Electrolyte solution, lithium-ion battery and formation method therefor, and electric apparatus

Abstract

Embodiments of the present application disclose an electrolyte solution, a lithium-ion battery and a formation method therefor, and an electric apparatus. The electrolyte solution comprises a film-forming additive and metal ions. The reduction potential φ(Mn+ / M) of the metal ions satisfies φ(Mn+ / M)+(RTlnC) / F<φX, where Mn+ represents the metal ions, n represents the valence of the metal ions, R represents the ideal gas constant, T represents the temperature, C represents the molar concentration of the metal ions in the electrolyte solution, F represents the Faraday constant, and φX represents the reduction decomposition potential of the film-forming additive. When the electrolyte solution is used for a lithium-ion battery, the phenomenon of non-uniform current density of an electrode sheet during electrode sheet cycling can be effectively improved and lithium precipitation can be inhibited, thereby helping to increase the capacity retention rate and the cycling performance of the lithium-ion battery.

Description

Electrolyte, lithium-ion battery, formation method thereof, and power-consuming device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent document claims priority to and the benefit of Chinese patent application No. 202310797777.4, filed on June 30, 2023, entitled "Electrolyte, Lithium-ion Battery, Formation Method Thereof, and Electrical Device." The entire contents of the aforementioned patent application are incorporated by reference into this patent document. Technical Field

[0003] The present application relates to the field of batteries, and more specifically, to an electrolyte, a lithium-ion battery, a formation method thereof, and an electrical device. Background Art

[0004] In recent years, lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields, and have thus achieved great development.

[0005] Due to limitations in production processes and operating environments, the internal physical and chemical properties of lithium-ion batteries, as well as the current during charging, are non-uniform. This results in non-uniform current flow in different regions of the positive and negative electrodes during the charge and discharge process. In areas where the local current is excessive, the potential of the negative electrode is too low, which can easily damage the structure of the negative electrode active material and lead to lithium deposition, resulting in a decrease in the reversible capacity and cycle life of the lithium-ion battery. Therefore, how to improve the non-uniformity of the electrode current density during cycling is a technical problem that needs to be solved urgently.

[0006] Summary of the Invention

[0007] This application is made in response to the above-mentioned technical problems and aims to provide an electrolyte, a lithium-ion battery, a formation method thereof, and an electrical device. The electrolyte comprises a film-forming additive and metal ions, which can effectively improve the uneven current density of the electrode during cycling and inhibit lithium deposition, thereby helping to improve the capacity retention and cycling performance of the lithium-ion battery.

[0008] In a first aspect, an electrolyte is provided, comprising a film-forming additive and metal ions; wherein the reduction potential of the metal ions is satisfy: Among them, M n+ represents the metal ion, n represents the valence of the metal ion, R represents the ideal gas constant, T represents the temperature, C represents the molar concentration of the metal ion in the electrolyte, F represents the Faraday constant, represents the reductive decomposition potential of the film-forming additive.

[0009] It should be understood that the reduction potential of the metal ion and the reduction decomposition potential of the film-forming additive are the reduction potentials of the two relative to the same standard electrode.

[0010] In the embodiments of the present application, the electrolyte includes a film-forming additive and metal ions. The film-forming additive helps form a dense SEI film on the negative electrode surface. Since the metal ions have a reduction potential lower than the reduction decomposition potential of the film-forming additive, they are not reduced or are reduced only to a very small extent during the process of the film-forming additive decomposing to form the SEI film, resulting in the presence of free metal ions in the electrolyte of the lithium-ion battery after formation. As a result, the metal ions can improve the problem of uneven current density of the negative electrode sheet during the cycle of the lithium-ion battery, thereby helping to improve the capacity retention rate and cycle performance of the lithium-ion battery.

[0011] In a possible implementation, a mass ratio m1 / m2 of the film-forming additive to the electrolyte satisfies: 0.1%≤m1 / m2≤10%.

[0012] In the embodiments of the present application, controlling the amount of the film-forming additive in the electrolyte within a suitable range helps to form a dense SEI film.

[0013] In a possible implementation, the molar concentration C of the metal ions in the electrolyte satisfies: 0.001M≤C≤2M.

[0014] In the embodiments of the present application, by controlling the concentration of metal ions in the electrolysis within a suitable range, it helps to uniformize the current density of the negative electrode during the cycle of the lithium-ion battery while reducing the impact of metal ions on the self-discharge of the lithium-ion battery.

[0015] In a possible implementation, the reduction potential of the metal ions is higher than the reduction potential of lithium ions.

[0016] In the embodiments of the present application, by selecting metal ions with a reduction potential higher than the reduction potential of lithium ions, once lithium deposition occurs on the negative electrode of the lithium-ion battery, the free metal ions in the electrolyte can be reduced to metal elements by lithium, and then form a lithium-metal alloy with lithium, thereby further inhibiting lithium deposition.

[0017] In a possible implementation, the film-forming additive includes at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, vinyl sulfite, propylene sulfite, and lithium difluorooxalatoborate.

[0018] In a possible implementation, the metal ions include: Na + , K + 、Cs+ , Ca 2+ Mg 2+ 、Zn 2+ 、Sn 4+ At least one of .

[0019] In one possible implementation, the electrolyte includes: an inorganic salt, the inorganic salt includes the metal ions and anions; the anions include: acetate, fluorophosphate, tetrafluoroborate, perchlorate, nitrate, carbonate, acetate, bis(trifluoromethylsulfonyl)imide, trifluoromethanesulfonate, difluorooxalatoborate, dioxalatoborate, methanesulfonate, hexafluorophosphate, and at least one of halogen anions.

[0020] In one possible implementation, the electrolyte includes: a solvent; the solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate or butyl propionate.

[0021] In a possible implementation, the electrolyte includes a lithium salt; the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(trifluoromethylsulfonylimide), and lithium bis(oxaloyl)borate.

[0022] In a possible implementation, the molar concentration C' of the lithium salt in the electrolyte satisfies: 0.05M≤C'≤2M.

[0023] In a second aspect, a lithium-ion battery is provided, wherein the lithium-ion battery includes the electrolyte in any possible implementation of the first aspect.

