Electrolyte, lithium ion battery, formation method of lithium ion battery and electric device

Abstract

The embodiment of the invention discloses an electrolyte, a lithium ion battery, a formation method of the lithium ion battery and a power utilization device. The electrolyte comprises a film-forming additive and metal ions, wherein the reduction potential # imgabs0 # of the metal ions meets the formula # imgabs1 #, 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, F represents the Faraday constant, and # imgabs2 # represents the reductive decomposition potential of the film-forming additive. When the electrolyte is applied to the lithium ion battery, the phenomenon that the current density of a pole piece is not uniform in the pole piece circulation process can be effectively improved, lithium precipitation is inhibited, and the capacity retention ratio and the circulation performance of the lithium ion battery are improved.

Description

Technical Field

[0001] 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

[0002] 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 power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields, and have thus achieved great development.

[0003] Due to the limitations of production processes and usage environments, the physical and chemical properties of lithium-ion batteries and the current during the charging process are all non-uniform, resulting in non-uniform currents in different areas of the positive and negative electrodes of lithium-ion batteries during the charging and discharging process. In areas where the local current is too large, the potential of the negative electrode is too low, which can easily destroy the structure of the negative electrode active material and easily lead to lithium precipitation, resulting in a decrease in the reversible capacity of the lithium-ion battery and a shortened cycle life. Therefore, how to improve the non-uniformity of the current density of the electrode during the cycle is a technical problem that needs to be solved urgently. Summary of the invention

[0004] This application is made in view of the above technical problems, and its purpose is to provide an electrolyte, a lithium-ion battery and its formation method, and an electrical device. The electrolyte includes a film-forming additive and metal ions, which can effectively improve the phenomenon of uneven current density of the pole piece during the pole piece cycle and inhibit lithium precipitation, helping to improve the capacity retention rate and cycle performance of the lithium-ion battery.

[0005] In a first aspect, an electrolyte is provided, the electrolyte 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.

[0006] It should be understood that the reduction potential of the metal ions and the reduction decomposition potential of the film-forming additive are the reduction potentials of the two relative to the same standard electrode.

[0007] In the embodiments of the present application, the electrolyte includes a film-forming additive and metal ions. The film-forming additive helps to form a dense SEI film on the surface of the negative electrode, and the metal ions, because their reduction potential is lower than the reduction decomposition potential of the film-forming additive, will not be reduced or will be reduced in very small amounts during the process of the film-forming additive decomposing to form the SEI film, so that free metal ions exist in the electrolyte of the lithium-ion battery after formation. Therefore, 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.

[0008] In a possible implementation, a mass ratio m1 / m2 of the film-forming additive to the electrolyte satisfies: 0.1%≤m1 / m2≤10%.

[0009] 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.

[0010] In a possible implementation, the molar concentration C of the metal ions in the electrolyte satisfies: 0.001M≤C≤2M.

[0011] In the embodiments of the present application, by controlling the concentration of metal ions in the electrolysis within a suitable range, it helps to even out the current density of the negative electrode sheet during the cycle of the lithium-ion battery while reducing the effect of metal ions on the self-discharge of the lithium-ion battery.

[0012] In a possible implementation, the reduction potential of the metal ions is higher than the reduction potential of lithium ions.

[0013] In the embodiments of the present application, by selecting metal ions whose reduction potential is higher than that 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 by lithium to metal elements, and then form lithium-metal alloys with lithium, thereby further inhibiting lithium deposition.

[0014] 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.

[0015] In a possible implementation, the metal ions include: Na + , K + , Cs + , Ca 2+ Mg 2+ 、Zn 2+ Sn 4+ At least one of .

[0016] In a possible implementation, the electrolyte includes: an inorganic salt, the inorganic salt includes the metal ions and anions; the anions include: at least one of acetate, fluorophosphate, tetrafluoroborate, perchlorate, nitrate, carbonate, acetate, bistrifluoromethylsulfonyl imide, trifluoromethanesulfonate, difluorooxalatoborate, dioxalatoborate, methanesulfonate, hexafluorophosphate, and halogen anions.

[0017] In a 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.

