Precisely Controlled Atomic Layer Deposition of Nanostructured Li2s for High-Performance Lithium-Sulfur Batteries
Authors: Meng Xiangbo , Fister Timothy , Fenter Paul , Elam J. W. 
Published: February 2020

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 studies3-5 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.

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