Electrolyte and lithium battery

Abstract

The invention provides an electrolyte and a lithium battery. Specifically, the electrolyte comprises an unsaturated double-bond polymer monomer, an initiator and an additive, wherein the structural formula of the additive is as shown in formula (I); in the formula (I), R1 and R2 are the same or different and are independently selected from H, C1-C4 straight chain or branched chain alkyl; wherein based on the total mass of the electrolyte, the mass fraction of the additive is 0.1%-1%. According to the electrolyte and the additive, the mechanical property of a polymer skeleton can be enhanced, lithium ion transmission kinetics can be optimized, interface failure and side reaction can be effectively inhibited while rapid charging of the battery is realized, and high safety of the battery is ensured.

Description

Technical Field

[0001] This disclosure relates to the field of battery technology, and more particularly to an electrolyte and a lithium battery. Background Technology

[0002] In-situ solidification technology refers to injecting a liquid precursor containing polymer monomers, initiators, etc., into the battery. Through heating or ultraviolet irradiation, the precursor polymerizes in situ within the battery to form a gel-like solid electrolyte, thus achieving the transformation from liquid to solid state. Currently, semi-solid-state batteries using in-situ solidification technology generally pursue excellent safety performance at high energy density. However, the presence of the solidified polymer backbone makes it difficult to balance electrical performance and safety performance. Summary of the Invention

[0003] In view of this, the purpose of this disclosure is to provide an electrolyte and a lithium battery.

[0004] For the purposes described above, the first aspect of this disclosure provides an electrolyte comprising an unsaturated double-bonded polymer monomer, an initiator, and an additive; wherein the additive has the structural formula shown in formula (I): (I); In formula (Ⅰ), R1 and R2 may be the same or different, and each is independently selected from: H, C1-C4 straight-chain or branched alkyl; The additive has a mass fraction of 0.5% to 1% based on the total mass of the electrolyte.

[0005] In some embodiments, the additive has the following structural formula: (II).

[0006] In some embodiments, the unsaturated double-bonded polymer monomer is selected from any one or a combination of at least two of methyl methacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, acrylonitrile, vinylene carbonate, ethylene oxide, or 1,3-dioxolane.

[0007] In some embodiments, the mass fraction of the unsaturated double-bonded polymer monomer is 2% to 5% based on the total mass of the electrolyte.

[0008] In some embodiments, the initiator has a mass fraction of 0.05% to 1% based on the total mass of the unsaturated double-bonded polymer monomer and the additive.

[0009] In some embodiments, the mass ratio of the additive to the unsaturated double-bonded polymer monomer is not greater than 0.5 and not less than 0.1.

[0010] In some embodiments, an organic solvent is also included, said organic solvent comprising carboxylic esters and carbonates; The carboxylic acid ester includes any one or a combination of at least two of ethyl acetate, methyl acetate, methyl formate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, propyl butyrate, butyl butyrate, isopropyl acetate, and isoamyl acetate; the carbonate includes any one or a combination of at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. The mass fraction of the carboxylic acid ester is 4% to 40% based on the total mass of the electrolyte.

[0011] In some embodiments, the electrolyte further comprises a lithium salt, which includes any one or a combination of at least two of LiFSI, LiTFSI, LiPF6, LiBF4, LiClO4 or LiAsF6; The lithium salt has a mass fraction of 8% to 20% based on the total mass of the electrolyte.

[0012] In some embodiments, the electrolyte further includes fluoroethylene carbonate; Wherein, based on the total mass of the electrolyte, the mass fraction of the fluoroethylene carbonate is not higher than 20%.

[0013] In some embodiments, the invention further includes unsaturated additives; wherein the unsaturated additives include at least one or a combination of at least two of cyclic carbonate additives, cyclic sulfonyl lactone additives, and cyclic sulfate additives. The cyclic carbonate additive includes any one or a combination of at least two of vinylene carbonate and ethylene ethylene carbonate. The cyclic sulfonyl lactone additive includes any one or a combination of at least two of 1,3-propane sulfonyl lactone and / or 1,3-propene sulfonyl lactone. The cyclic sulfate additive includes vinyl sulfate; Wherein, based on the total mass of the electrolyte, the mass fraction of the unsaturated additive is not less than 0.2% and not more than 3%.

