A binder for a silicon negative electrode, and a negative electrode sheet and a battery including the same

Abstract

The present application relates to the technical field of lithium ion batteries, and particularly relates to a binder for a silicon negative electrode, a negative electrode sheet comprising the binder and a battery. The first component and the second component described in the present application can uniformly adhere the carbon-based negative electrode material, the silicon-based negative electrode material and the conductive agent together, avoid the possibility of the negative electrode coating powder falling off when the silicon-based negative electrode material expands, ensure the smoothness of the electronic and lithium ion channels of all active substances in the negative electrode coating, and play the performance of all active substances.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more particularly to a binder for silicon anodes, and a cathode sheet and battery comprising the binder. Background Technology

[0002] Currently, most commercially available lithium-ion batteries use graphite as the negative electrode. Due to their excellent energy density, considerable cycle life, and environmental friendliness, lithium-ion batteries are widely used in portable electronic products such as mobile phones and laptops, as well as new energy vehicles. However, with the rapid updates and replacements of these products, the energy density of traditional lithium-ion batteries using graphite (theoretical specific capacity ~370mAh / g) as the negative electrode is becoming increasingly limited, and it is difficult to break through the energy density barrier.

[0003] To achieve higher energy density lithium-ion batteries, silicon anodes with higher specific capacity have attracted widespread attention. Nano-silicon materials (~4200 mAh / g), silicon-carbon composites (>1700 mAh / g), and silicon suboxide materials (>1500 mAh / g) have been gradually developed and applied as anode materials. However, silicon does not possess a layered structure like graphite. Its lithium storage mechanism, like other metals, involves alloying and dealloying with lithium ions. The charge / discharge electrode reaction is as follows: Si + xLi + +xe - ——>Li x During the initial discharge, as the voltage decreases, a core-shell structure initially forms, consisting of both lithium-intercalated and non-lithium-intercalated crystalline silicon phases. With increasing lithium intercalation depth, lithium ions react with the internal crystalline silicon to form a lithium-silicon alloy, ultimately converting to Li. 15 The silicon exists in alloy form. This process increases the volume of silicon by about 1.5 to 3 times compared to the original state. The huge volume effect causes the structure of the silicon anode to be destroyed, and the active material loses electrical contact with the current collector and between active materials. The lithium ion insertion and extraction process cannot proceed smoothly, resulting in huge irreversible capacity.

[0004] In other words, the expansion of the silicon anode, which damages the anode paste, the anode paste / current collector interface, and the anode paste / separator interface, will severely affect the normal transport of electrons and lithium ions at the anode, thereby deteriorating the electrochemical performance of the silicon anode. Summary of the Invention

[0005] Currently, higher energy density is a continuously challenged goal for lithium-ion batteries, making the introduction of silicon anodes both reasonable and necessary. Research has found that to address the issues of silicon expansion causing damage to the anode paste and two interfaces, as mentioned above, it is necessary to construct novel binder systems to enhance cohesion and avoid powder shedding and deformation of the anode paste caused by silicon expansion. Simultaneously, it is necessary to improve the adhesion of the anode paste / current collector interface and the anode paste / separator interface to ensure normal electron and lithium-ion transport at the anode end during battery cycles. Solving these two key problems can guarantee the normal function of the anode sheet during cycling, which is of great significance for the large-scale commercial application of silicon anodes.

[0006] To address the shortcomings of existing technologies, this invention provides a binder for silicon anodes, as well as a cathode sheet and a battery incorporating the binder. This invention provides a novel binder to stabilize the cathode paste, the cathode paste / current collector interface, and the cathode paste / separator interface, ensuring normal electron and lithium-ion transport at the cathode during battery cycles, maintaining the normal electrode state, thereby improving battery cycle performance, suppressing battery expansion during cycling, and further enhancing the initial charge / discharge efficiency and positive electrode specific capacity.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] An adhesive comprising a first component and a second component, wherein the first component is a multi-component copolymer and the second component is styrene-butadiene rubber (SBR) and / or polytetrafluoroethylene (PTFE);

[0009] The multi-component copolymer is obtained by reacting a first comonomer and a second comonomer.

