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 material and preparation method thereof, positive electrode sheet, secondary battery and application

[0001] Cross-references

[0002] This application refers to 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 into this application in its entirety by reference. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a positive electrode active material and a preparation method thereof, a positive electrode sheet, a secondary battery and applications. Background Art

[0004] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0005] In recent years, the application of secondary batteries has become increasingly widespread. They are widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. This tremendous development of secondary batteries has led to higher demands for their cycling performance. Cathode active materials are a key factor influencing secondary battery performance. Modifying these materials to improve the initial coulombic efficiency and cycling performance of secondary batteries remains a pressing technical challenge.

[0006] Summary of the Invention

[0007] The present application provides a positive electrode active material and a preparation method thereof, a positive electrode plate, a secondary battery and applications, aiming to improve the first coulombic efficiency and cycle performance of a battery containing the positive electrode active material.

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

[0009] The fluoride having a perovskite structure has a strong skeleton structure and a relatively spacious lithium ion transmission channel, which can improve the lithium ion transmission capacity of the positive electrode active material. At the same time, the coating layer containing the above fluoride is coated on 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 the charge and discharge cycle, reduce the area of ​​direct contact between the lithium-containing positive electrode material and the electrolyte, reduce the side reaction 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 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 positive electrode active material.

[0010] In some embodiments, the mass percentage of the fluoride in the positive electrode active material is 3.2% to 5.3%, thereby further improving the initial coulombic efficiency and cycle performance of the battery.

[0011] In some embodiments, the molar proportion of Li element is 90% to 100% of the total molar amount of element A in the fluoride. In this design, the fluoride can be used as a lithium source to further improve the cycle performance of the battery.

[0012] In some embodiments, the A element further comprises K. The atomic radius of K is larger than that of Li. The inclusion of some K element in the fluoride can improve kinetics, thereby further improving the cycle performance of the battery.

[0013] In some embodiments, the M element includes at least Mn, and the molar proportion of Mn in the total molar amount of the fluoride M element is 25% to 85%. As a result, the material with the molecular formula AMF3 has a more stable perovskite structure, facilitating lithium ion transport, thereby further improving the battery's cycling performance.

[0014] In some embodiments, the molar proportion of Mn in the total molar amount of the fluoride M element is 40% to 60%. As a result, the material with the molecular formula AMF3 has a more stable perovskite structure, which facilitates lithium ion transport, thereby further improving the cycle performance of the battery.

[0015] In some embodiments, the mass percentage of fluorine in the positive electrode active material is 1.3% to 2.5%. This design can reduce stress and strain during the charge and discharge cycle, improve the stability of the positive electrode active material structure, and thus further improve the cycle performance of the battery.

[0016] In some embodiments, the fluoride comprises a fluoride having the 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 of F3.

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

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

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

[0020] Mixing a lithium-containing positive electrode material, a salt containing an element A, a salt containing an element M, a fluorine-containing metal salt, and a solvent to obtain a mixed solution; 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] removing the solvent 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 having a perovskite structure, the fluoride includes a material with the molecular formula AMF3, and the core includes a lithium-containing positive electrode material.

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

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

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

[0026] mixing the lithium-containing positive electrode material with a second solvent to disperse the lithium-containing positive electrode material in the second solvent to obtain a second solution;

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

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

[0029] In some embodiments, the step of removing the solvent from the mixed solution includes: performing a spray granulation process on 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 the M element includes at least one of nitrate, sulfate, and carbonate.

[0032] In a third aspect of the present application, a positive electrode plate is provided, comprising at least one of the positive electrode active material described in the first aspect of the present application and the positive electrode active material prepared by the preparation method described in the second aspect of the present application.

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

[0034] In a fourth aspect of the present application, a secondary battery is provided, comprising the positive electrode sheet described in the third aspect of the present application.

[0035] The secondary battery of the present application includes the positive electrode sheet provided by the present application, and thus has at least the same advantages as the positive electrode sheet.

[0036] In a fifth aspect of the present application, an electrical device is provided, comprising the secondary battery described in the fourth aspect of the present application.

[0037] The electric device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery.

[0038] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG1 is a schematic structural diagram of a positive electrode active material according to an embodiment of the present application.

