Electrolyte and lithium ion battery

Abstract

The embodiment of the invention discloses an electrolyte and a lithium ion battery. The electrolyte comprises a lithium salt, a non-aqueous solvent and an additive, the additive is prepared from 1, 1, 2, 2-tetrafluoroethyl-2, 2, 3, 3-tetrafluoropropyl ether, a triazole compound and 2-sulfydryl-4-(4-pyridyl) thiazole. According to the embodiment of the invention, the additive is added into the electrolyte, a compact, uniform and stable composite CEI film can be constructed on the surface of the positive electrode, and the composite CEI film can more effectively inhibit the oxidation reaction of the surface of the positive electrode under high voltage and high temperature, so that electrolyte decomposition and positive electrode structure collapse are better inhibited; the chemical stability of the electrolyte under high voltage and high temperature is guaranteed; meanwhile, the additive can better fix / complex transition metal ions and effectively prevent the transition metal from being deposited on a negative electrode after being dissolved out, so that the cycle performance of the lithium ion battery is remarkably improved.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, specifically to an electrolyte and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are widely used in portable devices such as mobile phones, cameras, and laptops due to their advantages including high specific capacity, long cycle life, low self-discharge rate, no memory effect, and environmental friendliness. Currently, with the application of lithium-ion batteries in electric vehicles, higher demands are being placed on their energy density.

[0003] Increasing the operating voltage can improve the energy density of lithium-ion batteries. However, conventional lithium-ion electrolytes face two main challenges above 4.2V, leading to performance degradation:

[0004] 1. Positive electrode interface oxidation: When the charging voltage exceeds 4.2V, solvent molecules (such as carbonates) in the electrolyte undergo severe irreversible oxidative decomposition on the surface of the positive electrode material, producing by-product deposition, increasing interfacial impedance, consuming active lithium, and leading to reduced initial efficiency and capacity decay. 2. Poor high-temperature stability: The above oxidation reaction accelerates rapidly at high temperatures. Simultaneously, the solid electrolyte interphase (SEI) film on the negative electrode side may become unstable, leading to continuous side reactions and electrolyte consumption, causing a rapid deterioration in high-temperature cycling performance.

[0005] Therefore, how to improve the electrochemical performance of lithium-ion batteries under high voltage is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this application is to provide an electrolyte and a lithium-ion battery.

[0007] To achieve the above objectives, the embodiments of this application propose the following technical solutions:

[0008] In a first aspect, embodiments of this application provide an electrolyte, the electrolyte comprising:

[0009] Lithium salts

[0010] Non-aqueous solvents, and

[0011] additive;

[0012] The additives include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, triazole compounds, and 2-mercapto-4-(4-pyridyl)thiazole;

[0013] The triazole compound has the general structural formula shown in Formula I:

[0014]

[0015] Formula I;

[0016] R is selected from alkyl, fluoroalkyl, H, cycloalkyl, heterocycloalkyl, vinyl or ethynyl.

[0017] As one embodiment of this example, R is selected from alkyl groups having 1 to 6 carbon atoms, fluoromethyl groups, 1-fluoroethyl groups, 2-fluoroethyl groups, 1-fluoropropyl groups, 2-fluoropropyl groups, saturated or unsaturated five-membered or six-membered rings, or saturated five-membered or six-membered heterocycles.

[0018] As one embodiment of this example, the triazole compound is selected from at least one of 1,2,4-triazole, 1-methyl-1,2,4-triazole, 1-ethyl-1,2,4-triazole, and 3-(trifluoromethyl)-1H-1,2,4-triazole.

[0019] As one embodiment of this example, the content of the triazole compound is 0.5-5%, based on the total mass of the electrolyte.

[0020] As one embodiment of this example, the content of the 2-mercapto-4-(4-pyridyl)thiazole is 0.1-5%, based on the total mass of the electrolyte.

[0021] As one embodiment of this example, the content of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is 0.5-3.5%, based on the total mass of the electrolyte.

[0022] As one embodiment of this example, the non-aqueous solvent is selected from one or more of propylene carbonate, ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, γ-butyrolactone, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, difluoroethyl acetate, and ethyl 2,2,2-trifluoroethyl acetate.

[0023] As one embodiment of this example, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium difluorooxalate phosphate, lithium difluorooxalate borate, lithium tetrafluorooxalate phosphate, and lithium difluorosulfonylimide.

[0024] The lithium salt content is 5-20%, based on the total mass of the electrolyte.

[0025] Secondly, embodiments of this application provide a lithium-ion battery, the lithium-ion battery comprising:

[0026] Positive electrode sheet;

[0027] Negative electrode plate;

[0028] Diaphragm; and

[0029] The electrolyte described in the first aspect.

[0030] In one embodiment of this invention, the positive electrode sheet includes a positive electrode active material; the positive electrode active material satisfies: Li(Ni x Co y Mn z O2;

[0031] Among them, 0<x<1, 0<y<1, 0<z<1, x+y+z=1;

[0032] The lithium-ion battery operates at a voltage of 2.75-4.4V.

[0033] Thirdly, embodiments of this application provide an electrical device, which includes a lithium-ion battery as described in the second aspect.

[0034] Compared with the prior art, the embodiments of this application have at least the following beneficial effects:

[0035] In this embodiment, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE458), triazole compounds, and 2-mercapto-4-(4-pyridyl)thiazole are added as functional additives to the electrolyte. This allows for the construction of a dense, uniform, and stable composite CEI film on the positive electrode surface. This composite CEI film can more effectively suppress the oxidation reaction on the positive electrode surface under high voltage and high temperature, thereby better suppressing electrolyte decomposition and positive electrode structure collapse, ensuring the chemical stability of the electrolyte under high voltage and high temperature. At the same time, the above additives can better fix / complex transition metal ions, effectively preventing transition metals from dissolving and depositing on the negative electrode, thus significantly improving the cycle performance of lithium-ion batteries.

[0036] Therefore, the electrolyte in this embodiment can significantly suppress the dissolution of transition metal ions, thereby improving the high-temperature cycle performance and high-temperature storage performance of the battery.

[0037] Additional aspects and advantages of this application will be set forth in part in the description which follows, and will become apparent from the description or may be learned by practice of this application. Detailed Implementation

[0038] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0039] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0040] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0041] The electrolyte, lithium-ion battery, and power supply device of this application are described in detail below.

[0042] First, let me explain the electrolyte according to the first aspect of this embodiment.

[0043] Electrolyte.

