Free-Standing T-Nb₂O₅/Graphene Composite Papers with Ultrahigh Gravimetric/Volumetric Capacitance for Li-Ion Intercalation Pseudocapacitor

Enhancing the Lithium Storage Performance of the Nb2O5 Anode via Synergistic Engineering of Phase and Cu Doping

Nb2O5 has been viewed as a promising anode material for lithium-ion batteries by virtue of its appropriate redox potential and high theoretical capacity. However, it suffers from poor electric conductivity and low ion diffusivity. Herein, we demonstrate the controllable fabrication of Cu-doped Nb2O5 with orthorhombic (T-Nb2O5) and monoclinic (H-Nb2O5) phases through annealing the solvothermally presynthesized Nb2O5 precursor under different temperatures in air, and the Cu doping amount can be readily controlled by the concentration of the precursor solution, whose effect on the lithium storage behaviors of the Cu-doped Nb2O5 is thoroughly investigated. H-Nb2O5 shows obvious redox peaks (Nb5+/Nb4+ and Nb4+/Nb3+) with much higher capacity and better cycling stability than those for the widely investigated T-Nb2O5. When introducing appropriate Cu doping, the optimized H-Cu0.1-Nb2O5 electrode shows greatly enhanced conductivity and lower diffusion barrier as revealed by the theoretical calculations and electrochemical characterizations, delivering a high reversible capacity of 203.6 mAh g-1 and a high capacity retention of 140.8 mAh g-1 after 5000 cycles at 1 A g-1, with a high initial Coulombic efficiency of 91% and a high rate capacity of 144.2 mAh g-1 at 4 A g-1. As a demonstration for full-cell application, the H-Cu0.1-Nb2O5||LiFePO4 cell displays good cycling performance, exhibiting a reversible capacity of 135 mAh g-1 after 200 cycles at 0.2 A g-1. More importantly, this work offers a new synthesis protocol of the monoclinic Nb2O5 phase with high capacity retention and improved reaction kinetics.

Competitive Redox Chemistries in Vanadium Niobium Oxide for Ultrafast and Durable Lithium Storage

Niobium pentoxide (Nb2O5) anodes have gained increasing attentions for high-power lithium-ion batteries owing to the outstanding rate capability and high safety. However, Nb2O5 anode suffers poor cycle stability even after modified and the unrevealed mechanisms have restricted the practical applications. Herein, the over-reduction of Nb5+ has been demonstrated to be the critical reason for the capacity loss for the first time. Besides, an effective competitive redox strategy has been developed to solve the rapid capacity decay of Nb2O5, which can be achieved by the incorporation of vanadium to form a new rutile VNbO4 anode. The highly reversible V3+/V2+ redox couple in VNbO4 can effectively inhibit the over-reduction of Nb5+. Besides, the electron migration from V3+ to Nb5+ can greatly increase the intrinsic electronic conductivity for VNbO4. As a result, VNbO4 anode delivers a high capacity of 206.1 mAh g-1 at 0.1 A g-1, as well as remarkable cycle performance with a retention of 93.4% after 2000 cycles at 1.0 A g-1. In addition, the assembled lithium-ion capacitor demonstrates a high energy density of 44 Wh kg-1 at 5.8 kW kg-1. In summary, our work provides a new insight into the design of ultra-fast and durable anodes.

Pseudohexagonal Nb2O5 Anodes for Fast-Charging Potassium-Ion Batteries

High-rate batteries will play a vital role in future energy storage systems, yet while good progress is being made in the development of high-rate lithium-ion batteries, there is less progress with post-lithium-ion chemistry. In this study, we demonstrate that pseudohexagonal Nb₂O₅(TT-Nb₂O₅) can offer a high specific capacity (179 mAh g^-1 ∼ 0.3C), good lifetime, and an excellent rate performance (72 mAh g^-1 at ∼15C) in potassium-ion batteries (KIBs), when it is composited with a highly conductive carbon framework; this is the first reported investigation of TT-Nb₂O₅ for KIBs. Specifically, multiwalled carbon nanotubes are strongly tethered to Nb₂O₅ via glucose-derived carbon (Nb₂O₅@CNT) by a one-step hydrothermal method, which results in highly conductive and porous needle-like structures. This work therefore offers a route for the scalable production of a viable KIB anode material and hence improves the feasibility of fast-charging KIBs for future applications.

Effect of strontium doping on the electrochemical pseudocapacitance of Y1-xSrxMnO3-δ perovskites

