Efficient Sodium Storage in Rolled-Up Amorphous Si Nanomembranes

Alleviating the volume expansion of silicon anodes by constructing a high-strength ordered multidimensional encapsulation structure

The application of silicon-based nanomaterials in fast-charging scenarios is hindered by volume expansion during lithiation and side reactions induced by surface effects. Constructing a robust encapsulation structure with high mechanical strength and conductivity is pivotal for optimizing the electrochemical performance of nanostructured silicon anodes. Herein, we propose a multifaceted hierarchical encapsulation structure featuring excellent mechanical strength and high conductivity by sequentially incorporating SiO x , hard carbon, and closed-pore carbon layers around silicon quantum dots, thereby enabling stable cycling at high current densities. In this structure, the ultra-thin SiO x layer strengthens the Si-C interface, while the outermost carbon matrix with closed pores functions both as a conductive network and a barrier against electrolyte intrusion. Notably, the synthesized material exhibits a specific capacity of 1506 mA h g-1 with 90.17% retention after 300 cycles at 1.0 A g-1. After 500 cycles at 5.0 A g-1, it retains 640.4 mA h g-1, over 70% of its initial capacity.

Multilevel Gradient-Ordered Silicon Anode with Unprecedented Sodium Storage

While cost-effective sodium-ion batteries (SIBs) with crystalline silicon anodes promise high theoretical capacities, they perform poorly because silicon stores sodium ineffectively (capacity <40 mAh g-1 ). To address this issue, herein an atomic-order structural-design tactic is adopted for obtaining unique multilevel gradient-ordered silicon (MGO-Si) by simple electrochemical reconstruction. In situ-formed short-range-, medium-range-, and long-range-ordered structures construct a stable MGO-Si, which contributes to favorable Na-Si interaction and fast ion diffusion channels. These characteristics afford a high reversible capacity (352.7 mAh g-1 at 50 mA g-1 ) and stable cycling performance (95.2% capacity retention after 4000 cycles), exhibiting record values among those reported for pure silicon electrodes. Sodium storage of MGO-Si involves an adsorption-intercalation mechanism, and a stepwise construction strategy of gradient-ordered structure further improves the specific capacity (339.5 mAh g-1 at 100 mA g-1 ). Reconstructed Si/C composites show a high reversible capacity of 449.5 mAh g-1 , significantly better than most carbonaceous anodes. The universality of this design principle is demonstrated for other inert or low-capacity materials (micro-Si, SiO2 , SiC, graphite, and TiO2 ), boosting their capacities by 1.5-6 times that of pristine materials, thereby providing new solutions to facilitate sodium storage capability for better-performing battery designs.

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

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

Recent progress and strategic perspectives of inorganic solid electrolytes: fundamentals, modifications, and applications in sodium metal batteries

Solid-state electrolytes (SEs) have attracted overwhelming attention as a promising alternative to traditional organic liquid electrolytes (OLEs) for high-energy-density sodium-metal batteries (SMBs), owing to their intrinsic incombustibility, wider electrochemical stability window (ESW), and better thermal stability. Among various kinds of SEs, inorganic solid-state electrolytes (ISEs) stand out because of their high ionic conductivity, excellent oxidative stability, and good mechanical strength, rendering potential utilization in safe and dendrite-free SMBs at room temperature. However, the development of Na-ion ISEs still remains challenging, that a perfect solution has yet to be achieved. Herein, we provide a comprehensive and in-depth inspection of the state-of-the-art ISEs, aiming at revealing the underlying Na⁺ conduction mechanisms at different length scales, and interpreting their compatibility with the Na metal anode from multiple aspects. A thorough material screening will include nearly all ISEs developed to date, i.e., oxides, chalcogenides, halides, antiperovskites, and borohydrides, followed by an overview of the modification strategies for enhancing their ionic conductivity and interfacial compatibility with Na metal, including synthesis, doping and interfacial engineering. By discussing the remaining challenges in ISE research, we propose rational and strategic perspectives that can serve as guidelines for future development of desirable ISEs and practical implementation of high-performance SMBs.

