Silicon-carbon negative electrode material and preparation method thereof

Abstract

The application provides a silicon-carbon negative electrode material and a preparation method thereof, and relates to the technical field of lithium ion battery negative electrode material preparation. The silicon-carbon negative electrode material comprises a core, wherein the core comprises one or more spherical porous carbon matrices with surface pores, and the surface pores of the spherical porous carbon matrices are distributed with nanosilicon; and a coating layer, wherein the coating layer coats the core, and the coating layer comprises a passivation carbon layer and a highly-conductive outer carbon layer; the passivation carbon layer coats the core; the highly-conductive layer coats the passivation carbon layer; and the highly-conductive outer carbon layer is diffused with nanosilver; and the silicon-carbon negative electrode material has small resistivity and excellent rate performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery negative electrode material preparation, and in particular to a silicon-carbon negative electrode material and a preparation method thereof. BACKGROUND

[0002] At present, lithium ion batteries are widely used in various consumer electronic products, including mobile phones, notebook computers and electric tools, and are also applied to electric vehicles, power grid energy storage markets and aerospace and marine application fields due to their high energy, power density, fast charging capability and long cycle life. Lithium ion batteries include positive electrode materials, negative electrode materials, separators and electrolytes, wherein the negative electrode material plays a key role in the performance of lithium ion batteries.

[0003] At present, the commonly reported negative electrode materials include silicon negative electrode materials, and the common types of silicon negative electrode materials are pre-lithium silicon oxide and new silicon-carbon. Among them, the new silicon-carbon becomes a research hotspot of silicon negative electrode materials because of its good nanometerization cycle.

[0004] However, the resistivity of the new silicon-carbon is 10-30 Ω·cm, and the powder resistivity is generally 1 order of magnitude higher than that of pre-lithium silicon oxide (pre-lithium silicon oxide powder resistivity: 1 Ω·cm). After compounding with graphite, the film resistance of the electrode sheet is also high, which affects the rate performance of the battery cell. In addition, the porous channel structure causes poor compression resistance of the material, and the material breaks and exposes the silicon material under high compaction, which causes side reactions with the electrolyte and affects the cycle of the battery cell. Therefore, there are many technical difficulties to be solved in the new silicon-carbon technology. SUMMARY

[0005] (I) Technical problems solved

[0006] In view of the deficiencies of the prior art, the present application provides a silicon-carbon negative electrode material and a preparation method thereof, which solves the technical problem of high resistivity of the new silicon-carbon.

[0007] (II) Technical solutions

[0008] To achieve the above purposes, the present application is implemented by the following technical solutions:

[0009] On the one hand, the present application provides a silicon-carbon negative electrode material, which comprises

[0010] a core comprising one or more spherical porous carbon matrices with surface channels, wherein nano-silicon is distributed in the surface channels of the spherical porous carbon matrices, and

[0011] a coating layer covering the core, wherein the coating layer comprises a passivation carbon layer covering the core and a high-conductivity outer carbon layer covering the passivation carbon layer, and nano-silver is dispersedly distributed in the high-conductivity outer carbon layer.

[0012] Preferably, the silicon-carbon negative electrode material is in the form of particles, with a particle size D50 of 6-10 μm; the passivation carbon layer accounts for 3-6% of the mass of the single particle silicon-carbon negative electrode material, and the high-conductivity outer carbon layer accounts for 2-5% of the mass of the single particle silicon-carbon negative electrode material.

[0013] In another aspect, the present application provides a method for preparing a silicon-carbon negative electrode material, comprising the following steps:

[0014] 1) mixing n-hexane and ethanol in a mass ratio of 1:1-5 to obtain a mixed solution A;

[0015] The mixed solution of n-hexane and ethanol is used to remove soluble organic impurities.

[0016] 2) adding medium-temperature coal tar to part of the mixed solution A, mixing and heating to 100-150°C under stirring at a speed of 90-120 r / min, maintaining for 2-4 h, and then filtering to obtain insoluble substances B;

[0017] 3) mixing dimethyl silicone oil with the insoluble substances B, mixing and heating to 300-400°C under stirring at a speed of 100-300 r / min, maintaining for 3-6 h, to obtain spherical carbon precursors C, with a particle size D50 of 1-4 μm;

