Porous hollow composites assembled by NixCo1-xSe2 nanosheets rooted on carbon polyhedra for superior lithium storage capability

Nanostructured conversion-type anode materials of metal-organic framework-derived spinel XMn2O4 (X = Zn, Co, Cu, Ni) to boost lithium storage

Bimetallic spinel transition metal oxides play a major part in actualizing eco-friendly electrochemical energy storage systems (ESSs). However, structural precariousness and low electrochemical capacitance restrict their actual implementation in lithium-ion batteries (LIBs). To address these demerits, the sacrificial template approach has been considered as a prospective way to strengthen electrochemical stability and rate performance. Herein, metal-organic frameworks (MOFs) derived XMn₂O₄-BDC (H₂BDC = 1,4-dicarboxybenzene, X = Zn, Co, Cu, Ni) are prepared by a hydrothermal approach in order to discover the effects of various metal cations on the electrochemical performance. Among them, ZnMn₂O₄-BDC displays best electrochemical properties (1321.5 mAh g^-1 at the current density of 0.1 A g^-1 after 300 cycles) and high efficiency with accelerated Li⁺ diffusivity. Density functional theory (DFT) calculations confirm the ZnMn₂O₄ possesses the weakest adsorption energy on Li⁺ with a minimized value of -0.92 eV. In comparison with other XMn₂O₄ through traditional fabrication method, MOF-derived XMn₂O₄-BDC possesses a higher number of Li⁺ transport channels and better electric conductivity. This tactic provides a feasible and effective method for preparing bimetallic transition metal oxides and enhances energy storage applications.

Engineering hierarchically ZnS/NiS/NiS2 hollow porous urchin-like composite towards exceptional lithium storage

Complex hollow structure nanostructure is regarded as the desired approach to alleviating the volume change of lithium-ion batteries (LIBs). In this work, ZnS/NiS/NiS₂ composite with a distinctive hierarchical hollow porous urchin-like structure was prepared through pyrolysis of bimetal-organic frameworks obtained by one-step solvothermal and firstly used as anodes for LIBs. Varying the metal molar ratios allows the control of the surface area and pore size distribution of ZnS/NiS/NiS₂. The obtained composite with a hollow porous urchin-like structure exhibits high porosity, large specific surface area, and strong synergetic interaction between ZnS and NiS/NiS₂ can greatly buffer the volume expansion to keep the mechanical stability, ensure sufficient contact region between electrolyte and electrodes and shorten the Li⁺ transfer distance, meanwhile, the carbon derived from organic ligand of bimetal-organic frameworks also constructs the conductive matrix to accelerate electrons transfer. Based on the above outstanding properties, the obtained material delivers excellent rate capacity, superior reversible capacity, and long-cycle stability, especially disclosing a capacity of 615 mAh·g^-1 after 300 cycles at 2 A·g^-1. This work proposes a feasible strategy to obtain a unique hollow porous urchin-like structure through pyrolysis of bimetal organic frameworks, it can be extended to fabricate other mixed metal sulfides nanostructures with excellent electrochemical performances.

Self-induced matrix with Li-ion storage activity in ultrathin CuMnO2 nanosheets electrode

Conversion anode materials such as Mn₃O₄ draw much attention due to their considerable theoretical capacity for lithium-ion batteries (LIBs). However, poor conductivity, slow solid-state Li-ion diffusion, and huge volume expansion of the active materials during charge/discharge lead to unsatisfied electrochemical performance. Despite several strategies like nanocrystallization, fabricating hierarchical nanostructures, and introducing a matrix are valid to address these crucial issues, the achieved electrochemical performance still needs to be further enhanced. What is worse, the matrix with less or no Li-ion storage activity may lower the achieved capacity of the electrodes. Herein, ultra-thin CuMnO₂ nanosheets with the thickness of 5-8 nm were evaluated for LIBs. The ultra-thin sheet-like nanostructure offers sufficient contact areas with electrolyte and shortens the Li-ion diffusion distance. Moreover, the in-situ generated Mn and Cu along with their oxides could play the role of matrix and conductive agent in turn at different stages, relieving the stress brought by volume expansion. Therefore, the as-prepared ultra-thin CuMnO₂ nanosheets electrode displays a remarkable reversible capacity, long cycling stability, and outstanding rate capability (a reversible capacity of 1160.5 mAh g^-1 at 0.1A g^-1 was retained after 100 cycles with a capacity retention of 95.1 %, and 717.8 mAh g^-1 at 2.0 A g^-1 after 400 cycles).