[0018] 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(trifluoromethylsulfonyl)imide, and lithium bis(oxalyl)borate.

[0019] In a possible implementation, the molar concentration C' of the lithium salt in the electrolyte satisfies: 0.05M≤C'≤2M.

[0020] In a second aspect, a lithium-ion battery is provided, wherein the lithium-ion battery comprises the electrolyte in any possible implementation of the first aspect.

[0021] In a third aspect, a formation method of the lithium ion battery in the second aspect is provided, the formation method comprising a charging stage, the charging stage comprising: a first charging stage, charging the lithium ion battery with a first current I1 to a first voltage U1 with 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 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.

[0022] In the embodiments of the present application, for a lithium-ion battery in which the electrolyte includes metal ions and a film-forming additive, during the formation process, a second charging stage is set up so that the film-forming additive in the electrolyte can be fully decomposed to form a 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 additive, during the constant voltage charging stage in which the film-forming additive decomposes to form a film, the metal ions will not be reduced, or will be reduced in very small amounts, thereby helping to even out the current density on the negative electrode sheet during the subsequent cycle of the lithium-ion battery.

[0023] 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.

[0024] In a possible implementation, 0 min<T≤60 min; optionally, 10 min≤T≤20 min.

[0025] In the embodiments of the present application, by controlling the charging time of the second charging stage within a suitable range, the film-forming additive is helped to fully decompose and form a film.

[0026] 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.

[0027] In a possible implementation, the first current I1 satisfies: 0.01C≤I1≤0.1C.

[0028] In the embodiments of the present application, by controlling the charging current in the first charging stage within a suitable 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.

[0029] In a possible implementation, the molar concentration C of the metal ions in the electrolyte satisfies: 0.001M≤C≤2M.

[0030] 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.

[0031] In a possible implementation, the metal ions include: Na + , K+ , Cs + , Ca 2+ Mg 2+ 、Zn 2+ Sn 4+ At least one of .

[0032] In a possible implementation, the electrolyte includes: an inorganic salt, the inorganic salt includes the metal ions and anions; the anions include: at least one of acetate, fluorophosphate, tetrafluoroborate, perchlorate, nitrate, carbonate, acetate, bistrifluoromethylsulfonyl imide, trifluoromethanesulfonate, difluorooxalatoborate, dioxalatoborate, methanesulfonate, hexafluorophosphate, and halogen anions.

[0033] In a fourth aspect, an electrical device is provided, the electrical device comprising the lithium-ion battery in the second aspect, and / or a lithium-ion battery formed according to the formation method in any possible implementation of the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. 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 paying creative work.

[0035] Figure 1 The present invention is a schematic flow chart of a lithium-ion battery formation method.

[0036] Figure 2 Another schematic flow chart of a lithium-ion battery formation method of the present application

[0037] Figure 3 A schematic diagram of a battery cell of a lithium-ion battery.

[0038] Figure 4 A schematic diagram of a battery module for a lithium-ion battery.

[0039] Figure 5 A schematic diagram of a lithium-ion battery.

[0040] Figure 6 Another schematic diagram of a lithium-ion battery. DETAILED DESCRIPTION

[0041] Hereinafter, the electrolyte of the lithium-ion battery, the lithium-ion battery and its formation method, and the implementation mode of the electric device of the present application are specifically disclosed with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures 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.

[0042] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a 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 a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present 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 real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it 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.

[0043] In the description of this application, it should be noted that, unless otherwise specified, "multiple" means more than two; the terms "upper", "lower", "left", "right", "inner", "outer", etc., indicating directions or positional relationships, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting this application. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0044] If not specifically stated, in this application, the term "and / or" is inclusive. For example, the phrase "A and / or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A and / or B": 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).

[0045] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably 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, the method may further include step (c), which means 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.

[0046] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0047] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their generally accepted meanings in the art.

[0048] 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 to form a galvanic cell. The standard electrode is generally a standard hydrogen electrode. In some other examples, the standard electrode can also be a saturated calomel electrode, etc. For example, in a lithium-ion battery, the standard electrode can be a lithium electrode. In addition, the reduction potential of a substance relative to a standard electrode can also be calculated by the reduction potentials of two substances relative to a standard hydrogen electrode.

