Electrolyte additive, electrolyte and battery

Abstract

The invention relates to the technical field of batteries, in particular to an electrolyte additive, an electrolyte and a battery. The structural general formula of the additive a is as follows: # imgabs0 #; R1, R2, R3, R4, R5, R6 and R7 are respectively and independently selected from one of hydrogen atoms, halogen atoms, alkyl with the carbon atom number of 1-10, unsaturated alkyl with the carbon atom number of 2-10, alkoxy with the carbon atom number of 1-10, alkanoyl with the carbon atom number of 2-10 and phenyl; hydrogen atoms in the alkane group, the unsaturated alkyl group, the alkoxy group and the alkanoyl group can be partially or completely substituted by one or more of halogen atoms, cyano groups, carboxyl groups and sulfonic acid groups. The electrolyte additive provided by the invention can endow the battery with excellent cycle and high-temperature storage performance.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to an electrolyte additive, an electrolyte and a battery. Background Art

[0002] Conventional organic carbonate electrolytes suffer from continuous oxidative decomposition at high voltages, as well as dissolution of transition metal ions in the cathode material, limiting the capacity and application of high-voltage cathode materials. Developing high-voltage electrolyte solvents and additives is a cost-effective and effective approach to improving battery performance, ultimately enabling stable electrolytes at high voltages. Summary of the Invention

[0003] The first object of the present invention is to provide an electrolyte additive, which, when added to the electrolyte, can enable the battery to have excellent cycle and high-temperature storage performance.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] An electrolyte additive includes an additive a, wherein the general structural formula of the additive a is as follows:

[0006]

[0007] Wherein, R1, R2, R3, R4, R5, R6 and R7 are independently selected from one of a hydrogen atom, a halogen atom, an alkane group having 1 to 10 carbon atoms, an unsaturated hydrocarbon group having 2 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkanoyl group having 2 to 10 carbon atoms and a phenyl group, and the hydrogen atoms in the alkane group, the unsaturated hydrocarbon group, the alkoxy group and the alkanoyl group may be partially or completely substituted by one or more of a halogen atom, a cyano group, a carboxyl group and a sulfonic acid group.

[0008] Wherein, the additive a comprises one or more compounds of formula 1 to formula 5,

[0009] The structural formulas of Formula 1 to Formula 5 are as follows:

[0010]

[0011]

[0012]

[0013] The electrolyte additive further includes additive b, and the additive b includes at least one of ethylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, propylene sulfite, vinyl sulfate, 4-methylethylene sulfate, succinic anhydride, adiponitrile and 1,3,6-hexanetrionitrile.

[0014] Wherein, the mass ratio of the additive a to the additive b is 1-10:15.

[0015] A second object of the present invention is to provide an electrolyte comprising the above electrolyte additive.

[0016] Wherein, the electrolyte further includes a lithium salt electrolyte and an organic solvent.

[0017] The lithium salt electrolyte includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, and lithium difluorooxalatoborate.

[0018] Wherein, the organic solvent includes a cyclic organic solvent and a chain organic solvent.

[0019] Wherein, the cyclic organic solvent includes at least one of ethylene carbonate, propylene carbonate, and butylene carbonate; and / or,

[0020] The chain organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0021] A third object of the present invention is to provide a battery comprising the above-mentioned electrolyte, a positive electrode sheet, a negative electrode sheet and a separator.

[0022] Beneficial effects of the present invention:

