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A novel strategy in which palladium(II)-catalyzed tandem cyclization is used to obtain N-heterocyclic architectures containing a seven-membered ring has been developed and used to synthesize a series of derivatives. The reaction uses an eco-friendly mixed solvent (water : EtOH = 2 : 1) instead of DMSO and maintains a high yield (91%). Its potential application value and reaction mechanism have also been explored. [ABSTRACT FROM AUTHOR]

Introducing metals into phosphorus to form metal phosphide materials as anodes for potassium ion batteries (PIBs) is an effective strategy to improve the electronic conductivity and alleviate the volume change during cycling, although with a compromise of capacity. Herein, we explore a CuP2/C composite as a novel anode for PIBs, which delivers a high reversible capacity of >450 mA h g−1. Unexpectedly, our results reveal that the POx components existing in the prepared composite are reversible, through a quantitative analysis via high-resolution solid-state 31P NMR and synchrotron X-ray diffraction tests. Their potassiation products K3PO4 and K4P2O7 can react with K–P alloys and turn back to POx during depotassiation, which probably accounts for the high capacity of the prepared material. The results also illustrate a crystallization–amorphization evolution process during cycling involving nanocrystalline α-K4P6, K4P3 and KP, and amorphous K4P6, KP and K3P phases, among which, the amorphous phases are identified for the first time. [ABSTRACT FROM AUTHOR]

To address the issues of the particle fracture and loss of electrical connectivity of high capacity silicon anodes, herein, we propose a novel strategy that combines surface carbon coating and bulk boron doping. Heavily boron doped polycrystalline photovoltaic Si particles are used as starting materials. The bulk boron doping is demonstrated to enhance both electron transportation and lithium-ion diffusion, which contributes to superior high-rate performance. Taking advantage of the fast kinetics and stable interphase with the electrolyte, the carbon coated boron doped Si electrode exhibits higher capacity retention. For example, the capacity retentions are 668 mA h g−1, 293 mA h g−1 and 79 mA h g−1 at a high rate of 0.5C (1C = 4000 mA g−1) after 500 cycles for 3900 ppm, 120 ppm, and 10 ppm boron doped Si, respectively. In addition, an improved mass loading of 2.0 mg cm−2, high areal capacity (3.9 mA h cm−2) and high-volume capacity (2111 mA h cm−3) are achieved. Our work opens a new horizon for designing stable high loading Si anodes, which is applicable for other alloy electrode materials. [ABSTRACT FROM AUTHOR]

Nanostructured transition metal oxide anodes have attracted considerable attention for high-performance lithium-ion batteries (LIBs). However, their low rate capability and rapid capacity decline resulting from their low electronic conductivities and inevitable substantial volumetric changes prevent them from being commercialized as anodes for LIBs. Herein, we design a high-performance anode for LIBs consisting of a yolk–shell structured Fe2O3@C nanoring (NR) composite that comprises a NR-like Fe2O3 core entirely protected by a fine porous carbon (C) shell to overcome such obstacles. This advantageous yolk–shell structural design can buffer the significant volume variations of Fe2O3 cores without damaging the microstructure of the electrode. Thanks to the unique structural features, the as-built electrode shows a remarkable electrochemical performance, namely, a large specific capacity of 846 mA h g−1 after 100 cycles at 0.2 A g−1, a superior rate performance of 688 mA h g−1 at 4 A g−1, and a remarkable cycling life (300 cycles, 945 mA h g−1 at 4.0 A g−1). Hence, this electrode is much better than a pure Fe2O3 NR electrode. [ABSTRACT FROM AUTHOR]

Li/CFx cells possess the highest energy density among all lithium primary batteries. Here, the electrochemical lithiation process is elucidated through high-resolution 19F NMR, in situ7Li NMR and TEM methods. Fluorinated carbon CFL (L is around 0.06 or less) is identified for the first time to be generated in the discharge process of CFx (x ≥ 0.5) besides LiF and carbon. Moreover, the morphological evolution of the formed LiF, which affects the impedance of the battery during discharge, is illustrated as crystal nuclei of LiF, with a size of around 10 nm, which keep forming and growing into crystal grains of LiF, with a size of around 200 nm, until the surface of the CFx particles is saturated by LiF and then both crystal nuclei and grains enlarged promptly towards the end of lithiation. This work reveals the electrochemical reaction mechanism of CFx and provides crucial guidance to enhance the performance of the materials. [ABSTRACT FROM AUTHOR]

Micrometer Si (MSi) particles are an attractive alternative as high energy-density lithium-ion battery anodes. To maintain the structural integrity and resolve the electrical conduction problem of MSi-based anodes, we propose novel MSi/C/reduced graphene oxide (RGO) through simple ball milling liquid polyacrylonitrile (PAN) with MSi and graphene oxide nanosheets, followed by thermal reduction. This structure capitalizes on the interaction of MSi and carbonized PAN with RGO sheets to provide a robust microarchitecture. The mechanical integrity of the in situ formed porous configuration can be dramatically improved by manipulating the size of unreacted Si nanocrystals. In addition, the Si–N–C layer serves as an electrolyte blocking layer, which helps to build a stable SEI layer and results in a high initial coulombic efficiency of 91.7%. Furthermore, the RGO binding to MSi/C acts as a flexible buffer during galvanostatic cycling, allowing microparticles to expand and fractured nanoparticles to anchor, while retaining electrical connectivity at both the particle and electrode levels. As a result, this hierarchical structure exhibits a superior reversible capacity of 1572 mA h g−1 with no capacity loss for 160 cycles at 0.2 A g−1 and over 628 mA h g−1 for 1000 cycles at 2 A g−1. [ABSTRACT FROM AUTHOR]

