Manganese iron precursor, manganese iron lithium phosphate positive electrode material and preparation method thereof and lithium ion battery

Abstract

The present application relates to manganese iron lithium phosphate positive material preparation technical field, provide a kind of manganese iron precursor, manganese iron lithium phosphate positive material and its preparation method and lithium ion battery.The preparation method of manganese iron precursor is as follows: inert gas is introduced into reaction vessel, and acidic ferrous ion complex base solution is added, then divalent manganese salt solution, doped metal salt solution is added, and fully stirred to mix uniformly;Subsequently, alkaline precipitant solution is added, and pH is adjusted to make metal ion precipitate;Reaction vessel is heated to set temperature while stirring, and heat preservation aging crystallization is carried out, precipitate is filtered, washed, dried, and manganese iron hydroxide is obtained;Manganese iron hydroxide is low-temperature calcined and dehydrated to obtain the present application.The manganese iron precursor provided by the present application can realize the uniform distribution of manganese and iron at atomic level, and the manganese iron lithium phosphate positive material prepared thereby has better electrochemical comprehensive performance;The preparation method of the present application is more close to the production process of iron phosphate and lithium iron phosphate, and the equipment modification cost is lower.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of lithium ion battery positive electrode materials, specifically to lithium iron manganese phosphate positive electrode materials and their preparation, and more particularly to a manganese iron precursor, a lithium iron manganese phosphate positive electrode material and its preparation method and a lithium ion battery. Background Art

[0002] In recent years, with increasing public awareness of lithium-ion battery safety and advancements in battery technology, lithium iron phosphate (LFP), as a lithium-ion battery cathode material, has seen its market share gradually increase, surpassing ternary cathode materials to become the mainstream cathode material. Compared to ternary materials, LFP cathode materials offer long cycle life and excellent safety performance. However, their lower discharge capacity, powder compaction density, and discharge voltage result in lower energy density. While current battery technologies, particularly BYD's Blade Battery technology, have significantly improved the energy density of LFP batteries, users' growing concerns about battery life necessitate further improvements in energy density. The inclusion of manganese in LFP significantly increases the battery's energy density, while maintaining the safety performance of LFP. This allows LFP to achieve a platform voltage of 4.1V and a medium voltage of 3.9V, significantly improving the battery's energy density and making it a highly promising alternative to LFP cathode materials.

[0003] Currently, the method for large-scale industrial production of lithium iron phosphate on the market is the solid-phase method. Its main raw materials are iron phosphate and lithium carbonate. Through wet grinding, spray drying, and solid-phase sintering, this process is simple, relatively low-cost, and the product has a high compaction density and good uniformity. Although lithium manganese iron phosphate has been commercialized, its production process route is uncertain. Some use soluble salts for hydrothermal production, but the equipment is expensive and the high-pressure production conditions are prone to safety issues. There are also solid-phase production methods using a mixture of manganese oxide and iron phosphate. Although the process is simple, the product uniformity and purity are poor.

[0004] To achieve large-scale and cost-effective industrial production of lithium iron phosphate (LFP), it is necessary to closely adhere to existing LFP production processes, minimizing the R&D investment in new equipment and the cost of modifying existing production lines. Therefore, breakthroughs can be made in two areas: first, preparing a manganese iron precursor similar to iron phosphate. The manganese and iron elements in this precursor must be evenly distributed at the atomic level to ensure the production of high-performance LFP. At the same time, this must be done as closely as possible to existing iron phosphate production processes to control equipment investment costs. Second, the LFP production process using this precursor must be similar to the existing LFP production process.

[0005] Existing Chinese patent document CN 114644328 B proposes a method for preparing a manganese iron oxide precursor by a solid phase method. Since this method uses high-temperature solid-phase mixing, it is difficult to ensure the uniform distribution of manganese and iron elements at the atomic level, and additional equipment is required. Chinese patent document CN 117923453 A proposes a method for preparing a manganese iron oxide precursor by using a manganese iron aerosol at high temperature. This method also requires additional equipment for precursor preparation. Chinese patent document CN 118005082A proposes a method for preparing a manganese iron oxide precursor by oxidizing divalent iron and a manganese source and then precipitating it. This method uses sodium hydroxide for precipitation. After the actual divalent iron is oxidized to trivalent iron, the solubility product will drop sharply by several orders of magnitude, and it will not be able to precipitate evenly with the manganese source.

