A low-sulfur type cation-doped manganese iron pyrophosphate precursor, carbon-coated modified manganese iron lithium phosphate and a preparation method and application thereof

Abstract

The application belongs to the technical field of new energy materials, and particularly relates to a low-sulfur cation-doped manganese iron pyrophosphate precursor, carbon-coated modified manganese iron lithium phosphate and a preparation method and application thereof. A low-sulfur cation-doped manganese iron pyrophosphate precursor is successfully prepared. By adding an appropriate amount of a phosphoric acid source to the prepared metal cation-doped manganese iron ammonium phosphate precursor, the sulfur content is effectively reduced, and the molar ratio of manganese, iron, a doped element and phosphorus is slightly less than 1, so that the tap density of the precursor is effectively improved. The precursor can effectively inhibit gas generation in a high-temperature sintering process, avoid pore defects and ensure the compactness of the structure of the prepared carbon-coated modified manganese iron lithium phosphate material, so that the cycle stability of the material is significantly improved. The lithium ion battery constructed based on the material exhibits excellent electrochemical performance. In addition, the preparation process of the precursor is simple, the raw material conversion rate is high and the precursor is suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of new energy technology. More specifically, it relates to a low-sulfur cation-doped pyrophosphoric iron precursor, carbon-coated modified manganese iron lithium phosphate and its preparation method and application. BACKGROUND

[0002] With the rapid development of new energy technology, the positive material as the key factor of the performance of lithium ion battery is receiving more and more attention. Lithium iron phosphate (LiFePO4) material as the positive material of lithium ion battery, due to its high safety, long cycle life, relatively low cost and other advantages, has been widely used in electric vehicles, energy storage systems and other fields. However, its tap density is low, resulting in low volume energy density; at the same time, the conductivity is relatively poor, and conductive agent needs to be added to improve it, which increases the cost to some extent and affects the overall performance of the battery.

[0003] At the same time, manganese iron lithium phosphate positive material gradually stands out with its higher voltage platform, energy density and more excellent low temperature performance, and becomes the new focus of current positive material industrialization research and development. In recent years, carbon coating and cation doping strategies have become a research hotspot. Among them, carbon coating can effectively improve the conductivity of the material, avoid direct contact between manganese iron lithium phosphate and electrolyte, and inhibit the excessive growth of nanoparticles in the sintering process; cation doping can effectively lengthen the Li-O bond in the manganese iron lithium phosphate lattice, facilitate lithium ion migration and improve the structural stability of the material. However, the mainstream solid phase sintering method is to mix iron single element, manganese source, phosphorus source, lithium source, carbon source and dopant according to a certain stoichiometric ratio to sinter manganese iron lithium phosphate, which cannot effectively ensure the uniform distribution of atoms in the bulk phase, thereby affecting the performance of the positive material. For example, Chinese patent application CN117715861A discloses a sheet-like manganese iron pyrophosphate and manganese iron lithium phosphate material, and the obtained manganese iron lithium phosphate material has excellent tap density, and the battery prepared therefrom also has good capacity and initial efficiency. However, similar manganese iron lithium phosphate materials often use low-cost manganese sulfate in the manganese doping process, which is economical but inevitably causes high sulfur content in the material, thereby exacerbating the challenge of its electrochemical performance. These problems result in unsatisfactory performance of manganese iron lithium phosphate positive material in terms of charge and discharge capacity and cycle stability, so it is necessary to further improve the performance of manganese iron lithium phosphate material. SUMMARY

[0004] The technical problem to be solved by the present application is to overcome the defects and shortcomings in the prior art that the sulfur content in the manganese iron pyrophosphate precursor is high, thereby affecting the electrochemical performance of manganese iron lithium phosphate, and to provide a preparation method of a low-sulfur cation-doped manganese iron pyrophosphate precursor.

[0005] Another object of the present application is to provide a low-sulfur cation-doped manganese iron pyrophosphate precursor prepared by the above preparation method.

[0006] Another object of the present application is to provide a preparation method of carbon-coated modified manganese iron lithium phosphate.

[0007] Another object of the present application is to provide carbon-coated modified manganese iron lithium phosphate prepared by the above preparation method.

[0008] Another object of the present application is to provide a lithium ion battery anode comprising the aforementioned carbon-coated modified manganese iron lithium phosphate.

[0009] Another object of the present application is to provide a lithium ion battery comprising the aforementioned lithium ion battery anode.

[0010] The above objects of the present application are achieved by the following technical solutions.

[0011] The present application protects a preparation method of a low-sulfur cation-doped manganese iron pyrophosphate precursor, comprising the following steps:

[0012] S1. Using manganese sulfate as a manganese salt to prepare a metal cation-doped manganese iron ammonium phosphate precursor;

[0013] S2. Mixing the metal cation-doped manganese iron ammonium phosphate precursor obtained in step S1 with a phosphoric acid source solution, adjusting the pH of the solution to 7-11, and fully reacting at 50-150℃, filtering, washing the precipitate, and drying to obtain a low-sulfur cation-doped manganese iron ammonium phosphate precursor;

[0014] S3. Fully calcining the low-sulfur cation-doped manganese iron ammonium phosphate precursor obtained in step S2 at 400-600℃ to obtain a low-sulfur cation-doped manganese iron pyrophosphate precursor;

[0015] The metal cation is selected from at least one of Mg, Ti, V, Co, Ni, Cr, Zn, Cu, Zr, Nb, Mo, Al, Ta, W, and Ca, without repetition among them;

[0016] The low-sulfur cation-doped manganese iron pyrophosphate precursor has the expression (Mn x Fe 1-x-y M y )2P2O7, 0

[0017] The addition amount of the phosphoric acid source (based on the amount of substance of phosphate) is at least 0.1 times the amount of substance of the metal cation-doped manganese iron ammonium phosphate precursor;

[0018] Steps S1-S3 are all carried out in a protective gas atmosphere.

[0019] The manganese iron lithium phosphate material is often prepared by using low-cost manganese sulfate in the process of manganese doping. Although this method is economical, it inevitably causes the problem of excessive sulfur content in the material, because the sulfur impurities (sulfate) are wrapped inside the prepared metal cation-doped manganese iron ammonium phosphate precursor particles or adsorbed on the surface, resulting in high sulfur impurity content of the obtained precursor. The inventors found that adding an appropriate amount of phosphoric acid source to the synthesized metal cation-doped manganese iron ammonium phosphate precursor can induce recrystallization to expose the sulfur impurities and separate them from the precursor particles, and then through subsequent post-processing of filtration and washing, the sulfur impurities are transferred, thereby achieving the purpose of removing the sulfur impurities. At the same time, the addition of the phosphoric acid source can control the molar ratio of the sum of manganese, iron and doped metal elements in the metal cation-doped manganese iron ammonium phosphate precursor Mn x Fe 1-x-y M y PO4 to the molar ratio of phosphorus element, so that it is slightly less than 1, realizing the uniform substitution and coordination of different elements in the precursor. This control ensures the regular distribution of the doped metal, manganese and iron elements at the atomic level in the precursor lattice, forming a single solid solution phase, thereby further improving the structural stability of the prepared low-sulfur cation-doped manganese iron pyrophosphate precursor and greatly reducing its sulfur content.

[0020] Further, as a common expression, M in (Mn x Fe 1-x-y M y )2P2O7 represents multiple (such as 4) metal cation doping, and A, B, C and D represent 4 different metal cations, respectively.

[0021] Further, as a common expression, when the doped metal cation is 4, the expression of the low-sulfur cation-doped manganese iron pyrophosphate precursor is (Mn x Fe 1-x-a-b-c-d A a B b C c D d )2P2O7, and 0 < x ≤ 0.9, 0 < a ≤ 0.1, 0 < b ≤ 0.1, 0 < c ≤ 0.1, 0 < d ≤ 0.1, a + b + c + d ≤ 0.1.

[0022] Further, as a common expression, M in (Mn x Fe 1-x-y M y )2P2O7 represents multiple (such as 5) metal cation doping, and A, B, C, D and E represent 5 different metal cations, respectively.

[0023] Further, as a common expression, when the doped metal cation is 5 kinds, the expression of the low-sulfur type cation-doped manganese iron pyrophosphate precursor is (Mn x Fe 1-x-a-b-c-d-e A a B b C c D d E e )2P2O7, and 0

[0024] Further, in step S1, the preparation method of the metal cation-doped manganese iron ammonium phosphate precursor specifically includes the following steps:

[0025] SI. Prepare a mixed solution I containing manganese sulfate and doped metal cation salt;

[0026] SII. Mix the elemental iron and the phosphoric acid source solution and fully react to obtain a ferrous phosphate solution system II;

[0027] SIII. At 70-150°C, add the mixed solution I obtained in step SI and the oxidizing agent to the ferrous phosphate solution system II obtained in step SII, mix and fully react to make the divalent manganese ions and the divalent iron ions oxidize into trivalent manganese ions and trivalent iron ions, respectively, to obtain an intermediate system III, adjust the pH to 7-11, fully react, and post-treat to obtain the metal cation-doped manganese iron ammonium phosphate precursor;

[0028] Wherein, the steps SI-SIII are carried out in a protective gas atmosphere.

[0029] Further, in step SI, the metal cation salt includes one or more of sulfate, chloride, nitrate, acetate, ammonium salt, carbonate, phosphate, oxalate, basic salt, and alcohol salt.

[0030] Further, in step SI, the Mg is selected from one or more of magnesium chloride, magnesium sulfate, magnesium chloride, magnesium acetate, magnesium nitrate, magnesium oxalate, magnesium carbonate, and magnesium citrate.

[0031] Further, in step SI, the Ti is selected from one or more of titanium sulfate, titanium chloride, oxotitanium ammonium oxalate, and titanium oxysulfate.

[0032] Further, in step SI, the V is selected from one or more of vanadium oxysulfate, dichloro oxovanadium, vanadium oxalate, and oxovanadium oxalate.

[0033] Further, in step SI, the Co is selected from one or more of cobalt sulfate, cobalt chloride, cobalt acetate, cobalt nitrate.

[0034] Further, in step SI, the Ni is selected from one or more of nickel sulfate, nickel chloride, nickel acetate, nickel nitrate.

[0035] Further, in step SI, the Cr is selected from one or more of chromium sulfate, chromium chloride, chromium acetate, chromium oxalate.

[0036] Further, in step SI, the Zn is selected from one or more of zinc sulfate, zinc chloride, zinc acetate, zinc oxalate, zinc nitrate.

[0037] Further, in step SI, the Cu is selected from one or more of copper sulfate, copper chloride, copper acetate, copper nitrate.

[0038] Further, in step SI, the Zr is selected from one or more of zirconium sulfate, zirconium tetrachloride, zirconium acetate, zirconium oxychloride, zirconium nitrate.

[0039] Further, in step SI, the Nb is selected from ammonium niobium oxalate and / or niobium oxalate.

[0040] Further, in step SI, the Mo is selected from one or more of molybdenum sulfate, molybdenum chloride, molybdenum acetate, ammonium molybdate, molybdenum nitrate.

[0041] Further, in step SI, the Al is selected from one or more of aluminum sulfate, aluminum chloride, aluminum nitrate.

[0042] Further, in step SI, the Ta is selected from one or more of tantalum sulfate, tantalum pentachloride, tantalum ethoxide, tantalum butoxide, tantalum isopropoxide.

[0043] Further, in step SI, the W is selected from one or more of tungsten nitrate, tungsten chloride, tungsten phosphate.

[0044] Further, in step SI, the Ca is selected from one or more of calcium bicarbonate, calcium dihydrogen phosphate, calcium chloride, calcium acetate, calcium nitrate.

