A modified silicon anode binder for lithium batteries and its application in anode sheets and batteries.

Abstract

This invention provides a modified lithium-ion battery silicon anode binder and its applications in anode sheets and batteries, belonging to the field of lithium-ion batteries. This invention utilizes chitosan as the main chain, pre-assembling it with a crosslinking agent integrating dual functional units of ion concentration sensing and electrochemical potential response. By leveraging the concentration gradient during electrode pretreatment to drive spontaneous crosslinking and gradient network formation, a smart binder with gradient structure and potential-triggered dynamic adjustment capabilities is prepared. This binder is used in the preparation of silicon anode sheets and the assembly of lithium-ion batteries, solving the problems of existing binders' inability to adaptively coordinate the requirements of high-elasticity buffers and rigid ion channels, their inability to suppress dendrite growth at high rates, and their difficulty in balancing long-cycle stability and high-rate safety. This anode binder can be used to prepare high-rate fast-charging lithium-ion battery silicon anodes, possessing great development potential in high-end power batteries and energy storage systems.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, specifically to a modified lithium battery silicon anode binder and its application in anode sheets and batteries. Background Technology

[0002] Currently, research on silicon anode binders in lithium-ion battery research still faces a series of challenges. For example, silicon materials may experience a massive volume expansion exceeding 300% during battery cycling, leading to issues such as electrode pulverization, capacity decay, and interfacial imbalance. These challenges represent a core bottleneck restricting their widespread application. As a key component within the electrode, the core function of binders has evolved from the traditional single adhesive role to requiring multiple properties simultaneously, including stress dissipation, interfacial stability, and ion transport promotion.

[0003] Existing research on binders struggles to maintain a robust mechanical support network while simultaneously constructing a high-speed and stable lithium-ion transport channel. Furthermore, it lacks dynamic response capabilities to the complex electrochemical environment within the battery, resulting in a difficulty in synergistically achieving high specific capacity, high rate capability, and long cycle life. CN121022314A discloses a silicon anode binder, its preparation method, and its application. A comb-shaped graft copolymer is prepared as the silicon anode binder. The main chain of the comb-shaped structure consists of polyurethane segments, with polyacrylic acid segments and fluorinated segments covalently linked on the side chains. Utilizing the synergistic function of each segment, the electrode's tolerance to silicon volume expansion is effectively improved. The resulting silicon anode binder exhibits a balance of rigidity and flexibility, along with good interfacial stability, maintaining a high capacity of the anode even after 500 cycles. However, this polymer network structure is uniform and lacks spatial functional partitioning design tailored to the ion transport requirements within the electrode. This results in high ion migration resistance at high rates, leading to limited ionic conductivity and a tendency to polarize at high currents, significantly limiting the battery's rate performance.

[0004] Current research on silicon anode binders mainly focuses on enhancing mechanical properties, but shortcomings in rate performance still exist. Therefore, binder systems with ion transport functions are gradually being developed. CN120966427A discloses a method for preparing a lignin-polyoxyethylene composite binder and its application in hard carbon anodes. In this invention, acid-precipitated lignin is chemically modified to obtain quaternized sodium lignin carboxylate, which is then chemically crosslinked with polyoxyethylene to prepare a lignin-polyoxyethylene binder with a three-dimensional network structure. The abundant active functional groups on the molecular chain provide electrostatic spatial repulsion between hard carbon particles, achieving efficient dispersion and reducing surface defects. The quaternary ammonium and other groups improve ion conductivity, providing efficient ion transport channels, thereby improving the rate performance of the anode. At the same time, the three-dimensional network formed by chemical crosslinking also enhances the mechanical and cycle performance of the anode. However, the ion-conducting network constructed by this binder is a static system that is spatially uniform and temporally solidified. The material performance requirements are different at different locations inside the battery, and the electrochemical microenvironment inside the battery is also dynamic during high-rate or long-cycle operation. Therefore, the static binder network system cannot meet these differentiated requirements.

[0005] In summary, given the current shortcomings of silicon anode binders for lithium-ion batteries, there is an urgent need to develop a multifunctional integrated binder that can actively adapt to changes in silicon volume, ensure high-rate ion transport, and intelligently respond to potential risks to suppress dendrite growth. This would be of great significance for promoting the application of silicon anodes in high-end electric vehicles and high-power energy storage electronic devices, which have high requirements for energy density, power density, and safety. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a modified lithium-ion battery silicon anode binder and its applications in anode sheets and batteries. This invention utilizes chitosan as the main chain, pre-assembling it with a crosslinking agent integrating dual functional units of ion concentration sensing and electrochemical potential response. By leveraging the concentration gradient during electrode pretreatment to drive spontaneous crosslinking and gradient network formation, a smart binder with gradient structure and potential-triggered dynamic adjustment capabilities is prepared. This binder is then used in the fabrication of silicon anode sheets and the assembly of lithium-ion batteries, solving the problems of existing binders' inability to adaptively coordinate the requirements of high-elasticity buffers and rigid ion channels, their inability to suppress dendrite growth at high rates, and their difficulty in simultaneously ensuring long-cycle stability and high-rate safety.

