Solvent composition, positive electrode slurry

Abstract

The application discloses a solvent composition and a positive electrode slurry. The solvent composition comprises: a first component, the first component comprising a silicon-based difluorophosphate compound; and a second component, the second component comprising one of a beta-alkyloxypropionamide and an alpha-alkyloxyacetamide; wherein the mass ratio of the first component to the second component is (0.2:100) to (10:100). Thus, the positive electrode slurry adopting the solvent composition has better stability, the baking effect after coating is better, and the decomposition product of the first component can improve the cycle performance of a battery.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to solvent compositions and positive electrode slurries. 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.

[0003] It should be noted that the above statements are only used to provide background information related to this application and do not necessarily constitute prior art. Summary of the Invention

[0004] In a first aspect of this application, a solvent composition is provided, comprising:

[0005] The first component comprises a silicon-based difluorophosphate compound, which includes at least one compound satisfying the formula shown in Formula 1.

[0006] Equation 1, where,

[0007] R1, R2, and R3 each independently include any one of H, F, C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C2-C4 fluoroalkynyl, C3-C4 cycloalkanes, R4-substituted phenyl, and R5-substituted benzyl. R1, R2, and R3 may be the same as or different from each other. R4 and R5 each independently include any one of C1-C4 alkyl, C2-C4 alkenyl, C2-C4 alkynyl, C1-C4 fluoroalkyl, C2-C4 fluoroalkenyl, and C2-C4 fluoroalkynyl. The second component includes one of β-alkoxypropionamide and α-alkoxyacetamide. The mass ratio of the first component to the second component is (0.2:100) to (10:100). Therefore, the positive electrode slurry using this solvent composition has better stability, better baking effect after coating, and the decomposition products of the first component can improve the cycle performance of the battery.

[0008] In some embodiments, the first component includes at least one of the following compounds:

[0009] Formula 1-1 Formula 1-2 Formula 1-3 Formula 1-4 Formulas 1-5 Equations 1-6. This can further improve the stability of the cathode slurry and enhance the cycle performance of the battery.

[0010] In some embodiments, the second component includes at least one selected from 3-methoxy-N,N-dimethylpropionamide, 2-methoxy-N,N-dimethylacetamide, 3-ethoxy-N,N-dimethylpropionamide, 2-ethoxy-N,N-dimethylacetamide, 3-methoxy-N,N-diethylpropionamide, 2-methoxy-N,N-diethylacetamide, and 3-ethoxy-N,N-diethylpropionamide. Therefore, the second component is removed more thoroughly after baking.

[0011] In a second aspect of this application, a positive electrode slurry is provided, comprising the solvent composition of the first aspect of this application. In the positive electrode slurry, the first component has a mass percentage of 0.1%-2% based on the total mass of the positive electrode slurry. Thus, residual alkali on the material surface can be effectively removed with a small amount of the first component, thereby improving the stability of the positive electrode slurry.

[0012] In some embodiments, the mass fraction of the second component is 20%-50% based on the total mass of the cathode slurry. This helps to improve the stability of the cathode slurry.

[0013] In some embodiments, the method further includes: a positive electrode active material, the positive electrode active material comprising a first positive electrode active material, wherein the first positive electrode active material satisfies the general formula LiNi. x M 1-x O2, 0.6≤x<1, M includes at least one of Co, Mn, Al, and Mg. This helps to improve the energy density of batteries made using this cathode slurry.

[0014] In some embodiments, the mass ratio of the first positive electrode active material to the solvent composition in the positive electrode slurry is (1.0-3.7):1. Therefore, a small amount of the second component is sufficient to achieve complete dissolution of both the first positive electrode active material and the first component, which is beneficial for removing residual alkali from the surface of the first positive electrode active material and improving the stability of the positive electrode slurry.

[0015] In some embodiments, based on the total mass of the cathode slurry, the mass fraction of the first cathode active material is 46%-78%, and the mass fraction of the solvent composition is 20.1%-52%. This is beneficial for improving the stability of the cathode slurry.

