Ionogel electrolyte based on porous graphitic C3N4 nanosheets for room temperature to 150 °C quasi-solid-state lithium batteries

Abstract

Ionogels, generally formed by immobilizing ionic liquids (ILs) with polymer gelators, hold considerable promise as quasi-solid-state electrolytes (QSSEs) for lithium metal batteries (LMBs) due to their high safety and electrode compatibility. However, their practical use in high-temperature LMBs suffers from the softened polymer chains of gelator at high temperatures, leading to liquid leakage and severe growth of Li dendrite. Here, a novel inorganic ionogel (PCNIL) combining lithium salt-containing IL with porous graphitic carbon nitride nanosheets (PCN) is developed through direct physical mixing. PCNIL exhibits a superior ionic conductivity (0.75 mS cm⁻¹) at room temperature similar to that of neat IL electrolyte (Li-IL) and a Li⁺ transference number (0.56) greatly higher than that of Li-IL (0.20). Furthermore, PCNIL maintains a temperature-independent shear storage modulus of up to 5 MPa from room temperature to 150 °C. Consequently, the Li|PCNIL|Li symmetrical cell demonstrates extended reversible lithium plating/stripping over 1200 h without dendritic growth. The robust mechanical strength, excellent thermal stability, and electrochemical stability of PCNIL allow Li|PCNIL|LiFePO₄ cells to operate stably in a wide temperature range of 25–150 °C.