Electrolyte, lithium ion battery and electric device

Abstract

The embodiment of the invention discloses an electrolyte, a lithium ion battery and a power utilization device, the electrolyte comprises metal ions, and the metal ions comprise at least one of K < + >, Rb < + > and Cs < + >; and the molar concentration CM of the metal ions in the electrolyte satisfies 0.03 M < = CM. When the electrolyte is applied to the lithium ion battery, the risk of lithium precipitation of a negative electrode can be effectively reduced, and the safety performance of the lithium ion battery is improved.

Description

Technical Field

[0001] 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

[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] 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. Summary of the invention

[0004] The present 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 deposition in the negative electrode sheet and improve the safety performance of the lithium-ion battery.

[0005] In a first aspect, an electrolyte is provided, the electrolyte comprising: metal ions, the metal ions comprising K + , Rb + , Cs + At least one of; the molar concentration of the metal ion in the electrolyte C M Satisfy: 0.03M≤C M .

[0006] 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 of the negative electrode sheet where the current density 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.

[0007] In a possible implementation, optionally, 0.03M≤C M ≤0.25M; 0.05M≤C M ≤0.15M.

[0008] 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 the form of ions, thereby effectively alleviating / improving lithium deposition on the negative electrode sheet. In addition, by controlling the concentration of metal ions within a suitable range, the lithium-ion battery can also have a good capacity retention rate.

[0009] In a possible implementation, the metal ions are electrochemically inert within an operating voltage range of the lithium-ion battery.

[0010] In one possible implementation, the metal ions include K + .

[0011] In an 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 locations on the negative electrode sheet where the current density is uneven and lithium deposition is likely to occur, effectively making the current density on the negative electrode sheet uniform and improving the efficiency of electrostatic shielding.

[0012] In a possible implementation, the electrolyte further includes lithium ions, and the molar concentration C of the lithium ions in the electrolyte is Li Satisfy: 0.8M≤C Li ≤1.2M.

[0013] In a possible implementation, the electrolyte includes an inorganic salt, and the inorganic salt includes the metal ions and anions; the anions include at least one of hexafluorophosphate, tetrafluoroborate, perchlorate, nitrate, carbonate, bistrifluoromethylsulfonyl imide, trifluoromethanesulfonate, difluorooxalatoborate, dioxalatoborate, methanesulfonate, and halogen anions.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] In a possible implementation, 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.

[0018] In the embodiment 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 precipitation is prone to occur, thereby inhibiting lithium precipitation. Considering that the electrostatic shielding effect of the metal ions may also affect the electrochemical reaction rate at this 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 on the negative electrode plate is greater than the capacity of the positive electrode active material per unit area on 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 negative electrode plate's capacity to accommodate lithium ions. Therefore, the electrolyte including metal ions in the lithium-ion battery combined with the design of a large CB value helps to further reduce the risk of lithium precipitation in the low CB value area of ​​the negative electrode plate and improve the safety performance of the lithium-ion battery.

[0019] 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.

[0020] In a third aspect, an electrical device is provided, wherein the electrical device comprises a lithium-ion battery according to any possible implementation of the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] 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.

[0022] Figure 1 A schematic diagram of a method for inhibiting lithium deposition in lithium-ion batteries.

[0023] Figure 2 A schematic diagram of a low CB value region.

[0024] Figure 3 A schematic diagram of a battery cell.

[0025] Figure 4 A schematic diagram of a battery module.

[0026] Figure 5 A schematic diagram of a battery.

[0027] Figure 6 Another schematic diagram of a battery. DETAILED DESCRIPTION

[0028] Hereinafter, the embodiments of the lithium-ion battery and the electrical device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there 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.

[0029] "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.

[0030] 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.

[0031] If not otherwise specified, in this application, 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).

[0032] 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.

[0033] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0034] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their generally accepted meanings in the art.

