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Lithium metal is recognized as a promising anode material for next-generation high-energy-density batteries, but uncontrollable lithium dendrites inhibit their further applications. In this paper, fluorine-containing functional groups were grafted on a commercial polypropylene (PP) separator by a simple and efficient plasma functionalization technique. The grafted polar groups enhance the affinity of the PP separator for Li-ions, thus resulting in improved wettability and ion conductivity as well as an enhanced lithium-ion transference number of the separator. Moreover, the introduced fluorine-containing functional groups participate in the formation of a LiF-rich solid electrolyte interface (SEI) film, which regulates the uniform deposition of lithium ions and inhibits lithium dendrite growth. As a result, Li‖Li symmetric batteries equipped with fluorinated PP separators exhibit a long lifespan of nearly 7000 h (1 mA cm−2, 1 mA h cm−2) with a low overpotential of 48 mV. This work introduces a simple method to induce the formation of a LiF-rich SEI film, which can be extended to a variety of energy storage systems and provides new routes for the construction of high-performance energy storage technologies. [ABSTRACT FROM AUTHOR]

It is instructive to explain the mechanism of action of additives as much as possible for the development of electrolytes. Recently, lithium disfluorobis(oxalato)phosphate (LiDFBOP) has been reported to show significant improvements in the solid electrolyte interphase (SEI) and battery performance in Li–S battery. In this work, the action mechanism of LiDFBOP in ether electrolyte was investigated in detail by a first-principles study. It was found that LiDFBOP preferentially decomposes on the anode, and the local environment after decomposition has a significant influence on the subsequent reaction. In addition, the participation of DFBOP− significantly affected the solvated structure and the trend in molecular decomposition. The addition of appropriate LiDFBOP weakened the strong binding between Li ion and the FSI− anion, and increased the content of 1,3-dioxolane in the solvated structure, thus improving the formation of the organic SEI. On the other hand, the LUMO redistribution induced by LiDFBOP is beneficial for protection of solvents. The possible characteristics of the new additive and the importance of dosage are also summarized in terms of the mechanism of action. [ABSTRACT FROM AUTHOR]

By employing first-principles simulations, we present theoretical predictions regarding the modification of structural, electronic and optical properties of 2H- and 1T′-MoS2 monolayers by covalent mono- and bisfunctionalization. Specifically, non-aromatic groups (–F, –NH2, –CH3, –CH2CH2 CN and –CH2CH2 OH) and aromatic (–Ph, –PhNO2 and PhOH) groups are utilized for monofunctionalization, and –F/–NH2, –NH2/–CH3 and –CH3/–Ph for bisfunctionalization. The stability of functionalized 2H- and 1T′-MoS2 monolayers mainly depends on the bonded groups and their surface coverage. In particular, the mixed bisfunctionalization with –F/–CH3 and –NH2/–CH3 groups enhances the stability of 2H-MoS2 through the formation of intermolecular hydrogen bonds. Both 2H- and 1T′-MoS2 can serve not only as electron donors, but also as electron acceptors, subject to the charge transfer behavior of the attached groups. Furthermore, mono- and bisfunctionalization are predicted to be efficient approaches to control the electronic band gaps in 2H- and 1T′-MoS2, where the corresponding values can be tuned by varying the coverage of the absorbed groups. At the same time, the choice of the chemical groups and their coverage also effectively determines the optical adsorption range and intensity. Therefore, our work shows that chemical functionalization of 2D materials with varying coverage can be an important approach to extend the scope of 2D materials in specific electronic and optoelectronic applications. [ABSTRACT FROM AUTHOR]

