2011 IR&D Annual Report

Pulsed-Laser Synthesis of Group IV Clatrates for Energy Storage Applications, 18-R8180

Principal Investigators
Kwai S. Chan
Michael A. Miller

Inclusive Dates:  10/01/08 – 09/30/10

Background — Energy storage and battery materials represent a major growth market for fundamental research, applied research and technology development. The U.S. Department of Energy (DOE) has established an extensive technology program to advance the development of Li-based batteries to enable a larger market penetration of hybrid electrical vehicles, plug-in hybrid electrical vehicles and electric vehicles. The pulsed-laser synthesis capability was needed to fabricate silicon, germanium, and tin clathrates, which are potential electrode materials for lithium-ion batteries. These results were needed to support a proposal to DOE.

Figure 1.  (A) Experimental setup for plasma magnetron synthesis of silicon clathrates. (B) Image of 
			plasma interaction with a pool of ionic liquid. (C) As-deposited nanoparticles of silicon in pool of  ionic liquid. (D) Fully 
			dispersed nanoparticles of silicon clathrates in ionic liquid recovered from the PEMS process.
Figure 1. (A) Experimental setup for plasma magnetron synthesis of silicon clathrates. (B) Image of plasma interaction with a pool of ionic liquid. (C) As-deposited nanoparticles of silicon in pool of ionic liquid. (D) Fully dispersed nanoparticles of silicon clathrates in ionic liquid recovered from the PEMS process.

Approach — A pulsed laser (mode-locked YAG with frequency doubling) and power supply system (Coherent Antares™, Model 76-S) were received from SP2 Carbon and installed in the Laser Raman Laboratory at SwRI. The pulsed-laser was set up on an air-suspended optical table in line with an SwRI-developed vacuum target-chamber. However, there were several issues with the laser cavity that required some repairs and alignment. The laser was repaired but the optical path could not be sufficiently aligned to cause lasing. To achieve the project goal, researchers redirected the project efforts to develop an alternative method of fabricating Si clathrates using an ionization-enhanced plasma magnetron sputtering technique.

Accomplishments — A plasma-enhanced magnetron sputtering (PEMS) vacuum deposition chamber was set up to explore the synthesis of guest-free silicon clathrate particles by directing a silicon-argon plasma into a pool of ionic liquid (IL), as illustrated in Figure 1(A). This synthesis process involved purchasing a silicon sputtering target based on SwRI's design specifications. The Si target was sputtered, and the sputtered Si-argon plasma was directly deposited into a pool of ionic liquid in vacuum, as shown in Figure 1(B). The suspended particles, Figure 1(C), were then separated from the ionic liquid, Figure 1(D), and structurally characterized via powder X-ray diffraction and Raman spectroscopy. The results indicated that small amounts of empty silicon clathrates, Si 46 , were synthesized using this technique. This technique is currently being used to make silicon clathrates in an external project supported by the DOE through the Lawrence Berkeley National Laboratory.

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04/15/14