Pastor-incessant
BATTERIES FOR ELECTRIC
VEHICLES
Background. The 1995 BTAP assessment
found that several advanced
battery types
with the potential to meet the mid-term
performance and
cost targets of the United
States Advanced Battery Consortium (USABC)
had
reached the pre-prototype stage. That Panel also
concluded that
even the leading candidates
among these were unlikely to be commercially
available before 20002001, and this only in a
complete success scenar
Io that required, in
particular, firm commitments to battery production
plants no later than 19989~99。In the absence
of historic precedent,
the 1995 BTAP study had
to leave open the question of whether
availability of batteries meeting or, at
least, coming close to USABC
mid-term targets
would lead to successful commercialization of
electric
vehicles (EVs). The study??s battery-
cost survey indicated [(1), Table
II.4] that
the costs of the batteries being developed were
likely to
be well above USABC mid-term
targets, except possibly in large-scale
production, adding to the uncertainty about
the prospects of EVs.
Over the past five
years, battery developers and automobile
manufacturers devoted large efforts to the
continued advancement of
EV-battery technology
and the development of a new generation of
electric vehicles. Under the MoA between the
six leading automobile
manufacturers and the
California Air Resources Board, a substantial
number of these vehicles has been deployed.
Nevertheless, since they
are produced in
limited volume only, the vehicles??including their
batteries??are expensive, and vehicle leases
had to be subsidized
heavily to attract early
users. As the time approaches for critical
decision on actions needed to implement the
current ZEV provisions,
the question again
arises whether batteries with the required
performance and cost characteristics could be
available in time for
commercialization of
broadly marketable EVs by 2003. The most important
requirements that must be met by EV batteries
are re-examined below
from today??s
perspective, and they are used in Section II.2 to
identify
the candidate EV batteries that were
examined more closely by BATTERY
TARGETSREQUIREMENTS
A
technical team drawn primarily from the major U.S.
automobile
manufacturers derived the long-term
battery targets in Table II.1
nearly a decade
ago from the postulate that, to be competitive, an
EV
intended for the same purpose as an
internal combustion engine
(ICE)-powered
vehicle had to match that vehicle with
respect
to all key characteristics:
performance, durability, safety,
convenience
and cost. The target ICE vehicle assumed in that
derivation
was a mass-produced (45-passenger)
family sedan with characteristics
similar to
the Chevrolet Lumina, Ford Taurus or Chrysler
Concorde.
Recognizing the difficulty of
emerging EV-battery technology meeting
the very demanding long-term targets,
USABC also defined a less severe
set of near-
term targets (see Table II.1) for the batteries of
EVs that
might find limited applications.
Recently, USABC defined a set of
battery
?°Commercialization?± targets that, if met, should
permit EVs
to begin entering the market. As
shown in Table II.1, the
commercialization
targets for performance fall generally between
the near and long-term values. The
commercialization targets for
cycle and
calendar life are as demanding as the long-term
values, while
the cost target is relaxed to
the near-term value of $$150kWh. The most
important requirements for EV batteries are
reviewed below from
today??s perspective and
compared to the USABC targets.
1.1.
Performance
Specific Energy. As shown in
Appendix C, today??s state-of-the-art
45-passenger vehicles (Table C.1) have
practical ranges of about
75-100 miles (Table
C.2, lines 4B and 4C) with 29-32 kWh batteries.
These batteries weigh between 450kg (NiMH) and
360kg (Li Ion), and they
represent
approximately 30% and 20%, respectively, of
vehicle curb
weights. The specific energy of
the NiMH batteries used varies from
about 50
to 64 Whkg; it is nearly 90 Whkg for the Li Ion
battery.
