Modified silicon-carbon negative electrode material, negative electrode plate, preparation method of modified silicon-carbon negative electrode material and negative electrode plate, and solid-state lithium ion battery

Abstract

The invention discloses a modified silicon-carbon negative electrode material, a negative electrode plate, a preparation method of the negative electrode plate and a solid-state lithium ion battery, and relates to the technical field of solid-state lithium ion batteries. The preparation method of the modified silicon-carbon negative electrode material comprises the following steps: mixing a silicon-carbon negative electrode material, an amine compound and ethanol according to a mass ratio of 1: (5-10): (5-10), and then sequentially carrying out ball milling, filtering and drying to obtain the modified silicon-carbon negative electrode material, wherein the technological parameters of the ball milling are as follows: the rotating speed is 190-400r / min, the time is 1440-1600min, and the ball-to-material ratio is (10-30): 1. The amino group and the hydroxyl group are grafted on the surface of the silicon-carbon negative electrode material through ball milling, and the amino group and the hydroxyl group have a synergistic effect to form a rapid lithium ion transmission channel, improve the ionic conductivity, form a three-dimensional net-shaped constraint network to buffer the volume change of silicon, and improve the cycling stability and the rate capability of the solid-state lithium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state lithium-ion batteries, and particularly to a modified silicon-carbon negative electrode material, a negative electrode sheet, a preparation method thereof, and a solid-state lithium-ion battery. Background Art

[0002] At present, as a power battery for electric vehicles, a liquid lithium-ion battery mainly uses an organic liquid electrolyte, and is prone to catch fire and burn due to short circuit after an accident occurs in an electric vehicle, thus threatening driving safety and hindering the popularization and application of power batteries. While a solid-state lithium-ion battery uses a solid electrolyte, which can effectively improve the battery safety factor and prevent safety problems such as combustion to a certain extent.

[0003] In the field of solid-state lithium-ion batteries, the capacity of a graphite negative electrode has approached the theoretical specific capacity (372 mAh·g -1 ), and it cannot meet the increasing demand for energy density. Silicon (Si) has been widely studied due to its high theoretical specific capacity (4200 mAh·g -1 ), low working voltage (about 0.28 V, while graphite is about 0.18 V), and high abundance (the second most abundant element on the earth). However, silicon will generate a huge volume expansion during the lithiation process, resulting in the failure of the electrode structure and affecting the cycle stability of the solid-state lithium-ion battery. Moreover, in a solid-state lithium-ion battery, the contact mode between the silicon negative electrode and the solid electrolyte is solid-solid contact, and the infiltration effect in a liquid lithium-ion battery cannot be achieved, resulting in a low initial ionic conductivity and further affecting the cycle stability. By coating porous carbon on the surface of silicon to form a silicon-carbon negative electrode material, the ionic conductivity can be improved to a certain extent and the cycle stability can be improved, but the rate performance and cycle performance of a solid-state lithium-ion battery based on the silicon-carbon negative electrode material still cannot meet the actual requirements.

[0004] Therefore, there is an urgent need to modify the silicon-carbon negative electrode material to improve the rate performance and cycle performance of a solid-state lithium-ion battery based on the silicon-carbon negative electrode material. Summary of the Invention

[0005] Based on the above deficiencies of the prior art, the purpose of the present invention is to provide a modified silicon-carbon negative electrode material, a negative electrode sheet, a preparation method thereof, and a solid-state lithium-ion battery, aiming to solve the problem that the rate performance and cycle performance of a solid-state lithium-ion battery based on the existing silicon-carbon negative electrode material still need to be further improved.

[0006] The technical solution of the present invention is as follows: In the first aspect of the present invention, a preparation method of a modified silicon-carbon negative electrode material is provided, which includes the following steps: Mix a silicon-carbon negative electrode material, an amine compound, and ethanol according to a mass ratio of 1:(5-10):(5-10) to obtain a mixture. After successively ball-milling, filtering, and drying the mixture, the modified silicon-carbon negative electrode material is obtained. Among them, the process parameters of ball-milling are as follows: The rotation speed is 190 - 400 r / min, the time is 1440 - 1600 min, and the ball-to-material ratio is (10 - 30):1.

