FIELD OF THE INVENTION

The present invention relates to a lithium ion secondary battery having excellent life characteristics.

BACKGROUND OF THE INVENTION

Lithium ion secondary batteries typical of non-aqueous electrolyte secondary batteries have high electromotive force and high energy density. Thus, lithium ion secondary batteries are in an increasing demand as a main power supply of mobile communication devices and portable electronic devices.

For the development of lithium ion secondary battery, it is an important technical issue to enhance the reliability of the battery. A positive electrode of lithium ion secondary battery contains a lithium composite oxide such as Li_xCoO₂or Li_xNiO₂(x is changeable depending on charge and discharge of battery). These lithium composite oxides contain Co⁴⁺ or Ni⁴⁺ having high valence and reactivity at the time of charging. Due to this, decomposition reaction of electrolyte pertaining to lithium composite oxide is accelerated in a high temperature environment, generating a gas in a battery. Consequently, sufficient cycle characteristic or storage characteristic at high temperature cannot be obtained.

In order to inhibit the reaction between an active material and an electrolyte, it is suggested to treat the surface of a positive electrode active material with a coupling agent (Japanese Patent Laid-Open Nos. 11-354104, 2002-367610, and 8-111243). This allows a stable coating to be formed on the surface of active material particle. Therefore, the decomposition reaction of electrolyte pertaining to lithium composite oxide is inhibited.

Further, from the viewpoint of inhibiting the reaction between the active material and the electrolyte and improving cycle characteristic and storage characteristic at high temperature, addition of various elements to a positive electrode active material is suggested (Japanese Patent Laid-Open Nos. 11-16566, 2001-196063, 7-176302, 11-40154, and 2004-111076).

Furthermore, improvement of water resistance is a problem regarding Li_xNiO₂. Therefore, it is suggested that a coupling agent is used to make the surface of Li_xNiO₂hydrophobic so that the stability of the active material is enhanced (Japanese Patent Laid-Open No. 2000-281354).

The technology for inhibiting gas generation by using a coupling agent has the following points to be improved. Many of lithium ion secondary batteries are used for various portable devices. Various portable devices are not always used immediately after battery charge is completed. There are many cases wherein a battery is kept in charge condition for a long period, and thereafter discharge starts. However, the cycle life characteristic of battery is generally evaluated under a condition different from such practical use condition.

For example, a standard cycle life test is conducted in a condition wherein a short rest (intermission) period is given after charging. The rest period is about 30 minutes, for example. If such condition is applied for evaluation, the cycle life characteristic can be improved to some extent by conventionally suggested technologies.

However, it is necessary to consider that intermittent cycles are repeated on the assumption of practical use conditions. If charge-discharge cycles are repeated with a longer rest period (e.g. rest period of 720 minutes) after charging, the above technologies cannot provide sufficient life characteristic. In other words, a conventional lithium ion secondary battery still has a problem, that is improvement of intermittent cycle characteristic.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a lithium ion secondary battery that comprises a chargeable and dischargeable positive electrode, a chargeable and dischargeable negative electrode, and a non-aqueous electrolyte. The positive electrode includes an active material particle, and the active material particle includes a lithium composite oxide represented by the general formula (1): Li_xM_1-yL_yO₂, wherein 0.85â‰¦xâ‰¦1.25 and 0â‰¦yâ‰¦0.50; M is at least one selected from the group consisting of Ni and Co; and L is at least one selected from the group of alkaline earth elements, transition elements, rare earth elements, and elements of Group IIIb and Group IVb. The lithium composite oxide is treated with a coupling agent having a plurality of hydrolyzable groups and the remaining hydrolyzable group that does not form a bond with the lithium composite oxide is inactivated.

When the lithium composite oxide is treated with the coupling agent, a part of the hydrolyzable groups usually remains uncombined to the surface of the lithium composite oxide. The present invention has one feature of inactivating the remaining hydrolyzable group by various methods.

In the general formula (1), when 0<y, L preferably includes at least one selected from the group consisting of Al, Mn, Ti, Mg, Zr, Nb, Mo, W and Y.

The coupling agent is preferably a silane coupling agent. In this case, the coupling agent binds to the lithium composite oxide via Siâ€”O bond. Thus, on the surface of the active material particle, a silicide compound is formed.

The silane coupling agent preferably has as a hydrolyzable group at least one selected from the group consisting of alkoxy group and chlorine atom, and further preferably has at least one selected from the group consisting of mercapto group, alkyl group, and fluorine atom.

The amount of the coupling agent is preferably 2% by weight or less with respect to the lithium composite oxide.

The remaining hydrolyzable group is inactivated by a predetermined stabilizer.

The remaining hydrolyzable group is inactivated by a reaction with, for example, at least one hydroxyl group-containing substance (stabilizer) selected from the group consisting of inorganic hydroxide and inorganic oxyhydroxide. Here, as the hydroxyl group-containing substance, usable is at least one selected from the group consisting of LiOH, NaOH, manganese benzoate, and Mn(OH)₂.

The remaining hydrolyzable group is inactivated by reaction with, for example, a ligating (coordination) compound (stabilizer) having two or more reactive groups. In this case, each of the two or more reactive groups preferably is hydroxyl group, carbonyl group, carboxyl group, or alkoxy group.

The remaining hydrolyzable group is inactivated by a reaction with, for example, a silylating agent (stabilizer) having only one reactive group. In this case, the remaining group of the silylating agent is preferably an organic group with a carbon number of 5 or less.

In treating the lithium composite oxide with a coupling agent, a part of hydrolyzable groups of the coupling agent remains. Inactivation of the remaining hydrolyzable groups (for example, chlorine atom and alkoxy group), improves intermittent cycle properties. It is supposed that the inactivation of the remaining hydrolyzable groups inhibits removal of the coupling agent or a compound derived therefrom the active material particle.

While the novel features of the invention are set forth particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a vertical cross-sectional view of a cylindrical lithium ion secondary battery according to Examples of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

First, a positive electrode of the present invention is described. The positive electrode contains the following active material particles.

The active material particle contains a lithium composite oxide (Ni/Co lithium composite oxide) including nickel and/or cobalt as a main component. The form of the lithium composite oxide is not particularly limited. The lithium composite oxide forms an active material particle in a primary particle condition, and in some cases forms an active material particle in a secondary particle condition. Secondary particles may be formed by agglomeration of a plurality of active material particles.

The average particle diameter of the active material particle (or Ni/Co lithium composite oxide particle) is not particularly limited, but it is preferably 1 to 30 Î¼m, particularly preferably 10 to 30 Î¼m. The average particle diameter can be measured by, for example, a wet laser particle size analyzer available from Microtrac Inc. In this case, 50% value by volume (median diameter: D50) can be considered as the average particle diameter.

The Ni/Co lithium composite oxide is represented by the general formula (1) Li_xM_1-yL_yO₂. The general formula (1) satisfies 0.85â‰¦xâ‰¦1.25 and 0â‰¦yâ‰¦0.50.

Element M is at least one selected from the group of Ni and Co.

Element L is at least one selected from the group of alkaline earth elements, transition elements other than Ni and Co, rare earth elements, and elements of Group IIIb and Group IVb. Element L imparts an effect of thermal stability improvement to the lithium composite oxide. In addition, element L is considered to have an effect of enhancing binding power between the coupling agent and the lithium composite oxide. Thus, element L is preferably present more abundantly on the surface layer than inside the active material particle of the lithium composite oxide.

When 0<y, the lithium composite oxide preferably contains as elemen L at least one selected from the group consisting of Al, Mn, Ti, Mg, Zr, Nb, Mo, W and Y. These elements may be contained in the lithium composite oxide as element L either alone or in combination of two or more thereof. Among these, Al is suitable as element L since it has strong binding power with oxygen. Mn, Ti, and Nb are also suitable. If element L includes Ca, Sr, Si, Sn, B, and the like, it is preferable to include Al, Mn, Ti, Nb, and the like at the same time.

The range x representing Li content may fluctuate in accordance with charge and discharge of a battery. In the completely discharged condition, an initial condition immediately after battery assembly, or a condition immediately after the synthesis of lithium composite oxide, the range x may be 0.85â‰¦xâ‰¦1.25, preferably 0.93â‰¦xâ‰¦1.1.

