September 20, 2006
Thin Film Batteries The Ticket For Electric Cars?
An article in MIT's Technology Review reports on the potential of thin film batteries to replace lithium ion batteries and to make electric cars feasible.
These new batteries replace the liquid or gel electrolyte with thin layers of solid glass-like or polymer materials, which are more stable. "Nothing can leak, nothing can freeze, nothing can boil, rupture, or explode," says Tim Bradow, vice president of business development at Infinite Power Solutions of Golden, CO, a leading developer of thin-film batteries.
All those recent exploding and burning laptop battery stories do not mean we've hit a technological limit in battery development. Thin film batteries will lower costs, increase safety, and increase capacity all at the same time.
MIT battery researcher Donald Sadoway says the use of solid electrolytes allows the use of pure lithium in the battery anode and this maximizes the amount of electricity that can be stored. Plus, this approach is amenable to use of a much lower cost manufacturing process.
In contrast to the glass-like electrolyte used by Infinite Power Solutions and others, Sadoway has developed a solid-polymer electrolyte (today's lithium-ion polymer batteries use a gel) for use in thin-film batteries. This electrolyte, he says, could be processed in rolls like newspaper, or some other high-throughput process. Such a process for thin-film batteries, although not now being developed by industry, could bring down costs, he says, while innovative ways of packaging electrodes could reduce size. "We've made batteries in the laboratory that are 300 watt-hours per kilogram," he says. "That's two times the best lithium-ion [battery] on the market today."
Low cost and high capacity could open the door to electric cars. Electric cars could end our dependence on liquid fuels for ground transportation. This would allow nuclear, coal, solar, and wind to compete directly oil, gasoline, and diesel fuel.
Note that battery energy storage capacity does not have to equal the energy content of gasoline or even of ethanol in order to make electric cars that will go as far on a charge as a car can go on a tank of gasoline. A shift to pure electric vehicles would allow the elimination of a heavy engine and a heavy transmission. Some of the weight budget currently allocated to the drivetrain could instead go to batteries. Then the car could be powered by electric motors located in each wheel.No need for a transmission and axle to turn the wheels.
I wonder if a failsafe mechanism can be built into the motors so that if one of the motors goes dead, there is no possibility that its failure mode will "engine brake" just that one wheel. "engine brake" here means the motor is generating electricity and drawing energy from its wheel. Of course, there are other failure modes that can result in an independently-driven wheel to independently stop and I expect they are more likely than one of the front wheels independently stopping/dragging in a rear-wheel drive car.
You saw this too I expect:
“Brown University engineers have created a new battery that uses plastic, not metal, to conduct electrical current. The hybrid device marries the power of a capacitor with the storage capacity of a battery. A description of the prototype is published in Advanced Materials.” http://www.physorg.com/news77371085.html
Don't forget the roughly 85% waste in an internal combustion engine, vs the roughly 20% waste in a battery and electric motor.
You only need about 20% as much energy in a battery as you need in a gas tank.
By the time the batteries are ready in a few years, we must have the energy source to create the electricity to
charge these batteries.
Here is a web site about the efficiency of burning switchgrass directly to produce energy from turbines. Basically
it says that growing switchgrass as fuel to burn directly, requires a lot less energy input than corn-ethanol.
The ratio of energy input efficiency is 14 to 1. This means a lot, since it is easy to grow switchgrass in
regions that are not used for agriculture, including near cities, and this is a carbon-neutral system, since
it emits only the carbon dioxide that was absorbed from the atmosphere into the switchgrass.
EXCERPT: What this article above says is that:
Switchgrass pellet fuel heating as an energy production and land use strategy
A switchgrass field yielding 10 tonne/ha generates 175.8 GJ of fuel pellet energy.
Using the energy output to input ratio of 14.6:1, 163.1 GJ/ha of net energy are gained per hectare. In comparison, co-firing switchgrass with coal produces a net energy gain of 47.2 GJ/ha, the production of switchgrass ethanol yields 57.1 GJ/ha and the production of corn-derived ethanol yields 21.4 GJ/ha.
In terms of net energy produced from a given land area, pelletized switchgrass is:
3.5X more efficient than co-firing switchgrass with coal for electricity production;
2.9X more efficient than cellulosic ethanol production;
7.6X more efficient than grain corn ethanol production.
