How do they get more mAhs into those batteries?

Ever wonder....?

Take a few apart, weight them, uses a micrometer, etc.

Seriously, its not a good idea to take them apart unless you know what you are doing and have a method to dispose of the hazardous materials safely (Your garbage can is NOT disposing of them safely).

But the easy way is to talk to some of the folks at the R&D departments of the major battery companies.

My understanding is that the major improvements in the beginning was the density of the metallic film in the batteries. But that soon peaked, hence the 2000mAh batteries.

To get past the 2000mAh barrier, some packed a few extra turns of foil in, and the 2100 and 2300 mAh batteries were born, but with some that also came with a slight increase in diameter.

AS of late......i.e. the 2500mAh and above batteries. Some are fine tuning their metallic film alloys and/or cathode anode structures, but MOST are actually using a thinner seperator material (i.e. Energizer) so they can get a few 'more' turns of foil in there. Hence the high self discharge rates that we are seeing in the 2500 and above batteries.

figures, thin everything till it fails, use "better" materials that can be thinnner, change the properties of the anode and cathode, make it a bit fatter, trying to stay within spec.

dont forget it also becomming even more prone to damage with thin stuff, a drop or dent. or even more imporatant that guy driving the forklift into the whole pallett of them the UPS guy playing basketpackage with your shipment, and the guy who drops everything off the shelfs of the store.

Hello Turak,

In addition, they "adjust" the ration of positive to negative electrode. The negative electrode is larger than the positive one. This gives protection against damage from over charging and over discharging, but you loose some capacity. If you move toward equalizing the electrodes, you gain capacity, but loose the ability of the cell to recover from an over charged or over discharged condition.

All in all, it seems that the high capacity cells are more fragile.

Tom

SilverFox said:

Hello Turak,

In addition, they "adjust" the ration of positive to negative electrode. The negative electrode is larger than the positive one. This gives protection against damage from over charging and over discharging, but you loose some capacity. If you move toward equalizing the electrodes, you gain capacity, but loose the ability of the cell to recover from an over charged or over discharged condition.

All in all, it seems that the high capacity cells are more fragile.

Tom

Click to expand...

Exactly. Higher capacity cells utilize thinner separators (easier to damage by large crystals) and have a lower cathode/anode mass ratio. That's why if you charge a 2500 mAh cell at 1C it would run 3-5 degrees C hotter than, say 1700 mAh one. Lower capacity cells have larger reserve in anode material that recombines the gasses emitted by the cathode during overcharge, thus running at lower pressures and temperatures.

You mean they're *NOT* using magic fairy dust?!

Hello NiOOH,

I haven't noticed a temperature increase when charging 2500, 2600, and 2700 mAh cells at 1C. As a matter of fact, there is very little temperature difference between charging those cells and cells of 1800, 2000, and 2200 mAh capacity. My Schulze charger does a very good job and the cells come off warm, but not hot.

However, this discussion may be only academic because there are very few consumer chargers that are capable of charging higher capacity cells at 1C.

Tom

There are quite a few consumer chargers that can charge even faster. I can think of all 15 and 30 min chargers from Energizer, Duracell, Sanyo, Ansmann, Varta, Sony, GP and possibly others. You can run an experiment using one of these charging a Sanyo 2500 or 2700 mAh cell and compare to a Sanyo 1700 mAh one (these are excellent BTW despite thir low capacity, very long service life, relatively low self discharge and low IR) and report the results. The effect is already present if you use 1C for the lower capacity one, i.e you can use 1700 mA current on the c9000 for instance. Even though as a C-rate it will belower for the high capacity cell the temperature profile will be different and the temperature will be higher towards the end of charge. On a secon thought the newer version of the c9000 is not the best tool for this, since it terminates quite conservatively, so you may not see the dT at the very end of charge.

these tighter and tighter film windings also increase the risk of internal short circuits in the battery, which is why I would go with high quality LG cells, especially when unprotected.

Hello NiOOH,

I agree. Real fast charging (charging at a rate greater than 1C) does heat the cells up. If you require "hot off the charger" performance, 30 minute (2C) or 15 minute (4C) charging will often give you that extra little bit of performance you are after. Cycle life is reduced when exceeding 1C charging, but some people find 100 - 150 cycles adequate for their needs.

As I mentioned earlier, there are very few consumer chargers that allow for 1C charging of the higher capacity cells. For example, how many chargers are you aware of that can charge at 2.5 amps to do a 1C charge on a 2500 mAh cell?

Tom

Yes, it is true that the so-called 1 hour chargers are most often rated at 2A, but that was not my point. My point was that the old school AA NiMH cells (<2Ah) have more gas recombination capacity and run cooler during fast charging as a result. As I said, you can test this with any -dV charger that runs around 2A charging current, even though in the case of <2Ah cell the charging current will actually exceed 1C, while in the case of a 2.5 Ah cell it will be below 1C. Just try it. I've done it and the results, at least with Sanyo and GP cells speak for themselves. The newer, high capacity cells run 2-4 degrees Celsius hotter towards the end of the charge compared to to the older lower capacity cells. This was my point.

Turak said:

AS of late......i.e. the 2500mAh and above batteries. Some are fine tuning their metallic film alloys and/or cathode anode structures, but MOST are actually using a thinner seperator material (i.e. Energizer) so they can get a few 'more' turns of foil in there. Hence the high self discharge rates that we are seeing in the 2500 and above batteries.

Click to expand...

:mecry:My Sanyo 2700 have a high self discharge rate, I should have done a little more reading before buying them. Are Eneloops the best way to go, or lower capacity low self discharge cells? I'm only drawing 3-4A with a WA1111.