Method for preparing high-pressure lithium iron phosphate using mixed iron sources and iron phosphate

Abstract

This invention discloses a method for preparing high-compaction lithium iron phosphate (LFP) cathode material using a mixed iron source, comprising the following steps: S1, preparing the acidic mixture; S2, adjusting the pH of the acidic mixture to 0.8–2.0 using phosphoric acid, followed by solid-liquid separation to obtain an acidic clarified solution; S3, pretreating the acidic clarified solution to obtain a first slurry; S4, adding excess hydrogen peroxide to the first slurry for oxidation, and aging at 60–100°C for 2–6 hours to obtain a white-pink slurry; S5, performing solid-liquid separation on the white-pink slurry to obtain a filter cake, which is then washed, dried, and calcined to obtain high-compaction LFP. Its advantages are: 1) It can significantly improve the compaction density of the lithium iron phosphate cathode material; 2) The method of this invention is simple and flexible to operate, low in cost, and suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to a battery manufacturing technology, and more particularly to a lithium iron phosphate cathode material manufacturing technology. Background Technology

[0002] Compared to ternary cathode materials, lithium iron phosphate (LFP) cells have lower compaction density, limiting their energy density and leading to their initial suppression by ternary cathode materials. However, LFP is less expensive, more environmentally friendly, and has higher safety performance, making it an ideal cathode material for lithium-ion batteries. Furthermore, with increasing emphasis on safety in passenger vehicles, LFP's market share is growing. If the low compaction issue can be resolved, the energy density of LFP cathode materials could be further improved. Summary of the Invention

[0003] To address the problem of low compaction density of electrode sheets in lithium iron phosphate battery cells, this invention provides a method for preparing high-compact lithium iron phosphate using a mixed iron source.

[0004] The technical solution adopted in this invention is: a method for preparing high-pressure lithium iron phosphate using mixed iron sources, including the step of preparing an acidic mixed solution, wherein the acidic mixed solution includes ferrous ions and ferric ions.

[0005] As a further improvement of the present invention, the molar ratio of ferrous ions to ferric ions in the acidic mixture is 1:0.005 to 0.05.

[0006] The acidic mixture can be prepared by adding an oxidizing agent (such as hydrogen peroxide) to a ferrous phosphate solution in a predetermined ratio to oxidize a portion of the ferrous ions to ferric ions, thereby obtaining the acidic mixture. Alternatively, the acidic mixture can be prepared by adding soluble ferrous salts and soluble ferric salts to a phosphoric acid solution in a predetermined ratio, thereby obtaining the acidic mixture.

[0007] As a further improvement of the present invention, the method further includes the step of adjusting the pH of the acidic mixture to 0.8-2.0 using phosphoric acid, followed by solid-liquid separation to obtain a clear acidic solution. More preferably, the concentration of total iron ions, consisting of ferrous and ferric ions, in the acidic mixture is 0.5-1.5 mol / L.

[0008] More preferably, the method further includes a pretreatment step for the acidic clarified liquid, wherein the pretreatment specifically involves heating the acidic clarified liquid to 50-70°C under stirring conditions at a heating rate of 3-10°C / min and holding it at that temperature for 5-20 minutes.

[0009] The method for preparing high-pressure lithium iron phosphate using a mixed iron source according to the present invention can be implemented according to the following steps:

[0010] S1. Prepare the acidic mixture;

[0011] S2. The pH of the acidic mixture is adjusted to 0.8-2.0 using phosphoric acid, and then a clear acidic solution is obtained by solid-liquid separation;

[0012] S3. The acidic clarifying liquid is pretreated to obtain a first slurry;

[0013] S4. Add excess hydrogen peroxide to the first slurry for oxidation, and age it at 60-100℃ for 2-6 hours to obtain a white-pink slurry.

[0014] S5. The white powder slurry is subjected to solid-liquid separation to obtain a filter cake. The filter cake is then washed, dried, and calcined to obtain high-pressure lithium iron phosphate.

[0015] The molar ratio of hydrogen peroxide added to ferrous ions in the first slurry is 1.1 to 1.5:1.

[0016] The present invention also discloses a high-pressure lithium iron phosphate iron phosphate, which is prepared by the method of preparing high-pressure lithium iron phosphate iron phosphate by the mixed iron source of the present invention.

