CN111682165A

CN111682165A - Positive electrode sheet, electrochemical device, and electronic device

Info

Publication number: CN111682165A
Application number: CN202010586264.5A
Authority: CN
Inventors: 王慧鑫; 丰炳梅; 卞春花; 汪颖
Original assignee: Dongguan Poweramp Technology Ltd
Current assignee: Dongguan Poweramp Technology Ltd
Priority date: 2020-06-24
Filing date: 2020-06-24
Publication date: 2020-09-18

Abstract

Embodiments of the present application provide positive electrode sheets, electrochemical devices, and electronic devices. The positive pole piece comprises a current collector, a first layer and a second layer. The first layer includes at least one of a ceramic material, a carbon-based material, a first active material, or an organic. The second layer is disposed between the current collector and the first layer, the second layer includes a second active material, and a surface of the second layer is alkaline. This application has avoided the surface to be direct contact between alkaline second floor and the barrier film coating through setting up the second floor between mass flow body and first layer to the second active material of second floor has been avoided chemical destructive effect to the barrier film coating, has promoted the adhesion force between positive pole piece and the barrier film, has improved electrode subassembly in use's deformation, has improved electrochemical device's life.

Description

Positive electrode sheet, electrochemical device, and electronic device

Technical Field

The present application relates to the field of electronic technologies, and in particular, to a positive electrode sheet, an electrochemical device, and an electronic device.

Background

In the prior electrode assembly structure, the positive electrode plate is directly contacted with a separation film with a bonding layer, and particularly in some electrode assemblies, the surface of a separation film substrate is coated with a polyacrylate material. It has been proved that the polyacrylate coating layer of the separator has a strong adhesive force with a negative active material (e.g., graphite), and the polyacrylate coating layer is coated by an aqueous solution, which is coated on both sides of the separator substrate, and has low processing cost, environmental friendliness and contribution to industrial production, so that it is an industry trend to coat the polyacrylate coating layer on the separator.

However, in the electrode assembly structure of the positive electrode plate containing the active material (for example, ternary material) with an alkaline surface, the surface of the positive electrode plate containing the active material has a strong alkalinity, so that the active material and some high molecular components of the coating of the separator are chemically damaged, the adhesion force between the positive electrode plate and the separator is very weak, and the electrode assembly is seriously deformed when the positive electrode plate and the separator do not have enough adhesion force.

Disclosure of Invention

The first layer with the isolation effect is used for avoiding the chemical damage effect of the anode piece with the alkaline surface and containing the active material on the isolating film coating, so that the adhesive force between the anode piece and the isolating film is improved.

The application provides a positive pole piece, it includes mass flow body, first layer and second floor. The first layer includes at least one of a ceramic material, a carbon-based material, a first active material, or an organic. The second layer is disposed between the current collector and the first layer, the second layer includes a second active material, and a surface of the second layer is alkaline.

In the above positive electrode sheet, wherein the second active material comprises a transition metal oxide having a chemical formula of Li_αNi_xCo_yM1_zN1_βO₂Wherein 0.7 is not less than α is not less than 1.3, 0.3 is not less than x is less than 1, 0 is not less than Y is not less than 0.4, 0 is not less than β is not less than 0.05, x + Y + z + β is 1, M1 is selected from at least one of Mn or Al, N1 is selected from at least one of Mg, B, Ti, Fe, Cu, Zn, Sn, Ca, W, Si, Zr, Nb, Y, Cr, V, Ge, Mo or Sr.

In the above positive electrode sheet, the positive electrode sheet at least satisfies one of the following conditions: the ceramic material comprises at least one of alumina, titania, zirconia, boehmite, or magnesium hydroxide; the carbon-based material comprises at least one of carbon black, carbon nanotubes, graphene, graphite or carbon fibers; the first active material comprises at least one of lithium iron phosphate, lithium ferric manganese phosphate, lithium cobaltate or lithium manganate; the organic matter comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyimide, aramid fiber or polyether.

