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

Abstract

The present application provides a silicon-based composite material, a secondary battery, and an electronic device. The silicon-based composite material comprises a silicon substrate and a first layer located on at least part of the surface of the silicon substrate. The first layer comprises a conductive agent and a fluorine-containing lithium phosphate compound. The thickness of the first layer is H nm, wherein 5 ≤ H ≤ 200. The fluorine-containing lithium phosphate compound in the silicon-based composite material provided by the present application can improve the interface stability of the SEI film and improve the cycle performance and expansion performance of the silicon-based composite material.

Description

Silicon-based 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-based composite material, a secondary battery using the silicon-based 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. Secondary batteries usually use silicon materials as negative electrode materials. Silicon materials are considered to be the most promising negative electrode materials that can replace graphite due to their high theoretical specific capacity (Li 15 Si4, 3579 mAh / g) and suitable working voltage (<0.5 V vs. Li / Li + ). However, the low electrical conductivity and the huge volume expansion during alloying / de-alloying affect the cycle performance of the secondary battery. SUMMARY

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

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

[0005] The present application provides a silicon-based composite material, comprising a silicon substrate and a first layer located on at least part of the surface of the silicon substrate, the first layer comprising a conductive agent and a fluorine-containing lithium phosphate compound, the thickness of the first layer being H nm, 5≤H≤200.

[0006] When the silicon-based composite material of the present application is applied to a secondary battery, the fluorine-containing lithium phosphate compound in the first layer will undergo a reduction reaction to form inorganic salt components such as LiF, Li3PO4 or Li3P during the charging process of the secondary battery, and participate in the formation of a solid electrolyte interface film (SEI film). The inorganic salt components improve the strength and ionic conductivity of the SEI film, thereby improving the interface stability of the SEI film, improving the cycle performance and expansion performance of the silicon-based composite material. At the same time, the addition of the conductive agent in the first layer can further improve the electrical conductivity of the silicon-based composite material, thereby improving the kinetic performance of the silicon-based composite material; while improving the stability of the SEI film, it is also beneficial to relatively reduce the thickness of the SEI film, reduce the interface transmission impedance of the SEI film, and thereby improve the lithium precipitation phenomenon. The thickness of the first layer is within the above range, which can improve the specific capacity of the silicon-based composite material while protecting the silicon substrate, improving the interface stability of the SEI film, and further improving the cycle performance and expansion performance of the silicon-based composite material.

[0007] In some possible implementation manners based on the first aspect, the fluorine-containing lithium phosphate compound is selected from at least one of lithium difluorophosphate, lithium difluorobisoxalate phosphate, or lithium tetrafluoroxalate phosphate. The fluorine-containing lithium phosphate compound can all undergo a reduction reaction to form inorganic salt components such as LiF, Li3PO4, or Li3P, so as to improve the interface stability of the SEI film and improve the cycle performance and expansion performance of the silicon-based composite material.

[0008] In some possible implementation manners based on the first aspect, the conductive agent includes at least one of a single-walled carbon nanotube or a multi-walled carbon nanotube. The conductive agent is a linear conductive agent, which can provide a better ion transmission channel and improve the electrical conductivity of the silicon-based composite material, thereby improving the kinetic performance of the silicon-based composite material.

[0009] In some possible implementation manners based on the first aspect, 5≤H≤64, which is beneficial to further improve the stability of the SEI film by the first layer and improve the cycle performance and expansion performance of the silicon-based composite material.

[0010] In some possible implementation manners based on the first aspect, the particle size Dv50 of the silicon-based composite material is X μm, and 4≤X≤13. This is beneficial to reduce the contact between the silicon-based composite material and the electrolyte, and in turn reduce the side reaction between the silicon-based composite material and the electrolyte, thereby improving the cycle performance of the silicon-based composite material.

[0011] In some possible implementation manners based on the first aspect, 0.56≤H / X≤22.22, which is beneficial to make the silicon-based composite material have better kinetic performance, cycle performance, and expansion performance.

[0012] 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 1≤y≤30. This is beneficial to make the conductive agent have better dispersibility and improve the electrical conductivity of the silicon-based composite material, thereby improving the kinetic performance and cycle performance of the silicon-based composite material. The average length of the conductive agent is L nm, and 1000≤L≤2000. This is beneficial to make the silicon-based composite material have better dispersibility and improve the long-range electrical conductivity of the active ions, thereby improving the rate performance of the silicon-based composite material.

[0013] In some possible implementation manners based on the first aspect, 1≤H / y≤50. By adjusting the relationship between the thickness of the first layer and the average diameter of the conductive agent, the conductive agent can maintain a suitable average diameter when the thickness of the first layer is relatively large, thereby improving the overall stability and ion conductivity of the silicon-based composite material.

[0014] In some possible implementation manners based on the first aspect, the sphericity of the silicon matrix is S, and S is greater than or equal to 0.8. The greater the sphericity of the silicon matrix, the more uniform the active ion insertion into the silicon-based composite material, and the more uniform the first layer coating and the stability of the silicon matrix, thereby improving the stability of the SEI film and the cycle performance of the silicon-based composite material.

[0015] In some possible implementation manners based on the first aspect, 1052 / L / S is less than or equal to 2105. In the case of a high sphericity, there is a gap between the silicon-based composite materials, and the relationship between the average length of the conductive agent and the sphericity is adjusted. In the case of a high sphericity, a longer conductive agent length is used to form a connected active ion transmission channel between the conductive agents, thereby improving the active ion transmission rate and the rate performance of the silicon-based composite material.

