Preparation method and application of starch-based lithium ion battery silicon negative electrode binder

Abstract

The invention belongs to the technical field of lithium ion batteries, and relates to a preparation method and application of a starch-based lithium ion battery silicon negative electrode binder. The method comprises the following steps: adding starch and lithium fluoride into a solvent, heating, stirring and uniformly mixing to obtain a modified starch polymer binder; the mass ratio of the starch to the lithium fluoride is (20-50): 1. The binder disclosed by the invention has excellent binding performance: through chemical modification and three-dimensional cross-linking design, the binder can remarkably improve the binding power of a silicon monoxide negative electrode, effectively fix an active material and inhibit the active material from falling off. The three-dimensional cross-linked network structure enables the binder to effectively alleviate the volume change problem of silicon monoxide, and avoids the damage to the electrode structure. The natural starch is used as a basic raw material, so that the adhesive is green, environment-friendly and wide in source, and meets the requirement of sustainable development. The binder disclosed by the invention is simple in preparation process, suitable for large-scale production and suitable for manufacturing requirements of various negative electrode materials at the same time.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a method for preparing and applying a starch-based lithium-ion battery silicon anode binder. Background Technology

[0002] In recent years, lithium-ion batteries have been widely used in electric vehicles and large-scale energy storage devices due to their excellent energy density and cycle life. However, the overall performance of the battery is largely affected by the anode material. Although commercially available graphite-based carbon-based anode materials have good cycle performance, their theoretical specific capacity is only 372 mAh g⁻¹. -1 This cannot meet the demand for higher energy densities. Therefore, non-carbon-based anode materials, especially those with high theoretical specific capacity (approximately 2000 mAh g⁻¹), are insufficient. -1 Silicon suboxide (SiO) has gradually become a research hotspot.

[0003] Similar to silicon, silicon suboxide undergoes significant volume expansion and contraction (approximately 200%) during lithium-ion insertion / extraction, leading to electrode pulverization and mechanical damage, resulting in rapid degradation of cycle performance. Furthermore, SiO partially decomposes during charge / discharge to generate irreversible byproducts (such as Li₂O), further reducing its capacity utilization. Therefore, developing a high-performance binder system to immobilize and protect the SiO anode material is crucial to overcoming these issues.

[0004] Traditionally, polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) have been widely used as binders and solvents in lithium-ion batteries. However, PVDF only fixes SiO particles to the current collector through van der Waals forces, making it difficult to effectively alleviate the stress caused by volume changes. Furthermore, the volatility and potential toxicity of PVDF and NMP pose threats to the environment and human health. Therefore, in recent years, environmentally friendly water-soluble binder materials have gradually become a research focus. These materials are not only environmentally friendly but also typically possess superior stability in anode materials.

[0005] Lithium-ion battery anode binders are key materials affecting electrode structural stability and cycle performance. Existing binder technologies mainly focus on traditional polymer binders, water-soluble polymer binders, and their modified forms, but these technologies still have the following shortcomings:

[0006] (1) Traditional polymer adhesives

[0007] Traditional polymer binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) interact with the anode material through van der Waals forces, but lack effective buffering capacity for anode materials with large volume changes, such as silicon or silicon suboxide. Because they cannot effectively absorb the stress generated by volume expansion, the electrode structure is easily damaged, leading to rapid degradation of cycle performance. Furthermore, PVDF requires dissolution with the organic solvent NMP, which may cause environmental and operator pollution during the preparation process, limiting its application in the green energy field.

[0008] (2) Water-soluble polymeric adhesives

[0009] In recent years, water-soluble polymer binders such as polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), and chitosan (CS) have attracted attention due to their environmentally friendly properties. These materials typically improve the bonding strength between the anode material and the current collector by forming hydrogen bonds or ionic bonds, partially alleviating the volume expansion problem. However, water-soluble binders with a single linear structure still have shortcomings in terms of mechanical properties and cycling stability, failing to provide sufficient electrode stability. Furthermore, these materials may experience a decline in bonding performance due to swelling or decomposition during long-term cycling, thus affecting the overall electrode performance.

