I worked some on batteries back in the 80s.  Common cause of failure is separator breakdown.  In those days, you could get high-temperature NiCd with a polypropylene separator, or consumer versions with nylon.  

Earliest implanted medical Li batteries were LiI, to my knowledge.  I think the 'separator' formed from reaction of lithium and iodine.  Power output, via the low-ionic-conductivity separator, as opposed to the relatively high-conductivity fabric-liquid electrolyte systems, was low. But there was no chance of the batteries shorting.  
Louis Hart

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tan Geok Ang
Sent: Wednesday, October 12, 2016 8:11 PM
To: [log in to unmask]
Subject: Re: [TN] Samsung Galaxy Note7

Personally, I noticed that I can see and feel the "shape" of the battery in iphone as compared to Samsung after about 1.5 years. This might means the casing material "play" a big role to cater for battery expansion/heat. I didn't go in detail... 

-----Original Message-----
From: Tan Geok Ang
Sent: Thursday, 13 October 2016 8:05 AM
To: [log in to unmask]
Subject: RE: [TN] Samsung Galaxy Note7

My takes is that the battery heated-up due to activities (charging, running apps, etc.), which resulted in battery expansion but it is between casings/items thus the "expansion force" is forced inwards, towards the layer of "insulator" between the cathode and anode, resulted breakdown of the layer. Hence, this problem is not a result of how many percent of power the battery is at. Just my opinion.