Metal Sulfide Artificial Solid-Electrolyte Interface for Improved Lithium Anode Stability
Authors: Loganathan Archana , Ghimire Govinda , Hamal Dambar , Awadallah Osama , El-Zahab Bilal 
Published: November 2022

In the last decade, lithium metal has burgeoned into a potential anode material from Li-ion battery to next generation battery systems because of the low redox potential (-3.040 V vs SHE.) and high gravimetric energy density [1-3]. Unlike conventional batteries, the major challenges to be addressed in lithium metal anodes are the dendritic growth, continuous lithium depletion, rapid capacity loss and low Columbic efficiency [4]. These challenges can be averted using electrolyte additives or creating artificial solid electrolyte (SEI) interphases [5]. In the present work, nanostructured transition metal sulfide (MS) and lithium transition metal sulfide (LMS) are used as artificial SEI on lithium metal anode by modifying the lithium metal/electrolyte interfaces and homogenous lithium deposition.
The nanostructured transition metal sulfide and lithium transition metal sulfide were synthesized by a simple wet chemical route at relatively low temperatures (150-200 °C). The synthesized LMS were typically of high purity and were filtered, washed, ball-milled, and calcined prior to use in the battery. The microstructure, structure and chemical analysis of the synthesized metal sulfide was characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Figure 1(a) shows the morphology of the ball-milled LMS as a layered structure with varying sizes of 10 µm to 100 nm. The EDS analysis of the ball-milled powder majorly showed an M/S ratio of 1:1 and 1:2.
The LSM was deposited on Li metal substrate by sputtering technique from a LSM target in Ar atmosphere. This film deposition was carried out at different sputtering time (10 sec -100 sec) and processing pressures. Homogeneous deposition of this LSM of few tens of nanometers thickness was successfully achieved. The electrochemical performance of the LSM artificial SEI was investigated in symmetric cells of two coated Li electrodes and compared to bare Li (Figure 1(b)). At different current densities of 0.5 and 1 mA/cm2, repeated Li plating and stripping revealed an enhanced cycling performance of metal sulfide coated Li compared to bare Li electrode. To better understand the interfacial stability, electrochemical impedance spectroscopy (EIS) studies were performed at different stages of cycling. The cycling performance of coated and bare Li anode was performed in a full cell containing NMC811 as cathode. After cycling, the microstructural changes in lithium metal anode were explored using SEM.

Figure 1: (a) SEM image of the ball-milled layered lithium metal sulfide and (b) Time-voltage profiles of the symmetric cells with Li anode and coated Li anode at the current density of 0.5 mA/cm2

References

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Figure 1