[0045] Further, in step SI, the molar ratio of manganese in the manganese sulfate and the doped metal in the doped metal cation salt M solution is f: g, the f is 0 < f ≤ 0.9, and the g is 0 < g ≤ 0.1.

[0046] Further, in step SI, the concentration of the mixed solution I is the molar concentration of the total metal cations.

[0047] Further, in step SI, the concentration of the mixed solution I is 0.1-10 mol / L, preferably 3 mol / L.

[0048] Further, in step SI, the protective gas comprises one or more of nitrogen, helium, and argon.

[0049] Further, in step SII, the iron source is one or more of iron block, iron powder, and iron sheet.

[0050] Further, in step SII, the phosphoric acid source comprises one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, sodium hydrogen phosphate, lithium dihydrogen phosphate, ammonium phosphate, lithium phosphate, sodium phosphate, ammonium hypophosphite, ammonium polyphosphate, sodium hypophosphite, sodium metaphosphate, and sodium tripolyphosphate.

[0051] Further, in step SII, the molar ratio of the iron source to the phosphoric acid source is 1:(2-5).

[0052] Further, in step SII, the reaction time is 0.5-20 h.

[0053] Further, in step SII, the phosphoric acid source has weak oxidizing property, and in the protective gas atmosphere, the iron source is only oxidized to the divalent state, and thus ferrous phosphate is generated.

[0054] Further, in step SIII, the oxidizing agent comprises one or more of hydrogen peroxide, oxygen, and ozone. One of the purposes of adding the oxidizing agent is to oxidize the Mn 2+ in the mixed solution I obtained in step SI to Mn 3+ ; the other purpose is to oxidize the Fe 2+ in the ferrous phosphate solution system II obtained in step SII to Fe 3+ .

[0055] Further, in step SIII, the molar ratio of the oxidizing agent to the divalent manganese salt in the mixed solution I obtained in step SI is at least 0.5 times the molar amount of the divalent manganese salt.

[0056] Further, in step SIII, the reaction time is 2-36 h.

[0057] Further, in step SIII, the pH 7-11 is adjusted by adding an alkaline reagent.

[0058] Further, the alkaline reagent comprises one or more of urea, ammonia, and urea phosphate. By using these alkaline reagents to adjust the pH of the solution, Mn 3+ and Fe 3+The metal cation doped manganese iron ammonium phosphate precursor is formed by co-precipitation of the metal cation and the phosphate source in the phosphate system, and the introduction of alkali metal impurities such as Na and K is avoided by not using sodium hydroxide and potassium hydroxide.

[0059] Further, in step SIII, the post-treatment includes filtering, washing, and drying.

[0060] Further, the filtering is pressure filtration, i.e., the solution containing the metal cation doped manganese iron ammonium phosphate precursor is subjected to pressure filtration to separate the solid and the liquid, and a filter cake is obtained.

[0061] Further, the washing is washing the filter cake after pressure filtration with water for 3-5 times.

[0062] Further, the drying is flash evaporation, i.e., the filter cake after washing is transferred into a flash evaporator to perform heat exchange to rapidly evaporate the surface moisture.

[0063] Specifically, in step SIII, the post-treatment includes filtering the solution containing the metal cation doped manganese iron ammonium phosphate precursor to separate the solid and the liquid, washing the filter cake after pressure filtration with water for 3-5 times, and transferring the filter cake after washing into a flash evaporator to perform heat exchange to rapidly evaporate the surface moisture.

[0064] Further, in step S2, the phosphate source includes one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, lithium dihydrogen phosphate, lithium phosphate, ammonium hypophosphite, and ammonium polyphosphate.

[0065] Further, in step S2, the molar ratio of the metal cation doped manganese iron ammonium phosphate precursor to the phosphate source is 1:(0.1-20), which ensures that the phosphate source is excessive relative to the precursor. If the amount of the phosphate source added is too much, unnecessary resources will be wasted.

[0066] Further, in step S2, the mixing time is 0.5-20h.

[0067] Further, in step S2, the pH of 7-11 is adjusted by adding an alkaline reagent.

[0068] Further, the alkaline reagent includes one or more of urea, ammonia, and urea phosphate.

[0069] Further, in step S2, the reaction time is 2-36h.

[0070] Further, in step S2, the filtering is pressure filtration, i.e., the solution containing the low-sulfur type metal cation doped manganese iron ammonium phosphate precursor is subjected to pressure filtration to separate the solid and the liquid.

[0071] Further, in step S2, the precipitate washing is performed by washing the filtered precipitate with water for 3-5 times.

[0072] Further, in step S2, the drying is performed by flash evaporation, i.e. transferring the washed precipitate into a flash evaporator for heat and moisture exchange to rapidly evaporate the surface moisture.

[0073] Further, in step S3, the sufficient calcination is performed for 1-4 hours.

[0074] The low-sulfur cation-doped pyrophosphate manganese iron precursor prepared by the preparation method is protected.

[0075] The application protects a preparation method of carbon-coated modified manganese iron lithium phosphate, comprising the following steps:

[0076] Si. The lithium salt, the phosphoric acid source, the aforementioned low-sulfur cation-doped pyrophosphate manganese iron precursor, the carbon source and the alcohol solution are uniformly mixed to obtain a slurry, the obtained slurry is ground and dried to obtain a powder;

[0077] Sii. The powder obtained in step Si is pre-calcined at 450-550℃ for 0.5-8 hours under a protective gas atmosphere, then heated to 650-900℃ for sufficient calcination, and post-treated to obtain the carbon-coated modified manganese iron lithium phosphate.

[0078] The application uses the low-sulfur cation-doped pyrophosphate manganese iron as the precursor for preparing the carbon-coated modified manganese iron lithium phosphate material, which has the following advantages: in the high-temperature sintering process, the generation of gas can be effectively prevented, thereby avoiding the formation of void defects, ensuring the compactness of the structure of the carbon-coated modified manganese iron lithium phosphate material, which not only effectively improves the compaction density of the material, but also relieves the manganese dissolution problem, thereby greatly improving the cycle stability of the material. Compared with the traditional ammonium manganese iron phosphate precursor, the ammonia gas is generated during the high-temperature sintering of the traditional ammonium manganese iron phosphate precursor, which causes the material to form a loose porous structure, which is not conducive to improving the compaction density and subsequent battery performance optimization.

[0079] Further, in step Si, the lithium salt includes one or more of lithium carbonate, lithium dihydrogen phosphate, lithium hydrogen phosphate, lithium phosphate, lithium hydroxide, lithium nitrate, and lithium acetate.

[0080] Further, in step Si, the phosphoric acid source includes one or more of lithium dihydrogen phosphate, lithium phosphate, ammonium dihydrogen phosphate, ammonium hydrogen phosphate, ammonium phosphate, phosphoric acid, ammonium hypophosphite, and ammonium polyphosphate.

[0081] Further, in step Si, the carbon source includes one or more of polyethylene glycol, polyethylene, polyvinyl alcohol, glucose, fructose, sucrose, starch, graphene oxide, polyvinylpyrrolidone, polyvinylidene fluoride, lauric acid, ascorbic acid, and citric acid.

[0082] Further, in step Si, the molar ratio of the lithium salt, the phosphoric acid source, the low-sulfur cation-doped manganese iron pyrophosphate precursor obtained above is 1 : (0.8-1.2) : (0.9-1.1). The lithium salt and the phosphoric acid source are appropriately added in excess to ensure that the reaction proceeds sufficiently and completely.

[0083] Further, in step Si, the mass ratio of the low-sulfur cation-doped manganese iron pyrophosphate precursor to the carbon source is 1 : (0.01-1) in step Si.

[0084] Further, in step Si, the alcohol solution is a mixed solution of an alcohol reagent and water. The alcohol reagent not only serves as a dispersion medium, but also helps the solution to dry quickly due to its fast evaporation rate.

[0085] Still further, the alcohol reagent includes one or more of ethanol, methanol, and ethylene glycol.

[0086] Preferably, the alcohol reagent is ethanol.

[0087] More preferably, the volume ratio of the alcohol reagent to water is 1 : (1-5).

[0088] Further, in step Si, the solid content of the slurry is 10%-45%.

[0089] Further, in step Si, the particle size of the ground slurry is 0.35 μm≤D 50 ≤0.4 μm.

[0090] Further, in step Si, the drying is spray drying.

[0091] Still further, the conditions for the spray drying are an inlet air temperature of 200-260°C, an outlet air temperature of 90-110°C, and an outlet particle size of 6 μm≤D 50 ≤9 μm.

[0092] Further, in step Sii, the protective gas includes one or more of nitrogen, helium, and argon.

[0093] Further, in step Sii, the calcination device is a box furnace, a roller kiln, or a tube furnace, preferably a box furnace.

[0094] Still further, the heating rate for the calcination is 1-10°C / min.

[0095] Further, in step Sii, the time for the sufficient calcination is 2-20 h. The stepwise calcination method is conducive to the formation of a single phase of the carbon-coated modified manganese iron lithium phosphate.

[0096] The carbon-coated modified lithium manganese iron phosphate prepared by the preparation method is protected.

[0097] The carbon-coated modified lithium manganese iron phosphate material prepared in the application presents a single solid solution phase structure, which ensures that there is no mixture of iron, manganese and manganese-iron related phases in the material, thereby ensuring the structural stability, compaction density and conductivity of the material. In addition, the doped cations are uniformly distributed in the lithium manganese iron phosphate material, rather than being locally aggregated or only distributed on the surface, which fundamentally improves the electronic structure and electrochemical performance of the lithium manganese iron phosphate, avoids the problem of insufficient performance adjustment, and provides a strong guarantee for the high performance of the battery.

[0098] The application protects a lithium ion battery positive electrode, which comprises a current collector and a positive electrode active material loaded on the current collector, and the positive electrode active material comprises the aforementioned carbon-coated modified lithium manganese iron phosphate.

[0099] Preferably, the current collector is an aluminum foil or a carbon-coated aluminum foil.

[0100] Further, as a preferred mode, the preparation method of the lithium ion battery positive electrode comprises the following steps: dispersing the carbon-coated modified lithium manganese iron phosphate, the conductive agent carbon black and the binder polyvinylidene fluoride in an N-methylpyrrolidone dispersant to obtain a positive electrode slurry, and then coating the positive electrode slurry on an aluminum foil, and after vacuum drying at 80-140℃ for 12-24h, the positive electrode is obtained.

[0101] Further, the mass ratio of the carbon-coated modified lithium manganese iron phosphate, the conductive agent carbon black and the binder polyvinylidene fluoride is 1:(0.03-0.125):(0.03-0.125).

[0102] The application protects a lithium ion battery, which comprises a positive electrode, a negative electrode, a separator and an electrolyte, and the positive electrode is the aforementioned lithium ion battery positive electrode.

[0103] The lithium ion battery prepared in the application exhibits excellent compaction density, charge and discharge capacity, capacity retention rate and cycle stability.

[0104] Further, as a preferred mode, the positive electrode of the lithium ion battery is the aforementioned lithium ion battery positive electrode, the negative electrode is a metal lithium sheet, the separator is a polyethylene film, and the electrolyte is prepared by dissolving 1mol / L of LiPF6 in a mixed solvent of dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethylene carbonate (EC) in a volume ratio of 1:1:1.

