Lithium ion battery and electric apparatus

Abstract

Disclosed in the embodiments of the present application are a lithium ion battery and an electric apparatus. The lithium ion battery comprises: an electrolyte, which comprises metal ions, wherein the reduction potential of the metal ions is higher than the reduction potential of lithium ions; and a low CB value region, wherein the CB value of the lithium ions in the low CB value region satisfies: 0<CB<1, and the CB value is the ratio of the capacity of an anode active material per unit area to the capacity of a cathode active material per unit area. The lithium ion battery provided in the present application can effectively ameliorate the problem of lithium plating in the low CB value region.

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. 202310794171.5, filed on June 30, 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] During the manufacturing process of lithium-ion batteries, process limitations inevitably lead to areas where the positive and negative electrode capacities do not match, known as low CB value regions. These low CB value regions are prone to lithium plating on the negative electrode sheet, adversely affecting the capacity and safety of the lithium-ion battery. Therefore, mitigating the impact of lithium plating on lithium-ion battery performance is a pressing technical challenge.

[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 includes an electrolyte containing metal ions, which can effectively improve the lithium plating problem in the low CB value area.

[0008] In a first aspect, a lithium-ion battery is provided, comprising: an electrolyte, the electrolyte comprising metal ions, the reduction potential of the metal ions being higher than the reduction potential of lithium ions; and a low CB value region, wherein the CB value of the lithium-ion battery in the low CB value region satisfies the following: 0<CB<1, where the CB value is the ratio of the capacity per unit area of ​​the negative electrode active material to the capacity per unit area of ​​the positive electrode active material.

[0009] In the low CB value area of ​​the lithium-ion battery, the CB value is less than 1. In other words, in the low CB value area, the capacity of the positive electrode active material per unit area is greater than the capacity of the negative electrode active material per unit area. Therefore, during the cycle, lithium deposition is likely to occur at the negative electrode piece corresponding to the low CB value area. In the embodiment of the present application, metal ions with a reduction potential higher than that of lithium ions are introduced into the electrolyte. When lithium deposition occurs at the negative electrode piece corresponding to the low CB value area, the metal ions in the electrolyte can freely move to the position of lithium deposition and be reduced to a metal element by lithium. Thus, the lithium deposition in the low CB value area is improved, helping to improve the reversible capacity and cycle performance of the lithium-ion battery.

[0010] In one possible implementation, the lithium-ion battery includes a negative electrode plate, and the percentage X of the area of ​​the negative electrode plate corresponding to the low CB value region to the area of ​​the negative electrode plate satisfies: 0% < X; optionally, 0% < X ≤ 10%; optionally, 0% < X ≤ 2%.

[0011] In a possible implementation, the CB value of the lithium-ion battery in the low CB value region satisfies: 0.5<CB<1.

[0012] In one possible implementation, the reduction potential of the metal ion is satisfy: Among them, M n+ represents the metal ion, n represents the valence of the metal ion, C represents the molar concentration of the metal ion in the electrolyte, R represents the ideal gas constant, T represents the temperature, and F represents the Faraday constant. Represents the standard electrode potential of lithium ions.

[0013] In the embodiments of the present application, by selecting metal ions whose reduction potentials satisfy the above conditions, the metal ions can be reduced to metal elements by the precipitated lithium, thereby improving the lithium precipitation problem in the low CB value region.

[0014] In one possible implementation, the reduction potential of the metal ion is satisfy:

[0015] In the embodiments of the present application, by selecting metal ions whose reduction potential meets the above conditions, while the metal ions can be reduced by lithium, it helps to reduce the oxidizing properties of the metal ions, thereby reducing the impact of the metal ions on the electrolyte and the positive and negative electrode plates.

[0016] In a possible implementation, the molar concentration C of the metal ions in the electrolyte satisfies: 0.001M≤C≤0.2M.

[0017] In the embodiments of the present application, by controlling the concentration of metal ions in the electrolyte within a suitable range, lithium deposition is suppressed while also helping to reduce the self-discharge of the lithium-ion battery.

[0018] In one possible implementation, the metal ions include Mg 2+ 、Al 3+ 、Zn 2+ 、Sb 2+ At least one of .

[0019] In a second aspect, a lithium-ion battery is provided, comprising: a low CB value region, wherein the CB value of the lithium-ion battery in the low CB value region satisfies the following: 0.5<CB<1; and a negative electrode plate, wherein the content of a metal element per unit area at the negative electrode plate corresponding to the low CB value region is greater than the content of the metal element per unit area at the negative electrode plate corresponding to the high CB value region; wherein the CB value of the lithium-ion battery in the high CB value region satisfies the following: CB≥1; 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; and the reduction potential of the metal ion corresponding to the metal element is higher than the reduction potential of the lithium ion.

