Three-dimensional porous silicon-carbon composite negative electrode material and preparation method thereof

Abstract

According to the three-dimensional silicon-carbon composite negative electrode material and the preparation method thereof provided by the invention, the carbon material with a graphitized structure and a three-dimensional porous structure is firstly synthesized, then nano silicon and the carbon material with the three-dimensional porous structure are directly used for in-situ compounding, and then the surface is coated with a layer of carbon material, so that the three-dimensional silicon-carbon composite negative electrode material is obtained. And the possibility that the silicon-carbon composite material reacts with air or water in the storage process is reduced. According to the three-dimensional porous carbon material with the graphitized structure, the conductivity of macroporous carbon is improved due to graphitization, and meanwhile, the three-dimensional porous structure provides a space for expansion and contraction of a silicon material in the charging and discharging process, so that the invalidation of a negative electrode material and the reduction of the bonding force of a current collector caused by the volume change of silicon are avoided. The particle size of the three-dimensional porous structure silicon-carbon composite material is in a micron level, meanwhile, the compaction density of the material is guaranteed, and the space for industrial application of the material is enlarged.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a silicon-carbon anode material for lithium-ion batteries and a preparation method thereof. Background Art

[0002] Currently, the anode material of commercial lithium-ion batteries is usually graphite. Graphite materials have a low lithium intercalation potential, good cycle life, and a small expansion coefficient. However, the theoretical capacity of graphite is 372 mAh / g, and for high energy density, the specific capacity of graphite is relatively low. The theoretical capacity of silicon anode material can reach 4200 mAh / g, which is considered to be a preferred anode material for high energy density batteries. However, the volume change of silicon material during charge and discharge can reach 300%, which also leads to pulverization and fragmentation of silicon particles, seriously affecting the cycle performance of the material. At the same time, the pulverization and fragmentation of the material also reduce the adhesion between the silicon material and the foil, resulting in a decrease in adhesion. Another major problem of silicon material is its low electronic conductivity and large internal resistance of the battery, which affects its application.

[0003] In order to suppress the volume change of silicon during charge and discharge, CN 111755684 A reduces the absolute volume expansion of silicon and improves the kinetics of nanosilicon in the anode material by nanosizing silicon powder and then coating it with a gaseous carbon source. CN 115954481 A designs a silicon-carbon composite material with a multi-level buffer structure to solve the problems existing in the silicon anode material itself, such as volume expansion, poor conductivity, and unstable interface. In the above solutions, the silicon source is mechanically crushed nanosilicon, with a low tap density, and the direct contact between nanosilicon and the current collector leads to a decrease in adhesion. In order to effectively suppress the volume expansion of silicon and improve its surface electronic conductivity, the present invention deposits nanosilicon on the designed three-dimensional porous surface by a deposition technique and performs surface coating. The designed three-dimensional multi-layer pore structure silicon-carbon composite material can effectively suppress expansion and at the same time has good electronic conductivity. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of a silicon-carbon anode material with three-dimensional pores, and the method includes the following steps:

[0005] S1: Prepare a salt solution of nickel or iron or cobalt;

[0006] S2: Take a superabsorbent polymer (SAP), and add the superabsorbent polymer to the salt solution in S1;

[0007] S3: Dry the resin obtained in S2 to obtain a mixture of SAP and salt,

[0008] S4: Carry out high-temperature carbonization on the mixture of the resin and salt obtained in step S3 under an inert atmosphere to obtain a mixture of carbon material and salt;

[0009] S5: Wash the material in step S4 with an acid to obtain three-dimensional porous carbon;

[0010] S6: Introduce silane gas into a reactor containing the three-dimensional porous carbon material in step S5 for thermal decomposition to form nano-silicon, obtaining a semi-finished three-dimensional porous silicon-carbon anode material;

[0011] S7: Introduce a hydrocarbon gas into the semi-finished three-dimensional porous silicon-carbon anode material obtained in step S6 for carbon coating to obtain a carbon-coated finished product.

