Preparation method of lithium ion battery and lithium ion battery

Abstract

The invention belongs to the technical field of lithium ion battery production, and relates to a preparation method of a lithium ion battery and the lithium ion battery, the preparation method comprises the following steps: respectively preparing a positive pole piece and a negative pole piece; the method comprises the following steps: mixing a lithium salt, a lithium salt ligand, a film-forming additive and a solvent in proportion to prepare eutectic electrolyte; sequentially stacking a positive electrode, a separator and a negative electrode, injecting the eutectic electrolyte, and standing; and finally performing formation and drying treatment. By introducing the low-viscosity solvent (the viscosity is less than or equal to 0.7 cp), the problems of low ion migration rate, poor electrode wettability, large internal resistance and the like caused by overhigh viscosity of the traditional eutectic electrolyte are effectively solved; and meanwhile, a stable and compact solid electrolyte interface film (SEI film) is formed on the surface of the electrode by utilizing the film-forming additive, so that the cycling stability and the interface compatibility of the battery are improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery production technology, and in particular to a method for preparing a lithium-ion battery and a lithium-ion battery. Background Technology

[0002] As lithium-ion batteries develop towards higher energy density, higher power density, and wider temperature ranges, the electrolyte, as a core component, must possess high thermal stability, a wide electrochemical window, and efficient ion transport capabilities. Eutectic electrolytes, with their unique solvation structures (such as hydrogen bond networks or ion coordination), exhibit low volatility, high safety, and adaptability to extreme temperature / voltage environments, making them potential candidate materials for high-voltage and high-temperature battery systems. However, the dense solvation network formed by strong intermolecular forces in eutectic electrolytes results in significantly high viscosity. This inherent defect severely limits practical applications: high viscosity not only reduces electrolyte flowability and ion migration rate, increases battery internal resistance, and weakens rate performance, but also leads to poor interfacial contact and intensified polarization due to insufficient wettability of electrode materials. Furthermore, for high-energy-density systems such as silicon-based anodes and lithium metal anodes, traditional eutectic electrolytes lack effective control over the electrode / electrolyte interface, making it difficult to suppress the volume expansion effect of silicon anodes or the dendrite growth problem of lithium metal. Such highly active anode surfaces are prone to forming unstable solid electrolyte interphase (SEI) films, leading to loss of active materials, intensified interfacial side reactions, and rapid degradation of cycle performance.

[0003] Most existing systems are designed around lithium salts and coordination solvents, lacking the introduction of film-forming additives. As a result, although they have excellent bulk stability, they are not good at electrode interface control. Other studies have tried to introduce film-forming components, but have failed to combine them with a suitable "formation first, drying later" process. This makes it difficult for additive molecules to be effectively reconstructed on the electrode surface and form a dense and stable SEI layer, thus limiting their actual performance in high-energy-density batteries.

[0004] Therefore, without sacrificing the thermal stability and electrochemical window of the eutectic electrolyte, optimizing the ion transport behavior and interface of the eutectic electrolyte through the rational selection of solvent systems and the introduction of specific film-forming additives, combined with a "formation first, drying later" process route, is key to improving the overall performance of lithium-ion batteries. This method not only effectively improves the kinetic characteristics of the electrolyte but also forms an interfacial protective layer with high mechanical strength and ion conductivity, which is crucial for improving the cycle performance of lithium-ion batteries. Summary of the Invention

[0005] To address the aforementioned problems, this invention discloses a method for preparing a lithium-ion battery and a lithium-ion battery itself. The technical solution of this invention is implemented as follows:

[0006] The first aspect of this invention discloses a method for preparing a lithium-ion battery, the method comprising:

[0007] S1. Prepare the positive electrode and the negative electrode respectively;

[0008] S2. A eutectic electrolyte is obtained by mixing lithium salt, lithium salt ligand, film-forming additive and solvent in a certain proportion.

[0009] S3. Stack the positive electrode, the separator, and the negative electrode in sequence, then inject the eutectic electrolyte and let it stand.

[0010] S4, transformation;

[0011] S5. Drying.

[0012] Furthermore, the positive electrode sheet includes a positive current collector and a positive active material layer, wherein the positive active material layer includes a positive active material, a conductive agent, a binder; and / or

[0013] The negative electrode sheet is a lithium metal negative electrode or is composed of a structure including a negative electrode current collector and a negative electrode active material layer;

[0014] The negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder.

[0015] Furthermore, the film-forming additive includes one or more of the following: vinylene carbonate, vinyl sulfate, fluorovinyl carbonate, propylene carbonate, methane disulfonate, tris(trimethylsilane) phosphate, vinyl sulfite, and propylene sulfite.

