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• A flexible aqueous Al-ion battery was reported for the first time. • The flexible Al-ion battery exhibits exceptional flexibility and safety. • The Al-ion battery delivers excellent electrochemical cycling stability. • This work paves the way for Al-ion battery application in wearable electronics. With the fast development of flexible and wearable electronics, the design of secondary energy storage system based on aqueous metal ion battery with outstanding flexibility, safety and low cost is critical for their practical application. As low-cost alternatives to lithium ion battery, multivalent metal ion technologies including Mg2+, Zn2+, Ca2+, and Al3+ are investigated increasingly in the past few years. The investigation based on Al-ion chemistry is also underway considering the aluminum's advantages of natural abundance, small ion size together with three-electron-redox properties. Herein, a flexible aqueous Al-ion battery is successfully fabricated for the first time with copper hexacyanoferrate cathode and polypyrrole (PPy) coated MoO 3 anode sandwiched by gel electrolyte. The as-assembled Al-ion battery based on intercalation chemistry exhibits an excellent cycling stability of 83.2% capacity retention after 100 cycles and good rate capability benefiting from the conductive PPy coating layer on MoO 3 anode. Besides, the battery demonstrates impressive flexibility and safety to sustain various deformations and mechanical abuse including bending, squeezing, folding, twisting as well as arbitrary drilling and tailoring into any desired shapes. Obviously, the flexible aqueous Al-ion battery developed in this study paves the way of multivalent metal ion battery as energy storage device towards various wearable electronics. [ABSTRACT FROM AUTHOR]

Highlights: A 2.4 V high-voltage flexible aqueous ZIB was fabricated, and superiors performances were achieved: extremely flat charging/discharging voltage plateaus (1.9/1.8 V), the smallest plateau voltage gap of 0.1 V, high energy density of 120 Wh kg−1, high power density of 3700 W kg−1, and excellent rate capability of 25 C. The battery posed application potential in wearable electronics with extreme safety against tough destructions including hammering, sewing, punching, and soaking. Flexible rechargeable aqueous zinc-ion batteries (ZIBs) have attracted extensive attentions in the energy storage field due to their high safety, environmental friendliness, and outstanding electrochemical performance while the exploration of high-voltage aqueous ZIBs with excellent rate capability is still a great challenge for the further application them in flexible and wearable electronics. Herein, we fabricated a 2.4 V high-voltage flexible aqueous ZIB, being among the highest voltage reported in aqueous ZIBs. Moreover, it exhibits extremely flat charging/discharging voltage platforms and the dropout voltage is only 0.1 V, which is the smallest gap in all aqueous batteries to our best knowledge. Furthermore, the prepared ZIB performs high rate capability of 25 C and energy density of 120 Wh kg−1 and exhibits excellent safety under various destructive conditions including hammering, sewing, punching, and soaking. These extraordinary results indicate the great application potential of our high-voltage flexible aqueous ZIB in wearable electronics. [ABSTRACT FROM AUTHOR]