Toyota will delay for at least two years the introduction of hybrid vehicles that use lithium ion batteries.  According to a report in the Wall Street Journal, the plan had been for Toyota to introduce 12 different vehicles using lithium ion batteries, starting with the 2008 model year. 
   
Now, it won’t be doing that.
   
The problem is safety.  Toyota believes that the lithium ion batteries are susceptible to overheating, which could cause fires or, potentially, explosions.  
   
The delay is potentially embarrassing to Toyota, as it is known that General Motors is actively pursuing lithium ion battery technology.  Had Toyota been able to meet their original timetable, they would have been first to market with a lithium ion battery.  Though they are currently testing vehicles using lithium ion batteries in Japan, the decision indicates that Toyota may not be ahead on battery technology and may not be the first to produce a commercially viable lithium ion battery hybrid.
   
The lithium ion battery technology, if it can be made safe, offers a substantial advantage over the nickel hydride battery currently used in hybrid vehicles, such as Toyota’s Prius.  Toyota believes that using lithium ion batteries could double the gas mileage of hybrid cars.