A Self‐Forming Composite Electrolyte for Solid‐State Sodium Battery with Ultralong Cycle Life

TLDR

Solid electrolytes can improve battery safety, but their low ionic conductivity and high interfacial resistance limit solid‑state battery performance. The study proposes a self‑forming composite electrolyte to enhance ionic conductivity. The authors synthesize a Na‑based NASICON composite and add a small amount of nonflammable ionic liquid at the cathode to improve interfacial kinetics. The Na‑based composite electrolyte delivers 3.4 mS cm⁻¹ at 25 °C and 14 mS cm⁻¹ at 80 °C, and when paired with a small amount of ionic liquid at the cathode, the resulting Na₃V₂(PO₄)₃/IL/SE/Na solid‑state battery retains ~90 mAh g⁻¹ after 10 000 cycles at 10 C, demonstrating ultralong cycle life and high rate capability.

Abstract

Replacing organic liquid electrolyte with inorganic solid electrolytes (SE) can potentially address the inherent safety problems in conventional rechargeable batteries. However, solid‐state batteries (SSBs) have been plagued by the relatively low ionic conductivity of SEs and large charge‐transfer resistance between electrode and SE. Here, a new design strategy is reported for improving the ionic conductivity of SE by self‐forming a composite material. An optimized Na + ion conducting composite electrolyte derived from the Na 1+ n Zr 2 Si n P 3− n O 12 NASICON (Na Super Ionic Conductor) structure is successfully synthesized, yielding ultrahigh ionic conductivity of 3.4 mS cm −1 at 25 °C and 14 mS cm −1 at 80 °C. On the other hand, in order to enhance the charge‐transfer rate at the electrode/electrolyte interface, an interface modification strategy is demonstrated by utilization of a small amount of nonflammable and nonvolatile ionic liquid (IL) at the cathode side in SSBs. The IL acts as a wetting agent, enabling a favorable interface kinetic in SSBs. The Na 3 V 2 (PO 4 ) 3 /IL/SE/Na SSB exhibits excellent cycle performance and rate capability. A specific capacity of ≈90 mA h g −1 is maintained after 10 000 cycles without capacity decay under 10 C rate at room temperature. This provides a new perspective to design fast ion conductors and fabricate long life SSBs.