Employing S(-I)/S(-II) Redox Chemistry in Quasi-1D Niobium Trisulfide-Graphene Cathodes for High-Capacity Magnesium–Lithium Hybrid Ion Batteries

Magnesium–lithium hybrid ion batteries (MLIBs) offer a compelling alternative to traditional lithium-ion batteries (LIBs) due to their enhanced safety, abundant magnesium resources, and high theoretical capacities. However, their practical deployment is constrained by the scarcity of high-capacity cathode materials. Herein, we report a quasi-one-dimensional (1D) pseudolayered niobium trisulfide (NbS3), incorporated with graphene, as a novel cathode that leverages disulfide (S22–) redox chemistry to achieve remarkable electrochemical performance. The electrode exhibits excellent cycling performance, retaining high lithium/magnesium cointercalation capacities of 251 mA h g–1 after 150 cycles at 100 mA g–1 and 181 mA h g–1 over 1000 cycles at 1000 mA g–1. Mechanistic investigations using in operando PXRD and ex situ XPS/XAS reveal a two-step phase evolution during initial cycling, involving sequential sulfur anion (S22–/S2–) and niobium cation (Nb4+/Nb3+) redox processes. Over extended cycling, the Nb4+/Nb3+ redox fades, leaving the S22–/S2– redox associated with a single reversible phase as the dominant contributor to the performance. The primary cause of capacity fade is attributed to the irreversible structural and redox changes related to the Nb4+/Nb3+ process, along with exfoliation-induced detachment of active material. This study provides comprehensive insights into the energy storage mechanisms of NbS3-based cathodes and underscores the potential of disulfide anion-containing trisulfides as promising candidates for next-generation, high-capacity magnesium-based batteries.