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Jun 22

The Chevy Bolt Battery Pack Possibilities


By BillR

On June 19, 2015, the feature article on the GM-Volt website examined how the new Chevy Bolt was likely derived from the Chevy Sonic, and some of the comparisons between the Spark EV, Sonic, and Bolt.

So now the question becomes; what will Chevy use for a battery pack?
Since the Spark EV has a range of 82 miles, and utilizes a 96S2P battery arrangement, a 2.5 scale-up would give 205 miles of range, thus the new pack would be a 96S5P. Sounds pretty simple and straightforward.

However, let’s look at this arrangement. Figure 1 is an illustration of the Spark EV chassis.

Figure 1

Over the rear wheels, we can see the large composite housing that contains the batteries. Imagine the size of this battery system if we need to increase its size by a factor of 2.5! Not only would it take up most of the undercarriage, but it would raise the height of the floorboards by the better part of 12 inches. This doesn’t fit the mission that Reuss stated, “5-passenger with utility”. Figure 2 provides another look at the Spark EV battery pack.

Figure 2

Again, imagine trying to place 2.5 of these battery packs in the Bolt.
There has to be a better way.

One major step in shrinking the size of the battery pack is to increase the energy density of the individual cells. Apparently, LG Chem has been working on this for an EV. It seems that there are tradeoffs between energy density and power density. A smaller battery pack, such as the 18.4 kWh pack in the Volt, needs cells with medium power density, but that compromises the energy density potential. However, a larger battery pack that would be used in a 200-mile EV could have low power density cells (since there are many more of them). This would allow the designers to optimize the chemistry for high energy density.

This is discussed by LG Chem’s CEO Prabhakar Patil in this link, but also in subsequent linked articles.

In fact, in his interview, Mark Reuss states that it is more challenging to build a flat battery pack, and “…the battery chemistry and the development of the battery pack coincides with the ability to package something like this. This is quite different from the Volt.”

So it seems that we are seeing not only a different package (flat platform battery pack), but that the cell chemistry has been optimized for the application (long range EV).

Let’s now look at a video of the Bolt at this website.

Please see the Bolt EV Interiors B-Roll video.

At 1:13 in the video, and also at 2:02, we get a glimpse of the floor thickness. It doesn’t appear to be much thicker than that of a conventional car. At 2:28, we see an energy diagram on the main screen, and an X-ray view reveals what looks like a mattress under the passenger compartment. Unlike many hippie vans of the ‘60’s, this mattress is actually the battery pack (although not likely drawn exactly to scale).

To fit within the required volume, this mattress-sized battery pack might be about 6” high, 40” wide, and 70” long (estimate only). This equates to 275 liters. I’m not sure of any volume data on the Spark EV battery pack, however, the Gen 2 Volt’s 18.4 kWh battery pack displaces 154 liters (see Figure 3).


Figure 3
So even two measly Volt battery packs (28 kWh usable) could not fit in this space. So it seems that Reuss is correct, this new battery pack will be quite different from the Volt.

So how will GM construct this battery pack? How do you package cells (such as those from the Spark EV and the Volt) that are approximately 5 inches wide and 7 inches tall (see Figure 4) in only 6 inches of height? How do all the coolant lines fit in this small package?

Figure 4. Each of the Gen 1 Volt’s cells is a “building block” within the
larger battery module and pack. An individual cell is about the size of
a 5-inch by 7-inch (12.7-cm by 17.7-cm) photo frame, is less than a
quarter-inch thick and weighs nearly a pound.

So it is obvious that there needs to be not only improved chemistry that is geared towards higher energy density, but also there needs to be a more optimized cell geometry for the package. What would be the best configuration, and what would be the best cooling scheme?

As I searched the internet, I found that LG Chem has been working on a new battery system in cooperation with the DOE. Here is a link to a 2013 progress report.

There is a great deal of information on cell life and other improvements, however, I took great interest in their low profile battery pack that is cooled by refrigerant. This battery pack is shown in Figure 5.

