Silicon-carbon composite material, secondary battery, and electronic device

Abstract

The present application provides a silicon-carbon composite material, a secondary battery, and an electronic device. The silicon-carbon composite material comprises a silicon substrate and a first layer at least partially located on the silicon substrate, wherein the first layer comprises a conductive agent and a silicon-oxygen organic substance. The silicon-carbon composite material provided by the present application enhances the interface stability between a silicon substrate and an electrolyte solution, improves the cycling performance of a secondary battery, and can also reduce the decomposition and gas production of an SEI film during the overdischarging of the secondary battery, thereby ameliorating the problem of gas production during the overdischarging of the secondary battery.

Description

Silicon-carbon composite material, secondary battery and electronic device TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical energy storage, in particular to a silicon-carbon composite material, a secondary battery using the silicon-carbon composite material and an electronic device using the secondary battery. BACKGROUND

[0002] In recent years, secondary batteries (such as lithium ion batteries) have developed rapidly in the field of new energy vehicles and large-scale energy storage. However, during the charging process of the secondary battery, the SEI film formed on the surface of the negative electrode will decompose and produce gas, which will affect the cycle performance of the lithium ion battery. SUMMARY

[0003] The present application provides a silicon-carbon composite material capable of improving the cycle performance.

[0004] In addition, the present application also provides a secondary battery using the silicon-carbon composite material and an electronic device.

[0005] The present application provides a silicon-carbon composite material, which comprises a silicon matrix and a first layer at least partially on the silicon matrix, the first layer comprising a conductive agent and a silicon-oxygen organic matter.

[0006] When the silicon-carbon composite material of the present application is applied to a secondary battery, the silicon-oxygen groups (Si-O-) in the silicon-oxygen organic matter can react with hydrogen fluoride (HF) in the electrolyte, thereby reducing or eliminating the etching of the silicon matrix by HF, improving the interface stability of the silicon matrix and the electrolyte, and improving the cycle performance of the secondary battery. At the same time, it can also reduce the corrosion of HF to the SEI film, thereby improving the stability of the SEI film. Furthermore, the silicon-oxygen organic matter can not only improve the stability of the SEI film, but also inhibit the decomposition of the solvent in the SEI film, reduce the organic components in the SEI film, thereby realizing the high-pressure stability of the SEI film, reducing lithium precipitation, and reducing the decomposition of the SEI film during over-discharge of the secondary battery, thereby improving the gas production problem during over-discharge of the secondary battery. The addition of the conductive agent in the first layer is beneficial to improving the interface conductivity of the silicon-carbon composite material, thereby improving the kinetic performance of the silicon-carbon composite material. The combination of the silicon-oxygen organic matter and the conductive agent in the silicon-carbon composite material makes the silicon-carbon composite material have good cycle performance, swelling performance and kinetic performance. At the same time, the silicon-oxygen organic matter can form a network structure, which can improve the toughness and strength of the surface of the silicon-carbon composite material, thereby further improving the interface stability between the SEI films, and thereby improving the cycle performance and swelling performance of the silicon-carbon composite material. The conductive agent is dispersed in the network structure formed by the silicon-oxygen organic matter, which can further improve the interface conductivity of the silicon-carbon composite material, thereby improving the kinetic performance of the silicon-carbon composite material.

[0007] In some possible implementation manners based on the first aspect, the siloxane organic matter comprises at least one of polymethylhydrosiloxane, polysilsesquioxane, vinyltrimethoxysilane or vinyltriethoxysilane. The siloxane and silane can reduce or eliminate etching of the silicon substrate by HF, improve the interface stability of the silicon substrate and the electrolyte, thereby improving the cycle performance of the secondary battery, and can also reduce lithium deposition and reduce the decomposition of the SEI film to produce gas when the secondary battery is over-discharged, thereby improving the gas production problem of the secondary battery when over-discharged.

[0008] In some possible implementation manners based on the first aspect, the conductive agent comprises at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes. The conductive agent has good conductivity, which is conducive to improving the conductivity of the silicon-carbon composite material, thereby providing a good transmission channel for active ions and improving the charge-discharge efficiency and cycle life of the secondary battery.

[0009] In some possible implementation manners based on the first aspect, the mass ratio of the silicon substrate and the conductive agent is 100:(0.5-0.9). This is conducive to improving the conductivity of the silicon-carbon composite material while also having good specific capacity, and the coated silicon-carbon composite material has excellent kinetic performance.

[0010] In some possible implementation manners based on the first aspect, the mass ratio of the conductive agent and the siloxane organic matter is (0.5-5):2. This is conducive to the siloxane organic matter being fully coated on the silicon substrate, which is conducive to improving the integrity of the siloxane organic matter coated on the silicon substrate, thereby sufficiently reducing etching of the silicon substrate by the electrolyte, and the silicon-carbon composite material has good conductivity, and the silicon-carbon composite material has good kinetic performance and cycle performance.

[0011] In some possible implementation manners based on the first aspect, the conductive agent has a linear structure, the average diameter of the conductive agent is y nm, and 0.5≤y≤20. This is conducive to improving the dispersity of the conductive agent while improving the electrical conductivity of the silicon-carbon composite material, thereby improving the rate performance and cycle performance of the silicon-carbon composite material. The average length of the conductive agent is L nm, and 500≤L≤1000. This is conducive to improving the dispersity of the conductive agent while providing the active ions with good long-range conductivity, thereby improving the kinetic performance of the silicon-carbon composite material.

[0012] In some possible implementation manners based on the first aspect, the particle size Dv50 of the silicon-carbon composite material is D μm, and 4≤D≤13. This is conducive to reducing side reactions between the silicon-carbon composite material and the electrolyte, improving the cycle performance of the silicon-carbon composite material, and improving the gas production problem of the secondary battery when overcharged.

[0013] In some possible implementation manners based on the first aspect, the thickness of the first layer is Hnm, 5≤H≤100, which is conducive to making the silicon-carbon composite material have better specific capacity, and meanwhile, the first layer can protect the silicon matrix and improve the gas generation problem of the secondary battery during overcharge.

