Composite material, negative electrode sheet, electrochemical apparatus, and electronic device

Abstract

The present invention relates to the technical field of energy storage, and provides a composite material, a negative electrode sheet, an electrochemical apparatus, and an electronic device. The composite material comprises graphite, silicon carbon and hard carbon. The average particle size of the graphite is D1, the average particle size of the silicon carbon is D2, and the average particle size of the hard carbon is D3, wherein 0.5≤D2 / D1≤0.7, and 0.7≤D3 / D1≤0.9. The synergistic cooperation effect of the particle size relationships of the components can effectively improve the compaction density of the negative electrode sheet, optimize ion transport pathways, and promote the formation of more uniform and stable SEI films, thereby significantly improving the energy density, charging and discharging efficiency and cycle life of secondary batteries.

Description

Composite material, negative electrode sheet, electrochemical device and electronic equipment TECHNICAL FIELD

[0001] The present application belongs to the technical field of energy storage, and specifically relates to a composite material, a negative electrode sheet, an electrochemical device and an electronic equipment. BACKGROUND

[0002] As a core component of electrochemical energy storage devices, the negative electrode active material has a decisive influence on the overall performance of the electrochemical device. In the charge and discharge cycle, the negative electrode active material plays a key role in storing and releasing active substances, directly determining the energy density, cycle efficiency and safety and stability of the battery.

[0003] The negative electrode active material in the prior art shows a diversified development trend, mainly including carbon-based materials and silicon-based materials. Among them, carbon-based materials, especially graphite, are widely used due to their excellent electrical conductivity and structural stability. However, the relatively low specific capacity of graphite limits its application in high-energy-density secondary batteries. In contrast, although silicon-based materials have a high theoretical specific capacity, they have problems such as poor cycle stability and significant volume effect. With the rapid development of the application field of secondary batteries, the requirements for their performance are increasing, especially in terms of energy density and cycle life. Therefore, a negative electrode active material with high energy density and cycle performance is needed to meet the requirements of different application scenarios.

[0004] SUMMARY

[0005] To solve the above problems, the present application provides a composite material, a negative electrode sheet, an electrochemical device and an electronic equipment, which controls the average particle size of graphite, silicon-carbon and hard carbon, and the three materials cooperate to inhibit the volume effect of silicon, thereby improving the energy density and cycle performance of the secondary battery.

[0006] A composite material includes graphite, silicon-carbon and hard carbon; the average particle size of the graphite is D1, the average particle size of the silicon-carbon is D2, and the average particle size of the hard carbon is D3; 0.5≤D2 / D1≤0.7, and 0.7≤D3 / D1≤0.9. The present application controls the average particle size of graphite, silicon-carbon and hard carbon in the above range, which can produce a synergistic effect, so that the size of each material is suitable for dense packing and the electrical conduction path is optimized. When applied in a negative electrode sheet, the compaction density can be improved, thereby improving the energy density and rate performance of the secondary battery. On the other hand, graphite and hard carbon can cooperate to inhibit the volume effect of silicon and form a more uniform and stable solid electrolyte interface film (SEI film), thereby improving the stability of the negative electrode active material during the charge and discharge process, and further improving the cycle performance of the secondary battery.

[0007] In some embodiments, the composite material satisfies at least one of the following conditions:

[0008] (1) 0.54≤D2 / D1≤0.65.

[0009] (2) 0.74≤D3 / D1≤0.83.

[0010] (3) 4μm≤D1≤23.3μm, preferably 4μm≤D1≤20μm, more preferably 10μm≤D1≤20μm.

[0011] (4) 2μm≤D2≤11.65μm, preferably 2μm≤D2≤10μm, more preferably 2μm≤D2≤4μm.

[0012] (5) 3.6μm≤D3≤21μm, preferably 5μm≤D3≤21μm, more preferably 2μm≤D3≤10μm.

[0013] The composite material satisfying the above conditions can better play the synergistic effect of the ternary material, and improve the internal resistance, rate performance and cycle performance of the secondary battery.

[0014] In some embodiments, the mass percentage of graphite is M1, the mass percentage of silicon carbon is M2, and the mass percentage of hard carbon is M3, based on the mass of the composite material; 30.7%≤M2≤79.6%; 10.3%≤M3≤19.5%. Based on the above particle size relationship of the composite material, the mass ratio of silicon carbon and hard carbon in the composite material is adjusted to be within the above range, which can further improve the synergistic effect of the composite material, and optimize the internal resistance, rate performance and cycle performance of the secondary battery.

[0015] In some embodiments, 0.5≤M3 / M1≤2. When the mass ratio of hard carbon and graphite is within the range, the conductive network system of the negative electrode can be further optimized, and the quality of the SEI film can be improved, thereby improving the rate performance and cycle performance of the secondary battery.

[0016] In some embodiments, the intensity ratio of D peak and G peak in the Raman spectrum of graphite is N1, and 0.35≤N1≤0.7; the intensity ratio of D peak and G peak in the Raman spectrum of hard carbon is N2, and 0.7≤N2≤1.3; the intensity ratio of D peak and G peak of graphite and hard carbon particles is set within the above specific range, which can optimize the structural order degree of the material, and improve the rate performance and cycle performance of the secondary battery when applied in the secondary battery.

[0017] In some embodiments, the interlayer spacing of graphite is d1, where 0.335 nm ≤ d1 ≤ 0.35 nm; and the interlayer spacing of hard carbon is d2, where 0.35 nm ≤ d2 ≤ 0.38 nm. By controlling the interlayer spacing of graphite and hard carbon within the above ranges, this application can optimize the storage space of active matter and the electron transport channels, thereby further improving the rate performance and cycle performance of the secondary battery.

[0018] In some embodiments, the mass content of silicon element is S1, 85% ≤ S1 ≤ 90%, based on the mass of silicon carbon. By controlling the silicon element content in silicon carbon within the above range, this application can further improve the cycle performance, internal resistance, and rate performance of the secondary battery.

[0019] In some embodiments, the interlayer spacing of the carbon material in silicon-carbon is d3, where 0.35 nm ≤ d3 ≤ 0.38 nm. Controlling the interlayer spacing of the carbon material in silicon-carbon within this range is beneficial for improving the electrochemical activity of active material insertion and extraction, thereby improving the rate performance and cycle performance of the secondary battery.

