Positive electrode active materials and their preparation methods, positive electrode sheets, batteries and electrical devices

Abstract

This application provides a positive electrode active material and its preparation method, a positive electrode sheet, a battery, and an electrical device, relating to the field of batteries. The positive electrode active material includes a layered transition metal oxide, a first coating layer covering the surface of the layered transition metal oxide, and a second coating layer covering the surface of the first coating layer; wherein, the first coating layer includes M x O y M includes at least one of Mg, Al and transition metals from group III to group VIB, 0 < x, 0 < y, the second coating layer includes a positive metal phosphate salt; the total thickness of the first coating layer and the second coating layer is H, H ≤ 3 nm, and the battery containing the above positive electrode active material has good energy density, as well as good cycle performance and good high-temperature storage performance in full charge state.

Description

Technical Field

[0001] This application relates to the field of batteries, and more specifically, to a positive electrode active material and its preparation method, a positive electrode sheet, a battery, and an electrical device. Background Technology

[0002] With the development of new energy vehicles and energy storage, the market demands increasingly higher energy density for power batteries. Layered transition metal oxides have very high volumetric energy density, which further increases with the increase of charging cut-off voltage, and dominate the 3C market. However, batteries containing them experience rapid performance degradation after being stored at a high temperature of 60°C when fully charged, making them unsuitable for long-term storage and exhibiting poor cycle performance. Summary of the Invention

[0003] In view of the above problems, this application provides a positive electrode active material and its preparation method, a positive electrode sheet, a battery and an electrical device, which can effectively improve the problems of poor battery cycle performance and poor high-temperature storage performance in a fully charged state while enabling batteries containing layered transition metal oxides to have better energy density.

[0004] In a first aspect, embodiments of this application provide a positive electrode active material, comprising: a layered transition metal oxide, a first coating layer covering the surface of the layered transition metal oxide, and a second coating layer covering the surface of the first coating layer; wherein the first coating layer includes M x O y M includes Mg, Al and at least one of Group III to VIB transition metals, 0 < x, 0 < y, the second coating layer includes a positive metal phosphate salt; the total thickness of the first coating layer and the second coating layer is H, H ≤ 3 nm.

[0005] In the technical solution of this application embodiment, a first coating layer is used to coat the layered transition metal oxide to alleviate the dissolution of the transition metal under high voltage. A second coating layer is disposed on the outer layer to protect the first coating layer from being eroded and damaged by the electrolyte. Furthermore, the positive metal phosphate salt, which has the property of a lithium-ion transport channel, can act as a fast ion conductor to improve the kinetic performance of the positive electrode active material. By ensuring that the total thickness of the first and second coating layers is H≤3nm, the influence of the coating layer on the conductivity and ion conduction characteristics of the layered transition metal oxide is mitigated. The combined effect of these features enables the battery containing the above-mentioned positive electrode active material to effectively improve the battery's cycle performance and high-temperature storage performance under full charge while maintaining a good energy density.

[0006] In some embodiments, 1nm < H ≤ 3nm; optionally, 1nm < H ≤ 2nm. This helps to mitigate the energy density loss of batteries containing the above-mentioned positive electrode active material and can effectively improve the cycle performance and high-temperature storage performance of batteries using this positive electrode active material.

[0007] In some embodiments, the thickness of the second coating layer is h, where 0.7 nm ≤ h ≤ 2 nm; alternatively, 1 nm ≤ h ≤ 1 / 2 H. Within the above range, it is beneficial to effectively improve the cycle performance and high-temperature storage performance of the battery containing the positive electrode active material while maintaining a better energy density.

[0008] In some embodiments, the surface of the layered transition metal oxide is doped with metal element M from the first coating layer. By doping with metal element M, a transition is formed between the layered transition metal oxide and the first coating layer. Furthermore, doping helps to enhance the bond-breaking energy barrier between the transition metal and oxygen originally contained in the layered transition metal oxide, suppressing the dissolution and oxygen release reactions of the transition metal originally contained in the layered transition metal oxide. This is beneficial for improving the cycle performance and high-temperature storage performance of the battery using this cathode active material.

[0009] In some embodiments, M includes at least one selected from Mg, Al, Ti, Zr, Nb, Ta, and W. The selection of these metal oxides provides excellent doping effects, which helps to prevent the dissolution and oxygen release of transition metal oxides in the layered transition metal oxides, thereby improving the performance of the cathode active material.

[0010] In some embodiments, the phosphate positive metal salt includes at least one selected from lithium phosphate, sodium phosphate, potassium phosphate, calcium phosphate, and aluminum phosphate. These phosphate positive metal salts are stable and not easily decomposed, and can exist stably under high temperature, high pressure, and hydrofluoric acid environments, which is beneficial for improving the cycle performance and high-temperature storage performance of batteries using this positive electrode active material.

[0011] Secondly, this application provides a method for preparing the positive electrode active material in the above embodiments, which includes: depositing a first coating layer on the surface of a layered transition metal oxide by vapor deposition to obtain an intermediate product; and depositing a second coating layer on the surface of the intermediate product by vapor deposition.

[0012] The preparation method provided in this application is beneficial to achieving a first coating layer and a second coating layer with high coating integrity, strong bonding force, relatively uniform thickness and thinness, which is beneficial to improving the cycle performance and high-temperature storage performance of batteries using this positive electrode active material.

[0013] Optionally, vapor deposition methods include atomic layer deposition.

[0014] In some embodiments, the preparation method further includes annealing the intermediate product before depositing a second coating layer on the surface of the intermediate product, wherein the annealing temperature is not lower than 600°C, optionally 600-800°C, and further optionally 650-800°C.

[0015] Annealing the intermediate product at a temperature not lower than 600°C before depositing the second coating layer on its surface enables the M in the first coating layer to be deposited. x O y The surface doping of layered transition metal oxides with metal element M is beneficial to improving the cycle performance and high-temperature storage performance of batteries using this positive electrode active material.

[0016] Alternatively, the annealing time is 3-5 hours.

[0017] In some embodiments, the preparation method further includes: depositing a second coating layer on the surface of the intermediate product, and then sintering it at 400-550°C for 3-5 hours. Optionally, the sintering temperature is 400-500°C. Using the above-mentioned low-temperature sintering method is beneficial for improving the structural stability of the positive electrode active material and can effectively remove impurities such as carbon introduced during the preparation process in the first and / or second coating layers, thereby improving the purity of the positive electrode active material.

[0018] Thirdly, this application provides a positive electrode sheet, which includes the positive active material in the above embodiments.

