Recent Advances in Designing High-Capacity Anode Nanomaterials for Li-Ion Batteries and Their Atomic-Scale Storage Mechanism Studies

Engineered Two-Dimensional Transition Metal Dichalcogenides for Energy Conversion and Storage

Designing efficient and cost-effective materials is pivotal to solving the key scientific and technological challenges at the interface of energy, environment, and sustainability for achieving NetZero. Two-dimensional transition metal dichalcogenides (2D TMDs) represent a unique class of materials that have catered to a myriad of energy conversion and storage (ECS) applications. Their uniqueness arises from their ultra-thin nature, high fractions of atoms residing on surfaces, rich chemical compositions featuring diverse metals and chalcogens, and remarkable tunability across multiple length scales. Specifically, the rich electronic/electrical, optical, and thermal properties of 2D TMDs have been widely exploited for electrochemical energy conversion (e.g., electrocatalytic water splitting), and storage (e.g., anodes in alkali ion batteries and supercapacitors), photocatalysis, photovoltaic devices, and thermoelectric applications. Furthermore, their properties and performances can be greatly boosted by judicious structural and chemical tuning through phase, size, composition, defect, dopant, topological, and heterostructure engineering. The challenge, however, is to design and control such engineering levers, optimally and specifically, to maximize performance outcomes for targeted applications. In this review we discuss, highlight, and provide insights on the significant advancements and ongoing research directions in the design and engineering approaches of 2D TMDs for improving their performance and potential in ECS applications.

Tailoring Alkalized and Oxidized V2CTx as Anode Materials for High-Performance Lithium Ion Batteries

V2CTx MXenes have gained considerable attention in lithium ion batteries (LIBs) owing to their special two-dimensional (2D) construction with large lithium storage capability. However, engineering high-capacity V2CTx MXenes is still a great challenge due to the limited interlayer space and poor surface terminations. In view of this, alkalized and oxidized V2CTx MXenes (OA-V2C) are envisaged. SEM characterization confirms the accordion-like layered morphology of OA-V2C. The XPS technique illustrates that undergoing alkalized and oxidized treatment, V2CTX MXene replaces -F and -OH with -O groups, which are more conducive to pseudocapacitive properties as well as Na ion diffusion, providing more active sites for ion storage in OA-V2C. Accordingly, the electrochemical performance of OA-V2C as anode materials for LIBs is evaluated in this work, showing excellent performance with high reversible capacity (601 mAh g-1 at 0.2 A g-1 over 500 cycles), competitive rate performance (222.2 mAh g-1 and 152.8 mAh g-1 at 2 A g-1 and 5 A g-1), as well as durable long-term cycling property (252 mAh g-1 at 5 A g-1 undergoing 5000 cycles). It is noted that the intercalation of Na+ ions and oxidation co-modification greatly reduces F surface termination and concurrently increases interlayer spacing in OA-V2C, significantly expediting ion/electron transportation and providing an efficient way to maximize the performance of MXenes in LIBs. This innovative refinement methodology paves the way for building high-performance V2CTx MXenes anode materials in LIBs.

Bio-Inspired Electrodes with Rational Spatiotemporal Management for Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are currently the predominant energy storage power source. However, the urgent issues of enhancing electrochemical performance, prolonging lifetime, preventing thermal runaway-caused fires, and intelligent application are obstacles to their applications. Herein, bio-inspired electrodes owning spatiotemporal management of self-healing, fast ion transport, fire-extinguishing, thermoresponsive switching, recycling, and flexibility are overviewed comprehensively, showing great promising potentials in practical application due to the significantly enhanced durability and thermal safety of LIBs. Taking advantage of the self-healing core-shell structures, binders, capsules, or liquid metal alloys, these electrodes can maintain the mechanical integrity during the lithiation-delithiation cycling. After the incorporation of fire-extinguishing binders, current collectors, or capsules, flame retardants can be released spatiotemporally during thermal runaway to ensure safety. Thermoresponsive switching electrodes are also constructed though adding thermally responsive components, which can rapidly switch LIB off under abnormal conditions and resume their functions quickly when normal operating conditions return. Finally, the challenges of bio-inspired electrode designs are presented to optimize the spatiotemporal management of LIBs. It is anticipated that the proposed electrodes with spatiotemporal management will not only promote industrial application, but also strengthen the fundamental research of bionics in energy storage.

