Sulfur‐Impregnated,Sandwich‐Type,Hybrid Carbon Nanosheets with Hierarchical Porous Structure for High‐Performance Lithium‐Sulfur Batteries

Sandwich‐type hybrid carbon nanosheets (SCNMM) consisting of graphene and micro/mesoporous carbon layer are fabricated via a double template method using graphene oxide as the shape‐directing agent and SiO₂ nanoparticles as the mesoporous guide. The polypyrrole synthesized in situ on the graphene oxide sheets is used as a carbon precursor. The micro/mesoporous strcutures of the SCNMM are created by a carbonization process followed by HF solution etching and KOH treatment. Sulfur is impregnated into the hybrid carbon nanosheets to generate S@SCNMM composites for the cathode materials in Li‐S secondary batteries. The microstructures and electrochemical performance of the as‐prepared samples are investigated in detail. The hybrid carbon nanosheets, which have a thickness of about 10–25 nm, high surface area of 1588 m² g^?1, and broad pore size distribution of 0.8–6.0 nm, are highly interconnected to form a 3D hierarchical structure. The S@SCNMM sample with the sulfur content of 74 wt% exhibits excellent electrochemical performance, including large reversible capacity, good cycling stability and coulombic efficiency, and good rate capability, which is believed to be due to the structure of hybrid carbon materials with hierarchical porous structure, which have large specific surface area and pore volume.     

Ligand‐Assisted Assembly Approach to Synthesize Large‐Pore Ordered Mesoporous Titania with Thermally Stable and Crystalline Framework

A novel ligand‐assisted assembly approach is demonstrated for the synthesis of thermally stable and large‐pore ordered mesoporous titanium dioxide with a highly crystalline framework by using diblock copolymer poly(ethylene oxide)‐b‐polystyrene (PEO‐b‐PS) as a template and titanium isopropoxide (TIPO) as a precursor. Small‐angle X‐ray scattering, X‐ray diffraction (XRD), transmission electron microscopy (TEM), high‐resolution scanning electron microscopy, and N₂‐sorption measurements indicate that the obtained TiO₂ materials possess an ordered primary cubic mesostructure with large, uniform pore diameters of about 16.0 nm, and high Brunauer–Emmett–Teller surface areas of ～112 m² g^?1, as well as high thermal stability (～700 °C). High resolution TEM and wide‐angle XRD measurements clearly illustrate the high crystallinity of the mesoporous titania with an anatase structure in the pore walls. It is worth mentioning that, in this process, in addition to tetrahydrofuran as a solvent, acetylacetone was employed as a coordination agent to avoid rapid hydrolysis of the titanium precursor. Additionally, stepped evaporation and heating processes were adopted to control the condensation rate and facilitate the assembly of the ordered mesostructure, and ensure the formation of fully polycrystalline anatase titania frameworks without collapse of the mesostructure. By employing the obtained mesoporous and crystallized TiO₂ as the photoanode in a dye‐sensitized solar cell, a high power‐conversion efficiency (5.45%) can be achieved in combination with the N719 dye, which shows that this mesoprous titania is a great potential candidate as a catalyst support for photonic‐conversion applications.     

Surface Engineering Strategies of Layered LiCoO2 Cathode Material to Realize High‐Energy and High‐Voltage Li‐Ion Cells

Battery industries and research groups are further investigating LiCoO₂ to unravel the capacity at high‐voltages (>4.3 vs Li). The research trends are towards the surface modification of the LiCoO₂ and stabilize it structurally and chemically. In this report, the recent progress in the surface‐coating materials i.e., single‐element, binary, and ternary hybrid‐materials etc. and their coating methods are illustrated. Further, the importance of evaluating the surface‐coated LiCoO₂ in the Li‐ion full‐cell is highlighted with our recent results. Mg,P‐coated LiCoO₂ full‐cells exhibit excellent thermal stability, high‐temperature cycle and room‐temperature rate capabilities with high energy‐density of ≈1.4 W h cc^?1 at 10 C and 4.35 V. Besides, pouch‐type full‐cells with high‐loading (18 mg cm^?2) electrodes of layered‐Li(Ni,Mn)O₂ ‐coated LiCoO₂ not only deliver prolonged cycle‐life at room and elevated‐temperatures but also high energy‐density of ≈2 W h cc^?1 after 100 cycles at 25 °C and 4.47 V (vs natural graphite). The post‐mortem analyses and experimental results suggest enhanced electrochemical performances are attributed to the mechanistic behaviour of hybrid surface‐coating layers that can mitigate undesirable side reactions and micro‐crack formations on the surface of LiCoO₂ at the adverse conditions. Hence, the surface‐engineering of electrode materials could be a viable path to achieve the high‐energy Li‐ion cells for future applications.     

