Electrolyte, lithium-ion battery, and electric device

Abstract

Disclosed in embodiments of the present application are an electrolyte, a lithium-ion battery, and an electric device. The electrolyte comprises a metal ion including at least one of K+, Rb+, and Cs+; and the molar concentration CM of the metal ion in the electrolyte satisfies: 0.03M≤CM. When applied in lithium-ion batteries, the electrolyte can effectively reduce the risk of lithium plating on the negative electrode and improve the safety performance of the lithium-ion batteries.

Description

Electrolyte, lithium-ion battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent document claims priority to and the benefit of Chinese patent application No. 202311523508.5, filed on November 15, 2023, entitled “Electrolyte, Lithium-ion Battery, and Electric 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, 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] With the widespread application of lithium-ion batteries, higher requirements are placed on the safety performance of lithium-ion batteries. How to improve the safety performance of lithium-ion batteries is crucial to the development and application of lithium-ion batteries.

[0006] Summary of the Invention

[0007] This application is made in view of the above technical problems, and its purpose is to provide an electrolyte, a lithium-ion battery and an electrical device. The electrolyte can effectively improve / mitigate lithium plating of the negative electrode sheet and improve the safety performance of the lithium-ion battery.

[0008] In a first aspect, an electrolyte is provided, wherein the electrolyte comprises: metal ions, wherein the metal ions include K + , Rb + 、Cs + At least one of; the molar concentration of the metal ion in the electrolyte C M Meets: 0.03M≤C M .

[0009] In the embodiments of the present application, there is an appropriate amount of free metal ions in the electrolyte, which can move to the position where the current density of the negative electrode sheet is uneven and lithium deposition is prone to occur to form electrostatic shielding or steric hindrance, thereby alleviating / improving lithium deposition on the negative electrode sheet during the cycle of the lithium-ion battery, thereby improving the safety performance of the lithium-ion battery.

[0010] In one possible implementation, optionally, 0.03M≤C M ≤0.25M; 0.05M≤C M≤0.15M.

[0011] In the embodiments of the present application, metal ions with a molar concentration of 0.03M to 0.25M can be relatively stably present in the electrolyte in ionic form, thereby effectively alleviating / improving lithium deposition on the negative electrode. Furthermore, by controlling the concentration of the metal ions within an appropriate range, the lithium-ion battery can also achieve good capacity retention.

[0012] In a possible implementation, the metal ions are electrochemically inert within an operating voltage range of the lithium-ion battery.

[0013] In one possible implementation, the metal ions include K + .

[0014] In the embodiment of the present application, potassium ions with a Stokes radius smaller than that of lithium ions are selected as metal ions. They can move faster than lithium ions to the positions on the negative electrode sheet where the current density is uneven and lithium deposition is likely to occur, effectively uniformizing the current density on the negative electrode sheet and improving the efficiency of electrostatic shielding.

[0015] In a possible implementation, the electrolyte further includes lithium ions, and the molar concentration of the lithium ions in the electrolyte is C Li Meets: 0.8M≤C Li ≤1.2M.

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

[0017] In a possible implementation, the electrolyte includes a solvent, the solvent includes a non-aqueous solvent, and the non-aqueous solvent includes a carbonate solvent.

[0018] In a possible implementation, the carbonate solvent includes: ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate and at least one of the halides of the above carbonates.

[0019] 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.

[0020] In a possible implementation, the CB value of the lithium-ion battery satisfies: 1.03≤CB≤1.2, where the CB value is the ratio of the capacity of the negative electrode active material per unit area to the capacity of the positive electrode active material per unit area.

[0021] In the embodiments of the present application, the metal ions in the electrolyte of the lithium-ion battery can form electrostatic shielding or steric hindrance at the position where the current density is uneven and lithium deposition is prone to occur, thereby inhibiting lithium deposition. Taking into account that the electrostatic shielding effect of the metal ions may also affect the electrochemical reaction rate at the position, the CB value of the lithium-ion battery is set to be within the range of 1.03 to 1.2, that is, the capacity of the negative electrode active material per unit area of ​​the negative electrode plate is greater than the capacity of the positive electrode active material per unit area of ​​the positive electrode plate, so that the negative electrode plate per unit area has more lithium ion active sites that can accommodate lithium ions that cannot be embedded in the corresponding position due to the influence of electrostatic shielding, and the larger the CB value, the stronger the capacity of the negative electrode plate to accommodate lithium ions. Therefore, the design of the electrolyte including metal ions in the lithium-ion battery combined with a large CB value helps to further reduce the risk of lithium deposition in the low CB value area of ​​the negative electrode plate and improve the safety performance of the lithium-ion battery.

[0022] In a possible implementation, the lithium-ion battery includes a negative electrode plate, the negative electrode plate includes a negative electrode active material, and the negative electrode active material includes graphite.

[0023] In a third aspect, an electrical device is provided, wherein the electrical device includes the lithium-ion battery in any possible implementation of the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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.

