Iron-manganese oxide precursor, and preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion battery positive electrode materials, and particularly relates to an iron manganese oxide precursor and a preparation method and application thereof. The preparation method comprises the following steps: mixing a mixed alkali solution and an iron-manganese mixed metal salt solution, and carrying out a co-precipitation reaction; filtering, washing and drying the reaction liquid to obtain an iron and manganese oxide precursor; the mixed alkali solution is an aqueous solution of hydroxide and carbonate or bicarbonate; the total concentration of the mixed alkali solution is 4.0 mol / L to 10.0 mol / L; the molar ratio of the carbonate or bicarbonate to the total metal elements of iron and manganese is (0.5-0.7): 1; the molar ratio of the hydroxide to the total metal elements of iron and manganese is (2.1-2.4): 1; the pH value of the coprecipitation reaction is 13.0-14.0. The preparation method disclosed by the invention is simple, low in cost, free from environmental protection pressure and suitable for industrial popularization and application, and the lithium ferric manganese phosphate / carbon composite material with excellent electrochemical performance can be finally prepared by using the iron manganese oxide prepared by the method as a lithium ferric manganese phosphate precursor.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery positive electrode materials, and in particular relates to an iron-manganese oxide precursor, a preparation method and application thereof. Background Art

[0002] Lithium iron manganese phosphate, like lithium iron phosphate, has an olivine structure and has excellent safety and thermal stability. Compared with lithium iron phosphate, lithium iron manganese phosphate has a similar specific capacity, but a higher voltage platform, higher energy density, and better low-temperature capacity and rate performance. It is a lithium-ion battery positive electrode material with great potential. From a crystal structure perspective, lithium iron manganese phosphate can be regarded as a solid solution of lithium iron phosphate and lithium manganese phosphate, with iron and manganese occupying the same sites; from a kinetic perspective, the lithium diffusion coefficients of lithium iron phosphate and lithium manganese phosphate are not in the same order of magnitude (lithium iron phosphate is higher); from a cycling perspective, manganese is more easily dissolved than iron during the charge and discharge cycle, resulting in cycle degradation. Therefore, uniform distribution of iron and manganese, avoiding two-phase separation and composition segregation are the keys to preparing high-quality lithium iron manganese phosphate.

[0003] Currently, the main preparation process routes for lithium iron manganese phosphate can be divided into liquid phase method and solid phase method. The liquid phase method uses soluble iron source, soluble manganese source, soluble lithium source and soluble phosphorus source as raw materials, and reacts in an organic / inorganic mixed system or under a high temperature and high pressure hydrothermal environment to achieve the synthesis of lithium iron manganese phosphate positive electrode with uniform distribution of iron and manganese; however, this method not only involves the use of large amounts of high-pressure liquid phase equipment and organic solvents, but also requires the recovery and treatment of large amounts of lithium-containing mother liquor. The process is complex and difficult to achieve large-scale industrialization. In the solid phase method, iron and manganese elements are derived from different raw materials. Due to the principles of sand grinding and sintering reactions, this route is difficult to achieve uniform distribution of iron and manganese.

[0004] Therefore, by following the design concept of the iron red preparation process route of lithium iron phosphate, and using iron-manganese oxide as the raw materials for iron and manganese elements, a uniform distribution of manganese and iron elements can be achieved, while lithium and phosphorus elements can be more evenly distributed through sand grinding and sintering reactions. Chinese invention patent CN118637668A provides a method for preparing an iron-manganese oxide precursor: ultrasonically atomizing and pyrolyzing an iron-manganese mixed metal salt solution to obtain an iron-manganese basic salt, and then calcining it at high temperature to obtain an iron-manganese oxide precursor; however, this process route requires high energy consumption and is costly for large-scale industrialization. Chinese invention patent CN119503892A provides a method for preparing an iron-manganese oxide precursor: dripping ammonium bicarbonate, a precipitant, and ammonia water, a pH regulator, into an iron-manganese mixed metal salt solution to carry out a co-precipitation reaction to synthesize a ferrous manganese carbonate precursor with a uniform distribution of iron and manganese elements, and then sintering it once to synthesize an iron-manganese oxide precursor; however, this process route not only involves the use of a large amount of ammonia-containing solution, but also requires a high-temperature sintering process, making its production cost high and putting great pressure on the environment. Chinese invention patent CN104868123A provides a method for preparing an iron-manganese oxide precursor: a sodium hydroxide precipitant is dripped into a mixture of manganese and iron ions, and the mixture is kept at a certain temperature to obtain an iron-manganese oxide precursor. Although this method can prepare an oxide precursor with uniform distribution of iron and manganese in a liquid phase system in one step and the process is relatively simple, the molar ratio of iron and manganese can only be fixed at 1:2, and the precursor has strong magnetic properties, which does not have great industrial significance.

[0005] In view of this, there is an urgent need in the art for a preparation method of an iron-manganese oxide precursor with simple production process, low cost, uniform distribution of iron and manganese elements and adjustable ratio, suitability for industrial production, and good electrochemical properties. Summary of the Invention

[0006] To address the deficiencies in the prior art, the present invention provides an iron-manganese oxide precursor, a preparation method, and applications thereof. The present invention draws on the preparation method of layered double hydroxides (LDHs) and utilizes their unique lattice positioning effect to prepare the iron-manganese oxide precursor, which features uniform distribution of iron and manganese elements, a large specific surface area, low impurity content, an adjustable iron-manganese ratio, a simple preparation process (no high-temperature sintering process), low cost, no environmental pressure, and suitability for industrial production. The lithium iron-manganese phosphate / carbon composite material prepared using the iron-manganese oxide precursor exhibits excellent electrochemical properties.

[0007] To achieve the above objectives, the technical solutions provided by the present invention are as follows:

[0008] In a first aspect, the present invention provides a method for preparing an iron-manganese oxide precursor, comprising the following steps:

[0009] (1) mixing a mixed alkali solution and an iron-manganese mixed metal salt solution to perform a coprecipitation reaction;

[0010] (2) filtering, washing, and drying the reaction solution of step (1) to obtain an iron-manganese oxide precursor;

[0011] The mixed alkaline solution is an aqueous solution of hydroxide and carbonate or bicarbonate;

[0012] The total concentration of the mixed alkali solution is 4.0 mol / L-10.0 mol / L;

[0013] The molar ratio of the carbonate or bicarbonate to the total metal elements of iron and manganese is (0.5-0.7):1;

[0014] The molar ratio of the hydroxide to the total metal elements of iron and manganese is (2.1-2.4):1;

[0015] The pH value of the coprecipitation reaction is 13.0-14.0.

