The present invention is directed to all-solid-state lithium-ion electrochemical cells comprising

- (A) a cathode comprising
  - (a) a particulate electrode active material according to general formula Li_1+xTM_1-xO₂, wherein TM is Ni and, optionally, at least one of Co and Mn, and, optionally, at least one element selected from Al, Mg, and Ba, transition metals other than Ni, Co, and Mn, and x is in the range of from zero to 0.2, wherein at least 50 mole-% of the transition metal of TM is Ni, wherein said electrode active material is coated with a continuous layer containing an oxide compound of Mo or W, and wherein said particulate electrode active material has an average particle diameter (D50) in the range of from 2 to 20 μm, wherein the continuous layer contains metallic Mo and an oxide compound of Mo or metallic W and an oxide compound of W
- (B) an anode, and
- (C) a solid electrolyte comprising lithium, sulphur and phosphorus.

Lithium ion secondary batteries are modern devices for storing energy. Many application fields have been and are contemplated, from small devices such as mobile phones and laptop computers through car batteries and other batteries for e-mobility. Various components of the batteries have a decisive role with respect to the performance of the battery such as the electrolyte, the electrode materials, and the separator. Particular attention has been paid to the cathode materials. Several materials have been suggested, such as lithium iron phosphates, lithium cobalt oxides, and lithium nickel cobalt manganese oxides. Although extensive research has been performed the solutions found so far still leave room for improvement.

One problem of lithium ion batteries lies in undesired reactions on the surface of the cathode active materials. Such reactions may be a decomposition of the electrolyte or the solvent or both. It has thus been tried to protect the surface without hindering the lithium ion exchange during charging and discharging. Examples are attempts to coat the surface of the cathode active materials with, e.g., aluminium oxide or calcium oxide, see, e.g., U.S. Pat. No. 8,993,051.

Another attempt to resolve the above problem is by using all-solid-state lithium-ion electrochemical cells, also called solid state lithium-ion cells. In such all-solid-state lithium-ion electrochemical cells, an electrolyte that is solid at ambient temperature is used. As electrolytes, certain materials based on lithium, sulphur and phosphorus have been recommended. However, side reactions of the electrolyte are still not excluded.

It has, on the other hand, also been reported that solid electrolytes based on lithium, sulphur and phosphorus may be incompatible with a nickel-containing complex layered oxide cathode material or other metal oxide cathode material when in direct contact with such cathode material, thereby impeding reversible operation of a respective solid-state or all solid-state lithium-ion electrochemical cell (battery) in certain cases. Several attempts have therefore been made to avoid direct contact between a nickel-containing layered oxide cathode material or other metal oxide cathode material and a respective solid electrolyte, e.g. by covering the oxidic cathode material on its surface with a shell or coating of certain materials, thus aiming at obtaining high oxidative stability and at the same time high lithium-ion conductivity of the oxidic cathode material and to so achieve or improve stable cycling performance of a solid-state or all solid-state lithium-ion electrochemical cell comprising said aforementioned components.

It was therefore an objective of the present invention to provide a lithium-ion electrochemical cell that overcomes the disadvantages of the prior art systems, and it was an objective to provide a process for manufacture of such lithium-ion electrochemical cells.

Accordingly, the all-solid-state lithium-ion electrochemical cells as defined at the outset have been found, hereinafter also defined as inventive electrochemical cells. In the context of the present invention, the terms all-solid-state lithium-ion electrochemical cells and solid-state lithium-ion electrochemical cells will be used interchangeably.

Inventive electrochemical cells comprise a cathode (A) and an anode (B) and a solid electrolyte (C), each of them being described in more detail below.

Cathode (A) comprises

- (a) a particulate electrode active material according to general formula Li_1-xTM_1-xO₂, wherein TM is Ni and, optionally, at least one of Co and Mn, and, optionally, at least one element selected from Al, Mg, and Ba, transition metals other than Ni, Co, and Mn, and x is in the range of from zero to 0.2, preferably 0.005 to 0.05, wherein at least 50 mole-% of the transition metal of TM is Ni, wherein said electrode active material is coated with a continuous layer containing an oxide of tungsten or oxide of molybdenum and wherein said particulate electrode active material has an average particle diameter (D50) in the range of from 2 to 20 μm, and wherein the continuous layer contains metallic Mo and an oxide compound of Mo or metallic W and an oxide compound of W.

