Electrolyte and lithium ion battery

Abstract

The embodiment of the invention provides an electrolyte and a lithium ion battery. The electrolyte comprises a lithium salt, a non-aqueous solvent and an additive, the additive comprises 1, 1, 2, 2-tetrafluoroethyl-2, 2, 3, 3-tetrafluoropropyl ether, cyanomethyl benzoate and a compound with a structure as shown in a formula I which is described in the specification. According to the embodiment of the invention, 1, 1, 2, 2-tetrafluoroethyl-2, 2, 3, 3-tetrafluoropropyl ether, cyanomethyl benzoate and the compound with the structure as shown in the formula I are added into the electrolyte, the electrolyte is applied to the lithium ion battery, the obtained lithium ion battery has more excellent high-temperature cycle performance and high-temperature storage performance, and dissolution of transition metal ions can be remarkably inhibited.

Description

Technical Field

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

[0002] Lithium-ion batteries, as a relatively mature battery technology, are widely used in digital products, energy storage, and power applications. Currently, with the increasing use 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, in conventional lithium-ion electrolytes, at voltages above 4.2V, solvent molecules undergo severe irreversible oxidative decomposition on the surface of the cathode material. This leads to the dissolution of transition metals in the cathode material, resulting in byproduct deposition, narrowing of lithium-ion migration channels, and increased interfacial impedance, thus reducing initial efficiency. Furthermore, the dissolution of transition metals further consumes active lithium, causing capacity decay in the lithium-ion battery and affecting its room-temperature cycling performance. Simultaneously, the aforementioned oxidation reaction accelerates dramatically at high temperatures, and the solid electrolyte interphase (SEI) film on the negative electrode side may become unstable, leading to continuous side reactions and electrolyte consumption, resulting in a rapid deterioration of high-temperature cycling performance. Summary of the Invention

[0004] The purpose of this application is to provide an electrolyte and a lithium-ion battery.

[0005] To achieve the above objectives, the embodiments of this application propose the following technical solutions:

[0006] In a first aspect, embodiments of this application provide an electrolyte, the electrolyte comprising:

[0007] Lithium salts

[0008] Non-aqueous solvents, and

[0009] additive;

[0010] The additives include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, cyanobenzoate, and compounds with the structure shown in Formula I:

[0011]

[0012] Formula I.

[0013] In one embodiment, the content of the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is 1-5%, based on the total mass of the electrolyte.

[0014] In one embodiment, the content of cyanomethyl benzoate is 0.5-3%, based on the total mass of the electrolyte.

[0015] In one embodiment, the content of the compound with the structure shown in Formula I is 0.5-5%, based on the total mass of the electrolyte.

[0016] In one embodiment, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalate borate, and lithium bis(oxalate borate).

[0017] The lithium salt content is 5-25%, based on the total mass of the electrolyte.

[0018] In one embodiment, the non-aqueous solvent is selected from at least one of carbonates, fluorocarbonates, carboxylic acid esters, fluorocarboxylic acid esters, ethers, and fluoroethers.

[0019] In one embodiment, the non-aqueous solvent is selected from at least one 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.

[0020] The content of the non-aqueous solvent is 64-92%, based on the total mass of the electrolyte.

[0021] In one embodiment, the electrolyte also includes other additives;

[0022] The other additives also include at least one of vinylene sulfate and propylene-1,3-sulfonyl lactone;

[0023] The content of the other additives is 0.5-4%, based on the total mass of the electrolyte.

[0024] Secondly, embodiments of this application provide a lithium-ion battery, the lithium-ion battery comprising:

[0025] Positive electrode sheet;

[0026] Negative electrode plate;

[0027] Diaphragm; and

[0028] The electrolyte described in the first aspect.

[0029] In one embodiment, the positive electrode sheet includes a positive electrode active material, which includes Li(Ni)x Co y Mn z )O2, 0<x<1, 0<y<1, 0<z<1, x+y+z=1;

[0030] The lithium-ion battery operates at a voltage of 3.0-4.4V.

[0031] Compared with the prior art, the embodiments of this application have at least the following beneficial effects:

[0032] In this embodiment, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, cyanomethyl benzoate, and the compound with the structure shown in Formula I are added to the electrolyte as additives. 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether preferentially forms films on the surfaces of the positive and negative electrodes, respectively, forming initial CEI and initial SEI films. Then, HFE458, cyanomethyl benzoate, and the compound with the structure shown in Formula I work together to repair the initial CEI and initial SEI films. Simultaneously, HFE458, cyanomethyl benzoate, and the compound with the structure shown in Formula I can reduce the migration of transition metal ions, ensuring the crystal structure of the positive electrode material under high voltage. This ensures that the positive electrode still has a large number of active sites for reversible insertion and extraction of lithium ions under high voltage, ultimately ensuring that the lithium-ion battery still has superior high-temperature cycle performance and high-temperature storage performance under high voltage conditions, and significantly suppressing the dissolution of transition metal ions.

[0033] Therefore, the electrolyte in this embodiment can significantly improve the high voltage resistance, high temperature cycle performance, and high temperature storage performance of lithium-ion batteries.

[0034] 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

[0035] 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.

[0036] 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.

[0037] It should also be understood that the terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application. As used in the embodiments of this application and the appended claims, unless the context clearly indicates otherwise, the singular forms "a," "an," and "the" are intended to include the plural forms.

[0038] Below, we will first explain some of the terms and materials used in this embodiment to facilitate understanding by those skilled in the art.

[0039] HFE458: 1,1,2,2-Tetrafluoroethyl-2,2,3,3-Tetrafluoropropyl ether.

[0040] Compound I: The compound with the structure shown in Formula I.

[0041] PST: Propylene-1,3-sulfonyl lactone.

[0042] EC: Ethylene carbonate.

[0043] EMC: Ethyl methyl carbonate.

[0044] The electrolyte and lithium-ion battery of this application are described in detail below.

[0045] First, the electrolyte of the first aspect of this embodiment will be described.

[0046] Electrolyte.

