CN112299387A - Regenerated lithium iron phosphate positive electrode material and preparation method thereof - Google Patents
Regenerated lithium iron phosphate positive electrode material and preparation method thereof Download PDFInfo
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Abstract
The invention relates to the field of treatment of lithium iron phosphate waste materials, and discloses a regenerated lithium iron phosphate anode material and a preparation method thereof. The positive electrode material includes: the core comprises a core and a shell layer wrapping the core; in the core, lithium: iron: the molar ratio of phosphorus is 1:1:1, in the shell layer, lithium: iron: molar ratio of phosphorus (1.03-1.15): 1: (1.01-1.05). The qualified and usable regenerated lithium iron phosphate anode material can be prepared from the lithium iron phosphate waste, and the reutilization of the lithium iron phosphate waste is realized. The provided lithium iron phosphate anode material can have a core-shell structure, and the electrochemical performance of the material is improved.
Description
Technical Field
The invention relates to the field of treatment of waste materials of lithium iron phosphate anode materials, in particular to a regenerated lithium iron phosphate anode material and a preparation method thereof.
Background
At present, the recovery method of lithium iron phosphate waste or lithium iron phosphate battery anode recovery waste comprises the following steps:
firstly, the solution is completely dissolved by strong acid, carbon is removed from the coating, then alkali liquor or lithium hydroxide is used for coprecipitation, after the proportion of lithium, iron and phosphorus in the solution system is adjusted, a hydrothermal method or other methods are used for preparing a lithium iron phosphate precursor from metal elements again, then a reductive carbon source is coated, and the regenerated lithium iron phosphate is obtained by high-temperature roasting. The method needs a large amount of acid dissolution, a large amount of alkali precipitation and a large amount of waste in the process.
And secondly, a selective lithium extraction process is adopted, an acid and oxidant (generally hydrogen peroxide) system with specific concentration is adopted to extract lithium with higher value to prepare lithium salt, and the rest iron and phosphorus elements can be used for preparing iron phosphate or other purposes.
And thirdly, directly supplementing a lithium source with a certain proportion into the waste lithium iron phosphate material, and regenerating the lithium iron phosphate positive electrode material by a high-temperature calcination method, wherein effective targeted lithium supplement cannot be realized by the method, the outer layer is coated with carbon, so that the lithium supplement effect is not good, lithium ions are difficult to diffuse into the center of the microsphere during lithiation sintering, the content of residual lithium on the surface of a finished product material is high, and the electrochemical capacity and the cycle performance of the regenerated lithium iron phosphate are influenced.
And fourthly, roasting to decompose carbon on the surface in air or an oxidizing atmosphere, then supplementing lithium, adjusting the proportion of lithium, iron and phosphorus, adding a reducing carbon source, grinding and mixing uniformly, and roasting in an inert atmosphere to obtain a finished lithium iron phosphate product.
It can be seen that a more appropriate method needs to be found for recycling the lithium iron phosphate waste or the lithium iron phosphate battery positive electrode recycling waste.
Disclosure of Invention
The invention aims to overcome the problems existing in the prior art of recycling waste lithium iron phosphate or recycling waste of a lithium iron phosphate battery positive electrode, and provides a regenerated lithium iron phosphate positive electrode material and a preparation method thereof. The regenerated lithium iron phosphate anode material has a core-shell structure.
In order to achieve the above object, a first aspect of the present invention provides a regenerated lithium iron phosphate positive electrode material, including: the core comprises a core and a shell layer wrapping the core; in the core, lithium: iron: the molar ratio of phosphorus is 1:1:1, in the shell layer, lithium: iron: molar ratio of phosphorus (1.03-1.15): 1: (1.01-1.05).
Preferably, in the regenerated lithium iron phosphate cathode material, the ratio of lithium: iron: molar ratio of phosphorus (1.01-1.05): 1: (1.001-1.02).
Preferably, the average particle size of the particles of the inner core is 200-1000nm, and the thickness of the shell layer is 50-100 nm.
