Solvent composition and positive electrode slurry

Abstract

The invention discloses a solvent composition and positive electrode slurry. The solvent composition comprises a first component and a second component, wherein the first component comprises a silicon-based difluorophosphate compound; the second component is prepared from one of beta-alkoxy propionamide and alpha-alkoxy acetamide, and the second component is prepared from one of beta-alkoxy propionamide and alpha-alkoxy acetamide; wherein the mass ratio of the first component to the second component is (0.2: 100)-(10: 100). Therefore, the positive electrode slurry adopting the solvent composition has relatively excellent stability, the baking effect after coating is relatively good, and the cycle performance of the battery can be improved by the decomposition product of the first component.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular, to a solvent composition and a positive electrode slurry. BACKGROUND

[0002] With the continuous expansion of the application field of lithium ion batteries, the performance requirements of lithium ion batteries in different application fields are quite different. Among them, when used as power batteries, higher energy density and longer cycle life have become the mainstream demand direction of the market.

[0003] It should be noted that the above statements are only used to provide background technical information related to the present application, and do not necessarily constitute the prior art. SUMMARY

[0004] In a first aspect of the present application, a solvent composition is provided, comprising: A first component, the first component comprising a silicon-based difluorophosphate compound, the silicon-based difluorophosphate compound comprising at least one compound satisfying Formula 1, Formula 1, wherein, R1, R2, and R3 each independently comprise 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 cycloalkane, R4-substituted phenyl, and R5-substituted benzyl, R1, R2, and R3 being the same or different from each other; R4 and R5 each independently comprise any one of C1-C4 alkyl, C2-C4 alkenyl, C2-C4 alkynyl, C1-C4 fluoroalkyl, C2-C4 fluoroalkenyl, and C2-C4 fluoroalkynyl; and a second component, the second component comprising one of a β-alkoxypropionamide and an α-alkoxyacetamide; wherein the mass ratio of the first component to the second component is (0.2:100)-(10:100). Thus, the positive electrode slurry using the solvent composition has better stability, the baking effect after coating is better, and the decomposition products of the first component can improve the cycle performance of the battery.

[0005] In some embodiments, the first component comprises at least one of the following compounds: Formula 1-1, Formula 1-2, Formula 1-3, Formula 1-4, Formula 1-5, Formula 1-6. Thus, the stability of the positive electrode slurry can be further improved, and the cycle performance of the battery can be improved.

[0006] In some embodiments, the second component includes at least one of 3-methoxy-N,N-dimethylpropanamide, 2-methoxy-N,N-dimethyacetamide, 3-ethoxy-N,N-dimethylpropanamide, 2-ethoxy-N,N-dimethylacetamide, 3-methoxy-N,N-diethylpropanamide, 2-methoxy-N,N-diethylacetamide, and 3-ethoxy-N,N-diethylpropanamide. Thus, the second component is removed more cleanly after baking.

[0007] In a second aspect of the present application, the present application provides a positive electrode slurry including the solvent composition of the first aspect of the present application, and in the positive electrode slurry, the mass percentage of the first component in the positive electrode slurry is 0.1%-2% based on the total mass of the positive electrode slurry. Thus, the surface residual alkali of the material can be effectively removed by a small amount of the first component, and the stability of the positive electrode slurry is improved.

[0008] In some embodiments, the mass fraction of the second component is 20%-50% based on the total mass of the positive electrode slurry. Thus, the stability of the positive electrode slurry is improved.

[0009] In some embodiments, the positive electrode active material includes a first positive electrode active material, and the first positive electrode active material satisfies the general formula LiNi x M 1-x O2, 0.6≤x<1, and M includes at least one of Co, Mn, Al, and Mg. Thus, the energy density of the battery prepared by using the positive electrode slurry is improved.

[0010] In some embodiments, 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. Thus, the first positive electrode active material and the first component can be sufficiently dissolved by a small amount of the second component, and the surface residual alkali of the first positive electrode active material is removed, and the stability of the positive electrode slurry is improved.

[0011] In some embodiments, 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% based on the total mass of the positive electrode slurry. Thus, the stability of the positive electrode slurry is improved.

