WO2017152624A1

WO2017152624A1 - Electrolyte and lithium ion battery

Info

Publication number: WO2017152624A1
Application number: PCT/CN2016/101765
Authority: WO
Inventors: 石俊黎; 夏永高; 刘兆平; 杨光华
Original assignee: 中国科学院宁波材料技术与工程研究所
Priority date: 2016-03-09
Filing date: 2016-10-11
Publication date: 2017-09-14
Also published as: TW201733194A; TWI606626B; CN105552430A

Abstract

The invention provides an electrolyte comprising lithium salt, a non-aqueous solvent and a first additive, wherein the first additive is selected from compounds adopting a structure shown in a formula (I). An ionic liquid oligomer with an amphiphilic function is added into the electrolyte to serve as the first additive. This type of ionic liquid oligomer can be taken as a surfactant and can effectively improve the wettability of the electrolyte on a diaphragm and an electrode material when the adding amount is controlled within a certain composition, and the initial efficiency and the charge-discharge capacity of a lithium ion battery are further improved. As a matter of fact that an ionic liquid can be also taken as a solvent of the lithium salt, the solubility of the lithium salt cannot be affected by addition of the ionic liquid. Besides, a second additive is added while the first additive is added. The second additive can participate in formation of an interfacial film in charge-discharge processes of the battery, so that the stable interfacial film can be formed between the electrolyte and the electrode material, thereby avoiding a side reaction between the electrolyte and the electrode material, and further improving the cycle stability of the lithium ion battery.

Description

Electrolyte and lithium ion battery

The present application claims priority to Chinese Patent Application No. 201610132763.0, entitled "An Electrolyte and a Lithium Ion Battery", filed on March 9, 2016, the entire contents of which is incorporated herein by reference. in.

Technical field

The invention belongs to the technical field of lithium ion batteries, and in particular relates to an electrolyte and a lithium ion battery.

Background technique

Lithium-ion batteries have become one of the most attractive new high-energy batteries due to their high specific energy and long cycle life. In recent years, the development of battery technology, the application range of lithium-ion batteries has become more and more extensive. New application areas continue to impose new requirements on the performance of lithium batteries, such as higher energy density, better safety and so on. At present, in order to improve the energy density of lithium-ion batteries, researchers mainly develop high-capacity, high-voltage positive electrode materials, such as increasing the working voltage of lithium-cobalt composite oxide or developing high-voltage lithium-nickel-manganese composite oxide. Wait. A high-voltage positive electrode material represented by a new material such as lithium nickel manganese oxide (LiNi _0.5 Mn _1.5 O ₄ ) or lithium cobalt phosphate (LiCoPO ₄ ) can have a discharge voltage of up to 5 V. To this end, a high-voltage electrolyte matching this is developed. It is of great significance.

However, the conventional electrolyte solution composed of a carbonate solvent and lithium hexafluorophosphate (lithium salt concentration of 0.5 to 2 mol/L) is difficult to work stably in a 5V-type high-voltage lithium ion battery, mainly due to the carbonate solvent itself. The oxidation potential is relatively low, and oxidative decomposition occurs at 4.2 V or higher. At present, the high-pressure electrolyte widely studied mainly improves the performance of the conventional electrolyte by adding certain additives, and forms a passivation film by reacting the additive with the electrode material, especially the positive electrode material, to prevent oxidation of the carbonate solvent. Decomposes to ensure that the electrolyte works relatively stably inside the battery.

By increasing the lithium salt concentration to a certain level (high concentration electrolyte), a high solvation between the internal solvent of the electrolyte and lithium ions (Li ⁺ ) is formed, and the solvent component is charged with a certain positive charge, which can effectively improve The oxidation resistance of the solvent inside the electrolyte allows the electrolyte system to work stably in a high voltage system of 5 V (J. Am. Chem. Soc. 2014, 136, 5039-5046). However, such electrolytes still have certain disadvantages, such as poor wettability of the electrolyte with the separator and the electrode material, which limits the effective insertion/deintercalation of lithium ions in the electrode material, so that the lithium ion battery using the electrolyte is used. For the first time, the efficiency is low and the first discharge capacity is low.

Summary of the invention

In view of this, the technical problem to be solved by the present invention is to provide an electrolyte and a lithium ion battery, and the lithium ion battery prepared by the electrolyte provided by the invention has high first efficiency and first charge and discharge capacity.

The invention provides an electrolyte comprising a lithium salt, a non-aqueous solvent and a first additive;

The first additive is selected from the group consisting of compounds having the structure of Formula I:

R _{1 is} selected from C _x1 H _y1 , 1≤x ₁ ≤3, y ₁ ≥0;

R _{2 is} selected from C _x2 H _y2 O _z N _w , 2≤x ₂ ≤120, y ₂ ≥0, z≥0, w≥0;

X ^{- is} selected from the group consisting of PF ₆ ^- , BF ₄ ^- , ClO ₄ ^- , [N(SO ₂ F) ₂ ] ^- , [N(SO ₂ CF ₃ ) ₂ ] ^- , B(C ₂ O ₄ ) ₂ ^- , B (C ₂ F ₂ O ₄ ) ^- or PO ₂ F ₂ ^- .

