Positive pole piece and preparation method thereof, battery monomer, battery and power utilization device

Abstract

The invention provides a positive pole piece and a preparation method thereof, a battery monomer, a battery and an electric device. The positive pole piece comprises a current collector, a first positive active material layer and a second positive active material layer, the first positive electrode active material layer is arranged on at least one side of the current collector, and the second positive electrode active material layer is arranged on the first positive electrode active material layer; the first cathode active material layer comprises a first cathode active material, the second cathode active material layer comprises a second cathode active material, the first cathode active material comprises a lithium-containing phosphate of an olivine structure, and the second cathode active material comprises a lithium metal oxide containing cobalt. The positive pole piece can effectively improve the influence of concentration polarization of the battery on the performance of the battery, and helps to improve the capacity and cycle performance of the battery.

Description

Positive electrode sheet and preparation method thereof, battery cell, battery and electrical device Technical Field

[0001] The present application relates to the field of batteries, and more specifically, to a positive electrode plate and a preparation method thereof, a battery cell, a 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 in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields, and have achieved great development. Therefore, higher requirements are placed on the capacity and cycle performance of lithium-ion batteries.

[0003] Battery polarization is one of the factors that affects the capacity and cycle performance of lithium-ion batteries, limiting their development. Therefore, how to reduce the impact of battery polarization on battery performance has become a technical problem that needs to be solved urgently.

[0004] Summary of the Invention

[0005] This application is made in view of the above-mentioned technical problems, and its purpose is to provide a positive electrode plate and its preparation method, a battery cell, a battery, and an electrical device. The positive electrode plate is used in a battery to effectively improve the effects of the battery's electrochemical polarization and electrolyte concentration polarization on battery performance, thereby helping to improve the battery's capacity and cycle performance.

[0006] In a first aspect, a positive electrode plate is provided, comprising a current collector, a first positive electrode active material layer and a second positive electrode active material layer, wherein the first positive electrode active material layer is arranged on at least one side of the current collector, and the second positive electrode active material layer is arranged on the first positive electrode active material layer; the first positive electrode active material layer comprises a first positive electrode active material, and the second positive electrode active material layer comprises a second positive electrode active material, wherein the first positive electrode active material comprises a lithium-containing phosphate with an olivine structure, and the second positive electrode active material comprises a lithium metal oxide containing cobalt.

[0007] In the embodiments of the present application, the positive electrode film layer on the positive electrode plate has a double-layer structure, with a cobalt-containing lithium metal oxide disposed on the upper layer and a lithium phosphate containing an olivine structure disposed on the lower layer. The upper and lower layers of the positive electrode film layer are configured so that the lithium ion kinetics of the upper layer of the positive electrode film layer are superior to those of the lower layer. In other words, the lithium ion conductivity of the upper layer of the positive electrode film layer is superior to that of the lower layer of the positive electrode film layer. Thus, a second positive electrode active material with better lithium ion kinetics is disposed on the upper layer of the positive electrode film layer, which is better soaked in the electrolyte, and a first positive electrode active material is disposed on the lower layer of the positive electrode film layer, which is less soaked in the electrolyte than the upper layer. This ensures that the current density distribution in the thickness direction of the positive electrode plate matches the ion kinetic properties of the positive electrode active material, thereby reducing the charge polarization voltage of the positive electrode plate and helping to improve the capacity performance and cycle performance of the battery.

[0008] It should be understood that the upper layer of the positive electrode film layer described in this application is the positive electrode active material layer on the positive electrode plate close to the electrolyte, such as the second positive electrode active material layer; the lower layer of the positive electrode film layer is the positive electrode active material layer on the positive electrode plate close to the current collector, such as the first positive electrode active material layer.

[0009] In some embodiments, the manganese-based transition metal lithium phosphate comprises a compound represented by formula (I): Li (1+x1) Mn a1 M1 (1-a1) P (1-m) O (4-n) (I)

[0010] Wherein, M1 represents a metal element, -0.2≤x1≤0.2, 0.1≤a1≤0.9, 0≤m≤0.1, 0≤n≤0.1.

[0011] In some embodiments, M1 includes one or more of Fe, Al, Cu, Cr, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb, and Ge.

[0012] In some embodiments, the cobalt-containing lithium metal oxide comprises a layered cobalt-containing lithium metal oxide.

[0013] In some embodiments, the cobalt-containing lithium metal oxide comprises a compound represented by formula (II): Li (1+x2) Co a2 M2 (1-a2) O (2-y) A y (II)

[0014] Wherein, M2 represents a metal element, A represents an oxygen-site doping element, A includes one or more of S, F, Cl and Br, -0.2≤x2≤0.2, 0.02≤a2≤0.5, 0≤y<2.

[0015] It should be understood that the battery will be accompanied by Li deintercalation and consumption during the charging and discharging process. The molar content of Li is different when the battery is discharged to different states. The above limitations on x1 and x2 include the molar content of Li in different charging and discharging states of the battery (usually the battery voltage is between 2.0V and 5.0V).

