2) Dispersing a crosslinker and an initiator in the organic solvent to obtain a solution B;

3) Injecting the foregoing two solutions concurrently by using a coaxial spinning apparatus, where the solution A is located in the core layer, and the solution B is located in the shell layer; and

4) The ejected coaxial fibers are the coaxial nanofibers. The coaxial nanofibers may be directly collected from the surface of the positive electrode plate and/or the negative electrode plate.

The inorganic particles are not particularly limited, and may be, for example, at least one selected from HfO₂, SrTiO₃, SnO₂, CeO₂, MgO, NiO, CaO, BaO, ZnO, ZrO₂, Y₂O₃, Al₂O₃, TiO₂, SiO₂, boehmite, magnesium hydroxide, aluminum hydroxide, lithium phosphate, lithium titanium phosphate, lithium aluminum titanium phosphate, lithium lanthanum titanate, lithium germanium thiophosphate, lithium nitride, SiS₂glass, P₂S₅glass, Li₂O, LiF, LiOH, Li₂CO₃, LiAlO₂, Li₂O—Al₂O₃—SiO₂—P₂O₅—TiO₂—GeO₂ceramic, or garnet ceramic. One of such inorganic particles may be used alone, or two or more thereof may be used in combination.

The average particle diameter of the inorganic particles is not particularly limited, and may be, for example, 0.01 μm to 10 μm, and preferably 20 nm to 5 μm. A ratio of the diameter of the nanofibers to the average particle diameter of the inorganic particles is not particularly limited, and may be, for example, 1:2 to 1:200, and preferably 1:3 to 1:20.

The number of the inorganic particles in the porous layer may be 5×10⁷/m²to 3×10¹⁹/m².

The mass of the inorganic particles in the porous layer may be 0.004 g/m²to 60 g/m².

The thickness of the porous layer is not particularly limited, and is preferably less than the thickness of a separator in the prior art. For example, the thickness of the porous layer according to this application may be 1 μm to 20 μm, and preferably 5 μm to 10 μm. Because the thickness of the porous layer according to this application is less than the thickness of the separator in the prior art, the porous layer increases the energy density of the battery.

The porosity of the porous layer is not particularly limited, but is preferably 30% to 95% in order to improve electrolyte retainability. The air permeability of the porous layer is not particularly limited in this application, as long as the objectives of this application can be achieved. For example, the air permeability may be 5 s/100 cm³to 400 s/100 cm³. Without being limited to any theory, the inventor of this application holds that the ion conductivity is further improved by controlling the air permeability within the range specified above.

The average pore diameter of the porous layer according to this application is not particularly limited, and may be 20 nm to 10 μm. The pore diameters of the porous layer according to this application may be uniformly distributed in the entire porous layer, or distributed in the porous layer according to a given rule, without being particularly limited, as long as the objectives of this application can be achieved. For example, in a preferred embodiment of this application, the pore diameters of the porous layer in a thickness direction from a region farther away from the electrode plate to a region closer to the electrode plate decrease linearly. In another preferred embodiment of this application, the pore diameters of the porous layer in the thickness direction from a region farther away from the electrode plate to a region closer to the electrode plate decrease nonlinearly. In another embodiment of this application, the pore diameters of the porous layer in the thickness direction from a region farther away from the electrode plate to a region closer to the electrode plate decrease discontinuously, that is, vary between layers. The number of layers is not particularly limited, and, for ease of preparation, may be 2 to 10 layers, and preferably 2 to 5 layers.

In some embodiments of this application, as shown in FIG. 3, one or more inorganic material layers 3 may overlay the outer surface between the pore-diameter-varying fiber layers inside the porous layer 2 to further improve the mechanical strength and ensure high insulation performance. The inorganic material layer is of some mechanical strength, and is electronically insulative, and preferably is an inorganic material capable of conducting lithium ions. The thickness of the inorganic material layer 3 is 0.1 μm to 20 μm. A deficient thickness brings no effects of improving the mechanical strength and suppressing particle penetration and lithium dendrite growth. An excessive thickness impedes lithium ion conduction, increases battery polarization, and hinders exertion of performance. The porosity of the inorganic material layer is 10% to 40%, and the average pore diameter thereof is 0.1 μm to 1 μm. Generally, the electronic resistivity of the inorganic material layer is greater than 10⁷Ω·m. Preferably, the electronic resistivity is greater than 10¹⁰Ω·m. The ionic conductivity of the inorganic material layer is required to range from 10⁻²S/cm to 10⁻⁸S/cm.