[0007] This invention discloses a modified lithium battery silicon anode binder, which is a pre-assembled solid composite powder formed by physical blending of highly active chitosan and bifunctional polyethylene glycol dialdehyde crosslinking agent. The bifunctional crosslinking agent has crown ether derivative units and bipyridine metal complex units covalently grafted onto its molecular backbone, and the two functional units are respectively grafted onto both ends of the polymer backbone.

[0008] This invention also discloses a method for preparing a modified lithium battery silicon anode binder, such as... Figure 1 As shown, the specific technical solution is as follows:

[0009] Step 1: Using a dual-terminal active polymer as a flexible backbone, the two ends of the polymer are first modified to aldehyde groups through an amidation reaction. Then, without separating the intermediates, a cyclic ligand unit with lithium ion coordination ability is first introduced, followed by a potential-responsive unit with reversible redox properties. The difference in reactivity of the amino groups of the two functional units is used to achieve directional grafting. The two functional units are covalently grafted to both ends of the polymer backbone through a Schiff base condensation reaction. After precipitation, washing and vacuum drying, a solid crosslinking agent with both ion sensing and potential response functions is obtained.

[0010] Step 2: Dissolve chitosan powder in dilute acid aqueous solution to protonate and dissolve it to form a homogeneous colloid. Then, add the solution dropwise into an excess of cold alkali solution to precipitate chitosan. After separation, the precipitate is repeatedly washed with deionized water until neutral, and then freeze-dried to obtain a loose and porous solid powder.

[0011] Step 3: Place the bifunctional crosslinking agent solid powder and the highly active chitosan solid powder together in the grinding jar of a planetary ball mill for ball milling to achieve uniform dispersion and close contact of the two powders at the submicron scale. The uniform dry powder obtained by sieving is the pre-assembled composite binder.

[0012] This invention also discloses a modified lithium battery silicon anode binder application for anode sheets and batteries. The anode sheet is formed by coating a slurry made by mixing anode active material, binder, conductive carbon black and a small amount of lithium nitrate. After low-temperature moisturizing pre-crosslinking, the mixture is gradually heated and dried. Subsequently, the anode sheet, positive electrode sheet and separator are encapsulated together to form a lithium-ion battery.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] 1. Stable and reversible redox pairs such as 4,4'-diamino-2,2'-bipyridine cobalt(II) are covalently incorporated into the crosslinking agent molecular chain. This unit serves as a built-in potential sensor (standard reduction potential is 0.15~0.35V vs Li). + / Li, matching silicon anode operating potential 0.01~0.5V vs Li +When the electrochemical potential of the microregion containing Co decreases to a specific threshold, a reversible redox reaction occurs, i.e., Co... 2+ / Co 3+ The valence state transition triggers an instantaneous change in molecular conformation and polarity. This change can reversibly regulate the local entanglement state and ion migration ability of the surrounding polymer network, thereby achieving adaptive regulation of ion flux in high-risk regions where lithium dendrites may germinate.

[0015] 2. By integrating the two functions mentioned above into the same crosslinking agent through molecular design, and utilizing the difference in reactivity of the functional unit amino groups to achieve directional grafting, the spatial arrangement is completed in a one-step process during the manufacturing stage. In the pretreatment stage, a static mechanical-transport gradient substrate is formed based on concentration sensing. During the battery operation stage, the potential response unit implanted in the substrate is in a static standby state until it is triggered by an abnormal potential. This design, which combines one-time construction and on-demand response, realizes the unity of pre-optimization of electrode structure and immediate handling of operational risks at the molecular level, expanding the functional dimensions of binder materials.

[0016] 3. Utilizing the lithium salt concentration gradient formed during electrode pretreatment (low-temperature moisturizing pre-crosslinking) as the driving force, and lithium nitrate as the lithium salt source, after slurry coating, the solvent evaporation rate of the surface layer is faster than that of the bottom layer, resulting in a higher Li+ concentration on the surface layer than on the bottom layer, forming a concentration gradient from the surface layer to the current collector; the crown ether functional units in the slurry can specifically respond to changes in local lithium ion concentration, and regulate the kinetics of the Schiff base crosslinking reaction by changing the polarity and steric hindrance of the local microenvironment. This process occurs spontaneously in the combined process of low-temperature moisturizing pre-crosslinking and gradual heating drying, ultimately forming a binder matrix with continuously changing crosslinking density and network structure in the electrode thickness direction, realizing the synchronous gradient design of mechanical support and ion transport performance. Attached Figure Description

[0017] Appendix Figure 1 This is a flowchart illustrating the preparation process of the silicon anode binder of the present invention.

[0018] Appendix Figure 2 This is a schematic diagram showing the specific discharge capacity of lithium batteries prepared with binders in the embodiments and comparative examples of the present invention at different discharge rates.

