We want to help the (automotive) customer optimize the solution,we can work in the mode where we are providing the black box, we go one step further and we look at [the consumer] and their requirements whether it’s acceleration, fuel economy, etc. and help optimize the battery pack so it doesn’t end up being over-designed based on one criteria.

We want to be a one stop shop, a center of excellence, for engineering and manufacturing located in North America because when I was on the other side as a Chief Engineer for the Escape Hybrid at Ford that was one thing I was looking for but couldn't find very easily.

—Prabhakar Patil

CPI considers the safety of their chemistry as well as the flexibility of their packaging to be key reasons why they GM selected them for the Volt.

The critical thing is to make sure there isn’t any kind of a mishap that occurs because of immature design or inadequate validation. Most people ... don’t distinguish between the chemistries ... Back in ’98 when I was trying to decide on the Escape, I deliberately ruled out Li-ion because there were too many issues and you don’t want to have even on instance of what happened with the laptops, but those issues have been addressed

Generic Li-ion cell and various component technologies. In Li-ion batteries, Li ions (Li+) leave the cathode during charging and move through the electrolyte and separator to intercalate into the anode. The reverse happens on discharge. Source: DOE, ALBAA 2008. Click to enlarge.

All Li-ion cells are built with a cathode, anode, separator, and electrolyte contained in a package. CPI considers its separator, cathode chemistry and packaging to be competitive strengths. In previous Li-ion batteries, microscopic amounts of manufacturing debris that are undetectable in end-of-line testing have penetrated the separator and led to fires resulting from the characteristics of the chemistries of the materials used in the battery.

CPI’s Safety Reinforcing Separator (SRS) separator is 5x stronger than the industry norm and is more robust to debris migration as well as overcharges and they view this as a long term competitive advantage.

Cathode chemistry is one of the main variables in determining Li-ion battery performance with at least eight different sub chemistries being actively pursued within the industry. For the Volt, CPI is using manganese-spinel (LiMnO₂) which features high stability and resistance to thermal runaway. “People frequently say they can handle cell safety issues with exterior circuitry but these cannot really help if something happens inside the cell,” Patil said.

Manganese is also abundant and low-cost and with the use of proprietary additives, CPI believes a calendar life of more than 15 years is achievable within a vehicle with proper design and operation.

In terms of chemistry ...one of the advantages I have with LG Chem as a parent company is materials is their DNA and we continue to look at chemistries beyond what we have. We need to obsolete our own, otherwise competitors will do it. We will look for other alternatives.

Right now the primary attention is on the cathode side. As the technology gets fixed, the anode is more of an issue related to fast charge. Right now that is not that big of a deal because most houses don’t have the electrical infrastructure to support a 10 minute fast charge ... it would bring down the neighborhood ... but as PHEVs proliferate there will be a need for fast charging at service stations and highway rest stops then the anode will play a role.

“Mini-cells” Source: LG Chem, ALBAA 2008. Click to enlarge.

The cell is the smallest part of the battery pack that can be handled independently. Each cell is made of many “mini-cells”, with each mini-cell having a cathode, anode and separator. The storage capacity of a cell can vary by as much as 10x depending up the number and size of the mini-cells. For a PHEV CPI expects ten to twenty cells to make up a module and ten to twenty modules make up the pack.

CPI will use a laminated flat (prismatic) package for the Volt’s cells instead of a cylindrical package. The laminated packaging is more forgiving than a metal can to abuse conditions. The flat pack can be customized to fit the available space in the vehicle. Flat packages have a higher surface area to volume ratio than cylinders facilitating heat removal during operation which is significant since elevated temperatures are the primary contributor to life degradation.

Example of high thermal efficiency for the prismatic cell. The center cell is the test item. Discharge was carried out at the rate of 30C. Source: Alamgir and Sastry (2008). Click to enlarge.

“All vehicle battery packs require cooling ...in consumer electronics the battery is in the same environment as people and automatically temperature controlled.” For a traditional HEV pack it can be as simple as circulating air while for the “Volt, we had to go to liquid cooling because there isn’t enough room” for air cooling.

Extreme cold generally isn’t a durability concern but can impact available power until the pack naturally warms up. For frigid climates like the Minnesota and Canada pack warming can be integrated with the overnight charging for a PHEV.

By measuring each cell’s voltage individually and selected temperature monitoring within the pack “the monitoring system is smart enough so that it knows when a cell or a group of cells is starting to fall out of the band and it can provide enough warning to have maintenance done on the battery rather than having it fail.”

Although repair plans will vary by car manufacturer, it is likely for the initial PHEV programs servicing a battery pack at a dealer would be limited to pack swapping. “Initially when the production volumes are low and with the reliability we expect from these systems the technician is not going to get much practice working on these technologies,” Patil said, and it makes sense for the repairs to be done at a central location.

