CN115548439A - Electrolyte for secondary battery and secondary battery - Google Patents

Electrolyte for secondary battery and secondary battery Download PDF

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CN115548439A
CN115548439A CN202110742394.8A CN202110742394A CN115548439A CN 115548439 A CN115548439 A CN 115548439A CN 202110742394 A CN202110742394 A CN 202110742394A CN 115548439 A CN115548439 A CN 115548439A
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secondary battery
electrolyte
additive
water
alkyl
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任建新
王圣
谢泽中
陶蒙
段柏禹
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BYD 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
    • H01M10/052—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
    • H01M10/0567—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
    • H01M10/42—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
    • 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 application provides a secondary battery electrolyte, including electrolyte salt, organic solvent and dewatering additive, dewatering additive includes the compound that the structural formula is shown as formula (1):
Figure DDA0003140083250000011
wherein R is 1 And R 3 Independently selected from any one of hydrogen, fluorine, alkyl, fluoroalkyl, alkenyl alkyl, alkynyl alkyl, alkenyl and alkynyl; r 2 And R 4 Independently selected from any one of fluorine, alkyl, fluoroalkyl, alkenyl alkyl, alkynyl alkyl, alkenyl, alkynyl, aryl and fluoroaryl. The water removal additive in the electrolyte of the secondary battery can remove water in the electrolyte, and reaction products of the water removal additive and water can be arranged on the positive electrode and the negative electrode of the batteryThe compact interfacial film is formed on the surface, and the interfacial film can improve the stability of the battery, reduce the impedance of the battery and ensure that the battery has good cycle performance and safety performance. The present application also provides a secondary battery.

Description

Electrolyte for secondary battery and secondary battery
Technical Field
The application relates to the technical field of secondary batteries, in particular to a secondary battery electrolyte and a secondary battery.
Background
Lithium secondary batteries have been widely used in terminal products (smart phones, digital cameras, notebook computers, electric vehicles, etc.) due to advantages of high energy density, high operating voltage, long service life, low self-discharge rate, environmental friendliness, etc. With the rapid development of the industry, higher requirements are made on the performance of lithium secondary batteries.
In the use of the lithium secondary battery, the direct contact of the anode material and the electrolyte is easy to generate side reaction, so that the electrolyte is oxidized and decomposed, a large amount of gas is generated, and the battery cycle attenuation and even the safety problem are caused. In addition, when the electrolyte contains a minute amount of water, the electrolyte salt reacts with water to generate a series of byproducts, which in turn causes the performance of the lithium secondary battery to be degraded. In order to solve the above problems, it is necessary to develop a new electrolyte system to improve the cycle performance and safety performance of the lithium secondary battery.
Disclosure of Invention
In view of the above, the present application provides a secondary battery electrolyte, in which a water removal additive in the secondary battery electrolyte can not only remove water in the electrolyte, but also a reaction product of the water removal additive and water can form a dense interface film on the surfaces of a positive electrode and a negative electrode of a battery, and the interface film can inhibit the reaction between the electrolyte and the positive and negative electrode materials, thereby improving the stability of the battery, reducing the impedance of the battery, and enabling the battery to have good cycle performance and safety performance.
The application provides a secondary battery electrolyte in a first aspect, which comprises electrolyte salt, an organic solvent and a water removal additive, wherein the water removal additive comprises a compound with a structural formula shown as a formula (1):
Figure BDA0003140083230000021
wherein, R is 1 And R 3 Independently selected from any one of hydrogen, fluorine, alkyl, fluoroalkyl, alkenyl alkyl, alkynyl alkyl, alkenyl and alkynyl; the R is 2 And R 4 Independently selected from any one of fluorine, alkyl, fluoroalkyl, alkenyl alkyl, alkynyl alkyl, alkenyl, alkynyl, aryl and fluoroaryl.
In the electrolyte of the secondary battery, the water removal additive comprises oxazaphosphorine, and sulfonyl and phosphoryl in an oxazaphosphorine structure have strong electron-withdrawing capability, so that P-O-C bonds in the water removal additive are easy to hydrolyze, so that water in the electrolyte is removed, and hydrolysis products of the water removal additive can form uniform and compact interface films on the surfaces of a positive electrode and a negative electrode of the battery, and the interface films can effectively prevent side reactions caused by direct contact of the electrolyte and the positive electrode and the negative electrode, so that the cycle performance and the safety performance of the battery are improved.
Alternatively, the R is 1 、R 2 、R 3 And R 4 At least one of which is fluorine or fluoroalkyl.
Alternatively, the R is 1 、R 2 、R 3 And R 4 At least one of which is fluorine.
Alternatively, the R is 1 、R 2 、R 3 And R 4 Is alkenylalkyl, alkynylalkyl, alkenyl, or alkynyl.
Optionally, the number of carbon atoms of the alkyl group, the fluoroalkyl group, the alkenylalkyl group, the alkynylalkyl group, the alkenyl group, and the alkynyl group is 1-10.
