In situ atomic‐scale observation of size‐dependent (de)potassiation and reversible phase transformation in tetragonal FeSe anodes

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.

Unveiling the Nature of Ultrastable Potassium Storage in Bi0.48Sb1.52Se3 Composite

“…Meanwhile, BiPS 4 /CNTs composite showed an excellent rate capability . Interestingly, the conductivity of Se (1 × 10 –3 S m –1 ), a member of the group VI element, is several orders higher than that of S (5 × 10 –28 S m –1 ). , Afterward, a series of multicomponent metal selenides (such as CoPSe/NC, BiSbSe 3 , etc .) have also been reported. , The performance of these conversion alloy anodes has been improved sharply based on rational structural engineering and composite electrode design.…”

Modulations in Superconductors: Probes of Underlying Physics

“…[ 118 ] Interestingly, the FeSe nanoflakes are also investigated as anodes in potassium‐ion batteries due to the reversible and large accommodation of K + ions. [ 124 ] Typically, the step‐by‐step process for device fabrication is shown in Figure 3e. [ 119 ] The SIC used is lithium‐ion conductive glass ceramics Li 2 Al 2 SiP 2 TiO 13 , working as both the substrate and gate medium.…”

Enabling highly-efficient and stable potassium-ion storage by exposing atomic-dispersed super-coordinated antimony O2Sb1N4 sites on N-doped carbon nanosheets

“…Potassium-ion batteries (PIBs) have been recognized as one of the promising complementary alternatives to lithium-ion batteries owing to the utilization of earth-abundant potassium and the comparable redox potential (K/K + , À2.93 V vs. standard hydrogen potential) to that of Li/Li + (À3.04 V). [1][2][3][4][5][6] Although much progress has been made, critical problems such as the massive volume expansion and sluggish reaction kinetics during cycling caused by large K + ions (1.38 Å) result in unsatisfactory performance, being an obstacle to the practical deployment of PIBs with high energy density and long cycle lifespan. [7][8][9] Exploring suitable electrode materials for PIBs, especially for anodes with a robust structure, superior rate capability, and cyclability remains challenging.…”