Amorphous Phosphorus/Nitrogen-Doped Graphene Paper for Ultrastable Sodium-Ion Batteries

Nitrogen-Doped Graphene-Like Carbon Intercalated MXene Heterostructure Electrodes for Enhanced Sodium- and Lithium-Ion Storage

MXene is investigated as an electrode material for different energy storage systems due to layered structures and metal-like electrical conductivity. Experimental results show MXenes possess excellent cycling performance as anode materials, especially at large current densities. However, the reversible capacity is relatively low, which is a significant barrier to meeting the demands of industrial applications. This work synthesizes N-doped graphene-like carbon (NGC) intercalated Ti3C2Tx (NGC-Ti3C2Tx) van der Waals heterostructure by an in situ method. The as-prepared NGC-Ti3C2Tx van der Waals heterostructure is employed as sodium-ion and lithium-ion battery electrodes. For sodium-ion batteries, a reversible specific capacity of 305 mAh g-1 is achieved at a specific current of 20 mA g-1, 2.3 times higher than that of Ti3C2Tx. For lithium-ion batteries, a reversible capacity of 400 mAh g-1 at a specific current of 20 mA g-1 is 1.5 times higher than that of Ti3C2Tx. Both sodium-ion and lithium-ion batteries made from NGC-Ti3C2Tx shows high cycling stability. The theoretical calculations also verify the remarkable improvement in battery capacity within the NGC-Ti3C2O2 system, attributed to the additional adsorption of working ions at the edge states of NGC. This work offers an innovative way to synthesize a new van der Waals heterostructure and provides a new route to improve the electrochemical performance significantly.

Interlayer Affected Diamond Electrochemistry

Diamond electrochemistry is primarily influenced by quantities of sp3-carbon, surface terminations, and crystalline structure. In this work, a new dimension is introduced by investigating the effect of using substrate-interlayers for diamond growth. Boron and nitrogen co-doped nanocrystalline diamond (BNDD) films are grown on Si substrate without and with Ti and Ta as interlayers, named BNDD/Si, BNDD/Ti/Si, and BNDD/Ta/Ti/Si, respectively. After detailed characterization using microscopies, spectroscopies, electrochemical techniques, and density functional theory simulations, the relationship of composition, interfacial structure, charge transport, and electrochemical properties of the interface between diamond and metal is investigated. The BNDD/Ta/Ti/Si electrodes exhibit faster electron transfer processes than the other two diamond electrodes. The interlayer thus determines the intrinsic activity and reaction kinetics. The reduction in their barrier widths can be attributed to the formation of TaC, which facilitates carrier tunneling, and simultaneously increases the concentration of electrically active defects. As a case study, the BNDD/Ta/Ti/Si electrode is further employed to assemble a redox-electrolyte-based supercapacitor device with enhanced performance. In summary, the study not only sheds light on the intricate relationship between interlayer composition, charge transfer, and electrochemical performance but also demonstrates the potential of tailored interlayer design to unlock new capabilities in diamond-based electrochemical devices.

Amorphous Materials for Lithium-Ion and Post-Lithium-Ion Batteries

Lithium-ion and post-lithium-ion batteries are important components for building sustainable energy systems. They usually consist of a cathode, an anode, an electrolyte, and a separator. Recently, the use of solid-state materials as electrolytes has received extensive attention. The solid-state electrolyte materials (as well as the electrode materials) have traditionally been overwhelmingly crystalline materials, but amorphous (disordered) materials are gradually emerging as important alternatives because they can increase the number of ion storage sites and diffusion channels, enhance solid-state ion diffusion, tolerate more severe volume changes, and improve reaction activity. To develop superior amorphous battery materials, researchers have conducted a variety of experiments and theoretical simulations. This review highlights the recent advances in using amorphous materials (AMs) for fabricating lithium-ion and post-lithium-ion batteries, focusing on the correlation between material structure and properties (e.g., electrochemical, mechanical, chemical, and thermal ones).  We  review both the conventional and the emerging characterization methods for analyzing AMs and present the roles of disorder in influencing the performances of various batteries such as those based on lithium, sodium, potassium, and zinc. Finally,  we  describe the challenges and perspectives for commercializing rechargeable AMs-based batteries.

All-Nitrogen Energetic Material Cubic Gauche Polynitrogen: Plasma Synthesis and Thermal Performance

Numerous theoretical calculations have demonstrated that polynitrogen with an extending polymeric network is an ultrahigh-energy all-nitrogen material. Typical samples, such as cubic gauche polynitrogen (cg-N), have been synthesized, but the thermal performance of polynitrogen has not been unambiguously determined. Herein, macroscopic samples of polynitrogen were synthesized utilizing a coated substrate, and their thermal decomposition behavior was investigated. Polynitrogen with carbon nanotubes was produced using a plasma-enhanced chemical vapor deposition method and characterized using infrared, Raman, X-ray diffraction X-ray photoelectron spectroscopy and transmission electron microscope. The results showed that the structure of the deposited polynitrogen was consistent with that of cg-N and the amount of deposition product obtained with coated substrates increased significantly. Differential scanning calorimetry (DSC) at various heating rates and TG-DSC-FTIR-MS analyses were performed. The thermal decomposition temperature of cg-N was determined to be 429 °C. The apparent activation energy (Ea) of cg-N calculated by the Kissinger and Ozawa equations was 84.7 kJ/mol and 91.9 kJ/mol, respectively, with a pre-exponential constant (lnAk) of 12.8 min-1. In this study, cg-N was demonstrated to be an all-nitrogen material with good thermal stability and application potential to high-energy-density materials.

