Negative pole piece, electrochemical device comprising negative pole piece and electronic equipment

Abstract

The invention discloses a negative pole piece, an electrochemical device containing the negative pole piece and electronic equipment, and belongs to the technical field of batteries. According to the negative electrode plate disclosed by the invention, the two negative electrode active material layers and the outer protection layer are arranged on at least one side surface of the current collector, and the two negative electrode active material layers can obviously improve the conductivity of the electrode plate, reduce the interface impedance, improve the reaction kinetics in the electrode plate and improve the cycle performance of the battery; and the protective layer can effectively resist the corrosion effect of electrolyte, reduce surface side reaction, relieve local heat accumulation, improve heat conduction and improve the stability of the negative pole piece, so that the cycle performance and the safety performance of the battery are improved.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, and in particular to negative electrode plates and electrochemical devices and electronic devices containing them. Background Technology

[0002] With the increasing demand for high capacity and high energy density in lithium-ion batteries, the silicon content in anode materials is constantly increasing, leading to more severe volume expansion during charging. Furthermore, as the battery cycles, the volume effect of the silicon anode worsens significantly, easily causing rapid capacity decay, decreased cycle stability, and localized separator failure, posing safety hazards. In addition, silicon anode sheets also suffer from poor conductivity, high internal resistance, poor interface stability with the electrolyte, and severe side reactions, resulting in increased battery impedance, reduced electrolyte retention coefficient, and significantly deteriorated cycle stability. Summary of the Invention

[0003] The purpose of this application is to solve the technical problems of high expansion rate, high impedance, low electrolyte retention coefficient and poor cycle performance of silicon-based negative electrodes in the prior art, and to propose a negative electrode sheet and an electrochemical device and electronic device containing it.

[0004] To achieve the above objectives, in a first aspect, this application provides a negative electrode current collector, and a first negative electrode active material layer, a second negative electrode active material layer, and a protective layer stacked on at least one surface of the negative electrode current collector, wherein the first negative electrode active material is close to and in contact with the current collector, and the second negative electrode active material layer is disposed between the first negative electrode active material layer and the protective layer. The first negative electrode active material layer includes a first silicon-carbon material and a metal phosphide; The second negative electrode active material layer includes a second silicon-carbon material and graphite; The protective layer comprises a metal nitride.

[0005] In the negative electrode sheet of this application, two layers of negative electrode active material and an outer protective layer are present on at least one side surface of the current collector. The first negative electrode active material layer contains a metal phosphide (MPa). x During the charging and discharging process of a battery, the following reaction occurs: MP x +Li++xe - =M+LiP xIn this process, the MP bonds between the metal and phosphorus elements in the metal phosphide are broken, forming nano-metal particles and lithium phosphate. These nano-metal particles improve the local conductive network, reduce impedance, and enhance the reaction kinetics of the first negative electrode active material layer. The second negative electrode active material layer, composed of graphite and silicon-carbon materials, further improves surface kinetics and reduces interfacial impedance. A protective layer includes a metal nitride, a ceramic material with high stability and thermal conductivity. Located on the outer surface of the two negative electrode active material layers, it effectively resists electrolyte corrosion, reduces surface side reactions, alleviates local heat accumulation, improves heat conduction, and enhances the stability of the negative electrode, thereby improving the battery's cycle performance and safety. Furthermore, the metal phosphide in the first negative electrode active material layer improves conductivity, balancing the charge state between the two layers and preventing severe volume expansion caused by deep lithium intercalation in the surface silicon-carbon layer, effectively reducing the battery's expansion rate.

[0006] In some embodiments, the first negative electrode active material layer satisfies the following relationship: 4≤x1 / z≤7.5, where x1 is the weight part of the first silicon carbide material in the first negative electrode active material layer, and z is the weight part of the metal phosphide in the first negative electrode active material layer.

[0007] In some embodiments, the metal phosphide in the first negative electrode active material layer includes at least one of tin phosphide, copper phosphide, iron phosphide, cobalt phosphide, nickel phosphide, zinc phosphide, and aluminum phosphide.

[0008] In some embodiments, the negative electrode sheet satisfies the following relationship: 10%≤x2≤90%, 10%≤y≤90%, where x2 is the mass percentage of the second silicon-carbon material in the second negative electrode active material layer, and y is the mass percentage of graphite in the second negative electrode active material layer.

[0009] In some embodiments, the Dv50 of the first silicon-carbon material in the first negative electrode active material layer is 10-20 μm.

[0010] In some embodiments, the Dv50 of the second silicon-carbon material is less than 10 μm.

[0011] In some embodiments, the negative electrode sheet satisfies the following relationship: 0.2≤L1 / L0≤2.5, where L0 is the thickness of the first negative electrode active material layer in μm; and L1 is the thickness of the second negative electrode active material layer in μm.