[0105] Compared with the prior art, the application has the following beneficial effects:

[0106] The application provides a low-sulfur type cation-doped manganese iron pyrophosphate precursor. By adding an appropriate amount of a phosphoric acid source to the prepared metal cation-doped manganese iron ammonium phosphate precursor, the sulfur content is effectively reduced, and the molar ratio of manganese, iron, a doped element and phosphorus is controlled to be slightly less than 1, so that the tap density of the precursor is effectively improved. The precursor can effectively inhibit gas generation during high-temperature sintering, avoid pore defects, ensure the compactness of the structure of the carbon-coated modified manganese iron lithium phosphate material prepared, and significantly improve the cycle stability of the material. The lithium ion battery constructed based on the material exhibits excellent electrochemical performance. In addition, the preparation process of the precursor is simple, the raw material conversion rate is high, and the precursor is suitable for industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0107] Fig. 1 SEM image of the low-sulfur type cation-doped manganese iron pyrophosphate precursor (Mn 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 )2P2O7 prepared for Example 1.

[0108] Fig. 2 SEM image of the low-sulfur type cation-doped manganese iron pyrophosphate precursor (Mn 0.7 Fe 0.25 Mg 0.01 V 0.0 1W 0.01 Zn 0.01 Al 0.01 )2P2O7 prepared for Example 2.

[0109] Fig. 3 SEM image of the low-sulfur type cation-doped manganese iron pyrophosphate precursor (Mn 0.4 Fe 0.55 Ti 0.02 V 0.03 )2P2O7 prepared for Example 3. DETAILED DESCRIPTION

[0110] The application will be further described below in conjunction with the accompanying drawings and specific examples, but the examples do not limit the application in any form. Unless otherwise specified, the reagents, methods and equipment used in the application are conventional reagents, methods and equipment in the technical field.

[0111] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0112] Example 1 A low-sulfur type cation-doped manganese iron pyrophosphate precursor, a carbon-coated modified manganese iron lithium phosphate, a lithium ion battery and a preparation method thereof

[0113] 1. A low-sulfur cation-doped manganese iron pyrophosphate precursor (Mn 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 )2P2O7

[0114] Into a nitrogen-purged dissolving tank, 16.81 kg of manganese sulfate monohydrate, 730.9 g of sodium tungstate, 664 g of vanadium oxalate, 1338.1 g of niobium oxalate, 236.8 g of anhydrous magnesium chloride, and 161.5 g of anhydrous cobalt chloride were dissolved to prepare a 3 mol / L metal salt mixed solution I.

[0115] Into a sealed synthesis reactor containing 8.2 L of ultrapure water, 766 g of iron powder was added, and the temperature of the reactor was set to 40°C. Nitrogen was introduced into the reactor, and the reactor was stirred at a speed of 800 r / min for 10 min. Then, 14.34 kg of 85 wt% concentrated phosphoric acid solution was slowly pumped into the reactor, and the mixture was stirred uniformly for 3 h to form a ferrous phosphate solution system II. Subsequently, the reactor was heated to 76°C, and after the temperature of the system stabilized, the metal salt mixed solution I and hydrogen peroxide (7.69 kg of 27.5 wt%) were simultaneously and slowly pumped into the ferrous phosphate solution system II at a molar ratio of 2:1. After the two were completely pumped into the ferrous phosphate solution system II to form an intermediate system III, the intermediate system III was stirred and reacted for 30 min. Then, 384.4 g of 27.5 wt% hydrogen peroxide solution was pumped into the intermediate system IV at the same feeding rate as above. Ammonia water was used to adjust the pH of the system IV to 7.3, and then the intermediate system IV was aged at 76°C for 2 h. Finally, the obtained slurry was pressure-filtered using a vertical pressure filter to obtain a filter cake, which was washed with high-purity water until the conductivity of the washing water reached 125 μs / cm, and then subjected to flash evaporation treatment to obtain a dry metal cation-doped manganese iron ammonium phosphate precursor (NH4Mn 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 PO4).

[0116] Under a nitrogen protective atmosphere, the metal cation-doped manganese iron ammonium phosphate precursor NH4Mn 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01PO4) into a 20 L ultrapure water as the base liquid high-efficiency closed synthesis reactor to disperse and make slurry, and 85 wt% concentrated phosphoric acid solution is slowly pumped into the above precursor slurry at a molar ratio of precursor: phosphoric acid = 2: 1, and stirred for 30 min to obtain intermediate system V, then ammonia is used to adjust the pH of system V to 7.3, and then system V is aged for 4 h. Finally, a vertical filter press is used to filter the obtained slurry to obtain a filter cake, and high-purity water is used to wash until the conductivity of the washing water is 108 μs / cm, and then flash treatment is performed to obtain a low-sulfur type cation-doped ammonium manganese iron phosphate precursor (NH4Mn 0.8 Fe 0.1 1W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 PO4).

[0117] The low-sulfur type cation-doped ammonium manganese iron phosphate precursor NH4Mn 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 PO4 is placed in a graphite crucible and placed in a nitrogen atmosphere box furnace (oxygen content less than 10 ppm), and heated to 450°C at a heating rate of 10°C / min and held for 2 h to prepare a low-sulfur type cation-doped manganese iron pyrophosphate precursor ((Mn 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 )2P2O7).

[0118] 2. Preparation of carbon-coated modified lithium manganese iron phosphate LiMn 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 PO4

[0119] The corresponding lithium carbonate, lithium dihydrogen phosphate, low-sulfur type cation-doped manganese iron pyrophosphate precursor (Mn 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co0.01 )2P2O7 and polyethylene glycol and glucose (6.5 wt% of low-sulfur cation-doped manganese iron phosphate precursor, and the mass ratio of polyethylene glycol and glucose is 2:1) are dispersed in ultrapure water and ethanol (the volume ratio of ultrapure water and ethanol is 2:1) to obtain a slurry with a solid content of 35%, and the slurry is subjected to coarse grinding and fine grinding to a particle size D 50 of 0.38 μm using a horizontal sand mill system, and then the slurry is transferred to a spray granulation dryer for spray drying to obtain a spray powder. Subsequently, the spray powder is subjected to staged temperature sintering using an atmosphere box furnace under a nitrogen protective atmosphere, and the temperature is raised to 500°C at a rate of 5°C / min and maintained for 4 h, and then the temperature is raised to 760°C at a rate of 10°C / min and maintained for 10 h. After the atmosphere box furnace is naturally cooled to room temperature, a carbon-coated modified lithium manganese iron phosphate (LiMn 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 PO4) is obtained.

[0120] 3. Preparation of a lithium ion battery

[0121] The carbon-coated modified lithium manganese iron phosphate obtained above, carbon black as a conductive agent, and polyvinylidene fluoride as a binder are dissolved in N-methyl pyrrolidone dispersant in a mass ratio of 94:3:3, mixed uniformly to obtain a positive electrode slurry, and then coated on an aluminum foil. After vacuum drying at 105°C for 24 h, a lithium ion battery positive electrode is obtained.

[0122] A lithium ion battery is assembled in an argon-filled glove box. The positive electrode is the lithium ion battery positive electrode described above, the negative electrode is a metal lithium sheet, the separator is a polyethylene film, and the electrolyte is prepared by dissolving 1 mol / L of LiPF6 in a mixed solvent of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethylene carbonate (EC) in a volume ratio of 1:1:1.

[0123] Example 2: A low-sulfur cation-doped manganese iron pyrophosphate precursor, a carbon-coated modified lithium manganese iron phosphate, a lithium ion battery, and a preparation method thereof

[0124] 1. Preparation of a low-sulfur cation-doped manganese iron pyrophosphate precursor (Mn 0.7 Fe 0.25 Mg 0.01 V 0.01 W 0.01 Zn 0.01 Al 0.01 )2P2O7

[0125] Into a nitrogen purged dissolving tank, 6.47 kg of manganese sulfate monohydrate, 65.9 g of magnesium sulfate, 146.1 g of vanadium oxalate, 160.8 g of sodium tungstate, 88.3 g of zinc sulfate, and 187.2 g of aluminum sulfate were dissolved to prepare a 2 mol / L metal salt mixed solution I.

[0126] Into a closed synthesis reactor containing 16.2 L of ultrapure water, 766 g of iron powder was added, and the temperature of the reactor was set to 45°C. Nitrogen was introduced into the reactor, and stirring was performed at a speed of 800 r / min for 10 min. Then, 6.31 kg of 85 wt% concentrated phosphoric acid solution was slowly pumped into the reactor, and uniform stirring was performed for 3 h to form a ferrous phosphate dihydrogen solution system II. Subsequently, the temperature of the reactor was increased to 75°C, and after the temperature of the system was stabilized, the metal: hydrogen peroxide (3.38 kg of 27.5 wt%) in a molar ratio of 2:1 in the aforementioned mixed metal source solution I was simultaneously and slowly pumped into the ferrous phosphate dihydrogen solution system II. After the two were completely pumped into the ferrous phosphate dihydrogen solution system II to form an intermediate system III, the intermediate system III was fully stirred and reacted for 30 min. Then, 169.1 g of 27.5 wt% hydrogen peroxide solution was pumped in at the same feeding rate as above to form an intermediate system IV. Ammonia water was used to adjust the pH of the system IV to 7.8, and then the intermediate system IV was aged at 75°C for 2 h. Finally, the obtained slurry was pressure-filtered using a vertical pressure filter to obtain a filter cake, which was washed with high-purity water until the conductivity of the washing water was 144 μs / cm, and then subjected to flash evaporation treatment to obtain a dry metal cation-doped manganese iron ammonium phosphate precursor (NH4Mn 0.7 Fe 0.25 Mg 0.01 V 0.01 W 0.01 Zn 0.01 Al 0.01 PO4).

[0127] Under a nitrogen protective atmosphere, the metal cation-doped manganese iron ammonium phosphate precursor NH4Mn 0.7 Fe 0.25 Mg 0.01 V 0.01 W 0.01 Zn 0.01 Al 0.01PO4 was added to a tightly sealed reactor with 20L of ultrapure water as the base solution and dispersed to form a slurry. An 85wt% concentrated phosphoric acid solution was slowly pumped into the reactor at a precursor:phosphoric acid molar ratio of 2:1 and stirred for 30 minutes to obtain intermediate system V. Then, system V was adjusted to pH 7.8 using ammonia water and aged for 4 hours. Finally, the obtained slurry was filtered using a vertical filter press to obtain a filter cake, which was washed with high-purity water until the wash water conductivity reached 112 μS / cm. The cake was then subjected to flash evaporation to obtain a low-sulfur cationic doped manganese iron ammonium phosphate precursor (NH4Mn). 0.7 Fe 0.25 Mg 0.01 V 0.01 W 0.01 Zn 0.01 Al 0.01 PO4).

[0128] Low-sulfur cation-doped manganese iron ammonium phosphate precursor NH4Mn 0.7 Fe 0.25 Mg 0.01 V 0.01 W 0.01 Zn 0.01 Al 0.01 PO4 was placed in a graphite crucible and heated to 450℃ in a nitrogen atmosphere box furnace (oxygen content less than 10 ppm) at a heating rate of 10℃ / min and held for 3 hours to prepare a low-sulfur cation-doped manganese iron pyrophosphate precursor ((Mn) 0.7 Fe 0.25 Mg 0.01 V 0.01 W 0.01 Zn 0.01 Al 0.01 )2P2O7).

