Lithium ion battery electrolyte and lithium ion battery

Abstract

According to the lithium ion battery electrolyte and the lithium ion battery provided by the invention, specific dimethyl sulfate, the compound shown in the general formula (I) and 1-ethyl-3-methylimidazolium difluorophosphate are added into the electrolyte to achieve a synergistic effect to form good SEI, so that the properties such as initial resistance characteristic, high-temperature durability, cycle characteristic and the like are improved; and the requirements of application scenes such as electronic equipment and vehicle batteries on the battery are met.

Description

Technical Field

[0001] The invention belongs to the field of lithium ion battery electrolyte, and in particular relates to a lithium ion battery electrolyte and a lithium ion battery. Background Art

[0002] In recent years, lithium-ion batteries have been widely used in electronic devices such as personal computers and communication equipment, and have attracted particular attention in electric vehicles, hybrid vehicles, fuel cell vehicles, and power storage devices.

[0003] Lithium secondary batteries are mainly composed of positive and negative electrodes containing materials that can absorb and release lithium, and electrolytes containing lithium salts and non-aqueous solvents. Positive electrode active materials commonly use lithium metal oxides, such as LiCoO2, LiNiO2, LiMnO2, etc. Negative electrode active materials are active substances that can absorb and release lithium, such as metallic lithium, lithium-containing alloys, coke, artificial graphite, natural graphite, etc. The electrolyte commonly uses a non-aqueous solvent mixed with Li electrolytes, and the non-aqueous solvent includes carbonate mixed solvents such as ethylene carbonate and methyl carbonate, and Li electrolytes such as LiClO4, LiAsF6, LiPF6, LiBF4, LiAlF4, LiN (SO2CF2CF3) and other inorganic lithium.

[0004] During the initial charge, lithium cations are embedded in the negative electrode, and the negative electrode reacts with the lithium cations, or the negative electrode reacts with the electrolyte solvent to form a film mainly composed of lithium carbonate and lithium oxide on the surface of the negative electrode, namely the solid electrolyte interface film (SEI). How to form a stable SEI with high lithium ion conductivity, low electronic conductivity and good durability is the key to improving battery performance. By adding a small amount of additives to the electrolyte to form a good SEI, the high temperature durability, initial resistance, cycle characteristics and other performance are improved to meet the requirements of batteries in application scenarios such as electronic equipment and automotive batteries. Summary of the invention

[0005] In order to overcome the problems existing in the prior art, the purpose of the present invention is to provide a lithium ion battery electrolyte and a lithium ion battery, by adding specific dimethyl sulfate, a compound represented by general formula (I) and 1-ethyl-3-methylimidazolium difluorophosphate to the electrolyte to form a good SEI synergistically, improve the initial resistance characteristics, high temperature durability, cycle characteristics and other properties, and meet the requirements of batteries for application scenarios such as electronic equipment and automotive batteries.

[0006] The objective of the present invention is achieved through the following technical solutions: An electrolyte comprises a non-aqueous solvent, an electrolyte salt, dimethyl sulfate, a compound selected from the group consisting of general formula (I) and 1-ethyl-3-methylimidazolium difluorophosphate.

[0007] Wherein, the general formula (I) is R1 R 2 N-SO3M 1 ; R 1 and R 2 The same or different, are straight-chain or branched alkyl groups having 1 to 6 carbon atoms, or cycloalkyl groups having 3 to 6 carbon atoms; M 1 is one or more selected from Li, Na, K and Cs; Preferably, the compound represented by general formula (I) is (CH3)2NSO3Li.

[0008] Preferably, the content of dimethyl sulfate in the electrolyte is preferably 0.01% to 10% by mass, more preferably 0.05% to 5% by mass, and particularly preferably 0.1% to 2% by mass, based on the total amount of the electrolyte.

[0009] Preferably, the content of the compound selected from the group consisting of compounds represented by general formula (I) in the electrolyte is preferably 0.01 to 10% by mass, more preferably 0.05 to 5% by mass, and particularly preferably 0.1 to 2% by mass, relative to the total amount of the electrolyte.

