Effect of ball milling energy on the structure and electrochemical behavior of CoS alloys as anode materials for aqueous secondary batteries

Abstract Co-based alloys exhibit high reversible electrochemical capacity and superior electrocatalytic activity as anode materials for aqueous secondary batteries, yet several underlying mechanisms remain unclear. Herein, we systematically investigate the effect of ball milling energy on the structure and electrochemical performance of CoS alloy, and elucidate the electrochemical reaction mechanism of CoS alloy anode in aqueous alkaline electrolyte. This study demonstrates that the CoS alloy electrode undergoes redox reactions in the alkaline aqueous electrolyte, with reversible interconversion between Co and Co(OH)2, which contributes to the electrochemical capacity. And the CoS alloy synthesized via low-energy ball milling, which lacks a formed compound phase, exhibits higher electrochemical activity than the compound-phase-containing CoS alloy obtained through high-energy ball milling. Specifically, the milled CoS alloy with ball-to-powder ratio of 5:1, 10:1 and 20:1, without formed compound phase, exhibits initial discharge capacities of 473.7, 492.5 and 454.1 mAh/g, respectively, at a current density of 300 mA/g, and retains 322.5, 292.4 and 274.3 mAh/g after 100 cycles, respectively. In contrast, the sample with a ball-to-powder ratio of 30:1 forms of the Co1-xS and Co4S3 phases, which are electrochemically inactive in alkaline electrolyte and thus unable to participate in redox reactions, resulting in a lower initial discharge capacity of 350.2 mAh/g and a retained capacity of 84.4 mAh/g after 100 cycles.