Two-dimensional　(2D)　transition　metal　chalcogenides　have　been　widely　studied　and　utilized　as　electrode　materials　for　lithium　ion　batteries　due　to　their　unique　layered　structures　to　accommodate　reversible　lithium　insertion.　Real-time　observation　and　mechanistic　understanding　of　the　phase　transformations　during　lithiation　of　these　materials　are　critically　important　for　improving　battery　performance　by　controlling　structures　and　reaction　pathways.　Here,　we　use　in　situ　transmission　electron　microscopy　methods　to　study　the　structural,　morphological,　and　chemical　evolutions　in　individual　copper　sulfide　(CuS)　nanoflakes　during　lithiation.　We　report　a　highly　kinetically　driven　phase　transformation　in　which　lithium　ions　rapidly　intercalate　into　the　2D　van　der　Waals-stacked　interlayers　in　the　initial　stage,　and　further　lithiation　induces　the　Cu　extrusion　via　a　displacement　reaction　mechanism　that　is　different　from　the　typical　conversion　reactions.　Density　functional　theory　calculations　have　confirmed　both　the　thermodynamically　favored　and　the　kinetically　driven　reaction　pathways.　Our　findings　elucidate　the　reaction　pathways　of　the　Li/CuS　system　under　nonequilibrium　conditions　and　provide　valuable　insight　into　the　atomistic　lithiation　mechanisms　of　transition　metal　sulfides　in　general.