Positive pole piece, lithium ion battery and electric device

Abstract

The embodiment of the invention discloses a positive pole piece, a lithium ion battery and a power utilization device. The positive pole piece comprises a current collector and a positive pole film layer arranged on at least one side of the current collector, the positive electrode film layer comprises metal salt, the metal salt comprises metal ions, the reduction potential of the metal ions is larger than that of lithium ions, and the difference value between the reduction potential of the metal ions and the reduction potential of the lithium ions is smaller than or equal to 0.8 V. When the positive pole piece is applied to the lithium ion battery, lithium precipitation can be effectively inhibited, and the cycle performance of the lithium ion battery can be improved.

Description

Technical Field

[0001] The present application relates to the field of batteries, and more specifically, to a positive electrode sheet, 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 been greatly developed. However, the limited reserves and uneven distribution of lithium resources have become a major problem restricting the development of lithium-ion batteries.

[0003] During the cycle of lithium-ion batteries, due to limitations in process, use environment and other factors, lithium deposition occurs on the negative electrode sheet, which in severe cases leads to the growth of lithium dendrites, threatening the reversible capacity and cycle life of lithium-ion batteries. Therefore, how to improve lithium deposition in lithium-ion batteries has become 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 positive electrode sheet, a lithium-ion battery and an electric device. The positive electrode sheet applied to a lithium-ion battery can effectively inhibit lithium precipitation and help improve the cycle performance and coulomb efficiency of the lithium-ion battery.

[0005] In a first aspect, a positive electrode plate is provided, the positive electrode plate comprising: a current collector and a positive electrode film layer arranged on at least one side of the current collector; the positive electrode film layer comprises a metal salt, the metal salt comprises metal ions, the reduction potential of the metal ions is greater than the reduction potential of lithium ions, and the difference between the reduction potential of the metal ions and the reduction potential of the lithium ions is less than or equal to 0.8V.

[0006] In the embodiment of the present application, by introducing a metal salt into the positive electrode sheet, the metal salt can be dissolved or partially dissolved in the electrolyte, so that when the positive electrode sheet is applied to a lithium-ion battery, there are free metal ions in the electrolyte. This part of the free metal ions can move freely to a position with a lower potential on the negative electrode sheet, and the reduction potential is close to the reduction potential of lithium ions (the difference is less than or equal to 0.8V), so that a local positive charge electrostatic field can be formed, thereby uniforming the current density on the negative electrode sheet and suppressing lithium precipitation. Thus, by the positive electrode sheet provided in the present application, lithium precipitation can be effectively suppressed, the side reactions during the lithium-ion battery cycle are reduced, and the cycle performance and coulomb efficiency of the lithium-ion battery are helped to be improved.

[0007] In a possible implementation, the positive electrode film layer includes a positive electrode active material layer, and the positive electrode active material layer is disposed on the current collector; the positive electrode active material layer includes the metal salt.

[0008] In a possible implementation, the positive electrode active material layer includes a positive electrode active material; and an average volume particle size Dv50 of particles of the metal salt is equal to an average volume particle size Dv50 of the positive electrode active material.

[0009] After the metal salt is dissolved in the electrolyte, pores will be left in the positive electrode active material layer. In the embodiment of the present application, by selecting metal salt particles with an average volume particle size equal to that of the positive electrode active material, it is helpful to leave pores in the positive electrode active material layer, increase the contact area between the positive electrode active material and the electrolyte, and reduce the risk of instability of the positive electrode active material layer structure due to the dissolution of the metal salt.

[0010] In a possible implementation, the average volume particle size Dv50 of the metal salt particles satisfies: 0.05 μm≤Dv50≤70 μm; optionally, 0.5 μm≤Dv50≤60 μm.

[0011] In a possible implementation, based on the total mass of the positive electrode active material layer, the mass content a of the metal salt satisfies: 1%≤a≤50%; optionally, 5%≤a≤40%.

[0012] In the embodiments of the present application, by controlling the mass content of the metal salt in the positive electrode active material layer within a suitable range, it helps to suppress lithium precipitation while reducing the effect of the metal salt on the energy density of the lithium-ion battery.

[0013] In a possible implementation, the positive electrode film layer includes a positive electrode active material layer and a coating layer, the positive electrode active material layer is disposed on the current collector, and the film layer is disposed on the positive electrode active material layer; the coating layer includes the metal salt.

[0014] In a possible implementation, the thickness d of the coating satisfies: 0.05 μm≤d≤100 μm; optionally, 0.1 μm≤d≤50 μm.

[0015] In a possible implementation, based on the total mass of the positive electrode film layer, the mass content b of the metal salt satisfies: 1%≤b≤40%; optionally, 5%≤b≤30%.

[0016] In the embodiments of the present application, by controlling the mass content of the metal salt in the positive electrode film layer within a suitable range, it helps to suppress lithium precipitation and also can reduce the effect of the metal salt on the energy density of the lithium-ion battery.

[0017] In a possible implementation, the metal salt includes at least one of a sodium salt, a potassium salt, a calcium salt, a magnesium salt, and a cesium salt.

[0018] In a possible implementation, the metal salt includes anions, and the anions include one or more of fluorine, phosphorus, sulfur, and nitrogen.

[0019] In a possible implementation, the solubility S of the metal salt in the electrolyte satisfies: S≥0.005 g / mL.