Molten salt synthesis of disordered spinel CoFe2O4 with improved electrochemical performance for sodium-ion batteries

Sodium-ion (Na-ion) batteries are currently being investigated as an attractive substitute for lithium-ion (Li-ion) batteries in large energy storage systems because of the more abundant and less expensive supply of Na than Li. However, the reversible capacity of Na-ions is limited because Na possesses a large ionic radius and has a higher standard electrode potential than that of Li, making it challenging to obtain electrode materials that are capable of storing large quantities of Na-ions. This study investigates the potential of CoFe2O4 synthesised via the molten salt method as an anode for Na-ion batteries. The obtained phase structure, morphology and charge and discharge properties of CoFe2O4 are thoroughly assessed. The synthesised CoFe2O4 has an octahedron morphology, with a particle size in the range of 1.1-3.6 μm and a crystallite size of ∼26 nm. Moreover, the CoFe2O4 (M800) electrodes can deliver a high discharge capacity of 839 mA h g-1 in the first cycle at a current density of 0.1 A g-1, reasonable cyclability of 98 mA h g-1 after 100 cycles and coulombic efficiency of ∼99%. The improved electrochemical performances of CoFe2O4 can be due to Na-ion-pathway shortening, wherein the homogeneity and small size of CoFe2O4 particles may enhance the Na-ion transportation. Therefore, this simple synthetic approach using molten salt favours the Na-ion diffusion and electron transport to a great extent and maximises the utilisation of CoFe2O4 as a potential anode material for Na-ion batteries.

Modulating Zinc Metal Reversibility by Confined Antifluctuator Film for Durable and Dendrite-Free Zinc Ion Batteries

Aqueous Zn ion batteries are promising systems due to their intrinsic safety, low cost, and non-toxicity, and the Zn corrosion and dendrite growth will cause the poor reversibility of Zn anode. Herein, the porous Zn@C solid, hollow, and yolk-shell microsphere films are developed as Zn anode antifluctuator (ZAAF). The prepared yolk-shell microspheres (Zn@C yolk-shell microsphere [ZCYSM]) film with superior buffering can effectively restrict the deposition of Zn metal in its interior and inhibit the volume expansion during plating/stripping process, thus modulating the Zn2+ flux and enabling stable Zn cycling. As a proof of concept, the ZCYSM@Zn symmetric cells achieve the excellent cyclic stability over 4000 h and cumulative plated capacity of 4 Ah cm-2  at a high current density of 10 mA cm-2 . Concomitantly, the suppressed corrosion reactions and dendrite-free ZAAF significantly improve the durability of full cells (coupled to CaV6 O16 ·3H2 O). Additionally, durable pouch cell and electrochemical neuromorphic inorganic device (ENIDe) are integrated to simulate neural network, providing a strategy for extreme interconnectivity comparable to the human brain.

Renaissance of elemental phosphorus materials: properties, synthesis, and applications in sustainable energy and environment

The polymorphism of phosphorus-based materials has garnered much research interest, and the variable chemical bonding structures give rise to a variety of micro and nanostructures. Among the different types of materials containing phosphorus, elemental phosphorus materials (EPMs) constitute the foundation for the synthesis of related compounds. EPMs are experiencing a renaissance in the post-graphene era, thanks to recent advancements in the scaling-down of black phosphorus, amorphous red phosphorus, violet phosphorus, and fibrous phosphorus and consequently, diverse classes of low-dimensional sheets, ribbons, and dots of EPMs with intriguing properties have been produced. The nanostructured EPMs featuring tunable bandgaps, moderate carrier mobility, and excellent optical absorption have shown great potential in energy conversion, energy storage, and environmental remediation. It is thus important to have a good understanding of the differences and interrelationships among diverse EPMs, their intrinsic physical and chemical properties, the synthesis of specific structures, and the selection of suitable nanostructures of EPMs for particular applications. In this comprehensive review, we aim to provide an in-depth analysis and discussion of the fundamental physicochemical properties, synthesis, and applications of EPMs in the areas of energy conversion, energy storage, and environmental remediation. Our evaluations are based on recent literature on well-established phosphorus allotropes and theoretical predictions of new EPMs. The objective of this review is to enhance our comprehension of the characteristics of EPMs, keep abreast of recent advances, and provide guidance for future research of EPMs in the fields of chemistry and materials science.

Nitrogen-Rich WN Clusters with Atomic Disorders and Non-Grain Boundaries Confined in Carbon Nanosheets Boosting Sodium-Ion Storage

Sodium-ion batteries (SIBs) as economic candidates have received considerable attention for large-scale energy storage applications. However, crystalline metal compounds with specific transport routes and rigid structures restrict their practical applications. Herein, the atomically dispersed N-rich amorphous WN clusters confined in the carbon nanosheets (WN/CNSs) are reported. Through advanced tests and calculations, the structural advantages, reaction mechanisms, and kinetic behaviors of the clusters are systematically analyzed. Compared with the crystalline W₂ N with low theoretical capacity (only 209.3 mAh g^-1 ), the amorphous WN clusters have the advantages of atomic disorders and non-grain boundaries and can afford abundant active sites (unsaturated dangling bonds) and isotropic charge transfer channels, which can be further enhanced by the N-rich characteristics and high electronegativity of the clusters. The encapsulation of CNSs has high conductivity and structural stability, which promotes electron transfer and effectively buffers volume expansions. As a SIB anode, the reversible capacity of WN/CNSs reaches 421.2 mAh g^-1 at 0.1 A g^-1 . Even at 20 A g^-1 , the reversible capacity of 170.7 mAh g^-1 is maintained after 8000 cycles. This study focuses on the advantages of amorphous nitrides, which have important guiding significance for the design of atomic clusters for high-performance metal ion batteries.

