CN112366350A - Electrolyte additive, electrolyte containing additive and lithium ion battery - Google Patents

Electrolyte additive, electrolyte containing additive and lithium ion battery Download PDF

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Publication number
CN112366350A
CN112366350A CN202010119672.XA CN202010119672A CN112366350A CN 112366350 A CN112366350 A CN 112366350A CN 202010119672 A CN202010119672 A CN 202010119672A CN 112366350 A CN112366350 A CN 112366350A
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electrolyte
lithium
additive
carbonate
lithium ion
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汪仕华
许梦清
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Wanxiang A123 Systems Asia Co Ltd
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Wanxiang Group Corp
Wanxiang A123 Systems Asia Co Ltd
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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
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • 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
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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Abstract

The invention relates to the technical field of lithium ion batteries, and discloses an electrolyte additive, an electrolyte containing the additive and a lithium ion battery. The electrolyte additive changes carbon atoms between two sulfur atoms in MMDS into nitrogen atoms, is easier to be oxidized and decomposed during formation, and forms a stable SEI film on the surface of a positive electrode, so that the decomposition of the lithium ion battery electrolyte, the structural change of a positive electrode material and high-temperature gas generation at high temperature can be more effectively inhibited, the problems of battery capacity attenuation, cycle life decline, internal resistance reduction and the like during high-temperature cycle or storage can be better prevented, and the high-temperature performance of the lithium ion battery is improved; also, the electrolyte additive does not have a discoloration problem during storage.

Description

Electrolyte additive, electrolyte containing additive and lithium ion battery
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to an electrolyte additive, an electrolyte containing the additive and a lithium ion battery.
Background
The lithium ion battery is a high-performance battery which realizes charging and discharging by moving lithium ions between a positive electrode and a negative electrode, and the basic structure of the lithium ion battery comprises a positive electrode, a negative electrode, electrolyte and a diaphragm. In the charging and discharging process, the electrolyte is mainly used as an ion conductor to transmit lithium ions between a positive electrode and a negative electrode; besides, the electrolyte plays another important role in participating in the film-forming reaction of a Solid Electrolyte Interface (SEI) film on the surface of the pole piece. Most of the electrolytes used in commercial lithium ion batteries are nonaqueous electrolytes, and mainly consist of three parts, namely an organic solvent, an electrolyte lithium salt and an additive. The additive has the function of improving the performance of the electrolyte, so that the performance of the battery is improved, and the additive comprises an SEI film forming additive, an overcharge protection additive, a flame retardant additive, a conductive capability additive, a wetting agent and the like.
Methylene Methanedisulfonate (MMDS) is a reported positive electrode film forming additive and can improve the high-temperature performance of the lithium ion battery. Electrolyte decomposition and structural change of the anode material are two important reasons for influencing the high-temperature performance of the lithium ion battery. In a high-temperature environment, the anode of the lithium ion battery and the electrolyte undergo oxidation-reduction reaction, so that the structure of the anode material is changed, and the battery capacity is rapidly reduced. For example, the capacity of the common positive electrode material LiMn2O4 rapidly decays above 55 ℃, mainly due to the reaction of LiPF6 in the electrolyte with a trace amount of moisture in the electrolyte to generate HF, Mn3+Disproportionation reaction under acidic condition to produce Mn2+And Mn4+And LiMn2O4Mn in (1)2+Is easily dissolved in the electrolyte at high temperature, resulting in a rapid decrease in capacity. In addition, thermal decomposition of the positive electrode material and oxidation of the electrolyte at the positive electrode may be generated as CO2The predominant gas, i.e., high temperature gas generation, causes the battery to swell, which increases the thickness of the battery and affects the safety performance. The MMDS can be preferentially oxidized and decomposed in the formation film-forming process of the anode film-forming additive, a layer of compact SEI film with good thermal stability is formed on the surface of the anode, the decomposition of the electrolyte at high temperature is inhibited, the anode material and the electrolyte solvent are separated, and the structural change of the anode material and high-temperature gas generation at high temperature are prevented, so that the high-temperature performance of the lithium ion battery is improved.
For example, chinese patent application No. CN201110125874.6 discloses an electrolyte for improving the high-temperature storage performance of a lithium ion secondary battery, which contains a lithium salt, an organic solvent, an additive and a high-temperature film forming agent, wherein the high-temperature film forming agent is a mixture of MMDS and 4-methyl ethylene sulfite, and the mass ratio of the MMDS to the 4-methyl ethylene sulfite is 3: 2. After the MMDS is added, the capacity retention rate and the capacity recovery rate of the lithium ion battery during high-temperature storage are obviously improved, the thickness increase rate is obviously reduced, and compared with other high-temperature additives (such as propenyl sultone), the MMDS can not cause the internal resistance of the battery to be obviously increased, so that the MMDS is a lithium ion battery electrolyte additive with better performance. However, MMDS has a great room for improvement of high-temperature performance of the battery, particularly for inhibition of high-temperature gassing, and MMDS has an unstable molecular structure, has a discoloration problem during storage, and requires low-temperature storage.