[0018] 4) mixing the spherical carbon precursors C with the mixed solution of n-hexane and ethanol, heating to 100-150°C under stirring at a speed of 90-120 r / min, maintaining for 2-4 h, filtering, washing with ethanol, and drying to obtain a spherical carbon matrix, mixing the spherical carbon matrix with KOH in a mass ratio of 1:1-1:3, calcining at 600-900°C in an inert atmosphere for 1-4 h, then washing with 0.5-1 M hydrochloric acid, washing with deionized water, and drying, to obtain a spherical porous carbon matrix D with uniform pore distribution;

[0019] The dimethyl silicone oil acts as a dispersant, and the dimethyl silicone oil and the insoluble substances B generate spherical small-particle-size carbon matrix (particle size D50 of 1-4 μm, non-fine powder) with uniform particle size under continuous stirring due to surface tension and pressure. The carbon matrix has uniform particle size and regular spherical shape, and the material has uniform pore size and uniform pore distribution after pore formation, and the nano-silicon is easily and uniformly deposited in the pores after silane deposition, forming a material with uniform structure and high material structure strength. In addition, the stress generated in the transverse direction due to the volume effect of the spherical material during charging and discharging can be partially offset, improving the cycle performance of the material. The small volume of the carbon matrix reduces the lithium ion transmission path, improves the rate performance of the material, and reduces the absolute volume expansion of the material during charging and discharging, improving the expansion and cycle of the material.

[0020] 5) the first mixed gas is introduced into the spherical porous carbon matrix D, heated to 400-700 DEG C for 2-6h, the second mixed gas is introduced, 650 DEG C-750 DEG C for 1-3h, to obtain product E;

[0021] 6) the third mixed gas is introduced into the product E, the gas flow ratio is 2:1-1:2, heated to 650-750 DEG C for 1-4h, to obtain silicon-carbon material precursor F;

[0022] Step 5) After the deposition of nanosilicon, first carbon coating is carried out for surface passivation, and then secondary carbon coating is carried out in step 6) to reduce the specific surface area of the material, increase the conductivity, and also completely isolate the nanosilicon in the matrix pores from the outside.

[0023] 7) the medium temperature coal pitch is added into 0.1M silver nitrate solution, stirred for 1-3h, the stirring speed is 900-1200r / min, to form a solution with solid content of 40-60%, then the solution is filtered and dried to form a composite carbon source G;

[0024] 8) the composite carbon source G and the silicon-carbon material precursor F are mixed and stirred at a mass ratio of 5:95-10:90 and a stirring speed of 300-500r / min, heated to 350 DEG C-500 DEG C, and kept for 1-3h to complete the granulation, then calcined at 650 DEG C-900 DEG C for 2-4h in an inert atmosphere, to obtain a silicon-carbon negative electrode material I.

[0025] Steps 7) and 8) are carried out by mixing silver nitrate solution with cheap medium temperature pitch, and then carrying out pitch carbonization in step 9) to form a high-conductive dense carbon layer, which improves the conductivity and reduces the specific surface area, and binds the nanosilicon expansion in the charging and discharging process, while the silver ions are reduced to nanosilver particles by the hydroxyl and carboxyl groups of the pitch, which are uniformly dispersed in the high-conductive dense carbon layer to form a three-dimensional conductive network, thereby improving the conductivity of the material.

[0026] Preferably, in step 2), the softening point of the medium temperature coal pitch is 280 DEG C, and the mass ratio of the medium temperature pitch to the solution A is 1:1-1:3.

[0027] Preferably, in step 3), the mass ratio of dimethyl silicone oil to the insoluble substance B is 1:2-1:5, which ensures that the insoluble substance B can be fully dispersed, and at the same time controls the particle size of the spherical carbon precursor C.

[0028] Preferably, in step 4), the mass ratio of the spherical carbon precursor C to the solution A is 1:1-1:3, the drying temperature is 60 DEG C-80 DEG C, and the particle size D50 of the spherical porous carbon matrix D is 1-4μm, to obtain a spherical small particle size carbon matrix with uniform particle size (particle size D50 is 1-4μm, non-fine powder), which shortens the lithium ion transmission particle size, and makes the material have excellent cycle performance.

[0029] Preferably, in the step 5), the first mixed gas comprises silane and hydrogen, and the volume ratio of the silane and hydrogen is 10:1-2:1, which can provide a high reduction atmosphere and ensure the required silicon source for the nanosilicon.

[0030] Preferably, in the step 5), the second mixed gas comprises acetylene and argon, and the volume ratio of the acetylene and argon is 2:1-1:3, which can ensure the amount of the second mixed gas to keep the flow state and the amount of the carbon source acetylene required for coating.