[0020] In a possible implementation, the percentage X of the area of ​​the negative electrode sheet corresponding to the low CB value region to the area of ​​the negative electrode sheet satisfies: 0% < X; optionally, 0% < X ≤ 10%; optionally, 0% < X ≤ 2%.

[0021] In a possible implementation, the CB value of the lithium-ion battery in the low CB value region satisfies: 0.5<CB<1.

[0022] In a possible implementation, the metal element includes at least one of Mg, Al, Zn, and Sb.

[0023] In a possible implementation, the lithium-ion battery includes an electrolyte, the electrolyte includes metal ions, and the metal ions are ions corresponding to the metal element.

[0024] In a possible implementation, the molar concentration C' of the metal ions in the electrolyte satisfies: 0M≤C'<0.2M.

[0025] In a third aspect, an electrical device is provided, wherein the electrical device includes the lithium-ion battery in any possible implementation of the first aspect and / or the lithium-ion battery in any possible implementation of the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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.

[0027] Figure 1 is a schematic diagram of the principle of metal ions inhibiting lithium dendrites.

[0028] FIG2 is a schematic diagram of a low CB value region.

[0029] FIG3 is a schematic diagram of a battery cell.

[0030] FIG4 is a schematic diagram of a battery module.

[0031] FIG5 is a schematic diagram of a battery.

[0032] FIG6 is another schematic diagram of a battery. DETAILED DESCRIPTION

[0033] 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.

[0034] " 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.

[0035] 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," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0036] 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).

[0037] 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.

[0038] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0039] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their generally accepted meanings in the art.

[0040] 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.

[0041] Where mentioned, the “low CB value region” refers to a region in the battery where the CB value is less than 1.

[0042] Where mentioned, the “high CB value region” refers to the region in the battery where the CB value is greater than or equal to 1.

[0043] If mentioned, Refers to the standard electrode potential of lithium ions. The standard electrode potential of a substance is the electrode potential measured when the substance is combined with a standard hydrogen electrode in a galvanic cell. For example, the standard electrode potential of lithium relative to hydrogen is -3.04V. In this application, electrode potential is also referred to as reduction potential.

[0044] If mentioned, "3V vs.Li + / Li” means that lithium is used as the counter electrode and the electrode potential relative to the lithium electrode is 3 V.

[0045] Next, embodiments of the present application are introduced.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] In the production process of lithium-ion batteries, a slurry containing active materials needs to be coated onto the current collector to form a pole piece. Due to limitations such as the coating process and the different drying speeds of the slurry at different positions on the pole piece after coating, it is usually impossible to obtain a pole piece with completely uniform thickness. This results in a low CB value area in the lithium-ion battery. During the cycle of the lithium-ion battery, since the capacity of the negative electrode pole piece corresponding to the low CB value area is relatively low, it cannot fully accommodate the lithium ions released from the positive electrode pole piece corresponding to the low CB value area, making it impossible for the excess lithium ions to be embedded in the negative electrode active material, resulting in lithium precipitation. As lithium ions continue to precipitate, the growth of lithium dendrites continuously consumes active lithium ions, resulting in a decrease in the capacity and cycle life of the battery.

[0050] In view of this, an embodiment of the present application provides a lithium-ion battery and an electrical device, wherein the electrolyte of the lithium-ion battery includes metal ions, which can improve lithium deposition and inhibit the growth of lithium dendrites during the cycle of the lithium-ion battery, thereby helping to improve the capacity retention rate and cycle performance of the lithium-ion battery.

[0051] 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.

[0052] First, a lithium-ion battery is provided, which includes an electrolyte, the electrolyte includes metal ions, and the reduction potential of the metal ions is higher than the reduction potential of lithium ions; a low CB value region, the CB value of the lithium-ion battery in the low CB value region satisfies: 0<CB<1, 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.

[0053] Specifically, the CB value in the low CB value region can be any value between 0 and 1, or within the range obtained by combining any two values ​​between 0 and 1. Since the CB value in the low CB value region of a lithium-ion battery is less than 1, lithium deposition is likely to occur during cycling. Figure 1 is a schematic diagram of the principle of suppressing lithium deposition in a lithium-ion battery according to an embodiment of the present application.

[0054] As shown in Figure 1, the negative electrode plate 1 includes a negative electrode current collector 11 and a negative electrode active material layer 12 disposed on the negative electrode current collector 11. After the lithium-ion battery is formed, the negative electrode plate 1 also includes a solid electrolyte interface (SEI) film 13 formed on the surface of the negative electrode active material layer 12. Region a corresponds to the low CB value region, and region b corresponds to the high CB value region. As lithium is continuously deposited in the low CB value region, lithium dendrites 14 grow, puncturing the SEI film 13.

