Positive electrode active material and preparation method thereof, positive electrode plate, battery and electric device

Abstract

The invention provides a positive active material and a preparation method thereof, a positive pole piece, a battery and an electric device, and relates to the field of batteries. The positive electrode active material comprises a layered transition metal oxide, a first coating layer coating the surface of the layered transition metal oxide, and a second coating layer coating the surface of the first coating layer; wherein the first coating layer comprises MxOy, M comprises Mg, Al and at least one of transition metals from the group III to the group VIB, x is greater than 0 and y is greater than 0, and the second coating layer comprises positive metal phosphate; the total thickness of the first coating layer and the second coating layer is H, H is less than or equal to 3nm, and the battery containing the positive electrode active material has relatively good cycle performance and relatively good high-temperature storage performance in a full charge state on the premise of relatively good energy density.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular, to a positive electrode active material and a preparation method thereof, a positive electrode sheet, a battery and an electrical device. Background Art

[0002] With the development of new energy vehicles and energy storage, the market has higher and higher requirements for the energy density of power batteries. Layered transition metal oxides have very high volume energy density, which further increases with the increase of charging cut-off voltage, and they dominate the 3C market. However, the performance of batteries containing them decays quickly after being stored at a high temperature of 60°C under full charge, and they cannot be stored for a long time, and the cycle performance is poor. Summary of the invention

[0003] In view of the above problems, the present application proposes a positive electrode active material and a preparation method thereof, a positive electrode plate, a battery and an electrical device, which can enable a battery containing layered transition metal oxides to have a better energy density while effectively improving the problems of poor battery cycle performance and poor high-temperature storage performance in a fully charged state.

[0004] In a first aspect, the present invention 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 M x O y , M includes Mg, Al and at least one of the transition metals of Groups III to VIB, 0<x, 0<y, the second coating layer includes metal orthophosphate; the total thickness of the first coating layer and the second coating layer is H, H≤3nm.

[0005] In the technical solution of the embodiment of the present application, the first coating layer is used to coat the layered transition metal oxide to alleviate the dissolution of transition metals in the layered transition metal oxide under high voltage, the second coating layer is arranged on the outer layer to protect the first coating layer from being corroded and damaged by the electrolyte, and the metal phosphate salt has the property of lithium ion transmission channel, which can be used as a fast ion conductor to improve the kinetic properties of the positive electrode active material. The total thickness of the first coating layer and the second coating layer is H≤3nm, which alleviates the influence of the coating layer on the conductive and ion-conductive properties of the layered transition metal oxide. The combined effect of the above-mentioned features enables the battery containing the above-mentioned positive electrode active material to effectively improve the cycle performance and high-temperature storage performance of the battery in the fully charged state while having a better energy density.

[0006] In some embodiments, 1nm<H≤3nm; optionally, 1nm<H≤2nm. This is helpful to alleviate the energy density loss of the battery containing the above-mentioned positive electrode active material, and can effectively improve the cycle performance and high-temperature storage performance of the battery using the positive electrode active material in a fully charged state.

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

[0008] In some embodiments, the surface of the layered transition metal oxide is doped with the metal element M in the first coating layer. By doping with the metal element M, on the one hand, a transition is formed between the layered transition metal oxide and the first coating layer, and on the other hand, doping is beneficial to enhance the bond breaking energy barrier between the transition metal and oxygen originally contained in the layered transition metal oxide, inhibit the dissolution and oxygen release reaction of the transition metal originally contained in the layered transition metal oxide, and is beneficial to improve the cycle performance and high-temperature storage performance of the battery using the positive electrode active material in the fully charged state.

[0009] In some embodiments, M includes at least one of Mg, Al, Ti, Zr, Nb, Ta and W. The selection of the above metal oxides has a good doping effect, which is beneficial to prevent the dissolution and oxygen release of the transition metal oxide in the layered transition metal oxide, and improve the performance of the positive electrode active material.

[0010] In some embodiments, the metal phosphate includes at least one of lithium phosphate, sodium phosphate, potassium phosphate, calcium phosphate and aluminum phosphate. Each of the metal phosphates is stable and not easy to decompose, and can stably exist in a high temperature, high pressure and hydrofluoric acid environment, which is beneficial to improving the cycle performance and high temperature storage performance of the battery using the positive electrode active material in a fully charged state.

[0011] In a second aspect, the present application provides a method for preparing the positive electrode active material in the above-mentioned embodiment, which comprises: 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 the present application is conducive 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 conducive to improving the cycle performance and high-temperature storage performance of a battery using the positive electrode active material in a fully charged state.

[0013] Optionally, the vapor deposition method includes an atomic layer deposition method.

[0014] In some embodiments, the preparation method further comprises: before depositing the second coating layer on the surface of the intermediate product, annealing the intermediate product, wherein the annealing temperature is not less than 600°C, can be 600-800°C, and can further be 650-800°C.

[0015] Before depositing the second coating layer on the surface of the intermediate product, the intermediate product is annealed at a temperature not lower than 600° C., so that the M x O y The surface doping of the layered transition metal oxide by the metal element M is beneficial to improving the cycle performance and high-temperature storage performance of the battery using the positive electrode active material in the fully charged state.

