Si/Ag composite with bimodal micro-nano porous structure as a high-performance anode for Li-ion batteries

Rational engineering of a carbon skeleton supported tin dioxide nanocomposite from MOF on graphene precursor for superior lithium and sodium ion storage

Tin dioxide (SnO2) is being investigated as a promising anode material for both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). Effectively dispersing small sized SnO2 crystals in well-designed carbonaceous matrices using eco-friendly materials and simplified methods is an urgent task. Herein, gallic acid (GA) molecules, abundant in plant kingdom, are firstly selected to react with few-layered graphene oxide (GO) in mild hydrothermal condition, and the GA modulated reduced graphene oxide (GA@RGO) supporting skeleton can be obtained. Then Sn-GA metal-organic framework (MOF) domains can be directly engineered on the surface of the GA@RGO sheets with controlled size and improved dispersion. Finally, the well-designed Sn-GA@RGO precursor is converted to the SnO2/C/RGO nanocomposite with significantly optimized microstructure. The SnO2/C/RGO sample delivers an excellent specific capacity of 823.6 mAh·g-1 after 700 cycles at 1000 mA·g-1 in half-cells and 741.3 mAh·g-1 after 50 cycles at 200 mA·g-1 in full-cells for LIBs, a specific capacity of 370.3 mAh·g-1 after 600 cycles at 200 mA·g-1 in half-cells for SIBs. The sample preparation strategy is rationally established by comprehensively understanding the interactions between GO sheets, Sn2+ ions and GA molecules, and the engineered SnO2/C/RGO nanocomposite has good prospects in wider fields.

Turning Complexity into Simplicity: In Situ Synthesis of High-Performance Si@C Anode in Battery Manufacturing Process by Partially Carbonizing the Slurry of Si Nanoparticles and Dual Polymers

For Si/C anodes, achieving excellent performance with a simple fabrication process is still an ongoing challenge. Herein, we report a green, facile and scalable approach for the in situ synthesis of Si@C anodes during the electrode manufacturing process by partially carbonizing Si nanoparticles (Si NPs) and dual polymers at a relatively low temperature. Due to the proper mass ratio of the two polymer precursors and proper carbonization temperature, the resultant Si-based anode demonstrates a typical Si@C core-shell structure and has strong mechanical properties with the aid of dual-interfacial bonding between the Si NPs core and carbon shell layer, as well as between the C matrix and the underlying Cu foil. Consequently, the resultant Si@C anode shows a high specific capacity (3458.1 mAh g-1 at 0.2 A g-1), good rate capability (1039 mAh g-1 at 4 A g-1) and excellent cyclability (77.94% of capacity retention at a high current density of 1 A g-1 after 200 cycles). More importantly, the synthesis of the Si@C anode is integrated in situ into the electrode manufacturing process and, thus, significantly decreases the cost of the lithium-ion battery but without sacrificing the electrochemical performance of the Si@C anode. Our results provide a new strategy for designing next-generation, high-capacity and cost-effective batteries.

Dealloyed Porous NiFe2O4/NiO with Dual-Network Structure as High-Performance Anodes for Lithium-Ion Batteries

As high-capacity anode materials, spinel NiFe₂O₄ aroused extensive attention due to its natural abundance and safe working voltage. For widespread commercialization, some drawbacks, such as rapid capacity fading and poor reversibility due to large volume variation and inferior conductivity, urgently require amelioration. In this work, NiFe₂O₄/NiO composites with a dual-network structure were fabricated by a simple dealloying method. Benefiting from the dual-network structure and composed of nanosheet networks and ligament-pore networks, this material provides sufficient space for volume expansion and is able to boost the rapid transfer of electrons and Li ions. As a result, the material exhibits excellent electrochemical performance, retaining 756.9 mAh g^-1 at 200 mA g^-1 after cycling for 100 cycles and retaining 641.1 mAh g^-1 after 1000 cycles at 500 mA g^-1. This work provides a facile way to prepare a novel dual-network structured spinel oxide material, which can promote the development of oxide anodes and also dealloying techniques in broad fields.

