Modified lithium-rich manganese-based positive electrode material, preparation method thereof and battery

Abstract

The invention provides a modified lithium-rich manganese-based positive electrode material, a preparation method thereof and a battery. The modified lithium-rich manganese-based positive electrode material comprises a lithium-rich manganese-based active core, and a lithium iron phosphate transition layer, a nitrogen-doped modified iron cobaltate nanosheet-nitrogen-doped carbon composite coating layer and a fast ion conductor-polymer composite coating layer which sequentially coat the surface of the lithium-rich manganese-based active core. The lithium-rich manganese-based positive electrode material is subjected to multiple coating, multiple coating layers have a synergistic effect, a coating system with electron / ion high-speed conduction, a stable interface and a stable structure is constructed, and the electrochemical performance of the lithium-rich manganese-based positive electrode material is comprehensively improved.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and relates to a modified lithium-rich manganese-based cathode material, its preparation method, and a battery. Background Technology

[0002] Among numerous energy storage technologies, lithium batteries have become a focus of research and application due to their high energy density, long cycle life, and excellent charge-discharge performance. Meanwhile, lithium-rich manganese-based cathode materials, with their unique advantages, are gradually emerging in the lithium battery field and have become a hot topic of common interest in both academia and industry.

[0003] Lithium-rich manganese-based cathode materials possess extremely high theoretical specific capacities, exceeding 300 mAh / g, far surpassing the widely used lithium iron phosphate and traditional ternary materials. Simultaneously, due to its manganese-based composition, this material exhibits a significant cost advantage, with raw material costs reduced by 20%–30% compared to some ternary materials. This promises to substantially lower the manufacturing costs of lithium batteries and drive the large-scale application of energy storage technologies. With its dual advantages of high energy density and low cost, lithium-rich manganese-based materials are considered an ideal choice for next-generation lithium battery cathode materials, becoming a key research focus for numerous research teams and companies.

[0004] CN120613388A discloses a modified lithium-rich manganese-based cathode material, its preparation method, and a lithium-ion battery. The method involves multi-element site doping of the matrix material to enhance the structural stability of the polycrystalline material, suppress transition metal ion migration and interlayer dislocations, improve internal lattice strength, and create a stable matrix material core. The heterostructure layer can significantly improve the surface structure phase transition and transition metal dissolution under high voltage, increasing the stability of the matrix material surface. Furthermore, the in-situ generated three-dimensional ion channels can improve the material's rate performance. The coating layer can effectively reduce solid-liquid interface side reactions, improve surface metal ion dissolution, and enhance the material's cycle performance.

[0005] CN120878786A discloses a lithium-rich manganese-based cathode material, wherein the lithium-rich manganese-based cathode material includes a matrix and a cerium oxide-cobalt oxide composite coating layer on the surface of the matrix.

[0006] The above-mentioned scheme produces lithium-rich manganese-based cathode materials with poor interfacial stability between the coating layer and the core, and the coating layer lacks flexibility, making it prone to cracking during cycling. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a modified lithium-rich manganese-based cathode material, its preparation method, and a battery. The present invention performs multiple coatings on the lithium-rich manganese-based cathode material, and the synergistic effect of the multiple coating layers constructs a coating system with high-speed electron / ion conduction, stable interface, and stable structure, thereby comprehensively improving the electrochemical performance of the lithium-rich manganese-based cathode material.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a modified lithium-rich manganese-based cathode material, the modified lithium-rich manganese-based cathode material comprising a lithium-rich manganese-based active core and a lithium iron phosphate transition layer, a nitrogen-doped modified cobalt oxide nanosheet-nitrogen-doped carbon composite coating layer, and a fast ion conductor-polymer composite coating layer sequentially coated on the surface of the lithium-rich manganese-based active core.

