A cerium-lanthanum co-doped modified manganese iron phosphate, its preparation method and cathode
By co-doping with cerium and lanthanum and synergistic modification with lithium molybdate and polymethyl methacrylate coating, the structural stability and conductivity issues of lithium manganese iron phosphate during cycling were solved, thereby improving the cycle life and high-rate performance of the battery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- GEM CO LTD
- Filing Date
- 2025-11-19
- Publication Date
- 2026-07-31
AI Technical Summary
Existing technologies cannot effectively solve the battery performance degradation problems caused by Mn3+ distortion, Fe2+ dissolution, low ionic conductivity and volume expansion during the cycling process of lithium manganese iron phosphate, and cannot simultaneously improve bulk stability, ion transport efficiency and interface compatibility.
A synergistic modification method involving cerium-lanthanum co-doping and lithium molybdate layer and polymethyl methacrylate coating layer was adopted. Through atomic layer deposition and emulsion polymerization spraying technology, the bulk structure stability was enhanced, the ionic conductivity was improved and the electrolyte decomposition was suppressed, and the charge and discharge volume changes were adapted.
It significantly improves the cycle life, high-rate performance and interface compatibility of lithium manganese iron phosphate, and solves the core performance defects of traditional modification methods.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of battery technology and relates to a lithium manganese iron phosphate cathode material, particularly to a cerium-lanthanum co-doped modified lithium manganese iron phosphate, its preparation method, and the cathode. Background Technology
[0002] Lithium-ion batteries, with their advantages of high energy density and long cycle life, are widely used in new energy vehicles, energy storage equipment, and other fields. Lithium manganese iron phosphate (LMFP), as a novel cathode material, combines the high safety and low cost of lithium iron phosphate (LFP) with the high voltage advantage of lithium manganese phosphate (LMP), achieving a theoretical capacity of 170 mAh / g and showing broad application prospects.
[0003] However, LMFP faces three major technical bottlenecks in practical applications: First, during the loop process, Mn 3+ Jahn-Teller distortion is prone to occur, and Fe 2+ It is easily oxidized and dissolved by the electrolyte, leading to the collapse of the material's crystal structure and rapid capacity decay; secondly, its intrinsic ionic conductivity is only 10. -10 ~10 -8 The S / cm ratio is far lower than that of commercially available LFP batteries, which limits the high-rate charge and discharge performance of the batteries. Thirdly, the volume expansion and contraction caused by lattice changes during charge and discharge can easily lead to electrode particle cracks and active material shedding during long-term cycling, further deteriorating cycle stability.
[0004] To address the aforementioned problems, existing technologies mostly employ doping or coating modification strategies. However, these technologies have significant drawbacks; for example, using a single dopant element fails to synergistically suppress Mn. 3+ Distortion and Fe 2+ Dissolution; the coating layer has low ionic conductivity, making it difficult to improve high-rate performance.
[0005] Furthermore, existing technologies employing single doping, single coating, or conventional composite modification methods cannot simultaneously address the three core deficiencies of LMFPs: bulk stability, ion transport efficiency, and interface compatibility, thus hindering their large-scale application in high-performance lithium-ion batteries. Therefore, developing a method for LMFP modification that synergistically optimizes bulk, interface, and ion transport performance has become an urgent problem to be solved in this field. Summary of the Invention
[0006] To address the shortcomings of existing technologies, the present invention aims to provide a cerium-lanthanum co-doped modified lithium manganese iron phosphate, its preparation method, and a cathode. This invention improves bulk stability, suppresses Jahn-Teller distortion of trivalent manganese ions and oxidative dissolution of ferrous ions, enhances ionic conductivity, resists HF corrosion, inhibits electrolyte decomposition and excessive SEI film growth, and adapts to volume changes to prevent particle breakage. The three elements synergistically reduce interfacial impedance, simultaneously improving the material's cycle life, high-rate performance, and interfacial compatibility.
[0007] To achieve this objective, the present invention employs the following technical solution:
[0008] In a first aspect, the present invention provides a method for preparing cerium-lanthanum co-doped modified lithium manganese iron phosphate, the method comprising the following steps:
[0009] Solid-state preparation of cerium-lanthanum co-doped lithium manganese iron phosphate precursor;
[0010] A lithium molybdate layer was coated on the surface of the cerium-lanthanum co-doped lithium manganese iron phosphate precursor by atomic layer deposition (ALD).
[0011] The cerium-lanthanum co-doped modified manganese iron phosphate was obtained by coating the surface of the lithium molybdate layer with a polymethyl methacrylate (PMA) coating layer through emulsion polymer spraying.
