Preparation method of multi-element doped ferromanganese oxide positive electrode precursor

Abstract

The invention discloses a preparation method of a multi-element doped ferromanganese oxide positive electrode precursor, and belongs to the technical field of lithium ion battery positive electrode material preparation. The molar ratio of manganese to iron in the multi-element doped ferromanganese oxide positive electrode precursor is x: (1-x), 0.2 lt; xlt; and the doping element accounts for 0.1-10% of the total mole number of manganese and iron. According to the multi-element doped ferromanganese oxide positive electrode precursor prepared by the invention, the coprecipitation intermediates are manganese carbonate and ferrous carbonate, and Ksp of the manganese carbonate and the ferrous carbonate are relatively close, so that the uniformity of ferromanganese can be ensured, meanwhile, metal ion doping is carried out in a liquid phase synthesis precursor stage, and the probability that doped ions enter compound lattices is greatly improved. The multi-element doped ferromanganese oxide positive electrode precursor has relatively high stability and good conductivity, and is beneficial to improving the capacity, the cycle life and the compaction density of a lithium iron manganese phosphate positive electrode material.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery positive electrode material preparation, and in particular to a method for preparing a multi-element doped manganese iron oxide positive electrode precursor. Background Art

[0002] Positive electrode materials are an important component of lithium-ion batteries. In the future, positive electrode materials for lithium batteries will gradually move towards high energy density and high cost performance. At present, there are two main types of positive electrode materials for automotive batteries: ternary positive electrode and lithium iron phosphate positive electrode. Among them, the ternary positive electrode has the advantages of high energy density and good low-temperature performance, but its price is high and its cycle performance is poor; although the lithium iron phosphate positive electrode has excellent cycle performance, its energy density and low-temperature performance are poor and it is difficult to meet the use scenarios of power batteries in cold regions.

[0003] Lithium iron manganese phosphate cathode has a higher voltage platform, higher energy density and excellent low-temperature performance, and its raw material cost is low, which can effectively solve the pain points of the first two. If its cycle performance can be effectively improved, lithium iron manganese phosphate is expected to become a new generation of automotive lithium-ion battery cathode material after ternary cathode and lithium iron phosphate cathode.

[0004] In order to meet the application requirements of long cycle and high rate of lithium batteries, the uniformity of manganese iron elements and ion doping in the lithium manganese iron phosphate positive electrode material are very important. Therefore, in the selection of process routes, we try our best to choose the process route of precursor materials with uniform manganese iron, and carry out high conductivity ion doping from the precursor synthesis stage. The process routes currently used by competitors are mainly: ①FeSO4+MnSO4+Li3PO4 as raw materials, and high temperature and high pressure hydrothermal reaction to achieve carbon-free lithium manganese iron phosphate pure phase precursor synthesis, and on this basis, element supplementation and carbon coating sintering are carried out to achieve uniform manganese iron. However, this method involves high-pressure liquid phase equipment and the recovery of a large amount of lithium-containing mother liquor, which is difficult to achieve large-scale mass production. ②Fe3O4 (Fe 1-x / Mn x )3O4 and LiH2PO4 are used as the main raw materials and produced by the solid phase method; the ferroferric oxide part is used as the main material in the production process. The main material itself is magnetic, and it is difficult to use the demagnetization process in the process. Therefore, it is difficult to ensure that the content of magnetic foreign matter in the finished product does not exceed the standard, and it is difficult to apply it to automotive positive electrode materials. ③Mn3O4+FePO4+LiH2PO4+Li2CO3 is used as raw materials. The process steps mainly involve mixing, grinding, spraying, sintering and crushing processes. The iron and manganese in the raw materials come from different raw materials, and the manganese iron is uneven. Limited by the principles of grinding and solid phase sintering reactions, this route is difficult to achieve uniform manganese iron at the atomic level. Therefore, the cycle performance of the finished product is difficult to guarantee, and when doping, only surface coating can be performed, and it is difficult to achieve intra-lattice doping.

