Sandwiching Defect-Rich TiO 2−δ Nanocrystals into a Three-Dimensional Flexible Conformal CarbonHybrid Matrix for Long-Cycling and High-Rate Li/Na-Ion Batteries

Developing flexible power sources is crucially important to fulfill the need for wearable electronic devices, but state-of-the-art flexible electrodes cannot meet the requirements of practical applications because of their heavy weight and unsatisfactory mechanical properties. Here, we highlight a design strategy for constructing a novel robust three-dimensional (3D) flexible electrode with a unique sandwichlike N-doped carbon sponge/TiO2−δ/reduced graphene oxide (NCS/TiO2−δ/RGO) configuration. In this electrode architecture, ultrafine defect-rich TiO2−δ nanocrystals are spatially sandwiched by a 3D conformal carbon hybrid matrix, where the 3D porous NCS provides an interconnected open diffusion channel for efficient ionic accessibility while the conformal RGO coating layer serves as an additional upper current collector, resulting in a double continuous conductive network for fast electronic transport and guaranteeing excellent electrochemical reaction kinetics. Hence, the as-built NCS/TiO2−δ/RGO flexibl...