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A cutaway view of the NiMH battery pack being used by Toyota in various hybrid-electric vehicles. (Toyota)

Toyota still favors nickel-metal hydride batteries for HEVs

Toyota isn’t taking a one-size-fits-all approach to electrified-vehicle battery chemistry.

Toyota has no immediate plans to drop its decades-long history of using NiMH (nickel-metal hydride) batteries, a stark contrast to other automakers solely offering electrified vehicles with lithium-ion batteries. “NiMH is reserved solely for our hybrid-electric vehicle applications,” said Scott Ankeney, senior engineering manager for the EV materials and catalyst design group at Toyota Motor North America in Ann Arbor, Michigan. The group’s tasks include battery-cell material design for hybrid-electric, plug-in hybrid vehicles (PHEVs) and EVs.

Ankeney spoke with SAE Media at a recent ride-and-drive program in Saline, Michigan for the 2024 Toyota Grand Highlander. The three-row SUV is offered with three propulsion choices: a turbocharged 2.4-L 4-cylinder gasoline engine, a 2.5-L 4-cylinder hybrid and a 2.4-L 4-cylinder turbo Hybrid Max. Both HEV variants of the Grand Highlander use NiMH batteries. In North America, the majority of the automaker’s HEVs use NiMH; exceptions include a lithium-ion battery pack for the Corolla Hybrid sedan.

NiMH battery packs — which the automaker debuted in 1997 via the first-generation Toyota Prius HEV in Japan — typically offer a cost advantage compared to lithium-ion chemistry. “NiMH also provides the power that’s needed to give assistance to the Toyota Hybrid System and provide a fuel-economy boost,” Ankeney said. The front-wheel drive Grand Highlander’s ICE-only powertrain achieves 24 mpg (9.8 L/100 km) combined, while estimated efficiency for the front-wheel-drive-configured SUV jumps to a 36 mpg (6.5 L/100 km) combined for the 2.5-L HEV and a 27 mpg (8.7 L/100 km) combined for the more-powerful 2.4-L Hybrid Max.

For a plug-in HEV or an EV, lithium-ion technology is chosen in large part because of that chemistry’s higher energy density versus NiMH, according to Ankeney. “We try to match the selected battery chemistry to customer vehicle expectations,” he said. For example, if a specific electrified vehicle’s target audience values fuel economy over high performance, those metrics dramatically influence what battery chemistry is specified.

“Most customers generally don’t buy a vehicle based on the chemistry of the battery,” Ankeney said.

The battery chemistry that will dominate Toyota’s electrified-vehicle portfolio in the future depends on several factors, including safety considerations. “Any energy-dense material has to be treated with care, so we make sure that safety is always our focus,” Ankeney said.

Solid-state batteries as well as the different chemical formulations around lithium-ion technology are among the ongoing research activities well underway at automakers and battery suppliers. One of the primary wants: development of a battery chemistry that is even more energy-dense than what’s currently in use for electrified vehicles. “We have to develop battery technologies that are safe and durable for automotive applications,” Ankeney stressed. “We have a pretty robust advanced development group that continues to work on next-generation battery technologies.”

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