In Situ Probing of Mass Exchange at the Solid Electrolyte Interphase in Aqueous and Nonaqueous Zn Electrolytes with EQCM-D

Abstract

Multivalent chemistry provides intriguing benefits of developing beyond lithium ion energy storage technologies and has drawn extensive research interests. Among the multivalent candidates, metallic zinc anodes offer an attractive high volumetric capacity at a low cost for designing the secondary ion batteries. However, the interfacial mass exchange at the Zn electrolyte/anode boundary is complicated. The least understood solid electrolyte interphase (SEI) occurs simultaneously with the reversible metal deposition, and its dynamic progression is unclear and difficult to capture. One major challenge to investigate such a dynamic interface is the lack of in situ analytical methods that offer direct mass transport information to reproduce the realistic battery operating conditions in an air-sensitive, nonaqueous electrolyte environment with a high iR drop. Work reported here reveals an in-depth analysis of the complex and dynamic SEI at the Zn electrolyte/electrode interface utilizing a multiharmonic quartz crystal microbalance with a dissipation method combined with the spectroscopic analysis. Key differences are observed for the SEI formation in the nonaqueous Zn(TFSI) 2 electrolyte in contrast to the aqueous ZnCl 2 electrolyte for reversible Zn deposition. A large disproportional loss of coulombs relative to the gravimetric mass change is prominently observed at the initial electrochemical cycles in the nonaqueous Zn electrolyte, and results suggest an in situ formation of an ionically permeable SEI layer that is compositionally featured with a rich content of organic S and N components. Further overtone-dependent dissipation analysis implies the changes in viscoelasticity at the electrode interface during the early SEI formation in the nonaqueous Zn(TFSI) 2 electrolyte.

Recent Advances in Electrolytes for “Beyond Aqueous” Zinc‐Ion Batteries

“…Moreover, it was reported that the aqueous ZnCl 2 electrolyte exhibited reversible Zn electrodeposition, while the nonaqueous Zn(TFSI) 2 organic electrolyte system showed complex interfacial reactions which result in the formation of an ionically permeable SEI layer with rich content of organic S and N components at initial electrochemical cycles (Figure 4c), leading to the high Coulombic efficiency of the organic electrolyte. [91] Although the electrochemical window (3.0 V) of Zn(TFSI) 2 organic electrolytes is limited by the poor oxidation stability compared with other zinc salts, it can still satisfy most high voltage cathode materials. For instance, as shown in Figure 5a, Zhang et al reported high-voltage Zn/graphite battery with 1 m Zn(TFSI) 2 /AN organic electrolyte exhibited the highest average output voltage of 2.2 V (Figure 5b), which is mainly attributed to electrolytes with high oxidative/reductive stability enabling good compatibility with the graphite cathode.…”

“…[ 97 ] The reason of this phenomenon was demonstrated to be related to the adhesion of TFSI − on the surface of the electrode in Zn(TFSI) 2 electrolyte. [ 91 ] Naveed et al. developed an organic electrolyte composed of Zn(OTf) 2 , TMP, and DMC, as shown in Figure , which shows highly reversible Zn plating/stripping without any dendritic growth on Zn anode after plating/stripping for 1000 cycles (2000 h).…”

“…[97] The reason of this phenomenon was demonstrated to be related to the adhesion of TFSI − on the surface of the electrode in Zn(TFSI) 2 electrolyte. [91] Naveed et al developed an organic electrolyte composed of Zn(OTf) 2 , TMP, and DMC, as shown in Figure 7, which shows highly reversible Zn plating/stripping without any dendritic growth on Zn anode after plating/ stripping for 1000 cycles (2000 h). The Zn/VS 2 battery with the Zn(OTf) 2 /DMC/TMP electrolyte delivered excellent cycling stability of over 5000 h and electrochemical performance with almost 95% capacity retention after 500 cycles with dendritefree flat morphology.…”

“…Copyright 2016, American Chemical Society. c) FTIR spectra of electrochemically cycled EQCM-D resonator in a 0.2 m Zn(TFSI) 2 /AN and in 0.2 m ZnCl 2 /H 2 O. Reproduced with permission [91]. Copyright 2021, American Chemical Society.…”

Understanding Electrochemical Intercalation of Al3+ Cation into the WO3 Electrochromic Electrode from Solid Electrolyte Interphase and Mass Changes

“…11 The formation of an ionically permeable SEI layer has been confirmed in the Zn 2+ -based electrolyte/electrode interface in previous literature. 12 However, as far as we know, in situ EQCM has not been performed during the investigation of the Al 3+ -based electrolyte for electrochromic batteries or devices.…”