Composite material, negative electrode sheet, preparation method thereof, electrochemical device, and electronic equipment

Abstract

A composite material, a negative electrode sheet and a preparation method thereof, an electrochemical device and an electronic equipment. The composite material comprises silicon-oxygen particles and hard carbon particles, the particle size Dv50 of the silicon-oxygen particles is D 1, the particle size Dv50 of the hard carbon particles is D 2, and D 1≤0.414D 2. By matching the hard carbon particles with large particle size with the silicon-oxygen particles with small particle size, and controlling the particle size D 1 of the silicon-oxygen particles and the particle size D 2 of the hard carbon particles to satisfy D 1≤0.414D 2, the electrochemical device using the composite material as the negative electrode active material has high energy density and good cycle performance.

Description

Technical Field

[0001] This application relates to the field of energy storage technology, and in particular to a composite material, a negative electrode sheet and its preparation method, an electrochemical device and an electronic device. Background Technology

[0002] Further improvements in the energy density of lithium-ion batteries are of great significance, and employing high-specific-capacity anode materials is an effective means to enhance this energy density. Silicon-based anode materials exhibit significantly higher specific capacity than carbon-based anode materials, making their application a crucial technological direction for developing next-generation high-energy-density lithium-ion batteries. However, due to the significant volume expansion of silicon-based anode materials and the reduced energy density gain caused by the rise in anode potential, they are typically used in combination with graphite. Nevertheless, a series of problems arise during cycling, including the loss of the ionic and electronic conductivity network due to volume expansion and the mismatch between lithium insertion and extraction potentials between silicon-based anode materials and graphite. These issues lead to rapid capacity decay and poor cycle performance. Summary of the Invention

[0003] In view of this, this application provides a composite material, a negative electrode sheet and its preparation method, an electrochemical device and an electronic device. The electrochemical device using the composite material as the negative electrode active material has both high energy density and good cycle performance.

[0004] The first aspect of this application provides a composite material comprising silicon oxide particles and hard carbon particles, wherein the particle size Dv50 of the silicon oxide particles is D1, and the particle size Dv50 of the hard carbon particles is D2, and D1 ≤ 0.414D2. The composite material provided in this application, by combining large-diameter hard carbon particles with small-diameter silicon oxide particles, and controlling the particle sizes D1 of the silicon oxide particles and D2 of the hard carbon particles to satisfy D1 ≤ 0.414D2, enables electrochemical devices using this composite material as the negative electrode active material to possess both high energy density and good cycle performance.

[0005] In some embodiments, the content of silicon-oxygen particles in the composite material is M1, and the content of hard carbon particles in the composite material is 1-M1, where 10wt%≤M1≤35wt%. This can further improve the compaction density of the electrode, increase the energy density of the electrochemical device, and enhance its cycle performance.

[0006] In some embodiments, the specific surface area of ​​the silicon-oxygen particles is B1, and the specific surface area of ​​the hard carbon particles is B2, where 1.25 ≤ B1 / B2 ≤ 4. This can further improve the cycle performance of the electrochemical device.

[0007] In some embodiments, the composite material satisfies at least one of the following conditions: (1) 1 μm ≤ D1 ≤ 15 μm; (2) 5 μm ≤ D2 ≤ 22.5 μm; (3) the specific surface area of ​​the silicon-oxygen particles is B1, 0.15 m².2 / g≤B1≤15m 2 / g; (4) The specific surface area of ​​the hard carbon particles is B2, 0.15m 2 / g≤B2≤12m 2 / g. This can further improve the cycle performance and energy density of electrochemical devices.

[0008] In some embodiments, the composite material satisfies at least one of the following conditions: (5) the compaction density of the silicon-oxygen particles is C1, 1.3 g / cm³. 3 ≤C1≤1.6g / cm 3 (6) The compacted density of the hard carbon particles is C2, 0.9 g / cm³. 3 ≤C2≤1.0g / cm 3 (7) The compaction density of the composite material is C3, 1 g / cm³. 3 ≤C3≤1.4g / cm 3 (8) The potential of hard carbon particles at 25% lithium insertion depth is 0.1–0.3 V higher than that of the silicon oxide particles at 25% lithium insertion depth vs Li / Li. + (9) The potential of the hard carbon particles at 75% delithiation depth is 0.1–0.3 Vvs Li / Li higher than that of the silicon oxide particles at 75% delithiation depth. + This can further improve the cycle performance and energy density of electrochemical devices.

