Engineering　the　particle　morphology　of　high-nickel　layered　cathode　materials　is　critical　for　tackling　the　instability　developed　in　their　structures　upon　electrochemical　cycling　owing　to　anisotropic　lattice　strain　generated　during　lithium　insertion/deinsertion.　This　study　reports　on　the　designer　particle　morphology　of　LiNi0.90Co0.05Mn0.05O2　(NCM90)　cathode　materials　realized　by　processing　them　in　pressurized　oxygen　atmospheres　(1-10　MPa).　Without　conventional　doping　or　coating,　the　NCM90　cathode　materials　exhibit　a　surprisingly　small　primary　particle　size　and　significantly　increased　(approximately　four　times)　particle　number　at　a　high　oxygen　pressure,　for　example,　≥5　MPa.　The　NCM90　cathode　materials,　whose　intercomparable　morphological　information　was　evaluated　for　the　first　time　by　deep　learning,　effectively　eliminate　the　accumulation　of　cycling-induced　local　strain　owing　to　the　randomized　orientation　of　primary　particles　and　the　homogenized　distribution　of　small　primary　particles.　Consequently,　these　cathode　materials　with　a　designer　particle　morphology　exhibit　an　excellent　electrical　cycling　performance.　©　2023　American　Chemical　Society