Negative electrode binder, negative electrode plate and battery
By introducing acrylic structural units, cross-linking structural units, and grafting units into the negative electrode binder, a three-dimensional cross-linking network and claw-shaped branched structure are constructed, which solves the problem of volume expansion of silicon negative electrodes and improves the stability and cycle stability of the electrode structure.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHENZHEN HAODYNE TECH CO LTD
- Filing Date
- 2026-03-25
- Publication Date
- 2026-05-15
AI Technical Summary
Existing anode binders cannot effectively suppress the volume expansion of silicon anodes during charge and discharge processes, leading to electrode structure damage and poor cycle stability.
A negative electrode binder is used, comprising acrylic structural units, cross-linked structural units, and grafted units, which are connected by chemical bonding to construct a three-dimensional cross-linked network. Carboxyl and sulfonic acid groups are introduced to enhance the interfacial anchoring ability and stress buffering ability.
It significantly improves the stability and cycle life of the electrode structure, suppresses the pulverization of silicon particles and the disintegration of the electrode structure, reduces repeated rupture of the SEI film, and enhances the cycle stability of the battery.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of secondary battery technology, specifically relating to a negative electrode binder, a negative electrode sheet, and a battery. Background Technology
[0002] Lithium-ion batteries, due to their high energy density, long cycle life, and low self-discharge rate, have become the primary power source for modern portable electronic devices, electric vehicles, and energy storage systems. Current lithium-ion batteries mainly use graphite-based materials as the negative electrode. However, with the continuous upgrading of portable electronic devices and electric vehicles, the demand for higher energy density lithium-ion batteries is increasing. The theoretical specific capacity of graphite-based negative electrode materials is only 372 mAh / g, which is insufficient to meet the development needs of high-energy-density lithium-ion batteries.
[0003] Currently, nano-silicon materials (~4200 mAh / g), silicon-carbon composites (>1700 mAh / g), and silicon suboxide materials (>1500 mAh / g) are gradually being developed and applied as anode materials. However, silicon anodes experience significant volume expansion during charge and discharge (up to 300% or more of their original volume). This massive expansion leads to structural breakage, loss of electrical contact between the active material and the current collector, and between active materials themselves. This disrupts the lithium-ion insertion / extraction process, resulting in a large, irreversible capacity and rapid capacity decay. Therefore, effectively controlling the volume expansion of silicon and improving its cycle stability is a key research focus in the field of silicon-based anodes. One approach is to use anode binders to buffer the expansion / contraction of the active material during charge and discharge, thereby improving battery cycle stability. However, traditional anode material binders such as sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) are not well-suited to handle the significant volume changes caused by silicon-based anodes, leading to electrode structure damage during cycling. Water-based polyacrylic acid (PAA) binders are difficult to adapt to the continuous dynamic volume changes of silicone, and their effect in suppressing expansion and pulverization is limited.
[0004] Therefore, there is an urgent need for a new type of anode binder to suppress the volume expansion of silicon anodes, maintain the integrity of the electrode structure, achieve excellent electrochemical performance, and improve the cycle stability of the anode. Summary of the Invention
[0005] This invention addresses the problem that existing negative electrode binders cannot effectively suppress the volume expansion of silicon negative electrodes. This invention provides a negative electrode binder, a negative electrode sheet, and a battery.
[0006] To solve the above-mentioned technical problems, the present invention provides a negative electrode binder, the negative electrode binder comprising a polymer, the polymer comprising acrylic structural units, crosslinked structural units and grafting units, at least a portion of the acrylic structural units being chemically bonded to the grafting units, the grafting units containing carboxyl groups and sulfonic acid groups.
[0007] Preferably, the mass ratio of the acrylic structural unit to the grafted unit is 1:0.05~0.3.
[0008] Preferably, the number of carboxyl groups and sulfonic acid groups in each grafting unit is the same.
[0009] Preferably, the mass ratio of the acrylic structural unit to the crosslinked structural unit is 1:0.0002~0.002.
