A secondary battery and an electric device

Abstract

The application relates to the technical field of secondary batteries, in particular to a secondary battery and a power consumption equipment. A secondary battery comprises electrolyte, the electrolyte comprises an additive; the additive comprises at least one of compounds as shown in formula I; wherein X and Y each independently comprise any one of C1-C20 fluorine-containing and / or silicon-containing hydrocarbon groups; R1, R2, R3 and R4 each independently comprise any one of C1-C20 fluorine-containing and / or silicon-containing hydrocarbon groups. The additive in the electrolyte of the secondary battery of the application is coupled through multiple actions, can further stabilize the positive and negative electrode interface film, comprehensively has the film forming effect, and further improves the cycle performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and in particular to a secondary battery and an electrical device. Background Technology

[0002] Lithium-ion batteries possess advantages such as high operating voltage and long lifespan. With continuous technological advancements, the requirements for energy density, cycle life, and safety of lithium-ion batteries are constantly increasing. During use, factors such as elevated ambient temperature can cause lithium-ion batteries to operate under high temperature and high pressure, leading to increased reactivity of the positive electrode. This can cause reactions between the electrolyte and the positive electrode material, posing a significant challenge to practical applications. Developing suitable electrolyte additives is one of the most economical and effective methods to improve the electrochemical performance of lithium-ion batteries. Therefore, designing a class of film-forming additives to improve the positive electrode interface film is crucial for further enhancing the overall performance of high-power battery systems.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] One objective of this invention is to provide a secondary battery in which the electrolyte can simultaneously form a passivation film with low impedance and stability at both the positive and negative electrode interfaces, thereby protecting the positive and negative electrodes and suppressing transitional side reactions.

[0005] Another object of the present invention is to provide an electrical device comprising the aforementioned secondary battery.

[0006] To achieve the above-mentioned objectives of this invention, the following technical solution is adopted:

[0007] A secondary battery includes an electrolyte, the electrolyte comprising an additive; the additive comprising at least one compound as shown in Formula I.

[0008]

[0009] Wherein, X and Y each independently contain C1 to C20 fluorine-containing and / or silicon-containing hydrocarbon groups, Any one of them;

[0010] R1, R2, R3 and R4 each independently contain any one of the C1 to C20 fluorine-containing and / or silicon-containing hydrocarbon groups.

[0011] Furthermore, the additive comprises at least one of the compounds shown in formulas I1, I2, and I3:

[0012]

[0013] R5 and R6 each independently contain any one of the C1 to C20 fluorine-containing and / or silicon-containing hydrocarbon groups.

[0014] Furthermore, the C1-C20 fluorinated and / or silicon-containing hydrocarbon groups include any one of the C1-C20 fluorinated and / or silicon-containing alkyl groups, the C1-C20 fluorinated and / or silicon-containing alkenyl groups, and the C1-C20 fluorinated and / or silicon-containing alkynyl groups.

[0015] Furthermore, the compound represented by Formula I contains silicon-containing hydrocarbon groups, and the number of silicon-containing hydrocarbon groups is greater than three.

[0016] Furthermore, the additive includes at least one of the compounds shown in the following structural formulas:

[0017]

[0018] Furthermore, the amount of the additive is 0.1% to 5% of the total mass of the electrolyte.

[0019] Furthermore, the secondary battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes a material with the chemical formula Li. a Ni x Co y Mn (1-x-y) M e One of O2, LiCoO2 and LiMn2O4, wherein 0.9 < a ​​< 1.1, 0 ≤ e ≤ 0.1, 0 < x < 1, 0 < y < 1, x + y < 1, and M includes at least one of Al, Zr, Sr, Ti, B, Mg, Sn, W, Y, Ba, Nb, Mo, Ta, Si, La, Er, Nd, Gd, and Ce.

[0020] Furthermore, the secondary battery includes a positive electrode sheet, which comprises a positive current collector and an active material layer disposed on at least one surface of the positive current collector, wherein the thickness of the active material layer of the positive electrode sheet is 20–80 μm.