[0016] In some embodiments, M2 includes one or more of Ni, Fe, Cr, Mn, Ti, Zn, V, Al, and Zr.

[0017] In some embodiments, the positive electrode active material includes the first positive electrode active material and the second positive electrode active material, the mass ratio of the first positive electrode active material to the positive electrode active material is m, and the mass ratio of the second positive electrode active material to the positive electrode active material is n, wherein 0<m<1, 0<n<1, and 0<m+n≤1.

[0018] In some embodiments, the first positive electrode active material and the second positive electrode active material satisfy: 0.2≤K≤0.6;

[0019] in,

[0020] In the embodiments of the present application, by controlling the value of K within an appropriate range, the lithium ion kinetic distribution of the positive electrode active material in the thickness direction of the positive electrode sheet can be flexibly adjusted, so that it can better match the current density distribution caused by the concentration polarization of the electrolyte, and effectively improve the effects of electrochemical polarization and electrolyte concentration polarization on battery performance.

[0021] In some embodiments, in a battery cell including the positive electrode sheet, the conductivity σ of the electrolyte satisfies: 3.3 mS cm -1 ≤σ≤13mS cm -1 .

[0022] In a second aspect, a method for preparing a positive electrode plate is provided, the method comprising: providing a current collector; arranging a first positive electrode active material layer on the current collector; arranging a second positive electrode active material layer on the first positive electrode active material layer; wherein the first positive electrode active material layer comprises a first positive electrode active material, the second positive electrode active material layer comprises a second positive electrode active material, the first positive electrode active material comprises a lithium-containing phosphate with an olivine structure, and the second positive electrode active material comprises a lithium metal oxide containing cobalt.

[0023] In a third aspect, a battery cell is provided, wherein the battery cell comprises the positive electrode sheet in any embodiment of the first aspect, or the positive electrode sheet prepared according to the method in any embodiment of the second aspect.

[0024] In some embodiments, the battery cell includes an electrolyte, and the conductivity σ of the electrolyte satisfies: 3.3 mS cm -1 ≤σ≤13mS cm -1 .

[0025] In a fourth aspect, a battery is provided, comprising the battery cell according to any one of the embodiments of the third aspect.

[0026] In a fifth aspect, an electrical device is provided, which includes the battery cell in any embodiment of the third aspect and / or the battery in any embodiment of the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. Those skilled in the art can also derive other drawings based on the drawings without inventive effort. In the drawings, the drawings are not drawn to scale.

[0028] FIG1 is a schematic structural diagram of a positive electrode plate of the present application.

[0029] FIG2 is a SEM image of a positive electrode sheet of the present application.

[0030] FIG3 is a schematic flow chart of a method for preparing a positive electrode sheet of the present application.

[0031] FIG4 is a schematic diagram of a battery cell of the present application.

[0032] FIG5 is a schematic diagram of a battery module of the present application.

[0033] FIG6 is a schematic diagram of a battery according to the present application.

[0034] FIG. 7 is another schematic diagram of a battery according to the present application. DETAILED DESCRIPTION

[0035] Below, with appropriate reference to the accompanying drawings, the embodiments of the positive electrode sheet and its preparation method, battery cell, battery and electrical device of the present application are specifically disclosed in detail. 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 structure 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.

[0036] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] 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", "inside", "outside", 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 a limitation on 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. "Vertical" is not strictly perpendicular, but is within the allowable error range. "Parallel" is not strictly parallel, but is within the allowable error range.

[0038] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0039] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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).

[0040] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0041] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0042] Unless otherwise specified, all technical features and optional technical features of this 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] Typically, a battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the battery's charge and discharge process, active ions are embedded in and out of the positive and negative electrode sheets. The electrolyte acts as an ion conductor between the positive and negative electrode sheets. The separator is placed between the positive and negative electrode sheets, primarily to prevent a short circuit between the positive and negative electrodes while allowing ions to pass through. In some embodiments, the battery described herein is also referred to as a secondary battery.

[0045] This application uses lithium-ion batteries as an example. Lithium-ion batteries are a typical type of secondary battery. Because they rely on the chemical reaction of lithium ions intercalating and disintercalating between the positive and negative electrodes to charge and discharge, lithium-ion batteries are also called rocking-chair batteries. During charging, lithium ions are released from the positive electrode, moved to the negative electrode, and then intercalated. During discharge, lithium ions are released from the negative electrode, moved to the positive electrode, and then intercalated.

[0046] It should be understood that the "lithium insertion" and "intercalation" processes described in this application refer to the process in which lithium ions are embedded in the positive electrode material and the negative electrode material due to electrochemical reactions, and the "de-lithiumization", "de-lithiumization" and "de-intercalation" processes described in this application refer to the process in which lithium ions are removed from the positive electrode material and the negative electrode material due to electrochemical reactions.