[0031] Preferably, in the step 6), the third mixed gas comprises acetylene and inert atmosphere. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0033] Figure 1 The XRD graph of the silicon-carbon negative electrode material in the embodiment 3 of the present application.

[0034] Figure 2 The structural schematic diagram of the silicon-carbon negative electrode material of the present application.

[0035] Figure 3 The full-cell cycle result of the silicon-carbon negative electrode material in the embodiment 3 of the present application. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application are described clearly and completely. Obviously, the described embodiments are some embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0037] The embodiments of the present application provide a silicon-carbon negative electrode material and a preparation method thereof, and solve the technical problems of high resistivity and poor compression resistance of the existing new type silicon-carbon electrode.

[0038] The technical solutions in the embodiments of the present application are as follows to solve the above technical problems:

[0039] 1. Currently, novel silicon-carbon materials are typically produced by crushing biomass, petroleum coke, or resin into irregular blocks, which are then pore-formed to form a blocky porous carbon matrix. This method often results in uneven particle size distribution in the carbon matrix, with fine powder (particle size <1μm, large specific surface area, many side reactions) or large particles (>20μm, long lithium-ion transport path, poor rate performance). The matrix's structure is prone to large pore defects due to side reactions or the preparation environment. Furthermore, differences in particle size and formation lead to varying local surface energies, resulting in uneven pore formation, affecting deposition uniformity and the material's electrochemical performance. In addition, after depositing nano-silicon within the pores of the aforementioned carbon matrix, the volume effect of silicon during charge and discharge causes varying stresses in different local areas of the irregularly shaped material, making it prone to breakage and pulverization, thus affecting the material's cycle performance. This invention uses inexpensive, medium-temperature coal tar pitch as raw material. In step 1), a mixed solution of hexane and ethanol is used to remove soluble organic impurities. In step 3), dimethyl silicone oil is used as a dispersant. The mixture is continuously stirred in a reactor under surface tension and pressure to generate uniformly sized spherical carbon matrix particles (1–4 μm, not fine powder). Due to the uniform particle size and regular spherical shape of the carbon matrix, the pore size is uniform after pore formation, and the pores are evenly distributed. After silane deposition, nano-silicon is easily and uniformly deposited within the pores, forming a material with a uniform structure and high structural strength. Furthermore, the spherical material can partially offset the stress generated by the volume effect in the lateral direction during charging and discharging, improving the material's cycle performance. The smaller carbon volume not only reduces the lithium-ion transport path, improving the material's rate performance, but also reduces the absolute volume expansion during charging and discharging, improving material expansion and cycle life.

[0040] 2. In step 5) of the present invention, after depositing nano-silicon, a first carbon coating is performed for surface passivation, and then a second carbon coating is performed in step 6) to reduce the material specific surface area and increase conductivity. At the same time, the nano-silicon in the matrix channel is completely isolated and passivated from the outside.

[0041] 3. In steps 7) and 8) of this invention, silver nitrate solution is mixed with inexpensive medium-temperature asphalt, and then in step 9) the asphalt is carbonized into a highly conductive dense carbon layer, which improves conductivity, reduces specific surface area, and restricts the expansion of nano-silicon during charging and discharging. At the same time, silver ions are reduced by the hydroxyl and carboxyl groups of the asphalt into nano-silver particles, which are uniformly dispersed in the highly conductive dense carbon layer to form a three-dimensional conductive network and improve the conductivity of the material.

[0042] 4. The structure of this invention is a novel silicon-carbon (nano-silicon deposited within the pores of a porous carbon matrix) composite material with a core of small size and uniform particle size. One or more cores are then combined through granulation to form a slightly larger finished product. The structural advantages include:

[0043] 1) Due to the porous structure of the carbon matrix in the novel silicon-carbon material, ion transport needs to bypass the pores, resulting in poor ion conductivity. Using a small core can shorten the lithium-ion transport path and improve the lithium-ion transport rate.

[0044] 2) Employing medium-temperature pitch granulation and carbonization to composite multiple cores reduces the material's specific surface area (increased particle size), minimizes negative reactions with the electrolyte, and improves initial efficiency (reduced SEI film). This better encapsulates the cores, further suppressing volume changes during charge and discharge. This comprehensive core encapsulation improves the situation where fresh silicon is exposed to the electrolyte due to volume changes during cell cycling, effectively reducing negative reactions and enhancing the material's cycle performance.

