Metal　oxides　hold　the　promise　of　high-capacity　anodes　for　Li-ion　batteries.　Lithiation　of　binary　metal　oxides　proceeds　with　two　typical　mechanisms:　insertion　and　conversion.　We　characterize　the　two-step　lithiation　behavior　of　alpha-MoO3,　namely,　Li　intercalation　in　the　layered　alpha-MoO3　leads　to　the　formation　of　crystalline　Li2MoO3　in　the　early　stage　of　lithiation,　and　further　Li　insertion　coverts　LixMoO3　to　metallic　Mo　and　amorphous　Li2O.　The　intercalation　process　is　thermodynamically　more　favorable　and　is　accompanied　with　a　minor　volumetric　change,　while　the　conversion　reaction　is　kinetically　slow　and　induces　large　deformation.　Furthermore,　instead　of　showing　significant　Li-embrittlement　as　seen　in　typical　oxides,　alpha-MoO3　remains　defects　free　despite　the　nearly　100%　repetitive　volumetric　change　during　lithiation　cycles.　The　reaction　mechanism,　structural　evolution,　and　mechanical　behaviors　are　unveiled　through　coordinated　in-situ　transmission　electron　microcopy　experiments　on　alpha-MoO3　nanobelts　and　first-principles　computational　studies.　The　results　provide　fundamental　perspectives　in　the　course　of　developing　reliable　high-capacity　electrodes　for　Li-ion　batteries.　(C)　2016　Elsevier　Ltd.　All　rights　reserved.