A manganese iron lithium phosphate cathode material with consistent morphology, a preparation method and a cathode

Abstract

The present application relates to a kind of morphology consistent lithium manganese iron phosphate positive electrode material, preparation method and positive electrode, the preparation method includes the following steps: (1) preparation fluorine indium co-doped lithium iron phosphate matrix;(2) using atomic layer deposition on the surface of the fluorine indium co-doped lithium iron phosphate matrix preparation AlF3-InF3 Covering layer, obtain inner layer coated lithium manganese iron phosphate material;(3) on the surface of the AlF3-InF3 Covering layer is coated MXene covering layer, obtain the morphology consistent lithium manganese iron phosphate positive electrode material.The preparation method provided by the present application solves the Jahn-Teller distortion of LMFP, ion elution, low conductivity and volume change problem by doping and double-layer coating modification simultaneously, significantly improves the cycle life, rate performance and high temperature stability of material, and preparation process controllability is strong, suitable for industrialization mass production.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and relates to a battery material, particularly to a lithium manganese iron phosphate cathode material with consistent morphology, its preparation method, and the cathode itself. Background Technology

[0002] Lithium-ion batteries, due to their high energy density, long cycle life, and environmental friendliness, have been widely used in consumer electronics, electric vehicles, and energy storage systems. As a core component of lithium-ion batteries, the performance of the cathode material directly determines the battery's energy density, rate capability, and safety performance. Lithium manganese iron phosphate (LMFP), as a novel cathode material, combines the high safety of lithium iron phosphate (LFP) with the high voltage advantage of lithium manganese phosphate (LMP), achieving a theoretical capacity of up to 170 mAh / g. Furthermore, its low raw material cost and good environmental compatibility have made it one of the research hotspots for lithium-ion battery cathode materials in recent years.

[0003] However, LMFPs still face many key technical bottlenecks in practical applications: On the one hand, the Mn³⁺ in the LMFP crystal structure is prone to Jahn-Teller distortion during charge-discharge cycles, leading to local collapse of the crystal structure. Simultaneously, Fe²⁺ is easily oxidized and dissolved in the electrolyte, causing not only loss of active materials but also the formation of inert byproducts at the electrode-electrolyte interface, significantly accelerating battery capacity decay. On the other hand, the intrinsic ionic conductivity of LMFPs is only 10⁻⁶. -9 S / cm~10 -7 S / cm, far lower than commercial LFP (10 -6 S / cm~10 -3 The low efficiency (S / cm) results in hindered lithium-ion migration within the material, leading to low capacity utilization during high-rate charging and discharging, which makes it difficult to meet the fast-charging performance requirements of power batteries.

[0004] To address these issues, existing technologies primarily employ modification methods such as elemental doping and surface coating. For instance, doping with metal ions like Mg²⁺ and Ni²⁺ suppresses Jahn-Teller distortion in Mn³⁺, but single doping has limited effect on improving ionic conductivity. Surface coating with inorganic materials like Al₂O₃ and LiPO₃ can reduce the dissolution of active ions, but traditional coatings are often dense and rigid structures, making it difficult to buffer volume changes during LMFP charging and discharging. After long-term cycling, particle cracks still appear, leading to coating failure. Furthermore, existing coating processes struggle to precisely control the coating thickness and uniformity, easily resulting in incomplete coating or excessively thick coatings that hinder lithium-ion transport, failing to simultaneously ensure material cycle stability, rate performance, and structural integrity. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a lithium manganese iron phosphate cathode material with consistent morphology, a preparation method, and a cathode. The preparation method provided by the present invention solves the problems of Jahn-Teller distortion, ion dissolution, low conductivity, and volume change of LMFP through synergistic modification of doping and double-layer coating, significantly improving the cycle life, rate performance, and high-temperature stability of the material. Moreover, the preparation process is highly controllable and suitable for industrial mass production.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a lithium manganese iron phosphate cathode material with uniform morphology, the preparation method comprising the following steps:

[0008] (1) Preparation of fluorine-indium co-doped lithium iron manganese phosphate matrix;

[0009] (2) An AlF3-InF3 coating layer was prepared on the surface of the fluorine-indium co-doped lithium iron manganese phosphate substrate by atomic layer deposition to obtain an inner-layer coated lithium iron manganese phosphate material;

[0010] (3) An MXene coating layer is coated on the surface of the AlF3-InF3 coating layer to obtain the lithium manganese iron phosphate cathode material with consistent morphology.

[0011] This invention achieves significant benefits through the synergistic effect of fluorine-indium co-doping, an AlF3-InF3 coating layer, and an MXene coating layer. The AlF3-InF3 coating layer adheres tightly to the surface of the fluorine-indium co-doped lithium iron manganese phosphate (LMFP) substrate, effectively suppressing the dissolution of Mn²⁺ and Fe²⁺ into the electrolyte and preventing decomposition caused by direct contact between the electrolyte and the substrate. It also significantly reduces side reactions at 60°C. The outer MXene coating layer, with its excellent flexibility, effectively buffers volume changes during the charging and discharging process of LMFP, preventing particle cracking. Furthermore, its two-dimensional layered structure can construct a continuous conductive network, improving the material's low intrinsic conductivity. The combination of these two layers not only solves the problem of low intrinsic conductivity in LMFP due to Mn²⁺... 3+ The Jahn-Teller distortion and structural collapse caused by the dissolution of active ions were overcome, and the particle breakage defects caused by volume changes were also overcome, ultimately significantly improving the cycle life and electrochemical performance of LMFPs, meeting the high requirements of power batteries, energy storage batteries and other scenarios.

