Positive electrode slurry solvent and preparation method therefor, positive electrode slurry, and secondary battery

Abstract

The present application provides a positive electrode slurry solvent and a preparation method therefor, a positive electrode slurry, and a secondary battery. The positive electrode slurry solvent comprises 3-methoxy-N,N-dimethylpropanamide and 3-methoxypropanoic acid. Based on the mass of the positive electrode slurry solvent, the mass percentage content of 3-methoxy-N,N-dimethylpropanamide is W, wherein W≥99.7%, and the mass percentage content of 3-methoxypropanoic acid is A, wherein 0.001%≤A≤0.2%. By controlling the mass percentage content of 3-methoxy-N,N-dimethylpropanamide and the mass percentage content of 3-methoxypropanoic acid to be within the ranges specified in the present application, the content of residual alkali in the positive electrode slurry is reduced, the phenomenon of gelation in the positive electrode slurry is mitigated, the viscosity of the slurry is reduced, and the dispersity and stability of the positive electrode slurry are improved. In addition, lithium 3-methoxypropanoate generated by reaction is dispersed on the surface of a positive electrode, which is conducive to improving the stability of an interfacial film, suppressing an interfacial reaction, reducing the decomposition of an electrolyte, and reducing interfacial impedance, thereby improving the high-temperature storage performance and high-temperature cycle performance of secondary batteries.

Description

A positive electrode slurry solvent, a preparation method thereof, a positive electrode slurry and a secondary battery

[0001] The present application claims priority to the Chinese patent application No. 202510074387.3 filed on January 17, 2025, and entitled "A positive electrode slurry solvent, a preparation method thereof, a positive electrode slurry and a secondary battery", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the field of electrochemistry, in particular to a positive electrode slurry solvent, a preparation method thereof, a positive electrode slurry and a secondary battery. BACKGROUND

[0003] Secondary batteries, such as lithium ion batteries, have the advantages of high working voltage, large specific energy density, long cycle life, low self-discharge rate, no memory effect, and little environmental pollution, and are widely used in many fields such as 3C electronic products, electric vehicles and energy storage power stations.

[0004] At present, the positive electrode slurry of the secondary battery usually contains a positive electrode active material, a conductive agent, a binder and an organic solvent. N-methyl pyrrolidone (NMP) is widely used as an organic solvent for the positive electrode slurry due to its low viscosity, low volatility, excellent chemical and thermal stability, and unlimited miscibility with water and other organic solvents. However, the thermal decomposition of NMP produces irritating or toxic gases, which has a great impact on the environment and human body, and NMP is expensive, which seriously limits the application of this type of solvent. In addition, the positive electrode active material often contains lithium salt residues on the surface of the material, which can easily react with moisture to generate Li2CO3, LiOH and other alkaline substances; in addition, in order to improve the capacity of the secondary battery with lithium iron phosphate as the positive electrode active material in the early stage of the cycle, a lithium-rich ferric acid is usually used to supplement the loss of lithium in the early stage of the cycle, but the lithium-rich ferric acid is sensitive to moisture and can easily decompose to produce alkaline substances, resulting in strong alkalinity of the positive electrode slurry. Li2CO3 can cause decomposition to produce gas when the battery is stored at high temperature and high potential, and LiOH can react with the lithium salt in the electrolyte to generate HF, which can deteriorate the performance of the battery. In addition, the presence of alkaline substances can also cause the slurry to gel, reduce the stability of the slurry and affect the coating of the electrode sheet. Therefore, it is urgent to develop a new green solvent to replace NMP as a positive electrode slurry solvent and solve the problem of residual alkaline in the positive electrode slurry. SUMMARY

[0005] The application aims to provide a positive electrode slurry solvent and a preparation method thereof, a positive electrode slurry and a secondary battery.

[0006] The first aspect of the application provides a positive electrode slurry solvent, which comprises 3-methoxy-N,N dimethyl propanamide and 3-methoxy propionic acid, the mass percentage of 3-methoxy-N,N dimethyl propanamide is W, W is greater than or equal to 99.7%, and the mass percentage of 3-methoxy propionic acid is A, 0.001% is less than or equal to A and 0.2%, based on the mass of the positive electrode slurry solvent.

[0007] The second aspect of the application provides a preparation method of the positive electrode slurry solvent of the first aspect of the application, which comprises the following steps:

[0008] (1) taking 3-methoxy propionic acid methyl ester and dimethylamine as raw materials, and performing an amidation reaction at a temperature of 30-50 DEG C to obtain a first mixed solution;

[0009] (2) performing distillation treatment on the first mixed solution to remove dimethylamine and methanol, and obtaining a second mixed solution;

[0010] (3) cooling the second mixed solution to a temperature of-20-20 DEG C, adding an acid solution, controlling the temperature of the second mixed solution to be within 20 DEG C during the addition of the acid, adjusting the pH of the second mixed solution to be 4-5, and then performing rectification under a vacuum degree of-0.09-0.1 MPa, a temperature of 115-140 DEG C and a reflux ratio of 2-7:1, and collecting a fraction in a temperature range of 110-125 DEG C to obtain the positive electrode slurry solvent.

[0011] The third aspect of the application provides a positive electrode slurry, which comprises the positive electrode slurry solvent of the first aspect of the application or the positive electrode slurry solvent prepared by the preparation method of the second aspect of the application, and further comprises a positive electrode active material, a binder and a conductive agent.

[0012] The fourth aspect of the application provides a secondary battery, which comprises a positive electrode sheet prepared by the positive electrode slurry provided by the third aspect of the application.

[0013] The application has the following beneficial effects:

[0014] This application provides a positive electrode slurry solvent and its preparation method, a positive electrode slurry, and a secondary battery. The positive electrode slurry solvent includes 3-methoxy-N,N-dimethylpropionamide and 3-methoxypropionic acid. Based on the mass of the positive electrode slurry solvent, the mass percentage of 3-methoxy-N,N-dimethylpropionamide is W, where W ≥ 99.7%, and the mass percentage of 3-methoxypropionic acid is A, where 0.001% ≤ A ≤ 0.2%. By controlling the mass percentages of 3-methoxy-N,N-dimethylpropionamide and 3-methoxypropionic acid within the range of this application, it is beneficial to reduce the residual alkali content in the positive electrode slurry, improve the gelation phenomenon of the positive electrode slurry, reduce the viscosity of the slurry, and improve the dispersibility and stability of the positive electrode slurry. The lithium 3-methoxypropionate generated by the reaction is dispersed on the positive electrode surface, which is beneficial to improve the stability of the interfacial film, inhibit interfacial reactions, reduce electrolyte decomposition, and reduce interfacial impedance, thereby improving the high-temperature storage performance and high-temperature cycle performance of the secondary battery.