Manufacturing

For the Volt project, CPI is providing prototype packs to GM until the automaker brings its new module and pack assembly operation online. The cells for the CPI-produced packs and cells to go directly to GM will come from Korea.

Originally we wanted to manufacture the pack for the Volt. For various reasons, GM wants to do it in house and of course we support them as a partner but we are at the same time prepared to manufacture for other customers.

We delivered 50 packs to GM last year and delivering close to 400 packs this year. Although it is being done on a prototype line we are emulating the processes that will be used in high volume production.

CPI’s long term goal to produce the cells in the US once they get a critical mass of business. Unlike their competitors A123Systems and EnerDel, they have not applied for any ATVMIP money.

[ATVMIP] is something we are looking into. For me the business equation has to be sustainable without incentives because incentives cannot last forever but at the same time incentives can help accelerate a technology’s acceptance and growth.

CPI’s manufacturing strategy is dynamic. If they have 50,000/year or more of the same pack in a given vehicle assembly plant they would build a satellite pack assembly plant close to the customer otherwise they would ship from a central plant servicing multiple programs.

Li-ion in traditional hybrid applications

With recent improvements in high temperature life and cell safety CPI is excited about increasing Li-ion’s role in traditional hybrids like the Toyota Prius. Compared with today’s NiMH batteries deployed in hybrids, the LG Chem lithium polymer batteries deliver the same power with 30% less weight, 50% less volume and 10% greater efficiency. LG Chem will be supplying a Lithium polymer pack for the Hyundai Blue Drive system expected to be released in 2009. (Earlier post.)

In general, the price of gasoline needs to be above US$3.50/gallon for traditional hybrids to be financially attractive, assuming a $3,500/vehicle premium of which a third is spent on the battery pack, CPI says.

CPI believes that people make an unreasonable comparison to consumer electronics (CE) pricing when discussing Li-ion for automotive traction (AT) applications. CPI believes four factors need to be taken into account to make a valid comparison:

• First, CE pricing is based on the beginning-of-life capacity whereas AT pricing is based upon end-of-life capacity and even for a highly durable chemistry the ratio of end-of-life to beginning-of-life is 75%.

• Second, the AT application is sized for a 70% depth of discharge, the gap between minimum and maximum charge levels, which allows space on the high end for regenerative braking and space on the low end to provide enough power for charge sustaining operation.

• Third, the AT market has more stringent requirements on the validation of the individual cells.

• Fourth, a vehicle pack battery pack has non-cell costs such as a monitoring system.

All four of these items together justify a 2.5x premium for the AT application (or approximately $ 1,000/available kWh) compared to the $350/stated kWh of a CE system, CPI says.

Long term barriers to widespread electric vehicle use

CPI sees three long term barriers to the subsidy-free adoption of electric vehicles. The first is the cost of the battery pack.

From a historical perspective over the past 17-18 years the cost has come down by a factor of 15x. In the next 5-10 years we should be able to come down by an incremental 2-4x and we will have to do that to accelerate the penetration of the technology.

The second barrier is capturing the residual value of the battery pack. When purchasing a PHEV or EV the consumer is spending a significant amount of money on a battery that, if properly implemented, will depreciate more slowly than the rest of the vehicle. After 10 years of operation the battery will still have 75% of its energy storage potential and could be used for non-automotive applications like load leveling for the grid to accommodate renewable energy. Properly capturing this residual value can have a significant impact on the financial viability of an electric vehicle.

People don’t make their decision on life cycle cost, they make it on transaction cost and we need to find a way to make it attractive. If you get a consortium of companies (i.e. power providers) to buy the battery and lease them to the customer we can make the lease payment very attractive in the end. Because what we call end of life is maybe a 25% loss of power or energy but it is still 3x more than what you get from lead acid ... but the consumer cannot realize this value on their own ... they need help.

The third barrier is peoples’ expectations for range.

One of the issues with the acceptance of pure EVs is if you want to provide a 100-mile range...you end up putting so much battery in that it ends up being used only 10% of the time or less and yet you are saddling the customer with that cost ...we need to find a better way so when they go on the occasional long trip or need that range...they can get something or rent something. With that being said, there are practical issues we need to deal with, for example even something as simple as being able to drop the battery pack out and put a new one in is a challenge because these high power connectors aren’t designed to be disconnected and reconnected on a regular basis.

That is why to me the plug in or range extended hybrid is a good stepping stone because it tries to balance the value equation with providing the amount of battery that would be used 80% of the time but addressing this range issue and the emotional issue of running out of battery with a relatively small and inexpensive engine and generator. People will start to feel comfortable and realize forty miles isn’t that bad ... and re-evaluate their expectations for range.

[Contributing writer Bill Cooke has been an engineer and manager with Ford and Visteon.]

Resources

• Mohamed Alamgir and Ann Marie Sastry (2008) Efficient Batteries for Transportation Applications. (Convergence 2008, 08CNVG-0036)