CN114583263B - Electrolyte, positive electrode, lithium ion battery and vehicle - Google Patents

Electrolyte, positive electrode, lithium ion battery and vehicle Download PDF

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CN114583263B
CN114583263B CN202011373676.7A CN202011373676A CN114583263B CN 114583263 B CN114583263 B CN 114583263B CN 202011373676 A CN202011373676 A CN 202011373676A CN 114583263 B CN114583263 B CN 114583263B
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electrolyte
additive
lithium
positive electrode
carbonate
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CN114583263A (en
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刘行
王圣
刘刚
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
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • 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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

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Abstract

The application discloses an electrolyte, a positive electrode, a lithium ion battery and a vehicle. The electrolyte comprises: lithium salt, organic solvent and additive; the additive comprises a first additive, wherein the first additive is an alkyl thiomorpholine compound, and the structural formula of the alkyl thiomorpholine compound is as follows:wherein R is selected from C 1 ‑C 10 Alkyl, C 2 ‑C 10 Alkenyl, C 2 ‑C 10 Alkynyl, C 3 ‑C 10 Cycloalkyl, C 6 ‑C 30 Aryl, C 3 ‑C 10 Thiazinyl and C 4 ‑C 10 At least one of thienyl; c (C) 1 ‑C 10 Alkyl, C 2 ‑C 10 Alkenyl, C 2 ‑C 10 Alkynyl, C 3 ‑C 10 Cycloalkyl, C 6 ‑C 30 Aryl, C 3 ‑C 10 Thiazinyl and C 4 ‑C 10 The hydrogen atoms in the thienyl group may be partially or fully substituted with substituents. The additive of the electrolyte has more substituents and complexing sites, has high reduction potential, is favorable for forming an interface protective film on a negative electrode, complexes metal ions dissolved out by a positive electrode, and improves the cycle stability of the battery under high voltage.

Description

Electrolyte, positive electrode, lithium ion battery and vehicle
Technical Field
The application relates to the field of new energy sources, in particular to electrolyte, a positive electrode, a lithium ion battery and a vehicle.
Background
The lithium ion battery has the advantages of high working voltage, large specific capacity, long cycle life, no memory effect, environmental friendliness and the like, and has been widely applied to electronic products such as communication tools, notebook computers and the like. With the application of lithium ion batteries in electric automobiles and hybrid electric automobiles, higher requirements are put on the energy density, especially the mass energy density, of the lithium ion batteries, and the high-nickel ternary positive electrode material is widely used as a positive electrode material due to higher energy density and specific capacity (especially when the charge cut-off voltage reaches 4.5V).
However, the existing electrolyte system composed of carbonate and lithium hexafluorophosphate is unstable at high voltage (4.5V), oxidative decomposition is easy to occur, the generated byproducts can accelerate metal dissolution and structural collapse of the positive electrode material, the impedance of the positive electrode surface is increased, and the high-nickel material can generate oxygen evolution phenomenon at high potential, so that the oxidative decomposition and gas production of the carbonate electrolyte are accelerated, the electrolyte is rapidly consumed and degraded, and finally, the battery expansion, the battery interface stability is poor, the impedance is increased and the battery performance is reduced.
Disclosure of Invention
In view of the above-described drawbacks or deficiencies of the prior art, it is desirable to provide an electrolyte, a positive electrode, a lithium ion battery, and a vehicle.
In a first aspect, the present application provides an electrolyte comprising: lithium salt, organic solvent and additive;
the additive comprises a first additive, wherein the first additive is an alkyl thiomorpholine compound, and the structural formula of the alkyl thiomorpholine compound is as follows:
wherein R is selected from C 1 -C 10 Alkyl, C 2 -C 10 Alkenyl, C 2 -C 10 Alkynyl, C 3 -C 10 Cycloalkyl, C 6 -C 30 Aryl, C 3 -C 10 Thiazinyl and C 4 -C 10 At least one of thienyl;
C 1 -C 10 alkyl, C 2 -C 10 Alkenyl, C 2 -C 10 Alkynyl, C 3 -C 10 Cycloalkyl, C 6 -C 30 Aryl, C 3 -C 10 Thiazinyl and C 4 -C 10 The hydrogen atoms in the thienyl group may be partially or fully substituted with substituents.
Preferably, the substituent includes at least one of amino, carboxyl, hydroxyl and cyano.