Facile preparation of magnetic graphene double‐sided mesoporous composites for the selective enrichment and analysis of endogenous peptides

In this work, magnetic graphene double‐sided mesoporous nanocomposites (mag‐graphene@mSiO₂) were synthesized by coating a layer of mesoporous silica materials on each side of magnetic grapheme. The surfactant (CTAB) mediated sol‐gel coating was performed using tetraethyl orthosilicate as the silica source. The as‐made magnetic graphene double‐sided mesoporous silica composites were treated with high‐temperature calcination to remove the hydroxyl on the surface. The novel double‐sided materials possess high surface area (167.8 cm²/g) and large pore volume (0.2 cm³/g). The highly open pore structure presents uniform pore size (3.2 nm) and structural stability. The hydrophobic interior pore walls could ensure an efficient adsorption of target molecules through hydrophobic–hydrophobic interaction. At the same time, the magnetic Fe₃O₄ particles on both sides of the materials could simplify the process of enrichment, which plays an important role in the treatment of complex biological samples. The magnetic graphene double‐sided nanocomposites were successfully applied to size‐selective and specific enrichment of peptides in standard peptide mixtures, protein digest solutions, and human urine samples. Finally, the novel material was applied to selective enrichment of endogenous peptides in mouse brain tissue. The enriched endogenous peptides were then analyzed by LC‐MS/MS, and 409 endogenous peptides were detected and identified. The results demonstrate that the as‐made mag‐graphene@mSiO₂ have powerful potential for peptidome research.     

Grafting Benzenediazonium Tetrafluoroborate onto LiNixCoyMnzO2 Materials Achieves Subzero‐Temperature High‐Capacity Lithium‐Ion Storage via a Diazonium Soft‐Chemistry Method

Subzero‐temperature Li‐ion batteries (LIBs) are highly important for specific energy storage applications. Although the nickel‐rich layered lithium transition metal oxides(LiNi_xCo_yMn_zO₂) (LNCM) (x > 0.5, x + y +z = 1) are promising cathode materials for LIBs, their very slow Li‐ion diffusion is a main hurdle on the way to achieve high‐performance subzero‐temperature LIBs. Here, a class of low‐temperature organic/inorganic hybrid cathode materials for LIBs, prepared by grafting a conducting polymer coating on the surface of 3 µm sized LiNi_0.6Co_0.2Mn_0.2O₂ (LNCM‐3) material particles via a greener diazonium soft‐chemistry method is reported. Specifically, LNCM‐3 particles are uniformly coated with a thin polyphenylene film via the spontaneous reaction between LNCM‐3 and C₆H₅N₂⁺BF₄^?. Compared with the uncoated one, the polyphenylene‐coated LNCM‐3 (polyphenylene/LNCM‐3) has shown much improved low‐temperature discharge capacity (≈148 mAh g^?1 at 0.1 C, ?20 °C), outstanding rate capability (≈105 mAh g^?1 at 1 C, ?20 °C), and superior low‐temperature long‐term cycling stability (capacity retention is up to 90% at 0.5 C over 1150 cycles). The low‐temperature performance of polyphenylene/LNCM‐3 is the best among the reported state‐of‐the art cathode materials for LIBs. The present strategy opens up a new avenue to construct advanced cathode materials for wider range applications.     