Optionally, the aryl group and the fluorinated aryl group have 6 to 20 carbon atoms.
Optionally, the water removal additive is 0.1 to 3 mass% in the secondary battery electrolyte. Further, the water removal additive accounts for 0.5-1.5% of the electrolyte of the secondary battery by mass.
Optionally, the additive further comprises a film forming additive.
Optionally, the film-forming additive comprises one or more of vinylene carbonate, fluoroethylene carbonate, methylene methanedisulfonate, lithium difluorophosphate, lithium difluorooxalato borate, propylene sulfite, vinyl sulfate, 1,3-propane sultone, and tripropylene phosphate.
Optionally, the mass percentage of the film forming additive in the secondary battery electrolyte is 0.1-5%.
Optionally, the mass ratio of the water-removing additive to the film-forming additive is 1 (0.1-10).
Optionally, the organic solvent includes one or more of a carbonate-based solvent, an ether-based solvent, and a carboxylate-based solvent.
Optionally, the electrolyte salt includes at least one of a lithium salt, a sodium salt, and a potassium salt.
In a second aspect, the present application provides a secondary battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte comprises the secondary battery electrolyte according to the first aspect of the present application.
Drawings
Fig. 1 is a schematic structural view of a secondary battery according to an embodiment of the present application;
fig. 2 is a scanning electron microscope image of the positive electrode plate of the battery provided in embodiment 1 of the present application;
FIG. 3 is a scanning electron microscope image of the positive electrode plate of the battery provided in comparative example 3 of the present application.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
When the battery electrolyte contains water, the reaction of the electrolyte lithium salt with water produces a series of by-products, such as HF, PF 5 、HPO 2 F 2 、H 2 PO 3 F and H 3 PO 4 And the like, the substances can cause irreversible damage to the lithium ion battery, for example, HF can dissolve interfacial films on the surfaces of the anode and the cathode of the battery, so that electrolyte is decomposed on the surfaces of the anode and the cathode, and the service life of the battery is shortened. The existing water removal additive can remove water in the electrolyte, but can not form a complete protective film, so that the electrolyte is continuously oxidized at the positive electrode, and the battery performance is deteriorated. The application provides a water removal additive, which not only can remove water and acid in electrolyte and reduce side reactions in a battery, but also has good film-forming property of a reaction product of the water removal additive and the water, and can form an interface film with stable performance on the surfaces of a positive electrode and a negative electrode of the battery, so that the positive electrode and the negative electrode materials of the battery are protected, the side reactions of the electrolyte on the surfaces of the positive electrode and the negative electrode of the battery are inhibited, and the performance of the battery is improved.
The water removal additive provided by the application comprises oxathiazaphosphine, and the structural formula of the oxathiazaphosphine is shown as a formula (1):
Figure BDA0003140083230000041
in the application, the oxathiazaphosphine contains various heteroatoms, and the positions of the heteroatoms and the substitution positions of the substituent groups ensure that the oxathiazaphosphine has higher stability and is not easy to decompose. The sulfonyl and phosphoryl in the oxathiolane structure have strong electron-withdrawing ability, so that P-O-C bonds in the water removal additive are easy to hydrolyze, water in the electrolyte is removed, and P, N, S heteroatoms in a hydrolysis product can greatly improve the thermal stability of a CEI film and an SEI film, so that the occurrence of positive and negative side reactions under a high-temperature condition is inhibited, and the lithium secondary battery has good high-temperature resistance.
In the embodiments of the present application, R 1 And R 3 Independently selected from any one of hydrogen, fluorine, alkyl, fluoroalkyl, alkenyl alkyl, alkynyl alkyl, alkenyl and alkynyl, R 2 And R 4 Independently selected from any one of fluorine, alkyl, fluoroalkyl, alkenyl alkyl, alkynyl alkyl, alkenyl, alkynyl, aryl and fluoroaryl.In the present embodiment, when the substituent group is selected from alkyl, the alkyl group may be any one of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, neopentyl, n-hexyl, cyclopropyl or cyclobutyl; when the substituent group is selected from fluoroalkyl, the fluoroalkyl group may be any one of trifluoromethyl, trifluoroethyl, trifluoropropyl, pentafluoropropyl, trifluorobutyl, and pentafluorobutyl; when the substituent group is selected from alkenyl alkyl, the alkenyl alkyl can be any one of allyl, alkenyl butyl, alkenyl isobutyl, alkenyl amyl and alkenyl isoamyl; when the substituent group is selected from alkynyl alkyl, the alkynyl alkyl can be any one of propargyl, alkynisobutyl, propargyl and alkynisopentyl; when the substituent group is selected from alkenyl, the alkenyl can be any one of vinyl, propenyl and butenyl; when the substituent group is selected from alkynyl, the alkynyl can be any one of ethynyl and propynyl; when the substituent group is selected from aryl, the aryl can be any one of phenyl, methylphenyl and dimethylphenyl; when the substituent group is selected from the group consisting of fluoroaryl groups, the fluoroaryl group may be any of p-fluorophenyl, p-trifluorophenyl, and p-trifluoroethylphenyl. In the embodiments of the present application, R 1 、R 2 、R 3 And R 4 May be the same or different groups.
