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

Ideal solid 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 of these criteria has remained a considerable bottleneck in the advancement of lithium metal batteries. In this study, we present a design strategy combining all of those requirements in a balanced manner to realize quasi-solid-state electrolyte-enabled Li metal batteries (LMBs). 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 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 4.4 V, excellent compatibility with Li metal electrodes, and high stability during Li deposition/stripping cycles. The high performance is attributed to charge delocalization in the backbone, mimicking the concept of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 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 quasi-solid-state electrolytes and a LiFePO cathode showed an initial capacity of 114 mAh g and 86.7% retention up to 200 cycles.