Positive pole piece, lithium ion battery comprising positive pole piece, and electronic device comprising positive pole piece

Abstract

The invention discloses a positive pole piece, a lithium ion battery comprising the same and an electronic device, the positive pole piece comprises a current collector, at least one surface of the current collector is provided with a first coating, a second coating and a third coating, the first coating is located between the current collector and the second coating, and the third coating is located between the first coating and the second coating. The second coating is positioned between the first coating and the third coating; the first coating comprises lithium iron phosphate, lithium manganese iron phosphate and a fast ion conductor in a mass ratio of (0-6): (6-12): 1; the second coating comprises nickel cobalt lithium manganate, lithium manganese iron phosphate and a fast ion conductor; and the third coating comprises a conductive agent and a fast ion conductor. According to the positive pole piece, by using the first coating, the second coating and the third coating containing specific components, the purpose of improving the rate capability of the lithium ion battery while maintaining high energy density is achieved.

Description

Technical Field

[0001] This application relates to the field of energy storage technology, and more specifically, to a positive electrode, and a lithium-ion battery and electronic device comprising the same. Background Technology

[0002] The low energy density of lithium-ion batteries means that for the same amount of power, the battery is larger and heavier, requiring more materials such as positive and negative electrodes, separators, and electrolytes to achieve the same capacity. This leads to increased costs for lithium-ion batteries and increases the overall weight and shorten the battery life of devices using them. The poor rate performance of lithium-ion batteries stems from their inability to efficiently and safely perform lithium-ion insertion / extraction under high-current charging and discharging scenarios. This shortcoming directly results in unmet fast-charging needs, inability to power high-power devices, and a significantly shortened cycle life. Specifically, the inability to meet fast-charging needs manifests as extremely slow charging speeds, incomplete or nonexistent charging, and greater difficulty in charging at low temperatures. The inability to power high-power devices manifests as a sharp drop in output voltage under high-power loads, reduced discharge capacity, and incompatibility with high-power devices.

[0003] Therefore, it is of great significance to develop a positive electrode that can improve the rate performance of lithium-ion batteries while maintaining high energy density. Summary of the Invention

[0004] The purpose of this application is to address the shortcomings of the prior art by providing a positive electrode, and a lithium-ion battery and electronic device comprising the same.

[0005] To achieve the above objectives, the technical solution adopted in this application is as follows: In a first aspect, this application provides a positive electrode sheet, including a current collector, wherein at least one surface of the current collector is provided with a first coating, a second coating and a third coating, wherein the first coating is located between the current collector and the second coating, and the second coating is located between the first coating and the third coating; The first coating comprises lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), and a fast ion conductor in a mass ratio of (0-6):(6-12):1. The second coating comprises lithium nickel cobalt manganese oxide (NCM), lithium manganese iron phosphate (LMFP), and a fast ion conductor; The third coating comprises a conductive agent and a fast ion conductor.

[0006] The positive electrode sheet of this application achieves the goal of improving the rate performance of lithium-ion batteries while maintaining high energy density by using a first coating, a second coating and a third coating containing specific components.

[0007] Specifically, in a multilayer structure system consisting of a first coating, a second coating, and a third coating, the first coating uses a specific mass ratio of LFP, LMFP, and fast ion conductors to increase the number of lithium-ion insertion sites and improve the energy density of the lithium-ion battery. The second coating, which uses NCM, LMFP, and fast ion conductors, not only improves the energy density of the lithium-ion battery but also reduces lithium-ion transport resistance and shortens the lithium-ion diffusion path, thereby improving the rate performance of the lithium-ion battery. The third coating forms a conductive network by using conductive agents and fast ion conductors, which can improve electronic conduction efficiency and is beneficial to improving the rate performance of the lithium-ion battery.

[0008] Meanwhile, the inventors have verified that the structural order and composition of each coating in the positive electrode sheet described in this application are crucial. If other inappropriate settings are used, such as swapping the order of the first and second coatings, or replacing the composition of the first or second coating, the expected effect cannot be achieved.

[0009] Preferably, in the first coating, the mass ratio of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), and fast ion conductor is one of or between any two of the following: 0:9:1, 1:12:1, 4:9:1, and 6:6:1.

[0010] More preferably, in the first coating, the mass ratio of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), and fast ion conductor is (1-6):(6-12):1.

[0011] Preferably, in the second coating, the mass ratio of lithium nickel cobalt manganese oxide (NCM), lithium manganese iron phosphate (LMFP), and fast ion conductor is (100-700):(20-300):1.

[0012] More preferably, in the second coating, the mass ratio of lithium nickel cobalt manganese oxide (NCM), lithium manganese iron phosphate (LMFP), and fast ion conductor is one of or between any two of the following: 100:300:1, 280:220:1, 420:140:1, 560:50:1, and 700:20:1.

