All Solid-State Li/Li[sub x]MnO[sub 2] Polymer Battery Using Ceramic Modified Polymer Electrolytes

All solid-state lithium/polymer battery ~LPB! using a metallic lithium anode and solvent-free polymer electrolyte has been demonstrated to be the most promising secondary battery for electric vehicle applications because of its low risk of liquid electrolyte leakage, higher energy density, and shape flexibility compared to other systems. The main problems that are still to be solved are related to a low conductivity at ambient temperature. Many efforts have been devoted to the development and improvement of the electrolyte’s ionic conductivity for such batteries. 1-6 One of the most successful approaches is to add a small-particle size ceramic powder in the polymer electrolyte. 7-10 Most studies have focused primarily on investigating the influence of the addition of ceramic powders on the ionic conductivity and interfacial stability with lithium. Indeed, these new types of composite polymer electrolytes result in an increase in the ionic conductivity and enhanced lithium/polymerelectrolyte interface stability. However, very few studies have been devoted to measure its electrochemical profile in a real battery system, specially the electrochemical stability of the polymer electrolyte on a cathode. The high ionic conductivity and interface stability with lithium is of primary importance when it was applied into a lithium/polymer battery in combination with a composite cathode, and the electrochemical stability against a high voltage is also important. Until now, the evaluation of the electrochemical stability was normally characterized by linear sweep voltammetry ~LSV! or cyclic voltammetry ~CV! of the polymer electrolyte on a smooth stainless steel blocking electrode. The polymer electrolytes with or without the ceramic additive have been reported to be stable at least above 4 V vs. Li/Li 1 . 4,6 However, when a composite electrolyte works as an electrolyte separator combined with a positive electrode in a real battery system, it contacts the porous composite electrode containing active material and conductive material, e.g., carbon black, acetylene black, graphite, etc., rather than a smooth inert electrode. In the present study, we are interested in investigating the battery performance of the Li/LixMnO2 cell based on the ceramicadditive polymer electrolyte, rather than the ion conductivity evaluation. We found that some of the ceramic modified composite polymer electrolytes behave in a manner similar to that of the ceramicfree polymer electrolyte, showing a poor charge/discharge efficiency due to poly~ethylene oxide !~ PEO! decomposition during cycling even they showed increased ionic conductivity, whereas the PEO decomposition suppression was observed on these doped components which form a stable interreaction between the ceramic surface and the PEO segment. The possible PEO decomposition mechanism was discussed.