All ternary metal selenide nanostructures for high energy flexible charge storage devices

The design of three-dimensional (3D) nanoarchitectures on a flexible substrate has emerged as a novel strategy for fabricating cutting-edge wearable and portable power sources. Herein, we propose a simple and versatile approach towards the fabrication of hierarchical nanoporous manganese nickel selenide (Mn_xNi_1-xSe₂) and manganese iron selenide (Mn_xFe_1-xSe₂) nanosheets as positive and negative electrodes for flexible charge storage devices to achieve ultra-high energy density. The Mn substitution into Ni/Fe-selenide results in hierarchical architecture with highly altered electronic structure, offering enhanced electrical conductivity, increased catalytic activity, and improved stability of Ni/Fe phases upon cycling. Under optimized conditions, the Mn_0.33Ni_0.67Se₂ and Mn_0.33Fe_0.67Se₂ electrodes showed high specific capacities of ∼333 and 251 mAh g⁻¹ at a current density of 1 mA cm⁻², superior rate capabilities of 81.4 and 80.9% capacity retention at 50 mA cm⁻², respectively, and outstanding cycling stability. Most importantly, in flexible solid-state assembly, the Mn_0.33Ni_0.67Se₂//Mn_0.33Fe_0.67Se₂ based SC delivers the excellent energy density of 87.2 Wh kg⁻¹ at a power density of 0.672 kW kg⁻¹, along with ultra-long durability of 96.2% capacity retention after 10,000 cycles at 30 mA cm⁻². Thus, it would be believed this new fabrication strategy certainly promising for flexible electronics devices in the near future.