Aluminum Borate Coating on High-Voltage Cathodes for Li-Ion Batteries

Abstract

Li-rich layered-layered nickel manganese cobalt oxides (LLNMC) of the type Li2MnO3-LiMO2 (M = Mn, Co, Ni) are promising cathode materials due to their higher specific capacities and discharge voltages compared to state of art materials. However, these materials have yet to exhibit adequate cycle life and power characteristics in practical cells, partly due to the instability of electrolytes at these high voltages. Thin coatings of inorganic materials such as Al2O3, AlPO4, and AlF3 have been shown to minimize these degradation processes, especially on high voltage cathodes. Here, we report the use of a new aluminum borate-based coating material on the LLNMC cathode at high active mass loadings. AlBO3-coated cathodes demonstrate a sevenfold increase in lifetime compared to uncoated material, as well as higher specific discharge energies vs. analogous AlPO4-coated materials. SEM and TEM confirm the thin coatings of amorphous material. Detailed electrochemical studies including Tafel polarization, PITT, and Electrochemical Impedance Spectroscopy (EIS) show that the AlBO3 coating improves the kinetics of electron transfer.