[0014] In some possible implementation manners based on the first aspect, the relationship between H and Dv50 satisfies the relationship: 0.55≤H / D≤12.5, which is conducive to making the silicon-carbon composite material have better rate performance and cycle performance, and is also conducive to improving the interface stability between the silicon-carbon composite material and the electrolyte, and further improving the gas generation problem of the SEI film during overcharge of the secondary battery.

[0015] In some possible implementation manners based on the first aspect, the silicon matrix comprises a silicon-carbon material, the silicon-carbon material comprises silicon elements and carbon elements, and the mass percentage of the silicon elements in the silicon elements and the carbon elements in the silicon matrix is 41.8% to 57.9%. This is conducive to making the silicon matrix have good electrical conductivity, and is also conducive to making the silicon matrix have good capacity contribution of silicon, and making the silicon-carbon composite material have good cycle performance.

[0016] In some possible implementation manners based on the first aspect, the average diameter of the conductive agent is ynm, and 1≤H / y≤25. This is conducive to making the first layer have a certain thickness and good electrical conductivity, and is conducive to improving the cycle stability, energy density of the secondary battery, and improving the over-discharge gas generation of the secondary battery.

[0017] The second aspect of the present application also provides a secondary battery, which comprises a battery cell, the battery cell comprising a negative electrode sheet, a positive electrode sheet and an electrolyte, the negative electrode sheet further comprising a silicon-carbon composite material, and the silicon-oxygen organic matter in the silicon-carbon composite material can improve the interface stability between the silicon matrix and the electrolyte, reduce the decomposition gas generation of the SEI film during over-discharge of the secondary battery, improve the cycle performance of the secondary battery and improve the gas generation performance of the secondary battery.

[0018] In some possible implementation manners based on the second aspect, when the voltage of the battery cell is 3V to 3.95V, the thickness of the battery cell is H0, and when the battery cell is discharged to 0.5V, the thickness of the battery cell is H2, and 0.58<H2 / H0≤1.36. The gas generation problem in the battery cell is improved, and the battery cell can maintain good stability, thereby improving the cycle performance and service life of the secondary battery.

[0019] The third aspect of the present application provides an electronic device comprising a secondary battery. The secondary battery supplies power to the electronic device, and the secondary battery comprises a silicon-carbon composite material, which can improve the cycle life of the secondary battery, and further improve the service life of the electronic device. BRIEF DESCRIPTION OF DRAWINGS

[0020] The above and / or additional aspects and advantages of the present application will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings, in which:

[0021] Figure 1 is a scanning electron microscope image of the silicon-carbon composite material prepared in Example 1.

[0022] Figure 2 is a scanning electron microscope image of the silicon substrate without any coating in Comparative Example 1.

[0023] Figure 3 is a plot of the change in cell thickness and voltage of the assembled cell of the silicon-carbon composite material prepared in Example 1 when discharged from 3.19 V to 0.5 V. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be described clearly and in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Unless otherwise defined, all the technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing the specific embodiments and are not intended to limit the present application.

[0025] In the related art, during over-discharge of a lithium ion battery, the lithium ion battery continuously discharges, and the negative electrode potential continuously rises to the oxidation potential at which the solid electrolyte interface film (SEI film) is oxidized and decomposed, which causes the SEI film to be oxidized and decomposed and a large amount of gas to be generated, affecting the cycle performance and safety performance of the lithium ion battery.

[0026] The present application provides a silicon-carbon composite material, which comprises a silicon substrate and a first layer at least partially on the silicon substrate, the first layer comprising a conductive agent and a silicon-oxygen organic compound containing Si-O-R. When the silicon-carbon composite material of the present application is applied to a secondary battery, the silicon-oxygen groups (Si-O-) in the silicon-oxygen organic compound can react with hydrogen fluoride (HF) in the electrolyte, thereby reducing or eliminating the etching of the silicon substrate by HF, improving the interface stability of the silicon substrate and the electrolyte, and improving the cycle performance of the secondary battery. At the same time, the corrosion of the SEI film by HF can also be reduced, thereby improving the stability of the SEI film. The silicon-oxygen organic compound, while improving the stability of the SEI film, can also inhibit the decomposition of the solvent in the SEI film, reduce the organic components in the SEI film, thereby achieving high-pressure stability of the SEI film, reducing lithium precipitation, and reducing the decomposition of the SEI film and gas generation during over-discharge of the secondary battery, thereby improving the gas generation problem during over-discharge of the secondary battery. The addition of the conductive agent in the first layer is conducive to improving the interface conductivity of the silicon-carbon composite material, thereby improving the kinetic performance of the silicon-carbon composite material. The combination of the silicon-oxygen organic compound and the conductive agent in the silicon-carbon composite material makes the silicon-carbon composite material have good cycle performance, swelling performance, and kinetic performance.

[0027] In some embodiments, the first layer can completely coat the outer surface of the silicon substrate, or the first layer can only coat part of the outer surface of the silicon substrate, for example, the surface area of the first layer can account for one-half or one-third of the outer surface area of the silicon substrate.

[0028] In some embodiments, the siloxane organic matter includes at least one of polymethylhydrosiloxane, polysilsesquioxane, vinyltrimethoxysilane or vinyltriethoxysilane. The siloxane or Si-O bond in the siloxane organic matter can reduce or eliminate the etching of HF to the Si or silicon compound material interface in the silicon substrate, improve the interface stability of the silicon substrate and the electrolyte, and further improve the cycle performance of the secondary battery. It can also reduce the decomposition of the SEI film during over-discharge of the secondary battery, and improve the gas production problem of the secondary battery during over-discharge. At the same time, the network structure formed by the above-mentioned siloxane organic matter can also improve the toughness and strength of the surface of the silicon-carbon composite material, thereby further improving the stability of the SEI film, and further improving the cycle performance and expansion performance of the silicon-carbon composite material. The conductive agent dispersed in the network structure formed by the siloxane organic matter can further improve the interface conductivity of the silicon-carbon composite material, thereby improving the kinetic performance of the silicon-carbon composite material.