[0012] The preparation method provided by this invention can significantly improve the electrochemical performance of lithium manganese iron phosphate. Specifically, the co-doping of Ce and La enhances the bulk structural stability and effectively suppresses Mn. 3+ Jahn-Teller distortion and Fe 2+ Oxidation and dissolution; the atomic layer deposition of lithium molybdate can improve ionic conductivity and resist corrosion by HF in the electrolyte; the emulsion polymerization spraying of polymethyl methacrylate layer can inhibit electrolyte decomposition and excessive growth of SEI film, while preventing particle breakage by elastically adapting to charge and discharge volume changes; the synergistic effect of the three significantly reduces interfacial impedance, and simultaneously improves the cycle life, high rate performance and interfacial compatibility of the material, solving the core performance defects of traditional lithium manganese iron phosphate.
[0013] In some embodiments, the cerium-lanthanum co-doped lithium manganese iron phosphate precursor includes a dopant element and lithium manganese iron phosphate; the dopant element is cerium and lanthanum, and the total doping amount of cerium and lanthanum is 0.5% to 5% of the total metal molar amount in the lithium manganese iron phosphate, for example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, but is not limited to the listed values, and other unlisted values within the range are also applicable.
[0014] In some embodiments, the molar ratio of cerium to lanthanum is (1~3):(1~3), for example, it can be 1:1, 1:2, 1:3, 2:1 or 3:1, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0015] In some embodiments, the thickness of the lithium molybdate layer is 10nm to 50nm, for example, it can be 10nm, 20nm, 30nm, 40nm or 50nm, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0016] In some embodiments, the thickness of the polymethyl methacrylate coating layer is 50 nm to 200 nm, for example, it can be 50 nm, 60 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm or 200 nm, but is not limited to the listed values, and other unlisted values within the range are also applicable.
[0017] In some embodiments, the solid-state method includes: mixing lithium, iron, manganese, phosphorus, cerium, and lanthanum sources, followed by wet ball milling and a first vacuum drying, and then sintering in a protective atmosphere to obtain the cerium-lanthanum co-doped manganese iron phosphate precursor.
[0018] In some embodiments, the protective atmosphere may be nitrogen.
[0019] In some embodiments, the lithium source includes any one or a combination of at least two of lithium carbonate, lithium hydroxide, or lithium acetate. Typical but non-limiting combinations include combinations of lithium carbonate and lithium hydroxide, combinations of lithium hydroxide and lithium acetate, combinations of lithium carbonate and lithium acetate, or combinations of lithium carbonate, lithium hydroxide, and lithium acetate.
[0020] In some embodiments, the iron source includes any one or a combination of at least two of ferrous sulfate, ferrous chloride, or ferrous oxalate. Typical but non-limiting combinations include combinations of ferrous sulfate and ferrous chloride, ferrous chloride and ferrous oxalate, ferrous sulfate and ferrous oxalate, or combinations of ferrous sulfate, ferrous chloride, and ferrous oxalate.
[0021] In some embodiments, the manganese source includes any one or a combination of at least two of manganese sulfate, manganese chloride, or manganese oxalate. Typical but non-limiting combinations include combinations of manganese sulfate and manganese chloride, manganese chloride and manganese oxalate, manganese sulfate and manganese oxalate, or manganese sulfate, manganese chloride, and manganese oxalate.
[0022] In some embodiments, the phosphorus source includes any one or a combination of at least two of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or phosphoric acid. Typical but non-limiting combinations include a combination of ammonium dihydrogen phosphate and diammonium hydrogen phosphate, a combination of diammonium hydrogen phosphate and phosphoric acid, a combination of ammonium dihydrogen phosphate and phosphoric acid, or a combination of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid.
[0023] In some embodiments, the cerium source includes cerium nitrate and / or cerium acetate.
[0024] In some embodiments, the lanthanum source includes lanthanum nitrate and / or lanthanum acetate.
[0025] In some embodiments, the temperature of the first vacuum drying is 60°C to 80°C, and the time is 12h to 24h.
[0026] The temperature for vacuum drying is 60℃~80℃, for example, it can be 60℃, 65℃, 70℃, 75℃ or 80℃, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0027] The vacuum drying time is 12h to 24h, for example, it can be 12h, 15h, 18h, 20h, 21h or 24h, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0028] In some embodiments, the sintering temperature is 600℃~800℃ and the time is 8h~12h.
[0029] The sintering temperature is 600℃~800℃, for example, it can be 600℃, 650℃, 700℃, 750℃ or 800℃, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0030] The sintering time is 8h to 12h, for example, it can be 8h, 9h, 10h, 11h or 12h, but it is not limited to the listed values. Other unlisted values within the range are also applicable.
[0031] In some embodiments, the lithium source precursor used for the atomic layer deposition includes lithium tert-butoxide, and the molybdenum source precursor used includes molybdenum hexacarbonyl.
[0032] In some embodiments, during the atomic layer deposition, the pulse time for each precursor is 0.1s to 1s, for example, it can be 0.1s, 0.3s, 0.5s, 0.6s, 0.8s or 1s, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0033] This invention does not limit the number of atomic layer deposition cycles, as long as the thickness of the resulting lithium molybdate layer meets the process requirements.
