Preparation method and application of ferric manganese phosphate precursor

Abstract

The invention discloses a preparation method and application of a ferric manganese phosphate precursor, and belongs to the technical field of lithium ion battery positive electrode materials. The technical problem to be solved is to simplify the preparation process and ensure good electrochemical performance. According to the technical scheme, the preparation method of the ferric manganese phosphate precursor comprises the following steps: dissolving an iron source, a manganese source and an oxidizing agent in water to obtain a metal salt solution; adding the phosphorus source solution into the metal salt solution for reaction, and after reaction, carrying out solid-liquid separation, washing, drying and dehydrating to obtain a ferric manganese phosphate precursor; the ratio of the molar weight of the phosphorus source to the total molar weight of iron and manganese is (1.0-2.0): 1; the ratio of the molar weight of the oxidizing agent to the total molar weight of iron and manganese is (0.6-1.5): 1; the reaction temperature in the step (2) is 80-100 DEG C, and the reaction time is 3-6 hours; the preparation method does not need to adjust the pH value.

Description

Technical Field

[0001] This invention provides a method for preparing and applying an iron-manganese phosphate precursor, belonging to the field of lithium-ion battery cathode material technology. Background Technology

[0002] For understanding the technical content of this invention: Currently, the most promising power batteries are lithium-ion batteries, characterized by high energy density, fast charge / discharge current, and long cycle life. Among them, lithium iron phosphate (LFP) has become one of the most widely used cathode materials due to its high safety performance and relatively low cost. However, LFP cathode materials have drawbacks such as poor conductivity and a low operating voltage platform. Meanwhile, lithium iron manganese phosphate (LMP) has a higher output voltage and higher capacity compared to LFP. Therefore, LMP has broad development prospects.

[0003] Currently, there are various methods for preparing lithium iron manganese phosphate precursors, among which the most important synthetic routes are the solid-state method and the co-precipitation method. The high-temperature solid-state method is relatively simple and is the most easily adopted method for industrial production.

[0004] Relevant patent documents retrieved: This document, published in China (CN119191363) on December 27, 2024, discloses a method for preparing and applying iron-manganese oxide. It involves complexing a metal salt, adding a precipitant to control the pH, and then generating Mn. 0.6 Fe 0.4 (OH)2; air-dried oxidation produces Mn 0.6 Fe 0.4 OOH; then high-temperature calcination to generate iron-manganese oxides. This method involves metal salt complexation precipitation, drying, and sintering to generate uniformly distributed iron-manganese oxides. However, it uses organic complexing agents multiple times, increasing wastewater treatment costs. The process is cumbersome and difficult to industrialize.

[0005] This document, published in China (CN119285457) on January 10, 2025, discloses a method for preparing a precursor of ferromanganese oxalate. The method involves adding ammonium oxalate to a metal salt to synthesize ferromanganese oxalate; then adding a phosphorus source and a lithium source, mixing and ball milling, and finally sintering to obtain lithium iron manganese phosphate cathode material. Ferromanganese oxalate is easier to synthesize than ferromanganese phosphate, but the synthesis of lithium iron manganese phosphate generates a large amount of CO2, affecting compaction density and cycle performance.

[0006] The document, published in China (CN118782788) on October 15, 2024, discloses a lithium iron manganese phosphate cathode material, its preparation method, cathode sheet, and lithium-ion battery. The preparation method involves sequentially grinding and dehydrating a mixture of raw materials including a lithium source, iron source, manganese source, phosphorus source, and water to obtain a precursor compound. Then, a mixture of raw materials including the precursor compound, an M metal source, a dispersant, and water is sequentially ball-milled, dried, pre-sintered, and sintered to obtain the lithium iron manganese phosphate cathode material.

[0007] This method improves electrochemical performance by doping with different metal elements, but the iron and manganese are not evenly distributed at the atomic level. The Jahn-Teller effect of manganese will seriously affect the cycle and rate performance of the battery.

[0008] Relevant non-patent literature retrieved: Journal or book title: Mining and Metallurgical Engineering; Article title: Mn 0.6 Fe 0.4 "Preparation and Electrochemical Performance Study of PO4 / C Cathode Material", Volume 44, Issue 4, Publication Date: August 2024. This document discloses Mn... 0.6 Fe 0.4 The preparation method of the PO4 / C cathode material precursor involves dissolving manganese salt, iron salt, and ascorbic acid in water to obtain a mixed salt solution; adjusting the pH to 4.5 with ammonia and sulfuric acid; adding the solution to a reaction vessel; and maintaining the reaction pH at 4.5 with ammonia. Although the initial discharge specific capacity at 1C is 145.5 mAh / g, this method requires pH adjustment, and subsequent ammonia removal is necessary due to the use of ammonia. The process is cumbersome and difficult to industrialize. The aforementioned literature represents at least the following unresolved technical problems or defects: Existing technologies require complex preparation processes to achieve good electrochemical performance; relevant evidence includes: [Mn...] 0.6 Fe 0.4 The study on the preparation and electrochemical performance of PO4 / C cathode materials requires multiple uses of acids and bases and repeated pH adjustments to achieve an initial discharge specific capacity of 145.5 mAh / g at 1C. Due to the use of ammonia, subsequent ammonia removal treatment is also necessary. The process is cumbersome and difficult to industrialize. Chinese patent CN119191363 uses organic complexing agents multiple times, increasing wastewater treatment costs; the process is also cumbersome and difficult to industrialize. Summary of the Invention

[0009] The purpose of this invention is to provide: A method for preparing an iron-manganese phosphate precursor, and related technologies, to solve technical problems such as simplifying the preparation process while ensuring good electrochemical performance, or a combination thereof.

[0010] Terminology Explanation: Unless otherwise defined, all technical terms in this document have the same meanings as commonly understood by one of ordinary skill in the art to which the subject matter of the claims pertains. Unless otherwise stated, all patents, patent inventions, and publications cited in this document are incorporated herein by reference in their entirety. If multiple definitions exist for terms in this document, the definitions in this chapter shall prevail.

[0011] It should be understood that the above brief description and the following detailed description are exemplary and for illustrative purposes only, and do not limit the subject matter of the invention in any way. In this invention, unless specifically stated otherwise, the singular is used to include the plural. It should also be noted that unless otherwise stated, the use of “or” or “or” means “and / or”. Furthermore, the definitions of the terms used can be found in the reference “Applied Electrochemistry, Yang Hui and Lu Wenqing, Science Press”.

[0012] Unless otherwise stated, conventional methods within the scope of the art, such as compaction density measurement and electrochemical performance measurement, shall be used.

[0013] Unless specifically defined herein, the use of all commercially available products herein employs standard techniques. For example, it may be carried out using the manufacturer's instructions for use with the kit, or in accordance with methods known in the art or the description of this invention. The techniques and methods described herein can generally be implemented according to conventional methods well known in the art, based on the descriptions in the various summary and more specific documents cited and discussed in this specification.

[0014] The term "washing" as used in this article refers to the removal of impurities or other soluble contaminants from the surface of a material using a solvent, thereby improving the purity of the material and the efficiency of subsequent processing.

[0015] The term "drying" as used in this article refers to the removal of moisture or other volatile solvents from materials to prevent the presence of moisture from causing a decline in material properties or abnormal reactions during subsequent processing.

[0016] The term "sintering" as used in this article refers to the physical and chemical bonding between material particles through high-temperature treatment to form a dense solid.

[0017] The term "solid-liquid separation" as used in this article refers to the process of separating solid particles from a liquid. This is a common physical operation widely used in fields such as chemistry, chemical engineering, pharmaceuticals, food science, and environmental science. The purpose of solid-liquid separation is to separate solid particles from liquids in order to recover the solid, purify the liquid, or achieve separate processing of both.

[0018] In a first aspect, the present invention provides: a method for preparing an iron-manganese phosphate precursor, characterized by comprising the following steps: (1) Dissolve the iron source, manganese source, and oxidant in water to obtain a metal salt solution; (2) Add the phosphorus source solution to the metal salt solution to react. After the reaction, separate the solid and liquid, wash, dry and dehydrate to obtain the iron-manganese phosphate precursor. The molar ratio of the phosphorus source to the total molar ratio of iron and manganese is 1.0-2.0:1. The molar ratio of the oxidant to the total molar ratio of iron and manganese is 0.6-1.5:1. The reaction temperature in step (2) is 80-100℃ and the time is 3-6 hours. The preparation method does not require pH adjustment.

[0019] The iron source for the technical feature is selected from at least one of ferrous sulfate, ferrous nitrate and ferrous chloride.

[0020] The manganese source for the technical feature is selected from at least one of manganese sulfate, manganese nitrate, and manganese chloride.

[0021] The oxidant used in this technical feature is selected from: ammonium persulfate or a mixture of ammonium persulfate and hydrogen peroxide.

[0022] Among them, the molar ratio of the mixture of ammonium persulfate and hydrogen peroxide is (4-8):1.