[0006] Therefore, it is urgent to propose a method for preparing manganese iron precursors and manganese iron phosphate lithium positive electrode materials that can ensure uniform distribution of manganese iron elements and can be applied to existing industrial iron phosphate and lithium iron phosphate production lines, greatly reducing the cost of new equipment or equipment modification. Summary of the Invention

[0007] The technical problem addressed by the present invention is to provide a manganese iron precursor, a lithium iron manganese phosphate cathode material, a preparation method thereof, and a lithium-ion battery. The present invention first produces a manganese iron hydroxide with a uniform distribution of manganese and iron at the atomic level, then further calcines and dehydrates it at low temperature to produce a manganese iron oxide precursor with a similarly uniform distribution of manganese and iron elements. The lithium iron manganese phosphate cathode material prepared from this raw material exhibits improved overall electrochemical performance.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing a ferromanganese precursor, which specifically comprises the following steps:

[0010] (1) introducing an inert gas into a reaction vessel, adding an acidic ferrous ion complex base liquid, and adjusting the pH of the acidic ferrous ion complex base liquid; then adding a divalent manganese salt solution and a doping metal salt solution, stirring them thoroughly, and mixing them evenly; then adding an alkaline precipitant solution, adjusting the pH, and precipitating the metal ions; then heating the reaction vessel to a set temperature while stirring, performing heat preservation, aging, and crystallization, filtering the precipitate, washing, and drying to obtain ferromanganese hydroxide;

[0011] (2) The ferromanganese hydroxide precursor is subjected to low-temperature calcination and dehydration to obtain ferromanganese oxide, that is, the ferromanganese precursor.

[0012] Furthermore, the acidic ferrous ion complex base liquid in step (1) is prepared from a ferrous salt solution, a complexing agent solution, and an acidic solution, and the specific process is as follows: first, the acidic solution is added to a reaction container into which an inert gas is introduced, then the ferrous salt solution is added, and then the complexing agent solution is added and stirred thoroughly, and then the pH of the mixed solution is adjusted to obtain the acidic ferrous ion complex base liquid.

[0013] Since the divalent iron in the ferrous salt aqueous solution is easily oxidized, inert gas is first introduced and acidic solution is added during the preparation of the acidic ferrous ion complex base liquid to keep the solution in the reaction container weakly acidic, which can protect the divalent iron from being immediately oxidized to trivalent iron.

[0014] Furthermore, the ferrous salt solution is prepared by dissolving a ferrous salt in deionized water. The ferrous salt includes at least one of ferrous sulfate and its hydrate, ferrous nitrate and its hydrate, and ferrous chloride and its hydrate, preferably ferrous sulfate and its hydrate.

[0015] Furthermore, the complexing agent solution is prepared by dissolving a complexing agent in deionized water. The complexing agent includes at least one of disodium ethylenediaminetetraacetic acid, diethylaminepentaacetic acid, tartaric acid, sodium gluconate, and ethylenediamine, preferably disodium ethylenediaminetetraacetic acid.

[0016] Furthermore, the acidic solution is an aqueous solution of an organic acid and / or an inorganic acid. The inorganic acid includes at least one of dilute sulfuric acid, dilute hydrochloric acid, and dilute nitric acid; and the organic acid includes at least one of citric acid, ethylenediaminetetraacetic acid, and acetic acid. Preferably, the solution is an aqueous solution of citric acid.

[0017] Furthermore, the divalent manganese salt solution in step (1) is prepared by dissolving a divalent manganese salt in deionized water. The divalent manganese salt includes at least one of manganese sulfate, manganese nitrate, and manganese chloride, preferably manganese sulfate.

[0018] Furthermore, the doped metal salt solution in step (1) is an aqueous solution containing a soluble salt of the doped metal element.

[0019] Furthermore, the doping metal element contained in the doping metal salt is at least one of titanium, magnesium, vanadium, niobium, aluminum, cobalt, molybdenum, nickel, zirconium, lanthanum, and tungsten.

[0020] Furthermore, the alkaline precipitant in step (1) is at least one of a combined solution of sodium hydroxide and sodium carbonate, a combined solution of sodium hydroxide and sodium bicarbonate, and aqueous ammonia.

[0021] Furthermore, in step (1), the molar ratio of manganese, iron and doping element in the reaction solution is controlled to be x:1-xy:y, wherein 0.5≤x<1, 0.01≤y≤0.03.

[0022] Further, x:1-x in step (1) includes but is not limited to 0.5:0.5, 0.6:0.4, 0.7:0.3, 0.8:0.2, 0.9:0.1.

[0023] Further, the inert gas in step (1) includes but is not limited to nitrogen, argon.

[0024] Further, the pH of the acidic ferrous ion complex-based solution in step (1) is controlled at 3-5.

[0025] Preferably, the amount of the complexing agent added in the acidic ferrous ion complex-based solution accounts for 1%-10% of the total amount of manganese and iron substances.

[0026] Further, the pH of the addition of the basic precipitant to precipitate metal ions in step (1) is controlled at 7.8-9.7.

[0027] Further, the aging temperature of the heating reactor in step (1) is 60-85℃, and the aging time is 4-24h.

[0028] Further, the conditions of the low-temperature calcination in step (2) are as follows: the calcination temperature is 400℃-650℃, and the time is 4-16h.

[0029] Further, the calcination atmosphere in step (2) is at least one of air and nitrogen.

[0030] In the second aspect, the present application provides a manganese-iron precursor prepared by the above preparation method.

