Next-Generation Batteries.

Abstract

The Next-Generation Battery Symposium was held in 2016 at the Institute of Superconducting and Electronic Materials (ISEM), University of Wollongong, Australia. 2016 marks the 22nd anniversary of ISEM. The total number of attendees was around 150. Most of the attendees were newly established researchers. This symposium provided an opportunity for all the young researchers to get together and share their knowledge and their current research work. The discussions and presentations were of very high quality and mainly on next-gene­­ration batteries. “Next-generation” batteries, in our opinion, are all about materials and systems that are currently not commercially available, but could be commercialized in the near future. With the help of Dr. Esther Levy (Consulting Editor for Advanced Materials), we proposed this special issue based on selected presentations at that symposium for Advanced Materials. This issue is composed of Reviews, Research News, and Communications. We have tried to cover all the aspects of promising next-generation battery systems, including high-energy Li-ion batteries, Na-ion batteries, LiS batteries, LiO2 batteries, NaO2 batteries, Al-ion batteries, and flow batteries. Supercapacitors and solid-oxide fuel cells are also introduced and reviewed in this issue. From the materials point of view, this issue covers different materials, designs, configurations, and morphologies, such as 2D materials, porous materials, and 3D nanostructures. Different kinds of active materials and electrolyte materials, from inorganic materials to organic materials, are also reviewed for battery applications. Li-ion batteries are playing an important role in our daily lives. One important issue is how to meet the rapidly growing demand for electric vehicles and energy storage. Li-ion batteries are facing great challenges to further improve energy density, cycle life, and operational safety. Developing high-capacity cathode materials is one of the major problems to be solved. Dingguo Xia and Biao Li (article number 1701054) review previous work on anionic redox, which is considered as a crucial reaction in the further development of high-capacity cathode materials for Li-ion batteries, to provide a better understanding of anionic-redox mechanisms. The involvement of oxygen redox can achieve multiple electron transfer, resulting in high capacity. High capacity also brings less structural stability, however. Although the challenge still exists for high-energy-density cathode materials for the Li-ion battery, anionic redox could provide new scope for the design of superior electrodes. Zaiping Guo's group (article number 1605807) reviews cathode surface-coating technology for high-energy Li-ion batteries, as well as other battery systems. High-energy anode materials for lithium-ion batteries, including Si and Sn, are also reviewed and reported in this issue. Yinzhu Jiang (article number 1606499) reports a high-performance Sn-based alloying anode boosted by pseudocapacitance at interfaces of Fe/Sn/Li2O, while Wei Luo, Dongyuan Zhao, and co-workers (article number 1700523) report an elastic coating of amorphous TiO2 to significantly improve the cycling stability. Novel 2D materials are also reviewed by Ziqi Sun's group (article number 1700176) for next-generation batteries. In particular, Yi Du's group (article number 1606716) highlights silicene as a novel 2D material that could serve as an interesting anode material for future Li-ion-battery applications. Hierarchically porous micro-/nanostructures are also outlined by Weishan Li's group (article number 1607015) for battery applications. From the sustainability point of view, organic redox compounds containing earth-abundant elements (C, H, O, N, etc.) will be ideal electrode materials for renewable energy applications and are environmentally benign. Jun Chen and co-workers (article number 1607007) summarize a molecular engineering approach for tuning the capacity, potential, kinetics, and stability of carbonyl electrode materials for both Li-ion batteries and flow batteries. Lithium–sulfur (LiS) batteries have been considered as energy-storage devices with high specific-energy density, along with the advantages of low cost and natural abundance. LiS batteries have been investigated over the past decade, and significant progress has been made. Feng Li's group (article number 1606823) summarizes the status of and prospects for LiS batteries. More research needs to be done, however, with the emphasis on integral design, including optimization of the sulfur cathode, lithium anode, and electrolyte to achieve reliable LiS batteries with satisfactory performance for possible market penetration. The electrolyte is one of the key points that affect the cycle life of LiS batteries. Jiazhao Wang and co-workers (article number 1700449) report on the relationship between the molecular structure and the properties of common organic electrolytes, along with their effects on LiS batteries. Guoxiu Wang's group (article number 1700587) reports on the performance of a novel Prussian Blue cathode with sulfur and soluble polysulfides that could significantly improve the cycle life and rate capability. Renjie Chen's group (article number 1700598) reports that large-scale production of 18.6 A h pouch cells with specific energy of 460 A h kg−1 has been achieved with modular-assembled carbon microstructures as the sulphur host. LiS batteries are near commercialization, as more and more prototype large-scale batteries have been achieved. The application of LiS batteries in drones could be promising due to their high specific-energy density at the current stage. The use of LiS batteries in transportation will have to wait for a solution to the safety issue posed by lithium metal on the anode side due to the growth of Li dendrites. Therefore, Ying Chen's group (article number 1700542) summarizes the strategies toward anode improvement for LiS batteries, including inserting an interlayer, modifying the separator and electrolyte, using artificial protection layers, and using alternative anodes to replace the Li-metal anode. The sodium-ion battery, as a promising low-cost battery system, could