WO2021208955A1 - Electrolyte additive, secondary battery electrolyte, secondary battery and terminal - Google Patents

Abstract

An electrolyte additive. The chemical structural formula thereof is shown in formula (I), wherein R₁, R₂, R₃, R₄, R₅ and R₆ are respectively selected from any one of alkyl, halogenated alkyl, alkoxy, halogenated alkoxy, alkenyl, halogenated alkenyl, alkenyloxy, halogenated alkenyloxy, aryl, halogenated aryl, aryloxy and halogenated aryloxy, R₇ is halogenated alkyl, and X is selected from O or S. By using the electrolyte additive, a stable interfacial film can be formed on the surface of a negative electrode of a battery, side reactions of the electrolyte and a negative electrode material can be reduced, and the coulombic efficiency and the cycling stability of the battery can be improved.

Description

Electrolyte additives, secondary battery electrolyte, secondary batteries and terminals

This application claims the priority of the Chinese patent application filed with the Chinese Patent Office on April 14, 2020, the application number is 202010290478.8, and the application name is "electrolyte additive, secondary battery electrolyte, secondary battery and terminal", all of which The content is incorporated in this application by reference.

Technical field

This application relates to the technical field of secondary batteries, in particular to an electrolyte additive, a secondary battery electrolyte, a secondary battery and a terminal.

Background technique

Lithium-ion batteries have been widely used in terminal products (smartphones, digital cameras, notebook computers, electric vehicles, etc.) due to their high energy density, high working voltage, long service life, low self-discharge rate, and environmental friendliness. . With the development of economy and technology, the energy density of commercial lithium-ion batteries using graphite as a negative electrode material has approached the upper limit, which cannot meet people's higher requirements for battery energy density. Using higher theoretical capacity silicon-based, tin-based, metallic lithium and other anode materials to partially or completely replace graphite anodes is an effective way to increase battery energy density. However, these types of high theoretical capacity anode materials have large volume expansion and are active High, in the process of battery charging and discharging, a large amount of electrolyte will be consumed, resulting in low coulombic efficiency of the battery and poor overall performance of the battery. To improve this problem, a negative electrode film-forming additive is usually added to the electrolyte to form a SEI (Solid Electrolyte Interphase) film on the surface of the negative electrode to prevent the electrolyte from contacting the negative electrode material and improve the Coulomb efficiency. However, the traditional negative electrode film-forming additives (such as vinylene carbonate, fluoroethylene carbonate and vinyl sulfate, etc.) have no obvious effect on the high volume expansion of silicon-based, tin-based and lithium metal negative materials, and can only improve the Coulomb efficient.

Summary of the invention

In view of this, the embodiments of the present application provide an electrolyte additive, which can form a stable interface film on the surface of the negative electrode of the battery, and effectively improve the coulombic efficiency and cycle stability of the battery.

The first aspect of the embodiments of the present application provides an electrolyte additive. The chemical structural formula of the electrolyte additive is as shown in formula (I),

In formula (I), the R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , and R ₆ are respectively selected from alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, haloalkenyl, Any one of alkenyloxy, halogenated alkenyloxy, aryl, halogenated aryl, aryloxy, and halogenated aryloxy; said R ₇ is a halogenated alkyl group, and said X is selected from O or S.

In the embodiment of the present application, the number of carbon atoms of the alkyl group, halogenated alkyl group, alkoxy group, and halogenated alkoxy group is 1-20; The number of carbon atoms is 2-20; the number of carbon atoms of the aryl group, halogenated aryl group, aryloxy group, and halogenated aryloxy group is 6-20.

In the embodiment of the present application, the halogen in the halogenated alkyl group, halogenated alkoxy group, halogenated alkenyl group, halogenated alkenyloxy group, halogenated aryl group and halogenated aryloxy group includes fluorine, chlorine, bromine, and iodine. Halogenation is fully halogenated or partially halogenated.

In the embodiment of the present application, the R ₇ is a fluoroalkyl group having 1-20 carbon atoms.

The second aspect of the embodiments of the present application provides an electrolyte for a secondary battery, including an electrolyte salt, a non-aqueous organic solvent, and an additive. The additives include the electrolyte additive described in the first aspect of the embodiments of the present application.

In the embodiment of the present application, the mass percentage of the electrolyte additive in the secondary battery electrolyte is 0.1%-10%.

In the embodiment of the present application, the electrolyte salt includes at least one of lithium salt, sodium salt, potassium salt, magnesium salt, zinc salt, and aluminum salt.

In the embodiment of the application, the electrolyte salt includes MClO ₄ , MBF ₄ , MPF ₆ , MAsF ₆ , MPF ₂ O ₂ , MCF ₃ SO ₃ , MTDI, MB(C ₂ O ₄ ) ₂ (MBOB), MBF ₂ C ₂ O ₄ (MDFOB), M[(CF ₃ SO ₂ ) ₂ N], M[(FSO ₂ ) ₂ N] and M[(C _m F _2m+1 SO ₂ )(C _n F _2n+1 SO ₂ )N One or more of ], wherein M is Li, Na or K, and m and n are natural numbers.

In the embodiment of the present application, the molar concentration of the electrolyte salt in the electrolyte of the secondary battery is 0.01 mol/L-8.0 mol/L.

In the embodiment of the present application, the non-aqueous organic solvent includes one or more of carbonate-based solvents, ether-based solvents, and carboxylate-based solvents.

In the embodiment of the application, the additive further includes other additives, and the other additives include biphenyl, fluorobenzene, vinylene carbonate, trifluoromethyl ethylene carbonate, vinyl ethylene carbonate, 1,3-propanesulfon Acid lactone, 1,4-butane sultone, vinyl sulfate, vinyl sulfite, succinonitrile, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane and 1,3 , One or more of 6-hexane trinitrile.

A third aspect of the embodiments of the present application provides a secondary battery, including a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte includes the secondary battery electrolyte described in the second aspect of the embodiments of the present application.

In the embodiment of the application, the negative electrode includes 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, a potassium negative electrode, a magnesium negative electrode, a zinc negative electrode, and an aluminum negative electrode.

In the embodiment of the present application, the carbon-based negative electrode includes one or more of graphite, hard carbon, soft carbon, and graphene, and the silicon-based negative electrode includes one of silicon, silicon carbon, silicon oxygen, and silicon metal compound. One or more types, the tin-based negative electrode includes one or more of tin, tin carbon, tin oxide, and tin metal compound. Lithium negative electrode, sodium negative electrode, potassium negative electrode, magnesium negative electrode, zinc negative electrode, aluminum negative electrode can be lithium, sodium, potassium, magnesium, zinc, aluminum metal simple substance or its alloy, also can be the above-mentioned metal or its alloy with current collector, namely It includes a current collector and the foregoing metal element or alloy layer provided on the current collector. Taking the lithium negative electrode as an example, the lithium negative electrode can be pure metal lithium or a lithium alloy, such as a lithium foil, or it can include a current collector and a metal lithium or lithium alloy disposed on the current collector, such as a lithium-copper composite tape.

