Formation of a Surficial Bifunctional Nanolayer on Nb O for Ultrastable Electrodes for Lithium-Ion Battery.

Safe and long cycle life electrode materials for lithium-ion batteries are significantly important to meet the increasing demands of rechargeable batteries. Niobium pentoxide (Nb O ) is one of the highly promising candidates for stable electrodes due to its safety and minimal volume expansion. Nevertheless, pulverization and low conductivity of Nb O have remained as inherent challenges for its practical use as viable electrodes. A highly facile method is proposed to improve the overall cycle retention of Nb O microparticles by ammonia (NH ) gas-driven nitridation. After nitridation, an ultrathin surficial layer (2 nm) is formed on the Nb O , acting as a bifunctional nanolayer that allows facile lithium (Li)-ion transport (10-100 times higher Li diffusivity compared with pristine Nb O microparticles) and further prevents the pulverization of Nb O . With the subsequent decoration of silver (Ag) nanoparticles (NPs), the low electric conductivity of nitridated Nb O is also significantly improved. Cycle retention is greatly improved for nitridated Nb O (96.7%) compared with Nb O (64.7%) for 500 cycles. Ag-decorated, nitridated Nb O microparticles and nitridated Nb O microparticles exhibit ultrastable cycling for 3000 cycles at high current density (3000 mA g ), which highlights the importance of the surficial nanolayer in improving overall electrochemical performances, in addition to conductive NPs.