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

Carbon encapsulated nanoparticles: materials science and energy applications

The technological implementation of electrochemical energy conversion and storage necessitates the acquisition of high-performance electrocatalysts and electrodes. Carbon encapsulated nanoparticles have emerged as an exciting option owing to their unique advantages that strike a high-level activity-stability balance. Ever-growing attention to this unique type of material is partly attributed to the straightforward rationale of carbonizing ubiquitous organic species under energetic conditions. In addition, on-demand precursors pave the way for not only introducing dopants and surface functional groups into the carbon shell but also generating diverse metal-based nanoparticle cores. By controlling the synthetic parameters, both the carbon shell and the metallic core are facilely engineered in terms of structure, composition, and dimensions. Apart from multiple easy-to-understand superiorities, such as improved agglomeration, corrosion, oxidation, and pulverization resistance and charge conduction, afforded by the carbon encapsulation, potential core-shell synergistic interactions lead to the fine-tuning of the electronic structures of both components. These features collectively contribute to the emerging energy applications of these nanostructures as novel electrocatalysts and electrodes. Thus, a systematic and comprehensive review is urgently needed to summarize recent advancements and stimulate further efforts in this rapidly evolving research field.

In Situ Construction of Crumpled Ti3C2Tx Nanosheets Confined S-Doping Red Phosphorus by Ti-O-P Bonds for LIBs Anode with Enhanced Electrochemical Performance

Red phosphorus (RP) with a high theoretical specific capacity (2596 mA h g-1) and a moderate lithiation potential (∼0.7 V vs Li+/Li) holds promise as an anode material for lithium-ion batteries (LIBs), which still confronts discernible challenges, including low electrical conductivity, substantial volumetric expansion of 300%, and the shuttle effect induced by soluble lithium polyphosphide (LixPPs). Here, S-NRP@Ti3C2Tx composites were in situ prepared through a phosphorus-amine-based method, wherein S-doped red phosphorus nanoparticles (S-NRP) grew and anchored on the crumpled Ti3C2Tx nanosheets via Ti-O-P bonds, constructing a three-dimensional porous structure which provides fast channels for ion and electron transport and effectively buffers the volume expansion of RP. Interestingly, based on the results of adsorption experiments of polyphosphate and DFT calculation, Ti3C2Tx with abundant oxygen functional groups delivers a strong chemical adsorption effect on LixPPs, thus suppressing the shuttle effect and reducing irreversible capacity loss. Furthermore, S-doping improved the conductivity of red phosphorus nanoparticles, facilitating Li-P redox kinetics. Hence, the S-NRP@Ti3C2Tx anode demonstrates outstanding rate performance (1824 and 1090 mA h g-1 at 0.2 and 4.0 A g-1, respectively) and superior cycling performance (1401 mAh g-1 after 500 cycles at 2.0 A g-1).

Simultaneous Catalytic Acceleration of White Phosphorus Polymerization and Red Phosphorus Potassiation for High-Performance Potassium-Ion Batteries

Red phosphorus (P) as an anode material of potassium-ion batteries possesses ultra-high theoretical specific capacity (1154 mAh g-1 ). However, owing to residual white P during the preparation and sluggish kinetics of K-P alloying limit its practical application. Seeking an efficient catalyst to address the above problems is crucial for the secure preparation of red P anode with high performance. Herein, through the analysis of the activation energies in white P polymerization, it is revealed that the highest occupied molecular orbital energy of I2 (-7.40 eV) is in proximity to P4 (-7.25 eV), and the lowest unoccupied molecular orbital energy of I2 molecule (-4.20 eV) is lower than that of other common non-metallic molecules (N2 , S8 , Se8 , F2 , Cl2 , Br2 ). The introduction of I2 can thus promote the breaking of the P─P bond and accelerate the polymerization of white P molecules. Besides, the ab initio molecular dynamics simulations show that I2 can enhance the kinetics of P-K alloying. The as-obtained red P/C composites with I2 deliver excellent cycling stability (358 mAh g-1 after 1200 cycles at 1 A g-1 ). This study establishes catalysis as a promising pathway to tackle the challenges of P anode for alkali metal ion batteries.