[0014] In some embodiments, a lithium salt additive is further included; wherein the lithium salt additive includes any one or a combination of at least two of lithium difluorophosphate, lithium dioxalate borate, lithium tetrafluoroborate, or lithium difluorooxalate phosphate. Wherein, based on the total mass of the electrolyte, the mass fraction of the lithium salt additive is not less than 0.05% and not more than 1.5%.

[0015] Based on the same inventive concept, a second aspect of this disclosure also provides a lithium battery, comprising: Positive electrode, including positive electrode active material; Negative electrode, including negative electrode active material; and Electrolyte, wherein the electrolyte includes the electrolyte described in any of the first aspects; The positive electrode active material includes Li x Ni y Mn z M m O 0.5x+1.5y+1.5z+1.5m Wherein, 0.9≤x≤1.1, 0.8≤y≤1, 0≤z≤0.2, 0≤m≤0.2; and M is selected from one or more of Fe, Ti, Co, Cr, V, Cu, Zn, Zr, Al, and Nb. The negative electrode active material comprises a mixture of silicon-containing material and graphite; and based on the total mass of the negative electrode active material, the mass fraction of the silicon-containing material is not higher than 30%.

[0016] As can be seen from the above, the present disclosure provides an electrolyte and a lithium battery, wherein the electrolyte comprises an unsaturated double-bonded polymer monomer, an initiator, and an additive; wherein the structural formula of the additive is shown in formula (I): (I); In formula (I), R1 and R2 may be the same or different, and are each independently selected from: H, C1-C4 straight-chain or branched alkyl groups; wherein, based on the total mass of the electrolyte, the mass fraction of the additive is 0.1%~1%. In such an electrolyte, the additive can enhance the mechanical properties of the polymer skeleton, optimize lithium-ion transport kinetics, and effectively suppress interfacial failure and side reactions while achieving rapid battery charging, ensuring high battery safety. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments.

[0018] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this disclosure should have the ordinary meaning as understood by one of ordinary skill in the art to which this disclosure pertains.

[0019] In this disclosure, the term "range" is used to define a range in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~130 and 70~120 are listed for a specific parameter, it is expected that ranges of 60~120 and 70~130 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this disclosure, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0020] Unless otherwise specified, all embodiments and optional embodiments of this disclosure can be combined to form new technical solutions.

[0021] Unless otherwise specified, all technical features and optional technical features of this disclosure can be combined to form new technical solutions.

[0022] Unless otherwise specified, the terms "comprising" and "including" as used in this disclosure can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0023] Unless otherwise specified, the term "or" is inclusive in this disclosure. For example, the phrase "A or B" means "A, B, or both A and B".

[0024] Semi-solid-in-situ curing battery systems generally use unsaturated double-bonded monomers to construct the polymer skeleton, and cyclic carbonates (such as ethylene carbonate EC and propylene carbonate PC) and linear carbonates (such as dimethyl carbonate DMC, ethyl methyl carbonate EMC and diethyl carbonate DEC) are used as solvents. Lithium salts are mainly lithium hexafluorophosphate or lithium bisfluorosulfonyl imide. Additives often include vinylene carbonate (VC), fluoroethylene carbonate (FEC) or nitrile compounds to improve performance.

[0025] The inventors of this disclosure have noted that the polymer backbone formed by the polymerization of unsaturated monomers is prone to volume expansion during long-term cycling, leading to microcracks at the electrode / electrolyte interface and exacerbating the unevenness of lithium-ion deposition. Simultaneously, the low elastic modulus of the polymer backbone cannot effectively suppress the generation of dead lithium, and the repeated rupture-repair process of the SEI film during high-rate charge-discharge causes continuous loss of active lithium, resulting in a rapid decline in capacity retention. Furthermore, the polymer undergoes chain segment relaxation at high temperatures, reducing backbone porosity and hindering lithium-ion transport pathways, leading to an increase in polarization voltage. Moreover, the swelling effect between the polymer and the electrolyte solvent (e.g., EMC) is intensified, triggering interfacial stratification and accelerating lithium salt hydrolysis and acid production (HF concentration > 200 ppm), causing dissolution of the positive electrode CEI film and dissolution of transition metals.

