Batteries for Plug-in Hybrid Electric Vehicles (PHEVs): Goals and the State of Technology circa 2008
Jonn Axn
jaxn@ucdavis.edu
Andrew Burke
afburke@ucdavis.edu
Ken Kurani
knkurani@ucdavis.edu
Institute of Transportation Studies
University of California
Davis, CA
UCD-ITS-RR-08-14
May 2008
Abstract
This report discuss the development of advanced batteries for plug-in hybrid electric vehicle (PHEV) applications. We discuss the basic design concepts of PHEVs, compare three ts of influential technical goals, and explain the inherent trade-offs in PHEV battery design. We then discuss the current state of veral battery chemistries, including nickel-metal hydride (NiMH) and lithium-ion (Li-Ion), comparing their abilities to meet PHEV goals, and potential trajectories for further improvement. Four important conclusions are highlighted. First, PHEV battery “goals” vary according to differing assumptions of PHEV design, performance, u patterns and consumer demand. Second, battery development is constrained by inherent tradeoffs among five main battery attributes: power, energy, longevity, safety and cost. Third, Li-Ion battery designs are better suited to meet the demands of more aggressive PHEV goals than the NiMH batteries currently ud for HEVs. Fourth, the flexible nature of Li-Ion technology, as well as concerns over safety, has prompted veral alternate paths of continued technological development. Due to the differences among the development paths, the attributes of one type of Li-Ion battery cannot necessarily be generalized to other types. This paper is not intended to be a definitive analysis of technologies; instead, it is more
of a primer for battery non-experts, providing the perspective and tools to help understand and critically review rearch on PHEV batteries.
Executive Summary
In this report we address the state of battery development for plug-in hybrid electric vehicles (PHEVs). This executive summary highlights our fundamental points, avoiding many of the technological details described in our full report. However, a full reading of our report is recommend for readers eking to better understand and critically review PHEV battery rearch. A glossary of PHEV terms and acronyms is provided on pages 24-26.
Basic PHEV Design Concepts: Figure E-1 portrays the two basic modes of a PHEV: charge depleting (CD) and charge sustaining (CS). For a distance, the “fully” charged PHEV is driven in CD mode—energy stored in the battery is ud to power the vehicle, gradually depleting the battery’s state of charge (SOC). Once the battery is depleted to a minimum level, the vehicle switches to CS mode, sustaining the battery SOC by relying primarily on the gasoline engine to drive the vehicle (like a conventional hybrid electric vehicle). CD range is the distance a fully charged PHEV can travel in CD mode before switching to CS mode (without being plugged in). A PH
EV with a CD range of 10 miles is referred to as a PHEV-10 (although notation can differ among reports). In CD mode, a PHEV can be designed to u grid electricity exclusively (all-electric ) or electricity and gasoline (blended ). All el equal, a PHEV designed for all-electric operation requires a more powerful battery than a PHEV designed for blended operation. The CD range and operation capabilities of a PHEV will depend on the assumed drive cycle , that is, how aggressively and under what conditions the vehicle is driven.
Figure E-1: Illustration of Typical PHEV Discharge Cycle
Distance
B a t t e r y S t a t e o f
C h a r g e (S O C )Charge Sustaining (CS Mode)
路西弗Charge Depleting (CD Mode)Gasoline Only
All Electric or
Blended Source: Adapted from Kromer and Heywood (2007, p31). Ud with permission from authors.
Battery Goals: Table E-1 summarizes PHEV battery goals from three different sources: The U.S. Advanced Battery Consortium (USABC), the Sloan Automotive Laboratory at
MIT, and the Electric Power Rearch Institute (EPRI). Battery goals are contingent on many assumptions, including CD range, CD operation (all-electric vs. blended), drive cycle, vehicle mass, battery mass, and other issues. We focus on USABC goals (Pesaren et al., 2007), which we compile into 5 main categories: power, energy, life, safety and cost. For power density, the PHEV-10 battery target is 830 W/kg, and the PHEV-40 target is 380 W/kg. The corresponding energy density targets are 100 Wh/kg and 140 Wh/kg, respectively. Not shown in Table E-1 are USABC safety goals, which are determined through abu testing, and bad on a general rating of “acceptability”. Targeted battery costs are $200-$300 per kWh. We note that there are inherent tradeoffs among the attributes categories: increasing power density requires higher voltage that reduces longevity and safety and increas cost; increasing energy density tends to reduce power density; attempts to simultaneously optimize power, energy, longevity, and safety will increa battery cost.