Advanced Anode Materials for Rechargeable Sodium-Ion Batteries

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

Morphology Engineering of Hybrid Supercapacitor Electrodes from Hierarchical Stem-like Carbon Networks with Flower-like MoS2 Structures

There is a critical need to develop high-performance supercapacitors that can complement and even rival batteries for energy storage. This work introduces a strategy to drastically enhance the energy storage performance of a supercapacitor by engineering electrode morphologies with ternary composites offering distinct benefits for the energy storage application. The electrodes were fabricated with conductive networks of carbon nanotubes (CNTs) coated with a zeolitic imidazole framework (ZIF) for high ion diffusivity and ion-accumulating molybdenum disulfide (MoS₂) with various morphologies. These include flower-like (fMoS₂), stacked-plate (pMoS₂), and exfoliated-flake (eMoS₂) structures from topochemical synthesis. CNT-ZIF-fMoS₂ demonstrates an excellent energy density, reaching almost 80 Wh/kg, and a maximum power density of approximately 3000 W/kg in a half-cell. This is far superior to the electrodes containing pMoS₂ and eMoS₂ and attributed to the increased surface area and the faradaic reactivity offered by fMoS₂. Additionally, the CNT-ZIF-fMoS₂ electrode demonstrates exceptional stability with an ∼78% of capacitance retention over 10,000 cycles. This work suggests that the electrode morphologies can dominate the energy storage behaviors and that the heteromaterial approach may be crucial in designing next-generation supercapacitors.

Yolk-Shell Sb@Void@Graphdiyne Nanoboxes for High-Rate and Long Cycle Life Sodium-Ion Batteries

Antimony (Sb) has been pursued as a promising anode material for sodium-ion batteries (SIBs). However, it suffers from severe volume expansion during the sodiation-desodiation process. Encapsulating Sb into a carbon matrix can effectively buffer the volume change of Sb. However, the sluggish Na⁺ diffusion kinetics in traditional carbon shells is still a bottleneck for achieving high-rate performance in Sb/C composite materials. Here we design and synthesize a yolk-shell Sb@Void@graphdiyne (GDY) nanobox (Sb@Void@GDY NB) anode for high-rate and long cycle life SIBs. The intrinsic in-plane cavities in GDY shells offer three-dimensional Na⁺ transporting channels, enabling fast Na⁺ diffusion through the GDY shells. Electrochemical kinetics analyses show that the Sb@Void@GDY NBs exhibit faster Na⁺ transport kinetics than traditional Sb@C NBs. In situ transmission electron microscopy analysis reveals that the hollow structure and the void space between Sb and GDY successfully accommodate the volume change of Sb during cycling, and the plastic GDY shell maintains the structural integrity of NBs. Benefiting from the above structural merits, the Sb@Void@GDY NBs exhibit excellent rate capability and extraordinary cycling stability.

Tin nanoparticle in-situ decorated on nitrogen-deficient carbon nitride with excellent sodium storage performance

Tin (Sn)-based electrodes, featuring high electrochemical activity and suitable voltage plateau, gain tremendous attention as promising anode materials for sodium-ion batteries. However, the application of Sn-based electrodes has been largely restricted by the serious pulverization upon repeated cycling due to their large volume expansion, especially at high current densities. Herein, a unique three-dimensional decorated structure was designed, containing ultrafine Sn nanoparticles and nitrogen-deficient carbon nitride (Sn/D-C₃N₄), to efficiently alleviate the expansion stress and prevent the aggregation of Sn nanoparticles. Furthermore, the density functional theory calculations have proved the high sodium adsorption ability and improved diffusion kinetics through the hybridization of D-C₃N₄ with Sn nanoparticles. Further combining the high electronic/ionic conductivity provided by the porous C₃N₄ matrix, high charge contribution from capacitive behavior, and high sodium storage activity of ultrafine Sn nanoparticles, the resultant Sn/D-C₃N₄ can achieve an ultrahigh reversible capacity of 518.3 mA g^-1 after 300 cycles at 1.0 A g^-1, and even maintaining a reversible capacity of 436.1 mAh g^-1 up to 500 cycles (5.0 A g^-1). What's more, the optimized Sn/D-C₃N₄∥Na₃V₂(PO₄)₃/C full cell can keep a high capacity retention of 87.1% at 1.0 A g^-1 even after 5000 cycles, manifesting excellent sodium storage performance.

Microsized Gray Tin as a High-Rate and Long-Life Anode Material for Advanced Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are developed to address the serious concern about the limited resources of lithium. To achieve high energy density, anode materials with a large specific capacity and a low operation voltage are highly desirable. Herein, microsized particles of gray Sn (α-Sn) are explored as an anode material of SIBs for the first time. The distinct structure of α-Sn endows it the reduced volume change, the improved interaction with polymer binders and the in situ formation of amorphous Sn, as supported by in situ XRD, TEM and DFT calculations. Therefore, α-Sn exhibits an excellent electrochemical performance, much better than β-Sn widely used before. Even microsized particles of α-Sn without any treatments deliver a capacity of ∼451 mAh g^-1 after 3500 cycles at 2 A g^-1 or ∼464 mAh g^-1 at 4 A g^-1 in a rate test. The results indicate the promising potential of α-Sn in SIBs.