In the embodiment of the present application, the lithium alloy includes 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 the embodiment of the present application, the secondary battery includes a lithium secondary battery, a potassium secondary battery, a sodium secondary battery, a magnesium secondary battery, a zinc secondary battery, or an aluminum secondary battery.

An embodiment of the present application further provides a terminal, including a housing, and electronic components and batteries contained in the housing. The battery supplies power to the electronic components, and the battery includes the third aspect of the embodiments of the present application. The secondary battery.

The electrolyte additives provided in the embodiments of the present application, on the one hand, the additives can preferentially reduce the non-aqueous organic solvents in the electrolyte on the surface of the negative electrode to form stable compounds such as metal halides, carbon-nitrogen bond-containing compounds, and silanes. The interface film reduces the side reactions between the electrolyte and the anode material, thereby improving the coulombic efficiency and cycle stability of the battery; on the other hand, the N-Si bond in the additive can interact with the small amount of hydrofluoric acid (HF) in the electrolyte containing lithium hexafluorophosphate The reaction inhibits the further decomposition of lithium hexafluorophosphate and improves the stability of the electrolyte.

Description of the drawings

FIG. 1 is a schematic structural diagram of a secondary battery provided by an embodiment of the present application;

FIG. 2 is a schematic structural diagram of a terminal provided by an embodiment of the present application;

3 is a cycle curve diagram of the lithium secondary battery of Example 1-2 and Comparative Example 1 of the present application;

4 is a cycle curve diagram of the lithium secondary battery of Example 3-4 and Comparative Example 2 of the present application;

FIG. 5 is a cycle curve diagram of lithium secondary batteries of Examples 5-8 and Comparative Examples 3-5 of the present application;

Fig. 6 is a linear sweep voltammetry (LSV) curve diagram of the electrolyte of Example 5 and Comparative Example 3 of the present application;

Figures 7, 8 and 9 are the XPS (X-ray photoelectron spectroscopy, X-ray photoelectron spectroscopy, X-ray photoelectron spectroscopy) corresponding to the F1s, N1s, and Si2p spectra of the graphite pole piece surface after cycling the lithium secondary battery of Example 1 and Comparative Example 1 of the present application. Spectrum) detection map;

10, 11, and 12 are XPS detection diagrams corresponding to F1s, N1s, and Si2p spectra on the surface of the lithium sheet after cycling the lithium secondary battery of Example 5 and Comparative Example 3 of the present application.

Detailed ways

The embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application.

As shown in FIG. 1, the core components of a secondary battery (take a lithium ion battery as an example) include a positive electrode material 101, a negative electrode material 102, an electrolyte 103, a separator 104, and corresponding connecting accessories and circuits. During charging, lithium ions are extracted from the crystal lattice of the positive electrode material 101 and deposited on the negative electrode after passing through the electrolyte 103; During the charging and discharging process, the electrolyte and the electrode material react on the solid-liquid interface to form an interface film. This interface film significantly affects the performance of the battery. The instability of the interface protection film will cause serious side reactions, which will reduce the Coulomb efficiency and battery cycle. life. In order to obtain a stable negative interface film, reduce side reactions between the electrolyte and the negative electrode, and improve the coulombic efficiency and cycle life of the battery, the embodiments of the present application provide an electrolyte additive. A small amount of the electrolyte additive is added to the electrolyte of the secondary battery. It can significantly improve the functionality of the electrolyte and enhance the overall performance of the battery.

The chemical structural formula of the electrolyte additive provided in the embodiments of the present application is as shown in formula (I),

In formula (I), R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ may be independently selected from alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, haloalkenyl , Alkenyloxy, halogenated alkenyloxy, aryl, halogenated aryl, aryloxy, and halogenated aryloxy; R ₇ is a halogenated alkyl group, and X can be selected from O or S.

The electrolyte additives provided in the embodiments of the present application have lower LUMO energy and higher reduction potential, and can be reduced on the surface of the negative electrode prior to the non-aqueous organic solvent in the electrolyte, forming rich metal halides and carbon-nitrogen bonds. The stable interface film of the compound and silane and other compounds can reduce the side reaction between the electrolyte and the negative electrode material, and improve the coulombic efficiency and cycle stability of the battery. In addition, the N-Si bond in the additive can also interact with the small amount of HF in the electrolyte containing lithium hexafluorophosphate. The reaction inhibits the further decomposition of lithium hexafluorophosphate and improves the stability of the electrolyte.

Among them, the metal halide formed in the interface film varies according to different secondary battery systems. Specifically, the metal halide can be a lithium halide (such as lithium fluoride), a sodium halide (such as sodium fluoride), and a potassium halide. (Such as potassium fluoride).

In secondary batteries, non-aqueous organic solvents generally include carbonate-based solvents, ether-based solvents, and carboxylate-based solvents. _{Since the carbon-halogen bond in R 7} and the Si-N, Si-O or Si-S bond in the electrolyte additive provided in the embodiments of the application are unstable and easy to break, they have a higher reduction potential (greater than the reduction of organic solvents). Potential), which is easier to be reduced than organic solvents. After being reduced, a stable interface film rich in metal halides, carbon-nitrogen bond-containing compounds and silanes and other compounds is formed to cover the surface of the negative electrode, inhibiting the reduction and decomposition of the electrolyte on the negative electrode surface , Thereby improving cycle stability. Among them, taking a lithium secondary battery with an electrolyte containing ethylene carbonate (EC) in the solvent as an example, when R ₇ in the additive of the embodiment of the present application is a fluoroalkyl group, the possible mechanism of action of the electrolyte additive is:

From the above-mentioned mechanism, the electrolyte additives of the examples of this application are added to the lithium secondary battery system containing ethylene carbonate (EC) in the electrolyte, and finally compounds such as lithium fluoride, silane and polyester containing carbon-nitrogen bonds are formed. .

In an embodiment of the present application, X is an oxygen atom O, and the chemical structural formula of the electrolyte additive is shown in formula (II):

In another embodiment of the present application, X is a sulfur atom S, and the chemical structural formula of the electrolyte additive is shown in formula (III):

In the embodiment of the present application, when X is a sulfur atom S, the electrolyte additive can also react in the electrolyte system to generate sulfide, thereby improving ion conductivity.