[0034] In some embodiments, the temperature for atomic layer deposition is 150°C to 250°C, for example, 150°C, 180°C, 200°C, 210°C, 240°C or 250°C, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0035] In some embodiments, the vacuum degree of the atomic layer deposition is 1 Pa to 10 Pa, for example, it can be 1 Pa, 3 Pa, 5 Pa, 6 Pa, 8 Pa or 10 Pa, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0036] In some embodiments, the emulsion polymer spraying includes: spraying a PMA prepolymer emulsion onto the surface of a lithium molybdate layer, followed by a second vacuum drying process to cure the PMA prepolymer emulsion and form a polymethyl methacrylate (PMMA) coating layer.
[0037] In some embodiments, the preparation method of the PMA prepolymer emulsion includes: mixing methyl methacrylate (MMA), emulsifier and deionized water in a mass ratio of (10~20):(0.5~2):(80~90), stirring and mixing, adding an initiator, and prepolymerizing at a temperature of 60℃~80℃ to obtain the PMA prepolymer emulsion.
[0038] The emulsifier can be SDS, and the initiator can be AIBN.
[0039] In some embodiments, the amount of initiator added is 0.5% to 2% of the mass of MMA, for example, it can be 0.5%, 1%, 1.5% or 2%, but is not limited to the listed values, and other unlisted values within the range are also applicable.
[0040] In some embodiments, the spraying pressure is 0.2MPa to 0.5MPa, for example, it can be 0.2MPa, 0.3MPa, 0.4MPa or 0.5MPa, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0041] In some embodiments, the spraying temperature is 80°C to 120°C, for example, it can be 80°C, 90°C, 100°C, 110°C or 120°C, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0042] In some embodiments, the temperature of the second vacuum drying is 100°C to 120°C, for example, 100°C, 105°C, 110°C, 115°C or 120°C, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0043] In some embodiments, the second vacuum drying time is 4h to 6h, for example, it can be 4h, 5h or 6h, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0044] As a preferred embodiment of the preparation method described in the first aspect of the present invention, the preparation method includes the following steps:
[0045] (1) Mix lithium source, iron source, manganese source, phosphorus source, cerium source and lanthanum source, wet ball mill, and then perform first vacuum drying at 60℃~80℃ for 12h~24h, and sinter at 600℃~800℃ for 8h~12h in a protective atmosphere to obtain cerium lanthanum co-doped manganese iron phosphate precursor.
[0046] The cerium-lanthanum co-doped lithium manganese iron phosphate precursor includes doping elements and lithium manganese iron phosphate. The doping elements are cerium and lanthanum. The total doping amount of cerium and lanthanum is 0.5% to 5% of the total metal molar amount in the lithium manganese iron phosphate, and the molar ratio of cerium to lanthanum is (1~3):(1~3).
[0047] (2) By atomic layer deposition, a lithium molybdate layer with a thickness of 10 nm to 50 nm is coated on the surface of the cerium-lanthanum co-doped lithium manganese iron phosphate precursor;
[0048] The lithium source precursor used in the atomic layer deposition includes lithium tert-butoxide, and the molybdenum source precursor used includes molybdenum hexacarbonyl; during the atomic layer deposition, the pulse time for each precursor is 0.1s to 1s; the temperature of the atomic layer deposition is 150℃ to 250℃, and the vacuum degree is 1Pa to 10Pa;
[0049] (3) Spray the PMA prepolymer emulsion onto the surface of the lithium molybdate layer, and perform a second vacuum drying at 100℃~120℃ for 4h~6h to solidify the PMA prepolymer emulsion. Coat the surface of the lithium molybdate layer with a polymethyl methacrylate coating layer with a thickness of 50nm~200nm to obtain the cerium lanthanum co-doped modified manganese iron phosphate.
[0050] The preparation method of the PMA prepolymer emulsion includes: mixing methyl methacrylate, emulsifier SDS and deionized water in a mass ratio of (10~20):(0.5~2):(80~90), stirring and mixing, adding initiator AIBN, and carrying out prepolymerization at a temperature of 60℃~80℃ to obtain the PMA prepolymer emulsion.
[0051] The spraying pressure is 0.2MPa~0.5MPa, and the temperature is 80℃~120℃.
[0052] In a second aspect, the present invention provides a cerium-lanthanum co-doped modified lithium manganese iron phosphate, wherein the cerium-lanthanum co-doped modified lithium manganese iron phosphate is prepared by the preparation method described in the first aspect.
[0053] Thirdly, the present invention provides a positive electrode, the positive electrode comprising cerium-lanthanum co-doped modified lithium manganese iron phosphate prepared by the preparation method described in the first aspect, or comprising cerium-lanthanum co-doped modified lithium manganese iron phosphate as described in the second aspect.
[0054] 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.
