Building the homogeneous ionic interfaces and channels for high compatible composite PVDF/SiO2 solid electrolyte by grafting sulfonate betaine

Abstract

Poor solid–solid interfacial compatibility has been a troubling challenge to the development of solid-state lithium metal batteries. For this purpose, inspired by mussel mimetic chemistry, the homogeneous ionic interfaces and channels between PVDF matrix and SiO2 nanospheres were built by grafting sulfonate betaine (SB) on their surfaces via Schiff base reaction and ring opening reaction. Furthermore, the influence of SB-SiO2 content on the structure, mechanical properties, thermal stability and electrochemical performances of the composite solid-state electrolyte was also studied. Desirably, Li+ transference number and ionic conductivity of 8%SB-SiO2/SB-PVDF/LiTFSI electrolyte membrane were as high as 0.50 and 5.5 × 10−5 S/cm, respectively, much higher than those of the counterparts in literatures. Uniform dispersion of SB-SiO2 nanospheres in 8%SB-SiO2/SB-PVDF/LiTFSI electrolyte membrane built the homogeneous continuous ion channels, while the homogeneous structure of SB-PVDF and PVDF binder in the electrode also facilitated the interface compatibility of the membrane/electrode, and thus the synergistic effect improved the Li+ transference number. The reversible specific capacity of LiFePO4//8%SB-SiO2/SB-PVDF/LiTFSI//Li battery was 129.7 mAh/g at 1.0 C for 200 cycles, higher than those of other two electrolyte membranes, meanwhile, high-voltage LCO//8%SB-SiO2/SB-PVDF/LiTFSI//Li battery also exhibited good Li-storage performance, indicating high feasibility of 8%SB-SiO2/SB-PVDF/LiTFSI electrolyte membrane in solid-state lithium metal batteries.