A preparation method of a coated and modified lithium iron manganese phosphate cathode material

Abstract

The present invention discloses a preparation method of a coated and modified lithium iron manganese phosphate cathode material, belonging to the technical field of lithium ion batteries. In the method of the present invention, by doping titanium and modifying polyvinyl alcohol, the electronic conductivity and lithium ion diffusion rate of the material are effectively improved, and at the same time, the capacity of the lithium iron phosphate cathode material is increased. Therefore, the doping of titanium and the modification of polyvinyl alcohol in the present invention have a synergistic effect. Especially when the molar amount of doped titanium is 0.02, the prepared battery has a high capacity and excellent rate performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium - ion batteries, and particularly relates to a preparation method of a coated and modified lithium iron manganese phosphate cathode material. Background Art

[0002] Lithium iron manganese phosphate (LMFP) has the same olivine structure as lithium iron phosphate, with stable structure, high voltage platform and high energy density, and is a new type of high - energy cathode material. However, during the charge - discharge process of LMFP material, the dissolution of transition metal manganese inevitably occurs. On the one hand, the dissolution of manganese will affect the structure of the cathode material and the lithium storage capacity of the cathode. On the other hand, the dissolved manganese deposits on the anode, affecting the diffusion of lithium ions. At the same time, the deposited manganese will catalyze the decomposition of the electrolyte, resulting in the consumption of active lithium and the formation of a thicker solid electrolyte interface film.

[0003] The patent with the patent number CN201911308409.9 relates to a method for preparing a lithium iron manganese phosphate precursor and a method for preparing lithium iron manganese phosphate. The method for preparing the lithium iron manganese phosphate precursor includes the following steps: (1) preparing liquid material A and liquid material B, where liquid material A is a mixed solution of manganese salt and iron salt, and liquid material B is an oxalic acid or phosphoric acid solution; (2) carrying out a co - precipitation reaction of liquid material A and liquid material B in a high - gravity rotating bed to obtain a first slurry; (3) washing and filtering the first slurry to obtain a filter cake; (4) mixing the filter cake and water, and adding a carbon source, and stirring evenly to obtain a second slurry; (5) homogenizing the second slurry; (⑥) drying the homogenized second slurry to obtain a lithium iron manganese phosphate precursor.

[0004] The patent application with the publication number CN105470510A claims a modified lithium iron manganese phosphate cathode material and its preparation method. The chemical composition of the modified lithium iron manganese phosphate cathode material is Li l-y Ti y Fe 1-x Mn x PO4, where the range of x is 0.2 ≤ x ≤ 0.6, and the range of y is 0.01 ≤ y ≤ 0.1. First, a lithium iron manganese phosphate precursor doped with titanium is prepared by a high - speed shear emulsification mechanism, and then the precursor and a carbon source are mixed and sintered to finally prepare a modified lithium iron manganese phosphate material. This method has a short reaction time, simple operation, reacts under normal pressure, the particle size of the precursor is controllable, and the yield is over 99%. Its electrochemical performance is excellent, the initial discharge specific capacity at 0.1C rate is 155.8 mAh / g, the capacity retention rate after 100 cycles at 1C rate is 97.4%, and the 8C discharge specific capacity is 115.4 mAh / g. However, its initial discharge specific capacity still cannot reach a better level. Summary of the Invention

[0005] In view of the prior art, it is of great significance to improve the electronic conductivity and lithium ion diffusion rate of the material through the preparation method of the lithium iron manganese phosphate cathode material coated with modified polyvinyl alcohol. To solve the technical problems proposed in the above background art, the present invention proposes a preparation method for a coated and modified lithium iron manganese phosphate cathode material.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A preparation method for a coated and modified lithium iron manganese phosphate cathode material, the general formula of the coated and modified lithium iron manganese phosphate cathode material is LiFe 1-x-y Mn y Ti x PO4@C1@C2, where 0.01 ≤ x ≤ 0.03, 0.61 ≤ x + y ≤ 0.63, the carbon source used for C1 is the first organic carbon source, and the carbon source used for C2 is the second organic carbon source.

