Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
Randy—
It is no problem for the feedback. I actually enjoy it when I am in disagreement with someone as you. It helps me question what I know, double check my assumptions, and follow links to data that I wasn’t always aware of. It makes it that much easier that you aren’t disagreeable. We are just to people looking at a set of data and coming to different conclusions.
The two issues I have with cycle life is that it can be doctored, for lack of a better term and that automotive cycle life is nothing like simple charge discharge cycles. It is highly dependent on the voltage range, temperature, rates, and at what point is the test stopped so it can be very easy to get caught up in the number of cycles. I agree about higher Wh/kg cells usually being needed for longer range pure-EVs. I would also argue that the correct cell choice would lessen the need for cells and/or environmental management.
While I am not entirely familiar with the GS Yuasa cells, what follows is educated speculation. As I understand it, the Yuasa cells are designed to handle 5C rate continuous discharges, as opposed to a pulse discharge (which I typically think of as <10sec, but that’s a personal opinion). The Yuasa cells could probably handle 10 or 15C pulses. The electrodes likely have much thinner coatings than the NCR 18605s, which means that there is a higher ratio of the substrate material. This causes the cell weight to go up quickly while the cell capacity is going down.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
Randy--
ABSL is one of several companies that has been using 18650s to build larger arrays, but their specialty is space applications, so they would be most familiar with the requirements. There are a number of other companies that have been doing similar things for space, aviation, military, and automotive applications.
That is why I simultaneously chuckle and grimace when I hear about how Tesla's pack technology is so much better and unique than everyone else. There are a lot of other companies who have been doing similar things for a very long time.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
Randy--
18650s slow thermal runaway, but only to a degree. Slowing comes almost as much from pack design. While a larger number of small cells allows redundancy, I have encountered the argument that it makes it harder to QC large packs due to the number of interconnects needed. There are merits to both points of view.
ABSL (which is part of EnerSys since 2011) has been making aerospace and satellite batteries out of 18650s since the 1980s or 1990s is one of the biggest in this area.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
Benthicity--
"Ridiculously optimistic?..."
Yes it is optimistic. Changing from the original 2.2Ah cells to the 2.9Ah cells was a cathode chemistry change, along with some internal mechanical design changes. Going from 2.9Ah to 3.1Ah was playing in the margins with the internal electrode design. I suspect going from 3.1Ah to 3.4Ah is the same. The mythical 4.0Ah cell that everyone brings up was first talked about in 2009, with a 2012-2013 target. As of a Panasonic tech roadmap dated July 2012, it isn’t even in the pilot planning yet.
And Tesla likely accounts for <5%, if not less than 1% of 18650 cell production. There are cell lines from Panasonic/Sanyo that produce several hundred million cells per year per type. There are at least 20 different cell lines from Panasonic alone, not even counting another 20 or so from Samsung and LG, plus a host of other vendors producing 18650s.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
Randy--
"The reason W-hr/kg is important..." "And $/kWh actually does matter..."
Both are irrelevant unless we are talking about true battery pack Wh/kg or $/kWh. Manufacturers quote cell level specific energies and costs, as opposed to true pack costs. Tesla may be using a cell ~250Wh/kg, but their pack is much closer to 150Wh/kg. The cell-level costs might be ~$200/kWh, but the pack is probably closer to ~$400 or $500/kWh. When people talk real battery costs, I will be happy to give some level of confirmation to correctness. Until then, I am happy to point out the flaws in PR campaigns.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
Randy--
"Just asking, but do you think Boeing might end up with an 18650 solution for their battery in order to satisfy the FAA reliability / safety concerns?"
Short answer: No.
Long(er) Answer: Form factor is pretty irrelevant when discussing safety. The FAA puts all Li-ion flavors and form factors in the same group of "Li-ion." They have had problems with batteries across a number of different chemistries and form factors, and right now are skittish about all of them. Actually, the FAA is a little behind the times on that bandwagon. The Navy has been like that for 4+ years now.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
Randy—
I had a look at the links you provided over the weekend. A couple of comments:
1) The first link does show a module that can handle 2C charge and discharge rates. That is due to the cell choice that they have listed however. The EAX is a lower capacity design (~2Ah), with a different chemistry and electrode mechanical design than the NCR cells used by Tesla.
2) For the second link, the cycle life was estimated.
3) The third link is 3 years old. I had seen it previously. To be honest, most pack construction with 18650s is virtually the same. Only the outer box usually changes.