[0012] In some embodiments, the positive electrode active material includes a second positive electrode active material and a lithium-rich material, and 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 O4a+2b Q comprises at least one of Ni, Co, Mn, Fe, 0.5≤a≤1, 0≤b≤0.5, a+b=1. Thus, the cycle performance of the battery prepared by using the positive electrode slurry is improved.

[0013] 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). Thus, the battery prepared by using the positive electrode slurry has a better cycle performance.

[0014] 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. Thus, the second positive electrode active material and the first component can be fully dissolved by a small amount of the second component, which is conducive to removing the residual alkali on the surface of the lithium-rich material and improving the stability of the positive electrode slurry.

[0015] In some embodiments, 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% based on the total mass of the positive electrode slurry. Thus, the stability of the positive electrode slurry is improved. DETAILED DESCRIPTION

[0016] The embodiments of the present application are described in detail below, but there will be cases of omission of unnecessary detailed description. For example, there are cases of omission of detailed description of matters well known, repeated description of actually identical structures. This is to avoid the following description from becoming unnecessarily long, facilitating understanding by those skilled in the art.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used in the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; unless otherwise specified, the numerical values of the parameters mentioned in the application can be measured by various measurement methods commonly used in the art (for example, tests can be performed according to the methods given in the embodiments of the application).

[0018] The terms "comprise" and "have" and any variations thereof in the specification and claims of the present application are open-ended expressions, i.e., include the contents indicated by the present application, but do not exclude other aspects.

[0019] In the description of the present application, all the numbers disclosed herein are approximate values. The value of each number can vary by 10% or less, or a reasonable variation as recognized by those skilled in the art, such as 1%, 2%, 3%, 4% or 5%.

[0020] In the description of the present application, "A and / or B" can include the case of A alone, the case of B alone, any one of the cases of A and B, where A, B are used for example only, which can be any technical feature connected by "and / or" in the present application.

[0021] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0022] Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0023] In the preparation process of the battery, it is necessary to disperse the positive active material, conductive agent, adhesive and other substances in the solvent to form a positive electrode slurry, and then the positive electrode slurry is arranged on the surface of the positive electrode current collector by coating or other methods. After baking to remove the solvent, the positive active material layer is obtained. However, the surface of the positive active material or the surface of the lithium-rich material in the related art often has residual alkaline substances. For example, by using high-nickel ternary material as the positive active material, the energy density of the battery can be effectively improved. However, as the Ni content increases, the temperature in the high-nickel ternary sintering process is lower, which reduces the volatilization amount of raw material lithium salt, and then increases the content of lithium salt remaining on the surface of the material, thereby forming Li2O. After Li2O adsorbs CO2 and H2O in the air, Li2CO3 and LiOH and other residual alkali are formed on the surface of the material. By using lithium iron phosphate material as the positive active material, the cycle life of the battery can be improved. At the same time, the lithium iron phosphate material also has the problem of relatively fast capacity attenuation in the early stage of the cycle. After mixing the lithium iron phosphate material with the lithium-rich material, such as lithium-rich ferrite, the active lithium ions released by the lithium-rich material can effectively supplement the active lithium loss caused by the capacity attenuation in the early stage of the cycle, thereby improving the performance of the lithium iron phosphate material. However, the lithium-rich material is often very sensitive to moisture and is easy to absorb water to decompose and produce alkaline substances, thereby forming surface residual alkali.

[0024] When the positive active material or the lithium-rich material has surface residual alkali, it will greatly affect the stability of the positive electrode slurry. During the mixing process of the positive electrode slurry, gelation is easy to occur, which affects 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 active material or the lithium-rich material will attack the C-F bond on the PVDF, causing the PVDF to generate a double bond by losing HF, which is further oxidized in the air to form a peroxide. The peroxide decomposes to produce free radicals, which then couple themselves to cause cross-linking failure of the PVDF, losing the bonding effect. At the same time, the positive electrode slurry gels and settles, which cannot be applied to the coating process.

