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Al-air batteries are generally fabricated by rigid and heavyweight materials such as metal or plastic, meanwhile a bulky electrolyte solution either in static or circulation is requisite to ensure their steady operation. Therefore, they are less suitable for powering flexible and portable devices with lower power demand, such as wearable electronics, point-of-care test assays, RFID tags, etc. This work develops a flexible and lightweight Al-air battery with much less electrolyte storage, which is totally fabricated on a cellulose paper. The Al foil anode is embedded inside the paper substrate during paper-making process, while the air-breathing cathode is deposited onto the paper surface using an oxygen reduction ink. Despite its simple structure and low cost, this flexible Al-air battery can deliver a satisfactory power density of 19 mW cm−2 with alkaline electrolyte, and its operation lifespan is as long as 58 h with only 25 mg Al when saline electrolyte is employed. The corresponding Al specific capacity is as high as 2338 mA h g−1. In addition, this battery exhibits an excellent flexibility when facing different bending angles from 60 to 180° and multiple bending times greater than 1000. Furthermore, a flexible current or voltage output can be easily obtained by scaling up or stacking the present flexible Al-air battery, respectively, and the corresponding stacking efficiency is as high as 94%. In the future, non-metal oxygen catalyst will be employed to improve its environmental friendliness, and hot-pressing will be adopted to further increase its robustness to external deformation. • A flexible Al-air battery is developed for powering flexible and portable devices. • Al anode is embedded inside the paper, while ink cathode is deposited on the paper. • Peak power density of 19 mW cm−2 and specific capacity of 2338 mA h g−1 is obtained. • Battery performance is very stable even it is bended to 180° and by 1000 times. • Battery scaling-up and stacking is very convenient and highly-efficient (94%). [ABSTRACT FROM AUTHOR]

A printable Al-air battery is successfully developed for the first time by printing the Al ink and the oxygen reduction ink onto a cellulose paper. Currently, the printable Al-air battery can provide an open-circuit voltage of 1 V, a peak power density of 6.6 mW cm−2 and a maximum current density of 40 mA cm−2 when using salt water as the electrolyte. With 6 mg Al, the battery can discharge at 1 mA cm−2 for almost 6 h, leading to a high specific capacity of 951 mA h g−1. It is found that a moderate concentration of the polymer binder and a high concentration of the carbon support are of great importance to the ink functionality, while the hot-press treatment can dramatically improve the electrode performance and robustness. Finally, screen-printed battery prototypes with a specific electrode pattern are demonstrated for powering a small electric fan and a light-emitting diode. The present printable Al-air battery is a novel type of primary power source with low fabrication cost, high energy density and great environmental friendliness, which is especially suitable for powering various disposable printed electronics in the future. Image 1 • An all screen-printed Al-air battery is proposed for powering printed electronics. • The Al ink is composed of Al microsphere, carbon nanotube and cellulose binder. • Peak power density of 6.6 mW cm−2 and current density of 40 mA cm−2 can be obtained. • The battery discharge specific capacity is as high as 951 mA h g−1. • Hot-pressing is found to significantly improve the printed anode integrity. [ABSTRACT FROM AUTHOR]

• A paper-based Al-air battery successfully developed for miniwatt applications. • The battery can work with limited electrolyte supply without external pumping. • Low-cost and low-grade Al employed with satisfactory discharge efficiency. • The paper substrate suppresses the Al self-corrosion with alkaline electrolyte. • An efficient and modular stacking strategy for battery pack development. Conventional Al-air battery is not suitable for mini-watt applications due to bulky liquid storage and complex water management. To achieve successful simplification and miniaturization, an innovative paper-based Al-air battery is developed in this study, which employs cellulose paper as electrolyte substrate, low-grade Al foil as anode and carbon paper as cathode. Despite its simple structure and low cost, this battery achieves satisfactory power output together with high efficiency. With alkaline electrolyte, an open-circuit voltage of 1.6 V, a peak power density of 21 mW cm−2 and a specific capacity of 1273 mA h g−1 are obtained. With saline electrolyte, the battery can continuously work at 1 mA cm−2 for 5.6 h with only 3.5 mg Al. In addition, it is found that the paper-based electrolyte delivery can suppress Al corrosion in alkaline environment, enabling the direct utilization of low-grade Al resources. Moreover, the battery performance is improved by optimizing properties of its components, such as cathode catalyst, electrode area ratio and paper substrate thickness. Finally, a 5-cell battery pack is successfully developed, achieving an open-circuit voltage of 7.7 V and a stacking efficiency as high as 97%. By further scaling-up, this battery pack is successfully demonstrated for charging portable electronics. [ABSTRACT FROM AUTHOR]

In this work, a lightweight, ultrathin and flexible paper-based gel electrolyte is developed for liquid-free Al-air batteries, which employs a natural cellulose paper to store an alkaline gel. The as-fabricated electrolyte can be applied in either mechanical-rechargeable or single-use Al-air batteries, providing an open-circuit voltage (OCV) of 1.5 V and a peak power density around 3.5 mW cm−2. In addition, the battery discharge specific capacity is as high as 900 mA h g−1 even with low-purity Al. Moreover, a flexible Al-air battery can be obtained, which exhibits a stable performance under different bending angles. By optimizing the electrolyte properties including polymer concentration, gel loading and solution casting time, the battery power output can be further improved to 6.4 mW cm−2. Finally, two stacking strategies are investigated for developing Al-air battery packs, including both vertical stacking and planar stacking. Benefited from the complete ionic isolation among the single cells, both stacking strategies are demonstrated viable, with a normal OCV of 5.6 V for a 4-cell stack and a stacking efficiency as high as 87.5%. Such kind of liquid-free Al-air batteries are especially suitable for powering portable electronic devices with small rated power. • A paper-based gel electrolyte is developed for liquid-free Al-air battery. • The battery can provide an OCV of 1.5 V and a peak power density of 6.4 mW cm−2 • A high specific capacity of 900 mA h g−1 can be achieved even with low-purity Al. • A flexible Al-air battery is also successfully developed. • A convenient and efficient stacking of Al-air battery pack is demonstrated. [ABSTRACT FROM AUTHOR]