[0013] More preferably, in the second coating, the mass ratio of lithium nickel cobalt manganese oxide (NCM), lithium manganese iron phosphate (LMFP), and fast ion conductor is (280-560):(50-220):1.

[0014] In a multilayer structure system consisting of a specific first coating, a second coating, and a third coating, the second coating uses NCM, LMFP, and fast ion conductors in a specific mass ratio. This not only further improves the energy density of lithium-ion batteries but also further reduces lithium-ion transport resistance and shortens the lithium-ion diffusion path, thereby further improving the rate performance of lithium-ion batteries.

[0015] Preferably, in the third coating, the mass ratio of the conductive agent to the fast ion conductor is (5-900):1.

[0016] More preferably, in the third coating, the mass ratio of the conductive agent to the fast ion conductor is one or any two of the following: 5:1, 10:1, 15:1, 18:1, 20:1, 50:1, 70:1, 100:1, 150:1, 200:1, 250:1, 300:1, 350:1, 400:1, 450:1, 480:1, 500:1, 550:1, 600:1, 650:1, 700:1, 750:1, 800:1, 850:1, and 900:1.

[0017] More preferably, in the third coating, the mass ratio of the conductive agent to the fast ion conductor is (18-900):1.

[0018] In a multilayer structure system consisting of a specific first coating, a second coating, and a third coating, the third coating uses a conductive network formed by a conductive agent and a fast ion conductor with a specific mass ratio, which can better improve the electron conduction efficiency, thereby further improving the rate performance of lithium-ion batteries.

[0019] Preferably, in the third coating, the conductive agent is at least one of sheet-like carbon material, linear carbon material, spherical carbon material, polymer conductive agent, and metal conductive agent.

[0020] In this application, the sheet-like carbon material includes, but is not limited to, graphene; the linear carbon material includes, but is not limited to, at least one of multi-walled carbon nanotubes and single-walled carbon nanotubes; the spherical carbon material includes, but is not limited to, at least one of conductive carbon black, acetylene black, conductive graphite, and carbon microspheres; the polymer conductive agent includes, but is not limited to, at least one of polyaniline (PANI) and poly(3,4-ethylenedioxythiophene) (PEDOT); and the metal conductive agent includes, but is not limited to, at least one of silver (Ag) powder, copper (Cu) powder, nickel (Ni) powder, gold (Au) powder, and aluminum (Al) powder.

[0021] More preferably, in the third coating, the conductive agent includes linear carbon material, polymer conductive agent and metal conductive agent, and the mass ratio of linear carbon material, polymer conductive agent and metal conductive agent is 1:(0-20):(0-20).

[0022] More preferably, the mass ratio of the linear carbon material, the polymer conductive agent, and the metal conductive agent is one of or between any two of the following: 1:0:10, 1:10:0, 1:0.05:20, 1:5:15, 1:10:10, 1:15:5, and 1:20:0.05.

[0023] More preferably, the mass ratio of the linear carbon material, the polymer conductive agent, and the metal conductive agent is 1:(0.05-20):(0.05-20).

[0024] In a multilayer structure system consisting of a specific first coating, a second coating, and a third coating, the conductive agent in the third coating can construct a continuous, short electron transport distance, low contact resistance, and stable conductive network by using a specific mass ratio of linear carbon material, polymer conductive agent, and metal conductive agent. This further improves electron conduction efficiency and thus better enhances the rate performance of lithium-ion batteries.

[0025] More preferably, the mass ratio of the linear carbon material, the polymer conductive agent, and the metal conductive agent is 1:(5-15):(5-15).

[0026] More preferably, in the third coating, the conductive agent includes linear carbon material, polymer conductive agent and spherical carbon material, and the mass ratio of linear carbon material, polymer conductive agent and spherical carbon material is 1:(0-20):(0-20).

[0027] More preferably, the mass ratio of the linear carbon material, the polymer conductive agent, and the spherical carbon material is 1:(0.05-20):(0.05-20).

[0028] More preferably, the mass ratio of the linear carbon material, the polymer conductive agent, and the spherical carbon material is 1:(5-15):(5-15).

[0029] More preferably, the particle size of the metal conductive agent is 5-50 nm, specifically 8-40 nm or 10-30 nm.

[0030] More preferably, the particle size of the spherical carbon material is 10-60 nm, specifically 30-45 nm.

[0031] Preferably, the fast ion conductor includes at least one of LATP (lithium aluminum titanium phosphate), LAGP (lithium germanium aluminum phosphate), LLTO (lithium lanthanum titanate), and LLZO (lithium lanthanum zirconium oxide).

