Silicon-based negative electrode material and preparation method and application thereof

Abstract

The application discloses a silicon-based negative electrode material and a preparation method and application thereof, and belongs to the technical field of lithium ion batteries. The silicon-based negative electrode material comprises a carbon matrix and sodium-magnesium co-doped silicon monoxide deposits; the silicon monoxide deposits are in a core-shell structure, and comprise a silicon monoxide inner core uniformly doped with magnesium elements and a silicon monoxide outer shell co-doped with sodium and magnesium. The preparation method comprises the following steps: (1) mixing silicon powder, silicon dioxide powder and magnesium powder; (2) depositing the mixed powder in carbon powder; and (3) mixing the intermediate product with a sodium salt to react, and then introducing carbon source gas to continue the reaction. The silicon-based negative electrode material has good initial coulomb efficiency, good expansion performance and cycle stability, and can be used as a negative electrode material of a lithium ion battery; the preparation process is simple and easy to operate, has high adaptability to existing production equipment, and can effectively improve the production efficiency and yield of the negative electrode material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery electrode materials, and particularly relates to a silicon-based negative electrode material and a preparation method and application thereof. BACKGROUND

[0002] The silicon-based negative electrode material is widely considered as an ideal alternative to graphite negative electrode due to its ultra-high theoretical specific capacity (4200 mAh / g, 10 times that of graphite negative electrode), low voltage platform (~0.4 V vs. Li / Li+) and abundant reserves in nature. However, the silicon-based material also has problems such as peeling off from the conductive agent and the binder and forming an unstable SEI after the particles are broken due to the large volume change during the lithium extraction / insertion process, which limits its commercialization.

[0003] To solve the above problems, the prior art such as CN115621433A and CN118198291A discloses that silicon monoxide material is deposited in a porous matrix material, the porous matrix provides structural support and reserved space for volume expansion when lithium is inserted, so that the prepared silicon-based negative electrode material has excellent rate performance and expansion performance. However, silicon monoxide itself has the problem of low first coulomb efficiency, and after being deposited into the porous matrix, the first coulomb efficiency of the material is also poor, which is difficult to meet the actual application requirements. SUMMARY

[0004] The present application provides a silicon-based negative electrode material and a preparation method and application thereof to solve the technical problem of poor first coulomb efficiency of the prior art negative electrode material mentioned in the background.

[0005] To solve the above technical problems, the technical solution provided by the present application is as follows:

[0006] A silicon-based negative electrode material, comprising a carbon matrix and sodium-magnesium co-doped silicon monoxide deposits filled in the pores of the carbon matrix; the silicon monoxide deposits have a core-shell structure, comprising a silicon monoxide inner core uniformly doped with magnesium elements and a sodium-magnesium co-doped silicon monoxide outer shell, and the doping amount of sodium elements in the sodium-magnesium co-doped silicon monoxide outer shell gradually decreases from the outside to the inside.

[0007] The design idea of the technical solution is that the silicon-based negative electrode material has deposited silicon monoxide, and the deposited silicon monoxide is different from the prior art and has a core and a shell, the core is uniformly magnesium-doped silicon monoxide, and the shell is sodium-magnesium co-doped silicon monoxide with a gradually decreasing sodium ion concentration from outside to inside. The uniformly magnesium-doped silicon monoxide core can significantly improve the first coulomb efficiency of the silicon-based negative electrode material, solve the problem of the first efficiency reduction of the material caused by the simple deposition of silicon monoxide in the prior art, and meanwhile, the sodium-magnesium co-doped silicon monoxide shell can form a loose accumulation structure, facilitating the embedding and extraction of lithium ions, and further reducing the expansion of the material, reducing the risk of material pulverization and cracking in the process of lithiumation and delithiation, and improving the expansion performance and cycle stability of the material.

[0008] As a further preferred embodiment of the above technical solution, the sodium-magnesium co-doped silicon monoxide deposit accounts for 25% to 70% of the mass of the silicon-based negative electrode material; the doping amount of magnesium element is 1% to 30% of the mass of the sodium-magnesium co-doped silicon monoxide deposit, and the doping amount of sodium element is 0.2% to 6.5% of the mass of the silicon-based negative electrode material.