Figure 5

The cooling system shown utilizes a refrigerant and refrigeration cycle, similar to an air conditioner. The cold refrigerant flows through a cold plate at the bottom of the pack. Between each pair of Li-Ion cells is a thermal fin, which conducts heat away from the cells and down to the cold plate. With temperature sensors and controls, the temperature of the cells can be maintained within a few degrees of optimum.

It also seems that there are distinct advantages to utilizing refrigerant in lieu of direct water cooling, including lower flow rates and reduced pumping losses. The following link on this type of cooling system from Parker Hannifin, states that pumping losses are only 10 percent of a direct water-cooled system.

The lower flow rates should equate to lower volume in the battery pack (less fluid to move). Another advantage would be the ability to maintain the cells at ~ 70° F, even when ambient air temperatures are much higher.

Further in my search, I located a patent application by LG Chem that seems to be related to this battery pack system.

If you click on the link “Download PDF 20140322563”, you can view the entire patent application and its associated images. Figure 6 below is a basic schematic of the system in the LG Chem patent application.

Figure 6

So, these low-profile battery systems could be placed in the Bolt’s skateboard chassis to provide the needed electrical energy, however, air passageways would be required for the necessary cooling air. This could add a great deal of duct work, which adds more volume.
But, if this battery pack could be integrated with the Bolt’s heating and air conditioning system, there are some significant advances that can be achieved.
So let’s look at how the Bolt’s heat/AC could be configured. See Figure 7.


Figure 7
This heating/AC system (air module) utilizes dampers to control the temperature and air flow in the car. Recirculated inside air and outside air is mixed and delivered to the blower. The position of the inlet damper determines the mix of inside and outside air. The heater core damper determines the amount of air that goes through the heater core. Other dampers determine which car vents supply the air. A similar air module could be employed in the Bolt.

So now imagine an integrated heat/AC and battery cooling system.
For the battery pack, the low-profile LG Chem configuration (seen in Figure 5) could be utilized, using the most energy dense cell chemistry for this application. However, the packs would include only the cells, thermal fins, cold plates, and any necessary electronics; no refrigeration system or equipment would be included. This power-dense battery pack would have external connections for “refrigerant in” and “refrigerant out”.
Now, let’s see Figure 8 for a schematic of a possible integrated system.

Figure 8

As seen in Figure 8, a motor driven compressor is utilized in the refrigerant system. This could be a variable speed motor whose speed is modulated to meet the demands of the system. As I describe this system, I will use four different temperature nomenclatures; hot, warm, cool, and cold.

The refrigerant is compressed in the motor driven compressor, and exits as hot refrigerant (S1). This hot refrigerant is directed to the heater core in the Bolt’s air module. This can now provide heat to the Bolt’s cabin, if necessary. The hot refrigerant continues from the air module via S2 to a radiator at the front of the car, probably located directly behind the Bolt’s front grill. After being cooled by the incoming air flow across the radiator, the warm refrigerant is directed to the expansion valve.

After expanding through this valve, the refrigerant is cold. From here it goes to the ambient air evaporator. In cool weather, this evaporator will draw heat from the ambient air. Next the refrigerant goes to the air module. Here the cabin evaporator can absorb heat and provide cool air to the cabin. The cold refrigerant then continues to the battery pack to cool the battery cells and then to an evaporator at the power unit. This would cool the power electronics and also the oil used in the motor/final drive. The cool refrigerant would now return to the motor driven compressor.

On hot days, the motor driven compressor would be working at higher load, and the heater core in the air module would be isolated. After being cooled in the radiator, the cold refrigerant exiting the expansion valve would bypass the ambient air evaporator (or this evaporator could be isolated, as we don’t want to add heat to the refrigerant in this mode). The cold refrigerant then goes to the cabin evaporator to provide cool air to the occupants, and then goes to the battery pack and power unit to provide additional cooling.

On cool days, the hot refrigerant from the motor driven compressor provides heat to the occupants through the heater core. The ambient air evaporator draws heat from the air and then continues through the system collecting heat from the battery pack and the drive unit (cabin evaporator is isolated). So now the system is acting like a heat pump, deriving heat not only from the ambient air, but also from the battery pack and the drive unit.

