Ammonium ferrous manganese phosphate precursor and preparation method and application thereof

Abstract

The present invention relates to the technical field of lithium-ion batteries, and in particular to an ammonium ferrous manganese phosphate precursor, a preparation method thereof, and an application thereof. The ammonium ferrous manganese phosphate precursor of the present invention comprises ammonium ferrous manganese phosphate crystals and carbon atoms located inside the lattice and / or on the lattice surface of the ammonium ferrous manganese phosphate crystals; in the ammonium ferrous manganese phosphate precursor, the content of C is ≥0.3wt%. The preparation method of the ammonium ferrous manganese phosphate precursor comprises the following steps: reacting a mixed solution containing a phosphorus source, an iron source, a manganese source, and a reducing carbon source with ammonia water under an inert atmosphere to obtain the ammonium ferrous manganese phosphate precursor. The ammonium ferrous manganese phosphate precursor of the present invention has no impurities, and a material with better conductivity and specific capacity can be obtained by calcining the precursor.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to an ammonium manganese ferrous phosphate precursor and a preparation method and application thereof. Background Art

[0002] Currently, the commonly used positive electrode materials for power batteries are lithium iron phosphate and ternary materials. Among them, lithium iron phosphate has increased its market share year by year due to its excellent cycle performance and safety. Lithium iron phosphate is a typical representative of olivine structure positive electrode materials, and its chemical formula is LiMPO. 4 (M=Mn, Fe, Co, etc.), the theoretical specific capacity is 170mAh / g, the voltage platform is different, the relative voltage of lithium iron phosphate, lithium manganese phosphate, lithium cobalt phosphate and lithium nickel phosphate are 3.5V, 4.1V, 4.8V and 5.2V (relative to Li+ / Li), but because the price of cobalt and nickel is high and not conducive to practical application, the price of metal iron and manganese is low, and lithium iron phosphate is more stable than lithium manganese phosphate, therefore, lithium iron phosphate was the first to be commercialized. In order to improve the energy density of lithium iron phosphate, lithium manganese iron phosphate came into being, which can increase the voltage platform of the positive electrode material on the basis of maintaining the stability of lithium iron phosphate, thereby increasing the energy density of the material. Its chemical formula is LiMn x Fe 1-x PO 4 (0 <x<1)。

[0003] Precursor calcination is a commonly used method for preparing positive electrode materials. Currently, common precursors for lithium manganese iron phosphate include ferromanganese oxalate, ferromanganese carbonate, ferromanganese phosphate and ammonium ferromanganese phosphate. Among them, the compaction density of the ferromanganese oxalate precursor is low, resulting in a low battery energy density; the capacity and compaction of the ferromanganese carbonate precursor are difficult to meet the target requirements; the manganese and iron ions in the ferromanganese phosphate precursor are all trivalent or higher, and a reducing agent needs to be added during the calcination process for reduction, but the capacity is low because some metal ions cannot be completely reduced; the ammonium ferromanganese phosphate precursor prepared by the co-precipitation method has a high reaction pH, and divalent iron is easily oxidized during the reaction, resulting in the formation of an iron hydroxide impurity phase.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The first purpose of the present invention is to provide an ammonium manganese ferrous phosphate precursor, in which the carbon atoms remain in the lattice or lattice surface of the ammonium manganese ferrous phosphate crystal, and the C content is ≥0.3wt%. After calcination, it is beneficial to improve the conductivity of the positive electrode material, thereby improving the specific capacity of the positive electrode material.

[0006] The second object of the present invention is to provide a method for preparing the ammonium manganese ferrous phosphate precursor as described above. By adding a reducing carbon source during the preparation process, it is beneficial to prevent the oxidation of metal ions during the preparation of the precursor, and the steps are simple and no impurities are generated; it is beneficial to improve the performance of the prepared precursor.

