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Solid-state electrolytes (SSEs) have brought significant advancements to secondary battery technology, but phosphides remain relatively unexplored compared to the extensively studied oxides, sulfides, and halides. In this study, we introduce a hierarchical approach for designing a Na-rich phosphide SSE. Starting with Na3P, one of the most Na-rich materials, we apply the concept of dilute element compounds, incorporating a small amount of a dopant element to preserve its Na-richness. This leads us to identify Na7TaP4 as a promising candidate. Subsequently, through phase engineering utilizing the inorganic crystal structure database, we pinpoint a superior phase for Na7TaP4 that exhibits significantly enhanced Na diffusion kinetics. Lastly, employing defect engineering, we determine that partial substitution of Ta with Zr or Hf can stabilize Na7TaP4 in the desired phase over the experimentally synthesized phase. This hierarchical approach not only reduces the Na diffusion activation energy of the initial material Na3P from 0.67 to 0.25 eV but also increases its band gap from 1.0 to 2.4 eV. These advancements show considerable promise for SSE applications. Furthermore, this design strategy is expected to find broad applicability in the development of SSEs for various types of secondary batteries. [ABSTRACT FROM AUTHOR]

Lithium (Li) incorporation in many metal oxides can form a disordered rock-salt (DRS) structure. Such Li-containing oxides are widely employed as high energy density electrode materials in Li-ion batteries. Here, we show that the atomic structures of these DRS oxides can only be correctly understood by using dynamical statistics. Taking LixV2O5 (3 ≤ x ≤ 5) as an example of Li-excess DRS materials, using first-principles molecular dynamics simulations assisted with machine-learning potentials, we show that the Li ions mostly occupy the octahedral sites and only the excess Li ions occupy the tetrahedral sites, which is different from the Li ion redistribution mechanism proposed previously based on the static statistics. Our study shows that when x > 3 the Li ions at the octahedral sites tend to be off center, benefiting their diffusion. Moreover, when x = 5 the volume expansion is found to be as high as 20%, significantly higher than the previously reported value of 5.9%, suggesting that the actual capacity of Li3V2O5 as an anode material might be significantly overestimated. [ABSTRACT FROM AUTHOR]

Lead halide perovskites have been intensively developed to be high-performance photovoltaic and optoelectronic materials, where the unique defect tolerance properties are believed to contribute to their excellence. However, defect tolerance, especially for the donors, has not been conclusively understood yet. Using hybrid functional calculations including spin–orbit coupling (SOC), we study the intrinsic defects of γ-CsPbI3. With a sufficiently large supercell and full structural relaxation, we show that most of the donor levels are deep in hybrid functional calculations, but become shallow due to the strong SOC effect, which reconstructs the potential energy surfaces of the donors by eliminating the large structural distortions. By quantifying the variation of electronic and elastic energies associated with defects, we show how the SOC effect changes the energy balance and reconstructs the defect structures. We reveal the decisive role of degeneracy of electronic states in the SOC effect, which significantly downshifts the conduction band minimum due to the quasi-three-fold degeneracy of Pb 6p orbitals, but has little effect on the non-degenerate defect states. [ABSTRACT FROM AUTHOR]