Using X-ray Microscopy To Understand How Nanoporous Materials Can Be Used To Reduce the Large Volume Change in Alloy Anodes

CoSe2 nanoparticles anchored on porous carbon network structure for efficient Na-ion storage

Cobalt selenide, as a star material in battery industry, has attracted much attention. However, when it is applied solely in sodium ion batteries, it will cause large volume expansion and material agglomeration, which will seriously affect the overall performance of batteries. In this work, we use ice bath impregnation to combine CoSe₂ nanoparticles with porous nitrogen-doped carbon networks (NC) as advanced anodes for ultra-long cycle life sodium ion batteries (SIBs). CoSe₂ nanoparticles are evenly attached to NC with strong interfacial contacts in CoSe₂@NC. The strong contact of CoSe₂ on the porous carbon network, along with the carbon network's unique network cross-linking structure, results in rapid electron transfer and Na ion diffusion kinetics of CoSe₂@NC, resulting in superior electrochemical performance. Besides, we have synthesized CoSe₂@NC with different loading by changing Co²⁺ concentration. The results show that CoSe₂@NC anode thus provides a high reversible capacity of 406 mAh/g. In addition, at high current 5 A/g, it can keep a reversible capacity of 300 mAh/g after 4500 cycles with an average capacity loss of less than 0.01 % per cycle. The excellent anchoring structure enables it to form stable solid electrolyte film (SEI) and reduce the amount of dead sodium in the first charge-discharge process, showing high Initial Coulombic Efficiency (ICE) (89.2 %). Finally, CoSe₂@NC and Na₃V₂(PO₄)₃ (NVP) are assembled into a full cell and the results shows an ultra-long cycle stability at 0.1 A/g. This strategy will facilitate the application of transition metal selenides in next-generation energy storage systems.

A Stable Core–Shell Si@SiOx/C Anode Produced via the Spray and Pyrolysis Method for Lithium-Ion Batteries

In the critical situation of energy shortage and environmental problems, Si has been regarded as one of the most potential anode materials for next-generation lithium-ion batteries as a result of the relatively low delithiation potential and the eminent specific capacity. However, a Si anode is subjected to the huge volume expansion–contraction in the charging–discharging process, which can touch off pulverization of the bulk particles and worsens the cycle life. Herein, to reduce the volume change and improve the electrochemical performance, a novel Si@SiO_x/C anode with a core–shell structure is designed by spray and pyrolysis methods. The SiO_x/C shell not only ensures the structure stability and proves the high electrical conductivity but also prevents the penetration of electrolytes, so as to avoid the repetitive decomposition of electrolytes on the surface of Si particle. As expected, Si@SiO_x/C anode maintains the excellent discharge capacity of 1,333 mAh g⁻¹ after 100 cycles at a current density of 100 mA g⁻¹. Even if the current density reaches up to 2,000 mA g⁻¹, the capacity can still be maintained at 1,173 mAh g⁻¹. This work paves an effective way to develop Si-based anodes for high-energy density lithium-ion batteries.

Understanding Stabilization in Nanoporous Intermetallic Alloy Anodes for Li-Ion Batteries Using Operando Transmission X-ray Microscopy

Tin-based alloying anodes are exciting due to their high energy density. Unfortunately, these materials pulverize after repetitive cycling due to the large volume expansion during lithiation and delithiation; both nanostructuring and intermetallic formation can help alleviate this structural damage. Here, these ideas are combined in nanoporous antimony-tin (NP-SbSn) powders, synthesized by a simple and scalable selective-etching method. The NP-SbSn exhibits bimodal porosity that facilitates electrolyte diffusion; those void spaces, combined with the presence of two metals that alloy with lithium at different potentials, further provide a buffer against volume change. This stabilizes the structure to give NP-SbSn good cycle life (595 mAh/g after 100 cycles with 93% capacity retention). Operando transmission X-ray microscopy (TXM) showed that during cycling NP-SbSn expands by only 60% in area and then contracts back nearly to its original size with no physical disintegration. The pores shrink during lithiation as the pore walls expand into the pore space and then relax back to their initial size during delithiation with almost no degradation. Importantly, the pores remained open even in the fully lithiated state, and structures are in good physical condition after the 36th cycle. The results of this work should thus be useful for designing nanoscale structures in alloying anodes.

