Preparation method of hydroxyl ferric manganese oxide precursor, lithium ferric manganese phosphate / carbon composite material and preparation method of lithium ferric manganese phosphate / carbon composite material

Abstract

The invention relates to the technical field of lithium ion battery positive electrode materials, in particular to a preparation method of a hydroxyl ferric manganese oxide precursor, a lithium ferric manganese phosphate / carbon composite material and a preparation method of the lithium ferric manganese phosphate / carbon composite material. The preparation method comprises the following steps: (1) preparing a complexing solution A by adopting a complexing agent; preparing a metal salt solution B by adopting an iron source, a manganese source and a reducing agent; preparing a precipitation solution C by adopting a precipitator; preparing an oxidizing solution D by adopting an oxidizing agent; (2) adding a metal salt solution B into the complexing solution A, then sequentially adding a precipitation solution C and an oxidation solution D for reaction, and carrying out solid-liquid separation to obtain a hydroxyl ferric manganese oxide precursor; the method has the advantages of higher purity, higher yield of iron and manganese elements and larger specific surface area.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery positive electrode materials, and in particular to a method for preparing an iron manganese oxyhydroxide precursor, an iron manganese phosphate lithium / carbon composite material and a preparation method thereof. Background Art

[0002] Among the current lithium-ion battery cathode materials, lithium iron phosphate (LIFP) is widely used in electric vehicles and energy storage due to its low cost and high safety. However, LFP suffers from poor low-temperature performance and has historically faced technical bottlenecks in energy density. Meanwhile, compared to LFP, LMP presents significant potential as a lithium-ion battery cathode material. Currently, the precursor preparation process for LMP is still under development and optimization.

[0003] The preparation process of lithium manganese iron phosphate precursor mainly includes the following routes: manganese iron phosphate precursor, manganese iron oxalate precursor, iron manganese oxide precursor, etc. Among them, because the K of Fe3(PO4)2 sp =10 -36 , K of Mn3(PO4)2 sp =1.3×10 -32 , it is difficult to generate trivalent ferromanganese phosphate precipitation as ferrophosphate, therefore ferromanganese phosphate precursor usually needs to adopt nitric acid-ethanol system, or reacts under high temperature and high pressure or high temperature calcination conditions, to achieve the purpose of uniform distribution of each element.As Chinese invention patent publication number CN119490169A provides a kind of preparation method of ferromanganese phosphate precursor, by by mixing complex iron salt solution, manganese source solution and phosphorus source solution, adding oxidant and alkali liquor to carry out coprecipitation reaction, carry out drying and roasting after reaction terminates, so as to obtain ferromanganese phosphate precursor.High temperature calcination is needed by this method, and oxygen needs to be passed through synchronously in the reaction process simultaneously, so cost is higher, is difficult to be applied in industrial production.

[0004] The manganese and iron in the manganese iron oxalate precursor are easier to mix evenly, and can be used to prepare lithium manganese iron phosphate positive electrode materials with better performance. However, because oxalate will be discharged in the form of CO2, it will affect the material's circulation, compaction and other properties, so it is also not suitable for large-scale industrial production.

[0005] Iron-manganese oxide precursors are more uniform and stable, can be prepared under relatively mild conditions, and are currently a relatively low-cost preparation process. For example, Chinese Invention Patent Publication No. CN119284859A provides a method for preparing ferromanganese oxide. A metal salt and a precipitant are dripped into a base solution for co-precipitation, followed by high-temperature calcination to obtain the ferromanganese oxide precursor. This method does not use a phosphoric acid and oxalic acid system as a precursor, resulting in a uniform distribution of iron and manganese. However, high-temperature calcination is still required, which is costly and difficult. Chinese invention patent publication number CN119191363A provides a method for preparing manganese iron oxide, which comprises simultaneously dripping an iron-manganese mixed solution, a complexing liquid, and a sodium hydroxide solution into a base liquid, and then drying and oxidizing the obtained product by air blower drying, and then calcining it at high temperature to obtain a manganese iron oxide precursor. This method effectively compensates for the solubility product difference between Fe(OH)2 and Mn(OH)2 through the use of a complexing agent, so that the iron and manganese elements are evenly mixed, thereby changing the product purity and other properties. However, in addition to requiring high-temperature calcination, this method has a relatively cumbersome and complicated preparation process, and when applied to industrial production, the production cycle is long and the cost is high.

[0006] The preparation process for ferromanganese oxyhydroxide precursors can avoid the high-temperature calcination step based on the preparation process of iron-manganese oxide, resulting in a relatively low cost. Furthermore, the preparation process for ferromanganese oxyhydroxide precursors, which offers a simple process flow and high purity, is currently in urgent need of development.

[0007] Chinese invention patent publication number CN118771456A discloses a method for preparing a ferromanganese oxyhydroxide precursor and lithium iron manganese phosphate, comprising the following steps: S1: preparing a complex solution containing an iron source, a manganese source, and a complexing agent; S2: adding an oxidant, a precipitant, and a growth inhibitor to the complex solution, heating the reaction, and obtaining the ferromanganese oxyhydroxide precursor after solid-liquid separation. However, this method requires the addition of a growth inhibitor to control the precursor particle size, making the process more complicated, and using a large amount of organic solvents during the preparation process, making wastewater and exhaust gas treatment more difficult. In addition, the purity of the prepared ferromanganese oxyhydroxide precursor, the yield of iron and manganese elements, and the specific surface area need to be improved, and the battery performance of the resulting lithium iron manganese phosphate needs to be further improved. Summary of the Invention

[0008] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for preparing a flaky, hexagonal ferromanganese oxyhydroxide precursor with high purity, high yield of iron and manganese elements, and high specific surface area, as well as a lithium ferromanganese phosphate / carbon composite material and a preparation method thereof.

[0009] The present invention is achieved through the following technical solutions: The first aspect of the present invention provides a method for preparing a manganese ferrous oxyhydroxide precursor, comprising the following steps: (1) A complexing agent is used to prepare a complexing solution A; an iron source, a manganese source and a reducing agent are used to prepare a metal salt solution B; a precipitating agent is used to prepare a precipitation solution C; an oxidizing agent is used to prepare an oxidizing solution D; (2) Add metal salt solution B to complex solution A, and then add precipitation solution C and oxidation solution D in sequence to react, separate the solid and liquid, and obtain ferromanganese hydroxide precursor.

[0010] As an embodiment of the present invention, the concentration of the complexing solution A is 6.0-13.0 mol / L.

[0011] As an embodiment of the present invention, the ratio of the complex ions (ammonium ions) in the complex solution A to the total molar number of Mn in the manganese source and Fe in the iron source, that is, n complex ions / n(Mn+Fe)=0.5-2.

[0012] As an embodiment of the present invention, the complexing agent is ammonia water; As an embodiment of the present invention, the iron source is a divalent iron source.

[0013] Preferably, the divalent iron source is one or more of ferrous sulfate, ferrous nitrate and ferrous chloride.

[0014] As an embodiment of the present invention, the manganese source is a divalent manganese source.

[0015] Preferably, the manganese source is one or more of manganese sulfate, manganese nitrate, manganese chloride and manganese citrate.

[0016] As an embodiment of the present invention, the reducing agent is ascorbic acid.

[0017] As an embodiment of the present invention, the total concentration of Mn and Fe in the metal salt solution B is 1.0-3.0 mol / L.

[0018] As an embodiment of the present invention, the molar ratio of Mn to Fe in the metal salt solution B is x / (1-x), where x is 0.5-0.9.

[0019] As an embodiment of the present invention, the molar ratio of the reducing agent to Mn in the manganese source and Fe in the iron source in the metal salt solution B is n reducing agent / n (Mn + Fe) = 0.01-0.03.

[0020] As an embodiment of the present invention, the precipitant is one or more of sodium hydroxide and potassium hydroxide.

[0021] As an embodiment of the present invention, the total concentration of the precipitant in the precipitation solution C is 6.0-12.0 mol / L.

[0022] As an embodiment of the present invention, the ratio of the hydroxide in the precipitation solution C to the total molar number of Mn in the manganese source and Fe in the iron source, that is, nOH - / n(Mn+Fe)=1.6-2.5.