[0047] With the increasing use of lithium-ion batteries, higher requirements are placed on the capacity and cycle performance of batteries. Battery polarization is one of the reasons that easily cause capacity loss and cycle performance degradation during the charge and discharge process of lithium-ion batteries. Battery polarization is generally divided into ohmic polarization, electrochemical polarization and concentration polarization. Among them, concentration polarization is caused by the diffusion rate of lithium ions participating in the battery electrochemical reaction in the liquid or solid phase is lower than the electron transmission rate in the electrochemical reaction. Electrochemical polarization is a polarization phenomenon in which the electrode potential deviates from the equilibrium potential due to the sluggishness of the electrochemical reaction. Especially in the late stage of battery charging, when the electrode assembly is in a high charge state, the electrochemical polarization and concentration polarization at the positive electrode plate increase significantly, seriously affecting the battery's charging capacity, and then affecting the subsequent discharge capacity, resulting in a decrease in battery capacity. In addition, as the battery cycles, the polarization phenomenon intensifies, causing adverse effects on the battery's cycle performance.

[0048] In view of this, embodiments of the present application provide a positive electrode sheet, wherein the film layer on the positive electrode sheet includes a first positive electrode active material layer disposed on a current collector and a second positive electrode active material layer disposed on the first positive electrode active material layer; the first positive electrode active material layer includes a first positive electrode active material, and the second positive electrode active material layer includes a second positive electrode active material; the first positive electrode active material includes an olivine-structured lithium-containing phosphate, and the second positive electrode active material includes a cobalt-containing lithium metal oxide. By disposing the first positive electrode active material with higher lithium ion kinetics in the first positive electrode active material layer and the second positive electrode active material in the second positive electrode active material layer, the effects of electrochemical polarization and concentration polarization on battery performance can be effectively improved, thereby helping to improve the battery's capacity and cycle performance.

[0049] Next, the positive electrode sheet, negative electrode sheet, separator and other parts of the battery are introduced in detail.

[0050] [Positive electrode]

[0051] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material. It should be understood that the positive electrode film layer is a film layer disposed on the positive electrode current collector.

[0052] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0053] In some embodiments, 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.).

[0054] FIG1 is a schematic structural diagram of a positive electrode plate provided in an embodiment of the present application.

[0055] As shown in FIG1 , the positive electrode sheet 1 includes a current collector 11 and a film layer 12 disposed on at least one side of the current collector 11 .

[0056] The membrane layer 12 includes a first positive electrode active material layer 121 and a second positive electrode active material layer 122 . The first positive electrode active material layer 121 is disposed on the positive electrode current collector, and the second positive electrode active material layer 122 is disposed on the first positive electrode active material layer 121 .

[0057] The first positive electrode active material layer 121 includes a first positive electrode active material, and the second positive electrode active material layer 122 includes a second positive electrode active material. The first positive electrode active material includes an olivine-structured lithium-containing phosphate, and the second positive electrode active material includes a cobalt-containing lithium metal oxide.

[0058] Generally speaking, the upper layer of the membrane layer 12 of the positive electrode plate 1 is fully in contact with the electrolyte and has a good degree of infiltration, allowing a large current to pass during an electrochemical reaction. However, the lower layer of the membrane layer 12 is less infiltrated than the upper layer, allowing a smaller current to pass during an electrochemical reaction. Therefore, during battery polarization, the upper layer of the positive electrode plate 1 will be more polarized than the lower layer, further exacerbating the battery polarization and detrimental to the battery's capacity retention and cycling stability.

[0059] In this embodiment, the membrane layer 12 is the aforementioned positive electrode membrane layer. In the positive electrode sheet 1, the first positive electrode active material layer 121, disposed on at least one side of the current collector, comprises an olivine-structured lithium-containing phosphate. The second positive electrode active material layer 122, closer to the electrolyte, comprises a cobalt-containing lithium metal oxide. Compared to the olivine-structured lithium-containing phosphate, the cobalt-containing lithium metal oxide has higher lithium ion kinetics, allowing the number of lithium ions it can transfer during charging to match the higher current. The olivine-structured lithium-containing phosphate, disposed in the lower layer of the membrane layer 12, has lithium ion kinetics that match the lower current.

[0060] Therefore, the embodiment of the present application designs the first positive electrode active material layer 121 and the second positive electrode active material layer 122 on the positive electrode plate 1 so that the kinetic properties of the positive electrode active material in the thickness direction of the positive electrode plate 1 match the current density distribution during the charging process, effectively improving the concentration polarization during the charging process, so that the capacity of the positive electrode active material on the positive electrode plate 1 can be fully utilized, which helps to maintain the capacity of the battery and helps improve the cycle stability of the battery.

[0061] FIG2 is a scanning electron microscope (SEM) image of a positive electrode sheet 1 provided in an embodiment of the present application.

[0062] Figure 2 shows the SEM morphology of a cross-section of the positive electrode sheet 1 along its thickness. It can be seen that the positive electrode sheet 1 has a clear three-layer structure: from bottom to top, a current collector 11 with a smooth and flat morphology, a first positive electrode active material layer 121 with a relatively dense powder morphology, and a second positive electrode active material layer 122 with a relatively loose powder morphology.