As a preferred embodiment, the alkylthio morpholinyl compound is selected from at least one of the following compounds:
preferably, the mass fraction of the first additive is 0.1% -10% based on the total mass of the electrolyte.
As a preferred embodiment, the additive further comprises: and the second additive is at least one selected from at least one of ethylene carbonate, fluoroethylene carbonate, ethylene sulfite, methylene methane disulfonate, 1, 3-propane sulfonate lactone, 1, 3-propylene sultone, ethylene sulfate, lithium difluorophosphate, lithium difluorobisoxalato phosphate and lithium tetrafluorooxalato phosphate.
Preferably, the mass fraction of the second additive is 0.1% -10% based on the total mass of the electrolyte.
Preferably, the lithium salt is at least one selected from the group consisting of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium difluorooxalato borate, lithium bis (trifluoromethylsulfonyl) imide and lithium difluorosulfimide.
Preferably, the organic solvent is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methylethyl carbonate, methylpropyl carbonate, gamma-butyrolactone, methyl formate, ethyl acetate, methyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate and butyl propionate.
As a preferable scheme, the organic solvent is ethylene carbonate and diethyl carbonate, and the mass ratio of the ethylene carbonate to the diethyl carbonate is 1 (1-2.5).
In a second aspect, the application provides a positive electrode of a lithium ion battery, which comprises a positive electrode current collector and a positive electrode active material layer positioned on the surface of the positive electrode current collector, wherein an interface protection film is arranged on the surface of the positive electrode active material layer, and the interface protection film is obtained by electrolytic solution according to the first aspect.
In a third aspect, the present application provides a lithium ion battery comprising: the electrolyte of the first aspect and/or the positive electrode of the second aspect.
In a fourth aspect, the present application provides a vehicle comprising: the lithium ion battery of the third aspect.
The electrolyte provided by the application comprises the first additive, wherein the first additive is an alkyl thiomorpholine compound, and the alkyl thiomorpholine compound is provided with a plurality of substituents and a plurality of complexing sites, so that the overall electron cloud density is higher, an interface protection film is formed on the positive electrode, and the positive electrode metal ions with strong oxidability are complexed, thereby effectively inhibiting the dissolution of the positive electrode metal ions and the oxidative decomposition of the electrolyte under high voltage; meanwhile, the additive has higher reduction potential, and a stable sulfur-containing polymer film can be formed on the surface of the negative electrode in the battery formation stage, so that the elasticity of the negative electrode interface protective film is improved, the stability of an electrode/electrolyte interface is maintained, and the cycle stability of the battery under high voltage is further improved.
Detailed Description
The present application will be described in further detail with reference to examples. It is to be understood that the specific embodiments described herein are merely illustrative of the application and are not limiting of the application.
It should be noted that, without conflict, the embodiments of the present application and features of the embodiments may be combined with each other. The present application will be described in detail with reference to examples.
When the high-nickel ternary material is charged to 4.5V, a large amount of tetravalent nickel ions are formed, carbonate in the electrolyte is oxidized by the strong oxidizing property of the tetravalent nickel ions, active lithium and the electrolyte are consumed, and the performance of the cracked electrolyte is accelerated by the oxidized byproducts including proton products such as water, and finally the capacity of the battery is quickly attenuated.
Based on the above-described problems, an embodiment of the present application provides an electrolyte, including: lithium salt, organic solvent and additive;
the additive comprises: a first additive;
the first additive is an alkyl thiomorpholine compound, and the structural formula of the alkyl thiomorpholine compound is as follows:
wherein R is selected from C 1 -C 10 Alkyl, C 2 -C 10 Alkenyl, C 2 -C 10 Alkynyl, C 3 -C 10 Cycloalkyl, C 6 -C 30 Aryl, C 3 -C 10 Thiazinyl and C 4 -C 10 At least one of thienyl;
C 1 -C 10 alkyl, C 2 -C 10 Alkenyl, C 2 -C 10 Alkynyl, C 3 -C 10 Cycloalkyl, C 6 -C 30 Aryl, C 3 -C 10 Thiazinyl and C 4 -C 10 The hydrogen atoms in the thienyl group may be partially or fully substituted with substituents.
