Manganese oxide/carbon yolk-shell nanorod anodes for high capacity lithium batteries

Construction of N-doped carbon encapsulated Mn2O3/MnO heterojunction for enhanced lithium storage performance

Owing to high theoretical capacity, low cost and abundant availability, manganese oxides are widely viewed as promising anodes for lithium-ion batteries (LIBs). Nonetheless, their practical application is significantly hindered by poor electrical conductivity, sluggish reaction kinetics and substantial volume change. In this work, an ingenious polypyrrole encapsulation followed by pyrolysis strategy is proposed to produce N-doped carbon encapsulated Mn2O3/MnO heterojunction (Mn2O3/MnO@NC) by using mechanically ground Mn3O4/C3N4 mixture as the precursor. The results show that the selection of precursor plays a pivotal role in the successful preparation of Mn2O3/MnO@NC hybrid. It is revealed that the uniform encapsulation by N-doped carbon significantly enhances the conductivity and structural stability of the final product. Concurrently, the Mn2O3/MnO heterojunction within the resultant hybrid exhibits a unique quantum-dot size, which effectively shortens ion transport pathways and exposes the active sites for lithium storage. Additionally, experimental observations and theoretical calculations demonstrate that the built-in electric fields generated at the interfaces of Mn2O3/MnO heterojunction accelerate the charge transfer and ion diffusion, thereby enhancing the electrochemical reaction kinetics. As a result, the Mn2O3/MnO@NC hybrid displays much enhanced lithium storage performance. Evidently, our work offers a good guidance for the design and synthesis of advanced transition metal oxide/carbon anodes for LIBs.

2D heterostructural Mn2O3 quantum dots embedded N-doped carbon nanosheets with strongly stable interface enabling high-performance sodium-ion hybrid capacitors

The ingenious architectural structural engineering is extensively identified as a cogent means for facilitating the electrochemical properties of conversion-type anode materials for sodium-ion storage. Herein, a delicate, scalable and controllable solvent-free strategy is proposed to synthesize ultrafine Mn2O3 quantum dots embedded into N-doped carbon to generate two-dimensional (2D) composites (MNC) with robust interfacial heterostructural interactions for high sodium ion storage and fast reaction kinetics, which averts the use of solvents and environmental pollution, greatly reduces time and production costs. The introduction of metallic Mn species simultaneously achieves the construction of ultrafine Mn2O3 quantum dots and strong interfacial heterostructural COMn bonds between metal species and 2D N-doped carbon matrix. The synergistic effect of the formation of oxide quantum dots, the combination of 2D N-doped carbon and the construction of robust interfacial interactions provides the stable electrode structure, fast reaction kinetics and high electrochemical storage capability of anode materials. Hence, MNC composites in SIBs convey remarkable reversible rate capability. Its superior capacity reaches 215 mAh g-1 for 50 cycles at 0.2 A g-1 and 155 mAh g-1 for 1000 cycles at a high current density of 5 A g-1, which shows good long-term stability. The assembled sodium-ion hybrid capacitors (SIHCs) device delivers outstanding energy density of 138 Wh kg-1 at a power density of 126 W kg-1 and 98% capacity retention after 2000 cycles at 2 A g-1, and tremendous capability for practical applications (69 LEDs can be easily lighted). This work not merely offers guidance for the rational interfacial engineering design of high-capacity Mn-based electrode materials in a feasible and scalable solvent-free tactics for Na+ storage, but also broadens the routes for projecting a better electrode material for other battery systems.

Fe3O4@void@C-Schiff-base/Pd yolk-shell nanostructures as an effective and reusable nanocatalyst for Suzuki coupling reaction

This article describes the synthesis of a novel Yolk-Shell structured Magnetic Yolk-Shell Nanomaterials Modified by Functionalized Carbon Shell with Schiff/Palladium Bases (Fe3O4@void@C-Schiff-base/Pd). The designed Fe3O4@void@C-Schiff-base/Pd catalyst was characterized using several techniques such as Fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometry (VSM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), thermal gravimetric analysis (TGA), powder X-ray diffraction (PXRD) and Inductively coupled plasma (ICP). The Fe3O4@void@C-Schiff-base/Pd was used as powerful catalyst for preparation Suzuki reaction in short reaction times and high yield in H2O at 60 °C and presence of potassium carbonate base. This nanocatalyst was magnetically recovered and reused several times with keeping its efficiency.

