Double-metal-coating-layer-containing silicon-carbon negative electrode material for all-solid-state battery and preparation method of silicon-carbon negative electrode material

Abstract

The invention relates to a preparation method of a double-metal-coating-layer-containing silicon-carbon negative electrode material for an all-solid-state battery, which comprises the following steps: (1) carrying out silicon deposition and carbon coating on porous carbon to obtain a silicon-carbon composite material; (2) dipping and modifying the silicon-carbon composite material in an aqueous solution of an anionic surfactant; (3) dissolving tin salt and second metal salt (indium salt or bismuth salt) in water according to a molar ratio of 1: (0.5-1.5), adding a nitrogen-containing organic reducing agent to form a mixed solution, and immersing the modified silicon-carbon composite material to obtain a silicon-carbon composite material containing a coating layer; and (4) carrying out heat treatment in an inert atmosphere to obtain the silicon-carbon negative electrode material containing the double metal coating layers. According to the invention, a Sn-In or Sn-Bi coating layer with a specific molar ratio is constructed on the surface of the silicon-carbon composite material, the coating layer can be lithiated in a grading manner in the charging and discharging process, an ion-electron bicontinuous network is cooperatively constructed, and N doping is synchronously realized through heat treatment; therefore, the silicon-carbon negative electrode material containing the coating layer shows excellent electrochemical performance in an all-solid-state battery.

Description

Technical Field

[0001] This invention belongs to the field of all-solid-state battery technology, specifically relating to a silicon-carbon anode material with a bimetallic coating for all-solid-state batteries and its preparation method. Background Technology

[0002] With the rapid development of electric vehicles and portable electronic devices, the market has an urgent need for energy storage devices with high energy density and high safety. All-solid-state batteries use non-flammable solid electrolytes to replace traditional organic electrolytes, fundamentally solving the risks of battery combustion and explosion. They also hold promise for achieving breakthroughs in energy density by matching higher-capacity positive and negative electrode materials, and are therefore widely regarded as an important development direction for next-generation lithium battery technology.

[0003] In the field of anode materials, silicon (Si) is favored due to its extremely high theoretical specific capacity (approximately 3579 mA·h / g) and suitable operating potential (approximately 0.3 V vs. Li). + Silicon (Li₂S) is considered one of the most promising next-generation anode materials. However, silicon materials experience significant volume changes (expansion rate > 300%) during lithium-ion insertion and extraction, leading to the cracking and pulverization of the active material, as well as repeated cracking and regeneration of the solid electrolyte interphase (SEI) film, resulting in rapid capacity decay. Furthermore, the low intrinsic electronic and ionic conductivity of silicon severely limits its rate performance.

[0004] To overcome the aforementioned drawbacks, silicon-carbon composite materials have emerged. Mainstream technologies embed silicon nanoparticles within a porous carbon matrix, utilizing the excellent conductivity and mechanical support of carbon materials to buffer the volume expansion of silicon and improve cycle stability to some extent. However, in all-solid-state battery systems, silicon-carbon anodes face more severe problems: 1) The solid-solid interface between the solid electrolyte and silicon-carbon particles is difficult to fully wet like a liquid electrolyte, resulting in a small effective ion transport contact area and high interfacial impedance; 2) Silicon nanoparticles are mainly distributed within the carbon framework, leading to long ion transport paths and slow kinetic processes. In existing technologies, to improve the electrochemical performance of silicon-carbon anodes for all-solid-state batteries, solid electrolytes and conductive agents are typically added to the silicon-based anode to enhance ionic and electronic conductivity, but this sacrifices the overall energy density of the electrode. Some studies have attempted to coat silicon-carbon composite materials, but most of these studies focus on single-component carbon layers or metal coatings. The main function of these coatings is limited to improving electronic conductivity or physically confining silicon volume expansion. They have limited contribution to building efficient ion transport channels and cannot fundamentally solve the core problem of interfacial ion transport dynamics in all-solid-state batteries.

[0005] Therefore, it is of great significance to develop an anode material that can maintain the high capacity and cycle stability of silicon-carbon composite materials while significantly improving their ion transport kinetics performance in all-solid-state batteries. Summary of the Invention

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a silicon-carbon anode material with a bimetallic coating for all-solid-state batteries includes the following steps:

[0008] (1) Porous carbon is subjected to silicon deposition and carbon coating treatment in sequence to obtain silicon-carbon composite material;

[0009] (2) The silicon-carbon composite material was dispersed in an aqueous solution of anionic surfactant and impregnated. After solid-liquid separation, solid washing and drying, the surface-modified silicon-carbon composite material was obtained.

[0010] (3) Dissolve tin salt and second metal salt together in water at a molar ratio of 1:0.5~1.5. The second metal salt is indium salt or bismuth salt. Then add nitrogen-containing organic reducing agent to form a mixed solution. Then immerse the surface-modified silicon-carbon composite material in the mixed solution. The mass ratio of the surface-modified silicon-carbon composite material, the total mass of tin salt and second metal salt and the mass of nitrogen-containing organic reducing agent is 100:(10~30):(5~10). After immersion, separate solid and liquid, wash the solid and dry to obtain silicon-carbon composite material with coating layer.

[0011] (4) The silicon-carbon composite material with the coating layer is heat-treated under an inert atmosphere to obtain a silicon-carbon anode material with a bimetallic coating layer.

