Coarse-grained reduced Mo Ti1−Nb2O7+ anodes for high-rate lithium-ion batteries

Abstract

High-volumetric-energy-density lithium-ion batteries require anode material with a suitable redox potential, a small surface area, and facile kinetics at both single-particle and electrode level. Here a family of coarse-grained molybdenum substituted titanium niobium oxides Mo[subscript x]Ti[subscript 1−x]Nb[subscript 2]O[subscript 7+y] (single crystals with 1~2 μm size) underwent hydrogen reduction treatment to improve electronic conduction was synthesized, which is able to stably deliver a capacity of 158.5 mAh g[superscript −1] at 6,000 mA g[superscript −1] (65.2 % retention with respect to its capacity at 100 mA g[superscript −1] ) and 175 mAh g[superscript −1] (73 % capacity retention over 500 cycles) at 2,000 mA g[superscript −1], respectively. Via careful in situ electrochemical characterizations, we identified the kinetic bottleneck that limits their high-rate applications to be mainly ohmic loss at the electrode level (which mostly concerns electron transport in the composite electrodes) rather than non-ohmic loss (which mostly concerns Li+ lattice diffusion within individual particles). Such a kinetic problem was efficiently relieved by simple treatments of Mo substitution and gas-phase reduction, which enable full cells with high electrode density, and high volumetric energy/power densities. Our work highlights the importance of diagnosis, so that modifications could be made specifically to improve full-cell performance.