A PVDF/g−C3N4-Based Composite Polymer Electrolytes for Sodium-Ion Battery
Kewei Shu, Jiazhen Zhou, Xiaojing Wu, Xuan Liu, Liyu Sun, Yu Wang, Siyu Tian, Huizhu Niu, Yihao Duan, Guangyu Hu, Haihua Wang
Abstract
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 C3N4 (g−C3N4) nanosheets as a novel nanofiller to form g−C3N4 composite solid polymer electrolytes (CSPEs). The analysis shows that the g−C3N4 filler can not only modify the structure in g−C3N4CSPEs 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−C3N4 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−C3N4. By applying the g−C3N4 CSPEs in the sodium-metal battery with Na3V2(PO4)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.