Grid-scale bulk energy storage solutions are needed to utilize the full potential of renewable energy technologies. Pseudocapacitive electrochemical energy storage can play a vital role in developing efficient energy storage solutions. The use of perovskites as anion intercalation-type pseudocapacitor electrodes has received significant attention in recent years. In this study, Sr-doped YMnO₃i.e. Y_1-xSr_xMnO_3-δ perovskite was prepared by the solid-state ceramic route and studied for electrochemical pseudocapacitance in aqueous KOH electrolyte. Microstructures, morphologies, and electrochemical properties of these materials were investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance method. The formation of the mostly cubic phase, with 50% strontium doped YMnO₃ (YSMO-50) provides an equivalent three-dimensional network and superior conductivity due to Mn³⁺-O^2--Mn⁴⁺ hopping conduction. YSMO-50 exhibited low intrinsic resistance, 1.45 Ω cm^-2, and the highest specific capacity, 259.83 F g^-1 at a current density of 1 A g^-1 in 2 M KOH aqueous electrolyte. Redox-mediated interconversion of oxide to hydroxide (M²⁺O^2- + H₂O + e^- ↔ M⁺OH^- + OH^-) in aqueous media is shown to be the reason behind the high capacitance of YSMO-50. The excellent electrochemical performance of YSMOs was attributed to the reversible interconversion of oxide-ion into hydroxide ion coupled with surface redox reaction of Mn²⁺/Mn³⁺ and Mn³⁺/Mn⁴⁺ occurring during the charge-discharge process. The maximum energy density of 65.13 W h kg^-1 was achieved at a power density of 0.45 kW kg^-1 for an asymmetric mode, in which YSMO serves as a negative electrode and Activated carbon (AC) as a positive electrode in the PVA-KOH gel electrolyte. Our study reveals that the doping of low valence atom (Sr) at the A-site in perovskite manganites (YMnO₃) may be an effective tool to enhance the pseudocapacitive performance of perovskite-based electrodes.

Operando X-ray Studies of Ni-Containing Heteropolyvanadate Electrode for High-Energy Lithium-Ion Storage Applications

Ni-containing heteropolyvanadate, Na₆[NiV₁₄O₄₀], was synthesized for the first time to be applied in high-energy lithium storage applications as a negative electrode material. Na₆[NiV₁₄O₄₀] can be prepared via a facile solution process that is suitable for low-cost mass production. The as-prepared electrode provided a high capacity of approximately 700 mAh g^-1 without degradation for 400 cycles, indicating excellent cycling stability. The mechanism of charge storage was investigated using operando X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), transition X-ray microscopy (TXM), and density functional theory (DFT) calculations. The results showed that V⁵⁺ was reduced to V²⁺ during lithiation, indicating that Na₆[NiV₁₄O₄₀] is an insertion-type material. In addition, Na₆[NiV₁₄O₄₀] maintained its amorphous structure with negligible volume expansion/contraction during cycling. Employed as the negative electrode in a lithium-ion battery (LIB), the Na₆[NiV₁₄O₄₀]//LiFePO₄ full cell had a high energy density of 300 W h kg^-1. When applied in a lithium-ion capacitor, the Na₆[NiV₁₄O₄₀]//expanded mesocarbon microbead full cell displayed energy densities of 218.5 and 47.9 W h kg^-1 at power densities of 175.7 and 7774.2 W kg^-1, respectively. These findings reveal that the negative electrode material Na₆[NiV₁₄O₄₀] is a promising candidate for Li-ion storage applications.

A Mechanically Flexible Necklace-Like Architecture for Achieving Fast Charging and High Capacity in Advanced Lithium-Ion Capacitors

Integration of fast charging, high capacity, and mechanical flexibility into one electrode is highly desired for portable energy-storage devices. However, a high charging rate is always accompanied by capacity decay and cycling instability. Here, a necklace-structured composite membrane consisting of micron-sized FeSe₂ cubes uniformly threaded by carbon nanofibers (CNF) is reported. This unique electrode configuration can not only accommodate the volumetric expansion of FeSe₂ during the lithiation/delithiation processes for structural robustness but also guarantee ultrafast kinetics for Li⁺ entry. At a high mass loading of 6.2 mg cm^-2 , the necklace-like FeSe₂ @CNF electrode exhibits exceptional rate capability (80.7% capacity retention from 0.1 to 10 A g^-1 ) and long-term cycling stability (no capacity decay after 1100 charge-discharge cycles at 2 A g^-1 ). The flexible lithium-ion capacitor (LIC) fabricated by coupling a pre-lithiated FeSe₂ @CNF anode with a porous carbon cathode delivers impressive volumetric energy//power densities (98.4 Wh L^-1 at 157.1 W L^-1 , and 58.9 Wh L^-1 at 15714.3 W L^-1 ). The top performance, long-term cycling stability, low self-discharge rate, and high mechanical flexibility make it among the best LICs ever reported.

Cobalt vanadium chalcogenide microspheres decorated with dendrite-like fiber nanostructures for flexible wire-typed energy conversion and storage microdevices

