Silicon-carbon composite negative electrode material and preparation method and application thereof

Abstract

The invention discloses a silicon-carbon composite negative electrode material and a preparation method and application thereof. The silicon-carbon composite negative electrode material comprises an inner core and a coating layer coating the inner core, the inner core comprises one or more silicon nanowires with the pipe diameter of 2-10 nm and the pipe length of 10-20 nm, magnesium silicate is dispersed and distributed on the surface layers of the silicon nanowires, the magnesium silicate is one or two of Mg2SiO4 and MgSiO3, fast ion conductors are uniformly distributed on the surfaces of the nanowires, and the fast ion conductors are uniformly distributed on the surfaces of the nanowires. The fast ion conductor is one of lithium aluminate, lithium metaphosphate and lithium phosphate; and the coating layer is a high-conductivity outer carbon layer. The silicon-carbon composite negative electrode material provided by the invention has the advantages that the rate performance and the cycle performance of the material are improved, and the structural strength of the material is also improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of composite material preparation, and particularly relates to a silicon-carbon composite negative material and a preparation method and application thereof. BACKGROUND

[0002] Silicon as anode material for lithium-ion batteries has high theoretical specific capacity, but it is accompanied by a huge volume effect during lithium extraction and insertion, resulting in poor cycle performance. At present, silicon and carbon are compounded to prepare silicon-carbon composite materials, which have high specific capacity and improved cycle performance. For example, Xu et al. (QUAN X, LI J Y, SUN J K, et al. Watermelon-Inspired Si / C Microspheres with Hierarchical Buffer Structures for Densely Compacted Lithium-Ion Battery Anodes[J]. Advanced Energy Materials, 2016, 7(3).) used nano-silicon, glucose, PVP and carboxymethyl cellulose sodium as raw materials to prepare silicon-carbon microspheres by a complex spray pyrolysis method and calcined at 900 ℃ in an atmosphere to obtain Si / C composite material with graphitized carbon layer. Chen et al. (CHEN X, YING H, CHEN J, et al. Preparation of graphene supported porous Si@C ternary composites and their electrochemical performance as high capacity anode materials for Li-ion batteries[J]. Ceramics International, 2015, 41(7):8533-8540.) prepared SiO2@C composite material by high-pressure hydrothermal reaction of hollow silica and GCP at 180 ℃ for 12 h. Jung et al. (Chul Ho Jung, Jong hyun Choi, Won-Sik Kim, Seong Hyeog Hyeon-Hong. An anopore-embedded graphitic carbon shell on silicon anode for high performance lithium ion batteries, 2018, 6, 8013) However, the material prepared by this method is generally micron-sized silicon, and the silicon-carbon material still has the problem of excessive internal stress due to expansion during the cycle process, and the particles are broken after multiple cycles, and the silicon-carbon composite is not uniform and the carbon layer structure is not strong, which cannot effectively inhibit the volume expansion of silicon during the cycle process and improve the conductivity. SUMMARY

[0003] In view of the defects of the prior art, the present application provides a silicon-carbon composite anode material.

[0004] The silicon-carbon composite negative electrode material provided by the application comprises: a core comprising one or more silicon-carbon nanowire arrays, silicon-carbon nanowires in the silicon-carbon nanowire arrays are distributed with magnesium silicate on the surface layer, and a fast ion conductor is distributed on the surface of the silicon-carbon nanowires distributed with magnesium silicate on the surface layer; a coating layer covering the core, and the coating layer is a high-conductivity outer carbon layer.

[0005] The application adopts the unique two-dimensional structure of silicon nanowires to improve the volume expansion and cycle performance of silicon, fills the carbon layer outside the silicon nanowires to improve the conductivity, provides a framework for inhibiting expansion, forms a magnesium silicate phase on the surface layer, and coats a fast ion conductor to improve the lithium ion fast transmission channel and the rate performance of the material, and further reduces the specific surface area of the material through asphalt granulation, reduces the side reaction, and further improves the cycle performance.

[0006] Further, the silicon-carbon nanowires can be silicon-carbon nanowires with a tube diameter of 2-10 nm and a tube length of 10-20 nm.

