Battery Types & Charging

An odd fact out the electric vehicle is that ‘volt heads’, or whatever you call them, never bother talking about the motor. It’s always all about the battery. The Internal Combustion Engine (ICE) deals with pistons, volatile chemicals, combustion and compression and in comparison to an AC induction motor, at all seems a bit improbable, as if the ICE was the invention that should never have happened. Containing about one-tenth the amount of moving parts, the only real exciting part for the EV mechanic is the possibility of getting electrocuted.

Battery Densities compared to Diesel

Two words explain the development of combustion over and above induction - energy density. Fact of the matter is that fossil fuels offer an enormous amount of energy in a pretty much ready-to-use form. The graph illustrates the amount in watt-hours per kilogram compared to the available battery chemistries and it’s pretty astounding. Lead-Acid batteries only store a very small fraction of the energy that diesel fuel holds. While the nickel and lithium technologies improve, they still don’t get even get close.

How, then, have manufacturers managed to run cars on this technology? The answer lies in efficiency. The well-to-wheel efficiency of a diesel car is about 25%. In other words, three quarters of your tank gets wasted. With electric cars the figure is more like 75% so you can afford to work with much less energy. But it has it’s limits. GM’s electric car from the 1990’s, the EV1, ran on lead acid and much of the technical challenges involved reducing drag. Tests showed that even a roof-affixed aerial could reduce the car’s range by a mile. A recent innovation (certainly with regard to the REVAi) has been the use of complex computer management and you notice it when you drive. In a nutshell, it takes plenty of energy to start a wheel spinning, but not much to keep it going. Onboard computers make a series of batteries intelligently share the load and the exact amount of power is delivered only when it’s needed. And then you’ve got regenerative braking to act as a top up.

Lead-Acid is a funny kind of technology. For example, you have to ‘water’ a REVAi every two or three weeks. It’s a very simple process (there’s a port on the car and it comes with a special tube along with some bottles of deionised water) but it’s definitely not something we’re used to. Even stranger is the behavior of the battery when it comes to making it to its stated range. Neglect it and it will perform badly. But drive it often and drive it well and it can be a very different story. GreenAer claim that one of their customers gets almost 100km out of his REVAi (the stated range is supposed to be 75km). It’s also possible to rehabilitate a battery that’s been sitting idle for a long time. This might explain that dismal review of the much awaited iMiEV by the Daily Telegraph:

In just 20 miles of gentle mixed motoring on an admittedly cold day, I used just under half the battery’s charge.

To be fair, if this was true it might just have been because the demo model was spending more time sitting an a cargo plane than being driven. But then again, this is supposed to be less of an issue with lithium technology so Mitsubishi’s claims to 160km for the iMiEV might go under some revision.

Nickel based (NiMH) batteries are primarily found in hybrid cars. Before lithium-ion, these were in our laptops and mobile phones. Of course, not many of us had either in the mid ninties since carrying around a brick wasn’t a desired fashion statement. This is also where many of us get our concerns about ‘memory’ from. Remember the days where you had to wait for your mobile to die before you charged it again? Thankfully, lithium-ion doesn’t have this drawback but it’s supposedly not quite a rugged and it’s still more expensive.

The EV industry seems to be settling with lithium-polymer for the next generation of vehicles. Initial concerns about safety and stability are just about overcome but it has taken years to get to this point. Cost is still a major issue. Some companies (Mitsubishi, for example) are hoping that economies of scale will bring the cost down but it’s a difficult business proposition. Are governments supposed to fund the first few million cars, or do the early adopters just take the brunt?

There is enough lithium on the planet to provide for bout 2.4 billion cars (there are less than 1 billion). Much of lies under salt-flats in South America and an intensive mining operation has yet to unfold. Two years ago, the technology cost about $750 per kWhr. Today, we’re down to about $500 and this should be pushed to less than $300.

The black swan might end up being an alternative chemistry and there’s some talk of a high-density ceramic technology but promises of results came to nothing last year. EEStor has recently shown some signs of encouragement for these ‘ultracapactiors’ but the jury is still out.

Lithium-sulphur and lithium-nano get talked about but they’re still several years away. So for the moment, success probably won’t lie in the battery so much as it will in the efficiency of the manufacturing operation of the vehicle as a whole. Costs will have to be kept down across the board. Saying that, keep an eye out for bipolar lead-acid, a technology which might break this year and claims to be a lot lighter and have an energy density comparable to nickel based technology (the assumption is that you get such performance at a fraction of the price).

The other big obstacle is charge time. We’ve gotten used to charging our phones every night so why shouldn’t this follow on to our cars? It might to a certain extent, but drivers will always want a relatively instant option. Better Place is pushing for ’swap technology’ but this requires both standardisation and a massive rollout of some fairly heavy duty infrastructure.

The head of GM recently remarked that the development of lithium batteries is moving at such a pace that you can charge them in 10 minutes! I’m sure this has some truth to it in a multi-million dollar lab somewhere, but commercial availability tells a different story. Mitsubishi’s iMiEV claims to charge up to 80% in 30 minutes, but this needs a special three-phase adaptor.

The same is true for REVA and their recently announced Fast Charger which supposedly fills the entire lithium battery in an hour. But it looks like this will be pricey. Upgrading a REVAi from lead-acid to lithium-ion looks set to cost something in the order of €100 a month (though under this leasing model, you don’t have to worry about replacing it down the road). A Fast Charger will probably cost a few grand but the good news is that there’s nothing stopping these being used as public charging points by local councils. But if you put the gizmos aside and keep to the normal charging cycles, then expect to charge overnight. A standard plug socket will do this.

A common feature of the charging cycle is that most batteries get to about 80% quite quickly. In two to three hours of charging you might be able drive a good 50km in a quadracycle. But there’s an anxiety issue here. It’s not as simple as ten minutes being enough to get you down to the shops and back. It’s probably safe to bet on an hour for something like a 10km round trip, but any chancer will eventually get caught out, not least because making a habit of short charges and close calls will probably affect the range of the battery.

The final, and perhaps most crippling aspect of battery technology is the lifespan. A three year life-cycle is perfect for consumer electronics (especially when they’ve got built in obsolescence) but drivers will always expect eight to ten years. This isn’t much of a financial issue with lead-acid. It’s just something you have to get used to and it probably won’t sabotage the possibility of making a saving. But with lithium or nickel based batteries the calculations become more complicated. Hybrids get ten years out of their batteries but that’s only by running them at 20% of their capacity. EVs need better or bigger batteries to get away with this strategy.

All the same, it might not be quite the issue many people think it is. Or, put another way, some won’t mind as long as it keeps them away from the pumps.There’s the added bonus of resale. AC induction motors don’t age like ICEs do so a new battery makes an EV not far off as good as new.

People talk about the ‘FCEV’ — the Fully Capable Electric Vehicle — and band about time frames like 2020. But it should be clear what this is getting at. It will be a great day when there’s an affordable car that goes 150kmph with a range of 400km, capable of being charged in 10 minutes with a battery warranty of 8-10 years, but just waiting for it to happen is not the answer. Getting there will mean starting small and it’s possible to use existing lead-acid technology do most urban journeys. The lithium cars will push this forward even more. If something comes out of the blue then we may be there much quicker than we expected to be. But failing that, it will be down to the pioneers and the early adopters to get this ball rolling.