Reconstruction and electronic properties of β-Li₃PS₄|Li₂S interface

Abstract

The morphology and properties of the interface between solid electrolyte and electrode have important impacts on all-solid-state lithium-sulfur batteries’ performance. We used the first-principles calculations to explore the interface between Li2S cathode and β-Li3PS4 (lithium thiophosphate, LPS) solid electrolyte, including lattice structure, mechanical, electrical properties, interface contact type, and charge distribution in real space. It is found that the interface is significantly reconstructed, and the Li atoms at the interface move mainly parallel to the interface plane. The interface density states introduce metallic properties, mainly contributed by the Li-s and S-s, -p orbitals in Li2S and S-p orbitals in LPS. The highest occupied molecular orbitals of the LPS electrolyte are lower than the electrochemical potential (Fermi level) of the Li2S cathode, thus the electrolyte and cathode materials are reasonable and stable in thermodynamics. Interface density of states shows electrons on the interface do not penetrate from Li2S into LPS, and do not leak electrons to cause electron conduct in LPS. Besides, the interface is an n-type Schottky barrier with a barrier value of 1.0 eV. The work-function of the interface indicates that there is a space charge layer by the redistribution of electrons, which is in agreement with the result of interface charge density difference. The electron/hole pairs will be separate, realizing high current charge and discharge capability because of the space charge layer.

Insights into the electrochemical properties of Li2FeS2 after FeS2 discharging

“…With the Li + migration energy barrier as the foundation, we estimated the diffusion coefficient (D) of Li + in Li 2 FeS 2 for comparison with the experimental data. Eqn (11) can be used to calculate the diffusion coefficient (D): 40…”

“…It is almost impossible for the space charge layer to be formed due to the increasing interface resistance. 11 To realize a high sulfur utilization and cycle stability of ASSLSBs, FeS 2 @S compound could efficiently improve the Li + diffusion rate to accelerate the redox reaction significantly, thus enhancing the sulfur utilization, and achieving a greater rate performance for ASSLSBs. 12 FeS 2 @S showed a superior electrochemical performance in Li–S batteries with temperate voltage plateaus of 1.5–2.8 V, a high theoretical specific capacity of 894 mA h g −1 for FeS 2 , 13 and a theoretical energy density of 1672 W h kg −1 for sulfur.…”

First‐principles Screening of Transition‐Metal Doped FeS2 As Sulfur Cathode Host for Sulfur Redox Chemistry

“…m slab 3), the surface free energy (g 0 ) of Fe 0.875 M 0.125 S 2 (001) with three different terminations was evaluated by the equation (3). [47]…”

“…The work function (W) refers to the minimum energy required to move an electron from the interior of a solid to the surface of the material. Equation ( 4) is applied for evaluating the work function, [47] as follows:…”

“…Fermi level of the cathode is higher than the lowest unoccupied molecule orbital (LUMO) of the electrolyte, causing the oxidation of electrolyte, and increasing the risk for battery short circuit. [47] Therefore, the electronic conductivity and the work function have significant effects on the sulfur cathode host Fe 0.875 M 0.125 S 2 . As shown in Figure 4g, the work function gradually increases from Fe 0.875 V 0.125 S 2 , to Fe 0.875 Cr 0.125 S 2 to Fe 0.875 Mn 0.125 S 2 except for Fe 0.875 Ti 0.125 S 2 , indicating that electrons are more difficult to overflow from Fe 0.875 M 0.125 S 2 (001), reducing the risk of electron leakage.…”