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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]

• A unique silane coupling agent derivative-coated Zn anode with ion perselectivity was demonstrated. • This modified Zn anode greatly restrained side reaction with desolvation of [Zn(H 2 O)6]2−. • Versatile coating with tightly contact of nano particles and organic network contributed to full-cell long cycling life. Although zinc anodes are extensively adopted to meet aqueous energy storage, serious dendrite formation and side reaction resulting in inferior lifetime have hindered the application. In this work, a unique interfacial engineering is proposed by a self-assembled artificial layer tightly contact to the surface of zinc anode with Zn2+ permselectivity. Such artificial layer via a facile hydrolysis consists of nano inorganic particles well dispersed in organic network. The screening for the bound water of Zn2+ enables excellent anticorrosion during cycling and rest situation. Meanwhile, the modified zinc anode can reduce the Zn2+ nucleation barrier for uniform distribution, which is beneficial to dendrite suppression. Consequently, the modified zinc anodes in both symmetric and full cells exhibit prominently electrochemical reversibility. Specifically, with a cycling area capacity of 3.0 mAh cm−2 at 1.0 mA cm−2, the modified zinc anode can tolerate superior plating/stripping behavior over 1000 h. When it is coupled with vanadium pentoxide cathode, the performance advantage of the modified full-cell is still impressive and high-capacity retention of ∼84 % after 1200 cycles is achieved. [ABSTRACT FROM AUTHOR]

• Organic-inorganic Ov-PVO/G heterostructures are prepared via a ball-milling approach. • The heterostructures contain expanded interlayer spacing, oxygen vacancy and heterointerface. • Freestanding Ov-PVO/G heterostructure cathodes with high mass-loading are fabricated. • The three-in-one Ov-PVO/G heterostructures exhibit accelerated reaction kinetics. • The freestanding Ov-PVO/G heterostructure cathodes for AZIBs deliver high areal capacity. Aqueous Zn-ion batteries (AZIBs) have great potential in large-scale energy storage, however, developing suitable cathodes with high energy/power densities remains highly challenging. Herein, a unique organic-inorganic heterostructures (denoted as O v -PVO/G) of poly(3,4-ethylenedioxythiophene) intercalated V 2 O 5 nanocrystals anchored on few-layer graphene by a simple and scalable ball-milling approach are demonstrated for high areal-capacity AZIBs cathodes, in which, adjusted interlayer spacing, abundant oxygen vacancies and robust heterointerfaces can be simultaneously constructed. Moreover, the feature of being well dispersed in different polar solvents (H 2 O, NMP, etc.) enable facile incorporation of the O v -PVO/G heterostructures into conductive networks of single-walled carbon nanotubes to fabricate freestanding composite cathodes. Electrochemical measurement and first-principles calculations indicate that such "Three-in-One" heterostructure can significantly enhance Zn2+ adsorption/desorption, electrical conductivity and charge transfer due to strong synergy, thereby exhibiting high-capacity and accelerated reaction kinetics during cycling. Specifically, at a practical mass loading of 12.0 mg/cm2, the freestanding O v -PVO/G cathodes show a high areal-capacity of 6.1 mAh/cm2 at 2.4 mA/cm2 and works stable with an area-capacity of 1.63 mAh/cm2 at 120 mA/cm2 after 500 cycles. More importantly, flexible soft-packaged AZIBs based on 3×3 cm2 high mass-loading O v -PVO/G cathodes deliver record-high and stable electric energy beyond 21.5 mAh at different bending states. This work paves a more promising way to practical application of high-performance AZIBs. [ABSTRACT FROM AUTHOR]