[0010] (3) Modified or composite adhesives

[0011] To further improve binder performance, researchers have attempted to enhance binder functionality through chemical modification or composite methods. For example, combining water-soluble polymers with functional groups or introducing inorganic particles to form a three-dimensional network structure. While these techniques can improve bonding performance, the preparation processes are complex and costly, and the modification effects are easily affected by environmental factors (such as humidity and temperature). Furthermore, the uniformity and stability of the composite materials are difficult to guarantee, potentially leading to inconsistencies in electrode performance.

[0012] (4) Shortcomings of starch-based binders

[0013] Although starch, as a natural and renewable resource, possesses abundant hydroxyl groups and good biocompatibility, showing potential in the field of lithium-ion battery binders, its natural form suffers from drawbacks such as uneven molecular weight distribution and insufficient mechanical properties. Unmodified starch is insufficient to meet the high-strength binder requirements of silicon suboxide anode materials. Furthermore, starch exhibits low solubility and stability in aqueous solutions, potentially leading to uneven dispersion during electrode processing.

[0014] Among these water-soluble binders, starch-based materials, as a natural and renewable resource, exhibit great application potential due to their wide availability, low cost, and good biocompatibility. Starch molecules contain numerous hydroxyl groups, which can interact with the surface of SiO particles through hydrogen bonds or chemical bonds, thereby mitigating stress caused by volume changes to some extent. Furthermore, chemical modification of starch molecules (such as esterification, etherification, or crosslinking modification) can further enhance their mechanical properties and stability. For example, crosslinked starch-based binders can form a three-dimensional network structure, which not only effectively restricts the displacement of SiO particles but also provides higher structural stability, thereby improving the cycle life and capacity retention of the SiO anode.

[0015] While existing binder technologies each have their advantages, there is still significant room for improvement in enhancing the cycle stability of silicon suboxide anodes, mitigating volume expansion issues, and achieving green manufacturing. Research indicates that starch-based binders can achieve synergistic effects by being combined with other functional materials (such as polyacrylic acid and chitosan) to improve their bonding performance in SiO anode applications. For example, some composite binders can simultaneously provide physical fixation and chemical stability for SiO particles, thereby significantly improving the mechanical integrity and electrochemical performance of the electrode.

[0016] In summary, starch-based binders, with their excellent performance and sustainable development characteristics, provide an environmentally friendly and efficient solution for the application of silicon suboxide anode materials in lithium-ion batteries. In the future, with further research into the structure-performance relationship of starch-based binders, their application prospects in high-performance lithium-ion batteries will be even broader. Summary of the Invention

[0017] To address the shortcomings of existing binders for silicon suboxide anode materials in lithium-ion batteries, this invention first provides a method for preparing a starch-based lithium-ion battery silicon anode binder.

[0018] Another objective of this invention is to provide a novel starch-based binder that has excellent bonding properties, mechanical strength, and environmental friendliness. It can effectively alleviate the stress concentration problem caused by the volume expansion of silicon suboxide anode materials during charging and discharging, and significantly improve the cycle stability and capacity retention of the electrode.

[0019] The starch-based binder of this invention, through chemical modification, utilizes the abundant hydroxyl groups in starch molecules to form strong hydrogen bonds or chemical bonds with the surface of silica particles, while simultaneously introducing ionic conductors with ionic conductivity and mechanical stability to construct a high-strength conductive SEI layer. This binder provides a stable bond between the negative electrode active material, the conductive agent, and the current collector, significantly improving the overall mechanical integrity and electrochemical performance of the electrode.

[0020] To achieve the above objectives, the present invention provides the following technical solution:

[0021] A method for preparing a starch-based silicon anode binder for lithium-ion batteries includes adding starch and lithium fluoride to a solvent, heating and stirring to mix evenly, to obtain a modified starch polymer binder; wherein the mass ratio of starch to lithium fluoride is 20~50:1.

[0022] Preferably, the solvent is dimethyl sulfoxide.

[0023] Preferably, the heating temperature is 55~70℃, and the stirring time is 3~5 hours.

