Preparation method of aluminum-doped submicron lithium iron manganese phosphate positive electrode material

Abstract

The invention relates to the technical field of lithium ion battery electrode materials, in particular to a preparation method of an aluminum-doped submicron lithium iron manganese phosphate positive electrode material. Aiming at the problems of relatively low conductivity, relatively low ion migration rate, relatively low cycle performance and relatively low rate capability of a lithium manganese iron phosphate positive electrode material, the submicron lithium manganese iron phosphate LiMn0. 6Fe0. 4PO4 (at) C / Al positive electrode material is prepared by taking aluminum oxide as a doping agent and adopting a coprecipitation method and a solid-phase sintering method. Through an electrochemical performance test, the first-circle discharge specific capacity of the embodiment is up to 164.3 mAh.g <-1 > under the current of 0.1 C. After 100 cycles of charge-discharge cycles under the current of 0.5 C, the specific discharge capacity of the material in the embodiment is 124.4 mAh.g <-1 >, and the capacity retention rate is as high as 91.6%, which is 9.7% higher than that of a comparative material. And the rate capability of the embodiment is also remarkably improved, and relatively high specific discharge capacity can be kept under a high-rate condition. The preparation method disclosed by the invention is simple, safe to operate, green and environment-friendly, and the cycle performance and the rate capability of the lithium manganese iron phosphate positive electrode material can be obviously improved.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery electrode materials, and in particular relates to a method for preparing an aluminum-doped submicron lithium manganese iron phosphate positive electrode material. Background Art

[0002] With the growing demand for sustainable energy supply, lithium-ion batteries have become a major focus as an energy conversion and storage system. In recent years, research on lithium-ion batteries has focused on improving the energy density and performance of their electrodes. However, concerns about safety issues have hindered the utilization of the maximum reversible capacity of layered cathode ternary materials (such as NCM). Compared with ternary materials, olivine-structured lithium iron phosphate cathode materials are extremely competitive due to their superior structural stability, excellent safety, high specific capacity, and natural abundance of iron (Fe) and phosphorus (P). However, compared with layered cathode materials, lithium iron phosphate materials have a lower redox potential, which leads to lower energy density and limits their widespread application. In order to overcome the limitation of energy density, an effective way is to use lithium iron manganese phosphate (LiMn) with an olivine structure. x Fe 1-x PO4) positive electrode material. This material replaces part of Fe with Mn in the LiFePO4 structure, making LiMn x Fe 1-x PO4 material can combine the advantages of LiFePO4's cycle stability and LiMnPO4's high operating voltage, thus becoming a research hotspot for high energy density lithium-ion battery systems.

[0003] However, the charge-discharge specific capacity and rate performance of lithium iron manganese phosphate materials are hindered by their own low electrical conductivity and lithium ion migration rate. In order to solve these problems, researchers have improved the electrochemical properties of lithium iron manganese phosphate materials through surface coating, ion doping, morphology control and other modification methods. Generally speaking, nano or submicron particles can shorten the diffusion path between lithium ions and electrons. At the same time, doping and coating of conductive materials or metal compounds can significantly improve electronic conductivity, allowing electrons to be quickly transmitted during lithiation and delithiation.

[0004] The present invention provides a method for preparing an aluminum-doped submicron lithium manganese iron phosphate positive electrode material based on a coprecipitation method and a solid phase sintering method. The preparation method is simple and can effectively improve the reversible capacity, cycle stability and rate performance of the lithium manganese iron phosphate positive electrode material. Summary of the invention

[0005] Purpose of the invention: In view of the problems existing in lithium manganese iron phosphate positive electrode materials themselves, the present invention provides a method for preparing aluminum-doped submicron lithium manganese iron phosphate positive electrode materials. The preparation method is simple and can effectively improve the reversible capacity, cycle stability and rate performance of lithium manganese iron phosphate positive electrode materials.

[0006] Technical solution: The present invention adopts coprecipitation method and solid phase sintering method to prepare an aluminum-doped submicron lithium manganese iron phosphate positive electrode material LiMn 0.6 Fe 0.4 PO4@C / Al.

