A stable cathode-solid electrolyte composite for high-voltage, long-cycle-life solid-state sodium-ion batteries

Abstract

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 the ion conductor Na3-xY1-xZrxCl6 (NYZC) that is both electrochemically stable (up to 3.8 V vs. Na/Na+) and chemically compatible with oxide cathodes. Its high ionic conductivity of 6.6 × 10−5 S cm−1 at ambient temperature, several orders of magnitude higher than oxide coatings, is attributed to abundant Na vacancies and cooperative MCl6 rotation, resulting in an extremely low interfacial impedance. A SSSB comprising a NaCrO2 + NYZC composite cathode, Na3PS4 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 halides for SSSB applications.

A cost-effective and humidity-tolerant chloride solid electrolyte for lithium batteries

“…This bottleneck arises from the fact that only 3+ cations may act as M in both Li 3 MCl 6 and Li 2 M 2/3 Cl 4 due to the charge balance requirement 7,14,[21][22][23][24][25][26] . Although cations with other valences may be introduced through aliovalent doping [32][33][34] , a considerable fraction of M still has to be 3+ ones. Then, after excluding the trivalent cations not sufficiently stable at 3+ and those too large or too small to fit in the crystal structure, the remaining options are almost confined to the aforementioned expensive elements, i.e., Y, Tb-Lu, Sc, and In.…”

Influence of Reduced Na Vacancy Concentrations in the Sodium Superionic Conductors Na11+xSn2P1–xMxS12 (M = Sn, Ge)

“…While defect formation enthalpies are often disregarded in superionic conductors, as they are thought to be negligible compared to migration enthalpy, recent reports suggest non-negligible influences of sodium or sodium vacancy concentrations in the fast ionic conductors Na3-xPS4-xClx and Na3-xM1-xZrxCl6. 9,47,48 Nevertheless, while it is difficult to assess the changing defect formation enthalpies experimentally, the found trend suggests some influence of the charge carrier density on the activation barrier in Na11+xSn2P1−xMxS12. S9).…”

Influence of Reduced Na Vacancy Concentrations in the Sodium Superionic Conductors Na11+xSn2P1−xMxS12 (M = Sn, Ge)

“…While defect formation enthalpies are often disregarded in superionic conductors, as they are thought to be negligible compared to migration enthalpy, recent reports suggest non-negligible influences of sodium or sodium vacancy concentrations in the fast ionic conductors Na3-xPS4-xClx and Na3-xM1-xZrxCl6. 9,47,48 Nevertheless, while it is difficult to assess the changing defect formation enthalpies experimentally, the found trend suggests some influence of the charge carrier density on the activation barrier in Na11+xSn2P1−xMxS12. Na11+xSn2+x(Sb1−yPy)xS12 (see Supporting information Figure S9).…”