[0047] Those skilled in the art will know that NCM batteries refer to those based on Li(Ni) x Co y Mn z Lithium-ion batteries made with O2 as the positive electrode, such as NCM batteries, have advantages such as high capacity, high energy density, and high operating voltage. Their operating voltage is generally between 3.6-4.2V, meaning the discharge cutoff voltage is 3.6V and the charging cutoff voltage is 4.2V. NCM batteries are commonly used in energy storage and power applications, such as electric vehicles. With the development of electric vehicles, the energy density requirements for pure electric vehicles, i.e., vehicles powered solely by batteries, are becoming increasingly higher. To further improve the energy density of NCM batteries, the Ni content in the positive electrode can be increased. For example, NCM811 represents Li(Ni) x Co y Mn z The ratio of Ni, Co, and Mn in O2 is 8:1:1, meaning the cathode material is Li(Ni) 0.8 Co 0.1 Mn 0.1O2 indicates that Ni is the most abundant of the three transition metals Ni, Co, and Mn. The role of Ni is to provide intercalation-deintercalation sites for lithium ions. The higher the Ni content, the more intercalation-deintercalation sites there are for lithium ions in the positive electrode, which means the larger the capacity of the lithium-ion battery. Under the same volume, the larger the capacity of the lithium-ion battery, the higher the energy density of the battery.

[0048] However, the higher the Ni content in the cathode, the less stable the cathode becomes. When the maximum acceptable charging cutoff voltage (typically 4.2V) is exceeded, the cathode performance rapidly degrades. This is because a high Ni content means relatively low contents of the other two transition metals, Co and Mn. Co and Mn stabilize the cathode's crystal structure, preventing instability and irreversible phase transitions at high voltages. Therefore, with a higher Ni content, at high voltages (above 4.2V), nickel ions undergo irreversible oxidative decomposition. The ionic radius of high-valence nickel ions shrinks, narrowing the lithium-ion migration channels and increasing interfacial impedance, leading to a decrease in initial efficiency. Furthermore, the dissolution of transition metals further consumes active lithium, causing lithium-ion battery capacity decay and consequently reducing the room-temperature cycling performance of the lithium-ion battery.

[0049] Furthermore, excessively high voltage can cause irreversible phase transitions in the cathode material, preventing lithium ions from intercalating or deintercalating into the cathode, resulting in permanent capacity decay and reduced cycle performance. Conversely, reducing the nickel content, i.e., correspondingly increasing the Co and / or Mn content, fails to meet the demands for high battery capacity and high energy density. Simultaneously, at high temperatures, the irreversible oxidative decomposition of the NCM battery cathode accelerates rapidly, and the SEI film on the negative electrode side may become unstable, leading to continuous side reactions and electrolyte consumption, ultimately causing a rapid deterioration in cycle performance.

[0050] In view of this, this application proposes an electrolyte for use in lithium-ion batteries. The electrolyte comprises: a lithium salt, a non-aqueous solvent, and additives; the additives include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE458), cyanobenzoate, and compound I; the structural formula of compound I is shown in Formula I:

[0051]

[0052] Formula I.

[0053] Specifically, the Chinese name of compound I is: N,N-diethyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxapentoborane-2-yl)aniline.

[0054] In this embodiment, by adding HFE458, cyanomethyl benzoate, and Compound I to the electrolyte, on the one hand, HFE458, cyanomethyl benzoate, and Compound I can reduce the migration of transition metal ions, ensuring the crystal structure of the cathode material under high voltage, and thus ensuring that the cathode still has a large number of active sites for reversible lithium ion insertion / extraction under high voltage. On the other hand, HFE458 preferentially forms films on the surfaces of the cathode and anode, respectively, forming initial CEI and initial SEI films. Then, cyanomethyl benzoate and Compound I work together to repair the initial CEI and initial SEI films; that is, the combination of HFE458, cyanomethyl benzoate, and Compound I can ensure that the CEI film on the surface of the cathode and the SEI film on the surface of the anode remain in good condition under high voltage. Furthermore, due to the repair of the initial CEI and initial SEI films by cyanomethyl benzoate and Compound I, the oxidation reaction of the cathode at high temperature is suppressed, and the stability of the SEI film at high temperature is improved.

[0055] The relevant components in the electrolyte of this embodiment will be further explained below.

[0056] 1,1,2,2-Tetrafluoroethyl-2,2,3,3-Tetrafluoropropyl ether.

[0057] In this embodiment, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE458) is used as a perfluoroether additive. Its molecule contains multiple CF bonds and ether bonds (-O-), exhibiting weak solvation ability. This reduces the direct contact between highly reactive solvent molecules (such as EC) in the electrolyte and the positive electrode, thereby improving the electrolyte's antioxidant capacity. Secondly, under high voltage, HFE458 preferentially decomposes compared to conventional carbonate solvents, forming LiF-rich CEI and SEI films on the positive and negative electrode surfaces, respectively, effectively isolating the positive and negative electrodes from the electrolyte. Furthermore, the weak solvation characteristics of HFE458 reduce the electrolyte's ability to complex and dissolve transition metal ions dissolved from the positive electrode, thus inhibiting transition metal ion dissolution. Additionally, during charge-discharge cycles, HFE458 generates fluorinated free radicals at high voltage. These fluorinated free radicals have strong electronegativity, reducing the oxidation state of trivalent nickel ions and inhibiting further nickel ion dissolution.

[0058] Understandably, HFE458 can improve the overall antioxidant capacity of the electrolyte. The initial CEI and SEI films it constructs can provide a uniform reaction substrate for the adsorption and oxidation of cyanobenzoate and compound I, avoiding the formation of thick films due to excessive local reactions of the above additives, which would lead to a significant increase in interfacial impedance.

[0059] Cyanobenzyl benzoate.

