A sheet-shaped silicon negative electrode having a stress relief effect and a method for manufacturing the same

Abstract

The application discloses a sheet-shaped silicon negative electrode with stress relieving effect and a preparation method thereof, and relates to a silicon negative electrode material and a preparation method thereof. The application removes metal elements from alloy silicon by acid etching under low temperature conditions, obtains porous silicon particles with uniform distribution of honeycomb structures, breaks the honeycomb structure porous silicon particles by physical and mechanical ball milling, realizes separation of pore walls, and obtains sheet-shaped silicon with a plane structure. After slurry casting and gradient heat treatment, a dense carbonized protective layer is coated on the surface of the sheet-shaped silicon. The prepared two-dimensional sheet-shaped silicon presents an irregular polygonal structure, a typical thickness is between 10-20 nm, and a transverse size is between 0.5-1.5 mu m. The two-dimensional sheet-shaped silicon can be used as a lithium ion battery silicon negative electrode with stress relieving effect. The application can improve the electrode tap density, realizes dense and efficient electron / ion transmission, the two-dimensional sheet-shaped silicon is in a plane stress state during lithiumation, has stress relieving effect, and significantly improves the mechanical properties of the electrode during the cycle process.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of silicon negative electrode material and its preparation method, specifically belongs to a kind of sheet silicon negative electrode material with stress relief function and its preparation method. BACKGROUND

[0002] With the increasing production of electronic devices and electric vehicles, the demand for lithium-ion batteries with higher specific power / energy, longer cycle life and lower cost is also increasingly urgent. Compared with traditional graphite materials, silicon has extremely high mass specific capacity (~3580 mAh g -1 ) and lower operating voltage (<0.5 V vs. Li / Li +), is the first choice of anode for lithium-ion batteries. However, silicon anode faces great challenges in alloying / de-alloying reaction with lithium ions, i.e. severe volume expansion / contraction, which leads to the concentration of internal stress of silicon anode during cycling, resulting in capacity fading and performance deterioration. The skilled person reduces the volume expansion by reducing the silicon material to critical nanoscale size (< 150 nm), such as nanoparticles, nanowires or nanorods, but the specific surface area of nanosilicon anode itself is large, which intensifies the side reaction of electrode and electrolyte, leading to the reduction of coulombic efficiency of nanosilicon in electrochemical reaction. In addition to this, the low tap density of nanosilicon electrode reduces the volumetric energy density of the electrode. In order to improve the coulombic efficiency of electrochemical reaction and the tap density of the electrode, while ensuring that the silicon particles will not be broken, scientists have done a lot of research, among which the combination of nanoscale structure and microporous silicon anode is an effective strategy. For example, Huo et al. in Scalable synthesis of ant-nest-like bulk porous silicon for high-performance lithium-ion battery anodes, Nature Communications, 2019, vol. 10, pp. 1447-1457, proposed that after the magnesium-silicon alloy was heated with nitrogen, the by-product Mg3N2 was removed in an acidic solution, obtaining an ant-nest-like three-dimensional interconnected nanoporous network, so that the Si nanoparticles in the lithiation / de-lithiation process undergo reversible inward expansion / contraction and are accommodated by the surrounding pores, thereby reducing the outward volume expansion change. Wang et al. in Controlled isotropic canalization of microsized silicon enabling stable high-rate and high-loading lithium storage, Advanced Materials, 2023, vol. 35, no. 2212157, pp. 1-10, proposed that the local difference in volume / pore change caused by different pore sizes will narrow or even interrupt the ion transport channel, and the regularly arranged nanosheets form regular straight channels in all directions of the particles, which can promote the fast transport of Li + -1 -1

[0003] ​​​However, the influence of stress form on the structure is not considered for the above porous structure and traditional three-dimensional structure silicon negative electrode. In the charging and discharging process, the traditional three-dimensional structure silicon is in a space stress state and must bear stress in multiple dimensions. When the stress direction is perpendicular to the structure plane (i.e. shear stress), it will cause the rupture of the three-dimensional silicon, which cannot withstand the mechanical stress change in the long-term cycle process, resulting in continuous capacity decline in the cycle process. More importantly, the three-dimensional structure silicon has unavoidable defects in the conductive contact between particles. The "point-to-point" contact mode cannot provide more efficient electron transmission, and it is difficult to meet the performance requirements of high-power batteries. SUMMARY

[0004] The purpose of the present application is to solve the above problems and provide a sheet-shaped silicon negative electrode with stress relief. On the basis of three-dimensional structure silicon, the influence of space stress and "point-to-point" contact in the traditional three-dimensional structure silicon negative electrode is solved, and a sheet-shaped silicon negative electrode material with stress relief and a preparation method thereof are provided. By acid etching alloy silicon under low temperature conditions, the metal elements are removed from the alloy, and porous silicon particles with uniform distribution of honeycomb structure are obtained. Then, the honeycomb structure porous silicon particles are broken by physical and mechanical ball milling to realize the separation of the pore wall, and the planar structure sheet-shaped silicon is obtained. After compounding with an organic polymer precursor, slurry casting is carried out, and then gradient heat treatment is carried out, and a dense carbonized protective layer is coated on the surface of the sheet-shaped silicon without adding additional binder. The two-dimensional sheet-shaped silicon obtained by mechanical ball milling presents an irregular polygonal structure, with a typical thickness of 10-20 nm and a lateral size of 0.5-1.5 μm, which can be used as a lithium ion battery silicon negative electrode with stress relief. The two-dimensional sheet-shaped silicon is in a planar stress state during lithiation, and has stress relief. The sheet-shaped silicon negative electrode based on face-to-face contact stacking can improve the tap density of the electrode, and at the same time realize dense and efficient electron / ion transmission, and significantly improve the electrochemical kinetic process in the electrode. The silicon negative electrode half-cell prepared therefrom still maintains 810 mAh g -1 of reversible specific capacity after 600 cycles at a silicon content of 81.3 wt% and a current density of 3.6 A g -1 The sheet-shaped silicon electrode obtained in the present application has good stress relief characteristics, high tap density, high electronic conductivity and fast ion transmission, and the battery prepared therefrom has high rate performance, high energy density and long cycle life.

[0005] Another purpose of the present application is to provide a preparation method of a sheet-shaped silicon negative electrode with stress relief.

[0006] The purpose of the present application is achieved by the following technical solutions.