[0020] In a possible implementation, the powder compaction density of the positive electrode film layer satisfies: ρ satisfies: 0.8 g / cm 3 ≤ρ≤4.0g / cm 3 ; Optionally, 1.0 g / cm 3 ≤ρ≤3.5g / cm 3 .

[0021] In a second aspect, a method for preparing a positive electrode plate is provided, the method comprising: arranging a positive electrode film layer on at least one side of a current collector to obtain the positive electrode plate; the positive electrode film layer comprises a metal salt, the metal salt comprises a metal ion, the reduction potential of the metal ion is greater than the reduction potential of the lithium ion, and the difference between the reduction potential of the metal ion and the reduction potential of the lithium ion is less than or equal to 0.8V.

[0022] In a possible implementation, providing a positive electrode film layer on at least one side of the current collector includes: providing a positive electrode active material layer on at least one side of the current collector, wherein the positive electrode active material layer includes the metal salt.

[0023] In one possible implementation, providing a positive electrode active material layer on at least one side of the current collector includes: preparing a first slurry, the first slurry including a positive electrode active material and the metal salt; applying the first slurry to at least one side of the current collector; drying the first slurry to form a first coating layer on the current collector; and rolling the current collector and the first coating layer to obtain the positive electrode sheet.

[0024] In a possible implementation, providing a positive electrode film layer on at least one side of the current collector includes: providing a positive electrode active material layer on at least one side of the current collector; providing a coating on the positive electrode active material layer; and the coating includes the metal salt.

[0025] In one possible implementation, providing a positive electrode active material layer on at least one side of the current collector includes: preparing a second slurry, the second slurry including a positive electrode active material; applying the second slurry to at least one side of the current collector; and drying the second slurry to form the positive electrode active material layer on the current collector.

[0026] In a possible implementation, providing a coating on the positive electrode active material layer includes: preparing a third slurry, wherein the third slurry includes the metal salt; applying the third slurry on the positive electrode active material layer; drying the third slurry to form the coating on the positive electrode active material layer; and rolling the dried current collector, the positive electrode active material layer and the coating to obtain the positive electrode sheet.

[0027] In a third aspect, a lithium-ion battery is provided, wherein the lithium-ion battery comprises a positive electrode sheet according to any possible implementation of the first aspect, and / or a positive electrode sheet prepared by the method according to any possible implementation of the second aspect.

[0028] In a possible implementation, the lithium-ion battery includes an electrolyte, and the electrolyte includes the metal ions.

[0029] In a possible implementation, based on the total weight of the electrolyte, the weight content c of the metal ions satisfies: 0.02%≤c≤30%; optionally, 0.03%≤c≤6%.

[0030] In a fourth aspect, an electrical device is provided, wherein the electrical device comprises a lithium-ion battery according to any possible implementation of the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] 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.

[0032] Figure 1 A schematic flow chart of a method for preparing a positive electrode sheet according to the present application.

[0033] Figure 2 A schematic diagram of a battery cell of a lithium-ion battery.

[0034] Figure 3 A schematic diagram of a battery module for a lithium-ion battery.

[0035] Figure 4 A schematic diagram of a lithium-ion battery.

[0036] Figure 5 Another schematic diagram of a lithium-ion battery. DETAILED DESCRIPTION

[0037] Hereinafter, the embodiments of the positive electrode plate and its preparation method, lithium-ion battery and electric device of the present application are specifically disclosed in detail with appropriate reference to the 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 descriptions 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.

[0038] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0039] 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.

[0040] If not specifically stated, in this application, the term "and / or" is inclusive. For example, 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).

[0041] 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.

[0042] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0043] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their generally accepted meanings in the art.

[0044] Where mentioned, "reduction potential" refers to the electrode potential of a substance relative to a standard hydrogen electrode. Specifically, the reduction potential is the electrode potential of a substance measured by placing the substance in a galvanic cell with a standard hydrogen electrode.

[0045] Where referred to, "metal salt" refers to a compound consisting of a metal cation and an anion.

[0046] Next, embodiments of the present application are introduced.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] During the cycle of lithium-ion batteries, the process of lithium ion embedding into the negative electrode active material is hindered by factors such as battery preparation technology and battery aging, and lithium deposition will occur on the surface of the negative electrode. The lithium metal deposited on the surface of the negative electrode tends to be in the form of dendrites. As lithium deposition continues, the lithium dendrites grow, and in severe cases, they pierce the SEI (solid electrolyte interface) membrane, react with the electrolyte, consume the active lithium ions in the battery, and cause the reversible capacity of the battery to decay and the cycle life to decrease. Once the lithium dendrites pierce the separator, it will also cause serious safety problems.

[0051] In view of this, the embodiments of the present application provide a positive electrode plate and a preparation method thereof, a lithium-ion battery and an electrical device, wherein the positive electrode plate includes a current collector and a positive electrode film layer arranged on at least one side of the current collector, the positive electrode film layer includes a metal salt, the metal salt includes metal ions, the reduction potential of the metal ions is greater than the reduction potential of the lithium ions, and the difference between the reduction potential of the metal ions and the reduction potential of the lithium ions is less than or equal to 0.8V.

