Lithium ion battery and electric device

Abstract

Disclosed in embodiments of the present application are a lithium ion battery and an electric device. The lithium ion battery comprises an electrolyte; the electrolyte comprises metal ions; the Stokes radius of the metal ions is smaller than that of lithium ions; and 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 a negative electrode active material per unit area to the capacity of a positive electrode active material per unit area. The lithium ion battery can effectively mitigate the problem of lithium precipitation, thereby improving the quick charging performance of the lithium ion battery.

Description

Lithium-ion batteries and electrical devices

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent document claims priority to and the benefit of Chinese patent application No. 202311525265.9, filed on November 15, 2023, entitled “Lithium-ion battery and power device.” The entire contents of the aforementioned patent application are incorporated by reference into this patent document. Technical Field

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

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

[0005] As people continue to pursue more efficient living, battery charging capacity 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.

[0006] Summary of the Invention

[0007] 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 uniform the current density of the negative electrode plate, improve the lithium plating problem, and give full play to the charging capacity of the lithium-ion battery.

[0008] In a first aspect, a lithium-ion battery is provided, comprising: an electrolyte, the electrolyte comprising metal ions, the Stokes radius of the metal ions being smaller than the Stokes radius of the lithium ions; and a CB value of the lithium-ion battery satisfying the following conditions: 1.06≤CB≤1.32, wherein the CB value is the ratio of the capacity per unit area of ​​the negative electrode active material to the capacity per unit area of ​​the positive electrode active material.

[0009] In the embodiment 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 of ​​the negative electrode sheet is greater than the capacity of the positive electrode active material per unit area of ​​the positive electrode sheet. In other words, the negative electrode sheet 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 plating 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 plating in the lithium-ion battery. Therefore, the lithium-ion battery provided in the embodiment of the present application can effectively reduce lithium plating and give full play to the charging capacity of the lithium-ion battery.

[0010] In a possible implementation, the molar concentration C of the metal ions in the electrolyte satisfies: 0.012M≤C≤0.05M.

[0011] In the embodiments of the present application, by controlling the molar concentration of metal ions within an appropriate 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.

[0012] In one possible implementation, the metal ions include K + 、Na + At least one of; Optionally, the metal ions include K + .

[0013] In a possible implementation, the conductivity σ of the electrolyte at room temperature satisfies: σ≥6mS·cm -1 .

[0014] 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, thereby reducing the risk of lithium plating in the lithium-ion battery.

[0015] In a possible implementation, the viscosity η of the electrolyte at room temperature satisfies: η≤5 Pa·s.

[0016] 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 plating in the lithium-ion battery.

[0017] 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.

[0018] In a possible implementation, the thickness h of the negative electrode film layer satisfies: 25 μm≤h≤60 μm.

[0019] In the embodiments of the present application, controlling the thickness of the negative electrode film layer within a suitable range helps to reduce the polarization of the lithium-ion battery and improve the charging capacity of the lithium-ion battery.

[0020] In one 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 .

[0021] 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 high energy density and a good charging capacity.

[0022] In a second aspect, an electrical device is provided, wherein the electrical device includes the lithium-ion battery in any possible implementation of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0024] FIG1 is a schematic diagram of a battery cell.

[0025] FIG2 is a schematic diagram of a battery module.

[0026] FIG3 is a schematic diagram of a battery.

[0027] FIG4 is another schematic diagram of a battery. DETAILED DESCRIPTION

[0028] Below, the embodiments of the lithium-ion battery and the electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0029] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0030] In the description of this application, it should be noted that, unless otherwise specified, "plurality" means more than two; terms such as "upper," "lower," "left," "right," "inner," and "outer" indicating directions or positional relationships are merely for the purpose of facilitating the description of this application and simplifying the description, and do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limiting this application. Furthermore, terms such as "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0031] Unless otherwise specified, in this application, the phrase "A and / or B" means "A, B, or both A and B". More specifically, the condition "A and / or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0032] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0033] Unless 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, the "Stokes radius" refers to the ratio of the drag coefficient of a particle moving in a Newtonian fluid to the particle's radius. It is also known as the particle's effective radius in solution or the solvated ion radius. The larger the Stokes radius, the greater the drag encountered by a particle in the fluid and the weaker its mobility.

