Lithium ion battery and electric device

Abstract

The embodiment of the invention discloses a lithium ion battery and a power utilization device, the lithium ion battery comprises an electrolyte, the electrolyte comprises metal ions, and the stokes radius of the metal ions is smaller than that of lithium ions; the CB value of the lithium ion battery meets the condition that CB is larger than or equal to 1.06 and smaller than or equal to 1.32, 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. The lithium ion battery can effectively solve the problem of lithium precipitation, and the fast charging 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 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] As people continue to pursue more efficient life, the charging capacity of batteries has become one of the important parameters for measuring battery quality. Therefore, how to improve the charging capacity of lithium-ion batteries is crucial to the development of lithium-ion batteries. Summary of the invention

[0004] This application is made in view of the above technical problems, and its purpose is to provide a lithium-ion battery and an electrical device. The lithium-ion battery can effectively even out the current density of the negative electrode sheet, improve the lithium precipitation problem, and give full play to the charging capacity of the lithium-ion battery.

[0005] In a first aspect, a lithium-ion battery is provided, comprising: an electrolyte, wherein the electrolyte comprises metal ions, wherein the Stokes radius of the metal ions is smaller than the Stokes radius of the lithium ions; and a CB value of the lithium-ion battery satisfies: 1.06≤CB≤1.32, wherein the CB value is the ratio of the capacity of a negative electrode active material per unit area to the capacity of a positive electrode active material per unit area.

[0006] In the embodiments of the present application, the CB value of the lithium-ion battery is set in the range of 1.06 to 1.32, 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. In other words, the negative electrode plate per unit area has more lithium ion active sites, and when the lithium-ion battery is charged at a high rate, a large number of lithium ions can be quickly embedded, thereby reducing the risk of lithium precipitation in the lithium-ion battery. At the same time, the electrolyte of the lithium-ion battery includes metal ions with a Stokes radius smaller than that of lithium ions. When the lithium-ion battery is charged at a high rate, the metal ions can migrate to places with higher current density faster than lithium ions, thereby reducing the impact of uneven current density on fast charging performance, and further reducing the risk of lithium precipitation in the lithium-ion battery. Therefore, the lithium-ion battery provided in the embodiments of the present application can effectively reduce lithium precipitation and give full play to the charging capacity of the lithium-ion battery.

[0007] In a possible implementation, the molar concentration C of the metal ions in the electrolyte satisfies: 0.012M≤C≤0.05M.

[0008] In the embodiments of the present application, by controlling the molar concentration of metal ions within a suitable range, the current density can be made more uniform while reducing the effect of metal ions on the viscosity of the electrolyte, helping to reduce concentration polarization inside the lithium-ion battery, thereby reducing lithium plating.

[0009] In one possible implementation, the metal ions include K + 、Na + At least one of; Optionally, the metal ion includes K + .

[0010] In a possible implementation, the conductivity σ of the electrolyte at room temperature satisfies: σ≥6mS·cm -1 .

[0011] In the embodiments of the present application, by controlling and selecting an electrolyte with a higher conductivity, it helps to reduce the impedance of the lithium-ion battery while helping to reduce the concentration polarization in the thickness direction of the electrode sheet, thereby reducing the risk of lithium deposition in the lithium-ion battery.

[0012] In a possible implementation, the viscosity η of the electrolyte at room temperature satisfies: η≤5 Pa·s.

[0013] In the embodiments of the present application, by selecting an electrolyte with a lower viscosity, the concentration polarization in the thickness direction of the electrode can be further reduced, thereby further reducing the risk of lithium deposition in the lithium-ion battery.

[0014] In a possible implementation, the lithium-ion battery includes a negative electrode plate, and the negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on the negative electrode current collector.

[0015] In a possible implementation, the thickness h of the negative electrode film layer satisfies: 25 μm≤h≤60 μm.

[0016] In the embodiments of the present application, by controlling the thickness of the negative electrode film layer within a suitable range, it is helpful to reduce the polarization of the lithium-ion battery and improve the charging capacity of the lithium-ion battery.

[0017] In a possible implementation, the loading amount m of the negative electrode film layer on the negative electrode current collector satisfies: 4 mg·cm -2 ≤m≤10mg·cm -2 .

[0018] In the embodiments of the present application, by controlling the loading amount of the negative electrode film layer on the negative electrode current collector within a suitable range, the lithium-ion battery can have both a higher energy density and a good charging capacity.

[0019] In a second aspect, an electrical device is provided, wherein the electrical device comprises a lithium-ion battery in any possible implementation of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] 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.

[0021] Figure 1 A schematic diagram of a battery cell.

[0022] Figure 2 A schematic diagram of a battery module.

[0023] Figure 3 A schematic diagram of a battery.