[0063] In some embodiments, the olivine-structured lithium-containing phosphate includes a compound represented by formula (I): Li (1+x1) Mn a1 M1 (1-a1) P (1-m) O (4-n) (I)

[0064] Wherein, M1 represents a metal element, -0.2≤x1≤0.2, 0.1≤a1≤0.9, 0≤m≤0.1, 0≤n≤0.1.

[0065] For example, x1 can be -0.2, -0.1, 0, 0.1, 0.2, or any combination thereof. a1 can be 0.5, 0.6, 0.7, 0.8, 0.9, or any combination thereof. m can be 0, 0.02, 0.04, 0.06, 0.08, 0.1, or any combination thereof. n can be 0.02, 0.04, 0.06, 0.08, 0.1, or any combination thereof.

[0066] In the embodiments of the present application, the olivine-structured lithium-containing phosphate that meets the above conditions has a high manganese content and can contribute to a higher voltage window in the electrochemical reaction. Therefore, selecting an olivine-structured lithium-containing phosphate that meets the above conditions helps further improve the energy density of the battery.

[0067] In some embodiments, M1 may include one or more of Fe, Al, Cu, Cr, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb, and Ge.

[0068] In some embodiments, the cobalt-containing lithium metal oxide comprises a layered cobalt-containing lithium metal oxide.

[0069] Cobalt-containing lithium metal oxides are a type of widely used positive electrode active material. They can include lithium nickel cobalt oxide, lithium manganese cobalt 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 its modified compounds, etc. It can include a hexagonal structure, a layered structure, etc.

[0070] In the embodiments of the present application, a layered cobalt-containing lithium metal oxide is selected, and its ordered layered structure can provide more lithium ion active sites for electrochemical reactions, thereby providing a higher capacity for the battery.

[0071] In some embodiments, the cobalt-containing lithium metal oxide comprises a compound represented by formula (II): Li (1+x2) Co a2 M2 (1-a2) O (2-y) A y (II)

[0072] Wherein, M2 represents a metal element, A represents an oxygen-site doping element, A includes one or more of S, F, Cl and Br, -0.2≤x2≤0.2, 0.02≤a2≤0.5, 0≤y<2.

[0073] For example, x2 can be -0.2, -0.1, 0, 0.1, 0.2, or any combination thereof. a2 can be 0.02, 0.04, 0.06, 0.08, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or any combination thereof. y can be 0, 0-2, or any combination thereof.

[0074] It should be understood that the battery will be accompanied by Li deintercalation and consumption during the charging and discharging process. The molar content of Li is different when the battery is discharged to different states. The above limitations on x1 and x2 include the molar content of Li in different charging and discharging states of the battery (usually the battery voltage is between 2.0V and 5.0V).

[0075] In some embodiments, M2 includes one or more of Ni, Fe, Cr, Mn, Ti, Zn, V, Al, and Zr.

[0076] In some embodiments, the positive electrode active material includes a first positive electrode active material and a second positive electrode active material, the mass ratio of the first positive electrode active material to the positive electrode active material is m, and the mass ratio of the second positive electrode active material to the positive electrode active material is n, wherein 0<m<1, 0<n<1, and 0<m+n≤1.

[0077] Specifically, the manganese content and cobalt content on the positive electrode plate 1 can be flexibly controlled by adjusting the mass ratio of the first positive electrode active material in the positive electrode active material and the mass ratio of the second positive electrode active material in the positive electrode active material, so that the positive electrode plate 1 meets different application requirements.

[0078] In addition, the positive electrode active material may further include a third positive electrode active material, for example, the third positive electrode active material includes lithium iron phosphate. In one example, the first positive electrode active material layer may include the first positive electrode active material and the third positive electrode active material. In another example, the second positive electrode active material layer may include the second positive electrode active material and the third positive electrode active material.

[0079] In some embodiments, the first positive electrode active material and the second positive electrode active material satisfy: 0.2≤K≤0.6;

[0080] in,

[0081] Specifically, the K value can be regulated by adjusting the values ​​of m, n, a1, and a2. Among them, m and n can be adjusted by controlling the amount of the first positive electrode active material and the second positive electrode active material, thereby achieving the regulation of the K value. The compound represented by formula (I) and the compound represented by formula (II) can be prepared using a synthesis method commonly used in the art. A1 and a2 can be adjusted by regulating the amount of the manganese source and the cobalt source during the synthesis process, thereby achieving the regulation of the K value.

[0082] In the embodiments of the present application, by controlling the value of K within an appropriate range, the lithium ion dynamics in the thickness direction of the positive electrode plate 1 can be flexibly controlled, so that the lithium ion dynamics of the upper layer of the film layer 12 can match the large current passing through the surface of the positive electrode plate 1 in the late stage of charging, and the lithium ion dynamics of the lower layer of the film layer 12 can match the current passing through the interior of the positive electrode plate 1, effectively improving the polarization of the positive electrode plate 1 during charging, thereby reducing the impact of concentration polarization on battery performance. By flexibly controlling the K value, the positive electrode plate 1 can be applied to batteries of different models and energy densities.

