In Situ, Atomic‐Resolution Observation of Lithiation and Sodiation of WS₂ Nanoflakes: Implications for Lithium‐Ion and Sodium‐Ion Batteries

Abstract

WS2 nanoflakes have great potential as electrode materials of lithium‐ion batteries (LIBs) and sodium‐ion batteries (SIBs) because of their unique 2D structure, which facilitates the reversible intercalation and extraction of alkali metal ions. However, a fundamental understanding of the electrochemical lithiation/sodiation dynamics of WS2 nanoflakes especially at the nanoscale level, remains elusive. Here, by combining battery electrochemical measurements, density functional theory calculations, and in situ transmission electron microscopy, the electrochemical‐reaction kinetics and mechanism for both lithiation and sodiation of WS2 nanoflakes are investigated at the atomic scale. It is found that compared to LIBs, SIBs exhibit a higher reversible sodium (Na) storage capacity and superior cyclability. For sodiation, the volume change due to ion intercalation is smaller than that in lithiation. Also, sodiated WS2 maintains its layered structure after the intercalation process, and the reduced metal nanoparticles after conversion in sodiation are well‐dispersed and aligned forming a pattern similar to the layered structure. Overall, this work shows a direct interconnection between the reaction dynamics of lithiated/sodiated WS2 nanoflakes and their electrochemical performance, which sheds light on the rational optimization and development of advanced WS2‐based electrodes.

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.…”

“…To reveal the origin of excellent electrochemical performance of WS 2 nanoflakes in SIBs, the dynamic process is studied by Wu's group [ 64 ] using in situ SAED and in situ TEM. The SAED pattern of the pristine WS 2 nanoflakes exhibits a single‐crystal structure along the [121] direction.…”

Ultrahigh Rate and Ultralong Life Span Sodium Storage of FePS3 Enabled by the Space Confinement Effect of Layered Expanded Graphite

“…Lithium-ion batteries (LIBs) have gradually occupied the main battery market to replace lead-acid batteries due to their long life span, high output voltage, and so forth. − However, the uneven global distribution and scarcity of lithium resources have brought concerns in terms of the sustainable development of LIBs. , In this context, sodium-ion batteries (SIBs) have regained the focus of research by virtue of their ample resources and similar intercalation/de-intercalation mechanism comparable to LIBs . More importantly, the lower cost and higher security of SIBs as well as the stronger environmental adaptability than LIBs make them potential new generation energy storage devices, especially in large-scale storage systems .…”

“…4,5 In this context, sodium-ion batteries (SIBs) have regained the focus of research by virtue of their ample resources and similar intercalation/de-intercalation mechanism comparable to LIBs. 6 More importantly, the lower cost and higher security of SIBs as well as the stronger environmental adaptability than LIBs make them potential new generation energy storage devices, especially in large-scale storage systems. 7 Unfortunately, the larger Na + diameter determines their slow kinetics, which causes SIBs of the same material to deliver a worse rate performance or lower capacity than LIBs.…”

Atomically Thin TaSe2 Film as a High‐Performance Substrate for Surface‐Enhanced Raman Scattering

“…[ 31 ] The partial phase transition from 2H to 1T is observed in many TMDs owing to the lithiation process. [ 35–37 ] Moreover, the high‐resolution TEM (HRTEM) image shows the coexistence of the 2H and 1T phases with some disorder close to the phase boundary, as observed in Figure S4 in the Supporting Information. Selected areas have been amplified in Figure S4 in the Supporting Information to demonstrate the typical 2H phase (Figure 2c) and the 1T phase of TaSe 2 (Figure 2d).…”