Photovoltaic Lithium-ion Battery with Layer-Structured Li2MnIII0.2MnIV0.8O2.9 Thin Film Chemically Fabricated for Cathodic Active Material

Dilithium manganese oxide (LMO) thin film was newly fabricated as an active material on a fluorinated-tin-oxide pre-coated glass electrode by a wet process. A stable LMO precursor solution was developed through the reaction of lithium and manganese acetates with butylamine in ethanol. A spin-coated precursor film was heat-treated at 500 °C in air for 0.5 h. The X-ray diffraction pattern indicates that the resultant film consists of layer-structured LMO crystals. The X-ray photoelectron spectra of LMO thin film suggests that the ratio of Mn3+/Mn4+ is 1/4, and the chemical formula can be expressed as Li2MnO2.9. A device was assembled with O-deficient LMO and TiO2 thin films as each active material, along with an electrolytic solution involving LiPF6. The charging voltages (2.67 and 1.45 V) of this device were recorded by applying a constant current of 0.2 mA and using 1-sun irradiation with no external power supply, respectively. The voltages delivered by this cobalt-free device were 0.63 and 0.13 V higher, respectively, than the corresponding device assembled with lithium cobalt oxide as a cathodic active material.