[0083] In some embodiments, the film layer 12 may further include a binder. For example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0084] In some embodiments, the film layer 12 may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0085] In some embodiments, the positive electrode sheet 1 can be prepared by the following method: the components for preparing the positive electrode sheet, such as the first 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 first positive electrode slurry; 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 second positive electrode slurry; the first positive electrode slurry and the second positive electrode slurry are coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet 1 can be obtained.

[0086] [Negative electrode]

[0087] The negative electrode sheet generally includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material. It should be understood that the negative electrode film layer is a film layer disposed on the negative electrode current collector.

[0088] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0089] Alternatively, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base layer (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0090] Alternatively, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon 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.

[0091] Optionally, the negative electrode film layer further includes a binder. The binder may 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).

[0092] Optionally, 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.

[0093] Optionally, the negative electrode film layer further includes other additives, such as a thickener (such as sodium carboxymethyl cellulose (CMC-Na)).

[0094] In some embodiments, the negative electrode sheet can be prepared by forming a negative electrode slurry from the components used to prepare the negative electrode sheet. For example, the negative electrode active material, conductive agent, binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form the negative electrode slurry. The negative electrode slurry is then coated onto the negative electrode current collector. After drying and cold pressing, the negative electrode sheet is obtained.

[0095] [Electrolytes]

[0096] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0097] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0098] In some embodiments, the electrolyte salt may 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.

[0099] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0100] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0101] In some embodiments, the conductivity σ of the electrolyte satisfies: 3.3 mS cm -1 ≤σ≤13mS cm -1 .

[0102] The conductivity σ of the electrolyte is related to factors such as the electrolyte, solute, solvent, and concentration of the electrolyte. In some examples, the conductivity σ of the electrolyte can be controlled by adjusting the concentration of the electrolyte or changing the type of electrolyte or solvent.

[0103] [Isolator]

[0104] In some embodiments, the battery further includes a separator. The present application has no particular limitation on the type of separator. For example, any known porous structure separator with good chemical and mechanical stability can be selected.

[0105] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0106] Next, the method for preparing the positive electrode plate 1 according to the embodiment of the present application is introduced in detail.

[0107] FIG3 is a schematic flow chart of a method for preparing a positive electrode sheet 1 according to an embodiment of the present application. As shown in FIG3 , the method 300 includes:

[0108] S301, providing a current collector 11.

[0109] S302 , disposing a first positive electrode active material layer 121 on at least one side of the current collector.

[0110] S303 , disposing the second positive electrode active material layer 122 on the first positive electrode active material layer 121 .

[0111] The first positive electrode active material layer 121 includes a first positive electrode active material, and the second positive electrode active material layer 122 includes a second positive electrode active material. The first positive electrode active material includes an olivine-structured lithium-containing phosphate, and the second positive electrode active material includes a cobalt-containing lithium metal oxide.

[0112] In this embodiment, the positive electrode sheet 1 prepared by the method 300 has a film layer 12 with a double-layer structure and has the technical effects corresponding to the positive electrode sheet 1 , which will not be described in detail here.

[0113] In some embodiments, the positive electrode sheet 1 , the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0114] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0115] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as 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. For example, FIG4 shows a battery cell 400 having a square structure as an example.

[0117] Figure 5 shows an example battery module 500. Referring to Figure 5 , in the battery module 500, multiple battery cells 400 may be arranged sequentially along the length of the battery module 500. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 400 may be secured together using fasteners.

[0118] Optionally, in one embodiment, the battery module 500 may further include a housing having an accommodation space, and the plurality of battery cells 400 may be accommodated in the accommodation space.

[0119] Optionally, in one embodiment, the battery modules 500 may be assembled into a battery. The battery may contain one or more battery modules 500. The specific number may be selected by those skilled in the art according to the application and capacity of the battery.

[0120] Figures 6 and 7 illustrate an example battery 600. Referring to Figures 6 and 7, battery 600 may include a battery box and multiple battery modules 500 disposed within the box. The battery box includes an upper box body 601 and a lower box body 602. The upper box body 601 can be placed over the lower box body 602 to form an enclosed space for accommodating the battery modules 500. The multiple battery modules 500 can be arranged in any manner within the battery box.

[0121] It should be understood that in other embodiments, the battery 600 is also referred to as a battery pack. The battery cells 400 may be first assembled into the battery module 500, and the battery 600 may be assembled from the battery module 500. Alternatively, the battery 600 may be directly assembled from the battery cells 400, omitting the intermediate battery module 500.

[0122] In addition, the present application also provides an electrical device, which includes at least one of the battery cell 400, battery module 500, or battery 600 provided in the present application. The battery cell 400, battery module 500, or battery 600 can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (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, satellites, energy storage systems, etc.

[0123] As an electric device, a battery cell 400 , a battery module 500 , or a battery 600 may be selected according to its usage requirements.

[0124] As an example of an electric device, the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module can be used.

[0125] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0126] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0127] [Examples and Comparative Examples]

[0128] Example 1

[0129] (1) Preparation of positive electrode sheet

[0130] The compound represented by formula (I), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were dissolved in solvent N-methylpyrrolidone (NMP) at a mass ratio of 97:1:2, and the mixture was thoroughly stirred and mixed to obtain a first positive electrode slurry.

