Silicon negative electrode surface modification material and modification method

Abstract

This invention discloses a silicon anode surface modification material and modification method, belonging to the field of lithium-ion battery technology. The invention includes the following steps: micron-sized silicon is subjected to high-energy ball milling in an inert atmosphere; the milled material is further ball-milled with active small molecules to prepare surface-modified silicon powder; the prepared surface-modified silicon powder, conductive carbon black, and a binder are mixed in a 7:1:2 ratio to form a slurry; the binder is prepared by adding a linear polymer and a crosslinking agent to a solvent in a certain proportion; the slurry is coated onto a copper foil current collector and dried under vacuum in stages to obtain a silicon-based anode material with a three-dimensional network structure. This invention utilizes the functional groups of active small molecules to effectively bond silicon powder to the binder network, which can improve the interaction between silicon powder and the binder network, generating various forces such as hydrogen bonds, covalent bonds, and ionic bonds between the binder and silicon powder. These various forces can maintain the structural stability of the silicon anode during expansion and contraction.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium-ion batteries, specifically relating to a silicon anode surface modification material and modification method. Background Technology

[0002] Currently, lithium-ion batteries are mainly used in portable electronic devices, electric vehicles, and energy storage power stations. As electronic products increasingly demand higher battery energy density and cycle life, higher requirements are being placed on the performance of the positive and negative electrode materials. Currently, graphite is the most widely used negative electrode material in commercially available lithium-ion batteries, but its theoretical specific capacity has reached its limit. Silicon negative electrodes have a capacity of 3579 mAh g⁻¹. -1 With its theoretical specific capacity, low lithiation potential, excellent fast-charging performance, abundant resources, and low cost, silicon has become an ideal choice for next-generation lithium-ion battery anode materials. To improve the cycle performance of silicon anodes, researchers have employed a series of methods, including silicon nano-sizing and porousing, constructing silicon-based composite materials, designing novel binders, surface coating silicon, and optimizing electrolyte composition.

[0003] Lithium-ion battery silicon anode binders have evolved from initial one-dimensional linear binders to three-dimensional network binders and now to multifunctional self-healing binders. Current binder systems mostly rely on the interaction between the silicon surface and hydroxyl groups. However, the distribution of these hydroxyl groups is affected by production and storage conditions. Furthermore, when hydroxyl groups are generated on the silicon surface, contact with oxygen in the air produces substances such as SiO2. These substances can cause side reactions in the silicon anode and, due to their non-conductivity, increase electrode polarization, further affecting the cycle performance of the electrode material. Summary of the Invention

[0004] The purpose of this invention is to provide a silicon anode surface modification material and modification method to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for modifying the surface of a silicon anode, comprising the following steps: S1. Micron-sized silicon is subjected to high-energy ball milling in an inert atmosphere to obtain silicon powder material A with dangling bonds on its surface; Add a small molecule compound B containing multiple functional groups to material A in a certain proportion, and ball mill or grind it under an inert atmosphere so that compound B is grafted onto the silicon powder surface through dangling bonds on the silicon surface to obtain material C. S2. Dissolve the composite binder composed of linear polymer and crosslinking agent in a solvent to form a binder solution, add material C and stir evenly to obtain slurry material D; S3. Material D is coated onto a copper foil current collector and dried by segmented vacuum baking to obtain a silicon-based anode material with a three-dimensional network structure confined within it.

[0006] In a preferred embodiment, the particle size of the micron-sized silicon is 2–8 μm, the ball mill speed is 500–1400 rpm, the ball milling time is 2–8 h, and the inert atmosphere is one or more combinations of argon and nitrogen.

[0007] In a preferred embodiment, the active small molecule compound B containing multiple functional groups should contain at least two functional groups selected from hydroxyl, carboxyl, and amino groups, including one or more of tannic acid, tyrosine, cysteine, lysine, gallic acid, glycine, resorcinol, p-cresol, 3,4-dihydroxyphenylalanine, m-cresol, pyrogallol, phlorogallol, phenethyl caffeate, α-naphthol, and β-naphthol, and its addition amount is 1 wt.%–40 wt.% of the silica powder mass.