Advances in Electrospun Materials and Methods for Li-Ion Batteries

Electronic devices commonly use rechargeable Li-ion batteries due to their potency, manufacturing effectiveness, and affordability. Electrospinning technology offers nanofibers with improved mechanical strength, quick ion transport, and ease of production, which makes it an attractive alternative to traditional methods. This review covers recent morphology-varied nanofibers and examines emerging nanofiber manufacturing methods and materials for battery tech advancement. The electrospinning technique can be used to generate nanofibers for battery separators, the electrodes with the advent of flame-resistant core-shell nanofibers. This review also identifies potential applications for recycled waste and biomass materials to increase the sustainability of the electrospinning process. Overall, this review provides insights into current developments in electrospinning for batteries and highlights the commercialization potential of the field.

Carbon nanoparticle-entrapped macroporous Mn3O4 microsphere anodes with improved cycling stability for Li-ion batteries

Manganese oxide (Mn₃O₄) has garnered substantial attention as a low-cost, environment-friendly anode material. It undergoes a conversion reaction involving the formation of Li₂O and metallic Mn to provide high-energy Li-ion batteries. However, its low electrical conductivity and significant volume change reduce its capacity during the initial lithiation/delithiation, hindering its practical application. To improve the cycle performance, we propose a new composite structure wherein we entrap carbon nanoparticles in macroporous Mn₃O₄ microspheres with a unique maze-like porous interior. We fabricate the Mn₃O₄/C composites using a scalable two-step process involving the thermal decomposition of MnCO₃ in water vapor and mixing in a carbon-dispersed solution. The fabricated Mn₃O₄/C composites with varying carbon contents exhibit a high maximum discharge capacity retention of 86% after 50 cycles, compared to the 18% given by bare Mn₃O₄. The entrapped carbon nanoparticles improve the cycle performance both electrochemically and physically. The microstructure of the composite particles and the fabrication process developed in this study will help improve the performance of other conversion-type anode materials that suffer from cycle degradation, including inexpensive transition metal oxides and sulfides.

Nanostructure and Advanced Energy Storage: Elaborate Material Designs Lead to High-Rate Pseudocapacitive Ion Storage

The drastic need for development of power and electronic equipment has long been calling for energy storage materials that possess favorable energy and power densities simultaneously, yet neither capacitive nor battery-type materials can meet the aforementioned demand. By contrast, pseudocapacitive materials store ions through redox reactions with charge/discharge rates comparable to those of capacitors, holding the promise of serving as electrode materials in advanced electrochemical energy storage (EES) devices. Therefore, it is of vital importance to enhance pseudocapacitive responses of energy storage materials to obtain excellent energy and power densities at the same time. In this Review, we first present basic concepts and characteristics about pseudocapacitive behaviors for better guidance on material design researches. Second, we discuss several important and effective material design measures for boosting pseudocapacitive responses of materials to improve rate capabilities, which mainly include downsizing, heterostructure engineering, adding atom and vacancy dopants, expanding interlayer distance, exposing active facets, and designing nanosheets. Finally, we outline possible developing trends in the rational design of pseudocapacitive materials and EES devices toward high-performance energy storage.

Boosting the lithium storage performance of tin dioxide by carbon nanotubes supporting and surface engineering

In order to reduce the negative impact of the extra carbon coating on the electrochemical properties of the commonly sandwiched carbon nanotubes@tin dioxide@carbon (CNT@SnO₂@C) composites, the external C coating has been designed as a porous carbon in this work. The well-designed porous carbon coating offers an attractive advantage compared to the common carbon coatings, namely, it can not only better mitigate the volumetric variation of SnO₂ by means of its spongy structure with better flexibility and rich free space, but also accelerate the lithium-ions diffusion by virtue of its open tunnel-like architecture. For this reason, this composite prepared here shows outstanding electrochemical performance stemming from the cooperative effect of inner CNT supporting and externally porous carbon coating, displaying 819.3 and 576.0 mAh g^-1 at 200 and even 1000 mA g^-1 after even 500 cycles, respectively. This surface engineering strategy may be valuable for enhancing the cyclical durability of other metal oxides with higher theoretical specific capacities.

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.

Nanocrystalline Cellulose Supported MnO2 Composite Materials for High-Performance Lithium-Ion Batteries

The rate capability and poor cycling stability of lithium-ion batteries (LIBs) are predominantly caused by the large volume expansion upon cycling and poor electrical conductivity of manganese dioxide (MnO₂), which also exhibits the highest theoretical capacity among manganese oxides. In this study, a nanocomposite of nanosized MnO₂ and pyrolyzed nanocrystalline cellulose (CNC) was prepared with high electrical conductivity to enhance the electrochemical performance of LIBs. The nanocomposite electrode showed an initial discharge capacity of 1302 mAh g⁻¹ at 100 mA g⁻¹ and exhibited a high discharge capacity of 305 mAh g⁻¹ after 1000 cycles. Moreover, the MnO₂-CNC nanocomposite delivered a good rate capability of up to 10 A g⁻¹ and accommodated the large volume change upon repeated cycling tests.

