Silicon-based composite material, preparation method of silicon-based composite material, negative electrode material, pole piece, lithium battery and electric device

Abstract

The invention relates to the field of lithium ion batteries, and discloses a silicon-based composite material, a preparation method of the silicon-based composite material, a negative electrode material, a pole piece, a lithium battery and an electric device. The silicon-based composite material comprises a silicon-based material inner core, a germanium metal middle layer arranged on the surface of the silicon-based material inner core, and a lithium titanate outer layer arranged on the surface of the germanium metal layer. The active metal germanium and the lithium titanate material are sequentially utilized to perform double-layer coating on the silicon-based material core to form the novel silicon-based composite material, so that the volume expansion of silicon can be effectively buffered, the conductivity of the material can be enhanced, the stability of the electrode structure is ensured, and the service life of the electrode is prolonged. The cycle performance is improved, and meanwhile, excellent rate capability can be shown, so that a series of negative conditions caused by the volume effect of the silicon material are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion batteries, in particular to a silicon-based composite material and a preparation method thereof, a negative electrode material, a negative electrode sheet, a lithium battery and an electric device. BACKGROUND

[0002] Silicon-based negative electrode materials are considered to be the next generation of negative electrode materials for lithium ion batteries, mainly because they have a theoretical specific capacity of up to 4200 mAh / g and a high reserve in the earth's crust (second only to oxygen, 27.6%). However, there are still some problems in the commercialization of silicon materials, mainly due to the poor cycle performance and low electrical conductivity caused by the volume effect of silicon materials.

[0003] In order to accelerate the use of silicon materials as negative electrodes, a series of modification methods have been explored, such as nanocrystallization of silicon materials, carbon coating, alloying, pre-lithiation, and adhesives and electrolyte additives matching silicon materials. In order to alleviate the volume effect of silicon materials, to inhibit, reduce or avoid silicon pulverization and to improve the conductivity of silicon-based negative electrode materials to improve the performance of silicon-based negative electrode materials. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a silicon-based composite material and a preparation method thereof, so that the silicon-based negative electrode material significantly improves the initial efficiency and cycle performance.

[0005] Another purpose of the present application is to provide a negative electrode material, a negative electrode sheet, a lithium ion battery and an electric device based on the above-mentioned silicon-based composite material.

[0006] In order to solve the above technical problems / achieve the above purposes or at least partially solve the above technical problems / achieve the above purposes, as a first aspect of the present application, a silicon-based composite material is provided, comprising a silicon-based material core, a germanium metal intermediate layer arranged on the surface of the silicon-based material core, and a lithium titanate outer layer arranged on the surface of the germanium metal layer.

[0007] Optionally, the weight ratio of the silicon-based material core to the germanium metal intermediate layer is (60-90):(10-40).

[0008] Optionally, the weight ratio of the silicon-based material core and the germanium metal intermediate layer to the lithium titanate outer layer is (70-95):(5-30).

[0009] Optionally, the silicon-based material includes one or more of silicon, silicon oxide, silicon-carbon composite material, and silicon alloy.

[0010] As a second aspect of the present application, a preparation method of the silicon-based composite material as described in the present application is provided, comprising:

[0011] The coating raw material is germane as a germanium metal intermediate layer, and the metal germanium is coated on the surface of the silicon-based material core by decomposing germane under high temperature conditions by using chemical vapor deposition, sol-gel method, hydrothermal synthesis method, high-temperature sintering method or solid-state diffusion doping method, to obtain a layer of coated silicon-based material.

[0012] The silicon-based composite material is obtained by calcining the layer of coated silicon-based material in a protective gas atmosphere after the layer of coated silicon-based material is in full contact with lithium titanate.

[0013] Optionally, the calcination temperature is 500-1000°C.

[0014] As a third aspect of the present application, a negative electrode material is provided, which comprises the silicon-based composite material described in the present application, and a binder and a conductive agent.

[0015] As a fourth aspect of the present application, a negative electrode sheet is provided, which comprises a current collector and the negative electrode material described in the present application coated on the surface of the current collector.

[0016] As a fifth aspect of the present application, a lithium ion battery is provided, which comprises a positive electrode sheet, the negative electrode sheet described in the present application, and a separator and an electrolyte.