[0010] The first comonomer is selected from at least one of carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (CMC-Na), lithium carboxymethyl cellulose (CMC-Li), polyacryl alcohol, and polyvinyl alcohol, or a combination thereof with at least one of polyacrylonitrile, polyacrylamide, or polyacrylate;

[0011] The second comonomer is selected from at least one of polyacrylic acid (PAA), alginate, perfluorosulfonic acid, polyacrylate, alginate, and perfluorosulfonate.

[0012] In this invention, the multi-component copolymer is a macromolecular copolymer synthesized by polymerization methods such as condensation reaction of monomers or polymers containing at least two different functional groups.

[0013] According to an embodiment of the present invention, the first comonomer is a carbophilic comonomer; the second comonomer is a silicaphilic comonomer.

[0014] According to an embodiment of the present invention, the first comonomer includes a hydrophilic group and a hydrophobic group. The first comonomer can be adsorbed to the carbon-based anode material (such as graphite) through the hydrophobic group (such as -CH2-), and the carbon-based anode material is dispersed by the steric hindrance repulsion of the hydrophilic group (such as -COOH, -OH, -CN, -CONH2, etc.) in the first comonomer adsorbed on its surface. Therefore, the first comonomer has the effect of being carbonophilic and can also play a role in dispersing the carbon-based anode material.

[0015] According to an embodiment of the present invention, the second comonomer can form a hydrogen bond bonding effect with silicon through -COOH or -COO-, has a connecting and dispersing effect on silicon, and at the same time has the effect of inhibiting silicon expansion.

[0016] According to an embodiment of the present invention, the mass ratio of the first comonomer to the second comonomer is 0 to 1:1, and 0:1 is not included. For example, it is 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1 or 1:1; when the mass ratio of the first comonomer to the second comonomer is 0 to 1:1 and 0:1 is not included, it can better achieve the dispersion of the binder for the anode active material and ensure the uniformity of the distribution of the silicon-based anode material and the carbon-based anode material.

[0017] According to an embodiment of the present invention, the multi-component copolymer satisfies 0 < m1 / m2 ≤ 1, where m1 is the mass of the first comonomer and m2 is the mass of the second comonomer; for example, m1 / m2 is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.

[0018] According to an embodiment of the present invention, the number average molecular weight of the multi-component copolymer is ≥ 1 million, preferably 1 million to 3 million. For example, it is 1 million, 1.2 million, 1.5 million, 1.8 million, 2 million, 2.2 million, 2.5 million, 2.8 million or 3 million.

[0019] According to an embodiment of the present invention, the multi-component copolymer is prepared by a dehydration condensation reaction between the carboxyl group or ester group in the second comonomer and the hydroxyl group in the first comonomer under vacuum and heating conditions.

[0020] The multi-component copolymer of this invention contains both carboxyphilic and silicaphilic groups, resulting in excellent dispersion properties and ensuring the uniformity of the distribution of carbon-based and silicon-based anode materials. Furthermore, the large molecular weight of the copolymer ensures sufficient cohesion, perfectly bonding the carbon-based, silicon-based, and conductive agents together. This prevents the anode paste from shedding powder during silicon expansion, ensuring unobstructed electron and lithium-ion channels within the anode paste and maximizing the performance of all active materials. Further, it is used in conjunction with styrene-butadiene rubber (SBR) and / or polytetrafluoroethylene (PTFE). The introduction of SBR or PTFE solves the adhesion problems at the anode paste / current collector and anode paste / separator interfaces, preventing detachment of the anode paste from the current collector or separator due to the impact on these interfaces during silicon expansion. This ensures unobstructed electron and lithium-ion channels and the stability of the anode sheet's structure and morphology throughout the battery's lifespan. Therefore, the use of the binder is beneficial for improving the cycle performance of the silicon anode, suppressing cycle expansion, and extending the cycle life of the battery. Simultaneously, because the binder ensures that the electron channels between the current collector and the active material, as well as between the active material and the current collector, remain unobstructed during charging and discharging of the silicon anode, the discharge capacity of the anode can be fully utilized. This avoids capacity loss caused by powder shedding and paste detachment from the current collector, thus significantly improving the battery's initial efficiency.