[0036] As mentioned, the "Cell Balance (CB) value" refers to the ratio of the negative electrode capacity to the positive electrode capacity on opposite sides of the battery, also known as the N / P (Negative / Positive) ratio. In other words, the CB value is equal to the ratio of the capacity of the negative electrode active material per unit area to the capacity of the positive electrode active material per unit area.

[0037] Next, embodiments of the present application are introduced.

[0038] In recent years, secondary batteries have been widely used in power tools, electronic products, electric vehicles, aerospace and other fields due to their high energy density and long service life, and have thus achieved great development. Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the charge and discharge process of the battery, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. Among them, the electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, which allows active ions to pass through while preventing the positive and negative electrodes from short-circuiting, so that the electrochemical reaction of the secondary battery proceeds normally.

[0039] Take lithium-ion batteries, for example. They are a typical secondary battery. Because they rely on the chemical reaction of lithium ions intercalating and deintercalating between the positive and negative electrodes for charging and discharging, they are also called rocking-chair batteries. During the charging process, lithium ions are released from the positive electrode active material, transferred through the electrolyte to the negative electrode, and then embedded in the negative electrode active material. During the discharge process, lithium ions are released from the negative electrode active material, transferred through the electrolyte to the positive electrode, and then embedded in the positive electrode active material.

[0040] It should be understood that the "lithium insertion" and "intercalation" processes described in this application refer to the process in which lithium ions are embedded in the positive electrode active material or the negative electrode active material due to an electrochemical reaction, and the "de-lithiumization", "de-lithiumization" and "de-intercalation" processes described in this application refer to the process in which lithium ions are removed from the positive electrode active material or the negative electrode active material due to an electrochemical reaction.

[0041] As the application scope of lithium-ion batteries becomes wider and wider, and the usage scenarios become more and more diverse, new demands 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 are affected by various factors such as concentration polarization inside the battery and low CB values ​​in local areas due to process limitations, which may cause lithium plating on the negative electrode. For high-capacity, high-energy-density lithium-ion batteries, the thickness of the electrode and the load of active materials on the electrode are higher than those of ordinary lithium-ion batteries, and the risk of lithium plating on the negative electrode during the cycle is higher. Therefore, in order to protect the battery and improve the safety of the battery, the actual charging capacity of the lithium-ion battery (for example, the charging rate) often cannot reach its theoretical value, resulting in a loss of charging capacity.

[0042] 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 to 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 sheet, reduce the polarization of the lithium-ion battery, reduce the risk of lithium plating of the negative electrode sheet, and enable the lithium-ion battery to fully exert its charging capacity, thereby improving the charging performance of the lithium-ion battery.

[0043] Typically, a lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. The lithium-ion battery provided in this application and its various components are described below.

[0044] 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.

[0045] Specifically, when designing the electrode, 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 higher capacity, increasing the loading amount of the active material on the negative electrode, 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 any value within the range obtained by combining any two of the above values.

[0046] 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 at a high current, a large number of lithium ions that move to the negative electrode sheet can be quickly embedded in the negative electrode active material, improving the embedding efficiency of lithium ions, thereby reducing the risk of lithium plating 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 process 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 plating 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 uniforming the current density of the negative electrode 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.

[0047] Therefore, the lithium-ion battery provided in the embodiment of the present application can effectively reduce the risk of lithium plating during high-current charging of the lithium-ion battery by controlling the range of the CB value and using an electrolyte including the aforementioned metal ions, thereby giving full play to the charging performance of the lithium-ion battery.