Porous Amorphous Silicon Hollow Nanoboxes Coated with Reduced Graphene Oxide as Stable Anodes for Sodium-Ion Batteries

Amorphous silicon (a-Si), due to its satisfactory theoretical capacity, moderate discharge potential, and abundant reserves, is treated as one of the most prospective materials for the anode of sodium-ion batteries (SIBs). However, the slow Na⁺ diffusion kinetics, poor electrical conductivity, and rupture-prone structures of a-Si restrict its further development. In this work, a composite (a-Si@rGO) consisting of porous amorphous silicon hollow nanoboxes (a-Si HNBs) and reduced graphene oxide (rGO) is prepared. The a-Si HNBs are synthesized through "sodiothermic reduction" of silica hollow nanoboxes at a relatively low temperature, and the rGO is covered on the surface of the a-Si HNBs by electrostatic interaction. The as-synthesized composite anode applying in SIBs exhibits a high initial discharge capacity of 681.6 mAh g^-1 at 100 mA g^-1, great stability over 2000 cycles at 800 mA g^-1, and superior rate performance (261.2, 176.8, 130.3, 98.4, and 73.3 mAh g^-1 at 100, 400, 800, 1500, and 3000 mA g^-1, respectively). The excellent electrochemical properties are ascribed to synergistic action of the porous hollow nanostructure of a-Si and the rGO coating. This research not only offers an innovative synthetic means for the development of a-Si in various fields but also provides a practicable idea for the design of other alloy-type anodes.

Expanding the ReS2 Interlayer Promises High-Performance Potassium-Ion Storage

Improving the electrochemical kinetics and the intrinsic poor conductivity of transition metal dichalcogenide (TMD) electrodes is meaningful for developing next-generation energy storage systems. As one of the most promising TMD anode materials, ReS₂ shows attractive performance in potassium-ion batteries (PIBs). To overcome the poor kinetic ion diffusion and limited cycling stability of the ReS₂-based electrode, herein, the interlayer distance expanding strategy was employed, and reduced graphene oxide (rGO) was introduced into ReS₂. Few-layered ReS₂ nanosheets were grown on the surface of the rGO with expanded interlayer distance. The prepared ReS₂ nanosheets show an expanded distance (∼0.77 nm). The synthesized EI-ReS₂@rGO composites were used in PIBs as anode materials. The K-ion storage mechanism of the ReS₂-based anode was investigated by in situ X-ray diffraction (XRD) technology, which shows the intercalation and conversion types. The EI-ReS₂@rGO nanocomposites show high specific capacities of 432.5, 316.5, and 241 mAh g^-1 under 0.05, 0.2, and 1.0 A g^-1 current densities and exhibit excellent reversibility at 1.0 A g^-1. Overall, this strategy, which finely tunes the local chemistry and orbital hybridization for high-performance PIBs, will open up a new field for other materials.

Hundred-gram scale fabrication of few-layered silicene by a continuous vapor-dealloying strategy for high-performance lithium storage

A continuous vapor de-alloying strategy for a hundred-gram scale fabrication of silicene is developed by etching CaSi₂ using waste polyvinyl chloride (PVC). The as-obtained few-layered silicene can be readily assembled with carbon nanotubes into flexible electrodes for lithium storage with excellent performance, which stably deliver a high capacity and stability. This strategy can be extended to other silicon analogs with various structures by selecting precursors such as Mg₂Si and Al/Si alloy.

Revealing Na-segregation at the Si/Graphene Interface and Its Implications toward the Na-storage Behavior of Si-Based Electrodes

