In Situ Visualization of Interfacial Sodium Transport and Electrochemistry between Few‐Layer Phosphorene

Abstract

For rechargeable batteries, ionic transport within the electrode materials is a critical process that controls the rate capability and energy efficiency of the battery. Despite substantial studies, the atomistic observation of the interfacial ionic transport and electrochemical reactions occurring between the solid‐state electrodes is lacking. Here, in situ transmission electron microscopy (TEM) is used to deliberately design an unusual sample configuration, enabling dynamic observation of the sodium ionic transport within a single‐crystal nanostructure and between different few‐layer phosphorene nanosheets. An unhindered and reversible ionic shuttling between few‐layer phosphorene is directly observed in real time. In addition, it is found that sodium transport kinetics are closely related to the interface orientation and the intimate contact between solid electrodes plays a significant role in inhibiting dendrite growth. Furthermore, by fast TEM imaging with ≈40 ms resolution a unique stripe‐like sodium transport behavior is observed in phosphorene, and the multiple sodium ionic transport pathways at the interfaces with atomic spatial resolution are revealed. This work may supply enlightening insights into understanding the solid–solid interfacial electrochemistry between electrode materials.

Unraveling the reaction mechanisms of electrode materials for sodium‐ion and potassium‐ion batteries by in situ transmission electron microscopy

“…In the past decade, the fast enhancement of in situ TEM provides unprecedented chances in exploring the basic mechanisms of electrochemical reactions in both SIBs and PIBs. In this review, we have systematically Hard carbon 330.8 mAh g −1 at 50 mA g −1 after 100 cycles [39] phosphorus-doped graphene 374 mAh g −1 after 120 cycles at 25 mA g −1 [45] Carbon nanofibers 245 mAh g −1 , 98% after a few initial cycles [59] Alloying reaction Phosphorene nanosheets 865 mA h g −1 for double-side Naadsorption [50] Single TiN coated Ge nanowire 623, 621 and 441 mAh g −1 in cycle 1, 2, and 20, respectively [48] Conversion reaction WS 2 nanoflakes 300 mAh g −1 at 100 mA g −1 after 100 cycles [64] FeS 2 nanotubes 360.3 mAh g −1f at 0.2 C after 50 cycles [65] Carbon-coated Sb 2 S 3 nanorods 570 mA h g −1 , 96% retention after 100 cycles [67] MoS 2 /C 484.9 mA h g −1 at 2.0 A g −1 after 1500 cycles [63] Potassium ion batteries Intercalation reaction G-TiO 2 nanotubes 222 mAh g −1 at 0.1 A g −1 over 400 cycles [68] nitrogen-dopedcarbon nanofibers 280 mAh g −1 at 0.1 A g −1 over 100 cycles [69] mesoporous carbon 70.7% after 1000 cycles at 1 A g −1 [70] Alloying reaction red P@N-PHCNFs 465 mAh g −1 at 2 A g −1 after 800 cycles [30] Carbon-coated Sb 2 S 3 nanowires 293 mAh g −1 at 0.05 A g −1 after 50 cycles [71] Sb@CNFs 338 mAh g −1 at 200 mAg −1 after 200 cycles [37] Conversion reaction Fluorographites 896.3 and 537.8 mAh g −1 at 0.5-4.5 V [74] FeS 2 ~400 mAh g −1 discharge capacity [73] Abbreviations: PIB, potassium ion batteries; SIB, sodium ion batteries.…”

“…Sun et al [ 46 ] revealed that alloying reaction in black phosphorous with Na ions consisted of intercalation first and alloying second. Xu et al [ 50 ] use in situ TEM to observe the Na ions transportation in the few‐layer phosphorene nanosheets by designing an unusual sample configuration. Figure 3A shows the diffusion pathways of Na ions in a nano cell when charging.…”

“…Reproduced with permission from ref. [50]. Copyright 2019, WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim.…”

Xenes as an Emerging 2D Monoelemental Family: Fundamental Electrochemistry and Energy Applications

“…The results indicated that the diffusion in the [ 98 ] direction, is more smooth than that in the [010] direction. [ 251 ] Very recently, the electrochemistry and Na transportation along the interfaces of few‐layer phosphorene was observed by applying the same approach by Zhu et al [ 25 ] The results indicated that the interface orientation can determine the kinetics of Na transportation. As shown in Figure 5e, when the zigzag direction is perpendicular to the interface, the quick Na ionic transport will lead to phosphorene transformation from crystal‐to‐amorphous.…”

“…Moreover, the properties of Xenes can be regulated at a wide range by various strategies including strain, [ 3–10 ] doping, [ 11–15 ] substrate, [ 16–18 ] functionalization. [ 14,19–22 ] Therefore, the research of Xenes has achieved great progress in theory and experiment in electrochemistry and energy, [ 23–25 ] electronics, [ 26 ] photonics, [ 27 ] logic transistors, [ 28 ] and biomedical technologies. [ 29 ]…”