Preparation method of lithium manganese iron phosphate material and application thereof

Abstract

The application provides a preparation method of a lithium manganese iron phosphate material, which comprises the following steps: preparing a manganese ferrous phosphate precursor by a liquid-phase coprecipitation method, removing crystallization water to obtain an anhydrous manganese ferrous phosphate precursor; mixing two groups of the anhydrous manganese ferrous phosphate precursor, a lithium source, a supplementary phosphorus source, an organic carbon source, a dopant and deionized water, stirring and dispersing, first wet grinding, spray drying, and second sintering to obtain two groups of lithium manganese iron phosphate intermediates; the addition proportion of the organic carbon source in the first group is lower than that in the second group, and the addition proportion of the dopant in the first group is greater than that in the second group; mixing the two groups of lithium manganese iron phosphate intermediates and supplementary organic carbon sources and deionized water, stirring and dispersing, second wet grinding, spray drying, third sintering, crushing to obtain the lithium manganese iron phosphate material, and the material has a high compacted density. The process flow is simple, and the application is suitable for large-scale production. The application further provides the lithium manganese iron phosphate material and a lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a method for preparing lithium manganese iron phosphate material, the lithium manganese iron phosphate material, and the application of the lithium manganese iron phosphate material. Background Technology

[0002] As the best performing secondary battery currently available, lithium-ion batteries have been commercialized since the 1990s. After years of research, lithium manganese iron phosphate has become one of the best performing technologies in the field of lithium-ion batteries.

[0003] Conventional methods for preparing lithium manganese iron phosphate and its precursors include high-temperature solid-state method, sol-gel method and co-precipitation method. Using conventional single preparation methods, the resulting precursors or lithium manganese iron phosphate materials have low compaction density, resulting in low electrochemical specific capacity when applied to cathode materials and corresponding batteries, which cannot meet the requirements of high-performance applications.

[0004] Currently known methods for preparing lithium manganese iron phosphate materials using a two-stage precursor formulation are problematic. This method introduces a grinding process to prepare precursor particles of different sizes, increasing process complexity and compromising the elemental uniformity of the material. Consequently, it is still not feasible to obtain lithium manganese iron phosphate materials that meet high-performance requirements. Summary of the Invention

[0005] In view of the above, the present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention proposes a method for preparing lithium manganese iron phosphate material, the lithium manganese iron phosphate material itself, and a lithium-ion battery. The method for preparing lithium manganese iron phosphate material provided by the present invention yields a stable graded structure, highly uniform distribution of lithium manganese iron phosphate elements and metal doping, and a dense and uniform carbon coating layer, which can preferentially improve the electrochemical performance of the material. Furthermore, the preparation method of this lithium manganese iron phosphate material has a simple process flow and is suitable for large-scale industrial production applications.

[0006] Therefore, in a first aspect, embodiments of the present invention provide a method for preparing lithium manganese iron phosphate material, the method comprising:

[0007] S10. Iron source, manganese source, phosphoric acid and deionized water are mixed and dissolved in a certain proportion, and a precursor of ferrous manganese phosphate is prepared by liquid phase co-precipitation. The precursor of ferrous manganese phosphate is subjected to a first sintering to remove the water of crystallization and obtain anhydrous ferrous manganese phosphate precursor.

[0008] S20, two groups of anhydrous manganese ferrous phosphate precursor, lithium source, supplemental phosphorus source, organic carbon source, dopant and deionized water are mixed in a certain proportion, stirring and dispersing, first wet grinding, spray drying, second sintering to obtain two groups of manganese iron lithium phosphate intermediates; wherein the first group of organic carbon source addition ratio is lower than the second group of organic carbon source addition ratio, the first group of dopant addition ratio is greater than the second group of dopant addition ratio;

[0009] S30, the two groups of manganese iron lithium phosphate intermediates and supplemental organic carbon source, deionized water are mixed in a certain proportion, stirring and dispersing, second wet grinding, spray drying, third sintering, crushing to obtain the manganese iron lithium phosphate material.

[0010] Preferably, the first group of organic carbon source addition ratio satisfies that the carbon content of manganese iron lithium phosphate intermediate is 0.05wt%-0.15wt%, the first group of dopant addition ratio satisfies that the doping metal accounts for 0.5%-1.0% of the iron manganese content in the anhydrous manganese ferrous phosphate precursor; the second group of organic carbon source addition ratio satisfies that the carbon content of manganese iron lithium phosphate intermediate is 0.45wt%-0.55wt%, and the second group of dopant addition ratio satisfies that the doping metal accounts for 0-0.5% of the iron manganese content in the anhydrous manganese ferrous phosphate precursor.

[0011] Preferably, the step S30 specifically comprises: the two groups of manganese iron lithium phosphate intermediates are mixed with organic carbon source and deionized water respectively in a certain proportion, stirring and dispersing, second wet grinding is carried out respectively in a first particle size and a second particle size, and then mixing, spray drying, third sintering and crushing are carried out to obtain the manganese iron lithium phosphate material.