The method of bonding between the inorganic material layer 3 and the porous layer 2 is not particularly limited. For example, the bonding may be implemented by the following methods:

1. Hot pressing and/or binding. In the hot pressing method, the hot pressing temperature needs to be a melting point of the inorganic material layer or a melting point of the porous layer, whichever is lower. The pressure needs to be 0.1 MPa to 1 MPa. In the binding method, the binder is not particularly limited, and may be, for example, one or more of polyamide, polyurethane, poly(ethylene-co-vinyl acetate) (EVA), poly(ethylene-co-vinyl alcohol) (EVOH), acrylate, or polyvinylidene difluoride.

2. If the inorganic material layer 3 is directly deposited on or applied to the porous layer 2, the binder is not necessarily used, and the bonding may be formed naturally.

The type of the lithium-ion battery according to this application is not particularly limited, and may be any type of lithium-ion battery, for example, a button-type, cylindrical, or pouch-type lithium-ion battery. The lithium-ion battery according to this application includes a positive electrode, a negative electrode, an electrolytic solution, and a porous layer according to this application. In an embodiment of this application, the porous layer may be formed on a surface of the positive electrode plate and a surface of the negative electrode plate, and then the “negative electrode plate+porous layer” and the “positive electrode plate+porous layer” are stacked together to form a stacked structure of the lithium-ion battery. In another embodiment of this application, the porous layer may be formed on both surfaces of the positive electrode plate, and then the negative electrode plate, and the “porous layer+positive electrode plate+porous layer” may be stacked together to form a stacked structure of the lithium-ion battery, without applying a porous layer onto the surface of the negative electrode plate. In another embodiment of this application, the porous layer may be formed on both surfaces of the negative electrode plate, and then the “porous layer+negative electrode plate+porous layer” and the positive electrode plate are stacked together to form a stacked structure of the lithium-ion battery. The stacked structure formed in this way may be further stacked in the foregoing sequence, or may be wound directly to form a multilayer stacked structure of the lithium-ion battery. The stacking method is not particularly limited in this application, and may be selected by a person skilled in the art as actually required.

In embodiments of this application, the positive electrode plate is not particularly limited, as long as the objectives of this application can be achieved. For example, the positive electrode plate generally includes a positive current collector and a positive active material layer, and the positive active material layer includes a positive active material. The positive current collector is not particularly limited, and may be any positive current collector well known in the art. For example, the positive current collector may be a copper foil, an aluminum foil, an aluminum alloy foil, or a composite current collector. The positive active material is not particularly limited, and may be any positive active material in the prior art. The positive active material is at least one selected from lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium cobaltate, lithium manganate, or lithium manganese iron phosphate.

Optionally, the positive electrode plate may further include a conductive layer. The conductive layer is located between the positive current collector and the positive active material layer. The composition of the conductive layer is not particularly limited, and may be a conductive layer commonly used in the art.

In embodiments of this application, the negative electrode plate is not particularly limited, as long as the objectives of this application can be achieved. For example, the negative electrode plate generally includes a negative current collector and a negative active material layer, and the negative active material layer includes a negative active material. The negative current collector is not particularly limited, and may be any negative current collector well known in the art. For example, the negative current collector may be a copper foil, an aluminum foil, an aluminum alloy foil, or a composite current collector. The negative active material is not particularly limited, and may be any negative active material well known in the art. For example, the negative active material may include at least one of artificial graphite, natural graphite, mesocarbon microbead, silicon, silicon carbon, silicon-oxygen compound, soft carbon, hard carbon, lithium titanium oxide, or niobium titanium oxide.

The electrolytic solution of the lithium-ion battery is not particularly limited, and may be any electrolytic well known in the art. The electrolytic solution may be in a gel state, a solid state, or a liquid state. For example, the liquid-state electrolytic solution includes a lithium salt and a nonaqueous solvent.

The lithium salt is not particularly limited, and may be any lithium salt well known in the art, as long as the objectives of this application can be achieved. For example, the lithium salt may be at least one selected from LiPF₆, LiBF₄, LiAsF₆, LiClO₄, LiB(C₆H₅)₄, LiCH₃SO₃, LiCF₃SO₃, LiN(SO₂CF₃)₂, LiC(SO₂CF₃)₃, or LiPO₂F₂. For example, the lithium salt may be LiPF₆.