Hierarchical MnV2O4 double-layer hollow sandwich nanosheets confined by N-doped carbon layer as anode for high performance lithium-ion batteries

Binary transition metal oxides, especially vanadate metal oxides, are highly desirable for lithium-ion batteries (LIBs) anode materials due to their low-budget and high theoretical lithium storage capacity. However, low conductivity and poor cycle stability caused by volume changes during charge and discharge limit their grid-scale applications. Herein, a novel spinel MnV₂O₄ double-layer hollow sandwich nanosheets enclosed in N-doped porous carbon layer (MnV₂O₄/NC) was efficiently synthesized in 5 min by microwave-assisted and in-situ pyrolysis the coated polydopamine. MnV₂O₄/NC shows the superior performance as anode for LIBs with a specific capacities of 760 mA h g^-1 at 1000 mA g^-1 and outstanding of cycling stability with a specific capacities of 525.5 mA h g^-1 after 1000 cycles even at 5000 mA g^-1, respectively, which due to its unique double-layer hollow sandwich microstructure, mixed lithium storage mechanism and in-situ coating of nitrogen-doped carbon layer.

Phase structure engineering of MnCo2Ox within electrospun carbon nanofibers towards high-performance lithium-ion batteries

Metal oxides are prospective alternative anode materials to the commercial graphite for lithium ion batteries (LIBs), while their practical application is seriously hampered by their poor conductivities and large volume changes. Herein, we report the controllable synthesis of amorphous/crystalline MnCo₂O_x nanoparticles within porous carbon nanofibers (marked as MCO@CNFs) through a facile electrospinning strategy and subsequent annealing reactions. The phase structures from Co/MnO_X to amorphous MnCo₂O_x and crystalline MnCo₂O_4.5 can be readily tuned by thermal reduction/oxidation under controlled atmosphere and temperature. When examined as anode for LIBs, the optimized MCO@CNFs delivers a high stable capacity of 780.3 mA h g^-1 at 200 mA g^-1 after 250 cycles, which is attributed to the synergistic effect of the distinctive amorphous structure and defective carbon nanofiber matrices. Specifically, the amorphous structure with rich defects offers more reactive sites and multiple pathways for the Li⁺ diffusion, while carbon hybridization sufficiently improves the electrode conductivities as well as buffers the volume changes. More importantly, we demonstrate a convenient synthesis strategy to control the metal-to-oxide structure evolution within carbon matrices, which is of great importance in exploring high-performance electrodes for next generation LIBs.

Binary-Metal Mn2SnO4 Nanoparticles and Sn Confined in a Cubic Frame with N-Doped Carbon for Enhanced Lithium and Sodium Storage

Sn-based materials have been popularly researched as anodes for energy storage due to their high theoretical capacity. However, the sluggish reaction kinetics and unsatisfied cycling stability caused by poor conductivity and dramatic volume expansion are still pivotal barriers for the development of Sn-based materials as anodes. In this work, the binary-metal Mn₂SnO₄ nanoparticles and Sn encapsulated in N-doped carbon (Sn@Mn₂SnO₄-NC) were fabricated by multistep reactions and employed as the anode for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). The coexistence of binary metals (Sn and Mn) can improve intrinsic conductivity. Simultaneously, hollow architecture along with carbon relieves internal stress and prevents structural collapse. A Sn@Mn₂SnO₄-NC anode delivers an appealing capacity of 1039.5 mAh g^-1 for 100 cycles at 100 mA g^-1 and 823.8 mAh g^-1 for 600 cycles at 1000 mA g^-1 in LIBs. When evaluated as an anode in SIBs, the Sn@Mn₂SnO₄-NC anode tolerates up to 7000 cycles at 2000 mA g^-1 and maintains a capacity of 185.8 mAh g^-1. Quantified kinetic investigations demonstrate the high contribution of pseudocapacitive effects during the cycle process. Furthermore, density functional theory (DFT) calculations further verify that introduction of the second metal (Mn) improves the conductivity of the material, which is favorable for charge transport. This work is expected to provide a feasible preparation strategy for binary-metal materials to enhance the performance of lithium- and sodium-ion batteries.