[0129] 2. Carbon-coated modified lithium manganese iron phosphate (LiMn) 0.7 Fe 0.25 Mg 0.01 V 0.01 W 0.01 Zn 0.01 Al 0.01 Preparation of PO4

[0130] Weigh the corresponding lithium carbonate, lithium dihydrogen phosphate, and low-sulfur cation-doped manganese iron pyrophosphate precursor (Mn) with a molar ratio of Li:P:(Mn+Fe+Mg+V+W+Zn+Al) of 1.08:1.04:1. 0.7 Fe 0.25 Mg 0.01 V 0.01 W 0.01 Zn 0.01 Al0.01 )2P2O7and polyethylene glycol and glucose (5.9 wt% low-sulfur cation-doped manganese iron pyrophosphate precursor, and the mass ratio of polyethylene glycol and glucose is 3:1) are dispersed in ultrapure water and ethanol (the volume ratio of ultrapure water and ethanol is 2:1) to obtain a slurry with a solid content of 38%, and the slurry is subjected to coarse grinding and fine grinding to a particle size D 50 of 0.39 μm using a horizontal sand mill system, and then the slurry is transferred to a spray granulation dryer for spray drying to obtain a spray powder. Subsequently, the spray powder is subjected to staged temperature sintering using an atmosphere box furnace under a nitrogen protective atmosphere, and the temperature is raised to 550°C at a rate of 5°C / min and maintained for 5 h, and then the temperature is raised to 720°C at a rate of 10°C / min and maintained for 9 h. After the atmosphere box furnace is naturally cooled to room temperature, a carbon-coated modified lithium manganese iron phosphate (LiMn 0.7 Fe 0.25 Mg 0.01 V 0.01 W 0.01 Zn 0.01 Al 0.01 PO4) is obtained.

[0131] 3. Preparation of a lithium ion battery

[0132] The carbon-coated modified lithium manganese iron phosphate obtained above, a conductive agent carbon black, and a binder polyvinylidene fluoride are dissolved in N-methylpyrrolidone dispersant in a mass ratio of 94:3:3, mixed uniformly to obtain a positive electrode slurry, and then coated on an aluminum foil. After vacuum drying at 105°C for 24 h, a lithium ion battery positive electrode is obtained.

[0133] A lithium ion battery is assembled in an argon-filled glove box. The positive electrode is the lithium ion battery positive electrode described above, the negative electrode is a metal lithium sheet, the separator is a polyethylene film, and the electrolyte is prepared by dissolving 1 mol / L of LiPF6 in a mixed solvent of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethylene carbonate (EC) in a volume ratio of 1:1:1.

[0134] Example 3: A low-sulfur cation-doped manganese iron pyrophosphate precursor, a carbon-coated modified lithium manganese iron phosphate, a lithium ion battery, and a preparation method thereof

[0135] 1. Preparation of a low-sulfur cation-doped manganese iron pyrophosphate precursor (Mn 0.4 Fe 0.55 Ti 0.02 V 0.03 )2P2O7

[0136] Into a nitrogen purged dissolving tank, 1.68 kg of manganese sulfate monohydrate, 147.3 g of ammonium titanyl oxalate, and 199.2 g of vanadium oxalate were dissolved to prepare a 2 mol / L mixed metal salt solution I.

[0137] Into a closed synthesis reactor containing 19.1 L of ultrapure water, 766 g of iron powder was added, and the temperature of the reactor was set to 50°C. Nitrogen was introduced into the reactor, and stirring was performed at a speed of 800 r / min for 10 min. Then, 2.87 kg of 85 wt% concentrated phosphoric acid solution was slowly pumped into the reactor, and uniform stirring was performed for 3 h to form a ferrous phosphate solution system II. Subsequently, the temperature of the reactor was increased to 72°C, and after the temperature of the system was stabilized, the mixed metal source solution I was slowly pumped into the ferrous phosphate solution system II in the form of a 2:1 molar ratio of metal to hydrogen peroxide (1.54 kg of 27.5 wt% hydrogen peroxide). After the two were completely pumped into the ferrous phosphate solution system II to form an intermediate system III, the intermediate system III was fully stirred and reacted for 30 min. Then, 76.9 g of 27.5 wt% hydrogen peroxide solution was pumped into the intermediate system III at the same feeding rate as above to form an intermediate system IV. Ammonia water was used to adjust the pH of the system IV to 7, and then the intermediate system IV was aged at 72°C for 2 h. Finally, the obtained slurry was pressure-filtered using a vertical pressure filter to obtain a filter cake, which was washed with high-purity water until the conductivity of the washing water was 153 μs / cm, and then subjected to flash evaporation treatment to obtain a dry metal cation-doped manganese iron ammonium phosphate precursor (NH4Mn 0.4 Fe 0.55 Ti 0.02 V 0.03 PO4)。

[0138] Under a nitrogen protective atmosphere, the metal cation-doped manganese iron ammonium phosphate precursor NH4Mn 0.4 Fe 0.55 Ti 0.02 V 0.03 PO4) prepared above was put into a high-efficiency closed synthesis reactor with 20 L of ultrapure water as a base liquid to disperse and form a slurry. An 85 wt% concentrated phosphoric acid solution was slowly pumped into the precursor slurry in the reactor at a molar ratio of precursor: phosphoric acid = 2:1, and stirring was performed for 30 min to obtain an intermediate system V. Then, ammonia water was used to adjust the pH of the system V to 7, and the system V was aged for 4 h. Finally, the obtained slurry was pressure-filtered using a vertical pressure filter to obtain a filter cake, which was washed with high-purity water until the conductivity of the washing water was 126 μs / cm, and then subjected to flash evaporation treatment to obtain a low-sulfur metal cation-doped manganese iron ammonium phosphate precursor (NH4Mn 0.4 Fe 0.55 Ti 0.02 V 0.03 PO4)。

[0139] A low-sulfur type cation-doped ammonium manganese iron phosphate precursor NH4Mn 0.4 Fe 0.55 Ti 0.02 V 0.03 PO4was placed in a graphite crucible and heated to 500℃ at a heating rate of 10℃ / min in a nitrogen atmosphere box furnace (oxygen content less than 10ppm) for 3h to prepare a low-sulfur type cation-doped ammonium manganese iron pyrophosphate precursor ((Mn 0.4 Fe 0.55 Ti 0.02 V 0.03 )2P2O7).

[0140] 2. Preparation of carbon-coated modified lithium manganese iron phosphate LiMn 0.4 Fe 0.55 Ti 0.02 V 0.03 PO4

[0141] The corresponding lithium carbonate, lithium dihydrogen phosphate, low-sulfur type cation-doped ammonium manganese iron pyrophosphate precursor ((Mn 0.4 Fe 0.55 Ti 0.02 V 0.03 )2P2O7) and polyethylene glycol and glucose (5.9wt% low-sulfur type cation-doped ammonium manganese iron pyrophosphate precursor, and the mass ratio of polyethylene glycol and glucose is 4:1) were weighed in a ratio of 1.06:1.02:1 of Li:P:(Mn+Fe+Ti+V) by mole, and dispersed in ultrapure water and ethanol (volume ratio of ultrapure water and ethanol is 2:1) to obtain a slurry with a solid content of 38%. The slurry was ground coarsely and finely to a particle size D 50 =0.37μm using a horizontal sand mill system, and then transferred to a spray granulation dryer for spray drying to obtain a spray powder. Subsequently, the spray powder was subjected to stepwise temperature sintering using an atmosphere box furnace under a nitrogen protective atmosphere, and heated to 500℃ at a heating rate of 5℃ / min for 5h, and then heated to 700℃ at a heating rate of 10℃ / min for 9h. After the atmosphere box furnace was naturally cooled to room temperature, a carbon-coated modified lithium manganese iron phosphate (LiMn 0.4 Fe 0.55 Ti 0.02 V 0.03 PO4) was obtained.

[0142] 3. Preparation of a lithium ion battery

[0143] The above-obtained carbon-coated modified lithium manganese iron phosphate was dissolved in N-methyl pyrrolidone dispersant and mixed uniformly with a conductive agent carbon black and a binder polyvinylidene fluoride in a mass ratio of 94:3:3 to obtain a positive electrode slurry, which was then coated on an aluminum foil. After vacuum drying at 105℃ for 24h, a lithium ion battery positive electrode was obtained.

[0144] The button lithium ion battery was assembled in a glove box filled with argon, the positive electrode was the above-mentioned lithium ion battery positive electrode, the negative electrode was a metal lithium sheet, the separator was a polyethylene film, and the electrolyte was prepared by dissolving 1 mol / L of LiPF6 in a mixed solvent of dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethylene carbonate (EC) in a volume ratio of 1:1:1.

[0145] Example 4 A low-sulfur cation-doped manganese iron pyrophosphate precursor, carbon-coated modified manganese iron lithium phosphate, lithium ion battery and preparation method thereof

[0146] 1. Preparation of a low-sulfur cation-doped manganese iron pyrophosphate precursor (Mn 0.6 Fe 0.35 Ti 0.05 )2P2O7

[0147] Into a nitrogen-purged dissolving tank, ultrapure water was added, and 3.96 kg of manganese sulfate monohydrate and 539.2 g of ammonium titanium oxalate were dissolved in the above-mentioned dissolving tank to prepare a 1 mol / L metal salt mixed solution I.

[0148] Into a closed synthesis reactor containing 22.3 L of ultrapure water, 766 g of iron powder was added, the temperature of the reactor was set to 40℃, nitrogen was introduced into the reactor and stirred at a speed of 800 r / min for 10 min, then 4.51 kg of 85wt% concentrated phosphoric acid solution was slowly pumped into the reactor, and stirred uniformly for 3 h to form a ferrous biphosphate solution system II. Then the reactor was heated to 78℃, and after the temperature of the system was stabilized, the metal: hydrogen peroxide (2.42 kg of 27.5wt%) in the above-mentioned mixed metal source solution I was slowly pumped into the ferrous biphosphate solution system II in a molar ratio of 2:1, and after the two were completely pumped into the ferrous biphosphate solution system II to form an intermediate system III, the intermediate system III was fully stirred and reacted for 30 min, and then 120.8 g of 27.5wt% hydrogen peroxide solution was pumped in at the same feeding rate as above to form an intermediate system IV. Ammonia water was used to adjust the pH of the system IV to 7.2, and then the intermediate system IV was aged at 78℃ for 2 h. Finally, the obtained slurry was pressure-filtered using a vertical pressure filter to obtain a filter cake, which was washed with high-purity water until the conductivity of the washing water was 141 μs / cm, and then subjected to flash evaporation treatment to obtain a dry metal cation-doped manganese iron ammonium phosphate precursor (NH4Mn 0.6 Fe 0.35 Ti 0.05 PO4).

[0149] Under a nitrogen protective atmosphere, the above-mentioned prepared metal cation-doped manganese iron ammonium phosphate precursor NH4Mn 0.6 Fe 0.35 Ti 0.05PO4) was prepared by placing the low-sulfur cation-doped manganese iron ammonium phosphate precursor (NH4Mn 0.6 Fe 0.35 Ti 0.05 PO4) into a graphite crucible and heating it in a nitrogen atmosphere box furnace (oxygen content less than 10 ppm) at a heating rate of 10°C / min to 480°C for 3h.

[0150] The low-sulfur cation-doped manganese iron ammonium phosphate precursor (NH4Mn 0.6 Fe 0.35 Ti 0.0 PO4) was placed in a graphite crucible and heated in a nitrogen atmosphere box furnace (oxygen content less than 10 ppm) at a heating rate of 10°C / min to 480°C for 3h to prepare the low-sulfur cation-doped manganese iron pyrophosphate precursor ((Mn 0.6 Fe 0.35 Ti 0.05 )2P2O7).