[0012] In some embodiments, the negative electrode sheet satisfies the following relationship: L0+L1+L2≤120μm, where L0 is the thickness of the first negative electrode active material layer in μm; L1 is the thickness of the second negative electrode active material layer in μm; and L2 is the thickness of the protective layer in μm.

[0013] In some embodiments, the negative electrode sheet satisfies the following relationship: 0.01 < L2 / L1 < 0.12, where L1 is the thickness of the second negative electrode active material layer in μm; and L2 is the thickness of the protective layer in μm.

[0014] In some embodiments, the metal nitride includes at least one of AlN, W2N, TiN, Zn3N2, and Mg3N2.

[0015] Secondly, this application provides an electrochemical device including the aforementioned negative electrode plate.

[0016] Thirdly, this application provides an electronic device including the aforementioned electrochemical device.

[0017] Compared with the prior art, the beneficial effects of this application are as follows: In the negative electrode sheet of this application, there are two layers of negative electrode active material and an outer protective layer on at least one side surface of the current collector. The two layers of negative electrode active material can significantly improve the conductivity of the electrode sheet, reduce the interfacial impedance, improve the reaction kinetics inside the electrode sheet, and improve the cycle performance of the battery. Moreover, the protective layer can effectively resist the corrosion of the electrolyte, reduce surface side reactions, alleviate local heat accumulation, improve heat conduction, and improve the stability of the negative electrode sheet, thereby improving the cycle performance and safety performance of the battery. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the negative electrode sheet in Example 1. In the figure, 1 is the first negative electrode active material layer, 2 is the second negative electrode active material layer, and 3 is the protective layer. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0021] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0022] In the detailed description and claims, a list of items connected by the terms "one of," "among," "a kind of," or other similar terms may mean any of the listed items. For example, if items A and B are listed, then the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, then the phrase "one of A, B, and C" means only A; only B; or only C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0023] In a first aspect, this application provides a negative electrode current collector, and a first negative electrode active material layer, a second negative electrode active material layer and a protective layer stacked on at least one surface of the negative electrode current collector, wherein the first negative electrode active material is close to and in contact with the current collector, and the second negative electrode active material layer is disposed between the first negative electrode material layer and the protective layer. The first negative electrode active material layer includes a first silicon-carbon material and a metal phosphide; The second negative electrode active material layer includes a second silicon-carbon material and graphite; The protective layer comprises a metal nitride.

[0024] In the negative electrode sheet of this application, two layers of negative electrode active material and an outer protective layer are disposed on at least one side surface of the current collector, wherein the first negative electrode active material layer contains metal phosphide (MPa). x During the charging and discharging process of a battery, the following reaction occurs: MP x +Li++xe - =M+LiP xIn this process, the MP bonds between the metal and phosphorus elements in the metal phosphide are broken, forming nano-metal particles and lithium phosphate. These nano-metal particles improve the local conductive network, reduce impedance, and enhance the reaction kinetics of the first negative electrode active material layer. The second negative electrode active material layer, composed of graphite and silicon-carbon materials, further improves surface kinetics and reduces interfacial impedance. A protective layer includes a metal nitride, a ceramic material with high stability and thermal conductivity. Located on the outer surface of the two negative electrode active material layers, it effectively resists electrolyte corrosion, reduces surface side reactions, alleviates local heat accumulation, improves heat conduction, and enhances the stability of the negative electrode, thereby improving the battery's cycle performance and safety. Furthermore, the metal phosphide in the first negative electrode active material layer improves conductivity, balancing the charge state between the two layers and preventing severe volume expansion caused by deep lithium intercalation in the surface silicon-carbon layer, effectively reducing the battery's expansion rate.

[0025] In some embodiments, the first negative electrode active material layer satisfies the following relationship: 4≤x1 / z≤7.5, where x1 is the weight part of the first silicon carbide material in the first negative electrode active material layer, and z is the weight part of the metal phosphide in the first negative electrode active material layer.

[0026] In some embodiments, based on a total weight of 100 parts of the first silicon carbide material and metal phosphide in the first negative electrode active material layer, x1 is 80-88 parts by weight. For example, it can specifically be 80 parts by weight, 81 parts by weight, 82 parts by weight, 83 parts by weight, 84 parts by weight, 85 parts by weight, 86 parts by weight, 87 parts by weight, or 88 parts by weight, or within the range of any two of the above values.

[0027] In some embodiments, based on a total weight of 100 parts of the first silicon carbide material and metal phosphide in the first negative electrode active material layer, z is 12-20 parts by weight; for example, it can specifically be 2 parts by weight, 12.5 parts by weight, 13 parts by weight, 13.5 parts by weight, 14 parts by weight, 14.5 parts by weight, 15 parts by weight, 15.5 parts by weight, 16 parts by weight, 16.5 parts by weight, 17 parts by weight, 17.5 parts by weight, 18 parts by weight, 18.5 parts by weight, 19 parts by weight, 19.5 parts by weight, 20 parts by weight, or within the range of any two of the above values.