The second aspect of the invention provides a preparation method of a regenerated lithium iron phosphate cathode material, which comprises the following steps:
1) under the protection of inert gas, the lithium iron phosphate anode material waste is contacted with an acid-containing solution for first grinding;
2) centrifugally washing and filtering the product obtained in the step 1);
3) taking the filter cake obtained in the step 2) as an inner core, and carrying out second grinding on the filter cake, iron phosphate, lithium carbonate, lithium phosphate, a reductive carbon source and deionized water to obtain mixed slurry;
4) and drying the mixed slurry, and roasting at a high temperature under the protection of inert gas to form a lithium iron phosphate shell outside the core, thereby obtaining the regenerated lithium iron phosphate anode material.
Through the technical scheme, the method can realize the regeneration preparation of the regenerated lithium iron phosphate anode material with the core-shell structure by recycling the lithium iron phosphate waste or the lithium iron phosphate battery anode waste, and realize the reutilization of the lithium iron phosphate waste. In addition, the content of lithium and phosphorus in the shell layer of the regenerated lithium iron phosphate cathode material provided by the invention is increased, namely the shell layer is rich in redundant micro lithium phosphate (Li)3P), lithium phosphate in the shell layer is good in conductivity, and Li is provided+The lithium ion transmission speed is accelerated by passing in and out the channels with the crystal structure of the lithium iron phosphate particles, thereby improving the conductivity, the charge and discharge capacity and the cycle service life of the lithium iron phosphate product。
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
The invention provides a regenerated lithium iron phosphate anode material in a first aspect, which comprises the following components: the core comprises a core and a shell layer wrapping the core; in the core, lithium: iron: the molar ratio of phosphorus is 1:1:1, in the shell layer, lithium: iron: molar ratio of phosphorus (1.03-1.15): 1: (1.01-1.05).
The regenerated lithium iron phosphate anode material provided by the invention is prepared from lithium iron phosphate waste or lithium iron phosphate battery anode recycling waste through regeneration, can form a core-shell structure, is used as a lithium iron phosphate anode material, and has better service performance. Wherein the inner core is made from lithium iron phosphate waste or lithium iron phosphate battery anode recycling waste and is formed into LiFePO4。
In the overall composition of the regenerated lithium iron phosphate positive electrode material provided by the present invention, the relationship between the components is preferably that, in the regenerated lithium iron phosphate positive electrode material, the ratio of lithium: iron: molar ratio of phosphorus (1.01-1.05): 1: (1.001-1.02).
In the composition of the regenerated lithium iron phosphate positive electrode material provided by the present invention, as described above, the molar amount of lithium and phosphorus in the core may be smaller than the molar amount in the shell, based on iron, that is, the composition of iron, lithium and phosphorus in the shell may be larger than the composition in the core, and the content of lithium and phosphorus may be larger. By realizing the composition and the structure, the regenerated lithium iron phosphate anode material has better service performance. In the structure of the regenerated lithium iron phosphate cathode material provided by the invention, lithium and phosphorus can have concentration gradient difference on the core and the shell, namely the concentration of the lithium and the phosphorus in the core is lower than that in the shell, and the shell is composed of lithium iron phosphate with high lithium and phosphorus concentrations.
In the present invention, preferably, the average particle size of the core is 200-1000nm, and the thickness of the shell layer is 50-100 nm.
The regenerated lithium iron phosphate anode material provided by the invention has the composition and structural characteristics, and can perform EDS element distribution qualitative and quantitative analysis on the shape/size of the material and a material micro-region through a scanning electron microscope energy spectrometer (SEM-EDS). On the obtained cross section SEM picture of the regenerated lithium iron phosphate cathode material, the concentration distribution of lithium and phosphorus in the inner core and the shell layer can be observed to be different. The overall chemical composition of the regenerated lithium iron phosphate cathode material can be determined by atomic absorption spectrometry.
The second aspect of the invention provides a preparation method of a regenerated lithium iron phosphate cathode material, which comprises the following steps:
1) under the protection of inert gas, the lithium iron phosphate anode material waste is contacted with an acid-containing solution for first grinding;
2) centrifugally washing and filtering the product obtained in the step 1);
3) taking the filter cake obtained in the step 2) as an inner core, and carrying out second grinding on the filter cake, iron phosphate, lithium carbonate, lithium phosphate, a reductive carbon source and deionized water to obtain mixed slurry;
4) and drying the mixed slurry, and roasting at a high temperature under the protection of inert gas to form a lithium iron phosphate shell outside the core, thereby obtaining the regenerated lithium iron phosphate anode material.