[0007] Further, the magnesium silicate can be one or both of Mg2SiO4 and MgSiO3.

[0008] Further, the fast ion conductor can be one or more of lithium aluminate, lithium metaphosphate, and lithium phosphate.

[0009] Further, the magnesium silicate is dispersedly distributed on the surface layer of the silicon-carbon nanowires, and the fast ion conductor is uniformly distributed on the surface of the silicon-carbon nanowires distributed with magnesium silicate on the surface layer.

[0010] The application further provides a preparation method of the silicon-carbon composite negative electrode material.

[0011] The preparation method of the silicon-carbon composite negative electrode material provided by the application comprises the following steps: 1) cutting a polished N-type semiconductor into a square N-type semiconductor sheet, and placing the N-type semiconductor sheet into a silicon etching solution system to perform etching, so that silicon nanowire arrays are formed on both sides of the N-type semiconductor sheet, to obtain a precursor B; 2) filling the silicon nanowires in the precursor B with amorphous carbon by using chemical vapor deposition to form a silicon-carbon nanowire precursor C; 3) separating the silicon-carbon nanowire arrays on both sides of the silicon-carbon nanowire precursor C from the N-type semiconductor substrate by using a plasma beam to form a silicon-carbon nanowire block, crushing the silicon-carbon nanowire block, uniformly mixing the crushed silicon-carbon nanowires with magnesium powder, and uniformly adding a fast ion conductor to obtain a mixture D; 4) calcining the mixture D under an inert atmosphere to obtain a composite material E; 5) Put the composite material E into an acid solution for washing, dry to obtain a composite material F; 6) Mix the composite material F with medium temperature coal pitch, and perform carbonization treatment in an inert atmosphere to obtain a finished silicon-carbon composite negative electrode material.

[0012] Further, in the step 1), the size of the square N-type semiconductor sheet can be 10*10 mm.

[0013] Further, in the step 1), the silicon etching solution system is an HF-AgNO3-H2O2 system, and the specific configuration method is as follows: 1 part of 2-4 mol / L hydrofluoric acid and 1 part of 0.1-1 mol / L hydrogen peroxide are uniformly mixed, and then 1 part of 0.1-0.3 mol / L silver nitrate solution is added and uniformly mixed to form the silicon etching solution system.

[0014] Further, in the step 1), the mass ratio of the square N-type semiconductor sheet to the silicon etching solution system is 1:1-1:4.

[0015] Further, in the step 1), the etching conditions are 20-40℃ for 5-15 min.

[0016] Further, in the step 2), the specific method of chemical vapor deposition includes: placing the precursor B in a CVD (chemical vapor deposition) furnace, and introducing N2 and C2H2 mixed gas, and keeping the temperature at 600-1000℃ for 6-10 h.

[0017] Further, the volume ratio of N2 and C2H2 in the mixed gas can be 1:1-1:3, specifically 1:1, 1:2 or 1:3.

[0018] Further, in the step 3), the silicon-carbon nanowire block is broken into small pieces with D50=2-4 μm.

[0019] Further, in the step 3), the silicon-carbon nanowire and magnesium powder are uniformly mixed at a mass ratio of 50:1-10:1, and the specific mass ratio can be 50:1, 40:1, 32:1 or 20:1.

[0020] Further, in the step 3), the fast ion conductor is one or more of lithium aluminate, lithium metaphosphate and lithium phosphate.

[0021] Further, in the step 3), the mass ratio of the silicon-carbon nanowire to the fast ion conductor is 1000:1-200:1, specifically 1000:1, 800:1, 700:1 or 300:1.

[0022] Further, in the step 4), the calcination condition is 600-900℃ for 2-4h.

[0023] Further, in the step 5), the acid solution is hydrochloric acid solution, and the concentration of the hydrochloric acid solution is 0.5-2mol / L.

[0024] Further, in the step 5), the drying mode is one of air drying and vacuum drying, and the temperature is 60-90℃.

[0025] Further, in the step 6), the softening point of the medium temperature coal pitch is 260-280℃.