Utility vehicles and vans (see Table
C.1) attain about 65-85 miles (Table
C.2) with
NiMH batteries having approximately the same
capacity, and battery weights represent
about 25% of the utility
vehicles?? 25-35%
higher curb weights. Only the lightweight,
aerodynamically very efficient 2-seat EV1 has
a practical range
substantially
Power
Density. The USABC targets for power density (see
Table II.1)
were set to give an EV acceptable
acceleration from a battery that meets
the
minimum specific energy requirements. These
targets need to be met
by a battery discharged
to 20% of its capacity at the lowest design
operating temperature, and until the end of
battery life when power
capability is
substantially degraded. (Fully charged, new
batteries
typically have much higher power
capability than needed by EVs.) Since
the
mass-produced ICE vehicles of today generally have
higher
acceleration capability than those of
5-10 years ago, the USABC
commercialization
target for power density probably should also be
considered a minimum requirement. In the
longer term, advances in
automobile
technology??especially substantial reductions of
weight and
aerodynamic drag??could result in
decreased EV-battery power and
capacity
requirements andor increases in EV performance, as
has been
demonstrated by GM??s EV1.
1.2.
DurabilityBattery Life
The useful service
life of a battery is limited by loss of its
ability
to meet certain minimum requirements
for delivery of energy and power.
For
EV batteries, the minimum requirements are
nominally set at 80%
of both the new
battery??s energy storage capacity and the EV??s
power
capability specification. Loss of power
capability (?°power fading?±)
and energy
capacity is caused by cycling batteries. It can
also occur
while batteries are not being
cycled, as a result of chemical processes
that
over time transform battery active materials
irreversibly into
inactive forms, andor reduce
the current carrying capability of the
battery. If these processes are relatively
rapid, battery life can
become unacceptably
short. Typically, power fading is the limiting
factor in EV-battery life. As will be
discussed in more detail below,
the likely
cost of nickel-metal hydride and other advanced EV
batteries
is such that, for acceptable life
cycle costs, these batteries need
to last for
at least 100-120 k miles, the nominal service-life
of the
vehicle. For a battery that can deliver
an EV range of 100 miles per
charge, the
100k-120k mile life requirement is equivalent to
the USABC
long-term target of at least 1000
deep cycles over its service life.
A 600 deep
cycle, 5-year life capability??the near-term USABC
target??is almost certainly insufficient in
view of the high cost of
battery replacement.
II.1.3. Safety
Today??s automobile
safety requirements are very stringent, and the
assurance of a very high level of safety will
be a critical requirement
for electric
vehicles deployed as a broadly available new
automotive
product. As a high-energy system,
the battery is the main safety
challenge
associated with electric vehicles. However, no
statistically
valid experience base exists for
defining and quantifying adequate
safety for
the advanced batteries used in EV propulsion.
Moreover, the
safety issues differ
substantially from one type of battery to another,
and even within a battery type from one design
to another. Given this
difficulty, USABC and
the battery and EV developers have resorted to
characterizing candidate advanced EV batteries
in terms of their
tolerance to a series of
10?°abuses?±, as a provisional indication of
the batteries?? level of safety.
Representative battery abuse tests
that EV-
battery developers apply routinely to cells and
modules are
summarized in Appendix D. It
needs to be emphasized, however, that there
are as yet no data correlating test results
and failure criteria with
safety-related
incidents experienced by vehicles equipped with
advanced EV batteries. Remarkably, such
incidents are extremely
rare or altogether
absent. Thus, while some of the abuse
tests probably represent a realistic failure
mode, others may not
simulate likely
occurrences, and an EV-battery failing to meet one
of
the standard abuse tests could conceivably
be safe under all but the
most extraordinary
and unlikely conditions. Conversely, it is noted
that unsafe situations may not be fully
captured by the existing abuse
tests but could
surface in the future.
1.4.
Convenience
Several battery
characteristics that may offer particular
advantages (or, conversely, pose limitations)
in EV applications can
be grouped under the
broad term ?°convenience?±: for example, quick
charging capability, low self-discharge rate,
and wide
battery-operating-temperature range.
