Beneficial Effects of Oxide-Based Additives on Li-and Mn-rich Cathode Active Materials

Abstract

Li- and Mn-rich layered oxides such as Li1.14(Ni0.26Co0.14Mn0.60)0.86O2 (LMR-NCM) are potential next-generation cathode active materials (CAMs) for lithium ion-batteries, promising an increased energy density at lower materials costs compared to state-of-the-art CAMs. However, its commercial viability is still inhibited by its strong gassing, poor cycling stability, and voltage fading, so various approaches such as post-treatments or additives are being investigated. Here, it will be shown that the cycling performance of LMR-NCM//graphite coin-cells is drastically improved when assembled with 300 °C dried glassfiber (GF) separators (“GF-cells”) compared to cells with Celgard (CG) separators dried at 70 °C (“CG-cells”). The origin of this phenomenon is investigated by online electrochemical mass spectrometry (OEMS), TGA-MS, water absorption, and XPS measurements. These reveal that the superior performance of the GF-cells can be ascribed to the bulk water absorption capability of the 300 °C dried glassfiber material as well as its ability to scavenge HF, whereby H2O and HF are produced by the (electro)chemical oxidation of the electrolyte and the decomposition of the LiPF6 salt. Similar performance enhancements can be observed for 300 °C dried SiO2 nanoparticles added to the LMR-NCM cathodes or for an HF/H+ scavenging electrolyte additive.