[0012] Preferably, the first particle size is 0.5-0.7pm, and the second particle size is 0.2-0.4pm.

[0013] Preferably, the addition amount of the supplemental organic carbon source is controlled according to the carbon content of the manganese iron lithium phosphate intermediate to satisfy that the target prepared manganese iron lithium phosphate material mass ratio is 1.3wt%-1.7wt%.

[0014] Preferably, the mixing ratio of the two groups of manganese iron lithium phosphate intermediates is 6:4-2:8.

[0015] Preferably, the addition amount of the anhydrous manganese ferrous phosphate precursor, the lithium source and the supplemental phosphorus source satisfies that the lithium and iron manganese molar ratio Li / (Fe+Mn) is 1.01-1.07, and the iron manganese and phosphorus molar ratio (Fe+Mn) / P is 0.96-0.99; and / or,

[0016] The organic carbon source includes at least one of glucose, sucrose, polyethylene glycol and citric acid; and / or

[0017] The dopant includes a compound of at least one of Ti, V, Nb, and Mg.

[0018] Preferably, the first sintering is in an air atmosphere, the sintering temperature is 500-650 DEG C, and the sintering time is 4-7 h; and / or,

[0019] The first wet grinding controls the particle size to be 0.3-0.5 μm; and / or,

[0020] The spray drying has an inlet temperature of 220 DEG C and an outlet temperature of 100 DEG C; and / or,

[0021] The second sintering is in a nitrogen atmosphere, the sintering temperature is 600-750 DEG C, and the sintering time is 4-8 h; and / or,

[0022] The third sintering is in a nitrogen atmosphere, the sintering temperature is 730-780 DEG C, and the sintering time is 8-10 h; and / or,

[0023] The pulverization controls the particle size to be D10≥0.3 μm, D50 is 0.5-1.1 μm, and D90≤12 μm.

[0024] In a second aspect, the embodiments of the present application further provide a lithium iron manganese phosphate material, which is prepared by the preparation method of the first aspect.

[0025] In a third aspect, the embodiments of the present application further provide a lithium ion battery, which includes a battery positive electrode prepared from the lithium iron manganese phosphate material of the second aspect.

[0026] The preparation method of the lithium iron manganese phosphate material provided by the embodiments of the present application adopts different carbon source addition ratios and dopant addition ratios in the sintering process of preparing the carbon-coated lithium iron manganese phosphate intermediate, forms carbon-coated lithium iron manganese phosphate intermediates with different morphologies, and then makes the carbon-coated lithium iron manganese phosphate intermediates with different morphologies graded and further form a dense and uniform carbon-coated layer through secondary carbon-coated mixed sintering, so that the carbon-coated lithium iron manganese phosphate intermediates with different morphologies are combined tightly to achieve high compaction density, thereby obtaining excellent electrochemical performance; the lithium ion battery further prepared by taking the lithium iron manganese phosphate material as a positive electrode material can also have excellent performance. Meanwhile, the process flow of the preparation method is simple, the equipment requirement is low, and the method is suitable for large-scale industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The preparation method flow chart of the lithium iron manganese phosphate material provided by an embodiment of the present application is shown in the figure.

[0028] Figure 2 The SEM image of the lithium iron manganese phosphate material prepared by the embodiment 1 of the present application is shown in the figure.

[0029] Figure 3 SEM image of the lithium manganese iron phosphate material prepared for Example 3 of the present application;

[0030] Figure 4 SEM image of the lithium manganese iron phosphate material prepared for Comparative Example 1 of the present application;

[0031] Figure 5 SEM image of the lithium manganese iron phosphate material prepared for Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0032] Embodiments of the present application are described in detail below with reference to the attached drawing figures, wherein the same or like component have the same or similar designations throughout the drawing figures and the detailed description. The embodiments described below are presented by way of example only and are not intended to be limiting of the application.

[0033] The disclosure that follows provides many different embodiments, or examples, for implementing different structures of the present application. For the purpose of simplicity, the elements and settings of the various examples are described in terms of specific placement, and / or configuration. These are by no means limiting of the present application. In their description, nonessential components are omitted and similar components are numbered with the same reference numerals throughout the several drawings.