[0019] Appendix Figure 3 A schematic diagram showing the specific capacity change of lithium batteries prepared with binders for embodiments and comparative samples of the present invention after 1000 charge-discharge cycles at 3C rate.

[0020] Appendix Figure 4 This diagram illustrates the specific discharge capacity of lithium batteries prepared with binders for embodiments and comparative samples of the present invention at different discharge rates at 55°C. Detailed Implementation

[0021] The following embodiments further explain and illustrate the technical solutions of the present invention. It should be specifically noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0022] This invention proposes a method for preparing a modified silicon anode binder for lithium batteries, such as... Figure 1 As shown, the specific technical solution is as follows:

[0023] 1. Synthesis of bifunctional crosslinking agents

[0024] Under anhydrous and oxygen-free conditions, crown ether derivative ionic coordination units and bipyridine metal complex potential-responsive units were covalently grafted to both ends of a bi-aldehyde-terminated polyethylene glycol (PEG) backbone via sequential amidation and directional Schiff base condensation reactions. The resulting bifunctional crosslinking agent solid was obtained after precipitation purification. Due to the good flexibility and compatibility of PEG segments with electrolytes, and the ease of chemical modification of its end groups, benzaldehyde end groups were introduced into its molecular chain ends, enabling it to undergo Schiff base crosslinking reactions with the amino groups of the functional units. The Schiff base reaction requires no additional condensing agent; directional grafting can be achieved by controlling the reaction sequence and the differences in the reactivity of the functional units. Furthermore, the cyclic ether oxygen structure of the crown ether derivative unit exhibits specific and reversible coordination ability with lithium ions. This coordination significantly alters the electron cloud distribution and spatial conformation of the crown ether unit itself, thereby affecting the local polarity and steric hindrance of the polymer fragments it connects to. During pretreatment, the difference in the degree of coordination between the crown ether and lithium ions under different lithium ion concentrations becomes a molecular switch regulating the differential Schiff base reaction rate in its vicinity. Bipyridine metal complex units (4,4'-diamino-2,2'-bipyridine cobalt(II)) react at the normal operating potential of the battery as Co 2+ The morphology remains stable, but a reversible redox reaction (Co) occurs when the local potential abnormally decreases. 2+ →Co 3+ This process transforms bipyridine metal complex molecules from a relatively hydrophobic and planar state to a relatively hydrophilic state with a slight conformational change. This microscopic change can reversibly push or relax the neighboring polymer chain network, thereby instantly regulating the ion migration ability of the local area.

[0025] 2. Preparation of highly active chitosan

[0026] Chitosan was dissolved in acid and then purified using an alkaline reprecipitation method to form a high specific surface area morphology. After washing and freeze-drying, highly active chitosan solid was obtained. Because chitosan molecular chains may partially aggregate or crystallize during processing, resulting in insufficient surface-accessible amino groups and uneven reactivity, dissolving chitosan in acid not only forms a homogeneous solution for subsequent processing but also protonates the amino groups on the chitosan chains to form ammonium salts. Under the action of electrostatic repulsion, the originally entangled or hydrogen-bonded molecular chains are fully extended, thereby exposing more active sites. The subsequent reprecipitation in a strong alkali solution deprotonates the chitosan, reducing its solubility and allowing it to recrystallize and aggregate at the molecular scale. However, small molecule impurities dissolved in the acid solution (such as proteins and pigments) remain in the mother liquor, thus purifying the chitosan molecules. Because the chitosan undergoes instantaneous precipitation from a homogeneous solution, it forms solid particles with smaller diameters, larger specific surface areas, and rougher, more porous surfaces. This type of chitosan exposes more active amino groups per unit mass, allowing subsequent freeze-drying to retain this microstructure to the greatest extent possible and preventing pore collapse and particle agglomeration caused by surface tension during conventional heat drying. The resulting chitosan particles have a high and easily accessible free amino content, dissolve or swell rapidly, and exhibit good reaction uniformity. This facilitates uniform pre-assembly mixing with crosslinking agent powder and allows for rapid and simultaneous large-area Schiff base reactions during pretreatment, forming a uniform and robust crosslinked network. The resulting chitosan particles have a high content of free amino groups that are easily accessible, dissolve or swell quickly, and exhibit good reaction uniformity. This is beneficial for achieving uniform pre-assembly mixing with the crosslinking agent powder and for rapidly and synchronously carrying out large-area Schiff base reactions during pretreatment, thereby forming a uniform and strong crosslinking network.