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

[0017] In some embodiments, the preparation method further comprises: after depositing the second coating layer on the surface of the intermediate product, sintering at 400-550°C for 3-5h. Optionally, the sintering temperature is 400-500°C. The above-mentioned low-temperature sintering method is conducive to improving the structural stability of the positive electrode active material, and can effectively remove impurities such as carbon introduced into the first and / or second coating layer during the preparation process, thereby improving the purity of the positive electrode active material.

[0018] In a third aspect, the present application provides a positive electrode plate, which includes the positive electrode active material in the above embodiment.

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

[0020] Wherein, 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 2 times greater than the mass percentage of CNT in the positive electrode active material layer;

[0022] Further optionally, 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%.

[0023] In a fourth aspect, the present application provides a battery, which includes the battery cell in the above embodiment.

[0024] In a fifth aspect, the present application provides an electrical device, which includes the battery in the above embodiment, and the battery is used to provide electrical energy.

[0025] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0027] Figure 1 A schematic diagram of the structure of a vehicle according to some embodiments of the present application;

[0028] Figure 2 A schematic diagram of the exploded structure of a battery according to some embodiments of the present application;

[0029] Figure 3 A schematic diagram of the exploded structure of a battery cell according to some embodiments of the present application;

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

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

[0032] Figure 6 This is a SEM image of the lithium cobalt oxide used in Example 1 of the present application before and after double-layer coating;

[0033] Figure 7 XPS test data of the first coating layer after coating and sintering provided in the embodiment of the present application;

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

[0035] Fig. 9 This is a comparison diagram of polarization voltage of batteries corresponding to Example 1 and Comparative Example 1 of the present application during the cycle process;

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

[0037] Fig.11This is a comparison chart of the anode Co deposition amount after battery storage EOL corresponding to Example 1, Example 2 and Comparative Example 1 of the present application.

[0038] The reference numerals in the specific implementation manner are as follows:

[0039] 1000-Vehicles;

[0040] 100-battery; 200-controller; 300-motor;

[0041] 10-box; 11-first part; 12-second part;

[0042] 20-battery cell; 21-housing; 22-electrode assembly; 23-electrode terminal; 24-pressure relief structure;

[0043] 211-housing; 212-cover;

[0044] 221 - positive electrode plate; 2211 - positive electrode current collector; 2212 - positive electrode ear; 2213 - positive electrode active material layer. DETAILED DESCRIPTION

[0045] The following embodiments of the technical solution of the present application will be described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0047] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0048] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0049] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0050] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0051] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0052] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

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

[0054] At present, from the perspective of market development, the application of power batteries is becoming more and more extensive. Power batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric cars, as well as military equipment and aerospace and other fields. With the continuous expansion of the application field of power batteries, the market demand is also constantly expanding.

[0055] Among them, layered transition metal oxides have very high volume energy density, which further increases with the increase of charging cut-off voltage, and they dominate the 3C market. However, existing layered transition metal oxides have the problem of poor high-temperature storage performance in a fully charged state. One of the main reasons for the above problem is that under high temperature and high voltage, the electrolyte will spontaneously generate HF (hydrofluoric acid), and HF will corrode the positive electrode material, resulting in capacity decay and storage performance degradation.

[0056] In order to alleviate the problem that a battery containing a layered transition metal oxide cannot take into account both good cycle performance and good high-temperature storage performance in a fully charged state on the basis of having a good energy density, 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 M x O y , M includes Mg, Al and at least one of the transition metals of Groups III to VIB, 0<x, 0<y, the second coating layer includes metal orthophosphate; the total thickness of the first coating layer and the second coating layer is H, H≤3nm.

[0057] In the above-mentioned positive electrode active material, the layered transition metal oxide is coated with the first coating layer to alleviate the dissolution and oxygen release of the transition metal of the layered transition metal oxide under high voltage, and the second coating layer is set on the outer layer to protect the first coating layer from being corroded and damaged by the electrolyte, and the metal phosphate has the property of lithium ion transmission channel, which can be used as a fast ion conductor to improve the kinetic performance of the positive electrode active material, and the total thickness of the first coating layer and the second coating layer is H≤3nm, which alleviates the influence of the coating layer on the conductive and ion-conductive properties of the layered transition metal oxide. The combined effect of the above-mentioned 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 in a fully charged state while having a better energy density.

[0058] The battery disclosed in the embodiment of the present application can be used in, but not limited to, electrical devices such as vehicles, ships or aircraft. A power supply system comprising the battery disclosed in the present application can be used to form the electrical device, which is conducive to alleviating and improving the initial coulomb efficiency and battery life of the battery.

[0059] The embodiment of the present application provides an electric device using a battery as a power source, and the electric device may be, but is not limited to, a mobile phone, a tablet, a laptop, an electric toy, an electric tool, a battery car, an electric car, a ship, a spacecraft, etc. Among them, the electric toy may include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, etc., and the spacecraft may include an airplane, a rocket, a space shuttle, and a spacecraft, etc.

[0060] For the convenience of description, the following embodiments are described by taking a vehicle 1000 as an example of an electrical device according to an embodiment of the present application.