Particulate electrode active material according to general formula Li_1-xTM_1-xO₂may be selected from lithiated nickel-cobalt aluminum oxides, lithiated nickel-manganese oxides, and lithiated layered nickel-cobalt-manganese oxides. Examples of layered nickel-cobalt-manganese oxides and lithiated nickel-manganese oxides are compounds of the general formula Li_1+x(Ni_aCo_bMn_cM¹_d)_1-xO₂, with M¹being selected from Mg, Ca, Ba, Al, Ti, Zn, Mo, Nb, V and Fe, the further variables being defined as follows:

- zero≤x≤0.2
- 0.50≤a≤0.99, preferably 0.60≤a≤0.90,
- zero≤b≤0.4, preferably zero<b≤0.2
- 0.01≤c≤0.3, preferably 0.1≤c≤0.2
- zero≤d≤0.1,
- and a+b+c+d=1.

In a preferred embodiment, particulate electrode active materials are selected from compounds according to general formula (I)

(Ni_aCo_bMn_c)_1-dM_d (I)

with

- a being in the range of from 0.6 to 0.99, preferably 0.8 to 0.98
- b being in the range of from 0.01 to 0.2, preferably 0.01 to 0.12
- c being in the range of from zero to 0.2, preferably 0 to 0.1, and
- d being in the range of from zero to 0.1, preferably 0 to 0.05,
- M is at least one of Al, Mg, Ti, Mo, W and Nb, and
- a+b+c=1.

and the further variables are defined as above.

Examples of lithiated nickel-cobalt aluminum oxides are compounds of the general formula Li[Ni_hCo_iAl_j]O_2+f. Typical values for f, h, i and j are:

- h is in the range of from 0.8 to 0.95,
- i is in the range of from 0.015 to 0.19,
- i is in the range of from 0.01 to 0.08, and
- f is in the range of from zero to 0.4.

Particularly preferred are Li_(1+x)[Ni_0.33Co_0.33Mn_0.33]_(1-x)O₂, Li_(1+x)[Ni_0.5Co_0.2Mn_0.3]_(1-x)O₂, Li_(1+x)[Ni_0.6Co_0.2Mn_0.2]_(1-x)O₂, Li_(1+x)[Ni_0.7Co_0.2Mn_0.1]_(1-x)O₂, and Li_(1+x)[Ni_0.3Co_0.1Mn_0.1]_(1-x)O₂, each with x as defined above, and Li[Ni_0.33Co_0.065Al_0.055]O₂and Li[Ni_0.91Co_0.045Al_0.045]O₂.

Some elements are ubiquitous. In the context of the present invention, traces of ubiquitous metals such as sodium, calcium, iron or zinc, as impurities will not be taken into account in the description of the present invention. Traces in this context will mean amounts of 0.02 mol-% or less, referring to the total metal content of TM.

In one embodiment of the present invention particles of particulate material such as lithiated nickel-cobalt aluminum oxide or layered lithium transition metal oxide, respectively, are cohesive. That means that according to the Geldart grouping, the particulate material is difficult to fluidize and therefore qualifies for the Geldart C region. In the course of the present invention, though, mechanical stirring is not required in all embodiments.

The particulate electrode active material has an average particle diameter (D50) in the range of from 2 to 20 μm, preferably from 2 to 15 μm, more preferably from 3 to 12 μm. The average particle diameter can be determined, e. g., by light scattering or LASER diffraction. The particles are usually composed of agglomerates from primary particles, and the above particle diameter refers to the secondary particle diameter.

In one embodiment of the present invention, said secondary particles are composed of agglomerated primary particles. Said primary particles may have an average particle diameter (D50) in the range of from 100 to 300 nm.

In one embodiment of the present invention, the particulate material has a specific surface, hereinafter also “BET surface”, in the range of from 0.1 to 1.5 m²/g. The BET surface may be determined by nitrogen adsorption after outgassing of the sample at 200° C. for 30 minutes or more and beyond this accordance with DIN ISO 9277:2010.

Said electrode active material is coated with a continuous layer containing an oxide compound of Mo (molybdenum) or W (tungsten), for example MoO₃, MoO₂, or WO₃. Further examples are selected from Li₂MoO₄, Li₂WO₄, Li₆WO₆, Li₄WO₅, Li₆W₂O₉, Li₂W₂O₇, Li₂W₄O₁₃, Li₂W₅O₁₆, and non-stoichiometric compounds, for example W or Mo bronze compounds of the formula LiwMO₃or Li_wWO₃with 0<w<1.

