Positive electrode active material and preparation method therefor, positive electrode sheet, secondary battery and use

Abstract

The present application relates to a positive electrode active material and a preparation method therefor, a positive electrode sheet, a secondary battery and the use. The positive electrode active material comprises a core and a coating layer that coats at least part of the surface of the core, wherein the coating layer comprises a fluoride having a perovskite structure, the fluoride comprising a material with a molecular formula of AMF3, where the element A comprises one or more of Li, Na and K, and the element M comprises one or more of Mn, Ni, Fe, Sr, Mg, Ca, Cu and Ce; and the core comprises a lithium-containing positive electrode material. Therefore, the initial coulombic efficiency and cycle performance of a battery are improved.

Description

Positive electrode active materials and their preparation methods, positive electrode sheets, secondary batteries and applications

[0001] Cross-referencing

[0002] This application incorporates Chinese Patent Application No. 202410353506.4, filed on March 26, 2024, entitled “Positive electrode active material and preparation method thereof, positive electrode sheet, secondary battery and application”, which is incorporated herein by reference in its entirety. Technical Field

[0003] This application relates to the field of battery technology, and in particular to a positive electrode active material and its preparation method, a positive electrode sheet, a secondary battery, and its applications. Background Technology

[0004] The statements herein are provided only as background information in connection with this application and do not necessarily constitute prior art.

[0005] In recent years, with the increasingly wide application of rechargeable batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. Due to the significant development of rechargeable batteries, higher requirements have been placed on their cycle performance. The positive electrode active material is one of the key factors affecting the performance of rechargeable batteries, and how to modify the positive electrode active material to improve the initial coulombic efficiency and cycle performance of rechargeable batteries is a pressing technical problem that needs to be solved.

[0006] Summary of the Invention

[0007] This application provides a positive electrode active material and its preparation method, a positive electrode sheet, a secondary battery, and its application, aiming to improve the first coulombic efficiency and cycle performance of batteries containing the positive electrode active material.

[0008] A first aspect of this application provides a positive electrode active material, comprising a core and a coating layer covering at least a portion of the surface of the core, the coating layer comprising a fluoride having a perovskite structure, the fluoride comprising a material with the molecular formula AMF3, the element A comprising one or more of Li, Na and K, the element M comprising one or more of Mn, Ni, Fe, Sr, Mg, Ca, Cu and Ce, and the core comprising a lithium-containing positive electrode material.

[0009] The perovskite-structured fluoride possesses a robust framework structure and a relatively wide lithium-ion transport channel, which can enhance the lithium-ion transport capability of the cathode active material. Simultaneously, the coating layer containing the aforementioned fluoride covers at least a portion of the core surface, protecting the lithium-containing cathode material, reducing the volume change of the lithium-containing cathode material during charge-discharge cycles, reducing the area of ​​direct contact between the lithium-containing cathode material and the electrolyte, reducing side reactions between the lithium-containing cathode material and the electrolyte, and to a certain extent reducing the dissolution of metal ions from the lithium-containing cathode material. Furthermore, the aforementioned fluoride can also serve as an alkali metal source and a fluorine source, thereby effectively improving the initial coulombic efficiency and cycle performance of the battery containing the aforementioned cathode active material.

[0010] In some embodiments, the fluoride comprises 3.2% to 5.3% by mass in the positive electrode active material. This can further improve the initial coulombic efficiency and cycle performance of the battery.

[0011] In some embodiments, the molar percentage of Li in the total molar amount of element A in the fluoride is 90% to 100%. This design allows the fluoride to serve as a lithium source, further improving the battery's cycle performance.

[0012] In some implementations, element A also includes K. K has a larger atomic radius than Li, and the presence of K in the fluoride can improve kinetics, thereby further enhancing the battery's cycle performance.

[0013] In some embodiments, the M element includes at least Mn, and the molar percentage of Mn in the total molar amount of the M element in the fluoride is 25% to 85%. Therefore, the material with the molecular formula AMF3 has a more stable perovskite structure, which facilitates lithium-ion transport and can further improve the cycle performance of the battery.

[0014] In some embodiments, the molar percentage of Mn in the total molar amount of M element in the fluoride is 40% to 60%. Therefore, the material with the molecular formula AMF3 has a more stable perovskite structure, which facilitates lithium-ion transport and can further improve the cycle performance of the battery.

[0015] In some embodiments, the fluorine content in the positive electrode active material is 1.3% to 2.5% by mass. This design reduces stress and strain during charge-discharge cycles, improves the stability of the positive electrode active material structure, and thus further enhances the cycle performance of the battery.

[0016] In some embodiments, the fluoride includes compounds with the molecular formula LiFe. 0.25 Ni 0.75 F3, Li 0.9 Na 0.1 Fe0.25 Ni 0.75 F3, Li 0.8 Na 0.2 Fe 0.25 Ni 0.75 F3, LiMn 0.25 Ni 0.75 F3, LiMn 0.6 Ni 0.4 F3, LiMn 0.85 Ni 0.15 F3, LiMn 0.7 Ni 0.3 F3, LiMn 0.4 Ni 0.6 F3, Li 0.9 K 0.1 Fe 0.25 Ni 0.75 F3, Li 0.9 Na 0.1 Sr 0.25 Fe 0.75 F3, Li 0.9 Na 0.1 Ce 0.25 Ca 0.75 F3 and Li 0.9 Na 0.1 Cu 0.25 Mg 0.75 One or more of the materials in F3.