[0031] Further, the manganese-iron precursor is a manganese-iron oxide doped with a metal element, and the molar ratio of manganese, iron and the doping element is x:1-x-y:y, wherein 0.5≤x<1 and 0.01≤y≤0.03.

[0032] Further, x:1-x includes but is not limited to 0.5:0.5, 0.6:0.4, 0.7:0.3, 0.8:0.2, 0.9:0.1.

[0033] Further, the doping metal element is at least one of titanium, magnesium, vanadium, niobium, aluminum, cobalt, molybdenum, nickel, zirconium, lanthanum and tungsten.

[0034] In the third aspect, the present application further provides a method for preparing a lithium manganese iron phosphate positive electrode material by using the above manganese-iron precursor, which comprises the following steps:

[0035] (1) the manganese iron precursor is mixed with a lithium source, a phosphorus source and a first carbon source, wherein the lithium source, the manganese iron precursor and the phosphorus source are weighed according to the molar ratio of Li:(Mn+Fe):P (1.0-1.1):1:(0.95-1.0), the first carbon source is weighed according to the mass ratio of (0.2-0.5):1 with the manganese iron precursor, after spray granulation, a first manganese iron lithium phosphate positive electrode material is obtained by low-temperature pre-sintering in a nitrogen atmosphere;

[0036] (2) the first manganese iron lithium phosphate positive electrode material is mixed with a second carbon source by secondary grinding, wherein the second carbon source is weighed according to the mass ratio of (0.1-0.4):1 with the first manganese iron lithium phosphate positive electrode material, after spray granulation, a second manganese iron lithium phosphate positive electrode material is obtained by high-temperature sintering in a nitrogen atmosphere and crushing.

[0037] Further, in step (1), the low-temperature pre-sintering temperature is 350-650 DEG C, and the sintering time is 4-16 h.

[0038] Further, in step (2), the high-temperature sintering temperature is 680-800 DEG C, and the sintering time is 6-16 h.

[0039] Further, in step (1), the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate and lithium phosphate.

[0040] Further, in step (1), the phosphorus source is at least one of lithium dihydrogen phosphate, lithium phosphate, diammonium hydrogen phosphate, phosphoric acid and ammonium dihydrogen phosphate.

[0041] Further, in step (1), the first carbon source is at least one of glucose, sucrose and starch.

[0042] Further, in step (2), the second carbon source is at least one of polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, citric acid and beta-cyclodextrin.

[0043] In a fourth aspect, the application further provides a manganese iron lithium phosphate positive electrode material prepared by the above method.

[0044] In a fifth aspect, the application further provides a lithium ion battery positive electrode sheet comprising the above manganese iron lithium phosphate positive electrode material.

[0045] In a sixth aspect, the application further provides a lithium ion battery comprising a positive electrode sheet, wherein the positive electrode sheet comprises the above manganese iron lithium phosphate positive electrode material.

[0046] The application has the following beneficial effects:

[0047] 1. The manganese iron precursor provided by the application can realize uniform distribution of manganese and iron at the atomic level, and the manganese iron lithium phosphate positive electrode material prepared from the raw material has better electrochemical comprehensive performance.

[0048] Specifically, the preparation method provided by the present invention comprises the following steps: first, adding a divalent manganese salt solution and a doping metal salt solution to a reaction vessel into which an inert gas is introduced and which is filled with an acidic iron salt-based liquid containing ferrous ions and a complexing agent thereof, and stirring and mixing the mixture thoroughly; then, adding an alkaline precipitant solution and adjusting the pH to precipitate the metal ions; then, heating the reaction vessel to a set temperature while stirring, performing heat preservation, aging, and crystallization, filtering the precipitate, washing, and drying to obtain ferromanganese hydroxide, wherein the ferromanganese elements are uniformly distributed in the obtained ferromanganese hydroxide.

[0049] This is due to the fact that Mn 2+ and Fe 2+ The solubility product constant of the hydroxide is closer, and the divalent ferrous ion (Fe 2+ ) and the complex formed by the complexing agent, is not easily oxidized in an acidic environment with an inert gas (this is because Fe 3+ The hydroxide solubility product of Mn 2+ The large difference in the solubility product of hydroxides will lead to the preferential precipitation of Fe(OH)3, affecting the uniform distribution of iron and manganese elements), and the complex of divalent ferrous ions can slowly release Fe 2+ , which makes it possible for manganese and iron to simultaneously generate hydroxide precipitation with uniformly distributed elements; the alkaline precipitant is a combined solution of sodium hydroxide and sodium carbonate, a combined solution of sodium hydroxide and sodium bicarbonate, and ammonia water. Due to the hydrolysis of carbonate or the ionization reaction of ammonia water, the manganese-iron hydroxide precipitation reaction is milder, which is conducive to the uniform distribution of manganese and iron elements.

[0050] Thereafter, the obtained ferromanganese hydroxide is calcined and dehydrated at low temperature to obtain ferromanganese oxide, namely the ferromanganese precursor provided by the present invention, which also has the same uniform distribution of manganese and iron elements as the ferromanganese hydroxide precursor.