[0044] Currently, with the widespread application of lithium-ion batteries in electric vehicles, the industry's requirements for their energy density are increasing, and increasing the operating voltage is an effective way to enhance the energy density of lithium-ion batteries. However, when the charging voltage of conventional lithium-ion batteries exceeds 4.2V, the cathode material will enter a strongly oxidized state due to the increased degree of delithiation (such as N in ternary cathodes). i2+ Deeply oxidized to Ni 4+ The strong oxidizing properties of its surface can disrupt the chemical stability of solvent molecules (such as carbonates) in the electrolyte. Specifically, the CO and CH bonds in carbonate molecules are oxidized and broken, resulting in severe irreversible oxidative decomposition reactions, producing by-product deposits, increasing interfacial impedance, consuming active lithium, and leading to reduced initial efficiency and capacity decay.

[0045] Secondly, high temperatures drastically accelerate the aforementioned oxidation reactions and increase the diffusion rate of oxidation products at the interface, leading to an exponential expansion of side reactions. Simultaneously, the dissolution of transition metals (Ni, Co, Mn) deposits on the negative electrode, damaging the SEI film and significantly reducing its stability. For example, organic components in the SEI film (such as alkyl lithium carbonate) undergo thermal decomposition, causing cracks or pores in the originally dense film structure, thus losing its insulating effect between the electrolyte and the negative electrode (such as graphite). This allows solvents and lithium salts in the electrolyte to continuously permeate through the damaged areas to the negative electrode surface, triggering new reduction reactions (such as solvent molecules embedding into the graphite interlayer and decomposing), further consuming active lithium and the electrolyte.

[0046] The aforementioned dual side reactions of the positive and negative electrodes promote each other, forming a vicious cycle of high temperature - accelerated oxidation - SEI film damage - intensified side reactions - more heat generation, ultimately causing the battery to rapidly decrease in capacity and drastically increase in impedance during high-temperature cycling.

[0047] In view of this, this embodiment proposes an electrolyte for use in lithium-ion batteries; the electrolyte includes lithium salt, non-aqueous solvent and additives; the additives include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE458), triazole compound and 2-mercapto-4-(4-pyridyl)thiazole.

[0048] In this embodiment, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE458), triazole compounds, and 2-mercapto-4-(4-pyridyl)thiazole are added as functional additives to the electrolyte. This allows for the construction of a dense, uniform, and stable composite CEI film on the positive electrode surface. This composite CEI film can more effectively suppress oxidation reactions on the positive electrode surface under high voltage and high temperature (enhancing the antioxidant capacity of the electrolyte itself), thereby better suppressing electrolyte decomposition and positive electrode structure collapse, ensuring the chemical stability of the electrolyte under high voltage and high temperature. At the same time, the above additives can better fix / complex transition metal ions, effectively preventing transition metals from dissolving and depositing on the negative electrode. The stable interface film and reduced side reactions mean less loss of active lithium and less damage to the electrode structure during charge-discharge cycles. This directly translates to the lithium-ion battery maintaining a high capacity after long-term cycling, which significantly improves the cycle performance of the lithium-ion battery.

[0049] Therefore, the electrolyte in this embodiment can significantly suppress the dissolution of transition metal ions, thereby improving the high-temperature cycle performance and high-temperature storage performance of the battery.

[0050] The relevant components in the electrolyte of this embodiment will be further explained below.

[0051] 1,1,2,2-Tetrafluoroethyl-2,2,3,3-Tetrafluoropropyl ether.

[0052] In this embodiment, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE458) is used as a fluorinated ether additive. Its molecular structure contains multiple strongly electronegative CF bonds and ether bonds (-O-), which preferentially decompose compared to conventional carbonate solvents in typical high-voltage lithium-ion battery systems (e.g., ≥4.2V). This results in the formation of a LiF-rich CEI film and SEI film on the positive and negative electrode surfaces, respectively, effectively preventing direct contact between the electrodes and the electrolyte. Simultaneously, the weak interaction between the ether bonds and lithium ions guides HFE458 to preferentially adsorb onto the positive electrode surface, and the strongly electronegative F atoms in its molecule selectively anchor Ni through strong coordination. 2+ Mn 2 + The presence of active transition metal ions significantly reduces transition metal ion dissolution and inhibits electrolyte chain decomposition. Furthermore, the weak coordination ability of HFE458 can regulate the composition and structure of the lithium salt solvation sheath, reducing Li... + Desolvation of the solubility barrier enhances the interfacial ion conductivity and lithium-ion migration kinetics.

[0053] It should be noted that HFE458 can improve the overall antioxidant capacity of the electrolyte and build preliminary interfacial protection. The CEI film it constructs can provide a uniform reaction substrate (laying the foundation) for the adsorption and oxidation of triazole compounds and 2-mercapto-4-(4-pyridyl)thiazole.

[0054] Triazole compounds.

[0055] The triazole compound used in this embodiment has the general structural formula I:

[0056]

[0057] Formula I;

[0058] Wherein, R is alkyl, fluoroalkyl, H, cycloalkyl, heterocycloalkyl, vinyl or ethynyl.

[0059] Preferably, the alkyl group is an alkyl group having 1 to 6 carbon atoms; such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, etc.; preferably methyl, ethyl, n-propyl, isopropyl; the fluoroalkyl group is preferably fluoromethyl, 1-fluoroethyl, 2-fluoroethyl, 1-fluoropropyl, 2-fluoropropyl; the cycloalkyl group is preferably a saturated or unsaturated five-membered or six-membered ring, wherein the unsaturated six-membered ring may be selected as a benzene ring; the heteroalkyl group may be a saturated five-membered or six-membered heterocycle, wherein the heterocycle is a nitrogen heterocycle, a sulfur heterocycle, an oxygen heterocycle, etc.

[0060] More preferably, the triazole compound is selected from at least one of 1,2,4-triazole, 1-methyl-1,2,4-triazole, 1-ethyl-1,2,4-triazole, and 3-(trifluoromethyl)-1H-1,2,4-triazole (CAS: 60406-75-9).

[0061] In this embodiment, the N atom in the triazole compound contains a lone pair of electrons, which can be adsorbed onto the positive electrode surface through coordination, reacting with metal ions (such as Mn). 2+ First, it forms monodentate coordination bonds, which initially fix metal ions in the micropores of the CEI membrane, and the heterocyclic structure is resistant to high-voltage oxidation. Second, the triazole compound has an intracyclic conjugated system, which can enhance the adsorption strength of the molecule on the electrode surface and easily form a cross-linked interface film after oxidation. At the same time, the triazole compound can participate in the interface reaction and improve the compactness of the interface film.

