Improving structural and thermal stability of LiNi0.8Co0.15Al0.05O2 by a fast-ionic-conductive LiAlSiO4 surface coating for Li-ion batteries. (10th August 2021) - Seenivasan, Manojkumar
Research Highlights: Ni0.8 Co0.15 Al0.05 (OH)2 was synthesized and its surface was successfully modified by LiAlSiO4 . The coated samples were extensively investigated through in situ XRD, thermal calorimetry, GITT, and EIS. In-situ XRD studies revealed that the LASO@NCA cathodes better withstood the mechanical stress during long cycling. LASO@NCA delivered excellent cyclability, rate capability, produced less heat. Surface coating inhibits side reactions and formation of residues on NCA during cycling. Abstract: In this study, we prepared Ni-rich Li[Ni0.8 Co0.15 Al0.05 ]O2 (NCA) as a cathode material for lithium-ion batteries (LIBs) through co-precipitation in a Taylor flow–assisted continuous reactor, and then using a wet-chemical process to coat the NCA with LiAlSiO4 (LASO). In situ X-ray diffraction, scanning electron microscopy, and transmission electron microscopy are used to characterize the structures and morphologies of the pristine and LASO-coated NCA materials. Relative to the pristine NCA, the LASO-coated NCA exhibited greater electrical conductivity and higher diffusivity of Li + ions and, thereby, improved cycling stability. Among our samples, the NCA coated with 1 wt.% LASO displays optimal electrochemical performance. The initial discharge capacity of pristine and 1 wt% coated LASO samples are, 198.9 and 194.1 mAh g −1 with columbic efficiencies of 87.6 and 90.2%, respectively. The capacity retention for LASO-coated material at 1 C (200 mA g –1 ) after 100 cycles is 91.2% at room temperature and 68.1% at 55 °C; for the pristine NCA, they are 73.2 and 37.4%, respectively. The coating effectively decreases anisotropic mechanical stress and, thus, prevents the formation of micro-cracks on the secondary particle surface. Electrochemical impedance spectroscopy and cyclic voltammetry reveal that the improvement in the electrochemical performance originates from lower surface impedance and higher Li + ion diffusivity. Furthermore, the thermal properties, measured using a multiple-module micro-calorimeter, reveals that the coated electrodes exhibited markedly lower heat-generated flux when cycled; post-mortem analysis after long-term cycling reveals that the amorphous LASO coating markedly inhibits any morphological changes to the structure, acts as relatively stable protective barriers, and provides pathways for rapid Li + ion diffusion. Thus, our LASO-modified NCA cathode materials appear to be promising candidates for application in high-energy-density LIBs. Graphical Abstract: Image, graphical abstract