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Synchrotron X-ray total scattering and pair distribution function analysis are used to investigate the structural changes during solution synthesis of the Li₇P₃S₁₁solid electrolyte. 

Silicon is considered an important anode material for solid-state batteries (SSBs) because of its unique properties in addressing key challenges associated with Li metal anodes such as dendrite formation and morphological instability. Despite many exciting results from previous reports on solid-state Si anodes, the initial Coulombic efficiency (ICE), a critical parameter that characterizes the electrochemical reversibility for the first cycle and directly influences the energy density of the battery, has not been well considered. Here we study the electrochemical stability between Si and three representative solid electrolytes (SEs), including a typical sulfide (75Li 2 S-25P 2 S 5 , LPS), an iodide-substituted sulfide (70(0.75Li 2 S-0.25P 2 S 5 )-60LiI, LPSI), and a hydride-based SE (3LiBH 4 -LiI, LBHI), to improve the ICE of solid-state Si anodes. Combining first-principles computations, electrochemical measurements, ex situ XPS characterizations, and mechanical measurements, we report that LBHI demonstrates superior electrochemical and chemical stability with Si anodes compared with sulfide-based SEs, enabling a high-performance solid-state Si anode with a record high ICE of 96.2% among all Si anodes reported to date. The excellent stability of LBHI with Si anode was also demonstrated in solid-state full cells with nickel-rich layered oxide cathodes. The research provides novel insights into developing high-performance Si anodes for practical applications. 

Abstract While significant efforts are being devoted to improving the ionic conductivity of lithium solid electrolytes (SEs), electronic transport, which has an important role in the calendar life, energy density, and cycling stability of solid‐state batteries (SSBs), is rarely studied. Here, the electronic conductivities of three representative SEs, including Li₃PS₄, Li₇La₃Zr₂O₁₂, and Li₃YCl₆, are reported. It is reported that the electronic conductivities of SEs are overestimated from the conventional measurements. By revisiting direct current polarizations using two‐blocking‐electrode cells and the Hebb‐Wagner approach, their sources of inaccuracy are provided and the anodic decomposition of SE is highlighted as the key source for the overestimated result. Modifications in the electrode selection and data interpretation are also proposed to approach the intrinsic electronic conductivity of SEs. A two‐step polarization method is also proposed to estimate the electronic conductivity of sulfides that decompose during measurement. Measured by the modified approach, the electronic conductivities of all SEs are one or two orders of magnitude lower than the reported value. Despite that, the electronic conductivity of sulfides seems to be still quite high to enable SSBs with a long calendar life of >10 years, highlighting the critical need for a more careful study of electronic transport in lithium SEs. 

Abstract Graphite anodes offer low volumetric capacity in lithium‐ion batteries. By contrast, tellurene is expected to alloy with alkali metals with high volumetric capacity (≈2620 mAh cm⁻³), but to date there is no detailed study on its alloying behavior. In this work, the alloying response of a range of alkali metals (A = Li, Na, or K) with few‐layer Te is investigated. In situ transmission electron microscopy and density functional theory both indicate that Te alloys with alkali metals forming A₂Te. However, the crystalline order of alloyed products varies significantly from single‐crystal (for Li₂Te) to polycrystalline (for Na₂Te and K₂Te). Typical alloying materials lose their crystallinity when reacted with Li—the ability of Te to retain its crystallinity is therefore surprising. Simulations reveal that compared to Na or K, the migration of Li is highly “isotropic” in Te, enabling its crystallinity to be preserved. Such isotropic Li transport is made possible by Te's peculiar structure comprising chiral‐chains bound by van der Waals forces. While alloying with Na and K show poor performance, with Li, Te exhibits a stable volumetric capacity of ≈700 mAh cm⁻³, which is about twice the practical capacity of commercial graphite.