[0025] In the related art, the acid-base of the positive electrode slurry is adjusted by adding acid substances such as oxalic acid and maleic acid to the positive electrode slurry. However, oxalate generated by neutralizing residual alkali from oxalic acid cannot be fully removed through the baking process (150°C-180°C). The oxalate remaining in the positive electrode tab catalyzes the decomposition of carbon dioxide and other gases under high-temperature conditions of the battery, such as high-temperature storage and high-temperature cycling, which negatively affects the high-temperature performance of the battery. Maleate generated by neutralizing residual alkali from maleic acid also cannot be fully removed through tab baking. The maleate remaining in the positive electrode tab has high impedance, which significantly degrades the performance of the battery.

[0026] In the present application, when the silicon-based difluorophosphate compound in the first component is used as a component of the positive electrode slurry, the surface residual alkali of the positive electrode active material or the lithium-rich material in the positive electrode slurry can be effectively removed. Specifically, the silicon-based difluorophosphate compound will first react with the residual moisture in the positive electrode slurry to hydrolyze and generate difluorophosphoric acid and silanol, reducing the side reactions of moisture consuming electrolyte during the subsequent battery charging and discharging cycle process. Further, the difluorophosphoric acid in the hydrolysis product can react with the residual alkali in the positive electrode slurry to generate difluorophosphate. The difluorophosphate, as an in-situ generated inorganic salt coating layer on the surface of the positive electrode active material, 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 interface side reactions. At the same time, the difluorophosphate has good lithium ion transport capacity, which can also reduce the interface impedance of the positive electrode active material and improve the cycle performance of the battery. The boiling point of the silanol in the hydrolysis product is low, which can be fully removed after the conventional tab baking process. A small amount of residual silanol can be further dehydrated to form a polymer interface film containing Si-O bonds after high-temperature baking, which has good flexibility and helps to improve the stability of the electrochemical interface on the surface of the positive electrode active material.

[0027] When N-methyl pyrrolidone is used as the solvent of the positive electrode slurry, the silanol in the aforementioned hydrolysis product reacts with N-methyl pyrrolidone to generate high-boiling silanol ester compounds such as N-methyl-4-hydroxyaminobutyric acid and N-hydroxymethyl-4-aminobutyric acid, which cannot be fully removed by the electrode baking process and thus remain in the positive electrode sheet, affecting the performance of the battery. Therefore, in the present application, by using β-alkoxypropionamide and / or α-alkoxyacetamide as a component of the positive electrode slurry in the second component, it has a similar Hansen solubility parameter with N-methyl pyrrolidone, is suitable for the dissolution and dispersion of various positive electrode active materials, binders, and the aforementioned additives, and the ether bond contained in the solvent structure can increase the solubility of the lithium salt in the solvent, so that the lithium difluorophosphate can be better dissolved and dispersed in the positive electrode slurry. The β-alkoxypropionamide and / or α-alkoxyacetamide also has good volatility and can be fully removed after baking, the time required for electrode baking is shorter, and there is almost no residue in the positive electrode sheet. In addition, β-alkoxypropionamide and / or α-alkoxyacetamide as a green and environmentally friendly solvent has many advantages such as no reproductive toxicity, no carcinogenicity, no mutagenicity, no teratogenicity, and less irritation compared with N-methyl pyrrolidone.

[0028] In summary, the positive electrode slurry in the present application consumes residual alkali by adding silicon-based difluorophosphate compounds, improves the stability of the positive electrode slurry, and further improves the cycle performance of the battery by neutralizing the difluorophosphate generated by the residual alkali. On this basis, combined with β-alkoxypropionamide and / or α-alkoxyacetamide which has good dispersibility and volatility, the positive electrode slurry can be uniformly dispersed, which can not only avoid the reaction between the conventional N-methyl pyrrolidone and the silanol in the hydrolysis product to generate a large amount of impurities, affecting the battery performance, but also can be quickly removed together with the silanol in the hydrolysis product through a simple and convenient electrode baking process, improving the baking efficiency of the positive electrode slurry.

[0029] Hansen solubility parameters are used to predict whether compounds can be mutually dissolved. It is based on a basic principle that substances tend to mix with other substances that have similar intermolecular forces. Hansen solubility parameters decompose intermolecular forces into three independent parts, in which δ d is the dispersion ability parameter, δ p is the polarity parameter, and δ h is the hydrogen bond and ability parameter. The smaller the difference between the Hansen solubility parameters of different substances, the higher the compatibility between them.

