Positive electrode slurry, positive electrode plate and battery

Abstract

The invention discloses positive electrode slurry, a positive electrode plate and a battery. The positive electrode slurry comprises a positive electrode active material and an additive, the additive comprises a silicon-based difluorophosphate compound, the silicon-based difluorophosphate compound satisfies a formula I and a formula I, R1, R2 and R3 are independently selected from C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C2-C4 fluoroalkynyl,-OP (= O) F2,-Si (R4) (R5) OP (= O) F2 or-OSi (R4) (R5) OP (= O) F2; r < 4 > and R < 5 > are respectively and independently selected from alkyl of C < 1 > to C < 4 >, fluoroalkyl of C < 1 > to C < 4 >, alkenyl of C < 2 > to C < 4 >, fluoroalkenyl of C < 2 > to C < 4 >, alkynyl of C < 2 > to C < 4 >, fluoroalkynyl of C < 2 > to C < 4 > or-OP (= O) F2. Therefore, the positive electrode slurry has relatively excellent stability, the baking effect after coating is relatively good, the cycle performance of the battery can be improved by the decomposition product of the additive, and the battery prepared from the positive electrode slurry has relatively excellent cycle performance and relatively high energy density.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to positive electrode slurry, positive electrode sheet, and battery. Background Technology

[0002] As the application fields of lithium-ion batteries continue to expand, the performance requirements of lithium-ion batteries vary greatly across different application areas. Among them, when used as power batteries, higher energy density and longer cycle life have become the mainstream demand in the current market. Summary of the Invention

[0003] In a first aspect, this application provides a positive electrode slurry comprising: a positive electrode active material and an additive, said additive comprising a silicon-based difluorophosphate compound satisfying Formula I. Formula I, R1, R2, and R3 are each independently selected from C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C2-C4 fluoroalkynyl, -OP(=O)F2, -Si(R4)(R5)OP(=O)F2, or -OSi(R4)(R5)OP(=O)F2; R4 and R5 are each independently selected from C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C2-C4 fluoroalkynyl, or -OP(=O)F2. Therefore, the cathode slurry exhibits superior stability, better baking performance after coating, and the decomposition products of the additives can improve the battery's cycle performance. Batteries made using this cathode slurry demonstrate superior cycle performance and lower interfacial impedance.

[0004] In some embodiments, the silicon-based difluorophosphate compound comprises at least one of the following structural formulas: Formula 1 Formula 2 Formula 3 Formula 4 Formula 5 Formula 6 Formula 7 Formula 8 Formula 9. This reduces side reactions between the binder and residual alkali on the surface of the positive electrode active material or lithium replenisher.

[0005] In some embodiments, the mass fraction of the additive is based on the total mass of the positive electrode slurry. oh A Satisfying 8≤ (a× oha -0.4×ln(b)+0.15× oh a -2.5× oh A ≤10, where: a is the initial pH of the positive electrode active material. oh a denoted by b, where b represents the mass percentage of the positive electrode active material in the positive electrode film layer, and b represents the solid content of the positive electrode slurry. Therefore, the positive electrode slurry exhibits a suitable pH, good viscosity and flowability, which is beneficial for improving the stability and processing performance of the positive electrode slurry.

[0006] In some embodiments, the additive in the cathode slurry is 0.1% to 2% by mass. Therefore, a small amount of additive can effectively remove residual alkali from the surface of the cathode active material or lithium supplement, improving the stability of the cathode slurry.

[0007] In some embodiments, the positive electrode active material includes a first positive electrode active material, the first positive electrode active material satisfying the general formula LiNi x M1 1-x O2, 0.6≤x<1, M1 includes at least one of Co, Mn, Al, and Mg; And / or, the positive electrode active material includes a second positive electrode active material, and the positive electrode slurry further includes a lithium supplementing agent, wherein the second positive electrode active material satisfies the general formula LiFe. 1-m M2 m PO4, 0≤m<1, M2 includes at least one of Co, Mn, Al, and Mg, and the lithium supplement satisfies the general formula Li 5a+2b Fe a Q b O 4a+2b Q includes at least one of Ni, Co, Mn, and Fe, 0.5≤a≤1, 0≤b≤0.5, and a+b=1.