Disclosure of Invention
In order to solve the technical problems, the invention provides an electrolyte additive, an electrolyte containing the additive and a lithium ion battery. The electrolyte additive is easier to be oxidized and decomposed during formation, and a stable SEI film is formed on the surface of the positive electrode, so that the high-temperature performance of the lithium ion battery can be more effectively improved; also, the electrolyte additive does not have a discoloration problem during storage.
The specific technical scheme of the invention is as follows:
an electrolyte additive having the formula:
Figure BDA0002392575260000021
wherein X is any one of the following cases:
a straight chain or branched chain alkyl group with 1-5 carbon atoms;
a linear or branched alkoxy group having 1 to 5 carbon atoms;
a straight or branched alkyl group in which some or all of the hydrogens are substituted with halogen atoms;
phenyl or substituted phenyl;
a carbonate group or a carbonate group substituted with a halogen atom;
a halogen atom;
a hydrogen atom.
When the lithium ion battery is circulated or stored in a high-temperature environment, the anode and the electrolyte generate oxidation-reduction reactionThe structure of the anode material is changed, so that the capacity of the battery is rapidly reduced, and the cycle life of the battery is declined; furthermore, the thermal decomposition of the positive electrode material and the oxidation of the electrolyte at the positive electrode may generate CO2The main gas, i.e. high-temperature gas generation, causes the expansion of the battery, so that the thickness of the battery is increased, the distance between the positive electrode and the negative electrode is increased, the internal resistance of the battery is greatly increased, and the safety performance of the battery is also influenced. The electrolyte additive is improved on the basis of the existing positive electrode film-forming additive MMDS, a carbon atom between two sulfur atoms is replaced by a nitrogen atom, and the electronegativity of the nitrogen atom is stronger than that of the carbon atom, so that the electron deviation degree after the nitrogen atom is bonded with the sulfur atom is larger, the electrophilicity of the sulfur atom can be increased, the structure is easier to be reduced under low voltage during formation, an SEI film is formed on the surface of a positive electrode, the decomposition of electrolyte at high temperature is inhibited, the positive electrode material and an electrolyte solvent are separated, and the structural change of the positive electrode material at high temperature is prevented, so that the high-temperature performance of a lithium ion battery is improved; in addition to the fact that the SEI film is more easily formed on the surface of the positive electrode, experiments show that the SEI film formed by the electrolyte additive is more stable compared with the MMDS, so that the effect of improving the high-temperature performance of the lithium ion battery is better.
In addition, the electrolyte additive of the present invention has no discoloration problem during storage, probably because a conjugated structure can be formed in its molecule, so that the molecular structure is more stable.
The electrolyte comprises a lithium salt, an organic solvent and an electrolyte additive, wherein the electrolyte additive is the electrolyte additive.
Preferably, the dosage of the electrolyte additive is 0.01-10% of the total mass of the electrolyte.
Further, the dosage of the electrolyte additive is 0.1-5% of the total mass of the electrolyte.
The dosage of the electrolyte additive is too small, so that a compact SEI film with good thermal stability is not formed on the surface of the anode; if the amount is too large, the internal resistance of the lithium ion battery is obviously increased. It is necessary to control the amount of the electrolyte additive within a suitable range.
Preferably, the lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis (fluorosulfonyl) imide, lithium bis (trifluoromethylsulfonyl) imide, lithium methylsulfonate, lithium trifluoromethylsulfonate, lithium bis (oxalato) borate, lithium difluoro (oxalato) phosphate and lithium tetrafluoro (oxalato) phosphate; the organic solvent is one or more of a carbonate solvent, a carboxylic ester solvent, an ether solvent, a sulfone solvent and a nitrile solvent.
Further, the carbonate solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl ethyl carbonate and dipropyl carbonate; the carboxylic ester solvent is one or more of ethyl acetate, methyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate and 1, 4-butyrolactone; the sulfone solvent is one or more of dimethyl sulfoxide, sulfolane, diphenyl sulfoxide, thionyl chloride and dipropyl sulfone; the nitrile solvent is one or more of acetonitrile, propionitrile, succinonitrile and adiponitrile.
Preferably, the concentration of the lithium salt is 0.5-1.3M.
Preferably, the organic solvent accounts for 80-90% of the total mass of the electrolyte.
A lithium ion battery comprising a positive electrode, a negative electrode, a separator and an electrolyte according to any one of claims 2 to 8.