[0007] A sheet-shaped silicon negative electrode with stress relief, characterized by being prepared by a method comprising the following steps:

[0008] Step one, preparation of three-dimensional honeycomb structure porous silicon particles: prepared by low-temperature dealloying method, the selection of alloy powder raw materials includes but is not limited to aluminum-silicon alloy (Al-Si), magnesium-silicon alloy (Mg-Si), iron-silicon alloy (Fe-Si) and the like; the selection of etching agent includes but is not limited to hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), phosphoric acid (H3PO4) and the like. 0.5-4 mol / L acid solution is configured as etching agent, alloy powder and acid solution are mixed in a flask at a ratio of 0.01-0.05 g / mL, and continuous stirring is carried out at a temperature of 1-10 ℃ in a cooling circulating water tank for 10-24 h, so that the metal elements are completely removed. Then the suspension is filtered and washed with excess deionized water until the washing liquid is neutral. The material is transferred to a freeze-drying box for freeze-drying for 1-8 h to sublimate the excess water, and then the porous silicon material is collected and stored in a drying box.

[0009] Step two, preparation of two-dimensional sheet structure silicon material: prepared by liquid phase mechanical ball milling method, the selection of dispersion solvent includes but is not limited to ethanol (C2H5OH), deionized water (H2O), N-methyl pyrrolidone (NMP), N, N-dimethylformamide (DMF) and the like. The collected porous silicon in step one is dispersed in the solvent at a mass concentration of 0.01-0.2 g / mL, mixed in a stainless steel ball milling tank at a ball-to-material ratio of 3:1 to 20:1, and then intermittently ball milled at a speed of 200-500 r / min for 2-20 h, with an intermittent time of 10-50 min for every 1 h of ball milling to prevent heat accumulation. After the tank body is cooled to room temperature, the mixture is filtered and washed with deionized water, and the material is transferred to a vacuum drying box for drying for 4-12 h to evaporate the excess water, and then the sheet-shaped silicon material is collected and stored in a drying box.

[0010] Step three, carbon-coated sheet silicon negative electrode tab preparation: prepared by slurry casting and gradient carbonization method, the selection of carbon precursor coating includes but is not limited to polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP), polydopamine (PDA), polytetrafluoroethylene (PTFE), resorcinol-formaldehyde resin (RF), etc.; The selection of solvent includes but is not limited to ethanol (C2H5OH), isopropanol (IPA), deionized water (H2O), N-methyl pyrrolidone (NMP), N,N-dimethylformamide (DMF), etc.; The conductive agent includes but is not limited to single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), conductive carbon black (SP), ketchen black (KB), etc. The sheet silicon, carbon precursor and conductive agent are weighed according to the mass ratio of (50-80):(10-40):(1-10), the powders are mixed and dissolved in the solvent at a mass ratio of 0.1-2 g / mL, and intermittent ultrasonic treatment is carried out at a power of 60-1000 W for 1-5 h, with 10 s of interval for every 30 s of ultrasonic treatment to prevent heat accumulation. The slurry is coated on the copper foil by an automatic coating machine at a coating speed of 0.5-10 m / min, and the thickness is controlled at 30-150 μm, then it is transferred to an oven for drying at 80 ℃ for 12-24 h, the dried electrode is heated to 280-300 ℃ at a rate of 2-5 ℃ / min and kept for 0.5-1 h under argon (Ar) or nitrogen (N2) atmosphere, then it is heated to 500-800 ℃ at a rate of 2-10 ℃ / min and calcined for 1-5 h, the carbon-coated sheet silicon negative electrode tab is stored in a drying box, and a sheet silicon negative electrode with stress relief function is obtained.

[0011] A preparation method of a sheet silicon negative electrode with stress relief function, characterized in that it comprises the following steps:

[0012] Step one, preparation of three-dimensional honeycomb structure porous silicon particles: prepared by low-temperature dealloying method, the selection of etching raw material includes but is not limited to aluminum-silicon alloy (Al-Si), magnesium-silicon alloy (Mg-Si), iron-silicon alloy (Fe-Si), etc.; The selection of etching agent includes but is not limited to hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), phosphoric acid (H3PO4), etc. An acid solution with a concentration of 0.5-4 mol / L is prepared as the etching agent, the alloy powder and the acid solution are mixed in a flask at a ratio of 0.01-0.05 g / mL, and the mixture is continuously stirred at a temperature of 1-10 ℃ in a cooling circulating water tank for 10-24 h to completely remove the metal elements. Then the suspension is filtered and washed with excess deionized water until the washing liquid is neutral. The material is transferred to a freeze-drying box for freeze-drying for 1-8 h to sublimate the excess water, and then the porous silicon material is collected and stored in a drying box.

[0013] Step two, preparation of two-dimensional sheet structure silicon material: prepared by liquid phase mechanical ball milling method, the selection of dispersion solvent includes but is not limited to ethanol (C2H5OH), deionized water (H2O), N-methyl pyrrolidone (NMP), N, N-dimethyl formamide (DMF) and the like. The porous silicon collected in step one is dispersed in the solvent at a mass concentration of 0.01-0.2 g / mL, mixed in a stainless steel ball milling tank at a ball-to-material ratio of 3:1 to 20:1, and then intermittently ball milled at a speed of 200-500 r / min for 2-20 h, with an intermittent time of 10-50 min for every 1 h of ball milling to prevent heat accumulation. After the tank body is cooled to room temperature, the mixture is filtered and washed with deionized water, and the material is transferred to a vacuum drying oven for drying for 4-12 h to evaporate the excess water, and then the sheet silicon material is collected and stored in a drying oven.

[0014] Step three, preparation of carbon-coated sheet silicon negative electrode sheet: prepared by slurry casting and gradient carbonization method, the selection of carbon precursor for coating includes but is not limited to polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP), polydopamine (PDA), polytetrafluoroethylene (PTFE), resorcinol-formaldehyde resin (RF) and the like; the selection of solvent includes but is not limited to ethanol (C2H5OH), isopropanol (IPA), deionized water (H2O), N-methyl pyrrolidone (NMP), N, N-dimethyl formamide (DMF) and the like; the conductive agent includes but is not limited to single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), conductive carbon black (SP), ketchen black (KB) and the like. The sheet silicon, carbon precursor and conductive agent are weighed according to a mass ratio of (50-80):(10-40):(1-10), the powders are mixed and dissolved in the solvent at a mass ratio of 0.1-2 g / mL, and intermittent ultrasonic treatment is performed at a power of 60-1000 W for 1-5 h, with an intermittent time of 10 s for every 30 s of ultrasonic treatment to prevent heat accumulation. The slurry is coated on a copper foil by an automatic coating machine at a coating speed of 0.5-10 m / min, with a thickness controlled at 30-150 μm, and then transferred to an oven for drying at 80 ℃ for 12-24 h, and the dried electrode is placed in a horizontal furnace under an argon (Ar) or nitrogen (N2) atmosphere, heated to 280-300 ℃ at a rate of 2-5 ℃ / min and kept for 0.5-1 h, and then heated to 500-800 ℃ at a rate of 2-10 ℃ / min and calcined for 1-5 h, and the carbon-coated sheet silicon negative electrode sheet is stored in a drying oven to obtain a sheet silicon negative electrode with stress relief effect.

