Silicon-based negative electrode material capable of synchronously realizing lithiation-carbon deposition and preparation method of silicon-based negative electrode material

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a silicon-based negative electrode material capable of synchronously realizing lithiation-carbon deposition and a preparation method of the silicon-based negative electrode material. Silicon dioxide is uniformly dispersed in a dimethylformamide aqueous solution, then Li-MOF grows on the surface of silicon dioxide through in-situ polymerization of lithium nitrate, pyromellitic acid and polyvinylpyrrolidone, silicon dioxide coating and synchronous introduction of the lithium element are achieved, the silicon and carbon compounding uniformity is improved, the preparation process is remarkably shortened, and the production cost is reduced. Then high-temperature treatment is performed in an inert atmosphere, so that an organic ligand of Li-MOF is carbonized to form a continuous conductive network to wrap an inner core, meanwhile, released metal lithium sublimates and reacts with silicon dioxide in a solid phase to generate active silicon and lithium silicate, the expansion stress of the inner core is effectively absorbed, an expansion space is provided, and the morphology stability of the material is maintained; the capacity retention ratio is greatly improved; and the cycle life of the battery is prolonged.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a silicon-based negative electrode material for synchronously realizing lithiation-carbon deposition and a preparation method thereof. BACKGROUND

[0002] The silicon-carbon negative electrode material is a new type of lithium ion battery negative electrode material, has advantages of high energy density and long cycle life, is usually formed by mixing nano-silicon and carbon material, and forms a shell-core structure to buffer stress and deformation generated in the process of lithium ion deintercalation.

[0003] However, the current main process for realizing the silicon-carbon negative electrode has many limitations. The mechanical ball milling method has low efficiency, the uniformity of the obtained composite material is poor, the volume expansion is difficult to effectively constrain, and the cycle performance is insufficient. Although the chemical vapor deposition method can realize fine structure control and excellent performance, the equipment investment is high, the large-scale production is difficult, and the cost is high. The existing methods all have the defects of complex process flow, low efficiency, poor uniformity of silicon and carbon composite, and low stability, and all need to rely on a complex pre-lithiation process to compensate for the low coulomb efficiency and poor cycle stability caused by the expansion of the silicon-carbon negative electrode, which significantly increases the manufacturing cost and process complexity, and brings potential risks to the stability of the silicon-carbon negative electrode material. SUMMARY

[0004] The application aims to provide a preparation method of a silicon-based negative electrode material for synchronously realizing lithiation-carbon deposition by in-situ growing lithium metal organic framework on the surface of a silicon source substrate, which can optimize the core-shell structure of the silicon-carbon negative electrode material and solve the problems of poor material stability and complex manufacturing process caused by silicon volume expansion and pre-lithiation.

[0005] To achieve the above-mentioned purpose, the application provides a preparation method of a silicon-based negative electrode material for synchronously realizing lithiation-carbon deposition, which comprises the following steps: S1, uniformly dispersing silicon dioxide powder in a dimethylformamide aqueous solution, then adding lithium nitrate to dissolve, and then adding pyromellitic acid and polyvinylpyrrolidone, stirring until the pyromellitic acid is dissolved, to obtain a mixed solution; S2, performing hydrothermal reaction on the mixed solution obtained in step S1, then performing filtration, washing and drying to obtain a Li-MOFs material in-situ coated on the surface of the silicon dioxide; the temperature of the hydrothermal reaction is 100-180 DEG C, and the time is 12-20 h; S3, performing high-temperature calcination treatment on the Li-MOFs material in-situ coated on the surface of the silicon dioxide obtained in step S2 in an inert gas atmosphere, program-controlled heating to 800-1200 DEG C for 1-2.5 h, then program-controlled cooling to 600 DEG C for 0.5 h, and finally naturally cooling to room temperature to obtain the silicon-based negative electrode material for synchronously realizing lithiation-carbon deposition.

[0006] In the above method, the volume ratio of dimethylformamide to deionized water in the dimethylformamide aqueous solution in S1 is 3~8:1~2.