Preferably, said continuous layer contains oxide compound(s) of either molybdenum or tungsten.

In the context of the present invention, the term “continuous layer” refers to a layer with an average thickness in the range of from 0.2 to 200 nm, preferably 1 to 100 nm and more preferred 5 to 50 nm of a coating wherein with the help of TEM or SEM no significant gaps can be detected. The thickness of said layer may differ in different particles of the same batch, and it may differ by ±50% in specific particles. A continuous layer is thus distinguished over discrete particles attached to the electrode active material.

Said continuous layer may contain more than one oxide compound of Mo or W, for example it may contain a combination of WO₃and Li₂WO₄. Said oxide compound may comprise cations other than Mo or W, respectively, for example Li.

Said continuous layer further contains metallic W or metallic Mo. Thus, said continuous layer contains metallic Mo and an oxide compound of Mo, or the layer contains metallic W and an oxide of W. Preferably, said continuous layer may contain either metallic Mo and an oxide compound of Mo or metallic W and an oxide compound of W. The molar ratio of W or Mo in metallic form is preferably in the range of from 1 to 50%, referring to total W—or Mo, respectively—in said coating.

Said continuous layer may further contain an oxide of at least one metal other than Mo or W.

The average thickness of such coating may be very low, for example 0.1 to 100 nm, for example 5 to 20 nm. In other embodiments, the average thickness may be in the range of from 25 to 50 nm. The average thickness in this context refers to an average thickness determined mathematically by calculating the amount of Mo (or W or Zr or Nb) oxide species per particle surface in m²and assuming a 100% conversion in steps in Mo or W or Zr or Nb deposition, respectively.

Cathodes (A) comprise a cathode active material (a) in combination with conductive carbon (b) and solid electrolyte (C). Cathodes (A) further comprise a current collector, for example an aluminum foil or copper foil or indium foil, preferably an aluminum foil.

Examples of conductive carbon (b) are soot, active carbon, carbon nanotubes, graphene, and graphite, and combinations of at least two of the aforementioned.

In a preferred embodiment of the present invention, inventive cathodes contain

- (a) 70 to 96% by weight cathode active material,
- (b) 2 to 10% by weight of conductive carbon,
- (C) 2 to 28% by weight of solid electrolyte, percentages referring to the sum of (a), (b) and (C).

Said anode (B) contains at least one anode active material, such as silicon, tin, indium, silicon-tin alloys, carbon (graphite), TiO₂, lithium titanium oxide, for example Li₄Ti₅O₁₂or Li₇Ti₅O₁₂or combinations of at least two of the aforementioned. Said anode may additionally contain a current collector, for example a metal foil such as a copper foil.

Inventive electrochemical cells further comprise

- (C) a solid electrolyte comprising lithium, sulfur and phosphorus, hereinafter also referred to as electrolyte (C) or solid electrolyte (C).

In this context, the term “solid” refers to the state of matter at ambient temperature.

In one embodiment of the present invention, solid electrolyte (C) has a lithium-ion conductivity at 25° C. of ≥0.1 mS/cm, preferably in the range of from 0.1 to 30 mS/cm, measurable by, e.g., impedance spectroscopy.

In one embodiment of the present invention, solid electrolyte (C) comprises Li₃PS₄, yet more preferably orthorhombic β-Li₃PS₄.

In one embodiment of the present invention, solid electrolyte (C) is selected from the group consisting of Li₂S—P₂S₅, Li₂S—P₂S₅—LiI, Li₂S—P₂S₅—Li₂O, Li₂S—P₂S₅—Li₂O—LiI, Li₂S—SiS₂—P₂S₅—LiI, Li₂SP₂S₅—Z_mS_nwherein m and n are positive numbers and Z is a member selected from the group consisting of germanium, gallium and zinc, Li₂S—SiS₂—Li₃PO₄, Li₂S—SiS₂—Li_yPO_z, wherein y and z are positive numbers, Li₇P₃S₁₁, Li₃PS₄, Li₁₁S₂PS₁₂, Li₇P₂S₈I, and Li_7-r-2sPS_6-r-sX_rwherein X is selected from chlorine, bromine, iodine, fluorine, CN, OCN, SCN, N₃(azide) or combinations of at least two of the aforementioned, preferably X is chlorine, and the variables are defined as follows:

- 0.8≤r≤1.7 and 0≤s≤(−0.25 r)+0.5.

