Battery Cell Technology
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scrambler
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21700 cells are nothing new, and are already used in some e-bike packs.
Their energy density is not much better than the 18650 at this point (about 2%) but being a bit bigger they can sometimes allow to fit more cell volumes in a specific space. Conversely, if the space is limited, being bigger can sometimes play in their disfavor as you may have to use significantly less cells to fit in the space.
So the potential gain in capacity is highly dependent on the space available. For example, a lot of packs arrange the cells perpendicular to the bike, so the packs are limited to 65mm of cells in the pack width direction. These cells are 71mm long and so a similar pack will be 9% wider with them.
Now there are also some potential advantages on the electric specs depending what the pack priorities are.
last, there is a promise that within 5 years, they could provide 20% more energy density. If that materializes, then they would be a definite plus.
Their energy density is not much better than the 18650 at this point (about 2%) but being a bit bigger they can sometimes allow to fit more cell volumes in a specific space. Conversely, if the space is limited, being bigger can sometimes play in their disfavor as you may have to use significantly less cells to fit in the space.
So the potential gain in capacity is highly dependent on the space available. For example, a lot of packs arrange the cells perpendicular to the bike, so the packs are limited to 65mm of cells in the pack width direction. These cells are 71mm long and so a similar pack will be 9% wider with them.
Now there are also some potential advantages on the electric specs depending what the pack priorities are.
last, there is a promise that within 5 years, they could provide 20% more energy density. If that materializes, then they would be a definite plus.
Ebiker33
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Their energy density is not much better than the 18650 at this point (about 2%)
I can tell you from the cordless tool market( which I deal with for a living) the 21700 cells are knocking it out of the park for all brands, everybody who uses them says they are better.
My favorite response from a customer that switched over said "The tool worked great before, no issues with power or run time, but the new battery was like finding a whole new gear for the same tool" that within the same voltage which was 18V, just a cell type change out from 18650 to 21700.
The 21700 is a bigger cell, physically. Most 18 volt stuff has been 5s2p stuff or 4ahr. That is a 2,000 mah 18650 cell. They don't make 21700 cells that low of density and you can get a 3,500 mah 18650 all day long and have been able to for 5 years.. Those 2,000 mah cells used for power drills are also fairly low in amperage delivery compared to any 21700 or newer 18650 cell. As I have said before, battery hype is huge and real battery advancements are painfully slow.
scrambler
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Yes, there are wide differences between cells of the same type like the 18650, so I would be cautious drawing any comparison without very specific technical information on each cell used in each case, as well as power requirement of the equipment using it.
I do think 21700 have things to offer, but it is not simply black and white
I do think 21700 have things to offer, but it is not simply black and white
Ebiker33
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I disagree, because I have been selling power tool batteries since the late 80's, they started with basic 7.2volt Makita in Ni-Cad, then they went to 9.6V then 12V then 14V eventually the industry settled on 18V, in between they ran
Nickel–metal hydride in all voltages, then came Lithium in 1.5V, slowly they began to move up the amp hours as the tools needed them. The latest is Dewalts dual voltage battery they call it flexvolt it runs it 60v or 20V(18) a marketing thing. But if you run at 60V your amp hours drops in half to 6 from 12.
Sure it took time but the advancements have been happening year after year, each company trying pass the other for bragging rights.
Check it out.
Dewalt Batteries
Also the new Milwaukee MX FUEL
MX FUEL runs at 72V Nominal (80V Max).
A real game changer, they have some really large tools for these like a 14" cut off that used to be gas
14" Saw
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harryS
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18650 is 18mm diameter and 65mm high. 21700 is only 3 mm wider and 5 mm longer, but that's 47% more volume. If we take away the metal case, you still get a lot more volume for the innards.
I just bought a 48V battery using 21700 generic chinese cells. They advertise it as 10 aH. That's small, but I only need it as an aux pack. If it comes off as 8AH, I'll be quite happy with it,
I just bought a 48V battery using 21700 generic chinese cells. They advertise it as 10 aH. That's small, but I only need it as an aux pack. If it comes off as 8AH, I'll be quite happy with it,
You can disagree all you want. What you are showing me is bigger batteries manufactured with the same technology, not new technology.