[0023] As an embodiment of the present invention, the oxidant is one or more of sodium peroxide, hydrogen peroxide and ozone.

[0024] As an embodiment of the present invention, the total concentration of the oxidant in the oxidizing solution D is 3.0-9.8 mol / L.

[0025] As an embodiment of the present invention, the molar ratio of the oxidant to Mn in the manganese source and Fe in the iron source in the oxidizing solution D is n oxidant / n (Mn + Fe) = 0.6-1.0.

[0026] As an embodiment of the present invention, the pH value of the reaction process in step (2) is controlled at 11.0-13.5.

[0027] As an embodiment of the present invention, the addition time of the metal salt solution B, the precipitation solution C and the oxidation solution D in step (2) is independently selected from 10 min to 120 min.

[0028] As an embodiment of the present invention, the addition temperatures of the metal salt solution B, the precipitation solution C and the oxidation solution D in step (2) are independently selected from 30°C to 80°C.

[0029] As an embodiment of the present invention, the metal salt solution B, the precipitation solution C and the oxidation solution D are added in step (2) with stirring, and the stirring speed is 250-600 rpm.

[0030] As an embodiment of the present invention, the reaction in step (2) is kept warm for 3-6 hours.

[0031] As an embodiment of the present invention, after the solid-liquid separation in step (2) is completed, a washing and drying step is also included.

[0032] Preferably, the washing agent is water, and the washing is performed until the conductivity is ≤300 μS / cm.

[0033] Preferably, the drying process parameters are 60-90° C. and 12-24 h. The drying method can be air drying or drying.

[0034] The reaction carried out in step (2) of the present invention is a coprecipitation reaction.

[0035] The ferromanganese oxyhydroxide precursor prepared by the present invention has a flaky morphology and a hexagonal crystal structure, and its chemical formula is Fe 1-X Mn X OOH, x is 0.5-0.9.

[0036] A second aspect of the present invention provides a lithium iron manganese phosphate / carbon composite material, which is prepared from an iron manganese oxyhydroxide precursor, wherein the iron manganese oxyhydroxide precursor is prepared by the above-mentioned preparation method.

[0037] A third aspect of the present invention provides a method for preparing the above-mentioned lithium iron manganese phosphate / carbon composite material, comprising the following steps: S1: mixing and grinding the ferromanganese oxyhydroxide precursor with lithium salt, phosphate salt and additives in a liquid phase system, spray drying the mixture, and sintering the powder obtained by spray drying under an inert atmosphere to obtain a pre-lithiated ferromanganese lithium phosphate precursor; S2: grinding and mixing the pre-lithiated lithium iron manganese phosphate precursor and the carbon source in a liquid phase system, and spray drying to obtain a lithium iron manganese phosphate / carbon composite material precursor; S3: taking the lithium manganese iron phosphate / carbon composite material precursor and sintering it in an inert atmosphere to obtain the lithium manganese iron phosphate / carbon composite material.

[0038] As an embodiment of the present invention, the lithium salt in step S1 is one or more of lithium carbonate, lithium hydroxide, lithium phosphate and lithium dihydrogen phosphate.

[0039] As an embodiment of the present invention, the phosphate salt in step S1 is one or more of ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, ammonium phosphate, lithium dihydrogen phosphate and lithium phosphate.

[0040] As an embodiment of the present invention, the additive in step S1 is any one or more of titanium dioxide, tetrabutyl titanate, magnesium hydroxide, magnesium oxide, magnesium acetate, magnesium nitrate, zirconium dioxide, zirconium hydroxide, niobium pentoxide, nickel acetate and nickel oxide.

[0041] As an embodiment of the present invention, the amount of the additive added in step S1 is 0.1%-1.0% of the mass of the pre-lithiated lithium manganese iron phosphate precursor.

[0042] As an embodiment of the present invention, the molar ratio of Li in the lithium salt, Mn and Fe in the manganese ferric oxyhydroxide precursor, and P in the phosphate salt in step S1 is Li:(Fe+Mn):P=(1.1-1.0):1:(1.1-1.0).

[0043] As an embodiment of the present invention, the sintering temperature in step S1 is 400-700° C. and the sintering time is 2-6 hours.

[0044] As an embodiment of the present invention, the liquid phase systems in step S1 and step S2 are independently selected from one or more of pure water, ethanol and methanol.

[0045] As an embodiment of the present invention, the grinding in step S1 and step S2 is independently controlled to have a particle size of 300-500 nm.

[0046] Preferably, the grinding is performed using a basket grinder for coarse grinding, the grinding time is 30 min to 60 min, and the particle size to be ground is controlled within D 50 =1-2 μm; then fine grinding is performed with a sand mill, and the particle size of the fine grinding slurry is controlled at 300-500nm.

[0047] As an embodiment of the present invention, the carbon source in step S2 is any one or more of glucose, crystal sugar, sucrose, fructose, polyethylene glycol, cyclodextrin, starch and cellulose.

[0048] As an embodiment of the present invention, in step S1 and step S2, the inlet temperature of the spray drying is 250-270°C, and the outlet temperature is 95-105°C.

[0049] As an embodiment of the present invention, the sintering temperature in step S3 is 675-780° C. and the sintering time is 4-10 hours.

[0050] As an embodiment of the present invention, the carbon content in the lithium iron manganese phosphate / carbon composite material is 1.2%-2.0%.

[0051] As an embodiment of the present invention, in step S1 and step S3, the inert atmosphere includes at least one of nitrogen, argon and helium.

[0052] As an embodiment of the present invention, in step S3, after the sintering is completed, a graded crushing process is further performed.

[0053] The beneficial effects of the present invention are: 1) The present invention provides a method for preparing a flaky, hexagonal ferromanganese oxyhydroxide precursor with a simple process and low cost. The method comprises adding a mixed metal salt solution of iron and manganese containing a reducing agent to a complex solution containing aqueous ammonia, and then sequentially adding a precipitant and an oxidant to carry out a coprecipitation reaction to obtain a lithium manganese ferrophosphate precursor. The entire preparation process does not require high-temperature calcination, is energy-efficient and low-consumption, and is suitable for industrial production. The Fe / Mn ratio is adjustable, and the yield of iron and manganese elements is high, reaching over 96%. At the same time, the prepared ferromanganese oxyhydroxide precursor has a low impurity content and a large specific surface area, which is conducive to improving the subsequent grinding efficiency.

[0054] 2) In the process of preparing ferromanganese oxyhydroxide of the present invention, the oxidation of some divalent metal salts is suppressed by using a reducing agent, which is more conducive to the co-precipitation of all divalent metal salts during the precipitation process. Then, an oxidizing agent is added to complete the oxidation of all divalent metal salts to trivalent metal salts, so that the metal salts are co-precipitated and oxidized in the same valence state (divalent or trivalent state), thereby obtaining ferromanganese oxyhydroxide with a purer crystal phase and more uniform co-precipitation of iron and manganese elements, thereby achieving the effect of improving the cycle performance of lithium iron manganese phosphate and reducing manganese dissolution.

[0055] 3) The present invention further optimizes the selection of iron and manganese sources and the dosage of each reagent. The prepared iron-manganese oxyhydroxide precursor is used to prepare a battery with a higher capacity and a higher platform efficiency, showing a higher energy density.

[0056] 4) The present invention also provides a method for preparing a lithium iron manganese phosphate / carbon composite material; by mixing and sintering a homemade lithium iron manganese phosphate precursor with a lithium salt, a phosphorus salt and an additive, and then mixing and grinding the sintered precursor with a carbon source again, and solid-phase sintering, a lithium iron manganese phosphate / carbon composite material with high battery capacity and high platform efficiency can be finally prepared. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 : SEM photograph of the lithium manganese iron phosphate precursor prepared in Example 1; Figure 2 : XRD pattern of the lithium manganese iron phosphate precursor prepared in Example 1; Figure 3 : Discharge curve of lithium manganese iron phosphate button prepared in Example 1. DETAILED DESCRIPTION

[0058] The present invention will be further described below with reference to specific embodiments, and the advantages and features of the present invention will become clearer as the description proceeds. However, these embodiments are merely exemplary and do not constitute any limitation to the scope of the present invention. It should be understood by those skilled in the art that the details and forms of the technical solutions of the present invention may be modified or replaced without departing from the spirit and scope of the present invention, and such modifications and replacements fall within the scope of protection of the present invention.