[0017] As a sixth aspect of the present application, an electrical equipment is provided, which comprises the lithium ion battery described in the present application, and the lithium ion battery provides electrical energy for the electrical equipment.

[0018] The silicon-based composite material is formed by successively coating the silicon-based material core with active metal germanium and lithium titanate material, which not only effectively buffers the volume expansion of silicon but also enhances the electrical conductivity of the material, ensures the stability of the electrode structure, improves the cycle performance, and exhibits excellent rate performance, thereby improving a series of negative situations caused by the volume effect of silicon material. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The structure of the silicon-based composite material of the present application is shown;

[0020] Figure 2 The preparation flowchart of the silicon-based composite material of the present application is shown;

[0021] Figure 3 The SEM images of the silicon-based composite material of the present application are shown: (a) 2K rate, (b) 5K rate, (c) 10K rate, and (a) 20K rate;

[0022] Figure 4 The room temperature cycle capacity retention rate results of soft pack batteries assembled with different silicon-based negative electrode materials are shown. DETAILED DESCRIPTION

[0023] The present application discloses a silicon-based composite material and a preparation method thereof, a negative electrode material, a pole piece, a lithium battery and an electric device. Those skilled in the art can refer to the content herein and appropriately improve the process parameters to achieve. It should be particularly pointed out that all similar replacements and changes are obvious to those skilled in the art, and they are considered to be included in the present application. The products, processes and applications described in the present application have been described by preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the preparation methods described herein without departing from the content, spirit and scope of the present application to achieve and apply the technology of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0024] It should be noted that in this text, if relationship terms such as "first" and "second", "step 1" and "step 2", and "(1)" and "(2)" appear, they are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between them. Moreover, the terms "include", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment. Without more limitations, the element defined by the statement "includes a" does not exclude the presence of another identical element in the process, method, article or equipment including the element. Meanwhile, the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0025] In the first aspect of the present application, a silicon-based composite material is provided, which comprises a silicon-based material core, a germanium metal intermediate layer arranged on the surface of the silicon-based material core, and a lithium titanate outer layer arranged on the surface of the germanium metal layer. The structural schematic diagram is shown in Figure 1 . The coating of active metal germanium not only improves the conductivity and buffering volume change of the material, but also provides additional capacity. Lithium titanate material is called "zero strain material", which can be used as a good buffer matrix for silicon volume expansion after coating, ensuring the stability of the electrode structure and improving the cycle performance. In addition, the high conductivity of active metal germanium and the fast charge-discharge characteristics of lithium titanate material can ensure that the material has excellent rate performance.

[0026] In some embodiments of the present application, the weight ratio of the silicon-based material core and the germanium metal intermediate layer is (60-90):(10-40). If the proportion of the silicon-based material core is too high, the overall weight of the material will be high, but the initial efficiency will gradually decrease, and the cycle performance will also deteriorate. If the proportion of the silicon-based material core is too low, the overall weight of the material will not meet the requirements, and the initial efficiency and cycle performance will have limited improvement. Therefore, the weight ratio of the silicon-based material core and the germanium metal intermediate layer is more preferably (60-65):(35-45). For example, 60:40, 65:35, 70:30, 75:25, 80:20, 85:15, 90:10, or any ratio between any two of them.

[0027] In some embodiments of the present application, the weight ratio of the silicon-based material core and the germanium metal intermediate layer and the lithium titanate outer layer is (70-95):(5-30). For example, 70:30, 75:25, 80:20, 85:15, 90:10, 95:5, or any ratio between any two of them. If the proportion of lithium titanate is too high, the overall weight of the material will decrease. If the proportion of lithium titanate is too low, the material will not be coated properly, and the cycle performance will be poor.

[0028] In some embodiments of the present application, the silicon-based material includes one or more of silicon, silicon oxide, silicon-carbon composite material, and silicon alloy. In some other embodiments of the present application, the silicon includes but is not limited to nano-silicon, micro-silicon, porous silicon, and thin-film silicon.

[0029] In some embodiments of the present application, the thickness of the germanium metal intermediate layer is 20-300 nm, and the thickness of the lithium titanate outer layer is 10-250 nm.