[0151] 2. Preparation of carbon-coated modified lithium manganese iron phosphate LiMn 0.6 Fe 0.35 Ti 0.05 PO4

[0152] The corresponding lithium carbonate, lithium dihydrogen phosphate, low-sulfur cation-doped manganese iron pyrophosphate precursor (Mn 0.6 Fe 0.35 Ti 0.05 )2P2O7, and polyethylene glycol and glucose (7.2wt% low-sulfur cation-doped manganese iron pyrophosphate precursor, and the mass ratio of polyethylene glycol and glucose is 2.5:1) were weighed in a ratio of Li:P:(Mn+Fe+Ti) molar ratio of 1.02:1.02:1, and dispersed in ultrapure water and ethanol (volume ratio of ultrapure water and ethanol is 2:1) to obtain a slurry with a solid content of 38%, and the above slurry was ground by a horizontal sand mill system to a particle size D 50When the particle size is 0.38 μm, the slurry is transferred to a spray granulation dryer for spray drying to obtain spray powder. Subsequently, the spray powder is subjected to staged temperature rising sintering in an atmosphere box furnace under a nitrogen protective atmosphere, and is heated to 520°C at a heating rate of 5°C / min for 5 h, and then heated to 760°C at a heating rate of 10°C / min for 9 h. After the atmosphere box furnace is naturally cooled to room temperature, the obtained furnace sintered powder is sieved to obtain carbon-coated modified lithium manganese iron phosphate (LiMn 0.6 Fe 0.35 Ti 0.05 PO4).

[0153] 3. Preparation of a lithium ion battery

[0154] The carbon-coated modified lithium manganese iron phosphate obtained above, carbon black as a conductive agent, and polyvinylidene fluoride as a binder are dissolved in N-methyl pyrrolidone dispersant in a mass ratio of 94:3:3, mixed uniformly to obtain a positive electrode slurry, which is then coated on an aluminum foil. After vacuum drying at 105°C for 24 h, a lithium ion battery positive electrode is obtained.

[0155] A lithium ion battery is assembled in an argon-filled glove box. The positive electrode is the lithium ion battery positive electrode described above, the negative electrode is a lithium metal sheet, the separator is a polyethylene film, and the electrolyte is prepared by dissolving 1 mol / L of LiPF6 in a mixed solvent of dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethylene carbonate (EC) in a volume ratio of 1:1:1.

[0156] Comparative Example 1: A cation-doped manganese iron pyrophosphate precursor, carbon-coated modified lithium manganese iron phosphate, lithium ion battery and preparation method thereof

[0157] The difference from Example 1 is that in Step 1, the ammonium manganese phosphate precursor is not treated with an appropriate amount of phosphoric acid source, i.e., a low-sulfur cation-doped ammonium manganese phosphate precursor NH4Mn 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 PO4.

[0158] 1. Preparation of a cation-doped manganese iron pyrophosphate precursor (Mn 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 )2P2O7

[0159] Into a nitrogen purged dissolving tank, 16.81 kg of manganese sulfate monohydrate, 730.9 g of sodium tungstate, 664 g of vanadium oxalate, 1338.1 g of niobium oxalate, 236.8 g of anhydrous magnesium chloride, and 161.5 g of anhydrous cobalt chloride were dissolved to prepare a 3 mol / L mixed metal salt solution I.

[0160] Into a closed synthesis reactor containing 8.2 L of ultrapure water, 766 g of iron powder was added, and the temperature of the reactor was set to 40°C. Nitrogen was introduced into the reactor, and stirring was carried out at a speed of 800 r / min for 10 min. Then, 14.34 kg of 85 wt% concentrated phosphoric acid solution was slowly pumped into the reactor, and uniform stirring was carried out for 3 h to form a ferrous phosphate dihydrogen solution system II. Subsequently, the reactor was heated to 76°C, and after the temperature of the system was stabilized, the mixed metal source solution I was slowly pumped into the ferrous phosphate dihydrogen solution system II in the form of a 2:1 molar ratio of metal to hydrogen peroxide (7.69 kg of 27.5 wt% hydrogen peroxide). After the two were completely pumped into the ferrous phosphate dihydrogen solution system II to form an intermediate system III, the intermediate system III was fully stirred and reacted for 30 min. Then, 384.4 g of 27.5 wt% hydrogen peroxide solution was pumped in at the same feeding rate as above to form an intermediate system IV. Ammonia water was used to adjust the pH of the system IV to 7.3, and then the intermediate system IV was aged at 76°C for 2 h. Finally, the obtained slurry was pressure-filtered using a vertical pressure filter to obtain a filter cake, which was washed with high-purity water until the conductivity of the washing water was 125 μs / cm, and then subjected to flash evaporation treatment to obtain a dry metal cation-doped manganese iron ammonium phosphate precursor (NH4Mn 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 PO4)。

[0161] The metal cation-doped manganese iron ammonium phosphate precursor NH4Mn 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 PO4 was placed in a graphite crucible and heated in a nitrogen atmosphere box furnace (oxygen content less than 10 ppm) at a heating rate of 10°C / min to 450°C for 2 h to prepare a cation-doped manganese iron pyrophosphate precursor ((Mn 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 )2P2O7).

[0162] 2. Carbon-coated modified lithium manganese iron phosphate LiMn 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 PO4

[0163] The corresponding lithium carbonate, lithium dihydrogen phosphate, cation-doped manganese iron pyrophosphate precursor (Mn 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0. 01 The above slurry is transferred to a spray granulation dryer for spray drying when the particle size D 50 is 0.38 pm, and the spray powder is obtained. Subsequently, the spray powder is subjected to stepwise temperature sintering using an atmosphere box furnace under a nitrogen protective atmosphere, and is heated to 500°C at a heating rate of 5°C / min for 4 h, and then heated to 760°C at a heating rate of 10°C / min for 10 h. After the atmosphere box furnace is naturally cooled to room temperature, carbon-coated modified lithium manganese iron phosphate (LiMn 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 PO4) is obtained.

[0164] 3. Preparation of a lithium ion battery

[0165] The above-obtained carbon-coated modified lithium manganese iron phosphate, conductive agent carbon black, and binder polyvinylidene fluoride are dissolved in N-methyl pyrrolidone dispersant in a mass ratio of 94:3:3, mixed uniformly to obtain a positive electrode slurry, and then coated on an aluminum foil. After vacuum drying at 105°C for 24 h, a lithium ion battery positive electrode is obtained.

[0166] The button lithium ion battery was assembled in an argon-filled glove box, the positive electrode was the above lithium ion battery positive electrode, the negative electrode was a metal lithium sheet, the separator was a polyethylene film, and the electrolyte was prepared by dissolving 1 mol / L of LiPF6 in a mixed solvent of dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethylene carbonate (EC) in a volume ratio of 1:1:1.

[0167] A cation-doped manganese iron pyrophosphate precursor, a carbon-coated modified manganese iron lithium phosphate, a lithium ion battery and a preparation method thereof

[0168] The difference from Example 2 is that in step 1, the ammonium manganese iron phosphate precursor is not treated with an appropriate amount of phosphoric acid source, i.e., a low-sulfur cation-doped ammonium manganese iron phosphate precursor NH4Mn 0.7 Fe 0.25 Mg 0.01 V 0.0 1W 0.01 Zn 0.01 Al 0.01 PO4.

[0169] 1. Preparation of a cation-doped manganese iron pyrophosphate precursor (Mn 0.7 Fe 0.25 Mg 0.01 V 0.01 W 0.01 Zn 0.01 Al 0.01 )2P2O7

[0170] Into a nitrogen-purged dissolving tank, ultrapure water was added, and 6.47 kg of manganese sulfate monohydrate, 65.9 g of magnesium sulfate, 146.1 g of vanadium oxalate, 160.8 g of sodium tungstate, 88.3 g of zinc sulfate and 187.2 g of aluminum sulfate were dissolved in the above dissolving tank to prepare a 2 mol / L metal salt mixed solution I.

[0171] Into a closed synthesis reactor containing 16.2 L of ultrapure water, 766 g of iron powder was added. The temperature of the reactor was set to 45 °C. Nitrogen was bubbled into the reactor and stirred at a speed of 800 rpm for 10 min. Then, 6.31 kg of 85 wt% phosphoric acid solution was slowly pumped into the reactor, and stirred uniformly for 3 h to form a ferrous phosphate solution system II. Subsequently, the reactor was heated to 75 °C. After the temperature of the system was stabilized, the aforementioned mixed metal source solution I was slowly pumped into the ferrous phosphate solution system II in the form of a 2:1 molar ratio of metal to hydrogen peroxide (3.38 kg of 27.5 wt%). After the two were completely pumped into the ferrous phosphate solution system II to form an intermediate system III, the intermediate system III was stirred and reacted for 30 min. Then, 169.1 g of 27.5 wt% hydrogen peroxide solution was pumped into the intermediate system IV at the same feeding rate as described above. The system IV was adjusted to a pH of 7.8 using ammonia water, and then the intermediate system IV was aged at 75 °C for 2 h. Finally, the obtained slurry was pressure-filtered using a vertical pressure filter to obtain a filter cake, which was washed with high-purity water until the conductivity of the washing water was 144 μ8 / cm, and then subjected to flash evaporation treatment to obtain a dry metal cation-doped ammonium manganese iron phosphate precursor (NH4Mn 0.7 Fe 0.25 Mg 0.01 V 0.01 W 0.01 Zn 0.01 Al 0.01 PO4)。

[0172] The metal cation-doped ammonium manganese iron phosphate precursor NH4Mn 0.7 Fe 0.25 Mg 0.01 V 0.01 W 0.01 Zn 0.01 Al 0.01 PO4was placed in a graphite crucible and heated in a nitrogen atmosphere box furnace (oxygen content less than 10 ppm) at a heating rate of 10 °C / min to 450 °C for 3 h to prepare a cation-doped manganese iron pyrophosphate precursor ((Mn 0.7 Fe 0.25 Mg 0.01 V 0.01 W 0.01 Zn 0.01 Al 0.01 )2P2O7)。

[0173] 2. Carbon-coated modified lithium manganese iron phosphate LiMn 0.7 Fe 0.25 Mg 0.01 V 0.01 W 0.01 Zn 0.01 Al 0.01Preparation of PO4

[0174] The corresponding lithium carbonate, lithium dihydrogen phosphate, cation-doped manganese iron pyrophosphate precursor (Mn 0.7 Fe 0.25 Mg 0.01 V 0.01 W 0.01 Zn 0.01 Al 0.01 )2P2O7, and polyethylene glycol and glucose (5.9wt% of the cation-doped manganese iron pyrophosphate precursor, and the mass ratio of polyethylene glycol and glucose is 3:1) were weighed in a proportion of 1.08:1.04:1 of the molar ratio of Li:P:(Mn+Fe+Mg+V+W+Zn+Al), and dispersed in ultrapure water and ethanol (volume ratio of ultrapure water and ethanol is 2:1) to obtain a slurry with a solid content of 38%. The slurry was subjected to coarse grinding and fine grinding using a horizontal sand mill system to a particle size D 50 = 0.39μm, and then transferred to a spray granulation dryer for spray drying to obtain a spray powder. Subsequently, the spray powder was subjected to staged temperature rising sintering using an atmosphere box furnace under a nitrogen protective atmosphere, and heated to 550℃ at a heating rate of 5℃ / min for 5h, and then heated to 720℃ at a heating rate of 10℃ / min for 9h. After the atmosphere box furnace was naturally cooled to room temperature, a carbon-coated modified lithium manganese iron phosphate (LiMn 0.7 Fe 0.25 Mg 0.01 V 0.01 W 0.01 Zn 0.01 Al 0.01 PO4) was obtained.

[0175] 3. Preparation of a lithium ion battery

[0176] The carbon-coated modified lithium manganese iron phosphate obtained above, carbon black as a conductive agent, and polyvinylidene fluoride as a binder were dissolved in N-methyl pyrrolidone dispersant in a mass ratio of 94:3:3, and uniformly mixed to obtain a positive electrode slurry, which was then coated on an aluminum foil. After vacuum drying at 105℃ for 24h, a lithium ion battery positive electrode was obtained.