[0016] In some possible implementation manners based on the first aspect, the mass percentage of lithium in the first layer is A%, 0.1≤A≤4, the mass percentage of phosphorus in the first layer is B%, 0.03≤B≤1.2, and the mass percentage of fluorine in the first layer is C%, 0.1≤C≤4, based on the mass of the silicon-based composite material. When the contents of lithium, phosphorus and fluorine are within the appropriate ranges, the first layer protects the silicon matrix, which is conducive to the silicon-based composite material having excellent specific capacity while improving the cycle performance and expansion performance of the silicon-based composite material.

[0017] In some possible implementation manners based on the first aspect, the silicon matrix includes a silicon-carbon material, the mass percentage of silicon is D%, 38≤D≤59, and the mass percentage of carbon is E%, 40≤E≤61, based on the mass of the silicon matrix. This is conducive to the silicon matrix having better specific capacity and initial efficiency while improving the interface stability of the silicon-based composite material, thereby improving the cycle performance and expansion performance of the silicon-based composite material.

[0018] In some possible implementation manners based on the first aspect, 0.003≤(A+B+C) / D≤0.19. The contents of lithium, phosphorus and fluorine in the first layer and the silicon content in the silicon matrix satisfy the above relationship, so that the elements in the first layer fully participate in the formation of the SEI film, which is conducive to improving the stability of the SEI film and the protection of the silicon matrix, thereby improving the cycle performance and expansion performance of the silicon-based composite material.

[0019] In some possible implementation manners based on the first aspect, 0.104≤H / D≤4.16. This is conducive to adjusting the thickness of the first layer while the silicon matrix has a certain silicon content, reducing the side reactions between the silicon matrix and the electrolyte, and thereby improving the cycle performance of the silicon-based composite material.

[0020] The second aspect of the present application provides a secondary battery, comprising a negative electrode sheet, a positive electrode sheet and an electrolyte, wherein the negative electrode sheet comprises a silicon-based composite material. The fluorine-containing lithium phosphate compound in the first layer can improve the interface stability of the SEI film and improve the cycle performance of the secondary battery.

[0021] 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 negative electrode sheet comprising a silicon-based composite material, which can improve the cycle performance of the secondary battery and thus improve the service life and charge-discharge rate of the electronic device. BRIEF DESCRIPTION OF DRAWINGS

[0022] 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:

[0023] FIG. 1 is a scanning electron microscope image of a silicon substrate before coating in Example 1 of the present application.

[0024] FIG. 2 is a scanning electron microscope image of a silicon-based composite material prepared after coating the silicon substrate in Example 1 of the present application. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as 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.

[0026] An embodiment of the present application provides a secondary battery, which comprises a shell, an electrode assembly and an electrolyte. The electrode assembly and the electrolyte are both located in the shell.

[0027] The shell can be a packaging bag obtained by packaging with a packaging film (such as an aluminum plastic film), such as 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.

[0028] The electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator film, and the separator film is arranged between the positive electrode sheet and the negative electrode sheet. The electrode assembly can be a laminated structure formed by laminating the positive electrode sheet, the separator film 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 film and the negative electrode sheet after being laminated.

[0029] Negative electrode sheet

[0030] The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer provided on the negative electrode current collector. The negative electrode 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 foil and a polymer substrate. The negative electrode active layer contains a negative electrode active material, and the negative electrode active material includes a silicon-based composite material.

[0031] The silicon-based composite material includes a silicon matrix and a first layer on at least part of the surface of the silicon matrix, the first layer including a conductive agent and a fluorine-containing lithium phosphate compound, and the thickness of the first layer being H nm, 5≤H≤200.

[0032] In the silicon-based composite material provided by the present application, the fluorine-containing lithium phosphate compound in the first layer will undergo a reduction reaction during the charging process of the secondary battery, forming inorganic salt components such as LiF, Li3PO4, or Li3P, and participating in the formation of a solid electrolyte interface film (SEI film). The inorganic salt components improve the strength and ionic conductivity of the SEI film, thereby improving the interface stability of the SEI film and the cycle performance and swelling performance of the silicon-based composite material. At the same time, the addition of the conductive agent in the first layer can further improve the conductivity of the silicon-based composite material, thereby facilitating the improvement of the rate performance of the silicon-based composite material and reducing lithium precipitation. By adjusting the thickness of the first layer within the above range, the silicon-based composite material can protect the silicon matrix while having a relatively high specific capacity, improve the interface stability of the SEI film, and further improve the cycle performance and swelling performance of the silicon-based composite material.

[0033] If H<5, the thickness of the first layer is small, and the protective effect on the silicon matrix is weak. The electrolyte can react with the silicon matrix and etch the silicon matrix, thereby deteriorating the cycle performance and swelling performance of the silicon-based composite material. If H>200, the thickness of the first layer is large, which affects the specific capacity of the silicon-based composite material. In some embodiments, the thickness H of the first layer can be 5, 6, 10, 15, 20, 25, 30, 40, 50, 75, 90, 100, 120, 125, 130, 150, 175, 180, 190, 200, or any value within the range formed by any two of the above values.

