Lithium iron phosphate composite material based on hydrothermal growth and preparation method thereof

Abstract

The invention belongs to the technical field of lithium ion battery materials, and particularly relates to a hydrothermal growth lithium iron phosphate composite material and a preparation method thereof. According to the technical scheme, the method comprises the following steps: respectively dissolving a lithium source and a phosphorus source in two containers, uniformly dissolving, taking an iron source and phosphorus source solution, slowly adding the dissolved lithium source into a mixed solution of the phosphorus source and the iron source, and transferring the mixed solution into a reaction kettle; putting the carbon fiber cloth material into a reaction kettle, carrying out high-temperature and high-pressure reaction for a period of time, washing and drying to obtain a reactant material; the preparation method comprises the following steps: adding a proper amount of a phosphorus source, a surfactant and ascorbic acid into pure water, dissolving to obtain a phosphorus source solution, sequentially adding a proper amount of an iron source and a lithium source into the phosphorus source solution, stirring, dissolving, transferring the obtained mixed solution into a reaction kettle, putting reactant materials into the reaction kettle, carrying out a high-temperature and high-pressure reaction for a period of time, and cooling to room temperature. The high-load lithium iron phosphate composite material is obtained; and preparing a mixed solution of a soluble carbon source and pure water, soaking the composite material in the carbon source mixed solution, drying, putting into a tubular furnace, and carrying out high-temperature sintering to obtain the final lithium iron phosphate positive electrode composite material.

Description

Background Art

[0001] The present invention belongs to the technical field of lithium-ion battery materials, and particularly relates to a lithium iron phosphate composite material grown by hydrothermal method and a preparation method thereof. Background Art

[0002] In order to address the current increasingly serious environmental pollution problems, numerous new energy sources and energy storage systems have been extensively developed and applied. As a safe and environmentally friendly energy storage device, lithium-ion batteries have been widely used in fields such as electric vehicles and large-scale energy storage systems. Among various cathode materials for lithium-ion batteries, lithium iron phosphate with an olivine structure has become the preferred material for lithium-ion batteries because lithium iron phosphate has advantages such as high capacity, high power, high cycle life, and high safety.

[0003] The preparation method of lithium iron phosphate is to mix a lithium source, an iron source, and a phosphorus source and then react them through various methods (such as solid-phase method, liquid-phase method, etc.). At present, most commercially produced lithium iron phosphate products use the solid-phase method. This method is simple and easy to operate, but the product consistency is poor. Moreover, the morphology of the prepared lithium iron phosphate finished product is relatively single. In order to improve the energy density of the battery, the solid-phase method usually uses methods such as nanosizing to improve the performance of the material. While nanosizing improves the performance, it will also make it difficult to disperse the materials during the slurry mixing process due to the too small particle size, ultimately affecting the battery performance. The hydrothermal method (liquid-phase method) can more precisely control the particle size or morphology of the material at the molecular level compared to the solid-phase method. The energy density of the battery is the most important performance of the battery, and the hydrothermal method is an effective method to improve the energy density of the battery. Summary of the Invention

[0004] In view of the above problems, the present invention provides a lithium iron phosphate composite material based on hydrothermal growth and a preparation method thereof. The lithium iron phosphate composite material prepared by the step-by-step hydrothermal process using a carbon fiber cloth and a substrate further improves the electrochemical performance of the material.

[0005] The present invention is achieved through the following technical solutions: The preparation method of the lithium iron phosphate composite material based on hydrothermal growth of the present invention includes the following steps: Dissolve the lithium source and the phosphorus source in two containers respectively. The molar ratio of the lithium source to the phosphorus source is (1 - 1.05):1. Use magnetic stirring to dissolve evenly. Weigh the iron source and add it to the phosphorus source solution. The addition amounts of the iron source and the phosphorus source are the same. Slowly add the dissolved lithium source to the mixed solution of the phosphorus source and the iron source, and finally transfer the obtained mixed solution to a reaction kettle. Put the carbon fiber cloth material into the reaction kettle. After a period of high-temperature and high-pressure reaction, take out the carbon fiber cloth, wash and dry it to obtain the reactant material. (3) Take an appropriate amount of phosphorus source, surfactant, and ascorbic acid, add them to pure water and dissolve to obtain a phosphorus source solution. Take an appropriate amount of iron source and lithium source, and add them to the phosphorus source solution in sequence, stir and dissolve. Transfer the obtained mixed solution to a reaction kettle. At the same time, put the reactant material obtained in (2) into the reaction kettle. After a period of high-temperature and high-pressure reaction, take out the reactant to obtain a high-loading lithium iron phosphate composite material; (4) Prepare a mixed solution of soluble carbon source and pure water. Immerse the composite material obtained in (3) in the carbon source mixed solution, dry it, and then put it into a tubular furnace for high-temperature sintering to obtain the final lithium iron phosphate cathode composite material.