[0177] A lithium ion battery was assembled in an argon-filled glove box. The positive electrode was the lithium ion battery positive electrode described above, the negative electrode was a lithium metal sheet, the separator was a polyethylene film, and the electrolyte was prepared by dissolving 1mol / L of LiPF6 in a mixed solvent of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethylene carbonate (EC) in a volume ratio of 1:1:1.

[0178] A cation-doped manganese iron pyrophosphate precursor, a carbon-coated modified lithium manganese iron phosphate, a lithium ion battery, and a method for preparing the same

[0179] The difference from Example 3 is that in Step 1, the manganese iron ammonium phosphate precursor is not doped with metal cations by treating with an appropriate amount of phosphoric acid source, i.e., a low-sulfur cation-doped manganese iron ammonium phosphate precursor NH4Mn 0.4 Fe 0.55 Ti 0.02 V 0.03 PO4.

[0180] 1. Preparation of a cation-doped manganese iron pyrophosphate precursor (Mn 0.4 Fe 0.55 Ti 0.02 V 0.03 )2P2O7

[0181] Into a nitrogen-purged dissolving tank, 1.68 kg of manganese sulfate monohydrate, 137.3 g of oxotitanium ammonium oxalate, and 199.2 g of vanadium oxalate were dissolved to prepare a 2 mol / L metal salt mixed solution I.

[0182] 766 g of iron powder was added to a closed synthesis reactor containing 19.1 L of ultrapure water, and the temperature of the reactor was set to 50°C. Nitrogen was introduced into the reactor and stirred at a speed of 800 r / min for 10 min. Then, 2.87 kg of 85 wt% concentrated phosphoric acid solution was slowly pumped into the reactor, and stirred uniformly for 3 h to form a ferrous phosphate dihydrogen solution system II. Then, the reactor was heated to 72°C, and after the temperature of the system was stabilized, the metal: hydrogen peroxide (1.54 kg of 27.5 wt%) in the mixed metal source solution I was slowly pumped into the ferrous phosphate dihydrogen solution system II at a molar ratio of 2:1. After the two were completely pumped into the ferrous phosphate dihydrogen solution system II to form an intermediate system III, the intermediate system III was fully stirred and reacted for 30 min. Then, 76.9 g of 27.5 wt% hydrogen peroxide solution was pumped in at the same feeding rate as above to form an intermediate system IV. The system IV was adjusted to pH 7 using ammonia water, and then the intermediate system IV was aged at 72°C for 2 h. Finally, the obtained slurry was pressure-filtered using a vertical pressure filter to obtain a filter cake, which was washed with high-purity water until the conductivity of the washing water was 153 μs / cm, and then subjected to flash evaporation treatment to obtain a dry metal cation-doped manganese iron ammonium phosphate precursor (NH4Mn 0.4 Fe 0.55 Ti 0.02 V 0.03 PO4).

[0183] The metal cation-doped manganese iron ammonium phosphate precursor NH4Mn 0.4 Fe 0.55 Ti 0.02 V 0.03PO4 was placed in a graphite crucible and heated to 500°C at a heating rate of 10°C / min in a nitrogen atmosphere box furnace (oxygen content less than 10 ppm) for 3 h to prepare a cation-doped manganese iron pyrophosphate precursor ((Mn 0.4 Fe 0.55 Ti 0.02 V 0.03 )2P2O7).

[0184] 2. Preparation of carbon-coated modified manganese iron lithium phosphate LiMn 0.4 Fe 0.55 Ti 0.02 V 0.03 PO4

[0185] The corresponding lithium carbonate, lithium dihydrogen phosphate, cation-doped manganese iron pyrophosphate precursor (Mn 0.4 Fe 0.55 Ti 0.02 V 0.03 )2P2O7, and polyethylene glycol and glucose (5.9 wt% cation-doped manganese iron pyrophosphate precursor, and the mass ratio of polyethylene glycol and glucose is 4:1) were weighed in a molar ratio of Li:P:(Mn+Fe+Ti+V) of 1.06:1.02:1, and dispersed in ultrapure water and ethanol (volume ratio of ultrapure water and ethanol is 2:1) to obtain a slurry with a solid content of 38%. The slurry was subjected to coarse grinding and fine grinding to a particle size D 50 = 0.37 μm using a horizontal sand mill system, and then transferred to a spray granulation dryer for spray drying to obtain a spray powder. Subsequently, the spray powder was subjected to stepwise temperature sintering using an atmosphere box furnace under a nitrogen protective atmosphere, and heated to 500°C at a heating rate of 5°C / min for 5 h, and then heated to 700°C at a heating rate of 10°C / min for 9 h. After the atmosphere box furnace was naturally cooled to room temperature, carbon-coated modified manganese iron lithium phosphate (LiMn 0.4 Fe 0.55 Ti 0.02 V 0.03 PO4) was obtained.

[0186] 3. Preparation of a lithium ion battery

[0187] The above-obtained carbon-coated modified manganese iron lithium phosphate was mixed with conductive agent carbon black and binder polyvinylidene fluoride in a mass ratio of 94:3:3 in N-methyl pyrrolidone dispersant to obtain a positive electrode slurry, which was then coated on an aluminum foil. After vacuum drying at 105°C for 24 h, a lithium ion battery positive electrode was obtained.

[0188] The button lithium ion battery was assembled in a glove box filled with argon, the positive electrode was the above lithium ion battery positive electrode, the negative electrode was a metal lithium sheet, the separator was a polyethylene film, and the electrolyte was prepared by dissolving 1 mol / L of LiPF6 in a mixed solvent of dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethylene carbonate (EC) in a volume ratio of 1:1:1.

[0189] A low-sulfur cation-doped ammonium manganese iron phosphate precursor, a carbon-coated modified lithium manganese iron phosphate, a lithium ion battery and a preparation method thereof

[0190] The difference from Example 1 is that in step 2, the low-sulfur cation-doped ammonium manganese iron phosphate precursor is directly used to prepare the carbon-coated modified lithium manganese iron phosphate.

[0191] 1. Preparation of a low-sulfur cation-doped ammonium manganese iron phosphate precursor NH4Mn 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 PO4

[0192] Into a nitrogen-purged dissolving tank, 16.81 kg of manganese sulfate monohydrate, 730.9 g of sodium tungstate, 664 g of vanadium oxalate, 1338.1 g of niobium oxalate, 236.8 g of anhydrous magnesium chloride, and 161.5 g of anhydrous cobalt chloride were dissolved to prepare a 3 mol / L metal salt mixed solution I.

[0193] 766 g of iron powder was added to a closed synthesis reactor containing 8.2 L of ultrapure water, and the temperature of the reactor was set to 40℃. Nitrogen was introduced into the reactor and stirred at a speed of 800 r / min for 10 min. Then, 14.34 kg of 85wt% concentrated phosphoric acid solution was slowly pumped into the reactor, and uniformly stirred for 3 h to form a ferrous phosphate dihydrogen solution system II. Then, the reactor was heated to 76℃, and after the temperature of the system was stabilized, the metal: hydrogen peroxide (7.69 kg of 27.5wt%) in the mixed metal source solution I was slowly pumped into the ferrous phosphate dihydrogen solution system II at a molar ratio of 2:1. After the two were completely pumped into the ferrous phosphate dihydrogen solution system II to form an intermediate system III, the intermediate system III was fully stirred and reacted for 30 min. Then, 384.4 g of 27.5wt% hydrogen peroxide solution was pumped in at the same rate to form an intermediate system IV. Ammonia water was used to adjust the pH of the system IV to 7.3, and then the intermediate system IV was aged at 76℃ for 2 h. Finally, the obtained slurry was pressure-filtered using a vertical pressure filter to obtain a filter cake, which was washed with high-purity water until the conductivity of the washing water was 125 μs / cm, and then subjected to flash evaporation treatment to obtain a dry metal cation-doped ammonium manganese iron phosphate precursor (NH4Mn0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 PO4).

[0194] Under a nitrogen protective atmosphere, the aforementioned metal cation-doped manganese iron ammonium phosphate precursor NH4Mn was subjected to... 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 The PO4 precursor was added to a high-efficiency sealed reactor with 20L of ultrapure water as the base solution and dispersed to form a slurry. An 85wt% concentrated phosphoric acid solution was slowly pumped into the precursor slurry at a precursor:phosphoric acid molar ratio of 2:1 and stirred for 30 min to obtain intermediate system V. Then, intermediate system V was adjusted to pH 7.3 using ammonia water and aged for 4 h. Finally, the obtained slurry was filtered using a vertical filter press to obtain a filter cake, which was washed with high-purity water until the wash water conductivity reached 108 μS / cm. The cake was then subjected to flash evaporation to obtain a low-sulfur cationic doped manganese iron ammonium phosphate precursor (NH4Mn). 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 PO4).

[0195] 2. Carbon-coated modified lithium manganese iron phosphate (LiMn) 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 Preparation of PO4

[0196] Weigh the corresponding lithium carbonate, lithium dihydrogen phosphate, and low-sulfur cation-doped manganese iron pyrophosphate precursor NH4Mn according to the molar ratio of Li:P:(Mn+Fe+W+V+Nb+Mg+Co) of 1.1:1.03:1. 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01PO4and polyethylene glycol and glucose (6.5wt% low-sulfur cation-doped manganese iron pyrophosphate precursor, and the mass ratio of polyethylene glycol and glucose is 2:1) are dispersed in ultrapure water and ethanol (the volume ratio of ultrapure water and ethanol is 2:1) to obtain a slurry with a solid content of 35%, and the slurry is subjected to coarse grinding and fine grinding to a particle size D 50 When the particle size D 0.8 Fe 0.11 W 0.02 V 0.02 Nb 0.02 Mg 0.02 Co 0.01 PO4) is 0.28μm, the slurry is transferred to a spray granulation dryer for spray drying to obtain a spray powder. Subsequently, the spray powder is subjected to staged temperature sintering using an atmosphere box furnace under a nitrogen protective atmosphere, and is heated to 500℃ at a heating rate of 5℃ / min for 4h, and then heated to 760℃ at a heating rate of 10℃ / min for 10h. After the atmosphere box furnace is naturally cooled to room temperature, a carbon-coated modified lithium manganese iron phosphate (LiMn 0.71 Fe 0.11 W 0.04 V 0.04 Nb 0.04 Mg 0.04 Co 0.02 )2P2O7is prepared

[0197] 3. Preparation of a lithium ion battery

[0198] The carbon-coated modified lithium manganese iron phosphate obtained above, a conductive agent carbon black, and a binder polyvinylidene fluoride are dissolved in N-methyl pyrrolidone dispersant at a mass ratio of 94:3:3 to obtain a positive electrode slurry, which is then coated on an aluminum foil. After vacuum drying at 105℃ for 24h, a lithium ion battery positive electrode is obtained.

[0199] A lithium ion battery is assembled in an argon-filled glove box. The positive electrode is the lithium ion battery positive electrode described above, the negative electrode is a metal lithium sheet, the separator is a polyethylene film, and the electrolyte is prepared by dissolving 1mol / L of LiPF6 in a mixed solvent of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethylene carbonate (EC) at a volume ratio of 1:1:1.

[0200] Preparation of a low-sulfur cation-doped manganese iron pyrophosphate precursor, a carbon-coated modified lithium manganese iron phosphate, and a lithium ion battery

[0201] The difference from Example 1 is that in step 1, an excess amount of cation doping is used to prepare a low-sulfur cation-doped manganese iron pyrophosphate precursor.