[0008] In a preferred embodiment, the compound containing multiple functional groups is one or more of the following: tannic acid, tyrosine, cysteine, lysine, gallic acid, glycine, resorcinol, p-cresol, 3,4-dihydroxyphenylalanine, m-cresol, pyrogallol, phlorogallol, phenethyl caffeate, α-naphthol, and β-naphthol.

[0009] In a preferred embodiment, in step S2: the linear polymer is selected from one or more combinations of polylactic acid, polylysine, chitosan, polyacrylamide, polyglycerol, polyacrylic acid, dextran, polypropylene glycol, polyethylene glycol, fructan, polyetherimide, and polyvinyl alcohol; The crosslinking agent is selected from one or more of citric acid, tartaric acid, lactic acid, phthalic acid, isophthalic acid, terephthalic acid, acetic acid, formic acid, oxalic acid, and glucose.

[0010] In a preferred embodiment, in step S2, the linear polymer accounts for 20 wt.%-80 wt.% of the binder solute, and the crosslinking agent accounts for 5 wt.%-40 wt.% of the binder solute.

[0011] In a preferred embodiment, in step S2, the solute content in the adhesive solution is 5wt.%-45wt.%.

[0012] In a preferred embodiment, in step S2, the solvent is selected from one or more combinations of benzene, toluene, acetone, butanone, cyclohexanone, cyclopentanone, tetrahydrofuran, anhydrous ethanol, and water.

[0013] As a preferred embodiment, in step S3, a segmented baking process is adopted, with the first segment baking temperature at 20-80 ℃ and the time at 2-6 h, and the second segment baking temperature at 80-150 ℃ and the time at 2-6 h.

[0014] The present invention also discloses a silicon anode surface modification material, which is prepared by the above-described silicon anode surface modification method; The present invention provides a silicon anode surface modification material prepared by the above method, which is applied to lithium-ion batteries.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention exposes a fresh surface to silicon powder through ball milling, simultaneously generating dangling bonds. These dangling bonds are then used to graft active small molecules containing various functional groups onto the silicon powder surface. The functional groups of these active small molecules effectively bond the silicon powder to a binder network. This method improves the interaction between the silicon powder and the binder network, generating various forces such as hydrogen bonds, covalent bonds, and ionic bonds between the binder and silicon powder. These forces maintain the structural stability of the silicon anode during expansion and contraction. The primary material preparation method used in this method is ball milling, a simple, low-cost, and easily scalable material preparation method, and is considered a highly commercially promising material synthesis method.

[0016] The raw materials used in the method provided by this invention are all commonly used industrial materials, which are low in cost, simple in process, highly controllable, highly scalable, and easy to industrialize. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the EPR results of the ball-milled silicon powder obtained in Example 1 of the present invention; Figure 2 XPS spectrum of the interaction between ball-milled silicon powder and active small molecules obtained in Example 1 of this invention; Figure 3 Example 1 and Comparative Example 1 of the present invention were compared in 1 A g. -1 A schematic diagram of the cycling performance at current density; Figure 4 This is a schematic diagram of the rate performance of Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0018] The present invention will be further described below with reference to embodiments.

[0019] The following embodiments are used to illustrate the present invention, but should not be used to limit the scope of protection of the present invention. The conditions in the embodiments can be further adjusted according to specific conditions, and simple improvements to the method of the present invention under the premise of the concept of the present invention are all within the scope of protection claimed by the present invention.

[0020] Please see Figures 1 to 4 This invention provides a method for modifying the surface of a silicon anode, comprising the following steps: S1. Micron-sized silicon is ball-milled in an inert atmosphere to expose fresh surfaces containing unpaired electrons, which are very easy to react with other substances.

