With the ever-increasing need for electrification across many application sectors, the development of new energy-storage technologies is of increasing relevance and critical importance. Electrification is progressing significantly within the traditional transportation sectors such as electric bikes, cars, buses, and other commercial vehicles, enabled by continued cell development and Gigafactory-scale mass production of Li-ion battery (LIB) technology. However, two key factors are starting to drive the need for new solutions to be found. One factor is the secure supply of key elements-mainly cobalt and nickelused in most of the conventional Li-ion cells which are becoming increasingly critical. The other is the performance requirements of desirable emerging application areas that are beyond the capabilities of traditional LIB technology. Examples include large commercial vehicles, [1] high-altitude long endurance (HALE), high-altitude pseudosatellites (HAPS), electric vertical takeoff and landing (eVTOL), [2] and electric passenger aircraft. The weight of the battery system (BSM) is an especially critical factor for these aviation applications. The battery systems' performance requirements differ across these applications: power, cycle life, system cost, etc. However, the need for a high gravimetric energy density, 400 Wh kg À1 and beyond, is common across them all. Higher energy battery systems will enable these vehicles to achieve extended range, a longer mission duration, lighter vehicle weight, or increased payload. In the following sections, key advantages, limitations, and progress made to extend cycle life, energy, power, and safety of Li-S battery management systems (BMS) are described. Further, recent advances regarding modeling, battery system management, and the integration of Li-S batteries into present as well as future real-world applications are summarized. 2. Lithium-Sulfur Battery Technology 2.1. Advantages LIB systems are the current technology of choice for many applications; however, the achievable specific energy reaches a maximum at around 240-300 Wh kg À1 at the cell level. [3] Emerging

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Lithium-Sulfur (Li-S) batteries offer a potential for higher gravimetric energy density in comparison to lithiumion batteries. Since they behave quite different from lithium-ion batteries, distinctive approaches to state estimation and battery management are required to be developed specifically for them. This paper describes an experimental work to model and perform real-time estimation of the progression of use-induced ageing in prototype Li-S cells. To do that, state-of-the-art 19 Ah Li-S pouch cells were subject to cycling tests in order to determine progressive changes in parameters of a nonlinear equivalent-circuit-network (ECN) model due to ageing. A stateof-health (SoH) estimation algorithm was then designed to work based on identifying ECN parameters using Forgetting-Factor Recursive Least Squares (FFRLS). Two techniques, nonlinear curve fitting and Support Vector Machine (SVM) classification, were used to generate SoH values according to the identified parameters. The results demonstrate that Li-S cell's SoH can be estimated with an acceptable level of accuracy of 96.7% using the proposed method under realistic driving conditions. Another important outcome was that the 'power fade' in Li-S cells happens at a much slower rate than the 'capacity fade' which is a useful feature for applications where consistency of power delivery is important.