WO2023236007A1

WO2023236007A1 - Electrolytic solution, lithium secondary battery comprising same, battery module, battery pack, and electric apparatus

Info

Publication number: WO2023236007A1
Application number: PCT/CN2022/097115
Authority: WO
Inventors: 范玉磊; 葛销明; 陈宇杰; 王慢慢
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2022-06-06
Filing date: 2022-06-06
Publication date: 2023-12-14
Also published as: CN118104030A

Abstract

An electrolytic solution, comprising an electrolyte lithium salt, an organic solvent for dissolving the electrolyte lithium salt, and a diluent, wherein the diluent is different from the organic solvent for dissolving the electrolyte lithium salt, and the diluent is selected from C6-C17 alkane. By adding the diluent into the electrolytic solution, the viscosity of the electrolytic solution is reduced, the conductivity of the electrolytic solution and the transmission capability of lithium ions in the electrolytic solution are improved, and a stable SEI film mainly composed of inorganic components is obtained, thereby inhibiting precipitation of lithium, and improving the cycle capability and the capacity retention ratio of a lithium secondary battery. The present application further relates to a lithium secondary battery comprising the electrolytic solution, a battery module, a battery pack, and an electric apparatus.

Description

Electrolyte and lithium secondary batteries containing the same, battery modules, battery packs, and electrical devices

Technical field

The present application relates to the technical field of lithium batteries, and in particular to an electrolyte and a lithium secondary battery, a battery module, a battery pack, and an electrical device containing the electrolyte.

Background technique

In recent years, as the application range of lithium secondary batteries has become more and more extensive, lithium secondary batteries are widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric Automobiles, military equipment, aerospace and other fields. As lithium secondary batteries have achieved great development, higher requirements have been placed on their cycle performance and safety performance.

In lithium secondary batteries, there is an SEI film (solid electrolyte interphase, solid electrolyte interface film) on the surface of the negative electrode. During the storage or use of the battery, its own structure is destroyed, causing contact between the negative electrode active material and the electrolyte. As the area increases, side reactions intensify and lithium precipitation occurs, which reduces the cycle performance of the battery and brings adverse safety risks. Therefore, developing and designing an SEI film with high stability has great practical value for improving the cycle performance and safety performance of lithium secondary batteries.

Contents of the invention

This application was made in view of the above problems, and its purpose is to provide an electrolyte that can effectively improve the cycle performance and capacity retention rate of lithium secondary batteries, and to provide lithium secondary batteries and battery modules including the electrolyte of the application. , battery packs and electrical devices.

In order to achieve the above object, a first aspect of the present application provides an electrolyte solution, which contains an electrolyte lithium salt, an organic solvent that dissolves the electrolyte lithium salt, and a diluent, the diluent and the organic solvent that dissolves the electrolyte lithium salt. The solvents are different, and the diluent is selected from C ₆ -C ₁₇ alkanes, optionally C ₈ -C ₁₅ alkanes, and further optionally C ₈ -C ₁₃ alkanes.

The electrolyte containing diluent of the present application is beneficial to reducing the viscosity of the electrolyte, improving the conductivity of the electrolyte and the transmission capacity of lithium ions in the electrolyte, and obtaining a stable SEI film mainly composed of inorganic components, thereby Suppresses the precipitation of lithium and improves the cycle capability and capacity retention rate of lithium secondary batteries.

In any embodiment, the diluent in the electrolyte of the present application is n-octane, n-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane or n-octane. At least one of pentadecane; optionally, the diluent is at least one of n-octane, n-nonane, n-decane, n-undecane, n-dodecane, and n-tridecane. As a result, the type of diluent is further limited, so that the electrolyte can form a good solvation structure and obtain an SEI film with better stability.

In any embodiment, in the electrolyte of the present application, the ratio of the mass W1 of the organic solvent to the mass W2 of the diluent is (0.1~12):1, optionally (0.14~11.10):1, and optionally ( 0.14～1.23):1. As a result, the solvation structure is changed, an SEI film mainly composed of inorganic components is formed, and the stability of the SEI film is improved.

In any embodiment, in the electrolyte of the present application, the ratio of the mass W1 of the organic solvent: the mass W2 of the diluent: the mass W3 of the electrolyte lithium salt is (0.05~2.5): (0.15~5.55): 1, which can be Selected as (0.09～1.67): (0.30～5.41): 1.

By further limiting the relative mass ratio of the organic solvent, diluent and electrolyte lithium salt contained in the electrolyte, on the one hand, the electrolyte lithium salt can be fully ionized and improve the conductivity of the battery; on the other hand, it is conducive to the formation of stable inorganic components ( The SEI film based on lithium salt anions (such as fluoride ions) improves the cycle performance of the battery.

In any embodiment, in the electrolyte of the present application, the electrolyte lithium salt includes: at least one of lithium hexafluorophosphate, lithium bisfluorosulfonimide, lithium bistrifluoromethylsulfonimide, and lithium difluoroxalate borate. , optionally lithium bisfluorosulfonyl imide. By introducing an electrolyte lithium salt containing anions such as fluoride ions, it is beneficial for fluoride ions to participate in film formation, improve the stability of the SEI film, and improve the cycle performance of the battery.

In any embodiment, in the electrolyte of the present application, the molar concentration of lithium bisfluorosulfonimide in the electrolyte is 0.05-5mol/l, optionally 0.1-4mol/l, and optionally 0.5- 4 mol/l, further optionally 1-3 mol/l, based on the total volume of the electrolyte. This is beneficial to improving the viscosity and conductivity of the electrolyte and improving the cycle performance of the battery.

In any embodiment, in the electrolyte of the present application, the organic solvent includes at least one of carbonates or ethers; optionally, the organic solvent includes: fluorinated ethylene carbonate, ethylene carbonate , propylene carbonate, dimethyl carbonate, diethyl carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran or 1,3-dioxolane At least one of; further optionally ethylene glycol dimethyl ether. As a result, the electrolyte lithium salt is dissociated under the action of the organic solvent, and the fluidity of the electrolyte is improved at the same time.

In any embodiment, the electrolyte of the present application also includes additives, the content of which is 0.1-5%, optionally 0.5-3%, based on the total mass of the electrolyte. This will help improve the stability of the SEI film and further improve the cycle performance of the battery.

In any embodiment, the additives in the electrolyte of the present application include: lithium nitrate, lithium fluoride, lithium carbonate, lithium difluoroxalate, ethyl sulfate, 1,3-propanesultone, tris(trimethyl) At least one of tris(trimethylsilane)borate, trimethylsilane)phosphate, and trimethylmethoxysilane. This further improves the stability of the SEI film of the battery and improves the cycle performance of the battery.

A second aspect of the present application provides a lithium secondary battery, which includes the electrolyte of the first aspect of the present application.

A third aspect of the present application provides a battery module, which includes the lithium secondary battery of the second aspect of the present application.

A fourth aspect of the present application provides a battery pack, which includes the battery module of the third aspect of the present application.