The application also provides an electrochemical device, which comprises a positive pole piece, a negative pole piece and an isolating membrane arranged between the positive pole piece and the negative pole piece. The positive pole piece comprises a current collector, a first layer and a second layer. The second layer is disposed between the current collector and the separator, and the first layer is between the second layer and the separator. The first layer includes at least one of a ceramic material, a carbon-based material, a first active material, or an organic substance, the second layer includes a second active material, and a surface of the second layer is alkaline.

In the above electrochemical device, wherein the separator comprises a porous substrate and a first adhesive layer, the first adhesive layer is located between the porous substrate and the first layer.

In the above electrochemical device, wherein the first adhesive layer comprises polyacrylate, and the first adhesive layer is in direct contact with the first layer.

In the above electrochemical device, wherein the second active material comprises a transition metal oxide having a chemical formula of Li_αNi_xCo_yM1_zN1_βO₂Wherein 0.7 is not less than α is not less than 1.3, 0.3 is not less than x is not less than 1, 0 is not less than y is not less than 0.4, 0 is not less than β is not less than 0.05, x + y + z + β is 1, M1 is selected from at least one of Mn or Al,n1 is at least one selected from Mg, B, Ti, Fe, Cu, Zn, Sn, Ca, W, Si, Zr, Nb, Y, Cr, V, Ge, Mo or Sr.

In the above electrochemical device, wherein the electrochemical device satisfies at least one of the following conditions: the ceramic material comprises at least one of alumina, titania, zirconia, boehmite, or magnesium hydroxide; the carbon-based material comprises at least one of carbon black, carbon nanotubes, graphene, graphite or carbon fibers; the first active material comprises at least one of lithium iron phosphate, lithium ferric manganese phosphate, lithium cobaltate or lithium manganate; the organic matter comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyimide, aramid fiber or polyether.

In the above electrochemical device, the separator further includes a second adhesive layer, and the second adhesive layer is located between the negative electrode sheet and the porous substrate. The second layer includes a first sublayer and a second sublayer on opposite sides of the current collector, respectively, and the first layer includes a third sublayer and a fourth sublayer. The first sublayer is arranged between the current collector and the third sublayer, the second sublayer is arranged between the current collector and the fourth sublayer, the third sublayer is in direct contact with the first bonding layer, and the first bonding layer comprises polyacrylate.

Embodiments of the present application also provide an electronic device including the electrochemical device described above.

This application is through being alkaline second floor setting with the surface between mass flow body and first layer, has avoided the surface to be direct contact between alkaline second floor and the barrier film coating to avoid the second floor to the chemical destruction effect of barrier film coating, promoted the adhesion stress between positive pole piece and the barrier film, improved electrode subassembly in use's deformation.

Drawings

Fig. 1 shows a schematic view of an electrode assembly of a conventional electrochemical device.

Fig. 2 shows a schematic diagram of a positive electrode sheet according to an embodiment of the present application.

Fig. 3 illustrates a schematic view of an electrode assembly of an electrochemical device according to an embodiment of the present application.

Detailed Description

The following examples are presented to enable those skilled in the art to more fully understand the present application and are not intended to limit the present application in any way.

As shown in fig. 1, a schematic view of an electrode assembly of a conventional electrochemical device is shown. The positive electrode plate comprises a current collector 3 and positive active material layers 2 and 4. The negative electrode tab includes a current collector 10 and negative electrode

active material layers

9, 11. The separator comprises a porous substrate 7 and adhesive layers 6, 8, wherein the adhesive layers 6, 8 may comprise polyacrylate. The isolating film is arranged between the positive pole piece and the negative pole piece. In some positive electrode active material layers 2 and 4 containing, for example, a ternary material, the surface of the positive electrode active material layers 2 and 4 is relatively highly alkaline, and when the positive electrode active material layer 4 and the adhesive layer 6 (for example, polyacrylate) are in direct contact, the positive electrode active material layer 4 exerts a chemical destruction effect on the adhesive layer 6, and the adhesive force between the positive electrode active material layer 4 and the adhesive layer 6 is relatively weak, so that the electrochemical device is easily deformed during the cycle.

