CN106953118B - Non-aqueous electrolyte for lithium ion battery and lithium ion battery - Google Patents

Non-aqueous electrolyte for lithium ion battery and lithium ion battery Download PDF

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CN106953118B
CN106953118B CN201611054855.8A CN201611054855A CN106953118B CN 106953118 B CN106953118 B CN 106953118B CN 201611054855 A CN201611054855 A CN 201611054855A CN 106953118 B CN106953118 B CN 106953118B
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phosphate
hydrocarbon group
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carbonate
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CN106953118A (en
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石桥
胡时光
林雄贵
贠娇娇
俱龙龙
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Huizhou Capchem Chemicals Co Ltd
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Priority to EP16922345.0A priority patent/EP3547433A4/en
Priority to PCT/CN2016/113649 priority patent/WO2018094843A1/en
Priority to US16/316,621 priority patent/US11362370B2/en
Priority to JP2018564811A priority patent/JP6814821B2/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0568—Liquid materials characterised by the solutes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0028—Organic electrolyte characterised by the solvent
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    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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    • Y02E60/10—Energy storage using batteries

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Abstract

The application discloses a non-aqueous electrolyte for a lithium ion battery and the lithium ion battery. The non-aqueous electrolyte comprises at least one of a first compound with a structural formula I and at least one of a second compound with a structural formula II; in the structural formula I, R1、R2Independently selected from a hydrocarbon group or a fluorinated hydrocarbon group having 1 to 5 carbon atoms, R1And R2At least one of which is a fluorinated hydrocarbon group in which at least two hydrogens are replaced with fluorine, and R in formula II3、R4、R5Independently selected from saturated hydrocarbon group, unsaturated hydrocarbon group or halogenated hydrocarbon group with 1-5 carbon atoms, R3、R4、R5At least one of them is an unsaturated hydrocarbon group. The nonaqueous electrolyte improves the high-temperature cycle performance of the high-voltage lithium ion battery and avoids decomposition and gas generation on the surface of the negative electrode through the synergistic effect of the first compound and the second compound. And the first compound part participates in the film forming reaction of the negative electrode, so that the interface condition of the negative electrode is improved, and the low-temperature discharge performance and the rate capability of the battery are guaranteed.

Description

Non-aqueous electrolyte for lithium ion battery and lithium ion battery
Technical Field
The application relates to the field of lithium ion battery electrolyte, in particular to a non-aqueous electrolyte for a lithium ion battery and the lithium ion battery.
Background
The lithium ion battery has the advantages of light weight, small volume, high working voltage, high energy density, large output power, no memory effect, long cycle life and the like, is widely applied to the field of digital products such as mobile phones, notebook computers and the like, and is considered to be one of the best choices of electric vehicles and large energy storage devices. At present, electronic digital products such as smart phones and tablet computers have higher and higher requirements on energy density of batteries, so that commercial lithium ion batteries are difficult to meet the requirements. Increasing the charging voltage of a lithium ion battery is one of the most effective ways to increase the energy density of the battery.
At present, the electrolyte of the lithium ion battery adopts carbonic ester as a solvent, and when the charging voltage of the lithium ion battery is more than 4.2V, the carbonic ester solvent can be oxidized and decomposed on the surface of a positive electrode material to generate gas and other decomposition products. On one hand, the generated gas may cause swelling of the battery, which may cause safety hazards to the battery, and on the other hand, the decomposition products thereof may significantly increase the impedance of the battery, thereby decreasing the respective performances of the battery. Therefore, for high voltage lithium ion batteries, it is necessary to develop solvents with higher oxidation potentials than carbonates. Chinese patent application CN104704657A discloses an electrolyte containing fluorine-substituted carboxylic ester and phosphoric ester, which can improve the high-temperature cycle performance of a high-voltage lithium ion battery. However, the applicant finds that the compatibility of the fluorocarboxylate with the carbon negative electrode material is poor, and the fluorocarboxylate can be reduced and decomposed on the surface of the negative electrode to generate a large amount of gas in the charging process of the battery, so that the battery brings great potential safety hazard and obviously deteriorates the performance of the battery. Although the phosphate ester can inhibit the decomposition of the fluorocarboxylic acid ester to some extent, the high-temperature cycle and high-temperature storage properties are desired to be further improved.