The nonaqueous solvent is not particularly limited, as long as the objectives of this application can be achieved. For example, the nonaqueous solvent may be at least one selected from carbonate compound, a carboxylate compound, an ether compound, a nitrile compound, or another organic solvent.

For example, the carbonate compound may be at least one selected from diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethylene propyl carbonate (EPC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methyl ethylene, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, or trifluoromethyl ethylene carbonate.

The method for depositing the nanofibers and the inorganic particles is not particularly limited, and may be any deposition method well known in the art. For example, the porous substrate may be prepared by electrospinning, air spinning, or centrifugal spinning, and the inorganic particles may be prepared by electrospraying. The sequence of depositing the nanofibers and the inorganic particles is not particularly limited, as long as the porous layer according to this application can be formed. The porous layer includes a nanofibrous porous substrate and inorganic particles distributed in the porous substrate. For example, the nanofibers and the inorganic particles may be deposited simultaneously.

The porous substrate may be implemented by using any spinning equipment known in the art, without being particularly limited, as long as the objectives of this application can be achieved. The spinning equipment may be any spinning equipment known in the art or commercially available.

Electrospraying is also known as electrostatic spraying. In a process of electrostatic spraying of particles, a spraying apparatus is filled with a particle suspension. Droplets of the suspension are retained at a nozzle by a surface tension under an externally applied electrical field. The surface of the suspension droplets accumulates charges as induced by the electrical field, and is subjected to an electrical field force exerted in a direction opposite to the surface tension. The suspension droplets at the nozzle leave the nozzle and move toward a deposition destination under the action of the electrical field, and are deposited on the destination.

The electro spraying may be implemented by any equipment known in the art, without being particularly limited, as long as the objectives of this application can be achieved. For example, the equipment may be any equipment known to a person skilled in the art or commercially available.

Another aspect of this application provides an electronic device. The electronic device includes the electrochemical device according to this application.

Terms and Definitions

Number of inorganic particles: the number of inorganic particles per unit area of the porous layer.

Average particle diameter of inorganic particles: The average particle diameter of inorganic particles is a particle diameter measured when a cumulative volume of measured particles reaches 50% of the total volume by counting from a small-sized particle side in a volume-based particle size distribution curve of the inorganic particles, where the particle size distribution curve is plotted by using a laser particle size analyzer.

Test Methods:

Self-Discharge Rate K of the Lithium-Ion Battery:

Discharging the lithium-ion battery at a current of 0.5 C until the voltage reaches 3.0 V, leaving the battery to stand for 5 minutes, then charging the lithium-ion battery at a constant current of 0.5 C until the voltage reaches 3.85 V, and then charging the battery at a constant voltage of 3.85 V until the current reaches 0.05 C. Leaving the battery to stand in a 25° C.±3° C. environment for two days, and measuring and recording the voltage OCV 1 at this time. Next, leaving the lithium-ion battery to stand in an environment of 25° C.±3° C. for two days, measuring and recording the voltage OCV2 at this time, and calculating a K value according to a formula: K (mV/h)=(OCV2−OCV1)/48 h×1000.

Porosity of the Porous Layer:

Disassembling the lithium-ion battery after the discharge, so as to obtain an electrode plate overlaid with a porous layer. Taking a part of the porous layer as a specimen, and measuring the porosity of the porous layer by conventional mercury intrusion porosimetry.

Capacity Retention Rate:

Charging a lithium-ion battery at a constant current of 0.5 C until the voltage reaches 4.4 V, then charging the battery at a constant voltage of 4.4 V until the current reaches 0.05 C, leaving the battery to stand for 10 minutes in a 25° C.±3° C. environment, and then discharging the battery at a current of 0.5 C until the voltage reaches 3.0 V, and recording a first-cycle discharge capacity as Q₁. Repeating the foregoing charge and discharge process for 50 cycles, and then recording the discharge capacity at this time as Q₅₀. Calculating a 50^th-cycle capacity retention rate η according to the following formula: η=Q₅₀/Q₁×100%.

Penetration Strength of the Porous Layer:

Measuring the penetration strength of the porous layer by using a microcomputer-controlled electronic universal tester (MTS-E44.104).

Test Process:

Disassembling a lithium-ion battery, and taking out a part of a stacked three-layer structure of a positive electrode plate, a porous layer, and a negative electrode plate to serve as a specimen. Oven-drying the specimen at 80° C. for 2 hours, and placing the specimen on an aluminum plate on a side of a pressure testing machine. Placing a steel ball (made of iron, 5 mm in diameter) on the specimen. Applying a 10 V voltage between tabs of the two electrode plates, and exerting a pressure on the surface of the specimen through the aluminum plates on both sides at a pressing speed of 0.1 mm/min in the vertical direction. When the resistance changes sharply, recording the pressure as the penetration strength.