Preferably, R _{1 is} selected from C _x1 H _y1 , 1≤x ₁ ≤2, and y ₁ >0;

R _{2 is} selected from C _x2 H _y2 O _z N _w , 2≤x ₂ ≤27, y ₂ >0, z≥0, w≥0;

X ^{- is} selected from BF ₄ ^- , [N(SO ₂ F) ₂ ] ^- or [N(SO ₂ CF ₃ ) ₂ ] ^- .

Preferably, the first additive is added in the electrolyte in an amount of 0.01% by weight to 20% by weight.

Preferably, a second additive is further included, the second additive being selected from the group consisting of a nitrile additive, a carbonate additive, a fluorocarbonate additive, an organophosphorus additive, a silicon-containing additive, a sulfur-containing additive, and a boron-containing additive.

Preferably, the second additive is acetonitrile, adiponitrile, succinonitrile, ethoxy (pentafluoro)cyclotriphosphazene, vinylene carbonate, ethylene carbonate, fluoroethylene carbonate, methyl (2,2,2-trifluoroethyl)carbonate, tris(2,2,2-trifluoroethyl)phosphite, triallyl phosphate, trimethyl phosphite, tris(trimethyl) Silicon based phosphite, allyloxytrimethylsilane, 1,3-propane sultone, propylene sulfite, dimethoyl methane, trifluoromethyl phenyl sulfide, trimethyl borate, three ( One or more of trimethylsilane) borate or tetramethyl borate.

Preferably, the second additive is added in the electrolyte in an amount of 0.01% by weight to 2% by weight.

Preferably, the lithium salt is selected from the group consisting of lithium hexafluorophosphate and its derivatives, lithium bis(fluorosulfonyl)imide and its derivatives, lithium bistrifluoromethanesulfonimide and its derivatives, lithium dioxalate borate and its derivatives , one of lithium difluorooxalate borate and its derivatives, lithium tetrafluoroborate and its derivatives, lithium perchlorate and its derivatives Or a variety.

Preferably, the concentration of the lithium salt in the electrolytic solution is from 3 to 4.5 mol/L.

Preferably, the nonaqueous solvent is selected from one or a mixture of two or more of a carbonate solvent, an ether solvent, a sulfone solvent, a nitrile solvent, a fluorocarbonate solvent or a fluoroether solvent.

Preferably, the carbonate solvent is at least ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). One type;

The ether solvent is tetrahydrofuran (THF), 2-methyltetrahydrofuran (2Me-THF), 1,3-dioxolane (DOL), dimethoxymethane (DMM), 1,2-dimethoxy At least one of ethane (DME) and diglyme (DG);

The sulfone solvent is at least one of dimethyl sulfoxide, diphenyl sulfoxide, thionyl chloride, sulfolane or dipropyl sulfone;

The nitrile solvent is at least one of acetonitrile, succinonitrile, and adiponitrile;

The fluorocarbonate-based solvent has the structure of Formula II or Formula III:

Wherein R1 to R4 are independently selected from C _x F _y H _z , 1≤x≤6, y>0, z≥0;

The fluoroether solvent has the structure of formula IV:

Wherein R5 to R6 are independently selected from C _m F _n H _t , 1 ≤ _m _≤ 6, n > 0, and t ≥ 0.

The present invention also provides a lithium ion battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, the electrolyte being selected from the electrolyte according to any one of claims 1 to 8.

Preferably, the material of the positive electrode is selected from a transition metal lithium intercalation compound, the material of the negative electrode is selected from a graphite material, and the separator is selected from any one of a porous polyolefin compound, cellulose or glass fiber.

In contrast to the prior art, the present invention provides an electrolyte comprising a lithium salt, a non-aqueous solvent and a first additive; the first additive being selected from the group consisting of compounds having the structure of Formula I:

R _{1 is} selected from C _x1 H _y1 , 1≤x ₁ ≤3, y ₁ ≥0; R _{2 is} selected from C _x2 H _y2 O _z N _w , 2≤x ₂ ≤120, y ₂ ≥0, z≥0, W≥0; X ^{- is} selected from PF ₆ ^- , BF ₄ ^- , ClO ₄ ^- , [N(SO ₂ F) ₂ ] ^- , [N(SO ₂ CF ₃ ) ₂ ] ^- , B(C ₂ O ₄ ) ₂ ^- , B(C ₂ F ₂ O ₄ ) ^- or PO ₂ F ₂ ^- . The present invention adds an amphiphilic ionic liquid oligomer as a first additive to the electrolyte. Since the ionic liquid oligomer can be used as a surfactant, when the addition amount is controlled to a certain composition, the wettability of the electrolyte to the separator and the electrode material can be effectively improved, thereby further improving the first efficiency of the lithium ion battery and Charge and discharge capacity. Since the ionic liquid can also act as a solvent for the lithium salt, its addition does not affect the solubility of the lithium salt. In addition, the second additive is added to the invention while the first additive is added. The second additive participates in the formation of the interface film (SEI film) during the charging and discharging process of the battery, so as to form a stable interface between the electrolyte and the electrode material. The membrane avoids side reactions between the two, thereby further improving the cycle stability of the lithium ion battery.

The results show that the first efficiency of the lithium ion battery prepared by the electrolyte provided by the invention is ≥82%, the first discharge capacity of 0.1C is ≥117mAh g ^-1 , and the number of cycles when the capacity is attenuated to 80% of the initial capacity is ≥205 times.

DRAWINGS

1 is a preparation flow of a first additive prepared in Example 1;

2 is a preparation flow of the first additive prepared in Example 2.

Detailed ways

R _{1 is} selected from C _x1 H _y1 , 1≤x ₁ ≤3, y ₁ ≥0;

In the present invention, an ionic liquid oligomer having an amphiphilic action is added to the electrolyte as a first additive. Since the ionic liquid oligomer can be used as a surfactant, when the addition amount is controlled to a certain composition, the wettability of the electrolyte to the separator and the electrode material can be effectively improved, thereby further improving the first efficiency of the lithium ion battery and Charge and discharge capacity. Since the ionic liquid can also act as a solvent for the lithium salt, its addition does not affect the solubility of the lithium salt.

In the present invention, the first additive is selected from the group consisting of compounds having the structure of formula I:

R _{1 is} selected from C _x1 H _y1 , 1≤x ₁ ≤3, y ₁ ≥0;

X ^{- is} selected from the group consisting of PF ₆ ^- , BF ₄ ^- , ClO ₄ ^- , [N(SO ₂ F) ₂ ] ^- , [N(SO ₂ CF ₃ ) ₂ ] ^- , B(C ₂ O ₄ ) ₂ ^- , B (C ₂ F ₂ O ₄ ) ^- or PO ₂ F ₂ ^- ;

Preferably, R _{1 is} selected from C _x1 H _y1 , 1≤x ₁ ≤2, and y ₁ >0;

Preferably, the first additive is selected from the group consisting of a compound having the structure of formula V, 1-methyl acetate-3-methylimidazolium bistrifluoromethylsulfonimide, 1-ethyl acetate-3-methyl Imidazole bistrifluoromethylsulfonimide, n-propyl acetate 1-methylimidazolium bistrifluoromethylsulfonimide, 1-methyl-p-methylbenzoate-3-methylimidazole Bis-trifluoromethylsulfonimide or ethyl 1-p-methylbenzoate-3-methylimidazolium bistrifluoromethylsulfonimide;

Wherein, in the formula V, n=3 or 4.

The source of the first additive in the present invention is not particularly limited, and may be a commercially available product or may be prepared by itself.

In the present invention, the amount of the first additive added in the electrolytic solution is preferably from 0.01% by weight to 20% by weight, more preferably from 0.1% by weight to 10% by weight. In some embodiments of the present invention, the first additive is added in an amount of 0.01 wt% in the electrolyte; in other embodiments of the invention, the first additive is added to the electrolyte in an amount of 0.05 wt%; In other embodiments of the invention, the first additive is added in an amount of 2 wt% in the electrolyte; in other embodiments of the invention, the first additive is in the electrolyte The addition amount is 5 wt%; in other embodiments of the invention, the first additive is added in an amount of 10 wt% in the electrolyte; in other embodiments of the invention, the first additive is in the electrolyte The amount added was 20% by weight.

Preferably, the electrolyte provided by the invention further comprises a second additive, which participates in the formation of the interface film (SEI film) during the charging and discharging process of the battery, so as to form a stable interface film between the electrolyte and the electrode material. To avoid side reactions between the two, thereby further improving the cycle stability of the lithium ion battery.

The second additive is selected from the group consisting of a nitrile additive, a carbonate additive, a fluorocarbonate additive, an organophosphorus additive, a silicon-containing additive, a sulfur-containing additive, and a boron-containing additive.