[0005] The currently disclosed preparation process of lithium iron manganese phosphate has not solved the problems of cycle stability and high-rate performance of the lithium iron manganese phosphate cathode, and it is still difficult to meet the commercial requirements of large-power lithium iron manganese phosphate for vehicles. Summary of the Invention

[0006] Based on the problems existing in the background technology, the present invention provides a multi-element doped manganese iron oxide precursor, a preparation method thereof, and a lithium iron manganese phosphate cathode material.

[0007] The present invention is implemented through the following technical solutions:

[0008] On the one hand, the present invention discloses a multi-element doped manganese iron oxide cathode precursor. The molar ratio of manganese to iron in the multi-element doped manganese iron oxide cathode precursor is x:(1 - x), where 0.2 < x < 0.8. The multi-element doping includes doping of one or more of magnesium, titanium, strontium, vanadium, niobium, cobalt, nickel, and lithium elements, and the doping element accounts for 0.1 - 10% of the total molar number of manganese and iron.

[0009] Furthermore, a preparation method of the multi-element doped manganese iron oxide cathode precursor includes the following steps:

[0010] (1) Prepare a manganese source, an iron source, and an ion dopant dissolved in pure water to obtain a manganese iron mixed solution, and first add it to a reaction kettle and stir as the bottom liquid;

[0011] (2) Prepare a soluble carbonate and an alkali, dissolve them in pure water to obtain a precipitant solution, which is used as the dropping liquid for the reaction;

[0012] (3) Control the temperature of the solution in the reaction kettle, start dropping the precipitant into the reaction kettle containing the bottom liquid, and at the same time measure the pH value in the reaction kettle. When the pH value reaches the set range, stop dropping and continue stirring the reaction;

[0013] (4) After the reaction reaches the end point, cool down, separate the solid-liquid mixture in the kettle, and wash the solid with pure water several times until the ionic conductivity of the washing water is lower than the set value;

[0014] (5) Put the separated solid into a drying device for drying, and then add it to a kiln for calcination to obtain the final multi-element doped manganese iron oxide cathode precursor.

[0015] Furthermore, in step (1), the manganese source is one or more of manganese sulfate, manganese chloride, and manganese nitrate; the iron source is one or more of ferrous sulfate, ferrous chloride, and ferrous nitrate; the ion dopant is one or more of magnesium acetate, magnesium sulfate, titanium dioxide, strontium sulfate, ammonium metavanadate, niobium pentoxide, cobalt sulfate, nickel sulfate, nickel acetate, and lithium sulfate.

[0016] Furthermore, in step (2), the soluble carbonate is one or more of ammonium bicarbonate, ammonium carbonate, sodium carbonate, and potassium carbonate; and the alkali is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and ammonia water.

[0017] Furthermore, in step (3), the temperature of the solution in the reaction kettle is 30-100° C.; the setting range of the pH value is 3-10, preferably 4-5.

[0018] Furthermore, the ion conductivity of the wash water in step (4) is ≤20000 μS / cm, preferably ≤2000 μS / cm.

[0019] Furthermore, the drying equipment in step (5) is one of an oven, a flash evaporator, and a rotary dryer, and the kiln is one of a box furnace, a tube furnace, a roller kiln, and a rotary kiln.

[0020] Furthermore, in step (5), the calcination temperature is 300-1000°C, preferably 500-800°C.

[0021] The second aspect of the present invention discloses a lithium manganese iron phosphate positive electrode material, which is prepared from the multi-element doped manganese iron oxide positive electrode precursor. The preparation steps are to mix the multi-element doped manganese iron oxide, phosphoric acid, lithium carbonate and glucose together, grind, dry, sinter and crush, and test the performance of the positive electrode material to study the performance of the multi-element doped manganese iron oxide positive electrode precursor.

[0022] Beneficial effects of the present invention:

[0023] 1. Compared with other methods, the multi-element doped manganese iron oxide positive electrode precursor synthesized by the present invention has the most uniform manganese and iron, and ion doping is performed between the precursor lattices. The multi-element doped manganese iron oxide positive electrode precursor prepared by this scheme is more uniform than ferromanganese phosphate, because in the manganese phosphate railway line, ferromanganese phosphate is coprecipitated, but the Ksp of manganese phosphate and ferrous phosphate are 1.30×10 -22 and 1.30×10 -32 The difference between the two is very large, so it cannot ensure the uniformity of manganese iron. The coprecipitation intermediates of the multi-element doped manganese iron oxide positive electrode precursor prepared in this scheme are manganese carbonate and ferrous carbonate, and the Ksp of the two are 1.80×10 -11 and 3.20×10 -11 , which is relatively close, manganese and ferrous ions can be precipitated at the same time, so the uniformity of ferromanganese can be guaranteed. And when carbonate is sintered to form oxide, the sintering process can also improve the uniformity of ferromanganese.