[0019] In some embodiments, the positive electrode sheet includes a positive active material layer, which includes a positive active material and a conductive agent, wherein the conductive agent includes Super P and CNT;

[0020] Among them, the mass percentage of Super P in the positive electrode active material layer is greater than the mass percentage of CNT in the positive electrode active material layer;

[0021] Optionally, the mass percentage of Super P in the positive electrode active material layer is at least twice the mass percentage of CNT in the positive electrode active material layer;

[0022] Further optionally, the conductive agent has a mass percentage of 0.9%-2% in the positive electrode active material layer, and the CNT has a mass percentage of less than or equal to 0.5% in the positive electrode active material layer.

[0023] Fourthly, this application provides a battery that includes the battery cell described in the above embodiments.

[0024] Fifthly, this application provides an electrical device that includes the battery described in the above embodiments, the battery being used to provide electrical energy.

[0025] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0026] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0027] Figure 1 This is a schematic diagram of the vehicle structure according to some embodiments of this application;

[0028] Figure 2 Exploded structural diagrams of batteries according to some embodiments of this application;

[0029] Figure 3 This is an exploded structural diagram of a battery cell according to some embodiments of this application;

[0030] Figure 4 This is a schematic diagram of the structure of the positive electrode sheet in some embodiments of this application;

[0031] Figure 5 This is a TEM image of the double-layer coated lithium cobalt oxide particles prepared in Example 1 of this application;

[0032] Figure 6 The images show SEM images of lithium cobalt oxide used in Example 1 of this application before and after double-layer coating.

[0033] Figure 7 XPS test data after the first coating layer is applied and after sintering, provided for embodiments of this application;

[0034] Figure 8 This is a schematic diagram of the capacity retention rate of lithium cobalt oxide double-layer coating before and after cycling at 25°C and 1C in Example 1 of this application;

[0035] Figure 9 This is a comparison diagram of the polarization voltage of the batteries corresponding to Embodiment 1 and Comparative Example 1 during cycling.

[0036] Figure 10 This is a schematic diagram showing the storage capacity retention rate of lithium cobalt oxide before and after double-layer coating in Example 1 of this application at 60°C, 100% SOC, and 0.33C.

[0037] Figure 11This is a comparison chart of the amount of Co deposited on the anode after the battery stores EOL in Examples 1, 2 and Comparative Example 1 of this application.

[0038] The reference numerals in the detailed embodiments are as follows:

[0039] 1000 - Vehicles;

[0040] 100 - Battery; 200 - Controller; 300 - Motor;

[0041] 10-Box body; 11-First part; 12-Second part;

[0042] 20-Battery cell; 21-Casing; 22-Electrode assembly; 23-Electrode terminal; 24-Pressure relief structure;

[0043] 211-Shell; 212-Cover;

[0044] 221-Positive electrode sheet; 2211-Positive current collector; 2212-Positive electrode tab; 2213-Positive active material layer. Detailed Implementation

[0045] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0047] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0048] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0049] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0050] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0051] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0052] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0053] In this application, the high-temperature storage performance under full charge refers to the storage performance of the battery at a high temperature of 60°C under full charge conditions, where SOC = 100% indicates that the battery is in a fully charged state, and SOC is the state of charge, i.e. the remaining power.

[0054] Currently, judging from market trends, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of power battery applications, market demand is also constantly increasing.

[0055] Layered transition metal oxides (LTMOs) possess very high volumetric energy density, which further increases with increasing charging cutoff voltage, giving them a dominant position in the 3C market. However, existing LTMOs suffer from poor high-temperature storage performance under full charge conditions. One of the main reasons for this problem is that under high temperature and high voltage, the electrolyte spontaneously generates HF (hydrofluoric acid), which corrodes the cathode material, leading to capacity decay and decreased storage performance.

[0056] To address the issue that batteries containing layered transition metal oxides, while achieving good energy density, cannot simultaneously achieve good cycle performance and good high-temperature storage performance under full charge, this application provides a positive electrode active material comprising a layered transition metal oxide, a first coating layer covering the surface of the layered transition metal oxide, and a second coating layer covering the surface of the first coating layer; wherein the first coating layer includes M x O y M includes Mg, Al and at least one of Group III to VIB transition metals, 0 < x, 0 < y, the second coating layer includes a positive metal phosphate salt; the total thickness of the first coating layer and the second coating layer is H, H ≤ 3 nm.

[0057] In the aforementioned positive electrode active material, a first coating layer is used to coat the layered transition metal oxide to mitigate the dissolution and oxygen release of the transition metal under high voltage. A second coating layer is disposed on the outer layer to protect the first coating layer from electrolyte erosion and damage. Furthermore, the lithium-ion transport channel property of the phosphate metal salt is utilized to act as a fast ion conductor, thereby improving the kinetic performance of the positive electrode active material. The total thickness of the first and second coating layers is H≤3nm, mitigating the impact of the coating layer on the conductivity and ion conduction properties of the layered transition metal oxide. The combined effect of these features allows batteries containing the aforementioned positive electrode active material to effectively improve cycle performance and high-temperature storage performance under full charge conditions while maintaining good energy density.

[0058] The batteries disclosed in this application can be used, but are not limited to, in electrical devices such as vehicles, ships, or aircraft. A power system comprising such an electrical device can be used, incorporating batteries disclosed in this application, which helps to mitigate and improve the battery's initial coulombic efficiency and battery life.

[0059] This application provides an electrical device that uses a battery as a power source. The electrical device can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0060] For ease of explanation, the following embodiments will be described using a vehicle 1000 as an example of an electrical device according to an embodiment of this application.

[0061] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of a vehicle 1000 provided in some embodiments of this application. The vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A battery 100 is disposed inside the vehicle 1000, and the battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The battery 100 can be used to power the vehicle 1000; for example, the battery 100 can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300, for example, to meet the power needs of the vehicle 1000 during startup, navigation, and driving.

[0062] In some embodiments of this application, the battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0063] In this application, battery 100 refers to a single physical module including one or more battery cells 20 to provide a certain voltage and capacity. It can be in the form of battery pack, battery module, etc. Battery 100 may also include a housing 10 for encapsulating one or more battery cells 20. The housing 10 can prevent liquids or other foreign objects from affecting the charging or discharging of the battery cells 20.

[0064] Please refer to Figure 2 , Figure 2This is an exploded view of a battery 100 provided in some embodiments of this application. The battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 provides a space for the battery cell 20 and can have various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, jointly defining a space for accommodating the battery cell 20. The second portion 12 may be a hollow structure with one open end, and the first portion 11 may be a plate-like structure, covering the open side of the second portion 12 so that the first portion 11 and the second portion 12 jointly define the space; alternatively, the first portion 11 and the second portion 12 may both be hollow structures with one open side, with the open side of the first portion 11 covering the open side of the second portion 12. Of course, the housing 10 formed by the first portion 11 and the second portion 12 can have various shapes, such as a cylinder, a cuboid, etc.

