Lithium ion battery electrolyte and application thereof

Abstract

The invention provides a lithium ion battery electrolyte and application thereof. The electrolyte comprises: a non-aqueous solvent; a lithium salt; the additive comprises a first additive, the first additive is at least one of compounds with a structure shown in a formula (I) or a formula (II), and in the formula (I), n is 0 or 1; in the formula (II), R1 and R2 are respectively selected from substituted or unsubstituted C1-8 alkyl groups, substituent groups are at least one of halogen, cyano groups, C3-6 silyl groups, C1-8 alkoxy groups, C1-8 alkyl groups, C2-8 alkenyl groups, C2-8 alkynyl groups, C6-10 aryl groups or C6-10 heterocyclic groups, heteroatoms in the heterocyclic groups are selected from at least one of oxygen, nitrogen, sulfur or phosphorus, and the number of the heteroatoms is 1-5. According to the lithium ion battery electrolyte and the application thereof provided by the invention, the safety performance and the cycle performance of the battery are improved.

Description

Technical Field

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

[0002] With the gradual popularization of new energy vehicles globally, the driving range of power batteries has become one of the key indicators for consumers when choosing new energy vehicles. The energy density of power batteries is positively correlated with the voltage of the cathode active material. Currently, the use of high-voltage cathode active materials such as ternary layered oxides, lithium nickel manganese oxide, lithium-rich manganese-based oxides, lithium manganese oxide, and lithium manganese iron phosphate can further improve the energy density of power batteries and alleviate range anxiety. However, high-voltage cathode active materials, such as ternary layered oxides, are prone to irreversible phase transitions during cycling. Lattice oxygen is released as oxygen free radicals or singlet oxygen and undergoes a violent oxidation reaction with the organic solvent in the electrolyte, generating gases such as carbon dioxide and carbon monoxide, as well as acidic substances. This leads to a sudden increase in internal battery pressure, posing a safety risk to the battery. Summary of the Invention

[0003] This invention proposes a lithium-ion battery electrolyte and its application, which can capture oxygen released from the positive electrode side and improve the performance of the CEI film, inhibit electrolyte decomposition, reduce the loss of active lithium at the negative electrode, and improve the cycle performance and safety performance of the battery.

[0004] To solve the above-mentioned technical problems, the present invention provides a lithium-ion battery electrolyte, comprising:

[0005] Non-aqueous solvents;

[0006] Lithium salts; and

[0007] The additive includes a first additive, which is at least one of a compound having a structure of formula (I) or formula (II):

[0008]

[0009] In formula (I), n is 0 or 1; in formula (II), R1 and R2 are each selected from substituted or unsubstituted C1-8 alkyl groups, and the substituent is at least one of halogen, cyano, C3-6 silyl, C1-8 alkoxy, C1-8 alkyl, C2-8 alkenyl, C2-8 alkynyl, C6-10 aryl or C6-10 heterocyclic group, wherein the heteroatom in the heterocyclic group is selected from at least one of oxygen, nitrogen, sulfur or phosphorus, and the number of heteroatoms is 1-5.

[0010] In one embodiment of the present invention, the first additive is selected from at least one of the following compounds:

[0011]

[0012]

[0013] In one embodiment of the present invention, the content of the first additive in the electrolyte is 0.1wt%-5wt%.

[0014] In one embodiment of the present invention, the content of the first additive in the electrolyte is 0.3wt%-1wt%.

[0015] In one embodiment of the present invention, the additive includes a second additive, which includes at least one of vinylene carbonate, 1,3-propanesulfonate lactone, fluoroethylene carbonate, vinyl sulfate, tris(trimethylsilane) phosphate, or tetravinylsilane.

[0016] In one embodiment of the present invention, the content of the second additive in the electrolyte is 3wt%-10wt%.

[0017] In one embodiment of the present invention, the non-aqueous solvent includes one or a combination of at least two of cyclic carbonates, linear carbonates, or linear carboxylic acid esters; the cyclic carbonate includes at least one of ethylene carbonate or propylene carbonate; the linear carbonate includes at least one of dimethyl carbonate, diethyl carbonate, or methyl ethyl carbonate; and the linear carboxylic acid ester is selected from at least one of methyl formate, ethyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, or ethyl butyrate.

[0018] In one embodiment of the present invention, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorosulfonylimide, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorooxalate phosphate, lithium dioxalate borate, or lithium difluorophosphate, and the content of the lithium salt in the electrolyte is 6wt%-25wt%.