[0025] FIG1 is a schematic diagram showing a method for inhibiting lithium deposition in lithium-ion batteries.

[0026] FIG2 is a schematic diagram of a low CB value region.

[0027] FIG3 is a schematic diagram of a battery cell.

[0028] FIG4 is a schematic diagram of a battery module.

[0029] FIG5 is a schematic diagram of a battery.

[0030] FIG6 is another schematic diagram of a battery. DETAILED DESCRIPTION

[0031] Below, the embodiments of the lithium-ion battery and the electrical device of the present application are described 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 structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0032] " 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.

[0033] 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.

[0034] Unless otherwise specified, in this application, the phrase "A and / or B" means "A, B, or both A and B". More specifically, the condition "A and / or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0035] 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.

[0036] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0037] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their generally accepted meanings in the art.

[0038] As mentioned, the "Stokes radius" refers to the ratio of the drag coefficient of a particle moving in a Newtonian fluid to the particle's radius. It is also known as the particle's effective radius in solution or the solvated ion radius. The larger the Stokes radius, the greater the drag encountered by a particle in the fluid and the weaker its mobility.

[0039] As mentioned, the "Cell Balance (CB) value" refers to the ratio of the negative electrode capacity to the positive electrode capacity on opposite sides of the battery, also known as the N / P (Negative / Positive) ratio. In other words, the CB value is equal to the ratio of the capacity of the negative electrode active material per unit area to the capacity of the positive electrode active material per unit area.

[0040] As mentioned, “electrochemically inert” refers to the property of not being electrochemically oxidized or electrochemically reduced, or the property of not undergoing electrochemical oxidation or electrochemical reduction.

[0041] Where mentioned, "non-aqueous solvent" refers to solvents other than water, for example, organic solvents, supercritical fluids, ionic liquids, etc.

[0042] Where mentioned, "carbonate solvents" refer to organic solvents containing a carbonate group (-OCO-O-) in their molecular structure. Examples include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), and linear carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0043] Next, embodiments of the present application are introduced.

[0044] 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.

[0045] Take lithium-ion batteries, for example. They are a typical secondary battery. Because they rely on chemical reactions involving the intercalation and deintercalation of lithium ions between the positive and negative electrodes for charging and discharging, they are also known as rocking-chair batteries. During charging, 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 discharge, 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.

[0046] 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.

[0047] During the production of lithium-ion batteries, a slurry containing active materials is applied to a current collector to form the electrode sheet. Due to limitations in the coating process and the varying drying rates of the slurry at different locations on the electrode sheet after coating, it is often impossible to obtain an electrode sheet with completely uniform thickness. This results in some areas of the negative electrode sheet having a lower gram capacity than the corresponding areas on the positive electrode sheet, resulting in a CB value less than 1 in these areas, i.e., a low CB value region in the lithium-ion battery. Furthermore, during the use of the lithium-ion battery, factors such as internal temperature variations can lead to uneven current density across the electrode sheet. At locations on the negative electrode sheet corresponding to low CB value regions or areas with higher current density on the negative electrode sheet, the state of charge (SOC) of the negative electrode sheet will preferentially reach saturation, resulting in a more negative local electric field and a greater attraction for positively charged ions, such as lithium ions. Because the SOC at these locations is already saturated, it cannot accommodate further lithium ion insertion. Consequently, lithium ions accumulate and precipitate at these locations. In other words, this leads to lithium plating, which adversely affects the safety performance of the lithium-ion battery.

[0048] In view of this, the present application provides an electrolyte, a lithium-ion battery and an electrical device. The electrolyte includes metal ions that can uniformly distribute the current density of the negative electrode. The application of the electrolyte in the lithium-ion battery can reduce the risk of lithium plating on the negative electrode and improve the safety performance of the lithium-ion battery.

[0049] 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.

[0050] [Electrolyte]

[0051] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte; it can be selected based on your needs. The electrolyte typically includes an electrolyte salt and a solvent.

[0052] First, the present application provides an electrolyte, which includes metal ions, including K + , Rb + 、Cs + At least one of; the molar concentration of metal ions in the electrolyte C M Meets: 0.03M≤C M ; Optionally, 0.03M≤C M ≤0.25M; optionally, 0.05M≤C M ≤0.15M.

[0053] Specifically, C M It can be 0.03M, 0.04M, 0.05M, 0.06M, 0.07M, 0.08M, 0.09M, 0.1M, 0.11M, 0.12M, 0.13M, 0.14M, 0.15M, 0.15M, 0.17M, 0.18M, ​​0.19M, 0.2M, 0.21M, 0.22M, 0.23M, 0.24M, 0.25M, or a value within the range obtained by combining any two of the above values. In another example, C M It can also be any value greater than or equal to 0.03M.