Preferably, the positive electrode includes a positive electrode active material, and the positive electrode active material is LiCoO2、LiNiO2、LiMn2O4、LiFePO4、LiNixCoyMnzO2Wherein x + y + z is 1; the negative electrode comprises a negative electrode active material, and the negative electrode active material is one or more of natural graphite, artificial graphite, lithium titanate, silicon and a silicon-carbon compound; the diaphragm is one or more of polyethylene, polypropylene, polyimide, aramid fiber, ceramic and PVDF.
Compared with the prior art, the invention has the following advantages: the electrolyte additive is easier to form an SEI film on the surface of the anode, and the formed SEI film is more stable, so that the decomposition of the electrolyte of the lithium ion battery, the structural change of the anode material and the high-temperature gas generation under high temperature can be more effectively inhibited, the problems of battery capacity attenuation, cycle life decline, internal resistance reduction and the like generated during high-temperature cycle or storage can be better prevented, and the high-temperature performance of the lithium ion battery is improved; in addition, the electrolyte additive disclosed by the invention is more stable in molecular structure, and the problem of color change does not exist in the storage process.
Detailed Description
The present invention will be further described with reference to the following examples.
Example 1
A lithium ion battery was prepared by the following method:
(1) preparing a non-aqueous electrolyte: mixing anhydrous solvents of ethylene carbonate and methyl ethyl carbonate according to the mass ratio of 3:7, adding metered lithium hexafluorophosphate to prepare electrolyte with the molar concentration of 1mol/L, then adding electrolyte additive with the dosage of 0.5 percent of the total mass of the electrolyte, and uniformly mixing until the solid is completely dissolved. The structural formula of the electrolyte additive is as follows:
Figure BDA0002392575260000041
(2) preparing a positive pole piece: LiNi of nickel cobalt lithium manganate is mixed according to the ratio of 93:3:40.8Co0.1Mn0.1O2Dispersing PVDF and a conductive agent in N-methyl pyrrolidone to obtain positive electrode slurry; and uniformly coating the positive electrode slurry on an aluminum foil, drying, rolling, slitting and punching to obtain the positive electrode plate.
(3) Preparing a negative pole piece: dispersing artificial graphite, carboxymethyl cellulose and a conductive agent in water according to a ratio of 95:2:3, and uniformly stirring to obtain negative electrode slurry; and uniformly coating the negative electrode slurry on a copper foil, drying, rolling, slitting and punching to obtain the negative electrode pole piece.
(4) Assembling the battery cell: and winding the positive pole piece, the diaphragm and the negative pole piece to form a sandwich structure, flattening the wound cylinder, welding a tab, packaging by using an aluminum plastic film to obtain a dry battery cell, and drying in vacuum at 85 ℃.
(5) Liquid injection and formation: and injecting the prepared electrolyte into the dry cell in a glove box, sealing, standing at normal temperature, forming, cutting the aluminum plastic film, exhausting air, and sealing for the second time to obtain the activated battery.
(6) High-temperature cycle test: the cell was charged at 45 ℃ to 4.2V with a 1C current constant current and constant voltage, with a 0.05C cutoff current. Then discharged to 3.0V at 1C current, and the initial discharge capacity D was recorded1. Repeating the above steps for N times until the discharge capacity DnThe test was stopped at 80% of the initial discharge capacity. The number of cycles was recorded. The data are recorded in table 1.
(7) High-temperature storage test: the battery was charged to 4.2V at a constant current and a constant voltage of 1C current, with a current cutoff of 0.05C. Then discharged to 3.0V at 1C current, and the initial discharge capacity D was recorded1And is fully charged again. Measuring the thickness of the cell is marked d1. After storing the cell at 60 ℃ for N days, the cell was taken out and cooled to room temperature, discharged to 3.0V at a current of 1C, and the discharge capacity D was recordedn. Capacity retention rate of Dn/D1X 100%. Charging to 4.2V with 1C current constant current and constant voltage, stopping current at 0.05C, and recording the thickness d of the battery2. Thickness growth rate of 100% × (d)2-d1)/d1. Discharge to 3.0V at 1C and record the initial discharge capacity Dn+1. Capacity recovery rate of Dn+1/D1X 100%. The data are recorded in table 1.
Example 2
A lithium ion battery was prepared by the following method:
(1) preparing a non-aqueous electrolyte: mixing anhydrous solvents of ethylene carbonate and methyl ethyl carbonate according to the mass ratio of 3:7, adding metered lithium hexafluorophosphate to prepare electrolyte with the molar concentration of 1mol/L, then adding an electrolyte additive, wherein the using amount of the electrolyte additive is 1% of the total mass of the electrolyte, and uniformly mixing until solids are completely dissolved. The structural formula of the electrolyte additive is as follows:
Figure BDA0002392575260000051
(2) preparing a positive pole piece: dispersing nickel cobalt lithium manganate LiNi0.8Co0.1Mn0.1O2, PVDF and a conductive agent in N-methylpyrrolidone according to the ratio of 93:3:4 to obtain positive electrode slurry; and uniformly coating the positive electrode slurry on an aluminum foil, drying, rolling, slitting and punching to obtain the positive electrode plate.