[0034] In some embodiments, preferably, 5≤H≤64. This facilitates further improvement of the stability of the SEI film by the first layer, and improvement of the cycle performance and swelling performance of the silicon-based composite material.

[0035] In some embodiments, the first layer can completely cover the outer surface of the silicon matrix, or the first layer can only cover part of the outer surface of the silicon matrix. 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 matrix, etc.

[0036] In some embodiments, the lithium phosphate compound containing fluorine is selected from at least one of lithium difluorophosphate, lithium difluorobisoxalate phosphate, or lithium tetrafluorooxalate phosphate. The lithium phosphate compound containing fluorine mentioned above can all undergo a reduction reaction to form inorganic salt components such as LiF, Li3PO4, or Li3P, so as to improve the interface stability of the SEI film and improve the cycle performance and expansion performance of the silicon-based composite material.

[0037] In some embodiments, the conductive agent includes at least one of single-walled carbon nanotubes (SWCNT) or multi-walled carbon nanotubes. The conductive agent mentioned above is a linear conductive agent, which can provide a better ion transmission channel and improve the conductivity of the silicon-based composite material, thereby improving the rate performance of the silicon-based composite material.

[0038] In some embodiments, the particle size Dv50 of the silicon-based composite material is X μm, and 4≤X≤13. Within the above range, it is beneficial to reduce the contact opportunities between the silicon-based composite material and the electrolyte, and to reduce the side reactions between the silicon-based composite material and the electrolyte, thereby improving the cycle performance and expansion performance of the silicon-based composite material. In some embodiments, the average particle size X of the silicon-based 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.

[0039] In some embodiments, 0.56≤H / X≤22.22, by adjusting the relationship between the thickness of the first layer and the average particle size of the silicon-based composite material, it is beneficial to make the silicon-based composite material have better rate performance and cycle performance. For example, when the particle size of the silicon-based composite material is relatively large, the stability is strong, but the kinetics is weak. By reducing the thickness of the first layer, the silicon-based composite material can maintain good rate performance. In some embodiments, H / X can be 0.56, 0.6, 0.7, 0.8, 1, 2, 3, 5, 7, 9, 10, 12, 15, 17, 19, 20, 22.22, or any value within the range formed by any two of the above values.

[0040] In some embodiments, the conductive agent has a linear structure, and the average diameter of the conductive agent is y nm, and 1≤y≤30. Within the above length range, it is beneficial to make the conductive agent have better dispersibility while improving the electrical conductivity of the silicon-based composite material, thereby improving the rate performance and cycle performance of the silicon-based composite material. In some embodiments, the average diameter y of the conductive agent can be 1, 2, 3, 5, 7, 9, 10, 12, 15, 17, 18, 20, 23, 25, 27, 30, or any value within the range formed by any two of the above values.

[0041] In some embodiments, the average length of the conductive agent is L nm, 1000≤L≤2000. The average length of the conductive agent within the above range is conducive to making the silicon-based composite material have better dispersibility while also being conducive to the active lithium ions having good long-range conductive capacity, thereby improving the kinetic performance of the silicon-based composite material. In some embodiments, the average length L of the conductive agent can be 1000, 1200, 1500, 1600, 1700, 1800, 1900, 2000, or any value within a range defined by any two of the above values.

[0042] In some embodiments, 1≤H / y≤50. By adjusting the relationship between the thickness of the first layer and the average diameter of the conductive agent, the conductive agent can have an average diameter within a set range when the thickness of the first layer is relatively thick, thereby facilitating improvement in the overall stability and ionic conductivity of the silicon-based composite material. In some embodiments, H / y can be 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 25, 30, 35, 40, 45, 50, or any value within a range defined by any two of the above values.

[0043] In some embodiments, the sphericity of the silicon matrix is S, S≥0.8. The greater the sphericity of the silicon matrix, the more conducive it is to improving the uniformity of the active ions embedded in the silicon-based composite material, and also conducive to improving the uniformity of the first layer coating and the stability of the silicon matrix, thereby facilitating improvement in the stability of the SEI film and further improvement in the cycle performance and expansion performance of the silicon-based composite material. In some embodiments, the sphericity S can be 0.8, 0.85, 0.9, 0.95, 0.99, or any value within a range defined by any two of the above values. In some embodiments, 0.8≤S<1.

[0044] In some embodiments, 1052≤L / S≤2105. At a higher sphericity, there is a gap between the silicon-based composite materials. By adjusting the relationship between the average length of the conductive agent and the sphericity, at a higher sphericity, a longer length of the conductive agent is used to form a connected active ion transmission channel between the conductive agents, thereby facilitating improvement in the lithium ion transmission rate and further improvement in the rate performance of the silicon-based composite material. In some embodiments, the ratio of L / S can be 1052, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2105, or any value within a range defined by any two of the above values.

[0045] In some embodiments, based on the mass of the silicon-based composite material, the mass percentage of lithium element in the first layer is A%, 0.1≤A≤4; the mass percentage of phosphorus element in the first layer is B%, 0.03≤B≤1.2; and the mass percentage of fluorine element in the first layer is C%, 0.1≤C≤4. When the contents of lithium element, phosphorus element and fluorine element are within the adaptive range, the thickness of the first layer can be reflected, so as to protect the silicon substrate, facilitate the silicon-based composite material to have excellent specific capacity, and improve the cycle performance and expansion performance of the silicon-based composite material. In some embodiments, A can be 0.1, 0.2, 0.5, 0.8, 1, 1.2, 1.5, 2, 2.2, 2.5, 3, 3.2, 3.5, 4, or any value within the range formed by any two of the above values. B can be 0.03, 0.05, 0.1, 0.2, 0.3, 0.5, 0.7, 0.9, 1, 1.2, or any value within the range formed by any two of the above values. C can be 0.1, 0.2, 0.5, 0.8, 1, 1.2, 1.5, 2, 2.2, 2.5, 3, 3.2, 3.5, 4, or any value within the range formed by any two of the above values.

