Modified silicon-carbon negative electrode material, negative electrode sheet and preparation method thereof and solid-state lithium-ion battery

Abstract

The present invention discloses a modified silicon-carbon anode material, a negative electrode plate, a preparation method thereof, and a solid-state lithium-ion battery, relating to the technical field of solid-state lithium-ion batteries. The preparation method of the modified silicon-carbon anode material comprises the following steps: mixing the silicon-carbon anode material, an amine compound, and ethanol in a mass ratio of 1:(5-10):(5-10), followed by ball milling, filtering, and drying to obtain the modified silicon-carbon anode material. The ball milling process parameters are: a rotation speed of 190-400 rpm, a time of 1440-1600 min, and a ball-to-material ratio of (10-30):1. The present invention grafts amino and hydroxyl groups onto the surface of the silicon-carbon anode material through ball milling. The synergistic effect of the two groups forms a rapid lithium ion transport channel, improves ionic conductivity, and forms a three-dimensional mesh-like constraint network to buffer silicon volume changes, thereby enhancing the cycling stability and rate performance 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 in particular 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] Currently, liquid lithium-ion batteries, the power batteries for electric vehicles, primarily use organic liquid electrolytes. These electrolytes are prone to short circuits and fires after an electric vehicle accident, threatening driving safety and hindering the widespread application of power batteries. Solid-state lithium-ion batteries, on the other hand, utilize solid electrolytes, which significantly improve battery safety and, to a certain extent, prevent safety issues such as fires.

[0003] In the field of solid-state lithium-ion batteries, the capacity of graphite negative electrode is close to the theoretical specific capacity (372mAh g -1 ), which cannot meet the increasing demand for energy density. Silicon (Si) has a high theoretical specific capacity (4200mAh g -1 ), low operating voltage (about 0.28V, while graphite is about 0.18V) and high abundance (the second most abundant element on Earth), and has been widely studied. However, silicon will produce a huge volume expansion during the lithiation process, which will cause the electrode structure to fail and affect the cycle stability of solid-state lithium-ion batteries. In addition, because the contact between the silicon negative electrode and the solid electrolyte in solid-state lithium-ion batteries is solid-solid contact, it is impossible to achieve the wetting effect in liquid lithium-ion batteries, resulting in low ionic conductivity in the early stage, which further affects the cycle stability. By coating the silicon surface with porous carbon 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 solid-state lithium-ion batteries based on silicon-carbon negative electrode materials still cannot meet actual requirements.

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

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

[0006] The technical solutions of the present invention are as follows:

[0007] A first aspect of the present invention provides a method for preparing a modified silicon-carbon negative electrode material, comprising the following steps:

[0008] The silicon-carbon negative electrode material, the amine compound and the ethanol are mixed in a mass ratio of 1:(5-10):(5-10) to obtain a mixture;

[0009] The mixture is subjected to ball milling, filtering and drying in sequence to obtain the modified silicon-carbon negative electrode material;

[0010] Among them, the process parameters of ball milling are:

[0011] The speed is 190~400r / min, the time is 1440~1600min, and the ball-to-material ratio is (10~30):1.

[0012] Optionally, the amine compound includes at least one of ethylenediamine, diethylamine, triethylamine and propylenediamine.

[0013] Optionally, the drying is vacuum drying, the temperature of the vacuum drying is 100 to 160° C., and the time of the vacuum drying is 600 to 1080 minutes.

[0014] In a 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.

[0015] According to a third aspect of the present invention, a negative electrode plate is provided, wherein the negative electrode plate comprises a negative electrode current collector and a dressing layer located on the surface of the negative electrode current collector, and the dressing layer comprises a conductive agent, a binder and the modified silicon-carbon negative electrode material of the present invention as described above.

[0016] Optionally, the mass ratio of the modified silicon-carbon negative electrode material, the conductive agent and the binder is (80-94):5:(1-15);

[0017] The conductive agent includes at least one of conductive carbon black and conductive graphite;

[0018] The binder includes at least one of polyvinylidene fluoride, polyacrylic acid, polyacrylonitrile and carboxymethyl cellulose.

