A negative electrode slurry, a negative electrode sheet, and a secondary battery

Abstract

This invention discloses a negative electrode slurry, a negative electrode sheet, and a secondary battery thereof. The negative electrode slurry of this invention includes a negative electrode active material, a slurry additive, a conductive agent, a binder, and a thickener. The negative electrode active material includes a graphite-based active material. The slurry additive includes compound A with the structure shown in Formula 1, wherein R1 and R2 are each independently selected from hydrogen, hydrocarbon groups, and tetrahydrofuran groups, and at least one of R1 and R2 is a tetrahydrofuran group. Due to the special structure of the slurry additive compound A in the negative electrode slurry of this invention, the wettability of the graphite-based negative electrode can be effectively improved, the high-temperature performance of the secondary battery can be effectively improved, and the risk of lithium plating is lower. Formula 1

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a negative electrode slurry, a negative electrode sheet, and a secondary battery thereof. Background Technology

[0002] Thick electrodes can improve battery energy density due to their high active material loading, but they face serious electrolyte wetting problems, leading to a decline in battery performance. Thick electrodes mainly face the following problems: (1) Structural resistance: Thick electrodes have high compaction density, high pore tortuosity, and uneven pore distribution, making it difficult for electrolyte to penetrate evenly and easily forming internal "dry areas"; (2) Kinetic limitations: The ion diffusion path is extended, and concentration polarization is aggravated; (3) The electrolyte viscosity is high, and the capillary force is insufficient to drive deep penetration; (4) Side reaction risk: Insufficient wetting leads to local lithium deposition, causing thermal runaway; residual moisture aggravates side reactions. Existing technologies mainly improve the wetting of thick electrodes in terms of process and materials. In terms of process, there are: (1) Process optimization gradient injection technology: The first injection (0.2~0.8M lithium salt) reduces viscosity and improves permeability; the second injection (3~9M) replenishes lithium ions, taking into account both SEI film uniformity and ion supply. (2) Vacuum-pressurization cycle: Vacuum reduces pore gas resistance, pressurization (0.2~1.0 MPa) enhances driving force, and fractional liquid injection avoids overflow and deformation. (3) Stepped aging / pre-charging: Combining room temperature and high temperature (35℃) aging, supplemented by stepped current pre-charging (0.05C→0.2C), the electrode is activated and the electrolyte distribution is optimized. In terms of materials, such as multi-gradient microstructure design, femtosecond laser to construct microporous networks, and surface and interface control of functional binders. These methods have improved the wetting of thick electrodes, but the resulting cost has increased significantly, and the original process production line needs to be changed.

[0003] Therefore, there is an urgent need for a negative electrode slurry, a negative electrode sheet and its secondary battery to effectively solve the problem of difficulty in wetting existing thick electrodes. Summary of the Invention

[0004] In view of the above problems, the purpose of this invention is to provide a negative electrode slurry, a negative electrode sheet and a secondary battery thereof. The negative electrode slurry has a special structure of slurry additives, which can effectively improve the wettability of graphite negative electrodes, effectively improve the high-temperature performance of secondary batteries, and have a lower risk of lithium plating.

[0005] To achieve the above objectives, a first aspect of the present invention provides a negative electrode slurry, comprising a negative electrode active material, a slurry additive, a conductive agent, a binder, and a thickener. The negative electrode active material comprises a graphitic active material, and the slurry additive comprises compound A with the structure shown in Formula 1.

[0006] Formula 1 R1 and R2 are each independently selected from hydrogen, hydrocarbon group, and tetrahydrofuran group, and at least one of R1 and R2 is tetrahydrofuran group.