[0007] Optionally, the amine compound includes at least one of ethylenediamine, diethylamine, triethylamine, and propylenediamine.

[0008] Optionally, the drying is vacuum drying, the temperature of the vacuum drying is 100 - 160 °C, and the time of the vacuum drying is 600 - 1080 min.

[0009] In the second aspect of the present invention, a modified silicon-carbon negative electrode material is provided, wherein the modified silicon-carbon negative electrode material is prepared by the preparation method of the modified silicon-carbon negative electrode material as described above in the present invention.

[0010] In the third aspect of the present invention, a negative electrode sheet is provided, wherein the negative electrode sheet includes a negative electrode current collector and a coating layer on the surface of the negative electrode current collector, and the coating layer includes a conductive agent, a binder, and the modified silicon-carbon negative electrode material as described above in the present invention.

[0011] Optionally, the mass ratio of the modified silicon-carbon negative electrode material, the conductive agent, and the binder is (80 - 94):5:(1 - 15); The conductive agent includes at least one of conductive carbon black and conductive graphite; The binder includes at least one of polyvinylidene fluoride, polyacrylic acid, polyacrylonitrile, and carboxymethyl cellulose.

[0012] In the fourth aspect of the present invention, a preparation method of the negative electrode sheet as described above in the present invention is provided, which includes the following steps: Mix the modified silicon-carbon negative electrode material, the conductive agent, the binder, and a polar solvent to obtain a negative electrode slurry; Coat the negative electrode slurry on the negative electrode current collector, and after vacuum curing, the negative electrode sheet is obtained.

[0013] Optionally, the polar solvent includes at least one of N-methylpyrrolidone, xylene, and chlorobenzene; The vacuum curing specifically includes the following steps: First, heat at 50 - 70 °C for 120 - 180 min; then heat under vacuum and at 70 - 100 °C for 600 - 720 min.

[0014] In a fifth aspect of the present invention, a solid-state lithium-ion battery is provided, wherein the solid-state lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, and a solid electrolyte located between the positive electrode sheet and the negative electrode sheet, and the negative electrode sheet is the negative electrode sheet as described above in the present invention.

[0015] Optionally, the solid electrolyte is a sulfide solid electrolyte.

[0016] Beneficial effects: The present invention adopts specific ball-milling process parameters, and based on the mechanochemical effect, a large number of amino groups and hydroxyl groups are grafted on the surface of the silicon-carbon negative electrode material particles. On the one hand, the amino groups and hydroxyl groups are combined on the surface of the silicon-carbon negative electrode material particles through chemical bonding to form a "bridge" for rapid lithium-ion transport, shortening the lithium-ion transport distance, effectively improving the ion and electron transport rates of the negative electrode itself, and thus effectively improving the cycle stability and rate performance of the solid-state lithium-ion battery; on the other hand, the amino groups and hydroxyl groups interact with each other, are connected by hydrogen bonds and form a three-dimensional network constraint network. The combined action of the three-dimensional network constraint network and the mechanical constraint formed by the carbon layer on the surface of the silicon-carbon negative electrode material particles better buffers the volume change of silicon during charge and discharge, reduces structural damage, and further improves the cycle stability of the solid-state lithium-ion battery.

[0017] In addition, for a solid-state lithium-ion battery using a sulfide solid electrolyte, after the amino groups are grafted on the surface of the silicon-carbon negative electrode material particles, due to the strong affinity between the amino groups and the sulfide solid electrolyte, the surface of the sulfide solid electrolyte can be passivated, further reducing the decomposition at the interface and the side reaction between the sulfide solid electrolyte and the silicon-carbon negative electrode material particles, thereby reducing the interface impedance and stabilizing the ion transport channel.