[0045] In addition, the carbon layer after asphalt carbonization has a large interlayer spacing, which provides a fast channel for electron and lithium-ion transport. The nano-silver dispersed in it further improves the conductivity of the material and improves the shortcomings of this type of material, such as high resistivity and poor rate performance.

[0046] 5. For example Figure 2 The present invention relates to a silicon-carbon anode material comprising a core comprising one or more spherical porous carbon matrices having surface channels, wherein nano-silicon is distributed within the surface channels of the spherical porous carbon matrix, and a coating layer covering the core. The coating layer comprises a passivated carbon layer and a highly conductive outer carbon layer, wherein the passivated carbon layer covers the core, the highly conductive layer covers the passivated carbon layer, and nano-silver is dispersedly distributed in the highly conductive outer carbon layer.

[0047] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0048] Example 1

[0049] This embodiment provides a method for preparing a long-cycle silicon-carbon anode material, as detailed below:

[0050] A mixture solution A is obtained by mixing n-hexane and ethanol with a mass ratio of 1:3, 280℃ softening point medium temperature coal tar pitch is added with a mass ratio of 1:1, and then placed in a reaction kettle and heated to 100℃ with stirring at 100r / min for 2h, followed by filtration. The obtained insoluble material B is mixed with dimethyl silicone oil with a mass ratio of 1:2, and then placed in a reaction kettle and heated to 300℃ with stirring at 100r / min for 3h to obtain spherical carbon precursor C. The spherical carbon precursor C is placed in a mixture solution of n-hexane and ethanol with a mass ratio of 1:1, and then placed in a reaction kettle and heated to 100℃ with stirring at 100r / min for 2h, followed by filtration and washing with ethanol, and then dried at 60℃ to obtain a spherical carbon matrix. The spherical carbon matrix is mixed with KOH with a mass ratio of 1:1, and then calcined at 600℃ in an inert atmosphere for 1h, followed by washing with 0.5M hydrochloric acid and deionized water, and then dried at 60℃ to obtain a spherical porous carbon matrix D with a particle size D50 of 1μm and uniform pore distribution.

[0051] The spherical porous carbon matrix D is placed in a fluidized bed, and then mixed gas of silane and hydrogen is introduced with a gas flow ratio of 10:1, heated to 400℃ and kept for 2h, and then mixed gas of acetylene and argon is introduced with a gas flow ratio of 2:1, heated to 650℃ and kept for 1h to obtain product E. The product E is placed in a CVD, and then mixed gas of acetylene and inert atmosphere is introduced with a gas flow ratio of 2:1, heated to 650℃ and kept for 1h to obtain long cycle silicon-carbon material precursor F. The medium temperature coal tar pitch is added into 0.1M silver nitrate solution, stirred at 1000r / min for 2h to form a 50% solid solution, and then filtered and dried to form a composite carbon source G.

[0052] The composite carbon source G and the long cycle silicon-carbon material precursor F are placed in a granulation kettle with a mass ratio of 5:95, stirred at 350r / min, heated to 350℃ and kept for 1h to complete granulation, and then calcined at 650℃ for 2h in an inert atmosphere to obtain a finished long cycle silicon-carbon material I with a particle size D50 of 6μm, wherein the passivation layer accounts for 3% of the mass ratio of the single particle long cycle silicon-carbon negative electrode material, and the high-conductivity outer carbon layer accounts for 2% of the mass ratio of the single particle long cycle silicon-carbon negative electrode material.

[0053] The obtained long cycle silicon-carbon negative electrode material and metal lithium are used to form a half-cell for electrochemical performance test, and the test rate is 0.1C (first time) + 0.5C (cycle), and the charge and discharge voltage is 0.005-0.8V. The results show that the discharge specific capacity of the negative electrode sheet can reach 1650mAh / g, the initial efficiency is 82.6%, and after 50 cycles, the capacity can still be maintained at 82.1%.

[0054] The obtained long cycle silicon-carbon negative electrode material was mixed with graphite at a mass ratio of 5:95 to obtain a composite negative electrode material. A 7 Ah soft package battery was assembled by performing the processes of slurry mixing, coating, rolling, slitting, die cutting, lamination, welding of the tabs, top side sealing, baking, liquid injection, and the like, using NCM622 as the positive electrode. After formation and capacity measurement, the battery was subjected to a normal temperature cycle test at a current density of 1C / 1C. The initial efficiency of the battery was 88%, and the capacity retention rate was 94.8% after 450 cycles.