[0016] Furthermore, the lithium salt includes one or more of LiTFSI, LiFSI, LiNO3, LiOTf, LiCl, LiDFOB, LiClO4, LiBr, LiI, LiSCN, LiBF4, LiAsF6, LiPF6, LiPO4F2, LiCF3SO3, and LiBETI.

[0017] Furthermore, the lithium salt ligand includes one or more of sulfones, urea, amides, nitriles, alcohols, imidazoles and their derivatives, and crown ethers. The lithium salt ligand and lithium salt are mixed to form a eutectic, which is then mixed evenly with film-forming additives and solvents to obtain a eutectic electrolyte.

[0018] The lithium salt ligands refer to organic molecules containing lone pairs of electrons or polarizable functional groups (such as carbonyl, nitrile, hydroxyl, etc.). They can disrupt the crystal structure of lithium salts by coordinating with lithium ions in lithium salts, forming eutectic mixtures through hydrogen bonding or ion-dipole interactions, thus forming eutectic mixtures.

[0019] Furthermore, the viscosity of the solvent at 25°C is ≤0.7cp.

[0020] Furthermore, the solvent includes one or more of acetonitrile, fluoroacetonitrile, propionitrile, dimethyl carbonate, ethyl acetate, ethyl propionate, diethyl carbonate, methyl formate, methyl acetate, isopropyl acetate, diethyl ether, and dimethoxymethane.

[0021] Furthermore, the mass ratio of the lithium salt, lithium salt ligand, and film-forming additive is (38%–70%): (29%–60%): (1%–25%).

[0022] Furthermore, the solvent accounts for 40% to 70% of the electrolyte by mass.

[0023] A second aspect of the present invention discloses a lithium-ion battery, which can be prepared by the preparation method described above.

[0024] The advantages of this invention are as follows:

[0025] The lithium-ion battery preparation method disclosed in this application incorporates film-forming additives and low-viscosity solvents during the preparation of the lithium-ion battery eutectic electrolyte, and combines this with a "formation first, drying later" process to synergistically solve the problems of high viscosity and interfacial instability. The traditional "dry first, formation later" process removes the solvent before any protection is formed at the electrode interface, resulting in the high-viscosity eutectic system directly contacting the electrode. This leads to insufficient wetting, violent and uncontrollable initial interfacial reactions, and difficulty in forming a uniform and stable SEI film. In contrast, the "formation first" step in this method, aided by a low-viscosity solvent, allows the electrolyte to fully wet the electrode, ensuring that the film-forming additives preferentially and uniformly reduce on the electrode surface during formation, constructing a stable and dense SEI film. This effectively suppresses interfacial side reactions and structural degradation during cycling. The low-viscosity solvent reduces the electrolyte viscosity, improves ion migration rate and wettability to porous electrodes, ensuring smooth lithium-ion migration and uniform SEI film formation. After formation, the remaining solvent is removed by drying, which not only preserves the inherent high safety and thermal stability of the eutectic electrolyte, but also avoids the risk of decomposition caused by long-term solvent residue.

[0026] This method optimizes lithium-ion transport and interface stability without disrupting the solvation structure of the eutectic electrolyte, significantly reducing interface impedance and thus improving the rate performance and cycle life of the battery. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only one embodiment of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 The graphs show the capacity retention test results of Embodiment 1 and Comparative Example 1 at 0.33C.

[0029] Figure 2 These are XPS test images of the negative electrode sheets after formation in Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0030] The technical solutions of the present invention will now be clearly and completely described with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used in the detailed description is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0032] The term "one or more" in this invention refers to the selection of one of the listed elements as a technical solution, or the selection of two or more mixed elements as a technical solution. Since the listed elements have similar physicochemical properties, they will not react chemically with each other. Those skilled in the art can choose appropriate mixed elements or single elements according to actual needs. This invention does not impose any restrictions on this.

[0033] In this invention, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0034] While ensuring the thermal stability or electrochemical window of the eutectic electrolyte, selecting appropriate solvents and additives is crucial for optimizing the ion transport kinetics of the eutectic electrolyte, constructing a stable interfacial film, and improving the cycle performance of lithium-ion batteries.

[0035] To address the above problems, this application proposes a technical solution.

[0036] The first aspect of this invention discloses a method for preparing a lithium-ion battery, the method comprising:

[0037] S1. Prepare the positive electrode and the negative electrode respectively;

[0038] S2. A eutectic electrolyte is obtained by mixing lithium salt, lithium salt ligand, film-forming additive and solvent in a certain proportion.

[0039] S3. Stack the positive electrode, the separator, and the negative electrode in sequence, then inject the eutectic electrolyte and let it stand.