In some embodiments of the present application, R 1 、R 2 、R 3 And R 4 At least one of which is fluorine or fluoroalkyl. In the present embodiment, when the substituent group includes fluorine or fluoroalkyl group, the water removal additive contains a certain amount of fluoride (e.g., liF) in the interface film formed on the surface of the electrode, thereby more effectively isolating the electrolyte from the electrode and further suppressing the occurrence of side reaction of the electrolyte on the surface of the electrode. Further, when R is 1 、R 2 、R 3 And R 4 When the plurality of substituent groups include fluorine or fluoroalkyl, the content of fluoride in the interfacial film is increased, and the protective performance of the interfacial film is improved. In some embodiments of the present application, R 1 、R 2 、R 3 And R 4 Is fluorine. When R is 1 、R 2 、R 3 And R 4 When at least one of the fluorine atoms is fluorine, the fluorine atoms have strong electron-withdrawing capability, so that the reaction activity of P-O-C bonds in the oxathiazaphosphine and water can be greatly improved, the reaction of the water removal additive and water is promoted, the reaction rate is improved, and the effective removal of water in the electrolyte is realized.
In the present application, when the substituent group contains an unsaturated double or triple bond, that is, R 1 、R 2 、R 3 And R 4 When at least one of the above-mentioned groups is alkenyl alkyl, alkynyl alkyl, alkenyl or alkynyl, the unsaturated double bond or triple bond has an electron-withdrawing ability, so that the reactivity of the P-O-C bond in the oxathiazaphosphine with water can be improved, thereby promoting the reaction of the water-removing additive with water, improving the reaction rate and realizing the effective removal of water in the electrolyte.
In the embodiments of the present application, the number of carbon atoms in the alkyl group, fluoroalkyl group, alkenylalkyl group, alkynylalkyl group, alkenyl group, and alkynyl group is 1 to 10, and the number of carbon atoms in the alkyl group, fluoroalkyl group, alkenylalkyl group, alkynylalkyl group, alkenyl group, and alkynyl group is 1 to 5. The number of carbon atoms of the alkyl group, fluoroalkyl group, alkenylalkyl group, alkynylalkyl group, alkenyl group, and alkynyl group may be specifically, but not limited to, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. When the number of carbon atoms is too high, the steric hindrance of the substituent is too large, the stability of the water removal additive is reduced, and the long chain length of the substituent causes the non-polarity of the water removal additive to be too strong, so that the solubility of the water removal additive in the electrolyte is reduced.
In the present embodiment, the carbon number of the aryl group and the fluoroaryl group is 6 to 20, and the carbon number of the aryl group and the fluoroaryl group is 6 to 10. The number of carbon atoms of the aryl group and the fluoroaryl group may specifically be, but not limited to, 6, 7, 8, 9, 10, 13, 17, or 20. The lower carbon atom number is beneficial to controlling the molecular weight of the water removal additive, so that the viscosity of the electrolyte is better controlled.
In some embodiments of the present application, the water removal additive may be any one or more of the compounds shown in table 1:
table 1 additive structure and name in some embodiments of the present application
Figure BDA0003140083230000061
Figure BDA0003140083230000071
Figure BDA0003140083230000081
The application provides a water removal additive includes that the major structure is the compound of oxygen sulfur nitrogen phosphine, the water removal additive of this structure can effectively detach the moisture in the electrolyte, reduce the emergence of side reaction, and the hydrolysis product of water removal additive can form the SEI membrane on the negative pole surface, restrain the destruction of electrolyte solvent to the negative pole structure, play the effect of protection negative pole, can form the CEI membrane on anodal surface again, prevent that anodal metal ion from dissolving out, stabilize anodal structure, and restrain anodal side electrolyte gas production, guarantee that the battery has higher energy density and cycle life. The formed SEI film and the CEI film have low impedance, which is beneficial to improving the internal dynamic characteristics of the lithium ion battery and reducing the interface impedance, thereby effectively improving the cycle performance, the high-temperature storage performance and the low-temperature performance of the lithium secondary battery. The water removal additive has good compatibility with anode and cathode materials, and has small influence on an electric core system.
The water removal additive can be prepared by different methods, and the specific preparation method is not limited. Taking the water removal additive 2-fluoro-1,5,4,2-oxathiazaphosphine-4-fluorosulfonyl-2,5,5-trioxide numbered 1 in table 1 as an example, the synthetic scheme of the water removal additive 1 is as follows:
Figure BDA0003140083230000091
the water removal additive numbered 1 in table 1 can be obtained through the above synthetic route, and accordingly, other water removal additives of the present application can be obtained by adjusting the substituent groups of the reactants, which is not described herein again.
The present application also provides a secondary battery electrolyte comprising an electrolyte salt, an organic solvent and an additive, the additive comprising the water scavenging additive described herein.