[0049] Where mentioned, "reductive decomposition potential" refers to the electrode potential of a substance relative to a standard electrode when it decomposes.

[0050] Next, embodiments of the present application are introduced.

[0051] 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 achieved great development. Usually, 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 a role in 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.

[0052] Take lithium-ion batteries as an example. Lithium-ion batteries are a typical secondary battery. Because they rely on the chemical reaction of lithium ions intercalating and disintercalating between the positive and negative electrodes for charging and discharging, lithium-ion batteries are also called rocking-chair batteries. During the charging process of lithium-ion batteries, lithium ions are released from the positive electrode active material, move to the negative electrode through the conduction of the electrolyte and embed into the negative electrode active material; and during the discharge process, lithium ions are released from the negative electrode active material, move to the positive electrode through the conduction of the electrolyte and embed into the positive electrode active material.

[0053] It should be understood that the "lithium insertion" and "embedding" 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 "extraction", "delithium" and "extraction" processes described in this application refer to the process in which lithium ions are extracted from the positive electrode active material or the negative electrode active material due to an electrochemical reaction.

[0054] Due to the limitations of production processes and other factors, the physical and chemical properties inside lithium-ion batteries are not uniform. This non-uniformity will be magnified in particular in environments with large temperature differences. Specifically, during the charging and discharging process of lithium-ion batteries, the current density is higher at locations with higher temperatures on the electrode. At locations with higher current density on the negative electrode, lithium deposition is very likely to occur due to low potential.

[0055] 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, there are free metal ions in the electrolyte, which can move freely 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.

[0056] 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, F is equal to 96485 C·mol -1 .

[0057] Specifically, the reduction potential of metal ions is lower than the reduction decomposition potential of film-forming additives, which means that during battery formation, when the film-forming additives decompose to form the SEI film, metal ions will not be reduced to metal elements, or only a very small amount of metal ions will be reduced to metal elements. In the subsequent cycle of lithium-ion batteries, these metal ions can move freely to the area where the local current density of the negative electrode is too high, 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.

[0058] In this embodiment, by introducing metal ions whose reduction potential is 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 the lithium-ion cycle can be effectively improved, thereby improving lithium precipitation and helping to improve the capacity retention rate and cycle performance of the lithium-ion battery.

[0059] It should be understood that the reduction potential of the metal ions and the reduction decomposition potential of the film-forming additives 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 ions is the reduction potential of the metal ions relative to the lithium electrode, and the reduction decomposition potential of the film-forming additive is the reduction decomposition potential of the film-forming additive relative to the lithium electrode. In another example, the reduction potential of the metal ions is the reduction potential of the metal ions relative to the 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 the standard hydrogen electrode.

[0060] Generally, a lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. Next, the lithium-ion battery provided in the present application and various parts of the lithium-ion battery are introduced.

[0061] [Negative electrode]

[0062] 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.

[0063] 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 any one or both of the two facing surfaces of the negative electrode current collector.

[0064] In one embodiment, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may 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 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0065] In one embodiment, the negative electrode active material may adopt the negative electrode active material for batteries 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 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 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.

[0066] 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).

[0067] In one embodiment, the negative electrode active material layer further includes a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0068] In one embodiment, the negative electrode active material layer further includes other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0069] In one embodiment, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet are formed into a negative electrode slurry. For example, the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a negative electrode slurry. Then, the negative electrode slurry is coated on the negative electrode current collector, and after drying, rolling and other processes, the negative electrode sheet can be obtained.

[0070] [Positive electrode]

[0071] 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.

[0072] 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 disposed on any one or both of the two facing surfaces of the positive electrode current collector.

[0073] 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 and a metal layer formed on at least one surface of the polymer material base. 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.).

[0074] In one embodiment, the positive electrode active material may adopt a positive electrode active material for a battery that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, 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 for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, 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 is 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 charge and discharge cycles. 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.

[0075] 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), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0076] 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.