[0021] According to an embodiment of the present invention, the mass ratio of the first component and the second component is 3 to 7:7 to 3, for example, 3:7, 4:6, 5:5, 6:4 or 7:3.

[0022] The present invention also provides a method for preparing the above-mentioned adhesive, the method comprising the following steps:

[0023] 1) The first comonomer and the second comonomer are mixed and subjected to a dehydration condensation reaction under vacuum and heating conditions to prepare the multi-component copolymer;

[0024] 2) The multi-component copolymer is mixed with the second component to prepare the adhesive.

[0025] According to an embodiment of the present invention, in step 1), the vacuum degree is >80kPa.

[0026] According to an embodiment of the present invention, in step 1), the heating temperature is 120°C to 300°C.

[0027] According to an embodiment of the present invention, in step 1), the reaction is carried out in the presence of a solvent, the solvent being selected from water, N,N-dimethylformamide (DMF), N,N-dimethylformamide (DMAc), etc.

[0028] The present invention also provides the application of the above-described binder in batteries.

[0029] According to an embodiment of the present invention, the binder serves as a binder in the negative electrode of the battery. Preferably, the binder serves as a binder in the silicon negative electrode of the battery.

[0030] The present invention provides a negative electrode sheet, the negative electrode sheet comprising the above-described binder.

[0031] According to an embodiment of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on at least one side surface of the negative electrode current collector, the negative electrode active material layer including the binder described above.

[0032] According to an embodiment of the present invention, the amount of the binder added accounts for 0.2 to 25 wt% of the total mass of the negative electrode active material layer, for example 0.5 to 15 wt%, or 1 to 5 wt%, for example 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%.

[0033] According to an embodiment of the present invention, the negative electrode active material layer further includes a negative electrode active material and a conductive agent.

[0034] According to an embodiment of the present invention, the negative electrode current collector is a single-sided smooth copper foil, a double-sided smooth copper foil, or a porous copper foil.

[0035] According to an embodiment of the present invention, the negative electrode active material includes silicon-based negative electrode material and carbon-based negative electrode material.

[0036] According to an embodiment of the present invention, the silicon-based anode material is selected from at least one of pure silicon, nano-silicon, silicon carbide, silicon-carbon composite material, or silicon suboxide.

[0037] According to an embodiment of the present invention, the carbon-based anode material is selected from at least one of artificial graphite, natural graphite, mesophase carbon microspheres, hard carbon, and soft carbon.

[0038] According to an embodiment of the present invention, the mass ratio of silicon-based anode material to carbon-based anode material in the negative electrode active material is 9:1 to 1:9, for example, 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2 or 9:1.

[0039] According to an embodiment of the present invention, the conductive agent is selected from at least one of graphite, conductive carbon black, acetylene black, graphene, and carbon nanotubes.

[0040] According to an embodiment of the present invention, the peeling force of the negative electrode sheet is ≥14N / m, preferably 15~20N / m.

[0041] According to an embodiment of the present invention, the peeling force of the negative electrode sheet after 20T cycles is ≥9N / m, preferably 12~20N / m.

[0042] The present invention also provides a method for preparing the above-mentioned negative electrode sheet, comprising the following steps:

[0043] (1) Mix the negative electrode active material, conductive agent and the above-mentioned binder evenly to obtain a negative electrode slurry;

[0044] (2) The negative electrode slurry is coated on the surface of the current collector and baked to obtain the negative electrode sheet.

[0045] According to an embodiment of the present invention, the method for preparing the negative electrode sheet includes at least the following steps:

[0046] Step 1:

[0047] A mixed solution of SWCNT and MP was prepared by stirring an aqueous solution of conductive single-walled carbon nanotubes (SWCNT) and a multi-component copolymer (MP) in a stirred tank. The weight ratio of SWCNT to MP was 1:3.

