Theoretical prediction of a highly conducting solid electrolyte for sodium batteries: Na₁₀GeP₂S₁₂

Abstract

Using first-principles simulations, we predict a high-performance solid electrolyte with composition Na 10 GeP 2 S 12 for use in sodium-sulfur (Na-S) batteries. The thermodynamic stability of its structure is established through determination of decomposition reaction energies and phonons, while Na-ionic conductivity is obtained using ab initio molecular dynamics at elevated temperatures. Our estimate of the room-temperature (RT) conductivity is 4.7 Â 10 À3 S cm À1 , which is slightly higher than those of other superionic solid electrolytes such as b 00 -alumina and Na 3 Zr 2 Si 2 PO 12 , currently used in practical hightemperature Na-S batteries. Activation energy obtained from the Arrhenius plot (in the range 800-1400 K) is 0.2 eV, which is slightly lower than the typical values exhibited by other ceramic conductors (0.25-1 V) (Hueso et al., Energy Environ. Sci., 2013, 6, 734). We show that soft Na-S phonon modes are responsible for its thermodynamic stability and the lower activation barrier for diffusion of Na-ions.Finally, the calculated electronic bandgap of 2.7 eV (a wide electrochemical window) augurs well for its safe use in sodium batteries. Opening up a possibility for realizing RT operation of Na-S batteries, our prediction of a new phase in the Na-Ge-P-S system will stimulate experimental studies of the material.

Vacancy‐Controlled Na+ Superion Conduction in Na11Sn2PS12

“…[20] Halide doping leads to the formation of Na + vacancies,w hich may facilitate Na + ion transport. [26] The predicted conductivity for the Ge compound was in good agreement with the previous report, [23] and the authors found the same composition/conductivity trend as known for the lithium compounds Li 10 TtP 2 S 12 ,n amely that the Na + ion conductivity decreases in the order Si!Ge!Sn. [20] In as ubsequent study,O ng and co-workers synthesized tetragonal Na 3Àx PS 4Àx Cl x with x = 6.25 %a nd achieved aconductivity of 1.14 mS cm À1 at 303 K. [21] Inspired by the very high Li + ion conductivity of compounds with composition Li 10 TtP 2 S 12 (Tt = Si, Ge, Sn), [5,6,22] some groups recently dedicated research efforts to the theoretical and experimental investigation of compounds in the quaternary sodium system with the same stoichiometry, namely Na 10 TtP 2 S 12 .I n2 015, Waghmare and co-workers computed the conductivity of Na 10 GeP 2 S 12 (NGPS) by means of density functional theory (DFT) and obtained av alue of 4.7 mS cm À1 ,which is even higher than the overall conductivity of commercial b''-alumina (2 mS cm À1 )a nd the overall conductivity of the best NASICON-type sodium-ion conductor Na 3.4 Sc 0.4 Zr 1.6 (SiO 4 ) 2 (PO 4 )( 4mScm À1 ).…”

“…[16] An even higher conductivity of 1.1-3 mS cm À1 was reported for the thioantimonate Na 3 SbS 4 .T his compound exhibits the highest Na + ion conductivity of all sulfide-based materials known so far, [17][18][19] but ad rawback is the toxicity of Sb.C onsequently, strategies for enhancing the ion conductivity of cubic Na 3 PS 4 via halide doping were analyzed by means of density functional theory molecular dynamics simulations. [23][24][25] Fort heir calculations,t hey assumed NGPS to crystallize in the same tetragonal P4 2 /nmc space group as the Li 10 GeP 2 S 12 (LGPS) homologue.I n2 016, Richards et al performed DFT studies on the entire Na 10 TtP 2 S 12 system with Tt = Si, Ge or Sn. In the simulations,i tw as found that av acancy concentration of only 2% can lead to ac onductivity enhancement of about one order of magnitude.…”

Na3SbSe4−xS x as Sodium Superionic Conductors

“…Promise has also been achieved in chalcogenide sodium-ion conductors. High conductivity was computationally predicted and then experimentally achieved in Na 10 MP 2 S 12 (M = Si, Ge, and Sn) 16,17 . A cubic Na 3 PS 4 phase with Na+ ion conductivity greater than 0.1 mS cm −1 at 25 °C was reported by Tatsumisago et al .…”

Room-Temperature All-solid-state Rechargeable Sodium-ion Batteries with a Cl-doped Na3PS4 Superionic Conductor

“…Chalcogenide-based (S, Se) chemistries offer the potential for higher ionic conductivities than oxides11121314151617181920. Though it is likely that sulfide and selenide-based solid electrolytes may exhibit lower intrinsic electrochemical stability, the formation of passivating phases at the electrode-solid electrolyte interface can potentially mitigate further reactions212223.…”