CN115832434A - Lithium ion battery electrolyte and lithium ion battery containing same - Google Patents

Abstract

The invention provides a lithium ion battery electrolyte and a lithium ion battery containing the same, and belongs to the technical field of lithium ion batteries. The lithium ion battery electrolyte comprises a lithium salt, a solvent and an additive part, wherein the additive part contains difluorophenyl phosphate and unsaturated isocyanurate. Through the combined use of the two additives, the impedance of the battery can not be greatly increased while the positive terminal is protected, and the battery is ensured to have high-temperature storage stability without deterioration of the cycle performance and the like of the battery.

Description

Lithium ion battery electrolyte and lithium ion battery containing same

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a lithium ion battery electrolyte and a lithium ion battery containing the same.

Background

With the increasing requirements of people on battery endurance and application environment, the lithium ion battery anode and cathode materials continuously break through theoretical limitations. Higher demands are also put forward on the change of the electrolyte aiming at the improvement of voltage and nickel content, the doping of different anode materials, the addition of lithium supplement additives and the like. How to reduce the oxidative decomposition of the electrolyte material under the catalysis of the anode and in a high-voltage (high-oxidation) environment is an effective way for improving the performances of the lithium ion battery such as cycle, high-temperature storage and the like at present.

The unsaturated compound is an effective additive for protecting the positive electrode. For example, patent CN201710297453.9 discloses tris (allyl) phosphate and tris (propargyl) phosphate, the double bond of which can effectively improve the HOMO level of the additive, and is more easily oxidized and polymerized at the positive electrode to form a protective layer; thereby suppressing decomposition of the electrolyte component while suppressing dissolution of the positive electrode material itself. Some of the other ingredients disclosed in this patent, such as ethoxypentafluorophosphazene, ethylene carbonate, etc., also have similar properties.

The introduction of unsaturated bonds can improve the HOMO energy level and reduce the LUMO energy level, so that the HOMO energy level can be reduced more easily at the negative electrode and deposited on the surface of the negative electrode to become a component of an SEI film. The excellent SEI film can inhibit the further reduction and decomposition of electrolyte components, reduce the consumption of active Li, inhibit the thickening and the impedance increase of the SEI film, and has important significance on improving the battery capacity. However, the SEI film formed by the conventional carbon-carbon double bond polymerization is lack of introduction of lone pair electrons of heteroatoms or defects, and often has higher internal resistance, so that the cycle performance of the battery is reduced.

In the fluorine-containing compound, the strong electronegativity of fluorine atoms can reduce the LUMO energy level of the compound, so that the fluorine-containing compound is easier to reduce at a negative electrode to form an inorganic component such as LiF, and the impedance of the negative electrode is effectively reduced. Therefore, developing an electrolyte capable of forming an excellent CEI film and an SEI film, and simultaneously protecting the positive electrode and the negative electrode and controlling the impedance is a research focus in the technical field of lithium ion batteries at present.

Disclosure of Invention

The invention provides a lithium ion battery electrolyte and a lithium ion battery containing the same, aiming at the problems in the prior art, and the lithium ion battery with good high-temperature storage performance and good cycle performance can be obtained by better coordinating the relation between the anode protection and the cathode impedance.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

as a first aspect of the present invention, there is provided a lithium ion battery electrolyte comprising a lithium salt, a solvent, an additive a, and an additive B. The additive A is selected from at least one of compounds shown as the following formula (I):

wherein n represents an integer of 1 to 5;

the additive B is selected from at least one of the compounds shown in the following formula (II):

wherein R is ₁ 、R ₂ 、R ₃ Each independently represents a fluorine atom, a C1-C10 alkyl group, a C2-C10 alkenyl group, a C2-C10 alkynyl group, a C1-C10 alkoxy group, a C1-C10 fluoroalkyl group, a C1-C10 fluoroalkoxy group, a C2-C10 cyanoalkyl group, or a C2-C10 isocyanatoalkyl group; and R is ₁ 、R ₂ 、R ₃ At least one of the groups contains an unsaturated bond, such as a carbon-carbon double bond, a carbon-carbon triple bond, an isocyanate bond, or the like.