[0016] In some embodiments, the method further includes: a positive electrode active material, which comprises a second positive electrode active material and a lithium-rich material, wherein the second positive electrode active material satisfies the general formula LiFe. 1-m M mPO4, 0≤m<1, M includes at least one of Co, Mn, Al, and Mg, and lithium-rich materials satisfy the general formula Li 5a+2b Fe a Q b O 4a+2b Q includes at least one of Ni, Co, Mn, and Fe, where 0.5 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, and a + b = 1. This helps to improve the cycle performance of batteries made using this cathode slurry.

[0017] In some embodiments, the mass ratio of the second positive electrode active material to the lithium-rich material in the positive electrode slurry is 100:(0.5-3). Therefore, the battery made using this positive electrode slurry exhibits superior cycle performance.

[0018] In some embodiments, the mass ratio of the positive electrode active material to the solvent composition in the positive electrode slurry is (0.9-2.2):1. Therefore, a small amount of the second component is sufficient to achieve complete dissolution of the second positive electrode active material and the first component, which is beneficial for removing residual alkali from the surface of the lithium-rich material and improving the stability of the positive electrode slurry.

[0019] In some embodiments, based on the total mass of the positive electrode slurry, the mass fraction of the second positive electrode active material is 46%-67%, and the mass fraction of the solvent composition is 30.1%-52%. This is beneficial for improving the stability of the positive electrode slurry. Detailed Implementation

[0020] 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 actually 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.

[0021] 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 the 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).

[0022] 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.

[0023] 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%.

[0024] 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.

[0025] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0026] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0027] 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 the solvent is removed by baking to obtain the positive electrode active material layer. However, the surface of the positive electrode active material or lithium-rich material in related technologies often has residual alkaline substances. For example, using high-nickel ternary materials as the positive electrode active material can effectively improve the energy density of the battery. 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. Using lithium iron phosphate (LFP) materials as the positive electrode active material can improve battery cycle life. However, LFP materials also suffer from relatively rapid capacity decay in the early stages of cycling. Mixing LFP materials with lithium-rich materials, such as lithium-rich ferric acid, allows the active lithium ions released by the lithium-rich material to effectively compensate for the active lithium loss during the early stages of cycling, thereby improving the performance of the LFP material. However, lithium-rich materials are often very sensitive to moisture, easily absorbing water and decomposing to produce alkaline substances, which then form residual alkali on the surface.

[0028] When the positive electrode active material or lithium-rich material 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-rich material 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. Simultaneously, the positive electrode slurry will gel and settle, making it unsuitable for coating processes.

[0029] 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.

[0030] In this application, when the silicon-based difluorophosphate compound in the first component is used as a component of the positive electrode slurry, it can effectively remove the surface residual alkali of the positive electrode active material or lithium-rich material in the positive electrode slurry. Specifically, the silicon-based difluorophosphate compound will first react with the residual water in the positive electrode slurry and hydrolyze to generate difluorophosphate and silanol, reducing the side reaction of water 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.

[0031] When N-methylpyrrolidone is used as the solvent for the positive electrode slurry, the silanol in the aforementioned hydrolysis products reacts with N-methylpyrrolidone to generate high-boiling-point silanol esters such as N-methyl-4-hydroxyaminobutyric acid and N-hydroxymethyl-4-aminobutyric acid. These compounds cannot be fully removed by the electrode baking process and remain in the positive electrode, affecting battery performance. Therefore, in this application, by using β-alkoxypropionamide and / or α-alkoxyacetamide as components of the positive electrode slurry in the second component, they have similar Hansen solubility parameters to N-methylpyrrolidone, making them suitable for dissolving and dispersing various positive electrode active materials, binders, and the aforementioned additives. Furthermore, the ether bonds contained in the solvent structure increase the solvent's solubility for lithium salts, resulting in better dissolution and dispersion of lithium difluorophosphate in the positive electrode slurry. β-alkoxypropionamide and / or α-alkoxyacetamide also have good volatility and are fully removed after baking, requiring less baking time for the electrode and leaving almost no residue in the positive electrode. Furthermore, β-alkoxypropionamide and / or α-alkoxyacetamide, as environmentally friendly solvents, offer numerous advantages over N-methylpyrrolidone, including no reproductive toxicity, no carcinogenicity, no mutagenicity, no teratogenicity, and low irritation.

