Silicon-based lithium ion battery negative electrode slurry, preparation method and application thereof

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a silicon-based lithium ion battery negative electrode slurry as well as a preparation method and application thereof. The preparation method of the silicon-based lithium ion battery negative electrode slurry comprises the following steps: S1: dissolving a binder in deionized water, heating and stirring to form a uniform and transparent binder solution; S2: dissolving a fluorine-containing metal salt in deionized water to prepare a fluorine-containing metal salt solution, blending the fluorine-containing metal salt solution with the binder solution, and then adding a silicon-based active material and a conductive agent to uniformly stir to obtain the silicon-based lithium ion battery negative electrode slurry; the binder comprises sodium carboxymethyl cellulose. The cycle stability and rate performance of the battery are remarkably improved by adding the fluorine-containing metal salt.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a silicon-based lithium-ion battery negative electrode slurry, its preparation method, and its application. Background Technology

[0002] With the rapid development of electric vehicles and energy storage systems, the demands on energy density and cycle stability of lithium-ion batteries are becoming increasingly stringent. The theoretical capacity of traditional graphite anodes (G) is only 372 mAh / g, which is insufficient to meet the development requirements of next-generation high-energy-density batteries. Silicon-based anodes, with their ultra-high theoretical capacity of 4200 mAh / g, low operating voltage, and environmental friendliness, have become the most promising alternative material.

[0003] However, the commercialization of silicon-based anodes faces severe challenges: the 300% volume expansion during lithiation can lead to electrode structure cracking, active material shedding, and repeated damage and regeneration of the solid electrolyte interphase (SEI) film. This process continuously consumes active lithium and electrolyte, resulting in increased SEI film thickness, increased lithium-ion transport resistance, and ultimately rapid battery capacity decay. Existing improvement strategies include structural optimization, composite system construction, and binder optimization, but these suffer from problems such as complex processes, high costs, or poor compatibility.

[0004] Existing technologies largely rely on external electrolyte regulation, making it difficult to achieve precise construction of the SEI film from within the electrode. There is an urgent need to develop a negative electrode slurry system that can fundamentally improve the stability of the SEI film, forming a dense SEI film with excellent ion conductivity through synergistic effects, thus solving the volume expansion problem of silicon-based negative electrodes. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a silicon-based lithium-ion battery anode slurry, its preparation method, and its applications. Starting from the internal regulation of the SEI film formation process within the electrode, and simultaneously optimizing the preparation process to meet industrial requirements, this invention overcomes the limitations of traditional methods that rely on external electrolyte regulation by directly introducing fluorine-containing metal salts into the anode slurry system. This solves the problems of SEI film damage and capacity decay caused by the volume expansion of silicon-based anodes.

[0006] The first objective of this invention is to provide a method for preparing a silicon-based lithium-ion battery negative electrode slurry, comprising the following steps: S1: Dissolve the adhesive in deionized water, heat and stir to form a uniform and transparent adhesive solution; S2: Dissolve the fluorine-containing metal salt in deionized water to prepare a fluorine-containing metal salt solution, mix it with the above binder solution, add silicon-based active material and conductive agent, and stir evenly to obtain the silicon-based lithium-ion battery negative electrode slurry; The binder includes sodium carboxymethyl cellulose.

[0007] Furthermore, the fluorine-containing metal salt is one or more of the following: sodium fluorosilicate, potassium fluorosilicate, magnesium fluorosilicate, zinc fluorosilicate, potassium fluoroaluminate, sodium fluoroaluminate, potassium fluorozirconate, sodium fluorozirconate, ammonium fluorozirconate, ammonium fluorotitanate, potassium fluorotitanate, sodium fluorotitanate, barium magnesium fluoride, and barium zinc fluoride.

[0008] Furthermore, the mass of the fluorine-containing metal salt is 0.5% to 2% of the sum of the masses of the fluorine-containing metal salt, binder, silicon-based active material, and conductive agent.

[0009] Furthermore, in the negative electrode slurry, the ratio of silicon-based active material: conductive agent: binder: fluorine-containing metal salt is 60:20:20-X:X, where X takes the value of 0.5 ~ 2.

[0010] Furthermore, the concentration of the adhesive solution in step S1 is 2%.

[0011] Furthermore, the mass concentration of the fluorine-containing metal salt solution in step S2 is 0.2% to 10%.

[0012] Furthermore, the adhesive also includes polyacrylic acid, sodium carboxymethyl cellulose and polyacrylic acid in a mass ratio of 2:1.

[0013] Furthermore, in step S2, the mixture is stirred at 40℃ ~ 90℃ for 12h ~ 24h.

[0014] Furthermore, the silicon-based active material is nano-silicon, micron-silicon, silicon-carbon, or silicon-oxygen; the conductive agent is SuperP, acetylene black, or carbon nanotubes.

[0015] A second objective of this invention is to provide a silicon-based lithium-ion battery negative electrode slurry prepared using the above-described preparation method.

[0016] A third objective of the present invention is to provide a silicon-based lithium-ion battery comprising a silicon-based negative electrode sheet made from the aforementioned negative electrode slurry.