[0016] Furthermore, the iron salt in the iron-manganese mixed metal salt in step (1) is a trivalent iron salt.

[0017] Preferably, the iron salt is at least one of ferric nitrate, ferric sulfate and ferric chloride.

[0018] Furthermore, the manganese salt in the iron-manganese mixed metal salt in step (1) is a divalent manganese salt.

[0019] Preferably, the manganese salt is at least one of manganese chloride, manganese acetate, manganese sulfate and manganese nitrate.

[0020] Furthermore, the total metal concentration in the iron-manganese mixed metal salt solution is 0.5 mol / L-5 mol / L, and the molar ratio of manganese to iron is x:(1-x), wherein x is 0.5-0.9.

[0021] Furthermore, the carbonate is at least one of ammonium carbonate, sodium carbonate, and potassium carbonate; the bicarbonate is at least one of ammonium bicarbonate, sodium bicarbonate, and potassium bicarbonate; the hydroxide is at least one of potassium hydroxide and sodium hydroxide; the coprecipitation reaction temperature is 50-70°C, and the reaction time is 2-8h.

[0022] Furthermore, the mixing is: adding the mixed alkali solution to the iron-manganese mixed metal salt solution.

[0023] Preferably, the adding method is dropwise addition.

[0024] Furthermore, the time for the simultaneous dropwise addition in step (1) is 15 min-120 min; and the dropwise addition temperature is 20-30°C.

[0025] Preferably, the coprecipitation reaction is carried out under stirring conditions, and the stirring speed is 400 rpm-800 rpm.

[0026] Furthermore, the washing process comprises washing the filtrate to a conductivity of less than 300 μS / cm;

[0027] Preferably, the drying temperature is 80°C-100°C, and the drying time is 8-12 hours.

[0028] In a second aspect, the present invention provides a method for preparing a lithium iron manganese phosphate / carbon composite material, comprising the following steps:

[0029] S1. Mixing and grinding the iron-manganese oxide precursor according to any one of claims 1 to 3 with a lithium salt, a phosphate salt, and an additive in a liquid phase system, drying, and sintering under an inert atmosphere to obtain a pre-lithiated iron-manganese phosphate lithium precursor;

[0030] S2. The pre-lithiated lithium iron manganese phosphate precursor obtained in step S1 and a carbon source are mixed and ground in a liquid phase system, and dried to obtain a lithium iron manganese phosphate / carbon composite material precursor;

[0031] S3. Sintering the lithium manganese iron phosphate / carbon composite material precursor obtained in step S2 under an inert atmosphere to obtain the lithium manganese iron phosphate / carbon composite material.

[0032] Furthermore, in step S1, the lithium salt is at least one of lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate.

[0033] Furthermore, the phosphate salt is at least one of ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, ammonium phosphate, lithium dihydrogen phosphate, and lithium phosphate.

[0034] Furthermore, the additive is at least one 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 0-1.0% of the mass of the pre-lithiated lithium iron manganese phosphate precursor and accounts for 0-1.0% of the mass of the final generated lithium iron manganese phosphate.

[0035] Furthermore, the molar ratio of Li:(Fe+Mn):P in the lithium salt, iron-manganese oxide precursor and phosphate salt is =(1.1-1.0):1(1.1-1.0).

[0036] Furthermore, in steps S1 and S2, the liquid phase system is any one of pure water, ethanol, and methanol.

[0037] Furthermore, the grinding is as follows: firstly coarse grinding to a particle size D 50 =1-2um, and then finely grind to a particle size of 300-500nm.

[0038] Preferably, the coarse grinding is performed using a basket grinder, and the coarse grinding time is 30-60 min.

[0039] Preferably, the fine grinding is performed using a sander, and the fine grinding time is 60-120 minutes.

[0040] Preferably, the drying in step S1 and step S2 is spray drying, with an inlet temperature of 250-270°C and an outlet temperature of 90-110°C.

[0041] Furthermore, the carbon source is at least one of glucose, crystal sugar, sucrose, fructose, polyethylene glycol, cyclodextrin, starch and cellulose.

[0042] Furthermore, the sintering temperature in step S1 is 400-700° C., and the sintering time is 2-6 hours; the sintering inert atmosphere is any one of nitrogen, argon, and helium.

[0043] Furthermore, the sintering temperature in step S3 is 675-780° C., the sintering time is 4-10 hours, and the sintering atmosphere is any one of nitrogen, argon, and helium.

[0044] Preferably, step S3 further comprises subjecting the lithium manganese iron phosphate / carbon composite material to graded crushing treatment, and the obtained lithium manganese iron phosphate / carbon composite material has a carbon content of 1.2%-2.5%.

[0045] In a third aspect, the present invention provides application of the preparation method in reducing impurities in iron-manganese oxide precursors and lithium iron-manganese phosphate / carbon composite materials.

[0046] In a fourth aspect, the present invention provides an iron-manganese oxide precursor prepared by the preparation method.

[0047] In a fifth aspect, the present invention provides a lithium manganese iron phosphate / carbon composite material prepared by the preparation method.

[0048] In a sixth aspect, the present invention provides a battery comprising the lithium manganese iron phosphate / carbon composite material prepared by the preparation method.

[0049] The beneficial effects of the present invention are:

[0050] 1) The present invention draws on the preparation method of layered double hydroxide (LDH) by using a first precipitant containing a carbonate and hydroxide solution, which is added dropwise to an iron-manganese mixed metal salt solution at a certain temperature to carry out a co-precipitation reaction. By leveraging the unique lattice positioning effect of the reaction intermediate and optimizing the reaction conditions, a unique iron-manganese oxide precursor with uniform distribution of iron and manganese elements can be prepared in one step. The precursor has a large specific surface area, low impurity content, high reactivity, an adjustable iron-manganese ratio, and an iron-manganese yield of up to 96%. At the same time, the preparation process is simple (no high-temperature sintering process), low cost, no environmental pressure, and is suitable for industrial production.

[0051] 2) The present invention also provides a method for preparing lithium iron manganese phosphate; by mixing the iron manganese oxide precursor of the present invention with a lithium source, phosphoric acid and an additive, sintering, and then mixing the sintered precursor with a carbon source again, grinding, and solid-phase sintering, a lithium iron manganese phosphate / carbon composite material with excellent electrochemical properties can be finally prepared. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 : SEM photograph of the iron-manganese oxide precursor prepared in Example 1.

[0053] Figure 2 : XRD pattern of the iron-manganese oxide precursor prepared in Example 1.

[0054] Figure 3 : SEM photograph of the lithium iron manganese phosphate / carbon composite material prepared in Example 1.