[0007] The present invention adopts the control experiment method, and the specific synthesis steps are as follows:

[0008] S1: Use a balance to weigh a certain amount of manganese sulfate monohydrate, ferrous sulfate heptahydrate and ascorbic acid, and completely dissolve them in 100 ml of deionized water, which is recorded as solution A.

[0009] S2: Use a balance to weigh a certain amount of oxalic acid dihydrate and ammonium oxalate monohydrate, and completely dissolve them in 100 ml of deionized water, which is recorded as solution B.

[0010] S3: Place solution A in a 50°C water bath, and add solution B dropwise into solution A using a peristaltic pump while stirring continuously.

[0011] S4: The pH of the AB mixed solution was adjusted to 3 with aqueous ammonia, and then the mixture was stirred continuously in a water bath at 50°C for several hours.

[0012] S5: After the reaction is complete, separate the supernatant and the precipitate using a centrifuge, transfer the precipitate to a Buchner funnel, and wash repeatedly with deionized water and ethanol until it becomes neutral.

[0013] S6: Put it into an oven, dry it thoroughly, grind it, and sieve it to obtain a manganese iron oxalate dihydrate precursor.

[0014] S7: Use a balance to weigh a quantitative precursor, lithium dihydrogen phosphate, and glucose, and mix them to obtain a mixture A.

[0015] S8: Place mixture A and alumina powder (0‰wt, 2‰wt) into a ball mill, add an appropriate amount of ethanol, and use a planetary ball mill to mix the materials evenly.

[0016] S9: Take it out and put it in the oven to dry it thoroughly.

[0017] S10: After grinding, calcining in a tube furnace. After cooling, taking out, grinding and sieving, 0‰ and 2‰ Al-doped submicron LiMn 0.6 Fe 0.4 PO4@C / Al material.

[0018] The above two materials were used as positive electrodes of lithium-ion batteries for electrochemical performance tests.

[0019] Beneficial effects: Compared with other modification methods of lithium manganese iron phosphate positive electrode materials, the method of the present invention is simpler and more environmentally friendly. The present invention found through comparative experiments that the cycle stability and rate performance of the lithium-rich manganese-based positive electrode material prepared with the assistance of agar are significantly improved, and the first discharge specific capacity is also very high. This has practical significance for the development of lithium-rich manganese-based positive electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The XRD patterns of the synthetic materials of the present invention and the comparative examples are shown in FIG.

[0021] Figure 2 The cycle performance diagram of the synthetic material of the embodiment of the present invention and the synthetic material of the comparative example is shown in FIG.

[0022] Figure 3 The rate performance diagram of the synthetic material of the embodiment of the present invention and the synthetic material of the comparative example DETAILED DESCRIPTION

[0023] The technical scheme of the present invention will be clearly and completely described below in combination with the embodiments and comparative examples of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative labor conditions belong to the scope of protection of the present invention.

[0024] Example:

[0025] Weigh MnSO4·H2O and FeSO4·7H2O according to the molar ratio of 6:4, and weigh a small amount of ascorbic acid to prevent oxidation, dissolve in 100ml deionized water, and record it as solution A. Weigh H2C2O4·2H2O and (NH4)2C2O4·H2O according to the molar ratio of 1:3, and dissolve in 100ml deionized water, record it as solution B. Move solution A into a water bath, set the temperature to 50℃, add solution B dropwise to solution A through a peristaltic pump, and stir evenly. Adjust the pH of the AB mixed solution to 3 with ammonia water, and stir continuously for several hours until the reaction is complete. Then use a centrifuge to separate the supernatant and the precipitate, transfer the precipitate to a Buchner funnel, wash it repeatedly with deionized water and ethanol until it is neutral, put it into an oven, dry it for 12 hours, grind and sieve it, and obtain a dihydrated manganese iron oxalate precursor. Weigh the quantitative precursor and lithium dihydrogen phosphate according to the molar ratio (Mn+Fe∶Li=1∶1.02), weigh glucose according to the mass fraction of 5%wt, and mix the above three substances to obtain mixture A. Weigh Al2O3 according to the mass fraction of 2‰wt, put mixture A and Al2O3 powder into a ball mill, add appropriate amount of ethanol, and use a planetary ball mill at 400rpm for 4h to mix the materials evenly. After taking out, put it in an oven and dry it thoroughly for 12h. After grinding, calcine it at 650℃ in a tube furnace under nitrogen atmosphere for 5h. After cooling, take it out, grind and sieve it to obtain 2‰Al-doped submicron LiMn0.6Fe0.4PO4@C / Al material.