[0034] Reference will now be made to Figure 1 In a first aspect, embodiments of the present application provide a preparation method of a lithium manganese iron phosphate material, the preparation method comprising:

[0035] S10, dissolving and mixing an iron source, a manganese source, phosphoric acid and deionized water in a certain proportion, preparing a ferromanganous phosphate precursor by liquid-phase co-precipitation, and removing crystal water by first sintering the ferromanganous phosphate precursor to obtain an anhydrous ferromanganous phosphate precursor;

[0036] S20, mixing two groups of anhydrous ferromanganous phosphate precursors, a lithium source, a supplementary phosphorus source, an organic carbon source, a dopant and deionized water in a certain proportion, stirring and dispersing, first wet grinding, spray drying and second sintering to obtain two groups of lithium manganese iron phosphate intermediates; wherein the addition proportion of the organic carbon source of the first group is lower than that of the second group, and the addition proportion of the dopant of the first group is greater than that of the second group;

[0037] S30, mixing the two groups of manganese iron lithium phosphate intermediates and supplemented organic carbon source, deionized water according to a certain proportion, stirring and dispersing, second wet grinding, spray drying, third sintering, crushing to obtain the manganese iron lithium phosphate material.

[0038] It can be understood that the step S10 uses a coprecipitation method to prepare a precursor, which can obtain a material with stable metal content, no impurities and uniform distribution, laying a good raw material foundation for subsequent preparation of target materials.

[0039] The step S20 is actually to prepare two different manganese iron lithium phosphate intermediates. The precursor raw materials, lithium sources, and supplemented phosphorus sources of the two groups are the same, but different amounts of carbon sources and dopant additives are used to prepare intermediates with different doping degrees and carbon source coatings through sintering. The material particle size is different.

[0040] The step S30 further mixes and carbon-coated sintering of the different morphology manganese iron lithium phosphate intermediates prepared in step S20 to realize the particle size grading of the two manganese iron lithium phosphate materials and further carbon-coated to improve the material performance.

[0041] Further, the first group of organic carbon source addition ratio meets the carbon content of manganese iron lithium phosphate intermediate at 0.05wt%-0.15wt%, and the dopant addition ratio of the first group meets the doping metal accounting for 0.5%-1.0% of the iron and manganese content in the anhydrous ferromanganous precursor; the second group of organic carbon source addition ratio meets the carbon content of manganese iron lithium phosphate intermediate at 0.45wt%-0.55wt%, and the dopant addition ratio of the second group meets the doping metal accounting for 0-0.5% of the iron and manganese content in the anhydrous ferromanganous precursor.

[0042] Specifically, in the present embodiment, the specific two groups of parameters of carbon source addition amount and dopant addition amount are used to achieve the purpose of preparing different particle material intermediates.

[0043] Further, the step S30 specifically includes: mixing the two groups of manganese iron lithium phosphate intermediates with organic carbon source and deionized water according to a certain proportion, stirring and dispersing, respectively wet grinding with a first particle size and a second particle size, then mixing, spray drying, third sintering, crushing to obtain the manganese iron lithium phosphate material.

[0044] In the present embodiment, in step S30, before mixing and sintering the two groups of different manganese iron lithium phosphate intermediates, wet grinding is performed with two different particle sizes, which can further obtain material particles with greater difference in morphology. After mixing and sintering, the micro-graded structure is more stable, and the material performance is further improved.

[0045] Specifically, the first particle size is 0.5-0.7 μm, and the second particle size is 0.2-0.4 μm.

[0046] Further, the addition amount of the supplementary organic carbon source is controlled according to the carbon content of the lithium iron manganese phosphate intermediate to satisfy the target preparation lithium iron manganese phosphate material mass ratio of 1.3-1.7 wt%.

[0047] Further, the mixing ratio of the two groups of lithium iron manganese phosphate intermediates is 6:4-2:8.

[0048] Further, the addition amounts of the anhydrous ferromanganous phosphate precursor, the lithium source, and the supplementary phosphorus source satisfy: the lithium to iron manganese molar ratio Li / (Fe+Mn) is 1.01-1.07, and the iron manganese to phosphorus molar ratio (Fe+Mn) / P is 0.96-0.99.

[0049] Further, the organic carbon source includes at least one of glucose, sucrose, polyethylene glycol, and citric acid.

[0050] Further, the dopant includes a compound of at least one of Ti, V, Nb, and Mg.

[0051] Further, the first sintering is in an air atmosphere, the sintering temperature is 500-650°C, and the sintering time is 4-7 h.

[0052] Further, the first wet grinding controls the particle size to be 0.3-0.5 μm.

[0053] Further, the spray drying has an inlet air temperature of 220°C and an outlet air temperature of 100°C.

[0054] Further, the second sintering is in a nitrogen atmosphere, the sintering temperature is 600-750°C, and the sintering time is 4-8 h.

[0055] Further, the third sintering is in a nitrogen atmosphere, the sintering temperature is 730-780°C, and the sintering time is 8-10 h.

[0056] Further, the pulverization controls the particle size to be D10≥0.3 μm, D50 is 0.5-1.1 μm, and D90≤12 μm.

[0057] In a second aspect, the embodiments of the present application further provide a lithium iron manganese phosphate material, which is prepared by the preparation method of the first aspect.

