Strengthening ion uptake and mitigating volume change via bimetallic telluride heterojunction for ultrastable K-ion hybrid capacitors

Abstract

Unitary transition-metal tellurides are appealing to supersede their oxide and sulfide congeners in the realm of K-ion storage because of advanced electrical conductivity. Nevertheless, the marked volume expansion of tellurides during K+ uptake/release giving rise to rapid capacity decay remains a daunting obstacle. Distinct from the previously reported singular telluride configurations, bimetallic heterojunction comprising Mo-Co telluride moiety and dual-carbon encapsulation is developed in this study to endow durable K-ion storage. Density functional theory calculations unlock the synergistic effects of bimetallic Mo-Co tellurides with respect to augmenting electrical conductivity and favoring K-ion adsorption. In situ transmission electron microscopy analysis clearly reveal the structural evolution of bimetallic Mo-Co telluride during a discharge/charge cycle, showing a mitigated volume expansion rate of 2.37 %. Accordingly, the heterojunction exhibits excellent cycling stability (160 mAh/g for 2000 cycles at 1.0 A/g) and favorable capacity output (322 mAh/g at 0.2 A/g), outperforming unitary MoTe2 or CoTe2 counterparts. Thus-derived K-ion hybrid capacitor full-cell manifests elongated lifespan over 6000 cycles at 1.0 A/g. This telluride heterojunction material might offer a valuable reference to rendering high-performance potassium-based energy storage devices.