[0062] As mentioned earlier, the fluorine-containing physical film formed by HFE458 first spreads on the positive and negative electrode surfaces, reducing interfacial tension. At the same time, it can provide a uniform reaction substrate for the adsorption and oxidation of triazole compounds and 2-mercapto-4-(4-pyridyl)thiazole, which can prevent triazole compounds from reacting excessively locally to form a thick film, resulting in a significant increase in interfacial impedance.

[0063] Understandably, during high-voltage charging, the nitrogen atom of the triazole ring preferentially adsorbs onto the positive electrode surface and coordinates with transition metal ions. Subsequently, some of the N-N bonds are oxidized and broken, generating a nitrogen-containing (such as CN, NO) cross-linked positive electrode interface CEI film. This CEI film has strong electronic insulation, which can prevent electrolyte oxidation caused by electron leakage, while retaining lithium ion conduction channels. Secondly, the nitrogen atom of the triazole ring can form stable coordination complexes with dissolved transition metal ions, reducing the concentration of free metal ions. The CEI film formed can also physically block metal ions from dissolving from the positive electrode. Furthermore, the triazole molecules adsorbed on the positive electrode surface can cover highly active transition metal sites, inhibiting the insertion and extraction of lattice oxygen at these sites.

[0064] 2-Mercapto-4-(4-pyridyl)thiazole.

[0065] The 2-mercapto-4-(4-pyridyl)thiazole (CAS No.: 77168-63-9) selected in this embodiment has the following structural formula:

[0066] .

[0067] Based on the above structural formula, 2-mercapto-4-(4-pyridyl)thiazole contains a pyridyl group (-C5H4N), a mercapto group (-SH), and a thiazole ring.

[0068] Among them, the N atom in the pyridinyl (-C5H4N) and thiazole rings contains lone pairs of electrons, giving them a stronger coordination ability for transition metal ions than triazole. Specifically, both the pyridinyl and thiazole rings have conjugated heterocyclic structures and lone pairs of electrons, allowing them to be firmly adsorbed onto the highly active cathode surface through coordination bonds or physical adsorption. This forms a dynamic protective film that physically blocks direct contact between the electrolyte and the cathode material, thereby suppressing oxidation side reactions. Furthermore, the thiol group (-SH) has a strong affinity for various transition metal ions (such as Co). 3+ Ni 2+ Mn 2+ It has a strong complexing ability, which can lock these dissolved ions in the electrolyte or fix them near the positive electrode interface, effectively preventing them from migrating and depositing to the negative electrode, thereby protecting the negative electrode SEI film and reducing the loss of active lithium; and the thiol group (-SH) has high reactivity and is easily oxidized to form disulfide (-SS-), which can fill the interface film defects and jointly participate in the construction of a robust and elastic organic-inorganic composite CEI layer.

[0069] Based on the above structure, firstly, in the 2-mercapto-4-(4-pyridyl)thiazole used in this embodiment, the pyridyl group, thiazole ring, and mercapto group can react with transition metal ions (such as Ni) in the electrolyte that are not captured by triazole compounds. 2+ Co 3+ First, it forms a more stable coordination complex, further eliminating the catalytic decomposition effect of free metal ions on the electrolyte (metal ions accelerate the hydrolysis and solvent oxidation of LiPF6). Second, the disulfides generated by the oxidation of mercapto groups on the electrode surface can be embedded in the pores or cracks of the CEI / SEI film, reducing the interfacial impedance. Third, the thiazole rings are adsorbed on the surface of the CEI / SEI film through π-π stacking, enhancing the mechanical strength of the CEI / SEI film and preventing the CEI / SEI film from breaking during charging and discharging. At the same time, the thiazole rings can form a weak interaction with the transition metal ions on the positive electrode surface, inhibiting the transformation of the positive electrode (such as NCM523) from a layered structure to a spinel / rock salt phase under high voltage, and reducing the capacity decay caused by lattice oxygen evolution.

[0070] The following section will further describe the principle behind the synergistic improvement of lithium-ion battery performance by HFE458, triazole compounds, and 2-mercapto-4-(4-pyridyl)thiazole.

[0071] First, in this embodiment, HFE458, the triazole compound, and 2-mercapto-4-(4-pyridyl)thiazole form a synergistic effect on the positive electrode side, which is the core of ensuring the high-voltage stability of the electrolyte. The multiple strongly electronegative CF bonds and ether bonds (-O-) in the HFE458 molecule preferentially decompose over conventional carbonate solvents in high-voltage lithium-ion battery systems (e.g., ≥4.2V), forming a LiF-rich CEI film and SEI film on the positive and negative electrode surfaces, respectively. This CEI film can initially block direct contact between the electrolyte and the positive electrode, while providing a uniform reaction substrate for the subsequent adsorption, coordination, and oxidative decomposition of additives. Next, the triazole compound, through the lone pair electrons of multiple N atoms in its molecule, reacts with the Li in the decomposition products of HFE458. + Alternatively, transition metal ions on the cathode surface can form coordination bonds, constructing an N-containing layer on the fluorine-containing substrate membrane. This not only enhances the mechanical strength of the CEI membrane but also provides abundant coordination sites for transition metal ions, laying the foundation for subsequent ion capture. The thiol group (-SH) of mercaptothiazole undergoes oxidative decomposition under high voltage, generating S-containing products such as Li₂S and organic sulfides, compensating for the insufficient ion conductivity of the LiF substrate membrane. Simultaneously, the pyridinium group and thiazole ring in its molecule can fill the micropores of the CEI membrane through intermolecular interactions, further improving the membrane density. Based on the combined effect of these additives, the problems of weak ion conductivity, insufficient mechanical strength, and high porosity of single CEI membranes are overcome, constructing a dense, uniform, and stable composite CEI membrane on the cathode surface. This composite CEI membrane can more effectively suppress oxidation reactions on the cathode surface under high voltage and high temperature, thereby better inhibiting electrolyte decomposition and cathode structure collapse, ensuring the chemical stability of the electrolyte under high voltage and high temperature.

