Lithium-ion battery and electric device

Abstract

The present application relates to a lithium-ion battery and an electric device. The lithium-ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte solution, wherein the electrolyte solution comprises additives, and the additives comprise a lithium cyano-imidazole compound and an S-containing ester compound. The S-containing ester compound comprises at least one structure selected from *-O-S(=O)2-O-*, *-O-S(=O)-O-*, and *-S(=O)2-O-*, wherein each * is independently connected to a carbon atom.

Description

Lithium-ion batteries and electrical devices Cross-references

[0001] This application claims priority to Chinese Patent Application No. 202411943349.9, filed on December 26, 2024, entitled "Lithium-ion Battery and Electrical Device", which is incorporated herein by reference in its entirety. Technical Field

[0002] This application relates to the field of battery technology, and in particular to a lithium-ion battery and an electrical device. Background Technology

[0003] In recent years, with the increasingly widespread application of lithium-ion batteries, they have been widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. Due to the significant advancements in lithium-ion battery technology, higher requirements have been placed on their high-temperature performance. Summary of the Invention

[0004] This application provides a lithium-ion battery and an electrical device, which aims to improve the high-temperature performance of the lithium-ion battery.

[0005] To achieve the above objectives, a first aspect of this application provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte contains additives, including cyano-containing imidazole lithium compounds and S-containing ester compounds;

[0006] The S-containing ester compounds include at least one of the structures *-OS(=O)2-O-*, *-OS(=O)-O-*, and *-S(=O)2-O-*, wherein each * is independently attached to a carbon atom.

[0007] In some embodiments of this application, the cyano-containing imidazole lithium compound includes one or more compounds satisfying formula (1):

[0008]

[0009] In formula (1), R1 and R2 are each independently selected from one of fluorinated or unsubstituted C0-C4 saturated alkylene groups and fluorinated or unsubstituted unsaturated hydrocarbon groups, and R3 is selected from one of fluorinated or unsubstituted C1-C4 saturated alkyl groups and fluorinated or unsubstituted unsaturated hydrocarbon groups.

[0010] In some embodiments of this application, the cyano-containing imidazole lithium compounds include 4,5-dicyano-2-(trifluoromethyl)imidazolium lithium.

[0011] In some embodiments of this application, the mass percentage of the 4,5-dicyano-2-(trifluoromethyl)imidazolium lithium in the electrolyte is 0.005% to 0.4%.

[0012] In some embodiments of this application, the mass percentage of the 4,5-dicyano-2-(trifluoromethyl)imidazolium lithium in the electrolyte is 0.02% to 0.4%.

[0013] In some embodiments of this application, one or more of the following conditions are met:

[0014] (1) The S-containing ester compounds include cyclic S-containing ester compounds;

[0015] (2) The mass percentage of the S-containing ester compound in the electrolyte is 0.007% to 2.9%.

[0016] In some embodiments of this application, the S-containing ester compound has a mass percentage content of 0.1% to 2% in the electrolyte.

[0017] In some embodiments of this application, one or more of the following conditions are met:

[0018] (1) The S-containing ester compounds include one or more of the compounds that satisfy formulas (2) to (4):

[0019]

[0020] R4, R5, and R6 are each independently selected from one of the following: H, F, fluorinated or unsubstituted C1-C10 saturated alkyl groups, fluorinated or unsubstituted unsaturated hydrocarbon groups, fluorinated or unsubstituted C6-C60 aryl groups, hydrocarbon carbonyl groups, carboxyl groups, hydrocarbon ester groups, cyano groups, silyl groups, and hydrocarbon oxy groups.

[0021] (2) The S-containing ester compounds include one or more of 1,3-propanesulfonic acid lactone, vinyl sulfate, vinyl disulfate, vinyl trisulfate, vinyl sulfite, and vinyl vinyl sulfite.

[0022] In some embodiments of this application, the additive further includes one or more of fluorocarbonate compounds, phosphate ester compounds, fluorobenzene compounds, and fluorophosphate compounds, wherein the fluorophosphate compound is lithium difluorophosphate.

[0023] In some embodiments of this application, one or more of the following conditions are met:

[0024] (1) The fluorocarbonate compound includes fluoroethylene carbonate, and the fluoroethylene carbonate has a mass percentage of 3% to 10% in the electrolyte;

[0025] (2) The phosphate ester compound includes tris(trimethylsilane) phosphate, wherein the mass percentage of tris(trimethylsilane) phosphate in the electrolyte is 0.05% to 0.5%;

[0026] (3) The electrolyte includes lithium difluorophosphate, and the mass percentage of lithium difluorophosphate in the electrolyte is 0.05% to 0.5%;

[0027] (4) The fluorobenzene compounds include one or more of monofluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene and trifluorotoluene;

[0028] (5) The additive includes fluorobenzene compounds, and the fluorobenzene compounds in the electrolyte have a mass percentage of 0.05% to 0.5%.

[0029] In some embodiments of this application, the electrolyte further comprises a non-aqueous solvent, which includes a highly conductive solvent, wherein the highly conductive solvent has the following characteristics: the conductivity of the highly conductive solvent at 25°C is 8 mS / cm to 20 mS / cm.

[0030] In some embodiments of this application, one or more of the following conditions are met:

[0031] (1) The highly conductive solvent includes a chain-like highly conductive solvent, which includes one or more of dimethyl carbonate, ethyl acetate and methyl acetate;

[0032] (2) The high conductivity solvent has a mass percentage content of 5% to 65% in the electrolyte.

[0033] In some embodiments of this application, the electrolyte further comprises an electrolyte lithium salt, which includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, wherein the molar concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.02 mol / L to 0.2 mol / L.

[0034] In some embodiments of this application, the negative electrode sheet includes a negative electrode active material layer, the negative electrode active material layer contains a negative electrode active material, and the negative electrode active material includes a silicon-based material.

[0035] In some embodiments of this application, the silicon-based material includes one or more of nano-silicon, micro-silicon, silicon-oxygen materials, and silicon-carbon materials.

[0036] In some embodiments of this application, the silicon-based material includes a silicon-carbon material, which satisfies one or more of the following conditions:

[0037] (1) The silicon-carbon material accounts for 3% to 40% of the mass of the negative electrode active material layer;

[0038] (2) In the silicon-carbon material, the mass ratio of silicon to carbon is (4-6):(6-4);

[0039] (3) The silicon-carbon material includes a porous silicon-carbon material, which includes a porous carbon matrix and silicon nanoparticles, wherein the silicon nanoparticles are loaded in the pores of the porous carbon matrix.

[0040] In some embodiments of this application, the pores include mesopores and micropores, wherein the pore diameter of the mesopores is 2nm to 10nm, and the pore diameter of the micropores is greater than or equal to 0.2nm and less than 2nm.

[0041] In some embodiments of this application, in the silicon-carbon porous material, the mesopores account for ≥50% of the number of pores.

[0042] In some embodiments of this application, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer contains a positive electrode active material, and the positive electrode active material includes at least one of nickel-cobalt-manganese-based positive electrode active material and lithium iron phosphate-based positive electrode active material.

[0043] In some embodiments of this application, the positive electrode active material includes a nickel-cobalt-manganese-based positive electrode active material, and the silicon-based material accounts for 3% to 45% of the mass of the negative electrode active material layer; or

[0044] The positive electrode active material includes lithium iron phosphate positive electrode active materials, and the silicon-based material accounts for ≤20% of the mass of the negative electrode active material layer.

[0045] In some embodiments of this application, the nickel-cobalt-manganese-based positive electrode active material includes lithium, nickel, cobalt, manganese and oxygen, wherein, based on the total atomic molar number of all transition metal elements, the atomic molar number of nickel accounts for 50% to 95%.

[0046] In some embodiments of this application, the nickel-cobalt-manganese-based cathode active material includes Li x’ Ni x Co y Mn 1-x-y O y’ , 0.7≤x≤0.95, 0 <y≤0.3,0.6≤x’≤1.2,1.6≤y’≤2.2。

[0047] In some embodiments of this application, the maximum charging cutoff voltage of the lithium-ion battery is greater than or equal to 4.3V, and the electrolyte satisfies the following characteristics: the mass fraction of dimethyl carbonate in the electrolyte is less than or equal to 30%.

[0048] Alternatively, the nickel-cobalt-manganese-based cathode active material includes a first nickel-cobalt-manganese-based cathode active material, and the electrolyte satisfies the following characteristics: the mass fraction of dimethyl carbonate in the electrolyte is less than or equal to 30%; wherein, in the first nickel-cobalt-manganese-based cathode active material, the atomic molar ratio of nickel element is 50% to 60% based on the total atomic molar number of all transition metal elements.

[0049] In some embodiments of this application, the first nickel-cobalt-manganese-based positive electrode active material includes Li x1’ Ni 0.5 Co y2 Mn 0.5-y2 O y1’ and Li x2’ Ni 0.6 Co y3 Mn 0.4-y3 O y2’ One or two of them, 0 <y2<0.5,0<y3<0.4,0.6≤x1’≤1.2,1.6≤y1’≤2.2,0.6≤x2’≤1.2,1.6≤y2’≤2.2。

[0050] In the lithium-ion battery provided in this application, cyano-containing imidazole lithium compounds and S-containing ester compounds are combined. Not only can the two play their individual roles to improve the stability of the electrode interface, but they also promote and synergize with each other, thereby improving the stability of the electrode interface and the high-temperature storage life of the battery.

[0051] A second aspect of this application provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte contains additives, including cyano-containing imidazole lithium compounds and S-containing ester compounds;

[0052] The S-containing ester compound includes at least one structure selected from *-OS(=O)2-O-*, *-OS(=O)-O-*, and *-S(=O)2-O-*, wherein each * is independently attached to a carbon atom, and the S-containing ester compound has a mass percentage content of 0.01% to 4% in the electrolyte.

[0053] A third aspect of this application provides an electrical device including a lithium-ion battery as described in the first aspect of this application.

[0054] The electrical device of this application includes the lithium-ion battery provided in this application, and therefore has at least the same advantages as the lithium-ion battery.