[0048] Step 2:

[0049] Take a 30% SWCNT-MP mixed solution and place it in a stirring tank. Add conductive agent carbon black SP and deionized water, stir, and a conductive adhesive is prepared. Then add silicon-based anode material and stir. SWCNT / MP material is coated on the surface of silicon-based anode material particles, which facilitates the dispersion of silicon-based anode material.

[0050] Step 3:

[0051] A carbon-based anode material is added to prepare a silicon-based anode material / carbon-based anode material hybrid anode material. Finally, the remaining 70% SWCNT-MP mixed solution, the second component, and deionized water are added and stirred to prepare an anode slurry. The anode slurry is coated on the surface of the current collector and baked to obtain the anode sheet.

[0052] The present invention also provides the application of the above-mentioned negative electrode sheet in batteries.

[0053] The present invention provides a battery comprising the binder described above.

[0054] According to an embodiment of the present invention, the battery includes the aforementioned negative electrode.

[0055] According to an embodiment of the present invention, the battery is a wound lithium-ion battery or a stacked lithium-ion battery.

[0056] According to an embodiment of the present invention, the battery is assembled from a positive electrode, a separator, a negative electrode, and an electrolyte. For example, the positive electrode, negative electrode, and separator are assembled into a battery using industry-standard winding or stacking methods, then encapsulated with an aluminum-plastic film, and subsequently undergo baking, electrolyte injection, formation, and secondary sealing processes to obtain a lithium-ion battery.

[0057] According to an embodiment of the present invention, the positive electrode active material is at least one of lithium iron phosphate, lithium iron manganese phosphate, ternary positive electrode materials (such as NCM622, NCM811, NCA, etc.), and lithium cobalt oxide.

[0058] The beneficial effects of this invention are:

[0059] (1) The first and second components described in this invention can work together to uniformly bond the carbon-based anode material, the silicon-based anode material and the conductive agent together, avoiding the possibility of powder falling off the anode paste when the silicon-based anode material expands, ensuring the smooth flow of electron and lithium-ion channels of all active materials inside the anode paste, and giving full play to the performance of all active materials.

[0060] (2) The first and second components of the present invention work together to ensure strong adhesion between the two interfaces of negative electrode paste / current collector and negative electrode paste / separator, avoiding the negative electrode paste from detaching from the current collector or separator due to the impact on the adhesion of the two interfaces when the silicon-based negative electrode material expands, and ensuring the smooth flow of electron channels and lithium-ion channels of the negative electrode and the stability of the structure and morphology of the negative electrode sheet throughout the entire life cycle of the battery.

[0061] (3) The first and second components of the present invention synergistically enhance the dispersion of carbon-based anode materials and silicon-based anode materials in the slurry, reduce the amount of CMC, increase the solid content of the slurry, and improve the processing performance of silicon-based anode sheets, making them suitable for large-scale production of silicon-based anode lithium-ion batteries. Attached Figure Description

[0062] Figure 1 This is a schematic diagram of the negative electrode sheet of the present invention.

[0063] Figure reference numerals: 1 is the diaphragm, 2 is the first component, 3 is the second component, 4 is the single-walled carbon nanotube, 5 is the carbon-based anode material, 6 is the conductive agent carbon black SP, 7 is the silicon-based anode material, and 8 is the anode current collector. Detailed Implementation

[0064] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0065] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0066] In the description of this invention, it should be noted that the terms "first," "second," etc., are used for descriptive purposes only and are not intended to indicate or imply relative importance.

[0067] Preparation Example 1

[0068] Preparation method of c-CMC-polyacrylol-PAA-alginic acid multi-component copolymer:

[0069] 25 wt.% CMC (4 wt.% aqueous solution of CMC, molecular weight > 250,000), 25 wt.% PAA (molecular weight > 250,000), 25 wt.% polyacrylol (molecular weight > 250,000), and 25 wt.% alginic acid (molecular weight > 250,000) were mixed and heated to 150°C under vacuum for 2–5 hours. Through the dehydration condensation reaction of -OH and -COOH, an aqueous multi-component copolymer of c-CMC-polyacrylol-PAA-alginic acid, with a molecular weight of 1 million, was formed.