[0024] In a third aspect, a formation method of the lithium ion battery of the second aspect is provided, wherein the formation method includes a charging stage, wherein the charging stage includes: a first charging stage, charging the lithium ion battery with a first current I1 to a first voltage U1 at a constant current; a second charging stage, charging the lithium ion battery with a constant voltage at the first voltage U1 for a duration of T; a third charging stage, charging the lithium ion battery with a constant current to a cut-off voltage; a fourth charging stage, charging the lithium ion battery with a constant voltage at the cut-off voltage until the current is less than or equal to the cut-off current; wherein the reduction potential of the metal ion is Lower than the reduction decomposition potential of the film-forming additive The negative electrode potential of the lithium ion battery at the first voltage U1 is less than the reduction decomposition potential of the film-forming additive. and greater than the reduction potential of the metal ion T>0min.

[0025] In the embodiments of the present application, for lithium-ion batteries whose electrolyte includes metal ions and film-forming additives, during the formation process, a second charging stage is set up so that the film-forming additives in the electrolyte can be fully decomposed to form an SEI film. At the same time, since the reduction potential of the metal ions is lower than the reduction decomposition potential of the film-forming additives, during the constant voltage charging stage where the film-forming additives decompose to form a film, the metal ions will not be reduced, or will be reduced in very small amounts, thereby helping to uniformly distribute the current density on the negative electrode during the subsequent cycles of the lithium-ion battery.

[0026] In a possible implementation, the formation method includes a discharge stage, and the discharge stage includes: discharging the lithium-ion battery at a constant current to a cut-off voltage.

[0027] In a possible implementation, 0 min<T≤60 min; optionally, 10 min≤T≤20 min.

[0028] In the embodiments of the present application, controlling the charging time of the second charging stage within an appropriate range helps the film-forming additive to fully decompose and form a film.

[0029] In a possible implementation, the first voltage U1 satisfies: U1=U X +U M Among them, U X represents the voltage of the lithium-ion battery when the film-forming additive begins to decompose, U M is a constant, 0V≤U M ≤0.3V; optionally, 0.05V≤U M ≤0.15V.

[0030] In a possible implementation, the first current I1 satisfies: 0.01C≤I1≤0.1C.

[0031] In the embodiments of the present application, by controlling the charging current in the first charging stage within an appropriate range, it helps to reduce the amount of metal ions reduced during the formation process, and at the same time helps to reduce the probability of increased self-discharge of the lithium-ion battery due to the reduction of metal ions.

[0032] In a possible implementation, the molar concentration C of the metal ions in the electrolyte satisfies: 0.001M≤C≤2M.

[0033] In a possible implementation, the film-forming additive includes at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, vinyl sulfite, propylene sulfite, and lithium difluorooxalatoborate.

[0034] In a possible implementation, the metal ions include: Na + , K+ 、Cs + , Ca 2+ Mg 2+ 、Zn 2+ 、Sn 4+ At least one of .

[0035] In one possible implementation, the electrolyte includes: an inorganic salt, the inorganic salt includes the metal ions and anions; the anions include: acetate, fluorophosphate, tetrafluoroborate, perchlorate, nitrate, carbonate, acetate, bis(trifluoromethylsulfonyl)imide, trifluoromethanesulfonate, difluorooxalatoborate, dioxalatoborate, methanesulfonate, hexafluorophosphate, and at least one of halogen anions.

[0036] In a fourth aspect, an electrical device is provided, comprising the lithium-ion battery of the second aspect, and / or a lithium-ion battery formed according to the formation method of any possible implementation of the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0038] FIG1 is a schematic flow chart of a formation method of a lithium-ion battery according to the present application.

[0039] FIG2 is another schematic flow chart of a lithium ion battery formation method of the present application

[0040] FIG3 is a schematic diagram of a battery cell of a lithium-ion battery.

[0041] FIG4 is a schematic diagram of a battery module of a lithium-ion battery.

[0042] FIG5 is a schematic diagram of a lithium-ion battery.

[0043] FIG6 is another schematic diagram of a lithium-ion battery. DETAILED DESCRIPTION

[0044] Below, the electrolyte of the lithium-ion battery, the lithium-ion battery and its formation method, and the embodiment of the electric device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of 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.

[0045] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0046] In the description of this application, it should be noted that, unless otherwise specified, "plurality" means more than two; terms such as "upper," "lower," "left," "right," "inner," and "outer" indicating directions or positional relationships are merely for the purpose of facilitating the description of this application and simplifying the description, and do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limiting this application. Furthermore, terms such as "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0047] Unless otherwise specified, the term "and / or" is inclusive in this application. For example, the phrase "A and / or B" means "A, B, or both A and B." More specifically, the condition "A and / or B" is satisfied if any of the following conditions are met: 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).

[0048] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0049] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0050] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their generally accepted meanings in the art.

[0051] As mentioned, "reduction potential" refers to the electrode potential of a substance relative to a standard electrode. Specifically, the reduction potential is the electrode potential of a substance measured by combining the substance with a standard electrode in a galvanic cell. The standard electrode is typically a standard hydrogen electrode, but in some other cases, it can also be a saturated calomel electrode. For example, in a lithium-ion battery, the standard electrode can be a lithium electrode. Alternatively, the reduction potential of a substance relative to a standard electrode can be calculated by measuring the reduction potentials of two substances relative to a standard hydrogen electrode.

[0052] Where mentioned, "reductive decomposition potential" refers to the electrode potential of a substance relative to a standard electrode when it decomposes.

[0053] Next, embodiments of the present application are introduced.

[0054] In recent years, secondary batteries have been widely used in power tools, electronic products, electric vehicles, aerospace and other fields due to their high energy density and long service life, and have thus achieved great development. Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the charge and discharge process of the battery, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. Among them, the electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, which allows active ions to pass through while preventing the positive and negative electrodes from short-circuiting, so that the electrochemical reaction of the secondary battery proceeds normally.

[0055] Take lithium-ion batteries, for example. They are a typical secondary battery. Because they rely on the chemical reaction of lithium ions intercalating and deintercalating between the positive and negative electrodes for charging and discharging, they are also called rocking-chair batteries. During the charging process, lithium ions are released from the positive electrode active material, transferred through the electrolyte to the negative electrode, and then embedded in the negative electrode active material. During the discharge process, lithium ions are released from the negative electrode active material, transferred through the electrolyte to the positive electrode, and then embedded in the positive electrode active material.

[0056] It should be understood that the "lithium insertion" and "intercalation" processes described in this application refer to the process in which lithium ions are embedded in the positive electrode active material or the negative electrode active material due to an electrochemical reaction, and the "de-lithiumization", "de-lithiumization" and "de-intercalation" processes described in this application refer to the process in which lithium ions are removed from the positive electrode active material or the negative electrode active material due to an electrochemical reaction.