[0027] 3. Composite adhesive pre-assembly

[0028] Crosslinking agent powder and chitosan powder are mixed at a certain mass ratio and then homogeneously mixed at the submicron level using high-speed ball milling to obtain a pre-assembled solid composite binder. By controlling the mass ratio of the two powders during mixing, the ratio of aldehyde and amino groups is indirectly regulated, ensuring the theoretical density of chemical crosslinking points in the final electrode from the source. This effectively controls the range of softness and hardness of the gradient structure. Simultaneously, the mechanical force of ball milling breaks up secondary agglomeration of the powder, allowing the bifunctional crosslinking agent particles and highly active chitosan particles to interpenetrate and closely embed, almost reaching a molecular-level proximity state. This achieves uniform dispersion of the two components at the microscale in the dry state. In this pre-assembled structure, each crosslinking agent molecule is surrounded by the active amino groups of multiple chitosan molecules, and each chitosan molecular chain is also close to the aldehyde functional groups of multiple crosslinking agent molecules. However, in the solid state, no covalent bonds have yet formed between them. Therefore, this physically mixed state is relatively stable and easy to store and transport. However, when this pre-assembled powder is used to prepare electrode slurry, the presence of solvent will simultaneously wet and swell both particles, causing them to rapidly dissociate, dissolve, or disperse. Since the functional groups of the two particles have achieved spatial uniformity and close proximity in the solid state, and a small amount of acetic acid has been added to the slurry as a catalyst, the Schiff base condensation reaction can be initiated immediately and uniformly throughout the slurry system once it comes into contact with the solvent. The chemical crosslinking process is completed in the subsequent low-temperature moisturizing pre-crosslinking stage, thereby avoiding local reactions that are too fast or too slow due to uneven mixing. This ensures that the crosslinking network generated in the entire electrode is macroscopically uniform, microscopically continuous and controllable.

[0029] 4. Negative electrode preparation and battery assembly

[0030] The binder is combined with the negative electrode active material, conductive agent and a small amount of lithium salt ( After mixing, a solvent is added to form a slurry, which is then coated onto copper foil. The mixture is first moisturized and pre-crosslinked, then gradually dried, and finally rolled, cut, and placed in a vacuum drying oven for vacuum drying. It is then assembled into a lithium-ion battery in an anhydrous and oxygen-free environment. During the moisturizing and pre-crosslinking stage, lithium nitrate serves as the lithium salt source. As the solvent slowly migrates, the surface solvent evaporates faster than the underlying layer, leading to a faster evaporation rate of the surface Li-ion layer. + The concentration is higher than that of the bottom layer, forming a concentration gradient from the surface to the current collector; the crown ether units in the binder molecules act as concentration sensors, differentially sensing local Li + In high-concentration regions, the Schiff base reaction is accelerated, forming rigid ion channels with high cross-linking density; in low-concentration regions, the reaction proceeds more slowly, forming an elastic buffer layer with low cross-linking density, thus spontaneously completing the one-time in-situ molding of the gradient structure during the assembly process. During battery operation, the bipyridine metal complex units embedded in this gradient network act as potential sensors, undergoing a reversible redox reaction (Co) when the local potential abnormally decreases to the dendrite growth risk threshold. 2+ / Co 3+Valence state transition), instantaneously adjust the entanglement state and ion flux of polymer network, actively suppress dendrite initiation, and realize the unity of pre-gradient optimization of electrode structure in the manufacturing stage and real-time dynamic response to risks in the operation stage at the molecular level.

[0031] The following are some specific embodiments of the present invention, and Table 1 shows the raw material information used in the embodiments.

[0032] Table 1 Raw Material Information Table

[0033]

[0034] Example 1

[0035] S1: In a glove box where the water and oxygen content are both less than 0.1 ppm, 10.0 g of polyoxyethylene diamine was weighed and dissolved in 40 mL of anhydrous DMF. The solution was then transferred to an ice-water bath at 0 °C. While stirring slowly, 5.9 g of 4-formylbenzoic acid succinimide ester was added dropwise to the system. The system was heated to 5 °C and stirred for 3 h to allow for amidation. Then, 4.2 g of 4''-aminobenzo-15-crown 5-ether was added, and the system was heated to 22 °C and stirred for 10 h. Next, 3.5 g of 4,4'-diamino-2,2'-bipyridine cobalt(II) was added, and the mixture was stirred for another 10 h to allow for Schiff base condensation. The reaction solution was then added dropwise to 450 mL of anhydrous diethyl ether pre-cooled to 2 °C to precipitate the product. The precipitate was collected by centrifugation at 9000 rpm and washed twice with cold diethyl ether. Finally, the product was dried under vacuum at 35 °C for 20 h to obtain a brownish-red solid powder.

[0036] S2: Weigh 20.0 g of chitosan and add it to 800 mL of acetic acid aqueous solution (2% by volume). Stir at 23 °C for 5 h to dissolve. Add the dissolved solution dropwise to 2000 mL of 2.5 mol / L NaOH aqueous solution pre-cooled to 8 °C at a rate of 3 mL / min. Stir at 400 rpm while adding the solution. Continue stirring for 50 min. Collect the precipitate by suction filtration using a Buchner funnel and wash with deionized water until the filtrate is neutral. Freeze the wet filter cake at -55 °C for 5 h and then freeze-dry at -55 °C for 42 h to obtain a white, fluffy powder.

[0037] S3: Weigh 15.2g of the brownish-red solid powder prepared in S1 and 3.36g of the white fluffy powder prepared in S2. Place both powders together in a 100mL zirconia grinding jar, add zirconia grinding balls with a diameter of 4mm to the jar, with a ball-to-powder ratio of 7:1, and ball mill at 300rpm for 4h. After the process, collect the powder through a 150-mesh sieve to obtain a light brownish-red pre-assembled solid composite binder.

