Calcium‐ and sulfate‐functionalized artificial cathode–electrolyte interphases of Ni‐rich cathode materials

Ni‐rich lithium nickel–cobalt‐manganese oxides (NCM) are considered the most promising cathode materials for lithium‐ion batteries (LIBs); however, relatively poor cycling performance is a bottleneck preventing their widespread use in energy systems. In this work, we propose the use of a dually functionalized surface modifier, calcium sulfate (CaSO 4 , CSO), in an efficient one step method to increase the cycling performance of Ni‐rich NCM cathode materials. Thermal treatment of LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) cathode materials with a CSO precursor allows the formation of an artificial Ca‐ and SO x ‐functionalized cathode–electrolyte interphase (CEI) layer on the surface of Ni‐rich NCM cathode materials. The CEI layer then inhibits electrolyte decomposition at the interface between the Ni‐rich NCM cathode and the electrolyte. Successful formation of the CSO‐modified CEI layer is confirmed by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy analyses, and the process does not affect the bulk structure of the Ni‐rich NCM cathode material. During cycling, the CSO‐modified CEI layer remarkably decreases electrolyte decomposition upon cycling at both room temperature and 45 °C, leading to a substantial increase in cycling retention of the cells. A cell cycled with a 0.1 CSO‐modified (modified with 0.1% CSO) NCM811 cathode exhibits a specific capacity retention of 90.0%, while the cell cycled with non‐modified NCM811 cathode suffers from continuous fading of cycling retention (74.0%) after 100 cycles. SEM, electrochemical impedance spectroscopy (EIS), X‐ray photoelectron spectroscopy (XPS), and inductively coupled plasma mass spectrometry (ICP‐MS) results of the recovered electrodes demonstrate that undesired surface reactions such as electrolyte decomposition and metal dissolution are well controlled in the cell because of the artificial CSO‐modified CEI layer present on the surface of Ni‐rich NCM811 cathodes.