Multifunctional scavengers in an MOF-Al2O3-based Janus separator for high-voltage lithium batteries

Abstract

LiPF₆-based electrolytes undergo degradation when exposed to even small humidity traces, generating HF that usually causes corrosion of Ni/Mn-based cathodes (e.g. LiNi_0.5Mn_1.5O₄ spinel, LNMO) with consequent loss of transition metal (TM) ions. This phenomenon leads to detrimental phenomena responsible for the significant reduction of both capacity and lifetime of Li-based batteries. Here, a multifunctional P(VDF-HFP)-based Janus separator for smart Li batteries is developed to prevent the above-mentioned degradation phenomena. The multi-functions consist of two different scavengers for HF and H₂O, respectively. Alumina nanoparticles are used as HF trapping agents, given their ability to react with hydrofluoric acid, while a metal–organic framework (HKUST-1) is chosen as a molecular sieve for the water molecules. The Janus membrane was tested as a separator in an LNMO half-cell under harsh conditions with a water-enriched (100 ppm) electrolyte. The Janus separator exhibits significantly enhanced cycling performance, with capacity retention exceeding 90% after 200 cycles at 1C (>120 mA h g⁻¹), in contrast to the bare P(VDF-HFP) film, showing capacity retention lower than 70%. Post-cycling ICP-OES analysis revealed that the leaching of TM metal ions from the spinel lattice upon cycling is halved in the case of cells with a Janus membrane as the separator. Moreover, the synergistic effects of the two scavengers (Al₂O₃ and an MOF) in the LNMO-based cells are remarkably beneficial in terms of enhanced resistance towards thermal runaway. The Janus separator, including scavenging functions, has great potential to enhance the quality, lifetime and safety of next-generation Li-based batteries.