Using nanoconfinement to inhibit the degradation pathways of conversion-metal oxide anodes for highly stable fast-charging Li-ion batteries†
Nanostructured hybrids that physically encapsulate highly morphable, high capacity Li-ion battery anodes can potentially enable much longer cycle life than straightforward deployment of the same chemistry. This study demonstrates improved reaction reversibility (longer cycle life) and increased reaction rate (faster charge/discharge) for conversion metal oxides (MOs) reacting with Li-ions in a new architecture where they are physically confined inside of nanostructured carbon. The specific system of focus is nickel oxide (NiO) nanoparticles that are selectively deposited inside of, and fully encapsulated by, carbon nanotubes (CNTs). The physical and electrochemical behavior of the resulting nano-confined NC-NiO@CNT10 anode shows that confinement, and more specifically isolation from the electrolyte, eliminates the primary mechanisms for degradation and coulombic efficiency loss in MO anodes. Importantly, the elimination of these parasitic degradation mechanisms allows a nano-confined NC-NiO@CNT10 anode to achieve a stable reversible capacity of ca. 700 mA h g−1 and >99.9% coulombic efficiency, even after 2000 deep charge/discharge cycles (0–100% state-of-charge) at 1C. These findings provide a blueprint for future understanding of the role of material confinement in controlling reactions that are not only applicable to achieving long-term cycle performance for future high rate MO@CNT anodes in Li-ion batteries, but other chemical and electrochemical systems as well.