Egyptian blue: from pigment to battery electrodes

Herein we report on using Egyptian blue as an anode material for Li-ion batteries. A 1^st cycle lithiation capacity of 594 mA h g^-1 and reversible capacity of 210 mA h g^-1 at 20 mA g^-1, and at 500 mA g^-1 a reversible capacity of 120 mA h g^-1 (stable over 1000 cycles) were achieved with coulombic efficiency more than 99.5%. Using X-ray diffraction, and FTIR and X-ray absorption spectroscopies we found that the material goes through a conversion reaction during the 1^st cycle that results in the formation of amorphous mixed oxides with copper nanoclusters.

Metal-Organic Framework-Derived Hierarchical MnO/Co with Oxygen Vacancies toward Elevated-Temperature Li-Ion Battery

Transition metal oxides for high-temperature lithium-ion batteries have captivated orchestrated efforts for next-generation high-energy-density anodes. However, due to inherent low tap density, poor conductivity, and structural instability, their poor cyclability capacity and rate performance at elevated temperatures hinder further implementation. Oxygen vacancies (O_v) engineered by manipulating the active sites and electrical conductivity is a promising method for superior lithium storage. Herein, hierarchical MnO/Co nanoparticle-embedded N-doped carbon nanotube (CNT)-assembled carbonaceous micropolyhedrons (O_v-MnO/Co NCPs) are constructed by a "4S" self-assembly, self-template, self-adaptive, and self-catalytic metal-organic framework template method with in situ oxygen vacancies introduced. Impressively, the internal nanoparticles with metallic Co and the external N-doped carbonaceous matrix entangled by fluffy self-generated CNTs synchronously constructed hierarchical micro/nano-secondary hybrids, facilitating highly compacted density, staggered conductive network, multidirectional diffusion pathways, and accelerated electrochemical kinetics. Experimental and density functional theory investigations systematically manifested that the O_v alongside the local built-in electric field within the crystal lattice induced the boosted electrical conductivity, additional active sites, and alleviated structural expansion, further achieving the exceptional diffusivity coefficient and pseudocapacitive capacity. Benefiting from the integrated structural and compositional optimization, the O_v-MnO/Co NCPs achieved distinguished "3C" performance with superior ultralong cyclability (a volumetric capacity of 1713.5 mAh cm^-3 at 1 A g^-1 up to 1000 cycles), good rate capacity (a well-maintained capacity of 670.2 mAh g^-1 even at 10 A g^-1), and considerable high-temperature capability at 60 °C.

Tin dioxide-based nanomaterials as anodes for lithium-ion batteries

The development of new electrode materials for lithium-ion batteries (LIBs) has attracted significant attention because commercial anode materials in LIBs, like graphite, may not be able to meet the increasing energy demand of new electronic devices. Tin dioxide (SnO2) is considered as a promising alternative to graphite due to its high specific capacity. However, the large volume changes of SnO2 during the lithiation/delithiation process lead to capacity fading and poor cycling performance. In this review, we have summarized the synthesis of SnO2-based nanomaterials with various structures and chemical compositions, and their electrochemical performance as LIB anodes. This review addresses pure SnO2 nanomaterials, the composites of SnO2 and carbonaceous materials, the composites of SnO2 and transition metal oxides, and other hybrid SnO2-based materials. By providing a discussion on the synthesis methods and electrochemistry of some representative SnO2-based nanomaterials, we aim to demonstrate that electrochemical properties can be significantly improved by modifying chemical composition and morphology. By analyzing and summarizing the recent progress in SnO2 anode materials, we hope to show that there is still a long way to go for SnO2 to become a commercial LIB electrode and more research has to be focused on how to enhance the cycling stability.

Planar Fully Stretchable Lithium-Ion Batteries Based on a Lamellar Conductive Elastomer

Stretchable lithium-ion batteries (LIBs) have attracted great attention as a promising power source in the emerging field of wearable electronics. Despite the recent advances in stretchable electrodes, separators, and sealing materials, building stretchable full batteries remains a big challenge. Herein, a simple strategy to prepare stretchable electrodes and separators at the full battery scale is reported. Then, electrostatic spraying is used to make the anode and cathode on an elastic current collector. Finally, a polyvinylidene fluoride/thermoplastic polyurethane nanofiber separator is hot-sandwiched between the cathode and anode. The fabricated battery shows stable electrochemical performance during repeatable release-stretch cycles. In particular, a stable capacity of 6 mA•h/cm² at the current rate of 0.5 C can be achieved for the fully stretchable LIB. More importantly, over 70% of the initial capacity can be maintained after 100 cycles with ∼150% stretch.