A particularly preferred example of solid electrolytes (C) is Li₆PS₅Cl, thus, r=1.0 and s=zero and X is chlorine.

In one embodiment of the present invention, electrolyte (C) is doped with at least one of Si, Sb, Sn. Si is preferably provided as element. Sb and Sn are preferably provided as sulfides.

In one embodiment of the present invention, inventive electrochemical cells comprise solid electrolyte (C) in a total amount of from 1 to 50% by weight, preferably of from 3 to 30% by weight, relative to the total mass of the cathode (A).

Inventive electrochemical cells further contain a housing.

Inventive electrochemical cells may be operated—charged and discharged—with an internal pressure in the range of from 0.1 to 300 MPa, preferably 1 to 100 MPa.

Inventive electrochemical cells may be operated at a temperature in the range of from −50° C. to +200° C., preferably from −30° C. to +120° C.

Inventive electrochemical cells show excellent properties even after multiple cycling, including very low capacity fading.

A further aspect of the present invention relates to a process for making inventive electrochemical cells, hereinafter also referred to as inventive process. The inventive process comprises the steps of

- (β) mixing an electrode active material (a) with carbon in electrically conductive form (b) and with a solid electrolyte (C) and, optionally, with a binder (c), and either
- (γ1) applying the mixture resulting from step (β) to a current collector, or
- (γ2) pelletizing the mixture resulting from step (β).

Electrode active material (a) and carbon in electrically conductive form (b) as well as solid electrolyte (C) have been described above.

Step (β) may be performed in a mill, for example a ball mill.

Step (β) may be performed in the presence of a solvent.

Step (γ1) may be performed with a squeegee, with a doctor blade, by drop casting, spin coating, or spray coating. Step (γ1) is preferably performed in the presence of a solvent.

Step (γ2) may be performed by compressing a dry powder in a die or in a mold. Step (γ2) is performed in the absence of a solvent. Preferably, pressure in the range of 50 MPa to 500 MPa is applied. A preferred suitable pressure is 375 MPa.

By the above steps, a cathode (A) is obtained.

In one embodiment of the present invention, the inventive process includes the manufacture of an electrode active material (a) by

- (α1) contacting a particulate electrode active material according to general formula Li_1+xTM_1-xO₂wherein the variables are defined as above, and wherein said electrode active material has lithium carbonate on the surface, with a to 0.2, wherein at least 50 mole-% of the transition metal of TM is Ni, and wherein said electrode active material has lithium carbonate on the surface, with a compound that is a carbonyl complex of Mo or W,
- (α2) performing a heat treatment on the mixture obtained in step (α1),
- (α3) treatment with an oxidant.

In the context of the present invention, carbonyl complexes of Mo are compounds that contain Mo and at least one CO ligand per Mo and mol compound. In the context of the present invention, carbonyl complexes of W are compounds that contain W and at least one CO ligand per W and mol compound.

Carbonyl complexs of Mo may bear ligands other than CO—for example NO. Carbonyl complexes of Mo may be ionic, for example anionic or cationic, with a counterion.

For carbonyl complexes of W the same applies mutatis mutandum.

Example of carbonyl complexes are Mo(CO)₂Cp*, Mo(CO)₃(EtCN)₃, W(CO)₄(MeCN)₂, and W(CO)₃(C₆H₃Me₃), with Cp* being pentymethylcyclopentadienyl, MeCn being acetonitrile, and C₆H₃being 1,3,5-trimethylbenzene. A particularly preferred example of carbonyl complexes of Mo is Mo(CO)s, and a particularly preferred example of carbonyl complexes of W is W(CO)s.

Step (α1) includes contacting a particulate electrode active material according to general formula Li_1+xTM_1−xO₂with a carbonyl complex of Mo or W in a solution, in a slurry, or with a carbonyl complex of Mo or W being in the gas phase.

