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| Fig. 1: (a) A thin layer of lithium metal is deposited on the copper current collector. (b)Interconnected hollow carbon nanospheres are fabricated on the copper current collector and then lithium is deposited underneath. (Source: J. Zhao) |
Lithium-ion batteries are widely used for consumer electronics and exhibit great potential for electrical vehicle and grid-scale energy storage. [1] For future applications, batteries with higher energy storage density than existing lithium ion batteries need to be developed. Lithium metal would be the optimal choice as an anode material, because it has the highest specific capacity (3860 mAh/g) and the lowest anode potential of all. [2] However, stable cycling of lithium metal anode is challenging due to the dendritic lithium formation and high chemical reactivity of lithium with electrolyte and nearly all the materials. [3]
For normal flat lithium metal foil, large volumetric changes during the lithium deposition process can easily lead to ramified growth of lithium dendrites and rapid consumption of the electrolytes. [4] Fig. 1b shows that coating the lithium metal anode with a monolayer of interconnected amorphous hollow carbon nanospheres helps isolate the lithium metal depositions and facilitates the formation of a stable solid electrolyte interphase. The advantages of our this approach are obvious: (1) amorphous carbon is chemically stable when in contact with lithium metal, (2) a hollow nanosphere layer is weakly bound to the metal current collector and can move up and down to adjust the availability of empty space during cycling. The top surface, formed from the hollow carbon nanospheres, is static and forms a stable, conformal SEI, while Li metal deposition takes place underneath, on the metal current collector. The stable SEI on the carbon nanosphere surface helps reduce the flow of Li ions towards the regions of broken SEI on the metal current collector. Therefore, the Coulombic efficiency improves to ~99% for more than 150 cycles. This is significantly better than the bare unmodified samples, which usually show rapid Coulombic efficiency decay in fewer than 100 cycles, which indicates that nanoscale interfacial engineering could be a promising strategy to tackle the intrinsic problems of lithium metal anodes.
This work demonstrates that the interfacial nanoscale engineering approach can improve Li metal cycling performance. The nanoengineering concepts described here may be a viable route towards lithium metal anode batteries and, more specifically, to high-energy-density batteries, such as lithium- sulfur and lithium-oxygen batteries.
© Jie Zhao. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] J. B. Goodenough and A. Manthiram, "A Perspective on Electrical Energy storage," MRS Commun. 4, 4135 (2014).
[2] H. Ota, et al., "Characterization of Lithium Electrode in Lithium Imides/Ethylene Carbonate and Cyclic Ether Electrolytes. II. Surface chemistry," J. Electrochem. Soc. 151, A437 (2004).
[3] K. Yan. et al., "Ultrathin Two-Dimensional Atomic Crystals as Stable Interfacial Layer For Improvement of Lithium Metal Anode," Nano Lett., 14, 6016 (2014).
[4] G.Zheng et al., "Interconnected Hollow Carbon Nanospheres For Stable Lithium Metal Anodes," Nat. Nanotechnol. 9, 618 (2014).