[0017] The core advantage of the fluorine-containing metal salt added in this invention lies in the fluoride ion (F... - It can preferentially react with the silicon-based surface oxide layer and electrolyte decomposition products to generate a highly stable LiF component, while the metal cations (Al³⁺) react with the electrolyte. + Na + Zr 4+LiF (such as sodium carboxymethyl cellulose) can be used as an inorganic framework dopant to construct LiF-rich SEI films. These SEI films possess both high density and excellent ionic conductivity, effectively buffering the volume expansion of silicon-based materials and suppressing continuous electrolyte decomposition. Furthermore, the high modulus of LiF also gives the electrode superior mechanical properties, effectively buffering the volume expansion effect of the silicon anode. For example, Na3AlF6 can form a uniform dispersion system with silicon-based active materials, conductive agents, and binders (such as sodium carboxymethyl cellulose) during slurry preparation, and cryolite Na3AlF6 contains F... - Al 3+ and Na + Active ions, of which F - It preferentially reacts with the oxide layer and electrolyte decomposition products on the silicon-based surface, participating in the formation of a stable SEI film containing more LiF and AlF3. This avoids problems such as additional electrolyte consumption and battery degradation caused by repeated SEI rupture, resulting in better battery cycle performance. Furthermore, a compound effect can be achieved by adding two or more fluorine-containing inorganic salts, effectively overcoming the limitation on the amount that can be added due to low solubility.

[0018] This invention achieves uniform coating of fluorine-containing metal salts on the surface of silicon-based active particles by blending an aqueous solution of fluorine-containing metal salts with a binder solution, avoiding excessively high or low local concentrations. The optimal parameter range was also explored to ensure sufficient LiF formation while avoiding increased ion conduction resistance caused by excessively thick SEI films.

[0019] The raw materials of this invention are readily available, the process is simple, no modification to existing production lines is required, and it is green, environmentally friendly, and cost-controllable, making it suitable for large-scale production.

[0020] The effects of the fluorine-containing metal salt added in this invention are as follows: (1) F - It preferentially participates in SEI film formation, increases LiF content, and enhances the mechanical strength and chemical stability of the film; (2) Metal cation doping optimizes the crystal structure of the SEI film and constructs a continuous lithium-ion transport channel; (3) Fluorine-containing metal salts and binders form a synergistic effect, improving the peel strength of the electrode (e.g., the peel strength of Example 2 reached 0.5217 kN / m, an increase of 34.9% compared to Comparative Example 5). This synergistic effect improves battery cycle performance from both interface stability and electrode mechanical properties (e.g., Figure 3 As shown, Example 2 achieved a capacity of 1034.1 mAh / g after 300 cycles at 0.5C, which is 48.9% higher than Comparative Example 5. Attached Figure Description

[0021] Figure 1 The process flow diagram for preparing the negative electrode slurry is shown for the examples and comparative examples; Figure 2 The bar chart shows the peel strength of the negative electrode sheets prepared using Examples 1, 6, 7 and Comparative Example 5. Figure 3 The graph shows the long-term cycling performance of the half-cells assembled using the negative electrode sheets prepared in Example 2 and Comparative Example 5 after 300 cycles at 0.5C. Figure 4 SEM images of the surface morphology of the negative electrode sheets prepared using Comparative Example 5 and Example 1 after assembling a half-cell and cycling for 50 cycles. Detailed Implementation

[0022] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0023] Example 1 S1. Preparation of binder: CMC solid powder binder is dissolved in deionized water and heated and stirred at 60°C for 6 h to obtain an aqueous binder. The concentration of the CMC binder solution is 2%.

[0024] S2. Preparation of the slurry: Dissolve the fluorine-containing metal salt in deionized water to prepare a fluorine-containing metal salt solution. Mix this solution with the aforementioned CMC binder solution, then add nano-silicon powder active material and conductive agent Super P. Heat at 60°C and stir continuously for 12 hours to prepare a uniformly dispersed silicon-based lithium-ion battery negative electrode slurry (e.g., Figure 1 (As shown in the figure). The proportions of each substance are shown in Table 1.

[0025] S3. Electrode preparation: Stir the slurry evenly, sonicate for 10 min, and then coat it onto the surface of copper foil using a coating machine to a thickness of 12 μm. Dry it under vacuum at 120℃ for 12 h, and cut it into circular electrode sheets with a radius of 7.5 mm for later use.

[0026] Examples 2-4 The amount of fluorine-containing metal salt added was changed, while other aspects remained the same as in Example 1.

[0027] Example 5 The adhesive used was CMC / PAA in a mass ratio of 2:1, and the rest was the same as in Example 1.

[0028] Example 6 The fluorine-containing metal salt was replaced with sodium fluorozirconate, and everything else was the same as in Example 1.

[0029] Example 7 The fluorine-containing metal salt was replaced with sodium fluorotitanate, and everything else was the same as in Example 1.

[0030] Comparative Example 1 The fluorine-containing metal salt, active material, and conductive agent are ground together for 15 to 30 minutes, and then an aqueous binder solution is added. The mixture is stirred at 40°C to 90°C for 12 to 24 hours.

