Anion anchored conjugated microporous polymers as solid electrolytes

Abstract

Improving the actual lithium ion conductivity and transference number of solid electrolytes has always been a bottleneck in the development of high energy density solid-state lithium-ion batteries. Chemically immobilizing anions in the solid electrolytes is the feasible method to remedy this problem. Herein, conjugated microporous polymers (CMP) with the desired designability and functionality were selected as a platform to study the correlation between anion anchor structure and solid electrolyte performance. We designed two types of anion modified CMP (denoted as CMP-SO3Li-1 and CMP-SO3Li-2) with different unit size monomers and they were explored as solid electrolytes in lithium-ion batteries. Both of them delivered high lithium ion migration number around 0.6, and CMP-SO3Li-1 with more abundant sulfonic acid anion exhibited a higher Li+ conductivity than CMP-SO3Li-2, which confirmed that the abundance of sulfonate functional groups was proportional to conductivity. Moreover, LFP|CMP-SO3Li-1|Li and LFP|CMP-SO3Li-2|Li full cells delivered a stable life over 60 cycles at 100 °C, with an initial discharge specific capacity of 143.7 mAh/g and 146.4 mAh/g, respectively. Benefit from the stable electrochemical windows over 4.6 V, CMP-SO3Li-1 also exhibited excellent cell performance with 4 V cathode in LCO|CMP-SO3Li-1|Li and NCM|CMP-SO3Li-1|Li full cells. This strategy of directly covalently riveting anions on the CMP framework has opened an avenue for the development of polymer solid electrolytes with high effective conductivity and migration number, and makes porous organic polymers as a notable potential candidate for solid electrolytes in high-temperature lithium ion batteries.