[0023] The electrolyte additive of the present invention comprises additive a, wherein NC and C≡N in additive a participate in forming a N-rich inorganic interface film, which can effectively isolate the electrode material from side reactions with the electrolyte, inhibit the dissolution of positive electrode metal ions under high voltage, and at the same time improve the high-voltage and high-temperature resistance of the electrolyte, thereby significantly improving the battery cycle performance and high-temperature storage performance. The phenoxy group in additive a can complex with the positive electrode, inhibit metal dissolution, improve the high-voltage resistance of the electrolyte, and thus improve the high-voltage cycle performance and high-temperature storage performance. The dioxy group enables additive a to provide multiple coordination sites with lithium ions, thereby reducing the viscosity of the electrolyte, thereby promoting the migration rate of lithium ions in the electrolyte, improving the ionic conductivity of the electrolyte, and thus improving the charge and discharge efficiency and cycle performance of the battery. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical scheme and technical effect of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention is clearly and completely described. The embodiments described below are part of the embodiments of the present invention, rather than all the embodiments. In combination with the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer; if the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0025] In the present description, the term "and / or" describes the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0026] In the description of the present invention, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0027] It should be understood that the weights of the relevant components mentioned in the embodiments of the present invention may not only refer to the specific content of each component, but also represent the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally increased or decreased according to the embodiments of the present invention, it is within the scope of the present invention. Specifically, the weights described in the embodiments of the present invention may be mass units known in the chemical industry, such as μg, mg, g, and kg.

[0028] In addition, unless the context clearly requires otherwise, expressions in the singular form of a word should be understood to include the plural form of the word. The terms "include" or "have" are intended to specify the presence of a feature, number, step, operation, element, part, or combination thereof, but are not used to exclude the presence or possibility of adding one or more other features, numbers, steps, operations, elements, parts, or combinations thereof.

[0029] An embodiment of the present invention provides an electrolyte additive, which includes additive a. The general structural formula of additive a is as follows:

[0030]

[0031] Wherein, R1, R2, R3, R4, R5, R6 and R7 are independently selected from one of a hydrogen atom, a halogen atom, an alkane group having 1 to 10 carbon atoms, an unsaturated hydrocarbon group having 2 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkanoyl group having 2 to 10 carbon atoms and a phenyl group, and the H in the alkane group, the unsaturated hydrocarbon group, the alkoxy group and the alkanoyl group may be partially or completely substituted by one or more of a halogen atom, a cyano group, a carboxyl group and a sulfonic acid group.

[0032] The electrolyte additive of the present invention comprises additive a, wherein NC and C≡N in additive a participate in forming a N-rich inorganic interface film, which can effectively isolate the electrode material from side reactions with the electrolyte, inhibit the dissolution of positive electrode metal ions under high voltage, and at the same time improve the high-voltage and high-temperature resistance of the electrolyte, thereby significantly improving the battery cycle performance and high-temperature storage performance. The phenoxy group in additive a can complex with the positive electrode, inhibit metal dissolution, improve the high-voltage resistance of the electrolyte, and thus improve the high-voltage cycle performance and high-temperature storage performance. The dioxy group enables additive a to provide multiple coordination sites with lithium ions, thereby reducing the viscosity of the electrolyte, thereby promoting the migration rate of lithium ions in the electrolyte, improving the ionic conductivity of the electrolyte, and thus improving the charge and discharge efficiency and cycle performance of the battery.

[0033] Preferably, the additive a comprises one or more substances of Formula 1 to Formula 5, and the structural formulas of Formula 1 to Formula 5 are as follows:

[0034]

[0035]

[0036] The substances of Formulas 1 to 5 all contain dimethoxy groups. By introducing dimethoxy groups, additive a can provide multiple coordination sites for lithium ions, thereby reducing the viscosity of the electrolyte, thereby promoting the migration rate of lithium ions in the electrolyte, improving the ionic conductivity of the electrolyte, and thus improving the battery's charge and discharge efficiency and cycle performance. Due to the improved ionic conductivity, the battery can operate at higher current densities without significant overheating or efficiency degradation, which helps to improve the battery's energy density and power density, making the battery more efficient, improving battery safety, and extending its life. Additive a in Formula 2 contains hydroxyl groups, which can form strong interactions with adsorbates through hydrogen bonds, thereby enhancing the adsorption effect of additive a in Formula 2 and improving the electrolyte infiltration effect. Additive a in Formula 3 contains multiple phenoxy groups, which can complex with the positive electrode, inhibit metal dissolution, improve the electrolyte's high-voltage resistance, and thus enhance high-voltage cycling performance and high-temperature storage performance. In the additive of Formula 4, the introduction of double C≡N forms a LiN-rich SEI film, inhibiting electrolyte decomposition and improving high-voltage cycling performance and storage performance.

