Carbon-coated silicon negative electrode particle and preparation method thereof

Abstract

The invention discloses a carbon-coated silicon negative electrode particle and a preparation method thereof, the surface of the silicon negative electrode particle is modified with silver particles, a carbon coating layer is arranged outside the silicon negative electrode particle, a cavity is arranged between the inner surface of the carbon coating layer and the surface of the silicon negative electrode particle, and the thickness of the cavity is greater than the particle size of the silicon negative electrode particle. Silicon negative electrode particles are taken as a core, the surface of the silicon negative electrode particles is modified with silver nanoparticles in situ, and the outer layer is coated with a carbon coating layer with a cavity, so that a buffer space is provided for silicon volume expansion, the electron transmission efficiency is enhanced, and meanwhile, the interface contact pressure between the negative electrode and sulfide electrolyte is reduced; and the cycling stability and practicability of the sulfide all-solid-state battery are finally improved.

Description

Technical Field

[0001] This invention relates to a silicon anode particle and its preparation method, and more particularly to a carbon-coated silicon anode particle and its preparation method. Background Technology

[0002] Sulfide-based all-solid-state batteries are widely considered a core technology for building next-generation high-energy-density energy storage systems due to the high ionic conductivity, low interfacial contact resistance, and excellent safety of their electrolytes. In this battery system, the anode material is the key component determining battery capacity, and elemental silicon, with its extremely high theoretical specific capacity, has become an ideal candidate material for the anode. However, the practical application of silicon anodes still faces two major challenges: First, during charging and discharging, the silicon anode undergoes a volume expansion of over 300%. This drastic volume change disrupts the solid-solid interface contact between the anode and the sulfide solid electrolyte, resulting in all-solid-state batteries requiring extremely high stacking pressure. Second, elemental silicon has low electronic conductivity, leading to low electron transport efficiency and poor electrode rate performance. Summary of the Invention

[0003] Purpose of the invention: The purpose of this invention is to provide a carbon-coated silicon anode particle with high electrical conductivity and capable of providing buffer space for the expansion of the silicon anode. Another purpose of this invention is to provide a method for preparing the carbon-coated silicon anode particle.

[0004] Technical solution: The present invention provides carbon-coated silicon anode particles, wherein the surface of the silicon anode particles is modified with silver particles, the silicon anode particles have a carbon coating layer, and there is a cavity between the inner surface of the carbon coating layer and the surface of the silicon anode particles, wherein the thickness of the cavity is greater than the particle size of the silicon anode particles.

[0005] The method for preparing carbon-coated silicon anode particles according to the present invention includes the following steps:

[0006] (1) Add silicon anode particles to an alkaline solution and mix to obtain hydroxylated silicon anode particles (Si-OH). Disperse the hydroxylated silicon anode particles with a solvent, add a grafting agent, and mix to obtain surface-grafted silicon anode particles.

[0007] (2) After dispersing the above surface-grafted silicon anode particles with a solvent, add silver precursor and reducing agent and mix to obtain surface silver-modified silicon anode particles (Si@Ag).

[0008] (3) After mixing the above-mentioned silver-modified silicon anode particles with the template, add carbon source and mix to obtain a precursor. After calcining the precursor, remove the template to obtain carbon-coated silicon anode particles.

[0009] Furthermore, in step (1), the silicon anode particles are elemental silicon (Si) particles.

[0010] Preferably, in step (1), the alkaline solution is an aqueous solution of sodium hydroxide (NaOH) with a concentration of 1 mol / L, used to hydroxylate the surface of the silicon anode particles, providing active sites for subsequent chemical modification.

[0011] Preferably, in step (1), the reaction conditions of silicon anode particles and NaOH aqueous solution are: stirring at 60°C for 30 min, and after the reaction is completed, washing them until neutral (pH=7) and then drying them.

[0012] In step (1), the grafting agent is an amino small molecule compound used to aminate the surface of silicon anode particles to obtain amino-grafted silicon anode particles (Si-NH2) to bind silver ions.

[0013] In step (1), the amino small molecule compound is 3-aminopropyltriethoxysilane (APTES), and its mass ratio with Si-OH is 1:10.

[0014] Preferably, in step (1), the reaction conditions for Si-OH and APTES are stirring at 50°C for 20 min, and drying after the reaction is completed.

[0015] In step (2), the silver precursor is a water-soluble silver salt, which is used to uniformly disperse silver ions on the Si-NH2 surface.

[0016] In step (2), the water-soluble silver salt is silver nitrate (AgNO3), which is inexpensive and easy to reduce.

[0017] In step (2), the reducing agent is sodium citrate, which is used to reduce silver ions on the surface of silicon anode particles in situ into nano-silver particles.

[0018] Preferably, in step (2), the molar ratio of silver nitrate to sodium citrate is 1:1.2, and the reducing agent is in excess to ensure that all silver nitrate is reduced.

[0019] In step (2), the mass ratio of the surface-grafted silicon anode particles to the silver precursor is 5:1 to 20:1 to regulate the silver loading on the surface of the silicon anode particles.

[0020] Preferably, in step (2), AgNO3 aqueous solution is added first, and the solution is stirred at room temperature for 30 min. Then, the solution is heated to 60°C, sodium citrate is added, and the mixture is stirred at this temperature for 1 h. After the reaction is complete, the solution is washed and dried.

[0021] In step (3), the template is polystyrene (PS) microspheres with a particle size of 2 to 10 times that of silicon anode particles, used to form a cavity between the carbon coating layer and the silicon anode particles, and the cavity thickness is the particle size of the PS microspheres.

[0022] In step (3), the carbon source is phenolic resin, and its amount is 0.5 to 1.2 times the sum of the mass of the surface silver-modified silicon anode particles and the template, and it is used to carbon-coat the surface silver-modified silicon anode particles and the template.

[0023] Preferably, in step (3), the mass ratio of the surface silver-modified silicon anode particles to the template is 1:2 to 1:5.

[0024] Preferably, in step (3), after the PS microspheres are dispersed in deionized water, Si@Ag is added, the mixture is stirred at room temperature for 6 h and dried, then dispersed in ethanol, phenolic resin is added, and the mixture is sonicated for 20 min to make it uniformly mixed.

