CN115911560A

CN115911560A - Electrolyte, secondary battery and electric equipment

Info

Publication number: CN115911560A
Application number: CN202211700975.6A
Authority: CN
Inventors: 傅佳乐; 许灿; 刘思; 潘炳昕; 乔飞燕; 褚春波; 张耀
Original assignee: Sunwoda Electronic Co Ltd
Current assignee: Sunwoda Electric Vehicle Battery Co Ltd
Priority date: 2022-12-28
Filing date: 2022-12-28
Publication date: 2023-04-04

Abstract

The application discloses electrolyte, secondary battery and consumer. The electrolyte includes a non-aqueous organic solvent, a lithium salt, and a first additive. The first additive of the present application contains both isocyanate groups and siloxane bonds. The isocyanate group can remove trace water in the electrolyte and inhibit the generation of hydrofluoric acid, the continuous decomposition of the electrolyte is reduced, the damage of the hydrofluoric acid to the interface film and the corrosion of the hydrofluoric acid to the silicon-carbon negative electrode are reduced, the dissolution of transition metal ions is inhibited, the structural stability of the interface film and the cycling stability of the battery are improved, and the high-temperature gas production performance of the battery is reduced. The silicon-oxygen bond can form an effective network structure on the surface of the silicon-carbon cathode, and the flexibility of an interface film is enhanced, so that the volume expansion of the silicon-carbon cathode is inhibited, and the cycle stability is improved to a certain extent. Therefore, the electrolyte of the present application can improve the performance of the secondary battery.

Description

Electrolyte, secondary battery and electric equipment

Technical Field

The application relates to the technical field of batteries, in particular to electrolyte, a secondary battery and electric equipment.

Background

Currently, one of the power sources of the electric vehicle is a lithium ion battery. Part of the lithium ion battery adopts a silicon-carbon cathode, fluorine-containing electrolyte and the like. When the fluorine-containing electrolyte and the silicon-carbon negative electrode are initially contacted, an inorganic or organic composite solid interfacial film (SEI film) is formed on the surface of the silicon-carbon negative electrode, which is very important for the cycle stability of the lithium ion battery. However, the existing fluorine-containing electrolyte contains trace moisture, the trace moisture can enable the fluorine-containing electrolyte to generate Hydrogen Fluoride (HF), and the HF can reduce the structural stability of the SEI film, so that the unstable SEI film is locally and gradually thickened in the circulation process, the film forming quality is poor, the capacity of the lithium ion battery in the circulation process is continuously reduced, and the circulation stability of the lithium ion battery is poor. Moreover, HF can also cause corrosion of the anode and the cathode, dissolution of transition metal ions and continuous decomposition of electrolyte, thereby causing serious problems of high-temperature storage and gas production and the like.

Disclosure of Invention

The embodiment of the application provides an electrolyte, a secondary battery and electric equipment, and solves the problems of poor cycle stability and serious high-temperature storage gas generation of the secondary battery with silicon carbon as a negative electrode active material.

The embodiment of the application provides an electrolyte, it includes: a non-aqueous organic solvent, a lithium salt and a first additive.

In some embodiments, the first additive comprises a compound having the structure shown in formula I:

wherein R is ₁ 、R ₂ Each independently selected from fluorine atom (-F), chlorine atom (-Cl), bromine atom (-Br) or hydrogen atom (-H).

R ₃ Selected from alkylene groups having 3 to 9 carbon atoms, substituted or unsubstituted with a first substituent; first, aSubstituents include methyl, ethyl, cyano or halogen groups.

R ₄ 、R ₅ 、R ₆ Each independently selected from alkyl groups having 1 to 3 carbon atoms substituted or unsubstituted with a second substituent comprising a halogen group.

In some embodiments, the structural formula of the first additive includes any one or more of the compounds represented by the following structural formulas:

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in some embodiments, the mass percentage of the first additive may be 0.1wt% to 3.0wt% based on the total mass of the electrolyte.

In some embodiments, the electrolyte further comprises a negative film forming additive comprising one or more of fluoroethylene carbonate, sulfate-based compounds, or sulfite-based compounds.

Alternatively, the sulphate-based compound comprises one or more of ethylene sulphate, 1, 3-propanediol cyclic sulphate, dimethyl sulphate, methyl ethyl sulphate, dipropyl sulphate or diisopropyl sulphate.

The sulfite ester compound comprises one or two of ethylene sulfite or vinyl sulfite.

In some embodiments, the negative film forming additive comprises fluoroethylene carbonate and ethylene sulfate.

In some embodiments, the fluoroethylene carbonate is 5.0wt% to 18.0wt% and the ethylene sulfate is 0.2wt% to 3.0wt% based on the total mass of the electrolyte.

Based on the total mass of the electrolyte, the mass percent of the fluoroethylene carbonate is W ₁ Percent, the mass percent of the ethylene sulfate is W ₂ % of the total weight of W ₁ And W ₂ Satisfies the relationship of (1) ₁ ＝(1.67～36)×W ₂ 。

In some embodiments, the mass percent of the first additive is M, based on the total mass of the electrolyte ₁ Percent, the mass percent of the negative electrode film forming additive is M ₂ % of, then M ₁ And M ₂ Satisfy the relationship of 0.65. Ltoreq. M ₁ +0.1×M ₂ ≤5.1。

The mass percent of the first additive is M based on the total mass of the electrolyte ₁ Percent, the mass percent of the negative film forming additive is M ₂ Percent, mass percent of lithium salt is M ₃ % of, then M ₁ 、M ₂ And M ₃ Satisfies the relationship of M ₃ ＜M ₁ +1.8×M ₂ 。

In some embodiments, the non-aqueous organic solvent includes any two or more of Ethylene Carbonate (EC), propylene Carbonate (PC), butylene Carbonate (BC), dimethyl carbonate (DMC), ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), ethyl Acetate (EA), propyl Acetate (PA), methyl Propionate (MP), ethyl Propionate (EP), propyl Propionate (PP), methyl Butyrate (MB), ethyl Butyrate (EB), γ -butyrolactone (γ -GBL), sulfolane (TMS).

