An electrolyte, a preparation method thereof, and a lithium secondary battery including the electrolyte

Abstract

The application provides an electrolyte, which comprises a lithium salt and an organic solvent, wherein the organic solvent comprises a cyclic uncoordinated solvent represented by the following formula (I), (I); in the formula (I), R1, R2, R3, R4, R5, R6, R7, R8, R9 and R10 are each independently selected from a hydrogen atom, a chlorine atom, a bromine atom, a fluorine atom, a C1-C3 alkyl group, a C1-C3 alkoxy group, a fluorine-substituted C1-C3 alkyl group or a fluorine-substituted C1-C3 alkoxy group. The electrolyte can be applied to a lithium metal secondary battery, can significantly improve the cycle stability, safety and cycle life of the battery, can effectively inhibit the decomposition of a coordination type solvent, realizes uniform deposition of metal lithium dendrites, thereby improving the stability of the electrolyte, and has obvious high-temperature storage gas production inhibition effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium secondary battery electrolyte, in particular, relates to an electrolyte and a lithium secondary battery comprising the same. BACKGROUND

[0002] Currently, the design of metal lithium electrolyte formula basically abandons the use of carbonate solvents, and the combination of coordination type ether and non-coordination diluent is currently the preferred combination. However, this electrolyte system can achieve good cycle in the early stage, and when cycled for hundreds of cycles, it starts to consume a large amount of electrolyte, and finally the electrolyte dries up, resulting in a sharp drop.

[0003] For example, in the Chinese patent with the application number "202311849057.4", an electrolyte and a lithium battery comprising the same are disclosed, which specifically discloses that the electrolyte includes a fluorine-containing ether solvent, a cosolvent and a diluent. The fluorine-containing ether solvent has an ether backbone and -F, -CH2F, -CHF2 or -CF3 introduced at both ends of the ether backbone, which can improve the Highest Occupied Molecular Orbital (HOMO) level and ultimately improve the oxidation ability of the electrolyte; the cosolvent is a nitrile solvent, a sulfone solvent or a phenyl ether with a DN value of 10-13 kcal / mol; the diluent is an aromatic or halogenated compound with a DN value less than 10 kcal / mol; the relative dielectric constant of the solvent, cosolvent and diluent is > 3.6. By using lithium salt, fluorine-containing ether solvent, nitrile solvent with a DN value of 10-13 kcal / mol as cosolvent and aromatic or halogenated compound with a DN value less than 10 kcal / mol as diluent and limiting the relative dielectric constant of the three reagents to be within a certain range, the overall high temperature resistance and high voltage resistance of the electrolyte can be significantly improved. Even at a lithium salt concentration of less than or equal to 1M, the proportion of contact ion pairs (CIP) and aggregates (AGG) coordination in the electrolyte is high, which promotes the generation of anion-derived SEI / CEI substances, and does not affect the dissolution of lithium salt, promotes the dissociation of solvated Li+, and greatly improves the cycle stability of the battery.

[0004] wherein the solution structure of the electrolyte is closely related to the DN value of the introduced diluent, when the DN value of the introduced solvent is less than 10, a local high concentration electrolyte (LHCE) can be obtained, which is independent of the type of lithium salt and coordinating solvent of the electrolyte. In the Chinese patent with application number "202311849057.4", the diluent used is an aromatic or halogenated compound with a DN value less than 10 kcal / mol, therefore, this local high concentration electrolyte system can achieve good cycle in the early stage, but when cycled for hundreds of times, it will start to consume a large amount of electrolyte, and finally the electrolyte dries up, resulting in a drop; and the diluent fluorobenzene used by it is easy to cause the battery to produce gas during the cycle process, thereby causing the battery to fail. SUMMARY

[0005] The purpose of the embodiments of the present application is to provide an electrolyte and a preparation method and a lithium secondary battery containing the electrolyte, in order to solve the technical problem that the electrolyte in the prior art starts to consume a large amount of electrolyte when cycled for hundreds of times, and finally the electrolyte dries up, resulting in a drop.

[0006] In a first aspect, the present application provides an electrolyte, comprising a lithium salt, an organic solvent, the organic solvent comprising a cyclic non-coordinating solvent represented by the following formula (I),

[0007] (I);

[0008] In formula (I), R1, R2, R3, R4, R5, R6, R7, R8, R9, R10 are each independently selected from a hydrogen atom, a chlorine atom, a bromine atom, a fluorine atom, a C1-C3 alkyl group, a C1-C3 alkoxy group, a fluorine-substituted C1-C3 alkyl group, or a fluorine-substituted C1-C3 alkoxy group.

