"Widely used lithium-ion batteries cannot satisfy the increasing requirement of energy storage systems in portable electronics and electric vehicles. New lithium metal anode batteries, like Li-S and Li-air batteries, are highly sought. Lithium metal provides an extremely high theoretical specific capacity, which is almost 10 times more energy than graphite," said Prof. Qiang Zhang, at the Department of Chemical Engineering, Tsinghua University.
"However, the practical applications of lithium metals are strongly hindered by lithium dendrite growth in continuous cycles. This induces safety concerns. The lithium dendrites may cause internal short circuits resulting in fire. Furthermore, the formation of lithium dendrites induces very low cycling efficiency."
The dendrite growth and unstable solid electrolyte interphase consume a large amount of lithium and electrolyte which leads to irreversible battery capacity losses and inhibiting the dendrites growth
Several approaches have been proposed to slow the growth of dendrites including electrolyte modification, artificial solid electrolyte interphase layers as well as electrode construction.
"We noticed that by decreasing the local current density heavily, lithium dendrite growth could be efficiently inhibited. Based on this concept, we employed unstacked graphene with an ultrahigh specific surface area to build a nanostructured anode. And it turned out to be a very efficient idea," said Rui Zhang, a Ph.D. student and the lead author. "Additionally, we have employed the dual-salt electrolyte to acquire more stable and more flexible solid electrolyte interphase, which can protect the lithium metal from further reactions with electrolyte."
The graphene-based anode offered improvement which included an ultralow local current density on the surface of graphene anode (a ten-thousandth of that on routine Cu foil-based anodes) induced by the large specific surface area of 1666 m2 g-1, which inhibited dendrite growth and brought uniform lithium deposition morphology.
The anode also offers a high stable cycling capacity of 4.0 mAh mg-1 induced by the high pore volume (1.65 cm3 g-1) of unstacked graphene, more than 10 times of the