[0035] As mentioned, "Stokes radius" refers to the ratio of the drag coefficient of a particle in a fluid to the particle radius when it moves in a Newtonian fluid. It is also called the effective radius of the particle in a solution, or the solvated ion radius. The larger the Stokes radius of a particle, the greater the drag it encounters when moving in the fluid, and the weaker its migration ability.

[0036] As mentioned, "CB (Cell balance) value" refers to the ratio of the negative electrode capacity to the positive electrode capacity on the opposite side 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.

[0037] 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.

[0038] Where mentioned, "non-aqueous solvent" refers to solvents other than water, for example, organic solvents, supercritical fluids, ionic liquids, and the like.

[0039] If mentioned, "carbonate solvents" refer to organic solvents containing carbonate groups (-OCO-O-) in their molecular structures. For example, cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), and chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0040] Next, embodiments of the present application are introduced.

[0041] 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.

[0042] 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 being embedded and released 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, moved to the negative electrode through the conduction of the electrolyte and embedded in the negative electrode active material; and during the discharge process, lithium ions are released from the negative electrode active material, moved to the positive electrode through the conduction of the electrolyte and embedded in the positive electrode active material.

[0043] 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.

[0044] In the production process of lithium-ion batteries, it is necessary to apply a slurry containing active materials to the current collector to form a pole piece. Due to the limitations of the coating process, the different drying speeds of the slurry at different positions on the pole piece after coating, etc., it is usually impossible to obtain a pole piece with completely uniform thickness. This makes the gram capacity of some areas on the negative pole piece lower than the gram capacity of the corresponding area on the positive pole piece, causing the CB value of this area to be less than 1, that is, a low CB value area appears in the lithium-ion battery. In addition, during the use of lithium-ion batteries, factors such as uneven temperature inside the lithium-ion battery can cause uneven current density on the pole piece. At the position of the negative pole piece corresponding to the low CB value area or the area with a larger current density on the negative pole piece, the state of charge (SOC) of the negative pole piece will first reach saturation, resulting in a more negative local electric field, which is easier to attract positively charged ions, such as lithium ions. Because the state of charge at this position is already saturated, it cannot accommodate more lithium ions to be embedded, which leads to the enrichment and precipitation of lithium ions at this position. In other words, it will cause lithium precipitation, which will have an adverse effect on the safety performance of lithium-ion batteries.

[0045] 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 plate. The electrolyte is applied to the lithium-ion battery to reduce the risk of lithium plating on the negative electrode plate and improve the safety performance of the lithium-ion battery.

[0046] 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.

[0047] [Electrolyte]

[0048] 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. The electrolyte usually includes electrolyte salt and solvent.

[0049] First, the present application provides an electrolyte, which includes metal ions, wherein the metal ions include K + , Rb + , Cs + At least one of; the molar concentration of metal ions in the electrolyte C M Satisfy: 0.03M≤C M ; Optionally, 0.03M≤C M ≤0.25M; optionally, 0.05M≤C M ≤0.15M.

[0050] 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.

[0051] In the embodiments of the present application, the metal ions in the electrolyte can move freely to the negative electrode plate. As mentioned above, at the negative electrode plate corresponding to the low CB value, or at the position with a larger current density on the negative electrode plate, the state of charge (SOC) of the negative electrode plate 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 embodiments 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 precipitate. As a result, the metal ions can effectively even out the current density of the negative electrode plate, inhibit lithium precipitation, and help improve the safety performance of lithium-ion batteries.

[0052] Furthermore, by controlling the concentration of metal ions within the range of 0.03M to 0.25M, the effect of metal ions on electrolyte viscosity can be reduced, thereby reducing the effect of metal ions on the DC impedance of lithium-ion batteries, thereby improving lithium deposition and enabling lithium-ion batteries to have good capacity retention.

