A secondary battery, a method of manufacturing the same, a power consuming device, a positive electrode active material, and a method of manufacturing the same

Abstract

The application relates to a secondary battery and a preparation method thereof, an electric device, a positive electrode active material and a preparation method thereof, and belongs to the technical field of secondary batteries; a first sublayer with oxygen vacancies is coated on a lithium cobalt phosphate material, the first sublayer can capture oxygen ions released by the lithium cobalt phosphate material at a high voltage in the operation process of the secondary battery, thereby reducing the possibility of oxidation and decomposition of the electrolyte, improving the gas swelling of the secondary battery, reducing the generation of acid, reducing the dissolution of the transition metal cobalt in the lithium cobalt phosphate material, and making the secondary battery have a good cycle life.

Description

Technical Field

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

[0002] The electrochemical performance of olivine-type positive electrode active materials such as lithium cobalt phosphate requires charging to a relatively high voltage (>4.9V). Under high voltage conditions, the surface interface structure of lithium cobalt phosphate materials is unstable, and oxygen ions in the surface structure are easily released. The released oxygen ions react with the electrolyte, causing the electrolyte to be oxidized and decomposed, generating a large amount of gas and causing the battery to swell. At the same time, the hydrofluoric acid produced by the oxidation and decomposition of the electrolyte is highly corrosive. After the lithium cobalt phosphate material is corroded, its transition metal element cobalt will gradually dissolve and continuously deposit on the negative electrode, causing continuous damage to the SEI film of the negative electrode, continuously consuming active lithium ions, and causing the battery capacity to decay rapidly. Summary of the Invention

[0003] In view of the above problems, this application provides a secondary battery and its preparation method, an electrical device, a positive electrode active material and its preparation method, which can improve the problem of oxidation reaction between oxygen ions released from lithium cobalt phosphate materials and the electrolyte.

[0004] In a first aspect, this application provides a secondary battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive active material layer, the positive active material layer comprising a positive active material, the positive active material comprising a first positive active material, the first positive active material comprising a core and a shell layer covering the core, the core comprising a lithium cobalt phosphate material, the shell layer comprising a first sublayer, the material of the first sublayer having oxygen vacancies.

[0005] In the technical solution of this application embodiment, by coating a first sublayer with oxygen vacancies onto a lithium cobalt phosphate material, the first sublayer can capture oxygen ions released by the lithium cobalt phosphate material under higher voltage during the operation of the secondary battery, thereby reducing the possibility of the electrolyte being oxidized and decomposed, improving the gas production and swelling of the secondary battery, and also reducing the generation of acid, thereby reducing the dissolution of the plating metal element cobalt in the lithium cobalt phosphate material, so that the secondary battery has a better cycle life.

[0006] In some embodiments, the oxygen vacancy content of the material of the first sublayer is not less than 20%.

[0007] In the above implementation process, the more oxygen vacancies in the material, the more oxygen ions released by lithium cobalt phosphate materials can be captured. By controlling the oxygen vacancy content of the first sublayer material to be no less than 20%, the oxygen ions released by lithium cobalt phosphate materials can be fully captured, effectively reducing the possibility of electrolyte oxidation and decomposition, and improving the problem of secondary battery swelling caused by gas generation. It also reduces acid production, thereby reducing the dissolution of cobalt, a plating metal element, from lithium cobalt phosphate materials, resulting in a better cycle life for the secondary battery.

[0008] In some embodiments, the oxygen vacancy content of the material of the first sublayer is 30% to 40%.

[0009] In the above implementation process, the higher the oxygen vacancy content of the material, the worse its stability. By controlling the oxygen vacancy content of the first sublayer material to 30%–40%, it achieves better stability and a better oxygen ion capture effect. This effectively captures oxygen ions released from lithium cobalt phosphate materials, reducing the possibility of electrolyte oxidation and decomposition, and mitigating the problem of secondary battery swelling caused by gas generation. It also reduces acid production, thereby reducing the dissolution of cobalt, a plating metal element, from lithium cobalt phosphate materials, resulting in a better cycle life for the secondary battery.

[0010] In some embodiments, the kernel and the first sublayer are in direct contact, and the contact area between the kernel and the first sublayer has a transition layer containing all elements of the material of the first sublayer.

[0011] In the above implementation process, by embedding the elements of the first sublayer material into the core to form a transition layer, the materials of the first sublayer and the lithium cobalt phosphate materials in the transition layer share oxygen atoms, causing electron transfer in the lithium cobalt phosphate materials in the transition layer, enhancing their electronegativity to oxygen, playing an oxygen-locking effect, and reducing the probability of oxygen evolution in the lithium cobalt phosphate materials of the surface transition layer.

[0012] In some embodiments, the material of the first sublayer includes a perovskite oxide.

[0013] In the above implementation process, perovskite oxides usually have the characteristics of oxygen vacancies and acid corrosion resistance. Using them as the material of the first sublayer can help improve the gas bulging and cycle life of secondary batteries.

[0014] In some embodiments, the material of the first sublayer includes N a O b N includes at least one of magnesium, calcium, cobalt, nickel, copper, zinc, aluminum, gallium, scandium, yttrium, lanthanum, titanium, chromium, vanadium, niobium, zirconium, or molybdenum, 0.5 ≥ a ≥ 0.1, b = Va / 2, and V is the valence number of element N.

[0015] In some embodiments, the first sublayer includes a plurality of attachment point layers, which are spaced apart on the kernel surface.

[0016] In the above implementation process, by distributing multiple attachment points at intervals on the core surface, that is, the entire first sublayer is distributed in an "island" shape, the influence of the first sublayer on the electron and ion transport of the entire first positive electrode active material can be reduced, which is beneficial to its rate performance and its own capacity.

[0017] In some embodiments, the mass percentage of the first sublayer in the first positive electrode active material is no more than 5%.

[0018] In the above implementation process, the lower the mass percentage of the first sublayer, the better it is for reducing the impact on the electron and ion transport of the entire first positive electrode active material. By controlling the mass percentage of the first sublayer to be no more than 5%, the first positive electrode active material can achieve better rate performance and its own capacity.

[0019] In some embodiments, the mass percentage of the first sublayer in the first positive electrode active material is 0.5% to 4%.

[0020] In the above implementation process, a higher mass percentage of the first sublayer is more conducive to capturing oxygen ions released from lithium cobalt phosphate materials. By controlling the mass percentage of the first sublayer to 0.5%–4%, oxygen ions released from lithium cobalt phosphate materials can be effectively captured, reducing the possibility of electrolyte oxidation and decomposition, and improving the problem of secondary battery swelling caused by gas generation. It also reduces acid production, thereby reducing the dissolution of cobalt, a plating metal element, from lithium cobalt phosphate materials, resulting in a better cycle life for the secondary battery. Furthermore, it also ensures that the first positive electrode active material has good rate performance and its own capacity.

[0021] In some embodiments, the shell further includes a second sublayer, the first sublayer being disposed between the core and the second sublayer, the second sublayer being made of carbon.

[0022] In the above implementation process, by setting a second sublayer on the surface of the cobalt phosphate lithium material to form a carbon coating, the electronic conductivity of the entire first positive electrode active material is improved.

[0023] In some embodiments, the second sublayer in the first positive electrode active material accounts for 0.1% to 5% of the total mass.

[0024] In the above implementation process, the larger the mass proportion of the second sublayer, the better it is for the electronic conductivity of the entire first positive electrode active material; conversely, the smaller the mass proportion of the second sublayer, the better it is for the specific capacity of the entire first positive electrode active material. By controlling the mass proportion of the second sublayer to be between 0.1% and 5%, both the electronic conductivity and specific capacity of the first positive electrode active material can be balanced.

[0025] In some embodiments, the lithium cobalt phosphate material includes: LiMPO4, where M includes Co and non-Co elements, and the non-Co elements include one or both of a first doping element and a second doping element, wherein the first doping element is a cobalt site doping and the second doping element is a phosphorus site doping.

[0026] Optionally, the first doping element includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Mn, Ni, Fe, Ga, Sn, Sb, Nb, and Ge.

[0027] Optionally, the first doping element includes at least two of Mn, Ti, V, Ni, Fe, and Mg.

[0028] Optionally, the second doping element includes one or more elements selected from B, S, Si, and N.

[0029] Optionally, lithium cobalt phosphate materials include Li 1+x Co 1-y A y P 1-z R z O4,

[0030] Where x is any value in the range of -0.100 to 0.100;

[0031] y is any value in the range of 0.001 to 0.500;

[0032] z is any value in the range of 0.001 to 0.100;

[0033] The A element includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Mn, Ni, Fe, Ga, Sn, Sb, Nb, and Ge.

[0034] The R includes one or more elements selected from B, S, Si, and N;

[0035] Optionally, lithium cobalt phosphate materials include Li a A e Co 1-f B f P 1-g C g O4-n D n ,

[0036] Wherein, A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W;

[0037] The B includes one or more elements selected from Ti, V, Zr, Mn, Ni, Mg, Fe, Ga, Sn, Sb, Nb, and Ge;

[0038] The C includes one or more elements selected from B, S, Si, and N;

[0039] The D includes one or more elements selected from S, F, Cl, and Br;

[0040] The value of a is selected from the range of 0.9 to 1.1, the value of e is selected from the range of 0.001 to 0.1, the value of f is selected from the range of 0.001 to 0.5, the value of g is selected from the range of 0.001 to 0.1, the value of n is selected from the range of 0.001 to 0.1, and the lithium cobalt phosphate material is electrically neutral.

[0041] In some embodiments, the core includes a core and a surface layer attached to the outside of the core. The core includes a first lithium cobalt phosphate material, and the surface layer includes a second lithium cobalt phosphate material. The second lithium cobalt phosphate material is doped with at least one of La, Mo, Y, or Sc, and the total molar content of La, Mo, Y, and Sc in the second lithium cobalt phosphate material is greater than the total molar content of La, Mo, Y, and Sc in the first lithium cobalt phosphate material.

