Graphite dual-ion batteries represent a potential battery concept for large-scale stationary storage of electricity, especially when constructed free of lithium and other chemical elements with ...limited natural reserves. Owing to their non-rocking-chair operation mechanism, however, the practical deployment of graphite dual-ion batteries is inherently limited by the need for large quantities of electrolyte solutions as reservoirs of all ions that are needed for complete charge and discharge of the electrodes. Thus far, lithium-free graphite dual-ion batteries have employed moderately concentrated electrolyte solutions (0.3-1 M), resulting in rather low cell-level energy densities of 20-70 Wh kg
. In this work, we present a lithium-free graphite dual-ion battery utilizing a highly concentrated electrolyte solution of 5 M potassium bis(fluorosulfonyl)imide in alkyl carbonates. The resultant battery offers an energy density of 207 Wh kg
, along with a high energy efficiency of 89% and an average discharge voltage of 4.7 V.
Dithiine linkage formation via a dynamic and self-correcting nucleophilic aromatic substitution reaction enables the de novo synthesis of a porous thianthrene-based two-dimensional covalent organic ...framework (COF). For the first time, this organo-sulfur moiety is integrated as a structural building block into a crystalline layered COF. The structure of the new material deviates from the typical planar interlayer π-stacking of the COF to form undulated layers caused by bending along the C–S–C bridge, without loss of aromaticity and crystallinity of the overall COF structure. Comprehensive experimental and theoretical investigations of the COF and a model compound, featuring the thianthrene moiety, suggest partial delocalization of sulfur lone pair electrons over the aromatic backbone of the COF decreasing the band gap and promoting redox activity. Postsynthetic sulfurization allows for direct covalent attachment of polysulfides to the carbon backbone of the framework to afford a molecular-designed cathode material for lithium–sulfur (Li–S) batteries with a minimized polysulfide shuttle. The fabricated coin cell delivers nearly 77% of the initial capacity even after 500 charge–discharge cycles at 500 mA/g current density. This novel sulfur linkage in COF chemistry is an ideal structural motif for designing model materials for studying advanced electrode materials for Li–S batteries on a molecular level.
Abstract
Two-dimensional (2D) membranes are emerging candidates for osmotic energy conversion. However, the trade-off between ion selectivity and conductivity remains the key bottleneck. Here we ...demonstrate a fully crystalline imine-based 2D polymer (2DPI) membrane capable of combining excellent ionic conductivity and high selectivity for osmotic energy conversion. The 2DPI can preferentially transport cations with Na
+
selectivity coefficient of 0.98 (Na
+
/Cl
−
selectivity ratio ~84) and K
+
selectivity coefficient of 0.93 (K
+
/Cl
−
ratio ~29). Moreover, the nanometer-scale thickness (~70 nm) generates a substantially high ionic flux, contributing to a record power density of up to ~53 W m
−2
, which is superior to most of nanoporous 2D membranes (0.8~35 W m
−2
). Density functional theory unveils that the oxygen and imine nitrogen can both function as the active sites depending on the ionization state of hydroxyl groups, and the enhanced interaction of Na
+
versus K
+
with 2DPI plays a significant role in directing the ion selectivity.
The anion-intercalation chemistries of graphite have the potential to construct batteries with promising energy and power breakthroughs. Here, we report the use of an ultrathin, positively charged ...two-dimensional poly(pyridinium salt) membrane (C2DP) as the graphite electrode skin to overcome the critical durability problem. Large-area C2DP enables the conformal coating on the graphite electrode, remarkably alleviating the electrolyte. Meanwhile, the dense face-on oriented single crystals with ultrathin thickness and cationic backbones allow C2DP with high anion-transport capability and selectivity. Such desirable anion-transport properties of C2DP prevent the cation/solvent co-intercalation into the graphite electrode and suppress the consequent structure collapse. An impressive PF
-intercalation durability is demonstrated for the C2DP-covered graphite electrode, with capacity retention of 92.8% after 1000 cycles at 1 C and Coulombic efficiencies of > 99%. The feasibility of constructing artificial ion-regulating electrode skins with precisely customized two-dimensional polymers offers viable means to promote problematic battery chemistries.
