Single–Ion Conducting Polymer Nanoparticles as Functional Fillers for Solid Electrolytes in Lithium Metal Batteries

Composite solid electrolytes including inorganic nanoparticles or nanofibers which improve the performance of polymer electrolytes due to their superior mechanical, ionic conductivity or lithium transference number are actively being searched for applications in lithium metal batteries. However, inorganic nanoparticles present limitations such as its tedious surface functionalization and agglomeration issues and poor homogeneity at high concentrations in polymer matrices. In this work, we report on polymer nanoparticles with lithium sulfonamide surface functionality (LiPNP) for application as electrolytes in lithium metal battery. The particles are prepared by semibatch emulsion polymerization, an easily up–scalable technique. LiPNPs are used to prepare two different families of particle reinforced solid electrolytes. When mixed with polyethylene oxide and lithium bis(trifluoromethane)sulfonimide (LiTFSI/PEO), the particles provoke a significant stiffening effect (E´ > 106 Pa vs. 105 Pa at 80 ºC) while retaining high ionic conductivity (σ = 6.6 × 10–4 S cm–1). Preliminary testing in LiFePO4 full cells, showed promising performance of the PEO nanocomposite electrolytes. By mixing the particles with propylene carbonate without any additional salt, we obtain true single ion conducting gel electrolytes as the lithium sulfonamide surface functionalities are the only sources of lithium ions in the system. The gel electrolytes are mechanically robust (up to G´ =106 Pa) and show ionic conductivity up to 10–4 S cm–1. Finally, the PC nanocomposite electrolytes were tested in symmetrical lithium cells. Our findings suggest that all–polymer nanoparticles could represent a new building block material for solid–state lithium metal battery applications.