[0007] Compared with existing technologies, the slurry additive compound A of this invention has a "fluoro-pyrimidinone-tetrahydrofuran" structure, making it amphiphilic. It is miscible with water and also soluble in organic solvents such as carbonates. When used as a slurry additive for the negative electrode, the polar groups (C=O, N atoms) of the pyrimidinone ring in compound A can form hydrogen bonds or π-π interactions with the negative electrode binder (such as SBR, PAA), enhancing the interfacial bonding between the graphite active material and the binder and reducing capacity decay caused by binder shedding during high-temperature cycling. Furthermore, in an electrolyte environment, part of compound A can dissolve in it. Compound A belongs to the fluoropyrimidinone derivative class, and its core structure includes fluorine atoms (F), a pyrimidinone ring, and tetrahydrofuran substituents. These structures work synergistically to improve the high-temperature performance of the battery. The fluorine atom, with its strong electronegativity, preferentially participates in the reaction on the negative electrode surface, forming a LiF-rich SEI film. LiF can suppress the decomposition and swelling of SEI at high temperatures, thereby maintaining the stability of the electrode interface, which is key to improving high-temperature cycle life and high-temperature storage capacity retention. The pyrimidinone ring is a rigid heterocyclic structure with good thermal stability and chemical inertness, reducing its own decomposition side reactions at high temperatures. Simultaneously, it interacts with Li in the electrolyte... + The weak interactions of the compounds regulate lithium-ion transport kinetics, preventing lithium dendrite growth or a sharp increase in interfacial impedance at high temperatures. The oxygen atoms in the tetrahydrofuran-based structure can form hydrogen bonds with electrolyte solvents (such as carbonates), enhancing the compatibility between the additive and the electrolyte. Simultaneously, its flexible chain buffers volume changes in the graphite anode during high-temperature cycling, reducing mechanical breakage of the SEI film and further stabilizing the interface. Therefore, the structural characteristics of compound A in this invention give it irreplaceable advantages in high-temperature cycling and storage: through fluorine atom film formation, pyrimidinone ring stabilization, and tetrahydrofuran flexible adaptation, it synergistically improves the anode interface stability. It also improves adhesion through hydrogen bonding and, synergistically with conductive agents and binders in the anode slurry, further enhances the wettability of the anode to the electrolyte.

[0008] Furthermore, R1 and R2 are each independently selected from hydrogen, alkyl groups having 1 to 6 carbon atoms, and 2-tetrahydrofuranyl groups, and at least one of R1 and R2 is 2-tetrahydrofuranyl.

[0009] Furthermore, compound A of the present invention comprises at least one of compounds A1 to A3:

[0010] Compound A1, Compound A2, Compound A3.

[0011] Specifically, the CAS number of compound A1 is 17902-23-7; the CAS number of compound A2 is 62987-05-7; and the CAS number of compound A3 is 64504-13-8.

[0012] Further, by weight, the present invention comprises 90-95 parts of negative electrode active material, 0.05-4.5 parts of slurry additive, 0.5-1.5 parts of conductive agent, 0.8-2.5 parts of binder, and 1.5-3 parts of thickener. Specifically, the weight percentage of the negative electrode active material may be, but is not limited to, 90, 91, 92, 93, 94, or 95 parts; the weight percentage of the slurry additive may be, but is not limited to, 0.05, 0.08, 0.1, 0.2, 0.5, 0.8, 1.0, 1.2, 1.5, 1.8, 2.0, 2.5, 3.0, 3.5, 4.0, or 4.5 parts; the weight percentage of the conductive agent may be, but is not limited to, 90-95 parts of negative electrode active material, 0.05-4.5 parts of slurry additive, 0.5-1.5 parts of conductive agent, 0.8-2.5 parts of binder, and 1.5-3 parts of thickener. The quantities are limited to 0.5 parts, 0.8 parts, 1.0 parts, 1.2 parts, 1.4 parts, and 1.5 parts; the quantities of adhesive may be, but are not limited to, 0.8 parts, 1.0 parts, 1.2 parts, 1.4 parts, 1.5 parts, 1.6 parts, 1.8 parts, 2.0 parts, 2.2 parts, and 2.5 parts; the quantities of thickener may be, but are not limited to, 1.5 parts, 1.8 parts, 2.0 parts, 2.2 parts, 2.4 parts, 2.5 parts, 2.6 parts, 2.8 parts, and 3.0 parts.

[0013] Furthermore, the graphite-based active material of the present invention includes at least one of artificial graphite, natural graphite, modified graphite, and composite graphite. Preferably, the graphite-based active material of the present invention is selected from artificial graphite or natural graphite.

[0014] Furthermore, the conductive agent of the present invention includes at least one of conductive carbon black and carbon nanotubes.

[0015] Furthermore, the adhesive of the present invention is selected from at least one of styrene-butadiene rubber, polyacrylonitrile, and polyacrylic acid.

[0016] Furthermore, the thickener of the present invention is selected from sodium carboxymethyl cellulose.

[0017] A second aspect of the present invention provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer, wherein the thickness of the negative electrode active material layer is 200 μm to 300 μm, and the negative electrode active material layer is prepared from the aforementioned negative electrode slurry. Specifically, the thickness of the negative electrode active material layer may be, but is not limited to, 200 μm, 210 μm, 220 μm, 230 μm, 240 μm, 250 μm, 260 μm, 270 μm, 280 μm, 290 μm, or 300 μm.