[0017] In some embodiments, the average thickness of the coating layer is 5 nm to 10 nm.

[0018] In some embodiments, the lithium-containing cathode material includes one or more of lithium transition metal oxides and their modified compounds, wherein the lithium transition metal oxides include one or more of lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0019] A second aspect of this application provides a method for preparing a positive electrode active material, comprising the following steps:

[0020] A mixed solution is obtained by mixing a lithium-containing cathode material, a salt containing element A, a salt containing element M, a fluorine-containing metal salt, and a solvent; the element A includes one or more of Li, Na, and K, and the element M includes one or more of Mn, Ni, Fe, Sr, Mg, Ca, Cu, and Ce.

[0021] The solvent is removed from the mixed solution to obtain the positive electrode active material;

[0022] The positive electrode active material includes a core and a coating layer covering at least a portion of the surface of the core. The coating layer includes a fluoride with a perovskite structure, and the fluoride includes a material with the molecular formula AMF3. The core includes a lithium-containing positive electrode material.

[0023] The above preparation method is simple and easy to operate, which is conducive to the mass production of positive electrode active materials.

[0024] In some embodiments, the step of mixing the lithium-containing cathode material, the salt containing element A, the salt containing element M, the fluorine-containing metal salt, and the solvent includes:

[0025] The salt containing element A, the salt containing element M, and the fluorine-containing metal salt are dissolved in a first solvent to obtain a first solution;

[0026] The lithium-containing cathode material is mixed with the second solvent to disperse the lithium-containing cathode material in the second solvent, thereby obtaining a second solution;

[0027] The first solution is mixed with the second solution to obtain a mixed solution; the solvent includes the first solvent and the second solvent, each of which independently includes one or more of water and ethanol.

[0028] In some embodiments, the first solvent further includes an inorganic acid, which includes one or more of sulfuric acid and hydrochloric acid.

[0029] In some embodiments, the step of removing the solvent from the mixed solution includes: spray granulation of the mixed solution to obtain the positive electrode active material.

[0030] In some embodiments, the salt containing element A includes a fluoride salt containing element A, the fluorine-containing metal salt includes a fluorine-containing alkali metal salt, and the fluoride salt containing element A and the fluorine-containing alkali metal salt each independently include at least one of LiF, KF and NaF.

[0031] In some embodiments, the salt containing element M includes at least one of nitrate, sulfate, and carbonate.

[0032] A third aspect of this application provides a positive electrode sheet, comprising at least one of the positive electrode active material described in the first aspect of this application and the positive electrode active material prepared by the preparation method described in the second aspect of this application.

[0033] The positive electrode sheet of this application includes at least one of the positive electrode active material provided in this application and the positive electrode active material prepared by the preparation method provided in this application, and therefore has at least the same advantages as the positive electrode active material.

[0034] A fourth aspect of this application provides a secondary battery, including the positive electrode sheet described in the third aspect of this application.

[0035] The secondary battery of this application includes the positive electrode provided in this application, and therefore has at least the same advantages as the positive electrode.

[0036] A fifth aspect of this application provides an electrical device including the secondary battery described in the fourth aspect of this application.

[0037] The electrical device of this application includes the secondary battery provided in this application, and therefore has at least the same advantages as the secondary battery.

[0038] Details of one or more embodiments of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0039] Figure 1 is a schematic diagram of the structure of the positive electrode active material according to an embodiment of this application.

[0040] Figure 2 is a structural diagram of a material with the molecular formula AMF3 according to an embodiment of this application.

[0041] Figure 3 is a schematic diagram of a battery cell according to one embodiment of this application.

[0042] Figure 4 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 3.

[0043] Figure 5 is a schematic diagram of a battery module according to one embodiment of this application.

[0044] Figure 6 is a schematic diagram of a battery pack according to one embodiment of this application.

[0045] Figure 7 is an exploded view of the battery pack of one embodiment of this application shown in Figure 6.

[0046] Figure 8 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of this application.

[0047] Figure 9 shows the X-ray diffraction (XRD) patterns of the fluorides prepared in Examples 1 and 7 of this application.

[0048] Figure 10 shows transmission electron microscopy (TEM) images of the positive electrode active materials prepared in Examples 4 and 12 of this application; Figure 10(a) is a TEM image of the positive electrode active material prepared in Example 4, and Figure 10(b) is a TEM image of the positive electrode active material prepared in Example 12.

[0049] Figure 11 is an X-ray energy dispersive spectroscopy (EDS) diagram of the positive electrode active material prepared in Example 6 of this application.

