A negative electrode binder composition, a negative electrode sheet, and a secondary battery

Abstract

To address the problem that existing negative electrode binders cannot effectively suppress the volume expansion of silicon negative electrodes, this invention provides a negative electrode binder composition, a negative electrode sheet, and a secondary battery. The negative electrode binder composition comprises a polysaccharide compound, a compound containing linear rigid chains, and a metal cation complexed with the polysaccharide compound. The mass ratio of the polysaccharide compound, the compound containing linear rigid chains, and the metal cation is (0.5-10):(10-40):(0.02-0.5). Both the polysaccharide compound and the compound containing linear rigid chains contain carboxyl groups. The pH value of the negative electrode binder composition is 5-8. At least partially, the carboxyl groups in the polysaccharide compound and the compound containing linear rigid chains are complexed with the metal cation, and the polysaccharide compound complexed with the metal cation forms a double helix structure. The negative electrode binder composition of this invention forms a self-healing network structure through the polysaccharide compound and the compound containing linear rigid chains, effectively preventing the breakage of negative electrode material particles and stabilizing the material interface.

Description

[0001] This application claims priority to Chinese Patent Application No. 202510470566.9, filed on April 15, 2025, entitled "A Negative Electrode Adhesive Composition, Negative Electrode Sheet, Secondary Battery", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention belongs to the field of secondary battery technology, specifically relating to a negative electrode binder composition, a negative electrode sheet, and a secondary battery. Background Technology

[0003] 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.

[0004] 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. However, binders such as polyacrylic acid (PAA) and polyacrylonitrile (PAN) have high glass transition temperatures and high hardness, resulting in brittle negative electrode sheets. During electrode sheet cutting, powder is easily shed, which affects battery performance.

[0005] 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

[0006] 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 composition, a negative electrode sheet, and a secondary battery.

[0007] To solve the above-mentioned technical problems, the present invention provides a negative electrode binder composition comprising a polysaccharide compound, a compound containing a linear rigid chain, and a metal cation, wherein the mass ratio of the polysaccharide compound, the compound containing a linear rigid chain, and the metal cation is (0.5-10):(10-40):(0.02-0.5).

[0008] Both the polysaccharide compound and the compound containing linear rigid chains contain carboxyl groups. The pH value of the negative electrode binder composition is 5-8. The carboxyl groups in the polysaccharide compound and the carboxyl groups in the compound containing linear rigid chains are at least partially complexed with the metal cations, and the polysaccharide compound complexed with the metal cations forms a double helix structure.

[0009] Preferably, the polysaccharide compound is gellan gum.

[0010] Preferably, the compound containing a linear rigid chain is polyacrylic acid.

[0011] Preferably, the molar ratio of the carboxyl group in the polysaccharide compound to the carboxyl group in the compound containing a linear rigid chain is 0.008:1 to 0.4:1.

[0012] Preferably, the metal cation includes at least one of divalent cations and monovalent cations.

[0013] Preferably, the metal cation includes Ca. 2+ Mg 2+ Ni 2+ Na + K + One or more of them.

[0014] Preferably, the metal cation is selected from Ca. 2+ Mg 2+ Ni 2+ One or more of them.

[0015] Preferably, the solid content of the negative electrode binder composition is 2%-20%, and the viscosity is 100-25000cp.

[0016] 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 the negative electrode binder composition described in any of the above claims.

[0017] Thirdly, this application provides a secondary battery, including the negative electrode sheet as described above.

