Morphological and Electrochemical Properties of ZnMn2O4 Nanopowders and Their Aggregated Microspheres Prepared by Simple Spray Drying Process

Phase-pure ZnMn₂O₄ nanopowders and their aggregated microsphere powders for use as anode material in lithium-ion batteries were obtained by a simple spray drying process using zinc and manganese salts as precursors, followed by citric acid post-annealing at different temperatures. X-ray diffraction (XRD) analysis indicated that phase-pure ZnMn₂O₄ powders were obtained even at a low post-annealing temperature of 400 °C. The post-annealed powders were transformed into nanopowders by simple milling process, using agate mortar. The mean particle sizes of the ZnMn₂O₄ powders post-treated at 600 and 800 °C were found to be 43 and 85 nm, respectively, as determined by TEM observation. To provide practical utilization, the nanopowders were transformed into aggregated microspheres consisting of ZnMn₂O₄ nanoparticles by a second spray drying process. Based on the systematic analysis, the optimum post-annealing temperature required to obtain ZnMn₂O₄ nanopowders with high capacity and good cycle performance was found to be 800 °C. Moreover, aggregated ZnMn₂O₄ microsphere showed improved cycle stability. The discharge capacities of the aggregated microsphere consisting of ZnMn₂O₄ nanoparticles post-treated at 800 °C were 1235, 821, and 687 mA h g⁻¹ for the 1st, 2nd, and 100th cycles at a high current density of 2.0 A g⁻¹, respectively. The capacity retention measured after the second cycle was 84%.

Template-free formation of one-dimensional mesoporous ZnMn2O4 tube-in-tube nanofibers towards lithium-ion batteries as anode materials

Mesoporous ZnMn2O4 tube-in-tube nanofibers are firstly synthesized via a template-free strategy as an anode material towards lithium-ion batteries, along with a tentative formation mechanism.

Structural Reorganization-Based Nanomaterials as Anodes for Lithium-Ion Batteries: Design, Preparation, and Performance

In recent years, with the growing demand for higher capacity, longer cycling life, and higher power and energy density of lithium ion batteries (LIBs), the traditional insertion-based anodes are increasingly considered out of their depth. Herein, attention is paid to the structural reorganization electrode, which is the general term for conversion-based and alloying-based materials according to their common characteristics during the lithiation/delithiation process. This Review summarizes the recent achievements in improving and understanding the lithium storage performance of conversion-based anodes (especially the most widely studied transition metal oxides like Mn-, Fe-, Co-, Ni-, and Cu-based oxides) and alloying-based anodes (mainly including Si-, Sn-, Ge-, and Sb-based materials). The synthesis schemes, morphological control and reaction mechanism of these materials are also included. Finally, viewpoints about the challenges and feasible improvement measures for future development in this direction are given. The aim of this Review is to shed some light on future electrode design trends of structural reorganization anode materials for LIBs.

β-MnO2 /Metal-Organic Framework Derived Nanoporous ZnMn2 O4 Nanorods as Lithium-Ion Battery Anodes with Superior Lithium-Storage Performance

Nanoporous ZnMn₂ O₄ nanorods have been successfully synthesized by calcining β-MnO₂ /ZIF-8 precursors (ZIF-8 is a type of metal-organic framework). If measured as an anode material for lithium-ion batteries, the ZnMn₂ O₄ nanorods exhibit an initial discharge capacity of 1792 mA h g^-1 at 200 mA g^-1 , and an excellent reversible capacity of 1399.8 mA h g^-1 after 150 cycles (78.1 % retention of the initial discharge capacity). Even at 1000 mA g^-1 , the reversible capacity is still as high as 998.7 mA h g^-1 after 300 cycles. The remarkable lithium-storage performance is attributed to the one-dimensional nanoporous structure. The nanoporous architecture not only allows more lithium ions to be stored, which provides additional interfacial lithium-storage capacity, but also buffers the volume changes, to a certain degree, during the Li⁺ insertion/extraction process. The results demonstrate that nanoporous ZnMn₂ O₄ nanorods with superior lithium-storage performance have the potential to be candidates for commercial anode materials in lithium-ion batteries.