The range y representing element L content may be 0â‰¦yâ‰¦0.50. However, when the balance of the capacity, cycle characteristic, and thermal stability is taken into consideration, the range y is preferably 0<yâ‰¦0.50, particularly preferably 0.001â‰¦yâ‰¦0.35.

When element L contains Al, the atom ratio a of Al with respect to the total of Ni, Co, and element L is suitably 0.005â‰¦aâ‰¦0.1, particularly suitably 0.01â‰¦aâ‰¦0.08.

When element L contains Mn, the atom ratio b of Mn with respect to the total of Ni, Co, and element L is suitably 0.005â‰¦bâ‰¦0.5, particularly suitably 0.01â‰¦bâ‰¦0.35.

When element L contains at least one selected from the group consisting of Ti and Nb, the total atom ratio c of Ti and Nb with respect to the total of Ni, Co, and element L is suitably 0.001â‰¦câ‰¦0.1, particularly suitably 0.001â‰¦câ‰¦0.08.

The atom ratio d of Ni with respect to the total of Ni, Co, and element L is preferably 60â‰¦dâ‰¦90, particularly suitably 70â‰¦dâ‰¦85.

The atom ratio e of Co with respect to the total of Ni, Co, and element L is preferably 5â‰¦eâ‰¦50, particularly suitably 10â‰¦dâ‰¦35.

The Ni/Co lithium composite oxide represented by the above general formula can be synthesized by sintering a raw material having a predetermined metal element ratio in an oxidizing atmosphere. The raw material includes lithium, nickel (and/or cobalt), and element L. The raw material includes oxides, hydroxides, oxyhydroxides, carbonates, nitrates, and organic complex salts of each metal element. These may be used either alone or in combination of two or more thereof.

From the viewpoint of facilitating the synthesis of Ni/Co lithium composite oxide, a solid solution containing a plurality of metal elements is preferably used. The solid solution containing a plurality of metal elements may be any of oxides, hydroxides, oxyhydroxides, carbonates, nitrates, and organic complex salts. For example, a solid solution containing Ni and Co, a solid solution containing Ni and element L, a solid solution containing Co and element L, and a solid solution containing Ni, Co, and element L are preferably used.

Temperature for sintering the raw material and oxygen partial pressure in an oxidizing atmosphere are dependent on the composition and amount of the raw material, and synthesis devices. A person skilled in the art can select appropriate conditions for them.

Other elements other than Li, Ni, Co, and element L may be mixed in industrial raw materials as impurities within such amounts that are usually contained therein. However, these impurities do not have large influences on the advantages of the present invention.

Lithium composite oxide is treated with a coupling agent having a plurality of hydrolyzable groups.

The coupling agent has at least one organic functional group and a plurality of hydrolyzable groups in a molecule thereof. The organic functional group has various hydrocarbon backbones. The hydrolyzable group imparts a hydroxyl group directly bonded to a metal atom (e.g. Siâ€”OH, Tiâ€”OH, and Alâ€”OH) by hydrolysis. Examples of the functional group include alkyl group, mercaptopropyl group, and trifluoropropyl group. Examples of the hydrolyzable group include hydrolyzable alkoxy group and chlorine atom.

In the specification, â€œtreatment with a coupling agentâ€ means that hydroxyl groups (OH group) present on the surface of lithium composite oxide are brought into reaction with the hydrolyzable groups of the coupling agent. For example, if the hydrolyzable group is an alkoxy group (OR group: R is an alkyl group), alcohol elimination reaction proceeds between the alkoxy and hydroxyl groups. In addition, if the hydrolyzable group is a chlorine atom (Cl group), hydrogen chloride (HCl) elimination reaction proceeds between the chlorine atom and hydroxyl groups.

The presence or absence of the treatment with the coupling agent can be confirmed through the formation of Xâ€”Oâ€”Si bond (X is the surface of lithium composite oxide), Xâ€”Oâ€”Ti bond, Xâ€”Oâ€”Al bond, etc. on the surface of a lithium composite oxide. When the lithium composite oxide contains Si, Ti, Al, etc. as element L, Si, Ti, and Al constituting the lithium composite oxide differs in structure from Si, Ti, and Al derived from the coupling agent. Thus, they are distinguishable.

As the coupling agent, usable are, for example, a silane coupling agent, aluminate coupling agent, titanate coupling agent. These may be either alone or in combination of plural kinds thereof. Among these, a silane coupling agent is particularly preferable. The silane coupling agent can form an inorganic polymer having siloxane bond as backbone. Coating of the surface of the active material with such an inorganic polymer inhibits side reaction. In other words, as a result of the surface treatment, the active material particle preferably carries a silicide compound.

Further, if the reactivity of the active material particle surface with the hydroxyl group is taken into consideration, the silane coupling agent preferably has as a hydrolyzable group at least one selected from the group consisting of alkoxy group and chlorine atom. Furthermore, from the viewpoint of inhibiting the side reaction with electrolyte, the silane coupling agent preferably has an organic functional group comprising at least one kind selected from the group consisting of mercapto group, alkyl group and fluorine atom.

The amount of coupling agent to be added to lithium composite oxide is preferably 2% by weight or less, more preferably 0.05 to 1.5% by weight. With respect to the lithium composite oxide If the amount of the coupling agent to be added exceeds 2% by weight, the surface of active material particle may be excessively coated with the coupling agent that does not engage in reaction.

In the present invention, the remaining hydrolyzable groups that have not been bonded to lithium composite oxide are inactivated. In this context, â€œinactivationâ€ means that the remaining hydrolyzable groups are brought into reaction to change to other structure.

For example, at least one kind of hydroxyl group-containing substance selected from the group consisting of inorganic hydroxide and inorganic oxyhydroxide is imparted to the surface of lithium composite oxide. The imparted hydroxyl group-containing substance reacts with the remaining hydrolyzable group, thereby inactivating the hydrolyzable group. In this case, it is considered that the hydrolyzable group is changed to, for example, hydroxyl group, peroxide group (OOM: M is a metal element) by the inactivation.

When hydroxyl group-containing substance is imparted to the surface of lithium composite oxide, for example, an aqueous solution or an organic solution having hydroxyl group-containing substance dissolved therein is prepared. Then, the lithium composite oxide treated with the coupling agent is dispersed in the obtained solution. Hydroxyl group-containing substance may be imparted to lithium composite oxide in advance. In this case, the lithium composite oxide that is not treated with the coupling agent is dispersed in an aqueous solution or an organic solution having hydroxyl group-containing substance dissolved therein, and then dried. Thereafter, a positive electrode is produced using the lithium composite oxide having hydroxyl group-containing substance, and the obtained positive electrode is treated with the coupling agent. The concentration of hydroxyl group-containing substance in an aqueous solution or an organic solution having hydroxyl group-containing substance dissolved therein is preferably 0.002 to 0.5 mol/L.

As the hydroxyl group-containing substance, usable are, for example, LiOH, NaOH, manganese benzoate, and Mn(OH)₂. These may be used either alone or in combination of plural kinds thereof.

The remaining hydrolyzable group can be inactivated by imparting a ligating compound having two or more reactive groups to the surface of lithium composite oxide. In this case, the imparted ligating compound reacts with the remaining hydrolyzable group. Specifically, two or more reactive groups of the ligating compound simultaneously react with two or more hydrolyzable groups. As a result, the hydrolyzable groups are inactivated. Each of two or more reactive groups of the ligating compound is preferably hydroxyl group, carbonyl group, carboxyl group, or alkoxy group. Further, two or more reactive groups are preferably the same kind of group.

In this invention, the ligating compound is a compound that can form the coordination compound reacting with the hydrolyzable group of the coupling agent. Examples of the ligating compound include Î²-diketone, alkanolamine, Î±-hydroxyketone, acid anhydrides, and diols. Particularly preferable are maleic acid, maleic anhydride, ethyl acetoacetate(Î²-diketone), 2,4-pentadion(Î²-diketone), triethanol amine(alkanolamine), 2-amino-2-methyl-1-propanol(alkanolamine), 4-hydroxy-2-butanone(Î±-hydroxyketone), 3-hydroxy-2-pentanone(Î±-hydroxyketone), 1-phenyl-1-oxo-2-hydroxypropane(Î±-hydroxyketone), phthalic anhydride (acid anhydride), and fumaric anhydride (acid anhydride).