Preferred are acetonitrile, adiponitrile, succinonitrile, ethoxy (pentafluoro)cyclotriphosphazene, vinylene carbonate, ethylene carbonate, fluoroethylene carbonate, methyl (2, 2, 2- Trifluoroethyl)carbonate, tris(2,2,2-trifluoroethyl)phosphite, triallyl phosphate, trimethyl phosphite, tris(trimethylsilyl)phosphite, Allyloxytrimethylsilane, 1,3-propane sultone, propylene sulfite, dimethoyl methane, trifluoromethyl phenyl sulfide, trimethyl borate, tris(trimethylsilane) boric acid One or more of ester, tetramethyl borate.

The second additive is added in the electrolyte in an amount of 0.01% by weight to 2% by weight, preferably 0.1% by weight to 1.5% by weight. In some embodiments of the present invention, the second additive is added in the electrolyte in an amount of 0.01 wt%; in other embodiments of the invention, the second additive is added in the electrolyte in an amount of 0.05 In other embodiments of the invention, the second additive is added in an amount of 0.1 wt% in the electrolyte; in other embodiments of the invention, the second additive is in the electrolyte The addition amount is 0.5 wt%; in other embodiments of the invention, the second additive is added in an amount of 1 wt% in the electrolyte; in other embodiments of the invention, the second additive is electrolyzed The amount added in the liquid was 1.5% by weight; in still other embodiments of the present invention, the second additive was added in an amount of 2.0% by weight in the electrolytic solution.

In some embodiments of the invention, the electrolyte further comprises an inorganic additive, preferably lithium difluorooxalate borate (LiDFOB) and/or LiPO ₂ F ₂ .

In the present invention, the electrolyte further includes a lithium salt selected from lithium hexafluorophosphate and derivatives thereof, lithium bis(fluorosulfonyl)imide and derivatives thereof, lithium bistrifluoromethanesulfonimide And one or more of its derivatives, lithium oxalate borate and its derivatives, lithium difluorooxalate borate and its derivatives, lithium tetrafluoroborate and its derivatives, lithium perchlorate and its derivatives, preferably It is LiPF ₆ , LiFSI, LiTFSI, LiBOB, LiDFOB, LiBF ₄ , LiClO ₄ or LiPF ₆ .

In the electrolytic solution, the concentration of the lithium salt is preferably from 3 to 4.5 mol/L, more preferably from 3.5 to 4 mol/L.

The solvent used in the electrolytic solution of the present invention is a nonaqueous solvent. In the present invention, the nonaqueous solvent is selected from the group consisting of a carbonate solvent, an ether solvent, a sulfone solvent, a nitrile solvent, and a fluorocarbonate solvent. Or one or a mixture of two or more of fluoroether solvents.

Preferably, the carbonate solvent is selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). At least one

The ether solvent is preferably tetrahydrofuran (THF), 2-methyltetrahydrofuran (2Me-THF), 1,3-dioxocyclopentane (DOL), dimethoxymethane (DMM), 1,2-dimethyl At least one of oxyethane (DME) and diglyme (DG), more preferably selected from the group consisting of 1,2-dimethoxyethane (DME) and diglyme (DG) At least one type;

The sulfone solvent is preferably at least one of dimethyl sulfoxide, diphenyl sulfoxide, thionyl chloride, sulfolane or dipropyl sulfone, more preferably at least one of dimethyl sulfoxide and sulfolane;

The nitrile solvent is preferably at least one of acetonitrile, succinonitrile, and adiponitrile, and more preferably at least one of acetonitrile and succinonitrile;

Preferably, the fluorocarbonate-based solvent is selected from the group consisting of CH ₃ -OCOO-CH ₂ CF ₃ .

The fluoroether solvent has the structure of formula IV:

Wherein R5 to R6 are independently selected from C _m F _n H _t , 1≤m≤6, n>0, t≥0;

Preferably, the fluoroether solvent is selected from the group consisting of CF ₃ CFHCF ₂ -O-CH ₂ CF ₃ .

In some embodiments of the present invention, in the electrolyte, the lithium salt/nonaqueous solvent is selected from LiPF ₆ / dimethyl carbonate (DMC), wherein the concentration of the LiPF ₆ in the electrolyte is preferably It is 3 to 3.5 mol/L.

In still another embodiment of the present invention, in the electrolyte, the lithium salt/nonaqueous solvent is selected from the group consisting of LiPF ₆ / ethyl methyl carbonate (EMC), wherein the concentration of the LiPF ₆ in the electrolyte It is preferably 3 to 5 mol/L.

In still another embodiment of the present invention, in the electrolyte, the lithium salt/nonaqueous solvent is selected from the group consisting of LiPF ₆ / diethyl carbonate (DEC), wherein the concentration of the LiPF ₆ in the electrolyte It is preferably 3 to 5 mol/L.

In still another embodiment of the present invention, in the electrolyte, the lithium salt/nonaqueous solvent is selected from the group consisting of LiPF ₆ / fluorocarbonate solvents, wherein the concentration of the LiPF ₆ in the electrolyte is preferably It is 3 to 5 mol/L.

