Stabilization of Zn anode via a multifunctional cysteine additive

Instability of Zn anode in aqueous electrolytes caused by severe dendrite growth and rampant side reactions limits the rapid development of aqueous zinc ion batteries (ZIBs). In detail, the [(Zn(H₂O)₆]²⁺ solvation structure, H₂O-riched anode/electrolyte interface (AEI) and unbalanced Zn²⁺ deposition kinetics are critical factors for the instability of Zn anode. Therefore, cysteine (Cys) rich in polar groups (–SH, –COOH, –NH₂) is introduced as a multifunctional additive to ZnSO₄ electrolyte for the stable Zn anode. Experimental and theoretical analysis prove that multiple polar groups of Cys can strongly interact with Zn²⁺ and Zn metal to enable the reconfiguration of solvation shell and AEI. The simultaneous optimization of the two is also conducive to improving the Zn²⁺ deposition kinetics. The synergistic effect of these functions effectively inhibits dendrite growth and side reactions, thus stabilizing the Zn anode. Consequently, the Zn//Zn symmetric cell can deliver an ultra-long cycle life (2300 h), and over tenfold life is extended under various test parameters. Even cycled at a harsh condition (5 mA, 5 mAh cm⁻²), the Zn anode delivers an ultra-high cumulative plated capacity of 1.36 Ah with a high CE of 99.4%. The proposed multifunctional additive provides new insight into electrolyte design for high-performance ZIBs.