In some embodiments, the lithium salt comprises lithium hexafluorophosphate (LiPF) ₆ ) And lithium bis (trifluoromethylsulfonyl) imide (LiTFSI), wherein the mass percent of the lithium salt is 10-15 wt% based on the total mass of the electrolyte.

An embodiment of the present application provides a secondary battery, including: positive electrode sheet, separator, negative electrode sheet and electrolyte in any of the above embodiments.

Wherein the negative plate comprises a negative active material comprising SiO _x X is more than or equal to 1 and less than or equal to 2.

The mass percentage of the first additive in the electrolyte and the SiO in the cathode active material _x The mass percentage ratio of (0.01-0.2): 1.

an embodiment of the present application provides an electric device, which includes the secondary battery in the above embodiment, and the secondary battery is used as a power supply source of the electric device.

The electrolyte of the embodiment of the application has at least the following technical effects:

the electrolyte solution of the present application is added with a first additive that contains both isocyanate groups (NCO) and siloxane bonds (Si-O). The isocyanate group (NCO) can remove trace water in the electrolyte, so that the generation of Hydrogen Fluoride (HF) is inhibited, the continuous decomposition of the electrolyte is reduced, the damage of HF to an SEI film and the corrosion of HF to a silicon-carbon negative electrode are reduced, the dissolution of transition metal ions is inhibited, the structural stability of the SEI film and the cycling stability of the battery are improved, and the high-temperature gas production performance of the battery is improved. Silicon-oxygen bonds (Si-O) can form an effective network structure on the surface of the silicon-carbon negative electrode, and the flexibility of the SEI film is enhanced, so that the volume expansion of the silicon-carbon negative electrode is inhibited, and the cycling stability is improved to a certain extent. Therefore, the electrolyte of the present application can improve the performance of the secondary battery.

Detailed Description

The technical solutions of the present application will be described clearly and completely with reference to various embodiments of the present application, and it should be understood that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

The embodiment of the application provides an electrolyte, a secondary battery and electric equipment. The following are detailed below. It should be noted that the following description of the embodiments is not intended to limit the preferred order of the embodiments.

In the present specification, the numerical range indicated by the term "to" means a range including numerical values described before and after the term "to" as the minimum value and the maximum value, respectively.

In the present application, "substituted" means that a hydrogen atom in a substituent is substituted by a substituent. "substituted or unsubstituted" means that the hydrogen atoms in the defined group may or may not be fully or partially substituted.

The embodiment of the application provides an electrolyte for a lithium ion battery. The electrolyte includes: a non-aqueous organic solvent, a lithium salt, and a first additive.

Wherein the first additive comprises a compound having a structure represented by formula I:

wherein R is ₁ 、R ₂ Each independently selected from fluorine atom (-F), chlorine atom (-Cl), bromine atom (-Br) or hydrogen atom (-H). R ₁ 、R ₂ The group may be one having a high electronegativity, and is preferably a fluorine atom, for example. The fluorocarbon bond (C-F bond) is easily broken. When the C-F bond is broken, a LiF-rich film can be formed on the surface of the silicon-carbon cathode, and the LiF-rich film serving as one component of an SEI film can enhance the mechanical strength of the LiF-rich film. Chlorine atoms (-Cl) or bromine atoms (-Br) can also perform similar functions, but are less effective than fluorine atoms.

R ₃ Selected from alkylene groups having 3 to 9 carbon atoms, substituted or unsubstituted with a first substituent. The first substituent mentioned above includes a methyl group, an ethyl group, a cyano group or a halogen group (-F, -Cl or-Br). R ₃ Plays a role of linking a fluorocarbon bond (C-F bond) with a silicon-oxygen bond (Si-O). R is ₃ The number of carbon atoms in the radical must not be too high, and if it is too high (for example higher than 9 carbon atoms), the viscosity of the first additive increases and the reactivity decreases. Thus, R ₃ The number of carbon atoms of (b) is preferably in the range of 3 to 9. By 3 to 9 carbon atoms in this application is meant that the number of carbon atoms may be 3, 4, 5, 6, 7, 8 or 9.

R ₄ 、R ₅ 、R ₆ Each independently selected from alkyl groups having 1 to 3 carbon atoms substituted or unsubstituted with a second substituent comprising a halogen group (-F, -Cl, or-Br). Alkyl of 1 to 3 carbon atoms may include methyl, ethyl or propyl (n-propyl or isopropyl), i.e. the number of carbon atoms may be 1,2 or 3.Si-O bonds can form an effective network structure on the surface of a silicon-carbon negative electrode, enhance the flexibility of an SEI film and inhibit silicon bodiesVolume expansion. R ₄ 、R ₅ 、R ₆ Must not be too numerous otherwise affecting the reticulation behaviour of the Si-O bonds, and therefore R ₄ 、R ₅ 、R ₆ Preferably methyl (-CH) ₃ ) Or ethyl (-CH) ₂ CH ₃ )。

The first additive described above contains isocyanate groups (NCO), which can scavenge trace amounts of water in the electrolyte, thereby suppressing the generation of hydrofluoric acid (HF). The possible mechanism is as follows: fluoride (e.g., liPF) is often included in fluorine-containing electrolytes ₆ Etc.) which decompose to lewis acids (e.g., PF) upon encountering trace amounts of water ₅ Etc.). The lewis acid reacts with the negative film-forming additive (e.g., fluoroethylene carbonate or FEC, etc.), causing the negative film-forming additive to decompose and produce hydrofluoric acid (HF). Hydrofluoric acid (HF) attacks the positive electrode material and/or the negative electrode material, thereby destroying the positive electrode and negative electrode structure of the lithium ion battery, and in severe cases, may cause the transition metal element contained in the positive electrode to escape, thereby changing the components of the electrolyte. In addition, the negative electrode film-forming additive is decomposed, so that a stable SEI film cannot be formed on the surface of the negative electrode, and the corrosion of hydrofluoric acid on the negative electrode is increased. The isocyanate group (NCO) of the present invention can react with a trace amount of water and hydrofluoric acid in the electrolyte (specifically, as shown in the following reaction equations 1 and 2), and thus eliminates a trace amount of water and hydrofluoric acid in the electrolyte, thereby suppressing side reactions caused by a trace amount of water and hydrofluoric acid in the electrolyte, improving the stability of the electrolyte, suppressing the destruction of hydrofluoric acid to the interface film and the corrosion of hydrofluoric acid to the positive electrode and the negative electrode, and suppressing the elution of metal ions.