[0012] In one embodiment of the present invention, step (1) of preparing the fluorine-indium co-doped lithium iron manganese phosphate matrix includes: mixing a lithium source, a manganese source, an iron source, a fluorine source and an indium source, ball milling to obtain a uniform slurry, spray drying to obtain precursor particles; sintering the precursor particles to obtain the fluorine-indium co-doped lithium iron manganese phosphate matrix.

[0013] For example, the dispersant used to obtain a homogeneous slurry through ball milling can be anhydrous ethanol.

[0014] For example, ball milling can be performed using a planetary ball mill.

[0015] In one embodiment of the present invention, the lithium source includes lithium dihydrogen phosphate.

[0016] In one embodiment of the present invention, the manganese source includes manganese carbonate.

[0017] In one embodiment of the present invention, the iron source comprises ferrous carbonate.

[0018] In one embodiment of the present invention, the fluorine source includes ammonium fluoride.

[0019] In one embodiment of the present invention, the indium source includes indium chloride.

[0020] In one embodiment of the present invention, the median particle size D50 of the precursor particles is 1 μm to 3 μm, for example, it can be 1 μm, 1.5 μm, 2 μm, 2.5 μm or 3 μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0021] The median particle size of the precursor particles is related to the parameters of spray drying. Optionally, the inlet temperature of spray drying can be 200℃~220℃, for example, 200℃, 205℃, 210℃, 215℃ or 220℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] The outlet temperature of spray drying can be 80℃~100℃, for example, 80℃, 85℃, 90℃, 95℃ or 100℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] In one embodiment of the present invention, the sintering is carried out in a protective atmosphere, including a pre-firing and a main firing performed sequentially;

[0024] The pre-firing includes heating to 300℃~400℃ at a heating rate of 2℃ / min~5℃ / min and holding at that temperature for 2h~3h;

[0025] The main firing process involves heating to 650℃~750℃ at a heating rate of 1℃ / min~3℃ / min and holding at that temperature for 8h~12h.

[0026] The preheating rate is 2℃ / min to 5℃ / min, for example, it can be 2℃ / min, 3℃ / min, 4℃ / min or 5℃ / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] The preheating temperature is 300℃~400℃, for example, it can be 300℃, 320℃, 350℃, 380℃ or 400℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] The preheating time is 2h to 3h, for example, it can be 2h, 2.5h or 3h, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] The heating rate of the main burner is 1℃ / min to 3℃ / min, for example, it can be 1℃ / min, 2℃ / min or 3℃ / min, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] The main firing temperature is 650℃~750℃, for example, it can be 650℃, 680℃, 700℃, 720℃ or 750℃, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] The main heat preservation time is 8h~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.

[0032] Optionally, the protective atmosphere may include nitrogen.

[0033] In one embodiment of the present invention, a single deposition cycle of the atomic layer deposition includes: using Ar gas as a carrier gas, introducing trimethylaluminum for 0.1s~0.3s, purging with Ar gas for 5s~10s, introducing hydrogen fluoride for 0.2s~0.5s, purging with Ar gas for 5s~10s, introducing triethylindium for 0.1s~0.3s, purging with Ar gas for 5s~10s, introducing hydrogen fluoride for 0.2s~0.5s, and purging with Ar gas for 5s~10s.

[0034] The number of cycles is related to the thickness of the AlF3-InF3 coating layer, but this invention does not impose a specific limitation on it. In one embodiment of this invention, the thickness of the AlF3-InF3 coating layer is 5nm to 20nm, for example, it can be 5nm, 8nm, 10nm, 12nm, 15nm, 18nm or 20nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] In one embodiment of the present invention, the temperature of the atomic layer deposition is 150°C to 200°C, for example, it can be 150°C, 160°C, 180°C, 190°C or 200°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] In one embodiment of the present invention, the MXene coating layer comprises: etching away the Al layer of Ti3AlC2 using hydrofluoric acid solution, and washing to obtain an MXene dispersion with a concentration of 0.5 mg / mL to 1 mg / mL;

[0037] The inner layer of lithium manganese iron phosphate material was mixed with the MXene dispersion, ultrasonically dispersed, stirred and dried to constant weight to obtain the lithium manganese iron phosphate cathode material with consistent morphology.

[0038] In one embodiment of the present invention, the solid-liquid ratio of the inner layer coated lithium manganese iron phosphate material to the MXene dispersion is 1:10 to 1:20, and the dimension of the solid-liquid ratio is g / mL. For example, it can be 1:10, 1:12, 1:15, 1:16, 1:18 or 1:20, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] In one embodiment of the present invention, the power of the ultrasonic dispersion is 300W to 500W, for example, it can be 300W, 350W, 400W, 450W or 500W, but is not limited to the listed values, and other unlisted values ​​within the range.