[0059] Example 1 Preparation of iron manganese oxyhydroxide precursor: Mix 93.57 mL of ammonia water (25%) with 31.43 mL of pure water to obtain complex solution A (molar ratio of ammonia water: total metal salts (Mn + Fe) = 1). Then, dissolve 140.41 g of ferrous sulfate heptahydrate (99%), 128.04 g of manganese sulfate monohydrate (99%), and 3.31 g of L-ascorbic acid (99.7%) (molar ratio of L-ascorbic acid: total metal salts = 0.015) in 416.67 mL of pure water to obtain mixed metal salt solution B. Then, add 104.0 g of NaOH (96%) (molar ratio of OH - : total metal salts (Mn + Fe) = 2.0) were dissolved in 249.6 mL of pure water to obtain precipitant C. 85.05 g of H2O2 (30%) solution was weighed and added to 170.10 g of pure water to obtain oxidant D (molar ratio H2O2:total metal salts = 0.6).

[0060] At 30 °C, the mixed metal salt solution B was added dropwise to a 2 L three-necked flask with complex solution A as the base liquid through a peristaltic pump at a rate of 23.33 mL / min. The addition time was 30 min. During the addition, the stirring speed was 300 rpm. After the addition was completed, the stirring was continued for 10 min. Then, the precipitant C was added dropwise to the reaction solution through a peristaltic pump at a rate of 9.17 mL / min. The addition time was 30 min. During the addition, the stirring speed was 300 rpm. After the addition was completed, the temperature was raised to 40 °C. Then, the oxidant D was added dropwise to the reaction solution through a peristaltic pump at a rate of 9.17 mL / min. The addition time was 30 min. During the addition, the stirring speed was 350 rpm. After the addition was completed, the reaction was kept warm for 3 h. The pH of the reaction system was 11.70. After the reaction was complete, the product was filtered, washed, and vacuum-filtered until the filtrate conductivity was <300 μS / cm. The filter cake was dried in a forced-air drying oven at 80°C for 12 hours, ultimately yielding 109.90 g of ferromanganese oxyhydroxide precursor. Analysis by a carbon-sulfur analyzer and ICP revealed a sulfur content of 0.030%, a sodium content of 131.77 ppm, and a specific surface area of 110.83 m 2 / g; the Fe content is 24.93%, the Mn content is 37.08%. After calculation, the molar ratio of Mn / Fe is 0.602:0.398, the Fe yield is 98.10%, and the Mn yield is 98.91%.

[0061] The obtained iron manganese oxyhydroxide precursor was observed by scanning electron microscopy. Figure 1 .from Figure 1It can be seen that the prepared iron manganese oxyhydroxide precursor is formed by the agglomeration of primary flake particles, and the primary particle length is about 250 nm. Compared with the existing technology, the particle size is smaller, which is not only conducive to improving the grinding efficiency, but also the smaller particle size is conducive to improving the transmission efficiency of lithium ions and enhancing the rate performance of the material. At the same time, XRD characterization was carried out, and the results are as follows Figure 2 From the spectrum, it can be seen that the diffraction peak of the ferromanganese oxyhydroxide precursor prepared in Example 1 is consistent with that of Fe 0.67 Mn 0.33 The OOH standard card (PDF card number #14-0557) corresponds to the above data, with no extra peaks and a hexagonal crystal structure. This indicates that iron and manganese elements exist in the ferric manganese oxyhydroxide crystal phase in the form of co-precipitation.

[0062] Preparation of lithium iron manganese phosphate / carbon composite material: The raw materials were added at a molar ratio of Li:(Fe+Mn):P = 1.06:1:1.03. 105.00g of ferromanganese oxyhydroxide precursor, 46.34g of lithium carbonate (99.5%), 140.92g of ammonium dihydrogen phosphate (99%), and 1.50g of magnesium hydroxide were added, in sequence, to a 2L measuring cup containing 800mL of pure water. The mixture was then ground in a basket mill at 2000r / min for 30min. After the slurry reached a particle size of 1-2μm, it was introduced into a sand mill for fine grinding. After the slurry reached a particle size of 300nm, it was spray-dried. After spray drying, the dried and crushed material was sintered in a tube furnace under a nitrogen atmosphere at 600°C for 4 hours. After the tube furnace cooled naturally to 80°C, the sintered material was crushed to obtain 175.12g of pre-lithiated lithium ferromanganese phosphate precursor.

[0063] 160.00g of pre-lithiated lithium iron manganese phosphate precursor, 13.00g of glucose, and 13.00g of polyethylene glycol 8000 were added to a 2L measuring cup containing 800mL of pure water in sequence, and placed in a basket grinder and ground at a speed of 2000r / min for 40min. After the slurry particle size reaches 1-2μm, the slurry is introduced into a sand mill for fine grinding. After the slurry particle size reaches 300nm, the slurry is spray-dried. After the spray drying is completed, the dried and crushed material is placed in a tubular furnace under a nitrogen atmosphere for sintering at a sintering temperature of 700℃ for 6 hours. After the tubular furnace is naturally cooled to 80℃, the sintered material is graded and crushed to finally obtain LiFe with a carbon content of 1.41%. 0.4 Mn 0.6 PO4 / C composite material.

[0064] Prepared LiFe 0.4 Mn 0.6PO4 / C composite material is used as the positive electrode material, acetylene black is used as the conductive agent, and polytetrafluoroethylene is used as the binder to make the electrode sheet. Metal lithium is used as the negative electrode to assemble into a button battery. At 2-4.3V and 25℃, different charge and discharge current conditions are used for testing. The discharge curve results are shown in the figure. Figure 3 The initial reversible capacity of charge and discharge at 0.1C is 156.6mAh / g, the first efficiency at 0.1C (first efficiency = (first discharge capacity / first charge capacity) × 100%) is 98.2%, the 0.1C 3.3V platform efficiency is 94.4%, the initial reversible capacity of charge and discharge at 0.2C is 154.1mAh / g, the initial reversible capacity of charge and discharge at 1C is 147.1mAh / g, and the capacity retention rate after 100 cycles at 1C is 97.8%.

[0065] Example 2 Preparation of iron manganese oxyhydroxide precursor: Mix 93.57 mL of ammonia water (NH3 25%) with 31.43 mL of pure water to obtain complex solution A (molar ratio of ammonia water: total metal salts = 1). Then, dissolve 175.51 g of ferrous sulfate heptahydrate (99%), 106.70 g of manganese sulfate monohydrate (99%), and 3.31 g of L-ascorbic acid (99.7%) (molar ratio of L-ascorbic acid: total metal salts = 0.015) in 416.67 mL of pure water to obtain mixed metal salt solution B. Then, add 104.0 g of NaOH (96%) (molar ratio of OH - : total metal salts = 2.0) was dissolved in 249.6 mL of pure water to obtain precipitant C. 85.05 g of H2O2 (30%) solution was weighed and added to 170.10 g of pure water to obtain oxidant D (molar ratio H2O2:total metal salts = 0.6).

[0066] At 30 °C, the mixed metal salt solution B was added dropwise to a 2 L three-necked flask with complex solution A as the base liquid through a peristaltic pump at a rate of 23.33 mL / min. The addition time was 30 min. During the addition, the stirring speed was 300 rpm. After the addition was completed, the stirring was continued for 10 min. Then, the precipitant C was added dropwise to the reaction solution through a peristaltic pump at a rate of 9.17 mL / min. The addition time was 30 min. During the addition, the stirring speed was 300 rpm. After the addition was completed, the temperature was raised to 40 °C. Then, the oxidant D was added dropwise to the reaction solution through a peristaltic pump at a rate of 9.17 mL / min. The addition time was 30 min. During the addition, the stirring speed was 350 rpm. After the addition was completed, the reaction was kept warm for 3 h. The pH of the reaction system was 11.60. After the reaction was complete, the product was filtered, washed, and vacuum-filtered until the filtrate conductivity was <300 μS / cm. The filter cake was dried in a forced-air drying oven at 80°C for 12 h, yielding 109.28 g of a manganese ferrohydroxide precursor. Analysis by a carbon-sulfur analyzer and ICP revealed a sulfur content of 0.028%, a sodium content of 184.11 ppm, and a specific surface area of 109.43 m 2 / g; the Fe content is 31.60%, the Mn content is 30.98%. After calculation, the molar ratio of Mn / Fe is 0.499:0.501, the Fe yield is 98.94%, and the Mn yield is 98.60%.