Further, a silylating agent may be imparted to the surface of lithium composite oxide. Preferably, the silylating agent has only one reactive group and the remaining group is an organic group with a carbon number of 5 or less. In this case, the imparted silylating agent reacts with the remaining hydrolyzable group. As a result, the hydrolyzable group is inactivated. Examples of the reactive group of the silylating agent include alkoxy group, chlorine atom, and mercapto group. Further, as the organic group with a carbon number of 5 or less, preferable are methyl group, ethyl group, propyl group, and pentyl group. Specific examples of the silylating agent include trialkylchlorosilane and trialkylalkoxysilane.

When a ligating compound or a silylating agent is imparted to the surface of lithium composite oxide, an aqueous solution or an organic solution having the ligating compound or the silylating agent dissolved therein, for example, is prepared. The lithium composite oxide treated with the coupling agent is dispersed in the obtained solution. The concentration of the ligating compound or silylating agent in the solution is preferably 0.01 to 2 mol/L.

Next, one exemplary method for producing a positive electrode is described.

(i) First Step

First, a lithium composite oxide represented by the general formula (1): Li_xM_1-yL_yO₂is prepared. The method for preparing the lithium composite oxide is not particularly limited. The lithium composite oxide can be synthesized by, for example, sintering a raw material having a predetermined metal element ratio in an oxidizing atmosphere. Sintering temperature, oxygen partial pressure in an oxidizing atmosphere, or the like may properly be selected depending on the composition and amount of a raw material, and the synthesis device.

(ii) Second Step

The obtained lithium composite oxide is treated with a coupling agent. The treatment method is not particularly limited. For example, only addition of the coupling agent to the lithium composite oxide is sufficient. However, it is preferable to allow the coupling agent to conform to the entire of lithium composite oxide. From this viewpoint, it is desirable to disperse the lithium composite oxide in a solution or a dispersion solution of the coupling agent, and thereafter to remove a solvent. It is preferable to stir the lithium composite oxide, for example, in the solution or dispersion solution of coupling agent at 20Â° C. to 40Â° C. for 5 to 60 minutes.

The solvent for dissolving or dispersing the coupling agent is not particularly limited, but preferable are: ketones such as dioxane, acetone, and methyl ethyl ketone (MEK); ethers such as tetrahydrofuran (THF); alcohols such as ethanol; N-methyl-2-pyrrolidone (NMP), and the like. Further, an alkaline water with pH of 10 to 14 is usable.

(iii) Third Step

The lithium composite oxide is immersed in a solution or a dispersion solution containing a hydroxyl group-containing substance, a ligating compound, or a silylating agent. This allows the remaining hydrolyzable groups to be inactivated.

(iv) Fourth Step

After the inactivation of the remaining hydrolyzable groups of the coupling agent, a mixture for positive electrode containing active material particles, a conductant agent, and a binder is dispersed in a liquid component to prepare a paste. The obtained paste is applied and dried onto a positive electrode core material (current collector for positive electrode), thereby obtaining a positive electrode. Temperature and time period for drying after the application of the paste onto the positive electrode core material are not particularly limited. It is sufficient to conduct the drying, for example, at approximately 100Â° C. for about 10 minutes.

In the lithium composite oxide, it is preferable that element L exists more abundantly on the surface layer than inside the active material particle. For example, the lithium composite oxide before the coupling treatment is allowed to carry a raw material for element L, and then the lithium composite oxide is sintered.

The sintering is conducted at 650Â° C. to 750Â° C. for 2 to 24 hours (preferably about 6 hours) in an oxygen or air atmosphere. In this case, the pressure of the oxygen atmosphere is preferably 10 kPa to 50 kPa. By this sintering process, it is possible to obtain an active material particle having element L on the surface layer more abundantly than the inside thereof.

As a binder to be included in the mixture for positive electrode, any of thermoplastic resins and thermosetting resins may be used, but thermoplastic resins are preferable. Examples of thermoplastic resins usable as a binder include polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-methylacrylate copolymer, and ethylene-methylmethacrylate copolymer. These may be used alone or in combination of two or more thereof. These may be used in the form of a cross-linked material with sodium ion or the like.

As the conductive material to be included in the mixture for positive electrode, any electronically conductive material may be used as long as it is chemically stable in a battery. Examples thereof include graphites such as natural graphite (scale-shaped graphite or the like) and artificial graphite; carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fiber such as carbon fiber and metal fiber; metallic powders such as aluminum; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxide such as titanium oxide; organic conductive materials such as polyphenylene derivative; and carbon fluoride. These may be used alone or in combination of two or more thereof. The amount of the conductive material to be added is not particularly limited, but it is preferably 1 to 50% by weight, more preferably 1 to 30% by weight, particularly preferably 2 to 15% by weight with respect to the active material particle contained in the mixture for positive electrode.

As the positive electrode core material (current collector for positive electrode), any electronically conductive material may be used as long as it is chemically stable in a battery. Usable are foils or sheets composed of, for example, aluminum, stainless steel, nickel, titanium, carbon, and conductive resin. Among these, aluminum foil, aluminum alloy foil, and the like are particularly preferable. On the surface of foil or sheet, a layer of carbon or titanium may be imparted or an oxide layer may be formed. Irregularities may be imparted to the surface of foil or sheet. The current collector may be used in the form of, for example, net, punched sheet, lath member, porous member, foam, and molded article of fibers. The thickness of the positive electrode core material is not particularly limited, but within a range of 1 to 500 Î¼m, for example.

The method for treating an active material particle composed of lithium composite oxide has been described above. Next, a method for treating an electrode plate is described.

(i) First Step

A lithium composite oxide represented by the general formula (1): Li_xM_1-yL_yO₂is prepared in the same manner in the case of treating an active material particle composed of lithium composite oxide with a coupling agent.

(ii) Second Step

The obtained lithium composite oxide is immersed in a solution of a hydroxyl group-containing substance, a ligating compound, or a silylating agent, and thereafter dried. This process allows a hydroxyl group-containing substance, a ligating compound, or a silylating agent to be attached to the lithium composite oxide.

(iii) Third Step

A mixture for positive electrode containing the obtained active material particle, a conductive agent, and a binder is dispersed in a liquid component to prepare a paste. The obtained paste is applied and dried onto a positive electrode core material (current collector for positive electrode), thereby obtaining a positive electrode. Temperature and time period for drying after the application of the paste onto the positive electrode core material are not particularly limited, but it is sufficient to conduct the drying, for example, at approximately 100Â° C. for about 10 minutes.

The hydroxyl group-containing substance, ligating compound, or silylating agent may be added to a paste before the paste is applied onto the positive electrode core material. In this case, second step can be omitted.

(iv) Fourth Step

The positive electrode containing the hydroxyl group-containing substance, ligating compound, or silylating agent is treated with a coupling agent. A treatment method is not particularly limited. For example, the positive electrode is immersed in a coupling agent for 5 to 10 minutes, and then dried at 110Â° C. for about 10 minutes. However, it is preferable to allow the coupling agent to conform to the entire of lithium composite oxide. From this viewpoint, it is desirable to use a solution or dispersion solution containing the coupling agent.

The solvent for dissolving or dispersing the coupling agent is not particularly limited, but preferable are: ketones such as dioxane, acetone, and methyl ethyl ketone (MEK); ethers such as tetrahydrofuran (THF); alcohols such as ethanol; N-methyl-2-pyrrolidone (NMP), and the like. Further, an alkaline water with pH of 10 to 14 is usable.

In the case for allowing element L to exist more abundantly on the surface layer than inside the active material particle, the active material particle is prepared in the same manner as in the case for treating the active material particle with the coupling agent.

As the binder, conductive material, and positive electrode core material (current collector for positive electrode), materials that are described for the case for treating the active material particle with the coupling agent can be used.

Hereafter, constituent elements other than positive electrode of the lithium ion secondary battery of the present invention are described. However, the lithium ion secondary battery has a feature of including the above-described positive electrode, and the other constituent elements are not particularly limited. Therefore, the following descriptions do not restrict the present invention.