[0060] First, cyanomethyl benzoate preferentially undergoes redox reactions on the electrode surface compared to basic electrolyte solvents (such as carbonates). For example, in NCM ternary batteries, especially under high-nickel (such as NCM622 or NCM811) or high-voltage operating conditions, the cathode material exhibits strong oxidizing properties and readily catalyzes the decomposition of the electrolyte solvent. In the molecular structure of cyanomethyl benzoate, the benzene ring provides a conjugated stabilizing effect, while the cyano group (-CN) possesses high electrochemical oxidation stability, enabling it to withstand higher potentials. Simultaneously, the cyano group has a strong lone pair of electrons, which can react with dissolved transition metal ions (such as Mn)... 2+ A complexation reaction occurs, forming a stable complex.

[0061] Secondly, under high voltage at the positive electrode, cyanomethyl benzoate undergoes oxidative decomposition on the surface of the fluorine-containing substrate film: the cyano group in cyanomethyl benzoate forms nitrogen-containing organic compounds. These nitrogen-containing compounds can not only interact with the transition metal atoms on the surface of the positive electrode material, anchoring the transition metals on the positive electrode surface and enhancing their lattice stability, but also inhibit the leaching and dissolution of transition metal ions from the lattice from the source. Furthermore, the nitrogen-containing compounds can also intertwine with the initial CEI film formed by HFE458, repairing the initial CEI film and enhancing its mechanical strength, thus preventing the oxidation rate of the positive electrode from being accelerated due to high temperature and high voltage.

[0062] On the negative electrode side, the decomposition products of cyanomethyl benzoate also contribute to the formation of a denser and more stable SEI film. For example, the components such as Li3N contained in its decomposition products, which have high lithium-ion conductivity, can optimize the structure of the SEI film. The SEI film formed by this combination can effectively prevent solvent molecules from co-intercalating into the graphite layered structure, avoid damage to the graphite structure, and reduce the consumption of active lithium during cycling.

[0063] Compound I.

[0064] The compound I selected in this embodiment is N,N-diethyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxapentobran-2-yl)aniline, which contains a pinacol borate ester group and a diethylamino group. First, the boron atom in the pinacol borate ester group is an electron-deficient center, which can interact with highly active and unstable high-valence transition metal ions on the surface of the cathode material. This interaction helps to stabilize the crystal structure on the surface of the cathode material and inhibit the dissolution of transition metal ions from the crystal lattice.

[0065] Secondly, even with the dissolution of small amounts of transition metal ions, the diethylamino (-N(C2H5)2) group in the molecule possesses a lone pair of electrons in its nitrogen atom, and the pinacol ester group in borate contains a boron atom, with the B and N atoms located at opposite ends of the molecule, separated by a certain distance. This structure allows compound I to simultaneously interact with metal ions using two coordinating atoms, forming a chelation effect. Since metal ions need to break multiple coordinating bonds simultaneously to escape the chelate ring, this is more difficult. Therefore, the chelate formed by this chelation effect is more stable than the simple complex formed by monodentate ligands. This chelation effect can greatly enhance the ability to immobilize transition metal ions, forming stable chelates and preventing their migration to the negative electrode. This will help prevent the catalytic destruction pathway of transition metal ions on the negative electrode SEI film (such as Mn...). 2+ (Catalyzed SEI decomposition) avoids the continuous consumption of active lithium and the sharp increase in battery internal resistance.

[0066] Furthermore, compound I can undergo electrochemical decomposition on the electrode surface. Its decomposition products (organic-inorganic complexes containing boron, nitrogen, and oxygen) can be embedded in the pores or cracks of the CEI / SEI film, enhancing the mechanical strength and ionic conductivity of the CEI / SEI film and preventing its rupture during charging and discharging. Based on the above effects, both the positive electrode CEI film and the negative electrode SEI film are more stable, and the interfacial impedance of the entire battery is suppressed, which is beneficial to improving rate performance and cycle life.

[0067] The principle behind the combined effect of the above additives to improve the performance of lithium-ion batteries will be further described below.

[0068] Understandably, HFE458, as a perfluorinated molecular structure, exhibits two main characteristics. First, its weak solvation ability reduces the direct contact between highly reactive solvent molecules (such as EC) in the electrolyte and the positive electrode, thereby enhancing the electrolyte's antioxidant capacity. Second, its weak solvation properties reduce the electrolyte's ability to complex and dissolve transition metal ions leached from the positive electrode, thermodynamically inhibiting their dissolution. Simultaneously, HFE458, due to its high oxidation stability, preferentially undergoes slight oxidation under high voltage compared to the solvent, generating fluorine-containing small molecule products. These products rapidly form a dense, initial fluorine-containing CEI film on the positive electrode surface, which can reduce Ni oxidation through physical barrier properties. 3+ Contact with the electrolyte inhibits its excessive oxidation to Ni. 4+ This reduces nickel ion dissolution and prevents irreversible oxidative decomposition of the cathode material.

[0069] Secondly, during charge-discharge cycles, HFE458 preferentially forms films on the positive and negative electrode surfaces: a fluorine-containing initial CEI film is formed on the positive electrode side, providing a uniform reaction substrate for the adsorption and oxidation of cyanomethyl benzoate and compound I; on the negative electrode side, HFE458 forms a fluorine-rich initial SEI film, laying the foundation for interfacial stability. Under the high-voltage environment of the positive electrode, cyanomethyl benzoate and compound I undergo oxidative decomposition on the surface of the fluorine-containing substrate film: cyanomethyl benzoate releases cyano-containing organic products, and compound I decomposes to produce small molecular species containing BO and BN. These two types of products coexist with the fluorine-containing substrate film, forming a composite CEI film rich in BO and BNC functional groups. In this compound, boron atoms in compound I, and the nitrogen-containing compounds formed by their decomposition, can coordinate with transition metal atoms on the surface of the cathode material, anchoring the transition metal on the cathode surface and enhancing its lattice stability. This inhibits the dissolution of transition metal ions from the lattice at the source. Simultaneously, the decomposition products can fill the initial CEI film formed by HFE458 and repair defects, significantly enhancing the mechanical strength of the CEI film. Therefore, a dense, uniform, and stable composite CEI film is constructed on the cathode surface, which can more effectively suppress the oxidation reaction on the cathode surface under high voltage and high temperature, thereby inhibiting electrolyte decomposition and cathode structure collapse, and ensuring the chemical stability of the electrolyte under extreme conditions.