[0057] Due to limitations in production processes and other factors, lithium-ion batteries exhibit heterogeneity in their internal physical and chemical properties. This heterogeneity is particularly amplified in environments with large temperature differences. Specifically, during the charge and discharge process of a lithium-ion battery, current density is higher at locations on the electrode where temperatures are higher. At locations on the negative electrode where current density is higher, lithium deposition is more likely to occur due to low potential.

[0058] In view of this, the embodiments of the present application provide an electrolyte for a lithium-ion battery, a lithium-ion battery and a formation method thereof, and an electrical device. The electrolyte of the lithium-ion battery includes a film-forming additive and metal ions, and the reduction potential of the metal ions is lower than the reduction decomposition potential of the film-forming additive. When the film-forming additive decomposes to form an SEI film, the metal ions in the electrolyte will not be reduced. Therefore, after the lithium-ion battery is formed, free metal ions exist in the electrolyte, which can freely move to the position where the local current of the negative electrode plate is too low, forming an electrostatic shield on the surface of the negative electrode plate, thereby uniformizing the current on the surface of the negative electrode plate.

[0059] First, an electrolyte for a lithium ion battery is provided, wherein the electrolyte comprises a film-forming additive and metal ions. satisfy: Among them, M n+ represents the metal ion, n represents the valence of the metal ion, R represents the ideal gas constant, T represents the temperature, C represents the molar concentration of the metal ion in the electrolyte, F represents the Faraday constant, Represents the reduction decomposition potential of the film-forming additive. Typically, R is equal to 8.314 J·K -1 ·mol -1 , T is in K, and F is equal to 96485 C·mol -1 .

[0060] Specifically, the reduction potential of the metal ions is lower than the reduction decomposition potential of the film-forming additives, which means that during battery formation, when the film-forming additives decompose to form the SEI film, the metal ions will not be reduced to metal elements, or only a very small amount of metal ions will be reduced to metal elements. During the subsequent cycles of the lithium-ion battery, these metal ions can freely move to the area of ​​excessive current density at the negative electrode, forming a local high-concentration positive charge electrostatic field in this area, thereby forming an electrostatic shield and uniformizing the current density on the negative electrode.

[0061] In this embodiment, by introducing metal ions with a reduction potential lower than the reduction decomposition potential of the film-forming additive into the electrolyte of the lithium-ion battery, the problem of uneven local current density of the electrode during lithium-ion cycling can be effectively improved, thereby improving lithium plating and helping to improve the capacity retention rate and cycle performance of the lithium-ion battery.

[0062] It should be understood that the reduction potential of the metal ion and the reduction decomposition potential of the film-forming additive mentioned in the embodiments of the present application are relative to the same standard electrode. For example, in one example, the reduction potential of the metal ion is the reduction potential of the metal ion relative to a lithium electrode, and the reduction decomposition potential of the film-forming additive is the reduction decomposition potential of the film-forming additive relative to a lithium electrode. In another example, the reduction potential of the metal ion is the reduction potential of the metal ion relative to a standard hydrogen electrode, and the reduction decomposition potential of the film-forming additive is the reduction decomposition potential of the film-forming additive relative to a standard hydrogen electrode.

[0063] Typically, a lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. The lithium-ion battery provided in this application and its various components are described below.

[0064] [Negative electrode]

[0065] The negative electrode sheet generally includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

[0066] As an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0067] In one embodiment, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate (such as a substrate made of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0068] In one embodiment, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode 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, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0069] In one embodiment, the negative electrode active material layer further includes a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0070] In one embodiment, the negative electrode active material layer further includes a conductive agent, which can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0071] In one embodiment, the negative electrode active material layer further includes other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0072] In one embodiment, the negative electrode sheet can be prepared by forming a negative electrode slurry using the aforementioned components for preparing the negative electrode sheet. For example, the negative electrode active material, conductive agent, binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form the negative electrode slurry. The negative electrode slurry is then coated onto the negative electrode current collector. After drying and roller pressing, the negative electrode sheet is obtained.

[0073] [Positive electrode]

[0074] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.

[0075] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is provided on either or both of the two facing surfaces of the positive electrode current collector.

[0076] In one embodiment, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. 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 may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0077] In one embodiment, the positive electrode active material may adopt the positive electrode active material for batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, 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 for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), 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 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and at least one of its modified compounds. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and at least one of a composite material of lithium iron manganese phosphate and carbon. The battery will be accompanied by the deintercalation and consumption of Li during the charging and discharging process, and the molar content of Li in the positive electrode active material is different when the battery is discharged to different states. In the enumeration of positive electrode active materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode active material is used in the battery system, and the molar content of Li will change after the charge and discharge cycle. In the enumeration of positive electrode active materials in this application, the molar content of O is only an ideal state value. The release of lattice oxygen will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0078] In one embodiment, the positive electrode active material layer further includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0079] In one embodiment, the positive electrode active material layer 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.

[0080] In one embodiment, the positive electrode sheet can be prepared by separately forming a positive electrode slurry from the components used to prepare the positive electrode sheet. For example, the first positive electrode active material and / or the second positive electrode active material, a conductive agent, a binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry. The positive electrode slurry is then coated on a positive electrode current collector. After drying and rolling, the positive electrode sheet can be obtained.

[0081] [Electrolyte]

[0082] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. This application has no specific restrictions on the type of electrolyte, and it can be selected according to needs.

[0083] The present application provides an electrolyte for a lithium ion battery, the electrolyte comprising a film-forming additive and metal ions. satisfy: Among them, M n+ represents the metal ion, n represents the valence of the metal ion, R represents the ideal gas constant, T represents the temperature, C represents the molar concentration of the metal ion in the electrolyte, and F represents the Faraday constant. Represents the reductive decomposition potential of the film-forming additive.

[0084] In this embodiment, metal ions with a reduction potential lower than the decomposition potential of the film-forming additive are introduced into the electrolyte. These metal ions are not reduced, or are reduced only to a very small extent, during the decomposition of the film-forming additive to form the SEI film. This results in the presence of free metal ions in the electrolyte after the lithium-ion battery is formed. Consequently, during the cycling of the lithium-ion battery, once a location with excessive current density appears on the negative electrode plate, the metal ions can freely migrate to that location, forming a localized positive electrostatic field there. This uniformizes the current density across the negative electrode plate, reduces the problem of lithium deposition and negative active material structural collapse caused by uneven current density, and helps improve the capacity retention and cycling performance of the lithium-ion battery.

[0085] In one embodiment, the mass ratio m1 / m2 of the film-forming additive to the electrolyte satisfies: 0.1%≤m1 / m2≤10%.

