Facet-Dependent Rock-Salt Reconstruction on the Surface of Layered Oxide Cathodes

Abstract

The surface configuration of pristine layered oxide cathode particles for Li-ion batteries significantly affects the electrochemical behavior, which is generally considered to be a thin rock-salt layer in the surface. Unfortunately, aside from its thin nature and spatial location on the surface, the true structural nature of this surface rocksalt layer remains largely unknown, creating the need to understand its configuration and the underlying mechanisms of formation. Using scanning transmission electron microscopy, we have found a correlation between the surface rock-salt formation and the crystal facets on pristine LiNi 0.80 Co 0.15 Al 0.05 O 2 primary particles. It is found that the originally (014̅ ) and ( 003) surfaces of the layered phase result in two kinds of rock-salt reconstructions: the (002) and (111) rock-salt surfaces, respectively. Stepped surface configurations are generated for both reconstructions. The (002) configuration is relatively flat with monatomic steps while the (111) configuration shows significant surface roughening. Both reconstructions reduce the ionic and electronic conductivity of the cathode, leading to a reduced electrochemical performance.

There and Back Again—The Journey of LiNiO2 as a Cathode Active Material

“…Although there is no doubt about the decomposition of the LNO surface to yield a rock salt‐type phase, the characterization of its structure is challenging and the exact Li/Ni ratio is mostly unknown. This is significant because the properties of rock salt Li δ Ni 1− δ O strongly depend on the Li concentration.…”

Hin und zurück – die Entwicklung von LiNiO2 als Kathodenaktivmaterial

“…Obwohl es keinen Zweifel an der Zersetzung der LNO‐Oberfläche zu einer steinsalzartigen Phase gibt, ist die Charakterisierung ihrer Struktur anspruchsvoll, und das genaue Li/Ni‐Verhältnis ist meist unbekannt. Das genaue stöchiometrische Verhältnis ist von Bedeutung, da die Eigenschaften der Steinsalzphase Li δ Ni 1− δ O stark von der Li‐Konzentration abhängen.…”

Surface regulation enables high stability of single-crystal lithium-ion cathodes at high voltage

“…To solve the deficiencies caused by different reasons, creative strategies are necessary to improve structural stability in NCM particles 15 . Ideal methods should be able to simultaneously tune structural and morphological characteristics to restrict both structural failure and intragranular cracks 13,16,17 .…”