[0040] FIG2 is a structural diagram of a material having the molecular formula AMF3 according to an embodiment of the present application.

[0041] FIG3 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0042] FIG. 4 is an exploded view of the battery cell shown in FIG. 3 according to an embodiment of the present application.

[0043] FIG5 is a schematic diagram of a battery module according to an embodiment of the present application.

[0044] FIG6 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0045] FIG. 7 is an exploded view of the battery pack shown in FIG. 6 according to an embodiment of the present application.

[0046] FIG8 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0047] FIG9 is an X-ray diffraction (XRD) pattern of the fluorides prepared in Examples 1 and 7 of the present application.

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

[0049] FIG11 is an X-ray energy dispersive spectrum (EDS) diagram of the positive electrode active material prepared in Example 6 of the present application.

[0050] Description of reference numerals:

[0051] 1. Battery pack; 2. Upper case; 3. Lower case; 4. Battery module; 5. Battery cell; 5. Casing; 5. Electrode assembly; 5. Cover; 6. Electrical device; 7. Positive electrode active material; 7.01 Core; 7.02 Coating layer; 7.03 Transition metal ions; 7.04 Electrolyte. DETAILED DESCRIPTION

[0052] Below, some embodiments of the positive electrode active material and its preparation method, positive electrode sheet, secondary battery and application of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0053] " scope " disclosed in the present application can be limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and any end value can be included or not included independently, and can be arbitrarily combined, that is, any lower limit can form a scope with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 are also listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is merely an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to listing the parameter as, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on. For example, when a parameter is expressed as an integer selected from "2-10", this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0054] In this application, "a plurality of" or "a plurality of" refers to a number greater than or equal to 2 unless otherwise specified. For example, "one or more" means one or more than or equal to two.

[0055] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0056] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive with other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments. References to "implementations" herein have a similar understanding.

[0057] It will be appreciated by those skilled in the art that, in the methods of various embodiments or examples, the order in which the steps are written does not imply a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible inherent logic. Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0058] In this application, in the open technical features or technical solutions described with words such as "contain", "include", and "include", unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions that also include additional members in addition to the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2, and a3" and the feature or solution of "A includes not only a1, a2, and a3, but also other members". In this application, unless otherwise specified, A (such as B) means 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, the terms "optionally," "optional," and "optional" are optional and refer to either option being present or absent. If a technical solution contains multiple "options," each option is considered independent unless otherwise specified and there are no conflicts or constraints.

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

[0061] Based on this, one embodiment of the present 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 including a fluoride having a perovskite structure, the fluoride including a material with a molecular formula AMF3, the A element including one or more of Li, Na and K, the M element including one or more of Mn, Ni, Fe, Sr, Mg, Ca, Cu and Ce, and the core including a lithium-containing positive electrode material.

[0062] In the above embodiment, the fluoride having a perovskite structure has a strong skeleton structure and a relatively spacious lithium ion transmission channel, which can improve the lithium ion transmission capacity of the positive electrode active material. At the same time, the coating layer containing the above fluoride is coated on 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 the charge and discharge cycle, reduce the area of ​​direct contact between the lithium-containing positive electrode material and the electrolyte, reduce the side reaction 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 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 positive electrode active material.

[0063] Alternatively, the structure and type of the fluoride may be tested using methods such as XRD, SEM (scanning electron microscope), TEM (transmission electron microscope), and EDX (energy dispersive X-ray spectrometer).

[0064] FIG1 shows a schematic diagram of the structure of a positive electrode active material according to an embodiment of the present 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 having a perovskite structure. The fluoride includes a material having the molecular formula AMF3. FIG2 shows a structural diagram of a material having the molecular formula AMF3 according to an embodiment of the present application. The material has a perovskite structure. With such a 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 mass proportion of fluoride in the positive electrode active material is 3.2% to 5.3%. This can further improve the initial coulombic efficiency and cycle performance of the battery. It is understood that the mass proportion 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, the A element includes at least Li, and the molar proportion of the Li element in the total molar amount of the A element in the fluoride is 90% to 100%. With this design, the fluoride can serve as a lithium source, further improving the cycle performance of the battery. It is understood that the molar proportion of the Li element in the total molar amount of the A element in the fluoride includes but is not limited to: 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, and 100%.