[0007] The third object of the present invention is to provide a lithium manganese iron phosphate, which is mainly obtained by calcining the above-mentioned ammonium ferromanganese phosphate precursor, a lithium source and a carbon source, and the temperature required during the calcination process is relatively low.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0009] The present invention provides an ammonium ferromanganese phosphate precursor, which comprises ammonium ferromanganese phosphate crystals and carbon atoms located inside the lattice and / or on the lattice surface of the ammonium ferromanganese phosphate crystals;

[0010] In the ammonium manganese ferrophosphate precursor, the content of C is ≥ 0.3 wt %.

[0011] Furthermore, the ammonium manganese ferrous phosphate precursor is a sheet-like structure.

[0012] Preferably, the sheet-like structure has a length of 10 to 30 μm and a width of 5 to 25 μm.

[0013] The present invention also provides a method for preparing the above-mentioned ammonium ferrous manganese phosphate precursor, comprising the following steps:

[0014] Under an inert atmosphere, a mixed solution containing a phosphorus source, an iron source, a manganese source and a reducing carbon source is reacted with aqueous ammonia to obtain the ammonium ferrous manganese phosphate precursor.

[0015] Furthermore, the pH of the mixed solution containing the phosphorus source, the iron source, the manganese source and the reducing carbon source is less than 2.

[0016] Furthermore, under an inert atmosphere, ammonia water is added to a mixed solution containing a phosphorus source, an iron source, a manganese source and a reducing carbon source until the pH of the mixed solution is 6-7, and then reacted at 60-100° C. to obtain the ammonium ferrous manganese phosphate precursor.

[0017] Furthermore, in the mixed solution containing the phosphorus source, the iron source, the manganese source and the reducing carbon source, the total concentration of Mn and Fe is 1 to 3 mol / L.

[0018] Furthermore, in the mixed solution containing the phosphorus source, iron source, manganese source and reducing carbon source, the ratio of the amount of Mn to the total amount of Mn and Fe is 0.5-0.7:1; the ratio of the amount of phosphate to the total amount of Mn and Fe is 1-1.2:1.

[0019] Furthermore, in the mixed solution containing the phosphorus source, the iron source, the manganese source and the reducing carbon source, the concentration of the reducing carbon source and the total concentration of Mn and Fe satisfy the following relationship: 10%≤T×S / (M+F)≤50%;

[0020] T is the concentration of the reducing carbon source, in mol / L;

[0021] S is the carbon content in the reducing carbon source;

[0022] M is the concentration of Mn, in mol / L;

[0023] F is the concentration of Fe, in mol / L.

[0024] Furthermore, the reducing carbon source includes at least one of glucose, fructose and maltose.

[0025] Preferably, the phosphorus source includes at least one of phosphoric acid, diammonium phosphate and monoammonium phosphate; the iron source includes a soluble iron salt; and the manganese source includes a soluble manganese salt.

[0026] The present invention also provides lithium manganese iron phosphate, which is mainly obtained by calcining the ammonium ferromanganese phosphate precursor as described above or the ammonium ferromanganese phosphate precursor prepared by the preparation method of the ammonium ferromanganese phosphate precursor as described above, a lithium source and a carbon source.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The ammonium ferromanganese phosphate precursor of the present invention contains carbon elements and has a flaky structure, which can improve the conductivity of the material after calcination, thereby improving the specific capacity of the material; the flaky structural feature is conducive to the reaction between the precursor and the lithium source during the sintering process, thereby facilitating the formation of lithium ferromanganese phosphate and reducing the temperature required for the calcination process.

[0029] The present invention prepares an ammonium ferrous manganese phosphate precursor by a hydrothermal method. By using a reducing carbon source as an additive, it is beneficial to prevent oxidation of metal ions in the precursor preparation process, the reaction process is simple, and no impurities are generated; and part of the carbon atoms of the ammonium ferrous manganese phosphate remain in the precursor lattice or on the lattice surface during precipitation, which is beneficial to improve the conductivity and specific capacity of the material after calcination. The filtrate in the preparation process of the present invention can be reused, thereby reducing the use of the reducing carbon source and water, and reducing the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 This is a SEM image of the ammonium ferrous manganese phosphate precursor prepared in Example 1 of the present invention.

