Investigation of Using Lithium-Sulfur Battery in an Electric Bus

摘要

Batteries are currently used as the main technology in the market for energy storage in electric vehicles (EVs) including a wide range of chemistries. Lithium-ion (Li-ion) battery is the dominant technology since it offers high specific energy with acceptable specific power, no memory effect and low self-discharge, when comparing to other technologies. It has been also claimed that Li-ion technology is approaching its theoretical energy density limits of 200-250 Wh/kg. At this point, Lithium-Sulfur (Li-S) batteries arise as one of the most promising battery technologies, since they provide a potential to achieve an energy density of 500-600 Wh/kg. Furthermore, Li-S batteries have the potential to be cheaper in mass production and provide more safety. Currently, Li-S cells have a good charge-discharge efficiency and are achieving a specific energy of 160-400 Wh/kg. The main disadvantages are its self-discharge and its modest cycle life, caused by a capacity fade due to cell components degradation. A prototype Li-S cell that is used in this study has a capacity of 12 Ah per cell and a specific energy of 300 Wh/kg is made by OXIS Energy Ltd.. Li-S battery can be considered as a promising technology for electrified transportation, since it provides higher energy density, increased safety and less cost in mass production, when comparing to current battery technologies used in the automotive market. The application of a Li-S battery pack in an electric bus is investigated in this study. Feasibility of using Li-S battery technology in an electric bus is assessed by proper sizing of a Li-S battery pack to be used in an electric bus model which has to fulfil the requirements of the standard London city bus. Battery pack sizing, modelling and simulation have been performed based on the new state-of-the-art Li-S cell that was tested under different conditions. As a result, an equivalent-circuit-network (ECN) model was developed for a single cell and then was used to build the pack model. The electric bus model was generated using MATLAB/Simulink including a Li-S battery pack. The vehicle movement over London drive cycle w as simulated to investigate performance of the prototype Li-S cell in such a real application. The pack sizing was performed using different approached such as maximum required power and/or required range of EV. Finally, simulation results of different Li-S battery packs were investigated to analyze how it accomplishes the requirements of the electric bus application. Furthermore, a comparison is performed between the proposed Li-S battery pack and current battery technologies available in the market.