[0010] This invention involves coating the surface of a lithium-rich manganese-based cathode material with multiple coating layers. LiFePO4, possessing a stable olivine structure and low oxidation potential, effectively suppresses irreversible lattice oxygen deposition from the core under high voltage and reduces direct contact between the core and subsequent coating layers or electrolyte, thereby significantly improving the initial coulombic efficiency and slowing capacity decay. In the nitrogen-doped modified iron cobalt oxide nanosheet-nitrogen-doped carbon composite coating layer, N... - Occupying oxygen sites in the FeCo2O4 lattice can improve electronic conductivity; the nanosheet structure shortens the Li + The diffusion pathway enhances electrolyte wettability; and the electronegativity of nitrogen enhances the adsorption of transition metal ions, reducing dissolution and oxygen release under high voltage, thus improving the stability of the coating layer. Nitrogen doping in the carbon layer improves the overall electronic conductivity of the material, and the FeCo2O4 nanosheet structure maximizes contact with the carbon network and core. Simultaneously, the composite layer formed by nitrogen-doped modified iron cobalt oxide nanosheets embedded in the nitrogen-doped carbon layer is more stable than a single carbon layer or oxide layer, better suppressing the dissolution of transition metal ions during cycling. The strong coupling between nitrogen-doped carbon and iron cobalt oxide nanosheets may produce a synergistic effect, promoting interfacial charge transport. Finally, a fast ion conductor-polymer composite coating layer is applied to the material surface. The polymer forms a stable interface with the electrolyte, blocking electrolyte erosion. Furthermore, the flexibility of the polymer layer buffers the stress caused by the volume expansion / contraction of the active material during charging and discharging, preventing coating layer rupture. The fast ion conductor nanoparticles assist ion conduction, avoiding conduction obstruction caused by polymer insulation, ensuring the material's rate performance.

[0011] Preferably, the chemical formula of the lithium-rich manganese-based active core is Li. 1+a [Ni β Co γ Mn 1-β-γ ] 1-aO2, where 0.08≤a≤0.15, 0.15≤β≤0.25, and 0.08≤γ≤0.12.

[0012] Preferably, the lithium-rich manganese-based active core further includes doping elements.

[0013] Preferably, the doping element includes Ti and / or Al.

[0014] Preferably, the molar percentage of dopant elements in the lithium-rich manganese-based active core is 0.1% to 0.5%, for example: 0.1%, 0.2%, 0.3%, 0.4% or 0.5%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] Preferably, the thickness of the lithium iron phosphate transition layer is 5nm to 15nm, for example: 5nm, 7nm, 9nm, 12nm or 15nm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] Preferably, the material of the nitrogen-doped modified iron cobalt oxide nanosheet-nitrogen-doped carbon composite coating layer includes nitrogen-doped carbon and nitrogen-doped modified iron cobalt oxide nanosheets.

[0017] Preferably, in the nitrogen-doped modified iron cobalt oxide nanosheet-nitrogen-doped carbon composite coating layer, the mass fraction of the nitrogen-doped modified iron cobalt oxide nanosheet is 80%~90%, for example: 80%, 82%, 85%, 88% or 90%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] Preferably, the nitrogen-doped modified iron cobalt oxide nanosheets have the chemical formula FeCo2O. 4-x N x , 0.03≤x≤0.07.

[0019] Preferably, the thickness of the nitrogen-doped modified iron cobalt oxide nanosheet-nitrogen-doped carbon composite coating layer is 5nm~20nm, for example: 5nm, 10nm, 15nm or 20nm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, the material of the fast ion conductor-polymer composite coating layer includes a fast ion conductor and a polar polymer.

[0021] Preferably, the fast ion conductor comprises LLZO.

[0022] Preferably, the polar polymer comprises PVDF and / or PVP.

[0023] Preferably, the mass fraction of fast ion conductor in the fast ion conductor-polymer composite coating layer is 60% to 80%, for example: 60%, 65%, 70%, 75% or 80%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] Preferably, the thickness of the fast ion conductor-polymer composite coating layer is 5nm to 15nm, for example: 5nm, 7nm, 9nm, 12nm or 15nm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] In a second aspect, the present invention provides a method for preparing the modified lithium-rich manganese-based cathode material as described in the first aspect, the method comprising the following steps:

[0026] The lithium-rich manganese-based active core material is dispersed in the first solvent, and then the first iron source, phosphorus source, lithium source and complexing agent are added. The pH is adjusted to the first pH to obtain a sol and the reaction is stirred. After the gel is dried, the precursor material is obtained by heat treatment.

[0027] The second iron source, cobalt source, nitrogen-containing carbon source and second solvent are mixed to obtain a mixed solution. The precursor material is mixed with the mixed solution, and an alkali source is added to adjust to the second pH. After hydrothermal reaction, the mixture is calcined in an atmosphere containing active nitrogen to obtain a sintered material.

[0028] The polymer, fast ion conductor and third solvent are mixed to obtain a coating liquid, which is then coated on the surface of the sintered material and dried to obtain the modified lithium-rich manganese-based cathode material.