[0055] Compared with the prior art, the present invention has the following beneficial effects:
[0056] The preparation method provided by this invention can significantly improve the electrochemical performance of lithium manganese iron phosphate. Specifically, the co-doping of Ce and La enhances the bulk structural stability and effectively suppresses Mn. 3+ Jahn-Teller distortion and Fe 2+ Oxidation and dissolution; the atomic layer deposition of lithium molybdate can improve ionic conductivity and resist corrosion by HF in the electrolyte; the emulsion polymerization spraying of polymethyl methacrylate layer can inhibit electrolyte decomposition and excessive growth of SEI film, while preventing particle breakage by elastically adapting to charge and discharge volume changes; the synergistic effect of the three significantly reduces interfacial impedance, and simultaneously improves the cycle life, high rate performance and interfacial compatibility of the material, solving the core performance defects of traditional lithium manganese iron phosphate. Detailed Implementation
[0057] 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.
[0058] 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.
[0059] 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.
[0060] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.
[0061] 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.
[0062] 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.
[0063] 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."
[0064] 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.
[0065] 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.
[0066] Example 1
[0067] This embodiment provides a method for preparing cerium-lanthanum co-doped modified manganese iron phosphate, comprising the following steps:
[0068] (1) Mix lithium carbonate, ferrous sulfate, manganese sulfate, ammonium dihydrogen phosphate, cerium nitrate and lanthanum nitrate, wet ball mill them, and then perform a first vacuum drying at 70°C for 18 hours. Then, sinter them at 700°C for 10 hours in a nitrogen atmosphere to obtain a cerium-lanthanum co-doped manganese iron phosphate precursor.
[0069] The cerium-lanthanum co-doped lithium manganese iron phosphate precursor includes doping elements and lithium manganese iron phosphate. The doping elements are cerium and lanthanum. The total doping amount of cerium and lanthanum is 2.5% of the total metal molar amount in the lithium manganese iron phosphate, and the molar ratio of cerium to lanthanum is 1:1.
[0070] The molar ratio of lithium, iron and manganese in lithium manganese iron phosphate is 1:0.4:0.6;
[0071] (2) A lithium molybdate layer with a thickness of 30 nm is coated on the surface of the cerium-lanthanum co-doped lithium manganese iron phosphate precursor by atomic layer deposition;
[0072] The lithium source precursor used in the atomic layer deposition includes lithium tert-butoxide, and the molybdenum source precursor used includes molybdenum hexacarbonyl; the pulse time for each precursor during the atomic layer deposition is 0.5 s; the temperature of the atomic layer deposition is 200 °C, and the vacuum degree is 5 Pa.
[0073] (3) Spray the PMA prepolymer emulsion onto the surface of the lithium molybdate layer, and perform a second vacuum drying at 110°C for 5 hours to solidify the PMA prepolymer emulsion. Coat the surface of the lithium molybdate layer with a polymethyl methacrylate coating layer with a thickness of 100 nm to obtain the cerium-lanthanum co-doped modified manganese iron phosphate.
[0074] The preparation method of the PMA prepolymer emulsion includes: mixing methyl methacrylate, emulsifier SDS and deionized water at a mass ratio of 15:1:85, stirring and mixing, adding initiator AIBN, and prepolymerizing at a temperature of 70°C to obtain the PMA prepolymer emulsion.
[0075] The spraying pressure is 0.4 MPa and the temperature is 100°C.
[0076] Example 2
[0077] This embodiment provides a method for preparing cerium-lanthanum co-doped modified manganese iron phosphate, comprising the following steps:
[0078] (1) Mix lithium carbonate, ferrous sulfate, manganese sulfate, ammonium dihydrogen phosphate, cerium nitrate and lanthanum nitrate, wet ball mill them, and then perform a first vacuum drying at 60°C for 24 hours. Then, sinter them at 600°C for 12 hours in a nitrogen atmosphere to obtain a cerium-lanthanum co-doped manganese iron phosphate precursor.
[0079] The cerium-lanthanum co-doped lithium manganese iron phosphate precursor includes doping elements and lithium manganese iron phosphate. The doping elements are cerium and lanthanum. The total doping amount of cerium and lanthanum is 0.5% of the total metal molar amount in the lithium manganese iron phosphate, and the molar ratio of cerium to lanthanum is 1:3.
[0080] The molar ratio of lithium, iron and manganese in lithium manganese iron phosphate is 1:0.4:0.6;
[0081] (2) A lithium molybdate layer with a thickness of 10 nm is coated on the surface of the cerium-lanthanum co-doped lithium manganese iron phosphate precursor by atomic layer deposition;
[0082] The lithium source precursor used in the atomic layer deposition includes lithium tert-butoxide, and the molybdenum source precursor used includes molybdenum hexacarbonyl; during the atomic layer deposition, the pulse time for each precursor is 0.1 s; the temperature of the atomic layer deposition is 150 °C, and the vacuum degree is 1 Pa;
[0083] (3) Spray the PMA prepolymer emulsion onto the surface of the lithium molybdate layer, and perform a second vacuum drying at 100°C for 6 hours to solidify the PMA prepolymer emulsion. Coat the surface of the lithium molybdate layer with a polymethyl methacrylate coating layer with a thickness of 50 nm to obtain the cerium-lanthanum co-doped modified manganese iron phosphate.