[0008] In some embodiments, 0.8 ≤ x < 1. Therefore, the specific capacity of the positive electrode active material is relatively high, which further contributes to improving the energy density of the battery made using this positive electrode slurry.

[0009] In some embodiments, the lithium replenishing agent includes at least one of Li5FeO4 (LFO) and Li2NiO2. Therefore, the lithium replenishing agent has a high lithium replenishment capacity, which can improve the cycle performance of batteries made using this cathode slurry. In some embodiments, 8 ≤ ((c×) oh c + d× oh d )-0.4×ln(b)+0.15×( ohc +oh d ) )-2.5× oh A ≤10, where b is the solid content of the positive electrode slurry, c is the initial pH of the second positive electrode active material, and d is the initial pH of the lithium supplement agent. oh c This represents the mass percentage of the second positive electrode active material in the positive electrode film layer. oh d This represents the mass percentage of lithium supplementation agent in the positive electrode film. Consequently, the positive electrode slurry exhibits a suitable pH, good viscosity, and good flowability, which is beneficial for improving the stability and processing performance of the positive electrode slurry.

[0010] In some embodiments, the slurry further includes a binder comprising polyvinylidene fluoride. This results in a more uniform dispersion of the binder in the cathode slurry and better stability of the cathode slurry.

[0011] In some embodiments, the mass fraction of the binder in the positive electrode slurry is 1%-3%. Thus, a small amount of binder can be used to firmly bond the positive electrode active material with the conductive agent, current collector, etc.

[0012] In a second aspect, this application proposes a positive electrode sheet prepared using the aforementioned positive electrode slurry. Therefore, this positive electrode sheet possesses all the features and advantages of the aforementioned positive electrode slurry, which will not be elaborated further here.

[0013] In a third aspect, this application proposes a battery including the aforementioned positive electrode. Consequently, this battery exhibits high energy density and superior cycle performance. Detailed Implementation

[0014] The embodiments of this application are described in detail below, but unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the following description is provided to enable those skilled in the art to fully understand this application and is not intended to limit the subject matter of the claims.

[0015] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0016] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0017] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0018] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0019] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0020] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0021] In battery manufacturing processes, positive electrode active materials, conductive agents, binders, and other substances need to be dispersed in a solvent to form a positive electrode slurry. This slurry is then coated onto the surface of the positive electrode current collector, and baked to remove the solvent, resulting in a positive electrode film. However, the surface of the positive electrode active material or lithium supplement in related technologies often has alkaline residues. For example, using high-nickel ternary materials as the positive electrode active material can effectively improve the battery's energy density. However, as the Ni content increases, the sintering temperature of the high-nickel ternary material decreases, leading to a reduction in the volatilization of the raw lithium salt. Consequently, the amount of lithium salt remaining on the material surface increases, forming Li₂O. After adsorbing CO₂ and H₂O from the air, Li₂O forms residual alkalis such as Li₂CO₃ and LiOH on the material surface.

[0022] Using lithium iron phosphate (LFP) materials as the positive electrode active material can improve the cycle life of batteries. However, LFP materials also suffer from relatively rapid capacity decay in the early stages of cycling. Mixing LFP materials with lithium replenishing agents, such as lithium-rich ferric acid, can effectively compensate for the active lithium loss caused by capacity decay in the early stages of cycling by releasing active lithium ions, thereby improving the performance of LFP materials. However, lithium replenishing agents are often very sensitive to moisture, easily absorbing water and decomposing to produce alkaline substances, which then form residual alkali on the surface.