[0010] Preferably, the acrylic structural unit and the grafted unit are chemically bonded together by amide bonds and / or ester bonds.
[0011] Preferably, the grafting unit is a structural unit formed by the participation of a grafting compound in the reaction, and the grafting compound includes at least one of DL-B-sulfoalanine, 2-amino-4-sulfobutyric acid, 2-amino-5-sulfovaleric acid, and 2-hydroxy-3-sulfopropionic acid.
[0012] Preferably, the crosslinked structural unit is a structural unit formed by the polymerization reaction of crosslinking monomers, and the crosslinking monomers include at least one of N,N'-methylenebisacrylamide and polyethylene glycol diacrylate.
[0013] Secondly, this application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material, a conductive agent and a negative electrode binder as described in any of the preceding claims.
[0014] Preferably, the mass ratio of the negative electrode active material, conductive agent and binder is (85~92):(5~10):(3~5).
[0015] Thirdly, this application provides a battery including the negative electrode sheet as described above.
[0016] In this application, acrylic structural units and cross-linked structural units in the negative electrode binder construct a three-dimensional cross-linked network, providing the binder with basic structural stability and volume expansion buffering capacity, preventing irreversible slippage of molecular chains, maintaining the integrity of the electrode structure, improving the overall strength and deformation resistance of the binder, and buffering the volume expansion stress of the silicon negative electrode. The grafting unit contains both carboxyl and sulfonic acid groups, which can form multiple hydrogen bonds with the hydroxyl groups on the silicon surface, significantly enhancing the interfacial anchoring ability, significantly strengthening the interfacial bonding force, and inhibiting the pulverization and shedding of active materials. At the same time, the introduced grafting unit, acrylic structural units, and cross-linked structural units construct a "claw-like" branched-network composite structure. The branches formed by the grafting unit constitute the elastic "claw tips" of the "claw-like" structure, which can flexibly disperse the stress generated by the volume change of silicon through their own deformation. With the synergistic effect of the rigidity of the network composite structure and the elasticity of the claw-like branches, the expansion stress during silicon cycling is effectively absorbed, significantly alleviating the volume expansion of silicon particles, inhibiting particle pulverization and electrode structure disintegration, achieving the dual function of structural buffering and strong interfacial bonding, and further reducing the repeated rupture and regeneration of the SEI film, significantly improving cycling stability. Detailed Implementation
[0017] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0018] One embodiment of this application provides a negative electrode binder, the negative electrode binder comprising a polymer, the polymer comprising acrylic structural units, crosslinked structural units and grafting units, at least a portion of the acrylic structural units being chemically bonded to the grafting units, the grafting units containing carboxyl groups and sulfonic acid groups.
[0019] In this embodiment, acrylic structural units and cross-linked structural units in the negative electrode binder construct a three-dimensional cross-linked network, providing the negative electrode binder with basic structural stability and volume expansion buffering capacity, preventing irreversible slippage of molecular chains, maintaining the integrity of the electrode structure, improving the overall strength and deformation resistance of the binder, and buffering the volume expansion stress of the silicon negative electrode. The grafting unit contains both carboxyl and sulfonic acid groups, which can form multiple hydrogen bonds with the hydroxyl groups on the silicon surface, greatly enhancing the interface anchoring ability, significantly strengthening the interface bonding force, and inhibiting the pulverization and shedding of active materials. At the same time, the introduced grafting unit, acrylic structural units, and cross-linked structural units construct a "claw-like" branched-network composite structure. The branches formed by the grafting unit constitute the elastic "claw tips" of the "claw-like" structure, which can flexibly disperse the stress generated by the volume change of silicon through their own deformation. With the synergistic effect of the rigidity of the network composite structure and the elasticity of the claw-like branches, the expansion stress during silicon cycling is effectively absorbed, significantly alleviating the volume expansion of silicon particles, inhibiting particle pulverization and electrode structure disintegration, achieving the dual effects of structural buffering and strong interface bonding, and further reducing the repeated rupture and regeneration of the SEI film, significantly improving cycle stability.