[0007] In the above method, the ratio of silica powder, dimethylformamide aqueous solution, lithium nitrate, pyromellitic acid and polyvinylpyrrolidone in S1 is (3~10)g:(500~1000)mL:(3~8)g:(6~12)g:(3~6)g.

[0008] In the above method, the stirring time in S1 is 35~45 min.

[0009] In the above method, the equipment for the hydrothermal reaction in S2 is a hydrothermal reactor.

[0010] In the above method, the inert gas in S3 is nitrogen, and the calcination equipment is a tube furnace.

[0011] In the above method, the heating rate of the programmed heating in S3 is 5℃ / min, and the cooling rate of the programmed cooling is 5℃ / min.

[0012] Furthermore, this application also provides silicon-based anode materials that simultaneously achieve lithiation-carbon deposition, prepared by any of the methods described above.

[0013] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages: 1. The preparation method provided in this application can achieve simultaneous pre-lithiation and carbon coating; by using the in-situ polymerization of lithium nitrate and pyromellitic acid on the surface of silicon dioxide to form a Li-MOF coating layer, the uniformity of silicon-carbon composite is improved, the process chain is greatly simplified, the preparation process is significantly shortened and the production cost is reduced.

[0014] 2. The silicon-based anode material of this application that simultaneously achieves lithiation-carbon deposition has high core-shell structure stability. During the high-temperature processing, the organic ligands of Li-MOF carbonize to form a continuous conductive network that wraps the core. At the same time, lithium metal sublimates and reacts with silicon dioxide in the solid phase to generate active silicon and lithium silicate, which effectively absorb the core expansion stress and provide expansion space, maintain the material morphology stability, and thus greatly improve the capacity retention rate and extend the battery cycle life.

[0015] 3. The silicon-based anode material of this application that simultaneously achieves lithiation-carbon deposition has an interface synergistic optimization effect; the uniform carbon layer effectively reduces charge transport impedance, while the pre-lithiation effect compensates for the first lithium loss. The two work together to significantly improve coulombic efficiency and specific capacity. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the preparation method provided in this application; Figure 2 This is an optical microscope image of the in-situ Li-MOFs material coated on the silica surface in Example 3; Figure 3 This is a scanning electron microscope (SEM) image of the silicon-based anode material that simultaneously achieves lithiation-carbon deposition, obtained in Example 3. Figure 4 The graphs show the electrochemical test data for the experimental and control groups; where a is the constant current charge-discharge data for the experimental group; b is the discharge specific capacity data for the experimental and control groups; c is the coulombic efficiency data for the experimental and control groups; and d is the capacity retention data for the experimental and control groups. Detailed Implementation

[0018] The technical solution of the present invention will be described below with reference to embodiments. However, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental and detection methods described in each embodiment are conventional methods; the reagents and materials described are commercially available unless otherwise specified. Unless otherwise specified, all percentages in the following embodiments refer to mass percentages. Unless otherwise specified, all proportions in the following embodiments refer to mass ratios.

[0019] Experimental apparatus: Leica DM2700 P optical microscope; purchased from Leica, Germany; Hydrothermal reactor: Model FJCF-150; Shanghai Fujing Instrument Co., Ltd. Tubular furnace: Model YMG1700-80; Suzhou Hongyu Electromechanical Technology Co., Ltd. Field emission scanning electron microscope (Nova Nano SEM); purchased from Thermo Fisher Scientific, USA. CT / CTE-4000 multi-channel button cell testing equipment; purchased from Shenzhen Xinwei; Electrochemical workstation CHI760f; purchased from Shanghai Chenhua.

[0020] Experimental materials: Commercial graphite anode powder material; purchased from BTR New Materials. Single-walled carbon nanotubes; purchased from Jiangsu Tiannai Technology. Super-P; purchased from DaCai Technology; PAA; purchased from Tianjin Haiyiwei Technology; CMC; purchased from DaCai Technology; Anhydrous ethanol; purchased from Sinopharm Xilong.