(3) Preparing a negative pole piece: dispersing artificial graphite, carboxymethyl cellulose and a conductive agent in water according to a ratio of 95:2:3, and uniformly stirring to obtain negative electrode slurry; and uniformly coating the negative electrode slurry on a copper foil, drying, rolling, slitting and punching to obtain the negative electrode pole piece.
(4) Assembling the battery cell: and winding the positive pole piece, the diaphragm and the negative pole piece to form a sandwich structure, flattening the wound cylinder, welding a tab, packaging by using an aluminum plastic film to obtain a dry battery cell, and drying in vacuum at 85 ℃.
(5) Liquid injection and formation: and injecting the prepared electrolyte into the dry cell in a glove box, sealing, standing at normal temperature, forming, cutting the aluminum plastic film, exhausting air, and sealing for the second time to obtain the activated battery.
(6) High-temperature cycle test: the cell was charged at 45 ℃ to 4.2V with a 1C current constant current and constant voltage, with a 0.05C cutoff current. Then discharged to 3.0V at 1C current, and the initial discharge capacity D was recorded1. Repeating the above steps for N times until the discharge capacity DnThe test was stopped at 80% of the initial discharge capacity. The number of cycles was recorded. The data are recorded in table 1.
(7) High-temperature storage test: the battery was charged to 4.2V at a constant current and a constant voltage of 1C current, with a current cutoff of 0.05C. Then discharged to 3.0V at 1C current, and the initial discharge capacity D was recorded1And is fully charged again. Measuring the thickness of the cell is marked d1. After storing the cell at 60 ℃ for N days, the cell was taken out and cooled to room temperature, discharged to 3.0V at a current of 1C, and the discharge capacity D was recordedn. Capacity retention rate of Dn/D1X 100%. Then charging to 4.2V with a constant current and a constant voltage of 1C, cutting off the current of 0.05C,recording the thickness d of the battery2. Thickness growth rate of 100% × (d)2-d1)/d1. Discharge to 3.0V at 1C and record the initial discharge capacity Dn+1. Capacity recovery rate of Dn+1/D1X 100%. The data are recorded in table 1.
Example 3
A lithium ion battery was prepared by the following method:
(1) preparing a non-aqueous electrolyte: mixing anhydrous solvents of ethylene carbonate and methyl ethyl carbonate according to the mass ratio of 3:7, adding metered lithium hexafluorophosphate to prepare electrolyte with the molar concentration of 1mol/L, then adding electrolyte additives, wherein the dosage is 10% of the total mass of the electrolyte, and uniformly mixing until solids are completely dissolved. The structural formula of the electrolyte additive is as follows:
Figure BDA0002392575260000061
(2) preparing a positive pole piece: dispersing nickel cobalt lithium manganate LiNi0.8Co0.1Mn0.1O2, PVDF and a conductive agent in N-methylpyrrolidone according to the ratio of 93:3:4 to obtain positive electrode slurry; and uniformly coating the positive electrode slurry on an aluminum foil, drying, rolling, slitting and punching to obtain the positive electrode plate.
(3) Preparing a negative pole piece: dispersing artificial graphite, carboxymethyl cellulose and a conductive agent in water according to a ratio of 95:2:3, and uniformly stirring to obtain negative electrode slurry; and uniformly coating the negative electrode slurry on a copper foil, drying, rolling, slitting and punching to obtain the negative electrode pole piece.
(4) Assembling the battery cell: and winding the positive pole piece, the diaphragm and the negative pole piece to form a sandwich structure, flattening the wound cylinder, welding a tab, packaging by using an aluminum plastic film to obtain a dry battery cell, and drying in vacuum at 85 ℃.
(5) Liquid injection and formation: and injecting the prepared electrolyte into the dry cell in a glove box, sealing, standing at normal temperature, forming, cutting the aluminum plastic film, exhausting air, and sealing for the second time to obtain the activated battery.