[0030] In some embodiments of the present application, the reversible specific capacity of the silicon-based composite material is above 1700 mAh / g, the initial efficiency is above 88%, and the capacity retention rate is significantly higher than that of other control groups during long-term cycling, reaching up to 90-95% at nearly 1000 cycles.

[0031] In a second aspect of the present application, a preparation method of the silicon-based composite material is provided, which comprises:

[0032] The germane is used as the coating raw material of the germanium metal intermediate layer. The chemical vapor deposition method, sol-gel method, hydrothermal synthesis method, high-temperature sintering method, or solid-state diffusion doping method is used to decompose the germane into metal germanium to coat the surface of the silicon-based material core under high-temperature conditions, thereby obtaining a layer of coated silicon-based material.

[0033] After the layer of coated silicon-based material is in full contact with lithium titanate, it is calcined in a protective gas atmosphere to obtain the silicon-based composite material.

[0034] In some embodiments of the present application, the silicon-based material is porous silicon prepared from silicon dioxide by magnesium thermal reduction method. In some other embodiments of the present application, the silicon dioxide particles are used as raw materials, and the silicon dioxide is reduced to elemental silicon by metal Mg at a certain temperature (SiO2+Mg→Si+MgO), and then the MgO is removed by hydrochloric acid to form porous silicon. In the reaction, the reduction temperature is 450-800°C, and the reduction time is 3-8h. The particle size of the silicon dioxide particles is 5-60μm, and the porosity of the core of the porous silicon particles is 10-45m 2 / g.

[0035] In some embodiments of the present application, the decomposition temperature of germane in the chemical vapor deposition method is 250-450°C, and the decomposition time is 2-5h.

[0036] In some embodiments of the present application, the sufficient contact includes but is not limited to grinding, ball milling, stirring, and oscillation. In some other embodiments of the present application, the coated silicon-based material is ball milled with the lithium titanate slurry, and then spray dried, and the weight ratio of the lithium titanate slurry to the coated silicon-based material is (10-20):(80-90), for example, 10:90, 15:85, 20:80, or any ratio between any two of them. The weight ratio of lithium titanate to water in the lithium titanate slurry is (15-30):(70-85), for example, 15:85, 20:80, 25:75, 30:70, or any ratio between any two of them. In some other embodiments of the present application, the rotation speed of the ball milling is 1500-4000r / min, and the time is 3-10h. The inlet temperature of the spray drying is 100-500°C, and the outlet temperature is 50-180°C.

[0037] In some embodiments of the present application, the calcination temperature is 500-1000°C, for example, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, or any value between any two of them; and the calcination time is 2-12h, for example, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, or any value between any two of them.

[0038] In some embodiments of the present application, the protective gas includes but is not limited to nitrogen and inert gas.

[0039] In a third aspect of the present application, a negative electrode material is provided, which comprises the silicon-based composite material described in the present application, and a binder and a conductive agent.

[0040] In some embodiments of the present application, the conductive agent can include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0041] In some embodiments of the present application, the binder comprises at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl chitosan (CMCS), sodium carboxymethyl cellulose (CMC), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorine-containing acrylate resin.

[0042] In some embodiments of the present application, the negative electrode material comprises the silicon-based composite material described herein, and conductive agent SP, conductive agent CNT, binder CMC glue, binder SBR, and their weight percentages are 93.5-95%: 1-2.0%: 0.1-0.2%: 1.4-2.0%: 2.3-2.5%, respectively, and the solid content of the CMC glue is 1.1%.

[0043] In a fourth aspect of the present application, a negative electrode sheet is provided, comprising a current collector and the negative electrode material described herein coated on the surface of the current collector. The negative electrode material is obtained by coating the negative electrode material described herein on the current collector after NMP pulping, rolling and sheeting to obtain the negative electrode sheet.

[0044] In some embodiments of the present application, the current collector can be a metal foil or a composite current collector. For example, as a metal foil, copper foil can be used. The composite current collector can comprise a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material base layer (such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0045] In a fifth aspect of the present application, a lithium ion battery is provided, comprising a positive electrode sheet, a negative electrode sheet described herein, and a separator and an electrolyte.