[0040] S4, transformation;

[0041] S5. Drying.

[0042] This invention employs a "formation-follow-solvent drying" method. During the preparation of the lithium-ion battery eutectic electrolyte, film-forming additives and a low-viscosity solvent are added. During formation, the high fluidity of the low-viscosity solvent ensures that the eutectic electrolyte fully wets the electrode material. In this process, the film-forming additives function uniformly, forming a stable and dense SEI film on the electrode surface, effectively suppressing interfacial side reactions and structural degradation during cycling. After the SEI film forms, the remaining solvent is removed through a drying step, preserving the inherent high safety and thermal stability of the eutectic electrolyte while avoiding the risk of decomposition side reactions that may be caused by long-term solvent residue.

[0043] It should be noted that in this invention, the solvent does not react with lithium salts and lithium salt ligands, and the additives also do not react with lithium salts and lithium salt ligands.

[0044] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer, wherein the positive active material layer includes a positive active material, a conductive agent, a binder; and / or

[0045] The negative electrode sheet is a lithium metal negative electrode or is composed of a structure including a negative electrode current collector and a negative electrode active material layer;

[0046] The negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder.

[0047] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0048] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0049] In some embodiments, the positive electrode active material may be a known positive electrode active material for batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0050] In some embodiments, the positive electrode active material layer may optionally include a binder. As examples, the binder may include at least one of vinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), nitrile butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR), styrene-ethylene-butene-styrene copolymer (SEBS), styrene-butadiene-styrene copolymer (SBS), polyacrylic acid (PAA), lithium polyacrylate (LiPAA), sodium polyacrylate (NaPAA), sodium alginate, and lithium alginate.

[0051] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0052] In some specific implementations, the specific type of negative electrode active material is not limited and can be selected according to requirements. Specifically, the negative electrode active material is selected from natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), 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 One or more of Li-Al alloys. Non-limiting examples of carbon materials include crystalline carbon, amorphous carbon, and mixtures thereof. Crystalline carbon can be amorphous or flake-shaped, small flake-shaped, spherical, or fibrous natural or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbides, calcined coke, etc.

[0053] In some specific implementations, elemental metals and metal compounds can also be selected as negative electrode active materials, such as compounds containing metals or metalloids such as Li, Ag, Al, Bi, Cu, Ga, Ge, In, Ni, Pb, Sb, Si, Sn, Sr, and Zn.

[0054] In some specific embodiments, the mass percentage of the negative electrode active material contained in the negative electrode active material layer can be 80%-99%, for example, 80%, 85%, 90%, 95%, 97%, 99%, etc., preferably 95%-97%.

[0055] In some specific embodiments, the negative electrode active material layer may include a binder; the binder improves the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector.

[0056] In some specific embodiments, non-limiting examples of adhesives include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0057] In some specific embodiments, the negative electrode active material layer can be obtained by coating a negative electrode slurry onto a negative electrode current collector and then performing operations such as drying. The negative electrode slurry includes at least a negative electrode active material and a negative electrode binder. When an aqueous solvent is used as the liquid medium for forming the negative electrode slurry, a thickener is preferably used for slurry formation. The thickener is typically used to adjust the viscosity of the slurry.

[0058] In some specific embodiments, the aforementioned thickener may be one or more of the following: carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein and their salts, etc.

[0059] In some specific embodiments, the mass percentage of the thickener in the negative electrode slurry can be 0.1%-5%, for example, 0.1%, 0.2%, 0.5%, 0.6%, 1%, 2%, 3%, 4%, 5%, etc., preferably 0.5%-3%, and more preferably 0.6%-2%.

[0060] In some specific embodiments, the negative electrode active material layer includes a conductive material, thereby making the electrode conductive. This conductive material can include any conductive material as long as it does not cause a chemical change. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powders, metal fibers, such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0061] In some specific embodiments, the negative current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0062] Preferably, the negative electrode is a lithium metal electrode.

[0063] The present invention does not impose any particular restrictions on the material and shape of the separator used in the battery, which can be any technology disclosed in the prior art.

[0064] It is understood that a separator is a component that isolates the positive and negative electrodes, preventing electrons from forming a path between them and causing a short circuit. This application does not specifically limit the separator; any known separator can be used in this application without departing from the inventive concept. The separator may be a diaphragm or a solid electrolyte membrane, as illustrated merely as an illustrative example and not a limitation on the scope of protection.

[0065] The separator typically has a porous structure, which can provide a lithium-ion transport channel. The separator can be one of PE, PP, PE / PP, PP / PE / PP, or PE / PP / PE.