[0032] More preferably, the general chemical formula of the LATP (lithium aluminum titanium phosphate) is Li. 1+a Al a Ti 2-a(PO4)3, where 0 < a ≤ 0.5.

[0033] More preferably, the chemical composition general formula of the LAGP (lithium aluminum germanium phosphate) is Li 1+b Al b Ge 2-b (PO4)3, where 0 < b ≤ 0.5.

[0034] More preferably, the chemical composition general formula of the LLTO (lithium lanthanum titanate) is Li 3c La 2 / 3-c Ti d T 1-d O3, where 0 < c < 2 / 3 and 0 < d ≤ 1, and wherein the T is independently selected from at least one of Nb, W, Hf, Ru, Mo, Nd, Ba, Ga, In, Ge, Sn, Sb, and Se.

[0035] More preferably, the chemical composition general formula of the LLZO (lithium lanthanum zirconium oxide) is Li 7-e La3Zr 2-e M e O 12 , where 0 ≤ e ≤ 1, and wherein the M is independently selected from at least one of Nb, Ta, Ti, Ga, Ge, Y, Gd, W, Mo, Sn, Sb, Se, Ru.

[0036] In the present application, the LATP (lithium aluminum titanium phosphate), LAGP (lithium aluminum germanium phosphate), LLTO (lithium lanthanum titanate), and lithium lanthanum zirconium oxide (LLZO) can be obtained commercially or prepared by conventional preparation methods in the art.

[0037] Preferably, the chemical composition general formula of the lithium nickel cobalt manganese oxide (NCM) is LiNi g Co h Mn 1-g-h O2, where 0.7 ≤ g ≤ 0.9 and 0.1 ≤ h ≤ 0.3.

[0038] Preferably, the chemical composition general formula of the lithium iron manganese phosphate (LMFP) is LiMn i Fe 1-i PO4, where 0.5 ≤ i ≤ 0.9.

[0039] In the present application, the lithium nickel cobalt manganese oxide (NCM) and lithium iron manganese phosphate (LMFP) can be obtained commercially or prepared by conventional preparation methods in the art.

[0040] Preferably, the first coating and / or the second coating and / or the third coating further includes a binder.

[0041] In this application, the adhesive includes, but is not limited to, at least one of polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone (PVP), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer.

[0042] More preferably, in the first coating, the ratio of the total mass of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP) and fast ion conductor to the mass of binder is (lithium iron phosphate + lithium manganese iron phosphate + fast ion conductor): binder = (80-98): (2-20).

[0043] More preferably, in the second coating, the ratio of the total mass of lithium nickel cobalt manganese oxide (NCM), lithium manganese iron phosphate (LMFP) and fast ion conductor to the mass of binder is (Nickel cobalt manganese oxide + Lithium manganese iron phosphate + Fast ion conductor): Binder = (85-97): (3-15).

[0044] More preferably, in the third coating, the ratio of the total mass of the conductive agent and the fast ion conductor to the mass of the binder is (conductive agent + fast ion conductor): binder = (85-97):(3-15).

[0045] Preferably, the first coating and / or the second coating further include a positive conductive agent.

[0046] More preferably, the positive electrode conductive agent includes at least one of conductive carbon black, graphite, expanded graphite, graphene, acetylene black, Ketjen black, carbon dots, carbon fibers, graphitized carbon sheets, carbon nanotubes, activated carbon, and mesoporous carbon, wherein the carbon nanotubes include, but are not limited to, at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0047] More preferably, in the first coating, the ratio of the total mass of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP) and fast ion conductor to the mass of positive electrode conductive agent is (lithium iron phosphate + lithium manganese iron phosphate + fast ion conductor): positive electrode conductive agent = (90-99.5):(0.5-10), specifically (96-99.5):(0.5-4).

[0048] More preferably, in the second coating, the ratio of the total mass of lithium nickel cobalt manganese oxide (NCM), lithium manganese iron phosphate (LMFP) and fast ion conductor to the mass of positive electrode conductive agent is (lithium nickel cobalt manganese oxide + lithium manganese iron phosphate + fast ion conductor): positive electrode conductive agent = (90-99.5):(0.5-10), specifically (96-99.5):(0.5-4).

[0049] Preferably, the thickness of the first coating is 10-20 μm, specifically 15-20 μm.

[0050] Preferably, the thickness of the second coating is 60-80 μm, specifically 60-70 μm.

[0051] Preferably, the thickness of the third coating is 8-20 μm, specifically 10-16 μm.

[0052] Preferably, the current collector is a metal foil or a composite current collector.

[0053] More preferably, the metal foil is aluminum foil.

[0054] Preferably, the thickness of the current collector is 10-20 μm.

[0055] In a second aspect, this application provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte as described in the first aspect.