[0055] In this embodiment, metal ions with a higher reduction potential than lithium ions are introduced into the lithium-ion battery, enabling the metal ions to be reduced by lithium. Consequently, once lithium dendrites grow and pierce the SEI membrane, the free metal ions in the electrolyte will migrate to the dendrites, reducing the precipitated lithium to elemental metal. This elemental metal can then form an alloy with lithium, thereby inhibiting lithium deposition and improving the capacity retention and cycle performance of the lithium-ion battery.

[0056] It should be understood that the low CB value region a in FIG1 is only an example of a low CB value region, which shows that the thickness of the negative active material layer 12 on the negative electrode sheet 1 is uniform, but due to the thicker thickness of the active material layer on the positive electrode sheet (not shown in the figure), this position is a low CB value region a. FIG2 shows another example of forming a low CB value region a. As shown in FIG2, the positive electrode sheet 2 includes a positive electrode current collector 21 and a positive electrode active material layer 22 disposed on the positive electrode current collector 21. In the case where the thickness of the positive electrode active material layer 22 is uniform, a thinner thickness of the negative electrode active material layer will also cause this position to become a low CB value region a.

[0057] In another possible scenario, the thicknesses of the positive electrode active material layer and the negative electrode active material layer at a certain location are not uniform. For example, the positive electrode active material layer is thicker while the negative electrode active material layer is thinner, which may also cause the location to become a low CB value area a.

[0058] In one embodiment, the lithium-ion battery includes a negative electrode plate, and the percentage X of the area of ​​the negative electrode plate corresponding to the low CB value region to the area of ​​the negative electrode plate satisfies: 0% < X; optionally, 0% < X ≤ 10%; optionally, 0% < X ≤ 2%.

[0059] Specifically, X can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a numerical range within the range obtained by combining any two of the above numerical values.

[0060] The low CB value region arises due to process limitations in lithium-ion battery production. Therefore, typically, 0% < X. On the other hand, based on existing lithium-ion battery production processes, the area of ​​the low CB value region cannot be infinitely large. Considering factors such as lithium-ion battery product yield, the value of X must also satisfy the following requirement: X ≤ 10%. It should be understood that, generally, the smaller the low CB value region, the smaller X, and the smaller the area on the negative electrode sheet prone to lithium deposition or dendrite growth, which is more beneficial to lithium-ion battery product yield.

[0061] In one example, since the position of the negative electrode sheet corresponding to the low CB value area is very prone to lithium deposition, the lithium-ion battery after the cycle can be disassembled and the area of ​​the lithium deposition area on the negative electrode sheet can be measured to approximate the area of ​​the negative electrode sheet corresponding to the low CB value area. In another example, in order to facilitate testing, some low CB value areas can be artificially created during the preparation of the lithium-ion battery so that the area of ​​the low CB value area can be artificially controlled and adjusted. During the test, the capacity of the specified area of ​​the positive electrode sheet and the negative electrode sheet can be measured to calculate the CB value of the specified area, thereby determining whether the area is a low CB value area.

[0062] In one embodiment, the CB value of the lithium-ion battery in the low CB value region satisfies: 0.5<CB<1.

[0063] Specifically, the CB value in the low CB value region may be any value between 0.5 and 1, or within a range obtained by combining any two values ​​between 0.5 and 1.

[0064] In one embodiment, the reduction potential of the metal ion satisfy:

[0065] Among them, M n+ represents the metal ion, n represents the valence of the metal ion, C represents the molar concentration of the metal ion in the electrolyte, R represents the ideal gas constant, T represents the temperature, and F represents the Faraday constant. Represents the standard electrode potential of lithium ions. Typically, R is equal to 8.314 J·K -1 ·mol - 1 , T is in K, and F is equal to 96485 C·mol -1 .

[0066] In one embodiment, the reduction potential of the metal ion satisfy:

[0067] In this embodiment, by selecting metal ions whose reduction potential meets the above conditions, when the reduction potential of the metal ions is higher than that of lithium ions and can be reduced by lithium; by controlling the upper limit of the reduction potential of the metal ions, metal ions with relatively weak oxidizing properties can be selected, thereby reducing the impact of metal ions on the electrolyte, positive electrode sheet, and negative electrode sheet.

[0068] In one embodiment, the molar concentration C of the metal ions in the electrolyte satisfies: 0.001M≤C≤1M; optionally, 0.001M≤C≤0.2M.

[0069] Specifically, C can be 0.001M, 0.002M, 0.003M, 0.004M, 0.005M, 0.006M, 0.007M, 0.008M, 0.009M, 0.01M, 0.02M, 0.03M, 0.04M, 0.05M, 0.06M, 0.07M, 0.08M, 0.09M, 0.1M, 0.2M, 0.3M, 0.4M, 0.5M, 0.6M, 0.7M, 0.8M, 0.9M, 1M, or its value is within the range obtained by combining any two of the above values.