[0019] A fourth aspect of the present invention provides a method for preparing the negative electrode sheet as described above, comprising the following steps:

[0020] Mixing a modified silicon-carbon negative electrode material, a conductive agent, a binder, and a polar solvent to obtain a negative electrode slurry;

[0021] The negative electrode slurry is coated on a negative electrode current collector and vacuum cured to obtain the negative electrode sheet.

[0022] Optionally, the polar solvent includes at least one of N-methylpyrrolidone, xylene and chlorobenzene;

[0023] Vacuum curing specifically includes the following steps:

[0024] First, heat at 50-70° C. for 120-180 min; then heat at 70-100° C. in vacuum for 600-720 min.

[0025] 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 of the present invention as described above.

[0026] Optionally, the solid electrolyte is a sulfide solid electrolyte.

[0027] Beneficial effects: The present invention adopts specific ball milling process parameters and grafts a large number of amino groups and hydroxyl groups on the surface of silicon-carbon negative electrode material particles based on the mechanochemical effect. 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, forming a "bridge" for rapid lithium ion transmission, shortening the transmission distance of lithium ions, and effectively improving the ion and electron transmission rate of the negative electrode itself, thereby 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, connecting through hydrogen bonds and forming a three-dimensional mesh constraint network. The three-dimensional mesh constraint network works together with the mechanical constraint formed by the carbon layer on the surface of the silicon-carbon negative electrode material particles to better buffer the volume change of silicon during the charge and discharge process, reduce structural damage, and further improve the cycle stability of the solid-state lithium-ion battery.

[0028] In addition, for solid-state lithium-ion batteries using sulfide solid electrolytes, after amino groups are grafted onto the surface of the silicon-carbon negative electrode material particles, the amino groups have a strong affinity with the sulfide solid electrolyte, which can passivate the surface of the sulfide solid electrolyte, further reducing the decomposition of the interface and the side reactions between the sulfide solid electrolyte and the silicon-carbon negative electrode material particles, thereby reducing the interface impedance and stabilizing the ion transmission channel.

[0029] In summary, the modified silicon-carbon negative electrode material prepared by the ball milling process forms a rapid lithium ion transmission channel based on the synergistic effect of surface amino groups and hydroxyl groups, effectively improves the lithium ion transmission path, improves the ion conductivity, forms a three-dimensional mesh constraint network to buffer the silicon volume change, effectively reduces interfacial side reactions, reduces interfacial impedance, and thereby improves the cycle stability, rate performance and reliability of solid-state lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the preparation process of modified silicon-carbon negative electrode materials.

[0031] Figure 2 This is a scanning electron microscope image of the silicon-carbon negative electrode material.

[0032] Figure 3 This is a scanning electron microscope image of the modified silicon-carbon negative electrode material prepared in Example 1.

[0033] Figure 4 This is a scanning electron microscope image of the modified silicon-carbon negative electrode material prepared in Example 2.

[0034] Figure 5 This is a scanning electron microscope image of the modified silicon-carbon negative electrode material prepared in Example 3.

[0035] Figure 6 The graph is a cycle curve of a solid-state lithium-ion battery prepared using the negative electrode sheets in Example 1, Example 2, Example 3 and Comparative Example 1 under 0.33C constant current charge and discharge.

[0036] Figure 7 The figure is a rate curve diagram of solid-state lithium-ion batteries prepared using the negative electrode sheets in Example 1, Example 2, Example 3 and Comparative Example 1 at different charge and discharge currents. DETAILED DESCRIPTION

[0037] The present invention provides a modified silicon-carbon anode material, a negative electrode sheet, a method for preparing the same, and a solid-state lithium-ion battery. To clarify the objectives, technical solutions, and effects of the present invention, the present invention is described in further detail below. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention.

