Drive Plugged In Column 105 Automotive Battery Development in Nevada

The Toyota Prius gasoline/electric hybrid car has been sold in the U.S. for over a decade with about 7 million vehicles distributed worldwide. After 10 years, the original Nickel-Metal Hydride battery cells in the traction battery pack for the electric motor have aged. The original warranty on the battery cells by local dealerships ranges from 100,000 to 150,000 miles, depending on the state where the vehicle was purchased.

These battery cells provide power directly to the electric-drive portion of the Synergy hybrid power train.

After stopping at an intersection, the gasoline engine in the Prius hybrid shuts down to avoid idling the engine and wasting fuel.

The electric motor starts the wheels of the vehicle moving from energy stored in the traction battery pack, until the vehicle accelerates to a level of speed where the gasoline engine can be restarted to supply more power to the wheels and also recharge the traction battery pack in time for the next stop.

During standard operation, the battery cells are only charged to about 60 percent capacity to preserve their operating life. The unused energy capacity is left as a cushion, to allow for intermittent transient voltages from the gasoline-powered generator when it turns on, as well as from intermittent surges of electricity sent back to the battery pack from regenerative braking operations by a free-wheeling electric

motor. This safety zone of operation helps optimize the lifecycle of the battery pack to exceed 150,000 miles of operation. The expected life of the individual battery cells is actually closer to 300,000 miles of operation, but daily stresses and strains can affect individual cells over time.

Panasonic’s acquisition of Sanyo in 2009 gave the company a big share of the NiMH market, as Sanyo supplied NiMH battery cells to Honda, Ford, and Volkswagen hybrid vehicles. Panasonic EV, a joint venture with Toyota, also supplied NiMH batteries to GM and Chrysler.

The original Nickel-Metal Hydride battery chemistry was developed in the U.S. during the late 1990s by ECD Ovonics Battery Co., with funding support from the U.S. Advanced Battery Consortium. The USABC was established as a joint venture by the Energy Department, U.S. automobile manufacturers and battery manufacturers to develop advanced battery technologies for the automotive industry.

NiMH technology was never developed or commercialized by U.S. battery manufacturers after the GM shares of the ECD Ovonics Battery Co. were sold to Chevron. However, licensing agreements with Japanese battery manufacturers allowed them to continue making refinements in the process technology for use by Toyota in its groundbreaking Prius gasoline/electric hybrid battery packs that began to appear in the U.S. in significant numbers during 2002.

During 2014, Toyota Prius hybrid owners must consider whether they want to replace their NiMH battery packs or trade up for a newer model car, as the battery cell storage capacity falls off with age. A replacement NiMH battery pack can cost about $2,300, depending on the distributor.

However, there is another option for hybrid car owners. Bring the hybrid vehicle to a battery refurbishing company like the Hybrid Shop, whose technicians will test and rebuild any bad cell modules for about $500. Restoring the energy capacity of the traction battery pack can improve overall fuel efficiency by up to five miles per gallon by also restoring the range that the vehicle can operate in “electric-only” mode, without the gasoline engine. For example, the battery pack in the Toyota Prius contains 38 sealed NiMH modules that provide a battery pack with a rating of 275 volts at 6.5 amp-hours, or about 1.8 kilowatt-hours of energy capacity. Each module has six “prismatic” — rectangular — battery cells wired together in series, with each cell providing 1.2 volts at 6.5 amp-hours.