[0025] Preferably, in step (3), the reaction conditions are to stir at 60°C until the ethanol evaporates, and then keep warm at 120°C for 2 hours to pre-cure it.

[0026] Preferably, in step (3), the calcination temperature is 650~750℃.

[0027] Preferably, in step (3), the calcination conditions are calcination at a heating rate of 5℃ / min under an inert atmosphere for 2 hours, followed by natural cooling.

[0028] Preferably, in step (3), the reaction conditions for removing the template are as follows: the cooled calcined product is dispersed in toluene, refluxed and stirred at 80°C for 8 h, then washed and dried.

[0029] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The present invention uses silicon anode particles as the core, and modifies them in situ with silver nanoparticles. The outer layer is covered with a carbon coating layer with cavities, which provides a buffer space for silicon volume expansion, enhances electron transport efficiency, and reduces the interfacial contact pressure between the anode and the sulfide electrolyte, ultimately improving the cycle stability and practicality of sulfide all-solid-state batteries. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the preparation process of the present invention;

[0031] Figure 2 This is a charge-discharge curve diagram of Embodiment 1 of the present invention;

[0032] Figure 3 This is a cycle capacity diagram of Embodiment 1 of the present invention. Detailed Implementation

[0033] The technical solution of the present invention will be further described below with reference to the embodiments and comparative examples. Unless otherwise stated, all reagents used are commercially available and are used directly without purification.

[0034] Example 1

[0035] (1) Weigh 0.5 g of silicon elemental particles with a particle size of 500 nm, add them to 50 mL of 1 mol / L NaOH aqueous solution, and stir at 60 °C for 30 min to allow hydroxylation reaction to occur. After the reaction is complete, centrifuge and wash until neutral, and dry at 60 °C to obtain Si-OH. Disperse the obtained Si-OH with 20 mL of ethanol, add 0.05 g of APTES (at this time, the mass ratio of Si-OH to APTES is 10:1), stir at 50 °C for 20 min, and centrifuge and dry to obtain Si-NH2.

[0036] (2) The obtained Si-NH2 was dispersed in 40 mL of deionized water, and an aqueous solution containing 0.05 g AgNO3 was added (the mass ratio of Si-NH2 to AgNO3 was 10:1). After stirring at room temperature for 30 min, the solution was heated to 60 °C, and an aqueous solution of sodium citrate (the molar ratio of AgNO3 to sodium citrate was 1:1.2) was added dropwise. The mixture was stirred at this temperature for 1 h. After the reaction was completed, the mixture was centrifuged, washed three times, and dried to obtain Si@Ag.

[0037] (3) Weigh 1 g of PS microspheres with a particle size of 3 μm, disperse them in 50 mL of deionized water, add 0.5 g of Si@Ag (at this time, the mass ratio of PS to Si@Ag is 2:1), stir at room temperature for 6 h, and centrifuge to dry. Disperse the dried product in 20 mL of ethanol, add 1.2 g of phenolic resin (at this time, the mass ratio of the dried product to phenolic resin is 1:0.8), sonicate for 20 min to mix it evenly, stir at 60℃ until the ethanol is completely evaporated, and keep at 120℃ for 2 h to pre-cur it to obtain the precursor.

[0038] (4) The above precursor was transferred to a tube furnace and calcined at 700°C for 2 h under a N2 atmosphere at a flow rate of 50 mL / min and a heating rate of 5°C / min. After calcination, the calcined product was allowed to cool naturally to room temperature and then dispersed with toluene and refluxed at 80°C for 8 h. After centrifugation and washing three times, the product was vacuum dried at 60°C to obtain carbon-coated silicon anode particles.

[0039] The obtained carbon-coated silicon anode particles were assembled with Li6PS5Cl sulfide electrolyte to form a sulfide all-solid-state battery. Using a Li-In alloy as the counter electrode, the initial discharge capacity was measured to be 2920 mAh / g at a charge / discharge rate of 0.1 C (1C = 4200 mAh / g) and a voltage range of 0.01–1.5 V. After 100 cycles, the capacity retention was measured to be 82%. At a charge / discharge rate of 2C, the initial discharge capacity was measured to be 1872 mAh / g. The conductivity was measured to be 85 S / m using the four-probe method, the charge / discharge volume expansion rate was 35%, and the packing pressure was 3 MPa.

[0040] Example 2

[0041] (1) Weigh 0.5 g of silicon elemental particles with a particle size of 500 nm, add them to 50 mL of 1 mol / L NaOH aqueous solution, and stir at 60 °C for 30 min to allow hydroxylation reaction to occur. After the reaction is complete, centrifuge and wash until neutral, and dry at 60 °C to obtain Si-OH. Disperse the obtained Si-OH with 20 mL of ethanol, add 0.05 g of APTES (at this time, the mass ratio of Si-OH to APTES is 10:1), stir at 50 °C for 20 min, and centrifuge and dry to obtain Si-NH2.

[0042] (2) The obtained Si-NH2 was dispersed in 40 mL of deionized water, and an aqueous solution containing 0.025 g AgNO3 was added (the mass ratio of Si-NH2 to AgNO3 was 20:1). After stirring at room temperature for 30 min, the solution was heated to 60 °C, and an aqueous solution of sodium citrate (the molar ratio of AgNO3 to sodium citrate was 1:1.2) was added dropwise. The mixture was stirred at this temperature for 1 h. After the reaction was completed, the mixture was centrifuged, washed three times, and dried to obtain Si@Ag.

[0043] (3) Weigh 1 g of PS microspheres with a particle size of 3 μm, disperse them in 50 mL of deionized water, add 0.5 g of Si@Ag (at this time, the mass ratio of PS to Si@Ag is 2:1), stir at room temperature for 6 h, and centrifuge to dry. Disperse the dried product in 20 mL of ethanol, add 1.2 g of phenolic resin (at this time, the mass ratio of the dried product to phenolic resin is 1:0.8), sonicate for 20 min to mix it evenly, stir at 60℃ until the ethanol is completely evaporated, and keep at 120℃ for 2 h to pre-cur it to obtain the precursor.