Tetrathiafulvalene-Based Metal-Organic Framework as a High-Performance Anode for Lithium-Ion Batteries

Metal-organic frameworks (MOFs) have aroused great interest as lithium-ion battery (LIB) electrode materials. In this work, we first report that a pristine three-dimensional tetrathiafulvalene derivatives (TTFs)-based zinc MOF, formulated [Zn₂(py-TTF-py)₂(BDC)₂]·2DMF·H₂O (1) (py-TTF-py = 2,6-bis(4'-pyridyl)tetrathiafulvalene and H₂BDC = terephthalic acid), can work as a high-performance electrode material for rechargeable LIBs. The TTFs-Zn-MOF 1 electrode displayed a high discharge specific capacity of 1117.4 mA h g^-1 at a current density of 200 mA g^-1 after 150 cycles along with good reversibility. After undergoing elevated discharging/charging rates, the electrode showed superior lithium storage performance in the extreme case of 20 A g^-1 and could finally recover the capability when the current rate was back to 200 mA g^-1. Particularly, specific capacities of 884.2, 513.8, and 327.8 mA h g^-1 were reached at high current densities of 5, 10, and 20 A g^-1 after 180, 175, and 300 cycles along with good reversibility, respectively. Such an excellent performance is first reported for the LIB anode materials. TTFs-Zn-MOF 2, namely, [Zn₂(py-TTF-py) (BDC)₂]·DMF·2H₂O (2), was prepared as a contrast to explore the relationship between the structures of the electrode materials and the electrochemical properties. Based on the structural analysis of 1 and 2 and ex situ X-ray photoelectron spectroscopy, the TTF moiety and the twofold TTF pillar play a key role in the excellent electrochemical performance. The full cell of MOF 1 with NMC 622 delivered the capacity of 131.9 mA h g^-1 at 100 mA g^-1 with the Coulombic efficiency of 99.45% after 70 cycles and exhibited the tolerance to high-current operation.

Cobalt vacancies assisted ion diffusion in Co2AlO4 carbon nanofibers for enhancing lithium battery performance

The rational design of one-dimensional nanofibers, concentrating on the compositions, morphology, structure and defects, has emerging importance in the preparation of anode materials with desired performance for lithium-ion batteries. In the present work, we prepared cobalt vacancies enriched Co₂AlO₄/carbon nanofibers coated with Co₂AlO₄ nanosheets by using electrospinning and multi-step sintering processes. As the anode of the lithium-ion battery, the as-prepared nanofibers show excellent cycling stability, and particularly the discharge capacity can remain at 627.4 mA h g^-1 after 500 cycles under 500 mA g^-1. We contributed the improved performances to the carbon-based networks, the presence of cobalt vacancy on Co₂AlO₄ and the larger specific surface area of the present species. Moreover, density functional theory (DFT) calculations have implied that introducing Co vacancies could reduce the energy barrier of ion diffusion, leading to a faster diffusion rate of lithium ions during cycling. Apparently, the present approach could afford many essential advantages for anode material preparation, such as carbon-based matrix, larger specific surface area and cation vacancy, and more importantly, it can be extended to other spinel mixed transition metal oxides.

Multi-Step Phase Transitions of Mn3 O4 During Galvanostatic Lithiation: An In Situ Transmission Electron Microscopic Investigation

For study of electrochemical reaction mechanisms at nanoscale, in situ electrochemical transmission electron microscopy (EC-TEM) exceeds many other methods due to its high temporal and spatial resolution. However, the limited amount of active materials used in previous in situ TEM studies prevents the model EC cells to operate in the constant-current (galvanostatic) charge/discharge mode that is required for accurate control of electrochemical processes. Herein, a new in situ EC-TEM technique is developed to investigate multi-step phase transitions of Mn₃ O₄ electrodes under the galvanostatic charge/discharge mode and constant-voltage discharge mode. In galvanostatic mode, the lithiation of Mn₃ O₄ undergoes multi-step phase transitions following a reaction pathway of Mn₃ O₄ + Li⁺ → LiMn₃ O₄ + Li⁺ → MnO + Li₂ O → Mn + Li₂ O. It is also found that lithium ions prefer to enter Mn₃ O₄ along the {101} direction to form LiMn₃ O₄ with the help of transitional boundary phase of Li_x Mn₃ O₄ . These results are in sharp contrast to that obtained under a constant-voltage discharge mode, where only a single-step lithiation process of Mn₃ O₄ + Li⁺ → Mn + Li₂ O is observed.

