NaF interfacial riveting and lattice doping enable high-density NZSP solid electrolyte with long-cycle performance

Abstract

Na3Zr2Si2PO12 (NZSP) shows great potential as candidate of solid electrolyte for solid-state sodium batteries. Herein, a high density NZSP solid electrolyte with space group of C2/c is synthesized by a new strategy. Such new strategy rivets most of NaF at the grain boundaries, effectively increasing the density of NZSP pellets. A small amount of F- doped into the lattice alters the lattice parameters of NZSP. The riveted NaF and doped F- cooperatively enhance the ionic conductivity of NZSP solid electrolyte. The optimized NZSP solid electrolyte, containing 3 wt%NaF additives and sintered at 1050 °C, exhibits a room-temperature Na+ conductivity of 7.2×10−4 S cm−1 and low activation energy of 0.23 eV. The solid-state battery using the optimized sample NZSP+3 wt%NaF as solid electrolyte has a wide electrochemical window of up to 7.0 V (vs. Na+/Na) and ultra-stable cycling capability towards the bare sodium metal. The corresponding symmetrical battery demonstrates stable and reversible cycle at 0.2 mA cm−2 for 700 h with negligible voltage polarization, the longest cycling time reported to date at this current density. At current density of 0.08 mA cm−2(0.5 C), all-solid-state battery of Na3V2(PO4)3/NZSP+3 wt%NaF/Na can deliver a discharge capacity of 62 mAh g−1 after 60 cycles. The interfacial rivet method offers valuable insights and inspiration for the development of other types of ceramic solid electrolytes.