[0012] In the present invention, the salt solution in step S1 is one or a mixture of nickel sulfate solution, nickel nitrate solution, iron sulfate solution, iron chloride solution, cobalt sulfate solution, and cobalt nitrate solution; the mass fraction of the salt solution is 5%-30%, preferably 10%-20%.

[0013] In the present invention, the superabsorbent polymer in step S2 is selected from sodium polyacrylate, potassium polyacrylate, and their derivatives. The mass ratio of the superabsorbent polymer to the salt solution is 1:(5 - 30). Preferably, the superabsorbent polymer is added to the stirred salt solution, and the preferred stirring methods are magnetic stirring and mechanical stirring. In this step, due to the high water absorption of SAP, the salt solution is evenly absorbed into the highly water-absorbent resin.

[0014] In the present invention, the drying method in step S3 adopts forced-air drying or freeze-drying. The temperature of forced-air drying is 60 - 90°C, and the drying time is 5 - 24 h; the temperature of freeze-drying is -20 - 40°C, and the drying time is 12 - 48 h; after drying, the salt is evenly adsorbed on the surface of the resin.

[0015] In the present invention, the inert atmosphere in step S4 is selected from nitrogen, argon, and helium; the carbonization temperature is 800°C - 1500°C, and the time is 1 h - 10 h, preferably 2 - 6 h; in step S4, due to the catalytic oxidation activity of the salt itself after high-temperature carbonization, graphite-like structures will be formed in the process of carbonization of SAP, thereby obtaining an amorphous and graphite-like carbon structure.

[0016] In the present invention, the acid in step S5 is hydrochloric acid, sulfuric acid, or nitric acid, preferably hydrochloric acid. The washing is preferably carried out with the assistance of magnetic stirring. After washing, the residual salt is washed out to obtain a pure carbon material. In step S5, due to the activation of sodium or potassium in SAP, a carbon material with a three-dimensional porous structure is formed.

[0017] In the present invention, the pore diameter of the three-dimensional porous carbon in step S5 is 2 - 10 7 nm; the specific surface area of the three-dimensional porous carbon is 1000 m 2 / g - 4000 m2 / g, preferably, the specific surface area of the three-dimensional porous carbon can be 1000 m 2 / g, 1500 m 2 / g, 2000 m 2 / g, 2500 m 2 / g, 3000 m 2 / g.

[0018] In the present invention, in the step S6, the silane gas is selected from at least one of silane, disilane, trichlorosilane, and dichlorosilane; the flow rate of the silane gas introduced is 0.2 - 3 L / min; the temperature of thermal decomposition is 400 - 700 °C, and the time of thermal decomposition is 10 - 60 min; the particle size of the nano-silicon is 0.5 nm - 20 nm. In the step S6, the nano-silicon and the three-dimensional porous carbon are in-situ compounded to form a semi-finished product of the three-dimensional porous silicon-carbon anode material. The mass ratio of the silicon element in the three-dimensional porous silicon-carbon anode material is 10 wt.% - 70 wt.%. The mass ratio of the three-dimensional porous carbon is 28.8 wt.% - 80 wt.%.

[0019] In the present invention, in the step S6, the hydrocarbon gas is selected from at least one of methane, ethane, propane, butane, ethylene, propylene, and acetylene; the flow rate of the introduced gas is 0.5 - 3 L / min, the temperature of carbon coating is 500 - 800 °C, the coating time is 0.5 - 4 h, and the thickness of the coating layer is 0.5 nm - 25 nm.

