Terrill B. Atwater

Determination of state-of-charge and state-of-health of batteries by fuzzy logic methodology

A practical method of predicting state-of-charge (SOC) and state-of-health (SOH) of battery systems has been developed and tested for several systems. The method involves the use of fuzzy logic mathematics to analyze data obtained by impedance spectroscopy and/or coulomb counting techniques. Fuzzy logic provides a powerful means of modeling complex, non-linear systems without the need for explicit mathematical models. New detailed impedance date has been obtained on the discharge performance of primary lithium/sulfur dioxide cells. Earlier data, obtained by Rutgers co-workers on nickel/metal hydride and other systems, have been reviewed and re-interpreted using fuzzy logic methodology. Devices are being developed for several systems, which will predict the SOC and SOH of batteries without the need to know their previous discharge and/or cycling history.

Man portable power needs of the 21st century: I. Applications for the dismounted soldier. II. Enhanced capabilities through the use of hybrid power sources

Abstract The Army is facing a number of challenges now and in the future. One of the major challenges is in the power sources arena. As the Army continues to move toward digitizing the battlefield, the need for portable power is increasingly becoming a technological hurdle that must be overcome in order for a soldier to exercise his electronics capabilities without being overburdened by the power sources size, weight and operating/logistical costs. Advanced electronic devices are becoming a critical piece of the soldiers personal battlefield equipment. A soldier with the latest version of the Single-Channel Ground and Airborne Radio System (SINCGARS) is one of the most dangerous weapon systems on the modern battlefield. The ability to accurately navigate and communicate multiplies the soldiers advantage over a less electronic capable enemy. Keeping his personal electronics operational is crucial to giving the soldier the capability to complete his mission successfully. Inherent in keeping the electronic equipment operating is keeping it supplied with batteries. Due to the increased emphasis placed on the modern soldiers electronic equipment, the importance of the portage of the power sources needed to keep this equipment operational has also increased. Recent efforts have focused on hybrid power sources that may enhance discussed capabilities by taking advantage of both high energy sources and high power systems for intermittent power application. This development could lead to a power source with enough energy to meet the Armys preference for a 72-h mission life before the need for resupply.

Fuel cell/electrochemical capacitor hybrid for intermittent high power applications

Abstract A hybrid power source was demonstrated to successfully power a simulated power load encountered in portable military electronics and communications equipment. The hybrid system consisted of a 25 W proton exchange membrane fuel cell (PEMFC) stack connected in parallel with a 70 F capacitor bank. The cyclic regime of 18.0 W for 2 min followed by 2.5 W for 18 min was chosen as the baseline for the simulation of power load. The operating potential cut-off voltage for pass/failure was set to 3.0 V. At room temperature (23–25°C), the PEMFC alone could not handle the described baseline regime with the PEMFC operating potential dropping below the cut-off voltage within 10 s. The hybrid, however, continuously powered the same regime for 25 h. Its operating potential never reached the voltage cut-off point, not even during the high load of 18.0 W. The tests with hybrid configuration were aborted after 25 h of operation with no signs of output degradation, suggesting that further extended operation was possible.

Dynamic characterization of small lead-acid cells

Abstract Three sizes of small valve regulated (VRLA) commercially available lead-acid cells were investigated and characterized for their dynamic properties by ac impedance spectroscopy and other electrochemical techniques. All cells were of the limited electrolyte type and no additional electrolyte was introduced during the studies. The data indicates a very significant increase in cell impedance at lower states of charge, as expected. In charging studies close to the fully charged state, some unexpected impedance data were observed. Complex impedance plots indicate a passive film formation, probably associated with the recombination surface film. The investigations included cells in various states of charge as well as cycling history including positional orientation studies. Equivalent circuits were derived from ac impedance spectroscopy and the parameters studied as a function of the cell’s state-of-charge. Furthermore, the voltage response of the cells was theoretically generated from the ac impedance spectroscopy using Fourier transform analysis and found to be similar to the measured cell responses.

