 (a) Cross-section SEM image of a representative aluminum anode all-solid-state thin-film battery before cycling. (b–d) Top down SEM images show how the aluminum anode surface evolves during the first cycling step. By increasing the charging current, the density of clusters also increases—(b) shows the effect of 10 nA after 50 min, (c) is 20 nA at 17 min, and (d) is 30 nA at 3 min—indicating that the aluminum–lithium alloy formation is a kinetically driven process. Courtesy of NIST