Porous oxygen-deficient TiNb2O7 spheres wrapped by MXene as high-rate and durable anodes for liquid and all-solid-state lithium-ion batteries

Abstract

TiNb2O7 (TNO) is an attractive anode material for high-safety lithium-ion batteries (LIBs) because of its medium working potential and competitive theoretical capacity. The main challenges associated with TNO anodes are ultralow electronic conductivity and structural instability, leading to poor power and cycling performances. Herein, we prepare MXene wrapped porous TNO spheres with oxygen vacancies (TNO-x@MXene). It is found that introducing MXene and oxygen vacancies into TNO anode can result in electronic conductivity enhancement about four orders of magnitude while building a porous structure allows Li+ (de-)intercalation reactions to dominantly occur at the material near-surface, boosting interfacial electron/ Li+ transfer kinetics. Meanwhile, 3D conductive networks constructed by flexible MXene nanoflakes also help retain electrical connectivity, minimizing electrode degradation during cycling. In half cells, the TNO-x@MXene material demonstrates high reversible capacity (264 mAh g−1 at 0.1C), superior cycling stability (0.03 % capacity fading per cycle during 1000 cycles at 4C), extraordinary rate capability (78 mAh g−1 at 100C), and high initial Coulombic efficiency (92.2 %). With LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode, the assembled liquid-state full cells exhibit excellent capacity retention of 91.5 % after 1000 cycles at 5C. Importantly, for the first time, we explore the potential of as-made TNO composite as the anode of all-solid-state LIBs with an inorganic sulfide electrolyte (Li6PS5Cl). The solid-state TNO-x@MXene//NCM811 batteries also demonstrate stable cycling ability (98 % capacity retention after 1000 cycles at 2C). The methodology can also be used to modify other electrode materials with low conductivity and structural instability for LIBs and beyond.