[0019] The present invention also provides a lithium-ion battery, comprising:

[0020] The positive electrode includes a positive electrode active material, which includes at least one of ternary layered oxide, lithium nickel manganese oxide, lithium-rich manganese-based oxide, lithium manganese oxide, or lithium manganese iron phosphate.

[0021] negative electrode;

[0022] A diaphragm is disposed between the positive electrode and the negative electrode;

[0023] The electrolyte is selected from the lithium-ion battery electrolytes described above.

[0024] The present invention also provides an electronic device comprising the lithium-ion battery described above.

[0025] In summary, this invention proposes a lithium-ion battery electrolyte and its application. By adding a first additive to the electrolyte, the selenium atoms in the first additive's structural formula can capture oxygen released from the positive electrode side and be oxidized to SeO2. The SeO2 is deposited on the positive electrode surface and participates in the formation of the positive electrode electrolyte interface film, reducing the positive electrode interface impedance. The six-membered ring containing S or P in the first additive decomposes to generate substances rich in lithium phosphate, lithium sulfate, or alkyl lithium sulfate, which further optimize the CEI film, improve the mechanical strength and ion transport efficiency of the CEI film, inhibit electrolyte decomposition, and improve the cycle performance of the lithium-ion battery. Furthermore, the free cyano groups are stored in the electrolyte to complex trace amounts of transition metals, reducing the loss of active lithium at the negative electrode and improving the battery's cycle performance and safety performance. Detailed Implementation

[0026] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0027] It should be understood that the invention can be embodied in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0028] The technical solution of the present invention will be further described in detail below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] This invention proposes a lithium-ion battery electrolyte, comprising a non-aqueous solvent, a lithium salt, and additives, wherein the additives include a first additive, which is, for example, at least one compound having the structure of formula (I) or formula (II):

[0030]

[0031] In formula (I), n is 0 or 1; in formula (II), R1 and R2 are each selected from substituted or unsubstituted C1-8 alkyl groups, and the substituents are at least one of halogen, cyano, C3-6 silyl, C1-8 alkoxy, C1-8 alkyl, C2-8 alkenyl, C2-8 alkynyl, C6-10 aryl, or C6-10 heterocyclic groups. The heteroatom in the heterocyclic group is selected from at least one of oxygen (O), nitrogen (N), sulfur (S), or phosphorus (P), and the number of heteroatoms is 1-5. The first additive can capture and absorb active oxygen released from the positive electrode side and participate in the positive electrode film formation, reduce the gas production of the battery, and improve the cycle performance and safety performance of the lithium-ion battery.

[0032] In one embodiment of the present invention, when the first additive is selected as a compound having the structure of formula (I) or formula (II), the selenium (Se) atoms in the structure of the first additive can capture oxygen released from the positive electrode side and be oxidized to SeO2. SeO2 is deposited on the positive electrode surface and participates in the formation of the cathode electrolyte interface (CEI film), reducing the positive electrode interface impedance. The six-membered ring portion containing S or P in the first additive decomposes to generate substances rich in lithium phosphate (Li3PO4), lithium sulfate (Li2SO3), or alkyl lithium sulfate (ROSO2Li), further optimizing the CEI film, improving its mechanical strength and ion transport efficiency, inhibiting electrolyte decomposition, and improving the cycle performance of the lithium-ion battery. The freed cyano groups are stored in the electrolyte to complex trace amounts of transition metals, reducing the loss of active lithium at the negative electrode.

[0033] In one embodiment of the present invention, the first additive is selected, for example, from any one or a combination of the following compounds: wait.

[0034] In one embodiment of the present invention, the content of the first additive in the electrolyte is, for example, 0.1wt%-5wt%, or, for example, 0.3wt%-1wt%. If the content of the first additive is too low, it cannot effectively achieve the technical effects of adsorbing active oxygen and forming a film to cover the solid-liquid interface. If the content of the first additive is too high, the formed CEI film is too thick, which hinders the transport speed of lithium ions, leading to an increase in the direct current resistance (DCR) of the lithium-ion battery, affecting the efficiency of the lithium-ion battery, and may also lead to a decrease in the cycle performance and safety performance of the lithium-ion battery. Therefore, controlling the content of the first additive can reduce gas production while exerting a good film-forming effect, thereby improving the cycle performance and safety performance of the battery.

[0035] In one embodiment of the present invention, the additive further includes a second additive, which includes at least one selected from vinylene carbonate (VC), 1,3-propanesultone (PS), fluoroethylene carbonate (FEC), 1,3,2-dioxathiolane 2,2-dioxide (DTD), tris(trimethylsilyl) phosphate (TMSP), or tetravinylsilane (TVSi). In a specific embodiment of the present invention, when the second additive is a combination of multiple substances, the content of each substance in the electrolyte is 0.1 wt%-5 wt%, and the total content of the second additive in the electrolyte is 3 wt%-10 wt%. The second additive can promote the formation of a solid electrolyte interface (SEI) film, and can synergistically improve the quality of the interface film and reduce lithium dendrite formation, thereby improving the cycle performance of the lithium battery.

