Conversion mechanism of NiCo_(2)Se_(4)nanotube sphere anodes for potassium-ion batteries

Given the abundance of potassium resources,potassium-ion batteries are considered a low-cost alternative to lithium-ion types.However,their electrochemical performance remains rather unsatisfactory because potassium ions have sluggish kinetics and large ionic radius.In this study,NiCo_(2)Se_(4)nanotube spheres are synthesized as efficient potassium storage hosts via a facile two-step hydrothermal process.The rationally designed electrode has various ameliorating morphological and functional features,including the following:(i)A hollow structure allows for relief of the volume expansion while offering an excellent electrochemical reac-tivity to accelerate the conversion kinetics;(ii)a high electrical conductivity for enhanced electron transfer;and(iii)myriad vacancies to supply active sites for electrochemical reactions.As such,the electrode delivers an initial reversible capacity of 458.1 mAh g^(−1)and retains 346.6 mAh g^(−1)after 300 cycles at 0.03 A g^(−1).The electrode sustains a high capacity of 101.4 mAh g^(−1)even at a high current density of 5 A g^(−1)and outperforms the majority of state-of-the-art anodes in terms of both cyclic capacity and rate capability,especially at above 1.0 A g^(−1).This study not only proves bimetallic selenides are promising candidates for potassium storage devices but also offers new insight into the rational design of electrode materials for high-rate potassium-ion batteries.