January 2012

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The UltraBattery retrofit project DP1.8 and Carbon Enriched project C3, performed by ECOtality North America (ECOtality) and funded by the U.S. Department of Energy (DOE) and the Advanced Lead Acid Battery Consortium (ALABC), are to demonstrate the suitability of advanced lead battery technology in Hybrid Electrical Vehicles (HEVs).A profile, termed the ‘Simulated Honda Civic HEV Profile’ (SHCHEVP) has been developed in project DP1.8 in order to provide reproducible laboratory evaluations of different battery types under ‘real-time’ HEV conditions. The cycle is based on the Urban Dynamometer Driving Schedule (UDDS) and Highway Fuel Economy Test (HWFET) cycles and simulates operation of a battery pack in a Honda Civic HEV. One pass through the SHCHEVP takes 2,140 seconds and simulates 17.7 miles of driving. A complete NiMH battery pack was removed from a Honda Civic HEV and operated under the SHCHEVP to validate the profile. The voltage behavior and energy balance of the battery during this operation was virtually the same as that displayed by the battery when in the Honda Civic operating on the dynamometer under the UDDS and HWFET cycles, thus confirming the efficacy of the simulated profile.An important objective of the project has been to benchmark the performance of the UltraBatteries from both Furukawa Battery Co., Ltd., Japan (Furakawa) and East Penn Manufacturing Co., Inc. (East Penn). Accordingly, UltraBattery packs from both Furakawa and East Penn have been characterized under a range of conditions. Resistance measurements and capacity tests at various rates show that both battery types are very similar in performance. Both technologies, as well as a standard lead-acid module (included for baseline data), were evaluated under a simple HEV screening test. Both Furakawa and East Penn UltraBattery packs operated for over 32,000 HEV cycles with minimal loss in performance, whereas the standard lead-acid unit experienced significant degradation after only 6,273 cycles. The high-carbon, ALABC battery manufactured in project C3, was also tested under the advanced HEV schedule. Its performance was significantly better than the standard lead-acid unit, but was still inferior compared with the UltraBattery. The batteries supplied by Exide as part of the C3 project performed well under the HEV screening test, especially at high temperatures. The results suggest that higher operating temperatures may improve the performance of lead-acid based technologies operated under HEV conditions – it is recommended that life studies be conducted on these technologies under such conditions.Individual Furakawa UltraBatteries have been operated according to the SHCHEVP under a range of state of charge (SOC) windows and temperatures. Battery cycling was conducted using three different SOC windows (43-53%, 53-63%, and 63-73%) and three different battery temperatures (10oC (50oF), 30oC (86oF), and 58oC (136oF)). The results suggest that an adequate compromise between vehicle acceleration and charging efficiency during regenerative braking is provided with a SOC window of 53-63% SOC. Also, low operating temperatures severely decrease the energy returned by simulated regenerative braking. At 30oC (86oF), the number of simulated vehicle miles covered before a simulated engine recharge is required is 142 miles; the number of miles drops to less than 18 miles at 10oC (50oF). As a result, operation in cooler climates where trip distances are short (i.e., where there is insufficient time for batteries to heat up) will result in increased fuel usage. The lower temperatures also decrease the available discharge power, although this change is small relative to the effect on the charging efficiency.In another test, an individual 12 volt (V) East Penn UltraBattery was cycled for 167,700 simulated vehicle miles under the SHCHEVP (at 30oC (86oF)). While the discharge capacity decreased from 7.6 to 4.5 Ah, the battery was still capable of providing the power required for acceleration. Also, the battery’s ability to accept energy from regenerative braking decreased significantly during the operating period. The effect of this behavior on fuel economy, however, is not known. This aside, the result is considered very promising, since the SHCHEVP used to cycle the battery has the same discharge/charge intensity and frequency that is used for the NiMH battery currently in the Honda Civic Hybrid (i.e., the power levels were not decreased for the UltraBattery). This result demonstrates that the UltraBattery packs can last the design life of modern HEVs.

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A 12V, NiMH module (from the Honda Civic vehicle) was tested for almost 80,000 simulated vehicle miles under the SHCHEVP (at 30oC (86oF)), and its capacity and performance remained unchanged during the test period. It consistently delivered 159 simulated vehicle miles between simulated engine recharges. The performance of the NiMH module also decreases when the temperature is lowered, although this drop is not as severe as for the UltraBattery. For example, at 10oC (50oF), the NiMH battery is still capable of operating for 71 simulated vehicle miles between simulated engine recharges, compared to only 18 miles for the UltraBattery. Therefore, the fuel usage at low temperatures of a NiMH-based HEV is expected to be lower than that of an equivalent UltraBattery-powered HEV. The extent of such a difference, however, is not known. An individual 12V, high-carbon ALABC module was also operated under the SHCHEVP, but failed after providing 40,391 miles of simulated service.

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A Furakawa UltraBattery pack operated trouble-free for 60,000 simulated miles under the SHCHEVP (at 30oC (86oF)) with a minimal drop in performance. A vehicle-sized pack of East Penn UltraBattery packs also delivered 60,000 miles under the SHCHEVP (at 30oC (86oF)). While there was an initial battery failure in this pack (at 10,000 miles), logging of individual 12V modules has shown that all units were still very close in performance at the end of the cycling period. These results are very promising, and combined with the results for the individual module cycling, suggest that UltraBattery packs may be capable of lasting the design life of a modern HEV (e.g., 160,000 miles). In the C3 project, a vehicle-sized pack of the high-carbon ALABC modules was operated under the SHCHEVP, although it failed after just 27,000 simulated miles. A vehicle-sized, high-carbon, lead-acid battery from Exide was also cycled under the SHCHEVP, but it failed after just 12,500 simulated miles.

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The project DP1.8 also consists of a retrofit of the original NiMH battery with a pack of 14 Ultra-Battery modules, manufactured by East Penn, in a new 2010 Honda Civic HEV. After completing the initial conversion, ECOtality tested the HEV in accordance with, and in cooperation with, Advanced Vehicle Testing Activity (AVTA) of DOEs FreedomCAR and Vehicle Technologies Program.

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ECOtality conducted a full vehicle baseline characterization on the converted HEV. A full dynamometer evaluation (e.g., measurement of fuel economy under standard driving schedules on the dynamometer) was completed by Argonne National Laboratory (ANL). This approach allowed direct performance comparisons with the UltraBattery against the technologies used in the unaltered HEVs.

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In October, 2011, the converted HEV was put into ECOtality’s fleet of test vehicles in Phoenix, Arizona, and it currently still being tested. The converted HEV accumulates approximately 5,000 miles on a monthly basis and is experiencing a wide range of driving conditions. The monthly data being collected from the vehicle is an array of battery parameters, such as:

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1. • most restrictive temperature

2. • pack voltage

3. • power

4. • vehicle parameters, such as speed

 

The individual module voltages and cell/module voltage deviation are being measured separately on a monthly basis, as well as monitoring the health of individual battery modules. The mileage driven and gallons of gasoline used monthly are being recorded to monitor the vehicle average fuel economy for the month.