Single-crystal based studies for correlating the properties and high-voltage performance of Li[NixMnyCo1−x−y]O2 cathodes†
Safe and stable cycling of lithium-ion battery cathodes at high voltages is essential for meeting next-generation energy storage demands, yet the lack of fundamental understanding of the correlation of a material's properties and reactivities largely hinders current progress. In the present study, we show how single-crystal samples with well-controlled physical characteristics can be used to unambiguously establish the relationships among specific properties, surface chemistry and electrochemical performance, enabling rational design of better performing cathode materials. Layered Li[NixMnyCo1−x−y]O2 (NMC) crystals, with four different particle shapes of an octahedron (Oct), truncated octahedron (T-Oct), polyhedron (Poly) and platelet (Plate), were prepared to vary the presence of (104), (001) and (012) family facets on the surface. This represents the first experimental verification of NMC morphologies that were theoretically calculated in the past. Systematic studies on the impact of isolated physical properties reveal the important roles of the Ni content, particle size and facet on surface stability and electrochemical performance. We show that compared to (012) surface dominated samples, high-voltage cycling stability was much improved on the (001) dominated Plate sample, suggesting that replacing the (012) surface with lower energy (001) and/or (104) surfaces can be effective in stabilizing NMCs during high energy applications. Our study further provides insights into how tailoring a material's surface properties can be used as an important route in balancing cathode capacity and stability.