[0067] In some embodiments, the A element further comprises K. The atomic radius of K is larger than that of Li. The inclusion of some K element in the fluoride can improve kinetics, thereby further improving the cycle performance of the battery.

[0068] In some embodiments, the M element includes at least Mn, and the molar proportion of the M element in the total molar amount of the M element in the fluoride is 25% to 85%. As a result, the material with the molecular formula AMF3 has a more stable perovskite structure, which facilitates lithium ion transport, thereby further improving the cycle performance of the battery. It can be understood that the molar proportion of the M element 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%, 85%. In some embodiments, the molar proportion of the M element in the total molar amount of the M element in the fluoride is 40% to 60%.

[0069] In some embodiments, the mass percentage of fluorine in the positive electrode active material is 1.3% to 2.5%. Such a design can effectively protect the CEI film (electrochemical interface film) of the positive electrode active material, reduce stress and strain during the charge and discharge cycle, and improve the stability of the positive electrode active material structure, thereby further improving the cycle performance of the battery. It is understood that the mass percentage of fluorine in the positive electrode active material 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 comprises a fluoride having the 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 materials of F3. Thus, the positive electrode active material can have a higher first coulombic efficiency and good cycle performance.

[0071] In some embodiments, the average thickness of the coating layer is 5 nm to 10 nm. This can further enhance the coating effect of the coating layer on the core and facilitate the diffusion and transport of lithium ions. 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 measured by TEM (transmission electron microscopy), for example, the maximum thickness and the minimum thickness of the coating layer can be measured 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 positive electrode material includes one or more of lithium transition metal oxides and modified compounds thereof, and the lithium transition metal oxide includes 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 and providing the above-mentioned coating layer can further improve the battery's cycling performance. It can be understood that the above-mentioned lithium manganese oxide includes lithium-rich manganese-based positive electrode materials, and lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide are 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 referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.8 Co 0.15 Al 0.05 O2.

[0077] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charge and discharge process, and the content of Li in the positive electrode plate is different when the battery is discharged to different states. In the list of positive electrode active materials in this application, unless otherwise specified, the content of Li is the initial state of the material. The positive electrode active material is applied to the positive electrode plate in the battery system, and after the charge and discharge cycle, the content of Li in the positive electrode active material contained in the plate will usually change. Among them, the content of Li can be measured by molar content, but is not limited to this. Regarding "the content of Li is the initial state of the material", the initial state of the material refers to the state before the material is added to the positive electrode slurry. It is understandable that new materials obtained by appropriate modification on the basis of 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 the molar content of oxygen to change, and the actual O content will fluctuate. The O content can be measured by molar content, but is not limited to this.

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

[0080] A lithium-containing positive electrode material, a salt containing an element A, a salt containing an element M, a fluorine-containing metal salt, and a solvent are mixed to obtain a mixed solution; 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;

[0081] removing the solvent from the mixed solution to obtain a 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, the fluoride includes a material with the molecular formula AMF3, and the core includes a lithium-containing positive electrode material.

[0083] In the above embodiment, the fluoride having a perovskite structure has a strong skeleton structure and a relatively spacious lithium ion transmission channel, which can improve the lithium ion transmission capacity of the positive electrode active material. At the same time, the coating layer containing the above fluoride is coated on 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 the charge and discharge cycle, reduce the area of ​​direct contact between the lithium-containing positive electrode material and the electrolyte, reduce the side reaction 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 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 positive electrode active material. Moreover, the above preparation method is simple and easy to operate, which is conducive to the mass production of positive electrode active materials.

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

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

[0086] mixing a lithium-containing positive electrode material with a second solvent to disperse the lithium-containing positive electrode material in the second solvent to obtain a second solution;

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

[0088] In some embodiments, the first solvent further comprises an inorganic acid, wherein the inorganic acid comprises 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 comprise LiF, the first solvent further comprises an inorganic acid, taking into account the solubility of LiF, so that LiF can be dissolved in the first solvent.

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

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

[0091] 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. It is understood that the salt containing element A can provide element A to the mixed solution, and the fluorine-containing metal salt can serve 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 the M element includes at least one of nitrate, sulfate, and carbonate.