[0040] In one embodiment of the present invention, the ultrasonic dispersion time is 30 min to 60 min, for example, it can be 30 min, 40 min, 50 min or 60 min, but is not limited to the listed values, and other unlisted values ​​within the range.

[0041] In one embodiment of the present invention, the temperature of the stirring and drying is 60°C to 80°C, for example, it can be 60°C, 65°C, 70°C, 75°C or 80°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] As a preferred embodiment of the preparation method provided by the present invention, the preparation method includes the following steps:

[0043] (1) Lithium dihydrogen phosphate, manganese carbonate, ferrous carbonate, ammonium fluoride and indium chloride are mixed and ball-milled to obtain a uniform slurry. The slurry is then spray-dried (inlet temperature 200℃~220℃, outlet temperature 80℃~100℃) to obtain precursor particles with a median particle size D50 of 1μm~3μm. The precursor particles are then sintered to obtain the fluorine-indium co-doped lithium iron manganese phosphate matrix.

[0044] The main component of the fluorine-indium co-doped lithium iron manganese phosphate matrix is ​​LiMn. 0.5 Fe 0.5 The doping concentrations of PO4 and F are 0.001 wt% to 0.005 wt%, and the doping concentrations of In are 0.002 wt% to 0.012 wt%.

[0045] The process is carried out in a nitrogen atmosphere and includes a pre-firing and a main firing performed sequentially. The pre-firing includes heating to 300℃~400℃ at a heating rate of 2℃ / min~5℃ / min and holding at that temperature for 2h~3h. The main firing includes heating to 650℃~750℃ at a heating rate of 1℃ / min~3℃ / min and holding at that temperature for 8h~12h.

[0046] (2) An AlF3-InF3 coating layer with a thickness of 5 nm to 20 nm was prepared on the surface of the fluorine-indium co-doped lithium iron manganese phosphate substrate by atomic layer deposition to obtain an inner-layer coated lithium iron manganese phosphate material;

[0047] The atomic layer deposition temperature is 150℃~200℃;

[0048] A single deposition cycle of the atomic layer deposition includes: using Ar gas as the carrier gas, introducing trimethylaluminum for 0.1s~0.3s, purging with Ar gas for 5s~10s, introducing hydrogen fluoride for 0.2s~0.5s, purging with Ar gas for 5s~10s, introducing triethylindium for 0.1s~0.3s, purging with Ar gas for 5s~10s, introducing hydrogen fluoride for 0.2s~0.5s, and purging with Ar gas for 5s~10s;

[0049] (3) Use hydrofluoric acid solution to etch and remove the Al layer of Ti3AlC2, and wash to obtain an MXene dispersion with a concentration of 0.5 mg / mL to 1 mg / mL; mix the inner layer coated lithium manganese iron phosphate material with the MXene dispersion, ultrasonically disperse at 300 W to 500 W for 30 min to 60 min, stir and dry at 60 °C to 80 °C until constant weight, and obtain the lithium manganese iron phosphate cathode material with consistent morphology;

[0050] The solid-liquid ratio of the inner layer coated lithium manganese iron phosphate material to the MXene dispersion is 1:10 to 1:20, and the dimension of the solid-liquid ratio is g / mL.

[0051] Secondly, the present invention provides a lithium manganese iron phosphate cathode material with uniform morphology, wherein the lithium manganese iron phosphate cathode material with uniform morphology is prepared by the preparation method described in the first aspect.

[0052] Thirdly, the present invention provides a positive electrode, the positive electrode comprising the lithium manganese iron phosphate positive electrode material with the same morphology as described in the second aspect.

[0053] 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.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] This invention achieves significant benefits through the synergistic effect of fluorine-indium co-doping, an AlF3-InF3 coating layer, and an MXene coating layer. The AlF3-InF3 coating layer adheres tightly to the surface of the fluorine-indium co-doped lithium iron manganese phosphate (LMFP) substrate, effectively suppressing the dissolution of Mn²⁺ and Fe²⁺ into the electrolyte and preventing decomposition caused by direct contact between the electrolyte and the substrate. It also significantly reduces side reactions at 60°C. The outer MXene coating layer, with its excellent flexibility, effectively buffers volume changes during the charging and discharging process of LMFP, preventing particle cracking. Furthermore, its two-dimensional layered structure can construct a continuous conductive network, improving the material's low intrinsic conductivity. The combination of these two layers not only solves the problem of low intrinsic conductivity in LMFP due to Mn²⁺... 3+ The Jahn-Teller distortion and structural collapse caused by the dissolution of active ions were overcome, and the particle breakage defects caused by volume changes were also overcome, ultimately significantly improving the cycle life and electrochemical performance of LMFPs, meeting the high requirements of power batteries, energy storage batteries and other scenarios. Attached Figure Description

[0056] Figure 1 The image shows a SEM image of the lithium manganese iron phosphate cathode material with consistent morphology obtained in Example 1. 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] 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.

[0067] 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℃.