[0030] In the first aspect of the present application, a solvent composition is provided, comprising: a first component, the first component comprising a silicon-based difluorophosphate compound, the silicon-based difluorophosphate compound comprising at least one compound satisfying formula 1, Formula 1, wherein 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 cycloalkane, R4-substituted phenyl, R5-substituted benzyl, R1, R2 and R3 are the same 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; a second component, the second component including one of a β-alkoxypropionamide, an α-alkoxyacetamide; wherein the mass ratio of the first component and the second component is (0.2:100)-(10:100). Thus, 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 the battery.

[0031] As an example, the mass ratio of the first component and 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.

[0032] In some embodiments, when R1, R2, R3 and the substituents in the substituted phenyl and the substituted benzyl are unsaturated groups, the unsaturated bonds contained therein can further induce polymerization crosslinking during the charging and discharging process of the battery, form a network structure, improve the structural stability of the positive active material, reduce the capacity loss caused by the breakage of the positive active particles, and improve the cycle performance of the battery.

[0033] In some embodiments, the first component includes at least one of the following compounds: Formula 1-1, Formula 1-2, Formula 1-3, Formula 1-4, Formula 1-5, Formula 1-6Thus, the stability of the positive electrode slurry can be further improved, and the cycle performance of the battery can be improved.

[0034] As an example, will react with the residual moisture in the positive electrode slurry to generate trimethylsilanol and difluorophosphoric acid, and the difluorophosphoric acid will react with the residual alkali on the surface of the positive active material or the lithium-rich material in the positive electrode slurry to generate lithium difluorophosphate.

[0035] As an example, will also directly react with the residual alkali to generate lithium difluorophosphate and trimethylsilanol.

[0036] As an example, the silicon-based difluorophosphate compound can be prepared by adding sodium difluorophosphate (50 mmol, moisture ≤20 ppm) into a reaction kettle under anhydrous conditions, then adding ultradry acetonitrile solvent (550 mmol), stirring and dissolving the solid at a temperature of 20-60°C, then slowly adding chlorosilane (50 mmol, moisture ≤20 ppm), maintaining a nitrogen atmosphere during the addition of chlorosilane and continuously stirring at 20-60°C for about 8 h. After the reaction is completed, the mixture is allowed to stand at room temperature for about 2 h, then the solid precipitate is removed by filtration, and then the solvent and volatile by-products are removed by nitrogen bubbling, thereby obtaining the desired silicon-based difluorophosphate compound.

[0037] In some embodiments, the second component includes at least one of 3-methoxy-N,N dimethyl propanamide, 3-methoxy-N,N-dimethyl acetamide, 3-ethoxy-N,N dimethyl propanamide, 2-ethoxy-N,N-dimethyl acetamide, 3-methoxy-N,N diethyl propanamide, 2-methoxy-N,N-diethyl acetamide, and 3-ethoxy-N,N diethyl propanamide. In this way, the second component is removed more cleanly after baking.

[0038] In a second aspect of the present application, a positive electrode slurry is provided, which includes the solvent composition of the first aspect of the present application. In the positive electrode slurry, the mass percentage of the first component in the positive electrode slurry is 0.1%-2% based on the total mass of the positive electrode slurry. In this way, the surface residual alkali of the material can be effectively removed by a small amount of the first component, thereby improving the stability of the positive electrode slurry.

[0039] By adding a small amount of the first component, the surface residual alkali of the positive electrode active material or lithium-rich material can be effectively removed, thereby generating an inorganic salt coating layer that helps to improve the cycle performance of the battery. At the same time, the mass percentage of the positive electrode active material in the positive electrode slurry is high, which helps to improve the energy density of the battery.

[0040] As an example, the Hansen solubility parameter (δ d = 16.9, δ p = 10, δ h = 8.7) of 3-methoxy-N,N dimethyl propanamide is close to that of PVDF (δ d = 17.2, δ p = 12.5, δ h = 9.2). In this way, the binder has a high solubility in the aforementioned second component, which helps to reduce the gelation of the positive electrode slurry and improve the dispersion uniformity of the positive electrode slurry.

[0041] In some embodiments, the mass fraction of the second component is 20%-50% based on the total mass of the positive electrode slurry. In this way, the stability of the positive electrode slurry is improved.

