ITEM: Now that Samsung has confirmed that faulty batteries were the cause of Galaxy Note 7s setting themselves on fire, the company has said it will be looking at ways to prevent future incidents. In which case I’d like to direct their attention to this paper from Stanford University researchers who have designed a lithium-ion battery with a built-in fire-extinguisher.
The “extinguisher” is a shell containing a flame-retardant chemical compound called triphenyl phosphate (TPP). The shell sits in the electrolyte fluid in the battery. When the temperature of the battery exceeds 150º Celsius, the shell melts and releases the TPP. Battery fires were extinguished in less than half a second in tests.
The paper, published by Science Advances, explains that safety problems remain a big issue for batteries as energy densities continue to increase, and this is “hindering further practical applications of the next generation of high-energy batteries.”
This isn’t news, of course, and battery R&D has been working on the problem for a long time. Proposed solutions include: “replacing the existing flammable electrolyte with nonflammable ones or using flame-retardant separators, detecting the dendrite via a smart separator for early warning, coating the separator with a ceramic layer, thermal-switching the current collector, and autonomic shutdown of lithium-ion batteries using thermoresponsive microspheres, among others.”
The problem, the paper says, is that these solutions only reduce the risk of fire rather than eliminate it, and in any case, each solution typically requires a sacrifice in battery performance.
Even the idea of adding flame-retardant additives to the electrolytes has been tried before, the paper says, but previous solutions require a sufficient amount of flame-retardant chemicals – and the more you put in, the worse your battery performance.
And so (from the abstract):
We have fabricated a novel “smart” nonwoven electrospun separator with thermal-triggered flame-retardant properties for lithium-ion batteries. The encapsulation of a flame retardant inside a protective polymer shell has prevented direct dissolution of the retardant agent into the electrolyte, which would otherwise have negative effects on battery performance. During thermal runaway of the lithium-ion battery, the protective polymer shell would melt, triggered by the increased temperature, and the flame retardant would be released, thus effectively suppressing the combustion of the highly flammable electrolytes.
And there you go.
The researchers add that this idea can be applied outside of smartphones:
It is anticipated that this type of smart separator can be used in other high-energy storage devices, which may encounter thermal runaway safety issues. In the future, mechanical (nail penetration test or crush test) or electrical abuse (overcharge or overdischarge) tests involving large-format cells will be needed for further practical applications.
It’s too soon to say if and/or when this idea will be commercially adopted, but battery makers are in desperate need of better ideas to improve battery technology, IHS senior analyst Ian Fogg told the BBC:
“There is enormous pressure to improve battery tech. It’s one of the areas that’s holding back mobile devices and a range of other products,” he told the BBC.
“Manufacturers have been balancing out consumer demand for longer-lived batteries, and more powerful devices with better graphics and larger more detailed displays, with the sophistication of battery tech.
“It’s very difficult to push up the capacity of batteries and there is always a risk that a battery in any device could fail.”