[0018] In this application, a composition with a self-healing network structure is formed by physical cross-linking of polysaccharide compounds, compounds containing linear rigid chains, and metal cations. The compounds containing linear rigid chains provide rigid support for the negative electrode binder composition, maintaining the integrity of the silicon negative electrode structure during charge-discharge cycles and releasing stress to stabilize the interface. Under the action of metal cations, the polysaccharide compounds can neutralize the electrostatic repulsion of the carboxylic acid groups in the polysaccharide compounds, promoting the formation of the double helix structure of the polysaccharide compounds, thus bringing better tensile properties to the binder system. Furthermore, the cross-linking network formed by the helical structure of the polysaccharide compounds can improve the tendency of compounds containing linear rigid chains to slip, thereby giving the polymer a certain degree of self-healing ability. After the metal cations complex with the polysaccharide compounds, the binder network is strengthened, the stress dispersion path is increased, and the mechanical properties of the binder are further optimized. In particular, the stretchable and recoverable double helix structure in the polysaccharide compounds, under the synergistic effect of compounds containing linear rigid chains, can provide sufficient mechanical support to buffer and suppress the volume change of the negative electrode material particles, thereby effectively preventing the breakage of the negative electrode material particles and stabilizing the material interface. Attached Figure Description

[0019] Figure 1 This is an infrared test image of an adhesive provided in Embodiment 1 of this application. Detailed Implementation

[0020] 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.

[0021] One embodiment of this application provides a negative electrode binder composition comprising a polysaccharide compound, a compound containing a linear rigid chain, and a metal cation, wherein the mass ratio of the polysaccharide compound, the compound containing the linear rigid chain, and the metal cation is (0.5-10):(10-40):(0.02-0.5).

[0022] Both the polysaccharide compound and the compound containing linear rigid chains contain carboxyl groups. The pH value of the negative electrode binder composition is 5-8. The carboxyl groups in the polysaccharide compound and the carboxyl groups in the compound containing linear rigid chains are at least partially complexed with the metal cations, and the polysaccharide compound complexed with the metal cations forms a double helix structure.

[0023] In this embodiment, a composition with a self-healing network structure is formed by physical cross-linking of polysaccharide compounds, compounds containing linear rigid chains, and metal cations. The compounds containing linear rigid chains provide rigid support for the negative electrode binder composition, maintaining the integrity of the silicon negative electrode structure during charge-discharge cycles and releasing stress to stabilize the interface. Under the action of metal cations, the polysaccharide compounds can neutralize the electrostatic repulsion of the carboxylic acid groups in the polysaccharide compounds, promoting the formation of the double helix structure of the polysaccharide compounds, thus providing better tensile properties to the binder system. Furthermore, the cross-linking network formed by the helical structure of the polysaccharide compounds can improve the tendency of compounds containing linear rigid chains to slip, thereby giving the polymer a certain degree of self-healing ability. After the metal cations complex with the polysaccharide compounds, the binder network is strengthened, the stress dispersion path is increased, and the mechanical properties of the binder are further optimized. In particular, the stretchable and recoverable double helix structure in the polysaccharide compounds, under the synergistic effect of compounds containing linear rigid chains, can provide sufficient mechanical support to buffer and suppress the volume change of the negative electrode material particles, thereby effectively preventing the breakage of the negative electrode material particles and stabilizing the material interface.

[0024] Specifically, the mass ratio of polysaccharide compounds, compounds containing linear rigid chains, and metal cations includes, but is not limited to, 0.5:10:0.02, 10:40:0.5, 5:25:0.0.2, 5:30:0.5, or 5:40:0.5.

[0025] In some embodiments, the polysaccharide compound is gellan gum. The carboxyl groups on gellan gum provide cross-linking active sites and also active sites for metal cation complexation. Furthermore, the carboxyl groups are beneficial for Li… + The transport of these components enhances rate performance. Gellan gum is an extracellular polysaccharide produced by the fermentation of Pseudomonas bacteria. Its basic structural unit is a tetrasaccharide repeating unit composed of glucose, glucuronic acid, and rhamnose. These units are linked by glycosidic bonds to form linear chains. However, in the presence of metal ions, the carboxyl groups (-COO⁻) on the gellan gum molecular chains form "ion bridges" with metal cations (especially divalent ions) through electrostatic interactions, causing the linear molecules to crosslink into a three-dimensional network. Therefore, it can be understood that in this embodiment, by selecting polysaccharide compounds that can form double helix structures after complexing with metal ions and synergistically combining them with compounds containing linear rigid chains, sufficient mechanical support is provided to buffer and suppress the volume changes of the negative electrode material particles, thereby effectively preventing the breakage of the negative electrode material particles and stabilizing the material interface. Furthermore, not all polysaccharide compounds can form double helix structures.