In the embodiment of the application, the water removal additive accounts for 0.1-3% of the electrolyte of the secondary battery by mass. In some embodiments of the present disclosure, the water removal additive is present in the electrolyte of the secondary battery in an amount of 0.5 to 1.5% by weight. The mass percentage of the water removal additive in the secondary battery electrolyte may be, but is not limited to, specifically 0.1%, 0.5%, 1%, 1.5%, 2%, or 3%. Within the mass percentage content range, the water removal additive can fully remove the water in the battery electrolyte, and the hydrolysate can form a complete protective layer on the surfaces of the positive and negative pole pieces, so that the stability of the battery pole pieces is effectively improved. It is considered that an excessively large thickness of the protective layer formed of the hydrolysate causes a large interface resistance, which hinders lithium ion transport and lowers discharge capacity. The concentration of water-removing additives should not be too high.
In some embodiments of the present application, the additive further comprises a film forming additive. The film forming additive can form an organic film on the surface of the electrode, and in the formation stage of the battery, the hydrolysate of the water removing additive and the film forming additive can act together to form an interface film with high density and good elastic performance. In some embodiments of the present application, the film-forming additive comprises one or more of Vinylene Carbonate (VC), vinyl Fluorocarbonate (FEC), methylene Methanedisulfonate (MMDS), lithium difluorophosphate (LiDFP), lithium difluorooxalato borate (liddob), vinyl sulfate (DTD), 1,3-Propane Sultone (PS), propylene sulfite, and tripropylene phosphate.
In the embodiment of the application, the mass percentage of the film forming additive in the electrolyte of the secondary battery is 0.1-5%. The content of the film-forming additive in the secondary battery electrolyte may be, but is not limited to, 0.1%, 0.5%, 1%, 2%, 3%, or 5% by mass. In the embodiment of the application, the mass ratio of the water removal additive to the film forming additive is 1 (0.1-10). In some embodiments of the present disclosure, the mass ratio of the water-removing additive to the film-forming additive is 1 (0.7-1.5), and within the above mass ratio range, the water-removing additive and the film-forming additive can perform a good coordination function, which is beneficial to forming a dense and elastic interfacial film. In the present application, the mass ratio of water-removing additive to film-forming additive may be, but is not limited to, 1.
In the embodiment of the present application, the electrolyte salt in the electrolyte solution of the secondary battery may be a lithium salt, a sodium salt, a potassium salt, or the like, depending on the secondary battery system. In some embodiments of the present application, the lithium salt comprises lithium hexafluorophosphate (LiPF) 6 ) Lithium difluoride imide (LiFSI), lithium bistrifluoromethylsulfonyl imide (LiTFSI), lithium tetrafluoroborate (LiBF) 4 ) Lithium hexafluoroarsenate (LiAsF) 6 ) Lithium hexafluoroantimonate (LiSbF) 6 ) Lithium perchlorate (LiClO) 4 ) Lithium bistrifluoromethylsulphonylimide (LiTFSI), lithium dioxalate borate (LiBOB), lithium difluorooxalate borate (liddob), lithium trifluoromethanesulfonate (LiCF) 3 SO 3 ) Lithium perfluorobutylsulfonate (LiC) 4 F 9 SO 3 ) Lithium bis (trifluoromethylsulfonyl) imide (Li (CF) 3 SO 2 ) 2 N), lithium bis (perfluoroethylsulfonyl) imide (Li (C) 2 F 5 SO 2 ) 2 N) is selected. In the present application, there is no particular requirement for the content of the electrolyte salt in the electrolyte of the secondary battery, and the content thereof may be determined by referring to the amount conventionally used in the art. In some embodiments of the present application, the concentration of the electrolyte salt in the electrolyte solution of the secondary battery is 0.1mol/L to 5mol/L, and further, the concentration of the electrolyte salt in the electrolyte solution of the secondary battery is 0.5mol/L to 1.5mol/L.
In the embodiment of the present application, the organic solvent includes one or more of a carbonate solvent, an ether solvent, and a carboxylate solvent. The carbonate solvent may be cyclic and/or linear, and the carboxylic acid ester solvent may be linear and/or branched. In some embodiments of the present disclosure, the organic solvent includes one or more of Ethylene Carbonate (EC), propylene Carbonate (PC), butylene carbonate, dimethyl carbonate (DMC), ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), propyl methyl carbonate (MPC), ethyl propyl carbonate, ethyl acetate, propyl acetate, ethyl propionate, ethyl butyrate, and the like, but is not limited thereto. In some embodiments of the present application, the organic solvent includes Ethylene Carbonate (EC), ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), and dimethyl carbonate (DMC), wherein a mass ratio of the Ethylene Carbonate (EC), the Ethyl Methyl Carbonate (EMC), the diethyl carbonate (DEC), and the dimethyl carbonate (DMC) is 1 (0.5-1.5): 0.1-1.