[0006] According to the preparation method of the lithium iron phosphate composite material based on hydrothermal growth, in (2), the high-temperature heating temperature is 150 - 200 °C, and the reaction time is 5 - 10 h. According to the preparation method of the lithium iron phosphate composite material based on hydrothermal growth, in (3), the high-temperature heating temperature is 150 - 250 °C, and the reaction time is 10 - 15 h.

[0007] According to the preparation method of the lithium iron phosphate composite material based on hydrothermal growth, in (2), the solution in the reaction kettle accounts for 50% - 80% of the total volume of the reaction kettle, and the high-pressure is 0.2 MPa - 2 MPa.

[0008] According to the preparation method of the lithium iron phosphate composite material based on hydrothermal growth, the soluble carbon source is one of glucose, sucrose, citric acid, or PEG, and the carbon source concentration in the carbon source solution is 0.1 - 0.5 M.

[0009] According to the preparation method of the lithium iron phosphate composite material based on hydrothermal growth, the sintering temperature of the tubular furnace is 500 - 800 °C, and the sintering time is 2 - 5 h.

[0010] According to the preparation method of the lithium iron phosphate composite material based on hydrothermal growth, the lithium source is lithium carbonate or lithium hydroxide.

[0011] According to the preparation method of the lithium iron phosphate composite material based on hydrothermal growth, the phosphorus source is phosphoric acid or ammonium monohydrogen phosphate.

[0012] According to the preparation method of the lithium iron phosphate composite material based on hydrothermal growth, the iron source is ferrous sulfate, ferrous chloride, or ferrous oxalate.

[0013] The composite material prepared by using the preparation method of the lithium iron phosphate composite material based on hydrothermal growth of the present invention.

[0014] The beneficial effects achieved by the present invention are: The present invention uses carbon fiber cloth as the substrate, and through a two-step hydrothermal process, lithium iron phosphate materials with two morphologies are successively compounded with the carbon fiber cloth, so that more active substances can be loaded on the carbon fiber cloth. The rod-shaped lithium iron phosphate on the surface of the composite material is more conducive to the insertion and extraction of ions, and the rod-shaped lithium iron phosphate material has a larger specific surface area and more active sites, which is beneficial to the performance of the capacity and rate of the lithium-ion battery. At the same time, the existence of part of the sheet structure avoids the problem of too large specific surface area of the pure rod-shaped structure, reduces the occurrence of side reactions, and improves the cycling performance. The hydrothermal growth preparation method avoids the use of binders, can provide higher capacity, and reduces the processing procedures. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a scanning diagram of the carbon fiber cloth in the present invention; Figure 2 It is a scanning diagram of the lithium iron phosphate composite material prepared by using (1) in Example 1; Figure 3 It is a scanning diagram of the high-loading lithium iron phosphate composite material in Example 1; DETAILED DESCRIPTION OF THE INVENTION

[0016] In order to better understand the technical solution of the present invention, the specific content of the present invention will be further described below. Obviously, based on the embodiments in the present invention, it is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0017] The preparation method of the lithium iron phosphate composite material based on hydrothermal growth of the present invention includes the following steps: Dissolve the lithium source and the phosphorus source in two containers respectively. The molar ratio of the lithium source to the phosphorus source is (1-1.05):1, and use magnetic stirring to dissolve evenly. Weigh the iron source and add it to the phosphorus source solution. The addition amounts of the iron source and the phosphorus source are the same. Slowly add the dissolved lithium source to the mixed solution of the phosphorus source and the iron source, and finally transfer the obtained mixed solution to a reaction kettle.

[0018] (2) Put the carbon fiber cloth material into the reaction kettle, and after a period of high-temperature and high-pressure reaction, the solution accounts for 50%-80% of the total volume of the reaction kettle, and the high-pressure is 0.2 MPa-2 MPa. Take out the carbon fiber cloth, wash and dry it to obtain the reactant material. The high-temperature heating temperature in this step is 150-200 °C, and the reaction time is 5-10 h.