[0042] In the above implementation process, by making the total molar content of La, Mo, Y and Sc in the second cobalt phosphate material on the surface greater than the total molar content of La, Mo, Y and Sc in the first cobalt phosphate material in the core, the cross-sectional structure of the core particles can be stabilized.

[0043] Secondly, this application provides a method for preparing a secondary battery, the method comprising:

[0044] Lithium cobalt phosphate materials were obtained;

[0045] The lithium cobalt phosphate material and the shell material are mixed in a solvent and then dried and granulated to obtain an intermediate powder.

[0046] The intermediate powder is sintered to obtain a positive electrode active material. The positive electrode active material includes a first positive electrode active material, which includes a core and a shell covering the core. The core includes a lithium cobalt phosphate material, and the shell includes a first sublayer. The material of the first sublayer has oxygen vacancies.

[0047] The positive electrode active material is prepared into a slurry and coated onto the positive electrode current collector to obtain a positive electrode sheet;

[0048] The positive electrode, separator, and negative electrode are assembled to obtain a secondary battery.

[0049] Thirdly, this application provides an electrical device, which includes a secondary battery provided in the first aspect or a secondary battery obtained by the method provided in the second aspect.

[0050] Fourthly, this application provides a positive electrode active material, the positive electrode active material comprising a first positive electrode active material, the first positive electrode active material comprising a core and a shell covering the core, the core comprising a lithium cobalt phosphate material, the shell comprising a first sublayer, the material of the first sublayer having oxygen vacancies.

[0051] In the technical solution of this application embodiment, by coating a first sublayer with oxygen vacancies onto a lithium cobalt phosphate material, when used as a positive electrode active material in a secondary battery, the first sublayer can capture oxygen ions released by the lithium cobalt phosphate material at a higher voltage, thereby reducing the possibility of the electrolyte being oxidized and decomposed, improving the gas production and swelling of the secondary battery, and also reducing the generation of acid, thereby reducing the dissolution of the plating metal element cobalt in the lithium cobalt phosphate material, so that the secondary battery has a better cycle life.

[0052] In some embodiments, the oxygen vacancy content of the material of the first sublayer is not less than 20%.

[0053] In the above implementation process, the higher the oxygen vacancy content of the material, the more oxygen ions released by lithium cobalt phosphate materials can be captured. By controlling the oxygen vacancy content of the first sublayer material to be no less than 20%, when used as the positive electrode active material of a secondary battery, it can fully capture oxygen ions released by lithium cobalt phosphate materials at higher voltages, effectively reducing the possibility of electrolyte oxidation and decomposition, and improving the problem of secondary battery swelling caused by gas generation. It also reduces acid production, thereby reducing the dissolution of the plating metal element cobalt from lithium cobalt phosphate materials, resulting in a better cycle life for the secondary battery.

[0054] In some embodiments, the kernel and the first sublayer are in direct contact, and the contact area between the kernel and the first sublayer has a transition layer containing all elements of the material of the first sublayer.

[0055] In the above implementation process, by embedding the elements of the first sublayer material into the core to form a transition layer, the materials of the first sublayer and the lithium cobalt phosphate materials in the transition layer share oxygen atoms, causing electron transfer in the lithium cobalt phosphate materials in the transition layer, enhancing their electronegativity to oxygen, playing an oxygen-locking effect, and reducing the probability of oxygen evolution in the lithium cobalt phosphate materials of the surface transition layer.

[0056] In some embodiments, the material of the first sublayer includes N a O b N includes at least one of magnesium, calcium, cobalt, nickel, copper, zinc, aluminum, gallium, scandium, yttrium, lanthanum, titanium, chromium, vanadium, niobium, zirconium, or molybdenum, 0.5 ≥ a ≥ 0.1, b = Va / 2, and V is the valence number of element N.

[0057] In some embodiments, the first sublayer includes a plurality of attachment point layers, which are spaced apart on the kernel surface.

[0058] In the above implementation process, by distributing multiple attachment points at intervals on the core surface, that is, the entire first sublayer is distributed in an "island" shape, the influence of the first sublayer on the electron and ion transport of the entire first positive electrode active material can be reduced, which is beneficial to its rate performance and its own capacity.

[0059] In some embodiments, the mass percentage of the first sublayer in the first positive electrode active material is no more than 5%.

[0060] In the above implementation process, the lower the mass percentage of the first sublayer, the better it is for reducing the impact on the electron and ion transport of the entire first positive electrode active material. By controlling the mass percentage of the first sublayer to be no more than 5%, the first positive electrode active material can achieve better rate performance and its own capacity.

[0061] In some embodiments, the shell further includes a second sublayer made of carbon, and the first sublayer is disposed between the core and the second sublayer.

[0062] In the above implementation process, by setting a second sublayer on the surface of the lithium cobalt phosphate material to form a carbon coating, the electronic conductivity of the entire first positive electrode active material is improved. At the same time, placing the first sublayer between the core and the second sublayer allows the material of the first sublayer to have an "oxygen-locking" effect on the lithium cobalt phosphate material, reducing the probability of oxygen ion evolution on the surface of the lithium cobalt phosphate material.

[0063] In some embodiments, the second sublayer in the first positive electrode active material accounts for 0.1% to 5% of the total mass.

[0064] In the above implementation process, the larger the mass proportion of the second sublayer, the better it is for the electronic conductivity of the entire first positive electrode active material; conversely, the smaller the mass proportion of the second sublayer, the better it is for the specific capacity of the entire first positive electrode active material. By controlling the mass proportion of the second sublayer to be between 0.1% and 5%, both the electronic conductivity and specific capacity of the first positive electrode active material can be balanced.

[0065] Fifthly, this application provides a method for preparing a positive electrode active material, the method comprising:

[0066] Lithium cobalt phosphate materials were obtained;

[0067] The lithium cobalt phosphate material and the shell material are mixed in a solvent and then dried and granulated to obtain an intermediate powder.

[0068] The intermediate powder is sintered to obtain a positive electrode active material. The positive electrode active material includes a first positive electrode active material, which includes a core and a shell covering the core. The core includes a lithium cobalt phosphate material, and the shell includes a first sublayer. The material of the first sublayer has oxygen vacancies.

[0069] In the technical solution of this application embodiment, by coating a first sublayer with oxygen vacancies onto a lithium cobalt phosphate material, when used as a positive electrode active material in a secondary battery, the first sublayer can capture oxygen ions released by the lithium cobalt phosphate material at a higher voltage, thereby reducing the possibility of the electrolyte being oxidized and decomposed, improving the gas production and swelling of the secondary battery, and also reducing the generation of acid, thereby reducing the dissolution of the plating metal element cobalt in the lithium cobalt phosphate material, so that the secondary battery has a better cycle life.

[0070] In some embodiments, the median particle size Dv50 of the lithium cobalt phosphate material is 1 μm to 5 μm, and the median particle size Dv50 of the shell material is 200 nm to 500 nm.

[0071] In the above implementation process, by controlling the median particle size Dv50 of the lithium cobalt phosphate material to be 1μm to 5μm and the median particle size Dv50 of the shell material to be 200nm to 500nm, a particle size difference is formed, which is beneficial for the shell material to adhere to the lithium cobalt phosphate material and form a coating layer.

[0072] In some embodiments, the method further includes carbon coating the positive electrode active material, wherein the carbon coating method includes chemical vapor deposition.

[0073] In the above implementation process, by using chemical vapor deposition for carbon coating, the probability of the first sublayer material being reacted into oxygen-free vacancy material during the carbon coating process, which would lead to a decrease in oxygen ion capture capacity, can be reduced.

[0074] In some embodiments, the lithium source used to obtain the lithium cobalt phosphate material includes at least one of lithium nitrate, lithium tetraborate, lithium fluoride, or lithium metaborate.

[0075] In the above implementation process, by using lithium nitrate, lithium tetraborate, lithium fluoride or lithium metaborate as lithium source, the sintering temperature of lithium cobalt phosphate materials can be reduced, making it possible to prepare the core and coating layer in one sintering process and achieve in-situ coating. Attached Figure Description

[0076] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0077] Figure 1 This application provides structural schematic diagrams of vehicles for some embodiments;

[0078] Figure 2 This is an exploded structural diagram of a secondary battery provided in some embodiments of this application;

[0079] Figure 3 This is a schematic diagram of the structure of a battery cell provided in some embodiments of this application;

[0080] Figure 4 Exploded views of a single battery cell provided in some embodiments of this application;

[0081] Figure 5 This is a schematic diagram illustrating the process of preparing a secondary battery according to some embodiments of this application;

[0082] Figure 6 This is an elemental distribution diagram of the positive electrode active material provided in Embodiment 1 of this application;

[0083] Figure 7 This is a schematic diagram of the surface morphology provided in Embodiment 1 of this application;

[0084] Figure 8 XPS image of the positive electrode active material provided in Example 1 of this application;

[0085] Figure 9 The image shows the XRD pattern of the positive electrode active material provided in Example 1 of this application.

[0086] The reference numerals in the detailed embodiments are as follows:

[0087] 1000 - Vehicle; 100 - Secondary battery; 200 - Motor; 300 - Controller; 10 - Housing; 11 - Accommodation space; 12 - First part; 13 - Second part; 20 - Battery cell; 21 - Housing; 211 - Opening; 22 - End cap assembly; 221 - End cap; 222 - Electrode terminal; 23 - Electrode assembly; 24 - Current collector; 25 - Insulation protection component. Detailed Implementation

[0088] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0089] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0090] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0091] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0092] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0093] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0094] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0095] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0096] Currently, judging from market trends, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of power battery applications, market demand is also constantly increasing.

