In-situ construction of passivation layer via trimethyl phosphate additive in electrolyte manipulation for high-performance zinc ion capacitors

Currently, protective layers for Zn metal anodes are commonly employed to suppress side reactions triggered by water solvent. However, their complex extra-treatment procedure and suboptimal structural stability remain unsatisfactory, hindering widespread deployment. Herein, the introduction of trimethyl phosphate (TMP) in the electrolyte enables in-situ formation of a Zn 3 (PO 4 ) 2 ·4H 2 O passivation layer, reducing water reactivity and ensuring uniform plating/stripping. Moreover, the oxygen-rich TMP molecules alter the original hydrogen bond structure by increasing strong hydrogen bonds from 42.1% to 63%, leading to enhanced electrolyte stability. Benefiting from these advantages, the assembled half cells achieve superior cycling stability with 99.68% Coulombic efficiency over 1700 cycles under 0.5 mA cm −2 , lasting 48 times longer than TMP-free cells. In the low-temperature environment, the addition of TMP significantly increases the cycle life of the Zn||active carbon capacitor by nearly 70 times. Proof-of-concept pouch cells deliver a robust cycling performance over 1300 cycles with 90.9% capacity retention. These findings provide an impetus for the practical utilization of Zn-based aqueous energy storage systems.