Twin　boundaries　(TBs)　as　a　common　defect　in　layered　cathodes　play　multiple　roles　in　affecting　materials＇　performance,　which　requires　a　deep　understanding　and　an　effective　regulation　method　to　realize　rational　design　of　superior　layered　cathodes.　Herein,　by　virtue　of　advanced　electron　microscopy,　we　demonstrate　that　TBs　can　be　quantitatively　estimated　and　characterized,　and　we　further　validate　that　TBs　can　initiate　massive　cracks　upon　electrochemical　cycling,　which　aggravates　the　performance　decay　of　LiNiO2.　Adjusting　the　synthesis　conditions　cannot　avoid　TB　formation　for　the　solid-state　method,　but　fortunately,　we　find　that　a　coprecipitation　method　can　effectively　eliminate　TBs;　thus,　the　improved　cycling　stability　of　LiNiO2　is　achieved.　We　further　validate　that　TB-free　LiCoO2　can　also　be　synthesized　by　the　coprecipitation　method,　which　demonstrates　improved　cycling　stability.