[0086] Specifically, m1 / m2 can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or its value is within the range obtained by combining any two of the above values.

[0087] Film-forming additives decompose during the battery's formation process and participate in the formation of the SEI film, helping lithium-ion batteries build a dense SEI film on the negative electrode surface. On the one hand, if the content of film-forming additives in the electrolyte is too low, the film-forming effect will be limited. On the other hand, if the content of film-forming additives in the electrolyte is too high, it may affect the viscosity of the electrolyte, thereby affecting the ion transport speed of the lithium-ion battery.

[0088] In this embodiment, by controlling the concentration of the film-forming additive in the electrolyte within an appropriate range, a dense SEI film can be formed on the surface of the negative electrode of the lithium-ion battery while reducing the effect of the film-forming additive on the electrolyte concentration.

[0089] It should be understood that the amount of film-forming additive varies before and after formation of a lithium-ion battery, and that the film-forming additive is at least partially consumed during the formation process. The above mass ratio of film-forming additive to electrolyte refers to the mass ratio of film-forming additive to electrolyte before formation of the lithium-ion battery.

[0090] In one embodiment, the molar concentration C of the metal ions in the electrolyte satisfies: 0.001M≤C≤2M.

[0091] Specifically, C can be 0.001M, 0.002M, 0.003M, 0.004M, 0.005M, 0.006M, 0.007M, 0.008M, 0.009M, 0.01M, 0.02M, 0.03M, 0.04M, 0.05M, 0.06M, 0.07M, 0.08M, 0.09M, 0.1M, 0.2M, 0.3M, 0.4M, 0.5M, 0.6M, 0.7M, 0.8M, 0.9M, 1M, 1.1M, 1.2M, 1.3M, 1.4M, 1.5M, 1.6M, 1.7M, 1.8M, 1.9M, 2M, or its value is within the range obtained by combining any two of the above values.

[0092] On the one hand, if the metal ion content in the electrolyte is too low, its effect on uniform current density is limited. On the other hand, if the metal ion content in the electrolyte is too high, the probability of forming metal on the surface of the negative electrode after reduction increases, which may lead to increased self-discharge of the lithium-ion battery.

[0093] Therefore, this embodiment controls the concentration of metal ions in the electrolyte within a suitable range, thereby uniformizing the current density of the negative electrode during the cycle of the lithium-ion battery and helping to reduce the self-discharge of the lithium-ion battery.

[0094] In one embodiment, the film-forming additive includes at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, vinyl sulfite, propylene sulfite, and lithium difluorooxalatoborate.

[0095] In one embodiment, the metal ions include: Na + , K + 、Cs + , Ca 2+ Mg 2+ 、Zn 2+ 、Sn 4+ At least one of .

[0096] In one embodiment, the electrolyte includes: an inorganic salt, the inorganic salt includes a metal ion and an anion; the anion includes: at least one of acetate, fluorophosphate, tetrafluoroborate, perchlorate, nitrate, carbonate, acetate, bis(trifluoromethylsulfonyl)imide, trifluoromethanesulfonate, difluorooxalatoborate, dioxalatoborate, methanesulfonate, hexafluorophosphate, and a halogen anion.

[0097] Specifically, metal ions can be introduced by adding inorganic salts into the electrolyte.

[0098] In one embodiment, the electrolyte includes a solvent; the solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate or butyl propionate.

[0099] In one embodiment, the electrolyte includes a lithium salt; the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(oxaloyl)borate.

[0100] In one embodiment, the molar concentration C' of the lithium salt in the electrolyte satisfies: 0.05M≤C'≤2M.

[0101] Specifically, C' can be 0.05M, 0.06M, 0.07M, 0.08M, 0.09M, 0.1M, 0.2M, 0.3M, 0.4M, 0.5M, 0.6M, 0.7M, 0.8M, 0.9M, 1M, 1.1M, 1.2M, 1.3M, 1.4M, 1.5M, 1.6M, 1.7M, 1.8M, 1.9M, 2M, or its value is within the range obtained by combining any two of the above values.

[0102] In one embodiment, the electrolyte may further include additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0103] [Isolator]

[0104] In one embodiment, the battery further includes a separator. The present application has no particular limitation on the type of separator. For example, any known porous structure separator with good chemical and mechanical stability can be selected.

[0105] In one embodiment, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0106] The present application also provides a lithium-ion battery comprising the electrolyte of any of the aforementioned embodiments. Based on similar principles, the lithium-ion battery comprising the electrolyte of the aforementioned embodiments can achieve corresponding technical effects, which will not be described in detail here.

[0107] [Forming method]

[0108] Next, the formation method of the lithium-ion battery in the aforementioned embodiment is introduced.

[0109] The present application also provides a formation method for a lithium-ion battery. FIG1 is a schematic flow chart of the formation method.

[0110] As shown in FIG1 , a lithium-ion battery formation method 100 includes a charging stage 101. The charging stage 101 includes:

[0111] S1011, a first charging stage, constant-current charging the lithium-ion battery with a first current I1 to a first voltage U1.

[0112] S1012, a second charging stage, constant-voltage charging of the lithium-ion battery at a first voltage U1 for a duration of T.

[0113] S1013, the third charging stage, charging the lithium-ion battery with a constant current to a cut-off voltage.

[0114] S1014, a fourth charging stage, charging the lithium-ion battery at a constant voltage at the cut-off voltage until the current is less than or equal to the cut-off current.

[0115] Among them, lithium-ion batteries include electrolytes, which include film-forming additives and metal ions. The reduction potential of the metal ions is Lower than the reduction decomposition potential of film-forming additives The negative electrode potential of the lithium ion battery at the first voltage U1 is lower than the reduction decomposition potential of the film-forming additive. and higher than the reduction potential of the metal ion T>0min.

[0116] For the lithium-ion battery mentioned in the above embodiment, multiple charging stages are set during its formation process. By controlling the lithium-ion battery to charge for a period of time T at the first voltage U1, the film-forming additive is fully decomposed to form a film at the first voltage U1. At the same time, the metal ions are not reduced at the first voltage U1, or only a very small number of metal ions are reduced. As a result, the metal ions can help to uniform the current density on the negative electrode during the subsequent cycles of the lithium-ion battery, thereby helping to suppress lithium plating and improve the capacity retention rate and cycle performance of the lithium-ion battery.

