Tailoring the interface in tungsten doped cobalt sulfide positive electrode with ultrathin cobalt oxide atomic layer for high performance energy storage application

Enhancing energy density remains a key focus in the designing of high-capacitance positive electrodes in energy storage systems. While metal sulfides have shown promise as an efficient electrode material, their applicability is hindered by stability issues and poor capacitance retention at high current densities due to limitations in electronic conductivity and suboptimal micro-/nanostructure. Addressing these challenges, the current study focuses on enhancing electrochemical performance by incorporating tungsten into cobalt sulfide (denoted as WCS). Through a hydrothermal fabrication process on a Ni-foam substrate, coupled with precisely controlled atomic layer deposition of ultrathin CoOx over WCS, a self-standing WCS10 positive electrode is developed. Remarkably, the optimized 10 nm CoOx atomic layer on WCS positive electrode demonstrated a high specific capacitance of 1720 F/g at a current density of 6 A/g, surpassing the pristine WCS by 200 F/g. Notably, WCS10 exhibits exceptional cyclic stability retaining similar to 97.5 % (whereas only 45 % in WCS) of its capacitance after 10,000 cycles at a high current density of 11 A/g. Furthermore, an asymmetric device was assembled using the WCS10 as the positive electrode and rGO as a negative electrode achieving a remarkable energy density of 93.125 Wh/kg at a power density of 750 W/kg at a current density of 1 A/g. A capacity retention of 80.6 % is achieved after 5000 charge-discharge cycles at a current density of 20 A/g. This study provides a simple and efficient route in preparing high performance positive electrode and offering a pathway towards more efficient and durable energy storage solutions.