[0055] Example 2

[0056] The present embodiment provides a preparation method of a long cycle silicon-carbon negative electrode material, which is as follows:

[0057] The obtained long cycle silicon-carbon negative electrode material was mixed with graphite at a mass ratio of 5:95 to obtain a composite negative electrode material. A 7 Ah soft package battery was assembled by performing the processes of slurry mixing, coating, rolling, slitting, die cutting, lamination, welding of the tabs, top side sealing, baking, liquid injection, and the like, using NCM622 as the positive electrode. After formation and capacity measurement, the battery was subjected to a normal temperature cycle test at a current density of 1C / 1C. The initial efficiency of the battery was 88%, and the capacity retention rate was 94.8% after 450 cycles.

[0058] The obtained long cycle silicon-carbon negative electrode material and metal lithium are combined to form a half battery for electrochemical performance test, the test rate is 0.1C (first time) + 0.5C (cycle), and the charge-discharge voltage is 0.005-0.8V. The results show that the discharge specific capacity of the negative electrode sheet can reach 1680mAh / g, the first efficiency is 82.9%, and after 50 cycles, the capacity can still be maintained at 84.1%.

[0059] The obtained long cycle silicon-carbon negative electrode material is mixed with graphite at a mass ratio of 5:95 to form a composite negative electrode material, NCM622 is used as a positive electrode, and a 7Ah soft package battery is assembled through processes such as slurry mixing, coating, rolling, slitting, die cutting, lamination, welding of tabs, top side sealing, baking, liquid injection and the like. After formation and capacity measurement, the battery is subjected to a normal temperature cycle test at a current density of 1C / 1C, the first efficiency of the battery cell is 88%, and after 450 cycles, the capacity retention rate is 95.2%.

[0060] Example 3

[0061] The present embodiment provides a preparation method of a long cycle silicon-carbon negative electrode material, which is specifically as follows:

[0062] The n-hexane and ethanol are mutually soluble in a mass ratio of 1:5, the softening point of the medium temperature coal pitch is 280℃, and the medium temperature coal pitch is added in a mass ratio of 1:3, and placed in a reaction kettle and heated to 150℃, and stirred at 120r / min for 4h, and then filtered, and the obtained insoluble substance is placed in a reaction kettle with dimethyl silicone oil in a mass ratio of 1:2.5, heated to 380℃, and kept for 4h, and stirred at 150r / min, to obtain spherical carbon precursors, and the spherical carbon precursors are placed in a n-hexane and ethanol mixed solution in a mass ratio of 1:2, placed in a reaction kettle and heated to 130℃, and stirred at 100r / min for 3h, and then filtered, and washed with ethanol, and dried at 70℃ to obtain a spherical carbon matrix, and the spherical carbon matrix is mixed with KOH in a mass ratio of 1:2, calcined at 800℃ in an inert atmosphere for 3h, and then washed with 0.9M hydrochloric acid, and deionized water, and dried at 70℃ to obtain a spherical porous carbon matrix with a particle size D50 of 3μm and uniform pore distribution, and placed in a fluidized bed, and a mixture of silane and hydrogen gas is introduced in a gas flow ratio of 8:1, heated to 500℃ and kept for 4h, and then a mixture of acetylene and argon gas is introduced in a gas flow ratio of 1:1.5, and kept at 700℃ for 2h, and the product is placed in a CVD, and a mixture of acetylene and inert atmosphere is introduced in a gas flow ratio of 1:1, and kept at 700℃ for 2h, to obtain a long cycle silicon-carbon material precursor, and the medium temperature coal pitch is added into a 0.1M silver nitrate solution, stirred for 2h at a stirring speed of 1000r / min, to form a 50% solid solution, and then filtered and dried to form a composite carbon source. The composite carbon source and the long cycle silicon-carbon material precursor are placed in a granulation kettle in a mass ratio of 7:90, heated to 400℃ and kept for 2h with stirring at 400r / min, to complete granulation, and then calcined at 700℃ for 3h in an inert atmosphere, to obtain a finished long cycle silicon-carbon negative electrode material with a particle size D50 of 8μm, wherein the passivation layer accounts for 4.5% of the mass ratio of the single particle long cycle silicon-carbon negative electrode material, and the high-conductivity outer carbon layer accounts for 4% of the mass ratio of the single particle long cycle silicon-carbon negative electrode material. As shown in Figure 1 the XRD pattern of the material, there is no obvious silicon characteristic peak, indicating that the internal structure of the material is uniform, and the material has good cycle performance.

