Synthesis of LiNiO2 at Moderate Oxygen Pressure and Long-Term Cyclability in Lithium-Ion Full Cells.

Abstract

The widespread adoption of electric vehicles necessitates higher-energy-density and longer-life cathode materials for Li-ion batteries. LiNiO2 offers a higher energy density at a lower cost than other high-Ni-content cathodes containing additional transition-metal ions. However, detrimental phase transformations and impedance growth, resulting from structural defects formed during synthesis, lead to poor cyclability and limit the practical viability of LiNiO2. Herein, we demonstrate a considerably improved cycle life for LiNiO2 by synthesizing it under a pressurized oxygen environment. The capacity retention in pouch-type full cells with a graphite anode after 1000 cycles is increased from 59 to 76% by applying a mere 1.7 atm of oxygen pressure during the synthesis of LiNiO2. With iodometric titration and inductively coupled plasma optical emission spectroscopy analysis, we provide clear evidence that oxygen pressure during synthesis reduces the occurrence of lattice oxygen vacancies and increases the content of Ni3+ in LiNiO2, improving its structural integrity and cyclability. Post-mortem analysis of the cycled cathodes provides insights into the sources of degradation occurring during long-term cycling. This work demonstrates a practically viable, synthetic approach combined with doping and coating to achieve improved performance with high-Ni layered oxide materials. Furthermore, this work represents the first report of extended cycling of LiNiO2 in pouch full cells with graphite anode and will, therefore, serves as an important benchmark for future research on LiNiO2.