A series of low-valence titanium oxides (TiO and Ti2O) were fabricated by the electric field control approach and their stoichiometric ratios were precisely regulated by adjusting the electrolytic voltage and time. The Na-storage behaviours of the low-valence titanium oxides were investigated for the first time. Compared to conventional TiO2, low-valence titanium oxides undergo conversion reactions with excellent electrochemical performances. The Ti2O electrode delivers a high reversible capacity of 515 mA h g−1, outstanding rate capability of 173 mA h g−1 at 20 A g−1 and superior long-term cycling stability over 1800 cycles. Ex situ characterization reveals the reversible transformation of Ti2O to Ti and Na2O during repeated cycling. Density functional theory (DFT) calculations confirm that the low Ti–O bond energy is in favor of the fracture and recombination of Ti–O bonds, resulting in high capacity through multi-electron conversion reactions. The high conductivity of low-valence titanium oxides is conducive to the rapid transfer of electrons, achieving high electrochemical utilization. In addition, the porous nanostructure generated in situ by chemical conversion reactions could improve Na+ diffusion kinetics and buffer volume changes during sodiation/desodiation processes, thus realizing superior cycling stability and ultrafast charge/discharge ability. Moreover, a full cell coupled with a carbon-coated Na3V2(PO4)3 (Na3V2(PO4)3/C) cathode was assembled, which exhibited a high reversible capacity of 258.4 mA h g−1 and extraordinary cycling performance of 86.5% capacity retention over 100 cycles, demonstrating the potential of low-valence titanium oxides in sodium ion batteries. [ABSTRACT FROM AUTHOR]

Though high capacity and stable cycling of hard carbon anode Na-ion batteries have been achieved, critical safety issues, low discharge potential and unsatisfactory rate performance, present a huge challenge for their practical application. Herein, a slope-dominated mechanism strategy has been designed by preparing hybrid nanostructure carbon materials (HNCs) using a CVD-like method, providing hard carbon with excellent rate performances and high average discharge potential as an anode for Na-ion batteries. The HNCs integrate the advantages of carbon nanotubes and carbon nanosheets, presenting short ion/electron transfer distance and high surface area for abundant active sites. In addition, their microstructural properties including disorder degree and existing state of heteroatom sulfur, can be regulated via different synthetic temperatures providing effective nanovoids and bonding sites. Based on the reaction kinetics analysis, the Na-ion storage mechanism of HNCs can be determined as a capacitive-controlled process, which is essential for improving rate performances. This work demonstrates a novel method to develop a hybrid nanostructure hard carbon, and design of an electrochemical storage mechanism for high-performance and high-safety Na-ion batteries. [ABSTRACT FROM AUTHOR]

The insulation of S/Li2S and highly soluble nature of polysulfides largely limit the practical use of Li–S batteries. To overcome these issues, tremendous effort has been made for exploring efficient host materials and new battery construction. Herein, we propose to prepare high conductivity Ti2O by a molten salt electrochemical synthesis method; the synthesized Ti2O is developed to serve as an advanced host and used as a functional separator modification material for the first time. XPS analysis and DFT calculations verified that Ti2O can chemically anchor polysulfides through the abundant surface vacancies, and its high electronic conductivity can further enhance the redox kinetics of intermediate polysulfides. The cells based on the Ti2O–Super P/S cathode exhibit a high sulfur utilization and superb rate capability (553 mA h g−1 at 4C). Moreover, the cells assembled with a host-interlayer integrated electrode (2.5 mg cm−2) could achieve a low decay rate of 0.04% over 500 cycles at 0.5C. A high areal capacity of 6.8 mA h cm−2 can be also achieved even under 7.5 mg cm−2 sulfur loading. Overall, the controllable synthesis and application strategies of Ti2O present a way of regulation and optimization of the electrochemical performance of a Ti-based sulfur host through surface vacancy engineering for advanced Li–S batteries. [ABSTRACT FROM AUTHOR]

First-principle calculations within many-body perturbation theory are carried out to investigate the influence of the adsorbed molecules and sulfur (S) defects on the electronic and optical properties of the MoS2 monolayer. The exciton binding energy in the range of 0.05 eV to 1.14 eV is observed as a function of molecular coverage, when NO and 1,3,5-triazin (C3H3N3) are adsorbed on the pristine surface. These results can be explained by the interaction between the exciton and the adsorbed molecule. Furthermore, the combined effect of molecular functionalization and defective doping is studied. Our results show that both the electronic and optical band gaps of the MoS2 monolayer strongly depend on the molecular species and the defective coverage, and can be tuned up to ∼2 eV. This work demonstrates the great potential of controlling the MoS2 monolayer's excitonic properties by molecular functionalization and defective engineering. [ABSTRACT FROM AUTHOR]

