Three-dimensional covalently attached sp2 hybrid graphite micropipes enhance the cycling stability of lithium metal negative

Lithium metal is considered as the most ideal lithium battery anode material due to its extremely high capacity (theoretical specific capacity of 3860 mA h g-1) and low potential (-3.040 V vs. standard hydrogen electrode). However, unlike graphite or silicon negative electrodes that achieve energy storage by forming lithium-based compounds, metallic lithium negative electrodes store energy by deposition / delamination of lithium at the electrode / electrolyte interface, which causes the lithium metal to react electrochemically Almost infinite volume changes occur, unstable solid electrolyte interface membrane (SEI) and the formation of lithium metal dendrites. These problems can eventually lead to battery shorts, low Coulombic efficiency and low metal lithium utilization. Recently nanostructured current collectors have been used to accommodate metallic lithium to inhibit the growth of lithium dendrites and improve the cycling stability of metallic lithium cathodes. However, this strategy still needs to be improved in the following aspects to meet practical needs: (i) nanostructures result in increased side reactions resulting in lower coulombic efficiencies than embedded anode materials; (ii) lithium metal in long cycle tests (<50 mA h cm-2) needs to be improved to meet the demand of lithium-sulfur, lithium-air and other high energy density batteries (> 10 mA h cm-2). How to further optimize the current collector microstructure and obtain the high performance metal lithium anode composite material that meets the application requirements is one of the important research directions of the metal lithium electrode.

Recently, the project team of Professor Ji Hengxing of China University of Science and Technology proposed a three-dimensional covalently connected sp2 hybrid graphite tube as the current collector of lithium metal anode in order to inhibit lithium dendrites and limit the occurrence of side reactions to achieve high efficiency lithium metal use. The advantage of this structure is that (i) the backbone structures formed by the sp2 hybrid carbon atoms have an extremely high conductivity; (ii) structural units covalently attached at the atomic scale form three-dimensional blocks of macroscopic size, Eliminating interfacial resistance between micro / nano structural units; (iii) micron-sized framework structures with optimized specific surface area while limiting the formation of lithium dendrites and SEIs. The three-dimensional covalently bonded sp2 hybrid graphite tube with a lithium metal anode can be cycled for 3000 hours without short-circuiting at a recycling capacity of 10 mA h cm-2 and a metal lithium utilization of 91%. The lithium metal negative can still achieve a surface capacity of 10 mA h cm-2 even at a current density of 10 mA cm-2. This three-dimensional covalently connected sp2 hybrid graphite micro-tube current collector design ideas for other types of metal batteries also have reference. Related research findings are published in “High Areal Capacity and Lithium Utilization in Anode Made of Covalently-Connected Graphite-Microtubes” in Advanced Materials, 2017, Doi: 10.1002 / adma.201700783. The first author of the dissertation is Jinsong, Ph.D., Department of Materials Science and Engineering, University of Science and Technology of China.

The above research has been supported by the National Natural Science Foundation of China, the Chinese Academy of Sciences “Hundred Talents Program”, energy materials chemistry collaborative innovation center.


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