[0009] A second aspect of this application provides a negative electrode sheet, including a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a conductive agent, a binder, and the aforementioned composite material.

[0010] In some embodiments, the compaction density of the negative electrode active material layer is 0.96 g / cm3 to 1.2 g / cm3, and the porosity of the negative electrode active material layer is 14% to 27%.

[0011] The third aspect of this application provides a method for preparing the aforementioned negative electrode sheet, comprising:

[0012] The composite material and dispersant are dry-mixed to obtain a mixture;

[0013] The solvent, a portion of the binder, and the conductive agent are mixed uniformly to obtain the first slurry;

[0014] The first slurry is added to the mixture and stirred until it is evenly mixed to obtain the second slurry;

[0015] The solvent is added to the second slurry and stirred until evenly mixed to obtain the third slurry;

[0016] Add the remaining binder to the third slurry, add solvent, and stir to mix evenly to obtain the negative electrode slurry;

[0017] A negative electrode slurry is coated onto at least one surface of a negative electrode current collector to obtain a negative electrode sheet.

[0018] In the method for preparing the negative electrode sheet provided in this application, the required binder is added in two steps, in which part of the binder is premixed with the conductive agent, which can achieve optimized distribution of the conductive agent and the binder, and is beneficial to improving the cycle performance of the electrochemical device.

[0019] A third aspect of this application provides an electrochemical device comprising a negative electrode prepared by the above-described method. It exhibits good cycle performance and high energy density.

[0020] A fourth aspect of this application provides an electronic device including the electrochemical device described above. Detailed Implementation

[0021] The following embodiments are intended to enable those skilled in the art to fully understand this application, but do not limit this application in any way.

[0022] This application provides a composite material comprising silicon oxide particles and hard carbon particles, wherein the particle size Dv50 corresponding to 50% of the volume distribution of the silicon oxide particles is D1, and the particle size Dv50 corresponding to 50% of the volume distribution of the hard carbon particles is D2, and D1≤0.414D2.

[0023] Hard carbon, by definition, refers to carbon that is difficult to graphitize, even at temperatures above 2500°C. Hard carbon is typically obtained from precursors such as pyrolytic polymers. Hard carbon possesses high reversible specific capacity, which is beneficial for improving the energy density of lithium-ion batteries. Hard carbon also has a highly porous structure, facilitating ion extraction and insertion, but this limits its compaction density, thus affecting energy density. Silicon-oxygen materials have high specific capacity, which is beneficial for improving the energy density of lithium-ion batteries, but they exhibit significant volume expansion and contraction during lithium insertion and extraction.

[0024] This application combines large-diameter hard carbon particles with small-diameter silicon-oxygen particles, and controls the particle sizes D1 of the silicon-oxygen particles and D2 of the hard carbon particles to satisfy D1≤0.414D2. This improves the low compaction density of hard carbon particles, increases the compaction density of the negative electrode sheet using this composite material as the negative electrode active material, and thus enhances the energy density of electrochemical devices (such as lithium-ion batteries) using this negative electrode sheet. Simultaneously, because the hardness of silicon-oxygen particles is greater than that of hard carbon particles, the silicon-oxygen particles can act as rollers during the cold pressing process of the negative electrode sheet, alleviating the locking caused by the sharp edges of the hard carbon particles, facilitating particle slippage, and further improving the compaction density of the negative electrode sheet. On the other hand, the small-diameter silicon-oxygen particles are distributed in the interstices of the large-diameter hard carbon particles. During lithium intercalation, the hard carbon particles exert a force on the silicon-oxygen particles that are expanding in volume, mitigating the capacity loss caused by the volume expansion of silicon-oxygen particles and improving the cycle performance of the electrochemical device.

[0025] In some embodiments, the hard carbon particles include at least one of resin carbon particles, organic polymer pyrolytic carbon particles, or carbon black particles, and the silicon oxide particles include at least one of Si, SiO, or SiO2.