Free‐Standing 3D Nanoporous Duct‐Like and Hierarchical Nanoporous Graphene Films for Micron‐Level Flexible Solid‐State Asymmetric Supercapacitors

High energy density and power density within a limited volume of flexible solid‐state supercapacitors are highly desirable for practical applications. Here, free‐standing high‐quality 3D nanoporous duct‐like graphene (3D‐DG) films are fabricated with high flexibility and robustness as the backbones to deposit flower‐like MnO₂ nanosheets (3D‐DG@MnO₂). The 3D‐DG is the ideal support for the deposition of large amount of active materials because of its large surface area, appropriate pore structure, and negligible volume compared with other kinds of carbon backbones. Moreover, the 3D‐DG preserve the distinctive 2D coherent electronic properties of graphene, in which charge carriers move rapidly with a small resistance through the high‐quality and continuous chemical vapor deposition‐grown graphene building blocks, which results in a high rate performance. Marvelously, ultrathin (≈50 μm) flexible solid‐state asymmetric supercapacitors (ASCs) using 3D‐DG@MnO₂ as the positive electrode and 3D hierarchical nanoporous graphene films as the negative electrode display ultrahigh volumetric energy density (28.2 mW h cm^?3) and power density (55.7 W cm^?3) at 2.0 V. Furthermore, as‐prepared ASCs show high cycle stability clearly demonstrating their broad applications as power supplies in wearable electronic devices.     

Superior Multifunctional Activity of Nanoporous Carbons with Widely Tunable Porosity: Enhanced Storage Capacities for Carbon‐Dioxide,Hydrogen, Water,and Electric Charge

Nanoporous carbons (NPCs) with engineered specific pore sizes and sufficiently high porosities (both specific surface area and pore volume) are necessary for storing energy in the form of electric charges and molecules. Herein, NPCs, derived from biomass pine‐cones, coffee‐grounds, graphene‐oxide and metal‐organic frameworks, with systematically increased pore width (<1.0 nm to a few nm), micropore volume (0.2–0.9 cm³ g^?1) and specific surface area (800–2800 m² g^?1) are presented. Superior CO₂, H_2, and H₂O uptakes of 35.0 wt% (≈7.9 mmol g^?1 at 273 K), 3.0 wt% (at 77 K) and 85.0 wt% (at 298 K), respectively at 1 bar, are achieved. At controlled microporosity, supercapacitors deliver impressive performance with a capacity of 320 and 230 F g^?1 at 500 mA g^?1, in aqueous and organic electrolytes, respectively. Excellent areal capacitance and energy density (>50 Wh kg^?1 at high power density, 1000 W kg^?1) are achieved to form the highest reported values among the range of carbons in the literature. The noteworthy energy storage performance of the NPCs for all five cases (CO₂, H₂, H₂O, and capacitance in aqueous and organic electrolytes) is highlighted by direct comparison to numerous existing porous solids. A further analysis on the specific pore type governed physisorption capacities is presented.     

High Capacity All‐Solid‐State Lithium Batteries Enabled by Pyrite‐Sulfur Composites

As the theoretical limit of intercalation material‐based lithium‐ion batteries is approached, alternative chemistries based on conversion reactions are presently considered. The conversion of sulfur is particularly appealing as it is associated with a theoretical gravimetric energy density up to 2510 Wh kg^?1. In this paper, three different carbon‐iron disulfide‐sulfur (C‐FeS₂‐S) composites are proposed as alternative positive electrode materials for all‐solid‐state lithium‐sulfur batteries. These are synthesized through a facile, low‐cost, single‐step ball‐milling procedure. It is found that the crystalline structure (evaluated by X‐ray diffraction) and the morphology of the composites (evaluated by scanning electron microscopy) are greatly influenced by the FeS₂:S ratio. Li/LiI‐Li₃PS₄/C‐FeS₂‐S solid‐state cells are tested under galvanostatic conditions, while differential capacity plots are used to discuss the peculiar electrochemical features of these novel materials. These cells deliver capacities as high as 1200 mAh g_(FeS2+S)^?1 at the intermediate loading of 1 mg cm^?2 (1.2 mAh cm^?2), and up to 3.55 mAh cm^?2 for active material loadings as high as 5 mg cm^?2 at 20 °C. Such an excellent performance, rarely reported for (sulfur/metal sulfide)‐based, all solid‐state cells, makes these composites highly promising for real application where high positive electrode loadings are required.     