[0018] In summary, the modified silicon-carbon negative electrode material prepared by the ball-milling process forms a rapid lithium-ion transport channel based on the synergistic effect of surface amino groups and hydroxyl groups, effectively improves the lithium-ion transport path, increases the ionic conductivity, forms a three-dimensional network constraint network to buffer the volume change of silicon, effectively reduces the interface side reaction, reduces the interface impedance, and further improves the cycle stability, rate performance and reliability of the solid-state lithium-ion battery. Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the preparation process of the modified silicon-carbon negative electrode material.

[0020] Figure 2 It is a scanning electron microscope image of the silicon-carbon negative electrode material.

[0021] Figure 3 It is a scanning electron microscope image of the modified silicon-carbon negative electrode material prepared in Example 1.

[0022] Figure 4Scanning electron microscope image of the modified silicon-carbon negative electrode material prepared in Example 2.

[0023] Figure 5 Scanning electron microscope image of the modified silicon-carbon negative electrode material prepared in Example 3.

[0024] Figure 6 Cycling curve of the solid-state lithium-ion battery prepared using the negative electrode sheets in Example 1, Example 2, Example 3, and Comparative Example 1 under a constant current charge-discharge at 0.33C.

[0025] Figure 7 Rate performance curve of the solid-state lithium-ion battery prepared using the negative electrode sheets in Example 1, Example 2, Example 3, and Comparative Example 1 at different charge-discharge currents. Detailed implementation manners

[0026] The present invention provides a modified silicon-carbon negative electrode material, a negative electrode sheet, and their preparation methods and a solid-state lithium-ion battery. To make the objectives, technical solutions, and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the description of the present invention are only for the purpose of describing specific implementation manners and are not intended to limit the present invention.

[0028] In the present invention, the silicon-carbon negative electrode material (a commercial product) is granular. For example, it can be obtained by the following method: Using porous carbon as the skeleton, depositing silicon on the surface, and then performing carbon coating to form a carbon layer.

[0029] An embodiment of the present invention provides a preparation method of a modified silicon-carbon negative electrode material, which, as Figure 1 shown, includes the following steps: S11. Mix the silicon-carbon negative electrode material, an amine compound, and ethanol according to a mass ratio of 1:(5 - 10):(5 - 10) to obtain a mixture; S12. After ball milling, filtering, and drying the mixture in sequence, obtain the modified silicon-carbon negative electrode material; Among them, the process parameters of ball milling are: The rotation speed is 190 - 400 r / min, the time is 1440 - 1600 min, and the ball-to-material ratio is (10 - 30):1.

[0030] In the embodiments of the present invention, specific ball milling process parameters are adopted. Based on the mechanochemical effect, a large number of amino groups and hydroxyl groups are grafted onto the surface of silicon-carbon anode material particles. On the one hand, the amino groups and hydroxyl groups are combined on the surface of the silicon-carbon anode material particles through chemical bonding to form a "bridge" for rapid lithium ion transport, shortening the transport distance of lithium ions, effectively improving the ion and electron transport rates of the anode itself, and thus effectively improving the cycle stability and rate performance of the solid-state lithium-ion battery. On the other hand, the amino groups and hydroxyl groups interact with each other, connect through hydrogen bonds and form a three-dimensional network constraint network. The combined action of the three-dimensional network constraint network and the mechanical constraint formed by the carbon layer on the surface of the silicon-carbon anode material particles better buffers the volume change of silicon during charge and discharge, reduces structural damage, and further improves the cycle stability of the solid-state lithium-ion battery.

[0031] In addition, for solid-state lithium-ion batteries using sulfide solid electrolytes, after amino groups are grafted onto the surface of silicon-carbon anode material particles, due to the strong affinity between the amino groups and the sulfide solid electrolyte, the surface of the sulfide solid electrolyte can be passivated, further reducing the decomposition at the interface and the side reaction between the sulfide solid electrolyte and the silicon-carbon anode material particles, thereby reducing the interface impedance and stabilizing the ion transport channel.

