Lithium iron manganese phosphate material, preparation method thereof, positive electrode sheet and lithium ion battery

Abstract

This application provides a lithium manganese iron phosphate material and its preparation method, a positive electrode sheet, and a lithium-ion battery, belonging to the field of lithium-ion battery technology. The lithium manganese iron phosphate material includes doped lithium manganese iron phosphate particles, the general formula of which is Li… 1‑a M 1a (M 2b Mn x Fe y‑b )P 1‑c B c O 4‑d X d Where 0.05≥a≥0, 0.05≥b>0, 0.07≥c>0, 0.081≥d>0, 1≥ x ≥0.5, 0.5≥ y >0, and x + y =1, M1 and M2 are doping elements. This application solves the problem of low electrochemical activity of lithium manganese iron phosphate from within, and solves the problem of Mn dissolution on the surface of lithium manganese iron phosphate by doping with anion X, thereby synergistically enhancing the electrochemical performance of lithium manganese iron phosphate materials such as cycle stability.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly relates to a lithium iron manganese phosphate material, a preparation method thereof, a positive electrode sheet and a lithium-ion battery. Background Art

[0002] Lithium iron manganese phosphate is a cathode material for lithium-ion batteries, with the chemical formula LiMn x Fe 1-x PO4 (0 < x < 1, abbreviated as LMFP). Compared with lithium iron phosphate (LFP), the working voltage of LMFP has increased from 3.4 V (LFP) to 4.1 V (LMFP), and the energy density has also increased from 580 Wh / kg (LFP) to 701 Wh / kg (LMFP). However, during the charge and discharge process of the LMFP cathode material, Mn 3+ will disproportionate and dissolve due to the Jahn-Teller effect, resulting in harmful structural disorder and irreversible phase transformation, making the cycle stability of the material poor. In addition, the strong P-O bond in LMFP limits the free movement of electrons, resulting in low electronic conductivity. Moreover, the olivine structure of the LMFP material causes its Li + diffusion channels to be one-dimensional. Compared with the layered ternary materials and spinel manganese oxides with tunnel structures, its Li + transport rate is smaller. Therefore, the low conductivity and Li + diffusion coefficient of LMFP still pose obstacles to its commercial application.

[0003] How to inhibit the Jahn-Teller effect of trivalent manganese in LMFP and improve the material conductivity and Li + diffusion coefficient is one of the research directions of current researchers. The most common carbon coating is one of the most common methods to improve the conductivity of LMFP, but carbon coating can only improve the external conductivity of the LMFP material.

[0004] Therefore, many researchers start from doping modification to improve the performance of LMFP. On the one hand, by doping divalent and tetravalent elements or even lower / higher-valent elements, the average valence state of Mn is adjusted to solve the problem of divalent manganese dissolution; on the other hand, doping can generate defects inside the LMFP lattice, increase Li + diffusion channels, and increase the carrier density of the material to improve the electrical conductivity of the material itself.

[0005] Common doping elements, such as low-valence aluminum (Al) and high-valence titanium (Ti) and vanadium (V), can replace transition metal ions in the crystal lattice with dopants of different valence states, which helps to alleviate the dissolution of divalent manganese and improve the ionic and electronic conductivity of LMFP materials. Meanwhile, dopants with different radii, such as magnesium (Mg) and cobalt (Co), can form pillars for the transition metal layers during interlayer doping, thus maintaining the crystal structure stability of LMFP. Furthermore, dopants such as tungsten (W) and niobium (Nb) can form stronger transition metal-oxygen bonds, thereby improving the thermal decomposition temperature and cycling performance of the material.

[0006] Therefore, in the LMFP precursor preparation stage, how to add one or more doping elements to the material to achieve the uniformity of actual doping inside the particles, introduce anions into the material surface through secondary doping methods, suppress Mn dissolution, and comprehensively improve the electrochemical performance of the cathode material has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] In view of the technical problems existing in the background art, this application provides a lithium manganese iron phosphate material and its preparation method, a positive electrode sheet and a lithium-ion battery, aiming to solve the problems of divalent manganese leaching and Li-ion leaching during the cycling process of lithium manganese iron phosphate material. + Technical problems related to the difference in diffusion rate and conductivity.

[0008] In a first aspect, embodiments of this application provide a lithium manganese iron phosphate material, which includes doped lithium manganese iron phosphate particles, the general formula of which is Li. 1-a M 1a (M 2b Mn x Fe y-b )P 1-c B c O 4-d X d Where 0.05≥a≥0, 0.05≥b>0, 0.07≥c>0, 0.081≥d>0, 1≥ x ≥0.5, 0.5≥ y >0, and x + y =1, M1 and M2 are doping elements, each independently selected from one or more of the following elements: magnesium, titanium, cobalt, nickel, copper, zinc, tin, barium, strontium, lead, aluminum, lanthanum, cerium, vanadium, zirconium, molybdenum, indium, and calcium; B is boron, and X is selected from one or more of the following elements: fluorine, bromine, iodine, chlorine, sulfur, and nitrogen.

[0009] The doped lithium manganese iron phosphate particles of this application Li1-a M 1a (M 2b Mn x Fe y-b )P 1-c B c O 4-d X d Containing a specific ratio of metal cations M1 and M2, and non-metal cations B and anions X, the doped lithium manganese iron phosphate particles exhibit core-shell doping characteristics through the synergistic effect of these dopants. Specifically, the interior of the doped lithium manganese iron phosphate particles is doped with metal / non-metal cations, while the surface is doped with anions, thereby synergistically enhancing the electrochemical performance of the lithium manganese iron phosphate material. In particular, metal cation M1 accelerates the Li... + The transport rate is increased. Meanwhile, the metal cation M2 enhances the stability of the Mn-O bond, improving the structural stability of lithium manganese iron phosphate materials. Simultaneously, the synergistic doping of metal cations M1 and M2 can effectively regulate the average valence state of Mn on the surface of doped lithium manganese iron phosphate particles, suppressing the dissolution of divalent manganese. The introduction of the non-metallic cation B forms BO3. 3- The presence of these groups not only enhances the flexibility of the lithium-ion diffusion channels but also broadens the Li-ion diffusion range. + The diffusion path is improved, thus significantly increasing the migration rate of lithium ions within the lithium manganese iron phosphate material. Anion X, as the anionic dopant, enhances the stability of the Mn-X or Mn-O bonds by increasing surface defects in the lithium manganese iron phosphate material, effectively suppressing the dissolution of Mn during charge and discharge, and preventing the degradation of the cycle performance of the lithium manganese iron phosphate material. Therefore, the doped lithium manganese iron phosphate particles of this application solve the problem of low electrochemical activity of lithium manganese iron phosphate from within through a composite doping strategy of metal cations M1, M2, and non-metal cation B, and solve the problem of Mn dissolution on the surface of lithium manganese iron phosphate through the doping of anion X, thereby synergistically enhancing the electrochemical performance of lithium manganese iron phosphate material, such as cycle stability.

[0010] Furthermore, in some embodiments, M1 replaces the Li element, and M1 includes M 11 and M 12 M 11 and M 12 Each element is independently selected from one or more of the following: magnesium, titanium, cobalt, nickel, copper, zinc, tin, barium, strontium, lead, aluminum, lanthanum, cerium, vanadium, zirconium, molybdenum, indium, and calcium. 11 and M 12 Different, M 11 and M 12The molar ratio is 1~4:4~1; and / or, M2 replaces Fe element, M2 includes M 21 and M 22 M 21 and M 22 Each element is independently selected from one or more of the following: magnesium, titanium, cobalt, nickel, copper, zinc, tin, barium, strontium, lead, aluminum, lanthanum, cerium, vanadium, zirconium, molybdenum, indium, and calcium. 21 and M 22 Different, M 21 and M 22 The molar ratio of the substances is 1~4:4~1; and / or, B replaces P; and / or, B, M1 and M2 are doped inside the doped lithium manganese iron phosphate particles; and / or, X replaces O, X is located on the surface of the doped lithium manganese iron phosphate particles, and X is distributed on the surface of the doped lithium manganese iron phosphate particles within 0.5%~5% of the particle diameter.

[0011] M1 replaces Li elements to create Li vacancies, thereby increasing the Li transport rate. M1 includes M 11 and M 12 And M 11 and M 12 This difference allows for more diverse doping of the metal cation M1, enabling more effective tuning of the internal electronic structure and Li content of lithium manganese iron phosphate materials. + The diffusion path is optimized to improve the conductivity and ion transport rate of lithium manganese iron phosphate materials. This is achieved by controlling M... 11 and M 12 When the molar ratio of substances is within the above range, it can promote M. 11 and M 12 Further optimization of the performance of lithium manganese iron phosphate materials will improve their electrochemical performance.

[0012] M2 replaces Fe, thereby enhancing the stability of the Mn-O bond. When M2 includes M... 21 and M 22 Furthermore, when the two differ, diverse cation-doped environments are formed within lithium manganese iron phosphate materials. This allows lithium manganese iron phosphate materials to simultaneously benefit from the properties of different elements within their internal structure, such as M. 21 It may optimize the migration path of lithium ions, while M 22 This enhances the structural stability and electronic conductivity of lithium manganese iron phosphate materials. This co-doping mechanism not only improves the electronic and ionic conductivity of lithium manganese iron phosphate materials and increases the lithium-ion diffusion rate, but also effectively suppresses Mn+ by altering the average valence state of transition metal ions. 2+The dissolution of [the substance] allows for precise control over the internal structure of lithium manganese iron phosphate materials, improving their cycle performance and overall stability. Furthermore, M […]. 21 and M 22 The ratio of the amounts of substances helps to form a more complex and ordered atomic arrangement, promoting the kinetic response of lithium manganese iron phosphate materials at high rates, thereby significantly improving the rate performance and cycle life of lithium manganese iron phosphate materials while maintaining high energy density.

[0013] Boron (B) replaces phosphorus (P), forming a planar triangular BO3 group. 3- This structure not only enhances the flexibility of the lithium-ion diffusion channels but also broadens the Li-ion diffusion path. + The diffusion path improves the electronic conductivity and Li content of lithium manganese iron phosphate materials. + Diffusion coefficient.

[0014] Using M1 and M2 as cationic dopants to replace Li and Fe elements respectively enhances the stability of the Mn-O bond, thereby effectively suppressing Mn 2+ The dissolution of Mn and the disordering of the structure of lithium manganese iron phosphate (LFP) materials significantly improve the cycling stability and conductivity of LFP materials. The introduction of M1 can regulate the average valence state of Mn, reduce the content of divalent manganese, and thus mitigate the negative impact of the Jahn-Teller effect; while the addition of M2 can act as a support between transition metal layers, maintaining structural stability and preventing the degradation of LFP materials during cycling. Simultaneously, the doping of boron (B) replaces some of the phosphorus (P) element, forming a stable BO3 group. 3- The structure enhances the flexibility and width of the lithium-ion diffusion channels. This multi-element composite doping strategy within lithium manganese iron phosphate provides enhanced electronic conduction pathways and increases the stability of the internal structure by synergistically regulating the internal chemical environment and structural characteristics of the particles. This fundamentally solves the common performance degradation problem of lithium manganese iron phosphate battery materials during charge-discharge cycles.

[0015] In the optimized scheme, X replaces O and is distributed on the surface of the doped lithium manganese iron phosphate particles. More preferably, X is distributed within 0.5% to 5% of the particle diameter depth on the surface of the doped lithium manganese iron phosphate particles. This design effectively enhances the stability of the Mn-X or Mn-O bonds, thereby suppressing Mn dissolution on the particle surface and inside, reducing the structural disorder and irreversible phase transition of the lithium manganese iron phosphate material caused by Mn dissolution, and significantly improving the cycle stability and safety of the lithium manganese iron phosphate material. Simultaneously, the anion doping on the surface acts as a protective layer, preventing direct contact between the electrolyte and the active components of the lithium manganese iron phosphate material, reducing the occurrence of electrochemical side reactions, and further improving the battery's cycle efficiency and lifespan.

[0016] The general formula of doped lithium manganese iron phosphate particles is Li 1-a M 1a (M 2b Mn x Fe y-b )P 1-c B c O 4-d X d In this process, the c value determines the degree of B doping, affecting lattice flexibility and Li. + The diffusion efficiency is determined by the d-value, which reflects the surface doping amount of anion X and plays a crucial role in suppressing Mn dissolution and improving the surface properties of lithium manganese iron phosphate materials. The x and y values ​​control the ratio of Mn and Fe, respectively, while the b value simultaneously determines the ratio of M2 and Fe, affecting the discharge capacity and voltage plateau stability of lithium manganese iron phosphate materials. The internal doping effects of M1, M2, and B enhance the intrinsic electronic and ionic conductivity of lithium manganese iron phosphate materials, while the surface doping of X strengthens the surface stability of lithium manganese iron phosphate materials.

[0017] Furthermore, in some embodiments, the lithium manganese iron phosphate material further includes a carbon coating layer on the surface of the doped lithium manganese iron phosphate particles, wherein the carbon content in the lithium manganese iron phosphate material is 1.5% to 3% by mass; and / or, the manganese leaching amount of the lithium manganese iron phosphate material is 50 ppm to 200 ppm; and / or, the lithium-ion diffusion coefficient of the lithium manganese iron phosphate material is 10. -12 cm 2 / s~10 -9 cm 2 / s; and / or, the electronic conductivity of lithium manganese iron phosphate material is 0.015S / m~0.030S / m; and / or, the D50 particle size of lithium manganese iron phosphate material is 2μm~5μm.