Hierarchical Carbide‐Derived Carbon Foams with Advanced Mesostructure as a Versatile Electrochemical Energy‐Storage Material

Highly porous carbide‐derived carbon (CDC) mesofoams (DUT‐70) are prepared by nanocasting of mesocellular silica foams with a polycarbosilane precursor. Ceramic conversion followed by silica removal and high‐temperature chlorine treatment yields CDCs with a hierarchical micro‐mesopore arrangement. This new type of polymer‐based CDC is characterized by specific surface areas as high as 2700 m² g^?1, coupled with ultrahigh micro‐ and mesopore volumes up to 2.6 cm³ g^?1. The relationship between synthesis conditions and the properties of the resulting carbon materials is described in detail, allowing precise control of the properties of DUT‐70. Since the hierarchical pore system ensures both efficient mass transfer and high capacities, the novel CDC shows outstanding performance as an electrode material in electrochemical double‐layer capacitors (EDLCs) with specific capacities above 240 F g^?1 when measured in a symmetrical two‐electrode configuration. Remarkable capacities of 175 F g^?1 can be retained even at high current densities of 20 A g^?1 as a result of the enhanced ion‐transport pathways provided by the cellular mesostructure. Moreover, DUT‐70 can be infiltrated with sulfur and host the active material in lithium–sulfur battery cathodes. Reversible capacities of 790 mAh g^?1 are achieved at a current rate of C/10 after 100 cycles, which renders DUT‐70 an ideal support material for electrochemical energy‐storage applications.     

Formation of Uniform N‐doped Carbon‐Coated SnO2 Submicroboxes with Enhanced Lithium Storage Properties

Rational design and preparation of SnO₂‐based materials with superior electrochemical performance for lithium‐ion batteries are highly desirable. In this work, the synthesis of SnO₂/nitrogen‐doped carbon (SnO₂/NC) submicroboxes with excellent lithium storage properties is reported. The as‐synthesized SnO₂/NC submicroboxes are highly porous with a high specific surface area of 125 m² g^?1, well‐defined hollow structure (around 400 nm in size) with a shell thickness of 40 nm, and ultrasmall SnO₂ nanoparticles uniformly coated with nitrogen‐doped carbon layer. As a result, the SnO₂/NC submicroboxes show outstanding electrochemical performance as an anode material for lithium‐ion batteries. A high reversible capacity of 491 mAh g^?1 can be retained after 100 cycles at a current density of 0.5 A g^?1.     

Biomimetic Spider‐Web‐Like Composites for Enhanced Rate Capability and Cycle Life of Lithium Ion Battery Anodes

It is crucial to control the structure and composition of composite anode materials to enhance the cell performance of such anode materials for lithium ion batteries. Herein, a biomimetic strategy is demonstrated for the design of high performance anode materials, inspired by the structural characteristics and working principles of sticky spider‐webs. Hierarchically porous, sticky, spider‐web‐like multiwall carbon nanotube (MWCNT) networks are prepared through a process involving ozonation, ice‐templating assembly, and thermal treatment, thereby integrating the networks with γ‐Fe₂O₃ particles. The spider‐web‐like MWCNT/γ‐Fe₂O₃ composite network not only traps the active γ‐Fe₂O₃ materials tightly but also provides fast charge transport through the 3D internetworked pathways and the mechanical integrity. Consequently, the composite web shows a high capacity of ≈822 mA h g^?1 at 0.05 A g^?1, fast rate capability with ≈72.3% retention at rates from 0.05 to 1 A g^?1, and excellent cycling stability of >88% capacity retention after 310 cycles with a Coulombic efficiency >99%. These remarkable electrochemical performances are attributed to the complementarity of the 3D spider‐web‐like structure with the strong attachment of γ‐Fe₂O₃ particles on the sticky surface. This synthetic strategy offers an environmentally safe, simple, and cost‐effective avenue for the biomimetic design of high performance energy storage materials.     

