Development and Application of Lithium Metal Phosphate to Achieve High Power Lithium-Ion Battery

Abstract

Due to the increase of lithium-ion battery (LIB) capacity, LIBs have been widely applied to hybrid or pure electric vehicles (EVs) and stationary energy storages. Simultaneously, the requirements of LIBs performance (ex. safety, long cycle life and power performance) have also been increased. Focusing on the cathode active materials, lithium iron phosphate (LFP) is an attractive material which possesses an excellent thermal stability and long cycle life originated from its specific crystal structure of lithium metal phosphate [1]. Although the recent demand of LFP has been growing for different industrial uses, its low average potential (~3.4 V vs. Li/Li+) still remains a main issue. In this study, we developed a unique lithium metal phosphate that shows high average potential and excellent power performance. The power performance is contributed to its fast transport of lithium-ions in the original crystal structure consisted of three-dimensional framework. The synthesized material demonstrates promising electrochemical properties analyzed by different methods. Moreover, the synthesized material blended with another cathode active material results in a higher power performance of LIBs.The lithium metal phosphate powder was synthesized by a liquid phase method. The electrode paste was prepared by mixing cathode active materials with carbon conductive agents and binders in N-methyl-2-pyrrolidone solvent. The paste was then used to prepare cathode on top of Al foil. Lithium metal foil or graphite anode electrode was used as a counter electrode. LiPF6 in organic carbonate solvent was used as electrolyte. The galvanostatic charge/discharge measurements were done at room temperature. Electrochemical impedance spectroscopy and cyclic voltammetry were used for analyzing lithium ion and electron transfer.The experimental discharge capacity of the synthesized material matches with theoretical capacity calculated from the synthesized chemical composition, with a higher average potential than conventional LFP (~3.4 V). As for the power performance, the capacity retention rate of the fabricated LIB was over 80% at 50C discharge rate. In addition, the mixture of the synthesized material and another cathode active material showed a positive effect on the power performance of LIBs. Lastly, the synthesized material can be applied for use of inkjet printing systems attributed to its micrometer-size particle based on our accumulated technological expertise. Here, a detail discussion about the characteristics of the synthesized material will be reported in this meeting. Reference [1] N. Nitta et al., Mater.Today, 18, 252-264, 2015.