Electrolyte, secondary battery, and electric device

Abstract

The application relates to the technical field of batteries, in particular to an electrolyte, a secondary battery and an electric device. The electrolyte comprises a compound shown as formula I: X1 and X2 are each independently selected from alkylene, alkenylene or alkynylene with a carbon number of 1-20; R1 and R2 are each independently selected from alkyl or halogenated alkyl; and Cy is a five-membered or six-membered ring group formed by surrounding connection in formula I. The compound shown as formula I used in the electrolyte has a lower LUMO, can be preferentially reduced by a solvent, and the electron-donating ability of the amine in the compound shown as formula I is strong, which is beneficial to the combination with Li + The solvent competes to participate in the formation of a solvated structure, solvent decomposition is inhibited, a better SEI film is formed on the surface of a graphite-based negative electrode, and the cycle performance of the battery is improved.

Description

Technical Field

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

[0002] With the rapid development of electric vehicles, people's requirements for the energy density, cycle life, and safety of lithium-ion batteries are constantly increasing. However, in traditional electrolyte systems, ternary cathode materials undergo drastic structural changes and interfacial side reactions under high pressure and high temperature, posing significant challenges to practical applications, especially the cycle life and safety of high-nickel ternary materials. Furthermore, the SEI film formed on the graphite anode plays a crucial role in battery performance; excessively high impedance in the formed SEI film can intensify battery polarization, easily leading to lithium plating on the anode surface and significantly reducing the battery's reversible capacity.

[0003] Developing suitable electrolyte additives is one of the most economical and effective methods to improve the electrochemical performance of lithium-ion batteries.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] One object of the present invention is to provide an electrolyte in which the compound represented by Formula I can preferentially undergo solvent reduction to form a better SEI film; and is advantageous for reaction with Li + It combines with the solvent to compete for the formation of solvation structures and inhibit solvent decomposition.

[0006] Another object of the present invention is to provide a secondary battery containing the above-mentioned electrolyte.

[0007] Another object of the present invention is to provide an electrical device including the above-mentioned secondary battery.

[0008] An electrolyte comprising a compound as shown in Formula I:

[0009] ;

[0010] X1 and X2 are each independently selected from alkylene, alkenylene, or ynylene groups having 1 to 20 carbon atoms;

[0011] R1 and R2 are each independently selected from alkyl or haloalkyl groups;

[0012] Cy is connected to Equation I. Five- or six-element ring bases formed by enclosure.

[0013] Furthermore, the five- or six-membered cyclic group includes any one of 2,4,5-imidazolinetrione, substituted or unsubstituted 2-imidazolidinone, and substituted or unsubstituted 1,3,5-triazine-2,4,6-trione.

[0014] Furthermore, at least one of R1 and R2 is halogenated.

[0015] Furthermore, the compound represented by Formula I includes at least one of structural formulas I1, I2, and I3:

[0016] , , .

[0017] Furthermore, the haloalkyl group includes a fluoroalkyl group; in the fluoroalkyl group, the number of fluorine atoms is ≥1.

[0018] Furthermore, the amount of the compound represented by Formula I is 0.1% to 5% of the total mass of the electrolyte.

[0019] The present invention also provides a secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte as described in any one of the above.

[0020] Furthermore, the negative electrode sheet includes a negative electrode active material, which includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon, nano carbon, and silicon-carbon composite.

[0021] The positive electrode includes a positive electrode active material, the chemical formula of which includes LiFePO4 and Li a Ni x Co y Mn （1-x-y） At least one of O2, wherein 0.9≤a≤1.1, 0<x<1, 0<y<1, and x+y<1.

[0022] Furthermore, the charging cutoff voltage of the secondary battery is 4.2 to 4.5V.

[0023] Furthermore, the thickness of the active material layer of the positive electrode is 20–90 μm.

[0024] The present invention also provides an electrical device comprising any one of the secondary batteries described above.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) The compound represented by Formula I used in the electrolyte of the present invention has a low LUMO and can preferentially undergo solvent reduction; and the amine in the compound represented by Formula I has a strong electron-donating ability, which is beneficial for reacting with Li + In combination, solvent competition participates in the formation of solvation structures, inhibiting solvent decomposition;

[0027] (2) The CF bond in the molecule of the compound represented by Formula I used in the electrolyte of the present invention helps to form LiF, form an SEI film on the negative electrode, improve the performance of the SEI film on the graphite negative electrode surface, and the fluorine-rich chain helps to reduce molecular interactions and prevent the electrolyte viscosity from increasing.