[0046] During the charging and discharging process of the battery, active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuiting of the positive and negative electrodes, while allowing ions to pass through.

[0047] The electrolyte is not particularly limited in the present application and can be selected as desired. For example, the electrolyte can be liquid, gel, or all-solid. In some embodiments of the present application, the electrolyte employs an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent. In some other embodiments of the present application, the electrolyte salt can include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoroboric oxalate, lithium boric oxalate, lithium difluoroboric dioxalate, or lithium tetrafluorophosphoric oxalate. In some other embodiments of the present application, the solvent can include at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, butyrosulfone, dimethyl sulfone, ethylene glycol dimethyl ether, methyl ethyl sulfone, or diethyl sulfone.

[0048] In some embodiments of the present application, the electrolytic solution can also optionally include an additive. The additive can include, for example, a negative electrode film-forming additive, a positive electrode film-forming additive, and an additive capable of improving certain properties of the battery, such as an additive capable of improving overcharge performance of the battery, an additive capable of improving high-temperature or low-temperature performance of the battery, and the like.

[0049] In some embodiments of the present application, the positive electrode sheet, the negative electrode sheet, and the separator film can be used to make an electrode assembly through a roll-pressing process or a stacking process.

[0050] In some embodiments of the present application, the lithium ion battery can include an outer package. The outer package can be used to encapsulate the electrode assembly and the electrolyte described above. In some other embodiments of the present application, the outer package of the lithium ion battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, and the like. The outer package of the lithium ion battery can also be a soft package, such as a pouch.

[0051] In a sixth aspect of the present application, a power-consuming device is provided, which includes the lithium ion battery described in the present application. The lithium ion battery provides power for the power-consuming device and can also be used as an energy storage unit for the power-consuming device. The power-consuming device can include, but is not limited to, a mobile device (such as a mobile phone, a laptop, and the like), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, and the like), an electric train, a ship or a satellite, an energy storage system, and the like.

[0052] In each set of comparative experiments provided in the present application, unless specifically stated, the experimental conditions, materials, etc. remain the same as the differences indicated in each set in order to have comparability. The experimental materials and reagents used in the examples can be obtained from commercial channels unless otherwise specified.

[0053] The silicon-based composite material and the preparation method thereof, the negative electrode material, the electrode sheet, the lithium battery and the electric device provided in the present application are further described below.

[0054] Example 1:

[0055] S1: SiO2 particles and Mg metal were mixed in a molar ratio, placed in a high-temperature reaction kettle, the sintering temperature was 600°C, the time was 5h, after cooling to room temperature, the mixture was taken out, and porous silicon was obtained by hydrochloric acid washing.

[0056] S2: Germane (GeH4) was used as the first alloy coating raw material, and chemical vapor deposition (CVD) method was used to decompose GeH4 under high temperature conditions to uniformly coat metal Ge on the surface of the porous silicon material, and a layer of coated silicon-based material was obtained.

[0057] The decomposition temperature of germane is 400°C, and the decomposition time is 4h.

[0058] The thickness of the metal coating layer is 100nm.

[0059] In the one-layer coated silicon-based material, the weight ratio of the porous silicon core layer to the metal coating layer is 70:30.

[0060] S3: Preparation of LTO two-layer coated porous silicon material

[0061] After LTO was added to deionized water and dispersed and ball milled to obtain LTO slurry, the one-layer coated silicon-based material in step S2 was added for mixing and ball milling, and then the established two-layer coated porous silicon-based negative electrode material was obtained after spray drying and calcination in a nitrogen atmosphere, and the preparation flow chart is shown in Figure 2 .

[0062] The weight ratio of LTO to water in the LTO slurry is 20:80; the weight ratio of the LTO slurry to the one-layer coated silicon-based material in S2 is 40:60.

[0063] The rotation speed of ball milling is 3000r / min, and the time is 8h.

[0064] The inlet temperature of the spray drying instrument is 400°C, and the outlet temperature is 120°C.

[0065] The calcination temperature is 800°C, and the time is 8h.

[0066] The thickness of the LTO coating layer is 150nm.

[0067] The weight ratio of the one-layer coated silicon-based material to the LTO coating layer in the negative electrode material is 75:25.