Graphene: A Path-Breaking Discovery for Energy Storage and Sustainability

The global energy situation requires the efficient use of resources and the development of new materials and processes for meeting current energy demand. Traditional materials have been explored to large extent for use in energy saving and storage devices. Graphene, being a path-breaking discovery of the present era, has become one of the most-researched materials due to its fascinating properties, such as high tensile strength, half-integer quantum Hall effect and excellent electrical/thermal conductivity. This paper presents an in-depth review on the exploration of deploying diverse derivatives and morphologies of graphene in various energy-saving and environmentally friendly applications. Use of graphene in lubricants has resulted in improvements to anti-wear characteristics and reduced frictional losses. This comprehensive survey facilitates the researchers in selecting the appropriate graphene derivative(s) and their compatibility with various materials to fabricate high-performance composites for usage in solar cells, fuel cells, supercapacitor applications, rechargeable batteries and automotive sectors.

High-value utilization of bamboo pulp black liquor lignin: Preparation of silicon-carbide derived materials and its application

The black liquor of bamboo pulp contains a large amount of silicon, which makes it difficult to separate industrial lignin, thus hindering its high-value utilization. Herein, this paper dedicates to exploring the high-value use of silica-containing lignin. Tetraethyl silicate (TEOS) was added to the above silicon-containing lignin for crosslinking with the lignin to prevent disintegration during carbonization and provide an additional source of silica. The carbonization is carried out at 600 °C (LT-6), 900 °C (LT-9) and 1200 °C (LT-12), and the structural evolution of SiO_xC_y is innovatively analyzed. The results show that LT-9 is dominated by the SiO₃C structure and has a specific surface area of 269 m² g^-1. The specific capacitance of LT-9 and LT-12 as supercapacitors electrodes is 78.6 F g^-1 and 74.8 F g^-1 at a current density of 1 A g^-1, and remains 95 % and 91.7 % after 10,000 cycles. Moreover, LT-9 has a high yield of 54 %. In this work, silicon-containing lignin is exploratively prepared as a silicon-carbide-derived material. Furthermore, the potential relationship between different SiO_xC_y molecular structures and electrochemical performance is evaluated, which is instructive for the high-value utilization of black liquor in bamboo pulp.

Carbon nanofibers derived from cellulose via molten-salt method as supercapacitor electrode

Carbon nanofibers (CNFs) have been paid much attention as supercapacitor electrode due to outstanding chemical stability, high electron transfer rate and large specific surface area. However, the preparation process of CNFs is always stalemated in electrospinning, heat stabilization and carbonization. The problems of solvent pollution in the electrospinning process, complex process and high energy consumption in conventional carbonization process can't be solved. Herein, CNFs have been innovatively prepared from nanofibrillated cellulose by the molten-salt method (NaCl/NaOH). Molten salt penetrates between the fibers, separates and activates the fibers. The obtained carbon nanofibers remain developed branching structures and have a large specific surface area (899 m² g^-1). The electrical properties are tested in a symmetrical two-electrode system. The specific capacitance is 150 F g^-1 at the current density of 1 A g^-1. Low equivalent series resistance (1.13 Ω) indicates that it has high electrode conductivity. This study has taken into account energy conservation, environmental protection, recyclability and simplified preparation process, which has a very far-reaching significance for the industrial production of CNFs.

Effects of Salt Concentration on the Water and Ion Self-Diffusion Coefficients of a Model Aqueous Sodium-Ion Battery Electrolyte

The aqueous sodium-ion battery is a promising alternative to the well-known lithium-ion battery owing to the large abundance of sodium ion resources. Although it is safer than the lithium-ion battery, the voltage window of the sodium-ion battery is narrower than that of the lithium-ion battery, thus limiting its practical implementation. Therefore, a highly concentrated electrolyte is required to address this issue. In the present work, the effect of the salt concentration on the transport properties of water molecules is investigated via theoretical analyses at the quantum mechanical level. A molecular dynamics simulation at the quantum mechanical level revealed that as the salt concentration increases, the ion-water interactions became stronger, leading to a lower diffusivity and a lower electronic band gap. These imply that the superconcentrated aqueous-based electrolytes have high potentials for the sodium-ion battery applications.

Tailoring Ordered Porous Carbon Embedded with Cu Clusters for High-Energy and Long-Lasting Phosphorus Anode

The natural insulating property and notorious pulverization of volume variation-induced materials during cycling pares the electrochemical activity of red phosphorous (RP) for lithium/sodium-ion batteries (LIBs/SIBs). To work out these issues, a tailored trimodal porous carbon support comprising highly ordered macropores and micro-mesoporous walls embedded with copper (Cu) nanoclusters (Cu-OMC) is proposed to confine RP. The construction of highly conductive copper-carbon wall facilitates fast electrons and ions transportation, while the interconnected and ordered porous structure not only creates enough space to resist the expansion effect of RP but also minimizes the ion diffusion length and enhances ion accessibility (the ion migration coefficient is ten times that of disordered porous carbon). Consequently, the resulting Cu-OMC@RP anode delivers a high reversible capacity (2498.7 mAh g^-1 at 0.3 C for LIBs; 2454.2 mAh g^-1 at 0.1 C for SIBs), superb rate properties (824.7 mAh g^-1 at 10 C for LIBs; 774.2 mAh g^-1 at 5 C for SIBs), and outstanding cycling stability (an ultralow decay rate of 0.057% per cycle after 1000 cycles at 10 C for LIBs and 0.048% per cycle at 5 C over 500 cycles for SIBs).