Nanospace-Confinement Synthesis: Designing High-Energy Anode Materials toward Ultrastable Lithium-Ion Batteries

Exploiting high-capacity and durable electrode materials is pivotal to developing lithium-ion batteries (LIBs) and their applications. Multiscaled nanomaterials have been demonstrated to efficiently couple the advantages of each component on different scales in energy storage fields. However, the precise control of the microstructure remains a great challenge for maximizing their contributions. Nanospace-confined synthesis provides a proactive strategy to build novel multiscaled nanomaterials with controllable internal void space for circumventing the intrinsic volume effects in the charge/discharge process. Herein, the rational design and synthesis of multiscaled high-capacity anode materials are mainly summarized according to their electrochemical mechanisms by choosing 1D channel, 2D interlayer, and 3D space as representative confinement reaction environments. The structure-performance relationships are clarified with the assistance of quantitative calculations, molecular simulations, and so forth. Finally, future potentials and challenges of such a synthesis tactic in designing high-performance electrode materials for next-generation secondary batteries are outlooked.

Yolk-Shell Nanostructures: Syntheses and Applications for Lithium-Ion Battery Anodes

Yolk-shell nanostructures have attracted tremendous research interest due to their physicochemical properties and unique morphological features stemming from a movable core within a hollow shell. The structural potential for tuning inner space is the focal point of the yolk-shell nanostructures in a way that they can solve the long-lasted problem such as volume expansion and deterioration of lithium-ion battery electrodes. This review gives a comprehensive overview of the design, synthesis, and battery anode applications of yolk-shell nanostructures. The synthetic strategies for yolk-shell nanostructures consist of two categories: templating and self-templating methods. While the templating approach is straightforward in a way that the inner void is formed by removing the sacrificial layer, the self-templating methods cover various different strategies including galvanic replacement, Kirkendall effect, Ostwald ripening, partial removal of core, core injection, core contraction, and surface-protected etching. The battery anode applications of yolk-shell nanostructures are discussed by dividing into alloying and conversion types with details on the synthetic strategies. A successful design of yolk-shell nanostructures battery anodes achieved the improved reversible capacity compared to their bare morphologies (e.g., no capacity retention in 300 cycles for Si@C yolk-shell vs. capacity fading in 10 cycles for Si@C core-shell). This review ends with a summary and concluding remark yolk-shell nanostructures.

SnS/N-Doped carbon composites with enhanced Li+ storage and lifetime by controlled hierarchical submicron- and nano-structuring

Hollow and dense hierarchical SnS microspheres coated with a nitrogen doped carbon layer were synthesised, tested and compared as anodes in lithium ion battery half cells.

A Nitrogen-Doped Manganese Oxide Nanoparticles/Porous Carbon Nanosheets Hybrid Material: A High-Performance Anode for Lithium Ion Batteries

A nitrogen-doped MnO nanoparticles/ porous carbon nanosheets (N-MnO/PCS) composite was synthesized by the room-temperature redox reaction between KMnO₄ and PCS followed by a facile carbothermal reduction, and a subsequent coating process of urea onto MnO/PCS and heat treatment. N-MnO nanoparticles with a grain size of about 30 nm are homogenously embedded on the surface of the N-PCS, corresponding to a high loading of 50.09 wt.% in the resulting composite. Benefiting from the enhanced reaction kinetics as well as electrical conductivity and continuous transport pathways of Li⁺ /electron resulting from the N-doping and hybridization of the cross-linked porous carbon substrate, the as-synthesized N-MnO/PCS-1 electrode delivers a large reversible specific capacity (1497.2 mA h g^-1 at 100 mA g^-1 after 160 cycles), outstanding rate capacities (710.6 mA h g^-1 at 1 A g^-1 and 640.1 mA h g^-1 at 2 A g^-1 ) and long-term cycling stability with specific capacity (976 mA h g^-1 at 0.5 A g^-1 after cycling 300 cycles). The simple and green synthesis and electronic properties of this composite mean that it has great potential as a high-capacity anode material for practical application in large-scale energy storage devices.

Facile Approach for Synthesizing High-Performance MnO/C Electrodes from Rice Husk

Pyrolysis is an effective way to convert biomass into biofuel while obtaining highly porous active carbon materials. In this study, a facile approach, involving hydrothermal and pyrolysis steps, is described for preparing hybrid metal oxide nanoparticle-embedded porous hard carbon matrices (MnO/C) from the biowaste rice husk and organometallic precursors. It was found that the pyrolysis/calcination temperature had a strong influence over the microstructure, especially over the porosity, but also over the carbon content and crystallinity of the nanocomposites; hence, the electrical properties can be controlled. Galvanostatic measurements showed that the nanocomposite obtained at 600 °C exhibited the highest charge/discharge capacity and best stability, delivering an initial discharge capacity of 1104 mA·h·g-1 at a current density of 200 mA·g-1, and retaining a value of 830 mA·h·g-1 after 200 cycles, suggesting excellent cycle stability. A discharge capacity of 581 mA·h·g-1 was obtained even at a current density as high as 2400 mA·g-1, demonstrating superb rate capability. This outstanding electrochemical performance, ascribed to high electrochemical activity of the embedded MnO nanoparticles enhanced by electrical conductivity provided through the high surface area of the active porous carbon support, is discussed in relation to the microstructure of the nanocomposite.