According to the method provided by the invention, the waste lithium iron phosphate or the waste recycled from the positive electrode of the lithium iron phosphate battery can be used for regeneration preparation, so that the waste is utilized. In the method, the lithium iron phosphate (LPF) is not completely dissolved by acid to obtain a solution containing lithium, phosphorus and iron for reuse, but the residual carbon coating layer coated on the surface of the LPF and the LPF material without lithium on the surface of the LPF are dissolved by weak acid and mechanical grinding, and the residual LPF is complete and can be used as a positive electrode active material. Further, LPF treated with acid is used as a core material, and the surface of the LPF is further subjected to treatmentAnd growing a new LPF to obtain an LPF product with a core-shell-like structure, thereby realizing the reutilization of the lithium iron phosphate waste. The filter cake as the inner core is composed of lithium iron phosphate waste or lithium iron phosphate battery anode recycling waste, namely LiFePO4。
In the method provided by the invention, a cross section is obtained by smearing a material and grinding ions, then an SEM image obtained by carrying out EDS element distribution qualitative and quantitative analysis, measurement and observation on the shape/size of the material and a material micro-area through a scanning electron microscope energy spectrometer (SEM-EDS) is obtained, and the content of lithium and phosphorus in a newly grown new LPF shell is increased, namely the shell is rich in redundant micro lithium phosphate (Li) in the shell3P), lithium phosphate in the shell layer is good in conductivity, and Li is provided+And the lithium ion transmission speed is accelerated by passing in and out the channels with the crystal structure of the lithium iron phosphate particles, so that the conductivity, the charge and discharge capacity and the cycle service life of the lithium iron phosphate product are improved.
In the method provided by the invention, preferably, the acid-containing solution is an aqueous solution of a weak organic acid.
In the method provided by the invention, preferably, the pH of the acid-containing solution is 1-5. In the preparation method of the regenerated lithium iron phosphate anode material, the waste material of the lithium iron phosphate anode material is pretreated better.
In the method provided by the present invention, preferably, the weak organic acid is selected from at least one of citric acid, acetic acid, tartaric acid and succinic acid.
In step 1) of the method provided by the invention, the usage amount of the acid-containing solution is such that the finally obtained regenerated lithium iron phosphate cathode material has the composition and structure provided by the invention. Preferably, the acid-containing solution in the step 1) is used in an amount of 1:2-1:10, preferably 1:4-1:6, based on the total weight of the weak organic acid and the water, of the waste lithium iron phosphate positive material to the acid-containing solution.
In the method provided by the invention, the step 1) of pretreating the lithium iron phosphate anode material waste material not only contacts with the acid-containing solution, but also mechanically grinds the lithium iron phosphate anode material waste material. Preferably, the first grinding conditions include: the first grinding temperature is 30-45 ℃, and the first grinding time is 0.5-4 h. The first grinding can be ball milling in a sand mill, zirconium balls with the diameter of 1-5mm are used as grinding balls, and the mass ratio of ball materials between the lithium iron phosphate anode material waste and the grinding balls is 5: 1-2: 1, the better effect of pretreating the lithium iron phosphate anode material waste can be obtained, the residual carbon coating layer on the surface of the lithium iron phosphate anode material waste is removed, and the part of the waste surface lacking lithium can be dissolved.
In the method provided by the invention, the step 2) can be used for washing the product obtained by the treatment in the step 1), washing the waste removed from the surface of the lithium iron phosphate waste material in the step 1), filtering, wherein the filtrate is the removed waste, and the filter cake is the treated material, and the following preparation steps can be carried out.
In the method provided by the invention, the step 3) can be used for preparing ingredients required by the shell layer. Preferably, in step 3), the ratio of lithium: iron: the molar ratio of phosphorus is 1:1: 1.
in the method provided by the present invention, preferably, the feeding amounts of the filter cake, iron phosphate, lithium carbonate, lithium phosphate, reducing carbon source and deionized water satisfy that, in the lithium iron phosphate shell layer, the ratio of lithium: iron: molar ratio of phosphorus (1.03-1.15): 1: (1.01-1.05).