In situconstruction of N-doped Ti3C2Txconfined worm-like Fe2O3nanoparticles by Fe-O-Ti bonding for LIBs anode with superior cycle performance

The development of Fe2O3as lithium-ion batteries (LIBs) anode is greatly restricted by its poor electronic conductivity and structural stability. To solve these issues, this work presentsin situconstruction of three-dimensional crumpled Fe2O3@N-Ti3C2Txcomposite by solvothermal-freeze-drying process, in which wormlike Fe2O3nanoparticles (10-50 nm)in situnucleated and grew on the surface of N-doped Ti3C2Txnanosheets with Fe-O-Ti bonding. As a conductive matrix, N-doping endows Ti3C2Txwith more active sites and higher electron transfer efficiency. Meanwhile, Fe-O-Ti bonding enhances the stability of the Fe2O3/N-Ti3C2Txinterface and also acts as a pathway for electron transmission. With a large specific surface area (114.72 m2g-1), the three-dimensional crumpled structure of Fe2O3@N-Ti3C2Txfacilitates the charge diffusion kinetics and enables easier exposure of the active sites. Consequently, Fe2O3@N-Ti3C2Txcomposite exhibits outstanding electrochemical performance as anode for LIBs, a reversible capacity of 870.2 mAh g-1after 500 cycles at 0.5 A g-1, 1129 mAh g-1after 280 cycles at 0.2 A g-1and 777.6 mAh g-1after 330 cycles at 1 A g-1.

Photothermal-Responsive Intelligent Hybrid of Hierarchical Carbon Nanocages Encapsulated by Metal-Organic Hydrogels for Sensitized Photothermal Therapy

Hierarchical carbon nanocages as emerging nanomaterials have a great potential for photothermal therapy due to their unique porous structure, high specific surface area, and excellent photothermal property. Herein, a hierarchical nitrogen-doped carbon nanocage (hNCNC) is introduced as a second near-infrared photothermal agent, and then functionalizes it with metal-organic hydrogel (MOG) to form a thermal-responsive switch for sensitized photothermal therapy. Upon 1064 nm light irradiation, the hNCNCs exhibit a remarkable photothermal conversion efficiency of 65.9% owing to a high near-infrared extinction coefficient. Meanwhile, due to the hierarchical structure, hNCNCs show 60.2% (wt./wt.) loading efficiency of quercetin, a heat shock protein (Hsp70) inhibitor. Through thermal-driven dry-gel transformation, the coating MOGs intelligently release the encapsulated quercetin for sensitizing cancer cells to heat. Based on the synergistic effect of hyperthermia elevation and thermal-driven drug release, the dual thermal utilization platform achieves effective photothermal tumor ablation in vivo under low concentration of hNCNCs and mild irradiation, which provides a new diagram of intelligent responsive photothermal agents for enhanced photothermal therapy.

Unlocking Deep and Fast Potassium-Ion Storage through Phosphorus Heterostructure

Potassium-ion battery represents a promising alternative of conventional lithium-ion batteries in sustainable and grid-scale energy storage. Among various anode materials, elemental phosphorus (P) has been actively pursued owing to the ideal natural abundance, theoretical capacity, and electrode potential. However, the sluggish redox kinetics of elemental P has hindered fast and deep potassiation process toward the formation of final potassiation product (K3 P), which leads to inferior reversible capacity and rate performance. Here, it is shown that rational design on black/red P heterostructure can significantly improve K-ion adsorption, injection and immigration, thus for the first time unlocking K3 P as the reversible potassiation product for elemental P anodes. Density functional theory calculations reveal the fast adsorption and diffusion kinetics of K-ion at the heterostructure interface, which delivers a highly reversible specific capacity of 923 mAh g-1 at 0.05 A g-1 , excellent rate capability (335 mAh g-1 at 1 A g-1 ), and cycling performance (83.3% capacity retention at 0.8 A g-1 after 300 cycles). These results can unlock other sluggish and irreversible battery chemistries toward sustainable and high-performing energy storage.

Advanced Anode Materials for Rechargeable Sodium-Ion Batteries

Rechargeable sodium-ion batteries (SIBs) have been considered as promising energy storage devices owing to the similar "rocking chair" working mechanism as lithium-ion batteries and abundant and low-cost sodium resource. However, the large ionic radius of the Na-ion (1.07 Å) brings a key scientific challenge, restricting the development of electrode materials for SIBs, and the infeasibility of graphite and silicon in reversible Na-ion storage further promotes the investigation of advanced anode materials. Currently, the key issues facing anode materials include sluggish electrochemical kinetics and a large volume expansion. Despite these challenges, substantial conceptual and experimental progress has been made in the past. Herein, we present a brief review of the recent development of intercalation, conversion, alloying, conversion-alloying, and organic anode materials for SIBs. Starting from the historical research progress of anode electrodes, the detailed Na-ion storage mechanism is analyzed. Various optimization strategies to improve the electrochemical properties of anodes are summarized, including phase state adjustment, defect introduction, molecular engineering, nanostructure design, composite construction, heterostructure synthesis, and heteroatom doping. Furthermore, the associated merits and drawbacks of each class of material are outlined, and the challenges and possible future directions for high-performance anode materials are discussed.