[0029] In some embodiments, the conductive agent includes at least one of single-walled carbon nanotubes (SWCNT) or multi-walled carbon nanotubes. The conductive agent has good conductivity, which is beneficial to improve the conductivity of the silicon-carbon composite material, and thus can provide a good transmission channel for active lithium ions, reduce the internal resistance of the secondary battery, and thus improve the charge-discharge efficiency and cycle life of the secondary battery.

[0030] In some embodiments, the silicon substrate includes a silicon-carbon material. The silicon-carbon material can include a porous carbon material and elemental silicon dispersed on the porous carbon material, and the porous carbon material is used to inhibit the volume expansion of the elemental silicon during the cycle process.

[0031] In some embodiments, the mass ratio of the silicon substrate and the conductive agent is 100:(0.5-0.9). The mass ratio of the conductive agent and the siloxane organic matter is within the above range, which is beneficial to improve the conductivity of the silicon-carbon composite material while having good specific capacity, and the coated silicon-carbon composite material has excellent kinetic performance. In some embodiments, the mass ratio of the conductive agent and the siloxane organic matter can be 100:0.5, 100:0.6, 100:0.65, 100:0.7, 100:0.75, 100:0.8, 100:0.85, 100:0.9, or any ratio within the range formed by any two of the above ratios.

[0032] In some embodiments, the mass ratio of the conductive agent and the siloxane organic matter is (0.5-5):2. The mass ratio of the conductive agent and the siloxane organic matter is within the above range, so that the siloxane organic matter can be sufficiently coated on the silicon substrate, which is conducive to improving the integrity of the siloxane organic matter coated on the silicon substrate, thereby sufficiently reducing the etching of the electrolyte on the silicon substrate, and making the silicon-carbon composite material have good electrical conductivity, so that the silicon-carbon composite material has good kinetic performance and cycle performance. In some embodiments, the mass ratio of the conductive agent and the siloxane organic matter can be 0.5:2, 1:2, 1.5:2, 2:2, 2.5:2, 3:2, 3.5:2, 4:2, 4.5:2, 5:2, or any value within the range formed by any two of the above values.

[0033] In some embodiments, the conductive agent has a linear structure, and the average diameter of the conductive agent is y nm, 0.5≤y≤20. Within the above length range, it is conducive to improving the dispersibility of the conductive agent while improving the electrical conductivity of the silicon-carbon composite material, thereby improving the rate performance and cycle performance of the silicon-carbon composite material. If the average diameter of the conductive agent is too large, such as y>20, the electrical conductivity of the silicon-carbon composite material will be reduced, and the cycle performance of the silicon-carbon composite material will be reduced. If the average diameter of the conductive agent is too small, such as y<0.5, the dispersibility of the conductive agent in the first layer is poor, the charge distribution on the surface of the silicon-carbon composite material is uneven, the interface stability is reduced, thereby reducing the cycle performance of the silicon-carbon composite material, and the over-discharge gas production will be worsened. In some embodiments, the average diameter y of the conductive agent can be 0.5, 1, 2, 3, 5, 7, 9, 10, 12, 15, 17, 18, 20, or any value within the range formed by any two of the above values.

[0034] In some embodiments, the average length of the conductive agent is L nm, 500≤L≤1000. Within the above range, it is conducive to improving the dispersibility of the conductive agent while making the active lithium ions have good long-range conductivity, and the conductive agent is dispersed on the network structure of the siloxane organic matter, so that the conductive agent provides an excellent conductive network, thereby improving the rate performance of the silicon-carbon composite material. In some embodiments, the average length of the conductive agent can be 500, 600, 700, 800, 900, 1000, or any value within the range formed by any two of the above values.

[0035] In some embodiments, the particle size Dv50 of the silicon-carbon composite material is D μm, 4≤D≤13. Within the above range, it is conducive to reducing the side reaction of the silicon-carbon composite material with the electrolyte, improving the cycle performance of the silicon-carbon composite material, and improving the gas problem of the secondary battery during overcharge. In some embodiments, the particle size D of the silicon-carbon composite material can be 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, or any value within the range formed by any two of the above values.

[0036] In some embodiments, the thickness of the first layer of the silicon-carbon composite material is Hnm, 5≤H≤100. The thickness of the first layer is within the above range, which is conducive to protecting the silicon matrix and improving the gas generation problem of the secondary battery during overcharge while making the silicon-carbon composite material have better gram capacity. In some embodiments, the thickness H of the first layer can be 5, 10, 15, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, or any value within the range consisting of any two of the above values. Preferably, 6≤H≤63.

[0037] In some embodiments, the relationship between H and Dv50 satisfies the relationship: 0.55≤H / D≤12.5. Controlling the relationship between the thickness of the first layer and the particle size D of the silicon-carbon composite material within a suitable range is conducive to making the silicon-carbon composite material have better rate performance and cycle performance, for example, the silicon-based composite material has relatively large particle size, strong stability, but weak kinetics, and by reducing the thickness of the first layer, the silicon-based composite material maintains good kinetics. At the same time, it is also conducive to improving the interface stability of the silicon-carbon composite material and the electrolyte, and thus improving the gas generation problem of the SEI film during overcharge of the secondary battery. In some embodiments, the ratio between H and D can be 0.55, 0.8, 0.9, 1, 2, 5, 8, 10, 11, 12, 12.5, or any value within the range consisting of any two of the above values.

[0038] In some embodiments, 1≤H / y≤25. When the relationship between the thickness of the first layer and the average diameter of the conductive agent satisfies the above relationship, the relationship between the thickness of the first layer and the average diameter of the conductive agent is balanced, which is conducive to the first layer having a certain thickness while also having good electrical conductivity, which is conducive to improving the cycle stability, energy density of the secondary battery and improving the over-discharge gas generation of the secondary battery. In some embodiments, H / y can be 1, 2, 5, 7, 8, 10, 12, 15, 17, 20, 23, 25, or any value within the range consisting of any two of the above values.