In still another embodiment of the present invention, in the electrolyte, the lithium salt/nonaqueous solvent is selected from the group consisting of LiPF ₆ /fluoroether solvents, wherein the concentration of the LiPF ₆ in the electrolyte is preferably 3 to 5 mol / L.

In still another embodiment of the present invention, in the electrolyte, the lithium salt/nonaqueous solvent is selected from lithium difluorooxalate borate LiDFOB/acetonitrile AN, wherein the lithium difluorooxalate borate LiDFOB is in the electrolyte The concentration in the mixture is preferably from 3.5 to 4.2 mol/L.

In still another embodiment of the present invention, in the electrolyte, the lithium salt/nonaqueous solvent is selected from lithium dioxalate borate LiBOB/acetonitrile AN, wherein the lithium dioxalate borate LiBOB is in the electrolyte The concentration is preferably 3.5 to 4.2 mol/L.

In still another embodiment of the present invention, in the electrolyte, the lithium salt/nonaqueous solvent is selected from the group consisting of LiTFSI/DMC, wherein the concentration of the LiTFSI in the electrolyte is preferably 4 to 5 mol/L.

In still another embodiment of the present invention, in the electrolyte, the lithium salt/nonaqueous solvent is selected from the group consisting of LiTFSI/ether, wherein the concentration of the LiTFSI in the electrolyte is preferably 4 to 5 mol/L. .

In still another embodiment of the present invention, in the electrolyte, the lithium salt/nonaqueous solvent is selected from the group consisting of LiTFSI/nitrile, wherein the concentration of the LiTFSI in the electrolyte is preferably 4 to 5 mol/L. .

In still another embodiment of the present invention, in the electrolyte, the lithium salt/nonaqueous solvent is selected from the group consisting of LiTFSI/sulfone, wherein the concentration of the LiTFSI in the electrolyte is preferably 4 to 5 mol/L. .

In still another embodiment of the present invention, in the electrolyte, the lithium salt/nonaqueous solvent is selected from the group consisting of LiFSI/DMC, wherein the concentration of the LiFSI in the electrolyte is preferably 4 to 5 mol/L.

In still another embodiment of the present invention, in the electrolyte, the lithium salt/nonaqueous solvent is selected from the group consisting of LiFSI/ether, wherein the concentration of the LiFSI in the electrolyte is preferably 4 to 5 mol/L. .

In still another embodiment of the present invention, in the electrolyte, the lithium salt/nonaqueous solvent is selected from the group consisting of LiFSI/nitrile, wherein the concentration of the LiFSI in the electrolyte is preferably 4 to 5 mol/L. .

In still another embodiment of the present invention, in the electrolyte, the lithium salt/nonaqueous solvent is selected from the group consisting of LiFSI/sulfone, wherein the concentration of the LiFSI in the electrolyte is preferably 4 to 5 mol/L. .

The invention also provides a preparation method of an electrolyte, comprising the following steps:

The lithium salt, the nonaqueous solvent, and the first additive are mixed and dissolved to obtain an electrolytic solution.

Preferably, the mixing further comprises a second additive.

The manner of the mixing of the present invention is not particularly limited, and a mixing method known to those skilled in the art may be used.

The present invention also provides a lithium ion battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, the electrolyte being selected from the electrolytes described above;

Preferably, the material of the positive electrode is selected from the group consisting of transition metal lithium intercalation compounds. In some embodiments of the present invention, the positive electrode material is selected from the group consisting of LiM _x Mn _2-x O ₄ , wherein 0≤x<2, M is a transition metal element, preferably, 0≤x≤1, M is selected from Ni, Co, Cs, Cr, Al or Bi.

In still other embodiments of the present invention, the positive electrode material is selected from the group consisting of xLi ₂ MnO ₃ -(1-x)LiNiCoMnO ₂ , wherein 0<x≤1, preferably, 0.2≤x≤0.71.

The material of the negative electrode is selected from a graphite material.

The separator is selected from any one of a porous polyolefin compound, cellulose or glass fiber.

The present invention adds an amphiphilic ionic liquid oligomer as a first additive to the electrolyte. Since the ionic liquid oligomer can be used as a surfactant, when the addition amount is controlled to a certain composition, the wettability of the electrolyte to the separator and the electrode material can be effectively improved, thereby further improving the first efficiency of the lithium ion battery and Charge and discharge capacity. Since the ionic liquid can also act as a solvent for the lithium salt, its addition does not affect the solubility of the lithium salt. In addition, the second additive is added to the invention while the first additive is added. The second additive participates in the formation of the interface film (SEI film) during the charging and discharging process of the battery, so as to form a stable interface between the electrolyte and the electrode material. The membrane avoids side reactions between the two, thereby further improving the cycle stability of the lithium ion battery.