[0026] In some embodiments, the compound containing linear rigid chains is polyacrylic acid (PAA). The carboxyl groups in PAA and the carboxyl groups in the polysaccharide compound respectively complex with metal cations, causing the polyacrylic acid and gellan gum to undergo physical cross-linking under the action of the metal cations. Additionally, the carboxyl groups in PAA form hydrogen bonds with the hydroxyl groups on the surface of the silicon anode particles, which can stabilize the electrode.

[0027] In some embodiments, the molar ratio of the carboxyl group in the polysaccharide compound to the carboxyl group in the compound containing a linear rigid chain is 0.008:1 to 0.4:1.

[0028] In some embodiments, the metal cation includes at least one of divalent and monovalent cations. The addition of metal cations promotes gel formation, strengthens the binder network, increases stress dispersion pathways, and further optimizes the mechanical properties of the binder. Specifically, the metal cations are obtained by adding soluble metal salts. Metal salts include, but are not limited to, calcium chloride, calcium nitrate, magnesium chloride, magnesium nitrate, nickel chloride, nickel sulfate, nickel nitrate, nickel acetate, sodium chloride, sodium sulfate, sodium carbonate, sodium nitrate, potassium chloride, potassium sulfate, potassium nitrate, and potassium carbonate.

[0029] Furthermore, the mass ratio of polysaccharide compounds, compounds containing linear rigid chains, and soluble metal salts is (0.5-10):(10-40):(0.1-1).

[0030] In some embodiments, the metal cation includes Ca 2+ Mg 2+ Ni 2+ Na + K + One or more of them.

[0031] In some embodiments, the metal cation is selected from Ca. 2+ Mg 2+ Ni 2+ One or more of these. By selecting divalent cations, the complexation with polysaccharide compounds is enhanced, which helps to form a stable gel structure. Specifically, Mg... 2+ Because of its small ionic radius and strong coordination and complexation ability, it can enhance the tendency of the contracted and tightened molecular chains to relax.

[0032] In some embodiments, the solid content of the negative electrode binder composition is 2%-20%, and the viscosity is 100-25000cp.

[0033] 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, wherein the negative electrode active material layer comprises the negative electrode binder composition described in any of the above claims.

[0034] Furthermore, the negative electrode active material layer also includes a negative electrode active material, a negative electrode conductive agent, and a thickener. Preferably, the peel strength of the negative electrode sheet is greater than 10 N / m.

[0035] Preferably, when the active material in the negative electrode active material layer is silicon-carbon or silicon, the binder in the above embodiments can provide sufficient mechanical support to buffer and suppress the volume change of silicon negative electrode material particles, thereby effectively preventing the breakage of silicon negative electrode material particles and stabilizing the silicon material interface.

[0036] An embodiment of the present invention also provides a secondary battery, including the negative electrode sheet as described above. The silicon negative electrode using the negative electrode binder composition of the above embodiments can exhibit excellent electrical contact integrity and surface stability, significantly improving the battery's rate capability, cycle stability, and other electrochemical performance.

[0037] The present invention will be further illustrated by the following examples.

[0038] Specifically, this invention discloses the negative electrode binder, negative electrode, and secondary battery.

[0039] Example 1

[0040] Negative electrode binder composition

[0041] S1: Weigh 5 parts of gellan gum GG and deionized water, heat and stir to dissolve;

[0042] S2: After GG is completely dissolved, add 0.5 parts of calcium nitrate and stir until completely dissolved;

[0043] S3: Continue to add 25 parts of polyacrylic acid (PAA) and continue heating and stirring until completely dissolved;

[0044] S4: Cool to 25°C, add deionized water to adjust the solid content and viscosity of the adhesive solution, add 20mM Tris buffer to make the pH value of the system between 5 and 8, so as to ensure that the calcium ions of PAA and gellan gum are complexed to obtain the negative electrode binder composition.

