  Sodium-ion batteries exhibit significant promise as a viable alternative to
current lithium-ion technologies owing to their sustainability, low cost per
energy density, reliability, and safety. Despite recent advancements in cathode
materials for this category of energy storage systems, the primary challenge in
realizing practical applications of sodium-ion systems is the absence of an
anode system with high energy density and durability. Although Na metal is the
ultimate anode that can facilitate high-energy sodium-ion batteries, its use
remains limited due to safety concerns and the high-capacity loss associated
with the high reactivity of Na metal. In this study, titration gas
chromatography is employed to accurately quantify the sodium inventory loss in
ether- and carbonate-based electrolytes. Uniaxial pressure is developed as a
powerful tool to control the deposition of sodium metal with dense morphology,
thereby enabling high initial coulombic efficiencies. In ether-based
electrolytes, the Na metal surface exhibits the presence of a uniform solid
electrolyte interphase layer, primarily characterized by favorable inorganic
chemical components with close-packed structures. The full cell, utilizing a
controlled electroplated sodium metal in ether-based electrolyte, provides
capacity retention of 91.84% after 500 cycles at 2C current rate and delivers
86 mAh/g discharge capacity at 45C current rate, suggesting the potential to
enable Na metal in the next generation of sodium-ion technologies with
specifications close to practical requirements.
