Chitosan‐Decorated Alumina Hybrid Nanoparticles as Smart Scavengers of HF and Dissolved Transition Metals in Lithium‐Ion Batteries

Lithium-ion cells encompassing LiPF6 as the lithium salt and high-voltage (LiNi0.5Mn1.5O4, LNMO) or high-capacity (LiNi0.8Mn0.1Co0.1O2, NMC811) cathode materials are prone to transition metal (TM) dissolution caused by HF, whose formation is catalyzed by H2O traces. TM ions can shuttle to the anodic compartment, increasing the cell degradation rate. Accordingly, specific self-healing strategies are helpful to develop scavengers able to eliminate HF and absorb TM ions so avoiding their shuttling. In this work, the fabrication and test of a bi-functional, autonomous scavenging agent made of Al2O3 particles decorated is reported with chitosan. The nanometric Al2O3 core is a trap for HF by chemical bonding. The chitosan coating is acid-sensitive, and the opening of such a capping layer is triggered in the presence of even small amounts of HF, leading to an efficient TM ion-trapping. In addition, chitosan is biocompatible, biodegradable, and abundant, which is relevant for design-for-recycling scopes. With ≈200 ppm of water in the electrolyte, 12 wt% of scavenger causes, after 200 cycles at 1C, an increase of capacity retention from 73% to 88% for LNMO, and, impressively, from 46% to 84% for NMC811. This autonomous self-healing mechanism is promising for application in next-generation smart cells without requiring any external sensing.