[0066] Solid electrolyte membranes are formed from solid electrolyte materials and can be one or more of the following: oxide solid electrolytes, sulfide solid electrolytes, halide solid electrolytes, polymer solid electrolytes, and boride solid electrolytes.

[0067] In some embodiments, the film-forming additive includes one or more of vinylene carbonate, vinyl sulfate, fluorovinyl carbonate, propylene carbonate, methane disulfonate, tris(trimethylsilane) phosphate, vinyl sulfite, and propylene sulfite.

[0068] By using the aforementioned additives, a dense and stable SEI film can be formed on the electrode surface, especially on the surface of silicon-based or lithium metal anodes. This SEI film can effectively suppress the continuous decomposition of the electrolyte, alleviate the volume effect of the silicon anode, and hinder the uncontrolled growth of lithium dendrites, thereby significantly reducing interfacial impedance, reducing the loss of active lithium and active materials during cycling, and ultimately improving the coulombic efficiency and long-cycle stability of the battery.

[0069] In some embodiments, the lithium salt includes one or more of LiTFSI, LiFSI, LiNO3, LiOTf, LiCl, LiDFOB, LiClO4, LiBr, LiI, LiSCN, LiBF4, LiAsF6, LiPF6, LiPO4F2, LiCF3SO3, and LiBETI.

[0070] In some embodiments, the lithium salt ligand includes one or more of sulfones, urea, amides, nitriles, alcohols, imidazoles and their derivatives, and crown ethers. The lithium salt ligand and lithium salt are mixed to form a eutectic, which is then mixed evenly with film-forming additives and solvents to obtain a eutectic electrolyte.

[0071] It is understood that this application does not have any particular requirements regarding the mixing order of lithium salt, lithium salt ligand, film-forming additive, and solvent to obtain a eutectic solution. Preferably, lithium salt and lithium salt ligand are premixed to form a eutectic, and then mixed with solvent and film-forming additive, or the obtained premixed solution is added to a mixed solution of solvent and film-forming additive for mixing; alternatively, lithium salt, lithium salt ligand, film-forming additive, and solvent can be directly mixed; furthermore, either lithium salt or lithium salt ligand can be first mixed with solvent and film-forming additive to obtain a premixed solution, and then the other can be added to the premixed solution.

[0072] It is understood that the technical solutions obtained by simply making conventional adjustments to the mixing order should still be considered within the scope of protection of this application.

[0073] In some embodiments, the solvent has a viscosity of ≤0.7cp at 25°C.

[0074] In some embodiments, the solvent includes one or more of acetonitrile, fluoroacetonitrile, propionitrile, dimethyl carbonate, ethyl acetate, ethyl propionate, diethyl carbonate, methyl formate, methyl acetate, isopropyl acetate, diethyl ether, and dimethoxymethane.

[0075] The introduction of low-viscosity solvents reduces the overall viscosity of the eutectic electrolyte, which not only improves the migration rate and transport efficiency of lithium ions, giving the battery excellent rate performance, but also ensures that the electrolyte can quickly and uniformly wet the entire porous electrode. This effectively solves the common problem of insufficient electrode wetting in high-viscosity eutectic electrolytes, reduces interfacial impedance, improves the stability of the SEI film, and extends the cycle life of the battery.

[0076] In some embodiments, the mass ratio of the lithium salt, lithium salt ligand, and film-forming additive is (38%–70%):(29%–60%):(1%–25%).

[0077] In practical applications, the mass ratio of lithium salt, lithium salt ligand, and film-forming additive can be selected as 38%:29%:1%, 38%:29%:5%, 38%:29%:10%, 38%:29%:10%, 38%:29%:25%, 40%:29%:1%, 40%:29%:5%, 40%:29%:10%, 45%:30%:1%, 45%:35%:5%, 50%:29%:5%, etc. The numerical ratios listed above are merely examples and not limitations. Those skilled in the art can freely implement any numerical ratio within the range of (38%–70%):(29%–60%):(1%–25%) without exceeding their understanding. Furthermore, it should be noted that when actually preparing the eutectic electrolyte, the lithium salt, lithium salt ligand, and film-forming additive weighed according to the above ratios must be mixed with the solvent. Therefore, the sum of the actual mass percentages of these three components in the final eutectic electrolyte must be less than 100%, with the remainder consisting of solvent.

[0078] In some preferred embodiments, the solvent accounts for 40% to 70% of the electrolyte by mass.

[0079] In specific applications, the mass ratio of solvent in electrolyte can be selected as 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, etc. The values ​​listed above are only examples and are not limitations. Without exceeding the understanding of those skilled in the art, those skilled in the art are free to implement any value in the range of 40% to 70%.

