So, why are these batteries in the Chevy Bolt ( 20170-2019 ) models more prone to thermal decomposition                                 ( Fire/Explosion) than other batteries?

 

  They are "High Voltage Batteries" and their voltage output is higher than other types of Lithium-Ion Batteries.  In contrast, Lithium Titanate Batteries are "Low Voltage Batteries" with a lower voltage output and a lower energy and power density..... but a much, much better safety profile and less propensity to undergo thermal decomposition, however they are more dense and so are not suitable for use in passenger EV automobiles. 

 

They are used in Electric Buses.  They do not contain Cobalt.  Anytime a battery contains Cobalt it increases its risk for thermal decomposition.  Size matters, but so does composition!!!   Especially when you are looking at "Lithium Ion Batteries", a garbage bag term that incorporates a wide variety of different battery chemistries with a wide variety of performance and safety profiles that are quite divergent from each other.  To lump all "Lithium Ion Batteries" under one name is like lumping all languages under the general term of "language". 

 

  With language and with Lithium Ion Batteries there are significant differences from one example to another as to type..... one size does NOT fit all!!

 

 

An August GTM article about the 2019 Arizona Public Service battery fire involving NMC batteries from LG Chemical does draw focus to the NMC type of Lithium-Ion battery and its increased risk of thermal decomposition vs, for instance, the LFP (Lithium Iron Phosphate) type of Lithium-Ion battery.  LG Chemicals, a Korean battery manufacturer, also has supplied NMC batteries to GM for the 2017-2019 Chevy Bolt that has now been the focus of battery fires when it is fully recharged to 100%.  This all illustrates that the type of Lithium-Ion Battery is extremely important and that different types of Lithium Ion Batteries have different safety profiles and different performance characteristics.  The LG Chem batteries using NMC ( Nickel, Manganese, Cobalt Oxide ) are more prone to thermal decomposition and thermal runaway, i.e. to fire and even explosion vulnerability as opposed to LFP Lithium-Ion Batteries, which do not contain cobalt.

 

"But the APS fire strikingly illustrated the explosive potential of those NMC batteries. Another chemistry, lithium-ferrous-phosphate or LFP, has gained ground due to a reputation for safety and lower costs, although it packs less energy density.

“The safety question has been one of several reasons why the energy storage market has given the Chinese LFP vendors a harder look,” said Daniel Finn-Foley, energy storage director at Wood Mackenzie. “As they’ve given them a second look, they’re liking what they see, and it’s moving LFP vendors toward a market-leading position.”

Indeed, NMC’s market share for grid storage has already peaked and will continue to decline as LFP gains ground, according to new research from Wood Mackenzie. LFP supplied just 10 percent of the market in 2015, but its share will reach 30 percent by 2030."

https://batteryuniversity.com/learn/article/bu_216_summary_table_of_lithium_based_batteries
https://batteryuniversity.com/learn/article/secondary_batteries
NMC batteries:  

"Thermal runaway

210°C (410°F) typical. High charge promotes thermal runaway"

Above quote is taken from the following article: