Insoluble polyanionic anthraquinones with two strong ionic O-K bonds as stable organic cathodes for pure organic K-ion batteries

Abstract

A new organic cathode namely potassium 2,6-dihydroxyanthraquinone (AQ26OK, theoretical capacity (CT) = 169 mA h g−1) is synthesized and fully characterized for K-ion batteries. AQ26OK is called polyanionic organic cathode because it has a polyanionic organic skeleton (−2 valent) and two strong ionic K-O bonds. Consequently, the polyanionic AQ26OK is hardly soluble into most organic liquid electrolytes. In half cells (0.3–3.4 V vs. K+/K) using 1 mol L−1 KPF6 in dimethoxyethane, AQ26OK delivers a highly stable specific capacity of 201 mA h g−1@50 mA g−1 over 450 cycles (4-month test) and realizes ~106 mA h g−1 for 3200 cycles at 500 mA g−1. Using the reduced state (K4TP) of potassium terephthalate (K2TP) as the organic anode, the resulting K4TP II AQ26OK organic potassium ion batteries can display a highly stable average discharge capacity of 135 mA h g−1cathode over 250 cycles at 100 mA g−1 and ~47 mA h g−1 for 1000 cycles at 500 mA g−1 during the working voltage of 0.01–3.1 V. To the best of our knowledge, AQ26OK is among the best stable cathodes reported for K ion batteries.