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

Abstract

The invention provides a positive active material and a preparation method thereof, a positive pole piece, a battery and electric equipment, and belongs to the technical field of batteries. The positive electrode active material comprises a substrate and an oxide layer positioned on the surface of the substrate; the matrix comprises Li < 1 + x > M < 1-y > A < y > P < 1-z > R < z > O < 4-t >, M comprises at least one of Fe, Co and Ni, A comprises at least one of Mn, Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R comprises at least one of B, S, Si and N; 0.1 < = x < = 0.1, 0 < = y < = 0.1, 0 < = z < = 0.1, and 0 < = t < = 0.1; the oxide layer includes an iron oxide. According to the positive electrode active material provided by the invention, the capacity of the matrix can be fully exerted, the positive electrode active material has relatively high electronic conductivity, and the lithium ion battery has relatively high cycle performance.

Description

Technical Field

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

[0002] In recent years, with the development of lithium-ion battery technology, lithium-ion batteries are widely used in energy storage power systems such as hydraulic, thermal, wind, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. The positive electrode active material is one of the key factors affecting the performance of lithium-ion batteries. Therefore, it has become an urgent technical problem to provide a positive electrode active material with high electronic conductivity, high specific capacity, and high cycle performance for lithium-ion batteries. Summary of the Invention

[0003] Aiming at the deficiencies of the prior art, the present application provides a positive electrode active material, a preparation method thereof, a positive electrode plate, a battery, and an electrical device, so that the capacity of the positive electrode active material can be fully exerted and has high electronic conductivity, and the lithium-ion battery has high cycle performance.

[0004] In a first aspect, the present application provides a positive electrode active material, which includes: a matrix and an oxide layer located on the surface of the matrix; the matrix includes Li 1+x M 1-y A y P 1-z R z O 4-t , where M includes at least one of Fe, Co, and Ni, A includes at least one of Mn, Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, R includes at least one of B, S, Si, and N; -0.1 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.1, 0 ≤ z ≤ 0.1, 0 ≤ t ≤ 0.1; the oxide layer includes iron oxide.

[0005] In the positive electrode active material provided by the present application, the surface of the matrix has an oxide layer containing iron oxide, and the iron oxide has high electronic conductivity, which can not only make the positive electrode active material have high electronic conductivity, but also make the capacity of the matrix fully exerted; in addition, compared with a lithium-ion battery prepared using only the matrix as the positive electrode active material, the lithium-ion battery prepared using the positive electrode active material provided by the present application has improved cycle performance.

[0006] In some embodiments, the matrix includes Li 1+x1 Fe 1-y1 A y1 PO 4-t1, A includes at least one of Mn, Al, Ti, V, Ni, and Zn; 0 ≤ x1 ≤ 0.05, 0 ≤ y1 ≤ 0.05, 0 ≤ t1 ≤ 0.02.

[0007] In some embodiments, in the Raman spectrum of the positive electrode active material, there is an O-Fe-O stretching vibration peak at a Raman shift of 200 cm -1 ~250 cm -1 position; and / or, in the Raman spectrum of the positive electrode active material, there is an O-Fe-O bending vibration peak at a Raman shift of 255 cm -1 ~300 cm -1 position. This can not only fully utilize the capacity of the matrix and make the positive electrode active material have a high electronic conductivity, but also make the lithium-ion battery prepared with this positive electrode active material have high cycling performance.

[0008] In some embodiments, the oxide layer includes iron(III) oxide; this can not only fully utilize the capacity of the matrix and make the positive electrode active material have a high electronic conductivity, but also make the lithium-ion battery prepared with this positive electrode active material have high cycling performance.

[0009] In some embodiments, the thickness of the oxide layer is ≤ 10 nm. When the thickness of the oxide layer is within the above range, it can not only fully utilize the capacity of the matrix and make the positive electrode active material have a high electronic conductivity, but also make the lithium-ion battery prepared with this positive electrode active material have high cycling performance.

[0010] In some embodiments, the thickness of the oxide layer is 1.5 nm to 4 nm. When the thickness of the oxide layer is within the above range, it is beneficial to further improve the full utilization of the capacity of the matrix and increase the electronic conductivity of the positive electrode active material, and at the same time is beneficial to further improve the cycling performance of the lithium-ion battery prepared with this positive electrode active material.

[0011] In some embodiments, the volume average particle size D V 50 of the positive electrode active material is 300 nm to 10.5 μm.

[0012] In a second aspect, the present application provides a method for preparing a positive electrode active material, the method including: treating a matrix to form an oxide layer on the surface of the matrix; the matrix includes Li 1+x M 1-y A y P 1-z R z O 4-t, wherein, M includes at least one of Fe, Co, and Ni, A includes at least one of Mn, Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge; -0.1 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.1, 0 ≤ z ≤ 0.1, 0.001 ≤ t ≤ 0.1; the oxide layer includes iron oxide.

[0013] In this application, an oxide layer containing iron oxide is formed on the surface of the substrate. The iron oxide has a high electronic conductivity, which can not only make the cathode active material have a high electronic conductivity, but also give full play to the capacity of the substrate. In addition, compared with a lithium-ion battery prepared using only the substrate as the cathode active material, using the cathode active material provided in this application can improve the cycling performance of the prepared lithium-ion battery.

[0014] In some embodiments, the substrate includes Li 1+x1 Fe 1-y1 A y1 PO 4-t1 , A includes at least one of Mn, Al, Ti, V, Ni, and Zn; 0 ≤ x1 ≤ 0.05, 0 ≤ y1 ≤ 0.05, 0 ≤ t1 ≤ 0.02; the substrate is oxidized to form an oxide layer on the surface of the substrate. In this application, by oxidizing the substrate containing Fe element, an in-situ oxidation reaction can occur on the surface of the substrate through a one-step oxidation operation to form an oxide layer containing iron oxide, which has the advantages of simple process and easy scaling up; and by using the method of in-situ oxidation on the surface of the substrate containing Fe element to form an oxide layer containing iron oxide, the combination between the oxide layer and the substrate can be relatively tight, and the distribution of iron oxide on the surface of the substrate is relatively uniform, which is beneficial to further fully exert the capacity of the substrate, and is beneficial to improving the electronic conductivity of the cathode active material and the cycling performance of the lithium-ion battery prepared using this cathode active material.

[0015] In some embodiments, the substrate is oxidized using an oxidation gas. By oxidizing the substrate containing Fe element with an oxidation gas, the oxidation gas can react with the surface of the substrate containing Fe element to form iron oxide, so that an oxide layer containing iron oxide is formed on the surface of the substrate, thereby giving full play to the capacity of the substrate in the prepared cathode active material, making the cathode active material have a high electronic conductivity, and making the lithium-ion battery prepared using this cathode active material have a high cycling performance.

[0016] In some embodiments, the oxidation gas includes at least one of oxygen and ozone.

[0017] In some embodiments, in the oxidation gas, the sum of the volumes of oxygen and ozone accounts for 10% to 100% of the total volume of the oxidation gas. The above technical solution is beneficial to increasing the formation rate of the oxide layer containing iron oxide formed on the surface of the substrate, and is beneficial to improving the preparation efficiency of the positive electrode active material.

[0018] In some embodiments, the temperature of the oxidation treatment ≥ 300 °C. When using the oxidation gas to perform oxidation treatment on the substrate containing Fe element, the temperature of the oxidation treatment ≥ 300 °C can cause the oxidation gas to react with the substrate containing Fe element to form iron oxide, so that an oxide layer containing iron oxide is formed on the surface of the substrate, and further the capacity of the substrate in the prepared positive electrode active material can be fully exerted, the positive electrode active material has a high electronic conductivity, and the lithium ion battery prepared using the positive electrode active material has a high cycle performance.

[0019] In some embodiments, the temperature of the oxidation treatment is 300 °C to 600 °C. When the temperature during the oxidation treatment is within the above range, the formation rate of the oxide layer containing iron oxide formed on the surface of the substrate containing Fe element can be relatively fast, which is beneficial to improving the preparation efficiency of the positive electrode active material.