Hierarchical structured Mn2O3 nanomaterials with excellent electrochemical properties for lithium ion batteries

A series of Mn2O3 nanomaterials with hierarchical porous structures was synthesized using three types of leaves as templates. In addition to their different morphologies, different porous nanostructures were achieved by choosing different leaves. The Mn2O3 nanomaterial prepared by using gingko leaves as a template provides a larger pore volume and a higher Brunauer-Emmett-Teller (BET) surface area. At the same time, this material also displays excellent electrochemical performance, that is, the specific capacities are 1274.6 mA h g-1 after 300 cycles and 381.5 mA h g-1 at current densities of 300 and 3000 mA g-1, respectively.

Mesoporous ZnMn2O4 Microtubules Derived from a Biomorphic Strategy for High-Performance Lithium/Sodium Ion Batteries

ZnMn₂O₄ microtubules (ZMO-MTs) with a mesoporous structure are fabricated by a novel yet effective biomorphic approach employing cotton fiber as a biotemplate. The fabricated ZMO-MT has approximately an inner diameter of 8.5 μm and wall thickness of 1.5 μm. Further, the sample of ZMO-MT displays a large specific surface area of 48.5 m² g^-1. When evaluated as a negative material for Li-ion batteries, ZMO-MT demonstrates an improved cyclic performance with discharge capacities of 750.4 and 535.2 mA h g^-1 after 300 cycles, under current densities of 200 and 500 mA g^-1, respectively. Meanwhile, ZMO-MT exhibits superior rate performances with high reversible discharge capacities of 614.7 and 465.2 mA h g^-1 under high rates of 1000 and 2000 mA g^-1, respectively. In sodium ion batteries applications, ZMO-MT delivers excellent high discharge capacities of 102 and 71.4 mA h g^-1 after 300 cycles under 100 and 200 mA g^-1, respectively. An excellent rate capability of 58.2 mA h g^-1 under the current density of 2000 mA g^-1 can also be achieved. The promising cycling performance and rate capability could be benefited from the unique one-dimensional mesoporous microtubular architecture of ZMO-MT, which offers a large electrolyte/electrode accessible contact area and short diffusion distance for both of ions and electrons, buffering the volume variation originated from the repeated ion intercalation/deintercalation processes.

Uniform MnCo2O4 Porous Dumbbells for Lithium-Ion Batteries and Oxygen Evolution Reactions

Three-dimensional (3D) binary oxides with hierarchical porous nanostructures are attracting increasing attentions as electrode materials in energy storage and conversion systems because of their structural superiority which not only create desired electronic and ion transport channels but also possess better structural mechanical stability. Herein, unusual 3D hierarchical MnCo₂O₄ porous dumbbells have been synthesized by a facile solvothermal method combined with a following heat treatment in air. The as-obtained MnCo₂O₄ dumbbells are composed of tightly stacked nanorods and show a large specific surface area of 41.30 m² g^-1 with a pore size distribution of 2-10 nm. As an anode material for lithium-ion batteries (LIBs), the MnCo₂O₄ dumbbell electrode exhibits high reversible capacity and good rate capability, where a stable reversible capacity of 955 mA h g^-1 can be maintained after 180 cycles at 200 mA g^-1. Even at a high current density of 2000 mA g^-1, the electrode can still deliver a specific capacity of 423.3 mA h g^-1, demonstrating superior electrochemical properties for LIBs. In addition, the obtained 3D hierarchical MnCo₂O₄ porous dumbbells also display good oxygen evolution reaction activity with an overpotential of 426 mV at a current density of 10 mA cm^-2 and a Tafel slope of 93 mV dec^-1.

Synthesis of ZnMn₂O₄ Nanoparticles by a Microwave-Assisted Colloidal Method and their Evaluation as a Gas Sensor of Propane and Carbon Monoxide

Spinel-type ZnMn₂O₄ nanoparticles were synthesized via a simple and inexpensive microwave-assisted colloidal route. Structural studies by X-ray diffraction showed that a spinel crystal phase of ZnMn₂O₄ was obtained at a calcination temperature of 500 °C, which was confirmed by Raman and UV-vis characterizations. Spinel-type ZnMn₂O₄ nanoparticles with a size of 41 nm were identified by transmission electron microscopy. Pellet-type sensors were fabricated using ZnMn₂O₄ nanoparticles as sensing material. Sensing measurements were performed by exposing the sensor to different concentrations of propane or carbon monoxide at temperatures in the range from 100 to 300 °C. Measurements performed at an operating temperature of 300 °C revealed a good response to 500 ppm of propane and 300 ppm of carbon monoxide. Hence, ZnMn₂O₄ nanoparticles possess a promising potential in the gas sensors field.

