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Interface density regulation of Ni 3 Se 4 /NiSe 2 heterostructures is achieved by controlled selenylation of Ni-MOFs. Compared with low-density interfaces, the high-density Ni 3 Se 4 /NiSe 2 heterostructures demonstrate superior lithium storage properties and electrocatalytic activity. [Display omitted] Biphasic or multiphase heterostructures hold attractive prospects in engineering advanced electrode materials for energy-related applications owing to the appealing synergistic effect; however, they still suffer from unsatisfied electrochemical activity and reaction kinetics. Herein, guided by density functional theory calculation, a well-engineered selenides heterostructure with high-density Ni 3 Se 4 -NiSe 2 biphasic interfaces that fastened in N, O-codoped carbon matrix, was developed for high-performance lithium storage and electrocatalysis. By controlled selenylation of metal–organic framework (MOF), a series of NiSe x @C hybrids (Ni 3 Se 4 @C, Ni 3 Se 4 /NiSe 2 @C-1, Ni 3 Se 4 /NiSe 2 @C-2, and NiSe 2 @C) with tunable biphasic components and grain sizes were prepared. Abundant two-phase interfaces with higher interface density are generated inside the Ni 3 Se 4 /NiSe 2 -1 induced by much smaller nanograins in comparison with the Ni 3 Se 4 /NiSe 2 -2, so that significant charge redistribution and faster electrons/Li+ ions transfer kinetics are achieved within the selenides, which are proved by the mutual verification of experiment and theoretical analysis. Benefitting from this optimized heterointerfaces, the Ni 3 Se 4 /NiSe 2 @C-1 electrode manifests reduced polarization, superior rate capability, and prolonged cyclic stability (621.3 mAh g−1 at 1 A g−1 for 1000 cycles; 362.3 mAh g−1 at 4 A g−1 for 2000 cycles) with respect to the Ni 3 Se 4 /NiSe 2 @C-2, as well as excellent performance in LiCoO 2 //Ni 3 Se 4 /NiSe 2 @C-1 full cell. Detailed electrochemical analysis confirmed rapid electrons/Li+ diffusion rates and more pseudocapacitive energy for the Ni 3 Se 4 /NiSe 2 @C-1. Therefore, the Ni 3 Se 4 /NiSe 2 @C-1 showcases superior hydrogen evolution reaction (HER) and lithium storage performance. This work demonstrates the significance of interface modulation to boost the electrochemical performance of multiphase heterostructures for energy storage and conversion. [ABSTRACT FROM AUTHOR]

Conducting polyaniline (PANI) exhibits interesting properties, such as high conductivity, reversible convertibility between redox states, and advantageous structural feature. It therefore receives ever‐increasing attention for various applications. This Minireview evaluates recent studies on application of PANI for Li‐ion batteries (LIBs), Li–S batteries (LSBs) and supercapacitors (SCPs). The flexible PANI is crucial for cyclability, especially for buffering the volumetric changes of electrode materials, in addition to enhancing the electron/ion transport. Furthermore, PANI can be directly used as an electroactive component in electrode materials for LIBs or SCPs and can be widely applied in LSBs due to its physically and chemically strong affinity for S and polysulfides. The evaluation of studies herein reveals significant improvements of electrochemical performance by physical/chemical modification and incorporation of PANI. [ABSTRACT FROM AUTHOR]

A large number of studies have shown that nitrogen‐doped carbon can effectively improve the electrochemical performance of renewable energy storage devices. Polyaniline, as a carbon precursor rich in nitrogen heteroatoms, can be pyrolyzed to introduce a high content of structural nitrogen atoms into the carbon skeleton to fundamentally change the global properties of carbon materials including physical properties (e. g. surface polarity, electric conductivity, and wettability) and chemical properties (e. g. basicity and additional pseudocapacitance). Thus, nitrogen doping is extensively applied in the field of Li‐ion batteries, Li‐sulfur batteries, and supercapacitors to obtain excellent performance. Doping with different kinds of nitrogen configurations (e. g. pyridinic N, pyrrolic N, and graphitic N) shows respective mechanisms for the electrode materials of different energy storage devices. These mechanisms and applications of pyrolytic polyaniline in Li‐ion batteries, Li‐sulfur batteries, and supercapacitors are illustrated in detail here. Energy matters: Some typical applications of pyrolytic polyaniline are emphasized to give a comprehensive understanding for the distinct roles and mechanisms of nitrogen doping. Remarkable electrochemical performance is realized in the renewable energy storage devices, owing to the synergetic effect of nitrogen doping and/or other active materials. The application of pyrolytic polyaniline is wide and promising. [ABSTRACT FROM AUTHOR]