[0051] 2. The ferromanganese precursor and lithium iron manganese phosphate preparation of the present invention are closer to the industrialized ferrophosphate and lithium iron phosphate production processes, and the equipment modification cost of the existing production line is lower, which has significant economic benefits. For example, the precipitation reaction of the present invention corresponds to the precipitation reaction of ferrophosphate; the aging reaction of the present invention corresponds to the aging process in the two-step ferrophosphate process; the dehydration reaction of the ferromanganese oxide preparation of the present invention corresponds to the dehydration process of dihydrate ferrophosphate by flash evaporation or rotary kiln; and the use of this precursor to prepare lithium iron manganese phosphate is completely consistent with the process of wet grinding, spray drying, and sintering of ferrophosphate and lithium carbonate, thus saving more production line modification costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 A schematic flow chart of a method for preparing a manganese iron oxide precursor provided in an embodiment of the present invention.

[0053] Figure 2 A schematic flow chart of a method for preparing lithium manganese iron phosphate provided in an embodiment of the present invention.

[0054] Figure 3 This is an SEM image of the ferromanganese oxide (i.e., ferromanganese precursor) obtained in Example 1.

[0055] Figure 4 This is the EDS surface scan of the main elements of the manganese iron oxide obtained in Example 1.

[0056] Figure 5 This is the SEM image of the lithium manganese iron phosphate prepared in Example 1. DETAILED DESCRIPTION

[0057] As used herein:

[0058] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0059] The conjunction "consisting of" excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed, excluding materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim, rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0060] When a parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values ​​and lower preferred values, this should be understood to specifically disclose all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed alone. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including the range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described in this article, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0061] In these examples, parts and percentages are by mass unless otherwise indicated.

[0062] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the accompanying drawings. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present disclosure.

[0063] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. Where specific conditions are not specified in the examples, the methods are carried out according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, they are conventional products that can be purchased commercially.

[0064] In order to better illustrate the technical solution of the present invention, the following embodiments are used as preferred examples for illustration, but the protection scope of the present invention is not limited to the following embodiments.

[0065] Example 1

[0066] This embodiment provides a method for preparing manganese iron hydroxide, comprising the following steps: dissolving a small amount of citric acid in deionized water to prepare an acidic solution with a concentration of 0.2 g / L, then placing the solution in a reaction vessel and introducing an inert nitrogen atmosphere. MnSO₄, FeSO₄·7H₂O, and MgSO₄ are weighed at a molar ratio of Mn:Fe:Mg = 0.6:0.38:0.02. The weighed FeSO4·7H2O is put into a reactor, and then the corresponding amount of chelating agent disodium ethylenediaminetetraacetate is weighed according to 4% of the total amount of manganese and iron elements to prepare a chelating agent solution, which is then put into the reactor and fully stirred. A citric acid solution with a concentration of 1 g / L is then added to adjust the pH of the mixed solution to 3.5 to form an acidic ferrous ion complex base liquid; then the weighed MnSO4 and MgSO4 are respectively dissolved in deionized water to form corresponding solutions, which are added to the above base liquid and fully stirred; sodium hydroxide and sodium carbonate are dissolved in deionized water in a mass ratio of 7:3 to prepare an alkaline precipitant solution, which is then slowly added dropwise until the pH of the solution is adjusted to 8.5, and the solution is kept warm at 70°C for 10 hours, filtered, washed, and dried to obtain manganese iron hydroxide.

[0067] This embodiment also provides a method for preparing ferromanganese oxide, specifically, calcining the prepared ferromanganese hydroxide at 500° C. for 6 h under a nitrogen flow for dehydration, and cooling to obtain ferromanganese oxide, i.e., ferromanganese precursor.

[0068] This embodiment also provides a method for preparing a lithium iron manganese phosphate positive electrode material, comprising the following steps: weighing lithium carbonate, a manganese iron precursor, and phosphoric acid at a molar ratio of Li / (Mn+Fe):P=1.038:1:0.96, weighing a first carbon source at a mass ratio of glucose to manganese iron oxide of 0.2:1, performing nano-sand milling and spraying, and pre-calcining the sprayed material at 500°C for 6 hours to obtain a first lithium iron manganese phosphate positive electrode material. Weighing a second carbon source at a mass ratio of polyethylene glycol to the first lithium iron manganese phosphate positive electrode material of 0.15:1, sand milling and spraying the second carbon source with the first lithium iron manganese phosphate positive electrode material, and sintering the sprayed material at 765°C for 10 hours to obtain a final lithium iron manganese phosphate product.