[0018] A third aspect of the present invention provides a secondary battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode is the aforementioned negative electrode.

[0019] Furthermore, the non-aqueous electrolyte of the present invention includes a film-forming aid, the film-forming aid comprising 0.5% to 5% by mass in the non-aqueous electrolyte. Specifically, the film-forming aid comprises 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, and 5.0% by mass in the non-aqueous electrolyte.

[0020] Furthermore, the film-forming aid of the present invention is selected from at least one of fluoroethylene carbonate (FEC), ethylene sulfite (ES), 1,3-propanesulfonate lactone (PS), 1,3-propenesulfonate lactone (PES), 1,4-butanesulfonate lactone (BS), ethylene sulfate (DTD), and succinic anhydride (SA).

[0021] Furthermore, the non-aqueous electrolyte of the present invention further includes a lithium salt and a non-aqueous organic solvent. Specifically, the lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluoro(oxalato)borate (LiDFOB), lithium lower aliphatic carboxylate, lithium difluoro(dioxalato)phosphate (LiDFBP), lithium bis(fluorosulfonyl)imide (LiFSI), lithium chloroborane, and lithium tetraphenylborate. The non-aqueous organic solvent is selected from at least one of ethylene carbonate (EC), propylene carbonate (PCA), butylene carbonate (BC), methyl pentyl carbonate (MPC), vinylene carbonate (VEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), propylene carbonate (PC), γ-butyrolactone (GBL), γ-valerolactone (GVL), δ-valerolactone (DVL), methyl acetate (MA), ethyl acetate (EA), ethyl propionate (EP), butyl acetate (BAC), propyl propionate (PP), propyl butyrate (PRB), dimethoxymethane (DMM), diethoxymethane (DEM), ethoxymethoxymethane (DCE), ethylene glycol di-n-propyl ether (EDP), ethylene glycol di-n-butyl ether (EDB), 1,3-dioxolane (DOL), 1,4-dioxane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), 2-trifluoromethyltetrahydrofuran (2-CF3-THF), and diethylene glycol dimethyl ether (DEGME). More specifically, the mass percentage of the lithium salt in the non-aqueous electrolyte is 8% - 20%. As an example, the mass percentage of the lithium salt in the non-aqueous electrolyte can be, but is not limited to, 8%, 10%, 12%, 14%, 15%, 16%, 18%, 19%, 20%; the mass percentage of the non-aqueous organic solvent in the non-aqueous electrolyte is 65% - 90%. As an example, the mass percentage of the non-aqueous organic solvent in the non-aqueous electrolyte for the graphite negative electrode can be, but is not limited to, 65%, 70%, 75%, 80%, 85%, 90%.

[0022] Furthermore, the positive electrode sheet of the present invention includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active substance in the positive electrode active material layer is selected from at least one of lithium iron phosphate and lithium manganese iron phosphate. Specifically, the positive electrode material can be lithium iron phosphate, and its chemical formula can be LiFePO4; also, for example, the positive electrode material can be lithium manganese iron phosphate, and its chemical formula can be LiMn x Fe 1-x PO4, where the doping ratio x of Mn is 0 - 0. <x<0.35; As an example, the positive electrode material of the present invention is LiFePO4. Detailed Implementation

[0023] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0024] Unless otherwise stated, all raw materials used in the embodiments and comparative examples of this invention were obtained from commercially available sources.

[0025] Example 1 (1) Preparation of negative electrode sheet The negative electrode slurry was prepared by thoroughly mixing 95g of artificial graphite (anode active material), 0.05g of slurry additive compound A1, 1.0g of conductive carbon black Super P (conductive agent), 2.4g of styrene-butadiene rubber (binder), and 1.55g of sodium carboxymethyl cellulose (thickener) in 95g of deionized water. The slurry was then coated onto copper foil, dried, and rolled to obtain a negative electrode sheet with a negative electrode active material layer thickness of 250µm.

[0026] (2) Preparation of positive electrode sheet 95g LiFePO4, 1g binder CMC and 4g conductive agent SuperP were mixed evenly in 95g deionized water to prepare a positive electrode slurry. The positive electrode slurry was coated on both sides of aluminum foil, dried and rolled to obtain a positive electrode sheet.