[0021] Furthermore, the secondary battery includes a negative electrode sheet, which comprises a negative current collector and an active material layer disposed on at least one surface of the negative current collector, wherein the thickness of the active material layer of the negative electrode sheet is 30–90 μm.

[0022] The present invention also provides an electrical device comprising any of the aforementioned secondary batteries.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) The secondary battery of the present invention contains PO bonds in the additive in its electrolyte. The free radicals generated by the breaking of the PO bonds diffuse to the positive electrode surface to form a CEI film, which can inhibit the dissolution of the transition metal at the positive electrode interface. Furthermore, the central atom B of the additive is in an electron-deficient state, which can act as an anion acceptor to increase the degree of dissociation of lithium salt and the migration number of lithium ions, reduce the content of LiF on the electrode surface, and thus reduce the interfacial impedance.

[0025] (2) The electrolyte of the secondary battery of the present invention can further stabilize the positive and negative electrode interface film through the coupling of multiple effects of additives, and improve the cycle performance of the battery by combining its film-forming effect. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. 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. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0027] A secondary battery includes an electrolyte, the electrolyte comprising an additive; the additive comprising at least one compound as shown in Formula I.

[0028]

[0029] Wherein, X and Y each independently contain C1 to C20 fluorine-containing and / or silicon-containing hydrocarbon groups, Any one of them;

[0030] R1, R2, R3 and R4 each independently contain any one of the C1 to C20 fluorine-containing and / or silicon-containing hydrocarbon groups.

[0031] The electrolyte used in the secondary battery of the present invention can simultaneously form a passivation film with low impedance and stability at both the positive and negative electrode interfaces, suppressing the transition side reactions between the positive electrode and the electrolyte, as well as problems such as the dissolution of transition metals and cracking of the positive electrode material; at the same time, it protects the negative electrode, forming a low impedance SEI film, allowing lithium ions to pass through quickly, reducing polarization, and improving the lithium plating window.

[0032] Specifically, the additives in the electrolyte contain PO bonds. The free radicals generated by the breaking of PO bonds diffuse to the positive electrode surface to form a CEI film, which can inhibit the dissolution of transition metals at the positive electrode interface. Furthermore, the central atom B in the additive is in an electron-deficient state, which can act as an anion acceptor to increase the degree of dissociation of lithium salt and the migration number of lithium ions, thereby reducing the content of LiF on the electrode surface and thus reducing the interfacial impedance. The R1, R2, R3 and R4 groups in the additive can react with HF to inhibit its corrosion of transition metals, or they can generate LiF, which can form a highly stable electrode-electrolyte interface structure.

[0033] The electrolyte of the secondary battery of the present invention can further stabilize the positive and negative electrode interface film through the coupling of multiple effects of additives, thereby improving the cycle performance of the battery by combining its film-forming effect.

[0034] In some specific embodiments of the present invention, the additive includes at least one of compounds represented by formulas I1, I2 and I3:

[0035]

[0036] R5 and R6 each independently contain any one of the C1 to C20 fluorine-containing and / or silicon-containing hydrocarbon groups.

[0037] In some specific embodiments of the present invention, the C1-C20 fluorinated and / or silicon-containing hydrocarbon groups include any one of C1-C20 fluorinated and / or silicon-containing alkyl groups, C1-C20 fluorinated and / or silicon-containing alkenyl groups, and C1-C20 fluorinated and / or silicon-containing alkynyl groups.

[0038] In some specific embodiments of the present invention, the compound represented by Formula I contains silicon-containing hydrocarbon groups, and the number of silicon-containing hydrocarbon groups is greater than 3.

[0039] In some specific embodiments of the present invention, the compound represented by Formula I contains a fluorinated hydrocarbon group, and the compound represented by Formula I has more than 6 fluorine atoms.

