The role of nanoscale-range vanadium treatment in LiNi0.8Co0.15Al0.05O2 cathode materials for Li-ion batteries at elevated temperatures

In order to overcome the inherent structural instability of bare LixNi0.8Co0.15Al0.05O2 (BNCA) containing large amounts of LiOH and Li2CO3 impurities at 60 and >200 degrees C, an effective nanoscale layer was generated by coating BNCA with an ammonium vanadate precursor, followed by annealing at 400 degrees C. This process forms a 17 nm thick surface layer containing V4+ ions in the transition metal 3b sites, thereby decreasing the thickness of the cation-mixing layer, which is the main factor responsible for destabilizing the surface structure. Such a coating also helps in substantially reducing the amount of surface impurities of LiOH, Li2CO3, and H2O by forming LiVO2, LiV2O5, VO2, and V2O5. Consequently, at 60 degrees C, vanadium-treated LiNi0.8Co0.15Al0.05O2 (VNCA) demonstrated excellent cyclability with a discharge capacity of 179 mA h g(-1) after 200 cycles (after 17 days) between 3 and 4.3 V, corresponding to 90% capacity retention, which is 18% higher than the capacity retention measured for BNCA. More importantly, VNCA exhibits a significantly reduced heat generation and a higher onset temperature for exothermic reactions.