A fifth aspect of the present application provides an electrical device, which includes at least one of the lithium secondary battery of the third aspect of the present application, the battery module of the fourth aspect of the present application, or the battery pack of the fifth aspect of the present application.

[beneficial effect]

The electrolyte of the present application changes the solvation structure of the electrolyte by containing an alkane diluent, which is conducive to the formation of a more stable SEI film, improves the transmission capacity of lithium ions and the conductivity of the electrolyte, thereby making the electrolyte containing the present application Liquid lithium secondary batteries have significantly improved cycle performance. Correspondingly, the battery pack, battery module and electrical device provided by the present application also have significantly improved cycle performance.

Description of the drawings

Figure 1 is a scanning electron microscope image of the surface morphology of the negative electrode of the lithium secondary battery of Examples 1-8 of the present application after the 100th cycle.

Figure 2 is a scanning electron microscope image of the surface morphology of the negative electrode of the lithium secondary battery of Comparative Example 1 after the 100th cycle.

Figure 3 is a Coulombic efficiency test of the lithium secondary battery of Comparative Example 1.

Figure 4 is a Coulombic efficiency test of the lithium secondary batteries in Examples 1-8 of the present application.

FIG. 5 is a schematic diagram of a lithium secondary battery according to an embodiment of the present application.

FIG. 6 is an exploded view of the lithium secondary battery according to the embodiment of the present application shown in FIG. 5 .

Figure 7 is a schematic diagram of a battery module according to an embodiment of the present application.

Figure 8 is a schematic diagram of a battery pack according to an embodiment of the present application.

FIG. 9 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 8 .

FIG. 10 is a schematic diagram of a power consumption device using a lithium secondary battery as a power source according to an embodiment of the present application.

Explanation of reference symbols:

1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 lithium secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly.

Detailed ways

Embodiments specifically disclosing the negative electrode sheet and its manufacturing method, the positive electrode sheet, the lithium secondary battery, the battery module, the battery pack, and the electrical device of the present application will be described in detail below with appropriate reference to the drawings. However, unnecessary detailed explanations may be omitted. For example, detailed descriptions of well-known matters may be omitted, or descriptions of substantially the same structure may be repeated. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

"Ranges" disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Furthermore, if the

minimum range values

1 and 2 are listed, and if the

maximum range values

3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-6. In this application, unless stated otherwise, the numerical range "a-b" represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in this article, and "0-5" is just an abbreviation of these numerical combinations. In addition, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

If there is no special description, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

If there is no special description, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

If there is no special instructions, all steps of the present application can be performed sequentially or randomly, and are preferably performed sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, mentioning that the method may also include step (c) means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c). , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b), etc.

If there is no special explanation, the words "include" and "include" mentioned in this application represent open expressions, which may also be closed expressions. For example, "comprising" and "comprising" may mean that other components not listed may also be included or included, or only the listed components may be included or included.

In this application, the term "or" is inclusive unless otherwise stated. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; Or both A and B are true (or exist).

Currently, electrolytes used in lithium secondary batteries mainly contain lithium salts and organic solvents. During the first charging process of a lithium secondary battery, lithium salt and organic solvent will react on the surface of the negative electrode to form a deposit with organic matter as the main component, that is, the SEI film. This film is crucial to the electrochemical performance of the lithium battery. . However, during the storage or use of lithium secondary batteries, the SEI film formed is unstable and will dissolve in the electrolyte, causing damage to the SEI film structure and greatly increasing the direct contact area between the negative electrode and the electrolyte. The occurrence of side reactions (mainly the deposition of by-products of electrolyte decomposition on the surface of the negative electrode and the production of gas from the electrolyte) ultimately deteriorates the cycle performance and safety performance of the battery.

In order to improve the cycle performance and safety performance of lithium secondary batteries, electrolytes with high lithium salt concentrations are now commonly used, but this will cause the viscosity of the electrolyte to be larger, reduce the lithium ion transmission capacity and the conductivity of the electrolyte, and make it difficult to industrialize.

The inventor developed an electrolyte system containing a diluent, which forms a solvation structure with a lower concentration of organic solvent components and a higher concentration of lithium salt anion components (such as fluoride ions), which can promote more lithium. Salt anions participate in film formation, forming a stable SEI film mainly composed of inorganic components, thus improving the cycle performance and safety performance of lithium secondary batteries.

[Electrolyte]

A first aspect of the application provides an electrolyte solution, which includes an electrolyte lithium salt, an organic solvent that dissolves the electrolyte lithium salt, and a diluent, the diluent is different from the organic solvent that dissolves the electrolyte lithium salt, and the The diluent is selected from C ₆ -C ₁₇ alkanes, optionally C ₈ -C ₁₅ alkanes, further optionally C ₈ -C ₁₃ alkanes.

In this application, the term "organic solvent that dissolves the electrolyte lithium salt" refers to dissociating the electrolyte lithium salt and meeting the conductivity requirements required by the battery.

In this application, the term "C ₆ -C ₁₇ alkanes" refers to straight-chain, branched-chain saturated alkanes having 6 to 17 carbon atoms. Examples include, but are not limited to, n-hexane and its isomers, n-heptane and its isomers, n-octane and its isomers, n-nonane and its isomers, n- Decane and its isomers, n-undecane and its isomers, n-dodecane and its isomers, n-tridecane and its isomers, n-tetradecane and its isomers, or n-pentadecane and its isomers. Among them, for example, n-hexane and its isomers refer to n-hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane alkyl. The above definition also applies to "C ₈ -C ₁₅ alkanes", which refers to straight-chain, branched-chain saturated alkanes having 8 to 15 carbon atoms. Similarly, the above definition also applies to "C ₈ -C ₁₃ alkanes", which refers to straight-chain, branched-chain saturated alkanes having 8 to 13 carbon atoms.

In this application, by adding an alkane or halogenated alkane diluent to the electrolyte, on the one hand, the organic solvent in the electrolyte can be diluted, the solvation structure is changed, and the degree of participation of the anions of the lithium salt in solvation is relatively increased. Therefore, even if Under low-concentration lithium salt conditions, a stable SEI film composed mainly of inorganic components can be formed, thereby solving the problem of lithium precipitation and improving the cycle performance of lithium secondary batteries; on the other hand, it reduces the electrolyte concentration The viscosity, lithium ion transport capacity and electrolyte conductivity are significantly improved.

In some embodiments, in the electrolyte, the diluent is n-octane, n-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane or n-decane. At least one of pentane; optionally, the diluent is at least one of n-octane, n-nonane, n-decane, n-undecane, n-dodecane, and n-tridecane.

By further defining the specific substance of the diluent, the composition of the electrolyte can be further optimized so that the electrolyte forms a good solvation structure. This structure promotes the electrolyte to form a more stable SEI film on the surface of the positive and negative electrodes, which not only can Avoiding or reducing electrolyte loss and inhibiting the growth of lithium dendrites can result in batteries with significantly improved cycle performance.