As a lithium-chargeable and dischargeable negative electrode, a negative electrode core material carrying a mixture for negative electrode can be used. The mixture for negative electrode includes, for example, a negative electrode active material and a binder, and as an optional component, includes a conductive material and a thickener. A negative electrode of this kind can be produced in the same manner as the positive electrode.

The negative electrode active material may be a material that can electrochemically charge and discharge lithium. For example, graphite, hard-to-graphitize carbon materials, lithium alloys, metal oxides, and the like can be used. The lithium alloy is preferably an alloy containing at least one selected from the group consisting of silicon, tin, aluminum, zinc, and magnesium. The metal oxide is preferably a silicon-containing oxide or a tin-containing oxide, and it is more preferable that the metal oxide is hybridized with a carbon material. The average particle size of the negative electrode active material is not particularly limited, but is preferably 1 to 30 Î¼m.

As a binder to be included in the mixture for negative electrode, any of thermoplastic resins and thermosetting resins may be used, but thermoplastic resins are preferable. Examples of thermoplastic resins usable as a binder include polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl acrylate copolymer, and ethylene-methyl methacrylate copolymer. These may be used alone or in combination of two or more thereof. These may be used in the form of a cross-linked material with sodium ion or the like.

As the conductive material to be included in the mixture for negative electrode, any electronically conductive material may be used as long as it is chemically stable in a battery. Examples thereof include graphites such as natural graphite (scale-shaped graphite or the like) and artificial graphite; carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fiber such as carbon fiber and metal fiber; metallic powders such as copper and nickel; and organic conductive materials such as polyphenylene derivative. These may be used alone or in combination of two or more thereof. The amount of the conductive material to be added is not particularly limited, but it is preferably 1 to 30% by weight, more preferably 1 to 10% by weight with respect to the active material particle contained in the mixture for negative electrode.

As the negative electrode core material (current collector for negative electrode), any electronically conductive material may be used as long as it is chemically stable in a battery. Usable are foils or sheets composed of, for example, stainless steel, nickel, copper, titanium, carbon, and conductive resin. Among these, copper foil, copper alloy foil, and the like are particularly preferable. On the surface of foil or sheet, a layer of carbon, titanium, or nickel may be imparted or an oxide layer may be formed. Irregularities may be imparted to the surface of foil or sheet. The current collector may be used in the form of, for example, net, punched sheet, lath member, porous member, foam, and molded article of fibers. The thickness of the negative electrode core material is not particularly limited, but within a range of 1 to 500 Î¼m, for example.

As a non-aqueous electrolyte, preferably used is a non-aqueous solvent having a lithium salt dissolved therein.

Examples of the solvent include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC); chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), and dipropyl carbonate (DPC); aliphatic carboxylic acid esters such as methyl formate, methyl acetate, methyl propionate, and ethyl propionate; lactones such as Î³-butyrolactone and Î³-valerolactone; chain ethers such as 1,2-dimethoxy ethane (DME), 1,2-diethoxy ethane (DEE), and ethoxymethoxy ethane (EME); cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran; dimethyl sulfoxide; 1,3-dioxolane; formamide; acetamide; dimethylformamide; dioxolane; acetonitrile; propylnitrile; nitromethane; ethyl monoglyme; phosphate trimester; trimethoxy methane; dioxolane derivative; sulfolane; methyl sulfolane; 1,3-dimethyl-2-imidazolidinone; 3-methyl-2-oxazolidinone; propylene carbonate derivative; tetrahydrofuran derivative; ethyl ether; 1,3-propanesultone; anisole; dimethyl sulfoxide; or N-methyl-2-pyrrolidone. These may be used alone but preferably two or more thereof may be mixed for use. Among these, preferable is a mixture solvent of a cyclic carbonate and a chain carbonate, or a mixture solvent of a cyclic carbonate, a chain carbonate, and an aliphatic carboxylic acid ester.

Examples of the lithium salt to be dissolved in the non-aqueous solvent include LiClO₄, LiBF₄, LiPF₆, LiAlCl₄, LiSbF₆, LiSCN, LiCl, LiCF₃SO₃, LiCF₃CO₂, Li(CF₃SO₂)₂, LiAsF₆, LiN(CF₃SO₂)₂, LiB₁₀Cl₁₀, lithium lower aliphatic carbonate, LiBr, LiI, LiBCl₄, lithium tetraphenylborate, and lithium imide salts. These may be used either alone or in combination of two or more thereof. However, at least LiPF₆is preferably used. The dissolution amount of the lithium salt with respect to the non-aqueous solvent is not particularly limited, but the concentration of lithium salt is preferably 0.2 to 2 mol/L, more preferably 0.5 to 1.5 mol/L.

For the purpose of improving charge-discharge properties of a battery, various additives can be added to the non-aqueous electrolyte. Examples of the additive include triethylphosphate, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, pyridine, hexaphosphate triamide, nitrobenzene derivatives, crown ethers, quaternary ammonium salts, and ethylene glycol dialkylether.

From the viewpoint of improving intermittent cycle properties, at least one additive selected from the group consisting of vinylene carbonate, vinylethylene carbonate, phosphazene, and fluorobenzene is preferably added to the non aqueous electrolyte. An appropriate content of these additives is 0.5 to 10% by weight of the non-aqueous electrolyte.

It is necessary to dispose a separator between the positive and negative electrodes. As the separator, an insulating fine porous thin film having high ion permeability and predetermined mechanical strength is preferably used. It is preferable that the separator has a function to close pores at a predetermined temperature or higher to increase resistance. As a material for the fine porous thin film, preferably used is polyolefin such as polypropylene and polyethylene, which has excellent resistance to organic solvents and hydrophobicity. A sheet, a nonwoven cloth, a woven cloth, and the like made of glass fiber are also used. The separator has a pore diameter of 0.01 to 1 Î¼m, for example. The separator generally has a thickness of 10 to 300 Î¼m. The separator generally has a porosity of 30 to 80%.

Instead of the separator, a non-aqueous electrolyte and a polymer material (polymer electrolyte) holding the electrolyte can be used. In this case, the polymer electrolyte is used integrally with the positive or negative electrode. As long as the polymer material can hold the non-aqueous electrolyte, any polymer material is usable, but a copolymer of vinylidene fluoride and hexafluoropropylene is particularly preferable.

Next, the present invention will be described in detail based on Examples, but the present invention is not limited to the following Examples.

EXAMPLE 1Battery A1

(i) Synthesis of Lithium Composite Oxide

A mixture of nickel sulfate, cobalt sulfate, and aluminum sulfate was prepared such that a molar ratio of Ni atom, Co atom, and Al atom is 80:15:5, and 3 kg of the mixture was dissolved in 10 L of water, obtaining a raw material solution. To the raw material solution, 400 g of sodium oxide was added to produce a precipitate. The precipitate was well washed with water and dried to obtain a co-precipitated hydroxide. A predetermined amount of lithium hydroxide was mixed with 3 kg of the obtained Niâ€”Coâ€”Al co-precipitated hydroxide, and sintered in an atmosphere with an oxygen partial pressure of 0.5 atmospheric pressure at a synthesis temperature of 750Â° C. for 10 hours to obtain a Ni/Co lithium composite oxide containing Al as element L (LiNi_0.8Co_0.15Al_0.05O₂).

(ii) Synthesis of Active Material Particle

The obtained composite oxide was treated with a coupling agent, and thereafter with a LiOH aqueous solution. Specifically, 2 kg of Ni/Co lithium composite oxide and 0.5% by weight of 3-mercaptopropyltrimethoxysilane with respect to the Ni/Co lithium composite oxide were inputted into 10 L of dehydrated dioxane, and the obtained dispersion solution was stirred at 25Â° C. for 3 hours. Then, 2 L of 0.2% by weight of LiOH aqueous solution was added to the dispersion solution, and further stirred at 25Â° C. for 2 hours. Thereafter, the composite oxide was filtrated, washed well with acetone, and dried at 100Â° C. for 2 hours.

