Preparation method of high-density lithium iron phosphate positive electrode material by using double iron sources and high-density lithium iron phosphate positive electrode material

Abstract

The application provides a preparation method of high-density lithium iron phosphate positive electrode material by using double-iron-source complex level matching, and the method comprises the following steps: adding ferrous sulfate and phosphoric acid into pure water and fully mixing to obtain a solution; the solution is divided into solution A and solution B; solution A is added into a certain amount of metal doping source material, an oxidizing agent and phosphoric acid, and the pH is controlled to be 1-3 to obtain iron phosphate; solution B is added into a certain amount of metal doping source material and ammonia water, and the pH is controlled to be 5-6 to obtain ferrous phosphate; the iron phosphate and the ferrous phosphate are respectively sand-mixed, sprayed with lithium source, carbon source and pure water according to a molar ratio to obtain yellow materials A and B; the yellow material A is calcined in a furnace to obtain a precursor A, the yellow material B is calcined in a furnace to obtain a precursor B, and the precursors A and B are mixed according to a certain mass ratio and then calcined to obtain a finished product. The process flow of the application is simple, can be combined with actual production, and is very effective for improving the compaction density and the electrical performance.

Description

Technical Field

[0001] This invention relates to a lithium-ion battery cathode material and its preparation method in the field of electrochemical energy storage, specifically to a method for preparing a high-pressure lithium iron phosphate cathode material using a dual-iron source composite stage. Background Technology

[0002] Lithium iron phosphate (LiFePO4) is widely used in portable electronic devices and new energy vehicles due to its advantages such as high safety, long cycle life, environmental friendliness, and low production cost. However, compared with ternary lithium batteries, the energy density of lithium iron phosphate is not superior. Therefore, at the material level, increasing its compaction density has become one of the optimal ways to improve the energy density of lithium iron phosphate. At the same time, the traditional high-temperature solid-state synthesis of lithium iron phosphate requires a carbon source for iron reduction. If lithium iron phosphate can be synthesized directly from the ferrous end, the cost can be further reduced. Summary of the Invention

[0003] The purpose of this invention is to improve the compaction density of lithium iron phosphate. This invention achieves this by controlling the pH of the iron phosphate slurry stage, preparing different iron sources, and synthesizing lithium iron phosphate using two pathways in the same reaction vessel. Finally, high and low temperature calcination is combined to achieve particle size distribution. This method has a simple process flow, produces environmentally friendly synthesized materials, and is easy to industrialize.

[0004] The method for solving the problem in this invention is achieved through the following technical solution:

[0005] Step (1): Add ferrous sulfate and phosphoric acid to pure water and mix thoroughly to obtain a solution, and then divide it into solution A and solution B;

[0006] Step (2): Add dopant, oxidant and phosphoric acid to solution A, and control the pH at 1-3 to obtain iron phosphate;

[0007] Step (3): Add dopant and ammonia to solution B, and control the pH at 5-6 to obtain ferrous phosphate;

[0008] Step (4): The iron phosphate obtained in step (2) is milled and sprayed with lithium source, carbon source and pure water to obtain lithium iron phosphate yellow material A; the ferrous phosphate obtained in step (3) is milled and sprayed with lithium source, carbon source and pure water to obtain lithium ferrous phosphate yellow material B;

[0009] Step (5): Place lithium iron phosphate yellow material A in a furnace and calcine to obtain precursor A. Place lithium iron phosphate yellow material B in a furnace and calcine to obtain precursor B. Mix precursor A and B in a certain mass ratio and then calcine to obtain the finished product.

[0010] The dopant in steps (2) and (3) is Mg 2+ Al 3+Ti 4+ V 5+ Bi 3+ One or more combinations thereof, wherein the dopants in steps (2) and (3) are the same or different.

[0011] The Mg 2+ It is selected from one or more of magnesium sulfate, magnesium chloride, magnesium carbonate, magnesium oxalate, magnesium acetate, and magnesium nitrate.

[0012] The Al 3+ It is selected from one or more of aluminum sulfate, aluminum chloride, aluminum carbonate, aluminum oxalate, aluminum acetate, and aluminum nitrate. The Ti... 4+ It is selected from one or more of titanium oxysulfate, titanium dioxide, tetrabutyl titanate, and tetraethyl titanate.