[0010] Preferably, the content of 1-ethyl-3-methylimidazolium difluorophosphate in the electrolyte is preferably 0.01 to 10% by mass, more preferably 0.05 to 5% by mass, and particularly preferably 0.1 to 2% by mass, relative to the total amount of the electrolyte.

[0011] Preferably, the mass ratio of dimethyl sulfate, the compound selected from the group consisting of compounds represented by general formula (I) and 1-ethyl-3-methylimidazolium difluorophosphate is 1-5:1-5:1-5, more preferably 1:2-5:2-5, more preferably 1:3:3.

[0012] The non-aqueous solvents include cyclic non-aqueous solvents (to improve the flash point of the solvent and the safety of the battery) and chain non-aqueous solvents.

[0013] The cyclic non-aqueous solvent is one or more of cyclic carbonate, cyclic carboxylate, cyclic sulfone, and cyclic ether. The cyclic carbonate is preferably one or more of ethylene carbonate, propylene carbonate, and 2,3-butylene carbonate. The cyclic carboxylate is preferably one or more of γ-butyrolactone and δ-valerolactone. The cyclic sulfone is preferably one or more of cyclopentane, dimethyl sulfone, and methyl ethyl sulfone. The cyclic ether is preferably dioxolane.

[0014] The mixing ratio of the cyclic aprotic solvent in the nonaqueous solvent is 10% to 100% by mass, more preferably 20% to 90% by mass, and particularly preferably 30% to 80% by mass. By achieving such a ratio, the conductivity of the electrolyte solution related to the charge and discharge characteristics of the battery can be improved.

[0015] The chain non-aqueous solvent is one or more of chain carbonate, chain carboxylic acid ester, chain ether and chain phosphate. Chain carbonate is preferably one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, dipropyl carbonate, dipentyl carbonate, dihexyl carbonate, ethyl octyl carbonate and dioctyl carbonate. Chain carboxylic acid ester is preferably methyl pivalate. Chain ether is preferably dimethoxyethane. Chain phosphate is preferably trimethyl phosphate.

[0016] The mixing ratio of the chain aprotic solvent in the nonaqueous solvent is 10% by mass to 100% by mass, more preferably 20% by mass to 90% by mass, and particularly preferably 30% by mass to 80% by mass.

[0017] Preferably, the non-aqueous solvent is a combination of a cyclic carbonate and a chain carbonate, which can improve the conductivity of the electrolyte and improve the charge and discharge characteristics of the battery. Cyclic carbonate and chain carbonate are represented by, and the mass ratio of cyclic carbonate: chain carbonate is 5:95-80-20, more preferably 10:90-70:30, and particularly preferably 15:85-55:45. By becoming such a ratio, the viscosity of the electrolyte can be suppressed from rising, and the dissociation degree of the electrolyte can be increased, so that the conductivity of the electrolyte related to the charge and discharge characteristics of the battery can be improved. In addition, the solubility of the electrolyte can be further improved. Accordingly, an electrolyte with excellent conductivity at room temperature or low temperature can be formed, so the load characteristics of the battery at room temperature to low temperature can be improved.

[0018] The electrolyte salt is a lithium salt, preferably one or more of LiPF6, LiBF4, LiClO4, LiAsF6, more preferably LiPF6.

[0019] The concentration of the electrolyte salt in the electrolyte solution is 0.1 mol / L to 3 mol / L, preferably 0.5 mol / L to 2 mol / L.

[0020] The electrolyte of the present invention may also contain other additives, such as metal oxides, glass, etc., as required.

[0021] The electrolytic solution of the present invention can be suitably used in electrochemical devices such as secondary batteries. An electrochemical device or secondary battery including the electrolytic solution of the present invention is also one of the present invention.

[0022] The lithium secondary battery of the present invention comprises a positive electrode, a negative electrode, a separator and the above-mentioned electrolyte.

[0023] (positive electrode) The positive electrode active material constituting the positive electrode can be used as long as it can electrochemically absorb and release lithium ions. As specific examples, lithium-containing transition metal composite oxides and lithium-containing transition metal phosphate compounds can be listed. Preferred are composite oxides containing lithium and transition metals such as LiCoO2, LiMnO2, LiMn2O4, LiNiO2, LiNiXCo(1-X)O2〔0<X<1〕, and LiFePO4.