[0024] Figure 4 Another schematic diagram of a battery. DETAILED DESCRIPTION

[0025] 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.

[0026] "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.

[0027] 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.

[0028] 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).

[0029] 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.

[0030] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0031] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their generally accepted meanings in the art.

[0032] 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.

[0033] 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.

[0034] Next, embodiments of the present application are introduced.

[0035] 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.

[0036] Take lithium-ion batteries as an example. Lithium-ion batteries are a typical secondary battery. Because they rely on the chemical reaction of lithium ions intercalating and disintercalating between the positive and negative electrodes for charging and discharging, lithium-ion batteries are also called rocking-chair batteries. During the charging process of lithium-ion batteries, lithium ions are released from the positive electrode active material, move to the negative electrode through the conduction of the electrolyte and embed into the negative electrode active material; and during the discharge process, lithium ions are released from the negative electrode active material, move to the positive electrode through the conduction of the electrolyte and embed into the positive electrode active material.

[0037] 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.

[0038] As the application scope of lithium-ion batteries becomes wider and wider, and the usage scenarios become more and more diverse, new requirements are put forward for the charging capacity of lithium-ion batteries. In some usage scenarios, lithium-ion batteries are required to have stable high-current charging capabilities. When charging lithium-ion batteries, lithium plating may occur on the negative electrode sheets due to various factors such as concentration polarization inside the battery and low CB values ​​in local areas caused by process limitations. For high-capacity, high-energy-density lithium-ion batteries, the thickness of the electrode sheets and the load of active materials on the electrode sheets are higher than those of ordinary lithium-ion batteries, and the risk of lithium plating on the negative electrode sheets during the cycle is higher. Therefore, in order to protect the battery and improve the safety of the battery, the actual charging capacity (for example, charging rate) of lithium-ion batteries often cannot reach their theoretical value, resulting in a loss of charging capacity.

[0039] In view of this, an embodiment of the present application provides a lithium-ion battery and an electrical device, wherein the CB value of the lithium-ion battery is set to 1.06-1.32, the negative electrode has more lithium insertion sites, and the electrolyte of the lithium-ion battery contains metal ions with a Stokes radius smaller than that of lithium ions, which can help improve the uniformity of the current density of the negative electrode plate, reduce the polarization of the lithium-ion battery, reduce the risk of lithium precipitation of the negative electrode plate, and enable the lithium-ion battery to fully exert its charging capacity, thereby improving the charging performance of the lithium-ion battery.

[0040] 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.

[0041] First, a lithium ion battery is provided. The lithium ion battery includes an electrolyte. The electrolyte includes metal ions. The Stokes radius of the metal ions is smaller than the Stokes radius of the lithium ions. The CB value of the lithium ion battery satisfies: 1.06≤CB≤1.32.

[0042] Specifically, when designing the pole piece, the CB value of the lithium-ion battery can be controlled within the range of 1.06 to 1.32 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: 1.06, 1.08, 1.1, 1.12, 1.14, 1.16, 1.18, 1.2, 1.22, 1.24, 1.26, 1.28, 1.3, 1.32, or a value within the range obtained by combining any two of the above values.

[0043] 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. When charging with a large current, a large number of lithium ions that move to the negative electrode sheet can be quickly embedded in the negative electrode active material, thereby improving the embedding efficiency of lithium ions and reducing the risk of lithium deposition at the negative electrode during high current charging. 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 formation of the lithium-ion battery, which is not conducive to the first-cycle coulomb efficiency of the lithium-ion battery. By controlling the CB value of the lithium-ion battery within the range of 1.06 to 1.32, it helps to reduce the risk of lithium deposition during the fast charging process of the lithium-ion battery. At the same time, metal ions are also introduced into the electrolyte of the lithium-ion battery. The Stokes radius of metal ions is smaller than that of lithium ions. Therefore, the migration rate of metal ions in the electrolyte is faster than that of lithium ions. When the current density of the negative electrode is uneven, they can move to the place with higher current density faster than lithium ions, thereby making the current density of the negative electrode uniform and making the distribution of lithium ions on the surface of the negative electrode more uniform, thereby further reducing the risk of lithium plating on the negative electrode.

[0044] Therefore, the lithium-ion battery provided in the embodiment of the present application can effectively reduce the risk of lithium plating when the lithium-ion battery is charged at a high current by controlling the range of the CB value and combining it with an electrolyte including the aforementioned metal ions, thereby giving full play to the charging performance of the lithium-ion battery.

[0045] In one embodiment, the molar concentration C of the metal ions in the electrolyte satisfies: 0.012M≤C≤0.05M.