[0019] (3) Take an appropriate amount of phosphorus source, surfactant, and ascorbic acid, add them to pure water and dissolve to obtain a phosphorus source solution, where the mass ratio of phosphoric acid, surfactant, and ascorbic acid is 100:(1 - 5):(1 - 5). Take an appropriate amount of iron source and lithium source, and add them to the phosphorus source solution in sequence, stir and dissolve. Transfer the obtained mixed solution to a reaction kettle. At the same time, put the reactant material obtained in (2) into the reaction kettle. After a period of high temperature and high pressure, the high temperature heating temperature is 150 - 250 °C, and the reaction time is 10 - 15 h. Take out the reactant to obtain a high-loading lithium iron phosphate composite material.

[0020] (4) Prepare a mixed solution of soluble carbon source and pure water. Immerse the composite material obtained in (3) in the carbon source mixed solution, dry it and then put it into a tube furnace for high-temperature sintering. The sintering temperature of the tube furnace is 500 - 800 °C, and the sintering time is 2 - 5 h to obtain the final lithium iron phosphate cathode composite material.

[0021] In the present invention, the soluble carbon source is selected from one of glucose, sucrose, citric acid, or PEG, and the carbon source concentration in the carbon source solution is 0.1 - 0.5 M; the lithium source is lithium carbonate or lithium hydroxide or a mixture of both; the phosphorus source is phosphoric acid or ammonium monohydrogen phosphate or a mixture of both. The iron source is one of ferrous sulfate, ferrous chloride, or ferrous oxalate or a mixture of two or more of them.

[0022] The present invention will be described in detail below in the manner of specific embodiments: Embodiment

[0023] (1) First, prepare two beakers and add pure water. Weigh lithium hydroxide and phosphoric acid according to the equal amount of substance of the lithium source and phosphorus source, and dissolve them in the two beakers respectively, and stir magnetically to dissolve evenly. Weigh an appropriate amount of ferrous sulfate according to the molar ratio of lithium source to iron source of 1.03:1, and add it to the phosphoric acid solution. At this time, slowly add the dissolved lithium hydroxide to the mixed solution of phosphoric acid and ferrous sulfate. Finally, transfer the obtained mixed solution to a reaction kettle. At the same time, put a carbon fiber cloth material of appropriate size into the reaction kettle. The high temperature heating temperature is 150 °C, and the reaction time is 10 h. After the reaction, take out the carbon fiber cloth, wash and dry it to obtain the reactant material.

[0024] (2) Take an appropriate amount of phosphoric acid, surfactant, and ascorbic acid, add them to pure water and dissolve. Weigh ferrous sulfate and lithium hydroxide according to the molar ratio of phosphorus source to iron source to lithium source of 1:1:1.03, and add them to the phosphoric acid solution in sequence, stir and dissolve. Transfer the obtained mixed solution to a reaction kettle. At the same time, put the reactant material obtained in (1) into the reaction kettle. The high temperature heating temperature is 150, and the reaction time is 15 h. After the reaction, take out the reactant to obtain a high-loading lithium iron phosphate composite material.

[0025] (3) Prepare a mixed solution of glucose and pure water with a concentration of 0.1 M. Immerse the composite material obtained in (2) in the glucose mixed solution, dry it, and then place it in a tube furnace for high-temperature sintering. The sintering temperature of the tube furnace is 500 °C, and the sintering time is 5 h. Example

[0026] (1) First, prepare two beakers and add pure water. Weigh lithium hydroxide and ammonium hydrogen phosphate according to the equal amount of substance of the lithium source and phosphorus source, and dissolve them in the two beakers respectively. Stir magnetically until dissolved evenly. Weigh an appropriate amount of ferrous oxalate according to the molar ratio of the lithium source to the iron source of 1.02:1, and add it to the ammonium hydrogen phosphate solution. Slowly add the dissolved lithium hydroxide to the mixed solution of ammonium hydrogen phosphate and ferrous oxalate. Finally, transfer the obtained mixed solution to a reaction kettle. At the same time, place a carbon fiber cloth material of appropriate size into the reaction kettle. The high-temperature heating temperature is 160 °C, and the reaction time is 9 h. After the reaction, take out the carbon fiber cloth, wash and dry it to obtain the reactant material.