Formaldehyde-Controlled Synthesis of Multishelled Hollow Mesoporous SiO2 Microspheres

We developed a facile one-pot method to synthesize multishelled hollow mesoporous SiO₂ microspheres (HMSs) with controllable interior structures including one-shell, double-shell, and yolk-shell. Single reagent formaldehyde could fully control the morphology of HMSs, in that formaldehyde was crucial to the SiO₂ precursor's hydrolysis rate and the template pore size.

A Mn3O4 nanospheres@rGO architecture with capacitive effects on high potassium storage capability

A two dimensional (2D) Mn₃O₄@rGO architecture has been investigated as an anode material for potassium-ion secondary batteries. Herein, we report the synthesis of a Mn₃O₄@rGO nanocomposite and its potassium storage properties. The strong synergistic interaction between high surface area reduced graphene oxide (rGO) sheets and Mn₃O₄ nanospheres not only enhances the potassium storage capacity but also improves the reaction kinetics by offering an increased electrode/electrolyte contact area and consequently reduces the ion/electron transport resistance. Spherical Mn₃O₄ nanospheres with a size of 30-60 nm anchored on the surface of rGO sheets deliver a high potassium storage capacity of 802 mA h g^-1 at a current density of 0.1 A g^-1 along with superior rate capability even at 10 A g^-1 (delivers 95 mA h g^-1) and cycling stability. A reversible potassium storage capacity of 635 mA h g^-1 is retained (90%) after 500 cycles even at a high current density of 0.5 A g^-1. Moreover, the spherical Mn₃O₄@rGO architecture not only offers facile potassium ion diffusion into the bulk but also contributes surface K⁺ ion storage. The obtained results demonstrate that the 2D spherical Mn₃O₄@rGO nanocomposite is a promising anode architecture for high performance KIBs.

1D Carbon-Based Nanocomposites for Electrochemical Energy Storage

Electrochemical energy storage (EES) devices have attracted immense research interests as an effective technology for utilizing renewable energy. 1D carbon-based nanostructures are recognized as highly promising materials for EES application, combining the advantages of functional 1D nanostructures and carbon nanomaterials. Here, the recent advances of 1D carbon-based nanomaterials for electrochemical storage devices are considered. First, the different categories of 1D carbon-based nanocomposites, namely, 1D carbon-embedded, carbon-coated, carbon-encapsulated, and carbon-supported nanostructures, and the different synthesis methods are described. Next, the practical applications and optimization effects in electrochemical energy storage devices including Li-ion batteries, Na-ion batteries, Li-S batteries, and supercapacitors are presented. After that, the advanced in situ detection techniques that can be used to investigate the fundamental mechanisms and predict optimization of 1D carbon-based nanocomposites are discussed. Finally, an outlook for the development trend of 1D carbon-based nanocomposites for EES is provided.

Uniform gallium oxyhydroxide nanorod anodes with superior lithium-ion storage

Exploration of a novel metal oxyhydroxide material provides potential candidates for lithium ion battery (LIB) anodes. In the present work, uniform GaOOH nanorods have been successfully synthesized via a simple hydrothermal method and employed as an anode material for LIBs for the first time. The obtained GaOOH nanorods show a high-purity phase with an average length of ∼1.4 μm and a width of ∼100 nm. As an anode, it delivers a stable capacity of ∼1089 mA h g^-1 at a 0.5 A g^-1 current density upon 300 cycles and a high rate capacity of ∼639 mA h g^-1 at 2 A g^-1, where the pseudocapacitance plays a dominant role with a capacity contribution ratio of about 83% at 2.0 mV s^-1. This enhanced storage performance can be attributed to a 1D nanostructure with efficient electron and ion transfer as well as strain relaxation upon multiple-cycling.