In one embodiment of the present invention, step (α1) is preferably performed by mixing particulate electrode active material according to general formula Li_1+xTM_1-xO₂to a slurry or dispersion of a nanoparticulate zirconia species, for example by adding a solution or slurry of a carbonyl complex of Mo or W in an organic solvent to particulate electrode active material according to general formula Li_1-xTM_1-xO₂or by adding particulate electrode active material according to general formula Li_1+xTM_1−xO₂to a solution or slurry of said carbonyl complex of Mo or W in an organic solvent, followed by a mixing operation like shaking or stirring. In this context, such organic solvent are aprotic solvents such as, but not limited to ethers, cyclic or non-cyclic, cyclic and acyclic acetals, aromatic hydrocarbons such as toluene, non-aromatic cyclic hydrocarbons such as cyclohexane and cyclopentane, and chlorinated hydrocarbons. It is preferred, though, to not use any solvent in step (α1) and to mix particulate electrode active material according to general formula Li_1-xTM_1-xO₂and carbonyl complexes of Mo or W in bulk, that is, in the absence of a solvent.

Preferred are carbonyl compounds of W or Mo.

In embodiments wherein in step (α1) said carbonyl complexes of Mo or W is in the gas phase, it is possible to evaporate such carbonyl complex of Mo or W and to contact said electrode active material with a stream of gas containing carbonyl complexes of Mo or W and, if desired, diluted with a carrier gas.

Examples of solvents are listed above. Examples of cyclic acetals are 1,3-dioxane and in particular 1,3-dioxolane. Examples of acyclic acetals are 1,1-dimethoxyethane, 1,1-diethoxyethane, and diethoxymethane. Examples of suitable acyclic ethers are, for example, diisopropyl ether, di-n-butyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, with preference being given to 1,2-dimethoxyethane. Examples of suitable cyclic ethers are tetrahydrofuran (“THF”) and 1,4-dioxane. Examples of chlorinated hydrocarbons are dichloromethane, chloroform, and 1,2-dichloroethane.

In one embodiment of the present invention, the contacting in step (α1) is performed at a temperature in the range of from zero to 120° C., preferably 10 to 50° C. Preferably, step (α1) is performed at ambient temperature.

In on embodiment of the present invention, the duration of mixing in step (α1) is in the range of from 1 second to 12 hours, preferably 60 seconds to 10 hours.

In one embodiment of the present invention, the residual moisture content of particulate electrode active material according to general formula Li_1-xTM_1-xO₂before treatment according to step (α1) is in the range of from 50 to 2,000 ppm, preferably from 100 to 400 ppm. The residual moisture content may be determined by Karl-Fischer titration.

In one embodiment of the present invention, the extractable lithium content of particulate electrode active material according to general formula Li_1-xTM_1-xO₂before treatment according to step (α1) is in the range of from zero to 10% by weight of the total lithium content, preferably 0.1 to 3% by weight. The extractable lithium content may be determined by dispersing electrode active material according to general formula Li_1-xTM_1-xO₂before treatment according to step (α1) in a pre-determined amount of aqueous HCl, for example in a pre-determined amount of aqueous 0.1 M HCl, followed by titration with base.

In one embodiment of the present invention, step (α1) is performed at 15 to 45° C., preferably 20 to 30% by weight, even more preferably at ambient temperature.

In one embodiment of the present invention, step (α1) has a duration in the range of from 10 to 60 minutes, preferably 20 to 40 minutes.

Step (α1) may be performed in any type of vessel that is suitable for mixing, for example stirred tank reactors, or rotary kilns or free-fall-mixers. On laboratory scale, beakers and round-bottom flasks are suitable as well. In embodiments wherein carbonyl complex of Mo or W is in the gas phase, fluidized bed reactors and rotary kilns are suitable as well.

After completion of step (α1) solvent—if applicable—may be removed by evaporation or by a solid-liquid separation method, for example by decanting or by filtration. In embodiments where a filtration is applied, the resulting filter cake may be dried, for example at reduced pressure and at a temperature in the range of from 50 to 120° C.

Step (α2) includes performing a heat treatment on the mixture obtained in step (α1). The heat treatment in step (α2) implies a temperature that is higher than the evaporation temperature or the decomposition temperature of the respective carbonyl complex, whatever is lower. Said decomposition temperature may be lower than the bulk decomposition temperature due to catalytic reactions.

In one embodiment of the present invention, step (α2) is performed at a temperature in the range of from 150 to 800° C., preferably 200 to 780° C., even more preferably 250 to 750° C.

