TE HVAC AND WASTE HEAT RECOVERY

Current vehicular HVAC technology heats and cools the thermal loads of the surrounding structures such as the headliner, windows, flooring, and seat backs in addition to the occupants. These systems require 3,500-4,500 W of cooled air at steady state.

Thermoelectric (TE) HVAC enables the use of distributed cooling/heating units. This approach would cool/heat the specific number of occupants rather than the whole cabin and its components. Preliminary analysis indicates that <700 W of cooling or heating per person and <3,000 W for a vehicle with five occupants would be adequate for occupant comfort.

In addition to decreasing engine load and thus increasing vehicle efficiency, TE HVAC will reduce or eliminate the need for conventional air conditioning working fluids, further reducing greenhouse gas emissions. Current air conditioner technology utilizes R-134a as the working fluid. R-134a has 1,300 times the global warming potential (GWP) of carbon dioxide. The European Union is prohibiting the use of R-134a in new model cars in 2011 and all new cars by 2017, and California is considering similar legislation.

While applicable to all commercial and passenger vehicles, TE HVAC is particularly attractive for hybrids (HEVs) and plug-in hybrids (PHEVs) where an electrically driven air conditioning system would be critical in maintaining occupant comfort when the engine cuts out, thereby disabling a belt-driven air conditioning compressor. Hybrid vehicles typically have small internal combustion engines which don’t have much exhaust heat; thus, some type of electrical resistance heating would be required to heat the cabin. A TE HVAC system could provide adequate occupant cooling and heating comfort (mode change involves a single electrical switch) with the same system.

Barriers to the deployment of thermoelectrics in this area are the early stage of thermoelectric generator (TEG) technological development; lack of information on their manufacturing capability; and unknown costs.

The DOE expects that the work solicited in this area will demonstrate the operational and economic viability of TE HVAC, with the goal of replacing or downsizing the current R134-a compressed refrigerant gas air conditioners.

Design features sought include:

• A coefficient of performance (COP) of > 1.3 for cooling and > 2.3 for the heating mode.

• Reduce the energy required by current compressed gas air conditioners by 1/3.

• TE HVAC systems developed under this area of interest should be targeted for introduction into production vehicles in the 2012 to 2015 timeframe.

A secondary objective is to improve the efficiency of TEGs for directly converting engine waste heat to electricity and to provide much of the power for operation of the TE HVAC. This requirement would apply to vehicles with engines that provide sufficient waste heat for commercially viable direct energy conversion. Applicants need not include work on this secondary objective in their application but may do so at their discretion to assist, as necessary, in achieving the prime objective.

The DOE is looking primarily to applicants which are high volume (greater than 1,000 personal or commercial vehicles produced annually) vehicle manufacturer currently producing vehicles in the United States with other team members being subcontractors to the applicant. In the case of TE HVAC and TEGs for Class 7 & 8 heavy-duty trucks, DOE encourages applicant to be a diesel engine manufacturer producing 1,000 engines annually in the United States.

DOE will only consider applications from non-OEM entities if a high volume vehicle manufacturer or a Class 7 & 8 Heavy Duty Diesel Engine manufacturer is a major and highly involved team member.

HIGH-ENERGY LI-ION BATTERIES FOR PHEVS

DOE intends this solicitation to support and to speed the development and deployment of advanced Lithium-ion batteries for PHEVs that can be produced in volume, can compete effectively in the market place with conventional/currently produced hybrid vehicles, and can therefore substantially reduce petroleum consumption.

This solicitation is broken down into four subtopic areas: new high-energy anode materials; lithium-ion internal short circuit testing, modeling, and mitigation; more stable, less expensive electrolyte salts and overcharge shuttles; and scalable manufacturing processes for Li-ion materials and components.

High-Energy Anode Materials. Most of the active negative electrode materials now being used in commercial lithium-ion batteries are based on graphite. Many of the recent performance improvements have come from relatively small adjustments in the chemical formulation or physical form of well-known materials, such as graphite and hard carbon.

The DOE is seeking research to identify, synthesize, and characterize new high-energy anode materials (including lithium alloys) for use in advanced lithium-ion batteries for PHEVs. Existing materials may be used for components that are not under development (cathode, electrolyte, binder). The task objective is the demonstration of cells that show practical and useful cycle life (750 cycles of ~70% state of charge (SOC) swing with less than 20% capacity fade) in large format cells with a significant (greater than two times) improvement in the specific capacity of the negative electrode over graphite-based electrodes.

Successful applicants must clearly explain and demonstrate all of the advantages (e.g., increased energy density, reduced cost, improved abuse tolerance) of the proposed anode material over existing ones, and describe why the material is expected to result in a significant improvement over current state of the art materials.

The DOE is ruling out consideration of materials that degrade other critical properties such as cost, power capability, life, or abuse tolerance, as compared to existing anode materials.

Specifically, the DOE is seeking:

• Negative electrode materials that exhibit usable specific capacities greater than twice that of graphite (or > 750mAh/g active material), and that result in a total electrode specific capacity of at least 600mAh/g. That is, the total electrode, including active material; conductive additive (if any), and binder (if any) must demonstrate a specific capacity of 600mAh/g.

• The active materials should be capable of being coated onto electrodes in thicknesses needed for high-energy batteries, ~50µm or more.

• The developer should be prepared to deliver (during the first six months of the agreement) negative electrodes capable of initial specific capacities of 650mAh/g and achieving ~50 full charge/discharge cycles in small laboratory scale cells (50 to 100mAh) at the 1C rate with less than 20% capacity fade.