[0052] When the positive electrode plate is applied to a lithium-ion battery, the metal salt can be dissolved or partially dissolved in the electrolyte, so that free metal ions exist in the electrolyte. This part of the free metal ions has a potential close to that of lithium ions, and since the metal salt can be regarded as an additive to the positive electrode film layer, the concentration of this part of the metal ions in the electrolyte is much smaller than that of lithium ions, so that the metal ions will not be reduced to metal elements. As a result, the metal ions can move freely to the position with lower potential on the negative electrode plate, that is, the position where lithium precipitation is likely to occur or has occurred, and form an electrostatic shield at this position, thereby uniformizing the current density on the negative electrode plate, inhibiting lithium precipitation, and reducing side reactions during the lithium ion cycle, thereby improving the cycle performance and coulomb efficiency of the lithium-ion battery.

[0053] 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.

[0054] [Positive electrode]

[0055] The present application first provides a positive electrode plate, which includes a current collector and a positive electrode film layer arranged on at least one side of the current collector.

[0056] It should be understood that the current collector in the positive electrode sheet is also called the positive current collector. As an example, the positive current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is arranged on any one or both of the two opposite surfaces of the positive current collector.

[0057] 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.).

[0058] In one embodiment, the positive electrode film layer includes a positive electrode active material layer, and the positive electrode active material layer is disposed on the positive electrode current collector; the positive electrode active material layer includes a metal salt.

[0059] Specifically, the metal salt may be introduced into the positive electrode active material layer. For example, the positive electrode active material and the metal salt may be mixed into a stable and uniform slurry during the preparation of the positive electrode active material layer, thereby introducing the metal salt into the positive electrode film layer.

[0060] In one embodiment, the positive electrode active material layer includes a positive electrode active material; and the average volume particle size Dv50 of particles of the metal salt is equal to the average volume particle size Dv50 of the positive electrode active material.

[0061] It should be understood that “the average volume particle size Dv50 of the metal salt particles is equal to the average volume particle size Dv50 of the positive electrode active material” can mean that the average volume particle size Dv50 of the metal salt particles is equal to the average volume particle size Dv50 of the positive electrode active material, or that the average volume particle size Dv50 of the metal salt particles is close to the average volume particle size Dv50 of the positive electrode active material. When the average volume particle size Dv50 of the metal salt particles is close to the average volume particle size Dv50 of the positive electrode active material, the absolute value of the difference between the average volume particle size of the metal salt particles and the average volume particle size of the positive electrode active material is less than or equal to 2μm.

[0062] When the positive electrode plate is used in a lithium-ion battery, the metal salt on the positive electrode plate will dissolve or partially dissolve in the electrolyte, thereby leaving pores in the positive electrode active material layer. In this embodiment, by controlling the average volume particle size of the metal salt particles to be equal to or similar to the average volume particle size of the positive electrode active material, pores can be left in the positive electrode active material layer, increasing the contact area between the positive electrode active material and the electrolyte while reducing the risk of excessive pores and collapse of the positive electrode active material layer.

[0063] In one embodiment, the average volume particle size Dv50 of the particles of the metal salt satisfies: 0.05 μm≤Dv50≤70 μm; optionally, 0.5 μm≤Dv50≤60 μm.

[0064] Specifically, the average volume particle size Dv50 of the metal salt particles can be 0.05μm, 0.06μm, 0.07μm, 0.08μm, 0.09μm, 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, or its value is within the range obtained by combining any two of the above values.

[0065] In one embodiment, based on the total mass of the positive electrode active material layer, the mass content a of the metal salt satisfies: 1%≤a≤50%; alternatively, 5%≤a≤40%.

[0066] Specifically, a can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, or its value is within the range obtained by combining any two of the above values.

[0067] On the one hand, if the metal salt content in the positive electrode active material layer is too low, the amount of metal salt that can be dissolved in the electrolyte is limited, which limits the inhibitory effect of metal ions on lithium precipitation. On the other hand, since metal salts do not participate in the charge and discharge reactions of lithium-ion batteries, excessive metal salt content in the positive electrode active material layer will affect the energy density of lithium-ion batteries.

[0068] In this embodiment, by controlling the mass content of the metal salt in the positive electrode active material layer within a suitable range, it is possible to suppress lithium precipitation while reducing the influence of the metal salt on the energy density of the lithium-ion battery.

[0069] In one embodiment, the positive electrode film layer includes a positive electrode active material layer and a coating layer, the positive electrode active material layer is disposed on the positive electrode current collector, and the film layer is disposed on the positive electrode active material layer; and the coating layer includes the metal salt.

[0070] Specifically, in addition to the scheme of introducing metal salts into the positive electrode active material layer, metal salts can also be introduced into the coating of the positive electrode film layer. For example, after the positive electrode active material layer is prepared on the positive electrode current collector, a slurry containing metal salts is coated on the positive electrode active material layer to form a coating. In this way, metal salts are introduced into the positive electrode film layer.

[0071] In one embodiment, the thickness d of the coating satisfies: 0.05 μm≤d≤100 μm; optionally, 0.1 μm≤d≤50 μm.

[0072] Specifically, d can be 0.05μm, 0.06μm, 0.07μm, 0.08μm, 0.09μm, 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, or its value is within the range obtained by combining any two of the above values.

[0073] In one embodiment, based on the total mass of the positive electrode film layer, the mass content b of the metal salt satisfies: 1%≤b≤40%; optionally, 5%≤b≤30%.

[0074] Specifically, b can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, or its value is within the range obtained by combining any two of the above values.

[0075] In this embodiment, by controlling the thickness of the coating and the mass content of the metal salt in the positive electrode film layer within a suitable range, it is possible to suppress lithium precipitation while reducing the effect of the metal salt on the energy density of the lithium-ion battery.