[0015] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Detailed Implementation

[0016] The technical solutions in this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0017] The first aspect of this application provides a positive electrode slurry solvent comprising 3-methoxy-N,N-dimethylpropionamide and 3-methoxypropionic acid. Based on the mass of the positive electrode slurry solvent, the mass percentage of 3-methoxy-N,N-dimethylpropionamide is W, where W ≥ 99.7%, and the mass percentage of 3-methoxypropionic acid is A, where 0.001% ≤ A ≤ 0.2%. For example, the mass percentage of 3-methoxypropionic acid can be 0.001%, 0.005%, 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.13%, 0.15%, 0.18%, 0.2%, or a range consisting of any two of these values.

[0018] 3-Methoxy-N,N-dimethylpropionamide, as an emerging green solvent, has advantages over NMP, including being green and non-toxic, having low viscosity, excellent chemical and thermal stability, being miscible with water and most organic solvents, and having high solubility for polyvinylidene fluoride (PVDF). It can replace NMP as a solvent for positive electrode slurry in secondary batteries. Furthermore, the inventors discovered that by including 3-methoxy-N,N-dimethylpropionamide and 3-methoxypropionic acid in the positive electrode slurry solvent and controlling the mass percentage of 3-methoxy-N,N-dimethylpropionamide and 3-methoxypropionic acid within the range specified in this application, on the one hand, 3-methoxypropionic acid can react with residual Li2CO3 and LiOH in the positive electrode active material, reducing the residual alkali content in the positive electrode active material; on the other hand, under strongly alkaline conditions, 3-methoxy-N,N-dimethylpropionamide will undergo trace hydrolysis to generate 3-methoxypropionic acid, further reducing the residual alkali content in the positive electrode material, thereby improving the gelation phenomenon of the positive electrode slurry, reducing the viscosity of the slurry, improving the stability of the positive electrode slurry, and facilitating the uniform coating of the positive electrode slurry. On the other hand, the lithium 3-methoxypropionic acid produced by the reaction of 3-methoxypropionic acid with residual alkali in the cathode slurry has relatively high solubility in 3-methoxy-N,N-dimethylpropionamide, exhibiting good dispersibility and stability. This improves the dispersion and stability of the cathode slurry, facilitating uniform coating. Furthermore, after the cathode slurry is coated onto the cathode current collector and the solvent is removed by drying, lithium 3-methoxypropionic acid is uniformly dispersed on the cathode surface, which helps improve the stability of the interfacial film, reduces direct contact between the cathode active material and the electrolyte, inhibits interfacial reactions, and reduces electrolyte decomposition. Simultaneously, lithium 3-methoxypropionic acid has good lithium-ion transport capacity and electrochemical stability, which helps reduce interfacial impedance and improve the high-temperature storage performance and high-temperature cycle performance of the secondary battery.

[0019] When the mass percentage of 3-methoxypropionic acid in the cathode slurry solvent is too low, for example, the value of A is less than 0.001%, the neutralization effect of 3-methoxypropionic acid on residual alkali in the cathode slurry is poor, and the improvement on the viscosity of the cathode slurry is not significant. When the mass percentage of 3-methoxypropionic acid is too high, for example, the value of A is higher than 0.2%, it will lead to a violent neutralization reaction, causing local heating of the cathode slurry. The water content generated by neutralization is too high, resulting in gelation of the cathode slurry. In addition, unreacted 3-methoxypropionic acid may remain after the electrode is baked, which will have a negative impact on the cathode active material. It is understood that in the cathode slurry solvent of this application, apart from 3-methoxy-N,N-dimethylpropionamide and 3-methoxypropionic acid, the remaining components are impurities that were not completely removed during the preparation process, such as N,N-dimethylacrylamide, methanol, and 3-dimethylamino-1,2-propanediol. Therefore, controlling the mass percentage W of 3-methoxy-N,N-dimethylpropionamide in the cathode slurry solvent within the range specified in this application is beneficial to improving the chemical and thermal stability of the cathode slurry solvent and reducing the viscosity of the cathode slurry.

[0020] The second aspect of this application provides a method for preparing the positive electrode slurry solvent of the first aspect of this application, which includes the following steps:

[0021] (1) Using methyl 3-methoxypropionate and dimethylamine as raw materials, an amidation reaction is carried out at a temperature of 30°C to 50°C to obtain a first mixed solution; the first mixed solution is a mixed solution mainly containing 3-methoxy-N,N-dimethylpropionamide. For example, the temperature for carrying out the amidation reaction can be 30°C, 33°C, 35°C, 38°C, 40°C, 43°C, 45°C, 48°C, 50°C, or a range of any two of these values.

[0022] (2) The first mixture is distilled to remove dimethylamine and methanol to obtain a second mixture;

[0023] (3) Cool the second mixture to a temperature T1 of -20°C to 20°C, add an acid solution, and control the temperature of the second mixture to within 20°C during the acid addition process. Adjust the pH of the second mixture to 4 to 5 and then carry out distillation with a vacuum of -0.09 MPa to -0.1 MPa. Raise the temperature to a temperature T2 of 115°C to 140°C and adjust the reflux ratio to (2 to 7):1. Collect the fraction in the temperature range of 110°C to 125°C to obtain the positive electrode slurry solvent. For example, T1 can be -20℃, -15℃, -10℃, -5℃, 0℃, 5℃, 10℃, 15℃, 20℃, or any two of these values; the pH of the second mixture is adjusted by adding acid to be 4, 4.2, 4.5, 4.8, 5, or any two of these values; the vacuum degree is controlled during distillation to be -0.09MPa, -0.092MPa, -0.095MPa, -0.098MPa, -0.1MPa, or any two of these values; the temperature T2 can be 115℃, 118℃, 120℃, 123℃, 125℃, 128℃, 130℃, 133℃, 135℃, 138℃, 140℃, or any two of these values; the reflux ratio can be 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, or any two of these values.

[0024] In some embodiments of this application, the molar ratio of methyl 3-methoxypropionate to dimethylamine is 1:(1.2-3). Preferably, the molar ratio of methyl 3-methoxypropionate to dimethylamine is 1:(2-3). For example, the molar ratio of methyl 3-methoxypropionate to dimethylamine can be 1:1.2, 1:1.5, 1:1.8, 1:2, 1:2.2, 1:2.5, 1:2.8, 1:3, or a range of any two of these values.

[0025] In some embodiments of this application, a polyol may be added as a solvent in the amidation reaction, and the molar ratio of methyl 3-methoxypropionate to polyol is 1:(0.5-2).

[0026] In some embodiments of this application, the polyol is selected from at least one of glycerol, ethylene glycol, 1,2-propanediol, 1,4-butanediol, and 1,6-hexanediol.

[0027] In some embodiments of this application, the acid solution is selected from sulfuric acid solution with a mass fraction of 10% to 80% or hydrochloric acid solution with a mass fraction of 5% to 37%. Adding the acid solution facilitates further removal of residual dimethylamine and trimethylamine from the second mixture and helps control the reaction temperature, thereby helping to control the mass percentage of 3-methoxypropionic acid within the range specified in this application.

[0028] The third aspect of the present application provides a positive electrode paste, which includes the positive electrode paste solvent of the first aspect of the present application or the positive electrode paste solvent prepared by the preparation method of the second aspect of the present application, and further includes a positive electrode active material, a binder, and a conductive agent.