[0032] In summary, the cathode slurry in this application, by incorporating silicon-based difluorophosphate compounds, not only consumes residual alkali and improves the stability of the cathode slurry, but also neutralizes the difluorophosphate generated by the residual alkali, further enhancing the battery's cycle performance. Furthermore, by combining β-alkoxypropionamide and / or α-alkoxyacetamide, which have good dispersibility and volatility, the cathode slurry achieves uniform dispersion while avoiding the reaction of conventional N-methylpyrrolidone with silanols in hydrolysis products to generate a large amount of impurities that affect battery performance. Simultaneously, the silanols in the hydrolysis products can be quickly removed through a simple and convenient electrode baking process, improving the baking efficiency of the cathode slurry.

[0033] The Hansen solubility parameter is used to predict whether compounds can dissolve in each other. It is based on the fundamental principle that substances tend to mix with other substances that have similar intermolecular forces. The Hansen solubility parameter decomposes intermolecular forces into three independent components, where δm... d It is the dispersion capability parameter, δ p It is related to the polarity parameter, δ h These are hydrogen bonds and solubility parameters. The smaller the difference in Hansen solubility parameters between different substances, the higher their compatibility.

[0034] In a first aspect, this application provides a solvent composition comprising: a first component comprising a silicon-based difluorophosphate compound, wherein the silicon-based difluorophosphate compound comprises at least one compound satisfying the formula shown in Formula 1.

[0035] Formula 1,

[0036] R1, R2, and R3 each independently include any one of H, F, C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C2-C4 fluoroalkynyl, C3-C4 cycloalkanes, R4-substituted phenyl, and R5-substituted benzyl. R1, R2, and R3 may be the same as or different from each other. R4 and R5 each independently include any one of C1-C4 alkyl, C2-C4 alkenyl, C2-C4 alkynyl, C1-C4 fluoroalkyl, C2-C4 fluoroalkenyl, and C2-C4 fluoroalkynyl. The second component includes one of β-alkoxypropionamide and α-alkoxyacetamide. The mass ratio of the first component to the second component is (0.2:100) to (10:100). Therefore, the solvent composition has better stability, better baking effect after coating, and the decomposition products of the first component can improve the cycle performance of the battery.

[0037] As an example, the mass ratio of the first component to the second component can be 0.2:100, 1:100, 2:100, 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, 9:100 or 10:100.

[0038] In some embodiments, when the substituents in R1, R2, R3, and the substituted phenyl or substituted benzyl groups 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.

[0039] In some embodiments, the first component includes at least one of the following compounds:

[0040] Formula 1-1 Formula 1-2 Formula 1-3 Formula 1-4 Formulas 1-5 Equations 1-6 thus further improve the stability of the positive electrode slurry and improve the cycle performance of the battery.

[0041] As an example, It will react with the residual moisture in the positive electrode slurry to generate trimethylsilanol and difluorophosphoric acid. The difluorophosphoric acid will react with the residual alkali on the surface of the positive electrode active material or lithium-rich material in the positive electrode slurry to generate lithium difluorophosphate.

[0042] As an example, It can also react directly with residual alkali to produce lithium difluorophosphate and trimethylsilanol.

[0043] As an example, the silicon-based difluorophosphate compound can be prepared by the following method: Under anhydrous conditions, sodium difluorophosphate (50 mmol, moisture ≤ 20 ppm) is added to a reaction vessel, followed by ultra-dry acetonitrile solvent (550 mmol). The solid is stirred and dissolved at a controlled temperature of 20℃-60℃. Then, a chlorosilane (50 mmol, moisture ≤ 20 ppm) is slowly added, maintaining a nitrogen atmosphere and stirring continuously at 20℃-60℃ for about 8 hours during the addition of the chlorosilane. After the reaction is complete, the mixture is allowed to stand at room temperature for about 2 hours, then filtered to remove the solid precipitate. Finally, nitrogen is bubbled to remove the solvent and volatile byproducts, thus obtaining the desired silicon-based difluorophosphate compound.