[0028] In some embodiments, the first negative electrode active material layer further includes at least one of a binder and a dispersant; based on a total weight of 100 parts of the first silicon carbide material and metal phosphide in the first negative electrode active material layer, the binder is 1-20 parts by weight and the dispersant is 0.1-5 parts by weight.

[0029] In some embodiments, the mass percentage of silicon in the first silicon-carbon active material and the second silicon-carbon active material is 5%-46%, respectively; for example, it can be 5%, 8%, 11%, 14%, 17%, 20%, 23%, 26%, 29%, 32%, 35%, 38%, 41%, 44%, 46%, or within any two of the above values.

[0030] In some embodiments, the Dv50 of the first silicon-carbon material in the first negative electrode active material layer is 10-20 μm. Exemplarily, it can be 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, 20 μm, or within the range of any two of the above values.

[0031] In some embodiments, the metal phosphide includes at least one selected from tin phosphide, copper phosphide, iron phosphide, cobalt phosphide, nickel phosphide, zinc phosphide, and aluminum phosphide. All of the above-mentioned metal phosphides undergo the following reaction during battery charging and discharging: MP x +Li++xe - =M+LiP x In this process, the MP bond between the metal element and the phosphorus element in the metal phosphide breaks, forming nano-metal particles and lithium phosphate. The nano-metal particles can improve the local conductive network, reduce impedance, and improve the reaction kinetics of the first negative electrode active material layer, thereby improving the cycle performance of the battery and reducing impedance.

[0032] In some embodiments, the Dv50 of the metal phosphide in the first negative electrode active material layer is 1-10 μm. For example, it can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 100 μm, or within any two of the above values.

[0033] In some embodiments, the negative electrode sheet satisfies the following relationship: 10%≤x2≤90%, 10%≤y≤90%, where x2 is the mass percentage of the second silicon-carbon material in the second negative electrode active material layer, and y is the mass percentage of graphite in the second negative electrode active material layer.

[0034] In some implementations, x2 is 10%-90%, and for example, it can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or within the range of any two of the above values.

[0035] In some implementations, y2 is 10%-90%, and for example, it can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or within the range of any two of the above values.

[0036] In some embodiments, the second negative electrode active material layer further includes at least one of a binder and a dispersant; the mass percentage of the binder in the second negative electrode active material layer is 1%-20%, and for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or within any two of the above values; the weight percentage of the dispersant is 0.1%-5%, and for example, it can be 0.1%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or within any two of the above values.

[0037] In some embodiments, the Dv50 of the second silicon-carbon material is less than 10 μm. For example, it can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 9.5 μm, or within the range of any two of the above values.

[0038] The larger particle size of the first silicon-carbon active material is beneficial for leaving gaps / pores to improve electrolyte wetting in the first negative electrode active material layer. This overcomes the defect that the first negative electrode active material layer is located close to the current collector side and below the second negative electrode active material layer and the protective layer, which makes it difficult to wet the electrolyte and thus affects its kinetics. This can further improve the performance of the battery.

[0039] In some embodiments, the graphite in the second negative electrode active material layer has a Dv50 of 1-10 μm. For example, it can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 100 μm, or within any two of the above values.

[0040] In some embodiments, the negative electrode sheet satisfies the following relationship: 0.2≤L1 / L0≤2.5, where L0 is the thickness of the first negative electrode active material layer in μm; and L1 is the thickness of the second negative electrode active material layer in μm.

[0041] In some implementations, L0 is 25-68 μm. For example, it can specifically be 25 μm, 27 μm, 29 μm, 31 μm, 33 μm, 35 μm, 37 μm, 39 μm, 41 μm, 43 μm, 45 μm, 47 μm, 49 μm, 51 μm, 53 μm, 55 μm, 57 μm, 59 μm, 61 μm, 63 μm, 65 μm, 67 μm, 68 μm, or within the range of any two of the above values.

[0042] In some embodiments, L1 is 17-67 μm, and exemplarily, it can be 17 μm, 19 μm, 21 μm, 23 μm, 25 μm, 27 μm, 29 μm, 31 μm, 33 μm, 35 μm, 37 μm, 39 μm, 41 μm, 43 μm, 45 μm, 47 μm, 49 μm, 51 μm, 53 μm, 55 μm, 57 μm, 59 μm, 61 μm, 63 μm, 65 μm, 67 μm, or within any two of the above values. In some embodiments, the negative electrode sheet satisfies the following relationship: L0 + L1 + L2 ≤ 120 μm, where L0 is the thickness of the first negative electrode active material layer in μm; L1 is the thickness of the second negative electrode active material layer in μm; and L2 is the thickness of the protective layer in μm.

[0043] In some embodiments, the negative electrode sheet satisfies the following relationship: 0.01 < L2 / L1 < 0.12, where L1 is the thickness of the second negative electrode active material layer in μm; and L2 is the thickness of the protective layer in μm.