[0055] Figure 4 : Discharge curve of the lithium manganese iron phosphate / carbon composite material prepared in Example 1.

[0056] The present invention will now be further described with reference to the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0057] The present invention is described below by way of specific examples to facilitate understanding and grasp of the technical solutions of the present invention, but the present invention is not limited thereto. The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified; and different sources do not significantly affect product performance.

[0058] Example 1

[0059] Preparation of iron-manganese oxide precursor:

[0060] 152.73 g of hydrated ferric sulfate (Fe content 22%) and 152.10 g of monohydrated manganese sulfate (purity 99.9%) were dissolved in 750 ml of deionized water to obtain a mixed metal salt solution A. 137.49 g of NaOH (purity 96%) (molar ratio of OH - : Total metal salt = 2.2), 95.40g Na2CO3 (purity 99%) (CO3 2- : total metal salt = 0.6:1) was dissolved in 750 ml of deionized water to obtain a first precipitant mixed alkaline solution B.

[0061] At 30°C, the first precipitant mixed alkali solution B was added dropwise to a 2L three-necked flask containing a mixed metal salt solution A at 25 mL / min through a peristaltic pump. The addition time was 30 min. During the entire addition process, the stirring speed was 350 rpm, and the pH of the reaction system was 13.3. After the addition was completed, the temperature was raised to 60°C and the reaction was carried out at a constant temperature for 4 hours. During the reaction, the stirring speed was 650 rpm. After the reaction was completed, the product was filtered, washed and filtered until the conductivity of the filtrate was <300 μS / cm; the filtered filter cake was placed in a 100°C forced drying oven and dried for 12 hours, and finally 122.86 g of iron phosphate manganese oxide precursor was obtained. After carbon sulfur analyzer and ICP detection and analysis, the precursor had an S content of 0.060%, a Na content of 133.2 ppm, and a specific surface area of 202.1 m 2 / g; the Fe content is 26.30%, the Mn content is 39.40%, and the molar ratio Mn / Fe is 0.604:0.396, the Fe yield is 96.2%, and the Mn yield is 97.9%.

[0062] The obtained iron-manganese oxide precursor was observed by scanning electron microscopy. Figure 1 .from Figure 1 It can be seen that the primary particles of the prepared iron-manganese oxide precursor are quasi-spherical and the primary particle size is relatively uniform, with a size of about 300nm. At the same time, the obtained iron-manganese oxide precursor was characterized by XRD, and the results are as follows Figure 2 .from Figure 2 It can be seen that the XRD pattern of the prepared iron-manganese oxide precursor is consistent with the standard pattern of Mn3O4 (PDF card number 80-0382), which indicates that iron and manganese elements exist in the prepared manganese tetraoxide crystal precursor in the form of co-precipitation.

[0063] Preparation of lithium iron manganese phosphate / carbon composite material:

[0064] The raw materials were added according to the molar ratio of Li:(Fe+Mn):P=1.06:1:1.03. 115.00g of iron manganese oxide precursor, 53.78g of lithium carbonate (purity 99.5%), 163.53g of ammonium dihydrogen phosphate (purity 99%), and 1.42g of magnesium oxide 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 30min. After the slurry particle size reached 1-2um, the slurry was introduced into a sand mill for fine grinding. After the slurry particle size reached 300nm, the slurry was spray-dried. After 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 600℃ for 4 hours. After the tubular furnace was naturally cooled to 80℃, the sintered material was crushed to obtain 208.92g of pre-lithiated iron manganese phosphate lithium precursor.

[0065] 200.00g of pre-lithiated lithium iron manganese phosphate precursor, 15.00g of glucose, and 15.00g 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 1-2um, 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 obtain a powder with a compaction density of 2.30g / cm 3 , LiFe with a carbon content of 1.41% 0.4 Mn 0.6 PO4 / C composite material.

[0066] The obtained lithium iron manganese phosphate / carbon composite material was observed by scanning electron microscope. Figure 3 .from Figure 3 It can be seen that the prepared lithium iron manganese phosphate / carbon composite material is composed of quasi-spherical primary particles, and the primary particles vary in size, with the particle size mainly concentrated in the range of 100-300 nm.

[0067] Prepared LiFe 0.4 Mn 0.6 PO4 / 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 4The initial reversible capacity of charge and discharge at 0.1C is 155.5mAh / g, the first efficiency of 0.1C is 98.1%, the initial reversible capacity of charge and discharge at 0.2C is 153.0mAh / g, and the initial reversible capacity of charge and discharge at 1C is 145.1mAh / g.

[0068] Example 2

[0069] Preparation of iron-manganese oxide precursor:

[0070] 114.24 g of hydrated ferric sulfate (Fe content 22%) and 177.45 g of monohydrated manganese sulfate (purity 99.9%) were dissolved in 750 ml of deionized water to obtain a mixed metal salt solution A. 134.37 g of NaOH (96%) (molar ratio of OH) - : total metal salt = 2.15), 103.35g Na2CO3 (99%) (molar ratio CO3 2- : total metal salt = 0.65: 1) was dissolved in 750 ml of deionized water to obtain a first precipitant mixed alkaline solution B.

[0071] At 30°C, the first precipitant mixed alkali solution B was added dropwise to a 2L three-necked flask containing a mixed metal salt solution A at 25 mL / min through a peristaltic pump. The addition time was 30 min. During the entire addition process, the stirring speed was 350 rpm, and the pH of the reaction system was 13.4. After the addition was completed, the temperature was raised to 60°C and the reaction was carried out at a constant temperature for 4 hours. During the reaction, the stirring speed was 650 rpm. After the reaction was completed, the product was filtered, washed and filtered until the conductivity of the filtrate was <300 μS / cm; the filtered filter cake was placed in a 100°C forced drying oven and dried for 12 hours, and finally 122.10 g of iron-manganese oxide precursor was obtained. According to the carbon-sulfur analyzer and ICP detection and analysis, the precursor had an S content of 0.035%, a Na content of 201.5 ppm, and a specific surface area of 126.5 m 2 / g; the Fe content is 19.81%, the Mn content is 46.06%, and the molar ratio Mn / Fe is 0.703:0.297, the Fe yield is 96.2%, and the Mn yield is 97.5%.

[0072] Preparation of lithium iron manganese phosphate / carbon composite material:

[0073] The raw material molar ratio Li: (Fe + Mn): P = 1.06: 1: 1.03 was used for feeding. 105.00g of iron-manganese oxide precursor, 54.00g of lithium carbonate (purity 99.5%), 164.22g of ammonium dihydrogen phosphate (purity 99%), 1.32g of magnesium acetate, and 0.560g of titanium dioxide were added to a 2L measuring cup containing 800mL of pure water in sequence, placed in a basket grinder and ground at 2000r / min for 30min until the slurry particle size reached 1-2um. The slurry was then introduced into a sand mill for fine grinding. After the slurry particle size reached 320nm, the slurry was spray-dried. After 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 700°C for 3 hours. After the tubular furnace was naturally cooled to 80° C., the sintered material was crushed to obtain 210.81 g of pre-lithiated lithium manganese iron phosphate precursor.