In the method provided by the present invention, preferably, the second grinding conditions include: the second grinding temperature is 20-30 ℃, and the second grinding time is 1-4 h. The first grinding can be ball milling in a sand mill, zirconium balls with the diameter of 0.1-0.5mm are used as grinding balls, and the mass ratio of the total amount of filter cakes, iron phosphate, lithium carbonate, lithium phosphate and the reducing carbon source to the ball material between the grinding balls is 6: 1-3: 1, further carrying out step 4) on the obtained mixed slurry to obtain the regenerated lithium iron phosphate cathode material with the composition and the structure provided by the invention.
In the method provided by the present invention, preferably, the reducing carbon source is selected from at least one of glucose, polyethylene glycol and sucrose. The polyethylene glycol may be 400-1000 in average molecular weight and is commercially available, for example, polypropylene glycol 500(PEG500, 500 in average molecular weight).
In the method provided by the invention, preferably, in the step 4), the drying temperature is 80-120 ℃, and the drying time is 1-4 h; the roasting temperature is 700-850 ℃, and the roasting time is 10-20 h. The drying may be spray drying. And 3) mixing materials to form a lithium iron phosphate shell layer outside the core, so as to obtain the regenerated lithium iron phosphate anode material provided by the invention.
The present invention will be described in detail below by way of examples.
In the following examples, the particle size, the core diameter and the shell thickness of the prepared regenerated lithium iron phosphate cathode material were measured by an ion mill (i.e., ri-4000) slicing method and a scanning electron microscope (e.g., zeiss, Gemini300) scanning cross-section method;
the core and shell of the regenerated lithium iron phosphate anode material are composed by a scanning electron microscope energy spectrometer (SEM-EDS) (Oxford X-MAX)N-80) measurement determination.
Example 1
Weighing 1.65kg of waste lithium iron phosphate reclaimed material and acid-containing liquid (250 g of citric acid, 5kg of deionized water and pH of 2), adding the waste lithium iron phosphate reclaimed material into a sand mill (1-5mm diameter zirconium balls with the ball material mass ratio of 3:1) under the protection of nitrogen, and grinding for 1h at 30 ℃;
centrifugally washing and filtering the ground lithium iron phosphate mixture to remove the desorbed carbon and partially dissolved lithium, iron and phosphorus solutions;
adding 1.58kg of filter cake (the molar ratio of lithium, iron and phosphorus is 1:1:1), 302g of iron phosphate, 102g of lithium carbonate, 1.04g of lithium phosphide, 53.5g of glucose and 5.5kg of deionized water into a sand mill (zirconium balls with the diameter of 0.1-0.5mm and the mass ratio of the balls to the materials being 3:1) and grinding for 50min at 25 ℃ to obtain mixed slurry;
and spray-drying the mixed slurry to obtain powder, roasting at the high temperature of 800 ℃ for 12 hours under the protection of inert gas, and air-crushing to obtain the regenerated lithium iron phosphate anode material.
The obtained regenerated lithium iron phosphate anode material is observed in structure and has a core-shell structure; the particle size, core diameter and shell thickness, core composition and shell composition were measured and the results are shown in Table 1.
Example 2
Weighing 2.0kg of waste lithium iron phosphate reclaimed materials and acid-containing liquid (450 g of alcohol-eating acid, 6kg of deionized water and 3.5 of pH), adding the waste lithium iron phosphate reclaimed materials into a sand mill (1-5mm diameter zirconium balls with the ball-material mass ratio of 4:1) under the protection of nitrogen, and grinding for 1.5h at 35 ℃;
centrifugally washing and filtering the ground lithium iron phosphate mixture to remove the desorbed carbon and partially dissolved lithium, iron and phosphorus solutions;
1896g of filter cake (wherein the molar ratio of lithium, iron and phosphorus is 1:1:1), 453g of iron phosphate, 155g of lithium carbonate, 3.12g of lithium phosphide, and PEG 800: 67.5g and 5kg of deionized water are added into a sand mill (zirconium balls with the diameter of 0.1-0.5mm and the mass ratio of the balls is 4:1) and ground for 50min at the temperature of 28 ℃ to obtain mixed slurry;
and spray-drying the mixed slurry to obtain powder, roasting at the high temperature of 720 ℃ for 15h under the protection of inert gas, and air-crushing to obtain the regenerated lithium iron phosphate anode material.
The obtained regenerated lithium iron phosphate anode material is observed in structure and has a core-shell structure; the particle size, core diameter and shell thickness, core composition and shell composition were measured and the results are shown in Table 1.