[0020] In some embodiments, the mass ratio of the acrylic structural unit to the grafted unit is 1:0.05~0.3. This mass ratio can achieve a good grafting density and interfacial bonding effect, ensuring that the grafted unit provides sufficient bipolar anchoring groups, while avoiding excessive grafting that would damage the main chain structure and film-forming properties, thus achieving an optimal balance between interfacial adhesion and structural strength.
[0021] In one specific embodiment, the acrylic structural unit includes at least one selected from acrylic acid structural units, methacrylic acid structural units, and itaconic acid structural units. The acrylic structural unit is derived from an acrylic monomer; the acrylic monomer includes at least one selected from acrylic acid, methacrylic acid, and itaconic acid.
[0022] Specifically, the mass ratio of acrylic structural units to grafting units includes, but is not limited to, 1:0.05, 1:0.1, 1:0.15, 1:0.2, 1:0.25, or 1:0.3. When the mass ratio of acrylic acid to grafting units is within the preferred range of this invention, optimal grafting density and interfacial bonding effect can be achieved, ensuring that the bipolar elastic "claw tips" of the graft can directly form more bonds with silicon and effectively alleviate the volume expansion of silicon particles.
[0023] In some embodiments, the number of carboxyl groups and sulfonic acid groups in each grafting unit is the same. By employing a structural design that simultaneously contains carboxyl and sulfonic acid groups within the same grafting unit, during the grafting reaction, each grafting site introduces the same functional unit containing equal amounts of carboxyl and sulfonic acid groups. The equal ratio of carboxyl and sulfonic acid groups ensures a uniform distribution of hydrogen bonding and electrostatic anchoring between the binder and the silicon surface, avoiding interfacial stress concentration caused by excessively dense or sparse local groups.
[0024] In some embodiments, the mass ratio of the acrylic structural unit to the crosslinked structural unit is 1:0.0002~0.002. Within this mass ratio range, a balance between the stability and toughness of the crosslinked network can be ensured, maintaining good toughness while guaranteeing structural strength, avoiding excessive crosslinking that leads to increased brittleness, and balancing structural support with volume expansion buffering capacity.
[0025] Specifically, the mass ratio of acrylic structural units to crosslinked structural units includes, but is not limited to, 1:0.0002, 1:0.0005, 1:0.0008, 1:0.0011, 1:0.0014, 1:0.0017 or 1:0.002.
[0026] In some embodiments, the acrylic structural unit and the grafted unit are chemically bonded together via amide bonds and / or ester bonds. The formation of a stable grafted structure through amide bonds and / or ester bonds ensures that the grafted unit does not detach or migrate under long-term cycling and electrolyte conditions, allowing the bipolar groups to function stably and continuously, thus improving the long-term reliability of the adhesive.
[0027] In some embodiments, the grafting unit is a structural unit formed by the reaction of a grafting compound. The grafting compound contains a carboxyl group, a sulfonic acid group, and a grafting reactive group, wherein the grafting reactive group includes at least one of amino and hydroxyl groups. The amino and hydroxyl groups can react with the carboxyl group of the acrylic structural unit to achieve stable grafting, while retaining the carboxyl and sulfonic acid groups as functional groups, thus achieving the dual function of dispersing the stress generated by the volume change of silicon and strong interface anchoring.
[0028] In some embodiments, the grafting compound includes at least one selected from DL-B-sulfonylalanine, 2-amino-4-sulfonylbutyric acid, 2-amino-5-sulfopenic acid, and 2-hydroxy-3-sulfonylpropionic acid. The spatial arrangement of the amino, sulfonic acid, and carboxyl groups in the above compounds is optimized, facilitating the grafting reaction between the amino or hydroxyl groups and the carboxyl groups of acrylic acid. Simultaneously, it facilitates the formation of multiple hydrogen bonds between the sulfonic acid and carboxyl groups in the grafting compound and the silanol groups, stably introducing bipolar groups and forming a "claw-like" anchoring structure, significantly enhancing the adsorption and adhesion capabilities to silicon-based active materials.