[0058] In a third aspect, the embodiments of the present application further provide a lithium ion battery, which includes a battery positive electrode prepared from the lithium iron manganese phosphate material of the second aspect.

[0059] The embodiment of the present application synthesizes the manganous iron source precursor by using the co-precipitation method, the reaction process is easy to control the reaction conditions, and the phase uniformity of the material is effectively improved, and the material repeatability is good.

[0060] The lithium manganese iron phosphate / carbon composite positive electrode material prepared by using the co-precipitation-three-step sintering combination method in the embodiment of the present application, by controlling the addition amount of the carbon source and the addition amount of the dopant, adjusting the gradation size between the particles, the material compaction density can be improved, the intermediate wet grinding particle size is further controlled, the gradation effect is further improved, and thus the material compaction density is improved.

[0061] The embodiment of the present application adopts the two-step carbon coating and ion doping method, which is beneficial to the migration of electrons and ions, and thus the charge and discharge performance of the battery is improved.

[0062] The following further specifically describes the specific process and effect of the preparation method of the lithium manganese iron phosphate material adopting the present application by combining some specific embodiments, but is not limited to the protection scope of the present application.

[0063] Embodiment 1

[0064] The present embodiment prepares a lithium manganese iron phosphate material, specifically including the following steps:

[0065] After the initial raw materials are uniformly mixed, the co-precipitation reaction is carried out, and after washing and drying, the first sintering is carried out, and the precursor A is obtained by crushing;

[0066] According to the precursor A and the lithium phosphate mixture Li / (Fe+Mn): 1.03, (Fe+Mn) / P: 0.98, the additive content of 0.60% mol relative to the (Fe+Mn) content in the precursor A, the intermediate product B is obtained by weighing 1000g of the precursor, 315.89g of lithium phosphate, 11.87g of glucose, 11.87g of polyethylene glycol, 11.87g of citric acid, 22.31g of magnesium acetate tetrahydrate, and 11.87g of ammonium metavanadate; the intermediate product C is obtained by weighing 30.85g of glucose, 11.16g of magnesium acetate tetrahydrate, 5.93g of ammonium metavanadate, and other raw materials of the same type and weight; the two intermediate products B and C are respectively prepared, ground, sprayed, and sintered.

[0067] The two batches of ingredients are respectively prepared according to the solid content of 45%, and the deionized water is used as the solvent for the first wet mixing, the slurry particle size D50 is controlled to be 0.4μm after grinding, the ground slurry is subjected to spray drying, the inlet air temperature is controlled to be 220℃, and the outlet air temperature is controlled to be 100℃; then sintering is carried out under the nitrogen atmosphere, the sintering parameters are 680℃, 6h, and the intermediate products B and C are obtained.

[0068] Take the intermediate products B and C by the proportion of 6:4, control the carbon content of the finished product manganese iron lithium phosphate to be 1.50%, and take two batches of raw materials respectively: ① intermediate product B 600g, glucose 30.00g, polyethylene glycol 33.00g, ② intermediate product C 400g, glucose 14.60g, polyethylene glycol 16.08g; both batches of raw materials are wet ground for the second time with the solid content of 42% and deionized water as the solvent, and the mixed slurry is ground to a particle size of: slurry B D50 is 0.5μm, and slurry C D50 is 0.2μm.

[0069] The ground slurry B and C are mixed uniformly by ball milling, the mixed slurry is spray dried by controlling the inlet air temperature to be 220℃ and the outlet air temperature to be 100℃, and then sintered under the nitrogen atmosphere with the sintering parameters of 740℃ and 10h, and the sintered material is airflow crushed to control the particle size of D10≥0.30μm, D50:0.5-1.1μm, and D90≤12μm, to obtain the high-compaction manganese iron lithium phosphate positive electrode material D, and relevant tests are carried out.

[0070] Figure 2 The SEM diagram of the manganese iron lithium phosphate material prepared in Example 1 can be seen from Figure 1 The primary particles are distributed in obviously different sizes, and the primary particles are connected closely.

[0071] Example 2

[0072] A manganese iron lithium phosphate material is prepared in this example, which specifically includes the following steps:

[0073] After the initial raw materials are mixed uniformly, the co-precipitation reaction, washing and drying are carried out, and then the first sintering is carried out to break the precursor A;

[0074] The precursor 1000g, lithium phosphate 315.89g, glucose 11.87g, polyethylene glycol 11.87g, citric acid 11.87g, magnesium acetate tetrahydrate 22.31g, and ammonium metavanadate 11.87g are taken according to the mixture of the precursor A and lithium phosphate Li / (Fe+Mn):1.03, (Fe+Mn) / P:0.98, the additive content of 0.60%mol relative to the (Fe+Mn) content in the precursor A, and the carbon content of 0.10% of the generated intermediate product B; the glucose 29.67g, magnesium acetate tetrahydrate 11.16g, ammonium metavanadate 5.93g, and other raw materials are taken with the same weight according to the additive content of 0.30%mol and the carbon content of 0.50% of the generated intermediate product C; the two intermediate products B and C are respectively dosed, ground, sprayed, and sintered.

