(Invited) in Situ Functional Imaging of Electrodes for All-Solid-State Batteries

Abstract

To date, the development of higher performance Li-ion all-solid-state batteries still entails the complete understanding of how the electrolyte and electrode materials change upon lithiation/delithiation. While macroscopic voltammograms are extremely informative, they do not provide information about how the material composing the active layers of the battery is changing upon lithiation/delithiation. Thus, to probe the mesoscale behavior of the batteries we combine real-time scanning electron microscopy in ultra-high vacuum with electrochemical cycling, in addition to ex situ characterization of the morphological, chemical, and electrical changes of the anodes and electrolyte upon lithiation. In particular, we will discuss the results using LiCoO2 (cathode), LiPON (electrolyte, deposited via sputtering), and Al and Si (anode) [1,2]. In the anode, Li ions are trapped by an AlLi alloy capped by a stable Al-Li-O is formed, leading to a rapid capacity fade, from 48.0 to 41.5 μ.Ah/cm2 in two cycles [1]. Surprisingly, the addition of a Cu protective layer is insufficient to avoid the device degradation because of the ultra fast Li diffusion within Al. Nevertheless, the Si anodes present extremely stable cycling: >92% of capacity retention after 100 cycles, with average Coulombic efficiency of 98% [2]. The in situ functional imaging platform presented here paves the way to diagnosing in real-time the changes that take place in all-solid-state batteries. [1] M. S. Leite et al., J. Mater. Chem. A. 2, 20552 (2014). Inside Cover. [2] C. Gong et al., ACS Appl. Materials and Interfaces. 7, 26007 (2015). Cover.