[0044] In some embodiments, the second component includes at least one selected from 3-methoxy-N,N-dimethylpropionamide, 3-methoxy-N,N-dimethylacetamide, 3-ethoxy-N,N-dimethylpropionamide, 2-ethoxy-N,N-dimethylacetamide, 3-methoxy-N,N-diethylpropionamide, 2-methoxy-N,N-diethylacetamide, and 3-ethoxy-N,N-diethylpropionamide. Therefore, the second component is removed more thoroughly after baking.

[0045] In a second aspect of this application, a positive electrode slurry is provided, comprising the solvent composition of the first aspect of this application. In the positive electrode slurry, the first component has a mass percentage of 0.1%-2% based on the total mass of the positive electrode slurry. Thus, residual alkali on the material surface can be effectively removed with a small amount of the first component, thereby improving the stability of the positive electrode slurry.

[0046] By adding a small amount of the first component, residual alkali on the surface of the positive electrode active material or lithium-rich material can be effectively removed, generating an inorganic salt coating layer that helps improve the battery cycle performance. At the same time, the positive electrode active material has a high mass ratio in the positive electrode slurry, which helps to improve the energy density of the battery.

[0047] As an example, the Hansen solubility parameter (δ) of 3-methoxy-N,N-dimethylpropionamide d =16.9, δ p =10, δ h =8.7) and PVDF(δ d =17.2, δ p =12.5, δ h =9.2) is close to that of the binder. Therefore, the binder has a high solubility in the second component mentioned above, which helps to reduce the gelation of the positive electrode slurry and improve the dispersion uniformity of the positive electrode slurry.

[0048] In some embodiments, the mass fraction of the second component is 20%-50% based on the total mass of the cathode slurry. This helps to improve the stability of the cathode slurry.

[0049] As an example, based on the total mass of the positive electrode slurry, the mass fraction of the second component can be 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, or 50%.

[0050] In some embodiments, the positive electrode slurry further includes: a positive electrode active material, the positive electrode active material including a first positive electrode active material, the first positive electrode active material satisfying the general formula LiNi x M 1-x O2, 0.6≤x<1, M includes at least one of Co, Mn, Al, and Mg. This helps to improve the energy density of batteries made using this cathode slurry.

[0051] High-nickel ternary materials have high energy density and fast lithium-ion insertion / extraction rates, making them suitable for high-power applications such as fast charging.

[0052] As an example, x can be 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95.

[0053] As an example, the first positive electrode active material may include LiNi. 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.8 Co 0.15 Al 0.05 O2), etc.

[0054] In some embodiments, the mass ratio of the first positive electrode active material to the solvent composition in the positive electrode slurry is (1.0-3.7):1. Therefore, a small amount of the second component is sufficient to achieve complete dissolution of both the first positive electrode active material and the first component, which is beneficial for removing residual alkali from the surface of the first positive electrode active material and improving the stability of the positive electrode slurry.

[0055] In some embodiments, based on the total mass of the positive electrode slurry, the mass fraction of the first positive electrode active material is 46%-78%, and the mass fraction of the solvent composition is 20.1%-52%.

[0056] In some embodiments, the positive electrode slurry further includes: a positive electrode active material, which comprises a second positive electrode active material and a lithium-rich material, wherein the second positive electrode active material satisfies the general formula LiFe. 1-m M m PO4, 0≤m<1, M includes at least one of Co, Mn, Al, and Mg, and lithium-rich materials satisfy the general formula Li 5a+2b Fe a Q b O 4a+2b Q includes at least one of Ni, Co, Mn, and Fe, where 0.5 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, and a + b = 1. This helps to improve the cycle performance of batteries made using this cathode slurry.

[0057] 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.

[0058] 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.

[0059] Lithium-rich iron acid has an anti-fluorite structure and its theoretical capacity can reach 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.

[0060] As an example, a can be 0.5, 0.6, 0.7, 0.8, 0.9, or 1.