[0032] In summary, the surface-modified silicon-carbon anode material prepared by the ball milling process forms a rapid lithium ion transport channel based on the synergistic effect of surface amino groups and hydroxyl groups, effectively improves the lithium ion transport path, increases the ionic conductivity, forms a three-dimensional network constraint network to buffer the volume change of silicon, to a certain extent avoids the electrode failure problem caused by silicon volume expansion, effectively reduces the interface side reaction, reduces the interface impedance, and further improves the cycle stability, rate performance and reliability of the solid-state lithium-ion battery.

[0033] During the ball milling process, amine compounds (such as ethylenediamine, etc.) undergo the cleavage of amino groups under the mechanical force of ball milling. The amino groups can undergo chemical bonding with the surface of the silicon-carbon anode material particles, and then the amino groups can be firmly anchored on the surface of the silicon-carbon anode material particles, forming a micro-nano composite structure with chemical bond connection. On the one hand, ethanol undergoes the cleavage of hydroxyl groups under the mechanical force, and the hydroxyl groups undergo chemical bonding with the surface of the silicon-carbon anode material particles, thereby realizing the grafting of hydroxyl groups. On the other hand, as a dispersant, it cooperates with the energy impact and shear force brought by ball milling, further disperses the agglomerates, and makes the grafting of amino groups more uniform, significantly improving the dispersion degree between the silicon-carbon anode material particles and the interfacial bonding force between the silicon-carbon anode material particles during the subsequent preparation of the anode electrode sheet, making the modified silicon-carbon anode material more stable during the subsequent pulping or coating process.

[0034] By adjusting the ball milling time, rotation speed, and ball-to-material ratio within the above ranges, the number of grafted groups on the surface of the silicon-carbon anode material particles and the degree of fragmentation of the silicon-carbon anode material particles can be controlled within an appropriate range. Under these ball milling conditions, excessive damage to the silicon-carbon anode material particles can be avoided, while a sufficiently good dispersion effect and a relatively appropriate grafting rate can be obtained, providing an adjustable space for different application requirements.

[0035] In step S11, the mass ratio of the silicon-carbon anode material, amine compound, and ethanol can be 1:5:5, 1:5:8, 1:5:10, 1:8:5, 1:8:8, 1:8:10, 1:10:5, 1:10:8, or 1:10:10, etc.

[0036] In some embodiments, the amine compound includes at least one of ethylenediamine, diethylamine, triethylamine, and propylenediamine, but is not limited thereto.

[0037] In some embodiments, the particle size of the silicon-carbon anode material is 4 - 10 μm.

[0038] In step S12, in some embodiments, the drying is vacuum drying, the temperature of the vacuum drying is 100 - 160 °C (for example, it can be 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C, or 160 °C, etc.), and the time of the vacuum drying is 600 - 1080 min (for example, it can be 600 min, 700 min, 800 min, 900 min, 1000 min, 1020 min, 1050 min, or 1080 min, etc.).

[0039] In some embodiments, the steps of obtaining the modified silicon-carbon anode material by successively ball milling, filtering, and drying the mixture specifically include: After ball milling the mixture, filter or centrifuge it, wash it three times with ethanol, and then perform vacuum drying to obtain the modified silicon-carbon anode material.

[0040] By filtration or centrifugation, the excess ethanol solvent and unreacted ethylenediamine are separated, and under vacuum conditions, it is dried to completely volatilize the residual ethylenediamine solvent or ethylenediamine physically adsorbed on the surface, obtaining a dry and pure modified silicon-carbon anode material powder, thereby reducing the negative impact on the performance of the solid-state lithium-ion battery.

[0041] The embodiment of the present invention also provides a modified silicon-carbon anode material, wherein the modified silicon-carbon anode material is prepared by the preparation method of the modified silicon-carbon anode material as described above in the embodiment of the present invention.

[0042] An embodiment of the present invention further provides a negative electrode sheet, wherein the negative electrode sheet includes a negative electrode current collector and a coating layer on the surface of the negative electrode current collector, and the coating layer includes a conductive agent, a binder, and the modified silicon-carbon negative electrode material as described above in the embodiment of the present invention.