[0053] In one embodiment, the metal ion is electrochemically inert in the operating voltage range of the lithium ion battery. It should be understood that whether the metal ion is electrochemically inert depends on a variety of factors, such as the concentration of the metal ion, the type of the metal ion, the influence of other substances in the electrolyte (such as electrolyte salts, solvents), the voltage of the lithium ion battery, etc.

[0054] 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.

[0055] In one embodiment, the metal ion is K + .

[0056] Specifically, the Stokes radius of lithium ions is usually The Stokes radius of potassium ions is usually The Stokes radius of potassium ions is smaller than that of lithium ions, and they have a faster migration rate in the electrolyte than lithium ions. Therefore, potassium ions can move faster to the negative electrode sheet corresponding to the low CB value, or to the area with a large local current density of the negative electrode sheet, and quickly form electrostatic shielding and steric hindrance, thereby improving / alleviating lithium deposition on the negative electrode sheet and helping to improve the safety performance of lithium-ion batteries.

[0057] In one embodiment, the electrolyte further includes lithium ions, and the molar concentration of lithium ions in the electrolyte is C Li Satisfy: 0.8M≤C Li ≤1.2M.

[0058] 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.

[0059] 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, which plays a role in uniform current density, inhibiting lithium deposition on the negative electrode sheet, and helping to improve the safety performance of the lithium ion battery.

[0060] In one embodiment, the electrolyte includes an inorganic salt, and the inorganic salt includes metal ions and anions; the anions include at least one of hexafluorophosphate ions, acetate ions, nitrate ions, and halogen ions.

[0061] Specifically, metal ions can be introduced by adding inorganic salts into the electrolyte.

[0062] In one embodiment, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethanesulfonyl imide), lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0063] 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, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate and halogenated products of the above carbonates.

[0064] 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 sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0065] 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.

[0066] [Negative electrode]

[0067] 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.

[0068] 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 any one or both of the two opposite surfaces of the negative electrode current collector.

[0069] 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.).

[0070] 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.

[0071] 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).

[0072] 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.

[0073] In one embodiment, the negative electrode film layer further includes other additives, such as a thickener (eg sodium carboxymethyl cellulose (CMC-Na)).

[0074] 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, cold pressing and other processes, the negative electrode sheet can be obtained.

[0075] [Positive electrode]

[0076] 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.

[0077] 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 any one or both of the two opposite surfaces of the positive electrode current collector.

[0078] 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.).

[0079] 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 LiNi1 / 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 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.

[0080] 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), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0081] 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.

[0082] 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, cold pressing and other processes, the positive electrode sheet can be obtained.

[0083] [Isolator]

[0084] 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.

[0085] 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.

[0086] 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.

[0087] [Lithium-ion battery]

[0088] The present application also provides a lithium-ion battery, which includes the electrolyte in any of the aforementioned embodiments.

[0089] By introducing the electrolyte in the embodiment of the present application into lithium ions, the current density on the surface of the negative electrode plate can be uniformly distributed through the metal ions in the electrolyte during the cycle of the lithium ion battery, thereby inhibiting lithium deposition and improving the safety performance of the lithium ion battery.

[0090] 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 of the negative electrode active material per unit area to the capacity of the positive electrode active material per unit area.

[0091] Specifically, when designing the pole piece, 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 a higher capacity, increasing the loading amount of the active material on the negative electrode pole piece, 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 a value within the range obtained by combining any two of the above values.

[0092] 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 the capacity of the positive electrode active material per unit area, and there are more lithium ion active sites on the negative electrode sheet, which improves the situation where lithium ions cannot be embedded in the negative electrode active material and lithium precipitation occurs. On the other hand, when the CB value is too large, more lithium ions will participate in the formation of the SEI film during the formation of the lithium-ion battery, which is not conducive to the first-cycle coulomb efficiency of the lithium-ion battery.

[0093] 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 in the negative electrode sheet.

[0094] 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 the limitations of technology and process, a low CB value area of ​​CB<1 will inevitably appear in lithium-ion batteries. The area of ​​the negative electrode sheet corresponding to the low CB value area has a higher current density, and lithium deposition is more likely to occur during the cycle of the lithium-ion battery.

