Assessing the potential of ion beam analytical techniques for depth profiling Li in thin film Li ion batteries

Depth resolution and probing depth for Li in lithium thin film batteries achievable using different ion beam analytical techniques were investigated. Experiments using protons for nuclear reaction analysis, He ions for time-of-flight (TOF) energy elastic recoil detection analysis (ERDA) in transmission geometry, as well as He and Li ions for coincidence ERDA in transmission geometry are performed. Experimental results are compared in terms of the obtained Li concentration in the separator layer. In coincidence ERDA experiments, significant loss of Li–Li and He–Li coincidence counts was observed due to multiple scattering of recoiled/scattered particles in the battery sample. The ideal achievable Li depth resolution was calculated for the ion beam techniques. A depth resolution of 750, 1030, 310, and 510 × 1015 atoms/cm2 could be achieved in the Nb2O5 cathode by nuclear reaction analysis (NRA) using 2 MeV H, TOF-ERDA using 8 MeV He, and coincidence ERDA using 8 MeV He and 8 MeV Li ions, respectively, upon optimization of the experimental setup. While a depth resolution of 120 × 1015 ions/cm2 could be achieved for Li by conventional TOF-ERDA using an solid-state detector energy detector and light primary ions such as O under gracing incidence, TOF-ERDA experiments are found to produce significantly higher beam damage in batteries than other techniques. The beam damage in NRA and coincidence ERDA as performed in this study is estimated to be of the order of 10−4 dpa.