Layered Heterostructure Ionogel Electrolytes for High‐Performance Solid‐State Lithium‐Ion Batteries

Ionogel electrolytes based on ionic liquids and gelling matrices offer several advantages for solid-state lithium-ion batteries, including nonflammability, wide processing compatibility, and favorable electrochemical and thermal properties. However, the absence of ionic liquids that are concurrently stable at low and high potentials constrains the electrochemical windows of ionogel electrolytes and thus their high-energy-density applications. Here, ionogel electrolytes with a layered heterostructure are introduced, combining high-potential (anodic stability: >5 V vs Li/Li⁺ ) and low-potential (cathodic stability: <0 V vs Li/Li⁺ ) imidazolium ionic liquids in a hexagonal boron nitride nanoplatelet matrix. These layered heterostructure ionogel electrolytes lead to extended electrochemical windows, while preserving high ionic conductivity (>1 mS cm^-1 at room temperature). Using the layered heterostructure ionogel electrolytes, full-cell solid-state lithium-ion batteries with a nickel manganese cobalt oxide cathode and a graphite anode are demonstrated, exhibiting voltages that are unachievable with either the high-potential or low-potential ionic liquid alone. Compared to ionogel electrolytes based on mixed ionic liquids, the layered heterostructure ionogel electrolytes enable higher stability operation of full-cell lithium-ion batteries, resulting in significantly enhanced cycling performance.