Honda (www.honda.com) currently uses NiMH batteries in all of its hybrid vehicles. It won't discuss the battery technology planned for a new hybrid model to be introduced in 2009.

The battery pack in Honda's Civic Hybrid stores electricity in a bank of 132 1.2 V NiMH cells that stores up to 158 V of electrical energy for the integrated motor assist (IMA) motor compared to 144 in previous versions. A new Panasonic dual-module casing reduces weight from previous hybrid battery packs and also allows it to increase efficiency of the electrical flow. The 12% smaller volume of the battery pack accommodates more cargo space.

Energy for the IMA motor is stored in a bank of 120 1.2 V NiMH cells that stores up to 144 V of electrical energy for the IMA motor, as in previous versions. A new Sanyo dual-module casing reduces weight from previous hybrid battery packs and also increases the efficiency of the electrical flow.

Honda has used ultracapacitors on its FCX fuel cell vehicle; however, its next-generation FCX will use Li-ion batteries for the same purpose because Li-ion batteries are lighter and more compact, and offer high output).

Li-ion technology is emerging as the primary candidate to replace NiMH in part because some required developments are supported by the growing dominance of Li-ion in consumer technology, according to Prabhakar Patil, chief executive officer of Compact Power Inc. (www.compactpower.com), a subsidiary of LG Chemicals (www.lgchem.com).

Patil noted that the weight advantage of Li-ion over NiMH materials gives Li-ion batteries a 2x to 3x advantage in energy and power density. “This is significant, as consumers are willing to pay a premium for longer usage time or lighter weight,” he said, adding “Li-ion batterycost on a $/kWh basis is already comparable to Ni-MH and is on track to go further down.”

Patil explained that when Sony (www.sony.com) commercialized Li-ion batteries in 1991, it introduced a graphite carbon as the anode material, pairing it with a metal oxide cathode (LiCoO2). “In Li-ion batteries, lithium ions leave the metal oxide cathode during charge and intercalate into the graphite carbon anode. The reverse happens on discharge,” he said.

Battery firms are focusing their research effort on development of new cathode materials, according to Patil, with a goal of replacing LiCoO2, which is costly because it contains cobalt and also has less than desirable abuse tolerance, especially on overcharge and internal shorting.

“The focus now is on Ni-based, layered cathodes that have better thermal stability than LiCoO2, but still have drawbacks based on price, abuse tolerance and low-temperature performance,” Patil said, adding that LiMn2O4 and LiFePO4 are robust with respect to thermal runaways on overcharge and internal shorts. “A combination of abuse-resistant cathode and chemistry, selection of appropriate voltage windows, and hardware and software system-level protection mechanisms can be used to make Li-ion batteries abuse-tolerant.”

Valence Technology Inc. (www.valence.com) offers U-Charge large-format Li-ion batteries based on the firm's Saphion technology, which is said to eliminate many of the safety issues associated with traditional oxide-based lithium-ion battery technologies. The batteries are said to deliver greater energy density and better reliability at a lower cost of ownership than lead-acid batteries, and to offer better cycle and battery life compared to NiMH nickel batteries of the same power.