Example 4
A lithium ion battery was prepared by the following method:
(1) preparing a non-aqueous electrolyte: mixing anhydrous solvents of ethylene carbonate and methyl ethyl carbonate according to the mass ratio of 3:7, adding metered lithium hexafluorophosphate to prepare electrolyte with the molar concentration of 1mol/L, then adding an electrolyte additive, wherein the using amount of the electrolyte additive is 0.01 percent of the total mass of the electrolyte, and uniformly mixing until the solid is completely dissolved. The structural formula of the electrolyte additive is as follows:
Figure BDA0002392575260000062
(2) preparing a positive pole piece: dispersing nickel cobalt lithium manganate LiNi0.8Co0.1Mn0.1O2, PVDF and a conductive agent in N-methylpyrrolidone according to the ratio of 93:3:4 to obtain positive electrode slurry; and uniformly coating the positive electrode slurry on an aluminum foil, drying, rolling, slitting and punching to obtain the positive electrode plate.
(3) Preparing a negative pole piece: dispersing artificial graphite, carboxymethyl cellulose and a conductive agent in water according to a ratio of 95:2:3, and uniformly stirring to obtain negative electrode slurry; and uniformly coating the negative electrode slurry on a copper foil, drying, rolling, slitting and punching to obtain the negative electrode pole piece.
(4) Assembling the battery cell: and winding the positive pole piece, the diaphragm and the negative pole piece to form a sandwich structure, flattening the wound cylinder, welding a tab, packaging by using an aluminum plastic film to obtain a dry battery cell, and drying in vacuum at 85 ℃.
(5) Liquid injection and formation: and injecting the prepared electrolyte into the dry cell in a glove box, sealing, standing at normal temperature, forming, cutting the aluminum plastic film, exhausting air, and sealing for the second time to obtain the activated battery.
Example 5
A lithium ion battery was prepared by the following method:
(1) preparing a non-aqueous electrolyte: mixing anhydrous solvents of ethylene carbonate and methyl ethyl carbonate according to the mass ratio of 3:7, adding metered lithium hexafluorophosphate to prepare electrolyte with the molar concentration of 1mol/L, then adding electrolyte additive, wherein the using amount of the electrolyte additive is 5% of the total mass of the electrolyte, and uniformly mixing until the solid is completely dissolved. The structural formula of the electrolyte additive is as follows:
Figure BDA0002392575260000071
(2) preparing a positive pole piece: dispersing nickel cobalt lithium manganate LiNi0.8Co0.1Mn0.1O2, PVDF and a conductive agent in N-methylpyrrolidone according to the ratio of 93:3:4 to obtain positive electrode slurry; and uniformly coating the positive electrode slurry on an aluminum foil, drying, rolling, slitting and punching to obtain the positive electrode plate.
(3) Preparing a negative pole piece: dispersing artificial graphite, carboxymethyl cellulose and a conductive agent in water according to a ratio of 95:2:3, and uniformly stirring to obtain negative electrode slurry; and uniformly coating the negative electrode slurry on a copper foil, drying, rolling, slitting and punching to obtain the negative electrode pole piece.
(4) Assembling the battery cell: and winding the positive pole piece, the diaphragm and the negative pole piece to form a sandwich structure, flattening the wound cylinder, welding a tab, packaging by using an aluminum plastic film to obtain a dry battery cell, and drying in vacuum at 85 ℃.
(5) Liquid injection and formation: and injecting the prepared electrolyte into the dry cell in a glove box, sealing, standing at normal temperature, forming, cutting the aluminum plastic film, exhausting air, and sealing for the second time to obtain the activated battery.
Example 6
A lithium ion battery was prepared by the following method:
(1) preparing a non-aqueous electrolyte: mixing anhydrous solvents of ethylene carbonate and methyl ethyl carbonate according to the mass ratio of 3:7, adding metered lithium hexafluorophosphate to prepare electrolyte with the molar concentration of 1mol/L, then adding an electrolyte additive, wherein the using amount of the electrolyte additive is 3% of the total mass of the electrolyte, and uniformly mixing until solids are completely dissolved. The structural formula of the electrolyte additive is as follows:
Figure BDA0002392575260000081
(2) preparing a positive pole piece: dispersing nickel cobalt lithium manganate LiNi0.8Co0.1Mn0.1O2, PVDF and a conductive agent in N-methylpyrrolidone according to the ratio of 93:3:4 to obtain positive electrode slurry; and uniformly coating the positive electrode slurry on an aluminum foil, drying, rolling, slitting and punching to obtain the positive electrode plate.
(3) Preparing a negative pole piece: dispersing artificial graphite, carboxymethyl cellulose and a conductive agent in water according to a ratio of 95:2:3, and uniformly stirring to obtain negative electrode slurry; and uniformly coating the negative electrode slurry on a copper foil, drying, rolling, slitting and punching to obtain the negative electrode pole piece.
(4) Assembling the battery cell: and winding the positive pole piece, the diaphragm and the negative pole piece to form a sandwich structure, flattening the wound cylinder, welding a tab, packaging by using an aluminum plastic film to obtain a dry battery cell, and drying in vacuum at 85 ℃.