[0009] As a further preferred embodiment of the above technical solution, the silicon-based negative electrode material is coated with a carbon coating layer, and the thickness of the carbon coating layer is 1 to 150 nm, and further preferably 5 to 20 nm. The carbon coating layer can further reduce the interface side reaction and improve the cycle stability of the material.

[0010] As a further preferred embodiment of the above technical solution, the carbon matrix is porous carbon, the particle size D50 of the porous carbon is 1 to 25 μm, the pore volume is 0.6 to 1.2 cm 3 / g, and the specific surface area is 1600 to 2200 m 2 / g.

[0011] Based on the same technical concept, the application further provides a preparation method of the silicon-based negative electrode material.

[0012] (1) mixing silicon powder, silicon dioxide powder and magnesium powder to obtain a mixed powder;

[0013] (2) placing the mixed powder in a reaction zone of a vacuum sintering furnace, placing carbon powder in a material collection zone of the vacuum sintering furnace, heating the vacuum sintering furnace to deposit the mixed powder in the carbon powder, and obtaining an intermediate product;

[0014] (3) mixing the intermediate product with a sodium salt to obtain a mixture, placing the mixture in a reaction furnace, reacting at 550 to 1000 ℃ under a protective atmosphere for 2 to 20 h, and then introducing a carbon source gas to continue the reaction for 2 to 5 h, to obtain the silicon-based negative electrode material.

[0015] The design concept of the above technical solution is that the present invention uses porous carbon as the matrix material, and further improves the first coulombic efficiency of silicon-based composite materials by depositing uniformly magnesium-doped silicon suboxide into the substrate. At the same time, the outer layer of the silicon suboxide deposit is treated with sodium-magnesium co-doping. Due to the presence of porous carbon, the decomposition of sodium salt can be promoted, and an unbalanced arrangement of O-Na and O-Mg bonds can be achieved. The O-Na bond is longer and the structure is loose; the O-Mg bond is shorter and the structure is dense. In the Li-NaMg-SiO system, the binary doping source will cause unbalanced repulsion, thereby forming a loose stacking structure on the outer layer of the deposit, which can facilitate lithium ion insertion and extraction, and improve the expansion performance and cycle stability of the material.

[0016] As a further preferred embodiment of the above technical solution, in step (2), the mass ratio of the mixed powder to the carbon powder is 1:(0.4~3.0).

[0017] As a further preferred embodiment of the above technical solution, in step (2), during the deposition process, the temperature of the reaction zone of the vacuum sintering furnace is controlled at 1300~1700℃, the temperature of the transition zone is controlled at 1200~1450℃, and the temperature of the receiving zone is controlled at 700~900℃. By implementing a three-stage gradient temperature control treatment on the sintering furnace, the influence of excessively high temperature heat radiation in the reaction zone on the material in the receiving zone is avoided, which can effectively improve the material recovery rate.

[0018] As a further preferred embodiment of the above technical solution, in step (2), the carbon powder is porous carbon, the particle size D50 of the porous carbon is 1~25μm, and the pore volume is 0.6~1.2 cm³. 3 / g, specific surface area is 1600 - 2200 m² 2 / g.

[0019] As a further preferred embodiment of the above technical solution, in step (1), the mass percentage of magnesium powder in the mixed powder is 1% to 30%, and more preferably 3% to 20%. When the magnesium content is too low, it cannot significantly improve the first coulombic efficiency of the material; when the magnesium content is too high, it will cause the synthetic material to have a low capacity.

[0020] As a further preferred embodiment of the above technical solution, in step (1), the molar ratio of silicon powder to silicon dioxide is (0.8~1.15):1, and more preferably (1~1.10):1. When the silicon content is too low, the material capacity and initial efficiency of the deposited material will be low. When the silicon content is too high, there will be a lot of unreacted silicon remaining in the furnace, resulting in material loss.

[0021] As a further preferred embodiment of the above technical solution, in step (3), the mass percentage of the sodium salt in the mixture is 1% to 30%, and more preferably 1% to 20%.

[0022] As a further preferred embodiment of the above technical solution, in step (3), the sodium salt includes at least one of sodium carbonate, sodium bicarbonate and sodium acetate.

