Negative pole piece and electrochemical device and electronic device comprising same

Abstract

The invention discloses a negative electrode pole piece and an electrochemical device and an electronic device comprising the negative electrode pole piece, and belongs to the technical field of energy storage. According to a negative electrode active material, the included angle between the sheet layer plane of crystalline flake graphite and a negative electrode current collector is controlled to be alpha degrees, and alpha is larger than or equal to 70 degrees and smaller than or equal to 90 degrees; the diameter-thickness ratio of the crystalline flake graphite, the mass percentage content of the crystalline flake graphite in the negative electrode active material and the Dv50 particle size of the silicon material meet the condition that (x * y) / z is greater than or equal to 0.09 and less than or equal to 85; and the cycle life of the electrochemical device is effectively prolonged.

Description

Technical Field

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

[0002] Electrochemical devices (especially lithium-ion batteries) are widely used in new energy vehicles, energy storage projects and other industries as energy storage devices because of their advantages such as high operating voltage, long cycle life, high energy density, low self-discharge and no memory effect.

[0003] As the application scope of secondary batteries continues to expand, the requirements for their cycle life are becoming increasingly stringent.

[0004] Therefore, this application is submitted. Summary of the Invention

[0005] The purpose of this application is to overcome the shortcomings of the existing technology and provide a negative electrode active material and a negative electrode sheet, an electrochemical device and an electronic device containing the same, wherein the negative electrode sheet can effectively improve the cycle life of the electrochemical device.

[0006] To achieve the above objectives, a first aspect of this application provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer comprises a negative electrode active material, which includes silicon material and flake graphite. The angle between the flake plane of the graphite sheet and the negative electrode current collector is α°, where 70 ≤ α ≤ 90°. The negative electrode sheet satisfies: 0.09 ≤ (x × y) / z ≤ 85°. Where x is the aspect ratio of the flake graphite; y represents the mass percentage of the flake graphite in the negative electrode active material; z μm is the Dv50 particle size of the silicon material.

[0007] In some implementations, the following condition is satisfied: 20 ≤ x ≤ 200.

[0008] In some implementations, the following condition is satisfied: 5≤y≤85.

[0009] In some implementations, the following condition is satisfied: 2≤z≤14.

[0010] In some embodiments, the silicon material has a mass percentage content of 15-95% in the negative electrode active material.

[0011] In some embodiments, the Dv50 particle size of the flake graphite is d μm, satisfying: 0.3≤d / z≤4.

[0012] In some implementations, the following condition is satisfied: 1.5 ≤ d ≤ 20.

[0013] In some embodiments, the flake graphite surface is coated with an iron oxide layer, and the thickness of the coating layer is 10-200 nm.

[0014] A second aspect of this application provides an electrochemical device comprising the negative electrode sheet described above.

[0015] A third aspect of this application provides an electronic device including the electrochemical device described above.

[0016] The beneficial effects of this application are as follows: By controlling the aspect ratio of flake graphite, the mass percentage of flake graphite in the negative electrode active material, and the Dv50 particle size of the silicon material, this application satisfies the following conditions: 0.09 ≤ (x×y) / z ≤ 85. The flake graphite constructs a continuous conductive network and reserves expansion buffer pores, effectively buffering the volume expansion of the silicon material and avoiding blocking the lithium-ion transport path, thus effectively promoting lithium-ion transport. Controlling the mass percentage of flake graphite in the negative electrode active material within a suitable range can effectively isolate the silicon material, better absorb expansion stress, and provide a continuous path for electron transport. Controlling the Dv50 particle size of the silicon material within a suitable range improves the dispersion and structural stability of the silicon material in the negative electrode active material layer, avoids structural damage during rolling, and improves the wettability of the electrolyte to the negative electrode sheet. This application improves the cycle life of the electrochemical device through the synergistic control of multiple parameters. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a traditional negative electrode.

[0018] Figure 2 This is a schematic diagram of the negative electrode sheet described in this application.

[0019] Figure 3 This is another structural schematic diagram of the negative electrode sheet described in this application. Detailed Implementation

[0020] 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.

[0021] 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.

[0022] 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.

[0023] In this application, there are no particular restrictions on the specific dispersion and mixing methods.

