Plug-in hybrid electric vehicles (PHEVs) are making headlines seemingly on a daily basis, offering some hope (along with other heavily hyped technologies such as biofuels) that the U.S. and other countries can actually reduce their dependence on foreign oil—and on a more altruistic level, perhaps make a positive impact on the environment.
Key to the ultimate success of PHEVs, as well as other hybrids and all-electric vehicles, is the battery technology, with lithium-ion batteries garnering much attention from automakers and suppliers, including lesser-known companies working with nanomaterials to enhance performance.
One such company is Reno, NV-based Altair Nanotechnologies, Inc. (Altairnano), which has developed a nano-lithium titanate (nLTO) spinel material for batteries that will power upcoming Phoenix Motorcars’ SUV and SUT models.
“Lithium titanate was produced in a nano size that in applying it to battery technology improved kinetics of that material compared to standard lithium titanate, which had previously been used in battery technology but was not considered active enough to be a good alternative,” said Bob Goebel, Vice President of Sales and Marketing for Altairnano.
Over the last 15 years, much of the work in battery technology with regard to Li-ion chemistry has been done on the cathode, while a graphite anode has remained intact, Goebel explained. While graphite is a good anode material, it does present some issues. “Graphite causes thermal runaway issues, and it does degrade through cycling because it’s a platelet-type structure that has a charge, and so those platelets have to move during charge and discharge as well as for lithium-ion insertion,” he said.
So Altairnano replaced the graphite with its nLTO material. “We’ve given up a little bit of energy density, but in spite of that we’ve got usable energy across a much broader temperature range and a much safer voltage range,” Goebel said, noting that “Li-ion has to be managed in a tight voltage window to avoid thermal runaways—the heat problem, the fire problems, and so forth.”
Altairnano’s nanocoating applied to an aluminum electrode enables a surface area 100 times larger than that in conventional Li-ion batteries, which have graphite on a copper electrode. This large surface area and the lack of a solid electrolyte interface layer allow outstanding charge/discharge rate performance.
The Nano-Titanate battery is about three times more efficient in storing brake energy vs. conventional Li-ion batteries, and it can be recharged in about 10 min compared to hours.
“Due to the rapid charge rate capability, the high amount of regenerative braking energy can be allowed directly into the battery, whereas other battery technologies heat up too fast with rapid charge due to the higher resistance and have to be charged at lower rates,” explained Goebel.
Durability is also up with the Nano-Titanate battery. “We have cell data and continue to gather full-size battery data that indicate far greater cycle life,” said Goebel. The data show the nLTO chemistry of Altairnano’s battery lasting up to 30 times longer than another new chemistry—iron phosphate (LiFePO4)/graphite.
“Cycle life can be extended compared to other chemistries with slower rates. The conventional Li-ion chemistry has even less cycle capability,” he added.
Replacing graphite with nLTO is about the same price from a material and build standpoint, according to Goebel. “The issue in the transportation industry is that the whole cost of displacing internal-combustion engines is the obstacle, not really [the cost of] one chemistry vs. the other.”
Altairnano is in the final stages of bringing its 1100-lb (500-kg), 35-kW·h battery package to market in the Phoenix vehicles. “As specific energy increases, we can use a smaller battery,” said Goebel, addressing the weight of the Phoenix battery. “The next generation of Altairnano battery chemistry will have improved energy density.”
Most of the large global automakers are looking at the Nano-Titanate battery, as are some Tier 1 suppliers. And the company has several ongoing projects with larger vehicles such as transit buses that use 70-kW·h packs.