It should be noted that the number of the substrates,
the alkylthio morpholines compounds comprise a sulfonyl group, a morpholin ring, and an alkyl group and various substituents, the alkyl group being attached to the morpholin ring. Due to the increase of substituents and the electron donating effect of alkyl, the overall electron cloud density of the alkyl thiomorpholine compound is higher, free electrons in the structure are more, compared with a solvent, the free electrons are more easily oxidized, an interface protection film is generated at the positive electrode, the oxidation of positive electrode metal ions to electrolyte is effectively prevented, the decomposition and consumption of the electrolyte are inhibited, the dissolution of the positive electrode metal ions accelerated by electrolyte byproducts is avoided, and the interface of the electrolyte/electrode is stabilized;
the sulfonyl, morpholine ring and substituent in the alkylthio morpholine ring compound provide a plurality of complexing sites, which is favorable for effectively complexing metal ions with oxidability in the electrolyte to generate organic metal chelate with stable low oxidability multi-ring structure, thereby preventing the oxidation of the electrolyte by the metal ions dissolved out by the positive electrode, and reducing the generation of side reaction products of the electrolyte and the dissolution and structural collapse of the positive electrode metal ions caused by the side reaction products; meanwhile, the alkyl thiomorpholine compound only forms a complex through strong electronegative atoms, so that the alkyl thiomorpholine compound has good compatibility with an electrolyte system containing carbonic ester, can be mutually dissolved, does not influence the physicochemical properties of the electrolyte, and has universal applicability;
the sulfonyl and morpholine rings in the alkylthio morpholine compound are taken as strong electron-withdrawing groups, so that the lowest unoccupied orbit LUMO energy of the molecule of the alkylthio morpholine compound can be reduced, and the alkylthio morpholine compound has higher reduction potential (proved by a cyclic voltammetry experiment to be far higher than the reduction potential of Ethylene Carbonate (EC)) according to the front orbit theory, so that an organic polymer can be generated on the surface of a negative electrode preferentially by the EC, the interface composition of the negative electrode and electrolyte is improved, and the electrode/electrolyte interface is stabilized;
the sulfonyl group in the alkylthio morpholines and a single atom on the morpholines can be reduced to Li 2 O、Li 2 S、Li 3 Inorganic components with high N plasma conductivity improve the conductivity of the electrolyte; meanwhile, the alkyl thiomorpholine compound is subjected to ring-opening polymerization in the electrochemical process to form a sulfur-containing organic polymer at the negative electrode, so that the interface protection film of the negative electrode has outstanding elastic performance, and the electrolyte/electrode interface of the negative electrode is effectively stabilized under the action of the interface protection film containing an organic layer and an inorganic layer. Therefore, the electrolyte of the application is beneficial to improving the cycle performance of the battery under high voltage.
In addition, C 1 -C 10 Alkyl, C 2 -C 10 Alkenyl, C 2 -C 10 Alkynyl, C 3 -C 10 Cycloalkyl, C 6 -C 30 Aryl, C 3 -C 10 Thiazinyl and C 4 -C 10 Thienyl, moderate carbon chain length, no significant increaseThe viscosity of the additive is added, but the wettability between the electrolyte and the electrode can be improved, so that the lithium ion transmission is facilitated; and C 1 -C 10 Alkyl, C 2 -C 10 Alkenyl, C 2 -C 10 Alkynyl, C 3 -C 10 Cycloalkyl, C 6 -C 30 Aryl, C 3 -C 10 Thiazinyl and C 4 -C 10 The hydrogen atoms in the thienyl can be partially or completely substituted by substituent groups, so that the activity of alkyl, alkenyl, alkynyl, cycloalkyl, aryl, thiazinyl or thienyl is further improved, an interface protection film is favorably generated at the positive electrode of the lithium ion battery, and the substituent groups provide more complexing sites of the alkylthio morpholine compound, so that the metal ions dissolved out by the positive electrode are favorably complexed, and the oxidative decomposition of the electrolyte under high voltage is reduced.
In summary, the electrolyte provided by the embodiment of the application has a plurality of substituents and complexing sites in the structure of the additive, which is beneficial to the oxidation of the additive preferential solvent on the surface of the positive electrode to form a stable interface protection film, thereby preventing metal ions from contacting with the electrolyte and stabilizing the electrolyte/electrode interface; meanwhile, tetravalent nickel ions with strong oxidability are effectively complexed, oxidation of metal ions to electrolyte is reduced, a stable polymer film is formed on the negative electrode, elasticity of a negative electrode interface protection film is improved, consumption of a solvent and damage of positive electrode metal ions to an SEI film due to dissolution are prevented, and further circulation stability of the lithium ion battery is improved.