[0075] Both batches of ingredients are mixed according to the first wet method with a solid content of 45% and deionized water as the solvent, and the particle size D50 of the slurry after grinding is controlled to be 0.4 μm. The ground slurry is spray dried with an inlet temperature of 220 ℃ and an outlet temperature of 100 ℃. Then, the sintering is carried out under a nitrogen atmosphere with a sintering parameter of 690 ℃ for 6 h to obtain intermediate products B and C.

[0076] Intermediate products B and C are weighed in a ratio of 5:5, and the carbon content of the finished product, manganese iron phosphate lithium, is controlled to be 1.50%. Two batches of raw materials are weighed: ① intermediate product B 500 g, glucose 25.00 g, polyethylene glycol 27.50 g, and ② intermediate product C 500 g, glucose 19.00 g, and polyethylene glycol 20.90 g. Both batches of raw materials are ground according to the second wet method with a solid content of 42% and deionized water as the solvent. The mixed slurry is ground to a particle size of D50: 0.5 μm for slurry B and D50: 0.2 μm for slurry C.

[0077] The ground slurry B and C are mixed uniformly in a ball mill, and the mixed slurry is spray dried with an inlet temperature of 220 ℃ and an outlet temperature of 100 ℃. Then, the sintering is carried out under a nitrogen atmosphere with a sintering parameter of 740 ℃ for 10 h. The sintered material is air-jet pulverized with a particle size D10≥0.30 μm, D50: 0.5-1.1 μm, and D90≤12 μm to obtain high-compaction manganese iron phosphate lithium cathode material D, which is then tested.

[0078] Example 3

[0079] This example prepares a manganese iron phosphate lithium material, which specifically includes the following steps:

[0080] After the initial raw materials are mixed uniformly, a coprecipitation reaction is carried out, and after washing and drying, the first sintering is carried out, and the precursor A is obtained by breaking.

[0081] According to the mixture of precursor A and lithium phosphate Li / (Fe+Mn): 1.03, (Fe+Mn) / P: 0.98, the additive content of (Fe+Mn) in the precursor A is 0.60% mol, and the carbon content of the corresponding intermediate product B is 0.10%. The precursor 1000 g, lithium phosphate 315.89 g, glucose 11.87 g, polyethylene glycol 11.87 g, citric acid 11.87 g, magnesium acetate tetrahydrate 22.31 g, and ammonium metavanadate 11.87 g are weighed. For the intermediate product C, the carbon content is 0.50% and the additive content is 0.30% mol. The glucose 29.67 g, magnesium acetate tetrahydrate 11.16 g, and ammonium metavanadate 5.93 g are weighed, and the other raw materials are the same. The two intermediate products B and C are respectively mixed, ground, sprayed, and sintered.

[0082] Both batches of ingredients were wet-mixed for the first time with a solid content of 45% and deionized water as the solvent. The particle size D50 of the slurry after grinding was controlled to be 0.4 μm. The ground slurry was then spray-dried with the inlet air temperature controlled at 220°C and the outlet air temperature controlled at 100°C. Then, it was sintered under a nitrogen atmosphere with sintering parameters of 700°C for 6 hours to obtain intermediate products B and C.

[0083] Weigh intermediate products B and C in a ratio of 4:6, and control the carbon content of the finished lithium manganese iron phosphate to be 1.50%. Weigh two batches of raw materials: ① 400g of intermediate product B, 20.00g of glucose, and 22.00g of polyethylene glycol; ② 600g of intermediate product C, 22.80g of glucose, and 25.08g of polyethylene glycol. Both batches of raw materials are subjected to a second wet grinding with deionized water as the solvent, with a solid content of 42%. The mixed slurries are ground to the following particle sizes: D50 of 0.6um for slurry B and 0.3um for slurry C.

[0084] The ground slurries B and C were ball-milled and mixed evenly. The mixed slurry was then spray-dried, with the inlet air temperature controlled at 220℃ and the outlet air temperature at 100℃. Then, it was sintered under a nitrogen atmosphere with sintering parameters of 750℃ for 10 hours. The sintered material was then subjected to air jet milling, with the particle size controlled at D10≥0.30um, D50:0.5-1.1um, and D90≤12um, to obtain high-pressure compacted lithium manganese iron phosphate cathode material D, and relevant tests were performed.

[0085] Figure 3 The image shows a SEM image of the lithium manganese iron phosphate material prepared in Example 3. Figure 3 As can be seen, the primary particles are distributed with significantly different particle sizes, and the primary particles are tightly connected.

