Lithium ion battery and electric device

Abstract

The embodiment of the invention discloses a lithium ion battery and a power utilization device, the lithium ion battery comprises an electrolyte, the electrolyte comprises metal ions, and the reduction potential of the metal ions is higher than that of lithium ions; and in the low CB value region, the CB value of the lithium ions in the low CB value region satisfies the following conditions: 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. The lithium ion battery provided by the invention can effectively improve the problem of lithium precipitation in a low CB value region.

Description

Technical Field

[0001] The present application relates to the field of batteries, and more specifically, to a lithium-ion battery and an electrical device. Background Art

[0002] In recent years, lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields, and have thus achieved great development.

[0003] In the preparation process of lithium-ion batteries, due to process limitations, there will inevitably be locations where the positive and negative electrode capacities do not match, that is, there will be low CB value areas. Lithium deposition is prone to occur on the negative electrode sheet corresponding to the low CB value area, which has an adverse effect on the capacity and safety of lithium-ion batteries. Therefore, how to improve the impact of lithium deposition on the performance of lithium-ion batteries is a technical problem that needs to be solved urgently. Summary of the invention

[0004] The present application is made in view of the above technical problems, and its purpose is to provide a lithium ion battery and an electric device. The lithium ion battery includes an electrolyte containing metal ions, which can effectively improve the lithium precipitation problem in the low CB value area.

[0005] In a first aspect, a lithium-ion battery is provided, the lithium-ion battery 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, 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 a negative electrode active material per unit area to the capacity of a positive electrode active material per unit area.

[0006] 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 prone 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 move freely 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.

[0007] In a 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%.

[0008] In a possible implementation, the CB value of the lithium-ion battery in the low CB value region satisfies: 0.5<CB<1.

[0009] 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.

[0010] 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.

[0011] In one possible implementation, the reduction potential of the metal ion is satisfy:

[0012] In the embodiments of the present application, by selecting metal ions whose reduction potentials satisfy 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.

[0013] In a possible implementation, the molar concentration C of the metal ions in the electrolyte satisfies: 0.001M≤C≤0.2M.

[0014] In the embodiments of the present application, by controlling the concentration of metal ions in the electrolyte within a suitable range, lithium precipitation is suppressed while also helping to reduce the self-discharge of the lithium-ion battery.

[0015] In a possible implementation, the metal ions include Mg 2+ 、Al 3+ 、Zn 2+ , Sb 2+ At least one of .

[0016] 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: 0.5<CB<1; 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 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.

[0017] 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%.

[0018] In a possible implementation, the CB value of the lithium-ion battery in the low CB value region satisfies: 0.5<CB<1.

[0019] In a possible implementation manner, the metal element includes at least one of Mg, Al, Zn, and Sb.

[0020] 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.

[0021] In a possible implementation, the molar concentration C' of the metal ions in the electrolyte satisfies: 0M≤C'<0.2M.

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

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

[0024] Figure 1 Schematic diagram of the principle of metal ion suppression of lithium dendrites.

[0025] Figure 2 A schematic diagram of a low CB value region.

[0026] Figure 3 A schematic diagram of a battery cell.

[0027] Figure 4 A schematic diagram of a battery module.

[0028] Figure 5 A schematic diagram of a battery.

[0029] Figure 6 Another schematic diagram of a battery. DETAILED DESCRIPTION

[0030] Hereinafter, the embodiments of the lithium-ion battery and the electrical device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0031] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can form a scope with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3,4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0032] In the description of this application, it should be noted that, unless otherwise specified, "multiple" means more than two; the terms "upper", "lower", "left", "right", "inner", "outer", etc., indicating directions or positional relationships, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting this application. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0033] If not otherwise specified, in this application, the phrase "A and / or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A and / or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0034] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0035] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0036] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their generally accepted meanings in the art.

