Reduced graphene oxide anchored with MnO2 nanorods as anode for high rate and long cycle Lithium ion batteries

A Hierarchical SnO2@Ni6MnO8 Composite for High-Capacity Lithium-Ion Batteries

Semiconductor-based composites are potential anodes for Li-ion batteries, owing to their high theoretical capacity and low cost. However, low stability induced by large volumetric change in cycling restricts the applications of such composites. Here, a hierarchical SnO₂@Ni₆MnO₈ composite comprising Ni₆MnO₈ nanoflakes growing on the surface of a three-dimensional (3D) SnO₂ is developed by a hydrothermal synthesis method, achieving good electrochemical performance as a Li-ion battery anode. The composite provides spaces to buffer volume expansion, its hierarchical profile benefits the fast transport of Li⁺ ions and electrons, and the Ni₆MnO₈ coating on SnO₂ improves conductivity. Compared to SnO₂, the Ni₆MnO₈ coating significantly enhances the discharge capacity and stability. The SnO₂@Ni₆MnO₈ anode displays 1030 mAh g^-1 at 0.1 A g^-1 and exhibits 800 mAh g^-1 under 0.5 A g^-1, along with high Coulombic efficiency of 95%. Furthermore, stable rate performance can be achieved, indicating promising applications.

Rational Construction of Yolk-Shell Bimetal-Modified Quinonyl-Rich Covalent Organic Polymers with Ultralong Lithium-Storage Mechanism

Covalent organic polymers are attracting more and more attention for energy storage devices due to their lightweight, molecular viable design, stable structure, and environmental benignity. However, low charge-carrier mobility of pristine covalent organic materials is the main drawback for their application in lithium-ion batteries. Herein, a yolk-shell bimetal-modified quinonyl-rich covalent organic material, Co@2AQ-MnO₂, has been designed and synthesized by in situ loading of petal-like nanosized MnO₂ and coordinating with Co centers, with the aim to improve the charge conductivity of the covalent organic polymer and activate its Li-storage sites. As investigated by in situ FT-IR, ex situ XPS, and electrochemical probing, the quinonyl-rich structure provides abundant redox sites (carbonyl groups and π electrons from the benzene ring) for lithium reaction, and the introduction of two types of metallic species promotes the charge transfer and facilitates more efficient usage of active energy-storage sites in Co@2AQ-MnO₂. Thus, the Co@2AQ-MnO₂ electrode exhibits good cycling performance with large reversible capacity and excellent rate performance (1534.4 mA h g^-1 after 200 cycles at 100 mA g^-1 and 596.0 mA h g^-1 after 1000 cycles at 1000 mA g^-1).

Sea Urchin-like Si@MnO2@rGO as Anodes for High-Performance Lithium-Ion Batteries

Si is a promising material for applications as a high-capacity anode material of lithium-ion batteries. However, volume expansion, poor electrical conductivity, and a short cycle life during the charging/discharging process limit the commercial use. In this paper, new ternary composites of sea urchin-like Si@MnO₂@reduced graphene oxide (rGO) prepared by a simple, low-cost chemical method are presented. These can effectively reduce the volume change of Si, extend the cycle life, and increase the lithium-ion battery capacity due to the dual protection of MnO₂ and rGO. The sea urchin-like Si@MnO₂@rGO anode shows a discharge specific capacity of 1282.72 mAh g⁻¹ under a test current of 1 A g⁻¹ after 1000 cycles and excellent chemical performance at different current densities. Moreover, the volume expansion of sea urchin-like Si@MnO₂@rGO anode material is ~50% after 150 cycles, which is much less than the volume expansion of Si (300%). This anode material is economical and environmentally friendly and this work made efforts to develop efficient methods to store clean energy and achieve carbon neutrality.

Co-Existence of Iron Oxide Nanoparticles and Manganese Oxide Nanorods as Decoration of Hollow Carbon Spheres for Boosting Electrochemical Performance of Li-Ion Battery

Here, we report that mesoporous hollow carbon spheres (HCS) can be simultaneously functionalized: (i) endohedrally by iron oxide nanoparticle and (ii) egzohedrally by manganese oxide nanorods (FexOy/MnO2/HCS). Detailed analysis reveals a high degree of graphitization of HCS structures. The mesoporous nature of carbon is further confirmed by N2 sorption/desorption and transmission electron microscopy (TEM) studies. The fabricated molecular heterostructure was tested as the anode material of a lithium-ion battery (LIB). For both metal oxides under study, their mixture stored in HCS yielded a significant increase in electrochemical performance. Its electrochemical response was compared to the HCS decorated with a single component of the respective metal oxide applied as a LIB electrode. The discharge capacity of FexOy/MnO2/HCS is 1091 mAhg-1 at 5 Ag-1, and the corresponding coulombic efficiency (CE) is as high as 98%. Therefore, the addition of MnO2 in the form of nanorods allows for boosting the nanocomposite electrochemical performance with respect to the spherical nanoparticles due to better reversible capacity and cycling performance. Thus, the structure has great potential application in the LIB field.