[0063] The obtained long cycle silicon-carbon negative electrode material and metal lithium are used to form a half-cell for electrochemical performance testing, and the test rate is 0.1C (first time) + 0.5C (cycle), and the charge and discharge voltage is 0.005-0.8V. The results show that the discharge specific capacity of the negative electrode sheet can reach 1648mAh / g, the first efficiency is 83.0%, and after 50 cycles, the capacity can still be maintained at 85.2%.

[0064] The obtained long cycle silicon-carbon negative electrode material was mixed with graphite at a mass ratio of 5:95 to obtain a composite negative electrode material. A 7 Ah soft package battery was assembled by performing the processes of slurry mixing, coating, rolling, slitting, die cutting, lamination, welding of the tabs, top side sealing, baking, liquid injection, and the like, using NCM622 as the positive electrode. After formation and capacity measurement, the battery was subjected to a normal temperature cycle test at a current density of 1C / 1C. The initial efficiency of the battery cell was 88% (dependent on the initial efficiency of the positive electrode). After 895 cycles, the capacity retention rate of the full battery was 93.7%.

[0065] Example 4

[0066] The present embodiment provides a preparation method of a long cycle silicon-carbon negative electrode material, which is as follows:

[0067] The obtained long cycle silicon-carbon negative electrode material was mixed with graphite at a mass ratio of 5:95 to obtain a composite negative electrode material. A 7 Ah soft package battery was assembled by performing the processes of slurry mixing, coating, rolling, slitting, die cutting, lamination, welding of the tabs, top side sealing, baking, liquid injection, and the like, using NCM622 as the positive electrode. After formation and capacity measurement, the battery was subjected to a normal temperature cycle test at a current density of 1C / 1C. The initial efficiency of the battery cell was 88% (dependent on the initial efficiency of the positive electrode). After 895 cycles, the capacity retention rate of the full battery was 93.7%.

[0068] The obtained long cycle silicon-carbon negative electrode material and metal lithium are combined to form a half battery for electrochemical performance test, the test rate is 0.1C (first time) + 0.5C (cycle), and the charge-discharge voltage is 0.005-0.8V. The results show that the discharge specific capacity of the negative electrode sheet can reach 1600mAh / g, the first efficiency is 82.8%, and after 50 cycles, the capacity can still be maintained at 84.9%.

[0069] The obtained long cycle silicon-carbon negative electrode material is mixed with graphite at a mass ratio of 5:95 to form a composite negative electrode material, NCM622 is used as a positive electrode, and a 7Ah soft package battery is assembled through the processes of slurry mixing, coating, rolling, slitting, die cutting, lamination, welding of tabs, top side sealing, baking, liquid injection and the like. After formation and capacity measurement, the normal temperature cycle test is carried out at a current density of 1C / 1C, the first efficiency of the cell is 88%, and after 450 cycles, the capacity retention rate of the full battery is 94.1%.

[0070] Example 5

[0071] The embodiment provides a preparation method of a long cycle silicon-carbon negative electrode material, and specifically as follows:

[0072] The n-hexane and ethanol are mutually soluble in a mass ratio of 1:3, the softening point of which is 280℃, and the medium temperature coal tar pitch is added in a mass ratio of 1:3, and placed in a reaction kettle and heated to 150℃, stirred at 100r / min for 4h, and then filtered, the obtained insoluble substance is mixed with dimethyl silicone oil in a mass ratio of 1:5, and placed in a reaction kettle, heated to 400℃, and kept for 6h, stirred at 300r / min, to obtain spherical carbon precursor, the spherical carbon precursor is placed in a n-hexane and ethanol mixed solution in a mass ratio of 1:3, placed in a reaction kettle and heated to 150℃, stirred at 100r / min for 4h, and then filtered, washed with ethanol, and dried at 75℃ to obtain a spherical carbon matrix, the spherical carbon matrix is mixed with KOH in a mass ratio of 1:3, calcined at 900℃ in an inert atmosphere for 4h, then washed with 1M hydrochloric acid, and deionized water, and dried at 80℃ to obtain a spherical porous carbon matrix product with a particle size D50 of 4μm and uniform pore distribution, placed in a fluidized bed, and mixed gas of silane and hydrogen is introduced in a gas flow ratio of 2:1, heated to 700℃ and kept for 6h, then mixed gas of acetylene and argon is introduced in a gas flow ratio of 1:3, kept at 750℃ for 3h, and the product is placed in a CVD, mixed gas of acetylene and inert atmosphere is introduced in a gas flow ratio of 1:2, kept at 750℃ for 4h, to obtain a long cycle silicon-carbon material precursor, the medium temperature coal tar pitch is added into a 0.1M silver nitrate solution, stirred for 2h at a stirring speed of 1000r / min, to form a 50% solid solution, then filtered and dried to form a composite carbon source. The composite carbon source and the long cycle silicon-carbon material precursor are placed in a granulating kettle in a mass ratio of 10:90, stirred at 500r / min, heated to 500℃ and kept for 3h, to complete granulation, then calcined at 900℃ in an inert atmosphere for 4h, to obtain a finished product of long cycle silicon-carbon negative electrode material with a particle size D50 of 10μm, wherein the passivation layer accounts for 6% of the mass ratio of the single particle long cycle silicon-carbon negative electrode material, and the high-conductivity outer carbon layer accounts for 5% of the mass ratio of the single particle long cycle silicon-carbon negative electrode material.

