Assessing the Reactivity of the Na₃PS₄ Solid-State Electrolyte with the Sodium Metal Negative Electrode Using Total Trajectory Analysis with Neural-Network Potential Molecular Dynamics

Abstract

Rechargeable batteries play a central role in the global shift from fossil fuels to renewable energy. Since the commercial introduction of lithium-ion batteries in the early 1990s, recent progress is focused on the development of solid-state materials and new battery chemistries. Specifically, solid-state sodium ion batteries are an attractive alternative alongside lithium-based rechargeable batteries, with improvements in safety, lifespan, sustainability, and price. Critical to the battery performance are electrode–electrolyte interfaces since undesirable side-reactions often proceed between electrode and electrolyte materials. In addition, atomistic or electronic-level knowledge on the reactions at the interface is limited due to technical difficulties of experimental observation. Computational studies on interfacial reactivity, such as first-principles techniques, have also long been limited by computational limitations. Recent advances using neural-network potential molecular dynamics simulations are allowing significantly larger systems and longer timescales to be simulated at a significantly reduced computational cost without loss of accuracy. In this study, the chemical stability of the glass–ceramic Na3PS4 solid-state electrolyte with the sodium metal electrode is investigated through a combined total trajectory analysis computational and experimental approach. PS4 groups in the Na3PS4 material were found to decompose sequentially into PS3, PS2, PS, and phosphide and sulfide species through the insertion of sodium atoms. Whereas the decomposition is thermodynamically favored, it is kinetically hindered due to steric effects in the PS3 intermediate. Machine learning-assisted analysis was found to be able to visualize the reactivity tendencies of individual element types. The formed SEI layer exhibited a good chemical stability and a low electronic conductivity. These findings provide new design principles to optimize and develop new solid-state electrolytes with an increased chemical stability toward the sodium metal electrode.

Increasing the Sodium Metal Electrode Compatibility with the Na3PS4 Solid‐State Electrolyte through Heteroatom Substitution

“…We confirmed no marked difference between both compounds, so that slow Na diffusivity is not a primary reason for the suppression of decomposition reaction in Na 3 PS 3 O. For sulfur, there was a sequential breakdown of P−S bonds as reported in our previous study [39] . For oxygen, the P−O bond was found to be very stable, with a very limited number of decomposition reactions of the neighboring P−S bonds.…”

“…The platinum electrode was used due to issues with sodium metal obscuring the band gap as explained in our previous study. [39] Cross-sectional DOS plots with the sodium metal electrode are shown in Figure S27. In both Figure 6c and Figure 6d (zoomed to the Fermi level), it can be observed that from oxygen towards tellurium the band gap decreases, indicating a greater reactivity towards tellurium.…”

“…To gain insights into the distribution of the density of states in the interface z‐coordinate, the cross‐sectional total density of states was plotted in Figure 6c and d for the oxygen, sulfur, selenium, and tellurium‐doped material for the 400 K relaxed input structure. The platinum electrode was used due to issues with sodium metal obscuring the band gap as explained in our previous study [39] . Cross‐sectional DOS plots with the sodium metal electrode are shown in Figure S27.…”

“…In our previous study [39] we investigated the chemical stability and degradation mechanisms of the Na 3 PS 4 solid‐state electrolyte material. The Na 3 PS 4 electrolyte is composed of regularly spaced PS 4 groups surrounded by loosely bound sodium ions which are able to migrate freely.…”

“…However, in recent years, developments in chemical databases, hardware, and machine learning, have led to the development of neuralnetwork potentials which are able to simulate reactivity and at a significantly lower computational cost, approaching the same accuracy as that of density functional theory (DFT). [36][37][38] In our previous study [39] we investigated the chemical stability and degradation mechanisms of the Na 3 PS 4 solid-state electrolyte material. The Na 3 PS 4 electrolyte is composed of regularly spaced PS 4 groups surrounded by loosely bound sodium ions which are able to migrate freely.…”