EMBODIMENTS
Preparation Example 1: Preparing A Negative Electrode Plate

Mixing artificial graphite as a negative active material, conductive carbon black (Super P), and the styrene butadiene rubber at a weight ratio of 96:1.5:2.5, adding deionized water as a solvent, and stirring evenly to obtain a slurry. Coating one surface of a 10-μm-thick negative current collector copper foil evenly with the slurry, and drying the slurry at a temperature of 110° C. to obtain a negative electrode plate coated with a 150-μm-thick negative active material layer on one side. Repeating the foregoing steps on the other surface of the negative electrode plate to obtain a negative electrode plate coated with the negative active material layer on both sides. Then cutting the negative electrode plate into a size of 41 mm×61 mm for future use.

Preparation Example 2: Preparing A Positive Electrode Plate

Mixing lithium cobalt oxide as a positive active material, conductive carbon black (Super P), and polyvinylidene difluoride at a weight ratio of 97.5:1.0:1.5, adding N-methyl pyrrolidone as a solvent, and stirring evenly. Coating a positive current collector aluminum foil evenly with the slurry, and drying the slurry at a temperature of 90° C. to obtain a positive electrode plate coated with a 100-μm-thick positive active material layer on one side. Repeating the foregoing steps on the other surface of the positive current collector aluminum foil to obtain a positive electrode plate of which both sides are coated with the positive active material layer. Then cutting the positive electrode plate into a size of 38 mm×58 mm for future use.

Preparation Example 3: Preparing an Electrolytic Solution

Mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) at a mass ratio of EC:EMC:DEC=30:50:20 in an dry argon atmosphere to form an organic solvent, then adding lithium salt hexafluorophosphate (LiPF₆) into the organic solvent to dissolve, and mixing the solution evenly to obtain an electrolytic solution in which a lithium salt concentration is 1.15 mol/L.

The following embodiments illustrate the preparation of an integrated porous layer of “nanofibrous porous substrate+inorganic particles” according to this application. The embodiments are illustrated by using a positive electrode plate as an example, and an integrated porous layer is deposited on both surfaces of the positive electrode plate. Understandably, the integrated porous layer may also be deposited on both surfaces of the negative electrode plate instead, or an integrated porous layer is deposited on one surface of the positive electrode plate and one surface of the negative electrode plate separately. Such implementation solutions can also achieve the objectives of this application. A person skilled in the art understands that such implementation solutions still fall within the protection scope of this application.

Embodiment 1

Dispersing 99.9 wt % polyvinylidene difluoride (PVDF), 0.09 wt % crosslinker acrylonitrile, and 0.01 wt % initiator boron trifluoride in a solvent of dimethylformamide and acetone mixed at a ratio of 7:3. In other words, adding the crosslinker and the initiator sparingly into a conventional electrospinning solution. Stirring evenly until the viscosity of the slurry is stable, so as to obtain a solution A with a solid content of 25 wt %. At the same time, dispersing 99.9 wt % boehmite, 0.09 wt % acrylonitrile, and 0.01 wt % boron trifluoride in a solvent of dimethylformamide and acetone mixed at a ratio of 7:3, and stirring evenly until the viscosity of the slurry is stable, so as to obtain a suspension B with a solid content of 40 wt %.

Making polyvinylidene difluoride nanofibers by using the solution A as an ingredient by electrospinning on the surface of the positive electrode plate prepared in Preparation Example 2, where the average diameter of the nanofibers is 100 nm. Electrospraying inorganic particles onto the surface of the positive electrode plate at the same time of spinning by using the suspension B as an ingredient, where the average particle diameter of the chosen inorganic particles is 500 nm, and a ratio of the average diameter of the nanofibers to the average particle diameter of the inorganic particles is 1:5. The thickness of the porous layer is 10 μm, the average pore diameter of the porous layer is 200 nm, and the porosity of the porous layer is 75%. Subsequently, repeating the foregoing steps on the other surface of the positive electrode plate, vacuum-drying at 40° C. to remove the solvents such as dimethylformamide, and then increasing the temperature to 80° C., and keeping the temperature for 6 hours so that crosslinking occurs under heat treatment to obtain a positive electrode plate coated with the porous layer on both sides. In the finally prepared porous layer, the weight percent of the polymer nanofibers is 95 wt %, the weight percent of the inorganic particles is 4.9 wt %, and the weight percent of the crosslinker plus the initiator is 0.1 wt %.