[0023] As a further preferred embodiment of the above technical solution, in step (3), the carbon source gas is acetylene, the protective atmosphere is nitrogen atmosphere, and the mass flow ratio of nitrogen to acetylene is 1:(1~0.25).

[0024] Based on the same technical concept, the present invention also provides an application of the silicon-based anode material described in the above technical solution or the silicon-based anode material prepared by the preparation method described in the above technical solution in lithium-ion batteries.

[0025] The present invention has the following beneficial effects:

[0026] (1) The silicon-based anode material of the present invention solves the problem of reduced first-time efficiency caused by simple deposition of silicon suboxide in the prior art. It has good first-time coulombic efficiency, low risk of pulverization and cracking of the material during lithiation and delithiation, good expansion performance and cycle stability, and can replace graphite anode as anode material for lithium-ion batteries.

[0027] (2) The preparation method of silicon-based anode material of the present invention is simple in process and easy to operate. It is highly compatible with the production equipment of the prior art and can effectively improve the production efficiency and yield of anode material. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the receiving area of ​​the vacuum sintering furnace in each embodiment.

[0029] Figure 2 This is a schematic diagram of the silicon-based anode material in each embodiment.

[0030] Figure 3 The image shows the XRD pattern of the silicon-based anode material in Example 1. Detailed Implementation

[0031] The following is a detailed description of the invention with reference to the accompanying drawings and embodiments.

[0032] Example 1:

[0033] like Figure 2 As shown, the silicon-based anode material in this embodiment includes a porous carbon matrix (the porous carbon has a particle size D50 of 1~25 μm and a pore volume of 0.6~1.2 cm³). 3 / g, specific surface area is 1600~2200 m² 2 / g) and sodium-magnesium co-doped silicon suboxide deposits filling the pores of a carbon matrix; the silicon suboxide deposits have a core-shell structure, including a uniformly magnesium-doped silicon suboxide core and a sodium-magnesium co-doped silicon suboxide shell. In the sodium-magnesium co-doped silicon suboxide shell, the amount of sodium doping gradually decreases from the outside to the inside, and the magnesium is uniformly distributed; the porous carbon matrix is ​​coated with a carbon coating layer. The XRD pattern of the silicon-based anode material in this embodiment is shown in the figure. Figure 3 As shown, the silicon-based anode material in this embodiment also contains sodium magnesium silicate (such as Na2Mg5Si). 12 O 30 Characteristic peaks of magnesium silicates (such as MgSiO3, etc.) and magnesium silicates (such as MgSiO3, etc.).

[0034] The silicon-based anode material in this embodiment is prepared by the following method:

[0035] (1) Weigh and mix silicon powder and silicon dioxide with a particle size of 3~5μm at a molar ratio of 1.05:1, and then add magnesium powder to obtain a mixed powder; the mass percentage of magnesium powder in the mixed powder is 9%;

[0036] (2) Place the mixed powder in the reaction zone of the vacuum sintering furnace; place the porous carbon (porous carbon D50 is 8.8μm, specific surface area is 1890 m²) in the reaction zone of the vacuum sintering furnace; 2 / g, pore volume 0.89 cm³ 3 / g) is placed in the receiving area 1 of the vacuum sintering furnace (structure as follows) Figure 1 As shown in the figure (1 is the receiving area, 2 is the keel lining, and 3 is the stainless steel screen), the inner wall of the receiving area is provided with a keel lining, and a stainless steel screen (such as...) is placed in the keel lining. Figure 1 As shown, porous carbon is thinly spread on a stainless steel sieve, with a thickness of less than 3 mm; the receiving zone and the reaction zone are connected. The mass ratio of the mixed powder to the porous carbon powder is 1:0.67. The vacuum reactor is heated, with the sintering temperature in the reaction zone controlled at 1380℃, the temperature in the transition zone controlled at 1240℃, and the temperature in the receiving zone controlled at around 800℃. The vacuum degree is controlled at 0.1~10 Pa, causing the mixed powder to deposit in the carbon powder to obtain the intermediate product.