[0036] In one embodiment of the present invention, the lithium salt includes, for example, one or a combination of at least two of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiDFOB), lithium difluorooxalate phosphate (LiDFOP), lithium dioxalate borate (LiBOB), or lithium difluorophosphate (LiPF2O2). The content of the lithium salt in the electrolyte is, for example, 6 wt%-25 wt%, preferably 10 wt%-17 wt%. In a specific embodiment of the present invention, the lithium salt is selected, for example, from lithium hexafluorophosphate and lithium bisfluorosulfonylimide to improve the ionic conductivity of the electrolyte, thereby improving the charge / discharge efficiency and energy density of the lithium-ion battery, enhancing the thermal stability of the electrolyte, and improving the safety performance of the battery.

[0037] In one embodiment of the present invention, the non-aqueous solvent includes, for example, one or a combination of at least two of cyclic carbonates, linear carbonates, or linear carboxylic acid esters. The cyclic carbonate includes, for example, at least one of ethylene carbonate (EC) or propylene carbonate (PC), meaning the cyclic carbonate can be ethylene carbonate, propylene carbonate, or a mixture of ethylene carbonate and propylene carbonate in any proportion. The linear carbonate includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), or ethyl methyl carbonate (EMC), meaning the linear carbonate can be one of the substances listed above, or a combination of any two or three of the listed species in any proportion. The linear carboxylic acid ester is selected from at least one of methyl formate (MF), ethyl formate (EF), butyl formate (BF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), butyl acetate (BA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), or ethyl butyrate (EB). That is, the linear carboxylic acid ester can be one of the substances listed above, or it can be a mixture of any two or more of the listed species in any proportion.

[0038] In one embodiment of the present invention, the content of cyclic carbonate in the electrolyte is, for example, 5 wt%-30 wt%, specifically, 5 wt%, 10 wt%, 20 wt%, or 30 wt%. The content of linear carbonate in the electrolyte is, for example, 10 wt%-50 wt%, specifically, 10 wt%, 20 wt%, 30 wt%, 40 wt%, or 50 wt%. The content of linear carboxylic acid ester solvent in the electrolyte is, for example, 10 wt%-40 wt%, specifically, 10 wt%, 20 wt%, 30 wt%, or 40 wt%. Cyclic carbonates possess high dielectric constants and polarity, effectively dissolving lithium salts and promoting their dissociation, thus providing the basic ionic conductivity of the electrolyte. Linear carbonates, with their low viscosity, low melting point, and good flowability, significantly reduce the overall viscosity of the electrolyte, increase ion migration rate, and improve battery rate performance. Linear carboxylic esters generally have even lower viscosity, and lithium-ion electrolytes containing carboxylic esters exhibit higher conductivity and lower initial DCR, resulting in superior fast-charging and low-temperature performance of lithium-ion batteries. By combining various solvents, their respective advantages can be leveraged to enhance the overall performance of the electrolyte.

[0039] In one embodiment of the present invention, when preparing the electrolyte, in a glove box with an inert gas atmosphere such as argon containing a moisture content and an oxygen content of less than or equal to 0.1 ppm, the solvent is mixed uniformly according to the mass ratio. Lithium salt is then added to the solvent and mixed uniformly. After the temperature of the lithium salt and solvent mixture drops below 15°C, additives are added and mixed uniformly to prepare the lithium-ion battery electrolyte. The content described in this application is a weight percentage calculated based on the total weight of the electrolyte.

[0040] This invention also proposes a lithium-ion battery, comprising a casing and a bare cell disposed within the casing. The bare cell includes a positive electrode, a separator, and a negative electrode. The separator is placed between the positive and negative electrodes to prevent short circuits and allow lithium ions to pass through. The positive electrode, separator, and negative electrode are stacked sequentially to ensure that a separator is present between any positive and negative electrode. A multi-layered stack is obtained by winding or folding, and this stack is then inserted into the battery casing as the bare cell. Finally, an electrolyte is injected into the casing once or in multiple stages to completely immerse the bare cell in the electrolyte. The electrolyte, for example, is selected from the aforementioned electrolytes and serves to conduct ions between the positive and negative electrodes. In one embodiment of this invention, the lithium-ion battery is, for example, a primary battery or a secondary battery. A secondary battery is, for example, a pouch battery, a hard-shell battery, or a cylindrical battery. This invention does not specifically limit the type of lithium-ion battery. In this embodiment, a pouch battery is used as an example to illustrate the lithium-ion battery.