[0023] When the positive electrode active material or lithium supplement has residual alkali on its surface, it will greatly affect the stability of the positive electrode slurry. During the mixing process, gelation is likely to occur, affecting the coating of the positive electrode slurry. Specifically, taking the common binder polyvinylidene fluoride (PVDF) as an example, the residual alkali on the surface of the positive electrode active material or lithium supplement will attack the CF bonds on PVDF, causing PVDF to lose HF and form double bonds. In the air, it will be further oxidized to form peroxides. The peroxides decompose to produce free radicals, which then self-couple, causing PVDF to cross-link and lose its binding effect. This results in an increase in the viscosity of the positive electrode slurry, causing gelation and sedimentation, making it unsuitable for coating processes.

[0024] Related technologies adjust the pH of the positive electrode slurry by adding acidic substances such as oxalic acid and maleic acid. However, the oxalate produced by neutralizing residual alkali with oxalic acid cannot be completely removed by baking (150℃-180℃). The oxalate remaining in the positive electrode will catalytically decompose to produce gases such as carbon dioxide under high-temperature battery conditions, such as high-temperature storage and high-temperature cycling, negatively impacting the battery's high-temperature performance. Similarly, the maleate produced by neutralizing residual alkali with maleic acid cannot be completely removed by baking. The maleate remaining in the positive electrode has high impedance, leading to a significant degradation in battery performance.

[0025] In this application, silicon-based difluorophosphate compounds are used as additives to effectively remove residual alkali from the surface of the positive electrode active material or lithium replenishing agent in the positive electrode slurry. Specifically, the silicon-based difluorophosphate compounds react with the residual moisture in the positive electrode slurry first, hydrolyzing to generate difluorophosphate and silanol, reducing the side reactions of moisture consuming electrolyte during subsequent battery charge and discharge cycles. Furthermore, the difluorophosphate in the hydrolysis products can react with the residual alkali in the positive electrode slurry to form difluorophosphate. As an inorganic salt coating layer generated in situ on the surface of the positive electrode active material, difluorophosphate improves the stability of the electrochemical interface on the surface of the positive electrode active material, reduces the direct contact between the positive electrode active material and the electrolyte, and inhibits the occurrence of interfacial side reactions. At the same time, difluorophosphate has good lithium-ion transport capacity and can also reduce the interfacial impedance of the positive electrode active material, thereby improving the cycle performance of the battery. The silanol in the hydrolysis products has a low boiling point and can be fully removed after conventional electrode baking process. The small amount of residual silanol can be further dehydrated after high-temperature baking to form a polymer interfacial film containing Si-O bonds, which has good flexibility and helps to improve the stability of the electrochemical interface on the surface of the positive electrode active material.

[0026] In a first aspect, this application provides a positive electrode slurry comprising: a positive electrode active material and an additive, said additive comprising a silicon-based difluorophosphate compound satisfying Formula I. Formula I, R1, R2, and R3 are each independently selected from C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C2-C4 fluoroalkynyl, -OP(=O)F2, -Si(R4)(R5)OP(=O)F2, or -OSi(R4)(R5)OP(=O)F2; R4 and R5 are each independently selected from C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C2-C4 fluoroalkynyl, or -OP(=O)F2. Therefore, the cathode slurry exhibits superior stability, better baking performance after coating, and the decomposition products of the additives can improve the battery's cycle performance. Batteries made using this cathode slurry demonstrate superior cycle performance and higher energy density.

[0027] In some embodiments, when R1, R2, and R3 are unsaturated groups, the unsaturated bonds contained therein can further induce polymerization and cross-linking during the charging and discharging process of the battery, forming a network structure, improving the structural stability of the positive electrode active material, reducing capacity loss caused by the breakage of positive electrode active particles, and improving the cycle performance of the battery.

[0028] In some embodiments, the silicon-based difluorophosphate compound comprises at least one of the following structural formulas: Formula 1 Formula 2 Formula 3 Formula 4 Formula 5 Formula 6 Formula 7 Formula 8 Formula 9. This reduces side reactions between the binder and residual alkali on the surface of the positive electrode active material or lithium replenisher.