[0046] In some embodiments, the silicon substrate includes a silicon-carbon material, based on the mass of the silicon substrate, the mass percentage of silicon element is D%, 38≤D≤59, and the mass percentage of carbon element is E%, 40≤E≤61. In the silicon substrate, the mass percentages of silicon element and carbon element are within the above ranges, which facilitates the silicon substrate to have better specific capacity and initial efficiency, and also improves the interface stability of the silicon-based composite material, thereby improving the cycle performance and expansion performance of the silicon-based composite material. In some embodiments, the mass percentage of silicon element D can be 38, 40, 42, 45, 48, 50, 52, 55, 59, or any value within the range formed by any two of the above values. In some embodiments, the mass percentage of carbon element E can be 40, 42, 45, 48, 50, 52, 55, 59, 61, or any value within the range formed by any two of the above values.

[0047] In some embodiments, 0.003≤(A+B+C) / D≤0.19. By adjusting the mass ratio of the sum of lithium element, phosphorus element and fluorine element in the first layer to the mass of carbon element in the silicon matrix, the influence of the first layer on the silicon matrix coating can be reflected. The sum of lithium, phosphorus and fluorine elements in the first layer and the silicon element in the silicon matrix satisfy the above relationship, so that the elements in the first layer fully participate in the formation of the SEI film, improve the stability of the SEI film and improve the protection of the silicon matrix by the first layer, thereby improving the cycle performance and expansion performance of the silicon-based composite material. If the above ratio is small, the improvement effect of the first layer on the SEI film is not obvious; if the above ratio is large, when the silicon-based composite material is applied to a secondary battery, more side reactions will occur during the formation stage, affecting the initial efficiency and energy density. In some embodiments, the ratio of (A+B+C) / D can be 0.003, 0.005, 0.01, 0.03, 0.05, 0.1, 0.13, 0.15, 0.18, 0.19 or any value within the range formed by any two of the above values.

[0048] In some embodiments, 0.104≤H / D≤4.16. Under the above relationship between the thickness of the first layer and the silicon matrix, the thickness of the first layer is adjusted while the silicon matrix has a certain silicon content, thereby reducing the side reactions between the silicon matrix and the electrolyte, thereby improving the cycle performance of the silicon-based composite material. In some embodiments, the ratio of H / D can be 0.104, 0.11, 0.12, 0.15, 0.2, 0.3, 0.5, 0.6, 1, 1.2, 1.5, 1.8, 2, 2.3, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.16 or any value within the range formed by any two of the above values.

[0049] In some embodiments, the content ratio of silicon element and carbon element in the silicon matrix ranges from 0.623 to 1.475. Within the above range, the silicon element and carbon element in the silicon matrix satisfy a certain mass ratio, thereby improving the specific capacity and initial efficiency of the silicon-based composite material. In some embodiments, the mass ratio of silicon element and carbon element in the silicon matrix can be 0.623, 0.65, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.475 or any value within the range formed by any two of the above values.

[0050] The preparation method of the silicon-based 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-based composite material can include but is not limited to the following steps: (1) dissolving and dispersing the conductive agent and the fluorine-containing lithium phosphate compound in the solvent and stirring uniformly; (2) adding the silicon matrix material to step (1), stirring and dispersing uniformly, and drying to obtain the silicon-based composite material.

[0051] The solvent used in step (1) includes at least one of water, ethanol, ethylene glycol, propylene glycol, and tetrahydrofuran.

[0052] The temperature for drying in step (2) is 80-220°C, and the drying time is 4-48 hours.

[0053] The preparation method of the silicon substrate 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 substrate includes: using a chemical vapor deposition method, a silicon source gas is deposited on a porous carbon to form silicon, and then a carbon source is introduced to form amorphous carbon on the surface of the silicon substrate, thereby obtaining the silicon substrate. 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.

[0054] In the preparation method of the silicon-based composite material, the thickness H of the first layer is adjusted by changing the mass ratio of the silicon substrate, the conductive agent, and the fluorine-containing lithium phosphate compound. The mass ratio of the silicon substrate, the conductive agent, and the fluorine-containing lithium phosphate compound is 100:(0.4-0.9):(0.5-5). Within the above suitable ratio range, if the mass ratio of the silicon substrate and the conductive agent is increased, the conductivity of the silicon-based composite material may be affected, and the cycle performance of the silicon-based composite material may be affected. If the mass ratio of the silicon substrate and the conductive agent is decreased, the specific capacity of the silicon-based composite material may be reduced, and the energy density of the lithium ion battery may be reduced. If the mass ratio of the silicon substrate and the fluorine-containing lithium phosphate compound is increased, the interface stability of the silicon-based composite material may be affected, and the cycle performance of the lithium ion battery may be reduced. If the mass ratio of the silicon substrate and the fluorine-containing lithium phosphate compound is decreased, the initial efficiency of the silicon-based composite material may be reduced, and the energy density of the lithium ion battery may be reduced. If the mass ratio of the fluorine-containing lithium phosphate compound and the conductive agent is increased, the conductivity of the silicon-based composite material may be affected, and the kinetic performance of the lithium ion battery may be reduced. If the mass ratio of the fluorine-containing lithium phosphate compound and the conductive agent is decreased, the interface stability of the silicon-based composite material may be affected, and the cycle performance of the lithium ion battery may be reduced.

