Breaking symmetry: Synergistic engineering of asymmetric Ru–O–Ti sites and polar N–Ti–O bonds to enhance sulfur-redox kinetics and suppress lithium dendrites

Flexible lithium–sulfur batteries (LSBs) are promising next-generation energy storage technology due to their exceptional energy density and cost effectiveness, yet their practical applications are hindered by the shuttling of lithium polysulfides (LiPSs), sluggish Li 2 S nucleation and decomposition kinetics, as well as uncontrolled Li dendrite growth. Herein, we design a flexible electrocatalyst featuring Ru single-atom and nitrogen dual-doped bronze-TiO 2 in situ grown on carbon cloth (Ru-NT@CC)—a new multifunctional host that simultaneously addresses aforementioned challenges via a symmetry-breaking strategy. X-ray absorption spectroscopy and theoretical calculations reveal that introducing Ru single atoms and N into nanometric TiO 2 creates atomically asymmetric Ru–O–Ti sites and polar N–Ti–O bonds, which break the symmetric configuration, upshift the d -band center, modulate the electronic distribution, and construct multi-metal sites in Ru-NT@CC. Electrochemical testing, theoretical calculations and ex/in situ characterization techniques further demonstrate these engineered sites combined with the freestanding conductive architecture, synergistically accelerate LiPS conversions, facilitate Li 2 S nucleation/decomposition, homogenize Li + flux, and enable dendrite-free Li plating/stripping. Consequently, the Ru-NT@CC/S cathode delivers an ultrahigh initial specific capacity of 872.8 mAh g −1 with just 0.027% per cycle degradation over 1000 cycles at 2.0 C. Even under a sulfur loading of 9.2 mg cm −2 and lean electrolyte of 5.6 μL mg −1 , it achieves a remarkable areal-capacity of 6.7 mAh cm −2 at 0.1 C after 50 cycles. The Ru-NT@CC/Li symmetrical-cell demonstrates an ultra-long cycling lifespan exceeding 2000 h. Notably, Ru-NT@CC/S||Ru-NT@CC/Li pouch cell maintains steady voltages under 180° folded condition. This work provides new insights into the rational design of electrocatalysts for sulfur conversion and paves the way for the development of advanced flexible LSBs. • Asymmetric Ru–O–Ti sites and polar N–Ti–O bonds break symmetric configuration for superior sulfur redox and Li deposition. • A freestanding, integrated host simultaneously optimizes both sulfur cathode and lithium anode. • Flexible pouch cell achieves high energy density and stable operation under 180° bending.