[0044] (4) The above precursor was transferred to a tube furnace and calcined at 650°C for 2 h under a N2 atmosphere at a flow rate of 50 mL / min and a heating rate of 5°C / min. After calcination, the calcined product was allowed to cool naturally to room temperature and then dispersed with toluene and refluxed at 80°C for 8 h. After centrifugation and washing three times, the product was vacuum dried at 60°C to obtain carbon-coated silicon anode particles.

[0045] The obtained carbon-coated silicon anode particles were assembled with Li6PS5Cl sulfide electrolyte to form a sulfide all-solid-state battery. Using a Li-In alloy as the counter electrode, the initial discharge capacity was measured to be 2850 mAh / g at a charge / discharge rate of 0.1 C (1C = 4200 mAh / g) and a voltage range of 0.01–1.5 V. After 100 cycles, the capacity retention was 78%. At a charge / discharge rate of 2C, the initial discharge capacity was measured to be 1672 mAh / g. The conductivity was 21 S / m, the charge / discharge volume expansion rate was 36%, and the packing pressure was 3 MPa.

[0046] Example 3

[0047] (1) Weigh 0.5 g of silicon elemental particles with a particle size of 500 nm, add them to 50 mL of 1 mol / L NaOH aqueous solution, and stir at 60 °C for 30 min to allow hydroxylation reaction to occur. After the reaction is complete, centrifuge and wash until neutral, and dry at 60 °C to obtain Si-OH. Disperse the obtained Si-OH with 20 mL of ethanol, add 0.05 g of APTES (at this time, the mass ratio of Si-OH to APTES is 10:1), stir at 50 °C for 20 min, and centrifuge and dry to obtain Si-NH2.

[0048] (2) The obtained Si-NH2 was dispersed in 40 mL of deionized water, and an aqueous solution containing 0.1 g AgNO3 was added (the mass ratio of Si-NH2 to AgNO3 was 5:1). After stirring at room temperature for 30 min, the solution was heated to 60 °C, and an aqueous solution of sodium citrate (the molar ratio of AgNO3 to sodium citrate was 1:1.2) was added dropwise. The mixture was stirred at this temperature for 1 h. After the reaction was completed, the mixture was centrifuged, washed three times, and dried to obtain Si@Ag.

[0049] (3) Weigh 1 g of PS microspheres with a particle size of 3 μm, disperse them in 50 mL of deionized water, add 0.5 g of Si@Ag (at this time, the mass ratio of PS to Si@Ag is 2:1), stir at room temperature for 6 h, and centrifuge to dry. Disperse the dried product in 20 mL of ethanol, add 1.2 g of phenolic resin (at this time, the mass ratio of the dried product to phenolic resin is 1:0.8), sonicate for 20 min to mix it evenly, stir at 60℃ until the ethanol is completely evaporated, and keep at 120℃ for 2 h to pre-cur it to obtain the precursor.

[0050] (4) The above precursor was transferred to a tube furnace and calcined at 700°C for 2 h under a N2 atmosphere at a flow rate of 50 mL / min and a heating rate of 5°C / min. After calcination, the calcined product was allowed to cool naturally to room temperature and then dispersed with toluene and refluxed at 80°C for 8 h. After centrifugation and washing three times, the product was vacuum dried at 60°C to obtain carbon-coated silicon anode particles.

[0051] The obtained carbon-coated silicon anode particles were assembled with Li6PS5Cl sulfide electrolyte to form a sulfide all-solid-state battery. Using a Li-In alloy as the counter electrode, the initial discharge capacity was measured to be 2893 mAh / g at a charge / discharge rate of 0.1 C (1C = 4200 mAh / g) and a voltage range of 0.01–1.5 V. After 100 cycles, the capacity retention was 81%. At a charge / discharge rate of 2C, the initial discharge capacity was measured to be 1923 mAh / g. The conductivity was 121 S / m measured using the four-probe method, the charge / discharge volume expansion rate was 36%, and the packing pressure was 3 MPa.

[0052] Example 4

[0053] (1) Weigh 0.5 g of silicon elemental particles with a particle size of 500 nm, add them to 50 mL of 1 mol / L NaOH aqueous solution, and stir at 60 °C for 30 min to allow hydroxylation reaction to occur. After the reaction is complete, centrifuge and wash until neutral, and dry at 60 °C to obtain Si-OH. Disperse the obtained Si-OH with 20 mL of ethanol, add 0.05 g of APTES (at this time, the mass ratio of Si-OH to APTES is 10:1), stir at 50 °C for 20 min, and centrifuge and dry to obtain Si-NH2.

[0054] (2) The obtained Si-NH2 was dispersed in 40 mL of deionized water, and an aqueous solution containing 0.05 g AgNO3 was added (the mass ratio of Si-NH2 to AgNO3 was 10:1). After stirring at room temperature for 30 min, the solution was heated to 60 °C, and an aqueous solution of sodium citrate (the molar ratio of AgNO3 to sodium citrate was 1:1.2) was added dropwise. The mixture was stirred at this temperature for 1 h. After the reaction was completed, the mixture was centrifuged, washed three times, and dried to obtain Si@Ag.

[0055] (3) Weigh 1 g of PS microspheres with a particle size of 1 μm, disperse them in 50 mL of deionized water, add 0.5 g of Si@Ag (at this time, the mass ratio of PS to Si@Ag is 2:1), stir at room temperature for 6 h, and centrifuge to dry. Disperse the dried product in 20 mL of ethanol, add 1.2 g of phenolic resin (at this time, the mass ratio of the dried product to phenolic resin is 1:0.8), sonicate for 20 min to mix them evenly, stir at 60℃ until the ethanol is completely evaporated, and keep at 120℃ for 2 h to pre-cure it to obtain the precursor.

[0056] (4) The above precursor was transferred to a tube furnace and calcined at 750°C for 2 h under a N2 atmosphere at a flow rate of 50 mL / min and a heating rate of 5°C / min. After calcination, the calcined product was allowed to cool naturally to room temperature and then dispersed with toluene and refluxed at 80°C for 8 h. After centrifugation and washing three times, the product was vacuum dried at 60°C to obtain carbon-coated silicon anode particles.

