Solid-state electrolytes (SSEs) are widely considered as an “enabler” to inhibit dendrite growth of lithium-metal anodes for high-energy and highly safe next-generation batteries. However, recent studies demonstrated that lithium dendrites form in working SSEs. Theoretically, dendrite inhibition can be achieved in perfect SSEs without any defects, while dendrite growth is extensively observed in practical SSEs with poor interface stability, large grain boundaries, voids, and partial electronic conductivity. In this Review, dendrite growth behaviors in SSEs, including polymer and inorganic electrolytes, are comprehensively summarized. The observed dendrite morphology in these SSEs, possible formation mechanisms, and some solutions are analyzed. Clear perspectives and some suggestions are also presented for the further development of SSEs in lithium-metal batteries. This Review intends to shed fresh light on the understanding of dendrite growth in SSEs and the rational design of the architecture and materials for SSEs matching the lithium-metal anode.
Context. The spiral structure of the Milky Way is not yet well determined. The keys to understanding this structure are to increase the number of reliable spiral tracers and to determine their distances as accurately as possible. HII regions, giant molecular clouds (GMCs), and 6.7 GHz methanol masers are closely related to high mass star formation, and hence they are excellent spiral tracers. The distances for many of them have been determined in the literature with trigonometric, photometric, and/or kinematic methods. Aims. We update the catalogs of Galactic HII regions, GMCs, and 6.7 GHz methanol masers, and then outline the spiral structure of the Milky Way. Methods. We collected data for more than 2500 known HII regions, 1300 GMCs, and 900 6.7 GHz methanol masers. If the photometric or trigonometric distance was not yet available, we determined the kinematic distance using a Galaxy rotation curve with the current IAU standard, R 0 = 8.5 kpc and Θ 0 = 220 km s −1 , and the most recent updated values of R 0 = 8.3 kpc and Θ 0 = 239 km s −1 , after velocities of tracers are modified with the adopted solar motions. With the weight factors based on the excitation parameters of HII regions or the masses of GMCs, we get the distributions of these spiral tracers.Results. The distribution of tracers shows at least four segments of arms in the first Galactic quadrant, and three segments in the fourth quadrant. The Perseus Arm and the Local Arm are also delineated by many bright HII regions. The arm segments traced by massive star forming regions and GMCs are able to match the HI arms in the outer Galaxy. We found that the models of three-arm and four-arm logarithmic spirals are able to connect most spiral tracers. A model of polynomial-logarithmic spirals is also proposed, which not only delineates the tracer distribution, but also matches the observed tangential directions.
Safe lithium (Li) metal batteries have been plagued by dendrite growth due to a heterogeneous solid electrolyte interphases (SEI) on the Li metal anode. Modulating the solvation sheath of Li ions enhances the uniformity and stability of SEI significantly. However, anion regulation in the solvation sheath for constructing stable SEI is rarely touched. Herein, the solvation structure of original bis(fluorosulfonyl)imide (FSI–) anions in the solvation sheath is altered by introduction of other anions, promoting the complete decomposition of FSI– and forming a stable SEI on the Li metal anode. Moreover, both the oxidation stability window of the electrolyte and current collector protection were enhanced. Furthermore, the components and structure of the solvation sheath were disclosed by combining 17O nuclear magnetic resonance and molecular dynamics simulations. This work provides fresh insight into the interrelation among various anions on regulating the solvation sheath of Li ions and demonstrates guidance in rationally designing electrolytes for stable and safe Li metal batteries.
High-energy-density lithium (Li) metal batteries are severely hindered by the dendritic Li deposition dictated by non-uniform solid electrolyte interphase (SEI). Despite its unique advantages in improving the uniformity of Li deposition, the current anion-derived SEI is unsatisfactory under practical conditions. Herein regulating the electrolyte structure of anions by anion receptors was proposed to construct stable anion-derived SEI. Tris(pentafluorophenyl)borane (TPFPB) anion acceptors with electron-deficient boron atoms interact with bis(fluorosulfonyl)imide anions (FSI À ) and decrease the reduction stability of FSI À . Furthermore, the type of aggregate cluster of FSI À in electrolyte changes, FSI À interacting with more Li ions in the presence of TPFPB. Therefore, the decomposition of FSI À to form Li 2 S is promoted, improving the stability of anion-derived SEI. In working Li j LiNi 0.5 Co 0.2 Mn 0.3 O 2 batteries under practical conditions, the anion-derived SEI with TPFPB undergoes 194 cycles compared with 98 cycles of routine anion-derived SEI. This work inspires a fresh ground to construct stable anion-derived SEI by manipulating the electrolyte structure of anions.
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