In post number 4 you said "that within the same voltage which was 18V, just a cell type change out from 18650 to 21700." Then you link to a higher voltage and larger capacity battery. Same old Same old. Manufacturing changes to the same old technology.
New technology would give you more power density for the same weight. Not more weight for a bigger battery. The problem with current technology on e bikes is weight. E bikes are limited range and handling because of this. Bicycle components just won't carry all that weight. You are into needing motorcycle parts and out of bicycles. I am pushing the limits at 49 amp hours but my bike is dog snot heavy at 80 pounds.
You will have to explain this one to me. You triple the voltage and only half the amp hours. That is a new one for me. Last I knew, Ohm's law is still on the books.
That has to be a 6P-3S Pack of 21700, 4,000 mah cells. That is more juice and more weight. At least the power density is much higher as they have moved to the current 15+ year old technology. E bikes generally have higher power density packs than this newer Dewalt battery.
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Ebiker33
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I guess our perception of what is new, is different then, we have different compositions and sizes and smart batteries with tech chips in them that communicate with both the chargers and tools which also now have chips in them too. I mentioned only 3 different compositions, but there is way more than that now, see chart.
If you think all these are the same, then I will respectfully agree to disagree.
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Your chart is deceiving and actually missing one. Your chart shows over a 6 fold increase in the last 100 years. That does not actually happen in practice. Go weight one of your new batteries and divide the total Wh by the weight and see where you are on the chart. Now do the same for a lead acid car battery. You will find the chart has a bit of built in bias going on. What is missing is Lithium Sulfur. Its been around since the late 2000's and more recently commercially viable in light weight high power applications but still suffers from low charge cycles. Max out there is pushing 400 Wh/Kg NCA has never been really commercially viable at the power density. Lithium Sulfur is promising after 15 years of development.
The problem with power density is also one of shock resistance (a reason your power tool batteries are older proven technology in a new wrapper) and charge cycles.
If you haven't figured it out, battery liars are a sore spot with me. They should be with you too. The extreme hype is because of the competition for grant money to study batteries, the heart of the sore spot with me. The waste of money on dead ends is mind boggling.
tomjasz
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onlineaddy
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If it were only that easy. You have to put it in a case and secure it with other 21700 cells. You may or may not retain that 6% in the end
scrambler
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Again devil is in the details.
Highest capacity 18650 cells are 3500mAh
Samsung 35E: 18.55mm x 65.25mm => volume of 17,634 mm3
3500 mAh => 0.1985 mAh / mm3
Highest capacity 21700 cells are 5000mAh
Samsung 50E: 21.1mm x 70.7 mm = volume of 24,722 mm3
5000 mAh => 0.2023 mAh / mm3
Both cells having the same Voltage, that is only 2% more energy density than the 18650 35E
But as mentioned previously this is only one little parameter in the many forming the equation of a specific battery requirements
Highest capacity 18650 cells are 3500mAh
Samsung 35E: 18.55mm x 65.25mm => volume of 17,634 mm3
3500 mAh => 0.1985 mAh / mm3
Highest capacity 21700 cells are 5000mAh
Samsung 50E: 21.1mm x 70.7 mm = volume of 24,722 mm3
5000 mAh => 0.2023 mAh / mm3
Both cells having the same Voltage, that is only 2% more energy density than the 18650 35E
But as mentioned previously this is only one little parameter in the many forming the equation of a specific battery requirements
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onlineaddy
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Right; that study is of cell (and not battery) comparison.
So far the higher the energy density, the more fragile is the cell and the more you have to protect it from shock loads. I am sure even so that shock loads reduce the number of cycles on high density cells. My batteries are all 18650, 3,500mah. Energy density is 285 Wh/Kg. I went and weighed one battery. 8.1lb for 720 Wh. That is an energy density of 196 Wh per Kg plus the battery cradle. Not bad for technology that actually works until you compare it to gasoline.
tomjasz
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I’m sorry but it become much ado about nothing and pretty much mental masturbation. The use of the word “new” and the subsequent correction adds nothing to the discussion. The reality is..we’re not what drives the market, not just yet. (Hoping)
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