[0026] In some embodiments, the content of silicon-oxygen particles in the composite material is M1, and the content of hard carbon particles in the composite material is 1-M1, where 10wt% ≤ M1 ≤ 35wt%. This can further improve the compaction density of the electrode, increase the energy density of the electrochemical device, and enhance its cycle performance. Optionally, M1 is a value within the range of any two of these values: 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, and 35wt%.

[0027] In some embodiments, 1 μm ≤ D1 ≤ 15 μm, and 5 μm ≤ D2 ≤ 22.5 μm. Optionally, D1 is a value within the range of 1 μm, 3 μm, 5 μm, 10 μm, 15 μm, or any combination of these values. Optionally, D2 is a value within the range of 51 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, 21 μm, 22.5 μm, or any combination of these values.

[0028] In some embodiments, the potential of hard carbon particles at 25% lithium insertion depth is 0.1–0.3 V higher than that of silicon oxide particles at 25% lithium insertion depth compared to Li / Li. + The potential of hard carbon particles at 75% delithiation depth is 0.1–0.3 V higher than that of silicon oxide particles at 75% delithiation depth vs. Li / Li. +Hard carbon particles have a higher potential than silicon-oxygen particles, allowing them to intercalate lithium before silicon-oxygen particles. This avoids the surface stress caused by reverse delithiation of silicon-oxygen particles during lithium-ion battery charging, which would inhibit the capacity of silicon-oxygen particles. Furthermore, during lithium-ion battery discharge, hard carbon particles ensure maximum lithium ion extraction from silicon-oxygen particles, preventing internal stress caused by incomplete delithiation from limiting subsequent charging capacity. It also minimizes lithium capture caused by incomplete delithiation of silicon-oxygen particles, further improving the cycle performance of lithium-ion batteries.

[0029] In some embodiments, the specific surface area of ​​the silicon oxide particles is B1, and the specific surface area of ​​the hard carbon particles is B2, where 1.25 ≤ B1 / B2 ≤ 4. This further increases the close contact between the hard carbon particles and the silicon oxide particles, thereby alleviating the expansion of the silicon oxide particles, improving the capacity loss caused by the volume expansion of the silicon oxide particles, and further enhancing the cycle performance of the electrochemical device. Optionally, B1 / B2 is a value within the range of 1.25, 1.5, 2, 2.5, 3, 3.5, 4, or any combination of these values.

[0030] In some embodiments, 0.15m 2 / g≤B1≤15m 2 / g, 0.15m 2 / g≤B2≤12m 2 / g. Optionally, B1 is 0.15m. 2 / g, 0.5m 2 / g, 1.5m 2 / g、2m 2 / g、4m 2 / g, 5.5m 2 / g、7m 2 / g, 9.5m 2 / g, 13.5m 2 / g, 15m 2 / g can be a value within a range of any two of these values. Optionally, B2 is 0.15m. 2 / g, 0.5m 2 / g, 1.5m 2 / g、2m 2 / g、4m 2 / g, 5.5m 2 / g、7m 2 / g, 9.5m 2 / g、12m 2 / g can be any value within a range of these values.

[0031] In some embodiments, the compaction density of the silicon-oxygen particles in the composite material is C1, the compaction density of the hard carbon particles in the composite material is C2, and the compaction density of the composite material is C3, 1.3 g / cm³. 3 ≤C1≤1.6g / cm 3 0.9g / cm 3 ≤C2≤1.0g / cm 3 1g / cm 3 ≤C3≤1.4g / cm 3 This further improves the low compaction density of hard carbon materials, increases the energy density of the electrochemical device, and further improves the expansion of silicon-oxygen particles, thereby enhancing the cycle performance of the electrochemical device. Optionally, C1 is 1.3 g / cm³. 3 1.35g / cm 3 1.4g / cm 3 1.45g / cm 3 1.5g / cm 3 1.55g / cm 3 1.6g / cm 3 Or it can be a value within a range of any two of these values. Optionally, C2 is 0.9 g / cm³. 3 0.92g / cm 3 0.95g / cm 3 0.97g / cm 3 1.0g / cm 3 Or it can be a value within a range of any two of these values. Optionally, C3 is 1 g / cm³. 3 1.2g / cm 3 1.3g / cm 3 1.4g / cm 3 Or it could be any two of these values ​​within a range.

