SO 3 Treatment of Lithium- and Manganese-Rich NCMs for Li-Ion Batteries: Enhanced Robustness towards Humid Ambient Air and Improved Full-Cell Performance

To increase the specific capacity of layered transition metal oxide based cathode active materials (CAMs) for Li-ion batteries such as NCMs (Li(Ni x Co y Mn z )O 2 , with x + y + z = 1), two major strategies are pursued: (i) increasing the Ni content (beyond, e.g., NCM811 with x = 0.8 and y = z = 0.1) or (ii) using Li- and Mn-rich NCMs (LMR-NCMs) which can be represented by the formula x Li 2 MnO 3 · (1−x) LiNi x Co y Mn z O 2 . Unfortunately, these materials strongly react with CO 2 and moisture in the ambient: Ni-rich NCMs due to the high reactivity of nickel, and LMR-NCMs due to their ≈10-fold higher specific surface area. Here we present a novel surface stabilization approach via SO 3 thermal treatment of LMR-NCM suitable to be implemented in CAM manufacturing. Infrared spectroscopy and X-ray photoelectron spectroscopy prove that SO 3 treatment results in a sulfate surface layer, which reduces the formation of surface carbonates and hydroxides during ambient air storage. In contrast to untreated LMR-NCM, the SO 3 -treated material is very robust towards exposure to ambient air at high relative humidity, as demonstrated by its lower reactivity with ethylene carbonate based electrolyte (determined via on-line mass spectrometry) and by its reduced impedance build-up and improved rate capability in full-cell cycling experiments.