[0026] Further, in the step 6), the mass ratio of the composite material F to the medium temperature coal pitch is 10:1-5:1.

[0027] Further, in the step 6), the carbonization condition is: mixing and heating under stirring to 300℃ for 2-4h, then heating to 600-900℃, and holding for 2-4h.

[0028] Further, in the step 6), the stirring speed is 90-120r / min.

[0029] The application further provides a lithium ion battery.

[0030] The lithium ion battery provided by the application comprises the silicon-carbon composite negative electrode material.

[0031] Compared with the prior art, the application has the following beneficial effects: The application uses N-type semiconductor as raw material, forms silicon nanowire array through surface corrosion, fills carbon between the nanowires to form a silicon-carbon composite precursor, cuts the silicon-carbon nanowire block through plasma beam, and prepares a unique two-dimensional structure of silicon nanowire to improve the volume expansion and cycle performance of silicon. The carbon layer filled outside the silicon nanowire can improve the conductivity and provide a framework for inhibiting expansion. After the silicon-carbon nanowire block is uniformly mixed with magnesium powder, the silicon on the surface of the silicon nanowire oxidized in the corrosion process is reduced through magnesium hot reduction, a magnesium silicate phase is formed on the surface layer to passivate the surface, prevent oxidation, and improve the initial efficiency of the material. Further, a fast ion conductor is coated to improve the lithium ion fast transmission channel and improve the rate performance of the material. Further, the asphalt granulation reduces the specific surface area of the material, reduces the side reaction, and further improves the cycle performance. In addition, the carbon coating layer formed by the silicon nanowire and the asphalt forms a steel bar-cement structure, improves the structural strength of the material, and is beneficial to improving the cycle performance of the material. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1A structure diagram of the high-performance silicon-carbon composite negative electrode material provided by the application.

[0033] Figure 2 A SEM image of the silicon nanowire array in Example 2.

[0034] Figure 3 A cycle performance diagram of the long-cycle silicon-carbon composite negative electrode material in Example 3. DETAILED DESCRIPTION

[0035] The application will be further described in detail below with reference to the specific embodiments, and the examples given are only for illustrating the application, and are not intended to limit the scope of the application. The examples provided below can serve as a guide for further improvement by those skilled in the art, and do not constitute any limitation on the application in any way.

[0036] In the following examples, the experimental methods are all conventional methods, and are performed according to the techniques or conditions described in the literature in the art or according to the product instructions, unless otherwise specified. The materials, reagents and the like used in the following examples can be obtained from commercial channels, unless otherwise specified.

[0037] Example 1, preparation of a long-cycle silicon-carbon composite negative electrode material 1 part of 2 mol / L hydrofluoric acid and 1 part of 0.1 mol / L hydrogen peroxide were mixed uniformly, 1 part of 0.1 mol / L silver nitrate solution was added, and mixed uniformly to form a mixed solution A. The polished N-type semiconductor was cut into 10*10 mm square N-type semiconductor pieces, and placed in solution A at a mass ratio of 1:1, and etched at 20°C for 5 min to form a silicon nanowire array on both sides of the N-type semiconductor piece. After washing with pure water and drying, a precursor B was obtained. The precursor B was placed in a CVD furnace, and heated at 600°C for 6 h, with N2 and C2H2 mixed gas as the gas, at a volume ratio of 1:1, so that the silicon nanowires were filled with amorphous carbon, forming a silicon-carbon nanowire precursor C.