In the obtained active material particle, the remaining hydrolyzable group (methoxy group) of the coupling agent is considered to be inactivated by reaction with LiOH added as a stabilizer.

(iii) Production of Positive Electrode

1 kg of the obtained active material particles (average particle diameter 12 Î¼m), 0.5 kg of PVDF #1320 (a solution of N-methyl-2-pyrrolidone (NMP) with a solid content of 12% by weight) available from Kureha Chemical Industry Co., Ltd., 40 g of acetylene black, and an appropriate amount of NMP were stirred with a double-arm kneader to prepare a mixture paste for positive electrode. This paste was applied onto both sides of an aluminum foil with a thickness of a 20 Î¼m (positive electrode core material), and dried. After drying, the obtained foil was rolled so as to have a total thickness of 160 Î¼m. Thereafter, the obtained electrode plate was slit to have such a width that it could be inserted into a 18650 cylindrical battery case, obtaining a positive electrode.

(iv) Production of Negative Electrode

3 kg of artificial graphite, 200 g of BM-400B available from Zeon Corporation (a dispersion solution of modified styrene-butadiene rubber with a solid content of 40% by weight), 50 g of carboxymethyl cellulose (CMC), and an appropriate amount of water were stirred with a double-arm kneader to prepare a mixture paste for negative electrode. This paste was applied to onto both sides of a copper foil with a thickness of 12 Î¼m (negative electrode core material), dried, and rolled so as to have a total thickness of 160 Î¼m. Thereafter, the obtained electrode plate was slit to have such a width that it could be inserted into a 18650 cylindrical battery case, obtaining a negative electrode.

(v) Preparation of Non-Aqueous Electrolyte

A mixed solvent of ethylene carbonate and methyl ethyl carbonate was prepared at a capacity ratio of 10:30. To the mixed solvent, 2% by weight of vinylene carbonate, 2% by weight of vinylethylene carbonate, 5% by weight of fluorobenzene, and 5% by weight of phosphazene were added, obtaining a mixed solution. LiPF₆was dissolved in this mixed solution at a concentration of 1.5 mol/L, obtaining a non-aqueous electrolyte.

(vi) Assembly of Battery

As shown in FIG. 1, a positive electrode 5 and a negative electrode 6 were wound via a separator 7 to form a group of electrode plates with a spiral shape. As the separator 7, a composite film of polyethylene and polypropylene (2300 available from Celgard Inc. with a thickness of 25 Î¼m) was used.

A positive lead 5a and a negative lead 6a both made of nickel were attached to the positive and negative electrodes 5 and 6, respectively. This group of electrode plates has an upper insulating plate 8a and a lower insulating plate 8b arranged on upper and lower faces thereof, and inserted into a battery case 1. Further, 5 g of the non-aqueous electrolyte was injected in the battery case 1.

Thereafter, a sealing plate 2 with an insulating gasket 3 arranged therearound and the positive electrode lead 5a were brought into conduction, and an opening of the battery case 1 was sealed with the sealing plate 2. Accordingly, a 18650 cylindrical lithium ion secondary battery (design capacity: 2000 mAh) was completed. This battery was used as an example Battery A1.

Battery A2

A lithium ion secondary battery was produced in the same manner as in Battery A1 except that an aqueous solution with 0.2% by weight of NaOH was used to inactivate the remaining hydrolyzable group of the coupling agent instead of an aqueous solution with 0.2% by weight of LiOH.

Battery A3

A lithium ion secondary battery was produced in the same manner as in Battery A1 except that an aqueous solution with 0.2% by weight of KOH was used to inactivate the remaining hydrolyzable group of the coupling agent instead of an aqueous solution with 0.2% by weight of LiOH.

Battery A4

A lithium ion secondary battery was produced in the same manner as in Battery A1 except that composite oxide having been treated with a coupling agent was treated with ethyl acetoacetate (Î²-diketone) to inactivate the remaining hydrolyzable group. Specifically, 2 kg of Ni/Co lithium composite oxide and 0.5% by weight of 3-mercaptopropyltrimethoxysilane with respect to Ni/Co lithium composite oxide were inputted into 10 L of dehydrated dioxane, and the obtained dispersion solution was stirred at 25Â° C. for 3 hours. Then, 0.2% by weight of ethyl acetoacetate with respect to the composite oxide was added to the dispersion solution, and further stirred at 25Â° C. for 2 hours, thereby inactivating the remaining hydrolyzable group. Thereafter, the composite oxdies were filtrated, washed with acetone, and dried at 100Â° C. for 2 hours.

Battery A5

A lithium ion secondary battery was produced in the same manner as in Battery A4 except that 2,4-pentadion(Î²-diketone) was used to inactivate the remaining hydrolyzable group of the coupling agent instead of ethyl acetoacetate.

Battery A6

A lithium ion secondary battery was produced in the same manner as in Battery A4 except that triethanol amine(alkanolamine) was used to inactivate the remaining hydrolyzable group of the coupling agent instead of ethyl acetoacetate.

Battery A7

A lithium ion secondary battery was produced in the same manner as in Battery A4 except that 2-amino-2-methyl-1-propanol(alkanolamine) was used to inactivate the remaining hydrolyzable group of the coupling agent instead of ethyl acetoacetate.

Battery A8

A lithium ion secondary battery was produced in the same manner as in Battery A4 except that 4-hydroxy-2-butanone(Î±-hydroxyketone) was used to inactivate the remaining hydrolyzable group of the coupling agent instead of ethyl acetoacetate.

Battery A9

A lithium ion secondary battery was produced in the same manner as in Battery A4 except that 3-hydroxy-2-pentanone(Î±-hydroxyketone) was used to inactivate the remaining hydrolyzable group of the coupling agent instead of ethyl acetoacetate.

Battery A10

A lithium ion secondary battery was produced in the same manner as in Battery A4 except that 1-phenyl-1-oxo-2-hydroxypropane(Î±-hydroxyketone) was used to inactivate the remaining hydrolyzable group of the coupling agent instead of ethyl acetoacetate.

Battery A11

A lithium ion secondary battery was produced in the same manner as in Battery A4 except that maleic anhydride (acid anhydride) was used to inactivate the remaining hydrolyzable group of the coupling agent instead of ethyl acetoacetate.

Battery A12

A lithium ion secondary battery was produced in the same manner as in Battery A4 except that phthalic anhydride (acid anhydride) was used to inactivate the remaining hydrolyzable group of the coupling agent instead of ethyl acetoacetate.

Battery A13

A lithium ion secondary battery was produced in the same manner as in Battery A4 except that fumaric anhydride (acid anhydride) was used to inactivate the remaining hydrolyzable group of the coupling agent instead of ethyl acetoacetate.

Battery A14

A lithium ion secondary battery was produced in the same manner as in Battery A4 except that trimethylchlorosilane (silylating agent) was used to inactivate the remaining hydrolyzable group of the coupling agent instead of ethyl acetoacetate.

Battery A15

A lithium ion secondary battery was produced in the same manner as in Battery A4 except that tripentylchlorosilane (silylating agent) was used to inactivate the remaining hydrolyzable group of the coupling agent instead of ethyl acetoacetate.

[Evaluation 1](Discharge Characteristic)

Pre-conditioning charge and discharge were conducted for each battery, followed by storage for 2 days under an environment at 40Â° C. Thereafter, each battery was subjected to the following two patterns of cycle tests. Here, the design capacity of the battery was 1 CmAh.

First Pattern (Ordinary Cycle Test)

(1) constant current charge (45Â° C.): 0.7 CmA (cut-off voltage 4.2 V)

(2) constant voltage charge (45Â° C.): 4.2 V (cut-off current 0.05 CmA)

(3) charge rest (45Â° C.): 30 minutes

(4) constant current discharge (45Â° C.): 1 CmA (cut-off voltage 2.5 V)

(5) discharge rest (45Â° C.): 30 minutes

Second Pattern (Intermittent Cycle Test)

(1) constant current charge (45Â° C.): 0.7 CmA (cut-off voltage 4.2 V)

(2) constant voltage charge (45Â° C.): 4.2 V (cut-off current 0.05 CmA)

(3) charge rest (45Â° C.): 720 minutes

(4) constant current discharge (45Â° C.): 1 CmA (cut-off voltage 2.5 V)

(5) discharge rest (45Â° C.): 720 minutes

Discharge capacities obtained after 500 cycles of first and second patterns were shown in Tables 1 to 22.