[0072] Understandably, the aforementioned CEI membrane can physically block direct contact between the positive electrode and the electrolyte, reducing lattice oxygen release and decreasing the dissolution rate of transition metal ions (hereinafter referred to as metal ions) from the source. Simultaneously, triazole compounds and 2-mercapto-4-(4-pyridyl)thiazole molecules will permeate to the surface of the positive electrode and undergo coordination reactions with a small amount of dissolved metal ions. Specifically, the N atom (lone pair electron) of the triazole compound can form a monodentate coordination bond with the metal ion, initially dissolving it; the pyridine N, mercapto, and N / S atoms of the thiazole ring in 2-mercapto-4-(4-pyridyl)thiazole can form a more stable bidentate chelate bond (such as Mn) with the metal ion. 2+ It can form a six-membered chelate ring with pyridine N and thiazole S, which can further capture metal ions that are not completely fixed by triazole compounds. Thus, the coordination system formed by triazole compounds and 2-mercapto-4-(4-pyridyl)thiazole can better fix metal ions and make them less prone to dissociation even under high voltage, thereby reducing the diffusion of metal ions from the source.

[0073] Secondly, even if a small amount of metal ions dissolve, the bi-complex system formed by the triazole compound and the 2-mercapto-4-(4-pyridyl)thiazole molecule in the electrolyte can further lock the metal ions, preventing them from migrating to the negative electrode. First, the lone pair electrons of the N atom of the triazole molecule dissolved in the electrolyte can rapidly form a monodentate coordination complex (triazole-metal complex) with the diffused metal ions. This complex is relatively unstable (easily dissociates), but it can temporarily lock the metal ions, slowing their diffusion rate and laying the foundation for the subsequent strong coordination of the mercaptothiazole. Next, the 2-mercapto-4-(4-pyridyl)thiazole molecule undergoes ligand exchange with the triazole-metal complex in the electrolyte: the pyridine N and thiazole N / S atoms in 2-mercapto-4-(4-pyridyl)thiazole replace the N atom of the triazole, forming a more stable bidentate complex with the metal ions. This bidentate complex is more stable and less prone to dissociation. Metal ions are firmly bound and cannot continue to diffuse to the negative electrode and deposit there.

[0074] Furthermore, regarding the negative electrode side, as mentioned earlier, during the initial stage of battery charging and discharging, HFE458 preferentially undergoes reduction on the surface of the negative electrode (such as graphite) to form a LiF-rich basic SEI film. Simultaneously, 2-mercapto-4-(4-pyridyl)thiazole, due to its properties, undergoes a reduction reaction on the negative electrode surface. The thiol groups and thiazole ring structure in its molecule allow it to decompose and form organic polymers or lithium salts containing elements such as sulfur and nitrogen. These organic products constitute the organic framework of the SEI film and possess good flexibility. This organic framework, covering the fluorine-rich basic film formed by HFE458, effectively buffers the volume changes of the negative electrode material during charging and discharging, preventing the cracking of the brittle inorganic layer and thus maintaining the integrity of the SEI film. Simultaneously, the nitrogen-containing groups of the triazole compound can be embedded into the organic framework formed by 2-mercapto-4-(4-pyridyl)thiazole, acting as cross-linkers or fillers, making the SEI film network structure more dense and stable, further enhancing its electronic insulation and ion conductivity.

[0075] More importantly, the stability of the CEI film on the positive electrode side indirectly assists the long-term performance of the SEI film on the negative electrode, jointly ensuring the electrochemical performance of lithium-ion batteries at high voltages (such as high-temperature cycling performance).

[0076] Therefore, the electrolyte in this embodiment can significantly suppress the dissolution of transition metal ions, thereby improving the high-temperature cycle performance and high-temperature storage performance of the battery.

[0077] It should be noted that in this embodiment, the content of HFE458 is 0.5-3.5%, the content of triazole compound is 0.5-5%, and the content of 2-mercapto-4-(4-pyridyl)thiazole is 0.1-5%, based on the total mass of the electrolyte.

[0078] For example, the amount of HFE458 used in the electrolyte includes, but is not limited to: 0.5%, 0.54%, 0.55%, 0.58%, 0.6%, 0.64%, 0.68%, 0.7%, 0.74%, 0.78%, 0.8%, 0.86%, 0.88%, 0.9%, 0.93%, 0.95%, 1.0%, 1.3%, 1.6%, 1.65%, 1.7%, 1.8%, 1.88%, 1.9%, 1.97%, 2.0%, 2.2%, 2.4%, 2.5%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, and 3.5%.

[0079] For example, the amounts of the above-mentioned triazole compounds used in the electrolyte include, but are not limited to: 0.5%, 0.55%, 0.6%, 0.7%, 0.88%, 0.96%, 1.1%, 1.3%, 1.6%, 1.65%, 1.7%, 1.8%, 1.88%, 1.9%, 1.95%, 2.0%, 2.1%, 2.4%, 2.6%, 2.8%, 3.0%, 3.2%, 3.3%, 3.5%, 3.52%, 3. 54%, 3.6%, 3.62%, 3.63%, 3.67%, 3.69%, 3.7%, 3.75%, 3.77%, 3.8%, 3.83%, 3.85%, 3.89%, 3.9%, 3.94%, 3.96%, 3.98%, 4.0%, 4.1%, 4.15%, 4.2%, 4.28%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%.

[0080] For example, the amount of the above-mentioned 2-mercapto-4-(4-pyridyl)thiazole used in the electrolyte includes, but is not limited to: 0.1%, 0.24%, 0.55%, 0.78%, 0.86%, 0.9%, 0.93%, 0.95%, 1%, 1.1%, 1.4%, 1.8%, 2%, 2.4%, 2.5%, 2.7%, 3.0%, 3.2%, 3.3%, 3.5%, 3.52%, 3.54%, 3.6%. %, 3.62%, 3.63%, 3.67%, 3.69%, 3.7%, 3.75%, 3.77%, 3.8%, 3.83%, 3.85%, 3.89%, 3.9%, 3.94%, 3.96%, 3.98%, 4.0%, 4.1%, 4.15%, 4.2%, 4.28%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%.

[0081] Lithium salts.

[0082] As an essential component of the electrolyte in this embodiment, the lithium salt can be selected from salts commonly used in non-aqueous electrolytes suitable for lithium-ion batteries. Specifically, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium difluorooxalate phosphate, lithium difluorooxalate borate, lithium tetrafluorooxalate phosphate, and lithium difluorosulfonylimide.