[0057] The obtained carbon-coated silicon anode particles were assembled with Li6PS5Cl sulfide electrolyte to form a sulfide all-solid-state battery. Using a Li-In alloy as the counter electrode, the initial discharge capacity was measured to be 2821 mAh / g at a charge / discharge rate of 0.1 C (1C = 4200 mAh / g) and a voltage range of 0.01–1.5 V. After 100 cycles, the capacity retention was 81%. At a charge / discharge rate of 2C, the initial discharge capacity was measured to be 1723 mAh / g. The conductivity was 85 S / m measured using the four-probe method, the charge / discharge volume expansion rate was 52%, and the packing pressure was 3.9 MPa.

[0058] Example 5

[0059] (1) Weigh 0.5 g of silicon elemental particles with a particle size of 500 nm, add them to 50 mL of 1 mol / L NaOH aqueous solution, and stir at 60 °C for 30 min to allow hydroxylation reaction to occur. After the reaction is complete, centrifuge and wash until neutral, and dry at 60 °C to obtain Si-OH. Disperse the obtained Si-OH with 20 mL of ethanol, add 0.05 g of APTES (at this time, the mass ratio of Si-OH to APTES is 10:1), stir at 50 °C for 20 min, and centrifuge and dry to obtain Si-NH2.

[0060] (2) The obtained Si-NH2 was dispersed in 40 mL of deionized water, and an aqueous solution containing 0.05 g AgNO3 was added (the mass ratio of Si-NH2 to AgNO3 was 10:1). After stirring at room temperature for 30 min, the solution was heated to 60 °C, and an aqueous solution of sodium citrate (the molar ratio of AgNO3 to sodium citrate was 1:1.2) was added dropwise. The mixture was stirred at this temperature for 1 h. After the reaction was completed, the mixture was centrifuged, washed three times, and dried to obtain Si@Ag.

[0061] (3) Weigh 1 g of PS microspheres with a particle size of 5 μm, disperse them in 50 mL of deionized water, add 0.5 g of Si@Ag (at this time, the mass ratio of PS to Si@Ag is 2:1), stir at room temperature for 6 h, and centrifuge to dry. Disperse the dried product in 20 mL of ethanol, add 1.2 g of phenolic resin (at this time, the mass ratio of the dried product to phenolic resin is 1:0.8), sonicate for 20 min to mix them evenly, stir at 60℃ until the ethanol is completely evaporated, and keep at 120℃ for 2 h to pre-cure it to obtain the precursor.

[0062] (4) The above precursor was transferred to a tube furnace and calcined at 750°C for 2 h under a N2 atmosphere at a flow rate of 50 mL / min and a heating rate of 5°C / min. After calcination, the calcined product was allowed to cool naturally to room temperature and then dispersed with toluene and refluxed at 80°C for 8 h. After centrifugation and washing three times, the product was vacuum dried at 60°C to obtain carbon-coated silicon anode particles.

[0063] The obtained carbon-coated silicon anode particles were assembled with Li6PS5Cl sulfide electrolyte to form a sulfide all-solid-state battery. Using a Li-In alloy as the counter electrode, the initial discharge capacity was measured to be 2880 mAh / g at a charge / discharge rate of 0.1 C (1C = 4200 mAh / g) and a voltage range of 0.01–1.5 V. After 100 cycles, the capacity retention was measured to be 80%. At a charge / discharge rate of 2C, the initial discharge capacity was measured to be 1857 mAh / g. The conductivity was measured to be 88 S / m using the four-probe method, the charge / discharge volume expansion rate was 28%, and the packing pressure was 2.5 MPa.

[0064] Example 6

[0065] (1) Weigh 0.5 g of silicon elemental particles with a particle size of 500 nm, add them to 50 mL of 1 mol / L NaOH aqueous solution, and stir at 60 °C for 30 min to allow hydroxylation reaction to occur. After the reaction is complete, centrifuge and wash until neutral, and dry at 60 °C to obtain Si-OH. Disperse the obtained Si-OH with 20 mL of ethanol, add 0.05 g of APTES (at this time, the mass ratio of Si-OH to APTES is 10:1), stir at 50 °C for 20 min, and centrifuge and dry to obtain Si-NH2.

[0066] (2) The obtained Si-NH2 was dispersed in 40 mL of deionized water, and an aqueous solution containing 0.05 g AgNO3 was added (the mass ratio of Si-NH2 to AgNO3 was 10:1). After stirring at room temperature for 30 min, the solution was heated to 60 °C, and an aqueous solution of sodium citrate (the molar ratio of AgNO3 to sodium citrate was 1:1.2) was added dropwise. The mixture was stirred at this temperature for 1 h. After the reaction was completed, the mixture was centrifuged, washed three times, and dried to obtain Si@Ag.

[0067] (3) Weigh 1 g of PS microspheres with a particle size of 3 μm, disperse them in 50 mL of deionized water, add 0.5 g of Si@Ag (at this time, the mass ratio of PS to Si@Ag is 2:1), stir at room temperature for 6 h, and centrifuge to dry. Disperse the dried product in 20 mL of ethanol, add 0.75 g of phenolic resin (at this time, the mass ratio of the dried product to phenolic resin is 1:0.5), sonicate for 20 min to mix them evenly, stir at 60℃ until the ethanol is completely evaporated, and keep at 120℃ for 2 h to pre-cur it to obtain the precursor.

[0068] (4) The above precursor was transferred to a tube furnace and calcined at 700°C for 2 h under a N2 atmosphere at a flow rate of 50 mL / min and a heating rate of 5°C / min. After calcination, the calcined product was allowed to cool naturally to room temperature and then dispersed with toluene and refluxed at 80°C for 8 h. After centrifugation and washing three times, the product was vacuum dried at 60°C to obtain carbon-coated silicon anode particles.

[0069] The obtained carbon-coated silicon anode particles were assembled with Li6PS5Cl sulfide electrolyte to form a sulfide all-solid-state battery. Using a Li-In alloy as the counter electrode, the initial discharge capacity was measured to be 2782 mAh / g at a charge / discharge rate of 0.1 C (1C = 4200 mAh / g) and a voltage range of 0.01–1.5 V. After 100 cycles, the capacity retention was 79%. At a charge / discharge rate of 2C, the initial discharge capacity was measured to be 1590 mAh / g. The conductivity was 78 S / m measured using the four-probe method, the charge / discharge volume expansion rate was 37%, and the packing pressure was 3.2 MPa.