[0070] The composite CEI membrane described above can physically block direct contact between the positive electrode and the electrolyte, reducing lattice oxygen release and decreasing the dissolution of transition metal ions at the source. Even if a small amount of metal ions break through the CEI membrane and enter the electrolyte, the cyano group (N atom with lone pair electrons) of the cyanomethyl benzoate molecule can react with the dissolved transition metal ions (such as Mn). 2+ The compound rapidly forms a monodentate complex, achieving initial fixation. Simultaneously, the B and N atoms at both ends of molecule I act as bidentate coordination sites, forming stable chelate structures (such as six-membered chelate rings) with metal ions, further capturing incompletely fixed metal ions from cyanomethyl benzoate and preventing their migration to the negative electrode. Therefore, the synergistic coordination system formed by molecules with two different coordination mechanisms can more firmly fix free metal ions in the electrolyte, ensuring the long-term effectiveness of the SEI film at the negative electrode and thus guaranteeing the electrochemical performance of the lithium-ion battery at high voltages.

[0071] Furthermore, on the negative electrode side, the reduction potentials of both cyanomethyl benzoate and compound I are lower than those of the solvent, preferentially undergoing reduction reactions to supplement and optimize the initial SEI film formed by HFE458: cyanomethyl benzoate is reduced to generate nitrogen-containing compounds (such as Li3N), while compound I decomposes to generate organic products containing boron, nitrogen, and oxygen, as well as inorganic products such as Li2O. These organic and inorganic products intertwine to form an organic-inorganic composite layer, covering the surface of the fluorine-rich base SEI film. In this composite layer, the organic phase imparts good flexibility to the SEI film, buffering the volume changes of the negative electrode material during charging and discharging, and preventing cracking of the brittle inorganic layer; the inorganic phase enhances the mechanical strength and stability of the SEI film, optimizing ion conduction efficiency. Simultaneously, because the positive electrode CEI film effectively reduces the dissolution of transition metal ions, the number of metal ions migrating to the negative electrode is significantly reduced. This avoids the side reactions of metal ions catalyzing SEI film decomposition and inducing dendrite growth, and synergizes with the aforementioned SEI film repair effect, further ensuring the stability of the SEI film under high voltage and high temperature conditions and preventing abnormal increases in interfacial impedance.

[0072] Therefore, the electrolyte of this embodiment, when applied to lithium-ion batteries, can significantly improve the high-temperature cycle performance and high-temperature storage performance of the batteries.

[0073] In summary, this embodiment uses HFE458, cyanomethyl benzoate, and Compound I as electrolyte additives. First, HFE458 preferentially forms the initial CEI / SEI film, reducing the extraction of transition metal ions and providing a uniform reaction substrate for the subsequent reactions of cyanomethyl benzoate and Compound I at the positive and negative electrodes. Second, through the coordination of transition metal ions with cyanomethyl benzoate and Compound I, the dissolution of transition metal ions is reduced at the source. That is, HFE458, cyanomethyl benzoate, and Compound I work together to significantly inhibit the dissolution of transition metal ions. Furthermore, cyanomethyl benzoate and Compound I react uniformly on the surface of the initial CEI / SEI film, and the reaction products replenish the initial CEI / SEI, improving the mechanical strength and ionic conductivity of the CEI / SEI film. Therefore, the electrolyte of this embodiment can significantly improve the high-voltage performance, high-temperature cycle performance, and high-temperature storage performance of lithium-ion batteries.

[0074] Further, the amount of HFE458 used in the electrolyte is 1-5%, based on the total mass of the electrolyte. For example, the amount of HFE458 used in the electrolyte includes, but is not limited to:

[0075] 1%, 1.1%, 1.11%, 1.25%, 1.3%, 1.4%, 1.44%, 1.48%, 1.5%, 1.52%, 1.56%, 1.75%, 1.79%, 1.8%, 1.85%, 1.9%, 2.0%, 2.01%, 2.05%, 2.09%, 2.1%, 2.2%, 2.4%, 2.5%, 2.6%, 2.8%, 3%, 3.1%, 3.15%, 3. 19%, 3.25%, 3.28%, 3.32%, 3.36%, 3.38%, 3.4%, 3.47%, 3.52%, 3.54%, 3.59%, 3.6%, 3.63%, 3.7%, 3.75%, 3.82%, 3.85%, 3.87%, 3.91%, 3.94%, 4%, 4.1%, 4.2%, 4.41%, 4.5%, 4.6%, 4.7%, 4.9%, 5%.

[0076] Further, the amount of cyanomethyl benzoate in the electrolyte is 0.5-3%, based on the total mass of the electrolyte. Exemplarily, the amount of cyanomethyl benzoate in the electrolyte includes, but is not limited to:

[0077] 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%, 1.1%, 1.2%, 1.21%, 1.23%, 1.25%, 1.3%, 1.4%, 1.46%, 1.49%, 1.5%, 1.53%, 1.55%, 1.78%, 1.8%, 1.83%, 1.9%, 1.91%, 1.96%, 1.97%, 2%, 2.01%, 2.05%, 2.09%, 2.1%, 2.2%, 2.4%, 2.5%, 2.6%, 2.8%, 3%.

[0078] Furthermore, the content of compound I is 0.5-5%, based on the total mass of the electrolyte. Exemplarily, the amount of compound I in the electrolyte includes, but is not limited to:

[0079] 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%, 1.1%, 1.2%, 1.22%, 1.25%, 1.28%, 1.3%, 1.4%, 1.43%, 1.49%, 1.5%, 1.54%, 1.57%, 1.76%, 1.8%, 1.85%, 1.9%, 2.0%, 2.01%, 2.03%, 2.05%, 2.07 %, 2.1%, 2.2%, 2.26%, 2.4%, 2.5%, 2.6%, 2.8%, 3%, 3.1%, 3.15%, 3.19%, 3.25%, 3.28%, 3.32%, 3.36%, 3.38%, 3.4%, 3.47%, 3.52%, 3.54%, 3.59%, 3.6%, 3.63%, 3.7%, 3.75%, 3.82%, 3.85%, 3.87%, 3.91%, 3.94%, 4%, 4.1%, 4.2%, 4.41%, 4.5%, 4.6%, 4.7%, 4.9%, 5%.

