Hi Bourgeoisdude,
My goal for the article is mostly to go over very lightly the basic concepts and technical terms (like V, and mAh, etc) and to crack open the black box (literally) and see what ticks underneath with one cocked at the exploding battery phenonenon. It's really by no means an deep explanation or technical analysis. It's an article in the vein of "What goes on beneath that manhole cover?" and while you can imagine all kinds of alligators and victorian pipeworks, it helps to shine a flashlight down there, snap some pictures and not so much discuss city blueprints as report what is seen and heard.
There were some parts that I've seen and experienced that I didn't go over. But if you want to hear more, just let me know.
As for NiMH vs. Li-ion--most new production laptops have moved to the Li-Ion packs. Most notebooks are designed to maximize battery life. And with the cost of designing custom battery packs being what they are (high!), the initial incremental cost of deploying Lithium-ion vs. NiMH is the same. Unless the battery pack is a standard mass produced part, NiMH gets cheaper more dramatically during mass production. So the manufacturer's rationale is often to deploy with a Lithium-Ion battery pack, and if you only ever sell a few thousand of that model laptop, a NiMH custom battery would not have been cheaper, and in the worst case, the battery life would have been pretty good. And furthermore, whoever got fired for choosing Sony?
Specifically, Sony admitted to metallic contamination of the Lithium-ion chemicals. If a metallic impurity (such as random particles of metal) gets inside the battery cell, chances are, nothing happens. The probability that these random particles randomly locate themselves into the formation similar to a wire, or a configuration that allows a short circuit to occur inside the cell is astronomically small. In fact, it might only ever occur to 5 in a million, or something small like that. That looks a lot like 0% probability if you round it up. But that was what happened. Somehow, random cells would short themselves out and do a runaway meltdown.
Basically, if you connect the + and the - side of a Lithium-ion cell, you better be far away, and fast. Luckily, the protective circuitry in between the + and the - prevents that from occuring. In the case of the Sony recall, it became possible for the + and - of an individual cell to *internally* get stuck together, and then, there is nothing in between to stop that reaction from getting away.
Thanks,
Calvin
Nearly all off the shelf rechargables are NiMH for reasons of safety, but, increasingly, NiMH is becoming pretty darn competitive with Li-ion.