ATOMIC LAYER DEPOSITION OF SOLID ELECTROLYTES FOR BEYOND LITHIUM-ION BATTERIES
Rubloff, Gary W
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This thesis outlines methodology and development of an atomic layer deposition (ALD) process for the well-known solid-state electrolyte lithium phosphorous oxynitride (LiPON). I have developed a quaternary ALD LiPON process through a novel stepwise additive development procedure. ALD process kinetics and chemistry were investigated using in-operando¬ spectroscopic ellipsometry and in-situ x-ray photoelectron spectroscopy (XPS). ALD LiPON exhibits a tunable ionic conductivity proportional to N content, with the highest conductivity of 6.5x10-7 S/cm at 16.3% N. Two applications of ALD LiPON are investigated: ALD LiPON films as a protection layer for next-generation lithium metal anodes in the lithium sulfur battery system, and as solid electrolytes in 3D thin film batteries with discussion towards development of an all ALD 3D battery. Lithium metal is considered the “holy grail” of battery anodes for beyond Li-ion technologies, however, the high reactivity of Li metal has until now prevented its commercial use. Here, ALD protection layers are applied directly to the Li anode to prevent chemical breakdown of the liquid electrolytes while allowing ion transport through the protection layer. Protection of lithium metal is investigated with two materials: low ionic conductivity ALD Al2O3, demonstrating a 60% capacity improvement in Li-S batteries by protecting the Li anode from sulfur corrosion during cycling, and high ionic conductivity ALD LiPON, demonstrating a 600% improvement in Li-S battery capacity over unprotected anodes. Interestingly, ALD LiPON also forms a self-healing protection layer on the anode surface preventing deleterious Li dendrite formation during high rate cycling. Solid Li-based inorganic electrolytes offer two profound advantages for energy storage in 3-D solid state batteries: enhanced safety, and high power and energy density. Until now, conventional solid electrolyte deposition techniques have faced hurdles to successfully fabricate devices on challenging high aspect ratio structures, required for improvements in both device energy and power density. In this thesis, I demonstrate fabrication of ALD heterostructures suitable for use in 3D solid batteries, and although this work is incomplete I discuss progress towards future use of ALD LiPON solid electrolytes in all ALD solid-state 3D batteries.