[0077] In one embodiment, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet are respectively formed into positive electrode slurries. For example, the first positive electrode active material and / or the second positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry. Then, the positive electrode slurry is coated on the positive electrode current collector, and after drying, rolling and other processes, the positive electrode sheet can be obtained.

[0078] [Electrolyte]

[0079] The electrolyte plays a role in conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs.

[0080] 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.

[0081] In this embodiment, metal ions with a reduction potential lower than the decomposition potential of the film-forming additive are introduced into the electrolyte, and will not be reduced or will be reduced in very small amounts during the process of the film-forming additive decomposing to form the SEI film, so that free metal ions exist in the electrolyte after the lithium-ion battery is formed. Therefore, during the cycle of the lithium-ion battery, once a position with excessive current density appears on the negative electrode plate, the metal ions can move freely to the position, forming a local positive charge electrostatic field at the position, thereby uniformizing the current density on the negative electrode plate, reducing the problem of lithium precipitation and collapse of the negative electrode active material structure due to uneven current density on the negative electrode plate, and helping to improve the capacity retention rate and cycle performance of the lithium-ion battery.

[0082] In one embodiment, the mass ratio m1 / m2 of the film-forming additive to the electrolyte satisfies: 0.1%≤m1 / m2≤10%.

[0083] 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.

[0084] Film-forming additives can decompose during the battery formation process, participate in the formation of SEI film, and help lithium-ion batteries build a dense SEI film on the surface of the negative electrode. On the one hand, if the content of film-forming additives in the electrolyte is too low, the film-forming effect is 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 transmission speed of the lithium-ion battery.

[0085] In this embodiment, by controlling the concentration of the film-forming additive in the electrolyte within a suitable 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.

[0086] It should be understood that the amount of the film-forming additive before and after the lithium-ion battery is formed is different, and the film-forming additive is at least partially consumed during the formation process. The mass ratio of the film-forming additive to the electrolyte is the mass ratio of the film-forming additive to the electrolyte before the lithium-ion battery is formed.

[0087] In one embodiment, the molar concentration C of the metal ions in the electrolyte satisfies: 0.001M≤C≤2M.

[0088] 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.

[0089] On the one hand, if the content of metal ions in the electrolyte is too low, the effect of uniform current density is limited. On the other hand, if the content of metal ions 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 lithium-ion batteries.

[0090] Therefore, this embodiment controls the concentration of metal ions in the electrolyte within a suitable range, which not only makes the current density of the negative electrode plate uniform during the cycle of the lithium-ion battery, but also helps to reduce the self-discharge of the lithium-ion battery.

[0091] 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.

[0092] In one embodiment, the metal ions include: Na + , K + , Cs + , Ca 2+ Mg 2+ 、Zn 2+ Sn 4+ At least one of .

[0093] 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, bistrifluoromethylsulfonyl imide, trifluoromethanesulfonate, difluorooxalatoborate, dioxalatoborate, methanesulfonate, hexafluorophosphate, and a halogen anion.

[0094] Specifically, metal ions can be introduced by adding inorganic salts into the electrolyte.

[0095] 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.

[0096] 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(oxalyl)borate.

[0097] In one embodiment, the molar concentration C' of the lithium salt in the electrolyte satisfies: 0.05M≤C'≤2M.

[0098] 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.

[0099] 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.

[0100] [Isolator]

[0101] 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 stability and mechanical stability can be selected.

[0102] In one embodiment, 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 membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0103] The present application also provides a lithium-ion battery, which includes the electrolyte in any of the above embodiments. Based on similar principles, the lithium-ion battery includes the electrolyte in the above embodiments and can achieve corresponding technical effects, which will not be described in detail here.

[0104] [Forming method]

[0105] Next, the formation method of the lithium-ion battery in the aforementioned embodiment is introduced.

[0106] The present application also provides a formation method for a lithium-ion battery, Figure 1 A schematic flow chart of the formation method is shown in FIG.

[0107] like Figure 1 As shown, the formation method 100 of a lithium-ion battery includes a charging stage 101. The charging stage 101 includes:

[0108] S1011, a first charging stage, charging the lithium-ion battery with a first current I1 to a first voltage U1.