[0037] As mentioned, "CB (Cell balance) value" refers to the ratio of the negative electrode capacity to the positive electrode capacity on the opposite side of the battery, also known as the N / P (Negative / Positive) ratio. In other words, the CB value is equal to the ratio of the capacity of the negative electrode active material per unit area to the capacity of the positive electrode active material per unit area.

[0038] Where mentioned, the "low CB value region" refers to the region in the battery where the CB value is less than 1.

[0039] 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.

[0040] If mentioned, Refers to the standard electrode potential of lithium ions. The standard electrode potential of a substance refers to the electrode potential of the substance measured when the substance is combined with a standard hydrogen electrode to form a primary cell. For example, the standard electrode potential of lithium relative to hydrogen is -3.04V. In this application, the electrode potential is also called the reduction potential.

[0041] 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.

[0042] Next, embodiments of the present application are introduced.

[0043] In recent years, secondary batteries have been widely used in power tools, electronic products, electric vehicles, aerospace and other fields due to their high energy density and long service life, and have achieved great development. Usually, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the charge and discharge process of the battery, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. Among them, the electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, which allows active ions to pass through while preventing the positive and negative electrodes from short-circuiting, so that the electrochemical reaction of the secondary battery proceeds normally.

[0044] Take lithium-ion batteries as an example. Lithium-ion batteries are a typical secondary battery. Because they rely on the chemical reaction of lithium ions intercalating and disintercalating between the positive and negative electrodes for charging and discharging, lithium-ion batteries are also called rocking-chair batteries. During the charging process of lithium-ion batteries, lithium ions are released from the positive electrode active material, move to the negative electrode through the conduction of the electrolyte and embed into the negative electrode active material; and during the discharge process, lithium ions are released from the negative electrode active material, move to the positive electrode through the conduction of the electrolyte and embed into the positive electrode active material.

[0045] It should be understood that the "lithium insertion" and "embedding" processes described in this application refer to the process in which lithium ions are embedded in the positive electrode active material or the negative electrode active material due to an electrochemical reaction, and the "extraction", "delithium" and "extraction" processes described in this application refer to the process in which lithium ions are extracted from the positive electrode active material or the negative electrode active material due to an electrochemical reaction.

[0046] In the production process of lithium-ion batteries, it is necessary to apply a slurry containing active materials to the current collector to form a pole piece. Due to 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 at 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. With the further precipitation of lithium ions, the growth of lithium dendrites continuously consumes active lithium ions, resulting in the attenuation of the battery's capacity and cycle life.

[0047] 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 precipitation 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.

[0048] Generally, a lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. Next, the lithium-ion battery provided in the present application and various parts of the lithium-ion battery are introduced.

[0049] 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.

[0050] Specifically, the CB value in the low CB value region can be any value between 0 and 1, or within a 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 the cycle. Figure 1 A schematic diagram of the principle of suppressing lithium deposition in a lithium-ion battery provided in an embodiment of the present application.

[0051] like Figure 1 As shown, the negative electrode plate 1 includes a negative electrode current collector 11 and a negative electrode active material layer 12 disposed on the negative electrode current collector 11. After the lithium-ion battery is formed, the negative electrode plate 1 also includes a solid electrolyte interface (SEI) film 13 formed on the surface of the negative electrode active material layer 12. Region a is the region corresponding to the low CB value region, and region b is the region corresponding to the high CB value region. As lithium is continuously precipitated in the low CB value region, lithium dendrites 14 grow and pierce the SEI film 13.

[0052] In this embodiment, metal ions with a higher reduction potential than lithium ions are introduced into the lithium-ion battery so that the metal ions can be reduced by lithium. Therefore, once lithium dendrites grow and pierce the SEI membrane, the free metal ions in the electrolyte will move to the lithium dendrites, and the precipitated lithium will be reduced to a metal element, which can further form an alloy or with lithium, thereby inhibiting lithium precipitation and helping to improve the capacity retention rate and cycle performance of the lithium-ion battery.

