Marinov, Alexandar Dimitrov; (2024) Big Data Electrochemical Studies and Ex Situ Material Characterisation of the Bulk MoS₂ Electrode Degradation Mechanism in Lithium-ion Batteries. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

With the ever-growing global impact of humankind’s reliance on fossil fuels and the political disruption of the global supply chains for critical energy storage materials, many countries have become dependent on the decisions of a few key exporters to meet their climate goals. With the political turmoil encompassing the globe in recent years, access to a diverse pool of energy storage options can only serve as a benefit to communities. With the commercial graphite-based lithium-ion battery reaching the limit of capacity optimisation, newer higher energy density materials are sought out to meet the world’s insatiable demand. As the export of battery grade graphite is becoming limited by embargoes and trade restrictions(1), alternative materials from different sources have an opportunity to rise to the occasion. Molybdenum disulphide (MoS2) has been studied in lithium-ion batteries for almost 50 years(2); however, its commercial implementation has not been achieved. The naturally abundant material, with established large-scale industrial mining, and a global supply chain make it a viable alternative. Especially, since it possesses a higher energy capacity than graphite. However, the commercially available top-down precursor MoS2 suffers from rapid loss of performance when fully discharged (3.00 – 0.01 V)(3). An in-depth ex situ analysis of MoS2 cells lithiated to 0.8 V, 0.6 V, 0.4 V, and 0.01 V, revealed an inhomogeneous radial lithiation gradient and an underuse of the electrode centre. By discharging to 0.01 V the MoS2 crystallographic structure is lost (3-6), limiting the application of material characterisation. Instead, long-term electrochemical cycling, numerical methods, and data analysis can be employed to gain a further understanding of the MoS2 operating mechanism. Electrochemical peak analysis enabled reaction profiles to be monitored over the course of hundreds of cycles, aiding to establish the redox pairs for the shallow (3.00 – 0.80 V) and deep (3.00 – 0.01 V) discharge ranges.

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