[0050] Explanation of reference numerals in the attached figures:

[0051] 1 Battery pack; 2 Upper casing; 3 Lower casing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate; 6 Electrical device; 70 Positive electrode active material; 701 Core; 702 Coating layer; 703 Transition metal ions; 704 Electrolyte. Detailed Implementation

[0052] The following describes in detail, with appropriate reference to the accompanying drawings, some embodiments of the positive electrode active material, its preparation method, positive electrode sheet, secondary battery, and applications of this application. However, some unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0053] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be combined arbitrarily, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when describing a parameter as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 for that parameter. For instance, when describing a parameter as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0054] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0055] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0056] 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 or implementation 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. The term "implementation" as used herein has a similar understanding.

[0057] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0058] In this application, open-ended technical features or solutions described using terms such as "containing," "comprising," or "including" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may also include other members or exclude additional members unless otherwise specified. This can be considered as providing both the feature or solution that "A consists of a1, a2, and a3" and the feature or solution that "A includes not only a1, a2, and a3, but also other members." In this application, unless otherwise specified, A (e.g., B) indicates that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0059] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0060] During repeated charge and discharge cycles, microcracks form inside the positive electrode active material of traditional lithium-ion batteries, and serious side reactions occur on the newly exposed surfaces, leading to a decrease in the battery's initial coulombic efficiency and cycle performance.

[0061] Based on this, one embodiment of this application provides a positive electrode active material, including a core and a coating layer covering at least a portion of the surface of the core. The coating layer includes a fluoride having a perovskite structure. The fluoride includes a material with the molecular formula AMF3. The A element includes one or more of Li, Na and K, and the M element includes one or more of Mn, Ni, Fe, Sr, Mg, Ca, Cu and Ce. The core includes a lithium-containing positive electrode material.

[0062] In the above embodiments, the fluoride with a perovskite structure has a robust framework structure and a relatively wide lithium-ion transport channel, which can improve the lithium-ion transport capability of the positive electrode active material. At the same time, the coating layer containing the above-mentioned fluoride covers at least part of the surface of the core, which can protect the lithium-containing positive electrode material, reduce the volume change of the lithium-containing positive electrode material during charge-discharge cycles, reduce the area of ​​direct contact between the lithium-containing positive electrode material and the electrolyte, reduce the side reactions between the lithium-containing positive electrode material and the electrolyte, and reduce the dissolution of metal ions in the lithium-containing positive electrode material to a certain extent. The above-mentioned fluoride can also serve as an alkali metal source and a fluorine source, thereby effectively improving the first coulombic efficiency and cycle performance of the battery containing the above-mentioned positive electrode active material.

[0063] Alternatively, methods such as XRD, SEM (scanning electron microscopy), TEM (transmission electron microscopy), and EDX (energy-dispersive X-ray spectroscopy) can be used to test the structure and types of fluorides.

[0064] Figure 1 shows a schematic diagram of the structure of a positive electrode active material according to an embodiment of this application. The positive electrode active material 70 includes a core 701 and a coating layer 702 covering at least a portion of the surface of the core 701. The coating layer 702 includes a fluoride with a perovskite structure, and the fluoride includes a material with the molecular formula AMF3. Figure 2 shows a structural diagram of a material with the molecular formula AMF3 according to an embodiment of this application, which has a perovskite structure. With this design, the coating layer 702 can protect the core 701, reduce side reactions between the core 701 and the electrolyte 704, and reduce the dissolution of transition metal ions 703 in the core 701 to a certain extent. At the same time, the fluoride can serve as an alkali metal source and a fluorine source, thereby improving the initial coulombic efficiency and cycle performance of the battery.

[0065] In some embodiments, the fluoride constitutes 3.2% to 5.3% of the positive electrode active material by mass. This can further improve the initial coulombic efficiency and cycle performance of the battery. It is understood that the mass percentage of fluoride in the positive electrode active material includes, but is not limited to: 3.2%, 3.5%, 3.7%, 4%, 4.2%, 4.5%, 4.7%, 5%, 5.1%, 5.2%, and 5.3%.

[0066] In some embodiments, element A includes at least Li, and the molar percentage of Li in the total molar amount of element A in the fluoride is 90% to 100%. This design allows the fluoride to serve as a lithium source, further improving the battery's cycle performance. It is understood that the molar percentage of Li in the total molar amount of element A in the fluoride includes, but is not limited to, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, and 100%.

[0067] In some implementations, element A also includes K. K has a larger atomic radius than Li, and the presence of K in the fluoride can improve kinetics, thereby further enhancing the battery's cycle performance.

[0068] In some embodiments, the M element includes at least Mn, and the molar percentage of Mn in the total molar amount of the M element in the fluoride is 25% to 85%. Therefore, the material with the molecular formula AMF3 has a more stable perovskite structure, which facilitates lithium-ion transport and further improves the cycle performance of the battery. It is understood that the molar percentage of Mn in the total molar amount of the M element in the fluoride includes, but is not limited to, 25%, 30%, 40%, 50%, 60%, 70%, 80%, and 85%. In some embodiments, the molar percentage of Mn in the total molar amount of the M element in the fluoride is 40% to 60%.