These are all feasible, although in the second link, I would crucify the PR and/or bizdev department(s) for putting the 5000 cycles in there. I have never said that cells will not improve. What I have consistently said was that they improve slowly and on the fringes more often than some massive breakthrough. More than anything, a judicious cell choice could eliminate the need for some improvements.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
teddy--
“Clearly you know nothing about how the Tesla works.”
That might be true, but I find it more likely that you know nothing about how battery chemistry works, and the strategies to improve life. I am well away aware of the SOC that a Tesla battery charges to. Other than I know that it isn’t to 100% SOC, anyone with a calculator can figure out the nominal cell voltage used to calculated the kWh rating, which is lower than the manufacturers reported nominal cell voltage.
That being said, even lowering the end of charge voltage still doesn’t prevent permanent capacity loss. Just leaving a cell on a shelf and not touching it will still cause permanent capacity loss over time. It is an unavoidable fact of Li-ion that this occurs. The only way that I have seen to mitigate that greatly is to store a battery and/or cells at virtually 0% SOC at <10degC. Even then one could see 1 or 2% permanent capacity loss per year.
As for Tesla being the best in the biz, that is just laughable. There are a number of companies that have been using commercial 18650s for a variety of applications infinitely more challenging than EVs, particularly space and aviation applications. These are things that have much greater environmental requirements, need multiple years of real data to support their usage, and have to handle much more extreme current and temperature conditions. Then again, you can just continue to believe what you believe…
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
Randy--
Maybe a better term would have been "mean specific energy (Wh/kg) across all cell types." Making a higher specific energy cell does not make it better, only higher specific energy. In order to build the best battery, the right cell has to be chosen for the application, which is not always the highest specific energy cell.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
Randy--
Both kW and kWh are a function of voltage as well. As a result, the current might be lower at high SOC, but will be significantly greater at low SOC. Charge doesn’t bother me too much, although at higher rates the heat generated can go up rather quickly. A 2C rate is achievable now on most cells. That being said, charging at 2C is a good way to shorten life unless your cell is designed for that.
PHEV applications are harder than pure EV applications. That being said, the big 3 and the DOE are writing the EV test manual as they go along. Both the requirements and the test procedures are evolving as things progress.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
See my above posts about what will happen as cells increase energy density. The pack will not necessarily get any lighter, since more cells will be needed to help lessen the current at the cell level. I also doubt that Panasonic, or anyone else is going to sell Tesla cells at cost, even if they were the biggest customer, which I doubt they ever will be. There are many cell lines from Sanyo/Panasonic that are produced on the order of hundreds of millions per year.
As for your assessment of cycle life, your lack of understanding of how the batteries will be cycled is appalling. Even if the pack is being cycled down 20% every day, the pack is going to be charged up nearly every night, at least that is what the true believers try and tell me. While shallow cycling is good for extending life, storage at a high state of charge is not. Then again, no one is going to have a simple constant current charge and constant current discharge. The charge might be simple, but the discharge will be anything but. This is the portion that will significantly tax the battery and will age it quicker than most people realize. That doesn’t even get into the storage effects, but that is a different story altogether.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
200Wh/kg is a pretty good average across all cell types. While there are cells higher, there are plenty that are significantly lower.
As for the Panasonic press release, as of the cell technology roadmap from Panasonic that I have seen dated July 2012, there is no 4.0Ah cell on the market, and none scheduled for pilot production through the end of 2014.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
Randy—
Your analysis of the changes in the coatings is correct in layman’s terms, which I mean as a complement. You would be surprised about how hard it is to get some people to understand even that much. There are a host of factors that are in play, but that is a good summary.
That being said, if you increase the anode capacity through a material change, your cell capacity does not go up unless you add more material on the positive. Typically cells have excess capacity on the anode for safety reasons. By adding to that capacity, the margin gets greater, but it is still the cathode that dictates the cell capacity. Because of this, one would have to make the positive material coating thicker, which is going to harm your power capabilities even more. While I agree that the particles themselves and how they are fabricated can help, that can only help so much.
I don’t know what type of rates would be needed. But I can tell you that at a cell level, the 18650s used by Tesla would be extremely taxed during a 2C discharge, let alone 4C (even for 10s), and forget about charging at a 2C rate. That is why I feel that they need so many cells. It just isn’t a range issue, but the cells themselves have a hard time handling the current demands. As a result they add enough to bring the charge and discharge rates to a level that can more easily handled by the cells.