[0117] It should be understood that the first voltage U1 is the full-cell voltage. The higher the full-cell voltage, the lower the negative electrode potential and the higher the positive electrode potential. The reduction potential mentioned above refers to the electrode potential of a single electrode. For example, in a lithium-ion battery, if the negative electrode potential is less than or equal to the reduction potential of the metal ions relative to lithium, the metal ions will be reduced, and the lithium-ion battery will have a corresponding full-cell voltage Ua. If the negative electrode potential is less than or equal to the reduction decomposition potential of the film-forming additive relative to lithium, the film-forming additive will decompose, and the lithium-ion battery will have a corresponding full-cell voltage Ub.

[0118] In the second charging stage, the negative electrode potential of the lithium-ion battery at the first voltage U1 is less than the reduction decomposition potential of the film-forming additive relative to lithium. Greater than the reduction potential of metal ions relative to lithium Therefore, at the first voltage U1, the film-forming additive is fully decomposed, and the metal ions are not reduced, or only a very small amount of metal ions are reduced. In other words, in the second charging stage, the first voltage U1 is greater than Ub and less than Ua.

[0119] FIG2 is another schematic flow chart of a formation method 100 provided in an embodiment of the present application.

[0120] In one embodiment, the formation method 100 includes a discharge phase 102, which includes:

[0121] S1021, discharge the lithium-ion battery at a constant current to a cut-off voltage.

[0122] In one embodiment, 0 min<T≤60 min; optionally, 10 min≤T≤20 min.

[0123] Specifically, T can be 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 12 min, 14 min, 16 min, 18 min, 20 min, 22 min, 24 min, 26 min, 28 min, 30 min, 32 min, 34 min, 36 min, 38 min, 40 min, 42 min, 44 min, 46 min, 48 min, 50 min, 52 min, 54 min, 56 min, 58 min, 60 min, or its numerical range is within the range obtained by combining any two of the above numerical values.

[0124] In one embodiment, the first voltage U1 satisfies: U1 = U X +U M Among them, U X Represents the voltage of the lithium-ion battery when the film-forming additive begins to decompose, U M is a constant, 0V≤U M ≤0.3V; optionally, 0.05V≤U M ≤0.15V.

[0125] Specifically, U M It can be 0V, 0.01V, 0.02V, 0.03V, 0.04V, 0.05V, 0.06V, 0.07V, 0.08V, 0.09V, 0.10V, 0.11V, 0.12V, 0.13V, 0.14V, 0.15V, 0.15V, 0.17V, 0.18V, 0.19V, 0.20V, 0.21V, 0.22V, 0.23V, 0.24V, 0.25V, 0.26V, 0.27V, 0.28V, 0.29V, 0.30V, or its value is within the range obtained by combining any two of the above values.

[0126] In this embodiment, the first voltage is set to be slightly higher than the voltage U of the lithium ion battery when the film-forming additive begins to decompose. X , so that the film-forming additives can be fully decomposed at the first voltage U1 and participate in the formation of the SEI film.

[0127] In one embodiment, the first current I1 satisfies: 0.01C≤I1≤0.1C.

[0128] Specifically, I1 can be 0.01C, 0.02C, 0.03C, 0.04C, 0.05C, 0.06C, 0.07C, 0.08C, 0.09C, 0.1C, or its value is within the range obtained by combining any two of the above values.

[0129] In this embodiment, by controlling the current in the first charging stage within an appropriate range, the possibility of metal ion reduction during the formation process is reduced, thereby reducing the amount of reduced metal ions. This also helps reduce the probability of increased self-discharge of the lithium-ion battery due to metal ion reduction.

[0130] Based on a similar principle, the lithium-ion battery formed by method 100 has metal ions in its electrolyte and can achieve the corresponding technical effects of the aforementioned lithium-ion battery, which will not be described in detail here.

[0131] In one embodiment, the negative electrode sheet, the positive electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0132] In one embodiment, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0133] In one embodiment, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0134] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square, or any other shape. For example, FIG3 shows a battery cell 300 having a square structure as an example.

[0135] It should be understood that the battery cell 300 may include the lithium-ion battery in the aforementioned embodiment.

[0136] Figure 4 shows an example battery module 400. Referring to Figure 4 , in the battery module 400, multiple battery cells 300 may be arranged sequentially along the length of the battery module 400. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 300 may be secured by fasteners. The multiple battery cells 300 may be of the same chemical system or of different chemical systems.

[0137] Optionally, in one embodiment, the battery module 400 may further include a housing having an accommodation space, and the plurality of battery cells 300 may be accommodated in the accommodation space.

[0138] Optionally, in one embodiment, the battery modules 400 may be assembled into a battery. The battery may contain one or more battery modules 400. The specific number may be selected by those skilled in the art according to the application and capacity of the battery.

[0139] Figures 5 and 6 illustrate an example battery 500. Referring to Figures 5 and 6, the battery 500 may include a battery box and multiple battery modules 400 disposed within the box. The battery box includes an upper case 501 and a lower case 502. The upper case 501 can be placed over the lower case 502 to form an enclosed space for accommodating the battery modules 400. The multiple battery modules 400 can be arranged in any manner within the battery box.

[0140] It should be understood that in other embodiments, the battery 500 is also referred to as a battery pack. The battery cells 300 may first be assembled into the battery module 400, and the battery 500 may be assembled from the battery module 400. Alternatively, the battery 500 may be assembled directly from the battery cells 300, omitting the intermediate battery module 400.

[0141] In addition, the present application also provides an electrical device, which includes at least one of the lithium-ion battery in the aforementioned embodiment or the lithium-ion battery prepared by method 100.

[0142] In another embodiment, an electrical device includes at least one of the battery cell 300, battery module 400, or battery 500 provided herein. The battery cell 300, battery module 400, or battery 500 can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0143] As an electric device, a battery cell 300 , a battery module 400 , or a battery 500 may be selected according to its usage requirements.

[0144] As an example of an electric device, the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module can be used.

[0145] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0146] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0147] [Examples 1-8 and Comparative Examples 1-2]

[0148] Example 1

[0149] (1) Preparation of negative electrode sheet

[0150] Dissolve 1 kg of artificial graphite (negative electrode active material), 10 g of acetylene black (conductive agent), 30 g of styrene-butadiene rubber (SBR) (binder), and 20 g of sodium carboxymethyl cellulose (CMC) (thickener) in 1 kg of deionized water and mix thoroughly to create a negative electrode slurry. The slurry is then evenly coated onto the negative electrode current collector copper foil. The negative electrode sheets are then cold pressed and slit.