[0080] In some embodiments, the eutectic electrolyte is prepared as follows:

[0081] In a dehumidified environment with a dew point below -40°C, lithium salt, lithium salt ligand, and film-forming additives are mixed at a mass ratio of (38–70):(29–60):(1–25) and stirred at 45°C–80°C for 5–10 hours to obtain a eutectic electrolyte. The eutectic electrolyte and solvent are then mixed and stirred at room temperature at a mass ratio of (30–60):(40–70) for 3 hours to obtain a eutectic electrolyte solution.

[0082] In specific applications, the stirring temperature for obtaining the eutectic electrolyte can be selected from 45℃, 48℃, 50℃, 52℃, 53℃, 55℃, 58℃, 60℃, 62℃, 65℃, 68℃, 70℃, 72℃, 75℃, 78℃, 80℃, etc.; the stirring time can be selected from 5h, 6h, 8h, 10h, etc.; the values ​​listed above are examples and are not limitations.

[0083] In some embodiments, the positive electrode sheet in S1 is prepared as follows:

[0084] The positive electrode active material, conductive agent, and binder are added to an appropriate amount of solvent (such as NMP) in a mass ratio of (95-98):(1-3):(1-2). The mixture is then stirred to form a uniform positive electrode slurry with a solid content of 40%-60%. The positive electrode slurry is then coated onto the positive electrode current collector, with a coating surface density of 200 g / m³. 2 ~550g / m 2 Subsequently, it was transferred to a vacuum oven and dried at 90℃~120℃ for 8h~16h. After drying, it was rolled (compacted density 2.6g / cm³). 3 ~3.5g / cm 3 After slitting, the positive electrode sheet is obtained. The die-cut electrode sheet is transferred to a vacuum oven and baked at 80℃~120℃ for 8h~48h until the moisture content of the positive electrode is <100ppm.

[0085] In specific applications, the mass ratio of the positive electrode active material, conductive agent, and binder can be selected as 95:3:2, 96:3:1, 96:2:2, 97:1:2, 97:2:1, 98:1:1, etc.; the solid content of the positive electrode slurry can be selected as 40%, 41%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, etc.; and the coating surface density of the positive electrode slurry can be selected as 200 g / m². 2 220g / m 2 250g / m 2 280g / m 2 300g / m 2 320g / m 2 350g / m 2 380g / m 2 400g / m 2 420g / m 2 450g / m 2 480g / m 2 500g / m 2 550g / m 2 The drying temperature of the positive electrode slurry can be selected from 90℃, 100℃, 110℃, 120℃, etc.; the drying time of the positive electrode slurry can be selected from 8h, 9h, 10h, 12h, 15h, 16h, etc.; the compaction density of the positive electrode slurry can be selected from 2.6g / cm³, 2.7g / cm³, 2.8g / cm³, 3g / cm³, 3.2g / cm³, etc. 3 3.3g / cm 3 3.5g / cm 3The baking temperature of the positive electrode sheet can be selected from 80℃, 90℃, 100℃, 110℃, 120℃, etc.; the baking time of the positive electrode sheet can be selected from 8h, 9h, 10h, 12h, 15h, 18h, 20h, 25h, 28h, 30h, 35h, 38h, 40h, 45h, 48h, etc. The values ​​listed above are examples and are not limitations.

[0086] In some embodiments, the negative electrode sheet in S1 is prepared as follows:

[0087] The negative electrode active material, conductive agent, and binder are mixed in a mass ratio of (92-96):(0.5-2):(3.5-6) ​​and added to an appropriate amount of solvent to form a uniform negative electrode slurry with a solid content of 30%-50%. The slurry is then coated onto the negative electrode current collector, with a coating surface density of 50 g / m². 2 ~200g / m 2 Subsequently, it was transferred to a vacuum oven and dried at 80℃~110℃ for 8h~16h. After drying, it was rolled (compacted density 1g / cm³). 3 ~1.5g / cm 3 After slitting, negative electrode sheets are obtained. The die-cut electrode sheets are transferred to a vacuum oven and baked at 80℃~100℃ for 8h~48h until the moisture content of the negative electrode is <150ppm.