[0020] On the other hand, the present invention provides a three-dimensional porous silicon-carbon composite anode material prepared by the above method;

[0021] The mass ratio of the coating layer material in the three-dimensional porous silicon-carbon anode material is 0.2 wt.% - 10 wt.%.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects:

[0023] The preparation method of the three-dimensional silicon-carbon composite anode material provided by the present invention first synthesizes a carbon material with a three-dimensional porous structure, then directly uses nano-silicon and the three-dimensional porous structure carbon material for in-situ compounding, and then coats a layer of carbon material on the surface to reduce the possibility of the silicon-carbon composite material reacting with air or water during storage. The three-dimensional porous carbon material with a graphitized structure improves the conductivity of the macroporous carbon due to graphitization. At the same time, its three-dimensional porous structure provides space for the expansion and contraction of the silicon material during charge and discharge, avoiding the failure of the anode material and the reduction of the adhesion force of the current collector caused by the volume change of silicon. The particle size of the three-dimensional porous silicon-carbon composite material is in the micron level, while ensuring the tap density of the material, improving the space for industrial application of the material. Detailed Embodiments

[0024] The technical scheme of the present invention and its effects are further described below by specific examples. The following examples are only used to illustrate the content of the present invention and are not used to limit the protection scope of the present invention. Simple changes made to the present invention by applying the concept of the present invention are all within the scope of the protection claimed by the present invention.

[0025] The devices and sources of raw materials used in the following examples and comparative examples are as follows:

[0026] Sodium polyacrylate resin, analytical grade, manufactured by Hangzhou Jutao Biotechnology Co., Ltd.;

[0027] Nickel sulfate, chemically pure, Aladdin;

[0028] Ferrous sulfate, chemically pure, Aladdin;

[0029] Hydrochloric acid, 36%, Yantai Sanhe Chemical Reagent Co., Ltd.;

[0030] Conductive carbon black, model: Superp, purity>99wt%, manufacturer: Yiruishi Graphite and Carbon;

[0031] Copper foil: Model BFR-1, thickness 8μm, copper purity> 99.8wt%, manufacturer is Taiwan Changchun Group;

[0032] Polyacrylate, model 1720, manufacturer Wanhua Chemical Group Co., Ltd.;

[0033] High-purity silane gas, purity 99.99%, the manufacturer is Zhongning Silicon Industry;

[0034] Acetylene gas, purity 99.9%, manufactured by Yantai Mingju;

[0035] Lithium metal sheets, high purity, manufactured by Shanghai Zhongli Industrial Co., Ltd.

[0036] Electrolyte, battery grade, manufactured by Sinochem Blue Sky;

[0037] Example 1

[0038] The present invention provides a method for preparing a three-dimensional porous silicon-carbon negative electrode material. The method comprises the following steps:

[0039] 1. Add 50 g of sodium polyacrylate resin to 500 g of 10% nickel sulfate hexahydrate solution under magnetic stirring to form a resin mixture after water absorption.

[0040] 2. The resin in step 1 is dried by forced air at 85° C. for 24 hours to obtain a mixture of sodium polyacrylate resin and nickel sulfate hexahydrate, wherein the nickel sulfate hexahydrate is uniformly adsorbed on the surface of the resin.

[0041] 3. Under a nitrogen atmosphere, heat the mixture of the resin and salt obtained in Step 2 above to 950 °C for 3 h of high-temperature carbonization to obtain a mixture of carbon material and salt.

[0042] 4. Magnetically stir the material in Step 3 above in 1 mol / L hydrochloric acid for 48 h, wash, centrifuge, and then dry in an oven at 85 °C for 24 h to form a carbon material with a three-dimensional porous structure.

[0043] 5. Take the carbon material (10.0 g) with a three-dimensional porous structure obtained in Step 4 and place it in a tube furnace. Under a nitrogen atmosphere, heat it to 450 °C, and then introduce silane gas into the chemical vapor deposition furnace at a rate of 0.5 L / min for silicon deposition and in-situ composite with the porous carbon, and maintain for 20 min; then introduce nitrogen again for 15 min to remove silane gas, and then introduce acetylene for chemical vapor deposition, and raise the furnace temperature to 550 °C for carbon coating on the sample surface, with a flow rate of 0.5 L / min and a deposition time of 1 h; finally, switch to nitrogen and cool the tube furnace to room temperature to obtain a three-dimensional porous silicon-carbon anode material.