[0109] S1012, a second charging stage, charging the lithium-ion battery at a constant voltage at a first voltage U1 for a duration of T.

[0110] S1013, the third charging stage, charging the lithium-ion battery with a constant current to a cut-off voltage.

[0111] S1014, a fourth charging stage, charging the lithium-ion battery at a constant voltage under the cut-off voltage until the current is less than or equal to the cut-off current.

[0112] The lithium-ion battery includes an electrolyte, the electrolyte includes a film-forming additive and metal ions, and the reduction potential of the metal ions 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.

[0113] For the lithium-ion battery mentioned in the above embodiment, multiple charging stages are set in 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 into a film at the first voltage U1. At the same time, the metal ions will not be reduced at the first voltage U1, or only a very small number of metal ions will be reduced. As a result, the metal ions can help to even out the current density on the negative electrode sheet during the subsequent cycle of the lithium-ion battery, thereby helping to inhibit lithium precipitation and improve the capacity retention rate and cycle performance of the lithium-ion battery.

[0114] 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 in the foregoing 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 has 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 has a corresponding full-cell voltage Ub.

[0115] 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 number 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.

[0116] Figure 2 Another schematic flow chart of a formation method 100 provided in an embodiment of the present application.

[0117] In one embodiment, the formation method 100 includes a discharge phase 102, and the discharge phase 102 includes:

[0118] S1021, discharge the lithium-ion battery at a constant current to a cut-off voltage.

[0119] In one embodiment, 0 min<T≤60 min; optionally, 10 min≤T≤20 min.

[0120] Specifically, T can be 1min, 2min, 3min, 4min, 5min, 6min, 7min, 8min, 9min, 10min, 12min, 14min, 16min, 18min, 20min, 22min, 24min, 26min, 28min, 30min, 32min, 34min, 36min, 38min, 40min, 42min, 44min, 46min, 48min, 50min, 52min, 54min, 56min, 58min, 60min, or its numerical range is within the range obtained by combining any two of the above numerical values.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] In one embodiment, the first current I1 satisfies: 0.01C≤I1≤0.1C.

[0125] 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.

[0126] In this embodiment, by controlling the current in the first charging stage within a suitable range, it helps to reduce the possibility of metal ions being reduced during the formation process, thereby reducing the amount of reduced metal ions. At the same time, it helps to reduce the probability of increased self-discharge of the lithium-ion battery due to the reduction of metal ions.

[0127] 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.

[0128] In one embodiment, the negative electrode sheet, the positive electrode sheet and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0129] In one embodiment, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0130] In one embodiment, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0131] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 3 The battery cell 300 is a square structure as an example.

[0132] It should be understood that the battery cell 300 may include the lithium-ion battery in the aforementioned embodiment.

[0133] Figure 4 4 is a battery module 400 as an example. Figure 4 In the battery module 400, the plurality of battery cells 300 may be arranged in sequence along the length direction of the battery module 400. Of course, they may also be arranged in any other manner. The plurality of battery cells 300 may be further fixed by fasteners. The plurality of battery cells 300 may be battery cells 300 of the same chemical system or battery cells 300 of different chemical systems.

[0134] Optionally, in one embodiment, the battery module 400 may further include a housing having an accommodation space, and the plurality of battery cells 300 are accommodated in the accommodation space.

[0135] Optionally, in one embodiment, the battery modules 400 may also be assembled into a battery. The number of battery modules 400 contained in the battery may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery.

[0136] Figure 5 and Figure 6 500 is an example of a battery. Figure 5 and Figure 6 The battery 500 may include a battery box and a plurality of battery modules 400 disposed in the battery box. The battery box includes an upper box body 501 and a lower box body 502. The upper box body 501 can cover the lower box body 502 and form a closed space for accommodating the battery modules 400. The plurality of battery modules 400 may be arranged in the battery box in any manner.

[0137] 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 form a battery module 400, and the battery 500 may be formed by the battery module 400. Alternatively, the battery 500 may be directly formed by the battery cells 300, omitting the intermediate form of the battery module 400.

[0138] 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.