Example 3
Weighing 825g of waste lithium iron phosphate reclaimed material and acid-containing liquid (acetic acid 162g, deionized water 2kg, pH 2.4), adding into a sand mill (1-5mm diameter zirconium balls, ball material mass ratio of 5:1) under the protection of nitrogen, and grinding for 0.45h at 36 ℃;
centrifugally washing and filtering the ground lithium iron phosphate mixture to remove the desorbed carbon and partially dissolved lithium, iron and phosphorus solutions;
adding 790g of filter cake (measured by the molar ratio of lithium to iron to phosphorus is 1:1:1), 151g of iron phosphate, 51g of lithium carbonate, 2.6g of lithium phosphide, 27g of sucrose and 3kg of deionized water into a sand mill (zirconium balls with the diameter of 0.1-0.5mm and the mass ratio of the balls is 5:1) and grinding for 50min at 26 ℃ to obtain mixed slurry;
and (3) spray-drying the mixed slurry to obtain powder, roasting at the high temperature of 750 ℃ for 10 hours under the protection of inert gas, and performing gas crushing to obtain the regenerated lithium iron phosphate anode material.
The obtained regenerated lithium iron phosphate anode material is observed in structure and has a core-shell structure; the particle size, core diameter and shell thickness, core composition and shell composition were measured and the results are shown in Table 1.
Example 4
Weighing 1kg of waste lithium iron phosphate reclaimed material and acid-containing liquid (141.6 g of succinic acid, 2kg of deionized water and pH 4), adding the waste lithium iron phosphate reclaimed material into a sand mill (1-5mm diameter zirconium balls with the ball material mass ratio of 2:1) under the protection of nitrogen, and grinding for 1.25h at 40 ℃;
centrifugally washing and filtering the ground lithium iron phosphate mixture to remove the desorbed carbon and partially dissolved lithium, iron and phosphorus solutions;
948g of filter cake (measured by the molar ratio of lithium to iron to phosphorus is 1:1:1), 180g of iron phosphate, 67g of lithium carbonate, 0.6g of lithium phosphide, 130g of glucose and 1.5kg of deionized water are added into a sand mill (zirconium balls with the diameter of 0.1-0.5mm and the mass ratio of balls is 6:1) and ground for 50min at 25 ℃ to obtain mixed slurry;
and spray-drying the mixed slurry to obtain powder, roasting at the high temperature of 810 ℃ for 18h under the protection of inert gas, and performing gas crushing to obtain the regenerated lithium iron phosphate anode material.
The obtained regenerated lithium iron phosphate anode material is observed in structure and has a core-shell structure; the particle size, core diameter and shell thickness, core composition and shell composition were measured and the results are shown in Table 1.
Comparative example 1
Weighing 1kg of waste lithium iron phosphate reclaimed material, 180g of iron phosphate, 67g of lithium carbonate, 0.6g of lithium phosphide, 130g of glucose and 1.5kg of deionized water, adding the materials into a sand mill (0.1-0.5mm diameter zirconium balls, the mass ratio of the balls to the materials is 6:1) and grinding for 50min at 25 ℃ to obtain mixed slurry;
and spray-drying the mixed slurry to obtain powder, roasting at the high temperature of 810 ℃ for 18h under the protection of inert gas, and performing gas crushing to obtain the regenerated lithium iron phosphate anode material.
Observing the structure of the obtained regenerated lithium iron phosphate anode material, wherein the obtained regenerated lithium iron phosphate anode material has no core-shell structure; the composition was measured and the results are shown in Table 1.
TABLE 1
As can be seen from the results in table 1, in the embodiment of the method provided by the present invention, the lithium iron phosphate cathode material having a core-shell structure can be prepared.
Test example
The waste lithium iron phosphate cathode materials used in example 1 and comparative example 1, the recycled material in example 1, the recycled lithium iron phosphate cathode material prepared in comparative example 1, and three cathode materials were prepared into CR2032 coin cells respectively, and the charging and discharging performance was compared, and the results are shown in table 2.