[0046] Specifically, the molar concentration C of the metal ions in the electrolyte can be: 0.012M, 0.014M, 0.016M, 0.018M, 0.02M, 0.022M, 0.024M, 0.026M, 0.028M, 0.03M, 0.032M, 0.034M, 0.036M, 0.038M, 0.04M, 0.042M, 0.044M, 0.046M, 0.048M, 0.05M, or its value is within the range obtained by combining any two of the above values.

[0047] By adding metal ions with a Stokes radius smaller than that of lithium ions to the electrolyte, the current density on the negative electrode plate can be effectively uniformized, reducing the risk of lithium precipitation on the negative electrode plate. If the molar concentration of the metal ions is too small, there are fewer metal ions in the electrolyte, and the inhibitory effect on lithium precipitation is limited; if the concentration of the metal ions is too high, there are too many metal ions in the electrolyte, which may increase the viscosity of the electrolyte. Based on this, the embodiments of the present application can effectively suppress lithium precipitation while reducing the effect of metal ions on the viscosity of the electrolyte by controlling the concentration of metal ions within the range of 0.012M to 0.05M.

[0048] In one embodiment, the metal ion comprises K + 、Na + At least one of; Optionally, the metal ion includes K + .

[0049] Specifically, the Stokes radius of lithium ions is usually The Stokes radius of a sodium ion is usually The Stokes radius of potassium ions is usually Taking potassium ions as an example, the possible mechanism by which the aforementioned metal ions can make the current density of the negative electrode plate uniform and improve lithium deposition is explained as follows: although it has more electron layers than lithium ions and a larger ion radius than lithium ions, the number of positive charges carried by potassium ions and lithium ions is the same, and the ion radius of potassium ions is larger. Therefore, its electric field strength is weaker than that of lithium ions, and its attraction to the negatively charged groups of solvent molecules is weaker. Therefore, its Stokes radius is smaller than that of lithium ions, and it has a higher migration rate in the solution. When the local current density is too high on the negative electrode plate, the metal ions can move to the position where the current density is too high faster than the lithium ions, thereby making the current density at that position uniform. Thus, the influence of the uneven current density of the negative electrode plate on the distribution of lithium ions on the surface of the negative electrode plate is reduced, and the lithium deposition at the position where the local current density is too high due to the uneven distribution of lithium ions on the surface of the negative electrode plate is effectively improved.

[0050] In one embodiment, the conductivity σ of the electrolyte at room temperature satisfies: σ≥6mS·cm -1 .

[0051] Specifically, the conductivity of the electrolyte at room temperature can be: 6mS·cm -1 、7mS·cm -1 、8mS·cm -1 、9mS·cm -1 、10mS·cm -1 、11mS·cm -1 、12mS·cm -1 、13mS·cm -1 、14mS·cm-1 、15mS·cm -1 、16mS·cm -1 、17mS·cm -1 、18mS·cm -1 、19mS·cm -1 、20mS·cm -1 wait.

[0052] The conductivity of the electrolyte can be controlled by adjusting parameters such as the solvent, solute and their respective concentrations. In the case of a thicker negative electrode sheet, the difference in wettability of the electrolyte in the thickness direction of the negative electrode sheet is amplified, and the concentration polarization of the negative electrode sheet in the thickness direction is also increased. Based on this, in the embodiment of the present application, by selecting a conductivity greater than or equal to 6mS·cm -1 The electrolyte with higher conductivity can improve the concentration polarization in the thickness direction of the negative electrode sheet. In addition, the electrolyte with higher conductivity can reduce the liquid phase transmission impedance inside the lithium-ion battery, thereby reducing the impedance inside the lithium-ion battery.

[0053] It should be understood that normal temperature can be understood as room temperature. For example, the normal temperature in my country is usually around 20°C to 25°C. For another example, the normal temperature in Russia is usually around 10°C. The above temperature range is only an example and does not constitute a limitation on "normal temperature".

[0054] In one embodiment, the viscosity η of the electrolyte at room temperature satisfies: η≤5 Pa·s.

[0055] Specifically, the viscosity η of the electrolyte at room temperature can be: 3Pa·s, 3.2Pa·s, 3.4Pa·s, 3.6Pa·s, 3.8Pa·s, 4Pa·s, 4.2Pa·s, 4.4Pa·s, 4.6Pa·s, 4.8Pa·s, 5Pa·s, or its value is within the range obtained by combining any two of the above values.

[0056] The viscosity of the electrolyte can be regulated by regulating the type of solute or solvent in the electrolyte, the concentration of the solute, and the concentration of the metal ions. Generally, the viscosity of the electrolyte affects the wettability of the electrode in the electrolyte. The better the wettability of the electrode, the higher the ion transmission efficiency and the lower the impedance. Therefore, in the embodiments of the present application, by selecting an electrolyte with a lower viscosity, the wettability of the negative electrode in the electrolyte can be improved, the concentration polarization in the thickness direction of the negative electrode can be reduced, and the risk of lithium precipitation of the negative electrode during high current charging can be reduced, thereby giving full play to the charging capacity of the lithium-ion battery and further improving the charging capacity of the lithium-ion battery.