The α-Fe2O3/graphite anode composites with enhanced electrochemical performance for lithium-ion batteries

The α-Fe₂O₃/graphite composites were prepared by a thermal decomposition method using the expanded graphite as the matrix. The α-Fe₂O₃ nanoparticles with the size of 15-30 nm were embedded into interlayers of graphite, forming a laminated porous nanostructure with a main pore distribution from 2 to 20 nm and the Brunauer-Emmett-Teller surface area of 33.54 m² g^-1. The porous structure constructed by the graphite sheets can alleviate the adverse effects caused by the huge volume change of the α-Fe₂O₃ grains during the charge/discharge process. The composite electrode exhibits a high reversible capacity of 1588 mAh g^-1 after 100 cycles at 100 mA g^-1, 702 mAh g^-1 at 5 A g^-1, 460 mAh g^-1 at 10 A g^-1 after 160 cycles, respectively, showing good cycle stability and outstanding rate capability at high current densities.

Calendering-Compatible Macroporous Architecture for Silicon-Graphite Composite toward High-Energy Lithium-Ion Batteries

Porous strategies based on nanoengineering successfully mitigate several problems related to volume expansion of alloying anodes. However, practical application of porous alloying anodes is challenging because of limitations such as calendering incompatibility, low mass loading, and excessive usage of nonactive materials, all of which cause a lower volumetric energy density in comparison with conventional graphite anodes. In particular, during calendering, porous structures in alloying-based composites easily collapse under high pressure, attenuating the porous characteristics. Herein, this work proposes a calendering-compatible macroporous architecture for a Si-graphite anode to maximize the volumetric energy density. The anode is composed of an elastic outermost carbon covering, a nonfilling porous structure, and a graphite core. Owing to the lubricative properties of the elastic carbon covering, the macroporous structure coated by the brittle Si nanolayer can withstand high pressure and maintain its porous architecture during electrode calendering. Scalable methods using mechanical agitation and chemical vapor deposition are adopted. The as-prepared composite exhibits excellent electrochemical stability of >3.6 mAh cm^-2 , with mitigated electrode expansion. Furthermore, full-cell evaluation shows that the composite achieves higher energy density (932 Wh L^-1 ) and higher specific energy (333 Wh kg^-1 ) with stable cycling than has been reported in previous studies.

Facile Synthesis of FeS@C Particles Toward High-Performance Anodes for Lithium-Ion Batteries

High energy density batteries with high performance are significantly important for intelligent electrical vehicular systems. Iron sulfurs are recognized as one of the most promising anodes for high energy density lithium-ion batteries because of their high theoretical specific capacity and relatively stable electrochemical performance. However, their large-scale commercialized application for lithium-ion batteries are plagued by high-cost and complicated preparation methods. Here, we report a simple and cost-effective method for the scalable synthesis of nanoconfined FeS in porous carbon (defined as FeS@C) as anodes by direct pyrolysis of an iron(III) p-toluenesulfonate precursor. The carbon architecture embedded with FeS nanoparticles provides a rapid electron transport property, and its hierarchical porous structure effectively enhances the ion transport rate, thereby leading to a good electrochemical performance. The resultant FeS@C anodes exhibit high reversible capacity and long cycle life up to 500 cycles at high current density. This work provides a simple strategy for the mass production of FeS@C particles, which represents a critical step forward toward practical applications of iron sulfurs anodes.

In Situ Focused Ion Beam Scanning Electron Microscope Study of Microstructural Evolution of Single Tin Particle Anode for Li-Ion Batteries

Tin (Sn) is a potential anode material for highenergy density Li-ion batteries because of its high capacity, safety, abundance and low cost. However, Sn suffers from large volume change during cycling, leading to fast degradation of the electrode. For the first time, the microstructural evolution of micrometer-sized single Sn particle was monitored by focused-ion beam (FIB) polishing and scanning electron microscopy (SEM) imaging during electrochemical cycling by in situ FIB-SEM. Our results show the formation and evolution of cracks during lithiation, evolution of porous structure during delithiation and volume expansion/contraction during cycling. The electrochemical performance and the microstructural evolution of the Sn microparticle during cycling are directly correlated, which provides insights for understanding Sn-based electrode materials.