[0029] In this application, Formula 1 corresponds to Compound 1, Formula 2 corresponds to Compound 2, Formula 3 corresponds to Compound 3, Formula 4 corresponds to Compound 4, Formula 5 corresponds to Compound 5, Formula 6 corresponds to Compound 6, Formula 7 corresponds to Compound 7, Formula 8 corresponds to Compound 8, and Formula 9 corresponds to Compound 9.

[0030] As an example, compound 1 reacts with residual moisture in the cathode slurry to generate trimethylsilanol and difluorophosphoric acid, which in turn reacts with residual alkali on the surface of the cathode active material or lithium supplement in the cathode slurry to generate lithium difluorophosphate.

[0031] As an example, compound 1 also reacts directly with residual base to produce lithium difluorophosphate and trimethylsilanol.

[0032] In some embodiments, the additive in the cathode slurry is 0.1% to 2% by mass. This helps to improve the stability of the cathode slurry.

[0033] By adding a small amount of additives, residual alkali on the surface of the positive electrode active material or lithium replenishing agent can be effectively removed, and an inorganic salt coating layer that helps improve the battery cycle performance can be generated. At the same time, the positive electrode slurry is still mainly composed of positive electrode active material, which helps to improve the energy density of the battery.

[0034] In some embodiments, the mass fraction of the additive is based on the total mass of the positive electrode slurry. oh A Satisfying 8≤ (a× oh a -0.4×ln(b)+0.15× oh a -2.5× oh A ≤10, where: a is the initial pH of the positive electrode active material. oh a denoted by b, where b represents the mass percentage of the positive electrode active material in the positive electrode film layer, and b represents the solid content of the positive electrode slurry. Therefore, the positive electrode slurry exhibits a suitable pH, good viscosity and flowability, which is beneficial for improving the stability and processing performance of the positive electrode slurry.

[0035] It is understood that the positive electrode slurry includes: positive electrode active material, conductive agent, binder, and solvent. The solid content 'b' of the positive electrode slurry is the proportion of components other than the solvent in the positive electrode slurry. oh a This refers to the proportion of the positive electrode active material to the components other than the solvent, i.e., the mass percentage of the positive electrode active material in the positive electrode film.

[0036] It should be noted that the initial pH of the positive electrode active material refers to the pH of the dry powder of the positive electrode active material.

[0037] The basic principle of the above formula is: pH 正极浆料 =pH 正极活性材料 +log(residual alkali dissolved / solvent volume)+ΔpH 添加剂 ; This can be further simplified to: pH 正极浆料 ≈a×ω a -k1×ln(b)+k2×ω a .

[0038] in: a represents the initial pH of the positive electrode active material; b represents the solid content of the positive electrode slurry; ω a This represents the mass percentage of the positive electrode active material in the positive electrode film layer. k1 and k2 are coefficients, calibrated experimentally (e.g., k1≈0.4, k2≈0.15). Therefore, the formula can be written as: pH 正极浆料 ≈a×ω a -0.4×ln(b)+0.15×ω a .

[0039] However, difluorophosphate compounds are polybasic acids, requiring a modification to the above formula, namely: pH 正极浆料 ≈(a×ω a -0.4×ln(b)+0.15×ω a -α×ω A ; Wherein: α is the neutralization efficiency, which is approximately 2.5 in this application.

[0040] Therefore, the amount of difluorophosphate compound added must be controlled to meet the following condition: 8 ≤ (a × oh a -0.4×ln(b)+0.15× oh a -2.5× oh A ≤10.

[0041] Under the above formula, the processing performance of the positive electrode slurry and the stability of the formed positive electrode sheet can be effectively balanced. If the amount of compound I added is too low, the slurry is highly alkaline and is prone to gelation or partial gelation, which affects the leveling of the positive electrode slurry and makes processing difficult. If the amount of compound I added is too high, the positive electrode slurry is low in alkalinity or acidic, and the corresponding decomposition products increase. On the one hand, the evaporation of decomposition products from the positive electrode sheet during the baking process of silanol may cause micropores or cracks on the electrode sheet, thereby causing lithium plating and performance degradation. On the other hand, the polysiloxane formed by the silanol that cannot be completely volatilized will increase in the positive electrode sheet, reduce interfacial ion conduction and increase interfacial impedance.