To overcome the above problems, some embodiments of the present application provide a positive electrode sheet including a current collector 3, positive active material layers 2, 4, and first layers 1, 5, as shown in fig. 2. In some embodiments, the current collector 3 may be an aluminum foil, but other positive current collectors commonly used in the art may also be used. In some embodiments, the surface of the positive electrode active material layer 2, 4 is alkaline. In some embodiments, the positive electrode active material layers 2, 4 may be referred to as second layers 2, 4, respectively. It should be understood that although the positive electrode active material layer and the first layer are shown in fig. 2 as being located on both sides of the current collector 3, in some embodiments, the positive electrode active material layer and the first layer may be provided on only one side of the current collector 3, for example, including only the positive electrode active material layer 4 and the first layer 5. Alternatively, the first layer may be provided only on one side of the current collector 3, that is, only the positive electrode active material layers 2 and 4 and the first layer 5 may be included. The positive electrode active material layer 4 and the first layer 5 will be described below as an example, and the positive electrode active material layer 2 and the first layer 1 may be provided accordingly.

In some embodiments, as described above, the positive electrode active material layer 4 is disposed between the current collector 3 and the first layer 5. In some embodiments, the first layer comprises at least one of a ceramic material, a carbon-based material, a first active material, or an organic. Through setting up the first layer for when positive pole piece and the barrier film that has the adhesive linkage contact, the surface is alkaline positive active material layer can not with adhesive linkage direct contact, thereby avoided the surface to be alkaline positive active material layer to the chemical destruction effect of adhesive linkage, promoted the adhesion stress between positive pole piece and the barrier film, stronger adhesion stress can strengthen the interface between positive pole piece and the barrier film, and then improves electrochemical device in use's deformation.

In some embodiments, the positive electrode active material layers 2, 4 each independently include a second active material including a transition metal oxide having a chemical formula of Li_αNi_xCo_yM1_zN1_βO₂Wherein 0.7. ltoreq. α. ltoreq.1.3, 0.3. ltoreq. x < 1, 0. ltoreq. Y < 0.4, 0. ltoreq. z < 0.4, 0. ltoreq. β. ltoreq.0.05, and x + Y + z + β.1, M1 is selected from at least one of Mn or Al, N1 is selected from at least one of Mg, B, Ti, Fe, Cu, Zn, Sn, Ca, W, Si, Zr, Nb, Y, Cr, V, Ge, Mo or Sr.

In some embodiments, the ceramic material comprises at least one of alumina, titania, zirconia, boehmite, or magnesium hydroxide. By using the ceramic material in the first layer, the adhesive force between the positive pole piece and the isolating membrane is improved, and meanwhile, the heating shrinkage rate of the isolating membrane can be reduced, the thermal stability is enhanced, and the short circuit at the edges of the positive pole piece and the negative pole piece is prevented. In addition, the ceramic material in the first layer is also beneficial to improving the infiltration between the electrolyte and the positive pole piece.

In some embodiments, the carbon-based material includes at least one of carbon black, carbon nanotubes, graphene, graphite, or carbon fibers. By using the carbon-based material in the first layer, the adhesion force between the positive pole piece and the isolating film is improved, and the conductivity of the positive pole piece can be enhanced at the same time, because the carbon-based material can play a good role in conducting electricity.

In some embodiments, the first active material comprises at least one of lithium iron phosphate, lithium manganese phosphate, lithium cobaltate, or lithium manganate. By using the first active material in the first layer, the capacity of the electrochemical device can be improved while the adhesion of the positive electrode sheet to the separator is improved, because the first active material can provide additional active species to participate in the deintercalation of lithium ions.

In some embodiments, the organic matter comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyimide, aramid, or polyether. By using organic substances in the first layer, the adhesive force between the positive electrode plate and the isolating film is improved, and the organic substances can be used as a waterproof layer to reduce the water content of the positive electrode plate, because the organic substances can block the positive electrode active material layer from contacting with moisture in the surrounding environment, for example, the positive electrode active material layer can be blocked from contacting with moisture in the air in the preparation process of the electrode assembly.

In some embodiments, the positive active material layer of the positive electrode tab may be coated on only a partial area of the current collector. In some embodiments, the first layer may be disposed on the entire area or only a partial area of the positive electrode active material layer. In some embodiments, the first layer may be provided only on a partial region of the positive electrode active material layer to be in contact with the adhesive layer. By adopting the partial area coating mode, the effect of preventing the positive active material layer with alkaline surface from damaging the adhesive layer can be achieved, the weight of the electrode assembly can be reduced, the thickness of the electrode assembly can be reduced, and the energy density can be improved.

