Abnormal phase-separated state of Li x Ni 0.8 Co 0.15 Al 0.05 O 2 in the first charge: Effect of electrode compaction

A planar electrochemical cell developed for operando/in situ neutron diffraction experiments at time-of-flight diffractometers was used to study a structural state of LixNi0.8Co0.15Al0.05O2 (NCA) electrodes with different degree of compaction. A two-phase-separated state of the NCA electrodes was observed in the first charge cycle. It was established that stronger compaction of the electrodes partially suppresses the phase separation of the cathode material: reduces a state of charge (SOC) range where two phases coexist, and decreases the difference between structural parameters of the phases. X-ray photoelectron spectroscopy has revealed a presence of Li2CO3 film at the surface of the NCA material in the amount that is unlikely to affect the NCA behavior during the first charge. It was suggested that the phase-separated state is caused by the morphology of the NCA material. This observation could be expanded to layered cathode materials with similar microstructures.