[0131] The compound represented by formula (II), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were dissolved in solvent N-methylpyrrolidone (NMP) at a mass ratio of 97:1:2, and the mixture was thoroughly stirred and mixed to obtain a second positive electrode slurry.

[0132] The first positive electrode slurry and the second positive electrode slurry are evenly coated on the positive electrode current collector aluminum foil once or in batches, with the first positive electrode slurry on the lower layer and the second positive electrode slurry on the upper layer. The positive electrode sheets are then dried, cold pressed, and cut.

[0133] In Example 1, m=0.4, n=0.6, a1=0.6, a2=0.24, and K=0.60.

[0134] (2) Preparation of negative electrode sheet

[0135] The negative electrode active material, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are dissolved in deionized water and mixed thoroughly to form a negative electrode slurry. The slurry is then evenly coated onto the negative electrode current collector copper foil. The negative electrode sheets are then cold pressed and slit.

[0136] (3) Assembly of battery cells

[0137] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order so that the separator is located between the positive electrode sheet and the negative electrode sheet and can isolate the positive electrode sheet from the negative electrode sheet; the stacked components are then wound to obtain an electrode assembly; the electrode assembly is placed in a shell, dried, and then injected with electrolyte; after undergoing processes such as formation and standing, a battery cell is obtained.

[0138] The electrolyte includes a carbonate solvent, and the conductivity of the electrolyte is σ = 4.4 mS cm -1 .

[0139] Example 2

[0140] Compared with Example 1, in Example 2, m=0.3, n=0.7, K=0.93, and the remaining parameters are the same as those in Example 1.

[0141] Example 3

[0142] Compared with Example 2, in Example 3, a1=0.7, a2=0.15, K=0.50, and the remaining parameters are the same as those in Example 2.

[0143] Example 4

[0144] Compared with Example 1, in Example 4, the second positive electrode active material layer further includes lithium iron phosphate (LiFePO 4 ), m=0.4, n=0.5, K=0.50, and the remaining parameters are the same as those in Example 1.

[0145] Example 5

[0146] Compared with Example 1, in Example 5, a1=0.1, a2=0.24, K=3.6, and the remaining parameters are the same as those in Example 1.

[0147] Example 6

[0148] Compared with Example 1, in Example 6, a1=0.9, a2=0.24, K=0.40, and the remaining parameters are the same as those in Example 1.

[0149] Example 7

[0150] Compared with Example 1, in Example 7, a1=0.6, a2=0.02, K=0.05, and the remaining parameters are the same as those in Example 1.

[0151] Example 8

[0152] Compared with Example 1, in Example 8, a1=0.6, a2=0.5, K=1.25, and the remaining parameters are the same as those in Example 1.

[0153] Example 9

[0154] Compared with Example 1, in Example 9, the conductivity of the electrolyte is σ=3.3mS cm -1 . , the remaining parameters are the same as those in Example 1.

[0155] Example 10

[0156] Compared with Example 1, in Example 10, the conductivity of the electrolyte is σ=13mS cm -1 , and the remaining parameters are the same as those in Example 1.

[0157] Example 11

[0158] Compared with Example 1, in Example 11, a2=0.12, m=0.5, n=0.5, K=0.20, and the remaining parameters are the same as those in Example 1.

[0159] Comparative Example 1

[0160] Compared to Example 1, the positive electrode sheet in Comparative Example 1 had a single-layer structure. Specifically, the compound represented by Formula (I), acetylene black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder were dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 97:1:2. The mixture was thoroughly stirred and mixed to produce a positive electrode slurry. The slurry was then evenly coated onto aluminum foil, the positive electrode current collector. The positive electrode sheet was then dried, cold-pressed, and slit.

[0161] Comparative Example 2

[0162] Compared with Example 1, the second positive electrode active material in Comparative Example 2 is lithium nickelate (LiNiO2), m=0.4, n=0.6, a1=0.6, K=0.6, σ=4.4mS cm -1 .

[0163] Please refer to Table 1 for specific parameter settings of the embodiment and comparative example.

[0164] In Table 1, active material 1 represents the first positive electrode active material, active material 2 represents the second positive electrode active material, I represents the compound represented by formula (I), and II represents the compound represented by formula (II).

[0165] The battery performance test results of the above examples and comparative examples are detailed in Table 2.

[0166] Table 2 Test results of battery charging time in different embodiments and comparative examples

[0167] In Example 1, membrane layer 12 has a double-layer structure and contains different active materials, while in Comparative Example 1, membrane layer 12 has only a single-layer structure and a single active material. A comparison of Example 1 and Comparative Example 1 shows that Example 1 has a capacity retention rate far exceeding that of Comparative Example 1, demonstrating excellent cycling and capacity performance. This demonstrates that by providing an olivine-structured lithium-containing phosphate on the upper layer of the positive electrode film layer 12 and a cobalt-containing lithium metal oxide on the lower layer of the positive electrode film layer 12, the lithium ion conductivity of the upper positive electrode film layer is superior to that of the lower positive electrode film layer, effectively improving battery polarization and enhancing the battery's capacity and cycling performance.