As a second aspect of the invention, the invention provides the use of the above-described electrolyte in the preparation of a lithium ion battery.

As a third aspect of the present invention, the present invention provides a lithium ion battery, comprising a positive electrode plate, a negative electrode plate, a separator and the above electrolyte.

Compared with the prior art, the invention has the following beneficial effects:

in the electrolyte disclosed by the invention, the anode low-impedance film-forming additive containing difluorophenylphosphate and the isocyanurate compound containing unsaturated bonds are matched, so that the components of an SEI film of the cathode can be optimized while the anode plate is protected, the internal resistance is kept in a controllable range, the high-temperature storage performance of the lithium ion battery is improved, and the cycle stability of the lithium ion battery is ensured.

Detailed Description

The lithium ion battery electrolyte and the lithium ion battery of the present invention will be described in detail below.

As a first aspect of the present invention, there is provided a lithium ion battery electrolyte comprising a lithium salt, a solvent, an additive a, and an additive B. The additive A is selected from at least one of compounds shown as the following formula I:

wherein n represents an integer of 1 to 5; specifically, n is 1,2,3, 4 or 5;

the additive B is selected from at least one of the compounds shown in the following formula II:

wherein R is ₁ 、R ₂ 、R ₃ Each independently represents a fluorine atom, a C1-C10 alkyl group, a C2-C10 alkenyl group, a C2-C10 alkynyl group, a C1-C10 alkoxy group, a C1-C10 fluoroalkyl group, a C1-C10 fluoroalkoxy group, a C2-C10 cyanoalkyl group, or a C2-C10 isocyanatoalkyl group; and R is ₁ 、R ₂ 、R ₃ At least one of the groups contains an unsaturated bond, such as a carbon-carbon double bond, a carbon-carbon triple bond, an isocyanate bond, or the like.

As an embodiment of the present invention, R ₁ 、R ₂ 、R ₃ Each independently represents a fluorine atom, a C1-C6 alkyl group, a C2-C6 alkenyl group, a C2-C6 alkynyl group, a C1-C6 alkoxy group, a C1-C6 fluoroalkyl group, a C1-C6 fluoroalkoxy group, a C2-C6 cyano groupAlkyl, isocyanatoalkyl of C2-C6; and R is ₁ 、R ₂ 、R ₃ At least one of the groups contains an unsaturated bond, such as a carbon-carbon double bond, a carbon-carbon triple bond, an isocyanate bond, or the like.

As an embodiment of the present invention, R ₁ 、R ₂ 、R ₃ Independently represent a fluorine atom, a C1-C3 alkyl group, a C2-C3 alkenyl group, a C2-C3 alkynyl group, a C1-C3 alkoxy group, a C1-C3 fluoroalkyl group, a C1-C3 fluoroalkoxy group, a C2-C3 cyanoalkyl group, a C2-C3 isocyanatoalkyl group; and R is ₁ 、R ₂ 、R ₃ At least one of the groups contains an unsaturated bond, such as a carbon-carbon double bond, a carbon-carbon triple bond, an isocyanate bond, or the like.

As an embodiment of the present invention, R ₁ 、R ₂ 、R ₃ Each independently represents a fluorine atom, a methyl group, an ethyl group, a vinyl group, an allyl group, an alkynyl group, a propargyl group, a methoxy group, an ethoxy group, a cyanomethyl group, a cyanoethyl group, or a cyanopropyl group; and R is ₁ 、R ₂ 、R ₃ At least one group contains an unsaturated bond, such as a carbon-carbon double bond, a carbon-carbon triple bond, an isocyanate bond, or the like.