[0043] In some embodiments, the mass ratio of the modified silicon-carbon negative electrode material, the conductive agent, and the binder is (80-94):5:(1-15), and for example, it can be 80:5:15, 85:5:10, 88:5:7, 90:5:5, 93:5:2, or 94:5:1, etc.

[0044] In some embodiments, the conductive agent includes at least one of conductive carbon black and conductive graphite, but is not limited thereto.

[0045] In some embodiments, the binder includes at least one of polyvinylidene fluoride, polyacrylic acid, polyacrylonitrile, and carboxymethyl cellulose, but is not limited thereto.

[0046] An embodiment of the present invention further provides a preparation method of the negative electrode sheet as described above in the embodiment of the present invention, which includes the following steps: S21. Mix the modified silicon-carbon negative electrode material, the conductive agent, the binder, and a polar solvent to obtain a negative electrode slurry; S22. Coat the negative electrode slurry on the negative electrode current collector and perform vacuum curing to obtain the negative electrode sheet.

[0047] In step S21, the mass ratio of the modified silicon-carbon negative electrode material, the conductive agent, and the binder refers to that described above and will not be elaborated here.

[0048] In some embodiments, the mass ratio of the modified silicon-carbon negative electrode material to the polar solvent is 1:(1.5-3), and for example, it can be 1:1.5, 1:2, 1:2.5, or 1:3, etc.

[0049] In some embodiments, the polar solvent includes at least one of N-methylpyrrolidone, xylene, and chlorobenzene, but is not limited thereto.

[0050] In some embodiments, the step of mixing the modified silicon-carbon negative electrode material, the conductive agent, the binder, and the polar solvent to obtain a negative electrode slurry specifically includes: Disperse the binder in the polar solvent and stir to obtain a binder solution; Mix the modified silicon-carbon negative electrode material, the conductive agent, and the binder solution to obtain a negative electrode slurry.

[0051] In a further embodiment, a magnetic stirrer is used to uniformly mix the modified silicon-carbon negative electrode material, the conductive agent, and the binder solution, so that the modified silicon-carbon negative electrode material and the conductive agent are fully dispersed and in uniform contact, reducing the possibility of agglomeration and improving the lithium-ion transport performance.

[0052] In step S22, the negative electrode slurry is coated on the negative electrode current collector to form a slurry layer. The thickness of the slurry layer can be determined according to actual needs. For example, the thickness of the slurry layer is 45-100 μm (such as 45 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or 100 μm, etc.).

[0053] In some embodiments, the vacuum curing specifically includes the following steps: First, under the condition of 50-70 °C (such as 50 °C, 60 °C, or 70 °C, etc.), heat for 120-180 min (such as 120 min, 130 min, 140 min, 150 min, 160 min, 170 min, or 180 min); then under the conditions of vacuum and 70-100 °C (such as 70 °C, 80 °C, 90 °C, or 100 °C), heat for 600-720 min (such as 600 min, 620 min, 650 min, 680 min, 700 min, or 720 min, etc.).

[0054] That is to say, first raise the ambient temperature to 50-70 °C, heat for 120-180 min, and the slurry layer is transformed into a semi-cured state; then evacuate to vacuum, raise the temperature to 70-100 °C, and heat for 600-720 min to complete the curing operation.

[0055] In some embodiments, the negative electrode current collector can be a copper foil, but is not limited thereto.

[0056] The embodiment of the present invention also provides a solid-state lithium-ion battery, wherein the solid-state lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, and a solid electrolyte located between the positive electrode sheet and the negative electrode sheet. The negative electrode sheet is the negative electrode sheet as described above in the embodiment of the present invention. Specifically, the solid electrolyte is a sulfide solid electrolyte.