[0020] In some embodiments, during the oxidation treatment, the flow rate of the oxidation gas is 200 sccm to 500 sccm. When the flow rate of the oxidation gas is within the above range, it is beneficial to form a relatively dense and uniform oxide layer covering the surface of the substrate on the surface of the substrate containing Fe element, and further beneficial to fully exert the capacity of the substrate and improve the electronic conductivity of the positive electrode active material, and the lithium ion battery prepared using the positive electrode active material has good cycle performance.

[0021] In some embodiments, the time of the oxidation treatment is 2 min to 60 min; when the time during the oxidation treatment is within the above range, the surface of the substrate containing Fe element can react fully with the oxidation gas, which is beneficial to making the mass fraction of the formed oxide layer containing iron oxide within a more appropriate range in the entire positive electrode active material. It can not only fully exert the capacity of the substrate in the positive electrode active material, make the positive electrode active material have a high electronic conductivity, but also make the lithium ion battery prepared using the positive electrode active material have a high cycle performance.

[0022] In a third aspect, the present application provides a positive electrode sheet, which includes a positive electrode current collector and a positive electrode active layer covering at least one surface in the thickness direction of the positive electrode current collector; wherein, the positive electrode active layer includes a first active material, and the first active material includes the positive electrode active material provided in any one of the above first aspects or the positive electrode active material prepared by the preparation method provided in any one of the above second aspects.

[0023] In some embodiments, the positive electrode active layer further includes a second active material, which is different from the first active material.

[0024] Fourthly, the present application provides a battery, which includes the positive electrode sheet provided in the third aspect above.

[0025] Fifthly, the present application provides an electrical device, which includes the battery provided in the fourth aspect above.

[0026] The above description is only an overview of the technical solution of the present application. In order to be able to understand the technical means of the present application more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of the present application more obvious and understandable, the specific embodiments of the present application are specifically exemplified below. Description of the Drawings

[0027] By reading the following detailed description of the preferred embodiments, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present application. And in all the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0028] Figure 1 It is a schematic structural diagram of a vehicle provided in some embodiments of the present application.

[0029] Figure 2 It is a schematic exploded view of a battery provided in some embodiments of the present application.

[0030] Figure 3 It is a schematic structural diagram of a battery cell provided in some embodiments of the present application.

[0031] Figure 4 It is an exploded view of a battery cell provided in some embodiments of the present application.

[0032] Figure 5 It is a schematic structural diagram of an electrode assembly provided in some embodiments of the present application.

[0033] Figure 6 It is a TEM-EDS diagram of the first active material prepared in Example 6 of the present application.

[0034] Figure 7 It is a TEM-EDS diagram of the first active material provided in Comparative Example 1 of the present application.

[0035] Figure 8 It is a comparative Raman spectrum diagram of the first active material prepared in Example 6 of the present application, the first active material prepared in Examples 9-10, and the first active material provided in Comparative Example 1.

[0036] Icons: 1000 - Vehicle; 100 - Battery; 10 - Box; 11 - Accommodating Space; 12 - First Part; 13 - Second Part; 20 - Battery Cell; 21 - Outer Shell; 211 - Opening; 22 - End Cap Assembly; 221 - End Cap; 222 - Electrode Terminal; 23 - Electrode Assembly; 231 - Positive Electrode Plate; 232 - Negative Electrode Plate; 233 - Separator; 24 - Current Collector Member; 25 - Insulating Protection Member; 200 - Controller; 300 - Motor. Detailed Embodiment

[0037] The embodiments of the technical solutions of the present application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to illustrate the technical solutions of the present application more clearly, and therefore are only examples and cannot be used to limit the protection scope of the present application.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled 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" and any variations thereof in the specification and claims of this application and the above drawings are intended to cover non-exclusive inclusion.

[0039] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary-secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality" is more than two, unless otherwise specifically defined.

[0040] Referring to "embodiments" herein means that the specific features, structures or characteristics described in connection with the embodiments may be included in at least one embodiment of this application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein may be combined with other embodiments.

[0041] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after.

[0042] In the description of the embodiments of the present application, the term "a plurality" 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).

[0043] In the description of the embodiments of the present application, the orientation or positional relationship indicated by technical terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the embodiments of the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the embodiments of the present application.

[0044] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", "connection", "fixation", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can also be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside 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 specific circumstances.

[0045] At present, from the perspective of the development of the market situation, the application of power batteries is becoming more and more extensive. Power batteries are not only used in energy storage power systems such as hydraulic, thermal, wind, and solar power stations, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric vehicles, as well as in multiple fields such as military equipment and aerospace. With the continuous expansion of the application fields of power batteries, the market demand is also continuously increasing.

[0046] The power battery can be a lithium-ion battery. During the charging process of the lithium-ion battery, lithium ions are released from the positive electrode active material, transported through the electrolyte, and pass through the separator membrane to be embedded in the negative electrode active layer. Among them, the positive electrode active material is one of the key factors affecting the performance of the lithium-ion battery.

[0047] However, at present, there is still room for improvement in the capacity of the positive electrode active material, the improvement of the electronic conductivity, and the improvement of the cycle performance of the lithium-ion battery.

[0048] Based on the above considerations, in order to fully utilize the capacity of the positive electrode active material and have high electronic conductivity, and to enable the lithium-ion battery to have high cycle performance, the present application designs a positive electrode active material, which includes: a matrix and an oxide layer located on the surface of the matrix; the matrix includes Li 1+x M 1-y A y P 1-z R z O4-t wherein, M includes at least one of Fe, Co, and Ni, A includes at least one of Mn, Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge; -0.1 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.1, 0 ≤ z ≤ 0.1, 0 ≤ t ≤ 0.1; the oxide layer includes iron oxide.

[0049] In such a cathode active material, the surface of the matrix has an oxide layer containing iron oxide, and the iron oxide has a high electronic conductivity, which can not only make the cathode active material have a high electronic conductivity, but also make the capacity of the matrix fully exerted; in addition, compared with a lithium-ion battery prepared using only the matrix as the cathode active material, using the cathode active material provided in this application can improve the cycling performance of the prepared lithium-ion battery.

[0050] This cathode active material can be used to prepare a cathode electrode sheet, and the cathode electrode sheet can be assembled into a battery. The battery can be a battery cell, a module, a battery pack, etc. The battery can be used in electrical equipment such as vehicles, ships, or aircraft. The power system of this electrical equipment can be composed of a battery disclosed in this application. In this way, it is beneficial to improve the cycling performance and service life of the battery at a relatively high temperature.

[0051] The embodiments of this application provide an electrical equipment using a battery as a power source. The electrical equipment can be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, an electric tool, etc. The vehicle can be a fuel vehicle, a gas vehicle, or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle, or an extended-range vehicle, etc.; the spacecraft includes an airplane, a rocket, a space shuttle, a spaceship, etc.; the electric toy includes a fixed or mobile electric toy, for example, a game console, an electric vehicle toy, an electric ship toy, an electric airplane toy, etc.; the electric tool includes a metal cutting electric tool, a grinding electric tool, an assembly electric tool, and a railway electric tool, for example, an electric drill, an electric grinder, an electric wrench, an electric screwdriver, a hammer drill, an impact drill, a concrete vibrator, and a planer, etc. The embodiments of this application do not impose special restrictions on the above-mentioned electrical equipment.

[0052] For the convenience of description, the following embodiments take the electrical equipment as a vehicle as an example for description.

[0053] Please refer to Figure 1 , Figure 1Schematic structural diagram of vehicle 1000 provided by some embodiments of the present application. Inside vehicle 1000, a battery 100 is provided. The battery 100 can be disposed at the bottom, head or tail of the vehicle 1000. The battery 100 can be used to supply power to the vehicle 1000. For example, the battery 100 can serve as the operating power source of the vehicle 1000.

[0054] Vehicle 1000 may further 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, it is used for the working power requirements during the start, navigation and driving of the vehicle 1000.

[0055] In some embodiments of the present application, the battery 100 can not only serve as the operating power source of the vehicle 1000, but also serve as the driving power source of the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0056] Figure 2 Exploded structural diagram of battery 100 provided by some embodiments of the present application. Please refer to Figure 2 , the battery 100 includes a box body 10 and battery cells 20, and the battery cells 20 are received in the box body 10.