As an embodiment of the present invention, the additive a is selected from at least one of the following formulas (1) to (6):

as an embodiment of the present invention, the additive B is selected from at least one of the following formulas (7) to (9):

the additive A is a difluorophenyl phosphate compound, and has good wettability on an interface; and the difluorophosphate group of the lithium-ion battery has the possibility of reacting to generate a lithium fluorophosphate component under the redox action, and has very low impedance in the lithium battery; the F-rich phenyl groups can be defluorinated to form an inorganic SEI film of lithium fluoride, further reducing the impedance. However, the SEI film formed by the material is mainly composed of inorganic components, and although the resistance can be reduced to a certain extent, the SEI film does not protect the surface of the electrode completely, and can cause continuous reaction of components such as solvents and the like with the electrode along with the progress of circulation, and particularly causes risks such as battery cycle deterioration, gas storage and the like under high temperature conditions. The additive B is an isocyanurate compound containing unsaturated bonds, has unsaturated bonds and a heterocyclic structure, has a lower LUMO energy level and a higher HOMO energy level, is easy to perform redox polymerization to form a compact protective film, can well protect an electrode under high-temperature storage and high voltage, and can inhibit electrode side reactions, battery gas generation and the like. However, such a dense protective film causes an increase in the internal resistance of the battery, and the cycle and low-temperature discharge properties are greatly affected. The additive A and the additive B have synergistic effect to form an SEI film compounded by organic components and inorganic components, so that the electrode is effectively protected, the rapid rise of the battery impedance is inhibited, and the performances of the battery such as high-temperature storage, cycle and the like are considered.

In the electrolyte of the invention, the additive A accounts for 0.1-10% of the electrolyte by mass percent, for example, 0.1-1%, 1-2%, 2-3%, 3-4%, 4-5%, 5-6%, 6-7%, 7-8%, 8-9%, 9-10% and any numerical value range in the interval; the addition amount of the additive A is preferably 0.3-3%; more preferably 1 to 3%. When the content of the additive A is too high, the inorganic components on the surface of the electrode are too much, so that the electrode is difficult to be effectively protected, and the side reaction of the electrolyte components is isolated; on the contrary, when the content of the additive a is too low, the inhibition effect on the increase in the impedance is not significant, and the cycle performance is still poor.

In the electrolyte of the invention, the additive B accounts for 0.1-5% of the electrolyte by mass percent, for example, 0.1-1%, 1-2%, 2-3%, 3-4%, 4-5% and any numerical value range in the interval; the addition amount of the additive B is preferably 0.3-2%; when the content of the additive B is too high, the SEI film on the surface of the electrode is too compact, the impedance is greatly increased, and although gas generation is effectively inhibited, the cycle performance and the discharge performance of the battery are deteriorated; on the contrary, when the content of the additive B is too low, effective protection of the electrode is difficult to achieve, and the battery capacity is easy to cause water jumping at the later stage of the cycle.

In the electrolyte of the invention, the mass ratio of the additive A to the additive B is 0.5. The cycle performance and the high-temperature storage effect can be further improved by the two under the appropriate adding proportion. If the relative content of the additive A is too high, the inorganic components on the surface of the electrode are too much, so that the electrode is difficult to be effectively protected, and finally, the circulation and high-temperature storage performance is poor; on the other hand, if the relative content of the additive a is too low, the battery impedance becomes high, and the battery gassing can be suppressed, but the battery cycle performance deteriorates seriously.

As an embodiment of the present invention, the electrolyte of the present invention may further optionally include other additives, and the kinds of the other additives may not be limited, and additives that are conventional in the art may be used. For example, one or a combination of more of Vinylene Carbonate (VC), vinyl sulfate (DTD), vinyl ethylene carbonate, fluoroethylene carbonate, methyl propargyl carbonate, ethyl propargyl carbonate, dipropargyl carbonate, maleic anhydride, succinic anhydride, 1,3-propanesultone, 1,4-butanesultone, methylene methanedisulfonate, lithium difluorobis (oxalate) phosphate, lithium bis (oxalate) borate, lithium tris (oxalate) phosphate, lithium difluorophosphate, and the like.

In the electrolyte of the present invention, the addition amount of other additives is 0 to 20% by mass, preferably 1 to 15% by mass of the electrolyte.

As an embodiment of the present invention, the lithium salt is selected from lithium hexafluorophosphate (LiPF) ₆ ) Lithium bis (fluorosulfonylimide) (LiFSI), lithium bis (trifluoromethyl) sulfonimide (LiTFSI), and lithium tetrafluoroborate (LiBF) ₄ ) One or more of; the total amount of the lithium salt accounts for 5-30% by mass of the electrolyte, and preferably 7-20% by mass of the electrolyte.