[0061] Please refer to Figure 1 , Figure 1 A schematic diagram of the structure of a vehicle 1000 provided for some embodiments of the present application. The vehicle 1000 may be a fuel vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A battery 100 is provided inside the vehicle 1000, and the battery 100 may be provided at the bottom, head or tail of the vehicle 1000. The battery 100 may be used to power the vehicle 1000, for example, the battery 100 may be used as an operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300, and the controller 200 is used to control the battery 100 to power the motor 300, for example, for starting, navigating and driving the vehicle 1000.

[0062] In some embodiments of the present application, the battery 100 can not only serve as an operating power source for the vehicle 1000, but also serve as a 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 the present application, the battery 100 refers to a single physical module including one or more battery cells 20 to provide a certain voltage and capacity, which may be in the form of a battery pack, a battery module, etc. The battery 100 may also include a box 10 for encapsulating one or more battery cells 20, and the box 10 may prevent liquid or other foreign matter from affecting the charging or discharging of the battery cells 20.

[0064] Please refer to Figure 2 , Figure 2An exploded view of a battery 100 provided in some embodiments of the present application. The battery 100 includes a box 10 and a battery cell 20, and the battery cell 20 is contained in the box 10. Among them, the box 10 is used to provide a storage space for the battery cell 20, and the box 10 can adopt a variety of structures. In some embodiments, the box 10 may include a first part 11 and a second part 12, the first part 11 and the second part 12 cover each other, and the first part 11 and the second part 12 jointly define a storage space for accommodating the battery cell 20. The second part 12 may be a hollow structure with one end open, the first part 11 may be a plate-like structure, and the first part 11 covers the open side of the second part 12, so that the first part 11 and the second part 12 jointly define a storage space; the first part 11 and the second part 12 may also be hollow structures with one side open, and the open side of the first part 11 covers the open side of the second part 12. Of course, the box 10 formed by the first part 11 and the second part 12 may be in a variety of shapes, such as a cylinder, a cuboid, etc.

[0065] In the battery 100, there may be multiple battery cells 20, and the multiple battery cells 20 may be connected in series, in parallel, or in a mixed connection. A mixed connection means that the multiple battery cells 20 are both connected in series and in parallel. The multiple battery cells 20 may be directly connected in series, in parallel, or in a mixed connection, and then the whole formed by the multiple battery cells 20 is accommodated in the box 10; of course, the battery 100 may also be a battery module formed by connecting multiple battery cells 20 in series, in parallel, or in a mixed connection, and then the multiple battery modules are connected in series, in parallel, or in a mixed connection to form a whole, and accommodated in the box 10. The battery 100 may also include other structures, for example, the battery 100 may also include a busbar component for realizing electrical connection between the multiple battery cells 20.

[0066] The battery cell 20 refers to the smallest unit constituting the battery 100. The battery cell 20 may be a lithium ion battery, a lithium sulfur battery, a sodium ion battery, or a magnesium ion battery, but is not limited thereto.

[0067] Please refer to Figure 3 , Figure 3 This is a schematic diagram of the exploded structure of a battery cell 20 provided in some embodiments of the present application. Figure 3 The battery cell 20 may include a housing 21 , an electrode assembly 22 and an electrolyte, and both the electrode assembly 22 and the electrolyte are contained in the housing 21 .

[0068] The housing 21 may include a shell 211 and a cover 212. The shell 211 is a component used to cooperate with the cover 212 to form an internal sealed space of the battery cell 20, wherein the formed sealed space can be used to accommodate the electrode assembly 22, electrolyte and other components. The cover 212 refers to a component that covers the opening of the shell 211 to isolate the internal environment of the battery cell 20 from the external environment. The shape of the cover 212 can be adapted to the shape of the shell 211 to cooperate with the shell 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 configured between the opening of the shell 211 and the cover 212 to achieve sealing between the shell 211 and the cover 212.

[0069] The shell 211 and the cover 212 can be of various shapes and sizes, such as a rectangular parallelepiped, a cylindrical shape, a hexagonal prism, etc. Specifically, the shapes of the shell 211 and the cover 212 can be determined according to the specific shape and size of the electrode assembly 22. The shell 211 and the cover 212 can be made of various materials, such as but not limited to metals such as copper, iron, aluminum, stainless steel, and aluminum alloy. The sealing ring can be made of various materials, such as but not limited to PP (polypropylene), PC (polycarbonate), PET (polyethylene terephthalate) and other materials that are resistant to electrolyte corrosion, high toughness and fatigue resistance. A coating can be formed on the outer surface of the shell 211, and the material of the coating can be various, such as but not limited to corrosion-resistant materials such as Ni and Cr.

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

[0071] The electrode assembly 22 includes a negative electrode sheet, a separator and a positive electrode sheet. The battery cell 20 mainly relies on the movement of metal ions between the positive electrode sheet and the negative electrode sheet to work. During the charge and discharge process, the active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet; the separator is arranged between the positive electrode sheet and the negative electrode sheet, which mainly prevents the positive and negative electrodes from short-circuiting, while allowing ions to pass through. The electrode assembly 22 can be a winding structure or a stacked structure, and the embodiments of the present application are not limited to this.