[0013] The V mentioned 5+ It is selected from one or more of ammonium metavanadate, vanadium pentoxide, and vanadium oxysulfate.

[0014] The Bi 3+ Selected from one or more of bismuth sulfate and bismuth nitrate.

[0015] In step (2), the molar ratio of metal ions to Fe in the dopant is 0.001-0.005:1, and the oxidant is one of hydrogen peroxide, oxygen, nitric acid, ammonium persulfate and potassium permanganate.

[0016] In step (3), the molar ratio of dopant to Fe is 0.005-0.02:1.

[0017] Specifically, in step (4), the lithium source is one or more of lithium carbonate and lithium bicarbonate, and the carbon source is one or more of glucose, sucrose, fructose, and polyethylene glycol.

[0018] Specifically, in step (4) Fe 3+ :Li:C=1:1-1.04:0.3-0.45, Fe 2+ The ratio of Li to C is 1:1-1.04:0.1-0.25, the solid content is controlled at 38-48%, the slurry particle size D50 is 300-450nm, and the spray outlet temperature is 75-85℃.

[0019] Specifically, in step (5), the calcination temperature of yellow material A is 650-700℃ and the holding time is 6-8h; the calcination temperature of yellow material B is 700-750℃ and the holding time is 6-8h; the mixing ratio of precursor A and B is 4-2:6-8; the calcination temperature is 750-800℃ and the holding time is 4-6h.

[0020] Compared with other lithium iron phosphate modification methods, the beneficial effects of this invention are:

[0021] By controlling the pH at the end of the ferric phosphate slurry, two iron sources, ferric phosphate and ferrous phosphate, are obtained. The experimental process is mature, the equipment is highly compatible, and the cost is low.

[0022] Two LFP precursors were synthesized using two iron sources with different valence states and different formulation processes. Due to the different valence states of ferrous phosphate and iron phosphate, the different rates of LFP formation from ferrous phosphate and iron, as well as the different sintering temperatures and times during the calcination process, ultimately resulted in different particle sizes, achieving the purpose of particle size distribution.

[0023] Doping at the iron source avoids interference from other raw materials at the downstream end, which could prevent the doping effect from being achieved or cause the loss of doping elements. At the same time, two different elements are doped at different iron sources. Titanium can improve the intrinsic conductivity of the material, while vanadium can refine the particles and improve the rate performance. In the final lithium iron phosphate, the two doping elements produce effects independently, avoiding the doping unevenness problem caused by dual doping. Attached Figure Description

[0024] Figure 1 This is a scanning electron microscope image of Example 1.

[0025] Figure 2 This is a scanning electron microscope image of Comparative Example 1. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0027] This invention discloses a method for preparing high-pressure lithium iron phosphate cathode material using a dual-iron source composite stage. The inventive concept is further illustrated below with specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. It should be understood that, based on the content of this invention, various modifications or alterations can be made to this invention by those skilled in the art, and these equivalent forms also fall within the scope defined by the appended claims.

[0028] Example 1

[0029] The purified ferrous sulfate was mixed with phosphoric acid to obtain ferric phosphate slurry, which was then divided into two parts, A and B.

[0030] In A, ammonium metavanadate was added at a molar ratio of vanadium:iron = 0.001:1. Then hydrogen peroxide and phosphoric acid were added, and the pH was tested. When the pH reached 2.5, the precipitate was collected, filtered, washed, and dried to obtain iron phosphate.

[0031] In B, tetrabutyl titanate was added according to a molar ratio of titanium:iron = 0.008:1. Ammonia was then added, and the pH was tested. When the pH reached 5.6, the precipitate was collected, filtered, washed, and dried to obtain ferrous phosphate.

[0032] Iron phosphate, lithium carbonate, glucose, and PEG were fed in a molar ratio of 1:1.01:0.3 (glucose and PEG were added as carbon sources in a 1:1 molar ratio, the same below). The solid content was 38%, the particle size D50 of the sand mill was 320 nm, and the spray drying outlet temperature was 75 °C to obtain yellow material A. Yellow material A was placed in a furnace, and nitrogen was used as the protective gas. The calcination temperature was 650 °C and the holding time was 6 h to obtain precursor A.