[0026] Comparative Example:

[0027] Weigh MnSO4·H2O and FeSO4·7H2O according to a molar ratio of 6:4, and weigh a small amount of ascorbic acid to prevent oxidation, dissolve in 100ml deionized water, and record it as solution A. Weigh H2C2O4·2H2O and (NH4)2C2O4·H2O according to a molar ratio of 1:3, and dissolve in 100ml deionized water, record it as solution B. Move solution A into a water bath, set the temperature to 50°C, add solution B dropwise to solution A through a peristaltic pump, and stir evenly. Adjust the pH of the AB mixed solution to 3 with ammonia water, and stir continuously for several hours until the reaction is complete. Then use a centrifuge to separate the supernatant and the precipitate, transfer the precipitate to a Buchner funnel, wash it repeatedly with deionized water and ethanol until it is neutral, put it in an oven, dry it for 12 hours, grind and sieve it, and obtain a dihydrated manganese iron oxalate precursor. According to the molar ratio (Mn+Fe∶Li=1∶1.02), weigh the quantitative precursor and lithium dihydrogen phosphate, weigh the glucose according to the mass fraction of 5%wt, and mix the above three substances to obtain mixture A. Put mixture A into a ball mill, add an appropriate amount of ethanol, and use a planetary ball mill at 400rpm for 4 hours to mix the materials evenly. After taking it out, put it in an oven and dry it thoroughly for 12 hours. After grinding, calcine it at 650℃ in a tube furnace under a nitrogen atmosphere for 5 hours. After cooling, take it out, grind and sieve it to obtain the comparative material.

[0028] The two materials of the embodiment and the comparative example were assembled with metal lithium sheets into button cells, and the electrochemical performance was tested. Cyclic performance test: The voltage window of the test was 2.0-4.5V, and the current of the first 4 cycles was 0.1C (1C = 170mAh·g -1 ), the current for 5-105 cycles is 0.5C. Rate performance test: The voltage window of the test is 2.0-4.5V, and the currents are 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, and 0.1C (4 cycles each). The cycle performance of the example materials and the comparative example materials is shown in Figure 2 At 0.1C current, the first cycle discharge capacity of the example material is 164.3 mAh g -1 After 100 cycles of charge and discharge at 0.5C current, the discharge capacity of the comparative material and the example material increased from the initial 131.1 mAh·g -1 、135.8mAh·g -1 Cycle to 107.3 mAh g -1 、124.4mAh·g -1 The capacity retention rate of the example material is as high as 91.6%, while the capacity retention rate of the comparative material is only 81.9%. The example material is 9.7% higher than the comparative material. Figure 3As can be seen from the figure, the rate performance of the embodiment material is more excellent, and it can maintain a high discharge specific capacity under high rate conditions. Through comparative experiments, it is found that the cycle and rate performance of the aluminum-doped submicron-level lithium manganese iron phosphate positive electrode material are significantly improved.

Claims

1. An aluminum-doped submicron lithium manganese iron phosphate positive electrode material, characterized in that: A submicron cathode material LiMn was prepared by coprecipitation and solid phase sintering using alumina as a dopant. 0.6 Fe 0.4 PO4@C / Al. Its preparation method is simple, safe to operate, green and environmentally friendly, and the prepared material particles are uniform and dense, which significantly improves the cycle performance and rate performance of lithium manganese iron phosphate positive electrode materials.

2. The aluminum-doped submicron lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The preparation method is simple, the operation is safe, and it is green and environmentally friendly.

3. The aluminum-doped submicron lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: Adding an appropriate amount of aluminum oxide as a dopant makes the synthesized lithium manganese iron phosphate positive electrode material LiMn 0.6 Fe 0.4 The electrochemical performance of PO4@C / Al is improved.

4. The aluminum-doped submicron lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The aluminum doping amount is 2‰wt, the glucose mixing amount is 5%wt, the water bath temperature during the reaction is 50°C, and the mixture is ball milled for more than 4 hours.

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