In some embodiments, the ratio of the mass W1 of the organic solvent contained in the electrolyte to the mass W2 of the diluent is (0.1~12):1, optionally (0.14~11.10):1, and optionally (0.14~11.10):1. 1.23): 1.

Optionally, the volume ratio of the organic solvent to the diluent is 9:1 to 1:9. Further optionally, the volume ratio of the organic solvent to the diluent is 1:1 to 9:1.

By further limiting the mass ratio of organic solvent to diluent in the electrolyte, the solvation structure is changed, an SEI film mainly composed of inorganic components is formed, and the stability of the SEI film is improved.

In some embodiments, the ratio of the mass W1 of the organic solvent contained in the electrolyte: the mass W2 of the diluent: the mass W3 of the electrolyte lithium salt is (0.05~2.5): (0.15~5.55): 1, optionally (0.09～1.67): (0.30～5.41): 1.

By further limiting the mass ratio of the organic solvent, diluent and electrolyte lithium salt in the electrolyte to keep the electrolyte lithium salt within an appropriate range, it is necessary to form a stable SEI film and maintain a low viscosity of the electrolyte, thereby Under the condition of good conductivity, the cycle performance and capacity retention rate of the battery are improved.

In some embodiments, in the electrolyte of the present application, the electrolyte lithium salt includes: lithium hexafluorophosphate (LiPF ₆ ), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethylsulfonyl imide (LiTFSI), At least one of lithium fluorosulfonyl borate (LiDFOB) can be selected from lithium bisfluorosulfonyl imide. By introducing an electrolyte lithium salt containing anions such as fluoride ions, it is beneficial for fluoride ions to participate in film formation, improve the stability of the SEI film, and improve the cycle performance of the battery.

In some embodiments, the molar concentration of lithium bisfluorosulfonimide in the electrolyte is 0.05-5mol/l, optionally 0.1-4mol/l, optionally 0.5-4mol/l, further optionally: 1-3 mol/l, based on the total volume of the electrolyte.

By further limiting the lithium ion content of the electrolyte lithium salt, it is beneficial to improve the viscosity and conductivity of the electrolyte and improve the cycle performance of the battery.

In some embodiments, in the electrolyte of the present application, the organic solvent includes at least one of carbonates or ethers; optionally, the organic solvent includes: fluorinated ethylene carbonate, ethylene carbonate Ester, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethylene glycol dimethyl ether, diglyme, tetraglyme, tetrahydrofuran or 1,3-dioxolane At least one of them; further optionally, ethylene glycol dimethyl ether. The function of these organic solvents is to dissociate lithium salts and meet the conductivity requirements of the battery.

In this application, the term "carbonate" refers to a compound in which the hydrogen atoms of the two hydroxyl groups (-OH) in the carbonic acid molecule are replaced by alkyl groups (R ₁ , R ₂ ), with the general formula R ₁ O-CO-OR ₂ , wherein R ₁ and R ₂ can be the same or different selected from C ₁ -C ₄ -alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl group, which is an open-chain carbonate, examples of which include but are not limited to dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc.; or R ₁ and R ₂ are connected to form an alkylene group such as C ₁ -C ₄ alkylene The group (-CH ₂ CH ₂ - or -CH ₂ CH ₂ CH ₂ ) is a cyclic carbonate, examples of which include but are not limited to ethylene carbonate, propylene carbonate, etc. Optionally, the carbonate may be substituted or unsubstituted, and the substituent may be selected from halogen, optionally a fluorine atom; examples thereof include, but are not limited to, fluorinated ethylene carbonate.

In this application, the term "ether" refers to the product of an alcohol in which the hydrogen in the hydroxyl group is replaced by a hydrocarbyl or alkylene group. Examples include, but are not limited to, polyglycol diethers, ethylene oxide, propylene oxide, tetrahydrofuran, dioxolane, etc.

In this application, the electrolyte contains an organic solvent with a mass fraction of 6.5% to 64%, a diluent with a mass fraction of 5.5% to 67%, and an electrolyte lithium salt with a mass fraction of 12% to 60%, based on the total electrolyte. Mass meter.

Further, in this application, the mass fraction of the organic solvent contained in the electrolyte is 6.5% to 37%, the mass fraction of the diluent is 20% to 55%, and the mass fraction of the electrolyte lithium salt is 33% to 36%, based on Total mass of electrolyte.

In some embodiments, the electrolyte further includes additives, the mass fraction of the additives is 0.1% to 5%, optionally 0.5% to 3%, further optionally, the mass fraction of the additives is 1%, based on the electrolyte Total mass meter. This further improves the stability of the SEI film, thereby avoiding or reducing electrolyte loss and inhibiting the growth of lithium dendrites, and the cycle performance and safety performance of the battery are significantly improved.

In some embodiments, additives in the electrolyte of the present application include lithium nitrate, lithium fluoride, lithium carbonate, lithium difluoroxalate, ethyl sulfate, 1,3-propanesultone, tris(trimethylsilane) ) at least one of phosphate, tris(trimethylsilane)borate, and trimethylmethoxysilane. It should be noted that each of the above substances is regarded as an additive when its mass fraction is no more than 5% (based on the total mass of the electrolyte). As a result, the stability of the SEI film is further improved and the cycle performance of the battery is improved.

It should be understood that the electrolyte of the present application can be used not only for lithium secondary batteries, but also for any other battery, battery module, battery pack or electrical device that needs to improve cycle performance.

The lithium secondary battery, battery module, battery pack and power consumption device of the present application are described below.

Lithium secondary battery

In one embodiment of the present application, a lithium secondary battery is provided, which includes the electrolyte of the present application.

Typically, lithium secondary batteries include positive electrode plates, negative electrode plates, electrolytes and separators. During the charging and discharging process of the battery, active ions are inserted and detached back and forth between the positive and negative electrodes. The electrolyte plays a role in conducting ions between the positive and negative electrodes. The isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows ions to pass through.

[Positive pole piece]

The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector.

As an example, the positive electrode current collector has two surfaces facing each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming metal materials (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the cathode active material may be a cathode active material known in the art for batteries. As an example, the cathode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials of batteries can also be used. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO ₂ ), lithium nickel oxides (such as LiNiO ₂ ), lithium manganese oxides (such as LiMnO ₂ , LiMn ₂ O ₄ ), lithium Nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (also referred to as NCM ₃₃₃ ), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (can also be abbreviated to NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (can also be abbreviated to NCM ₂₁₁ ), LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (can also be abbreviated to NCM ₆₂₂ ), LiNi At least one of _0.8 Co _0.1 Mn _0.1 O ₂ (also referred to as NCM ₈₁₁ ), lithium nickel cobalt aluminum oxide (such as LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) and its modified compounds. The olivine structure contains Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO ₄ (also referred to as LFP)), composites of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO ₄ ), lithium manganese phosphate and carbon. At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.

In some embodiments, the positive electrode film layer optionally further includes a binder. As examples, the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene tripolymer. At least one of a meta-copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer and a fluorine-containing acrylate resin.