[0038] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0039] In the present invention, the silicon-carbon negative electrode material (a commercial product) is in a granular form and can be obtained, for example, by the following method:

[0040] Using porous carbon as the skeleton, silicon is deposited on the surface, and then carbon coating is performed to form a carbon layer.

[0041] The embodiment of the present invention provides a method for preparing a modified silicon-carbon negative electrode material, wherein, Figure 1 As shown, the following steps are included:

[0042] S11, mixing the silicon-carbon negative electrode material, the amine compound, and ethanol in a mass ratio of 1:(5-10):(5-10) to obtain a mixture;

[0043] S12, ball milling, filtering and drying the mixture in sequence to obtain the modified silicon-carbon negative electrode material;

[0044] Among them, the process parameters of ball milling are:

[0045] The speed is 190~400r / min, the time is 1440~1600min, and the ball-to-material ratio is (10~30):1.

[0046] The embodiment of the present invention adopts specific ball milling process parameters and, based on the mechanochemical effect, grafts a large number of amino groups and hydroxyl groups 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, forming a "bridge" for the rapid transmission of lithium ions, shortening the transmission distance of lithium ions, and effectively improving the ion and electron transmission rate of the negative electrode itself, thereby 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, connecting through hydrogen bonds and forming a three-dimensional mesh constraint network. The three-dimensional mesh constraint network works together with the mechanical constraint formed by the carbon layer on the surface of the silicon-carbon negative electrode material particles to better buffer the volume change of silicon during the charge and discharge process, reduce structural damage, and further improve the cycle stability of the solid-state lithium-ion battery.

[0047] In addition, for solid-state lithium-ion batteries using sulfide solid electrolytes, after amino groups are grafted onto the surface of the silicon-carbon negative electrode material particles, the amino groups have a strong affinity with the sulfide solid electrolyte, which can passivate the surface of the sulfide solid electrolyte, further reducing the decomposition of the interface and the side reactions between the sulfide solid electrolyte and the silicon-carbon negative electrode material particles, thereby reducing the interface impedance and stabilizing the ion transmission channel.

[0048] In summary, the surface-modified silicon-carbon negative electrode material prepared by the ball milling process forms a rapid lithium ion transmission channel based on the synergistic effect of surface amino groups and hydroxyl groups, effectively improves the lithium ion transmission path, improves the ion conductivity, and forms a three-dimensional mesh constraint network to buffer the volume change of silicon. To a certain extent, it avoids the electrode failure problem caused by silicon volume expansion, effectively reduces interfacial side reactions, reduces interfacial impedance, and thus improves the cycle stability, rate performance and reliability of solid-state lithium-ion batteries.

[0049] During the ball milling process, amine compounds (such as ethylenediamine, etc.) undergo amino group cleavage under the mechanical force of ball milling. The amino group can chemically bond with the surface of the silicon-carbon negative electrode material particles, and then the amino group can be firmly anchored on the surface of the silicon-carbon negative electrode material particles, forming a micro-nano composite structure with chemical bond connection. On the one hand, ethanol undergoes hydroxyl group cleavage under the action of mechanical force, and the hydroxyl group chemically bonds with the surface of the silicon-carbon negative electrode material particles, thereby achieving the grafting of hydroxyl groups. On the other hand, it is used as a dispersant, cooperating with the energy impact and shear force brought by ball milling to further break up the agglomerates and make the grafting of amino groups more uniform, significantly improving the dispersion between the silicon-carbon negative electrode material particles and the interfacial bonding strength between the silicon-carbon negative electrode material particles in the subsequent preparation of the negative electrode sheet, making the modified silicon-carbon negative electrode material more stable in the subsequent slurrying or coating process.

[0050] By adjusting the ball-milling time, rotational speed, and ball-to-material ratio within the aforementioned ranges, the number of groups grafted onto the surface of the silicon-carbon anode material particles and the degree of particle fragmentation can be controlled within appropriate ranges. Under these ball-milling conditions, excessive damage to the silicon-carbon anode material particles is avoided while achieving a sufficiently good dispersion and a relatively suitable grafting rate, providing adjustable space for different application requirements.