[0023] The total molar concentration of iron and manganese in the technical characteristics is selected from 0.5-3.0 mol / L.

[0024] The preferred total molar concentration of iron and manganese is 1-2.5 mol / L.

[0025] Among them, technical feature A is further preferably 1 mol / L, 1.25 mol / L, 1.5 mol / L, 1.67 mol / L, 1.75 mol / L, 2 mol / L, 2.25 mol / L, and 2.5 mol / L.

[0026] Among them, technical feature A is further preferably 1 mol / L, 1.25 mol / L, 1.25 mol / L, 1.67 mol / L, or 2.5 mol / L.

[0027] Among them, the technical feature is that the molar ratio of iron to manganese is x:y, which is selected from: y is 0.5-0.9, x+y=1.

[0028] Among them, the preferred technical feature y is y=0.5-0.8.

[0029] Among them, the technical feature y is further preferably 0.5, 0.6, 0.7, or 0.8.

[0030] The phosphorus source for the technical feature is selected from at least one of the following: phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, and sodium phosphate.

[0031] The preferred phosphorus source is selected from at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate.

[0032] The preferred phosphorus source is selected from at least one of phosphoric acid, ammonium dihydrogen phosphate, and ammonium phosphate.

[0033] The concentration of the phosphorus source solution, as a technical feature, is selected from 0.5-3.0 mol / L.

[0034] The preferred concentration of the phosphorus source solution is 1-2.5 mol / L.

[0035] The concentration of the phosphorus source solution is further preferably 1.26-2.5 mol / L.

[0036] The concentration of the phosphorus source solution is further preferably 1.26 mol / L, 1.875 mol / L, 2.25 mol / L, 2.4 mol / L, or 2.42 mol / L.

[0037] The temperature at which the phosphorus source solution is added is selected from 80-100℃.

[0038] The preferred temperature for adding the phosphorus source solution is 90-97℃.

[0039] The preferred temperature for adding the phosphorus source solution is 90, 91, 92, 93, 94, 95, 96, or 97°C.

[0040] The technical feature is that the rate at which the phosphorus source solution is added is selected from 5-40 mL / min.

[0041] The preferred addition rate of the phosphorus source solution is 20-35 mL / min.

[0042] The preferred addition rate of the phosphorus source solution is 20, 25, 30, or 35 mL / min.

[0043] The technical feature of washing is: washing until the conductivity of the filtrate is below 300 μS / cm.

[0044] The ratio of the molar amount of phosphorus source to the total molar amount of iron and manganese is selected from 1.0-2.0:1.

[0045] The preferred ratio of the molar amount of phosphorus source to the total molar amount of iron and manganese is 1.00-1.90:1.

[0046] The preferred ratio of the molar amount of phosphorus source to the total molar amount of iron and manganese is 1.00-1.80:1.

[0047] The preferred ratio of the molar amount of phosphorus source to the total molar amount of iron and manganese is: 1.00, 1.01, 1.10, 1.20, 1.21, 1.30, 1.40, 1.50, 1.60, 1.70, or 1.80.

[0048] The ratio of the molar amount of the oxidant to the total molar amount of iron and manganese is selected from 0.6-1.5:1.

[0049] The preferred ratio of the molar amount of the oxidant to the total molar amount of iron and manganese is 0.9-1.2:1.

[0050] The preferred ratio of the molar amount of the oxidant to the total molar amount of iron and manganese is 0.9:1, 1:1, 1.1:1, or 1.2:1.

[0051] The ratio of the molar amount of the oxidant to the total molar amount of iron and manganese is further preferably 0.9:1, 1:1, or 1.2:1.

[0052] The temperature and time of the reaction in technical feature step (2) are selected from: temperature of 80-100℃ and time of 3-6h.

[0053] The temperature and time of the reaction in technical feature step (2) are more preferably: the temperature is 90-97℃ and the time is 4-6h.

[0054] The temperature and time of the reaction in technical feature step (2) are further preferably: the temperature is 90, 91, 92, 93, 94, 95, 96, or 97°C, and the time is 4h, 5h, or 6h.

[0055] Secondly, the present invention provides: an iron manganese phosphate precursor, prepared by the above-described preparation method.

[0056] Thirdly, the present invention provides the application of the iron manganese phosphate precursor in battery preparation.

[0057] Fourthly, the present invention provides a method for preparing a lithium iron manganese phosphate / carbon composite material, comprising the following steps: S1. Dehydrate the iron manganese phosphate precursor to obtain the dehydrated iron manganese phosphate precursor. S2. Take the lithium source, the dehydrated iron manganese phosphate precursor, the phosphorus source, the carbon source and the additives, grind, mix and dry them to obtain the lithium iron manganese phosphate / carbon composite material precursor. S3. The obtained lithium iron manganese phosphate / carbon composite material precursor is sintered in an inert gas atmosphere to obtain the lithium iron manganese phosphate / carbon composite material.

[0058] The technical features of dehydration include a temperature of 300-700℃, a time of 3-6 hours, and a dehydration atmosphere of at least one of air, nitrogen, and argon.

[0059] The preferred temperature and time for dehydration are: 500-550℃ and 4-6h.

[0060] The temperature and time for dehydration are further preferred to be: 500℃, 510℃, 520℃, 530℃, 540℃, and 550℃, and 4h, 5h, and 6h respectively.

[0061] The lithium source for the technical feature is selected from at least one of lithium carbonate, lithium hydroxide, and lithium acetate.

[0062] Among them, the ratio of the molar amount of lithium in the lithium source to the total molar amount of iron and manganese in the iron-manganese phosphate precursor is selected from 1.02-1.10:1.

[0063] The preferred ratio of the molar amount of lithium in the lithium source to the total molar amount of iron and manganese in the iron-manganese phosphate precursor is 1.04-1.08:1.

[0064] Among them, the ratio of the molar amount of lithium in the lithium source to the total molar amount of iron and manganese in the iron manganese phosphate precursor is further preferably 1.04:1, 1.06:1, or 1.08:1.

[0065] In particular, the ratio of the total molar amount of phosphorus in the phosphorus source to the total molar amount of iron and manganese in the iron-manganese phosphate precursor in technical feature step S2 is selected from: 1:0.96-0.99.

[0066] The preferred ratio of the total molar amount of phosphorus in the phosphorus source to the total molar amount of iron and manganese in the iron-manganese phosphate precursor is 1:0.97-0.985.

[0067] The ratio of phosphorus in the phosphorus source to the total molar amount of iron and manganese in the iron-manganese phosphate precursor, as described in technical feature step S2, is further preferably 1:0.97, 1:0.975, 1:0.98, or 1:0.985.

[0068] The carbon source for the technical feature is selected from at least one of glucose, rock sugar, sucrose, fructose, polyethylene glycol, cyclodextrin, starch, and cellulose.

[0069] The preferred amount of carbon source added is 8%-20% of the mass of the iron manganese phosphate precursor.

[0070] The technical feature additives are selected from at least one of the following: titanium dioxide, tetrabutyl titanate, magnesium acetate, magnesium oxide, magnesium hydroxide, magnesium nitrate, zirconium nitrate, zirconium dioxide, zirconium hydroxide, niobium pentoxide, nickel acetate, nickel nitrate, and nickel hydroxide.

[0071] The preferred technical additives are: magnesium oxide, niobium pentoxide, titanium dioxide, magnesium hydroxide, tetrabutyl titanate, and magnesium acetate.

[0072] The preferred technical additives are: magnesium oxide, niobium pentoxide, titanium dioxide, magnesium hydroxide, and magnesium acetate.

[0073] The preferred technical additives are: magnesium oxide, niobium pentoxide, titanium dioxide, and magnesium hydroxide.

[0074] The technical feature of grinding is that it is carried out in a liquid phase system.

[0075] The preferred liquid phase system for the technical feature is at least one of water, methanol, or ethanol.

[0076] The preferred grinding technique is as follows: first, coarse grinding is performed using a basket mill for 30-60 minutes, with the particle size controlled within D. 50 =1-2μm; then use a fine sand mill for fine grinding, the grinding time is 60-180min, and the particle size of the finely ground slurry is controlled at 200-500nm.

[0077] The sintering process described in technical step S3 is as follows: the temperature is 650-750℃ and the time is 6-12h.

[0078] The preferred sintering step S3 is at a temperature of 700-720℃ and a time of 10-12h.

[0079] The sintering described in technical feature step S3 is further preferably performed at temperatures of 700℃, 710℃, and 720℃, and for times of 10h, 11h, and 12h.

[0080] The preparation method further includes a graded crushing process.

[0081] Fifthly, the present invention provides: a lithium iron manganese phosphate / carbon composite material prepared by the above preparation method, wherein the carbon content is 1.2-2.5 wt.%.

[0082] In a sixth aspect, the present invention provides a battery comprising the lithium iron manganese phosphate / carbon composite material prepared by the above-described preparation method.