[0042] In some embodiments, the initial pH of the positive electrode active material can be selected from 9-14; the mass percentage of the positive electrode active material in the positive electrode film layer can be 85%-97%; and the solid content b of the positive electrode slurry can be 45%-70%.

[0043] In some embodiments, the positive electrode active material includes a first positive electrode active material, the first positive electrode active material satisfying the general formula LiNi x M1 1-x O2, 0.6≤x<1, M1 includes at least one of Co, Mn, Al, and Mg.

[0044] The first positive electrode active material includes high-nickel ternary materials, which have high specific capacity and fast lithium-ion insertion / extraction rate, making them suitable for high-power scenarios such as fast charging.

[0045] As an example, x can be 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95.

[0046] In some embodiments, 0.8 ≤ x < 1. Therefore, the specific capacity of the positive electrode active material is relatively high, which further contributes to improving the energy density of the battery made using this positive electrode slurry.

[0047] As an example, the first positive electrode active material may include LiNi. 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.8 Co 0.15 Al 0.05 O2), etc.

[0048] In some embodiments, the positive electrode active material includes a second positive electrode active material, and the positive electrode slurry further includes a lithium supplementing agent, wherein the second positive electrode active material satisfies the general formula LiFe. 1-m M2 m PO4, 0≤m<1, M2 includes at least one of Co, Mn, Al, and Mg, and the lithium supplement satisfies the general formula Li 5a+2b Fe a Q b O 4a+2b Q includes at least one of Ni, Co, Mn, and Fe, 0.5≤a≤1, 0≤b≤0.5, and a+b=1.

[0049] The second positive electrode active material includes lithium iron phosphate materials. Lithium iron phosphate materials have high structural stability, good cycle performance, are not prone to thermal runaway under high temperature conditions, have high safety, and low manufacturing cost.

[0050] As an example, m can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9.

[0051] In some embodiments, the lithium replenishing agent includes at least one of Li5FeO4 and Li2NiO2. Therefore, the lithium replenishing agent has a high lithium replenishment capacity, which can improve the cycle performance of batteries made using this cathode slurry.

[0052] The lithium replenishing agent includes lithium-rich ferric acid, which has an anti-fluorite structure and a theoretical capacity of 867 mAh / g. It can effectively improve the problem of low efficiency in the first cycle of the battery, thereby improving the battery capacity, cycle life and energy density.

[0053] As an example, a can be 0.5, 0.6, 0.7, 0.8, 0.9, or 1.

[0054] As an example, b can be 0, 0.1, 0.2, 0.3, 0.4, or 0.5.

[0055] In some embodiments, 8 ≤ ((c×) oh c + d× oh d )-0.4×ln(b)+0.15×( oh c +oh d ) )-2.5× oh A ≤10, where b is the solid content of the positive electrode slurry, c is the initial pH of the second positive electrode active material, and d is the initial pH of the lithium supplement agent. oh c This represents the mass percentage of the second positive electrode active material in the positive electrode film. oh d This represents the mass percentage of lithium supplementation agent in the positive electrode film. Consequently, the positive electrode slurry exhibits a suitable pH, good viscosity, and good flowability, which is beneficial for improving the stability and processing performance of the positive electrode slurry.

[0056] It is understood that the positive electrode slurry includes: the second positive electrode active material, conductive agent, binder, lithium supplementer, and solvent. The solid content b of the positive electrode slurry is the proportion of components other than the solvent in the positive electrode slurry. oh c This refers to the proportion of the second positive electrode active material in the components other than the solvent, i.e., the mass percentage of the second positive electrode active material in the positive electrode film. oh d This refers to the proportion of lithium replenishing agent in the components other than the solvent, i.e., the mass percentage of lithium replenishing agent in the positive electrode film.