Table E-1: Comparing PHEV Assumptions and Battery “Goals”
电汇手续费
Units USABC1MIT2EPRI3 Vehicle Assumptions
CD Range Miles 10 40 30 20 60
existence什么意思CD Operation - All-
electric
All-fraud
electric
Blended All-
angstelectric
All-
electric
德语入门学习
Body Type - Cross.
SUV Mid.
Car
Mid.
Car
Mid.
Car
Mid.
Car夏佩的奇妙冒险
Total Battery Mass kg 60 120 60 159 302 Total Vehicle Mass kg 1950 1600 1350 1664 1782 Battery “Goals”
Peak Power kW 50 46 44 54 99 Energy Capacity kWh 6 17 8 6 18 Calendar Life years 15 15 15 10 10 CD Cycle Life cycles 5,000 5,000 2,500 2,400 1,400 CS Cycle Life cycles 300,000 300,000 175,000 < 200,000 < 200,000 Sources:
1 Pesaren et al. (2007)
2 Kromer and Heywood (2007)
3 Graham et al. (2001)
Battery Technologies:We discuss two broad categories of battery chemistries:
nickel-metal hydride (NiMH) and lithium-ion (Li-Ion). Figure E-2 prents Ragone plots
of the chemistries adapted from Kalhammer et al. (2007). The light grey bands prent the power and energy capabilities, and tradeoffs, of lead-acid, nickel-cadmium, NiMH, ZEBRA, and Li-Ion chemistries. Onto Kalhammer et al.’s Ragone curves we plot USABC, MIT, and EPRI goals as dark stars. The grey squares reprent the performance
of two prototype PHEV batteries tested by Kalhammer et al. (2007): one NiMH (Varta), and one Li-Ion (Johnston Controls Saft—JCS). Whereas EPRI’s analysis suggests the performance goals for an all-electric PHEV-20 is achievable by current NiMH technology, the goals of the USABC and MIT are beyond even current Li-Ion technology capabilities. In any ca, Li-Ion battery technologies hold promi for achieving much higher power and energy density goals, due to lightweight material, pote
infernontial for high
voltage, and anticipated lower costs relative to NiMH. NiMH batteries could play an interim role in less demanding blended-mode designs, but it ems likely that falling Li-Ion battery prices may preclude even this role. However, Li-Ion batteries face drawbacks in longevity and safety which still need to be addresd for automotive applications. Figure E-2: Battery Potential and PHEV “Goals” (Ragone Plots)
= Cell “Goal”
= Actual Cell
EPRI PHEV-20
thirstyEPRI
PHEV-60
USABC
PHEV-10MIT
PHEV-30
USABC
沈奕斐
PHEV-40 Varta
NiMH
JCS
Li-Ion
Source: Image of battery chemistry “Ragone” plots from Kalhammer et al. (2007, p25).
Notes: All “goal” and “sample” points added by current authors.
Li-Ion Prospects:Li-Ion batteries can be constructed from a wide variety of materials, allowing battery developers to pursue veral different paths. The main Li-Ion cathode material ud for consumer applications (e.g. laptop computers and cell phones) is lithium cobalt oxide (LCO). However, due to safety concerns with using this chemistry for automotive applications, veral alternative chemistries
are being testing for PHEVs, including: lithium nickel, cobalt and aluminum (NCA), lithium iron phosphate (LFP), lithium nickel, cobalt and mangane (NCM), lithium mangane spinel (LMS), lithium titanium (LTO), and mangane titanium (MNS and MS). Table E-2 prents an illustrative snapshot of veral key Li-Ion technologies according to USABC goals. We u a simple rating scale bad on available literature: a rating of poor is far from reaching USABC goals in that category; a moderate rating shows some promi of meeting goals with further development; a good rating has shown evidence of being a good candidate to meet goals; and an excellent holds very strong promi of meeting USABC goals. Table E-2 further demonstrates the many inherent tradeoffs in battery development; a single battery has yet to meet power, energy, life, safety, and cost goals.
