Lithium-ion battery | Much more durable batteries than expected

Another argument of denigration of transport electrification has just fallen. Researchers at the Californian University of Stanford believe that electric vehicle batteries would be around 40 % more durable than we thought so far.

This is an assertion that only the prolonged road of electric vehicles makes it possible to make, specify the researchers. It is this use “in the real world, by real world” which forms the basis of their reflection.

According to them, everyday driving in town and on the highway – accelerations and braking, frequent and prolonged stays in parking lots – is poorly reproduced in initial laboratory tests which aim to establish the sustainability of technology. However, this driving would ensure a better lifespan of vehicles than the type of wear simulated by almost all laboratories that test new battery technologies.

Surprising result

For their study, the researchers tested 92 different types of batteries that are already on the market, over a period of two years. They established a “dynamic” test profile from the way the batteries are discharged and then recharged by electric vehicles actually on the road, and a “constant” profile as those simulated in the laboratory. They then applied the two profiles to determine if there was a difference in the way wear was formed in these batteries.

The result is surprising, of the very admission of academics. The more the tested profile is similar to the typical behavior of a normal motorist, “the more the lifespan increases”.

All things being also equal, the “dynamic discharge” (typical of normal driving) allowed them to extract an average of 38 % more recharge cycles from the tested batteries, compared to the “constant discharge” applied in the laboratory.

In other words, the lifespan of electric vehicles could be greater than the initial projections, which in most cases vary from 8 to 10 years depending on most car manufacturers.

To reassure their customers, the manufacturers added to the basic warranty on all their vehicles an additional warranty on the life of the batteries.

The most complete is that of the Kia and Hyundai brands. It stretches over 10 years or 160,000 kilometers. Toyota offers a guarantee of the same duration on the battery of its hybrid vehicles, but reduced to 8 years (with the same limit of 160,000 km) the warranty applicable to the BZ4X battery, the only fully electric vehicle in its catalog. The same is worth for Lexus RZ.

Obviously, the deadline for a warranty does not point out the useful end of life of an electrical or electronic product, whether it is an automobile, a telephone or a microwave. This is often a good indicator of the period during which the manufacturer believes that its products will behave as promised – which does not necessarily protect all buyers of different types of problems or malfunction.

Electronic management to review

Researchers have also compared how electronic controllers equip electric vehicles behave, to minimize the wear of batteries.

What they discovered is interesting: minimizing the number of charging cycles should be prioritized to prolong the useful life of electric vehicles that are constantly in circulation, such as buses or commercial vehicles. In contrast, it is the simple passage of time, rather than the number of charging cycles, which is the real enemy of the batteries of light vehicles led by individuals.

In all cases, researchers think that it would be possible for manufacturers to add a few years of useful life to most electric vehicles already on the road by revising the control software that teams them, in order to take into account more faithfully the way in which motorists use these vehicles, rather than systematically falling back on initial laboratory tests.

Extending the useful life of electric vehicles would have the additional advantage of making their retail price easier to absorb for buyers. Electric vehicles are always a little more expensive to buy than comparable format petrol vehicles, but their costs of use later are much lower, which makes it possible to amortize the surprise and, in the medium term, to pay less for your vehicle.

Consult the study “Dynamic Cycling Enhances Battery Lifetime” (in English)