Ionogels Based on Dynamically Cross-Linked Polyrotaxanes and Ionic Liquids for Lithium-Ion Batteries

Abstract

While liquid electrolytes are known for their inherent safety issues and solid polymer electrolytes suffer from their low ionic conductivity and high interfacial resistance at room temperature, ionogels combine the advantages of liquid electrolytes in terms of ionic conductivity and display acceptable mechanical properties compared to solid polymer electrolytes. Here, dynamically cross-linked poly(rotaxane) networks have been obtained by introducing dynamic and anion capturing centers based on boronic esters. Those networks have been further swelled by ionic liquids in order to obtain ionogels displaying superior ionic conductivities of 2.21×10− 3 S/cm at room temperature and a wide electrochemical stability window up to 4.8 V (vs. Li+/Li). In addition, those ionogels show high transference number for lithium ions because of the presence of the boron anion capturing groups. They also show the higher interfacial stability with lithium metal. When those ionogels are combined with a high voltage cathode LiNi0.6Co0.2Mn0.2O2, (NCM622), the resulting NCM622||ionogel||Li cell delivers superior discharge capacity at 0.1 C at room temperature, which is close to the theoretical capacity (170 mAh g−1) of NCM622. The cell also exhibits remarkable rate and cycling performance. This work demonstrates that the combination of ionogels and high-voltage cathode provides excellent electrochemical performance for the resulting batteries.