[0020] In some embodiments, the sphericity of graphite, silicon carbide, and hard carbon is all greater than or equal to 0.7. By controlling the shape characteristics of each component to meet the above sphericity condition, the composite material can have lower internal resistance, as well as higher rate performance and cycle performance.

[0021] Secondly, this application provides a negative electrode sheet, including a negative electrode additive layer, which comprises the composite material provided in the first aspect of this application. Because the negative electrode sheet of this application comprises the aforementioned composite material, it possesses the same advantages: lower internal resistance and the ability to achieve higher rate performance and cycle performance.

[0022] In some embodiments, the silicon content is S2, 20.5% ≤ S2 ≤ 72%, based on the mass of the negative electrode binder layer. By controlling the silicon content in the negative electrode binder layer within the above range, this application can further improve the cycle performance, internal resistance, and rate performance of the secondary battery.

[0023] Thirdly, this application provides an electrochemical device that includes the negative electrode provided in the second aspect of this application. Because the electrochemical device provided in this application includes the aforementioned negative electrode, it can achieve the same advantages, exhibiting excellent rate and cycle performance, and possessing significant advantages in fast charging and lifespan.

[0024] In some embodiments, the electrochemical device further comprises an electrolyte, the electrolyte comprising a first substance, the first substance comprising at least one of vinylene carbonate or vinyl ethylene carbonate. The mass percentage of the first substance in the electrolyte is M4, 0.01%≤M4≤4%. Preferably, 0.42%≤M4≤1.75%. By adding at least one of vinylene carbonate (VC) or vinyl ethylene carbonate (VEC) to the electrolyte, and by controlling the mass percentage of the first substance in the electrolyte, the present application can cooperate with the above-mentioned composite material to promote the formation of a more uniform and compact SEI film, reduce the decomposition of the electrolyte and the occurrence of side reactions, thereby improving the rate performance, cycle performance and safety performance of the secondary battery.

[0025] In a fourth aspect, the present application provides an electronic device comprising the electrochemical device provided in the third aspect of the present application. The electronic device of the present application can achieve the same advantages and has excellent endurance and fast charging performance, thereby having a high application prospect.

[0026] The beneficial effects of the present application at least include:

[0027] The composite material and the negative electrode sheet provided by the present application can effectively improve the compaction density of the negative electrode sheet, optimize the ion transmission path, and promote the formation of a more uniform and stable SEI film, thereby significantly improving the performance of the secondary battery, especially its energy density, charge and discharge efficiency and cycle life, which makes it have great application potential and market value in the field of electrochemical energy storage. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0029] In the research of improving the negative active material, the inventors found that graphite has excellent cycle stability, excellent electrical conductivity, low cost and high reversibility (can efficiently absorb and release active substances). Hard carbon has a larger interlayer distance and a porous structure, which makes the active substance can be more easily intercalated and has a shorter diffusion path, while hard carbon can provide a higher working potential, effectively reducing the risk of lithium dendrite formation, and maintaining good performance at low temperature. Although silicon-based materials face the problem of volume expansion, they have extremely high theoretical specific capacity and lower lithiation potential than graphite, and have great potential in developing high-energy-density materials.

[0030] In view of this, the application provides a composite material, comprising graphite, silicon-carbon and hard carbon; the average particle size of the graphite is D1, the average particle size of the silicon-carbon is D2, and the average particle size of the hard carbon is D3; 0.5≤D2 / D1≤0.7, and 0.7≤D3 / D1≤0.9. The composite material uses three different average particle sizes of materials to complement and synergize, wherein the graphite with a larger average particle size maintains a lower surface area, which can reduce the formation of a solid electrolyte interface film (SEI) and enhance the cycle stability. The hard carbon has a larger interlayer spacing and a porous structure, which can effectively fill the gaps between the graphite and construct a continuous network with the graphite under the average particle size relationship of the application, further promoting the electrical conductivity and the stability of the electrode structure. The silicon-carbon with a relatively small size is embedded between the graphite, which can improve the energy density of the secondary battery while also alleviating the impact of volume expansion. The application reduces the resistance by combining graphite and hard carbon, and improves the specific capacity of the composite material by using silicon-carbon materials. The synergistic effect of the ternary material composite can improve the compaction density of the negative electrode sheet, further improve the energy density of the secondary battery, and also help to improve the electronic conductivity, thereby optimizing the ion transport path and reducing the diffusion resistance of ions in the electrode. In addition, reasonable average particle size design helps to inhibit the volume expansion of silicon and lithium alloying by mixing hard carbon and graphite, and maintains the stability of the electrode capacity and volume. In terms of cycle stability, by controlling the average particle size of the silicon-carbon particles and combining graphite and silicon-carbon, the volume change during repeated charging and discharging can be effectively managed, and the damage to the electrode structure can be reduced. At the same time, the stable SEI film formed by the hard carbon and the graphite on the electrode surface can avoid the continuous consumption of active materials, so that the chemical stability can be guaranteed. In summary, the multi-element mixed anode design with careful matching of average particle sizes and complementary material properties successfully improves the energy density and charging and discharging performance of the secondary battery, and also reduces the internal resistance of the secondary battery and improves the rate performance, and ensures good cycle stability.

[0031] Exemplarily, the value of D2 / D1 can be 0.5, 0.52, 0.54, 0.57, 0.58, 0.60, 0.63, 0.65, 0.68, 0.7, or a value within a range consisting of any two of these values. The value of D3 / D1 can be 0.7, 0.72, 0.74, 0.76, 0.79, 0.81, 0.83, 0.87, 0.88, 0.9, or a value within a range consisting of any two of these values.

[0032] In some embodiments, D2 < D3. The average particle size of the silicon-carbon controlled by the present application is lower than that of the hard carbon, which can further increase the contact area of the silicon-carbon with the electrolyte, and is beneficial to reduce the internal resistance of the secondary battery and improve the rate performance. Meanwhile, the silicon-carbon with a smaller average particle size is more easily inserted into the gap between the graphite and the hard carbon, thereby reducing the volume expansion effect of the silicon-carbon and improving the structural stability of the negative active material, and further improving the cycle performance of the battery.