Self-assembled hierarchical porous NiMn2O4 microspheres as high performance Li-ion battery anodes

Hierarchical structured porous NiMn₂O₄ microspheres assembled with nanorods are synthesized through a simple hydrothermal method followed by calcination in air. As anode materials for lithium ion batteries (LIBs), the NiMn₂O₄ microspheres exhibit a high specific capacity. The initial discharge capacity is 1126 mA h g⁻¹. After 1000 cycles, the NiMn₂O₄ demonstrates a reversible capacity of 900 mA h g⁻¹ at a current density of 500 mA g⁻¹. In particular, the porous NiMn₂O₄ microspheres still could deliver a remarkable discharge capacity of 490 mA h g⁻¹ even at a high current density of 2 A g⁻¹, indicating their potential application in Li-ion batteries. This excellent electrochemical performance is ascribed to the unique hierarchical porous structure which can provide sufficient contact for the transfer of Li⁺ ion and area for the volume change of the electrolyte leading to enhanced Li⁺ mobility.

Hierarchical structured porous NiMn₂O₄ microspheres assembled with nanorods are synthesized through a simple hydrothermal method followed by calcination in air.

Formation of N-Doped Carbon-Coated ZnO/ZnCo2 O4 /CuCo2 O4 Derived from a Polymetallic Metal-Organic Framework: Toward High-Rate and Long-Cycle-Life Lithium Storage

Metal-organic frameworks (MOFs) are very promising self-sacrificing templates for the large-scale fabrication of new functional materials owing to their versatile functionalities and tunable porosities. Most conventional metal oxide electrodes derived from MOFs are limited by the low abundance of incorporated metal elements. This study reports a new strategy for the synthesis of multicomponent active metal oxides by the pyrolysis of polymetallic MOF precursors. A hollow N-doped carbon-coated ZnO/ZnCo₂ O₄ /CuCo₂ O₄ nanohybrid is prepared by the thermal annealing of a polymetallic MOF with ammonium bicarbonate as a pore-forming agent. This is the first report on the rational design and preparation of a hybrid composed of three active metal oxide components originating from MOF precursors. Interestingly, as a lithium-ion battery anode, the developed electrode delivers a reversible capacity of 1742 mAh g^-1 after 500 cycles at a current density of 0.3 mA g^-1 . Furthermore, the material shows large storage capacities (1009 and 667 mAh g^-1 ), even at high current flow (3 and 10 A g^-1 ). The remarkable high-rate capability and outstanding long-life cycling stability of the multidoped metal oxide benefits from the carbon-coated integrated nanostructure with a hollow interior and the three active metal oxide components.

Morphology-Conserved Transformations of Metal-Based Precursors to Hierarchically Porous Micro-/Nanostructures for Electrochemical Energy Conversion and Storage

To meet future market demand, developing new structured materials for electrochemical energy conversion and storage systems is essential. Hierarchically porous micro-/nanostructures are favorable for designing such high-performance materials because of their unique features, including: i) the prevention of nanosized particle agglomeration and minimization of interfacial contact resistance, ii) more active sites and shorter ionic diffusion lengths because of their size compared with their large-size counterparts, iii) convenient electrolyte ingress and accommodation of large volume changes, and iv) enhanced light-scattering capability. Here, hierarchically porous micro-/nanostructures produced by morphology-conserved transformations of metal-based precursors are summarized, and their applications as electrodes and/or catalysts in rechargeable batteries, supercapacitors, and solar cells are discussed. Finally, research and development challenges relating to hierarchically porous micro-/nanostructures that must be overcome to increase their utilization in renewable energy applications are outlined.

Graphene-oxide-wrapped ZnMn2O4 as a high performance lithium-ion battery anode

Cation distribution between tetrahedral and octahedral sites within the ZnMn₂O₄ spinel lattice, along with microstructural features, is affected greatly by the temperature of heat treatment. Inversion parameters can easily be tuned, from 5%-19%, depending on the annealing temperature. The upper limit of inversion is found for T = 400 °C as confirmed by x-ray powder diffraction and Raman spectroscopy. Excellent battery behavior is found for samples annealed at lower temperatures; after 500 cycles the specific capacity for as-prepared ZnMn₂O₄ is 909 mAh g^-1, while ZnMn₂O₄ heat-treated at 300 °C is 1179 mAh g^-1, which amounts to 101% of its initial capacity. Despite the excellent performance of a sample processed at 300 °C at lower charge/discharge rates (100 mAh g^-1), a drop in the specific capacity is observed with rate increase. This issue is solved by graphene-oxide wrapping: the specific capacity obtained after the 400th cycle for graphene-oxide-wrapped ZnMn₂O₄ heat-treated at 300 °C is 799 mAh g^-1 at a charge/discharge rate 0.5 A g^-1, which is higher by a factor of 6 compared to samples without graphene -oxide wrapping.