[0041] In an embodiment of the present invention, the positive electrode includes a positive electrode current collector and a positive electrode active layer coated at least on one surface of the positive electrode current collector. Among them, the positive electrode current collector is, for example, a foil formed after surface treatment of nickel, titanium, aluminum, silver, stainless steel, carbon, etc. In addition to the foil, the positive electrode current collector can also be used in any one or a combination of multiple forms such as film-like, mesh-like, porous, foam-like or non-woven fabric. Among them, the thickness of the positive electrode current collector is, for example, 8μm - 20μm. In this embodiment, the positive electrode current collector is, for example, an aluminum foil, and the thickness of the aluminum foil is, for example, 13μm.

[0042] In an embodiment of the present invention, the positive electrode active layer is disposed on either one or both of the two surfaces of the positive electrode current collector. The positive electrode active layer includes a positive electrode active material, a positive electrode binder, a positive electrode conductive agent, etc. Among them, the positive electrode active material, for example, includes one or more of ternary layered oxides (NCM), lithium nickel manganate (LiNi X Mn 2-x O4, 0 < x < 1), lithium-rich manganese-based (xLi2MnO3·(1 - x)NCM, 0.5 < x < 0.8), lithium manganate (LiMn2O4), and lithium iron manganese phosphate (LiFe x Mn 1-x PO4, 0 < x < 1), etc., to improve the energy density, cycle stability and safety of the lithium-ion battery. The positive electrode binder is, for example, selected from at least one of polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate (PAcr), polyvinyl ether (PVE), poly(methyl methacrylate) (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexafluoropropylene (PHFP), or styrene-butadiene rubber (SBR). The positive electrode conductive agent is, for example, selected from one of conductive carbon black (Super P), acetylene black, graphene, carbon nanotubes, carbon nanofibers, or porous carbon, or a combination of two or more in any proportion. The mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode active layer is, for example, (90 - 97):(1 - 5):(2 - 5).

[0043] In one embodiment of the present invention, the positive electrode active material is selected, for example, from a mixture of lithium manganese iron phosphate and ternary layered oxides, and the mass ratio of lithium manganese iron phosphate to ternary layered oxides is, for example, 3:7-8:2. In this embodiment, the positive electrode active material is selected, for example, from LiMn with a mass ratio of 5:5. 0.5 Fe 0.5 PO4 and LiNi 0.6 Mn 0.2 Co 0.2 O2, a positive electrode conductive agent selected from conductive carbon black and carbon nanotubes in a mass ratio of 1:1, and a positive electrode binder selected from polyvinylidene fluoride (PVDF) are used. The positive electrode active material, positive electrode conductive agent, and positive electrode binder are mixed, for example, in a mass ratio of 97:1:2. An organic solvent is then added, and the mixture is thoroughly stirred and homogenized under vacuum to obtain a positive electrode slurry. The organic solvent is, for example, N-methylpyrrolidone (NMP). The positive electrode slurry is uniformly coated onto aluminum foil, then air-dried at room temperature before being transferred to an oven for drying. The positive electrode is then obtained through cold pressing, edge trimming, cutting, and slitting processes. This application does not limit the method of preparing the positive electrode; in other embodiments, the positive electrode can also be obtained by any other method of forming a positive electrode.

[0044] In one embodiment of the present invention, the negative electrode includes, for example, a negative electrode current collector and a negative electrode active layer coated at least on one surface of the negative electrode current collector. The negative electrode current collector is selected, for example, from foils treated with nickel, titanium, gold, silver, chromium, molybdenum, copper, stainless steel, or carbon. Besides foils, the negative electrode current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam, or nonwoven fabric. The thickness of the negative electrode current collector is, for example, 6 μm-15 μm. In this embodiment, the negative electrode current collector is, for example, copper foil, and the thickness of the copper foil is, for example, 8 μm.