[0033] In some more preferred embodiments, 0.54≤D2 / D1≤0.65. In some other more preferred embodiments, 0.74≤D3 / D1≤0.83. By adjusting the average particle size relationship between the graphite and the silicon-carbon, or adjusting the average particle size relationship between the graphite and the hard carbon, the three can be better matched, and the compaction density of the negative electrode sheet can be further improved, the ion conduction network can be optimized, and the internal resistance, rate performance and cycle performance of the secondary battery can be improved.

[0034] In some embodiments, 4μm≤D1≤23.3μm. Exemplarily, D1 can be 4μm, 6μm, 7μm, 10μm, 11μm, 13μm, 15μm, 17μm, 19μm, 20μm, 23.3μm or a value within a range consisting of any two of these values.

[0035] In some embodiments, 2μm≤D2≤11.65μm. Exemplarily, D2 can be 2μm, 3μm, 4μm, 5μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11.65μm or a value within a range consisting of any two of these values.

[0036] In some embodiments, 3.6μm≤D3≤21μm. Exemplarily, D3 can be 3.6μm, 5μm, 7μm, 9μm, 10μm, 13μm, 14μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm or a value within a range consisting of any two of these values.

[0037] In some embodiments, based on the mass of the composite material, the mass percentage of graphite is M1, the mass percentage of silicon carbon is M2, and the mass percentage of hard carbon is M3; 30.7%≤M2≤79.6%; 10.3%≤M3≤19.5%. Optionally, M2 can be 30.7%, 31.8%, 34.2%, 36.1%, 40.0%, 43.5%, 44.8%, 47.7%, 49.4%, 53.3%, 54.0%, 57.1%, 60.0%, 62.1%, 66.5%, 68.4%, 70.9%, 73.0%, 74.6%, 79.2%, 79.6%, or a value within a range consisting of any two of these values. Optionally, M3 can be 10.3%, 10.7%, 11.2%, 11.7%, 12.2%, 12.6%, 12.8%, 13.4%, 13.9%, 14.2%, 14.8%, 15.2%, 15.9%, 16.3%, 16.8%, 17.4%, 17.6%, 18.1%, 18.6%, 19.1%, 19.5%, or a value within a range consisting of any two of these values. By respectively regulating the mass percentage of silicon carbon and hard carbon within the above ranges, the composite material can better cooperate to improve the energy density of the secondary battery, while further inhibiting the volume expansion effect of silicon, improving the internal resistance, rate performance, and cycle performance of the secondary battery.

[0038] In some embodiments, 0.5≤M3 / M1≤2. Illustratively, the value of M3 / M1 can be 0.5, 0.7, 0.8, 1.0, 1.2, 1.3, 1.5, 1.7, 1.8, 2, or a value within a range consisting of any two of these values. By regulating the mass ratio of hard carbon and graphite within the above ranges, the two can better cooperate to promote the conductive network system of the negative electrode, enabling the secondary battery to exhibit smaller internal resistance, further improving the stability of the SEI film, and reducing the volume change, thereby improving the cycle performance of the secondary battery.

[0039] In some embodiments, 5%≤M1≤40%. M1 can be 5%, 9%, 13%, 16%, 20%, 25%, 29%, 32%, 36%, 40%, or a value within a range consisting of any two of these values. By regulating the mass ratio of graphite within the above ranges, the internal resistance, rate performance, and cycle performance of the secondary battery can be further improved.

[0040] In some embodiments, the ratio of the intensity of the D peak and the G peak in the Raman spectrum of the graphite is N1, and 0.35≤N1≤0.7. Illustratively, N1 can be 0.35, 0.39, 0.43, 0.47, 0.50, 0.54, 0.57, 0.62, 0.65, 0.7, or a value within a range defined by any two of these values. In some embodiments, the ratio of the intensity of the D peak and the G peak in the Raman spectrum of the hard carbon is N2, and 0.7≤N2≤1.3; for example, N2 can be 0.7, 0.77, 0.83, 0.88, 0.98, 1.05, 1.13, 1.16, 1.26, 1.3, or a value within a range defined by any two of these values. Controlling the ratio of the D peak and the G peak of the graphite and the hard carbon within a specific range can regulate the degree of structural order of the two materials, and further improve the coordination of the two materials in the composite system of the present application, thereby improving the electronic conductivity and the stability of the SEI film, and optimizing the rate performance and the cycle performance of the secondary battery.

[0041] In some embodiments, the interlayer spacing of the graphite is d1, and 0.335 nm≤d1≤0.35 nm. Illustratively, d1 can be 0.335 nm, 0.337 nm, 0.338 nm, 0.340 nm, 0.342 nm, 0.343 nm, 0.344 nm, 0.346 nm, 0.347 nm, 0.35 nm, or a value within a range defined by any two of these values. Controlling the interlayer spacing of the graphite within the above range can further optimize the crystal structure thereof, improve the electrochemical activity of lithium ion intercalation and deintercalation, thereby reducing the internal resistance of the secondary battery, and promoting the improvement of the rate performance and the cycle performance thereof.

[0042] In some embodiments, the interlayer spacing of the hard carbon is d2, and 0.35 nm≤d2≤0.38 nm. Illustratively, d2 can be 0.35 nm, 0.354 nm, 0.356 nm, 0.360 nm, 0.363 nm, 0.366 nm, 0.369 nm, 0.372 nm, 0.374 nm, 0.38 nm, or a value within a range defined by any two of these values. Controlling the interlayer spacing of the hard carbon within the above specific range is conducive to optimizing the storage space of the active material and the electronic transmission channel, and improving the energy density, the rate performance, and the cycle performance of the secondary battery.

[0043] In the present application, silicon-carbon refers to a mixture composed of silicon elements and carbon elements, which may, for example, include but is not limited to at least one of coated silicon-carbon and embedded silicon-carbon. The coated silicon-carbon includes silicon particles and a layer of carbon material wrapped on the surface of the silicon particles; the embedded silicon-carbon includes a carbon material carrier and silicon particles located on the surface and inside of the carbon material carrier.

