Surface engineering of nanomaterials for improved energy storage - A review

Nanomaterials bring extreme promise for a future wave of energy storage materials with high storage capacity, fast recharging capability, and better durability than bulk material counterparts. However, this promise is often overshadowed by greater surface area and higher reactivity of nanostructured active materials - obstacles that must be overcome to be practical. Specifically for energy storage systems, many materials that exhibit promise in bulk form for high capacity or energy density exhibit surfaces that are unstable or reactive in electrochemical environments when downsized to nanometer length scales. As a result, surface engineering can be a powerful tool to decouple bulk material properties from surface characteristics that often bottleneck energy storage applications of nanomaterials. This review discusses advances made toward the surface engineering of nanostructures in the context of four mechanistic roles that surface engineering can play. This includes (i) chemical activation, where the surface layer plays the active role in facilitating a Faradaic chemical process, (ii) solid electrolyte interphase (SEI) control, where a surface layer can lead to a stable artificial interface for Faradaic processes to occur, (iii) chemical passivation, where near atomically thin surface protective layers can protect from corrosion or unwanted electrochemical reactions at interfaces, and (iv) mechanical stability, where a thin layer can provide mechanical support to inhibit fracturing or mechanical failure. This review elucidates surface engineering as a multi-faceted tool for engineering materials for energy storage that intersects the quest for new materials and the rediscovery of old materials to break new ground in energy storage applications. The discussion concludes by highlighting key current challenges in surface engineering for pure metal anodes in metal-ion batteries and polysulfide immobilization in lithium-sulfur batteries. (C) 2016 Elsevier Ltd. All rights reserved.