Self-assembled nanoflower-like FeSe2/MoSe2 heterojunction anode with enhanced kinetics for superior-performance Na-ion half/full batteries

Transition metal selenides are a research hotspot in sodium-ion batteries (SIBs). However, slow kinetics and rapid capacity decay due to volume changes during cycling limit their commercial applications. Heterostructures have the ability to accelerate charge transport and are widely used in energy storage devices due to their abundant active sites and lattice interfaces. A rational design of heterojunction electrode materials with excellent electrochemical performance is essential for SIBs. Herein, a novel anode material heterostructured FeSe₂/MoSe₂ (FMSe) nanoflower for SIBs was successfully prepared through a facile co-precipitation and hydrothermal route. The as-prepared FMSe heterojunction exhibits excellent electrochemical performance, including a high invertible capacity (493.7 mA h g^-1 after 150 cycles at 0.2 A g^-1), long-term cycling stability (352.2 mA h g^-1 even after 4200 cycles at 5.0 A g^-1) and competitive rate capability (361.2 mA h g^-1 at 20 A g^-1). By matching with a Na₃V₂(PO₄)₃ cathode, it can even exhibit ideal cycling stability (123.5 mA h g^-1 at 0.5 A g^-1 after 200 cycles). Furthermore, the sodium storage mechanism of the FMSe electrodes was systematically determined by ex situ electrochemical techniques. Theoretical calculation also reveals that the heterostructure on the FMSe interface enhances charge transport and promotes reaction kinetics.

Recent Progress of Hollow Carbon Nanocages: General Design Fundamentals and Diversified Electrochemical Applications

Hollow carbon nanocages (HCNCs) consisting of sp2  carbon shells featured by a hollow interior cavity with defective microchannels (or customized mesopores) across the carbon shells, high specific surface area, and tunable electronic structure, are quilt different from the other nanocarbons such as carbon nanotubes and graphene. These structural and morphological characteristics make HCNCs a new platform for advanced electrochemical energy storage and conversion. This review focuses on the controllable preparation, structural regulation, and modification of HCNCs, as well as their electrochemical functions and applications as energy storage materials and electrocatalytic conversion materials. The metal single atoms-functionalized structures and electrochemical properties of HCNCs are summarized systematically and deeply. The research challenges and trends are also envisaged for deepening and extending the study and application of this hollow carbon material. The development of multifunctional carbon-based composite nanocages provides a new idea and method for improving the energy density, power density, and volume performance of electrochemical energy storage and conversion devices.

Solid-State Electrolytes for Rechargeable Magnesium-Ion Batteries: From Structure to Mechanism

Rechargeable magnesium (Mg)-ion batteries have received growing attention as a next-generation battery system owing to their advantages of sufficient reserves, lower cost, better safety, and higher volumetric energy density than lithium-ion batteries. However, Mg as an anode can be easily passivated during charging/discharging by most common solvents, which are inconducive for magnesium deposition/stripping. Based on this, the development of Mg-ion solid-state electrolytes in the last decades led to the formulization of several concepts beyond previously reported designs. These exciting studies have once again sparked an interest in all-solid-state magnesium-ion batteries. In this review, Mg solid-state electrolytes, including inorganic (oxides, hydrides, and chalcogenides) and organic (metal-organic frameworks and polymers) materials are classified and summarized in detail. Moreover, the structural characteristics and the migration mechanism of Mg²⁺ ions are also discussed with a focus on pending questions and future prospects.