[0026] In addition, semi-solid-in-situ curing batteries undergo depolymerization in the early stages of thermal runaway (120-150℃), releasing a large number of free radicals and reducing the viscosity of the system. This makes it easier for flammable solvents to crosstalk with the positive and negative electrodes, triggering violent exothermic reactions. Furthermore, existing flame retardants cannot effectively penetrate into the polymer network to suppress the chain reaction.

[0027] In view of this, embodiments of the present disclosure provide an electrolyte comprising an additive having the structural formula (I) to improve the performance defects of semi-solid-in-situ cured batteries. Specifically, by forming an interpenetrating crosslinked structure with unsaturated double-bonded monomers, the additive enhances the mechanical strength of the polymer skeleton, suppresses volume expansion and interfacial microcrack formation during cycling; and the formimino groups in the additive selectively coordinate lithium salt anions, optimizing the transport path of lithium ions in the polymer pores, alleviating the increase in ion migration resistance caused by chain segment relaxation at high temperatures, and further improving the high-temperature stability of the battery, that is, achieving improved fast-charging performance of the battery while ensuring good battery safety.

[0028] To make the technical solutions of this disclosure clearer and easier to understand, the electrolyte and lithium battery provided in this disclosure will be described in detail below with reference to specific embodiments.

[0029] electrolyte In a first aspect, embodiments of this disclosure provide an electrolyte comprising an unsaturated double-bonded polymer monomer, an initiator, and an additive; wherein the additive has the structural formula shown in formula (I): (I); In formula (Ⅰ), R1 and R2 may be the same or different, and each is independently selected from: H, C1-C4 straight-chain or branched alkyl; wherein, based on the total mass of the electrolyte, the mass fraction of the additive is 0.5%~1%.

[0030] For example, R1 and R2 can each be independently methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, or tert-butyl. For instance, R1 is methyl and R2 is ethyl; or R1 is methyl and R2 is n-propyl; or R1 is methyl and R2 is n-butyl; or R1 is ethyl and R2 is ethyl; or R1 is ethyl and R2 is isopropyl; or R1 is ethyl and R2 is sec-butyl.

[0031] For example, the mass fraction of the additive may be 0.5%, 0.6%, 0.7%, 0.8%, 0.88%, or 1%.

[0032] Here, additives can be polymerized in situ with unsaturated polymer monomers to construct an interpenetrating cross-linked polymer framework with enhanced mechanical properties. This robust framework can effectively withstand the volume change stress generated by the electrode material during charge-discharge cycles, suppress electrode volume expansion and the generation and propagation of interfacial microcracks, thereby significantly improving the structural stability and cycle life of the battery.

[0033] Furthermore, the formimide groups introduced into the additive molecular structure possess the ability to selectively coordinate lithium salt anions. This coordination weakens the binding between lithium ions and anions, optimizes the transport path of lithium ions within the polymer pores, and increases the effective lithium ion transference number. Especially at high temperatures, this effect alleviates the increase in ion migration resistance that may be caused by polymer chain relaxation, further enhancing the battery's high-temperature stability and rate performance.

[0034] In some embodiments, the additive has the following structural formula: (II).

[0035] In some embodiments, the unsaturated double-bond polymer monomer is selected from any one or a combination of at least two of methyl methacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, acrylonitrile, vinylene carbonate, ethylene oxide, or 1,3-dioxolane. Exemplarily, the unsaturated double-bond polymer monomer may be vinylene carbonate or ethylene oxide; the unsaturated double-bond polymer monomer may be a combination of methyl methacrylate and vinylene carbonate, or a combination of acrylonitrile, vinylene carbonate, and ethylene oxide, which will not be further exemplified in this disclosure.

[0036] In some embodiments, the mass fraction of unsaturated double-bonded polymer monomers is 2% to 5% based on the total mass of the electrolyte, for example, 2.0%, 3.0%, 4.2%, or 5%. It should be noted that if the content of unsaturated double-bonded polymer monomers is less than 0.5%, it is difficult to effectively form a polymer backbone; if the content of unsaturated double-bonded polymer monomers is greater than 5%, it will lead to a significant deterioration in the electrical performance of the lithium battery.