[0024] 2. The present invention can achieve doping of multiple elements such as magnesium, titanium, strontium, vanadium, niobium, cobalt, nickel, lithium, etc. in the precursor section, which can significantly improve the doping effect of ions in the lattice and improve the fast charging performance and rate performance.

[0025] 3. The raw materials of the scheme of the present invention are widely available, the reaction device is simple, the process is mild, and it is easy to realize large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are used to provide further explanation of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0027] Figure 1 The present invention provides a process flow chart for preparing a multi-element doped manganese iron oxide positive electrode precursor.

[0028] Figure 2 This is a SEM image of ferromanganese carbonate, an intermediate product of the process of Example 1 of the present invention;

[0029] Figure 3 This is a SEM image of the multi-element doped manganese iron oxide positive electrode precursor of Example 1 of the present invention;

[0030] Figure 4 This is a SEM image of the positive electrode material prepared from the multi-element doped manganese iron oxide precursor of Example 1 of the present invention. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the following embodiments.

[0032] Example 1

[0033] The steps for preparing a multi-element doped manganese iron oxide positive electrode precursor are as follows:

[0034] 1) Dissolve 102.42 g of manganese sulfate monohydrate, 112.32 g of ferrous sulfate heptahydrate, 2.16 g of magnesium acetate tetrahydrate and 2.52 g of nickel acetate tetrahydrate in 1 L of pure water to obtain a manganese-iron mixed solution, first add it to a reactor as a base liquid, start the reactor and stir at 300 rpm;

[0035] 2) Prepare 87.78g of ammonium bicarbonate and dissolve it in pure water as a reaction precipitant; and prepare 25wt% ammonia solution as a dropwise addition liquid for the reaction;

[0036] 3) Control the temperature of the solution in the reactor to 60°C, and add the precipitant dropwise to the reactor containing the bottom solution while stirring; after the precipitant is added dropwise, start adding the ammonia solution dropwise, and measure the pH value in the reactor at the same time. When the pH value is greater than 4.5, stop adding dropwise and continue stirring the reaction;

[0037] 4) Keep the temperature in the kettle at 60°C, stir for 2 hours, turn off the circulating hot water and stirring paddle in the reactor, separate the solid-liquid mixture in the kettle, and wash the solid several times with pure water by centrifugation until the ion conductivity of the washing water is lower than the set value;

[0038] 5) placing the separated solid in a drying device for drying, and then adding it to a kiln for calcination to obtain the final multi-element doped manganese iron oxide positive electrode precursor;

[0039] 6) 160 g of the prepared multi-element doped manganese iron oxide positive electrode precursor was taken, and 115 g of 85 wt% phosphoric acid, 37 g of battery-grade lithium carbonate and 20 g of glucose monohydrate were sand-milled to d50 = 150 ± 5 nm, followed by spray drying and sintering in a box furnace at 600 ° C for 8 hours to obtain a manganese iron phosphate lithium positive electrode material. The 0.2C capacity was tested to be 152 mAh g -1 , the capacity retention rate after 200 cycles is 97%, and the compacted density is 2.15g / cc.