[0018] In the technical solution of this application embodiment, the carbon coating layer is beneficial to improving the electronic conductivity of lithium manganese iron phosphate material and reducing charge transport resistance, thereby significantly improving the discharge performance of the battery under high-rate conditions. Simultaneously, the carbon coating layer, as a physical barrier, can reduce direct contact between the electrolyte and the active material, reduce surface side reactions, improve the cycle stability and structural integrity of the lithium manganese iron phosphate material, limit the dissolution of Mn elements, and thus improve the capacity retention rate of the lithium manganese iron phosphate material during cycling. Preferably, the carbon coating layer with the above-mentioned carbon element content promotes a balanced improvement in the internal and external conductivity of the lithium manganese iron phosphate material, reducing the decrease in the proportion of active material and Li due to excessive coating. + The increased risk of diffusion pathways further enhances the overall electrochemical performance of lithium manganese iron phosphate materials.

[0019] Optimizing the above-mentioned appropriate manganese leaching amount helps to reduce the disproportionation and dissolution of Mn in lithium manganese iron phosphate materials due to the Jahn-Teller effect during charging and discharging. 3+ The resulting harmful structural disorder and irreversible phase transition reduce the risk of poor cycle stability in lithium manganese iron phosphate materials.

[0020] Optimizing the above-mentioned suitable lithium-ion diffusion coefficient helps reduce the risk of side reactions and uneven internal stress distribution, and improves the cycle stability and rate performance of lithium manganese iron phosphate materials.

[0021] By adjusting the content of doping elements M1 and M2, the electronic conductivity of lithium manganese iron phosphate material was increased to the above range, which significantly improved the conductivity performance of lithium manganese iron phosphate material, thereby improving the charge and discharge efficiency of lithium manganese iron phosphate material.

[0022] By optimizing the D50 particle size within a specific range and precisely controlling it, the uniformity of particle size is improved, thereby enhancing the contact efficiency between the active material and the electrolyte, accelerating the migration speed of lithium ions, and improving the rate performance of the battery. Furthermore, the uniform particle size distribution helps reduce agglomeration that may occur during electrode fabrication, increasing the compaction density of the lithium manganese iron phosphate material, and ultimately improving the energy density of the battery.

[0023] Secondly, embodiments of this application provide a method for preparing lithium manganese iron phosphate material. The method includes: mixing raw materials comprising a manganese source, an iron source, a first carbon source, a lithium source, a boron source, a cation doping source, and a phosphorus source, and then sequentially performing a first grinding and a first drying to obtain a cation-doped precursor; performing a first sintering of the cation-doped precursor under an inert atmosphere to obtain cation-doped lithium manganese iron phosphate; mixing raw materials comprising cation-doped lithium manganese iron phosphate, a second carbon source, and an anion doping source, and then sequentially performing a second grinding and a second drying to obtain an anion- and cation-doped precursors; and performing anion- and cation-doped precursors under an inert atmosphere. The bulk material undergoes a second sintering process to obtain lithium manganese iron phosphate material. The cation doping source includes M1 doping source and M2 doping source. M1 doping source and M2 doping source are each independently a doping source containing a metal element, which is selected from any one or more elements selected from magnesium, titanium, cobalt, nickel, copper, zinc, tin, barium, strontium, lead, aluminum, lanthanum, cerium, vanadium, zirconium, molybdenum, indium, and calcium. The anion doping source includes an element X, which is selected from any one or more elements selected from fluorine, bromine, iodine, chlorine, sulfur, and nitrogen.

[0024] The preparation method of the above-mentioned lithium manganese iron phosphate material in this application adopts a two-step solid-state method. First, in the first solid-state method, a cation doping source is introduced and subjected to a first grinding and a first drying process to obtain a cation-doped precursor. In the second solid-state method, an anion doping source is introduced and subjected to a second grinding and a second drying process to obtain an anion- and cation-doped precursors. The cation-doped precursor and the anion- and cation-doped precursors are then sintered to achieve dual doping of cations and anions. Specifically, the doping ions include metal cations M1 and M2, non-metal cations B, and anions X. Through the synergistic effect of these doping ions, a core-shell doping characteristic is formed in the doped lithium manganese iron phosphate particles. That is, metal / non-metal cations are doped inside the doped lithium manganese iron phosphate particles, and anions are doped on the surface of the doped lithium manganese iron phosphate particles, thereby synergistically enhancing the electrochemical performance of the lithium manganese iron phosphate material. Specifically, the incorporation of metal cation M1 can increase lithium vacancy defects inside the lithium manganese iron phosphate material, broadening the lithium content of lithium phosphate. + Diffusion channels increase conductive paths and accelerate Li + The M1 cation increases the transport rate and improves the carrier density of lithium manganese iron phosphate (LFP) materials. Meanwhile, the metal cation M2 enhances the stability of the Mn-O bond, improving the structural stability of LFP materials. Simultaneously, the synergistic doping of metal cations M1 and M2 can effectively regulate the average valence state of Mn on the surface of doped LFP particles, suppressing the dissolution of divalent manganese. The introduction of the non-metallic cation B forms BO3. 3- The presence of these groups not only enhances the flexibility of the lithium-ion diffusion channels but also broadens the Li-ion diffusion range. + The diffusion path is improved, thus significantly increasing the migration rate of lithium ions within the lithium manganese iron phosphate material. Anion X, as the anionic dopant, enhances the stability of the Mn-X or Mn-O bonds by increasing surface defects in the lithium manganese iron phosphate material, effectively suppressing the dissolution of Mn during charge and discharge, and preventing the degradation of the cycle performance of the lithium manganese iron phosphate material. Therefore, the doped lithium manganese iron phosphate particles of this application solve the problem of low electrochemical activity of lithium manganese iron phosphate from within through a composite doping strategy of metal cations M1, M2, and non-metal cation B, and solve the problem of Mn dissolution on the surface of lithium manganese iron phosphate through the doping of anion X, thereby synergistically enhancing the electrochemical performance of lithium manganese iron phosphate material, such as cycle stability. Furthermore, the above preparation method is simple, low-cost, and avoids the post-treatment problems of waste liquid caused by liquid-phase reactions.

[0025] Further, in some embodiments, the molar ratio of manganese from the manganese source, iron from the iron source, carbon from the first carbon source, lithium from the lithium source, boron from the boron source, metal from the cation dopant source, and phosphorus from the phosphorus source is 0.5~1:0~0.5:0.2~0.4:1~1.05:0.01~0.05:0.01~0.05:0.95~0.99; and / or, the M1 dopant source is selected from any one or more of sulfates, nitrates, oxalates, carbonates, and acetates containing the M1 element; and / or, M1 includes M 11 and M 12 M 11 and M 12 Each element is independently selected from any one of the following: magnesium, titanium, cobalt, nickel, copper, zinc, tin, barium, strontium, lead, aluminum, lanthanum, cerium, vanadium, zirconium, molybdenum, indium, and calcium. 11 and M 12 Different, M 11 and M 12 The molar ratio of M2 to M3 is 1-4:4-1; and / or, the M2 dopant source is selected from any one or more of sulfates, nitrates, oxalates, carbonates, and acetates containing the M2 element; and / or, M2 includes M2... 21 and M 22 M 21 and M 22 Each element is independently selected from one or more of the following: magnesium, titanium, cobalt, nickel, copper, zinc, tin, barium, strontium, lead, aluminum, lanthanum, cerium, vanadium, zirconium, molybdenum, indium, and calcium. 21 and M 22 Different, M 21 and M 22The molar ratio of the substances is 1~4:4~1; and / or, the boron source is selected from any one or more of boric acid, boron oxide, and lithium borate; and / or, the iron source is selected from any one or more of ferric phosphate, ferric oxide, ferrous oxide, ferric tetroxide, ferric nitrate, ferrous sulfate, and ferrous oxalate; and / or, the manganese source is selected from any one or more of manganese oxide, manganese tetroxide, manganese trioxide, manganese carbonate, manganese oxalate, manganese phosphate, manganese acetate, manganese sulfate, and manganese nitrate; and / or, the first carbon source is selected from any one or more of glucose, citric acid, sucrose, polyethylene glycol, polyvinyl alcohol, and ascorbic acid. Multiple sources are available; and / or the lithium source is selected from any one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium acetate, lithium phosphate, lithium nitrate, lithium tert-butoxide, lithium benzoate, lithium formate, lithium chromate, lithium citrate tetrahydrate, lithium tetrachloroaluminate, and lithium tetrafluoroborate; and / or the phosphorus source is selected from any one or more of phosphoric acid, lithium dihydrogen phosphate, lithium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate; and / or the cation doping amount in the cation-doped precursor is 1000ppm to 10000ppm, and the boron doping amount in the cation-doped precursor is 800ppm to 20000ppm.

[0026] Optimizing the above molar ratios is beneficial for precisely controlling the uniform distribution of dopant elements in the precursor and the expected stoichiometry. This precise control of molar ratios is crucial for achieving co-doping of cations and anions, which promotes the uniform distribution of M1 and M2 elements inside the doped lithium manganese iron phosphate particles; while the X element is mainly concentrated on the surface of the doped lithium manganese iron phosphate particles, forming a core-shell structure doping characteristic. That is, the metal / non-metal cations improve the conductivity and lithium-ion diffusion path inside; while the anions strengthen the surface and prevent the dissolution of Mn.

[0027] Preferential M1 doping sources of the above types help to achieve uniform doping of M1 cations during the synthesis of lithium manganese iron phosphate materials. M1 cations replace Li elements, forming Li vacancies and effectively improving the transport rate of Li ions.

[0028] Among the above preferred solutions, by selecting M of different types 11 and M 12 and control M 11 and M 12 The molar ratio helps to diversify cation doping, which can more effectively regulate the internal electronic structure and Li content of lithium manganese iron phosphate materials. + Diffusion pathways are improved to enhance conductivity and ion transport rate, thereby improving the cycle stability of lithium manganese iron phosphate materials. This is achieved by controlling M... 11 and M 12 The molar ratio can be adjusted to further optimize the performance of lithium manganese iron phosphate materials and improve their electrochemical performance.

[0029] Optimizing the selection of the above-mentioned M2 doping sources facilitates the effective incorporation of M2 elements into the lithium manganese iron phosphate (LFP) lattice during the synthesis of LFP materials, replacing Fe elements and optimizing the crystal structure of LFP materials. This operation not only helps enhance the stability of the Mn-O bond and suppress the dissolution of Mn divalent atoms, but also promotes the growth of Li by adjusting the valence state of the dopant element. + Rapid migration within lithium manganese iron phosphate materials significantly improves their conductivity and Li₂ content. + Diffusion rate. In a preferred embodiment, uniform doping of metal cations within the lithium manganese iron phosphate (LFP) material is achieved through the use of a specific M2 doping source, thereby enhancing the electrochemical activity and cycle stability of the LFP material. Simultaneously, the introduction of M2 element improves the electronic conduction path of the LFP material, enabling it to maintain high capacity even at high charge / discharge rates, thus improving the overall energy density and power density of the battery. Furthermore, M2 doping also contributes to improving the thermal stability and safety of the LFP material.

[0030] The preferred approach is to select different types of M. 21 and M 22 and control M 21 and M 22 The molar ratio of these elements allows lithium manganese iron phosphate materials to benefit from the properties of both elements simultaneously within their internal structure, such as M. 21 It may optimize the migration path of lithium ions, while M 22 This enhances the structural stability and electronic conductivity of lithium manganese iron phosphate materials. Furthermore, M 21 and M 22 The contrasting properties and appropriate proportions of these elements help to form a more complex and ordered atomic arrangement, promoting the kinetic response of lithium manganese iron phosphate materials at high rates. This significantly improves the rate performance and cycle life of lithium manganese iron phosphate materials while maintaining high energy density.

[0031] Preferential selection of the above boron sources helps to form a more stable BO3 group by partially replacing phosphorus in the synthesis of lithium manganese iron phosphate materials. 3- This structure enhances the flexibility and width of the lithium-ion diffusion channels within the lithium manganese iron phosphate material, thereby improving the Li-ion diffusion efficiency. + Transmission rate, while reducing Li + Diffusion barriers were overcome, and the crystal structure of lithium manganese iron phosphate materials was optimized.

[0032] By selecting the above-mentioned iron source types, not only are the necessary iron elements provided, but their own characteristics may also affect the synthesis process of lithium manganese iron phosphate materials, promoting a more uniform doping distribution, thereby enabling the final lithium manganese iron phosphate materials to exhibit higher capacity retention and more stable cycling performance.

[0033] The selection of the above-mentioned manganese source types promotes the uniform distribution of cation doping, enhances the electronic conductivity of lithium manganese iron phosphate materials, and improves the Li... + This improves diffusion efficiency and enhances the chemical stability and reactivity of lithium manganese iron phosphate materials during synthesis.

[0034] The preferred first carbon source can be converted into a carbon coating layer during the subsequent sintering process, which further improves the electronic conductivity and enhances the electrochemical performance of lithium manganese iron phosphate materials.

[0035] Optimizing the above-mentioned lithium source types helps to obtain a more uniform crystal structure and smaller grain size, improving the lithium-ion diffusion coefficient and cycle stability; at the same time, it reduces cation mixing, improving its discharge specific capacity and cycle stability. In addition, appropriate lithium sources, in combination with precursors, can better control the spherical secondary particle morphology of the final cathode material, improve tap density, and thus increase the volumetric energy density of the battery.

[0036] Optimizing the selection of phosphorus sources can effectively optimize the synthesis conditions of lithium manganese iron phosphate materials, further improving the structural uniformity and stability of the materials. This helps to form high-quality premixes, providing a foundation for subsequent uniform doping of cations and anions. Simultaneously, the phosphorus source not only participates in the formation of the main framework of lithium manganese iron phosphate materials but also promotes solid-state reactions between particles during subsequent heat treatment, forming a more complete crystal lattice structure, thereby improving the Li... + The diffusion pathway improves the conductivity and Li content of lithium manganese iron phosphate materials. + The rate of diffusion.