(5) Liquid injection and formation: and injecting the prepared electrolyte into the dry cell in a glove box, sealing, standing at normal temperature, forming, cutting the aluminum plastic film, exhausting air, and sealing for the second time to obtain the activated battery.
Example 7
A lithium ion battery was prepared by the following method:
(1) preparing a non-aqueous electrolyte: mixing anhydrous solvents of ethylene carbonate and methyl ethyl carbonate according to the mass ratio of 3:7, adding metered lithium hexafluorophosphate to prepare electrolyte with the molar concentration of 1mol/L, then adding electrolyte additive with the dosage of 0.5 percent of the total mass of the electrolyte, and uniformly mixing until the solid is completely dissolved. The structural formula of the electrolyte additive is as follows:
Figure BDA0002392575260000082
(2) preparing a positive pole piece: dispersing nickel cobalt lithium manganate LiNi0.8Co0.1Mn0.1O2, PVDF and a conductive agent in N-methylpyrrolidone according to the ratio of 93:3:4 to obtain positive electrode slurry; and uniformly coating the positive electrode slurry on an aluminum foil, drying, rolling, slitting and punching to obtain the positive electrode plate.
(3) Preparing a negative pole piece: dispersing artificial graphite, carboxymethyl cellulose and a conductive agent in water according to a ratio of 95:2:3, and uniformly stirring to obtain negative electrode slurry; and uniformly coating the negative electrode slurry on a copper foil, drying, rolling, slitting and punching to obtain the negative electrode pole piece.
(4) Assembling the battery cell: and winding the positive pole piece, the diaphragm and the negative pole piece to form a sandwich structure, flattening the wound cylinder, welding a tab, packaging by using an aluminum plastic film to obtain a dry battery cell, and drying in vacuum at 85 ℃.
(5) Liquid injection and formation: and injecting the prepared electrolyte into the dry cell in a glove box, sealing, standing at normal temperature, forming, cutting the aluminum plastic film, exhausting air, and sealing for the second time to obtain the activated battery.
Example 8
A lithium ion battery was prepared by the following method:
(1) preparing a non-aqueous electrolyte: mixing anhydrous solvents of ethylene carbonate and methyl ethyl carbonate according to the mass ratio of 3:7, adding metered lithium hexafluorophosphate to prepare electrolyte with the molar concentration of 1mol/L, then adding electrolyte additive with the dosage of 0.5 percent of the total mass of the electrolyte, and uniformly mixing until the solid is completely dissolved. The structural formula of the electrolyte additive is as follows:
Figure BDA0002392575260000091
(2) preparing a positive pole piece: dispersing nickel cobalt lithium manganate LiNi0.8Co0.1Mn0.1O2, PVDF and a conductive agent in N-methylpyrrolidone according to the ratio of 93:3:4 to obtain positive electrode slurry; and uniformly coating the positive electrode slurry on an aluminum foil, drying, rolling, slitting and punching to obtain the positive electrode plate.
(3) Preparing a negative pole piece: dispersing artificial graphite, carboxymethyl cellulose and a conductive agent in water according to a ratio of 95:2:3, and uniformly stirring to obtain negative electrode slurry; and uniformly coating the negative electrode slurry on a copper foil, drying, rolling, slitting and punching to obtain the negative electrode pole piece.
(4) Assembling the battery cell: and winding the positive pole piece, the diaphragm and the negative pole piece to form a sandwich structure, flattening the wound cylinder, welding a tab, packaging by using an aluminum plastic film to obtain a dry battery cell, and drying in vacuum at 85 ℃.
(5) Liquid injection and formation: and injecting the prepared electrolyte into the dry cell in a glove box, sealing, standing at normal temperature, forming, cutting the aluminum plastic film, exhausting air, and sealing for the second time to obtain the activated battery.
Comparative example 1
A lithium ion battery was prepared by the following method:
(1) preparing a non-aqueous electrolyte: mixing anhydrous solvents of ethylene carbonate and methyl ethyl carbonate according to the mass ratio of 3:7, adding metered lithium hexafluorophosphate to prepare electrolyte with the molar concentration of 1mol/L, then adding MMDS (sodium dodecyl benzene sulfonate) with the dosage of 0.5 percent of the total mass of the electrolyte, and uniformly mixing until the solid is completely dissolved.
(2) Preparing a positive pole piece: dispersing nickel cobalt lithium manganate LiNi0.8Co0.1Mn0.1O2, PVDF and a conductive agent in N-methylpyrrolidone according to the ratio of 93:3:4 to obtain positive electrode slurry; and uniformly coating the positive electrode slurry on an aluminum foil, drying, rolling, slitting and punching to obtain the positive electrode plate.
