With the unveiling of the National Electric Mobility Mission Plan 2020, Prime Minister Manmohan Singh has urged manufacturers to adopt electric vehicles in an attempt to reduce our dependence on imported oil. The ambitious plan aims to produce 6-7 million electric vehicles by 2020 with an estimated fuel savings of 2.2-2.5 million tonnes. Vehicle manufacturers in India have a tough road ahead in meeting this goal and tailoring electric vehicles for the Indian market.
In comparison to petrol/diesel cars, electric vehicles are propelled by an electric motor and a battery pack. In petrol/diesel cars, the tank size decides the driving range, while in electric vehicles, the battery pack determines the driving range. The success or failure of the electric vehicles rests firmly on the battery pack.
Thus far, the penetration of electric vehicles in India has been largely limited to the small odd-sized Reva cars, which were almost exclusively built using the nearly 200-year-old-lead acid battery technology. However, the main issue is that lead acid batteries are bulky and as a result, with a reasonably sized pack, these cars are limited to driving ranges of 25-50 km per charge. Even for the shortest of daily commutes, this driving range is crippling and there is a pressing need for better batteries.
The last few decades have seen the development of a host of different technologies but Li-ion battery has emerged as the battery of choice, especially for the electronics industry. Lightweight and reasonable durability among a host of features have made it standout among its competitors.
However, designing batteries for electric vehicles is more daunting than doing so for the electronics industry. Our laptops and smartphones live in the comfortable ‘office’ world with air-conditioning. Not to mention, the calendar life of electronic gadgets is 3-4 years. However, batteries for electric vehicles need to tough it out, especially Indian heat for many years. The automakers face the formidable task of picking the right Li-ion battery technology. For, any negative publicity for an emerging technology could easily spell its doom.
The working principle of a Li-ion battery is a relatively simple one of host-guest. When the battery is discharged, lithium ion moves into a host material and this movement generates electrical energy. When electrical energy is supplied, or, in other words, the battery is charged, the lithium ion moves out of the host material and reverts to its original state. Over the last 30 years, several suitable host materials have been identified that allow lithium ions to penetrate inside. The reliability of the battery rests solely on the choice of the host material.
Automakers Nissan, Toyota and Tesla have made their bet on different host materials. The ability of the host material to accept lithium ions gradually fades with time. The battery packs, as promised and marketed by the car makers in the U.S., were touted as losing only about 20 per cent of the capacity in nearly five years of operation. Recently, a class action lawsuit was brought up in California and Arizona against Nissan, citing that the battery packs in its electric vehicle, Nissan Leaf, prematurely lost battery life and driving range. A common feature between California and Arizona is the hot climate with temperatures in the range of 30-40 degree C in the summer, typical of the weather in most parts of India.
In a seminal work, the team of researchers at Dalhousie University in Canada showed using high-precision measurements that higher temperatures cause a faster fade simply due to an increase in parasitic reactions. In simpler terms, at higher temperatures, other unwanted reactions take place and these generate heat. This leads to rapid degradation and the automakers, aware of this issue, typically equip electric vehicles with a thermal management system that cools the battery. However, Nissan opted not to include such a system and the lawsuit alleges that this negligence is the cause of rapid fade of battery packs.
The road ahead for electric vehicles is long and arduous requiring clever technological choices by the automakers and an informed and involved consumer. Needless to say, active government support and drastic improvements in power generation are necessary ingredients for India to electrify even a small fraction of its road transportation.
( The writer’s email:venkvis@stanford.edu )
