Lithium-Ion Batteries for Electric Vehicles: Page 3 of 4

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

Longer life. While this can vary widely depending on factors such as daily depth of discharge and LA battery type (marine, golf-cart, AGM, industrial, etc.) regularly used and properly maintained EV-type FLAs have a typical life of about five years; LFP batteries have a typical life of 10 years. With only 12 years of data on LFP technology, their true longevity is uncertain.

The Main Disadvantage

While Li-ion batteries offer many benefits for EV applications, the main disadvantage (other than cost) compared to FLAs is the need for a battery management system (BMS), particularly while being charged. The job of a BMS is to monitor the voltage and temperature of each cell to protect them from excessive charging and discharging. While any battery system, whether it be FLA or Li-ion, can be improved with a BMS, they are not typically used with FLA cells because, as long as all the batteries in a pack are of the same manufacturer, model, and age (ideally from the same manufactured batch) and have been treated equally, the individual cells tend to behave the same while being charged. However, LFP cells, even of the same manufactured batch, can vary in capacity, leading to dangerously elevated voltages on the full cells as the others are still being charged.

FLA cells tend to be fairly tolerant of brief periods of high charge voltage (it is recommended to periodically elevate charge voltage, known as an equalization charge, which gasses the electrolyte vigorously in an effort to remove water/acid stratification and bring weaker cells up to full). With Li-ion batteries, even a fraction of an hour at elevated voltage can cause damage. Highly overcharged cells will swell and create internal gas pockets that prevent electrolyte contact with the electrodes. This usually permanently damages the cell (cells can be damaged and not show swelling). In extreme cases, the swelling can cause a cell case to rupture, releasing volatile organic solvent gases, which can be caustic and flammable. It should be noted that LA batteries have their share of dangers, including explosions, and a very hazardous electrolyte.

A BMS protects individual cells from over-voltage by shunting current around the full cells when they reach their “full” voltage, which allows the other cells to continue to charge. A good BMS can also detect when a cell is beginning to overheat (another sign of pending danger to cells) and shut off charging to the pack to protect all of the cells.

A BMS can also help during discharge by signaling for disconnection of the load when individual cells drop below their minimum voltage. Cells discharged too deeply can be permanently damaged or, at minimum, have their capacity or cycle life permanently reduced.

All factory EVs, such as the Leaf and the Volt, have a BMS that performs these functions. Some also manage air or liquid cooling of cells, both during charge and discharge, to prevent thermal runaway (a condition where one overheated cell causes its neighbors to begin generating heat), and to help maintain peak battery efficiency. Typical EV conversions using prismatic, hard-cased LFP cells usually don’t need active cooling for the cells because the cases have separators and air gaps built into them. This helps spread out the heat, and LFP chemistry (unlike some lithium-oxide-based chemistries) does not contain much internal oxygen, which can be a catalyst to thermal runaway.

The bottom line is that the risk of damage or danger is far too high to use Li-ion batteries without a battery management system. My upgraded conversion uses a relatively high-end BMS manufactured by Manzanita Micro (about $35 per cell). An optional display shows the state of each cell—both its voltage and temperature—in real time. Being a data-geek, I like to keep an eye on the whole system.

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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