[0095] Figure 1 A schematic diagram of the principle of suppressing lithium deposition in a lithium-ion battery provided in an embodiment of the present application.

[0096] like Figure 1 As shown, 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 region on the negative electrode plate corresponding to the low CB value region, and region b is other regions outside the low CB value region.

[0097] In the embodiment 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 precipitation. 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 area 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 precipitation.

[0098] It should be understood that the CB value of the lithium-ion battery is designed to be 1.03-1.2. 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 1.03-1.2. In addition, due to the limitations of the coating process, even if the CB value is designed to be 1.03-1.2, there will still be low CB value areas with CB values ​​less than 1 in some areas.

[0099] Figure 1 The low CB value area a in the figure is only an example of a low CB value area, which shows the situation that the thickness of the negative electrode active material layer 12 on the negative electrode plate 1 is uneven, resulting in the low CB value area a at this position. Figure 2 Another example of forming the low CB value region a is shown.

[0100] 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, the thickness of the positive active material layer 22 is relatively thick, which will also cause this position to become a low CB value area a.

[0101] In another possible situation, the thickness of the positive electrode active material layer and the negative electrode active material layer at a certain position 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 position to become a low CB value area a.

[0102] 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.

[0103] In one embodiment, a battery cell of a lithium-ion battery includes an outer package, which can be used to encapsulate the electrode assembly and the electrolyte.

[0104] In one embodiment, the outer packaging of the battery cell of the lithium-ion battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0105] The present application has no particular restrictions on the shape of the battery cell of the lithium-ion battery, which can be cylindrical, square or any other shape. For example, Figure 3 The battery cell 300 is a lithium-ion battery having a square structure as an example.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] Figure 5 and Figure 6 2 is a battery pack 500 of a lithium-ion battery as an example. Figure 5 and Figure 6 The battery pack 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.

[0110] It should be understood that the battery cells 300 may first form the battery module 400, and the battery pack 500 may be formed by the battery module 400. Alternatively, the battery pack 500 may be directly formed by the battery cells 300, omitting the intermediate form of the battery module 400.

[0111] In addition, the present application also provides an electrical device, which includes the lithium-ion battery in the aforementioned embodiment.

[0112] In another embodiment, the power-consuming device includes at least one of the battery cell 300, battery module 400, or battery pack 500 provided in the present application. The battery cell 300, battery module 400, or battery pack 500 can be used as a power source for the power-consuming device, or as an energy storage unit for the power-consuming device. The power-consuming 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 is not limited thereto.

[0113] As an electric device, the number of battery cells 300 , battery modules 400 , or battery packs 500 may be selected according to the usage requirements.

[0114] 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.

[0115] 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 light and thin, and a secondary battery may be used as a power source.

[0116] 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.

[0117] [Examples 1-15 and Comparative Examples 1-2]

[0118] Example 1

[0119] (1) Preparation of negative electrode sheet

[0120] The negative electrode active material artificial graphite (1kg), the conductive agent acetylene black (10g), the binder styrene butadiene rubber (30g), and the thickener sodium carboxymethyl cellulose (20g) were dissolved in the solvent deionized water (1kg), and mixed evenly to obtain the negative electrode slurry. Then the negative electrode slurry was evenly coated on the negative electrode current collector copper foil. After drying, rolling, and cutting, the negative electrode sheet was obtained.

[0121] The amount of negative electrode active material loaded on the negative electrode sheet can be controlled by controlling the thickness of the coating slurry, thereby controlling the CB value of the negative electrode sheet. For example, the amount of positive and negative electrode slurry coated by the coating equipment can be controlled so that the area of ​​the negative electrode sheet corresponding to the low CB value area in the negative electrode sheet after coating accounts for 10% of the area of ​​the negative electrode sheet, the CB' corresponding to the low CB value area is 0.9, and the CB corresponding to other areas is 1.1.

[0122] It should be understood that the area of ​​the negative electrode sheet corresponding to the low CB value region in the embodiment and the comparative example is controlled to account for 10% of the area of ​​the negative electrode sheet only for verifying the effect of the embodiment, and does not constitute a limitation on the low CB value region in the lithium-ion battery. In other words, there is not necessarily a low CB value region in the lithium-ion battery, and the area of ​​the negative electrode sheet corresponding to the CB value region does not necessarily account for 10% of the area of ​​the negative electrode sheet.

[0123] (2) Preparation of positive electrode sheet

[0124] The positive electrode active material LiNi5Co2Mn3O2 (1kg), the conductive agent carbon nanotube (20g), and the binder polyvinylidene fluoride (20g) were dissolved in the solvent N-methylpyrrolidone (1kg), and mixed evenly to obtain the positive electrode slurry. Then the positive electrode slurry was evenly coated on the positive electrode current collector aluminum foil. After drying, rolling, and cutting, the positive electrode sheet was obtained.

[0125] (3) Preparation of electrolyte

[0126] 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 an additive potassium hexafluorophosphate (KPF6) to make C M =0.1M, C Li =1M, stir evenly to obtain the electrolyte.

[0127] (4) Preparation of lithium-ion batteries

[0128] The positive electrode sheet, the isolation film, and the negative electrode sheet are stacked in order so that the isolation film 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 up and placed in a shell, and after drying, the electrolyte is injected to obtain the lithium-ion battery of Example 1.

[0129] The above battery was formed under the following specific formation conditions: using a blue power test system, the positive and negative electrodes were connected, left to stand for 1 minute, charged to 4.2V at a constant current of 0.1C, then charged at a constant voltage of 4.2V with a cut-off current of 0.05C, and the cumulative charging capacity X1 of the above process was recorded; then left to stand for 10 minutes, discharged at a constant current of 0.1C with a cut-off voltage of 2.5V, the discharge capacity X2 was recorded, and left to stand for 48 hours.

[0130] Thus, the CB of the lithium ion battery prepared in Example 1 is 1.1, CB' is 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.

[0131] Example 2

[0132] Compared with Example 1, in the electrolyte of Example 2, C M =0.03M.

[0133] Example 3

[0134] Compared with Example 1, in the electrolyte of Example 3, C M =0.05M.

[0135] Example 4

[0136] Compared with Example 1, in the electrolyte of Example 4, C M =0.15M.

[0137] Example 5

[0138] Compared with Example 1, in the electrolyte of Example 5, C M =0.2M.

[0139] Example 6

[0140] Compared with Example 1, in the electrolyte of Example 6, C M =0.25M.

[0141] Example 7

[0142] Compared with Example 1, lithium hexafluorophosphate (CsPF6) is added to the electrolyte of Example 7, and the metal ion is Cs + , C M =0.1M.

[0143] Example 8

[0144] 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 =0.1M.

[0145] Example 9

[0146] Compared with Example 1, in the electrolyte of Example 9, C Li =0.8M.

[0147] Example 10

[0148] Compared with Example 1, in the electrolyte of Example 10, C Li =1.2M.

[0149] Embodiment 11

[0150] Compared with Example 1, in the lithium ion battery of Example 11, CB=1.03.

[0151] Example 12

[0152] Compared with Example 1, in the lithium ion battery of Example 12, CB=1.2.

[0153] Example 13

[0154] Compared with Example 1, in the lithium ion battery of Example 13, CB=1.3.

[0155] Embodiment 14

[0156] Compared with Example 1, in the lithium ion battery of Example 14, CB'=0.8.

[0157] Embodiment 15

[0158] Compared with Example 1, in the lithium ion battery of Example 15, CB'=0.95.

[0159] Comparative Example 1

[0160] Compared with Example 1, the aforementioned metal ions are not added to the electrolyte of Comparative Example 1.