[0083] The beneficial effects of this invention are as follows: The present invention has at least the following beneficial effects: Compared with existing technologies, this invention has better technical effects in terms of simplifying the preparation process while ensuring good electrochemical performance.

[0084] According to experimental tests, the present invention simplifies the preparation process from the cumbersome steps of existing technologies, such as adjusting pH, using organic solvents, and removing ammonia, to a process that does not require pH adjustment, does not use organic solvents, and does not require ammonia removal.

[0085] According to experimental tests, the present invention enables the electrochemical performance to still achieve an initial reversible capacity of over 154.2 mAh / g at 0.1C charge / discharge, over 152.1 mAh / g at 0.2C charge / discharge, and over 145.0 mAh / g at 1C charge / discharge, even after simplifying the preparation process.

[0086] (1) In this invention, manganese and iron sources are first dissolved in pure water, and then an oxidant is added to obtain a metal salt solution. A phosphorus source solution is added to the metal salt solution, and the reaction is carried out at a certain temperature. After filtration, washing, and drying, manganese iron phosphate monohydrate is finally obtained. The entire reaction process is simple to operate, can be carried out under normal pressure, avoids the use of organic solvents such as ethanol, avoids adjusting the pH of the solution, is more environmentally friendly, and is easier to industrialize.

[0087] (2) The iron manganese phosphate salt prepared by the present invention has a high specific surface area and small particle size, which is beneficial for grinding, can shorten the grinding process time, and has good processing performance.

[0088] (3) The present invention also provides a method for preparing lithium iron manganese phosphate; by mixing, grinding and sintering the self-made iron manganese phosphate precursor with lithium carbonate, an excellent lithium iron manganese phosphate cathode material can be prepared.

[0089] Furthermore, based on the present invention: Based on the comparison between Examples 1-6 and Comparative Examples 1-6, this invention achieves new technical effects by employing a combination of specific co-precipitation reaction conditions, specific oxidant dosage, and specific phosphorus source dosage, simplifying the preparation process while ensuring good electrochemical performance. The combined technical effect is superior to the sum of the effects of each individual technique. Attached Figure Description

[0090] Figure 1 : A 50,000x SEM image of the iron manganese phosphate monohydrate precursor prepared in Example 1; Figure 2 XRD pattern of the iron manganese phosphate precursor prepared in Example 1.

[0091] Figure 3XRD pattern of lithium iron manganese phosphate prepared in Example 1; Figure 4 Discharge curve of lithium iron manganese phosphate button battery prepared in Example 1. Detailed Implementation

[0092] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way. The following content is merely an exemplary description of the scope of protection claimed by the present invention, and those skilled in the art can make various changes and modifications to the present invention based on the disclosed content, and such changes should also fall within the scope of protection claimed by the present invention.

[0093] The present invention will be further described below by way of specific embodiments. Unless otherwise specified, all instruments, devices, equipment, reagents, products, etc., used in the embodiments of the present invention are obtained through conventional commercial means.

[0094] Example 1 A precursor of iron-manganese phosphate, the preparation method of which includes the following steps: (1) Dissolve 112.33g of ferrous sulfate heptahydrate (99% purity) and 102.43g of manganese sulfate monohydrate (99% purity) in 800mL of deionized water, then add 279.43g of ammonium persulfate (98% purity) and dissolve to obtain a metal salt solution.

[0095] (2) Dissolve 138.86g of ammonium dihydrogen phosphate (purity 99.4%) in 500mL of deionized water to obtain a phosphorus source solution; add the phosphorus source solution dropwise to the metal salt solution at 95℃ at a dropwise rate of 20mL / min. During the entire dropwise addition process, the stirring speed is 350ppm. Start timing when the dropwise addition is completed and the solution temperature reaches 95℃. React for 4h while maintaining the stirring speed at 350rpm. After the reaction is completed, filter, wash and vacuum filter the product until the conductivity of the filtrate is <300μS / cm. Place the obtained iron manganese phosphate precursor filter cake in an 80℃ forced-air drying oven for 12 hours to finally obtain 163.6g of iron manganese phosphate precursor.

[0096] Analysis showed that the specific surface area of ​​this iron-manganese phosphate precursor was 89.35 m². 2 / g, of which Fe content is 13.63%, Mn content is 19.09%, and P content is 14.91%. The calculated molar ratio Mn / (Mn+Fe) is 0.587, the Fe yield is 99.854%, the Mn yield is 94.747%, and the P yield is 65.627%.

[0097] Scanning electron microscopy was performed on the iron-manganese phosphate precursor, and the results are as follows: Figure 1Simultaneously, the obtained iron-manganese phosphate precursor was characterized by XRD and subjected to phase analysis. The characterization results are as follows: Figure 2 As shown.

[0098] from Figure 1 It can be seen that the prepared iron-manganese phosphate precursor secondary particles are spherical with a diameter between 1-3 μm. From Figure 2 It can be seen that the XRD pattern of the prepared iron manganese phosphate precursor is consistent with the standard XRD pattern (PDF#44-0071 MnPO4·H2O) and there are no extra impurity peaks, indicating that the prepared iron manganese phosphate precursor is iron manganese phosphate monohydrate.

[0099] The above-mentioned iron-manganese phosphate precursor is used to prepare lithium iron-manganese phosphate / carbon composite materials. The preparation method of lithium iron-manganese phosphate / carbon composite materials includes the following steps: S1. The iron-manganese phosphate precursor was heated and dehydrated in a muffle furnace at 550℃ for 4 hours to obtain a dehydrated iron-manganese phosphate precursor (Fe content 16.22%, Mn content 22.95%, P content 18.44%). The raw materials were fed according to the raw material molar ratio Li / (Fe+Mn) = 1.06:1 and (Fe+Mn) / P = 0.975:1. 100g of the dehydrated iron-manganese phosphate precursor and 15.16g of dihydrogen phosphate were added... Ammonium (99.4 wt.%), 27.88 g lithium carbonate (99.5 wt.%), 9.21 g glucose, 3.45 g polyethylene glycol 20000, 0.46 g magnesium oxide, and 0.46 g titanium dioxide were added to 800 mL of anhydrous ethanol and ground in a basket mill at 1500 r / min for 60 min. After grinding, the slurry was fed into a sand mill and ground until the particle size of the slurry reached 400 nm. Then, the slurry was spray-dried. S2. After drying, the dried and crushed material is placed in a tube furnace under a nitrogen atmosphere for sintering at 700℃ for 10 hours. After the tube furnace cools down naturally to 80℃, the sintered material is graded and crushed to obtain a powder with a carbon content of 1.62% and a compacted density of 2.25 g / cm³. 3 LiFe 0.41 Mn 0.59 PO4 / C composite material. (Compacted density measurement: measured using a Sansi longitudinal and transverse compaction density meter) The obtained LiFe 0.41 Mn 0.59 The PO4 / C composite material was characterized by XRD and subjected to phase analysis. The characterization results are as follows: Figure 3 As shown. From Figure 3 It can be seen that LiFe 0.4 Mn 0.6XRD pattern of PO4 / C composite material and standard XRD pattern (PDF#89-7115Li(Fe) 0.77 Mn 0.23 The presence of PO4 and the absence of extra impurity peaks indicate that lithium iron manganese phosphate was prepared, with C existing as an amorphous carbon layer.

[0100] Prepared LiFe 0.41 Mn 0.59 PO4 / C composite material is used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder. The electrode sheets are made in a mass ratio of 90:5:5. Lithium metal is used as the negative electrode and assembled into a lithium iron manganese phosphate coin cell. Figure 4 The discharge curve of the prepared lithium iron manganese phosphate coin cell was obtained from... Figure 4 It can be seen that, under different charge and discharge current conditions at 2-4.3V and 25℃, the initial reversible capacity is 154.6mAh / g when charged and discharged at 0.1C, 152.8mAh / g when charged and discharged at 0.2C, and 145.2mAh / g when charged and discharged at 1C.

[0101] Example 2 A precursor of iron-manganese phosphate, the preparation method of which includes the following steps: (1) Dissolve 56.17g of ferrous sulfate heptahydrate (purity 99%) and 136.57g of manganese sulfate monohydrate (purity 99%) in 800mL of deionized water, then add 209.57g of ammonium persulfate (purity 98%), stir well to obtain a metal salt solution.

[0102] (2) Dissolve 138.86g of ammonium dihydrogen phosphate (purity 99.4%) in 500mL of deionized water to obtain a phosphorus source solution; add the phosphorus source solution dropwise to the metal salt solution at 90℃ at a dropwise rate of 20mL / min. During the entire dropwise addition process, the stirring speed is 350ppm. Start timing when the dropwise addition is completed and the solution temperature reaches 90℃. React for 6h while maintaining the stirring speed at 350rpm. After the reaction is completed, filter, wash and vacuum filter the product until the conductivity of the filtrate is <300μS / cm. Place the obtained iron manganese phosphate precursor filter cake in an 80℃ forced-air drying oven for 12 hours to finally obtain 164.55g of iron manganese phosphate precursor.