[0048] In one embodiment, the molar concentration C of the metal ions in the electrolyte satisfies: 0.012M≤C≤0.05M.

[0049] 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.

[0050] 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 deposition on the negative electrode plate. If the molar concentration of the metal ions is too low, there are fewer metal ions in the electrolyte, and its inhibitory effect on lithium deposition 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 deposition 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.

[0051] In one embodiment, the metal ion comprises K + 、Na + At least one of; Optionally, the metal ions include K + .

[0052] Specifically, the Stokes radius of lithium ions is typically 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 uniformly distribute the current density of the negative electrode and improve lithium deposition is explained as follows: although it has more electron layers and a larger ionic radius than lithium ions, the potassium ions and lithium ions carry the same number of positive charges, and the potassium ions have a larger ionic radius. 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, the metal ions can move to the position where the current density is too high faster than the lithium ions, thereby uniformizing the current density at that position. Thus, the influence of the uneven current density of the negative electrode on the distribution of lithium ions on the surface of the negative electrode 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 is effectively improved.

[0053] In one embodiment, the conductivity σ of the electrolyte at room temperature satisfies: σ≥6mS·cm -1 .

[0054] 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.

[0055] 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 the 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 internal impedance of the lithium-ion battery.

[0056] It should be understood that normal temperature can be understood as room temperature. For example, normal temperature in my country is generally around 20°C to 25°C. For another example, normal temperature in Russia is generally around 10°C. The above temperature ranges are merely examples and do not constitute a limitation on "normal temperature."

[0057] In one embodiment, the viscosity η of the electrolyte at room temperature satisfies: η≤5 Pa·s.

[0058] 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.

[0059] The viscosity of the electrolyte can be controlled 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 embodiment of the present application, by selecting an electrolyte with 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 deposition of the negative electrode during high current charging can be reduced, thereby fully utilizing the charging capacity of the lithium-ion battery and further improving the charging capacity of the lithium-ion battery.

[0060] Therefore, the lithium-ion battery provided in the embodiment of the present application can uniformly distribute the current density on the negative electrode sheet and has the charging capability of being charged to 35% SOC at a high rate (for example, 4C) without lithium deposition.

[0061] Next, the positive electrode sheet, negative electrode sheet, separator and electrolyte in the lithium-ion battery are introduced in detail.

[0062] [Negative electrode]

[0063] 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.

[0064] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0065] In one embodiment, the thickness h of the negative electrode film layer satisfies: 25 μm≤h≤60 μm.

[0066] 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.

[0067] 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.

[0068] 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 .

[0069] 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.

[0070] The charging capacity of lithium-ion batteries is affected not only by the thickness of the negative electrode film layer, but also 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 indirectly control the porosity of the negative electrode film layer by controlling the load of the negative electrode film layer on the negative electrode current collector within a suitable range, which helps the lithium-ion battery to have both higher energy density and good charging capacity.

[0071] When the negative electrode film layer is controlled to meet 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 can enable the lithium-ion battery to have both better charging capacity and energy density.

[0072] In one embodiment, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0073] In one embodiment, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0074] In one embodiment, the negative electrode film layer further includes a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0075] In one embodiment, the negative electrode film layer further includes a conductive agent, which can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

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

[0077] In one embodiment, the negative electrode sheet can be prepared by forming a negative electrode slurry using the aforementioned components for preparing the negative electrode sheet. For example, the negative electrode active material, conductive agent, binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form the negative electrode slurry. The negative electrode slurry is then coated onto the negative electrode current collector. After drying and cold pressing, the negative electrode sheet is obtained.