[0069] In some embodiments, the fluorine content in the positive electrode active material is 1.3% to 2.5% by mass. This design effectively protects the CEI film (electrochemical interface film) of the positive electrode active material, reduces stress and strain during charge-discharge cycles, and improves the structural stability of the positive electrode active material, thereby further improving the cycle performance of the battery. It is understood that the fluorine content in the positive electrode active material by mass includes, but is not limited to, 1.3%, 1.5%, 1.7%, 1.9%, 2%, 2.3%, and 2.5%.

[0070] In some embodiments, the fluoride includes the compound with the molecular formula LiFe. 0.25 Ni 0.75 F3, Li 0.9 Na 0.1 Fe 0.25 Ni0.75 F3, Li 0.8 Na 0.2 Fe 0.25 Ni 0.75 F3, LiMn 0.25 Ni 0.75 F3, LiMn 0.6 Ni 0.4 F3, LiMn 0.85 Ni 0.15 F3, LiMn 0.7 Ni 0.3 F3, LiMn 0.4 Ni 0.6 F3, Li 0.9 K 0.1 Fe 0.25 Ni 0.75 F3, Li 0.9 Na 0.1 Sr 0.25 Fe 0.75 F3, Li 0.9 Na 0.1 Ce 0.25 Ca 0.75 F3 and Li 0.9 Na 0.1 Cu 0.25 Mg 0.75 One or more of the F3 materials. This allows the positive electrode active material to possess high initial coulombic efficiency and good cycle performance.

[0071] In some embodiments, the average thickness of the coating layer is 5 nm to 10 nm. This further enhances the coating effect on the core while facilitating lithium-ion diffusion and transport. It is understood that the average thickness of the coating layer includes, but is not limited to, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, and 10 nm.

[0072] In this application, the unit "nm" refers to nanometers.

[0073] Alternatively, the average thickness of the coating layer can be determined by TEM (transmission electron microscopy). For example, the maximum and minimum thicknesses of the coating layer can be determined by TEM, and then the average of the two can be taken to obtain the average thickness of the coating layer.

[0074] In some embodiments, the lithium-containing cathode material includes one or more of lithium transition metal oxides and their modified compounds, wherein the lithium transition metal oxides include one or more of lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0075] Because lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide have strong oxidizing properties, using these materials as all or part of the core material, along with the aforementioned coating layer, can further improve the battery's cycle performance. It is understood that the aforementioned lithium manganese oxide includes lithium-rich manganese-based cathode materials, while lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide belong to ternary materials.

[0076] Non-limiting examples of lithium manganese oxides may include LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 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 Examples of lithium nickel cobalt aluminum oxides include LiNi, etc. 0.8 Co 0.15 Al 0.05 O2.

[0077] Understandably, lithium (Li) is intercalated and deintercalated during the charging and discharging process of a battery, and the Li content in the positive electrode varies depending on the state of discharge. In the examples of positive electrode active materials listed in this application, unless otherwise specified, the Li content refers to the initial state of the material. When positive electrode active materials are applied to the positive electrode in a battery system, the Li content in the positive electrode active material typically changes after charge-discharge cycles. The Li content can be measured using molar content, but is not limited to this. Regarding "Li content refers to the initial state of the material," the initial state of the material refers to its state before being added to the positive electrode slurry. It is understood that new materials obtained by appropriately modifying the listed positive electrode active materials are also within the scope of positive electrode active materials. The aforementioned appropriate modification refers to acceptable modification methods for positive electrode active materials, and non-limiting examples include coating modification.

[0078] In the examples of positive electrode active materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause changes in the molar content of oxygen, and the actual O content will fluctuate. The O content can be measured in molar content, but is not limited to this.

[0079] Another embodiment of this application provides a method for preparing a positive electrode active material, comprising the following steps:

[0080] A mixed solution is obtained by mixing a lithium-containing cathode material, a salt containing element A, a salt containing element M, a fluorine-containing metal salt, and a solvent; element A includes one or more of Li, Na, and K, and element M includes one or more of Mn, Ni, Fe, Sr, Mg, Ca, Cu, and Ce;

[0081] The solvent in the mixed solution is removed to obtain the positive electrode active material;

[0082] The positive electrode active material includes a core and a coating layer covering at least part of the surface of the core. The coating layer includes a fluoride with a perovskite structure, and the fluoride includes a material with the molecular formula AMF3. The core includes a lithium-containing positive electrode material.

[0083] In the above embodiments, the perovskite-structured fluoride possesses a robust framework structure and a relatively wide lithium-ion transport channel, which can enhance the lithium-ion transport capability of the cathode active material. Simultaneously, the coating layer containing the fluoride covers at least a portion of the core surface, protecting the lithium-containing cathode material, reducing the volume change of the lithium-containing cathode material during charge-discharge cycles, reducing the direct contact area between the lithium-containing cathode material and the electrolyte, reducing side reactions between the lithium-containing cathode material and the electrolyte, and to a certain extent reducing the dissolution of metal ions from the lithium-containing cathode material. The fluoride can also serve as an alkali metal source and a fluorine source, thereby effectively improving the initial coulombic efficiency and cycle performance of the battery containing the above-mentioned cathode active material. Furthermore, the above preparation method is simple and easy to operate, which is beneficial for the mass production of cathode active materials.

