Precisely Controlled Atomic Layer Deposition of Nanostructured Li2s for High-Performance Lithium-Sulfur Batteries

In our persistent quest for renewable clean energies, lithium-ion batteries (LIBs) as the primary electrical energy storage devices are essential ^1,2. LIBs, besides dominating portable consumer electronics, are being expected to go further for powering our transportation and smart grids. To this end, the current LIB technologies are not sufficient, suffering from energy density, cost, safety, and stability. Thus, new battery systems are in urgent need.

Lithium-sulfur (Li-S) batteries are very promising, in terms of its high energy density of 2600 Wh/kg accounting for five times that of LIBs. Furthermore, sulfur is abundant, cost-effective, and environmentally-friendly. However, lithium metal as the anode badly risk the battery safety due to its well-known dendrite growth during charge-discharge cycling. An alternative approach to avoid using Li metal is to replace with the prelithiated Li₂S ². As such, there will be many more choices of anode materials (e.g., Si and Sn) to pair with Li₂S, instead of Li metal. Thus, Li₂S is attracting  increasing research interest. Given the facts that Li₂S is electrically and ionically insulating, recent studies^3-5 unanimously demonstrated that Li₂S nanoscale composites showed much better performance than their microsized counterparts. Among the studies, ball milling was the most widely used for grinding commercial Li₂S micro-powers down to their nanoscale. There was to date little effort reported being viable for nanostructured Li₂S.

In this talk, we are going to present a new route via atomic layer deposition (ALD) to fabricate Li₂S nanofilms and various nanostructures based on different substrates. Using a lithium compound  and H₂S as precursors, the Li₂S ALD was systematically studied in the temperature range of 150 - 300 ^oC by a series of in situ techniques (e.g., QCM, QMS, and FTIR) and ex situ characterization tools (e.g., XRD, XRF, XPS, and XAS). The ALD Li₂S was further deposited on porous Cu foams, single-walled carbon nanotubes, graphene nanosheets. This ALD approach features its highly controllable film growth at the atomic level, excellent film uniformity and conformality on various substrates, and low growth temperature. The resultant Li₂S nanofilms and nanocompmosites were electrochemically tested as new cathode materials in Li-S batteries. Our new efforts demonstrated that the ALD-resultant Li₂S nanostructures are very promising in improving the electrochemical performance of Li-S batteries. In addition, the ALD-fabricated Li₂S also paved a new venue for developing superionic solid electrolytes for both thin film microbatteries and bulk-type batteries.

 

References:

                (1)           Thackeray, M. M.; Wolverton, C.; Isaacs, E. D. Energy & Environmental Science 2012, 5, 7854-7863.

                (2)           Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J. M. Nature Materials 2012, 11, 19-29.

                (3)           Cai, K. P.; Song, M. K.; Cairns, E. J.; Zhang, Y. G. Nano Letters 2012, 12, 6474-6479.

                (4)           Lin, Z.; Liu, Z. C.; Dudney, N. J.; Liang, C. D. Acs Nano 2013, 7, 2829-2833.

                (5)           Jeong, S.; Bresser, D.; Buchholz, D.; Winter, M.; Passerini, S. Journal of Power Sources 2013, 235, 220-225.