Further, the substituent includes at least one of amino, carboxyl, hydroxyl, cyano. The amino, carboxyl and hydroxyl groups are easier to oxidize, the positive electrode surface has good stability, and the cyano group has strong coordination capacity, and can be combined with active sites (such as high-valence metal ions, such as nickel) on the electrode surface to mask the active ions on the positive electrode surface, so that the decomposition of the electrode to electrolyte is reduced.
Preferably, the alkylthio morpholino ring compounds of the embodiments of the present application are selected from thiomorpholinoacetic acid-1, 1' -dioxide (formula I, CAS number: 155480-08-3), 4-benzylthiomorpholino-1, 1' -dioxide (formula II, CAS number: 26475-66-1), 4- (4 ' -carboxybenzyl) benzylthiomorpholino-1, 1' -dioxide (formula III, CAS number: 465514-21-0), 4-prop-2-ynylthiomorpholino-1, 1' -dioxide (formula IV, CAS number: 10442-03-2), 4- (2-methylthiophene) -1LAMBDA6,4-thiomorpholino-1, 1' -dioxide (formula V, CAS number: 175136-91-1), 4- (2-furanmethyl) -1LAMBDA6,4-thiomorpholino-thiazine-1, 1-dione (formula VI, VII number: 79206-94-3), 1-dioxo-4-thiomorpholino-1, 35-2-ethyl morpholine (formula IV, 3, CAS number: 10442-03-2), 4- (2-methylthio-thiomorpholino-1, 1' -dioxide (formula V, 3, 35-67) or at least one of formula (formula VI, 35-3).
As a realizable mode, the mass fraction of the first additive is 0.1% -10% based on the total mass of the electrolyte. The mass fraction range of the embodiment is favorable for forming an interface protection film on the positive electrode, so that the interface protection film can better prevent metal ions of the positive electrode from contacting with electrolyte, the electrolyte/electrode interface is stabilized, and meanwhile, complexing of metal ions dissolved out by the positive electrode is also favorable, and oxidative decomposition of the metal ions on the electrolyte is reduced; the other party can also improve the elasticity of the anode interface protective film, so that the stability of the electrolyte/electrode interface of the anode is maintained, and the cycle performance of the lithium ion battery is further effectively improved.
As a practical way, the additive further comprises: and a second additive selected from at least one of Vinylene Carbonate (VC), fluoroethylene carbonate (FEC), ethylene carbonate (VEC), ethylene Sulfite (ES), methylene Methane Disulfonate (MMDS), 1, 3-propane sulfonate lactone (PS), 1, 3-propylene sulfonate lactone (1, 3-PST), ethylene sulfate (VS), lithium Difluorophosphate (LD), lithium Difluorobisoxalato Phosphate (LDP) and Lithium Tetrafluorooxalato Phosphate (LTP).
The second additive in the electrolyte is mainly used for forming a film on a negative electrode, is beneficial to forming an SEI film with low impedance and high stability on the negative electrode of a lithium ion battery, has insolubility in an organic solvent, can exist stably in an organic electrolyte solution, and can not pass through the SEI film, so that co-intercalation of solvent molecules can be effectively prevented, damage to electrode materials caused by co-intercalation of the solvent molecules is avoided, and the cycle performance and the service life of the electrode are greatly improved.
As a realizable mode, the mass fraction of the second additive is 0.1% -10% based on the total mass of the electrolyte.
In a specific embodiment, the second additive is fluoroethylene carbonate (FEC), the mass percentage is 3%, a thinner and stable SEI film is formed on the negative electrode, and meanwhile, under the action of the first additive, the elasticity of the interface protection film of the negative electrode is further improved, so that the cycle stability of the lithium ion battery is improved.
As an achievable form, the lithium salt is at least one selected from lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium difluorooxalato borate, lithium bis (trifluoromethylsulfonyl) imide and lithium difluorosulfimide. Wherein, the lithium salt reduces the fluorine content, thereby reducing the generated hydrofluoric acid and further improving the high temperature performance of the electrolyte.
As a practical way, the concentration of the lithium salt is 0.1mol/L to 1.2mol/L. The concentration range of the embodiment of the application is favorable for moderate dielectric constant of the electrolyte and effective conduction of lithium ions.