[0061] As an example, b can be 0.5, 0.6, 0.7, 0.8, 0.9, or 1.

[0062] In some embodiments, lithium-rich materials include Li5FeO4, Li 3.5 Fe 0.5 Ni 0.5 O3, Li 3.5 Fe 0.5 Mn 0.5 At least one of O3. Therefore, the lithium-rich material has a high lithium replenishment capacity, which can improve the cycle performance and energy density of the battery made using this cathode slurry.

[0063] In some embodiments, the mass ratio of the second positive electrode active material to the lithium-rich material in the positive electrode slurry is 100:(0.5-3). Therefore, the battery made using this positive electrode slurry exhibits superior cycle performance.

[0064] 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 from the lithium-rich material 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 first component can effectively mitigate the impact of residual alkali on the surface of the lithium-rich material on the stability of the cathode slurry.

[0065] As an example, the mass ratio of the second positive electrode active material to the lithium-rich material in the positive electrode slurry can be 100:0.5, 100:1, 100:1.5, 100:2, 100:2.5 or 100:3.

[0066] Adding a small amount of lithium-rich material can effectively increase the initial capacity of the battery and improve its cycle performance. The positive electrode slurry still mainly consists of positive electrode active materials, which helps to improve the energy density of the battery.

[0067] In some embodiments, the mass ratio of the positive electrode active material to the solvent composition in the positive electrode slurry is (0.9-2.2):1. Therefore, a small amount of the second component is sufficient to achieve complete dissolution of the second positive electrode active material and the first component, which is beneficial for removing residual alkali from the surface of the lithium-rich material and improving the stability of the positive electrode slurry.

[0068] In some embodiments, based on the total mass of the cathode slurry, the mass fraction of the second cathode active material is 46%-67%, and the mass fraction of the solvent composition is 30.1%-52%. This is beneficial for improving the stability of the cathode slurry.

[0069] 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 positive electrode slurry.

[0070] The aforementioned binder can be fully dispersed in β-alkoxypropionamide and / or α-alkoxyacetamide. After forming the positive electrode active material layer, 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.

[0071] In some embodiments, the mass fraction of the binder in the positive electrode slurry is 1%-3%. Thus, the positive electrode active material can be firmly bonded to the conductive agent, current collector, etc. with a small amount of binder.

[0072] 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.

[0073] Example 1

[0074] 1) Preparation of positive electrode slurry

[0075] The solvent composition of the positive electrode slurry is a combination of the first component (Formula 1-1) and the second component 3-methoxy-N,N-dimethylpropionamide, with a mass ratio of 1:100. The mass fraction of the second component 3-methoxy-N,N-dimethylpropionamide in the positive electrode slurry is 30%. The positive electrode active material is LiNi. 0.8 Co 0.1 Mn 0.1 The active material is O2, the conductive agent is carbon black SP, the binder is polyvinylidene fluoride, and the first component is the compound shown in Formula 1-1. The mass ratio of the positive electrode active material to the first component is 100:0.3, and the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode slurry is 96.5:2:1.5. Specifically, polyvinylidene fluoride is dissolved in the second component to obtain a colloid, and then the positive electrode active material, conductive agent, and first component are added to the colloid and stirred until homogeneous to obtain the positive electrode slurry.

[0076] 2) Preparation of positive electrode sheet

[0077] The positive electrode slurry was uniformly coated onto the surface of the positive electrode current collector aluminum foil, with a coating density of 20 mg / cm³ on one side. 2 After drying at 150℃, rolling, baking, slitting and spot welding of tabs, positive electrode sheets are obtained.

[0078] 3) Preparation of negative electrode sheet

[0079] 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. The negative electrode slurry is then coated onto the surface of the negative electrode current collector copper foil, with a coating density of 12 mg / cm³ on one side. 2 After drying at 150℃, rolling, baking, slitting and spot welding of tabs, negative electrode sheets are obtained.

[0080] 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, electrolyte salt and organic solvent. The electrolyte salt is lithium hexafluorophosphate, and the mass fraction of lithium hexafluorophosphate in the electrolyte is 12%. The organic solvent is composed of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of EC:EMC = 3:7.

