Reinforced Poly(Ionic Liquid)-in-Salt Electrolytes for Highly Stable Solid-State Lithium Metal Batteries

Abstract

Solid-state polymer electrolytes (SPEs) are promising for high-safety, high-energy-density lithium metal batteries, but their adoption is limited by low room-temperature ionic conductivity and insufficient mechanical robustness. This study reports an improved SPE architecture consisting of a three-dimensional (3D) polyacrylonitrile (PAN)–Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) fibrous skeleton infused with a polymer electrolyte ionic liquid (PIL), which promotes lithium-salt dissociation, accelerates Li⁺ transport, and enhances mechanical strength. The resulting SPE achieves an ionic conductivity of up to 0.51 mS cm⁻¹. Li|Li symmetric cells using a 40-µm-thick SPE cycle stably for 2500 h at 0.2 mA cm⁻² with a low overpotential of 30 mV. In Li|LiFePO₄ (LFP) full cells, the electrolyte enables 86.8% capacity retention after 1000 cycles at 0.5 C and maintains stable operation at 130 °C. Flexible pouch-cell tests further confirm improved safety and durability under harsh conditions, highlighting the potential of this SPE design for high-voltage lithium metal batteries.

Graphical Abstract

Keywords

Solid-state battery / Polymer-in-salt / Polymeric ionic liquids / Fibrous skeleton / Solid-state polymer electrolyte / Lithium metal

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Funding

Departament de Salut, Generalitat de Catalunya(2021SGR01581)

Severo Ochoa program from Spanish MCIN / AEI(CEX2021-001214-S)

European Regional Development Fund(IU16-014206 (METCAM-FIB))

MCIN/AEI 10.13039/501100011033(MICIU/FEDER PID2024-156765OB-C21)

Major innovation projects for integrating science, education & industry of Qilu University of Technology (Shandong Academy of Sciences)(2025ZDZX19)

China Postdoctoral Science Foundation(2026M790106)

Fundació Institució dels Centres de Recerca de Catalunya (CERCA)

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