[0044] In some embodiments, the mass content of silicon element is S1, 85%≤S1≤90% based on the mass of the silicon-carbon. Exemplarily, S1 can be 85%, 85.5%, 86.2%, 86.6%, 87.4%, 87.9%, 88.0%, 88.6%, 89.7%, 89.7%, 90%, or a value within a range consisting of any two of these values. The application controls the content of silicon element in the silicon-carbon within the above range, which can improve the structural stability in the composite material system of the application, and can improve the conductivity and ion transport performance of the negative active material, thereby improving the cycle performance, internal resistance and rate performance of the secondary battery.

[0045] In some embodiments, the interlayer spacing of the carbon material in the silicon-carbon is d3, 0.35 nm≤d3≤0.38 nm. Exemplarily, d3 can be 0.35 nm, 0.354 nm, 0.356 nm, 0.360 nm, 0.363 nm, 0.366 nm, 0.369 nm, 0.372 nm, 0.374 nm, 0.38 nm, or a value within a range consisting of any two of these values. Controlling the interlayer spacing of the carbon material in the silicon-carbon within the above range can further optimize the rate performance and cycle performance of the secondary battery.

[0046] In some embodiments, the sphericity of the graphite, silicon-carbon and hard carbon is all greater than or equal to 0.7. For example, the sphericity of the graphite, silicon-carbon and hard carbon can be 0.7, 0.74, 0.76, 0.80, 0.82, 0.88, 0.88, 0.94, 0.95, 1.0, or a value within a range consisting of any two of these values. Controlling the sphericity of the three materials within the above range is conducive to uniform coating during the manufacturing process of the negative electrode sheet, and further optimizes the mechanical and electrochemical properties of the negative electrode sheet. At the same time, the interlayer spacing of the graphite and hard carbon particles is also precisely controlled within a specific nanometer scale, which optimizes the storage space for lithium ions and provides better electronic transmission channels, thereby improving the internal resistance, rate performance and cycle performance of the secondary battery.

[0047] In a second aspect, the application provides a negative electrode sheet, comprising the composite material provided in the first aspect of the application.

[0048] In the application, the composite material is included as a negative active material in the negative electrode binder layer of the negative electrode sheet. The negative electrode sheet of the application also includes a negative electrode current collector. In the application, the negative electrode binder layer can be disposed on one side of the surface in the thickness direction of the negative electrode current collector, or on both sides of the surface in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of the negative electrode current collector, or a partial area of the negative electrode current collector, which is not particularly limited in the application as long as the purpose of the application can be achieved.

[0049] The negative current collector is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the negative current collector includes, but is not limited to, a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a foamed nickel, a foamed copper, a composite current collector (e.g., a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector), a polymer substrate coated with an electrically conductive metal, and any combination thereof. In some embodiments, the negative current collector is a copper foil.

[0050] In the present application, a negative binder can also be included in the negative electrode mixture layer, which can improve the binding between the negative active material particles and each other, and can improve the binding between the negative active material and the negative current collector. The negative binder is not particularly limited in the present application, as long as the object of the present application can be achieved, and for example, can include, but is not limited to, at least one of polyvinyl alcohol, sodium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylic acid, butadiene-styrene rubber, acrylated butadiene-styrene rubber, an epoxy resin, or nylon.

[0051] In the present application, a conductive agent can also be included in the negative electrode mixture layer, which is used to improve the electrical conductivity of the negative electrode sheet. The type of the conductive agent in the negative electrode mixture layer is not particularly limited in the present application, as long as the object of the present application can be achieved, and for example, the conductive agent can include, but is not limited to, at least one of natural graphite, artificial graphite, conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, acetylene black, ketjen black, graphene, a metal material, or a conductive polymer. The above-mentioned carbon nanotubes can include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers can include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or nanocarbon fibers. The above-mentioned metal material can include, but is not limited to, metal powder and / or metal fibers, and specifically, the metal can include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above-mentioned conductive polymer can include, but is not limited to, at least one of a polyphenylene derivative, polyaniline, polythiophene, polyacetylene, or polypyrrole.

[0052] The mass ratio of the negative active material, the conductive agent, and the negative binder in the negative electrode mixture layer is not particularly limited in the present application, as long as the object of the present application can be achieved. In some embodiments, the structure of the negative electrode sheet is a negative electrode sheet structure that can be used for an electrochemical device, which is well known in the art.

[0053] In some embodiments, the method for preparing the negative electrode sheet is a method for preparing a negative electrode sheet for an electrochemical device known in the art. Illustratively, the negative electrode sheet can be obtained by mixing the negative electrode active material, the conductive agent, and the negative electrode binder in a solvent, and a thickening agent can be added as needed to prepare an active material composition, and the active material composition is coated on a negative electrode current collector. In some embodiments, the solvent can include, but is not limited to, water, N-methylpyrrolidone.

[0054] In a third aspect, the present application provides an electrochemical device comprising the negative electrode sheet provided in the second aspect of the present application.

[0055] The electrochemical device of the present application is not particularly limited, and it can include any device in which an electrochemical reaction occurs, such as a secondary battery. The present application will be described below with reference to embodiments of the present application in conjunction with a secondary battery. In some embodiments of the present application, the secondary battery can include, but is not limited to, a lithium ion secondary battery (lithium ion battery), a sodium ion battery, a lithium metal battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery, etc.

[0056] In some embodiments of the present application, the secondary battery further comprises a positive electrode sheet. The positive electrode sheet of the present application is not particularly limited, as long as it can achieve the purpose of the present application. For example, the positive electrode sheet comprises a positive electrode current collector and a positive electrode mixture layer on at least one surface of the positive electrode current collector. The "positive electrode mixture layer on at least one surface of the positive electrode current collector" means that the positive electrode mixture layer can be on one surface of the positive electrode current collector along the thickness direction of the positive electrode current collector, or on both surfaces of the positive electrode current collector along the thickness direction of the positive electrode current collector. It should be noted that the "surface" here can be the entire area of the surface of the positive electrode current collector, or can be part of the area of the surface of the positive electrode current collector, and the present application is not particularly limited, as long as it can achieve the purpose of the present application.