[0074] 200.00g of pre-lithiated lithium iron manganese phosphate precursor, 14.00g of fructose, and 6.00g of cyclodextrin 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 1-2um, the slurry is introduced into a sand mill for fine grinding. After the slurry particle size reaches 320nm, 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 730℃ for 8 hours. After the tubular furnace is naturally cooled to 80℃, the sintered material is graded and crushed to finally obtain a powder with a compaction density of 2.35g / cm 3 , LiFe with a carbon content of 1.55% 0.3 Mn 0.7 PO4 / C composite material.

[0075] Prepared LiFe 0.3 Mn 0.7 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 154.2mAh / g at 0.1C, with an initial efficiency of 97.8%. The initial reversible capacity at 0.2C was 151.9mAh / g, and at 1C was 144.9mAh / g.

[0076] Example 3

[0077] Preparation of iron-manganese oxide precursor:

[0078] 76.39 g of hydrated ferric sulfate (Fe content 22%) and 202.81 g of monohydrated manganese sulfate (99.9%) were dissolved in 750 ml of deionized water to obtain a mixed metal salt solution A. 131.24 g of NaOH (96%) (molar ratio of OH) was added. - : total metal salt = 2.10), 111.30g Na2CO3 (99%) (molar ratio CO3 2- : metal salt = 0.7:1) was dissolved in 750 ml of deionized water to obtain a first precipitant mixed alkaline solution B.

[0079] At 30°C, the first precipitant mixed alkali solution B was added dropwise to a 2L three-necked flask containing a mixed metal salt solution A at 25 mL / min through a peristaltic pump. The addition time was 30 min. During the entire addition process, the stirring speed was 350 rpm, and the pH of the reaction system was 13.5. After the addition was completed, the temperature was raised to 60°C and the reaction was carried out at a constant temperature for 4 hours. During the reaction, the stirring speed was 650 rpm. After the reaction was completed, the product was filtered, washed and filtered until the conductivity of the filtrate was <300 μS / cm; the filtered filter cake was placed in a 100°C forced drying oven and dried for 12 hours, and finally 121.31 g of iron-manganese oxide precursor was obtained. After carbon-sulfur analyzer and ICP detection and analysis, the precursor had an S content of 0.048%, a Na content of 207.3 ppm, and a specific surface area of 168.3 m 2 / g; the Fe content is 13.50%, the Mn content is 52.55%, and the molar ratio Mn / Fe is 0.798:0.202, the Fe yield is 97.5%, and the Mn yield is 96.7%.

[0080] Preparation of lithium iron manganese phosphate / carbon composite material:

[0081] The raw materials were added according to the molar ratio of Li:(Fe+Mn):P=1.05:1:1.03. 105.00g of iron-manganese oxide precursor, 53.73g of lithium carbonate (99.5% purity), 164.93g of ammonium dihydrogen phosphate (99% purity), 1.36g of zirconium oxide, and 0.45g of titanium dioxide were added to a 2L measuring cup containing 800mL of pure water, placed in a basket grinder and ground at 2000r / min for 30min. After the slurry particle size reached 1-2um, 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 600°C for 6 hours. After the tubular furnace was naturally cooled to 80° C., the sintered material was crushed to obtain 215.72 g of pre-lithiated lithium manganese iron phosphate precursor.

[0082] 200.00g of pre-lithiated lithium iron manganese phosphate precursor, 12.00g of glucose and 6.87g of starch 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 1-2um, the slurry is introduced into a sand mill for fine grinding. After the slurry particle size reaches 320nm, 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 8 hours. After the tubular furnace is naturally cooled to 80℃, the sintered material is graded and crushed to finally obtain a powder compaction density of 2.28g / cm 3 , LiFe with a carbon content of 1.56% 0.2 Mn 0.8 PO4 / C composite material.

[0083] Prepared LiFe 0.2 Mn 0.8 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 153.9mAh / g at 0.1C, with an initial efficiency of 97.5%. The initial reversible capacity at 0.2C was 151.5mAh / g, and at 1C was 143.2mAh / g.

[0084] Example 4

[0085] Preparation of iron-manganese oxide precursor:

[0086] 190.91 g of hydrated ferric sulfate (Fe content 22%) and 126.76 g of monohydrated manganese sulfate (purity 99.9%) were dissolved in 750 ml of deionized water to obtain a mixed metal salt solution A. 140.61 g of NaOH (purity 96%) (molar ratio of OH - : total metal salt = 2.25:1), 87.45g Na2CO3 (99%) (molar ratio CO3 2- : metal salt = 0.55:1) was dissolved in 750 ml of deionized water to obtain a first precipitant mixed alkaline solution B.

[0087] At 30°C, the first precipitant mixed alkali solution B was added dropwise to a 2L three-necked flask containing a mixed metal salt solution A at 25 mL / min through a peristaltic pump. The addition time was 30 min. During the entire addition process, the stirring speed was 350 rpm, and the pH of the reaction system was 13.4. After the addition was completed, the temperature was raised to 60°C and the reaction was carried out at a constant temperature for 4 hours. During the reaction, the stirring speed was 650 rpm. After the reaction was completed, the product was filtered, washed and filtered until the conductivity of the filtrate was <300 μS / cm; the filtered filter cake was placed in a 100°C forced drying oven and dried for 12 hours, and finally 123.63 g of iron-manganese oxide precursor was obtained. After carbon-sulfur analyzer and ICP detection and analysis, the precursor had an S content of 0.029%, a Na content of 215.9 ppm, and a specific surface area of 245.1 m 2 / g; the Fe content is 33.28%, the Mn content is 32.50%, and the molar ratio Mn / Fe is 0.498:0.502, the Fe yield is 98.0%, and the Mn yield is 97.5%.

[0088] Preparation of lithium iron manganese phosphate / carbon composite material:

[0089] The raw materials were added according to the molar ratio of Li:(Fe+Mn):P=1.05:1:1.02. 115.00g of iron-manganese oxide precursor, 53.24g of lithium carbonate (99.5% purity), 161.85g of ammonium dihydrogen phosphate (99% purity), 0.85g of niobium pentoxide, and 0.68g of magnesium oxide were added to a 2L measuring cup containing 800mL of ethanol, placed in a basket grinder and ground at 2000r / min for 30min. After the slurry particle size reached 1-2um, the slurry was introduced into a sand mill for fine grinding. After the slurry particle size reached 350nm, 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 600°C for 4 hours. After the tubular furnace was naturally cooled to 80° C., the sintered material was crushed to obtain 208.96 g of pre-lithiated lithium manganese iron phosphate precursor.