[0070] On the one hand, if the molar concentration of metal ions in the electrolyte is too low, its inhibitory effect on lithium dendrites is limited, and it is impossible to achieve continuous inhibition of lithium dendrites during the long cycle of lithium-ion batteries. On the other hand, if the molar concentration of metal ions in the electrolyte is too high, too many metal ions are reduced by lithium, and there is too much metal on the surface of the negative electrode, which reduces the insulation performance of the SEI film and increases the self-discharge of the lithium-ion battery.

[0071] Therefore, in this embodiment, by controlling the metal ion concentration in the electrolyte within a suitable range, it is possible to suppress lithium dendrites while reducing the impact of the reduced metal ions on the insulating properties of the SEI film, thereby helping to reduce the self-discharge of the lithium-ion battery.

[0072] In one embodiment, the metal ions include Mg 2+ 、Al 3+ 、Zn 2+ 、Sb 2+ At least one of .

[0073] It should be understood that the metal ions can be provided by a salt that can be dissolved in the electrolyte. Taking magnesium ions as an example, magnesium ions can be introduced by adding magnesium nitrate to the electrolyte. The metal salt includes an anion, and illustratively, the anion can be acetate ion, nitrate ion, hexafluorophosphate ion, or bis(fluorosulfonyl)imide ion.

[0074] In the above embodiment, a lithium-ion battery capable of suppressing lithium dendrites for a long time is introduced. Next, the lithium-ion battery after the above lithium-ion battery has been cycled is introduced.

[0075] An embodiment of the present application further provides a cycled lithium-ion battery, comprising a low CB value region, wherein the CB value of the lithium-ion battery in the low CB value region satisfies: 0.5<CB<1; and a negative electrode plate, wherein the content of the metal element per unit area at the negative electrode plate corresponding to the low CB value region is greater than the content of the metal element per unit area at the negative electrode plate corresponding to the high CB value region; wherein the CB value of the lithium-ion battery in the high CB value region satisfies: CB≥1; the CB value is the ratio of the capacity of the negative electrode active material to the capacity of the positive electrode active material; and the reduction potential of the metal ion corresponding to the metal element is higher than the reduction potential of the lithium ion.

[0076] It should be understood that in the embodiments of the present application, the cycled lithium-ion battery can be considered as a lithium-ion battery in which lithium deposition has occurred, that is, a lithium-ion battery after lithium deposition. As mentioned in the aforementioned embodiments, the electrolyte of the lithium-ion battery includes metal ions. Therefore, the cycled lithium-ion battery deposits lithium at the negative electrode piece corresponding to the low CB value area, and the deposited lithium is consumed by the metal ions, so that in the cycled lithium-ion battery, the metal element content per unit area at the negative electrode piece corresponding to the low CB value area is greater than the metal element content per unit area at the negative electrode piece corresponding to the high CB value area.

[0077] In one embodiment, the percentage X of the area of ​​the negative electrode piece corresponding to the low CB value region to the area of ​​the negative electrode piece satisfies: 0%<X; optionally, 0%<X≤10%; optionally, 0%<X≤2%.

[0078] In one embodiment, the CB value of the lithium-ion battery in the low CB value region satisfies: 0.5<CB<1.

[0079] In one embodiment, the metal element includes at least one of Mg, Al, Zn, and Sb.

[0080] In one embodiment, a lithium-ion battery includes an electrolyte, wherein the electrolyte includes metal ions, and the metal ions are ions corresponding to metal elements.

[0081] Specifically, as the number of cycles of a lithium-ion battery increases, the metal ions in the electrolyte are consumed by the precipitated lithium, and the concentration of the metal ions gradually decreases. Therefore, in a lithium-ion battery after cycling, the electrolyte may still contain some metal ions that have not been reduced by lithium.

[0082] In one embodiment, the molar concentration C' of the metal ions in the electrolyte satisfies: 0M≤C'<0.2M.

[0083] It should be understood that metal ions in a cycled lithium-ion battery may be completely consumed or partially residual, so C' may be 0 or non-0. Specifically, C' may be 0M, 0.02M, 0.04M, 0.06M, 0.08M, 0.1M, 0.12M, 0.14M, 0.16M, 0.18M, ​​0.2M, or a numerical range within the range obtained by combining any two of the above numerical values.

[0084] Next, the positive electrode sheet, negative electrode sheet, separator and electrolyte in the lithium-ion battery are introduced in detail.

[0085] [Negative electrode]

[0086] The negative electrode sheet generally includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

[0087] As an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0088] 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.).