[0027] (2) Take an appropriate amount of ammonium hydrogen phosphate, surfactant, and ascorbic acid, and dissolve them in pure water. Weigh ferrous oxalate and lithium hydroxide according to the molar ratio of the phosphorus source, iron source, and lithium source of 1:1:1.02, and add them to the ammonium hydrogen phosphate solution in sequence, and stir until dissolved. Transfer the obtained mixed solution to a reaction kettle. At the same time, place the reactant material obtained in (1) into the reaction kettle. The high-temperature heating temperature is 170 °C, and the reaction time is 14 h. After the reaction, take out the reactant to obtain a high-loading lithium iron phosphate composite material.

[0028] (3) Prepare a mixed solution of sucrose and pure water with a concentration of 0.2 M. Immerse the composite material obtained in (2) in the sucrose mixed solution, dry it, and then place it in a tube furnace for high-temperature sintering. The sintering temperature of the tube furnace is 600 °C, and the sintering time is 4 h. Example

[0029] (1) First, prepare two beakers and add pure water. Weigh lithium hydroxide and phosphoric acid according to the equal amount of substance of the lithium source and phosphorus source, and dissolve them in the two beakers respectively. Stir magnetically until dissolved evenly. Weigh an appropriate amount of ferrous sulfate according to the molar ratio of the lithium source to the iron source of 1.05:1, and add it to the phosphoric acid solution. Slowly add the dissolved lithium hydroxide to the phosphoric acid mixed solution. Finally, transfer the obtained mixed solution to a reaction kettle. At the same time, place a carbon fiber cloth material of appropriate size into the reaction kettle. The high-temperature heating temperature is 170 °C, and the reaction time is 8 h. After the reaction, take out the carbon fiber cloth, wash and dry it to obtain the reactant material.

[0030] (2) Take appropriate amounts of phosphoric acid, surfactant, and ascorbic acid, and dissolve them in pure water. Weigh phosphoric acid, ferrous sulfate, and lithium hydroxide according to the molar ratio of phosphorus source : iron source : lithium source of 1:1:1.05, and add them to the phosphoric acid solution in sequence, stirring to dissolve. Transfer the obtained mixed solution to a reaction kettle. At the same time, put the reactant material obtained in (1) into the reaction kettle. The high-temperature heating temperature is 190 °C, and the reaction time is 13 h. After the reaction, take out the reactant to obtain a high-loading lithium iron phosphate composite material.

[0031] (3) Prepare a mixed solution of PEG and pure water with a concentration of 0.3 M. Immerse the composite material obtained in (2) in the PEG mixed solution, dry it, and then put it into a tubular furnace for high-temperature sintering. The sintering temperature of the tubular furnace is 700 °C, and the sintering time is 3 h.

[0032] Comparative Example 1 (1) First, prepare two beakers and add pure water. Weigh lithium hydroxide and ammonium monohydrogen phosphate according to the equal amount of substance of lithium source and phosphorus source, and dissolve them in the two beakers respectively, stirring magnetically to dissolve evenly. Weigh an appropriate amount of ferrous oxalate according to the molar ratio of lithium source : iron source of 1.04:1, and add it to the ammonium monohydrogen phosphate solution. Slowly add the dissolved lithium hydroxide to the mixed solution of ammonium monohydrogen phosphate and ferrous oxalate. Finally, transfer the obtained mixed solution to a reaction kettle. At the same time, put a carbon fiber cloth material of appropriate size into the reaction kettle. The high-temperature heating temperature is 180 °C, and the reaction time is 7 h. After the reaction, take out the carbon cloth, wash and dry it to obtain the reactant material.

[0033] (2) Prepare a mixed solution of PEG and high-purity water with a concentration of 0.4 M. Immerse the composite material obtained in (2) in the PEG mixed solution, dry it, and then put it into a tubular furnace for high-temperature sintering. The sintering temperature of the tubular furnace is 700 °C, and the sintering time is 2 h.

[0034] Comparative Example 2 (1) Take appropriate amounts of phosphoric acid, surfactant, and ascorbic acid, and dissolve them in pure water. Weigh ferrous sulfate and lithium hydroxide according to the molar ratio of phosphorus source : iron source : lithium source of 1:1:1.05, and add them to the phosphoric acid solution in sequence, stirring to dissolve. Transfer the obtained mixed solution to a reaction kettle. At the same time, put the carbon fiber cloth into the reaction kettle. The high-temperature heating temperature is 220 °C, and the reaction time is 12 h. After the reaction, take out the reactant to obtain a high-loading lithium iron phosphate composite material.