[0090] 200.00g of pre-lithiated lithium iron manganese phosphate precursor, 16.00g of glucose and 4.00g of cyclodextrin were added to a 2L measuring cup containing 800mL of water in sequence, and placed in a basket grinder and ground at a speed of 2000r / min for 30min. After the slurry particle size reaches 1-2um, the slurry is introduced into a sand mill for fine grinding. After the slurry particle size reaches 350nm, 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 8 hours. After the tubular furnace is naturally cooled to 80℃, the sintered material is graded and crushed to obtain a powder with a compaction density of 2.33g / cm 3 , LiFe with a carbon content of 1.42% 0.5 Mn 0.5 PO4 / C composite material.

[0091] Prepared LiFe 0.5 Mn 0.5 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 156.5mAh / g at 0.1C, with an initial efficiency of 98.2%. The initial reversible capacity at 0.2C was 153.8mAh / g, and at 1C was 146.3mAh / g.

[0092] Example 5

[0093] Preparation of iron-manganese oxide precursor:

[0094] 242.39g of ferric nitrate nine hydrate (purity 99.9%) and 322.06g of 50% manganese nitrate solution were dissolved in 750ml of deionized water to obtain a mixed metal salt solution A. Then 143.73g of NaOH (purity 96%) (molar ratio of OH - : total metal salt = 2.3), 72.07g (NH4) 2CO3 (purity 99.9%) (molar ratio CO3 2- : total metal salt = 0.5:1) was dissolved in 750 ml of deionized water to obtain a first precipitant mixed alkaline solution B.

[0095] At 30°C, the first precipitant mixed alkali solution B was added dropwise to a 2L three-necked flask containing a mixed metal salt solution A at 12.5 mL / min through a peristaltic pump. The addition time was 120 min. During the entire addition process, the stirring speed was 350 rpm, and the pH of the reaction system was 13.6. After the addition was completed, the temperature was raised to 50°C and the reaction was kept at a constant temperature for 7 hours. During the reaction, the stirring speed was 750 rpm. After the reaction was completed, the product was filtered, washed and filtered until the conductivity of the filtrate was <300 μS / cm; the filtered filter cake was placed in a 100°C forced air drying oven and dried for 12 hours, and finally 122.13 g of iron-manganese oxide precursor was obtained. After carbon-sulfur analyzer, ion chromatograph and ICP detection and analysis, the precursor had an S content of 0.001%, an N content of 0.021%, a Na content of 184.6 ppm, and a specific surface area of 173.7 m 2 / g; the Fe content is 26.45%, the Mn content is 39.05%, and after calculation, the molar ratio of Mn / Fe is 0.600:0.400, the Fe yield is 96.2%, and the Mn yield is 96.5%.

[0096] Preparation of lithium iron manganese phosphate / carbon composite material:

[0097] The raw materials were added according to the molar ratio of Li:(Fe+Mn):P=1.03:1:1.03. 115.0g of iron manganese oxide precursor, 147.29g of lithium dihydrogen phosphate (99%), 0.85g of magnesium hydroxide, and 0.83g of titanium dioxide 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 30min. After the slurry particle size reached 1-2um, the slurry was introduced into a sand mill for fine grinding. After the slurry particle size reached 350nm, 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 650°C for 4 hours. After the tubular furnace was naturally cooled to 80°C, the sintered material was crushed to obtain 206.72g of pre-lithiated lithium iron manganese phosphate precursor.

[0098] 200.00g of pre-lithiated lithium iron manganese phosphate precursor, 16.00g of glucose, 2.0g of starch, and 3.0g of cyclodextrin were added to a 2L measuring cup containing 800mL of ethanol in sequence, and placed in a basket grinder and ground at a speed of 2000r / min for 30min. After the slurry particle size reaches 1-2um, 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 730℃ for 8 hours. After the tubular furnace is naturally cooled to 80℃, the sintered material is graded and crushed to obtain a powder with a compaction density of 2.38g / cm 3 , LiFe with a carbon content of 1.39% 0.4 Mn 0.6 PO4 / C composite material.

[0099] 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 155.8mAh / g at 0.1C, with an initial efficiency of 97.6%. The initial reversible capacity at 0.2C was 152.5mAh / g, and at 1C was 145.8mAh / g.

[0100] Example 6

[0101] Preparation of iron-manganese oxide precursor:

[0102] 97.32g of anhydrous ferric chloride (99%) and 178.11g of manganese chloride tetrahydrate (purity 99%) were dissolved in 750ml of deionized water to obtain a mixed metal salt solution A. Then 146.86g of NaOH (96%) (molar ratio of OH - : total metal salt = 2.35), 83.01g NH4HCO3 (purity 99%) (molar ratio CO3 2- : total metal salt = 0.7:1) was dissolved in 750 ml of deionized water to obtain a first precipitant mixed alkaline solution B.

[0103] At 30°C, the first precipitant mixed alkali solution B was added dropwise to a 2L three-necked flask containing a mixed metal salt solution A at 50 mL / min through a peristaltic pump. The addition time was 15 minutes. During the entire addition process, the stirring speed was 350 rpm, and the pH of the reaction system was 13.7. After the addition was completed, the temperature was raised to 70°C and the reaction was carried out at a constant temperature for 3 hours. During the reaction, the stirring speed was 550 rpm. After the reaction was completed, the product was filtered, washed and filtered until the conductivity of the filtrate was <300 μS / cm; the filtered filter cake was placed in a 100°C forced air drying oven and dried for 12 hours, and finally 121.95 g of iron-manganese oxide precursor was obtained. After carbon-sulfur analyzer, ion chromatograph and ICP detection and analysis, the precursor had an S content of 0.002%, a Cl content of 0.015%, a Na content of 205.1 ppm, and a specific surface area of 194.5 m 2 / g; the Fe content is 26.73%, the Mn content is 39.00%, and the molar ratio Mn / Fe is 0.597:0.403, the Fe yield is 97.0%, and the Mn yield is 96.2%.

