Enabling Uniform and Stable Lithium-Ion Diffusion at the Ultrathin Artificial Solid-Electrolyte Interface in Siloxene Anodes

Constructing a stable and robust solid electrolyte interphase (SEI) has a decisive influence on the charge/discharge kinetics of lithium-ion batteries (LIBs), especially for silicon-based anodes which generate repeated destruction and regeneration of unstable SEI films. Herein, a facile way is proposed to fabricate an artificial SEI layer composed of lithiophilic chitosan on the surface of two-dimensional siloxene, which has aroused wide attention as an advanced anode for LIBs due to its special characteristics. The optimized chitosan-modified siloxene anode exhibits an excellent reversible cyclic stability of about 672.6 mAh g-1 at a current density of 1000 mA g-1 after 200 cycles and 139.9 mAh g-1 at 6000 mA g-1 for 1200 cycles. Further investigation shows that a stable and LiF-rich SEI film is formed and can effectively adhere to the surface during cycling, redistribute lithium-ion flux, and enable a relatively homogenous lithium-ion diffusion. This work provides constructive guidance for interface engineering strategy of nano-structured silicon anodes.

Green Synthesis of CoZn-Based Metal-Organic Framework (CoZn-MOF) from Waste Polyethylene Terephthalate Plastic As a High-Performance Anode for Lithium-Ion Battery Applications

The recycling of discarded polyethylene terephthalate (PET) plastics produced metal-organic frameworks can effectively minimize environmental pollution and promote sustainable economic development. In this study, we developed a method using NaOH in alcohol and ether solvent environments to degrade PET plastics for synthesizing terephthalic acid. The method achieved a 97.5% degradation rate of PET plastics under a reaction temperature of 80 °C for 60 min. We used terephthalic acid as a ligand from the degradation products to successfully synthesize two types of monometallic and bimetallic CoZn-MOF materials. We investigated the impact of different metal centers and solvents on the electrochemical performance of the MOF materials. The result showed that the MOF-DMF/H2O material maintained a specific capacity of 1485.5 mAh g-1 after 100 cycles at a current density of 500 mA g-1, demonstrating excellent rate capability and cycling stability. In addition, our finding showed that the performance difference might be attributed to the synergistic effect of bimetallic Co2+ and Zn2+ in MOF-DMF/H2O, rapid lithium-ion diffusion and electron transfer rates, and the absence of coordinating solvents. Additionally, the non-in situ X-ray powder diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analysis results showed that lithium storage in the MOF-DMF/H2O electrode mainly depended on the aromatic C6 ring and carboxylate portions of the organic ligands in different charge and discharge states. Lithium ions can be reversibly inserted/removed into/from the electrode material. The physical adsorption on the MOF surface through electrostatic interactions enhanced both capacity and cycling stability. This research provides valuable insight for mitigating solid waste pollution, promoting sustainable economic development, and advancing the extensive applications of MOF materials in lithium-ion batteries.

Facile Construction of Advanced 1D Metal-Organic Coordination Polymer for Efficient Lithium Storage

Recently, coordination polymers (CPs) have been frequently reported in the field of energy storage as electrode materials for lithium-ion batteries (LIBs) due to their highly adjustable architectures, which have a variety of active sites and obviously defined lithium transport routes. A well-designed redox-active organic linker with potential active sites for storing lithium ions, pyrazine-2,3-dicarboxylate (H2PDA), was applied for generating CPs by a simple hydrothermal method. When employed as anode materials in LIBs, those two one-dimensional (1D) CPs with an isomorphic composition, [M(PDA)(H2O)2]n (M = Co for Co-PDA and Ni for Ni-PDA), produced outstanding reversible capacities and stable cycling performance. The Co-PDA displays a substantial reversible capacity of 936 mAh g-1 at 200 mA g-1 after 200 cycles, as well as an excellent cycling life at high currents. According to the ex situ characterizations, the high reversible specific capacity of the post-cycled electrodes was found to be a result of both the transition metal ions and the organic ligands, and Co-PDA and Ni-PDA electrode materials show reversible insertion/extraction processes that are accompanied by crystallization to an amorphous state.

Terminal Group-Oriented Self-Assembly to Controllably Synthesize a Layer-by-Layer SnSe2 and MXene Heterostructure for Ultrastable Lithium Storage

Heterostructured materials integrate the advantages of adjustable electronic structure, fast electron/ions transfer kinetics, and robust architectures, which have attracted considerable interest in the fields of rechargeable batteries, photo/electrocatalysis, and supercapacitors. However, the construction of heterostructures still faces some severe problems, such as inferior random packing of components and serious agglomeration. Herein, a terminal group-oriented self-assembly strategy to controllably synthesize a homogeneous layer-by-layer SnSe₂ and MXene heterostructure (LBL-SnSe₂ @MXene) is designed. Benefitting from the abundant polar terminal groups on the MXene surface, Sn²⁺ is induced into the interlayer of MXene with large interlayer spacing, which is selenized in situ to obtain LBL-SnSe₂ @MXene. In the heterostructure, SnSe₂ layers and MXene layers are uniformly intercalated in each other, superior to other heterostructures formed by random stacking. As an anode for lithium-ion batteries, the LBL-SnSe₂ @MXene is revealed to possess strong lithium adsorption ability, the small activation energy for lithium diffusion, and excellent structure stability, thus achieving outstanding electrochemical performance, especially with high specific capacities (1311 and 839 mAh g^-1 for initial discharge and charge respectively) and ultralong cycling stability (410 mAh g^-1 at 5C even after 16 000 cycles). This work conveys an inspiration for the controllable design and construction of homogeneous layered heterostructures.

Post-synthetic Fully π-Conjugated Three-Dimensional Covalent Organic Frameworks for High-Performance Lithium Storage

A fully π-conjugated nitrogen-rich three-dimensional covalent organic framework (PYTRI-COF-2) containing both pyrazine and triazine units was prepared through a post-synthetic strategy. The imine linkages in the pre-prepared PYTRI-COF-1 were converted into heterocyclic quinoline by the Povarov reaction. The obtained PYTRI-COF-2 displayed high Li-ion storage capacity and excellent cycling stability when it was used as the lithium (Li)-ion battery electrode.

Biomass Alginate Derived Oxygen-Enriched Carbonaceous Materials with Partially Graphitic Nanolayers for High Performance Anodes in Lithium-Ion Batteries

Lithium-ion batteries with high reversible capacity, high-rate capability, and extended cycle life are vital for future consumer electronics and renewable energy storage. There is a great deal of interest in developing novel types of carbonaceous materials to boost lithium storage properties due to the inadequate properties of conventional graphite anodes. In this study, we describe a facile and low-cost approach for the synthesis of oxygen-doped hierarchically porous carbons with partially graphitic nanolayers (Alg-C) from pyrolyzed Na-alginate biopolymers without resorting to any kind of activation step. The obtained Alg-C samples were analyzed using various techniques, such as X-ray diffraction, Raman, X-ray photoelectron spectroscopy, scanning electron microscope, and transmission electron microscope, to determine their structure and morphology. When serving as lithium storage anodes, the as-prepared Alg-C electrodes have outstanding electrochemical features, such as a high-rate capability (120 mAh g^-1 at 3000 mA g^-1) and extended cycling lifetimes over 5000 cycles. The post-cycle morphologies ultimately provide evidence of the distinct structural characteristics of the Alg-C electrodes. These preliminary findings suggest that alginate-derived carbonaceous materials may have intensive potential for next-generation energy storage and other related applications.

Accommodation of Two-Dimensional SiOx in a Point-to-Plane Conductive Network Composed of Graphene and Nitrogen-Doped Carbon for Robust Lithium Storage

Silicon oxides (SiO_x) are one of the most promising anode materials for next-generation lithium-ion batteries owing to their abundant reserve and low lost and high reversible capacity. However, the practical application of SiO_x is still hindered by their intrinsically low conductivity and huge volume change. In this regard, we design a novel anode material in which sheet-like SiO_x nanosheets are encapsulated in a unique point-to-plane conductive network composed of graphene flakes and nitrogen-doped carbon spheres. This unique composite structure demonstrates high specific capacity (867.7 mAh g^-1 at 0.1 A g^-1), superior rate performance, and stable cycle life. The electrode delivers a superior reversible discharge capacity of 595.8 mAh g^-1 after 200 cycles at 1.0 A g^-1 and 287.5 mAh g^-1 after 500 cycles at 5.0 A g^-1. This work may shed light on the rational design of SiO_x-based anode materials for next-generation high-performance lithium-ion batteries.