There are barriers that preclude a cell like Envia or CALiB, namely the fact that to make a high Wh/kg cell you typically have to make it a high energy cell. That means that the coatings on the current collectors are very thick and there is little electrode surface area. This cuts the power capability off at the knees. It is not uncommon for similar chemistries (sometimes even identical) to have vastly different Wh/kg based solely off of being either designed for power or for energy.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
It is no problem for the feedback. I actually enjoy it when I am in disagreement with someone as you. It helps me question what I know, double check my assumptions, and follow links to data that I wasn’t always aware of. It makes it that much easier that you aren’t disagreeable. We are just to people looking at a set of data and coming to different conclusions.
The two issues I have with cycle life is that it can be doctored, for lack of a better term and that automotive cycle life is nothing like simple charge discharge cycles. It is highly dependent on the voltage range, temperature, rates, and at what point is the test stopped so it can be very easy to get caught up in the number of cycles. I agree about higher Wh/kg cells usually being needed for longer range pure-EVs. I would also argue that the correct cell choice would lessen the need for cells and/or environmental management.
While I am not entirely familiar with the GS Yuasa cells, what follows is educated speculation. As I understand it, the Yuasa cells are designed to handle 5C rate continuous discharges, as opposed to a pulse discharge (which I typically think of as <10sec, but that’s a personal opinion). The Yuasa cells could probably handle 10 or 15C pulses. The electrodes likely have much thinner coatings than the NCR 18605s, which means that there is a higher ratio of the substrate material. This causes the cell weight to go up quickly while the cell capacity is going down.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
ABSL is one of several companies that has been using 18650s to build larger arrays, but their specialty is space applications, so they would be most familiar with the requirements. There are a number of other companies that have been doing similar things for space, aviation, military, and automotive applications.
That is why I simultaneously chuckle and grimace when I hear about how Tesla's pack technology is so much better and unique than everyone else. There are a lot of other companies who have been doing similar things for a very long time.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
18650s slow thermal runaway, but only to a degree. Slowing comes almost as much from pack design. While a larger number of small cells allows redundancy, I have encountered the argument that it makes it harder to QC large packs due to the number of interconnects needed. There are merits to both points of view.
ABSL (which is part of EnerSys since 2011) has been making aerospace and satellite batteries out of 18650s since the 1980s or 1990s is one of the biggest in this area.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
"Ridiculously optimistic?..."
Yes it is optimistic. Changing from the original 2.2Ah cells to the 2.9Ah cells was a cathode chemistry change, along with some internal mechanical design changes. Going from 2.9Ah to 3.1Ah was playing in the margins with the internal electrode design. I suspect going from 3.1Ah to 3.4Ah is the same. The mythical 4.0Ah cell that everyone brings up was first talked about in 2009, with a 2012-2013 target. As of a Panasonic tech roadmap dated July 2012, it isn’t even in the pilot planning yet.
And Tesla likely accounts for <5%, if not less than 1% of 18650 cell production. There are cell lines from Panasonic/Sanyo that produce several hundred million cells per year per type. There are at least 20 different cell lines from Panasonic alone, not even counting another 20 or so from Samsung and LG, plus a host of other vendors producing 18650s.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
"The reason W-hr/kg is important..."
"And $/kWh actually does matter..."
Both are irrelevant unless we are talking about true battery pack Wh/kg or $/kWh. Manufacturers quote cell level specific energies and costs, as opposed to true pack costs. Tesla may be using a cell ~250Wh/kg, but their pack is much closer to 150Wh/kg. The cell-level costs might be ~$200/kWh, but the pack is probably closer to ~$400 or $500/kWh. When people talk real battery costs, I will be happy to give some level of confirmation to correctness. Until then, I am happy to point out the flaws in PR campaigns.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
"Just asking, but do you think Boeing might end up with an 18650 solution for their battery in order to satisfy the FAA reliability / safety concerns?"
Short answer: No.
Long(er) Answer: Form factor is pretty irrelevant when discussing safety. The FAA puts all Li-ion flavors and form factors in the same group of "Li-ion." They have had problems with batteries across a number of different chemistries and form factors, and right now are skittish about all of them. Actually, the FAA is a little behind the times on that bandwagon. The Navy has been like that for 4+ years now.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
I had a look at the links you provided over the weekend. A couple of comments:
1) The first link does show a module that can handle 2C charge and discharge rates. That is due to the cell choice that they have listed however. The EAX is a lower capacity design (~2Ah), with a different chemistry and electrode mechanical design than the NCR cells used by Tesla.
2) For the second link, the cycle life was estimated.
3) The third link is 3 years old. I had seen it previously. To be honest, most pack construction with 18650s is virtually the same. Only the outer box usually changes.
