CN109873198B - Electrolyte solution and battery - Google Patents
Electrolyte solution and battery Download PDFInfo
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- CN109873198B CN109873198B CN201711271121.XA CN201711271121A CN109873198B CN 109873198 B CN109873198 B CN 109873198B CN 201711271121 A CN201711271121 A CN 201711271121A CN 109873198 B CN109873198 B CN 109873198B
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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- Y02E60/10—Energy storage using batteries
Abstract
An electrolyte and a battery are provided, the electrolyte including a fluorine-containing compound and an additive. The additive can form a stable solid electrolyte interface film (SEI film) on the surface of an anode in the battery formation process to inhibit the decomposition of other components in the electrolyte on the surface of the anode, and the fluorine-containing compound has excellent stability and extremely low surface tension and can form a liquid film on the surface of an electrode, so that the decomposition of the electrolyte on the surface of the electrode in the battery circulation process is relieved, and the circulation performance of the battery is improved; the electrolyte and the fluorine-containing compound have synergistic and cooperative effects, so that the cycle performance of the battery can be further improved, and the battery containing the fluorine-containing compound and the additive in the electrolyte has good cycle performance and long service life.
Description
Technical Field
The application relates to the field of batteries, in particular to an electrolyte and a battery.
Background
At present, lithium ion batteries have a wide application field, have the advantages of high energy density, no memory effect and the like, are applied to the fields of electric automobiles, consumer electronics products, energy storage devices and the like, and gradually become mainstream batteries in the fields. However, the current lithium ion battery commonly used by people has poor cycle performance, generally, after the lithium ion battery is used for two years, the cycle performance is obviously attenuated, the consumption experience of consumers is seriously influenced, and further the large-scale popularization of the lithium ion battery in the market is influenced, so that the current battery needs to be improved.
Disclosure of Invention
The present application is directed to solving, at least to some extent, one of the technical problems in the related art. Therefore, an object of the present invention is to provide an electrolyte solution capable of effectively improving cycle performance or service life of a battery, and a battery including the same.
In one aspect of the present application, an electrolyte is provided. According to an embodiment of the present application, the electrolyte includes a fluorine-containing compound and an additive. The inventor finds that the additive can form a stable solid electrolyte interface film (SEI film) on the surface of an anode in the battery formation process, and inhibit the decomposition of other components in the electrolyte on the surface of the anode, while the fluorine-containing compound has excellent stability and extremely low surface tension, and when the electrolyte containing the fluorine-containing compound is injected into the battery, a liquid film is formed on the surface of the electrode, so that the direct contact between the electrolyte and the surface of the electrode is avoided, the reaction consumption of the electrolyte on the surface of the electrode in the battery circulation process is relieved, and the cycle performance of the battery is improved; moreover, the inventor also finds that the battery using the electrolyte containing the fluorine-containing compound and the electrolyte additive has better cycle performance than the battery using the fluorine-containing compound or the electrolyte additive, the synergistic effect of the fluorine-containing compound and the electrolyte additive further enhances the thermal stability of the formed SEI film and slows down the continuous consumption of the electrolyte caused by the continuous decomposition and formation of the SEI film in the long-term cycle process, and the fluorine-containing compound and the electrolyte additive can be synergistic and matched, so that the cycle performance of the battery is remarkably improved, the service life is remarkably prolonged, and the service performance is very good.
In addition, the electrolyte according to the above-described embodiment of the present application may also have the following additional technical features:
according to embodiments herein, the fluorochemical is one or more of a perfluoropolyether and a perfluoroalkane. The perfluoropolyether and the perfluoroalkane form a liquid film on the surface of an electrode by virtue of lower surface tension of the perfluoropolyether and the perfluoroalkane, one or more of the perfluoropolyether and the perfluoroalkane is mixed with the electrolyte and injected into the battery, and the decomposition of the electrolyte on the surface of the electrode can be relieved in the battery circulation process, so that the circulation performance of the battery is improved.
According to an embodiment of the application, the additive is one or more selected from vinylene carbonate, fluoroethylene carbonate, lithium dioxalate borate and lithium difluorooxalate borate. Therefore, a stable solid electrolyte interface film (SEI film) can be formed on the surface of the anode in the battery formation process, the decomposition of other components in the electrolyte on the surface of the anode is inhibited, and the cycle performance of the battery is effectively improved.