The following reaction equation 1 is a reaction of an isocyanate group (NCO) with a trace amount of water in the electrolyte.

The value of n varies depending on the polymerization conditions and may be, for example, 5 to 20.

The following reaction equation 2 is a reaction of isocyanate groups (NCO) with hydrofluoric acid in the electrolyte.

Wherein x group represents a portion other than an isocyanate group (NCO) in the structural formula of the first additive.

Alternatively, in some embodiments herein, the structural formula of the first additive includes any one or more of the compounds represented by the following structural formula. Note that, the following only shows the structural formula of the first additive, and does not limit the conformation thereof.

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Optionally, in some embodiments of the present application, the mass percentage of the first additive is 0.1wt% to 3.0wt%, the mass percentage of the negative electrode film-forming additive is 5.0wt% to 21.0wt%, the mass percentage of the lithium salt is 10.0wt% to 15.0wt%, and the mass percentage of the nonaqueous organic solvent is the rest, based on the total mass of the electrolyte. The sum of the mass percentages of the first additive, the negative electrode film-forming additive, the lithium salt and the nonaqueous organic solvent is 100wt%.

In some embodiments of the present application, the mass percentage of the first additive based on the total mass of the electrolyte solution may also be 0.2wt% to 2.8wt%, may also be 0.5wt% to 2.5wt%, may also be 0.8wt% to 2.0wt%, may further be 1.0wt% to 1.8wt%, and may further be 1.2wt% to 1.6wt%. If the mass percentage of the first additive is less than 0.1wt%, the electrolyte contains too few isocyanate groups (NCO), fluorocarbon bonds (C-F bonds) and silicon-oxygen bonds (Si-O), and cannot completely cover the surface of the negative electrode, or a passivation film formed on the surface of the negative electrode is too thin and is easy to crack, and cannot inhibit the expansion of the silicon-carbon negative electrode, so that the final performance of the lithium ion battery is poor. If the mass percentage of the first additive is greater than 3.0wt%, a passivation film possibly formed on the surface of the negative electrode is too thick, which increases the impedance and polarization of the lithium ion battery and also affects the performance of the lithium ion battery.

In some embodiments of the present application, the electrolyte further comprises a negative film-forming additive. The negative film forming additive comprises one or more of fluoroethylene carbonate (FEC), sulfate compounds or sulfite compounds. Alternatively, the sulphate-based compound comprises one or more of ethylene sulphate (DTD), 1, 3-propanediol cyclic sulphate, dimethyl sulphate, methyl ethyl sulphate, dipropyl sulphate or diisopropyl sulphate. Optionally, the sulfite-based compound includes one or both of vinyl sulfite (ES) or vinyl sulfite.

In some embodiments of the present application, if the negative electrode film-forming additive is a single-component additive, the mass percentage of each negative electrode film-forming additive added alone may be any one of 5.0 to 21.0wt%, or 6.0 to 20.0wt%, or 10.0 to 18.0wt%, or 11.0 to 16.5wt%, or further 12.5 to 15.0wt%, based on the total mass of the electrolyte.

In some embodiments of the present application, if the negative film-forming additive is a two-component additive, i.e., the negative film-forming additive contains two components, the first component is fluoroethylene carbonate (FEC), and the second component is any one of a sulfate compound or a sulfite compound. Therefore, the mass percentage of the first component (fluoroethylene carbonate and FEC) is 5.0-18.0 wt%, and the mass percentage of the second component (sulfate compound or sulfite compound) is 0.2-3.0 wt% based on the total mass of the electrolyte. The mass percentage of the first component is larger than that of the second component. The first component (fluoroethylene carbonate, FEC) can make an interfacial film (SEI film) formed on the surface of the silicon-carbon anode rich in LiF and polyethylene oxide (PEO) to ensure the cycle performance of the silicon-carbon anode, and the more the silicon content in the silicon-carbon anode, the more the first component is added. The second component (sulfate compound or sulfite compound) can contain an inorganic component in the formed interface film to improve the ionic conductivity, but if the amount added is too high, the strength and toughness of the interface film are affected, and the cycle performance of the battery is affected. The mass percentage content of the first component (fluoroethylene carbonate, FEC) can be 7.0-16.0 wt%, 10.0-15.0 wt% or 12.0-13.0 wt%. The second component (sulfate compound or sulfite compound) can also be 0.3-2.9 wt%, 0.5-2.8 wt%, 0.8-2.5 wt%, or 1.0-2.0 wt%. For a single-component or double-component negative electrode film-forming additive, if the mass percent of the negative electrode film-forming additive is less than 5.0wt%, a stable SEI film cannot be formed, so that the silicon-carbon negative electrode is easily corroded, and the cycle performance and the service life are reduced. If the negative electrode film-forming additive is present in an amount of more than 21.0wt%, the SEI film becomes too thick, affecting the conductivity and the ion and electron transport rates, and also affecting the performance of the secondary battery.

