To overcome the shuttle effect in Li–S batteries, novel biomimetic molecule catalysts are synthesized by grafting hemin molecules to three functionalized carbon nanotube systems (CNTs–COOH, CNTs–OH, and CNTs–NH2). The Li–S battery using the CNTs–COOH@hemin cathode exhibits the optimal initial specific capacity (1637.8 mAh g−1) and cycle durability (up to 1800 cycles). Various in situ characterization techniques, such as Raman spectroscopy, Fourier‐transform infrared reflection absorption spectroscopy, and UV–vis spectroscopy, combined with density functional theory computations are used to investigate the structure–reactivity correlation and the working mechanism in the Li–S system. It is demonstrated that the unique structure of the CNTs‐COOH@hemin composite with good conductivity and adequate active sites resulting from molecule catalyst as well as the strong absorption to polysulfides entrapped by the coordinated Fe(III) complex with FeO bond enables the homogeneous dispersion of S, facilitates the catalysis and conversion of polysulfides, and improves the battery's performance.
The sluggish reaction
kinetics at the cathode/electrolyte interface
of lithium–sulfur (Li–S) batteries limits their commercialization.
Herein, we show that a dual-regulation system of iron phthalocyanine
(FePc) and octafluoronaphthalene (OFN) decorated on graphene (Gh),
denoted as Gh/FePc+OFN, accelerates the interfacial reaction kinetics
of lithium polysulfides (LiPSs). Multiple in situ spectroscopy techniques and ex situ X-ray photoelectron
spectroscopy combined with density functional theory calculations
demonstrate that FePc acts as an efficient anchor and scissor for
the LiPSs through Fe···S coordination, mainly facilitating
their liquid–liquid transformation, whereas OFN enables Li-bond
interaction with the LiPSs, accelerating the kinetics of the liquid–solid
nucleation and growth of Li2S. This dual-regulation system
promotes the smooth conversion reaction of sulfur, thereby improving
the battery performance. A Gh/FePc+OFN-based Li–S cathode delivered
an ultrahigh initial capacity of 1604 mAh g–1 at
0.2 C, with an ultralow capacity decay rate of 0.055% per cycle at
1 C over 1000 cycles.
Lithium–sulfur batteries possess high theoretical energy density but suffer from rapid capacity fade due to the shuttling and sluggish conversion of polysulfides. Aiming at these problems, a biomimetic design of cofactor‐assisted artificial enzyme catalyst, melamine (MM) crosslinked hemin on carboxylated carbon nanotubes (CNTs) (i.e., [CNTs–MM–hemin]), is presented to efficiently convert polysulfides. The MM cofactors bind with the hemin artificial enzymes and CNT conductive substrates through FeN5 coordination and/or covalent amide bonds to provide high and durable catalytic activity for polysulfide conversions, while π–π conjugations between hemin and CNTs and multiple Li‐bond networks offered by MM endow the cathode with good electronic/Li+ transmission ability. This synergistic mechanism enables rapid sulfur reaction kinetics, alleviated polysulfide shuttling, and an ultralow (<1.3%) loss of hemin active sites in electrolyte, which is ≈60 times lower than those of noncovalent crosslinked samples. As a result, the Li–S battery using [CNTs–MM–hemin] cathode retains a capacity of 571 mAh g−1 after 900 cycles at 1C with an ultralow capacity decay rate of 0.046% per cycle. Even under raising sulfur loadings up to 7.5 mg cm−2, the cathode still can steadily run 110 cycles with a capacity retention of 83%.
The
complicated reactions at the cathode–electrolyte interface
in Li–S batteries are a large barrier for their successful
commercialization. Herein, we developed a molecular design strategy
and employed three small molecules acting as interfacial mediators
to the cathodes of Li–S batteries. The theoretical calculation
results show that the incorporation of tris(4-fluorophenyl)phosphine
(TFPP) has a strong binding performance. The experimental results
demonstrate that the strong chemical interactions between polysulfides
and the F, P atoms in TFPP not only modify the kinetics of the electrochemical
processes in the electrolyte but also promote the formation of short-chain
clusters (Li2S
x
, x = 1, 2, 3, and 4) at the interface during the charge–discharge
process. As a result, an optimized electrode exhibits a low capacity
decay rate of 0.042% per cycle when the current rate is increased
to 5 C over 1000 cycles.
A high-performance catalyst, O-doped Sb2S3 nanosheets (SS-O NSs), is synthesized and introduced into lithium–sulfur batteries. Owing to their good conductivity, strong adsorbability/catalytic effect to polysulfides and fast Li+ diffusion, the...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.