Stable Zn electrodes enabled by an ultra-thin Zn phosphate protective layer

Abstract

Rechargeable zinc ion batteries are promising next-generation energy storage devices with inherent safety and low-cost advantages. However, unstable Zn/electrolyte interfaces cause detrimental dendrite growth and Zn anode corrosion, resulting in poor cycling stability. Herein, an ultra-thin (∼45 ± 5 nm) protective layer is created on Zn surfaces using a facile and rapid chemical treatment by polyphosphoric acid, which dramatically improves the stability of Zn/electrolyte interfaces. The uniformly coated protective layer serves as an artificial solid electrolyte interface to impede Zn corrosion and enable uniform Zn plating/stripping. The performance improvement is correlated with the thickness of protective layers, which can be easily adjusted using polyphosphoric acid at different concentrations. Protected Zn electrodes with an optimized protective layer thickness can cycle stably for 6500 h at a current density of 2 mA cm⁻² with a high cumulative plating capacity of 6.5 A h cm⁻². This improved stability can be retained even at a high current density of 10 mA cm⁻². Full Zn//MnO₂ cells are also demonstrated with a capacity retention of 78% after 500 cycles. This work offers a readily employable Zn electrode protection method for scalable applications. The findings on protective layer thickness also provide valuable insights into designing a surface protective layer for metal electrodes.