[0084] In some embodiments, the step of mixing the lithium-containing cathode material, the salt containing element A, the salt containing element M, the fluorine-containing metal salt, and the solvent includes:

[0085] A salt containing element A, a salt containing element M, and a fluorine-containing metal salt are dissolved in a first solvent to obtain a first solution.

[0086] The lithium-containing cathode material is mixed with the second solvent to disperse the lithium-containing cathode material in the second solvent, thus obtaining the second solution;

[0087] The first solution is mixed with the second solution to obtain a mixed solution; the solvent includes the first solvent and the second solvent, each of which independently includes one or more of water and ethanol.

[0088] In some embodiments, the first solvent further includes an inorganic acid, including one or more of sulfuric acid and hydrochloric acid. It is understood that when the salt containing element A and the salt containing element M each independently include LiF, the first solvent further includes an inorganic acid to allow LiF to dissolve in the first solvent, taking into account the solubility of LiF.

[0089] In some embodiments, the step of removing the solvent from the mixed solution includes spray granulation of the mixed solution to obtain a positive electrode active material.

[0090] It is understandable that positive electrode active materials can be prepared by spray granulation. This preparation method is simple, efficient, and suitable for large-scale production of positive electrode active materials. Moreover, the coating layer of positive electrode active materials prepared by spray granulation is relatively uniform.

[0091] In some embodiments, the salt containing element A includes a fluoride salt containing element A, and the fluorine-containing metal salt includes a fluorine-containing alkali metal salt. The fluoride salt containing element A and the fluorine-containing alkali metal salt each independently include at least one of LiF, KF, and NaF. It is understood that the salt containing element A can provide element A to the mixed solution, and the fluorine-containing metal salt can act as a fluorine source to provide fluorine to the mixed solution. It should be noted that the salt containing element A and the fluorine-containing metal salt can be the same or partially the same. When the fluorine-containing alkali metal salt includes at least one of LiF, KF, and NaF, it can provide element A to the mixed solution.

[0092] In some embodiments, the salt containing element M includes at least one of nitrates, sulfates, and carbonates.

[0093] By adjusting the parameters of the above preparation method, the positive electrode active material provided in one embodiment of this application can be obtained.

[0094] Another embodiment of this application provides a positive electrode sheet, including at least one of the positive electrode active materials described above and the positive electrode active materials prepared by the preparation method described above.

[0095] Another embodiment of this application provides a secondary battery, including the positive electrode sheet described above.

[0096] Another embodiment of this application provides an electrical device including the secondary battery described above.

[0097] In addition, the secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0098] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0099] Positive electrode sheet

[0100] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including the positive active material described above in this application.

[0101] As a non-limiting example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0102] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0103] In some embodiments, the positive electrode active material layer may optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0104] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0105] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto at least one surface of the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes. The solvent can be selected from, but is not limited to, any of the solvents described in the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface or both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40wt%-80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 mPa·s-25000 mPa·s. When coating the positive electrode slurry, the coating areal density per unit area, based on dry weight (excluding solvent), can be 15 mg / cm³. 2 -35mg / cm 2 The compaction density of the positive electrode sheet can be 3.0 g / cm³. 3 -3.6g / cm 3 3.3g / cm³ is an option. 3 -3.5g / cm 3 .

[0106] In this application, the unit "mPa·s" refers to millipascal-second, and the unit "mg / cm²" refers to millipascal-second. 2 "" refers to milligrams per square centimeter, with the unit "g / cm²". 3 "" refers to grams per cubic centimeter.

[0107] Negative electrode sheet

[0108] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0109] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0110] 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 polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on the polymeric material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0111] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As a non-limiting example, the negative electrode active material may include one or more 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 include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more 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.

[0112] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may include one or more 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).

[0113] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0114] 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)).

[0115] 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 (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto at least one surface of a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing, or other processes. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt%-60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa·s-10000mPa·s. When coating the negative electrode slurry, the coating unit areal density (dry weight, minus solvent) can be 75g / m³. 2 -220g / m 2 The compaction density of the negative electrode sheet can be 1.0 g / cm³. 3 -1.8g / cm 3 .

[0116] In this application, the unit "g / m 2 "" refers to grams per square meter.

[0117] electrolytes

[0118] Electrolytes function to conduct ions between the positive and negative electrode plates. This application does not impose any particular restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or completely solid.

[0119] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0120] In some embodiments, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0121] In some embodiments, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, ), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butene carbonate Fluoroethylene carbonate (FEC), 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.

[0122] 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.

[0123] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), etc.

[0124] Separating membrane

[0125] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0126] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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 may be the same or different, without particular limitation.

[0127] In some embodiments, the thickness of the isolation membrane is 6μm-40μm, and optionally 12μm-20μm.

[0128] In this application, the unit "μm" refers to micrometers.

[0129] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0130] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0131] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0132] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0133] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy, and generally includes at least a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the battery, active ions move back and forth between the positive and negative electrode plates, inserting and extracting. The electrolyte acts as a conductor for the active ions between the positive and negative electrode plates.

[0134] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 shows a square battery cell 5 as an example.

[0135] In some embodiments, referring to FIG4, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to actual needs.

