ABSTRACT
To overcome the shuttle effect in lithium-sulfur (Li-S) batteries, an sp/sp2 hybridized all-carbon interlayer by coating graphene (Gra) and hydrogen-substituted graphdiyne (HsGDY) with a specific surface area as high as 2184 m2 g-1 on a cathode is designed and prepared. The two-dimensional network and rich pore structure of HsGDY can enable the fast physical adsorption of lithium polysulfides (LiPSs). In situ Raman spectroscopy and ex situ X-ray photoelectron spectroscopy (XPS) combined with density functional theory (DFT) computations confirm that the acetylenic bonds in HsGDY can trap the Li+ of LiPSs owing to the strong adsorption of Li+ by acetylenic active sites. The strong physical adsorption and chemical anchoring of LiPSs by the HsGDY materials promote the conversion reaction of LiPSs to further mitigate the shuttling problem. As a result, Li-S batteries integrated with the all-carbon interlayers exhibit excellent cycling stability during long-term cycling with an attenuation rate of 0.089% per cycle at 1 C over 500 cycles.
ABSTRACT
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.
ABSTRACT
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 (Li2Sx, 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.
ABSTRACT
It is of great importance to develop a 3D scaffold that matches the bone in aspects of element and structure. In order to achieve this aim, the sugarcane aerogel derived borate glasses scaffolds were developed through in situ bioglass modification. Sol-gel-derived borate glasses of the 30-5B (Si/B ratio) have been prepared to produce 3D borate scaffolds with sugarcane morphologies. As a result, not only the elemental distribution but also the multilevel structure of this Gramineae plant derived implants were remarkably matched with natural bone. The subsequent animal implantation experiment found that the microstructural orientation of the implant had an important impact on the result of bone repair. The relative mechanisms were also discussed for the first time.
