Lasers Write Better Anodes

The laser light converts a polyimide­–urea polymer into three-dimensional hard carbon. (Source: Wiley-VCH / KAUST)

Sodium-ion batteries have potential to replace the currently used lithium-ion bat­teries by using the cheaper and more abundant sodium resource. This has parti­cular potential in Saudi Arabia, where sodium is readily available and easily extracted as a byproduct of water desa­lination, a signi­ficant source of potable water in the country. Yet normal graphite, the dominant anode material in lithium-ion batteries, struggles to store or inter­calate sodium ions because sodium ions are larger than lithium ions. Hard carbon is a type of disordered graphite that can store more sodium ions, hence increasing battery capacity. The problem is that making hard carbon requires tempera­tures of almost 1000°C.

The KAUST team led by Husam Alshareef has developed a process using a simple bench-top laser to make three-dimen­sional hard carbon directly on copper collectors without excessive tempera­tures or additional coating steps. The team formed a polymer – urea-containing poly­imide – sheet on copper and then exposed this sheet to strong laser light. By intro­ducing nitrogen gas during the process, the team could replace some of the carbon atoms with nitrogen atoms, reaching an extremely high nitrogen level (13 atomic %), which is unat­tainable by other techniques. Thus, the three-dimen­sional graphene was more conduc­tive, had expanded atomic spacing, and was directly bonded to the copper current collectors, eliminating the need for addi­tional processing steps.

“We wanted to find a way to make three-dimen­sional hard carbons without having to exces­sively heat our samples. This way we could form the hard carbon directly on copper collectors,” said Fan Zhang, a Ph.D. student in Alshareef’s group. The researchers fabri­cated sodium-ion batteries using their laser-formed anode material. Their device exhi­bited a coulombic effi­ciency that exceeds most reported carbona­ceous anodes, such as hard and soft carbon, and a sodium-ion capacity better than most previous carbon anodes in sodium-ion batteries. “This work opens a new direction in battery research, which can be extended to other energy-storage tech­nologies,” said Alshareef. (Source: KAUST)

Reference: F. Zhang et al.: Highly Doped 3D Graphene Na‐Ion Battery Anode by Laser Scribing Polyimide Films in Nitrogen Ambient, Adv. En. Mat. 8, 1800353 (2018); DOI: 10.1002/aenm.201800353

Link: Materials Science and Engineering, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology KAUST, Thuwal, Saudi Arabia

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