Lithium Storage Mechanisms and Electrochemical Behavior of a Molybdenum Disulfide Nanoparticle Anode

Abstract

This study investigates the electrochemical behavior of molybdenum disulfide (MoS₂) as an anode in Li-ion batteries, focusing on the extra capacity phenomenon. Employing advanced characterization methods such as in situ and ex situ X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy, the research unravels the complex structural and chemical evolution of MoS₂ throughout its cycling. A key discovery is the identification of a unique Li intercalation mechanism in MoS₂, leading to the formation of reversible Li_xMoS₂ phases that contribute to the extra capacity of the MoS₂ electrode. Density function theory calculations suggest the potential for overlithiation in MoS₂, predicting Li₅MoS₂ as the most energetically favorable phase within the lithiation–delithiation process. Additionally, the formation of a Li-rich phase on the surface of Li₄MoS₂ is considered energetically advantageous. After the first discharge, the battery system engages in two main reactions. One involves operation as a Li-sulfur battery within the carbonate electrolyte, and the other is the reversible intercalation and deintercalation of Li in Li_xMoS₂. The latter reaction contributes to the extra capacity of the battery. The incorporation of reduced graphene oxide as a conductive additive in MoS₂ electrodes notably improves their rate capability and cycling stability.