[0068] Example 1

[0069] This embodiment provides a method for preparing a lithium manganese iron phosphate cathode material with uniform morphology, the preparation method comprising the following steps:

[0070] (1) Lithium dihydrogen phosphate, manganese carbonate, ferrous carbonate, ammonium fluoride and indium chloride are mixed and ball-milled to obtain a uniform slurry. The slurry is then spray-dried (inlet temperature 210℃, outlet temperature 90℃) to obtain precursor particles with a median particle size D50 of 2μm. The precursor particles are then sintered to obtain a fluorine-indium co-doped lithium iron manganese phosphate matrix.

[0071] The main component of the fluorine-indium co-doped lithium iron manganese phosphate matrix is ​​LiMn. 0.5 Fe 0.5 The doping concentration of PO4 is 0.003 wt%, and the doping concentration of In is 0.008 wt%.

[0072] The process is carried out in a nitrogen atmosphere and includes a pre-firing and a main firing performed sequentially. The pre-firing includes heating to 350°C at a heating rate of 4°C / min and holding at that temperature for 2.5 hours. The main firing includes heating to 700°C at a heating rate of 2°C / min and holding at that temperature for 10 hours.

[0073] (2) An AlF3-InF3 coating layer with a thickness of 10 nm was prepared on the surface of the fluorine-indium co-doped lithium iron manganese phosphate substrate by atomic layer deposition to obtain an inner-layer coated lithium iron manganese phosphate material;

[0074] The atomic layer deposition temperature is 180°C;

[0075] A single deposition cycle of the atomic layer deposition includes: using Ar gas as the carrier gas, introducing trimethylaluminum for 0.2 s, purging with Ar gas for 8 s, introducing hydrogen fluoride for 0.4 s, purging with Ar gas for 8 s, introducing triethylin for 0.2 s, purging with Ar gas for 8 s, introducing hydrogen fluoride for 0.4 s, and purging with Ar gas for 8 s.

[0076] (3) Use hydrofluoric acid solution to etch and remove the Al layer of Ti3AlC2, and wash to obtain an MXene dispersion with a concentration of 0.8 mg / mL; mix the inner layer coated lithium manganese iron phosphate material with the MXene dispersion, ultrasonically disperse at 400 W for 45 min, stir and dry at 70 °C to constant weight to obtain the lithium manganese iron phosphate cathode material with consistent morphology.

[0077] The solid-liquid ratio of the inner layer coated lithium manganese iron phosphate material to the MXene dispersion is 1:15, and the dimension of the solid-liquid ratio is g / mL.

[0078] The SEM images of the lithium manganese iron phosphate cathode materials with consistent morphology obtained in this embodiment are as follows: Figure 1 As shown.

[0079] Example 2

[0080] This embodiment provides a method for preparing a lithium manganese iron phosphate cathode material with uniform morphology, the preparation method comprising the following steps:

[0081] (1) Lithium dihydrogen phosphate, manganese carbonate, ferrous carbonate, ammonium fluoride and indium chloride are mixed and ball-milled to obtain a uniform slurry. The slurry is then spray-dried (inlet temperature 200℃, outlet temperature 80℃) to obtain precursor particles with a median particle size D50 of 1μm. The precursor particles are then sintered to obtain a fluorine-indium co-doped lithium iron manganese phosphate matrix.

[0082] The main component of the fluorine-indium co-doped lithium iron manganese phosphate matrix is ​​LiMn. 0.5 Fe 0.5 The doping concentration of PO4 is 0.001 wt%, and the doping concentration of In is 0.002 wt%.

[0083] The process is carried out in a nitrogen atmosphere and includes a pre-firing and a main firing performed sequentially. The pre-firing includes heating to 300°C at a heating rate of 2°C / min and holding at that temperature for 3 hours. The main firing includes heating to 650°C at a heating rate of 1°C / min and holding at that temperature for 12 hours.

[0084] (2) An AlF3-InF3 coating layer with a thickness of 5 nm was prepared on the surface of the fluorine-indium co-doped lithium iron manganese phosphate substrate by atomic layer deposition to obtain an inner-layer coated lithium iron manganese phosphate material;

[0085] The atomic layer deposition temperature is 150°C;

[0086] A single deposition cycle of the atomic layer deposition includes: using Ar gas as the carrier gas, introducing trimethylaluminum for 0.2 s, purging with Ar gas for 8 s, introducing hydrogen fluoride for 0.4 s, purging with Ar gas for 8 s, introducing triethylin for 0.2 s, purging with Ar gas for 8 s, introducing hydrogen fluoride for 0.4 s, and purging with Ar gas for 8 s.

[0087] (3) Use hydrofluoric acid solution to etch and remove the Al layer of Ti3AlC2, and wash to obtain an MXene dispersion with a concentration of 0.5 mg / mL; mix the inner layer coated lithium manganese iron phosphate material with the MXene dispersion, ultrasonically disperse at 300 W for 60 min, stir and dry at 60 °C to constant weight to obtain the lithium manganese iron phosphate cathode material with consistent morphology.

[0088] The solid-liquid ratio of the inner layer coated lithium manganese iron phosphate material to the MXene dispersion is 1:10, and the dimension of the solid-liquid ratio is g / mL.