[0069] Example 2

[0070] This embodiment provides a method for preparing manganese iron hydroxide, comprising the following steps: mixing a small amount of nitric acid with deionized water to form an acidic solution with a mass concentration of 0.1%, then placing the solution in a reaction vessel and introducing an inert nitrogen atmosphere. Mn(NO₃)₂, Fe(NO₃)₂·9H₂O, and ammonium metavanadate are weighed in a molar ratio of Mn:Fe:V = 0.7:0.28:0.02. The weighed Fe(NO3)2·9H2O is put into a reactor, and then the corresponding amount of chelating agent disodium ethylenediaminetetraacetate is weighed according to 4% of the total amount of manganese and iron elements to prepare a chelating agent solution, which is then put into the reactor and fully stirred. A dilute nitric acid solution with a mass concentration of 5% is then added to adjust the pH to 4.1 to form an acidic ferrous ion complex base liquid; then the weighed Mn(NO3)2 and ammonium metavanadate are respectively dissolved in deionized water to form corresponding solutions, which are added to the above base liquid and fully stirred; an alkaline precipitant ammonia water is dropped until the solution pH is adjusted to 9.2, and the solution is kept warm and aged at 65°C for 12 hours, filtered, washed, and dried to obtain manganese iron hydroxide.

[0071] This embodiment also provides a method for preparing ferromanganese oxide, specifically, calcining the prepared ferromanganese hydroxide at 500° C. for 6 hours under a nitrogen flow for dehydration, and then cooling to obtain ferromanganese oxide, i.e., ferromanganese precursor.

[0072] This embodiment also provides a method for preparing a lithium iron manganese phosphate positive electrode material, comprising the following steps: weighing lithium carbonate, a manganese iron precursor, and lithium dihydrogen phosphate at a molar ratio of Li / (Mn+Fe):P=1.04:1:0.965, weighing a first carbon source at a mass ratio of sucrose to manganese iron oxide of 0.1:1, performing nano-sand milling and spraying, and pre-sintering the sprayed material at 500°C for 6 hours to obtain a first lithium iron manganese phosphate positive electrode material. A second carbon source at a mass ratio of polyvinyl alcohol to the first lithium iron manganese phosphate positive electrode material of 0.2:1 is weighed, and the second carbon source is sand milled and sprayed with the first lithium iron manganese phosphate positive electrode material, and the sprayed material is sintered at 755°C for 10 hours to obtain a final lithium iron manganese phosphate product.

[0073] Example 3

[0074] This embodiment provides a method for preparing manganese iron hydroxide, comprising the following steps: dissolving a small amount of hydrochloric acid in deionized water to prepare an acidic solution with a mass concentration of 0.01%, then placing the solution in a reaction vessel and introducing an inert nitrogen atmosphere. MnSO₄, FeCl₂·4H₂O, and Al(NO₃)₃ are weighed in a molar ratio of Mn:Fe:Al₃ = 0.6:0.38:0.02. The weighed FeCl2·4H2O is put into a reactor, and then the corresponding amount of chelating agent disodium ethylenediaminetetraacetate is weighed according to 4% of the total amount of manganese and iron elements to prepare a chelating agent solution, which is then put into the reactor and fully stirred. A dilute hydrochloric acid solution with a concentration of 1% is then added to adjust the pH of the mixed solution to 5.0 to form an acidic ferrous ion complex base liquid; then the weighed MnSO4 and Al(NO3)3 are respectively dissolved in deionized water to form corresponding solutions, which are added to the above base liquid and fully stirred; sodium hydroxide and sodium carbonate are dissolved in deionized water in a mass ratio of 7:3 to prepare an alkaline precipitant, and then slowly added dropwise until the pH of the solution is adjusted to 7.8. The solution is kept warm at 60°C for 24 hours, filtered, washed, and dried to obtain manganese iron hydroxide.

[0075] This embodiment also provides a method for preparing a ferromanganese precursor, specifically, calcining the prepared ferromanganese precursor at 400° C. for 16 hours under a nitrogen flow for dehydration, and then cooling to obtain ferromanganese oxide, namely, the ferromanganese precursor.

[0076] This embodiment also provides a method for preparing a lithium iron manganese phosphate positive electrode material, comprising the following steps: weighing lithium hydroxide, a manganese iron precursor, and phosphoric acid at a molar ratio of Li / (Mn+Fe):P=1.04:1:0.965, weighing a first carbon source at a mass ratio of glucose to manganese iron oxide of 0.5:1, performing nano-sand milling and spraying, and pre-calcining the sprayed material at 350°C for 16 hours to obtain a first lithium iron manganese phosphate positive electrode material. A second carbon source at a mass ratio of polyethylene glycol to the first lithium iron manganese phosphate positive electrode material of 0.15:1 is weighed, and the second carbon source is sand milled and sprayed with the first lithium iron manganese phosphate positive electrode material, and the sprayed material is sintered at 680°C for 16 hours to obtain a final lithium iron manganese phosphate product.