The feasibility of reversible alloying of Na with Si has led to Si being considered as a potential anode material for the upcoming Na-ion battery system. However, Si exhibits useful Na-storage capacity and associated electrochemical cyclic stability only in the presence of graphene-based interlayers/additives. Despite this, no knowledge exists concerning the characteristics/phenomena at the Si/graphene interface and the possible influence of the same toward Na-storage behavior/performance. Against this backdrop, a combination of first-principles-based calculations and experimental investigations has revealed here the occurrence of preferential Na-segregation at the Si/graphene interface. Bader charge analysis indicates that when positioned right at the interface, Na undergoes the greatest extent of charge transfer (to become positively charged), with electrons being transferred primarily to the more electronegative C (as compared to Si). More importantly, the binding energy of Na assumes the most negative value at the interface. Furthermore, the overall energy of the Na-Si-graphene system gets minimized to the greatest extent when the Na atom gets located at the Si/graphene interface. The abovementioned predictions have been verified by mapping the Na-concentrations from the surfaces of galvanostatically sodiated amorphous Si films down to bare Cu or graphene-coated Cu substrates (i.e., across Si film thickness) via depth profiling ToF-SIMS. Such measurements indicate that the overall Na-concentration in the sodiated Si film is considerably greater in the presence of a graphene-based interlayer between Si and Cu, thus agreeing with the as-observed enhanced Na-storage capacity. More importantly, the observation of a definite "hump" in the Na-concentration profile very close to the Si/graphene interface, in contrast to almost no Na-concentration close to the Si/Cu interface in the absence of a graphene-based interlayer, is direct evidence for preferential Na-segregation at the Si/graphene interface (unlike at the Si/Cu interface).

Modulating the Graphitic Domains of Hard Carbons Derived from Mixed Pitch and Resin to Achieve High Rate and Stable Sodium Storage

Resin derived hard carbons (HCs) generally demonstrate remarkable electrochemical performance for both sodium ion batteries (SIBs) and potassium-ion batteries (KIBs), but their practical applications are hindered by their high price and high temperature pyrolysis (≈1500 °C). Herein, low-cost pitch is coated on the resin surface to compromise the cost, and meanwhile manipulate the microstructure at a relatively low pyrolysis temperature (1000 °C). HC-0.2P-1000 has a large number of short graphitic layer structures and a relatively large interlayer spacing of 0.3743 nm, as well as ≈1 nm sized nanopores suitable for sodium storage. Consequently, the as produced material demonstrates a superior reversible capacity (349.9 mAh g^-1 for SIBs and 321.9 mAh g^-1 for KIBs) and excellent rate performance (145.1 mAh g^-1 at 20 A g^-1 for SIBs, 48.5 mAh g^-1 at 20 A g^-1 for KIBs). Furthermore, when coupled with Na₃ V₂ (PO₄ )₃ as cathode, the full cell exhibits a high energy density of 251.1 Wh kg^-1 and excellent stability with a capacity retention of 73.3% after 450 cycles at 1 A g^-1 .

Alkoxide hydrolysis in-situ constructing robust trimanganese tetraoxide/graphene composite for high-performance lithium storage

Herein we develop a novel and effective alkoxide hydrolysis approach to in-situ construct the trimanganese tetraoxide (Mn₃O₄)/graphene nanostructured composite as high-performance anode material for lithium-ion batteries (LIBs). This is the first report on the synthesis of Mn₃O₄/graphene composite via a facile hydrolysis of the manganese alkoxide (Mn-alkoxide)/graphene precursor. Before hydrolysis, two dimensional (2D) Mn-alkoxide nanoplates are closely adhered to 2D graphene nanosheets via Mn-O chemical bonding. After hydrolysis, the Mn-alkoxide in-situ converts to Mn₃O₄, while the Mn-O bond is preserved. This leads to a robust Mn₃O₄/graphene hybrid architecture with 15 nm Mn₃O₄ nanocrystals homogeneously anchoring on graphene nanosheets. This not only prevents the Mn₃O₄ nanocrystals agglomeration but also inversely mitigates the graphene nanosheets restacking. Moreover, the flexible and conductive graphene nanosheets can accommodate the volume change. This maintains the structural and electrical integrity of the Mn₃O₄/graphene electrode during the cycling process. As a result, the Mn₃O₄/graphene composite displays superior lithium storage performance with high reversible capacity (741 mAh g^-1 at 100 mA g^-1), excellent rate capability (403 mAh g^-1 at 1000 mA g^-1) and long cycle life (527 mAg g^-1 after 300 cycles at 500 mA g^-1). The electrochemical performance highlights the importance of rational design nanocrystals anchoring on graphene nanosheets for high-performance LIBs application.