[0012] This invention utilizes a liquid-phase impregnation and one-step heat treatment process to in-situ construct Sn-In or Sn-Bi coatings with specific molar ratios on the surface of a silicon-carbon composite material. Sn possesses high capacity and good electronic conductivity, while the second metal (In or Bi) exhibits a higher lithiation potential and lower volume expansion rate compared to silicon. Based on this, a stepped lithiation potential difference exists between the different metal components in the coating and between the coating and the silicon matrix, achieving graded lithiation during charge and discharge: the bimetallic coating with the higher potential is preferentially lithiated, pre-constructing a continuous ion transport network on the particle surface, providing a rapid channel for subsequent deep lithiation of silicon, and greatly improving the diffusion kinetics of lithium ions from the solid electrolyte to the active material, thereby significantly enhancing the battery's charge and discharge rate and capacity utilization. Simultaneously, this bimetallic coating utilizes the intrinsic high electronic conductivity of the metal to simultaneously establish an efficient electron transport channel on the particle surface, improving the overall electronic conductivity. Together with the aforementioned ion network, it constructs an "ion-electron" dual continuous network, fundamentally solving the solid-solid interface ion transport problem of the all-solid-state battery anode. In addition, during the heat treatment process, the gas (such as NH3) generated by the pyrolysis of the reducing agent reduces the metal salt while simultaneously doping the coating layer with nitrogen, effectively controlling the electronic structure of the coating layer, further enhancing the interfacial conductivity, and promoting the formation of a more stable and dense solid electrolyte interfacial film on the surface of the negative electrode particles.

[0013] Further, in step (1), porous carbon is obtained by pore formation through activation of a porous carbon precursor; the median particle size D50 of the porous carbon precursor is 5~10 μm, which can be selected from resin carbon or biomass carbon; the activation reagent is at least one of water vapor and carbon dioxide; the activation conditions are: holding at 800~950℃ for 8~12h; by controlling the activation conditions, the specific surface area of ​​the porous carbon is made to be 1700~2300 m². 2 / g, pore volume 0.9~1.2cm 3 / g.

[0014] The vapor-phase silicon deposition and carbon coating processes described in step (1) are techniques well known to those skilled in the art and are not particularly limited. For example, the conditions for vapor-phase silicon deposition are as follows: activated porous carbon is chemically vapor-deposited at 450-550°C for 2-4 hours under an inert atmosphere using an organosilicon source gas, and the ratio of activated porous carbon to organosilicon source gas is 1 kg: 150-250 L; the organosilicon source gas is selected from at least one of silane, dichlorosilane, trichlorosilane, silicon tetrachloride, silicon tetrafluoride, and disilane. The conditions for carbon coating are as follows: porous carbon after silicon deposition is reacted at 500-700°C for 1-3 hours under an inert atmosphere using a gaseous carbon source, and the ratio of porous carbon after silicon deposition to gaseous carbon source is 1 kg: 250-500 L; the gaseous carbon source is selected from at least one of C1-4 alkanes, C2-4 alkenes, and C2-4 alkynes.

[0015] Further, in step (1), the silicon content in the silicon-carbon composite material is 40~60wt%, preferably 48~55wt%, and the carbon coating layer accounts for 0.8~2wt% of the silicon-carbon composite material, preferably 1.2~2wt%.

[0016] Further, in step (2), the anionic surfactant is selected from at least one of sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS); the mass ratio of the silicon-carbon composite material to the volume of the aqueous solution of the anionic surfactant is 10g:500~1000mL, and the concentration of the aqueous solution of the anionic surfactant is 0.5~1.5wt%; the impregnation conditions are: stirring at 200~400rpm and 20~40℃ for 2~6h. During the impregnation process, the anionic surfactant modifies the surface of the silicon-carbon composite material, thereby providing more active sites for subsequent impregnation in a mixed solution composed of tin salt and a second metal salt.

[0017] Furthermore, in step (2), the washing is a pure water washing 2 to 4 times; the drying is vacuum drying at 60 to 80°C for 12 to 24 hours.

[0018] Preferably, in step (3), the molar ratio of the tin salt to the second metal salt is 1:0.8~1.2, for example, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2. It should be noted that the molar ratio of the tin salt to the second metal salt (indium salt or bismuth salt) is key to determining the synergistic effect of graded lithiation of the coating layer. When the amount of tin salt is excessive, the cycle performance is poor, possibly because the volume expansion (approximately 260%) caused by excessive tin weakens the mechanical stability of the coating layer; when the amount of the second metal salt is excessive, it reduces the overall capacity of the negative electrode, especially at high rates. Controlling the molar ratio of the tin salt to the second metal salt within the above range achieves a balance between suppressing expansion and maintaining capacity.

[0019] Preferably, in step (3), the mass ratio of the surface-modified silicon-carbon composite material, the total mass of the tin salt and the second metal salt, and the mass of the nitrogen-containing organic reducing agent is 100:(20~25):(7.5~10). The ratio of the three substances is intended to ensure the construction of a complete and uniform coating layer. If the amount of metal salt (tin salt and the second metal salt) is too low, the resulting coating layer will be too thin and discontinuous, and will not be able to completely coat the material; if the amount of metal salt is too high, the coating layer will be too thick, which will reduce the overall specific capacity of the entire negative electrode material. The nitrogen-containing organic reducing agent reduces the tin salt and the second metal salt in the subsequent heat treatment process, and also achieves N doping of the coating layer, which is beneficial to further improving the electrochemical performance. If the amount of nitrogen-containing organic reducing agent is too low, the metal salt will not be completely reduced, which will hinder lithium-ion transport and lead to a decrease in rate performance; if the amount of reducing agent is too high, excessive doping will also be detrimental to electron migration.