[0009] Further, in formula (I), R1, R2, R3, R4, R5, R6, R7, R8, R9, R10 are each independently selected from a hydrogen atom, a chlorine atom, or a fluorine atom.

[0010] Further, the cyclic non-coordinating solvent is selected from at least one of compounds 1-11:

[0011] .

[0012] Further, the organic solvent further comprises a linear uncoordinating solvent, the linear uncoordinating solvent comprising any one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, 1-(1,1,2,2-tetrafluoroethoxy)propane, 2-methyl-1-(1,1,2,2-tetrafluoroethoxy)propane, bis(2,2,2-trifluoroethyl) ether, tris(trifluoroethoxy)methane, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 2,2,2-trifluoroethyl-1,1,2,3,3,3-hexafluoropropyl ether, dichloromethane, hexafluoroisopropyl methyl ether, n-hexane, 2H,3H-decafluoropentane, and methyl nonafluorobutyl ether;

[0013] Further, the organic solvent further comprises a linear uncoordinating solvent, the linear uncoordinating solvent comprising any one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, 1-(1,1,2,2-tetrafluoroethoxy)propane, 2-methyl-1-(1,1,2,2-tetrafluoroethoxy)propane, bis(2,2,2-trifluoroethyl) ether, tris(trifluoroethoxy)methane, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 2,2,2-trifluoroethyl-1,1,2,3,3,3-hexafluoropropyl ether, dichloromethane, hexafluoroisopropyl methyl ether, n-hexane, 2H,3H-decafluoropentane, and methyl nonafluorobutyl ether;

[0014] Further, the organic solvent further comprises a linear uncoordinating solvent, the linear uncoordinating solvent comprising any one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, 1-(1,1,2,2-tetrafluoroethoxy)propane, 2-methyl-1-(1,1,2,2-tetrafluoroethoxy)propane, bis(2,2,2-trifluoroethyl) ether, tris(trifluoroethoxy)methane, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 2,2,2-trifluoroethyl-1,1,2,3,3,3-hexafluoropropyl ether, dichloromethane, hexafluoroisopropyl methyl ether, n-hexane, 2H,3H-decafluoropentane, and methyl nonafluorobutyl ether;

[0015] Further, the organic solvent further comprises a linear uncoordinating solvent, the linear uncoordinating solvent comprising any one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, 1-(1,1,2,2-tetrafluoroethoxy)propane, 2-methyl-1-(1,1,2,2-tetrafluoroethoxy)propane, bis(2,2,2-trifluoroethyl) ether, tris(trifluoroethoxy)methane, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 2,2,2-trifluoroethyl-1,1,2,3,3,3-hexafluoropropyl ether, dichloromethane, hexafluoroisopropyl methyl ether, n-hexane, 2H,3H-decafluoropentane, and methyl nonafluorobutyl ether;

[0016] Further, the organic solvent further comprises a linear uncoordinating solvent, the linear uncoordinating solvent comprising any one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, 1-(1,1,2,2-tetrafluoroethoxy)propane, 2-methyl-1-(1,1,2,2-tetrafluoroethoxy)propane, bis(2,2,2-trifluoroethyl) ether, tris(trifluoroethoxy)methane, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 2,2,2-trifluoroethyl-1,1,2,3,3,3-hexafluoropropyl ether, dichloromethane, hexafluoroisopropyl methyl ether, n-hexane, 2H,3H-decafluoropentane, and methyl nonafluorobutyl ether;

[0017] Further, the organic solvent further comprises a linear uncoordinating solvent, the linear uncoordinating solvent comprising any one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, 1-(1,1,2,2-tetrafluoroethoxy)propane, 2-methyl-1-(1,1,2,2-tetrafluoroethoxy)propane, bis(2,2,2-trifluoroethyl) ether, tris(trifluoroethoxy)methane, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 2,2,2-trifluoroethyl-1,1,2,3,3,3-hexafluoropropyl ether, dichloromethane, hexafluoroisopropyl methyl ether, n-hexane, 2H,3H-decafluoropentane, and methyl nonafluorobutyl ether;