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

[0094] Yet another embodiment of the present application provides a positive electrode plate, comprising at least one of the positive electrode active material described above and the positive electrode active material prepared by the preparation method described above.

[0095] Another embodiment of the present application further provides a secondary battery, comprising the above-mentioned positive electrode sheet of the present application.

[0096] Another embodiment of the present application further provides an electrical device, comprising the above-mentioned secondary battery of the present application.

[0097] In addition, the secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0098] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0099] Positive electrode

[0100] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material mentioned above in the present application.

[0101] As a non-limiting example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on either or both of the two facing surfaces of the positive electrode 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 base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

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

[0104] In some embodiments, the positive electrode active material layer may further include a conductive agent. As non-limiting examples, 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, a positive electrode sheet can be prepared by dispersing the components for preparing 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 on at least one side of a positive electrode current collector, and performing drying, cold pressing, and other processes to obtain a positive electrode sheet. The type of solvent can be selected from, but not limited to, any of the aforementioned 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 of the positive electrode current collector or both surfaces of the positive electrode current collector. The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40 wt% to 80 wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 mPa·s to 25000 mPa·s. When applying the positive electrode slurry, the coating unit area density based on dry weight (excluding solvent) can be 15 mg / cm 2 -35mg / cm 2 The compaction density of the positive electrode can be 3.0g / cm 3 -3.6g / cm 3 , optional 3.3g / cm 3 -3.5g / cm 3 .

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

[0107] Negative electrode

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

[0109] As a non-limiting example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two facing 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 polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0111] In some embodiments, the negative electrode active material may adopt negative electrode active materials for batteries that are well known in the art. As non-limiting examples, 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, lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials 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 further 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 further include a conductive agent, which 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 further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0115] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. 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 two 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 surface density on a dry weight basis (excluding the solvent) can be 75g / m 2 -220g / m 2 The compaction density of the negative electrode can be 1.0g / cm 3 -1.8g / cm 3 .

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

[0117] electrolytes

[0118] The electrolyte conducts ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0119] In some embodiments, the electrolyte is an electrolyte solution, which 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 bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorodioxalatophosphate (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP).

[0121] In some embodiments, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate One or more of 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, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[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), trifluoromethylethylene carbonate (TFPC), and the like.

[0124] Isolation film

[0125] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0126] In some embodiments, the material of the separator can include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

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

[0128] In this application, the unit "μm" means micrometer.

[0129] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0130] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the 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, a steel shell, etc. The outer packaging of the secondary battery can also be a soft shell, such as a pouch-type soft shell. The material of the soft shell can be plastic. Further, non-limiting examples of plastic can 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, a "battery cell" refers to a basic unit that can achieve the mutual conversion of chemical energy and electrical energy. Further, generally speaking, it includes at least a positive electrode plate, a negative electrode plate, and an electrolyte. During the battery's charge and discharge process, active ions are embedded in and out of the positive and negative electrode plates. The electrolyte plays the role of conducting active ions between the positive and negative electrode plates.

[0134] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG3 shows a battery cell 5 with a square structure as an example.

[0135] In some embodiments, referring to Figure 4, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0136] The secondary battery may be a battery module 4 or a battery pack 1 .

[0137] A battery module includes at least one battery cell. The number of battery cells contained 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] FIG5 shows an example battery module 4. Referring to FIG5 , in the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0139] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

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

[0141] Figures 6 and 7 illustrate an example battery pack 1. 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 comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed 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, the present application also provides an electrical device, which includes the secondary battery provided in the present application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, etc. Among them, mobile devices can be, for example, mobile phones, laptops, etc.; electric vehicles can 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 these.