Embodiments 2 to 5

Identical to Embodiment 1 except that the weight percent of the nanofibers and inorganic particles in the porous layer is adjusted separately according to Table 1, where a micrograph of the porous layer in Embodiment 2 is shown in FIG. 5.

Embodiment 6

Dispersing 99 wt % polyvinylidene difluoride, 0.9 wt % acrylonitrile, and 0.1 wt % boron trifluoride in a solvent of dimethylformamide and acetone mixed at a ratio of 7:3, and stirring evenly until the viscosity of the slurry is stable, so as to obtain a solution A with a solid content of 25 wt %. At the same time, dispersing 99 wt % boehmite, 0.9 wt % acrylonitrile, and 0.1 wt % boron trifluoride in a solvent of dimethylformamide and acetone mixed at a ratio of 7:3, and stirring evenly until the viscosity of the slurry is stable, so as to obtain a suspension B with a solid content of 40 wt %.

Performing the same method as in Embodiment 1 by using the solution A and the suspension B as ingredients, so as to make a positive electrode plate coated with the porous layer on both sides. In the finally prepared porous layer, the weight percent of the nanofibers is 69 wt %, the weight percent of the inorganic particles is 30 wt %, and the weight percent of the crosslinker plus the initiator is 1 wt %.

The rest is the same as Embodiment 1.

Embodiment 7

Dispersing 95 wt % polyvinylidene difluoride, 4.5 wt % acrylonitrile, and 0.5 wt % boron trifluoride in a solvent of dimethylformamide and acetone mixed at a ratio of 7:3, and stirring evenly until the viscosity of the slurry is stable, so as to obtain a solution A with a solid content of 25 wt %. At the same time, dispersing 95 wt % boehmite, 4.5 wt % acrylonitrile, and 0.5 wt % boron trifluoride in a solvent of dimethylformamide and acetone mixed at a ratio of 7:3, and stirring evenly until the viscosity of the slurry is stable, so as to obtain a suspension B with a solid content of 40 wt %.

Performing the same method as in Embodiment 1 by using the solution A and the suspension B as ingredients, so as to make a positive electrode plate coated with the porous layer on both sides. In the finally prepared porous layer, the weight percent of the nanofibers is 65 wt %, the weight percent of the inorganic particles is 30 wt %, and the weight percent of the crosslinker plus the initiator is 5 wt %.

The rest is the same as Embodiment 1.

Embodiment 8

Dispersing 93 wt % polyvinylidene difluoride, 6.3 wt % acrylonitrile, and 0.7 wt % boron trifluoride in a solvent of dimethylformamide and acetone mixed at a ratio of 7:3, and stirring evenly until the viscosity of the slurry is stable, so as to obtain a solution A with a solid content of 25 wt %. At the same time, dispersing 93 wt % boehmite, 6.3 wt % acrylonitrile, and 0.7 wt % boron trifluoride in a solvent of dimethylformamide and acetone mixed at a ratio of 7:3, and stirring evenly until the viscosity of the slurry is stable, so as to obtain a suspension B with a solid content of 40 wt %.

Performing the same method as in Embodiment 1 by using the solution A and the suspension B as ingredients, so as to make a positive electrode plate coated with the porous layer on both sides. In the finally prepared porous layer, the weight percent of the nanofibers is 63 wt %, the weight percent of the inorganic particles is 30 wt %, and the weight percent of the crosslinker plus the initiator is 7 wt %.

The rest is the same as Embodiment 1.

Embodiment 9

Identical to Embodiment 7 except that the polyvinylidene difluoride in the solution A is replaced with polyvinylidene difluoride-hexafluoropropylene (PVDF-HFP).

Embodiment 10

Identical to Embodiment 7 except that the boehmite in the suspension B is replaced with ZrO₂.

Embodiment 11

Identical to Embodiment 7 except that the crosslinker in the solution A is triethylene glycol diacrylate and the initiator is lauroyl peroxide.

Embodiment 12

Identical to Embodiment 7 except that the average particle diameter of the inorganic particles is adjusted to 200 nm.

Embodiment 13

Identical to Embodiment 7 except that the average particle diameter of the inorganic particles is adjusted to 1000 nm.

Embodiment 14

Identical to Embodiment 12 except that the average diameter of the nanofibers is adjusted to 50 nm, and the average particle diameter of the inorganic particles is adjusted to 10000 nm according to Table 1.