[0038] The silicon-carbon nanowire block is formed by separating the silicon-carbon nanowire array on both sides of the silicon-carbon nanowire precursor C from the N-type semiconductor substrate by a plasma beam, and is broken into small pieces with a particle size of D50 of 2 μm, wherein the silicon nanowire has a tube diameter of 2 nm and a tube length of 10 nm. The silicon-carbon nanowire is mixed with magnesium powder at a mass ratio of 50:1, and then lithium aluminate is added and mixed uniformly (obtaining a mixture D), and the mass ratio of the silicon-carbon nanowire to the lithium aluminate is 1000:1. The mixture is calcined at 600 ℃ for 2 h under an argon atmosphere, and MgSiO3 is formed on the surface of the silicon nanowire, and the surface is coated with lithium aluminate, thereby obtaining a composite material E. The composite material E is washed in 0.5 mol / L hydrochloric acid and dried by blowing air at 60 ℃, thereby obtaining a composite material F. The composite material F is mixed with medium-temperature coal pitch with a softening point of 260 ℃, and the mass ratio of the composite material F to the medium-temperature coal pitch is 10:1. The mixture is heated to 300 ℃ under stirring at a speed of 90 r / min in an argon atmosphere for 2 h, and then the temperature is increased to 600 ℃, and the mixture is kept at this temperature for 2 h, thereby obtaining a finished long-cycle silicon-carbon composite negative electrode material.

[0039] The obtained long-cycle silicon-carbon composite negative electrode material and lithium metal are used to form a half-cell for electrochemical performance test, and the test rate is 0.1 C (first time) + 0.5 C (cycle), and the charge and discharge voltage is 0.005-0.8 V. The results show that the discharge specific capacity of the negative electrode sheet can reach 1750 mAh / g, the first efficiency is 91.6%, and after 50 cycles, the capacity can still be maintained at 82.1%.

[0040] The obtained long-cycle silicon-carbon composite negative electrode material is mixed with graphite at a mass ratio of 5:95 to obtain a composite negative electrode material. NCM622 is used as a positive electrode to assemble a 7 Ah soft package battery through processes such as slurry mixing, coating, rolling, slitting, die cutting, lamination, tab welding, top side sealing, baking, and liquid injection. After formation and capacity distribution, the battery is subjected to a normal temperature cycle test at a current density of 1C / 1C, and the initial efficiency of the battery cell is 84%. After 850 cycles, the capacity retention rate of the full battery is 89.8%.

[0041] Example 2, preparation of a long-cycle silicon-carbon composite negative electrode material One part of 2.5 mol / L hydrofluoric acid and one part of 0.5 mol / L hydrogen peroxide are mixed uniformly, and one part of 0.15 mol / L silver nitrate solution is added and mixed uniformly to form a mixed solution A. A polished N-type semiconductor is cut into a square N-type semiconductor sheet with a size of 10*10 mm, and is placed in the solution A at a mass ratio of 1:2 at 25 ℃ for 10 min to form silicon nanowire arrays on both sides of the N-type semiconductor sheet. The precursor B is obtained after washing with pure water and drying. The precursor B is placed in a CVD furnace at 800 ℃ for 7 h, and the gas is a mixed gas of N2 and C2H2 with a volume ratio of 1:2, so that the silicon nanowires are filled with amorphous carbon to form a silicon-carbon nanowire precursor C.

[0042] Silicon nanowires were separated from the N-type semiconductor substrate by plasma beam separation of the silicon-carbon nanowire arrays on both sides of the silicon-carbon nanowire precursor C to form silicon-carbon nanowire blocks, which were then broken into small pieces with a diameter of 50~2μm. The silicon nanowires had a diameter of 3nm and a length of 13nm. The silicon-carbon nanowires were then mixed with magnesium powder at a mass ratio of 40:1, and lithium aluminate was added and mixed thoroughly. The mass ratio of silicon-carbon nanowires to lithium metaphosphate was 800:1. The mixture was calcined at 700℃ for 2.5h under an argon atmosphere. The surface of the rice noodles forms MgSiO3 and is coated with lithium metaphosphate. The mixture is washed in 0.8 mol / L hydrochloric acid and dried at 70°C by blowing air to obtain composite material F. Composite material F is then mixed with medium-temperature coal tar pitch with a softening point of 270°C at a mass ratio of 8:1. The mixture is heated to 300°C and held for 2.5 h under an argon atmosphere with a stirring speed of 100 r / min, and then heated to 700°C and held for 2.5 h to obtain the finished product.

[0043] The obtained long-cycle silicon-carbon composite anode material and lithium metal were used to assemble a half-cell for electrochemical performance testing. The test rates were 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltages ranged from 0.005 to 0.8V. The results showed that the discharge specific capacity of the anode sheet could reach 1737 mAh / g, with an initial efficiency of 89.6%, and after 50 cycles, it could still retain 82.1% of its capacity.

