Aqueous　zinc-ion　batteries　(AZIBs)　have　demonstrated　considerable　potential　for　utilization　in　large-scale　energy　storage　applications,　driven　by　their　environmental　sustainability,　inherent　safety　and　cost-effectiveness.　Nonetheless,　the　growth　of　Zn　dendrites　and　side　reactions,　resulting　in　degraded　cycling　stability,　poses　a　substantial　obstacle　to　the　practical　implementation　of　AZIBs.　Herein,　it　is　demonstrated　that　creatinine　(Cre),　a　metabolite　derived　from　muscle,　serves　as　a　multifunctional　electrolyte　additive　that　enhances　the　performance　of　AZIBs.　Both　experimental　and　theoretical　analyses　reveal　that　Cre,　when　used　as　an　electrolyte　additive,　fulfills　three　key　roles:　it　disrupts　the　solvation　structure　of　Zn2+　by　carbonyl　group;　it　forms　a　water-deficient　electric　double　layer,　thereby　reducing　the　likelihood　of　interfacial　water　decomposition;　and　it　promotes　the　deposition　of　Zn2+　on　the　(002)　planes,　facilitating　the　uniform　deposition.　The　Zn||Zn　symmetric　cell　utilizing　a　1 M　ZnSO4　electrolyte　with　the　addition　of　0.3 M　Cre　exhibits　stable　cycling　for　900　h　under　the　condition　of　1 mA　cm−2　and　1　mAh　cm−2,　representing　an　over　11-fold　increase　in　lifespan.　Furthermore,　the　Zn||VO2　full　cell　demonstrates　a　capacity　retention　of　≈105　mAh　g−1　after　300　cycles　at　a　rate　of　10　C.　©　2025　Wiley-VCH　GmbH.