Embodiment 15

Identical to Embodiment 13 except that the average pore diameter of the porous layer closer to the positive electrode plate is 200 nm, the average pore diameter of the porous layer farther away from the positive electrode plate is 1000 nm, the average pore diameter of the porous layer in the middle region increases linearly with the increase of the distance from the surface of the electrode plate, so that the average pore diameters of the porous layer change stepwise.

Embodiment 16

Identical to Embodiment 13 except that the electrospinning nozzle is a flat nozzle so as to obtain flat ribbon nanofibers, and, in a cross-section of a nanofiber, a long diameter is 100 nm, a length-to-width ratio is 20, and a ratio of the long diameter of the cross-section of the nanofiber to the average particle diameter of the inorganic particles is 1:10.

Embodiment 17

Dispersing PVDF in a solvent of dimethylformamide and acetone mixed at a ratio of 7:3, and stirring evenly until the viscosity of the slurry is stable, so as to obtain a solution A with a solid content of 25 wt %; and dispersing 95 wt % boehmite, 4.5 wt % acrylonitrile, and 0.5 wt % boron trifluoride in a solvent of dimethylformamide and acetone mixed at a ratio of 7:3, and stirring evenly until the viscosity of the slurry is stable, so as to obtain a suspension B with a solid content of 40 wt %. Dispersing 90 wt % acrylonitrile, and 10 wt % boron trifluoride in a solvent of dimethylformamide and acetone mixed at a ratio of 7:3, and stirring evenly until the viscosity of the slurry is stable, so as to obtain a solution C with a solid content of 25 wt %.

Preparing a coaxial PVDF/(acrylonitrile+boron trifluoride) nanofiber substrate by electrospinning on the surface of the positive electrode plate in Preparation Example 2 by using the solution A and the solution C as ingredients. Selecting a two-tube-sleeved nozzle as an electrospinning nozzle, in which the inner tube is configured to pass the solution A, and a space between the inner tube and the outer tube is configured to pass the solution C. Performing electrospinning to obtain coaxial nanofibers in which the core layer is PVDF fibers and the shell layer is “crosslinker+initiator”. The average diameter of the nanofibers is 100 nm, and a ratio of a core-layer fiber diameter to an outer diameter of a shell-layer fiber is 0.6. Electrospraying inorganic particles onto the surface of the positive electrode plate at the same time of spinning by using the suspension B as an ingredient, where the average particle diameter of the chosen inorganic particles is 1000 nm, and the ratio of the average diameter of the nanofibers to the average particle diameter of the inorganic particles is 1:10. The thickness of the porous layer is 10 μm, the average pore diameter of the porous layer is 200 nm, and the porosity of the porous layer is 75%. Subsequently, repeating the foregoing steps on the other surface of the positive electrode plate, vacuum-drying at 40° C. to remove the dispersants such as dimethylformamide, and then increasing the temperature to 80° C., and keeping the temperature for 6 hours so that crosslinking occurs under heat treatment to obtain a positive electrode plate coated with the porous layer on both sides. In the finally prepared porous layer, the weight percent of the nanofibers is 30 wt %, the weight percent of the inorganic particles is 30 wt %, and the weight percent of the crosslinker plus the initiator is 40 wt %.

Embodiment 18

Identical to Embodiment 17 except that the amount of the passed solution A and solution C in the electrospinning parameters is changed so that in the finally prepared porous layer, the weight percent of nanofibers is 55 wt %, the weight percent of crosslinker plus the initiator is 15 wt %, and the ratio of the core-layer fiber diameter to the outer diameter of the shell-layer fiber is adjusted to 0.85.

Embodiment 19

Identical to Embodiment 17 except that the amount of the passed solution A and solution C in the electrospinning parameters is changed so that in the finally prepared porous layer, the weight percent of nanofibers is 67 wt %, the weight percent of crosslinker plus the initiator is 3 wt %, and the ratio of the core-layer fiber diameter to the outer diameter of the shell-layer fiber is adjusted to 0.98.

Embodiment 20

Identical to Embodiment 13 except that the average particle diameter of the inorganic particles is adjusted to 5000 nm.

Embodiment 21

Identical to Embodiment 13 except that the average pore diameter of the porous layer is adjusted to 800 nm.

Embodiment 22

Identical to Embodiment 13 except that the thickness of the porous layer is adjusted to 5 μm.

Embodiment 23

Identical to Embodiment 13 except that the porosity of the porous layer is adjusted to 90%.