[0040] In some specific embodiments of the present invention, the compound represented by Formula I contains a fluorinated hydrocarbon group, and the compound represented by Formula I has more than 8 fluorine atoms.

[0041] In some specific embodiments of the present invention, the compound represented by Formula I contains a fluorinated hydrocarbon group, and the number of fluorine atoms in the compound represented by Formula I is less than 22.

[0042] In some specific embodiments of the present invention, the compound represented by Formula I contains a silicon-containing hydrocarbon group and

[0043] In some specific embodiments of the present invention, the compound represented by Formula I contains a fluorinated hydrocarbon group and

[0044] In different embodiments, the number of carbon atoms in the fluorinated and / or silicon-containing alkyl group can be 1, 2, 5, 8, 10, 12, 15, 18, 20, or any combination thereof; the number of carbon atoms in the fluorinated and / or silicon-containing alkenyl group can be 2, 5, 8, 10, 12, 15, 18, 20, or any combination thereof; the number of carbon atoms in the fluorinated and / or silicon-containing alkynyl group can be 2, 5, 8, 10, 12, 15, 18, 20, or any combination thereof.

[0045] The synthetic routes for the compounds shown in formulas I1, I2, and I3 above can be as follows:

[0046]

[0047] Z contains a group that can react with the hydroxyl groups of boric acid and phosphoric acid (such as amino groups, hydroxyl groups, etc.), and R contains any one of R1 to R6.

[0048] The compounds shown in formulas I1, I2 and I3 above can be prepared by the following methods:

[0049] (1) In a solvent containing phosphoric acid and a dehydrating agent, boric acid is slowly added, and then the mixture is heated and refluxed until no water is generated in the water separator. The intermediate product is obtained by vacuum distillation.

[0050] (2) The intermediate product is heated and reacted with one or more compounds containing R1 to R6 in a solvent. After the reaction is completed, the solvent is removed to obtain a crude product. The crude product is then separated and purified to obtain compound I1. Among them, the compounds containing one or more of R1 to R6 may include hexamethyldisilazane or 2,2,2-trifluoroethanol.

[0051] In preparing compound I1, in step (1), the molar ratio of boric acid to phosphoric acid, calculated as H3BO3 and H3PO4, is (0.95~1):1; in step (2), the molar ratio of any one or more compounds containing R1 to R6 to boric acid in step (1) is (2~2.05):1 or (4.1~4.3):1.

[0052] In preparing compound I2, in step (1), the molar ratio of boric acid to phosphoric acid, calculated as H3BO3 and H3PO4, is (1.9-2):1; in step (2), the molar ratio of any one or more compounds containing R1 to R6 to boric acid in step (1) is (3-3.08):1 or (5.1-5.3):1.

[0053] In preparing compound I3, in step (1), the molar ratio of boric acid to phosphoric acid, calculated as H3BO3 and H3PO4, is (2.85–3):1; in step (2), the molar ratio of any one or more compounds containing R1–R6 to boric acid in step (1) is (3–3.08):1 or (6.1–6.3):1.

[0054] In preparing compounds I1, I2, and I3, the solvents used in steps (1) and (2) may include toluene. In step (1), when boric acid is added, the system temperature can be 25–35°C. In step (1), the dehydrating agent may include sulfuric acid. In step (2), the heating temperature can be 95–105°C, and the reaction time can be adjusted according to the degree of reaction monitored by TLC, such as 3–6 hours. In actual operation, the products can be purified by column chromatography. The eluent used in column chromatography can be adjusted according to the actual situation, such as a mixture of petroleum ether and ethyl acetate, with a ratio of PE:EA = (1–4):1.

[0055] In some specific embodiments of the present invention, the additive includes at least one of the compounds represented by the following structural formulas:

[0056]

[0057] In some specific embodiments of the present invention, the electrolyte includes at least one of A1, B1 and C1, and at least one of A2, B2 and C2.