Highly conductive triple-layered hollow MnO2@SnO2@NHCS nanospheres with excellent lithium storage capacity for high performance lithium-ion batteries

Multilayered hollow MnO2@SnO2@NHCS nanospheres incorporate the merits of highly conductive N-doping and the synergistic effect of metal oxides.

Polypyrrole coated δ-MnO2 nanosheet arrays as a highly stable lithium-ion-storage anode

Manganese dioxide (MnO₂) with a conversion mechanism is regarded as a promising anode material for lithium-ion batteries (LIBs) owing to its high theoretical capacity (∼1223 mA h g^-1) and environmental benignity as well as low cost. However, it suffers from insufficient rate capability and poor cyclic stability. To circumvent this obstacle, semiconducting polypyrrole coated-δ-MnO₂ nanosheet arrays on nickel foam (denoted as MnO₂@PPy/NF) are prepared via hydrothermal growth of MnO₂ followed by the electrodeposition of PPy on the anode in LIBs. The electrode with ∼50 nm thick PPy coating exhibits an outstanding overall electrochemical performance. Specifically, a high rate capability is obtained with ∼430 mA h g^-1 of discharge capacity at a high current density of 2.67 A g^-1 and more than 95% capacity is retained after over 120 cycles at a current rate of 0.86 A g^-1. These high electrochemical performances are attributed to the special structure which shortens the ion diffusion pathway, accelerates charge transfer, and alleviates volume change in the charging/discharging process, suggesting a promising route for designing a conversion-type anode material for LIBs.

Double-shell SnO2@Fe2O3 hollow spheres as a high-performance anode material for lithium-ion batteries

Construction of novel electrode materials is an effective way to enhance the electrochemical performance of lithium ion batteries (LIBs).

High-Lithium-Affinity Chemically Exfoliated 2D Covalent Organic Frameworks

Covalent organic frameworks (COFs) with reversible redox behaviors are potential electrode materials for lithium-ion batteries (LIBs). However, the sluggish lithium diffusion kinetics, poor electronic conductivity, low reversible capacities, and poor rate performance for most reported COF materials limit their further application. Herein, a new 2D COF (TFPB-COF) with six unsaturated benzene rings per repeating unit and ordered mesoporous pores (≈2.1 nm) is designed. A chemical stripping strategy is developed to obtain exfoliated few-layered COF nanosheets (E-TFPB-COF), whose restacking is prevented by the in situ formed MnO₂ nanoparticles. Compared with the bulk TFPB-COF, the exfoliated TFPB-COF exhibits new active Li-storage sites associated with conjugated aromatic π electrons by facilitating faster ion/electron kinetics. The E-TFPB-COF/MnO₂ and E-TFPB-COF electrodes exhibit large reversible capacities of 1359 and 968 mAh g^-1 after 300 cycles with good high-rate capability.

Coaxial-cable hierarchical tubular MnO2@Fe3O4@C heterostructures as advanced anodes for lithium-ion batteries

Nanostructured manganese oxides have been regarded as promising anodes for lithium-ion batteries (LIBs) due to their high specific capacity, environmental friendliness and low cost. However, as conversion-type electrodes, their scalable utilization is hindered by intrinsically low reaction kinetics, large volume variation and high polarization. Herein, a coaxial-cable tubular heterostructure composed of a hollow carbon skeleton, Fe₃O₄ nanoparticles and ultrathin MnO₂ nanosheets from inside out, donated as MnO₂@Fe₃O₄@C, is synthesized via a facile two-step hydrothermal process. The unique design integrates conductive carbon and nanostructured MnO₂ and Fe₃O₄ into a one-dimensional (1D) hierarchically open architecture, which provides abundant electrode-electrolyte contact areas, favorable heterointerfaces and ultrafast electron/ion pathways. Benefiting from these features, the MnO₂@Fe₃O₄@C anode exhibits a high reversible capacity of 946 mAh g^-1 at 200 mA g^-1 after 160 cycles, and excellent cyclability with a specific capacity of 845 mAh g^-1 at 500 mA g^-1 after 600 cycles. This work might provide an insightful guideline for the design of novel electrode materials.

Smartly Designed Hierarchical MnO2 @Fe3 O4 /CNT Hybrid Films as Binder-free Anodes for Superior Lithium Storage

Nowadays, the development of advanced anode materials is highly desirable for the increasing demand for high-performance lithium-ion batteries (LIBs). Nanostructured MnO₂ has received utmost attention due to high theoretical capacity (1230 mA h g^-1 ), abundant resources, environmental benignity, and shortened electron and ion diffusion paths. Unfortunately, poor electronic conductivity and strong aggregation inclination of MnO₂ nanostructures result in disappointing electrochemical performances, which restrict their practical application as sole institute. Here, we propose smartly designed MnO₂ @Fe₃ O₄ /CNT hybrid films, in which MnO₂ nanosheets, Fe₃ O₄ nanoparticles and CNTs are hierarchically assembled in a unique stage of nanosheets-nanoparticles-nanotubes. The resulting MnO₂ @Fe₃ O₄ /CNT hybrid films can be directly used as anodes without any polymer binders, and exhibit significant synergistic interactions among three components, achieving excellent reversible capacity and rate performance.