[0084] The preparation method of the PMA prepolymer emulsion includes: mixing methyl methacrylate, emulsifier SDS and deionized water at a mass ratio of 10:0.5:80, stirring and mixing, adding initiator AIBN, and prepolymerizing at a temperature of 60°C to obtain the PMA prepolymer emulsion.
[0085] The spraying pressure is 0.2 MPa and the temperature is 120°C.
[0086] Example 3
[0087] This embodiment provides a method for preparing cerium-lanthanum co-doped modified manganese iron phosphate, comprising the following steps:
[0088] (1) Mix lithium carbonate, ferrous sulfate, manganese sulfate, ammonium dihydrogen phosphate, cerium nitrate and lanthanum nitrate, wet ball mill them, and then perform a first vacuum drying at 80°C for 12 hours. Then, sinter them at 800°C for 8 hours in a nitrogen atmosphere to obtain a cerium-lanthanum co-doped manganese iron phosphate precursor.
[0089] The cerium-lanthanum co-doped lithium manganese iron phosphate precursor includes doping elements and lithium manganese iron phosphate. The doping elements are cerium and lanthanum. The total doping amount of cerium and lanthanum is 5% of the total metal molar amount in the lithium manganese iron phosphate, and the molar ratio of cerium to lanthanum is 3:1.
[0090] The molar ratio of lithium, iron and manganese in lithium manganese iron phosphate is 1:0.4:0.6;
[0091] (2) A lithium molybdate layer with a thickness of 50 nm is coated on the surface of the cerium-lanthanum co-doped lithium manganese iron phosphate precursor by atomic layer deposition;
[0092] The lithium source precursor used in the atomic layer deposition includes lithium tert-butoxide, and the molybdenum source precursor used includes molybdenum hexacarbonyl; the pulse time for each precursor during the atomic layer deposition is 1 s; the temperature of the atomic layer deposition is 250 °C, and the vacuum degree is 10 Pa.
[0093] (3) Spray the PMA prepolymer emulsion onto the surface of the lithium molybdate layer, and perform a second vacuum drying at 120°C for 4 hours to solidify the PMA prepolymer emulsion. Coat the surface of the lithium molybdate layer with a polymethyl methacrylate coating layer with a thickness of 200 nm to obtain the cerium-lanthanum co-doped modified manganese iron phosphate.
[0094] The preparation method of the PMA prepolymer emulsion includes: mixing methyl methacrylate, emulsifier SDS and deionized water at a mass ratio of 20:2:90, stirring and mixing, adding initiator AIBN, and prepolymerizing at a temperature of 80°C to obtain the PMA prepolymer emulsion.
[0095] The spraying pressure is 0.5 MPa and the temperature is 80°C.
[0096] Example 4
[0097] This embodiment provides a method for preparing cerium-lanthanum co-doped modified manganese iron phosphate, which is the same as in Example 1 except that the thickness of the lithium molybdate layer is 5 nm.
[0098] Example 5
[0099] This embodiment provides a method for preparing cerium-lanthanum co-doped modified manganese iron phosphate, which is the same as in Example 1 except that the thickness of the lithium molybdate layer is 60 nm.
[0100] Example 6
[0101] This embodiment provides a method for preparing cerium-lanthanum co-doped modified manganese iron phosphate, which is the same as in Example 1 except that the thickness of the polymethyl methacrylate coating layer is 40 nm.
[0102] Example 7
[0103] This embodiment provides a method for preparing cerium-lanthanum co-doped modified manganese iron phosphate. Except for the thickness of the polymethyl methacrylate coating layer being 220 nm, the rest is the same as in Example 1.
[0104] Comparative Example 1
[0105] This comparative example provides a method for preparing cerium-doped modified manganese iron phosphate, comprising the following steps:
[0106] (1) Mix lithium carbonate, ferrous sulfate, manganese sulfate, ammonium dihydrogen phosphate and cerium nitrate, wet ball mill them, and then perform a first vacuum drying at 70°C for 18 hours. Then, sinter them at 700°C for 10 hours in a nitrogen atmosphere to obtain a cerium-doped lithium manganese iron phosphate precursor.
[0107] The cerium-doped lithium manganese iron phosphate precursor includes a dopant element and lithium manganese iron phosphate, wherein the dopant element is cerium, and the doping amount of cerium is 2.5% of the total molar amount of metal in the lithium manganese iron phosphate;
[0108] The molar ratio of lithium, iron and manganese in lithium manganese iron phosphate is 1:0.4:0.6;
[0109] (2) A lithium molybdate layer with a thickness of 30 nm is coated on the surface of the cerium-doped lithium manganese iron phosphate precursor by atomic layer deposition;
[0110] The lithium source precursor used in the atomic layer deposition includes lithium tert-butoxide, and the molybdenum source precursor used includes molybdenum hexacarbonyl; the pulse time for each precursor during the atomic layer deposition is 0.5 s; the temperature of the atomic layer deposition is 200 °C, and the vacuum degree is 5 Pa.