[0029] In some embodiments, the crosslinked structural unit is a structural unit formed by the polymerization reaction of crosslinking monomers, and the crosslinking monomers include at least one of N,N'-methylenebisacrylamide (MBAA) and polyethylene glycol diacrylate (PEGDA). Multifunctional crosslinking monomers have good compatibility with the acrylic acid backbone and high copolymerization efficiency, enabling the construction of a uniform and dense three-dimensional network, thereby improving the adhesive's resistance to swelling, powdering, and structural damage.
[0030] Furthermore, one embodiment of this application provides a method for preparing a negative electrode binder, comprising the following steps: Acrylic monomers, crosslinking monomers, and initiators are dissolved in deionized water and stirred until homogeneous to form a uniform precursor solution. The precursor solution is placed in an environment of 65-75°C and the crosslinking polymerization reaction is thermally initiated for 3-6 hours to obtain a crosslinked polyacrylic acid aqueous solution. The grafting compound was added to the above cross-linked polyacrylic acid aqueous solution and stirred at a constant temperature of 55~65℃ for 2~3h; then transferred to a vacuum oven and annealed at 140~160℃ for 12~16h. After cooling to 25~30℃, the negative electrode binder was obtained. Finally, deionized water was added to adjust the solid content to 10% negative electrode binder solution.
[0031] The mass ratio of crosslinking monomer to acrylic monomer is 0.0002~0.002:1, and the mass ratio of graft compound to acrylic monomer is 0.05~0.3:1.
[0032] The initiator includes at least one of ammonium persulfate (APS), potassium persulfate (KPS), and sodium persulfate.
[0033] The mass ratio of initiator to acrylic monomer is 0.0015~0.015:1 to ensure complete polymerization and no excess initiator residue.
[0034] As those skilled in the art know, the reactions in the above steps are conventional free radical polymerization and grafting reactions, and the specific methods and reaction conditions are common free radical polymerization and grafting methods in the prior art, which will not be described in detail in this invention.
[0035] In this invention, each of the aforementioned structural units represents the structural portion of the corresponding monomer present in the resulting polymer after the monomer participates in the polymerization reaction. The mass ratio of each structural unit is based on the mass content of the corresponding monomer in the total amount of monomers participating in the polymerization.
[0036] An embodiment of the present invention also provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector. The negative electrode active material layer comprises a negative electrode active material, a conductive agent, and the negative electrode binder described in any one of the preceding embodiments. Using the negative electrode binder of the present invention, a stable, strong, and highly elastic bonding network can be formed between the negative electrode active material, the conductive agent, and the current collector, effectively suppressing the volume expansion of the silicon-based negative electrode and maintaining the integrity of the conductive path and electrode structure.
[0037] In some embodiments, the mass ratio of the negative electrode active material, conductive agent, and binder is (85~92):(5~10):(3~5). This achieves excellent bonding and conductivity while ensuring high active material loading and high energy density, reducing impedance and improving the overall electrochemical performance of the battery.
[0038] Specifically, the mass ratio of the negative electrode active material, conductive agent and binder includes, but is not limited to, 85:10:5, 90:5:5, 92:3:5, 92:5:3, 90:7:3 or 90:6:4.
[0039] The negative electrode active material includes at least one of silicon and silicon-carbon.
[0040] The silicon loading in the negative electrode is 1.0~2.0 mg / cm³. 2 .
[0041] An embodiment of the present invention also provides a battery, including the negative electrode sheet as described above.
[0042] The present invention will be further illustrated by the following examples.
[0043] Specifically, this invention discloses the negative electrode binder, negative electrode sheet, and battery.