In order to further understand the present invention, the electrolyte solution and the lithium ion battery provided by the present invention will be described below in conjunction with the examples, and the scope of the present invention is not limited by the following examples.

Example 1

The preparation of the first additive was carried out in accordance with the literature "New co-initiator initiated epichlorohydrin polymerization". (Gao Hejun et al., New Co-initiator Initiates Epichlorohydrin Polymerization, Chemistry and Adhesion 2007, 29, 182-192)

The use of Best Company to provide AR grade epichlorohydrin polymerization. 20 mL of isopropanol was added as a solvent to a three-necked flask equipped with a stir bar, and 1 mL of ethylene glycol was added as a starter, and 2 mL of boron trifluoride diethyl ether was used as a catalyst. In the case of an ice water bath, 3 mL of epichlorohydrin was slowly added dropwise using a dropping funnel, and after completion, it was washed with water to obtain an oligomer 1.

Dissolve the bromine-containing intermediate polymer in dimethyl sulfoxide (DMSO) and add N-ethylimidazole (Alfa Aesar, 99%), kept the solution at 80 ° C and stirred for 36 h. Subsequently, the mixed solution was precipitated in ethyl acetate, and the precipitate was dried under vacuum at 80 ° C for 24 hours to obtain an ionic liquid oligomer 1.

The ionic liquid oligomer 1 was dissolved in deionized (DI) water to obtain an ionic liquid oligomer 1 solution. Lithium bis(fluorosulfonyl)imide (LiFSI) (Shanghai Hezhan Chemical New Material Co., Ltd.) was dissolved in deionized water to obtain a LiFSI solution. The LiFSI solution was added dropwise to the ionic liquid oligomer 1 solution and stirred for 6 hours, and the prepared ionic liquid oligomer 2 was precipitated in deionized water, and the precipitate was dried under vacuum at 80 ° C for 24 hours to obtain a desired product. The preparation process is shown in FIG. 1 , and FIG. 1 is a preparation process of the first additive prepared in Example 1.

Example 2

The preparation of the first additive was carried out in accordance with the method provided in the document "Journal of Membrane Science 2016, 499, 462-469".

A phenolic epoxy resin (PNE 177, Changchun Plastic, average molecular weight 1600 g ^-1 ) was precipitated with chloroform and n-hexane before use. Subsequently, the purified novolac epoxy resin was dissolved in chloroform (tedia, 99.9%) and the solution was cooled in an ice bath. Hydrobromide HBr was then slowly added to the solution and stirred for 6 hours to obtain a reaction mixture. Thereafter, the reaction mixture was washed with water to remove unreacted hydrobromic acid, and then the solvent was removed using a rotary evaporator to obtain a bromine-containing intermediate oligomer. The bromine-containing intermediate polymer was dissolved in dimethyl sulfoxide (DMSO), N-methylimidazole (Alfa Aesar, 99%) was added, the solution temperature was maintained at 80 ° C, and stirred for 36 h. Subsequently, the mixed solution was precipitated in ethyl acetate, and the precipitate was dried under vacuum at 80 ° C for 24 hours to obtain an ionic liquid oligomer 3.

The ionic liquid oligomer 1 was dissolved in deionized (DI) water to obtain an ionic liquid oligomer 1 solution. Lithium fluorosulfonate (LiTFSI) (Solvay) was dissolved in deionized water to obtain a LiTFSI solution. The LiTFSI solution was added dropwise to the ionic liquid oligomer 1 solution and stirred for 6 hours, and the prepared ionic liquid oligomer 4 was precipitated in deionized water, and the precipitate was dried under vacuum at 80 ° C for 24 hours to obtain a desired product. The preparation process is shown in FIG. 2, and FIG. 2 is a preparation process of the first additive prepared in Example 2.

Comparative example 1

The commercial high-voltage electrolyte 3015A provided by Cathay Huarong is the comparative example 1. The basic composition of the electrolyte is 1mol/L LiPF ₆ and ethylene carbonate (EC) and dimethyl carbonate (DMC), of which two solvents The volume ratio is 3:7 (as shown in Table 1).

Performance test: 1 mL of electrolyte was added to an iron shell with a solvent of 2 mL, and flammability test was performed using an open flame ignition. The contact angle of the electrolyte with the separator was measured using a contact angle meter (Dataphysics, OCA 20, Germany), the amount of the electrolyte was 1 μL, and the measurement temperature was 25 °C. An 18650 battery using LiNi _0.5 Mn _1.5 O ₄ as a positive electrode material and graphite as a negative electrode material was tested for the first time efficiency at 25 ° C, the first discharge capacity, and the number of cycles when the capacity was attenuated to 80% of the initial capacity. The test results are shown in Table 2.