[0078] [Positive electrode]

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

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

[0081] In one embodiment, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate made of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0082] In one embodiment, the positive electrode active material may adopt the positive electrode active material for batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.1 Al 0.05O2) 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 will be accompanied by the deintercalation and consumption of Li during the charging and discharging process, and the molar content of Li in the positive electrode active material is different when the battery is discharged to different states. In the enumeration of positive electrode active materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode active material is used in the battery system, and the molar content of Li will change after the charge and discharge cycle. In the enumeration of positive electrode active materials in this application, the molar content of O is only an ideal state value. The release of lattice oxygen will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0083] In one embodiment, the positive electrode film layer further includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0084] In one embodiment, the positive electrode film layer further includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0085] In one embodiment, the positive electrode sheet can be prepared by separately forming a positive electrode slurry from the components used to prepare the positive electrode sheet. For example, the first positive electrode active material and / or the second positive electrode active material, a conductive agent, a binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry. The positive electrode slurry is then coated on a positive electrode current collector. After drying and cold pressing, the positive electrode sheet can be obtained.

[0086] [Electrolyte]

[0087] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte; it can be selected based on specific needs. The electrolyte includes an electrolyte salt, a solvent, and a metal ion whose Stokes radius is smaller than that of a lithium ion.

[0088] In one embodiment, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0089] 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, methylpropyl carbonate, ethylpropyl 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, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0090] 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 a halogen anion.

[0091] 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 battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0092] [Isolator]

[0093] In one embodiment, the battery further includes a separator. The present application has no particular limitation on the type of separator. For example, any known porous structure separator with good chemical and mechanical stability can be selected.

[0094] In one embodiment, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0095] In one embodiment, the negative electrode sheet, the positive electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0096] In one embodiment, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0097] In one embodiment, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0098] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 100 having a square structure as an example.

[0099] It should be understood that the battery cell 100 may include the lithium-ion battery in the aforementioned embodiment.

[0100] Figure 2 shows an example battery module 200. Referring to Figure 2 , in the battery module 200, multiple battery cells 100 may be arranged sequentially along the length of the battery module 200. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 100 may be secured by fasteners. The multiple battery cells 100 may be of the same chemical system or of different chemical systems.

[0101] Optionally, in one embodiment, the battery module 200 may further include a housing having an accommodation space, and the plurality of battery cells 100 may be accommodated in the accommodation space.

[0102] Optionally, in one embodiment, the battery modules 200 may be assembled into a battery. The battery may contain one or more battery modules 200. The specific number may be selected by those skilled in the art according to the application and capacity of the battery.

[0103] Figures 3 and 4 illustrate an example battery pack 300. Referring to Figures 3 and 4, the battery pack 300 may include a battery box and multiple battery modules 200 disposed within the battery box. The battery box includes an upper case 301 and a lower case 302. The upper case 301 can be placed over the lower case 302 to form an enclosed space for accommodating the battery modules 200. The multiple battery modules 200 can be arranged in any manner within the battery box.

[0104] It should be understood that the battery cells 100 can first be assembled into the battery module 200, and the battery pack 300 can be assembled from the battery module 200. Alternatively, the battery pack 300 can be directly assembled from the battery cells 100, omitting the intermediate form of the battery module 200.

[0105] In addition, the present application also provides an electrical device, which includes the lithium-ion battery in the aforementioned embodiment.

[0106] In another embodiment, an electrical device includes at least one of the battery cell 100, battery module 200, or battery pack 300 provided herein. The battery cell 100, battery module 200, or battery pack 300 can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0107] 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.

[0108] As an example of an electric device, the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module can be used.

[0109] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0110] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0111] [Examples 1-10 and Comparative Example 1]

[0112] Example 1

[0113] (1) Preparation of negative electrode sheet

[0114] 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 deionized water at a mass ratio of 94:1:3:2. The mixture was mixed thoroughly to produce a negative electrode slurry. The slurry was then evenly coated onto the negative electrode current collector copper foil. The negative electrode sheets were then dried, rolled, and slit.