[0044] Example 2

[0045] The difference between this example and Example 1 is that the mass fraction of nickel sulfate hexahydrate is 20%, and the carbonization temperature in Step 3 is 1100 °C. The remaining raw materials and methods are the same as those in Example 1.

[0046] Example 3

[0047] The difference between this example and Example 1 is that nickel sulfate is changed to iron sulfate solution, the carbonization temperature in Step 3 is 1000 °C, and the carbonization time is 2 h. The remaining raw materials and methods are the same as those in Example 1.

[0048] Example 4

[0049] The difference between this example and Example 1 is that the mass of the nickel sulfate solution added is 750 g, and the silane deposition temperature in Step 5 is 500 °C, and the gas flow rate is 1 L / min. The remaining raw materials and methods are the same as those in Example 1.

[0050] Example 5

[0051] The difference between this example and Example 1 is that the silane deposition temperature in Step 5 is 500 °C, acetylene is used for chemical vapor deposition, and the furnace temperature is raised to 600 °C for carbon coating on the sample surface. The remaining raw materials and methods are the same as those in Example 1.

[0052] Example 6

[0053] The difference between this example and Example 1 is that in step 5, the flow rate of silane deposition is 1.5 L / min, the deposition time is 25 min, and the furnace temperature is raised to 600 °C to perform carbon coating on the sample surface for 1.5 h. The remaining raw materials and methods are the same as those in Example 1.

[0054] Comparative Example 1

[0055] The difference between this example and Example 1 is that the salt solution is changed to use pure water. The remaining raw materials and methods are the same as those in Example 1.

[0056] Comparative Example 2

[0057] The difference between this example and Example 1 is that step 5 deposition is not carried out. The remaining raw materials and methods are the same as those in Example 1.

[0058] Comparative Example 3

[0059] 50 g of sodium polyacrylate resin solid and 50 g of nickel sulfate hexahydrate are put into a stirrer for solid mixing to form a mixture of resin and salt. The difference between this comparative example and the example is that sodium polyacrylate resin and salt are blended as materials.

[0060] Test Example 1

[0061] The silicon-carbon composite materials provided in Examples 1-6 and the materials provided in Comparative Examples 1-3 are assembled into batteries. The steps are as follows:

[0062] 1. Electrode preparation: The negative electrode material, conductive agent (Super-P), and polyacrylic acid (PAA1720) binder are mixed in a mass ratio of 70:20:10 to prepare a slurry. After stirring and mixing evenly, it is coated on a copper foil current collector. After drying at room temperature, it is placed in a vacuum oven and further dried at 85 °C under vacuum conditions for 12 h to obtain the electrode.

[0063] 2. Battery assembly: The obtained electrode is cut into circular electrodes with a diameter of 14 mm, and the active material loading is 3.5.0 mg / cm 2 ; A lithium metal sheet is used as the counter electrode, 1 mol / L LiPF6 (the solvent is a mixed solution of ethylene carbonate and diethyl carbonate with a volume ratio of 1:1, adding 5% by volume of fluoroethylene carbonate) is used as the electrolyte, and a polypropylene microporous separator is used to assemble a 2032-type button battery in a glove box under an argon atmosphere. 60 μL of electrolyte is added to each battery. The obtained 2032-type button batteries are subjected to electrical performance tests: the charging cut-off voltage is 1.5 V, and the discharging cut-off voltage is 0.005 V. Then, activation is carried out under a 0.1C rate condition and charge-discharge cycle tests are carried out under a 0.5C rate condition. The obtained data are shown in Table 1 below.