[0028] (3) The secondary battery using the electrolyte of the present invention has good cycle performance. Detailed Implementation

[0029] 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.

[0030] An electrolyte comprising a compound as shown in Formula I:

[0031] ;

[0032] X1 and X2 are each independently selected from alkylene, alkenylene, or ynylene groups having 1 to 20 carbon atoms;

[0033] R1 and R2 are each independently selected from alkyl or haloalkyl groups;

[0034] Cy is connected to Equation I. Five- or six-element ring bases formed by enclosure.

[0035] The compound represented by Formula I used in the electrolyte of this invention has a low LUMO, enabling preferential solvent reduction; furthermore, the amine in the compound represented by Formula I has a strong electron-donating ability, which is beneficial for its reaction with Li. + In combination, solvent competition participates in the formation of solvation structures, inhibiting solvent decomposition; a better SEI film can be formed on the surface of graphite anode materials, thereby improving the problems existing in graphite anodes.

[0036] In some specific embodiments of the present invention, the five- or six-membered cyclic group includes any one of 2,4,5-imidazolinetrione, substituted or unsubstituted 2-imidazolidinone, and substituted or unsubstituted 1,3,5-triazine-2,4,6-trione.

[0037] The structural formulas of 2,4,5-imidazolinone, 2-imidazolidinone, and 1,3,5-triazine-2,4,6-trione are as follows: , , .

[0038] In some specific embodiments of the present invention, the compound represented by Formula I includes compounds such as those of structural formula I. a Ⅰ b or I c At least one of the following:

[0039] R3 and R4 are each independently selected from H, alkyl or substituted alkyl with 1 to 3 carbon atoms;

[0040] ;

[0041] R5 is selected from alkyl or substituted alkyl groups having 1 to 20 carbon atoms.

[0042] In some specific embodiments of the present invention, R5 is X3 is selected from alkylene, alkenylene, or ynylene with 1 to 18 carbon atoms; R6 is selected from alkyl or haloalkyl.

[0043] In different implementations, the number of carbons in X3 can be 1, 2, 5, 8, 10, 12, 15, 18, etc.

[0044] In some specific embodiments of the present invention, at least one of R1 and R2 is halogenated.

[0045] In some specific embodiments of the present invention, R1 and R2 are halogenated.

[0046] In some specific embodiments of the present invention, the number of halogens in R1 and R2 is greater than or equal to 2.

[0047] In some specific embodiments of the present invention, R1, R2 and R6 are each independently selected from alkyl or haloalkyl groups, and have 1 to 3 carbon atoms.

[0048] In some specific embodiments of the present invention, the haloalkyl group includes fluoroalkyl group.

[0049] In some specific embodiments of the present invention, the number of fluorine atoms in the fluoroalkyl group is ≥1.

[0050] The fluoroalkyl group may include one or more fluorine atoms, such as -CF3.

[0051] The CF bonds in the molecules of the compound represented by Formula I used in the electrolyte of this invention help to form LiF, which forms an SEI film on the negative electrode, improves the performance of the SEI film on the graphite negative electrode surface, and the fluorine-rich chain helps to reduce molecular interactions and prevent the electrolyte viscosity from increasing.

[0052] The alkylene groups with 1 to 20 carbon atoms mentioned in this invention refer to straight-chain or branched groups derived from alkanes containing 1 to 20 carbon atoms by removing two hydrogen atoms. Specific examples include, but are not limited to, methylene, ethylene, propylene, butylene, and pentylene.

[0053] The alkenyl group described in this invention refers to a straight-chain or branched group derived from a straight-chain or branched olefin containing a double bond by removing two hydrogen atoms. Specific examples include, but are not limited to, vinylidene, propenyl, butenyl, and pentenyl groups. Wherein, when X1 or X2 is an alkenyl group, the number of carbon atoms is at least 2.

[0054] The ynylene group described in this invention refers to a straight-chain or branched group derived from a straight-chain or branched alkyne containing a triple bond by removing two hydrogen atoms. Specific examples include, but are not limited to, ethynylene, propynylene, butynylene, and pentyynylene. Wherein, when X1 or X2 is an ynylene group, the number of carbon atoms is at least 2.

