BATTERY JOY AND THE CAR GUY: Cracking the Code of Lithium-Ion Batteries

As many of you may have picked up, I'm not really by standard definition a "car guy". I don't really like cars. I don't even like to drive. When we go out, my wife normally drives. Strange thing I wind up doing given that context.

But I am a battery guy. I've always been fascinated by telephones and batteries. That you can carry an electrical device around without a cord, never ceases to amaze me. At age four I thought flashlights were magic and I just never could put together how they could magically make light, and then how they would run down and COULDN'T make light. My later education in electronics didn't help much. Batteries were always kind of glossed over, largely because the instructors were electrical engineering types, batteries were kind of chemical, and beyond the basic textbook explanation, we kind of moved on to acknowledge that they could indeed produce voltage and current - for awhile.

Batteries have changed a lot in my lifetime. I recall entering a store called the Hobby Horse at age six and asking the guy for a dry cell and a miniature socket. He brought out a little blow up clown with sand in the bottom that you punched and it swung back up. He didn't know what a miniature socket was nor for that matter a "dry cell". I was confused that this adult was showing me a plastic toy when I wanted a battery and a bulb holder for a very basic experiment I found in a book. My disconnect with the populace of planet earth was pretty well completely formed by age 10 and I became convinced that I was supposed to be delivered to another planet and there was some heroic mixup in the postal system of the universe that had created this mess with me here instead. I've never really changed that position. An uncorrectable if tragic mistake that I will just have to learn to live with for now.

That you could move a car with batteries is indeed one of the most exciting things I've learned along the way. A 1979 experiment with a Ford Pinto was less than satisfactory. We had no PWM controllers. You switched batteries around in various combinations and an 11 mile range was the best I could do with a Baldor aircraft starter and some lead acid cells. I also learned a lesson about unobtainium as I ordered and paid for $5000 worth of Nickel Cadmium aircraft batteries and waited over a year before receiving my money back. As I was making about $19,000 per year and it WAS 1980, you can comprehend my lack of sympathy over battery prices today. IT would be the equivalent of a $50,000 purchase. After ayear, they DID send my money back. They simply had been unable to produce their brochure.

The Pinto kind of haunted the garage for a few years and was finally towed off to the junkyard.

Four years ago I ordered some very bad white Seiden LiFePo4 cells from China. 12 weeks later they showed up in my driveway. I had almost forgotten them. After a few months of playing around with them, it occurred to me that they would in fact drive a car somewhat better than the lead acid cells and I asked Brain to obtain a suitable lightweight vehicle. He picked a Speedster replica. I didn't even care what KIND of car it was.

But I fell in love with the Speedster. And I ordered seome Thundersky 90Ah cells to power it. We started work in September and rolled first on Christmas day. To say I had an EV grin was an understatement. I had calculated a range of 46 miles - we did 100 on the first charge. It went 94 miles per hour the first week. I had expected a very capable golf cart. I got a Porsche Speedster instead. Game on.

The central issue to me at the time was "If people knew about this shit, they'd be doing it RIGHT NOW". Some early EV pioneers had also ordered some Thundersky batteries in a group buy. They immediately tried to "equalize them" after the fashion of their beloved lead acid cells and ruined them all. I was following their progress quietly but intently. They've been heroically rewriting that historical episode ever since and I've watched that too. This was the beginning of the BMS crowd, which I struggle with to this day. They STILL do not understand these batteries.

As they come from China, the instructions with them were a little sparse. We were supposed to charge them to 4.2v per cell and Winston himself said that charging them to lesser voltages would "damage" his cells. The literature was totally rife with lead acid myths and carryovers. There was nothing to go by. We looked for Battery Management Systems and I actually bought several - typically at $2000-$2500 each. One from China had so much equipment and cables that the idea of instaling it in a Speedster was preposterous on the face of it. I would have needed Houston Control to mount all that stuff.