[0058] In some specific embodiments of the present invention, the total amount of A1, B1 and C1 in the electrolyte is in a mass ratio of 1:(0.3 to 15) to the total amount of A2, B2 and C2.

[0059] In different embodiments, the mass ratio of the total amount of A1, B1, and C1 to the total amount of A2, B2, and C2 in the electrolyte can be 1:0.3, 1:0.5, 1:0.8, 1:1, 1:2, 1:5, 1:8, 1:10, 1:12, 1:15, or any combination thereof.

[0060] The silane ethers in additives A1, B1, and C1 can react with HF to inhibit its corrosion of transition metals; the CF in additives A2, B2, and C2 can generate LiF, forming a highly stable electrode-electrolyte interface structure. Through cross-linking coupling, the positive and negative electrode interface films are further stabilized, and the combined film-forming effect improves the cycle performance of the battery.

[0061] In some specific embodiments of the present invention, the amount of the additive is 0.1% to 5% of the total mass of the electrolyte.

[0062] In different embodiments, the amount of the additive may be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or any combination thereof of the total mass of the electrolyte.

[0063] By using additives within the above dosage range, it is beneficial to form a passivation film of suitable thickness on the positive and negative electrode surfaces. The mechanical strength of the formed passivation film is sufficient to withstand the stress generated by the volume expansion of the positive and negative electrodes during cycling, and it is beneficial to promote the conduction of lithium ions while reducing the impedance of the battery.

[0064] In some specific embodiments of the present invention, the secondary battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes a material with the chemical formula Li. a Ni x Co y Mn (1-x-y) M e One of O2, LiCoO2 and LiMn2O4, wherein 0.9 < a ​​< 1.1, 0 ≤ e ≤ 0.1, 0 < x < 1, 0 < y < 1, x + y < 1, and M includes at least one of Al, Zr, Sr, Ti, B, Mg, Sn, W, Y, Ba, Nb, Mo, Ta, Si, La, Er, Nd, Gd, and Ce.

[0065] In some specific embodiments of the present invention, the secondary battery includes a positive electrode sheet, which comprises a positive current collector and an active material layer disposed on at least one surface of the positive current collector. The thickness of the active material layer of the positive electrode sheet is 20–80 μm. The positive current collector may have a single-sided active material layer region and a double-sided active material layer region. The thickness of the active material layer of the positive electrode sheet of the present invention is the thickness of the single-sided active material layer.

[0066] In different embodiments, the thickness of the active material layer of the positive electrode can be 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm or any combination thereof.

[0067] In some specific embodiments of the present invention, the secondary battery includes a negative electrode sheet, which comprises a negative current collector and an active material layer disposed on at least one surface of the negative current collector. The thickness of the active material layer of the negative electrode sheet is 30–90 μm. The negative current collector may have a single-sided active material layer region and a double-sided active material layer region. The thickness of the active material layer of the negative electrode sheet of the present invention is the thickness of the single-sided active material layer.

[0068] In different embodiments, the thickness of the active material layer of the negative electrode can be 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or any combination thereof.

[0069] In some specific embodiments of the present invention, the electrolyte further includes an organic solvent and a lithium salt.

[0070] In some specific embodiments of the present invention, the organic solvent includes one or more selected from ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate (BC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), diphenyl carbonate (DPhC), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), γ-butyrolactone (γ-GBL), acetonitrile (AN), and sulfolane (TMS). For example, the organic solvent includes ethylene carbonate (EC) and ethyl methyl carbonate (EMC).

[0071] In some specific embodiments of the present invention, the lithium salt includes lithium hexafluorophosphate (LiPF6) and / or a second lithium salt, wherein the second lithium salt includes at least one of lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiBOB), lithium difluorooxalato)borate (LiDFOB), lithium difluorodioxalato)phosphate (LiDFOP), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0072] In some specific embodiments of the present invention, the mass of the lithium salt is 10% to 15% of the total mass of the electrolyte.