[0032] Figure 2 This is an EDS image of the ammonium ferrous manganese phosphate precursor prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0033] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0034] The following is a detailed description of an ammonium manganese ferrous phosphate precursor according to an embodiment of the present invention and its preparation method and application.

[0035] In some embodiments of the present invention, an ammonium ferrous manganese phosphate precursor is provided, the ammonium ferrous manganese phosphate precursor comprising ammonium ferrous manganese phosphate crystals and carbon atoms located inside the crystal lattice and / or on the surface of the crystal lattice of the ammonium ferrous manganese phosphate crystals;

[0036] In the ammonium ferrous manganese phosphate precursor, the content of C is ≥ 0.3wt%.

[0037] The carbon atoms in the ammonium ferromanganese phosphate precursor of the present invention remain in the lattice or lattice surface of the ammonium ferromanganese phosphate crystals, and the carbon content is ≥0.3wt%, which is beneficial to improving the conductivity of lithium manganese iron phosphate obtained after calcining the ammonium ferromanganese phosphate precursor, thereby improving the specific capacity of the material.

[0038] In some embodiments of the present invention, the content of C in the ammonium manganese ferrous phosphate precursor is 0.3wt% to 2wt%; typically but not limiting, for example, the content of C in the ammonium manganese ferrous phosphate precursor is 0.3wt%, 0.5wt%, 1wt%, 1.5wt% or 2wt%, etc.

[0039] In some embodiments of the present invention, the ammonium manganese ferrous phosphate precursor is a sheet-like structure; preferably, the sheet-like structure has a length of 10 to 30 μm and a width of 5 to 25 μm.

[0040] The ammonium ferromanganese phosphate precursor with a flaky structure has a larger specific surface area, and the contact area between the precursor and the lithium source (such as lithium carbonate) is larger during the calcination process, which is beneficial to the reaction between the ammonium ferromanganese phosphate and the lithium source during the calcination process, thereby facilitating the formation of lithium iron manganese phosphate and reducing the temperature required for calcination.

[0041] In some embodiments of the present invention, a method for preparing the above-mentioned ammonium manganese ferrous phosphate precursor is also provided, comprising the following steps:

[0042] Under an inert atmosphere, a mixed solution containing a phosphorus source, an iron source, a manganese source and a reducing carbon source is reacted with ammonia water to obtain an ammonium ferrous manganese phosphate precursor.

[0043] The present invention prepares an ammonium ferrous manganese phosphate precursor containing carbon elements and having a flaky structure by a hydrothermal method, the reaction process is simple, and no impurities are generated; by adding a reducing carbon source as an additive during the preparation process, it is beneficial to prevent the oxidation of metal ions during the preparation of the precursor, and carbon remains in the precursor lattice or on the lattice surface during the precipitation of the ammonium ferrous manganese phosphate. The lithium manganese iron phosphate obtained by calcining the ammonium ferrous manganese phosphate precursor of the present invention is beneficial to improving the conductivity and specific capacity of the material; the ammonium ferrous manganese phosphate precursor has a larger specific surface area, and the flaky structure is beneficial to the reaction of the ammonium ferrous manganese phosphate precursor with a lithium source during the calcination process, thereby reducing the calcination temperature.

[0044] In some embodiments of the present invention, the pH of the mixed solution containing the phosphorus source, the iron source, the manganese source and the reducing carbon source is <2.

[0045] In some specific embodiments of the present invention, the preparation of a mixed solution containing a phosphorus source, an iron source, a manganese source and a reducing carbon source comprises: mixing the phosphorus source, the iron source, the manganese source, the reducing carbon source and water, and then adding an acid to adjust the pH of the solution to <2; preferably, the acid comprises at least one of sulfuric acid, hydrochloric acid and phosphoric acid.

[0046] In some embodiments of the present invention, the method for preparing the ammonium ferrous manganese phosphate precursor comprises the following steps:

[0047] Under an inert atmosphere, ammonia water is added to a mixed solution containing a phosphorus source, an iron source, a manganese source and a reducing carbon source until the pH of the mixed solution is 6-7, and then reacted at 60-100° C. to obtain an ammonium ferrous manganese phosphate precursor.

