Preferred planar crystal growth and uniform solid electrolyte interfaces enabled by anion receptors for stable aqueous Zn batteries

Abstract

Despite the intrinsic safety, abundant resource and low cost of Zn anodes and aqueous electrolytes, the implementation of rechargeable aqueous Zn batteries is still hampered by insufficient cyclability and notorious parasitic side reactions (i.e., dendrite growth, hydrogen evolution reaction, and corrosion). The construction of a reliable solid–electrolyte interphase (SEI) and/or the manipulation of crystal growth can effectively improve the reversibility of the Zn anode and mitigate side reactions. Herein, an anion receptor of imidazolidinyl urea (IU) is proposed to simultaneously manipulate the electric double layer (EDL) adsorption, Zn²⁺ bulk solvation structure and hydrogen bond network in a series of aqueous electrolytes (i.e., 2 M ZnSO₄, 2 M Zn(OTf)₂ and 2 M Zn(BF₄)₂), enabling a stable SEI and preferential growth of the Zn (002) plane. The 2 M ZnSO₄(IU)_0.25 aqueous electrolyte contributes to a layer-structured and tough SEI with inner inorganic ZnCO₃/ZnS_x and outer organic C–H/C–C components. Meanwhile, it forces Zn²⁺ ions to deposit on the (002) plane, resulting in a planar and compact deposition layer. Consequently, the Zn‖Zn symmetric cell shows exceptional reversibility and maintains long-term stability over 1500 h. The Zn‖Cu symmetric cell operates over 2000 cycles with a coulombic efficiency >99%. More importantly, a high-areal-capacity (∼5.7 mA h cm⁻²) Zn‖Br₂ full cell operating under the harsh condition of 84.03% Zn utilization sustainably runs 300 cycles with a capacity retention of 94.6% at ∼100% coulombic efficiency. This work provides an avenue to improve the reversibility of Zn metal anodes and develop high-energy aqueous Zn batteries.