Stable-cycling lithium metal batteries enabled by strategic lithium kinetics engineering

Innovative Highlights of the Work: • Pioneering Halogen-Borate Synergy for Lithium Kinetics Engineering: For the first time, we strategically synergized cesium iodide (CsI) with lithium difluoro(oxalato)borate (LiDFOB) for lithium metal batteries, restructuring the solvation sheath and precisely modulates lithium-ion solvation dynamics with reduced desolvation energy barriers. • Iodide-Mediated Directional Decomposition of LiDFOB toward Robust SEI: An iodide-mediated directional decomposition mechanism was identified that steered LiDFOB decomposition from B-F bond rupture to B-O bond rupture; As a result, a mechanically stable SEI was formed enriched with B–F and LiF components, effectively suppressing dendrite growth. • High-Loading Practical Cell Performance: The resulting Li||Cu half-cell exhibits high performance, maintaining a coulombic efficiency of 94% over 150 cycles at a current density of 2 mA cm⁻². Significantly, the Li||LiFePO₄ pouch cells with an industrial-level cathode loading of 24 mg cm⁻² retain 95% of their capacity after 150 cycles, even under stringent conditions (1C rate, 25 °C), outperforming all previously literature-reported additive systems, pointing to strong scalability for next-generation energy storage systems. Lithium metal anodes are hindered by dendrite growth, unstable solid electrolyte interphase (SEI), and irreversible dead lithium accumulation. Here we report a synergistic electrolyte design using cesium iodide and lithium difluoro(oxalato)borate (LiDFOB) that simultaneously regulates solvation structure, stabilizes the interface, and recovers inactive lithium. The cesium cation adsorbs on lithium protrusions to suppress dendrite nucleation through electrostatic shielding. The iodide anion performs dual functions: it generates an I 3 ⁻/I⁻ redox shuttle that reacted with trapped metallic lithium and Li₂O into soluble Li⁺ species, enabling lithium inventory recovery; more importantly, it selectively coordinates to the electrophilic oxygen in LiDFOB, redirecting its decomposition from thermodynamically favored B–F bond cleavage to kinetically accessible B–O scission (activation energy: 2.056 eV vs. 2.282 eV). This iodide-mediated regulation mechanism yields a dense SEI rich in boron fluoride and lithium fluoride, exhibiting high Li + conductivity and mechanical strength with a Young’s modulus of 7.9 GPa. Comprehensive spectroscopic and computational analyses confirm weakened Li + –solvent interactions, evidenced by elongation of the Li + -O DME bond from 2.02 Å to 2.63 Å, directly weakening Li⁺ solvation and facilitating desolvation. The resulting synergistic modulation of lithium-ion kinetics leads to significantly enhanced performance of Li||LFP full cells, which retain 85.5% of their capacity after 330 cycles at 1C. Moreover, a 1.1 Ah pouch cell with a 50-μm lithium foil and a high-loading LiFePO₄ cathode (24 mg cm⁻²) retains 95% of its capacity after 150 cycles at 1C. This work establishes a paradigm of functionally integrated electrolytes, which bridges solvation chemistry, interfacial engineering, and active material regeneration, addressing long-standing trade-offs in lithium-metal batteries. A synergistic organic-inorganic hybrid additive system, combining cesium iodide (CsI) and lithium difluoro(oxalate)borate (LiDFOB), is introduced into the electrolyte. Fundamentally, it alters interfacial chemistry by redirecting LiDFOB decomposition from B–F to B–O bond cleavage, leading to a robust solid electrolyte interphase (SEI). In parallel, iodide redox activity and electrostatic shielding of Cs + collectively regulate Li + kinetics, effectively suppressing dendritic growth and minimizing solvent decomposition, resulting in significantly enhanced battery performance.