Silver Doped Zinc Stannate (Ag-ZnSnO3) for the Photocatalytic Degradation of Caffeine under UV Irradiation

Contaminants of emerging concerns (CECs) spread across a wide range of organic product compounds. As biorecalcitrants, their removal from conventional wastewater treatment systems remains a herculean task. To address this issue, heterogenous solar driven advanced oxidation process based-TiO2 and other semiconductor materials has been extensively studied for their abatement from wastewater sources. In this study, we have synthesized by hydrothermal assisted co-precipitation Ag doped ZnSnO3. Structural and morphological characterizations were performed via X-ray diffraction (XRD), Fourier transform infra-red (FTIR), N2 adsorption-desorption at 77 K by Brunauer-Emmet-Teller (BET) and Barrett, Joyner, and Halenda (BJH) methods, Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy coupled with Energy dispersive spectroscopy (SEM-EDS), and UV-visible absorption in Diffuse reflectance spectroscopy (UV-vis/DRS) mode. Crystallite size estimate for Ag-ZnSnO3 and undoped form was 19.4 and 29.3 nm, respectively, while respective TEM particle size estimate was 79.0 nm and 98.2 nm. BET surface area and total pore volume by BJH for Ag-ZnSnO3 were estimated with respective values of 17.2 m2/g and 0.05 cm3/g in comparison to 18.8 m2/g and 0.06 cm3/g for ZnSnO3. Derived energy band gap (Eg) values were 3.8 eV for Ag-ZnSnO3 and 4.2 eV for ZnSnO3. Photocatalytic performance of Ag-ZnSnO3 was tested towards caffeine achieving about 68% removal under (natural) unmodified pH = 6.50 and almost 100% removal at initial pH around 7.5 after 4 h irradiation. The effect of initial pH, catalyst dosage, pollutant concentration, charge scavengers, H2O2, contaminant inorganic ions (anions) as well as humic acid (HA) on the photocatalyst activity over caffeine degradation were assessed. In accordance with the probation test of the reactive species responsible for photocatalytic degradation process, a reaction mechanism was deduced.

Architectural Engineering Achieves High-Performance Alloying Anodes for Lithium and Sodium Ion Batteries

Tremendous efforts have been dedicated to the development of high-performance electrochemical energy storage devices. The development of lithium- and sodium-ion batteries (LIBs and SIBs) with high energy densities is urgently needed to meet the growing demands for portable electronic devices, electric vehicles, and large-scale smart grids. Anode materials with high theoretical capacities that are based on alloying storage mechanisms are at the forefront of research geared towards high-energy-density LIBs or SIBs. However, they often suffer from severe pulverization and rapid capacity decay due to their huge volume change upon cycling. So far, a wide variety of advanced materials and electrode structures are developed to improve the long-term cyclability of alloying-type materials. This review provides fundamentals of anti-pulverization and cutting-edge concepts that aim to achieve high-performance alloying anodes for LIBs/SIBs from the viewpoint of architectural engineering. The recent progress on the effective strategies of nanostructuring, incorporation of carbon, intermetallics design, and binder engineering is systematically summarized. After that, the relationship between architectural design and electrochemical performance as well as the related charge-storage mechanisms is discussed. Finally, challenges and perspectives of alloying-type anode materials for further development in LIB/SIB applications are proposed.

Recent Progress on the Alloy-Based Anode for Sodium-Ion Batteries and Potassium-Ion Batteries

High-energy batteries with low cost are urgently needed in the field of large-scale energy storage, such as grid systems and renewable energy sources. Sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) with alloy-based anodes provide huge potential due to their earth abundance, high capacity, and suitable working potential, and are recognized as attractive alternatives for next-generation batteries system. Although some important breakthroughs have been reported, more significant improvements are still required for long lifetime and high energy density. Herein, the latest progress for alloy-based anodes for SIBs and PIBs is summarized, mainly including Sn, Sb, Ge, Bi, Si, P, and their oxides, sulfides, selenides, and phosphides. Specifically, the material designs for the desired Na⁺ /K⁺ storage performance, phase transform, ionic/electronic transport kinetics, and specific chemical interactions are discussed. Typical structural features and research strategies of alloy-based anodes, which are used to facilitate processes in battery development for SIBs and PIBs, are also summarized. The perspective of future research of SIBs and PIBs is outlined.

Recent Progress on Layered Cathode Materials for Nonaqueous Rechargeable Magnesium Batteries

Rechargeable magnesium batteries (RMBs) are promising candidates for next-generation energy storage systems owing to their high safety and the low cost of magnesium resources. One of the main challenges for RMBs is to develop suitable high-performance cathode materials. Layered materials are one of the most promising cathode materials for RMBs due to their relatively high specific capacity and facile synthesis process. This review focuses on recent progress on layered cathode materials for RMBs, including layered oxides, sulfides, selenides, and other layered materials. In addition, effective strategies to improve the electrochemical performance of layered cathode materials are summarized. Moreover, future perspectives about the application of layered materials in RMBs are also discussed. This review provides some significant guidance for the further development of layered materials for RMBs.