[0037] The optimal cation doping levels help to fully replace Li and Fe elements in the crystal lattice, forming Li and Fe vacancies, thereby improving Li... + This increases the transport rate and enhances the stability of the Mn-O bond. Preferred boron doping levels are beneficial for enhancing the flexibility of the lithium-ion diffusion channel and broadening the Li-ion diffusion path. + The preferred scheme, by controlling the doping amounts of cations and boron, not only optimizes the electronic and ion transport characteristics within the lithium manganese iron phosphate material, but also reduces the risk of divalent manganese dissolution during cycling by forming a stable doped structure, thus synergistically enhancing the electrochemical performance of the lithium manganese iron phosphate material, particularly in rate performance and cycle stability.

[0038] Furthermore, in some embodiments, the mass concentration of the slurry obtained from the first grinding is 1 g / mL to 20 g / mL.

[0039] Optimizing the appropriate mass concentration of the first grinding slurry improves the dispersibility and flowability of the material during the sand milling process, which is beneficial for improving the uniform distribution of dopant elements and forming more uniform precursor particles. By controlling the slurry concentration, the cation dopant source can be uniformly distributed inside the precursor, and the non-metallic cation boron source can also be uniformly doped in the particles, thereby improving the Li-P content of lithium manganese iron phosphate materials. + The diffusion channels and electronic conductivity were improved, and the doping concentration of anion X on the surface was optimized, effectively suppressing the dissolution of Mn and enhancing the chemical stability of the lithium manganese iron phosphate material surface.

[0040] Furthermore, in some embodiments, the air inlet rate of the first dryer is 10 mL / min to 100 mL / min, the inlet temperature is 180°C to 250°C, and the outlet temperature is 95°C to 120°C.

[0041] Among the above parameters, the air inlet rate helps to form uniform and fine particles, which not only increases the specific surface area of ​​the lithium manganese iron phosphate material, but also promotes the uniform distribution of elements during subsequent sintering. Appropriate inlet and outlet temperatures ensure that the moisture inside the particles evaporates rapidly without damaging their structure, avoiding agglomeration and thus guaranteeing particle dispersibility and crystallinity.

[0042] Furthermore, in some embodiments, the first sintering includes a first-stage sintering and a second-stage sintering performed sequentially. The temperature of the first-stage sintering is 100℃~150℃, and the holding time of the first-stage sintering is 2h~5h. The temperature of the second-stage sintering is 400℃~600℃, and the holding time of the second-stage sintering is 4h~10h.

[0043] In the preferred embodiment of the above scheme, the first stage of sintering is performed at a low temperature. Its main function is to perform secondary drying of the cation-doped precursor and effectively remove any air present, providing a purer inert atmosphere for subsequent synthesis processes. The low-temperature sintering helps promote uniform diffusion of ions within the cation-doped precursor, forming a stable doped structure and improving the Li... + The transmission efficiency. The temperature and time of the second sintering stage are mainly to promote the mild synthesis of cationic doped lithium manganese iron phosphate, while controlling the temperature below the conventional synthesis temperature reduces the risk of over-sintering of cationic doped lithium manganese iron phosphate at high temperatures and hinders abnormal particle size growth.

[0044] Further, in some embodiments, the anion doping source is selected from any one or more of ammonium fluoride, lithium fluoride, thiourea, ammonium chloride, ammonium bromide, ammonium iodide, lithium bromide, dicyandiamide, dicyandiamide, and lithium chloride; and / or, the second carbon source is selected from any one or more of glucose, citric acid, sucrose, polyethylene glycol, polyvinyl alcohol, and ascorbic acid; and / or, the molar ratio of the metal element in the cation-doped lithium manganese iron phosphate, the carbon element in the second carbon source, and the X element in the anion doping source is 1:0.01~0.2:0.05~0.4; and / or, the doping amount of anion in the anion-cation doping precursor is 1000ppm~10000ppm.

[0045] The preferred types of anion doping sources are introduced into the surface of lithium manganese iron phosphate materials to replace the O element and form a surface doping layer. This can enhance the stability of Mn-O bonds or Mn-anion bonding, effectively suppress Mn dissolution during cycling, reduce the disordered structure on the surface of lithium manganese iron phosphate materials, and optimize the surface chemical environment of lithium manganese iron phosphate materials, thus maintaining the structural integrity and electrochemical performance stability of lithium manganese iron phosphate materials.

[0046] The preferred second carbon source provides additional carbon elements, promoting the formation of a stable carbon coating layer on the surface of doped lithium manganese iron phosphate particles, thereby improving the electronic conductivity of the lithium manganese iron phosphate material. By introducing a specific carbon source, not only can the conductivity of lithium manganese iron phosphate material be enhanced, but it can also synergistically work with surface anion doping to further suppress Mn dissolution and enhance the stability of the particle surface.

[0047] The preferred molar ratio of the above-mentioned substances is beneficial for suppressing the dissolution of divalent manganese in lithium manganese iron phosphate materials during cycling, thereby improving the efficiency of Li... + The diffusion rate and conductivity are improved, thereby enhancing the cycle stability and rate performance of lithium manganese iron phosphate materials, while also optimizing the capacity retention and discharge specific capacity of lithium manganese iron phosphate materials.

[0048] The optimal anion doping level in the precursor within the specified range helps suppress Mn dissolution from the particle surface, while reducing the negative impact on the internal structure of lithium manganese iron phosphate materials and preserving the Li content of the lithium manganese iron phosphate materials. + Diffusion rate and electronic conductivity synergistically improve the overall performance of lithium manganese iron phosphate materials.

[0049] Furthermore, in some embodiments, the mass concentration of the slurry obtained from the second grinding is 1 g / mL to 20 g / mL.

[0050] Too low a concentration results in excessively fine atomized particles, increasing drying time and potentially wasting resources; while too high a concentration may make it difficult for the atomized particles to form uniform precursor particles during drying, affecting the structure and performance of the final lithium manganese iron phosphate material. The preferred mass concentration of the second grinding slurry allows the material to be uniformly atomized into particles of suitable size during spray drying. This ensures that doping elements are evenly distributed within and on the surface of the particles during subsequent calcination, and also helps to form particles with high sphericity and dispersibility, thereby effectively improving the synthesis quality and electrochemical performance of the lithium manganese iron phosphate material.

[0051] Furthermore, in some embodiments, the air inlet rate of the second dryer is 10 mL / min to 100 mL / min, the inlet temperature is 180°C to 250°C, and the outlet temperature is 95°C to 120°C.

[0052] Optimizing the above parameters promotes uniform drying of the slurry and the formation of particle morphology, enhancing the integrity of the internal structure and surface smoothness of the precursor particles. Specifically, optimizing these conditions reduces the risk of uneven particle internal structure caused by excessively rapid drying rates. Furthermore, appropriate inlet and outlet temperature ranges help maintain the chemical activity and stability of the material, reducing the risk of unnecessary chemical reactions or decomposition during the drying process. In the preferred embodiment, the second drying method is spray drying. By adjusting the spray drying parameters, the particle size is further refined, enhancing the agglomeration force between particles and helping to improve the compaction density of the material. In addition, a finer particle structure also helps to shorten the Li... + This improves the transmission path, enhances the conductivity of the material, and thus improves the rate performance and cycle life of the battery.

[0053] Furthermore, in some embodiments, the second sintering includes a first stage sintering, a second stage sintering, and a third stage sintering performed sequentially. The temperature of the first stage sintering is 350℃~600℃, and the holding time of the first stage sintering is 2h~5h; the temperature of the second stage sintering is 650℃~800℃, and the holding time of the second stage sintering is 1h~3h; the temperature of the third stage sintering is 480℃~600℃, and the holding time of the third stage sintering is 4h~10h.

[0054] In the technical solution of this application embodiment, in a preferred embodiment, the second sintering process is subdivided into a first-stage sintering, a second-stage sintering, and a third-stage sintering. The first-stage sintering primarily promotes the thermal decomposition and recombination of the anion and cation doping precursors, creating conditions for the subsequent diffusion of doping elements. The second-stage sintering aims to diffuse anions X onto the surface of the doped lithium manganese iron phosphate particles, enhancing the stability of Mn-X or Mn-O bonds and effectively suppressing Mn dissolution. Finally, the third-stage sintering optimizes the crystallinity of the material, and the short holding time reduces the risk of excessive diffusion of doping elements into the doped lithium manganese iron phosphate particles, improving the surface anion doping effect. Overall, the second sintering employs segmented sintering technology. By precisely controlling the temperature and time of each sintering stage, a synergistic effect is achieved between the metal / non-metal cations inside the doped lithium manganese iron phosphate particles and the surface anions, thereby improving the conductivity and Li- content of the lithium manganese iron phosphate material. + Diffusion coefficient and cycle stability.

[0055] Thirdly, embodiments of this application provide a positive electrode sheet, which includes the aforementioned lithium manganese iron phosphate material or the lithium manganese iron phosphate material prepared by the aforementioned preparation method.

[0056] The positive electrode obtained by the above preparation method ensures the uniform distribution and high dispersion of dopant elements in the material by controlling the doping amount of cations and anions and by using sand milling and spray drying technology. At the same time, the segmented calcination process enables the dopant elements to form a composite doping structure inside and on the surface of the material, realizing multiple modifications from the inside to the surface of the lithium manganese iron phosphate material. This synergistically improves the electrochemical performance of the lithium manganese iron phosphate material, resulting in the positive electrode of this lithium manganese iron phosphate material showing outstanding performance in rate capability and cycle stability.

[0057] Fourthly, embodiments of this application provide a lithium-ion battery, including a positive electrode, wherein the electrode used for the positive electrode is the aforementioned positive electrode sheet.

[0058] Lithium-ion batteries including the above positive electrode plates have high capacity and its retention rate, better rate performance and cycle performance. For example, the discharge specific capacity at 0.1C is 150mAh / g~160mAh / g, and the capacity retention rate after 500 cycles at 1C is as high as 92.5%~99.1%.

[0059] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0060] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0061] Figure 1 This is a SEM image of lithium manganese iron phosphate obtained in Example 1 of the present invention;

[0062] Figure 2 This is a TEM image of lithium manganese iron phosphate obtained in Example 1 of the present invention;

[0063] Figure 3 The XPS full spectrum of lithium manganese iron phosphate obtained in Example 1 of this invention;

[0064] Figure 4 The F element distribution diagram of lithium manganese iron phosphate obtained in Example 1 of the present invention;

[0065] Figure 5 The 5C charge-discharge curves of lithium manganese iron phosphate obtained in Example 1 and Comparative Example 1 of this invention are shown.

[0066] Figure 6 This is a 1C cycle diagram of lithium manganese iron phosphate obtained in Example 1 of the present invention;

[0067] Figure 7 This is a flowchart illustrating the preparation process of the lithium manganese iron phosphate material of the present invention. Detailed Implementation

[0068] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0069] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0070] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0071] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0072] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0073] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0074] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0075] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0076] To address the issues of divalent manganese leaching and Li+ leaching during the cycling process of lithium manganese iron phosphate materials... +To address the technical problems of poor diffusion rate and conductivity, this application provides a lithium manganese iron phosphate material, its preparation method, a positive electrode, and a lithium-ion battery. The method involves the synergistic doping of metal cations M1 and M2, non-metal cations B, and anions X into the doped lithium manganese iron phosphate particles, creating a core-shell doping characteristic. Specifically, metal / non-metal cations are doped inside the doped lithium manganese iron phosphate particles, while anions are doped on the surface. This synergistically enhances the electrochemical performance of the lithium manganese iron phosphate material, such as rate performance and cycle stability, thereby improving the overall electrochemical performance of the positive electrode and the lithium-ion battery.

[0077] The electrical devices provided in this application embodiment can be, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0078] In a first aspect, embodiments of this application provide a lithium manganese iron phosphate material, which includes doped lithium manganese iron phosphate particles, the general formula of which is Li0.05. 1-a M 1a (M 2b Mn x Fe y-b )P 1-c B c O 4-d X d Where 0.05≥a>0, 0.05≥b>0, 0.07≥c>0, 0.081≥d>0, 1≥ x ≥0.5, 0.5≥ y >0, and x + y =1, M1 and M2 are doping elements, each independently selected from one or more of the following elements: magnesium, titanium, cobalt, nickel, copper, zinc, tin, barium, strontium, lead, aluminum, lanthanum, cerium, vanadium, zirconium, molybdenum, indium, and calcium; B is boron, and X is selected from one or more of the following elements: fluorine, bromine, iodine, chlorine, sulfur, and nitrogen.

[0079] The doped lithium manganese iron phosphate particles of this application Li 1-a M 1a (M 2b Mn x Fe y-b )P 1-c Bc O 4-d X d Containing a specific ratio of metal cations M1 and M2, and non-metal cations B and anions X, the doped lithium manganese iron phosphate particles exhibit core-shell doping characteristics through the synergistic effect of these dopants. Specifically, the interior of the doped lithium manganese iron phosphate particles is doped with metal / non-metal cations, while the surface is doped with anions, thereby synergistically enhancing the electrochemical performance of the lithium manganese iron phosphate material. In particular, metal cation M1 accelerates the Li... + The transport rate is increased. Meanwhile, the metal cation M2 enhances the stability of the Mn-O bond, improving the structural stability of lithium manganese iron phosphate materials. Simultaneously, the synergistic doping of metal cations M1 and M2 can effectively regulate the average valence state of Mn on the surface of doped lithium manganese iron phosphate particles, suppressing the dissolution of divalent manganese. The introduction of the non-metallic cation B forms BO3. 3- The presence of these groups not only enhances the flexibility of the lithium-ion diffusion channels but also broadens the Li-ion diffusion range. + The diffusion path is improved, thus significantly increasing the migration rate of lithium ions within the lithium manganese iron phosphate material. Anion X, as the anionic dopant, enhances the stability of the Mn-X or Mn-O bonds by increasing surface defects in the lithium manganese iron phosphate material, effectively suppressing the dissolution of Mn during charge and discharge, and preventing the degradation of the cycle performance of the lithium manganese iron phosphate material. Therefore, the doped lithium manganese iron phosphate particles of this application solve the problem of low electrochemical activity of lithium manganese iron phosphate from within through a composite doping strategy of metal cations M1, M2, and non-metal cation B, and solve the problem of Mn dissolution on the surface of lithium manganese iron phosphate through the doping of anion X, thereby synergistically enhancing the electrochemical performance of lithium manganese iron phosphate material, such as cycle stability.