Topological transformation construction of CoSe2/N-doped carbon heterojunction with three-dimensional porous structure for high-performance sodium-ion half/full batteries

Transition metal selenides have been widely used as anode materials for sodium-ion batteries (SIBs) because of their considerable theoretical capacity and good conductivity. Nevertheless, the volume expansion is a serious...

Graphene-Based Nanomaterials for Flexible and Stretchable Batteries

Recently, as flexible and wearable electronic devices have become widely popular, research on light weight and large-capacity batteries suitable for powering such devices has been actively conducted. In particular, graphene has attracted considerable attention from researchers in the battery field owing to its good mechanical properties and its applicability in various processes to fabricate electrodes for batteries. Graphene is classified into two types: flake-type, fabricated from graphite, and film-type, synthesized using chemical vapor deposition. The unique processes involved in these two types enable the fabrication of flexible and stretchable batteries with various shapes and functions. In this article, the recent progress in the development of flexible and stretchable batteries based on graphene, as well as its important technical issues are reviewed.

Strategies for Developing Transition Metal Phosphides in Electrochemical Water Splitting

Electrochemical water splitting involving hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is a greatly promising technology to generate sustainable and renewable energy resources, which relies on the exploration regarding the design of electrocatalysts with high efficiency, high stability, and low cost. Transition metal phosphides (TMPs), as nonprecious metallic electrocatalysts, have been extensively investigated and proved to be high-efficient electrocatalysts in both HER and OER. In this minireview, a general overview of recent progress in developing high-performance TMP electrocatalysts for electrochemical water splitting has been presented. Design strategies including composition engineering by element doping, hybridization, and tuning the molar ratio, structure engineering by porous structures, nanoarray structures, and amorphous structures, and surface/interface engineering by tuning surface wetting states, facet control, and novel substrate are summarized. Key scientific problems and prospective research directions are also briefly discussed.

N, P-Codoped Graphene Dots Supported on N-Doped 3D Graphene as Metal-Free Catalysts for Oxygen Reduction

Nitrogen and phosphorus-codoped graphene dots supported on nitrogen-doped three-dimensional graphene (N, P-GDs/N-3DG) have been synthesized by a facile freeze-annealing process. On the surface of the 3D interconnected porous structure, the N, P-GDs are uniformly dispersed. The as-prepared N, P-GDs/N-3DG material served as a metal-free catalyst for oxygen reduction reaction (ORR) in an alkaline medium and evaluated by a rotating ring-disk electrode. The N, P-GDs/N-3DG catalyst exhibits excellent ORR activity, which is comparable to that of the commercial Pt/C catalyst. Furthermore, it exhibits a higher tolerance to methanol and better stability than the Pt/C. This enhanced electrochemical catalytic performance can be ascribed to the presence of abundant functional groups and edge defects. This study indicates that P-N bonded structures play a vital role as the active sites in ORR.

Emerging of Heterostructure Materials in Energy Storage: A Review

With the ever-increasing adaption of large-scale energy storage systems and electric devices, the energy storage capability of batteries and supercapacitors has faced increased demand and challenges. The electrodes of these devices have experienced radical change with the introduction of nano-scale materials. As new generation materials, heterostructure materials have attracted increasing attention due to their unique interfaces, robust architectures, and synergistic effects, and thus, the ability to enhance the energy/power outputs as well as the lifespan of batteries. In this review, the recent progress in heterostructure from energy storage fields is summarized. Specifically, the fundamental natures of heterostructures, including charge redistribution, built-in electric field, and associated energy storage mechanisms, are summarized and discussed in detail. Furthermore, various synthesis routes for heterostructures in energy storage fields are roundly reviewed, and their advantages and drawbacks are analyzed. The superiorities and current achievements of heterostructure materials in lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), lithium-sulfur batteries (Li-S batteries), supercapacitors, and other energy storage devices are discussed. Finally, the authors conclude with the current challenges and perspectives of the heterostructure materials for the fields of energy storage.

Three-Dimensional Graphene-Based Macrostructures for Electrocatalysis

Electrochemical energy storage and conversion is an effective strategy to relieve the increasing energy and environment crisis. The sluggish reaction kinetics in the related devices is one of the major obstacles for them to realize practical applications. More efforts should be devoted to searching for high-efficiency electrocatalysts and enhancing the electrocatalytic performance. 3D graphene macrostructures (3D GMs) are one kind of porous crystalline materials with 3D structures at both micro- and macro-scale. The unique structure can achieve large accessible surface area, expose many active sites, promote fast mass/electron transport, and provide wide room for further functional modification. All these features make them promising candidates for electrocatalysis. In this review, the authors focus on the latest progress of 3D GMs for electrocatalysis. First, the preparation methods of 3D GMs are introduced followed by the strategies for functional modifications. Then, their electrocatalytic performances are discussed in detail including monofunctional and bifunctional electrocatalysis. The electrocatalytic processes involve oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, and carbon dioxide reduction reaction. Finally, the challenges and perspectives are presented to offer a guideline for the exploration of excellent 3D GM-based electrocatalysts.

