Phase　boundary　movement　accomplishing　reversible　LiFePO4/FePO4　biphasic　transition　is　a　fundamental　Li-ion　intercalation/deintercalation　mechanism　for　LiFePO4　cathode.　Phase　boundary　energetically　favors　crack　nucleation　and　propagation;　thus,　postmortem　observation　on　cracks　becomes　a　feasible　approach　to　investigate　the　phase-transition　behavior　and　the　Li-ion　diffusion　mechanism.　The　previously　observed　(200)　plane　cracks　facilitate　the　＂domino＂　diffusion　model.　Herein,　our　microscopic　observations　reveal　another　type　of　cracks　along　the　(020)　planes　in　a　commercial　LiFePO4　cathode　cycled　at　moderate　rates　(0.1C,　0.33C,　and　1C).　Such　(020)　plane　cracks　are　more　detrimental　to　electrochemical　performance　because　they　can　cut　off　the　Li-ion　diffusion　pathway,　causing　inactive　segments　of　LiFePO4.　The　(020)　plane　cracks　indicate　the　LiFePO4/FePO4　phase　boundary　is　along　the　(020)　plane　and　moving　along　the　b-axis　during　battery　operation,　which　is　a　typical　bulk　diffusion-limited　Li-ion　diffusion　behavior.　Our　observations　stress　that　large　LiFePO4　primary　particle　(＞200　nm)　not　only　aggravates　cracking　degradation　but　also　switches　the　Li-ion　diffusion　mode　to　a　slow　bulk　diffusion　mechanism,　plunging　the　overall　battery　performance.