Li2So4 Coating of Co-Free, Li-Rich Layered Oxide Cathodes through a Carbonate Coating Method for Improving Cycle Performance

In the continued evolution toward high-performance lithium-ion batteries, cobalt has presented itself as a major obstacle due to its price and accessibility. Thus, Co-Free, Li-rich Layered Oxide Cathodes (CF-LLC) have become a promising cathode candidate for their exclusion of Cobalt and high theoretical capacity. Nevertheless, CF-LLC suffers from LLC issues such as phase transformation and voltage fade. Due to high overpotential from sluggish kinetics, the oxygen plateau of CF-LLC occurs at a higher-than-normal potential, leading to a shortened first cycle charge and lower discharge capacity. To mitigate this, we implemented a sulfate coating of the carbonate precursor; which upon lithiation, presents a Li 2 SO 4 coated LLC (S-CF-LLC). The Li-sulfate coating prevents agglomeration of the primary particles during lithiation, leading to a larger surface area and thus, faster kinetics. The coating also prevents increased degradation from the increased surface area by acting as a protective barrier. The S-CF-LLC was successfully synthesized using a hydrothermal synthesis method with a wet chemical coating step and the synthesis was confirmed using XRD, SEM, XPS, and HR-TEM techniques. Galvanostatic cycling showed that the first cycle improved from 236.1mAhg -1 to 263.5mAhg -1 after coating, owing to the improved kinetics. GITT analysis of the increased diffusion coefficient further confirmed the overall improved kinetics. Moreover, the efficacy of the coating was shown through cycle data after 100 cycles, which showed good coulombic efficiency with a high average of >99%, good capacity retention, and good voltage fade per cycle improvement. Overall, the successfully synthesized S-CF-LLC opens up the possibility of practical cobalt-free high-performance batteries.