Disclosure of Invention
The purpose of the application is to provide a novel lithium ion battery non-aqueous electrolyte and a lithium ion battery adopting the electrolyte.
In order to achieve the purpose, the following technical scheme is adopted in the application:
one aspect of the application discloses a nonaqueous electrolyte for a lithium ion battery, which comprises at least one selected from first compounds shown in a structural formula I and at least one selected from second compounds shown in a structural formula II;
structural formula (II)1COOR2，
In the structural formula I, R1、R2Each independently selected from a hydrocarbon group or a fluorinated hydrocarbon group having 1 to 5 carbon atoms, and R1And R2At least one of which is a fluorinated hydrocarbonA group; at least two hydrogens of the fluorinated hydrocarbyl group are replaced with fluorine;
structural formula II
Figure BDA0001162774840000021
In the structural formula II, R3、R4、R5Each independently selected from saturated hydrocarbon group, unsaturated hydrocarbon group or halogenated hydrocarbon group with 1-5 carbon atoms, and R3、R4、R5At least one of them is an unsaturated hydrocarbon group.
The nonaqueous electrolytic solution of the present invention is characterized in that a first compound represented by the structural formula one and a second compound represented by the structural formula two are used in combination, and the first compound and the second compound act synergistically. The first compound has high oxidation potential, so that the decomposition reaction of the electrolyte on the surface of the high-voltage positive electrode material can be reduced, but the first compound can be decomposed on the surface of the negative electrode, so that a large amount of gas is generated, and potential safety hazards are brought; the second compound contains unsaturated bonds in the molecular structure, so that a passivation film can be formed on the surface of the positive and negative electrode materials through a polymerization reaction in the first charging process of the lithium ion battery, but the passivation film has high impedance, and the low-temperature discharge performance and the rate capability of the battery are reduced. When the first compound and the second compound are used simultaneously, the second compound can preferentially generate a polymerization reaction on the surface of the negative electrode to form a passivation film, so that the decomposition reaction of the first compound on the surface of the negative electrode is inhibited, and the gas generation phenomenon of the lithium ion battery due to the decomposition of the structural formula I on the surface of the negative electrode in the charging process is inhibited. In addition, the first compound can also partially participate in the film forming reaction of the negative electrode, and the condition of the negative electrode interface is improved. The first compound and the second compound are used together, and the first compound and the second compound act in a coordinated manner, so that a special effect which cannot be achieved when the first compound and the second compound are used independently is generated.
In the present application, the first compound and the second compound are used simultaneously; the amount of the first compound can be added in a conventional amount, and for example, the amount of the first compound is preferably 10 to 80 percent of the total weight of the nonaqueous electrolyte. The second compound may be used in an amount corresponding to the conventional amount of the additive in the nonaqueous electrolytic solution, for example, about 0.8 to 1.2% by weight of the total weight of the nonaqueous electrolytic solution, and may be generally 0.01 to 5% by weight of the total weight of the nonaqueous electrolytic solution. The first compound may be used alone as the nonaqueous organic solvent of the nonaqueous electrolytic solution, or may be used in combination with other common organic solvents, and the use in combination with other organic solvents will be described in detail in the following embodiments.
It should be noted that the key point of the present application is to use the first compound and the second compound in the nonaqueous electrolytic solution, and as for other conventional components, such as lithium salt, reference may be made to the existing nonaqueous electrolytic solution, and even other common reagents may be added to the nonaqueous electrolytic solution to add corresponding functions, and are not limited herein. However, in the preferred embodiment of the present application, other organic solvents than the aqueous organic solvent, lithium salt and other reagents are particularly limited for achieving better effects, which will be described in detail in the subsequent embodiment.
