Negative electrode binder, negative electrode plate and lithium ion battery

Abstract

The invention provides a negative electrode binder, a negative plate and a lithium ion battery. The negative electrode binder comprises a basic binding phase, a dynamic crosslinking phase and a conductive reinforcing phase. According to the negative electrode binder, the negative electrode plate and the lithium ion battery, the negative electrode binder is a composite system, dopamine modified polyacrylic acid is taken as a basic framework, a dynamic hydrogen bond network is constructed by introducing boric acid, and meanwhile, PEDOT: PSS can be compounded to form a double-conductive network. Wherein dopamine is modified to improve the density of hydrogen bond sites, boric acid is introduced into a dynamic reversible hydrogen bond to realize room-temperature self-repairing, and PEDOT: PSS and SuperP cooperate to construct an electron and ion double-conduction channel. The silicon-based negative electrode plate adopting the binder can effectively relieve volume expansion of silicon in the charging and discharging process, the cycling stability and the energy density are remarkably improved, and the silicon-based negative electrode plate is suitable for the field of high-performance lithium ion batteries.

Description

A negative electrode binder, a negative electrode sheet and a lithium-ion battery Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a negative electrode binder, a negative electrode sheet, and a lithium-ion battery. Background Technology

[0002] Silicon (Si), with its ultra-high theoretical specific capacity of 4200 mAh・g⁻¹, is widely recognized as a core candidate material for next-generation high-energy-density lithium-ion battery anodes. Its application is expected to significantly break through the current battery energy density bottleneck and provide key technological support for new energy vehicles, high-end energy storage, and other fields. However, silicon-based materials undergo a dramatic volume expansion of over 300% during lithiation / delithiation. This inherent defect triggers a series of chain problems: huge stress inside the electrode leads to cracking, and the active material peels off from the current collector interface. At the same time, the repeatedly ruptured and regenerated solid electrolyte interphase (SEI) film continuously consumes electrolyte and lithium source, severely restricting the cycle stability of silicon-based anodes and becoming a core technological barrier for their commercial application.

[0003] Among numerous solutions, structural optimization and performance upgrades of binders have proven to be key means of mitigating silicon volume expansion and maintaining electrode structural integrity.

[0004] However, existing binders still have the following problems: While polyacrylic acid (PAA) possesses a certain adhesive strength by forming hydrogen bonds between its carboxyl groups and the hydroxyl groups on the silicon surface, its linear molecular structure lacks elastic adjustment capabilities, making it prone to slipping off the active material surface during repeated expansion and contraction of silicon, and difficult to maintain interfacial bonding over a long period. Poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS), although exhibiting excellent conductivity, suffers from insufficient mechanical stability due to its brittleness, making it unable to withstand structural impacts caused by volume changes. These single-functional binders generally cannot simultaneously meet the multiple core requirements of silicon-based anodes for high adhesion, high conductivity, and tolerance to volume expansion. More importantly, most existing binders lack dynamic self-healing capabilities and cannot repair microcracks generated during cycling. As the number of cycles increases, cracks accumulate and expand, eventually leading to the complete collapse of the electrode structure, further limiting the long cycle life and practical application value of silicon-based batteries.

[0005] This invention solves the core problems of silicon-based anode volume expansion, poor conductivity, and easy structural collapse through multi-component synergy and biomimetic design, providing key material and technical support for the development of high-energy-density lithium-ion batteries. Summary of the Invention

[0006] The present invention aims to solve the technical problems mentioned in the background art and provide a negative electrode binder, a negative electrode sheet and a lithium-ion battery.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a negative electrode binder, comprising a basic binder phase, a dynamic crosslinking phase, and a conductive reinforcing phase; the basic binder phase is dopamine-modified polyacrylic acid, obtained by an amidation reaction of polyacrylic acid and dopamine, with a mass ratio of 2-8:1; the dynamic crosslinking phase is boric acid, with a mass ratio of boric acid to dopamine-modified polyacrylic acid of 5-15:100; the conductive reinforcing phase is poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate), i.e., PEDOT:PSS, with a mass ratio of PEDOT:PSS to dopamine-modified polyacrylic acid of 1-5:10; the basic binder phase and the dynamic crosslinking phase are bonded by dynamic hydrogen bonds, and the basic binder phase and the conductive reinforcing phase are crosslinked by hydrogen bonds to form a three-dimensional network structure.