[0057] The box body 10 is used to provide a receiving space 11 for the battery cells 20. In some embodiments, the box body 10 may include a first part 12 and a second part 13. The first part 12 and the second part 13 are covered with each other to define a receiving space 11 for receiving the battery cells 20. Of course, the connection between the first part 12 and the second part 13 can be sealed by a sealing member (not shown in the figure), and the sealing member can be a sealing ring, sealant, etc.

[0058] The first part 12 and the second part 13 can be of various shapes. For example, a cuboid, a cylinder, etc. The first part 12 can be a hollow structure with an opening on one side to form a receiving cavity for receiving the battery cells 20. The second part 13 can also be a hollow structure with an opening on one side to form a receiving cavity for receiving the battery cells 20. The opening side of the second part 13 is covered with the opening side of the first part 12, then the box body 10 with the receiving space 11 is formed. Of course, as Figure 2 shown, it can also be that the first part 12 is a hollow structure with an opening on one side, and the second part 13 is a plate-like structure. The second part 13 is covered with the opening side of the first part 12, then the box body 10 with the receiving space 11 is formed.

[0059] In battery 100, there can be one or more battery cells 20. If there are multiple battery cells 20, they can be connected in series, parallel, or in a combined series-parallel configuration. A combined series-parallel configuration means that among the multiple battery cells 20, there are both series and parallel connections. The multiple battery cells 20 can be directly connected in series, parallel, or in a combined series-parallel manner and then the whole formed by the multiple battery cells 20 is accommodated in the box 10. Of course, it is also possible that multiple battery cells 20 are first connected in series, parallel, or in a combined series-parallel manner to form battery modules, and then multiple battery modules are connected in series, parallel, or in a combined series-parallel manner to form a whole and are accommodated in the box 10. The battery cell 20 can be in the shape of a cylinder, a flat body, a cuboid, or other shapes, etc. Figure 2 An exemplary case where the battery cell 20 is square is shown.

[0060] In some embodiments, the battery 100 may further include a busbar component (not shown in the figure). The multiple battery cells 20 can be electrically connected through the busbar component to achieve series, parallel, or combined series-parallel connection of the multiple battery cells 20.

[0061] Figure 3 It is a schematic structural diagram of the battery cell 20 provided by some embodiments of the present application. Figure 4 It is an exploded view of the battery cell 20 provided by some embodiments of the present application. Please refer to Figure 3 and Figure 4 , the battery cell 20 may include a housing 21, an end cap assembly 22, and an electrode assembly 23. The housing 21 has an opening 211, the electrode assembly 23 is accommodated in the housing 21, and the end cap assembly 22 is used to seal the opening 211.

[0062] The shape of the housing 21 can be determined according to the specific shape of the electrode assembly 23. For example, if the electrode assembly 23 has a cuboid structure, the housing 21 can be selected to have a cuboid structure. Figure 3 and Figure 4 An exemplary case where the housing 21 and the electrode assembly 23 are square is shown.

[0063] The material of the housing 21 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc. The embodiments of the present application do not make special restrictions on this.

[0064] The end cap assembly 22 includes an end cap 221 and an electrode terminal 222. The end cap assembly 22 is used to seal the opening 211 of the housing 21 to form a sealed installation space (not shown in the figure). The installation space is used to accommodate the electrode assembly 23. The installation space is also used to accommodate an electrolyte, such as an electrolyte solution. As a component for outputting the electrical energy of the electrode assembly 23, the electrode terminal 222 in the end cap assembly 22 is used to be electrically connected to the electrode assembly 23, that is, the electrode terminal 222 is electrically connected to the tab of the electrode assembly 23. For example, the electrode terminal 222 and the tab are connected through a current collector member 24 to achieve the electrical connection between the electrode terminal 222 and the tab.

[0065] It should be noted that the opening 211 of the outer shell 21 can be one or two. If the opening 211 of the outer shell 21 is one, the end cap assembly 22 can also be one, and two electrode terminals 222 can be arranged in the end cap assembly 22, and the two electrode terminals 222 are respectively used for electrically connecting with the positive electrode tab and the negative electrode tab of the electrode assembly 23. If the opening 211 of the outer shell 21 is two, for example, the two openings 211 are arranged on opposite sides of the outer shell 21, the end cap assembly 22 can also be two, and the two end cap assemblies 22 respectively cover the two openings 211 of the outer shell 21. In this case, the electrode terminal 222 in one end cap assembly 22 can be a positive electrode terminal for electrically connecting with the positive electrode tab of the electrode assembly 23; the electrode terminal 222 in the other end cap assembly 22 can be a negative electrode terminal for electrically connecting with the negative electrode tab of the electrode assembly 23.

[0066] In some embodiments, as Figure 4 shown, the battery cell 20 may further include an insulating protection member 25 fixed to the outer periphery of the electrode assembly 23, and the insulating protection member 25 is used for insulating and isolating the electrode assembly 23 from the outer shell 21. Exemplarily, the insulating protection member 25 is a tape adhered to the outer periphery of the electrode assembly 23. In some embodiments, the number of the electrode assemblies 23 is multiple, and the insulating protection member 25 surrounds the outer peripheries of the multiple electrode assemblies 23 and forms a whole structure of the multiple electrode assemblies 23 to keep the structure of the electrode assembly 23 stable. Among them, the electrode assembly 23 can be a wound electrode assembly or a stacked electrode assembly, and the embodiments of the present application are not limited thereto.

[0067] Figure 5 For the structural schematic diagram of the electrode assembly provided in some embodiments of the present application, please refer to Figure 5 , the electrode assembly 23 includes a positive electrode plate 231, a negative electrode plate 232 and a separator 233. The separator 233 is arranged between the positive electrode plate 231 and the negative electrode plate 232. The electrolyte is located in the installation space and fills the gaps of the electrode assembly 23.

[0068] The present application has no special limitations on the separator 233, the negative electrode plate 232 and the electrolyte.

[0069] For the separator 233, the separator 233 can be a PP (polypropylene) porous membrane, a PE (polyethylene) porous membrane, a polyimide porous membrane, and a porous membrane formed by composite of multiple polymers, etc.

[0070] For the negative electrode plate 232, the negative electrode plate 232 includes a negative electrode current collector and a negative electrode active layer covering at least one surface in the thickness direction of the negative electrode current collector; there is no particular limitation on the thickness of the negative electrode current collector and the negative electrode active layer in this application, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm, and the thickness of the negative electrode active layer on one side of the negative electrode current collector is 30 μm to 130 μm.

[0071] The material of the negative electrode current collector may include aluminum foil, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal, etc.; among them, the conductive metal includes, but is not limited to, copper, nickel, or titanium, and the material of the polymer substrate includes, but is not limited to, at least one of polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene terephthalate, poly(ethylene naphthalate), and poly(p-phenylene terephthalamide).

[0072] The negative electrode active material in the negative electrode active layer includes graphite, coke, etc., or the negative electrode active material in the negative electrode active layer includes lithium metal, an alloy formed by lithium and other metal elements or non-metal elements, where the metal elements include tin (Sn), zinc (Zn), aluminum (Al), magnesium (Mg), silver (Ag), gold (Au), gallium (Ga), indium (In), platinum (Pt), etc., and the non-metal elements include boron (B), carbon (C), silicon (Si), etc.

[0073] The conductive agent in the negative electrode active layer may include, but is not limited to, carbon materials, metals, or conductive polymers, etc. The carbon materials may include at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon nanofibers, natural graphite, artificial graphite, flake graphite, carbon dots, or graphene, etc. The metals may include metal powders or metal fibers such as copper, iron, aluminum, etc., and the conductive polymers may include at least one of polythiophene, polypyrrole, polyaniline, polyphenylene, and polyphenylene vinylene.

[0074] The binder in the negative electrode active layer may include, but is not limited to, at least one of polyvinyl alcohol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyamideimide, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinylpyrrolidone, polyethylene, polypropylene, epoxy resin, nylon, styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral, water-based acrylic resin, carboxymethyl cellulose (CMC), or sodium carboxymethyl cellulose (CMC-Na), etc.