[0037] Among them, the electrolyte additive also includes additive b, and additive b includes at least one of ethylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, 1,3-propane sulfonate, propylene sulfite, vinyl sulfate, 4-methylethylene sulfate, succinic anhydride, adiponitrile and 1,3,6-hexanetrionitrile.

[0038] By compounding the above-mentioned additive b with additive a to prepare an electrolyte composite additive, additive a and additive b act synergistically to form a more uniform, dense and lower-resistance SEI film, so that the additive of the present invention can further improve the cycle performance and high-temperature storage performance of the battery.

[0039] Among them, fluoroethylene carbonate can significantly improve the antioxidant capacity of the electrolyte, making it more stable under high voltage conditions and reducing the decomposition of the electrolyte. Succinic anhydride or adiponitrile can effectively form a protective film covering the surface of the positive electrode, preventing the transition metal ions in the positive electrode material from dissolving into the electrolyte, thereby maintaining the stability of the electrode structure and extending the battery life. 1,3-Propanesulfonic acid lactone, propylene sulfite, etc. help to form a stable SEI (solid electrolyte interface) film, which not only improves the cycle stability of the battery, but also enhances the safety of the battery under high temperature or overcharge conditions. Adiponitrile and 1,3,6-hexanetrinitrile help to lower the freezing point of the electrolyte and increase its fluidity in low temperature environments, thereby improving the working performance of the battery under low temperature conditions.

[0040] Among them, the appropriate proportion of additives a and b together can more effectively form a stable solid electrolyte interface (SEI) film, protecting the electrode surface from the continuous oxidative decomposition of the electrolyte, thereby extending the service life of the battery and improving its cycle stability. By adjusting this ratio, the instability problem of the electrolyte under high-voltage conditions can be effectively solved, so that the high-voltage positive electrode material can fully utilize its capacity advantage. Therefore, setting the mass ratio of additive a to additive b to 1-10:15 helps to optimize the performance of the electrolyte and improve the safety, cycle stability and life of the battery. When the content of additive a is too high or too low, it will affect the cycle performance and high-temperature storage performance of the battery, and will cause the viscosity of the electrolyte to become higher.

[0041] The second object of the present invention is to provide an electrolyte comprising the above-mentioned electrolyte additive, wherein the electrolyte has higher resistance to high voltage and high temperature, and can effectively improve the battery cycle performance and high-temperature storage performance.

[0042] The electrolyte also includes a lithium salt electrolyte and an organic solvent.

[0043] The lithium salt electrolyte and part of the organic solvent are evenly mixed to form a lithium salt solution with a concentration of 1.2 mol / L, and the lithium salt solution accounts for 15% of the total mass of the electrolyte.

[0044] The electrolyte additive includes additive a, which accounts for 1%-10% of the total mass of the electrolyte. In this embodiment, the remaining organic solvent accounts for 75%-84% of the total mass of the electrolyte. The NC and C≡N in additive a form a nitrogen-rich inorganic interface film, which effectively isolates the electrode material from side reactions with the electrolyte, inhibits the dissolution of positive electrode metal ions under high voltage, and enhances the electrolyte's high-voltage and high-temperature resistance, thereby significantly improving the battery's cycling performance and high-temperature storage performance.

[0045] In other embodiments, the electrolyte additive includes additive a and additive b, with additive a accounting for 1%-10% of the total mass of the electrolyte and additive b accounting for 15% of the total mass of the electrolyte. In this embodiment, the lithium salt electrolyte and a portion of the organic solvent are uniformly mixed to form a lithium salt solution with a concentration of 1.2 mol / L, with the lithium salt solution accounting for 15% of the total mass of the electrolyte and the remaining organic solvent accounting for 60%-69% of the total mass of the electrolyte. By compounding additive b with additive a to prepare an electrolyte composite additive, additive a and additive b act synergistically to form a more uniform, dense, and lower-resistance SEI film, allowing the additive of the present invention to further improve the battery's cycling performance and high-temperature storage performance.