[0055] The content of lithium, phosphorus, and fluorine elements of the fluorine-containing lithium phosphate compound on the silicon substrate is adjusted by adjusting the mass of the fluorine-containing lithium phosphate compound.

[0056] The value of the average diameter y and the value of the average length L of the conductive agent are changed by selecting conductive agent raw materials with different average diameters and average lengths.

[0057] The negative active layer can also include a binder to bind the negative active material particles to facilitate formation of the film layer and to improve the adhesion 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, polymeric ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, or nylon.

[0058] The negative active layer can also include a conductive material, which can include, 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 fiber, or any combination thereof. In some embodiments, the metal-based material can include, but is not limited to, metal powder or metal fiber, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer can be a polyphenylene derivative.

[0059] The negative active layer can also further include graphite. The graphite, which has a certain flexibility, can cooperate with the silicon-based composite material to alleviate the volume expansion of the negative active layer as a whole. Meanwhile, the graphite and the silicon-based composite material, which both serve as negative active materials, can take full advantage of both the silicon-based composite material and the graphite to achieve better electrochemical performance.

[0060] Positive electrode sheet

[0061] The positive electrode sheet includes a positive current collector and a positive active layer disposed on the positive current collector. The positive current collector can be an aluminum foil or a nickel foil, or any composite current collector known in the art, such as, but not limited to, a current collector formed by combining the aforementioned conductive foil and a polymer substrate. The positive active layer includes a positive active material, which includes a compound that reversibly intercalates and deintercalates lithium ions (i.e., a lithiated intercalation compound). In some embodiments, the positive 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 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 lithium manganate, spinel lithium nickel manganate, and lithium titanate.

[0062] 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, polyethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, or nylon.

[0063] 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, at least one of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material can include, but is not limited to, metal powder or metal fiber, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer can be a polyphenylene derivative.

[0064] Separator film

[0065] 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 of the techniques disclosed in the prior art. In some embodiments, the separator film includes a polymer or inorganic material formed of a material stable to the electrolyte of the present application, or the like.

[0066] For example, the separator film can include a base layer and a surface treatment layer. The base layer is a non-woven 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 non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.

[0067] 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 material. The inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from at least one 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, and barium sulfate.

[0068] 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 contained in the polymer layer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxide, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0069] Electrolyte solution

[0070] According to some embodiments of the present application, the electrolyte solution includes an organic solvent, a lithium salt, and an optional additive.

[0071] 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.

[0072] In some embodiments, the organic solvent includes an ether-based 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.

[0073] 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.

[0074] The application also applies the secondary battery to an electronic device, and the secondary battery supplies power to a load in the electronic device. The secondary battery in the electronic device contains a negative electrode material, and the negative electrode material includes a silicon-based composite material. A fluorine-containing lithium phosphate compound in the silicon-based composite material is reduced to form an inorganic salt during charging and discharging of the secondary battery, thereby improving the strength and ionic conductivity of the SEI film, and improving the cycle performance and charging efficiency of the secondary battery, and further improving the service life and charging efficiency of the electronic device.

[0075] The electronic device or apparatus of the application is not particularly limited. In some embodiments, the electronic device of the application includes, 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 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 audio 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.

[0076] 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.

[0077] Example 1-1

[0078] (1) 0.4 g of single-walled carbon nanotubes (SWCNT) and 0.2 g of lithium difluorophosphate dioxalate were dissolved and dispersed in a mixed solvent of water and ethanol, and stirred uniformly, the average diameter of the SWCNT was 5 nm, and the average length was 1500 nm; (2) 100 g of a silicon-based matrix material was added to step (1), the sphericity of the silicon-based matrix was 0.95, and the mass ratio of silicon element to carbon element in the silicon-based matrix was 48:51, and after stirring and uniform dispersion, the silicon-based composite material was obtained after drying at 180°C for 24 h.

[0079] Preparation of a lithium ion battery:

[0080] Preparation of a negative electrode sheet: the silicon-based composite material prepared above was used as an active material, acetylene black was used as a conductive agent, and sodium alginate was used as a binder. The mass ratio of the active material, acetylene black, and sodium alginate was 96:2:2. The active material and acetylene black were mixed and ground uniformly in proportion, and sodium alginate aqueous solution was added in proportion and stirred for 4 h. Finally, the mixture slurry was uniformly coated on a copper foil, and vacuum dried at 70°C for 12 h to obtain a negative electrode sheet.

[0081] Preparation of the positive electrode: Super-P was used as the conductive agent and PVDF as the binder, with the mass ratio of active material (lithium cobalt oxide), Super-P, and PVDF being 96:2:2. The active material and Super-P were thoroughly mixed in the specified ratio and ground until homogeneous. The prepared PVDF solution was then added in the specified ratio and stirred for 4 hours. Finally, the mixture was uniformly coated onto aluminum foil and vacuum dried at 70°C for 12 hours to obtain the positive electrode.