[0055] Details of one or more embodiments of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0056] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort. In the drawings:

[0057] Figure 1 is a schematic diagram of a battery cell according to one embodiment of this application.

[0058] Figure 2 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 1.

[0059] Figure 3 is a schematic diagram of a battery device according to an embodiment of this application.

[0060] Figure 4 is a schematic diagram of a battery pack according to one embodiment of this application.

[0061] Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4.

[0062] Figure 6 is a schematic diagram of an electrical device using a lithium-ion battery as a power source according to an embodiment of this application.

[0063] Reference numerals: 1 Battery pack; 2 Upper casing; 3 Lower casing; 4 Battery assembly; 5 Individual battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate; 6 Electrical device. Detailed Implementation

[0064] Hereinafter, some embodiments of this application are described in detail with appropriate reference to the accompanying drawings. However, some unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0065] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Ranges defined in this way can include or exclude endpoints. Any endpoint can be included or excluded independently, and they can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is expected that ranges of 60–110 and 80–120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are also listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0066] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0067] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0068] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0069] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0070] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0071] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0072] The term "cyano-containing imidazole lithium compounds" refers to compounds whose molecular structure contains a cyano group (-CN) and imidazole lithium. It is a general term for compounds.

[0073] The term "saturated alkyl" refers to a hydrocarbon group containing only a carbon-carbon single bond. Phrases containing this term, such as "C1-C10 saturated alkyl," refer to saturated alkyl groups containing 1 to 10 carbon atoms, and each occurrence can independently be C1 alkyl, C2 alkyl, C3 alkyl, C4 alkyl, C5 alkyl, C6 alkyl, C7 alkyl, C8 alkyl, C9 alkyl, or C10 alkyl. Suitable examples include, but are not limited to: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl, isohexyl, n-heptyl, octyl, etc.

[0074] The term "unsaturated hydrocarbon group" refers to a hydrocarbon group containing a carbon-carbon double bond (i.e., alkenyl), a carbon-carbon triple bond (i.e., alkynyl), or an aromatic group. Phrases containing this term, such as "C2–C9 unsaturated hydrocarbon group," refer to an alkenyl group containing 2–9 carbon atoms and / or an alkynyl group containing 2–9 carbon atoms, which, each time appearing, can independently be C2-alkenyl, C3-alkenyl, C4-alkenyl, C5-alkenyl, C6-alkenyl, C7-alkenyl, C8-alkenyl, or C9-alkenyl; and / or C2-alkynyl, C3-alkynyl, C4-alkynyl, C5-alkynyl, C6-alkynyl, C7-alkynyl, C8-alkynyl, or C9-alkynyl. Suitable examples include, but are not limited to: vinyl (-CH=CH2), allyl (-CH2CH=CH2), cyclopentenyl (-C5H7) and 5-hexenyl (-CH2CH2CH2CH2CH=CH2), ethynyl (-C≡CH) or propynyl (-CH2C≡CH), etc.

[0075] The term "alkylene" refers to the group formed by removing one hydrogen atom from each of the two carbon atoms in a saturated alkyl molecule, and can be represented by the general formula -(CH2). n -express.

[0076] The term "hydroalkyl group" refers to the group formed by removing one hydrogen atom from each of the two carbon atoms in an unsaturated hydrocarbon molecule.

[0077] The term "aryl" refers to an aromatic hydrocarbon group derived from an aromatic ring compound by removing one hydrogen atom. It can be a monocyclic aryl, a fused-ring aryl, or a polycyclic aryl; for polycyclic species, at least one is an aromatic ring system. For example, "C5–C20 aryl" refers to an aryl group containing 5–20 carbon atoms, which can be independently classified as C5, C6, C10, C14, C18, or C20 aryl. Suitable examples include, but are not limited to, benzene, biphenyl, naphthalene, anthracene, phenanthrene, dinaphthalene, triphenylene and their derivatives. Understandably, multiple aryl groups can also be interrupted by short non-aromatic units (e.g., <10% non-H atoms, such as C, N, or O atoms), specifically acenaphthene, fluorene, or 9,9-diarylfluorene, triarylamines, and diaryl ether systems should also be included in the definition of aryl.

[0078] The term "carbonyl" refers to

[0079] The term "hydrocarbonyl" refers to R' is a hydrocarbon group.

[0080] The term "carboxyl group" refers to

[0081] The term "ester group" refers to *-OC(=O)-*.

[0082] The term "hydrocarbon ester group" refers to *-OC(=O)-R1' or *-C(=O)O-R2', where R1' and R2' are both hydrocarbon groups.

[0083] The term "cyano" refers to *-C≡N.

[0084] The term "hydroxyl group" refers to *-O-R3', where R3' is a hydrocarbon group.

[0085] The term "silyl group" refers to a group formed by attaching a silicon atom (Si) to an alkyl group, which can be represented by the general formula *-Si-R4', where R4' is an alkyl group.

[0086] The term "carbonate compounds" refers to the collective term for compounds in which the hydrogen atoms of the two hydroxyl groups (*-OH) in a carbonic acid molecule are replaced by alkyl groups.

[0087] The term "phosphate esters" refers to ester derivatives of phosphate, a general term for compounds in which some hydroxyl hydrogen atoms in a phosphate molecule are replaced by alkyl groups.

[0088] The term "fluorobenzene compounds" refers to a group of compounds whose molecular structure contains fluorine atoms and a benzene ring, and one or more hydrogen atoms on the benzene ring are replaced by fluorine.

[0089] In all the above structural formulas, "*" represents a connection site.

[0090] High-temperature storage life of lithium-ion batteries is one of the important indicators for measuring the high-temperature performance of batteries. Traditional lithium-ion batteries usually have poor stability of the electrode interface under high temperature or high SOC conditions. The interface components are very prone to thermal decomposition or electrochemical decomposition processes, which leads to the destruction of the interface structure, resulting in a decrease in the high-temperature storage life and poor high-temperature performance of the battery.

[0091] To address the aforementioned technical problems, this application proposes a lithium-ion battery in which the high-temperature performance of the lithium-ion battery can be improved by combining cyanide-containing imidazole lithium compound additives and S-containing ester compound additives in the electrolyte. The lithium-ion battery will be described in detail below.

[0092] In a first aspect, this application provides a lithium-ion battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte contains additives, and the additives include cyano-containing imidazole lithium compounds and S-containing ester compounds;

[0093] The S-containing ester compounds include at least one of the structures *-OS(=O)2-O-*, *-OS(=O)-O-*, and *-S(=O)2-O-*, wherein each * is independently attached to a carbon atom.

[0094] The electrolyte of the aforementioned lithium-ion battery contains cyano-containing imidazole lithium compounds and S-containing ester compounds as additives. Among them, the cyano-containing imidazole lithium compounds contain unsaturated cyano groups (-CN) and N-containing unsaturated heterocycles. Such unsaturated groups have high reactivity and can preferentially participate in the film-forming reaction at the electrode interface in the battery, generating components resistant to electrochemical decomposition. This can suppress the consumption of electrolyte solvent and improve the stability of the electrode interface. At the same time, the lithium component in imidazole lithium promotes the participation of this type of compound in the film-forming reaction at the electrode interface, which is conducive to further improving the stability of the electrolyte interface. The S-containing ester compounds can participate in the film-forming reaction at the electrode interface to generate film components such as sulfates and sulfites, which are more stable than carbonates, thereby improving the high-temperature stability of the interface.

[0095] When cyano-containing imidazole lithium compounds and sulfur-containing ester compounds are combined and used in the interfacial film-forming reaction, the cyano-imidazole compounds, with their unsaturated triple bonds and cyclic structures, exhibit high reactivity and readily generate cross-linked organic components. The sulfur-containing ester compounds, on the other hand, produce inorganic sulfate interfacial components with good chemical stability. The combination of the two can form an organic-inorganic composite interface. This not only allows each compound to exert its individual effect to improve the stability of the electrode interface, but also promotes and synergizes with the other compound, further enhancing the stability of the electrode interface and the high-temperature storage life of the battery.

[0096] It can be understood that the "carbon atom" in the above "*each independently connected to a carbon atom" refers to the carbon atom contained in the structure of the sulfur-containing ester compound itself (i.e., the carbon atom of the sulfur-containing ester compound itself); the exemplary structural formulas are shown in formulas (2) to (4).

[0097] It should be noted that "high temperature" as used in this application refers to a temperature greater than or equal to 40°C, such as 60°C.

[0098] In some embodiments, the cyano-containing imidazole lithium compound comprises one or more compounds satisfying formula (1):

[0099]

[0100] In formula (1), R1 and R2 are each independently selected from one of fluorinated or unsubstituted C0-C4 saturated alkylene groups and fluorinated or unsubstituted unsaturated hydrocarbon groups, and R3 is selected from one of fluorinated or unsubstituted C1-C4 saturated alkyl groups and fluorinated or unsubstituted unsaturated hydrocarbon groups.

[0101] When at least one of R1, R2, or R3 contains a fluorine atom, it can protect the interface on the negative electrode side and help improve the stability of the interface on the negative electrode side.

[0102] In some embodiments, R3 is selected from fluorinated or unsubstituted C1-C3 saturated alkyl groups, further selected from fluorinated or unsubstituted C1-C2 saturated alkyl groups, even further selected from fluorinated or unsubstituted methyl groups, and even further selected from H.

[0103] In some embodiments, R3 is selected from fluorinated or unsubstituted C2-C3 unsaturated hydrocarbon groups, and may further be alkenyl groups.

[0104] In some embodiments, R2 and R4 are each independently selected from fluorinated or unsubstituted C1-C3 saturated alkylene groups, further selected from fluorinated or unsubstituted C1-C2 saturated alkylene groups, even further selected from fluorinated or unsubstituted methylene groups, and even further selected from single bonds (i.e., C0).

[0105] In some embodiments, R2 and R4 are each independently selected from fluorinated or unsubstituted C2-C3 unsaturated alkylene groups, further selected as alkenyl groups, and even further selected as single bonds (i.e., C0).

