Micro-hybrid vehicles using lithium-ion batteries provide a cost-effective way for automakers to improve fuel economy and comply with increasing CAFE standards. Lithium-ion batteries are superior to lead-acid batteries for micro-hybrid functions because they accept charges more quickly, allowing for improved recuperation of braking energy. Lithium-ion batteries also last longer and are lighter than lead-acid batteries, reducing replacement costs and weight over the vehicle's lifetime. Automakers will likely pursue a balanced strategy including micro-hybrids to cost-effectively improve fuel economy as required.

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Angela Duren
June 5, 2013
Lithium-Ion Batteries for
Micro-hybrids
-
CALSTART Leadership Circle

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2002 2004 2006 2008 2010 2012 2014 2016 2018 2020 2022 2024
CAFE
ACTUAL
By 2018, a major shift in
technology is required to
keep up with requirements.
US Passenger Vehicles
Fuel Economy Requirements
MPG
NHTSA projection of
requirements considering
the various credits*
* Source: US Federal Register, 15 Oct 2012, 2017–25 CAFE Final Rule
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Micro-hybrids are a cost effective solution for higher
volume impact on fuel economy requirements
A Balanced Strategy for CAFE
Fuel Economy
Requirements
EV
HEV
Micro-hybrid
* Source: US Federal Register, 15 Oct 2012, 2017–25 CAFE Final Rule
sales volume
Mild
NHTSA anticipates
U.S. penetration of
11% by 2020*

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Battery functions
Electrification and Voltage
EV
HEV
Micro-hybrid
Mild
High voltage
>60V
Low voltage
<60V
Battery supports
start-stop and
recuperation
Start-stop,
recuperation,
some power
assist
Battery
electric
driving

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Lithium-ion batteries have superior charge acceptance
Advanced Micro-hybrid Fuel Economy Gains
• Lithium-ion batteries have high rates of charge acceptance compared to
lead acid technology
• Kinetic energy from engine braking is quickly delivered to the battery for
storage and used when needed (recuperation)
• Less parasitic loss from engine-driven battery charging
decel stop
start &
accel drive decel stop
using stored
battery energy
parasitic loss
Battery
State of
Charge
SAVING FUEL
Li-Ion
Lead acid
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Advantages Over Lead-Acid
12V Nanophosphate™ Engine Start Battery
Mass reduction
Fewer replacements over vehicle life
• More than twice the life on today’s
micro-hybrid duty cycles
• Less mass than lead acid battery of
equivalent capacity
• Potential to downsize battery due to
greater usable energy
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Integrated
BMS/FET
Lower
enclosure
Cover
Terminal
bus bars
Prismatic
Module
20Ah prismatic cells
Construction of 12V Battery System
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AGM
baseline Li-ion
PbA+
small Li-ion
PbA +
ultracaps
PbA +
48V Li-ion
Battery 1 Lead-acid Lithium-ion Lead-acid Lead-acid Lead-acid
Battery 2 x x Lithium-ion Ultracaps Lithium-ion
Weight 26kg 10kg 17kg + 4kg 20kg + 5kg 17kg + 12kg
System component
upgrades:
x Stronger alternator Stronger alternator Stronger alternator
Starter-generator
with inverter
Additional
components
DC/DC (200W)
Battery sensor
x
Battery sensor
Cranking switch
DC/DC
Battery sensor
DC/DC (12V/48V)
Battery sensor
Total cost OEM $290 $600 $460 $615 $1,325
Total cost over life $540 $600 $520 $690 $1,385
Fuel economy
improvement*
2 - 5% 5 - 10% 15%
Comparison of Micro/mild-hybrid Solutions
+
+ +
10 year system cost assumptions
*compared to conventional vehicle
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MICRO ADVANCED MICRO MILD

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Comparison of Micro-hybrid Solutions
Increasingsystemcost(vehiclelife)
Increasing fuel economy
12V
PbA AGM
12V PbA
+ small 12V
Li-ion
12V PbA
+ ultracaps
12V PbA
+ 48V Li-Ion
Today‘s cost
over life in
stop-start
vehicles
12V
Li-ion
Cost vs. fuel economy improvement

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Summary and Outlook
• Due to cost and consumer acceptance, OEMs will likely
choose a more balanced strategy for electrification
• Micro-hybrid systems provide a value solution for significant
fuel economy improvement
• Lithium-ion batteries meet the requirements of tomorrow’s
advanced start-stop systems
+ Fuel economy improvement due to charge acceptance
+ Less weight than lead-acid
+ Longer life means warranty improvement and fewer replacements
for consumer
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