Effects of Electrolyte Flow Speed on the Performance of Zn-Ni Single Flow Batteries†

doi:10.7503/cjcu20130340

Abstract

Abstract:

The effects of current density, zinc deposition area capacity and electrolyte flow speed on the performance of Zn-Ni single flow batteries and zinc deposition morphology were investigated by electrochemical measurements combined with SEM observation and XRD analysis. The results show that the zinc deposition area capacity is the most important factor which influences the charge-discharge performance of Zn-Ni single flow batteries and zinc deposition morphology. The electrolyte flow speed should be neither high nor low. With the zinc deposition area capacity increasing, the charge-discharge efficiency and the cycling stability of test cells are more sensitive to the change of current density. Meanwhile, the preferable electrolyte flow speed range becomes narrow. The spongy zinc deposition is exhibited at zinc deposition area capacity beyond 25 mA·h/cm². But, at low zinc deposition area capacity and low electrolyte flow speed, the spongy zinc deposition is relatively uniform and compact. While, at higher zinc deposition area capacity, clusters and particles turn into larger and their irregularity is more serious. Only at the moderate electrolyte flow speed of 7.1 L/min, the zinc deposition is partly compact and regular and the preferable charge-discharge performance of the cell is exhibited.

Key words: Zn-Ni single flow battery, Zinc electro-deposition, Electrolyte flow speed, Zinc deposition area capacity, Charge-discharge performance

CLC Number:

O646.1

TrendMD:

SONG Shiye, PAN Junli, WEN Yuehua, CHENG Jie, PAN Junqing, CAO Gaoping. Effects of Electrolyte Flow Speed on the Performance of Zn-Ni Single Flow Batteries^†[J]. Chem. J. Chinese Universities, 2014, 35(1): 134.

Figures/Tables 8

Fig.1 Sketch map of single flow zinc-nickle cell

Fig.2 Charge-discharge efficiency vs. cycle number of test cells at a zinc deposition area capacity of 25 mA·h/cm2 Electrolyte flow speed/(L·min-1): (A) 2.9; (B) 7.1; (C) 9.2; (D) 10.0. Current density/(mA·cm-2): ■ □ 15; ● ○ 20; ▲ △ 25.

Fig.3 Charge-discharge efficiency vs. cycle number of test cells at a zinc deposition area capacity of 30 mA·h/cm2 Electrolyte flow speed/(L·min-1): (A) 2.9; (B) 4.7; (C) 9.2; (D) 10.0. Current density/(mA·cm-2): ■ □ 15; ● ○ 20; ▲ △ 25.

Fig.4 Charge-discharge efficiency vs. cycle number of test cells at the zinc deposition area capacity of 35 mA·h/cm2 Electrolyte flow speed/(L·min-1): (A) 2.9; (B) 7.1; (C) 9.2; (D) 10.0. Current density/(mA·cm-2): ■ □ 15; ● ○ 20; ▲ △ 25.

Fig.5 Variation of the average energy efficiency of batteries for 20 cycles at different zinc deposition area capacity and current density with electrolyte flow speed Area capacity of zinc deposition/(mA·h·cm-2): (A) 25; (B) 30; (C) 35. Current density/(mA·cm-2): ■ 15; ○ 20; ▲ 25.

Fig.6 Variation of average coulombic and energy efficiencies of test cells for 20 cycles with the zinc deposition area capacity at the electrolyte flow speed of 7.1 L/min and current density of 20 mA/cm2

Fig.7 Effects of electrolyte flow speed and deposition area capacity on the photographs(A—D) and SEM images(A'—D') of zinc deposits at current density of 20 mA/cm2 Deposition area capacity/(mA·h·cm-2): (A), (A'), (B), (B') 25; (C), (C'), (D), (D') 35. Electrolyte flow speed/(L·min-1): (A), (A'), (C), (C') 7.1; (B), (B'), (D), (D') 10.0.

Fig.8 XRD patterns of zinc deposits obtained at different electrolyte flow speed and deposition area capacityDeposition area capacity/(mA·h·cm-2): a, c. 25; b, d. 35. Electrolyte flow speed/(L·min-1): a, c. 7.1; b, d. 10.0.

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