New Insights on the Conversion Reaction Mechanism in Metal Oxide Electrodes for Sodium-Ion Batteries

Due to the abundance and low cost of exchanged metal, sodium-ion batteries have attracted increasing research attention for the massive energy storage associated with renewable energy sources. Nickel oxide (NiO) thin films have been prepared by magnetron sputtering (MS) deposition under an oblique angle configuration (OAD) and used as electrodes for Na-ion batteries. A systematic chemical, structural and electrochemical analysis of this electrode has been carried out. The electrochemical characterization by galvanostatic charge–discharge cycling and cyclic voltammetry has revealed a certain loss of performance after the initial cycling of the battery. The conversion reaction of NiO with sodium ions during the discharge process to generate sodium oxide and Ni metal has been confirmed by X-ray photoelectron spectra (XPS) and micro-Raman analysis. Likewise, it has been determined that the charging process is not totally reversible, causing a reduction in battery capacity.

Encapsulation of Red Phosphorus in Carbon Nanocages with Ultrahigh Content for High-Capacity and Long Cycle Life Sodium-Ion Batteries

Red phosphorus (RP) has attracted great attention as a potential candidate for anode materials of high-energy density sodium-ion batteries (NIBs) due to its high theoretical capacity, appropriate working voltage, and natural abundance. However, the low electrical conductance and huge volumetric variation during the sodiation-desodiation process, causing poor rate performance and cyclability, have limited the practical application of RP in NIBs. Herein, we report a rational strategy to resolve these issues by encapsulating nanoscaled RP into conductive and networked carbon nanocages (denoted as RP@CNCs) using a combination of a phosphorus-amine based method and evacuation-filling process. The large interior cavities volume of CNCs and controllable solution-based method enable the ultrahigh RP loading amount (85.3 wt %) in the RP@CNC composite. Benefiting from the synergic effects of the interior cavities and conductive network, which afford high structure stability and rapid electron transport, the RP@CNC composite presents a high systematic capacity of 1363 mA h g^-1 at a current density of 100 mA g^-1 after 150 cycles, favorable high-rate capability, and splendid long-cycling performance with capacity retention over 80% after 1300 cycles at 5000 mA g^-1. This prototypical design promises an efficient solution to maximize RP loading as well as to boost the electrochemical performance of RP-based anodes.

Pseudocapacitive behaviour in sol-gel derived electrochromic titania nanostructures

Nanostructured thin films are widely investigated for application in multifunctional devices thanks to their peculiar optoelectronic properties. In this work anatase TiO₂ nanoparticles (average diameter 10 nm) synthesised by a green aqueous sol-gel route are exploited to fabricate optically active electrodes for pseudocapacitive-electrochromic devices. In our approach, highly transparent and homogeneous thin films having a good electronic coupling between nanoparticles are prepared. These electrodes present a spongy-like nanostructure in which the dimension of native nanoparticles is preserved, resulting in a huge surface area. Cyclic voltammetry studies reveal that there are significant contributions to the total stored charge from both intercalation capacitance and pseudocapacitance, with a remarkable 50% of the total charge deriving from this second effect. Fast and reversible colouration occurs, with an optical modulation of ∼60% in the range of 315-1660 nm, and a colouration efficiency of 25.1 cm² C^-1 at 550 nm. This combination of pseudocapacitance and electrochromism makes the sol-gel derived titania thin films promising candidates for multifunctional 'smart windows'.

DFT and experimental study of nano red phosphorus anchoring on sulfurized polyacrylonitrile for lithium-ion batteries

Sulfur atoms can reconstruct the configuration of PAN, which makes the electron transfer more convenient and reduces the energy barriers during Li ion diffusion. The sulfurized polyacrylonitrile plays a crucial role in anchoring the P₄ molecule and electron transport simultaneously. Uniform RP nanoparticles (∼200 nm) are obtained using a simple liquid phase method. SPAN-RP shows an initial reversible capacity of 1214 mA h g^-1 at 0.2C and retains a capacity of 860 mA h g^-1 with a high coulombic efficiency of 99.6% after 200 cycles.

Enhancing the Cycling Stability by Tuning the Chemical Bonding between Phosphorus and Carbon Nanotubes for Potassium-Ion Battery Anodes

Phosphorus/carbon (P/C) composites as promising potassium-ion storage materials have been extensively investigated for its compound superiorities of high specific capacity and favorable electronic conductivity. However, the effects of different chemical bonding states between P and the carbon matrix for potassium-ion storage and cycling performance still need to be investigated. Herein, three P/C composites with different chemical bonding states were successfully fabricated through simply ball-milling red P with carboxylic group carbon nanotubes (CGCNTs), carbon nanotubes (CNTs), and reduced carboxylic group carbon nanotubes (RCGCNTs), respectively. When used as potassium-ion battery (PIB) anodes, the red P and CGCNT (P-CGCNT) composite deliver the most outstanding cycling stability (402.6 mAh g^-1 over 110 cycles) with a favorable capacity retention of 68.26% at a current density of 0.1 A g^-1, much higher than that of the phosphorus-CNT (P-CNT) composite (297.5 mAh g^-1 and 50.40%). Based on the results of X-ray photoelectron spectroscopy and electrochemical performance, we propose that the existence of a carboxyl functional group will be instrumental for the formation of the P-O-C bond. More importantly, when compared with the P-C bond, the P-O-C bond can lead to a higher reversible capacity and a better long-term cycling stability as a result of the more robust bonding energy of the P-O-C bond (585 KJ mol^-1) than that of the P-C bond (264 kJ mol^-1). This work provides some insights into designing high-performance P anodes for PIBs.