Preferably, in the structural formula I, the hydrocarbon group having 1 to 5 carbon atoms includes, but is not limited to, methyl, ethyl, propyl, vinyl, allyl, 3-butenyl, isobutenyl, 4-pentenyl, ethynyl, propargyl, 3-butynyl, 1-methyl-2 propynyl; fluorinated hydrocarbyl groups include, but are not limited to, difluoromethyl, trifluoromethyl, 2, 2-difluoroethyl, 2,2, 2-trifluoroethyl, 3, 3-difluoropropyl, 3,3, 3-trifluoropropyl, hexafluoroisopropyl; in the structural formula II, the saturated hydrocarbon group with 1-5 carbon atoms comprises but is not limited to methyl, ethyl and propyl; unsaturated hydrocarbon groups having 1 to 5 carbon atoms include, but are not limited to, vinyl, allyl, 3-butenyl, isobutenyl, 4-pentenyl, ethynyl, propargyl, 3-butynyl, 1-methyl-2-propynyl; the halogenated hydrocarbon group having 1 to 5 carbon atoms includes, but is not limited to, difluoromethyl, trifluoromethyl, 2, 2-difluoroethyl, 2,2, 2-trifluoroethyl, 3, 3-difluoropropyl, 3,3, 3-trifluoropropyl, hexafluoroisopropyl.
Preferably, the first compound is selected from H3CCOOCH2CF2H (abbreviated DFEA), H3CH2CCOOCH2CF2H (abbreviated DFEP), HF2CH2CCOOCH3(abbreviated as MDFP),HF2CH2CCOOCH2CH3(abbreviated EDFP), HF2CH2CH2CCOOCH2CH3(abbreviated EDFB), H3CCOOCH2CH2CF2H (abbreviated DFPA), H3CH2CCOOCH2CH2CF2H (abbreviated DFPP), CH3COOCH2CF3(abbreviated as TFEA), HCOOCH2CHF2(abbreviated DFEF), HCOOCH2CF3、CH3COOCH2CF2CF2H (abbreviated TFPA).
Preferably, the second compound is selected from at least one of tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, dipropargyl trifluoromethyl phosphate, dipropargyl 2,2, 2-trifluoroethyl phosphate, dipropargyl 3,3, 3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl 2,2, 2-trifluoroethyl phosphate, diallyl 3,3, 3-trifluoropropyl phosphate or diallyl hexafluoroisopropyl phosphate.
Preferably, the nonaqueous electrolytic solution further comprises one or more of unsaturated cyclic carbonate, unsaturated anhydride, cyclic sulfate, cyclic sultone and sulfone.
The unsaturated cyclic carbonate comprises at least one of vinylene carbonate (abbreviated as VC) and ethylene carbonate (abbreviated as VEC);
preferably, the cyclic sultone includes at least one of 1, 3-propane sultone (abbreviation 1, 3-PS), 1, 4-butane sultone (abbreviation BS), 1, 3-propene sultone (abbreviation PST), and methylene methanedisulfonate (abbreviation MMDS).
Preferably, the unsaturated acid anhydride includes at least one of succinic anhydride (abbreviated SA), maleic anhydride (abbreviated MA), and 2-methyl maleic anhydride (CA).
Preferably, the cyclic sulfate includes one or both of vinyl sulfate (abbreviated DTD) and propenyl sulfate (abbreviated TS).
Preferably, the sulfones include sulfolane (abbreviated SL).