[0073] The obtained long cycle silicon-carbon negative electrode material and metal lithium are used to form a half-cell for electrochemical performance test, the test rate is 0.1C(first time)+0.5C(cycle), and the charge and discharge voltage is 0.005-0.8V. The results show that the discharge specific capacity of the negative electrode sheet can reach 1580mAh / g, the first efficiency is 82.0%, and after 50 cycles, the capacity can still maintain 83.1%.

[0074] The obtained long cycle silicon-carbon negative electrode material is mixed with graphite in a mass ratio of 5:95 to form a composite negative electrode material, NCM622 is used as a positive electrode, and 7Ah soft package batteries are assembled through processes of slurry mixing, coating, rolling, slitting, die cutting, lamination, welding of tabs, top side sealing, baking, liquid injection, etc., after formation and capacity measurement, the batteries are tested for normal temperature cycle at a current density of 1C / 1C, the initial efficiency of the battery cell is 88%, and after 450 cycles, the capacity retention rate of the full battery is 92.5%.

[0075] Comparative Example 1

[0076] A porous carbon matrix with a D50 of 8 μm was placed in a fluidized bed, and a mixed gas of silane and hydrogen was introduced at a gas flow ratio of 2:1, heated to 700°C for 6 h, and then a mixed gas of acetylene and argon was introduced at a gas flow ratio of 1:3, 750°C for 3 h, to obtain a silicon-carbon negative electrode material. The obtained silicon-carbon negative electrode material and lithium metal were used to form a half-cell for electrochemical performance testing, with a test rate of 0.1C (first time) + 0.5C (circulation), and a charge-discharge voltage of 0.005-0.8V. The results showed that the discharge specific capacity of the negative electrode sheet could reach 1580 mAh / g, the first efficiency was 82.0%, and after 50 cycles, the capacity could still be maintained at 51.1%.

[0077] From the performance results of the examples, it can be seen that the long-cycle silicon-carbon negative electrode material of the present application is a new type of silicon-carbon (nano-silicon deposited in the pore channel of the porous carbon matrix) composite material with a small size and uniform particle size as the core. Then one or more cores are compounded by granulation to form a finished product with a slightly larger size. The structural advantages include: due to the multi-channel structure of the carbon matrix of the new type of silicon-carbon material, ion transmission needs to bypass the channel, and the ion conductivity is poor. The use of a small size core can shorten the lithium ion transmission path and improve the lithium ion transmission rate. The use of medium-temperature pitch granulation and carbonization method to compound multiple cores can reduce the specific surface area of the material (the particle size becomes larger), reduce the negative reaction with the electrolyte, and improve the first efficiency (SEI film reduction). The coating layer better wraps the core, further inhibiting the volume change of the material during charging and discharging. The core is wrapped in all directions, improving the situation that fresh silicon is exposed to the electrolyte due to the self-volume change of the silicon-based material during the cycle process of the battery, effectively reducing the negative reaction, and improving the cycle performance of the material. In addition, the interlayer spacing of the carbon layer after pitch carbonization is large, providing a fast channel for electron and lithium ion transport. The dispersed nano-silver further improves the electrical conductivity of the material, and improves the shortcomings of large resistivity and poor rate performance of this type of material.