[0075] The negative electrode plate 232 can be prepared according to conventional methods in the art. For example, the negative active material, conductive agent, binder, etc. described above are dispersed in a solvent, which can be N-methylpyrrolidone (NMP) or deionized water, to form a uniform negative electrode slurry. The negative electrode slurry is coated on the negative electrode current collector, and the negative electrode plate 232 is obtained through processes such as drying and cold pressing.

[0076] For the electrolyte, the electrolyte includes a sodium salt and a non-aqueous solvent, or the electrolyte includes a lithium salt and a non-aqueous solvent; wherein, the sodium salt can include NaPF 6 , NaClO 4 , NaBCl 4 , NaSO 3 CF 3 or Na(CH 3 )C 6 H 4 SO 3 and at least one of them; the present application has no special limitation on the concentration of the sodium salt in the electrolyte, as long as the object of the present application can be achieved. The lithium salt can include LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiB(C 6 H 5 ) 4 , LiCH 3 SO 3 , LiCF 3 SO 3 , LiN(SO 2 CF 3 ) 2 , LiC(SO 2 CF 3 ) 3 , Li 2 , SiF 6, at least one of lithium bis(oxalato)borate (LiBOB) or lithium difluoroborate; the present application does not particularly limit the concentration of the lithium salt in the electrolyte, as long as the object of the present application can be achieved. The present application does not particularly limit the above non-aqueous solvent, as long as the object of the present application can be achieved. For example, it may include but is not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents; the above carbonate compounds may include but are not limited to at least one of linear carbonate compounds, cyclic carbonate compounds or fluorinated carbonate compounds; the above linear carbonate compounds may include but are not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) or methyl ethyl carbonate (MEC); the above cyclic carbonates may include but are not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinylene carbonate (VEC); fluorinated carbonate compounds may include but are not limited to at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate or trifluoromethyl ethylene carbonate; the above carboxylate compounds may include but are not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone or caprolactone; the above ether compounds may include but are not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran; the above other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate.

[0077] For the positive electrode plate 231, the positive electrode plate 231 includes a positive electrode current collector and a positive electrode active layer covering at least one surface in the thickness direction of the positive electrode current collector; the material of the positive electrode current collector may include aluminum foil, aluminum foam, aluminum composite current collector (a current collector with a polymer support layer in the middle and aluminum metal layers on both surfaces of the support layer), nickel foil, nickel foam, etc. The binder in the positive electrode active layer is selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylate, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, ethylene-vinyl acetate copolymer, and ethylene-acrylic acid copolymer; the dispersant in the positive electrode active layer is selected from polyvinylpyrrolidone, etc.; the conductive agent in the positive electrode active layer is selected from at least one of conductive carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotube, graphene, activated carbon, graphite sheet, graphite particle, and mesophase carbon microsphere.

[0078] In the present application, the positive electrode active material in the positive electrode active layer includes a first active material, and the first active material includes: a matrix and an oxide layer located on the surface of the matrix; the matrix includes Li 1+x M 1-y A y P 1-z R z O 4-t , where M includes at least one of Fe, Co, and Ni, A includes at least one of Mn, Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and R includes at least one of B, S, Si, and N; -0.1 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.1, 0 ≤ z ≤ 0.1, 0 ≤ t ≤ 0.1; the oxide layer includes iron oxide.

[0079] Among them, "the oxide layer located on the surface of the matrix" means that: the oxide layer at least partially covers the surface of the matrix, which may be that the entire surface of the matrix is covered with the oxide layer, or only part of the surface area of the matrix is covered with the oxide layer.

[0080] "Iron oxide" means: an oxide of iron, a compound containing only iron and oxygen elements (Fe x O y , where 3 ≥ x ≥ 1, 4 ≥ y ≥ 1); for example, iron oxide can be ferrous oxide (FeO), ferric oxide (Fe 2 O 3 ) or / and magnetite (Fe 3 O 4 ) and other substances containing only iron and oxygen elements.

[0081] As an example, Li 1+x M 1-y A y P1-z R z O 4-t In it, the value of x can be any value among -0.1, -0.07, -0.05, -0.02, 0, 0.02, 0.05, 0.07, and 0.1 or the range value between any two of them; the value of y can be any value among 0, 0.001, 0.01, 0.02, 0.05, 0.07, 0.09, and 0.1 or the range value between any two of them; the value of z can be any value among 0, 0.01, 0.02, 0.05, 0.07, 0.09, and 0.1 or the range value between any two of them; the value of t can be any value among 0, 0.001, 0.01, 0.02, 0.05, 0.07, 0.09, and 0.1 or the range value between any two of them.

[0082] In the first active material provided by this application, the surface of the matrix has an oxide layer containing iron oxide. The iron oxide has a high electronic conductivity, which can improve the electronic conductivity performance of the first active material, and the capacity of the matrix in the first active material can be effectively exerted. In addition, compared with the lithium-ion battery prepared by using only the matrix as the positive electrode active material, the lithium-ion battery prepared by using the first active material provided by this application has improved cycle performance.

[0083] In some embodiments, the matrix includes Li 1+x1 Fe 1-y1 A y1 PO 4-t1 , A includes at least one of Mn, Al, Ti, V, Ni, and Zn; 0 ≤ x1 ≤ 0.05, 0 ≤ y1 ≤ 0.05, 0 ≤ t1 ≤ 0.02.

[0084] As an example, in Li 1+x1 Fe 1-y1 A y1 PO 4-t1 , the value of x1 can be any value among 0, 0.01, 0.02, 0.03, 0.04, and 0.05 or the range value between any two of them; the value of y1 can be any value among 0, 0.01, 0.02, 0.03, 0.04, and 0.05 or the range value between any two of them; the value of t1 can be any value among 0, 0.001, 0.005, 0.01, 0.015, 0.017, and 0.02 or the range value between any two of them.

[0085] Furthermore, in some embodiments, the matrix includes LiFePO 4 .

[0086] In some embodiments, in the Raman spectrum of the first active material, at a Raman shift of 200 cm-1 ~250 cm -1 has an O-Fe-O stretching vibration peak at the position; and / or, in the Raman spectrum of the first active material, there is an O-Fe-O bending vibration peak at the Raman shift of 255 cm -1 ~300 cm -1 position. The first active material having corresponding Raman characteristic peaks within the above wavenumber range can not only fully exert the capacity of the matrix and the first active material has a high electronic conductivity, but also enable the lithium-ion battery prepared with the first active material to have high cycling performance.

[0087] In some embodiments, the oxide layer includes iron(III) oxide (Fe 2 O 3 ). It can not only fully exert the capacity of the matrix and the first active material has a high electronic conductivity, but also enable the lithium-ion battery prepared with the first active material to have high cycling performance.

[0088] In some embodiments, along the direction from the outermost side of the oxide layer to the matrix, the content of iron oxide in the oxide layer gradually decreases.

[0089] In some embodiments, the thickness of the oxide layer ≤ 10 nm; it can not only fully exert the capacity of the matrix and the first active material has a high electronic conductivity, but also enable the lithium-ion battery prepared with the first active material to have high cycling performance.

[0090] Exemplarily, the thickness of the oxide layer can be any value among 10 nm, 8 nm, 7.5 nm, 6 nm, 5 nm, 4 nm, 3 nm, 2 nm, 1 nm, and 0.1 nm or the range value between any two of them.

[0091] In some embodiments, the thickness of the oxide layer is 1 nm - 8 nm. It can not only fully exert the capacity of the matrix and the first active material has a high electronic conductivity, but also enable the lithium-ion battery prepared with the first active material to have high cycling performance.

[0092] Exemplarily, the thickness of the oxide layer can be any value among 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 6 nm, 7.5 nm, and 8 nm or the range value between any two of them.

[0093] In some embodiments, the thickness of the oxide layer is 1.5 nm - 4 nm; which is beneficial to further improving the full exertion of the capacity of the matrix and increasing the electronic conductivity of the first active material, and at the same time is beneficial to further improving the cycling performance of the lithium-ion battery prepared with the first active material.

[0094] In some embodiments, the volume-average particle diameter D V 50 of the first active material is from 300 nm to 10.5 μm.

[0095] Exemplarily, the volume-average particle diameter D V 50 of the first active material can be any value among 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, and 10.5 μm or a range value between any two of them.

