Hexagonal prism-like morphology lithium manganese iron phosphate and preparation method thereof

Abstract

The invention relates to the field of preparation of new energy lithium ion battery positive electrode materials, in particular to hexagonal prism-like morphology lithium manganese iron phosphate and a preparation method thereof.The preparation method comprises the following steps that a proper amount of lithium hydroxide, deionized water, 85% phosphoric acid solution, manganese sulfate monohydrate and ferrous sulfate heptahydrate are taken and mixed, and a reaction solution is prepared; introducing the obtained reaction solution into a polytetrafluoroethylene lining, putting the polytetrafluoroethylene lining into a hydrothermal kettle, carrying out hydrothermal treatment at 100-240 DEG C for 10-18 hours, and then taking out the polytetrafluoroethylene lining; centrifugally washing the taken-out polytetrafluoroethylene lining with water for three times, and drying the obtained lithium manganese iron phosphate product in a drying oven to obtain light yellow powder for later use; and uniformly mixing the obtained light yellow powder with glucose, carrying out ball milling, transferring into a graphite ark, feeding into a high-temperature tube furnace, and carbonizing and coating a carbon layer to obtain the black lithium manganese iron phosphate. According to the invention, the lithium manganese iron phosphate with the hexagonal prism-like morphology is obtained, and the lithium manganese iron phosphate shows excellent electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the field of preparation of cathode materials for new energy lithium-ion batteries, and specifically to a lithium iron manganese phosphate with a quasi-hexagonal prism morphology and a preparation method thereof. Background Art

[0002] Benefiting from the development of the dual-carbon goal, new energy lithium-ion batteries have developed vigorously. Lithium iron phosphate is recognized as the most promising cathode material for lithium-ion power and energy storage batteries due to its good safety performance, long cycle life, wide range of raw material sources, and no environmental pollution. However, its actual energy density is close to the theoretical limit. As an upgraded version of lithium iron phosphate, lithium iron manganese phosphate is expected to gradually replace the latter in the field of power batteries and become the next-generation cathode material for lithium-ion batteries with an energy density 10%-20% higher than that of lithium iron phosphate. However, the existing electrochemical performance of lithium iron manganese phosphate still cannot meet the current needs. Summary of the Invention

[0003] In order to overcome the deficiencies of the prior art, the present invention provides a lithium iron manganese phosphate with a quasi-hexagonal prism morphology and a preparation method thereof, which has excellent electrochemical performance.

[0004] To achieve the above object, the specific technical solutions adopted by the present invention are as follows:

[0005] A preparation method of lithium iron manganese phosphate with a quasi-hexagonal prism morphology, comprising the following steps:

[0006] S1. Prepare a reaction solution:

[0007] Take an appropriate amount of lithium hydroxide, deionized water, 85% phosphoric acid solution, manganese sulfate monohydrate, and ferrous sulfate heptahydrate and mix them to prepare a reaction solution;

[0008] S2. Hydrothermal reaction:

[0009] Introduce the obtained reaction solution into a polytetrafluoroethylene inner liner, place it in a hydrothermal autoclave, and carry out hydrothermal treatment at 100-240°C for 10-18 h, and then take out the polytetrafluoroethylene inner liner;

[0010] S3. Wash to obtain the lithium iron manganese phosphate product:

[0011] Centrifuge and wash the taken-out polytetrafluoroethylene inner liner three times with water, and place the obtained lithium iron manganese phosphate product in an oven to dry to obtain a light yellow powder for standby; wherein, the centrifugation washing speed is 1000-9000 r / min, and the centrifugation time is 10-20 min;

[0012] S4. Carbonize and coat a carbon layer:

[0013] The obtained light yellow powder is uniformly mixed with glucose. After ball milling at 20 - 50 r / min for 6 - 12 h, it is transferred to a graphite ark and sent into a high-temperature tube furnace for carbonization to coat a carbon layer, obtaining the final black lithium iron manganese phosphate.

[0014] In the preparation method of lithium iron manganese phosphate with a quasi-hexagonal prism morphology of the present invention, 1 moL of lithium hydroxide is dissolved in 200 mL of deionized water, and then 1 moL of 85% phosphoric acid solution is added. Stir and mix at 100 - 400 r / min for 30 min, and then 0.6 moL of manganese sulfate monohydrate and 0.4 moL of ferrous sulfate heptahydrate are added. After stirring and mixing at 100 - 400 r / min for 30 min, a reaction solution is obtained.

[0015] In the preparation method of lithium iron manganese phosphate with a quasi-hexagonal prism morphology of the present invention, in the step S2, the obtained reaction solution is introduced into a polytetrafluoroethylene inner liner, loaded into a hydrothermal autoclave, with a pH of 6.5 - 8.7. After hydrothermal treatment at 140 °C for 10 h, the polytetrafluoroethylene inner liner is taken out.

