High-Performance Zinc-Bromine Rechargeable Batteries Enabled by In-Situ Formed Solid Electrolyte Interphase

Abstract

Aqueous zinc-bromine batteries (ZBBs) are promising candidates for renewable energy storage, offering advantages over lithium-ion batteries. However, their widespread adoption is hindered by challenges such as zinc dendrite formation and water decomposition, which lead to short circuits, electrode degradation and reduced cycle life. Therefore, this study presents a facile strategy for in-situ construction of a fluorinated solid electrolyte interphase (SEI) formed via coating graphite current collectors with a lubricant hydrophobic perfluoropolyether interlayer. During the initial charging process, a fluoride-rich SEI layer forms to regulate Zn nucleation and suppress dendrite growth. This SEI promotes uniform zinc deposition and inhibits hydrogen evolution by limiting water access to the electrode surface, thereby enhancing cycle life and energy efficiency. As a result, ZBBs incorporating this SEI exhibit a substantial reduction in potential hysteresis from 285 to 60 mV, deliver an energy density of nearly 20 Wh L^-1 and an areal capacity of 10.7 mAh cm^-2, and maintain >79% energy efficiency over 1000 cycles. This work offers a scalable approach to achieving high-performance ZBBs, advancing the development of next-generation anode-free zinc batteries.

Keywords: aqueous electrolyte; hydrogen evolution reaction; solid electrolyte interphase; zinc dendrites; zinc–bromine batteries.

Figure 1

Chemical characterization of the perfluoropolyether‐functionalized graphite (PFPE‐G) surface compared with that of bare graphite, analyzed by a) attenuated total reflection–Fourier transform infrared spectroscopy of the G, PFPE and PFPE‐G surfaces before cycling and after 200 cycles. b–d) X‐ray photoelectron spectra of C1s for the G and PFPE‐G current collectors before and after 200 cycles. In (c), the PFPE‐G electrode was left at room temperature for several weeks to investigate the coating stability and durability. Physical properties (wettability) of PFPE‐G. e) Contact angle measurements when a 5 µL droplet of 2.5 m ZnBr₂ electrolyte solution was dispersed onto the G and the PFPE‐G surfaces before and after 200 cycles. A schematic illustration of a proposed mechanism of PFPE coating at different cycle stages. f) The fluorinating agent (PFPE) layer is applied before the cycle. g) The Zn²⁺ ion‐transporting pathways through the PFPE layer before the reduction process to metallic Zn⁰ during the charging phase, with an inset description. h) In‐situ fluorinated interphase formed after the first cycle (terminated at the discharged state), with an inset description.

Figure 2

Characterization of the ZnF₂ interphase. a–f) X‐ray photoelectron spectroscopy (XPS) depth profiles of (a–c) F 1s and (d–f) C 1s after 0, 30, and 90 s of Ar⁺ sputtering for perfluoropolyether‐coated graphite (PFPE–G) samples after initial cycling, where Zn⁰ was stripped. g–i) Synchrotron soft X‐ray absorption spectrum of fluorine K‐edge, zinc L‐edge and carbon K‐edge for PFPE‐G current collectors before and after discharge. j) XRD patterns of discharged bare G and PFPE‐G current collectors. k) TEM and high‐resolution TEM images of the discharged PFPE‐G current collector, showing lattice fringes with corresponding d‐spacings for different ZnF₂ planes.

Figure 3

Visualization of the hydrogen evolution reaction and zinc plating morphology for the bare graphite (G) and perfluoropolyether‐coated G (PFPE‐G). a,d) Operando in‐situ observation of varying charging durations for Bare‐G and PFPE‐G electrodes in symmetrical cells, each charged at 5 mA for 30 min, captured using an optical microscope. b,e) Low‐magnification (100×) and c,f) high‐magnification (1000×). Scanning electron microscopy illustrates the zinc plating morphology on the Bare‐G and PFPE–G current collectors in a full nonflow ZBB. g) Cyclic voltammetry curves of the Zn half‐cell on the Bare‐G and PFPE‐G current collectors, recorded versus a saturated hydrogen calomel reference electrode, highlighting differences in redox behavior. h) Chronoamperometry analysis of the Bare‐G and PFPE‐G (treated) current collectors in a three‐electrode system at a fixed potential of −150 mV. i) Simulated Tafel analysis obtained from linear sweep voltammetry for the Bare‐G and PFPE‐G (Figure S13, Supporting Information) in a three‐electrode configuration, using Ag/AgCl as the reference electrode.

Figure 4

a,b) The electrochemical impedance spectroscopy (EIS) of (a) Bare‐G and (b) PFPE‐G), performed in a nonflow ZBB (NF‐ZBB) system and measured at 100 kHz–10 mHz by applying an AC potential (10 mV) between a working and reference electrode, with the simulated equivalent circuit to fit the EIS signals. c,d) Cycling performance of (c) bare‐G and (d) PFPE‐G in NF‐ZBBs at a current density of 25 mA cm⁻² and an areal capacity of 8.0 mAh cm⁻², under 1 m electrolyte concentrations. e) Coulombic, energy and voltage efficiencies and f) voltage profile of PFPE‐G over different cycles at 25 mA cm⁻² and an areal capacity of 10.7 mAh cm⁻², under 0.5 m electrolyte concentrations. g,h) Performance comparisons between the metrics of this study's battery and those of previously reported ZBBs at various efficiencies, current densities and areal capacities.