[0021] The preparation methods provided in Examples 1-4 are all as follows Figure 1 As shown, after dispersing silica in DMF aqueous solution, lithium nitrate is added as a lithium source, and the organic ligand pyromellitic acid is added. After mixing evenly, a hydrothermal reaction is carried out, and the product is filtered and washed to obtain Li-MOFs material with in-situ coating on the silica surface. Then, it is calcined at high temperature in a nitrogen atmosphere at a programmed temperature of 800~1200℃, so that the organic ligand is carbonized to form a carbon-coated conductive network. The lithium metal center sublimates and reacts with silica to generate active silicon and lithium silicate to achieve pre-lithiation, and finally obtains the silicon-based anode material that simultaneously achieves lithiation-carbon deposition provided in this application.

[0022] Detailed implementation examples are as follows: Example 1 This embodiment provides a silicon-based anode material that simultaneously achieves lithium-carbon deposition and its preparation method, including the following steps: S1. Disperse 0.3g of silica powder evenly in 80mL of DMF aqueous solution (DMF:H2O = 7:1 v / v), then add 0.3g of lithium nitrate to dissolve, then add 0.6g of pyromellitic acid and 0.3g of polyvinylpyrrolidone, stir for 35min until the pyromellitic acid dissolves to obtain a mixed solution; S2. The mixed solution obtained in step S1 is placed in a hydrothermal reactor, and after hydrothermal reaction, it is filtered, washed, and dried to obtain Li-MOFs material with in-situ coating on the surface of silica. The reaction temperature of the hydrothermal reaction is 180℃ and the reaction time is 12h. S3. The Li-MOFs material with in-situ coating on the silica surface obtained in step S2 is heated to 1000℃ for 2 hours in a nitrogen tube furnace at a heating rate of 5℃ / min, then cooled to 600℃ for 0.5 hours at a cooling rate of 5℃ / min, and finally naturally cooled to room temperature to obtain a silicon-based anode material that simultaneously achieves lithiation-carbon deposition.

[0023] Actual electrochemical testing verified that the silicon-based anode material prepared using this embodiment, which simultaneously achieves lithiation and carbon deposition, exhibits a first-cycle discharge specific capacity of 1475.01 mAh / g, a first-cycle coulombic efficiency of 79.34%, and a stable capacity retention of 74.91% after 19 cycles, fully demonstrating its technical advantages in interface synergistic optimization. Example 2 This embodiment provides a silicon-based anode material that simultaneously achieves lithium-carbon deposition and its preparation method, including the following steps: S1. Disperse 0.6g of silica powder evenly in 80mL of DMF aqueous solution (DMF:H2O=8:1v / v), then add 0.4g of lithium nitrate to dissolve, then add 0.8g of pyromellitic acid and 0.4g of polyvinylpyrrolidone, stir for 40min until the pyromellitic acid dissolves to obtain a mixed solution; S2. The mixed solution obtained in step S1 is placed in a hydrothermal reactor, and after hydrothermal reaction, it is filtered, washed, and dried to obtain Li-MOFs material with in-situ coating on the surface of silica. The reaction temperature of the hydrothermal reaction is 150℃ and the reaction time is 14h. S3. The Li-MOFs material coated on the silicon dioxide surface in step S2 is heated to 800℃ and calcined for 2.5h in a nitrogen tube furnace at a heating rate of 5℃ / min. Then, it is cooled to 600℃ and held for 0.5h at a cooling rate of 5℃ / min. Finally, it is naturally cooled to room temperature to obtain a silicon-based anode material that simultaneously achieves lithiation-carbon deposition.

[0024] Actual electrochemical testing verified that the silicon-based anode material prepared using this embodiment, which simultaneously achieves lithiation and carbon deposition, has a first-cycle discharge specific capacity of 1479.37 mAh / g, a first-cycle coulombic efficiency of 78.24%, and a stable capacity retention rate of 76.01% after 19 cycles, fully demonstrating its technical advantages in interface synergistic optimization.