[0097] The electrochemical performance of olivine-type cathode active materials, such as lithium cobalt phosphate, requires charging to a relatively high voltage (>4.9V), while the high-spin Co at the octahedral position of lithium cobalt phosphate... 3+ Unstable, prone to generating Co 2+ and Co 3+ The material exists in a mixed state, and the surface layer contains Co-O hybrid orbitals, which have low binding force on oxygen. Under high voltage conditions, the surface interface structure of lithium cobalt phosphate materials is unstable, and oxygen ions in the surface structure are easily released. The released oxygen ions react with the electrolyte, causing the electrolyte to be oxidized and decomposed, producing a large amount of gas and causing the battery to swell due to gas production. At the same time, the hydrofluoric acid produced by the oxidation and decomposition of the electrolyte is highly corrosive. After the lithium cobalt phosphate material is corroded, its transition metal element cobalt will gradually dissolve and continuously deposit on the negative electrode, causing continuous damage to the SEI film of the negative electrode, continuously consuming active lithium ions, and causing the battery capacity to decay rapidly.

[0098] To address these issues, some researchers have proposed doping lithium cobalt phosphate (LCP) materials with elements such as aluminum, magnesium, manganese, iron, titanium, and zirconium to stabilize the bulk structure and reduce structural degradation under higher voltages (>4.9V). However, elemental doping only stabilizes the bulk structure; the surface structure remains unstable. Under higher voltages (>4.9V), the surface structure still releases oxygen ions, causing electrolyte oxidation and decomposition, worsening the material structure, leading to rapid capacity decay and gas production in the secondary battery. Others have proposed coating the surface of LCP materials with inert oxides such as alumina, titanium oxide, lanthanum oxide, and zirconium oxide to reduce the contact area between the electrolyte and the LCP material, thereby reducing the corrosion of the material surface by hydrofluoric acid produced by electrolyte decomposition under higher voltages (>4.9V) and improving the cycle life of the secondary battery. While the surface oxide coating can reduce contact with acidic substances after the electrolyte's oxidation and decomposition, thus protecting lithium cobalt phosphate materials from corrosion, the intrinsic problem of oxygen ion release remains unresolved, and the following issues persist: 1. The inert oxide phase has weak lithium-ion transport performance. The olivine-structured lithium cobalt phosphate has a one-dimensional lithium-ion transport channel, and the oxide coating severely hinders lithium insertion and extraction, deteriorating the capacity of the secondary battery. 2. During the charging-discharging process, the lattice of lithium cobalt phosphate materials repeatedly contracts and expands. Due to the contraction and expansion forces, the core-shell structure coating layer is prone to detachment, exposing the lithium cobalt phosphate material itself, leading to corrosion and structural degradation. 3. The hydrofluoric acid produced after the electrolyte's oxidation and decomposition is highly corrosive and reacts chemically with the lithium cobalt phosphate material, causing metal ions to dissolve and deposit on the negative electrode, continuously consuming active lithium and rapidly reducing the cell capacity.

[0099] Based on the above considerations, in order to improve the problem of oxygen ions released from lithium cobalt phosphate materials reacting with the electrolyte in an oxidation reaction, this application proposes a secondary battery. The secondary battery includes a positive electrode sheet, the positive electrode sheet includes a positive active material layer, the positive active material layer includes a positive active material, the positive active material includes a first positive active material, the first positive active material includes a core and a shell layer covering the core, the core includes a lithium cobalt phosphate material, the shell layer includes a first sublayer, and the material of the first sublayer has oxygen vacancies.

[0100] This secondary battery uses a first sublayer with oxygen vacancies to coat a lithium cobalt phosphate material. This first sublayer can capture oxygen ions released by the lithium cobalt phosphate material under higher voltages during the operation of the secondary battery, thereby reducing the possibility of electrolyte oxidation and decomposition, improving gas production and swelling of the secondary battery, and also reducing acid production. This reduces the dissolution of cobalt, a metallic element, from the lithium cobalt phosphate material, resulting in a better cycle life for the secondary battery.

[0101] This secondary battery can be used in electrical equipment such as vehicles, ships, or aircraft. The power system of such electrical equipment can be constructed using the secondary battery disclosed in this application.

[0102] This application provides an electrical device that uses a battery as a power source. The electrical device can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0103] For ease of explanation, the following embodiments will use a vehicle as an example of an electrical device according to an embodiment of this application.

[0104] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of a vehicle provided in some embodiments of this application. The vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A secondary battery 100 is installed inside the vehicle 1000, and the secondary battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The secondary battery 100 can be used to power the vehicle 1000; for example, the secondary battery 100 can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 300 and a motor 200. The controller 300 is used to control the secondary battery 100 to supply power to the motor 200, for example, to meet the power needs of the vehicle 1000 during startup, navigation, and driving.

[0105] In some embodiments of this application, the secondary battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0106] In this application, the secondary battery 100 can refer to a single battery cell 20, or it can refer to a single physical module comprising multiple battery cells 20 to provide higher voltage and capacity, which can be in the form of a battery pack, battery module, etc. The secondary battery 100 may include a housing 10 for encapsulating multiple battery cells 20, and the housing 10 can prevent liquids or other foreign objects from affecting the charging or discharging of the battery cells 20.

[0107] Figure 2 This is an exploded structural diagram of a secondary battery 100 provided in some embodiments of this application. Please refer to... Figure 2 The secondary battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10.

[0108] The housing 10 provides a receiving space 11 for the battery cell 20. In some embodiments, the housing 10 may include a first portion 12 and a second portion 13, which overlap each other to define the receiving space 11 for accommodating the battery cell 20. Of course, the connection between the first portion 12 and the second portion 13 may be sealed by a sealant (not shown), such as a sealing ring, sealant, etc.

[0109] The first part 12 and the second part 13 can be of various shapes, such as cuboids, cylinders, etc. The first part 12 can be a hollow structure with an opening on one side to form a cavity for accommodating the battery cell 20, and the second part 13 can also be a hollow structure with an opening on one side to form a cavity for accommodating the battery cell 20. When the opening side of the second part 13 covers the opening side of the first part 12, a housing 10 with an accommodating space 11 is formed. Of course, as... Figure 2 As shown, the first part 12 can also be a hollow structure with an opening on one side, and the second part 13 can be a plate-like structure. The second part 13 covers the opening side of the first part 12, thus forming a box 10 with a accommodating space 11.

[0110] In the secondary 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 mixed configuration. A mixed configuration means that multiple battery cells 20 are connected in both series and parallel. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed configuration, and then the whole assembly of multiple battery cells 20 is housed in the housing 10. Alternatively, multiple battery cells 20 can first be connected in series, parallel, or in a mixed configuration to form a battery module, and then multiple battery modules can be connected in series, parallel, or in a mixed configuration to form a whole assembly, which is then housed in the housing 10. The battery cell 20 can be cylindrical, flat, cuboid, or other shapes. Figure 2 An example is shown where the battery cell 20 is square.

[0111] In some embodiments, the secondary battery 100 may further include a busbar (not shown), through which multiple battery cells 20 can be electrically connected to each other to achieve series, parallel, or mixed connection of multiple battery cells 20.

[0112] Figure 3 This is a schematic diagram of the structure of a battery cell 20 provided in some embodiments of this application. Figure 4 Exploded views of a battery cell 20 provided for some embodiments of this application. Please refer to... Figure 3 and Figure 4The 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 housed within the housing 21, and the end cap assembly 22 is used to seal the opening 211.

[0113] The shape of the outer casing 21 can be determined according to the specific shape of the electrode assembly 23. For example, if the electrode assembly 23 is a cuboid structure, the outer casing 21 can be a cuboid structure. Figure 3 and Figure 4 An example is shown where the housing 21 and electrode assembly 23 are square.

[0114] The outer shell 21 can also be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc. This application embodiment does not impose any special restrictions on this.

[0115] The end cap assembly 22 includes an end cap 221 and electrode terminals 222. The end cap assembly 22 is used to seal the opening 211 of the housing 21 to form a sealed mounting space (not shown) for accommodating the electrode assembly 23. The mounting space also accommodates an electrolyte, such as an electrolyte solution. As a component that outputs electrical energy to the electrode assembly 23, the end cap assembly 22 has electrode terminals 222 for electrical connection to the electrode assembly 23, specifically, the electrode terminals 222 are electrically connected to the tabs of the electrode assembly 23. For example, the electrode terminals 222 and the tabs are connected via a current collector 24 to achieve the electrical connection between the electrode terminals 222 and the tabs.

[0116] It should be noted that the opening 211 of the outer casing 21 can be one or two. If the outer casing 21 has one opening 211, the end cap assembly 22 can also be one, and two electrode terminals 222 can be provided in the end cap assembly 22. The two electrode terminals 222 are used to electrically connect to the positive electrode tab and the negative electrode tab of the electrode assembly 23, respectively. If the outer casing 21 has two openings 211, for example, the two openings 211 are located on opposite sides of the outer casing 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 casing 21. In this case, the electrode terminal 222 in one end cap assembly 22 can be a positive electrode terminal, used to electrically connect to 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, used to electrically connect to the negative electrode plate of the electrode assembly 23.

[0117] In some embodiments, such as Figure 4As shown, the battery cell 20 may further include an insulating protective member 25 fixed to the outer periphery of the electrode assembly 23. The insulating protective member 25 is used to insulate and isolate the electrode assembly 23 from the housing 21. Exemplarily, the insulating protective member 25 is adhesive tape bonded to the outer periphery of the electrode assembly 23. In some embodiments, there are multiple electrode assemblies 23, and the insulating protective member 25 surrounds the outer periphery of multiple electrode assemblies 23, forming a single integral structure to maintain the structural stability of the electrode assembly 23.