[0024] Preferably, the starch is one or both of amylose and amylopectin.

[0025] This invention also protects the starch-based lithium-ion battery silicon anode binder obtained by the preparation method.

[0026] Furthermore, the present invention also claims protection for the application of the starch-based lithium-ion battery silicon anode binder in the preparation of lithium-ion batteries.

[0027] Preferably, SiOx@C particles, Super P conductive agent and starch-based lithium-ion battery silicon anode binder are mixed in a mass ratio of 60:20:20, and a solvent is added and stirred evenly to obtain an electrode slurry.

[0028] Preferably, x in SiOx@C particles satisfies 0.5≤x≤1.5.

[0029] Preferably, the prepared electrode slurry is cast onto the surface of the copper foil current collector and uniformly coated using a doctor blade to form an electrode film of suitable thickness. The coated electrode is then dried under vacuum to ensure complete solvent evaporation. The electrode material loading after drying is controlled at 0.8 ~ 1 mg cm⁻¹. -2 between.

[0030] The starch-based lithium-ion battery silicon anode binder, its preparation method, and its application provided by this invention have the following advantages compared with existing technologies:

[0031] (1) Excellent adhesion performance: Through chemical modification and three-dimensional cross-linking design, this adhesive can significantly improve the adhesion of silicon suboxide anode, effectively fix the active material and inhibit its shedding.

[0032] (2) High mechanical stability: The three-dimensional cross-linked network structure enables the binder to effectively alleviate the volume change problem of silicon suboxide and avoid damage to the electrode structure.

[0033] (3) Environmental protection and sustainability: Based on natural starch, the binder is green and environmentally friendly, with a wide range of sources, which meets the needs of sustainable development.

[0034] (4) Simple preparation process: The binder of the present invention is simple to prepare, suitable for large-scale production, and applicable to the manufacturing needs of various negative electrode materials.

[0035] The starch-based binder of this invention, through chemical modification and cross-linking design, constructs a high-strength three-dimensional network structure. This not only overcomes the shortcomings of traditional starch but also significantly improves bonding performance and environmental friendliness, providing a new solution for high-performance lithium-ion batteries. The development of this starch-based binder not only significantly enhances the application performance of silicon suboxide anodes in lithium-ion batteries but also provides new ideas for the design of high-performance, environmentally friendly lithium battery materials, which is of great significance for the future industrial application of lithium-ion batteries in the fields of high energy density and long lifespan. Attached Figure Description

[0036] Figure 1 The image shows the SEM surface particle size (2 μm) of the starch-based electrode from Example 1.

[0037] Figure 2 The image shows the SEM surface particle pattern (500 nm) of the starch-based electrode in Example 1.

[0038] Figure 3 The graph shows the long-cycle performance test results of the starch-based electrode in this embodiment.

[0039] Figure 4 The rate performance diagram of the starch-based electrode in this embodiment is shown.

[0040] Figure 5 The image shows the cyclic voltammetry curve of the starch-based electrode in Example 1.

[0041] Figure 6 The graph shows the GITT test results of the starch-based electrode in Example 1.

[0042] Figure 7 The image shows the XRD pattern of the starch-based electrode from Example 1.

[0043] Figure 8 The image shows the XPS spectrum of the starch-based electrode from Example 1. Detailed Implementation

[0044] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods used in the embodiments of the present invention are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available reagents and materials.

[0045] This invention utilizes the synergistic modification of starch and LiF in DMSO, combined with SiOx@C particles (SiOx@C particles are SiOx particles coated with a nano-carbon layer, on which carbon nanotubes are grown in situ, wherein 0.5≤x≤1.5; a commonly used commercially available material) to construct an electrode material system, thereby improving the adhesion and electrochemical stability of silicon suboxide anode materials. The specific technical solution is as follows:

[0046] (1) Preparation of modified starch

[0047] Starch, dimethyl sulfoxide (DMSO), and lithium fluoride (LiF) were placed in a container and heated at 60°C with vigorous stirring for 4 hours. During the heating and stirring process, DMSO acted as a solvent to promote the unfolding of starch molecular chains, while LiF reacted with the hydroxyl groups in starch through ionic bonding, further enhancing the mechanical strength and adhesive properties of the starch, ultimately forming a modified starch polymer binder.

