Rechargeable batteries that use energy-dense multivalent metals as anodes (such as magnesium and calcium) could represent a major step forward in the transition to a renewable energy economy. When combined with sustainable and pliable organic cathodes, multivalent metal batteries can realize their full potential.[1] While offering good reversibility, organic electrodes continue to underperform in multivalent electrolytes, especially in terms of achievable capacities. Therefore, to improve existing and design better organic materials for Mg and Ca batteries, a deeper understanding of their kinetic constraints must be obtained.

A major obstacle to detailed kinetic studies of organic materials in multivalent electrolytes is the lack of reliable electrochemical setups that would allow both galvanostatic cycling and electrochemical impedance spectroscopy measurements. This is a direct consequence of large overpotentials of multivalent metal anodes, which can lead to the impedance response of organic cathode being completely concealed by large anode response. A stable reference electrode for multivalent systems has yet to be found, and the use of alternative counter electrodes, such as activated carbon, sometimes introduces more problems for electrochemical characterization than it solves. Therefore, we propose the use of cyclable symmetric cells, where two organic electrodes are used, with one electrode fully charged and the other fully discharged.[2] By using a model compound poly(anthraquinonyl sulfide) we demonstrate the feasibility of the approach in lithium batteries. We further show that, in multivalent electrolytes, this type of symmetric cell allows access to the true performance of organic electrodes, by successfully eliminating counter-electrode contribution and enabling both rate capability and long-term cycling experiments. On top of that, cyclable symmetric cells allow reliable impedance measurements. We show how the impedance response differs in shape and magnitude when organic polymers interact with Li, Mg, and Ca species. Besides opening the doors for discovering the true limits of organic materials coupled with multivalent charge carriers, cyclable symmetric cells could improve the comparability of the results obtained in the field of multivalent-metal organic batteries by eliminating the role of the anode/electrolyte interface in the electrochemical tests.