Water-processable liquid metal nanoparticles by single-step polymer encapsulation

Stabilizing metastable colloids such as gallium-based liquid metal nanoparticles (LM NPs) and using them in complex machining processes is a great challenge due to their simple and sensitive surface chemistry against ligand modification and solution processing. Water, a green solvent, is unfortunately not favored by LM NPs in the entire workflow from synthesis to functionalization and application. This dilemma is relieved herein by presenting a sonochemical polymer deposition technique that can produce a water-dispersible LM@polymer hybrid nanomaterial in one step. Water-soluble polymers such as poly(vinyl pyrrolidone) (PVP) can be directly deposited onto eutectic gallium indium (EGaIn) as a coating shell (up to 20 nm) and prevent their rapid and continuous oxidation in aqueous solutions. EGaIn@PVP NPs are stable after preservation for 30 days in water and 60 days in ethanol, and the polymer coating shows solvent-responsive swelling/shrinking behaviors. The LM@polymer NPs can be stably composited with other materials through complex processing and perform desired functions after composition. For demonstration, EGaIn@PVP NPs are employed as active electrode materials for lithium-ion batteries by compositing with water-soluble binders, and exhibit excellent cycling performances with no obvious decay (capacity retention >95%) in more than 700 cycles at 4 A g(-1). This strategy enriches the toolbox for surface engineering of LMs especially under harsh conditions, which can benefit the applications of LM NPs in various scenarios.