Silicon as the Anode Material for Multivalent-Ion Batteries: A First-Principles Dynamics Study

Due to its huge capacity, Si is a promising anode material for practical applications in lithium-ion batteries. Here, using first-principles calculations, we study the applicability of the amorphous Si anode in multivalent-ion batteries, which are of great interest as candidates for post-lithium-ion batteries. Of the multivalent Mg²⁺, Ca²⁺, Zn²⁺, and Al³⁺ ions, only Mg²⁺ and Ca²⁺ are able to form Mg_2.3Si and Ca_2.5Si by alloying with Si, delivering very high capacities of 4390 and 4771 mA h g^-1, respectively. Mg_2.3Si has an 8% smaller capacity than Ca_2.5Si, but its volume expansion ratio and ion diffusivity are ∼200% smaller and 3 orders of magnitude higher than those of Ca_2.5Si, respectively. The capacity, volume expansion, and ion diffusion of Mg_2.3Si are excellently high, moderately small, and fairly fast, respectively, when compared to those of Li_3.7Si, Na_0.75Si, and K_1.1Si. The high performance of Mg_2.3Si can be understood in terms of the coordination numbers of Si and the atomic size of Mg. This work suggests that, as a carrier ion for the amorphous Si anode, Mg²⁺ is the most competitive among the multivalent ions and is at least as good as monovalent ions.

Nanoframes@CNT Beads-on-a-String Structures: Toward an Advanced High-Stable Sodium-Ion Full Battery

Engineering intriguing electrode with exceptional kinetics behaviors is imperative for boosting sodium storage systems. Herein, the uniform nanoframes are threaded by the interwoven carbon nanotube (CNT) conductive network to form an ingenious beads-on-a-string structured NiFePBA nanoframe/CNT (NFPB-NF/CNT) cathode and the corresponding derivative NiFeSe nanoframe/CNT (NFS-NF/CNT) anode. NFPB-NF/CNT exhibited remarkable cycling life along with outstanding rate capability and low voltage decay per cycle. The fast Na⁺ conduction and sufficient sodiation reaction is proved using Na⁺ diffusion models. Meanwhile, an exceptional sodium storage capacity and prolonged cycling life is achieved using binary NFS-NF/CNT anode at a high rate. In situ and ex situ investigations are used to reveal the sodium storage mechanisms and structural evolution process. Furthermore, a sodium-ion full battery based on the above electrodes shows stable performance accompanied by high energy conversion efficiency. The material design strategy provides a new solution for exploiting smart multicomponent composites toward advanced energy storage devices.

Rational Design of Sb@C@TiO2 Triple-Shell Nanoboxes for High-Performance Sodium-Ion Batteries

Antimony is an attractive anode material for sodium-ion batteries (SIBs) owing to its high theoretical capacity and appropriate sodiation potential. However, its practical application is severely impeded by its poor cycling stability caused by dramatic volumetric variations during sodium uptake and release processes. Here, to circumvent this obstacle, Sb@C@TiO₂ triple-shell nanoboxes (TSNBs) are synthesized through a template-engaged galvanic replacement approach. The TSNB structure consists of an inner Sb hollow nanobox protected by a conductive carbon middle shell and a TiO₂ -nanosheet-constructed outer shell. This structure offers dual protection to the inner Sb and enough room to accommodate volume expansion, thus promoting the structural integrity of the electrode and the formation of a stable solid-electrolyte interface film. Benefiting from the rational structural design and synergistic effects of Sb, carbon, and TiO₂ , the Sb@C@TiO₂ electrode exhibits superior rate performance (212 mAh g^-1 at 10 A g^-1 ) and outstanding long-term cycling stability (193 mAh g^-1 at 1 A g^-1 after 4000 cycles). Moreover, a full cell assembled with a configuration of Sb@C@TiO₂ //Na₃ (VOPO₄ )₂ F displays a high output voltage of 2.8 V and a high energy density of 179 Wh kg^-1 , revealing the great promise of Sb@C@TiO₂ TSNBs as the electrode in SIBs.

State-of-the-Art Electrode Materials for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) were investigated as recently as in the seventies. However, they have been overshadowed for decades, due to the success of lithium-ion batteries that demonstrated higher energy densities and longer cycle lives. Since then, the witness a re-emergence of the SIBs and renewed interest evidenced by an exponential increase of the publications devoted to them (about 9000 publications in 2019, more than 6000 in the first six months this year). This huge effort in research has led and is leading to an important and constant progress in the performance of the SIBs, which have conquered an industrial market and are now commercialized. This progress concerns all the elements of the batteries. We have already recently reviewed the salts and electrolytes, including solid electrolytes to build all-solid-state SIBs. The present review is then devoted to the electrode materials. For anodes, they include carbons, metal chalcogenide-based materials, intercalation-based and conversion reaction compounds (transition metal oxides and sulfides), intermetallic compounds serving as functional alloying elements. For cathodes, layered oxide materials, polyionic compounds, sulfates, pyrophosphates and Prussian blue analogs are reviewed. The electrode structuring is also discussed, as it impacts, importantly, the electrochemical performance. Attention is focused on the progress made in the last five years to report the state-of-the-art in the performance of the SIBs and justify the efforts of research.