These are all feasible, although in the second link, I would crucify the PR and/or bizdev department(s) for putting the 5000 cycles in there. I have never said that cells will not improve. What I have consistently said was that they improve slowly and on the fringes more often than some massive breakthrough. More than anything, a judicious cell choice could eliminate the need for some improvements.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
“Clearly you know nothing about how the Tesla works.”
That might be true, but I find it more likely that you know nothing about how battery chemistry works, and the strategies to improve life. I am well away aware of the SOC that a Tesla battery charges to. Other than I know that it isn’t to 100% SOC, anyone with a calculator can figure out the nominal cell voltage used to calculated the kWh rating, which is lower than the manufacturers reported nominal cell voltage.
That being said, even lowering the end of charge voltage still doesn’t prevent permanent capacity loss. Just leaving a cell on a shelf and not touching it will still cause permanent capacity loss over time. It is an unavoidable fact of Li-ion that this occurs. The only way that I have seen to mitigate that greatly is to store a battery and/or cells at virtually 0% SOC at <10degC. Even then one could see 1 or 2% permanent capacity loss per year.
As for Tesla being the best in the biz, that is just laughable. There are a number of companies that have been using commercial 18650s for a variety of applications infinitely more challenging than EVs, particularly space and aviation applications. These are things that have much greater environmental requirements, need multiple years of real data to support their usage, and have to handle much more extreme current and temperature conditions. Then again, you can just continue to believe what you believe…
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
Many thanks. I don't know if I am amused or horrified by the way people treat higher Wh/kg cells as "better" when it just means higher Wh/kg.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
Maybe a better term would have been "mean specific energy (Wh/kg) across all cell types." Making a higher specific energy cell does not make it better, only higher specific energy. In order to build the best battery, the right cell has to be chosen for the application, which is not always the highest specific energy cell.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
Both kW and kWh are a function of voltage as well. As a result, the current might be lower at high SOC, but will be significantly greater at low SOC. Charge doesn’t bother me too much, although at higher rates the heat generated can go up rather quickly. A 2C rate is achievable now on most cells. That being said, charging at 2C is a good way to shorten life unless your cell is designed for that.
PHEV applications are harder than pure EV applications. That being said, the big 3 and the DOE are writing the EV test manual as they go along. Both the requirements and the test procedures are evolving as things progress.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
As for your assessment of cycle life, your lack of understanding of how the batteries will be cycled is appalling. Even if the pack is being cycled down 20% every day, the pack is going to be charged up nearly every night, at least that is what the true believers try and tell me. While shallow cycling is good for extending life, storage at a high state of charge is not. Then again, no one is going to have a simple constant current charge and constant current discharge. The charge might be simple, but the discharge will be anything but. This is the portion that will significantly tax the battery and will age it quicker than most people realize. That doesn’t even get into the storage effects, but that is a different story altogether.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
As for the Panasonic press release, as of the cell technology roadmap from Panasonic that I have seen dated July 2012, there is no 4.0Ah cell on the market, and none scheduled for pilot production through the end of 2014.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
Your analysis of the changes in the coatings is correct in layman’s terms, which I mean as a complement. You would be surprised about how hard it is to get some people to understand even that much. There are a host of factors that are in play, but that is a good summary.
That being said, if you increase the anode capacity through a material change, your cell capacity does not go up unless you add more material on the positive. Typically cells have excess capacity on the anode for safety reasons. By adding to that capacity, the margin gets greater, but it is still the cathode that dictates the cell capacity. Because of this, one would have to make the positive material coating thicker, which is going to harm your power capabilities even more. While I agree that the particles themselves and how they are fabricated can help, that can only help so much.
I don’t know what type of rates would be needed. But I can tell you that at a cell level, the 18650s used by Tesla would be extremely taxed during a 2C discharge, let alone 4C (even for 10s), and forget about charging at a 2C rate. That is why I feel that they need so many cells. It just isn’t a range issue, but the cells themselves have a hard time handling the current demands. As a result they add enough to bring the charge and discharge rates to a level that can more easily handled by the cells.
There are barriers that preclude a cell like Envia or CALiB, namely the fact that to make a high Wh/kg cell you typically have to make it a high energy cell. That means that the coatings on the current collectors are very thick and there is little electrode surface area. This cuts the power capability off at the knees. It is not uncommon for similar chemistries (sometimes even identical) to have vastly different Wh/kg based solely off of being either designed for power or for energy.
Tesla's Obscenely Expensive Cure For Range Anxiety [View article]
"Don't you just hate battery science where the gains you pick up on one hand are offset by sacrifices on the other?"
Some days, even I hate it.