In some embodiments of the present application, the fluoroethylene carbonate is present in a mass percent W based on the total mass of the electrolyte ₁ Percent, the weight percentage of the ethylene sulfate is W ₂ % of the total weight of W ₁ And W ₂ Satisfies the relationship of (1) ₁ ＝(1.67～36)×W ₂ 。W ₁ And W ₂ Can also satisfy W ₁ ＝(6～10)×W ₂ 。

In some embodiments of the present application, the mass percentage of the first additive is M, based on the total mass of the electrolyte ₁ Percent, the mass percent of the negative film forming additive is M ₂ % of, then M ₁ And M ₂ Satisfy the relationship of 0.65. Ltoreq. M ₁ +0.1×M ₂ ≤5.1。

Illustratively, the negative electrode film forming additive contains fluoroethylene carbonate (FEC) in an amount of 10.0 to 15.0wt% based on the total mass of the electrolyte and ethylene sulfate (DTD) in an amount of 1.0 to 2.0wt% based on the total mass of the electrolyte. Further, the negative electrode film forming additive contained fluoroethylene carbonate (FEC) in an amount of 10.0wt% based on the total mass of the electrolyte and ethylene sulfate (DTD) in an amount of 1.0wt% based on the total mass of the electrolyte.

In some embodiments of the present application, the non-aqueous organic solvent includes any two or more of Ethylene Carbonate (EC), propylene Carbonate (PC), butylene Carbonate (BC), dimethyl carbonate (DMC), ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), ethyl Acetate (EA), propyl Acetate (PA), methyl Propionate (MP), ethyl Propionate (EP), propyl Propionate (PP), methyl Butyrate (MB), ethyl Butyrate (EB), γ -butyrolactone (γ -GBL), sulfolane (TMS).

In some embodiments of the present application, the lithium salt serves as an electrolyte, which includes lithium hexafluorophosphate (LiPF) ₆ ) Lithium tetrafluoroborate (LiBF) ₄ ) One or more of lithium bis (oxalato) borate (LiBOB), lithium difluoro (oxalato) borate (LiDFOB), lithium difluoro (oxalato) phosphate (LiDFOP), lithium bis (fluorosulfonyl) imide (LiFSI), and lithium bis (trifluoromethanesulfonyl) imide (LiTFSI).

The lithium salt may be a bi-component lithium salt including lithium bis (fluorosulfonyl) imide (LiFSI) and lithium hexafluorophosphate (LiPF) ₆ ) The mass percent of the lithium salt is 10-15 wt% based on the total mass of the electrolyte. For example, the bi-component electrolyte lithium salt contains 5.0-7.5 wt% of bis (fluorosulfonyl) imide Lithium (LiFSI) and lithium hexafluorophosphate (LiPF) ₆ ) Accounting for 5.0 to 7.5 weight percent of the total mass of the electrolyte and accounting for 10.0 to 15.0 weight percent of the total mass of the electrolyte. For example, the bi-component electrolyte lithium salt contains lithium bis (fluorosulfonyl) imide (LiFSI) in an amount of 7.5wt% based on the total mass of the electrolyte, and lithium hexafluorophosphate (LiPF) ₆ ) The content of the electrolyte accounts for 5.0wt% of the total mass of the electrolyte, and the content of the electrolyte and the electrolyte accounts for 12.5wt% of the total mass of the electrolyte. The application in the preferred embodiment uses the bi-component electrolyte lithium salt to have the following beneficial effects: lithium hexafluorophosphate (LiP)F ₆ ) The non-aqueous organic solvent in the embodiment of the application has moderate ion migration number, moderate dissociation constant, good oxidation resistance and good passivation capability of a negative electrode current collector (such as aluminum foil and the like). The lithium bis (fluorosulfonyl) imide (LiFSI) has high dissociation degree and thermal stability and is insensitive to water, and has the effects of improving the stability of the electrolyte and the transference number of lithium ions. The synergistic effect of the two can improve the stability, conductivity and other properties of the electrolyte of the lithium ion battery. The mass percentage of the lithium salt is preferably within a range of 10.0 to 15.0wt% based on the total mass of the electrolyte. Since if the total content of the lithium salt is too low, the conductivity of the electrolyte is affected. If the total content of the lithium salt is too high, the viscosity of the electrolyte may be increased, which may affect not only the conductivity of the electrolyte but also the cycle performance of the lithium ion battery.

The embodiment of the present application further provides a preparation method of the first additive, which comprises the following steps:

wherein R is ₇ R in formula I ₃ Two carbon atoms are omitted. Thus, R ₃ Selected from the group consisting of alkylene groups having 3 to 9 carbon atoms which are substituted or unsubstituted with the first substituent, R ₇ Selected from alkylene groups having 1 to 7 carbon atoms, substituted or unsubstituted with a first substituent.

Specifically, taking the fluorosilicone isocyanate as an example, the preparation method comprises the following steps:

in the reaction process, 2-difluoroglutaric acid is used as a raw material, lithium aluminum hydride is used as a catalyst, and the molar ratio of the product 1, 2-difluoroglutaric acid to the lithium aluminum hydride obtained by the reaction at room temperature is 1:1. then, the product 1 is dehydrated at 300 ℃ by taking alumina as a catalyst to generate a product 2. Then taking chloroplatinic acid as a catalyst, and carrying out hydrosilylation reaction on the product 2 and trimethoxy silane at the temperature of 60 ℃ to obtain a product 3. Then the product 3 and diphenylphosphoryl azide (DPPA) are catalyzed by diisopropylethylamine at the temperature of 13-17 ℃ to obtain a product 4, and the product 4 is an acyl azide product. Then carrying out Curtius rearrangement reaction at 90 ℃ to obtain the target product (fluorosilicone isocyanate).

The embodiment of the application also provides a preparation method of the electrolyte, which comprises the following steps: uniformly mixing a plurality of components for forming the non-aqueous organic solvent according to a ratio in an inert gas environment at room temperature to obtain the non-aqueous organic solvent; gradually adding lithium salt into a nonaqueous organic solvent and uniformly mixing, wherein the temperature of the electrolyte is required to be increased to be not more than 2 ℃ in the adding process, otherwise, the components of the electrolyte are damaged; and then adding a first additive, and uniformly mixing to obtain the electrolyte. Optionally, when the first additive is added, a negative electrode film forming additive may also be added.