[0044] In some implementations, L2 is 1.2μm-3μm. For example, it can specifically be 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2.0μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, 2.5μm, 2.6μm, 2.7μm, 2.8μm, 2.9μm, 3.0μm, or within the range of any two of the above values.

[0045] In some embodiments, the metal nitride includes at least one of AlN, W2N, TiN, Zn3N2, and Mg3N2.

[0046] In some embodiments, the Dv50 of the metal nitride is 0.1-1.5 μm. Exemplarily, it can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, or within the range of any two of the above values.

[0047] In some embodiments, the mass percentage of metal nitride in the protective layer is 75%-98%, and for example, it can be 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or within any two of the above values.

[0048] In some embodiments, the protective layer further includes an adhesive, the adhesive in the protective layer having a mass percentage of 2%-25%, exemplarily 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or within any two of the above values. In some embodiments, both sides of the negative electrode current collector sequentially include a first negative electrode active material layer, a second negative electrode active material layer, and a protective layer, the first negative electrode active material layer being close to and in contact with the current collector, and the second negative electrode active material layer being disposed between the first negative electrode active material layer and the protective layer.

[0049] In some embodiments, the negative current collector is a metal foil or a composite current collector.

[0050] In some embodiments, the metal foil is a copper foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate.

[0051] In some embodiments, the conductive layer may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon tube, carbon nanotube, activated carbon, and mesoporous carbon.

[0052] In some embodiments, the binders in the first negative electrode active material layer, the second negative electrode active material layer, and the protective layer are each independently selected from 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, and polyester. The negative electrode binder of this application is not limited to the above materials, but also includes other materials that can be used as battery negative electrode binders. These materials include vinyl ester, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, 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 (PVDF), polyvinylpyrrolidone (PVP), and poly(vinylidene fluoride)-hexafluoropropylene.

[0053] In some embodiments, the dispersant in the first negative electrode active material layer and the second negative electrode active material layer includes carboxymethyl cellulose (CMC).

[0054] In some embodiments, the first negative electrode active material layer and / or the second negative electrode active material layer further include other negative electrode conductive agents. These conductive agents may include at least one of the following: carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, activated carbon, and mesoporous carbon. The negative electrode conductive agents in this application are not limited to the above-mentioned materials and also include other materials that can be used as battery negative electrode conductive agents.

[0055] In one embodiment, in the negative electrode sheet, the mass percentage content of the negative electrode conductive agent is 20%-50% based on the mass of the first negative electrode active material layer or the second negative electrode active material layer. In a second aspect, this application provides an electrochemical device including the aforementioned negative electrode sheet.

[0056] Electrochemical devices include any apparatus in which an electrochemical reaction occurs to convert chemical energy into electrical energy and vice versa, including, but not limited to, all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0057] In some embodiments, the electrochemical device includes a positive electrode, a negative electrode, an electrolyte, and a membrane located between the positive and negative electrodes.

[0058] In some embodiments, the positive electrode may include a positive current collector and a layer of positive active material disposed on at least one side of the positive current collector.

[0059] In some embodiments, the positive current collector is a metal foil or a composite current collector.

[0060] In some embodiments, the metal foil is aluminum foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate.

[0061] In some embodiments, the conductive layer may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon tube, carbon nanotube, activated carbon, and mesoporous carbon.

[0062] In some embodiments, the positive electrode active material layer may include a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent.

[0063] In some embodiments, the positive electrode active material is selected from LiCoO2, LiNiO2, and LiNi x Mn y O2, Li 1+ z Ni x Mn y Co 1-x-y O2, LiNi x Co y Al z The group consisting of O2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, Li2MnO3, LiFeO2, LiFePO4, LiMnPO4, and combinations thereof, wherein each x is independently 0.2 to 0.9; each y is independently 0.1 to 0.45; and each z is independently 0 to 0.2. The positive electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as positive electrode active materials.

[0064] In some embodiments, the positive electrode active material is Li 1+x Ni a Mn b Co c Al (1-a-b-c) O2; where -0.2≤x≤0.2, 0≤a<1, 0≤b<1, 0≤c<1 and a+b+c≤1.

[0065] In some embodiments, the positive electrode active material has the general formula Li 1+x Ni a Mn b Co c Al (1-a-b-c) O2, where 0.33≤a≤0.92, 0.33≤a≤0.9, 0.33≤a≤0.8, 0.5≤a≤0.92, 0.5≤a≤0.9, 0.5≤a≤0.8, 0.6≤a≤0.92 or 0.6≤a≤0.9; 0≤b≤0.5, 0≤b≤0.3, 0.1≤b≤0.5, 0.1≤b≤0.4, 0.1≤b≤0.3, 0.1≤b≤0.2 or 0.2≤b≤0.5; 0≤c≤0.5, 0≤c≤0.3, 0.1≤c≤0.5, 0.1≤c≤0.4, 0.1≤c≤0.3, 0.1≤c≤0.2 or 0.2≤c≤0.5.