Embodiment 24

Mixing conductive carbon black (Super P), and the styrene butadiene rubber (SBR) at a weight ratio of 97:3, adding deionized water (H₂O) as a solvent, blending the mixture into a slurry with a solid content of 85%, and stirring the slurry evenly. Coating a positive current collector aluminum foil with the slurry evenly, and drying at 110° C. to obtain a positive conductive layer that is 2 μm in thickness.

Mixing lithium cobalt oxide (LiCoO₂) as a positive active material, conductive carbon black (Super P), and polyvinylidene difluoride (PVDF) at a mass ratio of 97.5:1.0:1.5, adding N-methyl-pyrrolidone (NMP) as a solvent, blending the mixture into a slurry with a solid content of 75%, and stirring the slurry evenly. Coating the positive conductive layer of a 10-μm-thick positive current collector aluminum foil with the slurry evenly, and drying the current collector at a temperature of 90° C. to obtain a positive electrode plate on which the conductive layer is 2 μm thick. Repeating the foregoing steps on the other surface of the positive current collector aluminum foil to obtain a positive electrode plate coated with the conductive layer and the positive active material layer on both sides. Then cutting the positive electrode plate into a size of 38 mm×58 mm for future use.

Repeating the steps in Embodiment 13 on the surface of the positive electrode plate to obtain a positive electrode plate with a positive conductive layer.

Embodiment 25

Preparing a positive electrode plate according to the steps in Embodiment 13;

Mixing inorganic ceramic particles aluminum oxide (Al₂O₃) and polyvinylidene difluoride (PVDF) at a weight ratio of 95:5, Adding N-methyl-pyrrolidone (NMP) as a solvent, blending the mixture into a slurry with a solid content of 80%, and stirring the slurry evenly. Coating the porous layer on one side of the prepared positive electrode plate with the slurry evenly, and drying at a temperature of 90° C. to obtain an inorganic material layer. The thickness of the inorganic material layer is 3 μm, the porosity is 30%, and the average pore diameter is 0.8 μm.

Repeating the same steps on the other surface of the positive electrode plate to obtain a positive electrode plate coated with the inorganic material layer on both sides.

Embodiment 26

Identical to Embodiment 1 except that the suspension B contains neither the crosslinker nor the initiator.

Preparing a Lithium-Ion Battery

Aligning and stacking the negative electrode plate prepared in Preparation Example 1 and the positive electrode plate coated with a porous layer and obtained in each embodiment, as shown in FIG. 2. Fixing four corners of the entire stacked structure by using adhesive tape, and then placing the stacked structure into an aluminum plastic film package. Performing top-and-side sealing, injecting the electrolytic solution prepared in the Preparation Example 3, and sealing the package to obtain a stacked-type lithium-ion battery.

Comparative Embodiment 1

Using a 10 μm-thick polyethylene film as a separator, and placing the separator between the negative electrode plate and the positive electrode plate that are prepared in Preparation Example 1 and Preparation Example 2 respectively. Aligning the negative electrode plate, the positive electrode plate, and the separator and stacking them neatly. Fixing four corners of the entire stacked structure by using adhesive tape, and then placing the stacked structure into an aluminum plastic film package. Performing top-and-side sealing, injecting the electrolytic solution prepared in the Preparation Example 3, and sealing the package to obtain a stacked-type lithium-ion battery.

Comparative Embodiment 2

Dispersing 99.9 wt % PVDF, 0.09 wt % acrylonitrile, and 0.01 wt % boron trifluoride in a solvent of DMF and acetone mixed at a ratio of 7:3, and stirring evenly until the viscosity of the slurry is stable, so as to obtain a solution A with a solid content of 25 wt %.

Making a 10-μm-thick PVDF fiber layer by using the solution A as an ingredient by electrospinning on the surface of the positive electrode plate prepared in Preparation Example 2, where the average diameter of the fibers is 100 nm, the average pore diameter of the fiber layer is 400 nm, and the porosity is 75%. Repeating the foregoing steps on the other surface of the positive electrode plate, vacuum-drying at 40° C. to remove the dispersants such as DMF, and then increasing the temperature to 80° C., and keeping the temperature for 6 hours so that a crosslinking process is completed under heat treatment to obtain a positive electrode plate coated with the porous layer on both sides. In the obtained porous layer, the weight percent of polymer fibers is 99.9 wt %, and the weight percent of crosslinker plus the initiator is 0.1 wt %. A micrograph of the fiber layer of Comparative Embodiment 2 is shown in FIG. 4.

