Exploring　the　structure　transformation　mechanism　of　the　spent　cathodes　during　their　regeneration　process　is　the　key　to　optimizing　the　processing　protocol.　The　spent　cathode　materials　are　in　different　state　of　health　(SOH)　due　to　their　different　operation　history,　which　leads　to　the　challenge　of　restoring　them　in　one-pot.　Herein,　to　address　the　effect　of　SOH　on　the　direct　regeneration　protocol,　we　systematically　investigated　the　spent　LiCoO2　(LCO)　cathode　with　low　and　high　SOH.　We　find　that　lithium-deficiency　and　Al　impurity　are　the　two　important　factors　in　affecting　the　regeneration　quality　of　the　spent　LCO.　Lithium-deficiency　can　cause　void　defects　and　disordered　lattice　structure.　Al　impurity　is　brought　to　the　LCO　surface　during　lithium　replenishment　process,　which　further　diffuses　into　the　LCO　subsurface　layer　during　the　following　high　temperature　sintering.　Based　on　our　understanding　of　the　regeneration　process,　the　regeneration　protocol　is　optimized　accordingly,　which　can　successfully　restore　the　spent　LCO　with　different　SOH.　©　2023　Elsevier　Ltd