A Stable Cathode-Solid Electrolyte Composite for Long-Cycle-Life, High Voltage Solid-State Sodium-ion Batteries

Abstract

<p>Rechargeable solid-state sodium-ion batteries (SSSBs) hold great promise for safer and more energy-dense energy storage. However, the poor electrochemical stability between current sulfide-based solid electrolytes and high-voltage oxide cathodes has limited their long-term cycling performance and practicality. Here, we report the discovery of Na<sub>3-<i>x</i></sub>Y<sub>1-<i>x</i></sub>Zr<i><sub>x</sub></i>Cl<sub>6</sub> (NYZC) as an ion conductor that is both electrochemically stable (up to 3.8 V vs. Na/Na<sup>+</sup>) and chemically compatible with oxide cathodes. Its high ionic conductivity of 6.6 x 10<sup>-5</sup> S cm<sup>-1</sup><sub> </sub>at ambient temperature, several orders of magnitude higher than oxide coatings, is attributed to abundant Na vacancies and cooperative MCl<sub>6</sub> rotation, resulting in an extremely low interfacial impedance. A SSSB comprising a NaCrO<sub>2</sub>+NYZC composite cathode, Na<sub>3</sub>PS<sub>4</sub> electrolyte, and Na-Sn anode exhibits an exceptional first-cycle Coulombic efficiency of 97.1% at room temperature and can cycle over 1000 cycles with 89.3% capacity retention at 40°C. These findings highlight the immense potential of halide ion conductors for SSSB applications.</p>

High‐Entropy Solid‐State Na‐Ion Conductor for Stable Sodium‐Metal Batteries

“…They mostly exhibit good chemical and electrochemical stability, [4] in sharp contrast to sulfide SEs with narrow electrochemical window, which also easily get decom-posed upon exposure towards humidity and oxygen. [5] However, high temperature sintering process (> 1200 °C) is always indispensable for the synthesis of oxides; and the ionic conductivity of oxide electrolytes (10 À 4 ~10 À 3 S cm À 1 ) is usually one order of magnitude lower than that of sulfides (10 À 3 10 À 2 S cm À 1 ), which will undisputedly restrict the capacity and the rate performance of ASSBs. [6] Hence, it is of great importance to explore oxide SEs with high ionic conductivity and preferably low sintering temperature from energy-saving point of view.…”

Extending the Electrochemical Window of Na+ Halide Nanocomposite Solid Electrolytes for 5 V-Class All-Solid-State Na-Ion Batteries

“…The Xray diffraction (XRD) patterns of these samples revealed that the original trigonal P3m1 structure of Na 2 ZrCl 6 is retained across all variants (Figure 1a). 24,43 Specifically, up to x = 1.0, a gradual positive shift in the (301) peak at ∼30.5°with no emerging impurity phases suggests a lattice contraction in Na 2 ZrCl 6 , which is attributed to the smaller ionic radius of F − (133 pm) compared to that of Cl − (181 pm). 55 However, at x ≥ 1.5, the evolution of NaCl indicated a fluorination limit between x = 1.0 and 1.5.…”

“…40,41 While fewer Na + halide SEs have been identified compared to their Li + counterparts, their development has followed similar patterns. 25 Na + halide SEs developed via composition tuning include Na 3−x Er 1−x Zr x Cl 6 (0.04 mS cm −1 ), 42 Na 3−x Y 1−x Zr x Cl 6 (0.066 mS cm −1 ), 43 Na 3−x Yb 1−x Zr x Cl 6 (0.066 mS cm −1 ), 44 Na 3−x Cr 1−x Zr x Cl 6 (0.1 mS cm −1 ), 45 and Na 3−x In 1−x Zr x Cl 6 (∼0.01 mS cm −1 ). 46 A significant enhancement in ionic conductivity has been observed in several compounds prepared using the mechanochemical method, such as Na 2 ZrCl 6 , NaAlCl 4 , and Na 3 InCl 6 .…”

“…16 This new site facilitates the formation of a net-like 2D ionic conduction pathway within the ac-plane. However, the advancement of halide-based ASNBs is often hindered by the limited ionic conductivities of several halide SEs, typically at approximately 10 −5 S cm −1 , 24,25,42,43,48 except for NaAlCl 4−2x O x (1.3 mS cm −1 ) 49 and Ta-based materials (2.7 and 4.6 mS cm −1 for 0.5Na 2 O 2 −TaCl 5 and x[Na 0.75 (La/Sm) 1.75 Cl 6 ]•(1−x)-[NaTaCl 6 ], respectively). 50,51 Our group recently demonstrated a novel method for ameliorating the ionic conductivity of halide SEs through interfacial conduction by using a nanocomposite strategy.…”

“…52 In the realm of Na + halide SEs, studies on enhancing the electrochemical stability of Na + chloride SEs are still lacking, specifically with the absence of cases for fluorinated Na + chloride SEs. Furthermore, while most previous studies on Na + halide SEs have focused on the 3 Vclass NaCrO 2 cathode, 16,24,43 significant developments in various high-voltage Na + cathodes, such as Na-F e 0 . 5 5 M n 0 .…”