[0104] Preparation of lithium iron manganese phosphate / carbon composite material:

[0105] The raw materials were added according to the molar ratio of Li:(Fe+Mn):P=1.06:1:1.03. 120.00g of iron manganese oxide precursor, 53.80g of lithium carbonate (99.5%), 163.60g of ammonium dihydrogen phosphate (99%), and 1.50g of magnesium oxide were added to a 2L measuring cup containing 800mL of pure water in sequence and placed in a basket grinder for grinding at a speed of 2000r / min for 30min. After the slurry particle size reached 1-2um, the slurry was introduced into a sand mill for fine grinding. After the slurry particle size reached 380nm, 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 500℃ for 4 hours. After the tubular furnace was naturally cooled to 80℃, the sintered material was crushed to obtain 207.83g of pre-lithiated iron manganese phosphate lithium precursor.

[0106] 200.00g of pre-lithiated lithium manganese iron phosphate precursor, 8.00g of cyclodextrin, and 10.00g of glucose 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 30min. After the slurry particle size reaches 1-2um, the slurry is introduced into a sand mill for fine grinding. After the slurry particle size reaches 320nm, 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 10 hours. After the tubular furnace is naturally cooled to 80℃, the sintered material is graded and crushed to obtain a powder with a compaction density of 2.25g / cm 3 , LiFe with a carbon content of 1.63% 0.4 Mn 0.6 PO4 / C composite material.

[0107] 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 156.7mAh / g at 0.1C, with an initial efficiency of 98.2%. The initial reversible capacity at 0.2C was 153.5mAh / g, and at 1C was 147.1mAh / g.

[0108] Comparative Example 1

[0109] Compared with Example 1, the difference is that no sodium carbonate is added and the pH is 13.1.

[0110] Preparation of iron-manganese oxide precursor:

[0111] 152.73 g of hydrated ferric sulfate (Fe content 22%) and 152.10 g of monohydrated manganese sulfate (purity 99.9%) were dissolved in 750 ml of deionized water to obtain a mixed metal salt solution A. 137.49 g of NaOH (purity 96%) (molar ratio of OH - : total metal salt = 2.2) was dissolved in 750 ml of deionized water to obtain the first precipitant alkaline solution B.

[0112] At 30°C, the first precipitant alkaline solution B was added dropwise to a 2L three-necked flask containing a mixed metal salt solution A at 25mL / min through a peristaltic pump. The addition time was 30min. During the entire addition process, the stirring speed was 350rpm, and the pH of the reaction system was 13.1. After the addition was completed, the temperature was raised to 60°C and the reaction was carried out at a constant temperature for 4h. During the reaction, the stirring speed was 650rpm. After the reaction was completed, the product was filtered, washed and filtered until the conductivity of the filtrate was <300μS / cm; the filtered filter cake was placed in a 100°C forced drying oven and dried for 12h, and finally 120.07g of iron-manganese precursor was obtained. After carbon-sulfur analyzer and ICP detection and analysis, the precursor had an S content of 0.730%, a Na content of 7145.5ppm, and a specific surface area of 224.5m 2 / g; the Fe content is 25.42%, the Mn content is 37.02%, and the molar ratio Mn / Fe is 0.597:0.403, the Fe yield is 90.8%, and the Mn yield is 89.9%.

[0113] Compared with Example 1, the iron-manganese element yield of the iron-manganese precursor prepared in Comparative Example 1 is relatively low, and the impurities of S and Na are relatively high.

[0114] Preparation of lithium iron manganese phosphate / carbon composite material:

[0115] The raw materials were added according to the molar ratio of Li:(Fe+Mn):P=1.06:1:1.03. 115.00g of iron manganese oxide precursor, 51.10g of lithium carbonate (purity 99.5%), 155.40g of ammonium dihydrogen phosphate (purity 99%), and 1.42g of magnesium oxide were added to a 2L measuring cup containing 800mL of pure water in sequence, placed in a basket grinder and ground at 2000r / min for 30min. After the slurry particle size reached 1-2um, the slurry was introduced into a sand mill for fine grinding. After the slurry particle size reached 300nm, the slurry was spray-dried. After 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 600℃ for 4 hours. After the tubular furnace was naturally cooled to 80℃, the sintered material was crushed to obtain 201.91g of pre-lithiated iron manganese phosphate lithium precursor.

[0116] 200.00g of pre-lithiated lithium iron manganese phosphate precursor, 15.00g of glucose, and 15.00g 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 1-2um, 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 obtain a powder with a compaction density of 2.20g / cm 3 , LiFe with a carbon content of 1.45% 0.4 Mn 0.6 PO4 / C composite material.

[0117] Prepared LiFe 0.4 Mn 0.6 PO4 / 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 150.5mAh / g, the first efficiency of 0.1C is 96.1%, the initial reversible capacity of charge and discharge at 0.2C is 148.1mAh / g, and the initial reversible capacity of charge and discharge at 1C is 138.7mAh / g.

[0118] Comparative Example 2

[0119] Compared with Example 1, the difference is that the amount of sodium hydroxide added is 162.49g (molar ratio of OH - : total metal salts = 2.6), pH was 14.6.

[0120] Preparation of iron-manganese oxide precursor:

[0121] 152.73g of hydrated ferric sulfate (Fe content 22%) and 152.10g of monohydrated manganese sulfate (purity 99.9%) were dissolved in 750ml of deionized water to obtain a mixed metal salt solution A. Then 162.49g of NaOH (96%) (molar ratio of OH) was added. - : total metal salt = 2.6), 95.40g Na2CO3 (99%) (molar ratio CO3 2- : total metal salt = 0.6:1) was dissolved in 750 ml of deionized water to obtain a first precipitant mixed alkaline solution B.

[0122] At 30°C, the first precipitant mixed alkali solution B was added dropwise to a 2L three-necked flask containing a mixed metal salt solution A at 25 mL / min through a peristaltic pump. The addition time was 30 min. During the entire addition process, the stirring speed was 350 rpm, and the pH of the reaction system was 14.6. After the addition was completed, the temperature was raised to 60°C and the reaction was carried out at a constant temperature for 4 hours. During the reaction, the stirring speed was 650 rpm. After the reaction was completed, the product was filtered, washed and filtered until the conductivity of the filtrate was <300 μS / cm; the filtered filter cake was placed in a 100°C forced air drying oven and dried for 12 hours, and finally 119.51 g of iron-manganese oxide precursor was obtained. After carbon-sulfur analyzer and ICP detection and analysis, the precursor S content was 0.465%, the Na content was 4273.1 ppm, and the specific surface area was 120.9 m 2 / g; the Fe content is 26.14%, the Mn content is 39.88%, and the molar ratio Mn / Fe is 0.608:0.392, the Fe yield is 93.0%, and the Mn yield is 96.4%.

[0123] Compared with Example 1, the iron-manganese element yield of the iron-manganese precursor prepared in Comparative Example 2 is slightly lower, but the impurities of S and Na are higher.