[0040] Example 2

[0041] The steps for preparing a multi-element doped manganese iron oxide positive electrode precursor are as follows:

[0042] 1) Disperse 102.42 g of manganese sulfate monohydrate, 112.32 g of ferrous sulfate heptahydrate, 0.81 g of nano-grade titanium dioxide and 0.40 g of nano-magnesium oxide in 1 L of pure water to obtain a manganese-iron mixed solution, first add it into a reactor as a base liquid, start the reactor and stir at 300 rpm;

[0043] 2) Prepare 87.78g of ammonium bicarbonate and dissolve it in pure water as a reaction precipitant; and prepare 25wt% ammonia solution as a dropwise addition liquid for the reaction;

[0044] 3) Control the temperature of the solution in the reactor to 60°C, and add the precipitant dropwise to the reactor containing the bottom solution while stirring; after the precipitant is added dropwise, start adding the ammonia solution dropwise, and measure the pH value in the reactor at the same time. When the pH value is greater than 4.5, stop adding dropwise and continue stirring the reaction;

[0045] 4) Keep the temperature in the kettle at 60°C, stir for 2 hours, turn off the circulating hot water and stirring paddle in the reactor, separate the solid-liquid mixture in the kettle, and wash the solid several times with pure water by centrifugation until the ion conductivity of the washing water is lower than the set value;

[0046] 5) placing the separated solid in a drying device for drying, and then adding it to a kiln for calcination to obtain the final multi-element doped manganese iron oxide positive electrode precursor;

[0047] 6) 160 g of the prepared multi-element doped manganese iron oxide positive electrode precursor was taken, and 115 g of 85 wt% phosphoric acid, 37 g of battery-grade lithium carbonate and 20 g of glucose monohydrate were sand-milled to d50 = 150 ± 5 nm, followed by spray drying and sintering in a box furnace at 600 ° C for 8 hours to obtain a manganese iron phosphate lithium positive electrode material. The 0.2C capacity was tested to be 148 mAh g -1 , the capacity retention rate after 200 cycles is 93%, and the compacted density is 2.10g / cc.

[0048] Example 3

[0049] The steps for preparing a multi-element doped manganese iron oxide positive electrode precursor are as follows:

[0050] 1) Disperse 102.42 g of manganese sulfate monohydrate, 112.32 g of ferrous sulfate heptahydrate, 1.79 g of cobalt acetate tetrahydrate and 2.52 g of nickel acetate tetrahydrate in 1 L of pure water to obtain a manganese-iron mixed solution, first add it to a reactor as a base liquid, start the reactor and stir at 300 rpm;

[0051] 2) Prepare 87.78g of ammonium bicarbonate and dissolve it in pure water as a reaction precipitant; and prepare 25wt% ammonia solution as a dropwise addition liquid for the reaction;

[0052] 3) Control the temperature of the solution in the reactor to 60°C, and add the precipitant dropwise to the reactor containing the bottom solution while stirring; after the precipitant is added dropwise, start adding the ammonia solution dropwise, and measure the pH value in the reactor at the same time. When the pH value is greater than 4.5, stop adding dropwise and continue stirring the reaction;

[0053] 4) Keep the temperature in the kettle at 60°C, stir for 2 hours, turn off the circulating hot water and stirring paddle in the reactor, separate the solid-liquid mixture in the kettle, and wash the solid several times with pure water by centrifugation until the ion conductivity of the washing water is lower than the set value;

[0054] 5) placing the separated solid in a drying device for drying, and then adding it to a kiln for calcination to obtain the final multi-element doped manganese iron oxide positive electrode precursor;

[0055] 6) 160 g of the prepared multi-element doped manganese iron oxide positive electrode precursor was taken, and 115 g of 85 wt% phosphoric acid, 37 g of battery-grade lithium carbonate and 20 g of glucose monohydrate were sand-milled to d50 = 150 ± 5 nm, followed by spray drying and sintering in a box furnace at 600 ° C for 8 hours to obtain a manganese iron phosphate lithium positive electrode material. The 0.2C capacity was tested to be 151 mAh g -1 , the capacity retention rate after 200 cycles is 98%, and the compacted density is 2.20g / cc.