[0054] In the embodiment of the present application, the metal ions in the electrolyte can move freely to the negative electrode sheet. As mentioned above, at the negative electrode sheet corresponding to the low CB value, or at the position where the current density on the negative electrode sheet is relatively high, the state of charge (SOC) of the negative electrode sheet will preferentially reach saturation, resulting in a more negative local electric field, which is easier to attract positively charged metal ions. The electrolyte in the embodiment of the present application includes other metal ions besides lithium ions, which can move to the above-mentioned position and be enriched at this position, thereby forming electrostatic shielding and steric hindrance, so that lithium ions will not be enriched in this area and then lithium ions will be precipitated. As a result, the metal ions can effectively even out the current density of the negative electrode sheet, inhibit lithium precipitation, and help improve the safety performance of lithium-ion batteries.

[0055] Furthermore, by controlling the concentration of metal ions within the range of 0.03M to 0.25M, the effect of metal ions on the viscosity of the electrolyte can be reduced, thereby reducing the effect of metal ions on the DC impedance of the lithium-ion battery, thereby improving the lithium deposition situation while enabling the lithium-ion battery to have a good capacity retention rate.

[0056] In one embodiment, the metal ions are electrochemically inert within the operating voltage range of the lithium-ion battery. It should be understood that whether the metal ions are electrochemically inert depends on a variety of factors, such as the concentration of the metal ions, the type of metal ions, the influence of other substances in the electrolyte (e.g., electrolyte salts, solvents), the voltage of the lithium-ion battery, etc.

[0057] In the embodiments of the present application, the operating voltage range of the lithium-ion battery is generally 3.0V to 4.2V, and metal ions with a concentration range of 0.03M to 0.25M can stably exist in the electrolyte in ionic form within this voltage range, thereby improving / slowing down the release of lithium.

[0058] In one embodiment, the metal ion is K + .

[0059] Specifically, the Stokes radius of lithium ions is typically The Stokes radius of potassium ions is usually Potassium ions have a smaller Stokes radius than lithium ions and migrate faster in the electrolyte than lithium ions. As a result, potassium ions can more quickly move to the negative electrode sheet corresponding to a low CB value, or to areas of high local current density on the negative electrode sheet, quickly forming electrostatic shielding and steric hindrance, thereby improving / alleviating lithium deposition on the negative electrode sheet and helping to enhance the safety performance of lithium-ion batteries.

[0060] In one embodiment, the electrolyte further includes lithium ions, and the molar concentration of lithium ions in the electrolyte is C Li Meets: 0.8M≤C Li ≤1.2M.

[0061] Specifically, it can be 0.8M, 0.81M, 0.82M, 0.83M, 0.84M, 0.85M, 0.86M, 0.87M, 0.88M, 0.89M, 0.9M, 0.91M, 0.92M, 0.93M, 0.94M, 0.95M, 0.96M, 0.97M, 0.98M, 0.99M, 1M, 1.11M, 1.12M, 1.13M, 1.14M, 1.15M, 1.16M, 1.17M, 1.18M, ​​1.19M, 1.2M, or its value is within the range obtained by combining any two of the above values.

[0062] In the embodiments of the present application, the concentration of lithium ions is controlled within the range of 0.8M to 1.2M. At this lithium ion concentration, the concentration of metal ions is controlled within the range of 0.03M to 0.25M, so that the metal ions exist in the electrolyte as stable ions during the cycle of the lithium-ion battery, thereby achieving a uniform current density, inhibiting lithium plating from the negative electrode, and helping to improve the safety performance of the lithium-ion battery.

[0063] In one embodiment, the electrolyte includes an inorganic salt, the inorganic salt includes metal ions and anions; the anions include at least one of hexafluorophosphate ions, acetate ions, nitrate ions, and halogen ions.

[0064] Specifically, metal ions can be introduced by adding inorganic salts into the electrolyte.

[0065] In one embodiment, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0066] In one embodiment, the solvent includes a non-aqueous solvent, and the non-aqueous solvent includes a carbonate solvent. Optionally, the carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, and halogenated compounds of the above carbonates.

[0067] In another embodiment, the solvent may further include at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0068] In one embodiment, the electrolyte may further include additives, which may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the lithium-ion battery, such as additives that improve the overcharge performance of the lithium-ion battery, additives that improve the high temperature or low temperature performance of the lithium-ion battery, etc.

[0069] [Negative electrode]

[0070] The negative electrode sheet generally includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material.

[0071] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0072] 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 base layer and a metal layer formed on at least one surface of the polymer base material. 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 base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0073] 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.

[0074] In one embodiment, the negative electrode film 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).

[0075] In one embodiment, the negative electrode film 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.

[0076] In one embodiment, the negative electrode film layer further includes other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0077] 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 cold pressing, the negative electrode sheet is obtained.

[0078] [Positive electrode]

[0079] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0080] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0081] 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.).

[0082] 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 Mn 0.25 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 0.1 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.

[0083] In one embodiment, the positive electrode film 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.

[0084] In one embodiment, the positive electrode film 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.

[0085] 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 cold pressing, the positive electrode sheet can be obtained.