[0161] Comparative Example 2

[0162] Compared with Example 1, in the electrolyte of Comparative Example 2, C M =0.01M.

[0163] The data in Table 1 can be obtained by performing performance tests on the batteries in the embodiments and comparative examples. The specific test methods will be introduced later.

[0164] Product parameters of Examples 1-15 and Comparative Examples 1-2.

[0165] Table 1: Products and performance parameters of Examples 1-15 and Comparative Examples 1-2 Metal ions <![CDATA[C M (M)]]> <![CDATA[C Li (M)]]> CB CB' S ICE Capacity retention rate Example 1 <![CDATA[K + ]]> 0.1 1 1.1 0.9 7％ 90.4％ 82.0％ Example 2 <![CDATA[K + ]]> 0.03 1 1.1 0.9 46％ 90.8％ 88.0％ Example 3 <![CDATA[K + ]]> 0.05 1 1.1 0.9 18％ 90.3％ 84.6％ Example 4 <![CDATA[K + ]]> 0.15 1 1.1 0.9 ～0％ 90.2％ 78.7％ Example 5 <![CDATA[K + ]]> 0.2 1 1.1 0.9 ～0％ 90.4％ 70.1％ Example 6 <![CDATA[K + ]]> 0.25 1 1.1 0.9 ～0％ 89.9％ 62.3％ Example 7 <![CDATA[Cs + ]]> 0.1 1 1.1 0.9 18％ 91.0％ 79.4％ Example 8 <![CDATA[K + &Cs + ]]> 0.1&0.1 1 1.1 0.9 0％ 90.6％ 72.4％ Example 9 <![CDATA[K + ]]> 0.1 0.8 1.1 0.9 5％ 90.3％ 71.17％ Example 10 <![CDATA[K + ]]> 0.1 1.2 1.1 0.9 13％ 90.4％ 76.3％ Embodiment 11 <![CDATA[K + ]]> 0.1 1 1.03 0.9 37％ 91.8％ 80.9％ Example 12 <![CDATA[K + ]]> 0.1 1 1.2 0.9 8％ 89.5％ 83.1％ Example 13 <![CDATA[K + ]]> 0.1 1 1.3 0.9 ～0％ 86.5％ 83.2％ Embodiment 14 <![CDATA[K + ]]> 0.1 1 1.1 0.8 52％ 90.7％ 81.5％ Embodiment 15 <![CDATA[K + ]]> 0.1 1 1.1 0.95 ～0％ 90.0％ 81.7％ Comparative Example 1 / / 1 1.1 0.9 90％ 90.2％ 89.5％ Comparative Example 2 <![CDATA[K + ]]> 0.01 1 1.1 0.9 88％ 90.1％ 89.1％

[0166] 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 coulomb 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 plate to the area of ​​the negative electrode plate corresponding to the low CB value area after the lithium-ion battery is disassembled after the capacity retention rate test and full charge.

[0167] According to the embodiments and comparative examples in Table 1, by introducing metal ions with a molar concentration of 0.03M or more into the electrolyte, the embodiments all have a smaller S value, that is, the embodiments can effectively suppress the lithium precipitation of 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 the lithium precipitation of 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 where the current density of the negative electrode sheet is uneven and lithium precipitation is prone to occur, forming electrostatic shielding or steric hindrance, thereby effectively alleviating / improving the lithium precipitation of the negative electrode sheet and improving the safety performance of lithium-ion batteries.

[0168] 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 lithium-ion batteries decreases. The concentration of metal ions has a certain effect on the direct current resistance (DCR) of lithium-ion batteries. The higher the concentration, the greater the DCR, which makes the capacity retention rate of lithium-ion batteries 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 lithium-ion batteries while suppressing lithium precipitation.

[0169] According to the analysis and comparison of Examples 1, 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, proving 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, playing the role of electrostatic shielding or steric hindrance, thereby better uniforming the current density and inhibiting lithium precipitation.