In the embodiments of the present application, in R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , and R ₆ , the number of carbon atoms of the alkyl group, halogenated alkyl group, alkoxy group, and halogenated alkoxy group may be 1-20, and further , The number of carbon atoms can be 1-10, specifically the number of carbon atoms is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10; alkenyl, haloalkenyl, alkenyloxy, halogen The number of carbon atoms of the alkenyloxy group can be 2-20, and further, the number of carbon atoms can be 2-10, specifically, the number of carbon atoms is, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10. ; The number of carbon atoms of the aryl group, halogenated aryl group, aryloxy group, and halogenated aryloxy group can be 6-20, and further, the number of carbon atoms can be 7-10, specifically, the number of carbon atoms is, for example, 7, 8 , 9, 10.

Among them, when R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , and R ₆ are halogenated groups, the reduction potential of the electrolyte additive can be further increased, so that the electrolyte additive is more easily reduced.

In the embodiment of the application, R ₇ is a halogenated alkyl group. On the one hand, halogen is a strong electron-withdrawing group, which can improve the reducibility of electrolyte additives and increase the reduction potential. On the other hand, it is beneficial to form rich metal halides (such as fluorinated Lithium, sodium fluoride, etc.) stabilize the interface film to improve the stability of the negative electrode interface. In the embodiment of the present application, the _{number of carbon atoms of R 7} haloalkyl group can be 1-20, and further, the number of carbon atoms can be 1-10, specifically, the number of carbon atoms is, for example, 1, 2, 3, 4, 5, and 6. , 7, 8, 9, 10; In some embodiments of the present application, R ₇ is a fluoroalkyl group with 1-20 carbon atoms, and further, R ₇ is a fluoroalkyl group with 1-8 carbon atoms. Specifically, R ₇ may be, for example, trifluoromethyl, trifluoroethyl, pentafluoroethyl, or the like. A smaller number of carbon atoms is conducive to better dissolution of the additives in the electrolyte.

In the embodiments of this application _{, one or more of R 1} , R ₂ , R ₃ , R ₄ , R ₅ , and R ₆ are halogenated alkyl, halogenated alkoxy, halogenated alkenyl, halogenated alkenyloxy, halogenated aromatic It is helpful to enhance the flame retardant performance of electrolyte additives when it is based on or halogenated aryloxy group.

In the embodiments of the present application, the halogen in haloalkyl, haloalkoxy, haloalkenyl, haloalkenyloxy, haloaryl and haloaryloxy includes fluorine, chlorine, bromine, and iodine, and the halogenation can be Fully halogenated or partially halogenated. Alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkenyloxy, and haloalkenyloxy may be linear or branched.

In the embodiments of the present application, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ may be the same or different groups. In the embodiments of the present application, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ may also be the same or different groups _{from R 7.}

In the specific embodiment of the present application, the molecular structural formula of the electrolyte additive can be as shown in formulas (A)-(F):

[Correct 25.04.2021 according to Rule 91]

In the embodiments of the present application, the electrolyte additive represented by formula (I) can be prepared by different methods. In some embodiments of the present application, it can be prepared in the following manner:

Using pentane as solvent, add reactants R ₁ , R ₂ , R ₃ substituted chlorosilane M1, R ₄ , R ₅ , R ₆ substituted chlorosilane M2, and amide or sulfamide M3, and control the reaction temperature to 20-50 After the reaction is complete, the electrolyte additive of formula (I) can be obtained. Among them, amide or sulfamide is used as an acid binding agent. The reaction process is shown in formula (IV):

The embodiments of the present application also provide an electrolyte for a secondary battery, which includes an electrolyte salt, a non-aqueous organic solvent, and additives. The additives include the electrolyte additives described in the embodiments of the present application.

In the embodiments of the present application, the mass percentage content of the electrolyte additive in the electrolyte of the secondary battery may be 0.1%-10%. Further, the mass percentage content of the electrolyte additive in the electrolyte of the secondary battery may be 0.5%-8%, 1%-6%, 2%-5%, 0.5%-1%. In the embodiment of the present application, the addition of a lower content of electrolyte additives can effectively improve the coulombic efficiency of the battery. At the same time, the addition of a lower content of electrolyte additives can ensure that the viscosity of the electrolyte will not be too high and will not affect the battery performance.

In the embodiments of the present application, according to different secondary battery systems, the electrolyte salt may be a lithium salt, a sodium salt, a potassium salt, a magnesium salt, a zinc salt, an aluminum salt, and the like. Specifically, the lithium salt, sodium salt, and potassium salt may be MClO ₄ , MBF ₄ , MPF ₆ , MAsF ₆ , MPF ₂ O ₂ , MCF ₃ SO ₃ , MTDI, MB(C ₂ O ₄ ) ₂ (MBOB), MBF ₂ C ₂ O ₄ (MDFOB), M[(CF ₃ SO ₂ ) ₂ N], M[(FSO ₂ ) ₂ N] and M[(C _m F _2m+1 SO ₂ )(C _n F _2n+1 One or more of SO ₂ )N], wherein M is Li, Na or K, and m and n are natural numbers. Similarly, the magnesium salt, zinc salt, and aluminum salt may also be a salt substance formed of magnesium ion, zinc ion, aluminum ion, and anions in the above-mentioned lithium salt, sodium salt, and potassium salt.

In the embodiment of the present application, the molar concentration of the electrolyte salt in the electrolyte of the secondary battery is 0.01 mol/L-8.0 mol/L. Further, it may be 0.05 mol/L to 2 mol/L, 0.5 mol/L to 1.0 mol/L.

In the embodiment of the present application, the non-aqueous organic solvent includes one or more of carbonate-based solvents, ether-based solvents, and carboxylate-based solvents. Non-aqueous organic solvents can be mixed in any ratio. Among them, carbonate solvents include cyclic carbonates or chain carbonates. The cyclic carbonates may specifically be ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), butylene carbonate. One or more of (BC); the chain carbonate can specifically be dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate (DPC) One or more of. Ether solvents include cyclic ethers or chain ethers. Cyclic ethers can specifically be 1,3-dioxolane (DOL), 1,4-dioxane (DX), crown ether, tetrahydrofuran (THF), One or more of 2-methyltetrahydrofuran (2-CH ₃ -THF) and 2-trifluoromethyltetrahydrofuran (2-CF ₃ -THF); the chain ether may specifically be dimethoxymethane One or more of (DMM), 1,2-dimethoxyethane (DME), and diglyme (TEGDME). The carboxylic acid ester solvent may specifically be one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), butyl propionate or Many kinds.

In the embodiments of this application, in addition to the above-mentioned electrolyte additives, other additives can be added to the electrolyte of the secondary battery according to different performance requirements. The other additives can specifically be, but are not limited to, biphenyl, fluorobenzene, and vinylene carbonate. , Trifluoromethyl ethylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, 1,4-butane sultone, vinyl sulfate, vinyl sulfite, succinonitrile, hexamethylene One or more of nitrile, 1,2-bis(2-cyanoethoxy)ethane and 1,3,6-hexanetrinitrile.