[0056] Preferably, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side of the negative current collector.

[0057] More preferably, the negative electrode current collector is a metal foil or a composite current collector.

[0058] More preferably, the metal foil is a copper foil.

[0059] More preferably, the negative electrode active material layer includes a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent.

[0060] More preferably, the negative electrode active material includes natural graphite, synthetic graphite, hard carbon, soft carbon, mesophase carbon microspheres (MCMB), Sn, SnO2, SnO, and Li4Ti5O. 12 The material is selected from at least one of LTO, Si material, silicon-carbon (Si-C) composite material, silicon-nitrogen (Si-N) composite material, and silicon-oxygen (Si-O) composite material, wherein the silicon-carbon (Si-C) composite material includes, but is not limited to, silicon carbide (SiC). The negative electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as negative electrode active materials for batteries.

[0061] More preferably, the negative electrode binder comprises at least one of polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, polyacrylamide, styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylic acid-acrylonitrile-acrylamide copolymer, acrylic acid-acrylonitrile-acrylate copolymer, acrylonitrile-butadiene rubber, nitrile rubber, acrylonitrile-styrene-butadiene copolymer, acryloyl rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, sodium carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, carboxymethyl chitosan, polyester, polyamide, polyether, polyimide, polycarboxylic acid ester, polycarboxylic acid, polyurethane, alginate, fluorinated polymer, chlorinated polymer, polyvinylidene fluoride, and poly(vinylidene fluoride)-hexafluoropropylene. The negative electrode binder of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as battery negative electrode binders.

[0062] More preferably, the negative electrode conductive agent includes at least one of carbon, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon tubes, carbon nanotubes, activated carbon, and mesoporous carbon, wherein the carbon nanotubes include, but are not limited to, at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes. The negative electrode conductive agent of this application is not limited to the above materials, but also includes other materials that can be used as battery negative electrode conductive agents.

[0063] Commonly used diaphragms and electrolytes in this field can be used in this application.

[0064] Thirdly, this application provides an electronic device including a lithium-ion battery as described in the second aspect.

[0065] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. The electrochemical device described in this application is also not particularly limited in its use and can be used in any electronic device known in the prior art. According to some embodiments of this application, the electronic device includes, but is not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, and android robots.

[0066] Compared with the prior art, the beneficial effects of this application are as follows: The positive electrode sheet of this application achieves the goal of improving the rate performance of lithium-ion batteries while maintaining high energy density by using a first coating, a second coating and a third coating containing specific components.

[0067] Specifically, in a multilayer structure system consisting of a first coating, a second coating, and a third coating, the first coating uses a specific mass ratio of LFP, LMFP, and fast ion conductors to increase the number of lithium-ion insertion sites and improve the energy density of the lithium-ion battery. The second coating, which uses NCM, LMFP, and fast ion conductors, not only improves the energy density of the lithium-ion battery but also reduces lithium-ion transport resistance and shortens the lithium-ion diffusion path, thereby improving the rate performance of the lithium-ion battery. The third coating forms a conductive network by using conductive agents and fast ion conductors, which can improve electronic conduction efficiency and is beneficial to improving the rate performance of the lithium-ion battery.

[0068] Meanwhile, the inventors have verified that the structural order and composition of each coating in the positive electrode sheet described in this application are crucial. If other inappropriate settings are used, such as swapping the order of the first and second coatings, or replacing the composition of the first or second coating, the expected effect cannot be achieved. Detailed Implementation

[0069] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0070] The experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market.

[0071] In the following examples and comparative examples, the use of some reagents and materials is as follows: Single-walled carbon nanotubes, linear carbon materials, XFS28, 102908, Jiangsu Xianfeng Nanotechnology; Polyaniline (PANI), polymer conductive agent, P824522, McLean; Copper powder, metallic conductive agent, particle size 10-30nm, C804490, McLean; Conductive carbon black, spherical carbon material, particle size 30-45nm, C698937, McLean; Graphene, sheet-like carbon material, G835835, McLean; LLZO (lithium lanthanum zirconium oxide), Li 6.5 La3Zr 1.5 Ta 0.5 O 12The preparation method is as follows: weigh lithium carbonate, lanthanum oxide, zirconium oxide and tantalum oxide according to the molecular weight ratio, mix them; heat treat at 900℃ for 6h to obtain LLZO; LATP (lithium aluminum titanium phosphate), Li 1.3 Al 0.3 Ti 1.7 (PO4)3 is prepared by weighing lithium carbonate, aluminum oxide, titanium oxide and ammonium dihydrogen phosphate according to the molecular weight ratio, mixing them, and heat-treating at 800℃ for 15 h to obtain LATP. LLTO (lithium lanthanum titanate), Li 0.33 La 0.56 TiO3 is prepared by weighing lithium carbonate, lanthanum oxide and titanium dioxide according to the molecular weight ratio, mixing them and heat-treating them at 1100℃ for 12 h to obtain LLTO. LAGP (Lithium Aluminum Germanium Phosphate), Li 1.5 Al 0.5 Ge 1.5 (PO4)3 is prepared by weighing lithium carbonate, aluminum oxide, germanium oxide and ammonium dihydrogen phosphate according to the molecular weight ratio, mixing them, and heat-treating at 800℃ for 15 h to obtain LAGP. Lithium nickel cobalt manganese oxide (NCM), NCM811, LiNi 0.8 Co 0.1 Mn 0.1 O2, commercially available; Lithium manganese iron phosphate (LMFP), LiMn i Fe 1-i PO4, i=0.6, commercially available; Adhesive, polyvinylidene fluoride (PVDF), 768737, McLean.