[0106] In some embodiments, the cyano-containing imidazole lithium compound includes 4,5-dicyano-2-(trifluoromethyl)imidazolium lithium (LiTDI). ).

[0107] 4,5-Dicyano-2-(trifluoromethyl)imidazolium not only contains highly reactive -CN and N-containing unsaturated heterocycles, but the introduction of -CF3 can also increase its reduction reaction potential, which helps it to form a film at the negative electrode interface. At the same time, the LiF generated by -CF3 participating in the film formation reaction can further improve the stability of the interface, thereby further improving the high-temperature storage life of the battery.

[0108] In some embodiments, the mass percentage of lithium 4,5-dicyano-2-(trifluoromethyl)imidazolium in the electrolyte is 0.005% to 0.4%. For example, the mass percentage of lithium 4,5-dicyano-2-(trifluoromethyl)imidazolium in the electrolyte can be 0.005%, 0.01%, 0.02%, 0.04%, 0.06%, 0.08%, 0.1%, 0.12%, 0.14%, 0.16%, 0.18%, 0.2%, 0.21%, 0.23%, 0.25%, 0.27%, 0.29%, 0.3%, 0.32%, 0.34%, 0.36%, 0.38%, 0.4%, or within any range of the above values; optionally, it is 0.02% to 0.4%.

[0109] As a self-consuming component, lithium 4,5-dicyano-2-(trifluoromethyl)imidazolium has high reactivity. Appropriate control of its mass percentage in the electrolyte can not only improve the stability of the electrode interface, but also maintain high ion transport performance at the interface and reduce the increase of polarization.

[0110] In some embodiments, the S-containing ester compound includes cyclic S-containing ester compounds.

[0111] Cyclic S-containing esters have relatively stronger reactivity, which makes them more likely to participate in the interfacial film-forming reaction than electrolyte solvents. This helps to further reduce the consumption of electrolyte solvents and improve the stability of the interface.

[0112] In some embodiments, the S-containing ester compound in the electrolyte comprises 0.007% to 2.9% by mass. For example, the S-containing ester compound in the electrolyte may be 0.007%, 0.01%, 0.05%, 0.07%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, 1.5%, 2%, 2.5%, 2.9%, or within any range of the above values; optionally, it may be 0.1% to 1%.

[0113] By appropriately controlling the mass percentage of S-containing ester compounds in the electrolyte, the stability of the electrode interface can be improved, and the intrinsic stability of the electrolyte can be maintained at a high level.

[0114] In some embodiments, the S-containing ester compound includes one or more compounds satisfying formulas (2) to (4):

[0115]

[0116] R4, R5, and R6 are each independently selected from one of the following: H, F, fluorinated or unsubstituted C1-C10 saturated alkyl groups, fluorinated or unsubstituted unsaturated hydrocarbon groups, fluorinated or unsubstituted C6-C60 aryl groups, hydrocarbon carbonyl groups, carboxyl groups, hydrocarbon ester groups, cyano groups, silyl groups, and hydrocarbon oxy groups.

[0117] When cyclic sulfate compounds satisfying formula (2) or cyclic sulfite compounds satisfying formula (4) participate in interfacial film-forming reactions, they can generate film components such as sulfates or sulfites, which have higher stability than carbonates, which is beneficial to improving the high-temperature stability of the electrode interface. Cyclic sulfonate compounds satisfying formula (4) have an asymmetric structure, which can improve interfacial passivation and gas generation, and improve high-temperature performance.

[0118] In some embodiments, the S-containing ester compounds include cyclic sulfate compounds satisfying formula (2), cyclic sulfite compounds satisfying formula (4), and cyclic sulfonate compounds satisfying formula (4). When the three types of cyclic S-containing ester compounds are used in combination, they promote each other and have a better effect on improving interface passivation and high-temperature stability.

[0119] In some embodiments, the S-containing ester compound includes one or more of 1,3-propanesulfonate lactone, vinyl sulfate, vinyl disulfate, vinyl trisulfate, vinyl sulfite, and vinyl vinyl sulfite. This helps to further improve the high-temperature stability of the electrode interface and enhance the high-temperature performance of the battery.

[0120] In some embodiments, the additive further includes one or more of fluorocarbonate compounds, phosphate ester compounds, fluorobenzene compounds, and fluorophosphate compounds.

[0121] In some embodiments, the fluorocarbonate compound includes fluoroethylene carbonate (FEC). Fluoroethylene carbonate can effectively repair electrode interfaces, especially silicon-based anode interfaces, where the repair effect is particularly outstanding.

[0122] In some embodiments, the fluoroethylene carbonate ester is present in the electrolyte at a mass percentage of 3% to 10%. For example, the mass percentage of the fluoroethylene carbonate ester in the electrolyte may be 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or within any range of the above values.

[0123] By controlling the mass percentage of fluoroethylene carbonate in the electrolyte within a suitable range, it can effectively repair the electrode interface and reduce the occurrence of cycle-induced water drop caused by insufficient interface repair. On the other hand, it can also reduce the formation of acidic substances and improve the stability of the interface and its high-temperature stability.

[0124] In some embodiments, the phosphate ester compound includes one or more of tris(trimethylsilane) phosphate, tris(hexafluoroisopropyl) phosphate, and lithium difluorophosphate. These phosphate ester compounds facilitate the formation of Li3P at the electrode interface, have a low desolvation energy barrier, which facilitates lithium-ion interfacial transport and reduces interfacial impedance.

[0125] In some embodiments, the phosphate ester compound includes tris(trimethylsilane) phosphate. Tris(trimethylsilane) phosphate not only reduces interfacial impedance, but the trimethylsilane contained therein can also promote its reaction with water and acidic substances, thereby inhibiting the reaction between water and electrolyte lithium salts (such as LiPF6) and the damage to the interface by acidic substances (such as hydrofluoric acid), thus improving the stability of the interface.

[0126] In some embodiments, the tris(trimethylsilane)phosphate ester in the electrolyte comprises 0.05% to 0.5% by mass. For example, the mass percentage of tris(trimethylsilane)phosphate ester in the electrolyte may be 0.05%, 0.07%, 0.09%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or within any range of the above values.

[0127] By appropriately controlling the mass percentage of tris(trimethylsilyl)phosphate in the electrolyte, not only can the stability of the electrolytic interface be improved and the interfacial impedance reduced, but the intrinsic stability of the electrolyte can also be maintained at a high level.

[0128] In some embodiments, the fluorophosphate compound is lithium difluorophosphate. Certain positive electrode active materials in lithium-ion batteries, such as nickel-cobalt-manganese-based positive electrode active materials, especially when the nickel content is high, are prone to interacting with the electrolyte and undergoing catalytic reactions, resulting in gas production. Lithium difluorophosphate, however, can not only passivate the interface but also inhibit the reaction between the positive electrode active material and the electrolyte, thereby reducing gas production.

[0129] In some embodiments, the lithium difluorophosphate in the electrolyte has a mass percentage content of 0.05% to 0.5%. For example, the mass percentage content of lithium difluorophosphate in the electrolyte may be 0.05%, 0.07%, 0.09%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or within any range of the above values.

[0130] By appropriately controlling the mass percentage of lithium difluorophosphate in the electrolyte, not only can a better interface passivation effect be achieved, but the interface impedance can also be controlled within a suitable range, so as to achieve a balance between interface passivation and interface lithium-ion transport.

[0131] In some embodiments, the fluorobenzene compounds include one or more of monofluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, and trifluorotoluene. These fluorobenzene compounds exhibit preferential adsorption at interfaces, which can improve the wetting ability of the electrolyte at the interface; their adsorption at the interface is beneficial to the desolvation of lithium ions, thereby improving the interfacial charge transfer capacity, reducing interfacial impedance, and improving rate performance.

[0132] In some embodiments, the fluorobenzene compound includes one or both of monofluorobenzene and hexafluorobenzene. This is beneficial for further improving interfacial load transfer capability, reducing interfacial impedance, and enhancing rate performance.

[0133] In some embodiments, the fluorobenzene compound is present in the electrolyte at a mass percentage of 0.05% to 0.5%. For example, the mass percentage of the fluorobenzene compound in the electrolyte may be 0.05%, 0.07%, 0.09%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or within any range of the above values.

[0134] Fluorobenzene compounds do not participate in the solvation structure of lithium ions. By appropriately controlling their mass percentage in the electrolyte, not only can the interfacial charge transfer capacity be improved, but also the lithium ions can maintain a faster dissociation rate and thus maintain better liquid-phase transport kinetics.

[0135] In some embodiments, the electrolyte further comprises a non-aqueous solvent, including a highly conductive solvent, which has the following characteristic: a conductivity of 8 mS / cm to 20 mS / cm at 25°C. For example, the conductivity of the highly conductive solvent at 25°C can be 8 mS / cm, 10 mS / cm, 12 mS / cm, 14 mS / cm, 16 mS / cm, 18 mS / cm, 20 mS / cm, or within any range of the above values. The highly conductive solvent can improve the electrolyte kinetics and enhance the rate performance of the battery.

[0136] As an example, the conductivity of non-aqueous solvents at 25°C can be tested using the following method: Take the electrolyte from the battery and perform Fourier transform infrared spectroscopy (FTIR) on it. Determine the types of non-aqueous solvents in the electrolyte based on the position and intensity of the absorption peaks in the FTIR spectrum. Take the corresponding non-aqueous solvents and measure their conductivity at 25°C using a conductivity meter (such as the Shanghai Leici DDSJ-319L model). A specific testing method is as follows: First, rinse the conductivity cell and electrodes three times with distilled water. Then, rinse the conductivity cell and electrodes three times with a small amount of the non-aqueous solvent to be tested. Next, pour in the non-aqueous solvent to be tested, ensuring the liquid level is 1-2 cm above the platinum electrode in the conductivity cell. Place the conductivity cell in a thermostatic bath that has been preheated to the test temperature and maintain the temperature for 15-20 minutes. Set the "Calibration / Measurement" button to the "Measurement" position, select an appropriate measurement range, and test the conductivity of the non-aqueous solvent.

