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Rehargeable batteries

Electric vehicles are powered by electricity stored in large rechargeable batteries on the inside, enabling emission and noise-free operation (except for the tires noise). During the past decade we witnessed the improvement of batteries, their price decrease and their longer charging cycles, which boosted their storing capacity per weight unit and volume. Moreover, their memory effect has been suppressed and their operative life has increased. The improvement of batteries will carry on and mass media keep reporting on new batteries with new feature-enhancing materials. A growing number of companies is entering into this promising sector, since batteries support and enable cell phones, laptops and multiple consumption products. Road transport electrification is nowadays much more than a mere possibility.

Batteries are powered by electricity, which can be obtained in several ways. Their main impact is electricity self-generation. They can be recharged during off-peak hours (lower demand hours) and in the future they might even be able to deliver electricity into the network during peak hours (V2G). Unlike in hydrogen’s case, the distribution network exists and the basic infrastructure could be built in a short period of time with no major difficulties. However, important disadvantages should be considered. Firstly, the batteries capacity and cost. Lithium batteries increase capacity and vehicle autonomy but they are expensive and tend to overheat. Besides, there is an unsolved controversy regarding the lithium resources available for an intended manufacturing of millions of new vehicles. The price of a lithium tone rose from 350 dollars, in 2003, to 3,000 dollars, in 2008.

Other disadvantages are electric vehicles size and features, the time necessary for battery recharging, the current absence of battery recharging or replacement points and the changes that should take place in the electricity generation and distribution network. Nevertheless, mid- and short-term economic, political social and environmental advantages exceed actual disadvantages, which explains why many governments have given their support to rechargeable electric vehicles development.

Nonetheless, there is an irrefutable fact: gasoline and diesel provide higher energy density and flexibility than batteries: gasoline provides 13 kWh/kg (8.9 kWh per liter) and diesel, 12.7 kWh/kg, as opposed to 0.16 kWh, produced by last generation lithium batteries. Hydrocarbon higher energy density ensures more autonomy, despite its inefficiency in converting stored chemical energy into journey kilometers. Vehicles operating with hydrocarbon require only a few minutes to fill in the deposit, as opposed to the several hours required to recharge current electric vehicles. Moreover there is a well-developed gas station infrastructure, whereas this structure does not exist for electric vehicles.

Battery types

Electric vehicles future is in rechargeable batteries, which have been devoted a really small research effort when compared with other technologies: storing capacity has grown two-fold every ten years, figures that pale in comparison to development of computers or other technologies. Thanks to cell phones progress, and only in the last few years, important investments have been made, accelerated by the electric vehicle generalization foreseen from 2012 onwards.

The cost of an electric vehicle or plug-in hybrid is dependent, to a significant extent, on the battery. Battery type and capacity determine maximum speed, autonomy between recharges, recharge time and battery operative life. Battery prices have decreased in the last few years and will continue to do so as the demand increases and mass production expands.

The main technologies are the following:
Lead-acid: Lead-acid storage batteries are the oldest. They have a low accumulated electricity-weigh-volume ratio. They are quite bulky and heavy, but they are long lasting and low-cost and their recycling rate is higher than 90%. In order to achieve 50 km autonomy with a 70 km/h peak speed a 400kg lead-acid battery is required. The recharging period ranges between 8 and 10 hours.

Nickel-Cadmium (NiCd): These batteries use the Nickel anode and the Cadmium cathode. Cadmium is a highly toxic heavy metal, hence their ban within the European Union. They have a long operative life (over than 1,500 recharges) but a low energy density (50 Wh/kg), and they are also affected by memory effect.

Nickel-Metal Hydride batteries (NiMH): Nickel Metal Hydride rechargeable batteries are very similar to Nickel-Cadmium batteries except for the toxic metal, so their environmental impact is much lower. Nickel Metal Hydride rechargeable batteries store 2 or 3 times more electricity than Nickel Cadmium batteries with the same weight, although they are also affected by memory effect, in a lower proportion. Their energy density reaches 80 Wh/kg.

Lithium-ion: Lithium batteries owe their development to cell phone sector and they are very recent. Their energy density reaches 115 Wh/kg and they do not suffer the memory effect. Lithium-ion batteries are used in cell phones, computers, mp3 players and cameras and they will probably power the next generation of hybrid and network electric plug-in vehicles. Despite their unquestionable advantages, they also have disadvantages: overheating, high cost and, mostly, lithium reserves, subject to a great controversy.

Lithium polymer batteries: This technology is similar to Lithium ion batteries but it provides a higher energy density, an ultra light design (very useful for ultra light vehicles) and a higher discharge rate. Among its disadvantages we find batteries instability due to overcharging and when the discharging takes place under a certain voltage.

Zebra batteries (NaNiCl): Among the most promising batteries we find Zebra. It offers a high energy density but it operates in a temperature range between 270º and 350º, which requires isolation. It is suitable for buses. In Stabio, south of Tesino (Swiss canton), a plant is being built for mass battery production. Among its disadvantages, besides its operation temperature, we find thermal loss while the battery is not used. The Think City electric car is equipped with 17.5 kWh Zebra Na-NiCl batteries.