[0115] (2) Preparation of positive electrode sheet

[0116] The positive electrode active material, LiNi5Co2Mn3O2, the conductive agent, carbon nanotubes, and the binder, polyvinylidene fluoride, were dissolved in N-methylpyrrolidone at a mass ratio of 96:2:2 and mixed thoroughly to produce a positive electrode slurry with a solid content of 50%. The slurry was then evenly coated onto the positive electrode current collector, aluminum foil. The positive electrode sheets were then dried, rolled, and slit.

[0117] (3) Preparation of electrolyte

[0118] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), the electrolyte was prepared by uniformly mixing the organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), then adding appropriate amounts of lithium hexafluorophosphate (LiPF6) and potassium hexafluorophosphate (KPF6) to achieve a molar concentration of 1M for LiPF6 and 0.03M for KPF6.

[0119] (4) Preparation of reference electrode

[0120] 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 tab to prepare a reference electrode.

[0121] (5) Preparation of lithium-ion batteries

[0122] (5.1) Stack the positive electrode sheet, the separator, and the negative electrode sheet in order so that the separator is located 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, dry them, and inject the electrolyte to obtain the lithium-ion battery of Example 1.

[0123] (5.2) Stack the positive electrode sheet, separator, reference electrode, separator, and negative electrode sheet of a specific size in order so that the reference electrode is located between two layers of separators; then place the stacked components in a shell, dry them, and inject the electrolyte to obtain the reference cell of Example 1.

[0124] The lithium-ion batteries and reference batteries were formed using the following formation conditions: using a blue-electric test system, the positive and negative electrodes were connected, the battery rested for 1 minute, and then charged at a constant current of 0.1C to 4.2V. Then, the battery was charged at a constant voltage of 4.2V with a cutoff current of 0.02C. After resting for 10 minutes, the battery was discharged at a constant current of 0.1C to a cutoff voltage of 2.5V and rested for 48 hours. The formation process forms an SEI film and helps reduce battery polarization.

[0125] (6) Lithium plating of reference electrode

[0126] Before performing a performance test on the reference cell, the reference electrode of the reference cell needs to be activated. Specifically, the reference electrode of the reference cell needs to be plated with lithium. The specific process of lithium plating is as follows: connect the positive electrode to the reference electrode, charge at a constant current of 20μA for 2 hours, and after standing for 5 minutes, connect the negative electrode to the reference electrode, and discharge at a constant current of 20μA for 2 hours 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 cell after lithium plating to the lithium metal electrode is 40mV to 400mV, which is considered to be the completion of reference electrode activation.

[0127] 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 conditions; the performance of the reference battery represents the theoretical performance of the lithium-ion battery under the conditions.

[0128] 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 .

[0129] Example 2

[0130] Compared with Example 1, in the lithium ion battery of Example 2 and the reference battery, CB=1.06.

[0131] Example 3

[0132] Compared with Example 1, in the lithium ion battery of Example 3 and the reference battery, CB=1.24.

[0133] Example 4

[0134] Compared with Example 1, in the lithium ion battery of Example 4 and the reference battery, CB=1.32.

[0135] Example 5

[0136] Compared with Example 1, in the lithium ion battery of Example 5 and the reference battery, C = 0.012M, σ = 9.7mS·cm -1 .

[0137] Example 6

[0138] Compared with Example 1, in the lithium ion battery of Example 6 and the reference battery, C = 0.05M, σ = 9.1mS·cm-1 .

[0139] Example 7

[0140] 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 + .

[0141] Example 8

[0142] Compared with Example 1, in the lithium ion battery of Example 8 and the reference battery, σ=6mS·cm - 1 ,η=5Pa·s.

[0143] Example 9

[0144] Compared with Example 1, in the lithium ion battery of Example 9 and the reference battery, h = 25 μm, m = 4 mg·cm -2 .

[0145] Example 10

[0146] Compared with Example 1, in the lithium ion battery of Example 10 and the reference battery, h = 60 μm, m = 10 mg·cm -2 .

[0147] Comparative Example 1

[0148] Compared with Example 1, the lithium ion battery of Comparative Example 1 and the reference battery do not contain metal ions with a Stokes radius smaller than that of lithium ions.