[0111] (3) Spray the PMA prepolymer emulsion onto the surface of the lithium molybdate layer, and perform a second vacuum drying at 110°C for 5 hours to solidify the PMA prepolymer emulsion. Coat the surface of the lithium molybdate layer with a polymethyl methacrylate coating layer with a thickness of 100 nm to obtain the cerium-doped coated modified lithium manganese iron phosphate.
[0112] The preparation method of the PMA prepolymer emulsion includes: mixing methyl methacrylate, emulsifier SDS and deionized water at a mass ratio of 15:1:85, stirring and mixing, adding initiator AIBN, and prepolymerizing at a temperature of 70°C to obtain the PMA prepolymer emulsion.
[0113] The spraying pressure is 0.4 MPa and the temperature is 100°C.
[0114] Comparative Example 2
[0115] This comparative example provides a method for preparing lanthanum-doped modified manganese iron phosphate, comprising the following steps:
[0116] (1) Mix lithium carbonate, ferrous sulfate, manganese sulfate, ammonium dihydrogen phosphate and lanthanum nitrate, wet ball mill them, and then perform a first vacuum drying at 70°C for 18 hours. Then, sinter them at 700°C for 10 hours in a nitrogen atmosphere to obtain a lanthanum-doped manganese iron phosphate precursor.
[0117] The lanthanum-doped lithium manganese iron phosphate precursor includes a dopant element and lithium manganese iron phosphate, wherein the dopant element is lanthanum, and the amount of lanthanum doping is 2.5% of the total metal molar amount in the lithium manganese iron phosphate.
[0118] The molar ratio of lithium, iron and manganese in lithium manganese iron phosphate is 1:0.4:0.6;
[0119] (2) A lithium molybdate layer with a thickness of 30 nm is coated on the surface of the lanthanum-doped lithium manganese iron phosphate precursor by atomic layer deposition;
[0120] The lithium source precursor used in the atomic layer deposition includes lithium tert-butoxide, and the molybdenum source precursor used includes molybdenum hexacarbonyl; the pulse time for each precursor during the atomic layer deposition is 0.5 s; the temperature of the atomic layer deposition is 200 °C, and the vacuum degree is 5 Pa.
[0121] (3) Spray the PMA prepolymer emulsion onto the surface of the lithium molybdate layer, and perform a second vacuum drying at 110°C for 5 hours to solidify the PMA prepolymer emulsion. Coat the surface of the lithium molybdate layer with a polymethyl methacrylate coating layer with a thickness of 100 nm to obtain the lanthanum doped coated modified lithium manganese iron phosphate.
[0122] The preparation method of the PMA prepolymer emulsion includes: mixing methyl methacrylate, emulsifier SDS and deionized water at a mass ratio of 15:1:85, stirring and mixing, adding initiator AIBN, and prepolymerizing at a temperature of 70°C to obtain the PMA prepolymer emulsion.
[0123] The spraying pressure is 0.4 MPa and the temperature is 100°C.
[0124] Comparative Example 3
[0125] This comparative example provides a method for preparing cerium-lanthanum co-doped modified manganese iron phosphate, comprising the following steps:
[0126] (1) Mix lithium carbonate, ferrous sulfate, manganese sulfate, ammonium dihydrogen phosphate, cerium nitrate and lanthanum nitrate, wet ball mill them, and then perform a first vacuum drying at 70°C for 18 hours. Then, sinter them at 700°C for 10 hours in a nitrogen atmosphere to obtain a cerium-lanthanum co-doped manganese iron phosphate precursor.
[0127] The cerium-lanthanum co-doped lithium manganese iron phosphate precursor includes doping elements and lithium manganese iron phosphate. The doping elements are cerium and lanthanum. The total doping amount of cerium and lanthanum is 2.5% of the total metal molar amount in the lithium manganese iron phosphate, and the molar ratio of cerium to lanthanum is 1:1.
[0128] The molar ratio of lithium, iron and manganese in lithium manganese iron phosphate is 1:0.4:0.6;
[0129] (2) The PMA prepolymer emulsion was sprayed onto the surface of the cerium-lanthanum co-doped lithium manganese iron phosphate precursor and subjected to a second vacuum drying at 110°C for 5 hours to solidify the PMA prepolymer emulsion. A polymethyl methacrylate coating layer with a thickness of 100 nm was then coated onto the surface of the cerium-lanthanum co-doped lithium manganese iron phosphate precursor to obtain the cerium-lanthanum co-doped modified lithium manganese iron phosphate.
[0130] The preparation method of the PMA prepolymer emulsion includes: mixing methyl methacrylate, emulsifier SDS and deionized water at a mass ratio of 15:1:85, stirring and mixing, adding initiator AIBN, and prepolymerizing at a temperature of 70°C to obtain the PMA prepolymer emulsion.