[0008] A further preferred embodiment: The LiPAA is prepared by neutralization reaction of polyacrylic acid and lithium hydroxide, wherein the molar ratio of lithium hydroxide to acrylic acid units in polyacrylic acid is 0.5-1:1.

[0009] A negative electrode sheet includes a current collector and a negative electrode active layer, wherein the negative electrode active layer is coated on the surface of the current collector; the negative electrode active layer includes a negative electrode active material, a conductive additive, and any one of the negative electrode binders described above; wherein the conductive additive is SuperP.

[0010] A further preferred embodiment: the negative electrode active material is at least one of silicon powder and silicon-carbon composite material, and the silicon powder particle size is 60-100nm.

[0011] A further preferred embodiment: the mass ratio of the negative electrode active material, the negative electrode binder, and the conductive additive is 5-7:1.5-2.5:1.5-2.5.

[0012] A lithium-ion battery includes a positive electrode, a separator, an electrolyte, a negative electrode binder as described in any one of the above, or a negative electrode sheet as described in any one of the above.

[0013] A further preferred embodiment: the active material of the positive electrode is at least one of NCM, NCA, NCAM, LFP, and LFMP.

[0014] A further preferred embodiment: the electrolyte is 1.0 mol / L LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC:DEC=1:1, v / v), with 8-12 wt% fluoroethylene carbonate (FEC) added.

[0015] A further preferred embodiment: the diaphragm is a PP or PE diaphragm. Beneficial effects

[0016] This type of negative electrode binder, negative electrode sheet, and lithium-ion battery systematically solves the core problems of volume expansion, poor conductivity, and structural collapse of silicon-based negative electrodes through multi-component synergy and biomimetic design, providing key material and technical support for the development of high-energy-density lithium-ion batteries. It borrows the multi-tentacle bonding mechanism of ivy suction cups, and improves the hydrogen bond site density through dopamine modification, achieving a 180° peel force of 1.50N, an improvement of 89.9% compared to traditional PAA, effectively suppressing the shedding of active materials caused by silicon expansion. The dynamic reversible hydrogen bond network introduced by boric acid can repair microcracks generated by cycling at room temperature. After 50 cycles, the electrode thickness increase is only 61.0%, far lower than the 119.3% of PAA electrodes, firmly maintaining the integrity of the electrode structure. The electron-ion dual conduction network constructed by PEDOT:PSS and SuperP imparts an 8.53×10⁻ 4 With an ionic conductivity of 675.7 S·cm⁻¹ and an electronic conductivity of 675.7 S·cm⁻¹, it maintains a capacity of 1877 mAh·g⁻¹ even at a high rate of 8.0 A·g⁻¹. Moreover, the preparation does not require complex equipment, the water-based system is green and environmentally friendly, and it can be directly adapted to existing production lines. When applied in silicon-carbon composite materials, the capacity is still ≥1.0 mAh·cm⁻² after 400 cycles, which combines excellent performance with industrialization potential. Detailed Implementation

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention.

[0018] In this embodiment of the invention, a negative electrode binder includes a basic binder phase, a dynamic crosslinking phase, and a conductive reinforcing phase. The basic binder phase is dopamine-modified polyacrylic acid, prepared by an amidation reaction of polyacrylic acid and dopamine, with a mass ratio of 2-8:1. The dynamic crosslinking phase is boric acid, with a mass ratio of boric acid to dopamine-modified polyacrylic acid of 5-15:100. The conductive reinforcing phase is poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate), i.e., PEDOT:PSS, with a mass ratio of PEDOT:PSS to dopamine-modified polyacrylic acid of 1-5:10. The basic binder phase and the dynamic crosslinking phase are bonded by dynamic hydrogen bonds, and the basic binder phase and the conductive reinforcing phase are crosslinked by hydrogen bonds to form a three-dimensional network structure. LiPAA is prepared by a neutralization reaction of polyacrylic acid and lithium hydroxide, with a molar ratio of lithium hydroxide to acrylic acid units in polyacrylic acid of 0.5-1:1.