[0086] [Isolator]

[0087] 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.

[0088] 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.

[0089] The above describes the various components of the lithium-ion battery provided by the present application. Next, the lithium-ion battery involved in the present application is introduced.

[0090] [Lithium-ion battery]

[0091] The present application also provides a lithium-ion battery, which includes the electrolyte in any of the aforementioned embodiments.

[0092] By introducing the electrolyte of the embodiment of the present application into lithium ions, the current density on the surface of the negative electrode can be uniformly distributed through the metal ions in the electrolyte during the cycle of the lithium ion battery, thereby suppressing lithium deposition and improving the safety performance of the lithium ion battery.

[0093] In one embodiment, the CB value of the lithium-ion battery satisfies: 1.03≤CB≤1.2, where the CB value is the ratio of the capacity per unit area of ​​the negative electrode active material to the capacity per unit area of ​​the positive electrode active material.

[0094] Specifically, when designing the electrode, the CB value of the lithium-ion battery can be controlled within the range of 1.03 to 1.2 by selecting a negative electrode active material with higher capacity, increasing the loading of the active material on the negative electrode, etc. The CB value can be: 1.03, 1.04, 1.06, 1.08, 1.1, 1.12, 1.14, 1.16, 1.18, 1.2, or any value within the range obtained by combining any two of the above values.

[0095] On the one hand, when the CB value is greater than 1, the capacity of the negative electrode active material per unit area is greater than that of the positive electrode active material per unit area, and the negative electrode sheet has more lithium ion active sites, which improves the situation where lithium ions cannot be embedded in the negative electrode active material and lithium plating occurs. On the other hand, if the CB value is too large, more lithium ions will participate in the formation of the SEI film during the lithium-ion battery formation process, which is not conducive to the first cycle coulombic efficiency of the lithium-ion battery.

[0096] The present application controls the CB value of the lithium-ion battery within the range of 1.03 to 1.2, thereby enabling the lithium-ion battery to have a good coulombic efficiency while further reducing the risk of lithium plating on the negative electrode sheet.

[0097] It should be understood that although the CB value of lithium-ion batteries is designed to be 1.03 ≤ CB ≤ 1.2, as mentioned above, due to process and manufacturing limitations, low CB value regions (CB < 1) are unavoidable in lithium-ion batteries. The low CB value region corresponds to the area of ​​the negative electrode sheet with higher current density, making lithium deposition more likely during the cycling of the lithium-ion battery.

[0098] FIG1 is a schematic diagram showing the principle of suppressing lithium deposition in a lithium-ion battery according to an embodiment of the present application.

[0099] As shown in Figure 1, the negative electrode plate 1 includes a negative electrode current collector 11 and a negative electrode active material layer 12 disposed on the negative electrode current collector 11. After the lithium-ion battery is formed, the negative electrode plate 1 also includes a solid electrolyte interface (SEI) film 13 formed on the surface of the negative electrode active material layer 12. Region a is the area on the negative electrode plate corresponding to the low CB value region, and region b is the area outside the low CB value region.

[0100] In the embodiments of the present application, thanks to the metal ions in the electrolyte, they can move to the area on the negative electrode sheet corresponding to the low CB value area, or the area with higher current density on the negative electrode sheet, forming electrostatic shielding and steric hindrance, preventing lithium ions from enriching and then precipitating at this location, thereby inhibiting lithium deposition. In addition, the CB value of the lithium-ion battery is designed to be 1.03-1.2. In other words, the CB value of region b can reach 1.03-1.2, which can help accommodate lithium ions that cannot be accommodated in the area corresponding to the low CB value, further reducing the risk of lithium deposition.

[0101] It should be understood that the CB value of the lithium-ion battery is designed to be 1.03 to 1.2. This can be achieved by selecting suitable positive and negative active materials to achieve the desired gram capacity, controlling the coating weight of the positive and negative electrode sheets, etc. Once the lithium-ion battery is assembled, its CB value is a fixed value. Due to factors such as the manufacturing process, the CB value of different lithium-ion batteries may fluctuate, so the CB value of the lithium-ion battery is designed to be within a range of 1.03 to 1.2. In addition, due to the limitations of the coating process, even if the CB value is designed to be 1.03 to 1.2, there will still be low CB value areas with a CB value of less than 1 in some areas.

[0102] The low CB value region a in FIG1 is merely an example of a low CB value region, which illustrates the situation where the thickness of the negative active material layer 12 on the negative electrode sheet 1 is uneven, resulting in the low CB value region a at that location. FIG2 illustrates another example of forming the low CB value region a.

[0103] The positive electrode sheet 2 includes a positive current collector 21 and a positive active material layer 22 disposed on the positive current collector 21. When the thickness of the negative active material layer 12 is uniform, a thicker positive active material layer 22 may also cause this location to become a low CB value region a.

