Self-assembled nano-silica-embedded polyethylene separator with outstanding physicochemical and thermal properties for advanced sodium ion batteries

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Vol. 405; p. 125844
• Main Authors: Mun, Junyoung, Yim, Taeeun, Gap Kwon, Yong, Jae Kim, Ki
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.02.2021
• Subjects: Electrochemical performance; Poly(ethylene) separator; Silica; Sodium ion battery; Thermal stability; Wettability; Electrochemical performance; Sodium ion battery; Wettability; Poly(ethylene) separator; Silica; Thermal stability
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2020.125844

[Display omitted] •Nano-SiO2 is incorporated in the polyethylene (PE) for Na ion battery separator.•Nano-SiO2 is applied as coating of the PE backbone and internal nano particles.•SiO2 was accommodated with preserving the thickness of the separator.•SiO2-treatment enhance Na ion electrolyte wetting as well as thermal safety.•Credible µm thickness PE separator is firstly introduced to Na battery separator. Sodium ion batteries (NIBs) provide significant advantages for large-scale energy conversion and storage devices. NIBs are extensively investigated because of the global abundance of Na resources. The Na ion is similar to the Li ion; however, the conventional poly(ethylene) (PE) separator used in Li ion batteries is unsuitable for NIBs because of its extremely poor wettability by the Na+ electrolyte and its high thermal shrinkage. These properties can cause severe safety issues at elevated temperatures, as well as poor ionic conductivities. Therefore, the PE separator needs modification for use in high-performance NIBs. Here, we propose a unique nano-SiO2 impregnation method that preserves the thickness of the separator to ensure a high volumetric energy density. Silica matrices are incorporated into the PE separator through a simple chemical modification that includes embedding the hydroxyl group by benzoyl peroxide treatment, followed by Si–O condensation to introduce 3-(trimethyloxysilyl)propyl methacrylate auxiliaries. These steps allow the introduction of multiple Si–O functional groups onto the PE backbone through chemical reactions with tetraorthosilicate. The proposed separator exhibits high wettability and ionic conductivity while maintaining the initial separator thickness. The nano-SiO2-impregnated PE has significantly improved thermal stability and high dimensional stability even at an elevated temperature of 140℃. Na full-cell systems, consisting of Na0.9Li0.05Ni0.25Fe0.25Mn0.5O2 and hard carbon electrodes, exhibit considerably increased cycle lives and rate capabilities when fabricated with this nano-SiO2-impregnated PE separator.