[0019] A negative electrode sheet includes a current collector and a negative electrode active layer, wherein the negative electrode active layer is coated on the surface of the current collector; the negative electrode active layer includes a negative electrode active material, a conductive additive, and a negative electrode binder of any one of the above; the conductive additive is SuperP; the negative electrode active material is at least one of silicon powder and silicon-carbon composite material, wherein the silicon powder has a particle size of 60-100 nm; the mass ratio of the negative electrode active material, the negative electrode binder, and the conductive additive is 5-7:1.5-2.5:1.5-2.5.

[0020] A lithium-ion battery includes a positive electrode, a separator, an electrolyte, a negative electrode binder of any one of the above, or a negative electrode of any one of the above; the active material of the positive electrode is at least one of NCM, NCA, NCAM, LFP, and LFMP; the electrolyte is 1.0 mol / L LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC:DEC=1:1, v / v), and 8-12 wt% fluoroethylene carbonate (FEC) is added; the separator is a PP or PE separator.

[0021] The negative electrode binder of this invention is a ternary composite system consisting of a basic binder phase, a dynamic crosslinking phase, and a conductivity-enhancing phase: The basic binder phase (PD) uses polyacrylic acid (PAA) as a backbone, and introduces catechol groups through dopamine (DA) modification, which increases the hydrogen bond site density by 30%-50%. The amino groups in DA form amide bonds with the carboxyl groups in PAA, while the catechol groups can form strong hydrogen bonds with the hydroxyl groups on the silicon surface, significantly enhancing the interfacial bonding force between the binder and the active material; The dynamic crosslinking phase (BA) uses boron atoms in boric acid (BA) to form dynamic reversible hydrogen bonds with the hydroxyl and amino groups on the PD molecular chain. When the silicon volume expands, stress is released through hydrogen bond breakage, and self-repair is achieved through hydrogen bond recombination after expansion. It can repair ≥85% of microcracks within 24 hours at room temperature, maintaining the integrity of the electrode structure.

[0022] Conductivity-enhancing phase (PEDOT:PSS): The compounded PEDOT:PSS and SuperP form a molecular- and macroscopic dual conductive network: PEDOT:PSS achieves electronic coupling at the molecular level, while SuperP constructs electron percolation channels at the macroscopic level, maintaining the binder's electronic conductivity above 675.7 S·cm⁻¹. Simultaneously, Li⁺ in LiPAA (optional compound) can be rapidly transported via carboxyl peristalsis, achieving an ionic conductivity of 8.53 × 10⁻⁻⁻⁻⁶. 4 S·cm⁻¹ solves the problem of insufficient conductivity / ion conduction in traditional binders.

[0023] This invention does not strictly limit the positive electrode active material in the positive electrode sheet; it can be any positive electrode active material commonly used in lithium-ion batteries, such as at least one composite oxide of lithium with cobalt, manganese, nickel, or combinations thereof. More specifically, it can be at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium iron phosphate (LFP), lithium nickel manganese oxide, lithium-rich manganese-based materials, etc.

[0024] This invention does not strictly limit the negative electrode active material in the negative electrode sheet. It can be at least one of the negative electrode active materials commonly used in lithium-ion batteries, such as graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon suboxide and silicon-carbon negative electrode), and tin-based negative electrode materials (mainly including tin and tin alloy).

[0025] This invention does not strictly limit the choice of electrolyte, and may include one or more solvents commonly used in lithium-ion battery electrolytes, as well as lithium salts commonly used in lithium-ion electrolytes. For example, the solvent may be ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, methyl ethyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, γ-butyrolactone, etc.; the lithium salt may be one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0026] This invention does not strictly limit the choice of separator material. It can be one of the separator materials commonly used in lithium-ion batteries, such as polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), cellulose nonwoven separator, and separator with ceramic coating.