[0149] Product parameters of Examples 1-10 and Comparative Example 1.

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

[0151] In Table 1, "CB value" represents the CB value of the lithium-ion battery and the reference battery, "metal ion" represents the metal ion in the electrolyte whose Stokes radius is smaller than that of the lithium ion. "C" represents the molar concentration of the metal ion 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, and "m" represents the loading amount of the negative electrode film on the negative electrode current collector.

[0152] The battery performance tests were carried out on the above embodiments and comparative examples, and the measured performance data are detailed in Table 2.

[0153] Table 2: Product parameters of Examples 1-10 and Comparative Example 1

[0154] In Table 2, "Critical No-lithium Plating SOC of Reference Battery" indicates the state of charge of the reference battery when lithium plating is about to occur at the negative electrode of the reference battery as measured by the charging capacity test, "Critical No-lithium Plating SOC of Lithium-ion Battery" indicates the state of charge of the lithium-ion battery when lithium plating is about to occur at the negative electrode of the lithium-ion battery as measured by the charging capacity test, and "SOC Difference" indicates the difference between the critical no-lithium plating SOC of the reference battery and the critical no-lithium plating SOC of the lithium-ion battery. "Lithium plating is about to occur" means that during the charging capacity test of a lithium-ion battery or a reference battery being charged at a certain current, if more electricity is charged at the current, lithium plating will occur at the negative electrode.

[0155] 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.

[0156] Starting with a state of charge (SOC) of 0% for the reference battery, a constant current charge of 4C was performed. Charging was terminated when the negative electrode potential reached 0 mV relative to the reference electrode potential. The battery's SOC at the time of charge termination was recorded. This SOC represents the critical non-lithium deposition SOC of the reference battery of Example 1, which can represent the theoretical charge capacity of the lithium-ion battery of Example 1.

[0157] The charging capacity test of the lithium-ion battery in Table 2 can be carried out in the following steps:

[0158] Prepare multiple identical lithium-ion batteries and perform cycle testing on these multiple lithium-ion batteries. The specific test conditions are as follows: in a constant temperature chamber at 25°C, the lithium-ion batteries are allowed to rest for 2 hours, then discharged at a constant current of 0.33C to 2.5V. After resting for 5 minutes, the multiple lithium-ion batteries are each charged at a constant current of 4C to different states of charge, then charged at a constant current of 0.33C to 4.2V, and then charged at a constant voltage of 4.2V to a current of less than or equal to 0.05C. After 50 cycles, the multiple lithium-ion batteries are disassembled and observed for lithium deposition on the negative electrode plates. In the step of charging the multiple lithium-ion batteries at a constant current to different states of charge, the multiple different states of charge are set based on the critical state of charge (SOC) of the reference battery at which no lithium deposition occurs. For example, if the critical state of charge (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%, for example, 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 after 50 cycles, the lithium-ion battery is in a fully charged state, that is, the battery has been charged to 4.2V and constant voltage charged at 4.2V to a current of less than or equal to 0.05C.

[0159] By cycling the above-mentioned multiple identical lithium-ion batteries, negative electrode plates of the lithium-ion batteries charged to multiple different SOCs and cycled were obtained. The negative electrode plates corresponding to two adjacent SOCs exhibited lithium deposition and no lithium deposition, respectively. The SOC corresponding to the negative electrode plate that did not deposit lithium was recorded as the critical no-lithium deposition SOC of the lithium-ion battery.

[0160] The following is a brief introduction to the test methods for the physical and chemical parameters and performance parameters involved in the embodiments of this application. It should be understood that the following test methods are only examples, and other test methods known in the art can also be used for testing.