[0048] (2) Preparation of electrode paste

[0049] SiOx@C particles, Super P conductive agent (a general-purpose conductive agent), and modified starch binder were mixed at a mass ratio of 60:20:20. A suitable amount of solvent was added and the mixture was stirred until homogeneous, thus preparing a uniform electrode slurry. The high uniformity of this slurry contributes to the formation of a structurally stable electrode film.

[0050] (3) Electrode coating and drying

[0051] The prepared electrode slurry was cast onto the surface of the copper foil current collector and uniformly coated using a doctor blade to form an electrode film of suitable thickness. Subsequently, the coated electrode was dried under vacuum at 80°C to ensure complete solvent evaporation and thorough bonding between the binder and the active material. The loading of the dried electrode material was controlled at 0.8–1 mg cm⁻¹. -2 To ensure optimal electrochemical performance and stability.

[0052] (4) Battery assembly

[0053] In an inert atmosphere glove box, a 2023-type coin cell was assembled using lithium metal as the counter and reference electrode and silicon suboxide as the working electrode. Conventional lithium-ion battery electrolytes were used, and repeatability and reliability were ensured through precise control of the battery assembly process.

[0054] (5) Electrochemical performance testing

[0055] A series of silica half-cells based on binders modified with different starches were prepared and comparative tests were conducted. The performance of the binder in the silica anode material was analyzed using cyclic voltammetry, constant current charge-discharge, and cyclic voltammetry methods, verifying its superiority in capacity retention, cycle stability, and rate performance.

[0056] The following Examples 1 to 3 were conducted using different starches to demonstrate the versatility of the above-mentioned starch modification.

[0057] Example 1:

[0058] ① Preparation of amylopectin-based negative electrode slurry: Amylopectin (1g), dimethyl sulfoxide (DMSO, 5g), and lithium fluoride (LiF, 0.02g) were placed in a container and heated at 60℃ with vigorous stirring for 4 hours. Subsequently, SiOx@C particles and Super P conductive agent were added to the binder (the mass ratio of SiOx@, Super P, and binder was 60:20:20). The mixture was stirred evenly with an appropriate amount of solvent (deionized water) to prepare a uniform electrode slurry.

[0059] ② Preparation of silicon anode: The prepared electrode slurry was cast onto copper foil (coated evenly with a scraper) and dried under vacuum at 80°C. The Si particle mass loading level was set to 0.8 ~ 1 mg cm⁻¹. -2 .

[0060] ③ Battery assembly: The prepared copper foil is used as the silicon anode, and lithium foil, LiPF6 solution, and polypropylene film are used as the counter electrode, reference electrode, electrolyte, and separator, respectively. The cells are assembled into a 2032 type button cell in a glove box.

[0061] ④ Electrochemical performance testing: On a charge / discharge tester, set the voltage range to 0.01 to 2V and the current density to 0.1C for charge / discharge cycle testing; set the current density to 0.1, 0.2, 0.5, and 1C for rate testing; use an electrochemical workstation (IVIUM) at 0.1mV / s within the voltage range of 0.01-1.2V (vs. Li / Li+). -1Cyclic voltammetry measurements were performed at a scan rate; for GITT (given intermittent titration) testing, a constant current of 0.1C (1C = 2000 mA / g) was applied to the battery for 15 min during charge and discharge, followed by current relaxation for 30 min to allow the battery to reach equilibrium. Cycles were continued until the charge / discharge cutoff voltages (2V and 0.01V), respectively.