[0025] Example 3 This embodiment provides a silicon-based anode material that simultaneously achieves lithium-carbon deposition and its preparation method, including the following steps: S1. Disperse 0.5g of silica powder evenly in 50mL of DMF aqueous solution (DMF:H2O=3:2v / v), then add 0.4g of lithium nitrate to dissolve, then add 0.8g of pyromellitic acid and 0.4g of polyvinylpyrrolidone, stir for 40min until the pyromellitic acid dissolves to obtain a mixed solution; S2. The mixed solution obtained in step S1 is placed in a hydrothermal reactor, and after hydrothermal reaction, it is filtered, washed, and dried to obtain Li-MOFs material with in-situ coating on the surface of silica. The reaction temperature of the hydrothermal reaction is 120℃ and the reaction time is 16h. S3. The Li-MOFs material coated on the silicon dioxide surface in step S2 is heated to 1000℃ for 2 hours in a tube furnace under nitrogen atmosphere at a heating rate of 5℃ / min. Then, it is cooled to 600℃ and held for 0.5 hours at a cooling rate of 5℃ / min. Finally, it is naturally cooled to room temperature to obtain a silicon-based anode material that simultaneously achieves lithiation-carbon deposition.

[0026] The in-situ Li-MOFs material coated on the silica surface obtained in Example S2 was observed using an optical microscope, such as... Figure 2 As shown, the material has a distinct spherical structure with a uniform diameter, indicating that this application has achieved uniform growth of spherical Li-MOFs on the silica surface and uniform coating of silica.

[0027] The silicon-based anode material that simultaneously achieves lithiation-carbon deposition, obtained in this embodiment, was subjected to scanning electron microscopy to obtain... Figure 3 ,like Figure 3 As shown, under microscopic conditions, the material has uniform particle size and obvious carbon shell coating morphology, indicating that after high-temperature calcination, the organic ligands in Li-MOF are carbonized to form a carbon shell, which uniformly coats the silicon core.

[0028] Example 4 This embodiment provides a silicon-based anode material that simultaneously achieves lithium-carbon deposition and its preparation method, including the following steps: S1. Disperse 0.6g of silica powder evenly in 60mL of DMF aqueous solution (DMF:H2O = 5:1 v / v), then add 0.8g of lithium nitrate to dissolve, then add 1.2g of pyromellitic acid and 0.6g of polyvinylpyrrolidone, stir for 45min until the pyromellitic acid dissolves to obtain a mixed solution. S2. The mixed solution obtained in step S1 is placed in a hydrothermal reactor, and after hydrothermal reaction, it is filtered, washed, and dried to obtain Li-MOFs material with in-situ coating on the surface of silica. The reaction temperature of the hydrothermal reaction is 100℃ and the reaction time is 20h. S3. The Li-MOFs material coated on the silicon dioxide surface in step S2 is heated to 1200℃ for 1h in a nitrogen tube furnace at a heating rate of 5℃ / min, then cooled to 600℃ for 0.5h at a cooling rate of 5℃ / min, and finally naturally cooled to room temperature to obtain a silicon-based anode material that simultaneously achieves lithiation-carbon deposition.

[0029] Actual electrochemical testing verified that the silicon-based anode material prepared using this embodiment, which simultaneously achieves lithiation and carbon deposition, exhibits a first-cycle discharge specific capacity of 1476.27 mAh / g, a first-cycle coulombic efficiency of 78.17%, and a stable capacity retention of 75.95% after 19 cycles, fully demonstrating its technical advantages in interface synergistic optimization. Example 5 This embodiment provides a silicon-based anode material that simultaneously achieves lithium-carbon deposition and its preparation method, including the following steps: S1. Disperse 1.0g of silica powder evenly in 100mL of DMF aqueous solution (DMF:H2O=4:1 v / v), then add 0.8g of lithium nitrate to dissolve, then add 1.2g of pyromellitic acid and 0.6g of polyvinylpyrrolidone, stir for 45min until the pyromellitic acid dissolves to obtain a mixed solution; S2. The mixed solution obtained in step S1 is placed in a hydrothermal reactor, and after hydrothermal reaction, it is filtered, washed, and dried to obtain Li-MOFs material with in-situ coating on the surface of silica. The reaction temperature of the hydrothermal reaction is 140℃ and the reaction time is 16h. S3. The Li-MOFs material coated on the silicon dioxide surface in step S2 is calcined at 1000℃ for 2 hours in a nitrogen tube furnace, then cooled to 600℃ at a cooling rate of 5℃ / min and held for 0.5 hours, and finally cooled naturally to room temperature to obtain a silicon-based anode material that simultaneously achieves lithiation-carbon deposition.

