Improved Li-Ion Conduction and (Electro)Chemical Stability at Garnet-Polymer Interface through Metal-Nitrogen Bonding

摘要

Organic-inorganic composite solid electrolytes consisting of garnet fillersdispersed in polyvinylidene difluoride (PVDF) frameworks have shownpromise to enable high-energy solid-state Li-metal batteries. However, theair-sensitive garnets easily form poorly-conductive residues, which hindersfast Li-ion exchange at the garnet-polymer interface and results in low ionicconductivity. The highly alkaline residues trigger instant dehydrofluorinationof PVDF to form unsaturated CC bonds, which are unstable againsthigh-voltage cathode materials. Here it is shown that, by applying a 10-nmpolydopamine coating on the residue-removed garnet surface, the modifiedgarnet filler becomes air-stable and does not generate alkaline residues, soPVDF remains an intact structure. Surface characterizations reveal substantialmetal-nitrogen bonding between the La atoms of garnet and the aminogroups of polydopamine, which can invite stronger adsorption of Li ionsat the heterointerface. A new interparticle Li-ion conduction mechanism isdisclosed for the composite electrolyte, in which Li ions preferably migratethrough the garnet-polydopamine interface, forming an efficient ion-percolationnetwork. As a result, the composite electrolyte demonstrates aneffective room-temperature Li~+ conductivity of 1.52 × 10~(–4) S cm~(–1) and a highcutoff voltage of up to 4.7 V versus Li~+/Li to support stable operation of allsolid-state Li-LiCoO_2 batteries.