Graphdiyne structure (left) and its application in suppressing dendrite growth in lithium metal batteries (right).
Graphdiyne structure (left) and its application in suppressing dendrite growth in lithium metal batteries (right).

Lithium-ion batteries have revolutionized mobile electronics and are making in-roads on transport, but further improvements in lifetime and power will require new technologies. One option is lithium metal batteries, which last longer and charge faster, but this technology has a problem. Lithium deposits called dendrites tend to grow on the anode potentially creating short circuits, which can cause the battery to fail, catch fire, or explode.

Now researchers from Institute of Chemistry, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Nankai University, Shantou University, and Center for High Pressure Science and Technology Advanced Research in China have devised a thin film separator based on a carbon allotrope – known as graphdiyne – that acts as a filter for lithium ions and prevents dendrite growth [Shang et al., Materials Today Energy 10 (2018) 191-199].

Lithium-metal batteries are similar in concept to lithium-ion batteries but rely on a lithium metal anode. During the discharging process, the lithium metal anode donates electrons to the cathode via an external circuit. Upon charging, however, lithium metal is deposited on the anode. It is during this process that unwelcome dendrites can form.

This is where the separator film comes in. Made from ultrathin (10 nm) graphdiyne, a two-dimensional monolayer of carbon-atom hexagons bridged by butadiyne links, the thin film separator has some remarkable properties. Not only is graphdiyne simultaneously flexible and robust, its chemical structure creates a uniformly porous mesh that allows only one lithium ion to pass through each pore. This regulates the motion of ions through the film, rendering the diffusion of ions highly uniform. Importantly for batteries, this feature of the film effectively suppresses the growth of lithium dendrites.

“Suppressing lithium dendrites can stabilize the solid electrolyte interphase, thus improving the lifespan and coulombic efficiency [of the device],” explains Yuliang Li of the Institute of Chemistry, Chinese Academy of Sciences, who led the research. “It can avoid dendrite-related short circuits, thus increasing the safety of batteries.”

The researchers believe that graphdiyne films could overcome some of the until-now intractable problems facing lithium and other alkali metal batteries.

“Graphdiyne is a perfect material with a super-conjugated structure, intrinsic band gap, naturally large porous structure, and semiconducting properties, which shows great promises for solving a big scientific problem in this field,” says Li.

The two-dimensional material is also simple and easy to produce under normal lab conditions.

“Although more effort is needed to improve the quality of large-scale graphdiyne membranes, we think graphdiyne might bring some big breakthroughs in the safety of lithium batteries,” Li told Materials Today.