Two Co(II)/Ni(II) complexes based on nitrogenous heterocyclic ligand as high-performance electrocatalyst for hydrogen evolution reaction

Two transition metal complexes {[Co2(bpda)4(H2O)2]⋅4H2O}n(Co-1) and {[Ni(bpda)2(H2O)2]⋅2H2O}(Ni-2) (H2bpda = 2,2 '- bipyridine -4,4' - dicarboxylic acid) have been synthesized by hydrothermal method and characterized. These two compounds can be explored...

Realizing the enhanced cyclability of a cactus-like NiCo2O4 nanocrystal anode fabricated by molecular layer deposition

Lithium-ion batteries with conversion-type anode electrodes have attracted increasing interest in providing higher energy storage density than those with commercial intercalation-type electrodes. However, conversion-type materials exhibit severe structural instability and capacity fade during cycling. In this work, a molecular layer deposition (MLD)-derived conductive Al₂O₃/carbon layer was employed to stabilize the structure of the cactus-like NiCo₂O₄ nanocrystal (NC) anode. The conductive Al₂O₃/carbon network and cactus-like NiCo₂O₄ NCs are beneficial for fast Li⁺/e^- transport. Moreover, the Al₂O₃/carbon buffer-layer can prevent the NiCo₂O₄ NCs from agglomeration and form a steady solid electrolyte interphase (SEI), thus hampering the penetration of the electrolyte. Owing to these advantages, the assembled NiCo₂O₄@Al₂O₃/carbon half battery shows a high reversible capacity (931.2 mA h g^-1 at 2 A g^-1) and long-term stability of 290 mA h g^-1 at 5 A g^-1 over 500 cycles. Quantitative analyses further reveal the fast kinetics and the capacitance-battery dual model mechanism in the 3D core-shell structures. The design and introduction of MLD-derived hybrid coating may open a new way to conversion-type and alloy-type anode materials beyond NiCo₂O₄ to achieve high cyclability.

Dual-carbon coupled Co5.47N composites for capacitive lithium-ion storage

Transition metal nitrides are of great interest as potential anodes for lithium-ion batteries (LIBs) owing to their high theoretical capacity. However, poor cycling stability and rate performance greatly hinder their practical applications. To better alleviate these problems, a unique 3D hierarchical nanocomposite constructed by dual carbon-coated Co_5.47N nano-grains wrapped with carbon and reduced graphene oxide (Co_5.47N@C@rGO) was synthesized through one-step simultaneous nitridation and carbonization of zeolitic imidazolate frameworks@GO precursor. The 3D hierarchical Co_5.47N@C@rGO composite can combine the good conductivity and mechanical strength of rGO and a high theoretical capacity of Co_5.47N. When explored as anode material for LIBs, Co_5.47N@C@rGO exhibits a high reversible capacity of ~860 mAh g^-1 at a current density of 1.0 A g^-1 after 500 cycles and excellent high-rate capability (665 and 573 mAh g^-1 at current densities of 3.2 and 6.4 A g^-1, respectively). The excellent electrochemical performance of Co_5.47N@C@rGO can be ascribed to its hierarchically porous structure and the synergistic effect between Co_5.47N nano-grains and rGO.

Copper nanowires and copper foam multifunctional bridges in zeolitic imidazolate framework-derived anode material for superior lithium storage

Herein, a synthetic strategy for growing trimetallic zeolitic imidazolate framework (ZIF) polyhedrons on copper foam (CF) and interweaving with copper nanowires (CNWs) is proposed. Subsequently, in situ annealing under N₂ atmosphere leads to the formation of multi-doped CNWs/Cu_0.39Zn_0.14Co_2.47O₄-ZnO/CF (CNWs/CZCOZ/CF). The unique structural characteristics of CNWs/CZCOZ/CF allow it to be directly assembled as a working electrode, without additional conductive additives or binders. When it's used as the lithium-ion battery (LIB) anode, this electrode exhibits a significantly high capacity of 2305 mAh g^-1 at 0.1 A g^-1 after 500 cycles. More importantly, kinetic analysis on the basis of cyclic voltammograms (CVs) indicates that the pseudocapacitive effect is the primary contributor to the high lithium storage capacity and also accounts for the exceptionally high rate capacity of 713 mAh g^-1 even if the current density is at a maximum of 10 A g^-1. Moreover, the superior battery performance originates from their advantageous structural diversity and unique compositional features, including synergistic effects among polymetallic components and two highly conductive substrates (CNWs and CF), forming unhindered paths for fast charge transfer.