Two-Dimensional Ga2O3/C Nanosheets as Durable and High-Rate Anode Material for Lithium Ion Batteries

The self-healing feature of gallium (Ga) is unique, making Ga-based materials attract attention for their potential to solve the anode pulverization issue of lithium ion batteries. In this work, a hierarchical two-dimensional (2D) Ga₂O₃/C structure has been synthesized by a facile NaCl template method. Ga₂O₃ nanoparticles (3.8 nm) are uniformly embedded in 2D carbon nanosheets. The long horizontal length of the carbon nanosheets (10 μm) provides long-range electron conductivity, and the thin vertical thickness (75 nm) shortens the Li ion diffusion path. Benefited from the integrated 2D structure and the high electron conductivity, the obtained 2D Ga₂O₃/C nanosheets exhibit excellent overall performance, including high lithium storage capacity (1026 mAh g^-1 at 0.5 A g^-1), high rate capability (378 mAh g^-1 at 10.0 A g^-1), and high cyclability (500 cycles at 0.5 A g^-1). The lithiation/delithiation mechanism of 2D Ga₂O₃/C has been further studied with combined electrochemical and ex situ X-ray diffraction methods.

Engineering Na-Mo-O/Graphene Oxide Composites with Enhanced Electrochemical Performance for Lithium Ion Batteries

Sodium molybdate (Na−Mo−O) wrapped by graphene oxide (GO) composites have been prepared via a simple in‐situ precipitation method at room temperature. The composites are mainly constructed with one dimension (1D) ultra‐long sodium molybdate nanorods, which are wrapped by the flexible GO. The introduction of GO is expected to not merely provide more active sites for lithium‐ions storage, but also improve the charge transfer rate of the electrode. The testing electrochemical performances corroborated the standpoint: The Na−Mo−O/GO composites delivers specific capacities of 718 mAh g⁻¹ after 100 cycles at 100 mA g⁻¹, and 570 mAh g⁻¹ after 500 cycles at a high rate of 500 mA g⁻¹; for comparison, the bare Na−Mo−O nanorod shows a severe capacity decay, which deliver only 332 mAh g⁻¹ after 100 cycles at 100 mA g⁻¹. In view of the cost‐efficient and less time‐consuming in synthesis, and one‐step preparation without further treatment, these Na−Mo−O nanorods/GO composites present potential and prospective anodes for LIBs.

The rational design of hierarchical MoS2 nanosheet hollow spheres sandwiched between carbon and TiO2@graphite as an improved anode for lithium-ion batteries

Molybdenum disulfide (MoS₂) shows high capacity but suffers from poor rate capability and rapid capacity decay, which greatly limit its practical applications in lithium-ion batteries. Herein, we successfully prepared MoS₂ nanosheet hollow spheres encapsulated into carbon and titanium dioxide@graphite, denoted as TiO₂@G@MoS₂@C, via hydrothermal and polymerization approaches. In this hierarchical architecture, the MoS₂ hollow sphere was sandwiched by graphite and an amorphous carbon shell; thus, TiO₂@G@MoS₂@C exhibited effectively enhanced electrical conductivity and withstood the volume changes; moreover, the aggregation and diffusion of the MoS₂ nanosheets were restricted; this advanced TiO₂@G@MoS₂@C fully combined the advantages of a three-dimensional architecture, hollow structure, carbon coating, and a mechanically robust TiO₂@graphite support, achieving improved specific capacity and long-term cycling stability. In addition, it exhibited the high reversible specific capacity of 823 mA h g^-1 at the current density of 0.1 A g^-1 after 100 cycles, retaining almost 88% of the initial reversible capacity with the high coulombic efficiency of 99%.

A Double-Buffering Strategy to Boost the Lithium Storage of Botryoid MnOx /C Anodes

Transition metal oxides (TMOs) are regarded as promising candidates for anodes of lithium ion batteries, but their applications have been severely hindered by poor material conductivity and lithiated volume expansion. As a potential solution, herein is presented a facile approach, by electrospinning a manganese-based metal organic framework (Mn-MOF), to fabricate yolk-shell MnO_x nanostructures within carbon nanofibers in a botryoid morphology. While the yolk-shell structure accomodates the lithiated volume expansion of MnO_x , the fiber confinement ensures the structural integrity during charge/discharge, achieving a so-called double-buffering for cyclic volume fluctuation. The formation mechanism of the yolk-shell structure is well elucidated through comprehensive instrumental characterizations and cogitative control experiments, following a combined Oswald ripening and Kirkendall process. Outstanding electrochemical performances are demonstrated with prolonged stability over 1000 cycles, boosted by the double-buffering design, as well as the "breathing" effect of lithiation/delithiation witnessed by ex situ imaging. Both the fabrication methodology and electrochemical understandings gained here for nanostructured MnO_x can also be extended to other TMOs toward their ultimate implementation in high-performance lithium ion batteries (LIBs).