[0048] In some specific embodiments of the present invention, the stirring speed of the reaction is 400-800 rpm; and the reaction time is >6 h.

[0049] In some embodiments of the present invention, typically but not limiting, for example, the reaction temperature is 60°C, 70°C, 80°C, 90°C or 100°C, etc.

[0050] In some specific embodiments of the present invention, the gas of the inert atmosphere includes nitrogen.

[0051] In some specific embodiments of the present invention, the method for preparing the ammonium manganese ferrous phosphate precursor further comprises, after the reaction, sequentially performing solid-liquid separation, washing and drying; preferably, the drying temperature is 80-120° C., and the drying time is ≥12 h.

[0052] In some embodiments of the present invention, in the mixed solution containing a phosphorus source, an iron source, a manganese source and a reducing carbon source, the total concentration of Mn and Fe is 1 to 3 mol / L; typically but not limitatively, for example, in the mixed solution containing a phosphorus source, an iron source, a manganese source and a carbon source, the total concentration of Mn and Fe is 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L, etc.

[0053] In some embodiments of the present invention, in a mixed solution containing a phosphorus source, an iron source, a manganese source and a reducing carbon source, the ratio of the amount of Mn to the total amount of Mn and Fe is 0.5-0.7:1; the ratio of the amount of phosphate to the total amount of Mn and Fe is 1-1.2:1.

[0054] In some embodiments of the present invention, in a mixed solution containing a phosphorus source, an iron source, a manganese source and a reducing carbon source, the concentration of Mn and the concentration of Fe satisfy the following relationship: 0.5≤M / (M+F)≤0.7; the concentration of phosphate, the concentration of Mn and the concentration of Fe satisfy the following relationship: 1≤P / (M+F)≤1.2; wherein, M is the concentration of Mn (unit: mol / L); F is the concentration of Fe (unit: mol / L); and P is the concentration of phosphate (unit: mol / L).

[0055] In some embodiments of the present invention, in a mixed solution containing a phosphorus source, an iron source, a manganese source and a reducing carbon source, the concentration of the reducing carbon source and the total concentration of Mn and Fe satisfy the following relationship: 10%≤T×S / (M+F)≤50%; T is the concentration of the reducing carbon source, in mol / L; S is the carbon content in the reducing carbon source; M is the concentration of Mn, in mol / L; F is the concentration of Fe, in mol / L.

[0056] The general formula of ammonium ferromanganese phosphate is NH 4 Mnx Fe y PO 4 where 0 < x < 1, 0 < y < 1, and x + y = 1. By adopting the above proportional relationship in the present invention, it can ensure that the ratio of phosphorus to metal ions in the lithium iron phosphate manganese prepared by subsequent sintering is within a suitable range.

[0057] In some embodiments of the present invention, the reducing carbon source includes at least one of glucose, fructose, and maltose.

[0058] In some embodiments of the present invention, the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, and ammonium hydrogen phosphate.

[0059] In some embodiments of the present invention, the iron source includes soluble iron salts. Preferably, the iron source includes at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate.

[0060] In some embodiments of the present invention, the manganese source includes soluble manganese salts; preferably, the manganese source includes at least one of manganese sulfate, manganese nitrate, and manganese chloride.

[0061] In some embodiments of the present invention, a lithium iron phosphate manganese is also provided, which is mainly obtained by calcining the ammonium manganese iron phosphate precursor or the ammonium manganese iron phosphate precursor prepared by the preparation method of the ammonium manganese iron phosphate precursor, a lithium source, and a carbon source.

[0062] In some embodiments of the present invention, the lithium source includes lithium carbonate.

[0063] In some embodiments of the present invention, the calcination temperature is 600 - 650 °C.

[0064] The lithium iron phosphate manganese obtained by calcining the ammonium manganese iron phosphate precursor of the present invention and lithium carbonate has more excellent conductivity and specific capacity, and the required calcination temperature is lower.

