Electricity generated from renewable sources, such as solar and wind power, offers enormous potential for meeting future energy demands. But access to solar and wind energy is intermittent, whereas electricity must be reliably available for 24 hours a day: Even second-to-second fluctuations can cause major disruptions that cost tens of billions of dollars annually. Electrical energy storage devices will therefore be critical for effectively leveling the cyclic nature of renewable energy sources. (See the article by George Crabtree and Nathan Lewis, Physics Today 0031-9228 60 3 2007 37 https://doi.org/10.1063/1.2718755 Physics Today, March 2007 .) They are also a key enabler in numerous areas of technological relevance ranging from transportation to consumer electronics.
Electrical energy storage systems can be divided into two main categories: batteries and electrochemical capacitors. Batteries store energy in the form of chemical reactants, whereas ECs store energy directly as charge. Due to that fundamental difference between the...
