Coarse-grained reduced MoxTi1-xNb2O7+y anodes for high-rate lithium-ion batteries

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 MoxTi1-xNb2O7+y (single crystals with 1 similar to 2 mu m size) underwent hydrogen reduction treatment to improve electronic conduction was synthesized, which is able to stably deliver a capacity of 158.5 mAh g(-1) at 6,000 mA g(-1) (65.2 % retention with respect to its capacity at 100 mA g(-1)) and 175 mAh g(-1) (73 % capacity retention over 500 cycles) at 2,000 mA g(-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.

Automated summary

By treating and modifying coarse-grained oxide materials, researchers were able to improve electronic conduction and achieve high capacity and high-rate performance in lithium-ion batteries. Through careful electrochemical characterization, they identified and addressed the kinetic bottleneck, ultimately leading to the development of high-density and high energy/power density full cell designs.