Template-free fabrication of graphene-wrapped mesoporous ZnMn2O4 nanorings as anode materials for lithium-ion batteries

We rationally designed a facile two-step approach to synthesize ZnMn₂O₄@G composite anode material for lithium-ion batteries (LIBs), involving a template-free fabrication of ZnMn₂O₄ nanorings and subsequent coating of graphene sheets. Notably, it is the first time that ring-like ZnMn₂O₄ nanostructure is reported. Moreover, our system has been demonstrated to be quite powerful in producing ZnMn₂O₄ nanorings regardless of the types of Zn and Mn-containing metal salts reactants. The well-known inside-out Ostwald ripening process is tentatively proposed to clarify the formation mechanism of the hollow nanorings. When evaluated as anode material for LIBs, the resulting ZnMn₂O₄@G hybrid displays significantly improved lithium-storage performance with high specific capacity, good rate capability, and excellent cyclability. After 500 cycles, the ZnMn₂O₄@G hybrid can still deliver a reversible capacity of 958 mAh g^-1 at a current density of 200 mA g^-1, much higher than the theoretical capacity of 784 mAh g^-1 for pure ZnMn₂O₄. The outstanding electrochemical performance should be reasonably ascribed to the synergistic interaction between hollow and porous ZnMn₂O₄ nanorings and the three-dimensional interconnected graphene sheets.

Intricate Hollow Structures: Controlled Synthesis and Applications in Energy Storage and Conversion

Intricate hollow structures garner tremendous interest due to their aesthetic beauty, unique structural features, fascinating physicochemical properties, and widespread applications. Here, the recent advances in the controlled synthesis are discussed, as well as applications of intricate hollow structures with regard to energy storage and conversion. The synthetic strategies toward complex multishelled hollow structures are classified into six categories, including well-established hard- and soft-templating methods, as well as newly emerging approaches based on selective etching of "soft@hard" particles, Ostwald ripening, ion exchange, and thermally induced mass relocation. Strategies for constructing structures beyond multishelled hollow structures, such as bubble-within-bubble, tube-in-tube, and wire-in-tube structures, are also covered. Niche applications of intricate hollow structures in lithium-ion batteries, Li-S batteries, supercapacitors, Li-O₂ batteries, dye-sensitized solar cells, photocatalysis, and fuel cells are discussed in detail. Some perspectives on the future research and development of intricate hollow structures are also provided.

Nano-particle assembled porous core-shell ZnMn2O4 microspheres with superb performance for lithium batteries

Porous ZnMn₂O₄ microspheres were prepared via a facile co-precipitation method followed by calcination at various temperatures and evaluated as anode materials for lithium ion batteries. The sample prepared at 600 °C outperformed the other samples in terms of electrochemical performance with high reversible capacity, high-rate capability, and excellent cycling performance. The capacity of the sample remained as high as 999 mAh g^-1 at a current rate of 100 mA g^-1 after 50 cycles-one of the best ever reported for ZnMn₂O₄-based materials. A high reversible capacity of 400 mAh g^-1 was retainable at a current density of 2000 mA g^-1 after 2500 cycles. A novel electrochemical reaction mechanism of ZnMn₂O₄ anodes was established and investigated at length. The Mn₃O₄ observed during the charge process was largely responsible for the enhanced performance, as confirmed by x-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The relatively large surface area, abundant porosity, large ion exchange space, and strong mechanical stability of the porous connected 3D framework were responsible for the unique oxidation/reduction Mn²⁺ ↔ Mn³⁺ process we observed.

Hierarchical porous ZnMn2O4microspheres assembled by nanosheets for high performance anodes of lithium ion batteries

Hierarchical porous ZnMn₂O₄microspheres assembled by nanosheets are fabricated and they exhibit outstanding electrochemical performance for lithium-ion battery anodes.

