Comparative Studies of Polycrystal and Single-Crystal LiNi0.6Co0.2Mn0.2O2 in Terms of Physical and Electrochemical Performance

Abstract

Herein, the physical properties (structure, morphology, lattice strain, specific surface area, particle size, and compaction density) of polycrystal LiNi0.6Co0.2Mn0.2O2 (PC622) and single-crystal LiNi0.6Co0.2Mn0.2O2 (SC622) materials have been comparatively investigated. We have also investigated the electrochemical performance of PC622 and SC622 electrodes with different compaction densities. The results show that secondary particle collapse is widely observed in highly compacted PC622 electrodes. Moreover, the improvement in compaction density is beneficial for specific capacity and initial Coulombic efficiency. SC622 exhibits good cycling performance at room temperature (25 °C) and an elevated temperature (55 °C) even when the density increases to 3.52 g cm–3. The capacity retention values of SC622 are 86.0% (150 cycles, 1C, 25 °C) and 94.1% (100 cycles, 1C, 55 °C), which are significantly higher than PC622 (78.7 and 75.7%, respectively). Further studies via TEM on these electrodes with high compaction densities show that a thinner rock-salt phase region is found on the surface of the SC622 particles. Hence, SC622 maintains crystallite integration, excellent cycling performance, and thermal stability and can easily be manufactured into high compaction density electrodes.