In one embodiment of the present invention, step (α2) is performed under an inert gas, for example nitrogen, or a noble gas.

In one embodiment of the present invention, step (α2) has a duration in the range of from 1 second to 24 hours, preferably 10 minutes to 10 hours.

In one embodiment of the present invention, step (α2) is performed in an autoclave, in a rotary kiln, in a roller hearth kiln or in a pusher kiln. In laboratory scale embodiments, step (α2) may be performed in an oven such as a muffle oven or in a tube furnace, or in a sealed tube.

The pressure in step (α2) may be in the range of from 1 bar to 20 bar, preferred are 2 bar to 10 bar. In the course of step (α2), carbon monoxide is released, and step (α2) is then performed under an atmosphere with an increasing content of CO.

A material is obtained from step (α2). In the subsequent step (α3), the material from step (α2) is treated with an oxidant.

Examples of suitable oxidants are oxygen, ozone, mixtures of ozone and oxygen, peroxides such as organic peroxides and H₂O₂, wherein the oxygen may stem from air or from synthetic air.

In one embodiment of the present invention, step (α3) is performed at a temperature in the range of from 150 to 600° C., preferably 300 to 500° C., even more preferably 350 to 450° C.

In one embodiment of the present invention, step (α3) is performed in a fluidized bed, in a packed bed reactor, in a CVD/MOCVD/ALD reactor or in a counter flow reactor, in a rotary kiln, in a roller hearth kiln or in a pusher kiln. In laboratory scale embodiments, step (α3) may be performed in an oven such as a muffle oven or in a tube furnace.

In one embodiment of the present invention, step (α3) has a duration in the range of from 1 minute to 12 hours, preferably 10 minutes to 5 hours.

The inventive manufacture of electrode active material (a) may include further operations, especially flushing operations, for example with nitrogen or a rare gas after step (α1), one or more venting operations to remove carbon monoxide after step (α2), and de-agglomeration operations after step (α3).

The inventive process may further comprise the following steps:

- providing an anode (B) and a solid electrolyte (C),
- and assembling cathode (A), anode (B) and a solid electrolyte (C) in a housing, optionally with a separator. Preferably, an extra layer of solid electrolyte (C) may serve as separator, and no separators such as ethylene-propylene copolymers are required.

However, it is preferred to first combine solid electrolyte (C) with a cathode active material (a), for example by mixing or milling, in a mixer or in an extruder. Then, anode (B) and, if applicable, a separator is added and the combined cathode (A), anode (B) and a solid electrolyte (C) as separator are arranged in a housing.

It is even more preferred to first combine some solid electrolyte (C) with a cathode active material (a), for example by co-milling and subsequent compression, and separately combining an anode active material with solid electrolyte (C) and conductive carbon, for example by co-milling and subsequent compression, and to then combine a layer of the above cathode (A) and a layer of anode (B) and a further layer of solid electrolyte (C) under a pressure of from 1 to 450 MPa, preferably of from 50 to 450 MPa and more preferably of from 75 to 400 MPa.

A further aspect of the present invention relates to cathodes (A) comprising

- (a) a particulate electrode active material according to general formula Li_1-xTM_1-xO₂, wherein TM is Ni and, optionally, at least one of Co and Mn, and, optionally, at least one element selected from Al, Mg, Ba and B, transition metals other than Ni, Co, and Mn, and x is in the range of from zero to 0.2, wherein at least 50 mole-% of the transition metal of TM is Ni, wherein the of said electrode active material are coated with a continuous layer containing an oxide compound of Mo or W or Nb or Zr, preferably of Mo or W, and wherein said particulate electrode active material has an average particle diameter (D50) in the range of from 2 to 20 μm,
- (b) carbon in electrically conductive form, and
- (C) a solid electrolyte comprising lithium, sulfur and phosphorus.

Particulate electrode active material (a), carbon (b) and solid electrolyte (C) have been described above.

Optionally, a binder (c) may be present. Optionally, a current collector may be present.

Inventive cathodes (A) and all-solid-state batteries containing them exhibit good discharge specific capacities and most importantly improved capacity retention during cycling.

The invention is further illustrated by working examples.

Percentages are % by weight unless specifically noted otherwise.