TABLE 1Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example A13-mercaptopropyl-LiOH aqueous solution20011500Example A2trimethoxysilaneNaOH aqueous solution20001502Example A3KOH aqueous solution19991505Example A4ethyl acetoacetate (Î²-diketone)20001499Example A52,4-pentadion (Î²-diketone)20011502Example A6triethanol amine20021500Example A72-amino-2-methyl-1-propanol20031498Example A84-hydroxy-2-butanone19991499Example A93-hydroxy-2-pentanone20011500Example A101-phenyl-1-oxo-2-hydroxypropane20001497Example A11maleic anhydride (acid anhydride)20021497Example A12phthalic anhydride (acid anhydride)20021502Example A13fumaric anhydride (acid anhydride)20001502Example A14trimethylchlorosilane (silylating agent)20011499Example A15tripentylchlorosilane (silylating agent)19991502Comparativenone2002â€‚802Example A1

EXAMPLE 2

Batteries B1 to B15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that 3-methacryloxypropyltrimethoxysilane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 2.

TABLE 2Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example B13-methacryloxypropyl-LiOH aqueous solution20011500Example B2trimethoxysilaneNaOH aqueous solution20021500Example B3KOH aqueous solution20011502Example B4ethyl acetoacetate (Î²-diketone)19991503Example B52,4-pentadion (Î²-diketone)20001499Example B6triethanol amine20011498Example B72-amino-2-methyl-1-propanol20011497Example B84-hydroxy-2-butanone20021500Example B93-hydroxy-2-pentanone20001510Example B101-phenyl-1-oxo-2-hydroxypropane19991509Example B11maleic anhydride (acid anhydride)19981508Example B12phthalic anhydride (acid anhydride)19971507Example B13fumaric anhydride (acid anhydride)20001500Example B14trimethylchlorosilane (silylating agent)20011503Example B15tripentylchlorosilane (silylating agent)20021505Comparativenone2001â€‚800Example B1

EXAMPLE 3

Batteries C1 to C15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that 3,3,3-trifluoropropyltrichlorosilane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 3.

TABLE 3Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example C13,3,3-LiOH aqueous solution20031501Example C2trifluoropropyl-NaOH aqueous solution20001502Example C3trichlorosilaneKOH aqueous solution19991508Example C4ethyl acetoacetate (Î²-diketone)20001510Example C52,4-pentadion (Î²-diketone)20011509Example C6triethanol amine19991502Example C72-amino-2-methyl-1-propanol19981501Example C84-hydroxy-2-butanone20001504Example C93-hydroxy-2-pentanone20011505Example C101-phenyl-1-oxo-2-hydroxypropane20021507Example C11maleic anhydride (acid anhydride)20031508Example C12phthalic anhydride (acid anhydride)20001509Example C13fumaric anhydride (acid anhydride)19991502Example C14trimethylchlorosilane (silylating agent)19981500Example C15tripentylchlorosilane (silylating agent)19991508Comparativenone2000â€‚801Example C1

EXAMPLE 4

Batteries D1 to D15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that 3,3,4,4,5,5,6,6,6-nonafluorohexyltrichlorosilane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 4.

TABLE 4Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example D13,3,4,4,5,5,6,6,6-LiOH aqueous solution19991502Example D2nonafluorohexyl-NaOH aqueous solution20011507Example D3trichlorosilaneKOH aqueous solution19971500Example D4ethyl acetoacetate (Î²-diketone)19971507Example D52,4-pentadion (Î²-diketone)20021500Example D6triethanol amine19991503Example D72-amino-2-methyl-1-propanol20001504Example D84-hydroxy-2-butanone20011503Example D93-hydroxy-2-pentanone20021500Example D101-phenyl-1-oxo-2-hydroxypropane19991508Example D11maleic anhydride (acid anhydride)19981508Example D12phthalic anhydride (acid anhydride)20001503Example D13fumaric anhydride (acid anhydride)20011509Example D14trimethylchlorosilane (silylating agent)20031508Example D15tripentylchlorosilane (silylating agent)20011509Comparativenone2000â€‚799Example D1

EXAMPLE 5

Batteries E1 to E15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that 3,3,3-trifluoropropyltrimethoxysilane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 5.

TABLE 5Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example E13,3,3-trifluoropropyl-LiOH aqueous solution20031501Example E2trimethoxysilaneNaOH aqueous solution19991503Example E3KOH aqueous solution20011502Example E4ethyl acetoacetate (Î²-diketone)20001502Example E52,4-pentadion (Î²-diketone)20011500Example E6triethanol amine20001500Example E72-amino-2-methyl-1-propanol20011500Example E84-hydroxy-2-butanone19991507Example E93-hydroxy-2-pentanone20011503Example E101-phenyl-1-oxo-2-hydroxypropane19991508Example E11maleic anhydride (acid anhydride)20011497Example E12phthalic anhydride (acid anhydride)20021507Example E13fumaric anhydride (acid anhydride)20001509Example E14trimethylchlorosilane (silylating agent)19981500Example E15tripentylchlorosilane (silylating agent)20001510Comparativenone1999â€‚800Example E1

EXAMPLE 6

Batteries F1 to F15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that hexyltrimethoxysilane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 6.

TABLE 6Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example F1hexyl-LiOH aqueous solution19991502Example F2trimethoxysilaneNaOH aqueous solution19991508Example F3KOH aqueous solution20021500Example F4ethyl acetoacetate (Î²-diketone)19981508Example F52,4-pentadion (Î²-diketone)20031501Example F6triethanol amine20021500Example F72-amino-2-methyl-1-propanol20011505Example F84-hydroxy-2-butanone20011497Example F93-hydroxy-2-pentanone19981501Example F101-phenyl-1-oxo-2-hydroxypropane20011503Example F11maleic anhydride (acid anhydride)20011500Example F12phthalic anhydride (acid anhydride)20031508Example F13fumaric anhydride (acid anhydride)19991503Example F14trimethylchlorosilane (silylating agent)20001510Example F15tripentylchlorosilane (silylating agent)20001503Comparativenone2002â€‚800Example F1

EXAMPLE 7

Batteries G1 to G15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that decyltrichlorosilane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 7.

TABLE 7Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example G1decyltrichlorosilaneLiOH aqueous solution20011503Example G2NaOH aqueous solution20001507Example G3KOH aqueous solution20001510Example G4ethyl acetoacetate (Î²-diketone)19991509Example G52,4-pentadion (Î²-diketone)20001509Example G6triethanol amine19971500Example G72-amino-2-methyl-1-propanol19981502Example G84-hydroxy-2-butanone19991502Example G93-hydroxy-2-pentanone20021500Example G101-phenyl-1-oxo-2-hydroxypropane20001503Example G11maleic anhydride (acid anhydride)20011502Example G12phthalic anhydride (acid anhydride)20011498Example G13fumaric anhydride (acid anhydride)19981500Example G14trimethylchlorosilane (silylating agent)19991507Example G15tripentylchlorosilane (silylating agent)19991508Comparativenone2001â€‚800Example G1

EXAMPLE 8

Batteries H1 to H15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that 6-triethoxysilyl-2-norbornane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 8.

TABLE 8Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example H16-triethoxysilyl-2-LiOH aqueous solution19981501Example H2norborneneNaOH aqueous solution20001503Example H3KOH aqueous solution19991503Example H4ethyl acetoacetate (Î²-diketone)19991508Example H52,4-pentadion (Î²-diketone)20021500Example H6triethanol amine20011503Example H72-amino-2-methyl-1-propanol20001500Example H84-hydroxy-2-butanone19991502Example H93-hydroxy-2-pentanone20021500Example H101-phenyl-1-oxo-2-hydroxypropane20001504Example H11maleic anhydride (acid anhydride)20011500Example H12phthalic anhydride (acid anhydride)19991503Example H13fumaric anhydride (acid anhydride)20001510Example H14trimethylchlorosilane (silylating agent)20011498Example H15tripentylchlorosilane (silylating agent)20001509Comparativenone2001â€‚798Example H1

EXAMPLE 9

Batteries I1 to I15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that 3-methacryloxypropyltrimethoxysilane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 9.