[0033] Similarly, ferrous phosphate, lithium carbonate, glucose and PEG were fed in a molar ratio of 1:1.02:0.15, with a solid content of 39%, a sand milling particle size D50 of 330 nm, and a spray drying outlet temperature of 76 °C to obtain yellow material B. Yellow material B was placed in a furnace, with nitrogen as the protective gas, and calcined at 700 °C for 7 h to obtain precursor B.

[0034] Precursors A and B were uniformly mixed at a mass ratio of A:B=4:6 and placed in a furnace. Nitrogen was used as the protective gas, and the calcination temperature was 750℃ for 4 hours to obtain the finished product LFP.

[0035] Example 2:

[0036] The purified ferrous sulfate was mixed with phosphoric acid to obtain ferric phosphate slurry, which was then divided into two parts, A and B.

[0037] In A, ammonium metavanadate was added at a molar ratio of vanadium:iron = 0.003:1. Then hydrogen peroxide and phosphoric acid were added, and the pH was tested. When the pH reached 1.3, the precipitate was collected, filtered, washed and dried to obtain iron phosphate.

[0038] In B, tetrabutyl titanate was added at a molar ratio of titanium:iron = 0.01:1, followed by the addition of ammonia water. The pH was tested simultaneously. When the pH reached 5.4, the precipitate was collected, filtered, washed, and dried to obtain ferrous phosphate.

[0039] Iron phosphate, lithium carbonate, glucose and PEG were fed in a molar ratio of 1:1.02:0.2, with a solid content of 38%, a sand milling particle size D50 of 340 nm, and a spray drying outlet temperature of 75 °C to obtain yellow material A. Yellow material A was placed in a furnace, calcined at 660 °C with nitrogen as the protective gas, and held for 7 h to obtain precursor A.

[0040] Similarly, ferrous phosphate, lithium carbonate, glucose and PEG were fed in a molar ratio of 1:1.01:0.2, with a solid content of 39%, a sand milling particle size D50 of 330 nm, and a spray drying outlet temperature of 76 °C to obtain yellow material B. Yellow material B was placed in a furnace, with nitrogen as the protective gas, and calcined at 720 °C for 7 h to obtain precursor B.

[0041] Precursors A and B were uniformly mixed at a mass ratio of A:B=3:7 and placed in a furnace. Nitrogen was used as the protective gas, and the calcination temperature was 770℃. The holding time was 4h to obtain the finished product LFP.

[0042] Example 3:

[0043] The purified ferrous sulfate was mixed with phosphoric acid to obtain ferric phosphate slurry, which was then divided into two parts, A and B.

[0044] In A, ammonium metavanadate was added at a molar ratio of vanadium:iron = 0.005:1. Then hydrogen peroxide and phosphoric acid were added, and the pH was tested. When the pH reached 2.8, the precipitate was collected, filtered, washed, and dried to obtain ferric phosphate.

[0045] In B, tetrabutyl titanate was added at a molar ratio of titanium:iron = 0.02:1, followed by the addition of ammonia water. The pH was tested simultaneously. When the pH was below 5.2, the precipitate was collected, filtered, washed, and dried to obtain ferrous phosphate.

[0046] Iron phosphate, lithium carbonate, glucose and PEG were fed in a molar ratio of 1:1.04:0.45, with a solid content of 38%, a sand milling particle size D50 of 400 nm, and a spray drying outlet temperature of 75 °C to obtain yellow material A. Yellow material A was placed in a furnace, calcined at 680 °C with nitrogen as the protective gas, and held for 8 h to obtain precursor A.

[0047] Similarly, ferrous phosphate, lithium carbonate, glucose and PEG were fed in a molar ratio of 1:1.04:0.25, with a solid content of 39%, a sand milling particle size D50 of 380 nm, and a spray drying outlet temperature of 76 °C to obtain yellow material B. Yellow material B was placed in a furnace, with nitrogen as the protective gas, and calcined at 720 °C for 8 hours to obtain precursor B.

