http://www.androidauthority.com/samsung-finally-tells-us-galaxy-note-7-phones-catching-fire-744538/
In a nutshell, the batteries were poop!
The first batch, there was a design flaw and in the second "abnormally high welding bars formed during the ultra-sonic welding process to attach the positive tab. Due to the high-welding bars, penetration of the insulation tape and the separator resulted in direct contact with the negative electrode. In addition, we found a number of batteries that were missing the insulation tape." (so tl;dr, a manufacturing defect).
In a nutshell, the batteries were poop!
The first batch, there was a design flaw and in the second "abnormally high welding bars formed during the ultra-sonic welding process to attach the positive tab. Due to the high-welding bars, penetration of the insulation tape and the separator resulted in direct contact with the negative electrode. In addition, we found a number of batteries that were missing the insulation tape." (so tl;dr, a manufacturing defect).