Comparative example 2:

The electrolyte composition was 2.8 mol/L LiPF ₆ and dimethyl carbonate (DMC). After the solvent was removed by molecular sieves, the electrolyte was prepared in the glove box according to the above ratio (as shown in Table 1).

Performance test: 1 mL of electrolyte was added to an iron shell with a solvent of 2 mL, and flammability test was performed using an open flame ignition. The contact angle of the electrolyte with the separator (Celgard 2500) was measured using a contact angle meter (Dataphysics, OCA 20, Germany), the amount of the electrolyte was 1 μL, and the measurement temperature was 25 °C. An 18650 battery using LiNi _0.5 Mn _1.5 O ₄ as a positive electrode material and graphite as a negative electrode material was tested for the first time efficiency at 25 ° C, the first discharge capacity, and the number of cycles when the capacity was attenuated to 80% of the initial capacity. The test results are shown in Table 2.

Example 3

The composition of the electrolytic solution was 2.8 mol/L LiPF ₆ and dimethyl carbonate (DMC), and the piperidine-based ionic liquid oligomer 2 prepared in Example 1 having a mass content of 0.05% (as shown in Table 1).

After the solvent was removed by a molecular sieve, the electrolyte was prepared in a glove box according to the formulation ratio of Table 1.

Performance test: 1 mL of electrolyte was added to an iron shell with a solvent of 2 mL, and flammability test was performed using an open flame ignition. The contact angle of the electrolyte with the separator was measured using a contact angle meter (Dataphysics, OCA 20, Germany), the amount of the electrolyte was 1 μL, and the measurement temperature was 25 °C. When using LiNi _0.5 Mn _1.5 O ₄ as the positive electrode material, the separator is polyethylene (PE), and the graphite is the negative electrode material of 18650 battery, the first efficiency of the test battery at 25 ° C, the first discharge capacity, the capacity decay to 80% of the initial capacity The number of cycles. The test results are shown in Table 2.

Example 4

The electrolyte composition is shown in Table 1. The composition of the electrolyte was: 3 mol/L LiFSI and ethyl methyl carbonate (EMC), and acetonitrile having a mass content of 0.01% (as shown in Table 1).

After the solvent was removed by using a molecular sieve, the electrolyte was prepared in a glove box according to the above ratio.

Performance test: 1 mL of electrolyte was added to a 2 mL iron shell, and flammability test was performed using an open flame ignition. The contact angle of the electrolyte with the separator was measured using a contact angle meter (Dataphysics, OCA 20, Germany), the amount of the electrolyte was 1 μL, and the measurement temperature was 25 °C. An 18650 battery using LiNi _0.5 Mn _1.5 O ₄ as a positive electrode material, a separator of polyethylene (PE) and graphite as a negative electrode material, the first time efficiency of the test cell at 25 ° C, and the number of cycles when the capacity was attenuated to 80% of the initial capacity. The test results are shown in Table 2.

Example 5

The electrolyte composition is shown in Table 1. The composition of the electrolyte was: 4.5 mol/L LiBOB and fluorocarbonate CH ₃ -OCOO-CH ₂ CF ₃ , the ionic liquid polymer 4 prepared in Example 2 and the fluorine content of 0.01% by mass in a mass content of 10%. Ester (as shown in Table 1).

Performance test: 1 mL of electrolyte was added to an iron shell with a solvent of 2 mL, and flammability test was performed using an open flame ignition. The contact angle of the electrolyte with the separator was measured using a contact angle meter (Dataphysics, OCA 20, Germany), the amount of the electrolyte was 1 μL, and the measurement temperature was 25 °C. An 18650 battery using LiNi _0.5 Mn _1.5 O ₄ as a positive electrode material, a separator of polyethylene (PE) and graphite as a negative electrode material, the first time efficiency of the test cell at 25 ° C, and the number of cycles when the capacity was attenuated to 80% of the initial capacity. The test results are shown in Table 2.

Examples 6-15

See Table 1 for the electrolyte composition of Examples 6-15, and the preparation method of piperidine ionic liquids. References (Feng Lu et al. Determination and analysis of conductivity of five new synthetic ester-substituted imidazole ionic liquids, Journal of Chemical Industry and Engineering , 2015, 66 (S2), 466-472).

Performance test: 1 mL of electrolyte was added to an iron shell with a solvent of 2 mL, and flammability test was performed using an open flame ignition. The contact angle of the electrolyte with the separator was measured using a contact angle meter (Dataphysics, OCA 20, Germany), the amount of the electrolyte was 1 μL, and the measurement temperature was 25 °C. An 18650 battery using LiNi _0.5 Mn _1.5 O ₄ as a positive electrode material, a separator of polyethylene (PE) and graphite as a negative electrode material, the first time efficiency of the test cell at 25 ° C, and the number of cycles when the capacity was attenuated to 80% of the initial capacity. See Table 2 for performance data.