According to an embodiment of the present application, the fluorine-containing compound is in a liquid state at room temperature (25 ℃) and has a boiling point of not less than 80 ℃. Therefore, the fluorine-containing compound has the advantages of higher boiling point, stable electrochemical property, wider use temperature range and better low-temperature and high-temperature resistance, can effectively inhibit the components in the electrolyte from being decomposed on the surface of the electrode, can effectively improve the cycle performance of the battery when being applied to the battery, and prolongs the service life of the battery.
According to the embodiment of the application, the mass fraction of the fluorine-containing compound is 0.01-2% based on the total mass of the electrolyte. The mass fraction of the fluorine-containing compound in the above range can significantly improve the cycle performance of the battery, and ensure that the first charge and discharge of the battery has high efficiency.
According to embodiments herein, the perfluoropolyether is selected from one or more of the following:
wherein m and n may be the same or different and each represents an integer of more than 1. The perfluoropolyether containing the structures of the formulas 1 to 4 has low surface tension, and one or more of the perfluoropolyethers with the structures are injected into the battery together with the electrolyte, so that a protective liquid film can be formed on the surface of an electrode in the battery circulation process, the electrolyte is protected from being decomposed, and the circulation performance and the service life of the battery containing the perfluoropolyether are improved.
According to embodiments herein, the perfluoropolyether has a molecular weight greater than 400. Therefore, the perfluoropolyether can effectively form a protective liquid film on the surface of the electrode, so that the electrolyte containing the perfluoropolyether has long service life, and the battery containing the electrolyte has better cycle performance.
According to embodiments of the present application, the perfluoroalkane has the formula: cxF2x+2(formula 5), wherein x is selected from an integer greater than 5. The perfluoroalkane with the structure has low surface tension, and can form a protective liquid film on the surface of an electrode to protect electrolyte from being decomposed, so that the service life of the electrolyte containing the perfluoroalkane is prolonged, and the cycle performance of a battery containing the electrolyte is improved.
According to the embodiment of the application, the weight fraction of the vinylene carbonate is 0.1-4%, the weight fraction of the fluoroethylene carbonate is 0.5-20%, the weight fraction of the lithium dioxalate borate is 0.1-4%, and the weight fraction of the lithium difluorooxalate borate is 0.1-4% based on the total weight of the electrolyte. Therefore, the electrolyte additive in the battery has low manufacturing cost within the range, an SEI film can be fully formed on the surface of the anode of the battery, the cycle performance of the battery is obviously improved, the storage gas production performance of the battery is not deteriorated, the service life of the battery is prolonged, and the service performance of the battery is better.
According to an embodiment of the present application, the above electrolyte further includes a lithium salt selected from one or more of inorganic lithium salts and organic lithium salts; preferably, the lithium salt is selected from lithium hexafluorophosphate (LiPF)6) Lithium difluorophosphate (LiPO)2F2) Lithium tetrafluoroborate (LiBF)4) One or more of lithium hexafluoroarsenate, lithium perchlorate, lithium bis (fluorosulfonyl) imide (LiFSI), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI); further preferably, the lithium salt is lithium hexafluorophosphate (LiPF)6). The lithium salt has good electrochemical stability, is easy to dissolve in an organic solvent and dissociate, ensures that the electrolyte has higher lithium ion conductivity, has less influence on the environment by decomposition products, has environment-friendly performance, is easy to purify and prepare, and has lower price.
According to an embodiment of the present application, the electrolyte further includes an organic solvent selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1, 4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, and ethyl butyrate. The organic solvent has moderate viscosity and dielectric constant, good thermal stability, wide application temperature range, good chemical and electrochemical properties, high safety and environmental compatibility and low price.
In another aspect of the present application, a battery is provided. According to an embodiment of the application, the battery comprises the electrolyte as described above. The battery has obviously enhanced cycle performance, obviously prolonged service life and greatly improved user experience.
Detailed Description
Embodiments of the present application are described in detail below. The following description of the embodiments is merely exemplary in nature and is in no way intended to limit the present disclosure. The examples do not specify particular techniques or conditions, according to techniques or conditions described in the literature in the field or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.