[0032] Negative electrode sheet

[0033] This application also provides a negative electrode sheet, which 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 conductive agent, a binder, and the aforementioned composite material. The composite material is used as the negative electrode active material of the negative electrode active material layer. In other words, the negative electrode active material of the negative electrode active material layer includes hard carbon particles and silicon oxide particles.

[0034] Binders can improve the bonding between negative electrode active material particles and the bonding between the negative electrode active material and the negative electrode current collector. Binders can include any adhesive polymer. Examples of binders include, but are not limited to: polyacrylic acid, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, or mixtures thereof.

[0035] Conductive agents are used to improve the conductivity of the negative electrode. Conductive agents can include any conductive material that does not cause chemical changes. Examples of conductive agents include, but are not limited to: base materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal base materials (e.g., metal powders or metal fibers, including copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives, etc.), or mixtures thereof.

[0036] In some embodiments, the compaction density of the negative electrode active material layer is 0.96 g / cm³. 3 ~1.2g / cm 3 The porosity of the negative electrode active material layer is 14%–27%, which further ensures that the electrochemical device has high energy density and excellent cycle performance. Optionally, the compaction density of the negative electrode active material layer is 0.96 g / cm³. 3 0.98g / cm 3 0.10 g / cm 3 0.12g / cm 3 0.14 g / cm 3 0.17g / cm 3 1.2g / cm 3 Or a value within a range of any two of these values. Optionally, the porosity of the negative electrode active material layer is 14%, 16%, 17%, 19%, 22%, 24%, 27%, or a value within a range of any two of these values.

[0037] In some embodiments, the negative current collector includes, but is not limited to: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and any combination thereof. In some embodiments, the negative current collector is copper foil.

[0038] In some embodiments, the structure of the negative electrode is a negative electrode structure known in the art that can be used in electrochemical devices.

[0039] In some embodiments, the method for preparing the negative electrode sheet is a method known in the art for preparing negative electrode sheets that can be used in electrochemical devices. Exemplarily, the negative electrode sheet can be obtained by mixing a negative electrode active material, a conductive agent, and a binder in a solvent, and heating a thickener as needed to prepare an active material composition, and then coating the active material composition onto a negative electrode current collector. In some embodiments, the solvent may include, but is not limited to, water and N-methylpyrrolidone.

[0040] This application also provides a method for preparing the above-mentioned negative electrode sheet, comprising the following steps: (a) dry mixing the composite material and the dispersant to obtain a mixture; (b) uniformly mixing the solvent, a portion of the binder and the conductive agent to obtain a first slurry; (c) adding the first slurry to the mixture and stirring to mix evenly to obtain a second slurry; (d) adding the solvent to the second slurry and stirring to mix evenly to obtain a third slurry; (e) adding the remaining binder to the third slurry and adding the solvent, stirring to mix evenly to obtain a negative electrode slurry; (f) coating the negative electrode slurry onto at least one surface of the negative electrode current collector to obtain a negative electrode sheet.

[0041] In step (a), pre-dispersing the composite material with a dispersant can reduce the risk of agglomeration of hard carbon particles and silica particles in the composite material. In some embodiments, the dispersant includes at least one of sodium carboxymethyl cellulose, sodium carboxymethyl cellulose, sodium polyacrylate, and acrylamide.

[0042] In step (b), the binder portion of the negative electrode active material layer is premixed with the conductive agent, which can optimize the composition of the conductive agent and the binder, and is beneficial to improving the cycle performance of the electrochemical device.

[0043] The solvents used in steps (b), (d), and (e) may be the same or different. In some embodiments, the solvents used in steps (b), (d), and (e) each include at least one of deionized water, N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, and tetrahydrofuran.

[0044] This application also provides an electrochemical device comprising the aforementioned composite material. The electrochemical device includes any device in which an electrochemical reaction occurs. Examples of electrochemical devices include, but are not limited to, primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, which includes, but is not limited to, lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0045] In some embodiments, the electrochemical device includes the negative electrode, the positive electrode, the electrolyte, and the separator disposed between the positive electrode and the negative electrode.

[0046] Positive electrode sheet

[0047] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer includes a positive active material, and the specific type of positive active material is not specifically limited and can be selected according to requirements.