[0103] Analysis showed that the specific surface area of ​​this iron-manganese phosphate precursor was 85.31 m². 2 / g, of which Fe content is 6.71%, Mn content is 25.23%, and P content is 15.63%. The calculated molar ratio Mn / (Mn+Fe) is 0.793, the Fe yield is 98.857%, the Mn yield is 94.461%, and the P yield is 69.196%.

[0104] The above-mentioned iron-manganese phosphate precursor is used to prepare lithium iron-manganese phosphate / carbon composite materials. The preparation method of lithium iron-manganese phosphate / carbon composite materials includes the following steps: S1. The iron-manganese phosphate precursor was heated and dehydrated in a muffle furnace at 500℃ for 6 hours to obtain a dehydrated iron-manganese phosphate precursor (Fe content 8.12%, Mn content 30.22%, P content 18.88%). The raw materials were fed according to the raw material molar ratio Li / (Fe+Mn) = 1.04:1 and (Fe+Mn) / P = 0.97:1. 100g of the dehydrated iron-manganese phosphate precursor and 12.43g... Ammonium dihydrogen phosphate (99.4 wt.%), 26.86 g lithium carbonate (99.5 wt.%), 8.99 g glucose, 3.37 g polyethylene glycol 20000, and 0.9 g magnesium hydroxide were added to 800 mL of anhydrous ethanol and ground in a basket mill at 1500 r / min for 60 min. After grinding, the slurry was fed into a sand mill and ground until the particle size of the slurry reached 400 nm. Then, the slurry was spray-dried. S2. After drying, the dried and crushed material is placed in a tube furnace under a nitrogen atmosphere for sintering at 700℃ for 10 hours. After the tube furnace cools down naturally to 80℃, the sintered material is graded and crushed to obtain a powder with a carbon content of 1.65% and a compacted density of 2.24 g / cm³. 3 LiFe 0.21 Mn 0.79 PO4 / C composite material.

[0105] Prepared LiFe 0.21 Mn 0.79 A PO4 / C composite material was used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder. Electrode sheets were fabricated using a mass ratio of 90:5:5. Lithium metal was used as the negative electrode, and the cells were assembled to simulate a lithium iron manganese phosphate coin cell. Tests were conducted at 2-4.3V and 25℃ under different charge / discharge current conditions. The initial reversible capacity was 154.2 mAh / g at 0.1C, 152.5 mAh / g at 0.2C, and 145.3 mAh / g at 1C.

[0106] Example 3 A precursor of iron-manganese phosphate, the preparation method of which includes the following steps: (1) Dissolve 140.41g of ferrous sulfate heptahydrate (99% purity) and 85.36g of manganese sulfate monohydrate (99% purity) in 400mL of deionized water, then add 186.29g of ammonium persulfate (98% purity) and 22.69g of 30% hydrogen peroxide solution, stir well to obtain a metal salt solution.

[0107] (2) Dissolve 23.06g of 85% phosphoric acid and 92.58g of ammonium dihydrogen phosphate (purity 99.4%) in 800mL of deionized water to obtain a phosphorus source solution; add the phosphorus source solution dropwise to the metal salt solution at 97℃ at a dropwise rate of 35mL / min. During the entire dropwise addition process, the stirring speed is 350ppm; start timing when the dropwise addition is completed and the solution temperature reaches 97℃, and react for 4h while maintaining the stirring speed at 350rpm; after the reaction is completed, filter, wash and vacuum filter the product until the conductivity of the filtrate is <300μS / cm. Place the obtained iron manganese phosphate precursor filter cake in an 80℃ forced-air drying oven for 12 hours to finally obtain 162.98g of iron manganese phosphate precursor.

[0108] Analysis showed that the specific surface area of ​​this iron-manganese phosphate precursor was 78.66 m². 2 / g, of which Fe content is 16.54%, Mn content is 16.32%, and P content is 16.34%. The calculated molar ratio Mn / (Mn+Fe) is 0.501, the Fe yield is 96.542%, the Mn yield is 96.830%, and the P yield is 85.978%.

[0109] The above-mentioned iron-manganese phosphate precursor is used to prepare lithium iron-manganese phosphate / carbon composite materials. The preparation method of lithium iron-manganese phosphate / carbon composite materials includes the following steps: S1. The iron-manganese phosphate precursor was heated and dehydrated in a muffle furnace at 550℃ for 5 hours to obtain a dehydrated iron-manganese phosphate precursor (Fe content 19.43%, Mn content 19.11%, P content 19.56%). The raw materials were fed according to the raw material molar ratio Li / (Fe+Mn) = 1.08:1, (Fe+Mn) / P = 0.98:1. 100g of the dehydrated iron-manganese phosphate precursor and 9.08g of phosphorus... Ammonium dihydrogen phosphate (99.4 wt.%), 27.90 g lithium carbonate (99.5 wt.%), 8.73 g glucose, 3.27 g polyethylene glycol 20000, and 0.87 g magnesium hydroxide were added to 800 mL of anhydrous ethanol and ground in a basket mill at 1500 r / min for 60 min. After grinding, the slurry was fed into a sand mill and ground until the particle size of the slurry reached 400 nm. Then, the slurry was spray-dried. S2. After drying, the dried and crushed material is placed in a tube furnace under a nitrogen atmosphere for sintering at 700℃ for 12 hours. After the tube furnace cools down naturally to 80℃, the sintered material is graded and crushed to obtain a powder with a carbon content of 1.64% and a compacted density of 2.26 g / cm³. 3 LiFe 0.5 Mn 0.5 PO4 / C composite material.

[0110] Prepared LiFe 0.5 Mn 0.5 A PO4 / C composite material was used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder. Electrode sheets were fabricated using a mass ratio of 90:5:5. Lithium metal was used as the negative electrode, and the cells were assembled into lithium iron manganese phosphate coin cells. Tests were conducted at 2-4.3V and 25℃ under different charge / discharge current conditions. The initial reversible capacity was 154.8 mAh / g at 0.1C, 153.0 mAh / g at 0.2C, and 145.1 mAh / g at 1C.

[0111] Example 4 A precursor of iron-manganese phosphate, the preparation method of which includes the following steps: (1) Dissolve 84.25g of ferrous sulfate heptahydrate (99% purity) and 250.53g of 50% manganese nitrate solution in 1000mL of deionized water, then add 279.43g of ammonium persulfate (98% purity) and dissolve to obtain a metal salt solution.

[0112] (2) Dissolve 172.94g of 85% phosphoric acid and 34.72g of ammonium dihydrogen phosphate (purity 99.4%) in 800mL of deionized water to obtain a phosphorus source solution; add the phosphorus source solution dropwise to the metal salt solution at 95℃ at a rate of 30mL / min, and stir at 350ppm throughout the dropwise process; start timing when the dropwise addition is completed and the solution temperature reaches 95℃, and react for 4h while maintaining a stirring speed of 350rpm; after the reaction is completed, filter, wash and vacuum filter the product until the conductivity of the filtrate is <300μS / cm, and place the obtained iron manganese phosphate precursor filter cake in an 80℃ drying oven for 12 hours to finally obtain 161.67g of iron manganese phosphate precursor.

[0113] Analysis showed that the specific surface area of ​​this iron-manganese phosphate precursor was 83.56 m². 2 / g, of which Fe content is 10.16%, Mn content is 22.65%, and P content is 16.56%. The calculated molar ratio Mn / (Mn+Fe) is 0.694, the Fe yield is 98.043%, the Mn yield is 95.220%, and the P yield is 48.020%.

[0114] The above-mentioned iron-manganese phosphate precursor is used to prepare lithium iron-manganese phosphate / carbon composite materials. The preparation method of lithium iron-manganese phosphate / carbon composite materials includes the following steps: S1. The iron-manganese phosphate precursor was heated and dehydrated in a muffle furnace at 600℃ for 5 hours to obtain a dehydrated iron-manganese phosphate precursor (Fe content 12.36%, Mn content 27.35%, P content 19.33%). The raw materials were fed according to the raw material molar ratio Li / (Fe+Mn) = 1.06:1, (Fe+Mn) / P = 0.975:1. 100g of the dehydrated iron-manganese phosphate precursor and 13.14g of dihydrogen phosphate were added... Ammonium (99.4 wt.%), 28.31 g lithium carbonate (99.5 wt.%), 9.05 g glucose, 3.39 g polyethylene glycol 20000, 0.45 g magnesium oxide, and 0.46 g titanium dioxide were added to 800 mL of anhydrous ethanol and ground in a basket mill at 1500 r / min for 60 min. After grinding, the slurry was fed into a sand mill and ground until the particle size of the slurry reached 400 nm. Then, the slurry was spray-dried. S2. After drying, the dried and crushed material is placed in a tube furnace under a nitrogen atmosphere for sintering at 720℃ for 10 hours. After the tube furnace cools down naturally to 80℃, the sintered material is graded and crushed to obtain a powder with a carbon content of 1.61% and a compacted density of 2.23 g / cm³. 3 LiFe 0.31 Mn 0.69 PO4 / C composite material.