[0065] Example 1

[0066] The preparation method of the ammonium manganese iron phosphate precursor provided in this example includes the following steps:

[0067] (1) Mix ferrous sulfate, manganese sulfate, phosphoric acid, glucose, and water to obtain a 10 L mixed solution. In the mixed solution, the total concentration of Mn 2+ and Fe 2+ is 1 mol / L, the molar ratio of Mn 2+ and Fe 2+ is 6:4, the concentration of glucose is 225 g / L, and the amount of substance of PO 4 3- and the sum of Mn 2+ and Fe 2+The ratio of the total amount of substance is 1:1; then sulfuric acid is added to adjust the pH of the mixed solution to <2.

[0068] (2) The mixed solution after adjusting the pH is added to the hydrothermal kettle, stirred and nitrogen is passed for 1 hour, the flow rate of nitrogen is 0.5L / min, and then ammonia water is added to adjust the pH of the solution to 6, and then the hydrothermal kettle is heated to 60°C, and the reaction is stopped after 6 hours at 60°C and a stirring speed of 800rpm. After stirring to 25°C, the reaction solution is filtered and washed with 10L of deionized water. After washing, it is dried at 120°C for 12 hours to obtain ammonium ferrous manganese phosphate precursor. The filtrate obtained after the reaction solution is filtered is reused 4 times and then desulfurized by precipitation method, and then it can be used again.

[0069] According to the test, in the ammonium manganese ferrous phosphate precursor, the molar ratio of Mn to Fe is 60%:40%, and the C content is 0.35wt%.

[0070] The method for preparing lithium manganese iron phosphate provided in this embodiment comprises the following steps:

[0071] The ammonium ferrous manganese phosphate precursor is mixed with lithium carbonate at a Li:P molar ratio of 1:1 to obtain a mixture, and then glucose and carbon nanotubes are added, the mass of glucose is 6wt% of the mixture, and the mass of the carbon nanotubes is 0.3wt% of the mixture; then sand grinding is performed to particles of 100-300nm, and then spray drying is performed. Thereafter, the dried material is heated to 600°C at a rate of 1-2°C / min and calcined for 10h, and naturally cooled to obtain lithium ferrous manganese phosphate.

[0072] Example 2

[0073] The preparation method of the ammonium manganese ferrous phosphate precursor provided in this embodiment comprises the following steps:

[0074] (1) Ferrous sulfate, manganese sulfate, phosphoric acid, glucose and water are mixed to obtain 10L of mixed solution. In the mixed solution, Mn 2+ and Fe 2+ The total concentration is 3 mol / L, Mn 2+ and Fe 2+ The molar ratio is 5:5, the concentration of glucose is 135g / L, and the PO 4 3- The amount of substance and Mn 2+ and Fe 2+ The total amount of substance is 1.1:1; then phosphoric acid is added to adjust the pH of the mixed solution to <2.

[0075] (2) The mixed solution after adjusting the pH was added to a hydrothermal kettle, stirred and passed nitrogen for 1 hour, the nitrogen flow rate was 10 L / min, and then ammonia water was added to adjust the pH of the solution to 7. The hydrothermal kettle was heated to 100°C, and the reaction was stopped at 100°C and a stirring speed of 400 rpm for 10 hours. After continuing to stir to 25°C, the reaction solution was filtered and washed with 30 L of deionized water. After washing, it was dried at 120°C for 12 hours to obtain ammonium ferrous manganese phosphate precursor.

[0076] The preparation method of lithium iron manganese phosphate provided in this embodiment refers to Example 1, except that the ammonium ferrous manganese phosphate precursor used is the ammonium ferrous manganese phosphate precursor prepared in this embodiment.

[0077] Example 3

[0078] The preparation method of the ammonium manganese ferrous phosphate precursor provided in this embodiment comprises the following steps:

[0079] (1) Ferrous sulfate, manganese sulfate, phosphoric acid, fructose and water are mixed to obtain 10L of mixed solution. In the mixed solution, Mn 2+ and Fe 2+ The total concentration is 1 mol / L, Mn 2+ and Fe 2+ The molar ratio is 7:3, the concentration of glucose is 225g / L, and the PO 4 3- The amount of substance and Mn 2+ and Fe 2+ The total amount of substance is in a ratio of 1.2:1; then sulfuric acid is added to adjust the pH of the mixed solution to <2.

