Build a safer battery: Spectroscopic assistance

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  • Published: Jan 8, 2016
  • Author: David Bradley
  • Channels: Atomic
thumbnail image: Build a safer battery: Spectroscopic assistance

Current batteries can explode

Stanford researchers have developed a thin polyethylene film that prevents a lithium-ion battery from overheating, then restarts the battery when it cools. The film is embedded with spiky nanoparticles of graphene-coated nickel. Courtesy: Bao et al. Stanford

A new material that can rapidly shut down an overheating lithium-ion rechargeable battery and once cool, quickly restore power has been described by US researchers in the journal Nature Energy. The highly thermoresponsive material could make a wide range of battery-powered electronic devices much safer than they currently are.

Overheating and spontaneously combusting batteries are a serious problem for the tech user on the go, with laptop computers, mobile phones and other devices regularly appearing in the news for product recalls following conflagrational incidents and accidents.

The common lithium-ion batteries found in laptops, mobile phones and other devices consist of two electrodes and a liquid or gel electrolyte that carries ions between them. If the battery is overcharged, short-circuited or otherwise damaged, it generates heat. If the temperature reaches about 150 degrees Celsius, the battery separator starts to melt electrolyte can ignite and the battery can burst into flames or even explode.

Electrochemical impedance

Now, Yi Cui, Zhenan Bao and colleagues at Stanford University, in California, have used electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy to study the properties and behaviour of their composite. The material comprises graphene-coated spiky nanoparticles of nickel mixed in a polyethylene polymer network.

The team explains how their battery failsafe material works: As it begins to get hot, the polymer expands and pulls apart the conductive nickel nanoparticles within the matrix. This leads to a rapid drop in the conductivity of the composite by about seven to eight orders of magnitude within a second, thus quickly disabling the battery and precluding any further temperature rise and potential incinerating effects. The polymer then begins to cool again, contracting and allowing the nanoparticles to come into close contact once again and completing the circuit again so that the device can continue to function. The team says the loss of conductivity driven by polymer expansion is entirely reversible so there is no loss of conductivity. This was demonstrated in tests involving raising battery temperature to the hazard point of 70 degrees Celsius. Moreover, the system tested as a coating on the current collector of a standard lithium-ion battery offers a quick and essentially passive way to make such batteries much safer rather than relying on external temperature-sensing switching devices.

Reversible retarding battery fires

Several techniques have been used to prevent battery fires, such as adding flame retardants to the electrolyte or embedding a warning device that lets a user know their battery is getting dangerously hot. Most of the approaches to battery safety are irreversible, which means the battery cannot be used afterwards. "People have tried different strategies to solve the problem of accidental fires in lithium-ion batteries," explains chemical engineer Bao."We've designed the first battery that can be shut down and revived over repeated heating and cooling cycles without compromising performance." Bao adds that the safety material can be modified to change the cut-out temperature. "We can tune the temperature higher or lower depending on how many particles we put in or what type of polymer materials we choose," he explains Bao. For example, the battery could be disabled at any temperature between 50 and 150 degrees Celsius depending on requirements of the device.

"The next step will be to improve the thermal conductivity and room temperature conductivity to allow higher rate operation," team member, and first author, Zheng Chen told SpectroscopyNOW.com

Related Links

Nature Energy 2016, online: "Fast and reversible thermoresponsive polymer switching materials for safer batteries"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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