High rate-induced structural changes in thin-film lithium batteries on flexible substrate

An investigation is made of the high-rate capability (up to 10 C) of all-solid-state thin-film lithium batteries that comprise of Li/LiPON/LiCoO2 on a flexible substrate, as well as of the effect of high-rate cycling on the structure of these batteries. Raman spectroscopic analysis results reveal that an increase in the rate promotes film orientation of the LiCoO2 cathode with (1 0 1)/(1 0 4) planes and limited lithium intercalation and deintercalation within the layered hexagonal structure without a phase transition to monoclinic. Although with high-rate cycling the LiCoO2 columnar grains tend to aggregate and lose grain orientation, as observed by scanning electron microscopic imaging, the film morphology is efficiently preserved when there is exterior multilayered encapsulation on thin-film batteries. Encapsulated thin-film batteries at 10 C show excellent capacity retention of 95% over 800 cycles, delivering > 22 μAh cm−2 μm−1. The data contribute to a basic understanding of the structure–rate performance relationship of all-solid-state battery systems.