The USABC targets for these
characteristics
form a reasonable set of requirements, but none of
these
are as critical to the acceptability of
batteries for EV service as
are the targets
for performance, durability and safety. The
numerical
values listed in Table II.1 thus
appear to be desirable, rather than
required,
characteristics although some of them may prove to
be
important for acceptance of an EV in the
market. (Not mentioned
among the
requirements but also important is the
stipulation
that EV batteries must be
chemically and mechanically maintenance-free
to avoid the cost of skilled maintenance
labor andor the
inconvenience to the
owneroperator. This requirement does not
extend to electrical maintenance [such as cell
balancing, etc.] that
can be provided
automatically as part of the battery??s
electrical-
control functions during charging
or other phases of operation.)
1.5.
Cost
Background. By general agreement, the
costs of advanced EV batteries
having the
potential to meet the other critical requirements
for EV
service are a major barrier to the
competitiveness and widespread
introduction of
EVs. For example, the actual costs of the advanced
batteries in the EVs introduced in limited
numbers over the past several
years range
from nearly $$30,000 to more than $$80,000 per
pack,
requiring heavy subsidies by the EV
manufacturers to attract vehicle
lessees. The
specific costs target for advanced batteries
would be
substantially higher only if
motor-fuel costs increased
drastically
above $$2gal, or if the needed EV-battery
capacities were to decrease substantially
below 28kWh because of
much-reduced range
requirements andor greatly increased EV
efficiencies. None of these possibilities
seems likely in the
foreseeable future, at
least in the United States, although some of
them might materialize over the long term.
2. EV-BATTERY COST FACTORS
From the outset of this study, it was clear
that battery costs were
not only important
issues with the advanced systems currently used in
EVs, but were recognized as a major
economic barrier to the widespread
market
introduction of electric vehicles. Acquisition and
analysis of
battery-cost information,
therefore, became important aspects of the
Panel??s work. This section reviews the major
factors that contribute
to battery cost.
Additionally, an EV-battery-pack will have a
thermal
management system for heating,
cooling, or both, as well as electrical
and
electronic controls to regulate charge and
discharge, assure safety,
and prevent
electrical abuse. The level of sophistication and
complexity of the needed controls depends on
the requirements of
specific battery systems.
The major steps in EV-battery-pack production
are shown in Figure II.2. While production
activities up to the level
of modules are
exclusively the province of the battery
manufacturer,
pack assembly, electrical-
control integration, and reliability testing
are operations frequently carried out by the
EV-battery customer, the
vehicle manufacturer.
How these responsibilities are divided affects
the selling price of
the battery. Thus, while
the specific cost (in $$kWh) of the battery
pack ready for installation in the vehicle is
the most important battery
cost
characteristic, most of the cost data gathered and
reported in
this study are for module costs.
To arrive at the pack price, we have
added a
fixed amount to the module cost, using the
approximate numbers
provided by battery
developers and USABC.
Direct labor costs,
as a percentage of total costs, decline with
increasing capital investment in labor-saving
manufacturing equipment
that becomes
progressively more productive as battery
production
volume rises. At any given
production level, there is a tradeoff
between
the costs of direct labor and the ownership costs
of automated
production equipment. The
inherently greater efficiency and precision
that automation enables in most manufacturing
operations make large
contributions to the
decline in costs as production volume increases.
The third major contributor to costs is
manufacturing ?°overhead?±,
a category that
includes the ownership and operating costs of
plants
and equipment, as well as the costs of
manufacturing support services
(manufacturing
engineering, material handling, quality assurance,
etc.). The sum of materials and
component costs, labor costs
and
manufacturing overhead is usually termed the
(COG) for battery roduction.
how pack
costs aggregate from the cost components
identified above
through the various steps
involved in manufacturing batteries on a
commercial scale. In the larger manufacturing
facilities that could
be operational by 2003
if plant commitments were made in the near future,
costs and prices would be considerably lower
than present levels.
Economies of scale will
result from discounts on bulk purchases of
materials and components, higher efficiencies
in the use of labor and
equipment and,
especially, use of custom-designed automated
manufacturing equipment with high
production rates and product
yields.
Although depreciation charges related to this
equipment
will contribute significantly to the
factory costs of the batteries,
they will be
more than offset by the savings in labor costs
realized.