Ti 3 C 2 T x , a novel two-dimensional metal carbide, is regarded as a promising candidate for lithium-ion batteries (LIBs) due to its unique layered structure, good conductivity and low barrier for Li + diffusion. However, Ti 3 C 2 T x has low capacity and poor rate capability due to the severe interlayer stacking and functionalization group of hydroxyl, oxygen or fluorine existing in Ti 3 C 2 T x particles, limiting its widespread applications. Herein, we have firstly offered a relatively simple and rapid synthetic method to fabricate a 3D quaternary rGO/TiO 2 /Mn 3 O 4 /Ti 3 C 2 T x nanocomposite as LIBs anode material. Ti 3 C 2 T x acts as a conductive framework to enhance the electronic transport properties. Besides, this unique layered structure contributes partially to the enhancement of the total theoretical capacity of the active material. Mn 3 O 4 functions as the dominant part of the active material to contribute an extraordinarily high theoretical capacity. TiO 2 nanoparticles and rGO nanosheets can effectively shorten the electron/ion diffusion channels and construct a highly conductive matrix for the fast transfer of electron and Li + . Meanwhile, both of them can also efficaciously buffer the volume change effect during lithiation/delithiation process. As expected, rGO/TiO 2 /Mn 3 O 4 /Ti 3 C 2 T x material has presented significantly outstanding lithium ion storage capabilities, high Coulombic efficiency, excellent long-term cyclability and superior rate capability. For an example, the rGO/TiO 2 /Mn 3 O 4 /Ti 3 C 2 T x anode exhibits high specific capacity of 887.2 mA h g -1 at 0.05 A g −1 , almost 2.2 times as much as that of raw Ti 3 C 2 T x anode (404.9 mA h g -1 ). Even after 100 cycles at a current density of 0.5 A g −1 , the rGO/TiO 2 /Mn 3 O 4 /Ti 3 C 2 T x anode can still deliver a capacity of 221.5 mA h g −1 . Thus the rGO/TiO 2 /Mn 3 O 4 /Ti 3 C 2 T x anode can be ascribed to have a novel 3D sandwich-like collective benefit from the 0D/2D/3D particles/sheets/layers nanoarchitecture and can be used as a promising anode material for high performance LIBs. [ABSTRACT FROM AUTHOR]

As one of the novel two-dimensional metal carbides, Ti 3 C 2 T x has received intense attention for lithium-ion batteries. However, Ti 3 C 2 T x has low intrinsic capacity due to the fact that the surface functionalization of F and OH blocks Li ion transport. Herein a novel “plane-line-plane” three-dimensional (3D) nanostructure is designed and created by introducing the carbon nanotubes (CNTs) and SnO 2 nanoparticles to Ti 3 C 2 T x via a simple hydrothermal method. Due to the capacitance contribution of SnO 2 as well as the buffer role of CNTs, the as-fabricated sandwich-like CNTs@SnO 2 /Ti 3 C 2 T x nanocomposite shows high lithium ion storage capabilities, excellent rate capability and superior cyclic stability. The galvanostatic electrochemical measurements indicate that the nanocomposite exhibits a superior capacity of 604.1 mAh g −1 at 0.05 A g −1 , which is higher than that of raw Ti 3 C 2 T x (404.9 mAh g −1 ). Even at 3 A g −1 , it retains a stable capacity (91.7 mAh g −1 ). This capacity is almost 5.6 times higher than that of Ti 3 C 2 T x (16.6 mAh g −1 ) and 58 times higher than that of SnO 2 /Ti 3 C 2 T x (1.6 mAh g −1 ). Additionally, the capacity of CNTs@SnO 2 /Ti 3 C 2 T x for the 50th cycle is 180.1 mAh g −1 at 0.5 A g −1 , also higher than that of Ti 3 C 2 T x (117.2 mAh g −1 ) and SnO 2 /Ti 3 C 2 T x (65.8 mAh g −1 ), respectively. [ABSTRACT FROM AUTHOR]

• Nanosized monometallic selenides heterostructure are obtained by precisely controlled selenylation of MOFs. • Phase boundaries with interfacial charge redistribution and lattice dislocations promote rapid transfer of electrons and Li+. • Monometallic selenides heterostructure manifest superior lithium storage properties to the single-phase counterparts. Two-phase heterostructure with rich phase boundaries holds great potential in engineering advanced electrode materials. However, current heterostructures are largely generated by introducing exotic cations or anions, complicating synthetic procedures and disturbing real insights into the intrinsic effect of heterostructure. Herein, nanosized monometallic selenides heterostructures are developed by precisely controlled selenylation of metal organic frameworks, which are implanted into in-situ formed carbon (NiSe/NiSe 2 @C, CoSe/CoSe 2 @C). The disordered atoms arrangement at two-phase boundary leads to the redistribution of interfacial charge and generation of lattice distortions, promoting easy adsorption and swift transfer of Li+, and providing extra active sites. As a proof of concept, the NiSe/NiSe 2 @C exhibits far surpassing lithium storage properties to single-phase counterparts (NiSe@C and NiSe 2 @C), including higher reversible capacity of 1015.5 mAh g−1, better rate capability (500.8 mAh g−1 at 4 A g−1), and superior cyclic performance. As expected, the NiSe/NiSe 2 @C manifests lower charge transfer resistance, higher Li+ diffusion coefficient, and accelerated capacitive kinetics. Ex-situ X-ray diffraction, high-resolution transmission electron microscopy, and selected area electron diffraction combined with differential capacity versus voltage plots reveal multi-step redox mechanism of NiSe/NiSe 2 @C and the reason of conspicuous capacity enhancement. This work demonstrates the enormous potential of monometallic monoanionic heterostructure in energy-related field. [ABSTRACT FROM AUTHOR]