[0083] In this embodiment, the lithium salt content is 5-20%, including but not limited to: 5%, 5.1%, 5.2%, 5.5%, 5.8%, 6%, 6.4%, 7%, 7.3%, 7.4%, 7.8%, 8%, 8.3%, 8.6%, 9%, 9.3%, 9.5%, 10%, 12.5%, 13%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.2%, 17.6%, 18%, 18.6%, 18.8%, 19%, 19.2%, 19.5%, 19.8%, and 20%.

[0084] Non-aqueous solvent.

[0085] The electrolyte in this embodiment is the same as that of a general non-aqueous electrolyte, typically containing a non-aqueous solvent for dissolving the aforementioned lithium salt as its main component. There are no particular limitations on the non-aqueous solvent used here; any known organic solvent can be used. Specifically, the non-aqueous solvent is selected from at least one of the following: propylene carbonate, ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, γ-butyrolactone, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, difluoroethyl acetate, and ethyl 2,2,2-trifluoroethyl acetate.

[0086] It should be understood that, in the electrolyte of this embodiment, apart from the lithium salt and additives, the remaining components are all non-aqueous solvents. Therefore, after determining the amount of lithium salt and additives, the content of non-aqueous solvents can also be expressed as a balance.

[0087] Other additives.

[0088] In addition to the various components listed above, the electrolyte of this application may reasonably use other functional additives within a range that does not significantly impair the effect of this application. For example, other additives may be at least one of lithium difluorophosphate (LiPO2F2), vinylene carbonate (VC), vinyl sulfate (DTD), 1,3-propanesulfonyl lactone (PS), fluoroethylene carbonate (FEC), and lithium difluorooxalate borate (LiODFB).

[0089] For example, lithium difluorophosphate, vinylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, fluoroethylene carbonate, or lithium difluorooxalate borate can be used alone, or any two or more of lithium difluorophosphate, vinylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, fluoroethylene carbonate, and lithium difluorooxalate borate can be used in any ratio of any proportion.

[0090] In this embodiment, the content of the other additives is 0.1-5%, preferably 0.2-5%, more preferably 0.2-3%, based on the total mass of the electrolyte.

[0091] For example, the amounts of the other additives mentioned above used in the electrolyte include, but are not limited to: 0.5%, 0.54%, 0.55%, 0.58%, 0.6%, 0.64%, 0.68%, 0.7%, 0.74%, 0.78%, 0.8%, 0.86%, 0.88%, 0.9%, 0.93%, 0.95%, 1.0%, 1.3%, 1.6%, 1.65%, 1.7%, 1.8%, 1.88%, 1.9%, 1.97%, 2.0%, 2.3%, 2.5%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.3%, 3.5%, 3.7%, 3.8%, 3.9%, 4.0%, 4.2%, 4.4%, 4.6%, 4.8%, 4.9%, and 5%.

[0092] Next, the preparation method of the above electrolyte will be explained.

[0093] Preparation method.

[0094] The electrolyte of this application can be prepared using methods known in the art, for example:

[0095] In an argon atmosphere glove box with a water content of <10ppm, non-aqueous solvents are mixed in proportion, then fully dried lithium salts are dissolved in the mixed non-aqueous solvents, and then additives are added. After mixing evenly, an electrolyte is obtained.

[0096] This application does not impose any special limitations on the preparation method of the electrolyte.

[0097] Next, the lithium-ion battery according to the second aspect of this embodiment will be described.

[0098] Lithium-ion batteries.

[0099] The lithium-ion battery described in the second aspect of this embodiment includes: a positive electrode, a negative electrode, a separator, and an electrolyte as described in the first aspect; the operating voltage of the lithium-ion battery in this embodiment is 2.75-4.4V, that is, the operating voltage range of the lithium-ion battery is wider.

[0100] As can be understood, referring to the discussion of the electrolyte in the first aspect, the electrolyte used in this embodiment contains HFE458, triazole compounds, and 2-mercapto-4-(4-pyridyl)thiazole, which can construct a dense, uniform, and stable composite CEI film on the positive electrode surface and improve the antioxidant capacity of the electrolyte itself, enabling the electrolyte system to remain stable at higher potentials (such as 4.4V or even higher) and not easily decompose. At the same time, the above-mentioned additives can better fix / complex transition metal ions, effectively preventing the deposition of transition metals on the negative electrode after dissolution. The high-quality SEI / CEI film with good ionic conductivity is conducive to rapid lithium-ion conduction. The stable interface film and reduced side reactions mean that less active lithium is lost and less damage is done to the electrode structure during charge-discharge cycles. This directly translates into the lithium-ion battery maintaining a high capacity after long-term cycling, that is, significantly improving the cycle performance of the lithium-ion battery.

[0101] Therefore, the lithium-ion battery of this embodiment can significantly suppress the dissolution of transition metal ions, and the lithium-ion battery has superior high-temperature cycle performance and high-temperature storage performance.

[0102] Positive electrode sheet.

[0103] The positive electrode used in the lithium-ion battery of this embodiment includes a positive current collector and a positive active material layer located at least on one side of the positive electrode, wherein the positive active material layer includes a positive active material.

[0104] In some embodiments, the positive current collector can be a metal current collector or a composite current collector. Among them, the metal current collector includes, but is not limited to, aluminum foil current collectors.

[0105] In some embodiments, the positive electrode active material of a lithium-ion battery may include at least one of the following: layered structure positive electrode active material (e.g., nickel-cobalt-manganese ternary positive electrode material, nickel-cobalt-aluminum ternary positive electrode material, lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide, etc.), olivine-type phosphate active material (e.g., lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, etc.), and spinel structure positive electrode active material (e.g., spinel lithium manganese oxide, spinel lithium nickel manganese oxide, lithium-rich spinel lithium manganese oxide, and lithium nickel manganese oxide, etc.).

[0106] In some embodiments of this application, the cathode material may be selected from Li(Ni) x Co y Mn z O2; where 0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1. For example, the cathode material can be selected from Li(Ni) 0.8 Co 0.1 Mn 0.1 O2, Li(Ni) 0.6 Co 0.2 Mn0.2 O2, Li(Ni) 0.5 Co 0.2 Mn 0.3 )O2.

[0107] In some embodiments, the binder in the positive electrode active material layer may be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and terpolymer of PVDF-tetrafluoroethylene-propylene.

[0108] In some embodiments, the conductive agent in the positive electrode active material layer may be at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, carbon nanotubes, graphene, and carbon nanofibers.

[0109] Negative electrode sheet.

[0110] In some embodiments, the negative electrode sheet may include a negative current collector and a layer of negative active material disposed on at least one side of the surface of the negative current collector.

