Tuning the cathode/solid electrolyte interface for high-performance solid-state Na-ion batteries

This study examines and compares the impact of various interfacial modification strategies in optimizing the contact resistance between the rigid ceramic electrolyte and cathode active material (AM) in solid-state sodium-ion batteries (SSBs). All the cells are fabricated using Na_3.1V₂P_2.9Si_0.1O_12, Na_3.456Mg_0.128Zr_1.872Si_2.2P_0.8O₁₂, and Na as a cathode AM, solid electrolyte (SE) and anode, respectively. The AM/SE interface is modified by (1) wetting the interface with organic liquid electrolyte (LE), (2) slurry casting and sintering a thin layer of composite cathode, and (3) infiltrating AM precursors inside the porous SE structure followed by drying and sintering. Despite exhibiting a stable cyclability performance, the SSBs prepared using the LE modification and composite cathode approach possess a low AM loading of < 1 mg·cm⁻². On the other hand, the SSBs with infiltrated-cathode exhibit a superior discharge capacity of ∼ 102 mAh·g⁻¹ at 0.2C and less than 5% capacity fading after 50 cycles at room temperature. Notably, these cells contain a high AM loading of 2.12 mg·cm⁻². The microstructural analysis reveals the presence of AM particles inside the pores of the porous SE, allowing for the efficient insertion/removal of sodium ions. The porous scaffold of SE not only provides continuous sodium-ion conduction pathways inside the cathode structure but also renders stability by accommodating stress induced by volume change during repeated cycling. The outcomes of this work demonstrate the effectiveness of the wet-chemical infiltration technique in improving the AM loading and storage capacity performance of SSBs working at 25°C.