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

Abstract

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 (CaSO4, CSO), in an efficient one step method to increase the cycling performance of Ni-rich NCM cathode materials. Thermal treatment of LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode materials with a CSO precursor allows the formation of an artificial Ca- and SOx-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.