[0046] The lithium salt electrolyte includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, and lithium difluorooxalatoborate.

[0047] The above-mentioned types of lithium salts each have different dissociation abilities and can provide sufficient lithium ions in organic solvents, thereby improving the ionic conductivity of the electrolyte. Lithium hexafluorophosphate has higher ionic conductivity and can achieve rapid charging and discharging. Lithium tetrafluoroborate (LiBF4) has good stability at high temperatures, which helps the battery to work normally at higher temperatures. Lithium difluorooxalatoborate (LiBOB) can not only form a stable interface film on the positive electrode surface, reducing the oxidative decomposition of the electrolyte under high pressure conditions, but also inhibit the dissolution of transition metal ions in the positive electrode material, which is beneficial to improving the operating voltage and cycle life of the battery. Lithium perchlorate (LiClO4) can enhance the ionic conductivity of the electrolyte in low temperature environments and improve the low-temperature working performance of the battery.

[0048] In summary, selecting at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, and lithium difluorooxalatoborate as the lithium salt electrolyte can significantly optimize the performance of the electrolyte, improve the energy density, power density, cycle life and safety of the battery, and meet the needs of different application scenarios.

[0049] Among them, the organic solvent includes cyclic organic solvents and chain organic solvents.

[0050] Wherein, the cyclic organic solvent includes at least one of ethylene carbonate, propylene carbonate, and butylene carbonate; and / or,

[0051] The chain organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0052] Cyclic organic solvents have a high dielectric constant, which facilitates the dissociation of lithium salts, thereby increasing the free lithium ion concentration in the electrolyte and improving ionic conductivity. Chain organic solvents, on the other hand, have a low viscosity and promote ion migration. The combination of these two can significantly improve the overall ionic conductivity of the electrolyte. Cyclic organic solvents generally have good thermal and chemical stability, especially resistance to decomposition reactions at high temperatures. Although chain organic solvents have poor thermal stability when used alone, when mixed with cyclic solvents, they effectively balance the overall thermal and chemical stability, maintaining electrolyte stability over a wide temperature range. Cyclic organic solvents, such as ethylene carbonate (EC), can preferentially reduce on the anode surface, forming a strong and uniform SEI film. This film not only effectively prevents further electrolyte decomposition but also allows lithium ions to pass through, reducing irreversible capacity loss and extending battery life. The high viscosity of cyclic organic solvents increases electrolyte viscosity, allowing better adhesion to the electrode surface. The addition of chain organic solvents reduces the overall viscosity, improving the electrolyte's wettability to the separator and electrode materials, and promoting more efficient ion transport. In summary, the preparation of electrolyte by combining cyclic organic solvents and chain organic solvents can significantly improve the comprehensive performance of the electrolyte.

[0053] A third object of the present invention is to provide a battery comprising the above-mentioned electrolyte, a positive electrode sheet, a negative electrode sheet and a separator.

[0054] Specifically, the battery is a secondary battery, which may be a lithium ion battery, a sodium ion battery, a calcium ion battery, a magnesium ion battery, or a potassium ion battery. Preferably, the secondary battery is a lithium ion battery, which has good cycle performance and cycle storage performance.

[0055] A lithium ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator, a shell and the above-mentioned electrolyte. The separator is used to separate the positive electrode sheet and the negative electrode sheet, and the shell is used to package and install the positive electrode sheet, the negative electrode sheet, the separator and the above-mentioned electrolyte.

[0056] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material. The positive electrode active material may include but is not limited to a chemical formula of Li a Ni x Co y M z O 2-b Nb A combination of one or more of the compounds shown, wherein 0.95≤a≤1.2, x>0, y≥0, z≥0, and x+y+z=1, 0≤b≤1, M is selected from a combination of one or more of Mn and Al, N is selected from a combination of one or more of F, P, and S, and the positive electrode active material may also be, but is not limited to, LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, Li2NiMn3O8, LiNi 0.5 Mn 1.5 A combination of one or more of O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, TiS2, etc.