[0168] By comparing Example 1 and Comparative Example 2, it can be seen that the upper layer of the membrane layer 12 is provided with lithium nickelate, which also has a layered structure, but its lithium ion kinetics are inferior to those of cobalt-containing lithium metal oxide. The capacity retention rate of the battery in Comparative Example 2 after 200 cycles is also significantly lower than that of the battery in Example 1. Therefore, by providing a cobalt-containing lithium metal oxide with excellent lithium ion kinetics in the upper layer, the lithium ion transfer capacity of the surface of the positive electrode sheet 1 can be matched with the larger current on the surface of the positive electrode sheet 1, thereby effectively improving the battery polarization and helping to improve the battery's capacity performance and cycle performance.

[0169] Compared with Example 1, Examples 2-3 adjusted the values ​​of m and n, and adjusted the values ​​of a1 and a2, respectively. As a result, the K values ​​of Example 2 and Example 3 were 0.93 and 0.5, respectively. Among them, the K value of 0.93 in Example 2 exceeded the range of 0.2-0.6, while the K value of 0.5 in Example 3 fell within this range. The capacity retention rates of the batteries in Examples 2 and 3 were 91.0% and 92.2%, respectively, indicating that the performance of Examples 1 and 3 was better than that of Example 2. This shows that controlling the K value within an appropriate range is more conducive to improving battery polarization and improving the battery's cycle performance and capacity performance.

[0170] Compared to Example 1, the second active material layer 122 of Example 4 also includes lithium iron phosphate, where the mass ratio of lithium iron phosphate to the positive electrode active material is 0.1. The film layer 12 of the positive electrode plate 1 in Example 4 also has the same double-layer structure and corresponding materials as Example 1, and also exhibits excellent cycle performance and capacity performance.

[0171] Compared with Example 1, Examples 5-6 and 7-8 changed the values ​​of a1 and a2, respectively. In Example 5 and Example 6, the values ​​of a1 were 0.1 and 0.9, respectively, and the corresponding K values ​​were 3.6 and 0.4, respectively, and the capacity retention rates were 90.1% and 92.9%, respectively. As a1 increases, the K value decreases. Among them, the K value of Example 5 exceeds the range of 0.2-0.6, and the capacity retention performance of the battery in Example 5 is inferior to that of Example 1 and Example 6. In Example 7 and Example 8, the values ​​of a2 were 0.02 and 5, respectively, and the corresponding K values ​​were 0.05 and 1.25, respectively, and the capacity retention rates were 80.7% and 90.3%, respectively. As a2 increases, the K value increases. Among them, the K values ​​of Examples 7 and 8 are both beyond the range of 0.2-0.6. The capacity retention rates of the batteries in Examples 7 and 8 are both lower than that of Example 1 in which the K value falls within the range of 0.2-0.6. However, the capacity retention rate of Example 8 is better than that of Example 7, indicating that increasing the cobalt content in the positive electrode sheet is also helpful in improving the capacity retention rate of the battery.

[0172] Compared with Example 1, Examples 9-10 change the conductivity of the electrolyte. The values ​​of conductivity σ in Examples 9 and 10 are 3.3 mS cm and 3.3 mS cm, respectively. -1 and 13 mS cm -1 , all falling within 3.3 mS cm -1 -13mS cm -1 Within the value range of , the corresponding capacity retention rates are 93.5% and 94.0%, respectively, both showing good cycle performance and capacity performance.

[0173] Compared with Example 1, Example 11 changes a2, m, and n so that the K value is 0.2, which also falls within the value range of 0.2-0.6. Example 11 also exhibits good cycle performance and capacity performance.

[0174] Next, the testing methods of the physical parameters and performance parameters mentioned in the embodiments of this application are briefly introduced.

[0175] 1. Test method for battery capacity retention rate

[0176] The battery was subjected to charge and discharge tests at 25°C. The test conditions were as follows: using a Blue Electric test system, the positive and negative electrodes were connected, and the battery was subjected to a two-stage charge and discharge test. The first stage of the charge and discharge process involved a 1-minute rest period, followed by a constant-current charge at 8mA to 4.2V, followed by a constant-voltage charge at 4.2V with a cutoff current of 2mA. After a 10-minute rest period, the battery was discharged at a constant current of 8mA to a cutoff voltage of 2.5V, and then rested for 50 hours. This first stage of the test was used to form the SEI film and reduce polarization. The second stage of the charge and discharge process involved a 60mA constant-current charge at a cutoff voltage of 4.2V, a 4.2V constant-voltage charge at a cutoff current of 2mA, a 10-minute rest period, and a 60mA constant-current discharge at a cutoff voltage of 2.5V. After a second charge and discharge cycle of 500 cycles, the battery was charged to 4.2V before testing. The second stage of the test was used to test the battery's cycling performance. The first charge cycle refers to the battery's capacity after the first test, which is first charged at a constant current of 60mA to 4.2V, then charged at a constant voltage of 4.2V to a cutoff current of 2mA. The first discharge capacity refers to the capacity discharged by the battery when discharged at a constant current of 60mA to a voltage of 2.5V. The discharge capacity after 200 cycles is calculated, with the first-cycle discharge capacity as 100%. The ratio of this capacity to the first-cycle discharge capacity is the capacity retention rate after 200 cycles.