[0057] It should be noted that the initial pH of the second positive electrode active material refers to the pH of the dry powder of the second positive electrode active material, and the initial pH of the lithium supplement refers to the pH of the dry powder of the lithium supplement.

[0058] In some embodiments, the mass ratio of the second positive electrode active material to the lithium supplement in the positive electrode slurry is 100:(0.5-3). Therefore, the battery made using this positive electrode slurry exhibits superior cycle performance.

[0059] Lithium iron phosphate (LFP) materials suffer from relatively rapid capacity decay in the early stages of cycling. Mixing LFP materials with lithium-rich ferric acid allows the active lithium ions released by the lithium replenishment agent to effectively compensate for the loss of active lithium during the early stages of cycling, thereby improving the performance of the LFP materials. Furthermore, the aforementioned additives can effectively mitigate the impact of residual alkali on the surface of the lithium replenishment agent on the stability of the cathode slurry.

[0060] As an example, the mass ratio of the second positive electrode active material to the lithium supplement in the positive electrode slurry can be 100:0.5, 100:1, 100:1.5, 100:2, 100:2.5 or 100:3.

[0061] Adding a small amount of lithium supplement can effectively improve cycle performance. At this point, the positive electrode slurry still mainly consists of positive electrode active materials, which helps to improve the energy density of the battery.

[0062] In some embodiments, the slurry further includes a binder comprising at least one selected from polyvinylidene fluoride, polyacrylic acid, polyacrylonitrile, and polyimide. This results in a more uniform dispersion of the binder in the cathode slurry and better stability of the cathode slurry.

[0063] The aforementioned binder can be uniformly dispersed in the solvent of the positive electrode slurry, such as N-methylpyrrolidone. After forming the positive electrode film, it can firmly adhere the positive electrode active material, conductive agent, etc. in the positive electrode active material together and fix them on the surface of the positive electrode current collector, which helps to improve the mechanical strength and structural stability of the positive electrode sheet.

[0064] In some embodiments, the mass fraction of the binder in the positive electrode slurry is 1%-3%, for example, it can be 1%, 1.5%, 2%, 2.5%, or 3%. Thus, a small amount of binder can be used to firmly bond the positive electrode active material to the conductive agent, current collector, etc.

[0065] In a second aspect, this application proposes a positive electrode sheet prepared using the aforementioned positive electrode slurry. Therefore, this positive electrode sheet possesses all the features and advantages of the aforementioned positive electrode slurry, which will not be elaborated further here.

[0066] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector.

[0067] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0068] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0069] In a third aspect, this application proposes a battery including the aforementioned positive electrode. Consequently, this battery exhibits high energy density and superior cycle performance.

[0070] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0071] Example 1 1) Preparation of positive electrode slurry The solvent for the positive electrode slurry is N-methylpyrrolidone, and the positive electrode active material is LiNi. 0.6 Co 0.2 Mn 0.2 The active material is O2, the conductive agent is carbon black, the binder is polyvinylidene fluoride, and the additive is compound 1. The mass ratio of the positive electrode active material, conductive agent, binder, and additive in the positive electrode slurry is 95:2.67:2:0.33. Specifically, polyvinylidene fluoride is dissolved in a solvent to prepare a colloid, and then the positive electrode active material, conductive agent, and additive are added to the above colloid and stirred and mixed evenly to obtain a positive electrode slurry with a solid content of 65%.

[0072] 2) Preparation of positive electrode sheet The positive electrode slurry was uniformly coated onto the surface of the positive electrode current collector aluminum foil, with a coating density of 16.0 mg / cm³ on one side. 2 After drying at 150℃, rolling, baking, slitting and spot welding of tabs, positive electrode sheets are obtained.

