Triphase Heterogeneous Electrocatalysts of Ni and Co for High-Performing Li-O2 Batteries.

Abstract

The limited energy density of the current Li-ion batteries restricts the electrification of transportation to small- and medium-scale vehicles. On the contrary, Li-O2 batteries (LOBs), with their significantly higher theoretical energy density, can power heavy-duty transportation, if the sluggish electrode kinetics in these devices can be substantially improved. The use of solid electrocatalysts at the cathode is a viable strategy to address this challenge, but current electrocatalysts fail to provide sufficient discharge depths and cyclability, primarily due to the formation of the film-like discharge product, Li₂O₂, on catalytic sites, which obstructs charge transport and gas diffusion pathways. Here, we report that a triphase heterogeneous catalyst comprising NiCoP, NiCo2S4, and NiCo2O4, assembled into a hierarchical hollow architecture (NC-3@Ni), efficiently modulates the morphology and orientation of the discharge product, facilitating the sheet-like growth of Li2O2 perpendicular to the cathode surface. These modifications enable the assembled LOB to deliver a high discharge capacity of 25 162 mAh g−1 at 400 mA g−1, along with impressive cycling performance, achieving 270 cycles with a discharge depth of 1000 mAh g−1, exceeding 1350 h of continuous operation. This promising performance is attributed to the presence of individual electrophilic and nucleophilic phases within the heterogeneous microstructure of the triphase catalyst, collectively promoting the formation of sheet-like Li2O2.