All-Solid-State Rechargeable Air Batteries Using Redox Active Naphthoquinone in the Negative Electrode
Authors: Wada Suguru , Miyatake Kenji 
Published: December 2024

Typical air batteries are composed of metallic negative electrode, liquid electrolyte, and gas (oxygen) diffusion positive electrode. The use of metals often causes dendrite growth, which deteriorates the durability of the air batteries similar to the secondary batteries. The liquid electrolyte poses the risk of leakage, limiting application of air batteries to small devices. Recently, air batteries that use organic redox molecules as the negative electrode have been explored. This type of emerging air batteries can be charged/discharged by the redox reactions of the organic molecules associated with protons.
We have recently succeeded in developing an all-solid-state rechargeable air batteries (SSAB) combining a redox-active organic molecule as negative electrodes and a proton-conductive polymer membrane as solid electrolyte. We initially focused on 2,5-dihydroxy-1,4-benzoquinone (DHBQ) as the redox-active molecule and commercial Nafion as the solid electrolyte1 (Fig. 1a and b) to fabricate an SSAB. For improving the capacity and cyclability, polymeric DHBQ was also used. In the present study, the principle of SSAB was further verified with other redox-active organic molecules.
1,4-Naphthoquinone (NQ) was used for the negative electrode, which is known to undergo reversible redox reaction via two electrons / two protons transfer process (Fig. 2a). Nafion or a hydrocarbon-based polymer electrolyte membrane (SPP-QP)2 developed at the University of Yamanashi was used as the solid electrolyte (Fig. 2b). Pt/CB (TEC10E50E, Tanaka Kikinzoku) or Pt/GCB catalyst (TEC10EA50E, Tanaka Kikinzoku) was used for the oxygen electrode. NQ, carbon powder (Ketjen black, Tanaka Kikinzoku) and Nafion were used for the inks to be used for the negative electrode. The ink was sprayed onto one side of the electrolyte membrane. The ink for the oxygen electrode composed of Pt/CB or Pt/GCB and Nafion. was similarly sprayed onto the other side of the membrame to obtain catalyst-coated membrane (CCM). SSAB was tested at a cell temperature of 40 °C and 100% RH. Cyclic voltammograms (CV) were obtained at a scan rate of 20 mV s-1 and all charge-discharge cycling tests were performed at 15 C rate.
The redox potential of the negative electrode observed in the CV measurements was 0.47 V (vs RHE) for DHBQ and 0.34 V (vs RHE) for NQ, indicating that NQ with a lower redox potential could provide higher electromotive force. Fig. 3 shows the charge-discharge curves of SSABs, in which DHBQ or NQ was used as the negative electrode. The SSAB-DHBQ had an open circuit voltage of 0.80 V, a discharge capacity of 73 mAh g-1, and a Coulomb efficiency of 58%, while the SSAB-NQ had an open circuit voltage of 0.88 V, a discharge capacity of 78 mAh g-1, and a Coulomb efficiency of 85%. Replacing Nafion with the SPP-QP membrane resulted in improved Coulomb efficiency (98%) since SPP-QP was much less permeable than Nafion and thus suppressed oxygen permeation to the negative electrode.

Acknowledgement

This work was partly supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan, through Grants-in-Aid for Scientific Research (KAKENHI 23H02058).

References

1) M. Yonenaga, Y. Kaiwa, K. Oka, K. Oyaizu, K. Miyatake, Angew. Chem. Int. Ed., 62, e202304366(2023).
2) J. Miyake, R. Taki, T. Mochizuki, R. Shimizu, R. Akiyama, M. Uchida, K. Miyatake, Sci. Adv., 3, eaao0476 (2017).

Figure 1