[0053] It should be understood that Figure 1 The low CB value area a is only an example of a low CB value area, which shows that the thickness of the negative electrode active material layer 12 on the negative electrode plate 1 is uniform, but because the thickness of the active material layer on the positive electrode plate is thicker (not shown in the figure), this position is the low CB value area a. Figure 2 Another example of forming a low CB value region a is shown. Figure 2 As shown, the positive electrode sheet 2 includes a positive current collector 21 and a positive active material layer 22 disposed on the positive current collector 21. When the thickness of the positive active material layer 22 is uniform, a thinner thickness of the negative active material layer will also cause this position to become a low CB value area a.

[0054] In another possible situation, the thickness of the positive electrode active material layer and the negative electrode active material layer at a certain position are not uniform. For example, the positive electrode active material layer is thicker while the negative electrode active material layer is thinner, which may also cause the position to become a low CB value area a.

[0055] 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%.

[0056] 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 its numerical range is within the range obtained by combining any two of the above numerical values.

[0057] The low CB value area is generated due to the process limitations in the production process of lithium-ion batteries. Therefore, under normal circumstances, 0% < X. On the other hand, based on the existing production process of lithium-ion batteries, the area of ​​the low CB value area will not be unlimitedly large. Based on the consideration of factors such as the yield rate of lithium-ion battery products, the value of X also needs to meet the following requirements: X ≤ 10%. It should be understood that under normal circumstances, the smaller the area of ​​the low CB value area, the smaller X, the smaller the area on the negative electrode sheet where lithium deposition or lithium dendrite growth is likely to occur, and the more favorable it is for the product yield of lithium-ion batteries.

[0058] In one example, the position of the negative electrode sheet corresponding to the low CB value area is very prone to lithium deposition. Therefore, 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 it to 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 manufactured 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 CB value of the designated area can be calculated by measuring the capacity of the positive electrode sheet and the negative electrode sheet, thereby determining whether the area is a low CB value area.

[0059] In one embodiment, the CB value of the lithium-ion battery in the low CB value region satisfies: 0.5<CB<1.

[0060] 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.

[0061] In one embodiment, the reduction potential of the metal ion satisfy:

[0062] Among them, M n+ represents metal ions, n represents the valence of metal ions, C represents the molar concentration of metal ions 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. Usually, R is equal to 8.314 J·K -1 ·mol -1 , T is in K, F is equal to 96485 C·mol -1 .

[0063] In one embodiment, the reduction potential of the metal ion satisfy:

[0064] 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 influence of metal ions on the electrolyte, positive electrode plate, and negative electrode plate.

[0065] 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.

[0066] 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.

[0067] On the one hand, if the molar concentration of metal ions in the electrolyte is too low, the 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, there is too much metal on the surface of the negative electrode, the insulation performance of the SEI film is reduced, and the self-discharge of the lithium-ion battery is increased.

[0068] 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 effect of reduced metal ions on the insulating properties of the SEI film, thereby helping to reduce the self-discharge of the lithium-ion battery.

[0069] In one embodiment, the metal ions include Mg 2+ 、Al 3+ 、Zn 2+ , Sb 2+ At least one of .

[0070] It should be understood that the metal ions can be provided by salts 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 anions, and illustratively, the anions can be acetate ions, nitrate ions, hexafluorophosphate ions, and bis(fluorosulfonyl)imide ions.

[0071] 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.

[0072] An embodiment of the present application also provides a cycled lithium-ion battery, comprising a low CB value zone, wherein the CB value of the lithium-ion battery in the low CB value zone satisfies: 0.5<CB<1; 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 zone is greater than the content of the metal element per unit area at the negative electrode plate corresponding to the high CB value zone; wherein the CB value of the lithium-ion battery in the high CB value zone 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.

[0073] It should be understood that in the embodiments of the present application, the lithium-ion battery after cycling 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 lithium-ion battery after cycling 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 lithium-ion battery after cycling, 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.

[0074] In one embodiment, 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%.

