Affiliation:
1. Department of Chemistry and NanoScience Centre University of Jyväskylä JYU P.O.B. 35 Jyväskylä FI‐40014 Finland
2. Research Group of Battery Materials and Technologies Department of Mechanical and Materials Engineering University of Turku Vesilinnantie 5 Turku FI‐20014 Finland
3. Materials Chemistry Research Group Department of Chemistry University of Turku Henrikinkatu 2 Turku FI‐20500 Finland
Abstract
AbstractFluorenones are suitable candidates for negolytes in flow batteries, as they demonstrate the ability to store 2 electrons, and can achieve reversibility, solubility, and stability with appropriate molecular design. However, limitations persist such as the use of alkaline media, high redox potentials, and a limited scope for optimization. Herein, azoniafluorenones is reported as a novel class of negolytes. They can be readily accessed in a highly modular fashion from inexpensive commercially available materials (e.g., boronic acids). Variations in the substitution patterns reveal the 3‐substituted N‐alkylated AZON3, which demonstrates excellent solubility at neutral pH (1.64 m) with two low reversible redox potentials (−0.31 and −0.58 V vs Ag/AgCl). AZON3 exhibits high stability when evaluated at high concentration in a neutral supporting electrolyte (1 m in 3 m KCl), paired with BTMAP‐Fc on the positive side. Capacity retentions of 99.95% and 99.91% per cycle (99.35% and 99.21% per day) are achieved when cycling with 1 and 2 electrons, respectively, coupled with high volumetric capacity of 46.4 Ah L−1 (87% of capacity utilization).
Funder
Research Council of Finland
H2020 European Research Council
Luonnontieteiden ja Tekniikan Tutkimuksen Toimikunta
Turun Yliopisto