[0057] In this embodiment, after grafting amino groups and hydroxyl groups onto the surface of silicon-carbon anode material particles, a rapid lithium-ion transmission channel is formed, a more perfect conductive network is formed, the ion transmission efficiency is improved, and the internal resistance of the anode is reduced. The perfect conductive network not only improves the overall conductivity of the anode, but also enhances the performance of the anode during high-rate charge and discharge processes, ensuring the stability and efficiency of the solid-state lithium-ion battery under fast charge and discharge conditions. In addition, the amino groups and hydroxyl groups can form a three-dimensional network constraint network through forces such as hydrogen bonds, improving the mechanical stability of the anode during the swelling process and extending the service life of the solid-state lithium-ion battery. In addition, during the charge and discharge process, due to the high affinity of the amino groups in the modified silicon-carbon anode material for the sulfide solid electrolyte, the interfacial side reactions between the anode and the sulfide solid electrolyte can be effectively reduced, further reducing the interfacial impedance and increasing the ionic conductivity. Therefore, grafting amino groups and carboxyl groups onto the surface of silicon-carbon anode material particles in the present invention has a triple comprehensive effect of improving the interface, forming a three-dimensional network constraint network, and accelerating lithium-ion transmission, thereby improving the rate performance and cycling performance of the solid-state lithium-ion battery.

[0058] The following further illustrates the present invention through specific embodiments.

[0059] Example 1 This embodiment provides a method for preparing a negative electrode sheet, including the following steps: (1) Provide a silicon-carbon anode material (purchased from Shenzhen Solide New Materials Technology Co., Ltd., model GSC-1892), with a particle size of about 4-10 μm. Its scanning electron microscope image is as Figure 2 shown. It can be seen that its particles are complete. Mix the silicon-carbon anode material, ethylenediamine, and ethanol in a mass ratio of 1:5:5 to obtain a mixture; (2) Place the above-prepared mixture in a ball mill (purchased from Guangzhou Anheng Scientific Instruments Co., Ltd., named Miqi / vertical planetary ball mill, model YXQM-2L) for ball milling (rotation speed of 200 r / min, time of 1440 min, ball-to-material ratio of 20:1, diameter of grinding balls of 3 mm), then filter, wash three times with ethanol, and then perform vacuum drying (temperature of 150 °C, time of 720 min) to obtain a modified silicon-carbon anode material. Its scanning electron microscope image is as Figure 3 shown. It can be seen that its average particle size is about 4 μm. Compared with Figure 2 it is found that after ball milling, the structure of the obtained modified silicon-carbon anode material remains complete and the particles are clear; (3) Disperse polyvinylidene fluoride in N-methylpyrrolidone and stir to obtain a binder solution; Using a magnetic stirrer, the modified silicon-carbon anode material, conductive carbon black, and binder solution were uniformly mixed to obtain an anode slurry; among them, the mass ratio of the modified silicon-carbon anode material, conductive carbon black, polyvinylidene fluoride, and N-methylpyrrolidone was 90:5:5:240; (4) The above-prepared anode slurry was coated on a copper foil to form a slurry layer with a thickness of 50 μm, and then the ambient temperature was first raised to 60 °C and heated for 120 min, and the slurry layer was converted into a semi-cured state; subsequently, it was pumped to vacuum, the temperature was raised to 80 °C, and heated for 720 min to complete the curing operation to obtain an anode plate.

[0060] Example 2 This example provides a method for preparing an anode plate, and the difference from Example 1 is only that: In step (1), the silicon-carbon anode material, ethylenediamine, and ethanol were mixed according to a mass ratio of 1:10:10.

[0061] The scanning electron microscope image of the prepared modified silicon-carbon anode material is as Figure 4 shown. It can be seen that its average particle size is about 4 μm. Compared with Figure 2 it is found that after ball milling, the structure of the obtained modified silicon-carbon anode material remains intact and the particles are clear.

[0062] Example 3 This example provides a method for preparing an anode plate, and the difference from Example 1 is only that: In step (1), the silicon-carbon anode material, ethylenediamine, and ethanol were mixed according to a mass ratio of 1:10:10; In step (2), the ball milling speed was 400 r / min.