[0089] Example 3

[0090] This embodiment provides a method for preparing a lithium manganese iron phosphate cathode material with uniform morphology, the preparation method comprising the following steps:

[0091] (1) Lithium dihydrogen phosphate, manganese carbonate, ferrous carbonate, ammonium fluoride and indium chloride are mixed and ball-milled to obtain a uniform slurry. The slurry is then spray-dried (inlet temperature 220℃, outlet temperature 100℃) to obtain precursor particles with a median particle size D50 of 3μm. The precursor particles are then sintered to obtain a fluorine-indium co-doped lithium iron manganese phosphate matrix.

[0092] The main component of the fluorine-indium co-doped lithium iron manganese phosphate matrix is ​​LiMn. 0.5 Fe 0.5 The doping concentration of PO4 is 0.005 wt%, and the doping concentration of In is 0.012 wt%.

[0093] The process is carried out in a nitrogen atmosphere and includes a pre-firing and a main firing performed sequentially. The pre-firing includes heating to 400°C at a heating rate of 5°C / min and holding at that temperature for 2 hours. The main firing includes heating to 750°C at a heating rate of 3°C / min and holding at that temperature for 8 hours.

[0094] (2) An AlF3-InF3 coating layer with a thickness of 20 nm was prepared on the surface of the fluorine-indium co-doped lithium iron manganese phosphate substrate by atomic layer deposition to obtain an inner-layer coated lithium iron manganese phosphate material;

[0095] The atomic layer deposition temperature is 200°C;

[0096] A single deposition cycle of the atomic layer deposition includes: using Ar gas as the carrier gas, introducing trimethylaluminum for 0.2 s, purging with Ar gas for 8 s, introducing hydrogen fluoride for 0.4 s, purging with Ar gas for 8 s, introducing triethylin for 0.2 s, purging with Ar gas for 8 s, introducing hydrogen fluoride for 0.4 s, and purging with Ar gas for 8 s.

[0097] (3) Use hydrofluoric acid solution to etch and remove the Al layer of Ti3AlC2, and wash to obtain an MXene dispersion with a concentration of 1 mg / mL; mix the inner layer coated lithium manganese iron phosphate material with the MXene dispersion, ultrasonically disperse at 500 W for 30 min, stir and dry at 80 °C to constant weight to obtain the lithium manganese iron phosphate cathode material with consistent morphology.

[0098] The solid-liquid ratio of the inner layer coated lithium manganese iron phosphate material to the MXene dispersion is 1:20, and the dimension of the solid-liquid ratio is g / mL.

[0099] Comparative Example 1

[0100] This comparative example provides a method for preparing lithium manganese iron phosphate cathode material, the method comprising the following steps:

[0101] (1) Lithium dihydrogen phosphate, manganese carbonate, ferrous carbonate and indium chloride are mixed and ball-milled to obtain a uniform slurry. The slurry is then spray-dried (inlet temperature is 210℃, outlet temperature is 90℃) to obtain precursor particles with a median particle size D50 of 2μm. The precursor particles are then sintered to obtain an indium-doped lithium iron manganese phosphate matrix.

[0102] The indium-doped lithium iron manganese phosphate matrix is ​​mainly composed of LiMn. 0.5 Fe 0.5 The doping concentration of PO4 and F is 0.003 wt%.

[0103] The process is carried out in a nitrogen atmosphere and includes a pre-firing and a main firing performed sequentially. The pre-firing includes heating to 350°C at a heating rate of 4°C / min and holding at that temperature for 2.5 hours. The main firing includes heating to 700°C at a heating rate of 2°C / min and holding at that temperature for 10 hours.

[0104] (2) An AlF3-InF3 coating layer with a thickness of 10 nm was prepared on the surface of the indium-doped lithium iron manganese phosphate substrate by atomic layer deposition to obtain an inner-layer coated lithium iron manganese phosphate material;

[0105] The atomic layer deposition temperature is 180°C;

[0106] A single deposition cycle of the atomic layer deposition includes: using Ar gas as the carrier gas, introducing trimethylaluminum for 0.2 s, purging with Ar gas for 8 s, introducing hydrogen fluoride for 0.4 s, purging with Ar gas for 8 s, introducing triethylin for 0.2 s, purging with Ar gas for 8 s, introducing hydrogen fluoride for 0.4 s, and purging with Ar gas for 8 s.

[0107] (3) Use hydrofluoric acid solution to etch and remove the Al layer of Ti3AlC2, and wash to obtain an MXene dispersion with a concentration of 0.8 mg / mL; mix the inner layer coated lithium manganese iron phosphate material with the MXene dispersion, ultrasonically disperse at 400 W for 45 min, stir and dry at 70 °C to constant weight to obtain the lithium manganese iron phosphate cathode material.

[0108] The solid-liquid ratio of the inner layer coated lithium manganese iron phosphate material to the MXene dispersion is 1:15, and the dimension of the solid-liquid ratio is g / mL.