Correspondingly, the embodiment of the present application also provides a preparation method of the above-mentioned secondary battery electrolyte, which includes the following steps:

In an inert environment or a closed environment (such as a glove box filled with argon gas), add electrolyte additives to a non-aqueous organic solvent, then dissolve the fully dried electrolyte salt in the above solution, stir and mix uniformly to obtain a secondary Battery electrolyte.

Each operation in the above preparation method can be implemented according to the existing conventional electrolyte preparation process, wherein the specific selection of raw materials such as electrolyte salt, non-aqueous organic solvent, electrolyte additive, etc. are as described above, and will not be repeated here. When the electrolyte also includes other additives, they can be added together with the electrolyte additives.

The embodiments of the present application also provide a secondary battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte adopts the secondary battery electrolyte provided in the above-mentioned embodiments of the present application. The secondary battery provided in the embodiments of the present application, because the electrolyte additive mentioned in the present application is added to the electrolyte, can obtain higher coulombic efficiency and good cycle stability. In the embodiment of the present application, the secondary battery may be a lithium secondary battery, a potassium secondary battery, a sodium secondary battery, a magnesium secondary battery, a zinc secondary battery, an aluminum secondary battery, or the like. The secondary battery provided in the embodiments of this application can be used in terminal consumer products, such as mobile phones, tablet computers, mobile power supplies, portable computers, notebook computers, and other wearable or movable electronic devices, as well as automobiles and other products to improve product performance .

In the 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, a potassium negative electrode, a magnesium negative electrode, a zinc negative electrode, and an aluminum negative electrode. Among them, the carbon-based negative electrode can include graphite, hard carbon, soft carbon, graphene, etc.; the silicon-based negative electrode can include silicon, silicon carbon, silicon oxygen, silicon metal compound, etc.; the tin-based negative electrode can include tin, tin carbon, tin oxide, tin Metal compounds. Lithium negative electrode, sodium negative electrode, potassium negative electrode, magnesium negative electrode, zinc negative electrode, aluminum negative electrode can be lithium, sodium, potassium, magnesium, zinc, aluminum metal simple substance or its alloy, also can be the above-mentioned metal or its alloy with current collector, namely It includes a current collector and the foregoing metal element or alloy layer provided on the current collector. Taking the lithium negative electrode as an example, the lithium negative electrode can be pure metal lithium or a lithium alloy, such as a lithium foil, or it can include a current collector and a metal lithium or lithium alloy disposed on the current collector, such as a lithium-copper composite tape. 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 the embodiments of the present application, the positive electrode includes a positive electrode active material capable of reversibly intercalating/deintercalating metal ions (lithium ions, sodium ions, potassium ions, magnesium ions, zinc ions, aluminum ions, etc.). The selection of positive electrode active materials in this application There is no particular limitation, and it can be a positive electrode active material conventionally used in existing secondary batteries. Taking a lithium secondary battery as an example, the positive electrode active material can be lithium cobalt oxide (LiCoO ₂ ), lithium iron phosphate (LiFePO ₄ ), lithium nickel cobalt manganese oxide (LiNi _0.6 Co _0.2 Mn _0.2 ), and polyanionic lithium compound LiM _x ( PO ₄ ) _y (M is Ni, Co, Mn, Fe, Ti, V, 0≤x≤5, 0≤y≤5), etc.

In the embodiments of the present application, the current collector of the positive electrode may be metals such as aluminum, titanium, and tantalum or alloys thereof, and the current collector of the negative electrode may be materials such as copper, nickel, stainless steel, etc.

In the embodiment of the present application, the diaphragm can be an existing conventional diaphragm, including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP/PE, double-layer PP/PP, and three-layer PP/ Diaphragm such as PE/PP.

As shown in FIG. 2, the embodiment of the present application also provides a terminal. The terminal 200 may be a mobile phone, a tablet computer, a notebook computer, a portable computer, a smart wearable product, a car, etc. The terminal 200 includes a housing 201 and a housing 201. The electronic components and batteries (not shown in the figure) in the housing 201. The battery provides power for the electronic components. The battery is the secondary battery provided in the above embodiment of the application. The housing 201 may include The front cover on the side and the rear case assembled on the rear side, the battery can be fixed inside the rear case.

The following further describes the embodiments of the present application through specific embodiments.

Example 1

An electrolyte for lithium secondary batteries, including lithium salt (lithium hexafluorophosphate LiPF ₆ ), a non-aqueous organic solvent formed by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a mass ratio of 50:50, and including molecules The structural formula is the electrolyte additive shown in formula (A), wherein _{the concentration of lithium salt (LiPF 6} ) is 1.0 mol/L, and the mass percentage of electrolyte additive A is 0.5%,

Preparation of the electrolyte for the lithium secondary battery in this embodiment:

In a glove box filled with argon, mix EC and EMC to form a non-aqueous organic solvent, add electrolyte additive A to the above-mentioned non-aqueous organic solvent, and then _{dissolve fully dried lithium salt (LiPF 6} ) in the above-mentioned solvent , Stir and mix uniformly to prepare the lithium secondary battery electrolyte of Example 1 of the present application.

Preparation of lithium secondary battery

Weigh 2% polyvinylidene fluoride (PVDF), 2% conductive agent super P and 96% lithium cobalt oxide (LiCoO ₂ ), and add them to N-methylpyrrolidone (NMP) in turn, stir and mix thoroughly Evenly, the slurry is coated on the aluminum foil current collector, dried, cold pressed, and slit to prepare the positive pole piece.

Weigh 1.5% sodium carboxymethyl cellulose (CMC), 2.5% styrene-butadiene rubber (SBR), 1% acetylene black and 95% graphite, and add them to deionized water in turn, stir and mix well. The slurry is coated on the copper foil current collector, dried, cold pressed, and slit to prepare a negative electrode piece.

The positive pole piece, the negative pole piece and the commercial PE separator prepared above are made into batteries, and polymer packaging is used, and the lithium secondary battery electrolyte prepared in Example 1 of this application is poured into a soft pack after chemical conversion and other processes. Lithium secondary battery.

Example 2

An electrolyte for lithium secondary batteries, including lithium salt (LiPF ₆ ), a non-aqueous organic solvent formed by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a mass ratio of 50:50, and a molecular structural formula The electrolyte additive represented by formula (B), wherein _{the concentration of the lithium salt (LiPF 6} ) is 1.0 mol/L, and the mass percentage of the electrolyte additive B is 0.5%,

Preparation of the electrolyte for the lithium secondary battery in this embodiment:

In a glove box filled with argon gas, EC and EMC are mixed to form a non-aqueous organic solvent, electrolyte additive B is added to the above non-aqueous organic solvent, and then fully dried lithium salt (LiPF ₆ ) is dissolved in the above solvent , Stir and mix uniformly to prepare the lithium secondary battery electrolyte of Example 2 of the present application.