I. Manufacture of a Cathode Active Material

- (b.1): Super C65, TIMCAL
- (C.1): Li₆PS₅Cl, available from NEI
- rpm: revolutions per minute
- barg: bar gauge, bar above normal pressure

I.1 Providing a Precursor for Cathode Active Materials

As TM-OH.1, a co-precipitated hydroxide of Ni, Co and Mn was used, molar ratio Ni:Co:Mn 8.5:1:0.5, spherical particles, average particle diameter (D50) 3.52 μm, (D90) 5.05 μm, determined by LASER diffraction, uniform distribution of Ni, Co and Mn.

I.2. Manufacture of a Non-Treated Cathode Active Material

B-CAM.1 (Comparative): TM.1-OH was mixed with LiOH monohydrate in a molar ratio Li/TM of 1.02. The mixture was heated to 760° C. and kept for 10 hours in a forced flow of a mixture of 60% oxygen and 40% nitrogen (by volume). After cooling to ambient temperature, the powder was deagglomerated and sieved through a 32 μm mesh to obtain the base electrode active material B-CAM 1.

The D50 of the electrode active material B-CAM.1 was 3.5 μm, determined using the technique of LASER diffraction in a Mastersize 3000 instrument from Malvern Instruments. Residual moisture at 250° C. was determined to be 650 ppm.

II. Manufacture of Inventive Cathode Active Materials

II.1 Manufacture of Inventive CAM.1

Step (α1.1): 50 g of B-CAM.1 were mixed with 1.90 g of W(CO)₆in a 500 mL polypropylene screw-top bottle. A mixture was obtained.

Step (α2.1): A 300 ml stainless steel autoclave with glass liner and stirrer bar was charged with the mixture from step (α1.1). The autoclave was sealed under nitrogen atmosphere, then flushed three times by adding nitrogen to a pressure of 10 barg and depressurizing to 0 barg. Magnetic stirring at 100 rpm was started. Then the autoclave was heated to an outside temperature of 250° C. and maintained at 250° C. for 5 hours. During this time, the autoclave pressure rose to 5.0 barg. The autoclave was cooled to ambient temperature, depressurized to 0 barg and flushed twice with nitrogen as described above. It was then evacuated by a diaphragm pump and vented with ambient air. This step was performed three times. The autoclave was flushed with nitrogen one more time and opened under a nitrogen atmosphere to extract a material.

Step (α3.1): Subsequently, the material from step (α2.1) was transferred to a tube furnace and heated at 400° C. for 2 h (heating rate: 5° C. min⁻¹) under a flow of pure oxygen. The resulting product was collected, inventive CAM. 1.

As shown by SEM (scanning electron microscopy), the particles of CAM.1 had a continuous layer of a tungsten oxide compound.

II.2 Manufacture of Further Inventive Cathode Active Materials

The protocol II.1 was essentially repeated but with modifications according to Table 1.

TABLE 1

Data from CAM.1 to CAM.7 and B-CAM.1

Amount
Wt-%

of CO
of CO
Temperature
Duration

complex/
complex/
in step
of step

CO
50 g
50 g
(α3)
(α3)

complex
B-CAM.1
B-CAM.1
[° C.]
[h]

B.CAM.1
None
—
—
—
—

CAM.1
W(CO)₆
1.9
3.80
400
2

CAM.2
W(CO)₆
3.87
7.74
400
2

CAM.3
Mo(CO)₆
1.4
2.80
400
2

CAM.4
Mo(CO)₆
2.84
5.68
400
2

CAM.5
W(CO)₆
1.9
3.80
750
2

CAM.6
W(CO)₆
3.87
7.74
750
2

CAM.7
Mo(CO)₆
1.4
2.80
750
2

CAM.8
Mo(CO)₆
2.84
5.68
750
2

As shown by SEM (scanning electron microscopy), the particles of CAM.2 had a continuous layer of a tungsten oxide compound.

III Electrode Manufacture, Cell Manufacture and Testing

III.1 Electrode Manufacture

A cathode composition was made by mixing 70% of B-CAM.1 or any of CAM.1 to CAM.8 with 30 wt % (C.1), followed by addition of 1 wt % (b.1), said 1% referring to the sum of cathode active material and (C). For the cathode composite preparation, the active material was mixed under an argon atmosphere with (b.1) and (C.1) using a planetary ball milling (Fritsch) at 140 rpm for 30 min (ten ZrO₂balls with a diameter of 10 mm). In the cases of CAM.1, CAM.2, CAM.3 and CAM.4, inventive cathodes (A.1), (A.2), (A.3) or (A.4) were obtained. In the case of B-CAM.1, a comparative cathode C-(A.5) was obtained.