[0038] S4: SiO / C, conductive carbon black, binder, and lithium nitrate are mixed in a mass ratio of 80:8:6:1. Then, 70 wt% of 1,4-butyrolactone (containing 0.5% acetic acid by volume) is added dropwise. The mixture is stirred at 500 rpm for 30 min under vacuum, followed by stirring at 2000 rpm for 90 min. After stirring, the mixture is allowed to stand for 30 min to remove bubbles. The slurry is then coated onto copper foil and kept moist at 50°C and 50% relative humidity. After pre-crosslinking for 2.5 hours, the material was transferred to an oven and dried at 80°C for 30 minutes, then at 120°C for 60 minutes. Subsequently, it was rolled, cut, and placed in a vacuum drying oven at 150°C for 12 hours to obtain a negative electrode sheet prepared with modified silicon negative electrode binder. This negative electrode sheet was then assembled into a CR2032 type lithium-ion battery in an argon glove box. The positive electrode of the battery is lithium iron phosphate, and the electrolyte is a 1:1 mixture of ethylene carbonate and dimethyl carbonate containing 1 mol / L LiFSI.

[0039] Example 2

[0040] The preparation method according to Example 1 differs in that:

[0041] S1: 5.4 g of 4-formylbenzoic acid succinimide ester was added dropwise to the system. The amidation reaction temperature was 0℃ and the reaction time was 2.5 h. After adding 4''-aminobenzo-15-crown 5-ether, the mixture was stirred for 8 h. Then, 3.2 g of 4,4'-diamino-2,2'-bipyridine cobalt(II) was added and the mixture was stirred for another 8 h. The Schiff base condensation reaction temperature was 18℃.

[0042] S2: The volume fraction of the acetic acid aqueous solution is 1.5%, the concentration of the NaOH solution is 2 mol / L, and the temperature is 5℃;

[0043] S3: The white fluffy powder prepared in S2 was weighed in an amount of 3.02g. The ball-to-powder ratio during ball milling was 5:1, and the ball milling time was 3h.

[0044] S4: The pre-crosslinking temperature for moisturizing is 40℃, the humidity is 40%, and the time is 2 hours. All other steps are the same.

[0045] Example 3

[0046] The preparation method according to Example 1 differs in that:

[0047] S1: 6.4 g of 4-formylbenzoic acid succinimide ester was added dropwise to the system. The amidation reaction temperature was 8℃ and the reaction time was 4 h. After adding 4''-aminobenzo-15-crown 5-ether, the mixture was stirred for 12 h. Then, 3.8 g of 4,4'-diamino-2,2'-bipyridine cobalt(II) was added and the mixture was stirred for another 12 h. The Schiff base condensation reaction temperature was 28℃ and the reaction time was 24 h.

[0048] S2: The volume fraction of the acetic acid aqueous solution is 2.5%, the concentration of the NaOH solution is 3 mol / L, and the temperature is 15℃;

[0049] S3: The white fluffy powder prepared in S2 was weighed in an amount of 3.70g. The ball-to-powder ratio during ball milling was 8:1, and the ball milling time was 5h.

[0050] S4: Moisturize and pre-crosslink at 60°C and 60% humidity for 3 hours. All other steps are the same.

[0051] Example 4

[0052] The preparation method according to Example 1 differs in that:

[0053] S1: 5.9 g of 4-formylbenzoic acid succinimide ester was added dropwise to the system. The amidation reaction temperature was 8℃, the reaction time was 3.5 h, the condensation reaction temperature was 25℃, 4''-aminobenzo-15-crown 5-ether was added and stirred for 9 h, then 3.4 g of 4,4'-diamino-2,2'-bipyridine cobalt(II) was added and stirred for another 9 h. The Schiff base condensation reaction time was 18 h.

[0054] S2: The volume fraction of the acetic acid aqueous solution is 2.2%, the concentration of the NaOH solution is 2.8 mol / L, and the temperature is 12℃;

[0055] S3: The white fluffy powder prepared in S2 was weighed in an amount of 3.53g. The ball-to-powder ratio during ball milling was 6:1, and the ball milling time was 4.5h.

[0056] S4: Moisturizing pre-crosslinking temperature 55℃, humidity 55%, time 2.5h, the rest of the steps are the same.

[0057] Comparative Example 1

[0058] The preparation method according to Example 1 differs in that:

[0059] S1: Dissolve the obtained brownish-red solid in 100 mL of acetate-sodium acetate buffer solution with pH=5.0, and then add 2.0 g of 50% glutaraldehyde aqueous solution dropwise while stirring. Continue stirring at 25 °C for 12 h to obtain the crosslinking agent reaction solution.