In some embodiments, the positive active material layer of the positive electrode tab may include a second active material, a conductive agent, and a binder. The conductive agent of the positive electrode active material layer may include at least one of conductive carbon black, flake graphite, graphene, carbon nanotubes, or carbon fibers. The binder in the positive electrode active material layer may include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, a styrene-acrylate copolymer, a styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. In some embodiments, the mass percentage ratio of the second active material, the conductive agent and the binder in the positive electrode active material layer may be 70-90: 1-15: 1-15, but this is merely an example and any other suitable mass ratio may be employed.

In some embodiments, when a ceramic material, a carbon-based material, and/or a first active material is employed for the first layer, a binder may be added. The binder may include at least one of polyvinylidene fluoride, copolymers of vinylidene fluoride-hexafluoropropylene, styrene-acrylate copolymers, styrene-butadiene copolymers, polyamides, polyacrylonitrile, polyacrylates, polyacrylic acids, polyacrylates, sodium carboxymethylcellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ethers, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. In some embodiments, the mass percentage ratio of the ceramic material, the carbon-based material and/or the first active material to the binder in the first layer may be 80 to 99: 1-20, but this is merely exemplary and not intended to limit the present application, and other suitable ratios may be employed.

As shown in fig. 3, some embodiments of the present application provide an electrochemical device including a positive electrode tab, a negative electrode tab, and a separator disposed between the positive electrode tab and the negative electrode tab. As described above, the positive electrode sheet includes the current collector 3, the positive active material layers 2, 4, and the first layers 1, 5, and a detailed description can be found in the description of fig. 2 and will not be repeated here. In some embodiments, as described above, the positive electrode active material layers 2, 4 may be referred to as second layers 2, 4, respectively, and the second layers 2, 4 may each independently include a second active material. In some embodiments, one of the second layers 2, 4 may be referred to as a first sublayer and the other of the second layers 2, 4 may be referred to as a second sublayer. In some embodiments, one of the first layers 1, 5 may be referred to as a third sublayer, while the other of the first layers 1, 5 may be referred to as a fourth sublayer. In some embodiments, the adhesive layer 6 is referred to as a first adhesive layer, the first adhesive layer is located between the porous substrate 7 and the first layer, further, the first adhesive layer is located between the porous substrate 7 and the third sub-layer 5, and the first adhesive layer is in direct contact with the third sub-layer 5; the adhesive layer 8 is referred to as a second adhesive layer, which is located between the porous substrate 7 and the negative electrode tab.

In some embodiments, the negative electrode tab includes a current collector 10 and a negative

active material layer

9, 11. In some embodiments, current collector 10 of the negative electrode tab may comprise at least one of a copper foil, a nickel foil, or a carbon-based current collector. In some embodiments, the anode

active material layer

9, 11 may include an anode active material, a conductive agent, and a binder. In some embodiments, the negative active material may include at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, or hard carbon. In some embodiments, the negative electrode active material is 70% to 99% by mass of the active material layer. In some embodiments, the conductive agent in the negative electrode active material layer includes at least one of conductive carbon black, acetylene black, carbon nanotubes, ketjen black, conductive graphite, or graphene. In some embodiments, the conductive agent is present in an amount of 0.5% to 10% by mass of the negative electrode active material layer. In some embodiments, the binder in the negative electrode active material layer includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, or styrene butadiene rubber. In some embodiments, the binder is present in an amount of 0.5% to 10% by mass of the negative electrode active material layer. It should be understood that the above description of the negative pole piece is merely exemplary and that other suitable configurations may also be employed.