[0115] Prepared LiFe 0.31 Mn 0.69 A PO4 / C composite material was used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder. Electrode sheets were fabricated using a mass ratio of 90:5:5. Lithium metal was used as the negative electrode, and the cells were assembled into lithium iron manganese phosphate coin cells. Tests were conducted at 2-4.3V and 25℃ under different charge / discharge current conditions. The initial reversible capacity was 154.5 mAh / g at 0.1C, 152.9 mAh / g at 0.2C, and 145.4 mAh / g at 1C.

[0116] Example 5 A precursor of iron-manganese phosphate, the preparation method of which includes the following steps: (1) Dissolve 112.33g of ferrous sulfate heptahydrate (purity 99%) and 102.43g of manganese sulfate monohydrate (purity 99%) in 600mL of deionized water, then add 232.86g of ammonium persulfate (purity 98%) and dissolve to obtain a metal salt solution.

[0117] (2) Dissolve 46.12g of 85% phosphoric acid and 165.82g of ammonium phosphate trihydrate (purity 98%) in 500mL of deionized water to obtain a phosphorus source solution; add the phosphorus source solution dropwise to the metal salt solution at 90℃ at a dropwise rate of 25mL / min. During the entire dropwise addition process, the stirring speed is 350ppm; start timing when the dropwise addition is completed and the solution temperature reaches 90℃, and react for 6h while maintaining a stirring speed of 350rpm; after the reaction is completed, filter, wash and vacuum filter the product until the conductivity of the filtrate is <300μS / cm. Place the obtained iron manganese phosphate precursor filter cake in an 80℃ forced-air drying oven for 12 hours to finally obtain 166.86g of iron manganese phosphate precursor.

[0118] Analysis showed that the specific surface area of ​​this iron-manganese phosphate precursor was 76.58 m². 2 / g, of which Fe content is 12.79%, Mn content is 19.30%, and P content is 15.75%. The calculated molar ratio Mn / (Mn+Fe) is 0.604, the Fe yield is 95.539%, the Mn yield is 97.698%, and the P yield is 70.706%.

[0119] The above-mentioned iron-manganese phosphate precursor is used to prepare lithium iron-manganese phosphate / carbon composite materials. The preparation method of lithium iron-manganese phosphate / carbon composite materials includes the following steps: S1. The iron-manganese phosphate precursor was heated and dehydrated in a muffle furnace at 550℃ for 4 hours to obtain the dehydrated iron-manganese phosphate precursor (Fe content 15.46%, Mn content 23.44%, P content 19.68%). The raw materials were fed according to the raw material molar ratio Li / (Fe+Mn) = 1.04:1 and (Fe+Mn) / P = 0.985:1. 100g of the dehydrated iron-manganese phosphate precursor and 9.12g of ammonium dihydrogen phosphate were added. 99.4 wt.%, 27.17 g lithium carbonate (99.5 wt.%), 8.73 g glucose, 3.27 g polyethylene glycol 20000, 0.40 g magnesium oxide, and 0.47 g niobium pentoxide were added to 800 mL of anhydrous ethanol and ground in a basket mill at 1500 r / min for 60 min. After grinding, the slurry was fed into a sand mill and ground until the particle size of the slurry reached 400 nm. Then, the slurry was spray-dried. S2. After drying, the dried and crushed material is placed in a tube furnace under a nitrogen atmosphere for sintering at 700℃ for 12 hours. After the tube furnace cools down naturally to 80℃, the sintered material is graded and crushed to obtain a powder with a carbon content of 1.66% and a compacted density of 2.25 g / cm³. 3 LiFe 0.4 Mn 0.6 PO4 / C composite material.

[0120] Prepared LiFe 0.4 Mn 0.6 A PO4 / C composite material was used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder. Electrode sheets were fabricated using a mass ratio of 90:5:5. Lithium iron manganese phosphate coin cells were assembled using lithium metal as the negative electrode. Tests were conducted at 2-4.3V and 25℃ under different charge / discharge current conditions. The initial reversible capacity was 154.3 mAh / g at 0.1C, 152.7 mAh / g at 0.2C, and 145.0 mAh / g at 1C.

[0121] Example 6 A precursor of iron-manganese phosphate, the preparation method of which includes the following steps: (1) Dissolve 81.15g of ferrous chloride tetrahydrate (98% purity) and 119.95g of manganese chloride tetrahydrate (99% purity) in 800mL of deionized water, then add 279.43g of ammonium persulfate (98% purity) and dissolve to obtain a metal salt solution.

[0122] (2) Dissolve 115.29g of 85% phosphoric acid and 103.64g of ammonium phosphate trihydrate (purity 98%) in 800mL of deionized water to obtain a phosphorus source solution; add the phosphorus source solution dropwise to the metal salt solution at 95℃ at a rate of 30mL / min, and stir at 350ppm throughout the dropwise process; start timing when the dropwise addition is completed and the solution temperature reaches 95℃, and react for 5h while maintaining a stirring speed of 350rpm; after the reaction is completed, filter, wash and vacuum filter the product until the conductivity of the filtrate is <300μS / cm, and place the obtained iron manganese phosphate precursor filter cake in an 80℃ drying oven for 12 hours to finally obtain 162.5g of iron manganese phosphate precursor.

[0123] Analysis showed that the specific surface area of ​​this iron-manganese phosphate precursor was 84.35 m². 2 / g, of which Fe content is 13.42%, Mn content is 19.45%, and P content is 15.21%. The calculated molar ratio Mn / (Mn+Fe) is 0.596, the Fe yield is 97.625%, the Mn yield is 95.885%, and the P yield is 53.198%.

[0124] The above-mentioned iron-manganese phosphate precursor is used to prepare lithium iron-manganese phosphate / carbon composite materials. The preparation method of lithium iron-manganese phosphate / carbon composite materials includes the following steps: S1. The iron-manganese phosphate precursor was heated and dehydrated in a muffle furnace at 600℃ for 4 hours to obtain a dehydrated iron-manganese phosphate precursor (Fe content 16.08%, Mn content 23.14%, P content 18.83%). The raw materials were fed according to the raw material molar ratio Li / (Fe+Mn) = 1.06:1 and (Fe+Mn) / P = 0.975:1. 100g of the dehydrated iron-manganese phosphate precursor and 13.82g of ammonium dihydrogen phosphate were added. 99.4 wt.%, 27.91 g lithium carbonate (99.5 wt.%), 9.11 g glucose, 3.41 g polyethylene glycol 20000, 0.45 g magnesium oxide, and 0.46 g niobium pentoxide were added to 800 mL of anhydrous ethanol and ground in a basket mill at 1500 r / min for 60 min. After grinding, the slurry was fed into a sand mill and ground until the particle size of the slurry reached 400 nm. Then, the slurry was spray-dried. S2. After drying, the dried and crushed material is placed in a tube furnace under a nitrogen atmosphere for sintering at 700℃ for 10 hours. After the tube furnace cools down naturally to 80℃, the sintered material is graded and crushed to obtain a powder with a carbon content of 1.62% and a compacted density of 2.24 g / cm³. 3 LiFe 0.4 Mn 0.6 PO4 / C composite material.

[0125] Prepared LiFe 0.4 Mn 0.6 A PO4 / C composite material was used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder. Electrode sheets were fabricated using a mass ratio of 90:5:5. Lithium metal was used as the negative electrode, and the cells were assembled into lithium iron manganese phosphate coin cells. Tests were conducted at 2-4.3V and 25℃ under different charge / discharge current conditions. The initial reversible capacity was 154.2 mAh / g at 0.1C, 152.1 mAh / g at 0.2C, and 145.1 mAh / g at 1C.

[0126] Comparative Example 1 Unlike Example 1, in step (2) of preparing iron manganese phosphate, excess phosphoric acid is added to the phosphorus source solution.

[0127] (1) Dissolve 112.33g of ferrous sulfate heptahydrate (99% purity) and 102.43g of manganese sulfate monohydrate (99% purity) in 800mL of deionized water, then add 279.43g of ammonium persulfate (98% purity) and dissolve to obtain a metal salt solution.

[0128] (2) 288.24 g of 85% phosphoric acid was added to 500 mL of deionized water to obtain a phosphorus source solution. The phosphorus source solution was added dropwise to the metal salt solution at 95 °C at a rate of 20 mL / min. During the entire dropwise addition process, the stirring speed was 350 ppm. The reaction was started after the dropwise addition was completed and the solution temperature reached 95 °C. The reaction was carried out for 4 h while maintaining a stirring speed of 350 rpm. After the reaction was completed, the product was filtered, washed and vacuum filtered until the conductivity of the filtrate was <300 μS / cm. The obtained iron manganese phosphate precursor filter cake was placed in an 80 °C drying oven for 12 hours to finally obtain 156.33 g of iron manganese phosphate precursor.