[0024] When the conductivity of the positive electrode active material is insufficient, it can be used together with a conductive auxiliary agent to form a positive electrode. The conductive auxiliary agent is one or more carbon materials such as carbon black, amorphous whiskers, and graphite.

[0025] (negative electrode) The negative electrode is composed of a negative electrode active material layer containing a negative electrode active material and a current collector. The negative electrode active material constituting the negative electrode can be any material as long as it can electrochemically absorb and release lithium ions. As specific examples, one or more of carbonaceous materials, metal oxide materials, lithium metal, lithium-containing alloys, and lithium-containing metal composite oxide materials can be cited.

[0026] Preferably, the carbon material is one or more of carbon black, activated carbon, artificial graphite, natural graphite, hard carbon, coke, mesocarbon microbeads (MCMB) sintered below 1500° C., and mesophase pitch carbon fiber (MCF).

[0027] The negative electrode active material layer further contains a binder, a thickener, and a conductive material.

[0028] The above-mentioned binder can be the same as the above-mentioned binder that can be used for the positive electrode. The ratio of the binder to the negative electrode active material is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, particularly preferably 0.6% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less, and particularly preferably 8% by mass or less. When the ratio of the binder to the negative electrode active material exceeds the above range, the proportion of the binder that does not contribute to the battery capacity in the amount of binder increases, which sometimes leads to a decrease in the battery capacity. In addition, when it is lower than the above range, it sometimes leads to a decrease in the strength of the negative electrode.

[0029] Diaphragm A separator is provided between the positive electrode and the negative electrode to electrically insulate the positive electrode from the negative electrode and to allow lithium ions to pass therethrough. The separator is a porous film.

[0030] The separator is a porous sheet or nonwoven fabric, and is preferably one or more of a polyolefin porous film, a polyimide porous film, a polyvinylidene fluoride porous film, and a polyester porous film.

[0031] The polyolefin porous polymer film is preferably a porous polyethylene film, a porous polypropylene film, or a multilayer film of a porous polyethylene film and a polypropylene film.

[0032] The thickness of the separator is 1 μm to 50 μm, preferably 5 μm to 30 μm, and more preferably 8 μm to 30 μm.

[0033] The porosity of the diaphragm is 20%-95%, preferably 35%-85% or more, and more preferably 45%-75%. When the porosity is too small compared to the above range, the membrane resistance increases and there is a tendency for the rate characteristics to deteriorate. When the porosity is too large compared to the above range, there is a tendency for the mechanical strength of the diaphragm to decrease and the insulation to decrease.

[0034] The average pore size of the separator is 0.05 μm to 0.5 μm, preferably 0.05 μm to 0.2 μm. If the average pore size exceeds the above range, short circuit is likely to occur. If it is below the above range, the membrane resistance may increase and the rate characteristics may decrease.

[0035] Battery composition The positive plate and the negative plate are separated by the above-mentioned separator to form a laminated structure, or the positive plate and the negative plate are wound into a spiral structure through the above-mentioned separator to obtain an electrode group. The proportion of the volume of the electrode group in the battery internal volume (hereinafter referred to as the electrode group occupancy) is usually 40% or more, preferably 50% or more, and usually 90% or less, preferably 80% or less. The lithium secondary battery of the present invention can adopt various known shapes, and can be formed into cylindrical, coin-shaped, square, membrane-shaped and other arbitrary shapes.

[0036] Beneficial effects: By adding specific dimethyl sulfate, the compound represented by the general formula (I) and 1-ethyl-3-methylimidazolium difluorophosphate to the electrolyte, a good SEI is formed synergistically, thereby improving the initial resistance characteristics, high temperature durability, cycle characteristics and other properties, thereby meeting the requirements of batteries for application scenarios such as electronic equipment and automotive batteries. DETAILED DESCRIPTION

[0037] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The present invention is further explained below in conjunction with specific implementation modes.