[0066] In some embodiments, the positive electrode active material is doped with a dopant selected from the group consisting of Fe, Ni, Mn, Al, Mg, Zn, Ti, La, Ce, Sn, Zr, Ru, Si, Ge, and combinations thereof. In some embodiments, the dopant is not Fe, Ni, Mn, Mg, Zn, Ti, La, Ce, Ru, Si, or Ge. In some embodiments, the dopant is not Al, Sn, or Zr.

[0067] In some embodiments, the positive electrode active material may include LiNi. 0.33 Mn 0.33 Co 0.33 O2, LiNiO2, LiNi 0.4 Mn 0.4 Co 0.2 O2, LiNi 0.5 Mn 0.3 Co 0.2 O2, LiNi 0.6 Mn 0.2 Co 0.2 O2, LiNi 0.7 Mn 0.15 Co 0.15 O2, LiNi 0.8 Mn 0.1 Co 0.1 O2, LiNi 0.92 Mn 0.04 Co 0.04 O2, LiNi 0.8 Co 0.15 Al 0.05 At least one of O2.

[0068] In some embodiments, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-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. The positive electrode binder of this application is not limited to the above materials, but also includes other materials that can be used as battery positive electrode binders.

[0069] In some embodiments, the positive electrode conductive agent may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon tubes, carbon nanotubes, activated carbon, and mesoporous carbon.

[0070] The positive electrode conductive agent of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as positive electrode conductive agents for batteries.

[0071] The separator separates the negative and positive electrodes and provides a pathway for lithium-ion migration. The use of the separator is not particularly limited, as long as it is a separator commonly used in lithium-ion secondary batteries. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte permeability are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes formed from polyolefin-based polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, ethylene / methacrylate copolymers, etc.) or laminated structures with two or more layers. Alternatively, nonwoven fabrics formed from conventional porous nonwoven fabrics (e.g., glass fibers with high melting points, polyethylene terephthalate fibers, etc.) can be used. Furthermore, coated separators containing ceramic components or polymer materials to ensure heat resistance or mechanical strength can be used, and can optionally be used as single-layer or multi-layer structures.

[0072] Generally, a diaphragm includes a substrate and a coating applied to the surface of the substrate.

[0073] In some embodiments, the substrate is, but is not limited to, at least one of polyolefins, polyesters, polyacetals, polyamides, polyethylene terephthalate, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyacrylonitrile, polyvinylidene fluoride, polyoxymethylene, polyoxymethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polysulfone, and polymethyl methacrylate. Some non-limiting examples of polyolefins include at least one of polyethylene (PE), ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), polypropylene (PP), polyethylene-polypropylene copolymer (PE-PP), and polyethylene-polypropylene-polyethylene copolymer.

[0074] In some embodiments, the coating is disposed on one side of the substrate. In some embodiments, the coating is disposed on both sides of the substrate. The inorganic filler comprises Al2O3, SiO2, TiO2, ZrO2, Mg(OH)2, MgO, SnO2, CaCO3, BaSO4, TiN, AlN, Na2OmTiO2, K2OnTiO2, BaOx, MTiO3, and combinations thereof, wherein m is 3 or 6, n is 1, 2, 4, 6, or 8, x is 1 or 2, and M is Ba, Sr, or Ca. The inorganic filler may be spherical, flake-shaped, disc-shaped, needle-shaped, cylindrical, irregular, or other known particle shapes.

[0075] In some embodiments, the inorganic material is not spherical, sheet-like, disc-like, needle-like, cylindrical, or irregular in shape. The inorganic filler includes one or more of alumina, hydrated alumina, boehmite, magnesium hydroxide, magnesium oxide, titanium dioxide, zirconium oxide, and barium sulfate.

[0076] In some implementations, the binder is a water-soluble polymer.

[0077] In some implementations, the water-soluble polymer is a homopolymer or copolymer.

[0078] In some embodiments, the water-soluble binder includes at least one of polyamide, polycarboxylate, polycarboxylic acid, polyacrylic acid, polyacrylate, polymethacrylic acid, polymethacrylate, polyvinyl alcohol, polyvinyl acetate, polyacrylamide, cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, carboxymethyl cellulose (CMC), cyanoethyl cellulose, acrylonitrile rubber (NBR), styrene-butadiene rubber (SBR), and latex.

[0079] In some embodiments, the electrolyte may include at least one of a gel electrolyte, a solid electrolyte, and a liquid electrolyte.

[0080] In some embodiments, the liquid electrolyte may include a non-aqueous solvent and a lithium salt.

[0081] In some embodiments, the lithium salt may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate.

[0082] In some embodiments, the non-aqueous solvent may be at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds.

[0083] In some embodiments, the carbonate compound may include at least one of chain carbonate compounds, cyclic carbonate compounds, and fluorocarbonate compounds.

[0084] In some embodiments, the chain carbonate compound may include diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof.