[0057] Therefore, the lithium-ion battery provided in the embodiment of the present application can uniformly distribute the current density on the negative electrode plate, and has the charging capability of charging to 35% SOC at a high rate (for example, 4C) without lithium precipitation.

[0058] Next, the positive electrode sheet, negative electrode sheet, separator and electrolyte in the lithium-ion battery are introduced in detail.

[0059] [Negative electrode]

[0060] 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.

[0061] 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.

[0062] In one embodiment, the thickness h of the negative electrode film layer satisfies: 25 μm≤h≤60 μm.

[0063] Specifically, the thickness of the negative electrode film layer can be: 25μm, 28μm, 30μm, 32μm, 34μm, 36μm, 38μm, 40μm, 42μm, 44μm, 46μm, 48μm, 50μm, 52μm, 54μm, 56μm, 58μm, 60μm, or its value is within the range obtained by combining any two of the above values.

[0064] The thickness of the negative electrode film layer has a certain influence on the charging capacity of the lithium-ion battery. The reason is that the smaller the thickness of the negative electrode film layer, the more conducive it is to the diffusion and infiltration of the electrolyte, which can reduce the concentration polarization in the thickness direction of the negative electrode plate, reduce the risk of lithium precipitation of the negative electrode plate when charging with a large current, and help the charging capacity of the lithium-ion battery. In addition, the thickness of the negative electrode film layer also has a certain influence on the energy density of the lithium-ion battery. Under the same powder compaction density, the thicker the thickness of the negative electrode film layer, the higher the load of active material on the negative electrode plate, and the greater the energy density of the lithium-ion battery. Based on this, the embodiments of the present application help the lithium-ion battery to have both high energy density and good charging capacity by controlling the thickness of the negative electrode film layer within an appropriate range.

[0065] In one embodiment, the loading amount m of the negative electrode film layer on the negative electrode current collector satisfies: 4 mg·cm -2 ≤m≤10mg·cm -2 .

[0066] Specifically, the loading amount m of the negative electrode film layer on the negative electrode current collector can be: 4 mg cm -2 , 4.5mg·cm -2 , 5mg·cm-2 , 5.5mg·cm -2 , 6mg·cm -2 、6.5mg·cm -2 , 7mg·cm -2 、7.5mg·cm -2 , 8mg·cm -2 、8.5mg·cm -2 , 9mg·cm -2 、9.5mg·cm -2 、10mg·cm -2 , or its value is within the range obtained by combining any two of the above values.

[0067] In addition to being affected by the thickness of the negative electrode film layer, the charging capacity of a lithium-ion battery is also affected by the porosity. Generally speaking, the greater the porosity of the negative electrode film layer, the more conducive it is to the diffusion and infiltration of the electrolyte, the smaller the concentration polarization, and the better the charging capacity of the lithium-ion battery. On the other hand, when the thickness of the negative electrode film layer is constant, the greater the powder compaction density, the lower the porosity, the greater the load of the negative electrode film layer on the negative electrode current collector, and the greater the energy density of the lithium-ion battery. Based on this, the embodiments of the present application control the load of the negative electrode film layer on the negative electrode current collector within a suitable range, which is equivalent to indirectly controlling the porosity of the negative electrode film layer, which helps the lithium-ion battery to have both a higher energy density and good charging capacity.

[0068] When the negative electrode film layer is controlled to satisfy the above-mentioned thickness and load, it is equivalent to taking into account the porosity and thickness of the negative electrode film layer at the same time, which enables the lithium-ion battery to have both better charging capacity and energy density.

[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 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 0.05O2) 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] [Electrolyte]

[0084] 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 includes an electrolyte salt, a solvent, and a metal ion, and the Stokes radius of the metal ion is smaller than the Stokes radius of the lithium ion.

[0085] 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.

[0086] In one embodiment, the solvent can be selected from 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, 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.

[0087] In one embodiment, the metal ion is provided by an inorganic salt. In other words, the electrolyte includes an inorganic salt, and the inorganic salt includes the metal ion and an anion. Exemplarily, the anion includes at least one of hexafluorophosphate, tetrafluoroborate, perchlorate, nitrate, carbonate, bistrifluoromethylsulfonyl imide, trifluoromethanesulfonate, difluorooxalatoborate, dioxalatoborate, methanesulfonate, and halogen anions.

[0088] 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 performance of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high or low temperature performance of the battery, etc.

[0089] [Isolator]

[0090] 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.

[0091] 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.

[0092] 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.

[0093] In one embodiment, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0094] In one embodiment, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0095] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 1 The battery cell 100 is a square structure as an example.