[0082] The positive and negative electrode sheets have a unit area capacity of approximately 2.6 mAh cm⁻¹. -2 and 2.7mAh cm -2 The corresponding negative / positive capacity ratio (N / P) is approximately 1.045. The positive and negative electrode sheets are separated using a 7µm polyethylene (PE) membrane via a winding process. A mixture of ethylene carbonate / propylene carbonate / diethyl carbonate / propyl propionate (EC / PC / DEC / PP) in a volume ratio of 1:1:1:1 is added to the solvent along with 1M LiPF6, and the mixture is thoroughly mixed. Then, 5wt.% fluoroethylene carbonate (FEC) and 2wt.% 1,3,6-hexamethylenetrionitrile (HTCN) are added as electrolyte additives, resulting in an electrolyte retention coefficient of 1.6 g / Ah. After aging, formation, and capacity testing, a lithium-ion battery is manufactured.

[0083] Examples 1-2 to Examples 1-7

[0084] The difference between Examples 1-2 to 1-7 and Example 1-1 is that the amount of lithium difluorodioxalate phosphate added in the preparation of the silicon-based composite material is adjusted; the rest of the preparation process is exactly the same as in Example 1-1. Specific material preparation conditions are shown in Tables 1 and 2.

[0085] Examples 2-1 to 2-4

[0086] The difference between Examples 2-1 to 2-4 and Examples 1-7 is that the sphericity of the silicon matrix or the mass ratio of silicon in the silicon matrix is ​​adjusted in the silicon-based composite material; the rest of the preparation process is exactly the same as in Examples 1-7. Specific material preparation conditions are shown in Tables 3 to 5.

[0087] Examples 3-1 to 3-4

[0088] The difference between Examples 3-1 to 3-4 and Examples 1-7 is that the average diameter or average length of the conductive agent in the silicon-based composite material is adjusted; the rest of the preparation process is exactly the same as in Examples 1-7. The thickness of the first layer and the mass percentage of silicon are the same as in Examples 1-7. Specific material preparation conditions are shown in Table 6.

[0089] Examples 3-5 to Examples 3-8

[0090] Example 3-5 differs from Example 3-3 in that the particle size Dv50 of the silicon-based composite material is adjusted. The rest of the preparation process is exactly the same as Example 3-3. Example 3-6 differs from Example 3-4 in that the particle size Dv50 of the silicon-based composite material is adjusted. The rest of the preparation process is exactly the same as Example 3-4. The thickness of the first layer and the mass percentage of silicon are the same as in Example 1-7. The specific material preparation conditions are shown in Table 6.

[0091] Examples 3-7 to 3-8 differ from Example 3-4 in that the type of fluorine-containing lithium phosphate compound is adjusted and the particle size Dv50 of the silicon-based composite material is adjusted, and the rest of the preparation process is exactly the same as Example 3-4. The thickness of the first layer and the mass percentage of silicon are the same as in Example 1-7. The specific material preparation conditions are shown in Table 6.

[0092] Comparative Example 1

[0093] The difference from Example 1-1 is that in the preparation of the silicon-based composite material, the surface of the silicon substrate is not coated with any coating treatment, and the specific material preparation conditions are shown in Table 1 and Table 2. In Table 1 and Table 2, Comparative Example 1 uses “D1” to represent, and the subsequent comparative examples described below use the corresponding “D2”, “D3”, “D4”, “D5” to represent.

[0094] Comparative Example 2

[0095] The difference from Example 1-1 is that in the preparation of the silicon-based composite material, the surface of the silicon substrate is only coated with conductive agent SWCNT, and the specific material preparation conditions are shown in Table 1 and Table 2.

[0096] Comparative Example 3

[0097] The difference from Example 1-1 is that in the preparation of the silicon-based composite material, the surface of the silicon substrate is only coated with fluorine-containing lithium phosphate compound, and the specific material preparation conditions are shown in Table 1 and Table 2.

[0098] Comparative Example 4

[0099] The difference from Example 1-1 is that the amount of lithium difluorophosphate dioxalate added in the preparation of the silicon-based composite material is adjusted, and the rest of the preparation process is exactly the same as Example 1-1. The specific material preparation conditions are shown in Table 1 and Table 2.

[0100] Comparative Example 5

[0101] The difference from Example 1-1 is that the amount of lithium difluorophosphate dioxalate added in the preparation of the silicon-based composite material is adjusted, and the rest of the preparation process is exactly the same as Example 1-1. The specific material preparation conditions are shown in Table 1 and Table 2.

[0102] Test Method

[0103] (1) Test method of powder particle size: The particle size distribution of the silicon-based composite material is tested by using 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.

[0104] (2) Measurement method of thickness of the first layer:

[0105] The silicon-based composite material is sliced by using focused ion beam (FIB), and then characterized by high-resolution transmission electron microscope (HRTEM, model Talos F200X). In the same selected area range (500000 times magnification), the first layer in the particle is observed, the thickness of the first layer in the particle of the silicon-based composite material is measured, and optionally the thickness of fifty different positions in the first layer is 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.