[0129] Analysis showed that the specific surface area of ​​this iron-manganese phosphate precursor was 36.26 m². 2 The sample contains 10.52% Fe, 20.00% Mn, and 16.4% P. The calculated molar ratio of Mn / (Mn+Fe) is 0.659, resulting in a Fe yield of 73.623%, a Mn yield of 94.852%, and a P yield of 33.113%. Adding excessive phosphoric acid to the phosphorus source solution lowers the pH, leading to incomplete iron precipitation and a reduced yield.

[0130] The above-mentioned iron-manganese phosphate precursor is used to prepare lithium iron-manganese phosphate / carbon composite materials. The preparation method of lithium iron-manganese phosphate / carbon composite materials includes the following steps: S1. The iron-manganese phosphate precursor was heated and dehydrated in a muffle furnace at 550℃ for 4 hours to obtain a dehydrated iron-manganese phosphate precursor (Fe content 12.49%, Mn content 24.42%, P content 20.45%). The raw materials were fed according to the raw material molar ratio Li / (Fe+Mn) = 1.06:1 and (Fe+Mn) / P = 0.975:1. 100g of the dehydrated iron-manganese phosphate precursor and 2.90g of ammonium dihydrogen phosphate were added. 99.4 wt.%, 26.30 g lithium carbonate (99.5 wt.%), 9.21 g glucose, 3.45 g polyethylene glycol 20000, 0.46 g magnesium oxide, and 0.46 g titanium dioxide were added to 800 mL of anhydrous ethanol and ground in a basket mill at 1500 r / min for 60 min. After grinding, the slurry was fed into a sand mill and ground until the particle size of the slurry reached 400 nm. Then, the slurry was spray-dried. S2. After drying, the dried and crushed material is placed in a tube furnace under a nitrogen atmosphere for sintering at 700℃ for 10 hours. After the tube furnace cools down naturally to 80℃, the sintered material is graded and crushed to obtain a powder with a carbon content of 1.60% and a compacted density of 2.20 g / cm³. 3 LiFe 0.34 Mn 0.66 PO4 / C composite material.

[0131] Prepared LiFe 0.34 Mn 0.66 A PO4 / C composite material was used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder. Electrode sheets were fabricated using a mass ratio of 90:5:5. Lithium metal was used as the negative electrode, and the cells were assembled to simulate a lithium iron manganese phosphate coin cell. Tests were conducted at 2-4.3V and 25℃ under different charge / discharge current conditions. The initial reversible capacity was 148.6 mAh / g at 0.1C, 145.2 mAh / g at 0.2C, and 139.5 mAh / g at 1C.

[0132] Comparative Example 2 Unlike Example 1, in step (2) of preparing iron manganese phosphate, excess ammonium phosphate is added to the phosphorus source solution.

[0133] (1) Dissolve 112.33g of ferrous sulfate heptahydrate (99% purity) and 102.43g of manganese sulfate monohydrate (99% purity) in 800mL of deionized water, then add 279.43g of ammonium persulfate (98% purity) and dissolve to obtain a metal salt solution.

[0134] (2) Dissolve 518.19g of ammonium dihydrogen phosphate (purity 99.4%) in 750mL of deionized water to obtain a phosphorus source solution; add the phosphorus source solution dropwise to the metal salt solution at 95℃ at a dropwise rate of 20mL / min. During the entire dropwise addition process, the stirring speed is 350ppm; start timing when the dropwise addition is completed and the solution temperature reaches 95℃, and react for 4h while maintaining the stirring speed at 350rpm; after the reaction is completed, filter, wash and vacuum filter the product until the conductivity of the filtrate is <300μS / cm. Place the obtained iron manganese phosphate precursor filter cake in an 80℃ forced-air drying oven for 12 hours to finally obtain 206.33g of iron manganese phosphate precursor.

[0135] Analysis showed that the specific surface area of ​​this iron-manganese phosphate precursor was 27.54 m². 2 The product contains 10.59% Fe, 15.64% Mn, and 18.99% P. The calculated molar ratio of Mn / (Mn+Fe) is 0.600, with Fe yield of 97.824%, Mn yield of 97.898%, and P yield of 50.34%. Adding excess ammonium phosphate to the phosphorus source solution resulted in an excessively high pH, ​​leading to the formation of the impurity phase NH4Fe(HPO4)2 in the product.

[0136] The above-mentioned iron-manganese phosphate precursor is used to prepare lithium iron-manganese phosphate / carbon composite materials. The preparation method of lithium iron-manganese phosphate / carbon composite materials includes the following steps: S1. The iron-manganese phosphate precursor was heated and dehydrated in a muffle furnace at 550℃ for 4 hours to obtain a dehydrated iron-manganese phosphate precursor (Fe content 13.27%, Mn content 19.63%, P content 23.74%). The raw materials were fed according to the raw material molar ratio Li / (Fe+Mn)=1.06:1. 100g of the dehydrated iron-manganese phosphate precursor, 23.42g of lithium carbonate (99.5wt.%), 9.21g of glucose, 3.45g of polyethylene glycol 20000, 0.46g of magnesium oxide, and 0.46g of titanium dioxide were added to 800mL of anhydrous ethanol and placed in a basket mill and ground at 1500r / min for 60min. After grinding, the slurry was introduced into a sand mill for grinding. After the slurry particle size reached 400nm, the slurry was spray-dried. S2. After drying, the dried and crushed material is placed in a tube furnace under a nitrogen atmosphere for sintering at 700℃ for 10 hours. After the tube furnace cools down naturally to 80℃, the sintered material is graded and crushed to obtain a powder with a carbon content of 1.63% and a compacted density of 2.19 g / cm³. 3 LiFe 0.4 Mn 0.6 PO4 / C composite material.

[0137] Prepared LiFe 0.4 Mn 0.6 A PO4 / C composite material was used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder. Electrode sheets were fabricated using a mass ratio of 90:5:5. Lithium metal was used as the negative electrode, and the cells were assembled into lithium iron manganese phosphate coin cells. Tests were conducted at 2-4.3V and 25℃ under different charge / discharge current conditions. The initial reversible capacity was 142.1 mAh / g at 0.1C, 139.8 mAh / g at 0.2C, and 132.8 mAh / g at 1C.

[0138] Comparative Example 3 Unlike Example 1, in step (1) of preparing iron manganese phosphate, an excess of ammonium persulfate oxidant was added.

[0139] (1) Dissolve 112.33g of ferrous sulfate heptahydrate (99% purity) and 102.43g of manganese sulfate monohydrate (99% purity) in 800mL of deionized water, then add 465.71g of ammonium persulfate (98% purity) and dissolve to obtain a metal salt solution.

[0140] (2) Dissolve 138.86g of ammonium dihydrogen phosphate (purity 99.4%) in 500mL of deionized water to obtain a phosphorus source solution; add the phosphorus source solution dropwise to the metal salt solution at 95℃ at a dropwise rate of 20mL / min. During the entire dropwise addition process, the stirring speed is 350ppm. Start timing when the dropwise addition is completed and the solution temperature reaches 95℃. React for 4h while maintaining the stirring speed at 350rpm. After the reaction is completed, filter, wash and vacuum filter the product until the conductivity of the filtrate is <300μS / cm. Place the obtained iron manganese phosphate precursor filter cake in an 80℃ forced-air drying oven for 12 hours to finally obtain 145.4g of iron manganese phosphate precursor.

[0141] Analysis showed that the specific surface area of ​​this iron-manganese phosphate precursor was 68.28 m². 2 The sample contains 14.55% Fe, 18.33% Mn, and 14.85% P. The calculated molar ratio of Mn / (Mn+Fe) is 0.562, with Fe yield of 94.694%, Mn yield of 80.854%, and P yield of 58.099%. Adding excess ammonium persulfate as an oxidant inhibits manganese precipitation, thus reducing the yield.

[0142] The above-mentioned iron-manganese phosphate precursor is used to prepare lithium iron-manganese phosphate / carbon composite materials. The preparation method of lithium iron-manganese phosphate / carbon composite materials includes the following steps: S1. The iron-manganese phosphate precursor was heated and dehydrated in a muffle furnace at 550℃ for 4 hours to obtain a dehydrated iron-manganese phosphate precursor (Fe content 17.80%, Mn content 22.51%, P content 18.51%). The raw materials were fed according to the raw material molar ratio Li / (Fe+Mn) = 1.06:1, (Fe+Mn) / P = 0.975:1. 100g of the dehydrated iron-manganese phosphate precursor and 17.31g of dihydrogen phosphate were added... Ammonium (99.4 wt.%), 28.67 g lithium carbonate (99.5 wt.%), 9.21 g glucose, 3.45 g polyethylene glycol 20000, 0.46 g magnesium oxide, and 0.46 g titanium dioxide were added to 800 mL of anhydrous ethanol and ground in a basket mill at 1500 r / min for 60 min. After grinding, the slurry was fed into a sand mill and ground until the particle size of the slurry reached 400 nm. Then, the slurry was spray-dried. S2. After drying, the dried and crushed material is placed in a tube furnace under a nitrogen atmosphere for sintering at 700℃ for 10 hours. After the tube furnace cools down naturally to 80℃, the sintered material is graded and crushed to obtain a powder with a carbon content of 1.61% and a compacted density of 2.21 g / cm³. 3 LiFe 0.44 Mn 0.56 PO4 / C composite material.