[0051] In step S11, the mass ratio of the silicon-carbon negative electrode material, the amine compound and the 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.

[0052] In some embodiments, the amine compound includes at least one of ethylenediamine, diethylamine, triethylamine, and propylenediamine, but is not limited thereto.

[0053] In some embodiments, the particle size of the silicon-carbon negative electrode material is 4 to 10 μm.

[0054] In step S12, in some embodiments, the drying is vacuum drying, the vacuum drying temperature is 100-160°C (for example, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C or 160°C, etc.), and the vacuum drying time is 600-1080 min (for example, 600 min, 700 min, 800 min, 900 min, 1000 min, 1020 min, 1050 min or 1080 min, etc.).

[0055] In some embodiments, after the mixture is subjected to ball milling, filtering and drying in sequence, the steps of obtaining the modified silicon-carbon negative electrode material specifically include:

[0056] The mixture is ball-milled, filtered or centrifuged, washed three times with ethanol, and then vacuum-dried to obtain the modified silicon-carbon negative electrode material.

[0057] By filtering or centrifuging, excess ethanol solvent and unreacted ethylenediamine are separated, and the product is dried under vacuum conditions to completely volatilize the residual ethylenediamine solvent or ethylenediamine physically adsorbed on the surface, thereby obtaining a dry and pure modified silicon-carbon negative electrode material powder, thereby reducing the negative impact on the performance of solid-state lithium-ion batteries.

[0058] An embodiment of the present invention further provides a modified silicon-carbon negative electrode material, 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 embodiment of the present invention.

[0059] An embodiment of the present invention further provides a negative electrode plate, wherein the negative electrode plate includes a negative electrode current collector and a dressing layer located on the surface of the negative electrode current collector, and the dressing 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.

[0060] 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), for example, it can be 80:5:15, 85:5:10, 88:5:7, 90:5:5, 93:5:2 or 94:5:1.

[0061] In some embodiments, the conductive agent includes at least one of conductive carbon black and conductive graphite, but is not limited thereto.

[0062] In some embodiments, the binder includes at least one of polyvinylidene fluoride, polyacrylic acid, polyacrylonitrile, and carboxymethyl cellulose, but is not limited thereto.

[0063] The present invention also provides a method for preparing the negative electrode sheet as described above, comprising the following steps:

[0064] S21, mixing the modified silicon-carbon negative electrode material, the conductive agent, the binder and the polar solvent to obtain a negative electrode slurry;

[0065] S22, coating the negative electrode slurry on the negative electrode current collector, and vacuum curing to obtain the negative electrode plate.

[0066] In step S21, the mass ratios of the modified silicon-carbon negative electrode material, the conductive agent, and the binder are as described above and will not be repeated here.

[0067] In some embodiments, the mass ratio of the modified silicon-carbon negative electrode material to the polar solvent is 1:(1.5-3), for example, 1:1.5, 1:2, 1:2.5 or 1:3.

[0068] In some embodiments, the polar solvent includes at least one of N-methylpyrrolidone, xylene, and chlorobenzene, but is not limited thereto.

[0069] 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 the negative electrode slurry specifically includes:

[0070] Dispersing the binder in a polar solvent and stirring to obtain a binder solution;

[0071] The modified silicon-carbon negative electrode material, the conductive agent and the binder solution are mixed to obtain a negative electrode slurry.

[0072] 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, thereby reducing the possibility of agglomeration and improving the lithium ion transmission performance.

[0073] 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 (for example, 45 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm, etc.).

[0074] In some embodiments, vacuum curing specifically comprises the following steps:

[0075] First, heat at 50-70°C (for example, 50°C, 60°C or 70°C, etc.) for 120-180 min (for example, 120 min, 130 min, 140 min, 150 min, 160 min, 170 min or 180 min); then heat at 70-100°C (for example, 70°C, 80°C, 90°C or 100°C) in vacuum for 600-720 min (for example, 600 min, 620 min, 650 min, 680 min, 700 min or 720 min, etc.).

