Enhanced electrochemical lithium storage activity of LiCrO₂ by size effect

Cr₈O₂₁ was chemically lithiated using a lithium-biphenyl-dimethoxyethane solution. Lithiated Cr₈O ₂₁ shows a structure in which as-formed LiCrO₂ units are sandwiched between Cr₂O₃ superlattice layers. Chemically lithiated Cr₈O₂₁ shows a delithiation capacity of 200 mAh g^-1. It means that LiCrO₂ units in lithiated Cr ₈O₂₁ are electrochemically active. This finding is opposite to previous reports that LiCrO₂ materials have very poor Li-storage capacities. Our new result implies that LiCrO₂ with extremely small domain size could show enhanced reactivity. This proposal is proved unambiguously by the fact that LiCrO₂ powder materials with smaller grain size (<20 nm) show much higher capacities than LiCrO ₂ materials with larger grain size (>50 nm). In addition, it is found that the cation mixing is more significantly in LiCrO₂ materials with smaller grain size, which seems a key factor for the storage and transport of lithium in layered Cr-based materials. The cation mixing may also explain the result that the lattice parameters of LiCrO₂ do not change significantly upon lithium extraction and insertion, investigated by in situ and ex situ XRD techniques.