[0096] It should be understood that the battery cell 100 may include the lithium-ion battery in the aforementioned embodiment.

[0097] Figure 2 2 is a battery module 200 as an example. Figure 2 In the battery module 200, the plurality of battery cells 100 may be arranged in sequence along the length direction of the battery module 200. Of course, they may also be arranged in any other manner. The plurality of battery cells 100 may further be fixed by fasteners. The plurality of battery cells 100 may be battery cells 100 of the same chemical system or battery cells 100 of different chemical systems.

[0098] Optionally, in one embodiment, the battery module 200 may further include a housing having an accommodation space, and the plurality of battery cells 100 are accommodated in the accommodation space.

[0099] Optionally, in one embodiment, the battery modules 200 may also be assembled into a battery. The number of battery modules 200 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.

[0100] Figure 3 and Figure 4 300 is an example of a battery pack. Figure 3 and Figure 4 The battery pack 300 may include a battery box and a plurality of battery modules 200 disposed in the battery box. The battery box includes an upper box body 301 and a lower box body 302. The upper box body 301 can cover the lower box body 302 and form a closed space for accommodating the battery modules 200. The plurality of battery modules 200 may be arranged in the battery box in any manner.

[0101] It should be understood that the battery cells 100 may first form the battery module 200, and the battery pack 300 may be formed by the battery module 200. Alternatively, the battery pack 300 may be directly formed by the battery cells 100, omitting the intermediate form of the battery module 200.

[0102] In addition, the present application also provides an electrical device, which includes the lithium-ion battery in the aforementioned embodiment.

[0103] In another embodiment, the power-consuming device includes at least one of the battery cell 100, battery module 200, or battery pack 300 provided in the present application. The battery cell 100, battery module 200, or battery pack 300 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.

[0104] As an electric device, the number of battery cells 100, battery modules 200, or battery packs 300 can be selected according to its usage requirements.

[0105] 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.

[0106] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0107] 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.

[0108] [Examples 1-10 and Comparative Example 1]

[0109] Example 1

[0110] (1) Preparation of negative electrode sheet

[0111] The negative electrode active material artificial graphite (Dv50 = 15 μm), the conductive agent acetylene black, the binder styrene butadiene rubber, and the thickener sodium carboxymethyl cellulose were dissolved in the solvent deionized water according to the mass ratio of 94:1:3:2, 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.

[0112] (2) Preparation of positive electrode sheet

[0113] The positive electrode active material LiNi5Co2Mn3O2, the conductive agent carbon nanotubes, and the binder polyvinylidene fluoride are dissolved in the solvent N-methylpyrrolidone at a mass ratio of 96:2:2, and mixed evenly to obtain a positive electrode slurry with a solid content of 50%. The positive electrode slurry is then evenly coated on the positive electrode current collector aluminum foil. After drying, rolling, and cutting, the positive electrode sheet is obtained.

[0114] (3) Preparation of electrolyte

[0115] In an argon atmosphere glove box (H2O < 0.1ppm, O2 < 0.1ppm), the electrolyte was prepared. The specific process is: the organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) were mixed evenly, and then appropriate amounts of lithium hexafluorophosphate (LiPF6) and potassium hexafluorophosphate (KPF6) were added to make the molar concentration of LiPF6 1M and the molar concentration of KPF6 0.03M.

[0116] (4) Preparation of reference electrode

[0117] A copper wire with a diameter of 0.5 mm was soaked in concentrated sulfuric acid for 2 h, and then the surface of the copper wire was cleaned with deionized water and ethanol respectively. The cleaned copper wire was then placed in an oven at 60°C for 6 h and welded to a nickel electrode ear to prepare a reference electrode.

[0118] (5) Preparation of lithium-ion batteries

[0119] (5.1) Stack the positive electrode sheet, the isolation membrane, and the negative electrode sheet in order, so that the isolation membrane is between the positive electrode sheet and the negative electrode sheet and can isolate the positive electrode sheet from the negative electrode sheet; then wind the stacked components and place them in a shell, and inject the electrolyte after drying to obtain the lithium-ion battery of Example 1.

[0120] (5.2) The positive electrode sheet, the isolation membrane, the reference electrode, the isolation membrane, and the negative electrode sheet of a specific size are stacked in order so that the reference electrode is located between two layers of isolation membranes; the stacked components are then placed in a shell, dried, and injected with electrolyte to obtain the reference cell of Example 1.

[0121] The above lithium-ion battery and reference battery were formed under the following conditions: using a blue electric test system, the positive electrode and the negative electrode were connected, left to stand for 1 minute, and then charged to 4.2V at a constant current of 0.1C, and then charged at a constant voltage of 4.2V with a cut-off current of 0.02C, and then left to stand for 10 minutes, and then discharged at a constant current of 0.1C with a cut-off voltage of 2.5V, and left to stand for 48 hours. The SEI film is formed during the formation of the battery and helps to reduce the polarization of the battery.