[0044] The obtained long-cycle silicon-carbon composite anode material was mixed with graphite at a mass ratio of 5:95 to form a composite anode material. Using NCM622 as the positive electrode, a 7Ah soft-pack battery was assembled by performing processes such as slurry mixing, coating, rolling, slitting, die cutting, stacking, electrode tab welding, top and side sealing, baking, and electrolyte injection. After capacity testing, a room temperature cycle test was conducted at a 1C / 1C current density. The initial efficiency of the cell was 85%, and after 860 cycles of the full battery, the capacity retention rate was 90.6%.

[0045] Example 3: Preparation of long-cycle silicon-carbon composite anode material One part of 2.8 mol / L hydrofluoric acid and one part of 0.8 mol / L hydrogen peroxide were mixed thoroughly, and one part of 0.2 mol / L silver nitrate solution was added. The mixture was then thoroughly mixed to form solution A. The polished N-type semiconductor was cut into 10*10 mm square N-type semiconductor wafers, and the wafers were placed in solution A at a mass ratio of 1:2. The wafers were etched at 30°C for 13 min to form silicon nanowire arrays on both sides of the N-type semiconductor wafers. After washing with pure water and drying, precursor B was obtained. Precursor B was placed in a CVD furnace and kept at 800°C for 7 h in a 1:2 volume ratio of N2 and C2H2 gas to fill the spaces between the silicon nanowires with amorphous carbon, forming silicon-carbon nanowire precursor C.

[0046] The silicon-carbon nanowires were separated from the N-type semiconductor substrate on both sides of the silicon-carbon nanowire precursor C using a plasma beam to form silicon-carbon nanowire blocks, which were then broken into small pieces with a diameter of 50~2μm. The silicon nanowires had a diameter of 4nm and a length of 15nm. The silicon-carbon nanowires and magnesium powder were mixed evenly at a mass ratio of 32:1, and then lithium aluminate was added and mixed evenly. The mass ratio of silicon-carbon nanowires to lithium metaphosphate was 700:1. The mixture was calcined at 750℃ for 3h under an argon atmosphere to form Mg2SiO4 on the surface of the silicon nanowires, which was then coated with lithium metaphosphate. The mixture was washed in 1mol / L hydrochloric acid and dried at 75℃ by forced air. The composite material F was then mixed with medium-temperature coal tar pitch with a softening point of 270℃ at a mass ratio of 7:1. The mixture was stirred at 110r / min under an argon atmosphere and heated to 300℃ for 3h, then heated to 800℃ and held for 2.5h to obtain the finished product.

[0047] The obtained long-cycle silicon-carbon composite anode material and lithium metal were used to assemble a half-cell for electrochemical performance testing. The test rates were 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltages ranged from 0.005 to 0.8V. The results showed that the discharge specific capacity of the anode sheet could reach 1680 mAh / g, with an initial efficiency of 93.0%, and after 50 cycles, it could still retain 83.1% of its capacity.

[0048] The obtained long-cycle silicon-carbon composite anode material was uniformly mixed with graphite at a mass ratio of 5:95 to form the composite anode material. Using NCM622 as the positive electrode, a 7Ah soft-pack battery was assembled through processes including slurry preparation, coating, rolling, slitting, die-cutting, stacking, tab welding, top-side sealing, baking, and electrolyte injection. After capacity testing, a room-temperature cycle test was conducted at 1C / 1C current density. The initial efficiency of the cell was 86.2%, and after 932 cycles of the full battery, the capacity retention rate was 90.3%. Figure 3 As shown.