Unveiling the relationship between the multilayer structure of metallic MoS2 and the cycling performance for lithium ion batteries

Molybdenum disulfide (MoS₂) with a layered structure is a desirable substitute for the graphite anode in lithium ion storage. Compared with the semiconducting phase (2H-MoS₂), the metallic polymorph (1T-MoS₂) usually shows much better cycling stability. Nevertheless, the origin of this remarkable cycling stability is still ambiguous, hindering further development of MoS₂-based anodes. Herein, we assembled multilayered 1T-MoS₂ nanosheets directly on Ti foil to investigate the Li⁺ storage mechanism. Based on experimental observation and computational simulation, we found that the cycling stability correlates with the layer number of MoS₂. Multilayered 1T-MoS₂ can accommodate inserted Li⁺ in a ternary compound Li-Mo-S through a reversible reaction, which is favorable for retaining a substantial number of MoS₂ nanodomains upon Li intercalation. These residual MoS₂ nanodomains can serve as an anchor to adhere Li_xS species, thereby suppressing the "shuttle effect" of polysulfides and enhancing cycling stability. This work sheds light on the development of high-performance anodes based on metallic MoS₂ for LIBs.

Purification of silicon from waste photovoltaic cells and its value-added application in lithium-ion batteries

A facile and promising method was proposed to make full use of waste photovoltaic cell natural characteristics by fabricating the PSi/Li/N@C composite as high-performance LIB anode material.

Study of the Structure and Properties of ZnS Utilized in a Fluorescence Biosensor

ZnS materials have been widely used in fluorescence biosensors to characterize different types of stem cells due to their excellent fluorescence effect. In this study, ZnS was prepared by vulcanizing nano-Zn particles synthesized using a DC arc plasma. The composition and structure of the ZnS materials were studied by X-ray diffraction (XRD), and their functional group information and optical properties were investigated by using IR spectrophotometry and UV-vis spectrophotometry. It has been found that the synthesized materials consist of Zn, cubic ZnS, and hexagonal ZnS according to the vulcanization parameters. Crystalline ZnS was gradually transformed from a cubic to a hexagonal structure, and the cycling properties first increase, then decrease with increasing sulfurization temperature. There is an optimal curing temperature giving the best cycling performance and specific capacity: the material sulfurized thereat mainly consists of cubic β-ZnS phase with a small quantity of Zn and hexagonal α-ZnS. The cubic phase ZnS has better conductivity than hexagonal ZnS, as evinced by electrochemical impedance spectroscopy (EIS). The ZnS (as prepared) shows board absorption, which can be used in fluorescence biosensors in cell imaging systems.

SnSe, the rising star thermoelectric material: a new paradigm in atomic blocks, building intriguing physical properties

Thermoelectric (TE) materials, which enable direct energy conversion between waste heat and electricity, have witnessed enormous and exciting developments over last several decades due to innovative breakthroughs both in materials and the synergistic optimization of structures and properties. Among the promising state-of-the-art materials for next-generation thermoelectrics, tin selenide (SnSe) has attracted rapidly growing research interest for its high TE performance and the intrinsic layered structure that leads to strong anisotropy. Moreover, complex interactions between lattice, charge, and orbital degrees of freedom in SnSe make up a large phase space for the optimization of its TE properties via the simultaneous tuning of structural and chemical features. Various techniques, especially advanced electron microscopy (AEM), have been devoted to exploring these critical multidiscipline correlations between TE properties and microstructures. In this review, we first focus on the intrinsic layered structure as well as the extrinsic structural "imperfectness" of various dimensions in SnSe as studied by AEM. Based on these characterization results, we give a comprehensive discussion on the current understanding of the structure-property relationship. We then point out the challenges and opportunities as provided by modern AEM techniques toward a deeper knowledge of SnSe based on electronic structures and lattice dynamics at the nanometer or even atomic scale, for example, the measurements of local charge and electric field distribution, phonon vibrations, bandgap, valence state, temperature, and resultant TE effects.