[0042] For example, 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% based on the total mass of the positive electrode slurry.

[0043] In some embodiments, the positive electrode slurry further comprises: a positive electrode active material, the positive electrode active material comprising 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 comprising at least one of Co, Mn, Al, Mg. In this way, the energy density of the battery made by using the positive electrode slurry is improved.

[0044] High-nickel ternary materials have high energy density and fast lithium ion deintercalation rate, and are suitable for high-power scenarios such as fast charging.

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

[0046] For example, the first positive electrode active material can comprise LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05 O2, etc.

[0047] 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. In this way, the first positive electrode active material and the first component can be fully dissolved by a small amount of the second component, which is conducive to removing residual alkali on the surface of the first positive electrode active material and improving the stability of the positive electrode slurry.

[0048] In some embodiments, 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% based on the total mass of the positive electrode slurry.

[0049] In some embodiments, the positive electrode slurry further comprises: a positive electrode active material, the positive electrode active material comprising a second positive electrode active material and a lithium-rich material, the second positive electrode active material satisfying a general formula of LiFe 1-m M m PO4, 0≤m<1, M comprising at least one of Co, Mn, Al, Mg, the lithium-rich material satisfying a general formula of Li 5a+2b Fe a Q b O 4a+2b , Q comprising at least one of Ni, Co, Mn, Fe, 0.5≤a≤1, 0≤b≤0.5, a+b=1. Thus, the cycle performance of a battery made with the positive electrode slurry is improved.

[0050] The lithium iron phosphate material has high structural stability, good cycle performance, is not prone to thermal runaway under high temperature conditions, has high safety, and has low manufacturing cost.

[0051] 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.

[0052] The lithium-rich iron acid has an anti-fluorite structure, and the theoretical capacity thereof can reach 867 mAh / g, which can effectively improve the problem of low first cycle efficiency of a 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 0.5, 0.6, 0.7, 0.8, 0.9, or 1.

[0055] In some embodiments, the lithium-rich material comprises Li5FeO4, Li 3.5 Fe 0.5 Ni 0.5 O3, Li 3.5 Fe 0.5 Mn 0.5 O3. Thus, the lithium-rich material has high lithium supplement capacity, and the cycle performance and energy density of a battery made with the positive electrode slurry are improved.

[0056] In some embodiments, 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). Thus, the battery made with the positive electrode slurry has good cycle performance.

[0057] The lithium iron phosphate material has a relatively fast capacity attenuation problem in the early stage of cycling. Mixing the lithium iron phosphate material with the lithium-rich ferrite can effectively supplement the active lithium loss caused by the capacity attenuation in the early stage of cycling, thereby improving the performance of the lithium iron phosphate material. The first component can effectively alleviate the influence of the residual alkali on the surface of the lithium-rich material on the stability of the positive electrode slurry.

[0058] For 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.

[0059] By adding a small amount of lithium-rich material, the initial capacity of the battery can be effectively improved, and the cycle performance can be improved. The positive electrode slurry is still mainly composed of positive electrode active materials, which helps to improve the energy density of the battery.

[0060] 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. Thus, by a small amount of the second component, the second positive electrode active material and the first component can be fully dissolved, which is beneficial to remove the residual alkali on the surface of the lithium-rich material and improve the stability of the positive electrode slurry.

[0061] In some embodiments, 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%, based on the total mass of the positive electrode slurry. Thus, it is beneficial to improve the stability of the positive electrode slurry.

[0062] In some embodiments, further comprising: a binder, the binder comprising at least one of polyvinylidene fluoride, polyacrylic acid, polyacrylonitrile, and polyimide. Thus, the binder is uniformly dispersed in the positive electrode slurry.

[0063] The aforementioned binder can be fully dispersed in the β-alkoxy propionamide and / or α-alkoxy acetamide, and after forming the positive electrode active material layer, the positive electrode active material, conductive agent, etc. in the positive electrode active material can be firmly adhered together and fixed 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%. Thus, by a small amount of the binder, the positive electrode active material and the conductive agent, current collector, etc. can be firmly combined together.