[0029] This invention obtains a precursor by coating lithium iron phosphate onto the surface of a lithium-rich manganese-based active core using a sol-gel method. Then, nitrogen-doped iron cobalt oxide with a two-dimensionally preferentially grown nanosheet structure is generated on the precursor surface via a hydrothermal reaction. The nitrogen-containing carbon source in solution can play a surface control role, facilitating the formation of nanosheet iron cobalt oxide on the precursor material surface. Calcination in an active nitrogen atmosphere allows for the control of the nitrogen content in both the nitrogen-doped iron cobalt oxide and the nitrogen-doped carbon, resulting in a nitrogen-stable doped coating layer. Finally, a fast ion conductor-polymer composite coating layer can be formed through simple liquid-phase coating.

[0030] Preferably, the first iron source includes ferric nitrate.

[0031] Preferably, the phosphorus source includes lithium dihydrogen phosphate and / or phosphoric acid.

[0032] Preferably, the lithium source includes lithium phosphate and / or lithium dihydrogen phosphate.

[0033] Preferably, the complexing agent comprises citric acid.

[0034] Preferably, the first solvent includes ethanol and water.

[0035] Preferably, the volume ratio of ethanol to water is (0.5~1.5):1, for example: 0.5:1, 0.8:1, 1:1, 1.2:1 or 1.5:1, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] Preferably, a doped metal source is also added during the process of mixing the first iron source, phosphorus source, lithium source, complexing agent and first solvent.

[0037] Preferably, the first pH is 4 to 7, for example: 4, 4.5, 5, 6 or 7, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0038] Preferably, the temperature of the stirring reaction is 70℃~80℃, for example: 70℃, 72℃, 75℃, 78℃ or 80℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] Preferably, the mixture is dried after the stirring reaction.

[0040] Preferably, the drying temperature is 100℃~120℃, for example: 100℃, 105℃, 110℃, 115℃ or 120℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] Preferably, the heat treatment temperature is 500℃~700℃, for example: 500℃, 550℃, 600℃, 650℃ or 700℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] Preferably, the heat treatment time is 4h to 8h, for example: 4h, 5h, 6h, 7h or 8h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] Preferably, the atmosphere for the heat treatment includes nitrogen and / or argon.

[0044] Preferably, the second iron source comprises ferric nitrate.

[0045] Preferably, the cobalt source includes cobalt nitrate.

[0046] Preferably, the nitrogen-containing carbon source includes CTAB and / or PVP.

[0047] Preferably, the second solvent comprises deionized water.

[0048] Preferably, the alkali source includes any one or a combination of at least two of sodium hydroxide, potassium hydroxide, or ammonia water. Typical but non-limiting combinations include combinations of sodium hydroxide and potassium hydroxide, potassium hydroxide and ammonia water, or sodium hydroxide and ammonia water, etc.

[0049] Preferably, the second pH is 9 to 11, for example: 9, 9.5, 10, 10.5 or 11, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0050] Preferably, the temperature of the hydrothermal reaction is 120℃~180℃, for example: 120℃, 130℃, 150℃, 160℃ or 180℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0051] Preferably, the hydrothermal reaction time is 8h to 10h, for example: 8h, 8.5h, 9h, 9.5h or 10h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0052] Preferably, the active nitrogen atmosphere includes ammonia and an inert gas.

[0053] Preferably, the volume fraction of ammonia in the active nitrogen atmosphere is 2% to 10%, for example: 2%, 5%, 8% or 10%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0054] Preferably, the calcination temperature is 400℃~500℃, for example: 400℃, 420℃, 450℃, 480℃ or 500℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0055] Preferably, the calcination time is 2h to 3h, for example: 2h, 2.2h, 2.5h, 2.8h or 3h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0056] Preferably, the third solvent comprises N-methylpyrrolidone.

[0057] Preferably, the drying temperature is 100℃~120℃, for example: 100℃, 105℃, 110℃, 115℃ or 120℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0058] Thirdly, the present invention provides a battery comprising the modified lithium-rich manganese-based cathode material as described in the first aspect.

[0059] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] (1) This invention employs multiple coatings on lithium-rich manganese-based cathode materials. The lithium iron phosphate layer is used to suppress oxygen release, limit Mn dissolution, and stabilize the surface structure of the material. The nitrogen-doped iron cobaltate-nitrogen-doped carbon composite coating layer can improve the electronic conductivity of the coated material and reduce the direct contact between the material core and the electrolyte. The fast ion conductor-polymer composite coating layer on the surface can provide fast Li-ion exchange. + The system effectively channels and inhibits the formation of microcracks, preventing HF corrosion and thus constructing a coating system with high-speed electron / ion conduction, stable interface, and stable structure, comprehensively improving the electrochemical performance of lithium-rich manganese-based cathode materials.

