First-Principles Study on the Interfacial Cathode-Contact Stability and Li Diffusivity of N-Doped Li6Zr2O7 for All-Solid-State Li-Ion Batteries.

Abstract

Here, N-doped Li₆Zr₂O₇ (LZON) is investigated using first-principles density functional theory (DFT) methods to evaluate its (electro)chemical stability and Li-ion transport properties for its novel design as a practical dual-use Li ionic conductor, both as a cathode-coating layer (CCL) and solid electrolyte (SE) in all-solid-state Li-ion batteries (ASSBs). Thermodynamic free energy calculations showed that LZO, as CCL and SE, is chemically stable versus most known cathode materials. Focusing on LiCoO₂ (LCO) cathode, explicit hetero-interface modeling analysis of the low-energy LCO(104)|LZO(001) interface revealed that LZO can form a strongly adhered and a low-strain contact with LCO. The electronic structure of this interface has LCO-side states (Co-3d, O-2p) occupying the highest occupied states, thereby facilitating a stable cell charging. Climbing-image nudged elastic band calculations results suggested that the LCO(104)|LZO(001) interface also has interface-normal diffusion pathways with low Li ion migration energy. Meanwhile, ab-initio- and machine-learning-based molecular dynamics simulation results confirmed that Li diffusivity in bulk LZO can be greatly enhanced by several orders of magnitude via aliovalent N-doping with Li interstitial addition. For the LCO(104)|LZON(001) interface, the N dopant is determined to energetically prefer the LZON bulk region, the corresponding interface electronic structure that can also facilitate a stable ASSB cell charging.