Hierarchically Nanoporous Pyropolymers Derived from Waste Pinecone as a Pseudocapacitive Electrode for Lithium Ion Hybrid Capacitors

The non-aqueous asymmetric lithium ion hybrid capacitor (LIHC) is a tactical energy storage device composed of a faradic and non-faradic electrode pair, which aims to achieve both high energy and great power densities. On the other hand, the different types of electrode combinations cause severe imbalances in energy and power capabilities, leading to poor electrochemical performance. Herein, waste pinecone-derived hierarchically porous pyropolymers (WP-HPPs) were fabricated as a surface-driven pseudocapacitive electrode, which has the advantages of both faradic and non-faradic electrodes. The unique materials properties of WP-HPPs possessing high effective surface areas and hierarchically open nanopores led to high specific capacities of ~412 mA h g⁻¹ and considerable rate/cycling performance as a cathode for LIHCs. In particular, nanometer-scale pores, approximately 3 nm in size, plays a key role in the pseudocapacitive charge storage behaviors because open nanopores can transport solvated Li-ions easily into the inside of complex carbon structures and a large specific surface area can be provided by the effective active surface for charge storage. In addition, WP-HPP-based asymmetric LIHCs assembled with a pseudocapacitive counterpart demonstrated feasible electrochemical performance, such as maximum specific energy and specific power of ~340 Wh kg⁻¹ and ~11,000 W kg⁻¹, respectively, with significant cycling stability.

Enhanced sodium storage kinetics by volume regulation and surface engineering via rationally designed hierarchical porous FeP@C/rGO

Transition metal phosphides, such as iron phosphide (FeP), have been considered as promising anode candidates for high-performance sodium ion batteries (SIBs) owing to their high theoretical capacity. However, the development of FeP is limited by large volume change, low electrical conductivity and sluggish kinetics with sodium ions. Moreover, the sodium storage kinetics and dynamics behavior in FeP are still unclear. Herein, improved sodium storage ability of FeP is achieved by volume regulation and surface engineering via a rationally designed hierarchical porous FeP@C/rGO nanocomposite. This FeP@C/rGO nanocomposite exhibits excellent rate capability and long cycle life as the anode of SIBs. Specifically, the FeP@C/rGO nanocomposite delivers high specific capacities of 635.7 and 343.1 mA h g-1 at 20 and 2000 mA g-1, respectively, and stable cycling with 88.2% capacity retention after 1000 cycles. The kinetics and dynamics studies demonstrate that the superior performance is attributed to the rationally designed hierarchical porous FeP@C/rGO with a high capacitive contribution of 93.9% (at 2 mV s-1) and a small volume expansion of only 54.9% by in situ transmission electron microscopy (TEM) measurement. This work provides valuable insights into understanding the phase evolution of FeP during the sodiation/desodiation process for designing high-performance SIBs.

Si and Ge-Based Anode Materials for Li-, Na-, and K-Ion Batteries: A Perspective from Structure to Electrochemical Mechanism

Silicon and germanium are among the most promising candidates as anodes for Li-ion batteries, meanwhile their potential application in sodium- and potassium-ion batteries is emerging. The access of their entire potential requires a comprehensive understanding of their electrochemical mechanism. This Review highlights the processes taking place during the alloying reaction of Si and Ge with the alkali ions. Several associated challenges, including the volumetric expansion, particle pulverization, and uncontrolled formation of solid electrolyte interphase layer must be surmounted and different strategies, such as nanostructures and electrode formulation, have been implemented. Additionally, a new approach based on the use of layered Si and Ge-based Zintl phases is presented. The versatility of this new family permits the tuning of their physical and chemical properties for specific applications. For batteries in particular, the layered structure buffers the volume expansion and exhibits an enhanced electronic conductivity, allowing high power applications.