[0085] In some embodiments, the cyclic carbonate compound may include ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof.

[0086] In some embodiments, the fluorocarbonate compound may include at least one of 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-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate.

[0087] In some embodiments, the carboxylic acid ester compound may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonate lactone, caprolactone, and methyl formate.

[0088] In some embodiments, the ether compound may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

[0089] In some embodiments, the non-aqueous solvent may also include at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters.

[0090] Thirdly, this application provides an electronic device including the aforementioned electrochemical device.

[0091] 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 of this invention is not particularly limited in its application and can be used in any electronic device known in the prior art. According to some embodiments of the invention, 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.

[0092] Test method: (1) Expansion test and liquid retention coefficient calculation: A lithium-ion battery is considered fully charged when it is charged at a constant current and constant voltage of 0.5C to 4.55V (0.02C cutoff) and discharged at a constant current of 0.2C to 2.8V.

[0093] The lithium-ion battery is charged at a constant current and constant voltage of 0.5C to 4.0V (0.02C cutoff) as a half-charge state.

[0094] Lithium-ion battery expansion rate (%) = (full charge thickness H1 / half charge thickness H0) × 100%.

[0095] Liquid retention coefficient calculation: Liquid retention volume (g) / 2.8V discharge capacity (Ah).

[0096] (2) Hot box test The lithium-ion battery was placed in an oven, and the oven temperature was increased to above 130℃ at a rate of 5±2℃ / min. The upper limit temperature of the oven was obtained through multiple tests. The test was stopped after maintaining the upper limit temperature for 30 minutes. If the lithium-ion battery did not catch fire or explode at this time, the test was passed, and the upper limit temperature was recorded.

[0097] (3) Cyclic performance test Charging method: 17.6A constant current and constant voltage charging to 4.55V (0.02C cutoff). Discharge method: 0.7C constant current discharge to 3.0V; Using the above-mentioned charge-discharge cycle as one cycle, the capacity retention rate of the lithium-ion battery was tested after 300 cycles. Referring to the expansion rate test method in (1) above, the expansion rate of the lithium-ion battery at the initial full charge and the full charge expansion rate after 300 cycles were tested.

[0098] (4) Electrochemical impedance spectroscopy After the lithium-ion battery was fully charged, it was transferred to a constant temperature chamber at 25±3℃ and left for 2 hours. Electrochemical impedance spectroscopy (EIS) was performed using an AC current with a voltage amplitude of 5mV as a disturbance signal, with a frequency range of 10000-0.03Hz.

[0099] (5) Particle size test: The Dv50 of each material particle in the negative electrode sheet is tested by laser particle size analyzer.

[0100] (6) Negative electrode composition test: After scraping the coating of the negative electrode, thermogravimetric analysis was performed, and elemental analysis was performed by inductively coupled plasma spectrometry after powder digestion to obtain the content of metal elements, P, C, Si and other elements in the negative electrode.

[0101] Example 1 Lithium-ion batteries include a positive electrode, a negative electrode, a separator, and an electrolyte, and their preparation includes the following steps: S1, Negative Electrode: The structure of the negative electrode in this embodiment is as follows... Figure 1 As shown; the negative electrode sheet is prepared according to the following process: S11. A slurry is prepared by mixing and stirring the first silicon carbide material, tin phosphide, SBR binder, and CMC dispersant in deionized water at a weight ratio of 80:20:4:1. This slurry is then coated onto both sides of a 6μm thick copper foil to obtain a first negative electrode active material layer on the negative electrode current collector. The areal density of the first negative electrode active material layer coated on one side is 30.1 g / m². 2 ; S12. A slurry is obtained by mixing and stirring the second silicon-carbon material, graphite, binder (SBR), and dispersant (CMC) in deionized water at a mass ratio of 20:75:4:1. This slurry is then coated onto the first negative electrode active material layer to form the second negative electrode active material layer. The areal density of the second negative electrode active material layer coated on one side is 19.2 g / m². 2 The total surface area density of the coating on one side of the negative electrode sheet is 49.3 g / m². 2 The silicon mass percentage in the first and second silicon-carbon materials is 46%, respectively. S13. Mix metal nitride:PVDF:PVP in NMP at a mass ratio of 80:18:2, and then coat the mixture onto the second negative electrode active material layer to obtain a protective layer. S14. After rolling, slitting, and sheet forming, a wound negative electrode sheet is obtained.

[0102] S2. Lithium cobalt oxide, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 96.5:1.5:2. N-methylpyrrolidone (NMP) is added, and the mixture is stirred evenly under vacuum to obtain a positive electrode slurry. An 8μm aluminum foil is used as the positive electrode current collector, and the positive electrode slurry is uniformly coated onto the current collector. After drying, cold pressing, and cutting, the positive electrode sheet is obtained. The areal density of the positive electrode active material layer coated on one side of the positive electrode sheet is 177.9 g / m². 2 .

[0103] S3. A PE porous membrane with a thickness of 9μm is used as the separator.