It is to be noted that vinylene carbonate (abbreviated as VC), vinylethylene carbonate (abbreviated as VEC), fluoroethylene carbonate (abbreviated as FEC), or 1, 3-propane sultone (abbreviated as 1, 3PS), 1, 4-butane sultone (abbreviated as BS), 1, 3-propene sultone (abbreviated as PST), methylene methanedisulfonate (abbreviated as MMDS), succinic anhydride (abbreviated as SA), maleic anhydride (abbreviated as MA), 2-methylmaleic anhydride (abbreviated as CA), vinyl sulfate (abbreviated as DTD), propylene sulfate (abbreviated as TS), sulfolane (abbreviated as SL), and 1, 4-butyrolactone (abbreviated as GBL), which are conventional reagents for nonaqueous electrolytic solutions, are reported, and some of them, namely, may be used as additives and may also be used as solvents, for example, FEC, which is considered to be a nonaqueous organic solvent when used in a relatively large amount, the smaller amount thereof was regarded as an additive. For example, in the present invention, the amount of VC is preferably 0.1% to 4%, more preferably 0.5% to 1.5%, based on the total weight of the nonaqueous electrolytic solution. The amount of VEC is 0.1 to 3% by weight, more preferably 0.2 to 1.5% by weight, based on the total weight of the nonaqueous electrolytic solution. The amount of 1, 3-PS is 0.1-10%, more preferably 1-3% of the total weight of the nonaqueous electrolytic solution. The amount of BS is 0.1 to 10%, more preferably 1 to 3% based on the total weight of the nonaqueous electrolytic solution. The amount of PST is 0.1 to 3% by weight, more preferably 0.5 to 2% by weight, based on the total weight of the nonaqueous electrolytic solution. The amount of MMDS is 0.1 to 4% by weight, more preferably 0.5 to 2% by weight, based on the total weight of the nonaqueous electrolytic solution. The amount of SA is 0.1 to 4% by weight, more preferably 0.5 to 2% by weight, based on the total weight of the nonaqueous electrolytic solution. The amount of MA is 0.1 to 4% by weight, more preferably 0.5 to 2% by weight based on the total weight of the nonaqueous electrolytic solution. The amount of CA is 0.1 to 4% by weight, more preferably 0.5 to 2% by weight, based on the total weight of the nonaqueous electrolytic solution. The amount of DTD is 0.1 to 5% by weight, more preferably 0.5 to 3% by weight, based on the total weight of the nonaqueous electrolytic solution. The amount of TS is 0.1 to 4%, more preferably 0.5 to 3% based on the total weight of the nonaqueous electrolytic solution. The amount of SL is 0.1 to 30% by weight, more preferably 2 to 15% by weight, based on the total weight of the nonaqueous electrolytic solution. The GBL is used in an amount of 0.1 to 30% by weight, more preferably 2 to 15% by weight, based on the total weight of the nonaqueous electrolytic solution.
Preferably, the nonaqueous electrolytic solution further includes at least one selected from the group consisting of ethylene carbonate, fluoroethylene carbonate (abbreviated as FEC), propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and propyl methyl carbonate. The content thereof may vary widely, and preferably, the content thereof is 1% to 40% of the total weight of the nonaqueous electrolytic solution. It is understood that when a plurality of the above-mentioned substances are contained, the above-mentioned content ranges are the ratio of the total content of the above-mentioned substances.
More preferably, the nonaqueous electrolytic solution further includes at least one of ethylene carbonate, fluoroethylene carbonate, and propylene carbonate.
The application also discloses application of the non-aqueous electrolyte in a lithium ion battery or a storage capacitor.
The application also discloses a lithium ion battery, which comprises a positive electrode, a negative electrode, a diaphragm arranged between the positive electrode and the negative electrode, and electrolyte, wherein the electrolyte is the lithium ion battery non-aqueous electrolyte.
The lithium ion battery has the key points that the non-aqueous electrolyte is adopted, so that the passive films are formed on the surfaces of the anode and the cathode, the decomposition reaction of the electrolyte on the surfaces of the anode and the cathode is effectively inhibited, the structure of the anode material is inhibited from being damaged, the lithium precipitation phenomenon is reduced, and the high-low temperature performance and the rate capability of the battery are ensured. As for other components in the lithium ion battery, such as a positive electrode, a negative electrode, and a separator, a conventional lithium ion battery can be referred to. In a preferred embodiment of the present invention, the active material of the positive electrode is particularly limited.