Stabilization of Sn Anode through Structural Reconstruction of a Cu-Sn Intermetallic Coating Layer

The metallic tin (Sn) anode is a promising candidate for next-generation lithium-ion batteries (LIBs) due to its high theoretical capacity and electrical conductivity. However, Sn suffers from severe mechanical degradation caused by large volume changes during lithiation/delithiation, which leads to a rapid capacity decay for LIBs application. Herein, a Cu-Sn (e.g., Cu₃ Sn) intermetallic coating layer (ICL) is rationally designed to stabilize Sn through a structural reconstruction mechanism. The low activity of the Cu-Sn ICL against lithiation/delithiation enables the gradual separation of the metallic Cu phase from the Cu-Sn ICL, which provides a regulatable and appropriate distribution of Cu to buffer volume change of Sn anode. Concurrently, the homogeneous distribution of the separated Sn together with Cu promotes uniform lithiation/delithiation, mitigating the internal stress. In addition, the residual rigid Cu-Sn intermetallic shows terrific mechanical integrity that resists the plastic deformation during the lithiation/delithiation. As a result, the Sn anode enhanced by the Cu-Sn ICL shows a significant improvement in cycling stability with a dramatically reduced capacity decay rate of 0.03% per cycle for 1000 cycles. The structural reconstruction mechanism in this work shines a light on new materials and structural design that can stabilize high-performance and high-volume-change electrodes for rechargeable batteries and beyond.

Nanospace-Confinement Synthesis: Designing High-Energy Anode Materials toward Ultrastable Lithium-Ion Batteries

Exploiting high-capacity and durable electrode materials is pivotal to developing lithium-ion batteries (LIBs) and their applications. Multiscaled nanomaterials have been demonstrated to efficiently couple the advantages of each component on different scales in energy storage fields. However, the precise control of the microstructure remains a great challenge for maximizing their contributions. Nanospace-confined synthesis provides a proactive strategy to build novel multiscaled nanomaterials with controllable internal void space for circumventing the intrinsic volume effects in the charge/discharge process. Herein, the rational design and synthesis of multiscaled high-capacity anode materials are mainly summarized according to their electrochemical mechanisms by choosing 1D channel, 2D interlayer, and 3D space as representative confinement reaction environments. The structure-performance relationships are clarified with the assistance of quantitative calculations, molecular simulations, and so forth. Finally, future potentials and challenges of such a synthesis tactic in designing high-performance electrode materials for next-generation secondary batteries are outlooked.

Hollow structured cathode materials for rechargeable batteries

Hollow structuring has been intensively studied as an effective strategy to improve the electrochemical performance of the electrode materials for rechargeable batteries in terms of specific capacity, rate capability, and cycling performance. To date, hollow structured anode materials have been extensively investigated, while hollow structured cathode materials (HSCMs) are relatively less explored because of the difficulties in morphological control as well as the concern of reduced volumetric capacities. In this paper, we provide an overview of the research advances in the synthesis and evolution of HSCMs for metal (Li, Na, etc.) ion batteries. Attributing to the advantages of hollow structures including high surface area, excellent accessibility to active sites, and enhanced mass transport and diffusion, hollow structuring can significantly improve the performance of high-capacity cathode materials with low kinetics, such as lithium rich layered oxides, silicates, and V₂O₅. It is anticipated that the precise and facile control of the spatial configuration can balance the electrochemical performance of HSCMs and the volumetric capacities of HSCMs, leading to practical high-performance batteries.