[0076] In one embodiment, the metal salt includes at least one of a sodium salt, a potassium salt, a calcium salt, a magnesium salt, and a cesium salt.

[0077] In one embodiment, the metal salt includes anions, and the anions include one or more of fluorine, phosphorus, sulfur, and nitrogen.

[0078] Specifically, after the metal salt is dissolved or partially dissolved in the electrolyte, the electrolyte also includes free anions, which may participate in the formation of the SEI film. Therefore, by selecting anions including the above elements, it is beneficial to form a uniform and dense SEI film. In the case of lithium deposition on the negative electrode, a uniform and dense SEI film helps to induce uniform deposition of lithium ions. In other words, it makes lithium deposition more uniform, thereby further inhibiting the formation or growth of lithium dendrites and improving the cycle performance and coulomb efficiency of lithium-ion batteries.

[0079] Exemplarily, the anion includes sulfur, which means that the anion includes but is not limited to sulfide ion, sulfate ion, sulfite ion, etc. In another example, the anion includes acetate, fluorophosphate, nitrate, carbonate, bis(trifluoromethylsulfonyl)imide, hexafluorophosphate.

[0080] In one embodiment, the solubility S of the metal salt in the electrolyte satisfies: S≥0.005 g / mL.

[0081] For example, S may be 0.005 g / mL, 0.01 g / mL, 0.05 g / mL, or other values ​​greater than 0.005 g / mL.

[0082] The compacted density of the positive electrode film powder satisfies: ρ satisfies: 0.8g / cm 3 ≤ρ≤4.0g / cm 3 ; Optionally, 1.0 g / cm 3 ≤ρ≤3.5g / cm 3 .

[0083] Specifically, ρ can be 0.8 g / cm 3 , 0.85g / cm 3 , 0.9g / cm 3 , 0.95g / cm 3 , 1.0g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 , 2.0g / cm 3, 2.1g / cm 3 , 2.2g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 , 2.5g / cm 3 , 2.6g / cm 3 , 2.7g / cm 3 , 2.8g / cm 3 , 2.9g / cm 3 、3.0g / cm 3 、3.1g / cm 3 、3.2g / cm 3 , 3.3g / cm 3 、3.4g / cm 3 、3.5g / cm 3 、3.6g / cm 3 、3.7g / cm 3 、3.8g / cm 3 、3.9g / cm 3 , 4.0g / cm 3 , or its value is within the range obtained by combining any two of the above values.

[0084] In one embodiment, the positive electrode active material may adopt a positive electrode active material for a battery 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. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 、LiMn 2 O 4 ), 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 O 2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (also referred to as NCM523), LiNi 0.5 Co 0.25Mn 0.25 O 2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O 2 ) and its modified compounds, etc. Examples of lithium phosphates containing olivine structures may include, but are not limited to, lithium iron phosphate (such as LiFePO 4 (also referred to as LFP), composite materials of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), at least one of a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and 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 applied to 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. Lattice oxygen release will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0085] In one embodiment, the positive electrode film layer further includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0086] In one embodiment, the positive electrode film layer further includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0087] 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 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, rolling and other processes, the positive electrode sheet can be obtained.

[0088] [Negative electrode]

[0089] The negative electrode plate generally includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector.

[0090] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0091] 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.).

[0092] 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.

[0093] In one embodiment, the negative electrode film layer further includes a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0094] In one embodiment, the negative electrode film layer further includes a conductive agent, which can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0095] In one embodiment, the negative electrode active material layer further includes other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0096] 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, rolling and other processes, the negative electrode sheet can be obtained.

[0097] [Electrolyte]

[0098] The electrolyte plays a role in conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. The electrolyte includes electrolyte salt and solvent.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] [Isolator]

[0103] 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.

[0104] 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.

[0105] [Preparation method]

[0106] Next, the preparation method of the positive electrode plate in the aforementioned embodiment is introduced.

[0107] The present application also provides a method for preparing a positive electrode plate. Figure 1 A schematic flow chart of a method for preparing a positive electrode sheet.

[0108] like Figure 1 As shown, the method 100 includes:

[0109] S101, disposing a positive electrode film layer on at least one side of the current collector to obtain a positive electrode sheet.

[0110] The positive electrode film layer includes a metal salt, the metal salt includes a metal ion, and the difference between the reduction potential of the metal ion and the reduction potential of the lithium ion is less than or equal to 0.8V.

[0111] It should be understood that the current collector mentioned in method 100 is a positive electrode current collector.

[0112] Optionally, in S101 , disposing a positive electrode film layer on at least one side of the current collector includes: disposing a positive electrode active material layer on at least one side of the current collector, wherein the positive electrode active material layer includes a metal salt.

[0113] Optionally, in S101 , disposing a positive electrode film layer on at least one side of the current collector includes: disposing a positive electrode active material layer on at least one side of the current collector; and disposing a coating on the positive electrode active material layer, wherein the coating includes a metal salt.

[0114] In other words, the positive electrode film layer including the metal salt may be the positive electrode active material layer including the metal salt, or may be the coating on the positive electrode active material layer including the metal salt.

[0115] Optionally, providing a positive electrode active material layer on at least one side of the current collector comprises:

[0116] i) preparing a first slurry, wherein the first slurry includes a positive electrode active material and a metal salt.

[0117] ii) coating the first slurry on at least one side of a current collector.