On very cold days (less than 30° F), there will likely be a need for resistive heating elements.

In summary, Mark Reuss states that packaging the Bolt’s flat battery pack is more challenging than that of the Volt, and also states “…the battery chemistry and the development of the battery pack coincides with the ability to package something like this. This is quite different from the Volt.”

Therefore, it seems that to package the ~ 50 kWh of battery capacity into the limited volume skateboard chassis of the Bolt will require a more energy dense battery chemistry as well as an innovative battery cooling system. It appears that LG Chem has been working on such a system for several years with funding from the US Department of Energy.

By utilizing this new “cold plate” battery cooling system, and integrating the system with the Bolt’s heat/AC system, the Bolt could not only have a smaller and lighter weight battery pack, but may also have a system with lower coolant flows, smaller radiators, an integrated AC system, and a heat pump extraordinaire!


Dec 23

GM Planning to Triple or Quadruple Electric Car Volumes by 2015, LG Chem Says Batteries Not a Constraint


General Motors CEO Dan Akerson

[ad#post_ad]We have heard before that GM’s newest CEO Dan Akerson is particularly bullish about electric cars. It is clear he feels the Volt is a very significant vehicle for the company and projects that the currently high demand will continue to grow.

Thus far GM has committed to producing 15,000 Volts in 2011 and at least 45,000 in 2012.

There is also evidence the company is developing a crossover Voltec vehicle, a 2-mode plugin Cadillac SUV, and possibly a third Voltec car. The crossover may be called the Chevy Amp and could be unveiled next month at the Detroit Auto Show.

Akerson told reporters previously that GM was studying ways to double or triple electric car capacity. Bloomberg now reports that GM sources say Akerson has asked a team to look for ways to triple or even quadruple 2012 electric car production rates by as early as 2015. These volumes  potentially of 250,000 vehicles would be spread across several different vehilce types and brands.

Spreading the technology across brands and vehicles will help to lower costs. Lower costs are needed to increase sales volume. Only 7% of the US car buying public has been determined able to afford the Chevy Volt at its current price.

Akerson’s production plan aims to make GM the recognized global leader in electric vehicles, and is devised to prepare for higher gas prices in the future.

The new electric vehicles under development for the US will all be larger than the Volt and may include an SUV.

Aside from consumer demand and cost the only other theoretical limitation for increasing production is the availability of the lithium ion batteries.

Volt battery supplier LG Chem, however, has massive production capacity, has already started building one Michigan factory and has a second under development.  In fact, LG Chem Power CEO Prabhakar Patil tells GM-Volt that battery supply isn’t a limiting factor.

“GM will have to speak to their plans for future volumes,” said Patil. “But LG Chem stands ready to support them and does not expect battery capacity to be a constraint.”

Source (Bloomberg)



Mar 09

Report Reveals Lithium-ion Battery Prices Already Dropping Steeper Than Expected


[ad#post_ad]Electrification of the automobile is well underway, with the first mass produced cars expected to hit the roads later this year.

There have been many speculative reports about whether these cars will catch on and be sold in high volumes over the next few years.

These predictions hinge on cost to consumers, both for the cars and for gas.  Other than for early adopters, plug-in cars must offer better cost of operation than gas-powered cars to win in the marketplace.

The bulk of an electric vehicle’s cost, however, is the cost of its lithium-ion batteries.

Reports predicting low EV sales volumes often use $1000 per kwh as the price for lithium-ion batteries, but that is unrealisticly high and should no longer be used.

A new report issued by Deutsche Bank indicates prices that are considerably lower.  They write “we continue to believe that the market underestimates the potential for growth in this segment” and “we’ve noted evidence of steeper than-expected battery price declines which will likely bolster the consumer value proposition and potentially lead to stronger demand than we originally envisioned.”

The firm notes the average lithium-ion cell price in 2009 has been $650 per kwh, but claims automakers are already seeing bids for $450 per kwh from battery companies for delivery contracts in the 2011/2012 timeframe.

Furthermore, they predict an additional 25% decline in price over the next 5 years and a 50% decline over the next 10 years along with a doubling of performance over the next 7 years.

