Fig. 1. (a) SEM image of the zinc anode by electrically depositing onto a carbon cloth. Adopted with permission from Ref. [18], Copyright 2019, Royal Society of Chemistry. (b) SEM image and the photographs (the inset) of the MnO₂/rGO sample on carbon cloth. Adopted with permission from Ref. [19], Copyright 2018, Nature Publishing Group.

Fig. 2. (Color online) (a) The process diagram of SA-based hydrogel electrolyte. Adopted with permission from Ref. [22], Copyright 2020, Elsevier. (b) The schematic diagram of PAM-based hydrogel. Adopted with permission from Ref. [23], Copyright 2018, American Chemical Society. (c) The structure diagram of fabricating PVA-based self-healing electrolyte. Adopted with permission from Ref. [24], Copyright 2019, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fig. 3. (Color online) (a) The schematic process of design and (b) the cycle performance of ultrathin all-in-one ZIBs. Adopted with permission from Ref. [25], Copyright 2021, John Wiley & Sons. (c) Schematic illustration of fabrication procedures and (d) cycle performance of in-plane batteries. Adopted with permission from Ref. [ 26], Copyright 2020, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fig. 4. (Color online) (a) Illustrations of the Zn-MnO₂ battery i) being placed under foot and ii) going through car run-over. (b) Discharge curve of the battery after 2 days' everyday treading. (c) Discharge curve of the battery after 20 times of random run-over by cars on road. All the discharge curves were recorded at 0.924 A/g (3C rate). Adopted with permission from Ref. [28], Copyright 2019, Elsevier. (d) Schematics of the evolution of the Zn-reinforced SA-PAM SE hydrogel structure. (e) Tensile strength of the Zn-reinforced SA-PAM SE. (f) Capacity loss per cycle of all kinds of flexible ZIBs. Adopted with permission from Ref. [29], Copyright 2020, American Chemical Society. Optical images of a “ZIBs” LED powered by four all-in-one ZIBs in series (g) without bending and (h) under bending. (i) Cycling performance of the all-in-one and stacked ZIBs at 0.5 A/g under flat and different bending states. Adopted with permission from Ref. [30], Copyright 2019, Royal Society of Chemistry. (j) The flexible ZIB is subjected to fold deformation. (k) Galvanostatic charge/discharge curves of the ZIB cell under different mechanical deformations. Adopted with permission from Ref. [31], Copyright 2021, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fig. 5. (Color online) (a) Cycling performance of the obtained flexible Zn-MnO₂ battery before healing and after fourth healing. (b) Demonstration of a self-healing flexible Zn-MnO₂ battery powering an electric watch before and after cutting and after healing. Adopted with permission from Ref. [32], Copyright 2019, American Chemical Society. (c) Charging and discharging profiles of alkaline flexible NiCo-Zn batteries before and after multiple cutting/healing cycles. (d) Healing efficiency calculated from (c). (e) Demonstration of a self-healing flexible NiCo-Zn battery powering an electric watch before and after cutting and after healing. Adopted with permission from Ref. [33], Copyright 2018, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. (f) Demonstration of hydrogel electrolytes and the battery using all-in-one electrodes after each time of the self-healing process. Adopted with permission from Ref. [ 34], Copyright 2021, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fig. 6. (Color online) (a) The demonstration of AF-battery powered a series of electronic devices. Adopted with permission from Ref. [18], Copyright 2019, Royal Society of Chemistry. (b) The schematic diagram of anti-freezing gel electrolyte based on PAM/EG gel electrolyte. Adopted with permission from Ref. [35], Copyright 2020, Frontiers Media S.A. (c) The voltage curves of Zn plating-stripping in ZL-PAAm under different temperatures. Adopted with permission from Ref. [36], Copyright 2020, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fig. 7. (Color online) (a) The process of the smart reaction of flexible ZIBs when temperature changes. Adopted with permission from Ref. [37], Copyright 2018, Science China Press. (b) The schematic diagram of smart rection. Adopted with permission from Ref. [38], Copyright 2020, John Wiley & Sons. (c) The demonstration of practical submarine-use of flexible ZIBs assembled by XG-PAM/CNF hydrogel electrolyte. Adopted with permission from Ref. [ 39], Copyright 2020, American Chemical Society. (d) Ion conductivity of zwitterionic sulfobetaine/cellulose semi-interpenetrating networks gel (ZSC-gel). Adopted with permission from Ref. [40], Copyright 2020, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Table 1. The performance comparison of flexible ZIBs using in different situations.