TABLE 9Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example I13-LiOH aqueous solution20021500Example I2methacryloxypropyl-NaOH aqueous solution20011497Example I3trimethoxysilaneKOH aqueous solution19991502Example I4ethyl acetoacetate (Î²-diketone)20011509Example I52,4-pentadion (Î²-diketone)20011502Example I6triethanol amine19971500Example I72-amino-2-methyl-1-propanol20021507Example I84-hydroxy-2-butanone20001507Example I93-hydroxy-2-pentanone19981500Example I101-phenyl-1-oxo-2-hydroxypropane19981502Example I11maleic anhydride (acid anhydride)19971507Example I12phthalic anhydride (acid anhydride)20011509Example I13fumaric anhydride (acid anhydride)20031501Example I14trimethylchlorosilane (silylating agent)19991509Example I15tripentylchlorosilane (silylating agent)20021505Comparativenone2001â€‚799Example I1

EXAMPLE 10

Batteries J1 to J15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that dodecyltriethoxysilane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 10.

TABLE 10Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example J1dodecyl-LiOH aqueous solution20001500Example J2triethoxysilaneNaOH aqueous solution20001507Example J3KOH aqueous solution19971500Example J4ethyl acetoacetate (Î²-diketone)19991508Example J52,4-pentadion (Î²-diketone)20021500Example J6triethanol amine19991508Example J72-amino-2-methyl-1-propanol19971507Example J84-hydroxy-2-butanone20011505Example J93-hydroxy-2-pentanone20011503Example J101-phenyl-1-oxo-2-hydroxypropane20021505Example J11maleic anhydride (acid anhydride)19981508Example J12phthalic anhydride (acid anhydride)20031501Example J13fumaric anhydride (acid anhydride)19991503Example J14trimethylchlorosilane (silylating agent)20001509Example J15tripentylchlorosilane (silylating agent)20001510Comparativenone2000â€‚795Example J1

EXAMPLE 11

Batteries K1 to K15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that dimethoxymethylchlorosilane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 11.

TABLE 11Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example K1Dimethoxymethyl-LiOH aqueous solution20021500Example K2chlorosilaneNaOH aqueous solution20001503Example K3KOH aqueous solution20011500Example K4ethyl acetoacetate (Î²-diketone)19991502Example K52,4-pentadion (Î²-diketone)20001504Example K6triethanol amine20011509Example K72-amino-2-methyl-1-propanol20011502Example K84-hydroxy-2-butanone20011503Example K93-hydroxy-2-pentanone19991503Example K101-phenyl-1-oxo-2-hydroxypropane19991509Example K11maleic anhydride (acid anhydride)20011500Example K12phthalic anhydride (acid anhydride)20021507Example K13fumaric anhydride (acid anhydride)19981501Example K14trimethylchlorosilane (silylating agent)20031508Example K15tripentylchlorosilane (silylating agent)20011507Comparativenone2002â€‚800Example K1

EXAMPLE 12

Batteries L1 to L15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that 3-mercaptopropylmethyldimethoxysilane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 12.

TABLE 12Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example L13-mercaptopropyl-LiOH aqueous solution19991502Example L2methyldimethoxy-NaOH aqueous solution20001510Example L3silaneKOH aqueous solution20021505Example L4ethyl acetoacetate (Î²-diketone)19971507Example L52,4-pentadion (Î²-diketone)20021500Example L6triethanol amine20001504Example L72-amino-2-methyl-1-propanol20031508Example L84-hydroxy-2-butanone20021500Example L93-hydroxy-2-pentanone19981501Example L101-phenyl-1-oxo-2-hydroxypropane20011503Example L11maleic anhydride (acid anhydride)19981508Example L12phthalic anhydride (acid anhydride)19971500Example L13fumaric anhydride (acid anhydride)19991507Example L14trimethylchlorosilane (silylating agent)19991508Example L15tripentylchlorosilane (silylating agent)19981500Comparativenone2001â€‚802Example L1

EXAMPLE 13

Batteries M1 to M15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that 3,3,3-trifluoropropylmethyldichlorosilane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 13.

TABLE 13Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example M13,3,3-trifluoropropyl-LiOH aqueous solution19991509Example M2methyldichlorosilaneNaOH aqueous solution20011497Example M3KOH aqueous solution20001507Example M4ethyl acetoacetate (Î²-diketone)20011507Example M52,4-pentadion (Î²-diketone)19991503Example M6triethanol amine19991502Example M72-amino-2-methyl-1-propanol20011498Example M84-hydroxy-2-butanone20011500Example M93-hydroxy-2-pentanone20001500Example M101-phenyl-1-oxo-2-hydroxypropane20021507Example M11maleic anhydride (acid anhydride)20001502Example M12phthalic anhydride (acid anhydride)20031501Example M13fumaric anhydride (acid anhydride)19981502Example M14trimethylchlorosilane (silylating agent)20011509Example M15tripentylchlorosilane (silylating agent)20001510Comparativenone2001â€‚800Example M1

EXAMPLE 14

Batteries N1 to N15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that diethoxydichlorosilane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 14.

TABLE 14Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example N1diethoxy-LiOH aqueous solution20021507Example N2dichlorosilaneNaOH aqueous solution20031508Example N3KOH aqueous solution20001509Example N4ethyl acetoacetate (Î²-diketone)19981500Example N52,4-pentadion (Î²-diketone)20001503Example N6triethanol amine19991503Example N72-amino-2-methyl-1-propanol20011502Example N84-hydroxy-2-butanone19991508Example N93-hydroxy-2-pentanone19981508Example N101-phenyl-1-oxo-2-hydroxypropane20011505Example N11maleic anhydride (acid anhydride)20011498Example N12phthalic anhydride (acid anhydride)19991509Example N13fumaric anhydride (acid anhydride)20021505Example N14trimethylchlorosilane (silylating agent)20011503Example N15tripentylchlorosilane (silylating agent)19971507Comparativenone2001â€‚797Example N1

EXAMPLE 15

Batteries O1 to O15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that 3,3,3-trifluoropropylmethyldimethoxysilane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 15.

TABLE 15Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example O13,3,3-trifluoropropyl-LiOH aqueous solution20011509Example O2methyldimethoxy-NaOH aqueous solution19991507Example O3silaneKOH aqueous solution20001503Example O4ethyl acetoacetate (Î²-diketone)19971500Example O52,4-pentadion (Î²-diketone)20001500Example O6triethanol amine20001504Example O72-amino-2-methyl-1-propanol20001499Example O84-hydroxy-2-butanone20021500Example O93-hydroxy-2-pentanone19991503Example O101-phenyl-1-oxo-2-hydroxypropane19991502Example O11maleic anhydride (acid anhydride)19981501Example O12phthalic anhydride (acid anhydride)20011509Example O13fumaric anhydride (acid anhydride)20001510Example O14trimethylchlorosilane (silylating agent)20021500Example O15tripentylchlorosilane (silylating agent)20001510Comparativenone2002â€‚800Example O1

EXAMPLE 16

Batteries P1 to P15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 16.

TABLE 16Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example P12-(3,4-LiOH aqueous solution20011507Example P2epoxycyclohexyl)-NaOH aqueous solution20021500Example P3ethyltrimethoxysilaneKOH aqueous solution20021507Example P4ethyl acetoacetate (Î²-diketone)19971507Example P52,4-pentadion (Î²-diketone)20031501Example P6triethanol amine20011505Example P72-amino-2-methyl-1-propanol20011500Example P84-hydroxy-2-butanone20021500Example P93-hydroxy-2-pentanone20011503Example P101-phenyl-1-oxo-2-hydroxypropane20001503Example P11maleic anhydride (acid anhydride)20011498Example P12phthalic anhydride (acid anhydride)20001510Example P13fumaric anhydride (acid anhydride)19991503Example P14trimethylchlorosilane (silylating agent)20001504Example P15tripentylchlorosilane (silylating agent)20011509Comparativenone2001â€‚798Example P1

EXAMPLE 17

Batteries Q1 to Q15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that docosylmethyldichlorosilane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 17.