The increasing energy demand for next-generation portable and miniaturized electronics has drawn tremendous attention to develop microscale energy storage and conversion devices with light weight and flexible characteristics. Herein, we report the preparation of flower-like cobalt vanadium selenide/nickel copper selenide (CoVSe/NiCuSe) microspheres with three-dimensional hierarchical structure of micropore growth on copper wire for a flexible fiber microsupercapacitor (microSC) and overall water splitting. The CoV-LDH microspheres are anchored on the dendrite-like NiCu nanostructured Cu wire using a hydrothermal method (CoV-LDH/NiCu@CW). The sulfidation and selenization of CoV-LDH/NiCu was carried out through the ion-exchange reaction of OH^- with sulfide and selenide ions to obtain CoVS/NiCuS@CW and CoVSe/NiCuSe@CW electrodes, respectively. Benefitting from the unique structure, the flower-like CoVSe/NiCuSe@CW microspheres exhibit better electrochemical performance compared with other as-prepared fiber-shaped electrodes. As an electrode active material for microSC, CoVSe/NiCuSe microspheres exhibit a specific capacitance of 35.40 F cm^-3 at 4 mA cm^-2, and maintain 281.25 F cm^-3 even at a high current density of 83 mA cm^-2, indicating outstanding charge storage capacitance and excellent rate capability. Moreover, the assembled flexible solid-state asymmetric microSCs based on flower-like CoVSe/NiCuSe microspheres-coated Cu wire as the positive electrode and polypyrrole/reduced graphene oxide-coated carbon fiber as the negative electrode manifests a maximum energy density of 20.17 mW h cm^-3 at a power density of 624.32 mW cm^-3 and remarkable cycling stability (96.7% after 5000 cycles) with good mechanical stability. As an electrocatalyst for oxygen and hydrogen evolution reactions in alkaline medium, the CoVSe/NiCuSe electrode delivers an overpotential of 297 mV and 165 mV at 100 mA cm^-2. Furthermore, the CoVSe/NiCuSe-based electrolysis cell for overall water splitting presents a low cell voltage (1.7 V at 50 mA cm^-2) as well as high durability.

Coupling High Rate Capability and High Capacity in an Intercalation-Type Sodium-Ion Hybrid Capacitor Anode Material of Hydrated Vanadate via Interlayer-Cation Engineering

Layered metal vanadates with intercalation pseudocapacitive behaviors show great promise for applications in sodium-ion hybrid capacitor anode materials due to their large interlayer distances, which benefit the fast Na⁺ solid-state diffusion. However, their charge storage capacity is significantly constrained by the limited available sites that allow the intercalation of Na⁺ ions. In this work, by engineering the interlayer cations, Ni_0.12Zn_0.2V₂O₅·1.07H₂O is designed as a high-performance anode material in sodium-ion hybrid capacitors. The Ni/Zn codoping in the layered vanadate leads to the integration of high rate capability and high specific capacity. Specifically, the spacious interlayer spacing and the pillaring effects of Zn ions together lead to the high rate performance and decent cycling stability, while the redox reactions of the interlayer Ni ions efficiently upgrade the charge storage capacity of this layered material. Accordingly, this work offers a promising avenue to further optimizing the Na⁺ storage performance of layered vanadates via interlayer-cation engineering.

Using Metal Cation to Control the Microstructure of Cobalt Oxide in Energy Conversion and Storage Applications

Herein, a facile and efficient synthesis of microstructured Co₃ O₄ for both supercapacitor and water-splitting applications is reported. Metal cations (Fe³⁺ , Cu²⁺ ) serve as structure-directing agents regulating the structure of Co compounds, which are subsequently annealed to yield Co₃ O₄ . Detailed characterizations and density functional theory (DFT) calculations reveal that the in situ Cl-doping introduces oxygen defects and provides abundant electroactive sites, and narrows the bandgap, which enhances the electron excitation of the as-formed Co₃ O₄ . The as-prepared Cl-doped Co₃ O₄ hierarchical nanospheres (Cl-Co₃ O₄ -h) display a high specific capacitance of 1629 F g^-1 at 1 A g^-1 as an electrode for supercapacitors, with excellent rate capability and cyclability. The Cl-Co₃ O₄ -h//activated carbon (AC) asymmetric supercapacitor (ASC) electrode achieves a specific capacitance of 237 F g^-1 at 1 A g^-1 , with an energy density of 74 Wh kg^-1 at a power density of 807 W kg^-1 and even maintains 47 Wh kg^-1 at the higher-power density of 24.2 kW kg^-1 . An integrated electrolyzer for water-splitting with Cl-Co₃ O₄ -h as both cathode and anode can be driven by Cl-Co₃ O₄ -h//AC ASC. The electrolyzer provides a high current density of 35 mA cm^-2 at a cell voltage of 1.6 V, with good current density retention over 50 h.

"Porous and Yet Dense" Electrodes for High-Volumetric-Performance Electrochemical Capacitors: Principles, Advances, and Challenges

With the ever-rapid miniaturization of portable, wearable electronics and Internet of Things, the volumetric performance is becoming a much more pertinent figure-of-merit than the conventionally used gravimetric parameters to evaluate the charge-storage capacity of electrochemical capacitors (ECs). Thus, it is essential to design the ECs that can store as much energy as possible within a limited space. As the most critical component in ECs, "porous and yet dense" electrodes with large ion-accessible surface area and optimal packing density are crucial to realize desired high volumetric performance, which have demonstrated to be rather challenging. In this review, the principles and fundamentals of ECs are first observed, focusing on the key understandings of the different charge storage mechanisms in porous electrodes. The recent and latest advances in high-volumetric-performance ECs, developed by the rational design and fabrication of "porous and yet dense" electrodes are then examined. Particular emphasis of discussions then concentrates on the key factors impacting the volumetric performance of porous carbon-based electrodes. Finally, the currently faced challenges, further perspectives and opportunities on those purposely engineered porous electrodes for high-volumetric-performance EC are presented, aiming at providing a set of guidelines for further design of the next-generation energy storage devices.