[0137] In some embodiments, the highly conductive solvent includes a chain-like highly conductive solvent, which includes one or more of dimethyl carbonate (DMC), ethyl acetate (EA), and methyl acetate (MA).

[0138] The chain-like structure of these low-viscosity solvents gives them good fluidity in the electrolyte. The entanglement and obstruction between the molecular chains are relatively small, which enables the electrolyte to have a relatively low viscosity. The lower viscosity is conducive to the rapid diffusion of lithium ions in the electrolyte, which can improve the rate performance of the battery.

[0139] In some embodiments, the chain-like low-viscosity solvent includes one or both of ethyl acetate and methyl acetate, as well as dimethyl carbonate. Combining a chain-like low-viscosity solvent of the carboxylic acid ester with dimethyl carbonate can further enhance rate performance through the synergistic effect between the different solvents.

[0140] In some embodiments, the high-conductivity solvent has a mass percentage content of 5% to 65% in the electrolyte. For example, the mass percentage content of the high-conductivity solvent in the electrolyte can be 5%, 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or within any range of the above values. Controlling the mass percentage content of the high-conductivity solvent in the electrolyte within a suitable range can not only improve the electrolyte kinetics but also maintain the reaction at the positive and negative electrode interfaces at an appropriate reaction level, thus maintaining a good cycle life for the battery.

[0141] In some embodiments, the chain-like highly conductive solvent comprises dimethyl carbonate, wherein the dimethyl carbonate comprises 30% to 50% by mass in the electrolyte. For example, the mass percentage of dimethyl carbonate in the electrolyte can be 30%, 35%, 40%, 45%, 50%, or within any range of these values. This facilitates a better balance between electrolyte kinetics and the high-temperature performance of the battery.

[0142] In some embodiments, the chain-like highly conductive solvent comprises dimethyl carbonate, and the chain-like highly conductive solvent has a conductivity of 8 mS / cm to 11 mS / cm at 25°C. For example, the conductivity of the chain-like highly conductive solvent at 25°C can be 8 mS / cm, 9 mS / cm, 10 mS / cm, 11 mS / cm, or within any range of the above values.

[0143] In some embodiments, the chain solvent includes ethyl acetate, which comprises 20% to 40% by mass in the electrolyte. For example, the mass percentage of ethyl acetate in the electrolyte can be 20%, 25%, 30%, 35%, 40%, or any range thereof. This facilitates a better balance between electrolyte kinetics and the high-temperature performance of the battery.

[0144] In some embodiments, the chain-like highly conductive solvent includes ethyl acetate, and the chain-like highly conductive solvent has a conductivity of 10 mS / cm to 16 mS / cm at 25°C. For example, the conductivity of the chain-like highly conductive solvent at 25°C can be 10 mS / cm, 11 mS / cm, 12 mS / cm, 13 mS / cm, 14 mS / cm, 15 mS / cm, 16 mS / cm, or within any range of the above values.

[0145] In some embodiments, the chain solvent includes methyl acetate, which is present in the electrolyte at a mass percentage of 10% to 30%. For example, the mass percentage of methyl acetate in the electrolyte can be 10%, 15%, 20%, 25%, 30%, or any range thereof. This allows for a better balance between electrolyte kinetics and the high-temperature performance of the battery.

[0146] In some embodiments, the chain solvent comprises methyl acetate, and the chain solvent has a conductivity of 12 mS / cm to 20 mS / cm at 25°C. For example, the conductivity of the chain solvent at 25°C can be 12 mS / cm, 13 mS / cm, 14 mS / cm, 15 mS / cm, 16 mS / cm, 17 mS / cm, 18 mS / cm, 19 mS / cm, 20 mS / cm, or within any range of the above values.

[0147] In some embodiments, the electrolyte further comprises an electrolyte lithium salt, including lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonylimide (LiFSI).

[0148] In the electrolyte, lithium hexafluorophosphate is used as the main lithium salt, and when combined with lithium bisfluorosulfonylimide, lithium bisfluorosulfonylimide can not only participate in interfacial film formation, improve interfacial stability, and enhance the cycle life of the battery, but also has a better dissociation ability than lithium hexafluorophosphate, which can improve the liquid phase conductivity and enhance the lithium ion transport performance at the interface.

[0149] In some embodiments, the electrolyte comprises lithium bis(fluorosulfonyl)imide, wherein the molar concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.02 mol / L to 0.2 mol / L. For example, the molar concentration of lithium bis(fluorosulfonyl)imide in the electrolyte may be 0.02 mol / L, 0.05 mol / L, 0.07 mol / L, 0.09 mol / L, 0.1 mol / L, 0.12 mol / L, 0.14 mol / L, 0.16 mol / L, 0.18 mol / L, 0.2 mol / L, or within any range of the above values.

[0150] Controlling the molar concentration of LiFSI in the electrolyte within a suitable range can improve the ion transport and kinetic performance at the interface, as well as the cycle life of the battery. On the other hand, by controlling the molar concentration of LiFSI in the electrolyte within a suitable range, the structural stability of lithium-ion batteries, especially lithium-ion batteries composed of high-nickel cathodes and silicon-based anodes, can be improved.

[0151] It can be understood that the above-mentioned "high-nickel cathode" refers to a cathode including nickel-cobalt-manganese-based cathode active materials, and in the nickel-cobalt-manganese-based cathode active materials, the proportion of nickel atoms in the total atomic moles of all transition metal elements is ≥50%; the above-mentioned "silicon-based anode" refers to an anode including silicon-based materials.

[0152] In some embodiments, the negative electrode includes a negative electrode active material layer, the negative electrode active material layer comprising a negative electrode active material, the negative electrode active material including a silicon-based material.

[0153] Silicon-based materials have a high specific capacity, which helps improve the energy density of batteries. However, the volume expansion effect of silicon-based materials can easily lead to the destruction and reorganization of the negative electrode interface structure during battery cycling, adversely affecting cycle performance. By combining silicon-based materials with the electrolyte system described above, and leveraging the improvement effect of the electrolyte system on the negative electrode interface, especially since this improvement effect is particularly significant for silicon-based negative electrodes, not only can the energy density of the battery be improved, but the battery can also achieve better cycle performance.

[0154] As an example, the method for obtaining negative or positive active materials in a battery negative or positive electrode sheet is as follows: After disassembling the battery, remove the positive or negative electrode sheet and soak it in dimethyl carbonate for a certain period of time (e.g., 2h to 10h); then remove the positive or negative electrode sheet and dry it at a certain temperature and time (e.g., 60℃ for more than 4h); after drying, remove the positive or negative electrode sheet. Bake the dried positive or negative electrode sheet at a certain temperature and time (e.g., 400℃ for more than 2h); randomly select a region in the baked positive or negative electrode sheet and sample the positive or negative active material layer (sampling can be done by scraping powder with a blade); sieve the collected sample (e.g., sieve through a 200-mesh sieve) to finally obtain a positive or negative active material sample that can be used for testing.

[0155] In some embodiments, the silicon-based material includes one or more of nano-silicon, micro-silicon, silicon-oxygen materials, and silicon-carbon materials.

[0156] In some embodiments, the average particle size of the nano-silicon is 5 nm to 30 nm. For example, the average particle size of the nano-silicon can be 5 nm, 8 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, or within any range of the above values. This helps to reduce the volume expansion effect of silicon to a certain extent and improve cycle performance.

[0157] In some embodiments, the average particle size of micron-sized silicon is 2 μm to 6 μm. For example, the average particle size of micron-sized silicon can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, or within any range of these values. This helps to reduce the volume expansion effect of silicon to a certain extent and improve cycle performance.

[0158] The average particle size of nano-silicon or micron-silicon can be tested using methods known in the art. For example, it can be determined using a laser particle size analyzer (such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK) according to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0159] In some embodiments, the silicon-based material includes silicon-carbon materials. Silicon-carbon materials have a certain inhibitory effect on the expansion of silicon, which can improve cycle performance to some extent.

[0160] In some embodiments, the silicon-carbon material comprises 3% to 40% of the negative electrode active material layer by mass. For example, the mass percentage of silicon-carbon material in the negative electrode active material layer can be 3%, 5%, 8%, 10%, 13%, 15%, 18%, 20%, 22%, 25%, 27%, 29%, 30%, 32%, 34%, 36%, 38%, 40%, or any range thereof. This reduces the potential for increased interface damage when the mass percentage of silicon-carbon material is high, thus maintaining better cycle performance of the battery.

[0161] In some embodiments, the mass ratio of silicon to carbon in the silicon-carbon material is (4-6):(6-4). For example, the mass ratio of silicon to carbon can be 4:6, 4:5, 4:4, 5:6, 5:4, 6:4, or any range thereof. This helps to improve the suppression of silicon expansion and thus improves cycle performance.

[0162] As an example, the mass ratio of silicon to carbon in silicon-carbon materials can be tested using the following method: Take the negative electrode active material obtained above, and use inductively coupled plasma (ICP) emission spectroscopy to determine the silicon and carbon content, thereby obtaining the mass ratio of silicon to carbon.

[0163] In some embodiments, the silicon-carbon material includes a porous silicon-carbon material, which comprises a porous carbon matrix and silicon nanoparticles, wherein the silicon nanoparticles are loaded within the pores of the porous carbon matrix.

[0164] Silicon-carbon porous materials not only allow for easy control of the content of silicon nanoparticles loaded in a porous carbon matrix, but also reserve some volume space for buffering the expansion of silicon nanoparticles. By limiting the volume expansion of silicon nanoparticles during lithium insertion / extraction, the cycle performance of the battery can be improved.

[0165] In some embodiments, the pores include mesopores and micropores, wherein the pore size of the mesopores is 2 nm to 10 nm, and the pore size of the micropores is greater than or equal to 0.2 nm and less than 2 nm. For example, the pore size of the mesopores can be 2 nm, 3 nm, 5 nm, 7 nm, 9 nm, 10 nm, or any value within the range above; the pore size of the micropores can be 0.2 nm, 0.5 nm, 0.7 nm, 1 nm, 1.2 nm, 1.4 nm, 1.6 nm, 1.8 nm, or any value within the range above. In silicon-carbon porous materials, controlling the pore sizes of micropores and mesopores within a suitable range can enable the silicon-carbon porous materials to have a relatively high specific surface area, which can better suppress volume expansion, increase electrolyte wetting, and improve kinetics.