[0018] Further, the organic solvent further comprises a linear uncoordinating solvent, the linear uncoordinating solvent comprising any one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, 1-(1,1,2,2-tetrafluoroethoxy)propane, 2-methyl-1-(1,1,2,2-tetrafluoroethoxy)propane, bis(2,2,2-trifluoroethyl) ether, tris(trifluoroethoxy)methane, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 2,2,2-trifluoroethyl-1,1,2,3,3,3-hexafluoropropyl ether, dichloromethane, hexafluoroisopropyl methyl ether, n-hexane, 2H,3H-decafluoropentane, and methyl nonafluorobutyl ether;

[0019] and / or, the additive comprises any one of vinylene carbonate, 1,3-propane sultone inner ester;

[0020] Further, the sum of the mass percentages of the linear uncoordinating solvent and the cyclic uncoordinating solvent is 35.5%-84.9% based on the total mass of the electrolyte.

[0021] Further, the molar ratio of the linear uncoordinating solvent and the cyclic uncoordinating solvent is (1-3):(1-2).

[0022] Further, the mass percentage of the coordinating solvent is 10%-25% based on the total mass of the electrolyte.

[0023] and / or, the mass percentage of the lithium salt is 5%-35% based on the total mass of the electrolyte;

[0024] and / or, the mass percentage of the additive is 0.1%-4.5% based on the total mass of the electrolyte.

[0025] In a second aspect, the present application provides a preparation method of an electrolyte, comprising the following steps:

[0026] S1, under the protection of inert gas, a coordinating solvent is added to a configuration container, then a lithium salt is added to the configuration container and mixed uniformly;

[0027] S2, a linear uncoordinating solvent and a cyclic uncoordinating solvent are added to the configuration container and mixed uniformly;

[0028] S3, an additive is added to the configuration container and mixed uniformly to obtain the electrolyte.

[0029] In a third aspect, the present application provides a lithium secondary battery comprising the electrolyte described above; or comprising the electrolyte prepared by the preparation method described above.

[0030] The lithium secondary battery in the present application can be a lithium metal negative electrode battery or a negative electrode-free lithium metal battery. Due to the inclusion of the electrolyte in the present application, under the synergistic action of the linear uncoordinating solvent and the cyclic uncoordinating solvent, better reversible deintercalation can be achieved, the growth of lithium dendrites is inhibited, the deposition of lithium dendrites is reduced, the cycle stability, safety and cycle life of the battery can be significantly improved; at the same time, the decomposition of the coordinating solvent can be effectively inhibited, uniform deposition of metal lithium dendrites is achieved, thereby improving the stability of the electrolyte; and the high-temperature storage gas production inhibition effect is obvious, the vapor pressure is lower at the same temperature, thereby widening the use temperature range of the lithium metal battery.

[0031] The beneficial effects of the embodiments of the present application are as follows:

[0032] (1) The electrolyte in the present application can be applied to lithium secondary batteries, which can be lithium metal negative electrode batteries or negative electrode-free lithium metal batteries. The coordination type solvent realizes the dissociation of lithium salt through its high polarity, but the high concentration causes the viscosity of the electrolyte to be too large, which is not conducive to ion movement. The introduction of straight-chain non-coordination solvents can be used to adjust the overall viscosity and solvation structure of the electrolyte, forming more anion-cation aggregate solvation models, but the straight-chain non-coordination solvent has limited control over the solvation structure and cannot inhibit the chemical reactivity of lithium metal with the coordination solvent. The introduction of cyclic non-coordination solvents exhibits a specific constraint conformation, with a lower electron cloud density around the oxygen atom, which maximally reduces the coordination with lithium ions. Therefore, under the synergistic action of cyclic non-coordination solvents and straight-chain non-coordination solvents, anion-based interface regulation can be achieved, the interface forms inorganic components rich in LiF, Li3N, etc., improves the ion diffusion kinetics, and can achieve better reversible deintercalation, inhibit the growth of lithium dendrites, and reduce the deposition of lithium dendrites. Its application can significantly improve the cycle stability, safety and cycle life of the battery.

[0033] (2) The electrolyte in the present application has strong reducibility, and many solvents cannot achieve good chemical and electrochemical stability. The use of straight-chain non-coordination solvents and cyclic non-coordination solvents together can achieve good reaction inertness, reduce the decomposition of the highly polar coordination solvent in the first solvation sheath, effectively inhibit the decomposition of the coordination solvent, and achieve uniform deposition of lithium metal dendrites, thereby improving the stability of the electrolyte.

