Optimization of Na3Zr2Si2PO12 ceramic electrolyte and interface for high performance solid-state sodium battery

Abstract

Poor ionic conductivity of solid-state electrolyte (SE) and high interface resistances between the SE and electrodes are two major challenges for solid-state sodium batteries (SSBs). In this work, an integrate strategy is proposed for improving the ionic conductivity of SE and reducing the interfacial resistance between SE and cathode. The pure-phase Na3Zr2Si2PO12 (NZSP) is prepared by optimizing the composition ratios of the starting materials and is applied as SE for SSBs. The as-prepared NZSP SE achieves a relatively high ionic conductivity of 1.935 × 10−4 S cm−1 at 25 °C and a good electrochemical stability up to 5 V vs. Na+/Na. The solid-state Na|NZSP|Na symmetrical cell can perform a consistent cycling for 70 h, indicating the excellent chemical and electrochemical stability for SE and SE/Na interface. A composite cathode is fabricated using NZSP and Na3V2(PO4)3 (NVP) particles. The sodiated Nafion is particularly applied as the interface modifier for the cathode to facilitate the ionic contact. At 25 °C, the SSB with NZSP SE and the composite cathode modified by sodiated Nafion delivers a discharge capacity of 81.6 mA h g−1 at the current density of 20 mA g−1 and retains a high capacity of 62.23 mA h g−1 after 50 cycles. These results indicate that optimization of the NZSP electrolyte and the NZSP/NVP interface is an efficient method to achieve the high-performance SSB.