Recent Developments in Supercapacitor Electrodes: A Mini Review

The use of nonrenewable fossil fuels for energy has increased in recent decades, posing a serious threat to human life. As a result, it is critical to build environmentally friendly and low-cost reliable and renewable energy storage solutions. The supercapacitor is a future energy device because of its higher power density and outstanding cyclic stability with a quick charge and discharge process. Supercapacitors, on the other hand, have a lower energy density than regular batteries. It is well known that the electrochemical characteristic of supercapacitors is strongly dependent on electrode materials. The current review highlights advance in the TMOs for supercapacitor electrodes. In addition, the newly discovered hybrid/pseudo-supercapacitors have been discussed. Metal oxides that are employed as electrode materials are the focus of this study. The discovery of nanostructured electrode materials continues to be a major focus of supercapacitor research. To create high-performance electrode materials from a morphological standpoint, various efforts have been attempted. Lastly, we analyze the supercapacitor’s evolving trend and our perspective for the future generations of supercapacitors.

Insight into the effects of dislocations in nanoscale titanium niobium oxide (Ti2Nb14O39) anode for boosting lithium-ion storage

Defect engineering through induction of dislocations is an efficient strategy to design and develop an electrode material with enhanced electrochemical performance in energy storage technology. Yet, synthesis, comprehension, identification, and effect of dislocation in electrode materials for lithium-ion batteries (LIBs) are still elusive. Herein, we propose an ethanol-thermal method mediated with surfactant-template and subsequent annealing under air atmosphere to induce dislocation into titanium niobium oxide (Ti₂Nb₁₄O₃₉), resultant nanoscale-dislocated-Ti₂Nb₁₄O₃₉ (Nano-dl-TNO). High-resolution transmission electron microscope (HRTEM), fast Fourier transform (FFT), and Geometrical phase analysis (GPA) denote that the high dislocation density engraved with stacking faults forms into the Ti₂Nb₁₄O₃₉ lattice. The presence of dislocation could offer an additional active site for lithium-ion storage and tune the electrical and ionic properties of the Ti₂Nb₁₄O₃₉. The resultant Nano-dl-TNO delivers superior rate capability, high specific capacity, better cycling stability, and making Ti₂Nb₁₄O₃₉ a suitable candidate among fast-charging anode materials for lithium-ion batteries. Moreover, In-situ High-resolution transmission electron microscope (HRTEM) and Geometrical phase analysis (GPA) evinces that the removal of the dislocated area in the Nano-dl-TNO leads to the contraction of the lattice, alleviation of the total volume expansion, causing the symmetrization and preserves structural stability. The present findings and designed approach reveal the rose-colored perspective of dislocation engineering into mixed transition metal oxides as next-generation anodes for advanced lithium-ion batteries and all-solid-state lithium-ion batteries.

Advanced and Emerging Negative Electrodes for Li-Ion Capacitors: Pragmatism vs. Performance

Li-ion capacitors (LICs) are designed to achieve high power and energy densities using a carbon-based material as a positive electrode coupled with a negative electrode often adopted from Li-ion batteries. However, such adoption cannot be direct and requires additional materials optimization. Furthermore, for the desired device’s performance, a proper design of the electrodes is necessary to balance the different charge storage mechanisms. The negative electrode with an intercalation or alloying active material must provide the high rate performance and long-term cycling ability necessary for LIC functionality—a primary challenge for the design of these energy-storage devices. In addition, the search for new active materials must also consider the need for environmentally friendly chemistry and the sustainable availability of key elements. With these factors in mind, this review evaluates advanced and emerging materials used as high-rate anodes in LICs from the perspective of their practical implementation.

Novel aluminum vanadate as a cathode material for high-performance aqueous zinc-ion batteries

Rechargeable aqueous zinc-ion batteries (AZIBs) have garnered widespread attention as a new large-scale energy storage candidate owing to their low cost and high theoretical capacity. Because of the unique divalent state of Zn²⁺and the existence of a strong electrostatic repulsion phenomenon, researchers are currently focusing on how to prepare high-performance cathode materials. In this study, we synthesized aluminum vanadate (AlV₃O₉) as a cathode material for AZIBs using a solvothermal method. Al³⁺acted as a pillar in the resultant structure and stabilized it. Furthermore, this large interlayer spacing enhanced the ion diffusion coefficient and accelerated the ion transport process. Because of these advantages, the AlV₃O₉(AVO) cathode exhibited excellent electrochemical performance, including a high capacity of 421.0 mA h g^-1at 0.1 A g^-1and a stable rate capability of 348.2 mA h g^-1at 1 A g^-1. Moreover, it exhibited a specific capacity of 202 mA h g^-1even at a high current density of 3 A g^-1(the capacity retention rate reached 84.38% after 1600 cycles). The prepared ZIBs presented a high power density of 366.6 W kg^-1at an energy density of 286 W h kg^-1. These extraordinary results indicate the great application potential of AVO as a cathode material for AZIBs.