[0034] (3) Compared with the fluorobenzene family of the same ring diluent, it is easy to cause the lithium battery to produce gas during the cycle process, thereby causing the battery to fail. The electrolyte in the present application has obvious high-temperature storage gas inhibition effect for the applied cyclic non-coordination solvent, can inhibit gas production during the cycle process of the lithium secondary battery, and can significantly improve the cycle stability, safety and cycle life of the battery. And, the vapor pressure is lower at the same temperature, which widens the high temperature interval for the use of lithium metal batteries. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments of the present application. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0036] Figure 1 The schematic diagram of the cycle capacity retention rate of the lithium secondary battery in Example 1, Example 2 and Comparative Example 1. DETAILED DESCRIPTION

[0037] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0038] I. Embodiment:

[0039] Embodiment 1:

[0040] 1.1. An electrolyte, comprising:

[0041] a lithium salt, lithium bis(fluorosulfonyl)imide (LiFSI), with a mass percentage of 20%;

[0042] an additive, vinylene carbonate, with a mass percentage of 2%;

[0043] a complexing solvent, ethylene glycol dimethyl ether (DME), with a mass percentage of 23%,

[0044] a linear non-complexing solvent, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE);

[0045] a cyclic non-complexing solvent, compound 2 of the following formula (1);

[0046] (1)

[0047] the sum of the mass percentages of the linear non-complexing solvent and the cyclic non-complexing solvent is 55%, and the molar ratio of the linear non-complexing solvent to the cyclic non-complexing solvent is 1:1.

[0048] 1.2. Preparation method:

[0049] comprising the following steps:

[0050] S1. In an argon-filled glove box, first add the lithium salt to the weighed complexing solvent and mix well;

[0051] S2. Then add the linear non-complexing solvent and the cyclic non-complexing solvent and mix well;

[0052] S3. Finally, add the additive and mix well to prepare a clear and transparent electrolyte.

[0053] Embodiment 2:

[0054] The electrolyte in this embodiment is different from that in Embodiment 1 in that the lithium salt used is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and the others are the same as in Embodiment 1.

[0055] Embodiment 3:

[0056] The electrolyte in this example differs from that in Example 1 in that the cyclic non-coordinating solvent is Compound 1 of the following formula (2) and is otherwise the same as in Example 1.

[0057] (2)

[0058] Example 4:

[0059] The electrolyte in this example differs from that in Example 1 in that the cyclic non-coordinating solvent is Compound 3 of the following formula (3) and is otherwise the same as in Example 1.

[0060] (3)

[0061] Example 5:

[0062] The electrolyte in this example differs from that in Example 1 in that the cyclic non-coordinating solvent is Compound 4 of the following formula (4) and is otherwise the same as in Example 1.

[0063] (4)

[0064] Example 6:

[0065] The electrolyte in this example differs from that in Example 1 in that the cyclic non-coordinating solvent is Compound 5 of the following formula (5) and is otherwise the same as in Example 1.

[0066] (5)

[0067] Example 7:

[0068] The electrolyte in this example differs from that in Example 1 in that the cyclic non-coordinating solvent is Compound 6 of the following formula (6) and is otherwise the same as in Example 1.

[0069] (6)

[0070] Example 8:

[0071] The electrolyte in this example differs from that in Example 1 in that the cyclic non-coordinating solvent is Compound 7 of the following formula (7) and is otherwise the same as in Example 1.

[0072] (7)

[0073] Example 9:

[0074] The electrolyte in this example differs from that in Example 1 in that the cyclic non-coordinating solvent is Compound 8 of the following formula (8) and is otherwise the same as in Example 1.

[0075] (8)

[0076] Example 10:

[0077] The electrolyte in this example is different from that in Example 1 in that the cyclic non-coordinating solvent is compound 9 of the following formula (9) and the others are the same as in Example 1.

[0078] (9)

[0079] Example 11:

[0080] The electrolyte in this example is different from that in Example 1 in that the cyclic non-coordinating solvent is compound 10 of the following formula (10) and the others are the same as in Example 1.

[0081] (10)

[0082] Example 12:

[0083] The electrolyte in this example is different from that in Example 1 in that the cyclic non-coordinating solvent is compound 11 of the following formula (11) and the others are the same as in Example 1.

