Electrochemical Energy Reviews

Electrospun Flexible Nanofibres for Batteries: Design and Application

P. Robert Ilango, A. Dennyson Savariraj, Hongjiao Huang, Linlin Li, Guangzhi Hu, Huaisheng Wang, Xiaodong Hou, Byung Chul Kim, Seeram Ramakrishna, Shengjie Peng

2023, 6(4): 31. doi:10.1007/s41918-022-00148-4

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Flexible and free-standing electrospun nanofibres have been used as electrode materials in electrochemical energy storage systems due to their versatile properties, such as mechanical stability, superb electrical conductivity, and high functionality. In energy storage systems such as metal-ion, metal-air, and metal-sulphur batteries, electrospun nanofibres are vital for constructing flexible electrodes and substantially enhancing their electrochemical properties. The need for flexible batteries has increased with increasing demand for new products such as wearable and flexible devices, including smartwatches and flexible displays. Conventional batteries have several semirigid to rigid components that limit their expansion in the flexible device market. The creation of flexible and wearable batteries with greater mechanical flexibility, higher energy, and substantial power density is critical in meeting the demand for these new electronic items. The implementation of carbon and carbon-derived composites into flexible electrodes is required to realize this goal. It is essential to understand recent advances and the comprehensive foundation behind the synthesis and assembly of various flexible electrospun nanofibres. The design of nanofibres, including those comprising carbon, N-doped carbon, hierarchical, porous carbon, and metal/metal oxide carbon composites, will be explored. We will highlight the merits of electrospun carbon flexible electrodes by describing porosity, surface area, binder-free and free-standing electrode construction, cycling stability, and performance rate. Significant scientific progress has been achieved and logistical challenges have been met in promoting secondary battery usage; therefore, this review of flexible electrode materials will advance this easily used and sought-after technology. The challenges and prospects involved in the timely development of carbon nanofibre composite flexible electrodes and batteries will be addressed.

Ion Migration Mechanism Study of Hydroborate/Carborate Electrolytes for All-Solid-State Batteries

Huixiang Liu, Xian Zhou, Mingxin Ye, Jianfeng Shen

2023, 6(4): 32. doi:10.1007/s41918-023-00191-9

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Hydroborate/carborate electrolytes represent an emerging and newly rediscovered solid electrolyte used in various all-solid-state batteries (such as lithium-ion batteries and sodium-ion batteries). High ionic conductivity, wide chemical/electrochemical stability, low density, and favorable mechanical properties make hydroborate/carborate electrolytes a promising candidate for solving the difficult challenges faced by the device integration and processing of all-solid-state batteries. It is remarkable that the ionic conductivity of solid electrolytes can be simply adjusted up to 10^?3 S cm^?1, and the optimized ionic conductivity can even reach 10^?2 S cm^?1. Furthermore, hydroborate/carborate electrolytes have been successfully formed and applied to?~?5 V high-voltage solid-state batteries. However, due to certain characteristics of hydroborate/carborate electrolytes, such as anion rotation and phase transition, it is challenging to understand the mechanism of their high ionic conductivity. Therefore, in this review, we summarized the latest research progress on hydroborate/carborate electrolytes, highlighted various mechanisms underlying the conductivity, described emerging characterization techniques and theoretical calculations, and listed general guidelines to unravel the high conductivity of hydroborate/carborate compounds. Novel strategies and suggestions on hydroborate/carborate work are also proposed. Following emerging research trends, we project promising future development toward the realization of hydroborate/carborate electrolytes in practical applications.

Application of Solid Catalysts with an Ionic Liquid Layer (SCILL) in PEMFCs: From Half-Cell to Full-Cell

Xiaojing Cheng, Guanghua Wei, Liuxuan Luo, Jiewei Yin, Shuiyun Shen, Junliang Zhang

2023, 6(4): 33. doi:10.1007/s41918-023-00195-5

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The advantages of zero emission and high energy efficiency make proton exchange membrane fuel cells (PEMFCs) promising options for future energy conversion devices. To address the cost issue associated with Pt-based electrocatalysts, considerable effort over the past several years has been devoted to catalyst surface modification by means of novel electrocatalysts, such as solid catalysts with an ionic liquid layer (SCILL), which improves both the oxygen reduction reaction (ORR) activity and durability. However, despite numerous reports of dramatically enhanced ORR activity, as determined via the rotating disk electrode (RDE) method, few studies on the application of SCILLs in membrane electrode assembly (MEA) have been reported. The underlying reason lies in the well-acknowledged technological gap between half-cells and full-cells, which originates from the disparate microenvironments for three phase boundaries. Therefore, the objective of this review is to compare the detailed information about improvements in fuel cell performance in both half- and full-cells, thus increasing the fundamental understanding of the mechanism of SCILL. In this review, the concept of SCILL and its origin are introduced, the outstanding electrochemical performance of SCILL catalysts in both RDE and MEA measurements is summarized, and the durability of SCILL catalysts is analysed. Subsequently, proposed mechanisms for the enhanced ORR activity in half-cells, the improved oxygen transport in full-cells and the boosted stability of SCILL catalysts are discussed, while the effects of the IL chemical structure, IL loading as well as the operating conditions on the performance and lifetime of SCILL catalysts are assessed. Finally, comprehensive conclusions are presented, and perspectives are proposed in the last section. It is believed that the new insight presented in this review could provide guidance for the further development of SCILLs in low-Pt PEMFCs.