[0089] 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.

[0090] In one embodiment, the negative electrode active material layer further includes a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0091] In one embodiment, the negative electrode active material 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.

[0092] In one embodiment, the negative electrode active material layer further includes other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0093] 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.

[0094] [Positive electrode]

[0095] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.

[0096] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is provided on either or both of the two facing surfaces of the positive electrode current collector.

[0097] In one embodiment, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0098] 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 0.15 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.

[0099] In one embodiment, the positive electrode active material layer further includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0100] In one embodiment, the positive electrode active material layer further includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0101] 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.

[0102] [Electrolyte]

[0103] 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 metal ions with a higher reduction potential than lithium ions.

[0104] 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.

[0105] 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.

[0106] In one embodiment, the metal ions include Mg 2+ 、Al 3+ 、Zn 2+ 、Sb 2+ At least one of .

[0107] 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 acetate, nitrate, hexafluorophosphate, and perchlorate.

[0108] In one embodiment, the reduction potential of the metal ion satisfy: Among them, M n+ represents the metal ion, n represents the valence of the metal ion, C represents the molar concentration of the metal ion in the electrolyte, R represents the ideal gas constant, T represents the temperature, and F represents the Faraday constant. Represents the standard electrode potential of lithium ions.

[0109] In one embodiment, the reduction potential of the metal ion satisfy:

[0110] In one embodiment, in the lithium-ion battery before cycling, the molar concentration C of the metal ions in the electrolyte satisfies: 0.001M≤C≤1M; optionally, 0.001M≤C≤0.2M.

[0111] In one embodiment, in the cycled lithium-ion battery, the molar concentration C' of the metal ions in the electrolyte satisfies: 0M≤C'<0.2M.

[0112] 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.

[0113] [Isolator]

[0114] 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.

[0115] 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.

[0116] 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.

[0117] In one embodiment, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0118] 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.

[0119] 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, FIG3 shows a battery cell 300 having a square structure as an example.

[0120] It should be understood that the battery cell 300 may include the lithium-ion battery in the aforementioned embodiment.

[0121] Figure 4 shows an example battery module 400. Referring to Figure 4 , in the battery module 400, multiple battery cells 300 may be arranged sequentially along the length of the battery module 400. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 300 may be secured using fasteners. The multiple battery cells 300 may be of the same chemical system or of different chemical systems.

[0122] Optionally, in one embodiment, the battery module 400 may further include a housing having an accommodation space, and the plurality of battery cells 300 may be accommodated in the accommodation space.

[0123] Optionally, in one embodiment, the battery modules 400 may be assembled into a battery. The battery may contain one or more battery modules 400. The specific number may be selected by those skilled in the art according to the application and capacity of the battery.

[0124] Figures 5 and 6 illustrate an example battery 500. Referring to Figures 5 and 6, the battery 500 may include a battery box and multiple battery modules 400 disposed within the box. The battery box includes an upper case 501 and a lower case 502. The upper case 501 can be placed over the lower case 502 to form an enclosed space for accommodating the battery modules 400. The multiple battery modules 400 can be arranged in any manner within the battery box.

[0125] It should be understood that in other embodiments, the battery 500 is also referred to as a battery pack. The battery cells 300 may first be assembled into the battery module 400, and the battery 500 may be assembled from the battery module 400. Alternatively, the battery 500 may be assembled directly from the battery cells 300, omitting the intermediate battery module 400.

[0126] In addition, the present application also provides an electrical device, which includes the lithium-ion battery in the aforementioned embodiment.

[0127] In another embodiment, an electrical device includes at least one of the battery cell 300, battery module 400, or battery 500 provided herein. The battery cell 300, battery module 400, or battery 500 can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, 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.

[0128] As an electric device, a battery cell 300 , a battery module 400 , or a battery 500 may be selected according to its usage requirements.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] [Examples 1-10 and Comparative Example 1]

[0133] Example 1

[0134] (1) Preparation of negative electrode sheet

[0135] The negative electrode active material, artificial graphite (1 kg, 15 μm particle size), the conductive agent, acetylene black (10 g), the binder, styrene-butadiene rubber (30 g), and the thickener, sodium carboxymethyl cellulose (20 g), were dissolved in 1 kg of deionized water and mixed thoroughly to create 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.

[0136] (2) Preparation of positive electrode sheet

[0137] The positive electrode active material, LiNi5Co2Mn3O2 (1 kg), the conductive agent, carbon nanotubes (20 g), and the binder, polyvinylidene fluoride (20 g), were dissolved in 1 kg of N-methylpyrrolidone and mixed thoroughly to produce a positive electrode slurry. The slurry was then evenly coated onto the positive electrode current collector, aluminum foil. The positive electrode sheets were then dried, rolled, and slit.