[0084] (11)

[0085] Example 13:

[0086] The electrolyte in this example is different from that in Example 1 in that the linear non-coordinating solvent is 1H, 1H, 5H-octafluoropentyl-1, 1, 2, 2-tetrafluoroethyl ether; the cyclic non-coordinating solvent is compound 3 of the following formula (12); and the others are the same as in Example 1.

[0087] (12)

[0088] Example 14:

[0089] The electrolyte in this example is different from that in Example 1 in that the coordinating solvent is triethylene glycol dimethyl ether; the cyclic non-coordinating solvent is compound 6 of the following formula (13); and the others are the same as in Example 1.

[0090] (13)

[0091] Example 15:

[0092] 15.1. An electrolyte, comprising:

[0093] a lithium salt, lithium hexafluorophosphate, with a mass percentage of 25%;

[0094] an additive, 1, 3-propane sultone, with a mass percentage of 1%;

[0095] The coordination solvent used is 1,2-diethoxyethane, with a mass percentage of 15%.

[0096] A linear noncoordinate solvent, using 1-(1,1,2,2-tetrafluoroethoxy)propane;

[0097] A cyclic noncoordinate solvent, using compound 1 of formula (14);

[0098] (14)

[0099] The sum of the mass percentages of the linear noncoordinating solvent and the cyclic noncoordinating solvent is 59%, and the molar ratio of the linear noncoordinating solvent to the cyclic noncoordinating solvent is 2:1.

[0100] 15.2 Preparation method, same as in Example 1.

[0101] Example 16:

[0102] 16.1 An electrolyte, comprising:

[0103] The lithium salt used is lithium tetrafluoroborate, which accounts for 15% by mass.

[0104] The additive is fluoroethylene carbonate, which accounts for 1.5% by mass.

[0105] The coordination solvent used is 1,2-diethoxyethane, with a mass percentage of 13%.

[0106] A linear noncoordinate solvent is used, specifically 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether.

[0107] A cyclic noncoordinate solvent, using compound 2 of formula (15);

[0108] (15)

[0109] The sum of the mass percentages of the linear noncoordinating solvent and the cyclic noncoordinating solvent is 70%, and the molar ratio of the linear noncoordinating solvent to the cyclic noncoordinating solvent is 3:1.

[0110] 16.2 Preparation method, same as in Example 1.

[0111] Example 17:

[0112] 17.1 An electrolyte, comprising:

[0113] The lithium salt used is lithium hexafluorophosphate, which accounts for 25% by mass.

[0114] The additive is methylene methane disulfonate, which accounts for 3% by mass.

[0115] The coordinating solvent is tetraethylene glycol dimethyl ether, and the mass percentage is 10%,

[0116] The linear non-coordinating solvent is 1H, 1H, 5H-octafluoropentyl-1, 1, 2, 2-tetrafluoroethyl ether;

[0117] The cyclic non-coordinating solvent is compound 4 of the following formula (16);

[0118] (16)

[0119] The sum of the mass percentages of the linear non-coordinating solvent and the cyclic non-coordinating solvent is 62%, and the molar ratio of the linear non-coordinating solvent to the cyclic non-coordinating solvent is 3:2.

[0120] 17.2, Preparation method, same as example 1.

[0121] II. Comparative examples:

[0122] Comparative example 1:

[0123] The electrolyte in this comparative example is different from example 1 in that no cyclic non-coordinating solvent is used, and the mass percentage of the linear non-coordinating solvent is 55%, and the others are the same as example 1.

[0124] Comparative example 2:

[0125] The electrolyte in this comparative example is different from example 1 in that the cyclic non-coordinating solvent used is fluorobenzene; the others are the same as example 1.

[0126] Comparative example 3:

[0127] The electrolyte in this comparative example is different from example 1 in that the cyclic non-coordinating solvent used is m-fluorotoluene; the others are the same as example 1.

[0128] III. Experimental examples:

[0129] 1. The electrolytes in examples 1-17 and comparative examples 1-3 are respectively prepared into lithium secondary batteries, and the 25℃ cycle performance test, 55℃ cycle performance test and high temperature storage gas production test are carried out.

