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Current Affairs

Room temperature sodium sulphur battery

Date: 12 January 2020 Tags: Energy

Issue

Researchers at the Indian Institute of technology (IIT) Madras have designed a new sodium sulphur battery that can be operated at room temperature.

 

Background

Conventional sodium sulphur batteries require very high temperature (300 degree C) for operation.

 

Details

  • By operating the battery at room temperature, the team was able to achieve higher charge storage capacity (technically called the specific capacity) and nearly zero self-discharge when the battery is not being used.

  • The battery also showed 83% retention of capacity even at the end of 500 cycles of charging and discharging. 

  • The first step that the team took to operate the battery at room temperature was by changing the electrolyte used.

  • Conventionally, sodium sulphur batteries use a solid electrolyte (sodium beta alumina), which by default reduces the diffusion of sodium ions from the anode to the cathode at room temperature. It is to increase the diffusion of sodium ions that the temperature is raised to about 300 degree C.

  • In place of a solid electrolyte the researchers used a glass fibre separator soaked in ether-based electrolyte that allows the battery to be operated at room temperature.

  • Changing the electrolyte alone is not sufficient to improve battery performance as there are other problems with sodium sulphur batteries.

  • The first problem is that with increasing amount of polysuphides getting dissolved into the electrolyte, there is a net loss in the cathode sulphur. In addition, the dissolved polysuphides move towards the anode and form a coating over it. This reduces the performance of the battery.

  • To address the problem, the team added a shielding layer very close to the cathode. The shielding layer is made of white graphite mixed in a polymer matrix.

  • The polymer allows the sodium ions to pass through while the white graphite added to the polymer matrix prevents the migration of polysuphides to the anode.

  • Since the migration of the polysuphides to the sodium anode is prevented by the shielding layer, self-discharge of the battery is significantly reduced.

  • While conductive carbons are added to the sulphur to make it electrically conductive in conventional sulphur batteries, the researchers used partially exfoliated multiwalled carbon nanotubes.