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

TL;DR

This study investigates how moisture-induced cation exchange in LiNiO2 affects its crystal structure and electrochemical performance, revealing that H+ substitution narrows Li diffusion pathways and deteriorates rate capability.

Contribution

It provides a detailed analysis of structural changes due to Li+/H+ exchange and their impact on electrochemical properties using experimental and DFT methods.

Findings

H+ cation exchange confirmed by thermogravimetric analysis and titration.

Increased H concentration worsens low-temperature rate capability.

Cation exchange reduces lattice parameters and narrows Li-O layers, hindering Li+ diffusion.

Abstract

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.