In one embodiment of the present invention, the solvent is one or more selected from the group consisting of chain carbonates, cyclic carbonates, carboxylic acid esters, chain fluorocarbons, cyclic fluorocarbons, and fluoroethers.

Furthermore, the chain carbonates mainly comprise one or more of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; the cyclic carbonates mainly comprise one or more of ethylene carbonate, vinylene carbonate and propylene carbonate; the carboxylic ester mainly comprises one or more of ethyl acetate, ethyl propionate, methyl propionate, propyl propionate, methyl butyrate and ethyl butyrate; the chain fluoro carbonate mainly comprises one or more of methyl trifluoroethyl carbonate, ethyl trifluoroethyl carbonate and bis (trifluoroethyl) carbonate; the cyclic fluoro carbonate mainly comprises one or more of fluoroethylene carbonate, trifluoromethyl ethylene carbonate, bis (trifluoromethyl) carbonate and trifluoroethyl ethylene carbonate; the fluorocarboxylic acid ester mainly comprises one or more of methyl difluoroacetate, ethyl difluoroacetate, difluoroethyl acetate, ethyl trifluoroacetate and trifluoroethyl acetate; the fluoroether mainly comprises one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, fluoromethyl-1,1,1,3,3,3-hexafluoroisopropyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, tetrafluoromethyl butyl ether, 4-trifluoromethylanisole, 1,1,2,3,3,3-hexafluoropropyl 2,2,2-trifluoroethyl ether;

furthermore, the total content of the solvent accounts for 50-95% by mass of the electrolyte, and preferably 70-90% by mass of the electrolyte.

As a second aspect of the invention, the invention provides the use of the above-described electrolyte in the preparation of a lithium ion battery. The lithium ion battery prepared by the electrolyte can protect the positive terminal, does not greatly increase the impedance of the battery, ensures the high-temperature storage stability of the battery, and does not deteriorate the cycle performance of the battery and the like.

As a third aspect of the present invention, the present invention provides a lithium ion battery, comprising a positive electrode plate, a negative electrode plate, a separator and the above electrolyte. The lithium ion battery may be prepared using methods known to those skilled in the art.

As an embodiment of the present invention, the positive electrode sheet includes a positive electrode current collector, a positive electrode active material, a conductive agent, and a binder;

the positive electrode current collector includes, but is not limited to, metal foils and the like, for example, aluminum foil and the like; the positive active material includes, but is not limited to, one or a combination of more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, and the like; the conductive agent includes but is not limited to conductive carbon black, conductive graphite, carbon fiber, single-arm carbon nanotube, multi-wall carbon nanotube, etc.; the binder includes, but is not limited to, styrene Butadiene Rubber (SBR), polyvinylidene fluoride (PVDF), polyacrylate (PAA), polyimide (PI), polytetrafluoroethylene (PTFE), and the like.

In a preferred embodiment, the positive electrode active material is LiNi _1-x-y-z Co _x Mn _y Al _z O ₂ Wherein: x is more than or equal to 0 and less than or equal to 1,0 and less than or equal to 1,0 and less than or equal to 1, and x + y + z is more than or equal to 0 and less than or equal to 1;

as an embodiment of the present invention, the negative electrode sheet includes a negative electrode current collector, a negative electrode active material, a conductive agent, and a binder;

the negative electrode current collector includes, but is not limited to, metal foils and the like, for example, copper foils and the like; the negative active material includes but is not limited to one or more of artificial graphite, natural graphite, composite graphite, graphene, mesophase microspheres, nano-silicon, silicon-carbon composite material, silica/carbon composite material and the like; the conductive agent includes but is not limited to conductive carbon black, conductive graphite, carbon fiber, single-arm carbon nanotube, multi-wall carbon nanotube, etc.; the binder includes, but is not limited to, styrene Butadiene Rubber (SBR), polyvinylidene fluoride (PVDF), polyacrylate (PAA), polyimide (PI), and the like.

As an embodiment of the present invention, the separator may be a separator conventionally used in the art for lithium ion batteries, including but not limited to polyethylene, polypropylene, polyvinylidene fluoride, etc., and a multi-layered composite film thereof.