[0070] Example 7

[0071] (1) Weigh 0.5 g of silicon elemental particles with a particle size of 500 nm, add them to 50 mL of 1 mol / L NaOH aqueous solution, and stir at 60 °C for 30 min to allow hydroxylation reaction to occur. After the reaction is complete, centrifuge and wash until neutral, and dry at 60 °C to obtain Si-OH. Disperse the obtained Si-OH with 20 mL of ethanol, add 0.05 g of APTES (at this time, the mass ratio of Si-OH to APTES is 10:1), stir at 50 °C for 20 min, and centrifuge and dry to obtain Si-NH2.

[0072] (2) The obtained Si-NH2 was dispersed in 40 mL of deionized water, and 0.05 g of aqueous solution of AgNO3 was added (the mass ratio of Si-NH2 to AgNO3 was 10:1). After stirring at room temperature for 30 min, the solution was heated to 60 °C, and sodium citrate aqueous solution (the molar ratio of AgNO3 to sodium citrate was 1:1.2) was added dropwise. Stirring was continued at this temperature for 1 h. After the reaction was completed, the solution was centrifuged, washed three times, and dried to obtain Si@Ag.

[0073] (3) Weigh 1 g of PS microspheres with a particle size of 3 μm, disperse them in 50 mL of deionized water, add 0.5 g of Si@Ag (at this time, the mass ratio of PS to Si@Ag is 2:1), stir at room temperature for 6 h, and centrifuge to dry. Disperse the dried product in 20 mL of ethanol, add 1.8 g of phenolic resin (at this time, the mass ratio of the dried product to phenolic resin is 1:1.2), sonicate for 20 min to mix it evenly, stir at 60℃ until the ethanol is completely evaporated, and keep at 120℃ for 2 h to pre-cure it to obtain the precursor.

[0074] (4) The above precursor was transferred to a tube furnace and calcined at 700°C for 2 h under a N2 atmosphere at a flow rate of 50 mL / min and a heating rate of 5°C / min. After calcination, the calcined product was allowed to cool naturally to room temperature and then dispersed with toluene and refluxed at 80°C for 8 h. After centrifugation and washing three times, the product was vacuum dried at 60°C to obtain carbon-coated silicon anode particles.

[0075] The obtained carbon-coated silicon anode particles were assembled with Li6PS5Cl sulfide electrolyte to form a sulfide all-solid-state battery. Using a Li-In alloy as the counter electrode, the initial discharge capacity was measured to be 2890 mAh / g at a charge / discharge rate of 0.1 C (1C = 4200 mAh / g) and a voltage range of 0.01–1.5 V. After 100 cycles, the capacity retention was measured to be 80%. At a charge / discharge rate of 2C, the initial discharge capacity was measured to be 1670 mAh / g. The conductivity was measured to be 89 S / m using the four-probe method, the charge / discharge volume expansion rate was 33%, and the packing pressure was 2.9 MPa.

[0076] Comparative Example 1

[0077] (1) Weigh 0.5 g of silicon elemental particles with a particle size of 500 nm, add them to 50 mL of 1 mol / L NaOH aqueous solution, and stir at 60 °C for 30 min to allow them to undergo a hydroxylation reaction. After the reaction is complete, centrifuge and wash until neutral, and dry at 60 °C to obtain Si-OH.

[0078] (2) Weigh 1 g of PS microspheres with a particle size of 3 μm, disperse them in 50 mL of deionized water, add 0.5 g of Si-OH (at this time, the mass ratio of PS to Si-OH is 2:1), stir at room temperature for 6 h, and centrifuge to dry. Disperse the dried product in 20 mL of ethanol, add 1.2 g of phenolic resin (at this time, the mass ratio of dried product to phenolic resin is 1:0.8), sonicate for 20 min to mix it evenly, stir at 60℃ until the ethanol is completely evaporated, and keep at 120℃ for 2 h to pre-cure it to obtain the precursor.

[0079] (3) The above precursor was transferred to a tube furnace and calcined at 700°C for 2 h under a N2 atmosphere at a flow rate of 50 mL / min and a heating rate of 5°C / min. After calcination, the calcined product was allowed to cool naturally to room temperature and then dispersed with toluene and refluxed at 80°C for 8 h. After centrifugation and washing three times, the product was vacuum dried at 60°C to obtain carbon-coated silicon anode particles.

[0080] The obtained silicon anode particles were assembled with Li6PS5Cl sulfide electrolyte to form a sulfide all-solid-state battery. Using a Li-In alloy as the counter electrode, the initial discharge capacity was measured to be 1450 mAh / g at a charge-discharge rate of 0.1 C (1C = 4200 mAh / g) and a voltage range of 0.01–1.5 V. After 100 cycles, the capacity retention was 55%. At a charge-discharge rate of 2 C, the initial discharge capacity was measured to be 594 mAh / g. The conductivity was 0.28 S / m, the charge-discharge volume expansion rate was 36%, and the packing pressure was 3.0 MPa.

[0081] Comparative Example 2

[0082] (1) Weigh 0.5 g of silicon elemental particles with a particle size of 500 nm, add them to 50 mL of 1 mol / L NaOH aqueous solution, and stir at 60 °C for 30 min to allow hydroxylation reaction to occur. After the reaction is complete, centrifuge and wash until neutral, and dry at 60 °C to obtain Si-OH. Disperse the obtained Si-OH with 20 mL of ethanol, add 0.05 g of APTES (at this time, the mass ratio of Si-OH to APTES is 10:1), stir at 50 °C for 20 min, and centrifuge and dry to obtain Si-NH2.

[0083] (2) The obtained Si-NH2 was dispersed in 40 mL of deionized water, and an aqueous solution containing 0.05 g AgNO3 was added (the mass ratio of Si-NH2 to AgNO3 was 10:1). After stirring at room temperature for 30 min, the solution was heated to 60 °C, and an aqueous solution of sodium citrate (the molar ratio of AgNO3 to sodium citrate was 1:1.2) was added dropwise. The mixture was stirred at this temperature for 1 h. After the reaction was completed, the mixture was centrifuged, washed three times, and dried to obtain Si@Ag.

