Heteroatoms synergistic anchoring vacancies in phosphorus‑doped CoSe2 enable ultrahigh activity and stability in Li–S batteries

Lithium-sulfur (Li–S) batteries are hailed as next-generation energy storage stars, boasting an ultra-high theoretical energy density (2600 Wh kg^-1) and low cost. Yet, two critical bottlenecks—the shuttle effect of lithium polysulfides (LiPSs) and slow sulfur conversion kinetics—cause rapid capacity decay, holding back their commercialization. Now, a team led by Professors Xuebin Wang and Shaochun Tang from Nanjing University has published a breakthrough in Nano-Micro Letters, introducing a novel “heteroatoms synergistic anchoring vacancies” strategy. This innovation creates phosphorus-doped CoSe₂ with rich selenium vacancies (P-CS-Vo-0.5), resolving the long-standing “activity-stability trade-off” of catalysts and enabling Li–S batteries with exceptional performance.

Why This Catalyst Fixes Li–S Battery Woes

Traditional Li–S battery catalysts (e.g., pure CoSe₂) struggle to balance two key needs: strong LiPS adsorption (to suppress shuttling) and fast conversion kinetics (to boost capacity). Vacancy engineering—adding selenium vacancies (Vo) to CoSe₂—enhances activity by creating more active sites, but excess or unstable vacancies cause structural collapse and rapid deactivation. The Nanjing University team’s solution addresses this with precision:

• Volcano-Type Activity Control: Through systematic experiments and density functional theory (DFT) simulations, they found a “volcano relationship” between vacancy concentration and catalytic activity. The optimal CS-Vo-0.5 (CoSe₂ with 0.5 mol L^-1 NaBH₄-induced vacancies) strikes the perfect balance—enough vacancies to accelerate LiPS conversion, but not so many that the structure degrades.
• P Anchoring for Stability: Doping phosphorus (P) into CS-Vo-0.5 is the game-changer. P atoms fill partial selenium vacancies, reducing the vacancy surface energy by 56% (from 1.59 eV to 0.69 eV) and suppressing inward vacancy migration. This “anchoring” effect preserves active sites over cycles, solving the stability issue of vacancy-rich catalysts.
• Dual-Function Boost: P-CS-Vo-0.5 excels at both adsorption and conversion: it strongly binds LiPSs (adsorption energy for Li₂S₄ = −1.326 eV, 28% higher than pure CoSe₂) and lowers the activation energy for LiPS conversion by 2513.9 J mol^-1, accelerating reaction kinetics.

Core Innovation: How P-CS-Vo-0.5 Is Made

The team’s synthesis process is simple yet precise, ensuring uniform vacancies and stable P doping:

1. Create Vacancies: Treat CoSe₂ (derived from ZIF-67 and selenium powder) with 0.5 mol L^-1 NaBH₄. The reactive hydrogen from NaBH₄ etches selenium atoms, forming stable selenium vacancies (CS-Vo-0.5).
2. P Doping: Heat CS-Vo-0.5 with NaH₂PO₂ under argon. P atoms selectively occupy partial vacancies, forming P-CS-Vo-0.5 without disrupting CoSe₂’s cubic structure.
   Advanced characterizations confirm the design: spherical aberration-corrected STEM images show clear selenium vacancies, while XPS and XANES reveal that P doping modulates electron density around Co and Se, enhancing LiPS interactions.

Li–S Battery Performance: Ultra-High Capacity & Long Life

When integrated into a Li–S battery separator, P-CS-Vo-0.5 delivers remarkable results:

• High Initial Capacity: At 0.2C (1C = 1675 mA g^-1), the battery achieves an initial discharge capacity of 1306.7 mAh g^-1—80% of sulfur’s theoretical capacity, far exceeding pure CoSe₂ (516.0 mAh g^-1).
• Exceptional Cyclic Stability: At 4C (high rate), it retains 84.6% of its capacity after 400 cycles—four times better than CS-Vo-0.5 (50.3% retention) and pure CoSe₂ (20.5% retention).
• High Sulfur Loading: Even with a sulfur loading of 5.7 mg cm^-2 (critical for practical high-energy batteries), it maintains an areal capacity of 5.04 mAh cm^-2 with 95.1% retention after 80 cycles.
• Real-World Proof: The battery powers patterned LEDs, demonstrating its practical applicability. In situ Raman tests further confirm that P-CS-Vo-0.5 nearly eliminates the shuttle effect—only weak LiPS signals are detected during cycling, unlike pure CoSe₂ separators.

Future Impact: A New Path for Energy Storage

This work isn’t just a win for Li–S batteries—it provides a general strategy for designing stable, high-activity catalysts. By tuning local atomic environments (vacancies+ heteroatom doping), the team has opened doors to better catalysts for other energy systems, such as fuel cells and metal-air batteries. For Li–S batteries specifically, P-CS-Vo-0.5 brings commercialization closer: it addresses the core shuttle and kinetics issues while using low-cost, scalable materials.

As the global demand for high-energy, long-life batteries grows (for electric vehicles, grid storage, and portable electronics), innovations like P-CS-Vo-0.5 are critical. The Nanjing University team’s “heteroatoms synergistic anchoring” strategy proves that precision engineering—balancing activity and stability at the atomic level—is the key to next-generation energy storage.