The most critical obstacle preventing lithium–sulfur batteries (LSBs) from practical application is the shuttle effect. Herein, we present a zirconium based metal–organic framework (MOF) composite separator which effectively blocks polysulfides from shuttling without hampering the migration of lithium ions owing to the sieving effect of the MOFs. Moreover, owing to the high Brunauer–Emmett–Teller (BET) surface area of 1418 m2 g−1 and chemical interactions with zirconium and oxygen on the MOFs, the polysulfides can also be physically and chemically adsorbed on the surface of the MOFs, which further blocks the polysulfides from shuttling through the intergranular channels of the MOF particles. In addition, the wettability of the composite separator with the electrolyte is enhanced owing to the polar functional groups of –COOH and –OH on the MOFs. The battery with a composite separator delivers an initial discharge capacity of 1239 mA h g−1 at 0.2C and 1147.4 mA h g−1 at 0.5C. The reversible capacity is maintained at 964.1 mA h g−1 with an average fading of only 0.08% per cycle at 0.5C. The capacity at the 2C rate with the composite separator is 955.8 mA h g−1, which is far more than that of the pristine separator, which is 289.2 mA h g−1. [ABSTRACT FROM AUTHOR]

Herein, a high energy efficiency and long life aqueous Zn–I2 battery based on an activated carbon encapsulated I2 (I2@C-50) cathode is reported. It is found that an optimized electrolyte of Zn(CF3SO3)2 can significantly boost the initial coulombic efficiency from 61.1% to 91.3% due to the coordination effect, which accounts for the high energy efficiency of the battery. Moreover, the in situ formed solid electrolyte interphase (SEI) film on the Zn surface can effectively stabilize Zn stripping/plating and ensure the long-term cycling stability of the aqueous Zn–I2 battery. Besides, an activated carbon host with a large surface area, strong adsorption and spatial confinement suppresses the loss of active materials. As a result, the I2@C-50 cathode realizes a capacity of 210 mA h g−1 and a high energy efficiency of 96.7% at 0.1 A g−1, and exhibits a capacity retention of 66% after 10 000 cycles at 5 A g−1. In addition, pouch batteries with different sizes also demonstrate feasibility in practical applications. The results presented in this work provide insights on electrode, electrolyte and interface engineering to design high performance aqueous batteries. [ABSTRACT FROM AUTHOR]

Enhanced phosphorus (7.2 wt%) and sulfur (15.7 wt%) co-doped carbon (PSC) is synthesized via a one-step sintering of carbon disulfide and red phosphorus in a vacuum. It is found that S atoms can act as immobilization sites for phosphorus by covalently bonding with P atoms in the form of C–S–P, and thus high-level doping of phosphorus can be realized. Owing to the high-level doping, this co-doped carbon shows enlarged interlayer spacing, improved charge transfer capability and strong adsorption of Na+ ions. When tested as an anode for sodium ion batteries, this PSC delivers a high reversible capacity of 513.8 mA h g−1 at 100 mA g−1, excellent rate capability of 181.8 mA h g−1 at 10 A g−1 and superior cycling stability with a capacity of 290.1 mA h g−1 after 1000 cycles at 1 A g−1. [ABSTRACT FROM AUTHOR]

Polydiaminoanthraquinones, featured as redox-active quinone segments linked by polyaniline, were investigated as novel organic cathodes for K-ion batteries. With electron-withdrawing groups (CN) substituted, elevations of the redox potential and capacity utilization were achieved. [ABSTRACT FROM AUTHOR]