[0039] In some embodiments, the mass percentage of the carbon element is 38.2% to 61.3% and the mass percentage of the silicon element is 38.7% to 61.8% based on the sum of the mass of the silicon element and the carbon element in the silicon matrix. The content of the carbon element and the silicon element in the silicon matrix within the above range is conducive to making the silicon matrix have good electrical conductivity, contributing to the capacity of the silicon in the silicon matrix, and making the silicon-carbon composite material have good cycle performance. In some embodiments, the mass percentage of the carbon element in the silicon matrix can be 38.2%, 39%, 41%, 45%, 47%, 49%, 53%, 55%, 58%, 60%, 61.3%, or any value within the range formed by any two of the above values. The mass percentage of the silicon element in the silicon matrix can be 38.7%, 39%, 41.8%, 43%, 45%, 48%, 51%, 54%, 56%, 57%, 57.9%, 59%, 61%, 61.8%, or any value within the range formed by any two of the above values. Preferably, the mass percentage of the silicon element is 41.8% to 57.9%.

[0040] The preparation method of the silicon-carbon composite material is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the preparation method of the silicon-carbon composite material can include but is not limited to the following steps: (1) dissolving and dispersing the conductive agent and the silicon-oxygen organic compound containing Si-O-R in a solvent, and stirring uniformly; (2) adding the silicon matrix material to step (1), stirring and dispersing uniformly, and drying to obtain the silicon-carbon composite material.

[0041] The solvent used in step (1) includes at least one of water, ethanol, ethylene glycol, propylene glycol, and tetrahydrofuran.

[0042] In step (2), the stirring time is 1h to 24h, the stirring speed is 500r / min to 2500r / min, the drying temperature is 92℃-198℃, and the drying time is 2h-24h.

[0043] The preparation method of the silicon matrix is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the preparation method of the above-mentioned silicon matrix includes: using chemical vapor deposition method, the silicon source gas is deposited on the porous carbon to form silicon, and then the carbon source is introduced to form amorphous carbon on the surface of the silicon matrix, thereby obtaining the silicon matrix. The carbon source gas can include but is not limited to at least one of methane, acetylene, ethylene, ethane, propyne, propylene, propane, butyne, butene, or butane. The silicon source gas can include but is not limited to one or more of monosilane, disilane, trisilane, tetrasilane, chlorosilane, dichlorosilane, trichlorosilane, or tetrachlorosilane. The content of the silicon element in the silicon matrix can be adjusted by changing the introduction time of the silicon source gas.

[0044] In the preparation method of the silicon-carbon composite material, the mass ratio of silicon element and carbon element in the silicon matrix and the mass ratio of the silicon matrix, the conductive agent and the silicon-oxygen organic matter affect the cycle performance, lithium precipitation performance and over-discharge gas production of the silicon-carbon composite material. The mass ratio of the silicon matrix and the conductive agent is 100:(0.5-0.9); the mass ratio of the conductive agent and the silicon-oxygen organic matter is (0.5-5):2. Preferably, the mass ratio of the silicon matrix, the conductive agent and the silicon-oxygen organic matter is 100:0.5:2. Increasing the mass ratio of the silicon matrix and the conductive agent will reduce the cycle performance of the silicon-carbon composite material, and reducing the mass ratio of the silicon matrix and the conductive agent will reduce the specific capacity of the silicon-carbon composite material and the energy density of the secondary battery. Increasing the mass ratio of the silicon matrix and the silicon-oxygen organic matter will reduce the effect of the silicon-carbon composite material on improving over-discharge gas production. Reducing the mass ratio of the silicon matrix and the silicon-oxygen organic matter will reduce the kinetic performance (such as lithium precipitation performance) and cycle performance of the silicon-carbon composite material. Increasing the mass ratio of the silicon-oxygen organic matter and the conductive agent will reduce the kinetic performance and cycle performance of the silicon-carbon composite material, and reducing the mass ratio of the silicon-oxygen organic matter and the conductive agent will reduce the performance of the silicon-carbon composite material on improving over-discharge gas production of the secondary battery.

[0045] Based on the above mass ratio of the silicon matrix, the conductive agent and the silicon-oxygen organic matter, the thickness H of the first layer can be changed by adjusting the stirring time and rate in the case of changing the content of the silicon matrix.

[0046] The average diameter y and the average length L of the conductive agent are changed by selecting conductive agent raw materials with different average diameters and average lengths.

[0047] An embodiment of the present application provides a secondary battery, which comprises a shell and an electrode core. The electrode core is located in the shell.

[0048] The shell can be a packaging bag obtained by packaging with a packaging film (such as an aluminum plastic film), and the secondary battery can be a soft-packaged secondary battery. In other embodiments, the secondary battery can also be a steel shell secondary battery, an aluminum shell secondary battery, etc.

[0049] The electrode core comprises an electrode assembly and an electrolyte, and the electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator. The electrode assembly can be a laminated structure formed by laminating the positive electrode sheet, the separator and the negative electrode sheet. In other embodiments, the electrode assembly can also be a wound structure formed by winding the positive electrode sheet, the separator and the negative electrode sheet after lamination.

[0050] The negative electrode sheet

[0051] The negative electrode sheet includes a negative current collector and a negative active layer disposed on the negative current collector. The negative current collector can use at least one of a copper foil, a nickel foil, a stainless steel foil, a titanium foil, or a carbon-based current collector, and can also be any composite current collector disclosed in the prior art, such as but not limited to a current collector formed by combining the aforementioned conductive foils and a polymer substrate. The negative active layer contains a negative active material, which includes the silicon-carbon composite material described above.

[0052] The negative active layer also contains a binder to bind the negative active material particles to facilitate the formation of a film layer, and also to improve the bonding force between the negative active layer and the negative current collector. In some embodiments, the binder can include, 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, or nylon, etc.

[0053] The negative active layer can also include a conductive material, which includes but is not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, the carbon-based materials can include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, or any combination thereof. In some embodiments, the metal-based materials can include, but are not limited to, metal powders or metal fibers, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer can be a polyphenylene derivative.

[0054] The negative active layer can further contain graphite, which has a certain flexibility and can cooperate with the silicon-carbon composite material to alleviate the overall volume expansion of the negative active layer. At the same time, graphite and silicon-carbon composite material as negative active material can also take full advantage of the advantages of both silicon-carbon composite material and graphite to achieve better electrochemical performance.