[0068] Example 2:

[0069] S1: SiO2 particles and Mg metal are mixed in a molar ratio, placed in a high-temperature reaction kettle, the sintering temperature is 600°C, the time is 5h, after cooling to room temperature, the mixture is taken out, and porous silicon is obtained by hydrochloric acid washing.

[0070] S2: Germane (GeH4) is used as the first layer alloy coating raw material, and chemical vapor deposition (CVD) method is used to decompose GeH4 to uniformly coat metal Ge on the surface of the porous silicon material under high temperature conditions, to obtain a one-layer coated silicon-based material.

[0071] The decomposition temperature of germane is 400°C, and the decomposition time is 3h.

[0072] The thickness of the metal coating layer is 85nm.

[0073] In the one-layer coated silicon-based material, the weight ratio of the porous silicon core layer to the metal coating layer is 65:35.

[0074] S3: Preparation of LTO two-layer coated porous silicon material

[0075] LTO is added to deionized water for dispersion ball milling to obtain LTO slurry, then mixed with the one-layer coated silicon-based material in step S2 for ball milling, and then spray drying and calcination under nitrogen atmosphere to obtain the specified two-layer coated porous silicon-based negative electrode material.

[0076] The weight ratio of LTO to water in the LTO slurry is 20:80; the weight ratio of the LTO slurry to the one-layer coated silicon-based material in step S2 is 40:60.

[0077] The rotation speed of ball milling is 3000r / min, and the time is 8h.

[0078] The inlet temperature of the spray drying instrument is 400°C, and the outlet temperature is 120°C.

[0079] The calcination temperature is 800°C, and the time is 8h.

[0080] The thickness of the LTO coating layer is 150nm.

[0081] The weight ratio of the one-layer coated silicon-based material to the LTO coating layer in the negative electrode material is 75:25.

[0082] Example 3:

[0083] S1: SiO2 particles and Mg metal are mixed in a molar ratio, placed in a high-temperature reaction kettle, the sintering temperature is 600°C, the time is 5h, after cooling to room temperature, the mixture is taken out, and porous silicon is obtained by hydrochloric acid washing.

[0084] S2: GeH4 is used as the first alloy coating raw material, and chemical vapor deposition (CVD) method is used to decompose GeH4 under high temperature conditions to uniformly coat the surface of the porous silicon material with metal Ge, and a layer of coated silicon-based material is obtained.

[0085] The decomposition temperature of germane is 400°C, and the decomposition time is 4h.

[0086] The thickness of the metal coating layer is 100nm.

[0087] In the one-layer coated silicon-based material, the weight ratio of the porous silicon core layer and the metal coating layer is 60:40.

[0088] S3: Preparation of LTO two-layer coated porous silicon material

[0089] LTO is added to deionized water for dispersion ball milling to obtain LTO slurry, then mixed with the one-layer coated silicon-based material in step S2 for ball milling, and then spray drying and calcination under nitrogen atmosphere to obtain the specified two-layer coated porous silicon-based negative electrode material, and the SEM image is shown in Figure 3 .

[0090] The weight ratio of LTO to water in the LTO slurry is 20:80; the weight ratio of the LTO slurry to the one-layer coated silicon-based material in S2 is 40:60.

[0091] The rotation speed of ball milling is 3000r / min, and the time is 8h.

[0092] The inlet temperature of the spray drying instrument is 400°C, and the outlet temperature is 120°C.

[0093] The calcination temperature is 800°C, and the time is 8h.

[0094] The thickness of the LTO coating layer is 150nm.

[0095] In the negative electrode material, the weight ratio of the one-layer coated silicon-based material and the LTO coating layer is 75:25.

[0096] Comparative Example 1:

[0097] S1: SiO2 particles and Mg metal are mixed in a molar ratio, placed in a high-temperature reaction kettle, the sintering temperature is 600°C, the time is 5h, after cooling to room temperature, the mixture is taken out, and porous silicon is obtained by hydrochloric acid washing.

[0098] S2: GeH4 is used as the first alloy cladding raw material, and the metal Ge uniformly cladded on the surface of the porous silicon material is obtained by decomposing GeH4 under high temperature conditions by using a chemical vapor deposition (CVD) method.

