Sandwich‐Shell Structured CoMn₂O₄/C Hollow Nanospheres for Performance‐Enhanced Sodium‐Ion Hybrid Supercapacitor

Abstract

With the rapid depletion of petroleum and coal resources, the utilization of clean and sustainable energy (e.g., solar, hydropower, wind, and geothermal energy) has become particularly important. However, solar and wind energy have many intrinsic drawbacks, such as intermittence and instability, limiting their direct use. Therefore, it is urgent to develop high-performance electrochemical energy storage (EES) system to realize energy transfer. [1] Also, both electric vehicles and portable electronic devices need EES. With their increasing importance and large-scale applications, EES devices such as sodiumion batteries (SIBs), lithium-ion batteries (LIBs), and supercapacitors are receiving considerable attention. [2] Batteries provide superior energy density to supercapacitors, but their power density is much lower than that of supercapacitors. Hybrid supercapacitors (HSCs), as emerging EES devices, are commonly assembled by redox-type electrode as anode and capacitive electrode as cathode. HSCs provide an opportunity to achieve relatively-high energy density with concurrently superior power density. However, different charge storage mechanism in anode and cathode leads to in the electrochemical reaction kinetics, hindering the development of HSCs. [3] Engineering of architecture and component is efficient to achieving performance-enhanced HSCs.Sodium-ion HSCs (Na-HSCs) have attracted numerous attention due to their resource abundance as well as wide operating voltage range. Although the size of Na + is obviously larger than that of Li + , its lower desolvation energy makes it possible to develop high-rate devices. In comparison with lithium-ion HSCs, Na-HSCs are still in their infancy. Considering economic profits and resource-rich sodium, Na-HSCs are promising. [4] In addition, Na-HSCs can provide relatively high-power density and outstanding rate capability compared with SIBs. [5] Nevertheless, their current performance is far from satisfying practical application. Therefore, various novel electrode materials have been designed in order to enhance their comprehensive performance. To match the cathode with rapid faradaic reactions, anode materials experiencing fast redox reactions are desired. The nanostructure engineering coupled with the Sodium hybrid supercapacitors (Na-HSCs) are regarded as one promising electrochemical energy storage device, because of the low price of sodium, prolonged life cycle, and high-energy/power density. Nonetheless, the imparity between the fast capacitive reactions at cathode and the sluggish Faradaic reactions at the anode leads to an imbalance in the electrochemical reaction kinetics, limiting the development of Na-HSCs. Therefore, it is urgent to develop suitable anode materials for performance-enhanced Na-HSCs. Herein, sandwich-shell-structured CoMn 2 O 4 /C hollow spheres are synthesized by a facile hydrothermal reaction and subsequent calcination, where mesoporous carbon hollow spheres (CHSs) serve as nonsacrificial hard templates. CHSs with numerous mesoporous channels...

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