[0075] In one embodiment, the CB value of the lithium-ion battery in the low CB value region satisfies: 0.5<CB<1.

[0076] In one embodiment, the metal element includes at least one of Mg, Al, Zn, and Sb.

[0077] 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.

[0078] Specifically, as the number of cycles of the lithium-ion battery increases, the metal ions in the electrolyte are consumed by the precipitated lithium, thereby gradually reducing the concentration of the metal ions. Therefore, in the lithium-ion battery after the cycle, the electrolyte may also include some metal ions that have not been reduced by lithium.

[0079] In one embodiment, the molar concentration C' of the metal ions in the electrolyte satisfies: 0M≤C'<0.2M.

[0080] It should be understood that the metal ions in the lithium-ion battery after cycling may be completely consumed or partially residual, so C' may be 0 or not. 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 thereof within the range obtained by combining any two of the above numerical values.

[0081] Next, the positive electrode sheet, negative electrode sheet, separator and electrolyte in the lithium-ion battery are introduced in detail.

[0082] [Negative electrode]

[0083] 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.

[0084] 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 any one or both of the two facing surfaces of the negative electrode current collector.

[0085] In one embodiment, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0086] In one embodiment, the negative electrode active material may adopt the negative electrode active material for batteries known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0087] 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).

[0088] In one embodiment, the negative electrode active material layer further includes a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0089] In one embodiment, the negative electrode active material layer further includes other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0090] In one embodiment, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet are formed into a negative electrode slurry. For example, the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a negative electrode slurry. Then, the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0091] [Positive electrode]

[0092] 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.

[0093] 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 disposed on any one or both of the two facing surfaces of the positive electrode current collector.

[0094] In one embodiment, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0095] In one embodiment, the positive electrode active material may adopt a positive electrode active material for a battery that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and at least one of its modified compounds. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and at least one of a composite material of lithium iron manganese phosphate and carbon. The battery is accompanied by the deintercalation and consumption of Li during the charging and discharging process, and the molar content of Li in the positive electrode active material is different when the battery is discharged to different states. In the enumeration of positive electrode active materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode active material is used in the battery system, and the molar content of Li will change after charge and discharge cycles. In the enumeration of positive electrode active materials in this application, the molar content of O is only an ideal state value. The release of lattice oxygen will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0096] 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), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0097] 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.

[0098] In one embodiment, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet are respectively formed into positive electrode slurries. For example, the first positive electrode active material and / or the second positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry. Then, the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0099] [Electrolyte]

[0100] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. The electrolyte includes an electrolyte salt, a solvent, and a metal ion, and the reduction potential of the metal ion is higher than the reduction potential of the lithium ion.

[0101] In one embodiment, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethanesulfonyl imide), lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0102] In one embodiment, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0103] In one embodiment, the metal ions include Mg 2+ 、Al 3+ 、Zn 2+ , Sb 2+ At least one of .

[0104] 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.

[0105] In one embodiment, the reduction potential of the metal ion satisfy: Among them, M n+ represents metal ions, n represents the valence of metal ions, C represents the molar concentration of metal ions 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.

[0106] In one embodiment, the reduction potential of the metal ion satisfy:

[0107] 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.

[0108] 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.

[0109] In one embodiment, the electrolyte may further include additives, which may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain performance of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high or low temperature performance of the battery, etc.

[0110] [Isolator]

[0111] In one embodiment, the battery further includes a separator. The present application has no particular limitation on the type of separator, for example, any known porous structure separator with good chemical stability and mechanical stability can be selected.

[0112] In one embodiment, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0113] In one embodiment, the negative electrode sheet, the positive electrode sheet and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0114] In one embodiment, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0115] In one embodiment, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0116] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 3 The battery cell 300 is a square structure as an example.

[0117] It should be understood that the battery cell 300 may include the lithium-ion battery in the aforementioned embodiment.