[0021] S2. The ball-milled silicon is ball-milled or ground with active small molecules. The active small molecules react with the dangling bonds on the silicon surface, thereby grafting the active small molecules onto the silicon powder surface.

[0022] S3. After the active small molecules are effectively bonded to the silicon powder, the functional groups at the other end can form various forces such as hydrogen bonds, covalent bonds, and ionic bonds with the binder network. These forces can maintain the structural stability of the silicon anode during the expansion and contraction process.

[0023] In some examples, the active small molecule is one or more of phenol, catechol, tannic acid, hydroquinone, gallic acid, resorcinol, p-cresol, 3,4-dihydroxyphenylalanine, m-cresol, pyrogallol, dopa, pyrogallol, phenethyl caffeate, α-naphthol, and β-naphthol; the adhesive system used is a three-dimensional network crosslinking adhesive, wherein the linear polymer used is one or more of polyacrylic acid, polyacrylamide, polyimide, polylysine, polylactic acid, polymaleic acid, and polyvinyl alcohol, and the crosslinking agent in the adhesive system is one or more of tartaric acid, lactic acid, phthalic acid, citric acid, isophthalic acid, terephthalic acid, acetic acid, formic acid, oxalic acid, and glucose.

[0024] The ratio of active small molecules to silicon powder is 5 wt.%-25 wt.%; the crosslinking agent accounts for 10 wt.%-50 wt.% of the solute in the binder.

[0025] The ball milling time for micron-sized silicon is 2-8 hours, and the ball milling or grinding time for silicon powder and active small molecules after ball milling is 0.5-2 hours.

[0026] Example 1 A silicon anode surface modification material and modification method, the preparation method comprising the following steps: S1. 0.5 g of micron-sized silicon is ball-milled in a high-energy ball mill for 4 hours using an intermittent ball milling process (ball milling for 0.5 hours, then pause for 0.5 hours). The resulting powder is collected for subsequent use.

[0027] S2. The ball-milled silicon and active small molecule gallic acid were ball-milled for 1 h, with the active small molecule accounting for 10%, under an argon atmosphere.

[0028] S3, the linear adhesive uses polyacrylic acid, and the crosslinking agent uses tartaric acid.

[0029] Example 2 A silicon anode surface modification material and modification method, the preparation method comprising the following steps: S1. 0.5 g of micron-sized silicon is ball-milled in a high-energy ball mill for 4 hours using an intermittent ball milling process (ball milling for 0.5 hours, then pause for 0.5 hours). The resulting powder is collected for subsequent use.

[0030] S2. The ball-milled silicon and active small molecule tannic acid were ball-milled for 1 h, with the active small molecule accounting for 10%, under an argon atmosphere.

[0031] S3, the linear adhesive uses polyacrylic acid, and the crosslinking agent uses tartaric acid.

[0032] Example 3 A silicon anode surface modification material and modification method, the preparation method comprising the following steps: S1. 0.5 g of micron-sized silicon is ball-milled in a high-energy ball mill for 4 hours using an intermittent ball milling process (ball milling for 0.5 hours, then pause for 0.5 hours). The resulting powder is collected for subsequent use.

[0033] S2. The ball-milled silicon was ball-milled with active small molecule catechol for 1 h, with the active small molecule accounting for 10%, under an argon atmosphere.

[0034] S3, the linear adhesive uses polyacrylic acid, and the crosslinking agent uses tartaric acid.

[0035] Example 4 A silicon anode surface modification material and modification method, the preparation method comprising the following steps: S1. 0.5 g of micron-sized silicon is ball-milled in a high-energy ball mill for 4 hours using an intermittent ball milling process (ball milling for 0.5 hours, then pause for 0.5 hours). The resulting powder is collected for subsequent use.

