Li₂SO₄ coating for enhanced electrochemical performance of Co-free, Li-rich layered oxide cathode

In the continued evolution toward high-performance lithium (Li)-ion batteries, cobalt (Co) has presented itself as a major obstacle due to its price, toxicity and supply. Thus, Co-free, Li-rich layered oxide cathodes (CF-LLC) have garnered interest for their exclusion of cobalt and high theoretical capacity. Nevertheless, CF-LLC suffers from issues such as sluggish kinetics, voltage fade and low early capacity due to the increase in cation mixing resulting from the absence of cation-ordering cobalt. To mitigate this, a sulfate coating was applied to the cathode carbonate precursor prior to lithiation, resulting in the formation of a Li2SO4-coated CF-LLC. The Li2SO4 coating prevents the agglomeration of primary particles during lithiation, thereby reducing the primary particle sizes. As a result, Li diffusion pathways are shortened, enhancing Li diffusivity. The coating also prevents transition metal dissolution by acting as a protective barrier against electrolytic reactions. With the Li2SO4 coating, first cycle capacity increased from 205.1 mAh∙g-1 to 259.0 mAh∙g-1, and first cycle Coulombic efficiency also increased from 76.6% to 83.6%. Moreover, after 100 cycles, the Li2SO4-coated sample showed a good 84.7% capacity retention and an improved average voltage fade per cycle of 2.79 mV.