7 Degradation in Lithium–Sulfur Batteries

Rajlakshmi Purkayastha

OXIS Energy, E1 Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB, UK

7.1 Introduction

Degradation refers to the process of breakdown or deterioration that occurs when an object is put to use. For a lithium–sulfur (Li–S) battery, this breakdown of ability is measured in the deterioration of the usable capacity of the cell. For batteries in particular this refers to the breaking down/chemical transformation/deterioration of internal components, which leads to changes in the measured output characteristics, i.e. voltage and current over a period of time. Since fluctuations of voltage and current are possible due to changes in operating conditions as well, a better quantity to measure deterioration over time is the capacity of the battery. The capacity can be defined as the total available charge within the battery, and is expressed in units of ampere‐hour. The capacity is directly correlated to the active mass present within the battery, but is dependent on all components operating efficiently. Thus the degradation of the internal components will lead to the charge either becoming inaccessible (e.g. loss of connection of active material from the circuit) or being consumed in parasitic side reactions (e.g. solid–electrolyte interphase (SEI) formation, polysulfide shuttling). Thus the loss of capacity or capacity fade is a direct measure of the degradation processes within the battery. When the cell ...

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