[0109] Comparative Example 2

[0110] This comparative example provides a method for preparing lithium manganese iron phosphate cathode material, the method comprising the following steps:

[0111] (1) Lithium dihydrogen phosphate, manganese carbonate, ferrous carbonate and ammonium fluoride are mixed and ball-milled to obtain a uniform slurry. The slurry is then spray-dried (inlet temperature is 210℃, outlet temperature is 90℃) to obtain precursor particles with a median particle size D50 of 2μm. The precursor particles are then sintered to obtain a fluorine-doped lithium iron manganese phosphate matrix.

[0112] The main component of the fluorine-doped lithium iron manganese phosphate matrix is ​​LiMn. 0.5 Fe 0.5 The doping concentration of PO4 and F is 0.003 wt%.

[0113] The process is carried out in a nitrogen atmosphere and includes a pre-firing and a main firing performed sequentially. The pre-firing includes heating to 350°C at a heating rate of 4°C / min and holding at that temperature for 2.5 hours. The main firing includes heating to 700°C at a heating rate of 2°C / min and holding at that temperature for 10 hours.

[0114] (2) An AlF3-InF3 coating layer with a thickness of 10 nm was prepared on the surface of the fluorine-doped lithium iron manganese phosphate substrate by atomic layer deposition to obtain an inner-layer coated lithium iron manganese phosphate material;

[0115] The atomic layer deposition temperature is 180°C;

[0116] A single deposition cycle of the atomic layer deposition includes: using Ar gas as the carrier gas, introducing trimethylaluminum for 0.2 s, purging with Ar gas for 8 s, introducing hydrogen fluoride for 0.4 s, purging with Ar gas for 8 s, introducing triethylin for 0.2 s, purging with Ar gas for 8 s, introducing hydrogen fluoride for 0.4 s, and purging with Ar gas for 8 s.

[0117] (3) Use hydrofluoric acid solution to etch and remove the Al layer of Ti3AlC2, and wash to obtain an MXene dispersion with a concentration of 0.8 mg / mL; mix the inner layer coated lithium manganese iron phosphate material with the MXene dispersion, ultrasonically disperse at 400 W for 45 min, stir and dry at 70 °C to constant weight to obtain the lithium manganese iron phosphate cathode material.

[0118] The solid-liquid ratio of the inner layer coated lithium manganese iron phosphate material to the MXene dispersion is 1:15, and the dimension of the solid-liquid ratio is g / mL.

[0119] Comparative Example 3

[0120] This comparative example provides a method for preparing lithium manganese iron phosphate cathode material, the method comprising the following steps:

[0121] (1) Lithium dihydrogen phosphate, manganese carbonate and ferrous carbonate are mixed and ball-milled to obtain a uniform slurry. The slurry is then spray-dried (inlet temperature 210℃, outlet temperature 90℃) to obtain precursor particles with a median particle size D50 of 2μm. The precursor particles are then sintered to obtain a lithium iron manganese phosphate matrix.

[0122] The main component of the lithium iron manganese phosphate matrix is ​​LiMn. 0.5 Fe 0.5 PO4;

[0123] The process is carried out in a nitrogen atmosphere and includes a pre-firing and a main firing performed sequentially. The pre-firing includes heating to 350°C at a heating rate of 4°C / min and holding at that temperature for 2.5 hours. The main firing includes heating to 700°C at a heating rate of 2°C / min and holding at that temperature for 10 hours.

[0124] (2) An AlF3-InF3 coating layer with a thickness of 10 nm was prepared on the surface of the lithium iron manganese phosphate substrate by atomic layer deposition to obtain an inner layer coated lithium iron manganese phosphate material;

[0125] The atomic layer deposition temperature is 180°C;

[0126] A single deposition cycle of the atomic layer deposition includes: using Ar gas as the carrier gas, introducing trimethylaluminum for 0.2 s, purging with Ar gas for 8 s, introducing hydrogen fluoride for 0.4 s, purging with Ar gas for 8 s, introducing triethylin for 0.2 s, purging with Ar gas for 8 s, introducing hydrogen fluoride for 0.4 s, and purging with Ar gas for 8 s.

[0127] (3) Use hydrofluoric acid solution to etch and remove the Al layer of Ti3AlC2, and wash to obtain an MXene dispersion with a concentration of 0.8 mg / mL; mix the inner layer coated lithium manganese iron phosphate material with the MXene dispersion, ultrasonically disperse at 400 W for 45 min, stir and dry at 70 °C to constant weight to obtain the lithium manganese iron phosphate cathode material with consistent morphology.

[0128] The solid-liquid ratio of the inner layer coated lithium manganese iron phosphate material to the MXene dispersion is 1:15, and the dimension of the solid-liquid ratio is g / mL.

[0129] Comparative Example 4

[0130] This comparative example provides a method for preparing lithium manganese iron phosphate cathode material, the method comprising the following steps:

[0131] (1) Lithium dihydrogen phosphate, manganese carbonate, ferrous carbonate, ammonium fluoride and indium chloride are mixed and ball-milled to obtain a uniform slurry. The slurry is then spray-dried (inlet temperature 210℃, outlet temperature 90℃) to obtain precursor particles with a median particle size D50 of 2μm. The precursor particles are then sintered to obtain a fluorine-indium co-doped lithium iron manganese phosphate matrix.