[0057] The positive electrode active material may also be modified. Methods for modifying the positive electrode active material are known to those skilled in the art. For example, the positive electrode active material may be modified by coating, doping, or the like. The materials used for the modification may include, but are not limited to, a combination of one or more of Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, and W.

[0058] The positive electrode current collector is usually a structure or part that collects current. The positive electrode current collector can be any material in the art that is suitable for use as a positive electrode current collector for lithium-ion batteries. For example, the positive electrode current collector can include but is not limited to metal foil, and more specifically can include but is not limited to aluminum foil.

[0059] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material. The negative electrode active material can be one or more of graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microbeads, silicon-based materials, tin-based materials, lithium titanate or other metals that can form alloys with lithium.

[0060] Among them, graphite can be selected from one or more of artificial graphite, natural graphite and modified graphite; silicon-based materials can be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; tin-based materials can be selected from one or more of elemental tin, tin oxide compounds, and tin alloys.

[0061] The negative electrode current collector is generally a structure or part that collects current. The negative electrode current collector can be any material suitable for use as a negative electrode current collector for lithium-ion batteries in the art. For example, the negative electrode current collector can include but is not limited to metal foil, and more specifically can include but is not limited to copper foil.

[0062] The isolation membrane can be any material suitable for lithium-ion battery isolation membranes in the art, for example, it can be a combination of one or more materials including but not limited to polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester and natural fibers.

[0063] The shell is made of stainless steel or aluminum-plastic film.

[0064] In order to enable those skilled in the art to clearly understand the implementation details and operations of the present invention, and to significantly demonstrate the improved performance of the embodiments of the present invention, the above technical solutions are illustrated below through multiple embodiments.

[0065] Example 1

[0066] Positive electrode preparation:

[0067] 98 parts by weight of 4.55V high-voltage LiCoO2 cathode material, 1 part of PVDF (polyvinylidene fluoride) binder, and 1 part of CNT conductive agent were dispersed in 40 parts of NMP (N-methylpyrrolidone) organic solvent. The mixture was stirred in a vacuum mixer until stable and uniform, and then evenly coated on 10μm thick aluminum foil. The aluminum foil was dried at room temperature and then transferred to a 120°C forced air oven for 1 hour. The positive electrode sheet was then cold pressed and die-cut.

[0068] Negative electrode preparation:

[0069] 97 parts of commercial graphite, 2 parts of PVDF (a binder), and 1 part of CNT (a conductive agent) were mixed by weight and dispersed in 120 parts of deionized water. The mixture was stirred in a vacuum mixer until stable and uniform, and then evenly coated onto 8μm-thick copper foil. The aluminum foil was air-dried at room temperature and then transferred to a 120°C forced air oven for drying for 1 hour. The negative electrode sheet was then cold-pressed and die-cut.

[0070] Electrolyte preparation:

[0071] 1) In a nitrogen-filled glove box (O<2 ppm, H<3 ppm), an organic solvent was prepared, wherein the organic solvent consisted of EC (ethylene carbonate), PC (propylene carbonate), and PP (propyl propionate) in a weight ratio of 15:15:70;

[0072] 2) Slowly add LiPF6 to the organic solvent to prepare a lithium salt solution with a concentration of 1.2 mol / L;

[0073] 3) mixing a lithium salt solution, an organic solvent, an additive a, and an additive b in parts by weight of 15 parts, 69 parts, 1 part, and 15 parts to prepare an electrolyte, wherein the additive b is composed of 8 parts of FEC (fluoroethylene carbonate), 3 parts of PS (1,3-propane sultone), 2 parts of ADN (adiponitrile), and 2 parts of HTCN (1,3,6-hexanetrionitrile), for a total of 15 parts;

[0074] Additive a is a compound of formula 1, and additive a is commercially available, wherein the structure is shown below:

[0075]

[0076] Lithium-ion battery preparation:

[0077] The positive electrode sheet, separator, and negative electrode sheet are stacked in order and wound to obtain a bare battery cell. The lithium-ion battery is prepared by aluminum-plastic film packaging, re-baking, liquid injection, static standing, formation, fixture shaping, secondary sealing, and capacity testing.