In some embodiments, the separator comprises a porous substrate 7 and adhesive layers 6, 8, as described above. In some embodiments, the porous substrate 7 may comprise at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one of high density polyethylene, low density polyethylene, or ultra high molecular weight polyethylene. Particularly polyethylene and polypropylene, which have a good effect on preventing short circuits and can improve the stability of the electrochemical device through a turn-off effect. In some embodiments, the thickness of the porous substrate 7 is in the range of about 5 μm to 500 μm. In some embodiments, both adhesive layers 6, 8 may comprise polyacrylate, and both adhesive layers 6, 8 may have a thickness in the range of 5 μm to 100 μm. It should be understood that the above description of the isolation diaphragm is merely exemplary, and that other suitable isolation diaphragm configurations may also be employed. For example, a ceramic layer may be provided between the porous substrate 7 and the spacer adhesive layers 6, 8.

In some embodiments, the electrochemical device comprises a lithium ion battery, but the application is not so limited. In some embodiments, the electrochemical device may further include an electrolyte. In some embodiments, the electrolyte includes, but is not limited to, at least two of dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), Ethylene Carbonate (EC), Propylene Carbonate (PC), Propyl Propionate (PP). In addition, the electrolyte may additionally include at least one of Vinylene Carbonate (VC), fluoroethylene carbonate (FEC), or dinitrile compounds as an electrolyte additive. In some embodiments, the electrolyte further comprises a lithium salt.

In some embodiments of the present application, taking a lithium ion battery as an example, a positive electrode plate, a separator, and a negative electrode plate are sequentially wound or stacked to form an electrode assembly, and then the electrode assembly is packaged in, for example, an aluminum plastic film, and an electrolyte is injected into the electrode assembly, and then the electrode assembly is formed and packaged to obtain the lithium ion battery. And then, performing performance test and cycle test on the prepared lithium ion battery.

Those skilled in the art will appreciate that the above-described methods of making electrochemical devices (e.g., lithium ion batteries) are merely examples. Other methods commonly used in the art may be employed without departing from the disclosure herein.

Embodiments of the present application also provide an electronic device including the electrochemical device described above. The electronic device of the embodiment of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power source, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large household battery, a lithium ion capacitor, and the like.

In the following, some specific examples and comparative examples are listed to better illustrate the present application, wherein a lithium ion battery is taken as an example.

Example 1

Preparing a negative pole piece: the current collector adopts copper foil, and the thickness is 10 mu m. The negative active material adopts graphite, the conductive agent adopts acetylene black, and the binder adopts styrene butadiene rubber and sodium carboxymethylcellulose. Mixing a negative electrode active substance, acetylene black, styrene butadiene rubber and sodium carboxymethylcellulose in a mass percentage of 96: 1: 1.5: 1.5 dispersing the mixture in deionized water to form slurry, uniformly stirring the slurry, coating the slurry on a copper foil, drying the slurry to form a negative electrode active material layer, wherein the thickness of the negative electrode active material layer is 45 mu m, and cold pressing and stripping the negative electrode active material layer to obtain the negative electrode pole piece.

Preparing a positive pole piece: taking a second active material LiNi_0.5Co_0.2Mn_0.3O₂Acetylene black and a binder polyvinylidene fluoride (PVDF) in a mass percentage ratio of 94: 3: and 3, fully stirring and uniformly mixing in an N-methyl pyrrolidone solvent system, and coating on an aluminum foil to obtain a positive active material layer, wherein the thickness of the positive active material layer is 45 microns. Mixing alumina ceramic and a binder vinylidene fluoride according to the mass percentage of 95: 5 fully stirring and mixing the mixture evenly in an N-methyl pyrrolidone solvent systemAnd (3) uniformly coating the mixture on the positive active material layer to form a first layer, wherein the thickness of the first layer is 10 mu m, and drying and cold pressing are carried out to obtain the positive pole piece.

Preparing an isolating membrane: and stirring the polyacrylate to form uniform slurry, coating the slurry on the two side surfaces of the porous base material (polyethylene), and drying to form the isolating membrane.

Preparing an electrolyte: under the environment that the water content is less than 10ppm, lithium hexafluorophosphate and a nonaqueous organic solvent (ethylene carbonate (EC), diethyl carbonate (DEC), Propylene Carbonate (PC), Propyl Propionate (PP), Vinylene Carbonate (VC), wherein the mass percentage ratio of lithium hexafluorophosphate to the Vinylene Carbonate (VC) is 8: 92 was formulated to form an electrolyte having a lithium salt concentration of 1 mol/L.