[0166] In some embodiments, the mesopores in the silicon-carbon porous material account for ≥50% of the total pores. For example, the mesopore-to-pore ratio can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, or any of the above values. This facilitates a further increase in the specific surface area of ​​the silicon-carbon porous material, resulting in better improvement in volume expansion and cycle performance.

[0167] As an example, the ratio of mesopores to pores and the pore size of porous silicon-carbon materials can be tested using the following method: Take the negative electrode active material sample obtained above and perform scanning electron microscopy (SEM) to observe and confirm whether the morphology of the negative electrode active material is porous. After confirmation, place the porous silicon-carbon material sample in liquid nitrogen, adjust different test pressures, measure the amount of nitrogen adsorption, and plot the adsorption and desorption isotherms. Determine the pore shape based on the shape of the hysteresis loop, calculate the pore distribution according to different pore models, fit the pore size distribution curves of mesopores and macropores using the BJH model, and fit the pore size distribution curve of micropores using the DFT model to obtain the pore size distribution of mesopores and the pore size of micropores. Then, perform scanning electron microscopy on the porous silicon-carbon material again, select a certain area within the field of view (e.g., 100nm × 100nm), measure and record the pore size of all pores in this area to obtain the number of micropores and mesopores, and based on this, the ratio of mesopores to pores can be obtained.

[0168] In some embodiments, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer containing a positive electrode active material, the positive electrode active material including at least one of nickel-cobalt-manganese-based positive electrode active material and lithium iron phosphate-based positive electrode active material.

[0169] In some embodiments, the positive electrode active material includes a nickel-cobalt-manganese-based positive electrode active material, and the silicon-based material accounts for 3% to 45% of the mass of the negative electrode active material layer. For example, the mass percentage of the silicon-based material in the negative electrode active material layer can be 3%, 5%, 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or any range thereof. Thus, when the aforementioned electrolyte system is combined with the negative electrode, it further improves the stability of the negative electrode interface and its high-temperature stability, enabling the battery to have higher cycle life and high-temperature performance.

[0170] In some embodiments, the positive electrode active material includes lithium iron phosphate-based positive electrode active materials, and the silicon-based material accounts for ≤20% of the mass of the negative electrode active material layer. For example, the mass percentage of the silicon-based material in the negative electrode active material layer can be 1%, 5%, 8%, 10%, 13%, 15%, 17%, 20%, or any range thereof. This allows for capacity matching between the positive and negative electrodes while maintaining good cycle performance of the battery.

[0171] As an example, the mass percentage of silicon-based materials in the negative electrode active material layer can be tested using the following method: After disassembling the battery, remove the negative electrode sheet, scrape a sample onto the negative electrode active material layer (e.g., take a sample with a thickness of 2 / 3), place the sample in a container of known mass and weigh it, recording the initial mass; immerse the weighed sample in dimethyl carbonate for a certain period of time, and filter it after the inactive substances have fully dissolved; immerse the filtered sample in N-methylpyrrolidone for a certain period of time, filter it, and wash it to obtain the negative electrode active material. Weigh and record the weight of the negative electrode active material to obtain the mass percentage of silicon-based materials in the negative electrode active material layer.

[0172] In some embodiments, the nickel-cobalt-manganese-based cathode active material includes lithium, nickel, cobalt, manganese, and oxygen, wherein the atomic molar percentage of nickel is 50%–95% based on the total atomic molar percentage of all transition metal elements. For example, the atomic molar percentage of nickel can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or any range thereof. When the atomic molar percentage of nickel in the nickel-cobalt-manganese-based cathode active material reaches 50%–95%, it indicates a high nickel content (which can be referred to as a medium-high nickel material). High-nickel materials are prone to catalytic reactions, leading to electrolyte consumption, reduced cycle performance, and gas production. By combining this medium-high nickel material with the electrolyte system described above, based on the inhibitory effect of the electrolyte system on the catalytic reaction between the medium-high nickel material and the electrolyte, and the inhibitory effect of the additives on electrolyte solvent consumption during interfacial film formation, the cycle performance and gas production of the medium-high nickel material system can be improved.

[0173] In some embodiments, in the nickel-cobalt-manganese-based cathode active material, the proportion of nickel atoms is greater than 60% and less than or equal to 95% based on the total atomic moles of the transition metal elements. Thus, when the aforementioned electrolyte system is combined with this medium-to-high nickel material, the improvement in cycle performance and gas production is even better.

[0174] As an example, the elemental species and atomic mole numbers of the positive electrode active material can be tested by the following method: Take the positive electrode active material obtained above and test it using inductively coupled plasma (ICP), and the elemental distribution and the atomic mole numbers corresponding to each element can be obtained.

[0175] In some embodiments, the nickel-cobalt-manganese-based positive electrode active material includes Li x’ Ni x Co y Mn 1-x-y O y’ , where 0.7 ≤ x ≤ 0.95, 0 < y ≤ 0.3, 0.6 ≤ x' ≤ 1.2, 1.6 ≤ y' ≤ 2.2. Thus, not only can the positive electrode have a high specific capacity and energy density, but also the cycle performance of the battery can be further improved by the combination of this positive electrode active material and the electrolyte system described above.

[0176] In some embodiments, the nickel-cobalt-manganese-based positive electrode active material includes Li x’ Ni 0.9 Co y1 Mn 0.1-y1 O y’ , where 0 < y1 < 0.1, 0.6 ≤ x' ≤ 1.2, 1.6 ≤ y' ≤ 2.2. Thus, not only can the positive electrode have a high specific capacity and energy density, but also the cycle performance of the battery can be further improved by the combination of this positive electrode active material and the electrolyte system described above.

[0177] In some embodiments, the nickel-cobalt-manganese-based positive electrode active material includes a high-voltage material, the maximum charging cut-off voltage of the lithium-ion battery is greater than or equal to 4.3V, and the electrolyte satisfies the following characteristics: the mass fraction of dimethyl carbonate in the electrolyte is less than or equal to 30%. Thus, the cyclic gas generation of the electrolyte can be reduced.

[0178] It should be noted that the "high-voltage material" described in this application refers to a nickel-cobalt-manganese-based positive electrode active material whose maximum charging cut-off voltage can reach 4.3V or above.

[0179] It should be noted that based on the total atomic mole number of all transition metal elements, the atomic mole number ratio of nickel element is 50% - 60%, which can make the maximum charging cut-off voltage of the first nickel-cobalt-manganese-based positive electrode active material reach 4.3V or above. At this time, the first nickel-cobalt-manganese-based positive electrode material also belongs to the high-voltage material.

[0180] It should be noted that when the nickel-cobalt-manganese-based positive electrode active material includes a high-voltage material, or when the nickel-cobalt-manganese-based positive electrode active material includes a first nickel-cobalt-manganese-based positive electrode active material, the mass fraction of dimethyl carbonate in the electrolyte must be less than or equal to 30%. This means that when the battery containing the high-voltage material or the first nickel-cobalt-manganese-based positive electrode active material is used in a high-voltage scenario (such as when the battery is being charged, the maximum charging voltage is 4.3V or higher), the mass fraction of dimethyl carbonate in the electrolyte must be less than or equal to 30%.

[0181] It should be noted that when the nickel-cobalt-manganese-based positive electrode active material includes the above-mentioned high-voltage material and / or the first nickel-cobalt-manganese-based positive electrode active material, the mass fraction of carboxylic acid ester solvent in the electrolyte is less than or equal to 0.5%.

[0182] In some embodiments, the nickel-cobalt-manganese-based cathode active material includes a first nickel-cobalt-manganese-based cathode active material, wherein the mass fraction of dimethyl carbonate in the electrolyte is less than or equal to 30%; wherein, in the first nickel-cobalt-manganese-based cathode active material, the atomic molar ratio of nickel, based on the total atomic molar number of all transition metal elements, is 50% to 60%. This reduces the circulating gas generation of the electrolyte. In some embodiments, the first nickel-cobalt-manganese-based cathode active material includes Li... x1’ Ni 0.5 Co y2 Mn 0.5-y2 O y1’ and Li x2’ Ni 0.6 Co y3 Mn 0.4-y3 O y2’ At least one of them, 0 <y2<0.5,0<y3<0.4,0.6≤x1’≤1.2,1.6≤y1’≤2.2,0.6≤x2’≤1.2,1.6≤y2’≤2.2。

[0183] In some embodiments, the electrolyte contains dimethyl carbonate, and the mass percentage of dimethyl carbonate in the electrolyte is less than or equal to 30%. This reduces the gas generation during electrolyte circulation.

[0184] It should be noted that the above-mentioned "carboxylic acid ester solvents" refer to compounds formed by the dehydration condensation of carboxylic acids and alcohols, that is, compounds in which the -OH group of the carboxyl group is replaced by an alkoxy group.

[0185] In some implementations, lithium iron phosphate cathode active materials include one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0186] In some embodiments, nickel-cobalt-manganese based cathode active materials include LiNi0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 LiNi 0.9 Co 0.05 Mn 0.05 O2 (also known as NCM) 955 )wait.

[0187] Secondly, this application provides an electrolyte containing additives, said additives including cyano-containing imidazole lithium compounds and S-containing ester compounds;

[0188] The S-containing ester compounds include at least one of the structures *-OS(=O)2-O-*, *-OS(=O)-O-*, and *-S(=O)2-O-*, wherein each * is independently attached to a carbon atom.

[0189] In some embodiments, the electrolyte is the electrolyte in the lithium-ion battery described in the first aspect of this application.

[0190] Thirdly, this application provides a lithium-ion battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte contains additives, including cyano-containing imidazole lithium compounds and S-containing ester compounds;

[0191] The S-containing ester compound includes at least one structure selected from *-OS(=O)2-O-*, *-OS(=O)-O-*, and *-S(=O)2-O-*, wherein each * is independently attached to a carbon atom, and the S-containing ester compound has a mass percentage content of 0.01% to 4% in the electrolyte.