[0118] The electrode assembly 23 includes a positive electrode, a negative electrode, and a separator. The electrode assembly 23 can be a wound electrode assembly 23 or a stacked electrode assembly 23, and the embodiments of this application are not limited thereto.

[0119] The positive electrode sheet includes a positive current collector and a positive active material layer. The positive active material layer is coated on the surface of the positive current collector. The positive current collector without the positive active material layer protrudes from the positive current collector with the positive active material layer. The positive current collector without the positive active material layer serves as the positive electrode tab.

[0120] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0121] In some embodiments, when the secondary battery 100 is a lithium-ion battery, the positive electrode active material may be any one or more lithium cobalt phosphate-based materials provided in the embodiments of this application, as well as positive electrode active materials for lithium-ion batteries other than lithium cobalt phosphate-based materials known in the art. As an example, positive electrode active materials other than lithium cobalt phosphate-based materials may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNiO2). 1 / 3 Co 1 / 3 Mn1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 At least one of lithium nickel cobalt aluminum oxides and their modified compounds. Examples of lithium-containing phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0122] In some embodiments, when the secondary battery 100 is a sodium-ion battery, the positive electrode active material may be any one or more lithium cobalt phosphate-based materials known in the art for use in sodium-ion batteries, as well as those provided in the embodiments of this application. For example, at least one of sodium transition metal oxides, polyanionic compounds, and Prussian blue-based compounds may be used. However, this application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used.

[0123] As an optional technical solution in this application, the transition metal in the sodium transition metal oxide can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na. x M02, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, 0 <x≤1。

[0124] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (Y04). n-The price state.

[0125] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0126] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y ) n+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (Y04). n- The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) n+ The valence state; the halogen can be at least one of F, Cl and Br.

[0127] Polyanionic compounds include, for example, NaFePO4, Na3V2(PO4)3, NaM'PO4F (where M' is one or more of V, Fe, Mn, and Ni) and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0128] Prussian blue compounds can be a class of compounds containing sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Examples of Prussian blue compounds include Na. a Me b Me' c (CN)6 where Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 <a≤2,0<b<1,0<c<1。

[0129] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0130] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0131] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0132] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is coated on the surface of the negative electrode current collector. The negative electrode current collector without the negative electrode active material layer protrudes from the negative electrode current collector with the negative electrode active material layer. The negative electrode current collector without the negative electrode active material layer serves as the negative electrode tab.

[0133] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0134] In some embodiments, the negative electrode active material layer includes a negative electrode active material, which may be a negative electrode active material known in the art for use in batteries. 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, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0135] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0136] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0137] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0138] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0139] In other embodiments, the current collector of the negative electrode sheet may also include a current collector body and a base coating. The base coating may be disposed on at least one side of the current collector body. The base coating basically does not contain negative electrode active material, but may contain a small amount of carbon material. However, the carbon material forms a thin coating and cannot function as a negative electrode active material. In this embodiment, the negative electrode sheet can be an electrode sheet without a negative electrode active material layer. For a negative electrode sheet without a negative electrode active material layer, when the current collector of the negative electrode sheet does not contain a base coating, the film layer of the negative electrode sheet can be disposed on the surface of at least one side of the current collector body; when the current collector of the negative electrode sheet includes a base coating, the film layer of the negative electrode sheet can be disposed on the surface of the base coating away from the current collector body.

[0140] In some implementations, in order to ensure that a large current can pass through without melting, there are multiple positive electrode tabs stacked together, and multiple negative electrode tabs stacked together.

[0141] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0142] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0143] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0144] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0145] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0146] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0147] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0148] This application provides a secondary battery, which includes a positive electrode sheet, a positive electrode active material layer, a positive electrode active material layer, and a first positive electrode active material. The first positive electrode active material includes a core and a shell layer covering the core. The core includes a lithium cobalt phosphate material, and the shell layer includes a first sublayer. The material of the first sublayer has oxygen vacancies.

[0149] Lithium cobalt phosphate materials refer to at least one of lithium cobalt phosphate (LiCoPO4) and its modified materials, which may include coating, mixing or doping with other materials or elements.

[0150] The presence of oxygen vacancies in the first sublayer material refers to the detachment of oxygen atoms (oxygen ions) from the crystal lattice in metal oxides or other oxygen-containing compounds, resulting in oxygen loss and the formation of vacancies. Simply put, it refers to the defects left by oxygen ions escaping from the crystal lattice. These can be characterized using XPS (X-ray photoelectron spectroscopy), where the peaks of lattice oxygen and defect oxygen are clearly distinguishable (e.g., ...). Figure 8 (As shown).

[0151] It is understandable that the positive electrode active material can be only the first positive electrode active material, or it can be mixed with other lithium-containing positive electrode active materials or sodium-containing positive electrode active materials.

[0152] The secondary battery 100 coats a first sublayer with oxygen vacancies onto a lithium cobalt phosphate material. This first sublayer can capture oxygen ions released by the lithium cobalt phosphate material under higher voltages during the operation of the secondary battery, thereby reducing the possibility of electrolyte oxidation and decomposition, improving gas production and swelling of the secondary battery, and also reducing acid production. This, in turn, reduces the dissolution of cobalt, a metallic element, from the lithium cobalt phosphate material, giving the secondary battery a better cycle life.

[0153] In the technical solution of this application embodiment, the oxygen vacancy content of the material of the first sublayer is not less than 20%.

[0154] Oxygen vacancy content refers to the value of the defect oxygen peak area / (lattice oxygen peak area + defect oxygen peak area) after the material is characterized by X-ray photoelectron spectroscopy (O1S).

[0155] The more oxygen vacancies a material has, the more oxygen ions it can capture from lithium cobalt phosphate materials. By controlling the oxygen vacancy content of the first sublayer material to be no less than 20%, it is possible to fully capture oxygen ions released from lithium cobalt phosphate materials, effectively reducing the possibility of electrolyte oxidation and decomposition, and improving the problem of secondary battery swelling caused by gas generation. It also reduces acid production, thereby reducing the dissolution of cobalt, a plating metal element, from lithium cobalt phosphate materials, resulting in a better cycle life for the secondary battery.

[0156] Furthermore, the oxygen vacancy content of the first sublayer material is 30%–40%. A higher oxygen vacancy content results in lower stability. By controlling the oxygen vacancy content of the first sublayer material to 30%–40%, it achieves better stability and a better oxygen ion capture effect. This effectively captures oxygen ions released from lithium cobalt phosphate materials, reducing the possibility of electrolyte oxidation and decomposition, and mitigating the problem of secondary battery swelling caused by gas generation. It also reduces acid production, thereby reducing the dissolution of cobalt, a plating element, from lithium cobalt phosphate materials, resulting in a better cycle life for the secondary battery.

[0157] For example, the oxygen vacancy content of the material in the first sublayer can be 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, etc., or it can be any value in the range of not less than 20%.

[0158] In the technical solution of this application embodiment, the core and the first sub-layer are in direct contact, and the contact area between the core and the first sub-layer has a transition layer, which contains all the elements of the material of the first sub-layer.

[0159] The method for detecting whether the transition layer contains the material elements of the first sublayer can be as follows: first, determine the material and thickness of the first sublayer, and then use X-ray electron spectroscopy etching test method to detect elements at different depths to determine whether the elements of the first sublayer material can be identified.

[0160] In the technical solution of this application embodiment, by embedding the elements of the first sublayer material into the core to form a transition layer, the material of the first sublayer and the lithium cobalt phosphate material in the transition layer share oxygen atoms, causing electron transfer in the lithium cobalt phosphate material in the transition layer, enhancing its electronegativity to oxygen ions, playing an oxygen-locking effect, and reducing the probability of oxygen ion evolution in the lithium cobalt phosphate material of the surface transition layer.

[0161] In the technical solution of this application embodiment, the material of the first sublayer includes perovskite oxide. Perovskite oxide refers to a class of inorganic materials having a perovskite structure (generally cubic or octahedral in shape).

[0162] Perovskite oxides typically possess oxygen vacancies and acid resistance, making them beneficial for improving gas bulging and cycle life in secondary batteries when used as the first sublayer material.

[0163] In the technical solution of this application embodiment, the material of the first sub-layer includes N. a O b N includes at least one of magnesium, calcium, cobalt, nickel, copper, zinc, aluminum, gallium, scandium, yttrium, lanthanum, titanium, chromium, vanadium, niobium, zirconium, or molybdenum, 0.5 ≥ a ≥ 0.1, b = Va / 2, and V is the valence number of element N.

[0164] For example, the material of the first sublayer can be La2Mo2O9, CeO2, RuO2, Al2O3, ZnO2, LaMnO, LaCoO3, SrTiO3, BiFeO3, CaTiO3, CaFeO3, LaCo 0.12 Mn 0.88 O3, CsLaNb2O7, KLaNb2O7 or Pr 0.4 Sr 0.6 (Co0.7 Fe 0.2 Nb 0.1 )O etc.

[0165] In the technical solution of this application embodiment, the first sub-layer includes multiple attachment point layers, which are spaced apart on the core surface. By distributing the multiple attachment point layers spaced apart on the core surface, the entire first sub-layer is distributed in an "island" shape (e.g., Figure 7 As shown in the figure, it can reduce the influence of the first sublayer on the electron and ion transport of the entire first positive electrode active material, which is beneficial to its rate performance and its own capacity.

[0166] In the technical solution of this application embodiment, the mass percentage of the first sublayer in the first positive electrode active material is no more than 5%. The lower the mass percentage of the first sublayer, the better it is to reduce the impact on the electron and ion transport of the entire first positive electrode active material. By controlling the mass percentage of the first sublayer to be no more than 5%, the first positive electrode active material can have better rate performance and its own capacity can be fully utilized.