[0057] The positive electrode current collector of the present application is not particularly limited, as long as it can achieve the purpose of the present application. For example, the positive electrode current collector can comprise an aluminum foil, an aluminum alloy foil, or a composite current collector (such as an aluminum-carbon composite current collector), etc.

[0058] The positive electrode mixture layer of the present application comprises a positive electrode active material, and the type of the positive electrode active material of the present application is not particularly limited, as long as it can achieve the purpose of the present application. For example, the positive electrode active material can comprise lithium nickel cobalt manganese oxide (LiNi 0.90 Co 0.05 Mn 0.05O2(NCM955), NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate (LiCoO2), lithium manganate, lithium nickel manganate, lithium manganese iron phosphate, or lithium titanate, etc. In the present application, the positive electrode active material can also include a non-metal element, for example, the non-metal element includes at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur.

[0059] In the present application, the positive electrode mixture layer can also include a positive electrode binder and a conductive agent. The positive electrode binder can improve the binding between the positive electrode active material particles and each other, and can improve the binding between the positive electrode active material and the positive electrode current collector. The present application does not have a particular limitation on the type of positive electrode binder in the positive electrode mixture layer, as long as the purpose of the present application can be achieved, for example, the positive electrode binder can include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyolefins (such as polyethylene, polypropylene, etc.), styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0060] The present application does not have a particular limitation on the type of conductive agent in the positive electrode mixture layer, as long as the purpose of the present application can be achieved, for example, the conductive agent can be the same as the type of conductive agent in the negative electrode mixture layer described above. Non-limiting examples of conductive agents include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, etc.), metal-based materials (e.g., metal powder, metal fibers, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0061] The present application does not have a particular limitation on the mass ratio of the positive electrode active material, the conductive agent, and the positive electrode binder in the positive electrode mixture layer, and a person skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved. In some embodiments, the structure of the positive electrode sheet can be a positive electrode sheet structure known in the art that can be used in an electrochemical device.

[0062] In some embodiments, the method of preparing the positive electrode sheet is a method of preparing a positive electrode sheet known in the art that can be used in an electrochemical device. For example, the positive electrode sheet can be obtained by mixing the positive electrode active material, the conductive material, and the positive electrode binder in a solvent to prepare an active material composition, and coating the active material composition on the current collector. In some embodiments, the solvent can include water, N-methylpyrrolidone, etc., but is not limited thereto.

[0063] In some embodiments, the secondary battery of the present application further comprises an electrolyte.

[0064] In some embodiments, the electrolyte comprises a first substance, which comprises at least one of vinylene carbonate or vinyl ethylene carbonate. By adding at least one of vinylene carbonate (VC) or vinyl ethylene carbonate (VEC) into the electrolyte, the contact between the negative electrode and the electrolyte can be improved by the cooperation of the composite material in the negative electrode, thereby reducing the interfacial impedance, lowering the internal resistance of the secondary battery, and also facilitating the formation of a more uniform and compact SEI film, protecting the electrode surface and reducing the decomposition of the electrolyte and the occurrence of side reactions, thereby improving the cycle performance and safety performance of the secondary battery.

[0065] The mass percentage of the first substance is M4, 0.01%≤M4≤4%, based on the mass of the electrolyte. For example, M4may be 0.01%, 0.42%, 0.89%, 1.37%, 1.75%, 2.23%, 2.75%, 3.15%, 3.78%, 4.00%, or a value within a range defined by any two of these values. In some preferred embodiments, 0.42%≤M4≤1.75%. By regulating the mass percentage of the first substance within the above range, the cooperation effect of the first substance and the composite material can be promoted, and the stability of the SEI film can be further improved, so that the secondary battery can achieve higher cycle performance and safety performance.

[0066] The electrolyte can be divided into aqueous electrolyte and non-aqueous electrolyte. Compared with the aqueous electrolyte, the electrochemical device using the non-aqueous electrolyte can work in a wider voltage window, thereby achieving a higher energy density. In some embodiments, the non-aqueous electrolyte comprises an organic solvent and an electrolyte.

[0067] Electrolytes that can be used in the electrolyte of embodiments of the present application include, but are not limited to, inorganic lithium salts such as LiC104, LiAsF6, LiPF6, LiBF4, LiSbF6, LiSO3F, LiN(FSO2)2, and the like; fluorine-containing organic lithium salts such as LiCF3SO3, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,3-hexafluoropropanedisulfonimide lithium, cyclic 1,2-tetrafluoroethane disulfonimide lithium, LiPF4(CF3)2, LiN(CF3SO2)(C4F9SO2), LiC(CF3SO2)3, LiPF4(CF3SO2)2, LiPF4(C2F5)2, LiPF4(C2F5SO2)2, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2; dicarboxylic acid complex-containing lithium salts such as lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tris(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, and the like. Additionally, the above electrolytes can be used singly, or two or more kinds can be used simultaneously. For example, in some embodiments, the electrolyte includes a combination of LiPF6and LiBF4. In some embodiments, the electrolyte includes LiPF6.

[0068] The present application does not limit the content of the electrolyte in the electrolyte, as long as the purpose of the present application can be achieved. In some exemplary embodiments, the concentration of the electrolyte is in the range of 0.8 mol / L to 3 mol / L, such as in the range of 0.8 mol / L to 2.5 mol / L, in the range of 0.8 mol / L to 2 mol / L, in the range of 1 mol / L to 2 mol / L, and 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.

[0069] The organic solvent that can be used in the electrolyte of embodiments of the present application can be any organic solvent known in the art. In some embodiments, the organic solvent includes, but is not limited to, a carbonate compound, an ester-based compound, an ether-based compound, a ketone-based compound, an alcohol-based compound, an aprotic solvent, or a combination thereof. Among them, examples of the carbonate compound include, but are not limited to, a chain carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound, or a combination thereof.

[0070] 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.

[0071] The preparation method of the electrolyte of the embodiments of the present application is not limited, and can be prepared according to the conventional electrolyte. In some embodiments, the electrolyte of the present application can be prepared by mixing the components.