[0111] In some embodiments, the negative electrode active material layer may include a negative electrode active material, a thickener, a conductive agent, and a binder. The negative electrode current collector may be a metal foil, for example, a copper foil.

[0112] In some embodiments, the negative electrode active material may be a carbon-based material, a silicon-based material, a tin-based material, etc. Preferably, it is one or more of soft carbon, hard carbon, and graphite. More preferably, it is graphite.

[0113] In some embodiments, the binder in the negative electrode material layer may be at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyacrylamide (PAM), polyvinyl alcohol (PVA), and polymethacrylic acid (PMAA).

[0114] In some embodiments, the conductive agent in the negative electrode material layer may be at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, carbon nanotubes, graphene, and carbon nanofibers.

[0115] Diaphragm.

[0116] To prevent short circuits, a separator is typically sandwiched between the positive and negative electrodes. This application does not impose any particular restrictions on the material or shape of the separator; any known separator can be used as long as it does not significantly impair the effectiveness of this application. Materials such as resins, glass fibers, and inorganic materials formed from materials stable to the non-aqueous electrolyte of this embodiment can be used. Porous sheets or non-woven fabric-like materials with excellent liquid retention properties are preferred. For example, separators made of conventional materials such as polyethylene, polypropylene, and polytetrafluoroethylene can be used.

[0117] Next, the electrical device of the third aspect of this embodiment will be described.

[0118] Electrical appliances.

[0119] It should be noted that the features and effects described for the electrolyte in the first aspect and the lithium-ion battery in the second aspect of this embodiment are also applicable to this electrical device, and will not be repeated here.

[0120] In addition, it should be noted that the specific type of electrical device is not particularly limited, and those skilled in the art can choose flexibly according to actual needs, such as including but not limited to electronic devices (such as mobile phones, laptops, tablets, wearable devices, etc.) and vehicles (such as electric vehicles, electric cars, etc.).

[0121] The present application is further illustrated below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0122] Unless otherwise specified, all materials, reagents and instruments used in the following embodiments are commercially available.

[0123] For ease of explanation, the additives used in the following examples are abbreviated as follows:

[0124] 1,1,2,2-Tetrafluoroethyl-2,2,3,3-Tetrafluoropropyl ether: denoted as Compound I;

[0125] 2-Mercapto-4-(4-pyridyl)thiazole: denoted as compound II;

[0126] Triazole compounds: designated as compound III;

[0127] 1,2,4-Triazole: denoted as compound III-1;

[0128] 1-Methyl-1,2,4-triazole: denoted as compound III-2;

[0129] 1-Ethyl-1,2,4-triazole: designated as compound III-3;

[0130] 3-(trifluoromethyl)-1H-1,2,4-triazole: denoted as compound III-4.

[0131] The components and contents of the electrolytes in Examples 1-9 and Comparative Examples 1-7 are shown in Table 1 below.

[0132] Table 1: Components and contents of electrolytes in Examples 1-9 and Comparative Examples 1-7

[0133] Components Compound I Compound II Compound III <![CDATA[LiPO2F2]]> <![CDATA[LiPF6]]> non-aqueous solvents Example 1 0.5% 5.0% 2.0% Compound III-1 - 12.5% margin Example 2 2.4% 0.1% 5.0% Compound III-1 - 12.5% margin Example 3 3.0% 2.5% 2.0% Compound III-4 - 12.5% margin Example 4 1.8% 3.2% 2.5% Compound III-4 - 12.5% margin Example 5 2.0% 2.7% 2.8% Compound III-2 - 12.5% margin Example 6 0.8% 3.0% 3.7% Compound III-2 - 12.5% margin Example 7 3.0% 4.0% 0.5% Compound III-3 - 12.5% margin Example 8 3.5% 1.8% 2.2% Compound III-3 - 12.5% margin Example 9 3.0% 2.5% 2.0% Compound III-4 0.2% 12.5% margin Comparative Example 1 - - - - 12.5% margin Comparative Example 2 3.0% - - - 12.5% margin Comparative Example 3 - 2.5% - - 12.5% margin Comparative Example 4 - - 2.0% Compound III-4 - 12.5% margin Comparative Example 5 - 2.5% 2.0% Compound III-4 - 12.5% margin Comparative Example 6 3.0% 2.5% - - 12.5% margin Comparative Example 7 3.0% - 2.0% Compound III-4 - 12.5% margin

[0134] In Table 1, the total content of all components is 100%, and the non-aqueous solvent is composed of ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) in a mass ratio of 1:1:1.

[0135] In Table 1, 2.0% compound III-1 indicates that the triazole compound used is 1,2,4-triazole, and the amount of 1,2,4-triazole added is 2.0%; similarly, 2.0% compound III-4 indicates that the triazole compound used is 3-(trifluoromethyl)-1H-1,2,4-triazole, and the amount of 3-(trifluoromethyl)-1H-1,2,4-triazole added is 2.0%.

[0136] The preparation method of the above electrolyte includes: mixing ethylene carbonate (EC), diethyl carbonate (DEC) and methyl ethyl carbonate (EMC) in an argon atmosphere glove box with a water content of <10ppm at a mass ratio of EC:PC:PP=1:1:1; then dissolving fully dried lithium salt LiPF6 in the mixed non-aqueous solvent; then adding the above additives; and mixing evenly to obtain the electrolyte.

[0137] The electrolytes prepared in Examples 1-6 and Comparative Examples 1-7 were used to prepare the corresponding lithium-ion batteries, specifically including:

[0138] (1) Preparation of positive electrode sheet:

[0139] Will Li(Ni 0.5 Co 0.2 Mn 0.3 O2, conductive agent SuperP, binder PVDF, and carbon nanotubes (CNTs) were mixed in a mass ratio of 95.2:1.5:2.3:1. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum to prepare a uniform lithium-ion battery positive electrode slurry. The positive electrode slurry was then uniformly coated onto an aluminum foil with a thickness of approximately 12 μm, with a coating weight of 0.032 g / cm³. 2 The material is dried in an 85°C oven for 4 hours, and then cold-pressed and die-cut to form a positive electrode sheet.

[0140] (2) Preparation of negative electrode sheet:

[0141] Graphite was mixed with conductive agent SuperP, thickener CMC, and binder SBR (styrene-butadiene rubber latex) at a mass ratio of 95:1.5:1.5:2. Deionized water was added, and the mixture was stirred evenly under vacuum. The resulting slurry was then uniformly coated onto a copper foil with a thickness of approximately 12 μm, with a coating weight of 0.0225 g / cm³. 2 The material is dried in a forced-air oven at 85°C for 4 hours, and then cold-pressed and slit to obtain the negative electrode sheet.