[0073] 3) Preparation of negative electrode sheet The negative electrode active material is made of artificial graphite. Artificial graphite, conductive agent SP, binder SBR, and CMC are dissolved in deionized water at a mass ratio of 95:1.5:2:1.5 to obtain the negative electrode slurry. This slurry is then coated onto the surface of the copper foil used as the negative electrode current collector, with a coating density of 10.1 mg / cm³ on one side. 2 After drying at 90℃, rolling, baking, slitting and spot welding of tabs, the negative electrode sheet is obtained.

[0074] 4) Assemble the above positive electrode, negative electrode, separator, and electrolyte into a soft-pack battery with a designed capacity of 1750mAh. The separator is a polyethylene film with a ceramic coating on its surface. The electrolyte includes, by mass percentage, an electrolyte salt and an organic solvent. The electrolyte salt is lithium hexafluorophosphate, and the mass fraction of lithium hexafluorophosphate in the electrolyte is 12.5%. The organic solvent is composed of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of EC:EMC = 3:7.

[0075] The differences between the remaining embodiments and comparative examples and Embodiment 1 are shown in Table 1. In Examples 35-38 and Comparative Example 2, a lithium supplement agent was added to the positive electrode slurry. Specifically, in Example 35, the mass ratio of positive electrode active material, conductive agent, binder, additive, and lithium supplement agent was 94:1.39:2.0:0.61:2.0; in Example 36, the mass ratio was 94:1.41:2.0:0.59:2.0; in Example 37, the mass ratio was 95:1.40:2.0:0.60:1.0; in Example 38, the mass ratio was 93:1.38:2.0:0.62:3.0; and in Comparative Example 2, the mass ratio was 94:1.0:2.0:0:3.0.

[0076] Table 1

[0077] The gelation properties of the positive electrode slurry in the aforementioned examples and comparative examples were tested by visual observation. The test results are shown in Table 2. The batteries in the examples and comparative examples were subjected to the following performance tests, and the test results are shown in Table 2: Room temperature cycle performance test: The battery is charged at 1C constant current to 4.25V at room temperature (25℃), charged at constant voltage (4.25V) to cutoff current (0.05C), and then discharged at 1C to voltage (2.75V). This charge-discharge cycle is repeated 1000 times. The discharge capacity of the 1000th cycle is recorded and divided by the discharge capacity of the 1st cycle to obtain the capacity retention rate.

[0078] High-temperature cycle performance test: The battery is charged at a constant current of 1C to 4.25V at a high temperature of 45℃, and then charged at a constant voltage of 4.25V to the cutoff current of 0.05C. The battery is then discharged at 1C. This charge-discharge cycle is repeated for 800 cycles. The discharge capacity of the 800th cycle is recorded and divided by the discharge capacity of the 1st cycle to obtain the capacity retention rate.

[0079] High-temperature storage performance test: The battery was charged at room temperature (25℃) with a constant current of 1C to 4.25V, and then charged at a constant voltage of 4.25V until the cutoff current was 0.05C. The battery was then discharged at a constant current of 1C, and the discharge capacity was recorded as C1. At room temperature (25℃), the battery was charged at a constant current of 1C to 4.25V, and then charged at a constant voltage of 4.25V until the cutoff current was 0.05C. The battery was then transferred to a high temperature of 60℃ and stored for 14 days. It was then discharged at a constant current of 1C, and the discharge capacity was recorded as C2. The capacity retention rate at 60℃ = C2 / C1 × 100%.

[0080] DC Impedance Test: Place the battery in a 25℃ environment and discharge it at a constant current of 1C to the cutoff voltage of 2.75V. Let it rest for 5 minutes, then charge it at a constant current and constant voltage of 1C to the upper limit voltage of 4.25V, with a cutoff current of 0.05C. Discharge it at a constant current of 1C for 30 minutes. Place the battery, adjusted to 50% SOC, at 25℃ and let it rest for 5 minutes. Discharge it at a constant current of 2C for 10 seconds. The discharge current during 2C discharge is I. 2C Record the initial voltage V0 and the voltage V1 after 10 seconds of discharge. The formula for calculating the DC internal resistance of discharge at 50% SOC is as follows: DCR(mΩ)=(V0-V1) / I 2C ×1000.

