Greenhouse gas (GHG) emissions are the major cause of harsh climate change around the world, and transportation accounts for 15% of global GHG emissions. In the US, the transportation sector’s portion of GHG emissions accounts for 28%[1][2]. With the increasing number of automobile vehicles on the roads each day, there is a serious need to transform transportation technology. Electric Vehicles (EV) present a promising solution to GHG problems as they are considered zero emission vehicles. But, the bottleneck in electric vehicle technology is the battery. Vehicles powered with batteries that can be driven on roads for 500 km per charge, quickly charged from grid electricity and that are free from safety concerns are envisioned by many automobile manufactures. Tesla recently introduced the new all-electric and zero emission sedan Model-S car, with 85 kWh lithium-ion batteries that can run 300 miles (482 km) per charge [3]. Toyota, Mercedes, BMW, Ford and many other automobile manufacturers are investing huge dollars in electric vehicle development. A better battery will strengthen the case for battery electric vehicle (BEV) over gasoline powered automobiles in the near future.
The BEV is powered by primary or secondary batteries. First generation BEV’s used lead-acid battery and nickle-metal hydride battery. But due to less energy density of the battery, this BEV faced several challenges with respect to commercialization. In the 1990’s, the lithium-ion (Li-ion) battery was developed by Japanese technological giant, Sony [4], [5]. Since then, the lithium-ion battery has been considered the best option for electric vehicles due to several advantages. It has more energy density (kW/kg) than lead-acid batteries or nickle-metal hydride batteries and has greater efficiency. Improvements in battery component materials have helped reduced the limitations of Li-ion batteries. Today, nano-technology is fabricating electrodes and electrolytes of Li-ion batteries with lower degradation and improved safety. Li-ion batteries for Tesla’s BEVs were highly criticized after the accident in 2013 where Tesla’s BEV caught [6] fire in the battery compartment after the car hit road debris. This fire was caused by the electrolyte material present in the battery. New methods that improve the fire and impact resistance are crucial to make BEV’s safe from any hazard.
The comparison of BEV’s and internal combustion engines on an energy density basis shows that a better battery with higher energy density is crucial. A battery with less energy density increases vehicle weight and decreases driving range. Next generation metal-air (Li-air) batteries promise the high energy density that is required for greater automobile industry penetration. The energy density of gasoline fuelled vehicles is about 1.7 kW·h/kg after accounting for all the losses. On the other hand, the theoretical energy density of the lithium-air battery is 12 kW·h/kg (43.2 MJ/kg) [7]. This is higher because oxygen mass is excluded when taken directly from the surroundings. It is estimated that the same 1.7 kW·h/kg could reach the wheels using Li-air after all losses. Li-air batteries possess about 10 times the energy density than conventional li-ion technology [7]. Basic research and development is progressing with metal-air batteries and a lot of funds are being invested in the US and across the world. After successful deployment of li-air, or other metal-air batteries, the dream of BEV’s outclassing the internal combustion engine will come true.
The charging time of batteries is also a big challenge. Most BEV’s can be charged overnight with a household power connection and would therefore be reliable for daily commutation. But, long-distance travelling presents a greater challenge. Tesla provides super-charging stations which can charge a battery by 50% in just 30 minutes. A battery swapping option is also offered by Tesla and some other BEV manufacturers. Recently, Tesla displayed that they can automatically swap BEV batteries in 90 seconds [8]. So, to produce a better battery, charging time is critical and engineering materials with nano-technology will offer quick charging. Novel ways to quickly charge batteries are being investigated by scientists and engineers including super capacitors, quantum dots and many more concepts.
Another factor that makes BEVs less competitive than gasoline engine vehicles is the cost of the batteries. Gasoline engines represent mature technology that has been fine tuned in every aspect to reduce cost. In contrast, batteries use costly materials and manufacturing the technology is complex, resulting in increased costs. Next generation BEV batteries, including Li-Air and lithium iron phosphate (LiFePO4 ) batteries, will utilize cheap materials and will significantly reduce the cost of batteries [9]. Many efforts are being made to improve Li-ion battery by replacing Cobalt (Co) in its cathode with Magnesium (Co) or Iron (Fe).
Studies predict that the number of cars in the world will hit the two billion mark in 2020, which means global greenhouse gas emission trends will increase despite attempts to reduce GHGs [10]. As the number of cars on the road increases, the traffic jams also exacerbate the problems. A BEV powered by advanced battery technology is the feasible and necessary solution to post-2020 scenarios with more than two billion cars on the roads. An electric vehicle that is charged from the grid has more efficiency and less emissions because grid energy generation is already monitored by state policies. A better battery for automobile industry traction that powers a vehicle for 500 km per charge (with high safety characteristics) will transform transportation in the near future.
Taqi Mehran is majoring in Advanced Energy Technology. His research interests include the design and development of advanced energy conversion and storage technologies. Currently, he is working on improving performance and durability of Solid Oxide Fuel Cells (SOFC) for operation on direct coal, hydrocarbon and liquid fuels.
This article was originally posted on the Student Energy Blog and republished with permission.
Sources:
[1].http://www.ecofys.com/files/files/asn-ecofys-2013-world-ghg-emissions-flow-chart-2010.pdf[2].http://www.epa.gov/climatechange/ghgemissions/usinventoryreport.html[3].http://www.teslamotors.com/models/features#/performance [4].Lithium-Ion Batteries: Science and Technologies By Masaki Yoshio, Ralph J. Brodd, Akiya Kozawa http://books.google.co.kr/books?id=gkYhDYk6ftQC&printsec=frontcover&dq=lithium+ion+batteries&hl=en&sa=X&ei=cwpaU9nDN-36iQfX3YH4CA&ved=0CEUQ6AEwAg [5].Lithium Batteries: Advanced Technologies and Applications Bruno Scrosati, K. M. Abraham http://onlinelibrary.wiley.com/book/10.1002/9781118615515[6].http://www.technologyreview.com/view/519921/what-the-tesla-battery-fire-means-for-electric-vehicles/[7].Girishkumar et.al., (2010). “Lithium−Air Battery: Promise and Challenges”. The Journal of Physical Chemistry Letters 1 (14): 2193. doi:10.1021/jz1005384 [8].http://www.teslamotors.com/batteryswap [9].Fritz R. Kalhammer et.al. Status and Prospects for Zero Emissions Vehicle Technology :http://www.researchgate.net/publication/242603174_Status_and_Prospects_for_Zero_Emissions_Vehicle_Technology[10].Two Billion Cars: Driving Toward Sustainability by Daniel Sperling http://www.amazon.com/Two-Billion-Cars-Driving-Sustainability/dp/B0071UPDOA