[0099] The decomposition temperature of germane is 400℃, and the decomposition time is 4h.

[0100] The thickness of the metal cladding layer is 100nm.

[0101] In the metal germanium cladded silicon-based material, the weight ratio of the porous silicon core layer and the metal cladding layer is 70:30.

[0102] Comparative Example 2:

[0103] S1: SiO2 particles and Mg metal are mixed in a molar ratio, placed in a high-temperature reaction kettle, the sintering temperature is 600℃, the time is 5h, after cooling to room temperature, the mixture is taken out, and porous silicon is obtained by hydrochloric acid washing.

[0104] S2: LTO is added to deionized water for dispersion ball milling to obtain LTO slurry, then the porous silicon in the step S1 is mixed and ball milled, and LTO cladded porous silicon-based negative electrode material is obtained by spray drying and calcination under nitrogen atmosphere.

[0105] The weight ratio of LTO to water in the LTO slurry is 20:80; the weight ratio of the LTO slurry to the porous silicon of S1 is 40:60.

[0106] The rotation speed of ball milling is 3000r / min, and the time is 8h.

[0107] The inlet temperature of the spray drying instrument is 400℃, and the outlet temperature is 120℃.

[0108] The calcination temperature is 800℃, and the time is 8h.

[0109] The thickness of the LTO cladding layer is 150nm.

[0110] In the negative electrode material, the weight ratio of the porous silicon core layer and the LTO cladding layer is 70:30

[0111] Comparative Example 3:

[0112] S1: SiO2 particles and Mg metal are mixed in a molar ratio, placed in a high-temperature reaction kettle, the sintering temperature is 600℃, the time is 5h, after cooling to room temperature, the mixture is taken out, and porous silicon is obtained by hydrochloric acid washing.

[0113] S2: tributyl(6-hexylthieno[3,2-b]thiophen-2-yl)stannane (C 24 H 42S2 Sn) as the first alloy cladding material, C 12 H 28 Sn is uniformly coated on the surface of the porous silicon material, obtaining a metal tin-coated silicon-based material.

[0114] The decomposition temperature of tributyl(6-hexylthieno[3,2-b]thiophen-2-yl)stannane is 400°C, and the decomposition time is 3h.

[0115] The thickness of the metal coating layer is 100nm.

[0116] In the metal tin-coated silicon-based material, the weight ratio of the porous silicon core layer and the metal coating layer is 60:40.

[0117] S3: Preparation of LTO double-layer coated porous silicon material

[0118] After dispersing and ball milling LTO in deionized water to obtain LTO slurry, then adding the metal tin-coated silicon-based material in S2 step for mixing ball milling, and after spray drying and calcining in nitrogen atmosphere, the established double-layer coated porous silicon-based negative electrode material can be obtained.

[0119] Optionally, the weight ratio of LTO to water in the LTO slurry is 20:80; and the weight ratio of the LTO slurry to the metal tin-coated silicon-based material of S2 is 40:60.

[0120] The rotation speed of ball milling is 3000r / min, and the time is 8h.

[0121] The inlet temperature of the spray drying instrument is 400°C, and the outlet temperature is 120°C.

[0122] The calcination temperature is 800°C, and the time is 8h.

[0123] The thickness of the LTO coating layer is 150nm.

[0124] In the negative electrode material, the weight ratio of the metal tin-coated silicon-based material and the LTO coating layer is 75:25.

[0125] Experimental example:

[0126] The silicon-based composite materials of each example and comparative example are prepared into negative electrode sheets, and the conductive agent and binder used in each group are consistent, and are combined with lithium negative electrode to form a button cell, and the reversible specific capacity and initial efficiency are tested. The button cell test procedure is 0.1C current constant current constant voltage discharge to 0.005V, 0.1C constant current constant voltage charge to 1.5V, cutoff current: 0.02C; constant current discharge to 0.005V, cycle 3 times; the results are shown in Table 1 below.

