LiCoO2 and LiCo1-xAlxO2 Thin Film Cathodes Grown by Pulsed Laser Ablation

LiCoO₂ and LiCo_0.5Al_0.5O₂ thin films have been grown by pulsed laser ablation on SnO₂-coated glass substrates. For both stoichiometries, the resultant films are dense and uniaxially textured films with the Li and Co layers parallel to the substrate. In general, to grow LiCo_0.5Al_0.5O₂ films, a laser flux roughly 80 mJ pulse^-1 higher than that used for LiCoO₂ films is required to achieve a similar deposition rate. LiCoO₂ films grown at T_s = 600°C and p[O₂] = 2000 mTorr have a typical grain size of ∼ 100 nm. For constant current cycling between 3.8 and 4.2 V at 5 μ A, the LiCoO₂ films have an initial discharge capacity of ∼ 0.33 Li per LiCoO₂ (89 (mA h) g^-1) decreasing to ∼ 0.18 Li/LiCoO₂ (49 (mA h) g^-1) after 100 cycles and have a continued capacity loss of ∼ 0.25% per cycle. The LiCo_0.5Al_0.5O₂ films grown to date have roughly 3 times less capacity than the LiCoO₂ films and apparently a large asymmetry between Li extraction and reintercalation.