In Situ Investigations of Li‐MoS₂ with Planar Batteries

Abstract

We have designed a planar microbattery that allows in situ electrical transport measurement during electrochemical charge and discharge in micron-sized individual crystallites of 2D-layered nanosheets, as well as optical studies (transmittance, Raman spectroscopy), which can give information about the electronic structure of the active material. To demonstrate the utility of our microbattery platform, we study the lithiation of MoS 2 crystallites. We observe that the electrical conductivity of the 2D MoS 2 crystallites is highly dependent on thickness and the rate of lithiation in the fi rst cycle. We use in situ TEM to confi rm that upon rapid fi rst-cycle lithiation the formation of a Mo conductive network imbedded in the Li 2 S matrix leads to an enhanced electrical conductivity compared to the pristine MoS 2 . We applied the results in Li-MoS 2 coin cells with composite electrodes, demonstrating that batteries with fast lithiation on the fi rst cycle showed signifi cantly higher specifi c capacity than batteries lithiated slowly. The microbattery platform can be generally applied to other energy storage materials and a wide range of characterization techniques, and is thus a powerful tool to uncover the properties of nanoscale materials undergoing electrochemical modifi cation. As in the example demonstrated here, we expect this platform will lead to new insights into the operation of battery materials at the nanoscale, leading to new strategies in improving the cell performance.A schematic crystal structure of 2H-MoS 2 is illustrated in Figure 1 a, with the lattice parameters a = 3.16 Å and c = 12.29 Å. Our microbattery platform developed for the in situ measurement of the optical transmittance and electrical transport of 2D nanomaterials is illustrated in Figure 1 b. A MoS 2 crystal and lithium metal are deposited on top of the Cu transport electrodes and current collector, respectively. The MoS 2 fl ake can be charged/discharged by connecting transport electrodes and current collector to an electrochemical workstation. Coupling the microbattery with a transmission optical microscope/probe station, we can then carry out in situ optical transmittance and electrical transport measurements on the same MoS 2 crystal. Optical images of uniform-thickness mechanically exfoliated MoS 2 crystals are shown in Figure 1 c,d, with dimensions as large as 100 µm × 100 µm. We used atomic force microscopy (AFM) to determine the morphology and thickness of exfoliated MoS 2 , in Figure 1 e,f. A photograph of the complete microbattery device is shown in Figure 1 g. The region of the transport electrodes is expanded in Figure 1 h, showing a large uniform area of MoS 2 crystal spanning the electrodes.To understand the intrinsic resistance change during lithiation, an in situ electrical transport measurement was carried out using our microbattery setup. Figure 2 a shows the simultaneously measured resistance and electrochemical potential at a small constant lithiation current at 0.5 µA for a single MoS 2 crystal of thickness 35 n...

Approaching the Lithiation Limit of MoS2 While Maintaining Its Layered Crystalline Structure to Improve Lithium Storage

“…1.9, ca. [16] Therefore we attribute the peak at about 2.2 Vt ot he conversion reaction and the de-lithiation process of disordered MoS 2 .Wenote that this peak also appears in the dQ/dV curves of the cell cycled in 3.0-0.6 V, which is presumably due to some degree of conversion reaction under this voltage range.B ased on the initial charging/discharging curves,w e can calculate that about 20 %c onversion reaction has taken place in 3.0-0.6 V(see details in the Supporting Information, Figure S5). 2.5 Vc orresponding to the multistage deintercalation process.…”

Opening Two‐Dimensional Materials for Energy Conversion and Storage: A Concept

“…[30] Cui et al developed an electrochemical approach to continuously control the amount of Li + ions intercalated into the interlayer of vertically aligned MoS 2 nanofilms. Then, as shown in the reaction (2), with the increasing of intercalant concentration, 2H-MoS 2 reversibly transforms into 1T-MoS 2 .…”

Integration: An Effective Strategy to Develop Multifunctional Energy Storage Devices

“…They are generally realized by coating a thin layer of active materials onto a transparent current collector such as indium tin oxide (ITO) [ 21,[131][132][133][134] or preparing thin fi lm electrodes in the absence of current collectors. [ 138 ] The MoS 2 exhibited a bandgap at the range of visible light with low transmittance. [ 138 ] The MoS 2 exhibited a bandgap at the range of visible light with low transmittance.…”