Almost
every automaker interested in producing electric cars is betting on
improvements to lithium-ion batteries to make the cars cheaper and
extend their driving range.
But scientists at BASF
are exploring the possibilities of an older type of battery,
nickel-metal hydride, now used in hybrids. They recently doubled the
amount of energy that these batteries can store, making them comparable
to lithium-ion batteries. And they have a plan to improve them far more,
potentially increasing energy storage by an additional eight times.
The BASF researchers are aiming for batteries that cost $146 per
kilowatt-hour, roughly half as much as the cheapest lithium-ion electric
car batteries.
Lithium-ion batteries have been preferred in many applications
because they’re lighter and more compact—that’s why they’ve superseded
nickel-metal hydride batteries in most portable electronics.
But nickel-metal hydride batteries have some significant advantages
in cars, which is why they’ve been used in hybrids for decades. They’re
durable, and inherently safer than lithium-ion batteries, partly because
they don’t use flammable liquids, as lithium-ion batteries do—they
don’t catch fire if they overheat or are overcharged so their cooling
systems and electronic controls are far simpler. Safety systems can add
about 25 percent to the cost of a lithium-ion battery pack, and increase
their weight by 50 percent, based on data from the industry group U.S.
Advanced Battery Consortium.
To these inherent advantages, the BASF scientists added improvements
to the nickel-based materials used in the batteries. Changing the
microstructure helped make them more durable, which in turn allowed
changes to the cell design that saved considerable weight, enabling
storage of 140 watt-hours per kilogram.
Lithium-ion battery cells can store far more—230 watt-hours per
kilogram in some cases. But when you factor in the added weight of the
safety systems, and the fact that much of the energy is held in reserve
to reduce wear and tear and allow for energy storage capacity fade over
time, that advantage can disappear.One recent analysis found that the total usable amount of energy storage in lithium-ion electric car batteries is between 60 and 120 watt-hours per kilogram. Researchers still need to test whether BASF’s cells can last as long as conventional nickel-metal hydride batteries.
The next step for BASF is to introduce more radical changes to nickel-metal hydride batteries, swapping out the materials used now for ones that can store more energy and withstand higher voltages.