[0086] Example 4

[0087] This embodiment prepares a lithium iron manganese phosphate material, specifically including the following steps:

[0088] After the initial raw materials are mixed evenly, a co-precipitation reaction is carried out. After washing and drying, the first sintering is carried out and the precursor A is crushed.

[0089] The precursor A and lithium phosphate mixture material Li / (Fe+Mn): 1.03, (Fe+Mn) / : 0.98, the additive content of 0.60% mol relative to the (Fe+Mn) content in the precursor A, the carbon content of 0.10% in the intermediate product B generated, 1000g of the precursor, 315.89g of lithium phosphate, 11.87g of glucose, 11.87g of polyethylene glycol, 11.87g of citric acid, 22.31g of magnesium acetate tetrahydrate, and 11.87g of ammonium metavanadate; the carbon content of 0.50% in the intermediate product C generated, the additive content of 0.30% mol, 29.67g of glucose, 11.16g of magnesium acetate tetrahydrate, 5.93g of ammonium metavanadate, and the same types and weights of other raw materials; the two intermediate products B and C are respectively prepared, ground, sprayed, and sintered.

[0090] The two batches of materials are mixed according to the first wet method with a solid content of 45% and deionized water as the solvent, and the particle size D50 of the slurry after grinding is controlled to be 0.4um. The ground slurry is spray dried, and the inlet air temperature is controlled to be 220℃ and the outlet air temperature is controlled to be 100℃. Then, the sintering is carried out under nitrogen atmosphere, and the sintering parameters are 700℃ and 6h, to obtain the intermediate products B and C.

[0091] The intermediate products B and C are weighed according to the proportion of 2:8, and the carbon content of the finished product is controlled to be 1.50%. Two batches of raw materials are respectively weighed: ① intermediate product B 200g, glucose 10.00g, polyethylene glycol 11.00g, ② intermediate product C 800g, glucose 30.40g, polyethylene glycol 33.44g; the two batches of raw materials are respectively ground according to the second wet method with a solid content of 42% and deionized water as the solvent, and the mixed slurry is respectively ground to a particle size of: slurry B D50 is 0.7um, and slurry C D50 is 0.3um.

[0092] The ground slurry B and C are mixed uniformly by ball milling, and the mixed slurry is spray dried, and the inlet air temperature is controlled to be 220℃ and the outlet air temperature is controlled to be 100℃. Then, the sintering is carried out under nitrogen atmosphere, and the sintering parameters are 750℃ and 10h, to obtain the high-density lithium manganese iron phosphate positive electrode material D, and the related tests are carried out.

[0093] Comparative Example 1

[0094] The present comparative example prepares a lithium manganese iron phosphate material, which specifically includes the following steps:

[0095] After the initial raw materials are mixed uniformly, a coprecipitation reaction is carried out, and after washing and drying, a first sintering is carried out, and the precursor A is obtained by crushing.

[0096] The weighed raw materials are mixed in a first wet method with a solid content of 45% and deionized water as a solvent, the particle size D50 of the slurry after grinding is controlled to be 0.4 um, the ground slurry is spray dried, the inlet air temperature is controlled to be 220 DEG C, the outlet air temperature is controlled to be 100 DEG C, and then sintered under a nitrogen atmosphere, the sintering parameters are 680 DEG C, 6h, to obtain an intermediate product.

[0097] The weighed raw materials are mixed in a first wet method with a solid content of 45% and deionized water as a solvent, the particle size D50 of the slurry after grinding is controlled to be 0.4 um, the ground slurry is spray dried, the inlet air temperature is controlled to be 220 DEG C, the outlet air temperature is controlled to be 100 DEG C; then sintered under a nitrogen atmosphere, the sintering parameters are 680 DEG C, 6h, to obtain an intermediate product.

[0098] The carbon content of the finished product is controlled to be 1.50%, the intermediate product 1000g, glucose 50.00g, polyethylene glycol 55.00g, the second wet grinding is carried out with a solid content of 42% and deionized water as a solvent, and the mixed slurry is ground to a particle size D50 of 0.5um.

[0099] The ground slurry is spray dried, the inlet air temperature is controlled to be 220 DEG C, the outlet air temperature is controlled to be 100 DEG C; then sintered under a nitrogen atmosphere, the sintering parameters are 740 DEG C, 10h, the sintered material is air-pulverized, the particle size D10 is controlled to be greater than or equal to 0.30um, D50 is controlled to be 0.5-1.1um, and D90 is controlled to be less than or equal to 12um, to obtain a high-density lithium manganese iron phosphate positive electrode material D, and related tests are carried out.

[0100] Figure 4 The SEM diagram of the lithium manganese iron phosphate material prepared for the comparative example 1 can be seen from Figure 4 It can be seen that the particle size of the primary particles is small, the particle state is poor, part of the particles are lumped together, and the material morphology is poor.