The technical solutions of the present invention will be described clearly and completely by specific embodiments, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. In addition, the starting materials of the present invention are all common commercial products unless otherwise specified.

As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having," "contains" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

When an amount, concentration, or other value or parameter is expressed as a range, preferred range, or as a range of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted to include the ranges "1 to 4", "1 to 3", "1 to 2 and 4 to 5", "1 to 3 and 5", and the like. When a range of values is described herein, unless otherwise stated, the range is intended to include the endpoints thereof and all integers and fractions within the range.

The singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. "optional" or "any" means that the subsequently described event or events may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

The indefinite articles "a" and "an" preceding an element or component of the invention are not intended to limit the number requirement (i.e., the number of occurrences) of the element or component. Thus, "a" and "an" should be read to include one or at least one, and the singular form of an element or component also includes the plural unless the number clearly indicates the singular.

Further, the technical features of the embodiments of the present invention may be combined with each other as long as they do not conflict with each other.

Synthesis of Compounds

Synthesis of additive A:

76.6g (0.5 mol) of phosphorus oxychloride is added into a three-neck flask under the protection of nitrogen atmosphere, and the temperature is raised to 40 ℃; 46g (0.25 mol) of pentafluorophenol was added dropwise to the reaction mixture with stirring over a period of 30min. After the dropwise addition, the temperature was raised to 150 ℃ and the mixture was stirred under reflux for 12 hours. After the reaction is finished, distilling to remove unreacted phosphorus oxychloride to obtain a crude product of pentafluorophenyl dichlorophosphate.

The crude product was dissolved in acetonitrile, then 58g of dehydrated potassium fluoride reagent was added, the temperature was raised to 150 ℃ and the reaction was refluxed for 24h. And after the reaction is finished, carrying out reduced pressure distillation on the reaction liquid, collecting fractions at 110-140 ℃, and obtaining the compound shown in the formula (6) with the liquid phase analysis purity of more than 97%. And (3) synthesis of an additive B:

allyl alcohol (1.5 mol) was added to 100ml of water under a nitrogen atmosphere, the temperature was then raised to 60 ℃, isocyanuric acid (0.5 mol) was slowly added dropwise thereto under stirring, and the pH was adjusted to about 7. After the addition was complete, the temperature was raised to 80 ℃ and the reaction was refluxed for 12 hours. After the reaction was completed, the reaction product was cooled to 10 ℃ and ethanol and DMSO solvents were added, and solid salts were precipitated. After filtration, washing with acetone for several times, and then distilling under reduced pressure to obtain TAIC, i.e., the compound represented by formula (7).

The other compounds represented by additive B can be obtained by the same method by changing the kind and ratio of the alcohol.

Comparative example 1

The electrolyte is prepared by the following method: mixing Ethylene Carbonate (EC), diethyl carbonate (DEC) and Ethyl Methyl Carbonate (EMC) according to a volume ratio of 30/20/50 in a glove box, reducing the temperature to below 10 ℃, and then slowly adding lithium hexafluorophosphate to prepare a 1.1M lithium hexafluorophosphate solution; then, VC in a mass fraction of 0.5% and DTD in a mass fraction of 1% were added to the electrolytes, respectively, to obtain the electrolyte of comparative example 1.

The electrolyte of comparative example 1 was injected into a fully dried 4.3V NCM (nickel: cobalt: manganese = 6).

Comparative example 2

The comparative example 2 battery was prepared substantially identically to comparative example 1. Except that in the electrolyte of comparative example 2, compound (1) was added in a mass fraction of 1% in addition to VC and DTD.

Comparative example 3

The comparative example 3 cell was prepared substantially the same as comparative example 1. Except that in the electrolyte of comparative example 3, in addition to VC and DTD, compound (5) was added in a mass fraction of 1%.

Comparative example 4

The comparative example 4 cell was prepared substantially the same as comparative example 1. Except that in the electrolyte of comparative example 4, in addition to VC and DTD, compound (7) was added in a mass fraction of 0.3%.