Nanostructured metal chalcogenides confined in hollow structures for promoting energy storage

The engineering of progressive nanostructures with subtle construction and abundant active sites is a key factor for the advance of highly efficient energy storage devices. Nanostructured metal chalcogenides confined in hollow structures possess abundant electroactive sites, more ions and electron pathways, and high local conductivity, as well as large interior free space in a quasi-closed structure, thus showing promising prospects for boosting energy-related applications. This review focuses on the most recent progress in the creation of diverse confined hollow metal chalcogenides (CHMCs), and their electrochemical applications. Particularly, by highlighting certain typical examples from these studies, a deep understanding of the formation mechanism of confined hollow structures and the decisive role of microstructure engineering in related performances are discussed and analyzed, aiming at prompting the nanoscale engineering and conceptual design of some advanced confined metal chalcogenide nanostructures. This will appeal to not only the chemistry-, energy-, and materials-related fields, but also environmental protection and nanotechnology, thus opening up new opportunities for applications of CHMCs in various fields, such as catalysis, adsorption and separation, and energy conversion and storage.

Layered Transition Metal Dichalcogenide-Based Nanomaterials for Electrochemical Energy Storage

The rapid development of electrochemical energy storage (EES) systems requires novel electrode materials with high performance. A typical 2D nanomaterial, layered transition metal dichalcogenides (TMDs) are regarded as promising materials used for EES systems due to their large specific surface areas and layer structures benefiting fast ion transport. The typical methods for the preparation of TMDs and TMD-based nanohybrids are first summarized. Then, in order to improve the electrochemical performance of various kinds of rechargeable batteries, such as lithium-ion batteries, lithium-sulfur batteries, sodium-ion batteries, and other types of emerging batteries, the strategies for the design and fabrication of layered TMD-based electrode materials are discussed. Furthermore, the applications of layered TMD-based nanomaterials in supercapacitors, especially in untraditional supercapacitors, are presented. Finally, the existing challenges and promising future research directions in this field are proposed.

Construction of Mn-Zn binary carbonate microspheres on interconnected rGO networks: creating an atomic-scale bimetallic synergy for enhancing lithium storage properties

Transition metal carbonates (TMCs), as promising anode materials for high-performance lithium ion batteries, possess the advantages of abundant natural resources and high electrochemical activity; however, they suffer from poor Li+/e- conductivities and serious volume changes during the charge/discharge process. Constructing multicomponent carbonates by introducing binary metal atoms, as well as designing a robust structure at the micro and nanoscales, could efficiently address the above problems. Therefore, single-phase MnxZn1-xCO3 microspheres anchored on 3D conductive networks of reduced graphene oxide (rGO) are facilely synthesized via a one-pot hydrothermal method without any structure-directing agents or surfactants. Due to the well-designed architecture and atomic-scale bimetallic synergy, the MnxZn1-xCO3/rGO composites show superior lithium storage capacity, good rate capability and ultra-long cycling performance. Specifically, the Mn2/3Zn1/3CO3/rGO composites could deliver a high capacity of 1073 mA h g-1 at 200 mA g-1. After 1700 cycles at a high rate of 2000 mA g-1, a stable capacity of 550 mA h g-1 can be maintained with the capacity retention approaching 88.6%. Density functional theory (DFT) calculations indicate that the partial Zn substitution in MnCO3 could significantly decrease the band gap of the crystal, resulting in great improvement of electric conductivity. Moreover, the commercial potential of the MnxZn1-xCO3/rGO composites is investigated by assembling full cells, suggesting good practical adaptability of the composite anodes. This work would provide a feasible and cost-efficient method to develop high-performance anodes and stimulate many more related research studies on TMC-based electrodes.

