Lithium–sulfur batteries (LSBs) hold immense promise for next-generation energy storage, boasting a theoretical specific capacity of 1,675 mAh g-1 for sulfur and 3,860 mAh g-1 for lithium metal. Yet their practical deployment faces a fundamental kinetic bottleneck: the sluggish stepwise sulfur redox conversion involving soluble lithium polysulfides (LiPSs). Conventional "adsorption-catalysis" strategies—employing metal oxides, sulfides, and nitrides—have focused overwhelmingly on chemically suppressing LiPS shuttling and enhancing conversion kinetics, while systematically overlooking a crucial rate-limiting step: the high Li⁺-solvent desolvation energy barrier. In typical liquid electrolytes, Li⁺ exists predominantly in solvent-separated ion pair (SSIP) configurations with strong Li⁺-solvent coordination bonds that impose severe kinetic penalties on polysulfide conversion. Now, researchers led by Tan Wang, Zhenhua Wang, David Rooney, and Kening Sun have proposed a transformative catalyst desolvation strategy utilizing phosphorus-modulated cerium single-atom catalysts that fundamentally reconfigures the Li⁺ solvation environment, unlocking rapid sulfur redox kinetics and unprecedented cycling stability.
Innovative Design and Mechanism
The team engineered a P/Ce-NC catalyst featuring isolated cerium single atoms anchored on N-doped carbon, with phosphorus strategically incorporated into the second coordination sphere of the Ce–N4 site. This molecular architecture operates through a dual electronic modulation mechanism that addresses both Li⁺ transport and polysulfide containment.
Accelerated Li⁺ Desolvation: DFT calculations and molecular dynamics simulations reveal that phosphorus incorporation increases electron occupancy of the Ce f_{y3x3} and f_z3 orbitals, enhancing interaction between Ce and the oxygen atoms of solvent molecules (DME/DOL). This electronic reconfiguration effectively weakens Li⁺-solvent coordination: Li–O bond lengths elongate from 1.91 Å to 2.47 Å in DOL and from 2.02 Å to 3.23/2.33 Å in DME. Crystal orbital Hamilton population (COHP) analysis confirms substantially reduced binding strength, with integrated pCOHP values dropping to 0.02–0.12 versus the pure solvent system. Consequently, the desolvation energy barrier plummets from 1.8 eV/0.7 eV (blank electrolyte) to merely 0.3 eV/0.39 eV for DME/DOL in the P/Ce-NC system.
Solvation Structure Reorganization: The weakened Li⁺-solvent interaction promotes a fundamental shift in the Li⁺ solvation sheath from SSIP-dominated to anion-rich configurations. Raman spectroscopy confirms that in the P/Ce-NC system, the proportions of contact ion pairs (CIP) and aggregates (AGG) increase to 29.89% and 19.92%, respectively, compared to merely 23.52% and 8.84% in the PNC system. This reorganization accelerates Li⁺ desolvation while maintaining ionic conductivity (0.33 mS cm⁻¹) and enhancing the Li⁺ transference number from 0.11 to 0.45.
Strengthened f-d-p Orbital Hybridization: Simultaneously, the Ce-f orbital achieves maximized overlap with the S-p orbital, creating strengthened f-d-p hybridization that effectively inhibits polysulfide anion diffusion through the interlayer. This dual-action mechanism—accelerating Li⁺ transport while suppressing shuttle effects—establishes a robust catalytic interface for sulfur conversion.
Outstanding Performance
The electrochemical metrics demonstrate the transformative impact of this catalyst desolvation strategy. Cyclic voltammetry reveals sharper oxidation peaks with significantly smaller peak potential gaps (Gap 1: 0.32 V; Gap 2: 0.10 V vs. PNC), indicating rapid multiphase conversion kinetics. The Tafel slope decreases to 90 mV dec-1 (vs. 109 mV dec-1 for PNC), confirming superior electrochemical activity. Li⁺ diffusion coefficients are markedly enhanced across all redox stages, as quantified by scan-rate-dependent CV analysis.
At the cell level, the battery with P/Ce-NC delivers an initial discharge capacity of 1,134 mAh g-1 at 0.2 C, retaining 815 mAh g-1 (72.17%) after 200 cycles with a stable Coulombic efficiency of 99.65%. The high-voltage/low-voltage plateau capacity ratio (Q_L/Q_H = 2.46) surpasses PNC (2.23), confirming superior sulfur utilization. Rate capability testing demonstrates exceptional performance across the full spectrum: 1,374, 1,052, 891, 791, 710, 653, 607, 547, and 469 mAh g-1 at 0.1, 0.2, 0.5, 1, 2, 3, 4, 5, and 6 C, respectively, with excellent recovery to 801 mAh g-1 when returning to 0.5 C.
Under demanding high-loading conditions (5.31 mg cm-2 sulfur, E/S ratio of 8 μL mg-1), the battery achieves a superior reversible areal capacity of 5.85 mAh cm-2 with a minimal charge-discharge voltage gap of merely 0.19 V. A Li-S pouch cell with 45 mg sulfur mass delivers an initial capacity of 784.55 mAh g-1 at 0.1 C, maintaining 96.54% capacity retention after 200 cycles—underscoring exceptional practical viability.
Most remarkably, the battery achieves ultrastable long-term cycling with an ultralow decay rate of 0.036% per cycle over 1,700 cycles at 1 C, delivering a high specific capacity of 939 mAh g-1. This performance markedly surpasses the PNC system (0.058% decay over 1,000 cycles) and establishes a new benchmark among single-atom catalyst-based and solvation-modulation LSBs reported to date.
Stabilized Lithium Anode Interface: The accelerated Li⁺ desolvation synergistically stabilizes the lithium anode/electrolyte interface. In situ Raman spectroscopy confirms effective suppression of polysulfide shuttle effects, with consistently weak LiPS signals throughout charge-discharge cycles. XPS analysis of cycled lithium anodes reveals an inorganic-rich SEI featuring enhanced LiF and Li3N content, which promotes uniform Li⁺ deposition. Li//Li symmetric cells with P/Ce-NC exhibit a minimal overpotential of merely 0.01 V and achieve a prolonged cycling lifespan exceeding 1,000 hours at 0.5 mA cm-2.
Applications and Future Outlook
This work establishes catalyst desolvation as a paradigm-shifting strategy that moves beyond conventional adsorption-catalysis approaches to address the fundamental kinetic origin of sulfur redox limitations. By demonstrating that the Li⁺ desolvation process—conceptually analogous to intermediate adsorption in heterogeneous catalysis—can be effectively catalyzed through single-atom electronic structure engineering, this research opens promising avenues for next-generation high-energy batteries combining rapid kinetics, extended cycle life, and practical manufacturability. The demonstrated pouch cell performance and sub-0.04% capacity decay rate position this technology as a critical enabler for the commercialization of lithium-sulfur batteries in electric vehicles and grid-scale storage.
Stay tuned for more groundbreaking research from this collaborative team at Beijing Institute of Technology and Queen's University Belfast!