The present application also provides a secondary battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte comprises the secondary battery electrolyte as provided herein. Referring to fig. 1, fig. 1 is a schematic structural diagram of a secondary battery according to an embodiment of the present disclosure. The secondary battery includes a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte 40. When the secondary battery is charged, lithium ions are extracted from the positive electrode 10 and deposited to the negative electrode 20 after passing through the electrolyte 40; during discharge, lithium ions are extracted from the negative electrode 20, pass through the electrolyte 40, and are inserted into the positive electrode 10. The secondary battery provided by the application has good cycle performance and safety performance due to the adoption of the secondary battery electrolyte. In the embodiment of the present application, the secondary battery may be a lithium secondary battery, a potassium secondary battery, a sodium secondary battery, or the like.
In the present application, the negative electrode of the secondary battery may be any negative electrode known in the art. In an embodiment of the present application, the negative electrode may include one or more of a carbon-based negative electrode, a silicon-based negative electrode, a tin-based negative electrode, a lithium negative electrode, a sodium negative electrode, and a potassium negative electrode. Wherein the carbon-based negative electrode may include graphite, hard carbon, soft carbon, graphene, and the like; the silicon-based negative electrode can comprise silicon, silicon carbon, silicon oxygen, silicon metal compound and the like; the tin-based negative electrode may include tin, tin carbon, tin oxide, tin metal compounds; the lithium negative electrode may include metallic lithium or a lithium alloy. The lithium alloy may specifically be at least one of a lithium silicon alloy, a lithium sodium alloy, a lithium potassium alloy, a lithium aluminum alloy, a lithium tin alloy, and a lithium indium alloy. In some embodiments of the present disclosure, the current collector of the negative electrode is a copper foil, and the negative active material includes one or more of natural graphite, artificial graphite, hard carbon, soft carbon, lithium titanate, iron oxide, lithium titanium phosphate, titanium dioxide, silicon monoxide, tin, and antimony; the binder comprises one or more of polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), and styrene butadiene latex (SBR); the conductive agent comprises one or more of acetylene black, keqin carbon black, super-P, carbon nano tubes, carbon nano fibers, activated carbon and graphene. In the present application, any method known in the art may be used for the preparation of the negative electrode.
In the embodiments of the present application, the positive electrode of the secondary battery includes a positive electrode active material capable of reversibly intercalating/deintercalating metal ions (lithium ions, sodium ions, potassium ions, and the like), and the positive electrode of the secondary battery in the present application may be any positive electrode known in the art. Taking a lithium secondary battery as an example, the positive electrode active material may be, but is not limited to, lithium cobaltate (LiCoO) 2 ) Lithium iron phosphate (LiFePO) 4 )、LiNi 0.33 Co 0.33 Mn 0.33 O 2 (NCM111)，LiNi 0.4 Co 0.2 Mn 0.4 O 2 (NCM424)，LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523)，LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622)，LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM 811).
In the present embodiment, the separator of the secondary battery may be any separator known to those skilled in the art, and for example, the separator may be one or more of a polyolefin microporous film, polyethylene terephthalate, polyethylene felt, glass fiber felt, or ultra fine glass fiber paper.
In the embodiment of the present application, the battery may be prepared by any one of a lamination process and a winding process. In some embodiments of the present application, a battery is prepared using a lamination process.
The technical solution of the present application is further described below by referring to a plurality of examples.
Example 1
1) Preparation of electrolyte for secondary battery
An organic solvent was obtained by mixing 30g of Ethylene Carbonate (EC), 30g of Ethyl Methyl Carbonate (EMC), 30g of diethyl carbonate (DEC) and 10g of dimethyl carbonate (DMC),then 14g of lithium hexafluorophosphate (LiPF) 6 ) And 1g of Vinylene Carbonate (VC) are dissolved in the solvent, stirred and mixed into a uniform solution, and then the dewatering additive with the molecular structural formula shown as the formula (A) is added into the solution to obtain the electrolyte of the secondary battery. Wherein the mass of the water removal additive is 1g.
Figure BDA0003140083230000121
2) Preparation of lithium secondary battery
Mixing graphite, sodium carboxymethylcellulose (CMC) and Styrene Butadiene Rubber (SBR) according to a weight ratio of 100.
Mixing LiFePO 4 Acetylene black and polyvinylidene fluoride (PVDF) in a weight ratio of 95:3:2, adding N-methyl pyrrolidone, stirring to obtain uniform slurry, coating the slurry on an aluminum foil with the thickness of 12 mu m, drying at 120 ℃ for 24h, rolling and slitting to obtain the positive pole piece, wherein the water content of the positive pole piece is 50-400 ppm.
And (3) cutting the PE diaphragm with the thickness of 12 mu m into required sizes to obtain a battery diaphragm, winding the prepared positive pole piece, negative pole piece and battery diaphragm to prepare a battery core, filling the electrolyte of the secondary battery, and preparing the soft package lithium secondary battery S1 through the processes of formation and the like.
