Organic molecules for high capacity rechargeable batteries

11 Sep 2017. NUS chemists have developed molecule-based organic cathodes for ultra-stable high capacity rechargeable batteries.

Rechargeable batteries are the key energy storage components in many large-scale battery systems.  These include electric vehicles (EVs) and smart renewable energy grids. With increasing demand for battery-based storage systems, researchers are turning to more environmentally friendly methods of producing them. One such method is the use of organic materials as the battery electrode.

When compared to inorganic-based metal oxide electrodes which are more widely used, organic electrodes have lower environmental footprints, provide better safety, and allow eco-efficient production and disposal. They are also flexible and can be made easily into wearable parts. This makes them an attractive candidate for use in rechargeable batteries. However, their poor electrical conductivity and tendency to lose their energy storage ability after being charged multiple times limit their use in battery applications.

A team led by Prof LOH Kian Ping, from the Department of Chemistry, NUS has synthesised an organic molecule called 3Q (π-conjugated quinoxaline-based heteroaromatic molecules) with enhanced conductivity and energy retention capability. The new molecule has a conducting scaffold with up to six charge storage sites per molecular unit.  This means that on a per molecule basis, it has a very high energy density. When it is bonded with graphene and used in an ether-based electrolyte, the 3Q-based electrode displays a high electrical conductivity of 395 milliampere hour per gram. The results provide evidence that heteroaromatic molecules are promising candidates for developing high-energy density organic rechargeable batteries with a long cycle life.

“This study is expected to pave the way towards the development of small organic-molecule-based cathode materials for lithium ion batteries, which have superior energy density and a long lifespan,” said Prof Loh.

Figure shows the chemical structure of 3Q.  Each of the six nitrogen atoms (denoted by "N") can provide a storage site for electrical charges when used in batteries.

 

Reference

CX Peng; GH Ning; J Su; G Zhong; W Tang; B Tian; C Su; D Yu; L Zu; J Yang; MF Ng; YS Hu; Y Yang*; M Armand; KP Loh*, "Reversible multi-electron redox chemistry of π-conjugated N-containing heteroaromatic molecule-based organic cathodes" NATURE ENERGY Volume: 2 Article: 17074 DOI:10.1038/nenergy.2017.74   Published: 2017.

 

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