[0143] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0144] FIG8 shows an example of an electric device 6. The electric device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0145] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0146] Below, the embodiment of the present application is described. The embodiment described below is exemplary, is only used to explain the present application, and is not to be construed as limiting the present application. Where the technology or conditions are not specified in the embodiment, the technology or conditions described in the literature in this area or the product instructions are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0147] Example 1

[0148] The method for preparing the positive electrode active material comprises the following steps:

[0149] (1) dissolving ferric nitrate and nickel nitrate containing M elements in a molar ratio of 1:3 in 30 mL of deionized water and mixing them uniformly by ultrasonication for 30 minutes to form a solution A; M elements refer to iron and nickel;

[0150] (2) adding 0.06 mol of lithium fluoride to 10 mL of concentrated nitric acid and stirring continuously to form solution B, wherein the lithium fluoride acts as 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 g (g) of lithium-containing positive electrode material LiNi 0.7 Co 0.05 Mn 0.25 O2 was dissolved in 40 mL of anhydrous ethanol and subjected to ultrasonic vibration after dissolution to form solution D (second solution). Solution D was poured into solution C and stirred to uniformly disperse to obtain a mixed solution;

[0153] (5) The mixed solution obtained in step (4) is subjected to spray granulation. The process parameters of the spray granulation include: an inlet temperature of 200°C, an outlet temperature of 700°C, a spray pressure of 2 MPa, a nozzle diameter of 0.3 mm, a spray time of 60 min, and a 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, the coating layer is a fluoride LiFe with a perovskite structure 0.25 Ni 0.75 F3, the mass proportion of the fluoride in the positive electrode active material is 4.62%. In this application, the unit "L / min" refers to liters / minute.

[0154] Prepare lithium-ion batteries as follows:

[0155] (1) Preparation of positive electrode sheet

[0156] The above-mentioned positive electrode active material, conductive agent SP, conductive agent CNT, and binder PVDF were weighed in a mass ratio of 97%:1.7%:0.3%:1%, and NMP solvent was added and stirred to form a positive electrode slurry with a viscosity of 6000mPa·s~10000mPa·s. The slurry was then coated on both sides of a 13μm thick aluminum foil, dried in an oven at 120℃~140℃, and roll-pressed to obtain a positive electrode sheet.

[0157] (2) Preparation of negative electrode sheet

[0158] The negative electrode active material graphite, conductive agent Super P, binder CMC, and binder SBR were weighed in a mass ratio of 97%:0.7%:1%:1.3%, and deionized water was added and stirred to form a negative electrode slurry with a viscosity of 10000mPa·s to 15000mPa·s. The slurry was then coated on both sides of a 6μm thick copper foil, dried in an oven at 120°C to 140°C, and roll-pressed to obtain a negative electrode sheet.

[0159] (3) Battery assembly

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

[0161] Examples 2 to 16

[0162] The method is basically the same as Example 1, except that the type of lithium-containing positive electrode material, the type of fluoride, and the mass proportion of fluoride in the positive electrode 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 steps (2) of Examples 2 to 16 is replaced with potassium fluoride and / or sodium fluoride, it is necessary to replace all or part of the concentrated nitric acid in step (2) with an equal volume of deionized water so that the potassium fluoride and / or sodium fluoride is dissolved in the deionized water. The raw material ratios in Examples 2 to 16 can be calculated based on the product parameters of the positive electrode active material.

[0164] Comparative Example 1

[0165] The same as Example 1, except that the lithium-containing positive electrode material LiNi in Example 1 is directly 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 to 16 and the lithium ion battery of Comparative Example 1 were prepared in a similar manner to the lithium ion battery of Example 1, but used the positive electrode active materials prepared in the corresponding Examples.

[0167] Product parameter testing and performance testing

[0168] (1) Test on the molar proportion of Li element 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 by EDX (energy dispersive X-ray spectrometer), and the molar percentage of element Li was obtained by calculation.

[0170] (2) Test on the molar proportion of Mn element in the total molar amount of M element in fluoride

[0171] The content of M element in the fluoride of the coating layer was tested by EDX, and the molar ratio of Mn element was obtained by calculation.

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

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

[0174] (4) Test of the mass ratio of fluoride in positive electrode active materials

[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 proportion 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 3.4 V at 25°C and 0.1C, and then charged to 3.95 V at 0.33C. The charge capacity was recorded as C0.

[0178] Capacity test: First, discharge to 2.8V (discharge capacity is D0); then charge to 4.3V at a constant current of 0.33C. Then, charge to 0.05C at a constant voltage of 4.3V (charge capacity is C1). After 10 minutes, discharge to 2.8V at a constant current of 0.33C (discharge capacity is D1). Calculate the initial coulombic efficiency of the lithium-ion battery using the following formula.

