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Electric Vehicle Battery Development Gains Momentum

NREL's modeling, simulation, and testing activities include battery safety assessment, next-generation battery technologies, material synthesis and research, subsystem analysis, and battery second use studies.
Photo by Dennis Schroeder, NREL

Electric Vehicle Battery Development Gains Momentum

CAEBAT collaboration targets EDV batteries with longer range and lifespan, at a lower cost.

"When people get behind the wheel of an electric car, it should be a great driving experience. Period." Dr. Taeyoung Han, GM technical fellow, said, "Battery performance is vital in meeting drivers' expectations."

Electric-drive vehicles (EDVs) promise to curb greenhouse gas emissions and slash America's need for imported oil. However, designing high-performance, cost-effective, and safe energy storage systems can present considerable challenges.

Batteries, which are typically some of the most expensive EDV components, power the motor and other electrical systems, while storing grid-fed energy as well as kinetic energy from regenerative braking. To appeal to drivers, electric cars need to have a range of 250 to 300 miles between charges, placing greater pressure on the vehicles' battery packs.

At the same time, for EDVs to gain meaningful market share, the U.S. Department of Energy (DOE) has determined that battery costs need to be cut from $400-$600 per kilowatt hour (kWh) to $125/kWh, and battery lifespan needs to be extended to 15 years from its current eight years.

Powering Better Performance, Lower Costs

A photo of a man wearing safety glasses, a blue blazer, and red tie standing behind a table filled with lithium battery packs in a large, open laboratory (22817).

NREL Energy Storage Group Manager Ahmad Pesaran demonstrates advances in battery performance at NREL's Battery Thermal Management Test Facility.
Photo by Dennis Schroeder, NREL

To accelerate development of battery packs and wider adoption of EDVs, the National Renewable Energy Laboratory (NREL) is collaborating with a range of experts on the $14 million Computer-Aided Engineering for Electric Drive Vehicle Batteries (CAEBAT) project.

CAEBAT's goal is to develop sophisticated software tools to improve and accelerate battery design and boost EDV performance and consumer appeal — and ultimately diminish petroleum consumption and polluting emissions.

"Lithium-ion batteries are widely seen as the most feasible solution for electric vehicles in the next decade, but so far high cost, limited range, and long recharge times have been stumbling blocks for making electric vehicles realistic options for the broader market," said NREL Energy Storage Group Manager Ahmad Pesaran.

"Researchers and industry engineers need to work together to speed up advancements in performance while lowering costs," Pesaran went on to explain. "Even if a cell is developed that meets most of the EV requirements, a full battery pack consisting of many cells needs to meet the challenges posed by full system integration and operation under real world conditions."

The CAEBAT project addresses these issues with a suite of battery cell and pack engineering tools that:

  • Investigate a full range of chemistry, cell design, and battery pack options for particular vehicle platforms
  • Factor in electrochemical, thermal, and mechanical interactions
  • Shorten battery prototyping and optimization processes
  • Improve overall battery performance, safety, and lifespan
  • Reduce costs for suppliers, manufacturers, and consumers.

Combining Energy in Industry-Research Partnership

"We need to keep raising the bar with our electric car designs, and battery performance is a huge part of that," said Xiao Guang Yang of Ford, a CAEBAT principal investigator.

Most battery models and simulation tools developed prior to CAEBAT did not strike the balance of precision and ease-of-use battery developers, pack integrators, and automakers require. In 2011, DOE/NREL used a competitive procurement process to select three teams to develop three separate, competitive, validated, and easy-to-use CAEBAT software tools for battery pack design. The three teams include representatives from each key industry sector:

  • EC Power, Penn State University, Johnson Controls, and Ford
  • General Motors, ANSYS, and ESim
  • CD-adapco, Battery Design LLC, A123 Systems, and Johnson Controls.

While DOE's Office of Energy Efficiency and Renewable Energy Vehicle Technologies Office provided primary funding for this activity, these industry partners contributed 50% ($7 million) of the project budget.

Modeling at the Materials, Cell, and Pack Level

A computer-generated image of a prototype for a 24-cell module.

GM pack-level validation of CAEBAT tool using prototype for 24-cell module.

At the outset of the CAEBAT project, NREL unveiled a development crucial to filling a gap in existing tools: a predictive computer simulation of Lithium-ion batteries. This framework, known as the Multi-Scale Multi-Dimensional model, has a modular, flexible architecture that connects the physics of battery charge/discharge processes, thermal control, safety, and reliability in a computationally efficient manner. This makes it much easier to independently develop submodels at the cell and pack levels.

NREL provides technical support on electrochemical and thermal modeling to all of the CAEBAT teams as they work independently to develop and validate computer-aided engineering tools based on a variety of chemistries, cell geometries, and battery pack configurations.

CAEBAT has already produced models of alternatively stacked, wound-, and large-format cylindrical cell performance, as well as pack thermal networks. These models have been validated from the cell to the pack level. The software tools that have resulted from this collaboration are expected to become competitive marketplace offerings for battery engineers and EDV designers by the end of 2014.

"The simulation and automation tools that will come out of this project will impact the industry's ability to design energy storage systems at a faster pace," said Brian Sisk, director of Controls and Modeling for Johnson Controls Power Solutions. "We also believe this work will enable innovation in battery pack design and technology integration, leading to better electric vehicle performance."

In addition to computer-aided engineering and groundbreaking thermal evaluation and analysis, NREL also acts as a go-to resource in boosting efficiency and troubleshooting deficiencies in energy storage systems. This helps automakers and battery companies design better vehicles and meet challenging cost and performance targets.

Sustainable Transportation

Fall 2013 / Issue 5

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