[0045] In one embodiment of the present invention, the negative electrode active layer is disposed on any one or both surfaces of the negative electrode current collector. The negative electrode active layer includes a negative electrode active material, a negative electrode conductive agent, a negative electrode binder, and a thickener. The negative electrode active material is selected, for example, from graphite or silicon-containing composite materials, including natural graphite, artificial graphite, graphite / silicon-oxygen composite materials, graphite / silicon-carbon composite materials, graphite / elemental silicon composite materials, etc. The negative electrode binder is selected from at least one of the following: styrene-butadiene rubber, polyvinylidene fluoride, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), carboxylated polyvinyl chloride (CPVC), polyvinyl fluoride (PVF), polyvinylpyrrolidone (PVP), polyurethane (PU), polytetrafluoroethylene (PTFE), or acrylic-esterified styrene-butadiene rubber (A-SBR). The thickener is selected from, for example, sodium carboxymethyl cellulose (CMC-Na) or lithium carboxymethyl cellulose (CMC-Li). The negative electrode conductive agent is selected from, for example, one of conductive carbon black, Ketjen black, acetylene black, graphene, carbon nanotubes, carbon nanofibers, or porous carbon, or a combination of two or more in any proportion. The mass ratio of negative electrode active material, negative electrode conductive agent, negative electrode binder and thickener in the negative electrode active layer is, for example, (91-98.5):(0.5-2):(0.5-5):(0.5-2).

[0046] In one embodiment of the present invention, the negative electrode active material is selected from artificial graphite, the negative electrode conductive agent is selected from conductive carbon black, the thickener is selected from sodium carboxymethyl cellulose, and the negative electrode binder is selected from styrene-butadiene rubber. The negative electrode active material, negative electrode conductive agent, thickener, and negative electrode binder are mixed, for example, at a mass ratio of 97:0.5:0.5:2. Deionized water is added, and the mixture is thoroughly stirred and homogenized under vacuum to obtain a negative electrode slurry. The negative electrode slurry is coated onto copper foil, then air-dried at room temperature and transferred to an oven for drying. After cold pressing, edge trimming, sheet cutting, and slitting, the negative electrode is obtained. In other embodiments, the negative electrode can also be obtained by any other method of forming a negative electrode.

[0047] In one embodiment of the present invention, the separator is, for example, a conventional separator, a ceramic separator, a polymer separator, a non-woven fabric separator, or an inorganic-organic composite separator, and the thickness of the separator is, for example, 9μm-15μm. Specifically, the separator is, for example, a single-layer polypropylene (PP) membrane, a single-layer polyethylene (PE) membrane, a double-layer PP / PE membrane, a double-layer PP / PP membrane, or a triple-layer PP / PE / PP membrane. In one embodiment of the present invention, the separator is, for example, selected as an 8μm-10μm polyethylene base membrane, and a 2μm-4μm thick nano-alumina coating is coated on at least one side of the base membrane.

[0048] In one embodiment of the present invention, the positive electrode, separator, and negative electrode are placed sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. A bare cell is obtained by winding or stacking. The bare cell is then placed in an aluminum-plastic film, baked at 80°C-100°C to remove moisture, and then the electrolyte is injected into the aluminum-plastic film once or in multiple stages before sealing. Following these processes, a soft-pack lithium-ion battery is obtained through standing, hot and cold pressing, formation, clamping, and capacity testing.

[0049] The present invention will be explained in more detail below by referring to embodiments, which should not be construed as limiting. Appropriate modifications can be made within the scope of the invention and all such modifications fall within the technical scope of the invention. Unless otherwise stated, the raw materials and reagents used in the following embodiments are commercially available or can be prepared by conventional methods in the art, and the instruments used in the embodiments are also commercially available.

[0050] Example 1

[0051] Electrolyte preparation: In an argon-filled glove box with an oxygen content of 0.1 ppm and a water content of 0.1 ppm, ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and ethyl acetate were mixed uniformly in a mass ratio of 5:3.3:4:2 to obtain a mixed solvent. Dried LiPF6, LiFSI, and LiPO2F2 were added to the mixed solvent and mixed thoroughly. The mixture was then cooled to 15°C, and then additive compound 1 (first additive), and additives VC, DTD, TVSi, and TMSP were added to obtain the lithium-ion battery electrolyte. Specifically, based on the total mass of the lithium-ion battery electrolyte (100%), the content of LiPF6 was 10%, LiFSI was 4%, LiPO2F2 was 0.8%, additive compound 1 was 0.5%, VC was 2%, DTD was 0.5%, TMSP was 0.5%, and TVSi was 0.2%.

[0052] Preparation of the positive electrode: The positive electrode active material is LiMn in a mass ratio of 5:5. 0.5 Fe 0.5PO4 and LiNi 0.6 Mn 0.2 Co 0.2 O2, positive electrode conductive agent (conductive carbon black and carbon nanotubes in a 1:1 mass ratio), and positive electrode binder (polyvinylidene fluoride). The positive electrode active material, positive electrode conductive agent, and positive electrode binder are mixed in a mass ratio of 97:1:2, NMP is added, and the mixture is thoroughly stirred and homogenized under vacuum to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated onto aluminum foil, then air-dried at room temperature before being transferred to an oven for drying. The positive electrode is then obtained through cold pressing, edge trimming, sheet cutting, and slitting processes.