[0072] In some embodiments, the secondary battery of the present application is provided with a separator between the positive electrode sheet and the negative electrode sheet to prevent short circuit. The material and shape of the separator are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic substance formed of a material stable to the electrolyte of the present application, etc.

[0073] For example, in some embodiments, the separator comprises a substrate layer. The substrate layer is a non-woven fabric, a film or a composite film having 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 polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric or polypropylene-polyethylene-polypropylene porous composite film.

[0074] A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer can be a polymer layer, an inorganic layer or a layer formed by mixing polymer and inorganic substance. Specifically, the inorganic layer comprises inorganic particles and a binder. The inorganic particles can be selected from one or a combination of several of aluminum oxide, 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 can be selected from one or a combination of several of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.

[0075] The secondary battery of the present application further comprises a packaging bag for containing the positive electrode sheet, the negative electrode sheet, the separator and the electrolyte, and other components known in the art in the secondary battery, and the present application does not limit the above-mentioned other components. The packaging bag of the present application is not particularly limited, and can be a packaging bag known in the art as long as it can achieve the purpose of the present application.

[0076] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and the present application is not particularly limited, for example, can include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding, etc. as needed to obtain an electrode assembly with a winding structure, placing the electrode assembly into a packaging bag, injecting electrolyte into the packaging bag and sealing, to obtain a secondary battery; or stacking the positive electrode sheet, the separator and the negative electrode sheet in order, then fixing the four corners of the entire stack structure with adhesive tape to obtain an electrode assembly with a stack structure, placing the electrode assembly into a packaging bag, injecting electrolyte into the packaging bag and sealing, to obtain a secondary battery. In addition, a current protection element, a guide plate, etc. can also be placed in the packaging bag as needed, thereby preventing the pressure inside the secondary battery from rising and overcharging and discharging.

[0077] In a fourth aspect, the present application provides an electronic device comprising the electrochemical device provided in the third aspect of the present application.

[0078] The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. For example, the electronic device can include but is not limited to a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a head-mounted stereo headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, etc. In addition, the electrochemical device of the present application is applicable not only to the above-mentioned electronic devices, but also to energy storage power stations, sea-borne vehicles, and air-borne vehicles. The air-borne vehicles include air-borne vehicles within the atmosphere and air-borne vehicles outside the atmosphere.

[0079] The scheme of the present application will be described below with reference to the following specific examples taking lithium ion batteries as an example. Unless otherwise specified, the raw materials used in the following examples are all from ordinary commercially available products, and the devices or equipment used are all purchased from conventional market channels. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0080] Preparation of lithium ion batteries

[0081] 1. Preparation of negative electrode sheet

[0082] The composite material, conductive agent, polyacrylic acid (PAA), thickening agent (sodium carboxymethyl cellulose, CMC) in Table 1, Table 2 or Table 3 are mixed in a solvent (deionized water) in a weight ratio of 95.7:1.5:1.8:1 under sufficient stirring to form a uniform negative electrode slurry. The negative electrode slurry is uniformly coated on a negative electrode current collector (copper foil), dried, cold-pressed to form a negative electrode active material layer, and then cut and tabbed to obtain a negative electrode sheet.

[0083] 2. Preparation of a positive electrode sheet

[0084] The positive electrode active material (lithium nickel cobalt manganese oxide, NCM811), conductive agent (acetylene black), and binder (polyvinylidene fluoride, PVDF) are mixed in a solvent (N-methyl pyrrolidone, NMP) in a mass ratio of 96.3:2.2:1.5, and uniformly stirred under a vacuum stirrer to obtain a positive electrode slurry. The positive electrode slurry is coated on a positive electrode current collector (aluminum foil), dried, cold-pressed to form a positive electrode active material layer, and then cut and tabbed to obtain a positive electrode sheet.

[0085] 3. Preparation of an electrolyte

[0086] In a dry argon glove box, ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of EC:PC:EMC:DEC=10:30:30:30, followed by the addition of 2% fluoroethylene carbonate and 2% 1,3-propane sultone. After dissolution and sufficient stirring, lithium salt LiPF6 is added, and the mixture is uniformly mixed to obtain an electrolyte. The concentration of LiPF6 is 1 mol / L.

[0087] 4. Preparation of a separator

[0088] A porous polyethylene (PE) film is used as the separator.

[0089] 5. Preparation of a lithium ion battery

[0090] The obtained positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to serve as a separator. Then, the bare cell is obtained by winding. The bare cell is placed in an outer packaging aluminum plastic film, electrolyte is injected, and the lithium ion battery is obtained by vacuum packaging, standing, and formation.

[0091] Test method:

[0092] Silicon element content test:

[0093] The silicon content in the present application can be tested by methods known in the art, for example, the silicon content of the sample to be tested can be quantitatively tested by using Shimadzu / Kratos X-ray photoelectron spectrometer AXIS SUPRA+.

[0094] D peak and G peak intensity ratio test:

[0095] The ID / IG of the carbon material (such as graphite, hard carbon) can be tested by methods known in the art, for example, the carbon material sample can be scanned by using a laser microscopic confocal Raman spectrometer (Raman, HR Evolution, HORIBA Scientific Instrument Co., Ltd.), and the D peak and G peak of all sample particles in the area range are obtained, the data is processed by using LabSpec software to obtain the peak intensity of each sample particle, which is ID and IG respectively, the frequency of ID / IG is counted with a step of 0.02 to obtain a normal distribution graph, the (ID / IG)max and (ID / IG)min of these sample particles are counted, and the average value of ID / IG is calculated, which is the ID / IG value of the measured carbon material. The laser wavelength of the Raman spectrometer can be in the range of 532 nm to 785 nm.

[0096] Average particle size test:

[0097] The average particle size can be tested by methods known in the art, for example, a laser diffraction particle size distribution measuring instrument (Malvem Mastersizer 3000) can be used to measure the particle size distribution of the sample to be tested according to the particle size distribution laser diffraction method GB / T19077 2016, and then the average particle size of the sample to be tested is obtained. Also, a sample area can be selected on the negative electrode sheet, and a SEM image of the sample area is obtained, then, an image analysis software is used to randomly select 10 particles of the sample to be tested from the SEM image as samples, the areas of these samples are calculated, then, assuming that the sample to be tested is spherical, the area equivalent diameter R1 (diameter) of each sample to be tested is calculated by the following formula: 1 / 2 ; wherein S is the area of the sample to be tested. The R1 of the above-mentioned sample to be tested is calculated by processing 3 SEM images, and the area equivalent diameters of the 30 (10x3) samples to be tested are arithmetically averaged to obtain the average particle size of the sample to be tested.