[0139] In another embodiment, the electrical device includes at least one of the battery cell 300, battery module 400, or battery 500 provided in the present application. 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 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 thereto.

[0140] As an electric device, a battery cell 300, a battery module 400, or a battery 500 may be selected according to its usage requirements.

[0141] 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, etc. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module may be used.

[0142] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0143] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0144] [Examples 1-8 and Comparative Examples 1-2]

[0145] Example 1

[0146] (1) Preparation of negative electrode sheet

[0147] 1kg of artificial graphite, anode active material, 10g of acetylene black, 30g of styrene butadiene rubber (SBR), and 20g of carboxymethyl cellulose sodium (CMC) were dissolved in 1kg of deionized water and mixed evenly to obtain cathode slurry. Then, the cathode slurry was evenly coated on the cathode current collector copper foil. After cold pressing and slitting, the cathode pole sheet was obtained.

[0148] (2) Preparation of positive electrode sheet

[0149] 1 kg of positive electrode active material LiNi5Co2Mn3O2, 20 g of conductive agent carbon nanotubes, and 20 g of binder polyvinylidene fluoride (PVDF) were dissolved in 1 kg of N-methylpyrrolidone and mixed evenly to obtain positive electrode slurry. Then, the positive electrode slurry was evenly coated on the positive electrode current collector aluminum foil. After cold pressing and slitting, the positive electrode sheet was obtained.

[0150] (3) Preparation of electrolyte

[0151] 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 thereto, and the mixture was stirred evenly to obtain an electrolyte 1 including a film-forming additive and metal ions. The solvent of the 0.05M potassium hexafluorophosphate was EC:DMC:DEC in a volume ratio of 1:1:1. The mass fraction of VC in the electrolyte was 4%.

[0152] A commercially available 1 M lithium hexafluorophosphate (LiPF6) electrolyte solution is prepared. This electrolyte solution is referred to as electrolyte solution 2.

[0153] Electrolyte 3 was obtained by adding a film-forming additive VC to a 1M lithium hexafluorophosphate (LiPF6) electrolyte solution so that the mass fraction of VC in the electrolyte solution was 4%.

[0154] (4) Preparation of lithium-ion batteries

[0155] 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 separate 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 a lithium-ion battery is obtained after packaging.

[0156] The lithium-ion battery obtained after packaging was formed according to the following process, and the specific formation process was: standing for 1 minute, charging at a constant current of 8 mA to 2.3 V (the first charging stage); charging at a constant voltage of 2.3 V for 15 minutes (the second charging stage); charging at a constant current of 8 mA to 4.2 V (the third charging stage); charging at a constant voltage of 4.2 V with a cut-off current of 2 mA (the fourth charging stage); after standing for 10 minutes, discharging at a constant current of 8 mA with a cut-off voltage of 2.5 V (discharging stage); standing for 50 hours.

[0157] 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.

[0158] Example 2

[0159] Compared with Example 1, in the electrolyte of Example 2, m1 / m2=0.1%.

[0160] Example 3

[0161] Compared with Example 1, in the electrolyte of Example 3, m1 / m2=10%.

[0162] Example 4

[0163] Compared with Example 1, in the electrolyte of Example 4, C=0.001M.

[0164] Example 5

[0165] 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.

[0166] Example 6

[0167] 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.

[0168] Example 7

[0169] Compared with Example 1, in the electrolyte of Example 7, LiPF6 and cesium hexafluorophosphate (CsPF6) with a concentration of 0.05M are uniformly mixed, so that the metal ions in the electrolyte are Cs + .

[0170] Example 8

[0171] Compared with Example 1, in the electrolyte of Example 8, DTD is used as a film-forming additive, and m1 / m2=1%.

[0172] Comparative Example 1

[0173] 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.

[0174] Comparative Example 2

[0175] 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.

[0176] The products and performance parameters of Examples 1-8 and Comparative Examples 1-2 are detailed in Table 1.