[0078] Example 2

[0079] The difference between Example 2 and Example 1 is that the additive a in Example 2 is a compound of Formula 2, and the additive a is commercially available, and its structural formula is shown below:

[0080]

[0081] The other preparation methods of Example 2 are the same as those of Example 1 and are not described in detail here.

[0082] Example 3

[0083] The difference between Example 3 and Example 1 is that the additive a in Example 3 is a compound of formula 3, and the additive a is commercially available, and its structure is shown below:

[0084]

[0085] The other preparation steps of Example 3 are the same as those of Example 1 and are not described in detail here.

[0086] Example 4

[0087] The difference between Example 4 and Example 1 is that the additive a in Example 4 is a compound of formula 4, and the additive a is commercially available, and its structure is shown below:

[0088]

[0089] The other preparation steps of Example 4 are the same as those of Example 1 and are not described in detail here.

[0090] Example 5

[0091] The difference between Example 5 and Example 1 is that the additive a in Example 5 is a compound of Formula 5, and the additive a is commercially available, and its structure is shown below:

[0092]

[0093] The other preparation steps of Example 5 are the same as those of Example 1 and are not described in detail here.

[0094] Example 6

[0095] The difference between Comparative Example 6 and Example 1 is that the addition amounts of the components in the electrolyte are: lithium salt solution, organic solvent, additive a and additive b are 15 parts, 68 parts, 2 parts and 15 parts by weight.

[0096] The rest is the same as in Example 1 and will not be described in detail here.

[0097] Example 7

[0098] The difference between Example 7 and Example 1 is that the addition amounts of the components in the electrolyte are: lithium salt solution, organic solvent, additive a and additive b are 15 parts, 65 parts, 5 parts and 15 parts by weight.

[0099] The rest is the same as in Example 1 and will not be described in detail here.

[0100] Example 8

[0101] The difference between Example 8 and Example 1 is that the addition amounts of the components in the electrolyte are: lithium salt solution, organic solvent, additive a and additive b are 15 parts, 60 parts, 10 parts and 15 parts by weight.

[0102] The rest is the same as in Example 1 and will not be described in detail here.

[0103] Example 9

[0104] The difference between Example 9 and Example 1 is that the organic solvent of the electrolyte consists of EC (ethylene carbonate), DEC (diethyl carbonate), and BC (butylene carbonate) in a weight ratio of 15:15:70.

[0105] Comparative Example 1

[0106] The difference between Comparative Example 1 and Example 1 is that the addition amounts of the components in the electrolyte are: lithium salt solution, organic solvent, additive a and additive b are 15 parts, 50 parts, 20 parts and 15 parts by weight.

[0107] The rest is the same as in Example 1 and will not be described in detail here.

[0108] Comparative Example 2

[0109] The difference between Comparative Example 2 and Example 1 is that the addition amounts of the components in the electrolyte are: lithium salt solution, organic solvent, additive a and additive b are 15 parts, 69.5 parts, 0.5 parts and 15 parts by weight.

[0110] Comparative Example 3

[0111] The difference between Comparative Example 3 and Example 1 is that the addition amounts of the components in the electrolyte are: lithium salt solution, organic solvent, additive a and additive b are 15 parts, 70 parts, 0 parts and 15 parts by weight.

[0112] The rest is the same as in Example 1 and will not be described in detail here.

[0113] Comparative Example 4

[0114] The difference between Comparative Example 4 and Example 1 is that the addition amounts of the components in the electrolyte are: lithium salt solution, organic solvent, additive a and additive b are 15 parts, 84 parts, 1 part and 0 part by weight.

[0115] The rest is the same as in Example 1 and will not be described in detail here.

[0116] Specifically, the mass fractions of the electrolyte components in Examples 1-8 and Comparative Examples 1-4 are shown in Table 1.