[0062] ⑤ Results and Discussion: such as Figure 1 , Figure 2 As shown in Table 1, the SEM surface of the amylopectin-based electrode exhibits a uniform particle distribution with no obvious agglomeration, and the SiOx particles have a diameter of approximately 1 μm. To evaluate the peel strength of the electrode prepared with the binder material, a 180° peel test was conducted, revealing that the amylopectin-based electrode possesses a peel strength as high as 26 N / m. Figure 3 and 4 As shown, the electrode material exhibits excellent performance in long-cycle and rate performance tests. After 100 cycles at a current density of 0.1C, its specific capacity remains at 1037 mAh / g, with an initial coulombic efficiency of 83.1%. After a total of 50 rate tests (current density varying between 0.1C and 1C), the specific capacity remains as high as 1220 mAh / g when recovering to 0.1C. Figure 5 As shown, the electrochemical redox reaction of the electrode was studied using cyclic voltammetry (CV) in the range of 0.01 and 2 V at a scan rate of 0.1 mV / s. A cathode peak centered at 0.14 V and two anodic peaks centered at 0.52 V and 0.33 V were observed, corresponding to the typical alloying and dealloying behavior of amorphous silicon, respectively. The CV curve shape remained stable throughout the three cycles, indicating that the electrode exhibits good reversibility during charge and discharge. Figure 6 As shown in the figure, the GITT test results indicate that the lithium-ion diffusion curve exhibits a "W" shaped characteristic, with a diffusion rate ranging from 1.0 × 10⁻⁶. -8 ~ 1.0×10 -12 Between. For example Figure 7 As shown, the XRD pattern of the starch-based electrode exhibits distinct SiO and SiO₂ crystal peaks, proving that the active material of the starch-based electrode is SiO₂x. Figure 8 As shown, the XPS Si 2p, C 1s and O 1s spectra of the starch-based electrode indicate that its surface has abundant bonding groups, including Si-OS and Si-C interfacial bonds. The abundant bonding of the binder can effectively maintain the stable cycling performance of the electrode.

[0063] Example 2

[0064] ① Preparation of amylose-based negative electrode slurry: Amylose (1g), dimethyl sulfoxide (DMSO, 5g), and lithium fluoride (LiF, 0.02g) were placed in a container and heated at 60℃ with vigorous stirring for 4 hours. Subsequently, SiOx@C particles and Super P conductive agent were added to the binder (the mass ratio of SiOx@, Super P, and binder was 60:20:20). The mixture was stirred evenly with an appropriate amount of solvent (deionized water) to prepare a uniform electrode slurry.

[0065] ② Preparation of silicon anode: The prepared electrode slurry was cast onto copper foil (coated evenly with a scraper) and dried under vacuum at 80°C. The Si particle mass loading level was set to 0.8 ~ 1 mg cm⁻¹. -2 .

[0066] ③ Battery assembly: The prepared copper foil is used as the silicon anode, and lithium foil, LiPF6 solution, and polypropylene film are used as the counter electrode, reference electrode, electrolyte, and separator, respectively. The cells are assembled into a 2032 type button cell in a glove box.

[0067] ④ Electrochemical performance testing: On a charge / discharge tester, the voltage range was set between 0.01 and 2V, and the current density was set to 0.1C for charge / discharge cycle testing; rate testing was conducted with current densities of 0.1, 0.2, 0.5, and 1C respectively; for the GITT test, a constant current of 0.1C (1C = 2000mA / g) was applied to the battery for 15 min during charge / discharge, followed by current relaxation for 30 min to allow the battery to reach equilibrium. The cycles continued until the charge / discharge cutoff voltages (2V and 0.01V).

[0068] ⑤ Results and Discussion: As shown in Table 1, to evaluate the peel strength of the electrodes prepared with the binder material, a 180° peel test was conducted. The results showed that the peel strength of the amylose-based electrode was 21 N / m. Figure 3 and 4 As shown, to evaluate the cycling stability and rate performance of the electrode material, after 100 cycles at a current density of 0.1C, its specific capacity remained at 526 mAh / g, with an initial coulombic efficiency of 78.6%. After a total of 50 rate tests (current density varying between 0.1C and 1C), the specific capacity recovered to 1139 mAh / g at 0.1C.

