Built-in electric field-assisted surface-amorphized nanocrystals for high-rate lithium-ion battery.

High-power batteries require fast charge/discharge rates and high capacity besides safe operation. TiO2 has been investigated as a safer alternative candidate to the current graphite or incoming silicon anodes due to higher redox potentials in effectively preventing lithium deposition. However, its charge/discharge rates are reluctant to improve due to poor ion diffusion coefficients, and its capacity fades quickly with rate as only thinner surface layers can be effectively used in faster charge/discharge processes. Here, we demonstrate that surface-amorphized TiO2 nanocrystals greatly improve lithium-ion rechargeable battery performance: 20 times rate and 340% capacity improvement over crystalline TiO2 nanocrystals. This improvement is benefited from the built-in electric field within the nanocrystals that induces much lower lithium-ion diffusion resistance and facilitates its transport in both insertion and extraction processes. This concept thus offers an innovative and general approach toward designing battery materials with better performance.