[0045] Among them, gellan gum was selected from Shanghai Shifeng Biotechnology Co., Ltd., and polyacrylic acid was selected from Aladdin Reagent (Shanghai Co., Ltd.). In this application, 1 part is 100g, 5 parts of gellan gum weigh 500g, and the amount of carboxyl groups in the polysaccharide compound gellan gum is n1=0.73mol; 25 parts of PAA weigh 2500g, and the amount of carboxyl groups in the linear rigid chain compound polyacrylic acid is n2=34.69mol, n1:n2=0.02.

[0046] negative electrode sheet

[0047] 96% silicon carbide, 1% sodium carboxymethyl cellulose thickener, and 1% conductive carbon black were stirred at low speed, and water was added to adjust the solid content to 50%. After continued stirring, the mixture was kneaded, and 2% negative electrode binder was added. After medium-high speed dispersion, the mixture was defoamed under vacuum and discharged. The negative electrode slurry was then coated on both sides of the negative electrode current collector Cu foil, with a single-sided coating surface density of 120 g / m². 2 After drying and cold pressing (compacted density 1.7 g / cm³), 3 After processes such as cutting and slitting, the negative electrode sheet is obtained.

[0048] Positive electrode film

[0049] The positive electrode active material (nickel-cobalt-manganese ternary), conductive carbon black, and positive electrode binder were mixed at a mass ratio of 96.8:2:1.2, and NMP was added to prepare a positive electrode slurry. The positive electrode slurry was coated onto aluminum foil and dried to obtain the positive electrode sheet.

[0050] Secondary battery preparation

[0051] The negative electrode, separator (PE film), and positive electrode are wound in sequence, with the separator positioned between the positive and negative electrodes to provide isolation, thus forming an electrode assembly. The electrode assembly is then placed in an outer package, injected with commercially available electrolyte, and sealed. After processes such as electrolyte injection, formation, and venting, a secondary battery is obtained.

[0052] Examples 2-8

[0053] Examples 2-8 are largely the same as Example 1, except that they use the formulations in Table 1.

[0054] Comparative Examples 1-10

[0055] Most of the steps in Comparative Examples 1-10 and Example 1 are the same, except that the formulations in Table 1 are used.

[0056] Table 1

[0057]

[0058] The negative electrode sheets and secondary batteries prepared in the above embodiments and comparative examples were tested as follows.

[0059] 1) Battery charge-discharge cycle 100 cycles electrode expansion rate test:

[0060] The constant current method was used for charge-discharge cycling. After 100 charge-discharge cycles, the ratio of the increase in electrode thickness to the electrode thickness before charge-discharge was recorded as the electrode expansion rate, under the lithium-intercalated state of the electrode.

[0061] 2) Room temperature cycling test

[0062] After placing the battery in a constant temperature test chamber at 25℃±2℃ for 1 hour, charge it to 3.65V with a constant current and constant voltage of 1C and cut off the current at 0.05C; discharge it to 2.5V with a constant current of 1C and record the discharge capacity; repeat the above steps 500 times and calculate the capacity retention rate.

[0063] 3) Battery rate performance test:

[0064] After placing the battery in a constant temperature test chamber at 25℃±2℃ for 1 hour, charge it to 3.65V with a constant current and constant voltage of 1C and cut off current of 0.05C; discharge it to 2.5V with constant currents of 0.5C, 2C, and 5C, and record the discharge time, discharge capacity, and discharge plateau voltage; repeat the above steps 500 times and calculate the capacity retention rate.

