Rechargeable aqueous zinc batteries offer a safe, economical, and scalable solution for grid-scale storage of renewable energy. However, low coulombic efficiency and short cycle life resulting from the notorious dendrite formation and parasitic reactions of zinc anodes remain a grand challenge for the practical applications of this type of battery. The primary objective of this thesis is to tackle the aforementioned issues, thereby creating highly reversible zinc anodes for high-performance rechargeable aqueous batteries.

We begin with developing a hierarchical porous framework for zinc anodes by electroless plating a conformal nanoporous tin (Sn) layer on a copper mesh (NSH). The NSH can reduce the local current density, provide abundant nucleation sites for zinc deposition, homogeniz...[ Read more ]

Rechargeable aqueous zinc batteries offer a safe, economical, and scalable solution for grid-scale storage of renewable energy. However, low coulombic efficiency and short cycle life resulting from the notorious dendrite formation and parasitic reactions of zinc anodes remain a grand challenge for the practical applications of this type of battery. The primary objective of this thesis is to tackle the aforementioned issues, thereby creating highly reversible zinc anodes for high-performance rechargeable aqueous batteries.

We begin with developing a hierarchical porous framework for zinc anodes by electroless plating a conformal nanoporous tin (Sn) layer on a copper mesh (NSH). The NSH can reduce the local current density, provide abundant nucleation sites for zinc deposition, homogenize the ion flux and electric field at the electrode surface, and suppress the hydrogen evolution side reaction. As a result, the asymmetric Zn SH cell achieves a coulombic efficiency of 99.0% for over 200 cycles at 2 mA cm⁻². Nevertheless, the electrically conductive skeleton induces preferential zinc deposition near the electrode/separator interface, resulting in a low operating areal capacity. Hence, a non-conductive polybenzimidazole (PBI) nanofibers layer is electrospun onto a copper substrate (PBI-Cu). The PBI nanofiber framework with abundant polar groups and uniform microporous structure can uniformize and facilitate the transport of Zn²⁺ ions at the electrode surface, enabling bottom-up and dendrite-free zinc deposition. Consequently, a symmetric cell with Zn@PBI-Cu electrodes can stably cycle under a large current density (20 mA cm^-2) and high areal capacity (5 mAh cm^-2). To suppress the side reactions of zinc with electrolyte, an ultrathin and dense Zn²⁺-conductive sulfonated poly(ether ether ketone) (SPEEK) polymer film is homogeneously coated onto the zinc surface via facile spin-coating. This artificial protective layer simultaneously blocks the water molecules and anions, uniformizes the ion flux, and facilitates the desolvation process of Zn²⁺ ions, thereby considerably enhancing the stability and reversibility of zinc anodes.

In addition to electrodes, electrolyte modulation also represents an effective approach to improving the electrochemical performance of zinc anodes. In this regard, we first report a NH4Br electrolyte additive, of which the cations (i.e., NH₄⁺) preferentially absorb on the tips/protrusions and repel upcoming Zn²⁺ ions to the vicinity for deposition. The electrostatic shielding effect effectively mitigate the zinc dendrite formation and extend the cyclability of zinc anodes. To reduce active solvated water molecules near the zinc surface and thus suppress side reactions, we explore dimethylacetamide (DMAc) as a water blocker. It is revealed that DMAc in the electrolyte impedes the formation of hydrated Zn²⁺ solvation while facilitating the association of Zn²⁺ and SO₄²⁻, thereby effectively mitigating side reactions and dendrite growth. Finally, we formulate a new electrolyte to boost the reversibility of zinc anodes. With the guidance of theoretical calculations, dimethyl sulfoxide (DMSO) is added into a Zn(TFSI)₂ electrolyte, which effectively introduces TFSI^- anions into the solvation sheath of Zn²⁺ and enables preferable reduction of TFSI^- anions prior to zinc deposition, thus in-situ constructing a ZnF₂-rich interphase on the zinc surface. The resultant interphase not only regulates the uniform Zn²⁺ ion transport, thus suppressing the dendrite formation, but also effectively prevents the zinc anode from side reactions with the electrolyte. As a result, the newly formulated electrolyte enables a zinc symmetric cell to achieve a long cycle life of over 2,000 h. More excitingly, full cells with diverse cathodes and the new electrolyte all display impressive cycling performance, showing great promise for practical applications.

Keywords: Aqueous zinc batteries; zinc dendrite; interface modification; solid electrolyte interphase; electrolyte modulation