Red-phosphorus-impregnated carbon nanofibers for sodium-ion batteries and liquefaction of red phosphorus

Red phosphorus offers a high theoretical sodium capacity and has been considered as a candidate anode for sodium-ion batteries. Similar to silicon anodes for lithium-ion batteries, the electrochemical performance of red phosphorus is plagued by the large volume variation upon sodiation. Here we perform in situ transmission electron microscopy analysis of the synthesized red-phosphorus-impregnated carbon nanofibers with the corresponding chemo-mechanical simulation, revealing that, the sodiated red phosphorus becomes softened with a “liquid-like” mechanical behaviour and gains superior malleability and deformability against pulverization. The encapsulation strategy of the synthesized red-phosphorus-impregnated carbon nanofibers has been proven to be an effective method to minimize the side reactions of red phosphorus in sodium-ion batteries, demonstrating stable electrochemical cycling. Our study provides a valid guide towards high-performance red-phosphorus-based anodes for sodium-ion batteries.

Red phosphorus is a promising anode for Na-ion batteries but suffers from large volume change upon cycling. Here the authors show a red-phosphorus-impregnated carbon nanofiber design in which the sodiated red phosphorus is featured by a “liquid-like” behavior and ultra-stable electrochemical performance is realized.

Recent Progress of In Situ Transmission Electron Microscopy for Energy Materials

In situ transmission electron microscopy (TEM) is one of the most powerful approaches for revealing physical and chemical process dynamics at atomic resolutions. The most recent developments for in situ TEM techniques are summarized; in particular, how they enable visualization of various events, measure properties, and solve problems in the field of energy by revealing detailed mechanisms at the nanoscale. Related applications include rechargeable batteries such as Li-ion, Na-ion, Li-O₂ , Na-O₂ , Li-S, etc., fuel cells, thermoelectrics, photovoltaics, and photocatalysis. To promote various applications, the methods of introducing the in situ stimuli of heating, cooling, electrical biasing, light illumination, and liquid and gas environments are discussed. The progress of recent in situ TEM in energy applications should inspire future research on new energy materials in diverse energy-related areas.

Three-Dimensional Electronic Network Assisted by TiN Conductive Pillars and Chemical Adsorption to Boost the Electrochemical Performance of Red Phosphorus

The practical application of red phosphorus (P) for sodium-ion batteries (SIBs) is retarded by its poor reversibility and its unstable cycling life derived from its poor conductivity and huge volume expansion. Graphene is considered as an ideal matrix to remedy these weaknesses due to its excellent conductivity and two-dimensional structure. Its π-π restacking causes spatial collapse, however, meaning that graphene cannot effectively buffer volume expansion. Herein, multifunctional TiN is introduced into a P composite to fix this issue. TiN acts as conductive pillars, electron transfer bridges, and a chemical adsorbent of phosphorus in the composite, to prevent the graphene nanoplates from restacking, to bridge gaps between the graphene nanoplates, and to chemically adsorb the P, resulting in the formation of a three-dimensional electronic network and endowing the pulverized P particles with good contact with the conductive matrix to avoid forming insulating "dead P". Consequently, the P composite presents excellent performance for SIBs.

Highly Reversible and Rapid Sodium Storage in GeP3 with Synergistic Effect from Outside-In Optimization

The composite GeP₃/C@rGO as a sodium ion battery anode material was fabricated by introducing a carbon matrix into GeP₃ through high-energy ball milling, followed by encapsulating the resultant composite with graphene via a solution-based ultrasonic method. To delineate the individual role of carbon matrix and graphene, material characterization and electrochemical analyses were performed for GeP₃/C@rGO and three other samples: bare GeP₃, GeP₃ with graphene coating (GeP₃@rGO), and GeP₃ with carbon matrix (GeP₃/C). GeP₃/C@rGO exhibits the highest electric conductivity (5.89 × 10^-1 S cm^-1) and the largest surface area (167.85 m² g^-1) among the four samples. The as-prepared GeP₃/C@rGO delivered a reversible high capacity of 1084 mA h g^-1 at 50 mA g^-1, excellent rate capacity (435.4 mA h g^-1 at a high rate of 5 A g^-1), and long-term cycling stability (400 cycles with a reversible capacity of 823.3 mA h g^-1 at 0.2 A g^-1), all of which outperform the other three samples. The kinetics investigation reveals a "pseudocapacitive behavior" in GeP₃/C and GeP₃/C@rGO, where solely faradic reactions took place in bare GeP₃ and GeP₃@rGO with a typical "battery behavior". Based on ex-situ X-ray photoelectron spectroscopy and ex-situ electrochemical impedance spectroscopy, the carbon matrix serves to activate and stabilize the interior of the composite, while the graphene protects and restrains the exterior surface. Benefiting from the synergistic combination of these two components, GeP₃/C@rGO achieved extremely stable cycling stability as well as outstanding rate performance.