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

[0180] (6) Cyclic performance test

[0181] At 25°C, charge the lithium-ion battery at a constant current of 0.33C to 4.3V, then charge it at a constant voltage of 4.3V until the current is less than 0.05C. Then discharge it at a constant current of 0.33C to 2.5V. The discharge capacity at 0.5C is calculated as one cycle. Repeat the above charge and discharge steps until the capacity retention rate reaches 90% SOH. The number of cycles at this point represents the cycle performance of the battery.

[0182] Table 1

[0183]

[0184] Table 2

[0185] FIG9 is an XRD pattern of the fluorides prepared in Example 1 and Example 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 F3, as shown in FIG9 , 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 is a TEM image of the positive electrode active materials prepared in Example 4 and Example 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 dotted line portion in Figure 10 is 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 a perovskite structure is 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 5nm to 6nm, and the average thickness of the coating layer in Example 12 is 9nm to 10nm, 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] FIG11 is the EDS surface scan test result of the positive electrode active material prepared in Example 6. As can be seen from FIG11 , each element is evenly distributed on the surface of the positive electrode active material, and the presence of K, Fe, and F elements further proves that fluoride is successfully coated on the surface of the lithium-containing positive electrode material.

[0188] It can be seen from Tables 1 and 2 that, compared with Comparative Example 1, the batteries of Examples 1 to 16 have higher first coulombic efficiency and better cycle performance, indicating that the positive electrode active materials prepared in Examples 1 to 16 can improve the first coulombic efficiency and cycle performance of batteries containing the positive electrode active materials.

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

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

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

[0192] The above description of the various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced with each other and will not be repeated herein for the sake of brevity.

[0193] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode active material comprising a core and a coating layer covering at least a portion of the surface of the core, wherein the coating layer comprises a fluoride having a perovskite structure, the fluoride comprises a material having a molecular formula of AMF3, the A element comprises one or more of Li, Na and K, the M element comprises one or more of Mn, Ni, Fe, Sr, Mg, Ca, Cu and Ce, and the core comprises a lithium-containing positive electrode material.

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

3. The positive electrode active material according to claim 1 or 2, wherein The A element includes at least Li, and the molar proportion of the Li element in the total molar amount of the A element in the fluoride is 90% to 100%.

4. The positive electrode active material according to claim 3, wherein The A element also includes K.

5. The positive electrode active material according to any one of claims 1 to 4, wherein The M element includes at least Mn. In the total molar amount of the M element in the fluoride, the molar proportion of the Mn element is 25% to 85%.

6. The positive electrode active material according to claim 5, wherein In the total molar amount of the M element in the fluoride, the molar proportion of the Mn element is 40% to 60%.

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

8. The positive electrode active material according to claim 1 or 2, wherein The fluoride includes a molecular formula of 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 One or more of the materials of F3.

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

10. The positive electrode active material according to any one of claims 1 to 9, wherein The lithium-containing positive electrode material includes one or more of lithium transition metal oxides and modified compounds thereof, and the lithium transition metal oxide includes one or more of lithium manganese oxide, lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.

11. A method for preparing a positive electrode active material, comprising the following steps: Mixing a lithium-containing positive electrode material, a salt containing an element A, a salt containing an element M, a fluorine-containing metal salt, and a solvent to obtain a mixed solution; 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; removing the solvent from the mixed solution to obtain the positive electrode active material; in, 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, the fluoride includes a material with a molecular formula of AMF3, and the core includes a lithium-containing positive electrode material.

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

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

14. The preparation method according to any one of claims 11 to 13, wherein The step of removing the solvent from the mixed solution includes: performing a spray granulation process on the mixed solution to obtain the positive electrode active material.

15. The preparation method according to any one of claims 11 to 14, wherein The preparation method satisfies one or more of the following conditions: (1) 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; (2) The salt containing the M element includes at least one of nitrate, sulfate and carbonate. 16 . A positive electrode sheet comprising at least one of the positive electrode active material according to claim 1 and the positive electrode active material prepared by the preparation method according to claim 11 . 17 . A secondary battery comprising the positive electrode sheet according to claim 16 .

18. An electric device comprising the secondary battery according to claim 17.

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