[0008] The preparation method includes the following steps:

[0009] (1) According to the lithium iron manganese phosphate cathode material LiFe 1-x-y Mn y Ti x PO4@C1@C2 coated with modified polyvinyl alcohol, add the iron source, manganese source, lithium source, phosphorus source, titanium source and the first organic carbon source to the reaction vessel according to a certain molar stoichiometric coefficient ratio, grind and mix evenly, add water, and mix evenly again to obtain the lithium iron manganese phosphate precursor slurry;

[0010] The first organic carbon source is modified polyvinyl alcohol containing dioctadecyl;

[0011] (2) After drying the lithium iron manganese phosphate precursor slurry obtained in step (1), sinter it in a protective atmosphere to obtain the once-coated titanium-doped lithium iron manganese phosphate cathode material;

[0012] (3) After mixing the once-coated titanium-doped lithium iron manganese phosphate cathode material obtained in step (2) with the second organic carbon source, sinter it in a protective atmosphere to obtain the coated and modified lithium iron manganese phosphate cathode material.

[0013] The preparation method of the modified polyvinyl alcohol containing dioctadecyl includes the following steps:

[0014] S1: Carry out a graft reaction between polyvinyl alcohol and acryloyl chloride to obtain acryloyl polyvinyl alcohol;

[0015] S2: Carry out an amino addition reaction between the acryloyl polyvinyl alcohol obtained in step S1, dioctadecylamine, and 2,9,16,23-tetraaminophthalocyanine iron to obtain the modified polyvinyl alcohol containing dioctadecyl.

[0016] Preferably, the mass ratio of polyvinyl alcohol, acryloyl chloride, dioctadecylamine to 2,9,16,23-tetraaminophthalocyanine iron is 400-500∶600-1000∶10-12∶1.

[0017] Specifically, in step S1, the temperature of the grafting reaction is 50-60 °C; in step S2, the temperature of the amino addition reaction is 60-70 °C.

[0018] Specifically, the preparation method of the polyvinyl alcohol containing dioctadecyl includes the following steps:

[0019] S1: By weight, mix 10-20 parts of polyvinyl alcohol and 200-240 parts of dimethyl sulfoxide, soak for 0.5-2 h, dropwise add 10-15 parts of concentrated sulfuric acid, 20-30 parts of acryloyl chloride, heat and react for 30-100 minutes with stirring, add sodium hydroxide until pH = 8-10 to obtain an allyl polyvinyl alcohol solution;

[0020] S2: Add 0.2-0.6 parts of dioctadecylamine, 0.02-0.05 parts of 2,9,16,23-tetraaminophthalocyanine iron, and 2-4 parts of sodium ethoxide to the allyl polyvinyl alcohol solution, heat and react for 50-120 minutes, remove dimethyl sulfoxide to obtain the polyvinyl alcohol containing dioctadecyl.

[0021] For the polyvinyl alcohol containing dioctadecyl, through the amino addition reaction of the allyl polyvinyl alcohol solution with dioctadecylamine and 2,9,16,23-tetraaminophthalocyanine iron respectively, after carbon coating, due to the presence of long alkyl carbon chains, more carbon dioxide overflows, the generated porosity increases, the specific surface area can be increased, which is beneficial to improving the capacity of the lithium iron phosphate cathode material.

[0022] Specifically, the iron source is at least one of iron oxide, ferrous sulfate, ferric sulfate, iron phosphate, and ferrous oxalate;

[0023] The manganese source is at least one of manganese acetate, manganese dioxide, manganese oxalate, and manganese carbonate;

[0024] The lithium source is at least one of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate;

[0025] The phosphorus source is at least one of iron phosphate, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate;

[0026] The titanium source is at least one of titanium dioxide, titanium sulfate, lithium titanate, and iron titanate.

