Petia Guerrero and Arturo I. Sotomayor

1. Performance of Lithium Ion Battery for High Speed Train Application Petia Guerreroand Arturo I. Sotomayor Department of Mechanical Engineering, College of Engineering and Engineering Technology, Northern Illinois University Method The battery cell is placed in the environmental control chamber and connected to the Cadex battery testing system. The battery cell is then fully charged and discharged at the desired charge rate. Thermocouples are placed on the battery cell to collect temperature data using the LabVIEW software. The chambers viewing window allows the FLIR IR camera to observe the battery during the tests performed. Introduction In today’s world, to travel long distances people favor airplanes, buses or automobiles. These modes of transportation are inefficient, causing pollution and greenhouse gases. They can be stressful to travelers due to time wasted in traffic or going through airport security. However, in recent years, there has been a push to create a network of high speed  rail. High speed trains have faster travel times than conventional trains and cars, minimal waiting time at a station, and can be cheaper to the consumer than an airplane ticket. To make these high speed trains more efficient a regenerative braking system should be applied. Regenerative braking systems work by turning the kinetic energy of the wheel, as it turns, into another form of energy. This energy can either be used immediately or stored to be used at a later time. Lithium ion batteries should be used in this application because of their high energy density. Lithium ion batteries consist of a cathode, an electrolyte and an anode. The process involves a chemical reaction in which the free electrons flow through the system. Specifically, the lithium iron phosphate (LiFePO4) battery is preferred because it has a high energy density and long cycle life (over 2000 cycles). The LiFePO4 is a leading battery type in safety characteristics compared to other lithium ion batteries. During the experiments done in this project, the performance of a LiFePO4 cell was tested. Results The LiFePO4 battery cell was examined in various temperature settings and charge rates. These temperatures include -10, 1, 20, 30, and 50 degrees Celsius. The battery cell was tested at 5A (0.5C), 7.5A (0.75C) and 10A (1.0C) charge rates. The data taken from the experiments allowed us to calculate the capacity and efficiency for each trial. The results show that the LiFePO4 battery cell’s overall performance enhances as the charge rate decreases . The temperature also has an effect on the battery performance. The thermocouples and IR camera were used to measure temperature variations along the surface of the battery. From the results shown below, we can observe the trend of the battery’s efficiency, capacity, and temperature variations. Results Picture taken from IR camera using ExaminIR software (Above). Temperature profile of battery cell surface using IR camera (Above). Conclusions From these results we can conclude that in application to regenerative braking system, a battery operating at a lower charge rate is preferred for a wide range of temperatures. If the temperature in which the battery is operating is within the range of 20°C and 50°C either of the charge rates examined could be used. When designing a complete battery pack, it is important to create a housing system that takes into account the distribution of temperature across the surface of the battery cells to allow the optimum performance. FLIR IR camera positioned outside environmental chamber viewing window. Aim Much more work must be done on energy storage systems to be able to apply regenerative braking to high speed trains. To proceed with more testing, an experimental set up was developed to test how the lithium ion battery performs under different conditions such as different temperatures and different charge rates. An environmental control chamber is used to control the ambient temperature in which the battery will be tested. The Cadex battery testing system is used to charge and discharge the battery cell at different rates. This system is connected to the Battery Lab software which stores the data taken during the tests. Seven thermocouples are placed on the battery cell and one is placed in the chamber to measure the ambient temperature. An infrared camera is also used to observe the temperature variations along the surface of the battery cell. These tests are vital to determining how to place the battery cells when building a full battery unit for a regenerative braking system Location of thermocouples on LiFePO4 battery cell. Acknowledgments We would like to thank Dr. Pradip Majumdar for guidance and assistance in the Department of Mechanical Engineering. We would also like to thank Northern Illinois for hosting the Research Experience for Undergraduate summer program, which was made possible by support from The National Science Foundation (Grant #SMA-1156789) and Northern Illinois University, MESA, and the Lipp Family Foundation. More specifically, we would like to thank the College of Liberal Arts and Science, the College of Engineering and Engineering Technology, and the offices of the Vice Provost for Academic Affairs and the Vice President for Research and Graduate Studies. Cadex battery testing system.