Developments of high-voltage all-solid-state thin-film lithium ion batteries

Powders of Li2MMn3O8 (M = Fe, Co) were prepared by glycine nitrate combustion from the corresponding metal nitrates. The reaction products were pressed into pellets with the addition of 20 wt.% excess LiNO3, which were used as targets for e-beam evaporation. A high-voltage all-solid-state thin-film lithium ion battery was demonstrated by the sequential deposition of spinel structured Li2MMn3O8 (M = Co, Fe) as positive electrode by e-beam evaporation, LiPON as electrolyte, and metallic Al as negative electrode by sputtering in N2 and Ar gas mixtures with specific power and gas flow rates. A lithium ion conductivity of ∼10−6 S cm−1 was observed for the optimized thin-film LiPON electrolyte prepared under the condition of a chamber pressure of 2.6 × 10−2 mbar and a power of 60–100 W. The chemical diffusion coefficient (D˜) was found to be in the range 10−13 to 10−12 cm2 s−1 for any composition x of Li2−xMMn3O8 (M = Fe, Co) in the range from 0.1 to 1.6 by employing the galvanostatic intermittent titration technique (GITT). AC impedance studies revealed a charge transfer resistance of 260–290 Ω, a double layer capacity of ∼45–70 μF for an electrode area of 6.7 cm2.