[0015] The obtained sheet-shaped silicon negative electrode with stress relief function can be used for the preparation of button cell electrodes: using a punching machine to punch the negative electrode sheet prepared in step three, the negative electrode sheet is punched into a circular sheet with a diameter of 14-28 mm, the selection of positive electrode material includes but is not limited to lithium cobalt oxide (LCO), lithium iron phosphate (LFP), lithium nickel cobalt manganese oxide, lithium manganate, lithium nickel cobalt aluminum oxide, etc., the positive electrode sheet is punched into a circular sheet with a diameter of 12-16 mm, and a full battery is assembled, and a purchased lithium sheet is used as a reference electrode to assemble a half battery; the separator is punched into a circular sheet with a diameter of 16-20 mm; after the electrode sheet is prepared, it is placed in a 60°C vacuum drying oven, and after drying for 4-8 h, it can be used, and after use, it is placed back in the drying oven for storage.

[0016] The obtained sheet-shaped silicon negative electrode with stress relief function can be used for the assembly and liquid injection of the battery: the dried carbon-coated sheet-shaped silicon electrode sheet is used as the working electrode (positive electrode) of the button cell, and a purchased lithium sheet is used as the reference electrode (negative electrode), during assembly, the negative electrode shell is placed on the platform, then the negative electrode sheet, the separator, the positive electrode sheet, the electrolyte, the gasket and the spring are sequentially placed, and finally the positive electrode shell is covered, and the button cell packaging machine is used for packaging, the button half battery is assembled, and the button full battery is assembled by replacing the lithium sheet with the positive electrode in step four, all assembly processes are carried out in a glove box (H2O≤0.1 ppm; O2≤0.1 ppm) in an argon atmosphere, and the electrode adopts the punched sheet in step four.

[0017] The performance of the battery prepared above is tested in an electrochemical test cabinet, the half battery assembled according to the above steps has an ohmic resistance of 2-5 Ω and a lithium ion diffusion coefficient of (3-8.5)×10 -12 cm 2 s -1 , and has excellent electronic and ionic conductivity. The assembled half battery has a charge specific capacity of 2100-2300 mAh g -1 , and can still work normally at a current density of 5-7.2 A g -1 and has a charge specific capacity of 700-805 mAh g -1 , the electrode can reach 2-3.4 mAh cm -2 when the silicon content is 70-81.3wt% and the active material of the electrode is loaded with 1-1.68 mg cm -2The assembled half-battery has a cycle life of 100-600 cycles, and a coulomb efficiency of 99-99.8 %. The full battery prepared according to the above steps still has a high capacity retention rate of 90-92.3 % after 100-200 cycles. The prepared carbon-coated sheet-shaped silicon electrode has an electrode thickness expansion rate of only 4.5-10 % after 50-100 cycles, and the electrode has an expansion stress change of only 0.5-1.7 KPa during the first lithium intercalation process. The tap density of the sheet-shaped silicon material can reach 0.3-0.36 g cm -3 .

[0018] Specifically, the porous silicon with honeycomb pores is broken and separated by ball milling, the internal stress state in the electrochemical process is changed, the expansion stress is relieved, the ion transmission distance is shortened, the high-efficiency electron transmission channel of surface contact is constructed, the charge transmission efficiency is improved, and the electrode tap density is increased, so that the sheet-shaped silicon negative electrode material with high rate performance, energy density and long cycle life and stress relieving property is prepared.

[0019] The essential difference between the application and the three-dimensional structure silicon is that the two-dimensional silicon material belongs to a typical plane structure, the stress form is always constrained in the two-dimensional plane, the expansion stress in the charging and discharging process in the direction perpendicular to the structure plane (thickness) can be ignored compared with the three-dimensional silicon, and the in-plane strength can relieve the mechanical strain in the charging and discharging process. At the same time, the two-dimensional silicon material avoids the defects of "point-to-point" contact, the plane structure feature provides a "face-to-face" contact mode, and the effective surface contact improves the conductivity between materials and the tap density of the electrode. The two-dimensional structure silicon negative electrode has great potential in improving the electrochemical performance and cycle life, the negative electrode structure is redesigned on the basis of the three-dimensional porous silicon, the internal stress and the electrode thickness are minimized, the long-life silicon negative electrode with high electrochemical performance can be realized under high surface capacity, and therefore the new stress adaptive lithium ion battery silicon-based negative electrode material has great significance.