[0080] In summary, in this embodiment, when the contents of HFE458, cyanomethyl benzoate, and Compound I in the electrolyte are within a limited range, HFE458 preferentially forms films on the positive and negative electrodes, respectively, to form initial CEI and initial SEI films. Subsequently, HFE458, cyanomethyl benzoate, and Compound I work together to repair the initial CEI and initial SEI films, preventing an increase in interfacial impedance, suppressing the oxidation reaction of the positive electrode at high temperatures, and improving the stability of the SEI film at high temperatures. Simultaneously, HFE458, cyanomethyl benzoate, and Compound I can reduce the migration of transition metal ions, ensuring that the positive electrode still has a large number of active sites for reversible lithium ion insertion / extraction under high voltage. Ultimately, this ensures that the lithium-ion battery still possesses superior high-temperature cycle performance and high-temperature storage performance under high voltage conditions, and significantly suppresses the dissolution of transition metal ions.

[0081] Therefore, the combination of HFE458, cyanobenzoate, and compound I in this embodiment enables the battery prepared with the electrolyte to have better high-temperature cycling performance and high-temperature storage performance.

[0082] In this embodiment, the above-mentioned additives can be purchased directly or prepared in-house; specifically, HFE458 (CAS No.: 16627-68-2), cyanobenzoate (CAS No.: 939-56-0), and Compound I (CAS: 920304-57-0) can be purchased directly. HFE458 was purchased from Hubei Wande Chemical Co., Ltd., cyanobenzoate from Shanghai Ruisheng Chemical Technology Co., Ltd., and Compound I from Shanghai Mairui Biochemical Technology Co., Ltd.

[0083] Lithium salts.

[0084] Lithium salt is 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 bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalate borate, and lithium bis(oxalate borate).

[0085] Preferably, lithium hexafluorophosphate (LiPF6) is selected as the lithium salt. However, when using multiple lithium salts, their content is not particularly limited as long as it does not significantly impair the effectiveness of this application.

[0086] In this embodiment, the lithium salt content is 5-25%, preferably 5-20%, more preferably 10-20%, and even more preferably 12-18%, based on the total mass of the electrolyte.

[0087] For example, the amount of the lithium salt used in the electrolyte includes, but is not limited to: 5%, 5.06%, 5.11%, 5.2%, 5.3%, 5.5%, 5.6%, 5.9%, 6%, 6.1%, 6.3%, 6.5%, 7%, 7.4%, 7.6%, 7.8%, 8%, 8.1%, 8.4%, 8.7%, 9%, 9.2%, 9.5%, 9.8%, 10%, 11%, 12%, 13%, 13.3%, 14%, 14.7%, 15%, 15.5%, 16%, 16.6%, 17%, 17.2%, 17.5%, 18%, 18.4%, 18.8%, 19%, 19.2%, 19.5%, 19.7%, 20%, 21%, 22%, 23%, 24%, and 25%.

[0088] The lithium salt used in this embodiment can be purchased directly or prepared by ourselves; specifically, lithium hexafluorophosphate was purchased from Chengdu McCarthy Chemical Co., Ltd.

[0089] Non-aqueous solvent.

[0090] The electrolyte in this embodiment is similar to that of a typical non-aqueous electrolyte, usually 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 herein; any known organic solvent can be used. Preferably, organic solvents are selected from saturated cyclic carbonates, chain carbonates, chain carboxylic esters, cyclic carboxylic esters, etc., but are not particularly limited to these types. One, two, or more solvents can be used alone or in combination as the non-aqueous solvent.

[0091] Specifically, as a preferred embodiment, the non-aqueous solvent is selected from at least one of carbonates, fluorocarbonates, carboxylic acid esters, fluorocarboxylic acid esters, ethers, and fluoroethers.

[0092] In a preferred embodiment, the non-aqueous solvent is selected from at least one 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. The content of the non-aqueous solvent is 64-92%, based on the total mass of the electrolyte.

[0093] 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.

[0094] The non-aqueous solvents used in this embodiment can be purchased directly or prepared in-house; specifically, ethylene carbonate (EC) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., trifluoromethyl ethyl carbonate (FEMC) was purchased from Shanghai McLean Biochemical Technology Co., Ltd., and methyl ethyl carbonate (EMC) was purchased from Guangdong Runhe Biomedical Technology Co., Ltd.

[0095] Other additives.

[0096] In addition to the various components listed above, the electrolyte of this application may reasonably employ other functional additives without significantly impairing the effectiveness of this application. For example, at least one of vinylene sulfate and propylene-1,3-sulfonyl lactone may be used. Specifically, propylene-1,3-sulfonyl lactone may be used.

[0097] In this application, the content of other additives is 0.5-4%, preferably 0.8-4%, more preferably 1-4%, based on the total mass of the electrolyte.

[0098] For example, the amounts of the other additives mentioned above in the electrolyte include, but are not limited to: 0.5%, 0.53%, 0.55%, 0.59%, 0.6%, 0.64%, 0.68%, 0.7%, 0.73%, 0.77%, 0.8%, 0.82%, 0.88%, 0.9%, 0.93%, 0.96%, 1.0%, 1.3%, 1.6%, 1.7%, 1.8%, 1.88%, 1.9%, 1.97%, 2.0%, 2.3%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.5%, 3.8%, and 4.0%.

[0099] The additives used in this application can be purchased directly or prepared in-house; specifically, propylene-1,3-sulfonyl lactone was purchased from Shijiazhuang Jianxin Biotechnology Co., Ltd.

[0100] Next, the preparation method of the above electrolyte will be explained.

[0101] Preparation method.

[0102] The electrolyte of this application can be prepared using methods known in the art, for example:

[0103] 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.

[0104] This application does not impose any special limitations on the preparation method of the electrolyte.