[0027] (3) Preparation of non-aqueous electrolyte In an argon-filled glove box (O2 < 1 ppm, H2O < 1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and propylene carbonate (PC) were mixed in a weight ratio of EC:EMC:PC = 6:9:1 to prepare 84 g of non-aqueous organic solvent. After dissolving and stirring thoroughly, 16 g of lithium hexafluorophosphate was added and mixed evenly to obtain a graphite anode non-aqueous electrolyte.

[0028] (4) Preparation of lithium-ion batteries The positive electrode, separator, and negative electrode are wound together to form a soft-pack battery cell, which is then packaged in a polymer aluminum-plastic film and filled with the graphite negative electrode non-aqueous electrolyte prepared above. After formation, capacity testing, and other processes, a lithium-ion battery with a capacity of 1000mAh is produced.

[0029] Example 2 The difference between this embodiment and Embodiment 1 is that the slurry additive is compound A2, while the rest are the same as in Embodiment 1.

[0030] Example 3 The difference between this embodiment and Embodiment 1 is that the slurry additive is compound A3, while the rest are the same as in Embodiment 1.

[0031] Example 4 The difference between this embodiment and Example 1 is that the mass of compound A1 is 2g, while the rest are the same as in Example 1.

[0032] Example 5 The difference between this embodiment and Example 1 is that the mass of compound A1 is 4.5g, while the rest are the same as in Example 1.

[0033] Example 6 The difference between this embodiment and Embodiment 1 is that the mass of the artificial graphite is 93g, while the rest are the same as in Embodiment 1.

[0034] Example 7 The difference between this embodiment and Embodiment 1 is that the mass of conductive carbon black Super P is 1.3g, while the rest are the same as in Embodiment 1.

[0035] Example 8 The difference between this embodiment and Embodiment 1 is that the adhesive is polyacrylonitrile, while the rest are the same as in Embodiment 1.

[0036] Example 9 The difference between this embodiment and Embodiment 1 is that: (3) Preparation of non-aqueous electrolyte: In a glove box filled with argon (O2 < 1 ppm, H2O < 1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and propylene carbonate (PC) were mixed in a weight ratio of EC:EMC:PC = 6:9:1 to obtain 83 g of non-aqueous organic solvent. After dissolving and stirring thoroughly, 16 g of lithium hexafluorophosphate and 1 g of fluoroethylene carbonate (FEC) were added in sequence and mixed evenly to obtain the graphite negative electrode non-aqueous electrolyte.

[0037] Everything else is the same as in Example 1.

[0038] Example 10 The difference between this embodiment and Embodiment 1 is that: (3) Preparation of non-aqueous electrolyte: In a glove box filled with argon (O2 < 1 ppm, H2O < 1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and propylene carbonate (PC) were mixed in a weight ratio of EC:EMC:PC = 6:9:1 to obtain 83 g of non-aqueous organic solvent. After dissolving and stirring thoroughly, 16 g of lithium hexafluorophosphate and 1 g of succinic anhydride (SA) were added in sequence and mixed evenly to obtain the graphite negative electrode non-aqueous electrolyte.

[0039] Everything else is the same as in Example 1.

[0040] Comparative Example 1 The difference between this comparative example and Example 1 is as follows: (1) Preparation of negative electrode sheet: 95g of negative electrode active material artificial graphite, 1.0g of conductive agent conductive carbon black Super P, 2.4g of binder styrene-butadiene rubber and 1.55g of thickener sodium carboxymethyl cellulose are thoroughly mixed in 95g of deionized water to obtain a negative electrode slurry. The slurry is coated on copper foil, dried and rolled to obtain a negative electrode sheet with a negative electrode active material layer thickness of 250um.

[0041] Everything else is the same as in Example 1.

[0042] Comparative Example 2 The difference between this comparative example and Example 1 is as follows: (1) Preparation of negative electrode sheet: 95g of negative electrode active material artificial graphite, 1.0g of conductive agent conductive carbon black Super P, 2.4g of binder styrene-butadiene rubber and 1.55g of thickener sodium carboxymethyl cellulose are thoroughly mixed in 95g of deionized water to obtain a negative electrode slurry. The slurry is coated on copper foil, dried and rolled to obtain a negative electrode sheet with a negative electrode active material layer thickness of 250um.

[0043] (3) Preparation of non-aqueous electrolyte: In a glove box filled with argon (O2 < 1 ppm, H2O < 1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and propylene carbonate (PC) were mixed in a weight ratio of EC:EMC:PC = 6:9:1 to obtain 83.95 g of non-aqueous organic solvent. After dissolving and stirring thoroughly, 16 g of lithium hexafluorophosphate and 0.05 g of compound A1 were added in sequence and mixed evenly to obtain graphite anode non-aqueous electrolyte.

