A PVDF/g−C(3)N(4)-Based Composite Polymer Electrolytes for Sodium-Ion Battery

As one of the most promising candidates for all-solid-state sodium-ion batteries and sodium-metal batteries, polyvinylidene difluoride (PVDF) and amorphous hexafluoropropylene (HFP) copolymerized polymer solid electrolytes still suffer from a relatively low room temperature ionic conductivity. To modify the properties of PVDF-HEP copolymer electrolytes, we introduce the graphitic C(3)N(4) (g−C(3)N(4)) nanosheets as a novel nanofiller to form g−C(3)N(4) composite solid polymer electrolytes (CSPEs). The analysis shows that the g−C(3)N(4) filler can not only modify the structure in g−C(3)N(4)CSPEs by reducing the crystallinity, compared to the PVDF−HFP solid polymer electrolytes (SPEs), but also promote a further dissociation with the sodium salt through interaction between the surface atoms of the g−C(3)N(4) and the sodium salt. As a result, enhanced electrical properties such as ionic conductivity, Na(+) transference number, mechanical properties and thermal stability of the composite electrolyte can be observed. In particular, a low Na deposition/dissolution overpotential of about 100 mV at a current density of 1 mA cm(−2) was found after 160 cycles with the incorporation of g−C(3)N(4). By applying the g−C(3)N(4) CSPEs in the sodium-metal battery with Na(3)V(2)(PO(4))(3) cathode, the coin cell battery exhibits a lower polarization voltage at 90 mV, and a stable reversible capacity of 93 mAh g(−1) after 200 cycles at 1 C.