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The Fathers of Fast Charging: The Story of the First 250kW 10-Minute Fast Charge

image credit: Botsford

The Fathers of Fast Charging: The Story of the First 250 kW 10-Minute Fast Charge

Charles Botsford, P.E., Monrovia, California

The Fast Charge Event

On May 17, 2007, AeroVironment, Inc (AV) engineers fast charged a 35 kWh electric vehicle battery pack in 10 minutes [1]. Witnessing the event were Tony Andreoni and Craig Childers of the California Air Resources Board (ARB).

The pack, comprising Altairnano modules designed for Phoenix Motorcars’ electric sports utility truck, began at zero percent state of charge and ended at approximately ninety-five percent state of charge.

35kWh Lithium Titanate Battery Pack

Figure 1. 35kWh Lithium Titanate Battery Pack

The Battery Technology

Altainano used a lithium titanate battery chemistry for their packs. The advantages of lithium titanate chemistry over other lithium chemistries are:

  • Long cycle life – on the order of 5,000 full 100 percent depth of discharge (DoD) cycles
  • Long calendar life – twenty years?
  • True 10-minute fast charge rate – this translates to a 6c charge rate. 1c charge rate is a full battery charge in 60 minutes. 6c is six times that rate or a full charge in 10 minutes.
  • Highly safe – very low potential of thermal runaway compared with other lithium chemistries

The disadvantages of lithium titanate chemistry are:

  • Low specific energy – in the range of 60-80 kg/kWh, which translates to 50 percent heavier packs
  • High cost – approximately 20-30 percent more expensive than other lithium based chemistries. The low specific energy translates to more lithium required per kWh.

Thirteen years later (i.e., 2020), the high cost and low specific energy disadvantages have proven difficult to overcome relative to the light duty EV market. However, lithium titanate is still competitive for the heavy-duty vehicle market, especially transit buses.

This perspective is important in understanding why vehicle developers were interested in lithium titanate in the 2007 time frame. A battery pack that wouldn’t degrade, had lower thermal runaway risk, and last forever would solve most of the problems an automotive manufacturer faced as they developed a new EV model. The ability to fast charge in less than 10 minutes was not only icing on the cake, but meant a compelling way to address “range anxiety.”

At the time, Altairnano was the first company developing lithium titanate. Later on, Toshiba, with its SCiB technology, worked with several large automotive manufacturers, including Honda (the Fit) and Mitsubishi (i-MiEV) to commercialize the technology.

Proving the Battery Technology

By the early 2000s, AeroVironment (AV) had more than 20 years of battery testing and pack development experience, starting with the development of the GM Sunraycer and GM Impact in the late 1980s and early 1990s. That experience included extensive work with lead-acid, nickel metal hydride, myriad lithium chemistries, and many kinds of fuel cell technologies.

AV had been at the forefront of fast charging of EVs - starting with EV1, then the fast charging of battery electric forklifts. For electric cars, these efforts met with limited success since no battery chemistry was capable of accepting a fast charge at practical rates. This changed with the development of the lithium titanate oxide (LTO) batteries - and their practical implementation by Altairnano. AV recognized early that the fast charging capabilities of this battery chemistry merited attention.

To say that AV engineers were skeptical of new battery claims is an understatement. Battery developers regularly commissioned AV to test and validate their new and latest batteries. Often, the claims were truly unbelievable, and just as often proved wrong. One AeroVironment engineering manager had a saying, “There are liars, damn liars, and battery suppliers.”

When Altairnano came to AV with the claims listed above, the engineers were highly skeptical to say the least.

Testing began at the cell level. Cell testing is relatively inexpensive and quickly determines whether further testing at the module or pack level is warranted. It was. Much to the amazement of AV engineers, cell testing passed 6c charge and discharge testing from zero to 100 percent state-of-charge (SOC). After approximately 1000 full DoD cycles, no degradation was detected. Testing also included time in a thermal chamber and witnessing of nail penetration and other destructive testing to make sure that the cell meets the safety standards already established.

One surprising note was the capability of the cell to discharge to zero SOC, which is something highly discouraged universally by lithium battery manufacturers.

Next was the module level, where performance problems often crop up. A module comprises many cells and requires a battery management system for cell balancing, thermal monitoring, voltage control, and other management parameters. Due to the very low internal impedance of lithium titanate, the battery management system had no trouble with cell balancing and controlling the module. AV engineers spent much more time and effort with module testing because testing at the pack level is even more critical. The pack-level battery management system controls multiple modules—28 modules for the Altairnano pack.

The Pre-Test and Test

On the evening of May 16th, 2007, AV engineers conducted the first pack-level pre-test of the Altairnano pack using an AV-900 advanced battery cycler, which is rated at 250 kW. The purpose was to check all systems, especially safety. Pushing that much power into an EV pack had never been done before. The pack was discharged to zero percent SOC that night.

On May 17th, 2007, with everyone standing back and safety goggles in place, the AV-900 battery cycler began charging the pack.

The fully charged 35 kWh pack, in ten minutes, theoretically requires 210kW (35 x 6C = 210 kW). However, system losses from pack internal resistance, cabling, contactors, and battery management system, increased the actual power required from 215 to 240kW, pushing the AV-900 to its limits.

The charging proceeded as expected. AV engineers followed the increasing pack voltage, which indicated the pack was charging according to the SOC/voltage curve.