An embodiment of the present application also provides a secondary battery, including: the anode plate, the isolating film, the cathode plate and the electrolyte. The isolating film is positioned between the positive plate and the negative plate. The positive plate, the isolating film and the negative plate can be laminated or wound to form a battery intermediate product, and the secondary battery is obtained after electrolyte is injected and post-treatment steps are carried out.

The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on one or both surfaces of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material. The positive electrode active material layer may be one or more layers. Each of the multiple layers of the positive electrode active material may contain the same or different positive electrode active material. The positive electrode active material includes any material capable of reversibly intercalating and deintercalating active ions such as lithium ions.

In some embodiments, the positive active material includes a material containing lithium and at least one transition metal. In some embodiments of the present application, the positive active material includes Li _a Ni _1-x-y Co _x M _y O ₂ The compound of (1), wherein: x is more than or equal to 0.95 and less than or equal to 1.2, x is more than or equal to 0 and less than or equal to 0.5, y is more than or equal to 0 and less than or equal to 0.5, and x + y is more than or equal to 0 and less than or equal to 1, M comprises Mn and/or Al. Optionally, a positive electrodeThe active material is LiNi _0.8 Mn _0.1 Co _0.1 O ₂ (NMC811)。

The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer formed on one or both surfaces of the negative electrode current collector, the negative electrode active material layer containing a negative electrode active material. The anode active material layer may be one layer or a plurality of layers, and each layer of the plurality of layers may contain the same or different anode active materials. The negative electrode active material includes any material capable of reversibly inserting and extracting active ions such as lithium ions. In some embodiments, the chargeable capacity of the negative electrode active material is greater than the discharge capacity of the positive electrode active material to prevent lithium metal from being unintentionally precipitated on the negative electrode sheet during charging. The negative electrode active material includes SiO _x X is more than or equal to 1 and less than or equal to 2. The mass percentage of the first additive in the electrolyte and the SiO in the cathode active material _x The mass percentage ratio of (0.01-0.2): 1, may be 0.02: 1. 0.05:1. 0.10: 1. 0.12: 1. 0.15: 1. 0.16: 1. 0.18:1 or any two of the above ranges. SiO in the negative electrode active material _x The content of (b) is 0.5 to 15% by mass, and may be any value or a range of any two values among 1%, 2%, 5%, 8%, 10%, 12% and 14%.

The embodiment of the application also provides electric equipment, which comprises the secondary battery, and the secondary battery is used as a power supply of the electric equipment. The electric equipment of the present application includes, but is not limited to, a backup power source, a motor, an electric automobile, an electric motorcycle, a power-assisted bicycle, a bicycle, an electric tool, a household large-sized battery, and the like.

The following description is given with reference to specific examples.

Example 1

The present example provides an electrolyte consisting of a lithium salt, a non-aqueous organic solvent, a negative electrode film-forming additive, and a first additive.

Wherein, the first additive is a substance shown in the following structural formula, namely, fluorosilicone isocyanate. The mass percent of the first additive is 0.5wt% based on the total mass of the electrolyte.

The lithium salt is lithium hexafluorophosphate (LiPF) ₆ ). The mass percent of the lithium salt is 12.5wt% based on the total mass of the electrolyte.

The negative film forming additive is fluoroethylene carbonate (FEC). The mass percent of the negative electrode film forming additive is 10wt% based on the total mass of the electrolyte.

The non-aqueous organic solvent is a mixture of Ethylene Carbonate (EC), propylene Carbonate (PC), ethyl Methyl Carbonate (EMC) and diethyl carbonate (DEC), and the mass ratio of EC/PC/EMC/DEC is 1. The balance of the addition amount of the non-aqueous organic solvent is that the sum of the mass percentages of the lithium salt, the non-aqueous organic solvent, the negative electrode film-forming additive and the first additive is 100wt%.

The preparation method of the electrolyte provided by the embodiment comprises the following steps:

at room temperature, in a glove box filled with argon (H) ₂ O<1ppm,O ₂ <1 ppm), mixing EC, PC, EMC and DEC according to a mass ratio of 1:2:5:2 is mixed uniformly in proportion by

The molecular sieve is used for removing water to obtain a mixed solvent. Lithium salt LiPF accounting for 12.5wt% of the total mass of the electrolyte ₆ Successively adding the lithium salt LiPF into the obtained mixed solvent, continuously stirring and cooling to ensure that the temperature of the electrolyte is not higher than 2 ℃, and continuously adding the lithium salt LiPF ₆ Finally, colorless transparent liquid is obtained. Then, fluoroethylene carbonate (FEC) in an amount of 10wt% based on the total mass of the electrolyte and fluorosilicone isocyanate (first additive) in an amount of 0.5wt% based on the total mass of the electrolyte were added, respectively, and the mixture was stirred uniformly to obtain the electrolyte of this example.

The present embodiment also provides a method for manufacturing a secondary battery, which includes the following steps:

and stacking the positive plate, the isolating film and the negative plate in sequence to enable the isolating film to be positioned between the positive plate and the negative plate, obtaining a naked battery cell through winding, hot-pressing reshaping and tab welding, placing the naked battery cell in an outer packaging aluminum-plastic film, and baking for 24 hours in an oven at 85 +/-10 ℃ to obtain a battery intermediate product. The electrolyte (15 g) prepared above was injected into the dried battery intermediate, and the secondary battery (i.e., lithium ion pouch battery) was obtained by standing, formation, and capacity grading.