[0076] That is to say, first increase the ambient temperature to 50~70℃ and heat for 120~180min to convert the slurry layer into a semi-cured state; then evacuate to vacuum, increase the temperature to 70~100℃, and heat for 600~720min to complete the curing operation.

[0077] In some embodiments, the negative electrode current collector may be copper foil, but is not limited thereto.

[0078] An embodiment of the present invention further provides a solid-state lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, and a solid electrolyte positioned between the positive and negative electrode sheets. The negative electrode sheet is the negative electrode sheet described above in the embodiment of the present invention. Specifically, the solid electrolyte is a sulfide solid electrolyte.

[0079] In this embodiment, after amino groups and hydroxyl groups are grafted onto the surface of the silicon-carbon negative electrode material particles, a rapid lithium ion transmission channel is formed, forming a more complete conductive network, improving the ion transmission efficiency, and reducing the internal resistance of the negative electrode. The perfect conductive network not only improves the overall conductivity of the negative electrode, but also enhances the performance of the negative electrode during high-rate charge and discharge, ensuring the stability and efficiency of the solid-state lithium-ion battery under rapid charge and discharge conditions. In addition, the amino group and the hydroxyl group can form a three-dimensional network constraint network through forces such as hydrogen bonds, thereby improving the mechanical stability of the negative electrode during the expansion 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 group in the modified silicon-carbon negative electrode material with the sulfide solid electrolyte, the interface side reaction between the negative electrode and the sulfide solid electrolyte can be effectively reduced, further reducing the interface impedance and improving the ionic conductivity. Therefore, the present invention grafts amino groups and carboxyl groups onto the surface of the silicon-carbon negative electrode material particles, which has the triple comprehensive effects of improving the interface, forming a three-dimensional network constraint network and accelerating lithium ion transmission, thereby improving the rate performance and cycle performance of the solid-state lithium-ion battery.

[0080] The present invention will be further described below with reference to specific examples.

[0081] Example 1

[0082] This embodiment provides a method for preparing a negative electrode sheet, comprising the following steps:

[0083] (1) Provide silicon-carbon negative electrode material (purchased from Shenzhen Solid New Material Technology Co., Ltd., model GSC-1892), the particle size of which is about 4 to 10 μm, and its scanning electron microscope image is as follows: Figure 2 As shown, it can be seen that the particles are complete; the silicon-carbon negative electrode material, ethylenediamine and ethanol are mixed in a mass ratio of 1:5:5 to obtain a mixture;

[0084] (2) The mixture prepared above was placed in a ball mill (purchased from Guangzhou Anheng Scientific Instrument Co., Ltd., named Miqi / vertical planetary ball mill, model number YXQM-2L) for ball milling (rotation speed of 200r / min, time of 1440min, ball-to-material ratio of 20:1, and particle size of grinding balls of 3mm), then filtered and washed three times with ethanol, and then vacuum dried (temperature of 150℃, time of 720min) to obtain a modified silicon-carbon negative electrode material, the scanning electron microscope image of which is shown in FIG. Figure 3 As shown, it can be seen that the average particle size is about 4 μm, which is consistent with Figure 2 Comparison shows that after ball milling, the structure of the modified silicon-carbon anode material remains intact and the particles are clear;

[0085] (3) dispersing polyvinylidene fluoride in N-methylpyrrolidone and stirring to obtain a binder solution;

[0086] The modified silicon-carbon negative electrode material, conductive carbon black, and binder solution were uniformly mixed using a magnetic stirrer to obtain a negative electrode slurry; wherein the mass ratio of the modified silicon-carbon negative electrode material, conductive carbon black, polyvinylidene fluoride, and N-methylpyrrolidone was 90:5:5:240;

[0087] (4) The negative electrode slurry prepared above was coated on a copper foil to form a slurry layer with a thickness of 50 μm. The ambient temperature was then raised to 60°C and heated for 120 minutes to convert the slurry layer into a semi-cured state. The slurry layer was then evacuated to a vacuum state, heated to 80°C, and heated for 720 minutes to complete the curing operation and obtain a negative electrode sheet.

