Dual-anion ether electrolyte enables stable high-voltage Na3V2(PO4)2F3 cathode under wide temperatures

Abstract

Na3V2(PO4)2F3 (denoted as NVPF) is an attractive cathode for sodium ion batteries (NIB) owning to its high theoretical capacity (128 mAh g−1) and high working potential (3.9 V vs Na/Na+). However, NVPF often suffers from low electronic conductivity and unstable cathode electrolyte interphase (CEI), seriously hindering its practical application. Here, a uniform NVPF microsphere assembled by carbon-coated NVPF nanosheets (HM-NVPF@CN) is prepared and subsequently an inorganic-rich B, F species CEI layer on its surface in dual-anion ether electrolyte is constructed to address above drawbacks. The carbon-coated NVPF nanosheets can shorten the diffusion pathway for both Na+ and e−, and provide large electrochemical reaction area. In addition, the robust CEI layer can enhance the Na+ transport and suppress the parasitic reactions. The optimized electrode exhibits a good cycling stability (70 mAh g−1 after 2000 cycles) and outstanding low temperature performance (99 mAh g−1 at −25 °C). The full cell fabricated with a hard carbon (HC) anode achieves a high capacity retention (88% after 930 cycles) and superior high temperature performance (60 °C, 72 mAh g−1 at 5C). This work provides a novel idea to regulate interfacial chemistry of cathodes for the high-voltage NIB.