9 Battery Management Systems – State Estimation for Lithium–Sulfur Batteries

Daniel J. Auger Abbas Fotouhi Karsten Propp and Stefano Longo

Cranfield University, School of Aerospace, Transport and Manufacturing, Cranfield, MK43 0AL, UK

9.1 Motivation

Most batteries are vulnerable to being overdischarged; many are also vulnerable to overcharging. In lithium–sulfur, while overcharging is not seen as a “safety” issue [1], the high charge state “shuttle” phenomenon is associated with capacity fade [2]. Consequently, it is important to avoid extremes of charge state. As illustrated in Figure 9.1, our ability to access the full “usable capacity” depends on the ability to reliably estimate the state of charge at these extremes: uncertainty in state measurements translates directly into a reduced window of operation. This underlines the importance of reliable state estimation techniques: the effective capacity of a battery depends not only on the chemistry but also on the accuracy of the state estimation algorithms. Without these, an otherwise good battery technology can be rendered useless.

Schematic with a cylinder in horizontal orientation having parallel arcs (theoretical capacity) with a rightward arrow at the bottom (usable capacity) and a circle linked to outward arrows (estimation uncertainty).

Figure 9.1 Theoretical capacity and usable capacity. At extremes of state of charge, there is a risk of damage, avoided by operating within a restricted “usable capacity” range. Any uncertainty in the state estimate reduces the effective usable capacity even further. Source: Propp ...

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