[0170] 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 greater 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 with 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.

[0171] According to the analysis and comparison of Examples 1, 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 the design of metal ions with large CB values ​​can help 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, indicating 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.

[0172] According to the analysis and comparison of Examples 1, 14-15, it can be seen that regardless of the CB value of the low CB value zone, the metal ions can improve / inhibit the lithium precipitation of the negative electrode sheet corresponding to the region. Moreover, when the concentration of metal ions is constant, the higher the CB value of the low CB value zone, the lower the S value. It shows that the larger the CB value of the low CB value zone, the more lithium ions that can be accommodated in the region, 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, so that the S value decreases. It should be understood that the CB' in the embodiments and comparative examples is artificially set to verify the experimental effect. In actual production, the low CB value zone is generated due to the limitations of the process and process, and its specific CB value may not be artificially controlled, but the area size of the low CB value zone can be measured by testing means. Thus, the concentration of metal ions in the electrolyte can also be adjusted according to the size of the low CB value zone in the lithium ion battery. For example, in a lithium ion battery with a large low CB value zone, the concentration of metal ions is appropriately increased.

[0173] The following is a brief introduction to the test methods of 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 may also be used for testing.

[0174] 1. CB value test method

[0175] According to the embodiments of the present application, the reversible capacity test of the negative electrode is determined by the following steps: Take the negative electrode plate coated on one side and cut it into a disc with a diameter of 14 mm. Assemble button cells in a glove box, in which a small lithium metal disc is used as the counter electrode, and use the electrolyte prepared as described above. After standing for 6 hours at 25°C, 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.

[0176] 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 button cells in a glove box, in which 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.

[0177] The CB value of the battery can be calculated according to the formula CB = Ca / Cc, where Ca is the charge capacity obtained by the negative electrode reversible capacity test, and Cc is the discharge capacity obtained by the positive electrode reversible capacity test.

[0178] It should be understood that the capacity of the specified area of ​​the positive electrode sheet and the negative electrode sheet can be measured separately to calculate the CB value of the specified area. In the area where the CB value is less than 1, lithium deposition will occur on the negative electrode sheet during the test. Therefore, the corresponding low CB value area can be determined by testing the capacity of the positive and negative electrode sheets and observing where lithium deposition occurs on the negative electrode sheet, and then the area size corresponding to the low CB value area can be obtained according to the fitting calculation.

[0179] 2. Molar concentration test method

[0180] 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.

[0181] Exemplarily, 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.

[0182] 3. Test method for first cycle coulombic efficiency of lithium-ion batteries

[0183] As mentioned above, during the formation process of the lithium-ion battery, the charging capacity X1 and the discharging capacity X2 of the lithium-ion battery are recorded respectively, and the first cycle coulomb efficiency ICE of the lithium-ion battery is = X2 / X1×100%.

[0184] 4. Capacity retention test

[0185] Using the Blue Electric test system, the formed lithium-ion battery was allowed to stand for 10 minutes, and 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 allowed to stand for 10 minutes, and then 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, it was 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 allowed to stand for 10 minutes, and then 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, and the capacity retention rate of the lithium-ion battery = Y2 / Y1×100%.

[0186] 5. Lithium deposition test

[0187] After the capacity retention rate test, the lithium-ion battery was left 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 was charged at a constant voltage of 4.2V with a cut-off current of 0.05C. The fully charged lithium-ion battery was disassembled to observe whether the negative electrode sheet corresponding to the low CB value area was lithium-precipitated. The percentage S of the area of ​​the lithium-precipitated area and the area of ​​the negative electrode sheet corresponding to the low CB value area can be obtained by fitting calculation. Alternatively, the negative electrode sheet obtained after disassembly is photographed, the graphite area on the negative electrode sheet is golden yellow, and the lithium-precipitated 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 precipitation can be calculated.

[0188] 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 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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