[0056] Example 4

[0057] The steps for preparing a multi-element doped manganese iron oxide positive electrode precursor are as follows:

[0058] 1) Disperse 102.42 g of manganese sulfate monohydrate, 112.32 g of ferrous sulfate heptahydrate, 0.81 g of nano-TiO2 and 0.40 g of nano-magnesium oxide in 1 L of pure water to obtain a manganese-iron mixed solution, first add it into a reactor as a base liquid, start the reactor and stir at 300 rpm;

[0059] 2) Prepare 87.78g of ammonium bicarbonate and dissolve it in pure water as a reaction precipitant; and prepare 25wt% ammonia solution as a dropwise addition liquid for the reaction;

[0060] 3) Control the temperature of the solution in the reactor to 60°C, and add the precipitant dropwise to the reactor containing the bottom solution while stirring; after the precipitant is added dropwise, start adding the ammonia solution dropwise, and measure the pH value in the reactor at the same time. When the pH value is greater than 4.5, stop adding dropwise and continue stirring the reaction;

[0061] 4) Keep the temperature in the kettle at 60°C, stir for 2 hours, turn off the circulating hot water and stirring paddle in the reactor, separate the solid-liquid mixture in the kettle, and wash the solid several times with pure water by centrifugation until the ion conductivity of the washing water is lower than the set value;

[0062] 5) placing the separated solid in a drying device for drying, and then adding it to a kiln for calcination to obtain the final multi-element doped manganese iron oxide positive electrode precursor;

[0063] 6) 160 g of the prepared multi-element doped manganese iron oxide positive electrode precursor was taken, and 115 g of 85 wt% phosphoric acid, 37 g of battery-grade lithium carbonate and 20 g of glucose monohydrate were sand-milled to d50 = 120 ± 5 nm, followed by spray drying and sintering in a box furnace at 600 ° C for 8 hours to obtain a manganese iron phosphate lithium positive electrode material. The 0.2C capacity was tested to be 152 mAh g -1 , the capacity retention rate after 200 cycles is 96%, and the compacted density is 2.08g / cc.

[0064] Example 5

[0065] The steps for preparing a multi-element doped manganese iron oxide positive electrode precursor are as follows:

[0066] 1) Disperse 102.42 g of manganese sulfate monohydrate, 112.32 g of ferrous sulfate heptahydrate, 2.16 g of magnesium acetate tetrahydrate and 0.42 g of lithium hydroxide monohydrate in 1 L of pure water to obtain a manganese-iron mixed solution, first add it to a reactor as a base liquid, start the reactor and stir at 300 rpm;

[0067] 2) Prepare 87.78g of ammonium bicarbonate and dissolve it in pure water as a reaction precipitant; and prepare 25wt% ammonia solution as a dropwise addition liquid for the reaction;

[0068] 3) Control the temperature of the solution in the reactor to 60°C, and add the precipitant dropwise to the reactor containing the bottom solution while stirring; after the precipitant is added dropwise, start adding the ammonia solution dropwise, and measure the pH value in the reactor at the same time. When the pH value is greater than 4.5, stop adding dropwise and continue stirring the reaction;

[0069] 4) Keep the temperature in the kettle at 60°C, stir for 2 hours, turn off the circulating hot water and stirring paddle in the reactor, separate the solid-liquid mixture in the kettle, and wash the solid several times with pure water by centrifugation until the ion conductivity of the washing water is lower than the set value;

[0070] 5) placing the separated solid in a drying device for drying, and then adding it to a kiln for calcination to obtain the final multi-element doped manganese iron oxide positive electrode precursor;

[0071] 6) 160 g of the prepared multi-element doped manganese iron oxide positive electrode precursor was taken, and 115 g of 85 wt% phosphoric acid, 37 g of battery-grade lithium carbonate and 20 g of glucose monohydrate were sand-milled to d50 = 150 ± 5 nm, followed by spray drying and sintering in a box furnace at 600 ° C for 8 hours to obtain a manganese iron phosphate lithium positive electrode material. The 0.2C capacity was tested to be 155 mAh g -1 , the capacity retention rate after 200 cycles is 95%, and the compacted density is 2.13g / cc.