[0073] In different embodiments, the mass of the lithium salt may be 10%, 11%, 12%, 13%, 14%, 15% of the total mass of the electrolyte, or any combination thereof.

[0074] Use an appropriate lithium salt concentration to ensure the conductivity and viscosity of the electrolyte.

[0075] The present invention also provides an electrical device comprising any of the aforementioned secondary batteries.

[0076] The present invention will now be described in detail with reference to specific embodiments.

[0077] The synthetic routes and specific steps of compounds A1, B1, C1, A2, B2, and C2 used in the following examples are as follows:

[0078]

[0079] The specific preparation method of compound A1 may include: adding 0.98 g of phosphoric acid, 0.01 g of concentrated sulfuric acid, and 100 mL of toluene to a three-necked flask equipped with a magnetic stirrer and a water separator, starting stirring, and slowly adding 0.62 g of boric acid dropwise at 30 °C. After the addition is complete, the temperature is raised to 120 °C and refluxed until no water is generated in the water separator. The intermediate II1 is obtained by vacuum distillation. 3.2 g of hexamethyldisilazane and 100 mL of toluene are added to the above intermediate II1, and the mixture is heated to 100 °C and reacted for 5 h. The solvent is removed by vacuum distillation, and the crude product is subjected to column chromatography (eluent is petroleum ether and ethyl acetate in a volume ratio of 3:1) to obtain product A1 (2.24 g, yield 52%). 1 HNMR(DMSO,400MHZ)δ(ppm):0.21(s,36H). 13 C NMR (CDCl3, 100MHZ) δ (ppm): 4.8, 4.5.

[0080]

[0081] The specific preparation method of compound B1 may include: adding 1.96 g of phosphoric acid, 0.01 g of concentrated sulfuric acid, and 100 mL of toluene to a three-necked flask equipped with a magnetic stirrer and a water separator, starting stirring, and slowly adding 0.62 g of boric acid dropwise at 30 °C. After the addition is complete, the temperature is raised to 120 °C and refluxed until no water is generated in the water separator. The intermediate II2 is obtained by vacuum distillation. 4.8 g of hexamethyldisilazane and 100 mL of toluene are added to the above intermediate II2, and the mixture is heated to 100 °C and reacted for 5 h. The solvent is removed by vacuum distillation, and the crude product is subjected to column chromatography (eluent is petroleum ether and ethyl acetate in a volume ratio of 2.5:1) to obtain product B1 (2.62 g, yield 45%). 1 H NMR (DMSO, 400MHZ) δ (ppm): 0.21 (s, 45H). 13 C NMR (CDCl3, 100MHZ) δ (ppm): 4.8, 4.2.

[0082]

[0083] The specific preparation method of compound C1 may include: adding 2.94 g of phosphoric acid, 0.01 g of concentrated sulfuric acid, and 100 mL of toluene to a three-necked flask equipped with a magnetic stirrer and a water separator, starting stirring, and slowly adding 0.62 g of boric acid dropwise at 30 °C. After the addition is complete, the temperature is raised to 120 °C and refluxed until no water is generated in the water separator. The intermediate II3 is obtained by vacuum distillation. 4.8 g of hexamethyldisilazane and 100 mL of toluene are added to the above intermediate II3, and the mixture is heated to 100 °C and reacted for 5 h. The solvent is removed by vacuum distillation, and the crude product is subjected to column chromatography (eluent is petroleum ether and ethyl acetate in a volume ratio of 3.5:1) to obtain product C1 (3 g, yield 41%). 1 HNMR(DMSO,400MHZ)δ(ppm):0.21(s,54H). 13 C NMR (CDCl3, 100MHZ) δ (ppm): 4.8.

