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

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 O-3 and H2O as oxidant. The O-3-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 O-3-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.