[0049] Example 4: Preparation of long-cycle silicon-carbon composite anode material One part of 3.5 mol / L hydrofluoric acid and one part of 0.8 mol / L hydrogen peroxide were mixed thoroughly, and one part of 0.25 mol / L silver nitrate solution was added. The mixture was then thoroughly mixed to form solution A. The polished N-type semiconductor was cut into 10*10 mm square N-type semiconductor wafers, and placed in solution A at a mass ratio of 1:3.5. The wafers were etched at 35°C for 13 min to form silicon nanowire arrays on both sides of the N-type semiconductor wafers. After washing with pure water and drying, precursor B was obtained. Precursor B was placed in a CVD furnace and kept at 800°C for 8 h under a gas mixture of N2 and C2H2 at a volume ratio of 1:2 to fill the spaces between the silicon nanowires with amorphous carbon, forming silicon-carbon nanowire precursor C.

[0050] The silicon-carbon nanowires were separated from the N-type semiconductor substrate on both sides of the silicon-carbon nanowire precursor C using a plasma beam to form silicon-carbon nanowire blocks, which were then broken into small pieces with a diameter of 50~2μm. The silicon nanowires had a diameter of 7nm and a length of 18nm. The silicon-carbon nanowires and magnesium powder were mixed evenly at a mass ratio of 20:1, and then lithium aluminate was added and mixed evenly. The mass ratio of silicon-carbon nanowires to lithium phosphate was 300:1. The mixture was calcined at 850℃ for 3.5h under an argon atmosphere to form Mg2SiO4 on the surface of the silicon nanowires. The surface was then coated with lithium phosphate. The mixture was washed in 1.8mol / L hydrochloric acid and dried under vacuum at 85℃. The composite material F was then mixed with medium-temperature coal tar pitch with a softening point of 275℃ at a mass ratio of 6:1. The mixture was heated to 300℃ and held for 3.5h under an argon atmosphere with a stirring speed of 115r / min, and then heated to 850℃ and held for 3.5h to obtain the finished product.

[0051] The obtained long-cycle silicon-carbon composite anode material and lithium metal were used to assemble a half-cell for electrochemical performance testing. The test rates were 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltages ranged from 0.005 to 0.8V. The results showed that the discharge specific capacity of the anode sheet could reach 1690 mAh / g, with an initial efficiency of 92.2%, and it could still retain 80.1% of its capacity after 50 cycles.

[0052] The obtained long-cycle silicon-carbon composite anode material was mixed with graphite at a mass ratio of 5:95 to form a composite anode material. Using NCM622 as the positive electrode, a 7Ah soft-pack battery was assembled by performing processes such as slurry preparation, coating, rolling, slitting, die cutting, stacking, electrode tab welding, top and side sealing, baking, and electrolyte injection. After capacity testing, a room temperature cycle test was conducted at a 1C / 1C current density. The initial efficiency of the cell was 86.3%, and the capacity retention rate was 88.3% after 836 cycles of the entire battery.

[0053] Example 5: Preparation of long-cycle silicon-carbon composite anode material One part of 3.5 mol / L hydrofluoric acid and one part of 0.8 mol / L hydrogen peroxide were mixed thoroughly, and one part of 0.25 mol / L silver nitrate solution was added. The mixture was then thoroughly mixed to form solution A. The polished N-type semiconductor was cut into 10*10 mm square N-type semiconductor wafers, and placed in solution A at a mass ratio of 1:3.5. The wafers were etched at 35°C for 13 min to form silicon nanowire arrays on both sides of the N-type semiconductor wafers. After washing with pure water and drying, precursor B was obtained. Precursor B was placed in a CVD furnace and kept at 800°C for 10 h in a mixed gas of N2 and C2H2 at a volume ratio of 1:3 to fill the spaces between the silicon nanowires with amorphous carbon, forming silicon-carbon nanowire precursor C.