[0037] In some embodiments, the initiator has a mass fraction of 0.05% to 1% based on the total mass of the unsaturated double-bonded polymer monomers and additives, for example, 0.05%, 0.1%, 0.25%, 0.5%, 0.75%, or 1%. Exemplarily, the initiator may be azobisisobutyronitrile (AIBN).

[0038] In some embodiments, the mass ratio of the additive to the unsaturated double-bonded polymer monomer is not greater than 0.5 and not less than 0.1. Here, A represents the additive and C represents the double-bonded polymer monomer, then 0.1 ≤ A / C ≤ 0.5, for example, 0.1, 0.15, 0.25, 0.30, 0.35, 0.38, 0.40, 0.45, 0.5. It should be noted that if A / C < 0.1, the amount of additive added is insufficient and it is difficult to play the corresponding role; if A / C > 0.5, the amount of additive added is too large, which can easily lead to a decrease in the electrical performance of the lithium battery.

[0039] In some embodiments, the electrolyte further includes an organic solvent. Further, the organic solvent includes carboxylic acid esters and carbonates; wherein the carboxylic acid ester includes any one or a combination of at least two of ethyl acetate, methyl acetate, methyl formate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, propyl butyrate, butyl butyrate, isopropyl acetate, and isoamyl acetate; the carbonate includes any one or a combination of at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; wherein, based on the total mass of the electrolyte, the mass fraction of the carboxylic acid ester is 4% to 40%, for example, 4%, 10%, 20%, 25%, and 40%.

[0040] Optionally, the carboxylic acid ester includes any one or a combination of at least two of ethyl acetate, methyl acetate, propyl propionate, and ethyl propionate.

[0041] It should be noted that carboxylic esters can provide polymerizable sites, which is beneficial for forming a three-dimensional gel network and achieving "in-situ solidification." Carboxylic esters can also construct ion transport channels. In addition, the polar groups of carboxylic esters can have a good wetting effect on both positive and negative electrode surfaces, which can reduce interfacial impedance, suppress interfacial side reactions, and improve cycle life and interfacial stability.

[0042] In some embodiments, the electrolyte further comprises a lithium salt, which includes any one or a combination of at least two of LiFSI, LiTFSI, LiPF6, LiBF4, LiClO4, or LiAsF6. For example, the lithium salt may be LiPF6 or LiFSI.

[0043] In some embodiments, the mass fraction of the lithium salt is 8% to 20% based on the total mass of the electrolyte. Exemplarily, the mass fraction of the lithium salt can be 8%, 10%, 12%, 13%, 15%, 16%, 17%, or 20%.

[0044] In some embodiments, the electrolyte further includes fluoroethylene carbonate; based on the total mass of the electrolyte, the mass fraction of fluoroethylene carbonate is not higher than 20%, for example 1%, 2%, 5%, 8%, 10%, 12%, 15%, or 20%. Here, fluoroethylene carbonate can be used as a film-forming inducer, a low-temperature co-solvent, and a high-pressure / high-temperature interface stabilizer in the in-situ curing system.

[0045] In some embodiments, the invention further includes unsaturated additives; wherein the unsaturated additives include at least one or a combination of at least two of cyclic carbonate additives, cyclic sulfonyl lactone additives, and cyclic sulfate additives. Here, the unsaturated additives may include only cyclic carbonate additives, only cyclic sulfonyl lactone additives, or only cyclic sulfate additives; this disclosure does not limit the scope of the invention.

[0046] For example, the cyclic carbonate additive includes any one or a combination of at least two of vinylene carbonate and ethylene ethylene carbonate.

[0047] For example, the cyclic sulfonyl lactone additive includes any one or a combination of at least two of 1,3-propanesulfonyl lactone and / or 1,3-propenesulfonyl lactone.

[0048] For example, the cyclic sulfate additive includes vinyl sulfate.

[0049] In some embodiments, based on the total mass of the electrolyte, the mass fraction of the unsaturated additive is not less than 0.2% and not more than 3%, for example, 0.2%, 0.8%, 1.5%, 2.0%, 2.3%, or 3%.

[0050] In some embodiments, the electrolyte further includes lithium salt additives; wherein the lithium salt additives include any one or a combination of at least two of lithium difluorophosphate, lithium dioxalate borate, lithium tetrafluoroborate, or lithium difluorooxalate phosphate.

