Combined operando and ex-situ monitoring of the Zn/electrolyte interface in Zn-ion battery systems

Pornnapa Phummaree; Manaswee Suttipong; Theeraboon Jaroonsteanpong; Catleya Rojviriya; Rojana Pornprasertsuk; Soorathep Kheawhom; Jitti Kasemchainan

doi:10.1016/j.heliyon.2023.e18638

Combined operando and ex-situ monitoring of the Zn/electrolyte interface in Zn-ion battery systems

Heliyon. 2023 Jul 27;9(8):e18638. doi: 10.1016/j.heliyon.2023.e18638. eCollection 2023 Aug.

Authors

Pornnapa Phummaree¹, Manaswee Suttipong^{1

2}, Theeraboon Jaroonsteanpong¹, Catleya Rojviriya³, Rojana Pornprasertsuk^{2

4

5}, Soorathep Kheawhom^{5

6}, Jitti Kasemchainan^{1

2

5}

Affiliations

¹ Department of Chemical Technology, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand.
² Center of Excellence on Petrochemical and Materials Technology, 7th floor, Chulalongkorn University Research Building, Soi Chula, 12, Phayathai Rd, Bangkok, 10330, Thailand.
³ Synchrotron Light Research Institute (Public Organization), Nakhon Ratchasima, 30000, Thailand.
⁴ Department of Material Science, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand.
⁵ Center of Excellence on Advanced Materials for Energy Storage, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand.
⁶ Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok, 10330, Thailand.

Abstract

Operando optical microscopy enables imaging at the interface between the Zn electrode and the electrolyte of 1 M ZnSO₄(aq) in the symmetrical Zn/Zn cells assembled as the pouch cells with the mechanical load of 0.8 MPa. The imaging was executed during cycling of Zn plating and stripping at the different current densities of 0.5, 1.0, 2.0, and 4.0 mA cm^-2, and the areal capacity of 2 mAh·cm^-2. When the current densities are below 4.0 mA cm^-2, no intense Zn dendrites are observed. However, at 4.0 mA cm^-2, the severe Zn dendrites can penetrate through the separator and cause short-circuiting. From the electrochemical perspective, the voltage profile of such system drops to almost zero volt. Both operando optical and ex-situ synchrotron X-ray imaging further prove the appearance of the Zn dendrites. By Raman spectroscopy and X-ray diffraction, the cycled Zn electrode surface contains passivation species of Zn₄(OH)₆SO₄, ZnO, and Zn(OH)₂ that could limit the active surface area for the Zn plating/stripping, accelerating the localized current density and favoring the growth of Zn dendrites. With the SiO₂ additive of 0.5% w/v in 1 M ZnSO₄(aq), the severe Zn dendrites disappear, as well as the cycled Zn/electrolyte interface becomes close to the pristine state; low degree of the Zn electrode roughness and the Zn surface passivation is noticed. The appearance of the claimed Zn surface morphology was also confirmed by Scanning Electron Microscopy (SEM). In turn, too low or too high SiO₂ content in the electrolyte does not generate desirable effects. A high level of Zn dendrites and short circuiting are still recognized. Hence, both the operando and ex-situ characterizations can mutually validate the phenomena at the Zn/electrolyte interface.

Keywords: Operando optical microscopy; SiO2 additive; Surface characterization; Synchrotron X-ray imaging; Zn-ion batteries; Zn/electrolyte interface.