Controlled Synthesis of 2D Prussian Blue Analog Nanosheets with Low Coordinated Water Content for High-Performance Lithium Storage

Prussian blue analogs (PBAs) with open and porous frameworks have attracted wide attention in alkali metal ion batteries due to their high theoretical specific capacities and fast ion insertion/extraction kinetics. However, abundant coordinated water usually exists in traditional PBAs synthesized in aqueous systems. Consequently, the competition between coordinated water and alkali ions easily causes the rapid structural collapse of PBAs during the repeated discharge/charge cycles, lowering the cycling stability, and rate performance of batteries. Besides, most reported PBAs adopt the cubic/particle-like morphologies with large sizes, which usually suffer from insufficient ion diffusion especially at high rates. Herein, a facile and general strategy for the synthesis of 2D CoCo, CuFe, CuCeFe, and CuCeCo-based PBA nanosheets is reported. As a proof-of-concept application, Co₃ [Co(CN)₆ ]₂ nanosheets are evaluated as anode materials for lithium-ion batteries. Thanks to the lower coordinated water content, smaller impedance and higher lithium-ion diffusion coefficient, Co₃ [Co(CN)₆ ]₂ nanosheets deliver a superior reversible capacity of 810.4 mAh g^-1 at 100 mA g^-1 , better rate performance, and higher cycling stability compared to common Co₃ [Co(CN)₆ ]₂ cubes. Further studies indicate that the capacitance-controlled electrochemical behaviors dominate in the Co₃ [Co(CN)₆ ]₂ nanosheets, giving rise to their excellent structural stability and superior lithium storage performance even at high rates.

Endothermic Dehydrogenation-Driven Preventive Magnesiation of SiO for High-Performance Lithium Storage Materials

Silicon monoxide (SiO)-based materials have gained much attention as high-capacity lithium storage materials based on their high capacity and stable capacity retention. However, low initial Coulombic efficiency associated with the irreversible electrochemical reaction of the amorphous SiO₂ phase in SiO inhibits the wide usage of SiO-based anode materials for lithium-ion batteries. Magnesiation of SiO is one of the most promising solutions to improve the initial efficiency of SiO-based anode materials. Herein, we demonstrate that endothermic dehydrogenation-driven magnesiation of SiO employing MgH₂ enhanced the initial Coulombic efficiency of 89.5% with much improved long-term cycle performance over 300 cycles compared to the homologue prepared by magnesiation of SiO with Mg and pristine SiO. High-resolution transmission electron microscopy with thermogravimetry-differential scanning calorimetry revealed that the endothermic dehydrogenation of MgH₂ suppressed the sudden temperature rise during magnesiation of SiO, thereby inhibiting the coarsening of the active Si phase in the resulting Si/Mg₂SiO₄ nanocomposite.

Ultrahigh Lithium Storage Capacity of Al2C Monolayer in a Restricted Multilayered Growth Mechanism

Designing anode materials with high lithium specific capacity is crucial to the development of high energy density lithium (ion) batteries. Herein, a distinctive lithium growth mechanism, namely, the restricted multilayered growth for lithium, and a strategy for lithium storage are proposed to achieve a balance between ultrahigh specific capacity and the need to avert uncontrolled dendritic growth of lithium. In particular, based on first-principles computation, we show that the Al₂C monolayer with a planar tetracoordinate carbon structure can be an ideal platform for realizing the restricted multilayered growth mechanism as a two-dimensional (2D) anode material. Furthermore, the Al₂C monolayer exhibits the ultrahigh specific capacity of lithium of 4059 mAh/g, yet with a low diffusion barrier of 0.039-0.17 eV and low open circuit voltage in the range of 0.002-0.34 V. These novel properties render the Al₂C monolayer a promising anode material for future lithium (ion) batteries. Our study also offers a design of promising 2D anode materials with a high specific capacity, fast lithium-ion diffusion, and safe lithium storage.

Metaphosphate-Bridged Interface Boosts High-Performance Lithium Storage

Carbon materials with well-dispersed SnO_x particles exhibit excellent lithium-storage performance. However, the volume change of SnO_x and the weak interaction between SnO_x and carbon induce an unsteady SnO_x-C interface during the lithiation/delithiation process. This phenomenon results in enhanced charge transfer resistance and reduced electrical contact of active materials, which leads to low reversibility of tin oxidation, restricted capacity, sluggish kinetics, structural deterioration, and rapid capacity decay. Herein, tin oxide/carbon composites with a metaphosphate-bridged interface are synthesized to construct a robust interfacial contact between tin oxides and carbon. The metaphosphate group functions as a bridge between SnO_x and carbon and results in excellent electrochemical stability during the charge/discharge process, which is favorable for electrode structural integrity. The formation of the metaphosphate-bridged interface provides a steady transport channel for e^-/Li⁺ and thus improves the reversibility of the conversion reaction. The enhanced charge transfer and interaction can also boost the charge transfer between SnO_x and carbon, which leads to higher SnO_x utilization. Thus, the prepared P-SnO_x/C anode exhibits enhanced lithium-storage performance in terms of specific capacity, cycling stability, and rate performance.

Adjustable Dimensionality of Microaggregates of Silicon in Hollow Carbon Nanospheres: An Efficient Pathway for High-Performance Lithium-Ion Batteries

Silicon, as an anode candidate with great promise for next-generation lithium-ion batteries (LIBs), has drawn massive attention. However, the deficiencyies of tremendous volume change and intrinsic low electron/ion conductivity will hinder its further development. To cope with these bottlenecks, from the aspect of dimension design concept, the diverse dimensionality of microaggregates derived from cogenetic Si/C nano-building blocks was explored rather than the conventional strategies such as morphology control, structure design, and composition adjustment of Si/C. Herein, constructing silicon-carbon hybrid materials considering component dimensional variation and dimensional hybridization is beneficial to enhance lithium storage performance. Initiating from 0D silicon nanodots evenly immersed in the interior and skeleton of a hollow carbon shell (SHC) nanosphere, the 1D SHC nanospheres interconnected with nitrogen doping carbon necklace fiber, a 2D SHC nanospheres directional arranged plane, and a 3D SHC nanospheres self-aggregated microsphere will be elaborately and favorably designed and composed. Then, three different as-prepared dimensional materials deliver their inherent superiority in chemical, physical, and electronic properties containing 1D high aspect ratio, 2D fast electron/ion diffusion kinetics, and 3D efficient conductive networks, yielding effectively enhanced electrochemical performance, respectively.

Self-Optimizing Effect in Lithium Storage of GeO2 Induced by Heterointerface Regulation

Herein, a heterostructural hexagonal@tetragonal GeO₂ (HT-GeO₂ ) composite has been designed based on density functional theory (DFT) calculations and synthesized via an acidic-heating route dealt with rapid cooling, where the inner hexagonal GeO₂ (H-GeO₂ ) phase is covered by a porous layer of tetragonal GeO₂ (T-GeO₂ ) owing to HF etching. Interestingly, the HT-GeO₂ electrode has a self-optimizing effect in lithium storage induced by heterointerface regulation, where the porous T-GeO₂ layer on the surface of HT-GeO₂ can act as not only a Li⁺ /electron conducting layer, but also a buffer layer, while the inner H-GeO₂ phase can react preferentially with Li ions owing to lower intercalation energy, which is confirmed by operando XRD measurement contributing to thorough lithiation for HT-GeO₂ . Moreover, the heterointerface can enhance the pseudocapacitance effect, which can boost the Li storage and accelerate the discharge-charge process. As a result, a large capacity of 984 mAh g^-1 after 500 cycles at 2 A g^-1 and a capacity of 430 mAh g^-1 at a high current density of 20 A g^-1 are delivered. This work provides an easy and efficient way to improve the cycling stability of the GeO₂ anode, and the T-GeO₂ phase would be a novel anode material in energy storage devices.