[0020] In the preparation of silicon negative electrode material, the traditional method based on three-dimensional structure design focuses on reducing the volume expansion of silicon during lithiation. However, it ignores the influence of internal stress form on the stability of the structure, which leads to the structural collapse and failure of the electrode during long-term cycling, resulting in the decay of reversible capacity. During charging and discharging, the traditional three-dimensional structure silicon bears stress in multiple dimensions. When the stress direction is perpendicular to the structure plane (i.e. shear stress), it will cause the rupture of three-dimensional silicon. The feature of the present invention is to obtain a two-dimensional sheet structure silicon negative electrode by ball milling and breaking the three-dimensional porous silicon with a honeycomb structure. The purpose is to change the spatial internal stress state of the three-dimensional structure during the electrochemical process, so that the stress is constrained on the two-dimensional plane, and the effect of relieving the internal stress of the volume expansion of the silicon negative electrode is achieved. At the same time, unlike the extended ion transport channel of the three-dimensional structure silicon, based on the characteristics of the plane structure, the transport distance of lithium ions is shortened, which can improve the ion transport dynamics process. In addition, the two-dimensional sheet silicon provides a "face-to-face" contact mode, avoiding the defects of the "point-to-point" contact of the traditional three-dimensional structure silicon, and the effective surface contact improves the electronic conductivity between materials, and the dense stacking of the surface and the surface also improves the tap density of the electrode. The sheet silicon designed on the basis of three-dimensional porous silicon can also eliminate the crack defects in the three-dimensional structure in advance, avoiding the influence of defects on the cycle stability. The battery prepared therefrom has high rate performance, high energy density and long cycle life. After improvement by the present invention, the following advantages are obtained, first, the present invention proposes a method to construct a two-dimensional sheet silicon negative electrode with stress relief effect, which improves the defect that the traditional three-dimensional structure silicon negative electrode is easy to rupture. By mechanical ball milling treatment, the stress form borne by the porous silicon during charging and discharging is changed, the three-dimensional space stress is transformed into two-dimensional plane stress, the internal stress during the volume expansion of the silicon negative electrode is reduced, and the stability of the internal structure of the electrode is maintained; second, the prepared electrode has high electronic / ionic conductivity and high tap density. Based on the surface contact type plane stacking structure, the electronic transmission efficiency and the electrode tap density can be enhanced. The plane structure avoids the tortuous ion transport channel, shortens the lithium ion diffusion distance, and the sheet silicon can realize enhanced ion transport; third, the sheet silicon prepared by ball milling on the basis of three-dimensional porous silicon eliminates the crack defects in the three-dimensional structure in advance, avoiding the capacity decay of the electrode caused by defect expansion during long-term cycling; fourth, the lithium battery prepared realizes low expansion, low resistance, high lithium ion diffusion efficiency, high tap density, high capacity retention rate and long cycle life. The carbon-coated sheet silicon negative electrode shows reduced stress change and volume change during charging and discharging, and can still cycle stably under high current density and high load, and has high capacity retention rate in the full battery system. Therefore, the present invention successfully prepares a sheet silicon negative electrode material with low expansion stress, high reaction kinetics and long cycle life. This work provides an innovative way for the development of high specific energy / specific power silicon negative electrode battery. DETAILED DESCRIPTION

[0021] The following detailed description of the embodiments of the present application is given on the premise of the technical solutions of the present application, and detailed implementation manners and processes are given, but the protection scope of the present application is not limited to the following embodiments.

[0022] Embodiment 1.

[0023] Step one, preparation of three-dimensional honeycomb porous silicon particles: etching raw material is selected as Al-Si alloy; etchant is selected as HCl. 2 mol / L HCl solution is configured as etchant, Al-Si alloy powder is mixed with the hydrochloric acid solution in a flask at a ratio of 0.02 g / mL, and the Al element is completely removed by continuously stirring in a cooling circulating water tank at a temperature of 5 ℃ for 12 h. Then the suspension is filtered and washed with excess deionized water until the washing liquid is neutral. The material is transferred to a freeze-drying box for freeze-drying for 4 h to sublimate the excess water, and then the porous silicon material is collected and stored in a drying box.

[0024] Step two, preparation of two-dimensional sheet-shaped silicon material: the dispersion solvent is selected as C2H5OH. The collected porous silicon in step one is dispersed in the solvent at a mass concentration of 0.02 g / mL, mixed in a stainless steel ball mill jar at a ball-to-material ratio of 5:1, and then intermittently ball milled at a speed of 350 r / min for 5 h, with an intermittent time of 30 min for every 1 h of ball milling to prevent heat accumulation. After the tank body is cooled to room temperature, the mixture is filtered and washed with deionized water, and the material is transferred to a vacuum drying box for drying for 4 h to evaporate the excess water, and then the sheet-shaped silicon material is collected and stored in a drying box.

[0025] Step three, preparation of carbon-coated sheet-shaped silicon negative electrode sheet: the carbon precursor is selected as PAN; the solvent is selected as DMF; and the conductive agent is MWCNTs. The sheet-shaped silicon, carbon precursor and conductive agent are weighed at a mass ratio of 75:15:10, respectively, and the powders are mixed and dissolved in the solvent at a mass ratio of 0.1 g / mL, and are intermittently ultrasonically treated at a power of 900 W for 1 h, with an intermittent time of 10 s for every 30 s of ultrasonic treatment to prevent heat accumulation. The slurry is coated on a copper foil by an automatic coating machine at a coating speed of 5 m / min, and the thickness is controlled at 50 μm, and then is transferred to an oven for drying at 80 ℃ for 12 h, and the dried electrode is placed in a horizontal furnace and heated to 280 ℃ at a rate of 2 ℃ / min and kept for 0.5 h, and then heated to 500 ℃ at a rate of 10 ℃ / min and calcined for 2 h, and the carbon-coated sheet-shaped silicon negative electrode (FPSi@C) sheet is stored in a drying box.

[0026] Step four, button cell electrode preparation: the negative electrode sheet in step three is punched into a 14 mm diameter round sheet using a puncher. The separator is punched into a 18 mm diameter round sheet. After the electrode sheet is prepared, it is placed in a 60 °C vacuum drying oven and dried for 8 h before use. After use, it is stored in the drying oven.

[0027] Step five, battery assembly and liquid injection: the dried FPSi@C in step four is used as the working electrode (positive electrode) of the button cell, and the purchased lithium sheet is used as the reference electrode (negative electrode). During assembly, the negative electrode shell is placed on the platform, and then the negative electrode sheet, separator, positive electrode sheet, electrolyte, gasket, and spring are sequentially placed. Finally, the positive electrode shell is covered and sealed with a button cell packaging machine. The button cell assembly is completed, and all assembly processes are carried out in an argon atmosphere glove box (H2O≤0.1 ppm; O2≤0.1 ppm).

[0028] In this example, the above battery was subjected to impedance test (EIS). The EIS starting point of the FPSi@C half-cell is 3.4 Ω, which is less than the 4.5 Ω of the traditional carbon-coated three-dimensional porous silicon negative electrode (PSi@C) half-cell. The charge transfer resistance of the FPSi@C half-cell is 30 Ω, while the charge transfer resistance of the PSi@C half-cell is about 85 Ω, which is 2.8 times that of the FPSi@C half-cell. The prepared half-cell was cycled at a current density of 3.6 A g -1 -2 V, and with the increase of cycle number, the charge and discharge capacity and reaction activity remained stable, showing good electrochemical reversibility. The rate performance test was carried out at a current density of 0.36 A g -1 , 1.08 A g -1 , 1.8 A g -1 , 3.6 A g -1 , 7.2 A g -1 . At 0.36 A g -1 , the charge specific capacity of the FPSi@C half-cell was 2283 mAh g -1 , while the charge specific capacity of the PSi@C half-cell was only 2048 mAh g -1 . With the increase of current density, the FPSi@C half-cell can still maintain a high charge specific capacity, especially at an ultra-high current density of 7.2 A g -1 , the FPSi@C still has a specific capacity of 805 mAh g -1 , while the PSi@C half-cell rapidly decays to a specific capacity of 189 mAh g -1 .