[0077] Example 4

[0078] This embodiment provides a method for preparing manganese iron hydroxide, comprising the following steps: dissolving a small amount of acetic acid in deionized water to prepare an acidic solution with a concentration of 0.001 mol / L, then placing the solution in a reaction kettle and introducing an inert nitrogen atmosphere. MnSO₄, FeSO₄·7H₂O, and CoSO₄ are weighed at a molar ratio of Mn:Fe:Co = 0.6:0.38:0.02. The weighed FeSO4·7H2O is put into a reactor, and then the corresponding amount of chelating agent ethylenediamine is weighed according to 4% of the total amount of manganese and iron elements to prepare a chelating agent solution, which is put into the reactor and fully stirred. Then, an acetic acid solution with a concentration of 0.1 mol / L is added to adjust the pH to 3 to form an acidic ferrous ion complex base liquid; then, the weighed MnSO4 and CoSO4 are respectively dissolved in deionized water to form corresponding solutions, which are added to the above base liquid and fully stirred; sodium hydroxide and sodium bicarbonate are prepared into an alkaline precipitant solution in a mass ratio of 7:3, and then slowly added dropwise until the pH of the solution is adjusted to 9.7. The solution is kept warm at 85°C for 4 hours, filtered, washed, and dried to obtain manganese iron hydroxide.

[0079] This embodiment also provides a method for preparing a ferromanganese precursor, specifically, calcining the prepared ferromanganese hydroxide at 650° C. for 4 hours under a nitrogen flow for dehydration, and then cooling to obtain ferromanganese oxide, i.e., the ferromanganese precursor.

[0080] This embodiment also provides a method for preparing a lithium iron manganese phosphate positive electrode material, comprising the following steps: weighing lithium hydroxide, a manganese iron precursor, and phosphoric acid at a molar ratio of Li / (Mn+Fe):P=1.04:1:0.965, weighing a first carbon source at a mass ratio of glucose to manganese iron oxide of 0.25:1, performing nano-sand milling and spraying, and pre-sintering the sprayed material at 650°C for 4 hours to obtain a first lithium iron manganese phosphate positive electrode material. A second carbon source at a mass ratio of β-cyclodextrin to the first lithium iron manganese phosphate positive electrode material of 0.4:1 is weighed, and then sand milled and sprayed with the first lithium iron manganese phosphate positive electrode material. The sprayed material is then sintered at 800°C for 6 hours to obtain a final lithium iron manganese phosphate product.

[0081] Comparative Example 1

[0082] Manganese carbonate, ferrous oxalate and magnesium oxide were weighed and mixed according to the molar ratio of Mn:Fe:Mg=0.6:0.38:0.02, and then solid phase sintered at 800℃ to obtain (Mn 0.6 Fe 0.4 Mg 0.02 )2O3 oxide; lithium carbonate, (Mn 0.6 Fe 0.4 Mg 0.02 )2O3 and lithium dihydrogen phosphate were weighed in a molar ratio of Li / (Mn+Fe):P=1.04:1:0.965, and the mass of glucose accounted for (Mn 0.6Fe 0.4 Mg 0.02 )2O3 by weight, the mixture was sand-milled, spray-dried, and then solid-phase sintered at 765°C for 10 hours under a nitrogen flow to obtain lithium manganese iron phosphate.

[0083] Comparative Example 2

[0084] A manganese-iron mixed salt solution was prepared by weighing MnSO4·H2O and FeSO4·7H2O at a molar ratio of Mn:Fe:V = 0.7:0.28:0.02. Disodium ethylenediaminetetraacetic acid was added as a complexing agent, and ascorbic acid was added as an antioxidant. Oxygen was introduced into a reactor, along with the manganese-iron mixed salt solution and EDTA. The pH was adjusted to 8.0 with sodium hydroxide, and the reaction temperature was 30°C. The filter cake was then filtered, washed, and dried to obtain manganese-iron oxide powder.

[0085] Lithium carbonate, manganese iron oxide powder and lithium dihydrogen phosphate were weighed according to Li / (Mn+Fe):P=1.04:1:0.965, and mixed and sand-milled according to the mass ratio of sucrose: manganese iron oxide of 0.2:1. After spray drying, the mixture was pre-fired at 500°C for 6 hours and sintered at 755°C for 10 hours to obtain lithium manganese iron phosphate powder.

[0086] Comparative Example 3

[0087] A small amount of dilute nitric acid is mixed with deionized water to form a 0.1% acidic solution, which is then placed in a reactor and passed through an inert atmosphere. Fe(NO3)2·9H2O is added to the reactor at a molar ratio of Mn:Fe:V = 0.7:0.28:0.02. A 5% dilute nitric acid solution is then added to adjust the pH to 4.1, forming an acidic ferrous ion complex base solution. Subsequently, weighed Mn(NO3)2 and ammonium metavanadate are dissolved in deionized water to form a mixed solution, which is then added to the base solution and stirred thoroughly. A pure sodium hydroxide alkaline precipitant solution is then added dropwise until the solution pH is adjusted to 9.2. The solution is then aged at 65°C for 12 hours, filtered, washed, and dried, and then calcined at 500°C for 6 hours under a nitrogen stream for dehydration. After cooling, manganese iron oxide is obtained.