[0167] Furthermore, in the first positive electrode active material, the mass percentage of the first sublayer is 0.5% to 4%. A higher mass percentage of the first sublayer is more conducive to capturing oxygen ions released from lithium cobalt phosphate materials. By controlling the mass percentage of the first sublayer to 0.5% to 4%, oxygen ions released from lithium cobalt phosphate materials can be effectively captured, reducing the possibility of electrolyte oxidation and decomposition, and improving the problem of secondary battery swelling caused by gas generation. It also reduces acid production, thereby reducing the dissolution of cobalt, a plating element, from lithium cobalt phosphate materials, resulting in a better cycle life for the secondary battery. Additionally, it also ensures that the first positive electrode active material has good rate performance and its own capacity.

[0168] For example, the quality percentage of the first sub-layer can be 0.1%, 0.5%, 0.7%, 1.3%, 1.5%, 1.7%, 2%, 2.3%, 2.5%, 2.7%, 3%, 3.2%, 3.5%, 3.7%, 4%, 4.3%, 4.5%, 4.7%, 5%, etc., or it can be any value within the range of no more than 5%.

[0169] In the technical solution of this application embodiment, the shell layer further includes a second sub-layer, the material of which is carbon. By setting the second sub-layer on the surface of the lithium cobalt phosphate material to form a carbon coating, the electronic conductivity of the entire first positive electrode active material is improved.

[0170] In the technical solution of this application embodiment, the first sub-layer is disposed between the core and the second sub-layer. Disposing the first sub-layer between the core and the second sub-layer facilitates the "oxygen-locking" effect of the material in the first sub-layer on the lithium cobalt phosphate-based material, reducing the probability of oxygen ion evolution on the surface of the lithium cobalt phosphate-based material. Of course, in other embodiments, the positional relationship between the first and second sub-layers can also be that the second sub-layer is disposed between the core and the first sub-layer; this application does not impose limitations on this.

[0171] In the technical solution of this application embodiment, the mass percentage of the second sublayer in the first positive electrode active material is 0.1% to 5%. A higher mass percentage of the second sublayer is more beneficial to the electronic conductivity of the entire first positive electrode active material, while a lower mass percentage is more beneficial to the specific capacity of the entire first positive electrode active material. By controlling the mass percentage of the second sublayer to 0.1% to 5%, both the electronic conductivity and specific capacity of the first positive electrode active material can be balanced.

[0172] For example, the quality percentage of the second sub-layer can be 0.1%, 0.5%, 0.7%, 1.3%, 1.5%, 1.7%, 2%, 2.3%, 2.5%, 2.7%, 3%, 3.2%, 3.5%, 3.7%, 4%, 4.3%, 4.5%, 4.7%, 5%, etc., or it can be any value within the range of no more than 0.1% to 5%.

[0173] In the technical solution of this application embodiment, the lithium cobalt phosphate material includes: LiMPO4, where M includes Co and non-Co elements.

[0174] It should be noted that the above LiMPO4 is not a specific molecular structure formula, but a general expression of the Co-containing phosphate of lithium.

[0175] In some embodiments of this application, the non-Co element includes one or both of a first doping element and a second doping element, wherein the first doping element is cobalt-site doping and the second doping element is phosphorus-site doping.

[0176] In some embodiments of this application, the first doping element includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Ga, Sn, Sb, Nb, and Ge.

[0177] In some embodiments of this application, the first doping element includes at least two of Mn, Ti, V, Ni, Fe, and Mg.

[0178] In some embodiments of this application, the second doping element includes one or more elements selected from B, S, Si, and N.

[0179] In some embodiments of this application, the lithium cobalt phosphate material includes Li 1+x Co 1-y A y P 1-z R z O4, wherein is any value in the range of -0.100 to 0.100; y is any value in the range of 0.001 to 0.500; z is any value in the range of 0.001 to 0.100; A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Mn, Ni, Fe, Ga, Sn, Sb, Nb and Ge; and R includes one or more elements selected from B, S, Si and N.

[0180] In some embodiments of the technical solutions of this application, the compound Li 1+x Co 1-y A y P 1-z R z The method for preparing O4 may include the following steps:

[0181] (1) Dissolve and stir the iron source, the cobalt-doped element A source and acid in a solvent to generate a suspension of iron salt doped with element A. Filter the suspension and dry the filter cake to obtain cobalt salt doped with element A.

[0182] (2) The lithium source, phosphorus source, element R source, solvent and cobalt salt doped with element A obtained in step (1) are added to the reaction vessel, ground and mixed to obtain a slurry;

[0183] (3) The slurry obtained in step (2) is transferred to a spray drying equipment for spray drying and granulation to obtain granules;

[0184] (4) The particles obtained in step (3) are sintered to obtain compound Li. 1+x Co 1-y A y P 1-z R z O4.

[0185] In any embodiment, the cobalt source may be an iron-containing substance known in the art for the preparation of lithium cobalt phosphate, such as elemental cobalt, cobalt oxides, cobalt phosphate, cobalt oxalate, cobalt carbonate, or a combination thereof.

[0186] The acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and organic acids such as oxalic acid, for example, oxalic acid. The source of element R is selected from at least one of sulfates, borates, nitrates, and silicates of element R. The source of element A is selected from at least one of the elemental form, oxide, phosphate, oxalate, carbonate, and sulfate of A.

[0187] In some embodiments of this application, the cobalt-lithium phosphate material includes Li... a A e Co 1-f B f P 1-g C g O 4-n D n The positive electrode active material is electrically neutral. Specifically, A comprises one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; B comprises one or more elements selected from Ti, V, Zr, Mn, Ni, Mg, Fe, Ga, Sn, Sb, Nb, and Ge; C comprises one or more elements selected from B, S, Si, and N; D comprises one or more elements selected from S, F, Cl, and Br; a is selected from the range of 0.9 to 1.1; e is selected from the range of 0.001 to 0.1; f is selected from the range of 0.001 to 0.5; g is selected from the range of 0.001 to 0.1; n is selected from the range of 0.001 to 0.1.

[0188] It should be noted that Li a A e Co 1-f B f P 1-g C g O 4-n D n The compound is actually a specific LiMPO4 material. Its preparation method can be found in the Li... 1+x Co 1-y A y P 1-z R z O4 is not specified here.

[0189] The following uses Li 0.994 Mo 0.001 Mn 0.65 Co 0.35 P 0.999 Si 0.001 O 3.999 F 0.001The preparation process is further explained as follows: 1. Preparation of doped material: 1.3 mol of MnSO4·H2O and 0.7 mol of CoSO4·H2O were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction vessel, and 10 L of deionized water and 2 mol of oxalic acid dihydrate (calculated as oxalic acid) were added. The reaction vessel was heated to 80°C and stirred at 600 rpm for 6 hours until the reaction was terminated (no bubbles were generated), resulting in a doped suspension. The suspension was then filtered, and the filter cake was dried at 120°C and then ground to obtain the median particle size Dv. 50 The doped particles are approximately 100 nm in size. 2. Preparation of Li 0.994 Mo 0.001 Mn 0.65 Co 0.35 P 0.999 Si 0.001 O 3.999 F 0.001 1 mol of the above-mentioned doped particles, 0.497 mol of lithium carbonate, 0.001 mol of Mo(SO4)3, an 85% phosphoric acid aqueous solution containing 0.999 mol of phosphoric acid, 0.001 mol of H4SiO4, and 0.0005 mol of NH4HF2 were added to 20 L of deionized water. The mixture was transferred to a sand mill and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was then transferred to a spray drying equipment for spray drying granulation. The drying temperature was set at 250°C and the drying time was 4 hours to obtain granules. Under a protective atmosphere of nitrogen (90 vol%) + hydrogen (10 vol%), the above powder was sintered at 700°C for 10 hours to obtain Li. 0.994 Mo 0.001 Mn 0.65 Co 0.35 P 0.999 Si 0.001 O 3.999 F 0.001 .

[0190] It should be noted that during the charging and discharging process, Li or Na undergoes insertion / extraction and consumption, resulting in different molar contents of Li or Na at different discharge states. In the examples of positive electrode active materials in this application, the molar contents of Li or Na refer to the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to the battery system, the molar contents of Li or Na will change after charge-discharge cycles.

[0191] In the examples of positive electrode active materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0192] In some embodiments of this application, the core includes a core and a surface layer attached to the outside of the core. The core includes a first lithium cobalt phosphate material, and the surface layer includes a second lithium cobalt phosphate material. The second lithium cobalt phosphate material is doped with at least one of La, Mo, Y, or Sc. The total molar content of La, Mo, Y, and Sc in the second lithium cobalt phosphate material is greater than the total molar content of La, Mo, Y, and Sc in the first lithium cobalt phosphate material. By making the total molar content of La, Mo, Y, and Sc in the second lithium cobalt phosphate material of the surface layer greater than the total molar content of La, Mo, Y, and Sc in the first lithium cobalt phosphate material of the core, the cross-sectional structure of the core particles can be stabilized.

[0193] Having introduced the materials and structure of secondary batteries, the following section will provide a detailed description of their preparation methods.

[0194] Figure 5 Please refer to the schematic diagram of the process for preparing secondary batteries according to some embodiments of this application. Figure 5 The method for preparing a secondary battery provided in this application includes the following steps:

[0195] S0. Obtain lithium cobalt phosphate materials;

[0196] S1. Mix lithium cobalt phosphate materials and shell raw materials in a solvent, and then dry and granulate them to obtain intermediate powder.

[0197] S2. The intermediate powder is sintered to obtain a positive electrode active material with a first sublayer, wherein the material of the first sublayer has oxygen vacancies.

[0198] S3. Carbon coating is applied to the positive electrode active material.

