Structural manipulation approaches towards enhanced sodium ionic conductivity in Na-rich antiperovskites

Abstract

h i g h l i g h t s g r a p h i c a l a b s t r a c tA series of Na-rich antiperovskites were developed as advanced solid electrolytes.The materials are nonflammable, low-cost and suitable for thermoplastic processing. Enhanced sodium ionic conductivity was achieved by structural manipulation approaches. The Na ionic conductivity of Na 2.9 Sr 0.05 OBr 0.6 I 0.4 reaches 1.9 Â 10 À3 S/cm at 200 C. a b s t r a c tHigh-performance solid electrolytes are critical for realizing all-solid-state batteries with enhanced safety and cycling efficiency. However, currently available candidates (sulfides and the NASICON-type ceramics) still suffer from drawbacks such as inflammability, high-cost and unfavorable machinability.Here we present the structural manipulation approaches to improve the sodium ionic conductivity in a series of affordable Na-rich antiperovskites. Experimentally, the whole solid solutions of Na 3 OX (X ¼ Cl, Br, I) are synthesized via a facile and timesaving route from the cheapest raw materials (Na, NaOH and NaX). The materials are nonflammable, suitable for thermoplastic processing due to low melting temperatures (<300 C) without decomposing. Notably, owing to the flexibility of perovskite-type structure, it's feasible to control the local structure features by means of size-mismatch substitution and unequivalent-doping for a favorable sodium ionic diffusion pathway. Enhancement of sodium ionic conductivity by 2 magnitudes is demonstrated by these chemical tuning methods. The optimized sodium ionic conductivity in Na 2.9 Sr 0.05 OBr 0.6 I 0.4 bulk samples reaches 1.9 Â 10 À3 S/cm at 200 C and even higher at elevated temperature. We believe further chemical tuning efforts on Na-rich antiperovskites will promote their performance greatly for practical all-solid state battery applications.

Electronic, elastic, lattice dynamic and thermal conductivity properties of Na3OBr via first principles

“…To our knowledge, the melting temperature of Na 3 OBr is reported to be about 255 °C . Another work indicates that Na 3 OBr can be synthesized via solid‐state reaction at about 450 °C .…”

“…In 2013, Ramanna et al studied its structural, elastic, electronic, and optical properties using two different density functional methods within generalized gradient approximation. In 2015, Wang et al tried to improve Na + conductivity in Na 3 OBr by chemical manipulation techniques. In 2016, Zhu et al studied the transport mechanism of Na ions and found that they transport between the nearest Na ions in the NaO 6 octahedra.…”

Ab initioinvestigation of the stability of electrolyte/electrode interfaces in all-solid-state Na batteries

“…Recently, Zhu et al 46 analyzed their Naion transport mechanisms and reported low ionic conductivities (s z 10 À8 S cm À1 at RT, activation energy E a ¼ 0.6-0.7 eV). Nonetheless, chemical modications leave substantial room for improvement, e.g., by aliovalent substitution the conductivity of Na 2.9 Sr 0.05 OBr 0.6 I 0.4 reaches 0.19 mS cm À1 at 200 C. 47 Other oxides such as Na 2 SO 4 , Na 3 PO 4 , and Na 4 SiO 4 , are generally characterized by low ionic conductivity. However, they can be used as coating materials or end-members of better performing electrolyte solid-solutions such as Na 2 SO 4 / Na 4 SiO 4 , 48 Na 3 PO 4 /Na 2 SO 4 , 49,50 Na 3 AlF 6 /Na 2 SO 4 , 50 and Na 3 PO 4 / Na 4 SiO 4 .…”

Antiperovskites with Exceptional Functionalities

“…Larger Na + ions are better for stabilizing the antiperovskite structure, and hence, more NaRAPs are expected. In the solid solution Na 3 OX (X = Cl, Br, I), lattice mismatch and nonequivalent‐doping strategies have been successfully adopted to promote the performance . The optimized Na 2.9 Sr 0.05 OBr 0.6 I 0.4 exhibits a conductivity beyond 10 −2 S cm −1 when approaching the melting point.…”