[0020] Further, in step (3), the tin salt is selected from at least one of tin chloride (SnCl4), tin fluoride (SnF4), tin sulfate (Sn(SO4)2), stannous chloride (SnCl2), stannous sulfate (SnSO4), stannous nitrate Sn(NO3)2, and their hydrates; the indium salt is selected from at least one of indium chloride (InCl3), indium chloride (InBr3), indium iodide (InI3), and their hydrates; the bismuth salt is selected from at least one of bismuth chloride (BiCl3), bismuth bromide (BiBr3), and their hydrates; and the nitrogen-containing organic reducing agent is selected from at least one of dihydrodiamine and urea, preferably dihydrodiamine.

[0021] Further, in step (3), the mass ratio of the surface-modified silicon-carbon composite material to the volume ratio of the mixed solution is 1g:30~50mL; the impregnation conditions are: stirring at 300~500 rpm / min for 6~10h, and simultaneously subjected to ultrasonic treatment at 10~20kHz.

[0022] Further, in step (3), the washing is performed by alternating washing with ethanol and pure water, for a total of 2 to 4 times; the drying is performed by vacuum drying at 60 to 80°C for 12 to 24 hours.

[0023] Further, in step (4), the inert atmosphere is nitrogen and / or argon; the heat treatment conditions are: 800~950℃ for 6~8h. When the silicon-carbon composite material with the coating is heat-treated in an inert atmosphere, the reducing agent pyrolyzes to generate a reducing gas (such as NH3). The reducing gas can reduce tin salts, indium salts, and bismuth salts in situ to metal nanoparticles, which are then coated on the surface of the silicon-carbon composite material. At the same time, non-metallic elements (from the reducing agent) are doped, and finally, a silicon-carbon anode material with a bimetallic coating is obtained.

[0024] Secondly, the present invention also provides a silicon-carbon anode material with a bimetallic coating for all-solid-state batteries, which is prepared by the aforementioned preparation method, wherein the mass percentage of the bimetallic coating is 2-8%, preferably 4-6%.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. This invention utilizes a liquid-phase impregnation and one-step heat treatment process to in-situ construct a Sn-In or Sn-Bi coating layer with a specific molar ratio on the surface of a silicon-carbon composite material. This coating layer achieves graded lithiation during charge and discharge, synergistically constructing an "ion-electron" dual continuous network, fundamentally solving the problem of slow ion transport at the solid-solid interface of the negative electrode in all-solid-state batteries. Furthermore, during the heat treatment process, the reducing agent simultaneously achieves N doping of the coating layer, effectively controlling the electronic structure of the coating layer, further enhancing interfacial conductivity, and promoting the formation of a more stable and dense solid electrolyte interface film on the surface of the negative electrode particles.

[0027] 2. This invention achieves in-situ reduction, resulting in a tight bond and uniform coating between the generated nano-metal particles and the carbon substrate, which is beneficial for further improving cycle performance.

[0028] 3. The silicon-carbon anode material with a bimetallic coating of the present invention exhibits high initial coulombic efficiency (up to 82% or more), high specific capacity (up to 1800 mAh / g), excellent rate performance (still maintaining more than 550 mAh / g at 2C) and long cycle life (capacity retention of more than 90% after 100 cycles) when used in all-solid-state batteries. Attached Figure Description

[0029] Figure 1 The image shows a SEM image of the silicon-carbon anode material with a Sn-In coating prepared in Example 1.

[0030] Figure 2 The graphs show the electronic conductivity of the silicon-carbon anode materials prepared in Example 1 and Comparative Example 1.

[0031] Figure 3 The graph shows the first charge-discharge curves of the silicon-carbon anode materials prepared in Example 1 and Comparative Example 1 at a rate of 0.1C.

[0032] Figure 4 The rate performance diagrams are for the silicon-carbon anode materials prepared in Example 1 and Comparative Example 1.

[0033] Figure 5 The graphs show the cycling performance of the silicon-carbon anode materials prepared in Example 1 and Comparative Example 1 at 0.5C. Detailed Implementation

[0034] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0035] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0036] The resin carbon is phenolic resin carbon, which is a self-made phenolic resin carbonized material with a median particle size D50 of approximately 6.2 μm.

[0037] Example 1

[0038] (1) Place 200g of phenolic resin carbon in a tube furnace, introduce steam at 1.5L / min, and heat the tube furnace to 850℃ at a heating rate of 8℃ / min. Hold the temperature for 10h, then switch the steam to nitrogen, stop heating, and allow it to cool naturally to room temperature to obtain porous carbon (the specific surface area of ​​the porous carbon was measured to be 1988m² in a low-temperature nitrogen adsorption experiment). 2 / g, pore volume 1.09cm 3 / g); 30g of porous carbon was transferred into a fluidized bed, nitrogen was introduced at a flow rate of 5L / min, and the temperature was increased to 500℃ at a heating rate of 10℃ / min. The nitrogen flow rate was maintained and silane gas was introduced at a flow rate of 0.2 L / min for chemical vapor deposition for 2h. After the silane deposition was completed, the silane gas was stopped, and helium was introduced at a flow rate of 5L / min to remove excess silane gas. Subsequently, acetylene gas was introduced at 550℃ at a flow rate of 0.2L / min for vapor deposition for 1h. After the acetylene gas decomposed, a carbon coating layer was formed, and a silicon-carbon composite material was obtained.

[0039] According to GB / T 38823-2020, the silicon content in the silicon-carbon composite material was tested using a vario EL cube elemental analyzer from Elementar GmbH, Germany, and the mass percentage of the carbon coating layer was determined by the incremental method. Calculations showed that the silicon content in the prepared silicon-carbon composite material was 50.1 wt%, and the carbon coating layer accounted for 1.5 wt% of the composite material.