[0017] The beneficial effects of this invention are: 1) Using the iron phosphate obtained by the method of this invention as a raw material to prepare lithium iron phosphate can significantly improve the compaction density of lithium iron phosphate cathode materials. 2) The method of this invention is simple and flexible to operate, low in cost, and suitable for large-scale production. Attached Figure Description

[0018] Figure 1 This is a SEM image of the iron phosphate prepared in Example 1.

[0019] Figure 2 The image shows the PSD diagram of the iron phosphate prepared in Example 1.

[0020] Figure 3 The image shows the XRD pattern of iron phosphate prepared in Example 1.

[0021] Figure 4 The first charge-discharge curve at 0.1C is shown for lithium iron phosphate prepared from iron phosphate in Example 1.

[0022] Figure 5 This is a SEM image of the iron phosphate prepared in Comparative Example 1.

[0023] Figure 6 The image shows the PSD diagram of the iron phosphate prepared in Comparative Example 1. Detailed Implementation

[0024] The present invention will be further described below with reference to embodiments.

[0025] Example 1:

[0026] Ferric phosphate products were prepared according to the following method:

[0027] S1. Iron powder is dissolved in dilute phosphoric acid to obtain a ferrous phosphate solution. Hydrogen peroxide with a mass concentration of 10% is added to the ferrous phosphate solution to oxidize a portion of the ferrous ions to ferric ions, thereby obtaining an acidic mixture. The molar ratio of ferrous ions to ferric ions in the acidic mixture is 1:0.015.

[0028] S2. The pH of the acidic mixture is adjusted to 1.4 using 85% phosphoric acid, and then a clear acidic solution with a total iron ion concentration of 1 mol / L is obtained by solid-liquid separation.

[0029] S3. Pour the acidic clarified liquid into a glass reactor for pretreatment. Specifically, under stirring at 500 rpm, heat the acidic clarified liquid to 70°C at a heating rate of 5°C / min and keep it at that temperature for 10 minutes to obtain the first slurry.

[0030] S4. Add excess hydrogen peroxide to the first slurry at a rate of 5 mL / min for oxidation. After the addition is complete, keep warm for 0.5 h, and then continue to heat to 85 °C for aging for 2 h to obtain a white-pink slurry. The molar ratio of the added hydrogen peroxide to the ferrous ions in the first slurry is 1.2:1.

[0031] S5. The white-pink slurry is subjected to solid-liquid separation to obtain a filter cake. The filter cake is then washed, dried, and calcined at 600℃ for 2 hours to obtain the ferric phosphate product.

[0032] Example 2:

[0033] Ferric phosphate products were prepared according to the following method:

[0034] S1. Dissolve ferrous sulfate heptahydrate and ferric nitrate nonahydrate in dilute phosphoric acid to obtain an acidic mixture; the molar ratio of ferrous ions to ferric ions in the acidic mixture is 1:0.031.

[0035] S2. The pH of the acidic mixture is adjusted to 1.4 using 85% phosphoric acid, and then a clear acidic solution with a total iron ion concentration of 1 mol / L is obtained by solid-liquid separation.

[0036] S3. The acidic clarified liquid is poured into a glass reactor for pretreatment. Specifically, the acidic clarified liquid is heated to 70°C at a heating rate of 10°C / min under stirring at 350 rpm and kept at that temperature for 10 min to obtain the first slurry.

[0037] S4. Add excess hydrogen peroxide to the first slurry at a rate of 5 mL / min for oxidation. After the addition is complete, keep warm for 0.5 h, then heat to 85 °C and age for 2 h to obtain a white-pink slurry. The molar ratio of the added hydrogen peroxide to the ferrous ions in the first slurry is 1.2:1.

[0038] S5. The white-pink slurry is subjected to solid-liquid separation to obtain a filter cake. The filter cake is then washed, dried, and calcined at 600℃ for 2 hours to obtain the ferric phosphate product.

[0039] Example 3:

[0040] Ferric phosphate products were prepared according to the following method:

[0041] S1. Iron powder is dissolved in dilute phosphoric acid to obtain a ferrous phosphate solution. Hydrogen peroxide with a mass concentration of 10% is added to the ferrous phosphate solution to oxidize a portion of the ferrous ions to ferric ions, thereby obtaining an acidic mixture. The molar ratio of ferrous ions to ferric ions in the acidic mixture is 1:0.01.

[0042] S2. The pH of the acidic mixture is adjusted to 1.4 using 85% phosphoric acid, and then a clear acidic solution with a total iron ion concentration of 1 mol / L is obtained by solid-liquid separation.