[0053] Preparation of the negative electrode: Artificial graphite, conductive carbon black, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed in a mass ratio of 97:0.5:0.5:2. Deionized water is added and the mixture is thoroughly stirred and mixed under the action of a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry is coated on copper foil, and then dried at room temperature before being transferred to an oven for drying. After cold pressing, edge trimming, sheet cutting and slitting processes, the negative electrode is obtained.

[0054] Selection of diaphragm: A 12μm thick polypropylene membrane was selected as the diaphragm.

[0055] Battery fabrication: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. These stacked layers yield a bare cell. The bare cell is then placed in an aluminum-plastic film, baked at 100°C to remove moisture, injected with electrolyte, sealed, and subjected to formation to obtain a soft-pack lithium-ion battery.

[0056] Example 2

[0057] In the electrolyte, the content of compound 1 was 0.1 wt%, and the other steps were consistent with those in Example 1.

[0058] Example 3

[0059] In the electrolyte, the content of compound 1 was 0.3 wt%, and the other steps were consistent with those in Example 1.

[0060] Example 4

[0061] In the electrolyte, the content of compound 1 was 1 wt%, and the other steps were consistent with those in Example 1.

[0062] Example 5

[0063] In the electrolyte, the content of compound 1 was 3 wt%, and the other steps were consistent with those in Example 1.

[0064] Example 6

[0065] In the electrolyte, the content of compound 1 was 5 wt%, and the other steps were consistent with those in Example 1.

[0066] Example 7

[0067] In the electrolyte, compound 1 was replaced with compound 2, and the other steps were the same as in Example 1.

[0068] Example 8

[0069] In the electrolyte, compound 1 was replaced with compound 3, and the other steps were the same as in Example 1.

[0070] Example 9

[0071] In the electrolyte, compound 1 was replaced with compound 4, and the other steps were the same as in Example 1.

[0072] Example 10

[0073] In the electrolyte, compound 1 was replaced with compound 5, and the other steps were the same as in Example 1.

[0074] Example 11

[0075] In the electrolyte, compound 1 was replaced with compound 6, and the other steps were the same as in Example 1.

[0076] Example 12

[0077] In the electrolyte, compound 1 was replaced with compound 7, and the other steps were the same as in Example 1.

[0078] Example 13

[0079] In the electrolyte, the content of compound 1 was 0.05 wt%, and the other steps were consistent with those in Example 1.

[0080] Example 14

[0081] In the electrolyte, the content of compound 1 was 8 wt%, and the other steps were consistent with those in Example 1.

[0082] Example 15

[0083] No second additive was added to the electrolyte, and the other steps were the same as in Example 1.

[0084] Comparative Example 1

[0085] In the electrolyte, the first additive is not added, and the other steps are the same as in Example 1.

[0086] Comparative Example 2

[0087] In the electrolyte, neither the first nor the second additive is added, and the other steps are the same as in Example 1.

[0088] In this invention, lithium batteries were prepared using different electrolytes in Examples 1-15 and Comparative Examples 1-2, and the performance of the lithium batteries was tested. The formulations and test results of some electrolytes are shown in Table 1.

[0089] In one embodiment of the present invention, the initial DCR (Beginning Of Life DCR, BOL DCR) test is performed by adjusting the temperature of the constant temperature chamber to 25°C and letting the lithium battery stand in the constant temperature chamber for 1 hour; charging at a constant current of 0.3C to a cutoff voltage of 4.33V, then charging at a constant current of 4.33V to 0.05C, and letting it stand for 30 minutes; then discharging at a constant current of 0.33C to 2.8V, and letting it stand for 10 minutes, repeating this cycle twice, and taking the discharge capacity of the last discharge as C0. Charging at a constant current of 0.33C to 4.33V, then charging at a constant voltage to 0.05C, and letting it stand for 30 minutes, followed by discharging at a constant current of 0.33C to 50% C0, and letting it stand for 1 hour, recording the voltage V0 at the end of the standing period; then discharging at a constant current of 1C for 30 seconds, recording the voltage V1 and current I. Therefore, the initial DCR = (V0 - V1) / I.