Example 2
The electrolyte for a secondary battery and the lithium secondary battery in example 2 were prepared in the same manner as in example 1, except that the composition of the water-removing additive in example 2 was different, and the molecular structural formula of the water-removing additive in example 2 is shown in formula (B):
Figure BDA0003140083230000131
the soft-packed lithium secondary battery obtained in example 2 was named S2.
Example 3
The electrolyte for a secondary battery and the lithium secondary battery in example 3 were prepared in the same manner as in example 1, except that the composition of the water-removing additive in example 3 was different, and the molecular structural formula of the water-removing additive in example 3 is shown in formula (C):
Figure BDA0003140083230000132
the soft-packed lithium secondary battery obtained in example 3 was named S3.
Example 4
The electrolyte for a secondary battery and the lithium secondary battery in example 4 were prepared in the same manner as in example 1, except that the composition of the water-removing additive in example 4 was different, and the molecular structural formula of the water-removing additive in example 4 is shown in formula (D):
Figure BDA0003140083230000141
the soft-packed lithium secondary battery obtained in example 4 was named S4.
Example 5
The electrolyte for a secondary battery and the lithium secondary battery in example 5 were prepared in the same manner as in example 1, except that the composition of the water-removing additive in example 5 was different, and the molecular structural formula of the water-removing additive in example 5 is shown in formula (E):
Figure BDA0003140083230000142
the soft pack lithium secondary battery manufactured in example 5 was named S5.
Example 6
The electrolyte for a secondary battery and the lithium secondary battery in example 6 were prepared in the same manner as in example 1, except that the composition of the water-removing additive in example 6 was different, and the molecular structural formula of the water-removing additive in example 6 is shown by the formula (F):
Figure BDA0003140083230000143
the soft-packed lithium secondary battery obtained in example 6 was named S6.
Example 7
The electrolyte for a secondary battery and the lithium secondary battery in example 7 were prepared in the same manner as in example 1, except that the composition of the water-removing additive in example 7 was different, and the molecular structural formula of the water-removing additive in example 7 is shown in formula (G):
Figure BDA0003140083230000151
the soft-packed lithium secondary battery obtained in example 7 was named S7.
Example 8
The electrolyte for a secondary battery and the lithium secondary battery in example 8 were prepared in the same manner as in example 1, except that the composition of the water-removing additive in example 8 was different, and the molecular structural formula of the water-removing additive in example 8 is shown by the formula (H):
Figure BDA0003140083230000152
the soft-packed lithium secondary battery produced in example 8 was named S8.
Example 9
The electrolyte for a secondary battery and a lithium secondary battery in example 9 were prepared in the same manner as in example 1, except that the composition of the water-scavenging additive in example 9 was different, and the molecular structural formula of the water-scavenging additive in example 9 is shown by the formula (I):
Figure BDA0003140083230000153
the soft-packed lithium secondary battery obtained in example 9 was named S9.
Example 10
The electrolyte for a secondary battery and the lithium secondary battery in example 10 were prepared in the same manner as in example 1, except that the composition of the water-removing additive in example 10 was different, and the molecular structural formula of the water-removing additive in example 10 is shown by the formula (J):
Figure BDA0003140083230000161
the soft pack lithium secondary battery manufactured in example 10 was named as S10.
Example 11
The electrolyte for a secondary battery and the lithium secondary battery in example 11 were prepared in the same manner as in example 1, except that the composition of the water-removing additive in example 11 was different, and the molecular structural formula of the water-removing additive in example 11 was as shown in formula (K):
Figure BDA0003140083230000162
the soft pack lithium secondary battery produced in example 11 was named S11.
Example 12
The electrolyte for a secondary battery and the lithium secondary battery in example 12 were prepared in the same manner as in example 1, except that the composition of the water-removing additive in example 12 was different, and the molecular structural formula of the water-removing additive in example 12 is shown by the formula (L):
Figure BDA0003140083230000171
the soft pack lithium secondary battery produced in example 12 was named S12.
Example 13
A secondary battery electrolyte and a lithium secondary battery in example 13 were fabricated by the same method as in example 1, except that the composition of the water-scavenging additive in example 13 was different, and the molecular structural formula of the water-scavenging additive in example 13 is shown by the formula (M):
Figure BDA0003140083230000172
the soft pack lithium secondary battery obtained in example 13 was named as S13.
Example 14
A secondary battery electrolyte and a lithium secondary battery in example 14 were fabricated in the same manner as in example 1, except that the mass of the water-removing additive in example 14 was 0.1g. The soft-packed lithium secondary battery produced in example 14 was named S14.
Example 15
The secondary battery electrolyte and the lithium secondary battery in example 15 were prepared in the same manner as in example 1 except that the mass of the water-removing additive in example 15 was 4g. The soft pack lithium secondary battery obtained in example 15 was named S15.
Example 16
The electrolyte for a secondary battery and the lithium secondary battery in example 16 were prepared in the same manner as in example 1 except that vinylene carbonate was not added to example 16. The soft pack lithium secondary battery produced in example 16 was named S16.
To highlight the advantageous effects of the present application, the following comparative examples were provided.