[0024] Unless otherwise specified, all components, raw materials, or instruments used in the embodiments and comparative examples of this application are commercially available, and the components and raw materials used in each parallel experiment are the same.

[0025] In the following description, all figures disclosed herein are approximate values, regardless of whether the terms "about" or "approximately" are used in conjunction. They may vary by 1%, 2%, 5%, or sometimes 10% to 20%. Whenever a range of values ​​with a lower limit RL and an upper limit RU is disclosed, any values ​​falling within that range are specifically disclosed. Specifically, the following values ​​within this range are specifically disclosed: R = RL + k × (RU - RL), where k is a variable ranging from 1% to 100% with a 1% increment, i.e., k is 1%, 2%, 3%, 4%, 5%, ..., 50%, 51%, 52%, ..., 95%, 96%, 97%, 98%, 99%, or 100%. Furthermore, any range of values ​​defined by the two R values ​​as defined above are also specifically disclosed.

[0026] The term "negative electrode active material" (also known as anodic active material) is defined as a material that is electrochemically active in the negative electrode or anode. Active materials should be understood as materials capable of capturing and releasing Li and / or Na ions when subjected to voltage changes over a predetermined time period.

[0027] I. Negative electrode plate Studies have shown that silicon-based anode active materials (silicon materials) undergo volume expansion during charge and discharge (typically exceeding 300%), leading to mutual compression and cracking of silicon materials. This causes the silicon materials to detach from the anode current collector, resulting in a significant decrease in cycle life. Figure 1As shown, in traditional composite anode active materials (composite of silicon materials and graphite anode active materials), the graphite is randomly distributed and cannot effectively isolate silicon particles. The expansion stress is transmitted along the direction parallel to the current collector, causing the anode sheet to wrinkle or even break.

[0028] Therefore, based on the above problems, such as Figure 2 , Figure 3 As shown ( Figure 3 To show the angle between the flake graphite and the negative electrode current collector (only the flake graphite and the negative electrode current collector are shown), this application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, which includes silicon material and flake graphite. The angle between the flake plane of the flake graphite and the negative electrode current collector is α°, 70≤α≤90°. The negative electrode sheet satisfies: 0.09≤(x×y) / z≤85°. Where x is the aspect ratio of the flake graphite; y represents the mass percentage of the flake graphite in the negative electrode active material; z μm is the Dv50 particle size of the silicon material.

[0029] The inventors of this application have discovered that the distribution of flake graphite in the hybrid negative electrode active material (i.e., a hybrid negative electrode active material of silicon material and flake graphite) has a significant impact on the negative electrode electron conduction efficiency, ion diffusion rate, and volume expansion of silicon material.

[0030] In this application, the angle between the planar surface of the flake graphite and the negative electrode current collector is first adjusted to α°. This effectively reduces the conduction resistance between the negative electrode current collector and the negative electrode active material, lowers the interface resistance, effectively improves the uniformity of the conductive network structure, effectively promotes electron conduction, reduces polarization, and simultaneously forms a relatively continuous lithium-ion transport path. This reduces the transport distance of ions in the tortuous porous network and provides a pre-defined, directional buffer space for volume expansion during charging and discharging. The expansion can partially squeeze into these vertical channels, allowing the expanded silicon material to be orderly spaced, effectively absorbing expansion stress, significantly reducing the extrusion strength of silicon particles, and effectively improving the cycle life of the electrochemical device.

[0031] The inventors of this application have discovered that the cycle life of the electrochemical device and the volume expansion of the silicon material are related not only to the distribution of flake graphite, but also to the aspect ratio of the flake graphite, the mass percentage of flake graphite in the negative electrode active material, and the Dv50 particle size of the silicon material. This application controls the aspect ratio of the flake graphite, the mass percentage of flake graphite in the negative electrode active material, and the Dv50 particle size of the silicon material to satisfy: 0.09 ≤ (x×y) / z ≤ 85; the flake graphite constructs a continuous conductive network and reserves expansion buffer pores, effectively buffering the silicon expansion. The volume expansion of the material, while avoiding blockage of the lithium-ion transport path, effectively promotes lithium-ion transport; controlling the mass percentage of flake graphite in the negative electrode active material within a suitable range can effectively isolate the silicon material, better absorb expansion stress, and provide a continuous path for electron transport; controlling the Dv50 particle size of the silicon material within a suitable range improves the dispersion and structural stability of the silicon material in the negative electrode active material layer, avoids structural damage during rolling, and improves the wettability of the electrolyte to the negative electrode sheet; this application improves the cycle life of the electrochemical device through the synergistic control of multiple parameters.