[0063] The scanning electron microscope image of the prepared modified silicon-carbon anode material is as Figure 5 shown. It can be seen that its average particle size is about 1 μm, the particle size is small, and compared with Figure 2 it is found that its structure is significantly damaged, and the surface carbon layer is damaged during the ball milling process at a higher speed.

[0064] Comparative Example 1 This comparative example provides a method for preparing an anode plate, and the difference from Example 1 is only that: The silicon-carbon anode material (the same as the silicon-carbon anode material in Example 1) was not subjected to any modification treatment and was directly used to prepare an anode plate according to steps (3) to (4) in Example 1.

[0065] The negative electrode sheets prepared in Example 1, Example 2, Example 3 and Comparative Example 1 were cut and placed on one side of the solid-state lithium-ion battery shell, and the sulfide solid electrolyte powder (specifically Li6PS5Cl) was poured in and pressed into sheets at a pressure of 375MPa, and then a lithium-indium alloy sheet was placed as a counter electrode to prepare a solid-state lithium-ion battery. The charge and discharge cut-off voltage during the test was -0.595~0.9V, and the current density used for charge and discharge at different rates was: 0.1C=180mA·g -1 (It is based on the modified silicon-carbon negative electrode material contained in the solid-state lithium-ion battery. For example, when the solid-state lithium-ion battery contains 1g of modified silicon-carbon negative electrode material, the current used for charging and discharging at a rate of 0.1C is 180mA. When the solid-state lithium-ion battery contains 2g of modified silicon-carbon negative electrode material, the current used for charging and discharging at a rate of 0.1C is 360mA; the same applies to the other rates). 0.2C=360mA·g -1 , 0.33C=600mA·g -1 , 0.5C=900mA·g -1 , 0.8C=1440mA·g -1 1C=1800mA·g -1 . Then perform the following test: (1) Cyclic performance test at room temperature: first, charge and discharge once at a constant current of 0.1C, and then charge and discharge cycle at a constant current of 0.33C; (2) Rate performance test at room temperature: first, 0.1C constant current charge and discharge were performed, and then 0.2C, 0.5C, 0.8C, 1C and 0.1C constant current charge and discharge were performed in sequence.

[0066] The results are as follows Figure 6 , Figure 7 As shown in Tables 1 and 2.

[0067] Table 1. Cycle performance test results

[0068] Table 2. Rate performance test results

[0069] Examples 1 to 3 all utilize the mechanochemical effect of ball milling to graft amino groups and hydroxyl groups onto the surface of silicon-carbon negative electrode material particles in the presence of ethylenediamine and ethanol.

[0070] Compared with the solid-state lithium-ion battery prepared using the negative electrode sheet of Comparative Example 1, the solid-state lithium-ion battery prepared using the negative electrode sheet of Example 1 exhibits better cycle performance and rate performance when the first-cycle Coulombic efficiency and the first charge specific capacity are comparable. After cycling 100 times at a current of 0.33C, the capacity retention rate is as high as 97.61%, and it has higher capacity and smaller capacity decay at different discharge rates. This shows that modifying the surface of silicon-carbon anode material particles with amino groups and hydroxyl groups can, on the one hand, form fast lithium-ion transport channels, effectively improving ionic conductivity; on the other hand, under the interaction of amino groups and hydroxyl groups, the volume expansion of silicon can be effectively inhibited.