In some embodiments, the positive electrode film layer optionally further includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components in a solvent (such as N -methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode piece can be obtained.

[Negative pole piece]

The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, where the negative electrode film layer includes a negative electrode active material.

As an example, the negative electrode current collector has two opposite surfaces in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material. The composite current collector can be formed by forming metal materials (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the negative active material may be a negative active material known in the art for batteries. As an example, the negative active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, and the like. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon carbon composites, silicon nitrogen composites and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as battery negative electrode active materials can also be used. Only one type of these negative electrode active materials may be used alone, or two or more types may be used in combination.

In some embodiments, the negative electrode film layer optionally further includes a binder. The binder can be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polysodium acrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), poly At least one of methacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

In some embodiments, the negative electrode film layer optionally further includes a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

In some embodiments, the negative electrode film layer optionally includes other auxiliaries, such as thickeners, such as sodium carboxymethyl cellulose (CMC-Na), and the like.

In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative active materials, conductive agents, binders and any other components in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode piece can be obtained.

In some embodiments, when the negative electrode sheet uses copper foil, the preparation process of the negative electrode sheet includes: punching a 5-13 μm thick copper foil to obtain the negative electrode sheet.

[Isolation film]

In some embodiments, the lithium secondary battery further includes a separator film. The isolation film is arranged between the positive electrode piece and the negative electrode piece to play an isolation role. There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.

In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.

[Outer packaging]

In some embodiments, the lithium secondary battery may include an outer package for packaging the positive electrode tab, the negative electrode tab, and the electrolyte. As an example, the positive electrode sheet, the negative electrode sheet and the separator film can be laminated or rolled to form a laminated structure cell or a wound structure cell, and the cell is packaged in an outer package; the electrolyte can be electrolyte, and the electrolyte is infiltrated in the battery core. The number of cells in a lithium secondary battery can be one or several, which can be adjusted according to needs.

In one embodiment, the present application provides an electrode assembly. In some embodiments, the positive electrode piece, the negative electrode piece and the separator film can be made into an electrode assembly through a winding process or a lamination process. The outer packaging can be used to package the above-mentioned electrode components and electrolytes.

In some embodiments, the outer packaging of the lithium secondary battery may be a soft bag, such as a pouch-type soft bag. The soft bag may be made of plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), and the like. In some embodiments, the outer packaging of the lithium secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.

Preparation method of lithium secondary battery

In one embodiment, the present application provides a method for preparing a lithium secondary battery, in which the electrolyte provided in the first aspect of the present application is used.

The preparation of the lithium secondary battery may also include the step of assembling the negative electrode sheet, the positive electrode sheet and the electrolyte of the present application to form a lithium secondary battery. In some embodiments, the positive electrode piece, the isolation film, and the negative electrode piece can be wound or laminated in order, so that the isolation film plays an isolation role between the positive electrode piece and the negative electrode piece, thereby obtaining a battery core. The battery core is placed in the outer package, electrolyte is injected and sealed to obtain a lithium secondary battery. The battery margin of lithium secondary batteries is 90-95%.

In some embodiments, the preparation of the lithium secondary battery may further include the step of preparing a positive electrode sheet. As an example, the positive electrode active material, conductive agent and binder can be dispersed in a solvent (such as N-methylpyrrolidone, NMP for short) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, After drying, cold pressing and other processes, the positive electrode piece is obtained.

In some embodiments, the preparation of a lithium secondary battery includes the step of preparing a negative electrode sheet according to the method described herein.

This application has no particular limitation on the shape of the lithium secondary battery, which can be cylindrical, square or other arbitrary shapes. For example, FIG. 5 shows a lithium secondary battery 5 with a square structure as an example.

In some embodiments, referring to FIG. 6 , the outer package may include a housing 51 and a cover 53 . The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity. The positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the containing cavity. The electrolyte soaks into the electrode assembly 52 . The number of electrode assemblies 52 contained in the lithium secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

Power-consuming device, battery module or battery pack

In one embodiment, the present application provides an electrical device, a battery module or a battery pack, wherein the electrical device, battery module or battery includes a lithium secondary battery as described in the present application or a battery as described in the present application. Lithium secondary battery prepared by the method.

In some embodiments, secondary batteries can be assembled into battery modules, and the number of lithium secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

FIG. 7 shows the battery module 4 as an example. Referring to FIG. 7 , in the battery module 4 , a plurality of lithium secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 . Of course, it can also be arranged in any other way. Furthermore, the plurality of lithium secondary batteries 5 can be fixed with fasteners.

Optionally, the battery module 4 may further include a housing having an accommodation space in which a plurality of lithium secondary batteries 5 are accommodated.

In some embodiments, the above-mentioned battery modules can also be assembled into a battery pack. The number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.

8 and 9 show the battery pack 1 as an example. Referring to FIGS. 8 and 9 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box 2 and a lower box 3 . The upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 . Multiple battery modules 4 can be arranged in the battery box in any manner.

In addition, the present application also provides an electrical device, which includes at least one of the lithium secondary battery, battery module, or battery pack provided by the present application. The lithium secondary battery, battery module, or battery pack can be used as a power source for an electric device, or as an energy storage unit of the electric device. Electric devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric Trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

As an electrical device, lithium secondary batteries, battery modules or battery packs can be selected according to its usage requirements.

Figure 10 is an electrical device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the lithium secondary battery of the electrical device, a battery pack or battery module can be used.

As another example, the device may be a mobile phone, a tablet, a laptop, etc. This device is usually required to be thin and light, and a lithium secondary battery can be used as a power source.

Example

Hereinafter, examples of the present application will be described. The embodiments described below are illustrative and are only used to explain the present application and are not to be construed as limitations of the present application. If specific techniques or conditions are not specified in the examples, the techniques or conditions described in literature in the field or product instructions will be followed. If the manufacturer of the reagents or instruments used is not indicated, they are all commercially available conventional products commonly used in this field. The content of each component in the examples of this application is based on the mass without crystal water unless otherwise stated.

The following descriptive terms: "The electrolyte of Example 1-1" refers to the electrolyte used in the preparation process of the lithium secondary battery of Example 1-1; "The positive electrode sheet of Example 1-1" refers to the electrolyte of Example 1-1. The positive electrode sheet used in the preparation process of the lithium secondary battery of 1-1; "the negative electrode sheet of Example 1-1" refers to the positive electrode sheet used in the preparation process of the lithium secondary battery of Example 1-1 ; "Separation film of Example 1-1" refers to the separation film used in the preparation process of the lithium secondary battery of Example 1-1; "Lithium secondary battery of Example 1-1" refers to the separation film used in the preparation process of the lithium secondary battery of Example 1-1 Lithium secondary battery prepared from -1 positive electrode, separator, negative electrode and electrolyte.