[0029] Example 2.

[0030] Step one, preparation of three-dimensional honeycomb porous silicon particles: etching raw material selected Mg-Si alloy; etchant selected HNO3. 2 mol / L HNO3 solution was prepared as etchant, Mg-Si alloy powder and nitric acid solution were mixed in a flask at a ratio of 0.02 g / mL, and the mixture was continuously stirred at 2 ℃ in a cooling circulating water tank for 12 h to completely remove Mg element. Then the suspension was filtered and washed with excess deionized water until the washing liquid was neutral. The material was transferred to a freeze-drying box and freeze-dried for 4 h to sublimate the excess water, and then the porous silicon material was collected and stored in a dry box.

[0031] Step two, preparation of two-dimensional sheet-shaped silicon material: C2H5OH was selected as the dispersion solvent. The collected porous silicon in step one was dispersed in the solvent at a mass concentration of 0.02 g / mL, mixed in a stainless steel ball mill jar at a ball-to-material ratio of 5:1, and then intermittently ball-milled at a speed of 350 r / min for 5 h, with an intermittent time of 30 min for every 1 h of ball-milling to prevent heat accumulation. After the jar cooled to room temperature, the mixture was filtered and washed with deionized water, and the material was transferred to a vacuum drying box to dry for 4 h to evaporate the excess water, and then the sheet-shaped silicon material was collected and stored in a dry box.

[0032] Step three, preparation of carbon-coated sheet-shaped silicon negative electrode sheet: PAN was selected as the carbon precursor; DMF was selected as the solvent; SWCNTs were selected as the conductive agent. Sheet-shaped silicon, carbon precursor and conductive agent were weighed at a mass ratio of 75:20:5, mixed and dissolved in the solvent at a mass ratio of 0.1 g / mL, and intermittently ultrasonically treated at a power of 900 W for 1 h, with an intermittent time of 10 s for every 30 s of ultrasonic treatment to prevent heat accumulation. The slurry was coated on a copper foil at a coating speed of 5 m / min by using an automatic coating machine, and the thickness was controlled at 80 μm, and then transferred to an oven for drying at 80 ℃ for 12 h. The dried electrode was placed in a horizontal furnace and heated to 300 ℃ at a rate of 2 ℃ / min and kept for 1 h, and then heated to 500 ℃ at a rate of 10 ℃ / min and calcined for 2 h. The carbon-coated sheet-shaped silicon negative electrode (FPSi@C) sheet was stored in a dry box.

[0033] Step four, preparation of button cell electrode: the negative electrode sheet in step three was punched by using a sheet punching machine, and the negative electrode sheet was punched into a circular sheet with a diameter of 14 mm, and the positive electrode was selected as LFP, and the positive electrode sheet was punched into a circular sheet with a diameter of 12 mm, and assembled into a full cell; the separator was punched into a circular sheet with a diameter of 16.7 mm; after the electrode sheet was prepared, it was placed in a 60 ℃ vacuum drying box and dried for 10 h, and then could be used, and after use, it was stored in the drying box.

[0034] Step five, assembly and liquid injection of the battery: the sheet-shaped silicon electrode sheet in step four is used as the negative electrode of the button battery, and the LFP electrode is used as the positive electrode. When assembling, the negative electrode shell is first placed on the platform, and then the negative electrode sheet, the separator, the positive electrode sheet, the electrolyte, the gasket, and the spring are sequentially placed. Finally, the positive electrode shell is covered, and the button battery is packaged with a button battery packaging machine. All assembly processes are carried out in a glove box (H2O≤0.1 ppm; O2≤0.1 ppm) in an argon atmosphere

[0035] In this embodiment, the above-mentioned battery is subjected to impedance test (EIS), and the EIS starting point of the FPSi@C||LFP full battery is 2.8 Ω. The full battery is subjected to constant current charge and discharge test at 2.5-4 V voltage, and after 200 cycles at 1 C (=170 mAh g -1 ) rate, the prepared full battery still has a high capacity retention rate of 92.3 %. With the increase of the cycle number, the reaction peak of the charge and discharge curve of the battery does not change significantly, and the charge and discharge capacity and the reaction activity remain stable, which has good electrochemical reversibility. The rate performance test is carried out at 0.1 C, 0.2 C, 0.3 C, 0.5 C, 1 C

[0036] The discharge specific capacity of the FPSi@C||LFP full battery is 149 mAh g -1 at 0.1 C rate. With the increase of the rate, the FPSi@C||LFP can still maintain a relatively high discharge specific capacity, especially at a high rate of 1 C, the FPSi@C||LFP still has a specific capacity of 110 mAh g -1 .

[0037] Example 3.

[0038] Step one, preparation of three-dimensional honeycomb-shaped porous silicon particles: etching raw material is selected as Al-Si alloy; etchant is selected as HCl. 2 mol / L HCl solution is configured as the etchant, and the Al-Si alloy powder and the hydrochloric acid solution are mixed in a flask at a ratio of 0.02 g / mL. The Al element is completely removed by continuously stirring at a temperature of 5 °C in a cooling circulating water tank for 12 h. Then the suspension is filtered and washed with excess deionized water until the washing liquid is neutral. The material is transferred to a freeze-drying box for freeze-drying for 8 h to sublimate the excess water, and then the porous silicon material is collected and stored in a drying box.

[0039] Step two, preparation of two-dimensional sheet-like silicon material: the dispersion solvent is selected as NMP. The porous silicon collected in step one is dispersed in the solvent at a mass concentration of 0.05 g / mL, mixed in a stainless steel ball mill jar at a ball-to-material ratio of 5:1, and then intermittently ball milled at a speed of 350 r / min for 5 h, with an interval of 30 min for each 1 h of ball milling to prevent heat accumulation. After the jar is cooled to room temperature, the mixture is filtered, washed with deionized water, and the material is transferred to a vacuum drying oven to evaporate the excess water for 8 h, and then the sheet-like silicon material is collected and stored in a drying oven.