[0118] Figure 4 4 is a battery module 400 as an example. Figure 4 In the battery module 400, the plurality of battery cells 300 may be arranged in sequence along the length direction of the battery module 400. Of course, they may also be arranged in any other manner. The plurality of battery cells 300 may be further fixed by fasteners. The plurality of battery cells 300 may be battery cells 300 of the same chemical system or battery cells 300 of different chemical systems.

[0119] Optionally, in one embodiment, the battery module 400 may further include a housing having an accommodation space, and the plurality of battery cells 300 are accommodated in the accommodation space.

[0120] Optionally, in one embodiment, the battery modules 400 may also be assembled into a battery. The number of battery modules 400 contained in the battery may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery.

[0121] Figure 5 and Figure 6 500 is an example of a battery. Figure 5 and Figure 6 The battery 500 may include a battery box and a plurality of battery modules 400 disposed in the battery box. The battery box includes an upper box body 501 and a lower box body 502. The upper box body 501 can cover the lower box body 502 and form a closed space for accommodating the battery modules 400. The plurality of battery modules 400 may be arranged in the battery box in any manner.

[0122] 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 form a battery module 400, and the battery 500 may be formed by the battery module 400. Alternatively, the battery 500 may be directly formed by the battery cells 300, omitting the intermediate form of the battery module 400.

[0123] In addition, the present application also provides an electrical device, which includes the lithium-ion battery in the aforementioned embodiment.

[0124] In another embodiment, the electrical device includes at least one of the battery cell 300, battery module 400, or battery 500 provided in the present application. 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 mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0125] As an electric device, a battery cell 300, a battery module 400, or a battery 500 may be selected according to its usage requirements.

[0126] As an example of an electric device, the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module may be used.

[0127] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0128] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0129] [Examples 1-10 and Comparative Example 1]

[0130] Example 1

[0131] (1) Preparation of negative electrode sheet

[0132] The negative electrode active material artificial graphite (1kg, particle size 15μm), conductive agent acetylene black (10g), binder styrene butadiene rubber (30g), thickener sodium carboxymethyl cellulose (20g) were dissolved in solvent deionized water (1kg), mixed evenly to obtain negative electrode slurry. Then the negative electrode slurry was evenly coated on the negative electrode current collector copper foil. After drying, rolling and cutting, the negative electrode sheet was obtained.

[0133] (2) Preparation of positive electrode sheet

[0134] The positive electrode active material LiNi5Co2Mn3O2 (1kg), the conductive agent carbon nanotube (20g), and the binder polyvinylidene fluoride (20g) were dissolved in the solvent N-methylpyrrolidone (1kg), and mixed evenly to obtain the positive electrode slurry. Then the positive electrode slurry was evenly coated on the positive electrode current collector aluminum foil. After drying, rolling, and cutting, the positive electrode sheet was obtained.

[0135] (3) Preparation of electrolyte

[0136] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), electrolytes E1 and E2 were prepared, wherein 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 lithium-ion battery after formation, the volume ratio of E1 to E2 was 4:1.

[0137] Electrolyte E1 configuration: organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) were mixed evenly in a volume ratio of 1:1:1, and then 1.25 M lithium hexafluorophosphate (LiPF6) was added and dissolved in the solvent, and stirred evenly to obtain electrolyte E1.

[0138] Electrolyte E2 configuration: organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) were mixed evenly in a volume ratio of 1:1:1, and then 0.25 M magnesium bis(trifluoromethylsulfonyl)imide was added and dissolved in the solvent, and stirred evenly to obtain electrolyte E2.

[0139] (4) Preparation of lithium-ion batteries

[0140] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive electrode sheet and the negative electrode sheet and can separate the positive electrode sheet from the negative electrode sheet; then the stacked components are wound and placed in a shell, and the electrolyte E1 is injected after drying.