[0096] After the above introduction of the first active material, the preparation method of the first active material will be specifically introduced below.

[0097] In the present application, the substrate is treated to form an oxide layer on the surface of the substrate; the substrate includes Li 1+x M 1- y A y P 1-z R z O 4-t , where M includes at least one of Fe, Co, and Ni, A includes at least one of Mn, Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and R includes at least one of B, S, Si, and N; -0.1 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.1, 0 ≤ z ≤ 0.1, 0.001 ≤ t ≤ 0.1; the oxide layer includes iron oxide.

[0098] Wherein, "forming an oxide layer on the surface of the substrate" means that the oxide layer at least partially covers the surface of the substrate, which may be that the entire surface of the substrate is covered with the oxide layer, or only a partial area of the surface of the substrate is covered with the oxide layer.

[0099] Iron oxide refers to an oxide of iron, a compound containing only iron and oxygen elements (Fe x O y , where 3 ≥ x ≥ 1, 4 ≥ y ≥ 1); for example, the iron oxide can be ferrous oxide (FeO), ferric oxide (Fe 2 O 3 ) or / and magnetite (Fe 3 O 4 ) and other substances containing only iron and oxygen elements.

[0100] Exemplarily, in the matrix, the value of x can be any value among -0.1, -0.07, -0.05, -0.02, 0, 0.02, 0.05, 0.07, and 0.1 or a range value between any two of them; the value of y can be any value among 0, 0.01, 0.02, 0.05, 0.07, 0.09, and 0.1 or a range value between any two of them; the value of z can be any value among 0, 0.01, 0.02, 0.05, 0.07, 0.09, and 0.1 or a range value between any two of them; the value of t can be any value among 0, 0.001, 0.01, 0.02, 0.05, 0.07, 0.09, and 0.1 or a range value between any two of them.

[0101] In this application, an oxide layer containing iron oxide is formed on the surface of the matrix. The iron oxide has a high electronic conductivity, which can not only make the first active material have a high electronic conductivity but also give full play to the capacity of the matrix. In addition, compared with a lithium-ion battery prepared using only the matrix as the positive electrode active material, the lithium-ion battery prepared using the first active material provided in this application has improved cycling performance.

[0102] In some embodiments, the matrix includes Li 1+x1 Fe 1-y1 A y1 PO 4-t1 , where A includes at least one of Mn, Al, Ti, V, Ni, and Zn; 0 ≤ x1 ≤ 0.05, 0 ≤ y1 ≤ 0.05, 0 ≤ t1 ≤ 0.02; the matrix is oxidized to form an oxide layer on the surface of the matrix. In this application, by oxidizing the matrix containing Fe element, an in-situ oxidation reaction can occur on the surface of the matrix containing Fe element through a one-step oxidation operation to form an oxide layer containing iron oxide on the surface of the matrix, that is, the oxide layer containing iron oxide is formed by in-situ oxidation of the surface of the matrix containing Fe element.

[0103] It should be noted that in other feasible embodiments, the step of forming an oxide layer on the surface of the substrate can also be prepared in the following two ways; Method 1: Mix a slurry containing iron oxide with the substrate, and then dry and grind; Method 2: Mix an iron source with the substrate, and then oxidize the mixed system. Compared with the above two methods, the method of "oxidizing a substrate containing Fe element" provided in this application can cause an in-situ oxidation reaction on the surface of the substrate containing Fe element through a one-step oxidation operation to form an oxide layer containing iron oxide, which has the advantages of simple process and easy amplification; and by using the method of in-situ oxidation on the surface of the substrate containing Fe element to form an oxide layer containing iron oxide, the combination between the oxide layer and the substrate can be relatively tight, and the distribution of iron oxide on the surface of the substrate is relatively uniform, which is beneficial to further fully exert the capacity of the substrate and is beneficial to improving the electronic conductivity of the first active material and the cycle performance of the lithium-ion battery prepared by using the first active material.

[0104] As an example, Li 1+x1 Fe 1-y1 A y1 PO 4-t1 In [LiFePO₄]₁₋ₓ₁[Liₓ₁Fe₁₋ₓ₁Aₓ₁]PO₄₋ₓ₂[Liₓ₂Fe₁₋ₓ₂Aₓ₂]PO₄₋ₓ₃[Liₓ₃Fe₁₋ₓ₃Aₓ₃]PO₄₋ₜ₁, the value of x1 can be any value among 0, 0.01, 0.02, 0.03, 0.04, and 0.05 or the range value between any two of them; the value of y1 can be any value among 0, 0.01, 0.02, 0.03, 0.04, and 0.05 or the range value between any two of them; the value of t1 can be any value among 0, 0.001, 0.005, 0.01, 0.015, 0.017, and 0.02 or the range value between any two of them.

[0105] Furthermore, in some embodiments, the substrate is LiFePO₄. 4 .

[0106] In some embodiments, the substrate is oxidized by an oxidizing gas; when the substrate containing Fe element is oxidized by an oxidizing gas, the oxidizing gas can react with the surface of the substrate containing Fe element to form iron oxide, so that an oxide layer containing iron oxide is formed on the surface of the substrate, thereby fully exerting the capacity of the substrate in the prepared first active material, making the first active material have a high electronic conductivity, and making the lithium-ion battery prepared by using the first active material have a high cycle performance.

[0107] In some embodiments, the oxidizing gas includes at least one of oxygen and ozone.

[0108] Among them, "the oxidation gas includes at least one of oxygen and ozone" means that the oxidation gas can be only oxygen or only ozone, or the oxidation gas can only contain oxygen and ozone, or the oxidation gas can also contain other gases, for example, inert gases (including but not limited to nitrogen or / and argon, etc.); as an example, the oxidation gas can be air.

[0109] In some embodiments, in the oxidation gas, the sum of the volumes of oxygen and ozone accounts for 10% to 100% of the total volume of the oxidation gas. This is beneficial to increasing the formation rate of the oxide layer containing iron oxide formed on the surface of the substrate, and is beneficial to improving the preparation efficiency of the first active material.

[0110] As an example, in the oxidation gas, the volume fraction of the sum of the volumes of oxygen and ozone can be any value among 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100% or the range value between any two of them.

[0111] In some embodiments, the temperature of the oxidation treatment is ≥ 300 °C. This can enable the substrate containing Fe elements to undergo an oxidation reaction to form iron oxide, so that an oxide layer containing iron oxide is formed on the surface of the substrate, and further enables the capacity of the substrate in the prepared first active material to be fully exerted, enables the first active material to have a high electronic conductivity, and enables the lithium-ion battery prepared using this first active material to have high cycling performance.

[0112] The inventor speculates that for the substrate including LiFePO 4 when the temperature of the oxidation treatment is ≥ 300 °C, the reaction equation of the oxidation gas such as oxygen and LiFePO 4 is: 12LiFePO 4 + 3O 2 → 2Fe 2 O 3 + 4Li 3 Fe 2 (PO 4 ) 3 .

[0113] As an example, the temperature of the oxidation treatment can be 300 °C, 400 °C, 500 °C, 600 °C or 700 °C, etc.

[0114] In some embodiments, the temperature of the oxidation treatment is 300 °C to 600 °C. This can enable the formation rate of the oxide layer containing iron oxide formed on the surface of the substrate containing Fe elements to be relatively fast, and is beneficial to improving the preparation efficiency of the first active material.

[0115] Exemplarily, the temperature of the oxidation treatment can be any value among 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, and 600°C or a range value between any two of them.

[0116] In some embodiments, when oxidizing a matrix containing Fe element with an oxidation gas, the flow rate of the oxidation gas is 200 sccm to 500 sccm. This is beneficial for forming a relatively dense and uniformly covering oxide layer on the surface of the matrix containing Fe element, which is further beneficial for fully exerting the capacity of the matrix and improving the electronic conductivity of the first active material, and enabling the lithium-ion battery prepared with this first active material to have good cycling performance.

[0117] Exemplarily, when oxidizing a matrix containing Fe element with an oxidation gas, the flow rate of the oxidation gas can be any value among 200 sccm, 220 sccm, 250 sccm, 270 sccm, 300 sccm, 320 sccm, 350 sccm, 370 sccm, 400 sccm, 420 sccm, 450 sccm, 470 sccm, and 500 sccm or a range value between any two of them.

