Finding the economic balance of range against performance, energy density, and accumulator type versus cost challenges every EV manufacturer.
While most current highway-speed electric vehicle designs focus on lithium-ion and other lithium-based variants a variety of alternative batteries can also be used. Lithium based batteries are often chosen for their high power and energy density but have a limited shelf-life and cycle lifetime which can significantly increase the running costs of the vehicle. Variants such as Lithium iron phosphate and Lithium-titanate attempt to solve the durability issues with traditional lithium-ion batteries.
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| Prototypes of 75 watt-hour/kilogram lithium-ion polymer battery. Newer lithium-ion cells can provide up to 130 W·h/kg and last through thousands of charging cycl |
Other battery technologies include:
- Lead acid batteries are still the most used form of power for most of the electric vehicles used today. The initial construction costs are significantly lower than for other battery types, and while power output to weight is poorer than other designs, range and power can be easily added by increasing the number of batteries.
- NiCd - Largely superseded by NiMH
- Nickel metal hydride (NiMH)
- Nickel iron battery - Known for its comparatively long lifetime and low power density
- Zinc-air battery
- Molten salt battery
- Zinc-bromine flow batteries or Vanadium redox batteries can be refilled, instead of recharged, saving time. The depleted electrolyte can be recharged at the point of exchange, or taken away to a remote station.
The range of an electric car depends on the number and type of batteries used. The weight and type of vehicle, and the performance demands of the driver, also have an impact just as they do on the range of traditional vehicles. The range of an electric vehicle conversion depends on the battery type.
An alternative to quick recharging is to exchange the drained or nearly drained batteries (or battery range extender modules) with fully charged batteries, similar to how stagecoach horses were changed at coaching inns. Batteries could be leased or rented instead of bought, and then maintenance deferred to the leasing or rental company, and ensures availability.
Renault announced at the 2009 Frankfurt Motor Show that they have sponsored a network of charging stations and plug-in plug-out battery swap stations. Other vehicle manufacturers and companies are also investigating the possibility.
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| The Renault Fluence Z.E. will be the first electric car within the Better Place network, with sales scheduled to begin in Israel and Denmark by late 2011. |
A Smart grid allows BEVs to provide power to the grid, specifically:
- During peak load periods, when the cost of electricity can be very high. These vehicles can then be recharged during off-peak hours at cheaper rates while helping to absorb excess night time generation. Here the batteries in the vehicles serve as a distributed storage system to buffer power.
- During blackouts, as an emergency backup supply.
Lifespan
Battery life should be considered when calculating the extended cost of ownership, as all batteries eventually wear out and must be replaced. The rate at which they expire depends on the type of battery technology and how they are used - many types of batteries are damaged by depleting them beyond a certain level. Lithium-ion batteries degrade faster when stored at higher temperatures.
Future
The future of battery electric vehicles depends primarily upon the cost and availability of batteries with high specific energy, power density, and long life, as all other aspects such as motors, motor controllers, and chargers are fairly mature and cost-competitive with internal combustion engine components. Diarmuid O'Connell, VP of Business Development at Tesla Motors, estimates that by the year 2020 30% of the cars driving on the road will be battery electric or plug-in hybrid.