[0118] iii) drying the first slurry to form a first coating layer on the isolation film.

[0119] iv) rolling the current collector and the first coating layer to obtain a positive electrode sheet.

[0120] Thus, in the positive electrode sheet prepared through the above steps i) to iv), the positive electrode active material layer contains metal salt.

[0121] Optionally, providing a positive electrode active material layer on at least one side of the current collector comprises:

[0122] a) preparing a second slurry, wherein the second slurry includes a positive electrode active material.

[0123] b) applying the second slurry to at least one side of the current collector.

[0124] c) drying the second slurry to form a positive electrode active material layer on the separator.

[0125] Optionally, providing a coating layer on the positive electrode active material layer comprises:

[0126] 1) preparing a third slurry, wherein the third slurry includes a metal salt.

[0127] 2) Applying the third slurry on the positive electrode active material layer.

[0128] 3) Drying the third slurry to form a coating layer on the positive electrode active material layer.

[0129] 4) Roll-pressing the dried current collector, positive electrode active material layer and coating to obtain a positive electrode sheet.

[0130] Therefore, in the positive electrode sheet prepared through the above steps a)-c) and steps 1)-4), the positive electrode active material layer contains metal salt.

[0131] The present application also provides a lithium-ion battery, which includes the positive electrode sheet in any of the aforementioned embodiments, and / or the positive electrode sheet prepared by any of the aforementioned methods 100.

[0132] In one embodiment, a lithium ion battery includes an electrolyte including metal ions.

[0133] Specifically, after the aforementioned positive electrode plate is applied to a lithium-ion battery, the metal salt will dissolve or partially dissolve in the electrolyte to form free metal ions, thereby causing metal ions to exist in the electrolyte of the lithium-ion battery.

[0134] In one embodiment, based on the total weight of the electrolyte, the weight content c of the metal ions satisfies: 0.02%≤c≤30%; optionally, 0.03%≤c≤6%.

[0135] Specifically, c can be 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 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%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, or its value is within the range obtained by combining any two of the above values.

[0136] The present application also provides an electrical device, which includes the lithium-ion battery in any of the aforementioned embodiments.

[0137] 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.

[0138] In one embodiment, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0139] 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.

[0140] The present application has no particular restrictions on the shape of the battery cell, which can be cylindrical, square or any other shape. For example, Figure 2 The battery cell 200 is a square structure as an example.

[0141] It should be understood that the battery cell 200 may include the lithium-ion battery in the aforementioned embodiment.

[0142] Figure 3 300 is an example of a battery module. Figure 3 In the battery module 300, the plurality of battery cells 200 may be arranged in sequence along the length direction of the battery module 300. Of course, they may also be arranged in any other manner. The plurality of battery cells 200 may further be fixed by fasteners. The plurality of battery cells 200 may be battery cells 200 of the same chemical system or battery cells 200 of different chemical systems.

[0143] Optionally, in one embodiment, the battery module 300 may further include a housing having an accommodation space, and the plurality of battery cells 200 are accommodated in the accommodation space.

[0144] Optionally, in one embodiment, the battery modules 300 may also be assembled into a battery. The number of battery modules 300 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.

[0145] Figure 4 and Figure 5 400 is an example of a battery. Figure 4 and Figure 5 The battery 400 may include a battery box and a plurality of battery modules 300 disposed in the battery box. The battery box includes an upper box body 401 and a lower box body 402. The upper box body 401 can cover the lower box body 402 and form a closed space for accommodating the battery modules 300. The plurality of battery modules 300 may be arranged in the battery box in any manner.

[0146] It should be understood that in other embodiments, the battery 400 is also referred to as a battery pack. The battery cells 200 may first form a battery module 300, and the battery 400 may be formed by the battery module 300. Alternatively, the battery 400 may be directly formed by the battery cells 200, omitting the intermediate form of the battery module 300.

[0147] In addition, the present application also provides an electrical device, which includes the lithium-ion battery in the aforementioned embodiment.

[0148] In another embodiment, the power-consuming device includes at least one of the battery cell 200, battery module 300, or battery 400 provided in the present application. The battery cell 200, battery module 300, or battery 400 can be used as a power source for the power-consuming device, or as an energy storage unit for the power-consuming device. The power-consuming device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0149] As an electric device, a battery cell 200, a battery module 300, or a battery 400 may be selected according to its usage requirements.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] [Examples 1-23 and Comparative Examples 1-2]

[0154] Example 1

[0155] (1) Preparation of negative electrode sheet

[0156] 1kg of negative electrode active material artificial graphite, 10g of conductive agent acetylene black, 30g of binder styrene butadiene rubber (SBR), and 20g of thickener sodium carboxymethyl cellulose (CMC) were dissolved in 1kg of deionized water and mixed evenly to obtain negative electrode slurry. Then, the negative electrode slurry was evenly coated on the negative electrode current collector copper foil. After rolling and cutting, the negative electrode sheet was obtained.

[0157] (2) Preparation of positive electrode sheet

[0158] 1kg of positive electrode active material LiNi 5 Co 2 Mn 3 O 2 20g of metal salt potassium nitrate, 20g of conductive agent carbon nanotubes, and 20g of binder polyvinylidene fluoride (PVDF) were dissolved in 1kg of N-methylpyrrolidone and mixed evenly to obtain positive electrode slurry. The positive electrode slurry was then evenly coated on the positive electrode current collector aluminum foil. After drying in an oven at 80°C, the positive electrode active material layer was obtained, and then the positive electrode sheet was obtained by rolling and slitting.

