High performance sodium-ion batteries realized by design functional groups with the polar SrF2 reinforcement layer on modified cellulose separator

Abstract

Because separator serves as a pivotal component that determines the performance of sodium-ion batteries (SIBs), it is essential to develop a separator with excellent electrolyte wettability, exceptional electrochemical performance and superior safety. Herein, a high performance cellulose modified separator with numerous functional groups and a SrF₂ reinforcement layer on the surface has been fabricated through organic synthesis and in situ assembly, which not only endows the separator with an electrolyte-affinitive surface, but also effectively regulates interfacial interactions in the battery. These characteristics feature the separator to accelerate the transport of Na⁺ and form a more stable solid electrolyte interphase (SEI), thereby significantly augment the performance of SIBs. Notably, the Na||hard carbon (HC) cell assembled with the modified separator demonstrates a remarkable discharge capacity of 250.2 (mAh g⁻¹) at 0.5C, surpassing both unmodified cellulose separators (168.7 mAh g⁻¹) and conventional glass fiber (GF) separators (220.2 mAh g⁻¹). In addition, the cell with modified separator still maintains the highest discharge capacity (220.0 mAh g⁻¹) and excellent retention (87.9 %) after 1000 cycles. Furthermore, the prussian blue half cells of modified separator exhibit a high specific capacity of 95.3 mAh g⁻¹ at 1C, and show an enhanced initial specific capacity of 64.0 mAh g⁻¹ at 5C. This research offers a novel strategy for the design of high-performance separator for SIBs.