Li‐Ion Transport Mechanisms in Selenide‐Based Solid‐State Electrolytes in Lithium‐Metal Batteries: A Study of Li8SeN2, Li7PSe6, and Li6PSe5X (X = Cl, Br, I)

• Published in: Energy & environmental materials (Hoboken, N.J.) Vol. 7; no. 5; pp. 37 - n/a
• Main Authors: Xiao, Wenshan, Wu, Mingwei, Wang, Huan, Zhao, Yan, He, Qiu
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.09.2024; International School of Materials Science and Engineering,Wuhan University of Technology,Wuhan 430070,China%International School of Materials Science and Engineering,Wuhan University of Technology,Wuhan 430070,China; College of Materials Science and Engineering,Sichuan University,Chengdu 610065,China; The Institute of Technological Sciences,Wuhan University,Wuhan 430072,China%International School of Materials Science and Engineering,Wuhan University of Technology,Wuhan 430070,China
• Subjects: Activation energy; Conduction; Conduction bands; Conductivity; Diffusion barriers; Electrolytes; Insulation; Ion migration; Ion transport; Lithium; lithium argyrodites; lithium‐metal battery; Li‐ion transport; Mechanical properties; Metals; Molecular dynamics; Molten salt electrolytes; Selenide; Selenides; Solid electrolytes; solid‐state electrolytes; Li-ion transport; selenides; solid-state electrolytes; lithium argyrodites; lithium-metal battery
• ISSN: 2575-0356; 2575-0348; 2575-0356
• DOI: 10.1002/eem2.12729

To achieve high‐energy‐density and safe lithium‐metal batteries (LMBs), solid‐state electrolytes (SSEs) that exhibit fast Li‐ion conductivity and good stability against lithium metal are of great importance. This study presents a systematic exploration of selenide‐based materials as potential SSE candidates. Initially, Li8SeN2 and Li7PSe6 were selected from 25 ternary selenides based on their ability to form stable interfaces with lithium metal. Subsequently, their favorable electronic insulation and mechanical properties were verified. Furthermore, extensive theoretical investigations were conducted to elucidate the fundamental mechanisms underlying Li‐ion migration in Li8SeN2, Li7PSe6, and derived Li6PSe5X (X = Cl, Br, I). Notably, the highly favorable Li‐ion conduction mechanism of vacancy diffusion was identified in Li6PSe5Cl and Li7PSe6, which exhibited remarkably low activation energies of 0.21 and 0.23 eV, and conductivity values of 3.85 × 10−2 and 2.47 × 10−2 S cm−1 at 300 K, respectively. In contrast, Li‐ion migration in Li8SeN2 was found to occur via a substitution mechanism with a significant diffusion energy barrier, resulting in a high activation energy and low Li‐ion conductivity of 0.54 eV and 3.6 × 10−6 S cm−1, respectively. Throughout this study, it was found that the ab initio molecular dynamics and nudged elastic band methods are complementary in revealing the Li‐ion conduction mechanisms. Utilizing both methods proved to be efficient, as relying on only one of them would be insufficient. The discoveries made and methodology presented in this work lay a solid foundation and provide valuable insights for future research on SSEs for LMBs. This study presents highly potential selenide solid‐state electrolytes for lithium‐metal batteries and proposes an efficient and accurate paradigm for investigating Li‐ion migration mechanisms. First, the activation energy is determined by modeling the Arrhenius relationship using ion diffusion coefficients simulated by AIMD. Second, the diffusion paths are visualized through the density distribution of Li ions. Third, the migration routes of individual ions are traced. Finally, CI‐NEB calculations are conducted on crucial migration steps. Following this procedure, Li6PSe5Cl and Li7PSe6 are demonstrated with outstanding performance.