[0124] Preparation of lithium iron manganese phosphate / carbon composite material:

[0125] The raw materials were added according to the molar ratio of Li:(Fe+Mn):P=1.06:1:1.03. 115.00g of iron manganese oxide precursor, 54.05g of lithium carbonate (purity 99.5%), 164.34g of ammonium dihydrogen phosphate (purity 99%), and 1.42g of magnesium oxide 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 30min. After the slurry particle size reached 1-2um, the slurry was introduced into a sand mill for fine grinding. After the slurry particle size reached 300nm, the slurry was spray-dried. After 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 600℃ for 4 hours. After the tubular furnace was naturally cooled to 80℃, the sintered material was crushed to obtain 208.92g of pre-lithiated iron manganese phosphate lithium precursor.

[0126] 200.00g of pre-lithiated lithium iron manganese phosphate precursor, 15.00g of glucose, and 15.00g 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 1-2um, 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 obtain a powder with a compaction density of 2.23g / cm 3 , LiFe with a carbon content of 1.48% 0.4 Mn 0.6 PO4 / C composite material.

[0127] Prepared LiFe 0.4 Mn 0.6 PO4 / 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 151.0mAh / g, the first efficiency of 0.1C is 95.8%, the initial reversible capacity of charge and discharge at 0.2C is 148.7mAh / g, and the initial reversible capacity of charge and discharge at 1C is 137.9mAh / g.

[0128] Comparative Example 3

[0129] Compared with Example 1, the difference is that the added amount of sodium hydroxide is 112.49 g (molar ratio NaOH:metal salt=1.8), and the pH is 10.3.

[0130] Preparation of iron-manganese oxide precursor:

[0131] 152.73 g of hydrated ferric sulfate (Fe content 22%) and 152.10 g of monohydrated manganese sulfate (purity 99.9%) were dissolved in 750 ml of deionized water to obtain a mixed metal salt solution A. 112.49 g of NaOH (purity 96%) (molar ratio of OH - : total metal salt = 1.8), 95.40g Na2CO3 (purity 99%) (molar ratio CO3 2- : total metal salt = 0.6:1) was dissolved in 750 ml of deionized water to obtain a first precipitant mixed alkaline solution B.

[0132] At 30°C, the first precipitant mixed alkali solution B was added dropwise to a 2L three-necked flask containing a mixed metal salt solution A at 25mL / min through a peristaltic pump. The addition time was 30min. During the entire addition process, the stirring speed was 350rpm, and the pH of the reaction system was 10.3. After the addition was completed, the temperature was raised to 60°C and the reaction was carried out at a constant temperature for 4h. During the reaction, the stirring speed was 650rpm. After the reaction was completed, the product was filtered, washed and filtered until the conductivity of the filtrate was <300μS / cm; the filtered filter cake was placed in a 100°C forced drying oven and dried for 12h, and finally 140.38g of iron-manganese precursor was obtained. After carbon-sulfur analyzer and ICP detection and analysis, the precursor had an S content of 0.038%, a Na content of 8107.3ppm, and a specific surface area of 193.5m 2 / g; the Fe content is 19.59%, the Mn content is 34.02%, and the molar ratio Mn / Fe is 0.638:0.362, the Fe yield is 81.8%, and the Mn yield is 96.6%.

[0133] Compared with Example 1, the iron element yield of the iron-manganese precursor prepared in Comparative Example 3 is slightly lower, and the Na impurity content is higher. Preparation of lithium iron manganese phosphate:

[0134] The raw materials are added according to the molar ratio of Li:(Fe+Mn):P=1.06:1:1.03. 135.00g of iron manganese oxide precursor, 51.54g of lithium carbonate (99.5%), 156.73g of ammonium dihydrogen phosphate (99%), and 1.42g of magnesium oxide are 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 30min. After the slurry particle size reaches 1-2um, 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 600℃ for 4 hours. After the tubular furnace is naturally cooled to 80℃, the sintered material is crushed to obtain 201.32g of pre-lithiated iron manganese phosphate lithium precursor.

[0135] 200.00g of pre-lithiated lithium iron manganese phosphate precursor, 15.00g of glucose, and 15.00g 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 1-2um, 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 obtain a powder with a compaction density of 2.21g / cm 3 , LiFe with a carbon content of 1.44% 0.36 Mn 0.64 PO4 / C composite material.

[0136] Prepared LiFe 0.36 Mn 0.64 PO4 / 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 150.5mAh / g, the first efficiency of 0.1C is 95.1%, the initial reversible capacity of charge and discharge at 0.2C is 147.5mAh / g, and the initial reversible capacity of charge and discharge at 1C is 137.1mAh / g.

[0137] Comparative Example 4

[0138] Compared with Example 1, the difference is that the coprecipitation reaction temperature is 80°C.

[0139] Preparation of lithium manganese iron phosphate precursor:

[0140] 152.73 g of hydrated ferric sulfate (Fe content 22%) and 152.10 g of monohydrated manganese sulfate (purity 99.9%) were dissolved in 750 ml of deionized water to obtain a mixed metal salt solution A. 137.49 g of NaOH (purity 96%) (molar ratio of OH - : total metal salt = 2.2), 95.40g Na2CO3 (purity 99%) (molar ratio CO3 2- : total metal salt = 0.6:1) was dissolved in 750 ml of deionized water to obtain a first precipitant mixed alkaline solution B.

[0141] At 30°C, the first precipitant mixed alkali solution B was added dropwise to a 2L three-necked flask containing a mixed metal salt solution A at 25mL / min through a peristaltic pump. The addition time was 30min. During the entire addition process, the stirring speed was 350rpm, and the pH of the reaction system was 13.3. After the addition was completed, the temperature was raised to 80°C and the reaction was carried out at a constant temperature for 4h. During the reaction, the stirring speed was 650rpm. After the reaction was completed, the product was filtered, washed and filtered until the conductivity of the filtrate was <300μS / cm; the filtered filter cake was placed in a 100°C forced drying oven and dried for 12h, and finally 114.21g of iron-manganese precursor was obtained. After carbon-sulfur analyzer and ICP detection and analysis, the precursor had an S content of 0.634%, a Na content of 5814.7ppm, and a specific surface area of 49.3m 2 / g; the Fe content is 27.03%, the Mn content is 39.02%, and the molar ratio Mn / Fe is 0.595:0.405, the Fe yield is 91.9%, and the Mn yield is 90.1%.

[0142] Compared with Example 1, the iron-manganese element yield of the iron-manganese precursor prepared in Comparative Example 4 is slightly lower, and the impurity content of S and Na is higher.

