Functional ultrathin separators enabling stable zinc anodes for lean-electrolyte zinc-ion batteries

Abstract

Glass fiber separators are afflicted by zinc dendrite-caused failure and they require excess electrolytes due to large thickness (e.g., 260–780 μm), impairing the electrochemical performance of zinc-ion batteries (ZIBs). Herein, we report a 12 μm-thick functional ultrathin separator (MCNF) of a Cu/graphene interface-modified cellulose nanofiber membrane, realizing highly stable zinc anodes even in lean-electrolyte ZIBs. The MCNF separator optimizes the zinc deposition interface to achieve dendrite-free and highly reversible zinc anodes, since its nanoporous hydroxyl-rich cellulose nanofiber membrane and the conductive zincophilic Cu/graphene layer simultaneously optimize Zn²⁺ transport behavior including homogenizing ion flux and improving Zn²⁺ transference number, accelerate zinc desolvation-nucleation process and inhibit anode corrosion. As a result, zinc anodes coupled with the MCNF separator present a long cycle life of 700 h at 5 mA/cm² and 340 h at 10 mA/cm², far superior to those using glass fiber separators. Benefiting from the MCNF separator's ultrathin feature as well as the capability of enhancing zinc plating/stripping reversibility and inhibiting side reactions at the zinc deposition interface, Zn//VO₂ ZIBs present superior cycle stability exceeding 1800 cycles even under lean-electrolyte conditions. This work provides new inspirations for designing high-performance separators for high-energy-density ZIBs.