[0044] Everything else is the same as in Example 1.

[0045] Comparative Example 3 The difference between this comparative example and Example 1 is as follows: (1) Preparation of negative electrode sheet: 95g of negative electrode active material artificial graphite, 0.05g of slurry additive fluoroethylene carbonate (FEC), 1.0g of conductive agent conductive carbon black Super P, 2.4g of binder styrene-butadiene rubber and 1.55g of thickener sodium carboxymethyl cellulose are thoroughly mixed in 95g of deionized water to obtain negative electrode slurry. The slurry is coated on copper foil, dried and rolled to obtain a negative electrode sheet with a negative electrode active material layer thickness of 250um.

[0046] Everything else is the same as in Example 1.

[0047] Comparative Example 4 The difference between this comparative example and Example 1 is that the mass of compound A1 is 5g, while the rest are the same as in Example 1.

[0048] The negative electrode sheets prepared in Examples 1-10 and Comparative Examples 1-4 were subjected to wetting performance tests. The lithium-ion batteries prepared in the aforementioned examples and comparative examples were subjected to high-temperature cycling tests, high-temperature storage tests, thickness growth rate tests, and lithium plating tests, respectively. The specific test conditions are as follows, and the performance test results are shown in Table 1.

[0049] Wetting performance test: The prepared negative electrode sheet was cut into strips with a length x width of 15cm x 0.8cm. Each strip was immersed in 5mL of electrolyte with a fixed volume ratio of EC:EMC:DEC=1:1:1. The height of the electrode sheet wetted by the electrolyte was observed and recorded after 2 minutes.

[0050] High-temperature cycling capacity retention performance test: At a constant temperature of 25℃, the lithium-ion battery was charged at a constant current of 1C to a voltage of 3.65V, then charged at a constant voltage of 3.65V to a current of 0.05C, and then discharged at a constant current of 1C to a voltage of 2.5V. The first discharge capacity of the battery was recorded as C0. The lithium-ion battery was then placed in a constant temperature chamber at 45℃ and left to stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. After 600 cycles of 1C / 1C charge and discharge at 45℃, it was discharged at a constant current and constant voltage of 1C / 1C to 2.5V at a constant temperature of 25℃, and the discharge capacity was recorded as C1. The capacity retention rate of the lithium-ion battery after 600 cycles at a high temperature of 45℃ will be calculated using the following formula.

[0051] Capacity retention rate = C1 / C0 × 100%.

[0052] High-Temperature Storage Capacity Retention Test: At a constant temperature of 25℃, the lithium-ion battery was charged at a constant current of 1C to a voltage of 3.65V, then charged at a constant voltage of 3.65V to a current of 0.05C, and then discharged at a constant current of 1C to a voltage of 2.5V. The first discharge capacity of the battery was recorded as C0. The lithium-ion battery was then placed in a constant temperature chamber at 60℃ and stored for 30 days. After the storage period, the battery was removed and discharged at a constant temperature of 25℃ at a constant current and voltage of 1C / 1C to a voltage of 2.5V. The discharge capacity was recorded as C1. The capacity retention rate of the lithium-ion battery after 30 days of storage at 60℃ was calculated using the following formula.

[0053] Capacity retention rate = C1 / C0 × 100%.

[0054] Thickness growth rate test: The battery was charged to 3.65V at 0.5C constant current and constant voltage at 25℃. The mass of the fully charged battery was measured using the water displacement method and recorded as m1. After being stored at 60℃ for 30 days, the battery was removed and discharged to 2.5V at 0.5C constant current at room temperature (25℃). The mass of the battery was then measured using the water displacement method and recorded as m2.

[0055] Battery thickness growth rate after 30 days of high-temperature storage = (Battery thickness m2 after 30 days of storage - Battery thickness m1 after the first full charge) / Battery thickness m1 after the first full charge × 100%.

[0056] Lithium plating test: At a high temperature of 45℃, ① charge at 1C constant current and constant voltage to 3.65V, cutoff rate 0.05C, and let stand for 5 minutes; ② discharge at 1C constant current to 2.5V, and let stand for 5 minutes; ③ repeat steps ① to ② a total of 100 times; ④ charge at 1C constant current and constant voltage to 3.65V, cutoff rate 0.05C, and let stand for 5 minutes; ⑤ disassemble the interface and observe the lithium plating.