Going Beyond Lithium Hybrid Capacitors: Proposing a New High‐Performing Sodium Hybrid Capacitor System for Next‐Generation Hybrid Vehicles Made with Bio‐Inspired Activated Carbon

A novel sodium hybrid capacitor (NHC) is constructed with an intercalation‐type sodium material [carbon coated‐Na₃V₂(PO₄)₃, C‐NVP] and high surface area‐activated carbon derived from an eco‐friendly resource cinnamon sticks (CDCs) in an organic electrolyte. This novel NHC possesses a combination of high energy and high power density, along with remarkable electrochemical stability. In addition, the C‐NVP/CDC system outperforms present, well‐established lithium hybrid capacitor systems in all areas, and can thus be added to the list of candidates for future electric vehicles. A careful optimization of mass balance between electrode materials enables the C‐NVP/CDC cell to exhibit extraordinary capacitance performance. This novel NHC produces an energy density of 118 Wh kg^?1 at a specific power of 95 W kg^?1 and retains an energy density of 60 Wh kg^?1 with high specific power of 850 W kg^?1. Furthermore, a discharge capacitance of 53 F g^?1 is obtained from the C‐NVP/CDC cell at a 1 mA cm^?2 current density, along with 95% capacitance retention, even after 10 000 cycles. The sluggish kinetics of the Na ion battery system is successfully overcome by developing a stable, high‐performing NHC system.     

All‐Printed MnHCF‐MnOx‐Based High‐Performance Flexible Supercapacitors

Here, a simple active materials synthesis method is presented that boosts electrode performance and utilizes a facile screen‐printing technique to prepare scalable patterned flexible supercapacitors based on manganese hexacyanoferrate‐manganese oxide and electrochemically reduced graphene oxide electrode materials (MnHCF‐MnO_x/ErGO). A very simple in situ self‐reaction method is developed to introduce MnO_x pseudocapacitor material into the MnHCF system by using NH₄F. This MnHCF‐MnO_x electrode materials can deliver excellent capacitance of 467 F g^?1 at a current density of 1 A g^?1, which is a 2.4 times capacitance increase compared to MnHCF. In addition a printed, patterned, flexible MnHCF‐MnO_x/ErGO supercapacitor is fabricated, showing a remarkable areal capacitance of 16.8 mF cm^?2 and considerable energy and power density of 0.5 mWh cm^?2 and 0.0023 mW cm^?2, respectively. Furthermore, the printed patterned flexible supercapacitors also exhibit exceptional flexibility, and the capacitance remains stable, even while bending to various angles (60°, 90°, and 180°) and for 100 cycles. The flexible supercapacitor arrays integrated by multiple prepared single supercapacitors can power various LEDs even in the bent states. This approach offers promising opportunities for the development of printable energy storage materials and devices with high energy density, large scalability, and excellent flexibility.     

Surface Pseudocapacitive Mechanism of Molybdenum Phosphide for High‐Energy and High‐Power Sodium‐Ion Capacitors

Sodium‐based energy storage technologies are potential candidates for large‐scale grid applications owing to the earth abundance and low cost of sodium resources. Transition metal phosphides, e.g. MoP, are promising anode materials for sodium‐ion storage, while their detailed reaction mechanisms remain largely unexplored. Herein, the sodium‐ion storage mechanism of hexagonal MoP is systematically investigated through experimental characterizations, density functional theory calculations, and kinetics analysis. Briefly, it is found that the naturally covered surface amorphous molybdenum oxides layers on the MoP grains undergo a faradaic redox reaction during sodiation and desodiation, while the inner crystalline MoP remains unchanged. Remarkably, the MoP anode exhibits a pseudocapacitive‐dominated behavior, enabling the high‐rate sodium storage performance. By coupling the pseudocapacitive anode with a high‐rate‐battery‐type Na₃V₂O₂(PO₄)₂F@rGO cathode, a novel sodium‐ion full cell delivers a high energy density of 157 Wh kg^?1 at 97 W kg^?1 and even 52 Wh kg^?1 at 9316 W kg^?1. These findings present the deep understanding of the sodium‐ion storage mechanism in hexagonal MoP and offer a potential route for the design of high‐rate sodium‐ion storage materials and devices.     