Comparative example 5

The comparative example 5 cell was prepared substantially the same as comparative example 1. Except that in the electrolyte of comparative example 5, in addition to VC and DTD, compound (5) was added in a mass fraction of 4% and compound (7) was added in a mass fraction of 1%.

Comparative example 6

The comparative example 6 cell was prepared substantially the same as comparative example 1. Except that in the electrolyte of comparative example 5, in addition to VC and DTD, compound (5) was added in a mass fraction of 1% and compound (7) was added in a mass fraction of 2.5%.

Example 1

The example 1 cell was prepared substantially the same as in comparative example 1. Except that in the electrolyte of example 1, in addition to VC and DTD, compound (1) was added in a mass fraction of 1% and compound (7) was added in a mass fraction of 0.3%.

Example 2

The example 2 cell was prepared substantially the same as in comparative example 1. Except that in the electrolyte of example 2, in addition to VC and DTD, compound (2) was added in a mass fraction of 1% and compound (7) was added in a mass fraction of 0.3%.

Example 3

The example 3 cell was prepared substantially the same as comparative example 1. Except that in the electrolyte of example 3, in addition to VC and DTD, compound (3) was added at a mass fraction of 1% and compound (7) was added at a mass fraction of 0.3%.

Example 4

The example 4 cell was prepared substantially the same as comparative example 1. Except that in the electrolyte of example 4, in addition to VC and DTD, compound (4) was added at a mass fraction of 1% and compound (7) was added at a mass fraction of 0.3%.

Example 5

The example 5 battery was prepared substantially identically to comparative example 1. Except that in the electrolyte of example 5, in addition to VC and DTD, compound (5) was added in a mass fraction of 1% and compound (7) was added in a mass fraction of 0.3%.

Example 6

The example 6 battery was prepared substantially identically to comparative example 1. Except that in the electrolyte of example 6, in addition to VC and DTD, the compound (6) was added in a mass fraction of 1% and the compound (7) was added in a mass fraction of 0.3%.

Example 7

The example 7 cell was prepared substantially the same as in comparative example 1. Except that in the electrolyte of example 7, in addition to VC and DTD, the compound (1) was added in a mass fraction of 1% and the compound (8) was added in a mass fraction of 0.3%.

Example 8

The example 8 cell was prepared substantially the same as comparative example 1. Except that in the electrolyte of example 8, in addition to VC and DTD, compound (1) was added in a mass fraction of 1% and compound (9) was added in a mass fraction of 0.3%.

Example 9

The example 9 cell was prepared substantially the same as comparative example 1. Except that in the electrolyte of example 9, in addition to VC and DTD, compound (1) was added in a mass fraction of 1% and compound (7) was added in a mass fraction of 0.5%.

Example 10

The example 10 cell was prepared substantially the same as in comparative example 1. Except that in the electrolyte of example 10, in addition to VC and DTD, compound (5) was added in a mass fraction of 1% and compound (7) was added in a mass fraction of 0.5%.

Example 11

The example 11 battery was prepared substantially identically to comparative example 1. Except that in the electrolyte of example 11, in addition to VC and DTD, compound (5) was added in a mass fraction of 1% and compound (7) was added in a mass fraction of 1%.

Example 12

The example 12 cell was prepared substantially the same as comparative example 1. Except that in the electrolyte of example 12, in addition to VC and DTD, compound (5) was added in a mass fraction of 1% and compound (7) was added in a mass fraction of 2%.

Example 13

The example 13 cell was prepared substantially the same as comparative example 1. Except that in the electrolyte of example 13, in addition to VC and DTD, compound (5) was added in a mass fraction of 2% and compound (7) was added in a mass fraction of 1%.

Example 14

The example 14 cell was prepared substantially identically to comparative example 1. Except that in the electrolyte of example 14, in addition to VC and DTD, compound (5) was added in a mass fraction of 3% and compound (7) was added in a mass fraction of 1%.

Example 15

The example 15 cell was prepared substantially the same as example 10. Except that in the electrolyte of example 15, the lithium salt was selected from 1.1M LiPF ₆ LiPF changed to 0.9M ₆ 0.2M LiFSI was added.