[0051] In some embodiments, the mass fraction of lithium salt additive is not less than 0.05% and not more than 1.5% based on the total mass of the electrolyte, for example, 0.05%, 0.1%, 0.15%, 0.25%, 0.5%, 0.8%, 0.9%, 1.0%, 1.2%, and 1.5%.

[0052] lithium batteries A second aspect of this disclosure provides a lithium battery, including the electrolyte provided above. Here, the lithium battery can be a primary lithium battery or a secondary lithium battery; this disclosure does not limit the specific type.

[0053] In some embodiments, a lithium battery includes a positive electrode, a negative electrode, a separator located between the positive and negative electrodes, and an electrolyte. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0054] Positive electrode sheet The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0055] For example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0056] 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 (e.g., polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0057] In some embodiments, the positive electrode active material includes Li x Ni y Mn z M m O 0.5x+1.5y+1.5z+1.5m Wherein, 0.9≤x≤1.1, 0.8≤y≤1, 0≤z≤0.2, 0≤m≤0.2; and M is selected from one or more of Fe, Ti, Co, Cr, V, Cu, Zn, Zr, Al and Nb.

[0058] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0059] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0060] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0061] Negative electrode sheet The negative electrode includes a negative current collector and a film layer optionally disposed on at least one surface of the negative current collector.

[0062] For example, the film layer may include a negative electrode active material (e.g., artificial graphite), a conductive agent, a thickener, and a binder.

[0063] In some embodiments, the negative electrode active material comprises a mixture of silicon-containing material and graphite. Optionally, the silicon-containing material may comprise one or more of silicon-oxygen materials (e.g., silicon suboxide) or silicon-carbon materials (e.g., silicon-carbon composites, silicon carbide, silicon-carbon nanomaterials, porous silicon-carbon materials, etc.). Further, based on the total mass of the negative electrode active material, the mass fraction of the silicon-containing material is not higher than 30%, for example, 1%, 3%, 10%, 15%, 20%, 25%, or 30%.

[0064] In some embodiments, the negative electrode sheet can be prepared by dispersing the negative electrode active material, conductive agent, thickener, binder and any other components in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0065] Separating membrane In some embodiments, the secondary battery further includes a separator. This disclosure does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0066] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0067] Example The following describes embodiments of this disclosure. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0068] The specific preparation method of the secondary lithium battery of Embodiment 1 of this disclosure is as follows: (1) Preparation of lithium nickel cobalt manganese oxygen cathode: The positive electrode active material (LiNi) 0.9 Co 0.05 Mn 0.05 O2), polyvinylidene fluoride as a binder, and Super P as a conductive agent are mixed in a mass ratio of 98:1:1. N-methylpyrrolidone (NMP) is added, and the mixture is stirred under vacuum until the system is homogeneous and transparent to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated onto an aluminum foil. After the aluminum foil is dried at room temperature, it is transferred to an oven for drying. Then, it is cold-pressed and slit to obtain the positive electrode (electrode sheet).

[0069] (2) Preparation of graphite-silicon composite anode: Artificial graphite and silicon-carbon composite were mixed at the mass ratios shown in Table 1. The mixture served as the negative electrode active material, Super P as the conductive agent, sodium carboxymethyl cellulose (CMC-Na) as the thickener, and styrene-butadiene rubber (SBR) as the binder. The mixture was mixed at a mass ratio of 96:1:1:2, and deionized water was added. The negative electrode slurry was obtained under vacuum stirring. The negative electrode slurry was uniformly coated onto the negative electrode current collector copper foil. After the copper foil was dried at room temperature, it was transferred to an oven for drying. Then, it was cold-pressed and slit to obtain the negative electrode (electrode sheet).

[0070] (3) Preparation of electrolyte: In an argon-atmospheric glove box with a water content of <10 ppm, battery-grade ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and fluoroethylene carbonate (FEC) were mixed in a mass ratio of 1:1:3:45:1 to form a carbonate solvent. Lithium salt, carboxylic acid ester, initiator, and other components were added quantitatively according to the electrolyte composition of Example 1 in Table 1. The mixture was thoroughly mixed, and finally, the carbonate solvent was used to make up the total mass of the electrolyte.

