Lithium-Ion Batteries for Electric Vehicles

Intermediate

Inside this Article

GMC Sonoma
A converted GMC Sonoma.
Original FLA batteries
Eighteen of the original FLA batteries in a custom-built box in the truck bed. The six other batteries were housed under the truck’s hood.
Flooded lead-acid battery and lithium iron phosphate batteries
Compared to flooded lead-acid batteries, lithium iron phosphate batteries pack in more energy per physical size and weight.
The Sinopoly Lithium-Ion battery
The Sinopoly Lithium-Ion battery
The Sinopoly batteries installed
The Sinopoly batteries, with the battery management boards, newly installed in the truck.
The on-board 30-amp charger.
The on-board 30-amp charger.
A battery management system
A battery management system protects its cell by shunting current around it when it is full.
The AC input for the battery charger
The AC input for the battery charger is accessed through the old fuel filler door.
The truck’s in-cab battery monitors
The truck’s in-cab battery monitors show battery state-of charge (top), and BMS cell voltage and temperature (bottom).
The author with his truck
Randy shows off his Li-ion-powered truck.
GMC Sonoma
Original FLA batteries
Flooded lead-acid battery and lithium iron phosphate batteries
The Sinopoly Lithium-Ion battery
The Sinopoly batteries installed
The on-board 30-amp charger.
A battery management system
The AC input for the battery charger
The truck’s in-cab battery monitors
The author with his truck

In 2007, I converted a GMC Sonoma from its original gasoline propulsion to pure electric, using flooded lead-acid (FLA) batteries (see “Born to be Wired” in HP122). The type of FLA batteries most commonly used for EV conversions, golf cart batteries, have three 2 V cells and a capacity ranging from about 200 to 260 amp-hours (Ah). Moving the truck’s 3,200 pounds required a higher voltage than the 96 or 120 volts commonly used for lighter-weight vehicles, so I used 24 batteries for 144 V and an energy capacity (at 100% discharge) of about 37 kilowatt-hours (kWh).

However, the battery weight (approximately 1,800 pounds) brought the vehicle very close to its maximum gross weight of 5,000 pounds. I expected my batteries to have a five-year life, but in the third year, they started to show signs of failure.

The short life boiled down to maintenance. I knew that the best practice for FLA batteries is to re-water them monthly if they are being cycled frequently (as they usually are in an EV). The charging process causes evaporation through electrolysis. I was usually good at watering the batteries, but on a few occasions, I postponed it, only to find that enough of the electrolyte had evaporated to expose the top of the lead plates to air. Exposed lead oxidizes, making it harder for the plates to interact with electrolyte and, thus, reduces their capacity.

This undoubtedly contributed to a shorter life, but the nail in their coffin occurred when I was unexpectedly called away for several weeks during the summer. In my original design, a daily timer was set on the battery charger to ensure the batteries were fully charged before I left on my morning commute. Without daily driving, the charger was excessively charging the batteries. This boiled off a significant portion of the electrolyte and overheated the batteries, causing them to swell.

I didn’t realize this until I tried to drive my vehicle and heard a “bang” in the battery box, and the vehicle lost power. Several of the batteries in the middle of the pack (those that got the hottest) had swollen—one had swollen enough to cause an internal short circuit, which ignited the gasses at the top of the battery. I replaced the worst of the batteries, hoping that the remaining ones still had some life. But after testing, I found that all of the remaining batteries had a significant reduction in capacity—the only solution was to replace them all.

Battery Shopping

Because I wanted my next battery pack to give me better service, I started investigating lithium iron phosphate (LFP) batteries, which had dropped in price significantly—from $75,000 for a 31 kWh pack in 2006 to $12,000 in 2010 (since then, prices have remained fairly constant). A comparable FLA bank was more affordable (about $5,000), but I was convinced that Li-ion batteries would improve vehicle performance (power, acceleration, range, and energy economy) and render a long-term payoff.

Switching to LFPs shaved almost 1,000 pounds from the vehicle, more than doubled the vehicle’s range, gained back the vehicle’s original acceleration, and nearly halved its energy use per mile. To see why I experienced such a dramatic improvement, we need to compare the batteries themselves.

The FLA reference battery is a standard 225 Ah, 6-volt golf cart battery (e.g., Trojan T105). The LFP reference batteries are high-capacity (180 to 200 Ah), 3.2 volt prismatic batteries. There are a variety of manufacturers and distributors for this type of battery, the most popular and available being the CALB SE180AHA, the Sinopoly LPF200AHA, and the FluxPower BATVXLFP200AH. In comparing, keep in mind that a golf-cart battery has three cells for about 6 V, whereas the LFP prismatics come as single cells (packs of 4 cells for 12 V are also available). The comparison table values based on watt-hours (Wh) provide an apples-to-apples comparison because they relate to stored energy. Except where noted, the table characteristics come from manufacturers’ specification sheets. The LFP column is the average of the specifications for the three popular LFP models, whose values differ by 10% or less.

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Comments (3)

Jim and Elaine Stack's picture

Anniel, Lithium batteries are still 10 times safer than gas and millions safer than lead acid. Lead is the worst pollution of all time.

Jim and Elaine Stack's picture

I think combining ultra/super capacitors in parallel with lithium batteries will be a huge step. Bluecar in Italy does it and gets 150 miles per charge with a MiEV Mitsubishi sized vehicle.

With cooling on lithium batteries like my FORD Focus EV I think the batteries will last 16-20 years. With only a 1% drop each year. Tesla is doing battery than expected with their liquid cooled batteries.

Government testing show a 10-20 year life mostly depending on temperature and of course no running them way down or over charging. In comparison Lead Acid batteries in Vehicle are luck to last 2-3 years. Lithium is also considered non toxic by the EPA but do have 2nd life as solar back up and are recycled!

Richard Illyes's picture

Good information and interesting project.

Do you have an opinion on the EESTOR and ZENN project using super capacitors?

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