[0062] (2) The battery made from the composite modified lithium-rich manganese-based cathode material of the present invention has a discharge specific capacity of more than 248.9 mAh / g at 0.1C, more than 239.5 mAh / g at 0.2C, more than 226.3 mAh / g at 0.5C, and more than 216.3 mAh / g at 1C. The cycle capacity retention rate after 100 cycles at 1C is more than 87.8%. The lithium-rich manganese-based cathode material modified by the method of the present invention has significantly improved rate performance and cycle retention rate. The maximum 1C capacity can reach 224.6 mAh / g, and the maximum cycle retention rate can reach 92.3% after 100 cycles at 1C rate in the voltage range of 2-4.8V. Detailed Implementation

[0063] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0064] The "range" disclosed in this invention 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 the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, 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 specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. 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 invention, unless otherwise stated, the numerical range "a~b" 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 a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0065] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0066] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0067] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0068] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed 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, the method may also include step (c), meaning 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.

[0069] In this invention, open-ended technical features or solutions described using terms such as "comprising" 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, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0070] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0071] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0072] In this invention, "optional" means that something is optional, that is, it refers to any one of the two parallel solutions of "having" or "not having". If there are multiple "optional" options in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "optional" option is independent.

[0073] In this invention, "room temperature" generally refers to 4℃~35℃, and can refer to 20℃±5℃. In some embodiments of this invention, room temperature refers to 20℃~30℃.

[0074] Example 1

[0075] This embodiment provides a modified lithium-rich manganese-based cathode material, wherein the modified lithium-rich manganese-based cathode material comprises a chemical formula of Li 1.1 [Ni 0.2 Co 0.1 Mn 0.7 ] 0.9 The active core of O2 is a lithium-rich manganese-based active core, which is also doped with titanium and aluminum, wherein the molar percentage of titanium in the active core is 0.2% and the molar percentage of aluminum is 0.1%.

[0076] The surface of the lithium-rich manganese-based active core is sequentially coated with an 8 nm thick lithium iron phosphate transition layer, a 10 nm thick nitrogen-doped modified cobalt oxide nanosheet-nitrogen-doped carbon composite coating layer, and a 10 nm thick fast ion conductor-polymer composite coating layer.

[0077] The nitrogen-doped modified iron cobalt oxide nanosheet-nitrogen-doped carbon composite coating layer includes a nitrogen-doped carbon layer and FeCo2O embedded in the nitrogen-doped carbon layer. 3.95 N 0.05 The nitrogen-doped modified iron cobalt oxide nanosheets, wherein the nitrogen-doped modified iron cobalt oxide nanosheets-nitrogen-doped carbon composite coating layer comprises 85% by mass of the nitrogen-doped modified iron cobalt oxide nanosheets. The fast ion conductor-polymer composite coating layer comprises LLZO fast ion conductor and polar polymer PVDF, wherein the mass fraction of LLZO in the fast ion conductor-polymer composite coating layer is 70%.

[0078] The modified lithium-rich manganese-based cathode material was prepared by the following method:

[0079] The lithium-rich manganese-based active core material was dispersed in a mixed solvent of ethanol and water in a volume ratio of 1:1. Ferric nitrate and lithium dihydrogen phosphate were weighed in a molar ratio of 1:1 and added together to the mixture. Citric acid was added dropwise to adjust the pH to 5.8 to obtain a sol. The sol was stirred at 75°C for 2 hours, dried at 110°C, and then heat-treated at 600°C for 6 hours under a nitrogen atmosphere to obtain the precursor material.

[0080] Ferric nitrate, cobalt nitrate, and CTAB were mixed with water to obtain a mixed solution. The precursor material was mixed with the mixed solution, and the pH was adjusted to 10 with NaOH. The mixture was then placed in a high-pressure reactor and hydrothermally reacted at 150°C for 9 hours. The resulting solid material was calcined at 450°C for 2.5 hours under a mixed atmosphere of ammonia and argon (ammonia volume percentage of 8%) to obtain a sintered material.

[0081] PVDF and LLZO were mixed with NMP to obtain a coating solution, which was then coated onto the surface of the sintered material and dried at 120°C to obtain the modified lithium-rich manganese-based cathode material.

[0082] Example 2

[0083] This embodiment provides a modified lithium-rich manganese-based cathode material, wherein the modified lithium-rich manganese-based cathode material comprises a chemical formula of Li 1.1 [Ni 0.2 Co 0.1 Mn 0.7 ] 0.9 The lithium-rich manganese-based active core of O2 is further doped with titanium and aluminum, wherein the molar percentage of titanium in the lithium-rich manganese-based active core is 0.1% and the molar percentage of aluminum is 0.1%.

