Bulk synthesis of mixed transition metal dichalcogenide and performance as working electrode in Li, Na, and K-ion half cells

Nanosheets of mixed or cation-substituted Transition metal dichalcogenide (TMD) are promising materials for a range of applications, including electrodes for electrochemical energy storage devices. Yet such materials are expensive to produce in large quantities (gram levels or higher). Here, we report on a two-step process, which involves precursor pyrolysis and sulfur annealing for the preparation of bulk powders of Mo<i>_x</i>W_1-<i>x</i>S₂. The structural and morphological properties of the synthesized cation-substituted TMD alloy are compared with high-purity commercially sourced MoWS₂and MoS₂/WS₂hybrid specimens. Notably, the electrochemical characteristics of synthesized Mo<i>_x</i>W_1-<i>x</i>S₂exhibit exceptional first-cycle specific charge capacities for lithium-ion (638 mAh g^-1), sodium-ion (423 mAh g^-1), and potassium-ion (328 mAh g^-1) half-cells. All the cells showed capacity decay in longer-term cycling tests, arising from volume changes in TMD conversion-type electrodes. To mitigate the capacity decay, a voltage cut-off method is implemented, which minimizes irreversibility and structural distortion of TMD during cycling, even at higher cycling currents with nearly 100% average cycling efficiency. The findings of this study demonstrate a proficient and scalable synthesis methodology poised to be utilized across an array of layered TMD materials, with benefits to both industry and fundamental research into alkali-metal-ion energy storage.