Enhanced Lithium Storage Capacity of a Tetralithium 1,2,4,5-Benzenetetracarboxylate (Li4C10H2O8) Salt Through Crystal Structure Transformation

Because of their low price, design flexibility, and sustainability, organic-based electrode materials are considered one of the most promising next-generation alternatives to inorganic materials in Li-ion batteries. However, a clear understanding of the changes in the molecular crystal structure during Li-ion insertion/extraction and its relationship to excess capacity (over theoretical capacity) is still lacking. Herein, the tetralithium 1,2,4,5-benzenetetracarboxylate (Li₄C₁₀H₂O₈, Li₄BTC) salt was prepared using a simple ion-exchange reaction at room temperature and under solvothermal conditions (100 °C). The solvothermally synthesized salt (Li₄BTC-S) exhibited a well-ordered nanosheet morphology, whereas the room-temperature salt (Li₄BTC-R) was comprised of irregularly shaped particles. During the cycling of Li₄BTC-S, molecular rearrangement occurred to reduce the stress caused by repeated Li-ion insertion/extraction, resulting in a change in the crystal structure from triclinic to monoclinic and an increased free volume. This contributed to an increase in the reversible capacity to 1016 mAh g^-1 during the initial 25 cycles at 0.1 A g^-1, and finally the capacity stabilized at ca. 600 mAh g^-1 after 100 cycles, which is much higher than its theoretical capacity (234 mAh g^-1). Compared with Li₄BTC-R, Li₄BTC-S delivered a higher reversible capacity of 190 mAh g^-1 at a high current density of 2 A g^-1, with an excellent long-term cyclability of up to 1000 cycles, which was attributed to the straight free volume columns and the low-charge-transfer limitation.

Deterministic Design of Chemistry and Mesostructure in Li-Ion Battery Electrodes

All battery electrodes have complex internal three-dimensional architectures that have traditionally been formed through the random packing of the electrode components. What is now emerging is a new concept in battery electrode design, where the important electronic and ionic pathways, as well as the chemical interactions between the components of the electrode, are deterministically designed. Deterministic design enables far better properties than are possible through random packing, including dramatic improvements in both power and energy. Such a design approach is particularly attractive for emerging high-energy-density materials, which require available free volume as they swell during cycling. In addition to controlled structure, another important facet of the design of such systems is the stable chemical linkages between the active material and the conductive network that survive the lithiation and delithiation processes. In this Perspective, we discuss and provide our views on deterministically designed battery electrodes.

Metallic Sn-Based Anode Materials: Application in High-Performance Lithium-Ion and Sodium-Ion Batteries

With the fast-growing demand for green and safe energy sources, rechargeable ion batteries have gradually occupied the major current market of energy storage devices due to their advantages of high capacities, long cycling life, superior rate ability, and so on. Metallic Sn-based anodes are perceived as one of the most promising alternatives to the conventional graphite anode and have attracted great attention due to the high theoretical capacities of Sn in both lithium-ion batteries (LIBs) (994 mA h g-1) and sodium-ion batteries (847 mA h g-1). Though Sony has used Sn-Co-C nanocomposites as its commercial LIB anodes, to develop even better batteries using metallic Sn-based anodes there are still two main obstacles that must be overcome: poor cycling stability and low coulombic efficiency. In this review, the latest and most outstanding developments in metallic Sn-based anodes for LIBs and SIBs are summarized. And it covers the modification strategies including size control, alloying, and structure design to effectually improve the electrochemical properties. The superiorities and limitations are analyzed and discussed, aiming to provide an in-depth understanding of the theoretical works and practical developments of metallic Sn-based anode materials.

Enhancing the free corrosion dealloying rate with a catalytically driven reaction

Despite its high popularity, chemical dealloying that is widely used for the fabrication of nanoporous metals is a relatively slow process: dealloying a few milligrams of bulk material may take from several hours up to a few days, depending on the material system. Raising the temperature of the corroding medium is a common approach to speed up the dealloying process. However, high temperatures cause undesired ligament growth in dealloyed materials. Here we report for the first time the use of a catalytically driven reaction to speed up the dealloying process at ambient temperature and pressure. To demonstrate the concept, we show that the free corrosion dealloying of a silver-aluminum alloy is significantly faster with the help of a platinum catalyst. More importantly, the corresponding characteristic nanostructured size is much smaller than that without a catalyst. Our finding is expected to play a central role in scaling up the dealloying process from the laboratory to the industrial scale.