Lithium-rich　layered　oxides　have　been　considered　as　the　most　promising　candidate　for　offering　a　high　specific　capacity　and　energy　density　for　lithium-ion　batteries.　However,　their　practical　applications　are　still　suffered　by　the　cycle　instability　and　also　closely　related　thermal　stability.　Here,　microsized　crystalline　grains　with　good　dispersion　of　lithium-rich　layered　oxides　are　prepared　by　a　molten-salt　method,　while　a　spinel　structure　is　also　introduced　on　a　grain　surface　by　following　chemical　oxidation　and　annealing　process,　and　their　thermal　performance　with　different　cutoff　voltages　during　the　charge　process　is　systematically　studied　using　differential　scanning　calorimetry　method.　Results　have　shown　that　thermal　stability　of　microsized　crystalline　grains　is　better　than　that　of　spherical　secondary　agglomerates,　the　spinel　structure　introduction　on　the　grain　surface　of　microsized　crystalline　grains　can　contribute　obviously　to　their　thermal　stability,　in　which　the　onset　temperature　of　the　exothermic　peak　has　been　increased　by　103　degrees　C,　and　the　thermal　release　value　can　be　reduced　as　much　as　about　40%　when　the　battery　was　charged　to　4.8　V.　Furthermore,　the　electrochemical　performance,　especially　cycle　stability　under　a　high　temperature,　has　also　been　enhanced　for　spinel-modified　microsized　crystalline　grains.　This　work　not　only　develops　the　microsized　crystalline　grains　with　good　dispersion　of　lithium-rich　layered　oxides,　confirming　the　advantages　of　these　materials　compared　to　spherical　secondary　agglomerates,　but　also　reveals　the　method　to　improve　their　thermal　stability　by　grain　surface　structure　modification,　opening　the　way　to　optimize　the　comprehensive　performance　of　electrode　materials　for　batteries.