New-Type Hf-Based Nasicon Electrolyte For Solid-State Na-Ion Batteries With Superior Long-Cycling Stability And Rate Capability

The NASICON electrolyte with good chemical stability, suitable three-dimensional ion channel, high mechanical strength and wide electrochemical window, has been considered to be the one of most promising electrolytes for solid-state Na-ion batteries. However, the unsatisfactory ionic conductivity and large interface resistance severely limit its practical application. Herein, a new-type Hf-based NASICON electrolyte Na3.2Hf1.9Ca0.1Si2PO12 is synthesized, the conductivity of which can reach 1.07 x10(-3) S cm(-1) at room temperature and the stability electrochemical window can reach 8.80 V. In addition, a mixed-ion-electron interphase was constructed on the surface of Na3.2Hf1.9Ca0.1Si2PO12 which can guarantee a close contact and fast charge transfer between sodium and the electrolyte. The batteries with this new-type electrolyte can cycle stably more than 2400 h at room temperature and the critical current density can reach 1.9 mA cm(-2). Even the current density reaches 2.0 mA cm(-2), there was still no obvious short circuit, which was the highest value in similar works. The full cell of Na/Na3V2 (PO4)(3) with this electrolyte can maintain a capacity of 103.1 mAh g(-1) at 0.5 C without capacity decaying even after more than 300 cycles.