As a promising anode material, Ti 3 C 2 has got increasing attention in recent years for its brilliant performance in conductivity and hydrophilicity. However, the application of Ti 3 C 2 is limited by its low capacity. Herein, a sandwich-like three dimensional conductive network of MoS 2 intercalated p-Ti 3 C 2 (partially oxidized Ti 3 C 2 ) is fabricated by selective etching and subsequent hydrothermal treatment to overcome the shortcomings of Ti 3 C 2 . During the hydrothermal treatment, some TiO 2 nanocrystals are formed by partial oxidation of Ti 3 C 2 . The ultra high structural stability of TiO 2 nanocrystals upon lithium ion insertion and extraction process is beneficial to maintaining the cyclic stability of MoS 2 modified p-Ti 3 C 2 composites. In this architecture, MoS 2 acts as an intercalation agent to prevent the p-Ti 3 C 2 layers from restacking and facilitate the rapid transportation of electrons and ions between layers. The expanded interlayer space of p-Ti 3 C 2 provides extra free space to alleviate the volume change of MoS 2 . The optimal content of MoS 2 is 20% in this study. The synergistic effect of p-Ti 3 C 2 and 20 wt% MoS 2 endows composite with maximum discharge capacity of 656 mAh g −1 at 50 mA g −1 , which is significantly higher than the theoretical capacity of Ti 3 C 2 (320 mAh g −1 ). The sample also shows excellent cycling stability at 500 mAh g −1 . Even at high current density of 3000 mAh g −1 , a stable specific capacity of 153 mAh g −1 is obtained. These results clearly indicate that intercalation with MoS 2 is an effective strategy to improve the electrochemical performance of Ti 3 C 2 . [ABSTRACT FROM AUTHOR]

Three-dimensionally assembled LiFePO 4 /C/graphene nanofiber composites were successfully prepared via a suspension mixing method followed by heat-treatment at 400 °C. A faster electron transfer, lower electrochemical polarization as well as higher diffusion coefficient of Li + are obtained with the assistance of graphene nanofibers. The 5 wt% graphene nanofibers modified electrode (G-5) delivers the best electrochemical kinetics including the lowest charge transfer resistance and highest diffusion coefficient of Li + at 0 °C and −20 °C, respectively. Likewise, the G-5 exhibits the highest charge-discharge capability and the most stable cycling performance at low operation temperatures compared with those of LiFePO 4 /C, 3 wt% and 7 wt% graphene nanofibers modified LiFePO 4 /C (G-3 and G-7) composites. The G-5 electrode shows a capacity of 92.8 mAh g −1 with 92.0% capacity retention after 200 cycles at 1C at −20 °C. The reasons for the significant improvement of the low operation temperatures electrochemical performances can be ascribed to the enhanced conductivity and reduced agglomeration of pristine particles due to the introduction of graphene nanofibers. These excellent low temperature performances show that graphene nanofibers modified LiFePO 4 /C electrodes are promising cathode candidates for lithium-ion batteries applications at low temperatures. [ABSTRACT FROM AUTHOR]