TABLE 17Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example Q1docosylmethyl-LiOH aqueous solution19991503Example Q2dichlorosilaneNaOH aqueous solution20011500Example Q3KOH aqueous solution20011497Example Q4ethyl acetoacetate (Î²-diketone)20001503Example Q52,4-pentadion (Î²-diketone)19981508Example Q6triethanol amine20021505Example Q72-amino-2-methyl-1-propanol20001510Example Q84-hydroxy-2-butanone19991502Example Q93-hydroxy-2-pentanone19981500Example Q101-phenyl-1-oxo-2-hydroxypropane20001507Example Q11maleic anhydride (acid anhydride)20001502Example Q12phthalic anhydride (acid anhydride)20011503Example Q13fumaric anhydride (acid anhydride)19991508Example Q14trimethylchlorosilane (silylating agent)19991509Example Q15tripentylchlorosilane (silylating agent)20021500Comparativenone2001â€‚799Example Q1

EXAMPLE 18

Batteries R1 to R15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that dimethyldichlorosilane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 18.

TABLE 18Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example R1dimethyldichloro-LiOH aqueous solution20011500Example R2silaneNaOH aqueous solution20001504Example R3KOH aqueous solution20011507Example R4ethyl acetoacetate (Î²-diketone)20001510Example R52,4-pentadion (Î²-diketone)20001500Example R6triethanol amine20011509Example R72-amino-2-methyl-1-propanol19981508Example R84-hydroxy-2-butanone19971500Example R93-hydroxy-2-pentanone19991503Example R101-phenyl-1-oxo-2-hydroxypropane19991507Example R11maleic anhydride (acid anhydride)20011497Example R12phthalic anhydride (acid anhydride)20021507Example R13fumaric anhydride (acid anhydride)20011503Example R14trimethylchlorosilane (silylating agent)19991502Example R15tripentylchlorosilane (silylating agent)20011509Comparativenone1998â€‚797Example R1

EXAMPLE 19

Batteries S1 to S15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that dimethyldimethoxysilane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 19.

TABLE 19Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example S1dimethyldimethoxysilaneLiOH aqueous solution20021505Example S2NaOH aqueous solution20001510Example S3KOH aqueous solution19991503Example S4ethyl acetoacetate (Î²-diketone)20011500Example S52,4-pentadion (Î²-diketone)20031501Example S6triethanol amine20011505Example S72-amino-2-methyl-1-propanol19991508Example S84-hydroxy-2-butanone19971507Example S93-hydroxy-2-pentanone20011498Example S101-phenyl-1-oxo-2-hydroxypropane20031508Example S11maleic anhydride (acid anhydride)20001499Example S12phthalic anhydride (acid anhydride)20011502Example S13fumaric anhydride (acid anhydride)19981501Example S14trimethylchlorosilane (silylating agent)20021500Example S15tripentylchlorosilane (silylating agent)19991502Comparativenone2000â€‚795Example S1

EXAMPLE 20

Batteries T1 to T15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that methyltrimethoxysilane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 20.

TABLE 20Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example T1methyltrimethoxysilaneLiOH aqueous solution20021500Example T2NaOH aqueous solution19991502Example T3KOH aqueous solution19981501Example T4ethyl acetoacetate (Î²-diketone)20011503Example T52,4-pentadion (Î²-diketone)20011503Example T6triethanol amine19971500Example T72-amino-2-methyl-1-propanol20001500Example T84-hydroxy-2-butanone19991508Example T93-hydroxy-2-pentanone20011497Example T101-phenyl-1-oxo-2-hydroxypropane19981500Example T11maleic anhydride (acid anhydride)20011505Example T12phthalic anhydride (acid anhydride)20021500Example T13fumaric anhydride (acid anhydride)19991508Example T14trimethylchlorosilane (silylating agent)20011498Example T15tripentylchlorosilane (silylating agent)20011509Comparativenone2002â€‚800Example T1

EXAMPLE 21

Batteries U1 to U15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that diethoxymethyloctadecylsilane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 21.

TABLE 21Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example U1diethoxymethyl-LiOH aqueous solution19981502Example U2octadecylsilaneNaOH aqueous solution20001507Example U3KOH aqueous solution20001499Example U4ethyl acetoacetate (Î²-diketone)20001509Example U52,4-pentadion (Î²-diketone)19991502Example U6triethanol amine20021505Example U72-amino-2-methyl-1-propanol20001510Example U84-hydroxy-2-butanone20011500Example U93-hydroxy-2-pentanone20001510Example U101-phenyl-1-oxo-2-hydroxypropane19991507Example U11maleic anhydride (acid anhydride)20011502Example U12phthalic anhydride (acid anhydride)19991503Example U13fumaric anhydride (acid anhydride)20001504Example U14trimethylchlorosilane (silylating agent)20001502Example U15tripentylchlorosilane (silylating agent)20011509Comparativenone2001â€‚799Example U1

EXAMPLE 22

Batteries V1 to V15 were produced and evaluated in the same manner as in Batteries A1 to A15 of Example 1 except that diethoxydodecylmethylsilane was used as a coupling agent instead of 3-mercaptopropyltrimethoxysilane. The results are shown in Table 22.

TABLE 22Intermittent cycle characteristicCharge/Charge/Discharge restDischarge rest30 min.720 min.Discharge rate 1 CmAat 45Â° C.Coupling agentStabilizer(mAh)Example V1diethoxydodecyl-LiOH aqueous solution19991502Example V2methylsilaneNaOH aqueous solution20001500Example V3KOH aqueous solution20001509Example V4ethyl acetoacetate (Î²-diketone)20001510Example V52,4-pentadion (Î²-diketone)19981502Example V6triethanol amine20031501Example V72-amino-2-methyl-1-propanol20021500Example V84-hydroxy-2-butanone20011509Example V93-hydroxy-2-pentanone19991507Example V101-phenyl-1-oxo-2-hydroxypropane20001503Example V11maleic anhydride (acid anhydride)20001503Example V12phthalic anhydride (acid anhydride)19981501Example V13fumaric anhydride (acid anhydride)20021505Example V14trimethylchlorosilane (silylating agent)20011500Example V15tripentylchlorosilane (silylating agent)20001499Comparativenone1998â€‚800Example V1

Comparative Example

Comparative Example Batteries A1, B1, C1, D1, E1, F1, G1, H1, I1, J1, K1, L1, M1, N1, O1, P1, Q1, R1, S1, T1, U1, and V1 were prepared and evaluated in the same manners as in Batteries A1, B1, C1, D1, E1, F1, G1, H1, I1, J1, K1, L1, M1, N1, O1, P1, Q1, R1, S1, T1, U1, and V1, respectively, except that a stabilizer was not used. The results are shown in Tables 1 to 22.

In the above Examples, described are cases in which nickel-cobalt-aluminum composite oxide was used as a lithium composite oxide. However, lithium composite oxides having the general formula (1) have the similar crystal structure as LiCoO₂or LiNiO₂and have the similar properties, and thus the same effects are considered to be obtained from them. In addition, in cases wherein lithium composite oxides contain Mn, Ti, Mg, Zr, Nb, Mo, W or Y instead of aluminum, it has been confirmed that the similar results are obtained.

The present invention is useful in lithium ion secondary batteries that contain as active materials for positive electrode lithium composite oxides having a main component of nickel or cobalt to further enhance cycle characteristic more than conventional one in a condition (e.g. intermittent cycle) closer to a practical use condition.

The shape of lithium ion secondary battery of the present invention is not particularly limited, and may be formed in any shape, for example, a coin shape, button shape, sheet shape, cylindrical shape, flat shape, and square shape. Further, either of a winding type or stacking type may be used as a configuration of electrode plate group comprising positive and negative electrodes and a separator. Furthermore, the size of the battery may be small for use in small portable devices or large for use in electric vehicles. Thus, the lithium ion secondary battery of the present invention can be used as power sources of, for example, personal digital assistants, portable electronic devices, small power storage facilities for household use, two-wheeled motor vehicles, electric vehicles, and hybrid electric vehicles. However, the use application is not particularly limited.

Although the present invention has been described in terms of the presently preferred embodiments, it is to be understood that such disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains, after having read the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the true spirit and scope of the invention.