[0055] Positive electrode sheet

[0056] The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer disposed on the positive electrode current collector. The positive electrode current collector can use an aluminum foil or a nickel foil, or the like, and can be any composite current collector disclosed in the prior art, such as, but not limited to, a current collector formed by combining the aforementioned conductive foil and a polymer substrate. The positive electrode active layer includes a positive electrode active material, which includes a compound that reversibly intercalates and deintercalates lithium ions (i.e., a lithiated intercalation compound). In some embodiments, the positive electrode active material can include a lithium transition metal composite oxide. The 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 can include, but is not limited to, at least one of lithium cobaltate, lithium nickel manganese cobaltate, lithium nickel manganese aluminate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel-type lithium manganate, spinel-type lithium nickel manganate, and lithium titanate.

[0057] The positive electrode active layer also includes a binder to bind the positive electrode active material particles to facilitate formation of a film layer, and to improve the adhesion between the positive electrode active layer and the positive electrode current collector. In some embodiments, the binder can include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, an epoxy resin, or nylon.

[0058] The positive electrode active layer can also include a conductive material, which includes, but is not limited to, a carbon-based material, a metal-based material, a conductive polymer, or any combination thereof. In some embodiments, the carbon-based material can include, but is not limited to, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, or any combination thereof. In some embodiments, the metal-based material can include, but is not limited to, metal powder or metal fibers, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer can be a polyphenylene derivative.

[0059] Separator film

[0060] The material and shape of the separator film used in the electrochemical device of the present application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator film includes a polymer or an inorganic material formed of a material stable to the electrolyte of the present application, or the like.

[0061] For example, the separator film can include a base layer and a surface treatment layer. The base layer is a nonwoven fabric, a film, or a composite film having a porous structure, and the material of the base layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.

[0062] The surface treatment layer is provided on at least one surface of the base layer, and can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. The inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from at least one of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate.

[0063] The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxide, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer includes a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxide, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0064] Electrolyte solution

[0065] According to some embodiments of the present application, the electrolyte solution includes an organic solvent, a lithium salt, and an optional additive.

[0066] The organic solvent in the electrolyte solution of the present application can be any organic solvent known in the art as a solvent for an electrolyte solution. The electrolyte used in the electrolyte solution according to the present application is not limited, and can be any electrolyte known in the art. The additive of the electrolyte solution according to the present application can be any additive known in the art as an additive for an electrolyte solution. In some embodiments, the organic solvent includes, but is not limited to, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), or ethyl propionate.

[0067] In some embodiments, the organic solvent includes an ether solvent, such as including at least one of 1,3-dioxolane (DOL) and dimethoxyethane (DME). In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt includes, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis-trifluoromethanesulfonimide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalato)borate LiB(C2O4)2 (LiBOB), or lithium difluoro(oxalato)borate LiBF2(C2O4) (LiDFOB). In some embodiments, the additive includes at least one of fluoroethylene carbonate and adiponitrile.

[0068] According to some embodiments of the present application, the secondary battery of the present application includes, but is not limited to, a lithium ion battery.

[0069] In the battery cell formed by the above negative electrode sheet combination, the thickness of the battery cell is H0 when the voltage of the battery cell is 3V to 3.95V, and the thickness of the battery cell is H2 when the battery cell is discharged to 0.5V, and 0.58 < H2 / H0 ≤ 1.36. The negative electrode sheet in the battery cell includes the above-mentioned silicon-carbon composite material. The ratio of the thickness of the battery cell before and after discharge is within the above-mentioned range, the problem of gas production in the battery cell is improved, and the battery cell can maintain good stability, thereby improving the cycle performance and service life of the battery cell. When the thickness of the battery cell is H0, the corresponding voltage can be 3V, 3.1V, 3.2V, 3.3V, 3.4V, 3.5V, 3.6V, 3.7V, 3V, 3.8V, 3.95V, or any value within the range formed by any two of the above-mentioned values. In some embodiments, H2 / H0 can be 0.59, 0.6, 0.63, 0.7, 0.8, 0.9, 0.95, 1, 1.1, 1.15, 1.16, 1.2, 1.23, 1.3, 1.32, 1.36, or any value within the range formed by any two of the above-mentioned values. Preferably, 0.63 ≤ H2 / H0 ≤ 1.23, and more preferably, 0.9 ≤ H2 / H0 ≤ 1.16.

[0070] The thickness change of the above-mentioned battery cell is related to the interface stability in the battery cell, and the better the interface stability between the silicon-carbon composite material and the electrolyte, the smaller the thickness of the battery cell when the battery cell is discharged to 0.5V. The content of Si element in the silicon-carbon composite material, the content of Si-O bond, and the conductivity of the conductive agent affect the interface stability of the battery cell. The present application adjusts the above-mentioned influencing factors to change the thickness of the battery cell when it is discharged to 0.5V, so that the ratio of H2 / H0 is within a suitable range, so that the battery cell has good interface stability.

[0071] If the battery cell is discharged from the initial voltage to 2.5V, the volume change of the silicon-carbon composite material will be affected. If the battery cell is discharged from 2.5V, the main affected is the SEI film. If the battery cell is discharged from the initial voltage of 3V-3.95V to 0.5V, lithium ions are released from the negative active layer, the thickness of the negative electrode sheet decreases, and the first layer is formed on the silicon substrate in the silicon-carbon composite material. The silicon-carbon composite material itself has good stability and good interface stability between the silicon-carbon composite material and the electrolyte, reducing or eliminating the decomposition of the SEI film. Thus, the thickness of the battery cell decreases. If the battery cell is discharged from the initial voltage to 0.5V, the stability of the SEI film is poor, the SEI film will decompose and produce gas, and the thickness of the battery cell will increase, thereby affecting the ratio of H2 / H0.

[0072] The application also applies the secondary battery to an electronic device, and the secondary battery supplies power to the load of the electronic device. The secondary battery in the above-mentioned electronic device contains a negative active material, and the negative active material includes a silicon-carbon composite material. The first layer in the silicon-carbon composite material can reduce the etching of the silicon substrate by HF and improve the stability of the SEI film, thereby improving the cycle performance and charging efficiency of the secondary battery, and further improving the service life and charging efficiency of the electronic device.