[0048] Precursors A and B were uniformly mixed at a mass ratio of A:B=2:8 and placed in a furnace. Nitrogen was used as the protective gas, and the calcination temperature was 800℃ for 6 hours to obtain the finished product LFP.

[0049] Comparative Example 1:

[0050] The purified ferrous sulfate was mixed with phosphoric acid to obtain ferric phosphate slurry, which was then divided into two parts, A and B.

[0051] In A, ammonium metavanadate was added at a molar ratio of vanadium:iron = 0.001:1. Then hydrogen peroxide and phosphoric acid were added, and the pH was tested. When the pH reached 2.3, the precipitate was collected, filtered, washed, and dried to obtain ferric phosphate.

[0052] In B, tetrabutyl titanate was added according to a molar ratio of titanium:iron = 0.008:1. Ammonia was then added, and the pH was tested. When the pH reached 3.0, the precipitate was collected, filtered, washed, and dried to obtain ferric phosphate.

[0053] Iron phosphate, lithium carbonate, glucose and PEG were fed in a molar ratio of 1:1.01:0.3, with a solid content of 38%, a sand milling particle size D50 of 320 nm, and a spray drying outlet temperature of 75 °C to obtain yellow material A. Yellow material A was placed in a furnace, calcined at 650 °C with nitrogen as the protective gas, and held for 6 h to obtain precursor A.

[0054] Similarly, iron phosphate, lithium carbonate, glucose and PEG were fed in a molar ratio of 1:1.02:0.15, with a solid content of 39%, a sand milling particle size D50 of 330 nm, and a spray drying outlet temperature of 76 °C to obtain yellow material B. Yellow material B was placed in a furnace, with nitrogen as the protective gas, and calcined at 650 °C for 7 h to obtain precursor B.

[0055] Precursors A and B were uniformly mixed at a mass ratio of A:B=4:6 and placed in a furnace. Nitrogen was used as the protective gas, and the calcination temperature was 750℃ for 4 hours to obtain the finished product LFP.

[0056] Comparative Example 2:

[0057] The purified ferrous sulfate was mixed with phosphoric acid to obtain ferric phosphate slurry, which was then divided into two parts, A and B. In part A, ammonium metavanadate was added according to the molar ratio of vanadium:iron = 0.003:1. Then hydrogen peroxide and phosphoric acid were added, and the pH was tested. When the pH reached 4.6, the precipitate was collected, filtered, washed and dried to obtain ferric phosphate.

[0058] In ingredient B, tetrabutyl titanate was added at a molar ratio of titanium:iron = 0.01:1. Ammonia was then added, and the pH was tested. When the pH reached 5.5, the precipitate was collected, filtered, washed, and dried to obtain ferrous phosphate.

[0059] Iron phosphate, lithium carbonate, glucose and PEG were fed in a molar ratio of 1:1.02:0.2, with a solid content of 38%, a sand milling particle size D50 of 340 nm, and a spray drying outlet temperature of 75 °C to obtain yellow material A. Yellow material A was placed in a furnace, calcined at 720 °C with nitrogen as the protective gas, and held for 7 h to obtain precursor A.

[0060] Similarly, ferrous phosphate, lithium carbonate, glucose and PEG were fed in a molar ratio of 1:1.01:0.2, with a solid content of 39%, a sand milling particle size D50 of 330 nm, and a spray drying outlet temperature of 76 °C to obtain yellow material B. Yellow material B was placed in a furnace, with nitrogen as the protective gas, and calcined at 720 °C for 7 h to obtain precursor B.

[0061] Precursors A and B were uniformly mixed at a mass ratio of A:B=3:7 and placed in a furnace. Nitrogen was used as the protective gas, and the calcination temperature was 770℃. The holding time was 4h to obtain the finished product LFP.

[0062] Comparative Example 3:

[0063] The purified ferrous sulfate was mixed with phosphoric acid to obtain ferric phosphate slurry, which was then divided into two parts, A and B.

[0064] In A, ammonium metavanadate was added at a molar ratio of vanadium:iron = 0.001:1. Then hydrogen peroxide and phosphoric acid were added, and the pH was tested. When the pH reached 2.2, the precipitate was collected, filtered, washed, and dried to obtain ferric phosphate.

