Monday, November 28, 2011

What makes lithium ion batteries to swell ?



Well, today i will answer a very common question that people ask, probably because of their phones are powered by lithium ion batteries.
First a quote from a professor of Materials Chemistry at MIT who is an expert in advanced battery technologies, here is what he said;
“I’ve seen lithium-ion batteries that are so swollen you’d be tempted to prick them with a pin,” says Don Sadoway. The problem has to do with the chemistry of lithium ion batteries, that is how the batteries were manufactured, which reacts unfavorably to overcharging.
“There are strict limits on how much current can be put through a lithium-ion cell,” explains Sadoway. “During normal charging, you never see metallic lithium, which is inherently unstable. But during overcharging, the lithium builds up faster than it can dissipate. The result is that metallic lithium plates up on the anode. At the same time, the cathode becomes an oxidizing agent and loses stability.”
The big danger, says Sadoway, is that this chemical reaction is accompanied by heat because it is exothermic in nature and-- as every engineer knows -- warm gas occupies more space, which is what causes the battery to swell.
The bulging battery becomes a ticking bomb because if that battery is still kept on overcharge, it will get to a stage whereby the gases become so much that they cause the batteries to explode; in some cases that has happened.
As a safeguard, more recently manufactured batteries normally come with inbuilt  internal charging circuits, using charger ICs and vendor-supplied reference designs. Instead of controlling the charging directly like before, these internal battery pack circuits prevent an overcharge. And if they detect a limit, they shut down the battery.
Design of these circuits can be tricky, as consumers can accidentally connect the wrong power adaptor to a device. So engineers need to plan for almost any contingency.
And if they’ve been designing for nickel-metal-hydride batteries in the past, they need to throw the existing charger out as it will be incompatible with the new design. New phones nowadays inform the user when the battery is fully charged.....
I hope that has answered the question so when next your battery is full, disconnect it immediately to avoid overcharging....


3 comments:

  1. wow...thanks for the info

    ReplyDelete
  2. printf("now dats what i've been looking 4\n");

    ReplyDelete