Alkali etching metal silicates derived from bamboo leaves with enhanced electrochemical properties for solid-state hybrid supercapacitors

Abstract

Metal silicates are demonstrated to be potential electrode materials for rechargeable batteries and supercapacitors (SCs). However, their electrochemical properties applied to SCs in the literatures are far less than the expectation. Herein, we propose a strategy of alkali etching process to improve the electrochemical properties of metal silicates. First, nickel silicate (NiSi), cobalt silicate (CoSi) and manganese silicate (MnSi) with the interconnected nanosheets are derived from bamboo leaves (BLs) by a calcination in combination with a facile hydrothermal method. Then 3 M NaOH aqueous solution was used to soak the metal silicates for alkali etching to obtain the etching metal silicates (denoted as e-NiSi, e-CoSi, e-MnSi). The alkali etching can enlarge the accessibility for electrolyte ions and improve the electrochemical performance of metal silicates. In the three-electrode system, the e-NiSi-3, e-CoSi-3 and e-MnSi-3 exhibit higher specific capacitances and cycling performances than that of NiSi-3, CoSi-3 and MnSi-3. The solid-state hybrid supercapacitor (HSC) devices are fabricated by using the metal silicates as the positive material and activated carbon (AC) as the negative material. In the two-electrode system, the e-MSi-3//AC HSC devices (M = Ni, Co and Mn) deliver higher areal specific capacitances and energy densities and better cycle performance than those of MSi-3//AC HSC devices, for instance, e-NiSi-3//AC HSC device (412 mF cm−2 at 4 mA cm−2, 3.2 Wh m−2 at 3.8 W m−2) is superior to NiSi-3//AC HSC device (207 mF cm−2 at 4 mA cm−2, 1.6 Wh m−2 at 3.8 W m−2). This work proves that the alkali etching process can enhance the electrochemical performance of metal silicates and e-MSi-3 can be hopeful and prominent electrode materials applied to high-performance SCs.