An anode composition was made by mixing 30 wt % carbon-coated Li₄Ti₅O₁₂(NEI), 60 wt % (C.1), and 10 wt % (b.1) in a planetary ball mill. An anode composition (B.1) was obtained.

III.2 Cell Manufacture

For manufacture of solid-state electrochemical cells, an amount of 100 mg (C.1) was compressed at a pressure of 125 MPa to form a solid electrolyte pellet, then 65 mg anode (0.1) was pressed to the solid electrolyte pellet at 125 MPa, and either 11 to 12 mg cathode (A.1) to (A.4) or 12 mg comparative cathode C-(A.5) were pressed onto the other side at 375 MPa. The pellet so obtained was compressed in a cylindrical case composed of polyetheretherketone (PEEK) between two stainless steel rods. An electrochemical cell was obtained.

III.3 Cell Testing

The electrochemical testing was done in a custom-made two-electrode cell, including two stainless steel dies and a PEEK sleeve with an inner diameter of 10 mm. First, Li₆PS₅Cl (100 mg) solid electrolyte was pressed at a pressure of 0.5 t. Then, cathode composite (˜12 mg) was pressed at 3.5 t onto the solid electrolyte pellet, followed by pressing the anode composite (65 mg) onto the other side. A stable pressure of 55 MPa was maintained during electrochemical cycling. Galvanostatic dis-/charge and rate capability measurements were performed with a Maccor 3000 battery tester at 45° C. The cutoff voltages of as-assembled cells were 1.35 and 2.75 V with respect to Li₄Ti₅O₁₂/Li₇Ti₅O₁₂, and 1.0C is equal to 190 mA g_NCM⁻¹. The results are summarized in Table 2.

TABLE 2

Initial electrochemical test data

from CAM.1 to CAM.8 and B-CAM.

1st Discharge capacity (mAh/g)
1st cycle coulombic

CAM
Cathode
rated at C/10
efficiency [%]

B-CAM
A.0
185.22
80

CAM.1
A.1
205.07
89

CAM.2
A.2
190.03
88

CAM.3
A.3
192.36
85

CAM.4
A.4
193.08
85

CAM.5
A.5
201.37
86

CAM.6
A.6
195.40
86

CAM.7
A.7
190.92
85

CAM.8
A.8
194.16
84

TABLE 3

Rate-dependent electrochemical test

data CAM.1 to CAM.8 and B-CAM.

0.1 C
0.2 C
0.5 C
1.0 C

CAM
Cathode
(mAh/g)
(mAh/g)
(mAh/g)
(mAh/g)

B-CAM
A.0
185.22
152.69
112.19
74.45

CAM.1
A.1
205.07
191.35
161.13
126.88

CAM.2
A.2
190.03
175.24
143.74
109.73

CAM.3
A.3
192.36
167.07
127.50
91.22

CAM.4
A.4
193.08
165.12
126.65
92.16

CAM.5
A.5
201.37
175.88
129.58
90.47

CAM.6
A.6
195.40
172.85
131.63
94.11

CAM.7
A.7
190.92
161.39
117.24
76.91

CAM.8
A.8
194.16
169.08
127.87
92.99

TABLE 3

Cycling stability with pronlonged cycling electrochemical

test data CAM.1 to CAM.8 and B-CAM

10th
30th
50th
100th

Discharge
Discharge
Discharge
Discharge

CAM
Cathode
(mAh/g)
(mAh/g)
(mAh/g)
(mAh/g)

B-CAM
A.0
137.26
127.87
111.87
75.88

CAM.1
A.1
176.88
166.40
160.76
152.65

CAM.2
A.2
162.15
144.75
119.53
n.a.

CAM.3
A.3
153.72
147.19
145.69
139.65

CAM.4
A.4
132.61
121.40
117.01
111.71

CAM.5
A.5
154.75
149.31
150.88
137.48

CAM.6
A.6
158.37
153.00
141.25
106.58

CAM.7
A.7
143.31
137.22
136.36
135.15

CAM.8
A.8
147.12
137.58
136.43
111.54

n.a.: not available.