[0104] S4. In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) are mixed in a volume ratio of 1:1:4:4 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent at a ratio of 1 mol / L to prepare an electrolyte.

[0105] S5. Stack the positive electrode sheet, separator, and negative electrode sheet prepared above in sequence and wind them to obtain a battery cell. After packaging, baking, electrolyte injection, formation, secondary sealing, and capacity testing of the battery cell, a soft-pack lithium-ion battery is obtained.

[0106] Example 2 Compared with Example 1, the difference in this embodiment is that the slurry coating thickness of the first and second negative electrode active material layers in the preparation process of the negative electrode sheet is changed to change L0 and L1. At the same time, the content of the second silicon carbide material and graphite in the second negative electrode active material layer is changed (while the overall content is adjusted to 100wt% using binder SBR, the same below) to change x2 and y. The rest are the same. See Table 1-2 for details.

[0107] Example 3 Compared with Example 1, the difference in this embodiment is that the slurry coating thickness in the preparation process of the first and second negative electrode active material layers in the negative electrode preparation process is changed to change L0 and L1. At the same time, the content of the second silicon carbide material and graphite in the second negative electrode active material layer is changed to change x2 and y. At the same time, the amount of the first silicon carbide material and metal phosphide added in the first negative electrode active material (based on a total weight of 100 parts of the first silicon carbide material and metal phosphide, the same below) is changed to change x1 / z. The rest are the same. See Table 1-2 for details.

[0108] Example 4 The difference between this embodiment and Embodiment 1 is that the dosage of the first silicon carbide material and metal phosphide in the first negative electrode active material is changed to change x1 / z; at the same time, the content of the second silicon carbide material and graphite in the second negative electrode active material layer is changed to change x2 and y. The rest are the same, as detailed in Tables 1-2.

[0109] Examples 5-7 The difference between this embodiment and Embodiment 1 is that the type of metal phosphide is changed, as detailed in Tables 1-2; otherwise, they are the same.

[0110] Example 8 The difference between this embodiment and Embodiment 1 is that the Dv50 of the first silicon-carbon material in the first negative electrode active material layer is changed, as detailed in Tables 1-2; the rest are the same.

[0111] Example 9 The difference between this embodiment and Embodiment 1 is that the Dv50 of the first silicon-carbon material in the first negative electrode active material layer is changed, as detailed in Tables 1-2; the rest are the same.

[0112] Examples 10-11 The difference between this embodiment and Embodiment 1 is that the type of metal nitride is changed, as detailed in Tables 1-2; otherwise, they are the same.

[0113] Examples 12-13 The difference between this embodiment and embodiment 1 is that the thickness of the protective layer slurry coating is changed to change L2, and the Dv50 of the metal nitride is also changed, as detailed in Tables 1-2. The rest are the same.

[0114] Comparative Example 1 Compared with Example 1, the first negative electrode active material layer of this comparative example has no metal phosphide, but the rest is the same.

[0115] Comparative Example 2 The difference between this comparative example and Example 1 is that this comparative example does not have a second negative electrode active material layer, but the rest are the same.

[0116] Comparative Example 3 The difference between this comparative example and Example 1 is that this comparative example has no protective layer, but the rest are the same.

[0117] Comparative Example 4 Compared with Example 1, this comparative example differs in that the positions of the first negative electrode active material layer and the second negative electrode active material layer are interchanged. That is, the second negative electrode active material layer is first prepared on the negative electrode current collector, and then the first negative electrode active material layer is prepared on the second negative electrode active material layer. Specifically, the steps are as follows: S1. The negative electrode sheet is prepared according to the following process: S11. A slurry is obtained by mixing and stirring the second silicon-carbon material, graphite, binder (SBR), and dispersant (CMC) in deionized water at a mass ratio of 20:75:4:1. This slurry is then coated onto both sides of a 6μm thick copper foil current collector to obtain the second negative electrode active material layer. The areal density of the second negative electrode active material layer coated on one side is 19.2 g / m². 2 ; S12. A slurry is obtained by mixing and stirring the first silicon carbide material, tin phosphide, SBR binder, and CMC dispersant in deionized water at a mass ratio of 80:20:4:1. This slurry is then coated onto the surface of the second negative electrode active material layer, thus obtaining the first negative electrode active material layer on top of the second negative electrode active material layer. The areal density of the first negative electrode active material layer coated on one side is 30.1 g / m². 2 The total surface area density of the coating on one side of the negative electrode sheet is 49.3 g / m². 2 ; S13. Mix metal nitride:PVDF:PVP in NMP at a mass ratio of 80:18:2, and then coat the mixture onto the first negative electrode active material layer to obtain a protective layer. S14. After rolling, slitting, and sheet forming, a wound negative electrode sheet is obtained.