Preparing a lithium ion battery: and sequentially stacking the positive pole piece, the isolating film and the negative pole piece in sequence to enable the isolating film to be positioned between the positive pole piece and the negative pole piece to play an isolating role, and winding to obtain the electrode assembly. And (3) placing the electrode assembly in an outer packaging aluminum-plastic film, dehydrating at 80 ℃, injecting the electrolyte, packaging, and carrying out technological processes of formation, degassing, shaping and the like to obtain the lithium ion battery.

In examples 2 to 11 and comparative examples 1 to 3, the negative electrode sheet, the separator, the electrolyte and the lithium ion battery were prepared in the same manner as in example 1, and only the positive electrode sheet was prepared in a slightly different manner, and the differences in the parameters are shown in the corresponding tables.

In addition, in the present application, the following method is employed to measure the corresponding parameters.

And (3) testing the adhesive force:

the adhesion test using a universal tester generally requires at least 3 parallel samples. Disassembling an electrode assembly, taking a fixed position of the electrode assembly (ensuring consistency), shearing an isolation film and a pole piece (2 layers of isolation films and 1 layer of pole piece) at the same time, taking the width of the isolation film to be 2cm, removing one layer of isolation film, pasting a double-faced adhesive tape (2cm in width) on one steel plate, adhering the pole piece surface to the double-faced adhesive tape, and rolling the pole piece surface for 3 times by using 2kg of gravity. Tearing the other layer of isolating film for 5mm, sticking double-sided adhesive to the torn isolating film, and sticking white paper on the double-sided adhesive. The steel plate was mounted to the lower clamp and the white paper end was attached to the upper clamp, manipulated with the equipment software and the adhesion value read.

And (3) testing the deformation rate:

the deformation rate is (plate test thickness-micrometer thickness)/micrometer thickness × 100%.

The flat plate thickness test is carried out by a pressure flat plate thickness gauge, and mainly uses two planes to load pressure on an electrode assembly, generally 700g gravity is used, and the distance value between the planes is read, namely the flat plate thickness test.

Micrometer thickness is an electrode assembly thickness measurement using a 0.1 μm high precision micrometer (Mitutoyo brand), typically measuring three points in the middle of the electrode assembly and averaging.

And (3) hot box testing:

and (3) hanging the electrode assembly in a high-temperature furnace, and heating at the speed of 5 +/-3 ℃/min until the electrode assembly generates thermal runaway with smoking or ignition, and simultaneously carrying out thermocouple compatibility on the surface temperature of the electrode assembly by sticking and sensing on the surface of the electrode assembly, wherein the temperature at which the development temperature changes sharply is the thermal runaway temperature.

And (3) testing the wetting angle:

the method comprises the steps of horizontally placing a pole piece, dripping a drop of electrolyte on the surface of the pole piece, placing for 1min to enable the electrolyte to be soaked to a certain stable state, then photographing the drop in the horizontal direction by using a digital camera, measuring the soaking angle of the electrolyte and the pole piece in a data photo, and measuring by using ImageJ image processing software.

Testing the conductivity of the pole piece:

placing the pole piece in a fixture of a conductivity tester, contacting the upper and lower fixtures with the surface of the two sides of the pole piece, wherein the contact area is 1.54cm²And after the resistance value is read by the tester, the conductivity value is converted through the contact area and the thickness of the pole piece.

And (3) capacity testing:

the electrode assembly is used for carrying out discharge capacity test in a constant temperature room at 25 ℃ by using a Xinwei charge-discharge instrument, and the steps are charging to cut-off voltage by using 0.5C current, then carrying out constant voltage to 0.05C, then discharging to cut-off voltage by using 0.2C current, reading a capacity value, testing 10 samples and taking an average value.

Testing the moisture of the pole piece:

about 1g of the pole piece is put into a penicillin bottle, and a moisture tester is used for carrying out moisture test by a Karl Fischer volumetric method, wherein the test temperature is 170 ℃.

In examples 2 to 16, the same preparation method as in example 1 was used except that the material of the first layer and the kind of the second active material were different. In addition, in comparative examples 1 to 6, the first layer was not present.