Example 1-1

[Preparation of electrolyte]

In an argon atmosphere glove box with water content (H ₂ O) <10ppm and oxygen content (O ₂ ) <10ppm, add 28.06g LiFSI and 57.79g (66.66ml) respectively into the beaker, density ρ = 0.867g/ml ) ethylene glycol dimethyl ether (DME), 5.21g (7.41ml, density ρ = 0.703g/ml) n-octane, stir thoroughly and dissolve to obtain the electrolyte used in this example.

The total volume of the prepared electrolyte solution is 100 ml, in which the molar concentration of the lithium salt is 1.5 mol/l, based on the total mass of the electrolyte solution.

【Positive pole piece】

Lithium iron phosphate is evenly coated on the positive electrode current collector aluminum foil with a thickness of 13 μm. The surface capacity of the electrode piece is 2.85mAh/cm ² , and the rolling and punching area is 49.5mm*42mm.

【Negative pole piece】

A copper foil with a thickness of 8 μm is used as the negative electrode piece, and the area is punched into a size of 51mm*43.5mm.

【Isolation film】

A polypropylene film with a thickness of 9 μm was used as the isolation film.

[Preparation of lithium secondary batteries]

In an argon atmosphere glove box with water content (H ₂ O) <10ppm and oxygen content (O ₂ ) <10ppm, stack the positive electrode piece, isolation film, and negative electrode piece in order, so that the isolation film is in the positive and negative positions. The negative electrode plates play a role in isolating each other, and then the bare battery core is obtained by winding; the bare battery core with a capacity of 0.59Ah is placed in the outer packaging foil, and 0.25g of the electrolyte prepared above is injected into the dried battery. In the process, lithium secondary batteries are obtained through processes such as vacuum packaging, standing, formation, and shaping.

Example 1-2

The preparation process of the lithium secondary battery is generally based on Example 1-1. The difference is that the preparation steps of the electrolyte are: argon gas with water content (H ₂ O) <10 ppm and oxygen content (O ₂ ) <10 ppm. In the atmosphere glove box, add 28.06g LiFSI, 56.09g (64.70ml) ethylene glycol dimethyl ether (DME), and 6.50g (9.24ml) n-octane respectively into the beaker. Stir thoroughly and dissolve to obtain the electrolytic solution used in this example. liquid.

Example 1-3

The preparation process of the lithium secondary battery is generally based on Example 1-1. The difference is that the preparation steps of the electrolyte are: argon gas with water content (H ₂ O) <10 ppm and oxygen content (O ₂ ) <10 ppm. In the atmosphere glove box, add 28.06g LiFSI, 53.04g (61.18ml) ethylene glycol dimethyl ether (DME), and 8.81g (12.53ml) n-octane respectively into the beaker. Stir thoroughly and dissolve to obtain the electrolytic solution used in this example. liquid.

Examples 1-4

The preparation process of the lithium secondary battery is generally based on Example 1-1. The difference is that the preparation steps of the electrolyte are: argon gas with water content (H ₂ O) <10 ppm and oxygen content (O ₂ ) <10 ppm. In the atmosphere glove box, add 28.06g LiFSI, 51.02g (58.84ml) ethylene glycol dimethyl ether (DME), and 10.34g (14.71ml) n-octane respectively into the beaker. Stir thoroughly and dissolve to obtain the electrolytic solution used in this example. liquid.

Examples 1-5

The preparation process of the lithium secondary battery is generally based on Example 1-1. The difference is that the preparation steps of the electrolyte are: argon gas with water content (H ₂ O) <10 ppm and oxygen content (O ₂ ) <10 ppm. In the atmosphere glove box, add 28.06g LiFSI, 47.66g (54.97ml) ethylene glycol dimethyl ether (DME), and 12.88g (18.32ml) n-octane respectively into the beaker. Stir thoroughly and dissolve to obtain the electrolytic solution used in this example. liquid.

Examples 1-6

The preparation process of the lithium secondary battery is generally based on Example 1-1. The difference is that the preparation steps of the electrolyte are: argon gas with water content (H ₂ O) <10 ppm and oxygen content (O ₂ ) <10 ppm. In the atmosphere glove box, add 28.06g LiFSI, 31.17g (35.95ml) ethylene glycol dimethyl ether (DME), and 25.27g (35.95ml) n-octane respectively into the beaker. Stir thoroughly and dissolve to obtain the electrolytic solution used in this example. liquid.

Example 1-7

The preparation process of the lithium secondary battery is generally based on Example 1-1. The difference is that the preparation steps of the electrolyte are: argon gas with water content (H ₂ O) <10 ppm and oxygen content (O ₂ ) <10 ppm. In the atmosphere glove box, add 28.06g LiFSI, 15.25g (17.59ml) ethylene glycol dimethyl ether (DME), and 37.09g (52.76ml) n-octane respectively into the beaker. Stir thoroughly and dissolve to obtain the electrolytic solution used in this example. liquid.

Example 1-8

The preparation process of the lithium secondary battery is generally based on Example 1-1. The difference is that the preparation steps of the electrolyte are: argon gas with water content (H ₂ O) <10 ppm and oxygen content (O ₂ ) <10 ppm. In the atmosphere glove box, add 28.06g LiFSI, 12.14g (14.00ml) ethylene glycol dimethyl ether (DME), and 39.38g (56.01ml) n-octane respectively into the beaker. Stir thoroughly and dissolve to obtain the electrolytic solution used in this example. liquid.

Example 1-9

The preparation process of the lithium secondary battery is generally based on Example 1-1. The difference is that the preparation steps of the electrolyte are: argon gas with water content (H ₂ O) <10 ppm and oxygen content (O ₂ ) <10 ppm. In the atmosphere glove box, add 28.06g LiFSI, 10.29g (11.87ml) ethylene glycol dimethyl ether (DME), and 40.74g (57.95ml) n-octane respectively into the beaker. Stir thoroughly and dissolve to obtain the electrolytic solution used in this example. liquid.

Examples 1-10

The preparation process of the lithium secondary battery is generally based on Example 1-1. The difference is that the preparation steps of the electrolyte are: argon gas with water content (H ₂ O) <10 ppm and oxygen content (O ₂ ) <10 ppm. In the atmosphere glove box, add 28.06g LiFSI, 7.53g (8.69ml) ethylene glycol dimethyl ether (DME), and 42.76g (60.82ml) n-octane respectively into the beaker. Stir thoroughly and dissolve to obtain the electrolytic solution used in this example. liquid.

Example 1-11

The preparation process of the lithium secondary battery is generally based on Example 1-1. The difference is that the preparation steps of the electrolyte are: argon gas with water content (H ₂ O) <10 ppm and oxygen content (O ₂ ) <10 ppm. In the atmosphere glove box, add 28.06g LiFSI, 6.01g (6.93ml) ethylene glycol dimethyl ether (DME), and 43.87g (62.40ml) n-octane respectively into the beaker. Stir thoroughly and dissolve to obtain the electrolytic solution used in this example. liquid.