[0030] Actual electrochemical testing verified that the silicon-based anode material prepared using this embodiment, which simultaneously achieves lithiation and carbon deposition, exhibits a first-cycle discharge specific capacity of 1475.81 mAh / g, a first-cycle coulombic efficiency of 78.44%, and a stable capacity retention of 74.34% after 19 cycles, fully demonstrating its technical advantages in interface synergistic optimization. Example 6 This embodiment provides an example of preparing an electrode using a silicon-based anode material that simultaneously achieves lithiation and carbon deposition, as obtained in Example 3, and then conducting electrochemical tests. This demonstrates that the silicon-based anode material that simultaneously achieves lithiation and carbon deposition prepared by this invention can effectively absorb the expansion stress of the silicon core, provide expansion space, and thus improve the stability of the material when participating in electrochemical reactions, thereby enhancing the cycle life and capacity retention of the battery.

[0031] First, the electrode is prepared using the silicon-based anode material that simultaneously achieves lithium-carbon deposition, obtained in Example 3: The electrode paste was uniformly coated onto copper foil to a thickness of 150 μm and then dried in a vacuum oven at 85°C for 12 hours. The dried electrode sheets were then cut into 16 mm diameter discs. The solvent for the electrode paste was anhydrous ethanol and water in a volume ratio of 3:7. The solid content of the electrode paste was controlled at 10%–12%, and the proportions of each component are shown in Table 1. Table 1. Proportion of each component in the electrode paste Next, electrochemical tests were conducted: Experimental design: The above electrodes were assembled with a Li metal substrate to form a coin cell. A CHI760e electrochemical workstation was used for constant current charge-discharge testing (current density 2 mA / g) to determine the specific capacity. A Newway testing instrument was used for cycle stability testing. The specific steps are as follows: After standing for 15 minutes, constant current discharge (0.1C, 0.005V), after standing for 15 minutes, constant current discharge (0.05C, 0.005V), after standing for 15 minutes, constant current discharge (0.02C, 0.005V), after standing for 15 minutes, constant current charging (0.1C, 1.5V); perform cyclic constant current charge and discharge tests at a rate of 0.1C, with a discharge cutoff voltage of 0.005V and a charging cutoff voltage of 1.5V.

[0032] Control group design: Carbon-coated silicon-based composite material was prepared as follows: Silica powder was poured into a ceramic boat and placed in the center of a tube furnace. Acetylene (80 mL / min) and argon (160 mL / min) gases were used as feed gas. The temperature was raised to 500°C at a rate of 5°C / min and reacted for 2 hours. After natural cooling to room temperature, a carbon-deposited composite silicon-based anode was obtained. It was pressed into a 12 mm (diameter) disc, placed in a ceramic boat, and covered with 1 g of polyvinyl chloride powder. Then, it was heated to 300°C at a rate of 5°C / min in a nitrogen atmosphere and held at that temperature for 2 hours. The temperature was then raised to 900°C at the same rate and carbonized for 2 hours to obtain the carbon-coated silicon-based composite material.

[0033] Test results are as follows Figure 4 As shown in a, the Li-MOF-based anode material obtained in Example 3 exhibits the obvious constant-current charge-discharge electrochemical characteristics of silicon-based anode materials. Figure 4 As shown in b~d, the coulombic efficiency, specific capacity and capacity retention of the prepared Li-MOF-based anode material are significantly improved. Specific performance comparison data are shown in Table 2.

