Ion-sieving Janus separator modified by Ti3C2Tx toward dendrite-free zinc-ion battery

Aqueous zinc-ion batteries, as one of the promising substitutes for lithium-ion batteries, have received increasing attention due to their high safety, low cost, and non-toxicity. Nevertheless, the inevitable growth of zinc dendrites, hydrogen evolution, and side reactions on the Zn anode greatly hinder the further application of zinc-ion batteries. The current solutions mainly focused on electrolyte regulation, artificial interface layer introduction, and zinc alloy anode construction. MXene, as a novel generation of two-dimensional layered transition metals carbides/ nitrides, has been widely investigated in a variety of metal ion batteries in the last decade owing to excellent physical and chemical properties. Herein, we constructed an ion-sieving Janus separator for the aqueous zinc-ion battery by spraying Ti3C2Tx MXene ink on one side of the commercial glass fiber separator. Because of the advantages of MXene such as high conductivity, abundant surface functional groups, and highly matched lattice constants with the Zn anode, the composite separator can homogenize the surface electric field of the Zn anode, optimize the flux of Zn2+, and induce the uniform deposition of Zn2+. Most importantly, a unique ion sieving function was realized in the electrolyte because of the intrinsic electro-negativity of the MXene layer. The concentration of H+ and SO42- on the Zn anode side is largely reduced, and the hydrogen evolution and side reactions are greatly inhibited. Thus, for symmetrical cells, an ultralong cycling lifespan up to 2500 h and superior rate capability with dendrite-free deposition behavior were achieved. When further applying the Janus separator to aqueous zinc-ion batteries combined with the fabricated α-MnO2 cathode, Zn anode, and 2 M ZnSO4 + 0.2 M MnSO4 electrolyte, a superb capacity retention rate (85.7%) upon cycling for 500 cycles at 1.0 A g−1 was obtained. This ion-sieving separator possesses the giant potential for zinc-ion batteries.