A Functionalized Carbon Surface for High-Performance Sodium-Ion Storage

Sodium-ion batteries (SIBs) are promising for large-scale energy storage systems and carbon materials are the most likely candidates for their electrodes. The existence of defects in carbon materials is crucial for increasing the sodium storage ability. However, both the reversible capacity and efficiency need to be further improved. Functionalization is a direct and feasible approach to address this issue. Based on the structural changes in carbon materials produced by surface functionalization, three basic categories are defined: heteroatom doping, grafting of functional groups, and the shielding of defects. Heteroatom doping can improve the electrochemical reactivity, and the grafting of functional groups can promote both the diffusion-controlled bulk process and surface-confined capacitive process. The shielding of defects can further increase the efficiency and cyclic stability without sacrificing reversible capacity. In this Review, recent progresses in the ways to produce surface functionalization are presented and the related impact on the physical and chemical properties of carbon materials is discussed. Moreover, the critical issues, challenges, and possibilities for future research are summarized.

Partial Atomic Tin Nanocomplex Pillared Few-Layered Ti3C2Tx MXenes for Superior Lithium-Ion Storage

MXenes have attracted great interest in various fields, and pillared MXenes open a new path with larger interlayer spacing. However, the further study of pillared MXenes is blocked at multilayered state due to serious restacking phenomenon of few-layered MXene nanosheets. In this work, for the first time, we designed a facile NH4+ method to fundamentally solve the restacking issues of MXene nanosheets and succeeded in achieving pillared few-layered MXene. Sn nanocomplex pillared few-layered Ti3C2Tx (STCT) composites were synthesized by introducing atomic Sn nanocomplex into interlayer of pillared few-layered Ti3C2Tx MXenes via pillaring technique. The MXene matrix can inhibit Sn nanocomplex particles agglomeration and serve as conductive network. Meanwhile, the Sn nanocomplex particles can further open the interlayer spacing of Ti3C2Tx during lithiation/delithiation processes and therefore generate extra capacity. Benefiting from the "pillar effect," the STCT composites can maintain 1016 mAh g-1 after 1200 cycles at 2000 mA g-1 and deliver a stable capacity of 680 mAh g-1 at 5 A g-1, showing one of the best performances among MXene-based composites. This work will provide a new way for the development of pillared MXenes and their energy storage due to significant breakthrough from multilayered state to few-layered one.

Phosphorus-Amine-Based Synthesis of Nanoscale Red Phosphorus for Application to Sodium-Ion Batteries

Current methods for synthesizing nanoscale red phosphorus (NRP), including ball-milling and vaporization-condensation, have various limitations. More effective engineering of the properties of these materials would promote their application in sodium-ion batteries. Herein, we report a simple phosphorus-amine-based method for the scalable preparation of NRP with high yield. We confirm that red phosphorus is highly soluble in ethylenediamine and that addition of H⁺ precipitates a network of NRP, where the size distribution is controlled by the H⁺ concentration. Through the use of this method, uniform NRP with particle sizes of 5-10 nm was dispersed in situ on the surfaces of reduced graphene oxide (rGO) with a controllable loading ratio. We attribute the formation of this structure to strong adsorption between the red phosphorus-ethylenediamine complex and rGO. The binding between NRP/Na₃P and rGO effectively stabilized the NRP on rGO throughout charging/discharging processes, therefore enabling the NRP-rGO composite to deliver a high capacity of 2057 mA h g^-1 at a current density of 100 mA g^-1 and excellent long-cycling performance.

Integrated Paper-Based Flexible Li-Ion Batteries Made by a Rod Coating Method

Design and fabrication of flexible Li-ion batteries (FLIBs) with excellent electrochemical and structural stability via scalable fabrication techniques are important for their practical applications. A wide range of FLIBs with excellent flexibility have been reported. However, sophisticated designs and complex fabrication techniques are often used in fabricating FLIBS, making them difficult to be realized in industrial production. Here, we fabricate FLIBs with an integrated structure by assembling the LiFePO₄ cathode, Li₄Ti₅O₁₂ anode, graphene current collectors, and poly(vinylidene fluoride) (PVDF) electrolyte all together on commercial printing paper via conventional and scalable Meyer rod coating. In the design, the commercial paper serves as a flexible substrate to enable good flexibility of the device, and the paper is coated twice with PVDF to avoid the short-circuit problem and create a strong binding to integrate the device. The resultant integrated FLIBs exhibit excellent internal structural stability and good electrochemical performance under cycling bending for 100 times.

High-Performance Phosphorus-Graphite Dual-Ion Battery

Recently, dual-ion batteries (DIBs) are regarded as a promising alternative to well-developed lithium-ion batteries, and the development of high-performance and abundant-sodium-based DIBs (SDIBs) is being intensively pursued. In this work, a novel SDIB composed of a phosphorus (P)-based anode and graphite (G) cathode is successfully constructed for the first time. This P-G SDIB shows a high working voltage of around 3.9 V, a high reversible capacity of 373 mA h/g, good rate capability, and long cyclability, which are superior to those of the most reported DIBs. The ex situ X-ray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy tests reveal the insertion/extraction mechanism of Na⁺ ions into/from P-based anodes via reversible Na-P alloying reactions accompanied with high charge-storage capability. Moreover, the presodiation of P-based composites is found to be an efficient approach to boost the cycling performance of the P-G SDIB by forming a stable NaF-rich solid electrolyte interphase layer to alleviate electrolyte decomposition. Our results demonstrate that P-based SDIBs possess tremendous potential for practical electrochemical energy-storage applications.