[0118] S2. Lithium cobalt oxide, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 96.5:1.5:2. N-methylpyrrolidone (NMP) is added, and the mixture is stirred evenly under vacuum to obtain a positive electrode slurry. An 8μm aluminum foil is used as the positive electrode current collector, and the positive electrode slurry is uniformly coated onto the current collector. After drying, cold pressing, and cutting, the positive electrode sheet is obtained. The areal density of the positive electrode active material layer coated on one side of the positive electrode sheet is 177.9 g / m². 2 .

[0119] S3. A PE porous membrane with a thickness of 9μm is used as the separator.

[0120] S4. In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) are mixed in a volume ratio of 1:1:4:4 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent at a ratio of 1 mol / L to prepare an electrolyte.

[0121] S5. Stack the positive electrode sheet, separator, and negative electrode sheet prepared above in sequence and wind them to obtain a battery cell. After packaging, baking, electrolyte injection, formation, secondary sealing, and capacity testing of the battery cell, a soft-pack lithium-ion battery is obtained.

[0122] In Table 1-2, x1 represents the weight percentage of the first silicon-carbon material in the first negative electrode active material layer, d1 represents the Dv50 of the first silicon-carbon material, z represents the weight percentage of the metal phosphide in the first negative electrode active material layer, d2 represents the Dv50 of the metal phosphide; L0 represents the thickness of the first negative electrode active material layer; x2 represents the mass percentage of the second silicon-carbon material in the second negative electrode active material layer; d3 represents the Dv50 of the second silicon-carbon material; y represents the mass percentage of graphite in the second negative electrode active material layer; d4 represents the Dv50 of the graphite in the second negative electrode active material layer; L1 represents the thickness of the second negative electrode active material layer; d5 represents the D50 of the metal nitride; and L2 represents the thickness of the protective layer.

[0123] Table 1 Table 2 As can be seen from Examples 1-13 and Comparative Examples 1-4 above, the battery assembled in this application using a negative electrode sheet including a first negative electrode active material layer, a second negative electrode active material layer and a protective layer has a high cycle capacity retention rate (greater than 95%), a liquid retention coefficient (greater than 1.20 g / Ah) and a maximum temperature limit (greater than 130°C), as well as low resistance (less than 25 mΩ) and expansion rate (less than 10.5%).

[0124] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of this application and not 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 negative electrode sheet, characterized in that, It includes a negative electrode current collector, and a first negative electrode active material layer, a second negative electrode active material layer and a protective layer stacked on at least one surface of the negative electrode current collector, wherein the first negative electrode active material is close to and in contact with the current collector, and the second negative electrode active material layer is disposed between the first negative electrode material layer and the protective layer. The first negative electrode active material layer includes a first silicon-carbon material and a metal phosphide; The second negative electrode active material layer includes a second silicon-carbon material and graphite; The protective layer comprises a metal nitride.

2. The negative electrode sheet according to claim 1, characterized in that, The first negative electrode active material layer satisfies the following relationship: 4≤x1 / z≤7.5, where x1 is the weight part of the first silicon-carbon material in the first negative electrode active material layer, and z is the weight part of the metal phosphide in the first negative electrode active material layer.

3. The negative electrode sheet according to claim 1, characterized in that, The metal phosphide includes at least one of tin phosphide, copper phosphide, iron phosphide, cobalt phosphide, nickel phosphide, zinc phosphide, and aluminum phosphide.

4. The negative electrode sheet according to claim 1, characterized in that, The following relationship is satisfied: 10%≤x2≤90%, 10%≤y≤90%, where x2 is the mass percentage of the second silicon-carbon material in the second negative electrode active material layer, and y is the mass percentage of graphite in the second negative electrode active material layer.

5. The negative electrode sheet according to claim 1, characterized in that, Includes at least one of the following A and B: A. In the first negative electrode active material layer, the Dv50 of the first silicon-carbon material is 10-20 μm; B. In the second negative electrode active material layer, the Dv50 of the second silicon-carbon material is <10μm.

6. The negative electrode sheet according to claim 1, characterized in that, The following relationship is satisfied: 0.2≤L1 / L0≤2.5, where L0 is the thickness of the first negative electrode active material layer in μm; and L1 is the thickness of the second negative electrode active material layer in μm.

7. The negative electrode sheet according to claim 1, characterized in that, At least one of the following DE conditions must be met: D. L0+L1+L2≤120μm, where L0 is the thickness of the first negative electrode active material layer in μm; L1 is the thickness of the second negative electrode active material layer in μm; and L2 is the thickness of the protective layer in μm. E, 0.01 < L2 / L1 < 0.12, where L1 is the thickness of the second negative electrode active material layer in μm; L2 is the thickness of the protective layer in μm.

8. The negative electrode sheet according to claim 1, characterized in that, The metal nitride includes at least one of AlN, W2N, TiN, Zn3N2, and Mg3N2.

9. An electrochemical device, characterized in that, Includes the negative electrode sheet as described in claim 8.

10. An electronic device, characterized in that, Includes the electrochemical device as described in claim 9.

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