Freestanding all-solid-state rechargeable lithium batteries (Li/LiPON/LATP sheet/Au, SSB) operating at 2.3 V were developed. The electrochemical insertion of lithium into a white-colored Li+ conductive glass-ceramic solid electrolyte (LATP) sheet transformed the electrolyte into a blue-colored in-situ formed electrode, which provided a low-resistance electrode/solid electrolyte interface of ca. 100 Omega cm(2). In addition, the interfacial resistances at both Li/LiPON and LiPON/LATP were less than 100 Omega cm(2), and all the components in the SSB were combined with low-resistance interfaces. As a consequence, the resultant SSB delivered a clear redox peak at 100 mV s(-1) in the cyclic voltammetry measurements at 25 degrees C. The reaction region of the in-situ formed electrode was limited around the Au/LATP interface at 25 degrees C, but this region expanded into the LATP sheet at higher temperatures. At 100 degrees C, the resultant SSB delivered ca. 300 mu Ah cm(-2) and a volumetric energy density of 53 Wh L-1. The electronic conductivity of the in-situ formed electrode appeared to control the reaction region, and thus a SSB using a carbon-LATP composite sheet delivered a larger discharge capacity at 25 degrees C than that of the SSB using only LATP operated at 100 degrees C. The use of conductive LATP sheets may be a possible solution for developing SSBs that can be rationally designed according to the operational environments of the IoTs.