[0067] Preparation of lithium iron manganese phosphate / carbon composite material: The raw materials were added in a molar ratio of Li:(Fe+Mn):P = 1.06:1:1.03. 105.00g of ferromanganese oxyhydroxide precursor, 46.29g of lithium carbonate (99.5%), 140.76g of ammonium dihydrogen phosphate (99%), and 1.25g of magnesium oxide were added, in sequence, to a 2L measuring cup containing 800mL of pure water. The mixture was then ground in a basket mill at 2000r / min for 30min. After the slurry reached a particle size of 1-2μm, it was introduced into a sand mill for fine grinding. After the slurry reached a particle size of 320nm, it was spray-dried. After spray drying, the dried and crushed material was sintered in a tube furnace under a nitrogen atmosphere at 650°C for 4 hours. After the tube furnace cooled naturally to 80°C, the sintered material was crushed to obtain 172.92g of pre-lithiated lithium ferromanganese phosphate precursor.

[0068] 160.00g of pre-lithiated lithium manganese iron phosphate precursor, 13.00g of fructose, and 13.00g of polyethylene glycol 20000 were added to a 2L measuring cup containing 800mL of pure water in sequence, and placed in a basket grinder and ground at a speed of 2000r / min for 40min. After the slurry particle size reaches 1-2μm, the slurry is introduced into a sand mill for fine grinding. After the slurry particle size reaches 300nm, the slurry is spray-dried. After the spray drying is completed, the dried and crushed material is placed in a tubular furnace under a nitrogen atmosphere for sintering at a sintering temperature of 675℃ for 8 hours. After the tubular furnace is naturally cooled to 80℃, the sintered material is graded and crushed to finally obtain LiFe with a carbon content of 1.52%. 0.5 Mn 0.5 PO4 / C composite material.

[0069] Prepared LiFe 0.5 Mn 0.5 The PO4 / C composite material is used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. The battery is assembled into a button-type cell with metallic lithium as the negative electrode. Testing at 2-4.3V and 25°C using various charge and discharge current conditions revealed an initial reversible capacity of 156.3mAh / g at 0.1C, a first efficiency of 97.9% at 0.1C, and a plateau efficiency of 94.9% at 3.3V at 0.1C. Initial reversible capacities of 153.5mAh / g at 0.2C and 146.8mAh / g at 1C were achieved, with a capacity retention rate of 97.1% after 100 cycles at 1C.

[0070] Example 3 Preparation of iron manganese oxyhydroxide precursor: Mix 93.57 mL of ammonia water (NH3 25%) with 31.43 mL of pure water to obtain complex solution A (molar ratio of ammonia water: total metal salts = 1). Then, dissolve 105.31 g of ferrous sulfate heptahydrate (99%), 149.38 g of manganese sulfate monohydrate (99%), and 3.31 g of L-ascorbic acid (99.7%) (molar ratio of L-ascorbic acid: total metal salts = 0.015) in 416.67 mL of pure water to obtain mixed metal salt solution B. Then, add 104.0 g of NaOH (96%) (molar ratio of OH - : total metal salts = 2.0) was dissolved in 249.6 mL of pure water to obtain precipitant C. 85.05 g of H2O2 (30%) solution was weighed and added to 170.10 g of pure water to obtain oxidant D (molar ratio H2O2:total metal salts = 0.6).

[0071] At 30 °C, the mixed metal salt solution B was added dropwise to a 2 L three-necked flask with complex solution A as the base liquid through a peristaltic pump at a rate of 23.33 mL / min. The addition time was 30 min. During the addition, the stirring speed was 300 rpm. After the addition was completed, the stirring was continued for 10 min. Then, the precipitant C was added dropwise to the reaction solution through a peristaltic pump at a rate of 9.17 mL / min. The addition time was 30 min. During the addition, the stirring speed was 300 rpm. After the addition was completed, the temperature was raised to 40 °C. Then, the oxidant D was added dropwise to the reaction solution through a peristaltic pump at a rate of 9.17 mL / min. The addition time was 30 min. During the addition, the stirring speed was 350 rpm. After the addition was completed, the reaction was kept warm for 3 h. The pH of the reaction system was 11.63. After the reaction was complete, the product was filtered, washed, and vacuum-filtered until the filtrate conductivity was <300 μS / cm. The filter cake was dried in a forced-air drying oven at 80°C for 12 h, yielding 110.36 g of a manganese ferrohydroxide precursor. Analysis by a carbon-sulfur analyzer and ICP revealed a sulfur content of 0.032%, a sodium content of 119.57 ppm, and a specific surface area of 107.87 m 2 / g; the Fe content is 18.63%, the Mn content is 42.88%. After calculation, the molar ratio of Mn / Fe is 0.700:0.300, the Fe yield is 98.15%, and the Mn yield is 98.45%.

[0072] Preparation of lithium iron manganese phosphate / carbon composite material: The raw materials were added at a molar ratio of Li:(Fe+Mn):P=1.06:1:1.03. 105.00g of ferromanganese oxyhydroxide precursor, 46.04g of lithium carbonate (99.5%), 140.01g of ammonium dihydrogen phosphate (99%), 0.85g of titanium dioxide, and 0.75g of magnesium oxide were added to a 2L measuring cup containing 800mL of pure water. The mixture was then ground in a basket mill at 2000r / min for 30min. After the slurry reached a particle size of 1-2μm, it was finely ground in a sand mill. After the particle size reached 400nm, the slurry was spray-dried. After spray drying, the dried and crushed material was sintered in a tube furnace under a nitrogen atmosphere at 550°C for 4 hours. After the tubular furnace was naturally cooled to 80° C., the sintered material was crushed to obtain 170.65 g of pre-lithiated lithium manganese iron phosphate precursor.

[0073] 160.00g of pre-lithiated lithium iron manganese phosphate precursor, 13.00g of glucose, and 4.00g of starch were added to a 2L measuring cup containing 800mL of pure water in turn, placed in a basket grinder and ground at a speed of 2000r / min for 40min. After the slurry particle size reaches 1-2μm, the slurry is introduced into a sand mill for fine grinding. After the slurry particle size reaches 300nm, the slurry is spray-dried. After the spray drying is completed, the dried and crushed material is placed in a tubular furnace under a nitrogen atmosphere for sintering at a sintering temperature of 700℃ for 6 hours. After the tubular furnace is naturally cooled to 80℃, the sintered material is graded and crushed to finally obtain LiFe with a carbon content of 1.55%. 0.3 Mn 0.7 PO4 / C composite material.

[0074] Prepared LiFe 0.3 Mn 0.7 The PO4 / C composite material is used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. The battery is assembled into a button-type cell with metallic lithium as the negative electrode. Testing at 2-4.3V and 25°C using various charge and discharge current conditions revealed an initial reversible capacity of 154.3mAh / g at 0.1C, a 0.1C first-pass efficiency of 97.5%, and a 0.1C 3.3V plateau efficiency of 94.5%. Initial reversible capacities of 153.1mAh / g at 0.2C and 144.8mAh / g at 1C were achieved, with a capacity retention rate of 96.8% after 100 cycles at 1C.

[0075] Example 4 Preparation of iron manganese oxyhydroxide precursor: Mix 93.57 mL of ammonia water (NH3 25%) with 31.43 mL of pure water to obtain complex solution A (molar ratio of ammonia water: total metal salts = 1). Then, dissolve 70.20 g of ferrous sulfate heptahydrate (99%), 170.72 g of manganese sulfate monohydrate (99%), and 3.31 g of L-ascorbic acid (99.7%) (molar ratio of L-ascorbic acid: total metal salts = 0.015) in 416.67 mL of pure water to obtain mixed metal salt solution B. Then, add 104.0 g of NaOH (96%) (molar ratio of OH - : total metal salts = 2.0) was dissolved in 249.6 mL of pure water to obtain precipitant C. 85.05 g of H2O2 (30%) solution was weighed and added to 170.10 g of pure water to obtain oxidant D (molar ratio H2O2:total metal salts = 0.6).