[0071] Compared with the solid-state lithium-ion batteries prepared using the negative electrode sheets of Example 1 and Comparative Example 1, the solid-state lithium-ion batteries prepared using the negative electrode sheets of Example 2 and Example 3 have lower first-cycle Coulombic efficiency and lower first charge specific capacity. The first-cycle Coulombic efficiency of the solid-state lithium-ion battery prepared using the negative electrode sheet of Example 3 is only 66.75%. This is because, on the one hand, due to the use of a relatively high rotation speed during ball milling, the carbon layer of the silicon-carbon anode material is damaged, exposing the inner-layer silicon, and losing the mechanical stability and conductivity of the carbon layer coating, which affects the performance; on the other hand, a relatively high rotation speed and a relatively high ethylenediamine concentration will result in an excessive number of grafted amino groups on the surface. The amino groups will form a coordination interaction with lithium ions, and the negative factors of this coordination interaction will be greater than the positive factors brought by the improvement of conductivity by the amino groups, resulting in irreversible consumption of lithium ions. Therefore, controlling the ball milling rotation speed and the solid-liquid ratio can further limit the number of grafted amino groups and prevent the occurrence of more side reactions. However, when the coordination between the amino groups and lithium ions ends and a stable conductive layer is formed, the solid-state lithium-ion batteries prepared using the negative electrode sheets of Example 2 and Example 3 still show better cycle stability and rate performance than the solid-state lithium-ion battery prepared using the negative electrode sheet of Comparative Example 1. Among them, the solid-state lithium-ion battery prepared using the negative electrode sheet of Example 2 has a capacity retention rate of up to 98.06% after cycling 100 times at a current of 0.33C, further indicating that after grafting amino groups and hydroxyl groups, a "bridge" for fast lithium-ion transport can be effectively formed, forming a three-dimensional network constraint network to buffer the volume change of silicon during charge and discharge, and effectively improving the rate performance and cycle performance of the solid-state lithium-ion battery.

[0072] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A preparation method of a modified silicon-carbon anode material, characterized in that, It includes the following steps: Mix a silicon-carbon anode material, an amine compound, and ethanol in a mass ratio of 1:(5-10):(5-10) to obtain a mixed material; After successively ball-milling, filtering, and drying the mixed material, the modified silicon-carbon anode material is obtained; Among them, the process parameters of the ball-milling are: The rotation speed is 190-400 r / min, the time is 1440-1600 min, and the ball-to-material ratio is (10-30):

1.

2. The preparation method of the modified silicon-carbon anode material according to claim 1, wherein The amine compound includes at least one of ethylenediamine, diethylamine, triethylamine, and propylenediamine.

3. The preparation method of the modified silicon-carbon anode material according to claim 1, wherein The drying is vacuum drying, the temperature of the vacuum drying is 100-160 °C, and the time of the vacuum drying is 600-1080 min.

4. A modified silicon-carbon anode material, characterized in that, The modified silicon-carbon anode material is prepared by the preparation method of the modified silicon-carbon anode material according to any one of claims 1-3.

5. A negative electrode plate, characterized in that, The negative electrode sheet includes a negative electrode current collector and a dressing layer on the surface of the negative electrode current collector. The dressing layer includes a conductive agent, a binder, and the modified silicon-carbon anode material according to claim 4.

6. The negative electrode sheet according to claim 5, characterized in that, The mass ratio of the modified silicon-carbon anode material, the conductive agent, and the binder is (80-94):5:(1-15); The conductive agent includes at least one of conductive carbon black and conductive graphite; The binder includes at least one of polyvinylidene fluoride, polyacrylic acid, polyacrylonitrile, and carboxymethyl cellulose.

7. A method for preparing the negative electrode sheet according to any one of claims 5-6, characterized in that, It includes the following steps: Mix the modified silicon-carbon anode material, the conductive agent, the binder, and a polar solvent to obtain a negative electrode slurry; Coat the negative electrode slurry on the negative electrode current collector and, after vacuum curing, obtain the negative electrode sheet.

8. The method for preparing a negative electrode sheet according to claim 7, wherein, The polar solvent includes at least one of N-methylpyrrolidone, xylene, and chlorobenzene; The vacuum curing specifically includes the following steps: First, heat at 50-70 °C for 120-180 min; then heat under vacuum and at 70-100 °C for 600-720 min.

9. A solid-state lithium-ion battery, characterized in that, The solid-state lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, and a solid electrolyte between the positive electrode sheet and the negative electrode sheet. The negative electrode sheet is the negative electrode sheet according to any one of claims 5-6.

10. The solid-state lithium-ion battery according to claim 9, wherein, The solid electrolyte is a sulfide solid electrolyte.

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