Tuning the Electrolyte Solvation Structure to Suppress Cathode Dissolution, Water Reactivity, and Zn Dendrite Growth in Zinc‐Ion Batteries

Abstract

The cycle life of aqueous zinc-ion batteries (ZIBs) is limited by the notable challenges of cathode dissolution, water reactivity, and zinc dendrites. Here, it is demonstrated that by tuning the electrolyte solvation structure, the issues for both the electrodes and the electrolyte can be addressed simultaneously. Specifically, a fire-retardant triethyl phosphate (TEP) is demonstrated as a cosolvent with strong solvating ability in a nonaqueous/aqueous hybrid electrolyte. The TEP features a higher donor number (26 kcal mol −1 ) than H 2 O (18 kcal mol −1 ), preferring to form a TEP occupied inner solvation sheath around Zn 2+ and strong hydrogen bonding with H 2 O. The TEP coordinated electrolyte structure can inhibit the reactivity of H 2 O with V 2 O 5 and leads to a robust polymeric-inorganic interphase (poly-ZnP 2 O 6 and ZnF 2 ) on zinc anode effectively preventing the dendrite growth and parasitic water reaction. With such an optimized electrolyte, the Zn/Cu cells perform high average Coulombic efficiency of 99.5%, and the full cell with a low capacity ratio of Zn:V 2 O 5 (2:1) and lean electrolyte (11.5 g Ah −1 ) delivers a reversible capacity of 250 mAh g −1 for over 1000 cycles at 5 A g −1 . This study highlights the promise of a successful electrolyte regulation strategy for the development of highperformance and practical ZIBs.

Interfacial Engineering Strategy for High-Performance Zn Metal Anodes

“…Electrolyte additives are used to adjust the surface morphology of the Zn anode and inhibit side reactions, such as Zn dendrite growth, hydrogen evolution reaction, and Zn surface corrosion and passivation. Various electrolyte additives have been applied to RAZIBs to protect the Zn [84] anode by electrostatic shielding, crystallographic orientation induction, and modulation of the coordination status mechanism. According to previous research results, electrolyte additives can be divided into ionic and non-ionic additives.…”

“…Some additives can replace H 2 O in the Zn 2+ -solvated sheath, preferentially solvate with Zn ions, and remove H 2 O from the Zn 2+ -solvated sheath [ 83 ]. In addition, some additives also have a strong interaction with water, which reduces water activity and effectively inhibits parasitic water reactions and dendrite growth [ 84 ]. Furthermore, an in situ solid electrolyte interphase (SEI) layer can be constructed by adding additives to the electrolyte.…”

“…Furthermore, an in situ solid electrolyte interphase (SEI) layer can be constructed by adding additives to the electrolyte. The presence of additives not only adjusts the structure of the solvent sheath of Zn ions, allowing the rapid transmission of Zn 2+ , but also prevents H 2 O from penetrating the surface of the Zn anode, which greatly reduces the probability of side reactions [ 83 , 84 ].…”

“…13 f). Mao et al [ 84 ] used the flame-retardant triethyl phosphate (TEP) as a co-solvent by adjusting the solvation structure of the non-aqueous electrolyte. TEP preferentially forms a TEP-occupied inner solvation sheath around Zn 2+ and strong H bonding with H 2 O (Fig.…”

“…Characterization of the interphase on the cycled Zn surface: h XPS fitted curves of the F 1s, C 1s, and P 2p elements and i the interference reflection microscopy spectrum of the cycled Zn electrode and the acquired distribution of surface functional groups. Copyright 2021 Wiley-VCH [ 84 ] …”