[0076] At 30 °C, the mixed metal salt solution B was added dropwise to a 2 L three-necked flask with complex solution A as the base liquid through a peristaltic pump at a rate of 23.33 mL / min. The addition time was 30 min. During the addition, the stirring speed was 300 rpm. After the addition was completed, the stirring was continued for 10 min. Then, the precipitant C was added dropwise to the reaction solution through a peristaltic pump at a rate of 9.17 mL / min. The addition time was 30 min. During the addition, the stirring speed was 300 rpm. After the addition was completed, the temperature was raised to 40 °C. Then, the oxidant D was added dropwise to the reaction solution through a peristaltic pump at a rate of 9.17 mL / min. The addition time was 30 min. During the addition, the stirring speed was 350 rpm. After the addition was completed, the reaction was kept warm for 3 h. The pH of the reaction system was 11.70. After the reaction was complete, the product was filtered, washed, and vacuum-filtered until the filtrate conductivity was <300 μS / cm. The filter cake was dried in a forced-air drying oven at 80°C for 12 h, yielding 110.93 g of a manganese ferrohydroxide precursor. Analysis by a carbon-sulfur analyzer and ICP revealed a sulfur content of 0.029%, a sodium content of 157.56 ppm, and a specific surface area of 107.62 m 2 / g; the Fe content is 12.43%, the Mn content is 48.68%. After calculation, the molar ratio Mn / Fe is 0.799:0.201, the Fe yield is 98.73%, and the Mn yield is 98.30%.

[0077] Preparation of lithium iron manganese phosphate / carbon composite material: The raw materials were added at a molar ratio of Li:(Fe+Mn):P=1.05:1:1.02. 105.00g of ferromanganese oxyhydroxide precursor, 45.39g of lithium carbonate (99.5%), 137.97g of ammonium dihydrogen phosphate (99%), 0.50g of niobium pentoxide, and 1.00g of magnesium oxide were added, in that order, to a 2L measuring cup containing 800mL of pure water. The mixture was then ground in a basket mill at 2000r / min for 30min. After the slurry reached a particle size of 1-2μm, it was finely ground in a sand mill. After the particle size reached 320nm, the slurry was spray-dried. After spray drying, the dried and crushed material was sintered in a tube furnace under a nitrogen atmosphere at 580°C for 5 hours. After the tubular furnace was naturally cooled to 80° C., the sintered material was crushed to obtain 169.8 g of pre-lithiated lithium manganese iron phosphate precursor.

[0078] 160.00g of pre-lithiated lithium iron manganese phosphate precursor, 12.50g of crystal sugar, and 4.8g of cyclodextrin were added to a 2L measuring cup containing 800mL of pure water in sequence, placed in a basket grinder and ground at a speed of 2000r / min for 40min. After the slurry particle size reaches 1-2μm, the slurry is introduced into a sand mill for fine grinding. After the slurry particle size reaches 300nm, the slurry is spray-dried. After the spray drying is completed, the dried and crushed material is placed in a tubular furnace under a nitrogen atmosphere for sintering at a sintering temperature of 700℃ for 6 hours. After the tubular furnace is naturally cooled to 80℃, the sintered material is graded and crushed to finally obtain LiFe with a carbon content of 1.66%. 0.2 Mn 0.8 PO4 / C composite material.

[0079] Prepared LiFe 0.2 Mn 0.8 The PO4 / C composite material is used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. The battery is assembled into a button-type cell with metallic lithium as the negative electrode. Testing at 2-4.3V and 25°C using various charge and discharge current conditions revealed an initial reversible capacity of 154.5mAh / g at 0.1C, a 0.1C first-pass efficiency of 98.2%, and a 0.1C 3.3V plateau efficiency of 95.6%. Initial reversible capacities of 152.5mAh / g at 0.2C and 143.9mAh / g at 1C were achieved, with a capacity retention rate of 96.5% after 100 cycles at 1C.

[0080] Example 5 Preparation of iron manganese oxyhydroxide precursor: Mix 163.75 mL of ammonia water (NH3 25%) with 26.47 mL of pure water to obtain complex solution A (molar ratio of ammonia water: total metal salts = 1.75). Then, dissolve 140.41 g of ferrous sulfate heptahydrate (99%), 128.04 g of manganese sulfate monohydrate (99%), and 4.42 g of L-ascorbic acid (99.7%) (molar ratio of L-ascorbic acid: total metal salts = 0.02) in 416.67 mL of pure water to obtain mixed metal salt solution B. Then, add 88.5 g of NaOH (96%) (molar ratio of OH - : total metal salts = 1.7) was dissolved in 212.4 mL of pure water to obtain precipitant C. 113.4 g of H2O2 (30%) solution was weighed and added to 226.8 g of pure water to obtain oxidant D (molar ratio H2O2:total metal salts = 0.8).

[0081] At 30 °C, the mixed metal salt solution B was added dropwise to a 2 L three-necked flask with complex solution A as the base liquid through a peristaltic pump at a rate of 23.33 mL / min. The addition time was 30 min. During the addition, the stirring speed was 300 rpm. After the addition was completed, the stirring was continued for 10 min. Then, the precipitant C was added dropwise to the reaction solution through a peristaltic pump at a rate of 9.17 mL / min. The addition time was 25 min. During the addition, the stirring speed was 300 rpm. After the addition was completed, the temperature was raised to 60 °C. Then, the oxidant D was added dropwise to the reaction solution through a peristaltic pump at a rate of 9.17 mL / min. The addition time was 40 min. During the addition, the stirring speed was 350 rpm. After the addition was completed, the reaction was kept warm for 5 h. The pH of the reaction system was 11.27. After the reaction was complete, the product was filtered, washed, and vacuum-filtered until the filtrate conductivity was <300 μS / cm. The filter cake was dried in a forced-air drying oven at 80°C for 12 hours, yielding 109.73 g of a manganese ferrohydroxide precursor. Analysis by a carbon-sulfur analyzer and ICP revealed a sulfur content of 0.028%, a sodium content of 126.80 ppm, and a specific surface area of 108.81 m 2 / g; the Fe content is 25.03%, the Mn content is 37.01%. After calculation, the molar ratio of Mn / Fe is 0.601:0.399, the Fe yield is 98.34%, and the Mn yield is 98.57%.

[0082] Preparation of lithium iron manganese phosphate / carbon composite material: The raw materials were added in a molar ratio of Li:(Fe+Mn):P=1.03:1:1.03. 105.00g of ferromanganese oxyhydroxide precursor, 126.72g of lithium dihydrogen phosphate (99.5%), and 1.50g of magnesium oxide were added sequentially to a 2L measuring cup containing 800mL of pure water. The mixture was then ground in a basket mill at 2000r / min for 30min. After the slurry reached a particle size of 1-2μm, it was introduced into a sand mill for fine grinding. After the slurry reached a particle size of 350nm, it was spray-dried. After spray drying, the dried and crushed material was sintered in a tube furnace under a nitrogen atmosphere at 600°C for 4 hours. After the tube furnace cooled naturally to 80°C, the sintered material was crushed to obtain 178.52g of pre-lithiated lithium ferromanganese phosphate precursor.

[0083] 160.00g of pre-lithiated lithium iron manganese phosphate precursor, 13.00g of glucose, and 4.00g of starch were added to a 2L measuring cup containing 800mL of pure water in turn, placed in a basket grinder and ground at 2000r / min for 40min. After the slurry particle size reached 1-2μm, the slurry was introduced into a sand mill for fine grinding. After the slurry particle size reached 300nm, the slurry was spray-dried. After the spray drying was completed, the dried and crushed material was placed in a tubular furnace under a nitrogen atmosphere for sintering at a sintering temperature of 720°C for 8 hours. After the tubular furnace was naturally cooled to 80°C, the sintered material was graded and crushed to finally obtain LiFe with a carbon content of 1.39%. 0.4 Mn 0.6 PO4 / C composite material.

[0084] Prepared LiFe 0.4 Mn 0.6 The PO4 / C composite material is used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. The battery is assembled into a button-type cell with metallic lithium as the negative electrode. Testing at 2-4.3V and 25°C using various charge and discharge current conditions revealed an initial reversible capacity of 155.8mAh / g at 0.1C, a 0.1C first cycle efficiency of 97.8%, and a 0.1C 3.3V plateau efficiency of 94.5%. Initial reversible capacities of 153.6mAh / g at 0.2C and 145.3mAh / g at 1C were achieved, with a capacity retention rate of 97.3% after 100 cycles at 1C.

[0085] Example 6 Preparation of iron manganese oxyhydroxide precursor: Mix 70.18 mL of ammonia water (NH3 25%) with 54.82 mL of pure water to obtain complex solution A (molar ratio of ammonia water: total metal salts = 0.75). Then, dissolve 101.43 g of ferrous chloride tetrahydrate (98%), 149.93 g of manganese chloride tetrahydrate (99%), and 3.31 g of L-ascorbic acid (99.7%) (molar ratio of L-ascorbic acid: total metal salts = 0.015) in 416.67 mL of pure water to obtain mixed metal salt solution B. Then, add 125.0 g of NaOH (96%) (molar ratio of OH - : total metal salts = 2.4) was dissolved in 300.0 mL of pure water to obtain precipitant C. 85.05 g of H2O2 (30%) solution was weighed and added to 170.10 g of pure water to obtain oxidant D (molar ratio H2O2:total metal salts = 0.6).

[0086] At 30 °C, the mixed metal salt solution B was added dropwise to a 2 L three-necked flask with complex solution A as the base liquid through a peristaltic pump at a rate of 23.33 mL / min. The addition time was 30 min. During the addition, the stirring speed was 300 rpm. After the addition was completed, the stirring was continued for 10 min. Then, the precipitant C was added dropwise to the reaction solution through a peristaltic pump at a rate of 9.17 mL / min. The addition time was 36 min. During the addition, the stirring speed was 300 rpm. After the addition was completed, the temperature was raised to 60 °C. Then, the oxidant D was added dropwise to the reaction solution through a peristaltic pump at a rate of 9.17 mL / min. The addition time was 30 min. During the addition, the stirring speed was 350 rpm. After the addition was completed, the reaction was kept warm for 6 h. The pH of the reaction system was 13.04. After the reaction was complete, the product was filtered, washed, and vacuum-filtered until the filtrate conductivity was <300 μS / cm. The filter cake was dried in a forced-air drying oven at 80°C for 12 h, ultimately yielding 110.66 g of ferromanganese oxyhydroxide precursor. Analysis by a carbon-sulfur analyzer and ICP revealed a sulfur content of 0.005%, a sodium content of 177.23 ppm, and a specific surface area of 111.92 m 2 / g; the Fe content is 24.71%, the Mn content is 36.72%. After calculation, the molar ratio of Mn / Fe is 0.601:0.399, the Fe yield is 97.93%, and the Mn yield is 98.62%.

[0087] Preparation of lithium iron manganese phosphate / carbon composite material: The raw materials were added at a molar ratio of Li:(Fe+Mn):P = 1.05:1:1.03. 105.00g of ferromanganese oxyhydroxide precursor, 45.48g of lithium carbonate (99.5%), 139.60g of ammonium dihydrogen phosphate (99%), 0.50g of zirconium dioxide, and 1.00g of magnesium oxide were added, in that order, to a 2L measuring cup containing 800mL of pure water. The mixture was then ground in a basket mill at 2000r / min for 30min. After the slurry reached a particle size of 1-2μm, it was finely ground in a sand mill. After the particle size reached 350nm, the slurry was spray-dried. After spray drying, the dried and crushed material was sintered in a tube furnace under a nitrogen atmosphere at 680°C for 5 hours. After the tubular furnace was naturally cooled to 80° C., the sintered material was crushed to obtain 170.81 g of pre-lithiated lithium manganese iron phosphate precursor.

[0088] 160.00g of pre-lithiated lithium iron manganese phosphate precursor, 16.00g of glucose, and 20.00g of polyethylene glycol 20000 were added to a 2L measuring cup containing 800mL of pure water in turn, and placed in a basket grinder and ground at a speed of 2000r / min for 40min. After the slurry particle size reaches 1-2μm, the slurry is introduced into a sand mill for fine grinding. After the slurry particle size reaches 300nm, the slurry is spray-dried. After the spray drying is completed, the dried and crushed material is placed in a tubular furnace under a nitrogen atmosphere for sintering at a sintering temperature of 720℃ for 6 hours. After the tubular furnace is naturally cooled to 80℃, the sintered material is graded and crushed to finally obtain LiFe with a carbon content of 1.55%. 0.4 Mn 0.6 PO4 / C composite material.

[0089] Prepared LiFe 0.4 Mn 0.6 The PO4 / C composite material is used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. The battery is assembled into a button-type cell with metallic lithium as the negative electrode. Testing at 2-4.3V and 25°C using various charge and discharge current conditions revealed an initial reversible capacity of 155.8mAh / g at 0.1C, a 0.1C first-pass efficiency of 97.6%, and a 0.1C 3.3V plateau efficiency of 94.9%. Initial reversible capacities of 153.1mAh / g at 0.2C and 145.7mAh / g at 1C were achieved, with a capacity retention rate of 96.9% after 100 cycles at 1C.

[0090] Comparative Example 1 Compared with Example 1, the only difference is that the amount of oxidant added is reduced, the molar ratio of H2O2:total metal salt is 0.4, and the precursor product is a mixed crystal phase of manganese ferrohydroxide and manganese trimanganese tetraoxide.

[0091] Here are the results: Finally, 110.25 g of iron-manganese precursor was obtained. After carbon-sulfur analyzer and ICP analysis, the precursor had a S content of 0.285%, a Na content of 1616.14 ppm, and a specific surface area of 109.07 m 2 / g; the Fe content is 24.85%, the Mn content is 36.61%. After calculation, the molar ratio of Mn / Fe is 0.599:0.401, the Fe yield is 98.12%, and the Mn yield is 97.97%.

[0092] The obtained iron-manganese precursor was used to prepare lithium iron-manganese phosphate, and finally LiFe with a carbon content of 1.49% was obtained. 0.4 Mn 0.6 PO4 / C composite material. Prepared LiFe0.4 Mn 0.6 The PO4 / C composite material was used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. The battery was assembled into a button-type cell with metallic lithium as the negative electrode. Under different charge and discharge current conditions, testing at 2-4.3V and 25°C revealed an initial reversible capacity of 153.1mAh / g at 0.1C, a 0.1C first cycle efficiency of 96.1%, and a 0.1C 3.3V plateau efficiency of 93.5%. Initial reversible capacities at 0.2C and 150.1mAh / g, and at 1C, 139.9mAh / g, were achieved. After 100 cycles at 1C, the capacity retention rate was 90.1%.

[0093] Comparative Example 2 Compared with Example 1, the difference is that the amount of sodium hydroxide added is 78.0 g (molar ratio of OH - : total metal salt = 1.5), its precursor product is a mixed crystal phase of ferromanganese oxyhydroxide and trimanganese tetraoxide.

[0094] Here are the results: Finally, 119.63 g of iron-manganese precursor was obtained. The carbon-sulfur analyzer and ICP analysis showed that the precursor had a S content of 0.233%, a Na content of 174.19 ppm, and a specific surface area of 126.74 m 2 / g; the Fe content is 21.76%, the Mn content is 29.61%, and the molar ratio Mn / Fe is 0.580:0.420, the Fe yield is 93.24%, and the Mn yield is 85.98%. Compared with Example 1, the iron and manganese yield of Comparative Example 2 is lower.

[0095] The obtained iron-manganese precursor was used to prepare lithium iron-manganese phosphate, and finally LiFe with a carbon content of 1.46% was obtained. 0.42 Mn 0.58 PO4 / C composite material. Prepared LiFe 0.42 Mn 0.58 The PO4 / C composite material is used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. The battery is assembled into a button-type cell with metallic lithium as the negative electrode. Testing at 2-4.3V and 25°C using various charge and discharge current conditions revealed an initial reversible capacity of 153.3mAh / g at 0.1C, a 0.1C first-pass efficiency of 96.3%, and a 0.1C 3.3V plateau efficiency of 92.6%. Initial reversible capacities of 149.5mAh / g at 0.2C and 139.8mAh / g at 1C were achieved, with a capacity retention rate of 92.0% after 100 cycles at 1C.

