Ultrafast synthesis of K cations inserted birnessite-type MnO2 electrode in ethanolamine based deep eutectic solvents with improved supercapacitor performance

Abstract

Specific capacitance of energy storage devices depends on the electrode materials and various manganese oxides have recently been developed and attracted much attention due to their superior electrochemical performance with high capacitance, energy density, and cyclic stability. Herein, K cations inserted birnessite-type MnO2 was ultrafast synthesized by a facile room temperature wetchemical method under ethanolamine based deep eutectic solvents (DESs), where monoethanolamine (MEA), diethanolamine, and triethanolamine were used as hydrogen bond donor (HBD) and choline chloride (ChCl) was acted as hydrogen bond acceptor. The results indicate that K+ can be pre-inserted into the layers of birnessite-type MnO2 during the preparation process by the addition of ethanolamine based DESs. The morphology, crystallinity, and porosity of manganese oxides can be effectively adjusted by changed types of HBD in the DESs. The mesoporous granular K+ pre-inserted birnessite-type MnO2 prepared in [ChCl:2MEA] (MnOx-CM) with a high specific surface area of 220 m2/g and electrical conductivity exhibits the best electrochemical performance with high specific capacitance of 290 F/g at the current density of 0.1 A/g. The pre-inserted K+ ions participating in the redox process of birnessite-type MnO2 can efficiently improve the electrochemical energy storage and cycling stability. Thus, the MnOx-CM can still maintain 92.5% capacity retention after 8000 cycles.