[0080] In some embodiments, 'a' can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, etc., or other values ​​within the above range, which are not limited here.

[0081] In some embodiments, b can be 0.0024, 0.006, 0.0064, 0.008, 0.011, 0.012, 0.013, 0.018, 0.016, 0.034, 0.04, 0.05, etc., or other values ​​within the above range, which are not limited here.

[0082] In some embodiments, x can be 0.593, 0.594, 0.6, 0.7, 0.8, 0.9, 1.0, etc., or other values ​​within the above range, which are not limited here.

[0083] In some embodiments, y can be 0.1, 0.2, 0.3, 0.3974, 0.4, 0.401, 0.4044, 0.5, etc., or other values ​​within the above range, which are not limited here.

[0084] In some embodiments, c can be 0.019, 0.028, 0.03, 0.031, 0.041, 0.05, 0.061, 0.07, etc., or other values ​​within the above range, which are not limited here.

[0085] In some embodiments, d can be 0.01, 0.02, 0.03, 0.04, 0.045, 0.05, 0.051, 0.06, 0.07, 0.081, etc., or other values ​​within the above range, which are not limited here.

[0086] In some embodiments, the chemical formula of the doped lithium manganese iron phosphate particles may be selected from LiFe. 0.388 Mn 0.6 Ti 0.01 2P 0.97 B 0.03 O 3.95 F 0.05 LiFe 0.382 Mn 0.6 Mg 0.018 P 0.939 B 0.061 O 3.949 F 0.051 LiFe 0.388 Mn 0.6 Mg 0.012 P 0.969 B 0.03 1O 3.919 Cl 0.081 LiFe 0.384 Mn 0.6 Ca 0.016 P 0.969 B 0.031 O 3.949 F 0.051 LiFe 0.366 Mn 0.6 Ni 0.034 P 0.969 B 0.031 O 3.94 9F 0.051 LiFe 0.398 Mn 0.594 Ni 0.0016 Ca 0.0064 P 0.981 B 0.019 O 3.949 F 0.051 LiFe 0.395Mn 0.593 Ni 0.0096 Ca 0.002 4P 0.969 B 0.031 O 3.949 F 0.051 LiFe 0.395 Mn 0.593 Ni 0.006 Ca 0.006 P 0.969 B 0.031 O 3.949 F 0.051 LiFe 0.387 Mn 0.6 Ti 0.01 3P 0.959 B 0.041 O 3.955 F 0.045 LiFe 0.389 Mn 0.6 Ti 0.011 P 0.972 B 0.028 O 3.96 F 0.04 LiFe 0.388 Mn 0.6 Ti 0.012 P 0.96 9B 0.031 O 3.949 F 0.051 "etc." can also be other values ​​within the above range, and are not limited here.

[0087] Furthermore, in some embodiments, M1 replaces the Li element, and M1 includes M 11 and M 12 M 11 and M 12 Each element is independently selected from one or more of the following: magnesium, titanium, cobalt, nickel, copper, zinc, tin, barium, strontium, lead, aluminum, lanthanum, cerium, vanadium, zirconium, molybdenum, indium, and calcium. 11 and M 12 Different, M 11 and M 12 The molar ratio of the substances is 1~4:4~1.

[0088] M1 replaces Li elements to create Li vacancies, thereby increasing the Li transport rate. M1 includes M 11 and M 12 And M 11 and M 12 This difference allows for more diverse doping of the metal cation M1, enabling more effective tuning of the internal electronic structure and Li content of lithium manganese iron phosphate materials.+ The diffusion path is optimized to improve the conductivity and ion transport rate of lithium manganese iron phosphate materials. This is achieved by controlling M... 11 and M 12 When the molar ratio of substances is within the above range, it can promote M. 11 and M 12 Further optimization of the performance of lithium manganese iron phosphate materials will improve their electrochemical performance.

[0089] In some embodiments, M 11 and M 12 The ratio of the amounts of substances can be 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, etc., or other values ​​within the above range, which are not limited here.

[0090] In some embodiments, M2 replaces Fe, and M2 includes M 21 and M 22 M 21 and M 22 Each element is independently selected from one or more of the following: magnesium, titanium, cobalt, nickel, copper, zinc, tin, barium, strontium, lead, aluminum, lanthanum, cerium, vanadium, zirconium, molybdenum, indium, and calcium. 21 and M 22 Different, M 21 and M 22 The molar ratio of the substances is 1~4:4~1.

[0091] M2 replaces Fe, thereby enhancing the stability of the Mn-O bond. When M2 includes M... 21 and M 22 Furthermore, when the two differ, diverse cation-doped environments are formed within lithium manganese iron phosphate materials. This allows lithium manganese iron phosphate materials to simultaneously benefit from the properties of different elements within their internal structure, such as M. 21 It may optimize the migration path of lithium ions, while M 22 This enhances the structural stability and electronic conductivity of lithium manganese iron phosphate materials. This co-doping mechanism not only improves the electronic and ionic conductivity of lithium manganese iron phosphate materials and increases the lithium-ion diffusion rate, but also effectively suppresses Mn+ by altering the average valence state of transition metal ions. 2+ The dissolution of [the substance] allows for precise control over the internal structure of lithium manganese iron phosphate materials, improving their cycle performance and overall stability. Furthermore, M […]. 21 and M 22 The ratio of the amounts of substances helps to form a more complex and ordered atomic arrangement, promoting the kinetic response of lithium manganese iron phosphate materials at high rates, thereby significantly improving the rate performance and cycle life of lithium manganese iron phosphate materials while maintaining high energy density.

[0092] In some embodiments, M 21 and M 22 The ratio of the amounts of substances can be 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, etc., or other values ​​within the above range, which are not limited here.

[0093] In some embodiments, M2 can be Ti, Mg, Ni or Ca, or other values ​​within the above range, without limitation.

[0094] In some embodiments, M 21 Ni and M were 0.0016 ppm. 22 The Ca and M concentrations were 0.0064 ppm. 21 Ni and M were 0.0096 ppm. 22 The Ca concentration is 0.0024 ppm; or M 21 Ni and M were 0.006 ppm. 22 The value of Ca is 0.006 ppm; other values ​​within the above range are also acceptable and are not limited here.

[0095] In some embodiments, B replaces the P element.

[0096] Boron (B) replaces phosphorus (P), forming a planar triangular BO3 group. 3- This structure not only enhances the flexibility of the lithium-ion diffusion channels but also broadens the Li-ion diffusion path. + The diffusion path improves the electronic conductivity and Li content of lithium manganese iron phosphate materials. + Diffusion coefficient.

[0097] In some embodiments, B, M1, and M2 are doped inside the particles of doped lithium manganese iron phosphate.

[0098] Using M1 and M2 as cationic dopants to replace Li and Fe elements respectively enhances the stability of the Mn-O bond, thereby effectively suppressing Mn 2+ The dissolution of Mn and the disordering of the structure of lithium manganese iron phosphate (LFP) materials significantly improve the cycling stability and conductivity of LFP materials. The introduction of M1 can regulate the average valence state of Mn, reduce the content of divalent manganese, and thus mitigate the negative impact of the Jahn-Teller effect; while the addition of M2 can act as a support between transition metal layers, maintaining structural stability and preventing the degradation of LFP materials during cycling. Simultaneously, the doping of boron (B) replaces some of the phosphorus (P) element, forming a stable BO3 group. 3-The structure enhances the flexibility and width of the lithium-ion diffusion channels. This multi-element composite doping strategy within lithium manganese iron phosphate provides enhanced electronic conduction pathways and increases the stability of the internal structure by synergistically regulating the internal chemical environment and structural characteristics of the particles. This fundamentally solves the common performance degradation problem of lithium manganese iron phosphate battery materials during charge-discharge cycles.

[0099] In some embodiments, X replaces the O element, X is located on the surface of the doped lithium manganese iron phosphate particles, and X is distributed on the surface of the doped lithium manganese iron phosphate particles within a depth of 0.5% to 5% of the particle diameter.

[0100] In the optimized scheme, X replaces O and is distributed on the surface of the doped lithium manganese iron phosphate particles. More preferably, X is distributed within 0.5% to 5% of the particle diameter depth on the surface of the doped lithium manganese iron phosphate particles. This design effectively enhances the stability of the Mn-X or Mn-O bonds, thereby suppressing Mn dissolution on the particle surface and inside, reducing the structural disorder and irreversible phase transition of the lithium manganese iron phosphate material caused by Mn dissolution, and significantly improving the cycle stability and safety of the lithium manganese iron phosphate material. Simultaneously, the anion doping on the surface acts as a protective layer, preventing direct contact between the electrolyte and the active components of the lithium manganese iron phosphate material, reducing the occurrence of electrochemical side reactions, and further improving the battery's cycle efficiency and lifespan.

[0101] In some embodiments, X may be distributed on the surface of the doped lithium manganese iron phosphate particles at a depth of 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, or 5% of the particle size direction, or may be other values ​​within the above range, which are not limited here.

[0102] The general formula of doped lithium manganese iron phosphate particles is Li 1-a M 1a (M 2b Mn x Fe y-b )P 1-c B c O 4-d X d In this process, the c value determines the degree of B doping, affecting lattice flexibility and Li. + The diffusion efficiency is determined by the d-value, which reflects the surface doping amount of anion X and plays a crucial role in suppressing Mn dissolution and improving the surface properties of lithium manganese iron phosphate materials. The x and y values ​​control the ratio of Mn and Fe, respectively, while the b value simultaneously determines the ratio of M2 and Fe, affecting the discharge capacity and voltage plateau stability of lithium manganese iron phosphate materials. The internal doping effects of M1, M2, and B enhance the intrinsic electronic and ionic conductivity of lithium manganese iron phosphate materials, while the surface doping of X strengthens the surface stability of lithium manganese iron phosphate materials.

[0103] Furthermore, in some embodiments, the lithium manganese iron phosphate material further includes a carbon coating layer covering the surface of the doped lithium manganese iron phosphate particles, and the mass content of carbon element in the lithium manganese iron phosphate material is 1.5% to 3%.

[0104] In the technical solution of this application embodiment, the carbon coating layer is beneficial to improving the electronic conductivity of lithium manganese iron phosphate material and reducing charge transport resistance, thereby significantly improving the discharge performance of the battery under high-rate conditions. Simultaneously, the carbon coating layer, as a physical barrier, can reduce direct contact between the electrolyte and the active material, reduce surface side reactions, improve the cycle stability and structural integrity of the lithium manganese iron phosphate material, limit the dissolution of Mn elements, and thus improve the capacity retention rate of the lithium manganese iron phosphate material during cycling. Preferably, the carbon coating layer has the above-mentioned carbon content by mass. Further, controlling the carbon content in the lithium manganese iron phosphate material to be 2.1%~2.6% by mass promotes a balanced improvement in the internal and external conductivity of the lithium manganese iron phosphate material, reducing the decrease in the proportion of active material and Li due to excessive coating. + The increased risk of diffusion pathways further enhances the overall electrochemical performance of lithium manganese iron phosphate materials.

[0105] In some embodiments, the mass content of carbon in the lithium manganese iron phosphate material can be 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.8%, 3.0%, etc., or other values ​​within the above range, which are not limited here.

[0106] In some embodiments, the manganese leaching amount of the lithium manganese iron phosphate material is 50ppm to 200ppm.

[0107] Optimizing the above-mentioned suitable manganese leaching amount, further controlling the manganese leaching amount of lithium manganese iron phosphate material to 63ppm~185ppm helps to reduce the disproportionation and dissolution of Mn due to the Jahn-Teller effect during the charging and discharging process of lithium manganese iron phosphate material. 3+ The resulting harmful structural disorder and irreversible phase transition reduce the risk of poor cycle stability in lithium manganese iron phosphate materials.

[0108] In some embodiments, the manganese leaching amount of the lithium manganese iron phosphate material can be 50ppm, 55ppm, 60ppm, 63ppm, 70ppm, 76ppm, 78ppm, 85ppm, 90ppm, 92ppm, 100ppm, 105ppm, 115ppm, 120ppm, 125ppm, 130ppm, 132ppm, 140ppm, 145ppm, 150ppm, 155ppm, 160ppm, 162ppm, 170ppm, 175ppm, 180ppm, 185ppm, 190ppm, 195ppm, 200ppm, etc., or other values ​​within the above range, which are not limited here.

[0109] In some embodiments, the lithium-ion diffusion coefficient of lithium manganese iron phosphate material is 10. -9 cm 2 / s~10 -12 cm 2 / s.

[0110] The preferred lithium-ion diffusion coefficient is selected from the above, and further, the lithium-ion diffusion coefficient of the lithium manganese iron phosphate material is controlled to be 2.2 × 10⁻⁶. -12 cm 2 / s~6.9×10 -10 cm 2 / s helps reduce the risk of side reactions and uneven internal stress distribution, and improves the cycle stability and rate performance of lithium manganese iron phosphate materials.

