Optimization of LiMnPO4 Using Solid State Processes

The development of lithium ion battery over the years has been in leaps and bound. Research is still ongoing towards the development of better lithium ion batteries and utilization techniques to power devices and machines of the future ranging from hand tools to electric vehicle. Presently LiCoO₂is one of the most commercially available secondary batteries in the market right now.

Among the olivine battery materials LiFePO₄ is the most researched and understood material. Other olivine materials have higher energy density but some unfavorable characteristics hinder commercialization. LiCoPO₄ and LiNiPo₄ have really high voltages that is not in the operating range of presently usable electrolytes. LiMnPO₄ is a very promising olivine material, its operating voltage is higher than that of LiFePO₄ but still within the operating range of conventional electrolytes.

The low energy density of LiMnPO₄ at high rate cycling is a major problem that must be solved before it can be commercialized. Studies have shown that this is due to the low electronic conductivity, large volume change between LiMnPO4 and MnPO4 and high activation resistance ¹.

Many approaches have been applied to solve this problem. The poor electronic conductivity can be alleviated with the use of carbon coating. Using a one-step carbon coating process results in better coating and increased conductivity compared to two step coating as shown in figure 1¹. Isovalent co-doping has also been shown to increase the performance of the material. Some other interesting approach to the problem has also been employed. The use of grinding aid to reduce the size of the product has been shown to increase performance ³.  Use of oleic acid during fabrication reduces particle growth and agglomeration ⁴. Improved electrochemical performance was also gotten by the use of off stoichiometric mix of the precursor ².

The goal of our research is to combine these various methods that has been shown to increase performance of the material then characterize and analysis the material to see if the resulting material would be of higher performance as whole.

REFERENCES

1. Electrochemical Performance of LiMnPO₄ Synthesized with Off-Stoichiometry Byoungwoo Kang and Gerbrand Ceder

2. Rate Performance of LiMnPO₄ Based Materials from Different Carbon Source Addition Process Haisheng Fang, Enrui Dai, Kun Yang, Bin Yang, Yaochun Yao, Wenhui Ma, Yongnian Dai

3. Grinding aid-assisted preparation of high-performancecarbon-LiMnPO₄Lingbing Ran, Xiaoyan Liu, Qiwei Tang, Kunlei Zhu, Jianhua Tian,Jiangyong Du, Zhongqing Shan∗

4. Confined synthesis of hierarchical structured LiMnPO₄/C granules by a facile surfactant-assisted solid-state method for high-performance lithiumion batteries Longfei Zhang, Qunting Qu, Li Zhang,* Jing Li and Honghe Zhen