[0104] In another possible scenario, the thicknesses of the positive electrode active material layer and the negative electrode active material layer at a certain location are not uniform. For example, the positive electrode active material layer is thicker while the negative electrode active material layer is thinner, which may also cause the location to become a low CB value area a.

[0105] 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.

[0106] In one embodiment, a battery cell of a lithium-ion battery includes an outer packaging, which can be used to encapsulate the electrode assembly and the electrolyte.

[0107] In one embodiment, the outer packaging of the lithium-ion battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also 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.

[0108] The present application has no particular limitation on the shape of the battery cell of the lithium-ion battery, which can be cylindrical, square, or any other shape. For example, FIG3 shows a battery cell 300 of a lithium-ion battery with a square structure as an example.

[0109] 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 using fasteners. The multiple battery cells 300 may be of the same chemical system or of different chemical systems.

[0110] 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.

[0111] 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.

[0112] Figures 5 and 6 illustrate an example lithium-ion battery pack 500. Referring to Figures 5 and 6, the battery pack 500 may include a battery box and multiple battery modules 400 disposed within the battery 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.

[0113] It should be understood that the battery cells 300 can first be assembled into the battery module 400, and the battery pack 500 can be assembled from the battery module 400. Alternatively, the battery pack 500 can be directly assembled from the battery cells 300, omitting the intermediate form of the battery module 400.

[0114] In addition, the present application also provides an electrical device, which includes the lithium-ion battery in the aforementioned embodiment.

[0115] In another embodiment, an electrical device includes at least one of the battery cells 300, battery modules 400, or battery packs 500 provided herein. The battery cells 300, battery modules 400, or battery packs 500 can be used as a power source for the electrical device or as an energy storage unit for the electrical device. Electrical devices may include, but are 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.

[0116] As an electric device, the number of battery cells 300 , battery modules 400 , or battery packs 500 can be selected according to its usage requirements.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] [Examples 1-15 and Comparative Examples 1-2]

[0121] Example 1

[0122] (1) Preparation of negative electrode sheet

[0123] Dissolve 1 kg of artificial graphite (negative electrode active material), 10 g of acetylene black (conductive agent), 30 g of styrene-butadiene rubber (binder), and 20 g of sodium carboxymethyl cellulose (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 dried, rolled, and slit.

[0124] The amount of negative active material loaded on the negative electrode sheet, and thus the CB value of the negative electrode sheet, can be controlled by controlling the thickness of the coating slurry. For example, the amount of positive and negative electrode slurry applied by the coating equipment can be controlled so that the area of ​​the negative electrode sheet corresponding to the low CB value region accounts for 10% of the negative electrode sheet area after coating, the low CB value region corresponds to CB' = 0.9, and the other regions correspond to CB = 1.1.

[0125] It should be understood that the setting of the negative electrode sheet area corresponding to the low CB value region at 10% of the negative electrode sheet area in the Examples and Comparative Examples is intended solely to verify the effectiveness of the Examples and does not constitute a limitation on the low CB value region in lithium-ion batteries. In other words, a low CB value region does not necessarily exist in a lithium-ion battery, and the negative electrode sheet area corresponding to the CB value region does not necessarily account for 10% of the negative electrode sheet area.

[0126] (2) Preparation of positive electrode sheet

[0127] The positive electrode active material, LiNi5Co2Mn3O2 (1 kg), the conductive agent, carbon nanotubes (20 g), and the binder, polyvinylidene fluoride (20 g), were dissolved in 1 kg of N-methylpyrrolidone and mixed thoroughly to produce a positive electrode slurry. The slurry was then evenly coated onto the positive electrode current collector, aluminum foil. The positive electrode sheets were then dried, rolled, and slit.

[0128] (3) Preparation of electrolyte

[0129] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), the electrolyte was prepared by mixing organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) in a volume ratio of 1:1:1, and then adding 1M lithium hexafluorophosphate (LiPF6) and potassium hexafluorophosphate (KPF6) as an additive to make C M =0.1M, C Li =1M, and stir evenly to obtain the electrolyte.

[0130] (4) Preparation of lithium-ion batteries

[0131] The positive 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 is injected to obtain the lithium-ion battery of Example 1.

[0132] The above battery was formed under the following formation conditions: using a blue electric test system, the positive and negative electrodes were connected, and the battery was allowed to stand for 1 minute. The battery was then charged at a constant current of 0.1C to 4.2V, and then charged at a constant voltage of 4.2V with a cutoff current of 0.05C. The cumulative charge capacity X1 of the above process was recorded; then the battery was allowed to stand for 10 minutes, and discharged at a constant current of 0.1C with a cutoff voltage of 2.5V. The discharge capacity X2 was recorded, and the battery was allowed to stand for 48 hours.

[0133] Thus, the lithium ion battery prepared in Example 1 has a CB of 1.1 and a CB' of 0.9, and the metal ions in the electrolyte are K + , K + The molar concentration C in the electrolyte M =0.1M,Li + The molar concentration C in the electrolyte Li =1M.