[0027] Preferably, the first organic carbon source accounts for 5.4% of the total mass of the iron source, manganese source, lithium source, phosphorus source, titanium source and the reaction raw materials of the first organic carbon source, and the second organic carbon source accounts for 3.6% of the total mass of the carbon-coated lithium iron manganese phosphate cathode material and the reaction raw materials of the second organic carbon source;

[0028] The second organic carbon source is polyvinyl alcohol.

[0029] In step (2), the sintering temperature is 600-800 °C, and the sintering time is 6-10 h;

[0030] In step (3), the sintering temperature is 300-800 °C, and the sintering time is 3-5 h.

[0031] The present invention also provides a coated and modified lithium iron manganese phosphate cathode material prepared by the preparation method described above.

[0032] The present invention also provides the application of the coated and modified lithium iron manganese phosphate cathode material in the preparation of lithium ion batteries.

[0033] Beneficial effects of the present invention:

[0034] In the method of the present invention, by doping titanium and modifying polyvinyl alcohol, the electronic conductivity and lithium ion diffusion rate of the material are effectively improved, and at the same time, the capacity of the lithium iron phosphate cathode material is increased. Therefore, the doping of titanium and the modification of polyvinyl alcohol in the present invention have a synergistic effect. Especially when the molar amount of doped titanium is 0.02, the prepared battery has a high capacity and excellent rate performance. Description of the drawings

[0035] Figure 1 The first discharge curve of the battery assembled with the lithium iron phosphate cathode material prepared in Example 2 at 0.2C.

[0036] Figure 2 The first charge and discharge curve of the battery assembled with the lithium iron phosphate cathode material prepared in Example 2 at 0.1C.

[0037] Figure 3 The SEM image of the lithium iron phosphate cathode material prepared in Example 2.

[0038] Figure 4 The SEM image of the lithium iron phosphate cathode material prepared in Example 5. Detailed implementation manners

[0039] Example 1

[0040] The coated and modified lithium iron manganese phosphate cathode material is LiFe 1-x-y Mn y Ti xPO4@C1@C2, where x = 0.01, y = 0.6, the carbon source for C1 is glucose, and the carbon source for C2 is polyvinyl alcohol.

[0041] (1) Mixing and grinding: Mix FePO4, MnC2O4, Li2CO3, NH4H2PO4, and TiO2 in a molar ratio of 0.39∶0.6∶0.5∶1∶0.01 to obtain a mixed powder. Use glucose as the primary carbon source, and the addition amount is 5.4% of the total mass of the above raw materials. Add the mixed powder to deionized water and mix and grind it by means of ball milling for 4 h to obtain a lithium iron manganese phosphate precursor slurry.

[0042] (2) Drying: Dry and granulate the lithium iron manganese phosphate precursor slurry obtained in step (1) by spray drying (inlet air temperature 260 °C, outlet air temperature 110 °C) to obtain a precursor powder.

[0043] (3) Sintering: Sinter the precursor powder obtained in step (2) in a protective atmosphere (750 °C, 8 h) to obtain a sintered material; naturally cool it to room temperature to obtain a carbon-coated titanium-doped lithium iron manganese phosphate material.

[0044] (4) Secondary coating: Add the carbon-coated titanium-doped lithium iron manganese phosphate material obtained in step (3) and polyvinyl alcohol (PVA) as the secondary carbon source (3.6% of the total mass of the raw materials (carbon-coated titanium-doped lithium iron manganese phosphate material and PVA)) to deionized water, ultrasonically vibrate for 1 h, then perform suction filtration, and dry it in a vacuum drying oven at 120 °C for 4 h. Sinter the dried mixture in a protective atmosphere, raise the temperature to 350 °C at a rate of 10 °C / min and sinter for 1 h, then raise the temperature to 740 °C at a rate of 15 °C / min and sinter for 4 h, and then cool it to room temperature to obtain a secondary-coated lithium iron manganese phosphate cathode material. -1 of the rate to 350 °C and sinter for 1 h, and then raise the temperature to 740 °C at a rate of 15 °C / min -1 of the rate and sinter for 4 h, and then cool it to room temperature to obtain a secondary-coated lithium iron manganese phosphate cathode material.