[0136] The secondary battery can be either battery module 4 or battery pack 1.

[0137] A battery module includes at least one battery cell. The number of battery cells in a battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0138] Figure 5 shows a battery module 4 as an example. Referring to Figure 5, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0139] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0140] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the battery pack may contain one or more battery modules. Those skilled in the art can select an appropriate number based on the application and capacity of the battery pack.

[0141] Figures 6 and 7 illustrate a battery pack 1 as an example. Referring to Figures 6 and 7, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0142] In addition, this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to.

[0143] As an electrical device, a rechargeable battery can be selected based on its usage requirements.

[0144] Figure 8 shows an example of an electrical device 6. This electrical device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0145] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0146] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where the technology or conditions are not specified in the embodiments, they are performed according to the technology or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0147] Example 1

[0148] The preparation method of positive electrode active material includes the following steps:

[0149] (1) Dissolve iron nitrate and nickel nitrate, which contain element M, in 30 mL of deionized water at a molar ratio of 1:3, and sonicate for 30 min to mix them evenly to form solution A; element M refers to iron and nickel.

[0150] (2) Take 0.06 mol of lithium fluoride and add it to 10 mL of concentrated nitric acid. Stir continuously to form solution B. In this solution, lithium fluoride is both a salt containing element A and a fluorine-containing metal salt, providing element A (i.e. lithium) and fluorine to solution B.

[0151] (3) Pour solution B into solution A and heat continuously at 70 degrees Celsius (°C) for 10 minutes to form solution C (first solution);

[0152] (4) 4 grams (g) of lithium-containing cathode material LiNi 0.7 Co 0.05 Mn 0.25 O2 is dissolved in 40 mL of anhydrous ethanol. After dissolution, the solution is ultrasonically vibrated to form solution D (second solution). Solution D is poured into solution C and stirred to disperse evenly to obtain a mixed solution.

[0153] (5) The mixed solution obtained in step (4) is subjected to spray granulation. The process parameters for spray granulation include: inlet temperature of 200℃, outlet temperature of 700℃, spray pressure of 2 MPa, nozzle diameter of 0.3 mm, spray time of 60 min, and carrier gas flow rate of 1 L / min to 2 L / min. Finally, a positive electrode active material is obtained, the core of which is a lithium-containing positive electrode material LiNi. 0.7 Co 0.05 Mn 0.25 O2, with a coating layer consisting of LiFe fluoride with a perovskite structure. 0.25 Ni 0.75 F3, this fluoride accounts for 4.62% of the mass of the positive electrode active material. In this application, the unit "L / min" refers to liters per minute.

[0154] Lithium-ion batteries are prepared according to the following method:

[0155] (1) Preparation of positive electrode sheet

[0156] Weigh the above positive electrode active material, conductive agent SP, conductive agent CNT, and binder PVDF in a mass ratio of 97%:1.7%:0.3%:1%, add NMP solvent and stir to form a positive electrode slurry with a viscosity of 6000mPa·s to 10000mPa·s. Then, coat it on both sides of a 13μm thick aluminum foil, dry it in an oven at 120℃ to 140℃, and roll it to obtain the positive electrode sheet.

[0157] (2) Preparation of negative electrode sheet

[0158] Weigh out the negative electrode active material graphite, conductive agent Super P, binder CMC and binder SBR in a mass ratio of 97%:0.7%:1%:1.3%, add deionized water and stir to form a negative electrode slurry with a viscosity of 10000mPa·s to 15000mPa·s. Then coat it on both sides of a 6μm thick copper foil, dry it in an oven at 120℃ to 140℃, and roll it to obtain the negative electrode sheet.

[0159] (3) Battery assembly

[0160] Using LiPF6 / EC:DEC:EMC (volume ratio = 1:1:1) as the electrolyte and polyethylene film as the separator, the above positive and negative electrode sheets are cut and then assembled into bare cells in the order of separator, positive electrode sheet, separator, and negative electrode sheet. Electrolyte is then injected to obtain a lithium-ion battery.

[0161] Examples 2-16

[0162] The process is basically the same as in Example 1, except that the type of lithium-containing cathode material, the type of fluoride, and the mass percentage of fluoride in the cathode active material are changed, and the preparation parameters are changed accordingly.

[0163] It should be noted that the lithium fluoride used in step (2) of Example 1 is dissolved in concentrated nitric acid. When the lithium fluoride in step (2) of Examples 2-16 is replaced with potassium fluoride and / or sodium fluoride, all or part of the concentrated nitric acid in step (2) needs to be replaced with an equal volume of deionized water so that the potassium fluoride and / or sodium fluoride dissolve in the deionized water. The raw material ratio in Examples 2-16 can be calculated based on the product parameters of the positive electrode active material.

[0164] Comparative Example 1

[0165] Basically the same as Example 1, except that: the lithium-containing cathode material LiNi from Example 1 is directly used. 0.7 Co 0.05 Mn 0.25 O2 is used as the positive electrode active material.

[0166] The lithium-ion batteries of Examples 2-16 and Comparative Example 1 are prepared by methods similar to those of the lithium-ion battery of Example 1, but the positive electrode active materials prepared in the corresponding examples are used.