[0090] In one embodiment of the present invention, the high-temperature cycling test involves adjusting the temperature of the constant temperature chamber to 45°C, placing the lithium-ion battery in the constant temperature chamber for 2 hours to stabilize, charging it at a constant current of 1C to 4.33V, then charging it at a constant voltage of 0.05C, letting it stand for 10 minutes, and then discharging it at a constant current of 1C to 2.8V. After cycling this charge-discharge cycle 800 times, the discharge capacity C1 of the cell is recorded at the end of the 800 discharge cycles. The cycle capacity retention rate of the battery after 800 cycles at 45°C is calculated according to the following formula: Cycle capacity retention rate (%) = C1 / C0 × 100%.

[0091] In one embodiment of the present invention, the gas generation performance test of the lithium-ion battery involves adjusting the temperature of the constant temperature chamber to 25°C, placing the lithium-ion battery in the constant temperature chamber and letting it stand for 1 hour, then charging it to 4.33V at a constant current of 0.33C. The initial volume V1 of the cell is recorded using the water displacement method. The battery is then transferred to a constant temperature chamber at 60°C and stored for 90 days. During these 90 days, the battery is recharged every 15 days. Specifically, each time the battery is recharged, it is transferred to a constant temperature chamber at 25°C and left to stand for 2 hours, then charged to 4.33V at a constant current of 0.33C, and then charged to 0.05C at 4.33V. It is then transferred back to the constant temperature chamber at 60°C for further storage. After 90 days (d) of storage, the volume V2 of the cell after storage is recorded using the direct water displacement method. The storage capacity retention rate is calculated using the following formula: Storage gas generation rate = (V2 - V1) / V1 × 100%.

[0092] Table 1. Partial characteristics of the electrolytes and performance of lithium-ion batteries in Examples 1-15 and Comparative Examples 1-2.

[0093]

[0094] Please refer to Table 1. Comparing Example 1 and Comparative Examples 1-2, it can be seen that when only the second additive is added to the electrolyte, the initial impedance of the battery increases, and the high-temperature cycle capacity retention and high-temperature storage gas generation improve. When the first additive is added in addition to the second additive, the high-temperature cycle capacity retention and high-temperature storage gas generation of the battery are further improved. Comparing Examples 1 and 15, it can be seen that when the first additive is added to the electrolyte but the second additive is not added, the resistance of the lithium-ion battery decreases, but the high-temperature cycle capacity retention and high-temperature storage gas generation of the lithium-ion battery decrease. This indicates that the second additive can synergistically improve the quality of the interface film with the first additive. Since the increase in the thickness of the interface film slightly increases the initial impedance, it greatly improves the cycle performance of the lithium battery and reduces the high-temperature storage gas generation.

[0095] Comparing Examples 1-12 and Comparative Example 1, it can be seen that when the type and content of the second additive in the electrolyte are the same, adding the first additive to the electrolyte increases the high-temperature cycle capacity retention rate of the lithium-ion battery and reduces the high-temperature storage gas production. Therefore, the first additive can capture oxygen released from the positive electrode side and participate in the formation of the positive electrode electrolyte interface film, optimizing the CEI film, improving the mechanical strength and ion transport efficiency of the CEI film, inhibiting electrolyte decomposition, improving the cycle performance of the lithium-ion battery, and simultaneously reducing gas production.

[0096] Please refer to Table 1. Comparing Examples 1-6 and 13-14, it can be seen that as the content of the first additive in the electrolyte increases, the initial impedance increases, and the high-temperature cycle capacity of the lithium-ion battery initially increases and then decreases, while the gas production during high-temperature storage decreases. This is because when the content of the first additive is low, it cannot effectively achieve the technical effects of adsorbing active oxygen and forming a film covering the solid-liquid interface. As the content of the first additive increases, the adsorption of active oxygen is better, and the gas production decreases. However, the formed CEI film becomes too thick, hindering the transport speed of lithium ions, leading to an increase in the initial impedance of the lithium-ion battery, affecting the efficiency of the lithium-ion battery, and potentially causing a decrease in the cycle performance and safety performance of the lithium-ion battery. Therefore, controlling the content of the first additive can reduce gas production while exerting a good film-forming effect, thereby improving the cycle performance and safety performance of the battery.

[0097] Please refer to Table 1. Comparing Examples 1 and 7-12, it can be seen that when different compounds are selected as the first additive, the high-temperature cycle capacity retention rate and high-temperature storage gas generation of the lithium-ion battery are improved. However, different first additives have different effects on impedance, high-temperature cycle capacity retention rate and high-temperature storage gas generation, indicating that compounds with different structures have different effects. Based on the design requirements of lithium-ion batteries, different structures of first additives or combinations can be selected.

