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Sodium metal batteries have emerged as potential rivals to lithium‐ion batteries. Nevertheless, maintaining a stable sodium metal anode under harsh conditions (current density >10 mA cm−2) is extremely challenging. The primary issue is the highly reactive sodium metal continuously reacts with the electrolyte to form a thick and loose solid electrolyte film. The tip effect causes sodium ions (Na+) accumulated in the bulge resulting in uneven deposition. In this paper, a unique artificial interfacial layer (Ag nanoparticles distributed in NaClO4‐based matrix) is prepared on the surface of a metallic sodium anode using in situ displacement reaction. Ag particles arranged at the bottom of the artificial layer act as effective nucleation sites helping Na+ deposit uniformly, while the built‐in electric field formed between Ag in the middle/top of the artificial layer and the sodium accelerates the migration of Na+ in the interfacial layer during the deposition and reduce the polarization. Such important properties further allow the steady operation of modified sodium metal batteries in very harsh conditions. The symmetric battery achieves reversible stripping/plating for over 1000 h under high current density (10 mA cm−2). Moreover, the full cell coupled with a high‐loading Na3V2(PO4)3 cathode (20 mg cm−2) presents a stable cycle performance. [ABSTRACT FROM AUTHOR]

Electrolyte solvent, salt, and additive directly determine many battery indicators such as voltage limit, safe reliability, and temperature limit. In Ca‐metal batteries, suitable electrolyte and interphase are necessary to achieve reversible calcium plating/stripping, which is challenging for F‐based salts at room temperature. Ion transport and charge transfer in calcium batteries with Ca(BF4)2‐NaPF6 electrolyte are regulated for the first time by altering solvent and salt categories and ratios, achieving adjustable interphase species and microstructure, calcium deposition/dissolution overpotentials, and cycling stability. The optimized electrolyte of 0.1 m Ca(BF4)2‐0.9 m NaPF6 in ethylene carbonate/diethyl carbonate/dimethyl carbonate/ethyl methyl carbonate (7:1:6:6, v/v) contributes to the most stable Ca plating/stripping cycling and the weakest overpotential, as well as Na/Ca‐based hybrid solid electrolyte interphases including proper amount of organic matter. Ca‐metal batteries with the optimized electrolyte achieve an ultrahigh reversible capacity of ≈290 mAh g−1 (at 200 mA g−1 and 1.2–4.5 V), almost four times more than that of counterpart ones (≈65 mAh g−1), equivalent to energy/power performance of ≈616 Wh kg−1 at 429 W kg−1 among the best ones for multivalent ion rechargeable metal batteries. [ABSTRACT FROM AUTHOR]