[0039] Preparation Example 1 The electrolyte includes a non-aqueous solvent, an electrolyte salt, dimethyl sulfate, (CH3)2NSO3Li and 1-ethyl-3-methylimidazolium difluorophosphate. The preparation method thereof is as follows: Step 1: ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed at a mass ratio of 55:45 to obtain a non-aqueous solvent.

[0040] Step 2: dissolving LiPF6 as an electrolyte salt in the non-aqueous solvent obtained in step 1 to obtain an electrolyte salt solution, wherein the electrolyte salt concentration is 1 mol / L.

[0041] Step 3, dissolving dimethyl sulfate, (CH3)2NSO3Li and 1-ethyl-3-methylimidazolium difluorophosphate as additives in the electrolyte salt solution obtained in step 2 to obtain an electrolyte salt solution, wherein the content of the additives is 0.5wt% relative to the final electrolyte. The mass ratio of dimethyl sulfate, (CH3)2NSO3Li and 1-ethyl-3-methylimidazolium difluorophosphate is 1:3:3.

[0042] Comparative Preparation Example 1 The electrolyte includes a non-aqueous solvent, an electrolyte salt, (CH3)2NSO3Li and 1-ethyl-3-methylimidazolium difluorophosphate. The preparation method thereof is as follows: Step 1: ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed at a mass ratio of 55:45 to obtain a non-aqueous solvent.

[0043] Step 2: dissolving LiPF6 as an electrolyte salt in the non-aqueous solvent obtained in step 1 to obtain an electrolyte salt solution, wherein the electrolyte salt concentration is 1 mol / L.

[0044] Step 3, dissolving (CH3)2NSO3Li and 1-ethyl-3-methylimidazolium difluorophosphate as additives in the electrolyte salt solution obtained in step 2 to obtain an electrolyte salt solution, wherein the content of the additives is 0.5wt% relative to the final electrolyte solution. The mass ratio of (CH3)2NSO3Li and 1-ethyl-3-methylimidazolium difluorophosphate is 3:3.

[0045] Comparative Preparation Example 2 The electrolyte includes a non-aqueous solvent, an electrolyte salt, dimethyl sulfate and 1-ethyl-3-methylimidazolium difluorophosphate. The preparation method thereof is as follows: Step 1: ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed at a mass ratio of 55:45 to obtain a non-aqueous solvent.

[0046] Step 2: dissolving LiPF6 as an electrolyte salt in the non-aqueous solvent obtained in step 1 to obtain an electrolyte salt solution, wherein the electrolyte salt concentration is 1 mol / L.

[0047] Step 3, dissolving dimethyl sulfate and 1-ethyl-3-methylimidazolium difluorophosphate as additives in the electrolyte salt solution obtained in step 2 to obtain an electrolyte salt solution, wherein the content of the additives is 0.5wt% relative to the final electrolyte solution. The mass ratio of dimethyl sulfate to 1-ethyl-3-methylimidazolium difluorophosphate is 1:3.

[0048] Comparative Preparation Example 3 The electrolyte includes a non-aqueous solvent, an electrolyte salt, dimethyl sulfate and (CH3)2NSO3Li. The preparation method thereof is as follows: Step 1: ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed at a mass ratio of 55:45 to obtain a non-aqueous solvent.

[0049] Step 2: dissolving LiPF6 as an electrolyte salt in the non-aqueous solvent obtained in step 1 to obtain an electrolyte salt solution, wherein the electrolyte salt concentration is 1 mol / L.

[0050] Step 3, dissolving dimethyl sulfate and (CH3)2NSO3Li as additives in the electrolyte salt solution obtained in step 2 to obtain an electrolyte salt solution, wherein the content of the additives is 0.5wt% relative to the final electrolyte solution. The mass ratio of dimethyl sulfate to (CH3)2NSO3Li is 3:3.

[0051] Comparative Preparation Example 4 The electrolyte includes a non-aqueous solvent and an electrolyte salt. The preparation method thereof is as follows: Step 1: ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed at a mass ratio of 55:45 to obtain a non-aqueous solvent.

[0052] Step 2: dissolving LiPF6 as an electrolyte salt in the non-aqueous solvent obtained in step 1 to obtain an electrolyte salt solution, wherein the electrolyte salt concentration is 1 mol / L.