[0105] Next, the lithium-ion secondary battery according to the second aspect of this embodiment will be described.

[0106] Lithium-ion secondary batteries.

[0107] The lithium-ion secondary battery of this embodiment includes: a positive electrode, a negative electrode, a separator, and the electrolyte described above. The operating voltage of the lithium-ion battery is 3.0-4.4V.

[0108] Please refer to the description of the first aspect. Since the lithium-ion secondary battery of this embodiment contains the above-mentioned electrolyte, the lithium-ion battery of this embodiment has a wider operating voltage range and a higher charging cut-off voltage (4.4V).

[0109] Positive electrode sheet.

[0110] 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.

[0111] 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.

[0112] 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.).

[0113] In some embodiments, the positive electrode active material includes Li(Ni) x Co y Mn z )O2, where, 0<x<1, 0<y<1, 0<z<1, x+y+z=1.

[0114] Preferably, the cathode material may also be selected from Li(Ni) 0.5 Co 0.2 Mn 0.3 O2, Li(Ni) 0.6 Co0.2Mn0.2)O2, Li(Ni 0.8 Co 0.1 Mn 0.1 One or more of O2.

[0115] In this embodiment, Li(Ni) 0.6 Co 0.2 Mn 0.2 O2 is described as the positive electrode.

[0116] 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.

[0117] 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.

[0118] Negative electrode sheet.

[0119] 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.

[0120] 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.

[0121] In some embodiments, the negative electrode active material may be a carbon-based material, a silicon-based material, a tin-based material, etc. For example, the negative electrode active material may be selected from one or more of soft carbon, hard carbon, and graphite. Graphite is preferred.

[0122] 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).

[0123] 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.

[0124] Diaphragm.

[0125] To prevent short circuits, a separator is typically sandwiched between the positive and negative electrode plates. This embodiment 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. Suitable materials include resins, glass fibers, and inorganic materials formed from materials that stabilize the lithium-ion electrolyte of this embodiment. Porous sheets or non-woven fabric-like materials with excellent liquid retention properties are preferred.

[0126] For example, polyethylene, polypropylene and other polyolefins, polytetrafluoroethylene, polyethersulfone, glass filters, etc. can be used. Among them, glass filters and polyolefins are preferred, and polyolefins are even more preferred.

[0127] Next, the electrical device of the third aspect of this embodiment will be described.

[0128] Electrical appliances.

[0129] It should be noted that the features and effects described for the lithium-ion battery in the second aspect of this embodiment are also applicable to this electrical device, and will not be repeated here.

[0130] 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.).

[0131] 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.

[0132] Unless otherwise specified, all materials, reagents and instruments used in the following embodiments are commercially available.

[0133] The composition and content of the electrolytes in Examples 1-8 and Comparative Examples 1-8 are shown in Table 1 below.

[0134] Table 1: Components and contents (%) of electrolytes in Examples 1-8 and Comparative Examples 1-8

[0135] Components HFE458 cyanomethyl benzoate Compound I N,N-Diethylaniline PST <![CDATA[LiPF6]]> non-aqueous solvents Example 1 4 0.5 3 - - 13 margin Example 2 2.5 3 2 - - 13 margin Example 3 3 2 2.5 - - 13 margin Example 4 4.5 2.5 0.5 - - 13 margin Example 5 1 1.5 5 - - 13 margin Example 6 5 1 1.5 - - 13 margin Example 7 1.5 2 4 - - 13 margin Example 8 3 2 2.5 - 1 13 margin Comparative Example 1 - - - - - 13 margin Comparative Example 2 3 - - - - 13 margin Comparative Example 3 - 2 - - - 13 margin Comparative Example 4 - - 2.5 - - 13 margin Comparative Example 5 - 2 2.5 - - 13 margin Comparative Example 6 3 2 - - - 13 margin Comparative Example 7 3 - 2.5 - - 13 margin Comparative Example 8 3 2 - 2.5 - 13 margin

[0136] In Table 1, the total content of all components is 100%, and the non-aqueous solvent is composed of ethylene carbonate (EC), trifluoromethyl ethyl carbonate (FEMC), and methyl ethyl carbonate (EMC) in a mass ratio of 1:1:1.

[0137] Preparation of electrolyte: In an argon atmosphere glove box with a water content of <10ppm, ethylene carbonate (EC), trifluoromethyl ethyl carbonate (FEMC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC:FEMC:EMC=1:1:1. Then, fully dried lithium salt LiPF6 was dissolved in the mixed non-aqueous solvent. HFE458, cyanomethyl benzoate, compound I / N,N-diethylaniline and PST (if any) were then added and mixed thoroughly to obtain the electrolyte.

[0138] The electrolytes prepared in Examples 1-8 and Comparative Examples 1-8 were used to prepare the corresponding lithium-ion batteries, specifically including:

[0139] (1) Preparation of positive electrode sheet:

[0140] Li(Ni) nickel cobalt manganese oxide ternary material Li(Ni) 0.6 Co 0.2 Mn 0.2 O2, conductive agent SuperP, binder PVDF, and carbon nanotubes (CNTs) were mixed in a mass ratio of 96.8:1:1.2:1. 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 0.033 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.

[0141] (2) Preparation of negative electrode sheet:

[0142] 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.

[0143] (3) Preparation of the separating membrane:

[0144] A 10μm thick polyethylene film (purchased from Celgard) was selected.

[0145] (4) Preparation of lithium-ion secondary batteries:

[0146] 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 4.7 mm, the width is 56 mm, and the length is 60 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.

[0147] Battery performance testing.

[0148] The lithium-ion batteries prepared in Examples 1-8 and Comparative Examples 1-8 were subjected to the following performance tests, and the test results are shown in Table 2.

[0149] (1) High-temperature cycling performance test:

[0150] The lithium-ion battery was placed in a 45℃ 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 3.0V. 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.

[0151] 45℃, 500-cycle capacity retention (%) = C2 / C1 × 100%.

[0152] 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.

[0153] (2) Test of manganese leaching after high-temperature cycling:

[0154] 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.