Interfacial engineering of Ag nanodots/MoSe2 nanoflakes/Cu(OH)2 hybrid-electrode for lithium-ion battery

Although the Lithium ion batteries (LIBs) have attracted remarkable attentions, their practical development is hindered by the low rate performance and poor unit area capacity, which is significantly caused by the low conductivity of the active electrode materials. Herein, a three-dimensional (3D) architecture consisting of Ag nanodots embedded MoSe₂ sheets wrapping Cu(OH)₂ nanorods (Cu(OH)₂/MoSe₂/Ag) hybrids were in-situ synthesized on self-standing Cu- foam collector for LIBs application. The 2D MoSe₂ nanoflakes supported on 1D highly conductive Cu nanowires provides efficient pathways for both electrons and ions. The embedded Ag nanodots in the MoSe₂ as the internal-plane active sites not only improves the intrinsic conductivity but also allows the reversible formation and decompose of Ag-Li alloy, and thus leading to the promotion of Li⁺ ion storage. As a result, the Cu(OH)₂/MoSe₂/Ag electrode exhibits a high reversible discharge capacity of 1285.5 mAh g^-1 (current density of 0.2 C), good rate performance (discharge-specific capacity remained 544.8 mAh g^-1 at 5.0C), and excellent cycling stability (with almost no decay after 500 cycles). Significantly, the 3D Cu(OH)₂/MoSe₂/Ag electrode exhibits a high areal capacity of 2.50 mAh cm^-2 at a high current density of 1.82 mA cm^-2. This work provides the new insight into interfaces engineering for 3D architecture toward advanced self-standing LIB electrodes.

Three-dimensional mesoporous sandwich-like g-C3N4-interconnected CuCo2O4 nanowires arrays as ultrastable anode for fast lithium storage

Inspite of their impressive high theoretical capacity as Lithium-ion batteries (LIBs) anodes, spinel transition-metal oxides (TMOs) suffer serious volume expansion, aggregation and the pulverization of crystal structures during lithiation/delithiation, and this process severely restrict their industrial application. Multi-dimensional morphological engineering of spinel TMO nanostructures is an effective way to solve this issue. In this work, using facile hydrothermal synthetic methods, spinel CuCo₂O₄ nanowires arrays are synthesized and supported on g-C₃N₄ nanosheets, thus forming a unique sandwich-like interconnected three-dimensional mesoporous structure containing high amount of void spaces. Addition of g-C₃N₄ nanosheets to CuCo₂O₄ nanowire arrays may shorten the Li⁺ diffusion distance and electron transfer pathway, and may also provide more active sites for Li⁺ diffusion into electrolyte and buffer for the volume expansion and aggregation of CuCo₂O₄. As a LIB anode material, CuCo₂O₄@g-C₃N₄ shows initial lithiation capacity of 840.6 mAh g^-1, and capacity retention of 641.2 mAh g^-1 after 60 cycles at the current density of 0.1 A g^-1 and 499.2 mAh g^-1 after 40 cycles at high current of 1 A g^-1, which is significantly better than value of pure CuCo₂O₄ nanowires. This work affords a new way to tackle the problem of volume expansion of high capacity spinel TMO anode materials using g-C₃N₄ nanosheets as buffering agent.

Iron-Doping-Induced Phase Transformation in Dual-Carbon-Confined Cobalt Diselenide Enabling Superior Lithium Storage

Transition metal chalcogenides (TMCs) have been investigated as promising anodes for high-performance lithium-ion batteries, but they usually suffer from poor conductivity and large volume variation, thus leading to unsatisfactory performance. Although nanostructure engineering and hybridization with conductive materials have been proposed to address this concern, a better performance toward practical device applications is still highly desired. Herein, we report an iron-doping-induced structural phase transition from pyrite-type (cubic) to marcasite-type (orthorhombic) phases in porous carbon/rGO-coupled CoSe₂. The dual-carbon-confined orthorhombic CoSe₂ ( o-Fe _xCo_{1- x}Se₂@NC@rGO) composites exhibit dramatically enhanced lithium storage performance (920 mAh g^-1 after 1000 cycles at 1.0 A g^-1) over cubic CoSe₂-based composites ( c-CoSe₂@NC@rGO). The combined experimental studies and density functional theory calculations reveal that this doping-induced structural phase transformation strategy could create a favorable electronic structure and ensure a rapid charge transfer. These results demonstrate that the phase-transformation engineering may provide another opportunity in the design of high-performance TMC-based electrodes.