IEEE Electrification Magazine - September 2013 - 28

(a)

(b)

Figure 11. An in-wheel motor layout: (a) the overall cross section of the in-wheel motor with the tire and (b) the various components of the inwheel motor.

are lighter than lead-acid batteries of comparable power.
They are commonly used in many hybrid vehicles today,
including the Toyota Prius and Honda Insight. After testing
several alternatives, Toyota announced in 2009 its continued use of NiMH batteries in many of its hybrid vehicles.
Recently, manufacturers have extensively started using
-Li-ion as the preferred energy source, especially in EV and
PHEV applications.
In 2008, Li-ion batteries were considered too costly to
be used on a wide scale, costing around US$1,200/kWh to
deliver specific energy of 110 Wh/kg and power density of
1,000 W/kg. However, with the invention of new electrode
and electrolyte materials, the technology was advanced
and the cost reduced to US$700-800/kWh in 2011. The
specific energy and power density increased significantly
to more than 120 Wh/kg and 1,800 W/kg, respectively.
Currently, these batteries cost about US$400-500/kWh
and have a specific energy of 130-140 Wh/kg and a
power density of 2,400 W/kg. Their life is around 3,500
cycles. In 2015, the target cost for Li-ion batteries is

US$200-300/kWh for a PHEV. Specific energy and power
density t-argets are as high as 250-300 Wh/kg and
3,500 W/kg, respectively, in 2020, with a cost target of
US$100-150/kWh. The electric range targeted is approximately 150 mi in 2020. As of now, the range is approximately 38-40 mi for a midsize PHEV like the Chevy Volt
and approximately 100 mi for a full EV like the Mitsubishi
i-MiEV. Figure 12 explains the technological advancement
and future targets for Li-ion batteries from 2008 to 2020.

Harvesting Energy: Lessening Burden on the Battery Pack

Energy harvesting is another answer to reduce the load
on the battery pack. The generation of electricity on
board a vehicle without chemical conversion can significantly enhance the autonomy of electric driving
and extend the life and improve the performance of
energy storage devices. The e-tire concept is one of the
energy harvesting methods using the deflection of the
tire while the vehicle is in motion [8]. More specifically,
this new concept uses local changes in pressure and
shape of a vehicle tire to generate
electricity. The idea uses the principle of electromagnetism to genPower Density (W/Kg)
Cost (US$/kWh)
Specific Energy (Wh/Kg)
erate electricity inside the tire of
a vehicle in a new way that is yet
to be exploited in electrification
of vehicles. The rolling of the
wheel on the road causes local
changes in the tire's symmetric
shape and makes it flat at the
contact area with the road surface, as shown in Figure 13(a).
The dynamic deflection changes
the radial distance between the
2008
2010
2012
wheel axis and the circumfer2014
2016
2018
ence area of the tire when it is in
Year
2020
contact with the ground. This
Figure 12. The forecasted power density, specific energy, and cost of Li-ion batteries through 2020.
localized deflection in the tire

I E E E E l e c t r i f i c atio n Magaz ine / september 2013

Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2013