[0053] Example A lithium secondary battery was manufactured through the following steps.

[0054] Step 1: Preparation of negative electrode 97 parts by mass of artificial graphite, 1 part by mass of cellulose and 2 parts by mass of SBR latex were weighed, dissolved in water, and kneaded to obtain a paste-like negative electrode active material layer slurry, which was applied to a negative electrode collector made of a strip of copper foil with a thickness of 20 μm, dried, and rolled to obtain a sheet-like negative electrode including a negative electrode collector and a negative electrode active material layer. The coating density of the negative electrode active material layer at this time was 12 mg / cm 2 , the filling density is 1.3g / ml.

[0055] Step 2: Preparation of positive electrode Weigh 92 parts by mass of LiMnO2, 4 parts by mass of acetylene black and 4 parts by mass of PVDF, dissolve the above components in NMP, mix and obtain a paste-like positive electrode active material layer slurry, apply the slurry to a positive electrode collector of a strip-shaped aluminum foil with a thickness of 21 μm, dry and roll to obtain a sheet-like positive electrode including a positive electrode collector and a positive electrode active material layer. The coating density of the positive electrode active material layer at this time is 28 mg / cm 2 , the filling density is 2.3g / ml.

[0056] Step 3: Preparation of lithium-ion secondary battery The negative electrode, positive electrode and polyethylene separator prepared above were stacked in the order of negative electrode, separator and positive electrode to produce a battery element.

[0057] The battery element is inserted into a bag consisting of a laminate film whose both surfaces are coated with a resin layer of an aluminum sheet (thickness 40 μm), and the positive and negative terminals are made to protrude. Thereafter, the electrolytes described in the preparation example and the comparative preparation example are respectively injected into the bag, and vacuum sealing is performed to produce a sheet-shaped lithium-ion secondary battery.

[0058] The performance of the prepared lithium-ion secondary battery was characterized: 1. Initial characteristics of the battery: determination of initial resistance, initial discharge capacity and initial efficiency The lithium ion secondary battery was charged at a constant current of 1 mA and a constant voltage of 4.2 V, and discharged at a constant current of 1 mA until 2.85 V, and the cycle was repeated 10 times. At this time, the initial charge and discharge efficiency (initial efficiency) was calculated by the following formula from the charge capacity [mAh] of the first cycle and the discharge capacity [mAh] of the first cycle (initial discharge capacity).

[0059] Initial efficiency [%] = (discharge capacity of the first cycle [mAh] / charge capacity of the first cycle [mAh]) × 100 [%] According to the test results, the initial discharge capacity (relative value; %) of Example 1 and Comparative Examples 1-3 when the initial discharge capacity in Comparative Example 1 is set to 100%, and the initial efficiency (relative value; %) of Example 1 and Comparative Examples 1-3 when the initial efficiency in Comparative Example 4 is set to 100% are calculated respectively.

[0060] The above-mentioned lithium ion secondary battery was charged at a constant voltage of 4.0V, then, the charged lithium ion secondary battery was cooled to -20°C in a thermostatic chamber, and discharged at a constant current of 0.2mA at -20°C, and the potential drop at 10 seconds from the start of discharge was measured to measure the DC resistance [Ω] of the lithium ion secondary battery, and the obtained value was set as the initial resistance value [Ω] (-20°C).

[0061] The initial resistance value [Ω] (-20°C) in Comparative Example 4 is set to 100%, and the initial resistance values ​​(relative value; %) in Example 1 and Comparative Examples 1-3 are as follows: Initial battery resistance [%] = (initial resistance value [Ω] (-20°C) in Example 1 / initial resistance value [Ω] (-20°C) in Comparative Example 4) × 100 [%] 2. Cycle characteristics At 60°C, constant current-constant voltage charging (hereinafter referred to as CC / CV charging) (0.1C cut) is performed at a current equivalent to 0.2C until 4.9V, and then discharged at a constant current of 0.2C until 3V, which is regarded as 1 cycle, and the initial discharge capacity is calculated based on the discharge capacity of the third cycle. Here, 1C represents the current value that discharges the base capacity of the battery in 1 hour, for example, 0.2C represents a current value of 1 / 5 of it. After that, charge and discharge under the above conditions, and continue to cycle until it reaches 80% relative to the initial capacity, and the number of cycles to reach 80% is recorded in the table.