[0199] S4. The carbon-coated positive electrode active material is prepared into a positive electrode sheet, and then assembled with a separator and a negative electrode sheet to obtain an electrode assembly.

[0200] The assembly of the separator, positive electrode, and negative electrode can be either wound or stacked. Specifically, the separator, positive electrode, separator, and negative electrode are stacked sequentially, wound to form a flat structure, and then hot-pressed to obtain a wound electrode assembly; or, after preparing the positive electrode, the positive electrode, separator, negative electrode, separator, and so on are stacked sequentially to form a stacked electrode assembly.

[0201] S5. Assemble the electrolysis components to obtain a secondary battery.

[0202] The specific process for obtaining lithium cobalt phosphate materials is as follows: Cobalt source is dissolved in deionized water to obtain solution A; lithium source is dissolved in deionized water to obtain solution B; phosphoric acid is slowly added to solution A and stirred for 30 minutes to obtain solution C; then solution B is slowly added to solution C and stirred for 1 hour to obtain a mixed suspension; the suspension is poured into the inner liner of a reaction vessel and placed in a metal container; the hydrothermal reaction vessel is placed in a muffle furnace for heating and holding, followed by natural cooling; after the reaction is complete and cooled to room temperature, the inner liner of the reaction vessel is removed, and the precipitate and liquid are poured out. The obtained precipitate is filtered, washed, and dried to obtain the lithium cobalt phosphate precursor. The powder of the lithium cobalt phosphate precursor is placed in a nitrogen-filled box-type atmosphere furnace for sintering; after cooling, the material is pulverized and sieved to obtain the lithium cobalt phosphate material.

[0203] The shell material can be lanthanum source, molybdenum source, etc. Taking the preparation of lanthanum molybdate as the first shell material as an example, the specific preparation process is as follows: Lithium cobalt phosphate material powder is mixed with deionized water to obtain suspension D. Lanthanum oxide and molybdenum oxide are added to deionized water to obtain suspension E. The particle size of suspension E is ground with a sand mill until the median particle size Dv50 of the solid phase is 0.4 μm to obtain suspension F. Suspension F is added to suspension D and stirred continuously with a stirrer. Then, it is spray dried. The spray-dried powder is placed in a nitrogen box-type atmosphere furnace for sintering. Then, it is cooled to room temperature. After cooling, the material is crushed and sieved to obtain a positive electrode active material with lithium cobalt phosphate (LiCoPO4) as the core and lanthanum molybdate with oxygen-rich vacancies as the first sublayer of the coating.

[0204] The carbon coating process can be as follows: the first sublayer of the coating layer obtained above is a positive electrode active material composed of lanthanum molybdate rich in oxygen vacancies. It is placed in the rotating sample barrel of a plasma-enhanced chemical vapor deposition (RPS) device. After evacuation, methane and hydrogen are introduced as a mixed gas. The carbon deposition coating reaction is carried out in the RPS device. After the reaction is completed, the material is sieved.

[0205] In some embodiments of this application, the median particle size Dv50 of the lithium cobalt phosphate material is 1 μm to 5 μm, and the median particle size Dv50 of the shell material is 200 nm to 500 nm. By controlling the median particle size Dv50 of the lithium cobalt phosphate material to be 1 μm to 5 μm and the median particle size Dv50 of the shell material to be 200 nm to 500 nm, a particle size difference is created, which is beneficial for the shell material to adhere to the lithium cobalt phosphate material and form a coating layer.

[0206] For example, the median particle size Dv50 of lithium cobalt phosphate materials can be 1μm, 1.2μm, 1.4μm, 1.6μm, 1.8μm, 2μm, 2.2μm, 2.4μm, 2.6μm, 2.8μm, 3μm, 3.2μm, 3.4μm, 3.6μm, 3.8μm, 4μm, 4.2μm, 4.4μm, 4.6μm, 4.8μm, 5μm, etc., or it can be any value in the range of 1μm to 5μm. The median particle size Dv50 of the shell material can be 200nm, 220nm, 240nm, 260nm, 280nm, 300nm, 320nm, 340nm, 360nm, 380nm, 400nm, 420nm, 440nm, 460nm, 480nm, 500nm, etc., or it can be any value in the range of 200nm to 500nm.

[0207] In some embodiments of this application, the method further includes carbon coating of the positive electrode active material, wherein the carbon coating method includes chemical vapor deposition. The chemical vapor deposition can be microwave plasma-enhanced chemical vapor deposition, radio frequency plasma-enhanced chemical vapor deposition, bias plasma-enhanced chemical vapor deposition, etc. By using chemical vapor deposition for carbon coating, the probability of the first sublayer material being reacted into oxygen-free vacancy material during the carbon coating process, thus reducing the oxygen ion capture capacity, can be reduced.

[0208] In some embodiments of this application, the lithium source used to obtain lithium cobalt phosphate materials includes at least one of lithium nitrate, lithium tetraborate, lithium fluoride, or lithium metaborate. By using lithium nitrate, lithium tetraborate, lithium fluoride, or lithium metaborate as the lithium source, the sintering temperature of lithium cobalt phosphate materials can be reduced, allowing the core and coating layer to be prepared in a single sintering process, thus enabling in-situ coating.

[0209] The following examples will describe one or more embodiments in more detail. Of course, these examples do not limit the scope of the one or more embodiments.

[0210] Example 1

[0211] A positive electrode active material, the preparation process of which is as follows:

[0212] (1) After cobalt nitrate is dissolved in deionized water to obtain solution A, lithium hydroxide is dissolved in deionized water to obtain solution B. Phosphoric acid is slowly added to solution A and stirred for 30 min to obtain solution C. Then, solution B is slowly added to solution C and stirred for 1 h to obtain a mixed suspension. The suspension is poured into the inner liner of the reactor and placed in a metal container. The hydrothermal reactor is placed in a muffle furnace and heated to 220°C at 2°C / min. After holding at the temperature for 5 h, it is allowed to cool naturally. After the reaction is completed and cooled to room temperature, the inner liner of the reactor is removed, and the precipitate and liquid are poured out. The precipitate is filtered, washed, and dried to obtain the lithium cobalt phosphate precursor with the chemical formula LiCoPO4.

[0213] In the suspension, the molar ratio of lithium, cobalt, and phosphorus is 1:1:1; the concentration of cobalt nitrate in solution A is 2 mol / L; the concentration of lithium hydroxide in solution B is 4.29 mol / L; and the concentration of phosphoric acid is 85%.

[0214] (2) The powder from step (1) is placed in a nitrogen box-type atmosphere furnace and heated from room temperature to 700°C at a heating rate of 2°C / min. It is sintered for 16 hours. After cooling, the material is crushed and sieved to obtain lithium cobalt phosphate material.

[0215] Among them, the Dv50 of the lithium cobalt phosphate (LiCoPO4) matrix material is 1-3 μm, and the pore size of the sieve is 38 μm;

[0216] (3) The powder from step (2) is mixed with deionized water at a mass ratio of 2:8 to obtain suspension D. The raw materials of the first sublayer, lanthanum oxide and molybdenum oxide, are added to deionized water to obtain suspension E. The particle size of suspension E is ground to D50 of 0.4 μm using a sand mill to obtain suspension F. Suspension F is added to suspension D and stirred continuously using a stirrer. Then, spray drying is carried out under the conditions of inlet air temperature of 210℃ and outlet air temperature of 100℃.

[0217] The purity of lanthanum oxide is 99.8%, the purity of molybdenum oxide is 99.5%, the molar ratio of lanthanum oxide to molybdenum oxide is 1:2, and the mass ratio of lanthanum oxide + molybdenum oxide to deionized water is 1:9; the stirring speed is 600 rpm / min, and the peristaltic pump feeding rate of the spray dryer is 10 rpm / min.

[0218] (4) The spray-dried powder is placed in a nitrogen box-type atmosphere furnace and heated from room temperature to 500°C at a heating rate of 2°C / min. It is sintered for 12 hours and then cooled to room temperature at a slow rate of 1°C / min. After cooling, the material is crushed and sieved to obtain a positive electrode active material with a core of lithium cobalt phosphate and a first sublayer in the coating layer composed of lanthanum molybdate rich in oxygen vacancies (oxygen vacancies are 34.72%).

[0219] The first sublayer accounts for 0.3% of the mass of the positive electrode active material.

[0220] (5) Place the powder from step (4) in the rotating sample barrel of the plasma-enhanced chemical vapor deposition equipment. After evacuation, introduce methane and hydrogen as a mixed gas. Under the conditions of RPS (plasma generator) power of 800W and bias power of 200W, perform carbon deposition coating reaction for 5 minutes. After the reaction is completed, sieve the material to obtain a lithium cobalt phosphate cathode material with a core of lithium cobalt phosphate (LiCoPO4) - a first sublayer of lanthanum molybdate (La2Mo2O9) distributed in an "island" shape - and a second sublayer of carbon deposition coating.

[0221] The flow rate of methane (CH4) was 100 ml / min, the flow rate of hydrogen (H2) was 1500 ml / min, the rotation speed of the rotating sample container was 9 rpm / min, and the sieve aperture was 38 μm.

[0222] The elemental distribution of the positive electrode active material provided in Example 1 was tested, and the results are as follows: Figure 6 As shown in the figure, lanthanum and molybdenum are uniformly distributed on the surface of the positive electrode active material particles.

[0223] The surface morphology of the positive electrode active material provided in Example 1 was tested, and the results are as follows: Figure 7 As shown in the figure, the first sublayer is distributed in an "island" shape and is covered with a carbon layer on the outside.

[0224] XPS testing was performed on the positive electrode active material provided in Example 1, and the results are as follows: Figure 8 As shown in the figure, the oxygen vacancy rate of the positive electrode active material prepared in Example 1 is approximately 34.72%.

