All-Solid Lithium Metal Polymer Batteries; Effect of LiFePO4 Cathode Density and Thickness on Electrochemical Performance

Abstract

All-solid lithium metal polymer batteries (LMPBs) consisting of lithium transition metal cathode, polymer electrolyte and Li metal anode have been investigated for achieving much higher energy density than lithium-ion batteries (LIBs) or providing special design properties such as flexibility[1-2]. Unfortunately, commercially available LMPBs failed to go to market, because solid polymer electrolytes (SPEs) show low ionic conductivity and poor interfacial stability towards electrodes comparing to liquid electrolytes. However, most of researches on SPEs have been focused for electrolytes themselves without broad cell performance data such as cycle life and rate capability. Moreover, even though the cathode should be developed or optimized for LMPB systems, few researches on cathodes (for example, cathode thickness, density, or composition) unlike LIBs have been done systematically for LMPBs up to now [3]. So, in this work, we investigate the room temperature electrochemical properties of all-solid LMPBs while changing cathode thicknesses and densities. The LMPBs consist of LiFePO4/SPE/Li metal, in which SPEs for electrolyte and cathode binder are manufactured by in-situ thermal polymerization after cathode/high porous separator/Li cell assembly. The optimum thickness and density of LiFePO4 cathodes could be found by evaluating cycle performances at room temperatures and rate capability. At the same time, morphological changes within the cathode and electrochemical changes before and after polymerization are also compared precisely. Acknowledgements This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government(MEST)(2010-0025738).