[0029] In some embodiments of the present application, based on the mass of the positive electrode paste, the solid content of the positive electrode paste is B, and 50% ≤ B ≤ 80%. For example, the solid content of the positive electrode paste can be 50%, 53%, 55%, 58%, 60%, 63%, 65%, 68%, 70%, 73%, 75%, 78%, 80%, or a range composed of any two of these values. By adjusting the solid content of the positive electrode paste within the scope of the present application, it is beneficial to improve the dispersion and stability of the positive electrode paste and is beneficial to the uniform coating of the positive electrode paste.

[0030] The present application does not particularly limit the mass ratio of the positive electrode active material, the binder, and the conductive agent in the positive electrode paste, as long as the object of the present application can be achieved. For example, the mass ratio of the positive electrode active material, the binder, and the conductive agent can be (96 - 98):(0.5 - 2):(1 - 2.5).

[0031] In some embodiments of the present application, the positive electrode active material is selected from Li a (Ni x Co y M 1-x-y )O2, LiFe 1-m D m PO4, sodium iron nickel manganese, sodium vanadium phosphate, Prussian white, etc.; wherein, 0.5 ≤ a ≤ 1.3, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 < x + y ≤ 1, M is selected from at least one of Mn, Al, and Mg; 0 ≤ m ≤ 0.6, D is selected from at least one of Co, Mn, Ni, Al, and Mg. For example, the positive electrode active material can be selected from LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.7 Co 0.1 Mn 0.2 O2 (NCM712), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM111), LiNi 0.9 Co 0.05 Mn 0.05O2, LiFePO4, LiFe 0.4 Mn 0.6 PO4, LiFe 0.19 Mn 0.8 Ni 0.01 PO4.

[0032] In some embodiments of the present application, the positive electrode active material is selected from Li a (Ni x Co y M 1-x-y )O2, when 0.7 < x ≤ 1, 0.025% ≤ A ≤ 0.2% and [B / (1 - B)]×0.02% ≤ A ≤ [B / (1 - B)]×0.1%; when 0 ≤ x ≤ 0.7, 0.001% ≤ A ≤ [B / (1 - B)]×0.02%. In the preparation process of the Li a (Ni x Co y M 1-x-y )O2 material, generally, as the Ni content increases, the sintering temperature becomes lower, resulting in a decrease in the volatilization amount of residual lithium salts and an increase in the content of lithium salts remaining on the surface of the material. The remaining lithium salts are prone to react with moisture to generate Li2CO3 and LiOH. Therefore, when the value of x is different, the preferred value range of 3 - methoxypropionic acid in the positive electrode slurry solvent is different. When 0.7 < x ≤ 1, 0.025% ≤ A ≤ 0.2% and [B / (1 - B)]×0.02% ≤ A ≤ [B / (1 - B)]×0.1%; when 0 ≤ x ≤ 0.7, 0.001% ≤ A ≤ [B / (1 - B)]×0.02%. Through the above settings, it is beneficial to further reduce the content of residual alkali in the positive electrode slurry, improve the gel phenomenon of the positive electrode slurry, reduce the viscosity of the slurry, improve the dispersibility and stability of the positive electrode slurry. The lithium 3 - methoxypropionate generated by the reaction is dispersed on the surface of the positive electrode, which is beneficial to improving the stability of the interface film, inhibiting the interface reaction, reducing the decomposition of the electrolyte, and is also beneficial to reducing the interface impedance and further improving the high - temperature storage performance and high - temperature cycling performance of the secondary battery.

[0033] In some embodiments of the present application, the positive electrode active material is selected from LiFe<~ 1-m D m PO4, and the positive electrode slurry further includes a lithium supplement agent Li 5b+2c Fe b N c O 4b+2c , N is selected from at least one of Ni, Co, and Mn, 0.5 ≤ b ≤ 1, 0 ≤ c ≤ 0.5, and b + c = 1; based on the mass of the positive electrode active material, the lithium supplement agent Li 5b+2c Fe b N c O 4b+2cThe mass percentage content is C, where 0 ≤ C ≤ 1%. For example, the value of C can be 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or a range of any two of these values. For example, the lithium supplement can be selected from Li5FeO4 and Li2NiO2. The positive electrode slurry includes the lithium supplement Li... 5b+2c Fe b N c O 4b+2c This helps to replenish the lithium ion loss in the early stage of secondary battery cycle, thereby improving the reversible capacity of the secondary battery and improving its cycle performance.

[0034] In some embodiments of this application, the positive electrode active material is selected from LiFe. 1-m D m PO4, the cathode slurry also includes lithium supplementer Li. 5b+2c Fe b N c O 4b+2c N is selected from at least one of Ni, Co, and Mn, 0.5≤b≤1, 0≤c≤0.5, and b+c=1; based on the mass of the positive electrode active material, the lithium supplementer Li 5b+2c Fe b N c O 4b+2c The mass percentage content is C. When 0 ≤ C < 0.4%, 0.001% ≤ A ≤ [B / (1-B)] × 0.02%; when 0.4% ≤ C ≤ 1%, [B / (1-B)] × C × 0.02 ≤ A ≤ [B / (1-B)] × C × 0.05. When the positive electrode slurry includes lithium supplementer Li... 5b+2c Fe b N c O 4b+2c At that time, Li 5b+2c Fe b N c O 4b+2cSensitive to moisture, it easily absorbs water and decomposes to produce alkaline substances, leading to increased alkalinity in the positive electrode slurry and affecting its dispersibility and stability. Including 3-methoxypropionic acid in the positive electrode slurry solvent, and satisfying the following conditions: when 0 ≤ C < 0.4%, 0.001% ≤ A ≤ [B / (1-B)] × 0.02%; when 0.4% ≤ C ≤ 1%, [B / (1-B)] × C × 0.02 ≤ A ≤ [B / (1-B)] × C × 0.05, helps to further reduce the residual alkali content in the positive electrode slurry, improve the gelation phenomenon, reduce the viscosity of the slurry, and enhance its dispersibility and stability. The resulting lithium 3-methoxypropionic acid is dispersed on the positive electrode surface, which helps to improve the stability of the interfacial film, inhibit interfacial reactions, reduce electrolyte decomposition, and reduce interfacial impedance, further improving the high-temperature storage performance and high-temperature cycle performance of the secondary battery.

[0035] This application does not impose any particular restrictions on the types of conductive agents and binders in the positive electrode slurry, as long as they can achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of superconducting carbon black (Super P), acetylene black, Ketjen black, carbon nanotubes, graphene, or carbon fiber. For example, the binder may include, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorinated acrylate resin.

[0036] This application does not impose any particular restrictions on the preparation method of the positive electrode slurry, as long as it can achieve the purpose of this application. For example, the preparation method of the positive electrode slurry can be: dissolving the binder in the positive electrode slurry solvent to prepare a colloid, then adding the positive electrode active material and conductive agent to the above colloid, and stirring evenly to obtain the positive electrode slurry.

