Electrolyte-affinitive porous separators enabled by nitrile integration and polymerization-induced phase separation for stable lithium metal batteries

Abstract

Achieving long-term stability in lithium metal batteries (LMBs) requires separators that combine mechanical robustness, electrolyte wettability, and interfacial compatibility. Here, we report a porous separator, termed PHBA, fabricated via a one-step, environmentally benign polymerization-induced phase separation (PIPS) process. PHBA is constructed from three functional acrylate monomers: 1,6-hexanediol diacrylate (HDDA) for mechanical stiffness, butyl acrylate (BA) for elasticity, and acrylonitrile (AN) for electrolyte affinity. This synergistic monomer design yields a tunable, interconnected porous network that promotes uniform Li⁺ flux and fast ion transport. AN incorporation markedly improves wettability, enabling complete electrolyte spreading and absorption and resulting in a high ionic conductivity of 1.41 mS cm⁻¹. In Li/Li symmetric cells, PHBA supports stable lithium plating and stripping for over 775 h with low overpotential. In Li/NCM811 full cells, PHBA retains 65.1% capacity after 200 cycles at 2C, outperforming a commercial polyethylene (PE) separator (43.2%). Under elevated temperature (1C, 60 °C), PHBA maintains 85.6% capacity after 100 cycles, whereas PE retains only 46.9%. Post-mortem analyses reveal suppressed dendrite growth and improved interfacial contact with a stable LiF-rich solid electrolyte interphase. These results demonstrate that rational monomer selection combined with controlled phase separation enables multifunctional separators for stable LMBs.