The production of the lithium secondary battery was the same as in Example 1.

Example 3

An electrolyte for lithium secondary batteries, including lithium salt (LiPF ₆ ), mixed with ethylene carbonate (EC), diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) in a mass ratio of 30:60:10 The formed non-aqueous organic solvent, and the electrolyte additive having a molecular structural formula as shown in formula (C), wherein _{the concentration of the lithium salt (LiPF 6} ) is 1.0 mol/L, and the electrolyte additive C has a mass of 100% The sub-content is 1%,

Preparation of the electrolyte for the lithium secondary battery in this embodiment:

In a glove box filled with argon, EC, DEC, and FEC are mixed to form a non-aqueous organic solvent, electrolyte additive C is added to the above non-aqueous organic solvent, and then fully dried lithium salt (LiPF ₆ ) is dissolved in the above In the solvent, stir and mix uniformly to prepare the lithium secondary battery electrolyte of Example 3 of the present application.

Preparation of lithium secondary battery

Weigh 2% polyvinylidene fluoride (PVDF), 2% conductive agent super P and 96% lithium cobalt oxide (LiCoO ₂ ), and add them to N-methylpyrrolidone (NMP) in turn, stir and mix thoroughly Evenly, the slurry is coated on the aluminum foil current collector, dried, cold pressed, and slit to prepare the positive pole piece.

Weigh the mass percentages as 1.5% CMC, 2.5% SBR, 1% acetylene black and 95% silicon carbon, add them to deionized water in sequence, stir and mix well, coat the slurry on the copper foil current collector, and bake The negative pole piece is prepared by dry, cold pressing, and slitting.

The positive pole piece, the negative pole piece and the commercial PE separator prepared above are made into batteries, which are packaged by polymer, poured into the lithium secondary battery electrolyte prepared in Example 3 of this application, and are made into a soft pack after chemical conversion and other processes Lithium secondary battery.

Example 4

An electrolyte for lithium secondary batteries, including lithium salt (LiPF ₆ ), mixed with ethylene carbonate (EC), diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) in a mass ratio of 30:60:10 The formed non-aqueous organic solvent, and the electrolyte additive having a molecular structure such as formula (D), wherein _{the concentration of the lithium salt (LiPF 6} ) is 1.0 mol/L, and the electrolyte additive D has a mass of 100 The sub-content is 1%,

Preparation of the electrolyte for the lithium secondary battery in this embodiment:

In a glove box filled with argon gas, EC, DEC and FEC are mixed to form a non-aqueous organic solvent, electrolyte additive D is added to the above-mentioned non-aqueous organic solvent, and then fully dried lithium salt (LiPF ₆ ) is dissolved in the above In the solvent, stir and mix uniformly to prepare the lithium secondary battery electrolyte of Example 4 of the present application.

The production of the lithium secondary battery was the same as in Example 3.

Example 5

An electrolyte for lithium secondary batteries, including lithium salt (lithium hexafluorophosphate LiPF ₆ and lithium bisfluorosulfonimide LiFSI) composed of dimethyl carbonate (DMC) and fluoroethylene carbonate (FEC) in a mass ratio of 50:50 The non-aqueous organic solvent formed by mixing, and the electrolyte additive including the molecular structure shown in formula (A), wherein _{the concentration of the lithium hexafluorophosphate (LiPF 6} ) and the lithium bisfluorosulfonimide are 1.0 mol/L and 0.2mol/L, the mass percentage of the electrolyte additive A is 1%,

Preparation of the electrolyte for the lithium secondary battery in this embodiment:

In a glove box filled with argon, DMC and FEC are mixed to form a non-aqueous organic solvent, electrolyte additive A is added to the above non-aqueous organic solvent, and then fully dried lithium salts (LiPF ₆ and LiFSI) are dissolved in the above In the solvent, stir and mix uniformly to prepare the lithium secondary battery electrolyte of Example 5 of the present application.

Preparation of lithium secondary battery

Weigh 2% polyvinylidene fluoride (PVDF), 2% conductive agent super P, and 96% lithium cobalt oxide (LiCoO ₂ ), and add them to N-methylpyrrolidone (NMP) in turn, stir and mix them thoroughly Evenly, the slurry is coated on the aluminum foil current collector, dried, cold pressed, and slit to prepare the positive pole piece.

The positive pole piece, the metal lithium negative pole piece and the commercial PE separator prepared above are made into a battery cell, which is packaged by polymer, and filled with the lithium secondary battery electrolyte prepared in Example 5 of the present application, and is made after chemical conversion and other processes Soft pack lithium secondary battery.

Example 6

An electrolyte for lithium secondary batteries, including lithium salt (lithium hexafluorophosphate LiPF ₆ and lithium bisfluorosulfonimide LiFSI) composed of dimethyl carbonate (DMC) and fluoroethylene carbonate (FEC) in a mass ratio of 50:50 The non-aqueous organic solvent formed by mixing, and the electrolyte additive comprising the molecular structure shown in formula (E), wherein _{the concentration of the lithium hexafluorophosphate (LiPF 6} ) and lithium bisfluorosulfonimide (LiFSI) is 1.0 mol, respectively /L and 0.2mol/L, the mass percentage of the electrolyte additive E is 1%,

Preparation of the electrolyte for the lithium secondary battery in this embodiment:

In a glove box filled with argon, mix DMC and FEC to form a non-aqueous organic solvent, add electrolyte additive E to the above-mentioned non-aqueous organic solvent, and then _{dissolve fully dried lithium salts (LiPF 6} and LiFSI) in the above-mentioned non-aqueous organic solvent. In the solvent, stir and mix uniformly to prepare the lithium secondary battery electrolyte of Example 6 of the present application.

The production of the lithium secondary battery was the same as in Example 5.

Example 7

An electrolyte for lithium secondary batteries, including lithium salts (lithium bisfluorosulfonimide LiFSI and lithium difluorooxalate LiDFOB), consisting of dimethyl carbonate (DMC), fluoroethylene carbonate (FEC) and 1, 1,2,2-Tetrafluoroethyl-2,2,3,3-Tetrafluoropropyl ether (D2) is a non-aqueous organic solvent formed by mixing at a mass ratio of 50:10:40, and includes a molecular structure such as the formula ( F) The electrolyte additive shown in F), wherein the concentrations of the LiFSI and LiDFOB are 4.0 mol/L and 0.5 mol/L, respectively, and the electrolyte additive F has a mass percentage of 1%,

Preparation of the electrolyte for the lithium secondary battery in this embodiment:

In a glove box filled with argon, mix DMC, FEC and D2 to form a non-aqueous organic solvent, add electrolyte additive F to the above-mentioned non-aqueous organic solvent, and then dissolve fully dried lithium salts (LiFSI and LiDFOB) in In the above solvent, stir and mix uniformly to prepare the lithium secondary battery electrolyte of Example 7 of the present application.