[0088] Example 2

[0089] This embodiment provides a method for preparing a negative electrode sheet, which differs from the embodiment 1 only in that:

[0090] In step (1), the silicon-carbon negative electrode material, ethylenediamine and ethanol are mixed in a mass ratio of 1:10:10.

[0091] The scanning electron microscope image of the modified silicon-carbon negative electrode material prepared is as follows Figure 4 As shown, it can be seen that the average particle size is about 4 μm, which is consistent with Figure 2 By comparison, it was found that after ball milling, the structure of the modified silicon-carbon negative electrode material remained intact and the particles were clear.

[0092] Example 3

[0093] This embodiment provides a method for preparing a negative electrode sheet, which differs from the embodiment 1 only in that:

[0094] In step (1), the silicon-carbon negative electrode material, ethylenediamine and ethanol are mixed in a mass ratio of 1:10:10;

[0095] In step (2), the ball milling speed is 400 r / min.

[0096] The scanning electron microscope image of the modified silicon-carbon negative electrode material prepared is as follows Figure 5 As shown, the average particle size is about 1 μm, which is relatively small and Figure 2 By comparison, it was found that its structure was obviously damaged and the surface carbon layer was destroyed during the ball milling process at a higher speed.

[0097] Comparative Example 1

[0098] This comparative example provides a method for preparing a negative electrode sheet, which differs from Example 1 only in that:

[0099] The silicon-carbon negative electrode material (the same as the silicon-carbon negative electrode material in Example 1) is not subjected to any modification treatment and is directly used to prepare the negative electrode sheet according to steps (3) to (4) in Example 1.

[0100] The negative electrode sheets prepared in Examples 1, 2, 3, and Comparative Example 1 were cut and placed on one side of a solid-state lithium-ion battery shell. Sulfide solid electrolyte powder (specifically, Li6PS5Cl) was poured into the shell and pressed into sheets using a pressure of 375 MPa. A lithium-indium alloy sheet was then placed as a counter electrode to form a solid-state lithium-ion battery. The charge and discharge cutoff voltage during testing ranged from -0.595 to 0.9 V, and the current density used for charge and discharge at different rates was 0.1 C = 180 mA 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 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:

[0101] (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;

[0102] (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.

[0103] The results are as follows Figure 6 、 Figure 7 As shown in Tables 1 and 2.

[0104] Table 1. Cyclic performance test results

[0105]

[0106] Table 2. Rate performance test results

[0107]

[0108] In Examples 1 to 3, the mechanochemical effect of ball milling is utilized to graft amino groups and hydroxyl groups onto the surface of silicon-carbon negative electrode material particles in the presence of ethylenediamine and ethanol.

[0109] Compared to 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 exhibited better cycling and rate performance, with comparable first-cycle coulombic efficiency and first-charge specific capacity. After 100 cycles at a current of 0.33C, the capacity retention rate reached 97.61%, and it also had higher capacity and less capacity decay at different discharge rates. This shows that modifying the surface of the silicon-carbon negative electrode material particles with amino and hydroxyl groups can, on the one hand, form a rapid lithium ion transport channel, effectively improving ionic conductivity; on the other hand, the interaction between the amino and hydroxyl groups effectively suppresses the volume expansion of silicon.