[0096] Comparative Example 3 Compared with Example 1, the difference is that the amount of sodium hydroxide added is 135.5 g (molar ratio of OH - : total metal salt = 2.6), and its precursor product is iron manganese oxyhydroxide crystal phase.

[0097] Here are the results: Finally, 110.0 g of iron-manganese precursor was obtained. The carbon-sulfur analyzer and ICP analysis showed that the precursor had a S content of 0.24%, a Na content of 2814.86 ppm, and a specific surface area of 97.34 m 2 / g; the Fe content is 24.89%, the Mn content is 36.39%, and the molar ratio of Mn / Fe is 0.597:0.403, the Fe yield is 98.07%, and the Mn yield is 97.15%.

[0098] The obtained iron-manganese precursor was used to prepare lithium iron-manganese phosphate, and finally LiFe with a carbon content of 1.41% was obtained. 0.4 Mn 0.6 PO4 / C composite material. Prepared LiFe 0.4 Mn 0.6 The PO4 / C composite material was used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. The battery was assembled into a button-type cell with metallic lithium as the negative electrode. Testing at 2-4.3V and 25°C using various charge and discharge current conditions revealed an initial reversible capacity of 152.3mAh / g at 0.1C, a 0.1C first cycle efficiency of 95.9%, and a 0.1C 3.3V plateau efficiency of 93.2%. Initial reversible capacities at 0.2C and 148.7mAh / g were achieved, while those at 1C were 138.9mAh / g. After 100 cycles at 1C, the capacity retention rate was 91.1%.

[0099] Comparative Example 4 Compared with Example 1, the difference is that the amount of ammonia water added is 28.07 mL (molar ratio of ammonia water:total metal salt=0.3), and the precursor product is a manganese iron oxyhydroxide crystal phase.

[0100] Here are the results: Finally, 109.73 g of iron-manganese precursor was obtained. The carbon-sulfur analyzer and ICP analysis showed that the precursor had a S content of 0.367%, a Na content of 461.13 ppm, and a specific surface area of 62.56 m 2 / g; the Fe content is 24.96%, the Mn content is 36.68%. After calculation, the molar ratio of Mn / Fe is 0.599:0.401, the Fe yield is 98.07%, and the Mn yield is 97.67%.

[0101] The obtained iron-manganese precursor was used to prepare lithium iron-manganese phosphate, and finally LiFe with a carbon content of 1.48% was obtained. 0.4 Mn 0.6 PO4 / C composite material. Prepared LiFe 0.4 Mn 0.6 The PO4 / C composite material was used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. The battery was assembled into a button-type cell with metallic lithium as the negative electrode. Under different charge and discharge current conditions, testing at 2-4.3V and 25°C revealed an initial reversible capacity of 152.1mAh / g at 0.1C, a first efficiency of 95.4% at 0.1C, and a plateau efficiency of 93.8% at 3.3V at 0.1C. The initial reversible capacity at 0.2C was 148.9mAh / g, and at 1C was 139.5mAh / g. After 100 cycles at 1C, the capacity retention rate was 90.1%.

[0102] Comparative Example 5 Compared with Example 1, the difference is that the amount of ammonia water added is 205.86 mL (molar ratio of ammonia water:total metal salt=2.2), and the precursor product is a manganese iron oxyhydroxide crystal phase.

[0103] Here are the results: Finally, 109.9 g of iron-manganese precursor was obtained. The carbon-sulfur analyzer and ICP analysis showed that the precursor had a S content of 0.211%, a Na content of 164.45 ppm, and a specific surface area of 85.77 m 2 / g; the Fe content is 22.09%, the Mn content is 26.50%. After calculation, the molar ratio Mn / Fe is 0.549:0.451, the Fe yield is 86.93%, and the Mn yield is 70.69%. Compared with Example 1, the Fe and Mn element yields are relatively low, and the Fe / Mn ratio is significantly different from the designed value (0.4:0.6).

[0104] The obtained iron-manganese precursor was used to prepare lithium iron-manganese phosphate, and finally LiFe with a carbon content of 1.53% was obtained. 0.45 Mn 0.55 PO4 / C composite material. Prepared LiFe 0.45 Mn 0.55The PO4 / C composite material is used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. The battery is assembled into a button-type cell with metallic lithium as the negative electrode. Testing at 2-4.3V and 25°C using various charge and discharge current conditions revealed an initial reversible capacity of 151.1mAh / g at 0.1C, a 0.1C first-pass efficiency of 96.1%, and a 0.1C 3.3V plateau efficiency of 93.1%. Initial reversible capacities of 148.7mAh / g at 0.2C and 137.5mAh / g at 1C were achieved, with a capacity retention rate of 89.6% after 100 cycles at 1C.

[0105] Comparative Example 6 Compared with Example 1, the only difference is that during the preparation of the ferrous manganese oxyhydroxide precursor, the reaction temperature is 100° C., and the precursor product is a ferrous manganese oxyhydroxide crystal phase.

[0106] Here are the results: Finally, 111.1 g of iron-manganese precursor was obtained. The carbon-sulfur analyzer and ICP analysis showed that the precursor had a S content of 0.181%, a Na content of 213.47 ppm, and a specific surface area of 78.20 m 2 / g; the Fe content is 23.58%, the Mn content is 31.63%. After calculation, the molar ratio of Mn / Fe is 0.577:0.423, the Fe yield is 93.83%, and the Mn yield is 85.30%.

[0107] The obtained iron-manganese precursor was used to prepare lithium iron-manganese phosphate, and finally LiFe with a carbon content of 1.46% was obtained. 0.42 Mn 0.58 PO4 / C composite material. Prepared LiFe 0.42 Mn 0.58 The PO4 / C composite material is used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. The battery is assembled into a button-type cell with metallic lithium as the negative electrode. Testing at 2-4.3V and 25°C using various charge and discharge current conditions revealed an initial reversible capacity of 151.1mAh / g at 0.1C, a 0.1C first-pass efficiency of 96.1%, and a 0.1C 3.3V plateau efficiency of 93.1%. Initial reversible capacities of 148.7mAh / g at 0.2C and 136.8mAh / g at 1C were achieved, with a capacity retention rate of 91.6% after 100 cycles at 1C.

[0108] Comparative Example 7 Compared with Example 1, the difference is that the composition of the complexing agent is different, namely EDTA-2Na, and its precursor product is a ferromanganese oxyhydroxide crystal phase.

[0109] Here are the results: Finally, 98.86 g of iron-manganese precursor was obtained. The carbon-sulfur analyzer and ICP analysis showed that the precursor had a S content of 0.225%, a Na content of 3462.73 ppm, and a specific surface area of 154.66 m 2 / g; the Fe content is 24.85%, the Mn content is 36.79%, and the molar ratio Mn / Fe is 0.601:0.399, the Fe yield is 87.98%, and the Mn yield is 88.44%.

[0110] The obtained iron-manganese precursor was used to prepare lithium iron-manganese phosphate, and finally LiFe with a carbon content of 1.48% was obtained. 0.4 Mn 0.6 PO4 / C composite material. Prepared LiFe 0.4 Mn 0.6 The PO4 / C composite material was used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. The battery was assembled into a button-type cell with metallic lithium as the negative electrode. Testing at 2-4.3V and 25°C using various charge and discharge current conditions revealed an initial reversible capacity of 152.1mAh / g at 0.1C, a 0.1C first cycle efficiency of 95.2%, and a 0.1C 3.3V plateau efficiency of 92.4%. Initial reversible capacities at 0.2C and 148.1mAh / g were achieved, while those at 1C were 138.9mAh / g. After 100 cycles at 1C, the capacity retention rate was 92.5%.

[0111] Comparative Example 8 Compared with Example 1, the difference is that the reducing agent L-ascorbic acid is not added to the mixed metal salt solution, and the product is a mixed crystal phase of manganese ferric oxyhydroxide and trimanganese tetraoxide.