[0072] Example 1 This embodiment provides a positive electrode sheet, including a current collector (aluminum foil, 13μm thick). A first coating, a second coating, and a third coating are disposed on both surfaces of the current collector. The first coating is located between the current collector and the second coating, and the second coating is located between the first coating and the third coating. The first coating comprises lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), and fast ion conductor (LLZO) in a mass ratio of 4:9:1; The second coating comprises lithium nickel cobalt manganese oxide (NCM), lithium manganese iron phosphate (LMFP), and fast ion conductor (LLZO) in a mass ratio of 420:140:1; The third coating comprises a conductive agent and a fast ion conductor (LLZO) in a mass ratio of 480:1. The conductive agent comprises linear carbon material (single-walled carbon nanotubes), polymer conductive agent (polyaniline, PANI), and metal conductive agent (copper powder) in a mass ratio of 1:10:10. The first coating also includes a binder (polyvinylidene fluoride, PVDF) and a positive electrode conductive agent (conductive carbon black). The ratio of the total mass of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), and fast ion conductor (LLZO) to the mass of the binder (PVDF) is (lithium iron phosphate + lithium manganese iron phosphate + fast ion conductor): binder = 95:5. The ratio of the total mass of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), and fast ion conductor (LLZO) to the mass of the positive electrode conductive agent (conductive carbon black) is (lithium iron phosphate + lithium manganese iron phosphate + fast ion conductor): positive electrode conductive agent = 98:2. The second coating also includes a binder (polyvinylidene fluoride, PVDF) and a positive electrode conductive agent (conductive carbon black). The ratio of the total mass of lithium nickel cobalt manganese oxide (NCM), lithium manganese iron phosphate (LMFP), and fast ion conductor (LLZO) to the mass of the binder (PVDF) is (lithium nickel cobalt manganese oxide + lithium manganese iron phosphate + fast ion conductor): binder = 95:5. The ratio of the total mass of lithium nickel cobalt manganese oxide (NCM), lithium manganese iron phosphate (LMFP), and fast ion conductor (LLZO) to the mass of the positive electrode conductive agent (conductive carbon black) is (lithium iron phosphate + lithium manganese iron phosphate + fast ion conductor): positive electrode conductive agent = 98:2. The third coating also includes a binder (polyvinylidene fluoride, PVDF), and the ratio of the total mass of the conductive agent and the fast ion conductor (LLZO) to the mass of the binder (polyvinylidene fluoride, PVDF) is (conductive agent + fast ion conductor): binder = 95:5; The thickness of the first coating is 18 μm, the thickness of the second coating is 65 μm, and the thickness of the third coating is 14 μm; The above-mentioned method for preparing the positive electrode sheet includes the following steps: S1. Mix lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), fast ion conductor (LLZO), binder (polyvinylidene fluoride, PVDF), and positive electrode conductive agent (conductive carbon black) to obtain the first coating mixture. Add NMP at a ratio of 4500g first coating mixture: 3300g N-methylpyrrolidone (NMP), stir and mix to obtain the first coating slurry. A second coating mixture is prepared by mixing lithium nickel cobalt manganese oxide (NCM), lithium manganese iron phosphate (LMFP), fast ion conductor (LLZO), binder (polyvinylidene fluoride, PVDF), and positive electrode conductive agent (conductive carbon black). NMP is added at a ratio of 15000g second coating mixture to 10800g N-methylpyrrolidone (NMP), and the mixture is stirred to obtain a second coating slurry. The conductive agent, fast ion conductor (LLZO), and binder (polyvinylidene fluoride, PVDF) of the third coating are mixed to obtain the third coating mixture. NMP is added at a ratio of 2000g of the third coating mixture to 2400g of N-methylpyrrolidone (NMP), and the mixture is stirred to obtain the third coating slurry. S2. Coat one surface of the current collector aluminum foil (13μm thick) with the first coating slurry, dry it, coat the second coating slurry, dry it, coat the third coating slurry, and dry it to obtain a positive electrode sheet with a single-sided coating slurry; repeat the above steps on the other surface of the current collector aluminum foil to obtain a positive electrode sheet with a double-sided coating slurry. This embodiment also provides a lithium-ion battery, the preparation method of which includes the following steps: (1) A negative electrode active material silicon carbide (SiC), a negative electrode binder polyacrylic acid, a negative electrode conductive agent conductive carbon black, a negative electrode binder styrene-butadiene rubber, a negative electrode binder sodium carboxymethyl cellulose, and a negative electrode conductive agent single-walled carbon nanotubes are mixed in a mass ratio of 90:3.5:1.3:3.2:1.3:0.7 to obtain a negative electrode mixture. Deionized water is added at a ratio of 11500g negative electrode mixture: 9400g deionized water and stirred to obtain a negative electrode slurry. The negative electrode slurry is coated on one surface of a current collector copper foil (thickness 8μm) and dried to obtain a negative electrode sheet with a single-sided coating of negative electrode active material layer. The above steps are repeated on the other surface of the current collector copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode active material layer. The thickness of the negative electrode active material layer is 110μm. (2) Mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1 to obtain a solvent. Add solute LiPF6 to dissolve and mix evenly to obtain an electrolyte with a LiPF6 concentration of 1 mol / L. (3) The positive electrode sheet, separator (15μm thick polyethylene porous polymer film) and negative electrode sheet prepared above are stacked in sequence and wound to obtain an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried and injected with electrolyte. After vacuum sealing, standing, formation, degassing and edge trimming, a lithium-ion battery is obtained.