[0048] In some embodiments, the positive electrode active material comprises a compound that reversibly inserts and deintercalates lithium ions (i.e., a lithiation intercalation compound). In some embodiments, the positive electrode active material may comprise a lithium transition metal composite oxide. This lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive electrode active material is selected from at least one of: lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials (NCM), lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 (O4) or lithium iron phosphate (LiFePO4).

[0049] In some embodiments, the positive electrode active material layer further includes an adhesive, and optionally also includes a conductive material. The adhesive can improve the bonding between the positive electrode active material particles and the bonding between the positive electrode active material and the positive electrode current collector. In some embodiments, the adhesive includes, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon, etc.

[0050] In some embodiments, the positive electrode active material layer includes a conductive material, thereby imparting conductivity to the positive electrode. The conductive material may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powders, metal fibers, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0051] In some embodiments, the positive current collector is a metal, including but not limited to aluminum foil.

[0052] In some embodiments, the structure of the positive electrode is a positive electrode structure known in the art and suitable for use in electrochemical devices.

[0053] In some embodiments, the method for preparing the positive electrode is a method known in the art for preparing a positive electrode that can be used in electrochemical devices. For example, the positive electrode can be obtained by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and then coating the active material composition onto a current collector. In some embodiments, the solvent may include, but is not limited to, water, N-methylpyrrolidone, etc.

[0054] electrolyte

[0055] The electrolyte used in the embodiments of this application can be any electrolyte known in the prior art. Electrolytes can be classified as aqueous electrolytes and non-aqueous electrolytes. Compared to aqueous electrolytes, electrochemical devices using non-aqueous electrolytes can operate over a wider voltage window, thereby achieving higher energy densities. In some embodiments, the non-aqueous electrolyte includes an organic solvent, an electrolyte, and additives.

[0056] Electrolytes that can be used in the electrolytes of this application embodiments include, but are not limited to: inorganic lithium salts, such as LiClO4, LiAsF6, LiPF6, LiBF4, LiSbF6, LiSO3F, LiN(FSO2)2, etc.; fluorinated organic lithium salts, such as LiCF3SO3, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,3-hexafluoropropane disulfonylimide lithium, cyclic 1,2-tetrafluoroethane disulfonylimide lithium, LiPF4(CF3)2, LiN(C2F5SO2)2, etc. The electrolytes include LiC(CF3SO2)(C4F9SO2), LiPF4(CF3SO2)2, LiPF4(C2F5)2, LiPF4(C2F5SO2)2, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, and LiBF2(C2F5SO2)2; lithium salts containing dicarboxylic acid complexes, such as lithium bis(oxalate)borate, lithium difluorooxalate borate, lithium tri(oxalate)phosphate, lithium difluorobis(oxalate)phosphate, and lithium tetrafluoro(oxalate)phosphate. Furthermore, the above electrolytes can be used alone or in combination with two or more. For example, in some embodiments, the electrolyte includes a combination of LiPF6 and LiBF4. In some embodiments, the electrolyte includes LiPF6.

[0057] In some embodiments, the concentration of the electrolyte is in the range of 0.8 mol / L to 3 mol / L, for example, in the range of 0.8 mol / L to 2.5 mol / L, 0.8 mol / L to 2 mol / L, 1 mol / L to 2 mol / L, or for example, 1 mol / L, 1.15 mol / L, 1.2 mol / L, 1.5 mol / L, 2 mol / L, or 2.5 mol / L.

[0058] The additives that can be used in the electrolyte in the embodiments of this application can be additives known in the art that can be used to improve the electrochemical performance of the battery. In some embodiments, the additive includes, but is not limited to, at least one of polynitrile compounds, sulfur-containing additives, fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone (PS), and 1,4-butanesulfonate lactone.

[0059] The organic solvents that can be used in the electrolytes of this application embodiments can be any organic solvent known in the prior art. In some embodiments, the organic solvents include, but are not limited to: carbonate compounds, ester-based compounds, ether-based compounds, ketone-based compounds, alcohol-based compounds, aprotic solvents, or combinations thereof. Examples of carbonate compounds include, but are not limited to, chain carbonate compounds, cyclic carbonate compounds, fluorocarbonate compounds, or combinations thereof.

[0060] In some embodiments, the organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, methyl acetate, or ethyl propionate.

[0061] The preparation method of the electrolyte in this application is not limited and can be prepared in accordance with conventional electrolyte preparation methods. In some embodiments, the electrolyte of this application can be prepared by mixing the components.