[0060] S3: Weigh 10.08g of the white fluffy powder prepared in S2 and add it to the crosslinking agent reaction solution prepared in S1. Stir for 2 hours to form a homogeneous suspension. Then freeze-dry the suspension to remove the solvent and water. Ball mill the dried block solid and pass it through a 150-mesh sieve to obtain a powdered negative electrode binder.

[0061] S4: Without adding lithium nitrate, directly coat and dry; the remaining steps are the same.

[0062] This comparative example prepared a common crosslinking agent without crown ether units but with randomly distributed crosslinking points, a negative electrode binder without concentration gradient drive, and subsequently prepared a negative electrode sheet and a lithium-ion battery using this binder.

[0063] Comparative Example 2

[0064] The preparation method according to Example 1 differs in that:

[0065] S1: Replace 4,4'-diamino-2,2'-bipyridine cobalt(II) with 3.0 g of 4-aminoazobenzene, add 4''-aminobenzo-15-crown 5-ether and react for 10 h, then add 4-aminoazobenzene and react for another 10 h, then precipitate and dry to obtain an orange-red solid powder. The remaining steps are the same.

[0066] This comparative example shows the preparation of a binder without electrochemical response units, but using a crosslinking agent of non-matched response units, and subsequently using this binder to prepare a negative electrode and a lithium-ion battery.

[0067] Comparative Example 3

[0068] The preparation method according to Example 1 differs in that:

[0069] S1: The preparation of the brownish-red solid is cancelled, and the highly active chitosan, i.e., white fluffy powder, is prepared according to step S2 in Example 1;

[0070] S2: The white fluffy powder obtained in S1 is reacted with glutaraldehyde aqueous solution to form a uniform hydrogel. The hydrogel is freeze-dried and then ground to obtain porous sponge-like particles.

[0071] S3: Prepare ethanol solutions of 4''-aminobenzo-15-crown 5-ether and 4,4'-diamino-2,2'-bipyridine cobalt(II) and mix them. Immerse the porous particles obtained in S2 in the mixed solution, then remove and dry them. The remaining steps are the same.

[0072] This comparative preparation first performs basic cross-linking, then uses physical doping to load functional units onto the binder in the cross-linked network, and subsequently uses this binder to prepare the negative electrode sheet and lithium-ion battery.

[0073] Comparative Example 4

[0074] The preparation method according to Example 1 differs in that:

[0075] Commercial CMC was used directly as a binder without adding lithium nitrate and acetic acid. The coating was dried directly after coating. The electrolyte was a 1:1 mixture of ethylene carbonate and dimethyl carbonate containing 1 mol / L LiFSI. Subsequently, the negative electrode sheet was prepared and the lithium-ion battery was assembled according to step S4 in Example 1.

[0076] This comparative example shows the preparation of commercial lithium-ion batteries using conventional CMC binders.

[0077] Experimental Example 1

[0078] The CR2032 lithium-ion batteries prepared in Examples 1-4 and Comparative Examples 1-4 were placed in a 25°C constant temperature chamber and left to stand for 12 hours to allow the internal temperature of the batteries to equalize. Charge-discharge tests were performed on the batteries using the Blue Battery Testing System. In constant current-constant voltage (CC-CV) mode, the batteries were first charged at a constant current of 0.05C to the upper limit voltage of 3.65V, followed by constant voltage charging until the current decayed to 0.01C. After standing for 5 minutes, the batteries were then discharged at a constant current of 0.05C to the cutoff voltage of 2.0V using constant current mode. This charge-discharge process was repeated twice to activate the batteries. The above charge-discharge cycles were repeated at a 0.2C rate, and the charge-discharge specific capacity was recorded as the battery's baseline specific capacity C0. Then, the battery was charged at a constant current rate of 0.5C to 3.65V, followed by constant voltage charging until the current was less than 0.05C. Subsequently, the battery was discharged sequentially at 0.2C, 0.5C, 1C, 2C, 3C, and 5C to 2.0V, with three charge-discharge cycles performed at each discharge rate. The discharge data from the third cycle was used as the stable performance value for that discharge rate. A 5-minute rest period was set when switching between different discharge rates. Additionally, all batteries were discharged at a 0.5C rate to 2.0V, and then sequentially charged at constant current and constant voltage rates of 0.2C, 0.5C, 1C, 2C, and 3C to 3.65V, with three cycles performed at each charging rate. The charging data from the third cycle was used as the stable performance value for that discharge rate. A 5-minute rest period was set when switching between different discharge rates. After all the highest rate tests were completed, two more cycles were performed at 0.1C to test the recovery rate of the discharge specific capacity after high rate impact. The test results are shown in Table 2 and... Figure 2 As shown.