Abstract By skillfully designing the double-sided protective structure, WS 2 nanosheets in situ grow on reduced graphene oxide hollow spheres (Hs-rGO). Then nitrogen doped graphene (NG) is coated on the outer layer to obtained NG@WS 2 @Hs-rGO. Double-sided protective structure of NG@WS 2 @Hs-rGO is successfully fabricated via a facile synthesis strategy. When evaluated as an anode material for Lithium-ion batteries (LIBs), NG@WS 2 @Hs-rGO exhibits a high specific capacity of 1309.4 mAh g−1 at 100 mA g−1 and excellent rate capability (166.1 mAh g−1 at a high current density of 4000 mA g−1). More strikingly, at a high current density of 1000 mA g−1, the NG@WS 2 @Hs-rGO electrode delivers a discharge capacity of 300.9 mAh g−1 after 320 cycles. The capacity retention of the electrode material reaches as high as 106% of the discharge capacity after the 10th cycle. Internally, the elastic Hs-rGO provides space for the bulk expansion of WS 2. Externally, the outer layer of WS 2 coated with NG not only improves the conductivity, but also provides more active sites for Li ion storage. The double-sided protective structure makes NG@WS 2 @Hs-rGO a potential anode material for light and high-performance LIBs. Graphical abstract Image 1 Highlights • WS 2 nanosheets in situ grow on reduced graphene oxide hollow spheres. • N-doped graphene is coated to obtained double-sided protective structure. • The battery with 3D hollow spherical structure fully uses of graphene. • A high discharge capacity of 300.9 mAh g−1 is obtained after 320 cycles at 1000 mA g−1. • Full-cells with coin type were firstly assembled with LFP/C as cathode and NG@WS 2 @Hs-rGO as anode. [ABSTRACT FROM AUTHOR]

Cellulose paper-based energy storage devices have spurred significantly intrinsic advantages compared with the traditional batteries due to environmental benignity, recyclability and easy processing. In this work, the binary functional materials, which contains linear N-doped carbon nanotube (N-CNT, one-dimensional) and spherical C-coated MoS 2 (MoS 2 @C, zero-dimensional), are embedded into the porous recycled paper (RP, two-dimensional) derived from wastepaper via a facile and low-cost vacuum filtration method, and then the N-CNT/MoS 2 @C/RP film (N-M-RP film) featuring a unique compacted “point-line-plane” structure is obtained. In favor of the synergistic effect of high-conductive N-CNT, high-capacity MoS 2 @C and porous RP network, the prepared freestanding N-M-RP film presents a high strength of 35.2 MPa and a comparably low sheet resistance of 127.39 Ω sq −1 , and as an anode material for LIBs, the N-M-R film delivers a high reversible capacity, good cycling performance, superior rate capability and excellent electrochemical kinetics. Besides, the synergistic effect of “point-line-plane” structure on the improved electrochemical performances is also investigated. All the results indicate that the N-M-RP film comprised of 0D-1D-2D materials could be a potential candidate as a freestanding anode for LIBs. [ABSTRACT FROM AUTHOR]

Li 3 V 2 (PO 4 ) 3 /C was prepared as a pristine material by an improved sol-gel method. Then different amounts of CeO 2 were employed to modify Li 3 V 2 (PO 4 ) 3 /C cathode materials via a suspension mixing method assisted by polyvinyl alcohol. The 2 wt% CeO 2 modified sample (Ce-2) exhibits the best initial charge-discharge performance at −20 °C with a specific capacity of 70.4 mAh g −1 and 103.3 mAh g −1 at 1 C in the potential range of 3.0-4.3 V and 3.0-4.8 V, respectively. The Ce-2 electrode still delivers a stable cycling performance with 95.6 % and 92.7 % capacity retention after 50 cycles even at 5 C and at 0 °C in the potential range of 3.0-4.3 V and 3.0-4.8 V, respectively. The electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements indicate that the resistance and polarization of Ce-2 at low temperatures are lower than those of any other samples. In addition, the Ce-2 delivers the highest Li-ion diffusion coefficient derived from PSCA measurement, which further verifies that the electrochemical kinetics of Ce-2 is much more active than that of the pristine sample. The excellent low-temperature performances obtained in this work suggest that CeO 2 -modified Li 3 V 2 (PO 4 ) 3 /C material is a promising cathode candidate for battery applications at low temperature conditions. [ABSTRACT FROM AUTHOR]

Abstract: Lithium–sulfur battery is a promising energy storage system due to its high specific energy density, low cost and environmental friendliness. Layer-by-layer (LbL) assembly technique is introduced as a simple method to fabricate polymer-coated sulfur cathode materials for rechargeable lithium–sulfur batteries. Conductive polyaniline (PANI) were assembled on the outer shell of sulfur particles to provide an electron conducting paths for the charge and discharge of lithium–sulfur battery. The low permeability of sulfur shells was obtained by assembling the enough number of polyelectrolyte bilayers. A crosslinker and heat treatment were utilized to further reduce its permeability. The assembled polymer shells can be expected to be permeable for Li+ and slowly or hardly for sulfur and polysulfide during charge and discharge process. The obtained sulfur composite cathode materials were characterized by four-point probe instrument, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) patterns and Fourier transform infrared (FTIR) spectroscopy. The results demonstrated polymers have been coated on the surface of sulfur only by physical interaction and have no effect on sulfur. The conductive polymer-coated sulfur cathode also represents a well conductivity of 0.23Scm−1. Moreover, after coated by polymers, the crystal structure of sulfur still keeps its orthorhombic corresponding to cyclooctasulfur molecule (S8). [Copyright &y& Elsevier]