Amorphous Metal Fluorides Coatings By Atomic Layer Deposition for Stable Li-Ion Batteries
In order to reduce the unfavorable side reactions in Li-ion batteries, ultrathin metal oxides such as Al2O3, LiAlO2, and LiTaO3, deposited by atomic layer deposition, have been demonstrated [1,2] to significantly enhance both stability and safety of electrodes. However, metal oxide coatings are likely to be susceptible to hydrofluoric acid (HF) attack upon electrochemical cycling. Metal fluorides may be suitable alternatives for electrode coating materials due to their stability against HF attack and the strong bonding between metals and fluorine.
Here we report the atomic layer deposition of complex fluorides such as AlxWyFz and MgxWyFz utilizing WF6 as the source of both fluorine and the high valence metal with Al(CH3)3 (TMA) and Mg(Cp)2 . In-situ quartz crystal microbalance studies were performed during the deposition of these chemistries and in both cases the QCM data showed self-limiting, linear growth. Films were prepared at 200oC and the deposited layers of AlxWyFz and MgxWyFz were found to be x-ray amorphous in nature. SEM EDAX elemental mapping of these layers, deposited in high aspect ratio trenches, showed uniform and conformal distributions of the various elements within the films, Figure 1. We have used ~1 nm layers of AlxWyFz and MgxWyFz materials in an effort to improve the performance of a model Li-ion battery cathode, LiCoO2 . This presentation will present the results of ALD of these materials, characterization, and Li-ion battery stability tests.
(1) Jung, Y. S.; Cavanagh, A. S.; Dillon, A. C.; Groner, M. D.; George, S. M.; Lee, S.-H. Journal of The Electrochemical Society 2010, 157, A75.
(2) Park, J. S.; Meng, X.; Elam, J. W.; Hao, S.; Wolverton, C.; Kim, C.; Cabana, J. Chemistry of Materials 2014.
(3) Li, X.; Liu, J.; Banis, M. N.; Lushington, A.; Li, R.; Cai, M.; Sun, X. Energy & Environmental Science 2014, 7, 768.
(4) Anil U. Mane, and Jeffrey W. Elam, ALD (2014), Kyoto, Japan
(5) Park J. S, Mane A. U, Elam J. W., Croy J. R., Submitted to Chemistry of Materials