[0055] The alkyl group referred to in this invention refers to a straight-chain or branched alkyl group derived from an alkane by removing one hydrogen atom. Specific examples include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, 2-methylpropyl, 1-methylpropyl, 1,1-dimethylethyl, n-pentyl, etc.

[0056] The haloalkyl group described in this invention refers to a group derived from an alkyl group by substituting one or more halogen atoms; the halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms.

[0057] The five- or six-membered cyclic group described in this invention refers to a cyclic group containing five or six cyclic atoms.

[0058] In some specific embodiments of the present invention, the compound represented by Formula I includes at least one of structural formulas I1, I2, and I3:

[0059] , , .

[0060] In some specific embodiments of the present invention, the amount of the compound represented by Formula I is 0.1% to 5% of the total mass of the electrolyte.

[0061] In different embodiments, the amount of the compound represented by Formula I may be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% of the total mass of the electrolyte, or any combination thereof.

[0062] In some specific embodiments of the present invention, the electrolyte further includes an organic solvent, which includes ethylene carbonate and methyl ethyl carbonate; based on the total mass of the electrolyte, the content of ethylene carbonate is a%, the content of methyl ethyl carbonate is b%, and a and b satisfy the relationship: 80≤a+b≤89.

[0063] In different embodiments, a and b satisfy the following condition: a+b can be a range of 80, 82, 84, 86, 89, or any two of these. The sum of the contents of ethylene carbonate and methyl ethyl carbonate, within the range specified in this application, is beneficial for controlling the ion mobility in the solvent and improving the electronic conductivity of the compound represented by Formula I and the lithium salt in the solvent.

[0064] In some specific embodiments of the present invention, the organic solvent may further include any one or more of propylene carbonate, butene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, γ-butyrolactone, acetonitrile, and sulfolane.

[0065] In some specific embodiments of the present invention, the electrolyte further includes a lithium salt. Further, the lithium salt includes at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluorooxalatoborate, lithium difluorodioxalatophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

[0066] 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, such as 12% to 13%.

[0067] The present invention also provides a secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte as described in any one of the above.

[0068] In some specific embodiments of the present invention, the negative electrode sheet includes a negative electrode active material, which includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon, nano carbon, and silicon-carbon composite.

[0069] The positive electrode includes a positive electrode active material, the chemical formula of which includes LiFePO4 and Li a Ni x Coy Mn （1-x-y） At least one of O2, wherein 0.9≤a≤1.1, 0<x<1, 0<y<1, and x+y<1.

[0070] In some specific embodiments of the present invention, the charging cutoff voltage of the secondary battery is 4.2 to 4.5V.

[0071] In different embodiments, the charging cut-off voltage of the secondary battery can be a range of 4.2V, 4.3V, 4.4V, 4.5V, or any combination thereof.

[0072] In some specific embodiments of the present invention, the thickness of the active material layer of the positive electrode is 20–90 μm.

[0073] In different embodiments, the thickness of the active material layer of the positive electrode can be within the range of 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or any combination thereof. Controlling the thickness of the positive electrode within the range of this invention facilitates sufficient electrolyte wetting of the positive electrode and reduces the risk of breakage during rolling, thus ensuring the cycle performance of the battery.

[0074] The present invention also provides an electrical device comprising any one of the secondary batteries described above.

[0075] In some specific embodiments of the present invention, compound I a Ⅰ b and I c It can be prepared according to the following reaction route:

[0076]

[0077]

[0078] .

[0079] Furthermore, compounds I1, I2, and I3 can be prepared according to the following reaction route:

[0080]

[0081]

[0082] .

[0083] The reaction times involved in each of the above reaction routes can be adjusted according to the actual degree of reaction, and the specific degree of reaction can be monitored by conventional TLC.

[0084] Specifically, I1 was obtained from 1,3-bis(hydroxymethyl)-2-imidazolinone and (trifluoromethyl)trimethylsilane (TMSCF3) as raw materials, and silver trifluoromethanesulfonate (AgOTF) as catalyst, through a one-step reaction (yield 56%). The specific synthesis steps are as follows:

