RESUMEN
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.
RESUMEN
A porous carbon was synthesized via hydrothermal carbonization and CO2 activation. O2 and SO2 were successfully co-doped onto carbon surface by applying non-thermal plasma technique. Porous carbon possessing excellent textural properties is effective to adsorb the radicals generated by plasma. Plasma promotes the adsorption of O2 and SO2 on carbon surface with the formation of abundant CO, C-S and C-SOx (x = 1-3) groups. The O2/SO2 dual-doped porous carbon was utilized to adsorb elemental mercury (Hg0) from the flue gas of coal combustion. The Hg0 adsorption ability of the O2/SO2 dual-doped porous carbon is closely related with the concentrations of O2 and SO2 for plasma treatment and the treatment time. The optimal O2/SO2 dual-doped porous carbon exhibited far greater Hg0 adsorption capacity than a commercial brominated activated carbon. Density functional theory was employed to understand the Hg0 adsorption mechanism at the molecular level. CO, C-S and C-SOx (x = 1-3) groups enhanced the interaction of Hg0 with surface carbon atom. The activity of them for enhancing Hg0 adsorption is in the order of C-SO2 > CO > C-S > C-SO > C-SO3. Porous carbon can be activated by plasma in flue gas containing O2 and SO2, and used as superior sorbent for Hg0 removal.