The California South Coast Air Quality Management District (AQMD) today held a Plug-in Hybrid Electric Vehicle (PHEV) Forum and Technical Roundtable focused on the technical issues related to advanced batteries and their effect on the development and commercialization of PHEVs.
The mission was to accelerate the deployments of PHEVs and the goal for the meeting was threefold: to discuss and assess capabilities of advanced batteries; to identify requirements and issues; and to initiate dialogue between different participants in the market and to establish their respective roles.
AQMD’s focus on PHEVs comes more from the emissions control frame of reference. The four-county South Coast district has the worst air quality in the country. Although the progress has been made over the past years in reducing emissions, emissions have plateaued, and at levels above required standards.
With the most immediate gains being made, AQMD is looking for longer term changes—such as that represented by PHEVs—to alleviate the air quality issues. In March, the AQMD board directed staff to expand PHEV activities. This technical meeting was a first step in that direction.
Participating in the panel discussion were:
- Matt Miyasto, Technology Demonstrations Manager, AQMD
- Mark Duvall, Manager Technology Development, EPRI
- Tien Duong, Team leader Vehicle technologies, FreedomCAR (DOE)
- Ahmad Pesaran, Principal Engineer, NREL (DOE)
- Dan Doughty, Manager, Li-Ion Battery R&D, Sandia
- Michael Andrew, Johnson-Controls-SAFT
- Greg Hansen, Energy CS
- Loic Gaillac, Southern California Edison
The general sense of the panel was that from an electrochemistry point of view, lithium-ion cells note only were poised to become the predominant PHEV system in the short- to medium-terms, but that they were basically ready to go.
There exist, however, a number of significant barriers to the commercialization of Li-ion PHEV battery systems, among them being cost, cycle life, and safety management. While the chemistry may be ready, in other words, the barriers are primarily on the manufacturing side.
The other significant issue that emerged during the discussion was the question of the system design target, specifically whether or not the PHEV needed a pure electric mode, or whether it could use a blended approach.
Plug-in hybrids use a grid-rechargeable energy storage system to provide capabilities beyond those of conventional charge-sustaining hybrid systems. A PHEV essentially has two battery operating modes: a charge-sustaining mode [recharging the battery during operation via regenerative braking, for example] and a charge-depleting mode [drawing down the charge from the grid]. The total consumption benefits of a PHEV are a combination of the charge-depleting and charge-sustaining modes.
Characteristics of a PHEV battery pack include:
- Higher total energy capacity than those of HEVs;
- The cell design has lower power density but higher energy density than HEVs;
- The battery is deep discharged during driving to a lower minimum State of Charge than an HEV;
- The battery is grid-recharged;
- Total battery cost is higher than that of HEVs an represent a larger portion of the projected PHEV cost delta;
- Battery energy is directly related to the per mile electrical energy consumption and the desired range;
- Battery mass is greater but typically not to the extent that vehicle performance is significantly affected.
Tien Duong from the FreedomCAR project noted that the DOE has a draft goal of reducing the cost of PHEV batteries to $300 kWh by 2014. That would give a 10 kWh PHEV battery system a cost of about $3,000—about a quarter of the current cost. He also noted that the DOE is at work on a research roadmap for PHEVs, and that the draft roadmap should be ready by December.
Ahmad Pesaran from NREL pointed out that there is a broad spectrum of HEV-PHEV designs leading to different battery requirements. There are currently batteries that could meet the energy and power demands for PHEVs, he noted, but cost and the short cycle/calendar life are still major barriers.
While there are emission benefits with PHEVs, there are some differences between the emissions output of pure EV implementations and the blended EV range impacts that need to be understood. Specific points of discussion emerged around the current need for hybrids to fire up the engine to heat the catalytic converter at start-up. A PHEV with a robust EV mode would do so—but that in turn could confuse the existing testing regimens.
While NiMH systems have matured in power and energy, Li-ion systems support diverse chemistries and opportunities. Lithium-ion cells work basically on a shuttle mechanism, with the lithium ions moving back and for the between anode and cathode. Bsttery makers have an opportunity to change to the cathode and anode to improve characteristics such as recharge time or stability.
The lithium iron phosphate cathode chemistry used by Valence, for example, offers less potential watt output capacity than cobalt, but offers better safety characteristics. This is an exciting time for Li-ion, Pesaran noted, with new cathodes, new anodes and new electrolytes offering lower temperatures, better safety and lower cost.
All panel members agreed that one of the most pressing needs was larger demonstration PHEV fleets—on the order of several hundred vehicles in the aggregate.
I think what we heard today was that the best balance...is to put in a battery capable of only 20 kW rather than a full EV. Even in a vehicle like that (blended) you offer a lot of all-electric range. The evolution of the thing, if we have all electric range interspersed, or even just a Honda-type system where you are bleeding power into the system, will eventually evolve into more all-electric range, bigger and better all-electric range. If the automakers can get to the point where they can justify a 9 kWh battery or even 5 kWh on a car, then just as you saw with Toyota and Honda, you will see competition for providing more of that capability. And that will help all kinds of technologies.—Greg Hansen
I think the technology is fanning out. I envision that in the future when you go buy a Ford Escape, you will have an option of Battery A, Battery B, Battery C with different cost-benefit ratios, etc. Customers will make the choices. I think it will diversify rather than narrow.—Dan Doughty
Presentations and summary materials from the forum will be available on the AQMD website in several days.
Plug-In Hybrid Electric Vehicle Energy Storage System Design; Tony Markel and Andrew Simpson; National Renewable Energy Laboratory