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

[0073] Among them, the negative electrode current collector can be a metal foil or a composite current collector. For example, the material of the negative electrode current collector and the negative electrode tab can be copper. The composite current collector may include a polymer material base layer 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 polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0074] The negative electrode active material in the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material can be a negative electrode active material such as carbon and silicon. 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 can 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 can 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 can also be used.

[0075] According to some embodiments of the present application, the negative electrode active material layer may further 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 the present application, the negative electrode active material layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0077] According to some embodiments of the present application, the negative electrode active material layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0078] The isolation membrane is located between the positive electrode plate and the negative electrode plate and plays an isolation role. The embodiment of the present application has no particular restriction on the type of isolation membrane, and any known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.

[0079] According to some embodiments of the present application, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

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

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

[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 auxiliary agent.

[0083] As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. As an example, the auxiliary agent may include, for example, a dispersant, etc.

[0084] The positive electrode active material and the preparation method thereof proposed in the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[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 of 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 having a layered rock salt-type crystal structure and containing 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 having 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 having 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] The transition metals of Group III to VIB include Sc, Ti, V, Cr, Y, Zr, Nb, Mo, La, Hf, Ta and W. It is understood that M includes at least one of Mg, Al and the transition metals of Group III to VIB, which means that M includes at least one of Mg, Al, Sc, Ti, V, Cr, Y, Zr, Nb, Mo, La, Hf, Ta and W.

[0090] Orthometal phosphate refers to an orthophosphate whose cation is a metal. Orthometal phosphate is also called orthophosphate, which refers to a salt formed when the three hydrogens that can be ionized in phosphoric acid are replaced by metal ions. Orthometal phosphate has stable properties, is not easily decomposed by heat and is not decomposed by hydrofluoric acid. Therefore, as an outer layer, it is beneficial to improve the stability of the positive electrode active material, and is beneficial to improving the cycle performance of the battery of the positive electrode active material and the high-temperature storage performance of the fully charged state.

[0091] In addition to the influence of the selection of materials for the first coating layer and the second coating layer on the performance of the final positive electrode active material, the total thickness of the first coating layer and the second coating layer has a greater influence on its performance. If the total thickness is too thick, it will affect the transport of carriers, thereby significantly reducing the energy density and first coulombic efficiency of the battery. Therefore, the total thickness H of the first coating layer and the second coating layer is ≤3nm. Exemplarily, the total thickness H of the first coating layer and the second coating layer is any value of 0.5nm, 1nm, 2nm, 2.5nm, 3nm or between any two values.

[0092] In the above-mentioned positive electrode active material, the layered transition metal oxide is coated with the first coating layer to alleviate the dissolution of transition metals in the layered transition metal oxide under high voltage, and the second coating layer is set on the outer layer to protect the first coating layer from being corroded and damaged by the electrolyte, and the metal phosphate has the property of lithium ion transmission channel, which can be used as a fast ion conductor to improve the kinetic performance of the positive electrode active material. The total thickness of the first coating layer and the second coating layer is H≤3nm, which alleviates the influence of the coating layer on the conductive and ion-conductive properties of the layered transition metal oxide. The combined effect of the above-mentioned 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 in a fully charged state while having a better energy density.

[0093] It should be noted that the battery will be accompanied by the deintercalation and consumption of carriers during the charging and discharging process, and the molar content of carriers is different when the battery is discharged to different states. In the list of positive electrode materials in this application, the molar content of carriers is the initial state of the material, that is, the state before feeding. The positive electrode material is used in the battery system, and the molar content of carriers will change after the charge and discharge cycle. In the list of positive electrode materials in this application, the molar content of O is only a theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

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

[0095] Within the above range, the preparation difficulty is low, and the battery containing the above positive electrode active material has better cycle performance and better high-temperature storage performance in a fully charged state while having better energy density.

[0096] Exemplarily, H is 1.1 nm, 1.3 nm, 1.5 nm, 1.7 nm, 2 nm, 2.3 nm, 2.5 nm, 2.7 nm or 3 nm, etc.

[0097] Optionally, 1nm<H≤2nm.

[0098] Within the above range, it is beneficial to alleviate the energy density loss of the battery containing the above cathode active material, and can effectively improve the cycle performance and high-temperature storage performance of the battery using the cathode active material in a fully charged state.

[0099] Exemplarily, H is 1.1 nm, 1.3 nm, 1.5 nm, 1.7 nm or 2 nm, etc.

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

[0101] Since the second coating layer is located on the outside and is used to protect the first coating layer, if it is too thick, it will affect ion diffusion and electron conduction, and if it is too thin, it may cause incomplete coating and cause the positive electrode active material to be corroded and damaged by the electrolyte. Therefore, by limiting the thickness of the second coating layer to 0.7nm≤h≤2nm, it is beneficial to improve the stability and kinetic performance of the positive electrode active material, so that the battery containing the positive electrode active material can effectively improve the battery's cycle performance and high-temperature storage performance in the fully charged state while having a better energy density.

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

[0103] Optionally, 1nm≤h≤1 / 2H.

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

[0105] In this application, H and h refer to the average thickness. Systematic errors are inevitable during the coating and testing process, so the thickness at different locations is slightly different. Therefore, when testing the thickness of the coating layer, n points are randomly selected, for example, 10 points are used, and the average thickness of these points is calculated; when 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 clear interface, that is, the first coating layer does not dope the surface of the layered transition metal oxide.