[0138] (3) Preparation of electrolyte

[0139] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), electrolytes E1 and E2 were prepared, where E1 was used for the initial injection of the lithium-ion battery, and E2 was used for the secondary injection of the lithium-ion battery after formation; in the formed lithium-ion battery, the volume ratio of E1 to E2 was 4:1.

[0140] Electrolyte E1 preparation: Organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and 1.25 M lithium hexafluorophosphate (LiPF6) was added and dissolved in the solvent, and stirred to obtain electrolyte E1.

[0141] Electrolyte E2 preparation: Organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and 0.25 M magnesium bis(trifluoromethylsulfonyl)imide was added and dissolved in the solvent, and stirred to obtain electrolyte E2.

[0142] (4) Preparation of lithium-ion batteries

[0143] The positive electrode sheet, separator, and negative electrode sheet are stacked in order so that the separator is between the positive electrode sheet and the negative electrode sheet and can isolate the positive electrode sheet from the negative electrode sheet; then the stacked components are wound and placed in a shell, and after drying, the electrolyte E1 is injected.

[0144] The battery was formed using the following 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 0.33C to 4.2V. The battery was then charged at a constant voltage of 4.2V with a cutoff current of 0.05C. After resting for 10 minutes, the battery was discharged at a constant current of 0.33C to a cutoff voltage of 2.5V, and rested for 50 hours. The formation process forms an SEI film, which helps reduce polarization in the battery.

[0145] The formed battery is subjected to a second injection, wherein the electrolyte E2 is injected into the battery, and the lithium-ion battery is obtained after packaging.

[0146] The lithium-ion battery in Example 1 was tested. The area S1 of the negative electrode sheet corresponding to the low CB value region accounted for 5% of the total area S of the negative electrode sheet, that is, S1 / S = 5%. The CB value of the low CB value region was 0.95, and the CB value of the high CB value region was 1.1. The lithium ion concentration in the electrolyte was 1M, the molar concentration of magnesium ions was C = 0.05M, and the reduction potential of magnesium ions was 0.59V vs. Li + / Li.

[0147] Example 2

[0148] Compared with Example 1, in the lithium ion battery of Example 2, S1 / S=0.1%.

[0149] Example 3

[0150] Compared with Example 1, in the lithium ion battery of Example 3, S1 / S=10%.

[0151] Example 4

[0152] Compared with Example 1, in the lithium ion battery of Example 4, the CB value in the low CB value region is 0.9.

[0153] Example 5

[0154] Compared with Example 1, in the lithium ion battery of Example 5, the CB value in the low CB value region is 0.8.

[0155] Example 6

[0156] Compared with Example 1, in the lithium ion battery of Example 6, the CB value in the low CB value region is 0.7.

[0157] Example 7

[0158] Compared with Example 1, in the lithium ion battery of Example 7, the CB value in the low CB value region is 0.5.

[0159] Example 8

[0160] Compared with Example 1, in the lithium ion battery of Example 8, C=0.001M.

[0161] Example 9

[0162] Compared with Example 1, in the lithium ion battery of Example 9, C=0.2M.

[0163] Example 10

[0164] Compared with Example 1, the metal ions in the electrolyte of the lithium ion battery of Example 10 are aluminum ions, the molar concentration of aluminum ions is C=0.05M, and the reduction potential of aluminum ions is.

[0165] Comparative Example 1

[0166] Compared with Example 1, the electrolyte of the lithium ion battery of Comparative Example 1 does not contain metal ions. The process for preparing the E2 electrolyte in Comparative Example 1 is as follows: In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain the E2 electrolyte.

[0167] The product parameters and performance test parameters of Examples 1-10 and Comparative Example 1 are detailed in Table 1.

[0168] Table 1: Products and performance parameters of Examples 1-10 and Comparative Example 1

[0169] In Table 1, "metal ion" represents a metal ion in the electrolyte whose reduction potential is higher than the ion reduction potential. "S1 / S" represents the percentage of the area of ​​the negative electrode sheet corresponding to the low CB value region to the area of ​​the negative electrode sheet. "C" represents the molar concentration of the metal ion in the electrolyte. "500-cycle capacity retention rate" refers to the ratio of the discharge capacity after the lithium-ion battery is cycled 500 times to the discharge capacity of the first cycle. The specific calculation process will be introduced in the test method later and will not be repeated here. "m1 / m2" represents the ratio of the content m1 of the metal element on the negative electrode sheet corresponding to the low CB value region to the content m2 of the metal element on the negative electrode sheet corresponding to the high CB value region per unit area. "C'" represents the molar concentration of the metal ion in the electrolyte of the lithium-ion battery after cycling.