[0088] Lithium carbonate, manganese iron oxide, and lithium dihydrogen phosphate were weighed at a molar ratio of Li / (Mn+Fe):P=1.04:1:0.965, and a first carbon source was weighed at a mass ratio of sucrose:manganese iron oxide of 0.1:1. The mixture was nano-sand-milled and sprayed, and the sprayed material was pre-sintered at 500°C for 6 hours to obtain a first lithium manganese iron phosphate positive electrode material. A second carbon source was weighed at a mass ratio of polyvinyl alcohol:first lithium manganese iron phosphate positive electrode material of 0.2:1, and the second carbon source was sand-milled and sprayed with the first lithium manganese iron phosphate positive electrode material. The sprayed material was pre-sintered at 755°C for 10 hours to obtain the final lithium manganese iron phosphate product.

[0089] In order to verify the feasibility and effectiveness of the present invention, the following performance tests were performed on the lithium manganese iron phosphates prepared in the above embodiments and comparative examples:

[0090] 1. Microscopic morphology

[0091] The ferromanganese oxide prepared in Example 1 was subjected to scanning electron microscopy (SEM) testing and EDS surface scanning of the main elements of the ferromanganese oxide. The results are as follows: Figure 3 、 4 The lithium manganese iron phosphate prepared in Example 1 was tested by scanning electron microscope (SEM), and the results were as follows: Figure 5 shown.

[0092] from Figures 3-5 It can be seen that the manganese and iron elements in the manganese iron oxide precursor and the lithium manganese iron phosphate positive electrode material prepared in Example 1 are evenly distributed at the atomic level.

[0093] 2. Carbon content and powder compaction density test

[0094] 1. Carbon content test: Use carbon and sulfur analyzer, and the test method refers to GB / T 20123-2006.

[0095] 2. The powder compaction density is tested using Sansi Zongheng UTM7305 compaction density meter with a pressure of 3T.

[0096] 3. Electrical performance test

[0097] The electrochemical performance test method involves preparing a 3% adhesive solution containing polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP). The lithium manganese iron phosphate cathode material prepared in the aforementioned examples and comparative examples is then weighed, mixed with acetylene black, carbon black, and the adhesive solution in a mass ratio of 90:2.5:2.5:5, and coated onto aluminum foil to form a positive electrode sheet. A lithium sheet is used as the negative electrode sheet. A separator and an electrolyte are added. The electrolyte is a 1 mol / L LiPF6 solution, and the solvent is a mixture of EC, DEC, and DMC in a 1:1:1 volume ratio. The cells are assembled into a 2032-inch button cell in an argon-filled glove box. Testing is performed on a LAND battery tester at a current density of 0.05C, a voltage range of 2.5V to 4.5V, and a temperature of 25°C.

[0098] Table 1 Comparison of electrochemical performance of iron-manganese-lithium powder and corresponding button-type lithium-ion battery CR2032 in the embodiment and comparative example

[0099]

[0100]

[0101] As can be seen from the above table, the lithium manganese iron phosphate obtained in Examples 1-4 has advantages in compaction and capacity; since Comparative Example 1 is solid-phase sintering, the manganese and iron elements of the prepared manganese iron oxide precursor cannot achieve a uniform distribution at the atomic level, resulting in relatively poor electrochemical performance; and in Comparative Example 2, due to the introduction of oxygen, the ferrous ions will be oxidized to trivalent ferrous ions. Due to the difference in solubility product when encountering alkali, they will preferentially precipitate, making it impossible for the manganese and iron elements of the prepared manganese iron oxide precursor to achieve a uniform distribution at the atomic level, affecting its electrochemical performance; Comparative Example 3 lacks a chelating agent, and the alkaline precipitant is a strong base sodium hydroxide solution, which causes manganese and iron ions to precipitate too quickly, easily causing element enrichment to affect their uniform distribution, thereby affecting the performance of its electrochemical performance.

[0102] In summary, the ferromanganese precursor provided by the present invention can achieve a uniform distribution of manganese and iron at the atomic level, and the lithium iron manganese phosphate cathode material prepared from this raw material has better overall electrochemical performance. Moreover, the ferromanganese precursor and lithium iron manganese phosphate preparation described in the present invention are more closely aligned with the industrialized iron phosphate and lithium iron phosphate production processes, reducing the cost of equipment modification to existing production lines.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0104] Furthermore, those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of the present invention and to form different embodiments. For example, in the claims above, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is intended solely to enhance understanding of the overall background of the present invention and should not be construed as an admission or any form of implication that such information constitutes prior art known to those skilled in the art.