[0073] 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 headset, 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, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, etc.

[0074] The application is described below through specific examples and comparative examples. Those skilled in the art should understand that the preparation methods described in the application are only examples, and any other suitable preparation method is within the scope of the application.

[0075] Example 1

[0076] (1) Preparation of silicon-carbon composite material:

[0077] The single-walled carbon nanotubes and the polymethylhydrogen siloxane are dissolved and dispersed in a mixed solvent of water and ethanol at a mass ratio of 0.5:2, and are stirred uniformly to obtain a mixed slurry; (2) 100 g of a silicon matrix (based on the sum of silicon elements and carbon elements in the silicon matrix, the mass ratio of the carbon elements is 50.7%, and the mass ratio of the silicon elements is 49.3%) material is added to the mixed slurry in step (1), and is stirred at a stirring speed of 1000 r / min, and is uniformly dispersed after stirring for 4 h, and is dried at 168℃ to obtain a silicon-carbon composite material, wherein the Dv50 of the silicon-carbon composite material is 9 μm, the average diameter of the single-walled carbon nanotubes is 5 nm, and the average length of the single-walled carbon nanotubes is 800 nm.

[0078] (2) Preparation of a lithium ion battery:

[0079] Preparation of a negative electrode sheet: the silicon-carbon composite material, artificial graphite, negative electrode binder styrene-butadiene rubber (SBR), and negative electrode dispersant carboxymethyl cellulose (CMC) prepared above are mixed at a mass ratio of 10:88:1.6:0.4, and then deionized water is added as a solvent and stirred uniformly to prepare a negative electrode slurry with a solid content of 45 wt%. The negative electrode slurry is uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 6 μm, and the copper foil is dried at 85℃ for 4 h to obtain a negative electrode sheet with a single-sided coated negative electrode active material layer with a coating thickness of 80 μm. After cold pressing, sheet cutting, and slitting, the negative electrode sheet is dried under vacuum at 120℃ for 12 h to obtain a negative electrode sheet with a size of 76.6 mm x 875 mm. The cold pressing pressure is 20 tons (t), and the tap density of the negative electrode sheet is 1.78 g / cm 3 .

[0080] Preparation of a positive electrode sheet: the positive electrode active material lithium cobaltate, the positive electrode conductive agent acetylene black, and the positive electrode binder polyvinylidene fluoride (PVDF) are mixed at a mass ratio of 96.3:2.2:1.5, N-methyl pyrrolidone (NMP) is added as a solvent and stirred uniformly to prepare a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry is uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 13 μm, and is dried at 85℃ to obtain a positive electrode sheet with a single-sided coated positive electrode active material layer with a thickness of 130 μm. After cold pressing, sheet cutting, and slitting, the positive electrode sheet is dried under vacuum at 85℃ for 4 h to obtain a positive electrode sheet with a size of 74 mm x 867 mm. The cold pressing pressure is 20 t, and the tap density of the positive electrode sheet is 4.15 g / cm 3 .

[0081] Preparation of electrolyte: In a dry argon atmosphere glove box, organic solvents ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP) were mixed in a mass ratio of 3:1:3:3, then lithium salt LiPF6 was added, and the electrolyte was obtained after mixing uniformly. The mass percentage of lithium salt was 12.5% based on the mass of the electrolyte, and the rest was organic solvent.

[0082] Preparation of separator film: A porous polyethylene film (provided by Celgard) with a thickness of 15 μm was used as the separator film.

[0083] Assembly of lithium ion battery: The positive electrode sheet, the separator film, and the negative electrode sheet prepared above were stacked in order with the separator film between the positive electrode sheet and the negative electrode sheet to play a separating role, and then the electrode assembly was obtained by winding. After welding the tab, the electrode assembly was placed in an aluminum plastic film packaging bag and dried in a vacuum oven at 80°C for 12 hours to remove water. The electrolyte prepared above was injected, and the lithium ion battery (i.e. the battery cell) was obtained after vacuum packaging, standing, formation (0.02C constant current charging to 3.5V, and then 0.1C constant current charging to 3.9V), degassing, and edge cutting.

[0084] Examples 2 to 7

[0085] Examples 2 to 7 differ from Example 1 in that the type of siloxane organic matter or the mass ratio of the silicon matrix and the conductive agent or the mass ratio of the conductive agent and the siloxane organic matter is changed, and the rest of the preparation process is the same as that of Example 1.

[0086] Examples 8 to 10

[0087] Examples 8 to 10 differ from Example 1 in that the mass percentage of silicon element in the silicon matrix is changed, and the rest of the preparation process is the same as that of Example 1.

[0088] Examples 11 to 12

[0089] Examples 11 to 12 differ from Example 1 in that the particle size Dv50 of the silicon-carbon composite material is changed, and the rest of the preparation process is the same as that of Example 1.

[0090] Examples 13 to 16

[0091] Examples 13 to 16 differ from Example 1 in that the average diameter or average length of the conductive agent in the silicon-carbon composite material is changed, and the rest of the preparation process is the same as that of Example 1.

[0092] Example 17

[0093] Example 17 differs from Example 1 in that the stirring time in step (2) of preparing the silicon-carbon composite material is changed, and the stirring time is 10 min at a stirring speed of 1000 r / min, to obtain a first layer with a thickness of 5 nm, and the rest of the preparation process is the same as that of Example 1.

[0094] Example 18

[0095] Example 18 differs from Example 1 in that the stirring time in step (2) of preparing the silicon-carbon composite material is changed, and the stirring time is 1 h at a stirring speed of 1000 r / min, to obtain a first layer with a thickness of 36 nm, and the rest of the preparation process is the same as that of Example 1.

[0096] Example 19

[0097] Example 19 differs from Example 1 in that the stirring time in step (2) of preparing the silicon-carbon composite material is changed, and the stirring time is 8 h at a stirring speed of 1000 r / min, to obtain a first layer with a thickness of 72 nm, and the rest of the preparation process is the same as that of Example 1.