Hard carbon is one of the most promising anode materials for sodium ion batteries (SIBs) due to its low cost, high conductivity and suitable potential; however, its application is hindered by its relatively low capacity, and unsatisfactory rate capability and cyclability. Herein, we have reported a high performance SIB anode of S-doped interconnected carbon nanofibers (denoted as S-CNFs) that was directly derived from the industrial waste product bacterial cellulose, demonstrating great potential for practical application and sustainable development. The S-CNFs present high reversible capacities of 460 mA h g−1 at 0.05 A g−1 and 255 mA h g−1 at 10 A g−1, and preserved a capacity of 310 mA h g−1 at 1 A g−1 after 1100 cycles. Structural and electrochemical analyses revealed that multiple factors including the expanded (002) interlayer spacing, the electrochemically active –C–S–C– covalent bonds, the capacitive process induced by a large surface area and considerable defects as well as the stable structure associated with the cross-linked network contributed to their excellent performance. Furthermore, the first principles evaluations confirmed the sodium-storage mechanism of sulfur doping, which not only improved the interlayer distance for the mobility of Na+ but also promoted the electronegativity as well as the electrochemical activity and increased the adsorption of Na+. [ABSTRACT FROM AUTHOR]

Pyrite (FeS2) is considered an attractive Na-storage anode owing to its abundance, environment friendliness and high theoretical capacity (894 mA h g−1). However, it still remains great challenges to realize an applicable FeS2 electrode with both high reversible capacity and long cycle life. In this study, micron-sized FeS2@C composed of FeS2 nanoparticles uniformly embedded in carbon matrix was investigated as a conversion-type anode for sodium ion batteries by coupling with various electrolytes. It is demonstrated that the electrolyte formulations, i.e., both solvents and Na salts, play vital roles in the Na storage performance of FeS2. The combination of NaPF6 and DME was highly advantageous for constructing robust SEI films with high Na+ conductivity, guaranteeing fast and reversible conversion reactions in the wide electrochemical window of 0.005–3 V (vs. Na/Na+). Owing to the fast charge transfer kinetics and high chemical compatibility between the electrolyte and electrode, the as-prepared FeS2@C could deliver a high reversible capacity of 853 mA h g−1 at 0.2 A g−1 and 459 mA h g−1 at 40 A g−1, a remarkable initial coulombic efficiency of 84.7% and excellent cycling stability with capacity retention of 83.2% over 1000 cycles. These parameters prove the great potential of FeS2@C in fulfiling commercial demands for wide range of energy storage applications. [ABSTRACT FROM AUTHOR]

The permeation of dissolved lithium polysulfides across the porous polyolefin-based commercial separator is a major hindrance for using lithium sulfur batteries (LSBs). In this work, the poly(vinylidene fluoride) (PVDF)-based gel polymer electrolyte (GPE) with a compact morphology to block polysulfide penetration is prepared using a simple solution-casting method, and the strategy of incorporating poly(ethylene oxide) and nano zirconium dioxide is applied to guarantee electrolyte uptake and Li+ mobility. Superior to the commercial separator with liquid electrolyte, the LSB assembled with additive-free GPE exhibits a high initial capacity of 1429 mA h g−1, coulombic efficiency of 96% at 0.2C and improved rate performance. After 500 cycles at 1C, the LSB could still deliver a capacity of 847.2 mA h g−1, with a low fading rate of 0.05%. The LSB with high sulfur loading (5.2 mg cm−2) could attain a high areal capacity of 4.6 mA h cm−2. Results of scanning electron microscopy suggest that such a hybrid GPE could effectively protect the lithium anode from polysulfide corrosion. Therefore, this novel membrane of hybrid PVDF-based GPE provides a simple and effective method to establish high-performance LSBs. [ABSTRACT FROM AUTHOR]

A type of Na3V2(PO4)3/C (NVP/C) cathode material for sodium ion batteries was synthesized via a facile solid-phase method. Agarose, a natural polysaccharide from seaweed that can form a 3D network structure through hydrogen bonds in polar solvents, was used as a carbon source and a medium to form NVP/C particles as nanograins with a thin layer of carbon coating in a 3D carbon network. As the cathode, the NVP/C material exhibited a reversible capacity of 116 mA h g−1 at 1C, which is very close to its theoretical capacity (117.6 mA h g−1), with a capacity retention of 97.3% after 500 cycles. At 20C, the NVP/C had a capacity of 100 mA h g−1 and still kept a relatively stable capacity of 78 mA h g−1 after being cycled 7000 times. Based on the excellent performance of the obtained cathode material, a sodium ion full cell was assembled with S-doped carbon as the anode, which delivered 110 mA h g−1 of discharge capacity at 200 mA h g−1 (calculated using NVP as the cathode) and displayed an average voltage of around 1.7 V. All of these results imply that the prepared NVP/C has potential for application in sodium ion batteries for large-scale energy storage. [ABSTRACT FROM AUTHOR]