Lithium-Ion Capacitors: A Review of Design and Active Materials

Lithium-ion capacitors (LICs) have gained significant attention in recent years for their increased energy density without altering their power density. LICs achieve higher capacitance than traditional supercapacitors due to their hybrid battery electrode and subsequent higher voltage. This is due to the asymmetric action of LICs, which serves as an enhancer of traditional supercapacitors. This culminates in the potential for pollution-free, long-lasting, and efficient energy-storing that is required to realise a renewable energy future. This review article offers an analysis of recent progress in the production of LIC electrode active materials, requirements and performance. In-situ hybridisation and ex-situ recombination of composite materials comprising a wide variety of active constituents is also addressed. The possible challenges and opportunities for future research based on LICs in energy applications are also discussed.

Polyaniline–niobium oxide nanohybrids with photocatalytic activity under visible light irradiation

In this study, we reported the production of polyaniline and niobium oxide hybrids synthesized by the direct reaction between a niobium peroxyoxalate complex and anilinium salt in an aqueous medium.

Titanium niobate (Ti2Nb10O29) anchored on nitrogen-doped carbon foams as flexible and self-supported anode for high-performance lithium ion batteries

Assembling active materials on flexible conductive matrixes for fabricating high-rate, self-supported and durable anodes is essential for the development of high-power flexible lithium-ion batteries. In this study, we report an efficient combinational strategy for producing hybrid composites (TNO@MCF) of Ti₂Nb₁₀O₂₉ (TNO) anchored on melamine carbon foam (MCF) via a hydrothermal method. The N-doped MCF not only showed good electronic conductivity and flexibility, but also improved the ion transport performance of the composites. The TNO@MCF electrode exhibited remarkably high rate capacities (327 mA h g^-1 at 1 C, and 205 mA h g^-1 at 40 C) and excellent cycling stability with a high capacity retention of 81.4% after 1000 cycles at 10 C. After 100 compression-rebound cycles, the TNO@MCF electrode showed a reversible capacity of 315 mA h g^-1 at 1 C and exhibited a capacity retention of 72.3% for 1000 cycles at 10 C. This compressible structure design could provide guidelines for manufacture of other flexible electrodes for energy storage devices.

New Limits for Stability of Supercapacitor Electrode Material Based on Graphene Derivative

Supercapacitors offer a promising alternative to batteries, especially due to their excellent power density and fast charging rate capability. However, the cycling stability and material synthesis reproducibility need to be significantly improved to enhance the reliability and durability of supercapacitors in practical applications. Graphene acid (GA) is a conductive graphene derivative dispersible in water that can be prepared on a large scale from fluorographene. Here, we report a synthesis protocol with high reproducibility for preparing GA. The charging/discharging rate stability and cycling stability of GA were tested in a two-electrode cell with a sulfuric acid electrolyte. The rate stability test revealed that GA could be repeatedly measured at current densities ranging from 1 to 20 A g-1 without any capacitance loss. The cycling stability experiment showed that even after 60,000 cycles, the material kept 95.3% of its specific capacitance at a high current density of 3 A g-1. The findings suggested that covalent graphene derivatives are lightweight electrode materials suitable for developing supercapacitors with extremely high durability.

Recovery of niobium and tantalum by solvent extraction from Sn-Ta-Nb mining tailings

The slag from the extraction processes of metals from their ores may contain valuable components that, if adequately recovered, can be reintroduced in the technological life cycle. This is the case for the material obtained in Penouta mines in the North of Spain. These mineral sites are a main source of tin obtained from cassiterite. The mineral is submitted to a pyrometallurgical process to separate tin, however cassiterite is not the only mineral present in the veins, and large amounts of other minerals are normally discarded, constituting the slag. In the present case, besides cassiterite, one of the most abundant minerals in the ore is columbo tantalite, the source of the strategic coltan. In this work the raw material (slag) has been treated by acid leaching, using HF/H₂SO₄ as the leaching agent. Then liquid–liquid extraction of Nb and Ta was performed, with Cyanex®923 extractant, so that both metals were obtained separately. Then they were precipitated from the corresponding aqeuous solution, and calcined in order to yield Nb₂O₅ of 98.5% purity and tantalum salt, after calcination and purification, of 97.3% purity. The process described in this work opens a possibility to produce high quality materials that are considered critical by the EU from alternative sources exempt of criticality factors.

The slag from the extraction processes of metals from their ores may contain valuable components that, if adequately recovered, can be reintroduced in the technological life cycle.

Phononics of Graphene and Related Materials

In this Perspective, I present a concise account concerning the emergence of the research field investigating the phononic and thermal properties of graphene and related materials, covering the refinement of our understanding of phonon transport in two-dimensional material systems. The initial interest in graphene originated from its unique linear energy dispersion for electrons, revealed in exceptionally high electron mobility, and other exotic electronic and optical properties. Electrons are not the only elemental excitations influenced by a reduction in dimensionality. Phonons-quanta of crystal lattice vibrations-also demonstrate an extreme sensitivity to the number of atomic planes in the few-layer graphene, resulting in unusual heat conduction properties. I outline recent theoretical and experimental developments in the field and discuss how the prospects for the mainstream electronic application of graphene, enabled by its high electron mobility, gradually gave way to emerging real-life products based on few-layer graphene, which utilize its unique heat conduction rather than its electrical conduction properties.