[0043] S3. The acidic clarified liquid is poured into a glass reactor for pretreatment. Specifically, the acidic clarified liquid is heated to 70°C at a heating rate of 5°C / min under stirring at 300 rpm and kept at that temperature for 20 min to obtain the first slurry.

[0044] S4. Add excess hydrogen peroxide to the first slurry at a rate of 5 mL / min for oxidation. After the addition is complete, keep warm for 0.5 h, and then continue to heat to 85 °C for aging for 2 h to obtain a white-pink slurry. The molar ratio of the added hydrogen peroxide to the ferrous ions in the first slurry is 1.2:1.

[0045] S5. The white-pink slurry is subjected to solid-liquid separation to obtain a filter cake. The filter cake is then washed, dried, and calcined at 600℃ for 2 hours to obtain the ferric phosphate product.

[0046] Example 4:

[0047] Ferric phosphate products were prepared according to the following method:

[0048] S1. Iron powder is dissolved in dilute phosphoric acid to obtain a ferrous phosphate solution. Hydrogen peroxide with a mass concentration of 10% is added to the ferrous phosphate solution to oxidize a portion of the ferrous ions to ferric ions, thereby obtaining an acidic mixture. The molar ratio of ferrous ions to ferric ions in the acidic mixture is 1:0.05.

[0049] S2. The pH of the acidic mixture is adjusted to 1.4 using 85% phosphoric acid, and then a clear acidic solution with a total iron ion concentration of 1 mol / L is obtained by solid-liquid separation.

[0050] S3. Pour the acidic clarified liquid into a glass reactor for pretreatment. Specifically, under stirring at 500 rpm, heat the acidic clarified liquid to 70°C at a heating rate of 5°C / min and keep it at that temperature for 10 minutes to obtain the first slurry.

[0051] S4. Add excess hydrogen peroxide to the first slurry at a rate of 5 mL / min for oxidation. After the addition is complete, keep warm for 0.5 h, and then age at 70 °C for 2 h to obtain a white-pink slurry. The molar ratio of the added hydrogen peroxide to the ferrous ions in the first slurry is 1.2:1.

[0052] S5. The white-pink slurry is subjected to solid-liquid separation to obtain a filter cake. The filter cake is then washed, dried, and calcined at 600℃ for 2 hours to obtain the ferric phosphate product.

[0053] Example 5:

[0054] Ferric phosphate products were prepared according to the following method:

[0055] S1. Iron powder is dissolved in dilute phosphoric acid to obtain a ferrous phosphate solution. Hydrogen peroxide with a mass concentration of 10% is added to the ferrous phosphate solution to oxidize a portion of the ferrous ions to ferric ions, thereby obtaining an acidic mixture. The molar ratio of ferrous ions to ferric ions in the acidic mixture is 1:0.015.

[0056] S2. The pH of the acidic mixture is adjusted to 1.4 using 85% phosphoric acid, and then a clear acidic solution with a total iron ion concentration of 1 mol / L is obtained by solid-liquid separation.

[0057] S3. The acidic clarified liquid is poured into a glass reactor for pretreatment. Specifically, the acidic clarified liquid is heated to 60°C at a heating rate of 5°C / min under stirring at 500 rpm and kept at that temperature for 20 min to obtain the first slurry.

[0058] S4. Add excess hydrogen peroxide to the first slurry at a rate of 5 mL / min for oxidation. After the addition is complete, keep warm for 0.5 h, then heat to 80 °C and age for 2 h to obtain a white-pink slurry. The molar ratio of the added hydrogen peroxide to the ferrous ions in the first slurry is 1.2:1.

[0059] S5. The white-pink slurry is subjected to solid-liquid separation to obtain a filter cake. The filter cake is then washed, dried, and calcined at 600℃ for 2 hours to obtain the ferric phosphate product.

[0060] Example 6:

[0061] Ferric phosphate products were prepared according to the following method:

[0062] S1. Iron powder is dissolved in dilute phosphoric acid to obtain a ferrous phosphate solution. Hydrogen peroxide with a mass concentration of 10% is added to the ferrous phosphate solution to oxidize a portion of the ferrous ions to ferric ions, thereby obtaining an acidic mixture. The molar ratio of ferrous ions to ferric ions in the acidic mixture is 1:0.01.

[0063] S2. The pH of the acidic mixture is adjusted to 1.4 using 85% phosphoric acid, and then a clear acidic solution with a total iron ion concentration of 1.5 mol / L is obtained by solid-liquid separation.