[0080] (2) The mixed solution after adjusting the pH was added to a hydrothermal kettle, stirred and passed nitrogen for 1 hour, the nitrogen flow rate was 0.5 L / min, and then ammonia water was added to adjust the pH of the solution to 6. The hydrothermal kettle was heated to 60°C, and the reaction was stopped after 6 hours at 60°C and a stirring speed of 800 rpm. After continuing to stir to 25°C, the reaction solution was filtered and washed with 10 L of deionized water. After washing, it was dried at 120°C for 12 hours to obtain ammonium ferrous manganese phosphate precursor.

[0081] The preparation method of lithium iron manganese phosphate provided in this embodiment refers to Example 1, except that the ammonium ferrous manganese phosphate precursor used is the ammonium ferrous manganese phosphate precursor prepared in this embodiment.

[0082] Comparative Example 1

[0083] The preparation method of the ammonium manganese ferrous phosphate precursor provided in this comparative example is based on Example 1, except that in step (1), glucose is not added.

[0084] The preparation method of lithium iron manganese phosphate provided in this comparative example refers to Example 1, except that the ammonium ferrous manganese phosphate precursor used is the ammonium ferrous manganese phosphate precursor prepared in this comparative example.

[0085] Comparative Example 2

[0086] The preparation method of the ammonium manganese ferrous phosphate precursor provided in this comparative example refers to Example 1, with the only difference being that, in step (2), ammonia water is added to adjust the pH of the solution to 8, and then the hydrothermal autoclave is heated to 50°C, and the heating is stopped after reacting for 6 hours at 50°C and a stirring speed of 800 rpm.

[0087] The preparation method of lithium iron manganese phosphate provided in this comparative example refers to Example 1, except that the ammonium ferrous manganese phosphate precursor used is the ammonium ferrous manganese phosphate precursor prepared in this comparative example.

[0088] Test Example 1

[0089] The ammonium ferrous manganese phosphate precursor prepared in Example 1 was subjected to an electrochemical test, and the results are as follows: Figure 1 and Figure 2 shown. Figure 1 The a in the figure is a SEM image magnified 500 times. Figure 1 b is a SEM image magnified 3000 times; Figure 2 a is the EDS diagram of P element, Figure 2 b is the EDS diagram of Mn element. Figure 2 Figure c is the EDS graph of Fe element.

[0090] from Figure 1 and Figure 2 It can be seen that the ammonium manganese ferrophosphate precursor has a flaky structure and manganese iron and phosphorus are evenly distributed.

[0091] The lithium manganese iron phosphate prepared in Examples 1 to 3 and Comparative Examples 1 to 2 was used as the positive electrode active material, and the positive electrode active material: SP (superconducting carbon black): PVDF (polyvinylidene fluoride) was homogenized in a mass ratio of 90:5:5, and coated on a 20 μm thick aluminum foil to prepare a positive electrode sheet with a surface density of 8 mg / cm 2 , and then through drying, rolling, die cutting, punching into positive electrode sheets.

[0092] Use R2032 button battery shell for button battery assembly, use lithium sheet as negative electrode, adopt PE material diaphragm, add 80μmL of electrolyte (the electrolyte uses Xinzhoubang lithium-ion battery electrolyte, model LBC3401A60).

[0093] The electrochemical performance tests were carried out on the batteries prepared above. 1C cycle performance test was carried out at 25°C: the button batteries prepared above were tested using a blue electric tester; the prepared button batteries were placed in a high-temperature oven at 25°C for charge and discharge tests, with a voltage range of 2.0V to 4.35V, 0.1C charge and discharge activation for one cycle, and then charged at 0.5C constant current and constant voltage, with a cut-off current of 0.05C, and discharged at 1C current for 50 cycles, and the relevant data of parameters such as the first discharge specific capacity and the 50th cycle capacity retention rate were obtained. The test results are shown in Table 1.