Preferably, the active material of the positive electrode is LiNixCoyMnzL(1-x-y-z)O2、LiCox’L(1-x’)O2And LiNix”L’y’Mn(2-x”-y’)O4Wherein L is Al, Sr, Mg, Ti, Ca, Zr, Zn, Si or Fe, x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, x + y + z is more than 0 and less than or equal to 1, 0<x ' is not less than 1, x is not less than 0.3 and not more than 0.6, y ' is not less than 0.01 and not more than 0.2, and L ' is Co, Al, Sr, Mg, Ti, Ca, Zr, Zn, Si or Fe.
Due to the adoption of the technical scheme, the beneficial effects of the application are as follows:
the non-aqueous electrolyte is used by matching the first compound shown in the structural formula I and the second compound shown in the structural formula II, and the first compound and the second compound have synergistic effect, so that the high-temperature cycle performance of the high-voltage lithium ion battery is improved, and the phenomenon of gas generation caused by decomposition of the surface of a negative electrode is avoided. In addition, the first compound can also partially participate in the film forming reaction of the negative electrode, so that the interface condition of the negative electrode is improved, and the low-temperature discharge performance and the rate performance of the battery are further guaranteed.
Detailed Description
In a series of researches on the electrolyte, the applicant finds that the first compound can be decomposed to generate gas at a negative electrode when being used as a non-aqueous organic solvent, so that potential safety hazards exist; although the second compound can improve the high-temperature performance, the second compound generates polymerization reaction on the surfaces of the positive electrode and the negative electrode to form a passive film, the passive film has higher impedance, and the low-temperature discharge performance and the rate capability of the battery are reduced. After a large amount of researches and experiments, the application provides that the first compound and the second compound are mixed for use and have synergistic effect, so that the potential safety hazard of the first compound in decomposing and generating gas at the negative electrode is overcome, the influence of the second compound on the low-temperature discharge performance and the rate capability of the battery is relieved, and various performances of the battery are greatly improved.
The present application will be described in further detail with reference to specific examples. The following examples are intended to be illustrative of the present application only and should not be construed as limiting the present application.
Examples
In this example, an electrolyte was prepared according to the composition and formulation shown in table 1, wherein a plurality of non-aqueous electrolytes for lithium ion batteries of the present application were designed, and a plurality of comparative examples, detailed in table 1.
The preparation method of the electrolyte comprises the following steps: a nonaqueous organic solvent was prepared in the ratio shown in Table 1, and then lithium hexafluorophosphate was added thereto at a final concentration of 1.0mol/L, and further additives were added as shown in Table 1. The percentages in table 1 are weight percentages, i.e., the additive accounts for the total weight of the electrolyte, the lithium salt content in the electrolyte is 12.5%, and the balance is solvent-grade additives.
TABLE 1 electrolyte Components and amounts
Figure BDA0001162774840000071
In the lithium ion battery of this example, LiNi was used as the positive electrode active material0.5Co0.2Mn0.3O2The negative electrode adopts graphite and conductive carbon black, and the diaphragm adopts a polypropylene, polyethylene and polypropylene three-layer isolating membrane. The method comprises the following specific steps:
the preparation method of the anode comprises the following steps: according to the weight ratio of 96.8: 2.0: 1.2 Mass ratio Mixed Positive electrode active Material LiNi0.5Co0.2Mn0.3O2The conductive carbon black and the adhesive polyvinylidene fluoride are dispersed in N-methyl-2-pyrrolidone to obtain anode slurry, the anode slurry is uniformly coated on two sides of an aluminum foil, and the anode plate is obtained after drying, rolling and vacuum drying are carried out, and an aluminum outgoing line is welded by an ultrasonic welding machine, wherein the thickness of the anode plate is between 120 and 150 mu m.
