Rational Design of Flexible Zn-Based Batteries for Wearable Electronic Devices

Abstract

The advent of 5G and the Internet of Things has spawned a demand for wearable electronic devices. However, the lack of a suitable flexible energy storage system has become the “Achilles’ Heel” of wearable electronic devices. Additional problems during the transformation of the battery structure from conventional to flexible also present a severe challenge to the battery design. Flexible Zn-based batteries, including Zn-ion batteries and Zn–air batteries, have long been considered promising candidates due to their high safety, eco-efficiency, substantial reserve, and low cost. In the past decade, researchers have come up with elaborate designs for each portion of flexible Zn-based batteries to improve the ionic conductivities, mechanical properties, environment adaptabilities, and scalable productions. It would be helpful to summarize the reported strategies and compare their pros and cons to facilitate further research toward the commercialization of flexible Zn-based batteries. In this review, the current progress in developing flexible Zn-based batteries is comprehensively reviewed, including their electrolytes, cathodes, and anodes, and discussed in terms of their synthesis, characterization, and performance validation. By clarifying the challenges in flexible Zn-based battery design, we summarize the methodology from previous investigations and propose challenges for future development. In the end, a research paradigm of Zn-based batteries is summarized to fit the burgeoning requirement of wearable electronic devices in an iterative process, which will benefit the future development of Zn-based batteries.

Enhancing Two-Electron Reaction Contribution in MnO2 Cathode Material by Structural Engineering for Stable Cycling in Aqueous Zn Batteries

“…Rechargeable aqueous zinc batteries have caught great attentions as one of the promising “beyond Li-ion” technologies for energy storage recently. − The Zn metal anode delivers high capacity (820 mAh g –1 ) and low redox potential (−0.76 V vs standard hydrogen electrode) based on the highly reversible Zn/Zn 2+ process in aqueous electrolytes. − A few cathode materials have been studied in aqueous zinc batteries. − Among them, MnO 2 is promising with a discharge voltage around 1.4 V and theoretical capacity of 308 mAh g –1 with a one-electron redox reaction of Mn 4+ /Mn 3+ . − Early studies reveal the Zn 2+ /H + de/insertion into MnO 2 structures and/or conversion reactions during charge and discharge. , Later on, it is noted that MnO 2 may also undergo a dissolution/deposition process with Mn 2+ , and the two-electron transfer reaction provides double theoretical capacity . This process has been promoted by using acidic electrolytes or compositing a proton reservoir for the cathode. , Besides, it has been shown that acetate helps with the Mn dissolution process and thus enhances the two-electron reaction .…”

Coupling MnS and CoS Nanocrystals on Self-Supported Porous N-doped Carbon Nanofibers to Enhance Oxygen Electrocatalytic Performance for Flexible Zn-Air Batteries

“…At present, the cathode materials of flexible ZABs are mainly classified into two categories: (1) powder electrocatalysts supported on carbon cloth or other conductive substrates; (2) flexible binder-free positive electrodes with abundant active sites. For many traditional flexible electrodes, active substances are coated on the flexible substrate with a polymer binder, which is easy to cause the shedding of the active catalyst and the occurrence of side reaction. , On the other hand, self-supported air electrodes demonstrate several advantages over powder-type catalysts, such as a high specific surface area, exposing more active reaction centers, fast electron transport paths, short ion diffusion length, and strong stability. , Flexible carbon nanofibers with a three-dimensional interleaved network obtained by classical electrospinning technology are widely used in flexible electrode materials due to their admirable electrical conductivity, flexibility, and high stability. In addition, defect-rich carbon fibers (CF) could participate in the modulation of the electronic structure of the composite through the catalyst–support interaction and thus improve the electrocatalytic performance. , …”

“…44,45 On the other hand, selfsupported air electrodes demonstrate several advantages over powder-type catalysts, such as a high specific surface area, exposing more active reaction centers, fast electron transport paths, short ion diffusion length, and strong stability. 46,47 Flexible carbon nanofibers with a three-dimensional interleaved network obtained by classical electrospinning technology are widely used in flexible electrode materials due to their admirable electrical conductivity, flexibility, and high stability. In addition, defect-rich carbon fibers (CF) could participate in the modulation of the electronic structure of the composite through the catalyst−support interaction and thus improve the electrocatalytic performance.…”

Three-Dimensional Fe-N-C-Supported Amorphous NiFe alloy Nanoparticles as an Efficient Bifunctional Electrocatalyst for Zn-Air Batteries

“…Although researchers have made great progress in the research of bifunctional catalysts, it is still challenging to synthesize bifunctional catalysts with lower cost, higher performance, and longer life [3,4] . Because electrocatalysts suitable for OER usually exhibit poor ORR catalytic activity, and vice versa [5][6][7][8][9] .…”