Structural changes during water-mediated amorphization of semiconducting two-dimensional thio-stannates

Owing to their combined open-framework structures and semiconducting properties, two-dimensional thio-stannates show great potential for catalytic and sensing applications. One such class of crystalline materials consists of porous polymeric [Sn3S7 2-] n sheets with molecular cations embedded in-between. The compounds are denoted R-SnS-1, where R is the cation. Dependent on the cation, some R-SnS-1 thio-stannates transition into amorphous phases upon dispersion in water. Knowledge about the fundamental chemical properties of the thio-stannates, including their water stability and the nature of the amorphous products, has not yet been established. This paper presents a time-resolved study of the transition from the crystalline to the amorphous phase of two violet-light absorbing thio-stannates, i.e. AEPz-SnS-1 [AEPz = 1-(2-amino-ethyl)-piperazine] and trenH-SnS-1 [tren = tris-(2-amino-ethyl)-amine]. X-ray total scattering data and pair distribution function analysis reveal no change in the local intralayer coordination during the amorphization. However, a rapid decrease in the crystalline domain sizes upon suspension in water is demonstrated. Although scanning electron microscopy shows no significant decrease of the micrometre-sized particles, transmission electron microscopy reveals the formation of small particles (∼200-400 nm) in addition to the larger particles. The amorphization is associated with disorder of the thio-stannate nanosheet stacking. For example, an average decrease in the interlayer distance (from 19.0 to 15.6 Å) is connected to the substantial loss of the organic components as shown by elemental analysis and X-ray photoelectron spectroscopy. Despite the structural changes, the light absorption properties of the amorphisized R-SnS-1 compounds remain intact, which is encouraging for future water-based applications of such materials.

Unveiling the Interfacial Instability of the Phosphorus/Carbon Anode for Sodium-Ion Batteries

As a competitive anode material for sodium-ion batteries (SIBs), a commercially available red phosphorus, featured with a high theoretical capacity (2596 mA h g^-1) and a suitable operating voltage plateau (0.1-0.6 V), has been confronted with a severe structural instability and a rapid capacity degradation upon large volumetric change. In particular, the fundamental determining factors for phosphorus anode materials are yet poorly understood, and their interfacial stability against ambient air has not been explored and clarified. Herein, a high-performance phosphorus/carbon anode material has been fabricated simply through ball-milling the carbon black and red phosphorus, delivering a high reversible capacity of 1070 mA h g^-1 at 400 mA g^-1 after 200 cycles and a superior rate capability of 479 mA h g^-1 at 3200 mA g^-1. More importantly, we first reveal the significance of inhibiting the exposure of phosphorus/carbon electrode materials to air, even for a short period, for achieving a good electrochemical performance, which would sharply decrease the reversible capacities. With the assistance of synchrotron-based X-ray techniques, the formation and accumulation of insulating phosphate compounds can be spectroscopically identified, leading to the decay of electrochemical performance. At the same time, these passivation layers on the surface of electrode were found to occur via a self-oxidation process in ambient air. To maintain the electrochemical advantages of phosphorus anodes, it is necessary to inhibit their contact with air through a rational coating or an optimal storage condition. Additionally, the employment of a fluoroethylene carbonate (FEC) additive facilitates the decomposition of the electrolyte and favors the formation of a robust solid electrolyte interphase layer, which may suppress the side reactions between the active Na-P compounds and the electrolyte. These findings could help improve the surface protection and interfacial stability of phosphorus anodes for high-performance SIBs.

Crumpled Nitrogen-Doped Graphene-Wrapped Phosphorus Composite as a Promising Anode for Lithium-Ion Batteries

Red phosphorus (P) has recently gained wide attention because of the high theoretical capacity of 2596 mA h/g, which has been regarded as promising anode material for lithium-ion batteries (LIBs). However, the actual application of red P in LIBs is hampered by the huge expansion of volume and low electronic conductivity. Herein, we design a kind of red phosphorus/crumpled nitrogen-doped graphene (P/CNG) nanocomposites with high capacity density and great rate performance as anode material for LIBs. This anode material was rationally fabricated through the scalable ball-milling method. The nanocomposite structure of P/CNG improves the electron conductivity and alleviates volume change of raw red P because of the three-dimension (3D) framework, massive defects and active sites of CNG sheets. As expected, the P/CNG composite shows excellent electrochemical performances, including high capacity (2522.6 mA h/g at 130 mA/g), remarkable rate capability (1340.5 mA h/g at 3900 mA/g), and great cyclability (1470.1 mA h/g at 1300 mA/g for 300 cycles). This work may provide a broad prospect for a great rate performance of P-based anode material for LIBs.

First Principles Study of Penta-siligraphene as High-Performance Anode Material for Li-Ion Batteries

From first principles calculations, a novel pentagonal Si/C complexity is predicted to have potential applications as a promising anode material for Li-ion batteries. It is found that the structural and thermal stability of the penta-siligraphene (P-Si2C4) is better than penta-graphene that is composed of C atoms only. Electronic band structure analysis shows that the empty C-2pz state in the P-Si2C4 provides space to accommodate and stabilize electrons from Li, which makes Li storage energetically favorable. As a result, four Li atoms can be stored by one formula unit of the P-Si2C4, corresponding to a theoretical gravimetric Li storage capacity of 1028.7 mAhg-1. The metallic electronic structures of the Li-adsorbed P-LixSi2C4 as well as very small Li migration energy barriers are beneficial for fast charge/discharge performance of the battery. The mechanism on the Li adsorption interaction on the P-Si2C4 is discussed. These results demonstrate a novel strategy to design two-dimensional Si/C complex anode materials for high-performance Li-ion batteries.