[0177] Table 1: Products and performance parameters of Examples 1-8 and Comparative Examples 1-2

[0178] In Table 1, "m1 / m2" indicates the mass ratio of the film-forming additive to the electrolyte, "C" indicates the molar concentration of the metal ion in the electrolyte, "200 cycles capacity retention rate" indicates the capacity retention rate of the formed lithium-ion battery after 200 cycles, and "Whether the heating zone has lithium precipitates" indicates whether the negative electrode sheet corresponding to the heating zone after the lithium-ion battery cycle has lithium precipitates. The heating zone is the position of the negative electrode sheet corresponding to the heated part during the battery cycle test. For the specific test process, please refer to the physical and chemical parameter test section below.

[0179] According to the comparative analysis of the embodiments and comparative examples in Table 1, the electrolyte including the film-forming additive is applied to the lithium-ion battery, which can effectively improve the capacity retention rate of the lithium-ion battery, inhibit lithium precipitation, and thus improve the cycle performance of the lithium-ion battery. In particular, by comparing the embodiment 1 with the comparative example 2, it can be seen that the capacity retention rate and the number of cycles of the lithium-ion battery in the embodiment 1 are significantly better than those in the 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 precipitation and improving the capacity retention rate and cycle performance of the lithium-ion battery.

[0180] Through comparative analysis of Example 1 and Examples 4-6, it can be seen that the capacity retention rate of the lithium-ion battery 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 lithium-ion batteries while achieving a uniform current density on the negative electrode sheet.

[0181] It should be understood that the lithium-ion battery provided in the present application can be formed according to the formation method provided in the present application, or according to other formation methods. For example, the above-mentioned embodiments 1-8 and comparative examples 1-2 can also be formed according to the following method, and the specific formation process is: standing for 1 minute, charging to 4.2V at a constant current of 8mA; charging at a constant voltage of 4.2V, with a cut-off current of 2mA; after standing for 10 minutes, discharging at a constant current of 8mA, with a cut-off voltage of 2.5V, and standing for 50h.

[0182] 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.

[0183] [Examples 9-17 and Comparative Examples 3-5]

[0184] Example 9

[0185] Example 9 A lithium ion battery was prepared by 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: standing for 1 min, constant current charging to 2.3 V at a current of 8 mA (first charging stage); constant voltage charging at 2.3 V for 15 min (second charging stage); constant current charging to 4.2 V at a current of 8 mA (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 a constant current of 8 mA with a cut-off voltage of 2.5 V (discharging stage); standing for 50 h.

[0186] Among them, the first current I1=8mA, that is, I1=0.05C, the first voltage U1=2.3V, and T=15min.

[0187] Example 10

[0188] Compared with Example 9, during the formation process of the lithium ion battery of Example 10, T=10 min.

[0189] Embodiment 11

[0190] Compared with Example 9, during the formation process of the lithium ion battery of Example 11, T=20 min.

[0191] Example 12

[0192] Compared with Example 9, during the formation process of the lithium ion battery of Example 12, T=60 min.

[0193] Example 13

[0194] Compared with Example 9, during the formation process of the lithium ion battery of Example 13, U1 = 2.35V.

[0195] Embodiment 14

[0196] Compared with Example 9, during the formation process of the lithium ion battery of Example 14, U1 = 2.45V.

[0197] Embodiment 15

[0198] Compared with Example 9, during the formation process of the lithium ion battery of Example 15, U1 = 2.6V.

[0199] Example 16

[0200] Compared with Example 9, during the formation process of the lithium ion battery of Example 16, I1=0.01C.

[0201] Embodiment 17

[0202] Compared with Example 9, during the formation process of the lithium ion battery of Example 17, I1=0.1C.

[0203] Comparative Example 3

[0204] 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.

[0205] Comparative Example 4

[0206] 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.

[0207] Comparative Example 5

[0208] 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.

[0209] The products and performance parameters of Examples 9-17 and Comparative Examples 3-5 are detailed in Table 2.