[0098] This invention also provides an electronic device comprising at least one of the aforementioned lithium-ion batteries, which provides electrical energy. The electronic device can be a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, or power tool, etc. In one embodiment of this invention, the vehicle is, for example, a new energy vehicle, which can be a pure electric vehicle, a hybrid electric vehicle, or a range-extended electric vehicle, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. The electronic device includes the aforementioned lithium-ion battery, and therefore the advantages of including the aforementioned lithium-ion battery are not elaborated here.

[0099] In summary, this invention proposes a lithium-ion battery electrolyte and its application. By adding a first additive to the electrolyte, the selenium atoms in the first additive's structural formula can capture oxygen released from the positive electrode side and be oxidized to SeO2. SeO2 deposits on the positive electrode surface and participates in the formation of the positive electrode electrolyte interphase (CEI) film, reducing the positive electrode interfacial impedance. The six-membered rings containing S or P in the first additive decompose to generate substances rich in lithium phosphate, lithium sulfate, or alkyl lithium sulfate, further optimizing the CEI film, improving its mechanical strength and ion transport efficiency, inhibiting electrolyte decomposition, and improving the cycle performance of the lithium-ion battery. Furthermore, the freed cyano groups are stored in the electrolyte to complex trace amounts of transition metals, reducing the loss of active lithium at the negative electrode. Controlling the content of the first additive reduces gas production while exerting a good film-forming effect, improving the battery's cycle performance and safety. Adding a second additive based on the first additive can promote the formation of the solid electrolyte interfacial film, further improving the quality of the interfacial film, reducing lithium dendrite formation, and thus improving the cycle performance of the lithium battery.

[0100] The above description is merely a preferred embodiment of this application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept. For example, technical solutions formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application (but not limited to) each other.

[0101] Apart from the technical features described in the specification, the other technical features are known to those skilled in the art. To highlight the innovative features of this invention, the other technical features will not be described in detail here.

Claims

1. A lithium-ion battery electrolyte, characterized in that, include: Non-aqueous solvents; Lithium salts; as well as The additive includes a first additive, which is at least one of a compound having a structure of formula (I) or formula (II): In formula (I), n is 0 or 1; in formula (II), R1 and R2 are each selected from substituted or unsubstituted C1-8 alkyl groups, and the substituent is at least one of halogen, cyano, C3-6 silyl, C1-8 alkoxy, C1-8 alkyl, C2-8 alkenyl, C2-8 alkynyl, C6-10 aryl or C6-10 heterocyclic group, wherein the heteroatom in the heterocyclic group is selected from at least one of oxygen, nitrogen, sulfur or phosphorus, and the number of heteroatoms is 1-5.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, The first additive is selected from at least one of the following compounds:

3. The lithium-ion battery electrolyte according to claim 1, characterized in that, The content of the first additive in the electrolyte is 0.1wt%-5wt%.

4. The lithium-ion battery electrolyte according to claim 3, characterized in that, The content of the first additive in the electrolyte is 0.3wt%-1wt%.

5. The lithium-ion battery electrolyte according to claim 1, characterized in that, The additive includes a second additive, which includes at least one of vinylene carbonate, 1,3-propanesulfonate lactone, fluoroethylene carbonate, vinyl sulfate, tris(trimethylsilane) phosphate, or tetravinylsilane.

6. The lithium-ion battery electrolyte according to claim 5, characterized in that, The content of the second additive in the electrolyte is 3wt%-10wt%.

7. The lithium-ion battery electrolyte according to claim 1, characterized in that, The non-aqueous solvent includes one or a combination of at least two of cyclic carbonates, linear carbonates, or linear carboxylic acid esters; the cyclic carbonate includes at least one of ethylene carbonate or propylene carbonate; the linear carbonate includes at least one of dimethyl carbonate, diethyl carbonate, or methyl ethyl carbonate; and the linear carboxylic acid ester is selected from at least one of methyl formate, ethyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, or ethyl butyrate.

8. The lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorosulfonylimide, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorooxalate phosphate, lithium dioxalate borate, or lithium difluorophosphate, and the content of the lithium salt in the electrolyte is 6wt%-25wt%.

9. A lithium-ion battery, characterized in that, include: The positive electrode includes a positive electrode active material, which includes at least one of ternary layered oxide, lithium nickel manganese oxide, lithium-rich manganese-based oxide, lithium manganese oxide, or lithium manganese iron phosphate. negative electrode; A diaphragm is disposed between the positive electrode and the negative electrode; The electrolyte is selected from the lithium-ion battery electrolyte according to any one of claims 1-8.

10. An electronic device, characterized in that, Including the lithium-ion battery as described in claim 9.

Images