[0071] Based on the total mass of the electrolyte, the lithium salt comprises 12.5% ​​lithium hexafluorophosphate and 6% LiFSI; the initiator is azobisisobutyronitrile (AIBN) with a mass content of 0.1%; and the carboxylic acid ester has a mass content of 32%. In Table 1, the content of each component is a mass percentage calculated based on the total mass of the electrolyte.

[0072] It should be noted that, except for the component ratios specified in Table 1, the preparation methods of the negative electrode active materials and electrolytes in Examples 2-21 and the comparative examples are the same as those in Example 1. Polymer monomer (C) refers to methyl methacrylate; additive (A) refers to the compound corresponding to structural formula (II). In Examples 22-27 of Table 3, the proportion of silicon-carbon material in the negative electrode active material is 30%, and the preparation method of the electrolyte is the same as that in Example 1, except for the component ratios specified in Table 3.

[0073] (4) Preparation of the separating membrane: Polypropylene film is used as the separator.

[0074] (5) Preparation of secondary batteries: Using a 12 μm thick polypropylene (PP) film as the separator, the prepared positive electrode, separator, and negative electrode were stacked sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. Then, an aluminum-plastic film was wrapped around the separator, and the mixture was dried in a vacuum oven at 120 °C. After injecting 3.0 g / Ah of the prepared electrolyte, electrolytic liquefaction was performed. Following degassing, the mixture was placed in a vacuum oven at 60 °C for in-situ curing, ultimately yielding a 1 Ah soft-pack battery (i.e., an in-situ cured semi-solid-state battery).

[0075] Test methods The secondary batteries prepared in the above embodiments and comparative examples can be tested using the following methods: (1) Capacity retention rate of secondary batteries during room temperature fast charging cycles at 25 ℃ At 25 °C, the battery was charged at a constant current of 4C to 4.25 V, then charged at a constant voltage of 4.25 V until the current was less than 0.05 C. After resting for 10 min, it was discharged at a constant current of 1 C to 2.5 V. The discharge capacity of the battery at this time was tested, which is the discharge capacity of the first cycle. The battery was cycled multiple times under the above conditions, and the capacity retention rate of the battery after 400 cycles was calculated.

[0076] Calculate the capacity retention relative to the cycle using the following formula: Capacity retention rate (%) = (Discharge capacity after 400 cycles / Discharge capacity after the first cycle) × 100%.

[0077] (2) Capacity retention rate of secondary batteries under high-temperature cycling at 45 °C At 45 °C, the battery was charged at a constant current of 1C to 4.25 V, then charged at a constant voltage of 4.25 V until the current was less than 0.05 C. After resting for 10 min, it was discharged at a constant current of 1C to 2.5 V. The discharge capacity of the battery at this time was tested, which is the discharge capacity of the first cycle. The battery was cycled multiple times under the above conditions, and the capacity retention rate of the battery after 800 cycles was calculated.

[0078] Calculate the capacity retention relative to the cycle using the following formula: Capacity retention rate (%) = (Discharge capacity after 800 cycles / Discharge capacity during the first cycle) × 100%.

[0079] (3) High-temperature storage capacity recovery test of secondary batteries At 25 °C, the battery was charged at a constant current of 1 / 3C to 4.25 V, then charged at a constant voltage of 4.25 V until the current was less than 0.05 C. After resting for 10 min, it was discharged at a constant current of 1 / 3C to 2.5 V. The discharge capacity of the battery at this point was measured and recorded as the discharge capacity C0 for 0 days of cycling. The battery was then charged at a constant current of 1 / 3C to 4.25 V, then charged at a constant voltage of 4.25 V until the current was less than 0.05 C, and placed at 60 °C. The fully charged lithium-ion battery was stored at 60 °C for 60 days. The battery was then discharged at a constant current of 1 / 3C to 2.5 V at 25 °C, then charged at a constant current of 1 / 3C to 4.25 V, and then charged at a constant voltage until the current was 0.05 C. The battery was then discharged at a constant current of 1 / 3C to 2.5 V, and the discharge capacity was recorded as C1. The capacity recovery rate was (C1 / C0) × 100%.

[0080] (4) Volume expansion rate after 30 days of storage at 60 ℃: At 25 °C, the battery was charged at a constant current of 1C to 4.25 V, and then charged at a constant voltage to a current of 0.05 C. The volume of the battery was measured using the water displacement method and recorded as V0. The fully charged battery was then stored in a 60 °C oven for 30 days, and the volume after storage was measured using the water displacement method and recorded as V1.