[0159] (3) Preparation of lithium-ion batteries

[0160] The positive electrode sheet, the negative 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 after drying, lithium hexafluorophosphate (LiPF6) with a concentration of 1 mol / L is injected. 6 ) electrolyte, and a lithium-ion battery is obtained after packaging.

[0161] In Example 1, the positive electrode active material layer includes a metal salt, the metal salt is potassium nitrate, the metal ion is potassium ion, the difference between the reduction potential of the metal ion and the reduction potential of the lithium ion is 0.332V, the thickness of the positive electrode active material layer is 65μm, the average volume particle size of the metal salt particles Dv50=5μm, the solubility of the metal salt in the electrolyte S=0.032g / mL, the mass content of the metal salt in the positive electrode active material layer a=20%, the powder compaction density of the positive electrode film layer ρ=2.8, and the mass content of the metal ion in the electrolyte c=2.7%.

[0162] In order to verify the inhibitory effect of the positive electrode sheet provided in the present application on lithium precipitation and lithium dendrite growth, the CB value of the lithium-ion battery can be designed to be less than 1. Specifically, in Example 1, the CB value of the lithium-ion battery is 0.95.

[0163] Example 2

[0164] Compared with Example 1, the metal salt is magnesium nitrate, the metal ion is magnesium ion, the difference between the reduction potential of the metal ion and the reduction potential of the lithium ion is 0.672 V, Dv50=5 μm, S=0.054 g / mL, and c=4.7%.

[0165] Example 3

[0166] Compared with Example 1, in the isolation member of Example 3, the metal salts are potassium nitrate and magnesium nitrate, the metal ions are potassium ions and magnesium ions, the difference between the reduction potential of the metal ions and the reduction potential of the lithium ions are 0.332 V and 0.672 V respectively, S=0.047 g / mL, Dv50=5 μm, c=1.8% and 4.2%.

[0167] Example 4

[0168] Compared with Example 1, in Example 4, the metal salt is potassium hexafluorophosphate, Dv50=5 μm, S=0.035 g / mL, and c=2.9%.

[0169] Example 5

[0170] Compared with Example 1, in Example 5, the metal salt is barium sulfate, the difference between the reduction potential of the metal ion and the reduction potential of the lithium ion is 0.142 V, S=0.005 g / mL, Dv50=5 μm, and c=0.41%.

[0171] Example 6

[0172] Compared with Example 1, in Example 6, the average volume particle size of the metal salt particles Dv50=0.05 μm.

[0173] Example 7

[0174] Compared with Example 1, in Example 7, the average volume particle size of the metal salt particles Dv50=70 μm.

[0175] Example 8

[0176] Compared with Example 1, in Example 8, a=1%, c=0.02%.

[0177] Example 9

[0178] Compared with Example 1, in Example 9, a=50% and c=3.2%.

[0179] Example 10

[0180] Compared with Example 1, in Example 10, the preparation process of the positive electrode sheet is as follows: the positive electrode active material LiNi 5 Co 2 Mn 3 O 2 1 kg, 20g of conductive agent carbon nanotubes, and 20g of binder polyvinylidene fluoride (PVDF) are dissolved in 1kg of N-methylpyrrolidone and mixed evenly to obtain positive electrode slurry. Then the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil. After drying in an oven at 80°C, the positive electrode active material layer is obtained. 20g of metal salt potassium nitrate, 2g of PVDF and 20g of N-methylpyrrolidone are mixed and stirred into slurry and then coated on the positive electrode active material layer, and then rolled and cut to obtain the positive electrode sheet.

[0181] In other words, in Example 10, the coating layer includes a metal salt, the thickness of the coating layer is d=0.05 μm, the thickness of the positive electrode active material layer is 65 μm, and the mass content of the metal salt in the positive electrode film layer is b=1%, c=0.02%.

[0182] Embodiment 11

[0183] Compared with Example 10, in Example 11, d=0.1 μm and c=0.04%.

[0184] Example 12

[0185] Compared with Example 10, in Example 12, d=50 μm and c=3.2%.

[0186] Embodiment 13

[0187] Compared with Example 10, in Example 13, d=100 μm and c=3.2%.

[0188] Embodiment 14

[0189] Compared with Example 10, in Example 14, b=5% and c=0.09%.

[0190] Embodiment 15

[0191] Compared with Example 10, in Example 15, b=30% and c=2.9%.

[0192] Example 16

[0193] Compared with Example 1, in Example 16, ρ = 0.8 g / cm 3 , c = 2.76%.

[0194] Embodiment 17

[0195] Compared with Example 1, in Example 17, ρ = 1.0 g / cm 3 , c = 2.73%.

[0196] Embodiment 18

[0197] Compared with Example 1, in Example 18, ρ = 3.5 g / cm 3 , c = 2.64%.

[0198] Embodiment 19

[0199] Compared with Example 1, in Example 19, ρ = 4.0 g / cm 3 , c = 2.63%.

[0200] Embodiment 20

[0201] Compared with Example 1, in Example 20, a=1%, c=0.02%.

[0202] Embodiment 21

[0203] Compared with Example 1, in Example 21, a=1.5%, c=0.03%.

[0204] Embodiment 22

[0205] Compared with Example 1, in Example 22, the metal salt is sodium hexafluorophosphate, a=10%, and c=6%.

