Acid-Scavenging Separators: A Novel Route for Improving Li-Ion Batteries' Durability

Autocatalytic decomposition of LiPF₆, with generation of HF and Lewis acids is the root cause for Li-ion battery (LIB) performance degradation. Acidic species promote various parasitic reactions, among which transition metal ions' dissolution and the loss of electroactive as well as transport Li⁺ have the most detrimental consequences for LIB performance. Herein we report on the performance improvements enabled by an acid-scavenging separator in cells with graphite negative and LiMn₂O₄ or LiNi_0.6Mn_0.2Co_0.2O₂ positive electrodes. After 4 weeks of cycling at 55 °C, LiMn₂O₄∥graphite and LiNi_0.6Mn_0.2Co_0.2O₂∥graphite cells with functional separators retain 100 and 43% more capacity, respectively, than cells with plain polypropylene separators. Furthermore, cells with functionalized separators have half of the interfacial impedances of cells with baseline separators, irrespective of positive electrode. The benefits afforded by acid-scavenging separators thus extend to broader classes of cell chemistries, beyond those affected mainly by manganese dissolution and loss of electroactive Li⁺ ions.