The preparation method of the positive plate comprises the following steps: liNi serving as a positive electrode active material _0.8 Mn _0.1 Co _0.1 O ₂ The preparation method comprises the following steps of (NMC 811), acetylene black as a conductive agent (Super P) and polyvinylidene fluoride (PVDF) as a binder, uniformly mixing the components in a mass ratio of NMC811: super P: PVDF = 94.

The preparation method of the negative plate comprises the following steps: mixing SiO _x The preparation method comprises the following steps of uniformly mixing graphite, a conductive agent acetylene black (Super P) and a binder SBR according to a mass ratio of graphite to Super P to SBR = 9.4. The negative active material is made of SiO _x Is compounded with graphite and belongs to the field of composite Si-C material. Wherein SiO is _x The mass ratio to graphite was 9.4. In the negative electrode active material, siO _x Is 10% by mass. The mass percent of the first additive in the electrolyte is 0.5wt%, so the mass percent of the first additive in the electrolyte and the mass percent of SiO in the cathode active material _x The mass percentage of (A) is 0.05:1.

the component ratios of the respective examples and the respective comparative examples of the present application are shown in table 1, and the proportional relationship of the addition amounts is shown in table 2. The secondary batteries obtained in the respective examples and comparative examples of the present application were subjected to a battery performance test, and the test results are shown in table 3. The test method for the battery performance is as follows:

1. normal temperature initial DCR test: the pouch cell 1C thus obtained was charged to 4.25V at 25 ± 2 ℃, then discharged at 1C capacity for 30min, adjusted to 50% soc, then 5C constant current pulse discharged for 10s for recharging, and DCR = (voltage before pulse discharge-voltage after pulse discharge)/discharge current × 100% was calculated.

2. And (3) testing the normal-temperature cycle performance: and (3) carrying out charge-discharge cycle test on the obtained soft package battery at the temperature of 25 +/-2 ℃ at the charge-discharge rate of 1C/1C within the range of 2.8-4.25V, and recording the first cycle specific discharge capacity of the battery and the specific discharge capacity after 1000 cycles. Capacity retention rate at 1000 weeks = specific discharge capacity at 1000 weeks/specific discharge capacity at first week × 100%.

3. High-temperature storage performance: and (3) placing the obtained soft package battery at 60 +/-2 ℃, carrying out charge and discharge tests at the charge and discharge rate of 1C/1C within the range of 2.8-4.25V, recording the first cycle discharge specific capacity of the battery, then storing the battery for 120 days at the temperature of 60 +/-2 ℃, carrying out the charge and discharge tests again and recording the discharge specific capacity. High-temperature storage capacity retention = discharge specific capacity after 120 days/first-cycle discharge specific capacity × 100%.

4. High-temperature gas production test: and (3) charging the obtained soft package battery to 4.25V at the temperature of 25 +/-2 ℃ at a constant current of 1C rate, and then charging the soft package battery to a constant voltage of 4.25V until the current is lower than 0.05C, so that the soft package battery is in a full charge state of 4.25V. Testing the volume of the fully charged battery before storage by using a drainage method and recording the volume as V0; the fully charged cells were then placed in an oven at 60 + -2 deg.C, and after 50 days, the cells were removed and their stored volume was immediately tested and recorded as V1. Volume expansion rate = (V1-V0)/V0 × 100%.

Examples 2 to 5, comparative example 1

The above examples and comparative examples provide an electrolyte and a secondary battery. The above examples and comparative examples differ from example 1 in that: the amount of the first additive added was varied, and the rest was substantially the same as in example 1. The first additive was added in different amounts from example 1 to example 5. Comparative example 1 no first additive was added. The first additives of examples 2 to 4 were added in an amount of 0.1wt% to 3.0wt%. The first additive of example 5 was added in an amount of 5.0wt%, greater than 3.0wt%.

The experimental results of the above examples and comparative examples show that the addition of the first additive shown in formula I-1 to the silicon-carbon negative electrode system can improve the cycle retention rate of the secondary battery, improve the retention rate of high-temperature storage capacity, and reduce high-temperature gas generation; the main reasons are that isocyanate group NCO in the molecular structure of the first additive can remove trace water in the electrolyte, inhibit the generation of Hydrogen Fluoride (HF), improve the stability of the electrolyte, inhibit the damage of HF to an interface film and the corrosion of HF to a positive electrode and a negative electrode, and inhibit the dissolution of transition metal ions in a positive plate; si-O bonds can form an effective network structure on the surface of the silicon cathode, so that the flexibility of the SEI film is enhanced, and the volume expansion of silicon is inhibited; in addition, when the C-F bond is broken, a layer of SEI film rich in LiF can be generated on the surface of the silicon-carbon negative electrode, and the mechanical strength of the SEI film is enhanced.

In addition, as can be seen from the experimental results of the above examples and comparative examples, the addition of the first additive with a preferred content (0.1 wt% to 3.0 wt%) in the silicon-carbon negative electrode system can improve the cycle capacity retention rate of the secondary battery and the high-temperature storage capacity retention rate, and simultaneously reduce high-temperature gas generation; it can also be seen that, as the content of the first additive increases, the generated interfacial film (SEI film) becomes denser and denser, so that the initial DCR increases, the storage capacity retention rate becomes higher and higher, and the volume expansion rate becomes lower and lower, but the normal temperature cycle of the secondary battery tends to increase and decrease with the increase of the content of the first additive, mainly because the too dense interfacial film causes the polarization to increase, which affects the dynamic performance of the secondary battery. Therefore, the content of the first additive is not preferably as large as possible, and the mass percentage of the first additive is preferably in the range of 0.1 to 3.0wt% based on the total mass of the electrolyte.