[0044] Example 1 The preparation method of the negative electrode binder is as follows: Acrylic acid (AA) monomer, crosslinking agent N,N'-methylenebisacrylamide (MBAA), and initiator ammonium persulfate were dissolved in deionized water at a mass ratio of 1:0.001:0.008 and stirred until homogeneous to form a uniform precursor solution. The precursor solution was placed in a 70°C water bath and the crosslinking polymerization reaction was thermally initiated for 5 hours to obtain a crosslinked PAA aqueous solution. DL-B-sulfoalanine (AA to DL-B-sulfoalanine mass ratio 1:0.15) was added to the above cross-linked PAA aqueous solution and stirred at 60℃ for 2.5h. Then it was transferred to a vacuum oven and annealed at 150℃ for 14h. After cooling to 25℃, deionized water was added to adjust the solid content to 10% to obtain the negative electrode binder solution.
[0045] The method for preparing the negative electrode is as follows: Silicon carbon, conductive agent Super P, and negative electrode binder are blended in a mass ratio of 90:5:5, and then mixed with deionized water to prepare a slurry. The slurry was coated onto copper foil, dried, and then cut into negative electrode sheets of a fixed size. The silicon loading in the negative electrode active material layer was 1.5 mg / cm³. 2 .
[0046] The battery manufacturing method is as follows: After assembling the negative electrode, separator, and NCM811 positive electrode into a dry cell, a lithium battery is obtained by electrolyte injection. The electrolyte is a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a 1:1 mass ratio, and then LiPF6 is added until the molar concentration is 1.0 mol / L.
[0047] Examples 2-12 Examples 2-12 are largely the same as Example 1, except that they use the formulations in Table 1.
[0048] Comparative Examples 1-4 Most of the steps in Comparative Examples 1-4 are the same as those in Example 1, except that the formulations in Table 1 are used.
[0049] Table 1 The negative electrode binder, negative electrode sheet, and battery prepared in the above embodiments and comparative examples were tested as follows.
[0050] 1. Mechanical properties of the adhesive: Sample preparation method: The negative electrode adhesive liquid of the examples and comparative examples is spread evenly in the mold. The mold size is: length × width × depth = 8cm × 1.5cm × 0.5cm; put it in an oven and dry at 100°C for 2 hours.
[0051] The dried adhesive film was tested using a universal tensile testing machine at a tensile rate of 50 mm / min to measure the elongation at break, tensile strength, and toughness of the negative electrode adhesive.
[0052] 2. Electrode flexibility test: The negative electrode sheets of the examples and comparative examples were bent 180° using needles of different thicknesses, and the diameter of the needles when the first crack appeared was observed.
[0053] 3. Cyclic performance: In a constant temperature test chamber at 25℃±2℃, the batteries of the examples and comparative examples were placed for 1 hour, then charged to 3.65V with a constant current and constant voltage of 0.5C, and the cutoff current was 0.05C; then discharged to 2.5V with a constant current of 0.5C, and the discharge capacity was recorded; the above steps were repeated 150 times, and the capacity retention rate was calculated.
[0054] The test results are shown in Table 2.
[0055] Table 2 As shown in Table 2, the test results of the embodiments and comparative examples in this application demonstrate that the grafting unit, acrylic structural unit, and cross-linking structural unit construct a "three-dimensional cross-linked network-claw-shaped branch" structure. Combined with the interfacial anchoring effect of the bifunctional groups (carboxyl and sulfonic acid groups) in the grafting unit, this achieves a triple effect of structural support, stress buffering, and strong interfacial adhesion. This effectively suppresses the volume expansion of the silicon anode, maintains the integrity of the electrode structure, and significantly improves the battery cycle stability. In Comparative Example 1, the grafting compound in the anode binder contains only sulfonic acid groups, resulting in a single hydrogen bond interaction with the hydroxyl groups on the silicon surface. This leads to insufficient interfacial anchoring ability and an inability to form an efficient "claw-shaped" branch structure, resulting in poor stress dispersion. Consequently, the toughness of the anode binder, the flexibility of the electrode sheet, and the battery cycle stability are significantly inferior to those of the embodiments of this invention. In Comparative Example 2, the grafting compound in the anode binder contains only carboxyl groups, lacking sulfonic acid group-assisted adsorption. This prevents the formation of multiple hydrogen bonds with the silicon surface, resulting in weak interfacial adhesion, easy pulverization and detachment of silicon particles, and a low battery cycle retention rate.