[0062] Separating membrane

[0063] In some embodiments, a separator is provided between the positive and negative electrodes to prevent short circuits. The material and shape of the separator are not particularly limited and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0064] For example, in some embodiments, the separator includes a substrate layer. This substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure. The material of the substrate layer can be selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, the material of the substrate layer can be selected from a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane.

[0065] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by a mixture of polymers and inorganic substances. Specifically, the inorganic layer includes inorganic particles and a binder. The inorganic particles may be selected from one or a combination of several of the following: alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder may be selected from one or a combination of several of the following: polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0066] This application also provides an electronic device including the aforementioned electrochemical device. The composite material used in this application improves the cycle performance of the electrochemical device, making the resulting electrochemical device suitable for electronic devices in various fields, especially for electronic devices requiring long-term operation.

[0067] 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. For example, such electronic devices include, but are not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc. In addition to being applicable to the electronic devices exemplified above, the electrochemical device in this application is also applicable to energy storage power stations, marine transport vehicles, and air transport vehicles. Air transport vehicles include both intra-atmosphere and extra-atmosphere air transport vehicles.

[0068] The following specific embodiments are provided to better illustrate this application, wherein a lithium-ion battery is used as an example.

[0069] Examples 1-8 and Comparative Examples 1-2

[0070] I. Preparation of Lithium-ion Batteries

[0071] 1. Preparation of negative electrode sheet

[0072] The negative electrode active material / composite material (Dv50 is 8.4μm, specific surface area is 0.88m²) 2 / g of silica particles has a Dv50 of 20.3μm and a specific surface area of ​​0.83m². 2 The following ingredients (e.g., hard carbon granules), conductive agent, polyacrylic acid (PAA), and thickener (sodium carboxymethyl cellulose, CMC) are thoroughly mixed in a solvent (deionized water) at a weight ratio of 95.7:1.5:1.8:1 to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto a negative electrode current collector (copper foil), dried, and cold-pressed to form a negative electrode active material layer. After cutting and welding the tabs, the negative electrode sheet is obtained.

[0073] 2. Preparation of the positive electrode

[0074] The positive electrode active material (lithium iron phosphate), conductive agent (acetylene black), and binder (polyvinylidene fluoride, PVDF) are mixed in a solvent (N-methylpyrrolidone, NMP) at a mass ratio of 96.3:2.2:1.5 and thoroughly stirred under vacuum to obtain a positive electrode slurry. This positive electrode material is coated onto a positive electrode current collector (aluminum foil), dried, and cold-pressed to form a positive electrode active material layer. After cutting and welding the tabs, the positive electrode sheet is obtained.

[0075] 3. Preparation of electrolyte

[0076] In a dry argon-atmospheric glove box, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed thoroughly at a mass ratio of EC:PC:EMC:DEC = 10:30:30:30. Then, 2% fluoroethylene carbonate and 2% 1,3-propanesulfonyl lactone were added, dissolved, and stirred thoroughly. Lithium salt LiPF6 was then added and mixed thoroughly to obtain the electrolyte. The concentration of LiPF6 was 1 mol / L.

[0077] 4. Preparation of the separating membrane

[0078] Polyethylene (PE) porous polymer film is used as the separator.

[0079] 5. Preparation of lithium-ion batteries

[0080] The obtained positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode to provide isolation. The cells are then wound to obtain a bare cell. The bare cell is placed in an outer aluminum-plastic film, and electrolyte is injected. After vacuum sealing, settling, and formation processes, a lithium-ion battery is obtained.

[0081] The main difference between Examples 1-8 and Comparative Examples 1-2 is that the types and contents of the negative electrode active materials used are different, as detailed in Table 1.

[0082] II. Testing Methods

[0083] 1. Cycle performance testing of lithium-ion batteries

[0084] The cyclic performance test process is as follows:

[0085] (1) Adjust the furnace temperature to 25℃ and let it stand for 30 minutes;

[0086] (2) 1C DC to 2.5V;

[0087] (3) Let stand for 30 minutes;

[0088] (4) 1C CC to 4.3V, CV to 0.05C;

[0089] (5) Let stand for 5 minutes;

[0090] (6) 1C DC to 2.5V (record discharge capacity);

[0091] (7) Let stand for 5 minutes;

[0092] (8) Repeat steps 4 to 7 1000 times;

[0093] (9) The test is over.

