In Situ Direct Lithium Distribution Analysis Around Interfaces in an All‐Solid‐State Rechargeable Lithium Battery by Combined Ion‐Beam Method

Charge–discharge reaction in all‐solid‐state battery (SSB) is governed by Li‐ion movements and large resistance at solid–solid interface degrades rate capability of the SSBs. Thus, lithium (Li) distribution and its movement around interface in static or operated SSBs should be clarified well. Here, it is reported that combined ion beam analysis of high‐energy elastic recoil detection and Rutherford backscattering spectrometry probing 9.0 MeV O 4+ beams is a powerful technique to clarify static Li distribution around the interface, and that relative Li concentration change is correctly detected with reliable depth resolution in a few tens of nm scale. It is interesting to note that Li deficient region is formed inside the Li + ‐conductive crystalline glass solid electrolyte, LATP, at around the LiCoO 2 /LATP interface with the thickness of 120 ± 30 nm. Additionally, presence of hydrogen around both interfaces and their migration with the voltages are also detected.