[0141] The above battery was formed under the following conditions: using a blue electric test system, the positive electrode and the negative electrode were connected, left to stand for 1 minute, and then charged to 4.2V at a constant current of 0.33C, and then charged at a constant voltage of 4.2V with a cut-off current of 0.05C, and then left to stand for 10 minutes, and then discharged at a constant current of 0.33C with a cut-off voltage of 2.5V, and left to stand for 50 hours. The SEI film is formed during the formation of the battery and helps to reduce the polarization of the battery.

[0142] The formed battery is injected with electrolyte E2 for the second time, and the lithium-ion battery is obtained after packaging.

[0143] 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, 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.

[0144] Example 2

[0145] Compared with Example 1, in the lithium ion battery of Example 2, S1 / S=0.1%.

[0146] Example 3

[0147] Compared with Example 1, in the lithium ion battery of Example 3, S1 / S=10%.

[0148] Example 4

[0149] Compared with Example 1, in the lithium ion battery of Example 4, the CB value in the low CB value region is 0.9.

[0150] Example 5

[0151] Compared with Example 1, in the lithium ion battery of Example 5, the CB value in the low CB value region is 0.8.

[0152] Example 6

[0153] Compared with Example 1, in the lithium ion battery of Example 6, the CB value in the low CB value region is 0.7.

[0154] Example 7

[0155] Compared with Example 1, in the lithium ion battery of Example 7, the CB value in the low CB value region is 0.5.

[0156] Example 8

[0157] Compared with Example 1, in the lithium ion battery of Example 8, C=0.001M.

[0158] Example 9

[0159] Compared with Example 1, in the lithium ion battery of Example 9, C=0.2M.

[0160] Example 10

[0161] 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.

[0162] Comparative Example 1

[0163] Compared with Example 1, the electrolyte of the lithium ion battery of Comparative Example 1 does not include metal ions. The process of 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.

[0164] The product parameters and performance test parameters of Examples 1-10 and Comparative Example 1 are detailed in Table 1.

[0165] Table 1: Products and performance parameters of Examples 1-10 and Comparative Example 1

[0166] 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 zone 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 of the lithium-ion battery after 500 cycles to the discharge capacity of the first cycle. The specific calculation process will be introduced in the test method later, so it 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 zone to the content m2 of the metal element on the negative electrode sheet corresponding to the high CB value zone per unit area. "C'" represents the molar concentration of metal ions in the electrolyte of the lithium-ion battery after cycling.

[0167] 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.

[0168] According to the comparative analysis of the embodiments and the comparative examples, 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.

[0169] According to the analysis and comparison of Examples 1-3, the higher the percentage of the area of ​​the negative electrode sheet corresponding to the low CB value area in the lithium-ion battery to the area of ​​the negative electrode sheet, the larger the area of ​​the low CB value area, and the larger the area of ​​the region where lithium precipitation 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 area of ​​the negative electrode sheet corresponding to the low CB value area 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 area of ​​Example 3 accounts for a greater percentage of the area of ​​the negative electrode sheet than 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 precipitation 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 area to the area of ​​the negative electrode sheet of the lithium-ion battery, the greater the m1 / m2 after cycling, and the smaller the content C' of metal ions in the electrolyte. This shows that in lithium-ion batteries, the higher the percentage of the negative electrode plate area corresponding to the low CB value region to the negative electrode plate area, 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.

[0170] According to the analysis and comparison of Examples 1 and 4-7, the smaller the CB value in the low CB value zone, 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 precipitated on the negative electrode sheet corresponding to the low CB value zone. Under the same other conditions, it can be seen that the capacity retention rate of Examples 4-7 shows a gradually decreasing trend. Therefore, by controlling the CB value in the low CB value zone within an appropriate range, the probability of severe lithium precipitation of the battery caused by a too small CB value can be reduced. In addition, the smaller the CB value of the lithium-ion battery in the low CB value zone, the greater the m1 / m2 after cycling, and the smaller the content C' of metal ions in the electrolyte. The inhibitory effect of metal ions on lithium precipitation and lithium dendrites was verified again.

