High-Power and Ultralong-Life Aqueous Zinc-Ion Hybrid Capacitors Based on Pseudocapacitive Charge Storage

Highlights This work starts the research of pseudocapacitive oxide materials for multivalent Zn 2+ storage. The constructed RuO 2 ·H 2 O||Zn systems exhibit outstanding electrochemical performance, including a high discharge capacity, ultrafast charge/discharge capability, and excellent cycling stability. The redox pseudocapacitive behavior of RuO 2 ·H 2 O for Zn 2+ storage is revealed. Rechargeable aqueous zinc-ion hybrid capacitors and zinc-ion batteries are promising safe energy storage systems. In this study, amorphous RuO 2 ·H 2 O for the first time was employed to achieve fast and ultralong-life Zn 2+ storage based on a pseudocapacitive storage mechanism. In the RuO 2 ·H 2 O||Zn zinc-ion hybrid capacitors with Zn(CF 3 SO 3 ) 2 aqueous electrolyte, the RuO 2 ·H 2 O cathode can reversibly store Zn 2+ in a voltage window of 0.4–1.6 V (vs. Zn/Zn 2+ ), delivering a high discharge capacity of 122 mAh g −1 . In particular, the zinc-ion hybrid capacitors can be rapidly charged/discharged within 36 s with a very high power density of 16.74 kW kg −1 and a high energy density of 82 Wh kg −1 . Besides, the zinc-ion hybrid capacitors demonstrate an ultralong cycle life (over 10,000 charge/discharge cycles). The kinetic analysis elucidates that the ultrafast Zn 2+ storage in the RuO 2 ·H 2 O cathode originates from redox pseudocapacitive reactions. This work could greatly facilitate the development of high-power and safe electrochemical energy storage.