[0143] Prepared LiFe 0.44 Mn 0.56 A PO4 / C composite material was used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder. Electrode sheets were fabricated using a mass ratio of 90:5:5. Lithium metal was used as the negative electrode, and the cells were assembled to simulate a lithium iron manganese phosphate coin cell. Tests were conducted at 2-4.3V and 25℃ under different charge / discharge current conditions. The initial reversible capacity was 145.2 mAh / g at 0.1C, 143.8 mAh / g at 0.2C, and 136.8 mAh / g at 1C.

[0144] Comparative Example 4 Unlike Example 1, in step (1) of preparing iron manganese phosphate, a small amount of oxidant ammonium persulfate is added.

[0145] (1) Dissolve 112.33g of ferrous sulfate heptahydrate (purity 99%) and 102.43g of manganese sulfate monohydrate (purity 99%) in 800mL of deionized water, then add 116.43g of ammonium persulfate (purity 98%) and dissolve to obtain a metal salt solution.

[0146] (2) Dissolve 138.86g of ammonium dihydrogen phosphate (purity 99.4%) in 500mL of deionized water to obtain a phosphorus source solution; add the phosphorus source solution dropwise to the metal salt solution at 95℃ at a dropwise rate of 20mL / min. During the entire dropwise addition process, the stirring speed is 350ppm. Start timing when the dropwise addition is completed and the solution temperature reaches 95℃. React for 4h while maintaining the stirring speed at 350rpm. After the reaction is completed, filter, wash and vacuum filter the product until the conductivity of the filtrate is <300μS / cm. Place the obtained iron manganese phosphate precursor filter cake in an 80℃ forced-air drying oven for 12 hours to finally obtain 152.26g of iron manganese phosphate precursor.

[0147] Analysis showed that the specific surface area of ​​this iron-manganese phosphate precursor was 70.10 m². 2 The sample contains 14.59% Fe, 16.68% Mn, and 17.21% P. The calculated molar ratio Mn / (Mn+Fe) is 0.532, with Fe yield of 99.448%, Mn yield of 77.047%, and P yield of 70.509%. Adding a small amount of ammonium persulfate as an oxidant inhibits manganese precipitation, thus reducing the yield.

[0148] The above-mentioned iron-manganese phosphate precursor is used to prepare lithium iron-manganese phosphate / carbon composite materials. The preparation method of lithium iron-manganese phosphate / carbon composite materials includes the following steps: S1. The iron-manganese phosphate precursor was heated and dehydrated in a muffle furnace at 550℃ for 4 hours to obtain the dehydrated iron-manganese phosphate precursor (Fe content 17.31%, Mn content 20.51%, P content 20.15%). The raw materials were fed according to the raw material molar ratio Li / (Fe+Mn) = 1.06:1, (Fe+Mn) / P = 0.975:1. 100g of the dehydrated iron-manganese phosphate precursor and 5.82g of ammonium dihydrogen phosphate were added. 99.4 wt.%, 26.89 g lithium carbonate (99.5 wt.%), 9.21 g glucose, 3.45 g polyethylene glycol 20000, 0.46 g magnesium oxide, and 0.46 g titanium dioxide were added to 800 mL of anhydrous ethanol and ground in a basket mill at 1500 r / min for 60 min. After grinding, the slurry was fed into a sand mill and ground until the particle size of the slurry reached 400 nm. Then, the slurry was spray-dried. S2. After drying, the dried and crushed material is placed in a tube furnace under a nitrogen atmosphere for sintering at 700℃ for 10 hours. After the tube furnace cools down naturally to 80℃, the sintered material is graded and crushed to obtain a powder with a carbon content of 1.62% and a compacted density of 2.23 g / cm³. 3 LiFe 0.47 Mn 0.53 PO4 / C composite material.

[0149] Prepared LiFe 0.47 Mn 0.53 A PO4 / C composite material was used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder. Electrode sheets were fabricated using a mass ratio of 90:5:5. Lithium metal was used as the negative electrode, and the cells were assembled to simulate a lithium iron manganese phosphate coin cell. Tests were conducted at 2-4.3V and 25℃ under different charge / discharge current conditions. The initial reversible capacity was 143.5 mAh / g at 0.1C, 141.8 mAh / g at 0.2C, and 132.7 mAh / g at 1C.

[0150] Comparative Example 5 Unlike Example 1, in step (2) of preparing iron manganese phosphate, the reaction time is 2 hours.

[0151] (1) Dissolve 112.33g of ferrous sulfate heptahydrate (99% purity) and 102.43g of manganese sulfate monohydrate (99% purity) in 800mL of deionized water, then add 279.43g of ammonium persulfate (98% purity) and dissolve to obtain a metal salt solution.

[0152] (2) Dissolve 138.86g of ammonium dihydrogen phosphate (purity 99.4%) in 500mL of deionized water to obtain a phosphorus source solution; add the phosphorus source solution dropwise to the metal salt solution at 95℃ at a dropwise rate of 20mL / min. During the entire dropwise addition process, the stirring speed is 350ppm. Start timing when the dropwise addition is completed and the solution temperature reaches 95℃. React for 2h while maintaining the stirring speed at 350rpm. After the reaction is completed, filter, wash and vacuum filter the product until the conductivity of the filtrate is <300μS / cm. Place the obtained iron manganese phosphate precursor filter cake in an 80℃ forced-air drying oven for 12 hours to finally obtain 127.19g of iron manganese phosphate precursor.

[0153] Analysis showed that the specific surface area of ​​this iron-manganese phosphate precursor was 85.65 m². 2 The sample contains 15.31% Fe, 19.98% Mn, and 14.33% P. The calculated molar ratio Mn / (Mn+Fe) is 0.570, with Fe yield of 87.173%, Mn yield of 77.095%, and P yield of 49.043%. If the reaction time is too short, the yields of iron, manganese, and phosphorus all decrease.

[0154] The above-mentioned iron-manganese phosphate precursor is used to prepare lithium iron-manganese phosphate / carbon composite materials. The preparation method of lithium iron-manganese phosphate / carbon composite materials includes the following steps: S1. The iron-manganese phosphate precursor was heated and dehydrated in a muffle furnace at 550℃ for 4 hours to obtain a dehydrated iron-manganese phosphate precursor (Fe content 18.46%, Mn content 24.59%, P content 17.28%). It was fed with raw materials at a molar ratio of Li / (Fe+Mn) = 1.06:1 and (Fe+Mn) / P = 0.975:1. 100g of the dehydrated iron-manganese phosphate precursor and 27.80g of dihydrogen phosphate were added... Ammonium (99.4 wt.%), 30.63 g lithium carbonate (99.5 wt.%), 9.21 g glucose, 3.45 g polyethylene glycol 20000, 0.46 g magnesium oxide, and 0.46 g titanium dioxide were added to 800 mL of anhydrous ethanol and ground in a basket mill at 1500 r / min for 60 min. After grinding, the slurry was fed into a sand mill and ground until the particle size of the slurry reached 400 nm. Then, the slurry was spray-dried. S2. After drying, the dried and crushed material is placed in a tube furnace under a nitrogen atmosphere for sintering at 700℃ for 10 hours. After the tube furnace cools down naturally to 80℃, the sintered material is graded and crushed to obtain a powder with a carbon content of 1.62% and a compacted density of 2.11 g / cm³. 3 LiFe 0.43 Mn 0.57 PO4 / C composite material.

[0155] Prepared LiFe 0.43 Mn 0.57 A PO4 / C composite material was used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder. Electrode sheets were fabricated using a mass ratio of 90:5:5. Lithium metal was used as the negative electrode, and the cells were assembled to simulate a lithium iron manganese phosphate coin cell. Tests were conducted at 2-4.3V and 25℃ under different charge / discharge current conditions. The initial reversible capacity was 147.2 mAh / g at 0.1C, 144.9 mAh / g at 0.2C, and 138.1 mAh / g at 1C.

[0156] Comparative Example 6 Unlike Example 1, in step (2) of preparing iron manganese phosphate, the temperature at which the phosphorus source solution is added and the reaction temperature are both 30°C.

[0157] (1) Dissolve 112.33g of ferrous sulfate heptahydrate (99% purity) and 102.43g of manganese sulfate monohydrate (99% purity) in 800mL of deionized water, then add 279.43g of ammonium persulfate (98% purity) and dissolve to obtain a metal salt solution.