A Novel Salen-based Porous Framework Polymer as Durable Anode for Lithium-Ion Storage

Organic electrode materials with abundant resources, environmental friendliness and recyclability play a crucial role in rechargeable lithium-ion batteries (LIBs). However, the inferior electrical conductivity and unsatisfactory long-term cycling performance seriously impede their large-scale application in LIBs. Herein, a novel salen-based porous framework polymer (SPP) with a large conjugated skeleton was constructed and utilized as anode for LIBs. Owing to its unique architecture with a large conjugated skeleton facilitating the electron transport, rich pores accelerating the organic electrolyte infiltration, and stable skeleton structure improving the long-term cycling performance, SPP delivered a high specific capacity of 337 mA h g^-1 at 0.1 C (1 C=250 mA g^-1 ) after 100 cycles, and robust rate capacity of 95.5 mA h g^-1 at 32 C. Importantly, an impressive long-term cycling performance with a storage capacity of 155.7 mA h g^-1 at 8 C after 4000 cycles was obtained, showing a durable cyclic stability of SPP. Furthermore, the lithium storage mechanism of SPP was evaluated by ex-situ X-ray photoelectron spectroscopy, manifesting that the multiple active sites of C=N, -OH, and benzene ring were responsible for the superior lithium storage performance. The novel SPP presented in this work should be a promising organic electrode for energy storage applications.

Probing Mechanistic Insights into Highly Efficient Lithium Storage of C60 Fullerene Enabled via Three-Electron-Redox Chemistry

Renewable organic cathodes with abundant elements show promise for sustainable rechargeable batteries. Herein, for the first time, utilizing C₆₀ fullerene as organic cathode for room-temperature lithium-ion battery is reported. The C₆₀  cathode shows robust electrochemical performance preferably in ether-based electrolyte. It delivers discharge capacity up to 120 mAh g^-1 and specific energy exceeding 200 Wh kg^-1 with high initial Coulombic efficiency of 91%. The as-fabricated battery holds a capacity of 90 mAh g^-1 after 50 cycles and showcases remarkable rate performance with 77 mAh g^-1 retained at 500 mA g^-1 . Noteworthily, three couples of unusual flat voltage plateaus recur at ≈2.4, 1.7, and 1.5 V, respectively. Diffusion-dominated three-electron-redox reactions are revealed by cyclic voltammogram and plateau capacities. Intriguingly, it is for the first time unveiled by in situ X-ray diffraction (XRD) that the C₆₀ cathode underwent three reversible phase transitions during lithiation/delithiation process, except for the initial discharge when irreversible polymerization in between C₆₀ nanoclusters existed as suggested by the characteristic irreversible peak shifts in both in situ XRD pattern and in situ Raman spectra. Cs-corrected transmission electron microscope corroborated these phase evolutions. Importantly, delithiation potentials derived from density-functional-theory simulation based on proposed phase structures qualitatively consists with experimental ones.

Imine-Induced Metal-Organic and Covalent Organic Coexisting Framework with Superior Li-Storage Properties and Activation Mechanism

Due to the adjustable structure and the broad application prospects in energy and other fields, the exploration of porous organic materials [metal-organic polymers (MOPs), covalent organic frameworks (COFs), etc.] has attracted extensive attention. In this work, an imine-induced metal-organic and covalent organic coexisting framework (Co-MOP@COF) hybrid was designed based on the combination between the amino units from the organic ligands of Co-MOP and the aldehyde groups from COF. The obtained Co-MOP@COF hybrid with layer-decorated microsphere morphology exhibited good electrochemical cycling performance (a large reversible capacity of 1020 mAh g^-1 after 150 cycles at 100 mA g^-1 and a reversible capacity of 396 mAh g^-1 at 500 mA g^-1 ) as the anode for Li-ion batteries. The coexisting framework structure endowed the Co-MOP@COF hybrid with more surface area exposed in the exfoliated COF structure, which provided rapid Li-ion diffusion, better electrolyte infiltration, and effective activation of functional groups. Therefore, the Co-MOP@COF hybrid material achieved an enhanced Li storage mechanism involving multi-electron redox reactions, related to the Co^II center and organic groups (C=C groups of benzene rings and C=N groups), and furthermore improved electrochemical performance.

N-Enriched Porous Carbon/SiO2 Composites Derived from Biomass Rice Husks for Boosting Li-Ion Storage: Insight into the Effect of N-Doping

A N-enriched porous carbon/SiO₂ (SiO₂ /NC) composite from rice husks was prepared by ball milling and tested as a stable anode for lithium ion batteries (LIBs), in which the homogeneous dispersion of SiO₂ nanoparticles and carbon matrix, and high level of N-doping can be realized simultaneously. The influence of N-doping on a series of SiO₂ /NCs was systematically studied; this proved that the porosity, N-doping content, and electronic conductivity of SiO₂ /NC can be controlled by adjusting common nitrogen sources (urea and melamine) and doping routes, including dry and wet milling, to reach a desirable balance of high capacity, long-term cyclability, and rate property. The optimized SiO₂ /NC composite delivers a stably reversible capacity of 581 mA h g^-1 at the high current load of 1.0 A g^-1 at the 1000th cycle. The novel Li-storage mechanism of active silica in a composite was first proposed after observation of the N-doping effect that the redox reaction between SiO₂ and Li⁺ is accelerated to transform into an alloying reaction of generated Si and Li⁺ , thus enhancing the reversible capacity. Moreover, kinetics analysis confirms that there is a combined Li-storage mechanism of battery-capacitive pattern in composite that contributes to fast charge transfer and ion diffusion during cycle.

Oxygen Vacancies Boosting Lithium-Ion Diffusion Kinetics of Lithium Germanate for High-Performance Lithium Storage

Oxygen vacancies play a positive role in optimizing the physical and chemical properties of metal oxides. In this work, we demonstrated oxygen vacancy-promoted enhancement of Li-ion diffusion kinetics in Li₂GeO₃ nanoparticle-encapsulated carbon nanofibers (denoted as Li₂GeO_3-x/C) and accordingly boosted lithium storage. The introduction of the oxygen vacancies in Li₂GeO_3-x/C can enhance electronic conductivity and evidently decrease activation energy of Li-ion transport, thus resulting in evidently accelerated Li-ion diffusion kinetics during the lithiation/delithiation process. Thus, the Li₂GeO_3-x/C nanofibers exhibit an exceptionally large discharge capacity of 1460.5 mA h g^-1 at 0.1 A g^-1, high initial Coulombic efficiency of 81.3%, and excellent rate capability. This facile and efficient strategy could provide a reference for injecting the oxygen vacancies into other metal oxides for high-performance anode materials.

Insights into the Capacity and Rate Performance of Transition-Metal Coordination Compounds for Reversible Lithium Storage

Coordination compounds are well-known compounds that are being used as new materials for lithium storage because of their unique advantages, that is, designable structures, abundant active sites, and facile as well as mild synthetic routes. However, the electrode stability, low rate performance, and cycle life of coordination compounds are currently the main issues preventing their application as electrode materials, and the lithium-storage mechanism in coordination networks is not well understood. Herein, isostructural one-dimensional coordination compounds were synthesized to study their lithium-storage performance. Co-HIPA and Ni-HIPA showed superior electrolyte stability than other M-HIPAs, and Co-HIPA displayed a superior reversible capacity and cycle stability, excellent rate performance, and clear voltage platform. DFT calculations and kinetic analysis revealed the influence of the metal center with different electronic structures on the lithium-storage mechanism.