[0065] In battery 100, there can be multiple battery cells 20, which can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple battery cells 20 is housed within the housing 10. Alternatively, battery 100 can also be composed of multiple battery cells 20 first connected in series, parallel, or in a mixed manner to form a battery module, and then multiple battery modules are connected in series, parallel, or in a mixed manner to form a whole, which is also housed within the housing 10. Battery 100 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple battery cells 20.

[0066] Battery cell 20 refers to the smallest unit that makes up battery 100. Battery cell 20 can be a lithium-ion battery, lithium-sulfur battery, sodium-ion battery, or magnesium-ion battery, but is not limited to these.

[0067] Please refer to Figure 3 , Figure 3 This is an exploded structural diagram of a battery cell 20 provided in some embodiments of this application. See also... Figure 3 The battery cell 20 may include a housing 21, an electrode assembly 22 and an electrolyte, with the electrode assembly 22 and the electrolyte both housed within the housing 21.

[0068] The outer casing 21 may include a housing 211 and a cover 212. The housing 211 is an assembly that fits with the cover 212 to form an internal sealed space for the battery cell 20, wherein the formed sealed space can accommodate the electrode assembly 22, electrolyte, and other components. The cover 212 is a component that covers the opening of the housing 211 to isolate the internal environment of the battery cell 20 from the external environment. The shape of the cover 212 may be adapted to the shape of the housing 211 to fit the housing 211, and the cover 212 may also be provided with functional components such as electrode terminals 23 and pressure relief structures 24. A sealing ring may be provided between the opening of the housing 211 and the cover 212 to achieve a seal between the housing 211 and the cover 212.

[0069] The housing 211 and cover 212 can be of various shapes and sizes, such as cuboids, cylinders, and hexagonal prisms. Specifically, the shapes of the housing 211 and cover 212 can be determined according to the specific shape and size of the electrode assembly 22. The materials of the housing 211 and cover 212 can be various, such as, but not limited to, metals like copper, iron, aluminum, stainless steel, and aluminum alloys. The materials of the sealing ring can be various, such as, but not limited to, materials resistant to electrolyte corrosion, high toughness, and fatigue resistance, such as PP (polypropylene), PC (polycarbonate), and PET (polyethylene terephthalate). A plating layer can be formed on the outer surface of the housing 211, and the plating layer material can be various, such as, but not limited to, corrosion-resistant materials like Ni and Cr.

[0070] The battery cell 20 can also be in a pouch form, such as a bag-type pouch. The material of the pouch can be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0071] The electrode assembly 22 includes a negative electrode, a separator, and a positive electrode. The battery cell 20 primarily functions by the movement of metal ions between the positive and negative electrodes. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through. The electrode assembly 22 can be a wound structure or a stacked structure; this embodiment is not limited to either.

[0072] The negative electrode sheet includes a negative current collector, a negative electrode tab, and a negative active material layer. The negative active material layer is disposed on at least one side of the negative current collector, and a base coating layer may also be disposed between the negative current collector and the negative active material layer. The negative electrode tab protrudes from the negative current collector and is located, for example, at one end of the negative current collector or at opposite ends.

[0073] The negative electrode current collector can be a metal foil or a composite current collector. For example, the materials of the negative electrode current collector and the negative electrode tab can be copper. The composite current collector can include a polymer material substrate and a metal layer formed on at least one side of the polymer material substrate. The composite current collector can 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.).

[0074] The negative electrode active material layer includes negative electrode active materials, which can be carbon, silicon, or other negative electrode active material materials. As an example, the negative electrode active material material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials may also be used.

[0075] According to some embodiments of this application, the negative electrode active material layer may optionally include 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).

[0076] According to some embodiments of this application, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0077] According to some embodiments of this application, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0078] The separator is located between the positive electrode and the negative electrode, and plays a role in isolation. The embodiments of this application do not have any particular restrictions on the type of separator, and any well-known porous structure separator with good chemical and mechanical stability can be selected.

[0079] According to some embodiments of this application, 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.

[0080] like Figure 4 As shown, the positive electrode 221 includes a positive current collector 2211, a positive electrode tab 2212, and a positive active material layer 2213. The positive active material layer 2213 is disposed on at least one side of the positive current collector 2211. An undercoating layer or the like may also be disposed between the positive active material layer 2213 and the positive current collector 2211. The positive electrode tab 2212 protrudes from the positive current collector 2211 and is located, for example, at one end or at opposite ends of the positive current collector 2211.

[0081] The positive current collector 2211 can be a metal foil or a composite current collector. For example, the materials of the positive current collector 2211 and the positive electrode tab 2212 can be aluminum. The composite current collector may include a polymer material substrate and a metal layer formed on at least one side of the polymer material substrate. The composite current collector can 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.).

[0082] The positive electrode active material layer 2213 includes a positive electrode active material, and optionally a binder, optionally a conductive agent, and optionally an additive.

[0083] As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. As an example, the additive may include, for example, dispersants, etc.

[0084] The following describes in detail, with reference to the accompanying drawings, the positive electrode active material and its preparation method proposed in the embodiments of this application.

[0085] According to some embodiments of the present application, the present application provides a positive electrode active material, which includes: a layered transition metal oxide, a first coating layer coated on the surface of the layered transition metal oxide, and a second coating layer coated on the surface of the first coating layer; wherein, the first coating layer includes MxOy, M includes at least one of Mg, Al, and transition metals in Groups III to VIB, 0 < x, 0 < y, the second coating layer includes a normal metal phosphate; the total thickness of the first coating layer and the second coating layer is H, and H ≤ 3 nm.

[0086] The layered transition metal oxide refers to a transition metal oxide with a layered rock salt-type crystal structure and carriers. The carriers refer to metal ions that can move between the positive and negative electrodes of the battery, including alkali metal ions or alkaline earth metal ions. Specifically, the carriers include lithium ions, sodium ions, or magnesium ions, etc.

[0087] When the carrier is a lithium ion, the layered transition metal oxide refers to a lithium-containing material with a layered rock salt-type crystal structure. Exemplarily, it includes but is not limited to (1) LiNi x Co 1-x O2 (0 < x < 1), specifically, for example, LiCoO2, LiNiO2, LiMnO2, Li2MnO3, LiNi 0.8 Co 0.2 O2, etc.; (2) LiNi x Mn y Co 1-x-y O2 (x > 0, y > 0, x + y < 1), specifically, for example, LiNi<{ 1 / 3 Mn 1 / 3 Co 1 / 3 O2, etc.; (3) LiNi z Co x Al y O2, where 0.1 < x < 0.3, 0.01 < y < 0.15, 0 < z < 1, for example, Li(Ni 0.8 Co<{ 0.15 Al 0.05 )O2; (4) Li2MnO3 - LiAO2, where A is at least one of Co, Ni, Mn, etc., and those skilled in the art can select according to actual needs.