[0085] Under an argon atmosphere, 1.46 g of 1,3-bis(hydroxymethyl)-2-imidazolinone, 5.15 g of silver trifluoromethanesulfonate (AgOTf), 5.3 g of Selectfluor reagent, 1.75 g of KF, 1.94 g of 2-fluoropyridine, 2.85 g of TMSCF3, and 50 mL of ethyl acetate were added sequentially to a 250 mL round-bottom flask. The mixture was stirred at 50 °C for 12 h. The reaction was monitored by TLC until complete. The mixture was then washed with water, the organic phases were combined, and dried over anhydrous sodium sulfate. The crude product was finally purified by column chromatography (PE:EA = 3:1) to give 1.58 g of product I1 (yield 56%). 1 H NMR (DMSO, 300MHZ) δ (ppm): 5.24 (s, 4H), 3.42 (s, 4H),. 13 CNMR(CDCl3,100MHZ) δ(ppm):159.7, 125.2, 60.8, 38.5

[0086] I2. Using secganic acid and 2-chloroethanol as raw materials and potassium carbonate as a catalyst, a nucleophilic substitution reaction was carried out to obtain secganic acid containing a hydroxyl group; then, using AgOTF as a catalyst, it was reacted with TMSCF3 to obtain the final product (the two-step reaction yield was 45%). The specific synthetic steps are as follows:

[0087] In a 250 mL round-bottom flask, 1.14 g of secganic acid, 100 mL of DMF, and 2.76 g of K₂CO₃ were added sequentially. 0.16 g of 2-chloroethanol was slowly injected using a syringe. After the addition was complete, the reaction was allowed to proceed at room temperature, with TLC monitoring until the reaction was complete. The mixture was then washed with water, and the organic phases were combined and dried over anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA = 0.5:1) to obtain the intermediate product.

[0088] Under an argon atmosphere, the above intermediate, 5.15 g silver trifluoromethanesulfonate (AgOTf), 5.3 g Selectfluor reagent, 1.75 g KF, 1.94 g 2-fluoropyridine, 2.85 g TMSCF3, and 50 mL ethyl acetate were added sequentially to a 250 mL round-bottom flask. The mixture was stirred at 50 °C for 12 h. The reaction was monitored by TLC until complete. The mixture was then washed with water, the organic phases were combined, and dried over anhydrous sodium sulfate. The crude product was finally purified by column chromatography (PE:EA = 3:1) to give 1.52 g of the final product I2 (two-step yield 45%). 1H NMR(DMSO,300MHZ) δ(ppm): 3.67 (t, 4H), 3.35(t, 4H),. 13 CNMR(CDCl3,100MHZ) δ(ppm):158.7, 127.9,48.8, 43.2

[0089] I3 was obtained from 1,3,5-tris(2-hydroxyethyl)cyanuric acid and TMSCF3 as raw materials, with AgOTF as catalyst, through a one-step reaction (yield 65%). The specific synthesis steps are as follows:

[0090] Under an argon atmosphere, 2.61 g of 1,3,5-tris(2-hydroxyethyl)cyanuric acid, 7.72 g of silver trifluoromethanesulfonate (AgOTf), 7.95 g of Selectfluor reagent, 2.62 g of KF, 2.91 g of 2-fluoropyridine, 4.28 g of TMSCF3, and 50 mL of ethyl acetate were added sequentially to a 250 mL round-bottom flask. The mixture was stirred at 50 °C for 12 h. The reaction was monitored by TLC until complete. The mixture was then washed with water, the organic phases were combined, and dried over anhydrous sodium sulfate. The crude product was finally purified by column chromatography (PE:EA = 4:1) to give 3.02 g of the final product I3 (yield 65%). 1 H NMR(DMSO,300MHZ) δ(ppm): 3.67 (t, 6H), 3.35(t, 6H),. 13 CNMR(CDCl3,100MHZ) δ(ppm):148.3, 127.9, 48.3, 45.3.

[0091] The present invention will now be described in detail with reference to specific embodiments.

[0092] The examples and comparative examples respectively provide an electrolyte and a lithium-ion battery containing the electrolyte. The composition of the electrolyte is shown in Table 1.

[0093] The preparation method of lithium-ion batteries may include the following steps:

[0094] (1) Preparation of positive electrode sheet: The positive electrode active material Li(Ni) is prepared. 0.8 Mn 0.1 Co 0.1 O2 (NMC811), conductive agent acetylene black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of NMC811: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, a positive electrode sheet of the corresponding thickness is obtained.

[0095] (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 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.

[0096] (3) Fabrication of lithium-ion batteries: The 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 cell. The bare cell is placed in the outer packaging aluminum-plastic film and baked in an oven at 85 ± 10 ℃ for 24 h. 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.

