Micron　spherical　Sn　doping　Li1.2Ni0.2Mn0.8O2　cathode　materials　are　synthesized　via　a　carbonate　co-precipitation　method.　The　crystal　structure　and　morphology　of　the　pristine　and　Sn-doping　samples　are　characterized　by　a　joint　X-ray　diffraction　(XRD)　Rietveld　refinement　method　and　scanning　electron　microscopy　(SEM).　It　is　proved　that　Sn　successfully　doped　into　the　aimed　materials.　X-ray　photoelectron　spectroscopy　(XPS)　results　demonstrate　that　the　chemical　state　of　Sn　is　+4.　Appropriate　doping　contents　of　Sn　are　beneficial　to　improve　the　electrochemical　performance,　including　the　capacities　and　cycling　stability.　The　sample　with　1.0　mol%　Sn　delivers　high　initial　discharge　capacities　and　improved　rate　performance　(212.6　mAh/g　at　0.2C　and　137.8　mAh/g　at　5C,　respectively).　The　capacity　retention　is　96.2%　after　50　cycles　at　0.2C.　It　is　very　stable　for　the　doped　sample　with　2.0　mol%　Sn　after　160　cycles　at　0.2C,　the　capacity　retention　is　98.5%.　The　discharge　capacity　decreases　markedly　with　the　Sn　contents　increase　to　3.0　mol%,　since　Sn4+　can　not　participate　in　electrochemical　reaction.　Electrochemical　impedance　spectroscopy　(EIS)　results　demonstrate　that　the　charge　transfer　resistance　of　the　samples　with　1.0-2.0　mol%　Sn-doping　decreases　obviously.　It　reveals　that　doping　with　appropriate　Sn　substitution　not　only　improves　the　structure　stability,　but　also　increases　the　conductivity,　therefore　improves　their　rate　capability　and　cycling　stability.　(C)　2015　Elsevier　Ltd.　All　rights　reserved.