[0032] In some embodiments, the negative electrode plate satisfies: 0.78 ≤ (x×y) / z ≤ 13.26. In particular, when (x×y) / z is in this range, the cycle life of the electrochemical device can be further improved and the volume expansion can be reduced.

[0033] In some embodiments, the following condition is satisfied: 20≤x≤200. For example, it can be a range consisting of 20, 40, 50, 60, 80, 100, 120, 150, 160, 180, 200, or any two of these values. By controlling x within this range, it is possible to promote the formation of a continuous π-π conjugate conductive path, with a short electron transport path and no obvious breakpoints, thus promoting lithium-ion transport. At the same time, a suitable aspect ratio can prevent the migration and aggregation of silicon material, effectively isolate the silicon material, buffer the volume expansion of the silicon material, and further improve the cycle life of the electrochemical device.

[0034] In some implementations, the following condition is satisfied: 5≤y≤85. For example, it can be a range consisting of 5, 6, 8, 10, 12, 14, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 80, 85, or any two of these values. By controlling y within this range, a continuous conductive network structure is formed, buffering the volume change of silicon material and ensuring cycle stability.

[0035] In some implementations, the following condition is satisfied: 2≤z≤14, for example, it can be 2, 3, 4, 5, 6, 8, 10, 12, 14 or any two of these values. By controlling z within this range, the structural stability of the negative electrode can be effectively improved, lithium ion insertion / extraction can be promoted, lithium ion transport resistance can be reduced, polarization can be avoided, and the cycle life of the electrochemical device can be further improved.

[0036] In some embodiments, the mass percentage of silicon material in the negative electrode active material is 15-95%, for example, it can be 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or any two of these values. By controlling the mass percentage of silicon material in the negative electrode active material within this range, the specific capacity can be increased.

[0037] In some embodiments, the Dv50 particle size of the flake graphite is d μm, satisfying: 0.3≤d / z≤4, for example, it can be 0.3, 0.5, 0.6, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.5, 3, 3.5, 4 or any two of these values.

[0038] In some embodiments, the Dv50 particle size of the flake graphite is d μm, satisfying: 0.3≤d / z≤3. By controlling d / z within this range, an effective vertical barrier can be formed, preventing the silicon materials from squeezing against each other, improving the structural stability of the negative electrode sheet, while also preventing excessive bending or stacking of the flake graphite, avoiding the formation of a large area of ​​inert region on the negative electrode sheet, avoiding affecting the energy density of the negative electrode sheet, and further improving the cycle life of the negative electrode sheet.

[0039] In some implementations, the following condition is satisfied: 1.5≤d≤20, for example, it can be a range consisting of 1.5, 2, 3, 5, 6, 8, 10, 12, 14, 15, 16, 18, 20 or any two of these values, which effectively improves conductivity and effectively isolates the silicon material, better absorbs expansion stress, and provides a continuous path for electron transport.

[0040] In some embodiments, the flake graphite surface coating layer includes iron oxide, and the thickness of the coating layer is 10~200nm, for example, it can be 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 80nm, 100nm, 120nm, 150nm, 180nm, 200nm or any two of these values.

[0041] More specifically, the method for forming the coating layer on the surface of flake graphite is as follows: flake graphite is dispersed in an aqueous solution of Fe(NO3)3, stirred at 60~80℃ for 2~6h, ammonia water is added to adjust the pH to 9~11, stirred evenly, dried, and calcined to form the coating layer on the graphite surface.

[0042] In some embodiments, the molar concentration of the Fe(NO3)3 aqueous solution is 0.05~0.5 mol / L, for example, it can be 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L or any two of these values.

[0043] In some embodiments, the mass ratio of the flake graphite to the Fe(NO3)3 aqueous solution is (2~10):(90~98), for example, it can be 2:98, 4:96, 5:95, 6:94, 8:92, 10:90 or any two of these values.

