Progress has been made in the synthesis of high-performance nano-lithium iron phosphate, which can better meet the energy storage needs of lithium-ion batteries

Recently, the researcher Wang Xiaohui's research group of the Institute of Metal Research of the Chinese Academy of Sciences and the Nanjing University of Aeronautics and Astronautics professor Zhu Kongjun cooperated to increase the nucleation rate by reducing the nucleation window time based on the in-depth understanding of the LaMer nucleation growth mechanism, using microwave hydrothermal The synthesis method prepares nano-LiFePO4 in the synthesis environment of pure water. At the same time, the most valuable LiOH in the filtrate is recovered and reused by using the precipitating agent, and the effective utilization rate of the lithium source exceeds 90%, which greatly reduces the processing cost. The heart of an electric car is an electric motor driven by a battery or fuel-powered battery. With the increasing demand for electric vehicles, the demand for high-quality batteries is also increasing. Lithium-ion battery is the first choice for battery technology development, and its cathode material is one of the key components that determines battery performance. LiFePO4 also has excellent thermal stability, high reversibility and acceptable working voltage (3.45Vvs.Li+/Li), and has significant competitive advantages as a positive polarity material. Previously published articles mostly use solvothermal method to prepare nano-LiFePO4, and the product has good electrochemical performance, but the method has low yield and high cost, which cannot realize large-scale processing. Compared with solvothermal method, the cost of preparing LiFePO4 by hydrothermal method is lower, but the electrochemical performance of the product is poor. Moreover, regardless of solvothermal or hydrothermal synthesis, due to the limitations of the reaction (3LiOH+FeSO4+H3PO4u003dLiFePO4+Li2SO4), the effective utilization of the lithium source does not exceed one-third. Therefore, how to use the hydrothermal method to prepare high-performance nano-LiFePO4 and to recycle the lithium source is not only a technical problem in achieving large-scale hydrothermal preparation of nano-LiFePO4, but also an important scientific issue. Recently, the researcher Wang Xiaohui's research group of the Institute of Metal Research of the Chinese Academy of Sciences and the Nanjing University of Aeronautics and Astronautics professor Zhu Kongjun cooperated to increase the nucleation rate by reducing the nucleation window time based on the in-depth understanding of the LaMer nucleation growth mechanism, using microwave hydrothermal The synthesis method prepares nano-LiFePO4 in the synthesis environment of pure water. At the same time, the most valuable LiOH in the filtrate is recovered and reused by using the precipitating agent, and the effective utilization rate of the lithium source exceeds 90%, which greatly reduces the processing cost. The nano-LiFePO4 prepared by this method has the highest yield (1.3mol/L) so far, and exhibits excellent electrochemical performance. The specific discharge capacity is 167mAhg-1 at a rate of 0.1C, and the charge/discharge cycle is performed at a rate of 3C. After 1000 times, 88% of the initial capacity can still be maintained, which can meet the actual use of large-scale energy storage. This work is the first to realize the green and efficient synthesis of high-performance nano-LiFePO4 in a pure water synthesis environment, which will strongly promote its large-scale processing. The relevant results were published in the recently published 'Green Chemistry' (Green Chemistry, 2018, 20, 5215-5223) magazine. Figure 1 Classic LaMer nucleation and growth mechanism and test results. (A) Classical LaMer mechanism, a schematic diagram of the monomer concentration changes during the nucleation and growth of particles in solution. (B) Three kernel functions with Gaussian distribution. The width of the nucleation function () corresponds to the nucleation time window. (C) In-situ temperature vs. time curve under two heating modes: microwave heating and oil bath heating. (D) The size statistics of LiFePO4 prepared by two different heating modes along the [100] or [010] direction. The size of microwave heating is 63nm, while in the case of conventional oil bath heating, the size is 105nm. Figure 2 LiFePO4 nanocrystalline hydrothermal synthesis route and lithium recovery schematic diagram. LiOH, FeSO4 and H3PO4 are used as raw materials to prepare nano-LiFePO4. Use ba(OH) 2 as a precipitant to react with the filtrate, and then perform solid-liquid separation to recover LiOH. The illustration is a TEM photograph of LiFePO4. Figure 3 Comparison of the yield per unit volume of LiFePO4 prepared by the hydrothermal/solvothermal synthesis method. The illustration is an optical photograph of LiFePO4 synthesized in this work. Figure 4 The electrochemical performance curves of the original O-LiFePO4/C and the recovered R-LiFePO4/C. (A) Typical charge-discharge curve of O-LiFePO4/C in the range of 0.1-10C with different rates. (B) Rate performance. (C) Long-cycle stability of O-LiFePO4/C and R-LiFePO4/C at 3C rate. The charging or discharging time corresponding to 3C is 20 minutes. Lithium-ion battery 'Lithium-ion battery' is a type of battery that uses lithium metal or lithium alloy as the negative electrode material and uses a non-aqueous electrolyte solution. In 1912, the lithium metal battery was first proposed and studied by Gilbert N. Lewis. In the 1970s, M.S. Whittingham proposed and began to study lithium-ion batteries. Due to the very active chemical properties of lithium metal, the production, storage and use of lithium metal have very high environmental requirements. With the development of science and technology, lithium-ion batteries have now become the mainstream. Lithium ion batteries can be roughly divided into two categories: lithium metal batteries and lithium ion batteries. Lithium-ion batteries do not contain metallic lithium and are rechargeable. The fifth generation of rechargeable batteries, lithium metal batteries, was born in 1996, and its safety, specific capacity, self-discharge rate, and performance-price ratio are superior to those of lithium-ion batteries. Due to its own high-tech requirements, only a few companies in a few countries are processing this lithium metal battery. In October 2018, the research group of Professor Liang Jiajie and Chen Yongsheng of Nankai University and the research group of Lai Chao of Jiangsu Normal University successfully prepared a graphene three-dimensional porous carrier, which can realize ultra-high-speed battery charging and is expected to greatly extend the 'life' of lithium-ion batteries.