The present application has been completed based on the following findings and recognition by the inventors:
in the existing battery, in order to improve the cycle performance of the battery, the adopted method is to inject at least one of perfluoropolyether and perfluoroalkane and electrolyte into the lithium ion battery, and the perfluoropolyether or perfluoroalkane forms a coating on the surface of an electrode by virtue of lower surface tension of the perfluoropolyether or perfluoroalkane, so that the decomposition of the electrolyte on the surface of the electrode is relieved, and the cycle performance of the lithium ion battery is improved. However, the liquid film formed by the liquid perfluoropolyether and perfluoroalkane molecules has a limited protective effect on the electrode, and can only improve the cycle performance of the lithium ion battery to a certain extent. This limits the application of lithium ion batteries in the market and thus cannot meet the market demand. The inventor finds that the fluorine-containing compound with lower surface energy and the electrolyte additive are added into the electrolyte at the same time, and can cooperate and cooperate to form a protective film with better protection effect on the surface of the electrode, so that the cycle performance and the service life of the battery are obviously improved, the higher and higher market requirements are further met, and the user experience is improved.
In view of the above, in one aspect of the present application, an electrolyte is provided. According to an embodiment of the application, the electrolysis comprises a fluorine-containing compound and an additive. The inventor finds that the additive can form a stable solid electrolyte interface film (SEI film) on the surface of an anode in the battery formation process, inhibit the decomposition of other components in the electrolyte on the surface of the anode and improve the cycle performance of the battery, and the fluorine-containing compound has excellent stability and extremely low surface tension and is lower than the surface tension of the electrolyte, and when the fluorine-containing compound and the electrolyte are injected into a dry core of the battery together, a liquid film is formed on the surface of an electrode, so that the decomposition of the electrolyte on the surface of the electrode in the battery cycle process is relieved, and the cycle performance of the battery is improved; the electrolyte containing the fluorine-containing compound and the additive can cooperate with each other, so that the cycle performance of the battery containing the electrolyte is obviously improved, the service life is obviously prolonged, the service performance is very good, and the performance of the battery is obviously superior to that of the battery containing only one of the fluorine-containing compound and the additive of the electrolyte.
According to the embodiments of the present application, in order to improve the cycle performance of the battery, the properties of the fluorine-containing compound are not particularly limited, and those skilled in the art can flexibly select the fluorine-containing compound as long as the requirements of low surface energy and protection of the electrolyte from decomposition are satisfied. In some embodiments herein, the fluorochemical is liquid at room temperature (25 ℃) and has a boiling point of no less than 80 ℃. Therefore, the fluorine-containing compound has the advantages of higher boiling point, stable property, wider use temperature range and better low-temperature and high-temperature resistance, can effectively inhibit the decomposition of components in the electrolyte at the electrode, can effectively improve the cycle performance of the battery when being applied to the battery, and prolongs the service life of the battery.
According to the embodiment of the present application, the kind of the fluoride-containing compound is not particularly limited, and one skilled in the art can flexibly select the fluoride-containing compound as needed as long as it can satisfy the requirement of having a low surface tension. In some embodiments herein, the fluorochemical is selected from one or more of a perfluoropolyether and a perfluoroalkane. Therefore, the perfluoropolyether and the perfluoroalkane form a liquid film on the surface of the electrode by virtue of lower surface tension thereof, at least one of the perfluoropolyether and the perfluoroalkane is mixed with the electrolyte and injected into the battery, and the decomposition of the electrolyte on the surface of the electrode can be relieved in the battery circulation process, so that the battery circulation performance is improved.
The structure of the perfluoropolyether according to the embodiments of the present application is not particularly limited, and those skilled in the art can flexibly select the perfluoropolyether as long as the requirement of low surface tension can be satisfied. In some embodiments herein, the perfluoropolyether is selected from one or more of the following:
wherein m and n may be the same or different and each represents an integer of more than 1. Therefore, the perfluoropolyether containing the structures of the formulas 1 to 4 has low surface tension, and the perfluoropolyether containing the structures is injected into the battery together with the electrolyte, so that a protective liquid film can be formed on the surface of an electrode in the battery circulation process, the electrolyte is protected from being decomposed, and the circulation performance and the service life of the battery containing the perfluoropolyether are improved.