[0088] In specific applications, the mass ratio of the negative electrode active material, conductive agent, and binder can be selected as 92:2:6, 93:1:6, 93:2:5, 94:0.5:5.5, 94:1:5, 94:2:4, 95:0.5:4.5, 95:1.5:3.5, 95:2:3, 96:0.5:3.5, etc.; the solid content of the negative electrode slurry can be selected as 30%, 31%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, etc.; the coating surface density of the negative electrode slurry can be selected as 50 g / m². 2 80g / m 2 100g / m 2 120g / m 2 140g / m 2 150g / m 2 180g / m 2 200g / m 2 The drying temperature of the negative electrode slurry can be selected from 80℃, 90℃, 100℃, 110℃, etc.; the drying time of the negative electrode slurry can be selected from 8h, 9h, 10h, 12h, 15h, 16h, etc.; the compaction density of the negative electrode slurry can be selected from 1g / cm³, 1.1g / cm³, 1.2g / cm³, 1.3g / cm³, 1.4g / cm³, etc. 3 1.5g / cm3 The baking temperature of the negative electrode sheet can be selected as 80℃, 90℃, 100℃, etc.; the baking time of the negative electrode sheet can be selected as 8h, 9h, 10h, 12h, 15h, 18h, 20h, 25h, 28h, 30h, 35h, 38h, 40h, 45h, 48h, etc. The values ​​listed above are examples and are not limitations.

[0089] In some embodiments, in step S3, the battery after electrolyte injection is allowed to stand to ensure that the electrolyte fully wets the electrodes and separator. The standing conditions can be: standing at 25℃~45℃ for 24h~72h. In specific implementations, the standing temperature can be selected as 25℃, 30℃, 35℃, 40℃, 45℃, etc.; the standing time can be selected as 24h, 25h, 28h, 30h, 35h, 38h, 40h, 45h, 48h, 50h, 55h, 58h, 60h, 62h, 65h, 68h, 70h, 72h, etc. The values ​​listed above are only examples and are not limitations.

[0090] In some embodiments, the formation of S4 is performed using conventional methods in the art. For example, the lithium-ion battery after being immersed in electrolyte can be formed by a charge-discharge process: constant current charging at 0.05C to 3.85V at room temperature (25°C); standing for 30 minutes; constant current and constant voltage charging at 0.1C to 4.3V at room temperature (25°C), with a cutoff current of 0.05C; standing for 30 minutes; constant current discharging at 0.1C to 2.5V at room temperature (25°C).

[0091] After formation and before drying, the process includes a gas bag cutting and transfer step. Specifically, the formed battery is placed in a dehumidified environment with a dew point below -40°C, and the gas bag seal is cut open. The battery is then transferred to a vacuum oven for drying.

[0092] In some embodiments, the S5 drying step is performed under vacuum, specifically by controlling the vacuum level to be below 800 Pa and baking at a temperature of 45°C to 80°C for 24 to 48 hours. This process ensures that the remaining mass percentage of low-viscosity solvent within the battery is less than 1%, thereby essentially completely removing the free solvent and retaining only the functional eutectic electrolyte system.

[0093] As a non-limiting example, the vacuum baking temperature can be selected from 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, or 80℃; the baking time can be selected from 24h, 30h, 36h, 40h, or 48h. Those skilled in the art should understand that the specific values ​​listed above are merely examples to help understand this embodiment and are not intended to limit the scope of protection of this application. In practical applications, any adjustments and combinations can be made within the above range.

[0094] A second aspect of the present invention discloses a lithium-ion battery, which can be prepared by the preparation method described above.

[0095] The technical solution of the present invention will be described in more detail below through examples and comparative examples.

[0096] Example 1:

[0097] The cathode preparation process is as follows:

[0098] Li 1.2 Ni 0.2 Mn 0.6 O2, super-p, and PVDF were added to NMP solvent at a mass ratio of 97:2:1 to form a uniform positive electrode slurry. This slurry was then coated onto aluminum foil and transferred to a vacuum oven for drying at 100°C for 12 hours. After drying, the foil was rolled and slit to obtain the positive electrode sheet. The die-cut electrode sheet was then transferred to a vacuum oven and baked at 90°C for 24 hours until the moisture content of the positive electrode was <100 ppm.

[0099] The anode preparation process is as follows:

[0100] Silicon-carbon, Super-P, and CMC+SBR were mixed in deionized water at a mass ratio of 93:2:5 to form a uniform negative electrode slurry. This slurry was then coated onto copper foil and transferred to a vacuum oven, where it was dried at 90°C for 14 hours. After drying, the foil was rolled and slit to obtain the negative electrode sheet. The die-cut electrode sheet was then transferred to a vacuum oven and baked at 90°C for 24 hours until the moisture content of the negative electrode was <150 ppm.

[0101] The preparation process of the eutectic electrolyte is as follows:

[0102] Under an environment with a dew point below -40°C, LiTFSI, polyethersulfone (PES), and additive FEC were mixed in a mass ratio of 2:2:1 and stirred at 50°C for 8 hours to obtain a eutectic electrolyte. The eutectic electrolyte was then mixed with DMC in a mass ratio of 1:1 at room temperature and stirred for 3 hours to obtain a eutectic electrolyte solution.