[0072] Comparative Example 1

[0073] The steps for preparing a multi-element doped manganese iron oxide positive electrode precursor are as follows:

[0074] 1) Disperse 102.42 g of manganese sulfate monohydrate and 112.32 g of ferrous sulfate heptahydrate in 1 L of pure water to obtain a manganese-iron mixed solution, first add it into a reactor as a base liquid, start the reactor and stir at 300 rpm;

[0075] 2) Prepare 87.78g of ammonium bicarbonate and dissolve it in pure water as a reaction precipitant; and prepare 25wt% ammonia solution as a dropwise addition liquid for the reaction;

[0076] 3) Control the temperature of the solution in the reactor to 60°C, and add the precipitant dropwise to the reactor containing the bottom solution while stirring; after the precipitant is added dropwise, start adding the ammonia solution dropwise, and measure the pH value in the reactor at the same time. When the pH value is greater than 4.5, stop adding dropwise and continue stirring the reaction;

[0077] 4) Keep the temperature in the kettle at 60°C, stir for 2 hours, turn off the circulating hot water and stirring paddle in the reactor, separate the solid-liquid mixture in the kettle, and wash the solid several times with pure water by centrifugation until the ion conductivity of the washing water is lower than the set value;

[0078] 5) placing the separated solid in a drying device for drying, and then adding it to a kiln for calcination to obtain the final multi-element doped manganese iron oxide positive electrode precursor;

[0079] 6) 160 g of the prepared multi-element doped manganese iron oxide positive electrode precursor was taken, and 115 g of 85 wt% phosphoric acid, 37 g of battery-grade lithium carbonate and 20 g of glucose monohydrate were sand-milled to d50 = 150 ± 5 nm, followed by spray drying and sintering in a box furnace at 600 ° C for 8 hours to obtain a manganese iron phosphate lithium positive electrode material. The 0.2C capacity was tested to be 145 mAh g -1 , the capacity retention rate after 200 cycles is 85%, and the compacted density is 2.18g / cc.

[0080] Comparative Example 2

[0081] The steps for preparing a multi-element doped manganese iron oxide positive electrode precursor are as follows:

[0082] 1) Disperse 102.42 g of manganese sulfate monohydrate and 112.32 g of ferrous sulfate heptahydrate in 1 L of pure water to obtain a manganese-iron mixed solution, first add it into a reactor as a base liquid, start the reactor and stir at 300 rpm;

[0083] 2) Prepare 87.78g of ammonium bicarbonate and dissolve it in pure water as a reaction precipitant; and prepare 25wt% ammonia solution as a dropwise addition liquid for the reaction;

[0084] 3) Control the temperature of the solution in the reactor to 60°C, and add the precipitant dropwise to the reactor containing the bottom solution while stirring; after the precipitant is added dropwise, start adding the ammonia solution dropwise, and measure the pH value in the reactor at the same time. When the pH value is greater than 4.5, stop adding dropwise and continue stirring the reaction;

[0085] 4) Keep the temperature in the kettle at 60°C, stir for 2 hours, turn off the circulating hot water and stirring paddle in the reactor, separate the solid-liquid mixture in the kettle, and wash the solid several times with pure water by centrifugation until the ion conductivity of the washing water is lower than the set value;

[0086] 5) placing the separated solid in a drying device for drying, and then adding it to a kiln for calcination to obtain the final multi-element doped manganese iron oxide positive electrode precursor;

[0087] 6) 160 g of the prepared multi-element doped manganese iron oxide positive electrode precursor was taken, and 115 g of 85 wt% phosphoric acid, 37 g of battery-grade lithium carbonate, 2.16 g of magnesium acetate tetrahydrate, 2.52 g of nickel acetate tetrahydrate and 20 g of glucose monohydrate were sand-milled to d50 = 150 ± 5 nm, followed by spray drying and sintering in a box furnace at 600 ° C for 8 hours to obtain a manganese iron phosphate lithium positive electrode material, and its 0.2C capacity was tested to be 148 mAh g -1 , the capacity retention rate after 200 cycles is 87%, and the compacted density is 2.05g / cc.

[0088] The data comparison of the above examples and comparative examples is shown in Table 1.

[0089] Table 1

[0090]

[0091] The SEM images of the intermediate product ferromanganese carbonate prepared in Example 1, the SEM images of the multi-element doped ferromanganese oxide positive electrode precursor and the SEM images of the prepared positive electrode material are shown in Figure 1. Figure 2 , Figure 3 and Figure 4 . From the data, we can see that doping in the precursor synthesis stage can effectively improve the gram capacity and cycle performance of the positive electrode material without reducing the compaction density; and the doping effect of soluble ion dopants in the precursor stage is better than that of insoluble ion dopants, which is reflected in the higher capacity and higher compaction density of soluble dopants, and there is no need to control the grinding particle size to be very small.