[0070] Preparation Example 2

[0071] Preparation method of c-CMC-PAA multi-component copolymer:

[0072] 50 wt.% CMC (4 wt.% CMC aqueous solution, molecular weight > 500,000) and 50 wt.% PAA (molecular weight > 500,000) were mixed and heated to 150°C under vacuum for 2–5 hours. Through the dehydration condensation reaction of -OH and -COOH, an aqueous multi-component copolymer of c-CMC-PAA, MP2, was formed with a molecular weight of 1 million.

[0073] Preparation Example 3

[0074] Preparation method of c-polyacrylol-PAA multi-component copolymer:

[0075] 50 wt.% polyacrylol (10 wt.% aqueous polyacrylol solution, molecular weight > 500,000) and 50 wt.% PAA (molecular weight > 500,000) were mixed and heated to 150°C under vacuum for 2–5 hours. Through the dehydration condensation reaction of -OH and -COOH, an aqueous multi-component copolymer of c-polyacrylol-PAA, MP3, was formed with a molecular weight of 1 million.

[0076] Preparation Example 4

[0077] Preparation method of c-polyacrylol-alginic acid multi-component copolymer:

[0078] 50 wt.% polyacrylol (10 wt.% aqueous solution of polyacrylol, molecular weight > 500,000) and 50 wt.% alginic acid (molecular weight > 500,000) were mixed and heated to 150°C under vacuum for 2–5 hours. Through the dehydration condensation reaction of -OH and -COOH, a c-polyacrylol-alginic acid aqueous multi-component copolymer MP4 with a molecular weight of 1 million was formed.

[0079] Preparation Example 5

[0080] Preparation method of c-CMC-alginic acid multi-component copolymer:

[0081] 50 wt.% CMC (4 wt.% CMC aqueous solution, molecular weight > 500,000) and 50 wt.% alginic acid (molecular weight > 500,000) were mixed and heated to 150°C under vacuum for 2–5 hours. Through the dehydration condensation reaction of -OH and -COOH, an aqueous multi-component copolymer of c-CMC-alginic acid, MP5, was formed with a molecular weight of 1 million.

[0082] Example 1

[0083] (1) Preparation of negative electrode N1: The conductive agent single-walled carbon nanotubes (SWCNT) aqueous solution and the multi-component copolymer MP1 aqueous solution prepared in Preparation Example 1 were placed in a stirring tank and stirred for 60 min to obtain SWCNT-MP1 mixed solution.

[0084] A 30% SWCNT-MP1 mixed solution was placed in a stirred tank, and conductive agent carbon black SP and deionized water were added. The mixture was stirred for 60 minutes to obtain a conductive adhesive. Then, SiOx anode material was added, and the mixture was stirred for 90 minutes, resulting in the coating of SWCNT / MP1 material onto the surface of the SiOx particles, facilitating SiOx dispersion. Graphite was added to prepare a silicon-based / graphite hybrid anode material. Finally, the remaining 70% SWCNT-MP1 mixed solution, SBR binder, and deionized water were added, and the mixture was stirred for 2 hours to prepare a SiOx / graphite hybrid anode slurry. The slurry contained 28.95% SiOx: 67.55% graphite: 1% SP: 0.5% SWCNT: 1% MP1: 1% SBR binder.

[0085] The slurry has a solid content of 50 wt%. The slurry is evenly coated on both sides of the copper foil, dried, and compacted by a roller press to obtain the negative electrode sheet, denoted as N1.

[0086] (2) Preparation of positive electrode P1

[0087] The positive electrode active material, ternary nickel-cobalt-manganese NCM811, binder, and conductive carbon black were mixed and stirred at high speed to obtain a uniformly dispersed mixture. The mixture contained 95 wt% NCM, 2 wt% PVDF binder, and 3 wt% conductive carbon black as solids. The mixture was used as a solvent, N-methylpyrrolidone, to prepare a positive electrode active material slurry with a solids content of 70 wt%. This slurry was uniformly coated on both sides of an aluminum foil, dried, and compacted using a roller press to obtain the positive electrode sheet, denoted as P1.

