Cathodic ALD V2O5 thin films for high-rate electrochemical energy storage

Abstract

Atomic layer deposition (ALD) is attractive for next-generation electrical energy storage in forming passivation layers and more recently active storage material. Here we report a detailed study of ALD V₂O₅ as a high capacity cathode material, using vanadium tri-isopropoxide (VTOP) precursor with both O₃ and H₂O as oxidant. The O₃-based process produces polycrystalline films with generally higher storage capacity than the amorphous films resulting from the H₂O-based process over extended cycling (100 cycles). High capacities are achieved in V₂O₅ because of the ability to incorporate up to three Li per V₂O₅ formula unit. To address the central need for both high power and high energy, we identified the crucial tradeoff between higher gravimetric capacity with thinner films and higher material mass with thicker films. For the thickness regime 10–120 nm, we chose areal energy and power density as a useful metric for this tradeoff and found that it is optimized at 60 nm for the O₃-VTOP ALD V₂O₅ films. We believe the control of material quality, thickness, and conformality achievable with ALD processes is valuable as new nanoarchitectures for electrochemical energy storage come into sight.