We report for the first time that the dehydrogenation process of PAN was suppressed and the silicon oxide of the MSP surface was reduced during annealing in Ar + H2. Consequently, the remaining –NH bonds of the carbon chain can interact with the fresh amorphous Si on the surface of the MSPs to form a Si–N–C layer, which improves the adhesion between Si and C and serves as a stable electrolyte blocking layer. In addition, based on micron-sized MSPs, the structural stability of the electrode is dramatically enhanced through in situ formation of Si nanocrystals of less than 5 nm. The low Li+ diffusion kinetics of the Si–N–C layer and self limiting inhomogeneous lithiation in MSPs jointly create unlithiated Si nanocrystals, acting as supporting frames to prevent pulverization of the anode material. Our nitriding MSP anode has exhibited for the first time a 100% capacity retention (394 mA h g−1) after 2000 cycles (10 cycles each at 0.1, 0.5, 1, 2, and 1 and then 1950 cycles at 0.5 A g−1) and a 100% capacity retention at 0.1 A g−1 (540 mA h g−1) after 400 cycles. Thus, our work proposes a novel avenue to engineer battery materials with large volume changes. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) hierarchically porous transition metal oxides, particularly those involving different metal ions of mixed valence states and constructed from interconnected nano-building blocks directly grown on conductive current collectors, are promising electrode candidates for energy storage devices such as Li-ion batteries (LIBs) and supercapacitors (SCs). This study reports a facile and scalable chemical bath deposition process combined with simple calcination for fabricating 3D hierarchically porous Zn–Ni–Co oxide (ZNCO) nanosheet arrays directly grown on Ni foam with robust adhesion. The resulting nanostructures are then evaluated as a binder-free electrode for LIBs and SCs. Given its unique architecture and compositional advantages, the electrode exhibits a reversible capacity of 1131 mA h g−1 after 50 cycles at a current density of 0.2 A g−1, an excellent long-term cycling stability at a high current density of 1 A g−1 for 1000 cycles, and a desirable rate capability when tested as an anode for LIBs. When used for SCs, the electrode demonstrates a high specific capacitance (1728 F g−1 at 1 A g−1), an outstanding rate capability (72% capacitance retention from 1 A g−1 to 50 A g−1), and an excellent cycling stability (capacitance of 1655 F g−1 after 5000 cycles at a current density of 20 A g−1 with 108.6% retention). Overall, the unique 3D hierarchically porous ZNCO nanosheets hold a great promise for constructing high-performance energy storage devices. [ABSTRACT FROM AUTHOR]

The silicon material is the most promising candidate for developing new-generation lithium-ion batteries with high energy and power output. However, there remains a significant challenge due to poor electrical conductivity and pulverization of the silicon based anode during cycles. Aiming to solve these problems, in this work we fabricate a novel 3D composite architecture made of a Si@SiOx core-shell nanowire array grown on a 3D graphitic foam (Si CNW-3D GF) substrate by a well-designed multiple-step approach. The prepared Si CNW-3D GF composite shows the integrated advantages for high-performance lithium ion batteries, including its light weight, open macroporosity, high conductivity, high Si NW loading, excellent flexibility as well as SiOx buffer layers. As a result, the Si CNW-3D GF composite exhibits excellent performance such as high reversible lithium storage capacity (3603 mA h g-1 at a current density of 840 mA g-1), excellent cycling performance (up to 100 cycles) and superior rate capability (2299 mA h g-1 at 4200 mA g-1 and 1206 mA h g-1 at 8400 mA g-1), which is 2 times that of the Si CNW electrode where Si CNWs were grown directly on a stainless steel current collector without the presence of 3D GF. [ABSTRACT FROM AUTHOR]

Novel three-dimensional (3D) hierarchical NiSi[sub x]/Co[sub 3]O[sub 4] core-shell nanowire arrays composed of NiSi[sub x] nanowire cores and branched Co[sub 3]O[sub 4] nanosheet shells have been successfully synthesized by combining chemical vapor deposition and a simple but effective chemical bath deposition process followed by a calcination process. The resulting hierarchical NiSi[sub x]/Co[sub 3]O[sub 4] core-shell nanowire arrays directly serve as binder- and conductive-agent-free electrodes for lithium ion batteries, which demonstrate remarkably improved electrochemical performances with excellent capacity retention and high rate capability on cycling. They can maintain a stable reversible capacity of 1279 mA h g[sup -1] after 100 cycles at a current density of 400 mA g[sup -1] and a capacity higher than 340 mA h g[sup -1] even at a current density as high as 8 A g[sup -1]. Such superior electrochemical performance of the electrodes made by directly growing electro-active highly porous Co[sub 3]O[sub 4] on a nanostructured NiSi[sub x] conductive current collector makes them very promising for applications in high-performance lithium ion batteries. [ABSTRACT FROM AUTHOR]

A novel strategy in which palladium(II)-catalyzed tandem cyclization is used to obtain N-heterocyclic architectures containing a seven-membered ring has been developed and used to synthesize a series of derivatives. The reaction uses an eco-friendly mixed solvent (water : EtOH = 2 : 1) instead of DMSO and maintains a high yield (91%). Its potential application value and reaction mechanism have also been explored.