[0106] (3) Test method of average diameter and average length of conductive agent:

[0107] The 30000k magnification image is taken by scanning electron microscope (SEM), the image is processed by using image analysis software ImageJ, then the length and diameter of 20 CNTs are measured respectively, then the average value of the length values of 20 CNTs is taken, and the average length of CNTs is calculated; the average value of the diameter values of 20 CNTs is taken, and the average diameter of CNTs is calculated.

[0108] (4) Test method of mass ratio of silicon element and carbon element in silicon-based composite material:

[0109] The 1000 times magnification image is taken by scanning electron microscope (SEM), the silicon matrix part in the silicon-carbon material is selected, and EDS element analysis is performed to obtain the mass ratio of silicon element and carbon element.

[0110] (5) Test method of lithium element, phosphorus element and fluorine element in silicon-based composite material:

[0111] The silicon-based composite material is sliced by using focused ion beam (FIB), and then characterized by high-resolution transmission electron microscope (HRTEM, model Talos F200X). In the same selected area range (1000 times magnification), EDS element analysis is performed to obtain the mass ratio of lithium element, phosphorus element and fluorine element.

[0112] (6) Measurement method of sphericity:

[0113] The sphericity was evaluated by the following evaluation method using a flow particle image analyzer, FPIA-2100 (manufactured by SYSMEX Co., Ltd.).

[0114] The silicon matrix sample was dispersed in water containing a surfactant and introduced into the flow particle image analyzer by a syringe. A photograph of the sample (dispersed fine powder liquid) flowing in the core portion of the flow cell was taken every 1 / 30 seconds using a CCD camera and the still photograph was processed in real time. The sphericity was calculated by the following formula.

[0115] Sphericity = (circumference calculated from the diameter of the corresponding circle) / (circumference of the projection image of the particle)

[0116] The "diameter of the corresponding circle" is the diameter of a perfect circle having an area corresponding to the circumference of the actually taken projection image of the particle. The sphericity is obtained by dividing it by the value obtained with the circumference of the projection image of the actually taken particle. For example, in the case of an ideal circular ring, the sphericity is 1, and the more complex the shape of the particle image, the smaller the value of the sphericity. The average sphericity was calculated for each individual particle.

[0117] (7) Test method of scanning electron microscope (SEM):

[0118] The silicon-based composite material was tested using a scanning electron microscope of the type JEOL-JSM-6700F at a voltage of 5 kV and a current of 0.8 nA.

[0119] Performance test of lithium ion battery

[0120] 1. Test method of cycle performance:

[0121] The lithium ion battery was left to stand in a thermostat at 25°C ± 1°C for 30 minutes, charged at a constant current of 0.5 C to 4.45 V, then charged at a constant voltage of 4.45 V to 0.025 C, left to stand for 5 minutes, then discharged at 0.5 C to 3.0 V, which was one cycle of charge and discharge process, and the first cycle discharge capacity Co of the lithium ion battery was recorded. Thereafter, the above cycle process was repeated for 500 cycles. The cycle discharge capacity of the 500th cycle Ci was recorded. The 500-cycle cycle capacity retention rate = Ci / Co x 100%.

[0122] 2. Test method of expansion performance:

[0123] The lithium ion battery is charged to 3.95V at 0.5C constant current flow for the initial half-charged state, and the thickness of the lithium ion battery at the initial half-charged state is tested by a screw micrometer. When the above cycle performance test process is cycled to 500 times, the lithium ion battery is charged to 4.45V at 0.5C constant current flow for the full-charged state, and the thickness of the lithium ion battery at this time is tested by a screw micrometer. The 500-cycle expansion rate = (H1-H0) / H0x100%.

[0124] 3. Lithium precipitation performance test method:

[0125] The lithium ion battery is placed in a constant temperature oven at 25°C±1°C for 30 minutes, charged to 4.45V at 1C constant current, and then charged to 0.025C at 4.45V constant voltage, and then discharged to 3.0V at 0.5C, which is a one-time charge-discharge cycle process. After 10 cycles, the lithium ion battery is charged to 4.45V at 4C constant current, and then charged to 0.025C at 4.45V constant voltage, and then placed for 5 minutes. The lithium ion battery is disassembled to observe the lithium precipitation of the lithium ion battery. According to the above method, 1C is adjusted to 1.5C, 2C, 2.4C, 2.5C, 2.8C, 3C, 3.5C, 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 more lithium precipitation occurs, indicating that the lithium precipitation performance of the lithium ion battery is better. According to the state of the full-charged disassembled negative electrode phase contact separator being contaminated, when the negative electrode phase contact separator is white overall and the area showing gray is <2%, it is determined that no lithium precipitation occurs.

[0126] 4. Test method of energy density:

[0127] Take 5 lithium ion batteries from each group to be tested for the first time in a 25°C environment. Constant current charging is performed at a charge current of 0.5C until the upper limit voltage, and then constant voltage charging is performed at 0.02C. Then, constant current discharging is performed at a discharge 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 is calculated.

[0128] Charged to 50% SOC at 0.5C to obtain the lithium ion battery at 50% SOC. Measure the length, width and thickness of each lithium ion battery at 50% SOC to calculate the volume of the lithium ion battery. The volumetric 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.

[0129] Wherein, the upper limit voltage of the lithium ion battery is 4.45V, and the discharge cut-off voltage is 3.0V.