The production of the lithium secondary battery was the same as in Example 5.

Example 8

An electrolyte for lithium secondary batteries, including lithium salts (lithium bisfluorosulfonimide LiFSI and lithium difluorooxalate LiDFOB), consisting of ethylene glycol dimethyl ether (DME), fluoroethylene carbonate (FEC) and 1,1,2,2-Tetrafluoroethyl-2,2,3,3-Tetrafluoropropyl ether (D2) is a non-aqueous organic solvent formed by mixing 50:10:40 by mass ratio, and includes the molecular structure such as The electrolyte additive represented by formula (A), wherein the concentrations of the LiFSI and LiDFOB are 6.0 mol/L and 0.5 mol/L, respectively, and the electrolyte additive A has a mass percentage of 1%,

Preparation of the electrolyte for the lithium secondary battery in this embodiment:

In a glove box filled with argon, mix DME, FEC and D2 to form a non-aqueous organic solvent, add electrolyte additive A to the above-mentioned non-aqueous organic solvent, and then dissolve fully dried lithium salts (LiFSI and LiDFOB) in In the above solvent, stir and mix uniformly to prepare the lithium secondary battery electrolyte of Example 8 of the present application.

The production of the lithium secondary battery was the same as in Example 5.

Comparative example 1

An electrolyte for lithium secondary batteries, comprising lithium salt (lithium hexafluorophosphate LiPF ₆ ), a non-aqueous organic solvent formed by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a mass ratio of 50:50, wherein The concentration of the lithium salt (LiPF ₆ ) is 1.0 mol/L.

Preparation of the electrolyte for the lithium secondary battery in this comparative example:

In a glove box filled with argon gas, EC and EMC were mixed to form a non-aqueous organic solvent, and then fully dried lithium salt (LiPF ₆ ) was dissolved in the above solvent, stirred and mixed uniformly to prepare the lithium of Comparative Example 1 of the present application Secondary battery electrolyte.

Preparation of lithium secondary battery

Weigh 2% polyvinylidene fluoride (PVDF), 2% conductive agent super P and 96% lithium cobalt oxide (LiCoO ₂ ), and add them to N-methylpyrrolidone (NMP) in turn, stir and mix thoroughly Evenly, the slurry is coated on the aluminum foil current collector, dried, cold pressed, and slit to prepare the positive pole piece.

Weigh the mass percentages as 1.5% CMC, 2.5% SBR, 1% acetylene black and 95% graphite, add them to deionized water in turn, stir and mix well, coat the slurry on the copper foil current collector, and dry , Cold pressing, and slitting to make the negative pole piece.

The positive pole piece, the negative pole piece and the commercial PE separator prepared above are made into batteries, and polymer packaging is used, and the lithium secondary battery electrolyte prepared in Comparative Example 1 of the application is poured into a soft pack after chemical conversion and other processes. Lithium secondary battery.

Comparative example 2

An electrolyte for lithium secondary batteries, including lithium salt (LiPF ₆ ), mixed with ethylene carbonate (EC), diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) in a mass ratio of 30:60:10 In the formed non-aqueous organic solvent, _{the concentration of the lithium salt (LiPF 6} ) is 1.0 mol/L.

Preparation of the electrolyte for the lithium secondary battery in this comparative example:

In a glove box filled with argon gas, EC, DEC, and FEC were mixed to form a non-aqueous organic solvent, and then fully dried lithium salt (LiPF ₆ ) was dissolved in the above solvent, stirred and mixed uniformly, to prepare Comparative Example 2 of the present application Electrolyte for lithium secondary batteries.

Preparation of lithium secondary battery

Weigh 2% polyvinylidene fluoride (PVDF), 2% conductive agent super P and 96% lithium cobalt oxide (LiCoO ₂ ), and add them to N-methylpyrrolidone (NMP) in turn, stir and mix thoroughly Evenly, the slurry is coated on the aluminum foil current collector, dried, cold pressed, and slit to prepare the positive pole piece.

Weigh the mass percentages as 1.5% CMC, 2.5% SBR, 1% acetylene black and 95% silicon carbon, add them to deionized water in sequence, stir and mix well, coat the slurry on the copper foil current collector, and bake The negative pole piece is prepared by dry, cold pressing, and slitting.

The positive pole piece, the negative pole piece and the commercial PE separator prepared above are made into a battery cell, which is packaged by polymer, and filled with the lithium secondary battery electrolyte prepared in Comparative Example 2 of the application, and then a soft pack is made after chemical conversion and other processes. Lithium secondary battery.

Comparative example 3

An electrolyte for lithium secondary batteries, including lithium salt (lithium hexafluorophosphate LiPF ₆ and lithium bisfluorosulfonimide LiFSI) composed of dimethyl carbonate (DMC) and fluoroethylene carbonate (FEC) in a mass ratio of 50:50 In the non-aqueous organic solvent formed by mixing, the _{concentrations of the lithium hexafluorophosphate (LiPF 6} ) and lithium bisfluorosulfonimide (LiFSI) are 1.0 mol/L and 0.2 mol/L, respectively.

Preparation of the electrolyte for the lithium secondary battery in this comparative example:

In a glove box filled with argon gas, DMC and FEC were mixed to form a non-aqueous organic solvent, and then fully dried lithium salts (LiPF ₆ and LiFSI) were dissolved in the above solvent, stirred and mixed uniformly, to prepare Comparative Example 3 of the present application Electrolyte for lithium secondary batteries.

Preparation of lithium secondary battery

Weigh 2% polyvinylidene fluoride (PVDF), 2% conductive agent super P and 96% lithium cobalt oxide (LiCoO ₂ ), and add them to N-methylpyrrolidone (NMP) in turn, stir and mix thoroughly Evenly, the slurry is coated on the aluminum foil current collector, dried, cold pressed, and slit to prepare the positive pole piece.

The above-prepared positive pole piece, lithium metal negative pole piece and commercial PE diaphragm are made into batteries, which are packaged by polymer, and are filled with the lithium secondary battery electrolyte prepared in Comparative Example 3 of this application, and are made after chemical conversion and other processes Soft pack lithium secondary battery.

Comparative example 4

An electrolyte for lithium secondary batteries, including lithium salts (lithium bisfluorosulfonimide LiFSI and lithium difluorooxalate LiDFOB), consisting of dimethyl carbonate (DMC), fluoroethylene carbonate (FEC) and 1, A non-aqueous organic solvent formed by mixing 1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (D2) at a mass ratio of 50:10:40, wherein the LiFSI and LiDFOB The concentrations are 4.0mol/L and 0.5mol/L, respectively.