Table 1 shows the parameters and evaluation results of examples 1 to 4 and comparative examples 1 to 3.

TABLE 1

As can be seen from the comparison of example 1 and comparative example 1, the adhesion of the positive electrode tab including the first layer to the separator was improved from 0.35N/mm to 9.12N/mm, and the deformation rate of the electrode assembly after 500 cycles was reduced from 3.82% to 0.94% under strong adhesion. Generally > 2% is considered unacceptable deformation, thus demonstrating that the first layer acts to increase adhesion and improve deformation. In addition, the thermal stability was judged by the electrode assembly hot box test in the fully charged state, which increased from 126 ℃ to 137 ℃ from the thermal failure temperature of example 1 and comparative example 1. The first layer of alumina ceramic can reduce the heat shrinkage of the isolating film, so as to prevent the short circuit of the edges of the positive and negative pole pieces and prevent the short circuit of the positive and negative pole pieces on the main surface. Moreover, the first layer is found to reduce the wetting angle from 28.9 degrees to 5.4 degrees through the wetting angle test of the electrolyte and the pole piece, so that the problem of the wetting of the electrolyte and the pole piece in the electrode assembly manufacturing process is greatly improved. This benefit results from the higher electrolyte adsorption capacity of the small particle ceramic layer. As is clear from comparison between examples 2 to 4 and comparative examples 1 to 3, examples 2 to 4 can obtain the same effects as described above.

Table 2 shows the parameters and evaluation results of examples 5 to 8 and comparative examples 1, 4 to 5.

TABLE 2

It can be seen from the comparison of example 5 and comparative example 4 that the adhesion of the positive electrode tab including the first layer to the separator was improved from 0.43N/mm to 8.74N/mm, and the deformation rate of the electrode assembly after 500 cycles was reduced from 3.93% to 0.74% under strong adhesion. Generally > 2% is considered unacceptable deformation, thus demonstrating that the first layer acts to increase adhesion and improve deformation. In addition, the conductivity can be obtained by resistance testing of the positive electrode sheet, which is improved from 6.54mS/cm to 8.92mS/cm from the conductivity values of example 5 and comparative example 4. This is because the first layer including carbon black can perform a good conductive function, and eventually, the resistance of the electrode assembly becomes small. As is clear from comparison between examples 6 to 8 and comparative examples 1, 4 to 5, examples 6 to 8 can obtain the same effects as described above.

Table 3 shows the parameters and evaluation results of examples 9 to 12 and comparative examples 1 to 2, 4 and 6.

TABLE 3

It can be seen from the comparison of example 9 and comparative example 4 that the adhesion of the positive electrode tab including the first layer to the separator was improved from 0.43N/mm to 12.73N/mm, and the deformation rate of the electrode assembly after 500 cycles was reduced from 3.93% to 0.91% under strong adhesion. In general>2% was considered to be unacceptable distortion, thus demonstrating that the first layer acts to increase adhesion and improve distortion. In addition, as can be seen from the electrode assembly capacity values of example 9 and comparative example 4, 5122mAh was increased to 5143 mAh. This is due to the additional active LiCoO coating on the positive electrode surface₂Then, LiCoO₂Can also participate in the lithium ion extraction and contribute to the capacity, mostEventually increasing the capacity of the electrode assembly. As is clear from comparison of examples 10 to 12 with comparative examples 1 to 2, 4 and 6, the same effects as those described above can be obtained in the case of examples 10 to 12.

Table 4 shows the parameters and evaluation results of examples 13 to 16 and comparative examples 1 to 2 and 6.

TABLE 4

As can be seen from the comparison of example 13 with comparative example 1, the adhesion of the positive electrode tab including the first layer to the separator was improved from 0.35N/mm to 9.54N/mm, and the deformation rate of the electrode assembly after 500 cycles was reduced from 3.82% to 1.46% under strong adhesion. Generally > 2% is considered unacceptable deformation, thus demonstrating that the first layer acts to increase adhesion and improve deformation. In addition, as can be seen from the positive electrode moisture test data of example 13 and comparative example 1, the water content of the positive electrode sheet was reduced from 687ppm to 420ppm after 3 days of storage under the ambient condition of 25 ℃ temperature and 45% RH humidity. The PVDF high polymer material is covered on the surface of the positive pole compactly, so that the contact between an active material layer of the positive pole piece and moisture in the air can be blocked, and the effect of reducing the moisture content of the positive pole piece is finally achieved. As is clear from comparison of examples 14 to 16 with comparative examples 1 to 2 and 6, the working effects in accordance with those described above can be obtained in examples 14 to 16.