[0134] Example 2

[0135] Compared with Example 1, in the electrolyte of Example 2, C M =0.03M.

[0136] Example 3

[0137] Compared with Example 1, in the electrolyte of Example 3, C M =0.05M.

[0138] Example 4

[0139] Compared with Example 1, in the electrolyte of Example 4, C M =0.15M.

[0140] Example 5

[0141] Compared with Example 1, in the electrolyte of Example 5, C M =0.2M.

[0142] Example 6

[0143] Compared with Example 1, in the electrolyte of Example 6, C M =0.25M.

[0144] Example 7

[0145] Compared with Example 1, the electrolyte of Example 7 is added with lithium hexafluorophosphate (CsPF6), and the metal ion is Cs + , C M =0.1M.

[0146] Example 8

[0147] Compared with Example 1, in the electrolyte of Example 8, CsPF6 and KPF6 are added at the same time, and the metal lithium ions in the electrolyte are K + and Cs + , the concentration of the two metal ions in the electrolyte C M =0.1 M.

[0148] Example 9

[0149] Compared with Example 1, in the electrolyte of Example 9, C Li =0.8M.

[0150] Example 10

[0151] Compared with Example 1, in the electrolyte of Example 10, C Li =1.2M.

[0152] Example 11

[0153] Compared with Example 1, in the lithium ion battery of Example 11, CB=1.03.

[0154] Example 12

[0155] Compared with Example 1, in the lithium ion battery of Example 12, CB=1.2.

[0156] Example 13

[0157] Compared with Example 1, in the lithium ion battery of Example 13, CB=1.3.

[0158] Example 14

[0159] Compared with Example 1, in the lithium ion battery of Example 14, CB'=0.8.

[0160] Example 15

[0161] Compared with Example 1, in the lithium ion battery of Example 15, CB'=0.95.

[0162] Comparative Example 1

[0163] Compared with Example 1, the aforementioned metal ions are not added to the electrolyte of Comparative Example 1.

[0164] Comparative Example 2

[0165] Compared with Example 1, in the electrolyte of Comparative Example 2, C M =0.01M.

[0166] The data in Table 1 can be obtained by performing performance tests on the batteries in the examples and comparative examples. The specific testing methods will be introduced later.

[0167] Product parameters of Examples 1-15 and Comparative Examples 1-2.

[0168] Table 1: Products and performance parameters of Examples 1-15 and Comparative Examples 1-2

[0169] In Table 1, “metal ion” represents the metal ion added to the electrolyte, “CB” represents the CB value corresponding to other regions outside the low CB value region of the lithium-ion battery, “CB'” represents the CB value corresponding to the low CB value region of the lithium-ion battery, and “C M " represents the molar concentration of metal ions in the electrolyte, "C Li " represents the molar concentration of lithium ions in the electrolyte, "ICE" represents the first-cycle coulombic efficiency of the lithium-ion battery, "capacity retention rate" represents the capacity retention rate obtained after the capacity retention rate test of the lithium-ion battery, and "S" represents the percentage of the area of ​​the lithium deposition area on the negative electrode piece to the area of ​​the negative electrode piece corresponding to the low CB value area after the lithium-ion battery is disassembled after the capacity retention rate test and full charge.

[0170] According to the examples and comparative examples in Table 1, by introducing metal ions with a molar concentration of 0.03M or above into the electrolyte, the examples all have smaller S values, that is, the examples can effectively suppress lithium deposition in the negative electrode sheet corresponding to the low CB value area, while the S value of the comparative example is larger, indicating that there are no metal ions in the electrolyte or the concentration of metal ions is too small to suppress lithium deposition in the negative electrode sheet area corresponding to the low CB value area. Thus, it is proved that metal ions can stably exist in the electrolyte and move freely to the location of the negative electrode sheet where the current density is uneven and lithium deposition is prone to occur, forming electrostatic shielding or steric hindrance, thereby effectively alleviating / improving lithium deposition in the negative electrode sheet and improving the safety performance of lithium-ion batteries.

[0171] According to the analysis and comparison of Examples 1-6, it can be seen that as the molar concentration of metal ions in the electrolyte increases, the S value becomes smaller, and the S value of Examples 4-6 is even closer to 0%, indicating that the higher the concentration of metal ions, the better the inhibitory effect on lithium precipitation. On the other hand, as the concentration of metal ions increases, the capacity retention rate of the lithium-ion battery decreases. The concentration of metal ions has a certain effect on the direct current resistance (DCR) of the lithium-ion battery. The higher the concentration, the greater the DCR, which makes the capacity retention rate of the lithium-ion battery lower. Thus, it is shown that by controlling the concentration of metal ions in the range of 0.03M to 0.25M, it is also possible to take into account the capacity retention rate of the lithium-ion battery while suppressing lithium precipitation.