[0065] In ingredient B, tetrabutyl titanate was added at a molar ratio of titanium:iron = 0.008:1. Ammonia was then added, and the pH was tested. When the pH reached 5.7, the precipitate was collected, filtered, washed, and dried to obtain ferrous phosphate.

[0066] Iron phosphate, lithium carbonate, glucose and PEG were fed in a molar ratio of 1:1.01:0.3, with a solid content of 38%, a sand milling particle size D50 of 320 nm, and a spray drying outlet temperature of 75 °C to obtain yellow material A. Yellow material A was placed in a furnace, calcined at 650 °C with nitrogen as the protective gas, and held for 6 h to obtain precursor A.

[0067] Similarly, ferrous phosphate, lithium carbonate, glucose, and PEG were fed in a molar ratio of 1:1.02:0.15, with a solid content of 39%. The particle size D50 of the sand mill was 320 nm, and the spray drying outlet temperature was 76℃ to obtain yellow material B. Yellow material B was placed in a furnace and calcined at 670℃ with nitrogen as the protective gas for 7 hours to obtain precursor B.

[0068] Precursors A and B were uniformly mixed at a mass ratio of A:B=1:9 and placed in a furnace. Nitrogen was used as the protective gas, and the calcination temperature was 750℃ for 4 hours to obtain the finished product LFP.

[0069] Comparative Example 4:

[0070] The purified ferrous sulfate was mixed with phosphoric acid to obtain ferric phosphate slurry, which was then divided into two parts, A and B.

[0071] In A, ammonium metavanadate was added at a molar ratio of vanadium:iron = 0.003:1. Then hydrogen peroxide and phosphoric acid were added, and the pH was tested. When the pH was lower than 3, the precipitate was collected, filtered, washed and dried to obtain iron phosphate.

[0072] In ingredient B, tetrabutyl titanate was added at a molar ratio of titanium:iron = 0.01:1. Ammonia was then added, and the pH was tested. When the pH was below 6, the precipitate was collected, filtered, washed, and dried to obtain ferrous phosphate.

[0073] Iron phosphate, lithium carbonate, glucose and PEG were fed in a molar ratio of 1:1.02:0.2, with a solid content of 38%, a sand milling particle size D50 of 400 nm, and a spray drying outlet temperature of 75 °C to obtain yellow material A. Yellow material A was placed in a furnace, calcined at 620 °C with nitrogen as the protective gas, and held for 5 h to obtain precursor A.

[0074] Similarly, ferrous phosphate, lithium carbonate, glucose and PEG were fed in a molar ratio of 1:1.01:0.2, with a solid content of 39%, a sand milling particle size D50 of 400 nm, and a spray drying outlet temperature of 76 °C to obtain yellow material B. Yellow material B was placed in a furnace, with nitrogen as the protective gas, and calcined at 650 °C for 9 h to obtain precursor B.

[0075] Precursors A and B were uniformly mixed at a mass ratio of A:B=3:7 and placed in a furnace. Nitrogen was used as the protective gas, and the calcination temperature was 770℃. The holding time was 4h to obtain the finished product LFP.

[0076] Comparative Example 5:

[0077] The purified ferrous sulfate was mixed with phosphoric acid to obtain ferric phosphate slurry, which was then divided into two parts, A and B.

[0078] In A, ammonium metavanadate was added at a molar ratio of vanadium:iron = 0.005:1. Then hydrogen peroxide and phosphoric acid were added, and the pH was tested. When the pH was lower than 3, the precipitate was collected, filtered, washed and dried to obtain iron phosphate.

[0079] In ingredient B, tetrabutyl titanate was added at a molar ratio of titanium:iron = 0.02:1. Ammonia was then added, and the pH was tested. When the pH was below 6, the precipitate was collected, filtered, washed, and dried to obtain ferrous phosphate.

[0080] Iron phosphate, lithium carbonate, glucose and PEG were fed in a molar ratio of 1:1.04:0.45, with a solid content of 38%, a sand milling particle size D50 of 400 nm, and a spray drying outlet temperature of 75 °C to obtain yellow material A. Yellow material A was placed in a furnace, calcined at 720 °C with nitrogen as the protective gas, and held for 8 h to obtain precursor A.