Example 16

The example 16 cell was prepared substantially the same as example 10. Except that in the electrolyte of example 16, the lithium salt was selected from 1.1M LiPF ₆ LiPF changed to 0.7M ₆ 0.4M LiFSI was added.

The main components and the proportions of the various proportions and examples are shown in Table 1.

TABLE 1 Components and contents of electrolytes of comparative examples and examples

Lithium ion battery performance testing

Normal temperature cycle performance: charging the prepared lithium ion battery to 4.3V at a constant current and a constant voltage at 1C under the condition of normal temperature (25 ℃), then discharging to 2.8V under the constant current condition at 1C, and recording as a cycle, wherein the discharge capacity of the first cycle is recorded as DC ₁ (ii) a After 1000 cycles of such charge and discharge, the discharge capacity at 1000 th cycle was recorded as DC ₁₀₀₀ The capacity retention after the 1000 th cycle was calculated as follows:

high temperature cycle performance at 45 ℃: charging the prepared lithium ion battery to 4.3V at a constant current and a constant voltage of 1C under the condition of high temperature (45 ℃), then discharging to 2.8V under the condition of the constant current of 1C, and recording as a cycle, wherein the discharge capacity of the first cycle is recorded as DC ₁ (ii) a Thus, it is possible to provideAfter 800 cycles of charge and discharge, the discharge capacity at 800 th cycle was recorded as DC ₈₀₀ The capacity retention after the 800 th cycle was calculated as follows:

storage performance at 60 ℃: under the condition of normal temperature (25 ℃), the lithium ion battery is charged and discharged by 1C/1C once, and the average thickness of the battery is recorded as d ₁ Then charging the battery to 4.3V under the condition of 1C constant current and constant voltage, and storing the lithium ion battery in a high-temperature oven at 60 ℃ for 15 days; after 15 days, the cell was removed and tested for thickness d ₂ The thickness change rate at 60 ℃ for 15 days was calculated as follows:

the results of the battery tests of comparative examples 1 to 6 and examples 1 to 16 are shown in table 2 below.

Table 2 results of cell performance test for each comparative example and example

The electrolyte simultaneously containing two additives, namely fluorophenyl difluorophosphate and unsaturated isocyanurate, disclosed by the invention endows the lithium ion battery with better performance.

From the test results, the conclusion can be summarized as follows:

the high-temperature storage thickness change rates of the comparative example 1, the comparative example 4 and the comparative example 6, the examples 1, 10, 11, 12 and the like show that the unsaturated isocyanurate can effectively improve the gas generation condition of the battery; however, the addition of either alone or in excess may result in rapid degradation of the cycling performance of the cell, possibly due to its higher impedance;

the results of comparative example 5, examples 11, 13 and 14 show that the unsaturated isocyanurate compound and the fluorophenyl difluorophosphate can effectively improve the cycle performance of the battery, and the gas generation is less during high-temperature storage, probably because the fluorine-containing additive can effectively relieve the impedance increase caused by the unsaturated isocyanurate, and is significant in regulating the SEI film of the negative electrode. However, it should be noted that, as the content exceeds 3%, the cycle performance is reduced, indicating that the content cannot be too high, resulting in organic and inorganic imbalance of the negative electrode SEI film;

the results of examples 1-6, examples 7-9 show the difference in performance between compounds of the same structure when used as additives; among them, the compounds (1), (5), (6) and (7) are more effective. However, from the comparison between examples 1 and 9 and examples 5 and 10, the trend of the addition amount of the additive to the performance is not the same, and the collocation between different additives and the amount between the additives need to be further adjusted;

the results of example 10, example 15 and example 16 show that the addition of LiFSI can further improve the cycle performance and the high-temperature storage effect on the basis of the original results, so that the additive combination has more potential application.

Finally, it should be noted that the above-mentioned contents are only used for illustrating the technical solutions of the present invention, and not for limiting the protection scope of the present invention, and that the simple modifications or equivalent substitutions of the technical solutions of the present invention by those of ordinary skill in the art can be made without departing from the spirit and scope of the technical solutions of the present invention.