Constructing a Micrometer-Sized Structure through an Initial Electrochemical Process for Ultrahigh-Performance Li+ Storage

Orthorhombic niobium pentoxide (T-Nb₂O₅) is a promising anode to fulfill the requirements for high-rate Li-ion batteries (LIBs). However, its low electric conductivity and indistinct electrochemical mechanism hinder further applications. Herein, we develop a novel method to obtain a micrometer-sized layer structure of S-doped Nb₂O₅ on an S-doped graphene (SG) surface (the composite is denoted S-Nb₂O₅/SG) after the initial cycle, which we call "in situ electrochemically induced aggregation". In situ and ex situ characterizations and theoretical calculations were carried out to reveal the aggregation process and Li⁺ storage process. The unique merits of the composite with a micrometer-sized layer structure increased the reaction degree, structural stability, and electrochemical kinetics. As a result, the electrode exhibited a large capacity (∼598 mAh g^-1 at 0.1 A g^-1), outstanding cycling stability (∼313 mAh g^-1 at 5 A g^-1 and remains at ∼313 mAh g^-1 after 1000 cycles), and a high Coulombic efficiency and has a high fast-charging performance and excellent cycling stability.

Fully Active Bimetallic Phosphide Zn0.5Ge0.5P: A Novel High-Performance Anode for Na-Ion Batteries Coupled with Diglyme-Based Electrolyte

Metal phosphides are promising candidates for sodium-ion battery (SIB) anode owing to their large capacities with suitable redox potential, while the reversibility and rate performances are limited due to some electrochemically inactive transition-metal components and sluggish reaction kinetics. Here, we report a fully active bimetallic phosphide Zn_0.5Ge_0.5P anode and its composite (Zn_0.5Ge_0.5P-C) with excellent performance attributed to the Zn, Ge, and P components exerting their respective Na-storage merit in a cation-disordered structure. During Na insertion, Zn_0.5Ge_0.5P undergoes an alloying-type reaction, along with the generation of NaP, Na₃P, NaGe, and NaZn₁₃ phases, and the uniform distribution of these phases ensures the electrochemical reversibility during desodiation. Based on this reaction mechanism, excellent electrochemical properties such as a high reversible capacity of 595 mAh g^-1 and an ultrafast charge-discharge capability of 377.8 mAh g^-1 at 50C for 500 stable cycles were achieved within the Zn_0.5Ge_0.5P-C composite in a diglyme-based electrolyte. This work reveals the Na-storage reaction mechanism within Zn_0.5Ge_0.5P and offers a new perspective on designing high-performance anodes.

A high areal capacity sodium-ion battery anode enabled by a free-standing red phosphorus@N-doped graphene/CNTs aerogel

A novel and facile strategy for fabricating red phosphorus@nitrogen doped graphene/carbon nanotube aerogel (P@NGCA) is proposed as a free-standing anode for high energy sodium-ion batteries. Owing to an optimized structure of red P uniformly confined in porous NGCA with high conductivity and mechanical stability, the free-standing P@NGCA anode exhibits outstanding sodium storage performance with a high areal capacity of 3.3 mA h cm^-2 and superior initial Coulombic efficiency of 80%.

Regulating Dendrite-Free Zinc Deposition by Red Phosphorous-Derived Artificial Protective Layer for Zinc Metal Batteries

Rational architecture design of the artificial protective layer on the zinc (Zn) anode surface is a promising strategy to achieve uniform Zn deposition and inhibit the uncontrolled growth of Zn dendrites. Herein, a red phosphorous-derived artificial protective layer combined with a conductive N-doped carbon framework is designed to achieve dendrite-free Zn deposition. The Zn-phosphorus (ZnP) solid solution alloy artificial protective layer is formed during Zn plating. Meanwhile, the dynamic evolution mechanism of the ZnP on the Zn anode is successfully revealed. The concentration gradient of the electrolyte on the electrode surface can be redistributed by this protective layer, thereby achieving a uniform Zn-ion flux. The fabricated Zn symmetrical battery delivers a dendrite-free plating/stripping for 1100 h at the current density of 2.0 mA cm-2 . Furthermore, aqueous Zn//MnO2 full cell exhibits a reversible capacity of 200 mAh g-1 after 350 cycles at 1.0 A g-1 . This study suggests an effective solution for the suppression of Zn dendrites in Zn metal batteries, which is expected to provide a deep insight into the design of high-performance rechargeable aqueous Zn-ion batteries.