At just less than ten minutes into the test, one of the ARB representatives noticed that a cable connecter at a pack contactor was smoking. The test was immediately shut down. The pack was charged to approximately 95 percent SOC.

Over the next several months, battery testing at the module level confirmed the claimed attributes of the lithium titanate chemistry.

Test Implications

Demonstrating that a battery could be safely and fully charged in ten minutes was a major accomplishment for the EV industry. The Society of Automotive Engineers (SAE) J1772 DC charging subcommittee immediately began evaluating connector technology for the 250kW power level and initiated development of a new fast charge standard.

source: Botsford [2]

Figure 2. High Power DC Vehicle-Side Connector – early concepts

However, that effort was never completed, primarily due to fears by automotive manufacturers that batteries could not be fast-charged. Many years later (~2012), SAE adopted a 50kW combined charger system (CCS) standard, which would compete with the 50kW CHAdeMO (Japanese) standard already in place. Several years after that, SAE increased the power limit of CCS to approximately 400kW and a maximum charge current of 500 A.

The Heavy-Duty Market – A 500kW Transit Bus Charger

By 2010, Proterra, a transit bus manufacturer, had successfully developed an electric bus capable of  high-power charging using the Altairnano lithium titanate batteries. The first Proterra fast charge electric buses were put into revenue service at the Foothill Transit Agency (Southern California). AeroVironment developed the first 500kW charger, which comprised four 125kW power modules. A video of the charging system can be found at:

https://www.youtube.com/watch?v=zKM8v0Vdasc

 

The Fathers of Fast Charge

Phoenix Motorcars, Altairnano, and AeroVironment collaborated in developing and demonstrating the fast charge chemistry and technology. Those involved include:

Phoenix Motorcars

Rick Reinhard – Project engineer

Altairnano

Evan House, PhD – Battery specialist

Alan Gotcher – CEO

Bob Goebel – Business Development

AeroVironment, Inc.

Omo Velev – Project manager

Ron Norton – Standards engineer (Ron had a harness around his neck during the test, ready to pull the pack out of the high bay in case something went terribly wrong. This article is written in his memory.)

Adam Szczepanek – Lead engineer and topology designer of the 500kW fast charger

Bill Norris – Battery management specialist

Mike Vail – Power electronics engineer

Al Flack – Power electronics engineer

Scott Berman – Power electronics and software design engineer

Conclusion

Many projects were conducted and products developed in the 1990s on the fast charge of batteries of all types: lead acid, nickel metal hydride, and lithium chemistries. By the early 2000s, “extreme” 10-minute fast charging emerged as the holy grail. Meanwhile, one-hour fast charging was in the works for the many years of standards development that lie ahead.

The 2007 demonstration of true 10-minute fast charging at the pack level, with an actual EV battery pack, showed the standards developers they should set the limits to high power levels, 250kW and beyond. A decade later that’s what began to happen with both the combined charger system (CCS) and CHAdeMO standards.

 

References

 

1. Botsford, C., Testimony before California Air Resources Board on May 24, 2007.

2. Botsford, C, A. Szczepanek, “Fast Charging vs. Slow Charging: Pros and Cons for the New Age of Electric Vehicles”, EVS24, Paper No. 3960315, Stavanger, Norway, May 2009.

 

Author

Charles Botsford, PE is a professional chemical engineer in the State of California with 30 years’ experience in engineering process design, distributed generation, EV charging infrastructure, and environmental management. He has participated in California’s Vehicle Grid Integration (VGI) Working Group and participates in the Society of Automotive Engineers (SAE) J3072 AC Vehicle-to-Grid standards committee. Mr. Botsford holds a bachelor’s degree in chemical engineering from the University of New Mexico, and a master’s degree in chemical engineering from the University of Arizona.

Charles Botsford, PE's picture

Thank Charles for the Post!

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Discussions

Matt Chester's picture
Matt Chester on Sep 25, 2020 11:36 am GMT

Thanks for the history lesson, Charlie! Tech is moving along so quickly these days with everyone so eager to move onto the next breakthrough or next big idea that it's easy to forget to stop and pause and marvel at the great work being done all around us and what the direct impact of that work is/will be. This is a great reminder of that and shows how far we've come-- and will continue to go!

Charles Botsford, PE's picture
Charles Botsford, PE on Sep 28, 2020 10:58 pm GMT

Hi Matt,

Thanks. In 1987, AeroVironment (AV) built the Sunraycer for General Motors (GM), which won the solar race from Darwin to Adelaide. In 1989, AV built the Impact electric car for GM, which GM eventually turned into EV-1. By the 1990s, AV, GM, Ford, AC Propulsion, and a few other companies were trying to build the EV industry. Then the EV movement died down for about a decade, primarily waiting for battery technology to catch up. The early 2000s were exciting because of all the new tech development. By 2010, Nissan came along with the LEAF, and the EV movement was suddenly on again big time. Now we're into the 2020s and it's like a dream come true with all the EVs hitting the market, and the promise of EVs supporting the grid.

Matt Chester's picture
Matt Chester on Sep 29, 2020 11:37 am GMT

The EV market has been fascinating to watch-- I was surprised when I went to finally buy my first EV last year to find that the Leaf was already almost out of date with how many competitors it had that offered better ranges. This rate of progress is so encouraging!

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