[0069] Example 3

[0070] ① Preparation of corn starch-based negative electrode slurry: Corn starch (1g), dimethyl sulfoxide (DMSO, 5g), and lithium fluoride (LiF, 0.02g) were placed in a container and heated at 60℃ with vigorous stirring for 4 hours. Subsequently, SiOx@C particles and Super P conductive agent were added to the binder (the mass ratio of SiOx@, Super P, and binder was 60:20:20). The mixture was stirred evenly with an appropriate amount of solvent (deionized water) to prepare a uniform electrode slurry.

[0071] ② Preparation of silicon anode: The prepared electrode slurry was cast onto copper foil (coated evenly with a scraper) and dried under vacuum at 80°C. The Si particle mass loading level was set to 0.8 ~ 1 mg cm⁻¹. -2 .

[0072] ③ Battery assembly: The prepared copper foil is used as the silicon anode, and lithium foil, LiPF6 solution, and polypropylene film are used as the counter electrode, reference electrode, electrolyte, and separator, respectively. The cells are assembled into a 2032 type button cell in a glove box.

[0073] ④ Electrochemical performance testing: On a charge / discharge tester, the voltage range was set between 0.01 and 2V, and the current density was set to 0.1C for charge / discharge cycle testing; rate testing was conducted with current densities of 0.1, 0.2, 0.5, and 1C respectively; for the GITT test, a constant current of 0.1C (1C = 2000mA / g) was applied to the battery for 15 min during charge / discharge, followed by current relaxation for 30 min to allow the battery to reach equilibrium. The cycles continued until the charge / discharge cutoff voltages (2V and 0.01V).

[0074] ⑤ Results and Discussion: As shown in Table 1, to evaluate the peel strength of the electrodes prepared with the binder material, a 180° peel test was conducted. The results showed that the peel strength of the amylose-based electrode was 14 N / m. Figure 3 and 4 As shown, to evaluate the cycling stability and rate performance of the electrode material, after 100 cycles at a current density of 0.1C, its specific capacity remained at 184 mAh / g, with an initial coulombic efficiency of 73.5%. After a total of 50 rate tests (current density varying between 0.1C and 1C), the specific capacity recovered to 915 mAh / g at 0.1C.

[0075] Tables 1 and 2 show the performance test results of the negative electrode sheet and the initial charge-discharge performance test results of the constructed starch-based binder battery, respectively, for each embodiment.

[0076] Table 1. Performance test results of starch-based binder negative electrode sheets

[0077] Table 2. Initial charge-discharge performance test results of starch-based binder batteries

[0078] Obviously, the specific implementation schemes described above are merely a further detailed explanation of the purpose, technical solution and beneficial effects of the present invention. It should be understood that the above descriptions are only specific examples of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a starch-based lithium-ion battery silicon anode binder, characterized in that, Starch and lithium fluoride are added to a solvent, heated and stirred until homogeneous to obtain a modified starch polymer binder; the mass ratio of starch to lithium fluoride is 20~50:

1.

2. The preparation method according to claim 1, characterized in that, The solvent is dimethyl sulfoxide.

3. The preparation method according to claim 2, characterized in that, The heating temperature is 55~70℃, and the stirring time is 3~5 hours.

4. The preparation method according to claim 2, characterized in that, The starch is one or both of amylose and amylopectin.

5. The starch-based lithium-ion battery silicon anode binder obtained by any of the preparation methods described in claims 1 to 4.

6. The application of the starch-based lithium-ion battery silicon anode binder according to claim 5 in the preparation of lithium-ion batteries.

7. The application according to claim 6, characterized in that, SiOx@C particles, Super P conductive agent, and starch-based lithium-ion battery silicon anode binder are mixed in a mass ratio of 60:20:20, and then a solvent is added and stirred until homogeneous to obtain the electrode slurry.

8. The application according to claim 7, characterized in that, In SiOx@C particles, x satisfies 0.5 ≤ x ≤ 1.

5.

9. The application according to claim 7, characterized in that, The prepared electrode slurry was cast onto the surface of the copper foil current collector and uniformly coated using a doctor blade to form an electrode film of suitable thickness. The coated electrode was then dried under vacuum to ensure complete solvent evaporation. The electrode material loading after drying was controlled at 0.8–1 mg / cm³. -2 between.

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