[0045] Example 2

[0046] The coated and modified lithium iron manganese phosphate cathode material is LiFe 1-x-y Mn y Ti x PO4@C1@C2, where x = 0.02, y = 0.6, the carbon source for C1 is glucose, and the carbon source for C2 is polyvinyl alcohol.

[0047] (1) Hybrid grinding: Mix FePO4, MnC2O4, Li2CO3, NH4H2PO4, and TiO2 in a molar ratio of 0.38∶0.6∶0.5∶1∶0.02 to obtain a mixed powder. Use glucose as the primary carbon source, and the addition amount is 5.4% of the total mass of the above raw materials. Add the mixed powder to deionized water and mix and grind it by ball milling or other methods for 4 h to obtain a lithium iron manganese phosphate precursor slurry.

[0048] (2) Drying: Spray-dry (inlet air temperature 280 °C, outlet air temperature 130 °C) and granulate the lithium iron manganese phosphate precursor slurry obtained in step (1) to obtain a precursor powder.

[0049] (3) Sintering: Sinter the precursor powder obtained in step (2) in a protective atmosphere (750 °C, 8 h) to obtain a sintered material; naturally cool it to room temperature to obtain a carbon-coated titanium-doped lithium iron manganese phosphate material.

[0050] (4) Secondary coating: Add the carbon-coated titanium-doped lithium iron manganese phosphate material obtained in step (3) and PVA as the secondary carbon source (3.6% of the total mass of the raw materials (titanium-doped lithium iron manganese phosphate material and PVA)) to deionized water, ultrasonically vibrate for 1 h, then perform suction filtration, and dry it in a vacuum drying oven at 120 °C for 4 h. Sinter the dried mixture in a protective atmosphere, raise the temperature to 350 °C at a rate of 10 °C / min and sinter for 1 h, then raise the temperature to 740 °C at a rate of 15 °C / min -1 and sinter for 4 h, and then cool it to room temperature to obtain a secondary-coated lithium iron manganese phosphate cathode material. The SEM image of the obtained lithium iron manganese phosphate cathode material is as -1 shown. After SEM scanning, it can be observed that the lithium iron manganese phosphate particles still have a certain degree of uniformity through doping and coating. Figure 3 shown, and after SEM scanning, it can be observed that the lithium iron manganese phosphate particles still have a certain degree of uniformity through doping and coating.

[0051] Example 3

[0052] The coated and modified lithium iron manganese phosphate cathode material is LiFe 1-x-y Mn y Ti x PO4@C1@C2, where x = 0.03, y = 0.6, the carbon source for C1 is glucose, and the carbon source for C2 is polyvinyl alcohol.

[0053] (1) Hybrid grinding: Mix FePO4, MnC2O4, Li2CO3, NH4H2PO4, and TiO2 in a molar ratio of 0.37∶0.6∶0.5∶1∶0.03 to obtain a mixed powder. Use glucose as the primary carbon source, and the addition amount is 5.4% of the total mass of the raw materials. Add the mixed powder to deionized water and mix and grind it by ball milling or other methods for 4 h to obtain a lithium iron manganese phosphate precursor slurry.

[0054] (2) Drying: The slurry obtained in step (1) is spray-dried (inlet air temperature 300 °C, outlet air temperature 160 °C) to granulate and obtain precursor powder.

[0055] (3) Sintering: The precursor powder described in (2) is sintered in a protective atmosphere (750 °C, 8 h) to obtain the sintered material; it is naturally cooled to room temperature to obtain the carbon-coated lithium iron manganese phosphate material.