[0098] Sphericity test:

[0099] The sphericity can be tested by methods known in the art, for example, 10 particles of the material to be tested can be randomly selected from a sample area of the negative electrode sheet as samples, the circumferences of the samples are measured, and the area equivalent diameters R1 (diameter) of the samples are calculated by the following formula assuming that the samples are spherical: R1 = 2 x (S / π) 1 / 2 ; wherein S is the area of the sample, the circumference equivalent diameter R2 (diameter): R2 = 2 x (L / π); wherein L is the circumference of the sample. The sphericity of the material to be tested is calculated according to Q = R2 / R1, and the Q of 30 samples of the material to be tested from 3 SEM images is calculated, and then the sphericity of the material to be tested is obtained by arithmetic average.

[0100] X-ray powder diffraction (XRD) test:

[0101] The X-ray powder diffraction instrument (XRD, instrument model: Bruker D8 ADVANCE) is used for testing, the target material is CuKα, the voltage and current are 40KV / 40mA, the scanning angle range is 5° to 80°, the scanning step is 0.00836°, and the time for each step is 0.3s.

[0102] X-ray diffraction principle: when X-rays are irradiated on an object at an angle of θ, a part of the photons changes the direction of advancement due to collision with atoms, causing scattered rays. When the wavelength λ of the scattered rays is the same as that of the incident rays and has a certain phase relationship, the two interfere with each other to form a diffraction phenomenon, i.e., Bragg's law, 2dsinθ = λ (d is the interplanar spacing), so the interlayer spacing of the present application, i.e., the interplanar spacing d002 of the (002) crystal plane diffraction peak (referred to as 002 peak) is λ / 2 / sinθ, θ is the angle of the maximum peak intensity position of the 002 peak.

[0103] Direct current internal resistance test of lithium ion battery:

[0104] (1) the test temperature is 25°C;

[0105] (2) the lithium ion battery is charged at a current of 0.5C (CC) to 4.35V, and then charged at a constant voltage (CV) to 0.02C;

[0106] (4) stand for 5 minutes;

[0107] (5) discharge at a current of 1C (CC) for 1800 seconds (to 50% SOC), and record the terminal voltage;

[0108] (6) discharge at a current of 0.1C (CC) for 1 second, and record the terminal voltage, and calculate the terminal voltage difference and response current difference of steps 5 and 6;

[0109] (7) 50% SOC corresponding DC internal resistance is obtained by dividing the absolute value of the voltage difference at 5, 6 steps by the absolute value of the response current difference.

[0110] Cycle performance test of lithium ion battery:

[0111] (1) The test temperature is 25°C, and the lithium ion battery to be tested is placed for 30 min;

[0112] (2) The lithium ion battery to be tested is discharged (DC) at a current of 1C to 2.5V;

[0113] (3) Place for 30 min;

[0114] (4) Charge (CC) at a current of 1C to 4.35V, and then charge (CV) to 0.05C;

[0115] (5) Place for 5 min;

[0116] (6) Discharge at a current of 1C to 2.5V;

[0117] (7) Place for 5 min;

[0118] (8) Cycle steps 4 to 7 for 400 times, record the discharge capacity obtained in step (6) of the 3rd and 400th cycles, respectively, as the discharge capacity of the 3rd and 400th cycles;

[0119] (9) End of test.

[0120] Lithium ion battery capacity retention rate = discharge capacity of the 400th cycle / discharge capacity of the 3rd cycle x 100%.

[0121] Rate performance test of lithium ion battery

[0122] (1) The test temperature is 25°C;

[0123] (2) The lithium ion battery to be tested is placed for 5 min;

[0124] (3) The lithium ion battery to be tested is discharged at a current of 0.2C to 2.5V;

[0125] (4) Place for 5 min;

[0126] (5) Charge at a current of 0.5C to 4.3V, and then charge at a constant voltage to 0.02C;

[0127] (6) Place for 5 min;

[0128] (7) Discharge the lithium ion battery to be tested to 2.5V at a constant current, and the constant current discharge current is 0.2C. Record the discharge capacity obtained in this step as the 0.2C discharge capacity;

[0129] (8) Cycle step 4 to step 7, test under the condition of constant current discharge current respectively 4C rate, record the discharge capacity obtained in this step as 4C discharge capacity.

[0130] Lithium ion battery 4C capacity retention rate = 4C discharge capacity / 0.2C discharge capacity x 100%.

[0131] Thermal oven test performance test of lithium ion battery:

[0132] The thermal oven test procedure is as follows:

[0133] (1) The test temperature is 25℃, and the standing time is 5min;

[0134] (2) Constant current discharge at 1C current to 2.5V;

[0135] (3) Stand for 10min;

[0136] (4) Constant current charge (CC) to 4.35V, then constant voltage charge (CV) to 0.05C at 4.35V;

[0137] (5) Stand for 10min.

[0138] Take a photo before testing, measure the voltage resistance, and paste the temperature sensing line on the surface of the battery. Put the sample into the heating oven box, and increase the temperature to 155±2℃ at a rate of 5±2℃ / min and keep for 60min. Take a photo after testing, measure the voltage resistance. If the battery does not catch fire or explode, it is considered to have passed the thermal oven test, and the pass rate of 10 cells is used as the judgment index.

[0139] The performance test results of each embodiment and the comparative example are shown below.

[0140] The composite materials of each embodiment and the comparative example in Table 1 differ only in the average particle size D1 of graphite, the average particle size D2 of silicon carbon and / or the average particle size D3 of hard carbon from Example I-1. The specific differences and test results are shown in Table 1.