[0044] In some embodiments, the calcination temperature is 300~400°C, for example, it can be 300°C, 320°C, 350°C, 360°C, 380°C, 400°C or any two of these values.

[0045] In some embodiments, the calcination time is 0.5 to 5 hours, for example, it can be 0.5 hours, 1 hour, 2 hours, 4 hours, 5 hours or any two of these values.

[0046] In some embodiments, the thickness of the negative electrode active material layer is 25~150μm, for example, it can be 25μm, 30μm, 35μm, 40μm, 50μm, 60μm, 80μm, 100μm, 120μm, 140μm, 150μm or any two of these values.

[0047] In some embodiments, the thickness of the negative electrode current collector is 3.5~20μm, for example, it can be 3.5μm, 5μm, 6μm, 8μm, 10μm, 12μm, 14μm, 15μm, 16μm, 18μm, 20μm or any two of these values.

[0048] In some embodiments, the silicon material includes at least one of silicon-carbon composite materials, elemental silicon, silicon alloys, and silicon oxide.

[0049] In some embodiments, the silicon material includes a silicon-carbon composite material in which the mass percentage of silicon element is 25-90%, for example, it can be 25%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or any two of these values.

[0050] In this application, there are no particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collector, etc.

[0051] In some embodiments, the negative electrode active material layer further includes a negative electrode binder and a negative electrode conductive agent.

[0052] In some embodiments, the negative electrode binder includes at least one of the following: 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, 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. This application is not limited to the above materials and also includes other materials that can be used as battery negative electrode binders.

[0053] In some embodiments, the negative electrode conductive agent includes at least one of carbon, 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. This application is not limited to the above materials, but also includes other materials that can be used as negative electrode conductive agents in batteries.

[0054] II. Electrochemical Device This application provides an electrochemical device comprising the aforementioned negative electrode. In some embodiments, the electrochemical device further includes a positive electrode, a separator, and an electrolyte, wherein the separator is located between the positive and negative electrode.

[0055] The electrochemical device of this application includes any device in which an electrochemical reaction occurs, and specific examples include all kinds 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.

[0056] Positive electrode sheet The electrochemical device of this application includes a positive electrode, wherein the positive electrode includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector.

[0057] In some of these embodiments, the type of positive current collector is not particularly limited, and it may be any material known to be suitable for use as a positive current collector.

[0058] In some embodiments, the positive current collector includes metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper.

[0059] There are no particular restrictions on the form of the positive electrode current collector. When the positive electrode current collector is a metallic material, it can be in the form of metal foil, metal cylinder, metal strip, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, it can be in the form of carbon plate, carbon film, carbon cylinder, etc.

[0060] In some embodiments, the positive electrode active layer includes a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent.

[0061] 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.

[0062] In some embodiments, the positive electrode active material is Li 1+x Ni a Mnb 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.

[0063] 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.

[0064] 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.

[0065] In some embodiments, the positive electrode active material includes LiNi. 0.33 Mn 0.33 Co 0.33 O2(NMC333), LiNi 0.4 Mn 0.4 Co 0.2 O2, LiNi 0.5 Mn 0.3 Co 0.2 O2(NMC532), LiNi 0.6 Mn 0.2 Co 0.2 O2(NMC622), LiNi 0.7 Mn 0.15 Co 0.15 O2, LiNi 0.8 Mn 0.1 Co 0.1 O2(NMC811), LiNi 0.92 Mn 0.04 Co 0.04 O2, LiNi 0.8 Co 0.15 Al0.05 At least one of O2 (NCA) and LiNiO2 (LNO).

[0066] In some embodiments, the positive electrode binder includes binder materials comprising at least one of the following: 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. This application is not limited to the above materials and also includes other materials that can be used as battery positive electrode binders.

[0067] In some embodiments, the positive electrode conductive agent includes at least one of carbon, 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. This application is not limited to the above materials, but also includes other materials that can be used as positive electrode conductive agents in batteries.

[0068] diaphragm 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.

[0069] Generally, a diaphragm includes a substrate and a coating applied to the surface of the substrate.