[0158] (2) Dissolve 138.86g of ammonium dihydrogen phosphate (purity 99.4%) in 500mL of deionized water to obtain a phosphorus source solution; add the phosphorus source solution dropwise to the metal salt solution at 30℃ at a dropwise rate of 20mL / min. During the entire dropwise addition process, the stirring speed is 350ppm. Start timing when the dropwise addition is completed and the solution temperature reaches 30℃. React for 4h while maintaining the stirring speed at 350rpm. After the reaction is completed, filter, wash and vacuum filter the product until the conductivity of the filtrate is <300μS / cm. Place the obtained iron manganese phosphate precursor filter cake in an 80℃ forced-air drying oven for 12 hours to finally obtain 56.81g of iron manganese phosphate precursor.

[0159] Analysis showed that the specific surface area of ​​this iron-manganese phosphate precursor was 39.87 m². 2 The mixture contains 25.67% Fe, 1.83% Mn, and 16.08% P. The calculated molar ratio Mn / (Mn+Fe) is 0.068, with Fe yield of 65.293%, Mn yield of 3.154%, and P yield of 24.58%. At excessively low reaction temperatures, manganese hardly precipitates.

[0160] The above-mentioned iron-manganese phosphate precursor is used to prepare lithium iron-manganese phosphate / carbon composite materials. The preparation method of lithium iron-manganese phosphate / carbon composite materials includes the following steps: S1. The iron-manganese phosphate precursor was heated and dehydrated in a muffle furnace at 550℃ for 4 hours to obtain a dehydrated iron-manganese phosphate precursor (Fe content 33.43%, Mn content 2.36%, P content 20.97%). The raw materials were fed according to the raw material molar ratio Li / (Fe+Mn)=1.06:1. 100g of the dehydrated iron-manganese phosphate precursor, 25.25g of lithium carbonate (99.5wt.%), 9.21g of glucose, 3.45g of polyethylene glycol 20000, 0.46g of magnesium oxide, and 0.46g of titanium dioxide were added to 800mL of anhydrous ethanol and placed in a basket mill and ground at 1500r / min for 60min. After grinding, the slurry was introduced into a sand mill for grinding. After the slurry particle size reached 400nm, the slurry was spray-dried. S2. After drying, the dried and crushed material is placed in a tube furnace under a nitrogen atmosphere for sintering at 700℃ for 10 hours. After the tube furnace cools down naturally to 80℃, the sintered material is graded and crushed to obtain a powder with a carbon content of 1.59% and a compacted density of 2.26 g / cm³. 3 LiFe 0.93 Mn 0.07 PO4 / C composite material.

[0161] Prepared LiFe 0.93 Mn 0.07 A PO4 / C composite material was used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder. Electrode sheets were fabricated using a mass ratio of 90:5:5. Lithium metal was used as the negative electrode, and the cells were assembled to simulate a lithium iron manganese phosphate coin cell. Tests were conducted at 2-4.3V and 25℃ under different charge / discharge current conditions. The initial reversible capacity was 148.3 mAh / g at 0.1C, 145.4 mAh / g at 0.2C, and 136.4 mAh / g at 1C.

[0162] Verification of technical effectiveness and / or analysis of technical problem solving In Examples 1-6 of this invention, the initial reversible capacity during charge-discharge at 0.1C is 154.2 mAh / g or more, the initial reversible capacity during charge-discharge at 0.2C is 152.1 mAh / g or more, and the initial reversible capacity during charge-discharge at 1C is 145.0 mAh / g or more.

[0163] Comparative Examples 1-2 varied the amount of phosphorus source by adding excess phosphoric acid to the phosphorus source solution. The initial reversible capacity of Comparative Examples 1-2 under charge-discharge conditions at 0.1C was 142.1-148.6 mAh / g, at 0.2C it was 139.8-145.2 mAh / g, and at 1C it was 132.8-139.5 mAh / g. These values ​​are lower than those of Examples 1-6 of this invention.

[0164] Comparative Examples 3-4 varied the amount of oxidant used. The initial reversible capacity of Comparative Examples 3-4 under charge-discharge conditions of 0.1C was 143.5-145.2 mAh / g, the initial reversible capacity under charge-discharge conditions of 0.2C was 141.8-143.8 mAh / g, and the initial reversible capacity under charge-discharge conditions of 1C was 132.7-136.8 mAh / g. These values ​​are lower than those of Examples 1-6 of the present invention.

[0165] Comparative Examples 5-6 modified the conditions of the coprecipitation reaction. The initial reversible capacity of Comparative Examples 5-6 under charge-discharge conditions of 0.1C was 147.2-148.3 mAh / g, the initial reversible capacity under charge-discharge conditions of 0.2C was 144.9-145.4 mAh / g, and the initial reversible capacity under charge-discharge conditions of 1C was 136.4-138.1 mAh / g. These values ​​are lower than those of Examples 1-6 of the present invention.

[0166] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing a manganese iron phosphate salt precursor, characterized by, The preparation method comprises the following steps: (1) dissolving an iron source, a manganese source and an oxidizing agent in water to obtain a metal salt solution; (2) adding a phosphorus source solution into the metal salt solution to react, and then performing solid-liquid separation, washing, drying and dehydration on the reaction product to obtain a dehydrated iron manganese phosphate precursor; The molar ratio of the phosphorus source to the total molar amount of iron and manganese is 1.0-2.0:1; The molar ratio of the oxidizing agent to the total molar amount of iron and manganese is 0.6-1.5:1; The reaction temperature in step (2) is 80-100℃, and the reaction time is 3-6 hours; The preparation method does not need to adjust the pH value.

2. The production method according to claim 1, characterized by, In step (1), the iron source is at least one of ferrous sulfate, ferrous nitrate and ferrous chloride; and / or The manganese source is at least one of manganese sulfate, manganese nitrate and manganous chloride; and / or The total molar concentration of iron and manganese in the metal salt solution is 0.5-3.0 mol / L; and / or The molar ratio of iron to manganese in the metal salt solution is x:y, wherein y is 0.5-0.9, and x+y=1; and / or The oxidizing agent is ammonium persulfate or a mixture of ammonium persulfate and hydrogen peroxide.

3. The preparation method according to claim 1, characterized in that, In step (2), the phosphorus source is at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate and sodium phosphate; and / or The concentration of the phosphorus source solution is 0.5-3.0 mol / L; and / or The adding temperature of the phosphorus source solution is 80-100℃; and / or The adding speed of the phosphorus source solution is 5-40 mL / min; and / or The washing is performed until the conductivity of the filtrate is below 300 μS / cm.

4. The production method according to claim 3, characterized by, In step (2), the phosphorus source is at least one of phosphoric acid, ammonium dihydrogen phosphate and ammonium phosphate.

5. The iron manganese phosphate precursor prepared by the preparation method in any one of claims 1-4.

6. The use of the iron manganese phosphate precursor prepared by the preparation method in any one of claims 1-4 in battery preparation.

7. A method for preparing a lithium iron manganese phosphate / carbon composite material, characterized by, The preparation method comprises the following steps: S1, dehydrating the iron manganese phosphate precursor prepared by the preparation method in any one of claims 1-4 to obtain a dehydrated iron manganese phosphate precursor; S2, taking a lithium source, the dehydrated iron manganese phosphate precursor, a phosphorus source, a carbon source and an additive to perform grinding, mixing and drying to obtain an iron lithium manganese phosphate / carbon composite precursor; S3, sintering the obtained iron lithium manganese phosphate / carbon composite precursor in an inert gas atmosphere to obtain an iron lithium manganese phosphate / carbon composite material.

8. The production method according to claim 7, characterized by, In step S1, the dehydration temperature is 300-700℃, the dehydration time is 3-6 hours, and the dehydration atmosphere is at least one of air, nitrogen and argon; and / or In step S2, the lithium source is at least one of lithium carbonate, lithium hydroxide and lithium acetate, and the molar ratio of lithium in the lithium source to the sum of iron and manganese in the iron manganese phosphate precursor is 1.02-1.10:1; and / or The phosphorus source is at least one of diammonium hydrogen phosphate, ammonium dihydrogen phosphate and phosphoric acid, and the molar ratio of the sum of iron and manganese in the iron manganese phosphate precursor to phosphorus in the phosphorus source is 0.96-0.99:1; and / or The carbon source is at least one of glucose, granulated sugar, sucrose, fructose, polyethylene glycol, cyclodextrin, starch and cellulose, and the addition amount of the carbon source is 8%-20% of the mass of the manganese iron phosphate precursor; and / or The additive is at least one of titanium dioxide, tetrabutyl titanate, magnesium acetate, magnesium oxide, magnesium hydroxide, magnesium nitrate, zirconium nitrate, zirconium dioxide, zirconium hydroxide, niobium pentoxide, nickel acetate, nickel nitrate and nickel hydroxide, and the addition amount of the additive is 0-1.0% of the mass of the manganese iron phosphate precursor; and / or The sintering temperature in step S3 is 650-750℃, and the sintering time is 6-12 hours.

9. The lithium manganese iron phosphate / carbon composite material prepared by the preparation method in any one of claims 7-8.

10. A battery comprising the lithium manganese iron phosphate / carbon composite material prepared by the preparation method in any one of claims 7-8.

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