Sunder said:
Apparently delamination doesn't occur till about 4.35v, and you can tell how badly it has occurred by doing a few cycles through and seeing how quickly they become unbalanced. Because delamination is a physical process, the chance of it happeninging equally to a cell at the edge of a pack and at the centre is unlikely.
these packs kept close to perfect balance prior to this. if they fall out of balance in the next 3-5 cycles, I will probably throw them out. if they don't, apparently they're still 'safe
Im afraid you got some bad info. Nothing is laminated other than the edges of the foil pouch getting thermal-sealed. The layers just sit next to eachother in a stack, alternating aluminum and copper foil layers coated with the anode and cathode coatings, and the seperator layer wound between them like a fan.
At high voltages, two things happen. The physical volumetric change in the cathode is greater than the structure was designed to intercalate, and it breaks off chunks that no longer have a current path as a result.
The second effect is the decomposition of the solvents through electrolysis. This evolves hydrogen and some other gasses, which cause the cell to inflate (because pouches don't have vents like prismatics or cylindricals). As the pouch inflates with this gas, it takes the clamping load off the layers in the stack, and they develop gaps with gas pockets between them, and since lithium ions and electrons can't move through gas, bur rather only where the liquid solvent is wetting a path, then these areas become inactive, and the internal resistance climbs, lowering the C-rate and reducing capacity (because the areas with gas pockets can't be accessed to store and release charge anymore).
You can largely fix the gassing problem with the pin-prick method pioneered by AussieJester. (NOTE: it could explode in a fireball in your face, or just fix your pack
Never know)
The damage to the cathode structure is immediate though, and your cells will always have reduced capacity after a major over-charge.
For races where I know I need as much capacity as possible, I choose to over-charge to 4.35 or 4.4v sometimes with my Nano-Tech packs, it makes a 5Ah cell hold over 7Ah, but at the steep cost of taking many hundreds of lifecycles off the cells, and accepting that it will cause a permanent reduction in capacity afterwards.
Remember to make sure your insurance is paid up and your video camera is running.
