Abstract
A zinc rechargeable battery is one of the most promising candidates of next-generation energy storage devices with some merits such as a high energy density and a low-cost material, although no zinc has been used as the negative electrode for secondary uses. This is because some dendrites are generated on the zinc electrode during charge, which causes an internal short circuit. Our recent work [1] has developed a new zinc electrode that can operate at 1 C in alkaline aqueous solutions for 5,500 cycles or more, during which the charge and discharge voltages were stable and the initial capacity was kept over 90 %. In this work, we used this robust zinc electrode in zinc-nickel secondary batteries and examined high rate performance of the cell to know the cell resistance.
The new zinc electrode used a copper plate as the current collector, on which zinc had been deposited by electroplating, and was designed so that the electrolyte was separated in some parallel zones. A nickel electrode and a 6 mol/L KOH solution containing saturated ZnO were also used to fabricate a zinc-nickel cell. The cell was operated at room temperature and the cell voltages during charge and discharge were measured. The operation was carried out with the following rate pattern: 1 C (1 min.) → 2 C (2 sec.) → 1 C (1 min.) → 4 C (2 sec.) → 1 C (1 min.) → 6 C (2 sec.) → 1 C (1 min.) → 8 C (2 sec.) → 1 C (1 min.) → 10 C (2 sec.). This pattern was repeated three times during each of discharge and charge. The capacity of the zinc electrode was calculated from the weight of deposited zinc and the C rate was further determined with the electrode's capacity. The SOC range for charge and discharge was changed to know the effects on the rate performance and the cell resistance.
The discharge voltage was stable even at 10 C and changed immediately from 1 C to 10 C or vice versa. The plots of the discharge voltage and the current density showed a linear relationship, and the cell resistance ranged from 1.0 ohm cm2 to 1.2 ohm cm2 in the SOC region between 40 % and 100 %. These results suggest that it is possible for the cell to discharge at 10 C in maximum with such a low cell resistance and respond to the rate change. The charge voltage at 2 C or 4 C was almost constant in 2 sec., while that at 6C, 8C, or 10 C changed 20 mV in maximum during the short period. The charge voltage at 1 C after 10 C charge was almost the same as that before it, indicating a quick charge response to the rate change even during charge. The charge voltage was also linear to the current density, and the cell resistance was 1.2 ohm cm2 to 1.4 ohm cm2 from the Ⅰ-Ⅴ relationship which excluded the charge voltage data suggesting hydrogen evolution. From the above results, we demonstrated that the new zinc electrode worked well in the zinc-nickel secondary cell at high rate up to 10 C and responded well to a quick change in C rate without dendrite issues.
This work was financially supported by DOWA TECHNO FUND of DOWA Holdings, Co., Ltd.
Reference
[1] T. Okumura, K. Kawaguchi, M. Morimitsu, TMS 2020, San Diego (2020).