On Energy Storage Chemistry of Aqueous Zn-Ion Batteries: From Cathode to Anode

Xiujuan Chen, Wei Li, David Reed, Xiaolin Li, Xingbo Liu

2023, 6(4): 34. doi:10.1007/s41918-023-00194-6

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Rechargeable aqueous zinc-ion batteries (ZIBs) have resurged in large-scale energy storage applications due to their intrinsic safety, affordability, competitive electrochemical performance, and environmental friendliness. Extensive efforts have been devoted to exploring high-performance cathodes and stable anodes. However, many fundamental issues still hinder the development of aqueous ZIBs. Here, we critically review and assess the energy storage chemistries of aqueous ZIBs for both cathodes and anodes. First, this review presents a comprehensive understanding of the cathode charge storage chemistry, probes the existing deficiencies in mechanism verification, and analyzes contradictions between the experimental results and proposed mechanisms. Then, a detailed summary of the representative cathode materials and corresponding comparative discussion is provided with typical cases encompassing structural features, electrochemical properties, existing drawbacks, and feasible remedies. Subsequently, the fundamental chemical properties, remaining challenges, and improvement strategies of both Zn metal and non-Zn anodes are presented to thoroughly explore the energy storage chemistry of ZIBs and pursue the development of high-performance ZIBs. Furthermore, the progress of mechanistic characterization techniques and theoretical simulation methods used for ZIBs is timely reviewed. Finally, we provide our perspectives, critical analysis, and insights on the remaining challenges and future directions for development of aqueous ZIBs.

Printed Solid-State Batteries

Shiqiang Zhou, Mengrui Li, Peike Wang, Lukuan Cheng, Lina Chen, Yan Huang, Suzhu Yu, Funian Mo, Jun Wei

2023, 6(4): 35. doi:10.1007/s41918-023-00200-x

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Solid-state batteries (SSBs) possess the advantages of high safety, high energy density and long cycle life, which hold great promise for future energy storage systems. The advent of printed electronics has transformed the paradigm of battery manufacturing as it offers a range of accessible, versatile, cost-effective, time-saving and ecoefficiency manufacturing techniques for batteries with outstanding microscopic size and aesthetic diversity. In this review, the state-of-the-art technologies and structural characteristics of printed SSBs have been comprehensively summarized and discussed, with a focus on the cutting-edge printing processes. Representative materials for fabricating printed electrodes and solid-state electrolytes (SSEs) have been systematically outlined, and performance optimization methods of printed SSBs through material modification have been discussed. Furthermore, this article highlights the design principles and adjustment strategies of printing processes of advanced SSB devices to realize high performance. Finally, the persistent challenges and potential opportunities are also highlighted and discussed, aiming to enlighten the future research for mass production of printed SSBs.

Review on Low-Temperature Electrolytes for Lithium-Ion and Lithium Metal Batteries

Sha Tan, Zulipiya Shadike, Xinyin Cai, Ruoqian Lin, Atsu Kludze, Oleg Borodin, Brett L. Lucht, Chunsheng Wang, Enyuan Hu, Kang Xu, Xiao-Qing Yang

2023, 6(4): 36. doi:10.1007/s41918-023-00199-1

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Among various rechargeable batteries, the lithium-ion battery (LIB) stands out due to its high energy density, long cycling life, in addition to other outstanding properties. However, the capacity of LIB drops dramatically at low temperatures (LTs) below 0 °C, thus restricting its applications as a reliable power source for electric vehicles in cold climates and equipment used in the aerospace. The electrolyte engineering has proved to be one of the most effective approaches to mitigate LIB performance degradation at LTs. In this review, we summarize the important factors contributing to the deterioration in Li⁺ transport and capacity utilization at LTs while systematically categorize the solvents, salts and additives reported in the literature. Strategies to improve the Li⁺ transport kinetics, in the bulk electrolyte and across the interphases, are discussed. In particular, the formation mechanism of solid electrolyte interphase and its functionality for LT electrolytes are analyzed. Perspectives on the future evolution of this area are also provided.

Exploring More Functions in Binders for Lithium Batteries

Lan Zhang, Xiangkun Wu, Weiwei Qian, Kecheng Pan, Xiaoyan Zhang, Liyuan Li, Mengmin Jia, Suojiang Zhang

2023, 6(4): 37. doi:10.1007/s41918-023-00198-2

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As an indispensable part of the lithium-ion battery (LIB), a binder takes a small share of less than 3% (by weight) in the cell; however, it plays multiple roles. The binder is decisive in the slurry rheology, thus influencing the coating process and the resultant porous structures of electrodes. Usually, binders are considered to be inert in conventional LIBs. In the pursuit of higher energy density, many new binders are being developed for specific targets, such as the high-voltage (typically, ? 4.5 V) cathodes, conversion/alloy-type cathodes/anodes with large volume effect, and solid-state batteries (SSBs), in which these binders demonstrate their various functions. They may influence the solid electrolyte interface component, ensure the electrode/electrolyte interfacial stability, transport ions/electrons in the electrodes, provide adhesion and flexibility to solid-state electrolyte (SSE) films, etc. Here in this review, we try to summarize the advances on binders, among which the ones for high-voltage cathode materials, thick electrodes, micro-sized silicon particles, SSEs and SSBs are highlighted. We believe that the advanced functional binders would play decisive roles in the future development of high-energy–density LIBs and SSBs.

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