[0177] 2. Test method for electrolyte conductivity

[0178] The electrolyte conductivity test is performed using a conductivity meter (such as a Mettler Toledo conductivity meter) at room temperature (25°C) and the data is read.

[0179] 3.K value test method

[0180] By performing inductively coupled plasma (ICP) testing on the electrode, the content of specified elements in the electrode and the upper and lower layers of the film can be detected, a1*m and a2*n can be detected, and the K value can be calculated using the formula;

[0181] ICP test method: Use aqua regia (concentrated hydrochloric acid: concentrated nitric acid = 3:1) or reverse aqua regia (concentrated nitric acid: concentrated hydrochloric acid 3:1) to digest the electrode or the electrode after stripping the current collector, and then use an ICP tester to measure the element content.

[0182] 4. Scanning electron microscope test method of electrode

[0183] Weigh a certain area of ​​electrode (≤6×6cm 2 ) is adhered to the conductive glue, the conductive glue is placed on a sample stage and dried, and the treated sample stage is sent to a field emission scanning electron microscope (for example, a Zeiss Sigma300 scanning electron microscope can be used) to photograph the morphology of the material using the field emission scanning electron microscope.

[0184] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode sheet, characterized in that: The positive electrode sheet comprises: A current collector, a first positive electrode active material layer and a second positive electrode active material layer; The first positive electrode active material layer is disposed on at least one side of the current collector, and the second positive electrode active material layer is disposed on the first positive electrode active material layer; The first positive electrode active material layer includes a first positive electrode active material, and the second positive electrode active material layer includes a second positive electrode active material. The first positive electrode active material includes a lithium-containing phosphate having an olivine structure, and the second positive electrode active material includes a lithium metal oxide containing cobalt.

2. The positive electrode sheet according to claim 1, characterized in that: The olivine-structured lithium-containing phosphate comprises a compound represented by formula (I): Li (1+x1) Mn a1 M1 (1-a1) P (1-m) O (4-n) (I) Wherein, M1 represents a metal element, -0.2≤x1≤0.2, 0.1≤a1≤0.9, 0≤m≤0.1, 0≤n≤0.

1.

3. The positive electrode sheet according to claim 2, characterized in that: The M1 includes one or more of Fe, Al, Cu, Cr, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb and Ge.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that: The cobalt-containing lithium metal oxide includes a layered cobalt-containing lithium metal oxide.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The cobalt-containing lithium metal oxide includes a compound represented by formula (II): Li (1+x2) Co a2 M2 (1-a2) O (2-y) A y (II) Wherein, M2 represents a metal element, A represents an oxygen-doping element, A includes one or more of S, F, Cl and Br, -0.2≤x2≤0.2, 0.02≤a2≤0.5, 0≤y<2.

6. The positive electrode sheet according to claim 5, characterized in that: The M2 includes one or more of Ni, Fe, Cr, Mn, Ti, Zn, V, Al, and Zr.

7. The positive electrode sheet according to any one of claims 1 to 6, characterized in that: The positive electrode active material includes the first positive electrode active material and the second positive electrode active material; The mass ratio of the first positive electrode active material to the positive electrode active material is m, and the mass ratio of the second positive electrode active material to the positive electrode active material is m. The mass ratio of the material to the positive electrode active material is n, wherein 0<m<1, 0<n<1, and 0<m+n≤1.

8. The positive electrode sheet according to claim 7, characterized in that: The positive electrode sheet satisfies: 0.2≤K≤0.6; in, 9. The positive electrode sheet according to any one of claims 1 to 8, characterized in that: In the battery cell including the positive electrode sheet, the conductivity σ of the electrolyte satisfies: 3.3 mS cm -1 ≤σ≤13mS cm -1 .

10. A method for preparing a positive electrode sheet, characterized in that: The method comprises: providing a current collector; Disposing a first positive electrode active material layer on at least one side of the current collector; disposing a second positive electrode active material layer on the first positive electrode active material layer; The first positive electrode active material layer includes a first positive electrode active material, the second positive electrode active material layer includes a second positive electrode active material, the first positive electrode active material includes a lithium-containing phosphate with an olivine structure, and the second positive electrode active material includes a lithium metal oxide containing cobalt.

11. A battery cell, characterized in that: The battery cell comprises the positive electrode sheet according to any one of claims 1 to 9, or the positive electrode sheet prepared by the preparation method according to claim 10.

12. The battery cell according to claim 11, characterized in that: The battery cell includes an electrolyte, and the conductivity σ of the electrolyte satisfies: 3.3 mS cm -1 ≤σ≤13mS cm -1 .

13. A battery, characterized in that: The battery comprises the battery cell according to claim 11 or 12.

14. An electrical device, characterized in that: The electrical device comprises the battery cell according to claim 11 or 12, and / or the battery according to claim 13.

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