  LiNiO2 has high energy density but easily 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. 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 LiNiO2
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 due to increased
activation energy of Li+ diffusion owing to cation exchange. Rietveld analysis
of X-ray diffraction and DFT calculation confirmed that the c lattice parameter
and Li-O layer reduced because of the Li+/H+ cation exchange. These results
indicate that LiNiO2 modified in the atmosphere has a narrowed Li-O layer,
which is the Li diffusion path, and the rate characteristics are degraded.