[0167] Product parameter testing and performance testing

[0168] (1) Test the molar percentage of Li in the total molar amount of element A in fluoride.

[0169] The content of element A in the fluoride of the coating layer was tested using EDX (energy-dispersive X-ray spectroscopy), and the molar percentage of element Li was calculated.

[0170] (2) Test the molar percentage of Mn in the total molar amount of M in fluorides.

[0171] The content of M element in the fluoride of the coating layer was tested using EDX, and the molar percentage of Mn element could be calculated.

[0172] (3) Test of the mass percentage of fluorine in the positive electrode active material

[0173] A certain mass of positive electrode active material is weighed using a balance, and then the mass of fluorine in the positive electrode active material is tested using EDX. The mass percentage of fluorine in the positive electrode active material can be calculated.

[0174] (4) Test of the mass percentage of fluoride in positive electrode active material

[0175] A certain mass of positive electrode active material is weighed using a balance, and then the mass of fluoride in the positive electrode active material is tested using EDX. The mass ratio of fluoride in the positive electrode active material can be calculated.

[0176] (5) First Coulomb efficiency test

[0177] The unformed lithium-ion battery was first charged to 3.4V at 25°C and 0.1C, and then charged to 3.95V at 0.33C. The charging capacity was measured as C0.

[0178] Capacity testing: First, discharge to 2.8V, the discharge capacity is recorded as D0; then charge to 4.3V at a constant current of 0.33C, and then charge to 0.05C at a constant voltage of 4.3V, the charging capacity is recorded as C1; after resting for 10 minutes, discharge to 2.8V at a constant current of 0.33C, the discharge capacity is recorded as D1. Calculate the initial coulombic efficiency of the lithium-ion battery according to the following formula.

[0179] First coulomb efficiency (%) = D1 / (C0+C1-D0)×100%.

[0180] (6) Cyclic performance test

[0181] At 25°C, the lithium-ion battery was charged at a constant current of 0.33C to 4.3V, then charged at a constant voltage of 4.3V until the current was less than 0.05C. Next, the lithium-ion battery was discharged at a constant current of 0.33C to 2.5V. The discharge capacity at 0.5C was obtained, and this was counted as one cycle. The above charging and discharging steps were repeated until the capacity retention reached 90% SOH. The number of cycles at this point represents the battery's cycle performance.

[0182] Table 1

[0183]

[0184] Table 2

[0185] Figure 9 shows the XRD patterns of the fluorides prepared in Examples 1 and 7. The fluoride prepared in Example 1 is LiFe. 0.25 Ni 0.75 F3, the fluoride prepared in Example 7 is LiMn 0.25 Ni 0.75 As shown in Figure 9, even when the type of fluoride is changed, the fluoride can still maintain the characteristic peaks of the perovskite structure, indicating that the fluoride prepared in this application has a perovskite structure and its structural stability is relatively good.

[0186] Figure 10 shows TEM images of the positive electrode active materials prepared in Examples 4 and 12; Figure 10(a) is a TEM image of the positive electrode active material prepared in Example 4, and Figure 10(b) is a TEM image of the positive electrode active material prepared in Example 12. The dashed lines in Figure 10 represent the coating layer region. In Figure 10(a), lattice fringes belonging to the perovskite (110) crystal plane can be detected, indicating that the fluoride with the perovskite structure was successfully coated on the surface of the lithium-containing positive electrode material. As shown in Figure 10, the average thickness of the coating layer in Example 4 is 5 nm to 6 nm, and the average thickness of the coating layer in Example 12 is 9 nm to 10 nm, indicating that changing the mass ratio of fluoride in the positive electrode active material can control the change in the average thickness of the coating layer.

[0187] Figure 11 shows the EDS surface scan test results of the positive electrode active material prepared in Example 6. As can be seen from Figure 11, each element is evenly distributed on the surface of the positive electrode active material. Moreover, the presence of K, Fe and F elements further proves that the fluoride was successfully coated on the surface of the lithium-containing positive electrode material.

[0188] As shown in Tables 1 and 2, compared with Comparative Example 1, the batteries of Examples 1 to 16 have higher initial coulombic efficiency and better cycle performance, indicating that the positive electrode active material prepared in Examples 1 to 16 can improve the initial coulombic efficiency and cycle performance of batteries containing the positive electrode active material.

[0189] Comparing Examples 1 and 4-6, it can be seen that controlling the molar ratio of Li element in A element in fluoride to 90%-100% in Examples 1, 4 and 6 can further improve the cycle performance of the battery.

[0190] As can be seen from Examples 4 and 6, when the A element in the fluoride includes the Li element, the introduction of the K element into the fluoride in Example 6 can further improve the cycle performance of the battery.

[0191] Comparing Examples 1 and Examples 7-11, it can be seen that controlling the molar ratio of Mn element in the fluoride to M element in Examples 7-11 to be 25%-85% can further improve the cycle performance of the battery; further controlling the molar ratio of Mn element in the fluoride to M element in Examples 8 and 11 to be 40%-60% can further improve the cycle performance of the battery.