Comparative example 1
1) Preparation of electrolyte for secondary battery
At the water content<In a 2ppm argon glove box, 30g of Ethylene Carbonate (EC), 30g of Ethyl Methyl Carbonate (EMC), 30g of diethyl carbonate (DEC) and 10g of dimethyl carbonate (DMC) were mixed to obtain an organic solvent, and then 14g of lithium hexafluorophosphate (LiPF) was added 6 ) And 1g of Vinylene Carbonate (VC) were dissolved in the above solvent, stirred and mixed to a uniform solution, and then 1g of hexamethyldisilazane was added to the above solution to obtain a secondary battery electrolyte.
Preparation of lithium secondary battery
The positive electrode plate and the negative electrode plate were prepared in the same manner as in example 1, and the positive electrode plate, the negative electrode plate and the separator were wound to prepare a cell, and the above-mentioned secondary battery electrolyte was poured into the cell, and then the soft-packed lithium secondary battery C1 was prepared by processes such as formation.
Comparative example 2
The secondary battery electrolyte and the lithium secondary battery in comparative example 2 were prepared in the same manner as in comparative example 1 except that the mass of hexamethyldisilazane in comparative example 2 was 0.1g. The soft-packed lithium secondary battery manufactured in comparative example 2 was named C2.
Comparative example 3
1) Preparation of electrolyte for secondary battery
In an argon glove box having a water content of <2ppm, 30g of Ethylene Carbonate (EC), 30g of Ethyl Methyl Carbonate (EMC), 30g of diethyl carbonate (DEC) and 10g of dimethyl carbonate (DMC) were mixed to obtain an organic solvent, and then 14g of lithium hexafluorophosphate (LiPF 6) and 1g of Vinylene Carbonate (VC) were dissolved in the above solvent, and mixed with stirring to obtain a uniform solution, to obtain a secondary battery electrolyte.
2) Preparation of lithium secondary battery
And preparing a positive pole piece and a negative pole piece by the same method as the comparative example 1, winding the positive pole piece, the negative pole piece and the diaphragm to prepare a battery cell, filling the electrolyte of the secondary battery, and preparing the soft package lithium secondary battery C3 by processes such as formation and the like.
Effects of the embodiment
In order to strongly support the beneficial effects brought by the technical scheme of the embodiment of the application, the following tests are provided:
1) Taking a battery pole piece for appearance characterization after disassembling the soft package lithium secondary battery S1 in the embodiment 1 and the soft package lithium secondary battery C3 in the comparative example 3, please refer to fig. 2 and fig. 3, wherein fig. 2 is a scanning electron microscope image of the battery positive pole piece provided in the embodiment 1 of the application, and fig. 3 is a scanning electron microscope image of the battery positive pole piece provided in the comparative example 3 of the application. As can be seen from fig. 2, when the secondary electrolyte contains the water removal additive of the present application, the surface of the positive electrode of the battery has a granular deposition layer, which is a CEI film on the surface of the positive electrode of the battery, and the positive electrode can be well protected. As can be seen from fig. 3, when the electrolyte does not contain the water removal additive, the surface of the positive electrode of the battery is smooth, i.e., the positive electrode surface of the soft-packed lithium secondary battery C3 of comparative example 3 does not have a protective layer.
2) The soft-packed lithium secondary batteries of examples 1 to 16 and comparative examples 1 to 3 were subjected to cycle performance tests under specific conditions: the lithium-ion secondary battery was charged at a constant current of 0.05C to 15% soc at a temperature of 25C, further charged at 0.25C to 3.8V, constant-voltage to 0.02C, and then discharged at 0.33C to 2.5V, and the first charge-discharge capacity was recorded and the coulombic efficiency was calculated. Charging to 3.8V with 1C current, maintaining the voltage to 0.02C, and discharging to 2.5V with 200mA as the first cycle; after the charge-discharge cycle is repeated for 200 times, the discharge capacity of the 200 th cycle is recorded, the capacity retention rate after the 200 cycles is calculated, and the calculation formula is as follows: the capacity retention (%) after 200 cycles was not less than 200 cycles/first cycle discharge capacity × 100%, and the test results of the high temperature cycle performance of the pouch batteries of examples 1 to 16 and comparative examples 1 to 3 are shown in table 2.
TABLE 2 TABLE OF PERFORMANCE PARAMETERS OF SOFT-PACKAGE BATTERIES FOR EXAMPLES 1-16 AND COMPARATIVE EXAMPLES 1-3
Figure BDA0003140083230000191
Figure BDA0003140083230000201
As can be seen from table 2, the lithium-soft-pack secondary batteries of examples 1 to 16 of the present application have better cycle performance and show higher capacity retention after 200 cycles, compared to comparative examples 1 to 3, due to the addition of the water-removing additive of the present application to the electrolytes of examples 1 to 16. The water removal additive can effectively remove water in the electrolyte, and the hydrolysis product of the water removal additive can form a stable interface film on the surfaces of the positive electrode and the negative electrode of the battery, so that the side reaction of the electrolyte on the surfaces of the positive electrode and the negative electrode is prevented, and the cycle performance of the battery is improved.