[0064] Table 1 Electrochemical performance results of different materials

[0065] Sample Initial efficiency Capacity retention rate after 100 cycles Example 1 83.5％ 78.5％ Example 2 84.8％ 79.6％ Example 3 83.2％ 76.8％ Example 4 84.6％ 80.1％ Example 5 83.4％ 79.5％ Example 6 83.8％ 82.1％ Comparative example 1 81.3％ 68.6％ Comparative example 2 80.2％ 54.2％ Comparative example 3 79.5 50.3％

Claims

1. A preparation method of a three-dimensional porous silicon-carbon negative electrode material, the method comprising the following steps: S1: Prepare a salt solution of nickel, iron or cobalt; S2: Take a superabsorbent polymer (SAP), and add the superabsorbent polymer to the salt solution in S1; S3: Dry the resin obtained in S2 to obtain a mixture of SAP and salt; S4: Carry out high-temperature carbonization on the mixture of the resin and salt obtained in step S3 under an inert atmosphere to obtain a mixture of carbon material and salt; S5: Wash the material in S4 above with an acid to obtain three-dimensional porous carbon; S6: Pass silane gas into a reactor containing the three-dimensional porous carbon material in S5 above for thermal decomposition to form nano-silicon to obtain a semi-finished three-dimensional porous silicon-carbon anode material; S7: Pass the hydrocarbon gas into the semi-finished three-dimensional porous silicon-carbon anode material obtained in step S6 for carbon coating to obtain a carbon-coated finished product.

2. The preparation method according to claim 1, characterized in that, The salt solution in step S1 is one or a mixed solution of more of nickel sulfate solution, nickel nitrate solution, iron sulfate solution, iron chloride solution, cobalt sulfate solution, cobalt nitrate solution; the mass fraction of the salt solution is 5%-30%, preferably 10%-20%.

3. The preparation method according to claim 1 or 2, characterized in that, The superabsorbent polymer in step S2 is selected from sodium polyacrylate, potassium polyacrylate and their derivatives, and the mass ratio of the superabsorbent polymer to the salt solution is 1:(5-30).

4. The preparation method according to any one of claims 1-3, characterized in that, The drying method in step S3 adopts forced-air drying or freeze-drying. The temperature of forced-air drying is 60-90°C, and the drying time is 5-24h; the freeze-drying temperature is -20-40°C, and the drying time is 12-48h.

5. The preparation method according to any one of claims 1-4, characterized in that, The inert atmosphere in step S4 is selected from nitrogen, argon and helium; the carbonization temperature is 800°C-1500°C, and the time is 1h-10h, preferably 2-6h.

6. The preparation method according to any one of claims 1-5, characterized in that, The acid in step S5 is hydrochloric acid, sulfuric acid or nitric acid, preferably hydrochloric acid.

7. The preparation method according to any one of claims 1-6, characterized in that, The pore size of the three-dimensional porous carbon in the step S5 is 2-10 7 nm; the specific surface area of the three-dimensional porous carbon is 1000 m 2 / g - 4000 m 2 / g.

8. The preparation method according to any one of claims 1-7, characterized in that, The silane gas in step S6 is selected from at least one of silane, disilane, trichlorosilane and dichlorosilane; preferably, the flow rate of the silane gas passed in is 0.2-3L / min; the thermal decomposition temperature is 400-700°C, and the thermal decomposition time is 10-60min; the particle size of the nano-silicon is 0.5nm-20nm; and / or, the mass fraction of silicon element in the three-dimensional porous silicon-carbon anode material is 10wt.% - 70wt.%. The mass fraction of the three-dimensional porous carbon is 28.8wt.% - 80wt.%.

9. The preparation method according to any one of claims 1-8, characterized in that, The hydrocarbon gas in step S6 is selected from at least one of methane, ethane, propane, butane, ethylene, propylene and acetylene; and / or, the flow rate of the hydrocarbon gas passed in is 0.5-3L / min, the carbon coating temperature is 500-800°C, the coating time is 0.5-4h, and the coating layer thickness is 0.5nm-25nm.

10. A three-dimensional porous silicon-carbon composite negative electrode material prepared by the preparation method according to any one of claims 1-9; the mass ratio of the coating material in the three-dimensional porous silicon-carbon negative electrode material is 0.2 wt.% - 10 wt.%.