Search

A few safety challenges with lithium-ion batteries, stemming mostly from errors in assembly or from faulty electronics managing them, have created visibility and public concern. The ability to monitor all individual cells within large operational batteries containing many series/parallel cells, respectively, is challenging, and there is growing demand to identify new, non-invasive sensing technologies. Elevated temperatures, induced by either normal or abnormal operation, is a leading cause of failure. With traditional thermal sensing technology, it’s feasible to monitor a few spots within a large battery, introducing a high probability that elevated temperatures will not be measured by the managment system(s) intended to protect them. When abnormal conditions occur, a cell’s case expands and contracts in a measureable way. Detection of an abnormal stress/strain signature is another diagnostic that has great potential. The present study demonstrates the ability of an Optical Distributed Sensor Interrogator (ODiSI) to measure the surface temperature and case deformation of 18650 cells under normal and abnormal conditions, respectively. Multiple experiments have been performed to demonstrate the abilities of the ODiSI to measure temperature and stress/strain changes, respectively, and they show that the results are unique and repeatable making this a promising technique for monitoring lithium-ion cells. [ABSTRACT FROM AUTHOR]

The future fleet of the U.S. Navy vessels may be deployed with a number of high-power electrical loads that operate transiently. The transient nature of the loads will impart high stress on the traditional shipboard power system, possibly pushing it outside of the acceptable power quality standards. To restore power quality and increase system reliability, it is being proposed that electrochemical energy storage systems can be utilized to augment the existing generation systems. Lithium-ion batteries are of extreme interest due to their high combined power and energy density. The proposed energy storage systems will store a great deal of energy and could be designed with open-circuit potentials as high as 1 kV. Since size and weight aboard the vessel are limited, the batteries need to be designed as compact as possible. In the event of a battery failure, in which one or more cells are compromised, organic electrolyte may be vented within the air dielectric separating points of higher and lower potentials. How the vented electrolyte impacts the dielectric strength of the surrounding environment is of concern, especially given the battery’s high operational voltage, its compact construction, and the high energy it stores. The study documented here is aimed at studying the dielectric strength of the vented electrolyte from a lithium–iron–phosphate battery when exposed to potentials representative of a future shipboard energy storage system. [ABSTRACT FROM AUTHOR]

Li-ion cells offer excellent energy storage and conversion characteristics, but also suffer from performance and safety problems related to overheating due to insufficient heat removal during operation. Traditional thermal management approaches cool the cell at its outer surface, whereas it is more critical to cool the core of the cell where heat accumulation occurs. This paper investigates thermal performance of a 26650 Li-ion cell with a heat pipe inserted into the core. Heat pipe integrated cells are assembled starting from unfilled, unsealed cells. Thermal benefit of heat pipe insertion is characterized at a number of discharge rates. Advantages of heat pipe cooling compared to traditional surface-based cooling approach are quantified. It is shown that active cooling of the protruding tip of the heat pipe results in maximum thermal benefit, which is shown to reduce the core temperature to as low as, or even lower than the surface temperature. The heat pipe is shown to reduce temperature rise in case of anomalous increase in heat generation. While heat pipe insertion involves significant manufacturing challenges to ensure long-term reliability, the thermal benefits in doing so may potentially outweigh these challenges, and offer an effective thermal management approach for future Li-ion cell designs. [ABSTRACT FROM AUTHOR]

The U.S. Naval Research Laboratory is developing a rep-rate charger for a 60-kJ capacitor module. The charger is lithium-ion battery powered and must charge up the capacitive load 50 times over a 5-min period with roughly 1 s between each charge cycle. This paper examines some aspects of the design: lithium-ion battery energy storage, hard switched dc–dc converter, high-voltage rectifier, and capacitive load with pulsed power switching. The lithium-ion batteries are arranged in 12, 16-cell, 50 V modules that are connected in series to form a roughly 600 V prime power supply. A hard switched dc–dc converter with full-bridge rectifier is used to charge the capacitor and a pulse forming network is used to discharge the capacitor into the load. This paper will discuss the system design and available test data. [ABSTRACT FROM PUBLISHER]