[0057] Table 1. Performance test results of lithium-ion batteries

[0058] As shown in Table 1, compared with Comparative Example 1, the lithium-ion batteries of Examples 1 to 10 have better wetting performance and high-temperature performance, and no lithium plating was observed. In particular, Example 1 has the highest wetting height, the highest high-temperature cycle capacity retention rate, the highest high-temperature storage capacity retention rate, and the lowest thickness expansion rate after storage. It not only improves the wetting performance of the battery, but also improves the cycle and storage performance of the battery.

[0059] As can be seen from the comparison between Examples 1 and Examples 9-10, adding film-forming aids to non-aqueous electrolytes can further improve high-temperature cycling and high-temperature storage performance. This may be because film-forming aids can further increase interface stability, thereby improving the stability of the battery during high-temperature cycling and storage.

[0060] As can be seen from the comparison between Example 1 and Comparative Example 2, when the slurry additive is directly added to the non-aqueous electrolyte, the wetting performance deteriorates, the high-temperature cycling and high-temperature storage deteriorate, the thickness growth rate increases, and lithium plating is severe. This may be because the negative electrode active material of the battery electrode is relatively thick, making it difficult to form a good electrolyte diffusion channel, which leads to a reduction in electrolyte diffusion capacity and thus affects its electrochemical performance.

[0061] As can be seen from the comparison between Example 1 and Comparative Example 3, when using conventional FEC, which has the ability to improve high-temperature performance, as a slurry additive, the wetting performance and high-temperature performance deteriorate. This may be because FEC cannot be dissolved in deionized water, so it is impossible to obtain a uniform negative electrode slurry. In addition, FEC may react with the binder in the negative electrode slurry, causing the binder to lose its activity, thereby deteriorating the battery performance.

[0062] Compared with Example 1, Comparative Example 4 slightly improved the wettability of the battery, but its high-temperature cycle capacity retention rate did not improve, and there was slight lithium plating. This is because excessive addition of the additive will increase the battery impedance, leading to an increase in the interface resistance of the positive and negative electrodes, which hinders the insertion and extraction of lithium ions. Therefore, only by adding an appropriate amount can the battery cycle and storage performance be improved while improving the wettability of the battery.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A negative electrode slurry, characterized in that, The slurry includes a negative electrode active material, a slurry additive, a conductive agent, a binder, and a thickener. The negative electrode active material includes graphite-based active materials, and the slurry additive includes compound A with the structure shown in Formula 1. Formula 1 R1 and R2 are each independently selected from hydrogen, hydrocarbon group, and tetrahydrofuran group, and at least one of R1 and R2 is tetrahydrofuran group.

2. The negative electrode slurry according to claim 1, characterized in that, R1 and R2 are each independently selected from hydrogen, alkyl groups having 1 to 6 carbon atoms, and 2-tetrahydrofuranyl, and at least one of R1 and R2 is 2-tetrahydrofuranyl.

3. The negative electrode slurry according to claim 1 or 2, characterized in that, The compound A includes at least one of compounds A1 to A3: Compound A1, Compound A2, Compound A3.

4. The negative electrode slurry according to claim 1 or 2, characterized in that, By weight, it includes 90-95 parts of negative electrode active material, 0.05-4.5 parts of slurry additive, 0.5-1.5 parts of conductive agent, 0.8-2.5 parts of binder and 1.5-3 parts of thickener.

5. The negative electrode slurry according to claim 1 or 2, characterized in that, The graphite-based active materials include at least one of artificial graphite, natural graphite, modified graphite, and composite graphite.

6. The negative electrode slurry according to claim 1 or 2, characterized in that, The conductive agent includes at least one of conductive carbon black and carbon nanotubes, the binder is selected from at least one of styrene-butadiene rubber, polyacrylonitrile, and polyacrylic acid, and the thickener is selected from sodium carboxymethyl cellulose.

7. A negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer, characterized in that, The thickness of the negative electrode active material layer is 200um~300um, and the negative electrode active material layer is prepared from the negative electrode slurry according to any one of claims 1 to 6.

8. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode is the negative electrode as described in claim 7.

9. The secondary battery according to claim 8, characterized in that, The non-aqueous electrolyte includes a film-forming aid, and the film-forming aid accounts for 0.5% to 5% of the mass percentage of the non-aqueous electrolyte.

10. The secondary battery according to claim 9, characterized in that, The film-forming aid is selected from at least one of fluoroethylene carbonate, ethylene sulfite, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 1,4-butanesulfonate lactone, ethylene sulfate, and succinic anhydride.

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