3) After the soft-packed lithium secondary batteries of examples 1 to 16 and comparative examples 1 to 3 were cycled 200 times, an ac impedance test was performed at 80% soc, with a test frequency ranging from 0.1 HZ to 105HZ, to obtain the impedance of the batteries. Disassembling the tested battery, testing the content of iron element in the negative pole piece by an Inductively Coupled Plasma (ICP) instrument, testing for 200 times, taking an average value to obtain the iron dissolving amount in the negative pole piece, and testing the water content in the battery electrolyte. The results of pouch cell impedance, amount of dissolved iron, and water content for examples 1-16 and comparative examples 1-3 are shown in table 3.
Table 3 pouch cell parameter tables for examples 1-16 and comparative examples 1-3
Figure BDA0003140083230000202
Figure BDA0003140083230000211
As can be seen from table 3, the lithium secondary batteries with soft package according to examples 1 to 16 of the present application have lower impedance than those according to comparative examples 1 to 3, and when the water removal additive according to the present application is contained in the electrolyte, the water content in the electrolyte is greatly reduced, and the iron dissolution amount of the electrode sheet is also greatly reduced, so as to ensure that the batteries have higher capacity retention rate.
The foregoing is illustrative of the preferred embodiments of the present application and is not to be construed as limiting the scope of the application. It should be noted that modifications and embellishments could be made by those skilled in the art without departing from the principle of the present application and these are considered to be within the scope of the present application.

Claims (11)

1. A secondary battery electrolyte, which is characterized by comprising electrolyte salt, an organic solvent and a water removal additive, wherein the water removal additive comprises a compound shown as a structural formula (1):
Figure FDA0003140083220000011
wherein, R is 1 And R 3 Independently selected from any one of hydrogen, fluorine, alkyl, fluoroalkyl, alkenyl alkyl, alkynyl alkyl, alkenyl and alkynyl; the R is 2 And R 4 Independently selected from the group consisting of fluoro, alkyl, fluoroalkyl, alkenylalkyl, alkynylalkyl, alkenyl, alkynyl, aryl, fluoroarylAny one of them.
2. The secondary battery electrolyte of claim 1 wherein R is 1 、R 2 、R 3 And R 4 At least one of which is fluorine or fluoroalkyl.
3. The secondary battery electrolyte of claim 1 or 2 wherein R is 1 、R 2 、R 3 And R 4 Is fluorine.
4. The secondary battery electrolyte of claim 1 wherein R is 1 、R 2 、R 3 And R 4 Is alkenylalkyl, alkynylalkyl, alkenyl, or alkynyl.
5. The secondary battery electrolyte as claimed in any one of claims 1 to 4 wherein the alkyl group, the fluoroalkyl group, the alkenylalkyl group, the alkynylalkyl group, the alkenyl group, the alkynyl group have 1 to 10 carbon atoms; the number of carbon atoms of the aryl group and the fluorinated aryl group is 6 to 20.
6. The secondary battery electrolyte of any of claims 1-5 wherein the water scavenging additive is present in the secondary battery electrolyte in an amount of 0.1% to 3% by weight.
7. The secondary battery electrolyte of any of claims 1-6 wherein the additive further comprises a film forming additive; the film forming additive comprises one or more of vinylene carbonate, fluoroethylene carbonate, methylene methyl disulfonate, lithium difluorophosphate, lithium difluorooxalato borate, propylene sulfite, vinyl sulfate, 1,3-propane sultone and tripropylene phosphate.
8. The secondary battery electrolyte of claim 7 wherein the mass ratio of the water-scavenging additive to the film-forming additive is 1 (0.1-10).
9. The secondary battery electrolyte as claimed in any one of claims 1 to 8 wherein the organic solvent comprises one or more of a carbonate-based solvent, an ether-based solvent, and a carboxylic acid-based solvent.
10. The secondary battery electrolyte of any of claims 1-9 wherein the electrolyte salt comprises at least one of a lithium salt, a sodium salt, and a potassium salt.
11. A secondary battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, the electrolyte comprising the secondary battery electrolyte according to any one of claims 1 to 10.
CN202110742394.8A 2021-06-30 2021-06-30 Electrolyte for secondary battery and secondary battery Pending CN115548439A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115863768A (en) * 2023-02-22 2023-03-28 安徽盟维新能源科技有限公司 Electrolyte and lithium metal battery containing same
CN116565293A (en) * 2023-07-06 2023-08-08 宁德新能源科技有限公司 Electrochemical device and electronic device

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115863768A (en) * 2023-02-22 2023-03-28 安徽盟维新能源科技有限公司 Electrolyte and lithium metal battery containing same
CN115863768B (en) * 2023-02-22 2023-04-25 安徽盟维新能源科技有限公司 Electrolyte and lithium metal battery containing same
CN116565293A (en) * 2023-07-06 2023-08-08 宁德新能源科技有限公司 Electrochemical device and electronic device

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