In situ atomic‐scale observation of size‐dependent (de)potassiation and reversible phase transformation in tetragonal FeSe anodes
Ran Cai,
Lixia Bao,
Wenqi Zhang,
Weiwei Xia,
Chunhao Sun,
Weikang Dong,
Xiaoxue Chang,
Ze Hua,
Ruiwen Shao,
Toshio Fukuda,
Zhefei Sun,
Haodong Liu,
Qiaobao Zhang,
Feng Xu,
Lixin Dong
Affiliations
Ran Cai
Beijing Advanced Innovation Center for Intelligent Robots and Systems, School of Medical Technology Beijing Institute of Technology Beijing People's Republic of China
Lixia Bao
Analysis & Testing Center Beijing Institute of Technology Beijing People's Republic of China
Wenqi Zhang
Department of Biomedical Engineering City University of Hong Kong Hong Kong People's Republic of China
Weiwei Xia
Shaanxi Materials Analysis and Research Center, School of Materials Science and Engineering Northwestern Polytechnical University Xi'an People's Republic of China
Chunhao Sun
School of Environmental and Safety Engineering North University of China Taiyuan People's Republic of China
Weikang Dong
Analysis & Testing Center Beijing Institute of Technology Beijing People's Republic of China
Xiaoxue Chang
Analysis & Testing Center Beijing Institute of Technology Beijing People's Republic of China
Ze Hua
Analysis & Testing Center Beijing Institute of Technology Beijing People's Republic of China
Ruiwen Shao
Beijing Advanced Innovation Center for Intelligent Robots and Systems, School of Medical Technology Beijing Institute of Technology Beijing People's Republic of China
Toshio Fukuda
Beijing Advanced Innovation Center for Intelligent Robots and Systems, School of Medical Technology Beijing Institute of Technology Beijing People's Republic of China
Zhefei Sun
Department of Materials Science and Engineering, College of Materials Xiamen University Xiamen Fujian People's Republic of China
Haodong Liu
Department of Nanoengineering University of California San Diego La Jolla California USA
Qiaobao Zhang
Department of Materials Science and Engineering, College of Materials Xiamen University Xiamen Fujian People's Republic of China
Feng Xu
SEU‐FEI Nano‐Pico Center, Key Laboratory of MEMS of Ministry of Education Southeast University Nanjing People's Republic of China
Lixin Dong
Department of Biomedical Engineering City University of Hong Kong Hong Kong People's Republic of China
Abstract Potassium‐ion batteries (PIBs) are considered promising alternatives to lithium‐ion batteries owing to cost‐effective potassium resources and a suitable redox potential of −2.93 V (vs. −3.04 V for Li+/Li). However, the exploration of appropriate electrode materials with the correct size for reversibly accommodating large K+ ions presents a significant challenge. In addition, the reaction mechanisms and origins of enhanced performance remain elusive. Here, tetragonal FeSe nanoflakes of different sizes are designed to serve as an anode for PIBs, and their live and atomic‐scale potassiation/depotassiation mechanisms are revealed for the first time through in situ high‐resolution transmission electron microscopy. We found that FeSe undergoes two distinct structural evolutions, sequentially characterized by intercalation and conversion reactions, and the initial intercalation behavior is size‐dependent. Apparent expansion induced by the intercalation of K+ ions is observed in small‐sized FeSe nanoflakes, whereas unexpected cracks are formed along the direction of ionic diffusion in large‐sized nanoflakes. The significant stress generation and crack extension originating from the combined effect of mechanical and electrochemical interactions are elucidated by geometric phase analysis and finite‐element analysis. Despite the different intercalation behaviors, the formed products of Fe and K2Se after full potassiation can be converted back into the original FeSe phase upon depotassiation. In particular, small‐sized nanoflakes exhibit better cycling performance with well‐maintained structural integrity. This article presents the first successful demonstration of atomic‐scale visualization that can reveal size‐dependent potassiation dynamics. Moreover, it provides valuable guidelines for optimizing the dimensions of electrode materials for advanced PIBs.