[0141] Table 1

[0142] As can be seen from Table 1, the average particle sizes of the graphite, silicon-carbon and hard carbon are regulated to satisfy 0.5≤D2 / D1≤0.7 and 0.7≤D3 / D1≤0.9, which can produce a synergistic effect, reduce the direct current resistance of the lithium ion battery, and improve the energy density of the lithium ion battery while improving the rate performance and cycle performance of the lithium ion battery. When 0.54≤D2 / D1≤0.65 is further regulated, the internal resistance of the lithium ion battery can be significantly reduced, and the lithium ion battery can exhibit better rate performance and cycle performance. In particular, when the average particle sizes of the graphite and hard carbon satisfy 0.74≤D3 / D1≤0.83, the internal resistance, rate performance and cycle performance of the lithium ion battery can be further improved.

[0143] In particular, on the basis of the above average particle size relationship, the average particle size of the graphite is controlled to be 4 μm≤D1≤23.3 μm, the average particle size of the silicon-carbon is controlled to be 2 μm≤D2≤11.65 μm, and / or the average particle size of the hard carbon is controlled to be 3.6 μm≤D3≤21 μm, which can further improve the internal resistance, rate performance and cycle performance of the lithium ion battery.

[0144] The examples and comparative examples in Table 2 differ from Example I-1 only in that the mass percentage content M1 of the graphite, the mass percentage content M2 of the silicon-carbon and / or the mass percentage content M3 of the hard carbon are different. The specific differences and test results are shown in Table 2.

[0145] Table 2

[0146] As can be seen from Table 2, regulating the mass percentage content of the silicon-carbon in the composite material to be 30%≤M2≤80% and / or regulating the mass percentage content of the hard carbon to be 10%≤M3≤20% can further reduce the direct current resistance of the lithium ion battery and improve the rate performance and cycle performance of the lithium ion battery. In particular, controlling the mass content of the hard carbon and graphite to satisfy the relationship 0.5≤M3 / M1≤2 can significantly improve the rate performance and cycle performance of the lithium ion battery.

[0147] The examples and comparative examples in Table 3 differ from Example 1 only in that the interlayer spacing d1 of the graphite, the interlayer spacing d2 of the hard carbon, the mass content S1 of the silicon element in the silicon-carbon, the type and / or mass percentage content M4 of the first substance are different. The specific differences and test results are shown in Table 3.

[0148] Table 3

[0149] As can be seen from Table 3, the present application respectively regulates the interlayer spacing d1 of graphite to meet 0.335 nm≤d1≤0.35 nm, and the interlayer spacing d2 of hard carbon to meet 0.35 nm≤d2≤0.38 nm, which can optimize the storage space of active substances and the electronic transmission channel, further reduce the internal resistance of the lithium ion battery, and improve the rate performance and cycle performance of the lithium ion battery. In particular, when the content of silicon element S1 in the silicon-carbon meets 85%≤S1≤90%, the cycle performance, internal resistance and rate performance of the secondary battery can be further improved.

[0150] In particular, the first substance of at least one of vinylene carbonate or vinyl ethylene carbonate is added to the electrolyte, and the mass percentage content M4 of the first substance is regulated to meet 0.01%≤M4≤4%, which can improve the rate performance, cycle performance and safety performance of the secondary battery. In particular, when M4 meets 0.42%≤M4≤1.75%, the rate performance, cycle performance and safety performance of the secondary battery can be further optimized.

[0151] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the principles of the present application shall be included in the protection scope of the present application.

Claims

1. A composite material, characterized by, The composite material includes graphite, silicon carbide, and hard carbon; The average particle size of the graphite is D1, the average particle size of the silicon carbide is D2, and the average particle size of the hard carbon is D3; 0.5≤D2 / D1≤0.7, and 0.7≤D3 / D1≤0.

9.

2. The composite material of claim 1, wherein, The composite material satisfies at least one of the following conditions: (1) 0.54 ≤ D2 / D1 ≤ 0.65; (2) 0.74 ≤ D3 / D1 ≤ 0.83; (3) 4μm≤D1≤23.3μm; (4) 2μm≤D2≤11.65μm; (5) 3.6μm≤D3≤21μm.

3. The composite material of claim 1, wherein, Based on the mass of the composite material, the mass percentage of graphite is M1, the mass percentage of silicon-carbon is M2, and the mass percentage of hard carbon is M3; M1, M2, and / or M3 satisfy: 30.7% ≤ M2 ≤ 79.6%; 10.3% ≤ M3 ≤ 19.5%; and / or, 0.5≤M3 / M1≤2.

4. The composite material according to any one of claims 1 to 3, characterized in that, The composite material satisfies at least one of the following conditions: (1) In the Raman spectrum of the graphite, the intensity ratio of the D peak and the G peak is N1, 0.35≤N1≤0.7; (2) In the Raman spectrum of the hard carbon, the intensity ratio of the D peak and the G peak is N2, 0.7≤N2≤1.3; (3) The interlayer spacing of the graphite is d1, 0.335nm≤d1≤0.35nm; (4) The interlayer spacing of the hard carbon is d2, 0.35nm≤d2≤0.38nm.

5. The composite material according to any one of claims 1 to 3, characterized in that, The composite material satisfies at least one of the following conditions: (1) Based on the mass of the silicon carbon, the mass content of silicon element is S1, 85%≤S1≤90%; (2) The interlayer spacing of the carbon material in the silicon-carbon is d3, 0.35nm≤d3≤0.38nm; (3) The sphericity of the graphite, silicon carbide and hard carbon is greater than or equal to 0.

7.

6. A negative electrode sheet comprising a negative electrode mixture layer, characterized by The negative electrode compound layer comprises the composite material according to any one of claims 1 to 5.

7. An electrochemical device, characterized by, Includes the negative electrode sheet as described in claim 6.

8. The electrochemical device of claim 7, wherein, The electrochemical device further includes an electrolyte, which includes a first substance, the first substance including at least one of vinylene carbonate or vinyl ethylene carbonate; Based on the mass of the electrolyte, the mass percentage of the first substance is M4, where 0.01% ≤ M4 ≤ 4%.

9. The electrochemical device of claim 8, wherein, 0.42％≤M4≤1.75％。 10. An electronic device, comprising: The electrochemical device includes any one of claims 1 to 9.

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