[0192] It should be noted that the lithium-ion battery of the third aspect of this application is a lithium-ion battery before formation. After the lithium-ion battery is formed, the lithium-ion battery of the first aspect of this application can be obtained. Therefore, the content of each component in the lithium-ion battery of the third aspect is the content before formation.

[0193] It should be noted that the lithium-ion battery of the third aspect of this application is formed to obtain the lithium-ion battery of the first aspect of this application. The formation conditions can be selected according to actual needs and are not limited here.

[0194] In some embodiments, the cyano-containing imidazole lithium compound includes 4,5-dicyano-2-(trifluoromethyl)imidazolium lithium, which, prior to formation, has a mass percentage content of 0.01% to 1% in the electrolyte. For example, the mass percentage content of 4,5-dicyano-2-(trifluoromethyl)imidazolium lithium in the electrolyte may be 0.01%, 0.03%, 0.05%, 0.07%, 0.1%, 0.13%, 0.15%, 0.17%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, or within any range of the above values. Optionally, prior to formation, the mass percentage of lithium 4,5-dicyano-2-(trifluoromethyl)imidazolium in the electrolyte is 0.1% to 0.8%.

[0195] In some embodiments, prior to formation, the S-containing ester compound in the electrolyte comprises 0.01% to 4% by mass. For example, the mass percentage of the S-containing ester compound in the electrolyte may be 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.2%, 0.5%, 0.7%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or within any range of the above values. Optionally, prior to formation, the mass percentage of the S-containing ester compound in the electrolyte comprises 0.3% to 3% by mass.

[0196] In some embodiments, the additive further includes one or more of fluorocarbonate compounds, phosphate ester compounds, fluorobenzene compounds, and fluorophosphate compounds, wherein the fluorophosphate compound is lithium difluorophosphate.

[0197] In some embodiments, prior to formation, the fluoroethylene carbonate has a mass percentage content of 1% to 20% in the electrolyte. For example, the mass percentage content of the fluoroethylene carbonate in the electrolyte can be 1%, 2%, 4%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, or within any range of the above values. Optionally, prior to formation, the fluoroethylene carbonate has a mass percentage content of 5% to 15% in the electrolyte.

[0198] In some embodiments, prior to formation, the tris(trimethylsilane)phosphate ester has a mass percentage content of 0.01% to 2% in the electrolyte. For example, the mass percentage content of tris(trimethylsilane)phosphate ester in the electrolyte may be 0.01%, 0.03%, 0.05%, 0.07%, 0.09%, 0.1%, 0.5%, 0.8%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or within any range of the above values. Optionally, prior to formation, the mass percentage content of tris(trimethylsilane)phosphate ester in the electrolyte is 0.1% to 1%.

[0199] In some embodiments, the fluorophosphate compound is lithium difluorophosphate, and the lithium difluorophosphate has a mass percentage content of 0.01% to 1% in the electrolyte before formation. For example, the mass percentage content of lithium difluorophosphate in the electrolyte can be 0.01%, 0.03%, 0.05%, 0.07%, 0.1%, 0.13%, 0.15%, 0.17%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, or within any range of the above values. Optionally, the mass percentage content of lithium difluorophosphate in the electrolyte before formation is 0.1% to 0.8%.

[0200] In some embodiments, prior to formation, the fluorobenzene compound is present in the electrolyte at a mass percentage of 0.01% to 2%. For example, the mass percentage of the fluorobenzene compound in the electrolyte may be 0.01%, 0.03%, 0.05%, 0.07%, 0.09%, 0.1%, 0.5%, 0.8%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or within any range of the above values. Optionally, prior to formation, the fluorobenzene compound is present in the electrolyte at a mass percentage of 0.1% to 1%.

[0201] In some embodiments, the electrolyte further comprises an electrolyte lithium salt, including lithium hexafluorophosphate and lithium difluorosulfonylimide.

[0202] In some embodiments, prior to formation, the total molar concentration of the lithium electrolyte salt in the electrolyte is 0.5 mol / L to 2 mol / L. For example, the total molar concentration of the lithium electrolyte salt in the electrolyte can be 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.3 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, or within any range of these values. This allows the battery to possess higher rate performance.

[0203] In some embodiments, prior to formation, the molar concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.05 mol / L to 0.4 mol / L. For example, the molar concentration of lithium bis(fluorosulfonyl)imide in the electrolyte can be 0.05 mol / L, 0.07 mol / L, 0.09 mol / L, 0.1 mol / L, 0.12 mol / L, 0.14 mol / L, 0.18 mol / L, 0.2 mol / L, 0.23 mol / L, 0.25 mol / L, 0.28 mol / L, 0.3 mol / L, 0.32 mol / L, 0.35 mol / L, 0.37 mol / L, 0.4 mol / L, or within any range of the above values. Optionally, prior to formation, the molar concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.1 mol / L to 0.2 mol / L.

[0204] It should be noted that the electrolyte contained in the second aspect of this application and the lithium-ion battery contained in the third aspect, as well as the components contained in the electrolyte and the content of each component before and after formation, play similar roles to the electrolyte in the lithium-ion battery provided in the first aspect of this application, and will not be elaborated here.

[0205] In addition, the lithium-ion battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0206] Typically, a lithium-ion battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0207] Positive electrode sheet

[0208] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including a positive active material.

[0209] As a non-limiting example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0210] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on a polymeric material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0211] Understandably, lithium (Li) is intercalated and deintercalated during the charging and discharging process of a battery, and the Li content in the positive electrode varies depending on the state of discharge. Unless otherwise specified, the Li content in the examples of positive electrode materials listed in this application refers to the initial state of the material. When a positive electrode material is applied to a positive electrode in a battery system, the Li content in the positive electrode material typically changes after charge-discharge cycles. The Li content can be measured using molar content, but is not limited to this. Regarding "Li content refers to the initial state of the material," the initial state of the material refers to its state before being added to the positive electrode slurry. It is understood that new materials obtained by appropriately modifying the listed positive electrode materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to acceptable modification methods for the positive electrode material; non-limiting examples include coating modification.

[0212] In the examples of cathode materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause changes in the molar content of oxygen, and the actual O content will fluctuate. The O content can be measured in molar content, but is not limited to this.

[0213] In some embodiments, the positive electrode active material layer may optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0214] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0215] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto at least one surface of the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes. The solvent can be selected from, but is not limited to, any of the solvents described in the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or both surfaces of the positive electrode current collector.

[0216] Negative electrode sheet

[0217] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0218] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0219] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on the polymeric material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0220] In some embodiments, the negative electrode active material may include, in addition to silicon-based materials, one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, tin-based materials, and lithium titanate. Tin-based materials may include one or more of elemental tin, tin oxides, and tin alloys.

[0221] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0222] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0223] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0224] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto at least one surface of the negative electrode current collector, and then obtaining the negative electrode sheet after processes such as drying and cold pressing. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector.

[0225] electrolyte

[0226] The electrolyte includes lithium salt electrolyte and non-aqueous solvent.

[0227] In some embodiments, the electrolyte lithium salt may optionally include one or more of the following, in addition to lithium hexafluorophosphate and lithium bisfluorosulfonylimide: lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(trifluoromethanesulfonylimide) (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0228] In some embodiments, the non-aqueous solvent may optionally include one or more of the following, in addition to one or more of dimethyl carbonate (DMC), ethyl acetate, and methyl acetate: ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butenyl carbonate, methyl formate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0229] Separating membrane

[0230] In some embodiments, the lithium-ion battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0231] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0232] In some embodiments, the thickness of the isolation membrane is 6 μm to 40 μm.

[0233] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding process or a stacking process.

[0234] In some embodiments, the lithium-ion battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0235] In some embodiments, the outer packaging of the lithium-ion battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the lithium-ion battery can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0236] A lithium-ion battery includes at least one battery cell. A lithium-ion battery may include one or more battery cells.

[0237] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy, and generally includes at least a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the battery, active ions move back and forth between the positive and negative electrode plates, inserting and extracting. The electrolyte acts as a conductor for the active ions between the positive and negative electrode plates.

[0238] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square battery cell 5 as an example.

[0239] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to actual needs.

[0240] The lithium-ion battery can be a battery device 4 or a battery pack 1.

[0241] The battery device includes at least one battery cell. The number of battery cells in the battery device can be one or more, and those skilled in the art can select an appropriate number according to the application and capacity of the battery device.

[0242] Figure 3 shows a battery device 4 as an example. Referring to Figure 3, in the battery device 4, multiple battery cells 5 can be arranged sequentially along the length of the battery device 4. Of course, they can also be arranged in any other arbitrary way. Furthermore, the multiple battery cells 5 can be fixed in place by fasteners.

[0243] Optionally, the battery device 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0244] In some embodiments, the battery devices described above can also be assembled into a battery pack, and the number of battery devices contained in the battery pack can be one or more. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0245] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, the battery pack 1 may include a battery compartment and multiple battery devices 4 disposed within the battery compartment. The battery compartment includes an upper compartment 2 and a lower compartment 3, the upper compartment 2 covering the lower compartment 3 to form a closed space for accommodating the battery devices 4. The multiple battery devices 4 can be arranged in any manner within the battery compartment.

[0246] In addition, this application also provides an electrical device, which includes the lithium-ion battery provided in this application. The lithium-ion battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to.

[0247] As an electrical device, lithium-ion batteries can be selected based on its usage requirements.

[0248] Figure 6 shows an example of an electrical device 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the lithium-ion battery for this electrical device, a battery pack or battery device can be used.

[0249] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use lithium-ion batteries as their power source.

[0250] Example

[0251] The following describes some embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where the technology or conditions are not specified in the embodiments, they are performed according to the technology or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0252] Example 1

[0253] (1) Positive electrode plate

[0254] Using an 8μm thick aluminum foil as the positive electrode current collector, the ternary positive electrode material LiNi was... 0.9 Co 0.05 Mn 0.05O2 (NCM955), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were dissolved in N-methylpyrrolidone (NMP) at a weight ratio of 93:2:5. After thorough mixing, a positive electrode slurry with a solid content of 75 wt% was obtained. The positive electrode slurry was then uniformly coated onto both sides of the positive electrode current collector, with a coating density of 0.3 g / 1054.25 mm². 2 After drying, cold pressing, and slitting, the compacted density is approximately 3.5 g / cm³. 3 This yields the positive electrode sheet.

