Kinetically-Driven Phase Transformation during Lithiation in Copper Sulfide Nanoflakes

Abstract

Two-dimensional (2D) transition metal chalcogenides have been widely studied and utilized as electrode materials for lithium ion batteries due to their unique layered structures to accommodate reversible lithium insertion. Real-time observation and mechanistic understanding of the phase transformations during lithiation of these materials are critically important for improving battery performance by controlling structures and reaction pathways. Here, we use in situ transmission electron microscopy methods to study the structural, morphological, and chemical evolutions in individual copper sulfide (CuS) nanoflakes during lithiation. We report a highly kinetically driven phase transformation in which lithium ions rapidly intercalate into the 2D van der Waals-stacked interlayers in the initial stage, and further lithiation induces the Cu extrusion via a displacement reaction mechanism that is different from the typical conversion reactions. Density functional theory calculations have confirmed both the thermodynamically favored and the kinetically driven reaction pathways. Our findings elucidate the reaction pathways of the Li/CuS system under nonequilibrium conditions and provide valuable insight into the atomistic lithiation mechanisms of transition metal sulfides in general.

CuS and Cu2S as Cathode Materials for Lithium Batteries: A Review

“…To confirm this, XRD and SEM were used to characterize intermediate charge products. [29]. After the 10th and 20th discharge, however, the Li 2 S product became very evident.…”

“…The CuS nanoflakes are hexagonal with thicknesses between 5 and 20 nm and basal plane 200 nm. Using an in situ STEM setup (Figure 5b), He et al [29] revealed that there was no formation of intermediate Cu 2-x S phases during lithiation of CuS nanoflakes. Using an in situ STEM setup (Figure 5b), He et al [29] revealed that there was no formation of intermediate Cu 2-x S phases during lithiation of CuS nanoflakes.…”

“…Fu and Manthiram [31] believed that the decrease in this plateau is indicative of the formation of a charge product (other than Cu 2 S) that has a lower conversion energy barrier. [29] First, Li + intercalates into the lattice. Surprisingly, there were no peaks characteristic of crystalline Li 2 S detected after the first discharge (Figure 7b).…”

A Multifunctional Separator Enables Safe and Durable Lithium/Magnesium–Sulfur Batteries under Elevated Temperature

“…[11,14] Also, the high-resolution Cu 2p XPS spectra of the pristine CuNWs-GN/PI/ LLZO separator ( Figure S20, Supporting Information) shows the signals of partial copper oxides and metallic copper. [24,25] Based on these above results, the metallic copper nanowires are highly reactive toward soluble polysulfide species, which can be transformed to copper sulfide compounds as schematically shown in Figure 4. [21] It is clear that the Li 1s of polysulfide treated CuNWs-GN/PI/LLZO separator (Figure 3e) shows a single peak at around 54.6 eV, which is 1.7 eV lower than that of the pristine Li 2 S 6 according to previous literature.…”

Cu9S5 Nanoflower Cathode for Mg Secondary Batteries: High Performance and Reaction Mechanism

“…It is believed that suitable cathode materials could be well widened if a conversion mechanism is introduced into Mg batteries. As Mg 2+ is a harder acid than Li + , a softer base such as S 2− or Se 2− ions should be more advantageous to construct the cathode in light of the kinetics . In this work, a Cu 9 S 5 nanoflower with a hierarchical structure is prepared and used as the cathode for Mg batteries.…”