The molecular weight of the perfluoropolyether according to the examples of the present application is not particularly limited and can be flexibly selected by those skilled in the art as long as the requirement is satisfied. In some embodiments of the present application, the perfluoropolyether has a molecular weight greater than 400. Therefore, the chemical property of the perfluoropolyether is stable, the perfluoropolyether can effectively form a protective film layer on the surface of an electrode, the battery containing the perfluoropolyether is good in cycle performance and long in service life, and the battery containing the electrolyte is good in cycle performance.
The structure of perfluoroalkanes according to the examples of the present application is not particularly limited, and can be flexibly selected by one skilled in the art as long as the requirements are satisfied. In some embodiments of the present application, the perfluoroalkane has the formula: cxF2x+2Wherein x is an integer greater than 5, and the chemical structure of the compound can be a branched chain or a linear chain structure. Preferably, the perfluoroalkanes are chosen from those which are liquid at room temperature (25 ℃), such as perfluorododecane (C)12F26). Therefore, the perfluoroalkane with the structure has low surface tension, can form a protective film layer on the surface of an electrode and protect electrolyte from decomposition, so that the circulation performance of the battery can be improved by injecting the electrolyte containing the perfluoroalkane into the battery, the service life of the battery is prolonged, and the service performance is better.
According to the embodiment of the present application, in order to alleviate the decomposition of the electrolyte on the electrode surface, the mass fraction of the fluorine-containing compound is 0.01% to 2% based on the total mass of the electrolyte. The mass fraction of the fluorine-containing compound in the range can fully form a protective liquid film on the surface of the electrode, effectively relieve the decomposition of the electrolyte, obviously improve the cycle performance of the battery containing the fluorine-containing compound, and ensure that the first charge and discharge of the battery has higher efficiency. When the mass percentage of the fluorine-containing compound is less than 0.01%, a protective liquid film formed on the surface of the electrode is insufficient, the improvement on the cycle performance of the lithium ion battery is not obvious, and when the mass percentage of the fluorine-containing compound is more than 2%, the first charge-discharge efficiency of the lithium ion battery is reduced.
According to the embodiment of the application, in order to further improve the cycle performance of the battery, an appropriate amount of additive is added into the electrolyte, and the additive is selected from one or more of vinylene carbonate, vinyl fluorocarbonate, lithium bis (oxalato) borate and lithium difluoro (oxalato) borate. Therefore, the electrolyte additive has low cost, can form an SEI film on the surface of the anode in the battery formation process, inhibits the decomposition of other components in the electrolyte on the surface of the anode, and can obviously improve the cycle performance of the battery under the synergistic action of the additive and the fluorine-containing compound, so that the service life of the battery is prolonged, and the service performance of the battery is better.
In some embodiments of the present application, the mass fraction of the Vinylene Carbonate (VC) is 0.1% to 4% based on the total mass of the electrolyte, and thus, the mass fraction of the electrolyte additive vinylene carbonate in the battery is in the above range, the manufacturing cost is low, an SEI film can be sufficiently formed on the surface of the anode in the battery formation process, decomposition of other components in the electrolyte on the surface of the anode is inhibited, the cycle performance of the battery is significantly improved, and the storage gassing performance of the battery is not deteriorated, so that the service life of the battery is prolonged, and the service performance of the battery is better. When the mass percentage of the vinylene carbonate is less than 0.1%, an SEI film cannot be fully formed on the surface of an anode in the battery formation process, so that the improvement on the battery cycle performance is not obvious, and when the mass percentage of the vinylene carbonate is more than 4%, the storage gas production performance of the lithium ion battery is deteriorated, the service performance of the battery is influenced, and the manufacturing cost is increased.
In some embodiments of the present application, the mass fraction of the fluoroethylene carbonate (FEC) is 0.5% to 20% based on the total mass of the electrolyte. Therefore, the mass fraction of the electrolyte additive fluoroethylene carbonate in the battery is in the range, the manufacturing cost is low, an SEI film can be fully formed on the surface of the anode in the battery formation process, the cycle performance of the battery is obviously improved, the storage gas production performance of the battery is not deteriorated, the service life of the battery is prolonged, and the service performance of the battery is good. When the mass percentage of the fluoroethylene carbonate is less than 0.5%, an SEI film cannot be fully formed on the surface of the anode in the battery formation process, the improvement on the cycle performance of the lithium ion battery is not obvious, and when the mass percentage of the fluoroethylene carbonate is more than 20%, the cycle performance of the lithium ion battery is not further improved, the storage gas production performance of the lithium ion battery is deteriorated, and the manufacturing cost is increased.