The preparation method of the negative electrode comprises the following steps: according to the weight ratio of 96: 1: 1.2: mixing graphite, conductive carbon black, binder styrene butadiene rubber and carboxymethyl cellulose according to the mass ratio of 1.8, dispersing in deionized water to obtain negative electrode slurry, coating the negative electrode slurry on two sides of a copper foil, drying, rolling and vacuum drying, and welding a nickel outgoing line by using an ultrasonic welding machine to obtain a negative electrode plate, wherein the thickness of the negative electrode plate is between 120 and 150 mu m.
The preparation method of the diaphragm comprises the following steps: the three-layer isolating film of polypropylene, polyethylene and polypropylene is adopted, and the thickness is 20 mu m.
The battery assembling method comprises the following steps: placing three layers of isolating films with the thickness of 20 mu m between the positive plate and the negative plate, then winding a sandwich structure consisting of the positive plate, the negative plate and the diaphragm, flattening the wound body, then placing the flattened wound body into an aluminum foil packaging bag, and baking the flattened wound body in vacuum at 75 ℃ for 48 hours to obtain a battery cell to be injected with liquid; and injecting the prepared electrolyte into a battery cell, carrying out vacuum packaging, and standing for 24 h.
Formation of a battery: charging at 0.05C for 180min, charging at 0.1C to 3.95V, vacuum sealing twice, standing at 45 deg.C for 48h, further charging at 0.2C to 4.4V, and discharging at 0.2C to 3.0V.
In this example, the cycle number of the lithium ion battery with the electrolyte, in which the cycle capacity retention rate decays to 80% at 45 ℃ and 1C, and the capacity retention rate, the capacity recovery rate and the thickness expansion rate after 14 days of storage at 60 ℃ are respectively tested. Wherein storage at 60 ℃ for several days means that the electrolyte of the comparative example, the lithium ion battery of which was tested after storage at 60 ℃ for 7 days, and the test example, after storage at 60 ℃ for 14 days, were tested. The specific test method is as follows:
(1) the cycle frequency that the cycle capacity retention rate of 1C at 45 ℃ is attenuated to 80 percent actually represents the high-temperature cycle performance of the battery, and the specific test method comprises the following steps: and (3) charging the formed battery to 4.4V by using a 1C constant current and a constant voltage at 45 ℃, stopping the current to be 0.01C, then discharging to 3.0V by using the 1C constant current, circulating the steps until the capacity retention rate is attenuated to 80%, and counting the circulation times at the moment. The capacity retention rate calculation formula is as follows:
capacity retention (%) — (nth cycle discharge capacity/first cycle discharge capacity) × 100%.
(2) The method for testing the capacity retention rate, the capacity recovery rate and the thickness expansion rate after 14 days of storage at 60 ℃ comprises the following steps: charging the formed battery to 4.4V at a constant current and a constant voltage of 1C at normal temperature, stopping the current to be 0.01C, then discharging the battery to 3.0V at a constant current of 1C, measuring the initial discharge capacity of the battery, then charging the battery to 4.4V at the constant current and the constant voltage of 1C, stopping the current to be 0.01C, measuring the initial thickness of the battery, then storing the battery for 14 days at 60 ℃, measuring the thickness of the battery, then discharging the battery to 3.0V at the constant current of 1C, measuring the retention capacity of the battery, then charging the battery to 0.01C at the constant current and the constant voltage of 1C, then discharging the battery to 3.0V at the constant current of 1C, and measuring the recovery capacity of the battery. The calculation formula is as follows:
battery capacity retention (%) retention capacity/initial capacity × 100%
Battery capacity recovery (%) -recovery capacity/initial capacity X100%
The battery thickness swelling ratio (%) (thickness after 14 days-initial thickness)/initial thickness × 100%.