[0088] When the carrier is a sodium ion, the layered transition metal oxide refers to a sodium-containing material with a layered rock salt-type crystal structure, which includes but is not limited to NaFeO2 or Na 2 / 3 [Fe 1 / 2 Mn 1 / 2 O2, etc.

[0089] Group III to VIB transition metals include Sc, Ti, V, Cr, Y, Zr, Nb, Mo, La, Hf, Ta, and W. It is understood that M including Mg, Al, and at least one of Group III to VIB transition metals means that M includes at least one of Mg, Al, Sc, Ti, V, Cr, Y, Zr, Nb, Mo, La, Hf, Ta, and W.

[0090] Phosphate metal salts refer to phosphate salts with metal cations. Phosphate metal salts are also known as orthophosphates. They are salts formed when the three hydrogen atoms of phosphoric acid that can be ionized are replaced by metal ions. Phosphate metal salts are stable, not easily decomposed by heat, and are not decomposed by hydrofluoric acid. Therefore, as an outer layer, they are beneficial to improving the stability of the positive electrode active material and to improving the cycle performance and high-temperature storage performance of the battery under full charge.

[0091] Besides the selection of materials for the first and second coating layers affecting the performance of the final positive electrode active material, the total thickness of the first and second coating layers has a significant impact on its performance. If the total thickness is too thick, it will affect the transport of charge carriers, thereby significantly reducing the energy density and first coulombic efficiency of the battery. Therefore, the total thickness H of the first and second coating layers should be ≤3nm. For example, the total thickness H of the first and second coating layers can be any value of 0.5nm, 1nm, 2nm, 2.5nm, or 3nm, or between any two values.

[0092] In the aforementioned positive electrode active material, a first coating layer is used to coat the layered transition metal oxide to mitigate the dissolution of the transition metal under high voltage. A second coating layer is disposed on the outer layer to protect the first coating layer from electrolyte erosion and damage. Furthermore, the lithium-ion transport channel property of the phosphate metal salt is utilized to act as a fast ion conductor, thereby improving the kinetic performance of the positive electrode active material. The total thickness of the first and second coating layers is H≤3nm, mitigating the impact of the coating layer on the conductivity and ion conduction properties of the layered transition metal oxide. The combined effect of these features allows batteries containing the aforementioned positive electrode active material to effectively improve cycle performance and high-temperature storage performance under full charge conditions while maintaining good energy density.

[0093] It should be noted that during the charging and discharging process of a battery, there is intercalation and deintercalation of charge carriers, resulting in different molar contents of charge carriers at different discharge states. In the examples of cathode materials listed in this application, the molar contents of charge carriers refer to the initial state of the material, i.e., the state before material addition. When the cathode material is applied to the battery system, the molar contents of charge carriers will change after charge-discharge cycles. In the examples of cathode materials listed in this application, the molar contents of oxygen are only theoretical values. Lattice oxygen release will cause changes in the molar contents of oxygen, and the actual molar contents of oxygen will fluctuate.

[0094] According to some embodiments of this application, 1nm < H ≤ 3nm.

[0095] Within the aforementioned range, the preparation difficulty is low, and batteries containing the above-mentioned positive electrode active materials have good energy density, while also having good cycle performance and good high-temperature storage performance in a fully charged state.

[0096] For example, H can be 1.1nm, 1.3nm, 1.5nm, 1.7nm, 2nm, 2.3nm, 2.5nm, 2.7nm, or 3nm, etc.

[0097] Optionally, 1nm < H ≤ 2nm.

[0098] Within the aforementioned range, it is beneficial to alleviate the energy density loss of batteries containing the aforementioned positive electrode active material, and can effectively improve the cycle performance and high-temperature storage performance of batteries using this positive electrode active material under full charge.

[0099] For example, H can be 1.1nm, 1.3nm, 1.5nm, 1.7nm, or 2nm, etc.

[0100] According to some embodiments of this application, the thickness of the second coating layer is h, where 0.7nm ≤ h ≤ 2nm.

[0101] Since the second coating layer is located on the outside and serves to protect the first coating layer, excessive thickness can affect ion diffusion and electron conduction, while insufficient thickness may result in incomplete coating, leading to erosion and damage of the positive electrode active material by the electrolyte. Therefore, limiting the thickness of the second coating layer to 0.7 nm ≤ h ≤ 2 nm is beneficial for improving the stability and kinetic performance of the positive electrode active material. This allows batteries containing this positive electrode active material to effectively improve cycle performance and high-temperature storage performance under full charge conditions while maintaining good energy density.

[0102] For example, h is any value of 0.7m, 0.8m, 0.9m, 1.0nm, 1.1nm, 1.2nm, 1.3nm, 1.4nm, 1.5nm, 1.6nm, 1.7nm, 1.8nm, 1.9nm or 2.0nm or between any two values.

[0103] Optionally, 1nm≤h≤1 / 2H.

[0104] The thickness of the second coating layer is within the above range, which is beneficial to improving the cycle performance and high-temperature storage performance of the battery using the positive electrode active material.

[0105] In this application, H and h both refer to the average thickness. During the coating and testing process, systematic errors are inevitable, so the thickness varies slightly at different locations. Therefore, when testing the thickness of the coating layer, n points are randomly selected, for example, 10 points, and the average thickness of these points is calculated. If the error between the thickness of each point and the average thickness does not exceed 5%, the coating can be considered complete and uniform.

[0106] In some embodiments, the layered transition metal oxide and the first coating layer may have a defined interface, that is, the first coating layer does not dop the surface of the layered transition metal oxide.

[0107] In other embodiments, the surface of the layered transition metal oxide may be doped with a first coating layer, for example, the surface of the layered transition metal oxide may be doped with the metal element M in the first coating layer.

[0108] It is understandable that the doping of the metal element M in the first coating layer on the surface of the layered transition metal oxide means that the doped metal element M is located on the surface of the layered transition metal oxide, rather than the entire layered transition metal oxide being doped with the metal element M.

[0109] Since the surface of the layered transition metal oxide is doped with metal element M, the transition metal originally contained in the layered transition metal oxide is different from metal element M. In other words, if metal element M is only one element, then the layered transition metal oxide does not contain that element. If metal element M is only a combination of two or more elements, then the layered transition metal oxide does not contain at least one element in that combination.

[0110] By doping with metal element M, a transition is formed between the layered transition metal oxide and the first coating layer. On the other hand, doping helps to enhance the bond breaking energy barrier between the transition metal and oxygen originally contained in the layered transition metal oxide, suppresses the dissolution and oxygen release reaction of the transition metal originally contained in the layered transition metal oxide, and helps to improve the cycle performance and high-temperature storage performance of the battery using this positive electrode active material.

[0111] According to some embodiments of this application, M includes at least one of Mg, Al, Ti, Zr, Nb, Ta, and W.

