Synergy of Black Phosphorus-Graphite-Polyaniline-Based Ternary Composites for Stable High Reversible Capacity Na-Ion Battery Anodes

Controlled Growth Lateral/Vertical Heterostructure Interface for Lithium Storage

Artificial heterostructures with structural advancements and customizable electronic interfaces are fundamental for achieving high-performance lithium-ion batteries (LIBs). Here, a design idea for a covalently bonded lateral/vertical black phosphorus (BP)-graphdiyne oxide (GDYO) heterostructure achieved through a facile ball-milling approach, is designed. Lateral heterogeneity is realized by the sp2-hybridized mode P-C bonds, which connect the phosphorus atoms at the edges of BP with the carbon atoms of the terminal acetylene in GDYO. The vertical connection of the heterojunction of BP and GDYO is connected by P-O-C bond. Experimental and theoretical studies demonstrate that BP-GDYO incorporates interfacial and structural engineering features, including built-in electric fields, chemical bond interactions, and maximized nanospace confinement effects. Therefore, BP-GDYO exhibits improved electrochemical kinetics and enhanced structural stability. Moreover, through ex- and in-situ studies, the lithiation mechanism of BP-GDYO, highlighting that the introduction of GDYO inhibits the shuttle/dissolution effect of phosphorus intermediates, hinders volume expansion, provides more reactive sites, and ultimately promotes reversible lithium storage, is clarified. The BP-GDYO anode exhibits lithium storage performance with high-rate capacity and long-cycle stability (602.6 mAh g-1 after 1 000 cycles at 2.0 A g-1). The proposed interfacial and structural engineering is universal and represents a conceptual advance in building high-performance LIBs electrode.

Towards the Future of Polymeric Hybrids of Two-Dimensional Black Phosphorus or Phosphorene: From Energy to Biological Applications

With the advent of a new 2D nanomaterial, namely, black phosphorus (BP) or phosphorene, the scientific community is now dedicated to focusing on and exploring this 2D material offering elusive properties such as a higher carrier mobility, biocompatibility, thickness-dependent band gap, and optoelectronic characteristics that can be harnessed for multiple applications, e.g., nanofillers, energy storage devices, field effect transistors, in water disinfection, and in biomedical sciences. The hexagonal ring of phosphorus atoms in phosphorene is twisted slightly, unlike how it is in graphene. Its unique characteristics, such as a high carrier mobility, anisotropic nature, and biocompatibility, have attracted much attention and generated further scientific curiosity. However, despite these interesting features, the phosphorene or BP poses challenges and causes frustrations when it comes to its stability under ambient conditions and processability, and thus in order to overcome these hurdles, it must be conjugated or linked with the suitable and functional organic counter macromolecule in such a way that its properties are not compromised while providing a protection from air/water that can otherwise degrade it to oxides and acid. The resulting composites/hybrid system of phosphorene and a macromolecule, e.g., a polymer, can outperform and be exploited for the aforementioned applications. These assemblies of a polymer and phosphorene have the potential for shifting the paradigm from exhaustively used graphene to new commercialized products offering multiple applications.

Tunable Schottky and ohmic contacts in the Ti2NF2/α-Te van der Waals heterostructure

Two dimensional α-Te holds great promise in optoelectronic devices because of its high mobility and excellent environmental stability. In this study, the electronic structures and interfacial contact characteristics of the Ti₂NF₂/α-Te van der Waals heterostructure are investigated by means of first-principles calculations. It is found that p-type Schottky contacts with a Schottky barrier (SB) of 0.21 eV are formed at the Ti₂NF₂/α-Te interface. By applying external electric fields or controlling the interlayer coupling between the Ti₂NF₂ and α-Te monolayers, the SB height can be effectively tuned, and all the n-type Schottky, p-type Schottky, n-type ohmic and p-type ohmic contacts can be achieved. Such an extremely high tunability is further found to be closely associated with the charge transfer at the interface, as well as the interface dipole and the potential step. Our results provide an avenue for the design of future α-Te-based electronic devices with high performance.

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.

Phosphorus/Phosphide-Based Materials for Alkali Metal-Ion Batteries

Phosphorus- and phosphide-based materials with remarkable physicochemical properties and low costs have attracted significant attention as the anodes of alkali metal (e.g., Li, Na, K, Mg, Ca)-ion batteries (AIBs). However, the low electrical conductivity and large volume expansion of these materials during electrochemical reactions inhibit their practical applications. To solve these problems, various promising solutions have been explored and utilized. In this review, the recent progress in AIBs using phosphorus- and phosphide-based materials is summarized. Thereafter, the in-depth working principles of diverse AIBs are discussed and predicted. Representative works with design concepts, construction approaches, engineering strategies, special functions, and electrochemical results are listed and discussed in detail. Finally, the existing challenges and issues are concluded and analyzed, and future perspectives and research directions are given. This review can provide new guidance for the future design and practical applications of phosphorus- and phosphide-based materials used in AIBs.