[0036] S2. The ball-milled silicon was ball-milled with the active small molecule 3,4-dihydroxyphenylpropane for 1 h, with the active small molecule accounting for 10%, under an argon atmosphere.

[0037] S3, the linear adhesive uses polyacrylic acid, and the crosslinking agent uses tartaric acid.

[0038] Example 5 A silicon anode surface modification material and modification method, the preparation method comprising the following steps: S1. 0.5 g of micron-sized silicon is ball-milled in a high-energy ball mill for 4 hours using an intermittent ball milling process (ball milling for 0.5 hours, then pause for 0.5 hours). The resulting powder is collected for subsequent use.

[0039] S2. The ball-milled silicon was ball-milled with the active small molecule 3,4-dihydroxyphenylalanine for 1 h, with the active small molecule accounting for 20%, under an argon atmosphere.

[0040] S3, the linear adhesive uses polyacrylic acid, and the crosslinking agent uses tartaric acid.

[0041] Example 6 A silicon anode surface modification material and modification method, the preparation method comprising the following steps: S1. 0.5 g of micron-sized silicon is ball-milled in a high-energy ball mill for 4 hours using an intermittent ball milling process (ball milling for 0.5 hours, then pause for 0.5 hours). The resulting powder is collected for subsequent use.

[0042] S2. Ball mill the milled silicon with active small molecule tyrosine for 1 hour, with the active small molecule accounting for 20%, in an argon atmosphere.

[0043] S3. The linear binder uses polyacrylamide, and the crosslinking agent uses tartaric acid.

[0044] Example 7 A silicon anode surface modification material and modification method, the preparation method comprising the following steps: S1. 0.5 g of micron-sized silicon is ball-milled in a high-energy ball mill for 4 hours using an intermittent ball milling process (ball milling for 0.5 hours, then pause for 0.5 hours). The resulting powder is collected for subsequent use.

[0045] S2. The ball-milled silicon was ball-milled with the active small molecule 3,4-dihydroxyphenylalanine for 0.5 h, with the active small molecule accounting for 20%, under an argon atmosphere.

[0046] S3. The linear binder uses polyacrylamide, and the crosslinking agent uses citric acid.

[0047] Example 8 A silicon anode surface modification material and modification method, the preparation method comprising the following steps: S1. 0.5 g of micron-sized silicon is ball-milled in a high-energy ball mill for 4 hours using an intermittent ball milling process (ball milling for 0.5 hours, then pause for 0.5 hours). The resulting powder is collected for subsequent use.

[0048] S2. Grind the ball-milled silicon with the active small molecule 3,4-dihydroxyphenylalanine for 0.5 h, with the active small molecule accounting for 30%, under an argon atmosphere.

[0049] S3. The linear binder uses polyacrylamide, and the crosslinking agent uses citric acid.

[0050] Example 9 A silicon anode surface modification material and modification method, the preparation method comprising the following steps: S1. 0.5 g of micron-sized silicon is ball-milled in a high-energy ball mill for 4 hours using an intermittent ball milling process (ball milling for 0.5 hours, then pause for 0.5 hours). The resulting powder is collected for subsequent use.

[0051] S2. Grind the ball-milled silicon with the active small molecule 3,4-dihydroxyphenylalanine for 0.5 h, with the active small molecule accounting for 30%, under an argon atmosphere.

[0052] S3. The linear binder uses polyacrylamide, and the crosslinking agent uses citric acid.

[0053] Example 10 A silicon anode surface modification material and modification method, the preparation method comprising the following steps: S1. Mill 0.5 g of micron-sized silicon in a high-energy ball mill for 5 hours using an intermittent ball milling process (milling for 0.5 hours, then pausing for 0.5 hours). Collect the resulting powder for later use.

[0054] S2. Grind the ball-milled silicon with active small molecule tannic acid for 0.5 h, with the active small molecule accounting for 30%, under an argon atmosphere.

