Boosting the Ion Mobility in Solid Polymer Electrolytes Using Hollow Polymer Nanospheres as an Additive

Solid polymer electrolytes (SPEs) possess improved thermal and mechanical stability as safe energy storage devices. However, their low ion mobilities and poor electrochemical stabilities still hinder the wide industrial application of SPEs. Herein, we introduce an SPE design that provides an enormous number of electrochemically stable pathways and space for lithium-ion transport, blending polymer (polydopamine) hollow nanospheres with an inactive inorganic template into a poly(ethylene oxide) (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) based SPE. Hollow silica acts as a template for polydopamine processing a large contact area with the polymer electrolyte, and the interface between the polymer electrolyte and hollow composite fillers provides amounts of ion transport channels. In addition, theoretical calculations reveal a strong adsorption between polydopamine and TFSI^-, which suppresses the TFSI^- motion and meanwhile facilitates the selective Li⁺ transport. The hollow polydopamine can serve as a versatile platform for anion trapping and has large compatible and stable depression for a well-defined ion transfer interface layer, forming a three-in-one nanocomposite for the enhancement of ionic conductivity with no sacrifice of the mechanical properties. Experimental data confirmed the high mobility of ions within the composite electrolyte with an ionic conductivity of 0.189 mS cm^-1 in comparison to the SPE without additives (0.105 mS cm^-1) at 60 °C. The mobility of the Li⁺ increases after adding the polymer-coated inorganic additives, associated with a noticeable enlargement of the electrochemical window. Furthermore, an all-solid-state Li/LiFePO₄ battery with a hollow polydopamine nanoparticle-polymer composite electrolyte shows long life, high reversible capacity (134.9 mAh g^-1), and high capacity retention (97.2%) after 205 cycles at 0.2 C.