Wang Siliang,Wang Qiang,Zeng Wei,Wang Min,Ruan Limin,Ma Yanan
Restricted by their energy storage mechanism, current energy storage devices have certain drawbacks, such as low power density for batteries and low energy density for supercapacitors. Fortunately, the nearest ion capacitors, such as lithium-ion and sodium-ion capacitors containing battery-type and capacitor-type electrodes, may allow achieving both high energy and power densities. For the inspiration, a new zinc-ion capacitor (ZIC) has been designed and realized by assembling the free-standing manganese dioxide–carbon nanotubes (MnO 2 –CNTs) battery-type cathode and MXene (Ti 3 C 2 T x ) capacitor-type anode in an aqueous electrolyte. The ZIC can avoid the insecurity issues that frequently occurred in lithium-ion and sodium-ion capacitors in organic electrolytes. As expected, the ZIC in an aqueous liquid electrolyte exhibits excellent electrochemical performance (based on the total weight of cathode and anode), such as a high specific capacitance of 115.1 F g −1 (1 mV s −1 ), high energy density of 98.6 Wh kg −1 (77.5 W kg −1 ), high power density of 2480.6 W kg −1 (29.7 Wh kg −1 ), and high capacitance retention of ~ 83.6% of its initial capacitance (15,000 cycles). Even in an aqueous gel electrolyte, the ZIC also exhibits excellent performance. This work provides an essential strategy for designing next-generation high-performance energy storage devices.
MnO 2 as the cathode material of Zinc-ion batteries (ZIBs) has attracted great attention. In order to further improve the performance of ZIBs, MnO 2 hollow nanorobs and carbon nanotubes (CNTs) are compounded to obtain α-MnO 2 /CNTs nanocomposites in which robs and tubes are entangled with each other and present the cross-linked reticular structure. This structure of α-MnO 2 /CNTs electrode is obtained through hydrothermal strategy and provides large space for the volume variation of MnO 2 during the charge and discharge process. The α-MnO 2 /CNTs composite displays an excellent initial discharge capacity of 302 mAh·g −1 at 100 mA·g −1 , and keeps 116 mAh·g −1 at 2000 mA·g −1 (78.4% retention after 2000 cycles). This composite provides a new way for the further application of ZIBs.
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