Polyimide covalent organic frameworks as efficient solid-state Li+ electrolytes

Covalent organic frameworks (COFs) are attractive porous crystalline materials with extremely high stability, easy functionalization, and open channels, which are expected to be unique ion conductors/transporters in lithium ion batteries (LIBs). Despite recent advances, low ion conductivity and low transference number, resulting in low charging/discharging rate, low energy density, and short battery life, are the main issues that limit their direct application as solid electrolytes in LIBs. Here, we designed and synthesized a novel polyimide COF, namely, TAPA-PDI-COF, with abundant C=O groups, which has been successfully employed as high-performance solid electrolytes by doping TAPA-PDI-COF and succinonitrile (SN). Both the well-defined nanochannels of COFs and SN confined in the well-aligned channels restricted the free migration of anions, while C=O on COFs and CN groups of SN enhanced Li+ transport, thus achieving a high ion conductivity of 0.102 mS cm(-1) at 80 degrees C and a high lithium-ion transference number of 0.855 at room temperature. According to density functional theory (DFT) calculations, Li-ion migration mainly adopted in-plane transport rather than the axial pathway, which may be due to the shorter hopping distances in the planar pathway. The results suggest an effective strategy for the design and development of all-solid-state ionic conductors for achieving high-performance LIBs.