[0084] The surface of the lithium-rich manganese-based active core is sequentially coated with a lithium iron phosphate transition layer with a thickness of 5 nm, a nitrogen-doped modified cobalt iron nanosheet-nitrogen-doped carbon composite coating layer with a thickness of 5 nm, and a fast ion conductor-polymer composite coating layer with a thickness of 5 nm.

[0085] The nitrogen-doped modified iron cobalt oxide nanosheet-nitrogen-doped carbon composite coating layer includes a nitrogen-doped carbon layer and FeCo2O embedded in the nitrogen-doped carbon layer. 3.93 N 0.07 The nitrogen-doped modified iron cobalt oxide nanosheets, wherein the nitrogen-doped modified iron cobalt oxide nanosheets-nitrogen-doped carbon composite coating layer comprises 80% by mass of the nitrogen-doped modified iron cobalt oxide nanosheets. The fast ion conductor-polymer composite coating layer comprises LLZO fast ion conductor and polar polymer PVDF, wherein the mass fraction of LLZO in the fast ion conductor-polymer composite coating layer is 60%.

[0086] The modified lithium-rich manganese-based cathode material was prepared by the following method:

[0087] The lithium-rich manganese-based active core material was dispersed in a mixed solvent of ethanol and water in a volume ratio of 1:1. Ferric nitrate and lithium dihydrogen phosphate were weighed in a molar ratio of 1:1 and added together to the mixture. Citric acid was added dropwise to adjust the pH to 7 to obtain a sol. The sol was stirred at 70°C for 3 hours, dried at 100°C, and then heat-treated at 500°C for 8 hours under a nitrogen atmosphere to obtain the precursor material.

[0088] Ferric nitrate, cobalt nitrate, and PVP were mixed with water to obtain a mixed solution. The precursor material was mixed with the mixed solution, and the pH was adjusted to 11 with NaOH. The mixture was then placed in a high-pressure reactor and hydrothermally reacted at 120°C for 10 hours. The resulting solid material was calcined at 400°C for 3 hours under a mixed atmosphere of ammonia and argon (ammonia volume percentage of 2%) to obtain a sintered material.

[0089] PVP and LLZO were mixed with NMP to obtain a coating solution, which was then coated onto the surface of the sintered material and dried at 100°C to obtain the modified lithium-rich manganese-based cathode material.

[0090] Example 3

[0091] This embodiment provides a modified lithium-rich manganese-based cathode material, wherein the modified lithium-rich manganese-based cathode material comprises a chemical formula of Li 1.1 [Ni 0.2 Co 0.1 Mn 0.7 ] 0.9 The lithium-rich manganese-based active core of O2 is further doped with titanium and aluminum, wherein the molar percentage of titanium in the lithium-rich manganese-based active core is 0.2% and the molar percentage of aluminum is 0.2%.

[0092] The surface of the lithium-rich manganese-based active core is sequentially coated with a lithium iron phosphate transition layer with a thickness of 15 nm, a nitrogen-doped modified cobalt iron nanosheet-nitrogen-doped carbon composite coating layer with a thickness of 20 nm, and a fast ion conductor-polymer composite coating layer with a thickness of 15 nm.

[0093] The nitrogen-doped modified iron cobalt oxide nanosheet-nitrogen-doped carbon composite coating layer includes a nitrogen-doped carbon layer and FeCo2O embedded in the nitrogen-doped carbon layer. 3.97 N 0.03 The nitrogen-doped modified iron cobalt oxide nanosheets, wherein the nitrogen-doped modified iron cobalt oxide nanosheets-nitrogen-doped carbon composite coating layer comprises 90% by mass of the nitrogen-doped modified iron cobalt oxide nanosheets. The fast ion conductor-polymer composite coating layer comprises LLZO fast ion conductor and polar polymer PVDF, wherein the mass fraction of LLZO in the fast ion conductor-polymer composite coating layer is 80%.

[0094] The modified lithium-rich manganese-based cathode material was prepared by the following method:

[0095] The lithium-rich manganese-based active core material was dispersed in a mixed solvent of ethanol and water in a volume ratio of 1:1. Ferric nitrate and lithium dihydrogen phosphate were weighed in a molar ratio of 1:1 and added together to the mixture. Citric acid was added dropwise to adjust the pH to 7 to obtain a sol. The mixture was stirred at 80°C for 1.5 h, dried at 120°C, and then heat-treated at 700°C for 4 h under a nitrogen atmosphere to obtain the precursor material.

