This　review　aims　to　provide　an　insight　into　the　imidazolium　ionic　liquids　(ILs)　as　novel　phase　change　materials　(PCMs)　for　low　and　medium　temperature　thermal　energy　storage,　with　a　focus　on　their　multi-dimensional　thermophysical/nucleation　features　within　encapsulation　for　defect　regulation　during　solid–liquid　transition.　Imidazolium　ILs　have　been　emerging　as　novel　phase　transition-based　energy　storage　material　due　to　unique　properties　of　wide　liquidous　range,　rich　crystallization　behavior,　small　thermal　volumetric　expansion　and　environmental-friendly　properties,　but　suffer　from　defects　of　low　enthalpy　and　large　supercooling.　To　meet　the　challenge　acting　as　PCMs,　the　work　first　gave　a　brief　overview　on　supercooling　regulation　and　enthalpy　elevation　of　imidazolium　ILs,　and　proposed　micro-encapsulation　with　crystallization-promoting　porous　shell　to　regulate　their　defects.　Then　discussion　regarding　multi-dimensional　thermophysical　features　of　imidazolium　ILs　were　given,　including　features　within　micro-confined　capsule　core　(phase　transition,　melting　point,　thermal　stability,　specific　heat　capacity　and　thermal　conductivity),　nano-confined　nucleation　within　the　mesoporous　shell,　and　mesoporous　interfacial　nucleation.　Finally,　the　future　applications　of　imidazolium　ILs　and　microencapsulation　in　the　fields　of　infrared　stealthy,　solar　thermal　utilization,　thermal　management　in　extreme　environment　and　green　energy-saving　building　were　highlighted.　The　study　provides　a　timely　review　of　the　imidazolium　ILs　acting　as　thermal　energy　storage　(TES)　materials,　and　future　suggestion　like　functional　ILs　with　more　hydrogen　bonds　or　supercooling　utilization　for　seasonal　TES　may　help　concentrate　efforts　on　solving　the　key　issues　in　urgent　need.　©　2023　Elsevier　B.V.