This material consists of electrochemically stable graphene-coated spiky nickel nanoparticles mixed in a polymer matrix with a high thermal expansion coefficient. The as-fabricated polymer composite films show high electrical conductivity of up to 50 S cm−1 at room temperature. Conductivity decreases within one second by seven to eight orders of magnitude on reaching the transition temperature and spontaneously recovers at room temperature. This approach offers 103–104 times higher sensitivity to temperature changes than previous switching devices, the researchers said in an open-access paper published in the new journal Nature Energy.
To ensure good performance, LIBs [lithium-ion batteries] generally operate within a limited range of current density, voltage and temperature. However, at an abnormal temperature (for example, >150 ∘C), typically caused by shorting, overcharging or other abuse conditions, a series of exothermic reactions can be initiated and rapidly propagate to further increase the internal cell temperature and pressure, which results in catastrophic battery explosion and fire. Commercial LIBs are equipped with external pressure release vents and positive temperature coefficient (PTC) resistors on their cases to prevent overpressure and overheating. However, pressure and temperature increases inside cells can occur at much higher speeds than can be detected by these external devices. Thus, internal safety strategies are more effective in preventing thermal runaway.—Chen et al.
Read more at Stanford Team Develops Thermoresponsive Film Allowing Fast and Reversible Shutdown of Li-ion Batteries to Prevent Thermal Runaway
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