During the operation of a Lithium-Sulfur (Li-S) cell, structural changes take place within both positive and negative electrodes. During discharge, the sulfur cathode expands as solid products (mainly Li2S or Li2S/Li2S2) are precipitated on its surface, whereas metallic Li anode contracts due to Li oxidation/stripping. The opposite processes occur during charge, where Li anode tends to expand due to lithium plating and solid precipitates from the cathode side are removed, causing its thickness to decrease. Most research literature describe these processes as they occur within single electrode cell constructions. Since a large format Li-S pouch cell is composed of multiple layers of electrodes stacked together, and antagonistic effects (i.e. expansion and shrinkage) occur simultaneously during both charge and discharge, it is important to investigate the volumetric changes of a complete cell. Herein, we report for the first time the thickness variation of a Li-S pouch cell prototype. In these studies we used a laser gauge for monitoring the cell thickness variation under operation. The effects of different voltage windows as well as discharge regimes are explored. It was found that the thickness evolution of a complete pouch cell is mostly governed by Li anodes volume changes, which mask the response of the sulfur cathodes. Interesting findings on cell swelling when cycled at slow currents and full voltage windows are presented. A correlation between capacity retention and cell thickness variation is demonstrated, which could be potentially incorporated into Battery Management System (BMS) design for Li-S batteries

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This paper describes an open circuit voltage (OCV) prediction technique for lithium cells. The work contains an investigation to examine the charge and mixed state relaxation voltage curves, to analyse the potential for the OCV prediction technique in a practical system. The underlying principal of the technique described in this paper employs a simple equation paired with a polynomial to predict the equilibrated cell voltage after a small rest period. The polynomial coefficients are devised by the use of curve fitting and system identification techniques. The practical work detailed in this paper was conducted at the Centre for Automotive and Power System Engineering (CAPSE) battery laboratories at the University of South Wales.The results indicate that the proposed OCV prediction technique is highly effective and may be implemented with a simple battery management system.

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