Previously LG Chem subsidiary Compact Power’s CEO Prabahkar Patil told GM-Volt he expected cell cost to drop up to four-fold in the next 10 years, and said lithium ion cells for non automotive applications is already $350 per kwh.

Furthermore, last March GM vice president Jon Lauckner stated GM is already paying “many hundreds of dollars per kWh,” less than $1000 for the Volt’s lithium ion cells.

If one considers the Volt has a 16 kwh lithium ion battery, at $450 per kwh its total cell cost would be $7200.

Fuel costs about 2 cents per mile using electricity, and about 10 cents per mile using gas. At $450 per kwh at today’s gas prices, after 90,000 miles of electric driving fuel savings will cover the added cost of the battery.

Source (Deutsche Bank, PDF)


Oct 19

Q&A With the CEO of Compact Power Inc.


Prabakhar Patil is the CEO of Compact Power Inc.  CPI is a subsidiary for LG Chem, the Korean company that was awarded with the Chevy Volt cell supplier contract.  CPI helped GM to develop the packs for the Volt.  I had a chance to interview Dr. Patil on the current status of the relationship and operations.

Where are things with respect to pack development and considering GM’s announcement about in house pack and your relationship with them?
The relationship is good and unchanged because the decision for GM to manufacture the pack in-house after they got into volume production had been made some time ago. We agreed to it in the spirit of partnership because for strategic reasons it was important for GM to do this in house, even though we were prepared to support them in high volume production.

Right now nothing has really changed. As you know we shipped around 50 packs last year, this year we are shipping around 400 packs and that continues to happen. We are validating the pack design, the manufacturing process etc, and these are the prototype packs that are going into GM vehicles. That part is exactly the same as it would have been were we to make the high volume production packs.

So the prototype packs are currently being produced at your facility?
Yes, and they will continue to be made here until GM’s facility is up and running.

Are you helping GM to prepare their facility?
We work together. It’s a joint team that is actually at work.

As a subdivision of LG Chem, will you continue to work in GM’s facility?
No, once the production moves to their facility our role will be more supportive.

LG Chem got a $150 million DOE grant for setting up a cell manufacturing facility that will be locating in Michigan?
As you know, up to now the cells are made in Korea and we assemble, engineer, design and manufacture the pack here. The DOE grant is targeted at making the cells here. That has always been our plans and our footprint but this helps expedite the process.

So you are going to build a US battery factory from the ground up with that money?

When will you start construction?
We probably will complete the site selection process by the end of this year and then we’ll be breaking ground sometime next year. We have to go through all the permits and site preparation and all that stuff. More importantly in terms of production, the first of the cell lines in that new facility we expect to come on in production rates by second quarter of 2012. It will be fully done with all of the cell lines and electrode lines and all that stuff a year later. At that point, it will be capable of producing enough cells to support anywhere from 50,000 to 250,000 vehicle packs depending on how many cells the packs contain.

Is that factory going to solely be used for the Volt pack or might it be used for other automakers?
It is not tied to a single application or customer, that’s part of the flexibility that we will have that it can support different applications. Because as you know the cells for the Volt will initially come from Korea. In fact, that cell line is already up. It has to be in order for us to have certified cells that have to be ready well ahead of the vehicle launch so GM can go ahead with the pack validation and so forth.

That cell line is already up. That will be used to supply cells for the Volt until the cell line here comes on line, so we have a lot of flexibility.
As far as GM or any other customer is concerned they won’t be able to tell the difference as to whether the cell is made here or in Korea.

The cells for the Volt, are they pretty much going to be a standard LG automotive cell for all applications or are you developing differently nuanced cells for different applications?
There have to be different nuances. For example, if you go from a non plugin hybrid to a BEV there are three discrete types of cells that you need. On plugin HEV like hybrids, the power to energy ratio is high, because those hybrid configurations don’t need large pure electric range.

On the other end of the spectrum the battery electric vehicle where the energy density requirements are very significant when you get to 50 or 100 miles of range. The P to E ratio in that case is relatively low then. Plug in HEV cells like the Volt are in between in order for the cells to be optimized we have to tweak the chemistry or the recipe.


