Understanding the relationship between materials synthesis and electrochemical behaviors should provide valuable knowledge to further the advancement of lithium-ion batteries. In this work, layered cathode materials {e.g., LiNi 0.4 Mn 0.4 Co 0.18 Ti 0.02 O 2 (NMCs)} were prepared under three different annealing conditions, i.e., 900 C for 6 hours, 8 hours, and 12 hours, respectively. The resulting materials exhibit equivalent crystal structures and morphologies yet likely different surface chemical environments. These materials show distinctively different resistances against the surface passivation/ reconstruction (reduction of the transition metals in the layered structure to form rock-salt and/or spinel phases) during electrochemical cycling (2.0-4.7 V vs. Li + /Li). In general, the materials annealed for longer durations exhibited lower tendencies to form the surface passivation layer. Furthermore, the surface passivation became less severe when the electrode materials were cycled under mild conditions, such as slow constant current charging-discharging as opposed to cyclic voltammetry. The present study correlates the synthetic conditions with the surface instability and the electrochemical performance in cathode materials, and provides new insights into improving synthetic protocols for battery materials.

Layered LiNi 0.4 Mn 0.4 Co 0.18 Ti 0.02 O 2 cathode powders were ball-milled for various lengths of time. The structural properties of the pristine and milled powders, which have different particle sizes were examined with X-ray diffraction, soft X-ray absorption spectroscopy, and transmission electron microscopy to determine the effect of milling on structure. Electrochemical testing in halfcells was also carried out and shows that milling plays an important role in the performance of these cathode materials; as milling time increases, there is a decrease in initial discharge capacity. The first cycle irreversible capacity also increases for milled samples, as does capacity loss upon cycling under some regimes.The electrochemical degradation is strongly correlated with damage to the lamellar structure of cathode particles induced by milling, and lithium carbonate formation.