Optical properties and electrochemical performance of LiFePO₄ thin films deposited on transparent current collectors

LiFePO₄ thin film cathodes are deposited on various transparent conducting oxide thin films on glass, which are used as cathode current collectors. The XRD patterns show that the thin films have the phase of LiFePO₄ with an ordered olivine structure indexed to the orthorhombic Pmna space group. LiFePO₄ thin film deposited on various TCO glass substrates exhibits transmittance of about 53%. The initial specific discharge capacities of LiFePO₄ thin films are 25.0 μAh/cm² μ μm on FTO, 33.0 μAh/cm² μm on ITO, and 13.0 μAh/cm² μm on AZO coated glass substrates. Interestingly, the retention capacities of LiFePO₄ thin films are 76.0% on FTO, 31.2% on ITO, and 37.7% on AZO coated glass substrates at 20th cycle. The initial specific discharge capacity of the LiFePO₄/FTO electrode is slightly lower, but the discharge capacities of the LiFePO₄/FTO electrode relatively decrease less than those of the others such as LiFePO₄/ITO and LiFePO₄/AZO with cycling. The results reported here provide the high transparency of LiFePO₄ thin films cathode materials and the good candidate as FTO current collector of the LiFePO₄ thin film cathode of transparent thin film rechargeable batteries due to its high transparency and cyclic retention.