Numerous research efforts have been undertaken to improve the feasibility of fielding compact pulsed power systems for a wide variety of applications. Each of these research efforts focuses on specific areas of pulsed power, but few papers have focused on the performance of a grid independent prime power source. This critical component is often overlooked in mobile pulsed power systems. Though not within the pulsed power community, a great deal of work has been performed by those in the electrochemical energy storage community to improve the energy density, power density, working voltage, and cycle life of electrochemical cells. This paper has helped to develop new energy storage technologies for applications such as consumer electronics, electric vehicles, and electrical grid energy storage. However, these electrochemical cells were not developed with pulsed power applications in mind. For that reason, a large amount of research is needed to understand how to effectively use electrochemical cells in pulsed power applications. In this paper, a number of different energy storage chemistries, including lithium-ion batteries, lead acid batteries, and bi-polar nickel metal hydride batteries, have been evaluated for use in pulsed power applications as a result of their high power and energy densities. [ABSTRACT FROM PUBLISHER]

In recent years, energy storage manufacturers such as GAIA Advanced Lithium Battery Systems, Saft America, JM Energy, and Maxwell Corporation, among others, have greatly increased the power density of their respective electrochemical energy storage cells. Among the many types of high-power cells produced by the manufactures just listed are lithium-ion batteries, lithium-ion capacitors, and electric double-layer capacitors, respectively. The increased power density has made these types of portable energy storage devices more appealing and feasible for use as the prime power source of pulsed-power supplies that are used to drive systems such as electromagnetic launchers (EMLs). It has been previously shown by both Sitzman at the Institute for Advanced Technology, The University of Texas, Austin, and Allen and Neri at the U.S. Naval Research Laboratories that the prime power for small EMLs is derived from different types of batteries. In these types of pulsed-power systems, the batteries must be able to source pulsed currents at rates much higher than their continuous C rating. While this mode of operation has been shown to be possible, the elevated rate limitations of these types of devices are not well published, and it is unclear how the fundamental aging phenomena that occur inside these types of devices will be affected. Researchers at the University of Texas, Arlington, have ongoing experiments which are testing the limitations of these types of electrochemical cells for use in pulsed high-current applications. Experiments are also being performed to understand the aging characteristics when they are operated at elevated rates that are tens to hundreds of their rated C values. This paper describes the rationale behind the experiments, the experimental setup, and the research progress made thus far. [ABSTRACT FROM PUBLISHER]

Li-ion cells are a technologically important class of devices for electrochemical energy storage and conversion. Overheating of a Li-ion cell during operation is undesirable as it directly affects performance and safety. Although a number of methods have been used for temperature measurement in Li-ion cells, there is a lack of non-invasive techniques to determine the peak temperature at the core of the cell. Measuring only the outside surface temperature, while straightforward, is not sufficient since the core temperature may be much higher. This paper presents non-invasive measurement of the core temperature of a Li-ion cell using a recently developed technique that utilizes space and time integrals of the measured temperature field at the outside surface. The surface temperature field of an operating Li-ion cell is measured using infrared thermography at multiple discharge rates up to 10C, using which, the core temperature is predicted as a function of time. In each case, there is excellent agreement throughout the discharge period between the predicted core temperature and measurements from a thermocouple embedded at the core of the cell. These measurements quantify the temperature gradient within the cell, which is particularly high at large discharge rates. The non-invasive core measurement methods described here may contribute towards performance optimization and improved safety of Li-ion cells. [ABSTRACT FROM AUTHOR]

In this study, three identical LiNi x Co y Al 1−x−y O 2 , (NCA) batteries are evaluated to understand the impact of high rate discharge on the rate of capacity fade. The first of the three cells is repeatedly discharged in a pulse width modulated (PWM) manner at a frequency of 10 kHz, duty cycle of 50%, and peak rate of 83C (250 A). The second cell is repeatedly discharged at a constant current (CC) rate of 25C (75 A) while the third cell, which serves as the control cell, is discharged at its nominal CC rate of 1C (3 A). All three cells are recharged using a 1C CC recharge procedure to minimize the impact of recharge on cell aging. Novel and commercially procured battery cyclers are used to experimentally discharge and recharge the cells. Periodic baseline measurements, in which both capacity and electrochemical impedance spectroscopy (EIS) measurements show that the degradation mechanisms are enhanced under high rate pulse discharge cycling conditions. EIS modeling points to breakdown in the integrity of the anodic side double layer and increased charge transfer resistance as the largest contributors to impedance evolution in the cell. [ABSTRACT FROM AUTHOR]