[0027] The specific preparation steps of the negative electrode binder are as follows: S1, Dissolve 0.2-0.3g PAA (Mw≈450,000) in 30mL of phosphate buffer solution with pH=6, and stir magnetically until completely dissolved; Add 0.1-0.15g EDC and 0.05-0.08g NHS to activate the carboxyl groups of PAA for 30min; Then add 0.1-0.15g dopamine hydrochloride (DA·HCl) and stir at room temperature for 9h under a nitrogen atmosphere; Transfer the reaction solution to a 3500D dialysis bag and dialyze with ultrapure water for 3 days, changing the water 3 times a day to remove unreacted small molecules; Finally, freeze. Dry (-50℃, vacuum ≤10Pa) for 24h to obtain PD powder; S2, weigh PD and BA at a mass ratio of 90:10, dissolve in deionized water, and stir for 30min; if a conductive reinforcing phase needs to be added, add PEDOT:PSS solution at a mass ratio of PD:PEDOT:PSS=10:1, and continue stirring for 2h; transfer the mixture to a polytetrafluoroethylene mold, crosslink in situ at 120℃ under vacuum for 2h, and obtain an elastic composite binder after cooling; or directly retain the solution state for subsequent negative electrode slurry preparation; the ionic conductivity of the binder prepared by this method is not less than 8.53×10⁻ 4 S·cm⁻¹, 180° peel force not less than 1.50N, self-healing efficiency at room temperature not less than 85% (scratch healing time ≤24h).

[0028] In the negative electrode sheet of this invention, the negative electrode active layer is composed of silicon powder (60-100nm), negative electrode binder, and SuperP in a mass ratio of 6:2:2; if a silicon-carbon composite material is used, the mass ratio of silicon-carbon, binder, and SuperP is 8:1:1. The negative electrode active material, binder solution, and SuperP are added to deionized water in the specified proportions and stirred in a planetary mixer at 2000 r / min for 10 h to form a uniform, particle-free slurry. The slurry is then coated onto a 10 μm thick copper foil surface using a scraper, controlling the wet film thickness to be 150 μm to ensure… The dry film surface loading was 0.8-3.9 mg·cm⁻²; it was dried under vacuum at 100℃ for 12 h to remove moisture; then cut into 14 mm diameter discs to obtain the negative electrode; in an argon glove box (H₂O < 1 ppm, O₂ < 1 ppm), using the prepared negative electrode as the working electrode, the NCM811 positive electrode as the counter electrode, and PP as the separator, an electrolyte (1.0 mol / L LiPF₆-EC / DEC + 10 wt% FEC) was injected to assemble a CR2025 coin cell; the positive and negative electrode capacity ratio (n) was controlled during full cell assembly. The ratio of / p) is 1:1.12; after testing, the capacity retention rate is ≥90% after 300 cycles (silicon-based anode capacity 2538mAh·g⁻¹); the capacity reaches 1877mAh·g⁻¹ at 8.0A·g⁻¹, and rebounds to 2965mAh·g⁻¹ when it recovers to 0.125A·g⁻¹; with a negative electrode surface load of 3.89mg·cm⁻², the capacity is still ≥3mAh·cm⁻² after 50 cycles; after scratches on the electrode surface, the crack healing rate is ≥85% within 24 hours, and there is no through crack after 50 cycles; this battery passes... Dopamine modification increases hydrogen bond site density, achieving a 180° peel strength of 1.50N, an 89.9% improvement over traditional PAA (0.79N), effectively suppressing active material detachment caused by silicon expansion. The dynamic reversible hydrogen bonds introduced by boric acid can repair microcracks generated during cycling at room temperature; after 50 cycles, the electrode thickness increase is only 61.0%, far lower than the 119.3% increase of PAA electrodes, maintaining electrode structural integrity. The electronic and ionic dual conduction network constructed from PEDOT:PSS and SuperP achieves an ionic conductivity of 8.53 × 10⁻⁻⁻⁶ for the binder. 4 It has an electronic conductivity of 675.7 S·cm⁻¹ and a capacity of 1877 mAh·g⁻¹ at a high rate of 8.0 A·g⁻¹. Moreover, the preparation process does not require complex equipment, the water-based system is environmentally friendly, and it can be directly adapted to existing lithium-ion battery production lines. When used in silicon-carbon composite materials, the capacity is still ≥1.0 mAh·cm⁻² after 400 cycles.