And so I set out to learn all I could about large format Lithium Ion batteries. But as noted, there was almost no information available. I started hounding the Chinese by e-mail, and bit by bit did gain some communication with them in Chinglish. A guy in The Thundersky Yahoo group and I even devised a current shunt that worked with an LED and a Darlington transistor and I got it to shunt about 7 AMPERES across the cells. I also learned about thermal runaway of semiconductors and worse, that top balancing cells CAUSED cell death at the end of a drive - if you drove it far enough.

And so I started aquiring better volt meters and ammeters and power supplies and loads and experimenting with cells. I was crushed when I would lose one as they were expensive. Finally I decided to GET OVER THAT and just destroy them on purpose to see when and wny they failed. Enough accidents. Let's just do it on purpose.

I got to the point with Thundersky's that if I undercharged them to about 3.6 volts, they behaved very well and I really didn't have any less capacity than the spec sheet - often more in fact. Then I bought a Thundersky charger for 24 cells, which was what I had in the GEM. When I got it, it was really two little chargers bolted together. And it had NO controls on it at all. In fact, I opened the box and looked all through it. There was not a SINGLE trim pot in the entire device. It was hard wired for an output voltage of 87.4 volts as it turns out. Very interesting. Thunderksy, who still had 4.2v on their spec sheet at the time, was selling a charger for a fixed 24 cell system that charged the cells to 3.65 volts. I was off by 0.05 volts from what they were DOING not what they were SAYING.

The experience along the last four years has made me TOTALLY cynical about manufacturer specifications, battery experts, and the entire body of literature available on these cells. I distrust my own measurements and experiments, constantly questioning that I could be wrong, because of the variance between what I see and measure and what I read and hear. And over time, even more distrustful of others. I actually got in an argument with a guy on Endless Fear Sphorum and he sent me some graphs that were FAKED ENTIRELY. He just made these graphs up with software with no measurement at all. They had no outliers, no anomalies, they were gorgeous - albeit impossible. I questioned him on how he did the measurements and the story came unglued. I did the purported measurements, and showed my messy graphs that showed exactly the opposite, with the methodology I used and noted that he was either a liar or had faked the graphs entirely. He simply disappeared from the discussion.

So am I a little cynical about "experts" and self proclaimed "authorities" on the topic. Duh yayuh. Just a tad.

I also learned some interesting things about the Chinese. They will fill any blank on any form you want to present in order to close the sale. But consistently they UNDER promise and OVER deliver. Americans not only OVER promise and UNDER deliver, but there is a recurring admonishment that the Chinese products are shoddy in construction, unreliable, and probably dangerous - all coming from American companies in the space of course. The cynicism grows, and my nationalism fades, leaving two enormous fears. The first fear is that we will all wind up working for the Chinese. They believe this is their century and I can't make a case. The second fear of course is that they won't want us at all and will hire Brazilians instead.

In any event, the Sky Energy company received an enormous investment from the China Aviation Missile Academy and was reborn as the China Aviation Lithium Battery Company - CALB. We had kind of developed a bias in favor of the Sky Energy cells and they continued to manufacture them. We used them in most of our builds, although we also used a number of Winston battery company cells as they provided some cells and advertised with us for awhile. Over a year ago Keegan Han, the U.S. marketing rep for CALB, showed us some photos of their new "grey cells" that they were introducing. It was always a month or so away and this went on for over a year. Finally in June they became available. We got a few and tested them and not only ordered some, but began to discuss selling them.

Keegan provided us with an internal document describing the gains of the new grey cells. One of the claims was dramatically improved cold weather performance. So we set up a test of the SE180AH cell compared to the new CA180FI cell. The results were persuasive. The CAFI cell was dramatically better at -20C or about 0F. We also graphed the charge and discharge curve and noted that it was even flatter than the SE cells. We actually like flat charge/discharge curves as this moves a greater percentage of the capacity of the cell onto the safe "flat" part of the curve. This means we can cut off charging later, and cutoff discharging later and still be safe.

