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

Li- and Mn-rich layered oxides such as Li_1.14(Ni_0.26Co_0.14Mn_0.60)_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.