[0056] (4) Secondary coating: The carbon-coated lithium iron manganese phosphate material described in (3) and PVA (3.6% of the total raw material mass) as the secondary carbon source are added to deionized water, ultrasonically vibrated for 1 h, then filtered by suction, and dried in a vacuum drying oven at 120 °C for 4 h. The dried mixture is sintered in a protective atmosphere, heated to 350 °C at a rate of 10 °C / min and sintered for 1 h, then heated to 740 °C at a rate of 15 °C / min -1 and sintered for 4 h, and then cooled to room temperature to obtain the secondary-coated lithium iron manganese phosphate cathode material. -1 (4) Secondary coating: The carbon-coated lithium iron manganese phosphate material described in (3) and PVA (3.6% of the total raw material mass) as the secondary carbon source are added to deionized water, ultrasonically vibrated for 1 h, then filtered by suction, and dried in a vacuum drying oven at 120 °C for 4 h. The dried mixture is sintered in a protective atmosphere, heated to 350 °C at a rate of 10 °C / min and sintered for 1 h, then heated to 740 °C at a rate of 15 °C / min

[0057] Example 4

[0058] In this example, polyvinyl alcohol containing dioctadecyl is used to replace glucose as the primary carbon source in Example 1, and the remaining operation steps and feeding amounts are the same as those in Example 1.

[0059] Preparation method of polyvinyl alcohol containing dioctadecyl:

[0060] S1: Add 10 g of polyvinyl alcohol and 200 g of dimethyl sulfoxide to a stirring kettle, soak for 1 h, dropwise add 10 g of concentrated sulfuric acid and 20 g of acryloyl chloride, heat to about 50 °C under stirring, react for 60 minutes, add sodium hydroxide until pH = 9 to obtain an allyl polyvinyl alcohol solution;

[0061] S2: Then add 0.2 g of dioctadecylamine, 0.02 g of 2,9,16,23-tetraaminophthalocyanine iron, 2 g of sodium ethoxide, react at about 60 °C for 80 minutes, and remove dimethyl sulfoxide by vacuum distillation to obtain polyvinyl alcohol containing dioctadecyl.

[0062] The specific surface area of the lithium iron manganese phosphate material prepared by the above method is measured by BET to reach 16.798 m 2 / g.

[0063] Example 5

[0064] In this example, polyvinyl alcohol containing dioctadecyl is used to replace glucose as the primary carbon source in Example 2, and the remaining operation steps and feeding amounts are the same as those in Example 2.

[0065] Preparation method of polyvinyl alcohol containing dioctadecyl:

[0066] S1: Add 20 g of polyvinyl alcohol and 240 g of dimethyl sulfoxide into a stirring kettle, soak for 2 h, dropwise add 15 g of concentrated sulfuric acid and 30 g of acryloyl chloride, heat to about 60 °C under stirring, react for 80 minutes, add sodium hydroxide until pH = 9 to obtain an allyl polyvinyl alcohol solution;

[0067] S2: Then add 0.6 g of dioctadecylamine, 0.05 g of 2,9,16,23-tetraaminophthalocyanine iron, 4 g of sodium ethoxide, react at about 70 °C for 60 minutes, and remove dimethyl sulfoxide by vacuum distillation to obtain polyvinyl alcohol containing dioctadecyl.

[0068] The lithium iron phosphate manganese material prepared by the above method has a specific surface area as high as 18.433 m 2 / g measured by BET. The SEM diagram of the obtained lithium iron phosphate manganese cathode material is as Figure 4 shown. After SEM scanning, it can be observed that the lithium iron phosphate manganese particles still have a certain degree of uniformity through doping and coating.

[0069] Comparative Example 1

[0070] (1) Mixing and grinding: Mix FePO4, MnC2O4, NH4H2PO4, and Li2CO3 in a molar ratio of 0.4:0.6:0.5:1, use glucose as the primary carbon source, and the addition amount is 5.4% of the total mass of the raw materials. Add the mixed powder to deionized water and mix and grind by ball milling for 4 h to obtain a lithium iron phosphate manganese precursor slurry.