Spherical Sb Core/Nb2O5-C Double-Shell Structured Composite as an Anode Material for Li Secondary Batteries

Antimony (Sb)-based materials are considered to be attractive for use in Li secondary battery anodes because of their high capacity. However, their huge volume change during Li insertion-extraction cycling limits their cycle performance. The Sb-active material can be combined with intercalation-based active materials to address these issues. In this study, spherical Sb core/Nb2O5 shell structured composite materials were synthesized through a simple solvothermal process and a carbon coating was simultaneously added during heat treatment using a naphthalene precursor. The resulting double-shelled materials were characterized with X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and electron microscopy. The electrochemical test results showed that a reversible capacity of more than 450 mAh g−1 was retained after 100 cycles. This improved performance is ascribed to the double-shelled structure. The large volume change of the nano-sized Sb core material was alleviated by the double-shelled structure, which consisted of crystalline orthorhombic Nb2O5 and amorphous carbon. The shell materials also aided rapid charge transport.

Biomass-Derived Carbons for Sodium-Ion Batteries and Sodium-Ion Capacitors

In the past decade, the rapid development of portable electronic devices, electric vehicles, and electrical devices has stimulated extensive interest in fundamental research and the commercialization of electrochemical energy-storage systems. Biomass-derived carbon has garnered significant research attention as an efficient, inexpensive, and eco-friendly active material for energy-storage systems. Therefore, high-performance carbonaceous materials, derived from renewable sources, have been utilized as electrode materials in sodium-ion batteries and sodium-ion capacitors. Herein, the charge-storage mechanism and utilization of biomass-derived carbon for sodium storage in batteries and capacitors are summarized. In particular, the structure-performance relationship of biomass-derived carbon for sodium storage in the form of batteries and capacitors is discussed. Despite the fact that further research is required to optimize the process and application of biomass-derived carbon in energy-storage devices, the current review demonstrates the potential of carbonaceous materials for next-generation sodium-related energy-storage applications.

Two-Dimensional Transition Metal Chalcogenides for Alkali Metal Ions Storage

On the heels of exacerbating environmental concerns and ever-growing global energy demand, development of high-performance renewable energy-storage and -conversion devices has aroused great interest. The electrode materials, which are the critical components in electrochemical energy storage (EES) devices, largely determine the energy-storage properties, and the development of suitable active electrode materials is crucial to achieve efficient and environmentally friendly EES technologies albeit the challenges. Two-dimensional transition-metal chalcogenides (2D TMDs) are promising electrode materials in alkali metal ion batteries and supercapacitors because of ample interlayer space, large specific surface areas, fast ion-transfer kinetics, and large theoretical capacities achieved through intercalation and conversion reactions. However, they generally suffer from low electronic conductivities as well as substantial volume change and irreversible side reactions during the charge/discharge process, which result in poor cycling stability, poor rate performance, and low round-trip efficiency. In this Review, recent advances of 2D TMDs-based electrode materials for alkali metal-ion energy-storage devices with the focus on lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), potassium-ion batteries (PIBs), high-energy lithium-sulfur (Li-S), and lithium-air (Li-O₂ ) batteries are described. The challenges and future directions of 2D TMDs-based electrode materials for high-performance LIBs, SIBs, PIBs, Li-S, and Li-O₂ batteries as well as emerging alkali metal-ion capacitors are also discussed.

Stitching of Zn3(OH)2V2O7·2H2O 2D Nanosheets by 1D Carbon Nanotubes Boosts Ultrahigh Rate for Wearable Quasi-Solid-State Zinc-Ion Batteries

Several layer-structured vanadates of two-dimensional (2D) nanosheet morphologies have been investigated recently for flexible quasi-solid-state aqueous zinc-ion batteries (ZIBs), where one of the challenging issues is the poor electronic conductivity and mechanical stability especially in the cross-2D nanosheet direction, leading to insufficient rate capability and mechanical stability and shortened cycle life. Herein, we have devised a strategy of using one-dimensional (1D) carbon nanotubes (CNTs) to stitch zinc pyrovanadate (Zn₃(OH)₂V₂O₇·2H₂O, CNT-stitched ZVO) 2D nanosheets that are directly grown on oxidized CNT fiber (CNT-stitched ZVO NSs@OCNT fiber). With the CNT-stitched 2D nanosheet structure, the open frameworks of ZVO provide required spacing for reversible Zn²⁺ (de)intercalation, and the stitching CNTs offer the desperately needed electronic conductivity and mechanical robustness across the ZVO 2D nanosheets. As a result, the fiber-shaped quasi-solid-state ZIB, assembled using the CNT-stitched ZVO NSs@OCNT as the cathode and Zn NSs@CNT fiber (electrodeposited zinc nanosheets on CNT fiber) as the anode, demonstrates an ultrahigh rate capability (69.7% retention after a 100-fold increase in current density), an impressively stack volumetric energy density of 71.6 mWh cm^-3, together with a long-term stability (88.6% retention after 2000 cycles). The present work proves the proof-of-concept of developing 2D nanosheets purposely stitched together by 1D conducting nanotubes/nanowires as a class of advanced cathodes for quasi-solid-state ZIBs in future portable electronics.