[0206] Embodiment 23

[0207] Compared with Example 1, in Example 23, the metal salt is sodium bis(fluorosulfonyl)imide, a=40%, and c=30%.

[0208] Comparative Example 1

[0209] Compared with Example 1, in Comparative Example 1, the positive electrode film layer does not contain metal salt.

[0210] Comparative Example 2

[0211] Compared with Example 1, in Comparative Example 2, the metal salt is manganese nitrate, the metal ion is manganese ion, and the difference between the reduction potential of the metal ion and the reduction potential of the lithium ion is 1.86V.

[0212] The product parameters of Examples 1-23 and Comparative Examples 1-2 are detailed in Table 1.

[0213] Table 1: Product parameters of Examples 1-23 and Comparative Examples 1-2

[0214] In Table 1, S represents the solubility of the metal salt in the electrolyte; Dv50 represents the average volume particle size of the metal salt particles; ρ represents the powder compaction density of the positive electrode film layer; d represents the thickness of the coating; a represents the mass content of the metal salt based on the total mass of the positive electrode active material layer; b represents the mass content of the metal salt based on the total mass of the positive electrode film layer; c represents the mass content of the metal ion based on the total mass of the electrolyte.

[0215] The product performance tests of Examples 1-23 and Comparative Examples 1-2 are detailed in Table 2.

[0216] Table 2: Performance data of Examples 1-23 and Comparative Examples 1-2

[0217] In Table 2, "Number of cycles" indicates the number of cycles when the lithium-ion battery is cycled to SOH less than or equal to 80%. "Whether lithium dendrites appear" indicates whether obvious dendrite-like lithium precipitation appears on the negative electrode sheet obtained by disassembling the lithium-ion battery after the lithium-ion battery cycle is completed.

[0218] Through comparative analysis of Examples 1-23 and Comparative Examples 1-2, it can be seen that by introducing metal ions whose reduction potential difference with that of lithium ions is less than or equal to 0.8V into the positive electrode plate, lithium deposition and growth of lithium dendrites in the negative electrode plate can be effectively suppressed, thereby improving the cycle performance and average coulombic efficiency of lithium-ion batteries.

[0219] Through comparative analysis of Examples 1-4, it can be seen that the metal salt introduced into the positive electrode sheet can be potassium nitrate, magnesium nitrate, potassium nitrate and magnesium nitrate, and magnesium hexafluorophosphate, all of which are helpful in improving the cycle performance and average coulomb efficiency of lithium-ion batteries. Among them, in Example 4, by using fluorine-containing metal salts, it is helpful for lithium-ion batteries to form a uniform and dense SEI film, thereby further improving the cycle performance and average coulomb efficiency of lithium-ion batteries.

[0220] Through the comparative analysis of Examples 8-9, it can be seen that the performance of Example 8 with a lower metal salt content in the positive electrode active material layer is significantly inferior to that of Example 9 with a higher metal salt content in the positive electrode active material layer, indicating that the higher the mass content of the metal salt in the positive electrode active material layer, the higher the metal ion content in the electrolyte, and the better the inhibitory effect on lithium precipitation and lithium dendrites. In addition, since the metal salt does not participate in the charge and discharge reaction of the lithium ion battery and does not contribute to the capacity, the mass content of the metal salt in the positive electrode active material layer cannot be increased indefinitely. Therefore, by controlling the mass content of the metal salt in the positive electrode active material layer within a suitable range, it is possible to effectively suppress lithium precipitation while reducing the effect of the metal salt on the energy density of the lithium ion battery.

[0221] Through the comparative analysis of Examples 10-15, it can be seen that by providing a coating on the positive electrode active material layer, metal salts can also be introduced into the positive electrode plate to improve the lithium ion cycle performance. Under the same other conditions, as the coating thickness increases, the mass content of the metal salt in the positive electrode plate increases, and the inhibitory effect on lithium precipitation and lithium dendrite growth is enhanced.

[0222] 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.

[0223] 1. Test method of reduction potential

[0224] The substance to be tested is dissolved in an appropriate solvent, and then a reference electrode (such as a standard hydrogen electrode) and a working electrode (such as a glassy carbon electrode) are used to form a battery. The cyclic voltammetry curve is tested under different conditions (such as pH value, temperature, etc.), and the reduction peak potential of the substance to be tested is read to obtain the reduction potential of the substance to be tested.

[0225] 2. Test method for solubility of metal salts in electrolyte

[0226] Dissolve the metal salt in 100 mL of 1 mol / L lithium hexafluorophosphate electrolyte until crystals are precipitated, calculate the total amount of metal salt added m, and measure the total volume of the solution at this time V. The solubility S can be calculated by the following formula: S = m / V.

[0227] 3. Test method for average volume particle size

[0228] Laser particle size analyzer method: The laser particle size analyzer uses the principle of laser scattering to determine the particle size by measuring the scattering intensity of laser by particles in the substance.

[0229] Exemplarily, the average volume particle size of the metal salt particles involved in the present application can be tested by ion beam polishing (CP) in combination with a scanning electron microscope (SEM): after disassembling the lithium-ion battery, use a reagent identical to the solvent of the electrolyte to clean the positive electrode plate and dry it, perform ion beam polishing on the dried positive electrode plate, and observe the inner diameter of the cavity (the metal salt is completely dissolved) or semi-cavity (the metal salt is not completely dissolved) on the cross-section of the plate by SEM, and repeatedly measure the average value of the inner diameter, which can be approximated as the average volume particle size Dv50 of the metal salt particles.