[0071] (2) Drying: Dry and granulate the slurry obtained in step (1) by spray drying (inlet air temperature 280 °C, outlet air temperature 130 °C) to obtain a precursor powder.

[0072] (3) Sintering: Sinter the precursor powder obtained in (2) under a protective atmosphere (750 °C, 8 h) to obtain a sintered material; cool naturally to room temperature to obtain a carbon-coated lithium iron phosphate manganese material.

[0073] (4) Secondary coating: Add the carbon-coated lithium iron phosphate manganese material obtained in (3) and PVA as the secondary carbon source (3.6% of the total mass of the raw materials) to deionized water, ultrasonically oscillate for 1 h, then perform suction filtration, and dry in a vacuum drying oven at 120 °C for 4 h. Sinter the dried mixture in a protective atmosphere, raise the temperature to 350 °C at a rate of 10 °C / min and sinter for 1 h, then raise the temperature to 740 °C at a rate of 15 °C / min and sinter for 4 h, and then cool to room temperature to obtain a secondary-coated lithium iron phosphate manganese cathode material. -1 of the rate and sinter at 350 °C for 1 h, then raise the temperature to 740 °C at a rate of 15 °C / min -1 and sinter for 4 h, and then cool to room temperature to obtain a secondary-coated lithium iron phosphate manganese cathode material.

[0074] Test Example 1

[0075] (1) Weigh polyvinylidene fluoride binder (PVDF) with an analytical balance (accuracy 0.0001 g) into N-methylpyrrolidone (NMP), stir and dissolve completely; then add the cathode materials and carbon black conductive agent (SP) prepared in Examples 1 to 5 and Comparative Example 1, and stir evenly to obtain the cathode slurry; among them, the mass ratio of the composite material, PVDF, and SP is 8:1:1.

[0076] (2) Use a coater to evenly coat the cathode slurry on aluminum foil, and dry it in a vacuum drying oven. After removing the solvent NMP, then roll and punch it to obtain a circular sheet with a diameter of 16.0 mm as the cathode electrode.

[0077] (3) Using the above cathode electrode as the cathode, a lithium metal sheet as the anode, a PEPP composite film as the battery separator, and 1.0 molL -1 of LiPF6 / (DMC + DMC) as the electrolyte, where the volume ratio of EC to DMC is 1:1, assemble a CR2032 button cell.

[0078] (4) Perform cyclic charge and discharge tests on the above button cell at a charge and discharge rate of 0.2C, the test temperature is 25.0 °C, and the charge and discharge voltage is 2.5V - 4.5V; the test data is shown in Table 1.

[0079] Table 1

[0080]

[0081] From the data in Table 1, it can be seen that the initial discharge specific capacities of the lithium iron phosphate cathode materials prepared in Comparative Example 1 and Examples 1 to 5 are 141.6, 147.9, 157.8, 153.4, 155.2, and 158.5 mAh g -1 , respectively, and the initial charge and discharge efficiencies are 86.2%, 89.1%, 93.6%, 92.5%, 93.1%, and 93.8%, indicating that the doping of Ti can effectively improve the discharge performance of LiMn 0.6 Fe 0.4 PO4 / C. And polyvinyl alcohol containing dioctadecyl is beneficial to improving the capacity of the lithium iron phosphate cathode material. In addition, the lithium iron phosphate cathode material prepared in Example 5 has the highest capacity retention rate after 100 cycles, indicating that the modified polyvinyl alcohol as a secondary carbon coating source can effectively improve the structural stability of the material, thereby improving the battery cycle life of the lithium manganese iron phosphate material. In the initial discharge specific capacity test, the lithium manganese iron phosphate cathode materials with a Ti doping molar ratio of 0.02 in Example 2 and Example 5 have the most excellent discharge performance. According to Figure 1 and Figure 2, it can be known that the initial discharge specific capacity of the battery assembled with the lithium iron manganese phosphate cathode material prepared in Example 2 at 0.2C is 157.8 mAh g -1 , and the initial charge-discharge specific capacity at 0.1C is 164.6 mAh g -1 .