[0142] (3) Preparation of the separating membrane

[0143] A 10μm thick polyethylene film (purchased from Celgard) was selected.

[0144] (4) Preparation of lithium-ion secondary batteries

[0145] The positive electrode, separator, and negative electrode prepared above are sequentially stacked to form a stacked assembly, wherein the thickness of the stacked assembly is 4.8 mm, the width is 58 mm, and the length is 62 mm. The stacked assembly is baked under vacuum conditions and at 75°C for 12 hours, and then the electrolyte prepared above is injected. After vacuum sealing, standing, formation, final sealing, and capacity testing, a lithium-ion secondary battery is obtained.

[0146] Lithium-ion battery performance testing.

[0147] The following performance tests were conducted on the lithium-ion batteries prepared in Examples 1-9 and Comparative Examples 1-7, and the test results are shown in Table 2.

[0148] (1) High-temperature cycling performance test:

[0149] The lithium-ion battery was placed in a 45°C constant temperature chamber and left to stand for 2 hours. Then, the lithium-ion battery was charged at a constant current of 1C to a voltage of 4.4V (cutoff current of 0.05C). After the battery was fully charged, it was left to stand for 5 minutes. Then, it was discharged at a constant current of 1C to a voltage of 2.75V. The discharge capacity C1 after the first cycle was recorded. After 500 charge / discharge cycles, the discharge capacity C2 after the 500th cycle was recorded. The capacity retention rate of the lithium-ion battery was then determined.

[0150] 45℃, 500-cycle capacity retention (%) = C2 / C1 × 100%.

[0151] Among them, the high-temperature cycle performance of lithium-ion batteries is evaluated by the capacity retention rate at 45℃ and 500 cycles. The higher the capacity retention rate, the better the high-temperature cycle performance of the lithium-ion battery.

[0152] (2) Test of manganese leaching after high-temperature cycling:

[0153] The lithium-ion battery that had been cycled at high temperature (45°C) for 500 cycles was discharged to the lower limit voltage at a rate of 0.1C. The negative electrode was then disassembled, and the negative electrode powder was scraped off with a ceramic knife. After ICP testing, the amount of manganese dissolved on the negative electrode (ppm) was obtained, which is the amount of transition metal ion dissolved.

[0154] (3) High-temperature storage capacity retention test:

[0155] At 25°C, the lithium-ion battery was charged at a constant current of 1.0C to 4.4V, then charged at a constant voltage of 4.4V to the cutoff current of 0.05C. The battery was then discharged at a constant current of 1.0C to 2.75V. The discharge capacity was recorded as C0.

[0156] At 25℃, the lithium-ion battery was charged at a constant current of 1.0C to 4.4V, and then charged at a constant voltage of 4.4V to a cutoff current of 0.05C. The lithium-ion battery was then transferred to a 60℃ constant temperature chamber for storage for 30 days. After the storage period, the lithium-ion battery was removed and cooled to room temperature. At 25℃, the battery was discharged at a constant current of 1.0C to 2.75V, and the discharge capacity was recorded as C1. The high-temperature storage capacity retention rate of the lithium-ion battery was determined.

[0157] The formula for calculating the high-temperature storage capacity retention rate is: High-temperature storage capacity retention rate (%) = C1 / C0 × 100%.

[0158] Each performance test involved testing three batteries in parallel and taking the average value as the test result.

[0159] Table 2: Test results of lithium-ion batteries corresponding to Examples 1-9 and Comparative Examples 1-7

[0160] test group High-temperature storage capacity retention rate (%) after 30 days Capacity retention rate at 45℃ and 500 cycles (%) Leaching amount of transition metal manganese (ppm) Example 1 92.9 91.8 108 Example 2 90.9 90.0 120 Example 3 95.4 94.2 93 Example 4 94.8 93.8 96 Example 5 94.2 93.1 100 Example 6 93.3 92.4 104 Example 7 91.6 90.6 115 Example 8 93.6 92.6 102 Example 9 96.7 95.3 90 Comparative Example 1 37.3 34.5 345 Comparative Example 2 53.1 52.4 289 Comparative Example 3 62.2 60.8 238 Comparative Example 4 58.8 57.5 269 Comparative Example 5 75.7 71.2 159 Comparative Example 6 80.8 78.5 181 Comparative Example 7 78.5 76.1 201

[0161] Based on the test results in Table 2, it can be concluded that Examples 1-8, by adding 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, triazole compounds, and 2-mercapto-4-(4-pyridyl)thiazole to the electrolyte, can better suppress the dissolution of transition metal ions and significantly improve the high-temperature cycle performance and high-temperature storage performance of lithium-ion batteries. Among them, Example 3 (3.0% compound I, 2.5% compound II, 2.0% compound III-4) showed the best results.

[0162] Example 9 adds LiPO2F2 to Example 3, which can further effectively suppress the dissolution of transition metal manganese in the electrolyte and improve the high-temperature cycle performance and high-temperature storage performance of lithium-ion batteries.

[0163] Combining Comparative Example 1 and Example 3, it can be seen that Comparative Example 1, without additives, leads to the dissolution of a large amount of transition metal manganese, and its capacity retention rate decreases significantly after 30 days of high-temperature storage or 500 cycles at 45°C. This directly illustrates the importance of the additive system in improving the high-temperature storage stability of the electrolyte; without additives, the battery experiences severe capacity decay at high temperatures.

[0164] Based on the test results of Example 3 and Comparative Examples 2-4, compared with Example 3, the high-temperature cycle retention rates of Comparative Example 2 (containing only 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether), Comparative Example 3 (containing only 2-mercapto-4-(4-pyridyl)thiazole), and Comparative Example 4 (containing only 3-(trifluoromethyl)-1H-1,2,4-triazole) were 53.1%, 62.2%, and 58.8%, respectively. All of these improved the undesirable effects without additives to some extent, but were far lower than those of Example 3. Simultaneously, the dissolution of the transition metal manganese was also significantly increased, indicating that 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, triazole compounds, and 2-mercapto-4-(4-pyridyl)thiazole, when used alone, cannot achieve a breakthrough in high-temperature performance; they can only improve the electrochemical performance of lithium ions to a limited extent in the basic electrolyte.

