James F. Rohan

In this work we show high capacity and cycle‐life performance, for electrodeposited, crystalline V 2 O 5 thin film cathodes protected by a 1 nm ALD alumina deposit for use with Li‐metal and ionic liquid electrolyte based microbatteries. Al 2 O 3 coatings thicker than 1 nm are shown to decrease the performance of the V 2 O 5 thin film cathodes. The ionic liquid outperforms an organic electrolyte at 1 C rates with an initial capacity of 148 mAh g −1 and capacity retention of 97 % at cycle 50. A polymer gel analogue of the ionic liquid electrolyte in combination with the 1 nm Al 2 O 3 coated V 2 O 5 had an initial capacity of 139 mAh/g with a capacity retention of 93.5 % to cycle 800, illustrating high capacity and extended cycle life.