[0171] According to the comparative analysis of Examples 1, 8-9, 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 (such as Example 8), the inhibitory effect on lithium dendrites is limited. Therefore, it is shown that by controlling the concentration of metal ions in the electrolyte within a suitable range, it is helpful to improve the self-discharge of lithium-ion batteries while suppressing lithium precipitation and lithium dendrites.

[0172] The metal ion in Example 10 is Al 3+ , which shows that metal ions with a reduction potential higher than that of lithium ions can effectively inhibit lithium dendrites.

[0173] The following is a brief introduction to the test methods of the physical and chemical parameters and performance parameters involved in the embodiments of the present application. It should be understood that the following test methods are only examples, and other test methods known in the art may also be used for testing.

[0174] 1. Test method for reduction potential of metal ions

[0175] The reduction potential of metal ions can be obtained by measuring the potential difference between them and a standard electrode, or by calculating them based on the concentration and the Nernst equation. For example, the metal or metal ion solution to be tested, the standard hydrogen electrode or the lithium electrode can be used as the counter electrode to form a primary cell, and the potential difference between the two electrodes can be measured to obtain the reduction potential of the metal ions.

[0176] 2. CB value test method

[0177] Take the positive electrode sheet and negative electrode sheet per unit area, clean the surface with DMC, and assemble them with lithium sheets to form a positive or negative half-cell for lithium, charge / discharge at 0.04C current for 2 cycles, and take the charge capacity of the cathode and the discharge capacity of the anode in the second cycle as the active material capacity of the positive or negative electrode per unit area. CB value = (capacity of negative electrode active material per unit area) / (capacity of positive electrode active material per unit area).

[0178] 3. Molar concentration test method

[0179] 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.

[0180] Exemplarily, the ICP (Inductively coupled plasma) testing method process is as follows: the sample to be tested is digested with aqua regia (concentrated hydrochloric acid: concentrated nitric acid = 3:1) or reverse aqua regia (concentrated nitric acid: concentrated hydrochloric acid 3:1) and then the element content is measured using an ICP tester.

[0181] 4. Test method for the content of metal ions in negative electrode sheets

[0182] Take part of the sample to be tested (negative electrode piece) and directly measure the content of the target element in the sample through ICP test.

[0183] 5. Test method for self-discharge of lithium-ion batteries

[0184] Using the Blue Electric test system, the lithium-ion battery was charged to 3.8V at a constant current of 8mA; then it was left to stand for T=48h; the battery voltages before and after standing were V1 and V2 respectively; the K value (self-discharge rate) was calculated as (V1-V2) / T.

[0185] 6. Test method for 500-cycle capacity retention of lithium-ion batteries

[0186] Using the Blue Electric test system, first perform the first cycle of charge and discharge on the battery.

[0187] The first cycle charging 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 cut-off current of 2mA; the first cycle discharge capacity refers to the capacity W1 released by the battery when it is discharged to a voltage of 2.5V at a constant current of 60mA after formation.

[0188] Then the battery was tested for charge and discharge. The test process was: charging at a constant current of 60mA, with a cut-off voltage of 4.2V; constant voltage charging at 4.2V, with a cut-off current of 2mA; after standing for 10 minutes, discharging at a constant current of 60mA, with a cut-off voltage of 2.5V, and then charging to 4.2V after 500 cycles before the test was stopped. The discharge capacity after 500 cycles was W2. The capacity retention rate of lithium-ion batteries after 500 cycles was W2 / W1×100%.

[0189] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A lithium ion battery, characterized in that: The lithium-ion battery comprises: An electrolyte, the electrolyte comprising metal ions, the 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 φ(M n+ / M) satisfies: φ(M n+ / M)+(RTlnC) / F≥φ(Li + / Li); 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, F represents the Faraday constant, φ(Li + / Li) 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 φ(M n+ / M) satisfies: φ(M n+ / M)+(RTlnC) / F≤3V vs.Li + / Li.

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; 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; 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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