In some embodiments of the present application, the lithium bis (oxalato) borate (LiBOB) is present in a mass fraction of 0.1% to 4% based on the total mass of the electrolyte. Therefore, the electrolyte additive lithium bis (oxalato) borate in the battery has low manufacturing cost within the range, an SEI film can be fully formed on the surface of the anode in the battery formation process, the cycle performance of the battery is obviously improved, the storage gas production performance of the battery is not deteriorated, the service life of the battery is prolonged, and the service performance of the battery is good. When the mass percentage of the lithium dioxalate borate is less than 0.1%, an SEI film cannot be sufficiently formed on the surface of an anode in the battery formation process, the improvement on the cycle performance of the lithium ion battery is not obvious, and when the mass percentage of the lithium dioxalate borate is more than 4%, the storage gas production performance of the lithium ion battery is deteriorated and the manufacturing cost is increased.
In some embodiments of the present application, the lithium difluorooxalate borate (LiODFB) is present in a mass fraction of 0.1% to 4% based on the total mass of the electrolyte. Therefore, the electrolyte additive lithium difluoro (oxalato) borate in the battery has low manufacturing cost within the range, an SEI film can be fully formed on the surface of the anode in the battery formation process, the cycle performance of the battery is obviously improved, the storage gas production performance of the battery is not deteriorated, the service life of the battery is prolonged, and the service performance of the battery is better. When the mass percentage of the lithium difluoro oxalato borate is lower than 0.1%, an SEI film cannot be sufficiently formed on the surface of an anode in the battery formation process, the improvement on the cycle performance of the lithium ion battery is not obvious, and when the mass percentage of the lithium difluoro oxalato borate is higher than 4%, the storage gas production performance of the lithium ion battery is deteriorated, and the manufacturing cost is increased.
According to the embodiment of the present application, the electrolyte may further include a lithium salt, and the kind of the lithium salt is not particularly limited as long as the electrolyte can ensure high conductivity, and one skilled in the art can flexibly select the lithium salt according to needs. In some embodiments herein, the lithium salt is selected from one or more of inorganic lithium salts and organic lithium salts. The inorganic lithium salt may include, but is not limited to, lithium hexafluorophosphate (LiPF)6) Lithium difluorophosphate (LiPO)2F2) Lithium tetrafluoroborate (LiBF)4) One or more of lithium hexafluoroarsenate and lithium perchlorate, which may include, but is not limited to, lithium bis (fluorosulfonyl) imide (LiFSI), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF)3SO3) And lithium bis (trifluoromethylsulfonyl) imide (LiN (CF)3SO2)2) One or more of (a). The lithium salt has strong lithium ion transmission capacity, ensures that the electrolyte has higher lithium ion conductivity, has good electrochemical stability and chemical stability, is easy to dissolve in an organic solvent and dissociate, has less influence on the environment by a decomposition product, has environment-friendly performance, is easy to purify and prepare, and has lower price.
In some embodiments herein, the lithium salt is selected from lithium hexafluorophosphate (LiPF)6) Lithium difluorophosphate (LiPO)2F2) Lithium tetrafluoroborate (LiBF)4) One or more of lithium hexafluoroarsenate, lithium perchlorate, lithium bis (fluorosulfonyl) imide (LiFSI), and lithium bis (trifluoromethanesulfonyl) imide (LiTFSI). In some embodiments herein, the lithium salt is lithium hexafluorophosphate (LiPF)6). Therefore, the lithium salt has strong lithium ion transmission capacity, ensures that the electrolyte has higher lithium ion conductivity, has good electrochemical stability and chemical stability, is easy to dissolve in an organic solvent and dissociate, has less influence on the environment by decomposition products, has environment-friendly performance, and is easy to decomposeThe price is low for purification and preparation.