[0040] Step three, preparation of carbon-coated sheet-like silicon negative electrode sheet: the carbon precursor is selected as PVP; the solvent is selected as C2H5OH; and the conductive agent is SP. Sheet-like silicon, carbon precursor, and conductive agent are weighed at a mass ratio of 70:15:15, mixed at a mass ratio of 0.1 g / mL, and dissolved in the solvent, and then intermittently ultrasonically treated at a power of 600 W for 2 h, with an interval of 10 s for each 30 s of ultrasonic treatment to prevent heat accumulation. The slurry is coated on a copper foil at a coating speed of 4 m / min by using an automatic coating machine, and the thickness is controlled at 60 μm, and then transferred to an oven for drying at 80 ℃ for 12 h. The dried electrode is heated to 300 ℃ at a rate of 5 ℃ / min and kept for 0.5 h under a N2 atmosphere, and then heated to 800 ℃ at a rate of 10 ℃ / min and calcined for 2 h. The carbon-coated sheet-like silicon negative electrode (FPSi@C) sheet is stored in a drying oven.

[0041] Step four, preparation of a button cell electrode: the negative electrode sheet in step three is punched by using a sheet punching machine, and the negative electrode sheet is punched into a round sheet with a diameter of 14 mm; the separator is punched into a round sheet with a diameter of 16.7 mm; and the prepared electrode sheet is placed in a 60 ℃ vacuum drying oven, dried for 8 h, and then used after use and stored in the drying oven.

[0042] Step five, assembly and liquid injection of the battery: the dried FPSi@C in step four is used as the working electrode (positive electrode) of the button cell, and a purchased lithium sheet is used as the reference electrode (negative electrode). During assembly, the negative electrode shell is first placed on the platform, and then the negative electrode sheet, the separator, the positive electrode sheet, the electrolyte, the gasket, and the spring are sequentially placed, and finally the positive electrode shell is covered, and the button cell is packaged by using a button cell packaging machine. The button cell is assembled, and all the assembly processes are carried out in a glove box (H2O≤0.1 ppm; O2≤0.1 ppm) in an argon atmosphere.

[0043] In this example, the above-mentioned half-cell is subjected to constant current charge and discharge test at a voltage of 0.01-2 V. The specific capacity of the FPSi@C half-cell is 2202 mAh g -1 After 3 cycles, the specific charge capacity of the FPSi@C half-cell remains stable, reaching 2202 mAh g -1the initial specific capacity of the FPSi@C half-cell only decays by 11 mAh g -1 while the specific capacity of the conventional carbon-coated three-dimensional porous silicon negative electrode (PSi@C) half-cell decays from 2123 mAh g -1 to 1879 mAh g -1 , a decay of 244 mAh g -1 . After 500 cycles at 3.6 A g -1 , the FPSi@C half-cell still has a high specific capacity of 901 mAh g -1 , while the specific capacity of the PSi@C half-cell decays sharply to 0 mAh g -1 .

[0044] Example 4.

[0045] Step one, preparation of three-dimensional honeycomb-like porous silicon particles: etching raw material selected Al-Si alloy; etchant selected HCl. 2 mol / L HCl solution was prepared as etchant, and Al-Si alloy powder and hydrochloric acid solution were mixed in a flask at a ratio of 0.02 g / mL, and the Al element was completely removed by continuously stirring at a temperature of 10 °C in a cooling circulating water tank for 12 h. Then the suspension was filtered and washed with excess deionized water until the washing liquid was neutral. The material was transferred to a freeze-drying box for 4 h to sublimate the excess water, and then the porous silicon material was collected and stored in a dry box.

[0046] Step two, preparation of two-dimensional sheet-like silicon material: dispersion solvent selected C2H5OH. The collected porous silicon in step one was dispersed in the solvent at a mass concentration of 0.1 g / mL, mixed in a stainless steel ball mill jar at a ball-to-material ratio of 15:1, and then intermittently ball-milled at a speed of 500 r / min for 4 h, with an intermittent time of 30 min for every 1 h of ball-milling to prevent heat accumulation. After the tank body was cooled to room temperature, the mixture was filtered and washed with deionized water, and the material was transferred to a vacuum drying box for 12 h to evaporate the excess water, and then the sheet-like silicon material was collected and stored in a dry box.

[0047] Step three, preparation of carbon-coated sheet silicon negative electrode sheet: carbon precursor is PAN; solvent is DMF; conductive agent is MWCNTs. Sheet silicon, carbon precursor and conductive agent are weighed according to the mass ratio of 60:30:10, the powders are mixed and dissolved in the solvent according to the mass ratio of 2 g / mL, and intermittent ultrasonic treatment is performed at a power of 1000 W for 4 h, with an interval of 10 s for every 30 s of ultrasonic treatment to prevent heat accumulation. The slurry is coated on a copper foil by using an automatic coating machine at a coating speed of 10 m / min, and the thickness is controlled at 50 μm. Subsequently, the electrode is transferred to an oven for drying at 80 ℃ for 12 h. The dried electrode is heated to 300 ℃ at a rate of 5 ℃ / min and kept for 0.5 h under Ar atmosphere, and then heated to 700 ℃ at a rate of 10 ℃ / min and calcined for 2 h. The carbon-coated sheet silicon negative electrode (FPSi@C) sheet is stored in a drying box.

[0048] Step four, preparation of button cell electrode: the negative electrode sheet in step three is punched by using a sheet punching machine, and the negative electrode sheet is punched into a round sheet with a diameter of 13 mm; the separator is punched into a round sheet with a diameter of 17 mm; after the electrode sheet is prepared, it is placed in a 60 ℃ vacuum drying box, and can be used after drying for 12 h. After use, it is stored in the drying box.

[0049] Step five, assembly and liquid injection of the battery: the FPSi@C dried in step four is used as the working electrode (positive electrode) of the button cell, and the purchased lithium sheet is used as the reference electrode (negative electrode). During assembly, the negative electrode shell is placed on the platform, and then the negative electrode sheet, the separator, the positive electrode sheet, the electrolyte, the gasket and the spring are sequentially placed, and finally the positive electrode shell is covered. The button cell is packaged by using a button cell packaging machine, and the button cell assembly is completed. All the assembly processes are carried out in a glove box (H2O≤0.1 ppm; O2≤0.1 ppm) in an argon atmosphere.

