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Lithium, because of its ultra-high theoretical capacity of 3861 mAh g-1, has been successful in primary batteries. In practice, the performance of lithium falls short of its theoretical potential due to the formation of dendritic structures during the repeated plating or stripping processes, which reduces its cyclability, leaving it prone to short-circuiting and hazardous thermal failure.
One possible way to avoid dendrite formation is by constructing an interfacial layer that gradually fades from lithiophilic to lithiophobic properties. The performance of lithium anodes has been studied with a range of distinct interfacial layers which include carbon nanotubes; zinc oxide loaded carbon nanotubes, graphene, carbon black and carbon fibre.
Liqiang Mai and Yan Zhao from the Wuhan University of Technology, and Hao Zhang from the Research Institute of Chemical Defense worked with researchers at Beijing Institute of Technology and Beijing University of Chemical Technology in China to conclude that an interfacial layer that is lithiophobic, mechanically robust, and allows favorable Li-ion diffusion will suppress dendrite formation.
Mai and his colleagues found that long-term cycling caused mossy lithium deposits to build up under the interfacial layer hampering the battery’s performance.
To safeguard against the formation of mossy deposits and dendrites, researchers incorporated carbon nanotubes that were loaded with increasing quantities of zinc oxide. This changed the carbon nanotubes from lithiphobic to lithiophilic. The gradually faded blend of materials further improved the deposition behavior of lithium during cycling, leaving the battery stable after 520 cycles—whereas the nanotube-coated cell started to show signs of voltage divergence after 400 cycles. The differences in behavior became more apparent at higher current densities of 5 mA cm−2 and 10 mA cm−2.
Using scanning electron microscopy, researchers stated that lithium deposited on the electrode with a gradient interface layer had no crevices or dendrites. They also confirmed that there were no lithium deposits on the upper carbon nanotube layer, even after 520 cycles.
Mai says the gradient lithiophilic-lithiophobic interface strategy in lithium-sulphur batteries is an excellent candidate for companies developing a large-scale application.
