Multidimensional materials and device architectures for future hybrid energy storage

A chieving a secure, sustainable energy future is one of the greatest scientific and societal challenges of our time. Electrical energy storage (EES) plays a vital role in daily life because of our dependence on numerous electronic devices that require mobility. There is also a need for large-scale and inexpensive EES for grid and transportation applications. Electricity generated from renewable sources, such as solar and wind, is critical to meeting future energy demands. However, these intermittent renewable sources require efficient EES devices. Rechargeable (secondary) batteries, which use electrochemical reactions for energy storage, are commonly used for EES at small and medium scales1. Lithium-ion batteries currently dominate the market for electronic devices, and are rapidly penetrating the transportation segment and entering into grid scale storage. A multitude of other batteries are available commercially, including well known lead-acid batteries. However, modern technologies require much larger amounts of energy to be stored with a high energy density, quickly and at low cost. Electrochemical capacitors (ECs) can be charged in minutes if not seconds, ensuring fast energy collection, but they store 1–2 orders of magnitude less energy compared with batteries2. Thus, the development of new EES systems is needed in order for large-scale solarand wind-based electrical generation to be practical3,4. The time it takes to charge current batteries is long compared with what it takes to fuel our gasoline vehicles. Therefore, substantial improvements in the energy and power densities of EES systems are also needed to realize the electrification of transportation. Moreover, with the continued miniaturization of electronics, penetration of wireless devices into our homes and clothes, wide use of sensor networks and widely anticipated ‘Internet of Things’, there is an intensive effort to develop miniature, but powerful EES devices. Current thin-film batteries have a very small amount of active material relative to the packaging and other passive components. EES that have a much smaller content of DOI: 10.1038/ncomms12647 OPEN