[0081] Calculate the volume expansion rate of the battery relative to its initial state before storage using the following formula: Volume expansion rate (%) = [(V1-V0) / V0]×100%.

[0082] (5) Safety performance test of secondary battery hot box At 25 ℃, the battery is charged at a constant current of 1 / 3C to 4.25 V, and then charged at a constant voltage of 4.25 V until the current is less than 0.05 C. After resting for 10 min, the battery is placed in a hot chamber, and the temperature sensor is attached to the battery surface and the voltage sensor is clamped to the battery tab. After resting for 30 min, the temperature chamber is set to heat up to 130 ℃ at a heating rate of 5 ℃ / min and held at that temperature for 30 min. The battery is observed to see if thermal runaway occurs. If thermal runaway does not occur after 30 min, the heating is paused for 1 h. Then, the battery is heated at a heating rate of 5 ℃ / min until thermal runaway occurs, i.e., the battery catches fire or explodes. The temperature of the cell at this time is recorded as the thermal runaway temperature of the battery.

[0083] Table 1. Composition of electrolyte and negative electrode active material in different groups of examples and comparative examples.

[0084] Table 2 Performance data of different groups of embodiments and comparative examples

[0085] Under the same additive content, comparisons of examples with different polymer monomer contents (e.g., Examples 1, 5, 9, and 13; Examples 2, 6, 10, and 14; Examples 3, 7, 11, and 15; Examples 4, 8, 12, and 16) all showed that, with a fixed additive content, as the added polymer monomer content increased, the thermal runaway temperature of the cell in the hot box safety test and the capacity recovery rate after 60 days of full charge storage at 60°C generally increased. However, the capacity recovery rates of the cell after 500 cycles at 25°C and 400 cycles at 45°C exhibited a characteristic of first increasing and then decreasing. In summary, the overall performance of the cell is better when the polymer monomer content is between 2% and 5%.

[0086] Comparing Examples 1-4, Examples 5-8, Comparative Example 1 and Examples 9-12, and Examples 13-16, it can be observed that, with a fixed polymer monomer content, as the additive content increases, the thermal runaway temperature, capacity recovery rate after 500 cycles at 25°C, 400 cycles at 45°C, and 60 days of full-charge storage at 60°C in the hot box safety test all exhibit a characteristic of first increasing and then decreasing. In summary, the overall performance of the battery cell is best when the additive content is between 0.5% and 1%.

[0087] Furthermore, examining Examples 1 to 21 reveals that when the ratio of additive to polymer monomer is less than 0.1, the overall performance of the battery cell is poor due to the relatively low amount of additive added; when the ratio of additive to polymer monomer is greater than 0.5, the overall performance of the battery cell is also poor due to the relatively high amount of additive added.

[0088] Comparing Examples 17 to 21, it can be found that when the proportion of silicon-carbon material in the negative electrode active material is 30% and the polymer monomer in the electrolyte remains unchanged, increasing the amount of additives also results in a trend of first increasing and then decreasing the performance of the battery cell. The turning point of the trend occurs after the additive / polymer monomer ratio exceeds 0.5. This shows that the addition of additives can still improve the performance of the battery cell even after increasing the proportion of silicon-carbon material in the negative electrode active material, indicating that the additives provided in this disclosure have a relatively wide range of applications.

[0089] It should be noted that the compound corresponding to structural formula (II) is only representative of structural formula (I). Other compounds that satisfy structural formula (I) have similar effects in the battery cell as the compound corresponding to structural formula (II), and will not be described in detail here.

[0090] Table 3. Electrolyte composition and performance data for Examples 22-27

[0091] As shown in Table 3, with a fixed content of polymer monomers and additives, the capacity retention rate after 500 cycles at 25°C continuously increases with the increase of the carboxylic acid ester compound content. However, the capacity retention rate after 400 cycles at 45°C and the capacity recovery rate after 60 days of full-charge storage at 60°C both continuously decrease. In summary, the battery cell exhibits better overall electrical performance when the carboxylic acid ester compound content is within the range of 4% to 40%. Preferably, the carboxylic acid ester compound content is 16% to 40%.

