Structural Evolution of Electrochemically Lithiated MoS₂ Nanosheets and the Role of Carbon Additive in Li-Ion Batteries

Abstract

Understanding the structure and phase changes associated with conversion-type materials is key to optimizing their electrochemical performance in Li-ion batteries. For example, molybdenum disulfide (MoS2) offers a capacity up to 3-fold higher (∼1 Ah/g) than the currently used graphite anodes, but they suffer from limited Coulombic efficiency and capacity fading. The lack of insights into the structural dynamics induced by electrochemical conversion of MoS2 still hampers its implementation in high energy-density batteries. Here, by combining ab initio density-functional theory (DFT) simulation with electrochemical analysis, we found new sulfur-enriched intermediates that progressively insulate MoS2 electrodes and cause instability from the first discharge cycle. Because of this, the choice of conductive additives is critical for the battery performance. We investigate the mechanistic role of carbon additive by comparing equal loading of standard Super P carbon powder and carbon nanotubes (CNTs). The latter offer a nearly 2-fold increase in capacity and a 45% reduction in resistance along with Coulombic efficiency of over 90%. These insights into the phase changes during MoS2 conversion reactions and stabilization methods provide new solutions for implementing cost-effective metal sulfide electrodes, including Li–S systems in high energy-density batteries.

3D Metal‐Rich Cu7.2S4/Carbon‐Supported MoS2 Nanosheets for Enhanced Lithium‐Storage Performance

“…The high surface area should be implied the fact that MoS 2 nanosheets were well dispersed on 3D Cu 7.2 S 4 /C support to avoid from stacking, while it would provide more active sites for electrochemical reactions. [19,25,51] It was worth noting that the anode peak near 2.38 V gradually weakened in the subsequent CV scans compared to the first scan, and moved toward the negative potential to form a relatively broad anode peak. [42,47] The electrochemical performance of pristine MoS 2 nanosheets, Cu 7.2 S 4 /C nanocomposite and 3D core-shell Cu 7.2 S 4 / C@MoS 2 nanocomposite as anode for LIBs were investigated, which were assembled into coin cells and tested under the identical electrochemical condition.…”

“…[46,50] The apparent strong peak at around 2.38 V was considered to the oxidation of Li 2 S to S. [46] In the subsequent discharge process, an obvious cathode peak at around 1.18 V was attributed to form Li x MoS 2 . [19,25,51] It was worth noting that the anode peak near 2.38 V gradually weakened in the subsequent CV scans compared to the first scan, and moved toward the negative potential to form a relatively broad anode peak. While the corresponding anodic peaks at 1.91 V and 2.24 V during first scan remained almost unchanged, indicating that the MoS 2 /Mo couple dominated the redox process and gradually formed a highly reversible electrochemical reaction.…”

How does Molybdenum Disulfide Store Charge: A Minireview

“…The phase conversion and structural evolution of MoS 2 electrodes during the alkali metal ion (Li + , Na + , K + ) intercalation/ extraction process have been intensively studied by a series of in/ex situ characterization methods, such as in/ex situ X‐ray diffraction (XRD), in/ex situ Raman spectroscopy, scanning electron microscopy (SEM), in/ex situ transmission electron microscopy (TEM), and synchrotron X‐ray absorption spectroscopy (XAS) . Theoretical calculations using the density‐functional theory (DFT) were also used to perfect the proposed mechanisms . Nevertheless, researchers have not reached a consensus on some key issues owing to the complex charge‐storage process, such as the identification of intermediate phases at different charge/discharge periods, the reversibility of conversion reaction and the nature of extra capacity in MoS 2 electrodes.…”

Nanoconfined Oxidation Synthesis of N‐Doped Carbon Hollow Spheres and MnO2 Encapsulated Sulfur Cathode for Superior Li‐S Batteries

“…In recent years, it has been realized that polar function groups/surfacep lay as ignificantly role in suppressing the "shuttle effect", because they can increase the chemicali nteraction between the polysulfide and substrate materials. [21][22][23][24][25][26][27][28][29][30][31][32][33] Taking this into account, some nanostructured transition metal oxidesa nd sulfides with polarity, [21][22][23][24][25][26][27][28][29][30][31][32][33] such as MnO 2 , [21][22][23] TiO, [24] and TiO 2 , [25,26] have been found to confine sulfur.A lthought hese widely used transition sulfides/oxides with low electronic conductivityc annot efficientlyi mprovet he conductivity of sulfur cathode. The suitable solution is combining the well-conductive carbon andp olar functiong roups as matrix materials, which takest he advantage of synergetic effect of carbon and polar functiong roups to confine the "shuttle effect".…”