[0127] Table 1

[0128] Discharge gravimetric capacity (mAh / g) Charge gravimetric capacity (mAh / g) Initial efficiency (%) Example 1 2189.6 1937.8 88.5 Example 2 2012.2 1817.0 90.3 Example 3 1877.5 1731.1 92.2 Comparative Example 1 2850.8 2389.0 83.8 Comparative Example 2 2920.4 2465.2 84.4 Comparative Example 3 1810.1 1655.9 91.5

[0129] According to the results in Table 1, the first efficiency of the silicon-based composite material of the present application is above 88%, which is significantly higher than the silicon-based composite material not coated with the LTO coating layer in Comparative Example 1, and the silicon-based composite material not coated with the germanium metal layer in Comparative Document 2; Comparative Example 3 replaces the metal intermediate layer with tin, and its first efficiency is also slightly lower than that of Example 3 while maintaining the same other parameters as Example 3. In addition, by changing the weight ratio of the porous silicon core layer and the metal coating layer, the reversible gram capacity and first efficiency of the double-layer coated porous silicon-based negative electrode material will change to a certain extent.

[0130] The silicon-based composite materials and graphite of each embodiment and comparative example were used as the negative electrode main materials to make negative electrode sheets. The formula of negative electrode main materials is: sp: single-walled carbon nanotubes: SBR: CMC = 95%: 1.0%: 0.1%: 2.5%: 1.4%. The negative electrode sheet was combined with a ternary positive electrode sheet, a separator, and a silicon-carbon electrolyte to form a soft-pack lithium-ion battery. The room temperature cycle capacity retention rate of each group was tested. The results are shown in Figure 2. Figure 4 .

[0131] from Figure 4 It can be seen that the double-layer coated porous silicon-based anode material has better cycle performance than the metal-coated porous silicon-based anode material and the LTO-coated porous silicon anode material, and effectively buffers the volume expansion of silicon;

[0132] In addition, by changing the weight ratio of the porous silicon core layer and the metal coating layer, the cycle performance of the double-layer coated porous silicon-based negative electrode material changes significantly. Among them, the cycle performance of Example 3 is more outstanding, followed by the negative electrode material in which the tin metal coating is replaced on the basis of Example 3, and then the negative electrode materials of Examples 1 and 2 of this application. When the Comparative Examples 1 and 2 were cycled to 600 cycles, the capacity retention rate had dropped to 75%, while the capacity retention rates of the other groups remained above 80% at this stage.

[0133] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A silicon-based composite material, characterized in that: The invention comprises a silicon-based material core, a germanium metal intermediate layer arranged on the surface of the silicon-based material core, and a lithium titanate outer layer arranged on the surface of the germanium metal layer.

2. The silicon-based composite material according to claim 1, characterized in that The weight ratio of the silicon-based material core to the germanium metal intermediate layer is (60-90):(10-40).

3. The silicon-based composite material according to claim 1, characterized in that The weight ratio of the silicon-based material core and the germanium metal intermediate layer to the lithium titanate outer layer is (70-95):(5-30).

4. The silicon-based composite material according to claim 1, characterized in that The silicon-based material includes one or more of silicon, silicon oxide, silicon-carbon composite material, and silicon alloy.

5. A method for preparing the silicon-based composite material according to claim 1, characterized in that: include: Germane is used as the coating material for the germanium metal intermediate layer, and the germane is decomposed into metallic germanium by chemical vapor deposition, sol-gel method, hydrothermal synthesis method, high-temperature sintering method or solid-state diffusion doping method under high temperature conditions, and the metallic germanium is coated on the surface of the silicon-based material core to obtain a layer of coated silicon-based material; After the layer of coated silicon-based material is fully in contact with lithium titanate, it is calcined in a protective gas atmosphere to obtain the silicon-based composite material.

6. The preparation method according to claim 5, characterized in that The calcination temperature is 500-1000°C.

7. A negative electrode material, characterized in that The method comprises the silicon-based composite material according to any one of claims 1 to 4, and a binder and a conductive agent.

8. A negative electrode plate, characterized in that: The invention comprises a current collector and the negative electrode material according to claim 7 coated on the surface of the current collector.

9. A lithium-ion battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet as claimed in claim 8, a separator and an electrolyte.

10. An electrical device, characterized in that: The lithium-ion battery according to claim 9 is included, and the lithium-ion battery provides electrical energy for the electrical device.

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