As a practical form, the organic solvent is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methylethyl carbonate, methylpropyl carbonate, γ -butyrolactone, methyl formate, ethyl acetate, methyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate and butyl propionate.
In a specific embodiment, the organic solvent is ethylene carbonate and diethyl carbonate, and the mass ratio of the ethylene carbonate to the diethyl carbonate is 1 (1-2.5). Preferably 3:7. The cyclic ethylene carbonate has higher dielectric constant and high viscosity, and the linear diethyl carbonate has low viscosity, so that the ionic conductivity of the electrolyte is improved when the cyclic ethylene carbonate and the linear diethyl carbonate are matched for use, and the cyclic ethylene carbonate can also participate in the negative electrode to form an SEI film, thereby effectively preventing side reactions of the negative electrode.
The electrolyte provided by the embodiment of the application has the advantages that the first additive is provided with a plurality of substituents and complexing sites, so that the additive is beneficial to forming a stable interface protection film on the oxidized surface of the positive electrode by the preferential solvent of the additive, thereby preventing metal ions from contacting with the electrolyte and stabilizing the interface of the electrolyte/electrode; simultaneously, tetravalent nickel ions with strong oxidability are effectively complexed, so that the oxidation of metal ions to electrolyte is reduced; on the other hand, the first additive only forms a coordination complex through strong electronegative atoms, so that the first additive has good compatibility with a carbonate electrolyte system, is mutually soluble, does not influence the physicochemical properties of the electrolyte, and has universal applicability.
In addition, the first additive is beneficial to forming a polymer film on the negative electrode, the second additive is mainly used for forming a film on the negative electrode, and the first additive and the second additive are formed together on the negative electrode, so that the elasticity of an interface protection film of the negative electrode is improved, the electrolyte/electrode interface composition of the negative electrode is stabilized, and the cycle performance and the service life of the electrode are greatly improved.
In conclusion, the electrolyte provided by the application can not be subjected to oxidative decomposition under high voltage of the lithium ion battery, and can generate an interface protection film on the positive electrode and the negative electrode, so that the cycle performance of the lithium ion battery under the high voltage condition is improved.
In a second aspect, an embodiment of the present application provides a positive electrode of a lithium ion battery, where the positive electrode of the lithium ion battery includes a positive electrode current collector and a positive electrode active material layer located on a surface of the positive electrode current collector, and the surface of the positive electrode active material layer has an interface protection film, where the interface protection film is obtained by electrolytic solution according to the first aspect. This positive electrode has all the features and advantages of the above-described electrolyte, and will not be described in detail herein.
In a third aspect, embodiments of the present application provide a lithium ion battery. The lithium ion battery comprises the electrolyte of the first aspect and/or the positive electrode of the second aspect. Accordingly, the lithium ion battery has all of the features and advantages of the above-described electrolyte and/or the above-described positive electrode, and will not be described in detail herein. In general, the lithium ion battery has the advantages that the interface composition of the anode and the cathode can be improved, an interface protection film is generated, and the oxidative decomposition of electrolyte is inhibited, so that the lithium ion battery has good cycle performance under high voltage.
Wherein the positive electrode active material may be a ternary nickel cobalt manganese material, e.g., liNi 0.33 Co 0.33 Mn 0.33 O 2 (NCM 111 type), liNi 0.4 Co 0.2 Mn 0.4 O 2 (NCM 424 type), liNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM 523 type), liNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM 622 type), liNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM 811 type), liNi 0.85 Co 0.075 Mn 0.075 O 2 (NCM 811 model); the negative electrode may be artificial graphite, natural graphite, mesophase Carbon Microbeads (MCMB), silicon carbon negative electrode, or the like.
In a fourth aspect, the present application proposes a vehicle comprising the lithium ion battery of the third aspect. For example, a plurality of battery packs formed of the aforementioned lithium ion batteries may be included. Thus, the vehicle has all the features and advantages of the lithium ion battery described above, and will not be described in detail herein.
The present application will be illustrated by the following examples, which are given for illustrative purposes only and are not intended to limit the scope of the present application in any way, and unless otherwise specified, the conditions or procedures not specifically described are conventional and the reagents and materials employed are commercially available.
