Ever-growing energy demand in the world and the serious
environmental problems have greatly motivated considerable
research for sustainable energy conversion and storage devices,
such as batteries, fuel cells, and electrochemical capacitors, also
known as supercapacitors [1,2]. Among these energy storage
devices, supercapacitors are featured with faster chargeedischarge
rates, high power density (1e2 orders of magnitude higher than
batteries), much higher longevity (2e3 orders of magnitude longer
than batteries), high reliability and low manufacturing costs [3e5].
Even so, their practical applications are largely hindered by the low
energy density compared with rechargeable batteries [6]. Therefore,
in order to meet the future energy demands, it is essential to
develop advanced high-performance supercapacitors with high
energy density and superior cycling durability [7].