[0101] Comparative example 2

[0102] The present comparative example prepares a lithium manganese iron phosphate material, which specifically comprises the following steps:

[0103] After the initial raw materials are mixed uniformly, a co-precipitation reaction is carried out, washed and dried, and then a first sintering is carried out, and the precursor A is obtained by crushing.

[0104] The raw materials were weighed according to the mixture of precursor A and lithium phosphate, Li / (Fe+Mn): 1.03, (Fe+Mn) / P: 0.98, 0.30% mol of the additive relative to the content of (Fe+Mn) in precursor A, and the corresponding intermediate product carbon content was 0.50%. 1000g of precursor, 315.89g of lithium phosphate, 29.67g of glucose, 11.87g of polyethylene glycol, 11.87g of citric acid, 11.16g of magnesium acetate tetrahydrate, and 5.93g of ammonium metavanadate were weighed.

[0105] The weighed raw materials were mixed by a first wet method with a solid content of 45% and deionized water as a solvent, and the particle size D50 of the slurry after grinding was controlled to be 0.4um. The ground slurry was spray dried with an inlet temperature of 220°C and an outlet temperature of 100°C. Then, the sintering was carried out under a nitrogen atmosphere with a sintering parameter of 680°C for 6h to obtain an intermediate product.

[0106] The carbon content of the finished product was controlled to be 1.50%. 1000g of the intermediate product, 38.00g of glucose, and 41.80g of polyethylene glycol were weighed. Both batches of raw materials were ground by a second wet method with a solid content of 42% and deionized water as a solvent. The mixed slurry was ground to a particle size D50 of 0.2um.

[0107] The ground slurry was spray dried with an inlet temperature of 220°C and an outlet temperature of 100°C. Then, the sintering was carried out under a nitrogen atmosphere with a sintering parameter of 740°C for 10h. The sintered material was subjected to jet milling with a particle size D10≥0.30um, D50: 0.5-1.1um, and D90≤12um to obtain a high-density lithium manganese iron phosphate cathode material D, which was subjected to related tests.

[0108] Figure 5 The SEM image of the lithium manganese iron phosphate material prepared for Comparative Example 2 can be seen from Figure 5 which shows that the primary particle size is large, there are many gaps between the particles, the particles are not tightly combined, and the material morphology is poor.

[0109] The carbon content, specific surface area, powder compaction density, 0.1C and 1C discharge specific capacity of the products obtained in Examples 1-4 and Comparative Examples 1-2 were further tested, and the results are shown in Table 1.

[0110] Test method: The related physical and chemical properties and electrochemical properties were tested according to the national standard "Carbon composite lithium iron phosphate cathode material for lithium ion batteries" GB / T 30835-2014. The coin cell was prepared (the mass ratio of active material, conductive agent and binder was 90:5:5, and the charge and discharge voltage range was 2.0-4.5V).

[0111] Table 1 Performance test results of lithium manganese iron phosphate material

[0112]

[0113] According to the above results, it can be seen that, in the case of the same carbon content of the material, the compaction density and electrical properties of the lithium manganese iron phosphate composite material powder prepared by mixing the primary particles of different particle sizes prepared by adding different amounts of carbon sources and dopants in different mass ratios and then sintering again are obviously higher than those of the lithium manganese iron phosphate material prepared by adding a single carbon source and dopant.

[0114] The preparation method of the lithium manganese iron phosphate material provided in the embodiments of the present application uses different carbon source addition ratios and dopant addition ratios in the sintering process of the carbon-coated lithium manganese iron phosphate intermediate to form carbon-coated lithium manganese iron phosphate intermediates with different morphologies, and then the carbon-coated lithium manganese iron phosphate intermediates with different morphologies are mixed and sintered again to produce grading of the carbon-coated lithium manganese iron phosphate intermediates with different morphologies, further form a dense and uniform carbon-coated layer, and make the carbon-coated lithium manganese iron phosphate intermediates with different morphologies compact, so as to achieve high compaction density and obtain excellent electrochemical performance. The lithium ion battery further prepared by using the lithium manganese iron phosphate material as a positive electrode material can also have excellent performance. Meanwhile, the preparation method has a simple process flow, low equipment requirement, and is suitable for large-scale industrial production.

[0115] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples without contradiction.

[0116] Although the embodiments of the present application have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the claims and their equivalents.