[0161] 1. CB value test method

[0162] According to the embodiments of the present application, the reversible capacity test of the negative electrode is determined by the following steps: take a single-sided coated negative electrode sheet and cut it into a disc with a diameter of 14 mm. Assemble a button cell in a glove box, wherein a small lithium metal disc is used as the counter electrode and the electrolyte prepared above is used. After standing at 25°C for 6 hours, discharge at a constant current rate of 0.1C to 5mV, then discharge at a constant current rate of 0.01C to 5mV, then stand for 5 minutes, and charge at a constant current rate of 0.1C to 0.7V. The charging capacity is recorded as Ca in mAh.

[0163] According to the embodiments of the present application, the reversible capacity test of the positive electrode can be determined by the following steps: take a single-sided coated positive electrode sheet and cut it into a disc with a diameter of 14 mm. Assemble a button cell in a glove box, wherein a small lithium metal disc is used as the counter electrode and the electrolyte prepared 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.

[0164] The CB value of a battery can be calculated using the formula CB = Ca / Cc, where Ca is the charge capacity obtained through the negative electrode reversible capacity test, and Cc is the discharge capacity obtained through the positive electrode reversible capacity test.

[0165] 2. Molar concentration test method

[0166] 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.

[0167] Exemplarily, the test method is in accordance with HG / T 4067-2015, and the ICP (Inductively coupled plasma) test method is used 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.

[0168] 3. Test method for electrolyte viscosity

[0169] For specific test methods, please refer to "Viscosity Measurement Method": GB / T 10247-2008.

[0170] 4. Test method for electrolyte conductivity

[0171] The test method is in accordance with HG / T 4067-2015. The conductivity of the electrolyte to be tested is tested using a conductivity meter: about 100 ml of the sample to be tested is taken into 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.

[0172] 5. Load test method

[0173] Cut the negative electrode sheet to a specified area S and weigh the mass m1. Wash away the film layer on the surface of the negative electrode current collector and weigh the mass m2 of the negative electrode current collector. The loading amount of the negative electrode film layer on the negative electrode current collector is (m1-m2) / S.

[0174] 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 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, with a small difference, 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 fully exert its charging capacity. However, the critical non-lithium precipitation SOC of the lithium-ion battery of 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 of the Comparative Example is relatively poor. In other words, the lithium-ion battery of the Comparative Example cannot exert its charging capacity. Thus, it is shown that by introducing metal ions with a Stokes radius smaller than that of lithium ions into 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.

[0175] According to the comparative analysis of Examples 1-4, it can be seen that as the CB value increases, the critical non-lithium deposition SOC of the lithium-ion battery increases, which proves 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 non-lithium deposition SOC of the lithium-ion battery.

[0176] According to the comparative analysis of Examples 1, 5-6, the concentration of metal ions in Example 5 is lower, while the concentration of metal ions in Examples 1 and 6 is higher. Therefore, the suppression 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. The critical no-lithium precipitation SOC of the lithium-ion batteries in Examples 1 and 6 is greater than that in Example 5. The performance data of Examples 1 and 6 are not much different, indicating that within a certain range, increasing the concentration of metal ions is beneficial to suppressing lithium precipitation and improving the charging capacity of lithium-ion batteries.

[0177] Example 7 demonstrates that the introduction of sodium ions into the electrolyte has a similar effect as potassium ions.

[0178] According to the comparative analysis of Example 1 and Example 8, when the conductivity of the electrolyte is low, the critical no-lithium deposition SOC of the lithium-ion battery is also small, indicating that selecting an electrolyte with a higher conductivity helps to improve concentration polarization and thus inhibit lithium deposition, helping to improve the charging capacity of the lithium-ion battery.

[0179] According to the comparative analysis of Example 1 and Examples 9-10, Example 9, which has the smallest thickness of the negative electrode film layer, has the largest critical non-lithium deposition SOC of the lithium-ion battery, indicating 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 sheet, reduce the risk of lithium deposition on the negative electrode sheet, and improve the charging capacity of the lithium-ion battery.

[0180] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, the various technical features described in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. 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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