Charge-Delocalized Triptycene-Based Ionic Porous Organic Polymers as Solid Electrolytes for Lithium Metal Batteries

Abstract Ideal solid-state electrolytes for lithium (Li) metal batteries should conduct Li + rapidly with low activation energy, exhibit a high Li + transference number, form a stable interface with the Li anode, and be electrochemically stable. However, the lack of solid electrolytes that meet all these criteria has remained a considerable bottleneck in the advancement of lithium metal batteries. In this study, we present a design strategy combining all those requirements in a balanced manner. We prepared Li + -coordinated triptycene-based ionic porous organic polymers (Li + @iPOPs). The Li + @iPOPs with imidazolates and phenoxides exhibited a high conductivity of 4.38 mS cm −1 at room temperature, a low activation energy of 0.627 eV, a high Li + transference number of 0.95, a stable electrochemical window of up to 4.6 V, excellent compatibility with Li metal electrodes, and high stability during Li deposition/stripping cycling. The high performance can be attributed to charge delocalization in the backbone, which facilitates the diffusion of coordinated Li + through the porous space of the triptycene-based iPOPs. In addition, Li metal batteries assembled using Li + @Trp-Im-O-POPs as the solid electrolyte and a LiFeO 4 cathode showed an initial capacity of 114 mAh g −1 and retained 86.7% of the capacity after 200 cycles.