[0094] Lithium-ion battery capacity retention rate = Discharge capacity per cycle / Discharge capacity of the third cycle × 100%.

[0095] 2. Compacted density test of the negative electrode active material layer

[0096] An area of ​​1540.25 mm² was obtained from the surface of the negative electrode current collector along the negative electrode active material layer on the negative electrode sheet under test. 2 Small disc-shaped active material samples were taken. After removing the negative electrode current collector, the weight of the negative electrode active material was recorded. Twelve active material samples were taken from different locations in each group, and the weight per unit area of ​​the negative electrode active material layer was calculated.

[0097] Measure the thickness of the negative electrode active material layer on the negative electrode sheet in the direction perpendicular to the surface of the negative electrode current collector (excluding the current collector thickness). Take 12 active material samples at different locations in each group and calculate the compaction density of the negative electrode active material layer. Compaction density = weight of negative electrode active material / thickness in the direction perpendicular to the surface of the negative electrode current collector.

[0098] 3. Porosity test of the negative electrode active material layer

[0099] The gas displacement method is used for measurement. For details, please refer to the national standard GB / T24586-2009, "Determination of Apparent Density, True Density and Porosity of Iron Ore". Porosity P = (V1-V2) / V1×100%, where V1 represents the apparent volume and V2 represents the true volume.

[0100] III. Test Results

[0101] Table 1 lists the content of silicon-oxygen particles and hard carbon particles in the negative electrode active materials / composite materials of Examples 1-8. The negative electrode active material of Comparative Example 1 is only hard carbon particles, and the negative electrode active material of Comparative Example 2 is only silicon-oxygen particles. The table also shows the performance of the batteries corresponding to each example and comparative example.

[0102] Table 1

[0103]

[0104] As shown in Table 1, the negative electrode sheets of Examples 1-8 have high compaction densities, and the batteries of Examples 1-8 have high capacity retention rates, meaning that the batteries of Examples 1-8 combine high energy density and good cycle performance. This is because the combination of hard carbon particles and silicon oxide particles can improve the low compaction density of hard carbon particles; at the same time, since the hardness of silicon oxide particles is greater than that of hard carbon particles, the silicon oxide particles can act as rollers during the cold pressing process of the negative electrode sheet, further improving the compaction density of the negative electrode sheet; and the silicon oxide particles are distributed in the interstitial positions of hard carbon particles, so during the lithium intercalation process, the hard carbon particles exert a force on the silicon oxide particles that are expanding in volume, improving the capacity loss caused by the volume expansion of silicon oxide particles and improving the cycle performance of the electrochemical device. The negative electrode active material of Comparative Example 1, which only includes hard carbon particles, has the lowest compaction density, and the negative electrode active material of Comparative Example 2, which only includes silicon oxide particles, has the lowest capacity retention rate.

[0105] In Examples 2-7, the proportion of silicon-oxygen particles in the negative electrode active material is 10-35 wt%, the negative electrode sheet has a high compaction density, and the battery has a higher capacity retention rate.

[0106] Examples 9-14 and Comparative Example 3

[0107] The preparation and performance testing of the lithium-ion batteries in Examples 9-14 and Comparative Example 3 were carried out in accordance with Example 7, with the main difference being the different particle sizes of the silicon-oxygen particles and hard carbon particles, as detailed in Table 2. In Examples 9-14 and Comparative Example 3, the proportion of silicon-oxygen particles in the negative electrode active material was 35 wt%, and the proportion of hard carbon particles in the negative electrode active material was 65 wt%.

[0108] Table 2 lists the particle sizes of silicon oxide particles and hard carbon particles in Examples 7, 9-14 and Comparative Example 3, as well as the battery performance corresponding to each example and comparative example.

[0109] Table 2

[0110]

[0111]

[0112] Table 2 shows that when the particle size D1 of silicon-oxygen particles and the particle size D2 of hard carbon particles satisfy D1≤0.414D2, the battery exhibits both high energy density and good cycle performance. In Comparative Example 3, D1 / D2 is greater than 0.414, and both the compaction density and capacity retention rate decrease significantly.