(3) Low temperature discharge performance test
And (3) charging the formed battery to 4.4V at a constant current and a constant voltage of 1C at 25 ℃, then charging at a constant voltage until the current is reduced to 0.01C, then discharging to 3.0V at a constant current of 1C, and recording the discharge capacity at normal temperature. And then charging the battery to 4.4V at a constant current of 1C, then charging the battery at a constant voltage until the current is reduced to 0.01C, placing the battery in an environment at the temperature of minus 20 ℃ for standing for 12 hours, then discharging the battery to 3.0V at a constant current of 0.2C, and recording the discharge capacity at the temperature of minus 20 ℃.
The low-temperature discharge efficiency at-20 ℃ was 0.2C discharge capacity (-20 ℃) per 1C discharge capacity (25 ℃) x 100%.
The results of the tests are shown in Table 2.
TABLE 2 test results
Figure BDA0001162774840000081
Figure BDA0001162774840000091
As can be seen from the results of table 2, comparative example 1 employs only the second compound as an additive and does not employ the first compound as a solvent, and thus, the high-temperature cycle performance is weak, 80% remains of the capacity retention rate after 290 cycles, and the retention capacity and recovery capacity of storage at 60 ℃ for 14 days are also not ideal, especially the low-temperature discharge performance is poor. Comparative example 2, which used the first compound as a solvent and did not use the second compound as an additive, was poor in high-temperature storage properties and high-temperature storage properties. In comparative examples 3 to 9, the first compound was used as a solvent, and the saturated phosphate ester was used as an additive, and the solvent composition was also optimally adjusted, and although the high-temperature cycle performance and the high-temperature storage performance of the battery were greatly improved, the requirements could not be satisfied, and further improvement was desired. Examples 1-21 employed both the first compound as a solvent and the second compound as an additive, and optimized both the solvent combination and the additive combination, which significantly improved both the high temperature cycle performance and the high temperature storage performance, while also compromising the low temperature discharge performance. Example 21 has the best high temperature cycle performance, and can be cycled 662 times when the capacity retention rate decays to 80%, and the high temperature storage performance is quite excellent.
The foregoing is a more detailed description of the present application in connection with specific embodiments thereof, and it is not intended that the present application be limited to the specific embodiments thereof. For those skilled in the art to which the present application pertains, several simple deductions or substitutions may be made without departing from the concept of the present application, and all should be considered as belonging to the protection scope of the present application.

Claims (10)

1. A nonaqueous electrolyte for a lithium ion battery, characterized in that: comprises at least one selected from first compounds shown in a structural formula I and at least one selected from second compounds shown in a structural formula II;
structural formula (II)1COOR2，
In the structural formula I, R1、R2Each independently selected from a hydrocarbon group or a fluorinated hydrocarbon group having 1 to 5 carbon atoms, and R1And R2At least one of which is said fluorinated hydrocarbyl group; at least two hydrogens of said fluorinated hydrocarbyl group are replaced with fluorine;
structural formula II
Figure FDA0001988425020000011
In the structural formula II, R3、R4、R5Each independently selected from saturated hydrocarbon group, unsaturated hydrocarbon group or halogenated hydrocarbon group with 1-5 carbon atoms, and R3、R4、R5At least one of them is an unsaturated hydrocarbon group;
the unsaturated hydrocarbon group having 1 to 5 carbon atoms is at least one selected from the group consisting of a vinyl group, an allyl group, a 3-butenyl group, an isobutenyl group, a 4-pentenyl group, an ethynyl group, a propargyl group, a 3-butynyl group and a 1-methyl-2 propynyl group.