[0088] (3) Assembly of battery C1

[0089] After punching the positive electrode P1 and negative electrode N1, they are stacked in a Z-shape to form a bare cell, from which aluminum tabs and nickel-plated copper tabs are formed. The bare cell is then clamped with glass clamps at a force of 100 MPa / m. 2 The batteries are then vacuum-baked at 85°C for 24 hours and then encapsulated with aluminum-plastic film. This process is carried out in an environment with humidity <5%. The electrolyte used is a 1M lithium hexafluorophosphate electrolyte, with a solvent of ethylene carbonate / dimethyl carbonate / 1,2-propylene glycol carbonate in a 1:1:1 (volume ratio). After encapsulation, the batteries undergo formation and aging to obtain square soft-pack batteries with dimensions of 80mm × 60mm × 10mm.

[0090] Examples 2-6 and Comparative Examples 1-7

[0091] Examples 2-6 and Comparative Examples 1-7 differ from Example 1 in that the aqueous multi-component copolymers MP1 and / or SBR in (1) are replaced, and the specific selection of binders is shown in Table 1.

[0092] Table 1. Composition of the adhesives in the examples and comparative examples.

[0093] First component Second component Example 1 c-CMC-polyacrylol-PAA-algin copolymer MP1 SBR Example 2 c-CMC-PAA multi-component copolymer MP2 SBR Example 3 c-polyacrylol-PAA multi-component copolymer MP3 SBR Example 4 c-polyacrylol-alginic acid copolymer MP4 SBR Example 5 c-CMC-alginic acid copolymer MP5 SBR Example 6 c-CMC-polyacrylol-PAA-algin copolymer MP1 PTFE Comparative Example 1 Conventional CMC-Na SBR Comparative Example 2 PAA-Na SBR Comparative Example 3 c-CMC-polyacrylol-PAA-algin copolymer MP1 / Comparative Example 4 c-CMC-polyacrylol-PAA-algin copolymer MP1 Polyacrylate adhesives Comparative Example 5 A mixture of 50 wt.% PAA and 50 wt.% alginate SBR Comparative Example 6 A mixture of 50 wt.% CMC and 50 wt.% polyacrylol SBR Comparative Example 7 A mixture of 50 wt.% CMC and 50 wt.% PAA SBR

[0094] The positive and negative electrode active materials of the batteries in the above embodiments and comparative examples are kept in the same mass, and the designed capacity is kept in the same way. Based on this, the following performance tests were performed on the prepared batteries:

[0095] (1) Peel strength test method: Take negative electrode sheets of all the above embodiments and comparative examples cut to the same size, and test the peel strength according to the following method. Take the cut negative electrode sheet, cover the surface of the electrode sheet with peeling tape, peel it off with an electrode sheet peeler, and directly test its peel strength. Charge and discharge the batteries of the above embodiments and comparative examples 20 times at 100% DOD, dissect the batteries after 20 cycles and discharge them completely. When dissecting the batteries, observe the adhesion between the electrode sheet and the separator. Take the negative electrode sheet, dry the electrolyte, cut it to the same size as when testing the peel strength, and test the peel strength of the electrode sheet after 20T cycles according to the above method. At the same time, observe whether the negative electrode sheet sheds powder during cutting.

[0096] (2) Positive electrode specific capacity: The ratio of the capacity (mAh) of the battery during its first 0.33C discharge to the mass (g) of the positive electrode active material.

[0097] (3) First-time efficiency: The ratio of the battery’s first discharge capacity to its first charge capacity.

