Bottom-up formation of crystalline PEO/Na+ scaffolds in NaPF6-Diglyme-PEO and the electrochemical properties of the resulting electrolytes

Ultrahigh Molecular Weight polyethylene oxide (UHMW PEO) and NaPF 6 diglyme produce solid electrolytes with chemical and electrochemical stability in Prussian White (PW)//Hard Carbon (HC) and Na//Al cells. Both the NaPF 6 concentration and the polymer content rule the rheology, and the mechanical and electrochemical properties of the electrolytes. The use of UHMW PEO allows to incorporate minimum concentrations with maximum rheological impact. The solid character is achieved by the formation of rigid scaffold consisting of PEO/Na + crystalline complexes, which stops flow and provides a mechanical barrier between electrodes. To maximize the benefits of polymer addition, it is worthwhile to test formulations in which the concentration of Na + and PEO are varied. This is because the PEO/Na + crystalline complexes reduce the amount of mobile Na + cations. Na + complexation and crystalline phase distribution is studied by FTIR, XRD and DSC in NaPF 6 in diglyme solutions of concentration 0.9 to 1.5 m, and their solid electrolytes where PEO varies from 5 to 10 wt%. Ion mobility (conductivity and diffusivity) is studied in relation to their chemical composition and phase distribution, and their electrochemical behaviour is investigated in PW//HC and Na//Al cells. Cells with solid polymer electrolytes show remarkable performance even at room temperature and high current rate (1C). • NaPF 6 /diglyme electrolytes are studied as a function of the salt concentration. • PEO/NaPF 6 /diglyme electrolytes with different formulations are prepared. • In these electrolytes, crystalline PEO/Na complexes act as built-in separator. • The best PEO electrolytes perform well in PW//HC cells even at 1C and RT. • PEO electrolytes detach from the electrodes after cycling: component recovery.