[0097] The preparation method of the electrolyte includes the following steps:

[0098] At room temperature, in a glove box filled with argon (H2O < 1 ppm, O2 < 1 ppm), lithium salt is added to the organic solvent one by one while continuously stirring and cooling with dry ice. When the electrolyte temperature rises by no more than 2 °C, lithium salt can be added until the lithium salt reaches the preset mass fraction, and finally a colorless and transparent liquid is obtained. The compound shown in Formula I is then added and stirred evenly to obtain the electrolyte.

[0099] Electrochemical performance testing items include:

[0100] (1) Room temperature DCR test: At 25 ± 2 ℃, the lithium-ion batteries obtained in the examples and comparative examples were charged to 4.2 V with 1 C, then discharged at 1 C capacity for 30 min, adjusted to 50% SOC, and then pulsed discharged at 10 C constant current for 10 s. The SOC was then adjusted to 50% SOC according to the above method, and then charged for 10 s. The DCR was calculated as (voltage before pulse discharge – voltage after pulse discharge) / discharge current × 100%. After being stored at 60 ℃ for 30 days, the DCR was tested again when the battery was completely cooled to 25 ± 2 ℃. The DCR change rate was calculated as (DCR after 30 days – DCR before 30 days) / DCR before 30 days × 100%.

[0101] (2) High-temperature cycling performance test: At 45 ± 2 ℃, the lithium-ion batteries obtained in the examples and comparative examples were subjected to charge-discharge cycle tests in the range of 2.8 to 4.2 V at a charge-discharge rate of 1 C / 1 C. 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%.

[0102] (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 2.8 to 4.2 V. 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%.

[0103] Table 1. Electrolyte composition information and its lithium-ion battery performance

[0104]

[0105] Note: The percentage content of lithium salt and the compound shown in Formula I refers to their respective percentage content in the total mass of the electrolyte.

[0106] Comparing the experimental results of Examples 1-14 with Comparative Example 1, it can be seen that the compound represented by electrolyte formula I in this invention 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. Examples 1-6 also show that as the content of compound I1 increases, the initial internal resistance increases accordingly. This is because the generated interfacial film becomes increasingly dense, increasing the interfacial film impedance, which has a beneficial effect on suppressing the increasing trend of battery internal resistance during high-temperature storage and reducing irreversible losses during storage. Considering all performance aspects, the content of the compound represented by electrolyte formula I in this invention is preferably 0.5% to 1.5%.

[0107] The experimental results from Examples 4, 7-8, and Comparative Example 2 show that, compared to amide compounds containing only single conjugation, the multi-conjugated compounds I1, I2, and I3 exhibit better performance. This can be attributed to the multi-conjugated amide structures in the compounds I1, I2, and I3 represented by Formula I used in this invention, which result in lower LUMO orbitals in the molecules, preferentially reducing them to form an SEI film. Furthermore, the fluorine-rich chains in the molecules also help reduce molecular interactions and prevent an increase in electrolyte viscosity. In summary, electrolytes containing compounds represented by Formula I of this application can better improve the high-temperature storage and high-temperature cycling performance of battery cells.

[0108] 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. An electrolyte, characterized in that, Including compounds as shown in Formula I: ； X1 and X2 are each independently selected from alkylene, alkenylene, or ynylene groups having 1 to 20 carbon atoms; R1 and R2 are each independently selected from alkyl or haloalkyl groups; Cy is connected to Equation I. Five- or six-element ring bases formed by enclosure; The compound represented by Formula I includes at least one of structural formulas I1, I2, and I3: 、 、 。 2. The electrolyte according to claim 1, characterized in that, The amount of the compound represented by Formula I is 0.1% to 5% of the total mass of the electrolyte.

3. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and the electrolyte as described in any one of claims 1 to 2.

4. The secondary battery according to claim 3, characterized in that, The negative electrode sheet includes a negative electrode active material, which includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon, nano carbon, and silicon-carbon composite. The positive electrode includes a positive electrode active material, the chemical formula of which includes LiFePO4 and Li a Ni x Co y Mn （1-x-y） At least one of O2, wherein 0.9≤a≤1.1, 0<x<1, 0<y<1, and x+y<1.

5. The secondary battery according to claim 3, characterized in that, The charging cutoff voltage of the secondary battery is 4.2 to 4.5 V.

6. The secondary battery according to claim 3, characterized in that, The thickness of the active material layer of the positive electrode is 20–90 μm.

7. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 3 to 6.

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