[0111] In some embodiments, the lithium-ion diffusion coefficient of lithium manganese iron phosphate material can be 1.0 × 10⁻⁶. -12 cm 2 / s, 2.2×10 -12 cm 2 / s, 3.2×10 -12 cm 2 / s, 4.5×10 -12 cm 2 / s, 5.0×10 -12 cm 2 / s, 5.5×10 -12 cm 2 / s, 6.0×10 -12 cm 2 / s, 6.5×10 -12 cm 2 / s, 7.0×10 -12 cm 2 / s, 7.3×10 -12 cm 2 / s, 8.0×10 -12 cm 2 / s, 9.1×10 - 12 cm 2 / s, 1.3×10 -11 cm 2 / s, 2.1×10 -11 cm 2 / s, 3.0×10 -11 cm 2 / s, 4.0×10 -11 cm 2 / s, 5.5×10 - 11 cm 2 / s, 6.0×10 -11 cm 2 / s, 7.0×10 -11 cm 2 / s, 8.2×10 -11 cm 2 / s, 9.0×10 -11 cm 2 / s, 1.0×10 - 10 cm 2 / s, 2.5×10 -10 cm 2 / s, 3.1×10 -10 cm 2 / s, 4.7×10 -10 cm 2 / s, 6.9×10 -10 cm 2 / s, 7.5×10 - 10 cm 2 / s, 8.3×10 -10 cm 2 / s, 9.2×10 -10 cm 2 / s、10 -9 cm 2 / s, etc., can also be other values ​​within the above range, and are not limited here.

[0112] In some embodiments, the electronic conductivity of lithium manganese iron phosphate material is 0.015 S / m to 0.03 S / m.

[0113] By adjusting the content of doping elements M1 and M2, the electronic conductivity of lithium manganese iron phosphate material was improved to the above range. Furthermore, the electronic conductivity of lithium manganese iron phosphate material was controlled to be 0.017 S / m to 0.029 S / m, which significantly improved the conductivity performance of lithium manganese iron phosphate material, thereby improving the charge and discharge efficiency of lithium manganese iron phosphate material.

[0114] In some embodiments, the electronic conductivity of the lithium manganese iron phosphate material can be 0.015 S / m, 0.016 S / m, 0.017 S / m, 0.018 S / m, 0.019 S / m, 0.020 S / m, 0.021 S / m, 0.022 S / m, 0.023 S / m, 0.024 S / m, 0.025 S / m, 0.026 S / m, 0.027 S / m, 0.028 S / m, 0.029 S / m, 0.030 S / m, etc., or other values ​​within the above range, which are not limited here.

[0115] In some embodiments, the D50 particle size of the lithium manganese iron phosphate material is 2μm~5μm.

[0116] The D50 particle size is preferably within the above range. Further, the D50 particle size of the lithium manganese iron phosphate material is controlled to be 2.5 μm to 4.7 μm. Precise control improves the uniformity of particle size, thereby improving the contact efficiency between the active material and the electrolyte, accelerating the migration speed of lithium ions, and enhancing the rate performance of the battery. In addition, the uniform particle size distribution helps reduce agglomeration that may occur during electrode fabrication, increases the compaction density of the lithium manganese iron phosphate material, and thus improves the energy density of the battery.

[0117] In some embodiments, the D50 particle size of the lithium manganese iron phosphate material can be 2.0μm, 2.2μm, 2.5μm, 2.8μm, 3.0μm, 3.2μm, 3.5μm, 3.9μm, 4.0μm, 4.1μm, 4.3μm, 4.5μm, 4.7μm, 5.0μm, etc., or other values ​​within the above range, which are not limited here.

[0118] Please refer to Figure 7Secondly, embodiments of this application provide a method for preparing lithium manganese iron phosphate material. The method includes: mixing raw materials comprising a manganese source, an iron source, a first carbon source, a lithium source, a boron source, a cation doping source, and a phosphorus source, and then sequentially performing a first grinding and a first drying to obtain a cation-doped precursor; performing a first sintering of the cation-doped precursor under an inert atmosphere to obtain cation-doped lithium manganese iron phosphate; mixing raw materials comprising cation-doped lithium manganese iron phosphate, a second carbon source, and an anion doping source, and then sequentially performing a second grinding and a second drying to obtain an anion- and cation-doped precursors; and performing anion- and cation-doped precursors under an inert atmosphere. The bulk material undergoes a second sintering process to obtain lithium manganese iron phosphate material. The cation doping source includes M1 doping source and M2 doping source. M1 doping source and M2 doping source are each independently a doping source containing a metal element, which is selected from any one or more elements selected from magnesium, titanium, cobalt, nickel, copper, zinc, tin, barium, strontium, lead, aluminum, lanthanum, cerium, vanadium, zirconium, molybdenum, indium, and calcium. The anion doping source includes an element X, which is selected from any one or more elements selected from fluorine, bromine, iodine, chlorine, sulfur, and nitrogen.

[0119] The preparation method of the above-mentioned lithium manganese iron phosphate material in this application adopts a two-step solid-state method. First, in the first solid-state method, a cation doping source is introduced and subjected to a first grinding and a first drying process to obtain a cation-doped precursor. In the second solid-state method, an anion doping source is introduced and subjected to a second grinding and a second drying process to obtain an anion- and cation-doped precursors. The cation-doped precursor and the anion- and cation-doped precursors are then sintered to achieve dual doping of cations and anions. Specifically, the doping ions include metal cations M1 and M2, non-metal cations B, and anions X. Through the synergistic effect of these doping ions, a core-shell doping characteristic is formed in the doped lithium manganese iron phosphate particles. That is, metal / non-metal cations are doped inside the doped lithium manganese iron phosphate particles, and anions are doped on the surface of the doped lithium manganese iron phosphate particles, thereby synergistically enhancing the electrochemical performance of the lithium manganese iron phosphate material. Specifically, the incorporation of metal cation M1 can increase lithium vacancy defects inside the lithium manganese iron phosphate material, broadening the lithium content of lithium phosphate. + Diffusion channels increase conductive paths and accelerate Li + The M1 cation increases the transport rate and improves the carrier density of lithium manganese iron phosphate (LFP) materials. Meanwhile, the metal cation M2 enhances the stability of the Mn-O bond, improving the structural stability of LFP materials. Simultaneously, the synergistic doping of metal cations M1 and M2 can effectively regulate the average valence state of Mn on the surface of doped LFP particles, suppressing the dissolution of divalent manganese. The introduction of the non-metallic cation B forms BO3. 3- The presence of these groups not only enhances the flexibility of the lithium-ion diffusion channels but also broadens the Li-ion diffusion range.+ The diffusion path is improved, thus significantly increasing the migration rate of lithium ions within the lithium manganese iron phosphate material. Anion X, as the anionic dopant, enhances the stability of the Mn-X or Mn-O bonds by increasing surface defects in the lithium manganese iron phosphate material, effectively suppressing the dissolution of Mn during charge and discharge, and preventing the degradation of the cycle performance of the lithium manganese iron phosphate material. Therefore, the doped lithium manganese iron phosphate particles of this application solve the problem of low electrochemical activity of lithium manganese iron phosphate from within through a composite doping strategy of metal cations M1, M2, and non-metal cation B, and solve the problem of Mn dissolution on the surface of lithium manganese iron phosphate through the doping of anion X, thereby synergistically enhancing the electrochemical performance of lithium manganese iron phosphate material, such as cycle stability. Furthermore, the above preparation method is simple, low-cost, and avoids the post-treatment problems of waste liquid caused by liquid-phase reactions.

[0120] Furthermore, in some embodiments, the molar ratio of manganese from the manganese source, iron from the iron source, carbon from the first carbon source, lithium from the lithium source, boron from the boron source, metal from the cation doping source, and phosphorus from the phosphorus source is 0.5~1:0~0.5:0.2~0.4:1~1.05:0.01~0.05:0.01~0.05:0.95~0.99.

[0121] Optimizing the above molar ratios is beneficial for precisely controlling the uniform distribution of dopant elements in the precursor and the expected stoichiometry. This precise control of molar ratios is crucial for achieving co-doping of cations and anions, which promotes the uniform distribution of M1 and M2 elements inside the doped lithium manganese iron phosphate particles; while the X element is mainly concentrated on the surface of the doped lithium manganese iron phosphate particles, forming a core-shell structure doping characteristic. That is, the metal / non-metal cations improve the conductivity and lithium-ion diffusion path inside; while the anions strengthen the surface and prevent the dissolution of Mn.

[0122] In some embodiments, the D50 particle size of the lithium manganese iron phosphate material can be the molar ratio of manganese from the manganese source, iron from the iron source, carbon from the first carbon source, lithium from the lithium source, boron from the boron source, metal from the cation doping source, and phosphorus from the phosphorus source, which can be 0.5:0.2:0.2:1:0.01:0.01:0.95, 0.8:0.3:0.3:1.02:0.03:0.03:0.98, 1:0.5:0.4:1.05:0.05:0.05:0.99, etc., or other values ​​within the above range, which are not limited here.

[0123] In some embodiments, the M1 dopant source is selected from any one or more of sulfates, nitrates, oxalates, carbonates, and acetates containing the element M1.

[0124] Preferential M1 doping sources of the above types help to achieve uniform doping of M1 cations during the synthesis of lithium manganese iron phosphate materials. M1 cations replace Li elements, forming Li vacancies and effectively improving the transport rate of Li ions.

[0125] In some embodiments, M1 includes M 11 and M 12 M 11 and M 12 Each element is independently selected from any one of the following: magnesium, titanium, cobalt, nickel, copper, zinc, tin, barium, strontium, lead, aluminum, lanthanum, cerium, vanadium, zirconium, molybdenum, indium, and calcium. 11 and M 12 Different, M 11 and M 12 The molar ratio of the substances is 1~4:4~1.

[0126] The preferred approach is to select different types of M. 11 and M 12 and control M 11 and M 12 The molar ratio helps to diversify cation doping, which can more effectively regulate the internal electronic structure and Li content of lithium manganese iron phosphate materials. + Diffusion pathways are improved to enhance conductivity and ion transport rate, thereby improving the cycle stability of lithium manganese iron phosphate materials. This is achieved by controlling M... 11 and M 12 The molar ratio can be adjusted to further optimize the performance of lithium manganese iron phosphate materials and improve their electrochemical performance.

[0127] In some embodiments, M 11 and M 12 The ratio of the amounts of substances can be 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, etc., or other values ​​within the above range, which are not limited here.

[0128] In some embodiments, the M2 dopant source is selected from any one or more of sulfates, nitrates, oxalates, carbonates, and acetates containing the M2 element.

[0129] Optimizing the selection of the above-mentioned M2 doping sources facilitates the effective incorporation of M2 elements into the lithium manganese iron phosphate (LFP) lattice during the synthesis of LFP materials, replacing Fe elements and optimizing the crystal structure of LFP materials. This operation not only helps enhance the stability of the Mn-O bond and suppress the dissolution of Mn divalent atoms, but also promotes the growth of Li by adjusting the valence state of the dopant element. + Rapid migration within lithium manganese iron phosphate materials significantly improves their conductivity and Li₂ content.+ Diffusion rate. In a preferred embodiment, uniform doping of metal cations within the lithium manganese iron phosphate (LFP) material is achieved through the use of a specific M2 doping source, thereby enhancing the electrochemical activity and cycle stability of the LFP material. Simultaneously, the introduction of M2 element improves the electronic conduction path of the LFP material, enabling it to maintain high capacity even at high charge / discharge rates, thus improving the overall energy density and power density of the battery. Furthermore, M2 doping also contributes to improving the thermal stability and safety of the LFP material.

[0130] In some embodiments, M2 includes M 21 and M 22 M 21 and M 22 Each element is independently selected from one or more of the following: magnesium, titanium, cobalt, nickel, copper, zinc, tin, barium, strontium, lead, aluminum, lanthanum, cerium, vanadium, zirconium, molybdenum, indium, and calcium. 21 and M 22 Different, M 21 and M 22 The molar ratio of the substances is 1~4:4~1.

[0131] The preferred approach is to select different types of M. 21 and M 22 and control M 21 and M 22 The molar ratio of these elements allows lithium manganese iron phosphate materials to benefit from the properties of both elements simultaneously within their internal structure, such as M. 21 It may optimize the migration path of lithium ions, while M 22 This enhances the structural stability and electronic conductivity of lithium manganese iron phosphate materials. Furthermore, M 21 and M 22 The contrasting properties and appropriate proportions of these elements help to form a more complex and ordered atomic arrangement, promoting the kinetic response of lithium manganese iron phosphate materials at high rates. This significantly improves the rate performance and cycle life of lithium manganese iron phosphate materials while maintaining high energy density.

[0132] In some embodiments, the boron source is selected from any one or more of boric acid, boron oxide, and lithium borate.

[0133] Preferential selection of the above boron sources helps to form a more stable BO3 group by partially replacing phosphorus in the synthesis of lithium manganese iron phosphate materials. 3- This structure enhances the flexibility and width of the lithium-ion diffusion channels within the lithium manganese iron phosphate material, thereby improving the Li-ion diffusion efficiency. + Transmission rate, while reducing Li+ Diffusion barriers were overcome, and the crystal structure of lithium manganese iron phosphate materials was optimized.

[0134] In some embodiments, the iron source is selected from any one or more of ferric phosphate, ferric oxide, ferrous oxide, ferric tetroxide, ferric nitrate, ferrous sulfate, and ferrous oxalate.

[0135] By selecting the above-mentioned iron source types, not only are the necessary iron elements provided, but their own characteristics may also affect the synthesis process of lithium manganese iron phosphate materials, promoting a more uniform doping distribution, thereby enabling the final lithium manganese iron phosphate materials to exhibit higher capacity retention and more stable cycling performance.

