新加坡国立大学John Wang院士团队：异核双原子非对称极化调控d-p杂化增强锂硫电池双向的硫氧化还原动力学
学术
2024-12-13 09:02
上海
锂硫电池由于其高比能量（2600 Wh kg-1）和硫资源的丰富性，成为下一代可充电能源存储系统的有力候选。然而，锂硫电池在实际应用中面临多重问题，包括硫和Li2S的电绝缘性、充放电过程中体积膨胀（约80%）、锂多硫化物（LiPSs）的迁移效应和硫氧还原反应（SRR）动力学的慢速性等。这些问题限制了锂硫电池的实际应用和性能提升。为了解决这些问题，研究者们专注于开发新型电催化剂来改善SRR动力学和硫的利用率。单原子催化剂（SACs）和双原子催化剂（DACs）作为新兴的电催化剂类型，展示了较好的性能，特别是双原子催化剂（DACs）在优化中间体吸附、突破吸附能量标度关系（SRL）方面表现出色。然而，传统的双原子催化剂的催化机制和在锂硫电池中的应用仍不清楚，因此，本文提出并研究了异核CoFe双原子催化剂（CoFe DACs），旨在通过调节异核双原子催化剂非对称极化的电子结构，提升锂硫电池的性能。通讯作者：新加坡国立大学John Wang教授、沈磊高级讲师、新加坡科技局高性能计算研究所Yong-Wei Zhang教授、山东大学宋克鹏研究员。这篇文章介绍了异核CoFe双原子催化剂（DACs），通过利用其独特的非对称几何和电子构型，解决了锂硫电池（LiSBs）中硫还原反应（SRR）的动力学限制。研究发现，CoFe双原子催化剂能够有效加速Li2S2到Li2S的双向固-固转化以及Li2S分解的逆反应，显著提升了硫的利用效率和SRR动力学。在该催化剂中，Co原子的引入打破了Fe-3d轨道的局域化，提高了电子自旋态，从而提供了更多的空轨道，有助于SRR过程的进行。通过密度泛函理论（DFT）和态密度（DOS）分析，揭示了Fe的d带中心比Co更接近费米能级，导致Fe与吸附物种之间的反键态占据较低。这种电子结构的差异使得吸附倾向非对称地偏向Fe原子，进一步调节了电子轨道的杂化，削弱了Li-S键，促进了Li2S的分解。更为重要的是，研究还发现Li2S在Fe原子上的单位点吸附行为，这种单双位点吸附模式的灵活切换显著降低了SRR的能量壁垒，从而提高了硫的利用率和双向的氧化还原动力学。Material Synthesis
and Characterization.![]()
Figure 1. a) XRD pattern, b) Raman spectra, and c) Co and Fe 2p XPS
spectra of CoFe DACs. d) Co and Fe K-edge XANES, e) FT-EXAFS spectra, f)
FT-EXAFS fitting curves in R spaces, g) wavelet transform images of k2-weighted
EXAFS of DACs, h) HAADF-STEM image, and i) corresponding line-scanning
intensity profiles obtained on the zoomed areas in panel h for two bimetallic
Co-Fe sites. j) Statistical Co-Fe distance in the observed diatomic pairs. k)
CoFe DACs structure analyzed by EELS.Electrochemical Performance of Lithium Sulfur
Batteries.Figure 2.a) CV profiles of LiSBs. b) GCD profiles at 1 C. c) Rate performance of LiSBs
cells. d, e) Long-term cycling performance at 1 C and 3 C, respectively. f) DFT calculations of charge-density difference plots for Li2S8,
Li2S4, Li2S intermediates interacting with
CoFe DACs from top and side views. The yellow (blue)
distribution corresponds to charge accumulation (depletion). g) Free-energy
diagram of different DACs for SRR (the inset depicts the optimized geometries
of LiPSs adsorbed on CoFe DACs).Sulfur Redox
Kinetics Mechanism.Figure 3.a) CV
profiles of CoFe DACs across 1.7–3.0 V at various sweep rates. b) Linear correlation between peak current and square root
sweep rate for the redox peak. c) NTR values at diverse sweep rates. d-f) Potentiostatic discharge profiles
for Li2S precipitation. g) Potentiostatic charge profiles for Li2S dissociation. h) Tafel plots for symmetric cells, sweeping from -0.1 to 0.1
V at 0.1 mV s-1. i) CV profiles for symmetric cells in 0.25 M Li2S8 electrolyte at 1 mV s-1.Asymmetric
Charge Distribution and Orbital Hybridization.Figure 4. Projected density of states of (a) Co and (b) Fe
in CoFe DACs and their hybridization with Li2S in (c)
mono-adsorption configuration and (d) dual-adsorption configuration.Figure 5. -COHP diagram of (a) Co-S and (b) Fe-S bond in
spin up orbital and spin down orbital as well as Li-S bond in (c) spin up
orbital and (d) spin down orbital. -ICOHP values of (e) Fe-S/Co-S bonds and (f)
Li-S bonds. (g) Li2S decomposition barriers on FeFe, CoFe, CoCo
DACs. (h) Schematic of the formation of Fe/Co-S bonds. EF represents
the Fermi level. (i) The mechanism diagram illustrating the dynamic switching
between mono and dual adsorption sites.Asymmetric
Polarization Modulation of d–p Hybridization-Enhanced Bidirectional Sulfur
Redox Kinetics with Heteronuclear Dual-Atom Catalystshttps://pubs.acs.org/doi/10.1021/acsnano.4c09637.
