Lithium metal anodes (LMAs), featuring an extremely high theoretical specific capacity and the lowest redox potential among known anode materials, are widely recognized as a promising foundation for next-generation high-energy rechargeable batteries. Despite their unique advantages, the practical deployment of LMAs remains severely constrained by uncontrolled Li dendrite growth and low Coulombic efficiency. These issues mainly stem from the uneven deposition of lithium ions. Over the past decade, numerous strategies—such as artificial solid-electrolyte interphase (SEI) layers, and solid-state electrolytes—have been developed to address these bottlenecks. Among these methods, electrolyte additives are appealing due to their operational simplicity, low manufacturing cost, and high compatibility with practical battery configurations. Conventional additives typically function either as suppressors that inhibit Li nucleation at protrusions or as promoters that modify SEI composition to enhance interface stability. However, suppressors may lose their selectivity under high current densities because strong local electric fields can drive them toward both protrusions and recesses, weakening their suppressing capability. Meanwhile, selective accelerators that enhance Li⁺ reduction at recessed sites have been scarcely explored for LMAs, even though similar concepts are widely applied in industrial electroplating. In electroplating processes, leveling agents—often sulfur-containing molecules—can adsorb on the metal surface to accelerate bottom-up cation growth by the leveling effect of superfilling. Here, a synergistic dual-additive electrolyte strategy is proposed, combining N,N'-diethylthiourea (DTHU) with dodecyl trimethylammonium cations (DTA⁺). The two additives collaboratively regulate Li⁺ solvation, interfacial adsorption, and deposition kinetics, thus enabling smooth lithium plating even at elevated current densities.

Electrolytes were prepared by dissolving lithium salts in ether- or carbonate-based solvents, followed by the introduction of DTHU and/or DTA⁺ at controlled concentrations. Electrochemical evaluation was conducted using CR2032 coin-type symmetric cells and Li-Cu half cells assembled in an oxygen- and moisture-free glovebox. Long-term cycling, rate capability tests, and Coulombic efficiency measurements were performed under galvanostatic conditions. Full cells employing Li₄Ti₅O₁₂ (LTO) cathodes were assembled to examine the applicability of the additive strategy in practical battery environments.

To probe interfacial chemistry, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and energy-dispersive X-ray (EDX) mapping were employed. The adsorption behavior of DTHU and DTA⁺ on Li metal was elucidated through density-functional-theory calculations and molecular dynamics simulations. Moreover, the structural evolution of the SEI and ion-transport kinetics were further analyzed through electrochemical impedance spectroscopy and Arrhenius fitting.

A combination of theoretical calculations and experimental characterization revealed distinct yet complementary roles of the two additives. DTHU exhibited a significantly stronger adsorption affinity toward lithium metal compared with solvent molecules, enabling selective accumulation at recessed regions of the metal surface. EDX-mapping and time-dependent molecular simulations confirmed that DTHU molecules migrate toward pits during interfacial equilibration, aligning favorably to promote localized Li⁺ reduction. Conversely, DTA⁺ adsorbs preferentially on surface protrusions, as evidenced by a positive shift in the potential of zero charge obtained from AC voltammetry. This adsorption weakens the local electric field near convex regions and reduces the tip effect, which is responsible for accelerated dendrite growth in conventional electrolytes. When both additives are introduced simultaneously, Li⁺ flux is redistributed more homogeneously across the electrode surface. COMSOL simulations showed that the introduction of DTHU dramatically suppresses the unstable dendritic morphology that appears in the blank ether electrolyte. Instead, Li deposits in a dense and uniform manner.

In addition to altering deposition behavior, the dual-additive system significantly modifies the solvation structure of Li⁺ and the chemical makeup of the SEI. Raman spectroscopy revealed enhanced dissociation of lithium salt due to strong interactions between DTHU and anions. Molecular dynamics simulations further showed that the primary Li⁺ solvation sheath shifts toward a higher proportion of 1,3-dioxolane molecules, known precursors for forming polymeric SEI components. XPS analyses demonstrated that the combined additives promote the formation of a LiF-rich SEI, which possesses high mechanical robustness and ionic conductivity. Arrhenius analysis of charge-transfer resistance indicated a substantial reduction in Li⁺ desolvation energy, confirming accelerated interfacial kinetics.

These structural and interfacial benefits translated directly into superior electrochemical performance. Symmetric Li || Li cells using the dual-additive electrolyte cycled stably than 1500 h at 1.0 mA·cm^-2 with a low and stable overpotential of less than 80 mV. High-rate tests further demonstrated that the dual-additive electrolyte maintained smooth plating behavior even under 4.0 mA·cm^-2. Meanwhile, Cu-Li half cells exhibited higher Coulombic efficiencies and lower nucleation overpotentials, confirming improved initial Li deposition uniformity. In full-cell configurations, Li || LTO batteries employing the dual-additive electrolyte achieved stable cycling 500 cycles at 1.0 C with excellent capacity retention. This performance markedly exceeded that of full cells based on the baseline electrolyte, which suffered accelerated capacity fade due to dendrite-induced side reactions.

This study demonstrates a synergistic electrolyte-additive strategy inspired by industrial electroplating principles. By combining DTHU and DTA⁺, the approach simultaneously equalizes Li⁺ flux distribution, refines the ion-solvation environment, and guides the formation of a robust LiF-rich SEI. Together, these effects prevent dendrite formation even at high current densities and enable long-term cycling stability. The dual-additive electrolyte allows symmetric Li||Li cells to operate stably for over 1500 h and significantly improves the rate capability and cycle life of LTO full cells. The findings highlight the potential of electroplating-derived concepts as a practical and economical route to safe, dendrite-free lithium metal batteries. This strategy may be further extended to other monovalent and multivalent metal anode systems in future studies.