[0136] In some embodiments, the manganese source is selected from any one or more of manganese sulfide, manganese tetroxide, manganese trioxide, manganese carbonate, manganese oxalate, manganese phosphate, manganese acetate, manganese sulfate, and manganese nitrate.

[0137] The selection of the above-mentioned manganese source types promotes the uniform distribution of cation doping, enhances the electronic conductivity of lithium manganese iron phosphate materials, and improves the Li... + This improves diffusion efficiency and enhances the chemical stability and reactivity of lithium manganese iron phosphate materials during synthesis.

[0138] In some embodiments, the first carbon source is selected from any one or more of glucose, citric acid, sucrose, polyethylene glycol, polyvinyl alcohol, and ascorbic acid.

[0139] The preferred first carbon source can be converted into a carbon coating layer during the subsequent sintering process, which further improves the electronic conductivity and enhances the electrochemical performance of lithium manganese iron phosphate materials.

[0140] In some embodiments, the lithium source is selected from any one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium acetate, lithium phosphate, lithium nitrate, lithium tert-butoxide, lithium benzoate, lithium formate, lithium chromate, lithium citrate tetrahydrate, lithium tetrachloroaluminate, and lithium tetrafluoroborate.

[0141] Optimizing the above-mentioned lithium source types helps to obtain a more uniform crystal structure and smaller grain size, improving the lithium-ion diffusion coefficient and cycle stability; at the same time, it reduces cation mixing, improving its discharge specific capacity and cycle stability. In addition, appropriate lithium sources, in combination with precursors, can better control the spherical secondary particle morphology of the final cathode material, improve tap density, and thus increase the volumetric energy density of the battery.

[0142] In some embodiments, the phosphorus source is selected from any one or more of phosphoric acid, lithium dihydrogen phosphate, lithium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0143] Optimizing the selection of phosphorus sources can effectively optimize the synthesis conditions of lithium manganese iron phosphate materials, further improving the structural uniformity and stability of the materials. This helps to form high-quality premixes, providing a foundation for subsequent uniform doping of cations and anions. Simultaneously, the phosphorus source not only participates in the formation of the main framework of lithium manganese iron phosphate materials but also promotes solid-state reactions between particles during subsequent heat treatment, forming a more complete crystal lattice structure, thereby improving the Li... + The diffusion pathway improves the conductivity and Li content of lithium manganese iron phosphate materials. + The rate of diffusion.

[0144] In some embodiments, the doping amount of cations in the cation-doped precursor is 1000ppm to 10000ppm, and the doping amount of boron in the cation-doped precursor is 800ppm to 20000ppm.

[0145] The optimal cation doping levels help to fully replace Li and Fe elements in the crystal lattice, forming Li and Fe vacancies, thereby improving Li... + This increases the transport rate and enhances the stability of the Mn-O bond. Preferred boron doping levels are beneficial for enhancing the flexibility of the lithium-ion diffusion channel and broadening the Li-ion diffusion path. + The preferred scheme, by controlling the doping amounts of cations and boron, not only optimizes the electronic and ion transport characteristics within the lithium manganese iron phosphate material, but also reduces the risk of divalent manganese dissolution during cycling by forming a stable doped structure, thus synergistically enhancing the electrochemical performance of the lithium manganese iron phosphate material, particularly in rate performance and cycle stability.

[0146] In some embodiments, the doping amount of cations in the cation-doped precursor can be controlled to be from 1000ppm to 8340ppm, such as 1000ppm, 1080ppm, 1466ppm, 2000ppm, 2498ppm, 2503ppm, 2510ppm, 2544ppm, 3000ppm, 4150ppm, 4200ppm, 5000ppm, 6000ppm, 7000ppm, 8340ppm, etc., or other values ​​within the above range, which are not limited here.

[0147] In some embodiments, the boron doping amount in the cation-doped precursor can be controlled to be 800ppm to 1990ppm, such as 800ppm, 900ppm, 1012ppm, 1020ppm, 1032ppm, 1046ppm, 1053ppm, 1070ppm, 1079ppm, 1102ppm, 1335ppm, 1980ppm, 1990ppm, etc., or other values ​​within the above range, which are not limited here.

[0148] Furthermore, in some embodiments, the mass concentration of the slurry obtained from the first grinding is 1 g / mL to 20 g / mL.

[0149] Optimizing the appropriate mass concentration of the first grinding slurry improves the dispersibility and flowability of the material during the sand milling process, which is beneficial for improving the uniform distribution of dopant elements and forming more uniform precursor particles. By controlling the slurry concentration, the cation dopant source can be uniformly distributed inside the precursor, and the non-metallic cation boron source can also be uniformly doped in the particles, thereby improving the Li-P content of lithium manganese iron phosphate materials. + The diffusion channels and electronic conductivity were improved, and the doping concentration of anion X on the surface was optimized, effectively suppressing the dissolution of Mn and enhancing the chemical stability of the lithium manganese iron phosphate material surface.

[0150] In some embodiments, the mass concentration of the slurry obtained from the first grinding can be 1 g / mL, 3 g / mL, 5 g / mL, 6 g / mL, 8 g / mL, 9 g / mL, 10 g / mL, 12 g / mL, 14 g / mL, 16 g / mL, 18 g / mL, 20 g / mL, etc., or other values ​​within the above range, which are not limited here.

[0151] Furthermore, in some embodiments, the air inlet rate of the first dryer is 10 mL / min to 100 mL / min, the inlet temperature is 180°C to 250°C, and the outlet temperature is 95°C to 120°C.

[0152] Among the above parameters, the air inlet rate helps to form uniform and fine particles, which not only increases the specific surface area of ​​the lithium manganese iron phosphate material, but also promotes the uniform distribution of elements during subsequent sintering. Appropriate inlet and outlet temperatures ensure that the moisture inside the particles evaporates rapidly without damaging their structure, avoiding agglomeration and thus guaranteeing particle dispersibility and crystallinity.

[0153] In some embodiments, the air inlet rate of the first dryer can be 10 mL / min, 20 mL / min, 30 mL / min, 40 mL / min, 50 mL / min, 60 mL / min, 70 mL / min, 80 mL / min, 90 mL / min, 100 mL / min, etc., or other values ​​within the above range, which are not limited here.

[0154] In some embodiments, the inlet temperature can be 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, etc., or other values ​​within the above range, which are not limited here.

[0155] In some embodiments, the outlet temperature can be 95°C, 97°C, 99°C, 100°C, 102°C, 105°C, 108°C, 110°C, 112°C, 115°C, 118°C, 120°C, etc., or other values ​​within the above range, which are not limited here.

[0156] Furthermore, in some embodiments, the first sintering includes a first-stage sintering and a second-stage sintering performed sequentially. The temperature of the first-stage sintering is 100℃~150℃, and the holding time of the first-stage sintering is 2h~5h. The temperature of the second-stage sintering is 400℃~600℃, and the holding time of the second-stage sintering is 4h~10h.

[0157] In the preferred embodiment of the above scheme, the first stage of sintering is performed at a low temperature. Its main function is to perform secondary drying of the cation-doped precursor and effectively remove any air present, providing a purer inert atmosphere for subsequent synthesis processes. The low-temperature sintering helps promote uniform diffusion of ions within the cation-doped precursor, forming a stable doped structure and improving the Li... + The transmission efficiency. The temperature and time of the second sintering stage are mainly to promote the mild synthesis of cationic doped lithium manganese iron phosphate, while controlling the temperature below the conventional synthesis temperature reduces the risk of over-sintering of cationic doped lithium manganese iron phosphate at high temperatures and hinders abnormal particle size growth.

[0158] In some embodiments, the temperature of the first-stage sintering can be 100℃, 110℃, 120℃, 130℃, 140℃, or 150℃, and the holding time of the first-stage sintering can be 2h, 3h, 4h, 4.5h, or 5h, or other values ​​within the above range, which are not limited here.

[0159] In some embodiments, the temperature of the second-stage sintering can be 400℃, 450℃, 500℃, 550℃, or 600℃, and the holding time of the second-stage sintering can be 4h, 5h, 6h, 7h, 8h, 9h, or 10h, or other values ​​within the above range, which are not limited here.

[0160] Furthermore, in some embodiments, the anion doping source is selected from any one or more of ammonium fluoride, lithium fluoride, thiourea, ammonium chloride, ammonium bromide, ammonium iodide, lithium bromide, dicyandiamide, and lithium chloride.

[0161] The preferred types of anion doping sources are introduced into the surface of lithium manganese iron phosphate materials to replace the O element and form a surface doping layer. This can enhance the stability of Mn-O bonds or Mn-anion bonding, effectively suppress Mn dissolution during cycling, reduce the disordered structure on the surface of lithium manganese iron phosphate materials, and optimize the surface chemical environment of lithium manganese iron phosphate materials, thus maintaining the structural integrity and electrochemical performance stability of lithium manganese iron phosphate materials.

[0162] In some embodiments, the second carbon source is selected from any one or more of glucose, citric acid, sucrose, polyethylene glycol, polyvinyl alcohol, and ascorbic acid.

[0163] The preferred second carbon source provides additional carbon elements, promoting the formation of a stable carbon coating layer on the surface of doped lithium manganese iron phosphate particles, thereby improving the electronic conductivity of the lithium manganese iron phosphate material. By introducing a specific carbon source, not only can the conductivity of lithium manganese iron phosphate material be enhanced, but it can also synergistically work with surface anion doping to further suppress Mn dissolution and enhance the stability of the particle surface.

[0164] In some embodiments, the molar ratio of the metal element in the cationic doped lithium manganese iron phosphate, the carbon element in the second carbon source, and the X element in the anionic doped source is 1:0.01~0.2:0.05~0.4.

[0165] The preferred molar ratio of the above-mentioned substances is beneficial for suppressing the dissolution of divalent manganese in lithium manganese iron phosphate materials during cycling, thereby improving the efficiency of Li... + The diffusion rate and conductivity are improved, thereby enhancing the cycle stability and rate performance of lithium manganese iron phosphate materials, while also optimizing the capacity retention and discharge specific capacity of lithium manganese iron phosphate materials.

[0166] In some embodiments, the doping amount of anions in the anion-cation doped precursor is 1000ppm to 10000ppm.

[0167] The optimal anion doping level in the precursor within the specified range helps suppress Mn dissolution from the particle surface, while reducing the negative impact on the internal structure of lithium manganese iron phosphate materials and preserving the Li content of the lithium manganese iron phosphate materials. + Diffusion rate and electronic conductivity synergistically improve the overall performance of lithium manganese iron phosphate materials.

[0168] In some embodiments, the doping amount of anions in the anion-cation doped precursor can be 1000ppm, 1161ppm, 1175ppm, 1180ppm, 1182ppm, 1192ppm, 1194ppm, 1198ppm, 1203ppm, 1206ppm, 1210ppm, 1244ppm, 10000ppm, etc., or other values ​​within the above range, which are not limited here.

[0169] Furthermore, in some embodiments, the mass concentration of the slurry obtained from the second grinding is 1 g / mL to 20 g / mL.

[0170] Too low a concentration results in excessively fine atomized particles, increasing drying time and potentially wasting resources; while too high a concentration may make it difficult for the atomized particles to form uniform precursor particles during drying, affecting the structure and performance of the final lithium manganese iron phosphate material. The preferred mass concentration of the second grinding slurry allows the material to be uniformly atomized into particles of suitable size during spray drying. This ensures that doping elements are evenly distributed within and on the surface of the particles during subsequent calcination, and also helps to form particles with high sphericity and dispersibility, thereby effectively improving the synthesis quality and electrochemical performance of the lithium manganese iron phosphate material.

[0171] In some embodiments, the mass concentration of the slurry obtained from the second grinding can be 1 g / mL, 3 g / mL, 5 g / mL, 6 g / mL, 8 g / mL, 9 g / mL, 10 g / mL, 12 g / mL, 14 g / mL, 16 g / mL, 18 g / mL, 20 g / mL, etc., or other values ​​within the above range, which are not limited here.

[0172] Furthermore, in some embodiments, the air inlet rate of the second dryer is 10 mL / min to 100 mL / min, the inlet temperature is 180°C to 250°C, and the outlet temperature is 95°C to 120°C.

[0173] Optimizing the above parameters promotes uniform drying of the slurry and the formation of particle morphology, enhancing the integrity of the internal structure and surface smoothness of the precursor particles. Specifically, optimizing these conditions reduces the risk of uneven particle internal structure caused by excessively rapid drying rates. Furthermore, appropriate inlet and outlet temperature ranges help maintain the chemical activity and stability of the material, reducing the risk of unnecessary chemical reactions or decomposition during the drying process. In the preferred embodiment, the second drying method is spray drying. By adjusting the spray drying parameters, the particle size is further refined, enhancing the agglomeration force between particles and helping to improve the compaction density of the material. In addition, a finer particle structure also helps to shorten the Li... + This improves the transmission path, enhances the conductivity of the material, and thus improves the rate performance and cycle life of the battery.

[0174] In some embodiments, the air inlet rate of the second dryer can be 10 mL / min, 20 mL / min, 30 mL / min, 40 mL / min, 50 mL / min, 60 mL / min, 70 mL / min, 80 mL / min, 90 mL / min, 100 mL / min, etc., or other values ​​within the above range, which are not limited here.

[0175] In some embodiments, the inlet temperature of the second dryer can be 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, etc., or other values ​​within the above range, which are not limited here.

[0176] In some embodiments, the outlet temperature of the second dryer can be 95°C, 97°C, 99°C, 100°C, 102°C, 105°C, 108°C, 110°C, 112°C, 115°C, 118°C, 120°C, etc., or other values ​​within the above range, which are not limited here.