[0096] Ferric nitrate, cobalt nitrate, and PVP were mixed with water to obtain a mixed solution. The precursor material was mixed with the mixed solution, and the pH was adjusted to 9 with NaOH before being placed in a high-pressure reactor. The mixture was hydrothermally reacted at 180°C for 10 hours. The resulting solid material was calcined at 500°C for 2 hours under a mixed atmosphere of ammonia and argon (ammonia volume percentage of 10%) to obtain a sintered material.

[0097] PVDF and LLZO were mixed with NMP to obtain a coating solution, which was then coated onto the surface of the sintered material and dried at 110°C to obtain the modified lithium-rich manganese-based cathode material.

[0098] Example 4

[0099] The only difference between this embodiment and Embodiment 1 is that the mass fraction of nitrogen-doped modified iron cobalt oxide nanosheets in the nitrogen-doped carbon composite coating layer is 60%. All other conditions and parameters are exactly the same as in Embodiment 1.

[0100] Example 5

[0101] The only difference between this embodiment and Embodiment 1 is that the mass fraction of nitrogen-doped modified iron cobalt oxide nanosheets in the nitrogen-doped carbon composite coating layer is 90%. All other conditions and parameters are exactly the same as in Embodiment 1.

[0102] Example 6

[0103] The only difference between this embodiment and Embodiment 1 is that the thickness of the nitrogen-doped modified iron cobalt oxide nanosheet-nitrogen-doped carbon composite coating layer is 2 nm. All other conditions and parameters are exactly the same as in Embodiment 1.

[0104] Example 7

[0105] The only difference between this embodiment and Embodiment 1 is that the thickness of the nitrogen-doped modified iron cobalt oxide nanosheet-nitrogen-doped carbon composite coating layer is 20 nm. All other conditions and parameters are exactly the same as in Embodiment 1.

[0106] Example 8

[0107] The only difference between this embodiment and Embodiment 1 is that the mass fraction of LLZO in the fast ion conductor-polymer composite coating layer is 50%, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0108] Example 9

[0109] The only difference between this embodiment and Embodiment 1 is that the mass fraction of LLZO in the fast ion conductor-polymer composite coating layer is 90%, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0110] Comparative Example 1

[0111] The only difference between this comparative example and Example 1 is that the iron cobalt oxide nanosheets are not doped with nitrogen (after the iron cobalt oxide nanosheets are made, a nitrogen-containing carbon coating layer is prepared using CTAB and sintered in a pure argon atmosphere). All other conditions and parameters are exactly the same as in Example 1.

[0112] Comparative Example 2

[0113] The only difference between this comparative example and Example 1 is that the fast ion conductor-polymer composite coating layer is not provided; all other conditions and parameters are exactly the same as in Example 1.

[0114] Performance testing:

[0115] The positive electrode material, polyvinylidene fluoride, and conductive carbon black obtained in the examples and comparative examples were homogenized at a mass ratio of 97.2:1.3:1.5. Then, aluminum foil was laid flat on a coating machine for coating (area density of 16 mg / cm³). 2 After drying in a 100℃ forced-air drying oven for 12 hours, the cells were drilled, weighed, and the electrodes were baked to serve as the positive electrode. Metallic lithium was used as the negative electrode to fabricate a CR2032 coin cell. Finally, the cells were placed in a Blue Electric testing system for electrical performance testing. The test results are shown in Table 1.

[0116] Table 1

[0117]

[0118] As shown in Table 1, and based on Examples 1-9, the batteries made from the composite modified lithium-rich manganese-based cathode material of the present invention exhibit a discharge specific capacity of over 248.9 mAh / g at 0.1C, over 239.5 mAh / g at 0.2C, over 226.3 mAh / g at 0.5C, and over 216.3 mAh / g at 1C. The cycle capacity retention rate after 100 cycles at 1C is over 87.8%. The lithium-rich manganese-based cathode material modified by the method described in this invention shows significant improvements in both rate performance and cycle retention rate. The highest 1C capacity reaches 224.6 mAh / g, and the highest cycle retention rate reaches 92.3% after 100 cycles at 1C within a voltage range of 2-4.8V.

[0119] A comparison of Examples 1 and 4-5 shows that in the modified lithium-rich manganese-based cathode material of the present invention, the mass percentage of nitrogen-doped modified iron cobalt oxide nanosheets in the nitrogen-doped carbon composite coating layer affects its performance. When the mass percentage of nitrogen-doped modified iron cobalt oxide nanosheets in the nitrogen-doped carbon composite coating layer is controlled at 80%~90%, the modified lithium-rich manganese-based cathode material exhibits good performance. If the mass percentage of nitrogen-doped modified iron cobalt oxide nanosheets in the nitrogen-doped carbon composite coating layer is too low, the structural stability and the "anchoring" effect on suppressing phase transitions and oxygen loss in the lithium-rich core are limited, leading to a decrease in material performance. If the mass percentage of nitrogen-doped modified iron cobalt oxide nanosheets in the nitrogen-doped carbon composite coating layer is too high, the excessive iron cobalt oxide will interrupt the continuous conductive network formed by the carbon material, resulting in a decrease in the overall electronic conductivity of the coating layer, thereby affecting the material's performance.