[0225] XRD tests were performed on the positive electrode active material provided in Example 1, and the results are as follows: Figure 9 As shown in the figure, the main peak of the positive electrode active material prepared in Example 1 corresponds completely with the standard card of olivine-type lithium cobalt phosphate, indicating that the material synthesized in this example is indeed an olivine-type lithium cobalt phosphate material and that the coating does not affect the structure of the positive electrode active material.

[0226] Example 2

[0227] In this embodiment, except for step (4), which is adjusted to: placing the spray-dried powder into a nitrogen box-type atmosphere furnace, heating it from room temperature to 500°C at a heating rate of 2°C / min, sintering it for 12 hours, and then slowly cooling it back to room temperature at a rate of 5°C / min so that the oxygen vacancy content of the first sublayer lanthanum molybdate is 15%, the rest of the steps are the same as in Example 1.

[0228] Example 3

[0229] In this embodiment, except for step (4), which is adjusted to: placing the spray-dried powder into a nitrogen box-type atmosphere furnace, heating it from room temperature to 500°C at a heating rate of 2°C / min, sintering it for 12 hours, and then slowly cooling it back to room temperature at a rate of 3°C / min so that the oxygen vacancy content of the first sublayer lanthanum molybdate is 20%, the rest of the steps are the same as in Example 1.

[0230] Example 4

[0231] In this embodiment, except for step (4), which is adjusted to: placing the spray-dried powder into a nitrogen box-type atmosphere furnace, heating it from room temperature to 500°C at a heating rate of 2°C / min, sintering it for 12 hours, and then slowly cooling it back to room temperature at a rate of 1°C / min so that the oxygen vacancy content of the first sublayer lanthanum molybdate is 40%, the rest of the steps are the same as in Example 1.

[0232] Example 5

[0233] In this embodiment, except that the raw material of the first sublayer in step (3) is replaced with perovskite-type oxide calcium titanate, the other steps are the same as in Example 1.

[0234] Example 6

[0235] In this embodiment, except that the raw material of the first sublayer in step (3) is replaced with tungsten oxide, the other steps are the same as in Example 1.

[0236] Example 7

[0237] In this embodiment, except for changing the amount of suspension F and suspension D mixed in step (3) so that the mass ratio of the first sublayer in the positive electrode active material in step (4) is 0.1%, the other steps are the same as in Example 1.

[0238] Example 8

[0239] In this embodiment, except for changing the amount of suspension F and suspension D mixed in step (3) so that the mass ratio of the first sublayer in the positive electrode active material in step (4) is 1%, the other steps are the same as in Example 1.

[0240] Example 9

[0241] In this embodiment, except for changing the amount of suspension F and suspension D mixed in step (3) so that the mass ratio of the first sublayer in the positive electrode active material in step (4) is 5%, the other steps are the same as in Example 1.

[0242] Example 10

[0243] In this embodiment, except that the first sub-layer is completely covered, the other steps are the same as in Embodiment 9.

[0244] Example 11

[0245] In this embodiment, except for swapping the positions of the first sub-layer and the second sub-layer, everything else is the same as in Embodiment 1.

[0246] Example 12

[0247] A positive electrode active material, the preparation process of which is as follows:

[0248] Steps (1) to (4) are the same as steps (1) to (4) in Example 1.

[0249] (5) The powder, glucose and anhydrous ethanol in step (4) are added to a planetary ball mill jar at a mass ratio of 1:0.08:1. Zirconium beads are added and the mixture is mixed by planetary wet ball milling for 1 hour. After the zirconium beads are removed, the mixture is dried and sieved to obtain the glucose-coated LiCoPO4 lithium cobalt phosphate precursor.

[0250] The anhydrous ethanol had a purity of 99.5%, the planetary ball milling speed was 300 rpm / min, the zirconium beads had a diameter of 1 μm, the carbon source was glucose with a purity of 99.8%, and the addition amount was 8 wt% of the theoretical yield of lithium cobalt phosphate cathode material.

[0251] 6) The powder from step (5) is placed in a nitrogen-filled furnace and heated from room temperature to 700°C at a heating rate of 2°C / min. It is then sintered for 2 hours. After cooling, the material is crushed and sieved to obtain a lithium cobalt phosphate cathode material with a core of lithium cobalt phosphate (LiCoPO4), a first sublayer of lanthanum molybdate (La2Mo2O9) distributed in an "island" pattern, and a second sublayer of carbon layer coated with carbon produced by the decomposition of carbon source.

[0252] Comparative Example 1

[0253] In this comparative example, except for steps (3) and (4) which are not performed, all other contents are the same as in Example 1.

[0254] Comparative Example 2

[0255] In this comparative example, except for steps (3), (4) and (5) not being performed, all other contents are the same as in Example 1.

[0256] The main parameter controls for Examples 1 to 11 and Comparative Examples 1 to 2 are shown in the table below:

[0257]

[0258] In the table, " / " indicates that the substance does not exist or that the limitation does not exist.

[0259] The positive electrode active materials prepared in each embodiment and comparative example were used to prepare secondary batteries. The specific preparation process is as follows:

[0260] Preparation of the positive electrode sheet

[0261] A mother liquor was prepared by mixing polyvinylidene fluoride (PVDF), conductive carbon black (Super P), and N-methylpyrrolidone (NMP) at a mass ratio of 1:1:30. The positive electrode active material and the mother liquor were then mixed at a mass ratio of 9:16 using a planetary centrifuge to obtain a homogeneous positive electrode active slurry. This slurry was then coated onto aluminum foil and dried to obtain the positive electrode sheet. The loading of the positive electrode active material on the positive electrode sheet was 97.44 μg / mm². 2 .

[0262] Preparation of the negative electrode sheet

[0263] A lithium sheet with a thickness of 0.5 mm and a diameter of 18 mm was used as the negative electrode.

[0264] Preparation of Electrolyte

[0265] Ethylene carbonate, diethyl carbonate, and dimethyl carbonate were mixed in a volume ratio of 1:1:1. LiPF6 was then dissolved in this solution to obtain an electrolyte. The concentration of LiPF6 in this electrolyte was 1 mol / L.

[0266]

Isolation Film

[0267] A 20μm thick, Φ22mm diameter polypropylene film (uncoated) was used as the release membrane.

[0268] Preparation of Secondary Battery 100

[0269] Assemble the button cell battery in a glove box according to the following assembly sequence: negative electrode shell → nickel foam (diameter Φ20mm) → lithium sheet (diameter Φ18mm) → separator (diameter Φ22mm / thickness 20um) → positive electrode sheet (diameter Φ14mm) → positive electrode shell. Before and after placing the separator, use a pipette to inject 5ul of 1mol / L LiPF6 / (EC+DMC+EMC) electrolyte onto the lithium sheet and separator, respectively. The battery model is CR2430. Electrochemical tests were performed on the assembled battery using a Land battery tester. The test charge / discharge voltage was 2.0V. 5V.

[0270] The secondary batteries 100 prepared with the positive electrode active materials provided in each embodiment and comparative example were tested, including:

[0271] Acid corrosion resistance test: ① At 25℃, the button cell was charged at a constant current of 0.1C to 5V, then charged at a constant voltage of 0.05C, and left to stand for 5 minutes. After the test, the positive electrode was disassembled and removed in a glove box (water content < 1ppm, oxygen content < 1ppm). It was then soaked and washed three times in DMC (dimethyl carbonate) for 1 hour each time to remove impurities from the surface of the positive electrode. After that, it was air-dried in a glove box (>12 hours) to obtain a delithiated lithium cobalt phosphate positive electrode. ② Ethylene carbonate, diethyl carbonate, and dimethyl carbonate were mixed in a volume ratio of 1:1:1. LiPF6 was dissolved in the above solution to obtain the electrolyte. The concentration of LiPF6 in this electrolyte was 1 mol / L. Take 99.6g of the electrolyte prepared above and place it in a fluorination bottle. Add 0.4g of ultrapure water and shake well to obtain an electrolyte with a water content of 0.4%. ③ In a glove box (water content < 1ppm, oxygen content < 1ppm), take the electrode from step ① and place it in a 25ml fluorination bottle. Add 20ml of the 0.4% water content electrolyte from step ② to the bottle. After sealing, wrap the outer layer with a sealing film to ensure that it does not come into contact with the outside air. Then, place the fluorination bottle soaking the electrode in a 60℃ constant temperature oven and store it for 4 days, 8 days, 15 days, and 30 days. ④ Take 3ml of the electrolyte stored for 4 days, 8 days, 15 days, and 30 days in step ③ and filter it quickly using an organic filter membrane. Use an inductively coupled plasma atomic emission spectrometer to test the Co element content in the filtrate.

[0272] Specific capacity test: At 25℃, the button cell was charged at a constant current of 0.1C to 5V, then charged at a constant voltage to 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 0.1C to 2V. This charge-discharge cycle was repeated twice. Next, the cell was charged at a constant current of 1C to 5V, then charged at a constant voltage to 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 1C to 2V. This charge-discharge cycle was repeated twice. Specific capacity is calculated as discharge capacity / mass of positive electrode active material (positive electrode loading * positive electrode area * 90%).

[0273] High-temperature cycle test: At 45℃, the button battery is charged at a constant current of 0.1C to a voltage of 5V, then charged at a constant voltage of 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.1C to a voltage of 2V. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is the discharge capacity of the first cycle. After performing the cycle charge test in the above manner, the cycle ends when the discharge capacity decays to 80% of the initial value. The total number of cycles is the high-temperature cycle life.

[0274] High-temperature float charge life test: Following the same battery preparation steps as described above, the difference lies in using a CR2430 aluminum-plated positive electrode shell and a 7µm thick, Φ22mm diameter uncoated Celgard 2400 separator. All other aspects remain unchanged, resulting in a button cell. At 60℃, the button cell is charged at a constant current of 0.1C to a voltage of 5V, then charged at a constant voltage for 720 hours, allowed to stand for 5 minutes, and the current change is monitored. The point in time where a sudden current change occurs is the float charge life of the positive electrode material.