Mn-N-C Nanoreactor Prepared through Heating Metalloporphyrin Supported in Mesoporous Hollow Silica Spheres

Mesoporous hollow silica spheres have been drawing tremendous interest due to their special structure and properties and potential applications. Here we synthesized a nanoreactor via ship-in-bottle method, encapsulated with Mn-N-C by heating manganese porphyrin in nanocages of mesoporous hollow silica spheres. And manganese porphyrin is first encapsulated and confined in the hollow spheres. The nanoreactors are investigated through transmission electron microscopy (TEM) and high angle annular dark field scanning TEM (HAADF-STEM) as well as nitrogen adsorption-desorption isotherms. The results demonstrate that the mesoporous hollow spheres with well-defined morphology hold large pore volumes (0.29-0.46 cm³ g^-1), high specific surface areas (428-600 m² g^-1) and uniform pore sizes (4.0 nm). In addition, the ethylbenzene oxidation is conducted in order to explore the catalytic performance of the nanoreactors. And the nanoreactors are observed to possess remarkable catalytic activity and attractive stability for ethylbenzene oxidation, which should be ascribed to the special architectures and confined effect.

A novel one-step strategy toward ZnMn2O4/N-doped graphene nanosheets with robust chemical interaction for superior lithium storage

Ingenious hybrid electrode design, especially realized with a facile strategy, is appealing yet challenging for electrochemical energy storage devices. Here, we report the synthesis of a novel ZnMn2O4/N-doped graphene (ZMO/NG) nanohybrid with sandwiched structure via a facile one-step approach, in which ultrafine ZMO nanoparticles with diameters of 10-12 nm are well dispersed on both surfaces of N-doped graphene (NG) nanosheets. Note that one-step synthetic strategies are rarely reported for ZMO-based nanostructures. Systematical control experiments reveal that the formation of well-dispersed ZMO nanoparticles is not solely ascribed to the restriction effect of the functional groups on graphene oxide (GO), but also to the presence of ammonia. Benefitting from the synergistic effects and robust chemical interaction between ZMO nanoparticles and N-doped graphene nanosheets, the ZMO/NG hybrids deliver a reversible capacity up to 747 mAh g(-1) after 200 cycles at a current density of 500 mA g(-1). Even at a high current density of 3200 mA g(-1), an unrivaled capacity of 500 mAh g(-1) can still be retained, corroborating the good rate capability.

MoV2O8 nanostructures: controlled synthesis and lithium storage mechanism

A facile two-step strategy involving a solvothermal method and a subsequent calcining treatment was successfully developed for the preparation of MoV2O8 nanorods in the absence of any surfactants. Acetic acid was chosen as the solvent to provide an acidic environment. The as-synthesized MoV2O8 nanorods were evaluated as an anode material in lithium ion batteries, which showed excellent lithium storage performance in terms of its specific capacity, rate performance, and cycling stability. It could deliver a specific capacity of over 1325 mA h g(-1) after 50 cycles at 0.2 A g(-1), which is much higher than that of bulk MoV2O8 (617 mA h g(-1)). When the cell was cycled at a current density as high as 10.0 A g(-1), it still maintained a high specific capacity of around 570 mA h g(-1). The phase transformation, intercalation-deintercalation and partial redox processes are responsible for the lithium storage mechanism of MoV2O8 based on ex situ X-ray diffraction, X-ray photo electron spectroscopy and transmission electron microscopy studies, highlighting a new lithium storage mechanism for ternary metal oxides.

Influence of annealing temperature on microstructure and lithium storage performance of self-templated CuxCo3−xO4 hollow microspheres

Spinel Cu_xCo_3−xO₄ (x ≤ 0.30) hollow microspheres have been readily prepared via a self-templated solvothermal reaction followed by a thermal annealing step.

Enhanced microwave absorption capacity of hierarchical structural MnO2@NiMoO4 composites

MnO₂@NiMoO₄ exhibits enhanced microwave absorption capacity, which originates from the hierarchical hybrid nanostructures, multi-effective components, good impedance matching, and interfacial polarization between MnO₂ and NiMoO₄.

Self-sacrificial template formation of ultrathin single-crystalline ZnMn2O4 nanoplates with enhanced Li-storage behaviors for Li-ion batteries

Ultrathin single-crystalline ZnMn₂O₄ nanoplates were first designed and tailored as an anode for advanced Li-ion batteries via an efficient self-sacrificial template synthetic strategy, and delivered excellent Li-storage performance at high C rates.

A simple synthesis of hollow Mn2O3 core–shell microspheres and their application in lithium ion batteries

Hollow Mn₂O₃ core–shell microspheres were successfully fabricated via a mixed method including a solution method and a subsequent thermal decomposition.