High energy density hybrid Mg2+/Li+ battery with superior ultra-low temperature performance

Abstract

The development of high energy density rechargeable Mg-based batteries operating in a wide electrochemical window and ultra-low temperature remains a great challenge owing to parasitic side reactions between electrolytes and battery components when examined at high operating potentials (above 2.0 V vs. Mg²⁺/Mg). Herein we propose a flexible pyrolytic graphitic film (GF) as a reliable current collector of high-voltage cathodes for a hybrid Mg²⁺/Li⁺ battery within a pouch cell configuration. The utilization of such a highly electrochemical stable GF unlocks the critical bottleneck of incompatibility among all battery parts, especially parasitic corrosive reactions between electrolytes and currently available current collectors, which takes a big step forward towards the practical applications of Mg-based batteries. With an operating potential of 2.4 V, the hybrid Mg²⁺/Li⁺ battery designed by us can deliver a maximum energy density of 382.2 W h kg⁻¹, which significantly surpasses that of the conventional Mg battery (about 60 W h kg⁻¹), and the Al battery (about 40 W h kg⁻¹) as well as the state-of-the-art hybrid Na/Mg and Li/Mg batteries. The electrochemical property of the hybrid Mg²⁺/Li⁺ battery is also characterized by higher rate capability (68.8 mA h g⁻¹ at 3.0C), higher coulombic efficiency of 99.5%, and better cyclic stability (98% capacity retention after 200 cycles at 1.0C). In addition, the designed hybrid battery delivers excellent electrochemical performance at an ultra-low temperature of −40 °C, at which it retains 77% capacity compared to that of room temperature. Our strategy opens up a new possibility for widespread applications of graphitic current collectors towards high energy rechargeable Mg-based hybrid batteries, especially applied in polar regions, aerospace, and deep offshore waters.