[0081] Similarly, ferrous phosphate, lithium carbonate, glucose and PEG were fed in a molar ratio of 1:1.04:0.25, with a solid content of 39%, a sand milling particle size D50 of 380 nm, and a spray drying outlet temperature of 76 °C to obtain yellow material B. Yellow material B was placed in a furnace, with nitrogen as the protective gas, and calcined at 780 °C for 6 h to obtain precursor B.

[0082] Precursors A and B were uniformly mixed at a mass ratio of A:B=2:8 and placed in a furnace. Nitrogen was used as the protective gas, and the calcination temperature was 720℃ for 7 hours to obtain the finished product LFP.

[0083] Table 1: Parameter changes and results comparison between the examples and comparative examples

[0084]

[0085] Electrical performance testing methods

[0086] The materials from each embodiment and comparative example were mixed with a conductive agent (Super P) and a PVDF solution dissolved in NMP at a ratio of 90:5:5, and then coated onto carbon-coated aluminum foil. After vacuum drying at 110°C, they were pressed into 12mm diameter discs as positive electrodes, lithium metal sheets as negative electrodes, Celgard 2300 microporous membranes as separators, and a 1.0mol / L LiPF6 solution of ethylene carbonate (EC): dimethyl carbonate (DMC) = 1:1 as electrolyte. The R2025 coin cells were assembled in a glove box and allowed to stand at 25°C for 8 hours. Then, room temperature testing was performed using the Xinwei 3008 battery testing system: the cells were first charged to 3.75V at 0.1C and then discharged to 2V at 0.1C. After standing for 5 minutes, the cells were charged again at 0.1C and then discharged to 2V at 3C. The specific capacity at 0.1C and 3C was recorded.

[0087] Similarly, after standing at room temperature (25℃) for 8 hours, a high-temperature test at 45℃ was conducted using the Xinwei 3008 battery testing system: first, the battery was charged to 3.75V at 0.1C, then discharged to 2V at 0.1C, repeated 3 times. Next, the battery was charged to 3.75V at 0.1C, placed in a 45℃ constant temperature chamber for 5 minutes, and then discharged at 0.5C. The discharge specific capacity was recorded. The specific capacity at the 0.5C platform was calculated as: the capacity above 3.2V during 0.5C discharge / the total capacity during 0.5C discharge.

[0088] 1. Table 1 shows the parameter changes and results comparison between the examples and comparative examples. The compaction density of all three examples exceeds 2.6 g / cm³. 3At room temperature, both 0.1C and 3C maintain extremely high discharge specific capacity. Meanwhile, at a high temperature of 45℃, the plateau retention rate at 0.5C is also above 97%. The plateau retention rate reflects the polarization degree of lithium iron phosphate; a higher plateau retention rate indicates a lower polarization degree. These data demonstrate that within the optimal formulation range, the material can achieve excellent comprehensive performance. The five comparative examples show changes in the type of mixed iron source, the mixing mass ratio of the iron sources, the calcination temperature of the two iron sources, and the sintering temperature of the mixed iron source. It can be observed that when using a single iron source, the particle size tends to be uniform during calcination in both batches, resulting in low compaction density. After changing the mixing mass ratio of the iron sources, the particle size is not in the optimal gradation state, so the compaction density cannot be improved. Similarly, changing the calcination temperature of the two iron sources alters the particle size, crystallinity, and carbon content of the material, ultimately failing to achieve a high compaction state after mixing. Finally, the sintering temperature of the mixed iron source affects the carbon content and secondary growth state of the mixture, leading to a decrease in compaction density.

[0089] 2. When two iron sources are mixed, during calcination, due to the different valence states of iron, Fe... 3+ Fe needs to be obtained by first reducing the carbon obtained from the decomposition of organic carbon sources. 2+ It then participates in the synthesis of lithium iron phosphate; while Fe 2+ Lithium iron phosphate can then be synthesized directly. The different reaction steps of the two iron sources result in different particle growth rates. 3+ The slow growth rate and small particle size, combined with low calcination temperature and high carbon content, can improve electrical properties; Fe 2+ The growth rate is fast, the particles are large, and the calcination temperature is high with a low carbon content, which can improve compaction. Finally, two precursors in different states are obtained. After mixing them in a certain proportion and calcining them, a material with excellent compaction density and electrical properties is obtained.