[0064] S3. The acidic clarified liquid is poured into a glass reactor for pretreatment. Specifically, the acidic clarified liquid is heated to 80°C at a heating rate of 5°C / min under stirring at 800 rpm and kept at that temperature for 10 min to obtain the first slurry.

[0065] S4. Add excess hydrogen peroxide to the first slurry at a rate of 5 mL / min for oxidation. After the addition is complete, keep warm for 0.5 h, and then age at 70 °C for 2 h to obtain a white-pink slurry. The molar ratio of the added hydrogen peroxide to the ferrous ions in the first slurry is 1.2:1.

[0066] S5. The white-pink slurry is subjected to solid-liquid separation to obtain a filter cake. The filter cake is then washed, dried, and calcined at 600℃ for 2 hours to obtain the ferric phosphate product.

[0067] Example 7:

[0068] Ferric phosphate products were prepared according to the following method:

[0069] S1. Iron powder is dissolved in dilute phosphoric acid to obtain a ferrous phosphate solution. Hydrogen peroxide with a mass concentration of 10% is added to the ferrous phosphate solution to oxidize a portion of the ferrous ions to ferric ions, thereby obtaining an acidic mixture. The molar ratio of ferrous ions to ferric ions in the acidic mixture is 1:0.015.

[0070] S2. The pH of the acidic mixture is adjusted to 1.4 using 85% phosphoric acid, and then a clear acidic solution with a total iron ion concentration of 0.8 mol / L is obtained by solid-liquid separation.

[0071] S3. Pour the acidic clarified liquid into a glass reactor for pretreatment. Specifically, under stirring at 500 rpm, heat the acidic clarified liquid to 70°C at a heating rate of 5°C / min and keep it at that temperature for 10 minutes to obtain the first slurry.

[0072] S4. Add excess hydrogen peroxide to the first slurry at a rate of 5 mL / min for oxidation. After the addition is complete, keep warm for 0.5 h, then heat to 90 °C and age for 2 h to obtain a white-pink slurry. The molar ratio of the added hydrogen peroxide to the ferrous ions in the first slurry is 1.2:1.

[0073] S5. The white-pink slurry is subjected to solid-liquid separation to obtain a filter cake. The filter cake is then washed, dried, and calcined at 600℃ for 2 hours to obtain the ferric phosphate product.

[0074] Comparative Example 1:

[0075] This comparative example serves as a control experiment for Example 1, conducted according to the same steps and conditions as Example 1. The only difference is that the acidic mixture in step S1 (referred to as "ferrous phosphate solution" in Comparative Example 1) contains only ferrous ions and no ferric ions. The specific steps are as follows:

[0076] S1. Dissolve iron powder in dilute phosphoric acid to obtain ferrous phosphate solution.

[0077] S2. The pH of the ferrous phosphate solution is adjusted to 1.4 using 85% phosphoric acid, and then a clear acidic solution with a total iron ion concentration of 1 mol / L is obtained by solid-liquid separation.

[0078] S3. Pour the acidic clarified liquid into a glass reactor for pretreatment. Specifically, under stirring at 500 rpm, heat the acidic clarified liquid to 70°C at a heating rate of 5°C / min and keep it at that temperature for 10 minutes to obtain the first slurry.

[0079] S4. Add excess hydrogen peroxide to the first slurry at a rate of 5 mL / min for oxidation. After the addition is complete, keep warm for 0.5 h, then heat to 85 °C and age for 2 h to obtain a white-pink slurry. The molar ratio of the added hydrogen peroxide to the ferrous ions in the first slurry is 1.2:1.

[0080] S5. The white-pink slurry is subjected to solid-liquid separation to obtain a filter cake. The filter cake is then washed, dried, and calcined at 600℃ for 2 hours to obtain the ferric phosphate product.

[0081] Comparative Example 2:

[0082] This comparative example serves as a control experiment for Example 1, conducted according to the same steps and conditions as Example 1, except that it excludes the pretreatment step for the acidic clarifying solution. The specific steps are as follows:

[0083] S1. Iron powder is dissolved in dilute phosphoric acid to obtain a ferrous phosphate solution. Hydrogen peroxide with a mass concentration of 10% is added to the ferrous phosphate solution to oxidize a portion of the ferrous ions to ferric ions, thereby obtaining an acidic mixture. The molar ratio of ferrous ions to ferric ions in the acidic mixture is 1:0.015.

