Xiangbo Meng1,Xin Wang1
University of Arkansas1
Due to its high capacity and low cost, LiNi<sub>0.8</sub>Mn<sub>0.1</sub>Co<sub>0.1</sub>O<sub>2 </sub>(NMC811) is considered as the next promising cathode for commercial lithium-ion batteries. However, it is still suffering from serious performance degradation and safety hazard before large-scale commercialization. These existing issues are usually reflected as cation mixing, oxygen evolution, irreversible phase transition, transition metal ion dissolution, and microcracking. Aimed at addressing these problems, surface coating has been proven to be a widely accepted and effective approach. Among a variety of coating methods, atomic layer deposition (ALD) has emerged as a unique tool to deposit uniform and conformal coatings over NMCs, which have shown remarkable effects on improving battery performance.<sup>1-4</sup> Herein, for the first time we deposited ultrathin sulfide ALD coatings<sup>5</sup> over NMC811 composite electrodes. It was found that the sulfide coatings enable to noticeably enhance the cyclability and rate capability of NMC811 cathodes. To clarify the effects of the ALD sulfide coatings, we utilized a suite of characterization techniques, and the results revealed that the sulfide coatings can perfectly maintain the NMC structure during long cycling, consequently suppressing the crack formation. Furthermore, the sulfide layer has been verified to react with trace H<sub>2</sub>O in electrolyte and O<sub>2</sub> released from the NMC structure, forming oxidized sulfide layers. In addition, the measurements of electrochemical impedance spectroscopy confirms that the sulfide coatings physically protect the NMC surface from the electrode/electrolyte interfacial reactions. Based on our results, it can be foreseen that sulfides would be a new class of coating materials for addressing NMC issues. <br/><br/><b>References:</b><br/><b>1. </b>Meng, X.; Yang, X. Q.; Sun, X. L., <i>Advanced Materials </i><b>2012,</b> <i>24</i> (27), 3589-3615.<br/><b>2. </b>Liu, Y.; Wang, X.; Cai, J.; Han, X.; Geng, D.; Li, J.; Meng, X., <i>Journal of Materials Science & Technology </i><b>2020,</b> <i>54</i>, 77-86.<br/><b>3. </b>Wang, X.; Cai, J.; Liu, Y.; Han, X.; Ren, Y.; Li, J.; Liu, Y.; Meng, X., <i>Nanotechnology </i><b>2020,</b> <i>32</i> (11), 115401.<br/><b>4. </b>Gao, H.; Cai, J.; Xu, G.-L.; Li, L.; Ren, Y.; Meng, X.; Amine, K.; Chen, Z., <i>Chem. Mater. </i><b>2019,</b> <i>31</i> (8), 2723-2730.<br/><b>5. </b>Meng, X.; Comstock, D. J.; Fister, T. T.; Elam, J. W., <i>ACS Nano </i><b>2014,</b> <i>8</i> (10), 10963-10972.