Date Published: January 22, 2018
Publisher: John Wiley and Sons Inc.
Author(s): Jing Pan, Yang Yang Xu, Huan Yang, Zehua Dong, Hongfang Liu, Bao Yu Xia.
Zn–air batteries are becoming the promising power sources for portable and wearable electronic devices and hybrid/electric vehicles because of their high specific energy density and the low cost for next‐generation green and sustainable energy technologies. An air electrode integrated with an oxygen electrocatalyst is the most important component and inevitably determines the performance and cost of a Zn–air battery. This article presents exciting advances and challenges related to air electrodes and their relatives. After a brief introduction of the Zn–air battery, the architectures and oxygen electrocatalysts of air electrodes and relevant electrolytes are highlighted in primary and rechargeable types with different configurations, respectively. Moreover, the individual components and major issues of flexible Zn–air batteries are also highlighted, along with the strategies to enhance the battery performance. Finally, a perspective for design, preparation, and assembly of air electrodes is proposed for the future innovations of Zn–air batteries with high performance.
Recently, sustainable development became a hot topic and major concern of the modern society, especially due to the great pressure of serious environmental issues and increasing energy demands.1 Renewable energy including solar, wind, waves, and hydropower are being the promising alternatives to replace the traditional fossil fuels to achieve the goal of green, economical, and sustainable society.2 However, their power output varies significantly over seasons, climates, and locations, and often mismatches the energy demands, even poisons gridding power.3 The effective and feasible solution to address the mismatch is to exploit energy storage and conversion technologies, and they are becoming the top priorities of current research for the scientific community, commercial companies, and national governments.4 As one of the most promising electrochemical energy technologies, lithium (Li)‐ion batteries lead the market of energy storage, especially consumer batteries in electronics and power batteries in hybrid/electric vehicles and stationary power plants.5 However, the insufficient energy densities of rechargeable Li‐ion batteries (200–250 Wh kg−1) limit their further development and applications.6
Zn–air battery was initially proposed in 1878, while the silver wire acted as the air electrode.26 Few years later, a real gas diffusion electrode consisting porous carbon black and nickel current collector was reported in a so‐called Walker–Wilkins battery. Since the 1930s, a primary Zn–air battery was commercialized and was further applied in the hearing aids in 1970s.27 Now, its application has spread to seismic telemetry, railroad signaling, navigational buoys, remote communications, even electric vehicles and power grid.28, 29 However, hybrid/electric vehicles and power backup often need rechargeable batteries rather than primary ones.30
Except for the development of power battery, high market demands in consumer electronics especially portable and wearable devices also motive the new evolution of Zn–air batteries with some advanced features such as lightweight and shape conformability in the small unit.239 Therefore, developing suitable power supply system becomes imperative, Zn–air battery with flexibility and stretchability is then highly desirable.240 To successfully achieve this concept, flexibility of each component (cathode, anode, separator, and electrolyte) is the vital matter to obtain its stable battery performance during the repetitive external strain force.241 A summary of air electrodes and electrolytes employed in flexible Zn–air batteries could be seen in Table3.
Zn–air battery is one of the utmost potential energy technologies because of its high specific density and low cost, which would encounter the ever‐increasing energy demands for portable/wearable electronic devices and electric vehicles. Although considerable progresses have been made in recent years, there are still many problems need to be addressed. For power batteries in electric vehicles and power plants, the low practical energy density is the main hindrance, and consumer batteries also have to take into consideration the mechanical performance, safety and stability in flexible and portable devices. But all of these are closely related to air electrodes and their relevant components, including oxygen electrocatalysts, current collectors, and electrolytes. This review highlights their exciting advances and major issues in aspect of respective components. Thus, the intention of this review is to provide valuable understandings and insights for research community and application sectors to speed up innovation especially in air electrodes related parts for high performance Zn–air batteries.
The authors declare no conflict of interest.