Atomic layer deposition of Al2O3 on V2O5 xerogel film for enhanced lithium-ion intercalation stability

V2O5 xerogel films were fabricated by casting V2O5 sols onto fluorine-doped tin oxide glass substrates at room temperature. Five, ten and twenty atomic layers of Al2O3 were grown onto as-fabricated films respectively. The bare film and Al2O3-deposited films all exhibited hydrous V2O5 phase only. Electrochemical impedance spectroscopy study revealed increased surface charge-transfer resistance of V2O5 films as more Al2O3 atomic layers were deposited. Lithium-ion intercalation tests at 600 mAg−1 showed that bare V2O5 xerogel film possessed high initial discharge capacity of 219 mAhg−1 but suffered from severe capacity degradation, i.e., having only 136 mAhg−1 after 50 cycles. After deposition of ten atomic layers of Al2O3, the initial discharge capacity was 195 mAhg−1 but increased over cycles before stabilizing; after 50 cycles, the discharge capacity was as high as 225 mAhg−1. The noticeably improved cyclic stability of Al2O3-deposited V2O5 xerogel film could be attributed to the improved surface chemistry and enhanced mechanical strength. During repeated lithium-ion intercalation/de-intercalation, atomic layers of Al2O3 which were coated onto V2O5 surface could prevent V2O5 electrode dissolution into electrolyte by reducing direct contact between active electrode and electrolyte while at the same time acting as binder to maintain good mechanical contact between nanoparticles inside the film.