[0070] Substrate In some embodiments, the porous 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.

[0071] Inorganic particles 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, Na2O.mTiO2, K2O.nTiO2, 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.

[0072] In some embodiments, the inorganic filler includes one or more of alumina, hydrated alumina, boehmite, magnesium hydroxide, magnesium oxide, titanium dioxide, zirconium oxide, and barium sulfate.

[0073] Coating adhesive In some embodiments, the binder is a water-soluble polymer. In some embodiments, the water-soluble polymer is a homopolymer or copolymer.

[0074] 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, cyanoethyl cellulose, nitrile rubber (NBR), styrene-butadiene rubber (SBR), and latex.

[0075] In some embodiments, the monomers constituting the water-soluble polymer include monomers containing carboxylic acid groups and monomers containing amide groups. The monomer, a monomer containing a cyano group, and a monomer containing an ester group are selected from at least one of the following: a monomer containing a cyano group and a monomer containing an ester group.

[0076] In some embodiments, the monomers containing a carboxylic acid group include monocarboxylic acids, dicarboxylic acids, anhydrides of dicarboxylic acids, and derivatives thereof. Some non-limiting examples of monocarboxylic acids include acrylic acid, methacrylic acid, crotonic acid, 2-ethylacrylic acid, and isocrotonic acid. Some non-limiting examples of dicarboxylic acids include maleic acid, fumaric acid, itaconic acid, and methylmaleic acid. Some non-limiting examples of anhydrides of dicarboxylic acids include maleic anhydride, acrylic anhydride, methylmaleic anhydride, and dimethylmaleic anhydride.

[0077] In some embodiments, the monomer containing an amide group includes at least one of acrylamide and methacrylamide. In some embodiments, the monomer containing a cyano group includes at least one of acrylonitrile and α-alkylacrylonitrile. In some embodiments, the monomer containing a nitrile group is at least one of methacrylonitrile, α-ethylacrylonitrile, α-isopropylacrylonitrile, α-methoxyacrylonitrile, 3-methoxyacrylonitrile, and 3-ethoxyacrylonitrile.

[0078] In some embodiments, the monomer containing an ester group includes at least one of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n-butyl acrylate, and n-butyl methacrylate.

[0079] In some embodiments, the monomer accounts for 10-90% of the polymer. In some embodiments, the binder is an oil-soluble polymer.

[0080] In some of these embodiments, non-limiting examples of oil-soluble polymers include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyester, polyether, polyvinyl compounds, polyolefins, rubber, polyvinylpyrrolidone, polystyrene, nitrile rubber (NBR), styrene-butadiene rubber (SBR), latex, acrylonitrile-styrene-butadiene copolymer, halogenated polymers, fluorinated polymers, chlorinated polymers, unsaturated polymers, conjugated diene polymers, and combinations thereof.

[0081] electrolytes The electrochemical device of this application also includes an electrolyte.

[0082] In some embodiments, the electrolyte includes at least one of a gel electrolyte, a solid electrolyte, and a liquid electrolyte.

[0083] In some embodiments, the liquid electrolyte comprises a non-aqueous solvent and a lithium salt.

[0084] In some embodiments, the lithium salt includes at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate.

[0085] In some embodiments, the non-aqueous solvent may be at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds.

[0086] In some embodiments, the carbonate compound includes at least one of chain carbonate compounds, cyclic carbonate compounds, and fluorocarbonate compounds.

[0087] In some embodiments, the chain carbonate compound includes diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof. Examples of fluorocarbonate compounds are 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.

[0088] In some embodiments, examples of carboxylic acid ester compounds are 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, mevalonic acid lactone, caprolactone, and methyl formate.

[0089] In some embodiments, examples of ether compounds are dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

[0090] In some embodiments, the non-aqueous solvent also includes 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.

[0091] III. Electronic Devices This application also provides an electronic device, including the electrochemical device described in this application.

[0092] The application of the electrochemical device in this application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the electrochemical 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, android robots, etc.

[0093] IV. Testing Methods The Dv50 particle size mentioned in this application refers to the particle size corresponding to a cumulative volume distribution percentage of 50% for the material, which can be obtained by testing with a laser particle size analyzer.