[0170] For "m1 / m2" and "C'" in Table 1, the lithium-ion batteries in Examples 1-10 after 500 cycles can be disassembled to obtain the negative electrode plates, electrolyte and other parts after the cycle. Thus, the metal ion content m1 in the negative electrode plates corresponding to the low CB value area and the metal ion content m2 in the negative electrode plates corresponding to the high CB value area, as well as the metal ion concentration C' in the electrolyte can be detected.

[0171] According to the comparative analysis of the embodiment and the comparative example, it can be seen that by introducing metal ions into the electrolyte, the growth of lithium dendrites can be effectively inhibited, and the capacity retention rate and cycle performance of the lithium-ion battery can be improved.

[0172] According to the analysis and comparison of Examples 1-3, it can be seen that the higher the percentage of the area of ​​the negative electrode sheet corresponding to the low CB value region in the lithium-ion battery to the area of ​​the negative electrode sheet, the larger the area of ​​the low CB value region, and the larger the area of ​​the region where lithium deposition occurs on the negative electrode sheet after the lithium-ion battery is cycled. Under the same other conditions, the capacity retention rate of the lithium-ion battery will decrease as the percentage of the area of ​​the negative electrode sheet corresponding to the low CB value region to the area of ​​the negative electrode sheet increases. However, it can be seen from Example 3 and Comparative Example 1 that although the area of ​​the negative electrode sheet corresponding to the low CB value region of Example 3 accounts for a greater percentage of the area of ​​the negative electrode sheet than that of Comparative Example 1, the capacity retention rate of Example 3 is still higher than that of the Comparative Example, which illustrates the effective inhibition of lithium deposition and lithium dendrites by metal ions. In addition, the higher the percentage of the area of ​​the negative electrode sheet corresponding to the low CB value region to the area of ​​the negative electrode sheet of the lithium-ion battery, the greater the m1 / m2 after cycling, and the lower the content C' of metal ions in the electrolyte. This shows that in lithium-ion batteries, the higher the percentage of the area of ​​the negative electrode sheet corresponding to the low CB value region to the area of ​​the negative electrode sheet, the more metal ions are reduced to metal elements by lithium, which once again verifies the inhibitory effect of metal ions on lithium precipitation and lithium dendrites.

[0173] According to the analysis and comparison of Examples 1, 4-7, it can be seen that the smaller the CB value of the low CB value area, the more the capacity of the positive electrode active material per unit area exceeds the capacity of the negative electrode active material per unit area, and the more lithium is deposited on the negative electrode sheet corresponding to the low CB value area. Under the same other conditions, it can be seen that

[0174] The capacity retention rate of Examples 4-7 shows a gradually decreasing trend. Therefore, by controlling the CB value in the low CB value region within an appropriate range, the probability of severe lithium deposition in the battery caused by an excessively small CB value can be reduced. In addition, the smaller the CB value in the low CB value region of the lithium-ion battery, the greater the m1 / m2 after cycling, and the lower the content C' of metal ions in the electrolyte. This once again verifies the inhibitory effect of metal ions on lithium deposition and lithium dendrites.

[0175] A comparative analysis of Examples 1, 8, and 9 shows that the higher the metal ion concentration in the electrolyte, the greater the self-discharge of the lithium-ion battery. When the metal ion concentration in the electrolyte is too low (e.g., Example 8), the inhibitory effect on lithium dendrites is limited. This suggests that controlling the metal ion concentration in the electrolyte within an appropriate range can help improve the self-discharge of lithium-ion batteries while suppressing lithium deposition and dendrites.

[0176] The metal ion in Example 10 is Al 3+ , which shows that metal ions with a higher reduction potential than lithium ions can effectively inhibit lithium dendrites.

[0177] 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.

[0178] 1. Test method for reduction potential of metal ions

[0179] The reduction potential of a metal ion can be determined by measuring the potential difference between it and a standard electrode, or by calculating it based on its concentration and the Nernst equation. For example, a galvanic cell can be constructed using the metal or metal ion solution to be tested and a standard hydrogen electrode or lithium electrode as the counter electrode. The potential difference between the two electrodes is then measured to determine the reduction potential of the metal ion.

[0180] 2. CB value test method

[0181] Take a unit area of ​​positive and negative electrode sheets, clean their surfaces with DMC, and assemble them with lithium sheets to form a positive or negative-to-lithium half-cell. Perform two charge / discharge cycles at 0.04C. The cathode charge capacity and anode discharge capacity during the second cycle are used as the active material capacity per unit area of ​​the positive or negative electrode. CB value = (capacity of negative electrode active material per unit area) / (capacity of positive electrode active material per unit area).