[0255] (2) Negative electrode plate

[0256] Silicon-carbon porous material, graphite, conductive carbon black, and binder polyacrylic acid were mixed in a mass ratio of 2:6:1:1, and deionized water was added and stirred thoroughly to form a negative electrode slurry with a solid content of 48 wt%. The negative electrode slurry was then uniformly coated onto one surface of the negative electrode current collector copper foil, with a coating density of 0.12 g / 1054.25 mm² on one side. 2 After drying and cold pressing, the compacted density is approximately 1.6 g / cm³. 3 A negative electrode sheet is obtained, in which the mass ratio of silicon-based material in the negative electrode active material layer is 20%.

[0257] The silicon-carbon porous material used includes a porous carbon matrix and silicon nanoparticles loaded in the pores of the porous carbon matrix. The pores include mesopores with a pore size distribution of 2nm to 10nm and micropores with a pore size distribution of 0.2nm to 2nm. Mesopores account for 60% of the number of pores, micropores account for 40% of the number of pores, and the mass ratio of silicon to carbon is 5:5.

[0258] (3) Separating membrane

[0259] A 12μm thick polyethylene film was used as the separator.

[0260] (4) Electrolyte

[0261] Dimethyl carbonate (DMC), ethyl acetate (EA), methyl acetate (MA), and ethylene carbonate (EC) were mixed to obtain a non-aqueous solvent with a conductivity of 12 mS / cm at 25°C. Then, LiTDI, an S-containing ester compound (1,3-propanesulfonate lactone + vinyl sulfate + vinyl sulfite), FEC, and tris(trimethylsilane) phosphate were added to the electrolyte. Sufficiently dried lithium salts LiPF6 and LiFSI were then added and dissolved to prepare an electrolyte with a total molar concentration of 1 mol / L for LiPF6 and LiFSI (0.95 mol / L after formation). The initial molar concentration of LiFSI in the electrolyte was 0.1 mol / L (0.08 mol / L after formation).

[0262] In the electrolyte, the mass percentage of non-aqueous solvents is 72% (of which, DMC, EA, and MA account for 60%, 15%, and 15% of the non-aqueous solvents, respectively, and EC accounts for 10% of the non-aqueous solvents), the mass percentage of LiTDI in the electrolyte is 0.5% (0.2% after formation), and the total mass percentage of S-containing esters (1,3-propanesulfonate lactone + vinyl sulfate + vinyl sulfite) in the electrolyte is 2.5% (1.8% after formation). The electrolyte contains 1% by mass of 1,3-propanesulfonate lactone (0.9% after formation), 1% by mass of vinyl sulfate (0.6% after formation), 0.5% by mass of vinyl sulfite (0.3% after formation), 10% by mass of FEC (8.5% after formation), and 0.5% by mass of tris(trimethylsilane)phosphate (0.2% after formation).

[0263] (5) Battery assembly

[0264] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. They are then wound to obtain a bare cell. Tabs are welded to the bare cell, which is then placed in an aluminum casing and baked at 80°C to remove moisture. Electrolyte is then injected and the casing is sealed, resulting in a non-charged battery. The non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain a lithium-ion battery. The formation process involves charging at 0.02C constant current to 3.4V at 45°C, settling for 5 minutes, and then charging at 0.1C constant current to 3.75V.

[0265] Examples 2-9

[0266] Similar to the preparation method in Example 1, the main difference is that in step (4), the mass ratio of LiTDI and S-containing ester compounds in the electrolyte is adjusted, as detailed in Table 1 below.

[0267] Example 10

[0268] Similar to the preparation method in Example 1, the main difference is that in step (4), 1,3-propanesulfonic acid lactone is omitted from the S-containing ester compounds, but the total mass percentage of the S-containing ester compounds in the electrolyte remains unchanged, as detailed in Table 1 below.

[0269] Table 1

[0270] Example 11

[0271] Similar to the preparation method in Example 1, the main difference is that in step (4), hexafluorobenzene and lithium difluorophosphate are added to the electrolyte, as detailed in Table 2 below.

[0272] Example 12

[0273] The preparation method is similar to that in Example 1, the main difference is that in step (4), tris(trimethylsilane) phosphate is omitted, as detailed in Table 2 below.

[0274] Table 2

[0275] Examples 13-15

[0276] Similar to the preparation method in Example 1, the main difference is that in step (4), the molar concentration of LiFSI in the electrolyte is adjusted while the total molar concentration of lithium salt remains unchanged, as detailed in Table 3 below.

[0277] Table 3

[0278] Example 16

[0279] Similar to the preparation method in Example 1, the main difference is that in step (4), equal masses of EC and EMC are used to replace EA and MA, so that the mass ratio of non-aqueous solvents in the electrolyte remains unchanged, as detailed in Table 4 below.

[0280] Table 4

[0281] Example 17

[0282] Similar to the preparation method in Example 1, the main difference is that in step (2), the same mass of nano-silicon (average particle size 10nm) is used instead of silicon-carbon porous material, as detailed in Table 5 below.

[0283] Table 5

[0284] Examples 18-19

[0285] Similar to the preparation method in Example 1, the main difference is that in step (2), silicon-carbon porous materials with different mesopore ratios are used instead of the silicon-carbon porous materials in Example 1, as detailed in Table 6 below. The "mesopore ratio" and "micropore ratio" refer to the following in the silicon-carbon porous materials: mesopore ratio = number of mesopores / (number of mesopores + number of micropores), and micropore ratio = number of mesopores / (number of mesopores + number of micropores); "mass percentage" refers to the mass percentage of silicon-carbon porous materials and graphite in the negative electrode active material layer, respectively.

[0286] Table 6

[0287] Comparative Example 1

[0288] Similar to the preparation method in Example 8, the main difference is that in step (4), an equal mass of S-containing ester compounds is used instead of LiTDI, as detailed in Table 7 below.

[0289] Example 2

[0290] Similar to the preparation method in Example 8, the main difference is that in step (4), an equal mass of LiTDI is used instead of the S-containing ester compound, as detailed in Table 7 below.

[0291] Comparative Example 3

[0292] Similar to the preparation method in Example 1, the main difference is that in step (4), 2-(trifluoromethyl)imidazole of equal mass is used instead of LiTDI, as detailed in Table 7 below.

[0293] Comparative Example 4

[0294] Similar to the preparation method in Example 1, the main difference is that in step (4), 4,5-dicyano-2-(trifluoromethyl)imidazolium is used instead of LiTDI, as detailed in Table 7 below.

[0295] Table 7

[0296] The lithium-ion batteries obtained in Examples 1-19 and Comparative Examples 1-4 were subjected to performance tests, and the test results are listed in Tables 1-7 above. The mass percentages in Tables 1, 2, and 7 refer to the mass percentage of each component in the electrolyte.

[0297] Test section

[0298] (1) High-temperature storage life

[0299] At 25°C, the batteries prepared in each embodiment and comparative example were charged at a constant current rate of 0.5C to the charging cutoff voltage of 4.25V, then charged at a constant voltage rate until the current ≤0.05C, allowed to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to the discharge cutoff voltage of 2V, allowed to stand for 5 minutes. This constitutes one charge-discharge cycle. Then, the batteries were charged at a constant current rate of 0.5C to 4.25V, then charged at a constant voltage rate until the current ≤0.05C. After storing the batteries at 60°C for 100 days, the batteries were subjected to cyclic charge-discharge tests according to the above method, and the capacity retention rate of the lithium-ion batteries after 100 days of storage was calculated.

[0300] (2) Cyclic performance

[0301] At 25°C, the battery prepared above was charged to 4.25V at 0.5C, and then discharged to 2.5V at 1C. This constitutes one charge-discharge cycle. The discharge capacity at this point is recorded as the initial discharge capacity. The battery was then subjected to the same charge-discharge cycle test, and the discharge capacity after each cycle was recorded until the battery's discharge capacity decreased to 80% of the initial discharge capacity. The number of cycles at this point was recorded.

[0302] (3) DC internal resistance and ratio

[0303] At 25°C, a lithium-ion battery and a lithium-ion battery that has undergone 800 cycles at 25°C were charged to 4.3V at a constant current of 1C. Then, the battery was charged at a constant voltage of 4.3V until the current was less than 0.05C, and then discharged at 1C for 30 minutes, adjusting the battery's state of charge (SOC) to 50%. Next, the positive and negative probes of a TH2523A AC internal resistance tester were connected to the positive and negative terminals of the battery, respectively. The internal resistance values ​​were read using the tester and recorded as the initial battery internal resistance (mΩ) and the battery internal resistance after 800 cycles (mΩ). The DC internal resistance growth rate after 800 cycles at 1C can be calculated to characterize the battery's rate performance.

[0304] (4) Storage of gas production

[0305] At 25°C, the battery cells prepared in each embodiment and comparative example were charged at a constant current rate of 0.5C to 4.25V, and then charged at a constant voltage until the current was ≤0.05C. The batteries were then stored at 60°C for 100 days, and the internal pressure (MPa) of the batteries was measured using an external pressure gauge to characterize the storage gas generation of the batteries.

[0306] A comparison between Examples 1-19 and Comparative Examples 1-4 shows that by synergistically using cyano-containing imidazole lithium compounds and S-containing ester compounds, the cycle life of the battery can be improved, and the battery can also have good high-temperature storage life.

[0307] A comparison of Examples 1-5 shows that controlling the mass percentage of cyano-containing imidazole lithium compounds within a suitable range can achieve better cycle life, high-temperature storage life, and rate performance.

[0308] A comparison of Examples 1, 6-9 shows that controlling the mass percentage of S-containing ester compounds within a suitable range can achieve better cycle life, high-temperature storage life, and rate performance.