[0177] Furthermore, in some embodiments, the second sintering includes a first stage sintering, a second stage sintering, and a third stage sintering performed sequentially. The temperature of the first stage sintering is 350℃~600℃, and the holding time of the first stage sintering is 2h~5h; the temperature of the second stage sintering is 650℃~800℃, and the holding time of the second stage sintering is 1h~3h; the temperature of the third stage sintering is 480℃~600℃, and the holding time of the third stage sintering is 4h~10h.

[0178] In the technical solution of this application embodiment, in a preferred embodiment, the second sintering process is subdivided into a first-stage sintering, a second-stage sintering, and a third-stage sintering. The first-stage sintering primarily promotes the thermal decomposition and recombination of the anion and cation doping precursors, creating conditions for the subsequent diffusion of doping elements. The second-stage sintering aims to diffuse anions X onto the surface of the doped lithium manganese iron phosphate particles, enhancing the stability of Mn-X or Mn-O bonds and effectively suppressing Mn dissolution. Finally, the third-stage sintering optimizes the crystallinity of the material, and the short holding time reduces the risk of excessive diffusion of doping elements into the doped lithium manganese iron phosphate particles, improving the surface anion doping effect. Overall, the second sintering employs segmented sintering technology. By precisely controlling the temperature and time of each sintering stage, a synergistic effect is achieved between the metal / non-metal cations inside the doped lithium manganese iron phosphate particles and the surface anions, thereby improving the conductivity and Li- content of the lithium manganese iron phosphate material. + Diffusion coefficient and cycle stability.

[0179] In some embodiments, the sintering temperature of the first stage can be 350°C, 400°C, 450°C, 500°C, 550°C, or 600°C, and the holding time of the first stage sintering can be 2h, 3h, 4h, 5h, or other values ​​within the above range, which are not limited here.

[0180] In some embodiments, the temperature of the second sintering stage can be 650°C, 680°C, 700°C, 720°C, 750°C, or 800°C, and the holding time of the second sintering stage can be 1 hour, 2 hours, 3 hours, or other values ​​within the above range, which are not limited here.

[0181] In some embodiments, the sintering temperature of the third stage is 480℃, 500℃, 520℃, 550℃, or 600℃, and the holding time of the third stage sintering is 4h, 5h, 6h, 7h, 8h, 9h, or 10h, or other values ​​within the above range, which are not limited here.

[0182] Thirdly, embodiments of this application provide a positive electrode sheet, which includes the aforementioned lithium manganese iron phosphate material or the lithium manganese iron phosphate material prepared by the aforementioned preparation method.

[0183] The positive electrode obtained by the above preparation method ensures the uniform distribution and high dispersion of dopant elements in the material by controlling the doping amount of cations and anions and by using sand milling and spray drying technology. At the same time, the segmented calcination process enables the dopant elements to form a composite doping structure inside and on the surface of the material, realizing multiple modifications from the inside to the surface of the lithium manganese iron phosphate material. This synergistically improves the electrochemical performance of the lithium manganese iron phosphate material, resulting in the positive electrode of this lithium manganese iron phosphate material showing outstanding performance in rate capability and cycle stability.

[0184] Fourthly, embodiments of this application provide a lithium-ion battery, including a positive electrode, wherein the electrode used for the positive electrode is the aforementioned positive electrode sheet.

[0185] Lithium-ion batteries including the above positive electrode plates have high capacity and its retention rate, better rate performance and cycle performance. For example, the discharge specific capacity at 0.1C is 150mAh / g~160mAh / g, and the capacity retention rate after 500 cycles at 1C is as high as 92.5%~99.1%.

[0186] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0187] I. Preparation Method

[0188] Example 1:

[0189] Reference Figure 7 The process flow diagram for preparing lithium manganese iron phosphate material is shown. 10.8g lithium dihydrogen phosphate, 0.1g lithium carbonate, 6.08g iron phosphate, 6.92g manganese carbonate, 0.06g titanium dioxide (cationic dopant source), and 0.12g boric acid (boron source) are dispersed in deionized water containing 0.32g glucose (first carbon source) and stirred until homogeneous to obtain a first mixture. This first mixture is then stirred and refined in a sand mill for 2-3 hours (first grinding) at a stirring speed of 2200 rpm. The concentration of the first mixture is then adjusted to 5g / mL, followed by a single spray drying (first drying). The inlet air temperature is controlled at ℃, the outlet air temperature at 100℃, and the feed rate at 20mL / min to obtain the cation-doped precursor.

[0190] The cation-doped precursor was placed in a quartz crucible for the first sintering. The temperature was increased to 150℃ at 5℃ / min and held for 4h under a nitrogen atmosphere (first-stage sintering). Then the temperature was increased to 500℃ at 5℃ / min and held for 6h (second-stage sintering). The cooling rate was set to 5℃ / min. After cooling to room temperature, cation-doped lithium manganese iron phosphate was obtained.

[0191] Add 0.4g of glucose to 120g of deionized water and stir magnetically for 20 minutes to obtain a second carbon source solution. Add 10g of cation-doped lithium manganese iron phosphate, 1.02g of glucose, and 0.12g of ammonium fluoride to the second carbon source solution and mix for 20 minutes to obtain a suspension (second mixture). Sand mill the suspension (second grinding) for 2 hours and then perform a second spray drying (second drying). Control the inlet air temperature at ℃, the outlet air temperature at 110℃, and the feed rate at 12mL / min to obtain anion and cation doped precursors.

[0192] The anion and cation doped precursors were placed in a quartz crucible for a second sintering. The temperature was increased to 400℃ at 5℃ / min and held for 4h under a nitrogen atmosphere (first stage sintering), then increased to 700℃ at 5℃ / min and held for 1h (second stage sintering), and then decreased to 500℃ and held for 6h (third stage sintering). The cooling rate was set to 5℃ / min. After cooling to room temperature, lithium manganese iron phosphate material was obtained, wherein F was distributed on the surface of the doped lithium manganese iron phosphate particles within 0.6% of the particle diameter.

[0193] Example 2:

[0194] Compared with Example 1, the difference is that 0.06g of titanium dioxide was replaced with 0.045g of magnesium oxide, and the amount of boric acid added was 0.24g.

[0195] Example 3:

[0196] Compared with Example 2, the difference is that 0.12g of ammonium fluoride is replaced with 0.19g of ammonium chloride.

[0197] Example 4:

[0198] Compared with Example 1, the difference is that 0.06g of titanium dioxide was replaced with 0.058g of calcium oxide.

[0199] Example 5:

[0200] Compared with Example 1, the difference is that 0.06g of titanium oxide is replaced with 0.16g of nickel oxide.

[0201] Example 6:

[0202] Compared with Example 1, the difference is that 0.06g of titanium oxide is replaced with 0.011g of nickel oxide and 0.033g of calcium oxide, with a molar ratio of 1:4.

[0203] Example 7:

[0204] Compared with Example 1, the only difference is that 0.06g of titanium oxide is replaced with 0.045g of nickel oxide and 0.0085g of calcium oxide, with a molar ratio of 4:1.

[0205] Example 8:

[0206] Compared with Example 1, the only difference is that 0.06g of titanium oxide is replaced with 0.028g of nickel oxide and 0.021g of calcium oxide, with a molar ratio of 1:1.

[0207] Example 9:

[0208] Compared with Example 1, the difference is that the anion and cation doped precursors are placed in a quartz crucible, heated to 500°C at 5°C / min and held for 4 hours under a nitrogen atmosphere, then heated to 750°C at 5°C / min and held for 1 hour, and then cooled to 550°C and held for 6 hours. The cooling rate is set to 5°C / min. After cooling to room temperature, lithium manganese iron phosphate material is obtained, wherein F is distributed on the surface of the doped lithium manganese iron phosphate particles within 2.4% of the particle diameter.

[0209] Example 10:

[0210] Compared with Example 1, the difference is that the anion and cation doped precursors are placed in a quartz crucible, heated to 600°C at 5°C / min and held for 2 hours under a nitrogen atmosphere, then heated to 800°C at 5°C / min and held for 2 hours, and then cooled to 500°C and held for 6 hours. The cooling rate is set to 5°C / min. After cooling to room temperature, lithium manganese iron phosphate material is obtained, wherein F is distributed on the surface of the doped lithium manganese iron phosphate particles within 4.8% of the particle diameter.

[0211] Example 11:

[0212] Compared with Example 1, the difference is that the anion and cation doped precursors are placed in a quartz crucible, heated to 400°C at 5°C / min and held for 2 hours under a nitrogen atmosphere, then heated to 650°C at 5°C / min and held for 1 hour, and then cooled to 500°C and held for 4 hours. The cooling rate is set to 5°C / min. After cooling to room temperature, lithium manganese iron phosphate material is obtained, wherein F is distributed on the surface of the doped lithium manganese iron phosphate particles within 0.3% of the particle diameter.

[0213] Example 12:

[0214] Compared with Example 1, the difference is that the anion and cation doped precursors are placed in a quartz crucible, heated to 600°C at 5°C / min and held for 2 hours under a nitrogen atmosphere, then heated to 800°C at 5°C / min and held for 3 hours, and then cooled to 600°C and held for 10 hours. The cooling rate is set to 5°C / min. After cooling to room temperature, lithium manganese iron phosphate material is obtained, wherein F is distributed on the surface of the doped lithium manganese iron phosphate particles within 6.2% of the particle diameter.

[0215] Example 13:

[0216] Compared with Example 1, the difference lies in the molar ratio of manganese from the manganese source, iron from the iron source, carbon from the first carbon source, lithium from the lithium source, boron from the boron source, metal from the cation doping source, and phosphorus from the phosphorus source, which is 0.6:0.39:0.4:1.04:0.07:0.06:1, thus obtaining lithium manganese iron phosphate material.

[0217] Comparative Example 1:

[0218] Compared with Example 1, the difference is that titanium oxide and boric acid are not added during the first grinding process to obtain lithium manganese iron phosphate material.

[0219] Comparative Example 2:

[0220] Compared with Example 1, the difference is that ammonium fluoride is not added during the second grinding process to obtain lithium manganese iron phosphate material.

[0221] Comparative Example 3:

[0222] Compared with Example 1, the difference is that boric acid is not added during the first grinding and ammonium fluoride is not added during the second grinding, and lithium manganese iron phosphate material is finally obtained.

[0223] Comparative Example 4:

[0224] Compared with Example 2, the difference is that boric acid is not added during the first grinding and ammonium chloride is not added during the second grinding, and lithium manganese iron phosphate material is finally obtained.

[0225] Comparative Example 5:

[0226] Compared with Comparative Example 4, the difference is that magnesium oxide is not added during the first grinding, and lithium manganese iron phosphate material is finally obtained.

[0227] II. Testing Methods

[0228] 1. Property testing of lithium manganese iron phosphate materials:

[0229] The doped lithium manganese iron phosphate synthesized in Example 1 was characterized using a MERLIN Compact field emission scanning electron microscope (MESS). The SEM results are as follows: Figure 1 As shown, the synthesized material exhibits high sphericity and dispersibility, with high particle uniformity.

[0230] The doped lithium manganese iron phosphate material synthesized in Example 1 was characterized using a Thermo Fisher-Talos F200X high-resolution transmission electron microscope. The TEM results are as follows: Figure 2 As shown, the particle surface has a distinct secondary coating layer, and the particle interior is a dense lithium manganese iron phosphate material.

[0231] Metal ions and doping amount: The doped lithium manganese iron phosphate material synthesized in Example 1 was characterized by an Agilent 7900 inductively coupled plasma spectroscopy (ICP) instrument. The ICP results are shown in Table 1.

[0232] B element doping amount: The doped lithium manganese iron phosphate material synthesized in Example 1 was characterized by an Agilent-7900 inductively coupled plasma spectroscopy system. The ICP results are shown in Table 1.

[0233] Manganese leaching amount of lithium manganese iron phosphate material: The doped lithium manganese iron phosphate material synthesized in Example 1 was characterized by an Agilent-7900 inductively coupled plasma spectroscopy (ICP) instrument. The ICP results are shown in Table 2.

[0234] Lithium-ion diffusion coefficient of lithium manganese iron phosphate material: The doped lithium manganese iron phosphate material synthesized in Example 1 was tested by constant current intermittent titration using a CT2001A from Wuhan Landian Electronics Co., Ltd. The test results are shown in Table 2.

[0235] Electronic conductivity of lithium manganese iron phosphate material: The doped lithium manganese iron phosphate material synthesized in Example 1 was characterized using a China-Lattice-ST2643 resistivity meter, and the test results are shown in Table 2.

[0236] D50 particle size of lithium manganese iron phosphate material: The doped lithium manganese iron phosphate material synthesized in Example 1 was tested by constant current intermittent titration using a Malvern Panalytical-Mastersizer 3000 laser particle size analyzer. The test results are shown in Table 2.

[0237] Carbon content: The doped lithium manganese iron phosphate material synthesized in Example 1 was characterized using a Leco-CS844 carbon-sulfur analyzer. The test results are shown in Table 1.

[0238] Surface distribution of F within a certain depth along the particle size direction of doped lithium manganese iron phosphate particles: The F element doping in the sample was detected using an X-ray photoelectron spectroscopy (XPS) instrument from Thermo Fisher-K-Alpha (USA). The results are as follows: Figure 4 As shown

[0239] 2. Lithium-ion battery property testing:

[0240] The chemical state of Example 1 was characterized using a Thermo Fisher-K-Alpha X-ray photoelectron spectroscopy system. Figure 3 As shown, the anions in Example 1 were characterized using a JEOL-JEM-F200 field emission transmission electron microscope. Figure 4 As shown, it is clear that the material surface contains Ti and F components.