[0065] The application will be described in detail below through specific examples. It should be noted that the following examples are only used to illustrate the application and should not be regarded as limiting the scope of the application. If the specific technology or conditions are not specified in the examples, the technology or conditions described in the literature in the art or according to the product manual are used. If the reagent or instrument is not specified by the manufacturer, it is a conventional product that can be obtained by purchase.

[0066] Example 1 1) Preparation of the positive electrode slurry The solvent composition of the positive electrode slurry is a combined solvent of the first component (Formula 1-1) and the second component 3-methoxy-N,N-dimethylpropanamide, and the mass ratio of the two is 1:100. The mass fraction of the second component 3-methoxy-N,N-dimethylpropanamide in the positive electrode slurry is 30%. The positive electrode active material is LiNi 0.8 Co 0.1 Mn 0.1 O2, the conductive agent is carbon black SP, the binder is polyvinylidene fluoride, 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, the conductive agent, and the binder in the positive electrode slurry is 96.5:2:1.5. Specifically, the polyvinylidene fluoride is dissolved in the second component to obtain a colloid, and then the positive electrode active material, the conductive agent, and the first component are added to the above colloid and stirred and mixed uniformly to obtain the positive electrode slurry.

[0067] 2) Preparation of the positive electrode sheet The positive electrode slurry is uniformly coated on the surface of the positive electrode current collector aluminum foil, and the coating surface density of the single-sided surface is 20 mg / cm 2 After drying at 150°C, rolling, baking, slitting, and spot welding of the tabs, the positive electrode sheet is obtained.

[0068] 3) Preparation of the negative electrode sheet The negative electrode active material is artificial graphite. The artificial graphite, the conductive agent SP, the binder SBR, and the CMC are dissolved in deionized water at a mass ratio of 95:1.5:2:1.5 to obtain a negative electrode slurry. The negative electrode slurry is coated on the surface of the negative electrode current collector copper foil, and the coating surface density of the single-sided surface is 12 mg / cm 2 After drying at 150°C, rolling, baking, slitting, and spot welding of the tabs, the negative electrode sheet is obtained.

[0069] 4) Assembling the above positive electrode sheet, negative electrode sheet, separator and electrolyte into a soft package battery, and the design capacity of the battery is 1750 mAh; wherein the separator is a polyethylene film with a ceramic coating on the surface, and the electrolyte comprises electrolyte salt and organic solvent by mass percentage, wherein the electrolyte salt is lithium hexafluorophosphate, and the mass fraction of lithium hexafluorophosphate in the electrolyte is 12%, and the organic solvent is composed of ethylene carbonate (EC) and methyl ethyl carbonate (EMC) in a mass ratio of EC: EMC = 3:7.

[0070] The differences between the remaining examples and comparative examples and example 1 are shown in Table 1-1 and Table 1-2.

[0071] Table 1-1

[0072] Table 1-2

[0073] The batteries in the examples and comparative examples were subjected to the following performance tests, and the test results are shown in Table 2: The viscosity change rate of the positive electrode slurry (%, static for 24 h): after stirring the positive electrode slurry, the initial viscosity of the positive electrode slurry was tested by a viscometer and recorded as η0, and the viscosity of the positive electrode slurry after static for 24 h was tested and recorded as η 24 , and the viscosity change rate of the positive electrode slurry was (η 24 - η0) / η0 x 100%.

[0074] Normal temperature cycle performance test: charging the battery at room temperature 25℃ to the upper limit cut-off voltage at 1C constant current and constant voltage, and the cut-off current is 0.05C, then discharging the battery to the lower limit cut-off voltage at 1C, repeating the charge and discharge for 500 cycles, recording the discharge capacity of the 500th cycle and dividing by the discharge capacity of the 1st cycle, which is the capacity retention rate.

[0075] High temperature cycle performance test: charging the battery at high temperature 45℃ to the upper limit cut-off voltage at 1C constant current and constant voltage, and the cut-off current is 0.05C, then discharging the battery to the lower limit cut-off voltage at 1C, repeating the charge and discharge for 250 cycles, recording the discharge capacity of the 250th cycle and dividing by the discharge capacity of the 1st cycle, which is the capacity retention rate.