[0098] Example 20

[0099] Example 20 differs from Example 1 in that the stirring time in step (2) of preparing the silicon-carbon composite material is changed, and the stirring time is 24 h at a stirring speed of 1000 r / min, to obtain a first layer with a thickness of 100 nm, and the rest of the preparation process is the same as that of Example 1.

[0100] Comparative Example 1

[0101] Example 1 differs in that the surface of the silicon matrix is not coated with any coating during the preparation of the silicon-carbon composite material, and the specific material composition is shown in Table 1.

[0102] Comparative Example 2

[0103] Example 1 differs in that the surface of the silicon matrix is only coated with a conductive agent during the preparation of the silicon-carbon composite material, and the specific material composition is shown in Table 1.

[0104] Comparative Example 3

[0105] Example 1 differs in that the surface of the silicon matrix is only coated with a siloxane organic matter during the preparation of the silicon-carbon composite material, and the specific material composition is shown in Table 1.

[0106] The silicon-carbon composite materials prepared in the examples and comparative examples and the lithium ion batteries are subjected to the following tests, as shown in Tables 1 to 4.

[0107] Performance Test

[0108] (1) Test method of powder particle size Dv50:

[0109] The particle size distribution of the silicon-based composite material was tested by a Malvern particle size tester (instrument model Master Sizer 2000). The sample preparation method is as follows: about 0.02 g of powder sample is added to a 50 ml clean beaker, about 20 ml of deionized water is added, and 3 drops of surfactant sodium dodecyl sulfate are added to make the powder completely dispersed in the water. Ultrasonic cleaning machine for 5 minutes, get powder particle size test sample. In the volume-based particle size distribution of the material, from small particle size, to the particle size of 50% of the volume accumulation is Dv50.

[0110] (2) Measurement method of thickness of the first layer:

[0111] The silicon-carbon composite material was sliced by focused ion beam (FIB), and then characterized by high-resolution transmission electron microscope (HRTEM, model Talos F200X). In the same selected range (500000 times magnification), the first layer in the particle was observed, the thickness of the first layer in the particle of the silicon-carbon composite material was measured, and the thickness of fifty different positions in the first layer was optionally measured. The thickness can be measured according to the scale, and the average value of the fifty thickness values is calculated to obtain the thickness of the first layer.

[0112] (3) Test method of average diameter and average length of conductive agent:

[0113] The 30000k magnification image was taken by scanning electron microscope (SEM), and the image was processed by image analysis software ImageJ. Then the length and diameter of 20 CNTs were measured respectively, and then the average value of the length of 20 CNTs was calculated to obtain the average length of CNTs. The average value of the diameter of 20 CNTs was calculated to obtain the average diameter of CNTs.

[0114] (4) Test method of mass ratio of silicon element and carbon element in silicon matrix:

[0115] The 1000 times magnification image was taken by scanning electron microscope (SEM), and the silicon matrix part of the silicon-carbon material was selected for EDS element analysis to obtain the mass ratio of silicon element and carbon element.

[0116] (5) Test method of scanning electron microscope (SEM):

[0117] The silicon-based composite material was tested by JEOL-JSM-6700F type scanning electron microscope at a voltage of 5kV and a current of 0.8nA.

[0118] Lithium ion battery performance test

[0119] (1) Test method of cycle performance:

[0120] The lithium ion battery was placed in a thermostat at 25℃±1℃ for 30 minutes, charged at 0.5C current to 4.45V, then charged at 4.45V constant voltage to 0.025C, and then placed for 5 minutes, and then discharged at 0.5C to 3.0V, which was a cycle process, and the first cycle discharge capacity C0 of the lithium ion battery was recorded. Then, according to the above cycle process, 500 cycles were cycled. The cycle discharge capacity C1 of the 500th cycle was recorded. The 500-cycle cycle capacity retention rate = C1 / C0 x 100%.

[0121] (2) Measurement method of thickness of the cell before and after discharging:

[0122] The initial thickness of the cell (the voltage of the cell is 3V to 3.95V) was measured using a micrometer and recorded as H0, then discharged at 0.01C to 0.5V, the thickness of the cell was measured using a micrometer and recorded as H2, and the ratio of H2 / H0 was calculated.

[0123] (3) Test method or calculation formula of energy density:

[0124] 5 lithium ion batteries from each group were taken for the first time to charge and discharge in an environment of 25℃. Constant current charging was carried out at a charging current of 0.5C until the upper limit voltage, and then constant voltage charging was carried out at 0.02C, and then constant current discharging was carried out at a discharging current of 0.2C to the cut-off voltage, to obtain the discharge capacity of the lithium ion battery, and the average discharge voltage of the lithium ion battery was calculated.

[0125] Charged at 0.5C to 50% SOC to obtain the lithium ion battery at 50% SOC. The length, width and thickness of each lithium ion battery at 50% SOC were measured, and the volume of the lithium ion battery was calculated, and the volume energy density of the lithium ion battery = discharge capacity of the lithium ion battery x average discharge voltage of the lithium ion battery / volume of the lithium ion battery.

[0126] Wherein, the upper limit voltage of the lithium ion battery is 4.45V, and the discharge cut-off voltage is 3.0V.

[0127] (4) Test method of lithium precipitation performance:

[0128] The lithium ion battery was placed in a constant temperature box at 25℃±1℃ for 30 minutes, charged at 1.2C current to 4.45V, then charged at 4.45V to 0.025C, and stood for 5 minutes, then discharged at 0.5C to 3.0V, which was a one-time charge-discharge cycle process, and after repeating 10 cycle processes, the lithium ion battery was charged at 4C current to 4.45V, then charged at 4.45V to 0.025C, and stood for 5 minutes, and the lithium ion battery was disassembled to observe the lithium precipitation of the lithium ion battery. According to the above method, 1.2C was adjusted to 1.6C, 2C, 2.4C, 2.6C, 2.8C, 3C, 3.1C, 3.2C, 3.4C, 3.8C or 4C, respectively, to observe the lithium precipitation of the lithium ion battery under different charge rates. The higher the charge rate, the better the lithium precipitation performance of the lithium ion battery. According to the full charge disassembly of the negative electrode phase contact isolation film, the state of the contaminated isolation film was determined, and when the negative electrode phase contact isolation film showed white as a whole and the area showing gray was <2%, it was determined that no lithium precipitation occurred.

