IEEE Electrification Magazine - March 2017 - 44

currently on the road globally or are
planned to be launched soon. The
steady growth of xEV sales in the
United States is illustrated in Figure 1,
which shows the plug-in electric
vehicle sales in the United States
since 2010.
A historical account with a general review of the principle of the Li-ion
cell and its material requirements
was provided in this magazine in the
September 2015 issue with a focus on
residential energy storage (Restropo
et al., 2015). This article focuses on
aspects of Li-ion batteries relevant to
automotive applications.

OEMs are now more
focused on products'
market acceptance
and profitability
rather than on
building vehicles just
to meet fuel
economy regulations.

Trends in vehicle electrification
The trend in vehicle electrification around the globe is
affected by regional needs, regulations, and incentives. For
example, the overall driver for large-scale vehicle electrification in the United States still remains the regulatory
requirements such as those of the state of California,
which mandate that 10% of vehicles sold in the state by
any original equipment manufacturer (OEM) must have
zero emission by 2025, and the Federal Corporate Average
Fuel Economy (CAFE) target of 54.5 mi/gal by the year 2025.
Consequently, OEMs have considerable motivation for
electrification. Ford, for example, has announced that it
will spend over US$4.5 billion to have 40% of its vehicles
electrified by 2020.
In the United States, the main growth is in the BEV volume, while the sales for HEVs are either flat or decreasing.
In addition, the PHEV market is steady. However, OEMs are
now more focused on products' market acceptance and
profitability rather than on building vehicles just to meet
fuel economy regulations.
Although the focus in the European Union has been on
luxury PHEVs, the fallout from the so-called "Diesel-gate"
and the strict carbon-dioxide (CO2) emission targets
have motivated the OEMs to accelerate the electrification
of their fleets. While compact BEVs and luxury PHEVs are
considered the main platforms for the majority of the
regions, the OEMs are also adopting micro-HEVs such as
48- and 12-V systems for existing internal-combustion
engine (ICE) vehicles to meet fuel economy and CO2 regulations. Longer range BEVs (300 mi) and fast charging are
also gaining traction in the European Union.
In China, on the other hand, incentives for BEVs have
been the major driver for the increased BEV volume. This
has especially been the case for BEV buses where there
was an increase of more than 130% in bus volume from
2015 to 2016. One of the key goals for mass electrification
remains the cost parity of ICE and xEV vehicles so that
the mass acceptance does not rely on regulations and
incentives alone.

I E E E E l e c t r i f i c ati o n M agaz ine / march 2017

Trends in Battery Technologies
Batteries for BEVs

It is now clear that although the initial
focus for electrification was for HEVs,
the current focus is on BEVs and
PHEVs, since they achieve much better fuel economy. Of course, for BEVs,
the key objective is to remove the
range anxiety by offering a longerrange vehicle at an affordable price.
The challenge then is to develop a
high-energy battery at low cost.
The first generation of all BEVs
beginning in 2010 had a 100-mi range
or below. For example, the Nissan Leaf
and Ford Focus had ranges of about 70 mi. There are now a
number of offerings for BEVs that have ranges greater than
100 mi. Tesla, which is still a luxury brand, has been offering the Model S with a range greater than 200 mi for some
time now.
The Chevrolet Bolt, the first mass-marketed vehicle in
the long-range BEV class, was launched in January 2017
boasting a U.S. Environmental Protection Agency range of
238 mi (Figure 2). Vehicles with 300-500-mi ranges are also
being considered by some OEMs. Whether such vehicles
will have mass appeal remains to be seen.
The batteries for the first generation of BEVs were in the
25-kWh range. They were all about 350-V nominal systems
with peak powers of in the range of 100 kW and charging
time of about 3-8 h. Since Li-ion cells are usually about 3.6 V,
this means that about 100 cells (usually 96 cells or blocks of
cells) are in series. Porsche has recently unveiled a concept
car with an 800-V powertrain, which means that close to
200 cells have been placed in series to achieve the system
voltage. The future vehicle ranges from 300 to 500 mi imply
that BEV battery packs could be in the 60-100-kWh range
or as high as the 150-kWh range.
Virtually all BEV batteries used in passenger vehicles
are based on Li-ion cells using a layered cathode and a
graphite anode (Figure 3). Among all the cathode materials that are currently being deployed in xEVs, the layered
compounds have turned out to be the most effective
ones. They have the highest energy, both per weight
and volume, long life, and acceptable abuse tolerance.
These materials, typified by the Li(NiCoMn)O2 (NMC) or
LiNiCoAlO2 (NCA) formulas, are characterized by a
crystalline structure in which the MO2 (where M is a
transition-metal atom) and Li layers are alternately
stacked, and Li can shuttle back and forth into this structure during charge and discharge. They have specific energies of 150-200 mAh/g with a cell voltage of 3.6 V. Other
cathodes such as lithium iron phosphate (LFP) have a capacity of 150 mAh/g but at a much lower voltage of 3.2 V; thus,
the energy is lower, and these cathodes are not attractive
for passenger BEVs. However, this cathode material is

Table of Contents for the Digital Edition of IEEE Electrification Magazine - March 2017