2. The nonaqueous electrolytic solution of claim 1, wherein: in the structural formula I, the hydrocarbon group with 1-5 carbon atoms comprises but is not limited to methyl, ethyl, propyl, vinyl, allyl, 3-butenyl, isobutenyl, 4-pentenyl, ethynyl, propargyl, 3-butynyl and 1-methyl-2 propynyl; the fluorinated hydrocarbon group includes, but is not limited to, difluoromethyl, trifluoromethyl, 2, 2-difluoroethyl, 2,2, 2-trifluoroethyl, 3, 3-difluoropropyl, 3,3, 3-trifluoropropyl, hexafluoroisopropyl;
in the structural formula II, the saturated hydrocarbon group with 1-5 carbon atoms comprises but is not limited to methyl, ethyl and propyl; the halogenated hydrocarbon group having 1 to 5 carbon atoms includes, but is not limited to, difluoromethyl, trifluoromethyl, 2, 2-difluoroethyl, 2,2, 2-trifluoroethyl, 3, 3-difluoropropyl, 3,3, 3-trifluoropropyl, hexafluoroisopropyl.
3. The nonaqueous electrolytic solution of claim 1, wherein: the first compound is selected from H3CCOOCH2CF2H、H3CH2CCOOCH2CF2H、HF2CH2CCOOCH3、HF2CH2CCOOCH2CH3、HF2CH2CH2CCOOCH2CH3、H3CCOOCH2CH2CF2H、H3CH2CCOOCH2CH2CF2H、CH3COOCH2CF3、HCOOCH2CHF2、HCOOCH2CF3And CH3COOCH2CF2CF2And H.
4. The nonaqueous electrolytic solution of claim 1, wherein: the second compound is at least one selected from the group consisting of tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, dipropargyl trifluoromethyl phosphate, dipropargyl 2,2, 2-trifluoroethyl phosphate, dipropargyl 3,3, 3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl 2,2, 2-trifluoroethyl phosphate, diallyl 3,3, 3-trifluoropropyl phosphate and diallyl hexafluoroisopropyl phosphate.
5. The nonaqueous electrolytic solution of any one of claims 1 to 4, wherein: in the non-aqueous electrolyte, the amount of the first compound accounts for 10-80% of the total weight of the non-aqueous electrolyte; the second compound accounts for 0.01-5% of the total weight of the nonaqueous electrolyte.
6. The nonaqueous electrolytic solution of any one of claims 1 to 4, wherein: the non-aqueous electrolyte also comprises one or more of unsaturated cyclic carbonate, unsaturated anhydride, cyclic sulfate, cyclic sultone and sulfones.
7. The nonaqueous electrolytic solution of claim 6, wherein: the unsaturated cyclic carbonate is at least one of vinylene carbonate and ethylene carbonate; the unsaturated anhydride is selected from at least one of succinic anhydride, maleic anhydride and 2-methyl maleic anhydride; the cyclic sulfate is selected from one or two of vinyl sulfate and allyl sulfate; the cyclic sultone is selected from at least one of 1, 3-propane sultone, 1, 4-butane sultone, 1, 3-propene sultone and methylene methane disulfonate; the sulfone is sulfolane.
8. The nonaqueous electrolytic solution of any one of claims 1 to 4, wherein: the non-aqueous electrolyte also comprises at least one selected from ethylene carbonate, fluoroethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl methyl carbonate and 1, 4-butyrolactone; preferably, the nonaqueous electrolytic solution further includes at least one of ethylene carbonate, fluoroethylene carbonate, and propylene carbonate.
9. The utility model provides a lithium ion battery, includes positive pole, negative pole, arranges the diaphragm between positive pole and negative pole to and electrolyte, its characterized in that: the electrolyte is the nonaqueous electrolyte solution according to any one of claims 1 to 8.
10. The lithium ion battery of claim 9, wherein: the active material of the positive electrode is LiNixCoyMnzL(1-x-y-z)O2、LiCox’L(1-x’)O2And LiNix”L’y’Mn(2-x”-y’)O4Wherein L is Al, Sr, Mg, Ti, Ca, Zr, Zn, Si or Fe, x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, x + y + z is more than 0 and less than or equal to 1, 0<x ' is not less than 1, x is not less than 0.3 and not more than 0.6, y ' is not less than 0.01 and not more than 0.2, and L ' is Co, Al, Sr, Mg, Ti, Ca, Zr, Zn, Si or Fe.
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