[0202] 1. Preparation of a low-sulfur cation-doped manganese iron pyrophosphate precursor (Mn 0.71 Fe 0.11 W 0.04 V 0.04 Nb 0.04 Mg 0.04 Co 0.02 )2P2O7

[0203] Into a nitrogen purged dissolving tank, 14.92 kg of manganese sulfate monohydrate, 1461.5 g of sodium tungstate, 1327.9 g of vanadium oxalate, 1338.1 g of niobium oxalate, 473.6 g of anhydrous magnesium chloride, and 322.9 g of anhydrous cobalt chloride were dissolved to prepare a 3 mol / L mixed metal salt solution I.

[0204] Into a closed synthesis reactor containing 8.2 L of ultrapure water, 766 g of iron powder was added, and the temperature of the reactor was set to 40°C. Nitrogen was purged into the reactor, and the reactor was stirred at a speed of 800 r / min for 10 min. Then, 14.34 kg of 85 wt% concentrated phosphoric acid solution was slowly pumped into the reactor, and the mixture was stirred uniformly for 3 h to form a ferrous phosphate dihydrogen solution system II. Subsequently, the temperature of the reactor was increased to 76°C, and after the temperature of the system was stabilized, the mixed metal source solution I was slowly pumped into the ferrous phosphate dihydrogen solution system II in the form of a 2:1 molar ratio of metal to hydrogen peroxide (7.69 kg of 27.5 wt% hydrogen peroxide). After the two were completely pumped into the ferrous phosphate dihydrogen solution system II to form an intermediate system III, the intermediate system III was stirred and reacted for 30 min. Then, 384.4 g of 27.5 wt% hydrogen peroxide solution was pumped into the intermediate system IV at the same feeding rate as described above. The pH of the intermediate system IV was adjusted to 7.3 using ammonia water, and then the intermediate system IV was aged at 76°C for 2 h. Finally, the obtained slurry was pressure-filtered using a vertical pressure filter to obtain a filter cake, which was washed with high-purity water until the conductivity of the washing water was 167 μs / cm, and then subjected to flash evaporation treatment to obtain a dry metal cation-doped manganese iron ammonium phosphate precursor (NH4Mn 0.71 Fe 0.11 W 0.04 V 0.04 Nb 0.04 Mg 0.04 Co 0.02 PO4).

[0205] Under a nitrogen protective atmosphere, the metal cation-doped manganese iron ammonium phosphate precursor NH4Mn 0.71 Fe 0.11 W 0.04 V 0.04 Nb 0.04 Mg 0.04 Co 0.02The low-sulfur cation-doped manganese iron ammonium phosphate precursor (NH4Mn 0.7 1Fe 0.11 W 0.04 V 0.04 Nb 0.04 Mg 0.04 Co 0.02 PO4) is prepared by placing the low-sulfur cation-doped manganese iron ammonium phosphate precursor (NH4Mn

[0206] The low-sulfur cation-doped manganese iron ammonium phosphate precursor (NH4Mn 0.71 Fe 0.11 W 0.04 V 0.04 Nb 0.04 Mg 0.04 Co 0.02 PO4) is placed in a graphite crucible and heated to 400°C at a heating rate of 10°C / min in a nitrogen atmosphere box furnace (oxygen content less than 10 ppm) for 2 h to prepare a low-sulfur cation-doped manganese iron pyrophosphate precursor ((Mn 0.71 Fe 0.11 W 0.04 V 0.04 Nb 0.0 4Mg 0.04 Co 0.02 )2P2O7).

[0207] 2. Preparation of carbon-coated modified lithium manganese iron phosphate LiMn 0.71 Fe 0.11 W 0.04 V 0.04 Nb 0.04 Mg 0.04 Co 0.02 PO4

[0208] The corresponding lithium carbonate, lithium dihydrogen phosphate, and low-sulfur cation-doped manganese iron pyrophosphate precursor (Mn 0.71 Fe 0.11 W 0.04 V 0.04 Nb 0.04 Mg 0.04 Co0.02 )2P2O7 and polyethylene glycol and glucose (6.5wt% low-sulfur cation-doped manganese iron pyrophosphate precursor, and the mass ratio of polyethylene glycol and glucose is 3:1) are dispersed in ultrapure water and ethanol (the volume ratio of ultrapure water and ethanol is 2:1) to obtain a slurry with a solid content of 35%, and the slurry is subjected to coarse grinding and fine grinding to a particle size D 50 of 0.28μm using a horizontal sand mill system, and then the slurry is transferred to a spray granulation dryer for spray drying to obtain a spray powder. Subsequently, the spray powder is subjected to staged temperature sintering using an atmosphere box furnace under a nitrogen protective atmosphere, and the temperature is raised to 500℃ at a rate of 5℃ / min and maintained for 4h, and then the temperature is raised to 760℃ at a rate of 10℃ / min and maintained for 10h. After the atmosphere box furnace is naturally cooled to room temperature, a carbon-coated modified lithium manganese iron phosphate (LiMn 0.71 Fe 0.11 W 0.04 V 0.04 Nb 0.04 Mg 0.04 Co 0.02 PO4) is obtained.

[0209] 3. Preparation of a lithium ion battery

[0210] The carbon-coated modified lithium manganese iron phosphate obtained above, carbon black as a conductive agent, and polyvinylidene fluoride as a binder are dissolved in N-methyl pyrrolidone dispersant in a mass ratio of 94:3:3 to obtain a positive electrode slurry, which is then coated on an aluminum foil, and after vacuum drying at 105℃ for 24h, a lithium ion battery positive electrode is obtained.

[0211] A lithium ion battery is assembled in an argon-filled glove box, the positive electrode is the lithium ion battery positive electrode described above, the negative electrode is a metal lithium sheet, the separator is a polyethylene film, and the electrolyte is prepared by dissolving 1mol / L of LiPF6 in a mixed solvent of dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethylene carbonate (EC) in a volume ratio of 1:1:1.

[0212] Characterization of material composition and microstructure of experimental example 1

[0213] (1) SEM measurement

[0214] The low-sulfur cation-doped manganese iron pyrophosphate precursor prepared in Examples 1-3 is characterized by using a transmission scanning electron microscope, and the results are shown in Figs. 1-3 Fig. 1. The low-sulfur cation-doped manganese iron pyrophosphate precursor prepared in Examples 1-3 has a regular rod-like structure, which is beneficial to accelerating the grinding efficiency and nanocrystallization, and thus the carbon-coated modified lithium manganese iron phosphate can be prepared by fully mixing and uniformizing the carbon source and lithium source.

[0215] (2) Sulfur content and doped cation content detection

[0216] Appropriate amounts of the cation-doped manganese iron pyrophosphate precursors obtained in Examples 1-4 and Comparative Examples 1-5, as well as carbon-coated modified manganese iron lithium phosphate, were placed in centrifuge tubes. An appropriate amount of hydrochloric acid was added, and the mixture was heated and digested for 2 hours. After cooling and dilution, the samples were measured using an inductively coupled plasma atomic emission spectrometer.

[0217] (3) Determination of iron and phosphorus content

[0218] The iron and phosphorus contents of the cationic doped manganese iron pyrophosphate precursors obtained in Examples 1-4 and Comparative Examples 1-5 were determined. Iron content: determined by potassium dichromate titration; Phosphorus content: the precursor / lithium manganese iron phosphate was decomposed with perchloric acid, simultaneously removing carbon from the sample. In an acidic medium, orthophosphate ions reacted with a quinoline phosphomolybdate precipitant to form a yellow quinoline phosphomolybdate precipitate. After filtration, washing, drying, and weighing, the weight of the quinoline phosphomolybdate precipitate was obtained, from which the phosphorus content in the sample was calculated.

[0219] (4) Tap density

[0220] The weighed samples of the cation-doped manganese iron pyrophosphate precursors of Examples 1-4 and Comparative Examples 1-5 were placed into a three-sided graduated measuring cylinder and placed in a tap density tester. The test time of the density tester was adjusted. After the tap density tester stopped vibrating, the measuring cylinder was removed and the reading was taken to calculate the tap density of the powder.

[0221] Test data such as Figs. 1-3 As shown in Tables 1 and 2.

[0222] Table 1. Sulfur content, main / doped element content, and tap density in precursors / lithium manganese iron phosphate.

[0223]

[0224]

[0225] Note: / indicates that the content of this element was not detected.

[0226] Table 2 Doping metal element content of precursors

[0227]

[0228] Note: 15961 / W indicates that the content of metallic W in the precursor is 15961 ppm, and so on for others.

[0229] As can be seen from the data in Table 1, the sulfur impurity content of the low-sulfur cation-doped manganese iron ammonium phosphate precursor, the low-sulfur cation-doped manganese iron pyrophosphate precursor, and the carbon-coated modified manganese iron lithium phosphate prepared by treating the metal cation-doped manganese iron ammonium phosphate precursor with a phosphoric acid source in Examples 1-4 is all less than 10 ppm, which is much lower than the sulfur content of the metal cation-doped manganese iron ammonium phosphate precursor and the carbon-coated modified manganese iron lithium phosphate not treated with a phosphoric acid source in Comparative Examples 1-3. This is mainly due to the addition of an appropriate amount of phosphoric acid source to the synthesized metal cation-doped manganese iron ammonium phosphate precursor in Examples 1-4, which can induce recrystallization to expose and separate the sulfur impurities from the precursor particles, and then through subsequent filtration and washing post-processing, the sulfur impurities are transferred, thereby achieving the purpose of removing sulfur impurities and improving the crystallinity of the precursor, effectively avoiding the introduction of sulfur impurities during the preparation of the carbon-coated modified manganese iron lithium phosphate. In Comparative Examples 1-3, since the sulfur impurity content of the metal cation-doped manganese iron ammonium phosphate precursor exceeds the standard, these impurities are introduced as core sulfur sources during the subsequent preparation of the manganese iron pyrophosphate precursor and the manganese iron lithium phosphate, resulting in high sulfur impurity content in the finished manganese iron lithium phosphate, which severely limits the performance of the positive electrode material. In addition, after additional phosphoric acid source treatment, the ratio of n(Mn+Fe+M):n(P) can be slightly less than 1, which not only eliminates the cumbersome step of additional phosphorus source supplementation in the subsequent grinding stage, but also forms manganese iron metal site defects in the crystal lattice, which is beneficial to the insertion and extraction of lithium ions, improves the structural stability, and significantly improves the crystallinity of the manganese iron lithium phosphate, and effectively improves its electrochemical performance.

[0230] As can be seen from the ICP test results in Table 2, the main element content of the precursors prepared in Examples 1-4 and Comparative Examples 1-5 is basically consistent with the target doping molar ratio, with a deviation within an acceptable range. This result verifies the accuracy of the corresponding element ratio in the precursor expression, further confirms that the cation-doped manganese iron pyrophosphate / manganese iron ammonium phosphate precursor is successfully prepared according to the preset doping metal element molar ratio, and confirms the uniform distribution of the doping elements therein.