[0151] (2) Preparation of positive electrode sheet

[0152] 1 kg of the positive electrode active material LiNi5Co2Mn3O2, 20 g of the conductive carbon nanotubes, and 20 g of the binder polyvinylidene fluoride (PVDF) were dissolved in 1 kg of N-methylpyrrolidone and mixed thoroughly to create a positive electrode slurry. The slurry was then evenly coated onto the positive electrode current collector aluminum foil. The positive electrode sheets were then cold pressed and cut.

[0153] (3) Preparation of electrolyte

[0154] A 1M lithium hexafluorophosphate (LiPF6) electrolyte and a 0.05M potassium hexafluorophosphate (KPF6) electrolyte were uniformly mixed, and then a film-forming additive, VC, was added and stirred to obtain electrolyte 1 containing the film-forming additive and metal ions. The solvent for the 0.05M potassium hexafluorophosphate was a 1:1:1 ratio by volume of EC:DMC:DEC. The mass fraction of VC in the electrolyte was 4%.

[0155] A commercially available lithium hexafluorophosphate (LiPF6) electrolyte solution with a concentration of 1 M was prepared. This electrolyte solution was referred to as electrolyte solution 2.

[0156] Electrolyte 3 was obtained by adding VC, a film-forming additive, to a 1M lithium hexafluorophosphate (LiPF6) electrolyte solution so that the mass fraction of VC in the electrolyte solution was 4%.

[0157] (4) Preparation of lithium-ion batteries

[0158] The positive electrode sheet, the negative electrode sheet, the separator, and the negative electrode sheet are stacked in order so that the separator is between the positive electrode sheet and the negative electrode sheet and can isolate the positive electrode sheet from the negative electrode sheet; then the stacked components are wound and placed in a shell, and after drying, the electrolyte 1 is injected, and the lithium-ion battery is obtained after packaging.

[0159] The encapsulated lithium-ion battery was formed according to the following process: standing for 1 minute, constant current charging at 8 mA to 2.3 V (first charging stage); constant voltage charging at 2.3 V for 15 minutes (second charging stage); constant current charging at 8 mA to 4.2 V (third charging stage); constant voltage charging at 4.2 V with a cutoff current of 2 mA (fourth charging stage); standing for 10 minutes, discharging at 8 mA constant current to a cutoff voltage of 2.5 V (discharging stage); and standing for 50 hours.

[0160] In Example 1, electrolyte 1 is used, the mass ratio of film-forming additive to electrolyte is m1 / m2=4%, and the metal ion is K + , K + The molar concentration in the electrolyte is C=0.05M.

[0161] Example 2

[0162] Compared with Example 1, in the electrolyte of Example 2, m1 / m2=0.1%.

[0163] Example 3

[0164] Compared with Example 1, in the electrolyte of Example 3, m1 / m2=10%.

[0165] Example 4

[0166] Compared with Example 1, in the electrolyte of Example 4, C=0.001M.

[0167] Example 5

[0168] Compared with Example 1, in the electrolyte of Example 5, during the preparation of electrolyte 1, sodium hexafluorophosphate was added to the electrolyte, and the metal ion was Na + , Na + The molar concentration in the electrolyte is C=0.05M.

[0169] Example 6

[0170] Compared with Example 1, in the electrolyte of Example 6, during the preparation of electrolyte 1, sodium hexafluorophosphate was added to the electrolyte, and the metal ion was Na + , Na + The molar concentration in the electrolyte is C=2M.

[0171] Example 7

[0172] Compared with Example 1, in the electrolyte of Example 7, LiPF6 and cesium hexafluorophosphate (CsPF6) with a concentration of 0.05M are uniformly mixed, thereby the metal ions in the electrolyte are Cs + .

[0173] Example 8

[0174] Compared with Example 1, in the electrolyte of Example 8, DTD is used as a film-forming additive, and m1 / m2=1%.

[0175] Comparative Example 1

[0176] Compared with Example 1, Comparative Example 1 uses electrolyte 2. In other words, the electrolyte of the lithium ion battery of Comparative Example 1 does not contain film-forming additives and metal ions.

[0177] Comparative Example 2

[0178] Compared with Example 1, Comparative Example 2 uses Electrolyte 3. In other words, the electrolyte of the lithium ion battery of Comparative Example 2 includes a film-forming additive but does not include metal ions.

[0179] The products and performance parameters of Examples 1-8 and Comparative Examples 1-2 are detailed in Table 1.

[0180] Table 1: Products and performance parameters of Examples 1-8 and Comparative Examples 1-2

[0181] In Table 1, "m1 / m2" represents the mass ratio of the film-forming additive to the electrolyte, "C" represents the molar concentration of the metal ion in the electrolyte, "200 Cycle Capacity Retention" represents the capacity retention of the formed lithium-ion battery after 200 cycles, and "Whether Lithium Deposition Occurs in the Heating Zone" indicates whether lithium deposition occurs on the negative electrode sheet corresponding to the heating zone after cycling. The heating zone is the location of the negative electrode sheet corresponding to the heated portion during the battery cycling test. For detailed testing procedures, see the Physical and Chemical Parameter Testing section below.

[0182] According to the comparative analysis of the Examples and Comparative Examples in Table 1, the electrolyte containing the film-forming additive can be used in lithium-ion batteries to effectively improve the capacity retention rate of the lithium-ion battery, inhibit lithium plating, and thus improve the cycling performance of the lithium-ion battery. In particular, by comparing Example 1 and Comparative Example 2, it can be seen that the capacity retention rate and number of cycles of the lithium-ion battery in Example 1 are significantly better than those in Comparative Example 2. Therefore, it can be seen that by introducing metal ions into the electrolyte, the current density on the negative electrode sheet can be effectively uniformed, thereby inhibiting lithium plating and improving the capacity retention rate and cycling performance of the lithium-ion battery.

[0183] Through the comparative analysis of Example 1 and Examples 4-6, it can be seen that the capacity retention rate of the lithium-ion batteries of Example 1 and Example 5 is significantly better than that of Example 4, indicating that the concentration of metal ions increases, the effect on the uniform current density on the negative electrode sheet is enhanced, and lithium precipitation can be better suppressed. The capacity retention rate of the lithium-ion battery of Example 6 is lower than that of Example 4, indicating that the concentration of metal ions cannot be unlimitedly large. If the concentration of metal ions is too high, they are easily reduced to form a metal layer on the negative electrode sheet, thereby increasing the self-discharge of the lithium-ion battery. Therefore, through Examples 1 and Examples 4-6, it is shown that controlling the metal ions in the electrolyte within a suitable concentration range can reduce the effect of metal ions on the self-discharge of the lithium-ion battery while uniformizing the current density of the negative electrode sheet.