One of the claims was a 70% improvement in output power. All lithium cells face a design tradeoff. If you put more active material on the aluminum current collector, you get more energy in the same weight battery. But the migration path of electrons from the current collector to intercalation sites in the LiFePo4 material becomes longer and more tortuous, and at the same time, the migration path for lithium ions out of the electrolyte into the same material to join with the electron and so intercalate into the material becomes longer as well. This reduces the amount of current you can deliver at any one instant. And so the ENERGY density of a cell, that is its ability to store power, and its POWER density, it's ability to deliver power at impressive current levels, are almost mutually exclusive. We want more energy density for range. ANd we want more power to actually send 1000 amps for 15 seconds to our Soliton controller for example. This then is the central design tradeoff in Lithium ionic cells.

The CA180FI cells mostly come int at 196-198AH - typical of the Chinese propensity to under promise and over deliver. The CA180FI cells are expensive for 180 AH cells. They are pretty INEXPENSIVE for 200Ah cells. By contrast, we've NEVER had an American made A123 20Ah cell actually achieve 20Ah of capacity. Just doesn't happen.

But there was also a claim of 70% improved power output. Now I struggle with this. What does it mean? 70% of what. I have to assume that for the SAME decrease in output voltage, it would deliver 70% more current. Or conversely, might it mean if it delivers the same current, would their be a 70% decrease in the voltage drop? Or what?

A few weeks ago we carried some video of Damian McGuire heroically challenging a CA180FI cell we sent him with a SPANNER. A SPANNER is like a wrench, only white hot. He shorted a single cell with the spanner and recorded currents up to 1976Amps as I recall at least momentarily. And it appeared to hold 2.90volts at some impressive current levels. But the whole thing was sufficiently quick and uncontrolled that I couldnt' make much of it.

I don't have any real way to test 2000 amps beyond sticking a coat hanger in a bucket of water, hooking up a shunt to it, and praying that I don't blow all of us to Kingdom Come.

So on the assumption that the 40AH cell, the 60Ah cell, the 100Ah cell and the 180Ah cell are all different sizes of the same chemistry and construction, we ordered some 40Ah cells from Keegan and were disappointed to learn he was out of them. In fact, supplies of all the CA cells were uncertain as they were selling somewhat better than expected. Finally, they arrived last week.

The 40Ah cell is somewhat more manageable. 5C would be 200 amps and 10C consequently 400 amperes. I have loads that when used together can do 400 or 500 amps for brief periods in a controlled fashion. These are constant current loads.

Testing a single cell is problematical. When you only have 3.3v to start with, and it decreases to 2.5v, in order to do 400-500 amps you have to have very low resistances. Cables and connections and so forth become significant and you find you just can't make the current, not because the battery won't put it out, but because you can't load it sufficiently.

So we like to put 3 cells in series and get up to 10v or so to start. Our constant current loads can then maintain constant current and we can actually read our meters without going back to the video later to try to figure out what happened.

So we put three CA40FI cells in series and hooked it all up with a very accurate voltmeter and ammeter. We're within a hundredth of a volt and perhaps 0.3 amps on 100 amps.

I don't really need to get 40Ah SE cells to compare. First I cannot. But we had done a dynamometer test on Speedster Redux with a Soliton1 where we DID achieve 1000 amps, any way you want to measure it, by flooring it for 15 seconds in third gear under load. We had 188volts in our pack when we started, and 147volts at the point of highest current and lowest voltage. The SE cells did it pretty well, but our pack voltage dropped from 188volts to 147 volts a decrease of 41 volts and 23.4% of our original voltage.

This is kind of important actually. Had we maintained 188 volts, at 1000 amps, we would have had 188kW driving that car. In electrical horsepower, that is 252 horsepower. Unfortunately we didn't get 252 horsepower. The voltage dropped to 147 volts and at 1000 amps that is 147kW, a 41kW drop and more like 197 horsepower. In other words, we lost 55 horsepower to voltage sag.

1000 amps for a 180Ah cell is a current rate of 5.55C. In other words, 5.55 x the 180 rating in current. The higher the voltage at that current rate, very simply the more power and the faster the car will go.

In this weeks test, we attempted to duplicate this with the 40Ah cells. 5.5 x 40 is a much more manageable and measurable 220 amperes. So we set up the load to do 220 amps and switched it on for 15 seconds.