[0037] The fourth aspect of this application provides a secondary battery comprising a positive electrode sheet prepared from the positive electrode slurry provided in the third aspect of this application.

[0038] The positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that "surface" here can refer to the entire surface of the positive current collector or only a portion thereof; this application does not impose any particular limitation, as long as the purpose of this application is achieved. This application does not impose any particular limitation on the positive current collector, as long as the purpose of this application is achieved. For example, the positive current collector can be aluminum foil, aluminum alloy foil, or a composite positive current collector. The aforementioned composite positive current collector can be a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The material of the aforementioned polymer material base layer can be, but is not limited to, at least one of polypropylene (PP), polyethylene terephthalate (PET), or polybutylene terephthalate (PBT), and the material of the aforementioned metal layer can be, but is not limited to, at least one of aluminum, aluminum alloy, nickel, or nickel alloy. This application does not impose any particular limitation on the thickness of the positive electrode material layer and the positive electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the single-sided positive electrode material layer is 50 μm to 250 μm, and the thickness of the positive electrode current collector is 7 μm to 15 μm.

[0039] This application does not impose any particular limitation on the preparation method of the positive electrode sheet, as long as it achieves the purpose of this application. For example, the preparation method of the positive electrode sheet can be as follows: dissolving a binder in a positive electrode slurry solvent to prepare a colloid, then adding a positive electrode active material and a conductive agent to the colloid, stirring evenly to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated onto both surfaces of the positive electrode current collector, and dried to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After coating, the positive electrode sheet is obtained by cold pressing and cutting.

[0040] In this application, the secondary battery further includes a negative electrode sheet, which includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The phrase "the negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the negative electrode current collector, or only a portion of the surface area; this application has no particular limitation, as long as the purpose of this application is achieved.

[0041] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector. For example, the composite current collector may be lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.

[0042] The negative electrode material layer includes a negative electrode active material. This application does not impose any particular limitation on the negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include, but is not limited to, natural graphite, artificial graphite, mesophase micro carbon spheres, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 Or at least one of Li-Al alloys.

[0043] The negative electrode material layer may further include a negative electrode conductive agent and a negative electrode binder. This application does not impose any particular limitation on the types of negative electrode conductive agents and negative electrode binders, as long as they achieve the purpose of this application. For example, the negative electrode conductive agent may include, but is not limited to, at least one of superconducting carbon black (Super P), acetylene black, Ketjen black, carbon nanotubes, graphene, or carbon fibers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. For example, the negative electrode binder may include, but is not limited to, at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethyl methacrylate (PMAA), or carboxymethyl chitosan (CMCS). This application does not impose any particular limitation on the mass ratio of the negative electrode active material, negative electrode conductive agent, and negative electrode binder in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved. In some embodiments of this application, the negative electrode material layer may further include a thickener, which may include, but is not limited to, sodium carboxymethyl cellulose (CMC). This application does not impose any particular limitation on the mass ratio of the negative electrode active material, negative electrode conductive agent, negative electrode binder, and thickener in the negative electrode material layer; those skilled in the art can select these components according to actual needs, as long as the purpose of this application is achieved.

[0044] In this application, there are no particular limitations on the preparation method of the negative electrode sheet, as long as it can achieve the purpose of this application. For example, it can be prepared by the following method: adding negative electrode active material, negative electrode conductive agent, and negative electrode binder to deionized water and stirring evenly to obtain a negative electrode slurry with a solid content of 45wt% to 70wt%. The negative electrode slurry is uniformly coated on both surfaces of the negative electrode current collector, and after drying, a negative electrode sheet with a double-sided negative electrode material layer is obtained. Then, it is cold-pressed and cut to obtain the negative electrode sheet.

[0045] In this application, the secondary battery also includes a separator. This application does not impose any particular limitation on the separator, as long as it achieves the purpose of this application. For example, the separator material may include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), glass fiber, polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), and polyamide (PA). The type of separator may include at least one of woven membrane, nonwoven fabric, microporous membrane, composite membrane, rolled membrane, or spun membrane. In this application, the thickness of the separator is not particularly limited, as long as it achieves the purpose of this application; for example, the separator thickness may be from 4 μm to 20 μm.

[0046] In this application, the secondary battery also includes a casing for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it achieves the purpose of this application. For example, the casing can be a rigid casing or a flexible casing. The material of the rigid casing can be metal; this application does not limit the type of metal and can use known metal rigid casings, as long as they achieve the purpose of this application. The flexible casing can be a metal plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0047] In some embodiments of this application, the secondary battery may include, but is not limited to: lithium metal secondary battery, lithium-ion secondary battery (lithium-ion battery), sodium-ion secondary battery (sodium-ion battery), etc.

[0048] The fabrication process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the fabrication process of the secondary battery may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. Alternatively, stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent pressure rise and overcharging / discharging inside the secondary battery.

[0049] Example

[0050] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0051] Test methods and equipment:

[0052] Test of solvent composition of positive electrode slurry

[0053] The types and mass percentages of each component in the positive electrode slurry solvent were determined using a gas chromatograph (model: Agilent 8890).

[0054] Testing of positive electrode slurry

[0055] After stirring the positive electrode slurry, the initial viscosity of the positive electrode slurry was measured using a viscometer (model: Brookfield DV2THA) and recorded as η0. The viscosity of the positive electrode slurry was then measured after standing for 1 hour, 6 hours, and 24 hours, and recorded as η1, η6, and η24, respectively. The solid content of the upper and lower layers of the positive electrode slurry was also measured after standing for 24 hours. Small amounts of each layer were taken and spread evenly on aluminum foil of mass m, and the total weight was recorded as M. 上 and M 下 After baking in a 120℃ oven for 30 minutes, the total weight of the aluminum foil was M' 上 and M' 下 The solid content of the upper slurry was calculated to be (M' 上 -m) / (M 上 -m)×100%, the solid content of the lower layer slurry is (M' 下 -m) / (M 下 -m)×100%, the difference between the solid content of the upper slurry and the solid content of the lower slurry is denoted as △B.

[0056] After stirring the positive electrode slurry, take another 5g of positive electrode slurry, add 100g of deionized water at a temperature of (25±2)℃, and ultrasonically stir for 1min. Filter to obtain the filtrate. The pH value of the filtrate was tested using a pH meter, and the OH- ions were tested using a potentiometric titrator (model: Metrohm848Titrino plus). - and CO3 2- The concentration of [amount] was determined by titrating with a 0.1 mol / L hydrochloric acid solution. Titration principle: OH [[...]] - and CO3 2- Both OH- and CO32- can be titrated with hydrochloric acid, exhibiting a distinct jump point during potentiometric titration. 2- The mixed solution undergoes two steps of reaction during titration, resulting in two abrupt changes. The reaction corresponding to the first abrupt change is OH. - +H + =H2O, CO3 2- +H + =HCO3 - The reaction corresponding to the second jump point is HCO3. - +H + =H₂CO₃. In the test, pH ≈ 8 was chosen as the first abrupt change point and pH ≈ 5 as the second abrupt change point. The titration was stopped when the solution pH ≤ 3. Based on the molar amount of acid added at the aforementioned pH abrupt change points, the OH⁻... - and CO3 2- The content of.