TABLE 2
| Example 1 | Comparative example 1 | Waste material of lithium iron phosphate cathode material | |
| Specific charging capacity (mAh/g) | 163 | 157 | 154 |
| Specific discharge capacity (mAh/g) | 160 | 152 | 147 |
| 3.3V discharge fixed-point capacity (mAh) | 148 | 131 | 120 |
| Median voltage (V) | 3.36 | 3.37 | 3.35 |
| Constant pressure section ratio | 0.8％ | 1.3％ | 2.1％ |
| 3.3V site specific efficiency | 92.5％ | 86.18％ | 81.63％ |
| Coulombic efficiency | 98.16％ | 96.83％ | 95.45％ |
| 0.5C specific discharge capacity (mAh/g) | 145 | 130 | 120 |
| 1C specific discharge capacity (mAh/g) | 125 | 110 | 80 |
| Retention rate of discharge capacity after 100 cycles | 95.75％ | 92.5％ | 87.8％ |
Constant voltage charging segment ratio: in the whole charging process, the constant voltage charging capacity accounts for the ratio of the capacity of the whole charging process. The smaller the value, the better.
As shown in table 2, the regenerated lithium iron phosphate cathode material prepared by the method of the present invention has the above composition and structure (as shown in table 1), and can provide a further prepared cathode material with better electrochemical performance and better charge and discharge performance of the prepared lithium ion battery. The charge and discharge data of example 1 in table 2 is better than that of comparative example 1.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (10)
1. A regenerated lithium iron phosphate positive electrode material, comprising: the core comprises a core and a shell layer wrapping the core; in the core, lithium: iron: the molar ratio of phosphorus is 1:1:1, in the shell layer, lithium: iron: molar ratio of phosphorus (1.03-1.15): 1: (1.01-1.05).
2. The regenerated lithium iron phosphate positive electrode material according to claim 1, wherein, in the regenerated lithium iron phosphate positive electrode material, the ratio of lithium: iron: molar ratio of phosphorus (1.01-1.05): 1: (1.001-1.02).
3. The regenerative lithium iron phosphate positive electrode material as claimed in claim 1 or 2, wherein the average particle size of the core is 200-1000nm, and the thickness of the shell layer is 50-100 nm.
4. A preparation method of a regenerated lithium iron phosphate positive electrode material comprises the following steps:
1) under the protection of inert gas, the lithium iron phosphate anode material waste is contacted with an acid-containing solution for first grinding;
2) centrifugally washing and filtering the product obtained in the step 1);
3) taking the filter cake obtained in the step 2) as an inner core, and carrying out second grinding on the filter cake, iron phosphate, lithium carbonate, lithium phosphate, a reductive carbon source and deionized water to obtain mixed slurry;
4) and drying the mixed slurry, and roasting at a high temperature under the protection of inert gas to form a lithium iron phosphate shell outside the core, thereby obtaining the regenerated lithium iron phosphate anode material.
5. The process according to claim 4, wherein the acid-containing solution is an aqueous solution of a weak organic acid;
preferably, the pH of the acid containing solution is 1 to 5.
6. The method of claim 5, wherein the weak organic acid is selected from at least one of citric acid, acetic acid, tartaric acid, and succinic acid.
7. The method according to claim 5 or 6, wherein the acid-containing solution is used in the step 1), and the weight ratio of the lithium iron phosphate positive electrode material waste material to the acid-containing solution is 1:2-1: 10;
preferably, the first grinding conditions include: the first grinding temperature is 30-45 ℃, and the first grinding time is 0.5-4 h.
8. The method according to any one of claims 4 to 7, wherein in step 3), the ratio of lithium: iron: the molar ratio of phosphorus is 1:1: 1;
preferably, the feeding amount of the filter cake, the iron phosphate, the lithium carbonate, the lithium phosphate salt, the reducing carbon source and the deionized water meets the requirement that in the lithium iron phosphate shell layer, the ratio of lithium: iron: molar ratio of phosphorus (1.03-1.15): 1: (1.01-1.05);
preferably, the second grinding conditions include: the second grinding temperature is 20-30 ℃, and the second grinding time is 0.5-4 h.
9. The method of any one of claims 4-8, wherein the source of reducing carbon is selected from at least one of glucose, polyethylene glycol, and sucrose.
10. The method according to any one of claims 4 to 9, wherein in step 4), the drying temperature is 80 to 120 ℃ and the drying time is 1 to 4 hours; the roasting temperature is 700-850 ℃, and the roasting time is 10-20 h.
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