Atomic Sn Modification Promotes Vanadium-Based MXene Lithium Storage

source：beike new material Views：3290time：2020-08-10 QQ Academic Group: 1092348845

【Research Background】
Two-dimensional materials have attracted widespread attention, especially in the field of electrochemical energy storage. Due to the success of graphene, MXenes (two-dimensional transition metal carbides/nitrides) is expected to be one of the most promising candidates for lithium-ion batteries (LIBs) and capacitors because of its controllable chemical composition and unique structure. Electronic characteristics. In recent years, in-situ X-ray absorption fine structure (XAFS) has become a suitable technique for studying the mechanism of lithium ion insertion/extraction. In particular, XAFS can measure the dynamic valence state of metal atoms and the true structural evolution of materials during electrochemical reactions.

[Introduction]
In the study of ion-modified MXene, the National Synchrotron Radiation Laboratory of the University of Science and Technology of China, Song Li, found that Sn4+ ion-modified V2C has ultra-high lithium ion storage performance.
Ion intercalation is an important way to improve the energy storage performance of two-dimensional materials. The dynamic energy storage process of the MXene layered interlayer is very important, but it is still a challenge due to the lack of effective operation methods. This paper presents a unique atomic Sn4+ modified vanadium carbide (V2C) MXene that not only has a highly enhanced lithium ion battery (LIB) performance, but also has excellent performance due to the expansion of the interlayer space and the formation of VO-Sn bonds. Rate and cycle stability. Combined with in-situ test, the in-situ x-ray absorption fine structure measurement method was established, and the dynamic mechanism of V2C@SnMXene electrode in LIBs was discussed. The in-situ test results clearly reveal the valence state changes of vanadium (V) and tin (Sn), and the contribution of oxygen (O) atoms during charge and discharge, confirming their contribution to lithium storage capacity. Furthermore, the stability of the intercalated MXene electrode was further studied in situ, and the key role of the V-O-Sn bond was proved.
This article was published in the well-known journal Advanced Energy Material entitled: Atomic Sn4+ Decorated into Vanadium Carbide MXene Inter layers for Superior Lithium Storage

[Graphic introduction]

Figure 1 shows the synthesis process, surface morphology and static spectroscopy.

Figure 2 shows the electrochemical properties of V2C@Sn

Figure 3 is an in situ spectroscopy study of V2C@Sn electrode

Figure 4 shows the in-situ absorption fine structure spectrum of the V2C@Sn electrode.

[Article summary]
In this paper, the Sn4+ inserted V2C MXene was designed and successfully synthesized, and the 002 orientation lattice spacing was increased by about 19A, and the V-O-Sn bond was formed. The storage mechanism of lithium was investigated by in situ XAFS and Raman measurement methods in combination with conventional characterization methods. In situ x-ray diffraction (ex- situ XRD) results demonstrate the expansion and contraction of the V2C interlayer during lithium ion intercalation/extraction. The absorption of the fine structure spectrum indicates that O has a positive effect on the storage of lithium ions and F has a negative effect. More in more detail, our characterization of V, Sn in situ XAFS and Raman clearly demonstrates the reversible electrochemical activity of Sn and V atoms, resulting in excellent LIB capacity and cycling capacity. These results not only provide useful insights for a better understanding of the dynamic working process of MXenes-based electrodes, but also demonstrate that the combination of traditional in situ characterization and in situ spectroscopy techniques is of positive significance for future in situ studies.

Source: WeChat public number MXene Frontier

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