[0182] 3. Molar concentration test method

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

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

[0185] 4. Test method for metal ion content in negative electrode

[0186] Take part of the sample to be tested (negative electrode) and directly measure the content of the target element in the sample through ICP testing.

[0187] 5. Test method for self-discharge of lithium-ion batteries

[0188] Using a BlueDian test system, the lithium-ion battery was charged to 3.8V at a constant current of 8mA. The battery was then left to stand for 48 hours. The battery voltages before and after standing were V1 and V2, respectively. The K value (self-discharge rate) was calculated as (V1-V2) / T.

[0189] 6. Test method for 500-cycle capacity retention of lithium-ion batteries

[0190] Using the Blue Electric test system, first perform the first cycle of charge and discharge on the battery.

[0191] The first cycle charge refers to the battery being charged to 4.2V at a constant current of 60mA after formation, and then being charged at a constant voltage at 4.2V to a cutoff current of 2mA; the first cycle discharge capacity refers to the capacity W1 released by the battery when it is discharged to 2.5V at a constant current of 60mA after formation.

[0192] The battery was then subjected to a charge and discharge test. The test process was as follows: charging at a constant current of 60mA with a cutoff voltage of 4.2V; then constant voltage charging at 4.2V with a cutoff current of 2mA; after a 10-minute rest, discharging at a constant current of 60mA with a cutoff voltage of 2.5V; 500 cycles were repeated before charging to 4.2V before the test was terminated. The discharge capacity after 500 cycles was W2. The capacity retention rate of the lithium-ion battery after 500 cycles was W2 / W1 × 100%.

[0193] 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 metal ions having a reduction potential higher than a reduction potential of lithium ions; Low CB value area; The CB value of the lithium-ion battery in the low CB value region satisfies: 0<CB<1, 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 lithium-ion battery comprises: Negative electrode plate, the percentage X of the area of ​​the negative electrode plate corresponding to the low CB value region to the area of ​​the negative electrode plate satisfies: 0%<X; optionally, 0%<X≤10%; optionally, 0%<X≤2%.

3. The lithium ion battery according to claim 1 or 2, characterized in that: The CB value of the lithium-ion battery in the low CB value region satisfies: 0.5<CB<1.

4. The lithium ion battery according to any one of claims 1 to 3, characterized in that: The reduction potential of the metal ion satisfy: Among them, M n+ represents the metal ion, n represents the valence of the metal ion, C represents the molar concentration of the metal ion in the electrolyte, R represents the ideal gas constant, T represents the temperature, and F represents the Faraday constant. Represents the standard electrode potential of lithium ions.

5. The lithium ion battery according to any one of claims 1 to 4, characterized in that: The reduction potential of the metal ion satisfy:

6. The lithium ion battery according to any one of claims 1 to 5, characterized in that: The molar concentration C of the metal ions in the electrolyte satisfies: 0.001M≤C≤0.2M.

7. The lithium ion battery according to any one of claims 1 to 6, characterized in that: The metal ions include Mg 2+ 、Al 3+ 、Zn 2+ , Sb 2+ At least one of .

8. A lithium ion battery, characterized in that: The lithium-ion battery comprises: A low CB value region, wherein the CB value of the lithium-ion battery in the low CB value region satisfies: 0<CB<1; The negative electrode sheet, the content of the metal element per unit area at the negative electrode sheet corresponding to the low CB value area is greater than the content of the metal element per unit area at the negative electrode sheet corresponding to the high CB value area Content; Among them, the CB value of the lithium-ion battery in the high CB value area satisfies: CB≥1; 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 reduction potential of the metal ion corresponding to the metal element is higher than the reduction potential of the lithium ion.

9. The lithium-ion battery according to claim 8, characterized in that: The percentage X of the area of ​​the negative electrode sheet corresponding to the low CB value region to the area of ​​the negative electrode sheet satisfies: 0%<X; optionally, 0%<X≤10%; optionally, 0%<X≤2%.

10. The lithium ion battery according to claim 8 or 9, characterized in that: The CB value of the lithium-ion battery in the low CB value region satisfies: 0.5<CB<1.

11. The lithium ion battery according to any one of claims 8 to 10, characterized in that: The metal element includes at least one of Mg, Al, Zn and Sb.

12. The lithium ion battery according to any one of claims 8 to 11, characterized in that: The lithium-ion battery comprises: The electrolyte includes metal ions, and the metal ions are ions corresponding to the metal element.

13. The lithium ion battery according to claim 12, characterized in that: The molar concentration C' of the metal ions in the electrolyte satisfies: 0≤C'<0.2M.

14. An electrical device, characterized in that: The electrical device comprises a lithium ion battery as claimed in any one of claims 1 to 7 and / or a lithium ion battery as claimed in any one of claims 8 to 13.

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