[0016] In the preparation method of lithium iron manganese phosphate with a quasi-hexagonal prism morphology of the present invention, in the step S5, when carbonizing and coating the carbon layer, the temperature of the tube furnace is 600 - 800 °C, the oxygen content needs to be lower than 40 ppm, and high-temperature nitrogen sintering is carried out for 6 - 18 h.

[0017] The present invention also provides a lithium iron manganese phosphate with a quasi-hexagonal prism morphology, which is prepared by using the above-mentioned preparation method of lithium iron manganese phosphate with a quasi-hexagonal prism morphology, presenting a quasi-hexagonal prism morphology, and can well avoid the agglomeration of lithium iron manganese phosphate particles.

[0018] The present invention has the following characteristics and beneficial effects:

[0019] The present invention obtains a lithium iron manganese phosphate with a quasi-hexagonal prism morphology. Its quasi-hexagonal prism morphology avoids the agglomeration of lithium iron manganese phosphate particles, enables sufficient contact with the electrolyte, is beneficial to charge and discharge and processing performance, and exhibits excellent electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, objects and advantages of the present invention will become more obvious:

[0021] Figure 1 It is the morphology diagram of lithium iron manganese phosphate with a quasi-hexagonal prism morphology and excellent electrochemical performance in Example 1 of the present invention.

[0022] Figure 2 It is the morphology diagram of lithium iron manganese phosphate with a quasi-hexagonal prism morphology obtained in Example 2 of the present invention.

[0023] Figure 3Morphology diagram of lithium iron manganese phosphate obtained in Comparative Example 1. Detailed implementation manners

[0024] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0025] Example 1:

[0026] S1. Preparation of reaction solution:

[0027] Take 1 moL of lithium hydroxide and dissolve it in 200 mL of deionized water, then add 1 moL of 85% phosphoric acid solution, stir and mix at 250 r / min for 30 min, then add 0.6 moL of manganese sulfate monohydrate and 0.4 moL of ferrous sulfate heptahydrate, and stir and mix at 250 r / min for 30 min to obtain a reaction solution; the feeding method is selected as the dropping method, and the time is generally 10 - 55 min.

[0028] S2. Hydrothermal reaction:

[0029] Pour the obtained reaction solution into a polytetrafluoroethylene inner liner, place it in a hydrothermal autoclave, with the pH being 6.5 - 8.7, carry out hydrothermal treatment at 140 °C for 10 h, and then take out the polytetrafluoroethylene inner liner.

[0030] S3. Cleaning to obtain lithium iron manganese phosphate product:

[0031] Centrifuge and wash the taken-out polytetrafluoroethylene inner liner three times with water to obtain a lithium iron manganese phosphate product. The centrifugation speed is 5000 r / min, and the centrifugation time is 15 min. Place the obtained lithium iron manganese phosphate product in an oven to dry to obtain a light yellow powder for standby.

[0032] S4. Carbonization to coat a carbon layer:

[0033] Uniformly mix the obtained light yellow powder with glucose, use ball milling for mixing, the ball milling rate is 20 - 50 r / min, the ball milling time is 6 - 12 h, transfer the ball-milled material to a graphite ark, and send it into a high-temperature tube furnace for carbonization to coat a carbon layer. When carbonizing and coating the carbon layer, the temperature of the tube furnace is 700 °C, the oxygen content needs to be lower than 40 ppm, and sinter with high-temperature nitrogen for 6 - 18 h to obtain the final black product.

[0034] Example 2:

[0035] Extend the reaction time in Example 1 to 18 h. The ball milling rate is 20 r / min, and the ball milling time is 8 h. The sintering temperature is 700 °C, and the sintering time is 10 h, with the rest remaining unchanged.

[0036] Example 3:

[0037] Increase the phosphoric acid in Example 1 by 1%. The ball milling rate is 30 r / min, and the ball milling time is 8 h. The sintering temperature is 650 °C, and the sintering time is 12 h, with the rest unchanged.

[0038] Example 4:

[0039] Increase the phosphoric acid in Example 1 by 2%. The ball milling rate is 20 r / min, and the ball milling time is 8 h. The sintering temperature is 700 °C, and the sintering time is 10 h, with the rest unchanged.

[0040] Comparative Example 1:

[0041] Reduce the phosphoric acid in Example 1 to 99.5% of the original. The ball milling rate is 20 r / min, and the ball milling time is 8 h. The sintering temperature is 700 °C, and the sintering time is 10 h.

[0042] Comparative Example 2:

[0043] Reduce the phosphoric acid in Example 1 to 99% of the original. The ball milling rate is 20 r / min, and the ball milling time is 6 h. The sintering temperature is 700 °C, and the sintering time is 10 h.

