Achieving Rich-Mixed-Valence Polysulfides/Carbon Nanotube Films Toward Ultrahigh Volume Energy Density and Largely Deformable Pseudocapacitors

In this work, new insights into dependence of electrochemical performance enhancement on transition metals' rich-mixed-valence and their atomic ratio as well as redox active polysulfide are proposed. Especially the influence of atomic ratio is further demonstrated by both experiments and density functional theoretical calculation where increasing the Co/S leads to enlargement of both inter-atom distance and hole diameter in MnxCoySz cell. We rationally designed and prepared novel flexible electrode of rich-mixed-valence polysulfide MnxCoySz/carbon nanotube film (CNTF) through acid activation of a dense CNTF into hydrogel-like conductive matrix, growth of MnxCoy(CO3)0.5OH precursor on each CNT, followed by controlled sulfidation. Nanostructure control allows us to obtain fast electron/ion transfer and increased availability of active sites/interfaces. The optimal MnCo9S10/CNTF shows a specific capacitance reaching 450 F cm-3 at 10 mA cm-2, much higher than reported values for CNT-based electrodes. Also, it exhibits remarkable cycling stability with only 1.6% capacity loss after 10,000 cycles at a high current density of 80 mA cm-2. An all-solid-state asymmetric supercapacitor (ASC) applying the MnCo9S10/CNTF delivers exceptionally high volumetric energy density of 67 mWh cm-3 (at 10 W cm-3). Particularly, integrated electric sources with adjustable output voltages can be obtained by connecting several ASCs in series, and there are no structural failure and capacity loss during repeated large-angle twisting and vigorous hammering. This work provides a general route to energy storage devices with ultrahigh volumetric energy density and outstanding reliability for wearable electronics.