Basic Medium Heterogeneous Solution Synthesis of α-MnO₂ Nanoflakes as an Anode or Cathode in Half Cell Configuration (vs. Lithium) of Li-Ion Batteries

Nano α-MnO₂ is usually synthesized under hydrothermal conditions in acidic medium, which results in materials easily undergoing thermal reduction and offers single crystals often over 100 nm in size. In this study, α-MnO₂ built up of inter-grown ultra-small nanoflakes with 10 nm thickness was produced in a rapid two-step procedure starting via partial reduction in solution in basic medium subsequently followed by co-proportionation in thermal treatment. This approach offers phase-pure α-MnO₂ doped with potassium (cryptomelane type K_0.25Mn₈O₁₆ structure) demonstrating considerable chemical and thermal stability. The reaction pathways leading to this new morphology and structure have been discussed. The MnO₂ electrodes produced from obtained nanostructures were tested as electrodes of lithium ion batteries delivering initial discharge capacities of 968 mAh g⁻¹ for anode (0 to 2.0 V) and 317 mAh g⁻¹ for cathode (1.5 to 3.5 V) at 20 mA g⁻¹ current density. At constant current of 100 mA g⁻¹, stable cycling of anode achieving 660 mAh g⁻¹ and 145 mAh g⁻¹ for cathode after 200 cycles is recorded. Post diagnostic analysis of cycled electrodes confirmed the electrode materials stability and structural properties.

Synthesis, characterization of Hollandite Ag2Mn8O16 on TiO2 nanotubes and their photocatalytic properties for Rhodamine B degradation

In this research Ag2Mn8O16 nanocrystals/TiO2 nanotubes, photoelectrodes were successfully prepared through anodization and annihilation steps, followed by electrodeposition of MnO2 and Ag in a three electrodes cell. The obtained photoelectrodes were dried, then annealed for crystallization, the morphology and structure of the fabricated electrodes were characterized via scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The light absorption and harvesting properties were investigated through UV–visible diffuse reflectance spectrum (DRS), photocatalytic performances were evaluated by degradation of 50 mL of Rhodamine B (5 mg L−1) under Xenon light irradiation for 2 h. Results illustrated that the fabricated photoelectrodes show remarkable photo-degradation properties of organic pollutants in aqueous mediums.

Reduced Graphene Oxide-Wrapped Nickel-Rich Cathode Materials for Lithium Ion Batteries

The encapsulation of Ni-rich cathode materials (LiNi_0.6Co_0.2Mn_0.2O₂) for lithium ion batteries in reduced graphene oxide (rGO) sheets is introduced to improve electrochemical performances. Using (3-aminopropyl)triethoxysilane, the active materials are completely wrapped with several rGO layers of ∼2 nm thickness. By virtue of the great electrical conductivity of graphene, the rGO-coated cathode materials exhibit much enhanced electrochemical performances of cycling property and rate capability. In addition, it is shown that the structural degradation of the active materials, which is from the rhombohedral layered structure (R3̅m) to the spinel (Fd3̅m) or rock-salt phase (Fm3̅m), is significantly reduced as well as delayed due to the protection of the active materials in the rGO layers from direct contact with electrolytes and the consequent suppression of side reactions.

Freestanding graphene/MnO2 cathodes for Li-ion batteries

Different polymorphs of MnO₂ (α-, β-, and γ-) were produced by microwave hydrothermal synthesis, and graphene oxide (GO) nanosheets were prepared by oxidation of graphite using a modified Hummers' method. Freestanding graphene/MnO₂ cathodes were manufactured through a vacuum filtration process. The structure of the graphene/MnO₂ nanocomposites was characterized using X-ray diffraction (XRD) and Raman spectroscopy. The surface and cross-sectional morphologies of freestanding cathodes were investigated by scanning electron microcopy (SEM). The charge-discharge profile of the cathodes was tested between 1.5 V and 4.5 V at a constant current of 0.1 mA cm^-2 using CR2016 coin cells. The initial specific capacity of graphene/α-, β-, and γ-MnO₂ freestanding cathodes was found to be 321 mAhg^-1, 198 mAhg^-1, and 251 mAhg^-1, respectively. Finally, the graphene/α-MnO₂ cathode displayed the best cycling performance due to the low charge transfer resistance and higher electrochemical reaction behavior. Graphene/α-MnO₂ freestanding cathodes exhibited a specific capacity of 229 mAhg^-1 after 200 cycles with 72% capacity retention.

MnO2 nanotubes with a water soluble binder as high performance sodium storage materials

Well dispersed MnO₂ nanotubes were synthesized via a hydrothermal method.