[0129] Figure 1 is a scanning electron microscope image of the silicon-carbon composite material prepared in Example 1, and Figure 2 is a scanning electron microscope image of the silicon substrate without any coating in Comparative Example 1. From Figure 1 and Figure 2, the silicon substrate surface forms a single-walled carbon nanotube with a linear structure, and the silicon substrate surface is coated with a first layer. Figure 3 is a change trend of the initial voltage of the battery cell assembled in Example 1 from 3.19V to 0.5V and a change trend of the thickness of the battery cell, and during the discharging process, the thickness of the battery cell gradually decreases, and when discharged to 0.5V, the thickness of the battery cell is 4mm.

[0130] Table 1

[0131] Table 2 Note: " / " in Table 1 and Table 2 means not added or no relevant parameters.

[0132] As shown in Table 1 and Table 2, compared with Comparative Examples 1 to 3, in Example 1 to 7, the first layer contains both the conductive agent and the siloxane organic matter, which improves the cycle retention rate of the lithium ion battery and reduces lithium precipitation. This shows that both the conductive agent and the siloxane organic matter need to be coated in the first layer on the silicon substrate, and only one of the conductive agent and the siloxane organic matter will reduce the cycle retention rate of the lithium ion battery or the lithium precipitation performance. In Example 1 to 7, when both the siloxane organic matter and the conductive agent exist on the surface of the silicon-carbon composite material, the cycle performance of the silicon-carbon composite material is improved and the lithium precipitation is reduced. In the above examples, adjusting the mass ratio of the silicon substrate and the conductive agent, the mass ratio of the conductive agent and the siloxane organic matter, or using different types of siloxane organic matter, will affect the content of Si-O bond in the silicon-carbon composite material, which will affect the stability of the SEI film in the battery, thereby affecting the ratio of H2 / H0. Compared with Comparative Examples 1 to 3, in Example 1 to 7, the ratio of H2 / H0 is reduced, which also shows that when both the siloxane organic matter and the conductive agent exist in the silicon-carbon composite material, the decomposition gas of the SEI film is reduced or eliminated.

[0133] Table 3

[0134] Table 4

[0135] In combination with Table 1 to Table 4, in Example 8 to Example 9, adjusting the content of silicon element and carbon element in the silicon substrate will affect the cycle performance and lithium precipitation performance of the silicon-carbon composite material. The content of silicon element in the silicon substrate is within a suitable range, which is beneficial to make the secondary battery have good cycle performance and lithium precipitation performance. In Example 1, Example 11 and Example 12, the particle size Dv50 of the silicon-carbon composite material is adjusted, and when the particle size Dv50 of the silicon-carbon composite material and H / D are within a suitable range, the corresponding secondary battery has good energy density, and also has good cycle performance and lithium precipitation performance.

[0136] In Example 1, Example 13 to Example 16, by adjusting the average diameter and average length of the conductive agent, the corresponding secondary battery has good energy density, and also has good cycle performance and lithium precipitation performance.

[0137] In Example 1, Example 17 to Example 20, when preparing the silicon-carbon composite material, the stirring time is adjusted to adjust the thickness of the first layer in the silicon-carbon composite material, and when the thickness of the first layer is within a suitable range, the corresponding secondary battery has good energy density, and also has good cycle performance and lithium precipitation performance.

[0138] The above disclosure is only the preferred embodiment of the present application, and of course cannot be used to limit the present application, so equivalent changes made by the present application still fall within the scope of the present application.

Claims

1. A silicon-carbon composite material, characterized in that, It includes a silicon substrate and a first layer at least partially located on the silicon substrate, the first layer comprising a conductive agent and an organic silicon oxide compound.

2. The silicon-carbon composite material as described in claim 1, characterized in that, The siloxane includes at least one of polymethylhydrosiloxane, polysilsesquioxane, vinyltrimethoxysilane, or vinyltriethoxysilane.

3. The silicon-carbon composite material as described in claim 1 or 2, characterized in that, The conductive agent includes at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes. And / or, The silicon substrate includes silicon-carbon materials.

4. The silicon-carbon composite material according to any one of claims 1 to 3, characterized in that, The mass ratio of the silicon substrate to the conductive agent is 100:(0.5-0.9); the mass ratio of the conductive agent to the organic silicon oxide is (0.5-5):

2.

5. The silicon-carbon composite material according to any one of claims 1 to 4, characterized in that, The conductive agent has a linear structure, with an average diameter of y nm, where 0.5 ≤ y ≤ 20; and an average length of L nm, where 500 ≤ L ≤ 1000.

6. The silicon-carbon composite material according to any one of claims 1 to 5, characterized in that, The silicon-carbon composite material satisfies at least one of the following conditions: (1) The particle size Dv50 of the silicon-carbon composite material is Dμm, 4≤D≤13; (2) The thickness of the first layer is H nm, where 5 ≤ H ≤ 100; (3) The particle size Dv50 of the silicon-carbon composite material is Dμm, the thickness of the first layer is Hnm, and 0.55≤H / D≤12.5; (4) The silicon matrix includes silicon-carbon material, which includes silicon and carbon elements, and the mass percentage of silicon is 41.8% to 57.9% based on the sum of the masses of silicon and carbon elements in the silicon matrix.

7. The silicon-carbon composite material according to any one of claims 1 to 6, characterized in that, The thickness of the first layer is H nm, and the average diameter of the conductive agent is y nm, where 1 ≤ H / y ≤ 25.

8. A secondary battery, comprising a cell, characterized in that, The battery cell includes a negative electrode, a positive electrode, and an electrolyte, wherein the negative electrode further includes a silicon-carbon composite material as described in any one of claims 1 to 7.

9. The secondary battery as described in claim 8, characterized in that, The thickness of the battery cell is H0 when the cell voltage is between 3V and 3.95V, and the thickness of the cell is H2 when the cell is discharged to 0.5V. <H2 / H0≤1.36。 10. An electronic device, characterized in that, Includes the secondary battery as described in claim 8 or 9.

Images