[0084]

[0085] The specific preparation method of compound A2 may include: adding 0.98 g of phosphoric acid, 0.01 g of concentrated sulfuric acid, and 100 mL of toluene to a three-necked flask equipped with a magnetic stirrer and a water separator, starting stirring, and slowly adding 0.62 g of boric acid dropwise at 30 °C. After the addition is complete, the temperature is raised to 120 °C and refluxed until no water is generated in the water separator. The intermediate II1 is obtained by vacuum distillation. 4 g of 2,2,2-trifluoroethanol and 100 mL of toluene are added to the above intermediate II1, and the mixture is heated to 100 °C and reacted for 5 h. The solvent is removed by vacuum distillation, and the crude product is subjected to column chromatography (eluent is petroleum ether and ethyl acetate in a volume ratio of 1:1) to obtain product A2 (2.96 g, yield 63%). 1 HNMR(DMSO,400MHZ)δ(ppm):4.55(m,4H),4.38(m,4H). 13 C NMR (CDCl3, 100MHZ) δ (ppm): 125.5, 122.4, 67.0, 61.2.

[0086]

[0087] The specific preparation method of compound B2 may include: adding 1.96 g of phosphoric acid, 0.01 g of concentrated sulfuric acid, and 100 mL of toluene to a three-necked flask equipped with a magnetic stirrer and a water separator, starting stirring, and slowly adding 0.62 g of boric acid dropwise at 30 °C. After the addition is complete, the temperature is raised to 120 °C and refluxed until no water is generated in the water separator. The intermediate II2 is obtained by vacuum distillation. 5 g of 2,2,2-trifluoroethanol and 100 mL of toluene are added to the above intermediate II2, and the mixture is heated to 100 °C and reacted for 5 h. The solvent is removed by vacuum distillation, and the crude product is subjected to column chromatography (eluent is petroleum ether and ethyl acetate in a volume ratio of 1.5:1) to obtain product B2 (3.67 g, yield 58%). 1 HNMR(DMSO,400MHZ)δ(ppm):4.55(m,8H),4.38(m,2H). 13 C NMR (CDCl3, 100MHZ) δ (ppm): 125.2, 122.4, 66.5, 61.2.

[0088]

[0089] The specific preparation method of compound C2 may include: adding 2.94 g of phosphoric acid, 0.01 g of concentrated sulfuric acid, and 100 mL of toluene to a three-necked flask equipped with a magnetic stirrer and a water separator, starting stirring, and slowly adding 0.6 g of boric acid dropwise at 30 °C. After the addition is complete, the temperature is raised to 120 °C and refluxed until no water is generated in the water separator. The intermediate II3 is obtained by vacuum distillation. 6 g of 2,2,2-trifluoroethanol and 100 mL of toluene are added to the above intermediate II3, and the mixture is heated to 100 °C and reacted for 5 h. The solvent is removed by vacuum distillation, and the crude product is subjected to column chromatography (eluent is petroleum ether and ethyl acetate in a volume ratio of 2:1) to obtain product C2 (3.1 g, yield 39%). 1 H NMR (DMSO, 400MHZ) δ (ppm): 4.55 (m, 12H). 13 C NMR (CDCl3, 100MHZ) δ (ppm): 122.4, 61.2.

[0090] The examples and comparative examples each provide a lithium-ion battery containing an electrolyte, the composition of which is shown in Table 1.

[0091] The preparation method of lithium-ion batteries may include the following steps:

[0092] (1) Preparation of the positive electrode: The positive electrode active material Li(Ni) is prepared. 0.8 Mn 0.1 Co 0.1O2 (NMC811), conductive agent acetylene black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of NCM811:Super P:PVDF = 94:3:3, and then evenly dispersed in 1-methyl-2-pyrrolidone (NMP) to form a uniform black slurry. The mixed black slurry is coated on both sides of aluminum foil, and after baking, rolling, and cutting, the positive electrode sheet is obtained.