[0065] 4) Negative electrode peel strength test:

[0066] The coated single-sided negative electrode sheet was prepared at a ratio of 2.4 g / cm². 3 After compaction, a tensile testing machine with a range of 20N is used. The electrode is cut into pieces 20cm long and 3cm wide. 3M double-sided tape is attached to the steel plate. The coated side of the electrode is fixed to the tape on the steel plate with the coated side facing down. After rolling back and forth 6 times with a 2.5kg roller, the coating and copper foil are peeled off. The upper plate clamps the copper foil side. The electrode is stretched at a speed of 50mm / min and at 180°. The data of the stable tensile section is recorded as the peel strength (N / m).

[0067] The test results are shown in Table 2 below.

[0068] Table 2

[0069]

[0070] The test results from Example 1, Comparative Examples 1, 3, 9, and 10 show that when the polysaccharide compound is pectin, sodium alginate, or sodium carboxymethyl cellulose, these polysaccharide compounds cannot form a double helix structure under the action of cations. Therefore, the negative electrode binder composition cannot suppress the volume change of the silicon negative electrode material particles, resulting in increased electrode expansion, decreased peel strength, and deteriorated cycle performance and rate performance. When the negative electrode binder composition does not contain gellan gum, the electrode expansion rate increases, the peel strength decreases, and the cycle performance and rate performance deteriorate.

[0071] The test results of Examples 1-8 and Comparative Examples 4-8 show that when the mass ratio of gellan gum, polyacrylic acid and soluble metal salt is (0.5-10):(10-40):(0.1-1), the electrode has good rate performance. When the mass ratio of gellan gum, polyacrylic acid and soluble metal salt is not in the range of (0.5-10):(10-40):(0.1-1), the expansion rate of the electrode increases, the peel strength decreases, and the cycle performance and rate performance deteriorate.

[0072] As can be seen from the test results of Example 1 and Comparative Example 2, when the negative electrode binder composition does not contain metal cations, polyacrylic acid and gellan gum cannot form physical crosslinks and have a self-healing network structure, which reduces the adhesive performance of the binder, increases the expansion rate of the electrode, reduces the peel strength, and deteriorates the cycle performance and rate performance.

[0073] In summary, the binder composition prepared in this invention, when applied to silicon anode sheets, can suppress the volume change of silicon anode material particles, significantly reduce the expansion rate of the sheet, and improve cycle performance and rate performance.

[0074] 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 composition, characterized in that, The negative electrode binder composition comprises a polysaccharide compound, a compound containing a linear rigid chain, and a metal cation, wherein the mass ratio of the polysaccharide compound, the compound containing a linear rigid chain, and the metal cation is (0.5-10):(10-40):(0.02-0.5). Both the polysaccharide compound and the compound containing linear rigid chains contain carboxyl groups. The pH value of the negative electrode binder composition is 5-8. The carboxyl groups in the polysaccharide compound and the carboxyl groups in the compound containing linear rigid chains are at least partially complexed with the metal cations, and the polysaccharide compound complexed with the metal cations forms a double helix structure. The polysaccharide compound is gellan gum, and the compound containing linear rigid chains is polyacrylic acid.

2. The negative electrode binder composition according to claim 1, characterized in that, The molar ratio of the carboxyl group in the polysaccharide compound to the carboxyl group in the compound containing a linear rigid chain is 0.008:1 to 0.4:

1.

3. The negative electrode binder composition according to claim 1, characterized in that, The metal cation includes at least one of divalent and monovalent cations.

4. The negative electrode binder composition according to claim 3, characterized in that, The metal cation includes Ca. 2+ Mg 2+ Ni 2+ Na + K + One or more of them.

5. The negative electrode binder composition according to claim 4, characterized in that, The metal cation is selected from Ca. 2+ Mg 2+ Ni 2+ One or more of them.

6. The negative electrode binder composition according to claim 1, characterized in that, The negative electrode binder composition has a solid content of 2%-20% and a viscosity of 100-25000cp.

7. 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 the negative electrode binder composition according to any one of claims 1 to 6.

8. A secondary battery, characterized in that, Includes the negative electrode sheet as described in claim 7.

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