[0054] Silicon nanowires were separated from the N-type semiconductor substrate on both sides of the silicon-carbon nanowire precursor C using a plasma beam to form silicon-carbon nanowire blocks, which were then broken into small pieces with a diameter of 50~2μm. The silicon nanowires had a diameter of 3nm and a length of 13nm. The silicon-carbon nanowires and magnesium powder were mixed evenly at a mass ratio of 20:1, and then lithium aluminate was added and mixed evenly. The mass ratio of silicon-carbon nanowires to lithium phosphate was 300:1. The mixture was calcined at 850℃ for 3.5h under an argon atmosphere to form Mg2SiO4 on the surface of the silicon nanowires. The surface was coated with lithium phosphate. The mixture was washed in 1.8mol / L hydrochloric acid and dried under vacuum at 85℃. The composite material F was then mixed with medium-temperature coal tar pitch with a softening point of 275℃ at a mass ratio of 5:1. The mixture was heated to 300℃ and held for 3.5h under an argon atmosphere with a stirring speed of 115r / min, and then heated to 850℃ and held for 3.5h to obtain the finished product. The obtained long-cycle silicon-carbon composite anode material and lithium metal were used to assemble a half-cell for electrochemical performance testing. The test rates were 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltages ranged from 0.005 to 0.8V. The results showed that the discharge specific capacity of the anode sheet could reach 1683 mAh / g, with an initial efficiency of 93.0%, and it could still retain 81.1% of its capacity after 50 cycles.

[0055] The obtained long-cycle silicon-carbon composite anode material was mixed with graphite at a mass ratio of 5:95 to form a composite anode material. Using NCM622 as the positive electrode, a 7Ah soft-pack battery was assembled by performing processes such as slurry mixing, coating, rolling, slitting, die cutting, stacking, electrode tab welding, top and side sealing, baking, and electrolyte injection. After capacity testing, a room temperature cycle test was conducted at a 1C / 1C current density. The initial efficiency of the cell was 85.5%, and the capacity retention rate was 90.5% after 900 cycles of the full battery.

[0056] Comparative Example 1 A porous carbon matrix with a D50 of 8 μm was placed in a fluidized bed, and a mixture of silane and hydrogen gas was introduced at a gas flow ratio of 2:1. The mixture was heated to 700℃ and held for 6 hours. Then, a mixture of acetylene and argon gas was introduced at a gas flow ratio of 1:3 and held at 750℃ for 3 hours to obtain a silicon-carbon anode material.

[0057] The obtained silicon-carbon anode material and lithium metal were used to assemble a half-cell for electrochemical performance testing. The test rates were 0.1C (initial) + 0.5C (cycle), and the charge / discharge voltages ranged from 0.005 to 0.8V. The results showed that the discharge specific capacity of the anode sheet could reach 1580 mAh / g, with an initial efficiency of 82.0%, and after 50 cycles, it could still retain 51.1% of its capacity.

[0058] As can be seen from the performance results of the embodiments, this technical solution improves the volume expansion and cycling performance of silicon by: etching a silicon nanowire array on the surface of an N-type semiconductor, then cutting the silicon nanowires with a plasma beam to prepare a unique two-dimensional structure of silicon nanowires; reducing the silicon on the surface of the silicon nanowires that was partially oxidized during the etching process through magnesothermic reduction, while forming a magnesium silicate phase on the surface to passivate the surface, prevent oxidation, and improve the first efficiency of the material; then coating it with a fast ion conductor to enhance the fast lithium-ion transport channel and improve the rate performance of the material; then reducing the specific surface area of ​​the material through pitch granulation to reduce side reactions and further improve the cycling performance; in addition, the carbon coating layer formed by silicon nanowires and pitch forms a reinforced concrete structure, which improves the structural strength of the material and improves the cycling performance of the material.

[0059] The present invention has been described in detail above. For those skilled in the art, the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope, and without requiring unnecessary experiments. Although specific embodiments have been given, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including changes made using conventional techniques known in the art that depart from the scope disclosed herein. Some of the essential features can be applied within the scope of the following appended claims.

Claims

1. A silicon-carbon composite anode material, comprising: The core comprises one or more silicon-carbon nanowire arrays, wherein the surface of the silicon-carbon nanowires in the silicon-carbon nanowire array is distributed with magnesium silicate, and fast ion conductors are distributed on the surface of the silicon-carbon nanowires. A coating layer that covers the core, wherein the coating layer is a highly conductive outer carbon layer.

2. The silicon-carbon composite anode material according to claim 1, characterized in that: The silicon-carbon nanowires have a diameter of 2-10 nm and a length of 10-20 nm. And / or, the magnesium silicate is one or both of Mg2SiO4 and MgSiO3; And / or, the fast ion conductor is one or more of lithium aluminate, lithium metaphosphate, and lithium phosphate.