[0037] (3) Sodium carbonate and intermediate product are mixed to obtain a mixture, wherein sodium carbonate accounts for 2% of the mass of the mixture; the mixture is placed in a reactor and reacted at 850°C for 5 h under nitrogen atmosphere protection. After the reaction is completed, the furnace temperature is maintained, and acetylene is introduced for carbon deposition for 3 h. The mass flow ratio of nitrogen to acetylene gas is 1:0.5. After coating, the silicon-based anode material of this embodiment is obtained.

[0038] The silicon-based anode material in this embodiment can be used to manufacture lithium-ion batteries.

[0039] Example 2:

[0040] like Figure 2 As shown, the silicon-based anode material in this embodiment includes a porous carbon matrix (the porous carbon has a particle size D50 of 1~25 μm and a pore volume of 0.6~1.2 cm³). 3 / g, specific surface area is 1600 - 2200 m² 2 / g) and sodium-magnesium co-doped silica deposits filling the pores of a carbon matrix; the silica deposits have a core-shell structure, including a silica core uniformly doped with magnesium and a silica shell co-doped with sodium and magnesium. In the silica shell co-doped with sodium, the amount of sodium doping gradually decreases from the outside to the inside, and the magnesium is uniformly distributed; the porous carbon matrix is ​​coated with a carbon coating layer.

[0041] The preparation method of the silicon-based anode material in this embodiment is basically the same as that in Example 1, except that the mass ratio of the mixed powder to the porous carbon powder in step (2) is 1:1.

[0042] Comparative Example 1:

[0043] The preparation method of the silicon-based anode material in this comparative example is basically the same as that in Example 1, except that the temperature of the reaction zone and the transition zone of the furnace used is set to 1380℃.

[0044] Comparative Example 2:

[0045] The preparation method of the silicon-based anode material in this comparative example is basically the same as that in Example 1, except that sodium carbonate is not added in step (3).

[0046] Comparative Example 3:

[0047] Silicon-based anode materials were prepared in the same manner as in Example 1, except that magnesium powder was not added in step (1).

[0048] The silicon-based anode materials of each embodiment and comparative example were mixed with conductive agent (Super-p), binder (LA133) and water at a mass ratio of 8:1:1 to form a slurry. The dispersed slurry was coated on copper foil and dried, punched into an electrode sheet with a diameter of 16 mm, and then vacuum dried before being assembled into a CR2032 coin cell in a glove box. The prepared electrode sheet served as the positive electrode, the lithium metal sheet served as the negative electrode, and the electrolyte was 1 M LiPF6 (solvent: EC, DEC (volume ratio 1:1); solute: LiPF6; additives: 1% FEC, etc.). The prepared coin cells were left to stand at room temperature for 24 hours, and then constant current charge-discharge tests were performed on the Blue Electric test system. The cells were activated by charge-discharge at a current density of 0.1 C (designed according to 1C = 1500 mAh / g), and cycled at a current density of 0.5 C for up to 50 cycles. The charge-discharge cutoff voltage was 0.005~1.5 V. The specific capacity of the first charge, the efficiency of the first charge-discharge, and the capacity retention rate after 50 cycles were tested.

[0049] The deposition process recovery rate and full-charge expansion rate of the negative electrode sheets of coin cells made from silicon-based negative electrode materials of the above embodiments and comparative examples were also tested. The specific test process for the full-charge expansion rate was as follows: the thickness D1 of the negative electrode sheet of the coin cell made from the final material prepared in the embodiments and comparative examples after rolling was measured. Then, the full-charge thickness D2 of the negative electrode sheet was disassembled after the coin cell was fully charged to 100% SOC. Then the expansion rate was calculated: expansion rate = ((D2-D1) / D1)*100%; the deposition process recovery rate was calculated as follows: the mass of material added to the reaction zone is M1, the mass of material added to the receiving zone is M2, and the mass of material collected in the receiving zone after the deposition process is M3. Then: deposition process recovery rate = M3 / (M1+M2).

[0050] The test results are shown in Table 1.

[0051] Table 1: Test results of coin cells made with silicon-based anode materials from each embodiment and comparative example

[0052]

[0053] The Mg and Na content of the materials in each embodiment and comparative example was tested using inductively coupled plasma atomic emission spectrometry (ICP), and the C content of the materials was tested using a carbon-sulfur analyzer. The specific sample test results are shown in Table 2.