[0031] The fluorine-containing metal salt content is 2%, and the rest is the same as in Example 1.

[0032] Comparative Examples 2-4 The amount of fluorine-containing metal salt added was changed, while other aspects remained the same as in Comparative Example 1.

[0033] Comparative Example 5 A water-based binder was obtained by dissolving the binder solid powder in deionized water and heating and stirring at 60°C for 6 h. Silicon-based active materials and conductive agents were added, and the mixture was heated and stirred continuously at 60°C for 12 h to prepare a uniformly dispersed silicon-based lithium-ion battery negative electrode slurry.

[0034] The binder is CMC, the active material is nano-silicon powder, and the conductive agent is Super P.

[0035] Comparative Example 6 Prepare a CMC / PAA adhesive solution with a CMC to PAA mass ratio of 2:1, and other conditions are the same as in Comparative Example 5.

[0036] Comparative Example 7 PAA was used as the adhesive, and everything else was the same as in Example 2.

[0037] Comparative Example 8 Prepare the PAA adhesive solution, otherwise the same as in Comparative Example 5.

[0038] Table 1 shows the specific preparation parameters of the electrodes in the specific embodiments and comparative examples.

[0039] Table 2 shows the performance parameters of the electrodes in the specific embodiments and comparative examples.

[0040] Table 1

[0041] Table 2

[0042] According to Table 1, Table 2, Figure 2 , Figure 3 It can be known that: 1. The fluorine-containing additive material was determined. Through comparative experiments of Examples 1, 6, 7, and Comparative Example 5, it was found that sodium fluoroaluminate, as an additive, yielded the best performance in the relevant test results. Sodium fluorozirconate and sodium fluorotitanate, on the other hand, have lower complex ion stability, uneven F- release rates, and are prone to local over-fluorination, resulting in relatively thicker SEI films and relatively higher impedance. Therefore, their performance is somewhat worse than that of Example 1.

[0043] 2. Determination of Additive Content Range: Through comparative experiments of Examples 1-4 (wet process) and Comparative Examples 1-4 (dry process), the range of additive content was further limited. It was found that the overall battery performance was best when the additive content was 0.8% to 1.4%. Below this range, LiF generation was insufficient and the SEI film was unstable (as in Example 1, the capacity retention rate was low). Above this range, the SEI film was too thick and ion conduction was hindered (as in Example 4, the capacity decreased sharply). However, overall, the wet process of this invention performed better than the dry process.

[0044] 3. Determination of stirring temperature and time: The range of 40℃ ~ 90℃ and 12h ~ 24h was determined by testing the adhesive dissolution effect and slurry uniformity. Under these conditions, the adhesive can be fully dissolved to form a uniform and stable slurry system.

[0045] 4. As can be seen from Comparative Examples 7 and 8, not all adhesives can achieve a synergistic effect when used in combination with fluorine-containing metal salts. When the adhesive is PAA, the performance is actually reduced.

[0046] Figure 4 SEM images of the surface morphology of the negative electrode sheets prepared using Comparative Example 5 (left) and Example 1 (right) after assembling a half-cell and cycling for 50 cycles. Figure 4 It can be seen that the negative electrode sheet of the present invention still maintains good integrity after multiple cycles.

[0047] For any points not covered above, existing technologies shall apply.

[0048] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a silicon-based lithium-ion battery negative electrode slurry, characterized in that, Includes the following steps: S1: Dissolve the adhesive in deionized water, heat and stir to form a uniform and transparent adhesive solution; S2: Dissolve the fluorine-containing metal salt in deionized water to prepare a fluorine-containing metal salt solution, mix it with the above binder solution, add silicon-based active material and conductive agent, and stir evenly to obtain the silicon-based lithium-ion battery negative electrode slurry; The binder is sodium carboxymethyl cellulose or sodium carboxymethyl cellulose and polyacrylic acid, and the mass ratio of sodium carboxymethyl cellulose to polyacrylic acid is 2:1; The fluorine-containing metal salt is sodium fluoroaluminate; The mass of the fluorine-containing metal salt is 0.5% to 2% of the sum of the masses of the fluorine-containing metal salt, binder, silicon-based active material, and conductive agent. In the negative electrode slurry, the ratio of silicon-based active material: conductive agent: binder: fluorine-containing metal salt is 60:20:20-X:X, where X is 0.5~2. The mass concentration of the fluorine-containing metal salt solution in step S2 is 0.2% to 10%.

2. The preparation method according to claim 1, characterized in that, The concentration of the adhesive solution in step S1 is 2%.

3. The preparation method according to claim 1, characterized in that, In step S2, the mixture is stirred at 40℃ to 90℃ for 12h to 24h; the silicon-based active material is nano-silicon, micron-silicon, silicon-carbon, or silicon-oxygen; the conductive agent is Super P, acetylene black, or carbon nanotubes.

4. A silicon-based lithium-ion battery negative electrode slurry prepared by the preparation method according to any one of claims 1-3.

5. A silicon-based lithium-ion battery, characterized in that, It comprises a silicon-based negative electrode sheet made from the negative electrode paste of claim 4.

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