[0131] The spraying pressure is 0.4 MPa and the temperature is 100°C.
[0132] Performance Characterization
[0133] The lithium iron manganese phosphate (as the positive electrode active material) finally prepared in the above examples and comparative examples was used to prepare lithium-ion batteries, and the electrochemical performance was tested. The results are shown in Table 1.
[0134] Preparation of lithium-ion batteries:
[0135] The positive electrode active material, conductive carbon black (SP), and binder polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 8:1:1, and then N-methylpyrrolidone (NMP) solvent was added. The mixture was ball-milled to obtain a slurry. The slurry was coated onto the surface of aluminum foil and baked at 130°C for 3 hours, followed by vacuum baking at 100°C for 6 hours to ensure thorough drying. The areal density was controlled at 300 mg / cm³. 2 The R2032 lithium-ion battery was prepared by rolling and pressing, using lithium metal sheet as negative electrode, polypropylene separator, and 1 mol / L LiPF6 electrolyte (solvent: EC / DMC / EMC).
[0136] Charge the battery at a constant current rate of 0.2C to 4.5V, then charge it at a constant voltage rate of 4.5V until the current equals 0.05C. The charging capacity at this point is recorded as the first charge specific capacity. After resting for 5 minutes, discharge the battery at a constant current rate of 0.2C until the voltage reaches 2.5V. The discharge capacity at this point is recorded as the battery's first discharge specific capacity. After 100 cycles, the discharge capacity retention rate is recorded as the cycle capacity retention rate.
[0137] Table 1
[0138]
[0139] As can be seen from Examples 1 to 3 in the table, the first-cycle discharge specific capacity of the cerium-lanthanum co-doped modified manganese iron phosphate provided by the present invention reaches more than 154.9 mAh / g, and the cycle capacity retention rate is stable at more than 96.3%, demonstrating excellent electrochemical performance.
[0140] A comparison of Examples 4 and 5 with Example 1 shows that the thickness of the lithium molybdate layer needs to be controlled within a reasonable range to achieve optimal performance. When the lithium molybdate layer is too thin, it cannot sufficiently improve ionic conductivity and resist HF corrosion, resulting in a decrease in the first-cycle discharge specific capacity and cycle capacity retention. When the thickness is too thick, it increases the resistance of the ion transport path, leading to a decrease in the first-cycle discharge specific capacity and cycle capacity retention.
[0141] A comparison of Examples 6 and 7 with Example 1 shows that the thickness of the polymethyl methacrylate (PMMA) coating layer affects the material properties. When the coating layer is too thin, its ability to suppress electrolyte decomposition and excessive SEI film growth is limited, making it difficult to adapt to charge-discharge volume changes through elasticity, and particle breakage is likely to occur, resulting in a decrease in the first-cycle discharge specific capacity and cycle capacity retention rate. When the thickness is too thick, it will hinder the interfacial transport of lithium ions and weaken the elastic adaptation effect, resulting in a decrease in the first-cycle discharge specific capacity and cycle capacity retention rate.
[0142] A comparison of Comparative Examples 1 and 2 with Example 1 shows that only co-doping with Ce and La can simultaneously enhance bulk structural stability and suppress Mn. 3+ Jahn-Teller distortion and Fe 2+ Oxidative dissolution. While Ce doping alone can suppress structural distortion to some extent, it lacks the La-dependent effect on Fe. 2+ The selective stabilizing effect of Fe 2+ The oxidation and dissolution problem has not been effectively solved; when only La doping is performed, the reaction with Mn is not satisfactory. 3+ The distortion suppression effect is weaker than Ce, and long-term cycling can easily lead to loosening of the body structure.
[0143] A comparison of Comparative Example 3 and Example 1 shows that the synergistic effect of the lithium molybdate layer and the polymethyl methacrylate layer is key to improving interface performance. Without the lithium molybdate layer, the polymethyl methacrylate layer alone cannot resist HF corrosion, and the improvement in ionic conductivity is insufficient. It is difficult to form a synergistic effect of interface protection and ion transport with the polymethyl methacrylate layer, resulting in increased interface impedance, a first-cycle discharge specific capacity of only 151.8 mAh / g, and a cycle capacity retention of 91.7%.
[0144] In summary, the preparation method provided by this invention can significantly improve the electrochemical performance of lithium manganese iron phosphate. Specifically, the co-doping of Ce and La enhances the bulk structural stability and effectively suppresses Mn. 3+ Jahn-Teller distortion and Fe 2+ Oxidation and dissolution; the atomic layer deposition of lithium molybdate can improve ionic conductivity and resist corrosion by HF in the electrolyte; the emulsion polymerization spraying of polymethyl methacrylate layer can inhibit electrolyte decomposition and excessive growth of SEI film, while preventing particle breakage by elastically adapting to charge and discharge volume changes; the synergistic effect of the three significantly reduces interfacial impedance, and simultaneously improves the cycle life, high rate performance and interfacial compatibility of the material, solving the core performance defects of traditional lithium manganese iron phosphate.