[0118] In some embodiments, when oxidizing a matrix containing Fe element with an oxidation gas, the oxidation treatment time is 2 min to 60 min. This can enable the surface of the matrix containing Fe element to fully react with the oxidation gas, which is beneficial for making the mass fraction of the formed oxide layer containing iron oxide within a more appropriate range in the entire first active material. It can not only fully exert the capacity of the matrix in the first active material and make the first active material have a high electronic conductivity, but also enable the lithium-ion battery prepared with this first active material to have high cycling performance.

[0119] Exemplarily, when oxidizing a matrix containing Fe element with an oxidation gas, the oxidation treatment time can be any value among 2 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, and 60 min or a range value between any two of them.

[0120] In some embodiments, the oxidation treatment is carried out in a cyclone oxidation furnace. Passing an oxidation gas into the cyclone oxidation furnace to carry out an oxidation treatment on a substrate containing Fe elements can enable the oxidation gas to be in full contact with the surface of the substrate containing Fe elements, which is conducive to forming a relatively dense and uniform oxidation layer on the surface of the substrate containing Fe elements. Furthermore, it is conducive to further fully exerting the capacity of the substrate and improving the electronic conductivity of the first active material, and enabling the lithium-ion battery prepared with this first active material to have good cycling performance.

[0121] Exemplarily, the steps for oxidizing lithium iron phosphate include: laying the substrate containing Fe elements flat in the cyclone oxidation furnace, and placing the substrates containing Fe elements at intervals in the cyclone oxidation furnace. At 300°C to 600°C, introduce 200 sccm to 500 sccm of air into the furnace body for 2 min to 60 min.

[0122] It should be noted that the oxidation treatment can also be carried out in a tube oxidation furnace.

[0123] In some embodiments, in addition to the first active material provided above, the positive electrode active material in the positive electrode active layer further includes a second active material.

[0124] In some embodiments, the second active material includes: a body and a carbon layer located on the surface of the body; the body includes Li 1+m C 1-n D n P 1-s E s O 4-q , where C includes at least one of Fe, Co, and Ni, D includes at least one of Mn, Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, E includes at least one of B, S, Si, and N, 0.1 ≤ m ≤ 0.1, 0 ≤ n ≤ 0.1, 0 ≤ s ≤ 0.1, 0 ≤ q ≤ 0.1.

[0125] Among them, "the carbon layer located on the surface of the body" means that the surface of the body is covered with a carbon layer, and the carbon layer covers at least part of the surface of the body (it can be that the entire surface of the body is covered with the carbon layer, or only part of the surface area of the body is covered with the carbon layer).

[0126] Furthermore, in some embodiments, the body of the second active material includes LiFePO 4 .

[0127] In some embodiments, in the positive electrode active layer, the mass ratio of the first active material to the second active material is 1:(0.5 to 3). When the mass ratio of the first active material to the second active material is within the above range, the capacity of the positive electrode active material can be fully exerted, and it has a high electronic conductivity. Also, the lithium-ion battery prepared with this positive electrode active material can have good cycling performance.

[0128] Exemplarily, in the positive electrode active layer, the mass ratio of the first active material to the second active material can be any value among 1:0.5, 1:0.7, 1:1, 1:1.5, 1:2, 1:2.5, and 1:3 or the range value between any two of them.

[0129] In some embodiments, in the positive electrode active material, the carbon layer thickness of the second active material is 0.5 nm to 10 nm.

[0130] Exemplarily, the carbon layer thickness of the second active material can be any value among 0.5 nm, 1 nm, 1.5 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, and 10 nm or the range value between any two of them.

[0131] In some embodiments, for the second active material, the volume average particle size D V 50 is 0.5 μm to 5 μm.

[0132] Exemplarily, for the second active material, the volume average particle size D V 50 can be any value among 0.5 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 3 μm, 4 μm, and 5 μm or the range value between any two of them.

[0133] In some embodiments, in the second active material, the mass fraction of the carbon layer in the second active material is 0.5% to 5%.

[0134] Exemplarily, in the second active material, the mass fraction of the carbon layer in the second active material can be any value among 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, 3%, 4%, and 5% or the range value between any two of them.

[0135] In some embodiments, the material of the carbon layer in the second active material includes inorganic carbon or / and organic carbon. For example, the material of the carbon layer can include at least one of graphene, carbon black, conductive graphite, amorphous carbon, and carbon nanotubes.

[0136] It should be noted that this application does not limit the preparation method of the second active material.

[0137] It should be noted that the second active material in the positive electrode active layer is not limited to the above substances, and the second active material can be selected from one or a mixture of several of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-containing phosphate with an olivine structure. For example, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, lithium manganese oxide, etc.

[0138] The above positive electrode active material can be used to prepare the positive electrode plate 231. The positive electrode plate 231 can be prepared according to the conventional methods in the art. For example, the positive electrode active material, conductive agent, binder, etc. described above are dispersed in a solvent, and the solvent can be N-methylpyrrolidone (NMP) or deionized water to form a uniform positive electrode slurry. The positive electrode slurry is coated on the positive electrode current collector and the positive electrode plate 231 is obtained through processes such as drying and cold pressing.

[0139] The positive electrode plate 231 can be used to prepare the electrode assembly 23, and the electrode assembly can be used to prepare the battery 100, and this battery 100 can be used as the power source of the electrical equipment.

[0140] Next, one or more embodiments will be described in more detail with reference to the following examples. Of course, these examples do not limit the scope of one or more embodiments.

[0141] Experimental Example 1

[0142] (1) Preparation of the first active material:

[0143] Weigh 2 g of carbon-free LiFePO 4 , and spread it evenly in a corundum crucible with dimensions of 6 cm × 3 cm × 2 cm. Before the oxidation treatment, the cyclone oxidation furnace is preheated to the oxidation temperature of 400 °C, and air is introduced into the oxidation furnace as the oxidation gas at a gas flow rate of 400 sccm. When the temperature of the oxidation furnace is stable at the oxidation temperature, the corundum crucible carrying carbon-free LiFePO 4 is loaded into the oxidation furnace for a 10-minute oxidation treatment. After the oxidation treatment, the oxidized carbon-free LiFePO 4 powder is taken out and naturally cooled at room temperature. After its temperature drops to room temperature, the obtained powder is placed in a mortar and ground for 10 minutes to obtain the first active material.

[0144] Among them, "carbon-free LiFePO 4 " is: lithium iron phosphate without any coating layer treatment, and the D 4 50 of carbon-free LiFePO V is 2.3 μm.

[0145] (2) Preparation of the positive electrode plate:

[0146] Mix the cathode active material with a mass ratio of 92:2.5:5.5 (the cathode active material is a mixture of a first active material and a second active material, and the second active material is carbon-coated LiFePO 4 ), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF), add the solvent N-methylpyrrolidone (NMP), stir until the system becomes homogeneous, grind for 10 min, and then prepare a cathode slurry with a solid content of 50 wt%.

[0147] Among them, "carbon-coated LiFePO 4 " means: LiFePO 4 coated only with a carbon layer on the surface, and the volume average particle size D 4 50 of carbon-coated LiFePO V is 1.6 μm, the average thickness of the coated carbon layer is 1.5 nm, and the mass fraction of the carbon layer in the entire carbon-coated LiFePO 4 is 1.6 wt%; in the cathode active material, the mass ratio of the first active material to the second active material is 1:1.

[0148] Coat the cathode slurry evenly on both sides of the cathode current collector aluminum foil (with a thickness of 6 μm), dry at 120 °C for 4 h, then perform cold pressing, followed by trimming and slicing, and dry in a vacuum at 120 °C for 4 h to obtain the cathode plate, where the thickness of the single-sided cathode active material layer is 200 μm.

[0149] (3) Prepare a coin cell:

[0150] Use a lithium sheet (with a thickness of 0.5 mm) as the anode, and use a solution of 1 mol / L LiPF 6 in ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) with a volume ratio of 1:1:1 as the electrolyte, and assemble it with the above-prepared cathode plate into a CR2430 coin cell in a glove box.

[0151] Example 2

[0152] This example provides a coin cell. The difference between Example 2 and Example 1 is only that: the oxidation temperature in the preparation process of the first active material is 300 °C.

