Built-In “Vesicle-Like Structures” Electrolytes to Form Ion Channels for Dendrite-Free and Durable Zinc-Ion Hybrid Supercapacitors

Aqueous zinc-ion hybrid supercapacitors (ZHSCs) have stimulated wide attention due to their features of low cost and nontoxic nature. Nevertheless, the growth of zinc dendrites, parasitic reactions, and a narrow electrochemical stable window (ESW) have severely limited the development of ZHSCs. Here, the distinct vesicle-like structure using polyethylene glycol monomethyl ether (MPEG) and ethylene glycol dimethyl ether (DME) is creatively represented, which is named the bicelle electrolyte. In this unique vesicle-like structure, the O of -OH and C-O-C in MPEG extends to the interior, encapsulating aqueous Zn(ClO₄)₂. The hydrophobic groups of MPEG and DME accumulate due to hydrophobic interactions, forming a hydrophobic domain. Due to the presence of a hydrophobic domain, the internal active water molecules are prevented from directly contacting the Zn foil. The external hydrophilic groups form hydrogen bonds with free water, which also greatly suppress the activity of free water, thus inhibiting the harmful side reactions (hydrogen evolution reactions) related to water. The electrochemical stable window (ESW) was widened to 3.03 V. Furthermore, this vesicle-like structure formed by the head-to-head of MPEG and DME hydrophobic groups creates a Zn²⁺ channel that promotes rapid and uniform deposition of Zn²⁺, thereby inhibiting zinc dendrite growth and promoting the cycling stability of the cell. The experiments show that a high ion conductivity of 51.87 mS cm^-1 and a Zn²⁺ transference number (<i>t</i>_Zn²⁺) of 0.70 can be achieved in the bicelle system. The assembled asymmetric supercapacitor can have a specific capacity of 95.47 mAh g^-1 at 5 A g^-1, and it still maintains a high capacity retention rate of 84.40% after 8000 cycles. The symmetric cell delivers a long lifespan of over 1300 h at 1 mA cm^-2.