• Near the middle of the period of performance of the agreement, 18650 or larger format cells shall be assembled with the anode material, cycled, and examined to better characterize and understand any failure modes under cycling and calendar aging.

Lithium-ion Internal Short Circuit Testing, Modeling, and Mitigation. The potential hazard associated with a thermal runaway event in a large format HEV cell (~5Ah), PHEV cell (~10 to 40Ah) or full battery (~5kWh) is significant, according to the DOE. One abuse event of particular concern in vehicle applications is the internal short.

Internal shorts are presently extremely difficult to predict or detect prior to thermal runaway, and, therefore, mitigation techniques require additional active and passive protection devices that increase the cost, volume, and weight of the battery systems.

The DOE is seeking applications to:

• Develop an experimental method to “implant” internal short circuits that can be reproducibly and predictably activated in lithium-ion cells so that the resulting abuse event can be systematically studied as a function of SOC and temperature;

• Model the internal shorts using known electrochemical and thermal reactions, along with thermal propagation kinetics, so that lessons learned can be applied to additional chemistries and cell designs; and

• Develop methods to either mitigate the impact of internal shorts or to predict their imminent appearance to permit cell or battery shutdown.

Applicants will need to show how their experimental method is applicable to a wide range of cell geometries, including prismatic, flat plate/stacked, and cylindrical. Cell builds ranging in size from laboratory scale (50 to 100mAh) to 18650-scale (1-3 Ah) shall be used to demonstrate and validate the experimental approach. The approach shall then be used to demonstrate the impact of internal short circuits on the cell as a function of state of charge (SOC = 30, 50, 70, 90%) and temperature (T = 10, 20, 30, 40, and 50ºC). Following this, the contractor shall develop mitigation approaches and plan to demonstrate those approaches’ usefulness through additional testing of large format cells.

More Stable, Less Expensive Electrolyte Salts and Overcharge Shuttles. High-energy and high-power lithium-ion cells and batteries may be subject to inadvertent, abusive overcharge if the battery’s control mechanism fails. Even low levels of overcharge have been shown to make a cell more susceptible to thermal runaway. More extreme overcharge can produce rapid events such as venting with smoke and possibly flames.

Past work has indicated that this problem might be addressed by incorporating salts or additives into the cell’s electrolyte that become electro-active above a specified voltage (V_shunt) and then shunt or shuttle the current, thus maintaining the maximum voltage at V_shunt. These materials should have no effect on cell operation at normal voltages, yet provide a current path at elevated voltages.

The DOE is seeking applications to develop and demonstrate electroactive salts and/or additives that provide robust overcharge abuse tolerance. The material must provide overcharge protection up to and including C/3 charging rates, and must not result in degradation of other cell components or properties such as the electrolyte cost, discharge and regen power capability, or cycle and calendar life.

Nickelate and cobalt-based cathode materials are particularly susceptible to overcharge abuse, and thus overcharge shuttles that activate in the range of 4.1-4.5V are of particular interest. In addition, development of an alternative salt that is more stable and lower cost than existing salts (LiPF₆) will also be considered.

Scalable Manufacturing Processes for Li-ion Battery Materials and Components. The DOE is seeking applications for development of improved scalable manufacturing processes for the production of low-cost, high-quality Li-ion battery materials and components for PHEVs. Developers should clearly describe the process for production and material or component that will be improved, and what specific problem the proposed work will overcome (e.g. improved cathode stability, lower cost materials or components).

Developers may choose the particular battery materials or component to be used for the improved process method, but must clearly explain and demonstrate all of the advantages (e.g., reduced cost, improved quality, and improved performance) of the proposed production method and specific chemistry. Developers shall also describe what metric besides cost is to be used to measure material/component quality.

HEAVY-DUTY TRUCK TRAILERS

Earlier DOE work with the Truck Manufacturers Association (TMA) showed that substantial fuel economy improvements can be achieved through aggressive reductions in the aerodynamic drag of heavy-duty truck trailers.

The primary focus of this solicitation is to support the development of  trailers that achieve a 20% reduction in aerodynamic drag (leading to approximately a 10% improvement in fuel economy) compared to current, conventional trailers. An alternate option would be for proposing teams to present integrated aerodynamic solutions leading to a 15% improvement in fuel economy for the tractor/trailer combination.

Work under either the primary focus or the alternate option is expected to help focus industry efforts to identify and downselect aerodynamic devices; conduct fleet evaluations to glean relevant real world data; and coalesce aerodynamic options into saleable, comprehensive system solutions providing an attractive rate of return for fleet customers.

The DOE is encouraging applicants to be a high-volume Class VII or VIII heavy-duty trailer and/or truck/trailer manufacturer currently producing greater than 1,000 trailers or tractors/trailers annually in the United States with other team members being subcontractors to the applicant. Applications from other entities will only be considered if a high volume (greater than 1,000 trailers/tractors produced annually) manufacturer is a team member.

Advanced aerodynamic solutions developed under this program should be capable of being economically mass-produced, safe, and amenable to the broad commercial truck market. Factory installed aerodynamic solutions expected to achieve a 20% reduction in trailer aerodynamic drag or 15% improvement in overall fuel economy of the tractor/trailer combination shall be available for purchase by truck fleets within 2 1/2 years from project start date, according to the DOE.

Resources

• FY 08 Vehicle Technologies Program Wide FOA Funding Opportunity Number: DE-PS26-08NT01045-00