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

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[Ni 0.86 Co 0.07 Mn 0.07 ]O 2 to Li[Ni 0.67 Co 0.09 Mn 0.24 ]O 2 from the center to the outer surface. A thin shell composed of either Li[Ni 0.48 Co 0.26 Mn 0.26 ]O 2 or Li[Ni 0.56 Co 0.18 Mn 0.26 ]O 2 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.