[0073] Examples 2-4 and Comparative Examples 1-4 Examples 2-4 and Comparative Examples 1-4 provide different positive electrode sheets and lithium-ion batteries. The difference between them and Example 1 is that the mass ratio of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), and fast ion conductor (LLZO) in the first coating is different. All other aspects are the same as in Example 1, as shown in the table below: Table 1. Mass ratio of lithium iron phosphate, lithium manganese iron phosphate, and fast ion conductor in the first coating of Examples 1-4 and Comparative Examples 1-4. Examples 5-8 and Comparative Examples 5-7 Examples 5-8 and Comparative Examples 5-7 provide different positive electrode sheets and lithium-ion batteries. The difference between them and Example 1 lies in the mass ratio of lithium nickel cobalt manganese oxide (NCM), lithium manganese iron phosphate (LMFP), and fast ion conductor (LLZO) in the second coating. The rest are the same as in Example 1, as shown in the table below: Table 2. Mass ratios of lithium nickel cobalt manganese oxide, lithium manganese iron phosphate, and fast ion conductors in the second coating of Examples 1, 5-8, and Comparative Examples 5-7. Examples 9-11 Examples 9-11 provide different positive electrode sheets and lithium-ion batteries. The difference between them and Example 1 is that the mass ratio of conductive agent to fast ion conductor (LLZO) in the third coating is different. All other aspects are the same as in Example 1, as shown in the table below: Table 3. Mass ratio of conductive agent and fast ion conductor in the third coating of Examples 1 and 9-11 Examples 12-20 Examples 12-20 provide different positive electrode sheets and lithium-ion batteries. The difference between them and Example 1 is that the type of conductive agent in the third coating is different. All other aspects are the same as in Example 1, as shown in the table below: Table 4. Types of conductive agents in the third coating of Examples 1, 12-20 Example 21 This embodiment provides a positive electrode and a lithium-ion battery, which differs from Embodiment 1 in that: (1) Replace all of the LLZO (lithium lanthanum zirconium oxide) in Example 1 with LATP (lithium aluminum titanium phosphate); (2) In the first coating, the ratio of the total mass of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP) and fast ion conductor to the mass of positive electrode conductive agent (conductive carbon black) is = (lithium iron phosphate + lithium manganese iron phosphate + fast ion conductor): positive electrode conductive agent = 99.5:0.5; (3) In the second coating, the ratio of the total mass of lithium nickel cobalt manganese oxide (NCM), lithium manganese iron phosphate (LMFP) and fast ion conductor to the mass of positive electrode conductive agent (conductive carbon black) is = (lithium iron phosphate + lithium manganese iron phosphate + fast ion conductor): positive electrode conductive agent = 96:4; Everything else is the same as in Example 1.

