Lithium-sulfur battery charge and discharge cycle characteristics

The Japan Industrial Technology Research Institute (referred to as the Research Institute of Industry and Technology) announced on June 28, 2016 that it has jointly developed a lithium-sulfur battery with the University of Tsukuba. By using a metal-organic framework as a battery separator, a long-term stable charge and discharge cycle is realized characteristic. According to reports, the lithium-sulfur battery can still maintain a charging capacity of up to 900mAh/g after 1500 cycles of testing at a current density of 1 C (current value at the end of discharge after 1 hour of constant current discharge).

A lithium-sulfur battery using sulfur as a positive electrode of a lithium battery has a high positive electrode capacity (theoretical value is 1675mAh/g), and is expected as a new-generation battery. However, the problem with this type of battery is that the lithium sulfide, the intermediate product of the discharge reaction, is easily dissolved in the electrolyte. Therefore, as the charge and discharge cycle proceeds, the dissolved polysulfide ions initiate oxidation between the positive and negative electrodes. The reduction reaction (shuttle effect), which occurs repeatedly causes the battery capacity to deteriorate.

This time, the researchers did not take measures to prevent the dissolution of polysulfides, but instead used the "molecular sieve", a metal-organic framework that was often used for the adsorption and separation of gas molecules, to limit the movement of polysulfides to the negative electrode. The metal organic skeleton has three-dimensional micropores of sub-nanometer to several nanometers and fixed in size.

The membrane material is selected from a metal-organic framework in which the pore size is such that the polysulfide ions can pass through but the lithium ions can pass. And by mixing it into the graphene oxide layer, a flexible composite metal organic skeleton film was synthesized. Because it is a crystal, the metal organic skeleton has the disadvantage of being easily broken.

The researchers found that when the composite metal organic skeleton membrane is used as a lithium sulfur yellow battery separator, the shuttle effect which is regarded as a problem can be suppressed, and the charge and discharge capacity reduction and the cycle characteristics can be prevented from being lowered. After repeating 1500 charge and discharge cycles at room temperature, in terms of discharge capacity and coulombic efficiency, in addition to about 100 charge and discharge performed to perform initial activation, the discharge capacity of 100 to 1500 times hardly deteriorated, showing that Good cycle characteristics.

The future goal of the Research Institute is to develop lithium-sulfur batteries with excellent performance with the goal of practical use. The research results were published online on June 27 (British time) in the British academic journal Nature Energy.

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