[0110] Compared to the solid-state lithium-ion batteries prepared using the negative electrode sheets in Example 1 and Comparative Example 1, the solid-state lithium-ion batteries prepared using the negative electrode sheets in Example 2 and Example 3 had lower first-cycle coulombic efficiency and lower first-charge specific capacity. The solid-state lithium-ion battery prepared using the negative electrode sheet in Example 3 had a first-cycle coulombic efficiency of only 66.75%. This is because, on the one hand, the high ball milling speed destroys the carbon layer of the silicon-carbon negative electrode material, exposing the inner silicon layer, and losing the mechanical stability and conductivity of the carbon layer coating, which affects performance. On the other hand, the high ball milling speed and high ethylenediamine concentration lead to an excessive number of amino groups grafted onto the surface. The amino groups will form a coordination effect with lithium ions. The negative factor of this coordination effect will outweigh the positive factor brought by the amino groups' improved conductivity, resulting in irreversible consumption of lithium ions. Therefore, controlling the ball milling speed and solid-liquid ratio can further limit the number of grafted amino groups and prevent the occurrence of excessive side reactions. However, after the coordination between the amino group and the lithium ion is completed and a stable conductive layer is formed, the solid-state lithium-ion batteries prepared using the negative electrode sheets in Examples 2 and 3 still show better cycle stability and rate performance than the solid-state lithium-ion battery prepared using the negative electrode sheet in Comparative Example 1. Among them, the solid-state lithium-ion battery prepared using the negative electrode sheet in Example 2 has a capacity retention rate of up to 98.06% after 100 cycles at a current of 0.33C. This further illustrates that after grafting amino groups and hydroxyl groups, a "bridge" for rapid lithium ion transmission can be effectively formed, forming a three-dimensional mesh constraint network to buffer the volume change of silicon during charge and discharge, effectively improving the rate performance and cycle performance of the solid-state lithium-ion battery.

[0111] It should be understood that the application of the present invention is not limited to the above examples. For those skilled in the art, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for preparing a modified silicon-carbon negative electrode material, characterized in that: The steps include: The silicon-carbon negative electrode material, the amine compound and the ethanol are mixed in a mass ratio of 1:(5-10):(5-10) to obtain a mixture; The mixture is subjected to ball milling, filtering and drying in sequence to obtain the modified silicon-carbon negative electrode material; Among them, the process parameters of ball milling are: The speed is 190-400 r / min, the time is 1440-1600 min, and the ball-to-material ratio is (10-30):1; The amine compound includes at least one of ethylenediamine, diethylamine, triethylamine and propylenediamine; The silicon-carbon negative electrode material is obtained by the following method: Using porous carbon as the skeleton, silicon is deposited on the surface, and then carbon coating is performed to form a carbon layer.

2. The method for preparing the modified silicon-carbon negative electrode material according to claim 1, characterized in that: The drying is vacuum drying, the vacuum drying temperature is 100-160° C., and the vacuum drying time is 600-1080 min.

3. A modified silicon-carbon negative electrode material, characterized in that: The modified silicon-carbon negative electrode material is prepared by the preparation method of the modified silicon-carbon negative electrode material according to any one of claims 1-2.

4. A negative electrode plate, characterized in that: The negative electrode plate includes a negative electrode current collector and a dressing layer located on the surface of the negative electrode current collector, and the dressing layer includes a conductive agent, a binder and the modified silicon-carbon negative electrode material according to claim 3.

5. The negative electrode sheet according to claim 4, characterized in that: 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.

6. A method for preparing a negative electrode sheet according to any one of claims 4 to 5, characterized in that: The steps include: Mixing a modified silicon-carbon negative electrode material, a conductive agent, a binder, and a polar solvent to obtain a negative electrode slurry; The negative electrode slurry is coated on a negative electrode current collector and vacuum cured to obtain the negative electrode sheet.

7. The method for preparing a negative electrode sheet according to claim 6, wherein: The polar solvent includes at least one of N-methylpyrrolidone, xylene and chlorobenzene; Vacuum curing specifically includes the following steps: First, heat at 50-70° C. for 120-180 min; then heat at 70-100° C. in vacuum for 600-720 min.

8. 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 located 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 4 to 5.

9. The solid-state lithium-ion battery according to claim 8, characterized in that The solid electrolyte is a sulfide solid electrolyte.

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