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

[0108] It can be understood that doping 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 the metal element M, that is, the transition metal originally contained in the layered transition metal oxide is different from the metal element M. In other words, if the metal element M is only one element, the layered transition metal oxide does not contain this element; if the metal element M is only a combination of two or more elements, the layered transition metal oxide does not contain at least one element in the combination.

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

[0111] According to some embodiments of the present 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 is beneficial to prevent the dissolution and oxygen release of 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 the present application, the metal phosphate includes at least one of lithium phosphate, sodium phosphate, potassium phosphate, calcium phosphate and aluminum phosphate.

[0114] The above-mentioned metal phosphates are stable and not easy to decompose, and can stably exist in high temperature, high pressure and hydrofluoric acid environments, which is beneficial to improving the cycle performance and high-temperature storage performance of batteries using the positive electrode active materials in a fully charged state.

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

[0116] The volume particle size distribution Dv50 refers to a particle size distribution parameter determined by a particle size distribution measurement value. For example, the volume particle size distribution Dv50 is determined by a particle size analyzer-laser diffraction method. Specifically, reference may be made to the standard GB / T 19077-2016, and measurement may be performed using a laser diffraction scattering particle size analyzer.

[0117] Within the above range, the battery can have better cycle performance.

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

[0119] The preparation method provided in the present application is conducive 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 conducive to improving the cycle performance and high-temperature storage performance of a battery using the positive electrode active material in a fully charged state.

[0120] Specifically, the vapor deposition method includes atomic layer deposition (ALD), vapor deposition (CVD), physical vapor deposition (PVD) and thermal evaporation (PET).

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

[0122] It should be noted that the specific operation mode of the vapor deposition method is not limited in the present application. As long as the first coating layer and the second coating layer with high coating integrity and relatively uniform thickness can be formed, the specific operation can refer to the relevant technology.

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

[0124] Before depositing the second coating layer on the surface of the intermediate product, the intermediate product is annealed at a temperature not lower than 600°C, so that the metal element M in MxOy in the first coating layer can 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 in the fully charged state.

[0125] If the annealing temperature is too high, the doping elements will be dispersed and distributed, which will affect the doping effect. Therefore, the annealing temperature is optionally 600-800°C.

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

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

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

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

[0130] The annealing time affects the doping depth. Therefore, within the above annealing time range, the doping depth is appropriate, which is beneficial to improving the high-temperature storage performance of the battery in the fully charged state.

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

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

[0133] The above-mentioned low-temperature sintering method can, on the one hand, inhibit the internal doping of metal phosphates, and can enhance the bonding force between the layered transition metal oxide, the first coating layer and the second coating layer, thereby improving the structural stability of the positive electrode active material, which is beneficial for inhibiting the first and / or second coating layer from falling off when it is used in the production process of the positive electrode pole piece. On the other hand, it can effectively remove impurities such as carbon introduced into the first and / or second coating layer during the preparation process, thereby improving the purity of the positive electrode active material.

[0134] Exemplarily, the sintering temperature is any value among 400°C, 430°C, 450°C, 470°C, 500°C, 530°C, 550°C or between any two values, and the sintering time is any value among 3h, 3.5h, 4h, 4.5h, 5h or between any two values.

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

[0136] According to some embodiments of the present application, the present application provides a positive electrode plate, which includes the positive electrode material provided by the above embodiments.

[0137] According to some embodiments of the present application, the positive electrode plate includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material and a conductive agent, the conductive agent includes Super P and CNT, wherein 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.

[0138] Through the cooperation between Super P and CNT, it is beneficial to alleviate the deterioration of storage performance caused by oxidative decomposition of dispersant in CNT under high voltage while maintaining high conductivity, and it is beneficial to improve the high-temperature storage performance of the battery when it is fully charged.

[0139] In some optional embodiments, the mass percentage of Super P in the positive electrode active material layer is at least 2 times greater than 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 optional embodiments, 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%.

[0142] The above setting range is conducive to improving the high-temperature storage performance of the battery when it is fully charged.

[0143] Illustratively, 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 understandable that the contents of other components in the positive electrode active material can refer to the relevant technology. 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% auxiliary agent.

[0145] According to some embodiments of the present application, the present application also provides a battery, which includes the positive electrode plate of the above embodiments.

[0146] According to some embodiments of the present application, the present application also provides an electrical device, comprising a battery according to any of the above schemes.

[0147] The battery is used to provide electrical energy to an electrical device, which may be any of the aforementioned devices or systems using the battery.

[0148] Some specific embodiments are listed below to better illustrate the present application.

[0149] Example 1

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

[0151] S1. The first coating layer (component is aluminum oxide): undoped and coated lithium cobalt oxide powder is added as a substrate into the heating chamber of the ALD equipment, trimethylaluminum and water vapor are introduced at 125°C, and the substrate is stirred to achieve complete and uniform coating. The ALD is controlled for 1 hour to achieve a coating thickness of 0.28 nm. The coating thickness is controlled by the reaction time to obtain the first coating layer.

