Samsung Galaxy Note 7 - Official Investigation Finds, Two Reasons Behind Explosions

Samsung, after several months of in-depth investigations and finely announced the reasons behind the explosions of Note7 

Based on detailed analysis of the affected batteries, both Battery A from the 1st recall and Battery B from the 2nd recall, we identified separate factors that originated in and were specific to the two different batteries.                -Samsung official  

     

                                                                                              

Battery A assessment

I. There may be multiple contributing factors relating to battery assembly/manufacturing and design that when combined led to the failure of the Note 7 in the field

A. Battery assembly/manufacturing: 

• Deformation at the upper corners 

B. Battery design: 

• Thinner separator could lead to poorer protection and reduced tolerance to manufacturing defects 

• Higher energy density in general can exacerbate the severity of a battery failure 

II. One major failure mechanism is likely: A combination of deformation at the upper corners + thin separator + repeating mechanical stresses due to cycling, causing higher possibility of separator damage leading to an ISC between aluminum and copper foil at the corner

III. Additional investigation is needed to understand the root-cause of the deformations at the upper corners.

Battery B assessment

I. No evidence of device-level compatibility issues that may have contributed to the failure of the Note 7 in the field

II. There may be multiple contributing factors relating to production quality and battery design that when combined led to the failure of the Note 7 in the field

A. Production quality:
• Missing insulation tape on tab could result in higher possibility of ISC
• Bigger protrusion of welding points in tab could lead to higher possibility of separator puncture
• Misalignment of insulation tape and/or tab could bring more risk of ISC

B. Battery design:
• Thinner separator could lead to poorer protection and reduced tolerance to manufacturing defects
• Higher energy density in general can exacerbate the severity of a battery failure

III. One major failure mechanism for field incidents is likely: The combination of (1) missing insulation tape + (2) sharp edged protrusions on tab + (3) thin separator, all leading to a high possibility of an ISC between cathode tab and anode, subsequently resulting in heating and fire

IV. Further analysis is needed to understand the root-cause of the damage to the edge/corner of the battery which results in ISC at that location.

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