[0094] Test method for diameter-to-thickness ratio of flake graphite: (1) Test method for diameter-to-thickness ratio (x) of flake graphite: Use scanning electron microscope (SEM) to observe at least 100 flake graphite particles, measure the diameter and thickness of each particle, and calculate the average diameter-to-thickness ratio x = average diameter / average thickness.

[0095] Method for testing the angle between the flake plane of graphite and the negative electrode current collector: The cross-section of the negative electrode sheet is cut using ion beam polishing (CP) technology, and at least 50 interfaces between the graphite flakes and the current collector are observed by SEM. The angle between the flake plane of the graphite flakes and the normal of the current collector surface is measured.

[0096] The thickness of the coating layer can be measured using TEM (transmission electron microscopy).

[0097] The following uses a lithium-ion battery as an example and combines specific embodiments to illustrate the preparation of a lithium-ion battery. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.

[0098] Example 1 A method for preparing a lithium-ion battery includes the following steps: (1) Preparation of negative electrode sheet: The negative electrode active material, conductive agent Super-P, binder SBR and CMC are mixed evenly in a mass ratio of 96:2:1:1. Deionized water is added to adjust the solid content to 65%. The mixture is stirred at 2000 rpm for 10 minutes and then at 4000 rpm for 30 minutes to obtain a negative electrode slurry. The negative electrode slurry is coated on a 10 μm thick copper foil and dried at 80℃ for 5 minutes and then at 120℃ for 20 minutes. The dried electrode sheet is placed in a magnetic field with a magnetic field strength of 0.6T for 25 seconds to make the flake graphite oriented. Finally, it is rolled under a pressure of 10 MPa to make the thickness of the negative electrode active material layer reach 85 μm. It is then vacuum dried at 120℃ for 12 hours to obtain the negative electrode sheet. The negative electrode active material includes a silicon-carbon composite material (50% silicon content, 53% porosity) with a mass ratio of 8:2 and flake graphite.

[0099] (2) Preparation of the positive electrode: LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive agent acetylene black, and binder PVDF are mixed in a mass ratio of 96:2:2. NMP solvent is added to adjust the solid content to 72%. The mixture is stirred at 1500 rpm for 2 hours to obtain a positive electrode slurry. The positive electrode slurry is coated onto a 15 μm thick aluminum foil and dried at 80°C for 5 minutes and then at 120°C for 30 minutes. Finally, it is rolled under 20 MPa pressure and vacuum dried at 120°C for 12 hours to obtain a positive electrode sheet.

[0100] (3) Preparation of electrolyte: At room temperature, in a glove box filled with argon (H2O < 1 ppm, O2 < 1 ppm), ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC): propyl propionate (PP) were mixed evenly in a mass ratio of 20:30:20:30 to obtain a mixed organic solvent. Lithium salt LiPF6 was added to the mixed organic solvent and stirred evenly to obtain the electrolyte. The mass ratio of lithium salt LiPF6 to the mixed organic solvent was 12:88.

[0101] (4) Separator: A PE membrane with a thickness of 7 μm is used as the separator; (5) Assembly of lithium-ion batteries: The positive electrode, separator and negative electrode are stacked in sequence, so that the separator is between the positive and negative electrode to play a role in isolation. After being wound into a square bare cell, it is put into the outer packaging, then baked to remove water, injected with the corresponding electrolyte, sealed, and after standing, hot and cold pressing, formation and capacity testing, the lithium-ion battery is obtained.

[0102] The parameters of the negative electrode are shown in Table 1.

[0103] Examples 2-4 The difference between Examples 2-4 and Example 1 is that the aspect ratio of the flake graphite is changed, as shown in Table 1.

[0104] Examples 5-8 The difference between Examples 5-8 and Example 1 is that the mass ratio of flake graphite to silicon material is changed, as shown in Table 1.

[0105] Examples 9-11 The difference between Examples 9-11 and Example 1 is that the Dv50 particle size of the silicon material is changed, as shown in Table 1.

[0106] Examples 12-13, Comparative Examples 1-2 Examples 12-13 differ from Example 1 in that the Dv50 particle size of the silicon material, the aspect ratio of the flake graphite, and the mass ratio of the flake graphite to the silicon material are changed, as shown in Table 1.