According to the embodiment of the present application, the concentration of the lithium salt is not particularly limited, and may be flexibly selected by those skilled in the art as long as the requirement is satisfied. In some embodiments of the present application, the concentration of the lithium salt is from 0.5mol/L to 1.5mol/L, and in other embodiments of the present application, the concentration of the lithium salt is from 0.8mol/L to 1.2 mol/L. Therefore, the concentration of the lithium salt in the range can ensure that the electrolyte has higher lithium ion conductivity, and the electrolyte has moderate viscosity and lower cost.
According to an embodiment of the present application, the electrolyte may further include an organic solvent, and the kind of the organic solvent is not particularly limited, and may be flexibly selected by those skilled in the art as long as it can satisfy the requirement. In some embodiments herein, the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate, ethylmethyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, propylmethyl carbonate, propylethyl carbonate, 1, 4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, and ethyl butyrate. Therefore, the selected organic solvent has moderate viscosity and dielectric constant, good thermal stability, wide range of use temperature, good chemical and electrochemical properties, high safety and environmental compatibility and low price.
According to the embodiment of the present application, the preparation method of the electrolyte is not particularly limited, and those skilled in the art can flexibly select the electrolyte according to the need. In some embodiments of the present application, the electrolyte is prepared by conventional methods of mixing the materials. Therefore, the preparation method is simple, easy to realize, simple and convenient to operate and low in cost.
In another aspect of the present application, a battery is provided. According to an embodiment of the application, the battery comprises the electrolyte as described above. Therefore, the electrolyte is simple in structure, easy to realize and low in cost, the electrolyte is applied to the battery, the additive can form an SEI film on the surface of the anode of the battery, the fluorine-containing compound in the electrolyte can form a protective liquid film on the surface of an electrode, and the fluorine-containing compound and the protective liquid film can effectively improve the cycle performance of the battery under the synergistic action of the SEI film and the protective liquid film, so that the service performance of the battery is improved, and the market popularization is facilitated.
According to an embodiment of the present application, the lithium ion battery further includes a positive electrode sheet containing a positive electrode active material, a negative electrode sheet containing a negative electrode active material, and a separator. Here, the specific kind of the anode active material is not particularly limited, and those skilled in the art can flexibly select it as needed. In some embodiments of the present application, the negative active material is selected from natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO2Spinel-structured lithiated TiO2-Li4Ti5O12One or more of Li-Al alloy; the specific kind of the cathode active material is not particularly limited, and those skilled in the art can flexibly select it as desired. In some embodiments of the present application, the positive active material includes, but is not limited to, one or more of lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel cobaltate, lithium iron phosphate, lithium nickel cobalt aluminate, and lithium nickel cobalt manganate, and the above positive active material includes a prior art positive active material subjected to a doping or coating process. . The material for forming the isolation film is not particularly limited, and those skilled in the art can flexibly select the material as needed. In some embodiments of the present application, the separator comprises a Polyethylene (PE) separator, a polypropylene (PP) separator, or the like. Further, the separator includes one or more of an uncoated bare separator, an inorganic particle coated separator, and a polymer coated separator, depending on whether the surface of the separator contains a coating and the type of coating. . Therefore, the structure is simple and easy to realize, and the battery adopting the anode material, the cathode material and the isolating membrane is low in cost, good in stability and good in service performance.
According to the embodiment of the application, in a general battery, the protective film formed on the surface of the electrode by using liquid polymer molecules is used for protecting the components in the electrolyte from being decomposed, so that the decomposition of the electrolyte can be relieved to a certain extent, the cycle performance and the service performance of the battery cannot be obviously improved, and the market requirement cannot be further met. In the application, the composition of the electrolyte is adjusted, and the fluorine-containing compound capable of forming a protective liquid film on the surface of an electrode and the additive capable of forming a stable SEI film on the surface of an anode in the battery formation process are added into the electrolyte, so that the decomposition of the electrolyte on the surface of the electrode is inhibited, the cycle performance of the battery is obviously improved, the service performance is improved, the requirements of the current market are effectively met, and the user experience is improved.