[0155] (3) High-temperature storage capacity retention test:

[0156] At 25°C, the lithium-ion battery was charged to 4.4V at a constant current of 1.0C, then charged to a cutoff current of 0.05C at a constant voltage of 4.4V. The battery was then discharged to 3.0V at a constant current of 1.0C. The discharge capacity is recorded as C0.

[0157] At 25°C, 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 until the cutoff current of 0.05C. The lithium-ion battery was then transferred to a 60°C 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°C, the battery was discharged at a constant current of 1.0C to 3.0V, and the discharge capacity was recorded as C1. The high-temperature storage capacity retention rate of the lithium-ion battery was determined.

[0158] The formula for calculating the high-temperature storage capacity retention rate is: High-temperature storage capacity retention rate (%) = C1 / C0 × 100%.

[0159] Each performance test involved testing three batteries in parallel and taking the average value as the test result.

[0160] Table 2: Test results (%) of lithium ions for Examples 1-8 and Comparative Examples 1-8

[0161] test group High-temperature storage capacity retention rate (%) High-temperature cycling performance (%) Leaching amount of transition metal manganese (ppm) Example 1 91.6 90.9 105 Example 2 92.8 92.2 96 Example 3 94.5 93.1 94 Example 4 90.5 89.2 116 Example 5 92.4 91.6 91 Example 6 90.9 89.8 109 Example 7 93.3 92.7 90 Example 8 95.8 94.6 87 Comparative Example 1 35.2 32.2 356 Comparative Example 2 51.7 50.8 299 Comparative Example 3 55.6 54.4 277 Comparative Example 4 60.7 57.9 242 Comparative Example 5 71.8 70.4 158 Comparative Example 6 74.6 72.4 195 Comparative Example 7 77.8 74.9 172 Comparative Example 8 81.8 80.1 142

[0162] According to the test results in Table 2, compared with Comparative Example 1 (blank control group), Examples 1-7 significantly improved the high voltage resistance, high temperature cycle performance and high temperature storage performance of lithium-ion batteries by adding HFE458, cyanomethyl benzoate and compounds with the structure shown in Formula I as additives to the lithium-ion battery electrolyte.

[0163] Furthermore, Example 8 adds PST to Example 3, which can effectively improve the high voltage resistance, high temperature cycle performance and high temperature storage performance of lithium-ion batteries compared with Example 3.

[0164] By comparing Example 3 with Comparative Examples 2 and 4, Comparative Example 2 only added HFE458, Comparative Example 3 only added cyanomethyl benzoate, and Comparative Example 4 only added Compound I. The high-temperature storage capacity retention rate of Comparative Example 2 was 51.7%, the high-temperature cycling performance was 50.8%, and the transition metal dissolution was 299 ppm. This shows that using HFE458 alone, compared with the blank control group, can only improve the high-temperature storage capacity retention rate and high-temperature cycling performance of lithium-ion batteries to a limited extent, and the improvement in transition metal dissolution is not high. This may be because without cyanomethyl benzoate and Compound I, HFE458 alone cannot effectively anchor the transition metal to the positive electrode surface, resulting in insufficient lattice stability and a low degree of improvement in transition metal dissolution.

[0165] In Comparative Example 3, which only added cyanomethyl benzoate, the high-temperature cycling performance and high-temperature storage capacity of Comparative Example 3 showed only limited improvement compared to the blank control group, and the improvement in transition metal dissolution was not significant. This may be because, without HFE458 preferentially forming the film, the film formed by adding only cyanomethyl benzoate is thicker, resulting in an uneven CEI film and increased interfacial impedance. At the same time, since only cyanomethyl benzoate is added, it cannot simultaneously achieve film formation and complexation of transition metal ions, and lacks the weak solvation properties of HFE458. The electrolyte's ability to complex and dissolve transition metal ions dissolved from the positive electrode is enhanced, and too many transition metal ions dissolve in the electrolyte, resulting in the inability to completely capture and anchor them. As a result, the high-temperature storage capacity retention and high-temperature cycling performance of the lithium-ion battery showed only limited improvement compared to the blank control group, and the improvement in transition metal dissolution was not significant.

[0166] Comparative Example 4, which only added Compound I, showed only limited improvement in high-temperature cycling performance and high-temperature storage capacity compared to the blank control group, similar to Comparative Example 3. Furthermore, the improvement in transition metal dissolution was not significant. This may be due to the lack of HFE458 preferentially forming a film to provide a uniform reaction substrate for the adsorption and oxidation of Compound I, leading to localized overreaction of Compound I and the formation of a thick film. This resulted in an uneven CEI film and increased interfacial impedance. Additionally, the addition of only Compound I failed to simultaneously address film formation and chelation of transition metal ions. Furthermore, the lack of HFE458's weak solvation properties increased the electrolyte's ability to complex and dissolve transition metal ions dissolved from the cathode. Excessive dissolution of transition metal ions in the electrolyte prevented complete capture and anchoring, resulting in only limited improvement in the high-temperature storage capacity retention and high-temperature cycling performance of the lithium-ion battery compared to the blank control group, with minimal improvement in transition metal dissolution.

[0167] Further comparisons were made between Example 3 and Comparative Examples 5, 6, 7, and 8. Compared to Example 3, when Comparative Example 5 lacked HFE458, when Comparative Example 6 lacked Compound I, when Comparative Example 7 lacked cyanobenzoate, and when Comparative Example 8 used N,N-diethylaniline to replace Compound I, the high-temperature storage capacity retention and high-temperature cycling performance of the lithium-ion batteries of Comparative Examples 5, 6, 7, and 8 all decreased to varying degrees; and the amount of transition metal leaching in Comparative Examples 5, 6, 7, and 8 all increased to varying degrees. The principle may be as follows: For Comparative Example 5, the lack of HFE458 allows highly active solvent molecules in the electrolyte to directly contact the positive electrode, resulting in low antioxidant capacity of the electrolyte. Furthermore, the lack of the weak solvation properties of HFE458 increases the electrolyte's ability to complex and dissolve transition metal ions dissolved from the positive electrode. Excessive dissolution of transition metal ions in the electrolyte prevents cyanomethyl benzoate and Compound I from completely preventing the migration of transition metal ions. At the same time, due to the lack of HFE458, a uniform reaction substrate cannot be provided for the adsorption and oxidation of cyanomethyl benzoate and Compound I. This leads to a decrease in the high-temperature storage capacity retention and high-temperature cycling performance of the battery corresponding to the electrolyte of Comparative Example 5, and an increase in the amount of transition metal dissolved.