[0132] The main component of the fluorine-indium co-doped lithium iron manganese phosphate matrix is ​​LiMn. 0.5 Fe 0.5 The doping concentration of PO4 is 0.003 wt%, and the doping concentration of In is 0.008 wt%.

[0133] The process is carried out in a nitrogen atmosphere and includes a pre-firing and a main firing performed sequentially. The pre-firing includes heating to 350°C at a heating rate of 4°C / min and holding at that temperature for 2.5 hours. The main firing includes heating to 700°C at a heating rate of 2°C / min and holding at that temperature for 10 hours.

[0134] (2) The Al layer of Ti3AlC2 was removed by etching with hydrofluoric acid solution, and the MXene dispersion with a concentration of 0.8 mg / mL was obtained by washing. The fluorine-indium co-doped lithium iron manganese phosphate matrix was mixed with the MXene dispersion, ultrasonically dispersed at 400 W for 45 min, and stirred and dried at 70 °C to constant weight to obtain the lithium iron manganese phosphate cathode material.

[0135] The solid-liquid ratio of the fluorine-indium co-doped lithium iron manganese phosphate matrix to the MXene dispersion is 1:15, and the dimension of the solid-liquid ratio is g / mL.

[0136] Comparative Example 5

[0137] This comparative example provides a method for preparing lithium manganese iron phosphate cathode material, the method comprising the following steps:

[0138] (1) Lithium dihydrogen phosphate, manganese carbonate, ferrous carbonate, ammonium fluoride and indium chloride are mixed and ball-milled to obtain a uniform slurry. The slurry is then spray-dried (inlet temperature 210℃, outlet temperature 90℃) to obtain precursor particles with a median particle size D50 of 2μm. The precursor particles are then sintered to obtain a fluorine-indium co-doped lithium iron manganese phosphate matrix.

[0139] The main component of the fluorine-indium co-doped lithium iron manganese phosphate matrix is ​​LiMn. 0.5 Fe 0.5 The doping concentration of PO4 is 0.003 wt%, and the doping concentration of In is 0.008 wt%.

[0140] The process is carried out in a nitrogen atmosphere and includes a pre-firing and a main firing performed sequentially. The pre-firing includes heating to 350°C at a heating rate of 4°C / min and holding at that temperature for 2.5 hours. The main firing includes heating to 700°C at a heating rate of 2°C / min and holding at that temperature for 10 hours.

[0141] (2) An AlF3-InF3 coating layer with a thickness of 10 nm was prepared on the surface of the fluorine-indium co-doped lithium iron manganese phosphate substrate by atomic layer deposition to obtain lithium manganese iron phosphate cathode material;

[0142] The atomic layer deposition temperature is 180°C;

[0143] A single deposition cycle of the atomic layer deposition includes: using Ar gas as the carrier gas, introducing trimethylaluminum for 0.2 s, purging with Ar gas for 8 s, introducing hydrogen fluoride for 0.4 s, purging with Ar gas for 8 s, introducing triethylin for 0.2 s, purging with Ar gas for 8 s, introducing hydrogen fluoride for 0.4 s, and purging with Ar gas for 8 s.

[0144] Performance Characterization

[0145] The above-described embodiments and comparative examples involve mixing positive electrode material, conductive carbon black (SP), and binder polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1, then adding solvent N-methylpyrrolidone (NMP), and ball milling to obtain a slurry. The slurry is coated onto the surface of aluminum foil, vacuum baked at 110°C for 3 hours, and sliced ​​to obtain a positive electrode sheet. A lithium metal sheet is used as the negative electrode sheet, a polypropylene separator is used, and the electrolyte is 1 mol / L LiPF6 (solvent EC / DMC / EMC) to prepare a CR2032 type lithium-ion battery.

[0146] 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 500 cycles, the discharge capacity retention rate is recorded as the cycle capacity retention rate.

[0147] Table 1

[0148]

[0149] As can be seen from Examples 1 to 3 in the table, the lithium iron manganese phosphate material achieves excellent electrochemical performance through the synergistic effect of fluorine-indium co-doping, AlF3-InF3 coating layer and MXene coating layer, which can meet the requirements of high-demand scenarios.

[0150] Comparisons of Comparative Examples 1, 2, and 3 with Example 1 show that fluorine-indium co-doping is a crucial prerequisite for improving LMFP performance. When only fluorine doping or only indium doping is absent, the first-cycle capacity and cycle retention decrease slightly; however, without fluorine-indium co-doping, both the first-cycle capacity and cycle retention decrease significantly. This is because fluorine-indium co-doping synergistically suppresses Mn... 3+ The Jahn-Teller distortion reduces the dissolution of active ions and avoids structural collapse; single doping cannot achieve the same effect.

[0151] Comparisons of Comparative Examples 4 and 5 with Example 1 show that the synergistic coating of the AlF3-InF3 coating layer and the MXene coating layer is crucial for ensuring material performance. Without the AlF3-InF3 coating layer, Mn cannot be suppressed. 2+ Fe 2+ Dissolution and electrolyte decomposition lead to increased side reactions at high temperatures; the absence of the MXene coating layer prevents buffering of volume changes and the construction of a continuous conductive network, resulting in particle cracking and insufficient conductivity. The absence of either layer alone reduces the initial capacity and cycle retention; only the synergistic effect of both coating layers can simultaneously address the issues of ion dissolution, volume change, and conductivity.