[0084] S2. The pH of the acidic mixture is adjusted to 1.4 using 85% phosphoric acid, and then a clear acidic solution with a total iron ion concentration of 1 mol / L is obtained by solid-liquid separation.

[0085] S3. Add excess hydrogen peroxide to the acidic clarifying solution at a rate of 5 mL / min for oxidation. After the addition is complete, keep warm for 0.5 h, then heat to 85 °C and age for 2 h to obtain a white-pink slurry. The molar ratio of the added hydrogen peroxide to the ferrous ions in the first slurry is 1.2:1.

[0086] S4. The white-pink slurry is subjected to solid-liquid separation to obtain a filter cake. The filter cake is then washed, dried, and calcined at 600°C for 2 hours to obtain the ferric phosphate product.

[0087] Physicochemical property testing of iron phosphate and lithium iron phosphate:

[0088] The iron phosphate products obtained in the above examples and comparative examples were calcined with lithium carbonate and glucose at 700°C for 10 hours under the same conditions to obtain lithium iron phosphate products. The performance of the iron phosphate products and lithium iron phosphate products obtained in each example was tested separately, and the results are shown in Table 1.

[0089] Table 1 Comparison of physical parameters of iron phosphate and lithium iron phosphate prepared in each embodiment and comparative example.

[0090]

[0091] As can be seen from Table 1 and the accompanying drawings, compared with the prior art, the iron phosphate particles prepared by the method of this invention have larger particle sizes, wider particle size distribution, and higher tap density; and the lithium iron phosphate cathode material made from the iron phosphate prepared by the method of this invention has a tap density of 2.4–2.53 g / cm³. 3 Within its range, it is significantly superior to existing technologies.

[0092] As can be seen from the comparison between Example 1 and Comparative Example 1 in Table 1, the present invention significantly improves the particle size and tap density of iron phosphate by introducing the step of forming an acidic mixture with trivalent iron ions, and also significantly improves the compaction density of the prepared lithium iron phosphate cathode material.

[0093] As can be seen from the comparison between Example 1 and Comparative Example 2 in Table 1, the present invention can further improve the compaction density of lithium iron phosphate cathode material by adding a pretreatment step for acidic clarifying solution.

Claims

1. A method of preparing iron phosphate for high compaction lithium iron phosphate from mixed iron sources, characterized by: The preparation method comprises the following steps: S1, preparing an acid mixture, wherein the acid mixture comprises divalent iron ions and trivalent iron ions, the molar ratio of the divalent iron ions to the trivalent iron ions in the acid mixture is 1:0.005-0.05, and the acid mixture is prepared by adding an oxidizing agent into a ferrous phosphate solution in a set proportion to oxidize part of the divalent iron ions into trivalent iron ions, or by adding soluble divalent iron salt and soluble trivalent iron salt into a phosphoric acid solution in a set proportion; S2, adjusting the pH of the acid mixture to 0.8-2.0 by using phosphoric acid, and then performing solid-liquid separation to obtain an acid clarified liquid; S3, pretreating the acid clarified liquid to obtain a first slurry; S4, adding excess hydrogen peroxide to the first slurry for oxidation, and then aging at 60-100 ℃ for 2-6 h to obtain a white powder slurry; S5, performing solid-liquid separation on the white powder slurry to obtain a filter cake, and then sequentially performing washing, drying and calcination on the filter cake to obtain the iron phosphate for high-density lithium iron phosphate.

2. The process for preparing iron phosphate for high-density lithium iron phosphate using mixed iron sources according to claim 1, characterized by: The oxidizing agent is hydrogen peroxide.

3. The process for the preparation of iron phosphate for high density lithium iron phosphate using mixed iron source as claimed in claim 1, wherein: The total concentration of the divalent iron ions and the trivalent iron ions in the acid mixture is 0.5-1.5 mol / L.

4. The process for preparing iron phosphate for high-density lithium iron phosphate from mixed iron sources according to claim 1, characterized by: The method further comprises a pretreatment step of the acid clarified liquid, wherein the pretreatment is performed by heating the acid clarified liquid to 50-70 ℃ at a heating rate of 3-10 ℃ / min under stirring and then maintaining the temperature for 5-20 min.

5. The method of producing iron phosphate for high-density lithium iron phosphate according to claim 1, wherein In step S4, the amount of the hydrogen peroxide is determined according to the molar ratio of the hydrogen peroxide to the divalent iron ions in the first slurry, which is 1.1-1.5:1.

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