[0079] Table 2. Rate performance of the examples and comparative samples

[0080]

[0081] From Table 2 and Figure 2As can be seen, the sample from the examples exhibits significantly higher specific capacitance than the comparative sample under high-rate charge-discharge conditions. This indicates that the gradient ion channel in the sample from the examples ensures excellent ion transport kinetics, and the potential response mechanism guarantees interfacial stability at high rates, thereby improving the electrochemical performance of the silicon anode at high rates. The sample from Comparative Example 1 does not contain crosslinking of crown ether units, and Li... + The gradient concentration within the electrode is achieved solely through physical diffusion. At high rates, this diffusion leads to significant polarization, resulting in low discharge capacity. Similarly, the charging process is limited by ion diffusion and lacks a potential response unit, failing to alleviate lithium-ion depletion at the end of charging. In Comparative Example 2, the azobenzene derivative of the non-matched response unit replaces the electrochemically responsive 4,4'-diamino-2,2'-bipyridine cobalt(II) unit, causing the binder to be unable to effectively respond to local overpotentials during battery operation. Although the discharge capacity does not decrease significantly at high rates, the charge specific capacity decreases considerably under 3C fast charging conditions. This indicates that the potential response function of the 4,4'-diamino-2,2'-bipyridine cobalt(II) unit is crucial for suppressing anodic polarization and maintaining continuous lithium-ion charging during rapid lithium intercalation. Embedding plays a significant role, while non-matched response units fail to perform effectively. In Comparative Example 3, the functional units were physically doped later, lacking covalent connections with the polymer network and unable to penetrate into the cross-linked network. Consequently, they could neither form a stable gradient nor provide a sustained potential response. The electrode structure rapidly collapsed due to the loss of effective adaptive control, resulting in poor charge / discharge capacity and recovery ability. Comparative Example 4 is a common commercial lithium battery. The CMC binder used lacks an adaptive mechanical design to cope with silicon volume expansion. Under high-rate charge / discharge, the brittle CMC network cannot restrain the volume changes of silicon particles, leading to rapid electrode pulverization, severe damage to the electrode structure, and permanent capacity loss. Therefore, it exhibits the lowest charge / discharge specific capacity at high rates and poor recovery ability.

[0082] Experimental Example 2

[0083] The lithium-ion batteries prepared in Examples 1-4 and Comparative Examples 1-4 were subjected to two constant current constant voltage charge-discharge cycles at 25°C and a rate of 0.05C, followed by constant current constant voltage charge-discharge cycles at a rate of 0.1C, until the discharge capacity fluctuation of three consecutive cycles was less than 2%. The average discharge capacity of these three cycles was used as the baseline specific capacity C0. The batteries were then subjected to constant current constant voltage charge and discharge cycles at 25°C and a rate of 3C. After every 50 cycles at the 3C rate, a 0.5C rate charge-discharge cycle was performed, and the discharge specific capacity C0 was recorded. n A total of 1000 charge-discharge cycles were performed. The discharge specific capacity retention rate of the battery under 3C charge-discharge rate was calculated using the formula:

[0084]

[0085] The lithium-ion batteries prepared in Examples 1-4 and Comparative Examples 1-4 were placed in a 55°C constant temperature chamber and left to stand for 4 hours. They were then subjected to constant current and constant voltage charge-discharge cycles at a rate of 0.5C until the discharge capacity fluctuation of three consecutive cycles was less than 2%. The average discharge capacity of these three cycles was taken as the high-temperature reference specific capacity C. h0 Then, it was charged at a constant current and constant voltage rate of 0.5C, and then discharged sequentially at rates of 0.2C, 0.5C, 1C, 2C, 3C, and 5C. Each discharge rate was repeated 3 times. The discharge capacity of the third discharge cycle was taken as the stable capacity C at that rate. hn Calculate the high-temperature rate retention rate using the formula:

[0086]

[0087] The test results are shown in Table 3 and Figure 3 As shown.

[0088] Table 3. 3C cycle performance and high-temperature rate performance of the examples and comparative samples.

[0089]

[0090] From Table 3 and Figure 3 , Figure 4As can be seen, the specific capacity retention rates of the example samples at room temperature with 3C charge / discharge and at high temperature are significantly higher than those of the comparative sample, indicating that the examples have excellent rate performance and cycle retention at both room temperature and high temperature. Comparative Example 1, lacking the crown ether unit-driven gradient structure, results in lithium ions not preferentially passing through the ordered fast channels at high rates, leading to increased overall electrode polarization. Furthermore, the network cannot provide differentiated modulus in the thickness direction to synergistically buffer stress, causing localized stress concentration, accelerating electrode crack formation and active material shedding. Therefore, its retention rate after long-term cycling at room temperature is poor, and its discharge capacity at high-rate charge / discharge at high temperatures is also low. Comparative Example 2 has a gradient structure, thus exhibiting better performance in the initial capacity and early cycling stages. However, due to the lack of a matching electrochemical response unit inside the battery, it cannot adaptively adjust according to the actual potential. Therefore, during long-term high-rate cycling, uneven local lithium deposition occurs. Uniformity can also lead to the formation of a large number of dendrites, making it impossible to intervene in the risk of dendrite formation during cycling, resulting in poor capacity retention in later stages. Comparative Example 3 uses physical adsorption to dope functional units onto polymer chains, but the functional units cannot form a stable bond with the network and have difficulty contacting the active region. With prolonged cycling, the functional units gradually dissolve in the electrolyte, causing rapid functional decay. Comparative Example 4 uses commercial CMC as a binder. Since CMC is a rigid binder, the bonding effect is mainly through brittle hydrogen bonding. When silicon particles undergo huge volume expansion, it cannot provide elastic restraint, causing the electrode microstructure to begin to break after dozens of cycles. The active material loses connection with the conductive network, resulting in the worst capacity retention.