Claims

1. A preparation method of a coated and modified lithium iron manganese phosphate cathode material, characterized in that, The general formula of the coated and modified lithium iron manganese phosphate cathode material is LiFe 1-x-y Mn y Ti x PO4@C1@C2, where 0.01 ≤ x ≤ 0.03, 0.61 ≤ x + y ≤ 0.63, the carbon source of C1 is the first organic carbon source, and the carbon source of C2 is the second organic carbon source. The preparation method comprises the following steps: (1) According to the coated modified lithium iron manganese phosphate cathode material LiFe 1-x-y Mn y Ti x PO4@C1@C2, add the iron source, manganese source, lithium source, phosphorus source, titanium source and the first organic carbon source into the reaction vessel according to a certain molar stoichiometric coefficient ratio, grind and mix evenly, add water, and mix evenly again to obtain the lithium iron manganese phosphate precursor slurry; The first organic carbon source is modified polyvinyl alcohol containing dipalmityl; The preparation method of the polyvinyl alcohol containing dipalmityl comprises the following steps: S1: Grafting reaction is carried out on polyvinyl alcohol and acryloyl chloride to obtain allyl polyvinyl alcohol; S2: The allyl polyvinyl alcohol obtained in step S1 reacts with dipalmitylamine and 2,9,16,23-tetraaminophthalocyanine iron through amino addition reaction to obtain the modified polyvinyl alcohol containing dipalmityl; (2) After drying the lithium iron manganese phosphate precursor slurry obtained in step (1), sintering is carried out in a protective atmosphere to obtain a lithium iron manganese phosphate cathode material doped with titanium with a primary coating; (3) After mixing the lithium iron manganese phosphate cathode material doped with titanium with a primary coating obtained in step (2) with a second organic carbon source, sintering is carried out in a protective atmosphere to obtain the coated and modified lithium iron manganese phosphate cathode material.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the polyvinyl alcohol, acryloyl chloride, dipalmitylamine and 2,9,16,23-tetraaminophthalocyanine iron is 400-500∶600-1000∶10-12∶1.

3. The preparation method according to claim 1, characterized in that, In step S1, the temperature of the grafting reaction is 50-60°C; in step S2, the temperature of the amino addition reaction is 60-70°C.

4. The preparation method according to claim 1, characterized in that, The iron source is at least one of iron oxide, ferrous sulfate, ferric sulfate, iron phosphate, ferrous oxalate; The manganese source is at least one of manganese acetate, manganese dioxide, manganese oxalate, manganese carbonate; The lithium source is at least one of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate; The phosphorus source is at least one of iron phosphate, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate; The titanium source is at least one of titanium dioxide, titanium sulfate, lithium titanate, iron titanate.

5. The preparation method according to claim 1, characterized in that, The first organic carbon source accounts for 5.4% of the total mass of the iron source, manganese source, lithium source, phosphorus source, titanium source and the reaction raw materials of the first organic carbon source, and the second organic carbon source accounts for 3.6% of the total mass of the lithium iron manganese phosphate cathode material doped with titanium with a primary coating and the reaction raw materials of the second organic carbon source.

6. The preparation method according to claim 1, characterized in that, The second organic carbon source is polyvinyl alcohol.

7. The preparation method according to claim 1, characterized in that, In step (2), the sintering temperature is 600-800°C and the sintering time is 6-10h; In step (3), the sintering temperature is 300-800°C and the sintering time is 3-5h.

8. The coated and modified lithium iron manganese phosphate cathode material prepared by the preparation method according to any one of claims 1-7.

9. Application of the coated and modified lithium iron manganese phosphate cathode material according to claim 8 in the preparation of lithium ion batteries.

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