Preparation of the electrolyte for the lithium secondary battery in this comparative example:

In a glove box filled with argon, mix DMC, FEC and D2 to form a non-aqueous organic solvent, and then dissolve the fully dried lithium salt (LiFSI and LiDFOB) in the above solvent, stir and mix uniformly, to prepare the comparative example of this application 4 lithium secondary battery electrolyte.

The production of the lithium secondary battery was the same as that of Comparative Example 3.

Comparative example 5

An electrolyte for lithium secondary batteries, including lithium salts (lithium bisfluorosulfonimide LiFSI and lithium difluorooxalate LiDFOB), consisting of ethylene glycol dimethyl ether (DME), fluoroethylene carbonate (FEC) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (D2) is a non-aqueous organic solvent formed by mixing at a mass ratio of 50:10:40, wherein the LiFSI The concentrations of LiDFOB and LiDFOB are 6.0mol/L and 0.5mol/L, respectively.

Preparation of the electrolyte for the lithium secondary battery in this comparative example:

In a glove box filled with argon, mix DME, FEC and D2 to form a non-aqueous organic solvent, and then dissolve the fully dried lithium salt (LiFSI and LiDFOB) in the above solvent, stir and mix evenly to prepare the comparative example of the application 5. Lithium secondary battery electrolyte.

The production of the lithium secondary battery was the same as that of Comparative Example 3.

In order to strongly support the beneficial effects brought about by the technical solutions in Examples 1-8 and Comparative Examples 1-5 of this application, the following tests are provided:

Copper/lithium battery performance test: Assemble a copper sheet positive electrode, a metal lithium negative electrode and a separator to form a button battery, and drop 100 uL of the electrolyte described in the foregoing Examples 1-8 and Comparative Examples 1-5. Test according to the following test procedure, and the test results are listed in Table 1.

The copper/lithium battery test process is set as follows: the first charge and discharge current density is 0.5mA/cm ² , the first deposition volume is 4.0mAh/cm ² , the cycle discharge current density is 0.5mA/cm ² , and the cycle charge current density is 1.5mA/cm 2 cm ^2, a cyclic deposition amount 1.0mAh / cm ^2, cycle weeks 50 weeks, the first discharge capacity (Q _T) by comparing the battery, the cycle charge capacity (Q _C), and the last charging capacity (Q _S) calculated copper / Coulombic efficiency of lithium battery charge and discharge cycle.

Calculate the coulombic efficiency (CE) of the battery as follows:

Lithium secondary battery performance test: the lithium secondary batteries assembled in Examples 1-8 and Comparative Examples 1-5 were subjected to a charge-discharge cycle test at a charge-discharge rate of 0.2/0.5C, and the battery voltage range was 3.0V-4.45V , Record the capacity retention rate after 100 weeks, and the test results are shown in Table 1, Figure 3, Figure 4, and Figure 5.

Table 1 Battery Coulombic efficiency and cycle performance test results of Examples 1-8 and Comparative Examples 1-5

Example/Comparative Example	Coulombic efficiency of copper/lithium battery/%	Lithium secondary battery capacity retention rate/%
Example 1	95.2	95.7
Example 2	93.5	94.8
Example 3	97.8	92.9
Example 4	96.7	92.6
Example 5	98.8	90.9
Example 6	98.2	88.4
Example 7	99.4	85.7
Example 8	99.6	82.1

Comparative example 1	80.2	91.8
Comparative example 2	85.7	85.6
Comparative example 3	93.5	68.8
Comparative example 4	97.8	79.7
Comparative example 5	98.4	69.5

It can be known from the test results of Table 1 and Figure 3 that, compared with Comparative Example 1, Example 1 and Example 2 of the present application have added electrolyte additive A and electrolyte additive B to the electrolyte, respectively. Therefore, Example 1 of the present application And the 50-week average coulombic efficiency of the copper/lithium battery in Example 2 are both higher than the 50-week average Coulomb efficiency of the copper/lithium battery in Comparative Example 1, and the lithium cobaltate/graphite in Example 1 and Example 2 of the present application The capacity retention rate of the lithium secondary battery after 100 weeks was higher than the capacity retention rate of the lithium cobaltate/graphite lithium secondary battery in Comparative Example 1 after 100 weeks.

It can be known from the test results of Table 1 and Figure 4 that, compared with Comparative Example 2, Example 3 and Example 4 of the present application are respectively added with electrolyte additive C and electrolyte additive D in the electrolyte, so Example 3 of the present application The 50-week average coulombic efficiency of the copper/lithium battery in -4 is higher than the 50-week average coulombic efficiency of the copper/lithium battery in Comparative Example 2, and the lithium cobalt oxide/silicon carbon battery in Example 3-4 of the present application is 100 weeks The subsequent capacity retention rates are higher than those of the lithium cobalt oxide/silicon carbon battery in Comparative Example 2 after 100 weeks.

It can be known from the test results of Table 1 and Figure 5 that, compared to Comparative Example 3, Example 5 and Example 6 of the present application are respectively added with electrolyte additive A and electrolyte additive E in the electrolyte, therefore, Example 5 of the present application And the 50-week average coulombic efficiency of the copper/lithium battery in Example 6 are both higher than the 50-week average coulombic efficiency of the copper/lithium battery in Comparative Example 3, and the lithium cobaltate/lithium in Example 5 and Example 6 of the present application The capacity retention rate of the battery after 100 weeks is higher than the capacity retention rate of the lithium cobaltate/lithium battery in Comparative Example 3 after 100 weeks. Compared with Comparative Example 4, because the electrolyte additive F is added to the electrolyte in Example 7 of the present application, the 50-week average coulombic efficiency of the copper/lithium battery in Example 7 of the present application is higher than that of the copper/lithium battery in Comparative Example 4. The 50-week average coulombic efficiency of the lithium battery, and the capacity retention rate of the lithium cobalt oxide/lithium battery in Example 7 of the present application after 100 weeks is higher than the capacity retention rate of the lithium cobalt oxide/lithium battery in Comparative Example 4 after 100 weeks . Compared with Comparative Example 5, because the electrolyte additive A is added to the electrolyte in Example 8 of the present application, the 50-week average coulombic efficiency of the copper/lithium battery in Example 8 of the present application is higher than that of the copper/lithium battery in Comparative Example 5. The 50-week average coulombic efficiency of the lithium battery, and the capacity retention rate of the lithium cobalt oxide/lithium battery in Example 8 of the present application after 100 weeks is higher than the capacity retention rate of the lithium cobalt oxide/lithium battery in Comparative Example 5 after 100 weeks .