In the prepared electrolytes of Examples 1-1 to 1-11, the total volume of the electrolyte is 100 ml, and the molar concentration of the electrolyte lithium salt is 1.5 mol/l, but the volume ratio of DME to n-octane Different, they are 9:1, 7:1, 5:1, 4:1, 3:1, 1:1, 1:3, 1:4, 1:5, 1:7, 1:9, as shown in the table 1 shown.

Comparative example 1

The preparation process of the lithium secondary battery is generally based on Example 1-1. The difference is that the preparation steps of the electrolyte are: in an argon atmosphere with a water content (H ₂ O) <10 ppm and an oxygen content (O ₂ ) <10 ppm. In the glove box, add 15.19g LiFP ₆ , 53.31g ethylene carbonate, and 50.3g ethyl methyl carbonate (50ml, density ρ = 1.006g/ml) respectively into the beaker. Stir thoroughly and dissolve to obtain the electrolytic solution used in Comparative Example 2. liquid.

The total volume of the prepared electrolyte is 100 ml, in which the molar concentration of the electrolyte lithium salt is 1.0 mol/l. Based on the total mass of the electrolyte, the organic solvents used are ethylene carbonate and ethyl methyl carbonate.

Example 2-1

The preparation process of the lithium secondary battery is generally referred to Examples 1-8. The difference is that the preparation steps of the electrolyte are: in an argon atmosphere with a water content (H ₂ O) <10 ppm and an oxygen content (O ₂ ) <10 ppm. In the glove box, add 18.71g LiFSI, 13.87g (16.00ml) ethylene glycol dimethyl ether (DME), and 45.00g (64.01ml) n-octane respectively into the beaker, stir thoroughly and dissolve to obtain the electrolyte for this example. .

Example 2-2

The preparation process of the lithium secondary battery is generally referred to Examples 1-8. The difference is that the preparation steps of the electrolyte are: in an argon atmosphere with a water content (H ₂ O) <10 ppm and an oxygen content (O ₂ ) <10 ppm. In the glove box, add 37.41g LiFSI, 11.09g (12.79ml) ethylene glycol dimethyl ether (DME), and 35.96g (51.16ml) n-octane respectively into the beaker. Stir thoroughly and dissolve to obtain the electrolyte for this example. .

Example 2-3

The preparation process of the lithium secondary battery is generally referred to Examples 1-8. The difference is that the preparation steps of the electrolyte are: in an argon atmosphere with a water content (H ₂ O) <10 ppm and an oxygen content (O ₂ ) <10 ppm. In the glove box, add 56.12g LiFSI, 8.98g (10.36ml) ethylene glycol dimethyl ether (DME), and 29.13g (41.44ml) n-octane respectively into the beaker. Stir thoroughly and dissolve to obtain the electrolyte for this example. .

Example 2-4

The preparation process of the lithium secondary battery is generally referred to Examples 1-8. The difference is that the preparation steps of the electrolyte are: in an argon atmosphere with a water content (H ₂ O) <10 ppm and an oxygen content (O ₂ ) <10 ppm. In the glove box, add 9.35g LiFSI, 15.61g (18.00ml) ethylene glycol dimethyl ether (DME), and 50.62g (72.00ml) n-octane respectively into the beaker, stir thoroughly and dissolve to obtain the electrolyte for this example. .

Example 2-5

The preparation process of the lithium secondary battery is generally referred to Examples 1-8. The difference is that the preparation steps of the electrolyte are: in an argon atmosphere with a water content (H ₂ O) <10 ppm and an oxygen content (O ₂ ) <10 ppm. In the glove box, add 74.83g LiFSI, 6.87g (7.93ml) ethylene glycol dimethyl ether (DME), and 22.30g (31.72ml) n-octane respectively into the beaker. Stir thoroughly and dissolve to obtain the electrolyte for this example. .

In Examples 2-1 to 2-5, the total volume of the electrolyte is 100 ml, the volume ratio of DME to n-octane is 1:4, and the molar concentrations of the electrolyte lithium salts are different, respectively 1, 2, 3, 0.5, 4mol/l, as shown in Table 2.

Comparative example 2

The preparation process of the lithium-ion battery is generally referred to that of Example 1-1. The difference is that the preparation steps of the electrolyte are in an argon atmosphere with a water content (H ₂ O) <10 ppm and an oxygen content (O ₂ ) <0.1 ppm. In the glove box, add 74.83g LiFSI and 29.17g ethylene glycol dimethyl ether (DME) into the beaker respectively, stir thoroughly and dissolve to obtain the electrolyte used in Comparative Example 2.

Example 3-1

The preparation process of the lithium secondary battery is generally referred to Examples 1-8. The difference is that the preparation steps of the electrolyte are: in an argon atmosphere with a water content (H ₂ O) <10 ppm and an oxygen content (O ₂ ) <10 ppm. In the glove box, add 28.06g LiFSI, 12.24g (14.11ml) ethylene glycol dimethyl ether (DME), and 40.64g (56.45ml, density ρ = 0.72g/ml) n-nonane into the beaker, stir thoroughly to dissolve Finally, the electrolyte used in this example was obtained.

Example 3-2

The preparation process of the lithium secondary battery is generally referred to Examples 1-8. The difference is that the preparation steps of the electrolyte are: in an argon atmosphere with a water content (H ₂ O) <10 ppm and an oxygen content (O ₂ ) <10 ppm. In the glove box, add 28.06g LiFSI, 12.30g (14.18ml) ethylene glycol dimethyl ether (DME), and 41.53g (56.74ml, density ρ = 0.732g/ml) n-decane into the beaker, stir thoroughly to dissolve Finally, the electrolyte used in this example was obtained.

Example 3-3

The preparation process of the lithium secondary battery is generally referred to Examples 1-8. The difference is that the preparation steps of the electrolyte are: in an argon atmosphere with a water content (H ₂ O) <10 ppm and an oxygen content (O ₂ ) <10 ppm. In the glove box, add 28.06g LiFSI, 12.34g (14.24ml) ethylene glycol dimethyl ether (DME), and 42.14g (56.94ml, density ρ = 0.74g/ml) n-undecane respectively into the beaker, and stir thoroughly After dissolving, the electrolyte used in this example was obtained.

Example 3-4

The preparation process of the lithium secondary battery is generally referred to Examples 1-8. The difference is that the preparation steps of the electrolyte are: in an argon atmosphere with a water content (H ₂ O) <10 ppm and an oxygen content (O ₂ ) <10 ppm. In the glove box, add 28.06g LiFSI, 12.39g (14.30ml) ethylene glycol dimethyl ether (DME), and 42.89g (57.18ml, density ρ = 0.75g/ml) n-dodecane into the beaker, and stir thoroughly. After dissolving, the electrolyte used in this example was obtained.

Example 3-5

The preparation process of the lithium secondary battery is generally referred to Examples 1-8. The difference is that the preparation steps of the electrolyte are: in an argon atmosphere with a water content (H ₂ O) <10 ppm and an oxygen content (O ₂ ) <10 ppm. In the glove box, add 28.06g LiFSI, 12.44g (14.35ml) ethylene glycol dimethyl ether (DME), and 43.63g (57.41ml, density ρ = 0.76g/ml) n-tridecane into the beaker, and stir thoroughly. After dissolving, the electrolyte used in this example was obtained.