[0184] It should be understood that the lithium-ion battery provided herein can be formed according to the formation method provided herein or according to other formation methods. For example, the above Examples 1-8 and Comparative Examples 1-2 can also be formed according to the following method, wherein the formation process is as follows: standing for 1 minute, constant current charging at 8 mA to 4.2 V; constant voltage charging at 4.2 V with a cutoff current of 2 mA; standing for 10 minutes, discharging at 8 mA constant current to a cutoff voltage of 2.5 V, and standing for 50 hours.

[0185] Above, the embodiments and comparative examples related to the lithium-ion battery provided in the present application are introduced. Next, the embodiments and comparative examples related to the formation method provided in the present application are introduced.

[0186] [Examples 9-17 and Comparative Examples 3-5]

[0187] Example 9

[0188] Example 9 A lithium ion battery was prepared using the same preparation process as Example 1. The lithium ion battery was formed according to the following formation method, and the specific formation process was as follows: standing for 1 min, constant current charging at 8 mA to 2.3 V (first charging stage); constant voltage charging at 2.3 V for 15 min (second charging stage); constant current charging at 8 mA to 4.2 V (third charging stage); constant voltage charging at 4.2 V with a cut-off current of 2 mA (fourth charging stage); after standing for 10 min, discharging at 8 mA constant current with a cut-off voltage of 2.5 V (discharging stage); and standing for 50 h.

[0189] Wherein, the first current I1 =8 mA, that is, I1 =0.05C, the first voltage U1 =2.3 V, and T =15 min.

[0190] Example 10

[0191] Compared with Example 9, during the formation process of the lithium ion battery of Example 10, T=10 min.

[0192] Example 11

[0193] Compared with Example 9, during the formation process of the lithium ion battery of Example 11, T=20 min.

[0194] Example 12

[0195] Compared with Example 9, during the formation process of the lithium ion battery of Example 12, T=60 min.

[0196] Example 13

[0197] Compared with Example 9, during the formation process of the lithium ion battery of Example 13, U1 = 2.35V.

[0198] Example 14

[0199] Compared with Example 9, during the formation process of the lithium ion battery of Example 14, U1 = 2.45V.

[0200] Example 15

[0201] Compared with Example 9, during the formation process of the lithium ion battery of Example 15, U1 = 2.6V.

[0202] Example 16

[0203] Compared with Example 9, during the formation process of the lithium ion battery of Example 16, I1=0.01C.

[0204] Example 17

[0205] Compared with Example 9, during the formation process of the lithium ion battery of Example 17, I1=0.1C.

[0206] Comparative Example 3

[0207] The lithium-ion battery in Comparative Example 3 is a lithium-ion battery obtained by forming the lithium-ion battery in Example 1 using a common formation method.

[0208] Comparative Example 4

[0209] Compared with Example 9, the lithium ion battery of Comparative Example 4 is charged to 2.1 V at a constant current of 8 mA in the first charging stage. In other words, the lithium ion battery of Comparative Example 4 is charged to a voltage less than U1 in the first charging stage.

[0210] Comparative Example 5

[0211] Compared with Example 9, the lithium ion battery of Comparative Example 5 is charged to 2.5 V at a constant current of 8 mA in the first charging stage. In other words, the lithium ion battery of Comparative Example 5 is charged to a voltage greater than U1 in the first charging stage.

[0212] The products and performance parameters of Examples 9-17 and Comparative Examples 3-5 are detailed in Table 2.

[0213] Table 2: Products and performance parameters of Examples 11-19 and Comparative Example 3

[0214] In Table 2, "I1" represents the first current, "U1" represents the first voltage, "T" represents the duration of the second charging stage, "Capacity Retention" represents the capacity retention of the formed lithium-ion battery after 500 cycles, and "Whether Lithium Deposits in the Heating Zone" represents whether lithium is deposited on the negative electrode sheet corresponding to the heating zone after the lithium-ion battery cycles. The heating zone is the location of the negative electrode sheet corresponding to the heated portion during the battery cycle test. For the detailed test process, please refer to the physical and chemical parameter test section below.

[0215] The electrolyte provided by the embodiments of the present application is used in the lithium-ion batteries of the embodiments and comparative examples in Table 2. No matter whether it is the embodiment after formation using the formation method of the embodiments of the present application or the comparative example after formation without the formation method of the embodiments of the present application, no lithium precipitation occurs in the heating zone, which once again verifies the inhibitory effect of the electrolyte provided by the present application on lithium precipitation. In addition, the comparative examples in Table 2 all use the lithium-ion batteries provided by the present application including the aforementioned electrolyte. Although the formation method provided by the present application is not used, they still show good cycle performance, which proves that the lithium-ion batteries provided by the present application also have good cycle performance using other formation methods.

[0216] Through the comparative analysis of the examples and comparative examples in Table 2, it can be seen that the capacity retention rates of Examples 9-17 are all higher than those of Comparative Examples 3-5. This shows that on the basis of using the lithium-ion battery provided by the present application, combined with the formation method provided by the examples of the present application, the metal ions can be not reduced or reduced in very small amounts while the film-forming additives are fully decomposed to form an SEI film. As a result, the metal ions can evenly distribute the current density of the negative electrode sheets during subsequent cycles, inhibit lithium plating, and further improve the capacity retention rate of the lithium-ion battery. In summary, on the basis of using the lithium-ion battery provided by the present application, combined with the formation method provided by the present application, it is helpful to further inhibit the lithium plating of the lithium-ion battery and further improve the cycle performance of the lithium-ion battery. The following is a brief introduction to the test methods for the physical and chemical parameters and performance parameters involved in the examples of the present application. It should be understood that the following test methods are only examples, and other test methods known in the art can also be used for testing.

[0217] 1. Test method for reduction potential of metal ions

[0218] According to the electrolyte M n+ Metal ion concentration C and equation Obtained by calculation.

[0219] 2. Test method for reduction decomposition potential of film-forming additives

[0220] Before formation, batteries with a lithium metal reference electrode were subjected to cyclic voltammetry (CV) at a scan rate of 0.1 mV / s over a voltage range from the initial cell voltage to the upper cell voltage limit. The peak value of the CV curve was used to monitor the lithium reduction potential of the additive decomposition and the corresponding full cell potential.

[0221] 3. Test method for capacity retention of lithium-ion N-cycle batteries (N is a positive integer)

[0222] Using the Blue Electric test system, the formed lithium-ion battery is first charged and discharged for the first time.