Examples
The lithium ion batteries of examples 1 to 17 and comparative examples 1 to 18 were prepared according to the following preparation methods, with the compositions shown in table 1, as follows:
the preparation method comprises the following steps:
1. forming a lithium ion battery
(1) Preparation of positive plate
The positive electrode active material lithium cobaltate (LiCoO)2) Mixing a conductive agent Super P and a binding agent polyvinylidene fluoride according to the weight ratio of 97:1.4:1.6, adding N-methyl pyrrolidone (NMP), and stirring until the system becomes uniform and transparent to obtain anode slurry; uniformly coating the positive electrode slurry on a positive electrode current collector aluminum foil; and drying the aluminum foil at 85 ℃, then carrying out cold pressing, cutting into pieces, slitting and drying to obtain the positive plate.
(2) Preparation of negative plate
Mixing the negative active material artificial graphite, the conductive agent Super P, the thickening agent carboxymethylcellulose sodium (CMC) and the binder Styrene Butadiene Rubber (SBR) according to the weight ratio of 96.4:1.5:0.5:1.6, adding deionized water, and stirring to obtain negative slurry; uniformly coating the negative electrode slurry on a copper foil of a negative electrode current collector; and drying the copper foil at 85 ℃, and then carrying out cold pressing, cutting and slitting on the copper foil, and drying to obtain the negative plate.
(3) Preparation of electrolyte
Mixing Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and diethyl carbonate (DEC) in a dry argon atmosphere glove box according to the mass ratio of EC to EMC to DEC to 30:50:20, adding an additive, dissolving and fully stirring, and adding lithium salt LiPF6And mixing uniformly to obtain the electrolyte. Wherein, LiPF6The concentration of (2) was 1.05 mol/L. Used in the electrolyteThe specific kinds and contents of other electrolyte additives are shown in table 1. In table 1, the content of the electrolyte additive is a mass percentage calculated based on the total mass of the electrolyte.
(4) Preparation of the separator
A16 μm thick Polyethylene (PE) barrier film was used.
(5) Preparation of lithium ion battery
Stacking the positive plate, the isolating film and the negative plate in sequence to enable the isolating film to be positioned between the positive plate and the negative plate to play an isolating role, and then winding to obtain a bare cell; and injecting the prepared electrolyte into the dried battery cell, performing vacuum packaging, standing, formation (charging to 3.3V at a constant current of 0.02C and then charging to 3.6V at a constant current of 0.1C), shaping, capacity testing and other procedures to obtain the soft package lithium ion battery.
TABLE 1 kinds and amounts of additives in electrolytes of examples 1 to 17 and comparative examples 1 to 18
2. Lithium ion battery performance test process
(1) Lithium ion battery cycle performance test
And (3) placing the lithium ion battery in a constant temperature box at 25 ℃, and standing for 30 minutes to keep the temperature of the lithium ion battery constant. The lithium ion battery reaching a constant temperature was charged at a constant current of 0.7C to a voltage of 4.3V, then charged at a constant voltage of 4.3V to a current of 0.05C, and then discharged at a constant current of 1C to a voltage of 3.0V, which is a charge-discharge cycle. The first discharge capacity is 100%, the charge and discharge cycle is repeated until the discharge capacity is attenuated to 80%, the test is stopped, the cycle number is recorded and used as an index for evaluating the cycle performance of the lithium ion battery, and the test result is shown in table 2.
Meanwhile, the cycle performance of the lithium ion battery at 45 ℃ is tested, the test method is the same as the test method for the cycle performance at 25 ℃, and the test results are shown in table 2.
(2) High temperature storage test of lithium ion battery
And (3) placing the lithium ion battery in a constant temperature box at 25 ℃, and standing for 30 minutes to keep the temperature of the lithium ion battery constant. Charging to 4.4V at a constant current of 0.5C, charging to a current of 0.05C at a constant voltage, then discharging to 3.0V at a constant current of 0.5C, and recording the discharge capacity as the initial capacity of the lithium ion battery. And then charging to 4.4V at a constant current of 0.5C and charging at a constant voltage to a current of 0.05C, and testing and recording the thickness of the battery. And transferring the tested lithium ion battery into a 60 ℃ constant temperature box for storage for 21 days, testing and recording the thickness of the battery once every 3 days, transferring the battery into a 25 ℃ constant temperature box after the 21-day storage is finished, standing for 60 minutes, discharging to 3.0V at a constant current of 0.5C, and recording the discharge capacity as the residual capacity of the lithium ion battery. And (3) calculating the expansion rate of the storage thickness of the lithium ion battery, and taking the expansion rate as an index for evaluating the high-temperature storage gas production rate of the lithium ion battery, wherein the test result is shown in table 2.