[0309] By comparing Example 1 and Example 10, it can be seen that when the S-containing ester compound contains 1,3-propanesulfonic acid lactone, it can further improve the cycle life, high-temperature storage life and rate performance of the battery, and reduce gas production.

[0310] A comparison of Examples 1 and 11 shows that using fluorobenzene compounds and fluorophosphate compounds can further improve the cycle life and high-temperature storage life of the battery, while also reducing gas production. A comparison of Examples 1 and 12 shows that using phosphate ester compounds can further improve the cycle life of the battery, and also give the battery better high-temperature storage life and rate performance.

[0311] By comparing Example 1 with Examples 13-15, it can be seen that controlling the molar concentration of LiFSI within a suitable range can achieve better cycle life, high-temperature storage life, and rate performance.

[0312] By comparing Example 1 and Example 16, it can be seen that good cycle life, high temperature life and rate performance can be achieved by using different types of solvents. Among them, the performance is better when using high conductivity solvents EA and MA.

[0313] By comparing Example 1 and Example 17, it can be seen that different types of silicon-based materials can achieve good cycle life and high-temperature life, with silicon-carbon porous materials being better.

[0314] By comparing Example 1 with Examples 18-19, it can be seen that controlling the ratio of mesopores to micropores in silicon-carbon porous materials within a suitable range can achieve better cycle life and high-temperature storage life.

[0315] It should be noted that in the above embodiments and comparative examples, the reduction in the content of components in the electrolyte when the content changes (such as the reduction when the content of sulfur-containing ester compounds decreases from 4% to 0.01%) can be replenished by using the solvent ethylene carbonate.

[0316] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0317] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte contains additives, the additives comprising cyano-containing imidazole lithium compounds and S-containing ester compounds; The S-containing ester compounds include at least one of the structures *-OS(=O)2-O-*, *-OS(=O)-O-*, and *-S(=O)2-O-*, wherein each * is independently attached to a carbon atom.

2. The lithium-ion battery of claim 1, wherein, The cyano group-containing imidazole lithium compound includes one or more of the compounds satisfying formula (1) shown below: In formula (1), R1 and R2 are each independently selected from one of fluorinated or unsubstituted C0-C4 saturated alkylene groups and fluorinated or unsubstituted unsaturated hydrocarbon groups, and R3 is selected from one of fluorinated or unsubstituted C1-C4 saturated alkyl groups and fluorinated or unsubstituted unsaturated hydrocarbon groups.

3. The lithium-ion battery of claim 1 or 2, wherein, The cyano-containing imidazole lithium compounds include 4,5-dicyano-2-(trifluoromethyl)imidazolium lithium.

4. The lithium-ion battery of claim 3, wherein, The mass percentage of the 4,5-dicyano-2-(trifluoromethyl)imidazolium lithium in the electrolyte is 0.005% to 0.4%.

5. The lithium-ion battery of claim 3 or 4, wherein, The mass percentage of the 4,5-dicyano-2-(trifluoromethyl)imidazolium lithium in the electrolyte is 0.02% to 0.4%.

6. The lithium-ion battery according to any one of claims 1 to 5, wherein One or more of the following conditions must be met: (1) The S-containing ester compounds include cyclic S-containing ester compounds; (2) The mass percentage of the S-containing ester compound in the electrolyte is 0.007% to 2.9%.

7. The lithium-ion battery according to any one of claims 1 to 6, wherein The S-containing ester compound has a mass percentage of 0.1% to 2% in the electrolyte.

8. The lithium-ion battery according to any one of claims 1 to 7, wherein, One or more of the following conditions must be met: (1) the S-containing ester compound includes one or more of the compounds represented by formulae (2) to (4): R4, R5, and R6 are each independently selected from one of the following: H, F, fluorinated or unsubstituted C1-C10 saturated alkyl groups, fluorinated or unsubstituted unsaturated hydrocarbon groups, fluorinated or unsubstituted C6-C60 aryl groups, hydrocarbon carbonyl groups, carboxyl groups, hydrocarbon ester groups, cyano groups, silyl groups, and hydrocarbon oxy groups. (2) The S-containing ester compounds include one or more of 1,3-propanesulfonic acid lactone, vinyl sulfate, vinyl disulfate, vinyl trisulfate, vinyl sulfite, and vinyl vinyl sulfite.

9. The lithium-ion battery according to any one of claims 1 to 8, wherein, The additive also includes one or more of fluorocarbonate compounds, phosphate compounds, fluorobenzene compounds, and fluorophosphate compounds, wherein the fluorophosphate compound is lithium difluorophosphate.

10. The lithium-ion battery of claim 9, wherein, One or more of the following conditions must be met: (1) The fluorocarbonate compound includes fluoroethylene carbonate, and the fluoroethylene carbonate has a mass percentage of 3% to 10% in the electrolyte; (2) The phosphate ester compound includes tris(trimethylsilane) phosphate, wherein the mass percentage of tris(trimethylsilane) phosphate in the electrolyte is 0.05% to 0.5%; (3) The electrolyte includes lithium difluorophosphate, and the mass percentage of lithium difluorophosphate in the electrolyte is 0.05% to 0.5%; (4) The fluorobenzene compounds include one or more of monofluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene and trifluorotoluene; (5) The additive includes fluorobenzene compounds, and the fluorobenzene compounds in the electrolyte have a mass percentage of 0.05% to 0.5%.

11. The lithium-ion battery according to any one of claims 1 to 10, wherein, The electrolyte also contains a non-aqueous solvent, which includes a highly conductive solvent. The highly conductive solvent has the following characteristics: its conductivity at 25°C is 8 mS / cm to 20 mS / cm.

12. The lithium-ion battery of claim 11, wherein, One or more of the following conditions must be met: (1) The highly conductive solvent includes a chain-like highly conductive solvent, which includes one or more of dimethyl carbonate, ethyl acetate and methyl acetate; (2) The high conductivity solvent has a mass percentage content of 5% to 65% in the electrolyte.

13. The lithium-ion battery according to any one of claims 1 to 12, wherein, The electrolyte also contains an electrolyte lithium salt, which includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, wherein the molar concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.02 mol / L to 0.2 mol / L.

14. The lithium-ion battery according to any one of claims 1 to 13, wherein, The negative electrode sheet includes a negative electrode active material layer, the negative electrode active material layer contains a negative electrode active material, and the negative electrode active material includes a silicon-based material.

15. The lithium-ion battery of claim 14, wherein, The silicon-based materials include one or more of nano-silicon, micro-silicon, silicon-oxygen materials, and silicon-carbon materials.

16. The lithium-ion battery of claim 15, wherein, The silicon-based material includes silicon-carbon materials, and the silicon-carbon materials satisfy one or more of the following conditions: (1) The silicon-carbon material accounts for 3% to 40% of the mass of the negative electrode active material layer; (2) In the silicon-carbon material, the mass ratio of silicon to carbon is (4-6):(6-4); (3) The silicon-carbon material includes a porous silicon-carbon material, which includes a porous carbon matrix and silicon nanoparticles, wherein the silicon nanoparticles are loaded in the pores of the porous carbon matrix.

17. The lithium-ion battery of claim 16, wherein, The pores include mesopores and micropores. The pore size of the mesopores is 2nm to 10nm, and the pore size of the micropores is greater than or equal to 0.2nm and less than 2nm.

18. The lithium-ion battery of claim 17, wherein, In the silicon-carbon porous material, the mesopores account for ≥50% of the total number of pores.

19. The lithium-ion battery of any one of claims 1-18, wherein, The positive electrode sheet includes a positive active material layer, which contains a positive active material, including at least one of nickel-cobalt-manganese-based positive active material and lithium iron phosphate-based positive active material.

20. The lithium-ion battery of claim 19, wherein, The positive electrode active material includes a nickel-cobalt-manganese-based positive electrode active material, and the silicon-based material accounts for 3% to 45% of the mass of the negative electrode active material layer; or The positive electrode active material includes lithium iron phosphate positive electrode active materials, and the silicon-based material accounts for ≤20% of the mass of the negative electrode active material layer.

21. The lithium-ion battery of claim 20, wherein, The nickel-cobalt-manganese-based cathode active material includes lithium, nickel, cobalt, manganese, and oxygen, wherein, based on the total atomic molar number of all transition metal elements, the atomic molar number of nickel accounts for 50% to 95%.

22. The lithium-ion battery of claim 20 or 21, wherein, The nickel cobalt manganese-based positive electrode active material comprises Li x’ Ni x Co y Mn 1-x-y O y’ , 0.7≤x≤0.95, 0 23. The lithium-ion battery of any one of claims 20-22, wherein, The maximum charging cutoff voltage of the lithium-ion battery is greater than or equal to 4.3V, and the electrolyte meets the following characteristics: the mass fraction of dimethyl carbonate in the electrolyte is less than or equal to 30%. Alternatively, the nickel-cobalt-manganese-based cathode active material includes a first nickel-cobalt-manganese-based cathode active material, wherein the mass fraction of dimethyl carbonate in the electrolyte is less than or equal to 30%; wherein, in the first nickel-cobalt-manganese-based cathode active material, the atomic molar ratio of nickel is 50% to 60% based on the total atomic molar number of all transition metal elements.

24. The lithium-ion battery of claim 23, wherein, Li x1’ Ni 0.5 Co y2 Mn 0.5-y2 O y1’ and Li x2’ Ni 0.6 Co y3 Mn 0.4-y3 O y2’ one or both of 0 < y2 < 0.5, 0 < y3 < 0.4, 0.6 < x1' < 1.2, 1.6 < y1' < 2.2, 0.6 < x2' < 1.2, 1.6 < y2' < 2.

2.

25. A lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte contains additives, the additives comprising cyano-containing imidazole lithium compounds and S-containing ester compounds; The S-containing ester compound includes at least one structure selected from *-OS(=O)2-O-*, *-OS(=O)-O-*, and *-S(=O)2-O-*, wherein each * is independently attached to a carbon atom, and the S-containing ester compound has a mass percentage content of 0.01% to 4% in the electrolyte.

26. An electrical device comprising a lithium-ion battery as claimed in any one of claims 1 to 24.

Images