[0153] Example 3

[0154] This example provides a coin cell. The difference between Example 3 and Example 1 is only that: the oxidation temperature in the preparation process of the first active material is 500 °C.

[0155] Example 4

[0156] This embodiment provides a button cell. The difference between Embodiment 4 and Embodiment 1 is only that: the oxidation temperature in the preparation process of the first active material is 600 °C.

[0157] Embodiment 5

[0158] This embodiment provides a button cell. The difference between Embodiment 5 and Embodiment 1 is only that: the oxidation temperature in the preparation process of the first active material is 280 °C.

[0159] Embodiment 6

[0160] This embodiment provides a button cell. The difference between Embodiment 6 and Embodiment 1 is only that: the oxidation temperature in the preparation process of the first active material is 650 °C.

[0161] Embodiment 7

[0162] This embodiment provides a button cell. The difference between Embodiment 7 and Embodiment 1 is only that: the oxidation treatment time in the preparation process of the first active material is 2 min.

[0163] Embodiment 8

[0164] This embodiment provides a button cell. The difference between Embodiment 8 and Embodiment 1 is only that: the oxidation treatment time in the preparation process of the first active material is 60 min.

[0165] Embodiment 9

[0166] This embodiment provides a button cell. The difference between Embodiment 9 and Embodiment 1 is only that: the oxidation treatment time in the preparation process of the first active material is 20 min.

[0167] Embodiment 10

[0168] This embodiment provides a button cell. The difference between Embodiment 10 and Embodiment 1 is only that: the oxidation treatment time in the preparation process of the first active material is 30 min.

[0169] Embodiment 11

[0170] This embodiment provides a button cell. The difference between Embodiment 11 and Embodiment 1 is only that: the oxidation treatment time in the preparation process of the first active material is 1.8 min.

[0171] Embodiment 12

[0172] This embodiment provides a button cell. The difference between Embodiment 12 and Embodiment 1 is only that: the oxidation treatment time in the preparation process of the first active material is 65 min.

[0173] Embodiment 13

[0174] This embodiment provides a button cell. The difference between Embodiment 13 and Embodiment 1 is only that: the flow rate of the oxidation gas in the preparation process of the first active material is 200 sccm.

[0175] Embodiment 14

[0176] This embodiment provides a button cell. The difference between Embodiment 14 and Embodiment 1 is only that: the flow rate of the oxidation gas in the preparation process of the first active material is 500 sccm.

[0177] Embodiment 15

[0178] This embodiment provides a button cell. The difference between Embodiment 15 and Embodiment 1 is only that: the oxidation gas in the preparation process of the first active material is oxygen.

[0179] Embodiment 16

[0180] This embodiment provides a button cell. The difference between Embodiment 16 and Embodiment 1 is only that: the oxidation gas in the preparation process of the first active material is a mixed gas of ozone and argon with a volume ratio of 1:4.

[0181] Embodiment 17

[0182] This embodiment provides a button cell. The difference between Embodiment 17 and Embodiment 1 is only that: in the positive electrode active material, the mass ratio of the first active material to the second active material is 1:0.5.

[0183] Embodiment 18

[0184] This embodiment provides a button cell. The difference between Embodiment 18 and Embodiment 1 is only that: in the positive electrode active material, the mass ratio of the first active material to the second active material is 1:3.

[0185] Embodiment 19

[0186] This embodiment provides a button cell. The difference between Embodiment 19 and Embodiment 1 is only that: for the carbon-free LiFePO used to prepare the first active material 4 of D V 50 is 0.25 μm.

[0187] Embodiment 20

[0188] This embodiment provides a button cell. The difference between Embodiment 20 and Embodiment 1 is only that: for the carbon-free LiFePO used to prepare the first active material 4 of D V 50 is 8.2 μm.

[0189] Comparative Example 1

[0190] This comparative example provides a button cell. The difference between Comparative Example 1 and Example 1 is only that: the first active material is D V 50 is carbon-free LiFePO with a size of 2.3 μm 4 , and the positive electrode active material is only the first active material.

[0191] Among them, "carbon-free LiFePO 4 " means: lithium iron phosphate without any coating treatment.

[0192] Comparative Example 2

[0193] This comparative example provides a button cell. The difference between Comparative Example 1 and Example 1 is only that: the first active material is D V 50 is carbon-free LiFePO with a size of 2.3 μm 4 , the second active material is carbon-coated LiFePO 4 .

[0194] Among them, "carbon-free LiFePO 4 " means: lithium iron phosphate without any coating treatment; "carbon-coated LiFePO 4 " means: LiFePO with only a carbon layer coated on the surface 4 , and the volume average particle size D 4 50 of carbon-coated LiFePO is 1.6 μm, the average thickness of the coated carbon layer is 1.5 nm, and the mass fraction of the carbon layer in the entire carbon-coated LiFePO V is 1.6 wt%. 4

[0195] Table 1 Preparation parameters of the first active material and parameters of the positive electrode active material in Examples 1-20 and Comparative Examples 1-2

[0196]

[0197]

[0198] In Table 1, " / " means that the corresponding parameter does not exist.

[0199] Detect the performance of the first active material and the button cell:

[0200] (1) TEM-EDS analysis of the first active material

[0201] Using a cross-section polishing instrument (IB-09010CP argon ion cross-section polishing instrument from JEOL Ltd., Japan), a flat cross-section was cut from the core of the first active material; then, EDS elemental analysis combined with TEM (such as X-Max EDS from Oxford Instruments Group, UK, combined with Thermo Scientific-Talos F200S G2 TEM from Thermo Fisher Scientific Inc., USA) was used to scan and test the cross-section of the first active material to obtain the elemental distribution map in the cross-section.

[0202] The thickness of the oxide layer was obtained based on the elemental distribution of the cross-section; the average value of the thickness values of the oxide layer at 10 different positions on the test cross-section was taken as the thickness of the oxide layer.

[0203] (2) Raman spectroscopy analysis of the first active material

[0204] A LabRAM HR Evolution type laser micro-Raman spectrometer was used to measure the first active material. Among them, a solid-state laser with a wavelength of 523 nm was used as the light source, the beam diameter was 1.2 μm, and the power was 1 mW; the measurement mode was macro-Raman; a CCD detector was used.

[0205] (3) Volume average particle size D of the first active material V 50 test

[0206] Equipment model: Malvern 2000 (MasterSizer 2000) laser particle size analyzer, reference standard process: GB / T19077-2016 / ISO 13320:2009.

[0207] Specific test process: Take an appropriate amount of the first active material (the sample concentration should ensure a light transmittance of 8-12%), add 20 mL of absolute ethanol, and ultrasonically disperse the first active material for 5 min (53 KHz / 120 W). Then, according to the GB / T19077-2016 / ISO 13320:2009 standard, the volume average particle size D V 50 of the first active material was measured.

[0208] (4) Electronic conductivity test of the first active material

[0209] Using a powder resistivity meter (PRCD1100 model from Yuaneng Technology Co., Ltd.), the resistance of the first active material was measured under 100 MPa. Conductivity = powder thickness / (resistance value × powder area).

[0210] (5) Specific capacity test of the first active material

[0211] At 25 °C, the coin cells prepared in Examples 1 to 20 and Comparative Examples 1 to 2 were first charged at a constant current of 0.1C to 4.3V, then charged at a constant voltage of 4.3V until the current reached 0.01C, left standing for 5 min, and then discharged at 0.1C to 2.0V. The obtained discharge capacity was denoted as C1, and the capacity obtained by repeating the cycle for the second time was denoted as C2. Three parallel samples of the coin cells were prepared, and the average value of C2 of the three parallel samples was denoted as the average discharge capacity C0 (unit: mAh / g). The specific capacity of the first active material = (C0 - Cm × A 1 ) / A 2 , where Cm is the discharge capacity of the second active material, and its value is 150 mAh / g; A 1 is the mass percentage of the second active material in the positive electrode active material (unit: %), and A 2 is the mass percentage of the first active material in the positive electrode active material (unit: %).

