High-Performance Mg-Li Hybrid Batteries Based on Pseudocapacitive Anatase Ti 1-x Co x O 2-y Nanosheet Cathodes.

Despite the proposed safety, performance, and cost advantages, practical implementation of Mg-Li hybrid batteries is limited due to the unavailability of reliable cathodes compatible with the dual-ion system. Herein, a high-performance Mg-Li dual ion battery based upon cobalt-doped TiO 2 cathode was developed. Extremely pseudocapacitance-type Ti 1-x Co x O 2-y nanosheets consist of an optimum 3.57 % Co-atoms. This defective cathode delivered exceptional pseudocapacitance (maximum of 93 %), specific capacities (386 mAh g -1 at 25 mA g -1 ), rate performance (191 mAh g -1 at 1 A g -1 ), cyclability (3000 cycles at 1 A g -1 ), and coulombic efficiency (≈100 %) and fast charging (≈11 min). This performance was superior to the TiO 2 -based Mg-Li dual-ion battery cathodes reported earlier. Mechanistic studies revealed dual-ion intercalation pseudocapacitance with negligible structural changes. Excellent electrochemical performance of the cation-doped TiO 2 cathode was credited to the rapid pseudocapacitance-type Mg/Li-ion diffusion through the disorder generated by lattice distortions and oxygen vacancies. Ultrathin nature, large surface area, 2D morphology, and mesoporosity also contributed as secondary factors facilitating superior electrode-electrolyte interfacial kinetics. The demonstrated method of pseudocapacitance-type Mg-Li dual-ion intercalation by introducing lattice distortions/oxygen vacancies through selective doping can be utilized for the development of several other potential electrodes for high-performance Mg-Li dual-ion batteries.