Yes, I saw that report. I've also read other articles about the use of capacitors as batteries. But I've yet to see hard numbers in the capacitor approach in watt-hours per kilogram. That's the measure that Sadoway always uses (I've posted about Sadoway before) to compare batteries. If memory serves lead acid batteries are about 30 to 35 watt-hours per kg. So Sadoway is saying something a whole lot better is achievable with pure lithium and thin films.
If you or anyone else can point me to kilowatt-hours per kg numbers for these capacitors I'd like to see them. Then I could get excited enough to do a post about that approach.
Sadoway's claim of 300Wh/kg = 1 Mega Joule/Kg
Information on energy density:
Lithium ion battery 0.54 to 0.72 MJ/Kg
melting ice 0.335 MJ/Kg
compressed air at 20 bar (near compression limit) 0.27 MJ/Kg
NiMH Battery 0.22 MJ/Kg
lead acid battery 0.11 MJ/Kg
Supercapacitor 0.01 MJ/Kg
Capacitor 0.002 MJ/Kg
I kind of like melting Ice as an alternative. The enviromental and safety issues are very small.
There is a long thread about battery powered cars at GCC
Battery powered cars have been tested by DoE:
Advanced Vehicle Testing Activity (AVTA) is conducted jointly by the Idaho National Laboratory (INL) and the National Renewable Energy Laboratory (NREL). The data on the INL web site is generated by the testing activities of the INL. For more information about AVTA, go to the Department of Energy’s FreedomCAR & Vehicle Technologies Program web site.
I found this report: 2002-01-1916, Electric and Hybrid Vehicle Testing by James E. Francfort and Lee A. Slezak. [PDF]
I thought that the following was interesting and relevant to this discussion:
"As measured in km driven per kWh, the least efficient energy use occurred during fleet testing with the four vehicles averaging 2.7 km per kWh (Table 3). The average energy use for the four vehicles during the drive-cycle dynamometer testing (SAE J1634) was 5.4 km per kWh. The average EVAmerica charging efficiency results for the three vehicles was 3.5 km per kWh. The average fleet energy use results were 50% lower than the average drive cycle efficiency results and 23% lower than the EVAmerica charging efficiency results."
The four vehicles tested included Ford and Chevy small pick-ups converted to BEV, a Nissan medium-size station wagon, and the Toyota RAV4 EV. The RAV4 was the most efficient of the lot with 3.5km/kWh in fleet testing, 6.6km/kWh in dynamometer testing, and 3.7km/kWh in charging efficiency.
To convert km/kWh into MJ/100km, divide the number into 1 to make it kWh/km, multiply by 3.6 MJ/kWh and by 100.
I get 103MJ/100km fleet, 55MJ/100km dyno, 99MJ/100km charging for the RAV4.
Note that we can convert these figures to gasoline consumption by dividing by 30MJ/l. By that standard the RAV4 EV gets 3.4l/100km or 56mpg. So there is a real efficiency gain in going electric, my calculations are completely screwed up, or there is the illusion of a benefit because the heat engine is back at the electric company.
The on the GM EV1 [PDF], which was a sophisticated small vehicle purpose built to demonstrate EV technology showed:
DRIVING CYCLE RANGE
Range per SAE J1634: 78.2 miles
Energy Used: 12.84 kWh
Average Power: 4.06 kW
Efficiency: 164 Wh/mile
Specific Energy: 26.3 Wh/kg
Performance Goal: 60 miles
164 Wh/mile * 3600 J/Wh / 1.609Km/mi * 100 Km/100Km = 37MJ/100Km.
I think the RAV4 is a more realistic model for a small battery powered vehicle, but I do not gather any great hope for viable electric vehicles from it.
Here are the numbers from the paper you linked to:
ED = 8 Wh/kg at a PD = 100 to 10,000 W/kg
I didn't read the paper; just pulled those off the first page.
8 Wh/kg is really low.
Compared to a battery, yes. But within range for an ultracapacitor. To quote the Song and Palmore article further:
"Batteries are known for their high ED but low
PD (ED= 20–100 Wh kg–1 and PD= 50–200 Wkg–1), whereas
ultracapacitors are the opposite (ED= 1–10 Wh kg–1 and
PD= 1000–2000 Wkg–1)."
And when you consider an upper power density range of 10,000 W/kg, these polymer batteries look quite good compared to ultracapacitors.