[0084] (3) Weigh 1 g of PS microspheres with a particle size of 3 μm, disperse them in 50 mL of deionized water, add 0.5 g of Si-OH (at this time, the mass ratio of PS to Si-OH is 2:1), stir at room temperature for 6 h, and centrifuge to dry. Disperse the dried product in 20 mL of ethanol, disperse Si@Ag in 20 mL of ethanol, add 0.3 g of phenolic resin (at this time, the mass ratio of the dried product to phenolic resin is 1:0.2), sonicate for 20 min to make it uniformly mixed, stir at 60℃ until the ethanol is completely evaporated, and keep at 120℃ for 2 h to pre-cur it to obtain the precursor.

[0085] (4) The above precursor was transferred to a tube furnace and calcined at 700°C for 2 h under a N2 atmosphere at a flow rate of 50 mL / min and a heating rate of 5°C / min. After calcination, the calcined product was allowed to cool naturally to room temperature and then dispersed with toluene and refluxed at 80°C for 8 h. After centrifugation and washing three times, the product was vacuum dried at 60°C to obtain carbon-coated silicon anode particles.

[0086] The obtained silicon anode particles were assembled with Li6PS5Cl sulfide electrolyte to form a sulfide all-solid-state battery. Using a Li-In alloy as the counter electrode, the initial discharge capacity was measured to be 2070 mAh / g at a charge / discharge rate of 0.1 C (1C = 4200 mAh / g) and a voltage range of 0.01–1.5 V. After 100 cycles, the capacity retention was 32%, and electrode cracking and silicon particle pulverization occurred after 50 cycles. At a charge / discharge rate of 2 C, the initial discharge capacity was measured to be 980 mAh / g. The conductivity was 68 S / m measured using the four-probe method, the charge / discharge volume expansion rate was 280%, and the packing pressure was 40 MPa.

[0087] Comparative Example 3

[0088] (1) Weigh 0.5 g of silicon elemental particles with a particle size of 500 nm, add them to 50 mL of 1 mol / L NaOH aqueous solution, and stir at 60 °C for 30 min to allow hydroxylation reaction to occur. After the reaction is complete, centrifuge and wash until neutral, and dry at 60 °C to obtain Si-OH. Disperse the obtained Si-OH with 20 mL of ethanol, add 0.05 g of APTES (at this time, the mass ratio of Si-OH to APTES is 10:1), stir at 50 °C for 20 min, and centrifuge and dry to obtain Si-NH2.

[0089] (2) The obtained Si-NH2 was dispersed in 40 mL of deionized water, and an aqueous solution containing 0.05 g AgNO3 was added (the mass ratio of Si-NH2 to AgNO3 was 10:1). After stirring at room temperature for 30 min, the solution was heated to 60 °C, and an aqueous solution of sodium citrate (the molar ratio of AgNO3 to sodium citrate was 1:1.2) was added dropwise. The mixture was stirred at this temperature for 1 h. After the reaction was completed, the mixture was centrifuged, washed three times, and dried to obtain Si@Ag.

[0090] (3) Weigh 1 g of PS microspheres with a particle size of 3 μm, disperse them in 50 mL of deionized water, add 0.5 g of Si-OH (at this time, the mass ratio of PS to Si-OH is 2:1), stir at room temperature for 6 h, and centrifuge to dry. Disperse the dried product in 20 mL of ethanol, disperse Si@Ag in 20 mL of ethanol, add 2.25 g of phenolic resin (at this time, the mass ratio of the dried product to phenolic resin is 1:1.5), sonicate for 20 min to make it uniformly mixed, stir at 60℃ until the ethanol is completely evaporated, and keep at 120℃ for 2 h to pre-cur it to obtain the precursor.

[0091] (4) The above precursor was transferred to a tube furnace and calcined at 700°C for 2 h under a N2 atmosphere at a flow rate of 50 mL / min and a heating rate of 5°C / min. After calcination, the calcined product was allowed to cool naturally to room temperature and then dispersed with toluene and refluxed at 80°C for 8 h. After centrifugation and washing three times, the product was vacuum dried at 60°C to obtain carbon-coated silicon anode particles.

[0092] The obtained silicon anode particles were assembled with Li6PS5Cl sulfide electrolyte to form a sulfide all-solid-state battery. Using a Li-In alloy as the counter electrode, the initial discharge capacity was measured to be 1760 mAh / g at a charge / discharge rate of 0.1 C (1C = 4200 mAh / g) and a voltage range of 0.01–1.5 V. After 100 cycles, the capacity retention was 41%. At a charge / discharge rate of 2 C, the initial discharge capacity was measured to be 750 mAh / g. The conductivity was 68 S / m measured using the four-probe method, the charge / discharge volume expansion was 280%, and the packing pressure was 40 MPa.

[0093] Comparative Example 4

[0094] (1) Weigh 0.5 g of silicon elemental particles with a particle size of 500 nm, add them to 50 mL of 1 mol / L NaOH aqueous solution, and stir at 60 °C for 30 min to allow hydroxylation reaction to occur. After the reaction is complete, centrifuge and wash until neutral, and dry at 60 °C to obtain Si-OH. Disperse the obtained Si-OH with 20 mL of ethanol, add 0.05 g of APTES (at this time, the mass ratio of Si-OH to APTES is 10:1), stir at 50 °C for 20 min, and centrifuge and dry to obtain Si-NH2.

[0095] (2) The obtained Si-NH2 was dispersed in 40 mL of deionized water, and an aqueous solution containing 0.05 g AgNO3 was added (the mass ratio of Si-NH2 to AgNO3 was 10:1). After stirring at room temperature for 30 min, the solution was heated to 60 °C, and an aqueous solution of sodium citrate (the molar ratio of AgNO3 to sodium citrate was 1:1.2) was added dropwise. The mixture was stirred at this temperature for 1 h. After the reaction was completed, the mixture was centrifuged, washed three times, and dried to obtain Si@Ag.