[0054] Table 2: Elemental analysis and carbon content analysis results of silicon-based anode materials in each embodiment and comparative example.

[0055]

[0056] The above description is merely a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. For those skilled in the art, improvements and modifications obtained without departing from the inventive concept should also be considered within the scope of protection of the present invention.

[0057] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A silicon-based anode material, characterized in that, The material comprises a carbon matrix and a sodium-magnesium co-doped silicon suboxide deposit filling the pores of the carbon matrix. The silicon suboxide deposit has a core-shell structure, comprising a uniformly magnesium-doped silicon suboxide core and a sodium-magnesium co-doped silicon suboxide shell, wherein the sodium doping amount in the sodium-magnesium co-doped silicon suboxide shell gradually decreases from the outside to the inside. The sodium-magnesium co-doped silicon suboxide deposit accounts for 25% to 70% of the mass of the silicon-based anode material. The magnesium doping amount is 1% to 30% of the mass of the sodium-magnesium co-doped silicon suboxide deposit, and the sodium doping amount is 0.2% to 6.5% of the mass of the silicon-based anode material.

2. The silicon-based anode material according to claim 1, characterized in that, The silicon-based anode material is coated with a carbon coating layer, the thickness of which is 1~150nm.

3. The silicon-based anode material according to claim 1 or 2, characterized in that, The carbon matrix is ​​porous carbon with a particle size D50 of 1~25 μm and a pore volume of 0.6~1.2 cm³. 3 / g, specific surface area is 1600~2200 m² 2 / g.

4. A method for preparing the silicon-based anode material according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Mix silicon powder, silicon dioxide powder and magnesium powder to obtain a mixed powder; (2) The mixed powder is placed in the reaction zone of the vacuum sintering furnace, and the carbon powder is placed in the receiving zone of the vacuum sintering furnace. The vacuum sintering furnace is heated so that the mixed powder is deposited in the carbon powder to obtain an intermediate product. (3) The intermediate product is mixed with sodium salt to obtain a mixture. The mixture is placed in a reactor and reacted at 550~1000℃ for 2~20h under a protective atmosphere. Then carbon source gas is introduced to continue the reaction for 2~5h to obtain the silicon-based anode material.

5. The method for preparing the silicon-based anode material according to claim 4, characterized in that, In step (2), the mass ratio of the mixed powder to the carbon powder is 1:(0.4~3.0).

6. The method for preparing the silicon-based anode material according to claim 4, characterized in that, In step (2), during the deposition process, the temperature of the reaction zone of the vacuum sintering furnace is controlled at 1300~1700℃, the temperature of the transition zone is controlled at 1200~1450℃, and the temperature of the receiving zone is controlled at 700~900℃.

7. The method for preparing the silicon-based anode material according to claim 4, characterized in that, In step (2), the carbon powder is porous carbon with a particle size D50 of 1~25μm and a pore volume of 0.6~1.2 cm³. 3 / g, specific surface area is 1600-2200 m² 2 / g.

8. The method for preparing the silicon-based anode material according to any one of claims 4-7, characterized in that, In step (1), the magnesium powder accounts for 1% to 30% of the mass of the mixed powder.

9. The method for preparing the silicon-based anode material according to any one of claims 4-7, characterized in that, In step (1), the molar ratio of silicon powder to silicon dioxide is (0.8~1.15):

1.

10. The method for preparing the silicon-based anode material according to any one of claims 4-7, characterized in that, In step (3), the sodium salt accounts for 1% to 30% of the mass of the mixture.

11. The method for preparing the silicon-based anode material according to claim 10, characterized in that, In step (3), the sodium salt includes at least one of sodium carbonate, sodium bicarbonate and sodium acetate.

12. The method for preparing the silicon-based anode material according to any one of claims 4-7, characterized in that, In step (3), the carbon source gas is acetylene, the protective atmosphere is nitrogen atmosphere, and the mass flow ratio of nitrogen to acetylene is 1:(1~0.25).

13. The application of a silicon-based anode material according to any one of claims 1-3 or a silicon-based anode material prepared by any one of claims 4-12 in a lithium-ion battery.

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