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

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. Li_1-xH_xNiO₂ 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.