Synergistic Interactions of Different Electroactive Components for Superior Lithium Storage Performance

The fusion of different electroactive components of lithium-ion batteries (LIBs) sometimes brings exceptional electrochemical properties. We herein report the reduced graphene-oxide (rGO)-coated Zn₂SnO_4z@NiO nanofibers (ZSO@NiO@G NFs) formed by the synergistic fusion of three different electroactive components including ZnO, SnO₂, and NiO that exhibit exceptional electrochemical properties as negative electrodes for LIBs. The simple synthetic route comprised of electrospinning and calcination processes enables to form porous one-dimensional (1D) structured ZSO, which is the atomic combination between ZnO and SnO₂, exhibiting effective strain relaxation during battery operation. Furthermore, the catalytic effect of Ni converted from the surface-functional NiO nanolayer on ZSO significantly contributes to improved reversible capacity. Finally, rGO sheets formed on the surface of ZSO@NiO NFs enable to construct electrically conductive path as well as a stable SEI layer, resulting in excellent electrochemical performances. Especially, exceptional cycle lifespan of more than 1600 cycles with a high capacity (1060 mAh g^-1) at a high current density (1000 mA g^-1), which is the best result among mixed transition metal oxide (stannates, molybdates, cobaltates, ferrites, and manganates) negative electrodes for LIBs, is demonstrated.

Hollow Porous CoSnOx Nanocubes Encapsulated in One-Dimensional N-Doped Carbon Nanofibers as Anode Material for High-Performance Lithium Storage

CoSnO₃, as a high theoretical capacity electrode material (1235 mAh g^-1) for lithium storage, has been limited due to its low rate performance, huge volume expansion, and an unstable solid electrolyte interface (SEI). A rational design of the material structure including carbon coating can effectively solve the problems. To buffer the volume change and achieve a superior rate capability, hollow CoSnO_x nanocubes encapsulated in 1D N-doped carbon nanofibers (CNFs) were fabricated by electrospinning, showing a final discharge capacity of 733 mAh g^-1 with a 96% capacity retention after 800 cycles at a current rate of 1 A g^-1 and a brilliant rate performance (49% capacity maintenance with the current variation from 0.1 to 5 A g^-1). Absolutely, these outstanding characteristics are ascribed to the unique structure. The N-doped carbon fibers outside not only prevent the volume expansion during Li⁺ intercalation/extraction but also improve the electron transport in the electrode. Most significantly, the hollow structure offers enough vacant space to buffer the internal strain, while the porous structure shortens the Li⁺ diffusion distance. Combined with electrospinning technology, this study shares a novel idea for designing various composites with rational structures and outstanding electrochemical properties.

Interfacial Design on Graphene-Hematite Heterostructures for Enhancing Adsorption and Diffusion towards Superior Lithium Storage

Hematite (α-Fe₂O₃) is a promising electrode material for cost-effective lithium-ion batteries (LIBs), and the coupling with graphene to form Gr/α-Fe₂O₃ heterostructures can make full use of the merits of each individual component, thus promoting the lithium storage properties. However, the influences of the termination of α-Fe₂O₃ on the interfacial structure and electrochemical performance have rarely studied. In this work, three typical Gr/α-Fe₂O₃ interfacial systems, namely, single Fe-terminated (Fe-O₃-Fe-R), double Fe-terminated (Fe-Fe-O₃-R), and O-terminated (O₃-Fe-Fe-R) structures, were fully investigated through first-principle calculation. The results demonstrated that the Gr/Fe-O₃-Fe-R system possessed good structural stability, high adsorption ability, low volume expansion, as well as a minor diffusion barrier along the interface. Meanwhile, investigations on active heteroatoms (e.g., B, N, O, S, and P) used to modify Gr were further conducted to critically analyze interfacial structure and Li storage behavior. It was demonstrated that structural stability and interfacial capability were promoted. Furthermore, N-doped Gr/Fe-O₃-Fe-R changed the diffusion pathway and made it easy to achieve free diffusion for the Li atom and to shorten the diffusion pathway.

In Situ Confined Co5Ge3 Alloy Nanoparticles in Nitrogen-Doped Carbon Nanotubes for Boosting Lithium Storage

Ge-based materials have garnered much attention in lithium-ion batteries (LIBs) for their high theoretical capacity, but these materials suffer from huge volume changes and serious pulverization, which cause insufficient lithium storage performance. Herein, a composite composed of Co₅Ge₃- and nitrogen-doped carbon nanotube (Co₅Ge₃/N-CNT) was successfully synthesized using ZIF-67 and GeO₂ as precursors. There are interactions between the Co₅Ge₃ alloy nanoparticles and carbon nanotubes in the growth process, in which the Co₅Ge₃ alloy nanoparticles were confined in situ in N-CNTs and the in situ growth of N-CNTs was boosted in the existence of the Co₅Ge₃ catalyst. Density functional theory calculations revealed that the electronic conductivity of the Co₅Ge₃ alloy is much higher than that of Ge and the Li⁺ interaction energy of the former is lower than that of the latter. In addition, the interconnected carbon nanotubes not only offer Li⁺ diffusion pathways and electronic networks but also increase electronic conductivity. Importantly, carbon nanotubes and Co metal have a synergistic effect of buffering volume charge of Ge in the process of Li⁺ intercalation/deintercalation. As expected, the Co₅Ge₃/N-CNT composite demonstrated a high reversible capacity of 853.7 mA h g^-1 at 2 A g^-1 after 1500 cycles and attractive rate performance of up to 10 A g^-1.

CNT-Assembled Octahedron Carbon-Encapsulated Cu3P/Cu Heterostructure by In Situ MOF-Derived Engineering for Superior Lithium Storage: Investigations by Experimental Implementation and First-Principles Calculation

Conspicuously, metal-organic frameworks (MOFs) serve as homogenously and periodically atom-dispersed self-sacrificial template for in situ engineering of hierarchical porous carbon-encapsulated micro/nanoheterostructure materials, integrating the merits of micro/nanostructure to high-volumetric energy storage. Copper phosphide represents a promising candidate due to its compact material density compared to commercial graphite. Herein, micro/nanostructured Cu3P/Cu encapsulated by carbon-nanotube-assembled hierarchical octahedral carbonaceous matrix (Cu3P/Cu@CNHO) is constructed by an in situ MOF-derived engineering for novel anode material in LIBs, which achieves an extraordinary cycling stability (a well-maintained gravimetric/volumetric capacity of 463.2 mAh g-1/1878.4 mAh cm-3 at 1 A g-1 up to 1600 cycles) and distinguished rate capability (an ameliorated capacity of 317.7 mAh g-1 even at 10 A g-1), together with unprecedented heat-resistant capability (an elevated temperature of 50 °C for 1000 cycles maintaining 434.7 mAh g-1 at 0.5 A g-1). The superior electrochemical performance of Cu3P/Cu@CNHO is credited to the large specific surface area, conductive carbon matrix and metallic copper dopants, synergistic effects of the intrinsic Cu3P/Cu heterostructure, and well-defined micro/nanostructure, facilitating a boosted electrochemical conductivity and accelerated diffusion kinetics.

Insights into Lithium and Sodium Storage in Porous Carbon

The lithium and sodium storage behavior of porous carbon remains controversial, though it shows excellent cycling stability and rate performances. This Letter discloses the insertion, adsorption, and filling properties of porous carbon. ⁷Li nuclear magnetic resonance (NMR) spectroscopy recognized inserted and adsorbed lithium in this porous carbon but did not observe any other forms of lithium above 0.0 V vs. Li⁺/Li. In addition, although lithium insertion mainly takes place at low potentials, adsorption was found to be the main form of lithium storage throughout the investigated potential range. Such a storage feature is responsible for the excellent rate performance and high specific capacity of porous carbon. Raman spectroscopy further demonstrated the structural reversibility of the carbon in different potential ranges, verifying the necessity to optimize the potential range for a better cycling performance. These findings provide insights for the design and application of porous carbon.