[0230] 4. Test method for compacted powder density

[0231] After disassembling the lithium-ion battery, measure the total area P of the positive electrode sheet and cut off a certain area P 1 The positive electrode piece is weighed m 1 , measure thickness h 1 ; After washing away the positive electrode film layer, weigh m 2 And measure the thickness h 2 The metal salt content in the electrolyte was tested by ICP, and the P and P 1 The proportional relationship is P 1 The mass m of metal salt dissolved on the positive electrode with an area of ​​d 3 . The compacted density is (m 1 +m 3 -m 2 ) / (P 1 ×(h 1 -h 2 )).

[0232] 5. Test method for mass content

[0233] After disassembling the lithium-ion battery, weigh the total mass m of the positive electrode sheet. 3 , scrape the positive electrode film layer on the surface of the positive electrode plate, and obtain the mass m of the metal salt in the positive electrode film layer through ICP test 4 and the mass m of the metal salt in the electrolyte 5 , weigh the mass m of the remaining positive electrode sheet 6 The mass content of metal salt is (m 4 +m 5 ) / (m 3 +m 5 -m 6 ).

[0234] 6. Test method for the number of cycles of lithium-ion batteries

[0235] After formation aging, the lithium-ion battery is fully charged and discharged at a current of 0.33C, and the number of battery cycles is counted when the battery SOH reaches 80%.

[0236] 7. Test method for average coulombic efficiency of lithium-ion batteries

[0237] The discharge capacity of each cycle of the lithium-ion battery charge and discharge cycle is divided by the charge capacity to obtain the coulombic efficiency of each cycle, and then the coulombic efficiency of each cycle is added up and divided by the number of cycles to obtain the average coulombic efficiency.

[0238] 8. Test method for the presence of lithium dendrites

[0239] The cycled lithium-ion battery is disassembled to obtain the cycled negative electrode sheet, and whether dendrites appear on the negative electrode sheet can be directly observed.

[0240] 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 positive electrode sheet, characterized in that: The positive electrode sheet comprises: A current collector and a positive electrode film layer disposed on at least one side of the current collector; The positive electrode film layer includes a metal salt, the metal salt includes a metal ion, the reduction potential of the metal ion is greater than the reduction potential of the lithium ion, and the difference between the reduction potential of the metal ion and the reduction potential of the lithium ion is less than or equal to 0.8V.

2. The positive electrode sheet according to claim 1, characterized in that: The positive electrode film layer includes a positive electrode active material layer, and the positive electrode active material layer is arranged on the current collector; The positive electrode active material layer includes the metal salt.

3. The positive electrode sheet according to claim 2, characterized in that: The positive electrode active material layer includes a positive electrode active material; and the average volume particle size Dv50 of the particles of the metal salt is equal to the average volume particle size Dv50 of the positive electrode active material.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that: The average volume particle size Dv50 of the particles of the metal salt satisfies: 0.05 μm≤Dv50≤70 μm; optionally, 0.5 μm≤Dv50≤60 μm.

5. The positive electrode sheet according to any one of claims 2 to 4, characterized in that: Based on the total mass of the positive electrode active material layer, the mass content a of the metal salt satisfies: 1%≤a≤50%; optionally, 5%≤a≤40%.

6. The positive electrode sheet according to claim 1, characterized in that: The positive electrode film layer includes a positive electrode active material layer and a coating layer, wherein the positive electrode active material layer is disposed on the current collector, and the coating layer is disposed on the positive electrode active material layer; The coating includes the metal salt.

7. The positive electrode sheet according to claim 6, characterized in that: The thickness d of the coating satisfies: 0.05 μm≤d≤100 μm; optionally, 0.1 μm≤d≤50 μm.

8. The positive electrode sheet according to claim 6 or 7, characterized in that: Based on the total mass of the positive electrode film layer, the mass content b of the metal salt satisfies: 1%≤b≤40%; optionally, 5%≤b≤30%.

9. The positive electrode sheet according to any one of claims 1 to 8, characterized in that: The metal salt includes at least one of sodium salt, potassium salt, calcium salt, magnesium salt and cesium salt.

10. The positive electrode sheet according to any one of claims 1 to 9, characterized in that: The metal salt includes anions, and the anions include one or more of fluorine, phosphorus, sulfur, and nitrogen.

11. The positive electrode sheet according to any one of claims 1 to 10, characterized in that: The solubility S of the metal salt in the electrolyte satisfies: S≥0.005 g / mL.

12. The positive electrode sheet according to any one of claims 1 to 11, characterized in that: The powder compaction density of the positive electrode film layer satisfies: ρ satisfies: 0.8 g / cm 3 ≤ρ≤4.0g / cm 3 ; Optionally, 1.0 g / cm 3 ≤ρ≤3.5g / cm 3 .

13. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet according to any one of claims 1 to 12.

14. The lithium ion battery according to claim 13, characterized in that: The lithium ion battery includes an electrolyte, and the electrolyte includes the metal ions.

15. The lithium ion battery according to claim 13 or 14, characterized in that: Based on the total weight of the electrolyte, the weight content c of the metal ions satisfies: 0.02%≤b≤30%; optionally, 0.03%≤b≤6%.

16. An electrical device, characterized in that: The electrical device comprises a lithium-ion battery as claimed in any one of claims 13 to 15.

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