Claims

1. A modified lithium-ion battery silicon anode binder, comprising a main chain matrix and a crosslinking agent, characterized in that: The crosslinking agent is polyethylene glycol dialdehyde with functional units at both ends, obtained by directional grafting through amidation and Schiff base condensation reactions; the main chain matrix is ​​highly active chitosan with a large number of active amino groups on its surface, obtained by rapid precipitation and purification with alkali after acid dissolution; the functional units are ion sensing units and potential response units; the ion sensing unit is 4''-aminobenzo-15-crown 5-ether, and the potential response unit is 4,4'-diamino-2,2'-bipyridine cobalt; the crosslinking agent and the main chain matrix are combined by physical blending.

2. The method for preparing a modified lithium battery silicon anode binder according to claim 1, characterized in that, It is prepared by the following steps: S1: Using a double-ended active polymer as a flexible backbone, the two ends of the polymer are first modified to aldehyde groups through an amidation reaction. Then, without separating the intermediates, the two functional units are grafted in a directional manner by taking advantage of the difference in reactivity of the amino groups. The two functional units are grafted to the two ends of the polymer backbone in the form of covalent bonds through a Schiff base condensation reaction. After precipitation, washing and vacuum drying, a solid crosslinking agent is obtained. S2: Dissolve chitosan powder in acid to protonate and dissolve it to form a homogeneous colloid. Then, drop the solution into a cold alkaline solution to precipitate chitosan. After separation, the precipitate is repeatedly washed with deionized water until neutral. The loose and porous high-activity chitosan solid powder is obtained by freeze drying. S3: The solid crosslinking agent powder and the highly active chitosan solid powder are placed together in the grinding jar of a planetary ball mill for ball milling, and then sieved to obtain a uniform dry powder, which is the pre-assembled composite binder.

3. The method for preparing a modified lithium battery silicon anode binder according to claim 2, characterized in that: The dual-end active polymer in S1 is polyoxyethylene diamine, and the amidation reaction is a reaction between polyoxyethylene diamine and 4-formylbenzoic acid succinimide ester.

4. The method for preparing a modified lithium battery silicon anode binder according to claim 2, characterized in that: In the amidation reaction described in S1, the amino molar ratio of 4-formylbenzoic acid succinimide ester to polyoxyethylene diamine is (2.2:1) to (2.6:1), the reaction temperature is 0 to 8°C, and the reaction time is 2.5 to 4 h. The Schiff base condensation reaction is carried out at a temperature of 18 to 28°C and a reaction time of 16 to 24 h.

5. The method for preparing a modified lithium battery silicon anode binder according to claim 2, characterized in that: The acid solution in S2 is an aqueous solution of acetic acid, and the alkaline solution is an aqueous solution of NaOH.

6. The method for preparing a modified lithium battery silicon anode binder according to claim 2, characterized in that: The acid concentration in S2 is 1.5%~2.5% by volume, the cold alkali concentration is 2~3 mol / L, and the temperature is 5~15℃.

7. The method for preparing a modified lithium battery silicon anode binder according to claim 2, characterized in that: The mass ratio of the solid crosslinking agent to the highly active chitosan solid powder in S3 is (2.5:1) to (5:1), the mass ratio of the ball to the material in the ball mill is (5:1) to (8:1), and the ball milling time is 3 to 5 hours.

8. A negative electrode sheet using a modified lithium battery silicon negative electrode binder, characterized in that: A modified lithium-ion battery silicon anode binder according to any one of claims 1 to 7 is prepared by adding lithium nitrate as a concentration gradient inducer, using SiO / C as the anode active material; the binder, during low-temperature moisturizing pre-crosslinking in the anode sheet, uses crown ether units and bipyridine metal complexes as smart response units; the crown ether unit is a differential sensing Li + A concentration sensor for concentration, wherein the bipyridine metal complex is a potential sensor for locally sensing abnormal potentials.

9. A battery using a modified lithium-ion battery silicon anode binder, characterized in that: The negative electrode sheet comprising the modified lithium battery silicon negative electrode binder of claim 8, uses lithium iron phosphate as the positive electrode and a mixture of ethylene carbonate and dimethyl carbonate as the electrolyte, wherein the electrolyte is assembled with 1 mol / L bis(fluorosulfonyl)imide lithium and the volume ratio of ethylene carbonate to dimethyl carbonate is 1:

1.

10. A battery using a modified lithium-ion battery silicon anode binder according to claim 9, characterized in that: The discharge capacity retention rate after 5C charge-discharge at room temperature and 55℃ is ≥80%, and the discharge capacity retention rate after 1000 charge-discharge cycles at 3C rate is >80%.

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