[0093] (2) Preparation of negative electrode sheet: The negative electrode active material graphite, conductive agent acetylene black (Super P) and binder SBR are mixed evenly in a mass ratio of graphite:Super P:SBR = 94:3:3, and then evenly dispersed in deionized water to form a uniform black slurry. The mixed black slurry is coated on both sides of copper foil, and then baked, rolled, and cut into sheets to obtain the negative electrode sheet.

[0094] (3) Fabrication of lithium-ion batteries: The prepared positive electrode, separator and negative electrode are stacked in sequence, with the separator in the middle of the positive and negative electrode. After winding, hot pressing and shaping, the tabs are welded to obtain the bare battery. The bare battery is placed in the outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. The electrolyte is injected into the dried battery, and the battery is allowed to stand, form, and be divided into capacities to complete the preparation of the lithium-ion battery.

[0095] The preparation method of the electrolyte includes the following steps:

[0096] At room temperature, in an argon-filled glove box (H2O < 1 ppm, O2 < 1 ppm), lithium salt and additives are added to an organic solvent (EC:EMC mass ratio of 3:7). The mixture is stirred continuously and cooled with dry ice to ensure that the electrolyte temperature rise does not exceed 2°C. The mixture is then stirred until homogeneous to obtain the electrolyte.

[0097] Electrochemical performance testing items include:

[0098] (1) Room temperature DCR test: At 25±2℃, the lithium-ion batteries obtained in the examples and comparative examples were charged to 4.4V at 1C, then discharged at 1C capacity for 30 minutes. After adjusting to 50% SOC, they were pulsed at 10C constant current for 10 seconds. The SOC was then adjusted to 50% SOC again using the above method, and then charged for 10 seconds. The DCR was calculated as (voltage before pulse discharge – voltage after pulse discharge) / discharge current × 100%. After storage at 60℃ for 30 days, the DCR was tested again when the battery was completely cooled to 25±2℃. The internal resistance change rate was calculated as (DCR after 30 days – DCR before 30 days) / DCR before 30 days × 100%.

[0099] (2) Room temperature cycle performance test: At 25±2℃, the lithium-ion batteries obtained in the examples and comparative examples were subjected to charge-discharge cycle tests at a charge-discharge rate of 1C / 1C within the range of 2.8V to 4.4V, and the discharge specific capacity of the battery in the first cycle and the discharge specific capacity after 500 cycles were recorded. The capacity retention rate after 500 cycles = discharge specific capacity after 500 cycles / discharge specific capacity in the first cycle × 100%.

[0100] (3) High-temperature storage performance: The lithium-ion batteries obtained in the examples and comparative examples were placed at 60±2℃ and charged and discharged at a rate of 1C / 1C within the range of 2.8V to 4.4V. The discharge specific capacity of the batteries in the first week was recorded. After that, the batteries were stored at 60±2℃ for 7 days, and the charge and discharge test was carried out again, and the discharge specific capacity was recorded. High-temperature storage capacity retention rate = discharge specific capacity after 7 days / discharge specific capacity in the first week × 100%.

[0101] (4) High-Temperature Gas Generation Test: The lithium-ion batteries obtained in the examples and comparative examples were charged at a constant current rate of 1C to 4.4V at 25±2℃, and then charged at a constant voltage of 4.4V until the current was below 0.05C, so that they were in a fully charged state at 4.4V. The volume of the fully charged battery before storage was measured and recorded as V0; then the fully charged battery was placed in an oven at 60±2℃. After 7 days, the battery was taken out and its volume after storage was immediately measured and recorded as V1. Volume expansion rate = (V1 – V0) / V0 × 100%.

[0102] Table 1. Electrolyte composition information and its lithium-ion battery performance.

[0103]

[0104]

[0105]

[0106] Note: The dosage of lithium salt and each additive refers to their respective percentage content in the total mass of the electrolyte.