[0074] Example 22 This embodiment provides a positive electrode and a lithium-ion battery, which differs from Embodiment 1 in that: (1) Replace all of the LLZO (lithium lanthanum zirconium oxide) in Example 1 with LLTO (lithium lanthanum titanate); (2) In the first coating, the ratio of the total mass of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP) and fast ion conductor to the mass of positive electrode conductive agent (conductive carbon black) is (lithium iron phosphate + lithium manganese iron phosphate + fast ion conductor): positive electrode conductive agent = 96:4; (3) In the second coating, the ratio of the total mass of lithium nickel cobalt manganese oxide (NCM), lithium manganese iron phosphate (LMFP) and fast ion conductor to the mass of positive electrode conductive agent (conductive carbon black) is = (lithium iron phosphate + lithium manganese iron phosphate + fast ion conductor): positive electrode conductive agent = 99.5:0.5; Everything else is the same as in Example 1.

[0075] Example 23 This embodiment provides a positive electrode and a lithium-ion battery. The difference between this embodiment and Embodiment 1 is that LAGP (lithium aluminum germanium phosphate) is used instead of all LLZO (lithium lanthanum zirconium oxide) in Embodiment 1. All other aspects are the same as in Embodiment 1.

[0076] Comparative Example 8 This comparative example provides a positive electrode and a lithium-ion battery. The difference between this comparative example and Example 1 is that the first coating is not used in this comparative example, but all other aspects are the same as in Example 1.

[0077] Comparative Example 9 This comparative example provides a positive electrode and a lithium-ion battery. The difference between this comparative example and Example 1 is that this comparative example does not use a second coating, but otherwise it is the same as Example 1.

[0078] Comparative Example 10 This comparative example provides a positive electrode and a lithium-ion battery. The difference between this comparative example and Example 1 is that this comparative example does not use a third coating, but otherwise it is the same as Example 1.

[0079] Comparative Example 11 This comparative example provides a positive electrode sheet and a lithium-ion battery, which are different from those in Example 1 in that the positions of the first coating and the second coating are interchanged in this comparative example, that is, the second coating, the first coating and the third coating are sequentially provided on both surfaces of the current collector, and the rest are the same as those in Example 1.

[0080] Performance Test The lithium-ion batteries of the examples and comparative examples were subjected to performance tests, which are specifically as follows: 1. Energy density test In an environment of 25 °C, the lithium-ion battery was charged at a constant current and constant voltage of 0.33 C to 4.25 V, the cut-off current was 0.05 C, and it was left standing for 1 h. Then, it was discharged at a constant current of 1 C to 2.75 V. This cycle was repeated 3 times, and the discharge capacity R (unit: Ah) at the third cycle was recorded. At the same time, the mass m (unit: kg) and the average working voltage D (unit: V) of the lithium-ion battery were measured, and the energy density (unit: Wh / kg) of the lithium-ion battery was calculated according to the following formula: Energy density (unit: Wh / kg) = R × D / m; The qualified standard for the energy density is ≥ 310 Wh / kg; 2. Discharge duration test at 5C rate In an environment of 25 °C, the lithium-ion battery was charged at a constant current and constant voltage of 0.33 C to 4.25 V, the cut-off current was 0.05 C, and it was left standing for 1 h. Then, it was discharged at a constant current of 5 C to 2.75 V, and the discharge duration was recorded, which was denoted as the discharge duration at 5C rate (unit: h); the qualified standard for the discharge duration at 5C rate is ≥ 0.160 h; 3. Temperature rise test at 5C rate In an environment of 25 °C, the temperature on the surface of the lithium-ion battery was measured and denoted as T1 (unit: °C). Then, the lithium-ion battery was charged at a constant current and constant voltage of 0.33 C to 4.25 V, the cut-off current was 0.05 C, and then it was discharged at a constant current of 5 C to 2.75 V. At this time, the temperature on the surface of the lithium-ion battery was measured again and denoted as T2 (unit: °C). The temperature rise at 5C rate (unit: °C) was calculated according to the following formula: Temperature rise at 5C rate (unit: °C) = T2 - T1; The qualified standard for the temperature rise at 5C rate is ≤ 18.0 °C; The longer the discharge duration at 5C rate of the lithium-ion battery and the smaller the temperature rise at 5C rate, the better the rate performance of the lithium-ion battery; The experimental results are as follows: Table 5 Performance test results of each example and comparative example As shown in Table 5, the positive electrode sheet of this application achieves the goal of improving the rate performance of lithium-ion batteries while maintaining high energy density by using a first coating, a second coating and a third coating containing specific components.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A positive electrode plate, characterized in that, The device includes a current collector, on at least one surface of which a first coating, a second coating, and a third coating are disposed, wherein the first coating is located between the current collector and the second coating, and the second coating is located between the first coating and the third coating; The first coating comprises lithium iron phosphate, lithium manganese iron phosphate, and a fast ion conductor in a mass ratio of (0-6):(6-12):

1. The second coating comprises lithium nickel cobalt manganese oxide, lithium manganese iron phosphate, and a fast ion conductor; The third coating comprises a conductive agent and a fast ion conductor.