[0168] In Comparative Example 6, the absence of Compound I means that the additive composition lacks an additive that can interact with transition metal ions. This prevents the additive composition of Comparative Example 6 from effectively immobilizing the beneficial metal ions in the electrolyte system, thus failing to adequately prevent the migration of metal ions to the negative electrode. Simultaneously, the lack of Compound I prevents the formation of BO and BNC polymer structures and nitrogen-containing organic matter on the positive electrode surface, hindering the effective improvement of the mechanical strength of the CEI film. Furthermore, the absence of Compound I prevents the formation of boron-, nitrogen-, and oxygen-containing organic-inorganic complexes on the negative electrode surface, further hindering the effective improvement of the mechanical strength of the SEI film. Ultimately, this leads to a decrease in the high-temperature storage capacity retention and high-temperature cycling performance of the battery corresponding to the electrolyte of Comparative Example 6, and an increase in the dissolution of transition metals.

[0169] As for Comparative Example 7, it lacks cyanomethyl benzoate. Similar to Comparative Example 6, the absence of one of the additives capable of coordinating with transition metals prevents the additive composition of Comparative Example 7 from effectively immobilizing free transition metal ions in the electrolyte system, thus failing to adequately prevent the migration of metal ions to the negative electrode. Simultaneously, the lack of cyanomethyl benzoate prevents the formation of a denser and more stable SEI film on the negative electrode surface, ultimately leading to a decrease in the high-temperature storage capacity retention and high-temperature cycling performance of the battery corresponding to the electrolyte of Comparative Example 7, and an increase in the dissolution of transition metals.

[0170] For Comparative Example 8, N,N-diethylaniline was used instead of Compound I. The difference between N,N-diethylaniline and Compound I is that N,N-diethylaniline lacks the borate pinacol ester group, which prevents N,N-diethylaniline from interacting with the highly active and unstable high-valence transition metal ions on the cathode material surface. Therefore, it cannot more effectively suppress the dissolution of transition metals. Simultaneously, the lack of the borate pinacol ester group prevents N,N-diethylaniline from forming BO, BNC structure polymers and boron, nitrogen, and oxygen-containing organic-inorganic complexes. Consequently, the additive combination in Comparative Example 8 can only provide a limited improvement in the mechanical strength and ionic conductivity of the CEI / SEI film.

[0171] In summary, this embodiment incorporates HFE458, cyanomethyl benzoate, and compound I as additives into the electrolyte. HFE458 reduces the contact between nickel ions and the electrolyte through physical barrier, and its weak solvation properties reduce the electrolyte's ability to complex and dissolve transition metal ions dissolved from the positive electrode. Furthermore, during charge-discharge cycles, HFE458 preferentially forms films on the surfaces of the positive and negative electrodes, respectively, creating initial CEI and SEI films, providing a uniform reaction substrate for the subsequent reaction of cyanomethyl benzoate and compound I. Subsequently, HFE458, cyanomethyl benzoate, and the compound with the structure shown in Formula I work together to repair the initial CEI and SEI films. Meanwhile, HFE458, cyanomethyl benzoate, and the compound with the structure shown in Formula I can reduce the migration of transition metal ions, ensure the lattice structure of the cathode material under high voltage, and thus ensure that the cathode still has a large number of active sites for reversible insertion and extraction of lithium ions under high voltage. Ultimately, this ensures that the lithium-ion battery still has better high-temperature cycle performance and high-temperature storage performance under high voltage conditions, and can significantly suppress the dissolution of transition metal ions.

[0172] Therefore, the electrolyte in this embodiment can significantly improve the high voltage resistance, high temperature cycle performance, and high temperature storage performance of lithium-ion batteries.

[0173] 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 by, The electrolyte comprises: a lithium salt, a non-aqueous solvent, and an additive; the additive comprises 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, cyanomethyl benzoate and a compound of formula I: ； formula I.

2. 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 1-5% based on the total mass of the electrolyte.

3. The electrolyte of claim 1, wherein The content of the cyanomethyl benzoate is 0.5-3% based on the total mass of the electrolyte.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The content of the compound of formula I is 0.5-5% based on the total mass of the electrolyte.

5. The electrolyte of claim 1, wherein The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium difluorophosphate, lithium difluoro oxalato borate, lithium bisoxalato borate; The content of the lithium salt is 5-25% based on the total mass of the electrolyte.

6. The electrolyte of claim 1, wherein The non-aqueous solvent is selected from at least one of carbonates, fluorinated carbonates, carboxylic acid esters, fluorinated carboxylic acid esters, ethers, fluorinated ether solvents.

7. The electrolyte according to claim 1 or 6, characterized in that, The non-aqueous solvent is selected from at least one of propylene carbonate, ethyl methyl carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, fluorinated vinylene 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, ethyl 2,2,2-trifluoroacetate; The content of the non-aqueous solvent is 64-92% based on the total mass of the electrolyte.

8. The electrolyte of claim 1, wherein, The electrolyte further comprises other additives; The other additives further comprise at least one of vinylene sulfite, propenyl-1,3-sultone; The content of the other additives is 0.5-4% based on the total mass of the electrolyte.

9. A lithium-ion battery, characterized by The lithium ion battery comprises: a positive electrode sheet; a negative electrode sheet; a separator; and the electrolyte of any one of claims 1-8.

10. The lithium-ion battery of claim 9, wherein, The positive electrode sheet includes a positive electrode active material including Li(Ni x Co y Mn z )O2, 0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1; The working voltage of the lithium ion battery is 3.0-4.4 V.

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