[0107] Comparing the experimental results of Examples 1-9 and Comparative Example 1, it can be seen that adding the compound shown in Formula I can reduce the initial internal resistance of the battery and the increase in internal resistance during storage, and improve the capacity retention rate during high-temperature cycling and high-temperature storage. It can also be seen that as the content of the compound shown in Formula I increases, the initial internal resistance increases accordingly. This is because the generated interfacial film becomes increasingly dense, increasing the interfacial film impedance, which is beneficial in suppressing the increasing trend of battery internal resistance and volume expansion rate during high-temperature storage, and reducing irreversible losses during storage. However, excessive additive usage leads to a significant increase in initial impedance, which is detrimental to the battery's kinetic performance. Considering all performance factors, the preferred content of the compound shown in Formula I is 0.5% to 1.5%, and the optimal content can be determined according to specific requirements.

[0108] The experimental results from Examples 3, 5-9, and Comparative Examples 2-3 show that, compared to commercial additives TMSB and TMSP, the electrolyte of this invention containing the compound shown in Formula I results in better battery performance. This is because the free radicals generated by the breaking of the PO bond diffuse to the positive electrode surface to form a CEI film, which can inhibit the dissolution of Mn at the positive electrode interface; and the central atom B is in an electron-deficient state, which can act as an anion acceptor to increase the degree of dissociation of lithium salt and the transference number of lithium ions, thereby reducing interfacial impedance.

[0109] In summary, electrolytes containing the additives described in this application can better improve the high-temperature storage gas generation and high-temperature cycling performance of batteries. Specific usage can be adjusted according to the application scenario.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A secondary battery comprising an electrolyte, the electrolyte comprising an additive; the additive comprising at least one compound as shown in Formula I; ； in, X and Y each independently contain C1 to C20 fluorine-containing and / or silicon-containing hydrocarbon groups. Any one of them; R1, R2, R3 and R4 each independently contain any one of the fluorine-containing and / or silicon-containing hydrocarbon groups from C1 to C20; The amount of the additive is 0.1% to 5% of the total mass of the electrolyte.

2. The secondary battery according to claim 1, characterized in that, The additive includes at least one of the compounds shown in formulas I1, I2, and I3: 、 、 ； R5 and R6 each independently contain any one of the C1 to C20 fluorine-containing and / or silicon-containing hydrocarbon groups.

3. The secondary battery according to claim 1, characterized in that, The C1-C20 fluorinated and / or silicon-containing hydrocarbon groups include any one of the C1-C20 fluorinated and / or silicon-containing alkyl groups, C1-C20 fluorinated and / or silicon-containing alkenyl groups, and C1-C20 fluorinated and / or silicon-containing alkynyl groups.

4. The secondary battery according to claim 1, characterized in that, The compound represented by Formula I contains silicon-containing hydrocarbon groups, and the number of silicon-containing hydrocarbon groups is greater than 3.

5. The secondary battery according to claim 1, characterized in that, The additive includes at least one of the compounds shown in the following structural formulas: 、 、 、 、 、 。 6. The secondary battery according to claim 1, characterized in that, The secondary battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes materials selected from those with the chemical formula Li. a Ni x Co y Mn （1-x-y） M e One of O2, LiCoO2 and LiMn2O4, wherein 0.9 < a ​​< 1.1, 0 ≤ e ≤ 0.1, 0 < x < 1, 0 < y < 1, x + y < 1, and M includes at least one of Al, Zr, Sr, Ti, B, Mg, Sn, W, Y, Ba, Nb, Mo, Ta, Si, La, Er, Nd, Gd, and Ce.

7. The secondary battery according to claim 1, characterized in that, The secondary battery includes a positive electrode sheet, which comprises a positive current collector and an active material layer disposed on at least one surface of the positive current collector, wherein the thickness of the active material layer of the positive electrode sheet is 20–80 μm.

8. The secondary battery according to claim 1, characterized in that, The secondary battery includes a negative electrode sheet, which comprises a negative current collector and an active material layer disposed on at least one surface of the negative current collector, wherein the thickness of the active material layer of the negative electrode sheet is 30–90 μm.

9. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1 to 8.

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