Hybrid and Electric Systems R & D at DOE : Fiscal Year 2011-2012 Status

This paper presents an overview of the recent highlights and accomplishments, for fiscal years (FYs) 20112012, by the hybrid and electric systems (HES) R&D Team at the Vehicle Technologies Program (VTP) Office of the United States Department of Energy (DOE) Energy Efficiency and Renewable Energy (EERE) Office. There is significant U.S. commitment to HES R&D and additional responsibilities were assigned under the American Recovery and Reinvestment Act (ARRA) of 2009, an economic stimulus package from the 111th United States Congress. DOE has supported the development of HES technologies, including advanced automotive energy storage technologies, power electronics and electric machines, and simulation and testing tools, over the long term. This support has involved leveraging resources and expertise from automobile manufacturers, battery, motor, and electronics developers, small businesses, national laboratories, and universities to address the technical barriers which prevent the market introduction of vehicles which would use those advanced technologies. The HES R&D Team has had many significant accomplishments and continues to advance the state of the art for many technologies. This paper provides a discussion of the most recent highlights and a description of R&D coordination efforts with other government agencies in associated areas.


Introduction
The Hybrid Electric Systems (HES) subprogram of the Vehicle Technologies Program (VTP) in the U.S. Department of Energy (DOE) Energy Efficiency and Renewable Energy (EERE) Office spearheads R&D needed for the new generation of electric-drive vehicles.HES R&D is an important component of the VTP multi-year program plan [1] and includes R&D on energy storage, vehicle and system simulation and testing (VSST), and advanced power electronics and electric machines (APEEM).Status updates on these were regularly provided at prior EVS meetings (e.g., [2][3][4]).VTP leverages significant resources to address technical barriers preventing the commercialization of advanced transportation technologies like plug-in hybrid electric vehicles (PHEVs) and battery electric vehicles.Table 1 shows the FY 2003-2013 VTP budgets for HES R&D.
The fiscal year (FY) 2013 budget (President's Request) is approximately $259.8 million -nearly five times the FY 2003 budget.

Goals and Strategies
A current VTP goal is the commercialization of PHEVs and making them cost-competitive with conventional internal combustion engine vehicles.Intermediate goals include reducing the production cost of market-ready, high-energy, high-power batteries by 70% by 2014 (compared with 2009 costs) and reducing the cost of a market-ready advanced APEEM system at least 60% by 2015 (again, compared with 2009 costs).Technology development in collaboration with industry partners can enable rapid integration of new technologies into production vehicles.VTP works with industry, universities, and national laboratories to support research on the nextgeneration energy storage and electric-drive technologies to facilitate their commercialization.

