High-Energy Layered Oxide Cathodes with Thin Shells for Improved Surface Stability

Abstract

Core-shell, nickel-rich layered oxide materials with a full concentration gradient (FCG) core and thin shells with low nickel content have been investigated. Hierarchically structured core-shell materials have the same FCG core, where the composition gradually changes from Li[Ni0.86Co0.07Mn0.07]O2 to Li[Ni0.67Co0.09Mn0.24]O2 from the center to the outer surface. A thin shell composed of either Li[Ni0.48Co0.26Mn0.26]O2 or Li[Ni0.56Co0.18Mn0.26]O2 was applied to the outer surface of the FCG core. This hierarchical core-shell structure efficiently integrates the benefit of high energy from the Ni-rich core, structural stability and favorable transport of Li+ ions from the FCG core, and surface stability from the low-Ni and high-Mn shell. The core-shell cathodes demonstrate improved cycling performance at 55 °C even up to 4.5 V when compared to the FCG core-only cathode. Shells of low nickel content and a thickness of ∼300 nm provide sufficient surface stability, particularly at elevated temperatures. We suggest this novel core-shell structure as a suitable cathode for power sources such as electric vehicles, where safety and energy density are equally important. © 2014 American Chemical Society.