[0096] (3) Weigh 1 g of PS microspheres with a particle size of 0.1 μm, disperse them in 50 mL of deionized water, add 0.5 g of Si@Ag (at this time, the mass ratio of PS to Si@Ag is 2:1), stir at room temperature for 6 h, and centrifuge to dry. Disperse the dried product in 20 mL of ethanol, add 1.2 g of phenolic resin (at this time, the mass ratio of the dried product to phenolic resin is 1:0.8), sonicate for 20 min to mix it evenly, stir at 60℃ until the ethanol is completely evaporated, and keep it at 120℃ for 2 h to pre-cure it to obtain the precursor.

[0097] (4) The above precursor was transferred to a tube furnace and calcined at 700°C for 2 h under a N2 atmosphere at a flow rate of 50 mL / min and a heating rate of 5°C / min. After calcination, the calcined product was allowed to cool naturally to room temperature and then dispersed with toluene and refluxed at 80°C for 8 h. After centrifugation and washing three times, the product was vacuum dried at 60°C to obtain carbon-coated silicon anode particles.

[0098] The obtained silicon anode particles were assembled with Li6PS5Cl sulfide electrolyte to form a sulfide all-solid-state battery. Using a Li-In alloy as the counter electrode, the initial discharge capacity was measured to be 2120 mAh / g at a charge / discharge rate of 0.1 C (1C = 4200 mAh / g) and a voltage range of 0.01–1.5 V. After 100 cycles, the capacity retention was 34%. At a charge / discharge rate of 2 C, the initial discharge capacity was measured to be 1012 mAh / g. The conductivity was 79 S / m measured using the four-probe method, the charge / discharge volume expansion rate was 210%, and the packing pressure was 32 MPa.

[0099] Comparative Example 5

[0100] (1) Weigh 0.5 g of silicon elemental particles with a particle size of 500 nm, add them to 50 mL of 1 mol / L NaOH aqueous solution, and stir at 60 °C for 30 min to allow hydroxylation reaction to occur. After the reaction is complete, centrifuge and wash until neutral, and dry at 60 °C to obtain Si-OH. Disperse the obtained Si-OH with 20 mL of ethanol, add 0.05 g of APTES (at this time, the mass ratio of Si-OH to APTES is 10:1), stir at 50 °C for 20 min, and centrifuge and dry to obtain Si-NH2.

[0101] (2) The obtained Si-NH2 was dispersed in 40 mL of deionized water, and an aqueous solution containing 0.05 g AgNO3 was added (the mass ratio of Si-NH2 to AgNO3 was 10:1). After stirring at room temperature for 30 min, the solution was heated to 60 °C, and an aqueous solution of sodium citrate (the molar ratio of AgNO3 to sodium citrate was 1:1.2) was added dropwise. The mixture was stirred at this temperature for 1 h. After the reaction was completed, the mixture was centrifuged, washed three times, and dried to obtain Si@Ag.

[0102] (3) After dispersing Si@Ag with 20 mL of ethanol, add 0.4 g of phenolic resin (at this time, the mass ratio of Si@Ag to phenolic resin is 1:0.8), sonicate for 20 min to make it uniformly mixed, stir at 60℃ until the ethanol is completely evaporated, and keep at 120℃ for 2 h to pre-cur it to obtain the precursor.

[0103] (4) The above precursor was transferred to a tube furnace and calcined at 700°C for 2 h under a N2 atmosphere at a flow rate of 50 mL / min and a heating rate of 5°C / min. After calcination, the calcined product was allowed to cool naturally to room temperature and then dispersed with toluene and refluxed at 80°C for 8 h. After centrifugation and washing three times, the product was vacuum dried at 60°C to obtain carbon-coated silicon anode particles.

[0104] The obtained carbon-coated silicon anode particles were assembled with Li6PS5Cl sulfide electrolyte to form a sulfide all-solid-state battery. Using a Li-In alloy as the counter electrode, the initial discharge capacity was measured to be 2274 mAh / g at a charge / discharge rate of 0.1 C (1C = 4200 mAh / g) and a voltage range of 0.01–1.5 V. After 100 cycles, the capacity retention was 32%. At a charge / discharge rate of 2C, the initial discharge capacity was measured to be 1320 mAh / g. The conductivity was 68 S / m measured using the four-probe method, the charge / discharge volume expansion rate was 350%, and the packing pressure was 46 MPa.

[0105] Comparative Example 6

[0106] (1) Weigh 0.5 g of silicon elemental particles with a particle size of 500 nm, add them to 50 mL of 1 mol / L NaOH aqueous solution, and stir at 60 °C for 30 min to allow hydroxylation reaction to occur. After the reaction is complete, centrifuge and wash until neutral, and dry at 60 °C to obtain Si-OH. Disperse the obtained Si-OH with 20 mL of ethanol, add 0.05 g of APTES (at this time, the mass ratio of Si-OH to APTES is 10:1), stir at 50 °C for 20 min, and centrifuge and dry to obtain Si-NH2.

[0107] (2) The obtained Si-NH2 was dispersed in 40 mL of deionized water, and an aqueous solution containing 2.5 g AgNO3 was added (the mass ratio of Si-NH2 to AgNO3 was 1:5). After stirring at room temperature for 30 min, the solution was heated to 60 °C, and an aqueous solution of sodium citrate (the molar ratio of AgNO3 to sodium citrate was 1:1.2) was added dropwise. Stirring was continued at this temperature for 1 h. After the reaction was completed, the solution was centrifuged, washed three times, and dried to obtain Si@Ag.

[0108] (3) Weigh 1 g of PS microspheres with a particle size of 3 μm, disperse them in 50 mL of deionized water, add 0.5 g of Si@Ag (at this time, the mass ratio of PS to Si@Ag is 2:1), stir at room temperature for 6 h, and centrifuge to dry. Disperse the dried product in 20 mL of ethanol, add 1.2 g of phenolic resin (at this time, the mass ratio of the dried product to phenolic resin is 1:0.8), sonicate for 20 min to mix it evenly, stir at 60℃ until the ethanol is completely evaporated, and keep at 120℃ for 2 h to pre-cur it to obtain the precursor.

