It　is　promising　but　still　challenging　for　the　widespread　application　of　aqueous　zinc　batteries　due　to　the　poor　reversibility　of　the　zinc　anode　caused　by　prevalent　dendrite　growth　and　pronounced　interfacial　side　reactions.　Herein,　we　report　a　rare　soluble　and　water-stable　high-nuclearity　{Nd9Si4W39}　polyoxotungstate.　Interestingly,　upon　encountering　Zn2+　ions,　the　discrete　{Nd9Si4W39}　nanocluster　undergoes　a　structural　transformation　to　form　an　infinitely　extended　cluster-based　{[Zn(H2O)4]3[Nd9Si4W39]2}　two-dimensional　honeycomb　layer,　with　which　atomic-level　Zn2+　ion　effects　in　reconstructing　the　layer　are　determined.　More　interestingly,　we　demonstrate　that　the　structural　transformation　property　renders　the　{Nd9Si4W39}　cluster　an　efficient　electrolyte　additive　for　aqueous　zinc　batteries,　enabling　the　formation　of　the　2D　layer　as　a　protective　layer　on　the　zinc　anode,　significantly　enhancing　the　reversibility　of　the　zinc　anode.　Compared　to　the　pristine　Zn//Zn　symmetric　battery,　the　Zn//Zn　symmetric　battery　with　the　{Nd9Si4W39}　additive　exhibits　an　extended　lifespan　of　over　2000　hours　at　a　current　density　of　1　mA　cm-2.　In　situ　optical　microscopy,　Raman　spectroscopy,　and　molecular　dynamics　simulations　reveal　that　the　formation　of　the　protective　layer　effectively　promotes　uniform　zinc　deposition,　and　inhibits　zinc　agglomeration,　dendrite　growth,　and　side　reactions,　thereby　enabling　the　zinc　anode　to　exhibit　high　reversibility　and　long-term　service　life.