What Does Toyota Know That Nissan Doesn't?

By Bill Moore

Posted: 16 Sep 2009

Just before the start of the 63rd Frankfurt Auto Show in Germany, Toyota announced that after three years of secretly testing Priuses with lithium-ion batteries, it has reached the conclusion that it remained to be convinced that they made sense in terms of durability and cost, both inter-related. A battery that fails prematurely will cost Toyota -- and PEVE, it battery joint venture with Panasonic -- a lot of money.

So, it came as a double disappointment when Toyota announced with not a lot of fan fair that its 500 vehicle fleet of prototype plug-in Priuses will be able to drive upwards of 20 km (12 mi) on battery power alone.

Why such short range, was my first question? I've driven converted Priuses -- courtesy of Plug In Conversions Corporation -- that have that much range. My first thought was Toyota PHEV Priuses must be equipped with lower energy density nickel metal hydride batteries, especially in the light of their earlier announcement. But no, reading their press release and online brochure clearly states that the cars are, in fact, equipped with lithium-ion batteries.

So, what's going on?

The answer seems fairly obvious. Toyota clearly states they want to run real world tests of their technology, including lithium-ion batteries. That's what they'll learn from their fleets tests starting early next year. They might as well learn all they can, while they can, even if the original tests left them with serious concerns about lithium.

As to the relatively short range of 20 km, that's pretty easy to surmise. Most plug-in kits for the Prius plant the supplemental battery pack in the spare tire well, placing it squarely in the vehicle's crumble zone, which has raised some safety issues, though kit makers like PICC of San Diego point out that not only is their package securely bolted to the vehicle body but it also may, in fact, serve as an added crash buffer in a rear end collision, though no one has actually put that theory to the test.

Presumably, Toyota engineers are compelled to install the new lithium ion pack within the general location as the NiMH pack, behind and under the rear seat. 12 miles of driving range probably means the car has about a 4kWh pack, compared to the far smaller 1.3 kWh NiMH in the Generation Two car and presumably similarly-sized in the Gen. Three model. Even using lithium, it will probably take up a bit of interior real estate. I would expect the back seat to be a bit higher and likely the rear cargo deck than in the stock 2010 Prius, in order to accommodate. Toyota states the pack, whatever size it is, can be recharged using 230 volts in some 90 minutes time.

While Plug-In Hybrid advocates will find the 20 km (12 mi) range disappointing, Toyota points out that in Europe, the average commute in 25 km, 3 miles beyond the range of the prototype. While its nothing to write home about, it is a commendable, if cautious step in the right direction.

What I really would like to know is what did those three years of tests tell Toyota? They're a very bright company, so why are they going slow on lithium while just about everyone else -- except Honda -- is racing down the lithium road, especially Nissan and Renault who are betting the house on it, as is GM.

My guess is they're worried about calendar life: the slow, inevitable degradation over time of the battery's ability to hold a charge, regardless of how deeply or not the battery is discharged. It's a known issue with lithium battery chemistries, one that GM "solved" by simply doubling the size of the pack, thus adding significantly to its cost and complexity. Better Place and Renault-Nissan appear to be addressing it by simply not giving the car "buyer" ownership of the pack. Better Place will retain ownership of both the car and battery through its pay-by-the-mile contract. Renault-Nissan are exploring selling the car, but leasing the battery.

Toyota would, I believe, like to continue their highly successful "sell-it-and-forget" product quality strategy, especially in terms of warranty and potential early battery replacement problems. NiMH has proven it meets that criteria. Clearly lithium hasn't.... yet. And the only way to resolve the problem is to run out the calendar.

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