CoNi2S4‐Graphene‐2D‐MoSe2 as an Advanced Electrode Material for Supercapacitors

3D CoNi₂S₄‐graphene‐2D‐MoSe₂ (CoNi₂S₄‐G‐MoSe₂) nanocomposite is designed and prepared using a facile ultrasonication and hydrothermal method for supercapacitor (SC) applications. Because of the novel nanocomposite structures and resultant maximized synergistic effect among ultrathin MoSe₂ nanosheets, highly conductive graphene and CoNi₂S₄ nanoparticles, the electrode exhibits rapid electron and ion transport rate and large electroactive surface area, resulting in its amazing electrochemical properties. The CoNi₂S₄‐G‐MoSe₂ electrode demonstrates a maximum specific capacitance of 1141 F g^?1, with capacitance retention of ≈108% after 2000 cycles at a high charge–discharge current density of 20 A g^?1. As to its symmetric device, 109 F g^?1 at a scan rate of 5 mV s^?1 is exhibited. This pioneering work should be helpful in enhancing the capacitive performance of SC materials by designing nanostructures with efficient synergetic effects.     

Generalized Mechanochemical Synthesis of Biomass‐Derived Sustainable Carbons for High Performance CO2 Storage

Novel mechanochemical activation generates biomass‐derived carbons with unprecedented CO₂ storage capacity due to higher porosity than analogous conventionally activated carbons but similar pore size. The mechanochemical activation, or so‐called compactivation, process involves compression, at 740 MPa, of mixtures of activating agent (KOH) and biomass hydrochar into pellets/disks prior to thermal activation. Despite the increase in surface area and pore volume of between 25% and 75% compared to conventionally activated carbons, virtually all of the porosity of the biomass (sawdust and lignin) derived mechanochemically activated carbons is from small micropores (5.8–6.5 Å), which results in a dramatic increase in CO₂ storage capacity at 25 °C and low pressure (≤1 bar). The ambient temperature CO₂ uptake for a carbon derived from sawdust at 600 °C and a KOH/carbon ratio of 2, rises from 1.3 to 2.0 mmol g^?1 at 0.15 bar, and from 4.3 to 5.8 mmol g^?1 at 1 bar, which is the highest ever reported for carbonaceous materials. The mechanochemically activated carbons have a superior CO₂ working capacity for pressure swing adsorption and vacuum swing adsorption processes and, due to a high packing density, they exhibit excellent volumetric CO₂ uptake that is higher than for any material reported to date.     

Lithium‐Pretreated Hard Carbon as High‐Performance Sodium‐Ion Battery Anodes

Hard carbon (HC) is the state‐of‐the‐art anode material for sodium‐ion batteries (SIBs). However, its performance has been plagued by the limited initial Coulombic efficiency (ICE) and mediocre rate performance. Here, experimental and theoretical studies are combined to demonstrate the application of lithium‐pretreated HC (LPHC) as high‐performance anode materials for SIBs by manipulating the solid electrolyte interphase in tetraglyme (TEGDME)‐based electrolyte. The LPHC in TEGDME can 1) deliver > 92% ICE and ≈220 mAh g^?1 specific capacity, twice of the capacity (≈100 mAh g^?1) in carbonate electrolyte; 2) achieve > 85% capacity retention over 1000 cycles at 1000 mA g^?1 current density (4 C rate, 1 C = 250 mA g^?1) with a specific capacity of ≈150 mAh g^?1, ≈15 times of the capacity (10 mAh g^?1) in carbonate. The full cell of Na₃V₂(PO₄)₃‐LPHC in TEGDME demonstrated close to theoretical specific capacity of ≈98 mAh g^?1 based on Na₃V₂(PO₄)₃ cathode, ≈2.5 times of the value (≈40 mAh g^?1) with nontreated HC. This work provides new perception on the anode development for SIBs.     

