Full Organic Aqueous Battery Based on TEMPO Small Molecule with Millimeter-Thick Electrodes

Thick electrodes with sodium and even anion intercalation organic compounds integrated in a neutral-pH aqueous battery offer unique advantages in terms of round trip efficiency, environmental impact, and scalability for off- or on-grid renewable energy storage. Herein, we report the first anion-rocking chair/dual-ion organic battery. The latter reaches 35 Wh/kgmaterials at a C/8 rate. It shows remarkable cyclability and coulombic efficiency in a cheap and neutral NaClO4 electrolyte pouch cell with highly loaded millimeter-thick electrodes (5 mAh/cm2). This achievement is based on a thorough study of a commercial 2,2,6,6-tetramethylpiperidinyl-N-oxyl (TEMPO) (TEMPO) benzene derivative, namely, 4-hydroxy TEMPO benzoate, and its naphthalene analog (4-carboxy TEMPO naphthalate) as positive electrode materials and a bipyridinium–naphthalene oligomer as the negative electrode. Combined UV–vis spectroelectrochemistry and operando X-ray diffraction account for the much improved cyclability of the hydrophobic 4-carboxy TEMPO naphthalate at the expense of a lower specific capacity. This trend is reversed in the case of the 4-hydroxy TEMPO benzoate derivative. Results show that the kinetic limitations of 4-hydroxy TEMPO benzoate are associated with the surrounding composite electrode, whereas inner-grain ionic and/or electronic transports play a decisive role for 4-carboxy TEMPO naphthalate.