[0103] The battery assembly process is as follows:

[0104] The positive electrode, separator, and negative electrode are stacked sequentially. After injecting the eutectic electrolyte, the cells are left to stand at 45°C for 24 hours to ensure that the electrolyte fully wets the electrodes and separator. The lithium-ion battery after electrolyte injection is formed by charging and discharging using a charge-discharge process: charged at 0.05C constant current to 3.85V at 25°C, left to stand for 30 minutes, charged at 0.1C constant current and constant voltage to 4.3V at 25°C, cut off at 0.05C, left to stand for 30 minutes, and discharged at 0.1C constant current to 2.5V at 25°C. Then, the cells are dried: in a dehumidified environment with a dew point below -40°C, the air bag is cut open and sealed, and the cells are transferred to a vacuum oven. The cells are vacuum baked at 45°C to 80°C for 24 to 48 hours in an environment with a vacuum degree <800Pa, and finally, the cells are resealed.

[0105] Example 2:

[0106] The process of preparing the lithium-ion battery in this embodiment is basically the same as that in Example 1. The difference is that this embodiment uses lithium metal material as the negative electrode, and the negative electrode does not include negative electrode active material, conductive agent and binder; in addition, the preparation process of the electrolyte in this embodiment is as follows:

[0107] Under an environment with a dew point below -40°C, LiTFSI, PES and additive FEC were mixed at a mass ratio of 19:19:12 and stirred at 50°C for 8 hours to obtain a eutectic electrolyte. The eutectic electrolyte was then mixed with DME at a mass ratio of 1:1 and stirred at room temperature for 3 hours to obtain a eutectic electrolyte solution.

[0108] Apart from the differences mentioned above, the other processes in this embodiment are exactly the same as those in Embodiment 1.

[0109] Example 3:

[0110] The process of preparing lithium-ion batteries in this embodiment is basically the same as that in Example 1, the difference being that this embodiment uses LiNi 0.8 Co 0.1 Mn 0.1 O2 is used as the positive electrode active material; in addition, the preparation process of the electrolyte in this embodiment is as follows:

[0111] In an environment with a dew point below -40°C, LiTFSI, PES and additive FEC were mixed in a mass ratio of 22.5:22.5:5 and stirred at 50°C for 8 hours to obtain a eutectic electrolyte.

[0112] Apart from the differences mentioned above, the other processes in this embodiment are exactly the same as those in Embodiment 1.

[0113] Comparative Example 1:

[0114] The process of preparing lithium-ion batteries in this comparative example is basically the same as that in Example 1, except that the electrolyte in this comparative example does not contain the additive FEC.

[0115] Apart from the differences mentioned above, the other processes in this comparative example and Example 1 are exactly the same.

[0116] Comparative Example 2:

[0117] The process of preparing lithium-ion batteries in this comparative example is basically the same as that in Example 1. The difference is that the electrolyte in this comparative example does not contain the additive FEC. In addition, the mass ratio of LiTFSI to PES in this comparative example is 2:3 when preparing the eutectic electrolyte.

[0118] Apart from the differences mentioned above, the other processes in this comparative example and Example 1 are exactly the same.

[0119] Comparative Example 3:

[0120] The process of preparing lithium-ion batteries in this comparative example is basically the same as that in Example 1, except that the electrolyte in this comparative example does not contain the additive FEC; in addition, the positive electrode active material in this comparative example is LiNi. 0.8 Co 0.1 Mn 0.1 O2.

[0121] Apart from the differences mentioned above, the other processes in this comparative example and Example 1 are exactly the same.

[0122] Comparative Example 4: The preparation process was basically the same as in Example 1. The only difference was that the battery was dried first and then formed during the battery assembly process.

[0123] Comparative experiment:

[0124] Seven groups of samples, including Examples 1-3 and Comparative Examples 1-4, were tested as follows. Each group had 20 samples. All test results were averaged, and some data were rounded.

[0125] 1. Ionic conductivity test:

[0126] The ionic conductivity of each group of samples was tested at room temperature (25℃) using an ionic conductivity meter.

[0127] 2. Charge and discharge test:

[0128] Charge the battery at 0.33C constant current and constant voltage to 4.55V at 45℃, cut off current at 0.05C, let it stand for 30 minutes, and discharge it at 0.33C constant current to 2.3V. Repeat this charge-discharge cycle 200 times and record the discharge capacity of the 200th cycle as a function of the initial discharge capacity multiplied by 100%.

[0129] The test results are shown in the table below:

[0130] In addition, the capacity retention test curves of Example 1 and Comparative Example 1 at 0.33C are shown in the figure below. Figure 1 As shown.