[0055] S3. The linear binder uses polyimide, and the crosslinking agent uses tartaric acid.

[0056] Comparative Example 1 S1. 0.5 g of micron-sized silicon is ball-milled in a high-energy ball mill for 4 hours in an argon atmosphere using an intermittent ball milling process (0.5 hours of ball milling followed by a 0.5-hour pause). The resulting powder is collected for subsequent use.

[0057] S2. Mill the ball-milled silicon for 1 hour under an argon atmosphere, without adding any active small molecules.

[0058] S3, the linear adhesive uses polyacrylic acid, and the crosslinking agent uses tartaric acid.

[0059] Comparative Example 2 S1, micron-sized silicon that has not undergone any processing.

[0060] S2. Untreated micron-sized silicon and active small molecule tannic acid are ball-milled for 1 h, with the active small molecule accounting for 10%, under an argon atmosphere.

[0061] S3, the linear adhesive uses polyacrylic acid, and the crosslinking agent uses tartaric acid.

[0062] Table 1: Main raw materials and parameters involved in each embodiment

[0063] Performance testing EPR testing of ball-milled silicon powder confirmed the presence of unpaired electrons on its surface. XPS testing of silicon powder grafted with active small molecules demonstrated an interaction between the active small molecules and the silicon powder. Figure 1 As shown, the ball-milled silicon exhibits a significantly higher EPR signal compared to the unmilled silicon. Figure 2 As shown, after the active small molecules are grafted onto the ball-milled silicon powder, the XPS peaks of silicon shift, indicating that silicon interacts with the active small molecules.

[0064] The surface-modified silicon powder, conductive carbon black, and binder prepared in Examples 1-10 and Comparative Examples 1-2 were mixed in a ratio of 7:1:2 to form a slurry, with deionized water as the dispersant. The slurry was coated onto Cu foil and dried to obtain a negative electrode sheet. The negative electrode sheet was cut into 12 mm diameter discs, with lithium metal as the counter electrode and a 1 M LiPF6 / EC:DEC (1:1, v / v) solution containing 10% FEC and 1% VC additives as the electrolyte, to assemble a CR2032 coin cell.

[0065] All prepared batteries were tested using the Blue Electric testing system, with a voltage range of 0.005–1.0 V. Activation was performed at a charge / discharge rate of 100 mA / g for the first week, followed by cycling at 1 A / g. The test environment was room temperature, and the results are shown in Table 2.

[0066] Table 2: Performance data of the anode materials prepared in each embodiment and comparative example

[0067] As can be seen from Table 2, the binder network based on silicon surface grafted with active small molecules prepared in this invention is beneficial to improving the cycling performance of the material; Figure 3 It can be seen that the silicon anode material based on the bonding network confinement in Example 1 has a significantly improved capacity retention rate after 400 cycles at room temperature compared with Comparative Example 1.

[0068] In summary, this invention achieves a stable "silicon-active small molecule-binder" structure by forming a strong chemical interaction between the active small molecules and the dangling bonds on the silicon surface, and by chemically cross-linking the functional groups at the other end with the binder network. This covalent bond firmly connects the inorganic silicon particles and the organic binder network. The binder's interior is composed of a high-strength covalently cross-linked framework, while the introduction of active small molecules creates a rich network of reversible hydrogen bonds. The covalent bonds maintain the integrity of the electrode structure, while the reversible hydrogen bonds, acting as "sacrificial bonds," preferentially break to dissipate stress during silicon expansion and reform during contraction, endowing the electrode with self-healing capabilities and effectively buffering the mechanical impact caused by volume changes. The electrode operates at 1000 mA g... -1 It still maintains 1618 mAh g after 400 cycles.-1 This invention offers high capacity while maintaining excellent rate performance and rapid reaction kinetics. The introduction of active small molecules induces the formation of a thinner, more LiF-rich, stable SEI layer, effectively suppressing continuous electrolyte decomposition, reducing interfacial impedance, and providing interfacial protection for long-cycle stability. This invention proposes a novel strategy for constructing a robust interface through grafting active small molecules. Utilizing "molecular bridges," silicon particles are efficiently coupled to a three-dimensional cross-linked network, effectively suppressing volume expansion of the silicon anode and improving interfacial stability. This provides a valuable reference for the development of high-performance silicon-based anodes and other high-volume-expansion electrode materials. The method of this invention is simple to operate, low in cost, and highly controllable. It is also applicable to other common lithium-ion battery anode materials, showing very broad application prospects.