[0076] High temperature storage performance test: the battery was charged at room temperature 25℃ to the upper limit cut-off voltage at 0.5C constant current and constant voltage, and the cut-off current was 0.05C, then the battery was discharged at 1C constant current to the lower limit cut-off voltage, and the discharge capacity was recorded as C1. At room temperature 25℃, charge to the upper limit cut-off voltage at 1C constant current and constant voltage, the cut-off current was 0.05C to 4.25V, constant voltage 4.25V to the cut-off current 0.05C, then the battery was transferred to high temperature 60℃ for 14 days, then discharged at 1C constant current, the discharge capacity was recorded as C2, 60℃ capacity retention rate = C2 / C1 x 100%.

[0077] DC resistance test: the battery was placed in a 25℃ environment, discharged at 1C constant current to the cut-off voltage 2.75V, rested for 5min, charged to the upper limit voltage 4.25V at 1C constant current and constant voltage, the cut-off current was 0.05C, then discharged at 1C constant current for 30min, the battery adjusted to 50% SOC was rested for 5min at 25℃, discharged at 2C constant current for 10s, the discharge current at 2C was I 2C . Record the initial voltage V0 and the voltage V1 after discharging for 10s. The discharge DC resistance at 50% SOC is calculated as follows: DCR (mΩ) = (V0-V1) / I 2C x 1000.

[0078] Table 2

[0079] From the test results, according to the comparison of examples 1-8 and comparative examples 1, 4, it can be seen that in the high-nickel ternary system, when the first component of silicon-based difluorophosphate is added to the positive electrode slurry, the stability of the positive electrode slurry is better, and the lithium ion battery shows better room temperature and high temperature cycle capacity retention rate. The first component consumes residual alkali, improves the stability of the positive electrode slurry, at the same time, the difluorophosphate generated by neutralizing residual alkali can generate CEI film in situ, inhibit the decomposition of the second component in the electrolyte, enhance the Li + ion conductivity, reduce the impedance, and improve the room temperature and high temperature cycle stability of the battery.

[0080] According to the comparison of example 1 and comparative example 1, it can be seen that in the high-nickel ternary system, when 0.3% of the first component of silicon-based difluorophosphate is added to the positive electrode slurry, under the same solid content conditions, compared with N-methylpyrrolidone, under the condition that 3-methoxy-N,N-dimethylpropanamide is used as the second component, the initial viscosity of the positive electrode slurry is smaller, the viscosity change rate after standing for 24h is smaller, the first component and the generated difluorophosphate are more uniformly dispersed, the flowability and stability of the positive electrode slurry are better, the coating is more uniform, and the battery performance shows lower impedance and cycle performance.

[0081] As can be seen from the embodiment 15 and the comparative example 2, the superiority of 3-methoxy-N,N-dimethylpropanamide is more obvious under the condition of high solid content.

[0082] As can be seen from the comparison of the embodiment 23 and the comparative examples 3 and 5, in the lithium-rich material-containing lithium iron phosphate system, 3-methoxy-N,N-dimethylpropanamide also has the above advantages compared with N-methylpyrrolidone.

[0083] As can be seen from the embodiments 11-21, when the amount of the second component 3-methoxy-N,N-dimethylpropanamide 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 large, which has a slight adverse effect on coating.

[0084] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having substantially the same configuration and playing the same role and effect as the technical idea within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications of the embodiments that can be thought of by those skilled in the art, and other ways constructed by combining part of the components of the embodiments are also included in the scope of the present application.

Claims

1. A solvent composition, characterized in that, include: 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; The mass ratio of the first component to the second component is (0.2:100)-(10:100).

2. The solvent composition 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 solvent composition 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. A positive electrode slurry, characterized in that, The first component comprises the solvent composition according to any one of claims 1-3, wherein, 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%.

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

6. The positive electrode slurry according to claim 5, characterized in that, Further includes: The positive electrode active material includes 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.

7. The positive electrode slurry according to claim 6, 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.

8. The positive electrode slurry according to claim 6, 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%.

9. The positive electrode slurry according to claim 4, characterized in that, Further includes: The positive electrode active material includes 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.

10. The positive electrode slurry according to claim 9, 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).

11. The positive electrode slurry according to claim 9, characterized in that, In the positive electrode slurry, the mass ratio of the positive electrode active material to the solvent composition is (0.9-2.2):

1.

12. The positive electrode slurry according to claim 9, 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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