[0057] High-temperature cycling performance test

[0058] The lithium-ion battery was placed in a 45°C constant temperature chamber and left to stand for 4 hours. Then, the lithium-ion battery was charged at a constant current of 1C to the upper limit cutoff voltage, and then charged at a constant voltage to the cutoff current of 0.05C. After that, it was discharged at a constant current of 1C to the lower limit cutoff voltage. The initial discharge capacity was recorded as C1. This was one charge-discharge cycle. The above charge-discharge cycle was repeated for 500 times. The discharge capacity after the 500th cycle was recorded as C2.

[0059] 45℃ capacity retention rate (%) = C2 / C1 × 100%; The 45℃ capacity retention rate is used to evaluate the high-temperature cycle performance of lithium-ion batteries. The higher the capacity retention rate, the better the high-temperature cycle performance of lithium-ion batteries.

[0060] When the positive electrode active material is NCM811, the upper limit cutoff voltage in the above test steps is 4.25V and the lower limit cutoff voltage is 2.75V; when the positive electrode active material is NCM111, the upper limit cutoff voltage in the above test steps is 4.2V and the lower limit cutoff voltage is 2.75V; when the positive electrode active material is LiFePO4, the upper limit cutoff voltage in the above test steps is 3.6V and the lower limit cutoff voltage is 2V; when the positive electrode active material is LiFe... 0.4 Mn 0.6 For PO4, the upper cutoff voltage in the above test steps is 3.8V and the lower cutoff voltage is 2V.

[0061] High-temperature storage performance test

[0062] The lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 4 hours. Then, it was charged at a constant current of 0.5C to the upper cutoff voltage, followed by constant voltage charging until the cutoff current was 0.05C. Finally, it was discharged at a constant current of 1C to the lower cutoff voltage, and the discharge capacity was recorded as Q1. The lithium-ion battery was then charged at a constant current of 1C to the upper cutoff voltage, followed by constant current charging until the cutoff current was 0.05C. Afterward, the lithium-ion battery was placed in a 60°C explosion-proof oven and stored for 14 days. The battery was then removed and cooled to room temperature. At 25°C, it was discharged at a constant current of 1C to the lower cutoff voltage, and the discharge capacity at this point was recorded as Q2.

[0063] 60℃ storage capacity retention rate (%) = Q2 / Q1×100%. The 60℃ storage capacity retention rate is used to evaluate the high-temperature storage performance of lithium-ion batteries. The higher the capacity retention rate, the better the high-temperature storage performance of lithium-ion batteries.

[0064] When the positive electrode active material is NCM811, the upper limit cutoff voltage in the above test steps is 4.25V and the lower limit cutoff voltage is 2.75V; when the positive electrode active material is NCM111, the upper limit cutoff voltage in the above test steps is 4.2V and the lower limit cutoff voltage is 2.75V; when the positive electrode active material is LiFePO4, the upper limit cutoff voltage in the above test steps is 3.6V and the lower limit cutoff voltage is 2V; when the positive electrode active material is LiFe... 0.4 Mn 0.6 For PO4, the upper cutoff voltage in the above test steps is 3.8V and the lower cutoff voltage is 2V.

[0065] Example 1

[0066] <Preparation of Positive Electrode Slurry Solvent>

[0067] In a reaction vessel, 2.36 kg of methyl 3-methoxypropionate, 1.8 kg of dimethylamine, and 1.84 kg of glycerol were added at 0°C with a molar ratio of methyl 3-methoxypropionate:dimethylamine:glycerol of 1:2:1. The temperature was raised to 35°C, and the mixture was stirred for 5 hours. After the reaction was completed, the reaction solution was transferred to a flash evaporator and subjected to vacuum distillation at -0.098 MPa at 45°C to separate the dimethylamine and methanol mixture. The temperature of the remaining reaction solution was lowered to -10℃, and an 80% sulfuric acid solution was slowly added dropwise. The temperature was controlled within the range of -10℃ to 0℃. After adjusting the pH of the reaction solution to 4-5, it was transferred to a distillation column, heated to 120℃ under a vacuum of -0.098 MPa, with a reflux ratio of 7:1. The fraction collected between 115℃ and 120℃ was used to obtain the positive electrode slurry solvent. Based on the mass of the positive electrode slurry solvent, the mass percentage of 3-methoxy-N,N-dimethylpropionamide was 99.95%, the mass percentage of 3-methoxypropionic acid was 0.001%, and the remaining components included 0.048% N,N-dimethylacrylamide and 0.001% other impurities.

[0068] <Preparation of Positive Electrode Slurry>

[0069] 6.2g of the binder polyvinylidene fluoride (PVDF) was dissolved in 236g of the positive electrode slurry solvent prepared above to obtain a colloid. 500g of the positive electrode active material LiNi was then added. 0.8 Co 0.1 Mn 0.1 O2 and 10.3g of conductive agent acetylene black were added to the above colloid and stirred evenly to obtain the positive electrode slurry. The mass ratio of positive electrode active material, binder, and conductive agent was 96.8:1.2:2, and the solid content of the positive electrode slurry was 68.6%.

[0070] <Preparation of the positive electrode>

[0071] The prepared positive electrode slurry was directly and uniformly coated onto both surfaces of a 12 μm thick aluminum foil for positive electrode current collectors. After drying at 85°C, it was cold-pressed to obtain a positive electrode sheet with a double-sided coated positive electrode material layer. The thickness of the single-sided positive electrode material layer was 49 μm. Then, the sheets were trimmed, cut, and slit. After slitting, they were dried at 85°C under vacuum for 4 hours, and then tabs were welded to obtain positive electrode sheets with a size of 540 mm × 55 mm for later use.

[0072] <Preparation of Negative Electrode Sheets>

[0073] Artificial graphite (anode active material), styrene-butadiene rubber (SBR) (binder), sodium carboxymethyl cellulose (CMC) (thickener) (95:4:1 mass ratio) were mixed with deionized water as a solvent to form a slurry with a solid content of 50%. The slurry was then stirred evenly in a vacuum mixer to obtain the anode slurry. The anode slurry was uniformly coated onto both surfaces of a 9μm thick copper foil current collector. After drying at 85℃, it was cold-pressed to obtain a double-sided coated anode electrode sheet. The thickness of the single-sided anode material layer was 58μm. The sheet was then trimmed, cut, and slit. After slitting, it was dried at 85℃ under vacuum for 4 hours, and tabs were welded to obtain a 660mm × 59mm anode electrode sheet for later use.

[0074] <Preparation of the diaphragm>

[0075] The PE (polypropylene) ceramic-coated diaphragm is provided by Shenzhen Xingyuan Material Technology Co., Ltd. ， The model number is SH312E13, and the diaphragm thickness is 12.6μm.

