Grain boundary effects on Li-ion diffusion in a Li1.2Co0.13Ni0.13Mn0.54O2 thin film cathode studied by scanning probe microscopy techniques

This paper presents the results of in situ characterization of grain boundary effects on Li-ion diffusion in Li1.2Co0.13Ni0.13Mn0.54O2 thin film cathode by using various Scanning Probe Microscopy (SPM) techniques. In particular, conductive-AFM results show that grain boundaries are more conductive than those in the grain interior. With the increase of bias voltage, the high conductive regimes extend from grain boundaries to interiors. I-V curves show decreased current and increased voltage for current initiation when the tip is moved farther away from boundaries. Furthermore, positive and negative bias applied at grain boundary by biased-AFM can distinguish and manipulate the local Li-ion intercalation/de-intercalation processes at grain level in the cathode material without assembly of a full battery cell. Exfoliation and delamination, degradation and structural changes are observed when the Li-ions are move-out or move-into the layered structure of the cathode at the grain level. These results can provide important insights into understanding the Li-ion diffusion and aging mechanisms of cathode materials during charge/discharge processes.