Biju Shrestha

Pulsed Elevated Rate Discharge of Electrochemical Energy Storage Devices

A number of electrochemical energy storage devices have been developed and used widely to power portable applications. Lithium-ion batteries are extremely popular for use in portable devices as a result of their high energy density. Despite their high energy density, most commercial off-the-shelf cells are only modestly power dense, limiting them from being used to drive high power or pulsed power applications. Recently, new high power lithium-ion battery technologies such as the Saft VL5U cell have been developed, which are not readily available off the shelf, with power densities as high as 28.5 kW/kg [1] that are an attractive means for driving pulsed power systems. Additionally, advanced energy storage capacitors, such as electric double layer capacitors and lithium-ion capacitors, have been developed with high energy and power densities that also make them a suitable candidate for use in pulsed power applications. Previous research using these types of devices in applications other than as storage in hybrid electric vehicles and renewable energy platforms has been limited. The University of Texas at Arlington is currently engaged in research to understand the limitations of these types of devices and to understand their future potential for use in pulsed high current experiments. A test stand, similar to that of Chen [2], but with a higher electrical action capability, has been developed and used to further characterize the performance of these types of devices when they are discharged at rates 10s to 100s of times their rated C values in pulsed fashion. This paper describes the rationale behind the experiments, the experimental setup developed, and the research progress made thus far.

Capacity Fade of 26650 Lithium-Ion Phosphate Batteries Considered for Use Within a Pulsed-Power System’s Prime Power Supply

There is considerable need for a mobile, reliable, efficient, and compact prime power supply for use in a host of directed energy applications. Recent improvements in the energy and power density of electrochemical lithium-ion batteries have made them a very viable option for these types of applications where fast and rep-rate operation is of interest. Despite the proven ability of lithium-ion batteries to source high currents, it is still unclear how they age when they are used to repeatedly source high-rate currents in a pulsed manner, as they must when used in a repetitive rate prime power supply. Similarly, it is unclear how elevated rate recharge affects the life of the battery. Research has been performed at University of Texas at Arlington in which high-power, 2.6 Ah lithium-ion batteries have been repeatedly discharged and recharged at high pulsed rates. This paper will discuss the potential of lithium-ion batteries for use in these applications and will present experimental results performed when two 2.6 Ah cells were both discharged at 28 A (10.8C) and recharged at 9 A (3.5C) to 2.5 and 2.0 V, respectively.

Elevated Rate Cycling of High-Power Electrochemical Energy Storage Devices for Use as the Prime Power Source of an EM Launcher

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

Fast Recharge of Electrochemical Energy Storage Devices at Pulsed Elevated Rates

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Pulsed evaluation of high power electrochemical energy storage devices

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

Electrochemical Energy Storage Devices in Pulsed Power

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Elevated rate cycling of high power electrochemical energy storage devices for use as the prime power source of an EM launcher

values. This paper describes the rationale behind the experiments, the experimental setup, and the research progress made thus far.

Recharge of electrochemical energy storage devices at pulsed elevated rates

In the last decade, battery manufacturers have significantly reduced the internal series resistance of many electrochemical energy storage devices. This reduction has drastically increased the power density available from these electrochemical cells and opened up a whole new set of applications that they can be used to power, such as compact pulsed power systems and electric vehicles. It has been shown previously that high-power lithium-ion battery cells, such as the Saft VL8V and GAIA 27-Ah battery, are capable of discharging currents at rates much higher than their rated C values for time scales on the order of tens of milliseconds. While these cells are capable of elevated rate discharge, recharge at an elevated rate is traditionally thought of as being catastrophic to the cell lifetime. In all applications, there is always a desire to recharge electrochemical energy storage devices at a faster rate. Previous research in this area has applied charge rates to batteries that are a few times the cells rated C value in a steady-state application with findings that recharge time can be significantly reduced. The University of Texas at Arlington is conducting new research in this area. The aim of the research is to understand the charge rate limitations of electrochemical energy storage devices, such as lithium-ion batteries, supercapacitors, and lithium-ion capacitors, when the elevated charge is applied in a pulsed fashion. The effect that these types of elevated recharge rates have on the fundamental material properties inside the cells is being researched as well. This paper describes the rationale behind the experiments, the experimental setup developed, and the research progress made thus far.

Pulsed current limitations of high power electrochemical energy storage devices

Researchers and manufacturers of lithium-ion batteries (LIBs), electric-double-layer capacitors (EDLCs), and lithium-ion capacitors (LICs) have been able to produce devices with power densities previously thought to be impossible. As a result of their higher power density, these devices are able to source high currents to compact pulsed power loads. Though many pulsed power sources already exist which draw their prime power from electrochemical energy storage devices, the number of systems and their capabilities will increase substantially as energy storage technologies continue to advance. Though manufacturers often list the peak pulsed current capability on the electrochemical cells datasheet, sometimes the value listed can be limited by the hardware used to test the cells and not always the cells themselves. In order to experimentally validate the pulsed current limitations of newer electrochemical cells, a low impedance test stand, capable of extracting high pulsed current from individual cells has been developed. The impedance of the stand, roughly equal to or less than 1 milli-Ohm, is such that in most cases, the impedance of the cell dominates the discharge current. A description of the test stand, the 100 ms pulsed current limitations of many different cells, and experiments representative of how these devices can function in a pulsed power system will be presented.

Discharge of electrochemical energy storage devices at elevated rates for driving pulsed power applications

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.