[0078] It should be noted that, in this text, relational terms such as first and second are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such a process, method, article or device. Without more limitations, the element defined by the statement "including a" does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0079] The above examples are only used to illustrate the technical solutions of the present application, but not to limit the present application; although the present application has been described in detail with reference to the foregoing examples, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing examples can be modified, or some technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application. The present application does not detail the known technology of those skilled in the art.

Claims

1. A silicon-carbon anode material, characterized in that, The silicon-carbon anode material includes: The core comprises one or more spherical porous carbon matrices with surface channels, wherein nano-silicon is distributed within the surface channels of the spherical porous carbon matrix, and... A coating layer that coats the core, the coating layer comprising a passivated carbon layer and a highly conductive outer carbon layer, the passivated carbon layer coating the core, the highly conductive layer coating the passivated carbon layer, and nano-silver dispersed in the highly conductive outer carbon layer; The preparation method of the silicon-carbon anode material includes the following steps: 1) Mix hexane and ethanol at a mass ratio of 1:1 to 5 to obtain mixed solution A; 2) Add medium-temperature coal tar pitch to the mixed solution A, mix and heat to 100-150℃ under the condition of stirring speed of 90-120 r / min, keep warm for 2-4 h, and then filter to obtain insoluble substance B; 3) Mix dimethyl silicone oil with the insoluble substance B, stir at 100-300 r / min and heat to 300-400℃, keep warm for 3-6 h to obtain spherical carbon precursor C, wherein the particle size D50 of the spherical carbon precursor is 1-4 μm; 4) The spherical carbon precursor C is mixed with a mixed solution of n-hexane and ethanol, heated to 100-150°C with a stirring speed of 90-120 r / min, kept at the temperature for 2-4 h, filtered, washed with ethanol, and dried to obtain a spherical carbon matrix. The spherical carbon matrix is ​​mixed with KOH at a mass ratio of 1:1 to 1:3, calcined at 600-900°C under an inert atmosphere for 1-4 h, washed with 0.5M-1M hydrochloric acid, washed with deionized water, and dried to prepare a spherical porous carbon matrix D with uniform pore distribution. 5) Introduce the first mixed gas into the spherical porous carbon matrix D, heat it to 400-700℃ and keep it at that temperature for 2-6 hours, then replace it with the second mixed gas and keep it at 650-750℃ for 1-3 hours to obtain product E; 6) A third mixed gas is introduced into the product E with a gas flow ratio of 2:1 to 1:2, and heated to 650 to 750°C and held for 1 to 4 hours to obtain silicon-carbon material precursor F; 7) Add medium-temperature coal tar pitch to 0.1M silver nitrate solution and stir for 1-3 hours at a stirring speed of 900-1200 r / min to form a solution with a solid content of 40-60%. Then filter and dry the solution to form composite carbon source G. 8) The composite carbon source G and silicon-carbon material precursor F are mixed and stirred at a mass ratio of 5:95 to 10:90 and a stirring speed of 300 to 500 r / min. The mixture is then heated to 350°C to 500°C and held for 1 to 3 hours to complete granulation. Finally, the mixture is calcined at 650°C to 900°C for 2 to 4 hours under an inert atmosphere to obtain silicon-carbon anode material. In step 5), the first mixed gas includes silane and hydrogen, and the volume ratio of silane to hydrogen is 10:1 to 2:

1. In step 5), the second mixed gas includes acetylene and argon, and the volume ratio of acetylene to argon is 2:1 to 1:

3. In step 6), the third mixture includes acetylene and an inert atmosphere.

2. The silicon-carbon anode material according to claim 1, characterized in that, The silicon-carbon anode material is granular with a particle size D50 of 6–10 μm. The passivation carbon layer accounts for 3%–6% of the mass of a single silicon-carbon anode material, and the highly conductive outer carbon layer accounts for 2%–5% of the mass of a single silicon-carbon anode material.

3. The silicon-carbon anode material as described in claim 1, characterized in that, In step 2), the softening point of medium-temperature coal tar pitch is 280℃, and the mass ratio of medium-temperature pitch to solution A is 1:1 to 1:

3.

4. The silicon-carbon anode material as described in claim 1, characterized in that, In step 3), the mass ratio of dimethyl silicone oil to insoluble substance B is 1:2 to 1:

5.

5. The silicon-carbon anode material as described in claim 1, characterized in that, In step 4), the mass ratio of spherical carbon precursor C to solution A is 1:1 to 1:3, the drying temperature is 60℃ to 80℃, and the particle size D50 of spherical porous carbon matrix D is 1 to 4 μm.

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