[0117] Table 1:

[0118] Group Lithium salt solution (%) Solvent (%) Additive a(%) Additive b (%) Example 1 15 69 (EC, PC, PP) 1(Formula 1) 15 Example 2 15 69 (EC, PC, PP) 1(Formula 2) 15 Example 3 15 69 (EC, PC, PP) 1(Formula 3) 15 Example 4 15 69 (EC, PC, PP) 1(Formula 4) 15 Example 5 15 69 (EC, PC, PP) 1(Formula 5) 15 Example 6 15 68 (EC, PC, PP) 2(Formula 1) 15 Example 7 15 65 (EC, PC, PP) 5(Formula 1) 15 Example 8 15 60 (EC, PC, PP) 10(Formula 1) 15 Example 9 15 60 (EC, DEC, BC) 1(Formula 1) 15 Comparative Example 1 15 50(EC, PC, PP) 20(Formula 1) 15 Comparative Example 2 15 69.5 (EC, PC, PP) 0.5 (Formula 1) 15 Comparative Example 3 15 70 (EC, PC, PP) 0(Formula 1) 15 Comparative Example 4 15 84 (EC, PC, PP) 1(Formula 1) 0

[0119] Performance Testing

[0120] 1) Normal temperature / high temperature cycle test:

[0121] Place the battery in an oven at a constant temperature of 25℃ / 45℃ for 4 hours, then charge it to 4.55V at a constant current of 0.5C, then charge it at a constant voltage until the current drops to 0.05C, and then discharge it to 3.0V at a constant current of 1C. Repeat this cycle and record the initial capacity of the battery and the discharge capacity at the nth cycle. This test needs to record the discharge capacity at the 800th cycle and the 500th cycle.

[0122] Capacity retention rate = discharge capacity at the nth cycle / initial capacity × 100%.

[0123] 2) 85℃ high temperature storage test:

[0124] The lithium-ion battery was charged to 4.55V at a constant current of 0.5C in a 25°C environment, charged at a constant voltage until the current dropped to 0.02C, and then discharged to 3.0V at a constant current of 0.2C, and the cell thickness, internal resistance, and initial capacity at this time were recorded; then the battery was charged to 4.55V at a constant current of 0.5C, and then placed in an oven at a constant temperature of 85°C for 12 hours, and the cell thickness and internal resistance at this time were measured; the capacity discharged to 3.0V at a current of 0.2C was recorded as the residual capacity; the stored cell was charged to 4.55V at a constant current of 0.5C, charged at a constant voltage until the current dropped to 0.02C, and then discharged to 3.0V at a constant current of 0.2C, and recorded as the recovery capacity.

[0125] Capacity retention rate = remaining capacity / initial capacity × 100%;

[0126] Capacity recovery rate = recovery capacity / initial capacity × 100%;

[0127] Thickness expansion rate = (cell thickness after storage - cell thickness before storage) / cell thickness before storage × 100%.

[0128] 3) Electrolyte viscosity test:

[0129] Place the electrolyte in a constant temperature bath (e.g., 25±0.1°C), select a suitable spindle based on the estimated viscosity, calibrate with a standard solution, record the torque value after stabilization, and calculate the dynamic viscosity (unit: mPa·s).

[0130] The cycle capacity retention and 85°C storage performance of the batteries prepared in Examples 1-9 and Comparative Examples 1-4 were tested according to the above-mentioned normal temperature / high temperature cycle test method and 85°C high temperature storage test method. The viscosity of the electrolytes prepared in Examples 1-9 and Comparative Examples 1-3 was tested according to the above-mentioned electrolyte viscosity test method. The test results of each group are recorded in Table 2. Table 2:

[0131]