[0145] 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 method for preparing cerium and lanthanum co-doped coating-modified lithium iron manganese phosphate, characterized in that, The preparation method includes the following steps: Solid-state method for preparing cerium-lanthanum co-doped lithium manganese iron phosphate precursor; A lithium molybdate layer was coated onto the surface of the cerium-lanthanum co-doped lithium manganese iron phosphate precursor by atomic layer deposition. The cerium-lanthanum co-doped modified manganese iron phosphate was obtained by coating the surface of the lithium molybdate layer with a polymethyl methacrylate coating layer through emulsion polymer spraying.
2. The production method according to claim 1, characterized by, The cerium-lanthanum co-doped lithium manganese iron phosphate precursor includes doping elements and lithium manganese iron phosphate. The doping elements are cerium and lanthanum, and the total doping amount of cerium and lanthanum is 0.5% to 5% of the total metal molar amount in the lithium manganese iron phosphate.
3. The preparation method according to claim 1, characterized in that, The thickness of the lithium molybdate layer is 10 nm to 50 nm.
4. The method of claim 1, wherein, The thickness of the polymethyl methacrylate coating layer is 50 nm to 200 nm.
5. The preparation method according to claim 1, characterized in that, The solid-state method includes: mixing lithium source, iron source, manganese source, phosphorus source, cerium source and lanthanum source, wet ball milling followed by first vacuum drying, and sintering in a protective atmosphere to obtain the cerium-lanthanum co-doped manganese iron phosphate precursor.
6. The preparation method according to claim 5, characterized in that, The lithium source includes any one or a combination of at least two of lithium carbonate, lithium hydroxide, or lithium acetate.
7. The preparation method according to claim 5, characterized in that, The iron source includes any one or a combination of at least two of ferrous sulfate, ferrous chloride, or ferrous oxalate.
8. The preparation method according to claim 5, characterized in that, The manganese source includes any one or a combination of at least two of manganese sulfate, manganese chloride, or manganese oxalate.
9. The preparation method according to claim 5, characterized in that, The phosphorus source includes any one or a combination of at least two of the following: ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or phosphoric acid.
10. The preparation method according to claim 5, characterized in that, The cerium source includes cerium nitrate and / or cerium acetate.
11. The preparation method according to claim 5, characterized in that, The lanthanum source includes lanthanum nitrate and / or lanthanum acetate.
12. The preparation method according to claim 5, characterized in that, The temperature of the first vacuum drying is 60℃~80℃, and the time is 12h~24h.
13. The preparation method according to claim 5, characterized in that, The sintering temperature is 600℃~800℃, and the time is 8h~12h.
14. The preparation method according to claim 1, characterized in that, The lithium source precursor used in the atomic layer deposition includes lithium tert-butoxide, and the molybdenum source precursor used includes molybdenum hexacarbonyl.
15. The preparation method according to claim 1, characterized in that, During the atomic layer deposition, the pulse time for each precursor is 0.1s to 1s.
16. The preparation method according to claim 1, characterized in that, The atomic layer deposition temperature is 150℃~250℃.
17. The preparation method according to claim 1, characterized in that, The vacuum level of the atomic layer deposition is 1 Pa to 10 Pa.
18. The preparation method according to claim 1, characterized in that, The emulsion polymer spraying includes: spraying a PMA prepolymer emulsion onto the surface of a lithium molybdate layer, followed by a second vacuum drying process to cure the PMA prepolymer emulsion and form a polymethyl methacrylate coating layer.
19. The preparation method according to claim 18, characterized in that, The preparation method of the PMA prepolymer emulsion includes: mixing methyl methacrylate, emulsifier and deionized water in a mass ratio of (10~20):(0.5~2):(80~90), stirring and mixing, adding an initiator, and carrying out prepolymerization at a temperature of 60℃~80℃ to obtain the PMA prepolymer emulsion.
20. The preparation method according to claim 18, characterized in that, The spraying pressure is 0.2MPa~0.5MPa.
21. The preparation method according to claim 18, characterized in that, The spraying temperature is 80℃~120℃.
22. The preparation method according to claim 18, characterized in that, The temperature for the second vacuum drying is 100℃~120℃.
23. The preparation method according to claim 18, characterized in that, The second vacuum drying time is 4h~6h.
24. A cerium-lanthanum co-doped modified manganese iron phosphate, characterized in that, The cerium-lanthanum co-doped modified manganese iron phosphate is prepared by the preparation method described in any one of claims 1 to 23.
25. A positive electrode, characterized in that, The positive electrode comprises cerium-lanthanum co-doped modified lithium manganese iron phosphate prepared by the preparation method according to any one of claims 1 to 23, or cerium-lanthanum co-doped modified lithium manganese iron phosphate according to claim 24.