[0035] (2) Prepare a mixed solution of glucose and pure water with a concentration of 0.5 M. Immerse the composite material obtained in (2) in the glucose mixed solution, dry it, and then put it into a tubular furnace for high-temperature sintering. The sintering temperature of the tubular furnace is 750 °C, and the sintering time is 2 h.

[0036] The lithium iron phosphate composite material obtained through Example 1 was subjected to electron microscopy scanning to obtain asFigure 2 and Figure 3 Product micrograph, from which a more direct comparison can show that the lithium iron phosphate composite material after two hydrothermal treatments has a higher active material loading amount.

[0037] Meanwhile, the discharge specific capacity of the lithium iron phosphate materials prepared in Examples 1 to 3 and Comparative Examples 1 and 2 was tested. As shown by the comparison of the loading amount and specific capacity (0.1C) of the lithium iron phosphate composite materials, it can be found that the loading amount of the two-step hydrothermal composite material is significantly increased.

Claims

1. A preparation method of lithium iron phosphate composite material based on hydrothermal growth, characterized in that, It includes the following steps: (1) Dissolve the lithium source and the phosphorus source in two pure water containers respectively. The molar ratio of the lithium source to the phosphorus source is (1 to 1.05):

1. Use magnetic stirring to dissolve evenly. Weigh the iron source and add it to the phosphorus source solution. The addition amounts of the iron source and the phosphorus source are the same. Slowly add the dissolved lithium source to the mixed solution of the phosphorus source and the iron source. Finally, transfer the obtained mixed solution to a reaction kettle. (2) Put the carbon fiber cloth material into the reaction kettle. After a period of high-temperature and high-pressure reaction, take out the carbon fiber cloth. After washing and drying, obtain the reactant material. (3) Take appropriate amounts of the phosphorus source, surfactant, and ascorbic acid. The mass ratio of phosphoric acid, surfactant, and ascorbic acid is 100:(1 - 5):(1 - 5). Add them to pure water to dissolve and obtain a phosphorus source solution. Take appropriate amounts of the iron source and the lithium source and add them to the phosphorus source solution in sequence. Stir to dissolve. Transfer the obtained mixed solution to the reaction kettle. At the same time, put the reactant material obtained in (2) into the reaction kettle. After a period of high-temperature and high-pressure reaction, take out the reactant to obtain the high-loading lithium iron phosphate composite material. (4) Prepare a mixed solution of a soluble carbon source and pure water. Immerse the composite material obtained in (3) in the carbon source mixed solution. After drying, put it into a tubular furnace for high-temperature sintering to obtain the final lithium iron phosphate cathode composite material.

2. The preparation method of the lithium iron phosphate composite material based on hydrothermal growth according to claim 1, characterized in that, The high-temperature heating temperature in (2) is 150 - 200 °C, and the reaction time is 5 - 10 h.

3. The preparation method of the lithium iron phosphate composite material based on hydrothermal growth according to claim 1, characterized in that, The high-temperature heating temperature in (3) is 150 - 250 °C, and the reaction time is 10 - 15 h.

4. The preparation method of the lithium iron phosphate composite material based on hydrothermal growth according to claim 1, wherein, In (2), the solution in the reaction kettle accounts for 50% - 80% of the total volume of the reaction kettle, and the high-pressure is 0.2 MPa - 2 MPa.

5. The preparation method of the lithium iron phosphate composite material based on hydrothermal growth according to claim 1, wherein, The soluble carbon source is one of glucose, sucrose, citric acid, or PEG. The concentration of the carbon source in the carbon source solution is 0.1 - 0.5 M.

6. The preparation method of the lithium iron phosphate composite material based on hydrothermal growth according to claim 1, wherein The sintering temperature of the tubular furnace is 500 - 800 °C, and the sintering time is 2 - 5 h.

7. The preparation method of the lithium iron phosphate composite material based on hydrothermal growth according to claim 1, characterized in that, The lithium source is lithium carbonate or lithium hydroxide.

8. The preparation method of the lithium iron phosphate composite material based on hydrothermal growth according to claim 1, wherein, The phosphorus source is phosphoric acid or ammonium monohydrogen phosphate.

9. The preparation method of the lithium iron phosphate composite material based on hydrothermal growth according to claim 1, wherein, The iron source is ferrous sulfate, ferrous chloride, or ferrous oxalate.

10. A composite material prepared by the method for preparing a lithium iron phosphate composite material based on hydrothermal growth according to any one of claims 1 to 9.

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