[0122] (6) Lithium plating of reference electrode

[0123] Before the performance test of the reference battery, the reference electrode of the reference battery needs to be activated. Specifically, the reference electrode of the reference battery needs to be plated with lithium. The specific process of lithium plating is: connect the positive electrode to the reference electrode, charge at a constant current of 20μA for 2h, and after standing for 5min, connect the negative electrode to the reference electrode, and discharge at a constant current of 20μA for 2h to complete the lithium plating of the reference electrode. The reference electrode after lithium plating can also be called a lithium metal electrode. The voltage of the negative electrode of the reference battery after lithium plating to the lithium metal electrode is 40mV to 400mV, which is considered to be the activation of the reference electrode.

[0124] By setting up a lithium-ion battery and a corresponding reference battery, the charging capacity of the lithium-ion battery and the reference battery are tested simultaneously. The performance of the lithium-ion battery represents the actual performance of the lithium-ion battery under the condition; the performance of the reference battery represents the theoretical performance of the lithium-ion battery under the condition.

[0125] Thus, the CB value of the lithium ion battery and the reference battery prepared in Example 1 was set to 1.12, and the metal ion was K + , K + The molar concentration in the electrolyte is C = 0.03M, and the conductivity of the electrolyte is σ = 9.5mS·cm -1 , viscosity η = 3.9 Pa·s, thickness of negative electrode film h = 54 μm, loading amount of negative electrode film on negative electrode current collector m = 8.6 mg·cm -2 .

[0126] Example 2

[0127] Compared with Example 1, in the lithium ion battery of Example 2 and the reference battery, CB=1.06.

[0128] Example 3

[0129] Compared with Example 1, in the lithium ion battery of Example 3 and the reference battery, CB=1.24.

[0130] Example 4

[0131] Compared with Example 1, in the lithium ion battery of Example 4 and the reference battery, CB=1.32.

[0132] Example 5

[0133] Compared with Example 1, in the lithium ion battery of Example 5 and the reference battery, C = 0.012M, σ = 9.7mS·cm -1 .

[0134] Example 6

[0135] Compared with Example 1, in the lithium ion battery of Example 6 and the reference battery, C = 0.05M, σ = 9.1 mS·cm -1 .

[0136] Example 7

[0137] Compared with Example 1, in the lithium ion battery and the reference battery of Example 7, the metal lithium ions in the electrolyte are Na + .

[0138] Example 8

[0139] Compared with Example 1, in the lithium ion battery of Example 8 and the reference battery, σ=6mS·cm -1 , η=5Pa·s.

[0140] Example 9

[0141] Compared with Example 1, in the lithium ion battery of Example 9 and the reference battery, h = 25 μm, m = 4 mg·cm -2 .

[0142] Example 10

[0143] Compared with Example 1, in the lithium ion battery of Example 10 and the reference battery, h = 60 μm, m = 10 mg·cm -2 .

[0144] Comparative Example 1

[0145] Compared with Example 1, in the lithium ion battery of Comparative Example 1 and the reference battery, there is no metal ion whose Stokes radius is smaller than that of lithium ions.

[0146] Product parameters of Examples 1-10 and Comparative Example 1.

[0147] Table 1: Product parameters of Examples 1-10 and Comparative Example 1

[0148] In Table 1, "CB value" represents the CB value of lithium-ion batteries and reference batteries, "metal ions" represent metal ions in the electrolyte whose Stokes radius is smaller than that of lithium ions. "C" represents the molar concentration of metal ions in the electrolyte, "σ" represents the conductivity of the electrolyte at room temperature, "η" represents the viscosity of the electrolyte at room temperature, "h" represents the thickness of the negative electrode film layer, and "m" represents the loading amount of the negative electrode film layer on the negative electrode current collector.

[0149] The battery performance test was carried out on the above embodiments and comparative examples, and the measured performance data are shown in Table 2.

[0150] Table 2: Product parameters of Examples 1-10 and Comparative Example 1

[0151] In Table 2, "Critical non-lithium deposition SOC of reference battery" indicates the charge state of the reference battery when lithium deposition is about to occur at the negative electrode of the reference battery measured by the charging capacity test, "Critical non-lithium deposition SOC of lithium-ion battery" indicates the charge state of the lithium-ion battery when lithium deposition is about to occur at the negative electrode of the lithium-ion battery measured by the charging capacity test, and "SOC difference" indicates the difference between the critical non-lithium deposition SOC of the reference battery and the critical non-lithium deposition SOC of the lithium-ion battery. "Lithium deposition is about to occur" means that during the charging capacity test of a lithium-ion battery or a reference battery under a certain current, if more electricity is charged at the current, lithium deposition will occur at the negative electrode.

