Enhanced Electrochemical Performance of the Lithium-Manganese-Rich Cathode for Li-Ion Batteries with Na and F CoDoping.

ABSTRACT

The lithium-manganese-rich layered oxide cathode (LMR-NMC), xLi2MnO3·(1 - x)LiMO2 (M = Co, Ni, and Mn), is on demand because of its high specific capacity of over 250 mA h g-1 between the voltage range 2.0-4.8 V (vs Li/Li+). Because of the requirement of activating the Li2MnO3 phase in the first cycle, oxygen extraction from the lattice structure occurs. Consequently, capacity fading and voltage fading during cycling are still major obstacles to the commercialization of LMR-NMC in battery applications. Here, codoping Na and F into LMR-NMC via facile hydroxide coprecipitation followed by solid-state reaction is introduced. Na and F are partially substituted into Li and O sites, respectively. These dopant ions enlarge the Li slab, which in turn eases Li diffusion and minimizes oxygen loss, thereby stabilizing the structure. The codoped sample exhibits both high capacity retention (97%) and high voltage retention (91%) over 100 cycles with an initial discharge capacity of 260 mA h g-1 at 0.1 C. Compared to other reports on LMR-NMC as obtained by coprecipitation, results from this study show the best capacity retention. The developed codoping approach may provide a new strategy for designing high-performance LMR-NMC cathodes for next-generation lithium ion batteries.