[0090] 3. Through the comprehensive performance of the preparation method of high-compact lithium iron phosphate cathode material using a dual-iron source composite stage in the specific embodiments, it can be found that the present invention can simultaneously improve the electrical properties and compaction density of the material; in addition, the lithium iron phosphate obtained by the preparation method provided by the present invention under different combinations of lithium source, iron source, phosphorus source and vanadium source all have good electrochemical performance, indicating that the preparation method has good universality and is conducive to large-scale use.

Claims

1. A method for preparing high-pressure lithium iron phosphate cathode material using a dual-iron source composite stage, characterized in that, Includes the following steps: Step (1): Add ferrous sulfate and phosphoric acid to pure water and mix thoroughly to obtain a solution, and then divide it into solution A and solution B; Step (2): Add dopant, oxidant and phosphoric acid to solution A, and control the pH at 1-3 to obtain iron phosphate; Step (3): Add dopant and ammonia to solution B, and control the pH at 5-6 to obtain ferrous phosphate; Step (4): The iron phosphate obtained in step (2) is milled and sprayed with lithium source, carbon source and pure water to obtain lithium iron phosphate yellow material A; the ferrous phosphate obtained in step (3) is milled and sprayed with lithium source, carbon source and pure water to obtain lithium ferrous phosphate yellow material B; Step (5): Place lithium iron phosphate yellow material A in a furnace and calcine to obtain precursor A. Place lithium iron phosphate yellow material B in a furnace and calcine to obtain precursor B. Mix precursor A and B in a certain mass ratio and then calcine to obtain the finished product. The calcination temperature of lithium iron phosphate yellow material A is 650-700℃, and the holding time is 6-8h; The calcination temperature of lithium iron phosphate yellow material B is 700-750℃, and the holding time is 6-8h; The mixing ratio of precursors A and B is 4-2:6-8, the calcination temperature is 750-800℃, and the holding time is 4-6h.

2. The method for preparing high-pressure lithium iron phosphate cathode material using a dual-iron source composite stage according to claim 1, characterized in that, The dopant in steps (2) and (3) is Mg 2+ Al 3+ Ti 4+ V 5+ Bi 3+ One or more combinations thereof, wherein the dopants in steps (2) and (3) are the same or different.

3. The method for preparing high-pressure lithium iron phosphate cathode material using a dual-iron source composite stage according to claim 1, characterized in that, In step (2), the molar ratio of metal ions to Fe in the dopant is 0.001-0.005:1, and the oxidant is one of hydrogen peroxide, oxygen, nitric acid, ammonium persulfate and potassium permanganate. In step (3), the molar ratio of dopant to Fe is 0.005-0.02:

1.

4. The method for preparing high-pressure lithium iron phosphate cathode material using a dual-iron source composite stage according to claim 1, characterized in that, In step (4), the lithium source is one or more of lithium carbonate and lithium bicarbonate, and the carbon source is one or more of glucose, sucrose, fructose, and polyethylene glycol.

5. The method for preparing high-pressure lithium iron phosphate cathode material using a dual-iron source composite stage according to claim 1, characterized in that, In step (4), the lithium iron phosphate yellow material A is prepared, and the iron phosphate contains Fe. 3+ The molar ratio of Li to C in the lithium source is 1:1-1.04:0.3-0.

45.

6. The method for preparing high-pressure lithium iron phosphate cathode material using a dual-iron source composite stage according to claim 1, characterized in that, In the preparation of lithium iron phosphate yellow material B, Fe in ferrous phosphate 2+ The molar ratio of Li to C in the lithium source is 1:1-1.04:0.1-0.25, the solid content is controlled at 38-48%, and the slurry particle size D50 is 300-450nm.

7. A high-pressure lithium iron phosphate cathode material formulated using a dual-iron source composite stage, characterized in that, It is prepared by any one of the methods described in claims 1-6.

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