[0112] Here are the results: Finally, 106.62 g of iron-manganese precursor was obtained. After carbon-sulfur analyzer and ICP analysis, the precursor had a S content of 0.039%, a Na content of 206.17 ppm, and a specific surface area of 87.62 m 2 / g; the Fe content is 25.33%, the Mn content is 37.67%, and after calculation, the molar ratio Mn / Fe is 0.601:0.399, the Fe yield is 96.70%, and the Mn yield is 97.49%.

[0113] The obtained iron-manganese precursor was used to prepare lithium iron-manganese phosphate, and finally LiFe with a carbon content of 1.49% was obtained. 0.4 Mn 0.6 PO4 / C composite material. Prepared LiFe 0.4 Mn 0.6The PO4 / C composite material was used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. The battery was assembled into a button-type cell with metallic lithium as the negative electrode. Testing at 2-4.3V and 25°C using various charge and discharge current conditions revealed an initial reversible capacity of 152.1mAh / g at 0.1C, a 0.1C first cycle efficiency of 95.2%, and a 0.1C 3.3V plateau efficiency of 92.4%. Initial reversible capacities at 0.2C and 149.9mAh / g, and at 1C, 140.1mAh / g, were achieved. After 100 cycles at 1C, the capacity retention rate was 85.7%.

[0114] Comparative Example 9 Compared with Example 1, the difference is that the iron source in the mixed metal salt solution is a trivalent iron source (99.5% anhydrous ferric sulfate), the molar number of Fe is the same, and the product is a mixed crystal phase of ferric manganese oxyhydroxide and trimanganese tetraoxide.

[0115] Here are the results: Finally, 107.73 g of iron-manganese precursor was obtained. According to the carbon-sulfur analyzer and ICP analysis, the precursor had a S content of 0.331%, a Na content of 206.81 ppm, and a specific surface area of 158.17 m 2 / g; the Fe content is 25.17%, the Mn content is 37.49%, and the molar ratio Mn / Fe is 0.602:0.398, the Fe yield is 97.09%, and the Mn yield is 98.03%.

[0116] The obtained iron-manganese precursor was used to prepare lithium iron-manganese phosphate, and finally LiFe with a carbon content of 1.49% was obtained. 0.4 Mn 0.6 PO4 / C composite material. Prepared LiFe 0.4 Mn 0.6 The PO4 / C composite material was used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. The battery was assembled into a button-type cell with metallic lithium as the negative electrode. Testing at 2-4.3V and 25°C using various charge and discharge current conditions revealed an initial reversible capacity of 152.1mAh / g at 0.1C, a 0.1C first cycle efficiency of 95.2%, and a 0.1C 3.3V plateau efficiency of 91.4%. Initial reversible capacities of 148.1mAh / g at 0.2C and 137.1mAh / g at 1C were achieved, with a capacity retention rate of 88.9% after 100 cycles at 1C.

[0117] The above detailed description is a specific description of one feasible embodiment of the present invention. This embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or modification that does not depart from the present invention should be included in the scope of the technical solution of the present invention.

Claims

1. A method for preparing a manganese ferrous oxyhydroxide precursor, characterized in that: The steps include: (1) A complexing agent is used to prepare a complexing solution A; an iron source, a manganese source and a reducing agent are used to prepare a metal salt solution B; a precipitating agent is used to prepare a precipitation solution C; an oxidizing agent is used to prepare an oxidizing solution D; (2) Add metal salt solution B to complex solution A, and then add precipitation solution C and oxidation solution D in sequence to react, separate the solid and liquid, and obtain ferromanganese hydroxide precursor.

2. The preparation method according to claim 1, characterized in that The iron source is a divalent iron source; the manganese source is a divalent manganese source; the reducing agent is ascorbic acid; the total concentration of Mn and Fe in the metal salt solution B is 1.0-3.0 mol / L, wherein the molar ratio of Mn to Fe is x / (1-x), and x is 0.5-0.9; and the molar ratio of the reducing agent in the metal salt solution B to the Mn in the manganese source and the Fe in the iron source, i.e., n reducing agent / n(Mn+Fe)=0.01-0.

03.

3. The preparation method according to claim 2, characterized in that The divalent iron source is one or more of ferrous sulfate, ferrous nitrate and ferrous chloride; the manganese source is one or more of manganese sulfate, manganese nitrate, manganese chloride and manganese citrate.

4. The preparation method according to claim 1, characterized in that The complexing agent is ammonia water, the concentration of the complexing solution A is 6.0-13.0 mol / L, and the ratio of the complexing ions in the complexing solution A to the total molar number of Mn in the manganese source and Fe in the iron source, i.e., n complexing ions / n(Mn+Fe)=0.5-2.

5. The preparation method according to claim 1, characterized in that The precipitant is one or more of sodium hydroxide and potassium hydroxide; the total concentration of the precipitant in the precipitation solution C is 6.0-12.0 mol / L, and the ratio of hydroxide to the total molar number of Mn in the manganese source and Fe in the iron source, i.e., nOH - / n(Mn+Fe)=1.6-2.5; the oxidant is one or more of sodium peroxide, hydrogen peroxide and ozone; the total concentration of the oxidant in the oxidizing solution D is 3.0-9.8 mol / L; the molar ratio of the oxidant to Mn in the manganese source and Fe in the iron source, i.e., noxidant / n(Mn+Fe)=0.6-1.

0.

6. The preparation method according to claim 1, characterized in that The pH value of the reaction process in step (2) is controlled at 11.0-13.5; the addition time of the metal salt solution B, the precipitation solution C and the oxidation solution D are all 10 min-120 min, the addition temperature is 30°C-80°C, and stirring is accompanied during the addition process, and the stirring speed is 250-600 rpm; the heat preservation is carried out during the reaction process, and the time is 3-6 hours; after the solid-liquid separation is completed, washing and drying steps are also included, and the reagent used for washing is water, and the washing is carried out until the conductivity is ≤300 μS / cm.

7. A lithium iron manganese phosphate / carbon composite material, characterized in that: It is prepared from a ferrous manganese oxyhydroxide precursor, and the ferrous manganese oxyhydroxide precursor is prepared by the preparation method according to any one of claims 1 to 6.

8. A method for preparing the lithium manganese iron phosphate / carbon composite material according to claim 7, characterized in that: The steps include: S1: mixing and grinding the ferromanganese oxyhydroxide precursor with lithium salt, phosphate salt and additives in a liquid phase system, spray drying the mixture, and sintering the powder obtained by spray drying under an inert atmosphere to obtain a pre-lithiated ferromanganese lithium phosphate precursor; S2: grinding and mixing the pre-lithiated lithium iron manganese phosphate precursor and the carbon source in a liquid phase system, and spray drying to obtain a lithium iron manganese phosphate / carbon composite material precursor; S3: taking the lithium manganese iron phosphate / carbon composite material precursor and sintering it in an inert atmosphere to obtain the lithium manganese iron phosphate / carbon composite material.

9. The preparation method according to claim 8, characterized in that In step S1, the lithium salt is one or more of lithium carbonate, lithium hydroxide, lithium phosphate and lithium dihydrogen phosphate; the phosphate salt is one or more of ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, ammonium phosphate, lithium dihydrogen phosphate and lithium phosphate; the additive is any one or more of titanium dioxide, tetrabutyl titanate, magnesium hydroxide, magnesium oxide, magnesium acetate, magnesium nitrate, zirconium dioxide, zirconium hydroxide, niobium pentoxide, nickel acetate and nickel oxide, and the amount of the additive added is 0.1%-1.0% of the mass of the pre-lithiated lithium iron manganese phosphate precursor; the molar ratio of Li in the lithium salt, Mn and Fe in the ferromanganese oxyhydroxide precursor, and P in the phosphate salt is Li:(Fe+Mn):P=(1.1-1.0):1:(1.1-1.0); the sintering temperature is 400-700°C and the time is 2-6 h.

10. The preparation method according to claim 8, characterized in that The liquid phase system in step S1 and step S2 is one or more of pure water, ethanol and methanol; the grinding is controlled to have a particle size of 300-500 nm; the carbon source in step S2 is any one or more of glucose, crystal sugar, sucrose, fructose, polyethylene glycol, cyclodextrin, starch and cellulose; the sintering temperature in step S3 is 675-780°C and the sintering time is 4-10 hours; the carbon content in the lithium iron manganese phosphate / carbon composite material is 1.2%-2.0%.

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