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

[0153] S3, second coating layer (component: aluminum phosphate): in the heating chamber of the ALD equipment, trimethyl phosphate, ozone and trimethyl aluminum are introduced into the surface in turn at 230°C, and complete and uniform coating is achieved through sufficient stirring; the ALD is controlled to have a coating thickness of 0.3 nm for 1 hour, and the coating thickness is controlled by the reaction time to obtain the second coating layer.

[0154] S4. The double-layer coating of S3 is annealed at 400° C. for 5 hours to obtain a final positive electrode active material, which is recorded as double-layer coated lithium cobalt oxide.

[0155] The double-layer coated lithium cobalt oxide prepared in Example 1 was tested below. The specific test method and results are as follows:

[0156] (1) Figure 5 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 the first coating layer and the second coating layer are collectively referred to as the coating layer) is 2 nm. The thinner coating layer has less effect on the lithium ion deintercalation and charge transfer on the particle surface, achieving a very complete and uniform coating, which can comprehensively improve the cycling and high-temperature storage performance of the double-layer coated lithium cobalt oxide in the fully charged state.

[0157] The LEEQ0000D3 scanning electron microscope was used for testing, and then the standard JY / T010-1996 was used for testing to observe the sample morphology.

[0158] Figure 6 The SEM images of the lithium cobalt oxide used in Example 1 before and after double-layer coating are shown in FIG. Figure 6 Part a is before coating, and part b is after coating. Figure 6 It can be seen that the material morphology is basically the same before and after double-layer coating, that is, the ALD coating method has basically no effect 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) was measured by Auger spectroscopy. The AES data are shown in Table 1.

[0160] Table 1 AES data

[0161]

[0162]

[0163] According to Table 1, Al / P element signals were detected on the sample surface, and the Co signal content of the double-layer coated lithium cobalt oxide was very small, indicating that the surface of the lithium cobalt oxide particles was completely coated with AlPO4; the C element content was relatively high, and the main source was the adsorbed carbon on the particle surface.

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

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

[0166]

[0167] According to Table 2, the Dv50 of the double-layer coated lithium cobalt oxide particles is slightly lower than that of the uncoated lithium cobalt oxide particles, indicating that the coating layer is thin enough and does not increase the particle size; and the coating process is conducive to the dispersion of the particles, resulting in a slight decrease in Dv50. The BET is slightly reduced after coating, indicating that the coating layer is dense enough, rather than loose and porous.

[0168] (4) Inductively coupled plasma (ICP) emission spectroscopy was used to determine the content of Al and P in the double-layer coated lithium cobalt oxide. Specifically, the double-layer coated lithium cobalt oxide was taken as a sample, and the sample was digested with aqua regia and hydrofluoric acid HF. The solution after digestion was tested for the content of Al and P. The results are shown in Table 3.

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

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

[0171] According to Table 3, the content of P and Al in the double-layer coated lithium cobalt oxide is approximately 500-600 ppm, which means that the coating layer is thin enough and accounts for a very small proportion of the mass in the double-layer coated lithium cobalt oxide.

[0172] (5) The surface of the positive electrode active material after the first coating layer is coated and sintered is tested using a multifunctional X-ray photoelectron spectroscopy test instrument (XPS, instrument model: Shimadzu Axis Supra+). The XPS test data after the first coating layer is coated and sintered are as follows: Figure 7 As shown, Figure 7 Part a in the middle is the XPS signal diagram of Al2O3 coated with Al. Figure 7 Part b in the middle is the XPS signal diagram 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 It can be seen from parts a and b that the XPS signal of Al is enhanced after Al2O3 coating, and the signal peak of oxygen at 529.6eV is enhanced, indicating that the coating layer exists in the form of Al-O bonds; Figure 7 It can be seen from parts c and d that the XPS peak of AlPO4 coated Al moves toward the direction of high 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 comparative example and embodiment 1 are shown in Table 4.

[0176]

Preparation of positive electrode

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

[0178] After the prepared positive electrode slurry is stirred, the slurry viscosity is adjusted to 8000mPa.s, and the slurry coating weight is 0.3mg / 1540.25cm 2 After the single-sided coating is completed, the positive electrode sheet is prepared by drying, cold pressing, slitting and so on.

[0179]

Preparation of negative electrode sheet

[0180] 96.5wt% graphite, 1wt% conductive carbon black (Super P), 1wt% binder (styrene butadiene rubber), and 1.5wt% additive (sodium carboxymethyl cellulose) were mixed, added with deionized water, stirred, and dispersed to form negative electrode slurry. Then the negative electrode slurry was coated on Cu foil, and after both sides were completed, it was dried, cold pressed, cut, and sliced ​​to prepare the negative electrode sheet.

[0181]

Isolation film

[0182] PE (polyethylene) isolation film, thickness 12um.

[0183]

Electrolyte

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

[0185]

Battery preparation

[0186] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrodes, and wound to obtain a bare cell. The bare cell is placed in an aluminum-plastic bag, injected with the prepared electrolyte, and packaged, injected, and formed to obtain a single-layer laminated lithium-ion battery.

[0187]

First round of coulombic efficiency and gram capacity test

[0188] 1. The battery is kept at rest for 5 hours at 25°C; 2. Charged at 0.33C constant current to 4.48V; 3. Charged at 4.48V constant voltage until the current is ≤0.05C to obtain the first charge capacity; 4. Allowed to rest for 5 minutes at 25°C; 5. Discharged at 0.33C constant current to 2.5V to obtain the first discharge capacity; 6. Allowed to rest for 30 minutes at 25°C.