Integrated Design of Hierarchical CoSnO3@NC@MnO@NC Nanobox as Anode Material for Enhanced Lithium Storage Performance

Transition-metal oxides (TMOs) are potential candidates for anode materials of lithium-ion batteries (LIBs) due to their high theoretical capacity (∼1000 mA h/g) and enhanced safety from suppressing the formation of lithium dendrites. However, the poor electron conductivity and the large volume expansion during lithiation/delithiation processes are still the main hurdles for the practical usage of TMOs as anode materials. In this work, the CoSnO3@NC@MnO@NC hierarchical nanobox (CNMN) is then proposed and fabricated to solve those issues. The as-prepared nanobox contains hollow cubic CoSnO3 as a core and dual N-doped carbon-"sandwiched" MnO particles as a shell. As anode materials of LIBs, the hollow and carbon interlayer structures effectively accommodate the volume expansion while dual active TMOs of CoSnO3 and MnO efficiently increase the specific capacity. Notably, the dual-layer structure of N-doped carbons plays a critical functional role in the incorporated composites, where the inner layer serves as a reaction substrate and a spatial barrier and the outer layer offers electron conductivity, enabling more effective involvement of active anode materials in lithium storage, as well as maintaining their high activity during lithium cycling. Subsequently, the as-prepared CNMN exhibits a high specific capacity of 1195 mA h/g after the 200th cycle at 0.1C and an excellent stable reversible capacity of about 876 mA h/g after the 300th cycle at 0.5C with only 0.07 mA h/g fade per cycle after 300 cycles. Even after a 250 times fast charging/discharging cycle both at 5C, it still retains a reversible capacity of 422.6 mA h/g. We ascribe the enhanced lithium storage performances to the novel hierarchical architectures achieved from the rational design.

Facile Synthesis of Flower-Like MnCo2 O4 @PANi-rGO: A High-Performance Anode Material for Lithium-Ion Batteries

Flower-like MnCo₂ O₄ was prepared in a self-assembly process and used in the formation of MnCo₂ O₄ @polyaniline (MnCo₂ O₄ @PANi) that proceeds by a simple in situ polymerization. The MnCo₂ O₄ @PANi-reduced graphite oxide (MnCo₂ O₄ @PANi-rGO) composite was then synthesized by introducing rGO into MnCo₂ O₄ @PANi. This modification improves the overall electronic conductivity of the MnCo₂ O₄ @PANi-rGO because of the dual conductive functions of rGO and PANi; it also provides a buffer for the changes in electrode volume during cycling, thus improving the lithium-storage performance of MnCo₂ O₄ @PANi-rGO. The electrochemical performance of the samples was evaluated by charge/discharge cycling testing, cyclic voltammetry, and electrochemical impedance spectroscopy. MnCo₂ O₄ @PANi-rGO delivers a discharge capacity of 745 mAh g^-1 and a Coulombic efficiency of 100 % after 1050 cycles at a current density of 500 mA g^-1 , and is a promising anode material for lithium-ion batteries.

Micro/Nanoengineered α-Fe2 O3 Nanoaggregate Conformably Enclosed by Ultrathin N-Doped Carbon Shell for Ultrastable Lithium Storage and Insight into Phase Evolution Mechanism

The Fe-based transition metal oxides are promising anode candidates for lithium storage considering their high specific capacity, low cost, and environmental compatibility. However, the poor electron/ion conductivity and significant volume stress limit their cycle and rate performances. Furthermore, the phenomena of capacity rise and sudden decay for α-Fe₂ O₃ have appeared in most reports. Here, a uniform micro/nano α-Fe₂ O₃ nanoaggregate conformably enclosed in an ultrathin N-doped carbon network (denoted as M/N-α-Fe₂ O₃ @NC) is designed. The M/N porous balls combine the merits of secondary nanoparticles to shorten the Li⁺ transportation pathways as well as alleviating volume expansion, and primary microballs to stabilize the electrode/electrolyte interface. Furthermore, the ultrathin carbon shell favors fast electron transfer and protects the electrode from electrolyte corrosion. Therefore, the M/N-α-Fe₂ O₃ @NC electrode delivers an excellent reversible capacity of 901 mA h g^-1 with capacity retention up to 94.0 % after 200 cycles at 0.2 A g^-1 . Notably, the capacity rise does not happen during cycling. Moreover, the lithium storage mechanism is elucidated by ex situ XRD and HRTEM experiments. It is verified that the reversible phase transformation of α↔γ occurs during the first cycle, whereas only the α-Fe₂ O₃ phase is reversibly transformed during subsequent cycles. This study offers a simple and scalable strategy for the practical application of high-performance Fe₂ O₃ electrodes.

A Flexible and Boron-Doped Carbon Nanotube Film for High-Performance Li Storage

Boron-doped carbon nanotubes are a promising candidate for Li storage due to the unique electronic structure and high crystallinity brought by the boron dopants. However, the relatively low Li storage capacity has limited its application in the electrochemical energy storage field, which is mainly caused by the predominantly intact graphitic structure on their surface with limited access points for Li ion entering. Herein, we report a novel B-doped CNTs (py-B-CNTs) film, in which the CNTs possess intrinsically rough surface but flat internal graphitic structure. When used as a flexible anode material for LIBs, this py-B-CNTs film delivers significantly enhanced capacity than the conventional B-doped CNTs or the pristine CNTs films, with good rate capability and excellent cycling performance as well. Moreover, this flexible film also possesses excellent mechanical flexibility, making it capable of being used in a prototype flexible LIB with stable power output upon various bending states.

Bottom-Up Fabrication of 1D Cu-based Conductive Metal-Organic Framework Nanowires as a High-Rate Anode towards Efficient Lithium Storage

Conductive metal-organic frameworks (MOFs), as a newly emerging multifunctional material, hold enormous promise in electrochemical energy-storage systems owing to their merits including good electronic conductivity, large surface area, appropriate pore structure, and environmental friendliness. In this contribution, a scalable solvothermal strategy was devised for the bottom-up fabrication of 1D Cu-based conductive MOF, that is, Cu₃ (2,3,6,7,10,11-hexahydroxytriphenylene)₂ (Cu-CAT) nanowires (NWs), which were further utilized as a competitive anode for lithium-ion batteries (LIBs). The intrinsic Li storage mechanism of the Cu-CAT electrode was also explored. Benefiting from its structural virtues, the resultant 1D Cu-CAT NWs were endowed with superb Li⁺ diffusion coefficients and electrochemical conductivities and exhibited remarkably high-rate reversible capacities of approximately 631 mAh g^-1 at 0.2 A g^-1 and even approximately 381 mAh g^-1 at 2 A g^-1 , along with striking capacity retention of 81 % after 500 cycles at 0.5 A g^-1 . In addition, a Cu-CAT NWs-based full cell assembled with LiNi_0.8 Co_0.1 Mn_0.1 O₂ as the cathode displayed a large energy density of approximately 275 Wh kg^-1 as well as excellent cycling behavior. These results manifest the promising application of 1D conductive Cu-CAT NWs in advanced LIBs and even other potential versatile energy-related fields.

Ab Initio Screening of Doped Mg(AlH4)2 Systems for Conversion-Type Lithium Storage

In this work, we have explored the potential applications of pure and various doped Mg(AlH₄)₂ as Li-ion battery conversion electrode materials using density functional theory (DFT) calculations. Through the comparisons of the electrochemical specific capacity, the volume change, the average voltage, and the electronic bandgap, the Li-doped material is found to have a smaller bandgap and lower average voltage than the pure system. The theoretical specific capacity of the Li-doped material is 2547.64 mAhg⁻¹ with a volume change of 3.76% involving the electrode conversion reaction. The underlying reason for property improvement has been analyzed by calculating the electronic structures. The strong hybridization between Lis-state with H s-state influences the performance of the doped material. This theoretical research is proposed to help the design and modification of better light-metal hydride materials for Li-ion battery conversion electrode applications.