[0223] The first cycle charge refers to the battery being charged to 4.2V at a constant current of 60mA after formation, and then being charged at a constant voltage at 4.2V to a cutoff current of 2mA; the first cycle discharge capacity refers to the capacity W1 released by the battery when it is discharged to 2.5V at a constant current of 60mA after formation.

[0224] The battery is then subjected to charge and discharge tests. The test process is as follows: charging at a constant current of 60mA with a cut-off voltage of 4.2V; constant voltage charging at 4.2V with a cut-off current of 2mA; after standing for 10 minutes, discharging at a constant current of 60mA with a cut-off voltage of 2.5V, and then charging to 4.2V after N cycles before the test stops. The discharge capacity after N cycles is W2. The capacity retention rate of a lithium-ion battery after N cycles is W2 / W1×100%. For example, the discharge capacity after 200 cycles is W2', and the capacity retention rate of a lithium-ion battery after 200 cycles is W2' / W1×100%. For another example, the discharge capacity after 500 cycles is W2", and the capacity retention rate of a lithium-ion battery after 500 cycles is W2" / W1×100%.

[0225] 4. Test method for lithium ion battery heating area to see if lithium is deposited

[0226] During the cycle test of the lithium-ion battery, a 45°C heating plate is used to heat the lithium ion battery at one end along its length, and a water-cooling plate is used to accelerate heat dissipation at the other end, thereby simulating the uneven internal temperature of the lithium-ion battery during use.

[0227] For example, the length of the heating region may account for 20% of the length of the lithium-ion battery; and the length of the heat dissipation region may account for 50% of the length of the lithium-ion battery.

[0228] The cycled lithium-ion battery is disassembled to obtain the cycled negative electrode sheet, and whether lithium deposition occurs at the negative electrode sheet corresponding to the heated area can be directly observed.

[0229] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, the various technical features described in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. An electrolyte, characterized in that: The electrolyte includes a film-forming additive and metal ions; The reduction potential of the metal ion satisfy: Among them, M n+ represents the metal ion, n represents the valence of the metal ion, R represents the ideal gas constant, T represents the temperature, C represents the molar concentration of the metal ion in the electrolyte, F represents the Faraday constant, represents the reductive decomposition potential of the film-forming additive.

2. The electrolyte according to claim 1, characterized in that The mass ratio m1 / m2 of the film-forming additive to the electrolyte satisfies: 0.1%≤m1 / m2≤10%.

3. The electrolyte according to claim 1 or 2, characterized in that The molar concentration C of the metal ions in the electrolyte satisfies: 0.001M≤C≤2M.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The reduction potential of the metal ions is higher than the reduction potential of lithium ions.

5. The electrolyte according to any one of claims 1 to 4, characterized in that The film-forming additive comprises at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, vinyl sulfite, propylene sulfite and lithium difluorooxalate borate.

6. The electrolyte according to any one of claims 1 to 5, characterized in that The metal ions include: Na + , K + , Cs + , Ca 2+ Mg 2+ 、Zn 2+ Sn 4+ At least one of .

7. The electrolyte according to any one of claims 1 to 6, characterized in that The electrolyte includes: an inorganic salt, wherein the inorganic salt includes the metal ion and an anion; The anions include at least one of acetate, fluorophosphate, tetrafluoroborate, perchlorate, nitrate, carbonate, acetate, bistrifluoromethylsulfonyl imide, trifluoromethanesulfonate, difluorooxalatoborate, dioxalatoborate, methanesulfonate, hexafluorophosphate, and halogen anions.

8. The electrolyte according to any one of claims 1 to 7, characterized in that The electrolyte includes: a solvent; the solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate or butyl propionate.

9. The electrolyte according to any one of claims 1 to 8, characterized in that The electrolyte includes a lithium salt; the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(oxalyl)borate.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the electrolyte according to any one of claims 1 to 9.

11. A formation method for a lithium ion battery as claimed in claim 10, characterized in that: The formation method includes a charging stage, and the charging stage includes: In the first charging stage, the lithium-ion battery is charged with a first current I1 to a first voltage U1 at a constant current; In the second charging stage, the lithium-ion battery is charged at a constant voltage under the first voltage U1 for a duration of T; In the third charging stage, the lithium-ion battery is charged with a constant current to a cut-off voltage; In the fourth charging stage, the lithium-ion battery is charged at a constant voltage under the cut-off voltage until the current is less than or equal to the cut-off current; Wherein, the reduction potential of the metal ion Lower than the reduction decomposition potential of the film-forming additive The negative electrode potential of the lithium ion battery at the first voltage U1 is less than the reduction decomposition potential of the film-forming additive. and greater than the reduction potential of the metal ion T>0min.

12. The chemical formation method according to claim 11, characterized in that: The formation method includes a discharge stage, and the discharge stage includes: The lithium ion battery is discharged at a constant current to a cut-off voltage.

13. The chemical formation method according to claim 11 or 12, characterized in that: 0min<T≤60min; optionally, 10min≤T≤20min.

14. The chemical formation method according to any one of claims 11 to 13, characterized in that: The first voltage U1 satisfies: U1=U X +U M ; Among them, U X represents the voltage of the lithium-ion battery when the film-forming additive begins to decompose, U M Represents a constant, 0V≤U M ≤0.3V; Optionally, 0.05V≤U M ≤0.15V.

15. The chemical formation method according to any one of claims 11 to 14, characterized in that: The first current I1 satisfies: 0.01C≤I1≤0.1C.

16. The chemical formation method according to any one of claims 11 to 15, characterized in that: The molar concentration C of the metal ions in the electrolyte satisfies: 0.001M≤C≤2M.

17. The chemical formation method according to any one of claims 11 to 16, characterized in that: The film-forming additive comprises at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, vinyl sulfite, propylene sulfite and lithium difluorooxalate borate.

18. The chemical formation method according to any one of claims 11 to 17, characterized in that: The metal ions include: Na + , K + , Cs + , Ca 2+ Mg 2+ 、Zn 2+ Sn 4+ At least one of .

19. The chemical formation method according to any one of claims 11 to 18, characterized in that: The electrolyte includes: an inorganic salt, wherein the inorganic salt includes the metal ion and an anion; The anions include at least one of acetate, fluorophosphate, tetrafluoroborate, perchlorate, nitrate, carbonate, acetate, bistrifluoromethylsulfonyl imide, trifluoromethanesulfonate, difluorooxalatoborate, dioxalatoborate, methanesulfonate, hexafluorophosphate, and halogen anions.

20. An electrical device, characterized in that: The electrical device comprises the lithium ion battery according to claim 10, and / or a lithium ion battery formed by the formation method according to any one of claims 11-19.

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