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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.

In order to enhance the electrochemical performance and mechanical properties of poly(ethylene oxide) (PEO)-based solid polymer electrolytes, composite solid electrolytes (CSE) composed of single-ion conducting polymer-modified SiO 2 , PEO and lithium salt were prepared and used in lithium-ion batteries in this work. The pyridyl disulfide terminated polymer (py-ss-PLiSSPSI) is synthesized through RAFT polymerization, then grafted onto SiO 2 via thiol-disulfide exchange reaction between SiO 2 -SH and py-ss-PLiSSPSI. The chemical structure, surface morphology and elemental distribution of the as-prepared polymer and the PLiSSPSI- g -SiO 2 nanoparticles have been investigated. Moreover, CSEs containing 2, 6, and 10 wt% PLiSSPSI- g -SiO 2 nanoparticles (PLi- g -SiCSEs) are fabricated and characterized. The compatibility of the PLiSSPSI- g -SiO 2 nanoparticles and the PEO can be effectively improved owing to the excellent dispersibility of the functionalized nanoparticles in the polymer matrix, which promotes the comprehensive performances of PLi- g -SiCSEs. The PLi- g -SiCSE-6 exhibits the highest ionic conductivity (0.22 mS·cm -1 ) at 60 °C, a large t Li+ of 0.77, a wider electrochemical window of 5.6 V and a rather good lithium plating/stripping performance at 60 °C, as well as superior mechanical properties. Hence, the CSEs containing single-ion conducting polymer modified nanoparticles are promising candidates for all-solid-state lithium-ion batteries.