[0109] (4) The above precursor was transferred to a tube furnace and calcined at 700°C for 2 h under a N2 atmosphere at a flow rate of 50 mL / min and a heating rate of 5°C / min. After calcination, the calcined product was allowed to cool naturally to room temperature and then dispersed with toluene and refluxed at 80°C for 8 h. After centrifugation and washing three times, the product was vacuum dried at 60°C to obtain carbon-coated silicon anode particles.

[0110] The obtained carbon-coated silicon anode particles were assembled with Li6PS5Cl sulfide electrolyte to form a sulfide all-solid-state battery. Using a Li-In alloy as the counter electrode, the initial discharge capacity was measured to be 1672 mAh / g at a charge-discharge rate of 0.1 C (1 C = 4200 mAh / g) and a voltage range of 0.01–1.5 V. After 100 cycles, the capacity retention was 45%. At a charge-discharge rate of 2 C, the initial discharge capacity was measured to be 845 mAh / g. The conductivity was 151 S / m measured using the four-probe method, the charge-discharge volume expansion rate was 34%, and the packing pressure was 3 MPa.

[0111] The all-solid-state batteries composed of carbon-coated silicon anode particles and sulfide electrolytes prepared in Examples 1-7 all exhibit high discharge capacity, good cycle performance, high conductivity, and low stacking pressure. Furthermore, the electrochemical performance improves with increasing silver loading of the silicon anode particles, due to the good compatibility between silver nanoparticles and the sulfide electrolyte. The particle size of the PS microspheres used as templates can be used to control the cavity size between the silicon anode particles and the carbon coating layer. As the cavity size increases, the stacking pressure decreases significantly. This is because the cavity provides a buffer space for the expansion of the silicon anode particles, forming a "loose but compact" anode stacking structure outside, reducing the interfacial contact pressure with the sulfide electrolyte, and improving the cycle stability and practicality of the sulfide all-solid-state battery.

[0112] Comparing Example 1 and Comparative Examples 1-6, it can be seen that the carbon-coated silicon anode particles of the present invention have good electrochemical performance and low stacking pressure. This is the result of the synergistic effect of the surface-modified silver nanoparticles and the cavity-containing carbon coating layer. The cavity provides a dedicated buffer space for silicon volume expansion, and the silver nanoparticles construct an efficient electron channel between silicon and carbon, synergistically solving the problems of "expansion suppression-conductivity enhancement-low pressure adaptation". As shown in Examples 1-3 and Comparative Example 1, when the surface of the silicon anode particles is not modified with silver nanoparticles, the charge transfer efficiency of the all-solid-state battery composed of sulfide electrolyte decreases significantly, and a higher stacking pressure is required to maintain interfacial contact, resulting in poor cycle stability. However, as shown in Examples 1 and Comparative Example 6, when the silver load is excessive, since the specific capacity of silver as an anode (400~700 mAh / g) is much smaller than that of silicon (4200 mAh / g), a high silver content will affect the overall specific capacity of the anode. As shown in Examples 1, 4, 5 and Comparative Examples 4, 5, when the silicon anode particles are tightly coated with a carbon layer, but there is no cavity between the carbon layer and the anode particles, or the cavity volume is small, the expansion of silicon volume cannot be buffered, the electrode cracks, cannot be cycled multiple times, and the stacking pressure is high. As shown in Examples 1, 6, 7 and Comparative Examples 2, 3, the amount of phenolic resin determines the carbon coating effect. When the amount of phenolic resin is insufficient, the coated carbon layer becomes porous and easily detaches from the surface of the silicon anode particles. Therefore, within a certain range, the carbon coating effect improves with the increase of the amount of phenolic resin. However, when the amount of phenolic resin is excessive, the carbon layer agglomerates, the coating becomes thicker, and the charge transport efficiency is affected.

Claims

1. A carbon-coated silicon anode particle, characterized in that, The silicon anode particles are modified with silver particles on their surface and have a carbon coating layer on their exterior. There is a cavity between the inner surface of the carbon coating layer and the surface of the silicon anode particles, and the thickness of the cavity is greater than the particle size of the silicon anode particles.

2. A method for preparing carbon-coated silicon anode particles as described in claim 1, characterized in that, Includes the following steps: (1) Add silicon anode particles to an alkaline solution and mix to obtain hydroxylated silicon anode particles. Disperse the hydroxylated silicon anode particles with a solvent, add a grafting agent, and mix to obtain surface-grafted silicon anode particles. (2) After dispersing the above surface-grafted silicon anode particles with a solvent, add silver precursor and reducing agent, and mix to obtain surface silver-modified silicon anode particles. (3) After mixing the above-mentioned silver-modified silicon anode particles with the template, add carbon source and mix to obtain a precursor. After calcining the precursor, remove the template to obtain carbon-coated silicon anode particles.

3. The method for preparing carbon-coated silicon anode particles according to claim 2, characterized in that, In step (1), the grafting agent is an amino small molecule compound.

4. The method for preparing carbon-coated silicon anode particles according to claim 3, characterized in that, In step (1), the amino small molecule compound is 3-aminopropyltriethoxysilane.

5. The method for preparing carbon-coated silicon anode particles according to claim 2, characterized in that, In step (2), the silver precursor is a water-soluble silver salt.

6. The method for preparing carbon-coated silicon anode particles according to claim 5, characterized in that, In step (2), the water-soluble silver salt is silver nitrate.

7. The method for preparing carbon-coated silicon anode particles according to claim 2, characterized in that, In step (2), the reducing agent is sodium citrate.

8. The method for preparing carbon-coated silicon anode particles according to claim 2, characterized in that, In step (2), the mass ratio of the surface-grafted silicon anode particles to the silver precursor is 5:1 to 20:

1.

9. The method for preparing carbon-coated silicon anode particles according to claim 2, characterized in that, In step (3), the template is polystyrene microspheres with a particle size 2 to 10 times that of silicon anode particles.

10. The method for preparing carbon-coated silicon anode particles according to claim 2, characterized in that, In step (3), the carbon source is phenolic resin, and its amount is 0.5 to 1.2 times the sum of the mass of the silver-modified silicon anode particles and the template.

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