[0210] Table 2: Products and performance parameters of Examples 11-19 and Comparative Example 3 <![CDATA[I1(C)]]> <![CDATA[U1(V)]]> T(min) Capacity retention rate Is lithium deposited in the heating area? Example 9 0.05 2.3 15 94.3％ no Example 10 0.05 2.3 10 96.0％ no Embodiment 11 0.05 2.3 20 97.2％ no Example 12 0.05 2.3 60 96.5％ no Example 13 0.05 2.35 15 94.0％ no Embodiment 14 0.05 2.45 15 93.9％ no Embodiment 15 0.05 2.6 15 92.2％ no Example 16 0.01 2.3 15 95.4％ no Embodiment 17 0.1 2.3 15 93.8％ no Comparative Example 3 0.05 / / 90.2％ no Comparative Example 4 0.05 2.1 15 91.0％ no Comparative Example 5 0.05 3 15 91.5％ no

[0211] In Table 2, "I1" represents the first current, "U1" represents the first voltage, "T" represents the duration of the second charging stage, "Capacity retention rate" represents the capacity retention rate of the formed lithium-ion battery after 500 cycles, and "Whether lithium is deposited in the heating zone" represents whether lithium is deposited in the negative electrode sheet corresponding to the heating zone after the lithium-ion battery is cycled. The heating zone is the position of the negative electrode sheet corresponding to the heated part during the battery cycle test. For the specific test process, please refer to the physical and chemical parameter test section below.

[0212] 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 it is the embodiment after the formation method of the embodiments of the present application, or the comparative example after the formation method of the embodiments of the present application is not used, 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, but still show good cycle performance, proving that the lithium ion batteries provided by the present application also have good cycle performance using other formation methods.

[0213] Through the comparative analysis of the embodiments and comparative examples in Table 2, it can be seen that the capacity retention rates of embodiments 9-17 are all higher than those of comparative examples 3-5. It is explained that on the basis of using the lithium-ion battery provided by the present application, combined with the formation method provided in the embodiments 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 sheet during subsequent cycles, inhibit lithium precipitation, 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 in the present application, it is helpful to further inhibit the lithium precipitation 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 embodiments 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.

[0214] 1. Test method for reduction potential of metal ions

[0215] According to the electrolyte M n+ Metal ion concentration C and equation Obtained by calculation.

[0216] 2. Test method for reduction decomposition potential of film-forming additives

[0217] The battery with lithium metal reference electrode was subjected to cyclic voltammetry (CV) test before formation, with a scan rate of 0.1mV / s and a scan voltage range from the initial voltage of the battery to the upper limit voltage of the battery. The lithium reduction potential of the additive reduction decomposition and the corresponding full battery potential were monitored according to the peak value of the CV curve.

[0218] 3. Test method for capacity retention rate of lithium-ion N-cycle battery (N is a positive integer)

[0219] Using the Blue Electric test system, the formed lithium-ion battery is first charged and discharged for the first time.

[0220] The first cycle charging 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 cut-off current of 2mA; the first cycle discharge capacity refers to the capacity W1 released by the battery when it is discharged to a voltage of 2.5V at a constant current of 60mA after formation.

[0221] Then the battery is charged and discharged. The test process is: 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, discharge at a constant current of 60mA, with a cut-off voltage of 2.5V, and then charge to 4.2V after N cycles and stop the test. The discharge capacity after N cycles is W2. The capacity retention rate of lithium-ion batteries for N cycles is W2 / W1×100%. For example, the discharge capacity after 200 cycles is W2', and the capacity retention rate of lithium-ion batteries for 200 cycles is W2' / W1×100%. For another example, the discharge capacity after 500 cycles is W2", and the capacity retention rate of lithium-ion batteries for 500 cycles is W2" / W1×100%.

[0222] 4. Test method for lithium ion battery heating area to see if lithium is deposited

[0223] During the cycle test of the lithium-ion battery, a 45°C heating plate is used to heat one end along the length of the lithium ion, 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.

[0224] Exemplarily, the length of the heating area may account for 20% of the length of the lithium-ion battery; and the length of the heat dissipation area may account for 50% of the length of the lithium-ion battery.

[0225] The cycled lithium-ion battery is disassembled to obtain the cycled negative electrode plate, and whether lithium deposition occurs at the negative electrode plate corresponding to the heated area can be directly observed.

[0226] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned 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 includes all technical solutions falling 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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