Electrochemistry of P-C Bonds in Phosphorus-Carbon Based Anode Materials

Phosphorus-carbon anode materials for alkali-metal ion storage in rechargeable batteries can simultaneously achieve high-energy density and fast charging. The P-C-bonded structure in the phosphorus-carbon materials has been observed and acknowledged to be a critical structural feature that renders improved cycling stability and rate performance. However, the underlying mechanisms, especially the role played by P-C bonds, remain elusive. By combining computational simulations and spectroscopic characterizations, we reveal that the stability of P-C bonds is critical to the electrochemical performance. In the discharge process, P-P bonds are fragile, while the bonding state of the P-C bonds is almost unchanged since electrons were mainly received by the P atoms to form lone pairs. The preserved P-C clusters can effectively serve as a reunion center for the recovery of P-P bonds in the recharging process, leading to a moderate energy change and improved cycling reversibility and structural stability of the phosphorous for electrochemical energy storage.

Facile Separator Modification Strategy for Trapping Soluble Polyphosphides and Enhancing the Electrochemical Performance of Phosphorus Anode

Phosphorus anode is one of the most promising candidates for high-energy-density lithium-ion batteries. Recent studies found the lithiation process of phosphorus is accompanied by the soluble intermediates of lithium polyphosphides. The trans-separator diffusion of polyphosphides is responsible for the capacity decay. Herein, a facile separator modification strategy is proposed for improving the performance of phosphorus anode. The lightweight CNT-modified layer that has a continuous conductive skeleton, a dense structure, and a strong interaction with the soluble lithium polyphosphides can trap, stabilize, and reactivate the active material. Without sophisticated electrode structure design, the cyclability and high-rate performance of the phosphorus anode has been significantly improved, leading to a higher specific capacity of 1505 mAh/g at 250 mA/g (200th cycle) and 1312 mAh/g at 2 A/g. With the advantages of simplicity and low cost, the separator modification strategy provides a new feasible way for further improvement of the phosphorus-based anode.

Black Phosphorus/Polymers: Status and Challenges

As a newly emerged mono-elemental nanomaterial, black phosphorus (BP) has been widely investigated for its fascinating physical properties, including layer-dependent tunable band gap (0.3-1.5 eV), high ON/OFF ratio (10⁴ ), high carrier mobility (10³ cm² V^-1 s^-1 ), excellent mechanical resistance, as well as special in-plane anisotropic optical, thermal, and vibrational characteristics. However, the instability caused by chemical degradation of its surface has posed a severe challenge for its further applications. A focused BP/polymer strategy has more recently been developed and implemented to hurdle this issue, so at present BP/polymers have been developed that exhibit enhanced stability, as well as outstanding optical, thermal, mechanical, and electrical properties. This has promoted researchers to further explore the potential applications of black phosphorous. In this review, the preparation processes and the key properties of BP/polymers are reviewed, followed by a detailed account of their diversified applications, including areas like optoelectronics, bio-medicine, and energy storage. Finally, in accordance with the current progress, the prospective challenges and future directions are highlighted and discussed.

Applications of Carbon in Rechargeable Electrochemical Power Sources: A Review

Rechargeable power sources are an essential element of large-scale energy systems based on renewable energy sources. One of the major challenges in rechargeable battery research is the development of electrode materials with good performance and low cost. Carbon-based materials have a wide range of properties, high electrical conductivity, and overall stability during cycling, making them suitable materials for batteries, including stationary and large-scale systems. This review summarizes the latest progress on materials based on elemental carbon for modern rechargeable electrochemical power sources, such as commonly used lead–acid and lithium-ion batteries. Use of carbon in promising technologies (lithium–sulfur, sodium-ion batteries, and supercapacitors) is also described. Carbon is a key element leading to more efficient energy storage in these power sources. The applications, modifications, possible bio-sources, and basic properties of carbon materials, as well as recent developments, are described in detail. Carbon materials presented in the review include nanomaterials (e.g., nanotubes, graphene) and composite materials with metals and their compounds.