[0120] A comparison of Examples 1 and 6-7 shows that the thickness of the nitrogen-doped modified iron cobalt oxide nanosheet-nitrogen-doped carbon composite coating layer affects the performance of the modified lithium-rich manganese-based cathode material of the present invention. Controlling the thickness of the nitrogen-doped modified iron cobalt oxide nanosheet-nitrogen-doped carbon composite coating layer to 5 nm~15 nm results in better performance of the modified lithium-rich manganese-based cathode material. If the thickness of the nitrogen-doped modified iron cobalt oxide nanosheet-nitrogen-doped carbon composite coating layer is too thick, the ion and electron transport impedance increases. If the thickness of the nitrogen-doped modified iron cobalt oxide nanosheet-nitrogen-doped carbon composite coating layer is too thin, it cannot form a continuous and dense coverage on the surface of the lithium-rich manganese-based core, thus failing to effectively buffer the structural stress during cycling and having a weak effect on suppressing the structural phase transition of the core. Therefore, the improvement in cycle stability and voltage decay resistance is limited.

[0121] A comparison of Examples 1 and 8-9 shows that in the modified lithium-rich manganese-based cathode material of the present invention, the mass percentage of fast ion conductors in the fast ion conductor-polymer composite coating layer affects its performance. When the mass fraction of fast ion conductors in the fast ion conductor-polymer composite coating layer is controlled at 60%~80%, the modified lithium-rich manganese-based cathode material exhibits better performance. If the mass percentage of fast ion conductors in the fast ion conductor-polymer composite coating layer is too low, the ionic conductivity is too low, and it is impossible to construct a highly efficient Li-type cathode. + The channel does not significantly improve rate performance. If the mass ratio of fast ion conductors in the fast ion conductor-polymer composite coating is too high, the flexibility of the coating will decrease, the rigidity will be too strong, and the stability will be reduced.

[0122] A comparison of Example 1 and Comparative Example 1 shows that, in the nitrogen-doped modified iron cobalt oxide nanosheet-nitrogen-doped carbon composite coating layer of the present invention, N... -Occupying oxygen sites in the FeCo2O4 lattice can improve electronic conductivity; the nanosheet structure shortens the Li + The diffusion pathway improves electrolyte wettability; and the electronegativity of nitrogen enhances the adsorption of transition metal ions, reducing dissolution and oxygen release under high voltage, thus improving the stability of the coating layer. Nitrogen doping in the carbon layer can improve the overall electronic conductivity of the material, preventing the conductivity degradation problem that occurs with lithium iron phosphate coating layers.

[0123] As can be seen from the comparison between Example 1 and Comparative Example 2, the present invention provides a fast ion conductor-polymer composite coating layer on the surface of the material. The polymer can form a stable interface with the electrolyte, blocking electrolyte erosion. Moreover, the flexibility of the polymer layer can buffer the stress caused by the volume expansion / contraction of the active material during charging and discharging, preventing the coating layer from cracking. The fast ion conductor nanoparticles assist ion conduction, avoiding conduction obstruction caused by the insulation of the polymer, and further enhancing the rate performance of the material.

[0124] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A modified lithium-rich manganese-based cathode material, characterized in that, The modified lithium-rich manganese-based cathode material includes a lithium-rich manganese-based active core and a lithium iron phosphate transition layer, a nitrogen-doped modified iron cobalt oxide nanosheet-nitrogen-doped carbon composite coating layer, and a fast ion conductor-polymer composite coating layer sequentially coated on the surface of the lithium-rich manganese-based active core.

2. The modified lithium-rich manganese-based cathode material as described in claim 1, characterized in that, The chemical formula of the lithium-rich manganese-based active core is Li 1+a [Ni β Co γ Mn 1-β-γ ] 1-a O2, where 0.08≤a≤0.15, 0.15≤β≤0.25, and 0.08≤γ≤0.12; Preferably, the lithium-rich manganese-based active core further includes doping elements; Preferably, the doping element includes Ti and / or Al; Preferably, the molar percentage of doped elements in the lithium-rich manganese-based active core is 0.1% to 0.5%.

