A multifunctional and low-cost separator for long-life aqueous Zn metal batteries

Zinc metal batteries show great promise for energy storage applications in smart grids. However, Zn metal anodes pose significant challenges, mainly as a result of the uncontrollable growth of zinc dendrites on their surfaces, the accumulation of inert by-products, and the occurrence of the hydrogen evolution reaction. These obstacles can significantly reduce the cycling stability of the anodes. To solve these problems, we developed a boric acid-modified multifunctional cellulose separator to protect the zinc metal anode. The undissolved boric acid crystals in the separator facilitated the rapid transport of Zn²⁺ in the separator. The boric acid dissolved in the electrolyte buffered changes in pH and altered the dissolution sheath of Zn²⁺. Furthermore, it reacted with the zinc anode in the battery to form a zinc borate solid electrolyte interface layer, which served to isolate the anode from direct contact with the electrolyte. Thus, the Zn||Zn symmetric cell cycled stably for over 1500 h, whereas the Zn||MnO₂ full cell cycled stably for 4000 cycles under test conditions of 1A g⁻¹, and the capacity retention rate was 90.5%. This study introduces a novel approach to modifying zinc metal battery separators.