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Sandwiching Defect-Rich TiO2−δ Nanocrystals into a Three-Dimensional Flexible Conformal Carbon Hybrid Matrix for Long-Cycling and High-Rate Li/Na-Ion Batteries

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posted on 13.06.2019, 00:00 by Boya Wang, Wei Yuan, Xuemei Zhang, Mingwu Xiang, Yun Zhang, Heng Liu, Hao Wu
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 flexible electrodes exhibit high-rate capabilities and long-cycling life in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), and they also exhibit outstanding thermal stability under cycling at 55 °C. More remarkably, a flexible soft-package full battery based on a NCS/TiO2−δ/RGO anode and a LiNi1/3Co1/3Mn1/3O2 (for LIBs) or Na0.67Fe0.3Mn0.3Co0.4O2 (for SIBs) cathode shows stable electrochemical characteristics under bending and folding, holding great potential for flexible energy storage devices.