[0113] Examples 15-20

[0114] The preparation and performance testing of the lithium-ion batteries in Examples 15-20 were carried out in accordance with Example 7, with the main difference being the different specific surface areas of the silicon-oxygen particles and hard carbon particles, as detailed in Table 3. In Examples 15-20, the proportion of silicon-oxygen particles in the negative electrode active material was 35 wt%, and the proportion of hard carbon particles in the negative electrode active material was 65 wt%.

[0115] Table 3 lists the specific surface areas of silicon oxide particles and hard carbon particles in Examples 7, 15-20, as well as the performance of the batteries corresponding to each example.

[0116] Table 3

[0117]

[0118] As can be seen from Table 3, when 1.25≤B1 / B2≤4 is satisfied, the negative electrode sheet has a high compaction density, which in turn makes the battery have a high energy density and capacity retention rate.

[0119] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Therefore, any equivalent variations made in accordance with this application are still within the scope of this application.

Claims

1. A composite material, characterized by, The composite material comprises silicon-oxygen particles and hard carbon particles, the particle size Dv50 of the silicon-oxygen particles is D1, the particle size Dv50 of the hard carbon particles is D2, D1≤0.414D2, the specific surface area of the silicon-oxygen particles is B1, the specific surface area of the hard carbon particles is B2, 1.25≤B1 / B2≤4.

2. The composite material of claim 1, wherein, The content of the silicon-oxygen particles in the composite material is M1, the content of the hard carbon particles in the composite material is 1-M1, 10wt%≤M1≤35wt%.

3. The composite material of any one of claims 1-2, wherein, The composite material satisfies at least one of the following conditions: (1) 1μm≤D1≤15μm; (2) 5μm≤D2≤22.5μm; (3) the specific surface area of the silicon-oxygen particles is B1, 0.15 m 2 / g ≤ B1 ≤ 15 m 2 / g; (4) the specific surface area of the hard carbon particles is B2, 0.15 m 2 / g ≤ B2 ≤ 12 m 2 / g.

4. The composite material of any one of claims 1-2, wherein, The composite material satisfies at least one of the following conditions: (5) the compacted density of the silicon-oxygen particles is C1, 1.3 g / cm 3 ≤ C1≤ 1.6 g / cm 3 ; (6) the compacted density of the hard carbon particles is C2, 0.9 g / cm3≤ C2≤ 1.0 g / cm3 3 ≤ C2≤ 1.0 g / cm3 3 ; (7) the compacted density of the composite material is C3, 1 g / cm 3 ≤ C3≤ 1.4 g / cm 3 ; (8) the potential of the hard carbon particle at a 25% lithium intercalation depth is higher than the potential of the silicon-oxygen particle at a 25% lithium intercalation depth by 0.1 to 0.3 V vs. Li / Li + ; (9) the potential of the hard carbon particle at a 75% delithiation depth is higher than the potential of the silicon-oxygen particle at a 75% delithiation depth by 0.1 to 0.3 V vs. Li / Li + .

5. A negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, characterized by The negative electrode active material layer comprises a conductive agent, a binder and the composite material according to any one of claims 1-4.

6. The negative electrode sheet according to claim 5, wherein The compaction density of the negative active material layer is 0.96 g / cm 3 1.2 g / cm 3 The porosity of the negative active material layer is 14% to 27%.

7. The negative electrode sheet according to any one of claims 5-6, wherein the method for preparing the negative electrode sheet comprises: dry mixing the composite material and a dispersing agent to obtain a mixture; uniformly mixing a solvent, a part of the binder and the conductive agent to obtain a first slurry; adding the first slurry into the mixture and stirring to obtain a second slurry; adding a solvent into the second slurry and stirring to obtain a third slurry; adding the remaining binder into the third slurry and adding a solvent, and stirring to obtain a negative electrode slurry; coating the negative electrode slurry on at least one surface of the negative electrode current collector to obtain the negative electrode sheet.

8. An electrochemical device comprising a negative electrode sheet, characterized by The negative electrode sheet comprises the negative electrode sheet according to any one of claims 5-7.

9. An electronic device, comprising: The electrochemical device comprises the negative electrode sheet according to claim 8. The electrochemical device comprises the negative electrode sheet according to claim 8.

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