The novel ultra-thin two-dimensional polymer sheet, which is the organic analogue of graphene, heralds new opportunities for long lasting sodium rechargeable batteries
Polymers, such as plastic and synthetic textiles, are very useful technological commodities that have revolutionised daily life and industries. A research team from the National University of Singapore (NUS) has successfully pushed the frontier of polymer technology further by creating novel two-dimensional (2D) graphene-like polymer sheets.
In the last century, scientists have successfully developed molecules which can be crosslinked to form one-dimensional and three-dimensional polymers. These are used to produce a wide range of technological products. However, making 2D polymers has met with little success, as most molecules are not flat and they tend to rotate in solution, making it difficult to control their linking to a 2D plane,” said Professor Loh Kian Ping, Head of 2D Materials Research in the Centre for Advanced 2D Materials at NUS. He also holds an appointment with the Department of Chemistry at the NUS Faculty of Science.
Mr Liu Wei, who is the first author of the paper, added, “Our team developed a strategy to make 2D polymer sheets by prepacking flat molecules in a crystalline state and carrying out solid state polymerisation. This approach restricts the rotation of the molecules and allow the 2D polymerisation to take place to form carbon-carbon bonds.” Mr Liu is a PhD student at the NUS Department of Chemistry as well as NUS Graduate School for Integrative Sciences and Engineering.
The novel polymer sheets synthesised by the NUS team are unique because of their good electrical conductivities and highly regular, sub-nanometer sized pores, which can be used to store sodium ions efficiently and safely in sodium ion batteries. Sodium ion batteries are a type of rechargeable metal-ion battery that uses sodium ions as charge carriers. As there is an abundance of sodium, sodium ion batteries are cheaper to produce than lithium ion batteries. However, the disadvantage is that they do not last long. The 2D polymer developed by Prof Loh and his team can be mass produced at low cost for use as the electrode for sodium ion batteries, enabling such batteries to perform at high capacity for thousands of charge cycles.
The design and validation of the novel 2D polymer was published in the journal Nature Chemistry in January 2017. It has also been highlighted in Nature’s News & Views on 23 February 2017.