Red Phosphorus Anchored on Nitrogen-Doped Carbon Bubble-Carbon Nanotube Network for Highly Stable and Fast-Charging Lithium-Ion Batteries

A nitrogen-doped carbon bubble-carbon nanotube@red phosphorus (N-CBCNT@rP) network composite is fabricated, featuring an rP film embedded in a highly N-doped CBCNT network with hierarchical pores of different sizes and interior void spaces. Highly N-doped CBCNT with an optimized structure is utilized to achieve an ultrahigh rP content of 53 wt% in the N-CBCNT@rP composite by the NP bond, which shows a record rP content for rP-carbon composites by the vaporization-condensation process. When tested as an anode for lithium-ion batteries, the N-CBCNT@rP composite exhibits an ultrahigh initial Coulombic efficiency of 87.5%, high specific capacity, outstanding rate performance, and superior cycling stability at a high current density (capacity decay of 0.011% per cycle over 1500 cycles at 5 A g^-1 ), which is the lowest capacity fading rate of those previously reported for rP-based electrodes. The superior lithium-ion storage performance of the N-CBCNT@rP composite electrode is primarily attributed to its structure. The 3D hierarchical conducting network of the N-CBCNT@rP composite with abundant N-P bonds endows the entire electrode with maximized conductivity for superior ion and electron transfer kinetics. Moreover, N-CBCNT networks with hierarchical pores of different sizes can fix the location of rP, prevent agglomeration, and avoid volume expansion of rP.

Cluster Fragments in Amorphous Phosphorus and their Evolution under Pressure

Amorphous phosphorus (a-P) has long attracted interest because of its complex atomic structure, and more recently as an anode material for batteries. However, accurately describing and understanding a-P at the atomistic level remains a challenge. Here, it is shown that large-scale molecular-dynamics simulations, enabled by a machine-learning (ML)-based interatomic potential for phosphorus, can give new insights into the atomic structure of a-P and how this structure changes under pressure. The structural model so obtained contains abundant five-membered rings, as well as more complex seven- and eight-atom clusters. Changes in the simulated first sharp diffraction peak during compression and decompression indicate a hysteresis in the recovery of medium-range order. An analysis of cluster fragments, large rings, and voids suggests that moderate pressure (up to about 5 GPa) does not break the connectivity of clusters, but higher pressure does. The work provides a starting point for further computational studies of the structure and properties of a-P, and more generally it exemplifies how ML-driven modeling can accelerate the understanding of disordered functional materials.

Superfast Synthesis of Densely Packed and Ultrafine Pt-Lanthanide@KB via Solvent-Free Microwave as Efficient Hydrogen Evolution Electrocatalysts

At present, it is still a great challenge to synthesize refractory Pt-based electrocatalysts with excellent active specific surface area, specific activity, and stability by a simple method. Here, a superfast and solvent-free microwave strategy is reported to synthesize refractory ultrafine (≈3 nm) Pt-lanthanide@Ketjen Black (PtM@KB, M = La, Gd, Tb, Er, Tm, and Yb) alloy with densely packed as efficient hydrogen evolution electrocatalysts in a domestic microwave oven for the first time. The optimized Pt₆₁ La₃₉ @KB delivers excellent hydrogen evolution reaction (HER) activity with a low overpotential of 38 mV (10 mA cm^-2 ) and a high TOF value of 44.13 s^-1  (100 mV) in 0.5 m H₂ SO₄ , and performs well in 1.0 m KOH. This method can also be used to grow catalysts on carbon cloth (CC) directly. PtLa@CC shows an overpotential of 99 mV (1000 mA cm^-2 ) in 0.5 m H₂ SO₄ and can maintain activity after 500 h. Theoretical calculations reveal the enhanced stability and activity owing to the higher vacancy formation energy of Pt atoms and the optimized value of ΔG_H* . Solvent-free microwave strategy constitutes a significant insight into the development of refractory electrocatalyst with ultrafine size and highly dense, which can also work well at high current densities.

3D Carbon Networks: Design and Applications in Sodium Ion Batteries

As the key component of a new generation for low-cost energy storage systems, sodium-ion batteries (SIBs) have attracted enormous attention and research due to its promising potentiality in large-scale electrochemical energy storage. For practical application of SIBs, carbonaceous materials have been considered to be one of the best choices for electrodes in virtue of their abundant reserves, low cost, easy availability, and environmental friendliness. 3D carbon network (3D-carbon) is of particular interests, which has displayed outstanding features, including abundant active sites, interconnected multi-level pore structures, high electronic conductivity, and excellent mechanical stability. Herein, we review the structural advantages of 3D-carbon and its preparation methods, and then discuss recent progress in 3D carbon materials and their composites for SIBs. The superior functionalities of 3D-carbon are emphasized as support templates or encapsulation shell membranes. Finally, we summarize and outline the challenges and future prospects of 3D-carbon in SIBs.