[0069] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

[0070] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for modifying the surface of a silicon negative electrode, characterized by, Includes the following steps: S1. Micron-sized silicon is subjected to high-energy ball milling in an inert atmosphere to obtain silicon powder material A with dangling bonds on its surface; Add a small molecule compound B containing multiple functional groups to material A in a certain proportion, and ball mill or grind it under an inert atmosphere so that compound B is grafted onto the silicon powder surface through dangling bonds on the silicon surface to obtain material C. S2. Dissolve the composite binder composed of linear polymer and crosslinking agent in a solvent to form a binder solution, add material C and stir evenly to obtain slurry material D; S3. Material D is coated onto a copper foil current collector and dried by segmented vacuum baking to obtain a silicon-based anode material with a three-dimensional network structure confined within it.

2. The method of claim 1, wherein the method is characterized by: The micron-sized silicon has a particle size of 2–8 μm, the ball mill speed is 500–1400 rpm, the ball milling time is 2–8 h, and the inert atmosphere is one or more combinations of argon and nitrogen.

3. The method of claim 1, wherein the method is characterized by: The active small molecule compound B containing multiple functional groups should contain at least two functional groups selected from hydroxyl, carboxyl, and amino groups, including one or more of tannic acid, tyrosine, cysteine, lysine, gallic acid, glycine, resorcinol, p-cresol, 3,4-dihydroxyphenylalanine, m-cresol, pyrogallol, phlorogallol, phenethyl caffeate, α-naphthol, and β-naphthol, and its addition amount is 1 wt.%–40 wt.% of the silica powder mass.

4. The method of claim 1, wherein the method is characterized by: The linear polymer mentioned in step S2 is selected from one or more combinations of polylactic acid, polylysine, chitosan, polyacrylamide, polyglycerol, dextran, polypropylene glycol, polyethylene glycol, fructan, polyacrylic acid, polyacrylic acid, polyetherimide, and polyvinyl alcohol. The crosslinking agent is selected from one or more of citric acid, tartaric acid, lactic acid, phthalic acid, isophthalic acid, terephthalic acid, acetic acid, formic acid, oxalic acid, and glucose.

5. The method for modifying the surface of a silicon anode according to claim 1, characterized in that: In step S2, the linear polymer accounts for 20 wt.%-80 wt.% of the binder solute, and the crosslinking agent accounts for 5 wt.%-40 wt.% of the binder solute.

6. The method for modifying the surface of a silicon anode according to claim 1, characterized in that: In step S2, the solute content in the adhesive solution is 5wt.%-45wt.%.

7. The method for modifying the surface of a silicon anode according to claim 1, characterized in that: In step S2, the solvent is selected from one or more combinations of benzene, toluene, acetone, butanone, cyclohexanone, cyclopentanone, tetrahydrofuran, anhydrous ethanol, and water.

8. The method for modifying the surface of a silicon anode according to claim 1, characterized in that: In step S3, a segmented baking process is adopted. The first segment is baked at a temperature of 20-80 ℃ for 2-6 h, and the second segment is baked at a temperature of 80-150 ℃ for 2-6 h.

9. A silicon anode surface modification material, characterized in that, The silicon anode was prepared using the surface modification method described in any one of claims 1-9.

10. The application of the silicon anode surface modification material according to claim 9 in lithium-ion batteries.

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