[0143] Preparation of lithium iron manganese phosphate / carbon composite material:

[0144] The raw materials were added according to the molar ratio of Li:(Fe+Mn):P=1.06:1:1.03. 110.00g of iron manganese oxide precursor, 51.70g of lithium carbonate (purity 99.5%), 157.23g of ammonium dihydrogen phosphate (purity 99%), and 1.42g of magnesium oxide 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 30min. After the slurry particle size reached 1-2um, the slurry was introduced into a sand mill for fine grinding. After the slurry particle size reached 300nm, the slurry was spray-dried. After 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 600℃ for 4 hours. After the tubular furnace was naturally cooled to 80℃, the sintered material was crushed to obtain 201.32g of pre-lithiated iron manganese phosphate lithium precursor.

[0145] 200.00g of pre-lithiated lithium iron manganese phosphate precursor, 15.00g of glucose, and 15.00g 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 1-2um, 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 obtain a powder with a compaction density of 2.25g / cm 3 , LiFe with a carbon content of 1.41% 0.4 Mn 0.6 PO4 / C composite material.

[0146] Prepared LiFe 0.4 Mn 0.6 PO4 / 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 150.5mAh / g, the first efficiency of 0.1C is 95.2%, the initial reversible capacity of charge and discharge at 0.2C is 146.8mAh / g, and the initial reversible capacity of charge and discharge at 1C is 136.9mAh / g.

[0147] Examples 1-6 of the present invention have low impurity content, high specific surface area, and good electrochemical performance, which are not easy to achieve simultaneously. Among them, the iron-manganese oxide precursor prepared using metal sulfate has an S content of 0.029-0.06%, a Na content of 133.2-215.9 ppm, and good electrochemical performance. Comparative Example 1 does not add sodium carbonate, Comparative Examples 2-3 vary the amount of sodium hydroxide added, and Comparative Example 4 varies the coprecipitation reaction temperature, all of which result in increased impurity content and decreased electrochemical performance.

[0148] 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 an iron-manganese oxide precursor, characterized in that: The steps include: (1) mixing a mixed alkali solution and an iron-manganese mixed metal salt solution to perform a coprecipitation reaction; (2) filtering, washing, and drying the reaction solution of step (1) to obtain an iron-manganese oxide precursor; The mixed alkaline solution is an aqueous solution of hydroxide and carbonate or bicarbonate; The total concentration of the mixed alkali solution is 4.0 mol / L-10.0 mol / L; The molar ratio of the carbonate or bicarbonate to the total metal elements of iron and manganese is (0.5-0.7):1; The molar ratio of the hydroxide to the total metal elements of iron and manganese is (2.1-2.4):1; The pH value of the coprecipitation reaction is 13.0-14.

0.

2. The preparation method according to claim 1, wherein The iron salt in the iron-manganese mixed metal salt is a trivalent iron salt, and the manganese salt is a divalent manganese salt; The total metal concentration in the iron-manganese mixed metal salt solution is 0.5 mol / L-5 mol / L, and the molar ratio of manganese to iron is x:(1-x), wherein x is 0.5-0.9; The carbonate is at least one of ammonium carbonate, sodium carbonate, and potassium carbonate; The bicarbonate is at least one of ammonium bicarbonate, sodium bicarbonate and potassium bicarbonate; The hydroxide is at least one of potassium hydroxide and sodium hydroxide; The coprecipitation reaction temperature is 50-70° C., and the reaction time is 2-8 hours.

3. The preparation method according to claim 1, wherein The mixing comprises: adding the mixed alkali solution to the iron-manganese mixed metal salt solution; preferably, the adding is done by dropwise addition, the dropwise addition time is 15 min-120 min, and the dropwise addition temperature is 20-30° C.; and the washing comprises washing until the filtrate conductivity is lower than 300 μS / cm.

4. A method for preparing a lithium iron manganese phosphate / carbon composite material, characterized in that: The steps include: S1. Mixing and grinding the iron-manganese oxide precursor according to any one of claims 1 to 3 with a lithium salt, a phosphate salt, and an additive in a liquid phase system, drying, and sintering under an inert atmosphere to obtain a pre-lithiated iron-manganese phosphate lithium precursor; S2. The pre-lithiated lithium iron manganese phosphate precursor obtained in step S1 and a carbon source are mixed and ground in a liquid phase system, and dried to obtain a lithium iron manganese phosphate / carbon composite material precursor; S3. Sintering the lithium manganese iron phosphate / carbon composite material precursor obtained in step S2 under an inert atmosphere to obtain the lithium manganese iron phosphate / carbon composite material.

5. The preparation method according to claim 4, wherein In step S1, the lithium salt is at least one of lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate; The phosphate salt is at least one of ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, ammonium phosphate, lithium dihydrogen phosphate, and lithium phosphate; The additive is at least one of titanium dioxide, tetrabutyl titanate, magnesium hydroxide, magnesium oxide, magnesium acetate, magnesium nitrate, zirconium dioxide, zirconium hydroxide, niobium pentoxide, nickel acetate and nickel oxide; The additive is added in an amount of 0-1.0% of the mass of the pre-lithiated lithium manganese iron phosphate precursor; The molar ratio of Li:(Fe+Mn):P in the lithium salt, iron-manganese oxide precursor and phosphate salt in step S1 is (1.1-1.0):1(1.1-1.0); The sintering temperature in step S1 is 400-700°C and the sintering time is 2-6 hours; The inert atmosphere is any one of nitrogen, argon and helium; In steps S1 and S2, the liquid phase system is any one of water, ethanol, and methanol, and the grinding is as follows: first, coarse grinding to a particle size of D 50 =1-2um, then finely grind to a particle size of 300-500nm; The carbon source in step S2 is at least one of glucose, crystal sugar, sucrose, fructose, polyethylene glycol, cyclodextrin, starch and cellulose.

6. The preparation method according to claim 4, wherein The sintering temperature in step S3 is 675-780°C and the sintering time is 4-10 hours; The inert atmosphere is at least one of nitrogen, argon, and helium; The mass content of carbon in the lithium manganese iron phosphate / carbon composite material is 1.2%-2.0%.

7. Use of the preparation method according to any one of claims 1 to 3 and / or the preparation method according to any one of claims 4 to 6 in reducing impurities in an iron-manganese oxide precursor and a lithium iron-manganese phosphate / carbon composite material.

8. An iron-manganese oxide precursor prepared by the preparation method according to any one of claims 1 to 3.

9. A lithium iron manganese phosphate / carbon composite material prepared by the preparation method according to any one of claims 4 to 6.

10. A battery comprising the lithium iron manganese phosphate / carbon composite material prepared by the preparation method according to any one of claims 4 to 6.

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