[0081] For the differences between the remaining embodiments and comparative examples and Embodiment 1, please refer to Tables 1-1 and 1-2.

[0082] Table 1-1

[0083]

[0084] Table 1-2

[0085]

[0086] The batteries in the examples and comparative examples were subjected to the following performance tests, and the test results are shown in Table 2:

[0087] Viscosity change rate (%, after 24h of settling): After stirring the cathode slurry, the initial viscosity of the cathode slurry was measured with a viscometer and recorded as η0. Then, the viscosity of the cathode slurry after settling for 24h was measured and recorded as η. 24 The viscosity change rate of the positive electrode slurry is (η) 24 -η0) / η0×100%.

[0088] Room temperature cycle performance test: The battery is charged at room temperature (25°C) with constant current and constant voltage at 1C to the upper limit cutoff voltage, and the cutoff current is 0.05C. Then the battery is discharged at 1C to the lower limit cutoff voltage. The charge and discharge cycle is repeated for 500 cycles. The discharge capacity of the 500th cycle is recorded and divided by the discharge capacity of the 1st cycle to obtain the capacity retention rate.

[0089] High-temperature cycle performance test: The battery is charged at 45°C with constant current and constant voltage at 1C to the upper limit cutoff voltage, and the cutoff current is 0.05C. Then the battery is discharged at 1C to the lower limit cutoff voltage. The charge and discharge cycle is repeated for 250 cycles. The discharge capacity of the 250th cycle is recorded and divided by the discharge capacity of the 1st cycle to obtain the capacity retention rate.

[0090] High-temperature storage performance test: The battery was charged at room temperature (25℃) with a constant current and constant voltage of 0.5C to the upper limit cutoff voltage, with a cutoff current of 0.05C. Then, the battery was discharged at a constant current of 1C to the lower limit cutoff voltage, and the discharge capacity was recorded as C1. At room temperature (25℃), the battery was charged at a constant current and constant voltage of 1C to the upper limit cutoff voltage, with a cutoff current of 0.05C, to 4.25V. Then, it was charged at a constant voltage of 4.25V to the cutoff current of 0.05C. The battery was then transferred to a high temperature of 60℃ and left for 14 days. Then, it was discharged at a constant current of 1C, and the discharge capacity was recorded as C2. The capacity retention rate at 60℃ = C2 / C1 × 100%.

[0091] 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.

[0092] Table 2

[0093]

[0094] The test results show that, based on the comparison between Examples 1-8 and Comparative Examples 1 and 4, in the high-nickel ternary system, the addition of a silicon-based difluorophosphate ester as the first component to the cathode slurry results in better stability of the cathode slurry, and the lithium-ion battery exhibits better cycle capacity retention at both room temperature and high temperature. This first component, while consuming residual alkali and improving the stability of the cathode slurry, can also neutralize the difluorophosphate generated from the residual alkali to form a CEI film in situ, inhibiting the decomposition of the second component in the electrolyte and enhancing the Li-ion battery's performance. + Improves conductivity, reduces impedance, and enhances the battery's stability during both room temperature and high temperature cycling.

[0095] As can be seen from the comparison between Example 1 and Comparative Example 1, in the high-nickel ternary system, when 0.3% of silicon-based difluorophosphate esters are added as the first component to the cathode slurry, under the same solid content conditions, compared with N-methylpyrrolidone, 3-methoxy-N,N-dimethylpropionamide as the second component results in a lower initial viscosity, a smaller viscosity change rate after standing for 24 hours, more uniform dispersion of the first component and the generated difluorophosphate, better fluidity and stability of the cathode slurry, more uniform coating, and lower impedance and cycle performance of the battery.

[0096] As can be seen from Example 15 and Comparative Example 2, the superior properties of 3-methoxy-N,N-dimethylpropionamide are more pronounced under high solid content conditions.