[0044] Comparative Example 3:

[0045] Reduce the phosphoric acid in Example 1 to 98% of the original. The ball milling rate is 30 r / min, and the ball milling time is 11 h. The sintering temperature is 750 °C, and the sintering time is 10 h.

[0046] The morphology of the products obtained in each group was measured by SEM, and the results are shown in Figure 1 . It can be seen from Figure 1 that the products obtained in Examples 1 - 4 all exhibit significant characteristics of quasi-hexagonal prisms, with the upper and lower faces parallel and 6 side faces. This special morphology is beneficial for obtaining high electrochemical performance, can well avoid the aggregation of lithium iron phosphate particles, and is conducive to the diffusion of lithium ions, while the products in Comparative Examples 1 - 3 did not obtain the hexagonal prism morphology.

[0047] The electrochemical performance and specific surface area of each group were measured, and the results are shown in Table 1.

[0048] Table 1 Electrochemical performance and specific surface area of different examples

[0049]

[0050] As can be seen from Table 1, Examples 1-4 have excellent electrical properties with a 1C discharge capacity exceeding |46 mAh g-1. Compared with the electrical properties of the comparative examples, the 1C electrical properties have been greatly improved. This is due to the special morphology of the material. Additionally, at a high rate of 10C, the improvement even reaches above 50 mAh g-1, with an improvement amplitude exceeding 100%. It can be found that the higher the rate, the more excellent the electrical properties. This indicates that this morphology is very beneficial for improving the rate performance of the material, especially the high-rate performance.

[0051] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification are only preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of lithium iron manganese phosphate with a quasi-hexagonal prism morphology, characterized in that: It includes the following steps: S1. Prepare the reaction solution: Take appropriate amounts of lithium hydroxide, deionized water, 85% phosphoric acid solution, manganese sulfate monohydrate, and ferrous sulfate heptahydrate and mix them to prepare the reaction solution; S2. Hydrothermal reaction: Pour the obtained reaction solution into a polytetrafluoroethylene inner liner, place it in a hydrothermal autoclave, carry out hydrothermal treatment at 100 - 240 °C for 10 - 18 h, and then take out the polytetrafluoroethylene inner liner; S3. Wash and obtain the lithium iron manganese phosphate product: Centrifuge and wash the taken-out polytetrafluoroethylene inner liner three times with water, place the obtained lithium iron manganese phosphate product in an oven to dry, and obtain a light yellow powder for standby; S4. Carbonize and coat the carbon layer: Evenly mix the obtained light yellow powder with glucose, after ball milling, transfer it to a graphite boat, and send it into a high-temperature tube furnace for carbonization to coat the carbon layer, obtaining the final black lithium iron manganese phosphate.

2. The preparation method of lithium iron manganese phosphate with a quasi-hexagonal prism morphology as described in claim 1, characterized in that: In step S1, dissolve 1 moL of lithium hydroxide in 200 mL of deionized water, then add 1 moL of 85% phosphoric acid solution, stir and mix at 100 - 400 r / min for 30 min, then add 0.6 moL of manganese sulfate monohydrate and 0.4 moL of ferrous sulfate heptahydrate, and after stirring and mixing at 100 - 400 r / min for 30 min, obtain the reaction solution.

3. The preparation method of lithium iron manganese phosphate with a quasi-hexagonal prism morphology as described in claim 1, wherein: In step S2, pour the obtained reaction solution into a polytetrafluoroethylene inner liner, place it in a hydrothermal autoclave, with a pH of 6.5 - 8.7, carry out hydrothermal treatment at 140 °C for 10 h, and then take out the polytetrafluoroethylene inner liner.

4. The preparation method of lithium iron manganese phosphate with a quasi-hexagonal prism morphology as described in claim 1, characterized in that: In step S3, the centrifugation washing speed is 1000 - 9000 r / min, and the centrifugation time is 10 - 20 min.

5. The preparation method of lithium iron manganese phosphate with a quasi-hexagonal prism morphology as described in claim 1, characterized in that: In step S4, the ball milling rate is 20 - 50 r / min, and the ball milling time is 6 - 12 h.

6. The preparation method of lithium iron manganese phosphate with a quasi-hexagonal prism morphology as described in claim 1, characterized in that: In step S5, when carbonizing and coating the carbon layer, the temperature of the tube furnace is 600 - 800 °C, the oxygen content needs to be lower than 40 ppm, and sinter at high temperature with nitrogen for 6 - 18 h.

7. A lithium iron manganese phosphate with a quasi-hexagonal prism morphology, characterized in that: It is prepared by using the preparation method of lithium iron manganese phosphate with a quasi-hexagonal prism morphology as described in claims 1 - 6.

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