[0098] (4) 45℃ Cycles @ 80% Capacity Retention: At 45℃, within a charge / discharge window of 4.2V to 2.5V, 1C / 1C charge / discharge cycles were performed. The test process was as follows: first, 1C constant current charging to 4.2V, then constant voltage charging with a cutoff current of 0.05C, and finally 1C constant current discharging to 2.5V. This cycle test was repeated. The number of times the ratio of the discharge capacity to the initial discharge capacity (capacity retention) reached 80% was recorded and placed in Table 2. The ratio of the thickness of the fully charged battery at the end of the cycle to the thickness of the battery during the initial discharge was also recorded; this is the battery cycle expansion rate.

[0099] Table 2. Performance test data of the batteries in the examples and comparative examples.

[0100]

[0101] The test results in Table 2 show that the batteries in Examples 1-5 used a binder composition comprising a multi-component copolymer MP and SBR. The multi-component copolymer MP possesses both carbon-philic (preferably graphite) and silicon-philic functional groups, which can disperse and strengthen the cohesive force of the negative electrode paste. The strong adhesion between the negative electrode paste / current collector and the negative electrode paste / separator interfaces results in high peel strength of the negative electrode sheet, preventing powder shedding and membrane (separator, current collector) problems. Furthermore, the strong adhesion of the SBR binder to the negative electrode paste / current collector and negative electrode paste / separator interfaces ensures unobstructed electron channels provided by the current collector to the negative electrode and unobstructed lithium-ion channels provided by the separator to the negative electrode. This is mainly because the synergistic effect of MP / SBR, on the one hand, improves the interfacial structural stability between the negative electrode paste, negative electrode paste / current collector, and negative electrode paste / separator, mitigating the damage and deformation of the negative electrode sheet structure caused by the expansion of the silicon-based negative electrode material itself during charging and discharging, thus reducing cycle expansion and improving the cycle performance of the battery. On the other hand, the stable structure of the two interfaces of the negative electrode and the negative electrode paste ensures that the lithium-ion and electron channels at the negative electrode end remain unobstructed. This allows for full utilization of the capacity of the negative electrode active material, reduces polarization, improves the battery's initial efficiency (≥69%), increases the specific capacity of the positive electrode (≥164.95mAh / g), reduces DCIR changes during cycling, avoids excessive thickening of the SEI film at the negative electrode, reduces electrolyte side reactions, slows down the expansion of the negative electrode during cycling, and improves the battery's cycle performance. For example, for 45°C cycling, batteries using MP / SBR synergistic binders achieve over 1100 cycles with 80% capacity retention, and cycle expansion is controlled within 13%. Compared to other binders, this represents a significant improvement in cycle performance and cycle expansion.

[0102] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A negative electrode sheet characterized by comprising: The negative electrode sheet comprises a binder, the binder comprises a first component and a second component, the first component is a multi-component copolymer, and the second component is butadiene styrene rubber and / or polytetrafluoroethylene; The multi-component copolymer is a CMC-polyvinyl alcohol-PAA-alginic acid multi-component copolymer. The number average molecular weight of the multi-component copolymer is 1 million to 3 million.

2. The negative electrode sheet according to claim 1, characterized by The mass ratio of the first component to the second component is 3-7:7-3.

3. The negative electrode sheet according to claim 2, characterized by The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer located on at least one side surface of the negative electrode current collector, and the negative electrode active material layer comprises the binder.

4. The negative electrode sheet according to claim 2, characterized by The addition amount of the binder accounts for 0.2-25wt% of the total mass of the negative electrode active material layer.

5. The negative electrode sheet according to any one of claims 1 to 4, wherein The peeling force of the negative electrode sheet is ≥14N / m. And / or, the peeling force of the negative electrode sheet after 20T cycles is ≥9N / m.

6. The negative electrode sheet according to any one of claims 1 to 4, wherein The negative electrode active material comprises a silicon-based negative electrode material and a carbon-based negative electrode material; the silicon-based negative electrode material is selected from at least one of pure silicon, silicon carbide, silicon-carbon composite material or silicon monoxide; and the carbon-based negative electrode material is selected from at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon and soft carbon.

7. A battery, characterized by The battery comprises the negative electrode sheet according to any one of claims 1-6.

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