Examples 6 to 10

Examples 6 to 10 provide an electrolyte and a secondary battery. The formulations of the electrolytes provided in examples 6 to 10 are shown in table 1. The negative electrode film forming additive (fluoroethylene carbonate) of examples 6 to 8 was added in an amount of 5.0wt% to 18.0wt%. Example 9 no negative electrode film forming additive was added. The negative electrode film-forming additive (fluoroethylene carbonate) in example 10 was added in an amount of 25.0wt% or more and 18.0wt% or more. According to experimental results, if the negative electrode film-forming additive is not added, an SEI film can be generated, but the generated SEI film is unstable and has a thin thickness, and if the silicon-carbon negative electrode undergoes volume expansion or shrinkage during cycling, the SEI film can be broken; if the addition amount of the negative electrode film-forming additive is too high, the formed SEI is too thick and too dense, which is not favorable for ion and electron transmission, and can reduce the conductivity of the secondary battery. Therefore, the amount of the negative electrode film forming additive (fluoroethylene carbonate) is preferably in the range of 5.0wt% to 18.0wt%.

Examples 11 to 14

The above embodiments provide an electrolyte and a secondary battery. The above embodiment differs from embodiment 1 in that: the components and contents of the negative electrode film forming additive were different, and the rest was the same as in example 3. The negative electrode film forming additives of examples 11 and 12 used ethylene sulfate (DTD) and fluoroethylene carbonate (FEC) in combination. In example 11, the fluoroethylene carbonate was W in mass percentage based on the total mass of the electrolyte ₁ (10 wt%), ethylene sulfate in weight percentage of W ₂ (1.0 wt.%) then W ₁ And W ₂ Satisfies the relationship of (A) W ₁ ＝(1.67～36)×W ₂ . In example 12, the fluoroethylene carbonate was W in mass percentage based on the total mass of the electrolyte ₁ (15 wt%), ethylene sulfate in weight percent W ₂ (2.0 wt.%) then W ₁ And W ₂ Satisfies the relationship of (1) ₁ ＝(1.67～36)×W ₂ . The negative electrode film forming additives of examples 13 and 14 were added with only ethylene sulfate (DTD) alone. From the experimental results of example 1 and examples 11 to 14, it is found that the effect of ethylene sulfate (DTD) alone is not as good as that of the combined addition of ethylene sulfate (DTD) and fluoroethylene carbonate (FEC). The combination of FEC and DTD can be preferentially decomposed on the surface of the silicon-carbon negative electrode to form a stable and tough SEI film, effectively improve the volume expansion of silicon in the repeated charge-discharge process of the secondary battery, prevent the decomposition of electrolyte, improve the reversible capacity performance and the cycle performance of the secondary battery, and enable the secondary battery containing the silicon-carbon negative electrode to have good high-temperature performance.

Example 15 to example 16

The above embodiments provide an electrolyte and a secondary battery. The above embodiment differs from embodiment 11 in that: the composition and content of the lithium salt were varied, and the rest was the same as in example 11. As can be seen from the experimental results, a two-component lithium salt (e.g., with the addition of LiPF) ₆ And LiFSI) are better. The reason is as follows: lithium hexafluorophosphate in the non-aqueous organic solvent in the embodiment has moderate ion migration number, moderate dissociation constant, good oxidation resistance and good aluminum foil passivation capability. The lithium bis (fluorosulfonyl) imide has high dissociation degree and thermal stability and is insensitive to water, and has the effects of improving the stability of an electrolyte and the transference number of lithium ions, but the lithium bis (fluorosulfonyl) imide is easy to corrode an aluminum foil. The synergistic effect of the two components combines the advantages of the two components, the stability and the conductivity of the electrolyte can be improved, the initial impedance of the secondary battery is reduced, and the cycle performance, the high-temperature performance and other performances are improved.

Comparative examples 2 to 3

The above comparative example provides an electrolyte and a secondary battery. Comparative example 2 does not add the first additive, but a mixture of the second additive and the third additive, as compared to example 11. Comparative example 3 does not add the first additive, but a mixture of the second and third additives, relative to example 15.

The structural formula of the second additive is shown as formula II:

the structural formula of the third additive is shown as formula III:

the molar ratio of the second additive to the third additive is 1:1, the total addition amount of the second additive and the third additive is 1wt% based on the total mass of the electrolyte.

From the experimental results, it was found that the first additive of the present example simultaneously contains three functional groups including isocyanate group (NCO), siloxane bond (Si-O) in siloxane group and fluorocarbon bond (C-F), and the initial DCR of the resulting secondary battery was smaller than that of the secondary batteries of comparative examples 2 and 3, and the dynamic performance was better. The possible reasons are as follows: the three groups of the comparative example are distributed on different molecules, phenyl is easily oxidized on the positive electrode to form a CEI film with larger resistance, the initial DCR is large, the kinetics is poor, and the cycle performance is influenced, so that the effects of the two comparative examples are not as good as those of the related examples of the application.

Example 17 to example 20

The above embodiments provide an electrolyte and a secondary battery. The above embodiment differs from embodiment 3 in that: the first additive was different in structural formula and the rest was the same as in example 3.

Wherein the first additive of example 3 has the formula:

the first additive of example 17 has the formula:

the first additive of example 18 has the formula:

the first additive of example 19 has the formula:

the additive of example 20 has the formula:

according to experimental results, compared with a comparative example, the addition of the first additives shown in formulas I-2 to I-7 in the silicon-carbon negative electrode system can improve the cycle retention rate of the secondary battery, improve the retention rate of high-temperature storage capacity and reduce high-temperature gas generation; the main reasons are that isocyanate group NCO in the molecular structure of the first additive can remove trace water in the electrolyte, inhibit the generation of Hydrogen Fluoride (HF), improve the stability of the electrolyte, inhibit the damage of HF to an interface film and the corrosion of HF to a positive electrode and a negative electrode, and inhibit the dissolution of transition metal ions in a positive plate; si-O bonds can form an effective network structure on the surface of the silicon cathode, so that the flexibility of the SEI film is enhanced, and the volume expansion of silicon is inhibited; in addition, when the C-F bond is broken, a layer of SEI film rich in LiF can be generated on the surface of the silicon-carbon negative electrode, and the mechanical strength of the SEI film is enhanced.