[0040] (2) 20g of silicon-carbon composite material was dispersed in an aqueous solution of sodium dodecyl sulfate (SDS) with a concentration of 1000mL and stirred at 300rpm at 25℃ for 3h. Then, it was centrifuged, washed twice with pure water, and vacuum dried at 80℃ for 24h to obtain surface-modified silicon-carbon composite material.

[0041] (3) Dissolve 0.94 g (4.8 mmol) of tin fluoride (SnF4) and 1.06 g (4.8 mmol) of indium chloride (InCl3) in 250 mL of pure water, then add 0.75 g of dihydrodiamine and add pure water to make up to 300 mL to form a mixed solution. Then immerse 10 g of surface-modified silicon-carbon composite material in the above 300 mL mixed solution (i.e., the total mass of surface-modified silicon-carbon composite material, SnF4 and InCl3 and the mass ratio of dihydrodiamine are 100:20:7.5), stir at 400 rpm for 8 h, and simultaneously perform ultrasonic treatment at 15 kHz. After the immersion is completed, centrifuge the solid and wash it with ethanol and pure water alternately for a total of 4 times. Then vacuum dry at 80 °C for 24 h to obtain silicon-carbon composite material with coating layer.

[0042] (4) The silicon-carbon composite material with the coating layer is placed in a ceramic boat and then placed in a tube furnace. It is kept at 900°C for 7 hours under a nitrogen atmosphere. After the heat treatment is completed, it is naturally cooled to room temperature with the furnace to obtain the silicon-carbon anode material with a bimetallic coating layer, namely the silicon-carbon anode material with a Sn-In coating layer.

[0043] The mass percentage of the Sn-In coating layer was calculated using the weight gain method to be 4.5%.

[0044] Example 2

[0045] The rest is the same as in Example 1, except that in step (3), the total mass ratio of the surface-modified silicon-carbon composite material, SnF4 and InCl3, and dihydrodiamine is 100:10:5; specifically:

[0046] (1) Same as Example 1;

[0047] (2) Same as Example 1;

[0048] (3) Dissolve 0.47 g (2.4 mmol) of tin fluoride (SnF4) and 0.53 g (2.4 mmol) of indium chloride (InCl3) in 250 mL of pure water, then add 0.50 g of dihydrodiamine and add pure water to make up to 300 mL to form a mixed solution. Then immerse 10 g of surface-modified silicon-carbon composite material in the above 300 mL mixed solution (i.e., the total mass of surface-modified silicon-carbon composite material, SnF4 and InCl3 and the mass ratio of dihydrodiamine are 100:10:5), stir at 400 rpm for 8 h, and simultaneously perform ultrasonic treatment at 15 kHz. After the immersion is completed, centrifuge and wash the separated solid with ethanol and pure water alternately for a total of 4 times. Then vacuum dry at 80 °C for 24 h to obtain silicon-carbon composite material with coating layer.

[0049] (4) Same as in Example 1.

[0050] The mass percentage of the Sn-In coating layer was calculated using the weight gain method to be 2.4%.

[0051] Example 3

[0052] The rest is the same as in Example 1, except that in step (3), the total mass ratio of the surface-modified silicon-carbon composite material, SnF4 and InCl3, and dihydrodiamine is 100:15:5; specifically:

[0053] (1) Same as Example 1;

[0054] (2) Same as Example 1;

[0055] (3) Dissolve 0.70 g (3.6 mmol) of tin fluoride (SnF4) and 0.80 g (3.6 mmol) of indium chloride (InCl3) in 250 mL of pure water, then add 0.50 g of dihydrodiamine and add pure water to make up to 300 mL to form a mixed solution. Then immerse 10 g of surface-modified silicon-carbon composite material in the above 300 mL mixed solution (i.e., the total mass of surface-modified silicon-carbon composite material, SnF4 and InCl3 and the mass ratio of dihydrodiamine are 100:15:5), stir at 400 rpm for 8 h, and simultaneously perform ultrasonic treatment at 15 kHz. After the immersion is completed, centrifuge and wash the separated solid with ethanol and pure water alternately for a total of 4 times. Then vacuum dry at 80 °C for 24 h to obtain silicon-carbon composite material with coating layer.

[0056] (4) Same as in Example 1.

[0057] The mass percentage of the Sn-In coating layer was calculated using the weight gain method to be 3.5%.

[0058] Example 4

[0059] The rest is the same as in Example 1, except that in step (3), the mass ratio of the surface-modified silicon-carbon composite material, the total mass of SnF4 and InCl3, and the mass of dihydrodiamine is 100:25:10; specifically:

[0060] (1) Same as Example 1;

[0061] (2) Same as Example 1;

[0062] (3) Dissolve 1.17 g (6 mmol) of tin fluoride (SnF4) and 1.33 g (6 mmol) of indium chloride (InCl3) in 250 mL of pure water, add 1.0 g of dihydrodiamine, and add pure water to make up to 300 mL to form a mixed solution. Then, immerse 10 g of surface-modified silicon-carbon composite material in the above 300 mL mixed solution (i.e., the total mass of surface-modified silicon-carbon composite material, SnF4 and InCl3, and the mass ratio of dihydrodiamine is 100:25:10), stir at 400 rpm for 8 h, and simultaneously perform ultrasonic treatment at 15 kHz. After the immersion is completed, centrifuge the solid and wash it with ethanol and pure water alternately for a total of 4 times. Then, vacuum dry it at 80 °C for 24 h to obtain the silicon-carbon composite material with the coating layer.