[0112] That is, the first coating layer includes at least one of magnesium oxide, aluminum oxide, titanium oxide, zirconium oxide, niobium oxide, tantalum oxide and tungsten oxide. The selection of the above metal oxides has a good doping effect, which helps to prevent the dissolution and oxygen release of the transition metal oxides in the layered transition metal oxides and improve the performance of the positive electrode active material.

[0113] According to some embodiments of this application, the positive metal phosphate salt includes at least one of lithium phosphate, sodium phosphate, potassium phosphate, calcium phosphate, and aluminum phosphate.

[0114] The aforementioned phosphate metal salts are stable and not easily decomposed. They can exist stably under high temperature, high pressure and hydrofluoric acid environments, which is beneficial to improving the cycle performance and high temperature storage performance of batteries using this positive electrode active material.

[0115] According to some embodiments of this application, the volumetric particle size distribution Dv50 of the positive electrode active material is 5-25 μm.

[0116] Volumetric particle size distribution Dv50 refers to the particle size distribution parameter determined by particle size distribution measurement. For example, volumetric particle size distribution Dv50 is determined by particle size analyzer-laser diffraction method. Specifically, you can refer to standard GB / T 19077-2016, which uses a laser diffraction scattering particle size analyzer for measurement.

[0117] Within the above range, it is beneficial for the battery to have better cycle performance.

[0118] According to some embodiments of this application, this application also provides a method for preparing the above-mentioned positive electrode active material, which includes: depositing a first coating layer on the surface of a layered transition metal oxide by vapor deposition to obtain an intermediate product; and depositing a second coating layer on the surface of the intermediate product by vapor deposition.

[0119] The preparation method provided in this application is beneficial to achieving a first coating layer and a second coating layer with high coating integrity, strong bonding force, relatively uniform thickness and thinness, which is beneficial to improving the cycle performance and high-temperature storage performance of batteries using this positive electrode active material.

[0120] Specifically, vapor deposition methods include atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), and thermal evaporation deposition.

[0121] According to some embodiments of this application, the vapor deposition method is atomic layer deposition, which is a high-precision thin film deposition technology based on chemical vapor deposition. It is a technology that deposits material as a single-atom film on the surface of a substrate layer by layer based on chemical vapor deposition. Therefore, the film thickness can be precisely controlled by controlling the number of deposition cycles.

[0122] It should be noted that this application does not limit the specific operation method of vapor deposition, as long as it can achieve the formation of a first coating layer and a second coating layer with high coating integrity and relatively uniform thickness. For specific operation, please refer to relevant technologies.

[0123] According to some embodiments of this application, the preparation method further includes annealing the intermediate product before depositing a second coating layer on the surface of the intermediate product, wherein the annealing temperature is not lower than 600°C.

[0124] Annealing the intermediate product at a temperature of not less than 600°C before depositing the second coating layer on the surface of the intermediate product enables the metal element M in the MxOy of the first coating layer to dope the surface of the layered transition metal oxide, which is beneficial to improving the cycle performance and high-temperature storage performance of the battery using the positive electrode active material.

[0125] If the annealing temperature is too high, the dispersion of dopant elements will affect the doping effect. Therefore, the annealing temperature can be set to 600-800℃.

[0126] Within the aforementioned range, the doping is relatively uniform, which is beneficial to improving the structural stability of the positive electrode active material and to improving the cycle performance and high-temperature storage performance of the battery using the positive electrode active material.

[0127] For example, the annealing temperature is any value of 600°C, 630°C, 650°C, 680°C, 700°C, 725°C, 750°C, 775°C, or 800°C, or between any two values.

[0128] Optionally, the annealing temperature is 650-800℃.

[0129] Alternatively, the annealing time is 3-5 hours.

[0130] Annealing time affects doping depth. Therefore, within the above-mentioned annealing time range, the doping depth is appropriate, which is beneficial to improving the high-temperature storage performance of the battery under full charge.

[0131] For example, the annealing time is any value of 3h, 3.5h, 4h, 4.5h, 5h or between any two values.

[0132] According to some embodiments of this application, the preparation method further includes: depositing a second coating layer on the surface of the intermediate product and then sintering it at 400-550°C for 3-5 hours.

[0133] The above-mentioned low-temperature sintering method can, on the one hand, suppress the internal doping of phosphate positive metal salts and enhance the bonding force between layered transition metal oxides, the first coating layer and the second coating layer, thereby improving the structural stability of the positive electrode active material. This is beneficial for suppressing the shedding of the first and / or second coating layers when it is used in the fabrication of positive electrode sheets. On the other hand, it can effectively remove impurities such as carbon introduced into the first and / or second coating layers during the preparation process, thereby improving the purity of the positive electrode active material.

[0134] For example, the sintering temperature is any value of 400℃, 430℃, 450℃, 470℃, 500℃, 530℃, 550℃ or between any two values, and the sintering time is any value of 3h, 3.5h, 4h, 4.5h, 5h or between any two values.

[0135] Optionally, the sintering temperature is 400-500℃.

[0136] According to some embodiments of this application, this application provides a positive electrode sheet, which includes the positive electrode material provided in the above embodiments.

[0137] According to some embodiments of this application, the positive electrode sheet includes a positive active material layer, which includes a positive active material and a conductive agent. The conductive agent includes Super P and CNT, wherein the mass percentage of Super P in the positive active material layer is greater than the mass percentage of CNT in the positive active material layer.

[0138] The synergy between Super P and CNT helps to mitigate the deterioration of storage performance caused by the oxidation and decomposition of dispersants in CNTs under high voltage while maintaining high conductivity, and also helps to improve the high-temperature storage performance of the battery under full charge.

[0139] In some alternative implementations, the mass percentage of Super P in the positive electrode active material layer is at least twice the mass percentage of CNT in the positive electrode active material layer.

[0140] By limiting the mass percentage between the two, it is beneficial to improve the high-temperature storage performance of the battery when it is fully charged.

[0141] In some alternative embodiments, the conductive agent has a mass percentage of 0.9%-2% in the positive electrode active material layer, and the CNTs have a mass percentage of less than or equal to 0.5% in the positive electrode active material layer.

[0142] Within the above settings range, it is beneficial to improve the high-temperature storage performance of the battery when it is fully charged.

[0143] For example, the mass percentage of the conductive agent in the positive electrode active material layer is 0.9%, 1%, 1.3%, 1.5%, 1.7%, or 2%, etc.

[0144] It is understood that the content of other components in the positive electrode active material can be referenced with relevant technologies. For example, by mass percentage, the positive electrode active material includes 96.3-98.2% positive electrode active material, 0.9-2% conductive agent, 0.9-1.5% binder, and 0-0.2% additives.