[0062] Table 1 Lithium ion secondary battery performance

[0063] According to the results shown in Table 1, it can be seen from the comparison between Example 1 and Comparative Examples 1-3 and Comparative Example 4 that adding dimethyl sulfate, (CH3)2NSO3Li and 1-ethyl-3-methylimidazolium difluorophosphate as additives to the electrolyte has a synergistic effect, which can significantly reduce the initial battery resistance of the lithium secondary battery while maintaining the initial efficiency and initial discharge capacity, improve the initial resistance characteristics, and also improve the high temperature resistance cycle characteristics.

[0064] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. An electrolyte comprising a non-aqueous solvent, an electrolyte salt, dimethyl sulfate, a compound selected from the group consisting of general formula (I) and 1-ethyl-3-methylimidazolium difluorophosphate; in, The general formula (I) is R 1 R 2 N-SO3M 1 ; R 1 and R 2 The same or different, are straight-chain or branched alkyl groups having 1 to 6 carbon atoms, or cycloalkyl groups having 3 to 6 carbon atoms; M 1 is one or more selected from Li, Na, K and Cs; The contents of dimethyl sulfate, the compound represented by the general formula (I) and 1-ethyl-3-methylimidazolium difluorophosphate in the electrolyte are 0.01 mass % to 10 mass % relative to the total amount of the electrolyte; the mass ratio of dimethyl sulfate, the compound represented by the general formula (I) and 1-ethyl-3-methylimidazolium difluorophosphate is 1-5:1-5:1-5.

2. The electrolyte according to claim 1, characterized in that The content of dimethyl sulfate, the compound represented by the general formula (I) and 1-ethyl-3-methylimidazolium difluorophosphate in the electrolyte is 0.05% by mass to 5% by mass based on the total amount of the electrolyte.

3. The electrolyte according to claim 1, characterized in that The content of dimethyl sulfate, the compound represented by the general formula (I) and 1-ethyl-3-methylimidazolium difluorophosphate in the electrolyte is 0.1% to 2% by mass based on the total amount of the electrolyte.

4. The electrolyte according to claim 1, characterized in that The mass ratio of the dimethyl sulfate, the compound represented by the general formula (I) and 1-ethyl-3-methylimidazolium difluorophosphate is 1:2-5:2-5.

5. The electrolyte according to claim 1, characterized in that The mass ratio of the dimethyl sulfate, the compound represented by the general formula (I) and 1-ethyl-3-methylimidazolium difluorophosphate is 1:3:

3.

6. The electrolyte according to claim 1, characterized in that The compound represented by the general formula (I) is (CH3)2NSO3Li.

7. The electrolyte according to claim 1, characterized in that The non-aqueous solvent is a cyclic non-aqueous solvent and a chain non-aqueous solvent.

8. The electrolyte according to claim 7, characterized in that The cyclic non-aqueous solvent is one or more of cyclic carbonates, cyclic carboxylates, cyclic sulfones, and cyclic ethers; wherein the cyclic carbonates are selected from one or more of ethylene carbonate, propylene carbonate, and 2,3-butylene carbonate; the cyclic carboxylates are selected from one or more of γ-butyrolactone and δ-valerolactone; the cyclic sulfones are selected from one or more of cyclopentane sulfone, dimethyl sulfone, and methyl ethyl sulfone; and the cyclic ethers are selected from dioxolane.

9. The electrolyte according to claim 7, characterized in that The chain non-aqueous solvent is one or more of chain carbonates, chain carboxylates, chain ethers, and chain phosphates; wherein the chain carbonate is selected from one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, dipropyl carbonate, dipentyl carbonate, dihexyl carbonate, ethyl octyl carbonate, and dioctyl carbonate; the chain carboxylate is methyl pivalate, the chain ether is dimethoxyethane, and the chain phosphate is trimethyl phosphate.

10. A lithium secondary battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and the electrolyte according to any one of claims 1 to 9.

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