The above description is only a preferred embodiment of the application and is illustrative of the principles of the technology employed. It will be appreciated by those skilled in the art that the scope of the disclosure herein is not limited to the particular combination of features described above, but also encompasses other combinations of features described above or equivalents thereof. For example, the above features and the technical features having similar functions disclosed in the present application are mutually replaced to form the technical solution.

Claims

1. A positive electrode sheet, comprising:

a current collector;

a first layer comprising at least one of a ceramic material, a carbon-based material, a first active material, or an organic;

a second layer disposed between the current collector and the first layer, the second layer including a second active material, and a surface of the second layer being alkaline.

2. The positive electrode sheet according to claim 1, wherein the second active material comprises a transition metal oxide having a chemical formula of Li_αNi_xCo_yM1_zN1_βO₂Wherein 0.7 is not less than α is not less than 1.3, 0.3 is not less than x is less than 1, 0 is not less than Y is not less than 0.4, 0 is not less than β is not less than 0.05, x + Y + z + β is 1, M1 is selected from at least one of Mn or Al, N1 is selected from at least one of Mg, B, Ti, Fe, Cu, Zn, Sn, Ca, W, Si, Zr, Nb, Y, Cr, V, Ge, Mo or Sr.

3. The positive electrode sheet according to claim 1, wherein the positive electrode sheet satisfies at least one of the following conditions:

the ceramic material comprises at least one of alumina, titania, zirconia, boehmite, or magnesium hydroxide;

the carbon-based material comprises at least one of carbon black, carbon nanotubes, graphene, graphite or carbon fibers;

the first active material comprises at least one of lithium iron phosphate, lithium ferric manganese phosphate, lithium cobaltate or lithium manganate;

the organic matter comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyimide, aramid fiber or polyether.

4. An electrochemical device, comprising:

a positive electrode plate;

a negative pole piece;

the isolating film is arranged between the positive pole piece and the negative pole piece;

wherein, positive pole piece includes the mass flow body, first layer and second layer, the second layer sets up the mass flow body with between the barrier film, the first layer is located the second layer with between the barrier film, the first layer includes at least one in ceramic material, carbon-based material, first active material or the organic matter, the second layer includes the second active material, and the surface of second layer is alkaline.

5. The electrochemical device of claim 4, wherein the separator comprises a porous substrate and a first bonding layer, the first bonding layer being located between the porous substrate and the first layer.

6. The electrochemical device of claim 5, wherein the first bonding layer comprises a polyacrylate and the first bonding layer is in direct contact with the first layer.

7. The electrochemical device of claim 4, wherein the second active material comprises a transition metal oxide having a chemical formula of Li_αNi_xCo_yM1_zN1_βO₂Wherein 0.7 is not less than α is not less than 1.3, 0.3 is not less than x is less than 1, 0 is not less than Y is not less than 0.4, 0 is not less than β is not less than 0.05, x + Y + z + β is 1, M1 is selected from at least one of Mn or Al, N1 is selected from at least one of Mg, B, Ti, Fe, Cu, Zn, Sn, Ca, W, Si, Zr, Nb, Y, Cr, V, Ge, Mo or Sr.

8. The electrochemical device of claim 4, wherein the electrochemical device satisfies at least one of the following conditions:

9. The electrochemical device of claim 6, wherein the separator further comprises a second bonding layer between the negative electrode sheet and the porous substrate, the second layer comprising a first sublayer and a second sublayer on opposite sides of the current collector, respectively, the first layer comprising a third sublayer and a fourth sublayer, the first sublayer disposed between the current collector and the third sublayer, the second sublayer disposed between the current collector and the fourth sublayer, the third sublayer in direct contact with the first bonding layer.

10. An electronic device comprising the electrochemical device according to any one of claims 4 to 9.