[0056] The negative electrode binder in Comparative Example 3 does not contain grafting units and lacks the interfacial anchoring effect of carboxyl and sulfonic acid groups. As a result, the negative electrode binder cannot achieve effective stress buffering and interfacial bonding. The volume expansion of the silicon negative electrode cannot be suppressed, and the electrode structure is prone to disintegration, leading to the deterioration of the mechanical properties of the binder, the flexibility of the electrode sheet, and the cycle retention rate of the battery.
[0057] As can be seen from the test results of Examples 1, 10-12 and Comparative Example 4, the grafting unit in Comparative Example 4 contains sulfonic acid groups and carboxyl groups, which are formed by grafting carboxyl-containing grafting compounds and sulfonic acid-containing grafting compounds respectively. However, the grafting positions of sulfonic acid groups and carboxyl groups in the negative electrode binder cannot be determined, the grafting ratio is not easy to control, and sulfonic acid groups and carboxyl groups cannot form the claw-shaped branched structure in the embodiments of the present invention. The stress dispersion effect of the obtained negative electrode binder is poor, which reduces the toughness of the negative electrode binder, the flexibility of the electrode sheet and the cycle stability of the battery.
[0058] The test results of Examples 1-5 show that when the mass ratio of acrylic structural units to grafted units is 1:0.05~0.3, the toughness of the negative electrode binder, the flexibility of the electrode sheet, and the cycle stability of the battery can be further improved.
[0059] The test results of Examples 1 and 6-9 show that when the mass ratio of acrylic structural units to cross-linked structural units is 1:0.0002~0.002, the mechanical properties of the negative electrode binder, the flexibility of the electrode sheet, and the cycle performance of the battery can be further improved.
[0060] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A negative electrode binder, characterized in that, The negative electrode binder comprises a polymer, which includes acrylic structural units, crosslinked structural units, and grafting units. At least a portion of the acrylic structural units are chemically bonded to the grafting units, and the grafting units contain carboxyl groups and sulfonic acid groups.
2. The negative electrode binder according to claim 1, characterized in that, The mass ratio of the acrylic structural unit to the grafted unit is 1:0.05~0.
3.
3. The negative electrode binder according to claim 1, characterized in that, The number of carboxyl groups and sulfonic acid groups is the same in each grafting unit.
4. The negative electrode binder according to claim 1, characterized in that, The mass ratio of the acrylic structural unit to the crosslinked structural unit is 1:0.0002~0.
002.
5. The negative electrode binder according to claim 1, characterized in that, The acrylic structural units and the grafted units are chemically bonded together by amide bonds and / or ester bonds.
6. The negative electrode binder according to claim 5, characterized in that, The grafting unit is a structural unit formed by the participation of a grafting compound in a reaction, and the grafting compound includes at least one of DL-B-sulfoalanine, 2-amino-4-sulfobutyric acid, 2-amino-5-sulfovaleric acid, and 2-hydroxy-3-sulfopropionic acid.
7. The negative electrode binder according to claim 1, characterized in that, The cross-linked structural unit is a structural unit formed by the polymerization reaction of cross-linking monomers, and the cross-linking monomers include at least one of N,N'-methylenebisacrylamide and polyethylene glycol diacrylate.
8. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material, a conductive agent and a negative electrode binder as described in any one of claims 1 to 7.
9. The negative electrode binder according to claim 1, characterized in that, The mass ratio of the negative electrode active material, conductive agent and binder is (85~92):(5~10):(3~5).
10. A battery, characterized in that, Includes the negative electrode sheet as described in claim 8 or 9.