Table 1 Comparative Example and Electrolyte Composition of the Examples

Table 2 Performance test results of lithium ion batteries

The above description is only a preferred embodiment of the present invention, and it should be noted that those skilled in the art can also make several improvements and retouchings without departing from the principles of the present invention. It should be considered as the scope of protection of the present invention.

Claims

An electrolyte characterized by comprising a lithium salt, a nonaqueous solvent and a first additive;

The first additive is selected from the group consisting of compounds having the structure of Formula I:

R 1 is selected from C x1 H y1 , 1≤x 1 ≤3, y 1 ≥0;

R 2 is selected from C x2 H y2 O z N w , 2≤x 2 ≤120, y 2 ≥0, z≥0, w≥0;

X - is selected from PF 6 - , BF 4 - ; ClO 4 - , [N(SO 2 F) 2 ] - , [N(SO 2 CF 3 ) 2 ] - , B(C 2 O 4 ) 2 - , B (C 2 F 2 O 4 ) - or PO 2 F 2 - .
The electrolyte according to claim 1, wherein R 1 is selected from the group consisting of C x1 H y1 , 1 ≤ x 1 ≤ 2, and y 1 >0;

R 2 is selected from C x2 H y2 O z N w , 2≤x 2 ≤27, y 2 >0, z≥0, w≥0;

X - is selected from BF 4 - , [N(SO 2 F) 2 ] - or [N(SO 2 CF 3 ) 2 ] - .
The electrolytic solution according to claim 1, wherein the first additive is added in an amount of from 0.01% by weight to 20% by weight in the electrolytic solution.
The electrolyte according to claim 1, further comprising a second additive selected from the group consisting of a nitrile additive, a carbonate additive, a fluorocarbonate additive, an organophosphorus additive, and a silicon-containing additive One or more of an additive, a sulfur-containing additive, and a boron-containing additive.
The electrolyte according to claim 4, wherein the second additive is acetonitrile, adiponitrile, succinonitrile, ethoxy (pentafluoro)cyclotriphosphazene, vinylene carbonate, ethylene carbonate Ethyl ester, fluoroethylene carbonate, methyl (2,2,2-trifluoroethyl) carbonate, tris(2,2,2-trifluoroethyl)phosphite, triallyl phosphate, Trimethyl phosphite, tris(trimethylsilyl)phosphite, allyloxytrimethylsilane, 1,3-propane sultone, propylene sulfite, dimethylsulfonyl methane, trifluoromethyl One or more of phenyl sulfide, trimethyl borate, tris(trimethylsilane) borate, tetramethyl borate.
The electrolytic solution according to claim 1, wherein the second additive is added in an amount of from 0.01% by weight to 2% by weight in the electrolytic solution.
The electrolyte according to claim 1, wherein said lithium salt is selected from the group consisting of hexafluorophosphate Lithium and its derivatives, lithium bis(fluorosulfonyl)imide and its derivatives, lithium bistrifluoromethanesulfonimide and its derivatives, lithium dioxalate borate and its derivatives, lithium difluorooxalate borate and One or more of a derivative, lithium tetrafluoroborate and a derivative thereof, lithium perchlorate and a derivative thereof.
The electrolytic solution according to claim 1, wherein the concentration of the lithium salt in the electrolytic solution is from 3 to 4.5 mol/L.
The electrolytic solution according to claim 1, wherein the nonaqueous solvent is selected from the group consisting of a carbonate solvent, an ether solvent, a sulfone solvent, a nitrile solvent, a fluorocarbonate solvent or a fluoroether solvent. One or a mixture of two or more.
The electrolyte solution according to claim 9, wherein the carbonate solvent is at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate;

The ether solvent is at least one of tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxocyclopentane, dimethoxymethane, 1,2-dimethoxyethane and diglyme. ;

The sulfone solvent is at least one of dimethyl sulfoxide, diphenyl sulfoxide, thionyl chloride, sulfolane or dipropyl sulfone;

The nitrile solvent is at least one of acetonitrile, succinonitrile, and adiponitrile;

The fluorocarbonate-based solvent has the structure of Formula II or Formula III:

Wherein R1 to R4 are independently selected from C x F y H z , 1≤x≤6, y>0, z≥0;

The fluoroether solvent has the structure of formula IV:

Wherein R5 to R6 are independently selected from C m F n H t , 1 ≤ m ≤ 6, n > 0, and t ≥ 0.
A lithium ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, the electrolyte being selected from the electrolytes according to any one of claims 1 to 10.
The lithium ion battery according to claim 11, wherein the material of the positive electrode is selected from the group consisting of a transition metal lithium intercalation compound, the material of the negative electrode is selected from a graphite material, and the separator is selected from the group consisting of porous poly Any of an olefin compound, cellulose or glass fiber.