[0063] (4) Same as in Example 1.

[0064] The mass percentage of the Sn-In coating layer was calculated using the weight gain method to be 5.8%.

[0065] Example 5

[0066] The rest is the same as in Example 1, except that in step (3), the total mass ratio of the surface-modified silicon-carbon composite material, SnF4 and InCl3, and dihydrodiamine is 100:30:10; specifically:

[0067] (1) Same as Example 1;

[0068] (2) Same as Example 1;

[0069] (3) Dissolve 1.40 g (7.2 mmol) of tin fluoride (SnF4) and 1.60 g (7.2 mmol) of indium chloride (InCl3) in 250 mL of pure water, add 1.0 g of dihydrodiamine, and add pure water to make up to 300 mL to form a mixed solution. Then, immerse 10 g of surface-modified silicon-carbon composite material in the above 300 mL mixed solution (i.e., the total mass of surface-modified silicon-carbon composite material, SnF4 and InCl3, and the mass ratio of dihydrodiamine is 100:30:10), stir at 400 rpm for 8 h, and simultaneously perform ultrasonic treatment at 15 kHz. After the immersion is completed, centrifuge the solid and wash it with ethanol and pure water alternately for a total of 4 times. Then, vacuum dry it at 80 °C for 24 h to obtain the silicon-carbon composite material with the coating layer.

[0070] (4) Same as in Example 1.

[0071] The mass percentage of the Sn-In coating layer was calculated using the weight gain method to be 7.1%.

[0072] Example 6

[0073] The rest is the same as in Example 1, except that in step (3), the molar ratio of SnF4 to InCl3 is 1:0.5.

[0074] (1) Same as Example 1;

[0075] (2) Same as Example 1;

[0076] (3) Dissolve 1.28 g (6.6 mmol) of tin fluoride (SnF4) and 0.73 g (3.3 mmol) of indium chloride (InCl3) in 250 mL of pure water, then add 0.75 g of dihydrodiamine and add pure water to make up to 300 mL to form a mixed solution. Then immerse 10 g of surface-modified silicon-carbon composite material in the above 300 mL mixed solution (i.e., the total mass of surface-modified silicon-carbon composite material, SnF4 and InCl3 and the mass ratio of dihydrodiamine are 100:20:7.5), stir at 400 rpm for 8 h, and simultaneously perform ultrasonic treatment at 15 kHz. After the immersion is completed, centrifuge the solid and wash it with ethanol and pure water alternately for a total of 4 times. Then vacuum dry at 80 °C for 24 h to obtain silicon-carbon composite material with coating layer.

[0077] (4) Same as in Example 1.

[0078] The mass percentage of the Sn-In coating layer was calculated using the weight gain method to be 4.6%.

[0079] Example 7

[0080] The rest is the same as in Example 1, except that in step (3), the molar ratio of SnF4 to InCl3 is 1:0.8, specifically:

[0081] (1) Same as Example 1;

[0082] (2) Same as Example 1;

[0083] (3) Dissolve 1.05 g (5.4 mmol) of tin fluoride (SnF4) and 0.95 g (4.3 mmol) of indium chloride (InCl3) in 250 mL of pure water, then add 0.75 g of dihydrodiamine and add pure water to make up to 300 mL to form a mixed solution. Then immerse 10 g of surface-modified silicon-carbon composite material in the above 300 mL mixed solution (i.e., the total mass of surface-modified silicon-carbon composite material, SnF4 and InCl3 and the mass ratio of dihydrodiamine are 100:20:7.5), stir at 400 rpm for 8 h, and simultaneously perform ultrasonic treatment at 15 kHz. After the immersion is completed, centrifuge the solid and wash it with ethanol and pure water alternately for a total of 4 times. Then vacuum dry at 80 °C for 24 h to obtain silicon-carbon composite material with coating layer.

[0084] (4) Same as in Example 1.

[0085] The mass percentage of the Sn-In coating layer was calculated using the weight gain method to be 4.6%.

[0086] Example 8

[0087] The rest is the same as in Example 1, except that in step (3), the molar ratio of SnF4 to InCl3 is 1:1.2.

[0088] (1) Same as Example 1;

[0089] (2) Same as Example 1;

[0090] (3) Dissolve 0.85g (4.4mmol) tin fluoride (SnF4) and 1.15g (5.2mmol) indium chloride (InCl3) in 250mL of pure water, then add 0.75g dihydrodiamine and add pure water to make up to 300mL to form a mixed solution. Then immerse 10g of surface-modified silicon-carbon composite material in the above 300mL mixed solution (i.e., the total mass of surface-modified silicon-carbon composite material, SnF4 and InCl3 and the mass ratio of dihydrodiamine are 100:20:7.5), stir at 400 rpm for 8h, and simultaneously perform ultrasonic treatment at 15kHz. After the immersion is completed, centrifuge and wash the separated solid with ethanol and pure water alternately for a total of 4 times. Then vacuum dry at 80℃ for 24h to obtain silicon-carbon composite material with coating layer.

[0091] (4) Same as in Example 1.

[0092] The mass percentage of the Sn-In coating layer was calculated using the weight gain method to be 4.5%.

[0093] Example 9

[0094] The rest is the same as in Example 1, except that in step (3), the molar ratio of SnF4 to InCl3 is 1:1.5.

