Lithium metal has gravimetric capacity ∼10× that of graphite which incentivizes rechargeable Li metal batteries (RLMB) development. A key factor that limits practical use of RLMB is morphological instability of Li metal anode upon electrodeposition, reflected by the uncontrolled area growth of solid-electrolyte interphase that traps cyclable Li, quantified by the Coulombic inefficiency (CI). Here we show that CI decreases approximately exponentially with increasing donatable fluorine concentration of the electrolyte. By using up to 7 m of Li bis(fluorosulfonyl)imide in fluoroethylene carbonate, where both the solvent and the salt donate F, we can significantly suppress anode porosity and improve the Coulombic efficiency to 99.64%. The electrolyte demonstrates excellent compatibility with 5-V LiNiMnO cathode and Al current collector beyond 5 V. As a result, an RLMB full cell with only 1.4× excess lithium as the anode was demonstrated to cycle above 130 times, at industrially significant loading of 1.83 mAh/cm and 0.36 C. This is attributed to the formation of a protective LiF nanolayer, which has a wide bandgap, high surface energy, and small Burgers vector, making it ductile at room temperature and less likely to rupture in electrodeposition.

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Air-stability is one of the most important considerations for the practical application of electrode materials in energy-harvesting/storage devices, ranging from solar cells to rechargeable batteries. The promising P2-layered sodium transition metal oxides (P2-Na x TmO 2 ) often suffer from structural/chemical transformations when contacted with moist air. However, these elaborate transitions and the evaluation rules towards air-stable P2-Na x TmO 2 have not yet been clearly elucidated. Herein, taking P2-Na 0.67 MnO 2 and P2-Na 0.67 Ni 0.33 Mn 0.67 O 2 as key examples, we unveil the comprehensive structural/chemical degradation mechanisms of P2-Na x TmO 2 in different ambient atmospheres by using various microscopic/spectroscopic characterizations and first-principle calculations. The extent of bulk structural/chemical transformation of P2-Na x TmO 2 is determined by the amount of extracted Na + , which is mainly compensated by Na + /H + exchange. By expanding our study to a series of Mn-based oxides, we reveal that the air-stability of P2-Na x TmO 2 is highly related to their oxidation features in the first charge process and further propose a practical evaluating rule associated with redox couples for air-stable Na x TmO 2 cathodes.

Outlines of the multiphysics behaviors upon penetration and the comparisons of experiment and simulation.