The lithium ion batteries of examples 1-17 and comparative examples 1-2 were prepared as follows:
(1) Preparation of electrolyte:
mixing ethylene carbonate and diethyl carbonate according to a mass ratio of 3:7 to form a mixed solvent, and adding lithium hexafluorophosphate (LiPF) into the mixed solvent 6 ) And (3) adding the fluoroethylene carbonate serving as a second additive and the first additive into the mixture in sequence until the molar concentration is 1.0mol/L, and stirring the mixture uniformly to obtain the electrolyte. The specific types and the contents of the additives used in the electrolyte are shown in table 1, wherein the proportion of the additives is the mass percentage of the total mass of the electrolyte.
(2) Preparation of a positive plate:
LiNi in a mass ratio of 100:1:2:2 0.5 Co 0.2 Mn 0.3 O 2 (NCM 523), super-P, CNT and polyvinylidene fluoride (PVDF) are mixed into uniform paste, uniformly coated on aluminum foil with the thickness of 20um, and dried under vacuum at 80 ℃ for 24 hours to obtain the positive plate.
(3) Preparing a negative plate:
graphite, super-P, SBR (styrene butadiene rubber) and CMC (carboxymethyl cellulose) are mixed according to the mass ratio of 100:1:2.5:1.5 to form uniform paste, the uniform paste is uniformly coated on copper foil with 10um, and the paste is dried for 24 hours under vacuum at 80 ℃ to obtain the negative plate.
(4) Preparation of a lithium ion battery:
and preparing a soft package battery with the model SL582736, preparing a bare cell by a winding process of the positive plate, the negative plate and the isolating film in an argon glove box with the water content less than 5ppm, filling the cell into an aluminum plastic film package shell, injecting the electrolyte, sequentially sealing, and performing the procedures of standing, hot and cold pressing, formation, capacity division and the like to prepare the lithium ion battery.
Wherein, the formation process comprises the following steps: the simulated cell was first charged to 1.5V at 40mA (0.05C) and held at 1.5V for 10 hours to allow adequate wetting of the cell electrode sheet. After the constant voltage was completed, the battery was initially charged for 10 hours at a small current of 8mA (C/100) to form a stable and dense interface protective film, then charged to 4.35V at a current of 40mA (0.05C), and then discharged to 3.0V.
TABLE 1 specific types and contents of additives in examples 1 to 17 and comparative examples 1 to 2
The performance test procedure and test results of the lithium ion battery are described below:
(1) Expansion ratio test
The battery after completion of the formation of each example was charged at 0.5C (400 mA), and was charged at a constant voltage of 4.5V, further at a constant voltage of 4.5V, and at a current of 40mA. The full-charge battery was stored in a constant temperature oven at 60 ℃ for 5 days, 10 for each condition, and the average value was obtained. The thickness of the battery before and after storage is measured by a vernier caliper, and the expansion rate (%) of the battery is calculated by subtracting the thickness before storage from the thickness after storage and dividing the difference by the percentage obtained by the thickness before storage.
(2) Nickel element dissolution test
After the above battery was disassembled, the positive and negative electrode separator and the aluminum plastic film were repeatedly rinsed in 5mL of dichloromethane, and then a washing solution was subjected to Inductively Coupled Plasma (ICP) test, the test instrument being an inductively coupled plasma spectrometer of the samer product. 10 per condition, the results were averaged.
(3) High voltage cycling test of battery
The cells of the examples and comparative examples (10 for each condition, the average value was taken) were cycled between 2.75V and 4.5V at 1C (800 mA) for 200 times, respectively, by subtracting and evacuating the cell envelope. The tests were all carried out in a 25 ℃ incubator, and the capacity retention (%) was calculated as a percentage obtained by dividing the discharge capacity at the 200 th cycle by the initial discharge capacity at the first cycle.
The structures of the lithium ion batteries of examples 1-17 and comparative examples 1-2 tested according to the procedure and method described above are shown in table 2:
TABLE 2 test results for examples 1-17 and comparative examples 1-2
According to the results shown in table 2:
the lithium ion batteries of examples 1 to 17 have greatly improved expansion ratio, nickel dissolution rate and capacity retention ratio at high voltage, compared with comparative examples 1 and 2. The first additive and the second additive are not contained in the comparative example 1, and the second additive is only contained in the comparative example 2, so that the electrolyte is beneficial to reducing the expansion rate of the electrode and inhibiting the leaching amount of nickel element, and further improves the cycle stability of the lithium ion battery.