[0076] <Preparation of Electrolyte>

[0077] In an argon-filled glove box (moisture <10ppm, oxygen <1ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 3:7 to obtain a base solvent. Then, lithium hexafluorophosphate (LiPF6) was added to the base solvent to obtain the electrolyte. The mass percentage of LiPF6 was 12% based on the mass of the electrolyte, with the remainder being the base solvent.

[0078] <Preparation of Lithium-ion Batteries>

[0079] The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to act as a separator. The electrode assembly is then wound to obtain the electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag and vacuum-baked at 85°C for 48 hours. The electrolyte prepared above is then injected, and the lithium-ion battery is obtained through vacuum sealing, settling, formation, and shaping processes.

[0080] Example 2

[0081] Except for the preparation of the positive electrode slurry solvent, which is carried out according to the following method, the rest is the same as in Example 1.

[0082] <Preparation of Positive Electrode Slurry Solvent>

[0083] In a reaction vessel, 2.36 kg of methyl 3-methoxypropionate, 1.8 kg of dimethylamine, and 1.84 kg of glycerol were added at 0°C in a molar ratio of methyl 3-methoxypropionate:dimethylamine:glycerol of 1:2:1. The mixture was heated to 40°C and stirred for 5 hours. After the reaction was completed, the reaction solution was transferred to a flash evaporator and subjected to vacuum distillation at 45°C under a vacuum of -0.098 MPa to separate the dimethylamine and methanol mixture. The temperature of the remaining reaction solution was lowered to 0℃, and a 70% sulfuric acid solution was slowly added dropwise. The temperature was controlled within the range of 0℃ to 5℃. After adjusting the pH of the reaction solution to 4 to 5, it was transferred to a distillation column, heated to 120℃ under a vacuum of -0.098 MPa, with a reflux ratio of 5:1. The fraction collected in the temperature range of 116℃ to 122℃ was used to obtain the positive electrode slurry solvent. Based on the mass of the positive electrode slurry solvent, the mass percentage of 3-methoxy-N,N-dimethylpropionamide was 99.90%, the mass percentage of 3-methoxypropionic acid was 0.05%, and the remaining components included 0.012% methanol, 0.037% N,N-dimethylacrylamide, and 0.001% other impurities.

[0084] Example 3

[0085] Except for the preparation of the positive electrode slurry solvent, which is carried out according to the following method, the rest is the same as in Example 1.

[0086] <Preparation of Positive Electrode Slurry Solvent>

[0087] In a reaction vessel, 2.36 kg of methyl 3-methoxypropionate, 1.8 kg of dimethylamine, and 1.84 kg of glycerol were added at 0°C in a molar ratio of methyl 3-methoxypropionate:dimethylamine:glycerol of 1:2:1. The mixture was heated to 45°C and stirred for 5 hours. After the reaction was completed, the reaction solution was transferred to a flash evaporator and subjected to vacuum distillation at -0.098 MPa at 45°C to separate the dimethylamine and methanol mixture. The temperature of the remaining reaction solution was lowered to 5°C, and a 70% sulfuric acid solution was slowly added dropwise. The temperature was controlled between 5°C and 10°C. The pH of the reaction solution was adjusted to 4–5, and then transferred to a distillation column. Under a vacuum of -0.097 MPa, the temperature was raised to 125°C with a reflux ratio of 4:1. The fraction collected between 115°C and 124°C was used to obtain the positive electrode slurry solvent. Based on the mass of the positive electrode slurry solvent, the mass percentage of 3-methoxy-N,N-dimethylpropionamide was 99.82%, the mass percentage of 3-methoxypropionic acid was 0.1%, and the remaining components included 0.019% methanol, 0.06% N,N-dimethylacrylamide, and 0.001% other impurities.

[0088] Example 4

[0089] Except for the preparation of the positive electrode slurry solvent, which is carried out according to the following method, the rest is the same as in Example 1.

[0090] <Preparation of Positive Electrode Slurry Solvent>

[0091] In a reaction vessel, 2.36 kg of methyl 3-methoxypropionate, 1.8 kg of dimethylamine, and 1.84 kg of glycerol were added at 0°C in a molar ratio of methyl 3-methoxypropionate:dimethylamine:glycerol of 1:2:1. The mixture was heated to 50°C and stirred for 5 hours. After the reaction was completed, the reaction solution was transferred to a flash evaporator and subjected to vacuum distillation at -0.098 MPa at 45°C to separate the dimethylamine and methanol mixture. The temperature of the remaining reaction solution was lowered to 10℃, and a 70% sulfuric acid solution was slowly added dropwise. The temperature was controlled between 10℃ and 15℃. After adjusting the pH of the reaction solution to 4-5, it was transferred to a distillation column, heated to 130℃ under a vacuum of -0.095 MPa, with a reflux ratio of 3:1. The fraction collected between 115℃ and 125℃ was used to obtain the positive electrode slurry solvent. Based on the mass of the positive electrode slurry solvent, the mass percentage of 3-methoxy-N,N-dimethylpropionic acid was 99.72%, the mass percentage of 3-methoxypropionic acid was 0.2%, and the remaining components included 0.011% methanol, 0.068% N,N-dimethylacrylamide, and 0.001% other impurities.

[0092] Example 5

[0093] Except for replacing the types of positive electrode active materials according to Table 1 in the <Preparation of Positive Electrode Slurry> section, the rest is the same as in Example 1.

[0094] Example 6

[0095] Except for the preparation of the positive electrode slurry solvent, which is carried out according to the following method, the rest is the same as in Example 5.

[0096] In a reaction vessel, 2.36 kg of methyl 3-methoxypropionate, 1.8 kg of dimethylamine, and 1.84 kg of glycerol were added at 0°C in a molar ratio of methyl 3-methoxypropionate:dimethylamine:glycerol of 1:2:1. The mixture was heated to 40°C and stirred for 5 hours. After the reaction was completed, the reaction solution was transferred to a flash evaporator and subjected to vacuum distillation at 45°C under a vacuum of -0.098 MPa to separate the dimethylamine and methanol mixture. The temperature of the remaining reaction solution was lowered to -5℃, and a 70% sulfuric acid solution was slowly added dropwise. The temperature was controlled within the range of -5℃ to 0℃. After adjusting the pH of the reaction solution to 4-5, it was transferred to a distillation column, heated to 120℃ under a vacuum of -0.098 MPa, with a reflux ratio of 5.5:1. The fraction collected between 116℃ and 121℃ was used to obtain the positive electrode slurry solvent. Based on the mass of the positive electrode slurry solvent, the mass percentage of 3-methoxy-N,N-dimethylpropionic acid was 99.94%, the mass percentage of 3-methoxypropionic acid was 0.02%, and the remaining components included 0.012% methanol, 0.027% N,N-dimethylacrylamide, and 0.001% other impurities.

[0097] Example 7

[0098] Except for replacing the types of positive electrode active materials according to Table 1 in the <Preparation of Positive Electrode Slurry> section, the rest is the same as in Example 4.