[0095] (1) Same as Example 1;

[0096] (2) Same as Example 1;

[0097] (3) Dissolve 0.74 g (3.8 mmol) of tin fluoride (SnF4) and 1.26 g (5.7 mmol) of indium chloride (InCl3) in 250 mL of pure water, then add 0.75 g of dihydrodiamine and add pure water to make up to 300 mL to form a mixed solution. Then immerse 10 g of surface-modified silicon-carbon composite material in the above 300 mL mixed solution (i.e., the total mass of surface-modified silicon-carbon composite material, SnF4 and InCl3 and the mass ratio of dihydrodiamine are 100:20:7.5), stir at 400 rpm for 8 h, and simultaneously perform ultrasonic treatment at 15 kHz. After the immersion is completed, centrifuge the solid and wash it with ethanol and pure water alternately for a total of 4 times. Then vacuum dry at 80 °C for 24 h to obtain silicon-carbon composite material with coating layer.

[0098] (4) Same as in Example 1.

[0099] The mass percentage of the Sn-In coating layer was calculated using the weight gain method to be 4.5%.

[0100] Example 10

[0101] The rest is the same as in Example 1, except that: the impregnation conditions in step (2) are different; in step (3), equimolar amounts of tin chloride (SnCl4) are used to replace SnF4, equimolar amounts of bismuth chloride (BiCl3) are used to replace InCl3, and equimolar amounts of dihydrodiamine are used, and the impregnation conditions are different; the heat treatment conditions in step (4) are different; specifically:

[0102] (1) Same as Example 1;

[0103] (2) 20g of silicon-carbon composite material was dispersed in an aqueous solution of sodium dodecyl sulfate (SDS) with a concentration of 1500mL (0.8wt%), stirred at 300rpm at 25℃ for 4h, and then centrifuged, washed twice with pure water, and vacuum dried at 80℃ for 24h to obtain surface-modified silicon-carbon composite material.

[0104] (3) Dissolve 0.75g (4.0mmol) stannous chloride (SnCl2) and 1.25g (4.0mmol) bismuth chloride (BiCl3) together in 250mL of pure water, then add 0.75g urea and add pure water to make up to 300mL to form a mixed solution. Then immerse 10g of surface-modified silicon-carbon composite material in the above 300mL mixed solution (i.e., the mass ratio of surface-modified silicon-carbon composite material, SnCl2 and BiCl3 and urea is 100:20:7.5), stir at 400 rpm for 10h, and simultaneously perform ultrasonic treatment at 15kHz. After the immersion is completed, centrifuge and wash the separated solid with ethanol and pure water alternately for a total of 4 times. Then vacuum dry at 80℃ for 24h to obtain silicon-carbon composite material with coating layer.

[0105] (4) The silicon-carbon composite material with the coating layer is placed in a ceramic boat and then placed in a tube furnace. It is kept at 800°C for 8 hours under a nitrogen atmosphere. After the heat treatment is completed, it is naturally cooled to room temperature with the furnace to obtain the silicon-carbon anode material with a bimetallic coating layer, namely the silicon-carbon anode material with a Sn-Bi coating layer.

[0106] The mass percentage of the Sn-Bi coating layer was calculated to be 4.6% using the weight gain method.

[0107] Comparative Example 1

[0108] The rest is the same as in Example 1, except that in step (3), the molar ratio of SnF4 to InCl3 is 1:0.2, specifically:

[0109] (1) Same as Example 1;

[0110] (2) Same as Example 1;

[0111] (3) Dissolve 1.62 g (8.3 mmol) of tin fluoride (SnF4) and 0.38 g (1.7 mmol) of indium chloride (InCl3) in 250 mL of pure water, then add 0.75 g of dihydrodiamine and add pure water to make up to 300 mL to form a mixed solution. Then immerse 10 g of surface-modified silicon-carbon composite material in the above 300 mL mixed solution (i.e., the total mass of surface-modified silicon-carbon composite material, SnF4 and InCl3 and the mass ratio of dihydrodiamine are 100:20:7.5), stir at 400 rpm for 8 h, and simultaneously perform ultrasonic treatment at 15 kHz. After the immersion is completed, centrifuge the solid and wash it with ethanol and pure water alternately for a total of 4 times. Then vacuum dry at 80 °C for 24 h to obtain silicon-carbon composite material with coating layer.

[0112] (4) Same as in Example 1.

[0113] The mass percentage of the Sn-In coating layer was calculated using the weight gain method to be 4.5%.

[0114] Comparative Example 2

[0115] The rest is the same as in Example 1, except that in step (3), the molar ratio of SnF4 to InCl3 is 1:2, specifically:

[0116] (1) Same as Example 1;

[0117] (2) Same as Example 1;

[0118] (3) Dissolve 0.61 g (3.1 mmol) of tin fluoride (SnF4) and 1.39 g (6.2 mmol) of indium chloride (InCl3) in 250 mL of pure water, then add 0.75 g of dihydrodiamine and add pure water to make up to 300 mL to form a mixed solution. Then immerse 10 g of surface-modified silicon-carbon composite material in the above 300 mL mixed solution (i.e., the total mass of surface-modified silicon-carbon composite material, SnF4 and InCl3 and the mass ratio of dihydrodiamine are 100:20:7.5), stir at 400 rpm for 8 h, and simultaneously perform ultrasonic treatment at 15 kHz. After the immersion is completed, centrifuge the solid and wash it with ethanol and pure water alternately for a total of 4 times. Then vacuum dry at 80 °C for 24 h to obtain silicon-carbon composite material with coating layer.

[0119] (4) Same as in Example 1.

[0120] The mass percentage of the Sn-In coating layer was calculated using the weight gain method to be 4.5%.