[0130] FIG. 1 and FIG. 2 are scanning electron microscope images of the silicon substrate and the silicon-based composite formed after coating the silicon substrate in Example 1, respectively. As shown in FIG. 1 and FIG. 2, the surface of the silicon substrate is coated with the coating material, the surface smoothness is increased, and the fluorine-containing lithium phosphate compound and the conductive agent are attached to the silicon substrate.

[0131] Table 1

[0132] Table 2 Note: " / " in Table 1 and Table 2 means no addition or no relevant parameters.

[0133] Table 3

[0134] Table 4

[0135] In Table 1 and Table 2, in the examples and comparative examples, the surface of the silicon substrate is formed with the conductive agent and the fluorine-containing lithium phosphate compound, which improves the cycle performance, expansion performance of the lithium ion battery and reduces the lithium precipitation performance of the lithium ion battery.

[0136] The thickness H of the first layer affects the cycle performance and expansion performance of the lithium ion battery. Compared with Comparative Example 4 and Comparative Example 5, the thickness of the first layer in Example 1-1 to Example 1-7 is in a suitable range, which is beneficial to improve the cycle performance and expansion performance of the lithium ion battery. The sphericity of the silicon substrate also affects the cycle performance and expansion performance of the lithium ion battery.

[0137] In Table 3 and Table 4, it can be known from Example 1-7 and Example 2-1 to 2-2 that the greater the sphericity, the more beneficial to improve the uniformity of active ion embedded in the silicon-based composite material, the more beneficial to improve the stability of the SEI film, and thus the more beneficial to improve the cycle performance and expansion performance of the silicon-based composite material.

[0138] Table 5

[0139] The mass fraction of silicon element and carbon element also affects the cycle performance and expansion performance of the lithium ion battery. In Table 5, it can be known from Example 1-7 and Example 2-3 to 2-4 that the silicon element in the silicon substrate is in a suitable range and (A+B+C) / D is in a suitable range, and the lithium ion battery has good cycle performance, expansion performance and reduces lithium precipitation.

[0140] Table 6

[0141] The average diameter and average length of the conductive agent in the silicon-based composite material affect the cycle performance, expansion performance, and lithium precipitation performance of the lithium ion battery. In Table 6, it can be seen from Examples 1-7 and Examples 3-1 to 3-4 that the average diameter and average length of the conductive agent are within a suitable range, and the lithium ion batteries thereof all have good cycle performance, expansion performance, and reduced lithium precipitation.

[0142] The particle size Dv50 of the silicon-based composite material affects the cycle performance, expansion performance, and lithium precipitation performance of the lithium ion battery. In Table 6, in Examples 3-5 to 3-8, the silicon-based composite material has different particle sizes Dv50, and the lithium ion batteries thereof all have good cycle performance and expansion performance.

[0143] 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 according to the present application still fall within the scope of the present application.

Claims

1. A silicon-based composite material, wherein, It includes a silicon substrate and a first layer located on at least a portion of the surface of the silicon substrate, the first layer comprising a conductive agent and a fluorinated lithium phosphate compound, the thickness of the first layer being H nm, where 5 ≤ H ≤ 200.

2. The silicon-based composite material as described in claim 1, wherein, The fluorinated lithium phosphate compound is selected from at least one of lithium difluorophosphate, lithium difluorobis(oxalato) phosphate, or lithium tetrafluoro(oxalato) phosphate. or / and The conductive agent includes at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes.

3. The silicon-based composite material as described in claim 1 or 2, wherein, The silicon-based composite material satisfies at least one of the following conditions: (1)5≤H≤64； (2) The particle size Dv50 of the silicon-based composite material is X μm, 4≤X≤13; (3) The particle size Dv50 of the silicon-based composite material is X μm, and 0.56≤H / X≤22.

22.

4. The silicon-based composite material according to any one of claims 1 to 3, wherein, The conductive agent has a linear structure, with an average diameter of y nm, where 1 ≤ y ≤ 30; and an average length of L nm, where 1000 ≤ L ≤ 2000.

5. The silicon-based composite material as described in claim 4, wherein, 1≤H / y≤50.

6. The silicon-based composite material according to any one of claims 1 to 5, wherein, The sphericity of the silicon substrate is S, where S ≥ 0.

8.

7. The silicon-based composite material as described in claim 6, wherein, The average length of the conductive agent is Lnm, and 1052≤L / S≤2105.

8. The silicon-based composite material according to any one of claims 1 to 7, wherein, The silicon-based composite material satisfies at least one of the following conditions: (1) Based on the mass of the silicon-based composite material, the mass percentage of lithium in the first layer is A%, 0.1≤A≤4; (2) Based on the mass of the silicon-based composite material, the mass percentage of phosphorus in the first layer is B%, and 0.03≤B≤1.2; (3) Based on the mass of the silicon-based composite material, the mass percentage of fluorine in the first layer is C%, 0.1≤C≤4; (4) The silicon matrix includes silicon-carbon material. Based on the mass of the silicon matrix, the mass percentage of silicon is D%, 38≤D≤59, and the mass percentage of carbon is E%, 40≤E≤61. (5)0.003≤(A+B+C) / D≤0.

19.

9. The silicon-based composite material as described in claim 8, wherein, 0.104≤H / D≤4.

16.

10. A secondary battery, comprising a negative electrode, a positive electrode, and an electrolyte, wherein, The negative electrode sheet comprises a silicon-based composite material as described in any one of claims 1 to 9.

11. An electronic device, wherein, Includes the secondary battery as described in claim 10.

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