The results were nothing short of astounding. After 15 seconds at 220 amps, we had dropped from 9.935 volts to 9.263 volts - a drop of some 6.76%. This is a bit over a quarter of the drop the from the SE180AH cells at 23.4%.

What would this mean in Speedster Redux? Well, it means our 188 volts would have dropped to 175.3 volts and we would have produced 175.3kW instead of 147 kW, and produced 235 horsepower-e instead of 197 horsepower-e. With the same size and price of battery cell. That's 38 horsepower for free.

We repeated the test at a 30 second drain and the drop only increased to 7.66%. Again, compared to 23.4% at 15 seconds for the SE cells.

So we decided to go for broke and up the measurement to 12C or 480 amps. At 15 seconds, the drop increased to 15.94%. But that is OVER TWICE the current level and still over 7% LESS voltage sag than the SE cells. So we did a final test at 30 seconds and 12C. ANd we were STILL less voltage sag at 17% - more than 6% below the SE cells STILL.

Accelerating at full current for 30 seconds is actually preposterous. You will never do this in a car. You could go zero to 100 in a little over 20 seconds normally. If you can't you are doing direct drive and simply lack proper gearing for your vehicle.

Where to go with this? It pretty much obsoletes the A123 cells here at EVTV. True, they will do 20C. But the packaging requirements have proven daunting.

We have a new speedster coming our way from B&B Manufacturing in Granby Missouri. Recall they built the eCobra, which last week we welcomed back for some minor work before delivery. This Speedster will feature a carbon fiber body and a molytube chassis with rack and pinion steering and an IRS rear end. IT is supposed to come in at under 1000 pounds before adding wheels.

We'll use an AC-50 motor from High performance Electric Vehicles on this car - a three phase AC motor with a Curtis 1238-7601 controller. That controller can be fitted for 126volts but not over 130. And so sag is an issue. But it can also do 650 amps. If we had a 70Ah CALB cell, we have demonstrated it can do 12C or 840Amps. 38 cells at 3.3 each would give us 125.4 volts. At 840 amps, we could expect a voltage sag of 16% or 105 volts. Of course, it won't be that bad because our controller is limited to 650 amps. Let's call it 12% and 110 volts. That's 71.5 kW and 96 horsepower. That is not only FULL power, but much fuller power than we have ever been able to produce from this combination.

That's a very small pack at 8750 wH, but we should be down around 1550-1600 lbs total for perhaps 160 wH per mile. And so we could still hit a 55 mile range at 100% DOD or 43.75 miles at 80% DOD. That's still four miles past the 39.4 daily average in America.

And the price becomes attractive. At a little over $100 per cell, we have a battery pack at $3800. That's getting down toward Pb AGM cell prices.

And so the small pack short range vehicle at a lead acid price we were shooting for with the A123 cells becomes viable - without the packaging nightmare. And it's available now.

So we're a little excited about batteries. How about weight? The 70Ah cell should come in at just over five pounds each for a battery pack between 190 and 200 lbs. The curtis and motor come in at about 140 together. The wheels will probably be 160 lbs. And that's 1500 lbs for the car. Add a charger and DC-DC converter and cables and boxes and we will probably be 1550-1600 lbs. That's 450 lbs LESS than Speedster Duh, which was a 550 amp Curtis 1238-7501 controller. With the better voltage, the 100 additional amperes, and the 450 lb weight loss, I've got to believe this car will get out of its own way. I was actually enormously pleased with Speedster Duh's performance. But this one should scream. Rack and pinion front end and independent rear instead of swing axle should improve the handling.

AND Brian Anderson advises us he has a 6 x 9 inch channel 40 inches long under each door. It so happens, the 70Ah cells are about 5.5 x 8.5 inches and less than 2 inches thick. I could put 20 down both sides (actually I only need 38) and have NO forward cells and NO rear cells. A heroically low center of gravity and a MUCH improved polar moment on this car. It should handle heroically better, steer better, accelerate better, and literally dance down the road at 1600 lbs. Range anxiety? Keep your range. I don't need it. I need that Speedster, and it may just convert me to BE a car guy. If that won't, nothing ever will.

Jack Rickard