[0121] Comparative Example 3

[0122] The rest is the same as in Example 1, except that in step (3), the total mass ratio of the surface-modified silicon-carbon composite material, SnF4 and InCl3, and dihydrodiamine is 100:5:3; specifically:

[0123] (1) Same as Example 1;

[0124] (2) Same as Example 1;

[0125] (3) Dissolve 0.23 g (1.2 mmol) of tin fluoride (SnF4) and 0.27 g (1.2 mmol) of indium chloride (InCl3) in 250 mL of pure water, then add 0.30 g of dihydrodiamine and add pure water to make up to 300 mL to form a mixed solution. Then immerse 10 g of surface-modified silicon-carbon composite material in the above 300 mL mixed solution (i.e., the total mass of surface-modified silicon-carbon composite material, SnF4 and InCl3 and the mass ratio of dihydrodiamine are 100:5:3), stir at 400 rpm for 8 h, and simultaneously perform ultrasonic treatment at 15 kHz. After the immersion is completed, centrifuge the solid and wash it with ethanol and pure water alternately for a total of 4 times. Then vacuum dry at 80 °C for 24 h to obtain silicon-carbon composite material with coating layer.

[0126] (4) Same as in Example 1.

[0127] The mass percentage of the Sn-In coating layer was calculated using the weight gain method to be 1.2%.

[0128] Comparative Example 4

[0129] The rest is the same as in Example 1, except that in step (3), the total mass ratio of the surface-modified silicon-carbon composite material, SnF4 and InCl3, and dihydrodiamine is 100:40:15; specifically:

[0130] (1) Same as Example 1;

[0131] (2) Same as Example 1;

[0132] (3) Dissolve 1.87 g (9.6 mmol) of tin fluoride (SnF4) and 2.13 g (9.6 mmol) of indium chloride (InCl3) in 250 mL of pure water, then add 1.50 g of dihydrodiamine and add pure water to make up to 300 mL to form a mixed solution. Then immerse 10 g of surface-modified silicon-carbon composite material in the above 300 mL mixed solution (i.e., the total mass of surface-modified silicon-carbon composite material, SnF4 and InCl3 and the mass ratio of dihydrodiamine are 100:40:15), stir at 400 rpm for 10 h, and simultaneously perform ultrasonic treatment at 20 kHz. After the immersion is completed, centrifuge the solid and wash it with ethanol and pure water alternately for a total of 4 times. Then vacuum dry at 80 °C for 24 h to obtain silicon-carbon composite material with coating layer.

[0133] (4) Same as in Example 1.

[0134] The mass percentage of the Sn-In coating layer was calculated using the weight gain method to be 9.1%.

[0135] Applications and Testing

[0136] The silicon-carbon anode materials prepared in the above embodiments and comparative examples were used as anode active materials, and all-solid-state batteries were assembled according to the following method: The prepared silicon-carbon anode materials, vapor-grown carbon fibers (VGCF) and sulfide solid electrolyte (LPSC) were thoroughly ground and mixed in a mortar at a mass ratio of 65:5:30. The mixed powder was then pressed into anode sheets. The half-cell used lithium indium alloy as the counter electrode, and the all-solid-state battery used NCM811 as the positive electrode and lithium phosphorus sulfur chloride (LPSC) as the solid electrolyte. The solid-state batteries were assembled in an argon atmosphere in a Braun inert gas glove box in Germany.

[0137] The assembled batteries were subjected to performance tests at 25°C, with a charge / discharge voltage window of 0.05-1.5 V.

[0138] 1) Morphological analysis

[0139] Morphology analysis: The SEM image of the silicon-carbon anode material with Sn-In coating obtained in Example 1 is shown below. Figure 1 As shown, the material surface is uniformly coated with spherical nanoparticles, indicating that the surface coating of bimetal has been successfully achieved.

[0140] 2) Electrochemical performance testing

[0141] Conductivity testing: DC polarization IV tests were performed using a PARSTAT VersaSTAT instrument within a voltage range of 10mV to 50mV. 100 mg of the anode powder was pressed into a sheet under a pressure of 300 MPa, and the testing process was conducted under a constant pressure of 100 MPa. The electronic conductivity curves of the silicon-carbon anode materials prepared in Example 1 and Comparative Example 1 are shown below. Figure 2 As shown in the figure, the electronic conductivity of Example 1 is much higher than that of Comparative Example 1. The test results of the electronic conductivity of the other examples and comparative examples are shown in Table 1.

[0142] First-cycle performance: The first-cycle charge-discharge curves of the silicon-carbon anode materials prepared in Example 1 and Comparative Example 1 at a rate of 0.1C are shown in the figure below. Figure 3 As shown in the figure, the initial discharge specific capacity and initial coulombic efficiency of Example 1 are much higher than those of Comparative Example 1. The initial discharge specific capacity and initial coulombic efficiency of each example and comparative example are shown in Table 1.

[0143] Cycle performance and rate performance: The rate performance graphs of the silicon-carbon anode materials prepared in Example 1 and Comparative Example 1 are shown in the figure. Figure 4 As shown in the figure, its discharge specific capacity at a high rate of 2C is significantly higher than that of Comparative Example 1. The cycle performance curves of the silicon-carbon anode materials prepared in Example 1 and Comparative Example 1 at 0.5C are shown in the figure. Figure 5As shown in Table 1, the specific capacity at 0.2C, the specific capacity at 2C, and the capacity retention rate after 100 cycles at a 0.5C rate for each embodiment and comparative example are detailed in Table 1.

