Unveiling unique steric effect of threonine additive for highly reversible Zn anode

Aqueous Zn-ion batteries (ZIBs) exhibit a great potential for large scale energy storage applications due to their low cost and safe operating conditions. However, the dendritic growth of Zn caused by the random diffusion of Zn2+ ions on the Zn anode during operation shortens the cycle life of ZIBs. In this study, an ultra-trace amount of threonine (TH) was used as an electrolyte additive for the first time. Results showed that the TH molecules were adsorbed on the Zn anode surface. These molecules restricted the planar diffusion of Zn2+ ions through steric effects, which effectively inhibited the hydrogen evolution reaction and suppressed the dendritic growth of Zn. The assembled Zn//Zn symmetric cell with the TH additive showed stably cycling characteristics for over 580 h at 1 mA cm−2 with a capacity of 1 mAh cm−2, and the carbon cloth (CC)//Zn half-cell with the TH additive exhibited a high coulombic efficiency of 99.5%. Moreover, the Zn//CVO full cells with TH additive exhibited better capacity retention properties than the cell fabricated using the pure electrolyte. This work provides an encouraging path for development of low cost and efficient electrolyte additives for dendrite-free ZIBs.