Ti3C2Tx MXene Interface Layer Driving Ultra-Stable Lithium-Iodine Batteries with Both High Iodine Content and Mass Loading

Lithium-iodine (Li-I₂) batteries are promising candidates for next-generation electrochemical energy storage systems due to their high energy density and the excellent kinetic rates of I₂ cathodes. However, dissolution of iodine and iodide has hindered their widespread adoption for practical applications. Herein, a Ti₃C₂T_x MXene foam with a three-dimensional hierarchical porous architecture is proposed as a cathode-electrolyte interface layer in Li-I₂ batteries, enabling high-rate and ultrastable cycling performance at a high iodine content and loading mass. Theoretical calculations and empirical characterizations indicate that Ti₃C₂T_x MXene sheets with high metallic conductivity not only provide strong chemical binding with iodine species to suppress the shuttle effect but also facilitate fast redox reactions during cell cycling. As a result, the Li-I₂ battery using a cathode with 70 wt % I₂ cycled stably for over 1000 cycles at a rate of 2 C, even at an ultrahigh loading mass of 5.2 mg cm^-2. To the best of the authors' knowledge, this is the highest reported loading at such a high iodine content. This work suggests that using a Ti₃C₂T_x MXene interface layer can enable the design and application of high-energy Li-I₂ batteries.

Synthesis of CoTe nanowires: a new electrode material for supercapacitor with high stability and high performance

Highly dispersed CoTe electrode material were successfully prepared by using a facile one-step solvothermal process without any surfactants. Compared with the conventional hydrothermally prepared irregularly-shaped CoTe, a regular nanowire-formed CoTe can be obtained by a solvothermal process using ethylene glycol as a solvent. The prepared CoTe nanowire electrode can exhibit a relatively high specific capacity of 643.6 F g^-1 at a current density of 1 A g^-1 and remarkable cyclic stability with 76.9% of its specific capacitance retention after 5000 cycles at a high current density of 5 A g^-1. Besides, even at the high current density of 20 A g^-1, the specific capacitance of CoTe nanowire electrode still has 90.2% retention relative to 1 A g^-1, showing an excellent rate performance. In order to enlarge the potential window to increase the energy density, an asymmetric supercapacitor (ASC) is assembled by applying CoTe nanowires and activated carbon as the positive electrode and the negative electrode in 3 M KOH, which can enlarge the operating voltage to as high as 1.6 V, and shows a specific capacity of 92.5 F g^-1 with an energy density of 32.9 Wh kg^-1 and power density of 800.27 W kg^-1 at 1 A g^-1, and even after 5000 cycles of charge/discharge at 5 A g^-1, the ASC still retains 90.5% of its initial specific capacitance, showing excellent cycle stability.

Copper, zinc, and manganese niobates (CuNb2O6, ZnNb2O6, and MnNb2O6): structural characteristics, Li+ storage properties, and working mechanisms

Niobium-based oxides are considered promising anode materials for Li-ion batteries due to their high capacities, good cyclability, and excellent safety.

Orthorhombic Nb2O5-x for Durable High-Rate Anode of Li-Ion Batteries

Li₄Ti₅O₁₂ anode can operate at extraordinarily high rates and for a very long time, but it suffers from a relatively low capacity. This has motivated much research on Nb₂O₅ as an alternative. In this work, we present a scalable chemical processing strategy that maintains the size and morphology of nano-crystal precursor but systematically reconstitutes the unit cell composition, to build defect-rich porous orthorhombic Nb₂O_5-x with a high-rate capacity many times those of commercial anodes. The procedure includes etching, proton ion exchange, calcination, and reduction, and the resulting Nb₂O_5-x has a capacity of 253 mA h g^-1 at 0.5C, 187 mA h g^-1 at 25C, and 130 mA h g^-1 at 100C, with 93.3% of the 25C capacity remaining after cycling for 4,000 times. These values are much higher than those reported for Nb₂O₅ and Li₄Ti₅O₁₂, thanks to more available surface/sub-surface reaction sites and significantly improved fast ion and electron conductivity.

Coupling Niobia Nanorods with a Multicomponent Carbon Network for High Power Lithium-Ion Batteries

High power lithium-ion batteries require highly conductive electrodes. For an active electrode material that has limited electron conductivity, it is critical to build a carbon network that is not only highly conductive itself but also highly compatible with the electroactive material for efficient interfacial charge transfer. Herein, we design a multicomponent carbon network that is optimized for electrical coupling with the electroactive Nb₂O₅ nanorods for efficient electron injection. The self-support electrode is constructed by using 0D polypyrrole-derived (Ppy) carbon nanoparticles as glue to bind the Nb₂O₅ nanorods with 1D carbon nanotubes (CNTs) and 2D graphene nanosheets (GNSs). The 0D carbon nanoparticles also cross-link 1D CNTs with 2D GNSs, which can effectively prevent the GNSs from aggregation and form the 3D CNT/GNS network that provides continuous electronic and ionic pathways. This 3D Nb₂O₅@C self-support electrode exhibits a high discharge capacity of 246.3 mA h g^-1 at 0.5 C and 100 mA h g^-1 at 20 C and excellent Coulombic efficiency of 99.98% at 20 C. Even increasing the mass loading to 7.1 mg cm^-2, the Nb₂O₅@C electrode can still reach a discharge capacity of 172.4 mA h g^-1 at 0.5 C after 100 cycles. A high power density of 1043 W kg^-1 can be achieved at an energy density of 104.3 W h kg^-1 based on the electrode weight, which is among the highest values demonstrated so far for Nb₂O₅ electrodes. The results pave the way toward practical applications of Nb₂O₅ anodes in high-power lithium-ion batteries.