3. The modified lithium-rich manganese-based cathode material as described in claim 1 or 2, characterized in that, The thickness of the lithium iron phosphate transition layer is 5nm~15nm.

4. The modified lithium-rich manganese-based cathode material according to any one of claims 1-3, characterized in that, The materials of the nitrogen-doped modified iron cobalt oxide nanosheet-nitrogen-doped carbon composite coating layer include nitrogen-doped carbon and nitrogen-doped modified iron cobalt oxide nanosheets; Preferably, in the nitrogen-doped modified iron cobalt oxide nanosheet-nitrogen-doped carbon composite coating layer, the mass fraction of the nitrogen-doped modified iron cobalt oxide nanosheet is 80%~90%; Preferably, the nitrogen-doped modified iron cobalt oxide nanosheets have the chemical formula FeCo2O. 4-x N x , 0.03≤x≤0.07; Preferably, the thickness of the nitrogen-doped modified iron cobalt oxide nanosheet-nitrogen-doped carbon composite coating layer is 5 nm to 20 nm.

5. The modified lithium-rich manganese-based cathode material according to any one of claims 1-4, characterized in that, The material of the fast ion conductor-polymer composite coating layer includes a fast ion conductor and a polar polymer; Preferably, the fast ion conductor comprises LLZO; Preferably, the polar polymer comprises PVDF and / or PVP; Preferably, the mass fraction of the fast ion conductor in the fast ion conductor-polymer composite coating layer is 60%~80%; Preferably, the thickness of the fast ion conductor-polymer composite coating layer is 5 nm to 15 nm.

6. A method for preparing the modified lithium-rich manganese-based cathode material as described in any one of claims 1-5, characterized in that, The preparation method includes the following steps: The lithium-rich manganese-based active core material is dispersed in the first solvent, and then the first iron source, phosphorus source, lithium source and complexing agent are added. The pH is adjusted to the first pH to obtain a sol and the reaction is stirred. After the gel is dried, the precursor material is obtained by heat treatment. The second iron source, cobalt source, nitrogen-containing carbon source and second solvent are mixed to obtain a mixed solution. The precursor material is mixed with the mixed solution, and an alkali source is added to adjust to the second pH. After hydrothermal reaction, the mixture is calcined in an atmosphere containing active nitrogen to obtain a sintered material. The polymer, fast ion conductor and third solvent are mixed to obtain a coating liquid, which is then coated on the surface of the sintered material and dried to obtain the modified lithium-rich manganese-based cathode material.

7. The preparation method according to claim 6, characterized in that, The first iron source includes ferric nitrate; Preferably, the phosphorus source includes lithium dihydrogen phosphate and / or phosphoric acid; Preferably, the lithium source includes lithium phosphate and / or lithium dihydrogen phosphate; Preferably, the complexing agent comprises citric acid; Preferably, the first solvent comprises ethanol and water; Preferably, the volume ratio of ethanol to water is (0.5~1.5):1; Preferably, a doped metal source is also added during the process of mixing the first iron source, phosphorus source, lithium source, complexing agent and first solvent; Preferably, the first pH is 4-7; Preferably, the temperature of the stirring reaction is 70℃~80℃; Preferably, the mixture is dried after the stirring reaction; Preferably, the drying temperature is 100℃~120℃; Preferably, the heat treatment temperature is 500℃~700℃; Preferably, the heat treatment time is 4h to 8h; Preferably, the atmosphere for the heat treatment includes nitrogen and / or argon.

8. The preparation method according to claim 6 or 7, characterized in that, The second iron source includes ferric nitrate; Preferably, the cobalt source includes cobalt nitrate; Preferably, the nitrogen-containing carbon source includes CTAB and / or PVP; Preferably, the second solvent comprises deionized water; Preferably, the alkali source includes any one or a combination of at least two of sodium hydroxide, potassium hydroxide, or ammonia water; Preferably, the second pH is 9-11; Preferably, the temperature of the hydrothermal reaction is 120℃~180℃; Preferably, the hydrothermal reaction time is 8h~10h; Preferably, the active nitrogen atmosphere includes ammonia and an inert gas; Preferably, the volume fraction of ammonia in the active nitrogen atmosphere is 2% to 10%; Preferably, the calcination temperature is 400℃~500℃; Preferably, the calcination time is 2h to 3h.

9. The preparation method according to any one of claims 6-8, characterized in that, The third solvent includes N-methylpyrrolidone; Preferably, the drying temperature is 100℃~120℃.

10. A battery, characterized in that, The battery comprises the modified lithium-rich manganese-based cathode material as described in any one of claims 1-5.

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