Hydrangea-Shaped 3D Hierarchical Porous Magnesium Hydride-Carbon Framework with High Rate Performance for Lithium Storage

Magnesium hydride (MgH₂) is a promising anode material for lithium-ion batteries (LIBs) by virtue of its high theoretical specific capacity, suitable potential, and abundant source. However, the electrochemical performance of the MgH₂ electrode is still far from satisfactory due to its poor electronic conductivity and fast capacity decay. In this paper, a hydrangea-shaped three-dimensional (3D) hierarchical magnesium hydride-carbon framework (MH@HyC) comprising MgH₂ nanoparticles (NPs) uniformly self-assembled on hierarchical porous carbon (HyC) is fabricated for advanced lithium storage. Featuring high surface area and a well-defined macro-meso-micropore structure, HyC plays an ideal structure-directing role for the growth of MgH₂ NPs with size control, high loading, and a hydrangea-shape array. Taking advantage of the robust 3D hierarchical porous structure and the derived interactions, MH@HyC not only provides sufficient electrochemically active sites and enhances the electronic conductivity and channels for rapid transfer of electrons/Li ions but also relieves the agglomeration and accommodates the volumetric effects during cycling, leading to high capacity utilization, fast electrochemical kinetics, and well-sustained structural integrity. As a result, MH@HyC delivers a high reversible capacity of 554 mAh g^-1 after 1000 cycles at a high current rate of 2 A g^-1, enabling it a potential anode candidate for LIBs.

3D Graphene Networks Encapsulated with Ultrathin SnS Nanosheets@Hollow Mesoporous Carbon Spheres Nanocomposite with Pseudocapacitance-Enhanced Lithium and Sodium Storage Kinetics

The lithium and sodium storage performances of SnS anode often undergo rapid capacity decay and poor rate capability owing to its huge volume fluctuation and structural instability upon the repeated charge/discharge processes. Herein, a novel and versatile method is described for in situ synthesis of ultrathin SnS nanosheets inside and outside hollow mesoporous carbon spheres crosslinked reduced graphene oxide networks. Thus, 3D honeycomb-like network architecture is formed. Systematic electrochemical studies manifest that this nanocomposite as anode material for lithium-ion batteries delivers a high charge capacity of 1027 mAh g^-1 at 0.2 A g^-1 after 100 cycles. Meanwhile, the as-developed nanocomposite still retains a charge capacity of 524 mAh g^-1 at 0.1 A g^-1 after 100 cycles for sodium-ion batteries. In addition, the electrochemical kinetics analysis verifies the basic principles of enhanced rate capacity. The appealing electrochemical performance for both lithium-ion batteries and sodium-ion batteries can be mainly related to the porous 3D interconnected architecture, in which the nanoscale SnS nanosheets not only offer decreased ion diffusion pathways and fast Li⁺ /Na⁺ transport kinetics, but also the 3D interconnected conductive networks constructed from the hollow mesoporous carbon spheres and reduced graphene oxide enhance the conductivity and ensure the structural integrity.

Study of Li Adsorption on Graphdiyne Using Hybrid DFT Calculations

Promising applications of graphdiyne have often been initiated by theoretical predictions especially using DFT known as the most powerful first-principles electronic structure calculation method. However, there is no systematic study on the reliability of DFT for the prediction of the electronic properties of the graphdiyne. Here, we performed a study of Li adsorption on the graphdiyne using hybrid DFT with LC-ωPBE and compared the results with those of PBE, because accurate prediction of the Li adsorption is important for performance as a Li storage that was first theoretically suggested and then experimentally realized. Our results show that PBE overestimates the adsorption energy inside a pore and the barrier height at the transition state of in-plane diffusion compared to the those of LC-ωPBE. In particular, LC-ωPBE predicted almost barrier-less in-plane diffusion of Li on the graphdiyne because of the presence of both in-plane and out-of-plane π orbitals. Also, LC-ωPBE favors a high spin state due to the exact exchange energy when several Li atoms are adsorbed on the graphdiyne, whereas PBE favors a low spin state. Thus, the use of the hybrid DFT is critical for reliable predictions on the electronic properties of the graphdiyne.

Hierarchical Nanospheres Constructed by Ultrathin MoS2 Nanosheets Braced on Nitrogen-Doped Carbon Polyhedra for Efficient Lithium and Sodium Storage

MoS₂ has attracted a lot of attention for electrochemical energy storage. Herein, we design and fabricate unusual hierarchical composite nanospheres by cultivating a MoS₂ sheet-like nanostructure on nitrogen-doped carbon polyhedra (designated as CP@MoS₂ nanospheres). The nitrogen-doped carbon polyhedra are able to significantly boost the electrical conductivity of the hybrid architecture and largely mitigate the agglomeration of the MoS₂ nanostructure. The sheet-like MoS₂ nanostructure can render a great deal of storage sites toward lithium and sodium. When measured as a negative electrode for Li storage, these CP@MoS₂ nanospheres manifest a large charge capacity of approximately 549 mAh g^-1, a superior cycle life of 900 cycles, and excellent rate property. Furthermore, they also demonstrate improved electrochemical activity for Na⁺ ion storage.

Achieving High-Energy Full-Cell Lithium-Storage Performance by Coupling High-Capacity V2O3 with Low-Potential Ni2P Anode

To optimize the potential window and maximize the utilization of the capacity of both negative and positive electrodes, rational design of electrode materials are critically important in full-cell construction of rechargeable batteries. In this work, we propose and fabricate a carbon-confined V₂O₃/Ni₂P/C composite structure for excellent performance lithium ion batteries by taking advantage of the high capacity of V₂O₃ and low potential of Ni₂P. The full cell constructed with V₂O₃/Ni₂P/C as anode and commercial LiMn₂O₄ as cathode offers a record high energy density of 361.5 Wh kg^-1 and excellent cycle stability, outperforming the state-of-the-art work reported in literature.

Double-Holey-Heterostructure Frameworks Enable Fast, Stable, and Simultaneous Ultrahigh Gravimetric, Areal, and Volumetric Lithium Storage

Deliberate design of advantageous nanostructures holds great promise for developing high-performance electrode materials for electrochemical energy storage. However, it remains a tremendous challenge to simultaneously gain high gravimetric, areal, and volumetric capacities as well as high rate performance and cyclability to meet practical requirements mainly due to the intractable insufficient ion diffusion and limited active sites for dense electrodes with high areal mass loadings. Herein we report a double-holey-heterostructure framework, in which holey Fe₂O₃ nanosheets (H-Fe₂O₃) are tightly and conformably grown on the holey reduced graphene oxide (H-RGO). This hierarchical nanostructure allows for rapid ion and electron transport and sufficient utilization of active sites throughout a highly compact and thick electrode. Therefore, the free-standing flexible H-Fe₂O₃/H-RGO heterostructure anode can simultaneously deliver ultrahigh gravimetric, areal, and volumetric capacities of 1524 mAh g^-1, 4.72 mAh cm^-2, and 2621 mAh cm^-3, respectively, at 0.2 A g^-1 after 120 cycles, and extraordinary rate performance with a capacity of 487 mAh g^-1 (1.51 mAh cm^-2) at a high current density of 30 A g^-1 (93 mA cm^-2) as well as excellent cycling stability with a capacity retention of 96.3% after 1600 cycles, which has rarely been achieved before.

Controlled-Size Hollow Magnesium Sulfide Nanocrystals Anchored on Graphene for Advanced Lithium Storage

Magnesium sulfide (MgS), representative of alkaline-earth metal chalcogenides (AEMCs), is a potential conversion/alloy-type electrode material for lithium ion batteries (LIBs), by virtue of its low potential, high theoretical capacity, and abundant magnesium resource. However, the limited capacity utilization and inferior rate performance still hinder its practical application, and the progress is rather slow due to the challenging fabrication technique for MgS. Herein, we report a series of controlled-size hollow MgS nanocrystals (NCs) homogeneously distributed on graphene (MgS@G), fabricated through a metal hydride framework (MHF) strategy, and its application as advanced electrode material for LIBs. The hollow structure of MgS NCs is mainly attributed to the Kirkendall effect and the escape of hydrogen atoms from metal hydride during sulfuration. The as-synthesized MgS@G demonstrates robust nanoarchitecture and admirable interactions, which ensure a spatially confined lithiation/delithiation process, optimize the dynamics of two-steps conversion/alloying reactions, and induce a synergetic pseudocapacitive storage contribution. As a result, a representative MgS@G composite delivers a largely enhanced capacity of >1208 mAh g^-1 at a current density of 100 mA g^-1 and a long-term cycle stability at a high current density of 5 A g^-1 with a capacity of 838 mAh g^-1 over 3000 cycles, indicating well-sustained structural integrity. This work presents an effective route toward the development of high-performance magnesium-based material for energy storage.

