Lithium-ion-cell designs reduce size and weight compared to the battery technologies now being used in hybrid vehicles, but their costs remain higher than alternatives already in high volume. Battery researchers are examining every aspect of their materials and processes to make lithium technologies more cost-effective.
Global suppliers at the 1st International Conference on Advanced Lithium Batteries for Automotive Applications conference held by the U.S. Department of Energy’s Argonne National Lab in September discussed a number of programs aimed at reducing material costs.
While lithium-ion batteries are cost-effective for lightweight notebooks and cell phones, that is not the case for hybrids and electric vehicles. “The cost of a 1000-kW·h battery needs to be reduced two or three times,” said Tien Duong, Team Leader for the U.S. DOE.
Achieving that goal is still a ways out. But speakers said development programs are heading in the right direction, driven in part by help from government supported programs and industry consortia such as the U.S. Advanced Battery Consortium.
“We have a USABC program with a goal of $1200 per 40 kW,” said Frederic Bonhomme, Johnson Control-Saft USA’s Technical Representative. "We’re on the path to achieve that."
While part of this cost-reduction effort is on production techniques, a key aspect is materials research. Speakers said these materials dominate cell costs.
“In most cells, 50-60% of the cost is in materials,” said Jiqiang Wang, a spokesman from China’s Tianjin Institute of Power Source.
Speakers noted that there is some concern about the availability of materials. They also discussed ways to make sure that mining techniques let them get the most material for the least cost.
“Availability issues are crucial,” said Anna Teyssot, head of Renault’s Long Term R&D, who represented a European council consortium. “We may have to do research on the full life cycle, including mining.”
One way to trim costs is to get more with less material. That is a major focus area as lithium-technology researchers seek to improve the size benefits that give lithium alternatives the edge over the NiMH (nickel metal hydride) batteries that now dominate the hybrid vehicle market. Researchers are striving to boost the storage capacities of their cells.
“When we set our goals for 2002-2006, we were looking at energy density of 70 W·h/kg,” said Toshio Murata, Corporate R&D Director at GS Yuasa Corp. “The goal for 2007-2011 is a power density of 100 W·h/kg.”
That requires research in several different areas. Engineers and materials scientists are looking at every element within a battery, focusing on a number of different lithium-ion technologies that use manganese, phosphates, ferrous materials, and other alloys.
Researchers find that there are trade-offs with all these technologies, so battery makers will have to tune cells for different applications, such as longer lifetimes or higher energy.
“There is no silver bullet at this point,” Duong said.
That means researchers must look at every component and material in the battery in hopes of gaining a few percentage points improvement in performance. Much investigation is in electrolytes already used in laptops and cell phones. But there is also exploration with new compounds.
Toshiba Chief Scientist Norio Takami described a new electrode material, lithium titanium oxide. He says it has excellent safety characteristics, with no smoke or fire even when penetrated by a nail. It also showed no capacity loss after 3000 full depletion/full recharge cycles.
Another important component is the separator that keeps the anode and cathode from touching. Separators are thin films that are typically around 1 mm (0.04 in) thick. Though small, they are critical for both technical and financial reasons.
“The separator is the second largest material cost after the electrode,” said Jeon-Keun On, Team Leader at SK Energy Co. "Separators account for 19% of the material costs."
Both major corporations and start-ups feel they can improve separator performance and capture market share. Giant LG Chemical has developed a ceramic-coated separator. Colorado start-up Porous Power Technologies has developed a separator. The company is currently gearing up for volume manufacturing, said President Timothy Feaver.
Other materials in the cell are also being examined closely. “In electrolytes, companies are looking at liquid organic solvents, polymers, and gels,” Duong said.
Speakers noted that control systems and software must be closely intertwined with battery development to maximize overall performance. “The cell is 50% of it, but the battery management system is also very important,” said Naoki Ota, COO at EnerDel Lithium Power Systems.