[0145] According to some embodiments of this application, this application also provides a battery that includes the positive electrode sheet of the above embodiments.

[0146] According to some embodiments of this application, this application also provides an electrical device including a battery from any of the above-described solutions.

[0147] Batteries are used to provide electrical energy to electrical devices, which can be any of the aforementioned devices or systems that use batteries.

[0148] The following specific embodiments are provided to better illustrate this application.

[0149] Example 1

[0150] A positive electrode active material, the preparation method of which includes:

[0151] S1, First coating layer (composed of aluminum oxide): Undoped and uncoated lithium cobalt oxide powder is added to the heating chamber of the ALD device as a substrate. Trimethylaluminum and water vapor are introduced at 125°C. The substrate is stirred to achieve complete and uniform coating. The coating thickness is controlled to be 0.28 nm after 1 hour of ALD. The coating thickness is controlled by the reaction time to obtain the first coating layer.

[0152] S2. Anneal the product of S1 at 700℃ for 5 hours.

[0153] S3, Second coating layer (composed of aluminum phosphate): In the heating chamber of the ALD equipment, trimethyl phosphate, ozone and trimethyl aluminum are sequentially introduced onto its surface at 230°C. Complete and uniform coating is achieved through thorough stirring. The coating thickness is controlled to be 0.3 nm after 1 hour of ALD. The coating thickness is controlled by the reaction time to obtain the second coating layer.

[0154] S4. Anneal the double-layer coating of S3 at 400℃ for 5 hours to obtain the final positive electrode active material, denoted as double-layer coated lithium cobalt oxide.

[0155] The bilayer coated lithium cobalt oxide prepared in Example 1 was tested in the following ways, and the specific test methods and results are as follows:

[0156] (1) Figure 5 This is a TEM image of the double-layer coated lithium cobalt oxide particles prepared in Example 1. Figure 5 It can be seen that the total thickness H of the first coating layer and the second coating layer (hereinafter referred to as the coating layer) is 2nm. The thinner coating layer has less impact on the lithium ion insertion / extraction and charge transfer on the particle surface, achieving a very complete and uniform coating. It can comprehensively improve the cycling and high-temperature storage performance of double-coated lithium cobalt oxide in full charge state.

[0157] The morphology of the samples was observed using a LEEQ0000D3 scanning electron microscope and then tested in accordance with the standard JY / T010-1996.

[0158] Figure 6 The images shown are SEM images of the lithium cobalt oxide used in Example 1 before and after double-layer coating. Figure 6 Part a represents the area before encapsulation, and part b represents the area after encapsulation. The basis for this is... Figure 6 It can be seen that the morphology of the material before and after double coating is basically the same, that is, the coating method of ALD has basically no impact on the surface morphology of the material.

[0159] (2) The AES (Auger spectroscopy) data of the positive electrode active material (double-layer coated lithium cobalt oxide) were determined by Auger spectroscopy, and the AES data are shown in Table 1.

[0160] Table 1 AES Data

[0161]

[0162]

[0163] As shown in Table 1, Al / P element signals were detected on the sample surface. The Co signal content of the double-layer coated lithium cobalt oxide was very low, indicating that the surface of the lithium cobalt oxide particles was completely coated by AlPO4. The C element content was high, mainly from the adsorbed carbon on the particle surface.

[0164] (3) Referring to standard GB / T 19077-2016, the volumetric particle size distribution of lithium cobalt oxide before and after double-layer coating was measured using a laser diffraction scattering particle size analyzer. The specific surface area (BET) was measured using an ASAP 2460 high-performance specific surface area and pore size analyzer. The compaction density of the lithium cobalt oxide powder before and after double-layer coating under a pressure of 6 tons was also measured. The results are shown in Table 2. In Table 2, PD@6t / g / cm³ 3 It refers to the compaction density of the lithium cobalt oxide powder before and after double coating under a pressure of 6 tons.

[0165] Table 2 Physicochemical parameters of lithium cobalt oxide before and after double-layer coating

[0166]

[0167] As shown in Table 2, the Dv50 of double-coated lithium cobalt oxide particles is slightly lower than that of uncoated lithium cobalt oxide, indicating that the coating layer is thin enough and does not increase the particle size. Moreover, the coating process is beneficial to particle dispersion, thus causing a slight decrease in Dv50. The BET value is slightly lower after coating, indicating that the coating layer is sufficiently dense, rather than loose and porous.

[0168] (4) The Al and P content in bilayer coated lithium cobalt oxide was determined by inductively coupled plasma (ICP) emission spectroscopy. The specific steps were as follows: Bilayer coated lithium cobalt oxide was taken as a sample and digested with aqua regia and hydrofluoric acid (HF). The Al and P content of the digested solution was then tested. The results are shown in Table 3.

[0169] Table 3 ICP test data for double-layer coated lithium cobalt oxide

[0170] element Al P Al:P (mol) Content (ppm) 632 567 1.28

[0171] As can be seen from Table 3, the contents of P and Al in the double-layer coated lithium cobalt oxide are approximately 500–600 ppm, indicating that the coating layer is thin enough and accounts for a very small mass proportion in the double-layer coated lithium cobalt oxide.

[0172] (5) The surface of the positive electrode active material after the first coating layer was applied and after sintering was tested using a multifunctional X-ray photoelectron spectroscopy instrument (XPS, instrument model: Shimadzu Axis Supra+). The XPS test data after the first coating layer was applied and after sintering are as follows: Figure 7 As shown, where Figure 7 Part a in the middle is the XPS signal image of Al2O3 coated Al. Figure 7 Part b in the image shows the XPS signal of O after Al2O3 coating. Figure 7 Part c in the middle is the XPS signal diagram of Al after AlPO4 coating and sintering. Figure 7 Part b in the middle is the XPS signal diagram of O after AlPO4 coating and sintering.

[0173] according to Figure 7 As can be seen from parts a and b, the XPS signal of Al is enhanced after Al2O3 coating, and the signal peak of oxygen at 529.6 eV is enhanced, indicating that the coating layer exists in the form of Al-O bonds; according to Figure 7 As can be seen from parts c and d, the XPS peak of AlPO4 coated with Al shifts towards the direction of higher binding energy, and the signal is further enhanced after sintering, indicating that sintering can enhance the bonding ability between the coating layers.

[0174] Examples 2-10 and Comparative Examples 1-3

[0175] The differences between each embodiment and the comparative example and embodiment 1 are shown in Table 4.

[0176] Preparation of the positive electrode sheet

[0177] The positive electrode active materials provided in each embodiment and comparative example were mixed with 98 wt% positive electrode active material, 0.6 wt% conductive carbon black (Super P), 0.5 wt% carbon nanotubes (CNT), and 0.9 wt% polyvinylidene fluoride (PVDF), and then N-methylpyrrolidone was added and stirred to disperse, thus preparing a positive electrode slurry.