[0144] Table 1 Performance Tests

[0145]

[0146] As shown in Table 1, the electronic conductivity of the silicon-carbon anode material with a bimetallic coating prepared in the embodiments of the present invention is significantly improved. The assembled all-solid-state battery exhibits an initial coulombic efficiency of over 82% and a high specific capacity, especially exceeding 550 mAh / g at 2C high rate, while also demonstrating outstanding long-term cycle stability. In Comparative Examples 1 and 2, the molar ratio of the bimetallic coating is outside the scope of the present invention, and the synergistic effect of the bimetallic coating cannot be effectively utilized. Effective graded lithiation is not possible during charge and discharge, especially since cycle stability and capacity at high rates cannot be simultaneously achieved. Comparative Example 3 has an excessively low coating amount, resulting in poor conductivity and cycle performance. Comparative Example 4 has an excessively high coating amount, leading to a significant decrease in specific capacity.

[0147] In summary, the embodiments of the present invention achieve graded lithiation effect and synergistic effect with non-metal doping through a specific ratio of specific metal combinations (Sn-In, Sn-Bi), enabling the silicon-carbon anode material with a bimetallic coating to exhibit excellent kinetic performance and cycle stability when used in all-solid-state batteries.

Claims

1. A method for preparing a silicon-carbon anode material with a bimetallic coating for all-solid-state batteries, characterized in that, Includes the following steps: (1) Porous carbon is subjected to silicon deposition and carbon coating treatment in sequence to obtain silicon-carbon composite material; (2) The silicon-carbon composite material was dispersed in an aqueous solution of anionic surfactant and impregnated. After solid-liquid separation, solid washing and drying, the surface-modified silicon-carbon composite material was obtained. (3) Dissolve tin salt and second metal salt together in water at a molar ratio of 1:0.5~1.

5. The second metal salt is indium salt or bismuth salt. Then add nitrogen-containing organic reducing agent to form a mixed solution. Then immerse the surface-modified silicon-carbon composite material in the mixed solution. The mass ratio of the surface-modified silicon-carbon composite material, the total mass of tin salt and second metal salt and the mass of nitrogen-containing organic reducing agent is 100:(10~30):(5~10). After immersion, separate solid and liquid, wash the solid and dry to obtain silicon-carbon composite material with coating layer. (4) The silicon-carbon composite material with the coating layer is heat-treated under an inert atmosphere to obtain a silicon-carbon anode material with a bimetallic coating layer.

2. The preparation method according to claim 1, characterized in that, In step (1), porous carbon is obtained by activating and pore-forming a porous carbon precursor; the median particle size D50 of the porous carbon precursor is 5~10 μm, and it can be selected from resin carbon or biomass carbon; the activation reagent is at least one of water vapor and carbon dioxide; the activation conditions are: holding at 800~950℃ for 8~12h; by controlling the activation conditions, the specific surface area of ​​the porous carbon is made to be 1700~2300 m². 2 / g, pore volume 0.9~1.2cm 3 / g.

3. The preparation method according to claim 1, characterized in that, The silicon content in the silicon-carbon composite material in step (1) is 40~60wt%, preferably 48~55wt%, and the carbon coating layer accounts for 0.8~2wt% of the silicon-carbon composite material, preferably 1.2~2wt%.

4. The preparation method according to claim 1, characterized in that, In step (2), the anionic surfactant is selected from at least one of sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS); the mass ratio of the silicon-carbon composite material to the aqueous solution of the anionic surfactant is 10g:500~1000mL, and the concentration of the aqueous solution of the anionic surfactant is 0.5~1.5wt%; the impregnation conditions are: stirring at 200~400rpm and 20~40℃ for 2~6h; and / or, In step (2), the washing is a pure water wash 2 to 4 times; the drying is a vacuum drying at 60 to 80°C for 12 to 24 hours.

5. The preparation method according to claim 1, characterized in that, In step (3), the molar ratio of the tin salt to the second metal salt is 1:0.8~1.

2.

6. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of the surface-modified silicon-carbon composite material, the total mass of the tin salt and the second metal salt, and the mass of the nitrogen-containing organic reducing agent is 100:(20~25):(7.5~10).

7. The preparation method according to claim 1, characterized in that, In step (3), the tin salt is selected from at least one of tin chloride (SnCl4), tin fluoride (SnF4), tin sulfate (Sn(SO4)2), stannous chloride (SnCl2), stannous sulfate (SnSO4), stannous nitrate Sn(NO3)2, and their hydrates; the indium salt is selected from at least one of indium chloride (InCl3), indium chloride (InBr3), indium iodide (InI3), and their hydrates; the bismuth salt is selected from at least one of bismuth chloride (BiCl3), bismuth bromide (BiBr3), and their hydrates; and the nitrogen-containing organic reducing agent is selected from at least one of dihydrodiamine and urea, preferably dihydrodiamine.

8. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of the surface-modified silicon-carbon composite material to the volume ratio of the mixed solution is 1g:30~50mL; the impregnation conditions are: stirring at 300~500 rpm / min for 6~10h, and simultaneously subjected to ultrasonic treatment at 10~20kHz. In step (3), the washing is performed by alternating between ethanol and pure water, for a total of 2 to 4 times; the drying is performed by vacuum drying at 60 to 80°C for 12 to 24 hours.

9. The preparation method according to claim 1, characterized in that, In step (4), the inert atmosphere is nitrogen and / or argon; the heat treatment conditions are: 800~950℃ for 6~8h.

10. A silicon-carbon anode material with a bimetallic coating for use in all-solid-state batteries, prepared by the method according to any one of claims 1-8, characterized in that, The bimetallic coating has a mass percentage of 2-8%, preferably 4-6%.

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