Further, the lithium ion batteries of examples 10 to 17 were lower in the dissolution rate of nickel element at a high voltage expansion rate and higher in the capacity retention rate than comparative example 2. Examples 10-17 contained only the first additive and comparative example 2 contained only the second additive. Therefore, the first additive is beneficial to reducing the expansion rate of the electrode and inhibiting the dissolution of nickel element, thereby improving the cycle stability of the lithium ion battery.
Examples 1-6 and examples 8-9 show that the structural formula of the alkyl thiomorpholine compound is the influence of the compound I on the performance of a lithium ion battery, and the battery test result shows that the consumption of the alkyl thiomorpholine compound has a great influence on the battery performance. The electrodes of examples 1-6 had lower expansion rates and lower nickel dissolution rates than examples 8 and 9, while the batteries of examples 1-6 had higher capacity retention rates than examples 8 and 9. Therefore, the mass range of the alkyl thiomorpholine compound is favorable for forming an interface protection film on the surface of the positive electrode, and meanwhile, the alkyl thiomorpholine compound can complex metal ions dissolved out from the positive electrode, effectively inhibit oxidative decomposition of electrolyte and stabilize the electrode/electrolyte interface.
The battery test results of examples 1 and 7 show that the combination of the alkyl thiomorpholine compound and different negative electrode film forming additives has a significant effect on the electrical performance of the lithium ion battery, and the proper additive combination scheme has a certain effect on further improving the electrical performance of the lithium ion battery.
In conclusion, the electrolyte is favorable for forming an interface protection film on the positive electrode, so that the dissolution of metal ions of the positive electrode and the oxidative decomposition of the electrolyte under high voltage are effectively inhibited; meanwhile, the stable SEI film is formed on the surface of the negative electrode, the stability of an electrode/electrolyte interface is maintained, and the cycle stability of the battery under high voltage is further improved.
The above description is only illustrative of the preferred embodiments of the present application and of the principles of the technology employed. It will be appreciated by persons skilled in the art that the scope of the application referred to in the present application is not limited to the specific combinations of the technical features described above, but also covers other technical features formed by any combination of the technical features described above or their equivalents without departing from the inventive concept. Such as the above-mentioned features and the technical features disclosed in the present application (but not limited to) having similar functions are replaced with each other.

Claims (10)

1. An electrolyte, comprising: lithium salt, organic solvent and additive;
the additive comprises a first additive, wherein the first additive is an alkyl thiomorpholine compound, and the alkyl thiomorpholine compound is at least one of the following compounds:
a compound I; />A compound II;
a compound III; />A compound IV;
a compound V; />Compound VI;
a compound VII; />Compound VIII.
2. The electrolyte of claim 1 wherein the first additive is present in an amount of 0.1% to 10% by mass based on the total mass of the electrolyte.
3. The electrolyte of claim 1 or 2, wherein the additive further comprises: and the second additive is selected from at least one of ethylene carbonate, fluoroethylene carbonate, ethylene sulfite, methylene methane disulfonate, 1, 3-propane sulfonate lactone, 1, 3-propylene sultone, ethylene sulfate, lithium difluorophosphate, lithium difluorobisoxalato phosphate and lithium tetrafluorooxalato phosphate.
4. The electrolyte according to claim 3, wherein the mass fraction of the second additive is 0.1 to 10% based on the total mass of the electrolyte.
5. The electrolyte according to claim 1 or 2, wherein the lithium salt is at least one selected from the group consisting of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium difluorooxalato borate, lithium bis (trifluoromethylsulfonyl) imide and lithium difluorosulfimide.
6. The electrolyte according to claim 1 or 2, wherein the organic solvent is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methylethyl carbonate, methylpropyl carbonate, γ -butyrolactone, methyl formate, ethyl acetate, methyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, and butyl propionate.
7. The electrolyte according to claim 6, wherein the organic solvent is ethylene carbonate and diethyl carbonate, and the mass ratio of the ethylene carbonate to the diethyl carbonate is 1 (1-2.5).
8. A positive electrode of a lithium ion battery, characterized by comprising a positive electrode current collector and a positive electrode active material layer positioned on the surface of the positive electrode current collector, wherein the surface of the positive electrode active material layer is provided with an interface protection film, and the interface protection film is obtained by electrolytic liquefaction according to any one of claims 1-7.
9. A lithium ion battery, comprising: the electrolyte of any one of claims 1-7 and/or the positive electrode of claim 8.
10. A vehicle comprising the lithium-ion battery of claim 9.
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