Electrochemical Properties and Crystal Structure of Li+/H+Cation-Exchanged LiNiO2

Abstract

LiNiO2 has high energy density but readily reacts with moisture in the atmosphere and deteriorates. We performed qualitative and quantitative evaluations of the degraded phase of LiNiO2 and the influence of the structural change on the electrochemical properties of the phase. The formation of the Li1-xHxNiO2 phase with cation exchange between Li+ and H+ was confirmed by thermogravimetric analysis and Karl Fischer titration measurement. As the H concentration in Li1-xHxNiO2 increased, the rate capability deteriorated, especially in the low-temperature range and under low state of charge. Experimental and density functional theory (DFT) calculation results suggested that this outcome was attributed to an increased activation energy of Li+ diffusion because of cation exchange. Rietveld analysis of X-ray diffraction and DFT calculation confirmed that the c lattice parameter and Li-O layer decreased because of the Li+/H+ cation exchange. These results indicate that LiNiO2 reacting with moisture in the atmosphere has a narrowed Li-O layer, which is the Li diffusion path, and the rate characteristics are degraded.