[0092] Finally, it should be noted that the above-mentioned embodiments only express several implementation methods of the present invention and are not intended to limit the invention. For those skilled in the art, any modification, equivalent replacement, improvement, etc. made without departing from the concept of the present invention should be included in the protection scope of the invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A multi-element doped manganese iron oxide positive electrode precursor, characterized in that: The molar ratio of manganese to iron in the multi-element doped manganese-iron oxide cathode precursor is x:(1 - x), where 0.2 < x < 0.

8. The multi-element doping includes doping with one or more of magnesium, titanium, strontium, vanadium, niobium, cobalt, nickel, and lithium elements, and the doping element accounts for 0.1 - 10% of the total molar number of manganese and iron.

2. A method for preparing a multi-element doped manganese iron oxide positive electrode precursor as claimed in claim 1, characterized in that: It includes the following steps: (1) Prepare a manganese source, an iron source, and an ion dopant dissolved in pure water to obtain a manganese-iron mixed solution, and first add it to a reaction kettle and stir as the bottom liquid; (2) Prepare a soluble carbonate and an alkali, dissolve them in pure water to obtain a precipitant solution as the dropping liquid for the reaction; (3) Control the temperature of the solution in the reaction kettle, start dropping the precipitant into the reaction kettle containing the bottom liquid, and at the same time measure the pH value in the reaction kettle. When the pH value reaches the set range, stop dropping and continue stirring the reaction; (4) After the reaction reaches the end point, cool down, separate the solid-liquid mixture in the kettle, and wash the solid with pure water several times until the ionic conductivity of the washing water is lower than the set value; (5) Put the separated solid into a drying device for drying, and then add it to a kiln for calcination to obtain the final multi-element doped manganese-iron oxide cathode precursor.

3. The method for preparing a multi-element doped manganese iron oxide positive electrode precursor according to claim 2, characterized in that: In step (1), the manganese source is one or more of manganese sulfate, manganese chloride, and manganese nitrate; the iron source is one or more of ferrous sulfate, ferrous chloride, and ferrous nitrate; the ion dopant is one or more of magnesium acetate, magnesium sulfate, titanium dioxide, strontium sulfate, ammonium metavanadate, niobium pentoxide, cobalt sulfate, nickel sulfate, nickel acetate, and lithium sulfate.

4. The method for preparing a multi-element doped manganese iron oxide positive electrode precursor according to claim 2, characterized in that: In step (2), the soluble carbonate is one or more of ammonium bicarbonate, ammonium carbonate, sodium carbonate, and potassium carbonate; the alkali is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and ammonia water.

5. The method for preparing a multi-element doped ferromanganese oxide precursor according to claim 2, characterized in that: In step (3), the temperature of the solution in the reaction kettle is 30 - 100 °C; the set range of the pH value is 3 - 10, preferably 4 - 5.

6. The method for preparing a multi-element doped manganese iron oxide positive electrode precursor according to claim 2, characterized in that: In step (4), the ionic conductivity of the washing water is ≤20000 μS / cm, preferably ≤2000 μS / cm.

7. The method for preparing a multi-element doped manganese iron oxide positive electrode precursor according to claim 2, characterized in that: In step (5), the drying device is one of an oven, a flash dryer, and a rotary dryer, and the kiln is one of a box furnace, a tube furnace, a roller hearth kiln, and a rotary kiln.

8. The method for preparing a multi-element doped manganese iron oxide positive electrode precursor according to claim 2, characterized in that: In step (5), the calcination temperature is 300 - 1000 °C, preferably 500 - 800 °C.

9. A lithium manganese iron phosphate cathode material is prepared from the multi-element doped manganese-iron oxide cathode precursor described in claim 1. The preparation steps are to mix, grind, dry, sinter, and pulverize the multi-element doped manganese-iron oxide, phosphoric acid, lithium carbonate, and glucose, and test the performance of the cathode material to study the performance of the multi-element doped manganese-iron oxide cathode precursor.

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