Oct 02

Compact Power CEO on the Cost of Lithium-ion Batteries


Prabakhar Patil is the CEO of Compact Power Inc, the subsidiary of LG Chem that has been working with GM to produce the Volt’s battery packs.

I recently had the chance to ask him about the cost of lithium-ion batteries.  As some sources suggest cost could be as high as $1000 kwh, I asked him what the actual cost is in today’s market.  My question with his explanation follows:

What is the cost of lithium ion automotive batteries?
Is its risky or dangerous to quote direct numbers.

At the cell level, in consumer applications, 100% of the nominal capacity at the beginning of life is somewhere on the order of $350 per kwh.

First, we have to keep adding factors for in a vehicle application, when you look at it as a 10 year life and you have this 25% degradation, then your denominator goes down by 25%.

Secondly, if you’re not using all of the capacity, just the combination of those two factors will effectively cut the denominator in half in terms of usable capacity at the end of life as opposed to nominal capacity at the beginning of life. And that will raise the price in dollars per kwh, if you do it in terms of usable capacity at the end of life, by a factor of two

Third, if you add all of the other stuff you have to put in the pack, and it depends on what you consider inside the pack as opposed to outside, because that depends on vehicle architecture. So that’s why it gets very fuzzy and inconclusive to talk about gross level numbers unless you know specifically on how they are being defined.

The other perspective is that lithium ion in the 17 years since it was first introduced has come down by a factor of 14 in terms of dollars per kwh and it’s not done. It will continue to come down not at the same rate, but I fully expect over the next 5 to 10 years for the cost to get better by anywhere from a factor of 2 to 4 in terms of dollars per kwh as compared to where we are now.

One of the things that has nothing to do with the cell or any technology itself, is at the end of life if the battery still has 70 to 75% of its power and energy left.  Why throw it away when you can recapture it? If you could capture that residual value by effectively leasing the battery and putting it to work again in a utility application, at 50% of its initial value, it will cut the effective cost by a factor of two.


Sep 29

Compact Power/LG Chem to Produce and Assemble Battery Packs for GMs 2-Mode Plugin Hybrid, Not GM


GM has been developing a plugin 2-mode hybrid since 2006. It was at first to be deployed in the Saturn VUE.  The host vehicle was later changed to a compact Buick SUV when the Saturn division was sold. That decision too was scrapped, however, GM still intends to sell the drivetrain in some vehicle in 2011.

Although GM has decided to do pack assembly in-house for the Chevy Volt, apparently they have decided to let LG Chem subsidiary Compact Power assemble the packs for the plugin hybrid themselves.

“We will be supplying the production packs,” Compact Power CEO Prabahkar Patil told  “Those production packs will not be made by GM. We will actually be making them but in volume production.”

He explains that LG Chem and GM’s “relationship of course goes well beyond the Volt.”

The 2-mode plugin pack will be half the size of the Volt’s, consisting of 8 kwh of lithium ion cells.

“It’s a different form factor because its tailored to fit in the vehicle its intended for,” says Patil. “It is a different configuration, but there is quite a bit that is shared with Volt in terms of technology. The cell for example will be the same.”

He says that the thermal management system will also be “very similar” to the one used in the Volt.

“We try to commonize as much as we can,” he says. “That will always be our approach, to bring the cost down because of the volumes being higher and secondly because when you are reusing something it doesn’t require as much additional validation and testing and that also helps being the cost down and actually make the quality more robust.”

Patil says the packs will be made in a facility in Michigan that LG Chem just acquired in the past few months and refurbished.  He says that right now the facility is “still in the prototype phase as that’s where we are also making the Volt prototype packs.”

GM has not announced what production volume they expect for the 2-mode plugin hybrid.

Patil gives some guidance be explaining that when the current LG facility “gets some automation by the end of next year, it will have the capacity of 2500 of the large Volt type packs or as much as 10,000 of smaller packs.”

“The capacity depends on the nature and size of the pack,” he says.

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