Lithium-ion batteries (LIBs) have become immensely popular as the go-to power source for a wide variety of electronic devices and vehicles over the past two decades. Although it is hard to overstate the transformative effects that LIBs have had on modern societies, this technology has a fair share of disadvantages that cannot be ignored any further. These include the limited availability of lithium as well as safety and environmental concerns. These drawbacks have motivated scientists around the world to look for alternative battery technologies, such as aqueous batteries. Potassium-ion batteries (KIBs) are a prominent example; these batteries are made from abundantly available materials and are much safer than LIBs. Moreover, KIBs can utilize a water-in-salt electrolyte (WISE), which makes them more stable thermally and chemically.
锂离子电池（LIBs）在过去二十年中已成为各类电子设备和车辆的首选电源，广受欢迎。尽管LIBs对现代社会产生的变革性影响怎么强调都不为过，但这项技术也存在不少不容忽视的缺点，包括锂资源有限以及安全和环境问题。这些缺陷促使全球科学家寻找替代电池技术，例如水系电池。钾离子电池（KIBs）是一个典型例子；这些电池由储量丰富的材料制成，且比LIBs安全得多。此外，KIBs可采用water-in-salt electrolyte（WISE），这使其在热稳定性和化学稳定性方面表现更优。

However, the prevention of hydrogen evolution at the negative electrode for its stabilization is a major challenge in high-voltage aqueous batteries. While solid-electrolyte interphases (SEI) that form between these electrodes and the electrolyte solution help stabilize the electrodes in LIBs (by preventing electrolyte decomposition and self-discharge of the batteries), they have been scarcely researched in the context of KIBs.
然而，在高电压水系电池中，防止负极析氢以稳定其性能是一大挑战。尽管锂离子电池（LIBs）中电极与电解液之间形成的固体电解质界面相（SEI）能通过阻止电解液分解和电池自放电来稳定电极，但此类研究在钾离子电池（KIBs）领域仍极为匮乏。

To address this major knowledge gap, a research team from Tokyo University of Science- (TUS), Japan, has recently conducted a pioneering study to gain insights into SEI formation and their properties in WISE-based KIBs. Their findings were published online in the journal Angewandte Chemie International Edition on August 18, 2023. The study, led by TUS Professor Shinichi Komaba, is co-authored by Junior Associate Professor Ryoichi Tatara, Dr. Zachary T. Gossage, and Ms. Nanako Ito, all from TUS.
为填补这一重大知识空白，日本东京理科大学（TUS）的研究团队近期开展了一项开创性研究，旨在揭示基于WISE的KIBs中SEI膜的形成机制及其特性。该研究成果于2023年8月18日在线发表于期刊《Angewandte Chemie International Edition》。此项研究由TUS教授Shinichi Komaba领导，合著者包括TUS助理教授Ryoichi Tatara、Zachary T. Gossage博士以及Nanako Ito女士。

The researchers mainly employed two advanced analytical techniques -- scanning electrochemical microscopy (SECM) and operando electrochemical mass spectrometry (OEMS) -- to observe how SEI forms and reacts in real time during the operation of a KIB with a 3,4,9,10-perylenetetracarboxylic diimide negative electrode and 55 mol/kg K(FSA)_0.6(OTf)_0.4∙1H₂O, a WISE developed by the team in a previous study.
研究人员主要采用了两种先进的分析技术——扫描电化学显微镜（SECM）和操作电化学质谱（OEMS）——来观察在钾离子电池（KIB）运行过程中，采用3,4,9,10-苝四甲酰二亚胺负极和55 mol/kg K(FSA)(OTf)∙1H₂O（该团队在先前研究中开发的一种WISE电解质）时，SEI如何实时形成并发生反应。

The experiments revealed that SEI forms a passivating layer in WISE akin to that seen in LIBs, with slow apparent electron transfer rates, helping suppress hydrogen evolution. This can ensure stable performance and higher durability of KIBs. However, the researchers observed that the coverage of the SEI layer was incomplete at higher operating voltages, leading to hydrogen evolution.
实验表明，SEI在WISE中形成的钝化层与LIBs中的类似，具有较慢的表观电子转移速率，有助于抑制析氢反应。这可以确保KIBs的稳定性能和更高耐久性。然而，研究人员发现，在较高工作电压下，SEI层的覆盖不完全，导致析氢反应发生。

Taken together, the results reveal the need to explore potential avenues to enhance SEI formation in future aqueous batteries. "While our results reveal interesting details on the properties and stability of SEI found in one particular WISE, we should also focus on reinforcing the SEI network to achieve improved functionality," comments Prof. Komaba. "SEI could perhaps be improved by the development of other electrolytes that produce unique SEIs, but also through the incorporation of electrolyte additives or electrode surface pretreatment."
综上所述，研究结果表明有必要探索未来水系电池中增强SEI形成的潜在途径。小俣教授评论道：“虽然我们的研究结果揭示了在特定WISE中发现的SEI的特性和稳定性的有趣细节，但我们还应专注于强化SEI网络以实现更好的功能。SEI或许可以通过开发能产生独特SEI的其他电解液来改善，也可以通过引入电解液添加剂或电极表面预处理来实现。”

This study also highlights the power of SECM and OEMS for gaining a solid understanding of electrode-electrolyte interactions in next-generation batteries. "These techniques provide a powerful means for tracking the development, coverage, ion transfer, and stability of SEI and can easily be adapted for a variety of electrolytes and electrodes," explains Prof. Komaba. "We hope that this work encourages other researchers to further explore SECM and OEMS as advanced characterization methods that can be incorporated with traditional battery measurements to gain deeper insights."
这项研究还凸显了SECM和OEMS在深入理解下一代电池中电极-电解质相互作用方面的能力。“这些技术为追踪SEI的形成、覆盖范围、离子转移和稳定性提供了强有力的手段，并且可以轻松适用于各种电解质和电极，”Komaba教授解释道，“我们希望这项工作能鼓励其他研究人员进一步探索SECM和OEMS作为先进表征方法，将其与传统电池测量相结合，以获得更深入的见解。”

The development of aqueous batteries such as KIBs will be instrumental for sustainable societies in the future, since they could replace the expensive and hazardous LIBs currently used in electric vehicles, smart grids, renewable energy systems, and marine applications. By making energy storage more accessible, aqueous batteries will aid the transition toward carbon-neutral energy generation, paving the way for a greener future.
诸如KIBs等水系电池的发展对未来可持续社会至关重要，它们能替代当前电动汽车、智能电网、可再生能源系统和海事应用中使用的昂贵且存在安全隐患的LIBs。通过提高储能的普及性，水系电池将助力碳中性能源转型，为更绿色的未来铺平道路。