A hierarchical Ti2Nb10O29 composite electrode for high-power lithium-ion batteries and capacitors

Ti 2 Nb 10 O 29 (TNO) is a suitable electrode for high-performance lithium-ion batteries and capacitors because of its large lithium storage capacity and high Li + diffusivity . Currently, the rate or power capability of TNO-based systems is limited by the poor electronic conductivity of the material. Here we report our findings in design, synthesis, and characterization of a hierarchical N-rich carbon conductive layer wrapped TNO structure (TNO@NC) using a novel polypyrrole-chemical vapor deposition (PPy-CVD) process. It was found that carbon coating with PPy–carbon partially reduces Ti and Nb cations, forms TiN, and creates oxygen vacancies in the TNO@NC structure that further increase overall electronic and ionic conductivity . Various defect models and density functional theory (DFT) calculations are used to show how oxygen vacancies influence the electronic structure and Li-ion diffusion energy of the TNO@NC composite. The optimized TNO@NC sample shows notable rate capability in half-cells with a reversible capacity of 300 mAh g −1 at 1 C rate and maintains 211 mAh g −1 at a rate of 100 C, which is superior to that of most M x Nb y O z materials. Full cell LiNi 0.5 Mn 1.5 O 4 (LNMO)||TNO@NC lithium-ion batteries (LIB) and active carbon (AC)||TNO@NC hybrid lithium-ion capacitors (LIC) exhibited notable volumetric and gravimetric energy and power densities.