[0094] Table 1

[0095]

[0096]

[0097] As can be seen from Table 1, compared with Comparative Example 1, the positive electrode material prepared by calcining the ammonium ferrous manganese phosphate containing carbon element of the present invention has a more excellent specific capacity and capacity retention rate, and has better cycle performance. Compared with Comparative Example 2, the ammonium ferrous manganese phosphate precursor prepared by the preparation method of the present invention has a more excellent electrical property.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An ammonium ferrous manganese phosphate precursor, characterized in that: The ammonium manganese ferrous phosphate precursor includes ammonium manganese ferrous phosphate crystals and carbon atoms located inside the crystal lattice and / or on the surface of the crystal lattice of the ammonium manganese ferrous phosphate crystals; In the ammonium ferrous manganese phosphate precursor, the content of C is ≥ 0.3wt%; The ammonium manganese ferrous phosphate precursor is a sheet structure.

2. The ammonium ferrous manganese phosphate precursor according to claim 1, characterized in that: The sheet structure has a length of 10 to 30 μm and a width of 5 to 25 μm.

3. The method for preparing the ammonium ferrous manganese phosphate precursor according to claim 1 or 2, characterized in that: The following steps are included: Under an inert atmosphere, a mixed solution containing a phosphorus source, an iron source, a manganese source and a reducing carbon source is reacted with aqueous ammonia to obtain the ammonium ferrous manganese phosphate precursor.

4. The method for preparing the ammonium ferrous manganese phosphate precursor according to claim 3, characterized in that: The pH of the mixed solution containing the phosphorus source, the iron source, the manganese source and the reducing carbon source is less than 2.

5. The method for preparing the ammonium ferrous manganese phosphate precursor according to claim 3, characterized in that: Under an inert atmosphere, ammonia water is added to a mixed solution containing a phosphorus source, an iron source, a manganese source and a reducing carbon source until the pH of the mixed solution is 6-7, and then reacted at 60-100° C. to obtain the ammonium ferrous manganese phosphate precursor.

6. The method for preparing the ammonium ferrous manganese phosphate precursor according to claim 3, characterized in that: In the mixed solution containing the phosphorus source, the iron source, the manganese source and the reducing carbon source, the total concentration of Mn and Fe is 1-3 mol / L.

7. The method for preparing the ammonium ferrous manganese phosphate precursor according to claim 6, characterized in that: In the mixed solution containing the phosphorus source, iron source, manganese source and reducing carbon source, the ratio of the amount of Mn to the total amount of Mn and Fe is 0.5-0.7:1; the ratio of the amount of phosphate to the total amount of Mn and Fe is 1-1.2:

1.

8. The method for preparing the ammonium ferrous manganese phosphate precursor according to claim 7, characterized in that: In the mixed solution containing the phosphorus source, the iron source, the manganese source and the reducing carbon source, the concentration of the reducing carbon source and the total concentration of Mn and Fe satisfy the following relationship: 10%≤T×S / (M+F)≤50%; T is the concentration of the reducing carbon source, in mol / L; S is the carbon content in the reducing carbon source; M is the concentration of Mn, in mol / L; F is the concentration of Fe, in mol / L.

9. The method for preparing the ammonium ferrous manganese phosphate precursor according to claim 3, characterized in that: The reducing carbon source includes at least one of glucose, fructose and maltose; The phosphorus source includes at least one of phosphoric acid, diammonium phosphate and monoammonium phosphate; the iron source includes a soluble iron salt; and the manganese source includes a soluble manganese salt.

10. A lithium manganese iron phosphate, characterized in that: The method is mainly obtained by calcining the ammonium ferromanganese phosphate precursor prepared by the preparation method of the ammonium ferromanganese phosphate precursor described in claim 1 or 2 or the ammonium ferromanganese phosphate precursor described in any one of claims 3 to 9, a lithium source and a carbon source.

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