Claims

1. A method for preparing a lithium iron manganese phosphate material, characterized in that, The preparation method comprises: S10, according to a certain proportion, the iron source, manganese source, phosphoric acid and deionized water are mixed and dissolved, and a liquid phase co-precipitation method is used to prepare a ferromanganous phosphate precursor, the ferromanganous phosphate precursor is subjected to first sintering, and crystal water is removed, so as to obtain an anhydrous ferromanganous phosphate precursor; S20, according to a certain proportion, two groups of anhydrous ferromanganous phosphate precursors, a lithium source, a supplementary phosphorus source, an organic carbon source, a dopant and deionized water are mixed, stirring and dispersion, first wet grinding, spray drying, second sintering are carried out, and two groups of manganese iron lithium phosphate intermediates are obtained; wherein the addition proportion of the organic carbon source of the first group is lower than that of the second group, and the addition proportion of the dopant of the first group is greater than that of the second group; S30, according to a certain proportion, the two groups of manganese iron lithium phosphate intermediates and supplementary organic carbon source, deionized water are mixed, stirring and dispersion, second wet grinding, spray drying, third sintering and crushing are carried out, and the manganese iron lithium phosphate material is obtained; The addition proportion of the organic carbon source of the first group satisfies that the carbon content of the manganese iron lithium phosphate intermediate is 0.05wt%-0.15wt%, and the addition proportion of the dopant of the first group satisfies that the doping metal accounts for 0.5%-1.0% of the iron and manganese content in the anhydrous ferromanganous iron precursor; the addition proportion of the organic carbon source of the second group satisfies that the carbon content of the manganese iron lithium phosphate intermediate is 0.45wt%-0.55wt%, and the addition proportion of the dopant of the second group satisfies that the doping metal accounts for 0-0.5% of the iron and manganese content in the anhydrous ferromanganous iron precursor.

2. The method of claim 1, wherein the lithium iron manganese phosphate material is prepared by the steps of: The step S30 specifically comprises: according to a certain proportion, the two groups of manganese iron lithium phosphate intermediates are respectively mixed with an organic carbon source and deionized water, stirring and dispersion are carried out, second wet grinding is carried out respectively at a first particle size and a second particle size, and then mixing, spray drying, third sintering and crushing are carried out, so as to obtain the manganese iron lithium phosphate material. ​ 3. The method of claim 2, wherein the lithium iron manganese phosphate material is prepared by the steps of: mixing a lithium source, a manganese source, an iron source, and a phosphate source; and heating the mixture to a temperature of 600 to 800 °C for 1 to 10 hours. The first particle size is 0.5µm-0.7µm, and the second particle size is 0.2µm-0.4µm.

4. The method of claim 1, wherein the lithium iron manganese phosphate material is prepared by the steps of: mixing a lithium source, a manganese source, and an iron source; and heating the mixture to a temperature of 600 to 800 °C for 1 to 10 hours. The addition amount of the supplementary organic carbon source is controlled according to the carbon content of the manganese iron lithium phosphate intermediate to satisfy that the target preparation manganese iron lithium phosphate material mass ratio is 1.3wt%-1.7wt%.

5. The method of claim 1, wherein the lithium iron manganese phosphate material is prepared by the steps of: mixing a lithium source, a manganese source, an iron source, and a phosphate source; and heating the mixture to a temperature of 600 to 800 °C for 1 to 10 hours. The mixing proportion of the two groups of manganese iron lithium phosphate intermediates is 6:4-2:

8.

6. The method of claim 1, wherein the lithium iron manganese phosphate material is prepared by the steps of: mixing a lithium source, a manganese source, and an iron source; and heating the mixture to a temperature of 600 to 800 °C for 1 to 10 hours. The addition amount of the anhydrous ferromanganous iron precursor, the lithium source and the supplementary phosphorus source satisfies that the lithium and iron manganese molar ratio Li / (Fe+Mn) is 1.01-1.07, and the iron manganese and phosphorus molar ratio (Fe+Mn) / P is 0.96-0.99; and / or, The organic carbon source comprises at least one of glucose, sucrose, polyethylene glycol and citric acid; and / or The dopant comprises a compound of at least one of Ti, V, Nb and Mg.

7. The method of claim 1, wherein the lithium iron manganese phosphate material is prepared by the steps of: mixing a lithium source, a manganese source, and an iron source; and heating the mixture to a temperature of 600 to 800 °C for 1 to 10 hours. The first sintering is carried out in an air atmosphere, the sintering temperature is 500℃-650℃, and the sintering time is 4h-7h; and / or, The first wet grinding controls the particle size to be 0.3µm-0.5µm; and / or, The spray drying inlet temperature is 220℃, and the outlet temperature is 100℃; and / or, the second sintering is in a nitrogen atmosphere, the sintering temperature is 600-750℃, and the sintering time is 4-8h; and / or, the third sintering is in a nitrogen atmosphere, the sintering temperature is 730-780℃, and the sintering time is 8-10h; and / or, the particle size of the pulverization is controlled to D10≥0.3µm, D50 is 0.5-1.1µm, and D90≤12µm.

8. A lithium iron manganese phosphate material, characterized in that, The lithium iron manganese phosphate material is prepared by the preparation method in any one of claims 1-7.

9. A lithium-ion battery, characterized by The lithium ion battery comprises a battery positive electrode prepared from the lithium iron manganese phosphate material in claim 8.

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