[0152] The charging capacity test of the reference battery in Table 2 can be carried out in the following steps: in a constant temperature box at 25°C, the positive electrode and the negative electrode of the reference battery are connected, and constant current charging is performed at a current of 0.33C to 4.2V, and then constant voltage charging is performed at a voltage of 4.2V until the current is less than or equal to 0.05C. After standing for 10 minutes, constant current discharge is performed at a current of 0.33C to 2.5V. At this time, the state of charge of the battery is recorded as 0% SOC.

[0153] Starting from the reference battery having a state of charge of 0% SOC, it is charged at a constant current of 4C. When the negative electrode potential reaches 0mV compared to the reference electrode potential, the charging is terminated, and the state of charge of the battery at the time of charging termination is recorded. The state of charge is the critical non-lithium precipitation SOC of the reference battery in Example 1, and the critical non-lithium precipitation SOC of the reference battery can represent the theoretical charging capacity of the lithium-ion battery in Example 1.

[0154] The charging capacity test of the lithium-ion battery in Table 2 can be carried out in the following steps:

[0155] Prepare multiple identical lithium-ion batteries, and perform cycle tests on the multiple lithium-ion batteries. The specific test conditions are: in a constant temperature box at 25°C, let the lithium-ion battery stand for 2h, then discharge it to 2.5V at a constant current of 0.33C, let it stand for 5min, and then charge the multiple lithium-ion batteries to different states of charge at a current of 4C, and then charge them to 4.2V at a constant current of 0.33C, and then charge them to a current of less than or equal to 0.05C at a constant voltage of 4.2V. After 50 cycles, disassemble the multiple lithium-ion batteries to observe whether lithium precipitation occurs on the negative electrode sheet. In the step of charging the multiple lithium-ion batteries to different states of charge at a constant current, the multiple different states of charge are set according to the critical non-lithium precipitation SOC of the reference battery. For example, if the critical non-lithium precipitation SOC of the reference battery is measured to be 50%, then the multiple different states of charge can be set to multiple values ​​less than or equal to 50%, exemplarily, 49%, 48%, 47%, 46%, etc. The number of lithium-ion batteries used for testing can be set according to the test requirements. For example, 5, 10, or 15 lithium-ion batteries can be cycled. It should be understood that the lithium-ion battery after 50 cycles is in a fully charged state, that is, the battery has been charged to 4.2V and charged at a constant voltage of 4.2V to a current less than or equal to 0.05C.

[0156] By performing cycle tests on the above-mentioned multiple identical lithium-ion batteries, negative electrode plates of the lithium-ion batteries charged to multiple different SOCs and cycled are obtained, and the negative electrode plates corresponding to two adjacent SOCs respectively exhibit lithium deposition and no lithium deposition phenomena, and the SOC corresponding to the negative electrode plate without lithium deposition is recorded as the critical no-lithium deposition SOC of the lithium-ion battery.

[0157] 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.

[0158] 1. CB value test method

[0159] 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.

[0160] 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.

[0161] 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.

[0162] 2. Molar concentration test method

[0163] 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.

[0164] Exemplarily, the test method is in accordance with HG / T 4067-2015, and the ICP (Inductively coupled plasma) test method is used. The 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 by an ICP tester.

[0165] 3. Test method for electrolyte viscosity

[0166] For specific test methods, please refer to "Viscosity Measurement Method": GB / T 10247-2008.

[0167] 4. Test method for electrolyte conductivity

[0168] The test method is in accordance with HG / T 4067-2015. The conductivity of the electrolyte to be tested is tested with a conductivity meter: about 100 ml of the sample to be tested is taken from a dry, clean, corrosion-resistant sample bottle, and sealed in a constant temperature water bath at 25±0.5℃. When the temperature of the sample to be tested is constant, the sample bottle cap is replaced with a rubber stopper with an electrode inserted. When the temperature is within the range of 25±0.5℃, the data is read, which is the conductivity of the sample to be tested.

[0169] 5. Load test method

[0170] Cut the negative electrode sheet to a specified area S, weigh the mass m1, wash off the film layer on the surface of the negative electrode current collector, weigh the mass m2 of the negative electrode current collector, and the loading amount of the negative electrode film layer on the negative electrode current collector is (m1-m2) / S.