Nanostructural Uniformity of Ordered Mesoporous Materials: Governing Lithium Storage Behaviors

Nanostructured materials make a considerable impact on the performance of lithium-storage characteristics in terms of the energy density, power density, and cycle life. Direct experimental observation, by a comparison of controlled nanostructural uniformity of electrode materials, reveals that the lithium-storage behaviors of mesoporous MoO₂ and CuO electrodes are linearly correlated with their nanostructural uniformity. Reversible capacities of mesoporous MoO₂ and CuO electrodes with well-developed nanostructures (1569 mA h g^-1 for MoO₂ and 1029 mA h g^-1 for CuO) exceed their theoretical capacity based on the conversion reaction (838 mA h g^-1 for MoO₂ and 674 mA h g^-1 for CuO). Given that exact understanding of the origin of the additional capacity is essential in maximizing the energy density of electrode material, this work may help to gain some insights into the development of high energy-density lithium-storage materials for next-generation lithium rechargeable batteries.

Encapsulation of CoS x Nanocrystals into N/S Co-Doped Honeycomb-Like 3D Porous Carbon for High-Performance Lithium Storage

A honeycomb-like 3D N/S co-doped porous carbon-coated cobalt sulfide (CoS, Co9S8, and Co1-x S) composite (CS@PC) is successfully prepared using polyacrylonitrile (PAN) as the nitrogen-containing carbon source through a facile solvothermal method and subsequent in situ conversion. As an anode for lithium-ion batteries (LIBs), the CS@PC composite exhibits excellent electrochemical performance, including high reversible capacity, good rate capability, and cyclic stability. The composite electrode delivers specific capacities of 781.2 and 466.0 mAh g-1 at 0.1 and 5 A g-1, respectively. When cycled at a current density of 1 A g-1, it displays a high reversible capacity of 717.0 mAh g-1 after 500 cycles. The ability to provide this level of performance is attributed to the unique 3D multi-level porous architecture with large electrode-electrolyte contact area, bicontinuous electron/ion transport pathways, and attractive structure stability. Such micro-/nanoscale design and engineering strategies may also be used to explore other nanocomposites to boost their energy storage performance.

Few-Layer Silicene Nanosheets with Superior Lithium-Storage Properties

Silicene, a 2D silicon allotrope with unique low-buckled structure, has attracted increasing attention in recent years due to its many superior properties. So far, epitaxial growth is one of the very limited ways to obtain high-quality silicene, which severely impedes the research and application of silicene. Therefore, large-scale synthesis of silicene is a great challenge, yet urgently desired. Herein, the first scalable preparation of free-standing high-quality silicene nanosheets via liquid oxidation and exfoliation of CaSi₂ is reported. This new synthesis strategy successfully induces mild oxidation of the (Si²ⁿ )^2n- layers in CaSi₂ into neutral Si²ⁿ layers without damage of pristine silicene structure and promotes the exfoliation of stacked silicene layers. The obtained silicene sheets are dispersible and ultrathin ones with monolayer or few-layer thickness and exhibit excellent crystallinity. As a unique 2D layered silicon allotrope, the silicene nanosheets are further explored as new anodes for lithium-ion batteries and exhibit a nearly theoretical capacity of 721 mAh g^-1 at 0.1 A g^-1 and an extraordinary cycling stability with no capacity decay after 1800 cycles in contrast to previous most silicon anodes showing rapid capacity decay, thus holding great promise for energy storage and beyond.

Self-Assembly of Transition Metal Oxide Nanostructures on MXene Nanosheets for Fast and Stable Lithium Storage

Recently, a new class of 2D materials, i.e., transition metal carbides, nitrides, and carbonitrides known as MXenes, is unveiled with more than 20 types reported one after another. Since they are flexible and conductive, MXenes are expected to compete with graphene and other 2D materials in many applications. Here, a general route is reported to simple self-assembly of transition metal oxide (TMO) nanostructures, including TiO₂ nanorods and SnO₂ nanowires, on MXene (Ti₃ C₂ ) nanosheets through van der Waals interactions. The MXene nanosheets, acting as the underlying substrate, not only enable reversible electron and ion transport at the interface but also prevent the TMO nanostructures from aggregation during lithiation/delithiation. The TMO nanostructures, in turn, serve as the spacer to prevent the MXene nanosheets from restacking, thus preserving the active areas from being lost. More importantly, they can contribute extraordinary electrochemical properties, offering short lithium diffusion pathways and additional active sites. The resulting TiO₂ /MXene and SnO₂ /MXene heterostructures exhibit superior high-rate performance, making them promising high-power and high-energy anode materials for lithium-ion batteries.

Rapid Amorphization in Metastable CoSeO3·H2O Nanosheets for Ultrafast Lithiation Kinetics

The realization of high-performance anode materials with high capacity at fast lithiation kinetics and excellent cycle stability remains a significant but critical challenge for high-power applications such as electric vehicles. Two-dimensional nanostructures have attracted considerable research interest in electrochemical energy storage devices owing to their intriguing surface effect and significantly decreased ion-diffusion pathway. Here we describe rationally designed metastable CoSeO₃·H₂O nanosheets synthesized by a facile hydrothermal method for use as a Li ion battery anode. This crystalline nanosheet can be steadily converted into amorphous phase at the beginning of the first Li⁺ discharge cycling, leading to ultrahigh reversible capacities of 1100 and 515 mAh g^-1 after 1000 cycles at a high rate of 3 and 10 A g^-1, respectively. The as-obtained amorphous structure experiences an isotropic stress, which can significantly reduce the risk of fracture during electrochemical cycling. Our study offers a precious opportunity to reveal the ultrafast lithiation kinetics associated with the rapid amorphization mechanism in layered cobalt selenide nanosheets.

Green and Rational Design of 3D Layer-by-Layer MnO x Hierarchically Mesoporous Microcuboids from MOF Templates for High-Rate and Long-Life Li-Ion Batteries

Rational design and delicate control on the textural properties of metal-oxide materials for diverse structure-dependent applications still remain formidable challenges. Here, we present an eco-friendly and facile approach to smartly fabricate three-dimensional (3D) layer-by-layer manganese oxide (MnO _x) hierarchical mesoporous microcuboids from a Mn-MOF-74-based template, using a one-step solution-phase reaction scheme at room temperature. Through the controlled exchange of metal-organic framework (MOF) ligand with OH^- in alkaline aqueous solution and in situ oxidation of manganese hydroxide intermediate, the Mn-MOF-74 template/precursor was readily converted to Mn₃O₄ or δ-MnO₂ counterpart consisting of primary nanoparticle and nanosheet building blocks, respectively, with well-retained morphology. By X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy, high-resolution TEM, N₂ adsorption-desorption analysis and other techniques, their crystal structure, detailed morphology, and microstructure features were unambiguously revealed. Specifically, their electrochemical Li-ion insertion/extraction properties were well evaluated, and it turns out that these unique 3D microcuboids could achieve a sustained superior lithium-storage performance especially at high rates benefited from the well-orchestrated structural characteristics (Mn₃O₄ microcuboids: 890.7, 767.4, 560.1, and 437.1 mAh g^-1 after 400 cycles at 0.2, 0.5, 1, and 2 A g^-1, respectively; δ-MnO₂ microcuboids: 991.5, 660.8, 504.4, and 362.1 mAh g^-1 after 400 cycles at 0.2, 0.5, 1, and 2 A g^-1, respectively). To our knowledge, this is the most durable high-rate capability as well as the highest reversible capacity ever reported for pure MnO _x anodes, which even surpass most of their hybrids. This facile, green, and economical strategy renews the traditional MOF-derived synthesis for highly tailorable functional materials and opens up new opportunities for metal-oxide electrodes with high performance.

