An Experimental Study on Prototype Lithium–Sulfur Cells for Aging Analysis and State-of-Health Estimation

Abstract

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.

Correlations between precipitation reactions and electrochemical performance of lithium-sulfur batteries probed by operando scattering techniques

“…2 However, the low utilization of sulfur and the low reversibility of metallic lithium limit the specific energy density to around 400 W h kg À1 on the cell level so far. [3][4][5] Moreover, the reactions between the reactive lithium anode and the catholyte, i.e., cathode materials dissolved in an electrolyte, result in self-discharge and thus low Coulombic efficiency. 6 The low sulfur utilization, which is reflected by the ratio between the realized and theoretical specific capacity of the positive electrode expressed per unit mass of sulfur (1,672 mA h g À1 ), 1 stems from the complex reaction mechanism at the positive electrode.…”

Correlations between Precipitation Reactions and Electrochemical Performance of Lithium–Sulfur Batteries

“…2 However, the low utilization of sulfur and the low reversibility of metallic lithium limit the specific energy density to around 400 W h kg -1 on the cell level so far. [3][4][5] Moreover, the reactions between the reactive lithium anode and the catholyte, i.e. cathode materials dissolved in electrolyte, result in self-discharge and thus low Coulombic efficiency.…”

Economic Payback Time of Battery Pack Replacement for Hybrid and Plug-In Hybrid Electric Vehicles

“…In (9), the ICE can deliver positive torque only, while in (10) and in (11) the torques of the EMs can have negative values as well when generating electrical power. In (12), 𝐼𝐶𝐸 𝑜𝑛/𝑜𝑓𝑓 is a binary variable for the ICE state, and values of 0 and 1 relate to the ICE being off and on, respectively. Few constraints are imposed on the battery operation throughout the driving mission in ( 13) to (16).…”

“…As batteries age their properties change; internal electrical resistance increases, capacity decreases, and the opencircuit voltage characteristics may change, leading to reduced capability [10] [11]. Ageing of high-voltage batteries for electrified vehicles is a growing research topic as electrified vehicles become more prevalent and those in the field reach an advanced stage of life [12] [13]. In particular, a compelling research question arises concerning the convenience of replacing the battery pack over the electrified vehicle lifetime.…”