Partial sodiation induced laminate structure and high cycling stability of black phosphorous for sodium-ion batteries

Black phosphorus (BP) is a promising anode material for sodium ion batteries (SIBs) due to its extremely high theoretical capacity. However, the large volume change and breaking of the layered structure result in rapid capacity decay during cycling. Herein, our in situ transmission electron microscopy (TEM) study reveals the highly anisotropic Na diffusion and the formation of alternating layered and amorphous lamellas in BP nanosheets with small volume expansion induced by partial sodiation. Inspired by these results, we investigate systematically the cyclability of BP at controlled discharge capacities using half-cell SIBs, expecting to achieve good cyclability by sacrificing some of the capacity and preserving the layered structure of BP. Our results show that the cycling stability of BP is obviously improved by controlling the capacity appropriately. When the discharge capacity is limited at 400 mA h g^-1, the half-cell can sustain more than 100 cycles with an active material mass loading of ∼2 mg cm^-2, which is at least 4 times longer than when the capacity is limited at 600 mA h g^-1 or above. The in situ TEM and electrochemical tests indicate that maintaining the layered structure by controlling the capacity is key to improve the cyclability of BP as an anode in SIBs.

Molybdenum-doped tin oxide nanoflake arrays anchored on carbon foam as flexible anodes for sodium-ion batteries

Tin oxide (SnO₂) has been widely used as an anode material for sodium-ion storage because of its high theoretical capacity. However, it suffers from large volume expansion and poor conductivity. To overcome these limitations, in this study, we have designed and prepared Mo-doped SnO₂ nanoflake arrays anchored on carbon foam (Mo-SnO₂@C-foam with 38.41 wt% SnO₂ and 3.7 wt% Mo content) by a facile hydrothermal method. The carbon foam serves as a three-dimensional conductive network and a buffer skeleton, contributing to improved rate performance and cycling stability. In addition, Mo doping enhances the kinetics of sodium-ion transfer, and the interlaced SnO₂ nanoflake arrays is beneficial to promote the conversion reactions during the charge/discharge process. The as-prepared composite with a unique structure demonstrate a high initial capacity of 1017.1 mAh g^-1 at 0.1 A g^-1, with a capacity retention over three times higher than that of the control sample (SnO₂@C-foam) at 1 A g^-1, indicating a remarkable rate performance.

A Review on Applications of Layered Phosphorus in Energy Storage

Phosphorus in energy storage has received widespread attention in recent years. Both the high specific capacity and ion mobility of phosphorus may lead to a breakthrough in energy storage materials. Black phosphorus, an allotrope of phosphorus, has a sheet-like structure similar to graphite. In this review, we describe the structure and properties of black phosphorus and characteristics of the conductive electrode material, including theoretical calculation and analysis. The research progress in various ion batteries, including lithium-sulfur batteries, lithium–air batteries, and supercapacitors, is summarized according to the introduction of black phosphorus materials in different electrochemical applications. Among them, with the introduction of black phosphorus in lithium-ion batteries and sodium-ion batteries, the research on the properties of black phosphorus and carbon composite is introduced. Based on the summary, the future development trend and potential of black phosphorus materials in the field of electrochemistry are analyzed.

Recent Advances in Chemical Functionalization of 2D Black Phosphorous Nanosheets

Owing to their tunable direct bandgap, high charge carrier mobility, and unique in-plane anisotropic structure, black phosphorus nanosheets (BPNSs) have emerged as one of the most important candidates among the 2D materials beyond graphene. However, the poor ambient stability of black phosphorus limits its practical application, due to the chemical degradation of phosphorus atoms to phosphorus oxides in the presence of oxygen and/or water. Chemical functionalization is demonstrated as an efficient approach to enhance the ambient stability of BPNSs. Herein, various covalent strategies including radical addition, nitrene addition, nucleophilic substitution, and metal coordination are summarized. In addition, efficient noncovalent functionalization methods such as van der Waals interactions, electrostatic interactions, and cation-π interactions are described in detail. Furthermore, the preparations, characterization, and diverse applications of functionalized BPNSs in various fields are recapped. The challenges faced and future directions for the chemical functionalization of BPNSs are also highlighted.

Electrode Materials for High-Performance Sodium-Ion Batteries

Sodium ion batteries (SIBs) are being billed as an economical and environmental alternative to lithium ion batteries (LIBs), especially for medium and large-scale stationery and grid storage. However, SIBs suffer from lower capacities, energy density and cycle life performance. Therefore, in order to be more efficient and feasible, novel high-performance electrodes for SIBs need to be developed and researched. This review aims to provide an exhaustive discussion about the state-of-the-art in novel high-performance anodes and cathodes being currently analyzed, and the variety of advantages they demonstrate in various critically important parameters, such as electronic conductivity, structural stability, cycle life, and reversibility.