Organic fast ion-conductor with ordered Li-ion conductive nano-pathways and high ionic conductivity for electrochemical energy storage

Solid electrolyte (SE) is the most crucial factor to fabricate safe and high-performance all-solid-state lithium-ion batteries. However, the most commonly reported SE, including solid polymer electrolyte (SPE) and inorganic oxides and sulfides, suffer problems of low ionic conductivity at room temperature for SPE and large interfacial impedance with electrodes for inorganic electrolytes. Here we for the first time demonstrate a novel ionic plastic crystal lithium salt solid electrolyte (OLiSSE) fast ion-conductor dilithium (1,3-diethyl-4,5-dicarboxylate) imidazole bromide with ordered Li-ion conductive nanopathways and an exceptional ionic conductivity of 4.4 × 10−3 S cm−1 at 30 °C. The prepared OLiSSE exhibits apparent characters of typical ionic plastic crystals in the temperature range of −20 to 70 °C, and shows remarkable thermal stability and electrochemical stability below 150 °C and 4.7 V, respectively. No lithium dendrite or short circuit behavior is detected for the Li|OLiSSE|Li cell after the galvanostatic charge-discharge test for 500 h. The fabricated Li|OLiSSE|LiFePO4 all-solid-state cell without using any separator and liquid plasticizer directly delivers an initial discharge capacity of 151.4 mAh g−1 at the discharge rate of 0.1 C, and shows excellent charge-discharge cycle stability, implying large potential application in the next generation of safe and flexible all-solid-state lithium batteries.