Kirkendall Growth of Hollow Mn₃O₄ Nanoparticles upon Galvanic Reaction of MnO with Cu²⁺ and Evaluation as Anode for Lithium-Ion Batteries

We report the formation of high surface area hollow Mn₃O₄ nanoparticles that form as a result of the galvanic reaction of Cu²⁺ with MnO nanocrystals concomitant with a nanoscale Kirkendall effect. The MnO nanocrystals were prepared according to the ultralarge scale synthesis reported by Hyeon, which allowed the preparation of hollow Mn₃O₄ in multigram quantities. Ex-situ analyses with transmission electron microscopy and powder X-ray diffraction show the morphology and phase stability of the hollow particles correlate with DSC-TGA data and show collapse of the hollow particles at temperatures greater than 200 °C. Electrodes fabricated from hollow Mn₃O₄ exhibited excellent initial Li ion storage capability (initial discharge capacity = 1324 mAh/g) but poor cycling performance (97% loss of discharge capacity after 10th cycle), whereas Mn₃O₄-MWCNT electrodes exhibited good reversibility and discharge capacity of 760 mAh/g after 100 cycles.