[0165] Further comparison of Example 3 and Comparative Example 5 shows that, compared with Example 3, Comparative Example 5, which uses 2-mercapto-4-(4-pyridyl)thiazole and 3-(trifluoromethyl)-1H-1,2,4-triazole, shows an increase in the dissolution of transition metal manganese in Comparative Example 5. This indicates that in Example 3, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE458), triazole compounds, and 2-mercapto-4-(4-pyridyl)thiazole can construct a dense, uniform, and stable composite CEI film on the positive electrode surface, thereby better blocking the direct contact between the positive electrode and the electrolyte, reducing lattice oxygen release, and reducing the dissolution rate of transition metal ions from the source.

[0166] However, the high-temperature cycling and high-temperature storage performance of Comparative Example 5 showed a significant decrease. This is because the fluorinated physical film formed by 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether provides a uniform reaction substrate for the adsorption and oxidation of triazole compounds and 2-mercapto-4-(4-pyridyl)thiazole. In Comparative Example 5, the absence of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether leads to excessive localized reaction of triazole compounds and 2-mercapto-4-(4-pyridyl)thiazole, forming a thick film. This significantly increases the interfacial impedance, thereby affecting the high-temperature cycling and high-temperature storage performance of Comparative Example 5.

[0167] In addition, Comparative Examples 6 and 7 were modified by adding 2-mercapto-4-(4-pyridyl)thiazole or 3-(trifluoromethyl)-1H-1,2,4-triazole to Comparative Example 2. Compared with Comparative Example 1, Comparative Examples 2 and 3 could effectively improve the defects of HFE458 when used alone (weak ionic conductivity); however, compared with Example 3, the amount of manganese leached from the transition metal increased in Comparative Examples 6 and 7, and the high-temperature cycling performance and high-temperature storage performance decreased significantly.

[0168] This is because Comparative Example 6, lacking 3-(trifluoromethyl)-1H-1,2,4-triazole, resulted in an insufficient mechanical strength due to the absence of a nitrogen-containing intermediate layer in its CEI membrane. Furthermore, the lack of nitrogen atoms to form monodentate coordination bonds with metal ions led to a manganese leaching amount of 181 ppm, and its high-temperature storage and cycling performance were significantly lower than that of Example 3. Comparative Example 7, lacking the compound 2-mercapto-4-(4-pyridyl)thiazole, exhibited high porosity and poor ionic conductivity in its outer CEI membrane due to the absence of sulfur-containing structures. Simultaneously, the metal ions lost the strong binding of the bidentate chelate structure, resulting in even worse performance than Comparative Example 6.

[0169] This indicates that this embodiment is based on a coordination system formed by two compounds, triazole and 2-mercapto-4-(4-pyridyl)thiazole, in the electrolyte to better immobilize metal ions and inhibit excessive dissolution of manganese. At the same time, the synergistic, dense, and stable composite CEI film of the three compounds is used to improve the chemical performance of the lithium battery at high temperatures.

[0170] In summary, in the electrolyte of this embodiment, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, triazole compounds, and 2-mercapto-4-(4-pyridyl)thiazole, through the synergistic cooperation of base layer construction, intermediate layer reinforcement, and outer layer optimization, can form a dense and uniform composite CEI film on the positive electrode surface, improving the chemical stability of the electrolyte at high temperatures and blocking contact between the positive electrode and the electrolyte, thus reducing lattice oxygen release. At the same time, the above-mentioned additives can better fix / complex transition metal ions, effectively preventing the deposition of transition metals on the negative electrode after dissolution, thereby significantly improving the high-temperature cycle performance and high-temperature storage performance of lithium-ion batteries, providing key technical support for the long-term and stable application of high-voltage lithium-ion batteries.

[0171] The technical solutions provided by the embodiments of this application have been described in detail above. Specific examples have been used in this document to illustrate the principles and implementation methods of the embodiments of this application. The descriptions of the embodiments above are only for helping to understand the principles of the embodiments of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the embodiments of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. An electrolyte, characterized in that, The electrolyte comprises: Lithium salts Non-aqueous solvents, and additive; The additives include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, triazole compounds, and 2-mercapto-4-(4-pyridyl)thiazole; The triazole compound has the general structural formula shown in Formula I: ； Formula I R is selected from alkyl, fluoroalkyl, hydrogen, cycloalkyl, heterocycloalkyl, vinyl or ethynyl.

2. The electrolyte according to claim 1, characterized in that, The R is selected from alkyl groups having 1 to 6 carbon atoms, fluoromethyl groups, 1-fluoroethyl groups, 2-fluoroethyl groups, 1-fluoropropyl groups, 2-fluoropropyl groups, saturated or unsaturated five-membered or six-membered rings, or saturated five-membered or six-membered heterocycles.

3. The electrolyte according to claim 1 or 2, characterized in that, The triazole compound is selected from at least one of 1,2,4-triazole, 1-methyl-1,2,4-triazole, 1-ethyl-1,2,4-triazole, and 3-(trifluoromethyl)-1H-1,2,4-triazole.

4. The electrolyte according to claim 1, characterized in that, The content of the triazole compound is 0.5-5%, based on the total mass of the electrolyte.

5. The electrolyte according to claim 1, characterized in that, The content of the 2-mercapto-4-(4-pyridyl)thiazole is 0.1-5%, based on the total mass of the electrolyte.

6. The electrolyte according to claim 1, characterized in that, The content of the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is 0.5-3.5%, based on the total mass of the electrolyte.

7. The electrolyte according to claim 1, characterized in that, The non-aqueous solvent is selected from one or more of propylene carbonate, methyl ethyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, γ-butyrolactone, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, difluoroethyl acetate, and ethyl 2,2,2-trifluoroethyl acetate.

8. The electrolyte according to claim 1, characterized in that, The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium difluorooxalate phosphate, lithium difluorooxalate borate, lithium tetrafluorooxalate phosphate, and lithium difluorosulfonylimide. The lithium salt content is 5-20%, based on the total mass of the electrolyte.

9. A lithium-ion battery, characterized in that, The lithium-ion battery includes: Positive electrode sheet; Negative electrode plate; Diaphragm; and The electrolyte according to any one of claims 1-8.

10. The lithium-ion battery according to claim 9, characterized in that, The positive electrode sheet includes a positive electrode active material; the positive electrode active material satisfies: Li(Ni x Co y Mn z O2; Among them, 0<x<1, 0<y<1, 0<z<1, x+y+z=1; The lithium-ion battery operates at a voltage of 2.75-4.4V.

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