The above test results show that the use of the electrolyte containing the electrolyte additives of the embodiments of this application can significantly improve the coulombic efficiency and cycle performance of the battery. (Graphite negative electrode, silicon carbon negative electrode, lithium negative electrode) surface reduction to form a stable interface film rich in lithium fluoride, carbon-nitrogen bond-containing compounds, silane and other compounds, which not only reduces the side reactions between the electrolyte and the negative electrode, but also improves the battery coulomb Efficiency and cycle performance, and the N-Si bond in the electrolyte additive can react with a small amount of HF in the electrolyte containing lithium hexafluorophosphate, inhibiting the further decomposition of lithium hexafluorophosphate, and improving the stability of the electrolyte.

Fig. 6 is a linear scanning volt-ampere curve diagram of the electrolyte of Example 5 and Comparative Example 3 of the application. From the LSV curve in the figure, it can be seen that the reduction potential of the LSV curve of Comparative Example 3 without additives is about 0.9V. The reduction potential of the LSV curve of the additive added in Example 5 of this application is about 1.6V, which is significantly higher than the reduction potential of Comparative Example 3. This indicates that the additive is preferentially reduced to form a stable SEI film covering the surface of the negative electrode, which inhibits electrolysis. The reduction and decomposition of the liquid on the surface of the negative electrode improves the cycle stability of the battery.

7, 8 and 9 are XPS detection diagrams corresponding to F1s, N1s and Si2p spectra of the graphite pole piece surface after cycling the lithium cobalt oxide/lithium graphite secondary battery of Example 1 and Comparative Example 1 of the present application. 10, 11, and 12 are XPS detection diagrams corresponding to F1s, N1s and Si2p spectra on the surface of the lithium sheet after cycling the lithium cobalt oxide/lithium battery of Example 5 and Comparative Example 3 of the present application. It can be seen from the spectrum that the enhancement of Li-F, C-N and Si-C indicates that a stable interfacial film rich in compounds such as LiF, C-N and silane is formed on the surface of the negative electrode.

Comparing the data of Examples 7-8 and Comparative Examples 4-5, it can be found that the electrolyte additives provided in the examples of this application not only can effectively improve the coulombic efficiency and cycle performance of the battery in carbonate electrolytes, but also in ether solvents. The effect is also obvious in the electrolyte.

Claims (17)

1. An electrolyte additive, characterized in that the chemical structural formula of the electrolyte additive is as shown in formula (I),

   

   In formula (I), the R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , and R ₆ are respectively selected from alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, haloalkenyl, Any one of alkenyloxy, halogenated alkenyloxy, aryl, halogenated aryl, aryloxy, and halogenated aryloxy; said R ₇ is a halogenated alkyl group, and said X is selected from O or S.
2. The electrolyte additive according to claim 1, wherein the number of carbon atoms of the alkyl group, halogenated alkyl group, alkoxy group, and halogenated alkoxy group is 1-20; The number of carbon atoms of the oxy group and the halogenated alkenyloxy group is 2-20; the number of carbon atoms of the aryl group, the halogenated aryl group, the aryloxy group, and the halogenated aryloxy group are 6-20.
3. The electrolyte additive according to claim 1 or 2, wherein the halogen in the halogenated alkyl group, halogenated alkoxy group, halogenated alkenyl group, halogenated alkenyloxy group, halogenated aryl group and halogenated aryloxy group Including fluorine, chlorine, bromine, and iodine, the halogenation is perhalogenated or partially halogenated.
4. The electrolyte additive according to any one of claims 1 to 3, wherein the R ₇ is a fluoroalkyl group having 1-20 carbon atoms.
5. An electrolyte for a secondary battery, comprising an electrolyte salt, a non-aqueous organic solvent, and an additive, the additive comprising the electrolyte additive according to any one of claims 1-4.
6. The secondary battery electrolyte according to claim 5, wherein the weight percentage of the electrolyte additive in the secondary battery electrolyte is 0.1%-10%.
7. The secondary battery electrolyte according to claim 5 or 6, wherein the electrolyte salt includes at least one of lithium salt, sodium salt, potassium salt, magnesium salt, zinc salt, and aluminum salt.
8. The secondary battery electrolyte according to any one of claims 5-7, wherein the electrolyte salt comprises MClO ₄ , MBF ₄ , MPF ₆ , MAsF ₆ , MPF ₂ O ₂ , MCF ₃ SO ₃ , MTDI , MB(C ₂ O ₄ ) ₂ , MBF ₂ C ₂ O ₄ , M[(CF ₃ SO ₂ ) ₂ N], M[(FSO ₂ ) ₂ N] and M[(C _m F _2m+1 SO ₂ ) One or more of (C _n F _2n+1 SO ₂ )N], wherein M is Li, Na or K, and m and n are natural numbers.
9. The secondary battery electrolyte according to claim 5, wherein the molar concentration of the electrolyte salt in the secondary battery electrolyte is 0.01 mol/L-8.0 mol/L.
10. The secondary battery electrolyte according to claim 5, wherein the non-aqueous organic solvent comprises one or more of carbonate-based solvents, ether-based solvents, and carboxylate-based solvents.
11. The secondary battery electrolyte according to claim 5, wherein the additives further include other additives, and the other additives include biphenyl, fluorobenzene, vinylene carbonate, trifluoromethyl ethylene carbonate, carbonic acid Vinyl ethylene, 1,3-propane sultone, 1,4-butane sultone, vinyl sulfate, vinyl sulfite, succinonitrile, adiponitrile, 1,2-bis(2- One or more of cyanoethoxy)ethane and 1,3,6-hexane trinitrile.
12. A secondary battery, characterized by 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 5-11.
13. The secondary battery according to claim 12, wherein the negative electrode comprises a carbon-based negative electrode, a silicon-based negative electrode, a tin-based negative electrode, a lithium negative electrode, a sodium negative electrode, a potassium negative electrode, a magnesium negative electrode, a zinc negative electrode, and an aluminum negative electrode. One or more.
14. The secondary battery according to claim 13, wherein the carbon-based negative electrode comprises one or more of graphite, hard carbon, soft carbon, and graphene; the silicon-based negative electrode comprises silicon, silicon carbon, One or more of silicon oxygen and silicon metal compound; the tin-based negative electrode includes one or more of tin, tin carbon, tin oxygen, and tin metal compound; the lithium negative electrode includes metal lithium or a lithium alloy.
15. The secondary battery according to claim 14, wherein the lithium alloy includes 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.
16. The secondary battery according to claim 13, wherein the secondary battery comprises a lithium secondary battery, a potassium secondary battery, a sodium secondary battery, a magnesium secondary battery, a zinc secondary battery, or an aluminum secondary battery .
17. A terminal, characterized in that it comprises a casing, and electronic components and batteries contained in the casing, the battery provides power to the electronic components, and the battery comprises the one described in any one of claims 12-16. The secondary battery mentioned.

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