[0099] Examples 8 to 10

[0100] Except for replacing the types of positive electrode active materials and positive electrode slurry solvents according to Table 1 in the <Preparation of Positive Electrode Slurry> section, and adjusting the solid content of the positive electrode slurry, the rest is the same as in Example 1. Among them, the <Preparation of Positive Electrode Slurry Solvent> in Examples 8, 9 and 10 correspond to Examples 1, 6 and 4, respectively.

[0101] Examples 11 to 13

[0102] Except for the addition of lithium supplementer as per Table 1 in the <Preparation of Positive Electrode Slurry> section and the adjustment of the type of positive electrode slurry solvent, the rest is the same as in Example 8. When lithium supplementer is added, the mass percentage of positive electrode active material in the positive electrode material layer changes accordingly; the <Preparation of Positive Electrode Slurry Solvent> sections of Examples 11, 12, and 13 correspond to Examples 1, 2, and 4, respectively.

[0103] Examples 14 to 16

[0104] Except for replacing the types of positive electrode active materials and positive electrode slurry solvents according to Table 1 in the <Preparation of Positive Electrode Slurry> section, and adjusting the solid content of the positive electrode slurry, the rest is the same as in Example 1. Among them, the <Preparation of Positive Electrode Slurry Solvent> sections of Examples 14, 15, and 16 correspond to Examples 1, 6, and 4, respectively.

[0105] Examples 17 to 19

[0106] Except for the addition of lithium supplementer as per Table 1 in the <Preparation of Positive Electrode Slurry> and the adjustment of the type of positive electrode slurry solvent, the rest is the same as in Example 14. When lithium supplementer is added, the mass percentage of positive electrode active material in the positive electrode material layer changes accordingly; the <Preparation of Positive Electrode Slurry Solvent> in Examples 14, 15, and 16 correspond to Examples 1, 6, and 4, respectively.

[0107] Examples 20 to 23

[0108] Except for adjusting the type of positive electrode slurry solvent and the solid content of the positive electrode slurry according to Table 1 in the <Preparation of Positive Electrode Slurry> section, the rest is the same as in Example 1. Among them, the <Preparation of Positive Electrode Slurry Solvent> in Examples 20 and 22 is the same as in Example 2; the <Preparation of Positive Electrode Slurry Solvent> in Examples 21 and 23 is the same as in Example 4.

[0109] Comparative Example 1

[0110] Except for the preparation of the positive electrode slurry solvent, which is carried out according to the following method, the rest is the same as in Example 1.

[0111] <Preparation of Positive Electrode Slurry Solvent>

[0112] In a reaction vessel, 2.36 kg of methyl 3-methoxypropionate, 1.8 kg of dimethylamine, and 1.84 kg of glycerol were added at 0°C in a molar ratio of methyl 3-methoxypropionate:dimethylamine:glycerol of 1:2:1. The mixture was heated to 40°C and stirred for 5 hours. After the reaction was completed, the reaction solution was transferred to a flash evaporator and subjected to vacuum distillation at 45°C under a vacuum of -0.098 MPa to separate the dimethylamine and methanol mixture. Under a vacuum of -0.099 MPa, the temperature was raised to 120 °C, and the reflux ratio was 8:1. The fraction collected in the temperature range of 110 °C to 115 °C was obtained as the positive electrode slurry solvent. Based on the mass of the positive electrode slurry solvent, the mass percentage of 3-methoxy-N,N-dimethylpropionic acid was 99.95%, the mass percentage of 3-methoxypropionic acid was 0%, and the remaining components included 0.049% N,N-dimethylacrylamide and 0.001% other impurities.

[0113] Comparative Example 2

[0114] Except for the preparation of the positive electrode slurry solvent, which is carried out according to the following method, the rest is the same as in Example 1.

[0115] <Preparation of Positive Electrode Slurry Solvent>

[0116] In a reaction vessel, 2.36 kg of methyl 3-methoxypropionate, 1.8 kg of dimethylamine, and 1.84 kg of glycerol were added at 0°C in a molar ratio of methyl 3-methoxypropionate:dimethylamine:glycerol of 1:2:1. The mixture was heated to 50°C and stirred for 5 hours. After the reaction was completed, the reaction solution was transferred to a flash evaporator and subjected to vacuum distillation at -0.098 MPa at 45°C to separate the dimethylamine and methanol mixture. The temperature of the remaining reaction solution was lowered to 25°C, and a 90% sulfuric acid solution was slowly added dropwise while maintaining the temperature below 30°C. The pH of the reaction solution was adjusted to 4-5, and then transferred to a distillation column. Under a vacuum of -0.095 MPa, the temperature was raised to 130°C with a reflux ratio of 3:1. The fraction collected between 115°C and 125°C was used to obtain the positive electrode slurry solvent. Based on the mass of the positive electrode slurry solvent, the mass percentage of 3-methoxy-N,N-dimethylpropionamide was 99.61%, the mass percentage of 3-methoxypropionic acid was 0.3%, and the remaining components included 0.011% methanol, 0.078% N,N-dimethylacrylamide, and 0.001% other impurities.

[0117] Comparative Example 3

[0118] Except for the preparation of the positive electrode slurry solvent, which is carried out according to the following method, the rest is the same as in Example 1.

[0119] <Preparation of Positive Electrode Slurry Solvent>

[0120] In a reaction vessel, 2.36 kg of methyl 3-methoxypropionate, 1.8 kg of dimethylamine, and 1.84 kg of glycerol were added at 0°C in a molar ratio of methyl 3-methoxypropionate:dimethylamine:glycerol of 1:2:1. The mixture was heated to 60°C and stirred for 5 hours. After the reaction was completed, the reaction solution was transferred to a flash evaporator and subjected to vacuum distillation at -0.098 MPa at 45°C to separate the dimethylamine and methanol mixture. The temperature of the remaining reaction solution was lowered to -10℃, and an 80% sulfuric acid solution was slowly added dropwise. The temperature was controlled within the range of -10℃ to 0℃. After adjusting the pH of the reaction solution to 4-5, it was transferred to a distillation column, heated to 130℃ under a vacuum of -0.095 MPa, with a reflux ratio of 3:1. The fraction collected in the temperature range of 113℃ to 120℃ was used to obtain the positive electrode slurry solvent. Based on the mass of the positive electrode slurry solvent, the mass percentage of 3-methoxy-N,N-dimethylpropionic acid was 99.5%, the mass percentage of 3-methoxypropionic acid was 0.001%, and the remaining components included 0.126% methanol, 0.372% N,N-dimethylacrylamide, and 0.001% other impurities.

[0121] Comparative Example 4

[0122] Except for adjusting the type of positive electrode slurry solvent according to Table 1 in the <Preparation of Positive Electrode Slurry> section, and ensuring that the positive electrode slurry solvent does not contain 3-methoxypropionic acid, the rest is the same as in Example 5. The <Preparation of Positive Electrode Slurry Solvent> section is the same as in Comparative Example 1.