(3) Preparing a negative pole piece: dispersing artificial graphite, carboxymethyl cellulose and a conductive agent in water according to a ratio of 95:2:3, and uniformly stirring to obtain negative electrode slurry; and uniformly coating the negative electrode slurry on a copper foil, drying, rolling, slitting and punching to obtain the negative electrode pole piece.
(4) Assembling the battery cell: and winding the positive pole piece, the diaphragm and the negative pole piece to form a sandwich structure, flattening the wound cylinder, welding a tab, packaging by using an aluminum plastic film to obtain a dry battery cell, and drying in vacuum at 85 ℃.
(5) Liquid injection and formation: and injecting the prepared electrolyte into the dry cell in a glove box, sealing, standing at normal temperature, forming, cutting the aluminum plastic film, exhausting air, and sealing for the second time to obtain the activated battery.
(6) High-temperature cycle test: the cell was charged at 45 ℃ to 4.2V with a 1C current constant current and constant voltage, with a 0.05C cutoff current. Then discharged to 3.0V at 1C current, and the initial discharge capacity D was recorded1. Repeating the above steps for N times until the discharge capacity DnThe test was stopped at 80% of the initial discharge capacity. The number of cycles was recorded. The data are recorded in table 1.
(7) High-temperature storage test: the battery was charged to 4.2V at a constant current and a constant voltage of 1C current, with a current cutoff of 0.05C. Then discharged to 3.0V at 1C current, and the initial discharge capacity D was recorded1And is fully charged again. Measuring the thickness of the cell is marked d1. After storing the cell at 60 ℃ for N days, the cell was taken out and cooled to room temperature, discharged to 3.0V at a current of 1C, and the discharge capacity D was recordedn. Capacity retention rate of Dn/D1X 100%. Charging to 4.2V with 1C current constant current and constant voltage, stopping current at 0.05C, and recording the thickness d of the battery2. Thickness growth rate of 100% × (d)2-d1)/d1. Discharge to 3.0V at 1C and record the initial discharge capacity Dn+1. Capacity recovery rate of Dn+1/D1X 100%. The data are recorded in table 1.
Comparative example 2
A lithium ion battery was prepared by the following method:
(1) preparing a non-aqueous electrolyte: mixing anhydrous solvents of ethylene carbonate and methyl ethyl carbonate according to the mass ratio of 3:7, adding metered lithium hexafluorophosphate to prepare electrolyte with the molar concentration of 1mol/L, then adding MMDS (sodium dodecyl benzene sulfonate) with the dosage of 0.5 percent of the total mass of the electrolyte, and uniformly mixing until the solid is completely dissolved.
(2) Preparing a positive pole piece: dispersing nickel cobalt lithium manganate LiNi0.8Co0.1Mn0.1O2, PVDF and a conductive agent in N-methylpyrrolidone according to the ratio of 93:3:4 to obtain positive electrode slurry; and uniformly coating the positive electrode slurry on an aluminum foil, drying, rolling, slitting and punching to obtain the positive electrode plate.
(3) Preparing a negative pole piece: dispersing artificial graphite, carboxymethyl cellulose and a conductive agent in water according to a ratio of 95:2:3, and uniformly stirring to obtain negative electrode slurry; and uniformly coating the negative electrode slurry on a copper foil, drying, rolling, slitting and punching to obtain the negative electrode pole piece.
(4) Assembling the battery cell: and winding the positive pole piece, the diaphragm and the negative pole piece to form a sandwich structure, flattening the wound cylinder, welding a tab, packaging by using an aluminum plastic film to obtain a dry battery cell, and drying in vacuum at 85 ℃.
(5) Liquid injection and formation: and injecting the prepared electrolyte into the dry cell in a glove box, sealing, standing at normal temperature, forming, cutting the aluminum plastic film, exhausting air, and sealing for the second time to obtain the activated battery.
(6) High-temperature cycle test: the cell was charged at 45 ℃ to 4.2V with a 1C current constant current and constant voltage, with a 0.05C cutoff current. Then discharged to 3.0V at 1C current, and the initial discharge capacity D was recorded1. Repeating the above steps for N times until the discharge capacity DnThe test was stopped at 80% of the initial discharge capacity. The number of cycles was recorded. The data are recorded in table 1.
(7) High-temperature storage test: the battery was charged to 4.2V at a constant current and a constant voltage of 1C current, with a current cutoff of 0.05C. Then discharged to 3.0V at 1C current, and the initial discharge capacity D was recorded1And is fully charged again. Measuring the thickness of the cell is marked d1. After storing the cell at 60 ℃ for N days, the cell was taken out and cooled to room temperature, discharged to 3.0V at a current of 1C, and the discharge capacity D was recordedn. Capacity retention rate of Dn/D1X 100%. Charging to 4.2V with 1C current constant current and constant voltage, stopping current at 0.05C, and recording the thickness d of the battery2. Thickness growth rate of 100% × (d)2-d1)/d1. Discharge to 3.0V at 1C and record the initial discharge capacity Dn+1. Capacity recovery rate of Dn+1/D1X 100%. The data are recorded in table 1.
