Ex-situ EPR approach to explore the electrochemical behaviour of Arylboron-Linked conjugated microporous polymer cathode

Abstract

Electron paramagnetic resonance (EPR) spectroscopy is an important technique to probe the evolution of organic radicals during battery charging and discharging. Herein, we co-polymerize arylboron units and anthraquinone groups into a new organic electrode material, B-AQ, which has both the material characteristics of a conjugated microporous polymer and the special electronic properties of arylboron units and exhibits excellent thermodynamic stability and electrochemical properties. The experimental results show that the B-AQ cathode has fast charging/discharging capability at high current density and remarkable long cycle performance with very low capacity decay of 0.004 % per cycle over 2000 cycles. Adequate EPR method reveals the charging and discharging mechanism of the B-AQ electrode, i.e., the anthraquinone units gradually undergo anthraquinone radical species and enol lithium salt intermediates. In addition, comparative test studies show that inert gas protection of the discharge products in ex-situ EPR tests is necessary. This work will expand the research and application direction of boron-containing polymers and also provides an effective way to explore the reaction processes in organic lithium-ion batteries.