A flexible copper sulfide @ multi-walled carbon nanotubes cathode for advanced magnesium-lithium-ion batteries.

The hybrid magnesium-lithium-ion batteries (MLIBs) are promising alternatives in large-scale energy storage field owing to low cost and high safety of magnesium batteries and fast diffusion rate of Li-ion in the electrode. Herein, a free-standing and binder-free copper sulfide/Multi-walled carbon nanotubes film cathode (F-CuS-CNT), along with Mg-Li dual-salt electrolyte and dendrite-free Mg anode, is employed to construct the MLIBs. At room temperature (25 °C), the F-CuS-CNT electrode with a CuS content up to 70% exhibits a high initial specific capacity of 479 mAh g-1 (∼85.5% of the theoretical capacity) and a considerable cycling stability (165 mAh g-1 even after 100 cycles at the current density of 30 mA g-1), which far surpasses those of conventional CuS electrode. The excellent electrochemical performances of the F-CuS-CNTs electrode can be attributed to its excellent flexible network architecture as well as abundant pores, which provide more stable conductive buffering layers for CuS particles and higher Li+ diffusion dynamics during the charging/discharging process. This work demonstrates that constructing a flexible and free-standing film electrode could improve the electrochemical performances of MLIBs and may be an appropriate select of preparing flexible MLIBs.