The results of the high temperature cycle test and the storage test of examples 1, 2 and comparative examples 1, 2 are shown in table 1. As seen from the data in table 1, the cycle number of the battery of example 1 cycled to a capacity retention of 80% at 45 ℃ was significantly increased when the charge-discharge cycle was performed at 45 ℃ compared to that of comparative example 1; the cycle number of the battery of example 2 cycled to a capacity retention of 80% at 45 c was also significantly increased compared to that of comparative example 2, indicating that the additive of the present invention can more effectively prevent capacity fade and cycle life degradation of the battery during high temperature cycling compared to MMDS at the same amount. When stored at 60 ℃, the increase rate of the thickness of the battery of example 1 is significantly reduced, and the 30-day capacity retention rate and the 30-day capacity recovery rate are significantly increased, compared to comparative example 1; the thickness increase rate of the battery of example 2 was also significantly reduced, and the 30-day capacity retention rate and the 30-day capacity recovery rate were also significantly increased, compared to comparative example 2, which shows that the additive of the present invention can better inhibit the capacity fade and gassing and swelling of the lithium ion battery during high temperature storage, compared to MMDS, at the same amount. In summary, compared with the existing electrolyte additive MMDS, the additive provided by the invention has a better effect of improving the high-temperature performance of the lithium ion battery.
TABLE 1
Figure BDA0002392575260000111
Figure BDA0002392575260000121
The raw materials and equipment used in the invention are common raw materials and equipment in the field if not specified; the methods used in the present invention are conventional in the art unless otherwise specified.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all simple modifications, alterations and equivalents of the above embodiments according to the technical spirit of the present invention are still within the protection scope of the technical solution of the present invention.

Claims (10)

1. An electrolyte additive, wherein the electrolyte additive has a structural formula:
Figure FDA0002392575250000011
wherein X is any one of the following cases:
a straight chain or branched chain alkyl group with 1-5 carbon atoms;
a linear or branched alkoxy group having 1 to 5 carbon atoms;
a straight or branched alkyl group in which some or all of the hydrogens are substituted with halogen atoms;
phenyl or substituted phenyl;
a carbonate group or a carbonate group substituted with a halogen atom;
a halogen atom;
a hydrogen atom.
2. An electrolyte comprising a lithium salt, an organic solvent and an electrolyte additive, wherein the electrolyte additive is the electrolyte additive of claim 1.
3. The electrolyte of claim 2, wherein the electrolyte additive is present in an amount of 0.01 to 10% by weight of the total electrolyte.
4. The electrolyte of claim 3, wherein the electrolyte additive is present in an amount of 0.1 to 5% by weight of the total electrolyte.
5. The electrolyte of claim 2, wherein the lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis (fluorosulfonyl) imide, lithium bis (trifluoromethylsulfonyl) imide, lithium methylsulfonate, lithium trifluoromethylsulfonate, lithium bis (oxalato) borate, lithium difluorooxalato phosphate, and lithium tetrafluorooxalato phosphate; the organic solvent is one or more of a carbonate solvent, a carboxylic ester solvent, an ether solvent, a sulfone solvent and a nitrile solvent.
6. The electrolyte according to claim 5, wherein the carbonate solvent is one or more selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl ethyl carbonate, and dipropyl carbonate; the carboxylic ester solvent is one or more of ethyl acetate, methyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate and 1, 4-butyrolactone; the sulfone solvent is one or more of dimethyl sulfoxide, sulfolane, diphenyl sulfoxide, thionyl chloride and dipropyl sulfone; the nitrile solvent is one or more of acetonitrile, propionitrile, succinonitrile and adiponitrile.
7. The electrolyte of claim 5, wherein the lithium salt is present in a concentration of 0.5M to 1.3M.
8. The electrolyte of claim 5, wherein the organic solvent comprises 80-90% of the total electrolyte mass.
9. A lithium ion battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is the electrolyte according to any one of claims 2 to 8.
10. The lithium ion battery of claim 9, wherein the positive electrode comprises a positive active material, and the positive active material is LiCoO2、LiNiO2、LiMn2O4、LiFePO4、LiNixCoyMnzO2Wherein x + y + z is 1; the negative electrode comprises a negative electrode active material, and the negative electrode active material is one or more of natural graphite, artificial graphite, lithium titanate, silicon and a silicon-carbon compound; the diaphragm is one or more of polyethylene, polypropylene, polyimide, aramid fiber, ceramic and PVDF.
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