Energy Efficiency of Electric Vehicles

Figure 8. Vehicle with an electrochemical storage system
Using new processes central to nanotechnology, researchers create millions of identical
nanostructures with shapes tailored to transport energy as electrons rapidly to and from very
large surface areas where they are stored. Materials behave according to physical laws of
nature. The Maryland researchers exploit unusual combinations of these behaviors (called self-
assembly, self-limiting reaction, and self-alignment) to construct millions -- and ultimately
billions -- of tiny, virtually identical nanostructures to receive, store, and deliver electrical
energy [16].
2.4. Reduction of losses in the conductors and connectors
From the viewpoint of energy efficiency, choice of supply voltage, as well as quality contacts
in the connectors and cable section is very important. The designer is limited by other factors
such as the security problem (for battery overvoltage), limited space and cost. Therefore, it is
necessary to optimize the supply voltage and the conductor section with given constraints. It
is similar to the choice of connectors.
New Generation of Electric Vehicles
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Hybrid and electric vehicles have a high voltage battery pack that consists of individual
modules and cells organized in series and parallel. A cell is the smallest, packaged form a
battery can take and is generally on the order of one to six volts. A module consists of several
cells generally connected in either series or parallel. A battery pack is then assembled by
connecting modules together, again either in series or parallel [17]. The pack operates at a
nominal 375 volts, stores about 56 kilowatt hours (kWh) of electric energy and delivers up to
200 kilowatts of electric power. These power and energy capabilities of the pack make it
essential that safety be considered a primary criterion in the pack’s design and architecture [18].
Recent battery fires in electric vehicles have prompted automakers to recommend discharging
lithium ion batteries following serious crashes. However, completely discharging a vehicle’s
battery to ensure safety will permanently damage the battery and render it worthless. Self-
discharge effects and the parasitic load of battery management system electronics can also
irreversibly drain a battery.
Zero-Volt technology relies on manipulating individual electrode potentials within a lithium
ion cell to allow deep discharge without inflicting damage to the cell. Quallion has identified
three key potentials affecting the Zero-Volt performance of lithium ion batteries. First, the Zero
Crossing Potential (ZCP) is the potential of the negative electrode when the battery voltage is
zero. Second, the Substrate Dissolution Potential (SDP) is the potential at which the negative
electrode substrate begins to corrode. Finally, the Film Dissolution Potential (FDP) is the
potential at which the SEI begins to decompose. The crucial design parameter is to configure
the negative electrode potential to reach the ZCP before reaching either the SDP or the FDP at
the end of discharge. This design prevents damage to the negative electrode which would
result in permanent capacity loss. Figure 9 shows a schematic of the voltage profile during
deep discharge of Quallion’s Zero-Volt cells [18].