Wherein the thickness swell ratio (thickness-initial thickness after 21 days of storage)/initial thickness 100%
(3) First charge-discharge efficiency of lithium ion battery
First effect is first discharge capacity/first charge capacity 100%, and the test results are shown in table 2.
TABLE 2 results of performance test of lithium ion batteries of examples 1 to 17 and comparative examples 1 to 18
3. Analysis of results
From the data analysis in tables 1 and 2, it can be seen from comparative examples 1 and 2 to 9 that the addition of one or more of VC, FEC, LiBOB, and LiODFB can significantly improve the cycle performance and first-pass performance of the lithium ion battery without deteriorating the storage performance. However, in order to provide better consumer experience to consumers, the cycle performance of the lithium ion battery needs to be further improved.
From comparative example 1 and comparative examples 10 to 12, it is understood that the addition of one or more of perfluoropolyether and perfluorododecane can significantly improve the cycle performance of a lithium ion battery without deteriorating the storage performance. Also, the cycle performance of lithium ion batteries still needs to be improved.
As can be seen from comparative examples 2 to 12 and examples 1 to 17, combining at least one of perfluoropolyether and perfluorododecane with at least one of VC, FEC, LiBOB, and LiODFB can further improve the cycle performance of a lithium ion battery while hardly deteriorating the storage performance on the basis of adding at least one of perfluoropolyether and perfluorododecane alone or at least one of VC, FEC, LiBOB, and LiODFB.
It is clear from examples 1, 18 and 19 that the effect of perfluoropolyether on improving the performance of lithium ion batteries is hardly affected by its molecular structure when the molecular weights are close to each other.
From comparative examples 13 to 16 and examples 1, 3, 5, and 7, it is known that when the amount of VC added exceeds 5%, the storage performance of the lithium ion battery is seriously deteriorated; when the addition amount of the FEC exceeds 20%, the storage performance of the lithium ion battery is seriously deteriorated; when the addition amount of the LiBOB exceeds 5%, the storage performance of the lithium ion battery is seriously deteriorated; when the addition amount of the LiODFB exceeds 5%, the storage performance of the lithium ion battery is seriously deteriorated.
From comparative examples 17 to 18 and examples 1 to 2, it is understood that when the amount of perfluoropolyether or perfluorododecane added exceeds 2%, the first charge-discharge efficiency of the lithium ion battery is severely lowered.
In the description herein, reference to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the application. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present application, and that variations, modifications, substitutions and alterations may be made to the above embodiments by those of ordinary skill in the art within the scope of the present application.
Claims (8)
1. An electrolyte, comprising:
a fluorine-containing compound; and
an additive selected from lithium bis (oxalato) borate or lithium difluoro (oxalato) borate, wherein the mass fraction of the lithium bis (oxalato) borate is 0.1-4%, the mass fraction of the lithium difluoro (oxalato) borate is 0.1-4%,
the fluorine-containing compound is selected from one or more of perfluoropolyether and perfluorododecane, and the mass fraction of the fluorine-containing compound is 0.01% -2% based on the total mass of the electrolyte, wherein the perfluoropolyether is:
wherein m represents an integer greater than 1.
2. The electrolyte of claim 1, wherein the fluorine-containing compound is liquid at room temperature and has a boiling point of not less than 80 degrees celsius.
3. The electrolyte of claim 1, wherein the perfluoropolyether has a molecular weight greater than 400.
4. The electrolyte of claim 1, wherein the electrolyte further comprises a lithium salt selected from one or more of inorganic lithium salts and organic lithium salts.
5. The electrolyte of claim 4, wherein the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis (fluorosulfonyl) imide, lithium bis (trifluoromethanesulfonyl) imide.
6. The electrolyte of claim 5, wherein the lithium salt is lithium hexafluorophosphate.
7. The electrolyte of claim 1, wherein the electrolyte further comprises an organic solvent selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, propyl methyl carbonate, propyl ethyl carbonate, 1, 4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, and ethyl butyrate.
8. A battery comprising the electrolyte of any one of claims 1-7.
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