Fig. 4
Biocompatibility and thermal environmental testing for flexible battery. Progressive HEK 293 cellular growth on the top surface of the non-cytotoxic battery identified by conventional optical and fluorescent microscope images recorded at different times: a day 1, b day 3, and c day 5. (Left panels shows optical microscope images; right panels shows fluorescence microscope images). Large green stains corresponds to the growing number of living cells compared to the trivial red stains corresponding to dead cells. d CCK8 cell viability assay compares cell culture density on the flexible battery with a control group after 5 days of testing, which confirms the biocompatibility of the flexible lithium-ion battery. e Temperature effect on the operation of the flexible biocompatible battery compares the normalized discharge capacity at the first discharge cycle recorded for multiple flexible batteries heated at a designated temperature. The battery capacity increases with higher temperature as the battery’s internal resistance decreases. Thermal images of the battery are obtained during different temperatures
