Superior electrochemical properties of porous Mn2O3-coated LiMn2O4 thin-film cathodes for Li-ion microbatteries

Highlights: • Porous Mn2O3 thin-film was coated on LiMn2O4 thin-film cathode via sol–gel method. • Mn2O3-coated LiMn2O4 cathodes show superior capacity retention than pristine LiMn2O4. • Mn2O3-coated LiMn2O4 cathodes show better rate capability than pristine LiMn2O4. • Porous Mn2O3 film well protects the underlying LiMn2O4 film from the electrolyte. -- Abstract: Thin-film LiMn2O4 cathodes coated with Mn2O3 overlayer were prepared by a sol–gel method for Li-ion microbattery tests. The double-layered structure was fabricated on Pt(1 1 1) substrate through spin-coating the precursor solution for LiMn2O4 followed by that for Mn2O3. The Mn2O3 overlayer exhibited granular morphology with significant volume of pores while the LiMn2O4 film consisted of compacted grains. The electrochemical properties of the porous Mn2O3-coated LiMn2O4 (Mn2O3/LiMn2O4) cathodes characterized by charge–discharge (C–D) cycling performance, cyclic voltammetry, and rate capability were compared with those of the pristine LiMn2O4 cathodes. The Mn2O3/LiMn2O4 cathodes exhibited good cycle-life, only 0.007% capacity loss per cycle at 25 °C, thereby achieved discharge capacity retention of 80% after 3000 cycles, while the pristine LiMn2O4 cathodes retained only 35% of the initial capacity under the same C–D condition. The Mn2O3/LiMn2O4 cathodes also exhibited better rate capabilities compared to the pristine LiMn2O4 cathodes. The improved electrochemical performance is ascribed to the porous Mn2O3 overlayer that not only protects the underlying LiMn2O4 film from direct exposure to the electrolyte but also provides efficient Li+ diffusion path during the C–D cycling