[0050] In this example, the above battery is subjected to impedance test (EIS). The ohmic resistance of the FPSi@C half-cell after 50 cycles is 3.7 Ω, and the solid electrolyte interface resistance is 2.2 Ω, which is less than the ohmic resistance of 6.2 Ω and the solid electrolyte interface resistance of 4.7 Ω of the conventional carbon-coated three-dimensional porous silicon negative electrode (PSi@C) half-cell after 50 cycles. The above half-cell is subjected to constant current intermittent titration test (GITT), and the lithium ion diffusion coefficient of the FPSi@C half-cell is 8.5×10 -12 cm 2 s -1 , which is 10.5 times higher than that of the PSi@C half-cell. The above half-cell is subjected to constant current intermittent titration test (GITT) at 0.1 mV s -1 , 0.2 mV s -1 , 0.4 mV s -1 , 0.6 mV s -1 , 0.8 mV s-1 1 mV s -1 Cyclic voltammetry (CV) was performed at different scan rates, and the b value (peak current vs. scan rate) of the FPSi@C half-cell was 0.788, while the b value of the PSi@C half-cell was 0.7, indicating that FPSi@C had a faster ion transport kinetics process.

[0051] Example 5.

[0052] Step one, preparation of three-dimensional honeycomb porous silicon particles: etching raw material selected Al-Si alloy; etchant selected HCl. 2 mol / L HCl solution was prepared as etchant, and Al-Si alloy powder was mixed with the hydrochloric acid solution at a ratio of 0.02 g / mL in a flask, and the Al element was completely removed by continuously stirring at 5 ℃ in a cooling circulating water tank for 12 h. Then the suspension was filtered and washed with excess deionized water until the washing liquid was neutral. The material was transferred to a freeze-drying box for 4 h to sublimate the excess water, and then the porous silicon material was collected and stored in a dry box.

[0053] Step two, preparation of two-dimensional sheet-shaped silicon material: dispersion solvent selected C2H5OH. The collected porous silicon in step one was dispersed in the solvent at a mass concentration of 0.02 g / mL, mixed in a stainless steel ball mill jar at a ball-to-material ratio of 5:1, and then intermittently ball milled at a speed of 350 r / min for 5 h, with an intermittent time of 30 min for every 1 h of ball milling to prevent heat accumulation. After the tank body was cooled to room temperature, the mixture was filtered and washed with deionized water, and the material was transferred to a vacuum drying box for 4 h to evaporate the excess water, and then the sheet-shaped silicon material was collected and stored in a dry box.

[0054] Step three, preparation of carbon-coated sheet-shaped silicon negative electrode sheet: carbon precursor selected PAN; solvent selected DMF; conductive agent SP. Sheet-shaped silicon, carbon precursor, and conductive agent were weighed at a mass ratio of 75:15:10, mixed and dissolved in the solvent at a mass ratio of 0.1 g / mL, and intermittently ultrasonically treated at a power of 900 W for 1 h, with an intermittent time of 10 s for every 30 s of ultrasonic treatment to prevent heat accumulation. The slurry was coated on a copper foil at a coating speed of 5 m / min using an automatic coating machine, with a thickness controlled at 50 μm, and then transferred to an oven for drying at 80 ℃ for 12 h. The dried electrode was heated to 280 ℃ at a rate of 2 ℃ / min and kept for 0.5 h under N2 atmosphere, and then heated to 500 ℃ at a rate of 5 ℃ / min and calcined for 4 h. The carbon-coated sheet-shaped silicon negative electrode (FPSi@C) sheet was stored in a dry box.

[0055] Step 4, button cell electrode preparation: Use a punching machine to punch the negative electrode sheet from step 3 into a disc with a diameter of 12 mm; punch the separator into a disc with a diameter of 16 mm; after the electrode sheets are prepared, place them in a vacuum drying oven at 60 ℃ and dry for 8 h before use. After use, return them to the drying oven for storage.

[0056] Step 5, Battery Assembly and Electrolyte Filling: Use the dried FPSi@C from Step 4 as the working electrode (positive electrode) of the coin cell, and the purchased lithium sheet as the reference electrode (negative electrode). During assembly, first place the negative electrode shell on the platform, then put in the negative electrode sheet, separator, positive electrode sheet, electrolyte, gasket, and spring in sequence, and finally cover it with the positive electrode shell. Seal it with a coin cell packaging machine. The coin cell half-cell assembly is complete. All assembly processes are carried out in a glove box in an argon atmosphere (H2O≤0.1 ppm; O2≤0.1ppm).

[0057] In this embodiment, the expansion force of the aforementioned battery during discharge was tested. The expansion stress change of the conventional carbon-coated three-dimensional porous silicon anode (PSi@C) battery was 11.4 kPa, while that of the FPSi@C battery was only 1.7 kPa, making the expansion stress change of the PSi@C battery 6.7 times that of the FPSi@C battery. After 50 cycles, the expansion rate of the FPSi@C electrode was only 4.5%, while the expansion rate of the PSi@C electrode reached 35.3%. (The last sentence appears to be incomplete and possibly refers to a different battery model.) -2 Under the given areal load capacity, constant current charge-discharge tests were performed on the FPSi@C half-cell, which exhibited a capacity of 3.4 mAh cm⁻¹. -2 The surface capacity.