[0178] After the prepared positive electrode slurry was stirred, the viscosity was adjusted to 8000 mPa·s, and the slurry coating weight was 0.3 mg / 1540.25 cm². 2 After single-sided coating is completed, the electrode is dried, cold-pressed, slit, and prepared to obtain the positive electrode sheet.

[0179] Preparation of the negative electrode sheet

[0180] 96.5 wt% graphite, 1 wt% conductive carbon black (Super P), 1 wt% binder (polybutadiene styrene rubber), and 1.5 wt% additive (sodium carboxymethyl cellulose) were mixed, and deionized water was added and stirred to disperse and prepare a negative electrode slurry. The negative electrode slurry was then coated onto a Cu foil. After coating both sides, the foil was dried, cold-pressed, slit, and sheeted to prepare the negative electrode sheet.

[0181]

Isolation Film

[0182] PE (polyethylene) separator film, 12um thick.

[0183] Electrolyte

[0184] A 1 mol / L LiPF6 EC / DMC / DEC solution (EC / DMC / DEC volume ratio 1:1:1).

[0185] [Battery Manufacturing]

[0186] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the anode and cathode, and then wound to obtain a bare battery. The bare battery is placed in an aluminum-plastic bag, filled with prepared electrolyte, and then sealed, injected, and formed to obtain a single-layer stacked lithium-ion battery.

[0187] [First Round Coulomb Efficiency and Capacity Test]

[0188] 1. Allow the battery to stand still for 5 hours at 25℃; 2. Charge the battery with a constant current of 0.33C to 4.48V; 3. Charge the battery with a constant voltage of 4.48V until the current is ≤0.05C to obtain the initial charge capacity; 4. Allow the battery to stand still for 5 minutes at 25℃; 5. Discharge the battery with a constant current of 0.33C to 2.5V to obtain the initial discharge capacity; 6. Allow the battery to stand still for 30 minutes at 25℃.

[0189] In the above steps, the first discharge capacity measured in step 5 is the first discharge capacity of the material; the ratio of the first discharge capacity in step 5 to the first charge capacity in step 3 is the first coulombic efficiency.

[0190] The results are shown in Table 4.

[0191]

Cyclic Performance Test

[0192] 1. Let the battery stand at 25℃ for 5 hours; 2. Charge at a constant current of 0.33C to 4.48V; 3. Charge at a constant voltage of 4.48V until the current is ≤0.05C; 4. Let stand at 25℃ for 5 minutes; 5. Discharge at a constant current of 0.33C to 2.5V; 6. The capacity measured in step 5 is C0; 7. Charge at a constant current of 1C0 to 4.48V; 8. Charge at a constant voltage of 4.48V until the current is ≤0.05C0; 9. Discharge at a constant current of 1C0 to 2.5V; 10. Repeat steps 7-9 to achieve multiple cycles, with an additional 0.05C0 discharge to 2.5V every 50 cycles; 11. Let stand at 25℃ for 5 minutes.

[0193] The results are shown in Table 4 and Figure 8 As shown.

[0194] Figure 8 This diagram illustrates the capacity retention of the positive electrode active material (i.e., before and after lithium cobalt oxide coating) in Example 1 and Comparative Example 1 at 25°C and 1C cycling conditions. Figure 8 Comparative Example 1 is used as an example before coating, and Example 1 is used as an example after coating. According to Figure 8 It can be seen that the cycling performance of lithium cobalt oxide is significantly improved after ALD double-layer coating.

[0195] Figure 9 This is a comparison graph showing the polarization voltage of the batteries corresponding to Example 1 and Comparative Example 1 during cycling. Figure 9 Comparative Example 1 is used as an example before coating, and Example 1 is used as an example after coating. According to Figure 9 It can be seen that after ALD coating, the polarization voltage decreases and remains stable during battery cycling, indicating that the coating layer is beneficial to improving the charge-discharge kinetics performance of the material.

[0196] Storage Performance Test

[0197] 1. Let the battery stand at 25℃ for 5 hours; 2. Charge at a constant current of 0.33C to 4.48V; 3. Charge at a constant voltage of 4.48V until the current ≤0.05C; 4. Let the battery stand at 25℃ for 5 minutes; 5. Discharge at a constant current of 0.33C to 2.5V; 6. The capacity measured in step 5 is C0; 7. Charge at a constant current of 0.33C0 to 4.48V; 8. Charge at a constant voltage of 4.48V until the current ≤0.05C0 to achieve a full charge; 9. Store the battery in a 60℃ constant temperature chamber for 72 hours. 10. After storage, test the capacity of the battery at 25℃ after it is removed from the oven; 11. Discharge to 2.5V with a constant current of 0.33C0; 12. Discharge to 2.5V with a constant current of 0.05C0; 13. Let it stand for 5 minutes at 25℃; 14. Charge to 4.48V with a constant current of 0.33C0; 15. Let it stand for 5 minutes at 25℃; 16. Charge at 4.48V with a constant voltage until the current ≤0.05C0 to achieve full charge of the battery; 17. Repeat steps 9-16 to obtain the battery storage EOL time (EOL, End of Line, the end of battery life). The storage EOL time is defined as the time when the discharge capacity is 70% of the initial capacity. Each sample is tested with three parallel samples.

[0198] The results are shown in Table 4 and Figure 10 As shown.

[0199] Figure 10 This diagram illustrates the storage capacity retention of lithium cobalt oxide before and after double-layer coating at 60°C, 100% SOC, and 0.33°C. Figure 10 Comparative Example 1 is used as an example before coating, and Example 1 is used as an example after coating. According to Figure 10 It can be seen that the ALD double-layer coating significantly improves the storage capacity retention rate of the material at 60℃, 100% SOC, and 0.33C compared to Comparative Example 1, and the three parallel samples are basically completely overlapping, showing high consistency.

[0200] [Co Dissolution Test]

[0201] The batteries from Examples 1, 2, and Comparative Example 1 were disassembled after reaching the end of their battery life (EOL). The anode plates were cut into small, uniform-weight discs, with two discs cut from each anode plate. The mass percentage of Co on each disc was measured. After deducting the mass of the Cu foil current collector, the measured data represents the Co leaching amount. The results are as follows: Figure 11 As shown, Figure 11 Uncoated (numbers 1 and 2) correspond to Example 1, double-coated (numbers 3 and 4) correspond to Example 2, and coated + sintered (numbers 5 and 6) correspond to Example 1.

[0202] Figure 11 A comparison chart of Co deposition on EOL anodes in stacked storage, based on Figure 11It can be seen that the double-layer coating without sintering can reduce the amount of Co leaching during battery storage compared to the double-layer coating with sintering. In particular, the double-layer coating without sintering can reduce the amount of Co leaching during storage of stacked batteries by more than 30% compared to the uncoated method, indicating that double-layer coating has a significant effect on inhibiting Co leaching.