[0172] According to the analysis and comparison of Examples 1 and 7-8, in addition to potassium ions, the metal ions in the electrolyte can also be cesium ions, or potassium ions and cesium ions, which can also effectively inhibit lithium precipitation and play a similar role. Under the same other conditions, the S value of Example 1 is less than the S value of Example 7, indicating that potassium ions have a better inhibitory effect on lithium precipitation, and prove that potassium ions can move faster to the negative electrode sheet corresponding to the low CB value area or the position with a larger current density on the negative electrode sheet due to their smaller Stokes radius, thereby playing the role of electrostatic shielding or steric hindrance, thereby better uniforming the current density and suppressing lithium precipitation.

[0173] According to the analysis and comparison of Examples 1, 9-10, when the concentration of metal ions in the electrolyte remains unchanged, the higher the concentration of lithium ions in the electrolyte, the larger the S value. In other words, the inhibitory effect of metal ions on lithium precipitation weakens as the concentration of lithium ions increases. This shows that the metal ion concentration in the electrolyte can be designed to match the corresponding lithium ion concentration. For example, increasing the concentration of metal ions in an electrolyte with a higher lithium ion concentration can achieve a better improvement / inhibition of lithium precipitation.

[0174] According to the analysis and comparison of Examples 1 and 11-13, it can be seen that as the CB value of the lithium-ion battery increases, the S value decreases, and the S value of Example 13 is even closer to 0. This shows that when the metal ion concentration is constant, the larger the CB value, the better the effect of improving / suppressing lithium precipitation. It further shows that by designing with a large CB value of metal ions, it is helpful to further improve / suppress lithium precipitation and improve the safety and charging performance of lithium-ion batteries. On the other hand, as the CB value of the lithium-ion battery increases, the ICE of the lithium-ion battery decreases, which shows that the CB value of the lithium-ion battery cannot be designed to be too large. Therefore, it is shown that by controlling the CB value of the lithium-ion battery within a larger range and matching it with metal ions of appropriate concentration, it is possible to effectively suppress lithium precipitation while taking into account the ICE of the lithium-ion battery.

[0175] According to the analysis and comparison of Examples 1 and 14-15, it can be seen that regardless of the CB value of the low CB value area, the metal ions can improve / inhibit lithium plating of the negative electrode sheet corresponding to the area. Moreover, when the concentration of metal ions is constant, the higher the CB value of the low CB value area, the lower the S value. This shows that the larger the CB value of the low CB value area, the more lithium ions the area can accommodate, which helps to reduce the number of lithium ions that cannot be embedded in the negative electrode, that is, to reduce the number of lithium ions that can be enriched and then precipitated, thereby reducing the S value. It should be understood that the CB' in the examples and comparative examples is artificially set to verify the experimental results. In actual production, the low CB value area is generated due to the limitations of the process and manufacturing process, and its specific CB value may not be artificially controlled, but the area size of the low CB value area can be measured by testing means. Therefore, the concentration of metal ions in the electrolyte can also be adjusted according to the size of the low CB value area in the lithium-ion battery. For example, in a lithium-ion battery with a larger low CB value area, the concentration of metal ions is appropriately increased.

[0176] The following is a brief introduction to the test methods for the physical and chemical parameters and performance parameters involved in the embodiments of this 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.

[0177] 1. CB value test method

[0178] According to the embodiments of the present application, the reversible capacity test of the negative electrode is determined by the following steps: take a single-sided coated negative electrode sheet and cut it into a disc with a diameter of 14 mm. Assemble a button cell in a glove box, wherein a small lithium metal disc is used as the counter electrode and the electrolyte prepared above is used. After standing at 25°C for 6 hours, discharge at a constant current rate of 0.1C to 5mV, then discharge at a constant current rate of 0.01C to 5mV, then stand for 5 minutes, and charge at a constant current rate of 0.1C to 0.7V. The charging capacity is recorded as Ca in mAh.

[0179] According to the embodiments of the present application, the reversible capacity test of the positive electrode can be determined by the following steps: take a single-sided coated positive electrode sheet and cut it into a disc with a diameter of 14 mm. Assemble a button cell in a glove box, wherein a small lithium metal disc is used as the counter electrode and the electrolyte prepared as described above is used. After standing at 25°C for 6 hours, charge to 4.25V at a constant current rate of 0.1C, then charge to 4.25V at a constant current rate of 0.05C, then stand for 5 minutes, and discharge to 2.8V at a constant current rate of 0.1C. The discharge capacity is recorded as Cc in mAh.

[0180] The CB value of a battery can be calculated using the formula CB = Ca / Cc, where Ca is the charge capacity obtained through the negative electrode reversible capacity test, and Cc is the discharge capacity obtained through the positive electrode reversible capacity test.

[0181] It should be understood that the capacity of a specified area of ​​each positive and negative electrode can be measured separately to calculate the CB value of the specified area. In areas where the CB value is less than 1, lithium deposition will occur on the negative electrode during the test. Therefore, by testing the capacity of the positive and negative electrode sheets and observing where lithium deposition occurs on the negative electrode sheet, the corresponding low CB value area can be determined. The area corresponding to the low CB value area can then be calculated based on the fitting.