Claims

1. A method for preparing a ferromanganese precursor, characterized in that: The specific steps include: (1) Inert gas is introduced into the reaction vessel, and an acidic ferrous ion complex base liquid is added, and the pH of the acidic ferrous ion complex base liquid is adjusted to 3-5; then a divalent manganese salt solution and a doping metal salt solution are added, and the molar ratio of manganese, iron and doping elements in the reaction solution is controlled to be x:1-xy:y, wherein 0.5≤x<1, 0.01≤y≤0.03; the mixture is stirred thoroughly and mixed evenly; then an alkaline precipitant solution is added, and the pH is adjusted to 7.8-9.7 to precipitate the metal ions; then the reaction vessel is heated to a set temperature while stirring for heat preservation and aging crystallization, the heat preservation and aging temperature is 60-85°C, and the aging time is 4-24 hours; the precipitate is filtered, washed, and dried to obtain manganese iron hydroxide; The acidic ferrous ion complex base liquid is prepared from a ferrous salt solution, a complexing agent solution, and an acidic solution. The specific process is as follows: first, the acidic solution is added to a reaction vessel into which an inert gas is introduced, then the ferrous salt solution is added, and then the complexing agent solution is added and stirred thoroughly, and then the pH of the mixed solution is adjusted to obtain the acidic ferrous ion complex base liquid. The complexing agent solution is prepared by dissolving a complexing agent in deionized water, wherein the complexing agent includes at least one of disodium ethylenediaminetetraacetic acid, diethylaminepentaacetic acid, tartaric acid, sodium gluconate, and ethylenediamine; The acidic solution is an aqueous solution of an organic acid and / or an inorganic acid, wherein the inorganic acid comprises at least one of dilute sulfuric acid, dilute hydrochloric acid, and dilute nitric acid; and the organic acid comprises at least one of citric acid, ethylenediaminetetraacetic acid, and acetic acid. (2) The manganese iron hydroxide is calcined and dehydrated at a low temperature of 400°C to 650°C for 4 to 16 hours to obtain manganese iron oxide, i.e., manganese iron precursor.

2. The method for preparing a ferromanganese precursor according to claim 1, wherein: The ferrous salt solution is prepared by dissolving ferrous salt in deionized water, and the ferrous salt includes at least one of ferrous sulfate and its hydrate, ferrous nitrate and its hydrate, and ferrous chloride and its hydrate.

3. The method for preparing a ferromanganese precursor according to claim 1, wherein: The divalent manganese salt solution is prepared by dissolving a divalent manganese salt in deionized water, and the divalent manganese salt includes at least one of manganese sulfate, manganese nitrate, and manganese chloride.

4. The method for preparing a ferromanganese precursor according to claim 1, wherein: The doped metal salt solution is an aqueous solution containing a soluble salt of a doped metal element, and the doped metal element is at least one of titanium, magnesium, vanadium, niobium, aluminum, cobalt, molybdenum, nickel, zirconium, lanthanum, and tungsten; The alkaline precipitant is at least one of a combined solution of sodium hydroxide and sodium carbonate, a combined solution of sodium hydroxide and sodium bicarbonate, and ammonia water.

5. A ferromanganese precursor prepared by the preparation method according to any one of claims 1 to 4, characterized in that: The ferromanganese precursor is ferromanganese oxide doped with metal elements, and the molar ratio of manganese, iron and the doping element is x:1-xy:y, wherein 0.5≤x<1, 0.01≤y≤0.

03.

6. A method for preparing lithium iron manganese phosphate positive electrode material using the manganese iron precursor according to claim 5, characterized in that: The steps include: (1) Grinding and mixing the ferromanganese precursor with a lithium source, a phosphorus source, and a first carbon source, wherein the mass of the lithium source, the ferromanganese precursor, and the phosphorus source are weighed according to the molar ratio of Li:(Mn+Fe):P of (1.0-1.1):1:(0.95-1.0), and the first carbon source is weighed according to the mass ratio of the ferromanganese precursor to the ferromanganese precursor of (0.2-0.5):

1. After spray granulation, the mixture is pre-calcined at a low temperature in a nitrogen atmosphere to obtain a first manganese iron phosphate lithium positive electrode material; the low temperature pre-calcination temperature is 350-650°C, and the sintering time is 4-16 hours; (2) The first lithium iron manganese phosphate positive electrode material and the second carbon source are ground and mixed for a second time, wherein the second carbon source is weighed at a mass ratio of (0.1-0.4) to the first lithium iron manganese phosphate positive electrode material: 1, spray granulated, sintered at high temperature in a nitrogen atmosphere, and crushed to obtain the second lithium iron manganese phosphate positive electrode material; the high temperature sintering temperature is 680-800°C, and the sintering time is 6-16h.

7. The method according to claim 6, characterized in that In step (1), the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, and lithium phosphate; the phosphorus source is at least one of lithium dihydrogen phosphate, lithium phosphate, diammonium hydrogen phosphate, phosphoric acid, and ammonium dihydrogen phosphate; and the first carbon source is at least one of glucose, sucrose, and starch; In step (2), the second carbon source is at least one of polyethylene glycol, polyvinyl alcohol, polyvinyl pyrrolidone, citric acid, and β-cyclodextrin.

8. A lithium manganese iron phosphate positive electrode material prepared by the method according to claim 6 or 7.

9. A lithium-ion battery, characterized in that: It comprises a positive electrode plate, and the positive electrode plate comprises the lithium manganese iron phosphate positive electrode material according to claim 8.

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