A high-power lithium-ion hybrid capacitor based on a hollow N-doped carbon nanobox anode and its porous analogue cathode

Developing advanced lithium-ion hybrid capacitors (LIHCs) has a critical challenge of matching kinetics and capacity between the battery-type anode and the capacitive cathode. In this work, a novel "dual carbon" LIHC configuration is constructed to overcome such a discrepancy. Specifically, hollow nitrogen-doped carbon nanoboxes (HNCNBs) are synthesized by a simple template-assisted strategy. As an anode material (0.01-3 V vs. Li/Li⁺), the HNCNB electrode exhibits high specific capacity (850 mA h g^-1 at 0.1 A g^-1) and superior rate capability (321 mA h g^-1 at 20 A g^-1). After alkaline activation, the HNCNBs become highly porous (PHNCNBs), which offers better capacitance performance within the potential window from 2.5 to 4.5 V (vs. Li/Li⁺) than commercial activated carbon (AC). Coupling a pre-lithiated HNCNB anode with a PHNCNB cathode forms a dual-carbon LIHC. Since the similar hollow structure in both electrodes could diminish the diffusion distance, the as-prepared HNCNB//PHNCNB LIHC provides high energy densities of 148.5 and 112.1 W h kg^-1 at power densities of 250 and 25 000 W kg^-1, respectively, together with long-term cycling stability, which efficiently bridges the gap between supercapacitors and lithium ion batteries. Furthermore, the self-discharge behavior and the temperature-dependent performance are also investigated.

Towards fast-charging technologies in Li+/Na+ storage: from the perspectives of pseudocapacitive materials and non-aqueous hybrid capacitors

Since the discovery of the pseudocapacitive behavior in RuO₂ by Sergio Trasatti and Giovanni Buzzanca in 1971, materials with pseudocapacitance have been regarded as promising candidates for high-power energy storage. Pseudocapacitance-involving energy storage is predominantly based on faradaic redox reactions, but at the same time the charge storage is not limited by solid-state ion diffusion. Besides the search for pseudocapacitive materials, their implementation into non-aqueous hybrid capacitors stands for the strategy to increase power density by a rational design of the battery structure. Composed of a battery-type anode and a capacitor-type cathode, such devices show great promise to integrate the merits of both batteries and capacitors. Today, the availability of fast-charging technologies is of fundamental importance for establishing electric vehicles on a mass scale. Therefore, from the perspective of materials and battery design, understanding the basics and the recent developments of pseudocapacitive materials and non-aqueous hybrid capacitors is of great importance. With this goal in mind, we introduce here the fundamentals of pseudocapacitance and non-aqueous hybrid capacitors. In addition, we provide an overview of the latest developments in this fast growing research field.

Path towards graphene commercialization from lab to market

The ground-breaking demonstration of the electric field effect in graphene reported more than a decade ago prompted the strong push towards the commercialization of graphene as evidenced by a wealth of graphene research, patents and applications. Graphene flake production capability has reached thousands of tonnes per year, while continuous graphene sheets of tens of metres in length have become available. Various graphene technologies developed in laboratories have now transformed into commercial products, with the very first demonstrations in sports goods, automotive coatings, conductive inks and touch screens, to name a few. Although challenges related to quality control in graphene materials remain to be addressed, the advancement in the understandings of graphene will propel the commercial success of graphene as a compelling technology. This Review discusses the progress towards commercialization of graphene for the past decade and future perspectives.

S-Doped Carbon Fibers Uniformly Embedded with Ultrasmall TiO2 for Na+ /Li+ Storage with High Capacity and Long-Time Stability

Building a rechargeable battery with high capacity, high energy density, and long lifetime contributes to the development of novel energy storage devices in the future. Although carbon materials are very attractive anode materials for lithium-ion batteries (LIBs), they present several deficiencies when used in sodium-ion batteries (SIBs). The choice of an appropriate structural design and heteroatom doping are critical steps to improve the capacity and stability. Here, carbon-based nanofibers are produced by sulfur doping and via the introduction of ultrasmall TiO₂ nanoparticles into the carbon fibers (CNF-S@TiO₂ ). It is discovered that the introduction of TiO₂ into carbon nanofibers can significantly improve the specific surface area and microporous volume for carbon materials. The TiO₂ content is controlled to obtain CNF-S@TiO₂ -5 to use as the anode material for SIBs/LIBs with enhanced electrochemical performance in Na⁺ /Li⁺ storage. During the charge/discharge process, the S-doping and the incorporation of TiO₂ nanoparticles into carbon fibers promote the insertion/extraction of the ions and enhance the capacity and cycle life. The capacity of CNF-S@TiO₂ -5 can be maintained at ≈300 mAh g^-1 over 600 cycles at 2 A g^-1 in SIBs. Moreover, the capacity retention of such devices is 94%, showing high capacity and good stability.