[0189] In the above steps, the first discharge capacity measured in step 5 is the first-cycle 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-cycle coulomb efficiency.

[0190] The results are shown in Table 4.

[0191]

Cyclic performance test

[0192] 1. The battery was allowed to stand for 5 hours at 25°C; 2. Charged at 0.33C constant current to 4.48V; 3. Charged at 4.48V constant voltage until the current was ≤0.05C; 4. Allowed to stand for 5 minutes at 25°C; 5. Discharged at 0.33C constant current to 2.5V; 6. The capacity measured in step 5 was C0; 7. Charged at 1C0 constant current to 4.48V; 8. Charged at 4.48V constant voltage until the current was ≤0.05C0; 9. Discharged at 1C0 constant current to 2.5V; 10. Repeat steps 7-9 to achieve multiple cycles, where every 50 cycles, increase 0.05C0 to discharge to 2.5V; 11. Allowed to stand for 5 minutes at 25°C.

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

[0194] Figure 8 Schematic diagram of the capacity retention rate of the positive electrode active materials of Example 1 and Comparative Example 1 (i.e., before and after lithium cobalt oxide coating) at 25° C. and 1C cycle, Figure 8 In the example, Comparative Example 1 is used as an example before coating, and Example 1 is used as an example after coating. Figure 8 It can be seen that the cycle performance of lithium cobalt oxide is significantly improved after ALD double-layer coating.

[0195] Fig. 9 The polarization voltage comparison diagram of the battery corresponding to Example 1 and Comparative Example 1 during the cycle process is shown in FIG. Fig. 9 In the example, Comparative Example 1 is used as an example before coating, and Example 1 is used as an example after coating. Fig. 9 It can be seen that after ALD coating, the polarization voltage decreases and remains stable during the battery cycle, indicating that the coating layer is beneficial to improving the charge and discharge kinetics of the material.

[0196]

Storage performance test

[0197] 1. The battery is left at 25℃ for 5 hours; 2. 0.33C constant current charge to 4.48V; 3. 4.48V constant voltage charge until the current is ≤0.05C; 4. 25℃ condition for 5 minutes; 5. 0.33C constant current discharge to 2.5V; 6. The capacity measured in step 5 is C0; 7. 0.33C0 constant current charge to 4.48V; 8. 4.48V constant voltage charge until the current is ≤0.05C0 to achieve full charge of the battery; 9. The battery is stored in a 60℃ constant temperature box for 72 hours ; 10. After storage, the battery is taken out of the oven and the capacity is tested at 25℃; 11. 0.33C0 constant current discharge to 2.5V; 12. 0.05C0 constant current discharge to 2.5V; 13. Stand at 25℃ for 5 minutes; 14. 0.33C0 constant current charge to 4.48V; 15. Stand at 25℃ for 5 minutes; 16. 4.48V constant voltage charge until the current is ≤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 the battery's life). The storage EOL time is defined as the time when the discharge capacity is 70% of the initial capacity. Three parallel samples are used for each sample for testing.

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

[0199] Fig.10 Schematic diagram of storage capacity retention rate at 60°C, 100% SOC, and 0.33C before and after double-layer coating of lithium cobalt oxide. Fig.10 In the example, Comparative Example 1 is used as an example before coating, and Example 1 is used as an example after coating. Fig.10 It can be seen that the ALD double-layer coated material has significantly improved storage capacity retention at 60°C, 100% SOC, and 0.33C compared to comparative example 1, and the three parallel samples are basically completely overlapped with high consistency.

[0200]

Co dissolution test

[0201] The batteries of Example 1, Example 2 and Comparative Example 1 were disassembled after the storage EOL (End of Line), and the anode pole pieces were cut into small discs of uniform mass. Two small discs were cut from each anode pole piece, and the mass percentage of Co element on the small discs was tested. After deducting the mass of the Cu foil current collector, the measured data is the Co dissolution amount. The results are as follows: Fig.11 As shown, Fig.11 The uncoated ones (serial numbers 1 and 2) correspond to Example 1, the double-layer coated ones (serial numbers 3 and 4) correspond to Example 2, and the coated + sintered ones (serial numbers 5 and 6) correspond to Example 1.

[0202] Fig.11 Comparison chart of EOL anode Co deposition for stack storage, according to Fig.11It can be seen that the double-layer coated unsintered method can reduce the amount of Co dissolution during the storage process of the battery compared with the double-layer coated and sintered method. Among them, the double-layer coated unsintered method can reduce the amount of Co dissolution during the storage process of the laminated battery by more than 30% compared with the uncoated method, indicating that the double-layer coating has a significant effect on inhibiting Co dissolution.

[0203] Table 4 Differentiating parameters and test results of various embodiments and comparative examples

[0204]

[0205]

[0206] It can be seen from Table 4 that, compared with the comparative example, the embodiment of the present application can significantly improve the storage performance of the battery while taking into account the better first-cycle discharge capacity. That is, when the positive electrode active material prepared in the embodiment of the present application is used in the battery, the battery has both better energy density and better high-temperature storage performance in the fully charged state.