[0034] Table 2: Electrochemical data of experimental and control groups As shown in Table 2, the first-cycle discharge specific capacity of the experimental group reached 1479.82 mAh / g, which was significantly higher than that of the control group (1132.94 mAh / g), indicating a significant improvement in the utilization rate of active materials. The first-cycle coulombic efficiency of the experimental group was 80.34%, which was 4.32 percentage points higher than that of the control group, verifying the optimization of charge transport efficiency. More importantly, the capacity retention rate of the experimental group was 76.21%, which was far better than that of the control group (52.40%), fully demonstrating the cycling stability advantage of the material structure.

[0035] The above results demonstrate that this invention uniformly disperses silica in a DMF aqueous solution, followed by in-situ polymerization of lithium nitrate and pyromellitic acid to grow Li-MOF on its surface. This achieves simultaneous silica coating and lithium introduction, improving the uniformity of the silicon-carbon composite, significantly shortening the preparation process, and reducing production costs. Subsequently, high-temperature treatment in an inert atmosphere carbonizes the organic ligands of the Li-MOF, forming a continuous conductive network that encapsulates the core. Simultaneously, the released lithium metal sublimates and reacts with the silica solid phase to generate active silicon and lithium silicates. This effectively absorbs core expansion stress and provides expansion space, maintaining material morphological stability, thereby significantly improving capacity retention and extending battery cycle life.

[0036] As described above, the basic principles, main features, and advantages of the present invention have been well described. The above embodiments and specifications are merely descriptions of preferred embodiments of the present invention, and the present invention is not limited to the above embodiments. Various changes and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit and scope of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A method for preparing a silicon-based anode material for synchronous implementation of lithiation-carbon deposition, characterized in that, The method comprises the following steps: S1, uniformly dispersing silica powder in a dimethylformamide aqueous solution, then adding lithium nitrate to dissolve, and then adding pyromellitic acid and polyvinylpyrrolidone, and stirring until the pyromellitic acid is dissolved to obtain a mixed solution; S2, after the mixed solution obtained in step S1 is subjected to a hydrothermal reaction, the solution is filtered, washed, and dried to obtain a Li-MOFs material coated on the surface of silica in situ; the hydrothermal reaction is performed at a temperature of 100-180 DEG C for 12-20 h; S3, the Li-MOFs material coated on the surface of silica in situ obtained in step S2 is subjected to high-temperature calcination treatment in an inert gas atmosphere at a programmed temperature of 800-1200 DEG C for 1-2.5 h, then the temperature is programmed to decrease to 600 DEG C and maintained for 0.5 h, and finally the temperature is naturally cooled to room temperature to obtain a silicon-based negative electrode material which realizes lithiation-carbon deposition simultaneously.

2. The method of claim 1, wherein, In the dimethylformamide aqueous solution in step S1, the volume ratio of dimethylformamide to deionized water is 3-8:1-2.

3. The method of claim 1, wherein, In step S1, the amount ratio of the silica powder, the dimethylformamide aqueous solution, lithium nitrate, pyromellitic acid, and polyvinylpyrrolidone is (3-10) g:(500-1000) mL:(3-8) g:(6-12) g:(3-6) g.

4. The method of claim 1, wherein, In step S1, the stirring time is 35-45 min.

5. The method of claim 1, wherein, In step S2, the hydrothermal reaction equipment is a hydrothermal reaction kettle.

6. The method of claim 1, wherein, In step S3, the inert gas is nitrogen, and the calcination equipment is a tube furnace.

7. The method of claim 1, wherein, In step S3, the programmed temperature increasing rate is 5 DEG C / min, and the programmed temperature decreasing rate is 5 DEG C / min.

8. A silicon-based negative electrode material which realizes lithiation-carbon deposition simultaneously and is prepared by the method of any one of claims 1-7.

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