In Situ Synthesis of MoC1- x Nanodot@Carbon Hybrids for Capacitive Lithium-Ion Storage

In this study, in situ synthesis of carbon-coated MoC_{1- x} nanodots anchored on nitrogen-doped carbon (MoC_{1- x}@C) for lithium storage is reported. The obtained MoC_{1- x}@C hybrids exhibit intriguing structural characteristics including ultrafine particle size (ca. 1.2 nm) of MoC_{1- x} nanodots, porous structure of nitrogen-doped carbon matrix, and good robustness. When evaluated as anodes for lithium-ion batteries, the optimized MoC_{1- x}@C sample demonstrates a superior specific capacity (1099.2 mA h g^-1 at 0.1 A g^-1) and good rate capability (369.1 mA h g^-1 at 5 A g^-1). The MoC_{1- x}@C anode also presents remarkable cycling stability with a much higher specific capacity (657.9 mA h g^-1) than that of commercial bulk MoC (91.4 mA h g^-1) after 500 cycles at 1 A g^-1. Kinetics analysis of the anodes reveals the charge storage mechanism, which demonstrates the existence of capacitive redox reactions occurring at the shallow surface of the MoC_{1- x} nanodots and closely relating to the particle size. The outstanding electrochemical performance results from the synergistic effect of the elastic carbonaceous encapsulation to accommodate the huge volume expansion and the ultrafine MoC_{1- x} nanodots to provide more reactive sites for capacitive lithium storage.

POSS-Derived Synthesis and Full Life Structural Analysis of Si@C as Anode Material in Lithium Ion Battery

Polyhedral oligomeric silsesquioxane (POSS)-derived Si@C anode material is prepared by the copolymerization of octavinyl-polyhedral oligomeric silsesquioxane (octavinyl-POSS) and styrene. Octavinyl-polyhedral oligomeric silsesquioxane has an inorganic core (-Si₈O12) and an organic vinyl shell. Carbonization of the core-shell structured organic-inorganic hybrid precursor results in the formation of carbon protected Si-based anode material applicable for lithium ion battery. The initial discharge capacity of the battery based on the as-obtained Si@C material Si reaches 1500 mAh g-1. After 550 charge-discharge cycles, a high capacity of 1430 mAh g-1 was maintained. A combined XRD, XPS and TEM analysis was performed to investigate the variation of the discharge performance during the cycling experiments. The results show that the decrease in discharge capacity in the first few cycles is related to the formation of solid electrolyte interphase (SEI). The subsequent rise in the capacity can be ascribed to the gradual morphology evolution of the anode material and the loss of capacity after long-term cycles is due to the structural pulverization of silicon within the electrode. Our results not only show the high potential of the novel electrode material but also provide insight into the dynamic features of the material during battery cycling, which is useful for the future design of high-performance electrode material.

Structural and electrochemical behavior of a NiMnO3/Mn2O3 nanocomposite as an anode for high rate and long cycle lithium ion batteries

In this work, first time a pre-designed NiMnO₃/Mn₂O₃ nanocomposite is synthesized via a facile urea-assisted auto-combustion synthesis with the phase fraction ratio of ∼89% and ∼11%, respectively as an anode material for lithium-ion batteries.

2D-Pnictogens: alloy-based anode battery materials with ultrahigh cycling stability

There is an increasing demand for efficient energy storage systems in our modern mobile society for a wide range of applications such as smart grids, portable electronic devices, and electric vehicles. The performance of advanced batteries in terms of energy density, power density, cyclability, and safety is mainly determined by the primary functional components, particularly by the electrode materials. Black phosphorus (BP) and the following elements in group V (pnictogens) including arsenic, antimony, and bismuth with layered structures have attracted tremendous attention to replace the graphite anode. This is due to their extremely high specific-capacities for lithium and sodium storage based on the alloying reaction mechanism; however, the same mechanism causes an irreversible volume expansion and thus low cycling stability. Since the discovery of single layer BP and its outstanding physical properties such as tunable band gap, strong in-plane anisotropy, and high carrier mobility, the battery community have intensively studied this material as well as the 2D structures of other pnictogens. In this review, first, the preparation and properties of 2D-pnictogens including crystal structure and chemical stability are briefly described. Second, the theoretical and experimental details of the intercalation and alloying mechanisms are discussed. Finally, the excellent performance of 2D-pnictogens for lithium ion and sodium ion batteries and their principal advantages compared to their parent 3D structures are presented.