[0132] It can be seen from the experimental data results in Table 2 that the electrolyte additive of the present invention can significantly improve the cycle performance and high-temperature storage performance of the battery. Specifically, from the comparison of the test results of Examples 1 to 5, it can be seen that the use of additive a of Formula 1 can better improve the cycle performance of the battery, improve the battery life and the high-temperature storage stability of the battery; and the use of additive a of Formula 2, compared with Formula 1, Formula 2 contains a hydroxyl group, so that the cycle capacity retention rate and high-temperature storage performance of the battery of Example 2 are worse than those of Example 1; Example 3 is a battery prepared by using additive a of Formula 3. Compared with Formula 1, Formula 3 has one less methoxy group and one more phenoxy group, so that the cycle capacity retention rate and high-temperature storage performance of the battery of Example 3 at different temperatures are worse than those of Example 1. The cycle capacity retention rate of Example 3 is similar to that of Example 2, but the high-temperature storage performance is worse. The performance of Example 2 is poor, which shows that the methoxy group substituted by Formula 3 will affect the high-temperature storage performance of additive a; the battery of Example 4 is prepared using additive a of Formula 4, and the battery cycle capacity retention rate and high-temperature storage performance of Example 4 are much lower than those of Example 1. It can be seen that excessive C≡N will affect the cycle capacity retention rate and high-temperature storage performance of the battery; the battery prepared in Example 5 has the worst performance among Examples 1-5, which is because the R6 and R7 groups in Formula 5 are replaced by H, resulting in poor cycle capacity retention rate and high-temperature storage stability of the battery; however, by comparing Examples 1-5 with Comparative Example 3, it can be seen that additive a of the present invention can effectively improve the cycle capacity retention rate and high-temperature storage performance of the battery.

[0133] By comparing the test results of Example 1 and Examples 6-8 with Comparative Examples 1 and 2, it can be seen that the proportion of the electrolyte additive of the present invention is more conducive to improving the cycle performance and high-temperature storage performance of the battery. Compared with Example 1, Example 9 has better battery cycle capacity retention and high-temperature storage performance. This is because Example 9 uses a cyclic organic solvent and a chain organic solvent for compounding, which is more conducive to improving the battery cycle life and high-temperature storage stability. Comparing the test results of Example 1 with Comparative Examples 3 and 4, it can be seen that the compounding of additives a and additive b has a synergistic effect. Adding them to the electrolyte can better improve the cycle performance and high-temperature storage performance of the battery.

[0134] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. An electrolyte additive, characterized in that The additive a is included, and the general structural formula of the additive a is as follows: Wherein, R1, R2, R3, R4, R5, R6 and R7 are independently selected from one of a hydrogen atom, a halogen atom, an alkane group having 1 to 10 carbon atoms, an unsaturated hydrocarbon group having 2 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkanoyl group having 2 to 10 carbon atoms and a phenyl group, and the hydrogen atoms in the alkane group, the unsaturated hydrocarbon group, the alkoxy group and the alkanoyl group may be partially or completely substituted by one or more of a halogen atom, a cyano group, a carboxyl group and a sulfonic acid group.

2. An electrolyte additive according to claim 1, characterized in that: The additive a includes one or more compounds of Formula 1 to Formula 5, and the structural formulas of Formula 1 to Formula 5 are as follows:

3. An electrolyte additive according to claim 1 or 2, characterized in that: The invention also includes an additive b, which includes at least one of ethylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, propylene sulfite, vinyl sulfate, 4-methylethylene sulfate, succinic anhydride, adiponitrile and 1,3,6-hexanetrinitrile.

4. An electrolyte additive according to claim 3, characterized in that: The mass ratio of the additive a to the additive b is 1-10:

15.

5. An electrolyte, characterized in that The electrolyte additive comprises the electrolyte additive according to any one of claims 1 to 4.

6. An electrolyte according to claim 5, characterized in that: Also included are a lithium salt electrolyte and an organic solvent.

7. An electrolyte according to claim 6, characterized in that: The lithium salt electrolyte includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, and lithium difluorooxalatoborate.

8. An electrolyte according to claim 6, characterized in that: The organic solvent includes a cyclic organic solvent and a chain organic solvent.

9. An electrolyte according to claim 8, characterized in that: The cyclic organic solvent includes at least one of ethylene carbonate, propylene carbonate, and butylene carbonate; and / or, The chain organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

10. A battery, characterized in that: The electrolyte comprising the electrolyte according to any one of claims 5 to 9.

Images