Aligning and stacking this positive electrode plate and the negative electrode plate prepared in Preparation Example 1, as shown in FIG. 2. Fixing four corners of the entire stacked structure by using adhesive tape, and then placing the stacked structure into an aluminum plastic film package. Performing top-and-side sealing, injecting the electrolytic solution prepared in the Preparation Example 3, and sealing the package to obtain a stacked-type lithium-ion battery.

The data and test results of the embodiments and comparative embodiments are shown in Table 1.

TABLE 1

Ratio

of

Ratio

average
Ratio of

of

diameter
diameter

50^th-

of
of a first

Av-

Pene-

cycle

nano-
fiber to

Av-
erage

tration

dis-

fibers to
outer
Average
erage
pore

Po-
strength

charge

Weight
Weight
Weight

average
diameter
particle
di-
di-

rosity
P of
Self-
capacity

percent
percent
percent
Weight
particle
of a
diameter
ameter
ameter
Depth
of
porous
dis-
to first-

of
of
of
percent
diameter
second
of
of
of
of
po-
layer
charge
cycle

nano-
inorganic
cross-
of
of
fiber in a
inorganic
nano-
porous
porous
rous
(%)
rate of
dis-

fibers
particles
linker
initiator
inorganic
coaxial
particles
fibers
layer
layer
layer
(N/20
battery
charge

(%)
(%)
(%)
(%)
particles
structure
(nm)
(nm)
(nm)
(μm)
(%)
μm)
(mV/h)
capacity

Com-
—
—

—
—
—
—

—
10
30%
13.1
0.045
92.3%

parative

Embod-

iment 1

Com-
PVDF
—
Acrylo-
Boron
—
—
—
100
400
10
75%
6.4
0.059
93.5%

parative
99.9

nitrile
tri-

Embod-

0.09
fluoride

iment

0.01

2

Embod-
PVDF
Boehmite
Acrylo-
Boron
1:5
—
500
100
200
10
75%
16.6
0.025
95.9%

iment
95
4.9
nitrile
tri-

1

0.09
fluoride

0.01

Embod-
PVDF
Boehmite
Acrylo-
Boron
1:5
—
500
100
200
10
75%
21.3
0.021
96.4%

iment
69.9
30
nitrile
tri-

2

0.09
fluoride

0.01

Embod-
PVDF
Boehmite
Acrylo-
Boron
1:5
—
500
100
200
10
75%
21.6
0.022
96.3%

iment
49.9
50
nitrile
tri-

3

0.09
fluoride

0.01

Embod-
PVDF
Boehmite
Acrylo-
Boron
1:5
—
500
100
200
10
75%
20.1
0.022
96.2%

iment
29.9
70
nitrile
tri-

4

0.09
fluoride

0.01

Embod-
PVDF
Boehmite
Acrylo-
Boron
1:5
—
500
100
200
10
75%
18.2
0.024
96.0%

iment
4.9
95
nitrile
tri-

5

0.09
fluoride

0.01

Embod-
PVDF
Boehmite
Acrylo-
Boron
1:5
—
500
100
200
10
75%
23.4
0.019
96.4%

iment
69
30
nitrile
tri-

6

0.9
fluoride

0.1

Embod-
PVDF
Boehmite
Acrylo-
Boron
1:5
—
500
100
200
10
75%
25.0
0.016
96.3%

iment
65
30
nitrile
tri-

7

4.5
fluoride

0.5

Embod-
PVDF
Boehmite
Acrylo-
Boron
1:5
—
500
100
200
10
75%
25.5
0.016
96.0%

iment
63
30
nitrile
tri-

8

6.3
fluoride

0.7

Embod-
PVDF-
Boehmite
Acrylo-
Boron
1:5
—
500
100
200
10
75%
22.4
0.018
95.1%

iment
HFP
30
nitrile
tri-

9
65

4.5
fluoride

0.5

Embod-
PVDF
ZrO₂
Acrylo-
Boron
1:5
—
500
100
200
10
75%
26.6
0.016
95.9%

iment
65
30
nitrile
tri-

10

4.5
fluoride

0.5

Embod-
PVDF
Boehmite
Trieth-
Lauroy
1:5
—
500
100
200
10
75%
23.1
0.019
94.4%

iment
65
30
ylene
1

11

glycol
peroxide

dia-
0.5

crylate

4.5

Embod-
PVDF
Boehmite
Acrylo-