Si@SnS2 -Reduced Graphene Oxide Composite Anodes for High-Capacity Lithium-Ion Batteries

One of the key challenges for the development of lithium-ion batteries is the preparation of high-performance anode materials. In this paper, a micro/nanostructured Si@SnS₂ -rGO composite is reported in which Si nanoparticles with a particle size of 30 nm are electrostatically anchored on a 3D reduced graphene oxide (rGO) network and mixed with SnS₂ . The step-wise lithiation/delithiation of SnS₂ provided space-constraining effects to accommodate volume expansion and particle aggregation, thereby alleviating the volume expansion of Si during cycling as well as enhancing the structural stability, whereas the rGO in the 3D network stabilized the composite. The composite had a high specific capacity of 1480.1 mAh g^-1 after 200 cycles at a current density of 200 mA g^-1 and a high stability at rates of 200-3000 mA g^-1 . The capacity attenuation after cycling was only 89.18 %. A stable specific capacity (425.5 mAh g^-1 ) was achieved after 600 cycles at a current density of 3000 mA g^-1 . Therefore, the micro/nanostructured Si@SnS₂ -rGO composite is a promising anode material for use in lithium-ion batteries.

Boosting Sodium Storage of Fe1-xS/MoS2 Composite via Heterointerface Engineering

Improving the cycling stability of metal sulfide-based anode materials at high rate is of great significance for advanced sodium ion batteries. However, the sluggish reaction kinetics is a big obstacle for the development of high-performance sodium storage electrodes. Herein, we have rationally engineered the heterointerface by designing the Fe_1-xS/MoS₂ heterostructure with abundant "ion reservoir" to endow the electrode with excellent cycling stability and rate capability, which is proved by a series of in and ex situ electrochemical investigations. Density functional theory calculations further reveal that the heterointerface greatly decreases sodium ion diffusion barrier and facilitates charge-transfer kinetics. Our present findings not only provide a deep analysis on the correlation between the structure and performance, but also draw inspiration for rational heterointerface engineering toward the next-generation high-performance energy storage devices.

Thermal-controlled releasing and assembling of functional nanomembranes through polymer pyrolysis

Pyrolysis, which involves thermal decomposition of materials at elevated temperatures, has been commonly applied in the chemical industry. Here we explored the pyrolysis process for 3D nanofabrication. By strain engineering of nanomembranes on a thermal responsive polymer as the sacrificial layer, we demonstrated that diverse 3D rolled-up microstructures with different functions could be achieved without any additional solution and drying process. We carefully studied the effect of molecular weight of the polymer in the pyrolysis process and identified that the rapid breakdown of molecular backbone to a monomer is the key for nanomembrane releasing and rolling. Preferential rolling direction and corresponding dynamics were studied by analyzing the real-time video of the rolling process. We further demonstrated the versatile functions of the fabricated 3D structures as catalytic microengines and optical resonators. The simple fabrication methodology developed here may have great potential in producing functional 3D tubular micro-/nanostructures.

Three-Dimensional Chestnut-Like Architecture Assembled from NaTi3O6(OH)·2H2O@N-Doped Carbon Nanosheets with Enhanced Sodium Storage Properties

The application of sodium titanate anodes of low cost, feasible operating voltage, and nontoxic nature were severely hindered by their inferior cycling stability and poor rate capability. Here, three-dimensional (3D) chestnut-like NaTi₃O₆(OH)·2H₂O@N-doped carbon nanospheres (NTOH@CN) with loose crystal structures were prepared by a self-sacrificed template method. The nanospheres were composed of nanosheets and linked with nanowires, which interweaved to construct a meshwork structure. The growth mechanism of unique 3D NTOH@CN nanospheres was investigated by tracking the synthesis process of different hydrothermal durations. The rate performances of 3D NTOH@CN were superior to that of NaTi₃O₆(OH)·2H₂O irregular spheres assembled from nanosheets (3D NTOH) and NaTi₃O₆(OH)·2H₂O nanosheets (two-dimensional NTOH). Excellent cycling and rate performance were obtained due to their open crystal structure, unique 3D nanosphere morphology with short diffusion paths, N-doped carbon surrounding, and the solid solution reaction. In addition, the reaction mechanism, morphology change, and dynamics research during the sodium insertion/desertion process have been carefully studied. Based on varying ex situ analyses, the irreversible metallic titanium formation and the excellent structural stability of nanosphere morphology have been evidenced. The pseudocapacitive phenomenon was also detected, which effectively enhanced Na⁺ ion storage capability. The systematical and comprehensive study provide a holograph for the design and synthesis of sodium titanate nanostructures.

Improved gas sensing properties of silver-functionalized ZnSnO3 hollow nanocubes

Porous silver-functionalized ZnSnO₃ hollow nanocubes as a gas sensor with an ultra-fast response and recovery speed for acetone detection.