Claims (10)

1. A lithium ion battery electrolyte comprising a lithium salt, a solvent, an additive a and an additive B, wherein the additive a is selected from at least one of the compounds represented by the following formula (I):

wherein n represents an integer of 1 to 5;

the additive B is selected from at least one of the compounds shown in the following formula (II):

wherein R is ₁ 、R ₂ 、R ₃ Each independently represents a fluorine atom, a C1-C10 alkyl group, a C2-C10 alkenyl group, a C2-C10 alkynyl group, a C1-C10 alkoxy group, a C1-C10 fluoroalkyl group, a C1-C10 fluoroalkoxy group, a C2-C10 cyanoalkyl group, or a C2-C10 isocyanatoalkyl group; and R is ₁ 、R ₂ 、R ₃ At least one of the groups contains an unsaturated bond.

2. The electrolyte of claim 1, wherein:

R ₁ 、R ₂ 、R ₃ each independently represents a fluorine atom, a C1-C6 alkyl group, a C2-C6 alkenyl group, a C2-C6 alkynyl group, a C1-C6 alkoxy group, a C1-C6 fluoroalkyl group, a C1-C6 fluoroalkoxy group, a C2-C6 cyanoalkyl group, or a C2-C6 isocyanatoalkyl group; and R is ₁ 、R ₂ 、R ₃ At least one group contains an unsaturated bond;

preferably, R ₁ 、R ₂ 、R ₃ Each independently represents a fluorine atom, a C1-C3 alkyl group, a C2-C3 alkenyl group, a C2-C3 alkynyl group, a C1-C3 alkoxy group, a C1-C3 fluoroalkyl group, a C1-C3 fluoroalkoxy group, a C2-C3 cyanoalkyl group, or a C2-C3 isocyanatoalkyl group; and R is ₁ 、R ₂ 、R ₃ At least one group contains an unsaturated bond;

further preferably, R ₁ 、R ₂ 、R ₃ Each independently represents a fluorine atom, a methyl group, an ethyl group, a vinyl group, an allyl group, an alkynyl group, a propargyl group, a methoxy group, an ethoxy group, a cyanomethyl group, a cyanoethyl group, or a cyanopropyl group; and R is ₁ 、R ₂ 、R ₃ At least one of the groups contains an unsaturated bond.

3. The electrolyte of claim 1, wherein:

the additive A is selected from at least one of the following formulas (1) to (6):

4. the electrolyte of claim 1, wherein:

the additive B is selected from at least one of the following formulas (7) to (9):

5. the electrolyte of any one of claims 1 to 4, wherein: the additive A accounts for 0.1-10% of the electrolyte by mass percent; preferably 0.3 to 3%; further preferably 1 to 3%;

the additive B accounts for 0.1-5% of the electrolyte by mass percent, and preferably 0.3-2%.

6. The electrolyte as claimed in any one of claims 1 to 4, wherein: the mass ratio of the additive A to the additive B is 0.5.

7. The electrolyte of claim 1, wherein: the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis (fluorosulfonyl) imide, lithium bis (trifluoromethyl) sulfonyl imide and lithium tetrafluoroborate.

8. The electrolyte of claim 1, wherein: the solvent is selected from one or more of chain carbonates, cyclic carbonates, carboxylic esters, chain fluorocarbons, cyclic fluorocarbons, fluorocarbons and fluoroethers.

9. Use of the electrolyte of any of claims 1-8 in the preparation of a lithium ion battery.

10. A lithium ion battery comprising a positive electrode tab, a negative electrode tab, a separator and the electrolyte of any one of claims 1-8;

preferably, the positive electrode plate comprises a positive electrode current collector, a positive electrode active material, a conductive agent and a binder; the negative pole piece comprises a negative pole current collector, a negative pole active substance, a conductive agent and a binder;

more preferably, the positive electrode active material is LiNi _1-x-y-z Co _x Mn _y Al _z O ₂ Wherein: x is more than or equal to 0 and less than or equal to 1,0 and less than or equal to 1,0 and less than or equal to 1, and x + y + z is more than or equal to 0 and less than or equal to 1; the negative active material is one or a combination of more than one of artificial graphite, natural graphite, composite graphite, graphene, mesophase microspheres, nano-silicon, a silicon-carbon composite material and a silicon oxide/carbon composite material.