NiSx–rGOS is prepared via a facile and cost effective hydrothermal process, with the structure of ultrafine NiSx nanospheres uniformly wrapped in the in situ S-doped rGO matrix. The uniform nanostructural NiSx and high conductivity of S-doped rGO (rGOS) can effectively increase the ionic and electronic conductivity of the NiSx–rGOS composite, thus resulting in high capacity utilization of the active materials. Moreover, the buffering layer provided by the rGOS matrix can accommodate the volume change of the NiSx and protect the nanoparticles from aggregation during the repeated cycling process. The as-prepared NiSx–rGOS composite demonstrates a high reversible capacity of 516 mA h g−1 at 0.2 A g−1 with a capacity retention of 96.8% over 100 cycles and a remarkable rate performance of 414 mA h g−1 at 4 A g−1, possibly exhibiting the best electrochemical performances of nickel sulfide for sodium-ion batteries. [ABSTRACT FROM AUTHOR]

Metallic Sb has been extensively researched as a Na storage anode due to its high capacity and low cost, but it suffers from poor cycling stability stemming from its huge volume change (∼390%) during cycling. Herein, a unique two-dimensional hybrid structure of SbOx nanoplates encapsulated by carbon flakes (SbOx@CF) was fabricated by templating with soluble NaCl. Benefiting from its two-dimensional structure providing rapid Na+ ion uptake and removal and uniform coating endowing a stable buffer layer, the hybrid presents a high reversible capacity (451 mA h g−1) and excellent rate capability (114 mA h g−1 at 4 A g−1), as well as stable cycling (442 mA h g−1 after 100 cycles with 98% capacity retention). This work opens up a facile, controllable, economical and extendable approach to prepare advanced two-dimensional metal oxides for batteries and supercapacitors. [ABSTRACT FROM AUTHOR]

Sodium ion batteries are attractive alternatives to lithium ion batteries for stationary energy storage technology, and titanates are considered as promising anode materials for sodium ion batteries. Herein, a series of sodium titanates were synthesized via a simple, fast and controllable electrochemical route from solid TiO2 in molten salts of NaF–NaCl–NaI. For the first time, the as-prepared Na0.23TiO2 and Na0.46TiO2 were utilized as anode materials for sodium ion batteries, with a sodium storage capacity of 185 mA h g−1 and 215 mA h g−1 after 200 cycles, respectively. High rate and long term tests indicated the excellent cycle performance due to the formation of a 3D porous electrode structure during the long term charge/discharge processes. [ABSTRACT FROM AUTHOR]

A Na-rich cathode is developed by grafting the electron-withdrawing –SO3Na group on polyaniline chains. Due to the immobile doping and effective activation of the sulfonate group, this polymer demonstrates a high capacity (133 mA h g−1) and excellent cyclability through a cation-exchange reaction, offering a low cost and sustainable cathode for SIBs. [ABSTRACT FROM AUTHOR]

First-principle calculations within many-body perturbation theory are carried out to investigate the influence of the adsorbed molecules and sulfur (S) defects on the electronic and optical properties of the MoS 2 monolayer. The exciton binding energy in the range of 0.05 eV to 1.14 eV is observed as a function of molecular coverage, when NO and 1,3,5-triazin (C 3 H 3 N 3 ) are adsorbed on the pristine surface. These results can be explained by the interaction between the exciton and the adsorbed molecule. Furthermore, the combined effect of molecular functionalization and defective doping is studied. Our results show that both the electronic and optical band gaps of the MoS 2 monolayer strongly depend on the molecular species and the defective coverage, and can be tuned up to ∼2 eV. This work demonstrates the great potential of controlling the MoS 2 monolayer's excitonic properties by molecular functionalization and defective engineering.