[0029] The following specific example further illustrates the effectiveness of the technical solution of this application: First, 0.25g PAA was dissolved in 30mL of phosphate buffer solution with pH=6, 0.13g EDC and 0.07g NHS were added for activation for 30min, then 0.13g DA·HCl was added, and the mixture was stirred for 9h under a nitrogen atmosphere. After dialyzing, it was freeze-dried to obtain PD. PD was dissolved in deionized water at a mass ratio of PD:BA=90:10, and 10% of the mass of PEDOT:PSS was added. The mixture was crosslinked under vacuum at 120℃ for 2h to obtain PDB-PEDOT binder with an ionic conductivity of 8.53×10⁻. 4 The peel strength was 1.50 N. 60 mg of silicon powder (60-100 nm), 20 mg of PDB-PEDOT binder, and 20 mg of SuperP were dispersed in 1 mL of deionized water and stirred for 10 h to obtain a slurry. This slurry was coated onto copper foil, dried under vacuum at 100 °C for 12 h, and then cut to obtain a negative electrode with an areal load of 0.9 mg·cm⁻². After 50 cycles, the thickness increased by 61.0%, with no through cracks. The binder, negative electrode, positive electrode, electrolyte, and separator were assembled into a CR2025 coin cell (negative electrode + NCM811 positive electrode + PP separator + electrolyte). Tests showed an initial coulombic efficiency of 85.4%, a capacity of 2326 mAh·g⁻¹ after 300 cycles, and a rate capacity of 1877 mAh·g⁻¹ at 8.0 A·g⁻¹. The full cell capacity after 300 cycles was 1.2 mAh·cm⁻², meeting commercial requirements.

[0030] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention. In addition, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. Furthermore, various different embodiments of the present invention can also be arbitrarily combined, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A negative electrode binder, characterized in that: The structure comprises a base binder phase, a dynamic crosslinking phase, and a conductive reinforcing phase. The base binder phase is dopamine-modified polyacrylic acid, prepared by an amidation reaction of polyacrylic acid and dopamine, with a mass ratio of 2-8:

1. The dynamic crosslinking phase is boric acid, with a mass ratio of boric acid to dopamine-modified polyacrylic acid of 5-15:

100. The conductive reinforcing phase is poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate), i.e., PEDOT:PSS, with a mass ratio of PEDOT:PSS to dopamine-modified polyacrylic acid of 1-5:

10. The base binder phase and the dynamic crosslinking phase are bonded by dynamic hydrogen bonds, and the base binder phase and the conductive reinforcing phase are crosslinked by hydrogen bonds to form a three-dimensional network structure.

2. The negative electrode binder according to claim 1, characterized in that: The LiPAA is prepared by neutralization reaction of polyacrylic acid and lithium hydroxide, wherein the molar ratio of lithium hydroxide to acrylic acid units in polyacrylic acid is 0.5-1:

1.

3. A negative electrode sheet, characterized in that: It includes a current collector and a negative electrode active layer, wherein the negative electrode active layer is coated on the surface of the current collector; the negative electrode active layer includes a negative electrode active material, a conductive additive, and a negative electrode binder as described in any one of claims 1-2; wherein the conductive additive is SuperP.

4. A negative electrode sheet according to claim 3, characterized in that: The negative electrode active material is at least one of silicon powder and silicon-carbon composite material, and the silicon powder particle size is 60-100nm.

5. A negative electrode sheet according to claim 4, characterized in that: The mass ratio of the negative electrode active material, negative electrode binder, and conductive additive is 5-7:1.5-2.5:1.5-2.

5.

6. A lithium-ion battery, characterized in that: It includes a positive electrode sheet, a separator, an electrolyte, a negative electrode binder according to any one of claims 1-2, or a negative electrode sheet according to any one of claims 3-5.

7. A lithium-ion battery according to claim 6, characterized in that: The active material of the positive electrode is at least one of NCM, NCA, NCAM, LFP, and LFMP.

8. A lithium-ion battery according to claim 6, characterized in that: The electrolyte is 1.0 mol / L LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC:DEC=1:1, v / v), with 8-12 wt% fluoroethylene carbonate (FEC) added.

9. A lithium-ion battery according to claim 6, characterized in that: The diaphragm is a PP or PE diaphragm.