Example 3-6

The preparation process of the lithium secondary battery is generally referred to Examples 1-8. The difference is that the preparation steps of the electrolyte are: in an argon atmosphere with a water content (H ₂ O) <10 ppm and an oxygen content (O ₂ ) <10 ppm. In the glove box, add 28.06g LiFSI, 12.44g (14.35ml) ethylene glycol dimethyl ether (DME), and 43.63g (57.41ml, density ρ = 0.76g/ml) n-tetradecane into the beaker, and stir thoroughly. After dissolving, the electrolyte used in this example was obtained.

Example 3-7

The preparation process of the lithium secondary battery is generally referred to Examples 1-8. The difference is that the preparation steps of the electrolyte are: in an argon atmosphere with a water content (H ₂ O) <10 ppm and an oxygen content (O ₂ ) <10 ppm. In the glove box, add 28.06g LiFSI, 12.49g (14.41ml) ethylene glycol dimethyl ether (DME), and 44.39g (57.64ml, density ρ = 0.77g/ml) n-pentadecane into the beaker, and stir thoroughly. After dissolving, the electrolyte used in this example was obtained.

In Examples 3-1 to 3-7, the total volume of the electrolyte is 100 ml, the volume ratio of DME to n-octane is 1:4, and the molar concentration of the electrolyte lithium salt is 1.5 mol/l, but the dilution types are different. as shown in Table 3.

Example 4-1

The preparation process of the lithium secondary battery is generally referred to Examples 1-8. The difference is that the preparation steps of the electrolyte are: argon gas with water content (H ₂ O) <10 ppm and oxygen content (O ₂ ) <10 ppm. In the atmosphere glove box, add 28.06g LiFSI, 12.14g (14.00ml) ethylene glycol dimethyl ether (DME), 39.38g (56.01ml) n-octane, and 0.796g lithium nitrate respectively into the beaker, stir thoroughly and dissolve to obtain This embodiment uses electrolyte.

Examples 4-2 to 4-9

The preparation process of the lithium secondary battery is generally based on Example 4-1. The difference is that in the preparation step of the electrolyte, the types of additives are changed, as shown in Table 4.

In Examples 4-1 to 4-9, the total volume of the electrolyte is 100 ml, the volume ratio of DME to n-octane is 1:4, the molar concentration of the electrolyte lithium salt is 1.5 mol/l, and the mass fraction of the additive 1%, based on the total mass of the electrolyte. However, the types of additives are different, as shown in Table 4.

Comparative example 3

The preparation process of the lithium secondary battery is generally based on Example 1-1. The difference is that the preparation steps of the electrolyte are: in an argon atmosphere with a water content (H ₂ O) <10 ppm and an oxygen content (O ₂ ) <10 ppm. In the glove box, add 15.19g LiFP ₆ , 53.31g ethylene carbonate, 50.3g ethyl methyl carbonate (50ml, density ρ = 1.006g/ml), and 1.19g lithium nitrate respectively into the beaker. Stir thoroughly and dissolve to obtain the solution. The electrolyte used in proportion 3.

Example 5-1

The preparation process of the lithium secondary battery is generally referred to Examples 1-8. The difference is that the preparation of the negative electrode sheet is as follows:

Mix artificial graphite, conductive agent carbon black, and binder acrylate according to a mass ratio of 92:2:6, add deionized water, and obtain a negative electrode slurry under the action of a vacuum mixer; mix the negative electrode slurry with 0.18g (dry weight) )/1540.25mm ² is evenly coated on the negative electrode current collector copper foil with a thickness of 8 μm; the copper foil is dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then cold pressed and cut to obtain the negative electrode piece.

Examples 5-2 to 5-3

The preparation process of the lithium secondary battery is generally based on Example 5-1, with the following differences:

The preparation steps of the electrolyte of Example 5-2 are the same as those of Example 1-1, wherein the volume ratio of DME to n-octane is 9:1;

The preparation steps of the electrolyte of Example 5-3 are the same as those of Example 1-11, wherein the volume ratio of DME to n-octane is 1:9.

Examples 5-4 to 5-6

The preparation steps of the electrolyte of Embodiment 5-4 are the same as those of Embodiment 3-2, wherein the diluent is n-decane;

The preparation steps of the electrolyte of Embodiment 5-5 are the same as those of Embodiment 3-4, wherein the diluent is n-dodecane;

The preparation steps of the electrolyte of Example 5-6 are the same as those of Example 3-7, wherein the diluent is n-pentadecane.

Comparative example 4

The preparation process of the lithium secondary battery is generally based on Example 5-1. The difference is that the preparation steps of the electrolyte are: in an argon atmosphere with a water content (H ₂ O) <10 ppm and an oxygen content (O ₂ ) <10 ppm. In the glove box, add 15.19g LiFP ₆ , 53.31g ethylene carbonate, and 50.3g ethyl methyl carbonate (50ml, density ρ = 1.006g/ml) respectively into the beaker, stir thoroughly and dissolve to obtain the electrolytic solution used in Comparative Example 4. liquid.

The total volume of the prepared electrolyte is 100 ml, the molar concentration of the electrolyte lithium salt is 1.0 mol/l, and the organic solvents used are ethylene carbonate and ethyl methyl carbonate.

The relevant process parameters and performance data of Examples 5-1 to 5-6 and Comparative Example 6 are shown in Table 5.

【Battery performance test】

1. Surface observation of lithium metal negative electrode piece

After the lithium secondary batteries of the above examples and comparative examples were cycled for 100 cycles, the lithium secondary batteries were disassembled and the surface morphology of the metallic lithium negative electrode plate was observed with a metallographic optical microscope (Axio Observer Z1M) magnified 1000 times. Observe whether lithium dendrites are formed.

2. First time Coulomb efficiency and capacity retention rate

The lithium secondary batteries of the above embodiments and comparative examples were charged to 3.7V with a constant current and voltage of 0.285mA/ ^cm2 , left to stand for 10 minutes, and then discharged to 2.5V with a constant current of 1mA/ ^cm2 to obtain The Coulomb efficiency of the first cycle is the first Coulomb efficiency. Charge and discharge are repeated in this way to obtain the Coulombic efficiency of the 100th cycle.

The capacity retention rate is the ratio of the discharge capacity at a specified number of cycles to the first discharge capacity.

The above-mentioned embodiments and comparative examples were tested respectively according to the above-mentioned process. Please refer to Tables 1 to 5 for relevant process parameters and battery performance test result values. In Tables 1 to 5, V1 represents the volume of the organic solvent; W1 represents the mass of the organic solvent; V2 represents the volume of the diluent; W2 represents the mass of the diluent; W3 represents the mass of the electrolyte lithium salt; The volume ratio of the solvent (V1:V2); A represents the mass ratio of the organic solvent to the diluent in the electrolyte (W1:W2); B represents the mass ratio of the organic solvent, diluent, and electrolyte lithium salt in the electrolyte (W1:W2 :W3).