[0131]

[0132] XPS characterization curves of the negative electrode sheets after formation in Example 1 and Comparative Example 1 are shown below. Figure 2 As shown.

[0133] according to Figure 1 , Figure 2 As can be seen, Example 1, by adding the film-forming additive FEC during the preparation of the lithium-ion battery eutectic electrolyte and then adding the low-viscosity solvent DMC, allows FEC to preferentially decompose on the negative electrode surface during formation, forming a LiF-rich inorganic / organic composite SEI film, thus stabilizing the electrode interface. Simultaneously, the "formation first, solvent drying later" method utilizes the fluidity of the low-viscosity solvent during formation to better wet the electrode material with the eutectic electrolyte, ensuring a uniform SEI film with a stable LiF-rich composition, suppressing interface degradation during cycling, and achieving interface optimization. The drying process removes the solvent, preserving the characteristics of the eutectic electrolyte.

[0134] As shown in the table above, the examples demonstrate improvements in both ionic conductivity and cycle capacity retention compared to the comparative examples. This result verifies the effectiveness of the synergistic effect of the "film-forming additive + low-viscosity solvent" and "formation before drying" processes in this invention. The introduction of the low-viscosity solvent significantly improves the ionic conductivity of the examples, ensuring faster lithium-ion transport between the electrode and electrolyte, thereby enhancing the battery's rate performance and charge / discharge efficiency. The "formation before drying" process ensures that the film-forming additive reacts preferentially and uniformly on the electrode surface before solvent removal, forming a dense and stable SEI film. Compared to the "drying before formation" process, this method produces a superior SEI film structure, reduces interfacial impedance, and improves the battery's cycle capacity retention.

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

Claims

1. A method of producing a lithium ion battery, characterized by, The preparation method comprises: S1, respectively preparing a positive electrode sheet and a negative electrode sheet; S2, mixing lithium salt, lithium salt ligand, film-forming additive and solvent in proportion to obtain a eutectic electrolyte; S3, sequentially stacking the positive electrode, the separator and the negative electrode in order, then injecting the eutectic electrolyte and standing; S4, formation; S5, drying.

2. The method of claim 1, wherein the lithium ion battery is a lithium ion battery for a hybrid electric vehicle. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer comprises a positive electrode active material, a conductive agent and a binder; and / or The negative electrode sheet is a lithium metal negative electrode or is composed of a structure comprising a negative electrode current collector and a negative electrode active material layer; The negative electrode active material layer comprises a negative electrode active material, a conductive agent and a binder.

3. The method for preparing a lithium-ion battery according to claim 1, characterized in that, The film-forming additive comprises one or more of vinylene carbonate, vinyl sulfate, fluorinated vinyl carbonate, propylene carbonate, methane disulfonate methylene, tris(trimethylsilyl) phosphate, vinyl sulfite and propylene sulfite.

4. The method for preparing a lithium-ion battery according to claim 1, characterized in that, The lithium salt comprises one or more of LiTFSI, LiFSI, LiNO3, LiOTf, LiCl, LiDFOB, LiClO4, LiBr, LiI, LiSCN, LiBF4, LiAsF6, LiPF6, LiPO4F2, LiCF3SO3 and LiBETI.

5. The method of claim 1, wherein the lithium ion battery is a lithium ion battery for a hybrid electric vehicle. The lithium salt ligand comprises one or more of sulfone, urea, amide, nitrile, alcohol, imidazole and its derivatives, and crown ether; the lithium salt ligand and lithium salt are mixed to form a eutectic.

6. The method of claim 1, wherein the lithium ion battery is a lithium ion battery for a hybrid electric vehicle. The viscosity of the solvent at 25 DEG C is ≤0.7 cp.

7. The method for preparing a lithium-ion battery according to claim 6, characterized in that, The solvent comprises one or more of acetonitrile, fluorinated acetonitrile, propionitrile, dimethyl carbonate, ethyl acetate, ethyl propionate, diethyl carbonate, methyl formate, methyl acetate, isopropyl acetate, diethyl ether and dimethoxy methane.

8. The method of claim 1, wherein the lithium ion battery is a lithium ion battery for electric vehicles. The mass ratio of the lithium salt, the lithium salt ligand and the film-forming additive is (38% to 70%):(29% to 60%):(1% to 25%).

9. The method of claim 1, wherein the lithium ion battery is a lithium ion capacitor. The mass ratio of the solvent in the electrolyte is 40% to 70%.

10. A lithium-ion battery, characterized by, The lithium ion battery is prepared by the method of any one of claims 1 to 9.

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