Examples 21 to 22

The above embodiments provide an electrolyte and a secondary battery. The above embodiment differs from embodiment 1 in that: the mass percentage of the first additive in the electrolyte and the SiO in the cathode active material _x The ratio of the mass percent of (A) is different from that of (B), and the rest is the same as that of example 1.

In example 21, the negative electrode active material was made of SiO _x Is compounded with graphite and belongs to a silicon-carbon composite material. Wherein SiO is _x The mass ratio to graphite was 9.4. In the negative electrode active material, siO _x Is 10 percent by mass. The mass percent of the first additive in the electrolyte is 0.1wt%, so the mass percent of the first additive in the electrolyte and SiO in the cathode active material _x The mass percentage of (A) is 0.01:1.

in example 22, the anode active material was made of SiO _x Is compounded with graphite and belongs to the field of composite Si-C material. Wherein SiO is _x Mass ratio to graphite 13. In the negative electrode active material, siO _x Is 15 percent. Of a first additive in the electrolyteThe mass percent is 3.0wt%, so the mass percent of the first additive in the electrolyte and the SiO in the cathode active material _x The mass percentage of (A) is 0.2:1.

in the above embodiment, as the content of silicon in the negative active material increases, the mass percentage of the first additive in the electrolyte increases, thereby contributing to the improvement of the relevant performance of the battery.

TABLE 1 formulation table of electrolyte solutions of respective examples and comparative examples

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TABLE 2 ingredient addition relationship table for each example and comparative example

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Table 3 table of performance of secondary batteries of respective examples and comparative examples

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The present application is described in detail above, and the principles and embodiments of the present application are described herein by using specific examples, which are only used to help understand the method and the core idea of the present application; meanwhile, for those skilled in the art, according to the idea of the present application, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present application.

Claims

1. An electrolyte, comprising: a nonaqueous organic solvent, a lithium salt and a first additive; the first additive includes a compound having a structure represented by formula I:

wherein R is ₁ 、R ₂ Each independently selected from fluorine atom (-F), chlorine atom (-Cl), bromine atom (-Br) or hydrogen atom (-H);

R ₃ selected from alkylene groups having 3 to 9 carbon atoms substituted or unsubstituted with a first substituent; the first substituent comprises a methyl, ethyl, cyano or halogen group;

R ₄ 、R ₅ 、R ₆ each independently selected from alkyl groups having 1 to 3 carbon atoms substituted or unsubstituted with a second substituent comprising a halo group.

2. The electrolyte of claim 1, wherein the first additive has a structural formula comprising any one or more of the compounds represented by the following structural formulas:

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3. the electrolyte of claim 1, wherein the first additive is present in an amount of 0.1 to 3.0 wt.%, based on the total mass of the electrolyte.

4. The electrolyte of claim 1, further comprising a negative electrode film forming additive comprising one or more of fluoroethylene carbonate, sulfate ester compounds, or sulfite ester compounds;

optionally, the sulfate-based compound comprises one or more of ethylene sulfate, 1, 3-propanediol cyclic sulfate, dimethyl sulfate, methyl ethyl sulfate, dipropyl sulfate, or diisopropyl sulfate; and/or the presence of a gas in the gas,

the sulfite compound comprises one or two of ethylene sulfite or vinyl sulfite.

5. The electrolyte of claim 4, wherein the negative film forming additive comprises fluoroethylene carbonate and ethylene sulfate.

6. The electrolyte of claim 5, wherein the fluoroethylene carbonate is 5.0 to 18.0wt% and the ethylene sulfate is 0.2 to 3.0wt% based on the total mass of the electrolyte; and/or the presence of a gas in the gas,

based on the total mass of the electrolyte, the mass percent of the fluoroethylene carbonate is W ₁ Percent, the weight percentage of the ethylene sulfate is W ₂ % of the total weight of W ₁ And W ₂ Satisfies the relationship of (1) ₁ ＝(1.67～36)×W ₂ 。

7. The electrolyte of claim 4, wherein the first additive is present in a mass percentage of M based on the total mass of the electrolyte ₁ % of the negative electrode film-forming additiveIs M ₂ % of, then M ₁ And M ₂ Satisfy the relationship of 0.65. Ltoreq. M ₁ +0.1×M ₂ Less than or equal to 5.1; and/or the presence of a gas in the atmosphere,

the mass percent of the first additive is M based on the total mass of the electrolyte ₁ Percent, the mass percent of the negative electrode film forming additive is M ₂ Percent, the mass percent of the lithium salt is M ₃ % of, then M ₁ 、M ₂ And M ₃ Satisfies the relationship of M ₃ ＜M ₁ +1.8×M ₂ 。

8. The electrolyte of claim 1, wherein the non-aqueous organic solvent comprises any two or more of Ethylene Carbonate (EC), propylene Carbonate (PC), butylene Carbonate (BC), dimethyl carbonate (DMC), ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), ethyl Acetate (EA), propyl Acetate (PA), methyl Propionate (MP), ethyl Propionate (EP), propyl Propionate (PP), methyl Butyrate (MB), ethyl Butyrate (EB), gamma-butyrolactone (gamma-GBL), sulfolane (TMS).

9. The electrolyte of claim 1, wherein the lithium salt comprises lithium hexafluorophosphate (LiPF) ₆ ) And lithium bis (trifluoromethylsulfonyl) imide (LiTFSI), wherein the mass percent of the lithium salt is 10-15 wt% of the total mass of the electrolyte.

10. A secondary battery, characterized by comprising: a positive electrode sheet, a separator, a negative electrode sheet and the electrolyte according to any one of claims 1 to 9; the negative electrode sheet comprises a negative electrode active material, and the negative electrode active material comprises SiO _x X is more than or equal to 1 and less than or equal to 2;

11. an electric device, characterized by comprising the secondary battery according to claim 10 as a power supply source for the electric device.