[0192] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0193] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode active material, comprising an inner core and a coating layer coating at least part of a surface of the inner core, the coating layer comprising a fluoride having a perovskite structure, the fluoride comprising a material having a molecular formula of AMF 3, A elements comprising one or more of Li, Na and K, M elements comprising one or more of Mn, Ni, Fe, Sr, Mg, Ca, Cu and Ce, the inner core comprising a lithium-containing positive electrode material.

2. The positive electrode active material according to claim 1, wherein A mass percentage of the fluoride in the positive electrode active material is 3.2%-5.3%.

3. The positive electrode active material according to claim 1 or 2, wherein A elements at least comprise Li, a molar percentage of Li elements in a total amount of A elements of the fluoride is 90%-100%.

4. The positive electrode active material according to claim 3, wherein A elements further comprise K.

5. The positive electrode active material according to any one of claims 1 to 4, wherein M elements at least comprise Mn, a molar percentage of Mn elements in a total amount of M elements of the fluoride is 25%-85%.

6. The positive electrode active material according to claim 5, wherein A molar percentage of Mn elements in a total amount of M elements of the fluoride is 40%-60%.

7. The positive electrode active material according to any one of claims 1 to 6, wherein A mass percentage of fluorine elements in the positive electrode active material is 1.3%-2.5%.

8. The positive electrode active material according to claim 1 or 2, wherein The fluoride includes one or more of materials of formula LiFe 0.25 Ni 0.75 F3, Li 0.9 Na 0.1 Fe 0.25 Ni 0.75 F3, Li 0.8 Na 0.2 Fe 0.25 Ni 0.75 F3, LiMn 0.25 Ni 0.75 F3, LiMn 0.6 Ni 0.4 F3, LiMn 0.85 Ni 0.15 F3, LiMn 0.7 Ni 0.3 F3, LiMn 0.4 Ni 0.6 F3, Li 0.9 K 0.1 Fe 0.25 Ni 0.75 F3, Li 0.9 Na 0.1 Sr 0.25 Fe 0.75 F3, Li 0.9 Na 0.1 Ce 0.25 Ca 0.75 F3, and Li 0.9 Na 0.1 Cu 0.25 Mg 0.75 F3.

9. The positive electrode active material according to any one of claims 1 to 8, wherein An average thickness of the coating layer is 5nm-10nm.

10. The positive electrode active material according to any one of claims 1 to 9, wherein The lithium-containing positive electrode material comprises one or more of lithium transition metal oxides and modified compounds thereof, the lithium transition metal oxides comprising one or more of lithium manganese oxides, lithium nickel cobalt manganese oxides and lithium nickel cobalt aluminum oxides. 11.A method for preparing a positive electrode active material, comprising the following steps: mixing a lithium-containing positive electrode material, a salt containing A elements, a salt containing M elements, a fluorine-containing metal salt and a solvent to obtain a mixed solution, the A elements comprising one or more of Li, Na and K, the M elements comprising one or more of Mn, Ni, Fe, Sr, Mg, Ca, Cu and Ce; removing the solvent in the mixed solution to obtain the positive electrode active material; wherein, the positive electrode active material comprising an inner core and a coating layer coating at least part of a surface of the inner core, the coating layer comprising a fluoride having a perovskite structure, the fluoride comprising a material having a molecular formula of AMF 3, the inner core comprising a lithium-containing positive electrode material.

12. The method of making according to claim 11, wherein, The step of mixing a lithium-containing positive electrode material, a salt containing A elements, a salt containing M elements, a fluorine-containing metal salt and a solvent comprises: dissolving the salt containing A elements, the salt containing M elements and the fluorine-containing metal salt in a first solvent to obtain a first solution; mixing the lithium-containing positive electrode material and a second solvent to disperse the lithium-containing positive electrode material in the second solvent to obtain a second solution; mixing the first solution and the second solution to obtain a mixed solution, the solvent comprising the first solvent and the second solvent, the first solvent and the second solvent each independently comprising one or more of water and ethanol.

13. The method of making according to claim 12, wherein, The first solvent further comprises an inorganic acid, the inorganic acid comprising one or more of sulfuric acid and hydrochloric acid.

14. The method of making according to any one of claims 11 to 13, wherein, The step of removing the solvent in the mixed solution comprises: performing a spray granulation treatment on the mixed solution to obtain the positive electrode active material.

15. The method of manufacturing according to any one of claims 11 to 14, wherein, The method for preparing the positive electrode active material satisfies one or more of the following conditions: (1) the A element-containing salt includes an A element-containing fluorinated salt, the fluorinated metal salt includes a fluorinated alkali metal salt, and each of the A element-containing fluorinated salt and the fluorinated alkali metal salt independently includes at least one of LiF, KF, and NaF; (2) the M element-containing salt includes at least one of a nitrate, a sulfate, and a carbonate.

16. A positive electrode sheet comprising at least one of the positive electrode active material of any one of claims 1 to 10 and the positive electrode active material prepared by the production method of any one of claims 11 to 15.

17. A secondary battery comprising the positive electrode sheet of claim 16.

18. An electric device comprising the secondary battery of claim 17.

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