[0275] The test results are shown in the table below:

[0276]

[0277]

[0278] As can be seen from the table above, the positive electrode active material provided in the embodiments of this application has good corrosion resistance, and the secondary battery prepared with it has good cycle life and float charge life.

[0279] A comparison of data from Examples 1 to 6 shows that as the proportion of oxygen vacancies in the first sublayer material gradually increases, the corrosion resistance of the positive electrode active material gradually improves, and correspondingly, the cycle life and float charge life of the secondary battery gradually improve. By controlling the oxygen vacancy content of the first sublayer material to be no less than 20%, the capacity retention rate of the secondary battery after 100 cycles is above 89%. Furthermore, a comparison of data from Examples 2 and 6 shows that selecting lanthanum molybdate as the first sublayer material enables the positive electrode active material to have better corrosion resistance and results in a better cycle life for the secondary battery.

[0280] A comparison of data from Examples 1, 7 to 9 shows that as the mass percentage of the first sublayer increases, the corrosion resistance of the positive electrode active material gradually improves. However, the discharge specific capacity of the positive electrode active material exhibits a trend of first improving and then deteriorating, and the cycle life of the secondary battery also shows a trend of first improving and then deteriorating. Controlling the mass percentage of the first sublayer to no more than 5% ensures that the 0.1C discharge specific capacity of the secondary battery is no less than 139 mAh / g, and the 1C discharge specific capacity is no less than 129 mAh / g.

[0281] A comparison of the data from Examples 9 and 10 shows that the island-shaped coating of the second sublayer is more conducive to the utilization of the capacity of the positive electrode active material, so that the 0.1C discharge specific capacity of the secondary battery is not less than 139 mAh / g and the 1C discharge specific capacity is not less than 129 mAh / g.

[0282] A comparison of the data from Examples 1 and 11 shows that placing the first sublayer in the inner layer (i.e., closer to the core) is more beneficial to the corrosion resistance of the positive electrode active material and the cycle performance of the secondary battery. The reason for this is speculated to be that during the preparation process, the material of the first sublayer penetrates the core, forming a transition layer. The material of the first sublayer and the lithium cobalt phosphate-based material in the transition layer share oxygen atoms, causing electron transfer in the lithium cobalt phosphate-based material in the transition layer, enhancing its electronegativity towards oxygen, thus achieving an oxygen-locking effect and reducing the probability of oxygen evolution from the lithium cobalt phosphate-based material in the surface transition layer.

[0283] A comparison of the data from Examples 1 and 12 shows that using vapor deposition to prepare the second sublayer (i.e., the carbon layer) is more beneficial to the corrosion resistance of the positive electrode active material and the cycle performance of the secondary battery. The reason for this is speculated to be that this method reduces the probability of the first sublayer material being reacted into oxygen-free vacancy substances during the carbon coating process, thus decreasing the oxygen ion capture capacity.

[0284] The above are merely specific embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A secondary battery, characterized in that, The secondary battery includes a positive electrode sheet, the positive electrode sheet includes a positive active material layer, the positive active material layer includes a positive active material, the positive active material includes a first positive active material, the first positive active material includes a core and a shell layer covering the core, the core includes a lithium cobalt phosphate material, the shell layer includes a first sublayer, and the material of the first sublayer has oxygen vacancies.

2. The secondary battery according to claim 1, characterized in that, The oxygen vacancy content of the material in the first sublayer is not less than 20%.

3. The secondary battery according to any one of claims 1 to 2, characterized in that, The oxygen vacancy content of the material in the first sublayer is 30% to 40%.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The core and the first sublayer are in direct contact, and the contact area between the core and the first sublayer has a transition layer containing all the elements of the material of the first sublayer.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, The material of the first sublayer includes perovskite oxide.

6. The secondary battery according to any one of claims 1 to 5, characterized in that, The material of the first sublayer includes N a O b N includes at least one of magnesium, calcium, cobalt, nickel, copper, zinc, aluminum, gallium, scandium, yttrium, lanthanum, titanium, chromium, vanadium, niobium, zirconium, or molybdenum, 0.5 ≥ a ≥ 0.1, b = Va / 2, and V is the valence number of element N.

7. The secondary battery according to any one of claims 1 to 6, characterized in that, The first sub-layer includes multiple attachment point layers, which are spaced apart on the kernel surface.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, In the first positive electrode active material, the mass percentage of the first sublayer is no more than 5%.

9. The secondary battery according to any one of claims 1 to 8, characterized in that, In the first positive electrode active material, the mass percentage of the first sublayer is 0.5% to 4%.

10. The secondary battery according to any one of claims 1 to 9, characterized in that, The shell also includes a second sublayer, with the first sublayer disposed between the core and the second sublayer, the second sublayer being made of carbon.

11. The secondary battery according to claim 10, characterized in that, In the first positive electrode active material, the second sublayer accounts for 0.1% to 5% of the total mass.

12. The secondary battery according to any one of claims 1 to 11, characterized in that, The lithium cobalt phosphate material includes LiMPO4, where M includes Co and non-Co elements. The non-Co elements include one or both of a first doping element and a second doping element, wherein the first doping element is cobalt-site doping and the second doping element is phosphorus-site doping.

13. The secondary battery according to claim 12, characterized in that, The first doping element includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Mn, Ni, Fe, Ga, Sn, Sb, Nb, and Ge; and / or The second doping element includes one or more elements selected from B, S, Si, and N.

14. The secondary battery according to any one of claims 1 to 13, characterized in that, The core includes a core and a surface layer attached to the outside of the core. The core includes a first lithium cobalt phosphate material, and the surface layer includes a second lithium cobalt phosphate material. The second lithium cobalt phosphate material is doped with at least one of La, Mo, Y, or Sc. The total molar content of La, Mo, Y, and Sc in the second lithium cobalt phosphate material is greater than the total molar content of La, Mo, Y, and Sc in the first lithium cobalt phosphate material.

15. A method for preparing a secondary battery, characterized in that, The method includes: Lithium cobalt phosphate materials were obtained; The lithium cobalt phosphate material and the shell material are mixed in a solvent and then dried and granulated to obtain an intermediate powder. The intermediate powder is sintered to obtain a positive electrode active material. The positive electrode active material includes a first positive electrode active material, which includes a core and a shell covering the core. The core includes a lithium cobalt phosphate material, and the shell includes a first sublayer. The material of the first sublayer has oxygen vacancies. The positive electrode active material is prepared into a slurry and coated onto the positive electrode current collector to obtain a positive electrode sheet; The positive electrode, separator, and negative electrode are assembled to obtain a secondary battery.

16. An electrical appliance, characterized in that, The electrical equipment includes the secondary battery according to any one of claims 1 to 14 or the secondary battery obtained by the method of claim 15.

17. A positive electrode active material, characterized in that, The positive electrode active material includes a first positive electrode active material, which includes a core and a shell covering the core. The core includes a lithium cobalt phosphate material, and the shell includes a first sublayer. The material of the first sublayer has oxygen vacancies.

18. The positive electrode active material according to claim 17, characterized in that, The oxygen vacancy content of the material in the first sublayer is not less than 20%.

19. The positive electrode active material according to any one of claims 17 to 18, characterized in that, The core and the first sublayer are in direct contact, and the contact area between the core and the first sublayer has a transition layer containing all the elements of the material of the first sublayer.

20. The positive electrode active material according to any one of claims 17 to 19, characterized in that, The material of the first sublayer includes N a O b N includes at least one of magnesium, calcium, cobalt, nickel, copper, zinc, aluminum, gallium, scandium, yttrium, lanthanum, titanium, chromium, vanadium, niobium, zirconium, or molybdenum, 0.5 ≥ a ≥ 0.1, b = Va / 2, and V is the valence number of element N.

21. The positive electrode active material according to any one of claims 17 to 20, characterized in that, The first sub-layer includes multiple attachment point layers, which are spaced apart on the kernel surface.

22. The positive electrode active material according to any one of claims 17 to 21, characterized in that, In the first positive electrode active material, the mass percentage of the first sublayer is no more than 5%.

23. The positive electrode active material according to any one of claims 17 to 22, characterized in that, The shell also includes a second sublayer made of carbon, and the first sublayer is disposed between the core and the second sublayer.

24. The positive electrode active material according to claim 23, characterized in that, In the first positive electrode active material, the second sublayer accounts for 0.1% to 5% of the total mass.

25. A method for preparing a positive electrode active material, characterized in that, The method includes: Lithium cobalt phosphate materials were obtained; The lithium cobalt phosphate material and the shell material are mixed in a solvent and then dried and granulated to obtain an intermediate powder. The intermediate powder is sintered to obtain a positive electrode active material. The positive electrode active material includes a first positive electrode active material, which includes a core and a shell covering the core. The core includes a lithium cobalt phosphate material, and the shell includes a first sublayer. The material of the first sublayer has oxygen vacancies.

26. The method for preparing the positive electrode active material according to claim 25, characterized in that, The median particle size Dv50 of the lithium cobalt phosphate material is 1μm to 5μm, and the median particle size Dv50 of the shell material is 200nm to 500nm.

27. The method for preparing the positive electrode active material according to any one of claims 25 to 26, characterized in that, The method further includes carbon coating of the positive electrode active material, wherein the carbon coating method includes chemical vapor deposition.

28. The method for preparing the positive electrode active material according to any one of claims 25 to 27, characterized in that, The lithium source used to obtain the cobalt phosphate lithium-based material includes at least one of lithium nitrate, lithium tetraborate, lithium fluoride, or lithium metaborate.

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