[0171] According to the comparative analysis of Examples 1-10 and Comparative Example 1, it can be seen from the charging capacity tests of the examples and the comparative examples that the critical non-lithium precipitation SOC of the lithium-ion battery of the examples and the critical non-lithium precipitation SOC of the reference battery are relatively close, and the difference is small, indicating that the charging capacity of the lithium-ion battery in the examples is close to its theoretical charging capacity. In other words, the lithium-ion battery in the examples can give full play to its charging capacity. However, the critical non-lithium precipitation SOC of the lithium-ion battery in the comparative example and the critical non-lithium precipitation SOC of the reference battery are quite different, indicating that the charging capacity of the lithium-ion battery in the comparative example is poor. In other words, the lithium-ion battery in the comparative example cannot exert its charging capacity. Therefore, it is shown that by introducing metal ions with a Stokes radius smaller than lithium ions in the electrolyte and controlling the CB value of the lithium-ion battery within a suitable range, lithium precipitation can be effectively suppressed and the charging capacity of the lithium-ion battery can be improved.

[0172] According to the comparative analysis of Examples 1-4, it can be seen that as the CB value increases, the critical no-lithium SOC of the lithium-ion battery increases, proving that increasing the CB value can increase the lithium insertion sites on the negative electrode sheet, reduce the risk of lithium deposition in the lithium-ion battery, and thus improve the critical no-lithium SOC of the lithium-ion battery.

[0173] According to the comparative analysis of Examples 1, 5-6, the concentration of metal ions in Example 5 is relatively low, while the concentration of metal ions in Examples 1 and 6 is relatively high. Therefore, the inhibition of lithium precipitation by metal ions and the improvement of fast charging performance in Examples 1 and 6 are better than those in Example 5, and the critical non-lithium precipitation SOC of the lithium ion batteries of Examples 1 and 6 is greater than that of Example 5. The performance data of Examples 1 and 6 are not much different, indicating that within a certain range, an increase in the concentration of metal ions is beneficial to inhibiting lithium precipitation and improving the charging capacity of lithium ion batteries.

[0174] Example 7 demonstrates that the introduction of sodium ions into the electrolyte has a similar effect as potassium ions.

[0175] According to the comparative analysis of Example 1 and Example 8, when the conductivity of the electrolyte is low, the critical no-lithium precipitation SOC of the lithium-ion battery is also small, which means that selecting an electrolyte with a larger conductivity helps to improve concentration polarization and thus inhibit lithium precipitation, helping to improve the charging capacity of the lithium-ion battery.

[0176] According to the comparative analysis of Example 1 and Examples 9-10, Example 9 with the smallest thickness of the negative electrode film layer has the largest critical no-lithium deposition SOC of the lithium-ion battery, which means that the smaller the thickness of the negative electrode film layer, the more conducive it is to the diffusion and infiltration of the electrolyte, which can effectively reduce the concentration polarization in the thickness direction of the negative electrode plate, reduce the risk of lithium deposition on the negative electrode plate, and improve the charging capacity of the lithium-ion battery.

[0177] 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. A lithium ion battery, characterized in that: The lithium-ion battery comprises: An electrolyte, the electrolyte comprising metal ions, the Stokes radius of the metal ions being smaller than the Stokes radius of the lithium ions; The CB value of the lithium-ion battery satisfies: 1.06≤CB≤1.32, 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.

2. The lithium-ion battery according to claim 1, characterized in that The molar concentration C of the metal ions in the electrolyte satisfies: 0.012M≤C≤0.05M.

3. The lithium ion battery according to claim 1 or 2, characterized in that: The metal ions include K + 、Na + At least one of; Optionally, the metal ion includes K + .

4. The lithium ion battery according to any one of claims 1 to 3, characterized in that: The conductivity σ of the electrolyte at room temperature (25°C) satisfies: σ≥6mS·cm -1 .

5. The lithium ion battery according to any one of claims 1 to 4, characterized in that: The viscosity η of the electrolyte at room temperature (25° C.) satisfies: η≤5 Pa·s.

6. The lithium ion battery according to any one of claims 1 to 5, characterized in that: The lithium-ion battery comprises a negative electrode plate, and the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer arranged on the negative electrode current collector.

7. The lithium-ion battery according to claim 6, characterized in that: The thickness h of the negative electrode film layer satisfies: 25 μm≤h≤60 μm.

8. The lithium ion battery according to claim 6 or 7, characterized in that: The loading amount m of the negative electrode film layer on the negative electrode current collector satisfies: 4 mg·cm -2 ≤m≤10mg·cm -2 .

9. The lithium ion battery according to any one of claims 1 to 8, characterized in that: The electrolyte includes an inorganic salt, and the inorganic salt includes the metal ions and anions.

10. The lithium ion battery according to claim 9, characterized in that: The anions include at least one of hexafluorophosphate, tetrafluoroborate, perchlorate, nitrate, carbonate, bistrifluoromethylsulfonyl imide, trifluoromethanesulfonate, difluorooxalatoborate, dioxalatoborate, methanesulfonate, and halogen anions.

11. An electrical device, characterized in that: The electrical device comprises a lithium-ion battery as claimed in any one of claims 1 to 10.

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