Hybrid power sources for Land Warrior scenario

Hybrid systems utilizing a zinc-air battery or a Proton Exchange Membrane Fuel Cell (PEMFC) as the high energy density component coupled with a rechargeable battery (lead-acid or nickel-metal hydride) or electrochemical capacitor (EC) bank as the high power density component were tested under a high-pulse application load, Land Warrior (LW). The hybrid power sources successfully operated the LW cyclic load beyond the capabilities of the specific single chemistry systems studied. The zinc-air battery hybrids allowed approximately triple the operation time of PEMFC hybrids. The best performing hybrid system was the zinc-air battery/lead-acid battery. It provided the greatest operating voltage and longest operating time.

Power assisted fuel cell

A hybrid fuel cell demonstrated pulse power capability at pulse power load simulations synonymous with electronics and communications equipment. The hybrid consisted of a 25.0 W Proton Exchange Membrane Fuel Cell (PEMFC) stack in parallel with a two-cell lead-acid battery. Performance of the hybrid PEMFC was superior to either the battery or fuel cell stack alone at the 18.0 W load. The hybrid delivered a flat discharge voltage profile of about 4.0 V over a 5 h radio continuous transmit mode of 18.0 W.

Hybrid power sources for military applications

Hybrid power sources consisting of a high energy-density but low power density component, and high power density but low energy density component are the subject of this paper. Such systems could provide much needed capability of high current pulses and extend the operation time of comparable in size and weight battery system. This is especially true for the military applications. Several different hybrid power systems have been evaluated. A zinc-air/electrochemical capacitor (EC) hybrid under pulse load demonstrated power levels more than double of that of the zinc-air battery alone over extensive time of operation. Similar benefits were demonstrated in the fuel cell/electrochemical capacitor and fuel cell/sealed lead-acid battery systems.

Thermodynamic and Kinetic Study of the Li / MnO2 ⋅ Bi2 O 3 Electrochemical Couple

MnO 2 .(Bi 2 O 3 ) 0.06 cathode material showed improved performance over typical β-MnO 2 in primary lithium battery prototype cells. Studies indicate that Bi 2 O 3 surface-modified β-MnO 2 material provided alternative catalytic discharge mechanisms, which lower the activation energy of the cell reaction.

Hybrid fuel cell for pulse power applications

A hybrid fuel cell demonstrated pulse power capability. It successfully ran a pulse power load simulation synonymous with electronics and communications equipment. The hybrid consisted of a 25 W proton exchange membrane fuel cell (PEMFC) stack in parallel with a 70 farad capacitor assembly. A cyclic regime of 18.0 W for 2 minutes followed by 2.5 W for 18 minutes was chosen as the basic test regime. The operating potential cut-off voltage for pass/failure was set to 3.0 V. At room temperature (23-25/spl deg/C), the PEMFC alone could not successfully power the baseline regime previously described. The PEMFC operating potential dropped below 3.0 V within 10 seconds. The hybrid continuously powered the cyclic regime for 25 hours. The hybrids operating potential never reached the voltage cut-off, even during the high load of 18.0 W. The tests were aborted after 25 hours of operation with no signs of output degradation, suggesting that continuous operation is possible.

Improved impedance spectroscopy technique for status determination of production Li/SO/sub 3/ batteries

The authors address the development of a technique to provide reliable two-terminal impedance measurements on graduation cells. The techniques value as a quality control tool and field tester were criteria during its development. Accuracy and measurement time are two areas of concern. An impedance spectroscopy measurement system was set up using a Hewlett Packard HP9836 computer with hard drive and printer, a Schlumberger I286 electrochemical interface and a Schlumberger I250 frequency response analyzer. Since the concentration was on two terminal cells the working electrode of the electrochemical interface was connected to reference electrode 2 and the counter electrode was connected to reference electrode 1. Routine impedance measurements have been made on lithium/sulphur dioxide (Li/SO/sub 2/) cells using an equivalent electric circuit approach. The data obtained show that network analysis for production batteries can be achieved quickly and accurately.<<ETX>>