[0231] In summary, the sulfur impurity content of the low-sulfur cation-doped manganese iron pyrophosphate precursor and the carbon-coated modified manganese iron lithium phosphate in Examples 1-4 is significantly reduced by using a phosphoric acid source, which is superior to the precursors not treated with a phosphoric acid source in Comparative Examples 1-3, which is beneficial to improving the cycle performance of the lithium ion battery positive electrode material. At the same time, the molar ratio of the main elements in the precursor is also optimized, which improves the structural stability and electrochemical performance. The ICP test results further verify the accuracy of the element ratio in the precursor and the uniform distribution of the doping elements. The physical properties of the carbon-coated modified manganese iron lithium phosphate positive electrode material in Experimental Example 2 and the physicochemical performance test of the lithium ion battery based on the material

[0232] (1) Electrochemical performance test

[0233] The carbon-coated modified lithium manganese iron phosphate material obtained in Examples 1-4 and Comparative Examples 1-5 was used as a positive electrode active material. The active material, carbon black as a conductive agent, and polyvinylidene fluoride as a binder were weighed in a mass ratio of 94:3:3, dispersed in an N-methylpyrrolidone dispersant to form a uniformly dispersed positive electrode slurry, and then coated on an aluminum foil. After vacuum drying at 105°C for 24 h, the sheet was punched and weighed to obtain a round electrode sheet. A lithium metal sheet was used as a negative electrode, the prepared electrode sheet was used as a positive electrode, a polyethylene film was used as a separator, and an electrolyte was prepared by dissolving 1 mol / L LiPF6 in a mixed solvent of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethylene carbonate (EC) in a volume ratio of 1:1:1. A 2032 type lithium ion button cell was assembled in a Milan glove box (O2≤0.01 ppm, H2O≤0.01 ppm) and left to stand for 12 h before electrochemical performance testing at room temperature. The test voltage range was set to 2-4.5 V, and the charge and discharge test was performed at a rate of 0.1 C / 1 C current. The calculation formula is as follows:

[0234] First cycle discharge efficiency = first cycle discharge specific capacity / first cycle charge specific capacity x 100%;

[0235] Capacity retention rate = 100th cycle specific capacity / first cycle discharge specific capacity x 100%.

[0236] (2) Test method for powder compaction density and powder resistance

[0237] The carbon-coated modified lithium manganese iron phosphate positive electrode material prepared in Examples 1-4 and Comparative Examples 1-5 was used as a test sample. The powder compaction and powder resistance tester were used to test the powder compaction and powder conductivity.

[0238] The above test results are shown in Table 3

[0239] Table 3 Physical properties of carbon-coated modified lithium manganese iron phosphate positive electrode material and physicochemical performance test of lithium ion battery constructed based on the material

[0240]

[0241] From the data in Table 3, in terms of compaction density, Examples 1-4 used an appropriate amount of phosphoric acid source treatment on the metal cation-doped manganese ammonium phosphate precursor to form a low-sulfur type cation-doped manganese ammonium phosphate precursor, and used a low-sulfur type cation-doped manganese iron pyrophosphate as a precursor to prepare a carbon-coated modified lithium manganese iron phosphate material, and the compaction density was all above 2.3 g / cm 3Compared with Comparative Examples 1-3, the metal cation-doped ammonium manganese iron phosphate precursor is not treated with an appropriate amount of phosphoric acid source, the tap density of the ammonium manganese iron phosphate precursor is low, and the precursor is loose inside. When the ammonium manganese iron phosphate precursor is used as a precursor to prepare manganese iron pyrophosphate and lithium manganese iron phosphate, it is not conducive to the development of the tap density. In Comparative Example 4, the low-sulfur type metal cation-doped ammonium manganese iron phosphate precursor is directly used to prepare the lithium manganese iron phosphate positive electrode material. During the sintering process of the lithium manganese iron phosphate, ammonia gas is generated from the decomposition of the ammonium manganese iron phosphate and is removed from the material, resulting in a loose porous structure of the material, which is not conducive to the improvement of the tap density.

[0242] In terms of powder resistance, the powder resistance of the low-sulfur type carbon-coated modified lithium manganese iron phosphate material prepared in Examples 1-4 is less than 50 Ω·cm, which exhibits good electrical conductivity and is conducive to the development of the electrochemical performance. Compared with Comparative Examples 1-3, the metal cation-doped ammonium manganese iron phosphate precursor is not treated with an appropriate amount of phosphoric acid source, the crystallinity and particle morphology and packing mode are not ideal, and the powder resistance of the material is much higher than that of Examples 1-4. In Comparative Example 4, the low-sulfur type metal cation-doped ammonium manganese iron phosphate precursor is directly used to prepare the positive electrode material. During the sintering process, the precursor decomposes ammonia gas, which causes the structure of the positive electrode material to become loose, and the electronic migration path in the material becomes longer, resulting in a sharp increase in the powder resistance. In Comparative Example 5, the presence of excessive metal-doped ions affects the proportion of active substances in the positive electrode material, resulting in an increase in the powder resistance.

[0243] Further electrochemical performance tests show that, due to the use of the metal cation-doped ammonium manganese iron phosphate precursor with high tap density, low sulfur content, and n(Mn+Fe+M):n(P) ratio slightly less than 1, the carbon-coated modified lithium manganese iron phosphate positive electrode material prepared in Examples 1-4 exhibits more excellent tap density (>2.3 g / cm 3), first charge specific capacity (>153 mAh / g), first coulombic efficiency (>96%), cycle stability (>98%) and lower manganese elution (<100 ppm) performance. Among them, the lower n(Mn+Fe+M):n(P) ratio helps to construct manganese / iron site defects inside the lithium manganese iron phosphate crystal lattice, which can accelerate the migration of lithium ions and alleviate the volume expansion effect during charging and discharging, thereby improving the lithium storage performance of the material. On the contrary, Comparative Examples 1-3 use metal-doped ammonium manganese iron phosphate precursors with low tap density, high sulfur content, and high n(Mn+Fe+M):n(P), which perform poorly in terms of charge and discharge capacity and cycle stability. Comparative Example 4 directly uses a low-sulfur type of cation-doped ammonium manganese iron phosphate precursor for high-temperature sintering. During the sintering process, the ammonia gas generated by the decomposition of the ammonium manganese iron phosphate precursor causes a large number of pore defects to form inside the material. These pore defects not only reduce the density of the material, but also increase its specific surface area. During the charging and discharging cycle, these pore defects cause irreversible loss of lithium storage capacity, affecting the first cycle coulombic efficiency and cycle stability. Comparative Example 5 has too high a content of metal doping in the material, which reduces the proportion of effective electrochemical active metal sites in the prepared lithium manganese iron phosphate material. The excess doping of metals not only fails to contribute to the charge / discharge capacity, but also may hinder the migration of lithium ions, thereby negatively affecting the charge and discharge capacity.

[0244] In summary, the present application successfully prepares a low-sulfur type of cation-doped manganese iron pyrophosphate precursor. By adding an appropriate amount of phosphoric acid source to the prepared metal cation-doped ammonium manganese iron phosphate precursor, not only is the sulfur content of the precursor significantly reduced, but also the molar ratio of manganese, iron, doping elements, and phosphorus is slightly less than 1, which effectively improves the tap density of the precursor. This precursor can effectively suppress gas generation during high-temperature sintering, avoid pore defects, and ensure the density of the structure of the carbon-coated modified lithium manganese iron phosphate material prepared, significantly improving the cycle stability of the material. The lithium ion battery based on this lithium manganese iron phosphate material exhibits excellent compaction density, charge and discharge capacity, and cycle stability.

[0245] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above embodiments, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application are equivalent replacement methods and are included in the protection scope of the present application.

Claims

1. A method for preparing a low-sulfur type cation-doped manganese iron pyrophosphate precursor, characterized in that, The method comprises the following steps: S1. preparing a metal cation doped manganese iron ammonium phosphate precursor by using manganese sulfate as a manganese salt; S2. mixing the cation doped manganese iron ammonium phosphate precursor obtained in step S1 with a phosphoric acid source solution, adjusting the pH of the solution to 7-11, and fully reacting at 50-150 ℃, filtering, washing and drying the precipitate to obtain a low-sulfur cation doped manganese iron ammonium phosphate precursor; S3. fully calcining the low-sulfur cation doped manganese iron ammonium phosphate precursor obtained in step S2 at 400-600 ℃ to obtain a low-sulfur cation doped manganese iron pyrophosphate precursor; The metal cation is at least one selected from the group consisting of Mg, Ti, V, Co, Ni, Cr, Zn, Cu, Zr, Nb, Mo, Al, Ta, W and Ca, with no repetition among them; The expression for the low-sulfur cation-doped manganese pyrophosphate ferric precursor is (Mn x Fe 1-x-y M y )2P2O7, 0<x≤0.9, 0<y≤0.1; where M represents one or more metal cation doping; In step S2, the phosphoric acid source comprises one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, lithium dihydrogen phosphate, lithium phosphate, ammonium hypophosphite and ammonium polyphosphate; In step S2, the addition amount of the phosphoric acid source is at least 0.1 times the amount of substance of the metal cation doped manganese iron ammonium phosphate precursor; Steps S1-S3 are all carried out in a protective gas atmosphere; In step S1, the method for preparing the metal cation doped manganese iron ammonium phosphate precursor specifically comprises the following steps: SI. preparing a mixed solution I containing manganese sulfate and a doped metal cation salt; SII. mixing elemental iron and a phosphoric acid source solution and fully reacting to obtain a ferrous dihydrogen phosphate solution system II; SIII. adding the mixed solution I obtained in step SI and an oxidizing agent to the ferrous dihydrogen phosphate solution system II obtained in step SII at 70-150 ℃, fully reacting after mixing, oxidizing the divalent manganese ions and divalent iron ions into trivalent manganese ions and trivalent iron ions respectively, adjusting the pH to 7-11 with ammonia water, fully reacting, and post-treating to obtain the metal cation doped manganese iron ammonium phosphate precursor; Steps SI-SIII are all carried out in a protective gas atmosphere; In step SII, the phosphoric acid source comprises one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, sodium hydrogen phosphate, lithium dihydrogen phosphate, ammonium phosphate, lithium phosphate, sodium phosphate, ammonium hypophosphite, ammonium polyphosphate, sodium phosphite, sodium metaphosphate and sodium tripolyphosphate; In step SII, the molar ratio of elemental iron to the phosphoric acid source is 1: (2-5).

2. The low-sulfur cation doped manganese iron pyrophosphate precursor prepared by the preparation method in claim 1.

3. A method for preparing carbon-coated modified lithium iron manganese phosphate, characterized in that, The method comprises the following steps: Si. fully mixing lithium salt, a phosphoric acid source, the low-sulfur cation doped manganese iron pyrophosphate precursor in claim 2, a carbon source and an alcohol solution to obtain a slurry, grinding the slurry, and drying to obtain a powder; Sii. pre-calcining the powder obtained in step Si at 450-550 ℃ for 0.5-8 h under a protective gas atmosphere, fully calcining by increasing the temperature to 650-900 ℃, and post-treating to obtain a carbon-coated modified manganese iron lithium phosphate.

4. The preparation method according to claim 3, characterized in that, In step S1, the molar ratio of the lithium salt, the phosphoric acid source, and the low-sulfur cation-doped manganese iron pyrophosphate precursor is 1:(0.8-1.2):(0.9-1.1).

5. The preparation method according to claim 3, characterized in that, In step S1, the carbon source includes one or more of polyethylene glycol, polyethylene, polyvinyl alcohol, glucose, fructose, sucrose, starch, graphene oxide, polyvinylpyrrolidone, polyvinylidene fluoride, lauric acid, ascorbic acid, and citric acid.

6. The preparation method according to claim 3, characterized in that, In step S1, the mass ratio of the low-sulfur cation-doped manganese iron pyrophosphate precursor to the carbon source is 1:(0.01-1).

7. The carbon-coated modified lithium manganese iron phosphate prepared by the preparation method of any one of claims 3-6.

8. A lithium-ion battery cathode, characterized by, The lithium ion battery includes an electrolyte, a separator, a positive electrode, and a negative electrode, wherein the positive electrode includes the carbon-coated modified lithium manganese iron phosphate of claim 7.

9. A lithium-ion battery, characterized by The lithium ion battery includes an electrolyte, a separator, a positive electrode, and a negative electrode, wherein the positive electrode includes the lithium ion battery positive electrode of claim 8.

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