[0092] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this disclosure (including the claims) is limited to these examples; within the framework of this disclosure, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the embodiments of this disclosure as described above, which are not provided in detail for the sake of brevity.

[0093] This disclosure is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. An electrolyte, characterized in that, It includes unsaturated double-bonded polymer monomers, initiators, and additives; wherein the structural formula of the additives is shown in formula (I): （Ⅰ）； In formula (Ⅰ), R1 and R2 may be the same or different, and each is independently selected from: H, C1-C4 straight-chain or branched alkyl; The additive has a mass fraction of 0.5% to 1% based on the total mass of the electrolyte.

2. The electrolyte according to claim 1, characterized in that, The structural formula of the additive is as follows: (II).

3. The electrolyte according to claim 1, characterized in that, The unsaturated double-bonded polymer monomer is selected from any one or a combination of at least two of methyl methacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, acrylonitrile, vinylene carbonate, ethylene oxide, or 1,3-dioxolane; and / or Based on the total mass of the electrolyte, the mass fraction of the unsaturated double-bonded polymer monomer is 2% to 5%; and / or Based on the total mass of the unsaturated double-bonded polymer monomer and the additive, the mass fraction of the initiator is 0.05% to 1%.

4. The electrolyte according to claim 1, characterized in that, The mass ratio of the additive to the unsaturated double-bonded polymer monomer is not greater than 0.5 and not less than 0.

1.

5. The electrolyte according to claim 1, characterized in that, It also includes organic solvents, including carboxylic acid esters and carbonates; The carboxylic acid ester includes any one or a combination of at least two of ethyl acetate, methyl acetate, methyl formate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, propyl butyrate, butyl butyrate, isopropyl acetate, and isoamyl acetate; the carbonate includes any one or a combination of at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. The mass fraction of the carboxylic acid ester is 4% to 40% based on the total mass of the electrolyte.

6. The electrolyte according to claim 1, characterized in that, The electrolyte further comprises a lithium salt, which includes any one or a combination of at least two of LiFSI, LiTFSI, LiPF6, LiBF4, LiClO4 or LiAsF6; The lithium salt has a mass fraction of 8% to 20% based on the total mass of the electrolyte.

7. The electrolyte according to claim 1, characterized in that, The electrolyte also includes fluoroethylene carbonate; Wherein, based on the total mass of the electrolyte, the mass fraction of the fluoroethylene carbonate is not higher than 20%.

8. The electrolyte according to claim 1, characterized in that, It also includes unsaturated additives; wherein the unsaturated additives include at least one or a combination of at least two of cyclic carbonate additives, cyclic sulfonyl lactone additives, and cyclic sulfate additives; The cyclic carbonate additive includes any one or a combination of at least two of vinylene carbonate and ethylene ethylene carbonate. The cyclic sulfonyl lactone additive includes any one or a combination of at least two of 1,3-propane sulfonyl lactone and / or 1,3-propene sulfonyl lactone. The cyclic sulfate additive includes vinyl sulfate; Wherein, based on the total mass of the electrolyte, the mass fraction of the unsaturated additive is not less than 0.2% and not more than 3%.

9. The electrolyte according to claim 1, characterized in that, It also includes lithium salt additives; wherein the lithium salt additives include any one or a combination of at least two of lithium difluorophosphate, lithium dioxaborate, lithium tetrafluoroborate, or lithium difluorooxaborate. Wherein, based on the total mass of the electrolyte, the mass fraction of the lithium salt additive is not less than 0.05% and not more than 1.5%.

10. A lithium battery, characterized in that, include: Positive electrode, including positive electrode active material; Negative electrode, including negative electrode active material; as well as Electrolyte, wherein the electrolyte comprises the electrolyte according to any one of claims 1 to 9; The positive electrode active material includes Li x Ni y Mn z M m O 0.5x+1.5y+1.5z+1.5m Wherein, 0.9≤x≤1.1, 0.8≤y≤1, 0≤z≤0.2, 0≤m≤0.2; and M is selected from one or more of Fe, Ti, Co, Cr, V, Cu, Zn, Zr, Al, and Nb. The negative electrode active material comprises a mixture of silicon-containing material and graphite; and based on the total mass of the negative electrode active material, the mass fraction of the silicon-containing material is not higher than 30%.

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