[0152] In summary, this invention achieves significant beneficial effects through the synergistic effect of fluorine-indium co-doping, the AlF3-InF3 coating layer, and the MXene coating layer. The AlF3-InF3 coating layer adheres tightly to the surface of the fluorine-indium co-doped lithium iron manganese phosphate (LMFP) substrate, effectively suppressing the dissolution of Mn²⁺ and Fe²⁺ into the electrolyte and preventing decomposition caused by direct contact between the electrolyte and the substrate. It also significantly reduces side reactions at 60°C. The outer MXene coating layer, with its excellent flexibility, effectively buffers volume changes during the charging and discharging process of LFP, preventing particle cracking. Furthermore, its two-dimensional layered structure can construct a continuous conductive network, improving the low intrinsic conductivity of the material. The combination of these two layers not only solves the problem of low intrinsic conductivity in LMFP due to Mn²⁺... 3+ The Jahn-Teller distortion and structural collapse caused by the dissolution of active ions were overcome, and the particle breakage defects caused by volume changes were also overcome, ultimately significantly improving the cycle life and electrochemical performance of LMFPs, meeting the high requirements of power batteries, energy storage batteries and other scenarios.

[0153] 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 a lithium manganese iron phosphate cathode material with uniform morphology, characterized in that, The preparation method includes the following steps: (1) Preparation of fluorine-indium co-doped lithium iron manganese phosphate matrix; (2) An AlF3-InF3 coating layer was prepared on the surface of the fluorine-indium co-doped lithium iron manganese phosphate substrate by atomic layer deposition to obtain an inner-layer coated lithium iron manganese phosphate material; (3) An MXene coating layer is coated on the surface of the AlF3-InF3 coating layer to obtain the lithium manganese iron phosphate cathode material with consistent morphology; A single deposition cycle of the atomic layer deposition includes: using Ar gas as the carrier gas, introducing trimethylaluminum for 0.1s~0.3s, purging with Ar gas for 5s~10s, introducing hydrogen fluoride for 0.2s~0.5s, purging with Ar gas for 5s~10s, introducing triethylindium for 0.1s~0.3s, purging with Ar gas for 5s~10s, introducing hydrogen fluoride for 0.2s~0.5s, and purging with Ar gas for 5s~10s; The atomic layer deposition temperature is 150℃~200℃.

2. The preparation method according to claim 1, characterized in that, Step (1) involves preparing the fluorine-indium co-doped lithium iron manganese phosphate matrix by mixing a lithium source, a manganese source, an iron source, a fluorine source, and an indium source, ball milling to obtain a uniform slurry, spray drying to obtain precursor particles, and sintering the precursor particles to obtain the fluorine-indium co-doped lithium iron manganese phosphate matrix.

3. The preparation method according to claim 2, characterized in that, The lithium source includes lithium dihydrogen phosphate; And / or, the manganese source includes manganese carbonate; And / or, the iron source includes ferrous carbonate; And / or, the fluorine source includes ammonium fluoride; And / or, the indium source includes indium chloride.

4. The preparation method according to claim 2, characterized in that, The median particle size D50 of the precursor particles is 1 μm to 3 μm.

5. The preparation method according to any one of claims 2 to 4, characterized in that, The sintering is carried out in a protective atmosphere, including a pre-firing and a main firing performed sequentially. The pre-firing includes heating to 300℃~400℃ at a heating rate of 2℃ / min~5℃ / min and holding at that temperature for 2h~3h; The main firing process involves heating to 650℃~750℃ at a heating rate of 1℃ / min~3℃ / min and holding at that temperature for 8h~12h.

6. The preparation method according to claim 1, characterized in that, The thickness of the AlF3-InF3 coating layer is 5nm~20nm.

7. The preparation method according to claim 1, characterized in that, The MXene coating layer comprises: etching away the Al layer of Ti3AlC2 using hydrofluoric acid solution, and washing to obtain an MXene dispersion with a concentration of 0.5 mg / mL to 1 mg / mL; The inner layer of lithium manganese iron phosphate material was mixed with the MXene dispersion, ultrasonically dispersed, stirred and dried to constant weight to obtain the lithium manganese iron phosphate cathode material with consistent morphology.

8. The preparation method according to claim 7, characterized in that, The solid-liquid ratio of the inner layer coated lithium manganese iron phosphate material to the MXene dispersion is 1:10 to 1:20, and the dimension of the solid-liquid ratio is g / mL. And / or, the power of the ultrasonic dispersion is 300W~500W; And / or, the ultrasonic dispersion time is 30 min to 60 min; And / or, the temperature of the stirring and drying is 60℃~80℃.

9. A lithium manganese iron phosphate cathode material with uniform morphology, characterized in that, The morphologically consistent lithium manganese iron phosphate cathode material is prepared by the preparation method described in any one of claims 1 to 8.

10. A positive electrode, characterized in that, The cathode comprises the lithium manganese iron phosphate cathode material with consistent morphology as described in claim 9.

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