[0182] 2. Molar concentration test method

[0183] The molar concentration of metal ions in the electrolyte can be determined by various methods such as titration, electrochemical analysis, spectrophotometry, and inductively coupled plasma.

[0184] For example, the ICP (Inductively coupled plasma) testing method process is as follows: the sample to be tested is digested with aqua regia (concentrated hydrochloric acid: concentrated nitric acid = 3:1) or reverse aqua regia (concentrated nitric acid: concentrated hydrochloric acid 3:1) and then the element content is measured using an ICP tester.

[0185] 3. Test method for the first cycle coulombic efficiency of lithium-ion batteries

[0186] As mentioned above, during the formation process of the lithium-ion battery, the charge capacity X1 and discharge capacity X2 of the lithium-ion battery are recorded respectively. The first cycle coulombic efficiency ICE of the lithium-ion battery is = X2 / X1×100%.

[0187] 4. Capacity retention test

[0188] Using the Blue Electric test system, the formed lithium-ion battery was allowed to stand for 10 minutes, then charged at a constant current of 0.33C with a cut-off voltage of 4.2V, and then charged at a constant voltage at 4.2V with a cut-off current of 0.05C; then, after standing for 10 minutes, discharged at a constant current of 0.1C with a cut-off voltage of 2.5V, and the discharge capacity at this time was recorded as Y1; after standing for 10 minutes, then charged at a constant current of 0.33C with a cut-off voltage of 4.2V, and then charged at a constant voltage at 4.2V with a cut-off current of 0.05C; then, after standing for 10 minutes, discharged at a constant current of 4C with a cut-off voltage of 2.5V, and the discharge capacity at this time was recorded as Y2. The capacity retention rate of the lithium-ion battery = Y2 / Y1×100%.

[0189] 5. Lithium deposition test

[0190] After the capacity retention rate test, the lithium-ion battery is allowed to stand for 10 minutes, and then charged at a constant current of 0.33C with a cut-off voltage of 4.2V. Then, it is charged at a constant voltage of 4.2V with a cut-off current of 0.05C. The fully charged lithium-ion battery is disassembled to observe whether the negative electrode corresponding to the low CB value area is lithium-deposited. The percentage S of the area of ​​the lithium-deposited area and the area of ​​the negative electrode area corresponding to the low CB value area can be obtained by fitting calculation. Alternatively, the negative electrode obtained after disassembly is photographed. The graphite area on the negative electrode is golden yellow, and the lithium-deposited area is silver. The color difference is identified by a computer, and the area ratio of the silver area in the area corresponding to the low CB value is obtained, and the area ratio S of the lithium-deposited area can be calculated.

[0191] 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 comprises: Metal ions, the metal ions comprising K + , Rb + , Cs + At least one of; The molar concentration of the metal ion in the electrolyte is C M Satisfy: 0.03M≤C M .

2. The electrolyte according to claim 1, characterized in that 0.03M≤C M ≤0.25M; optionally, 0.05M≤C M ≤0.15M.

3. The electrolyte according to claim 1 or 2, characterized in that The metal ions are electrochemically inert within the operating voltage range of the lithium ion battery.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The metal ions include K + .

5. The electrolyte according to any one of claims 1 to 4, characterized in that The electrolyte also includes lithium ions, and the molar concentration of the lithium ions in the electrolyte is C Li Satisfy: 0.8M≤C Li ≤1.2M.

6. The electrolyte according to any one of claims 1 to 5, characterized in that The electrolyte includes an inorganic salt, and the inorganic salt includes the metal ion and an anion; The anions include at least one of hexafluorophosphate, tetrafluoroborate, perchlorate, nitrate, carbonate, bistrifluoromethylsulfonyl imide, trifluoromethanesulfonate, difluorooxalatoborate, dioxalatoborate, methanesulfonate, and halogen anions.

7. The electrolyte according to any one of claims 1 to 6, characterized in that The electrolyte includes a solvent, and the solvent includes a non-aqueous solvent; optionally, the solvent includes a carbonate solvent.

8. The electrolyte according to claim 7, characterized in that The carbonate solvent includes: at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate and halogenated products of the above carbonates.

9. A lithium ion battery, characterized in that: The lithium-ion battery comprises the electrolyte according to any one of claims 1 to 8.

10. The lithium ion battery according to claim 9, characterized in that: The CB value of the lithium-ion battery satisfies: 1.03≤CB≤1.2, and the CB value is the ratio of the capacity of the negative electrode active material per unit area to the capacity of the positive electrode active material per unit area.

11. The lithium ion battery according to claim 9 or 10, characterized in that: The lithium-ion battery comprises a negative electrode plate, the negative electrode plate comprises a negative electrode active material, and the negative electrode active material comprises graphite.

12. An electrical device, characterized in that: The electrical device comprises a lithium-ion battery as claimed in any one of claims 9 to 11.

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