be used for large-scale application in stationary batteries. Metal sulfides/selenides (MXs) with high specific capacity owing to the multi-electron reaction mechanisms are the earliest types of materials used for sodium intercalation and de-intercalation. Zhe Hu et al. (article number 1700606) review the current progress on MXs for next generation Na-ion batteries. Novel mechanisms and structures could shine light on future novel materials design. Alloy-based anode materials such as Sn, Sb, and P with high theoretical specific capacity are summarized by Wenping Sun's group (article number 1700622). Great progress has been achieved toward high-capacity and durable anode materials. Nevertheless, challenges such as low initial Coulombic efficiency, an unclear mechanism, and unstable solid electrolyte layers still remain. Yan Yu and co-workers (article number 1700431) give an overview of the recent approaches to enhance the electrical conductivity and structural stability of sodium superionic conductor (NASICON)-based electrode materials for anode, cathode, and electrolyte application. NASICON-type cathode materials are more high-power-oriented materials than energy-oriented materials owing to their high ionic conductivity and relatively low energy density. The search for batteries with higher energy density has led to metal–oxygen batteries, including LiO2 batteries (3456 W h kg−1Li2O2) and NaO2 batteries (1105 W h kg−1NaO2). Yong-Mook Kang's group (article number 1606572) compares both systems. The major drawbacks for LiO2 batteries include electrolyte instability and superoxide attack, unstable carbon electrodes, lithium-dendrite formation, low round-trip efficiency, short cycle life, and the requirement for pure oxygen. NaO2 batteries offer low cost and relatively high efficiency due to the corresponding discharge product NaO2 rather than Li2O2 as for LiO2 batteries. Zhangquan Peng, Guoxiu Wang, and co-workers (article number 1606816) report that nanostructured carbon materials with controlled porosity and pore-size distribution can control the morphology of the NaO2 discharge product, so as to develop high-performance NaO2 batteries. The study of both LiO2 and NaO2 batteries is still at an early stage, however. Achieving a fundamental understanding of the mechanism is still important. Shuangyin Wang and co-workers (article number 1606459) review the important role of defects in oxygen electrocatalysis. The types of defects, the strategies to generate defects in electrocatalysts, and the techniques to identify the defects are summarized. From previous commercial experience, personally speaking, we will have to wait for more than 30–50 years for such devices to be commercialized. If we consider 30 years as one generation, these devices will be for the next generation. Al-ion batteries are attractive next-generation batteries owing to their low cost and good safety. The low specific capacity (≈70 mA h g−1 for graphite) is one of their major drawbacks, however. Lianzhou Wang's group (article number 1606132) report that a 3D reduced-graphene-oxide-supported SnS2 nanosheet composite can provide high capacity (392 mA h g−1) and good cycling stability for Al-ion batteries. However, this system is only a new-born baby. Fundamental understanding and more advanced design and optimization will be needed for this kind of system to be commercialized. Recent advances in materials and related key components for solid-oxide fuel cells (SOFCs) operating below 500 °C are summarized by Wei Zhou, Zhonghua Zhu, and co-workers (article number 1700132) with a focus on the materials, structures, and techniques under development. As electricity gene­rators, SOFCs can convert the chemical energy in various fuels to electric power with high efficiency. If new materials and techniques could reduce the operating temperature down to 300 °C, the application of SOFCs could be extended to transportation, military applications, and portable devices in the near future. Jianli Kang's group (article number 1700515) reviews the current progress on pseudocapacitors in the design of 3D binder-free nanoarchitectures. Pseudocapacitors could fill the technology gap between capacitors and batteries to provide high power density and reasonable energy density due to the fast surface or near-surface redox charge transfer. It is worth noting that a battery is a system. A high-performance battery is a combination of well-performing components. Battery research, also involves all the different areas of knowledge in materials science, chemistry, physics, and materials engineering. The success of commercialization also depends on the cost factor, safety issues, chemical engineering, electrical engineering, and market readiness. We are in a rapi­­dly changing world, as we draw the future world in the cover picture. It is for sure that next-generation batteries will help our society to become renewable and sustainable. To close, we would like to thank Dr. Esther Levy and Dr. James Cook both from Wiley for their kind support for and contributions to this special issue. In the meantime, another special issue of Advanced Energy Materials has also been designed to complement the special issue in Advanced Materials. The other special issue only contains Reviews, including high-energy Si anodes for Li-ion batteries, carbon-based anodes, and cathode materials for sodium-ion batteries, LiS batteries, NaS batteries, and Liair batteries. Shulei Chou is a Senior Research Fellow in ISEM in the University of Wollongong (UOW). He obtained his bachelor's (1999) and master's degrees (2004) from Nankai University, China. His Ph.D. degree was granted by UOW in 2010. His research is focused on energy-storage materials for battery applications, especially on novel composite materials, new binders, and new electrolytes for Li-/Na-ion and metal–air batteries. Shi-Xue Dou is a Distingiushed Professor and Director of the Institute for Superconducting and Electronic Materials, Australian Institute of Innovative Materials, University of Wollongong. He received his Ph.D. in chemistry in 1984 at Dalhousie University, Canada. His research interests include energy storage, superconductors, and electronic materials.