3. The method for preparing the silicon-carbon composite anode material according to claim 1 or 2, comprising the following steps: 1) The polished N-type semiconductor is cut into square N-type semiconductor wafers and placed in a silicon etching solution system for etching, so that silicon nanowire arrays are formed on both sides of the N-type semiconductor wafers to obtain precursor B; 2) Chemical vapor deposition is used to fill the spaces between the silicon nanowires in the precursor B with amorphous carbon to form silicon-carbon nanowire precursor C; 3) The silicon-carbon nanowire arrays on both sides of the silicon-carbon nanowire precursor C are separated from the N-type semiconductor substrate using a plasma beam to form a silicon-carbon nanowire block. The silicon-carbon nanowire block is broken up, and the broken silicon-carbon nanowires are mixed evenly with magnesium powder. Then, a fast ion conductor is added and mixed evenly to obtain a mixture D. 4) The mixture D is calcined under an inert atmosphere to obtain composite material E; 5) The composite material E is washed in an acid solution and dried to obtain composite material F; 6) The composite material F is mixed with medium-temperature coal tar pitch and carbonized in an inert atmosphere to obtain the silicon-carbon composite anode material.

4. The preparation method according to claim 3, characterized in that: In step 1), the silicon etching solution system is an HF-AgNO3-H2O2 system, and the specific preparation method is as follows: mix 1 part of 2~4 mol / L hydrofluoric acid and 1 part of 0.1~1 mol / L hydrogen peroxide evenly, then add 1 part of 0.1~0.3 mol / L silver nitrate solution, and mix evenly to form the silicon etching solution system.

5. The preparation method according to claim 4, characterized in that: In step 1), the mass ratio of the square N-type semiconductor wafer to the silicon etching solution system is 1:1 to 1:

4. And / or, in step 1), the etching conditions are etching at 20~40℃ for 5~15 minutes.

6. The preparation method according to claim 3, characterized in that: In step 2), the specific method of chemical vapor deposition includes: placing the precursor B in a CVD furnace, introducing a mixed gas of N2 and C2H2, and maintaining the temperature at 600℃~1000℃ for 6~10h; wherein the volume ratio of N2 to C2H2 in the mixed gas is 1:1~1:

3.

7. The preparation method according to claim 3, characterized in that: In step 3), the silicon-carbon nanowire blocks are broken into small pieces with D50 = 2~4 μm; And / or, in step 3), the silicon-carbon nanowires and magnesium powder are mixed evenly at a mass ratio of 50:1 to 10:1; And / or, in step 3), the fast ion conductor is one or more of lithium aluminate, lithium metaphosphate, and lithium phosphate; And / or, in step 3), the mass ratio of the silicon-carbon nanowire to the fast ion conductor is 1000:1 to 200:

1.

8. The preparation method according to claim 3, characterized in that: In step 4), the calcination conditions are calcination at 600~900℃ for 2~4 hours.

9. The preparation method according to claim 3, characterized in that: In step 5), the acid solution is a hydrochloric acid solution with a concentration of 0.5~2 mol / L. And / or, in step 5), the drying method is one of blower drying and vacuum drying, and the temperature is 60~90℃.

10. The preparation method according to claim 3, characterized in that: In step 6), the softening point of the medium-temperature coal tar pitch is 260℃~280℃; And / or, in step 6), the mass ratio of the composite material F to the medium-temperature coal tar pitch is 10:1 to 5:1; And / or, in step 6), the carbonization treatment conditions are: mixing and heating to 300°C under stirring conditions and holding for 2-4 hours, then raising the temperature to 600-900°C and holding for 2-4 hours; And / or, in step 6), the stirring speed is 90-120 r / min.

11. A lithium-ion battery, characterized in that: The negative electrode of the lithium-ion battery comprises the silicon-carbon composite negative electrode material as described in claim 1 or 2, or the silicon-carbon composite negative electrode material prepared by the method described in any one of claims 3-10.

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