[0212] (6) Cycling performance test of coin cells

[0213] At 25 °C, the coin cells prepared in Examples 1 to 20 and Comparative Examples 1 to 2 were first charged to 4.3V at a constant current of 0.1C, then charged at a constant voltage of 4.3V until the current reached 0.01C, left standing for 5 min, and then discharged at 0.1C to 2.0V. This was one charge-discharge cycle process, and the discharge capacity this time was the discharge capacity of the 1st week cycle. The coin cells were subjected to 50-week cycle charge-discharge tests in the above manner, and the discharge capacity of the 50th week cycle was detected, and the capacity retention rate of the coin cells after cycling was calculated by the following formula.

[0214] Capacity retention rate (%) of coin cells after 50-week cycling = [Discharge capacity of the 50th week cycle / Discharge capacity of the 1st week cycle] × 100%.

[0215] Among them, the performance of the first active material and the coin cells is shown in Table 2:

[0216] Table 2 Performance of the first active material and coin cells

[0217]

[0218]

[0219] In Table 2, " / " means that there is no corresponding parameter; "thickness of the oxide layer" means: average thickness of the oxide layer; for Examples 1 to 20, the oxide layer refers to: iron oxide layer on the surface of lithium iron phosphate; "out of range" means: the corresponding data is too small to be measured.

[0220] Figure 6TEM-EDS diagram of the first active material prepared in Example 6 of this application Figure 7 TEM-EDS diagram of the first active material provided in Comparative Example 1 of this application

[0221] From Figure 6 it can be seen that the surface of the first active material prepared in Example 6 of this application has an iron-enriched surface layer ( Figure 6 The dotted line in indicates the interface between the iron-enriched surface layer of the first active material and the LiFePO 4 matrix), and the thickness of the surface layer is about 8 nm; From Figure 7 it can be seen that the first active material provided in Comparative Example 1 (i.e., carbon-free LiFePO 4 , LiFePO without any coating treatment 4 ) has a uniform distribution of phosphorus and iron throughout the particle and does not have an iron-enriched surface layer; It shows that after oxidation treatment, the first active material prepared in Example 6 of this application forms an iron-enriched surface layer on the surface of carbon-free LiFePO 4 .

[0222] Figure 8 Raman spectrum comparison diagram of the first active material prepared in Example 6 of this application, the first active materials prepared in Examples 9-10, and the first active material provided in Comparative Example 1

[0223] From Figure 8 it can be seen that the Raman spectra of the first active materials prepared in Example 6 and Examples 9-10 of this application after oxidation treatment for different times have two significant Raman characteristic peaks in the wavenumber range of 200 cm -1 ~300 cm -1 ; The positions of the two Raman characteristic peaks are at 225 cm -1 and 290 cm -1 respectively, corresponding to the υ(O-Fe-O) stretching vibration peak and the δ(O-Fe-O) bending vibration peak, indicating that the first active materials prepared in Example 6 and Examples 9-10 after oxidation treatment for different times form iron oxide (α-Fe 2 O 3 ). However, the Raman spectrum of the first active material provided in Comparative Example 1 (i.e., carbon-free LiFePO 4 , LiFePO without any coating treatment 4 ) does not have Raman characteristic peaks in the wavenumber range of 200 cm -1 ~300 cm -1 .

[0224] Combined with Figure 6 and Figure 8 it can be seen that for carbon-free LiFePO of this application 4After oxidation treatment, an oxide layer containing α-Fe 4 can be formed on the surface of carbon-free LiFePO 2 O 3 .

[0225] As can be seen from Table 2, the electronic conductivity and specific capacity of the first active materials prepared in Examples 1 to 20 of this application are both higher than those of the first active material provided in Comparative Example 1 (i.e., carbon-free LiFePO 4 , LiFePO without any coating treatment 4 ); it shows that: the first active material with an oxide layer provided in this application improves the disadvantages of low capacity and low electronic conductivity of carbon-free layer-coated LiFePO 4 .

[0226] As can also be seen from Table 2, the cycling performance of the coin cells corresponding to Examples 1 to 20 of this application is better than that of the coin cells corresponding to Comparative Examples 1 to 2; it shows that: the first active material with an oxide layer provided in this application improves the disadvantage of poor cycling performance of carbon-free layer-coated LiFePO 4 and has good cycling performance.

[0227] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of this application claimed, but merely represents selected embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without creative efforts fall within the scope of protection of this application.

Claims

1. A positive electrode active material, characterized in that, the positive electrode active material comprises: a substrate and an oxide layer located on the surface of the substrate; The matrix includes Li 1+x M 1-y A y P 1-z R z O 4-t , where M includes at least one of Fe, Co, and Ni, A includes at least one of Mn, Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge; -0.1 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.1, 0 ≤ z ≤ 0.1, 0 ≤ t ≤ 0.1; the oxide layer comprises iron oxide.

2. The positive electrode active material according to claim 1, characterized in that, The matrix includes Li 1+x1 Fe 1- y1 A y1 PO 4-t1 , where A includes at least one of Mn, Al, Ti, V, Ni, and Zn; 0 ≤ x1 ≤ 0.05, 0 ≤ y1 ≤ 0.05, 0 ≤ t1 ≤ 0.

02.

3. The positive electrode active material according to claim 1 or 2, characterized in that, In the Raman spectrum of the positive electrode active material, an O-Fe-O stretching vibration peak is present at a Raman shift of 200 cm -1 to 250 cm -1 position; And / or, in the Raman spectrum of the positive electrode active material, an O-Fe-O bending vibration peak is present at a Raman shift of 255 cm -1 to 300 cm -1 position.

4. The positive electrode active material according to any one of claims 1 to 3, characterized in that, the oxide layer comprises iron(III) oxide.

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that, the thickness of the oxide layer is ≤ 10 nm; optionally, the thickness of the oxide layer is 1.5 nm to 4 nm.

6. The positive electrode active material according to any one of claims 1 to 5, characterized in that, The volume average particle diameter D of the positive electrode active material V is 300 nm to 10.5 μm.

7. A method for preparing a positive electrode active material, characterized in that, comprises: treating a substrate to form an oxide layer on the surface of the substrate; The substrate includes Li 1+x M 1-y A y P 1-z R z O 4-t , where M includes at least one of Fe, Co, and Ni, A includes at least one of Mn, Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge; -0.1 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.1, 0 ≤ z ≤ 0.1, 0.001 ≤ t ≤ 0.1; the oxide layer comprises iron oxide.

8. The preparation method according to claim 7, characterized in that, The matrix includes Li 1+x1 Fe 1-y1 A y1 PO 4-t1 , A includes at least one of Mn, Al, Ti, V, Ni, and Zn; 0 ≤ x1 ≤ 0.05, 0 ≤ y1 ≤ 0.05, 0 ≤ t1 ≤ 0.02; the matrix is subjected to an oxidation treatment to form the oxide layer on the surface of the matrix.

9. The preparation method according to claim 8, characterized in that, oxidizing the substrate with an oxidizing gas; optionally, the oxidizing gas comprises at least one of oxygen and ozone; optionally, in the oxidizing gas, the sum of the volumes of the oxygen and the ozone accounts for 10% to 100% of the total volume of the oxidizing gas.

10. The preparation method according to claim 8 or 9, characterized in that, the temperature of the oxidation treatment is ≥ 300 °C; optionally, the temperature of the oxidation treatment is 300 °C to 600 °C.

11. The preparation method according to claim 9, characterized in that, during the oxidation treatment, the flow rate of the oxidizing gas is 200 sccm to 500 sccm; optionally, the time of the oxidation treatment is 2 min to 60 min.

12. A positive electrode tab, characterized in that, the positive electrode tab comprises a positive electrode current collector and a positive electrode active layer covering at least one surface in the thickness direction of the positive electrode current collector; wherein, the positive electrode active layer comprises a first active material, and the first active material comprises the positive electrode active material according to any one of claims 1 to 6 or the positive electrode active material prepared by using the preparation method according to any one of claims 7 to 11.

13. The positive electrode tab according to claim 12, characterized in that, the positive electrode active layer further comprises a second active material, and the second active material is different from the first active material.

14. A battery, characterized in that, the battery comprises the positive electrode tab according to claim 12 or 13.

15. An electrical device, characterized in that, the electrical device comprises the battery according to claim 14.

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