High-Crystallinity Urchin-like VS4 Anode for High-Performance Lithium-Ion Storage

VS₄ anode materials with controllable morphologies from hierarchical microflower, octopus-like structure, seagrass-like structure to urchin-like structure have been successfully synthesized by a facile solvothermal synthesis approach using different alcohols as solvents. Their structures and electrochemical properties with various morphologies are systematically investigated, and the structure-property relationship is established. Experimental results reveal that Li⁺ ion storage behavior in VS₄ significantly depends on physical features such as the morphology, crystallite size, and specific surface area. According to this study, electrochemical performance degrades on the order of urchin-like VS₄ > octopus-like VS₄ > seagrass-like VS₄ > flower-like VS₄. Among them, urchin-like VS₄ demonstrates the best electrochemical performance benefiting from its peculiar structure which possesses large surface area that accommodates the volume change to a certain extent, and single-crystal thorns that provide fast electron transportation. Kinetic parameters derived from EIS spectra and sweep-rate-dependent CV curves, such as charge-transfer resistances, Li⁺ ion apparent diffusion coefficients and stored charge ratio of capacitive and intercalation contributions, both support this claim well. In addition, the EIS measurement was conducted during the first discharge/charge process to study the solid electrolyte interface (SEI) formation on urchin-like VS₄ and kinetics behavior of Li⁺ ion diffusion. A better fundamental understanding on Li⁺ storage behavior in VS₄ is promoted, which is applicable to other vanadium-based materials as well. This study also provides invaluable guidance for morphology-controlled synthesis tailored for optimal electrochemical performance.

Functionalized Graphene Quantum Dot Modification of Yolk-Shell NiO Microspheres for Superior Lithium Storage

Yolk-shell NiO microspheres are modified by two types of functionalized graphene quantum dots (denoted as NiO/GQDs) via a facile solvothermal treatment. The modification of GQDs on the surface of NiO greatly boosts the stability of the NiO/GQD electrode during long-term cycling. Specifically, the NiO with carboxyl-functionalized GQDs (NiO/GQDsCOOH) exhibits better performances than NiO with amino-functionalized GQDs (NiO/GQDsNH₂ ). It delivers a capacity of ≈1081 mAh g^-1 (NiO contribution: ≈1182 mAh g^-1 ) after 250 cycles at 0.1 A g^-1 . In comparison, NiO/GQDsNH₂ electrode holds ≈834 mAh g^-1 of capacity, while the bald NiO exhibits an obvious decline in capacity with ≈396 mAh g^-1 retained after cycling. Except for the yolk-shell and mesoporous merits, the superior performances of the NiO/GQD electrode are mainly ascribed to the assistance of GQDs. The GQD modification can support as a buffer alleviating the volume change, improve the electronic conductivity, and act as a reservoir for electrolytes to facilitate the transportation of Li⁺ . Moreover, the enrichment of carboxyl/amino groups on GQDs can further donate more active sites for the diffusion of Li⁺ and facilitate the electrochemical redox kinetics of the electrode, thus together leading to the superior lithium storage performance.

Encapsulating Silica/Antimony into Porous Electrospun Carbon Nanofibers with Robust Structure Stability for High-Efficiency Lithium Storage

To address the volume-change-induced pulverization problems of electrode materials, we propose a "silica reinforcement" concept, following which silica-reinforced carbon nanofibers with encapsulated Sb nanoparticles (denoted as SiO₂/Sb@CNFs) are fabricated via an electrospinning method. In this composite structure, insulating silica fillers not only reinforce the overall structure but also contribute to additional lithium storage capacity; encapsulation of Sb nanoparticles into the carbon-silica matrices efficiently buffers the volume changes during Li-Sb alloying-dealloying processes upon cycling and alleviates the mechanical stress; the porous carbon nanofiber framework allows for fast charge transfer and electrolyte diffusion. These advantageous characteristics synergistically contribute to the superior lithium storage performance of SiO₂/Sb@CNF electrodes, which demonstrate excellent cycling stability and rate capability, delivering reversible discharge capacities of 700 mA h/g at 200 mA/g, 572 mA h/g at 500 mA/g, and 468 mA h/g at 1000 mA/g each after 400 cycles. Ex situ as well as in situ TEM measurements confirm that the structural integrity of silica-reinforced Sb@CNF electrodes can efficiently withstand the mechanical stress induced by the volume changes. Notably, the SiO₂/Sb@CNF//LiCoO₂ full cell delivers high reversible capacities of ∼400 mA h/g after 800 cycles at 500 mA/g and ∼336 mA h/g after 500 cycles at 1000 mA/g.

Designing flexible 2D transition metal carbides with strain-controllable lithium storage

Efficient flexible energy storage systems have received tremendous attention due to their enormous potential applications in self-powering portable electronic devices, including roll-up displays, electronic paper, and "smart" garments outfitted with piezoelectric patches to harvest energy from body movement. Unfortunately, the further development of these technologies faces great challenges due to a lack of ideal electrode materials with the right electrochemical behavior and mechanical properties. MXenes, which exhibit outstanding mechanical properties, hydrophilic surfaces, and high conductivities, have been identified as promising electrode material candidates. In this work, taking 2D transition metal carbides (TMCs) as representatives, we systematically explored several influencing factors, including transition metal species, layer thickness, functional group, and strain on their mechanical properties (e.g., stiffness, flexibility, and strength) and their electrochemical properties (e.g., ionic mobility, equilibrium voltage, and theoretical capacity). Considering potential charge-transfer polarization, we employed a charged electrode model to simulate ionic mobility and found that ionic mobility has a unique dependence on the surface atomic configuration influenced by bond length, valence electron number, functional groups, and strain. Under multiaxial loadings, electrical conductivity, high ionic mobility, low equilibrium voltage with good stability, excellent flexibility, and high theoretical capacity indicate that the bare 2D TMCs have potential to be ideal flexible anode materials, whereas the surface functionalization degrades the transport mobility and increases the equilibrium voltage due to bonding between the nonmetals and Li. These results provide valuable insights for experimental explorations of flexible anode candidates based on 2D TMCs.

Formation of N-Doped Carbon-Coated ZnO/ZnCo2 O4 /CuCo2 O4 Derived from a Polymetallic Metal-Organic Framework: Toward High-Rate and Long-Cycle-Life Lithium Storage

Metal-organic frameworks (MOFs) are very promising self-sacrificing templates for the large-scale fabrication of new functional materials owing to their versatile functionalities and tunable porosities. Most conventional metal oxide electrodes derived from MOFs are limited by the low abundance of incorporated metal elements. This study reports a new strategy for the synthesis of multicomponent active metal oxides by the pyrolysis of polymetallic MOF precursors. A hollow N-doped carbon-coated ZnO/ZnCo₂ O₄ /CuCo₂ O₄ nanohybrid is prepared by the thermal annealing of a polymetallic MOF with ammonium bicarbonate as a pore-forming agent. This is the first report on the rational design and preparation of a hybrid composed of three active metal oxide components originating from MOF precursors. Interestingly, as a lithium-ion battery anode, the developed electrode delivers a reversible capacity of 1742 mAh g^-1 after 500 cycles at a current density of 0.3 mA g^-1 . Furthermore, the material shows large storage capacities (1009 and 667 mAh g^-1 ), even at high current flow (3 and 10 A g^-1 ). The remarkable high-rate capability and outstanding long-life cycling stability of the multidoped metal oxide benefits from the carbon-coated integrated nanostructure with a hollow interior and the three active metal oxide components.

Facet-Selective Deposition of FeOx on α-MoO3 Nanobelts for Lithium Storage

One-dimensional heterostructures have attracted significant interests in various applications. However, the selective deposition of shell material on specific sites of the backbone material remains a challenge. Herein, a facile facet-selective deposition strategy has been developed for the construction of heterostructured α-MoO₃@FeO_x nanobelts. Because of the anisotropic feature of α-MoO₃ nanobelts, the FeO_x nanoparticles selectively deposit on the edges of α-MoO₃ nanobelts, that is, the {100} and {001} facets. Such a heterostructure facilitates the electron transfer in lithium storage. As a result, the α-MoO₃@FeO_x nanobelts exhibit high capacities of 913 mA h g^-1 after 100 cycles at 200 mA g^-1 and 540 mA h g^-1 after 100 cycles at 1000 mA g^-1. The facet-selective deposition strategy developed here would be extended to the construction of other novel heterostructures with fascinating physical/chemical properties and wide potential applications.