Why we re-visit this issue? Because it is highly related to the recent fire incident of the Korean energy storage systems (ESS).
Boeing 787 Battery Systems got fire in 2013
In 2013, the first year of service for the Boeing 787 Dreamliner, a widebody jet airliner, at least four aircraft suffered from electrical system problems stemming from its lithium-ion batteries.
The Boeing 787 Lithium-ion Battery System
8 cells of LVP65 Lithium Cobalt Oxide batteries are connecting in series to provide the required 32V 150A airplane power-up.
LVP65 can deliver up to 5C or 325A continuous current without any problem. The full specification of LVP65
Cells in a second lithium-ion battery on a Boeing 787 Dreamliner forced to make an emergency landing in Japan last month showed slight swelling, a Japan Transport Safety Board official.
One year later, no issues for Boeing 787 battery redesign
Flightglobal.com January 2014
The revised battery design increased the spacing between each of the eight internal cells, added ceramic heat shields between each cell, enclosed the battery in a stainless steel box and installed plumbing to vent any exhaust offboard.
If any individual cell begins to overheat, the new design should prevent the higher temperature from spreading to other cells in a condition called a thermal runaway.
Eight months later, the new battery installation has proven reliable so far.
The True Cause of the Problem
Lithium Cobalt Oxide batteries are high energy density battery cells. In principle, the battery cell can handle 5C continuous discharge current with sufficient ventilation of heat.
When 8 batteries cells were packed in a close environment discharging around 2.5C current, they will dissipate a lot of heat (P=I2R).
Power dissipation is equal to the square of discharge current multiply with the internal resistance of the battery cell. (P=I2R).
When the batteries are heated up, the internal resistance will increase and the swelling on the second battery cell is a phenomenon of an increase in internal resistance.
An increase in internal resistance will increase heat dissipation, which is called thermal runaway, eventually leading to the self-burning of battery cells.
Conclusion
The revised battery system design with more space and heat shields provide good ventilation of heat has concluded our findings.
Most of the electronics designers have little knowledge about the power dissipation of batteries and they simply based on the specification given by the manufacturers.
If safety is the utmost concern of a system, Lithium iron phosphate (LFP) batteries, containing Iron acting as an internal heatsink, are far safer than Lithium polymer type, high energy density, batteries such as LiCoO2, NCM, NMC, NCA.
The author has over 30 years of experience in the Lithium-ion battery industry from the laptop application, electric vehicle, to large energy storage.
To find LFP type Lithium-ion batteries, please visit everspring.net