Energy Storage R&D
Energy storage technologies, especially batteries, represent a critical enabling technology towards electrified transportation.Multiple DOE offices support R&D on energy storage.The Office of Basic Energy Sciences (BES) supports fundamental research to understand, predict, and control matter and energy at electronic, atomic, and molecular levels.The Advanced Research Projects Agency-Energy (ARPA-E) supports high-risk, translational research driven by the potential for significant commercial impact in the near-term.The Office of Electricity Delivery and Energy Reliability (OE) supports R&D on modernizing the electric grid, enhancing security/reliability of the energy infrastructure, and mitigating impacts of supply disruptions.Finally, the EERE Office supports work on advanced clean, reliable, sustainable, and affordable technologies which would reduce energy consumption.Figure 1 shows how these offices are positioned with respect to the current technology readiness levels (TRLs) of those technologies.Technologies at a lower TRL generally fall within the domain of BES and ARPA-E, whereas those at higher TRLs would generally be covered by EERE.To meet the DOE EV/PHEV goals and speed up the commercialization of those technologies, applied R&D is needed.Further, as seen in Figure 1, certain "beyond-Li-ion" chemistries (e.g., Li/S and Li/air) may actually exceed these goals.For example, lithium-sulfur batteries can have theoretical capacities substantially above those of lithium-ion batteries (because of how the ions are assimilated at the electrodes -at the sulfur electrode, each sulfur atom can host two lithium ions instead of the 0.5 to 0.7 for many typical lithium-ion chemistries) with possible specific energy values of up to 3,000 Wh/kg.However, taking advantage of the higher theoretical capacity is a challenge.In particular, sulfur is an insulating material and only atoms near the surface actually accept lithium ions.Another challenge is that the sulfur binds to lithium ions forming intermediate polysulfides which dissolve in the liquid electrolyte and settle in other areas of the battery, blocking the process of charging/discharging and drastically limiting the cycle life.Lithium/air batteries also have a theoretical specific energy of over 3,000 Wh/kg.However, the cycle life of Li/air cells has typically been much less than 100 cycles.The cell efficiency thus far has been less than 70 percent, due in part to the relatively low cell operating voltage and the polarization at the electrodes.Achieving a good power density is also a challenge.Such fundamental technical issues result in placing those technologies at a TRL level of 2. For lithium metal polymer batteries (theoretical specific energy: 990 Wh/kg), the lithium-salt electrolyte is held in a solid polymer composite (e.g., polyethylene oxide or polyacrylonitrile) instead of an organic solvent.This design can potentially lower the cost of manufacture, provide reliability and ruggedness, and be adaptable to a wide variety of packaging shapes.Although further along than lithium-sulfur, they face issues of a high internal resistance as well as comparatively long charge times and slow discharge rates-and therefore are also assigned a TRL of 2. Battery technologies employing silicon/metal alloy anodes and those employing high voltage cathodes (theoretical specific energy: 880 Wh/kg) are assigned a higher TRL of 3. Elements alloying with lithium have significantly higher volumetric and gravimetric capacities than graphite.Challenges to the implementation of alloy materials in commercial cells include maintaining the integrity of the alloy particles and the composite coating during cycling, forming a stable SEI layer on the alloy surface to avoid degradation of the electrolyte, ensuring good rate capability, thermal stability and accommodation of the alloy volume expansion to avoid cell swelling and electrode distortion or tearing.Furthermore, to be commercially viable an alloy anode needs to be made from low-cost raw materials and utilize practical manufacturing methods.Graphite and higher-voltage/higher-capacity cathodes (theoretical specific energy: 560 Wh/kg) are assigned TRLs of 3 and 4. Still further along are technologies based on graphite and nickel, manganese, iron cathodes (theoretical specific energy: 400 Wh/kg) which could be more readily commercialized if the costs could be further reduced.Both fundamental and applied research (more of the latter for higher TRL technologies) are needed to resolve associated issues to facilitate vehicular applications of these battery technologies and both are being conducted by VTP.

VSST R&D
Key VSST goals include demonstrating the market readiness of grid-connected vehicle technologies by 2015, supporting laboratory and field evaluations of large-scale demonstration fleets of advanced commercial and passenger PHEVs and EVs, collecting data on the interaction of electric-drive vehicles with charging infrastructure and the electric utility grid to understand electric-drive vehicle usage and charging patterns and their impacts, addressing associated codes and standards issues, developing and integrating technologies to greatly improve commercial vehicle efficiency, and validating in a systems context, performance targets for deliverables from the APEEM and Energy Storage R&D.The main barriers facing VSST's strategic goals include the risk aversion of manufacturers (who may be reluctant to invest in and introduce new technologies), costs, infrastructure issues and a lack of standardized test protocols.The VSST approach for overcoming them consists of activities in five main focus areas, including modeling and simulation, component and system evaluation, laboratory and field vehicle evaluations, codes and standards development, and heavy vehicle systems optimization.

APEEM R&D
The important elements of the APEEM R&D strategic approach include the development of a set of technologies that original equipment manufacturers (OEMs) and their suppliers can adopt (and modify, if necessary), dealing with a wide variety of technologies to make improvements to both the motor and the power electronics, pursuing high-risk concepts and reducing the overall risk of technical failure by pursuing more than one path toward each objective, and carrying out both short-term and long-term R&D to advance the technologies to a suitable point for industry to adopt.

Technical Barriers and Targets
It has been recognized for some time that the technical barriers to successful commercialization of advanced energy storage technologies (for transportation applications) are associated with cost, performance, life, and abuse tolerance -of which cost is the overriding factor.Also, it is critical for any new vehicle technology (including advanced energy storage systems) to operate safely under both routine and extreme conditions (including abuse conditions of high temperature, overcharge, or short circuit).Technical targets for individual battery applications have been developed in collaboration with the United States Advanced Battery Consortium (USABC) based on input from purchasers and end-users of these technologies.More recently, a significant focus of energy storage R&D has been the development of batteries for PHEV and EV applications.Current targets for PHEV batteries are tabulated in the VTP program plan [1].Additional performance targets (e.g., those for HEVs, EVs, and ultracapacitors) are available at the USABC partnership website [5] and reported in the VTP Energy Storage R&D annual progress report [6].The APEEM technical targets for peak power, costs, etc. can also be found in the corresponding section of the VTP multi-year program plan [1].

HES Grants under ARRA
The American Recovery and Reinvestment Act of 2009 (ARRA) (Public Law 111-5), an economic stimulus package enacted by the 111th United States Congress in February 2009, provided $2.4 billion in one-time grants to accelerate the manufacture and deployment of the next generation of U.S. batteries and electric vehicles.The awards, distributed across the U.S., include $1.5 billion in grants to U.S.-based manufacturers to produce batteries and their components and expand battery recycling capacity, approximately $500M to produce electric drives and their components, plus $400M in grants to purchase, deploy and evaluate PHEVs and all-electric vehicles for test demonstrations, to install electric charging infrastructures, and to support relevant outreach.These created numerous new projects to manufacture advanced batteries and EV components and to conduct deployment and demonstration.The manufacturing areas include those of material supply, cell components, cell fabrication, pack assembly, and recycling.The individual grants are described in the energy storage R&D annual progress report [6].All ARRA projects for battery and materials manufacturing facilities have been initiated.Production has begun at most facilities, including those listed in Table 2.

Energy Storage R&D
The energy storage R&D effort includes multiple activities, from hardware development with industry to mid-term R&D and focused fundamental research.The activities begin by establishing technical requirements for the energy storage technologies in cooperation with industry.Next, commercially available batteries are evaluated against those requirements.

Focused Fundamental Research
The Focused Fundamental Research activity, also called the Batteries for Advanced Transportation Technologies (BATT) activity, addresses fundamental issues of chemistries and materials associated with lithium batteries.It attempts to gain insight into system failures, develops models to predict failure and to optimize systems, and researches new and promising materials.It emphasizes the identification and mitigation of failure modes, coupled with materials synthesis and evaluation, advanced diagnostics, and improved electrochemical models.Battery chemistries are monitored continuously with periodic substitution of more promising components based on advice from within this activity, from outside experts and assessments of world-wide battery R&D.The work is carried out by a team headed by the Lawrence Berkeley National Laboratory (LBNL) and involves several other national labs, universities, and commercial entities.A list of the key projects for the BATT activity appears in Table 5.More information on BATT appears at its website [10] and in the VTP energy storage R&D Annual Progress Report [6].Some recent highlights for this activity are listed below:  MIT developed a new construction technique for thicker electrodes (almost 10 times more thickness), which uses sintered electrode architecture with aligned, low-tortuosity porosity (see Figure 2).Hardware-in-the-loop (HIL) simulation allows hardware components to be tested in the laboratory at vehicle level without requiring a prototype vehicle.
During benchmarking, both production vehicles and component technologies are extensively tested to verify any significant advances over current technologies.
Technology validation involves testing components/subsystems to evaluate them in a systems context.VSST works with industry partners to accurately measure real-world performance of advanced technology vehicles using a testing regime developed in partnership with industry stakeholders.In addition to baseline performance testing, fleet testing and accelerated reliability testing are also carried out.

Figure 1 :
Figure 1: Current energy storage R&D Focus and Technology Readiness Levels Figure 3: Volt L

Table 2 :
List of ARRA-funded battery facilities now in production

Table 3 :
An overview of battery development, system analysis, and testing projects in FY 2012 (from [6])

Table 4 .
More information on each project is available in the VTP Energy Storage R&D annual progress report[6].Some recent highlights for this activity are listed below.