[0130] 1.1, The preparation method of the lithium secondary battery comprises the following steps:

[0131] (1) Preparation of positive electrode sheet:

[0132] Polyvinylidene fluoride (PVDF) is uniformly dissolved in N-methyl pyrrolidone (NMP),

[0133] Then add the conductive agent Super P and mix thoroughly,

[0134] The positive active material LiNi0.8Co0.1Mn0.1O2 powder is gradually added again (the mass ratio of LiNi0.8Co0.1Mn0.1O2 powder, PVDF and conductive agent Super P is 97.4:1.3:1.3, and a positive electrode slurry is obtained (the discharge solid content of the positive electrode slurry is 65.1%),

[0135] The positive electrode slurry is coated on the current collector, and then dried, rolled, and slitted to obtain a positive electrode sheet that can be directly laminated.

[0136] (2) Cell production: The slitted positive electrode sheet and negative electrode sheet (lithium sheet) are laminated on a laminating machine, the separator is a PP / PE / PP three-layer material, and a soft package cell is assembled.

[0137] (3) Electrolyte: The electrolyte in Examples 1-17 and Comparative Examples 1-3 is used.

[0138] (4) Liquid injection, formation and aging:

[0139] After the cell is dried at high temperature, the electrolyte of the examples and comparative examples is injected into the soft package cell. After the electrolyte is injected, the lithium battery is subjected to a first packaging process, surface cleaning and other processes to complete the preliminary work, and is placed at room temperature for one day. The formation is performed by a step-by-step formation method, the first formation current is 0.05C, the constant current is charged for 2h, and the second formation current is 0.1C, and the constant current is charged until the voltage reaches 3.85V. After formation, it is subjected to 50℃ aging treatment for one day, cooled to room temperature for final sealing, and a lithium secondary battery is obtained.

[0140] 1.2 Test method:

[0141] (1) 25℃ cycle performance test: The batteries prepared in each example and comparative example are charged at 0.2C constant current and constant voltage to 4.2V at 25℃, and then discharged at 0.5C constant current to 3.0V, which is 1 cycle. Record the cycle number when the cell reaches 80% SOH.

[0142] (2) 55℃ cycle performance test: The batteries prepared in each example and comparative example are charged at 0.2C constant current and constant voltage to 4.2V at 25℃, and then discharged at 0.5C constant current to 3.0V, which is 1 cycle. Record the cycle number when the cell reaches 80% SOH.

[0143] (3) High-temperature storage gas production test: the battery prepared in each example and comparative example was charged at 0.2C constant current and constant voltage to 4.2V at 25°C, the capacity Qa of the battery (unit Ah) was recorded, the volume V1 of the battery was tested by drainage method (unit mL), then the battery was placed in a 70°C air oven for 21 days, after taking out and recovering to room temperature, the volume V2 of the battery was tested (unit mL);

[0144] Gas production calculation formula: (V2-V1) / Qa.

[0145] 1.3, the test results are shown in Table 1 below:

[0146] Table 1 test results

[0147]

[0148] From Table 1, it can be seen that:

[0149] (1) Through Comparative Example 1 and Examples 1-17, the combination of cyclic non-coordinating solvents and linear non-coordinating solvents can adjust the solvation structure, so that the coordination type solvent is less decomposed in the later stage of the cycle, which significantly improves the capacity retention rate of the soft package battery at room temperature and high temperature, significantly improves the cycle stability and cycle life of the battery, and improves the high-temperature cycle performance of the battery.

[0150] (2) It can be found from Comparative Examples 2 and 3 and Examples 1-17 that fluorobenzene, which is also a cyclic non-coordinating solvent, is far less effective than fluorotetrahydropyran non-coordinating solvent in improving cycle. The reason is that the combination of cyclic non-coordinating solvents and linear non-coordinating solvents in the present application has stronger inertness to lithium metal, which can reduce the decomposition of the coordination type solvent with strong polarity in the first solvation sheath, effectively inhibit the decomposition of the coordination type solvent, realize uniform deposition of metal lithium dendrites, improve the stability of the electrolyte, and thus more adapt to the irreversible consumption of the electrolyte caused by the strong reduction activity of the negative electrode.

