Survey of the transport properties of sodium superionic conductor materials for use in sodium batteries

New promising NASICON material as solid electrolyte for sodium-ion batteries: Correlation between composition, crystal structure and ionic conductivity of Na3+xSc2SixP3−xO12

“…The determined values of 0.3-0.35 eV have been reported very often for highly conductive NASICON materials [7]. The activation energy of the bulk conductivity, however, is significantly smaller and correlates better with the conductivity values since an increase was observed for x N 0.5.…”

“…Later, Losilla et al [28] tried to correlate the activation energy with the area of the smallest triangle, T1, for Na 1.4 In 0.4 M 1.6 (PO 4 ) 3 (M = Ti, Sn, Hf, Zr). This correlation was validated for approximately 30 NASICON materials with reported structural parameters [7].…”

“…The highest total conductivity of 6.9 × 10 −4 S cm −1 for x = 0.4 at 25°C places NSSiP 0.4 among the ten best NASICON sodium-conductive materials reported to date [7].…”

“…The conductivity of the NASICON materials is strongly related to their Na concentration and their crystallographic structure, which is influenced by the size of the M cations. It has been concluded from a literature survey [7] that the average ionic radius of M cations should be close to the ionic radius of Zr, i.e. r Zr = 0.72 Å [8], in order to obtain highly conductive materials comparable to β-and β″-alumina [9,10].…”

“…r Zr = 0.72 Å [8], in order to obtain highly conductive materials comparable to β-and β″-alumina [9,10]. In addition, the NASICON materials with the highest sodium ion conductivity contain 3-3.5 mol Na per formula unit and show a monoclinic distortion of the crystallographic lattice [7].…”