Ultrafast sulfur redox dynamics enabled by a PPy@N‑TiO2 Z‑scheme heterojunction photoelectrode for photo‑assisted lithium–sulfur batteries
2026-01-09
(Press-News.org)
While lithium–sulfur batteries (LSBs) promise 2600 Wh kg⁻¹, the sluggish liquid-solid conversion of polysulfides keeps practical capacities far below theory. Now, researchers at Northwestern Polytechnical University, led by Prof. Yibo He, report a free-standing PPy@N-TiO2/Carbon-Cloth photocathode that harvests sunlight to co-drive sulfur redox, delivering 1 653 mAh g-1 (98.7 % of theory) and 333 mAh g-1 after 5 h of pure photo-charging. Published in Nano-Micro Letters, the work realizes dual-mode energy harvesting in a single cell.
Why Photo-Assisted Strategy Matters
Polysulfide Bottleneck: Long-chain Li2S6/8 species shuttle and precipitate as electrically insulating Li2S, wasting active mass.
External-Field Boost: Optical fields lower activation energy via photocatalysis, yet single-semiconductor electrodes suffer wide band-gaps and fast carrier recombination.
Sun-in-Sulfur Vision: Integrating solar conversion and storage slashes grid demand during charging, ideal for high-altitude or off-grid devices.
Innovative Heterojunction Design
Z-Scheme p–n Junction: Vapor-phase polymerized polypyrrole (p-type) coats N-doped TiO2 nanorods (n-type), building an internal electric field that separates e⁻/h⁺ pairs.
Band-Engineered Alignment: narrowed gap (2.17 eV) extends visible harvest; CB electrons reduce S8→Li2S while VB holes oxidize Li2S→S8, closing a catalytic loop.
Free-standing Architecture: 3-D carbon cloth offers 599 mAh g-1 at 4 C and 3.3 mAh cm⁻² under 3 mg cm-2 sulfur, mitigating volume swing and blocking shuttle.
Performance Breakthroughs
Ultrafast Redox: Tafel slopes drop from 122 → 48 mV dec-1; Li2S nucleation time shortens from 3600 → 3 010 s with 17 % higher capacity.
Dual-Mode Harvesting: 0.33 % solar-to-output efficiency; coin cell powers toy car 288 cm under light vs 212 cm in dark, then 77 cm after 2 h re-charge under ambient sunlight.
Long-term Stability: 61.7 % retention over 328 cycles at 0.5 C; DRT analysis shows illuminated cell maintains lower R_SEI and R_PS, suppressing parasitic reactions.
Future Outlook
The plug-and-play photocathode design is scalable through roll-to-roll vapor coating, pointing toward solar-assisted EV packs and stratospheric drones where every photon counts.
END
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[Press-News.org] Ultrafast sulfur redox dynamics enabled by a PPy@N‑TiO2 Z‑scheme heterojunction photoelectrode for photo‑assisted lithium–sulfur batteries