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

[0208] According to Example 1 and Example 6, since the impurity removal sintering step is not performed in Example 6, its stability is lower than that in Example 1. Therefore, under the premise that the first-cycle discharge capacity and the first-cycle coulomb efficiency are equivalent, 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 surface of the layered transition metal oxide is doped with the first coating layer. According to Examples 1 and 7, doping the surface of the layered transition metal oxide with the first coating layer basically does not affect the first-cycle discharge capacity and the first-cycle coulomb efficiency, which is beneficial to significantly improve the storage EOL time.

[0210] According to Examples 1, 8-11, when the total coating thickness H≤3nm, the thickness of the second coating layer is 0.7-2nm, and further 1nm≤h≤1 / 2H, the battery has both better energy density and better high-temperature storage performance in a fully charged state.

[0211] According to Example 1 and Example 12, no matter the layered transition metal oxide is lithium cobalt oxide or NCM811, it can be coated by the preparation method provided in the present 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 in the fully charged state.

[0212] According to Examples 1 and 13-16, the temperature of doping annealing affects the storage EOL time. When the doping annealing temperature is 600-850°C, and can be selected as a doping annealing temperature of especially 600-800°C, when the prepared positive electrode active material is used in a battery, the battery has both better energy density and better high-temperature storage performance in a fully charged state.

[0213] According to Examples 1 and 17-18, the temperature of the impurity removal sintering affects the storage EOL time. The temperature of the impurity removal sintering is 400-550°C, especially at a temperature of 400-500°C for impurity removal sintering. When the prepared positive electrode active material is used in a battery, the battery has both better energy density and better high-temperature storage performance in a fully charged state.

[0214] According to Examples 1, 6-7 and Comparative Example 1, as long as double-layer coating is performed, regardless of whether doping or dedoping is performed, the first-cycle discharge capacity is equivalent to that of Comparative Example 1, and the storage EOL time is significantly improved.

[0215] According to Example 1 and Comparative Example 2, Comparative Example 2 only performs coating with the first coating layer and does not perform coating with the second coating layer. It can be seen that compared with Example 1, the storage EOL time is significantly reduced.

[0216] According to Example 1 and Comparative Example 3, it can be seen that the coating thickness of Comparative Example 3 is too thick, resulting in a significant decrease in its first-cycle discharge capacity, low application value, and no storage EOL time test was performed on it.

[0217] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A positive electrode active material, characterized in that: include: 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; Wherein, the first coating layer includes M x O y , the M comprises at least one of Mg, Al and transition metals from Group III to Group VIB, 0<x, 0<y, and the second coating layer comprises metal orthophosphate; The total thickness of the first cladding layer and the second cladding layer is H, where H≤3 nm.

2. The positive electrode active material according to claim 1, characterized in that 1nm<H≤3nm; Optionally, 1nm<H≤2nm.

3. The positive electrode active material according to claim 1 or 2, characterized in that: The thickness of the second coating layer is h, 0.7nm≤h≤2nm; Optionally, 1nm≤h≤1 / 2H.

4. The positive electrode active material according to any one of claims 1 to 3, characterized in that: The surface of the layered transition metal oxide is doped with the metal element M in the first coating layer.

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that: The M includes at least one of Mg, Al, Ti, Zr, Nb, Ta and W.

6. The positive electrode active material according to any one of claims 1 to 5, characterized in that: The metal phosphate salt includes at least one of lithium phosphate, sodium phosphate, potassium phosphate, calcium phosphate and aluminum phosphate.

7. The method for preparing a positive electrode active material according to claim 1, characterized in that: include: Depositing the first coating layer on the surface of the layered transition metal oxide by a vapor deposition method to obtain an intermediate product; Depositing the second coating layer on the surface of the intermediate product by a vapor deposition method; Optionally, the vapor deposition method includes an atomic layer deposition method.

8. The preparation method according to claim 7, characterized in that: The preparation method further comprises: before depositing the second coating layer on the surface of the intermediate product, annealing the intermediate product, wherein the annealing temperature is not less than 600° C., and may be 600-800° C., and may be further 650-800° C.; Optionally, the annealing time is 3-5h.

9. The preparation method according to claim 7 or 8, characterized in that: The preparation method further comprises: after depositing the second coating layer on the surface of the intermediate product, sintering at 400-550° C. for 3-5 hours; Optionally, the sintering temperature is 400-500°C.

10. A positive electrode sheet, characterized in that: The invention comprises the positive electrode active material as claimed in any one of claims 1 to 6.

11. The positive electrode sheet according to claim 10, characterized in that: The positive electrode sheet comprises a positive electrode active material layer, wherein the positive electrode active material layer comprises the positive electrode active material and a conductive agent, wherein the conductive agent comprises Super P and CNT; Wherein, the mass percentage of the Super P in the positive electrode active material layer is greater than the mass percentage of the CNT in the positive electrode active material layer; Optionally, 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; Further optionally, 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%.

12. A battery, characterized in that: A positive electrode sheet comprising the positive electrode sheet as described in any one of claims 10-11.

13. An electrical device, characterized in that: It comprises a battery as claimed in claim 12, said battery being used for providing electrical energy.

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