Claims

1. A sheet-shaped silicon negative electrode having a stress relaxation effect, characterized by: By alloying silicon etching in low temperature conditions, the metal elements are removed from the alloy, and the porous silicon particles with uniform distribution of honeycomb structure are obtained. Then, the honeycomb structure porous silicon particles are broken by physical and mechanical ball milling to realize the separation of the pore wall, and the planar structure of the silicon sheet is obtained. After compounding with the organic polymer precursor, the slurry casting is carried out, and then the gradient heat treatment is carried out, and the dense carbonized protective layer is coated on the surface of the sheet silicon without adding additional binder. The two-dimensional sheet silicon prepared presents irregular polygonal structure, the typical thickness is between 10-20 nm, and the lateral size is between 0.5-1.5 μm, which can be used as lithium ion battery silicon negative electrode with stress relief effect. ​ 2. The sheet-shaped silicon negative electrode having a stress relaxation effect according to claim 1, characterized by: Prepared by the method comprising the following steps: Step one, preparation of three-dimensional honeycomb structure porous silicon particles: using low temperature dealloying method, 0.5-4 mol / L acid solution is configured as etchant, alloy powder and acid solution are mixed in a flask at a ratio of 0.01-0.05 g / mL, and continuous stirring is carried out in a cooling circulating water tank at a temperature of 1-10 ℃ for 10-24 h to completely remove the metal elements; then the suspension is filtered and washed with excess deionized water until the washing liquid is neutral; the material is transferred to a freeze-drying box for freeze-drying for 1-8 h to sublimate the excess water, and then the porous silicon material is collected and stored in a dry box; Step two, preparation of two-dimensional sheet structure silicon material: the collected porous silicon in step one is dispersed in a solvent at a mass concentration of 0.01-0.2 g / mL, mixed in a stainless steel ball mill jar at a ball-to-material ratio of 3:1 to 20:1, and then intermittently ball milled at a speed of 200-500 r / min for 2-20 h, with an intermittent time of 10-50 min for every 1 h of ball milling to prevent heat accumulation; after the tank body is cooled to room temperature, the mixture is filtered and washed with deionized water, and the material is transferred to a vacuum drying box for drying for 4-12 h to evaporate the excess water, and then the sheet silicon material is collected and stored in a dry box; Step three, preparation of carbon-coated sheet silicon negative electrode sheet: sheet silicon, carbon precursor and conductive agent are weighed according to a mass ratio of 50-80:10-40:1-10, the powders are mixed and dissolved in a solvent at a mass ratio of 0.1-2 g / mL, and intermittent ultrasonic treatment is carried out at a power of 60-1000 W for 1-5 h, with an intermittent time of 10 s for every 30 s of ultrasonic treatment to prevent heat accumulation; the slurry is coated on a copper foil by an automatic coating machine at a coating speed of 0.5-10 m / min, and the thickness is controlled at 30-150 μm, and then transferred to an oven for drying at 80 ℃ for 12-24 h; the dried electrode is placed in a horizontal furnace under an argon or nitrogen atmosphere, heated to 280-300 ℃ at a rate of 2-5 ℃ / min and kept for 0.5-1 h, and then heated to 500-800 ℃ at a rate of 2-10 ℃ / min and calcined for 1-5 h, and the carbon-coated sheet silicon negative electrode sheet is stored in a dry box to obtain a sheet silicon negative electrode with stress relief effect.

3. The sheet-shaped silicon negative electrode having a stress relaxation effect according to claim 2, characterized by: The selection of the alloy powder raw material in step one includes but is not limited to aluminum-silicon alloy, magnesium-silicon alloy, iron-silicon alloy; the selection of the etchant includes but is not limited to hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid.

4. The sheet-shaped silicon negative electrode having a stress relaxation effect according to claim 2, characterized by: The selection of the dispersion solvent in step two includes but is not limited to ethanol, deionized water, N-methyl pyrrolidone, N, N-dimethylformamide.

5. The sheet-shaped silicon negative electrode having a stress relaxation effect according to claim 2, characterized by: The selection of the carbon precursor in step three includes but is not limited to polyacrylonitrile, polyvinylpyrrolidone, polydopamine, polytetrafluoroethylene, resorcinol-formaldehyde resin; the selection of the solvent includes but is not limited to ethanol, isopropanol, deionized water, N-methyl pyrrolidone, N, N-dimethylformamide; the conductive agent includes but is not limited to single-walled carbon nanotube, multi-walled carbon nanotube, conductive carbon black, ketchen black.

6. A method for producing a sheet-shaped silicon negative electrode having a stress relaxation effect, characterized by: The method comprises the following steps: Step one, preparation of three-dimensional honeycomb structure porous silicon particles: a low-temperature dealloying method is used, 0.5-4 mol / L acid solution is configured as an etchant, the alloy powder and the acid solution are mixed in a flask at a ratio of 0.01-0.05 g / mL, and continuous stirring is carried out in a cooling circulating water tank at a temperature of 1-10 ℃ for 10-24 h to completely remove the metal elements; then the suspension is filtered and washed with excess deionized water until the washing liquid is neutral; the material is transferred to a freeze-drying box for freeze-drying for 1-8 h to sublimate the excess water, and then the porous silicon material is collected and stored in a drying box; Step two, preparation of two-dimensional sheet structure silicon material: the collected porous silicon in step one is dispersed in a solvent at a mass concentration of 0.01-0.2 g / mL, mixed in a stainless steel ball mill jar at a ball-to-material ratio of 3:1 to 20:1, and then intermittently ball milled at a speed of 200-500 r / min for 2-20 h, with an intermittent time of 10-50 min for each ball milling of 1 h to prevent heat accumulation; after the jar is cooled to room temperature, the mixture is filtered and washed with deionized water, and the material is transferred to a vacuum drying box for drying for 4-12 h to evaporate the excess water, and then the sheet silicon material is collected and stored in a drying box; Step three, preparation of carbon-coated sheet silicon negative electrode sheet: sheet silicon, carbon precursor and conductive agent are weighed at a mass ratio of 50-80:10-40:1-10, the powders are mixed and dissolved in a solvent at a mass ratio of 0.1-2 g / mL, and intermittent ultrasonic treatment is carried out at a power of 60-1000 W for 1-5 h, with an intermittent time of 10 s for each ultrasonic treatment of 30 s to prevent heat accumulation; the slurry is coated on a copper foil by an automatic coating machine at a coating speed of 0.5-10 m / min, and the thickness is controlled at 30-150 μm, and then transferred to an oven for drying at 80 ℃ for 12-24 h; under an argon or nitrogen atmosphere, the dried electrode is heated to 280-300 ℃ at a rate of 2-5 ℃ / min and kept for 0.5-1 h, and then heated to 500-800 ℃ at a rate of 2-10 ℃ / min and calcined for 1-5 h, and the carbon-coated sheet silicon negative electrode sheet is stored in a drying box to obtain a sheet silicon negative electrode with stress relief effect.

7. The method of claim 6, wherein the method further comprises: The selection of the alloy powder raw material in step one includes but is not limited to aluminum-silicon alloy, magnesium-silicon alloy, iron-silicon alloy; the selection of the etchant includes but is not limited to hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid. ​ 8. The method of claim 6, wherein the method further comprises: The selection of the dispersion solvent in step two includes but is not limited to ethanol, deionized water, N-methyl pyrrolidone, N, N-dimethylformamide. ​ 9. The method of claim 6, wherein the method further comprises: The selection of the carbon precursor in step three includes but is not limited to polyacrylonitrile, polyvinylpyrrolidone, polydopamine, polytetrafluoroethylene, resorcinol-formaldehyde resin; the selection of the solvent includes but is not limited to ethanol, isopropanol, deionized water, N-methyl pyrrolidone, N, N-dimethylformamide; the conductive agent includes but is not limited to single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive carbon black, ketchen black. ​