[0081] Table 2

[0082] Table 2 shows that, comparing the battery performance test results of Example 1 and Comparative Example 1, the lithium-ion battery with added additives exhibits better capacity retention at both room temperature and high temperature cycling than Comparative Example 1. The results indicate that the additives can generate a CEI film in situ, inhibiting solvent decomposition in the electrolyte and enhancing the Li-ion battery's performance. + Improves conductivity, reduces impedance, and enhances stability during room temperature and high temperature cycling.

[0083] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode slurry, characterized by, Comprising: a positive electrode active material and an additive, the additive comprising a silicon-based difluorophosphate compound, the silicon-based difluorophosphate compound satisfying Formula I, Formula I, wherein R1, R2, and R3 are each independently selected from C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C2-C4 fluoroalkynyl, -OP(=O)F2, -Si(R4)(R5)OP(=O)F2, or -OSi(R4)(R5)OP(=O)F2; R4 and R5 are each independently selected from C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C2-C4 fluoroalkynyl, or -OP(=O)F2.

2. The positive electrode slurry according to claim 1, characterized by, The silicon-based difluorophosphate compound comprises at least one of the following structural formulas: Formula 1, Formula 2, Formula 3, Formula 4, Formula 5, Formula 6, Formula 7, Formula 8, Formula 9.

3. The positive electrode slurry according to claim 1, wherein a mass fraction of the additive based on a total mass of the positive electrode slurry ω A satisfies 8≤ (a× ω a -0.4×ln(b)+0.15× ω a )-2.5× ω A ≤10, wherein: a is an initial pH of the positive electrode active material, ω a is a mass proportion of the positive electrode active material in the positive electrode film layer, and b is a solid content of the positive electrode slurry.

4. The positive electrode slurry according to claim 3, characterized by, The mass percentage of the additive in the positive electrode slurry is 0.1% to 2%.

5. The positive electrode slurry according to any one of claims 1 or 2, characterized in that, The positive electrode active material includes a first positive electrode active material satisfying a general formula LiNi x M1 1-x O2, 0.6≤x<1, M1 includes at least one of Co, Mn, Al, Mg; and / or the positive electrode active material comprises a second positive electrode active material, the positive electrode slurry further comprises a lithium supplement agent, the second positive electrode active material satisfies a general formula LiFe 1-m M2 m PO4, 0≤m<1, M2 comprises at least one of Co, Mn, Al, Mg, the lithium supplement agent satisfies a general formula Li 5a+2b Fe a Q b O 4a+2b , Q comprises at least one of Ni, Co, Mn, Fe, 0.5≤a≤1, 0≤b≤0.5, a+b=1.

6. The positive electrode slurry according to claim 5, wherein 0.8≤x<1。 7. The positive electrode slurry according to claim 5, wherein The lithium supplement agent comprises at least one of Li5FeO4 and Li2NiO2.

8. The positive electrode slurry according to claim 5, wherein 8≤ ((c× ω c + d× ω d )-0.4×ln(b)+0.15×( ω c +ω d ) )-2.5× ω A ≤10, wherein b is the solid content of the positive electrode slurry, c is the initial pH of the second positive electrode active material, d is the initial pH of the lithium supplement agent, ω c is the mass ratio of the second positive electrode active material in the positive electrode film layer, ω d is the mass ratio of the lithium supplement agent in the positive electrode film layer.

9. The positive electrode slurry according to any one of claims 1 to 3, characterized by, Further comprising: a binder, the binder comprising polyvinylidene fluoride.

10. The positive electrode slurry according to claim 9, wherein The mass fraction of the binder in the positive electrode slurry is 1% to 3%.

11. A positive electrode sheet characterized by comprising: The positive electrode tab is prepared using the positive electrode slurry of any one of claims 1-10.

12. A battery, characterized by The positive electrode tab of claim 11 is included.

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