Nanotube network arrays with nickel oxide canopies as flexible high-energy anodes for lithium storage

Abstract NiO-based flexible anodes have provoked great interest due to their high theoretical capacity, benign redox reactivity, and chemical and thermal stability. However, the issues of their poor cyclability, low rate capability, and mechanical instability limit their practical applications. To approach the high-performance flexible devices, 3D NiO/TiO2 nanotube network arrays on flexible carbon cloth substrates are fabricated through a simple two-step, seed-free solvothermal method. The ultrathin NiO nanosheets provide remarkable charge-discharge cycle performance due to their slight volume expansion during the charge-discharge process. The flexible carbon cloth provides a conductive and bendable matrix. TiO2 nanotube arrays not only deliver a fast electron transfer path, but also excellent mechanical stability during bending. The porous network architecture results in a remarkable reduction in the irreversible capacity loss without sacrificing specific surface area. This unique structure creates a reversible capacity of 592.2 mAh g−1 after 1000 cycles at a current density of 200 mA g−1, and has a rate capacity of 439 mAh g−1 even at high current densities of 2000 mA g−1. Their full cells maintain excellent electrochemical performance and mechanical stability after multiple folds. The convenient synthetic process creates a window of opportunity for bringing flexible, high-performance energy storage devices to markets.