For the progressive development of spintronics as the next generation information technology source, it is essential to look for materials with high abundance, long spin lifetime, easy manipulation ...of spin current, and temperature/strain resistivity of spin properties. In this respect, the main group based two-dimensional (2D) semiconductors are systems of immense research interest in the field of spintronic devices for their novel characteristics and notable application in spintronics nanotechnology. The discovery of graphene set off the journey of 2D materials, and many of them have been identified as potential candidates for spintronics applications owing to their extraordinary properties and atomically thin structures. Since the last few decades, several theoretical and experimental reports agreed with the novel chemistry between 2D materials and nanoscale spintronic devices. This review highlights the most progressive and important theoretical and experimental studies of main group based 2D spintronics reported until present which have contributed to inspiring new spintronic devices and have given direction for further development. We have systematically discussed the main group based 2D spintronic materials in the two categories of metal incorporated and metal-free systems. Besides, vital focus is given to the useful theoretical techniques for spintronics studies and suitable designing of spintronic materials and devices. We have also briefly discussed the past, present, and future perspective of spintronic devices.
Presently, great attention is being directed toward the development of promising electrode materials for non-lithium rechargeable batteries which have the advantages of low cost, high energy storage ...density, and high rate capacity for substantial renewable energy applications. In this study, we have predicted that the C3N monolayer is a potential electrode material for Na- and K-ion batteries by first-principle calculations. The diffusion barriers are calculated to be as small as 0.03 eV for Na and 0.07 eV for K, which could lead to a very fast diffusion on the C3N monolayer surface, implying high mobility and cycle stability for batteries. The C3N monolayer is predicted to allow a high storage capacity of 1072 mAh/g by the inclusion of multilayer adsorption with an average voltage of 0.13 V for Na2C3N and 0.26 V for K2C3N systems, which is more promising than previously studied anode materials. All of these results ensure that the C3N monolayer could serve as an excellent anode material for Na- and K-ion batteries.
Developing a highly efficient catalyst with lower Pt content for the oxygen reduction reaction (ORR) is highly sought for fuel cell applications. The potential applicability of a cuboctahedral ...core–shell (Ti19@Pt60) nanocluster (NC) toward ORR activity has been investigated and compared with that of a pure Pt NC (Pt79). The energetic stability, thermal stability, and dissolution limit of Ti19@Pt60 NCs has been investigated for their possible synthesis and practical usages. Thermodynamic and kinetic parameters are explored to find out the most favored ORR pathway and product selectivity on the Ti19@Pt60 NC. Rate-determining steps (*O2 activation and *OH formation) are highly improved over the Ti19@Pt60 NC with respect to the cuboctahedral Pt NC (Pt79), pure metal (Pt, Pd, and Ag), and alloy (Pt3M; M = Ni, Co, Ti) based catalysts. Our detailed investigation reveals that the *O2-induced structural changes favor direct *O2 dissociation on the Ti19@Pt60 NC surface. Further, we find that a dual mechanism (ligand effect and charge transfer) plays an important role to improve the ORR activity. The results obtained in this study provide fundamental insight into the role of a core–shell NC toward ORR activity.
The emerging field of dual-ion batteries (DIBs) show better advantages compared to the commercial Li-ion batteries. Thus, the on-going experimental studies of DIBs require a clear understanding of ...the reaction mechanism as well as the resulting structural variation in the involved anions and cathode system. Therefore, in this work, using the first-principles calculations, we have studied the intercalation mechanism of PF6 – intercalation from the organic electrolyte into graphite. The intercalation energy characteristics indicate the favorable intercalation of PF6 – into graphite following the staging mechanism, also confirmed by X-ray diffraction simulations. PF6 – intercalation relatively acquiring a small interlayer distance in graphite than AlCl4 – and FSI– guarantees reduction in exfoliation of graphite to have a long battery cycle life, which is in accordance with the experimental reports (2000 cycles with 97.9% capacity retention). The cell voltage determined in the range 5.28–5.49 V having a maximum specific capacity of 124 mA h g–1 is in good agreement with experimental values. Through charge transfer analysis, we found that there is 0.97 |e| charge transfer from graphite to PF6 –, which clarifies that PF6 – intercalation into graphite is the charging process. Moreover, the metallic character of the PF6 – intercalated graphite system and a small diffusion barrier of 0.14 eV indicate a constant electronic conductivity and better rate performance, respectively. These results provide the clear understanding of PF6 – intercalation into graphite and also describe the role of staging behavior to obtain the precise values of electrochemical properties.
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