2. The positive electrode sheet as described in claim 1, characterized in that, Includes at least one of the following (a)-(d): (a) In the first coating, the mass ratio of lithium iron phosphate, lithium manganese iron phosphate and fast ion conductor is (1-6):(6-12):1; (b) In the second coating, the mass ratio of lithium nickel cobalt manganese oxide, lithium manganese iron phosphate and fast ion conductor is (100-700):(20-300):1; (c) In the third coating, the mass ratio of the conductive agent to the fast ion conductor is (5-900):1; (d) In the third coating, the conductive agent is at least one of sheet-like carbon material, linear carbon material, spherical carbon material, polymer conductive agent, and metal conductive agent.

3. The positive electrode sheet as described in claim 2, characterized in that, At least one of the following conditions (1)-(7) must be satisfied: (1) In the second coating, the mass ratio of lithium nickel cobalt manganese oxide, lithium manganese iron phosphate and fast ion conductor is (280-560):(50-220):1; (2) In the third coating, the mass ratio of the conductive agent to the fast ion conductor is (18-900):1; (3) The sheet-like carbon material includes graphene; (4) The linear carbon material includes at least one of multi-walled carbon nanotubes and single-walled carbon nanotubes; (5) The spherical carbon material includes at least one of conductive carbon black, acetylene black, conductive graphite, and carbon microspheres; (6) The polymer conductive agent includes at least one of polyaniline and poly(3,4-ethylenedioxythiophene); (7) The metal conductive agent includes at least one of silver powder, copper powder, nickel powder, gold powder, and aluminum powder.

4. The positive electrode sheet as described in claim 2, characterized in that, Includes at least one of the following (e)-(f): (e) In the third coating, the conductive agent includes linear carbon material, polymer conductive agent and metal conductive agent, and the mass ratio of linear carbon material, polymer conductive agent and metal conductive agent is 1:(0-20):(0-20); (f) In the third coating, the conductive agent includes linear carbon material, polymer conductive agent and spherical carbon material, and the mass ratio of linear carbon material, polymer conductive agent and spherical carbon material is 1:(0-20):(0-20).

5. The positive electrode sheet as described in claim 4, characterized in that, Includes at least one of the following (g)-(h): (g) The mass ratio of the linear carbon material, polymer conductive agent, and metal conductive agent is 1:(0.05-20):(0.05-20); (h) The mass ratio of the linear carbon material, the polymer conductive agent, and the spherical carbon material is 1:(0.05-20):(0.05-20).

6. The positive electrode sheet as described in claim 5, characterized in that, Includes at least one of the following (i)-(j): (i) The mass ratio of the linear carbon material, polymer conductive agent and metal conductive agent is 1:(5-15):(5-15); (j) The mass ratio of the linear carbon material, the polymer conductive agent and the spherical carbon material is 1:(5-15):(5-15).

7. The positive electrode sheet as described in claim 1, characterized in that, Includes at least one of the following (l)-(q): (l) The fast ion conductor includes at least one of LATP, LAGP, LLTO and LLZO; (m) The first coating and / or the second coating and / or the third coating also include an adhesive; (n) The first coating and / or the second coating further include a positive conductive agent; (o) The thickness of the first coating is 10-20 μm; (p) The thickness of the second coating is 60-80 μm; (q) The thickness of the third coating is 8-20 μm.

8. The positive electrode sheet as described in claim 7, characterized in that, At least one of the following (r)-(t) conditions must be satisfied: (r) The positive electrode conductive agent includes at least one of conductive carbon black, graphite, expanded graphite, graphene, acetylene black, Ketjen black, carbon dots, carbon fibers, graphitized carbon sheets, carbon nanotubes, activated carbon, and mesoporous carbon. (s) In the first coating, the ratio of the total mass of lithium iron phosphate, lithium manganese iron phosphate and fast ion conductor to the mass of positive electrode conductive agent is = (lithium iron phosphate + lithium manganese iron phosphate + fast ion conductor): positive electrode conductive agent = (90-99.5): (0.5-10); (t) In the second coating, the ratio of the total mass of lithium nickel cobalt manganese oxide, lithium manganese iron phosphate and fast ion conductor to the mass of positive electrode conductive agent is = (lithium nickel cobalt manganese oxide + lithium manganese iron phosphate + fast ion conductor): positive electrode conductive agent = (90-99.5): (0.5-10).

9. A lithium-ion battery, characterized in that, It includes the positive electrode, negative electrode, separator, and electrolyte as described in any one of claims 1-8.

10. An electronic device, characterized in that, Including the lithium-ion battery as described in claim 9.

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