[0123] Comparative Example 5

[0124] Except for adjusting the type of positive electrode slurry solvent according to Table 1 in the <Preparation of Positive Electrode Slurry> section, and ensuring that the positive electrode slurry solvent does not contain 3-methoxypropionic acid, the rest is the same as in Example 8. The <Preparation of Positive Electrode Slurry Solvent> section is the same as in Comparative Example 1.

[0125] Comparative Example 6

[0126] Except for adjusting the type of positive electrode slurry solvent according to Table 1 in the <Preparation of Positive Electrode Slurry> section, and ensuring that the positive electrode slurry solvent does not contain 3-methoxypropionic acid, the rest is the same as in Example 11. The <Preparation of Positive Electrode Slurry Solvent> section is the same as in Comparative Example 1.

[0127] Comparative Example 7

[0128] Except for adjusting the type of positive electrode slurry solvent according to Table 1 in the <Preparation of Positive Electrode Slurry> section, and ensuring that the positive electrode slurry solvent does not contain 3-methoxypropionic acid, the rest is the same as in Example 14. The <Preparation of Positive Electrode Slurry Solvent> section is the same as in Comparative Example 1.

[0129] Comparative Example 8

[0130] Except for adjusting the type of positive electrode slurry solvent according to Table 1 in the <Preparation of Positive Electrode Slurry> section, and ensuring that the positive electrode slurry solvent does not contain 3-methoxypropionic acid, the rest is the same as in Example 17. The <Preparation of Positive Electrode Slurry Solvent> section is the same as in Comparative Example 1.

[0131] Table 1 Note: In Table 1, " / " indicates that the corresponding substance or parameter does not exist.

[0132] As can be seen from Examples 1 to 23 and Comparative Examples 1 to 8, by selecting a positive electrode slurry solvent within the scope of this application and adjusting the mass percentage content of 3-methoxy-N,N-dimethylpropionic acid and 3-methoxypropionic acid in the positive electrode slurry solvent to be within the scope of this application, the obtained positive electrode slurry has a low viscosity and a small difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, indicating that the positive electrode slurry has good dispersibility and stability. The obtained lithium-ion battery has a high 45°C cycle capacity retention rate and a high 60°C storage capacity retention rate, indicating that the lithium-ion battery of the examples has good high-temperature cycle performance and high-temperature storage performance.

[0133] The solid content of the cathode slurry typically affects its dispersibility and stability, as well as the high-temperature cycle performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 2, 4, and 20 to 23, by adjusting the solid content of the cathode slurry within the range specified in this application, the viscosity of the cathode slurry can be reduced, and the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours is small, indicating that the cathode slurry has good dispersibility and stability. The resulting lithium-ion batteries exhibit high 45°C cycle capacity retention and high 60°C storage capacity retention, demonstrating that the lithium-ion batteries of these examples have good high-temperature cycle performance and high-temperature storage performance.

[0134] The type and mass percentage of lithium supplementation agents typically affect the dispersibility and stability of the cathode slurry, as well as the high-temperature cycle performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 8 to 13, Comparative Examples 5 to 6, Examples 14 to 19, and Comparative Examples 7 to 8, by adding lithium supplementation agents to the cathode slurry and adjusting the mass percentage of 3-methoxypropionic acid in the cathode slurry solvent within the range of this application, it is beneficial to further improve the high-temperature cycle performance and high-temperature storage performance of lithium-ion batteries. Simultaneously, it can reduce the viscosity of the cathode slurry, and the difference in solid content between the upper and lower layers of the slurry decreases after standing for 24 hours, indicating that the cathode slurry has good dispersibility and stability.

[0135] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A positive electrode slurry solvent comprising 3-methoxy-N,N-dimethylpropionamide and 3-methoxypropionic acid, wherein, based on the mass of the positive electrode slurry solvent, the mass percentage content of the 3-methoxy-N,N-dimethylpropionamide is W, W≥99.7%, and the mass percentage content of the 3-methoxypropionic acid is A, 0.001%≤A≤0.2%.

2. A method for preparing the positive electrode slurry solvent according to claim 1, comprising the following steps: (1) Using methyl 3-methoxypropionate and dimethylamine as raw materials, an amidation reaction was carried out at a temperature of 30°C to 50°C to obtain the first mixture. (2) The first mixture is distilled to remove dimethylamine and methanol to obtain a second mixture; (3) Cool the second mixture to -20℃ to 20℃, add acid solution, and control the temperature of the second mixture to within 20℃ during the acid addition process. Adjust the pH of the second mixture to 4 to 5 and then carry out distillation. The vacuum degree is -0.09MPa to -0.1MPa. Raise the temperature to 115℃ to 140℃ and adjust the reflux ratio to (2 to 7):

1. Collect the fraction in the temperature range of 110℃ to 125℃ to obtain the positive electrode slurry solvent.

3. A positive electrode slurry, comprising the positive electrode slurry solvent of claim 1 or the positive electrode slurry solvent prepared by the preparation method of claim 2, wherein the positive electrode slurry further comprises a positive electrode active material, a binder and a conductive agent.

4. The positive electrode slurry according to claim 3, wherein, Based on the mass of the positive electrode slurry, the solid content of the positive electrode slurry is B, where 50% ≤ B ≤ 80%.

5. The positive electrode slurry according to claim 3, wherein, The positive electrode active material is selected from at least one of Li a (Ni x Co y M 1-x-y )O2, LiFe 1-m D m PO4, sodium iron nickel manganese, sodium vanadium phosphate, Prussian white; wherein, 0.5 ≤ a ≤ 1.3, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 6. The positive electrode slurry according to claim 5, wherein, The positive electrode active material is selected from Li a (Ni x Co y M 1-x-y )O2, when 0.7 < x ≤ 1, 0.025% ≤ A ≤ 0.2% and [B / (1 - B)]×0.02% ≤ A ≤ [B / (1 - B)]×0.1%; when 0 ≤ x ≤ 0.7, 0.001% ≤ A ≤ [B / (1 - B)]×0.02%.

7. The positive electrode slurry according to claim 5, wherein, The positive electrode active material is selected from LiFe 1-m D m PO4, the positive electrode slurry also includes lithium supplementer Li. 5b+2c Fe b N c O 4b+2c N is selected from at least one of Ni, Co, and Mn, 0.5 ≤ b ≤ 1, 0 ≤ c ≤ 0.5, and b + c = 1; based on the mass of the positive electrode active material, the lithium supplementer Li 5b+2c Fe b N c O 4b+2c The mass percentage content is C, where 0 ≤ C ≤ 1%.

8. The positive electrode slurry according to claim 7, wherein, When 0 ≤ C < 0.4%, 0.001% ≤ A ≤ [B / (1-B)] × 0.02%; when 0.4% ≤ C ≤ 1%, [B / (1-B)] × C × 0.02 ≤ A ≤ [B / (1-B)] × C × 0.

05.

9. A secondary battery comprising a positive electrode sheet prepared from the positive electrode slurry according to any one of claims 3 to 8.

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