[0097] As can be seen from the comparison of Example 23 and Comparative Examples 3 and 5, in lithium iron phosphate systems containing lithium-rich materials, 3-methoxy-N,N-dimethylpropionamide also has the above-mentioned advantages compared with N-methylpyrrolidone.

[0098] As can be seen from Examples 11-21, when the amount of the second component 3-methoxy-N,N-dimethylpropionamide is too high, the initial viscosity of the positive electrode slurry is too low, the stability of the positive electrode slurry is relatively poor, the coating uniformity is reduced, and the cycle performance of the battery is slightly reduced; when the amount of the second component is too low, the viscosity of the positive electrode slurry is high, which has a slight adverse effect on the coating.

[0099] 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 in that, The solvent composition includes a solvent composition and a positive electrode active material, wherein the solvent composition comprises: The first component comprises a silicon-based difluorophosphate compound, said silicon-based difluorophosphate compound comprising at least one compound satisfying the formula shown in Formula 1. Equation 1, where, R1, R2, and R3 each independently include any one of H, F, C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C2-C4 fluoroalkynyl, C3-C4 cycloalkanes, R4-substituted phenyl, and R5-substituted benzyl. R1, R2, and R3 may be the same as or different from each other. R4 and R5 each independently include any one of C1-C4 alkyl, C2-C4 alkenyl, C2-C4 alkynyl, C1-C4 fluoroalkyl, C2-C4 fluoroalkenyl, and C2-C4 fluoroalkynyl. The second component includes one of β-alkoxypropionamide and α-alkoxyacetamide; Wherein, the mass ratio of the first component to the second component is (0.2:100)-(10:100), In the positive electrode slurry, based on the total mass of the positive electrode slurry, the mass percentage of the first component in the positive electrode slurry is 0.1%-2%. The positive electrode active material is a first positive electrode active material, wherein the first positive electrode active material satisfies the general formula LiNi. x M 1-x O2, 0.6≤x<1, M includes at least one of Co, Mn, Al, and Mg, or, The positive electrode active material is a second positive electrode active material and a lithium-rich material, wherein the second positive electrode active material satisfies the general formula LiFe. 1-m M m PO4, 0≤m<1, M includes at least one of Co, Mn, Al, and Mg, and the lithium-rich material 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.

2. The positive electrode slurry according to claim 1, characterized in that, The first component includes at least one of the following compounds: Formula 1-1 Formula 1-2 Formula 1-3 Formula 1-4 Formulas 1-5 Equations 1-6.

3. The positive electrode slurry according to claim 1, characterized in that, The second component includes at least one of 3-methoxy-N,N-dimethylpropionamide, 2-methoxy-N,N-dimethylacetamide, 3-ethoxy-N,N-dimethylpropionamide, 2-ethoxy-N,N-dimethylacetamide, 3-methoxy-N,N-diethylpropionamide, 2-methoxy-N,N-diethylacetamide, and 3-ethoxy-N,N-diethylpropionamide.

4. The positive electrode slurry according to claim 1, characterized in that, Based on the total mass of the positive electrode slurry, the mass fraction of the second component is 20%-50%.

5. The positive electrode slurry according to claim 1, characterized in that, In the positive electrode slurry, the mass ratio of the first positive electrode active material to the solvent composition is (1.0 - 3.7):

1.

6. The positive electrode slurry according to claim 1, characterized in that, Based on the total mass of the positive electrode slurry, the mass fraction of the first positive electrode active material is 46%-78%, and the mass fraction of the solvent composition is 20.1%-52%.

7. The positive electrode slurry according to claim 1, characterized in that, In the positive electrode slurry, the mass ratio of the second positive electrode active material to the lithium-rich material is 100:(0.5-3).

8. The positive electrode slurry according to claim 1, characterized in that, The positive electrode active material is a second positive electrode active material and a lithium-rich material. In the positive electrode slurry, the mass ratio of the positive electrode active material to the solvent composition is (0.9-2.2):

1.

9. The positive electrode slurry according to claim 1, characterized in that, Based on the total mass of the positive electrode slurry, the mass fraction of the second positive electrode active material is 46%-67%, and the mass fraction of the solvent composition is 30.1%-52%.

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