[0107] Examples 14-19 Examples 14-19 differ from Example 1 in that the Dv50 particle size of the flake graphite is changed, as shown in Table 1.

[0108] Examples 20-21, Comparative Example 3 Examples 20-21 and Comparative Example 3 differ from Example 1 in that the time and intensity of the magnetic field are changed.

[0109] The magnetic field duration in Example 20 was 15 seconds, and the magnetic field strength was 0.4 T.

[0110] The magnetic field duration in Example 21 was 30 seconds, and the magnetic field strength was 0.8 T.

[0111] The magnetic field duration for Comparative Example 3 is 5 seconds, and the magnetic field strength is 0.15 T.

[0112] Example 22 The difference between Example 22 and Example 1 is that the flake graphite in Example 22 has an iron oxide layer on its surface.

[0113] The method for forming the coating layer on the surface of flake graphite is as follows: flake graphite is dispersed in a 0.1 mol / L Fe(NO3)3 aqueous solution, stirred at 70°C for 4 hours, ammonia is added to adjust the pH to 10, stirred until homogeneous, dried, and calcined at 350°C for 3 hours to form the coating layer on the graphite surface. The thickness of the coating layer is between 10 and 200 nm. The mass ratio of the flake graphite to the Fe(NO3)3 aqueous solution is 8:92.

[0114] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that Comparative Example 4 was not magnetized, and the flake graphite was randomly distributed.

[0115] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that Comparative Example 5 did not contain flake graphite.

[0116] Table 1 Performance testing methods Volume expansion rate: The prepared lithium-ion battery was charged and discharged at 0.5C for 100 cycles at 25℃. The thickness change was measured by a PPG thickness gauge. Volume expansion rate (%) = (full charge thickness after cycle - initial half charge thickness) / initial half charge thickness × 100%.

[0117] Cycle capacity retention: The prepared lithium-ion battery was charged and discharged at 1C rate at 25℃, with a voltage range of 2.8V-4.2V. The first discharge capacity and the capacity after the 500th discharge were recorded. Cycle capacity retention (%) = capacity after the 500th discharge / capacity after the first discharge × 100%.

[0118] Table 2 As can be seen from Table 2, this application significantly suppresses volume expansion and improves the cycle life of the electrochemical device by controlling the aspect ratio of flake graphite, the mass percentage of flake graphite in the negative electrode active material, and the Dv50 particle size of the silicon material to satisfy: 0.09≤(x×y) / z≤85.

[0119] This application significantly suppresses volume expansion and improves the cycle life of the electrochemical device by controlling the angle between the flake plane of the graphite and the negative electrode current collector to α°, where 70 ≤ α ≤ 90.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention 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 the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A negative electrode sheet, characterized in that, The device includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, which includes silicon material and flake graphite. The angle between the flake plane of the graphite and the negative electrode current collector is α°, and 70 ≤ α ≤ 90°. The negative electrode sheet satisfies: 0.09 ≤ (x × y) / z ≤ 85°. Where x is the aspect ratio of the flake graphite; y represents the mass percentage of the flake graphite in the negative electrode active material; z μm is the Dv50 particle size of the silicon material.

2. The negative electrode sheet according to claim 1, characterized in that, It satisfies: 20≤x≤200.

3. The negative electrode sheet according to claim 1, characterized in that, It satisfies: 5≤y≤85.

4. The negative electrode sheet according to claim 1, characterized in that, It satisfies: 2≤z≤14.

5. The negative electrode sheet according to claim 1, characterized in that, The silicon material has a mass percentage content of 15-95% in the negative electrode active material.

6. The negative electrode sheet according to claim 1, characterized in that, The Dv50 particle size of the flake graphite is d μm, which satisfies: 0.3≤d / z≤4.

7. The negative electrode sheet according to claim 4, characterized in that, It satisfies: 1.5≤d≤20.

8. The negative electrode sheet according to claim 1, characterized in that, The flake graphite surface coating layer includes iron oxide, and the thickness of the coating layer is 10~200nm.

9. An electrochemical device, characterized in that, Includes the negative electrode sheet as described in any one of claims 1 to 8.

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

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