High‐Voltage‐Driven Surface Structuring and Electrochemical Stabilization of Ni‐Rich Layered Cathode Materials for Li Rechargeable Batteries

Layered lithium–nickel–cobalt–manganese oxide (NCM) materials have emerged as promising alternative cathode materials owing to their high energy density and electrochemical stability. Although high reversible capacity has been achieved for Ni‐rich NCM materials when charged beyond 4.2 V versus Li⁺/Li, full lithium utilization is hindered by the pronounced structural degradation and electrolyte decomposition. Herein, the unexpected realization of sustained working voltage as well as improved electrochemical performance upon electrochemical cycling at a high operating voltage of 4.9 V in the Ni‐rich NCM LiNi_0.895Co_0.085Mn_0.02O₂ is presented. The improved electrochemical performance at a high working voltage at 4.9 V is attributed to the removal of the resistive Ni²⁺O rock‐salt surface layer, which stabilizes the voltage profile and improves retention of the energy density during electrochemical cycling. The manifestation of the layered Ni²⁺O rock‐salt phase along with the structural evolution related to the metal dissolution are probed using in situ X‐ray diffraction, neutron diffraction, transmission electron microscopy, and X‐ray absorption spectroscopy. The findings help unravel the structural complexities associated with high working voltages and offer insight for the design of advanced battery materials, enabling the realization of fully reversible lithium extraction in Ni‐rich NCM materials.     

High‐Voltage Oxygen‐Redox‐Based Cathode for Rechargeable Sodium‐Ion Batteries

Recently, anionic‐redox‐based materials have shown promising electrochemical performance as cathode materials for sodium‐ion batteries. However, one of the limiting factors in the development of oxygen‐redox‐based electrodes is their low operating voltage. In this study, the operating voltage of oxygen‐redox‐based electrodes is raised by incorporating nickel into P2‐type Na_2/3[Zn_0.3Mn_0.7]O₂ in such a way that the zinc is partially substituted by nickel. As designed, the resulting P2‐type Na_2/3[(Ni_0.5Zn_0.5)_0.3Mn_0.7]O₂ electrode exhibits an average operating voltage of 3.5 V and retains 95% of its initial capacity after 200 cycles in the voltage range of 2.3–4.6 V at 0.1C (26 mA g^?1). Operando X‐ray diffraction analysis reveals the reversible phase transition: P2 to OP4 phase on charge and recovery to the P2 phase on discharge. Moreover, ex situ X‐ray absorption near edge structure and X‐ray photoelectron spectroscopy studies reveal that the capacity is generated by the combination of Ni²⁺/Ni⁴⁺ and O^2?/O^1? redox pairs, which is supported by first‐principles calculations. It is thought that this kind of high voltage redox species combined with oxygen redox could be an interesting approach to further increase energy density of cathode materials for not only sodium‐based rechargeable batteries, but other alkali‐ion battery systems.     

Engineering the Thermoelectric Transport in Half‐Heusler Materials through a Bottom‐Up Nanostructure Synthesis

Half‐Heusler (HH) alloys are among the best promising thermoelectric (TE) materials applicable for the middle‐to‐high temperature power generation. Despite of the large thermoelectric power factor and decent figure‐of‐merit ZT (≈1), their broad applications and enhancement on TE performance are limited by the high intrinsic lattice thermal conductivity (κ_L) due to insufficiencies of phonon scattering mechanisms, and the fewer powerful strategies associated with the microstructural engineering for HH materials. This study reports a bottom‐up nanostructure synthesis approach for these HH materials based on the displacement reaction between metal chlorides/bromides and magnesium (or lithium), followed by vacuum‐assisted spark plasma sintering process. The samples are featured with dense dislocation arrays at the grain boundaries, leading to a minimum κ_L of ≈1 W m^?1 K^?1 at 900 K and one of the highest ZT (≈1) and predicted η (≈11%) for n‐type Hf_0.25Zr_0.75NiSn_0.97Sb_0.03. Further manipulation on the dislocation defects at the grain boundaries of p‐type Nb_0.8Ti_0.2FeSb leads to enhanced maximum power factor of 47 × 10^?4 W m^?1 K^?2 and the predicted η of ≈7.5%. Moreover, vanadium substitution in FeNb_0.56V_0.24Ti_0.2Sb significantly promotes the η to ≈11%. This strategy can be extended to a broad range of advanced alloys and compounds for improved properties.