[0151] (3) The high-temperature storage gas production of Comparative Examples 1-3 and Examples 1-17 was compared. Comparative Example 1 used only a linear uncoordinating solvent; Comparative Example 2 used fluorobenzene in combination with a linear uncoordinating solvent; and Comparative Example 3 used m-fluorotoluene in combination with a linear uncoordinating solvent. In Examples 1-17, the high-temperature storage gas production of Example 5 and Example 10 was the lowest, 0.9 mL / Ah; and the high-temperature storage gas production of Example 6 was the highest, 2.7 mL / Ah. Compared with Example 5 and Example 10, the high-temperature storage gas production of Comparative Example 1 was 3.8 times that of Example 5 and Example 10, the high-temperature storage gas production of Comparative Example 2 was 6.6 times that of Example 5 and Example 10, and the high-temperature storage gas production of Comparative Example 3 was 10.2 times that of Example 5 and Example 10. Compared with Example 6, the high-temperature storage gas production of Comparative Example 1 was 1.3 times that of Example 6, the high-temperature storage gas production of Comparative Example 2 was 2.2 times that of Example 6, and the high-temperature storage gas production of Comparative Example 3 was 3.4 times that of Example 5 and Example 10. From the experimental results, it can be seen that in Examples 1-17 of the present application, the high-temperature storage gas production inhibiting effect of the cyclic uncoordinating solvent used is obvious, and the cyclic process of the lithium secondary battery can be inhibited to produce gas, which can significantly improve the cycle stability, safety and cycle life of the battery.

[0152] The above only describes the embodiments of the present application and is not used to limit the protection scope of the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An electrolyte comprising a lithium salt, an organic solvent, characterized in that, The organic solvent includes a cyclic non-coordinating solvent represented by at least one of compounds 1 to 11; The organic solvent further includes a linear non-coordinating solvent, the linear non-coordinating solvent including any one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, 1-(1,1,2,2-tetrafluoroethoxy)propane, 2-methyl-1-(1,1,2,2-tetrafluoroethoxy)propane, bis(2,2,2-trifluoroethyl) ether, tris(trifluoroethoxy)methane, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 2,2,2-trifluoroethyl-1,1,2,3,3,3-hexafluoropropyl ether, dichloromethane, hexafluoroisopropyl methyl ether, n-hexane, 2H,3H-decafluoropentane, and methyl nonafluorobutyl ether; The sum of the mass percentages of the linear non-coordinating solvent and the cyclic non-coordinating solvent is 35.5%-84.9% based on the total mass of the electrolyte, and the molar ratio of the linear non-coordinating solvent to the cyclic non-coordinating solvent is (1-3):(1-2).

2. The electrolyte according to claim 1, characterized in that, The organic solvent further includes a coordinating solvent, the coordinating solvent including any one or more of ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,2-diethoxyethane, acetonitrile, trimethyl phosphate, sulfolane, tetrahydrofuran, 1,4-dioxane, 1,3-dioxolane, dimethyl sulfite, methyl ethyl carbonate, vinyl carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, and methyl propyl carbonate; The lithium salt includes any one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium hexafluoroaluminate, lithium tetrafluoroborate, lithium fluorosulfate, lithium nitrate, lithium trifluoromethanesulfonate, and lithium perchlorate; The electrolyte further includes an additive, the additive including any one or more of vinylene carbonate, 1,3-propane sultone, fluoroethylene carbonate, vinylidene ethyl sulfate, vinyl sulfate, methylene methane disulfonate, vinylene vinyl ethyl sulfate, tris(trimethylsilyl) phosphate, and tris(trimethylsilyl) borate.

3. The electrolyte according to claim 2, characterized in that, The linear non-coordinating solvent includes any one or both of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether; The coordinating solvent includes any one or both of ethylene glycol dimethyl ether and triethylene glycol dimethyl ether; The lithium salt includes any one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium hexafluorophosphate, and lithium tetrafluoroborate; The additive includes any one of vinylene carbonate and 1,3-propane sultone.

4. The electrolyte of claim 2, wherein The mass percentage of the lithium salt is 5%-35% based on the total mass of the electrolyte; And / or, the mass percentage of the additive is 0.1%-4.5% based on the total mass of the electrolyte.

5. The method of claim 1-4, wherein the electrolyte is prepared by adding the electrolyte components to the solvent and stirring the mixture at a temperature of 20-30°C until the electrolyte is formed. The method comprises the following steps: S1, under the protection of inert gas, a coordination solvent is added into a configuration container, then a lithium salt is added into the configuration container and mixed uniformly; S2, a linear non-coordination solvent and a cyclic non-coordination solvent are added into the configuration container and mixed uniformly; S3, an additive is added into the configuration container and mixed uniformly to obtain an electrolyte.

6. A lithium secondary battery characterized by comprising: The electrolyte prepared by the method in claim 5 is also provided.

Images