The secondary lithium batteries corresponding to the Examples in Tables 1 to 4 and Comparative Examples 1-3 are lithium metal batteries, and the secondary batteries corresponding to the Examples and Comparative Example 4 in Table 5 are lithium ion batteries.

According to Table 1, it can be seen that the first Coulombic efficiency and capacity retention rate of the lithium metal batteries corresponding to Examples 1-1 to 1-11 are significantly higher than those of Comparative Example 1. From Example 1-1 to Example 1-11, when the molar concentration of the electrolyte lithium salt in the electrolyte is a constant value, the volume ratio X of the organic solvent to the diluent is in the range of 9:1 to 1:9, and the lithium metal battery The first cycle efficiency is higher than 83%, and the capacity retention rate is higher than 30%. Furthermore, when

According to Table 2, it can be seen that in Examples 1-8, 2-1 to 2-8, when the volume ratio X of the organic solvent and the diluent is a constant value, when the molar concentration of the electrolyte lithium salt in the electrolyte is From 0.5 to 4mol/l, the first cycle efficiency of lithium metal batteries is higher than 93%, and the capacity retention rate is higher than 55%. Furthermore, when the molar concentration of the electrolyte lithium salt in the electrolyte is 1 to 3 mol/l, the first cycle efficiency and capacity retention rate of the lithium metal battery are further improved.

Embodiment 2-5 of the present invention in Table 2 has higher first Coulombic efficiency and capacity retention rate than Comparative Example 1 in Table 1. Embodiment 2-1 of the present invention in Table 2 has higher first-time Coulomb efficiency and capacity retention rate than Comparative Example 2 in Table 2. Higher first coulombic efficiency, and significantly increased capacity retention. This shows that under the condition that the electrolyte solution contains the same molar concentration of electrolyte lithium salt, compared with the electrolyte solution that does not contain a diluent (Comparative Examples 1 and 2), when the electrolyte solution of the present invention contains a diluent, the performance of the lithium metal battery is improved. Both first-time Coulombic efficiency and capacity retention are significantly improved.

According to Table 3, when the volume ratio X of the organic solvent to the diluent in the electrolyte, the molar concentration of the electrolyte lithium salt are constant, and the diluent is a C ₈ -C ₁₅ alkane, the first cycle efficiency of the lithium metal battery is Higher than 92%, the capacity retention rates are all above 50%. Furthermore, when the diluent is a C ₈ -C ₁₃ alkane, the first cycle efficiency and capacity retention rate of the lithium metal battery are further improved.

According to Table 4, in the electrolyte, when the volume ratio of organic solvent to diluent The combination of additives is helpful to further improve the cycle performance of the battery.

According to Table 5, it can be seen that the capacity retention rates of the lithium ion batteries corresponding to Examples 5-1 to 5-6 are higher than those of Comparative Example 4.

The surface morphology of the lithium metal negative electrode in the lithium secondary battery of Examples 1-8 of the present application is shown in Figure 1, and the surface morphology of the lithium metal negative electrode in the lithium secondary battery of Comparative Example 1 is shown in Figure 2. It can be seen that the lithium dendrite growth of the lithium secondary battery according to the embodiment of the present application is suppressed.

The cycle Coulombic efficiency test results of the lithium secondary battery of Comparative Example 1 are shown in Figure 3, and the Coulombic efficiency test results of the lithium secondary batteries of Examples 1-8 of the present application are shown in Figure 4. It can be seen that the cycle performance of the lithium secondary battery with an electrolyte containing a diluent in the present application is significantly improved.

It should be noted that the present application is not limited to the above-described embodiment. The above-mentioned embodiments are only examples. Within the scope of the technical solution of the present application, embodiments that have substantially the same structure as the technical idea and exert the same functions and effects are included in the technical scope of the present application. In addition, within the scope that does not deviate from the gist of the present application, various modifications to the embodiments that can be thought of by those skilled in the art, and other forms constructed by combining some of the constituent elements in the embodiments are also included in the scope of the present application. .

Claims

An electrolyte solution, characterized in that it contains an electrolyte lithium salt, a diluent and an organic solvent that dissolves the electrolyte lithium salt. The diluent is different from the organic solvent that dissolves the electrolyte lithium salt. The diluent is selected from C 6 -C 17 alkane, optionally C 8 -C 15 alkane, further optionally C 8 -C 13 alkane.
The electrolyte according to claim 1, characterized in that the diluent is n-octane, n-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane Or at least one of n-pentadecane; optionally, the diluent is at least one of n-octane, n-nonane, n-decane, n-undecane, n-dodecane, and n-tridecane. kind.
The electrolyte according to claim 1 or 2, characterized in that the ratio of the mass W1 of the organic solvent to the mass W2 of the diluent is (0.1~12):1, optionally (0.14~11.10): 1, and optional (0.14~1.23): 1.
The electrolyte solution according to claim 1 or 2, characterized in that the ratio of the mass W1 of the organic solvent: the mass W2 of the diluent: the mass W3 of the electrolyte lithium salt is (0.05~2.5): ( 0.15～5.55): 1, optional (0.09～1.67): (0.30～5.41): 1.
The electrolyte solution according to any one of claims 1 to 4, characterized in that the electrolyte lithium salt includes: lithium hexafluorophosphate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, lithium difluoride At least one kind of lithium oxalate borate can be selected from lithium bisfluorosulfonyl imide.
The electrolyte according to claim 5, characterized in that the molar concentration of the lithium bisfluorosulfonimide in the electrolyte is 0.05-5mol/l, optionally 0.1-4mol/l, and optionally 0.5-4 mol/l, further optionally 1-3 mol/l, based on the total volume of the electrolyte.
The electrolyte according to any one of claims 1 to 6, wherein the organic solvent includes at least one of carbonates or ethers; optionally, the organic solvent includes fluorinated carbonic acid Ethylene, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran or 1 , at least one of 3-dioxolane; further optionally ethylene glycol dimethyl ether.
The electrolyte solution according to any one of claims 1-7, characterized in that the electrolyte solution further includes additives, and the mass fraction of the additives is 0.1-5%, optionally 0.5-3%, based on the Total mass of electrolyte.
The electrolyte according to claim 8, wherein the additives include lithium nitrate, lithium fluoride, lithium carbonate, lithium difluoroxalate, ethyl sulfate, 1,3-propanesultone, tris( At least one of trimethylsilane)phosphate, tris(trimethylsilane)borate, and trimethylmethoxysilane.
A lithium secondary battery, characterized by including the electrolyte solution according to any one of claims 1 to 9.
A battery module comprising the lithium secondary battery according to claim 10.
A battery pack, characterized by comprising the battery module according to claim 11.
An electrical device, characterized in that it includes at least one selected from the group consisting of the lithium secondary battery of claim 10, the battery module of claim 11, or the battery pack of claim 12.