[0203] Table 4. Difference parameters and test results for each embodiment and comparative example.

[0204]

[0205]

[0206] As shown in Table 4, compared to the comparative example, the embodiments of this application significantly improve the battery's storage performance while maintaining a better initial discharge capacity. In other words, when the positive electrode active material prepared in the embodiments of this application is applied to a battery, the battery achieves both better energy density and better high-temperature storage performance under full charge.

[0207] As can be seen from Examples 1, 2-5 and Comparative Example 4, the selection of the composition of the first coating layer will affect the final storage EOL time. When the metal M in the first coating layer includes at least one of Mg, Al and group III to VIB transition metals, the battery has both better energy density and better high-temperature storage performance in a fully charged state.

[0208] As can be seen from Examples 1 and 6, the stability of Example 6 is reduced compared to Example 1 because no impurity removal sintering step is performed. Therefore, under the premise that the first-cycle discharge specific capacity and the first-cycle coulombic efficiency are comparable, the storage EOL time is reduced.

[0209] In Example 7, the first coating layer does not dope the surface of the layered transition metal oxide. In Example 1, the first coating layer is used to dope the surface of the layered transition metal oxide. According to Examples 1 and 7, using the first coating layer to dope the surface of the layered transition metal oxide does not significantly affect the first-cycle discharge specific capacity and the first-cycle coulombic efficiency, which is beneficial to significantly improve the storage EOL time.

[0210] As can be seen from Examples 1 and 8-11, when the total thickness of the coating layer H ≤ 3nm, the thickness of the second coating layer is 0.7-2nm, and even more specifically when 1nm ≤ h ≤ 1 / 2H, the battery has both better energy density and better high-temperature storage performance under full charge.

[0211] As can be seen from Examples 1 and 12, regardless of whether the layered transition metal oxide is lithium cobalt oxide or NCM811, it can be coated using the preparation method provided in this application. After the coated positive electrode active material is applied to the battery, the battery has both better energy density and better high-temperature storage performance under full charge.

[0212] As can be seen from Examples 1 and 13-16, the doping annealing temperature affects the storage EOL time. When the doping annealing temperature is 600-850℃, especially 600-800℃, the prepared positive electrode active material can be used in the battery, and the battery has both better energy density and better high-temperature storage performance in a fully charged state.

[0213] As can be seen from Examples 1 and 17-18, the temperature of impurity removal sintering affects the storage EOL time. The impurity removal sintering temperature is 400-550℃, especially at the impurity removal sintering temperature of 400-500℃. When the prepared positive electrode active material is applied to the battery, the battery has both better energy density and better high-temperature storage performance under full charge.

[0214] As can be seen from Examples 1, 6-7 and Comparative Example 1, as long as double-layer coating is performed, regardless of whether doping or depurification is performed, the storage EOL time is significantly improved while the first-cycle discharge specific capacity is comparable to that of Comparative Example 1.

[0215] As can be seen from Example 1 and Comparative Example 2, Comparative Example 2 only performed the first coating layer coating and did not perform the second coating layer coating. It can be seen that compared with Example 1, its storage EOL time is significantly reduced.

[0216] As can be seen from Example 1 and Comparative Example 3, the coating thickness of Comparative Example 3 is too thick, which leads to a significant decrease in its first discharge capacity and low application value. Therefore, no storage EOL time test was conducted on it.

[0217] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This 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 active material, characterized by, The positive electrode active material comprises: a layered transition metal oxide, a first coating layer coated on a surface of the layered transition metal oxide, and a second coating layer coated on a surface of the first coating layer; The first coating layer comprises M x O y The M comprises Mg, Al and at least one of group III to group VI B transition metals, 0 a total thickness of the first coating layer and the second coating layer is H, and H≤3nm.

2. The positive electrode active material according to claim 1, characterized by 1nm<H≤3nm.

3. The positive electrode active material according to claim 1, characterized by 1nm<H≤2nm.

4. The positive electrode active material according to claim 1, characterized by a thickness of the second coating layer is h, and 0.7nm≤h≤2nm.

5. The positive electrode active material according to claim 1, characterized by 1nm≤h≤1 / 2H.

6. The positive electrode active material according to any one of claims 1 to 5, characterized by a surface of the layered transition metal oxide is doped with a metal element M in the first coating layer.

7. The positive electrode active material according to any one of claims 1 to 5, characterized by The M comprises at least one of Mg, Al, Ti, Zr, Nb, Ta and W.

8. The positive electrode active material according to any one of claims 1 to 5, characterized by The positive metal phosphate comprises at least one of lithium phosphate, sodium phosphate, potassium phosphate, calcium phosphate and aluminum phosphate.

9. The method for producing a positive electrode active material according to Claim 1, wherein The preparation method comprises: depositing the first coating layer on a surface of the layered transition metal oxide by a vapor deposition method to obtain an intermediate product; depositing the second coating layer on a surface of the intermediate product by a vapor deposition method.

10. The preparation method according to claim 9, characterized in that, The vapor deposition method comprises an atomic layer deposition method.

11. The preparation method according to claim 9, characterized in that, The preparation method further comprises: annealing the intermediate product before depositing the second coating layer on a surface of the intermediate product, wherein a temperature of the annealing is not lower than 600℃.

12. The method of claim 11, wherein, The temperature of the annealing is 600-800℃.

13. The preparation method according to claim 11, characterized in that, The temperature of the annealing is 650-800℃.

14. The method of claim 11, wherein, The annealing time is 3-5h.

15. The method of any one of claims 9-14, wherein, The preparation method further comprises: sintering at 400-550℃ for 3-5h after depositing the second coating layer on a surface of the intermediate product.

16. The method of claim 15, wherein, The sintering temperature is 400-500℃.

17. A positive electrode sheet characterized by comprising: The positive electrode active material comprises:

18. The cathode electrode of claim 17, wherein, The positive electrode plate comprises a positive electrode active material layer, the positive electrode active material layer comprising the positive electrode active material and a conductive agent, the conductive agent comprising Super P and CNT; wherein a mass percentage of the Super P in the positive electrode active material layer is greater than a mass percentage of the CNT in the positive electrode active material layer.

19. The cathode electrode of claim 18, wherein, The mass percentage of the Super P in the positive electrode active material layer is at least 2 times greater than the mass percentage of the CNT in the positive electrode active material layer.

20. The cathode sheet of claim 18 or 19, wherein, The mass percentage of the conductive agent in the positive electrode active material layer is 0.9%-2%, and the mass percentage of the CNT in the positive electrode active material layer is less than or equal to 0.5%.

21. A battery, characterized by The positive electrode plate comprises:

22. An electrical device, comprising: The battery is used to provide electric energy.

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