EKC2023

Understanding the influence of interlayer distance and particle size on lithium intercalation kinetics in MoS2

Aug 16, 2023, 1:50 PM

20m

Venus 1

Chemical Engineering and Material Science [CM1] Advancements in Battery Technology: From Materials to Applications

Speaker

Jaehoon Choi (Karlsruhe Institute of Technology)

Description

Pseudocapacitance is a mechanism that describes Faradaic charge storage reactions with an electrical signature closely resembling electric double-layer capacitance, holding promise to combine high specific energy and power.[1] It has been observed for electrode materials with certain intrinsic structural features, such as wide interlayer galleries in Ti3C2Tx MXenes offering facile diffusion pathways.[2] Nanostructuring can induce extrinsic pseudocapacitance to electrode materials that show classic battery-like behavior in their bulk form, such as LiCoO2, which can be explained by reduced diffusion distances and changes in site energies in the (near-)surface region.[3] It is challenging to clearly identify and separate such intrinsic and extrinsic influences on the charge storage mechanism in many emerging electrode materials that combine (atomic scale) structural features with nanosized crystalline domain sizes.

Layered transition metal dichalcogenides (TMDs), which have a chemical formula of MX2 (M = transition metal element, X = S, Se, or Te), have been investigated for electrochemical energy storage (EES) applications, such as batteries and capacitors.[4] Among them, molybdenum disulfide (MoS2) has been described to show pseudocapacitive lithium intercalation reactions in organic electrolytes, when the particle size is sufficiently nanostructured.[5] Furthermore, the material exhibits a relatively large interlayer spacing of 0.615 nm, which can be further expanded, for example, via the introduction of pillars. Hence it is a suitable model material to study intrinsic contributions from tuning interlayer distance and extrinsic contributions from tuning particle size, either individually or in combination. The former is expected to impact the intrinsic ionic transport properties in the host material, while the latter is reducing ion diffusion path length.

In this study, we investigate the pseudocapacitive behavior in MoS2-based materials as a function of their structure over several length scales. By synthesizing the material with high control over both interlayer distance at the (sub-)nanometer-scale and the particle size in the range from several tens to hundreds of nanometers, we can identify the individual contributions on the pseudocapacitive electrochemical signature. The aim of this contribution is to answer which structural modification to layered intercalation host materials (interlayer distance vs. particle size) is most effective to improve overall charge storage kinetics, and whether different modifications influence charge storage reactions at different time scales.

References

1. Fleischmann, S. et al. Pseudocapacitance: From Fundamental Understanding to High Power Energy Storage Materials. Chem. Rev. 120, 6738–6782 (2020).
2. Simon, P. & Gogotsi, Y. Materials for electrochemical capacitors. Nat. Mater. 7, 845–854 (2008).
3. Okubo, M. et al. Nanosize Effect on High-Rate Li-Ion Intercalation in LiCoO2 Electrode. J. Am. Chem. Soc. 129, 7444–7452 (2007).
4. Li, X. L. et al. Controllable Synthesis of Two‐Dimensional Molybdenum Disulfide (MoS2) for Energy‐Storage Applications. ChemSusChem 13, 1379–1391 (2020).
5. Cook, J. B. et al. Pseudocapacitive Charge Storage in Thick Composite MoS2 Nanocrystal‐Based Electrodes. Adv. Energy Mater. 7, 1601283 (2017).