[0241] The doped lithium manganese iron phosphate obtained in the above examples and comparative examples was mixed with conductive carbon black and binder (PVDF5130) at a mass ratio of 90:5:5 and coated onto a 12 μm thick Al foil. The electrode was then dried in a vacuum oven at 110°C, and then the electrode was pressed to 12 μm thickness. The diameter was measured, and the weight and mass of the active material were calculated. Subsequently, using lithium sheets as the counter electrode, CR2032 button half-cells were assembled using an LG2400 / 1000TS glove box manufactured by Wig Gas Purification Technology (Suzhou) Co., Ltd.

[0242] The performance of the obtained button cells was tested using a CT 2001A battery testing system manufactured by Wuhan Landian Electronics Co., Ltd., with a voltage range of 2-4.35V. The results are as follows: Figure 5 , Figure 6 As shown in Table 1. From Figure 5 As can be seen, the discharge specific capacity of the anion- and cation-doped lithium manganese iron phosphate corresponding to Example 1 is 135 mAh / g at 5C, while that of Comparative Example 1 is only 102.5 mAh / g. Doping greatly improves the rate performance of the material. Figure 6 The graph shows the performance of Example 1 after 500 cycles at 1C. The capacity retention rate of the material after cycling is as high as 99.1%, demonstrating excellent cycle stability.

[0243] All the test results are listed in Tables 1 and 2.

[0244] Table 1

[0245]

[0246]

[0247] Table 2

[0248]

[0249] Table 3

[0250]

[0251] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0252] The results in Table 1 show that the lithium manganese iron phosphate material exhibits high capacity after anion and cation doping.

[0253] The carbon coating in Example 1 was uniform (2.3%), with a small particle size (3.2 μm) and a high diffusion coefficient (2.5 × 10⁻⁶). -10 The high capacity and high stability of Ti doping indicate that Ti doping effectively suppresses Jahn-Teller distortion, B stabilizes PO bonds, and F reduces surface impedance. The three work together to achieve dual stability of the bulk phase and interface.

[0254] The capacity of Example 2 (Mg replacing Ti) was slightly lower than that of Example 1, possibly due to the lower capacity of Mg²⁺. + It has low electronegativity and its electronic conductivity is slightly inferior to that of Ti. 4+ However, it has the advantage of lower cost.

[0255] Example 3 (Cl) - Replace F - It is slightly inferior to Example 1 in suppressing Mn dissolution.

[0256] Example 4 (Ca replacing Ti) has a higher electronic conductivity, possibly due to the introduction of oxygen vacancies by Ca, but its capacity is slightly lower than that of Example 1.

[0257] Example 5 (Ni instead of Ti) improves capacity but sacrifices some cycle performance.

[0258] Example 6 (Ni:Ca molar ratio = 1:4) has performance close to that of Example 1, with high capacity, good stability, and extremely low total metal content (only about 1500 ppm), making it economically outstanding.

[0259] In Example 7 (Ni:Ca molar ratio = 4:1), Ni is dominant and Ca is auxiliary. The capacity is slightly lower than that of Example 6, but the cycle retention rate is better than that of Examples 5 and 6. This shows that an appropriate amount of Ni can improve capacity and stability, but the presence of trace amounts of Ca helps to maintain a high cycle retention rate.

[0260] Example 8 (Ni:Ca molar ratio = 1:1) exhibits balanced performance, slightly lower capacity, but excellent stability.

[0261] Although the Mn leaching amount (185ppm) increased in Example 9 (sintering temperature increased), the cycle retention rate was still relatively high, almost the same as in Example 1, indicating that the synergistic protective effect of B+F is strong and can partially offset the structural damage caused by high temperature.

[0262] The Mn leaching in Example 10 (with a higher sintering temperature) was 140 ppm, which was higher than that in Example 1, but the capacity and cycle retention were still better, indicating that the ternary doped system remained stable and had extremely strong stability even under harsh sintering conditions.

[0263] In Example 11 (Mn:Fe molar ratio = 0.6:0.39, Fe content reduced), the Fe content was reduced, but the capacity remained almost unchanged, and the cycle retention rate was still >96%, indicating that Fe is not the main contributor to capacity, and Mn dominates the capacity. The Ti+B+F system can stabilize the low-Fe formulation. The cost of Fe source (iron phosphate) is higher than that of Mn source, and reducing the Fe content can significantly reduce costs without sacrificing performance.

[0264] Comparative Example 1 (no cations, no boron) was doped with only F, with no cations or boron, and its performance was significantly worse than that of Example 1. This indicates that F... - Its effect is limited when used alone; it must work in conjunction with cations and boron to achieve stability.

[0265] Comparative Example 2 (no F, only cations + B) contained Ti and B, but no F. Mn dissolution was very high, while capacity and retention were both low. This indicates that F... - It is the key to inhibiting the dissolution of Mn; without F, the structure will collapse.

[0266] Comparative Example 3 (no B, no F, only cations) contains Ti but no B or F. Its performance is slightly better than Comparative Example 2, but far lower than the Example. This indicates that cation doping has some effect, but without B+F, interfacial side reactions cannot be controlled.

[0267] In Comparative Example 4 (no B, no F, but with Mg), even with the use of Mg (a superior cation to Ti), the performance was still severely degraded due to the absence of B+F. This demonstrates that B+F is an essential doping element, and cation doping further contributes to improved performance.

[0268] Comparative Example 5 (without Mg, B, or F) performed significantly worse than all other examples.

[0269] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A lithium manganese iron phosphate material, characterized in that, The lithium manganese iron phosphate material includes doped lithium manganese iron phosphate particles, the general formula of which is Li. 1-a M 1a (M 2b Mn x Fe y-b )P 1-c B c O 4-d X d Where 0.05≥a ≥0, 0.05≥b>0, 0.07≥c>0, 0.081≥d>0, 1≥ x ≥0.5, 0.5≥ y >0, and x + y =1, M1 and M2 are doping elements, wherein M1 and M2 are each independently selected from any one or more of magnesium, titanium, cobalt, nickel, copper, zinc, tin, barium, strontium, lead, aluminum, lanthanum, cerium, vanadium, zirconium, molybdenum, indium and calcium; B is boron, and X is selected from any one or more of fluorine, bromine, iodine, chlorine, sulfur and nitrogen.

2. The lithium manganese iron phosphate material according to claim 1, characterized in that, The M1 replaces the Li element, and the M1 includes M 11 and M 12 M 11 and M 12 Each element is independently selected from one or more of the following: magnesium, titanium, cobalt, nickel, copper, zinc, tin, barium, strontium, lead, aluminum, lanthanum, cerium, vanadium, zirconium, molybdenum, indium, and calcium. 11 and M 12 Unlike, the M 11 and the M 12 The molar ratio of the substances is 1~4:4~1; the M2 replaces the Fe element, and the M2 includes M 21 and M 22 M 21 and M 22 Each element is independently selected from one or more of the following: magnesium, titanium, cobalt, nickel, copper, zinc, tin, barium, strontium, lead, aluminum, lanthanum, cerium, vanadium, zirconium, molybdenum, indium, and calcium. 21 and M 22 Unlike, the M 21 and the M 22 The molar ratio of the substances is 1~4:4~1; And / or, the B element replaces the P element; And / or, B, M1 and M2 are doped inside the particles of the doped lithium manganese iron phosphate; And / or, the X replaces the O element, the X is located on the surface of the doped lithium manganese iron phosphate particles, and the X is distributed on the surface of the doped lithium manganese iron phosphate particles within a depth of 0.5% to 5% in the particle diameter direction.

3. The lithium manganese iron phosphate material according to claim 1 or 2, characterized in that, The lithium manganese iron phosphate material further includes a carbon coating layer on the surface of the doped lithium manganese iron phosphate particles, and the mass content of carbon in the lithium manganese iron phosphate material is 1.5%~3%; And / or, the manganese leaching amount of the lithium manganese iron phosphate material is 50ppm~200ppm; And / or, the lithium-ion diffusion coefficient of the lithium manganese iron phosphate material is 10. -12 cm 2 / s~10 -9 cm 2 / s; And / or, the electronic conductivity of the lithium manganese iron phosphate material is 0.015 S / m to 0.030 S / m; And / or, the D50 particle size of the lithium manganese iron phosphate material is 2μm~5μm.

4. A method for preparing lithium manganese iron phosphate material, characterized in that, The preparation method of the lithium manganese iron phosphate material includes: The raw materials, including manganese source, iron source, first carbon source, lithium source, boron source, cation doping source and phosphorus source, are mixed and then subjected to first grinding and first drying in sequence to obtain cation doped precursor; Under an inert atmosphere, the cation-doped precursor is subjected to a first sintering to obtain cation-doped lithium manganese iron phosphate. The raw materials, including the cation-doped lithium manganese iron phosphate, the second carbon source, and the anion-doped source, are mixed and then subjected to a second grinding and a second drying to obtain anion- and cation-doped precursors. Under an inert atmosphere, the anion and cation doped precursors are subjected to a second sintering to obtain the lithium manganese iron phosphate material; The cation doping source includes M1 doping source and M2 doping source; The M1 doping source and the M2 doping source are each independently a doping source containing a metal element, wherein the metal element is selected from any one or more elements selected from magnesium, titanium, cobalt, nickel, copper, zinc, tin, barium, strontium, lead, aluminum, lanthanum, cerium, vanadium, zirconium, molybdenum, indium, and calcium. The anion doping source is a doping source including element X, wherein element X is selected from any one or more of fluorine, bromine, iodine, chlorine, sulfur and nitrogen.

5. The preparation method according to claim 4, characterized in that, The molar ratio of manganese from the manganese source, iron from the iron source, carbon from the first carbon source, lithium from the lithium source, boron from the boron source, metal from the cation-doped source, and phosphorus from the phosphorus source is 0.5~1:0~0.5:0.2~0.4:1~1.05:0.01~0.05:0.01~0.05:0.95~0.99; And / or, the M1 dopant source is selected from any one or more of sulfates, nitrates, oxalates, carbonates and acetates containing the M1 element; And / or, the M1 includes M 11 and M 12 The M 11 and the M 12 M is independently selected from any one of the elements: magnesium, titanium, cobalt, nickel, copper, zinc, tin, barium, strontium, lead, aluminum, lanthanum, cerium, vanadium, zirconium, molybdenum, indium, and calcium. 11 and the M 12 Unlike, the M 11 and the M 12 The molar ratio of the substances is 1~4:4~1; And / or, the M2 dopant source is selected from any one or more of sulfates, nitrates, oxalates, carbonates and acetates containing the M2 element; And / or, the M2 includes M 21 and M 22 The M 21 and the M 22 M is independently selected from any one or more of the elements magnesium, titanium, cobalt, nickel, copper, zinc, tin, barium, strontium, lead, aluminum, lanthanum, cerium, vanadium, zirconium, molybdenum, indium, and calcium. 21 and the M 22 Unlike, the M 21 and the M 22 The molar ratio of the substances is 1~4:4~1; And / or, the boron source is selected from any one or more of boric acid, boron oxide, and lithium borate; And / or, the iron source is selected from any one or more of ferric phosphate, ferric oxide, ferrous oxide, ferric tetroxide, ferric nitrate, ferrous sulfate, and ferrous oxalate; And / or, the manganese source is selected from any one or more of manganese sulfide, manganese tetroxide, manganese trioxide, manganese carbonate, manganese oxalate, manganese phosphate, manganese acetate, manganese sulfate, and manganese nitrate; And / or, the first carbon source is selected from any one or more of glucose, citric acid, sucrose, polyethylene glycol, polyvinyl alcohol, and ascorbic acid; And / or, the lithium source is selected from any one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium acetate, lithium phosphate, lithium nitrate, lithium tert-butoxide, lithium benzoate, lithium formate, lithium chromate, lithium citrate tetrahydrate, lithium tetrachloroaluminate, and lithium tetrafluoroborate. And / or, the phosphorus source is selected from any one or more of phosphoric acid, lithium dihydrogen phosphate, lithium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate; And / or, the amount of cation doping in the cation-doped precursor is 1000ppm to 10000ppm, and the amount of boron doping in the cation-doped precursor is 800ppm to 20000ppm.

6. The preparation method according to claim 4 or 5, characterized in that, The first sintering includes a first-stage sintering and a second-stage sintering performed sequentially. The temperature of the first-stage sintering is 100℃~150℃, and the holding time of the first-stage sintering is 2h~5h. The temperature of the second-stage sintering is 400℃~600℃, and the holding time of the second-stage sintering is 4h~10h.

7. The preparation method according to claim 4 or 5, characterized in that, The anion doping source is selected from any one or more of ammonium fluoride, lithium fluoride, thiourea, ammonium chloride, ammonium bromide, ammonium iodide, lithium bromide, dicyandiamide, and lithium chloride; And / or, the second carbon source is selected from any one or more of glucose, citric acid, sucrose, polyethylene glycol, polyvinyl alcohol, and ascorbic acid; The molar ratio of the metal element in the cationic doped lithium manganese iron phosphate, the carbon element in the second carbon source, and the X element in the anionic doped source is 1:0.01~0.2:0.05~0.

4. And / or, the doping amount of anions in the anion and cation doped precursor is 1000ppm to 10000ppm.

8. The preparation method according to claim 4 or 5, characterized in that, The second sintering includes a first stage sintering, a second stage sintering, and a third stage sintering performed sequentially. The temperature of the first stage sintering is 350℃~600℃, and the holding time of the first stage sintering is 2h~5h. The temperature of the second stage sintering is 650℃~800℃, and the holding time of the second stage sintering is 1h~3h. The temperature of the third stage sintering is 480℃~600℃, and the holding time of the third stage sintering is 4h~10h.

9. A positive electrode sheet, characterized in that, The positive electrode sheet comprises lithium manganese iron phosphate material according to any one of claims 1 to 3 or lithium manganese iron phosphate material prepared by any one of claims 4 to 8.

10. A lithium-ion battery, comprising a positive electrode, characterized in that, The positive electrode used is the positive electrode sheet as described in claim 9.

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