Strategies for Controlling or Releasing the Influence Due to the Volume Expansion of Silicon inside Si-C Composite Anode for High-Performance Lithium-Ion Batteries

Currently, silicon is considered among the foremost promising anode materials, due to its high capacity, abundant reserves, environmental friendliness, and low working potential. However, the huge volume changes in silicon anode materials can pulverize the material particles and result in the shedding of active materials and the continual rupturing of the solid electrolyte interface film, leading to a short cycle life and rapid capacity decay. Therefore, the practical application of silicon anode materials is hindered. However, carbon recombination may remedy this defect. In silicon/carbon composite anode materials, silicon provides ultra-high capacity, and carbon is used as a buffer, to relieve the volume expansion of silicon; thus, increasing the use of silicon-based anode materials. To ensure the future utilization of silicon as an anode material in lithium-ion batteries, this review considers the dampening effect on the volume expansion of silicon particles by the formation of carbon layers, cavities, and chemical bonds. Silicon-carbon composites are classified herein as coated core-shell structure, hollow core-shell structure, porous structure, and embedded structure. The above structures can adequately accommodate the Si volume expansion, buffer the mechanical stress, and ameliorate the interface/surface stability, with the potential for performance enhancement. Finally, a perspective on future studies on Si-C anodes is suggested. In the future, the rational design of high-capacity Si-C anodes for better lithium-ion batteries will narrow the gap between theoretical research and practical applications.

Towards tuning the modality of hierarchical macro-nanoporous metals by controlling the dealloying kinetics of close-to-eutectic alloys

Largely inspired by nature, hierarchical porous materials are attractive for a wide range of applications as they provide a unique combination of transport and interfacial properties. Hierarchical macro-nanoporous metals (HMNPM) are of particular interest due to their high thermal and electrical conductivities, high volumetric macroporosity as well as their strong capillary forces, and large surface area due to their nanopores. However, tuning the porosity of HMNPMs remains challenging and often requires complex multi-step synthesis methods. Here we demonstrate that controlling the dealloying kinetics of close-to-eutectic alloys allows the selective tuning of the porosity of a hierarchical metal from tens of nanometers to hundreds of micrometers. This was demonstrated by dealloying the Cu-Mg-Zn alloy of close-to-eutectic composition to develop trimodal hierarchical macro-nanoporous copper with an impressive porosity of 94 vol% in the form of macroscopic self-supporting bulk samples. A combination of dealloying experiments and density functional theory calculations indicate that while selective corrosion of chemical phases in the Cu-Mg-Zn alloy is triggered according to their Volta potential, the kinetics can be altered by confinement and non-homogeneity effects. The obtained insights into the kinetics of close-to-eutectic alloy dealloying can be used to develop other hierarchical porous metals with tunable porosity and controlled shape.

Encapsulating silicon particles by graphitic carbon enables High-performance Lithium-ion batteries

Silicon combines the advantages of high theoretical specific capacity, low potential and natural abundance, which exhibits great promise as an anode for lithium-ion batteries. However, the main challenges associated with Si anode are continuous volume expansion upon cycling and intrinsic low electronic conductivity, leading to sluggish reaction kinetics and rapid capacity fading. Herein we propose a novel in-situ self-catalytic strategy for the growth of highly graphitic carbon to encapsulate Si nanoparticles by chemical vapor deposition, where the magnesiothermic reduction byproducts are used as templates and catalysts for the formation of three-dimensional (3D) conductive network architecture. Benefiting from the improved electronic conductivity and significant suppression of volume expansion, the as-synthesized Si carbon composites exhibit excellent lithium storage capabilities in terms of high specific capacity (2126 mAh g^-1 at 0.1 A g^-1), remarkable rate capability (750 mAh g^-1 at 5 A g^-1), and good cycling stability over 450 cycles. Furthermore, the as-fabricated full cell (Si//Ni-rich LiNi_0.815Co_0.185-xAl_xO₂) shows high energy density of 395.1 Wh kg^-1 and long-term stable cyclability. Significantly, this work demonstrates the effectiveness of in-situ self-catalysis reaction by using magnesiothermic reduction byproducts catalytically derived carbon matrix to encapsulate alloy-type anode material in giving rise to the overall energy storage performance.

Electrochemical Performance Enhancement of Micro-Sized Porous Si by Integrating with Nano-Sn and Carbonaceous Materials

Silicon is investigated as one of the most prospective anode materials for next generation lithium ion batteries due to its superior theoretical capacity (3580 mAh g-1), but its commercial application is hindered by its inferior dynamic property and poor cyclic performance. Herein, we presented a facile method for preparing silicon/tin@graphite-amorphous carbon (Si/Sn@G-C) composite through hydrolyzing of SnCl2 on etched Fe-Si alloys, followed by ball milling mixture and carbon pyrolysis reduction processes. Structural characterization indicates that the nano-Sn decorated porous Si particles are coated by graphite and amorphous carbon. The addition of nano-Sn and carbonaceous materials can effectively improve the dynamic performance and the structure stability of the composite. As a result, it exhibits an initial columbic efficiency of 79% and a stable specific capacity of 825.5 mAh g-1 after 300 cycles at a current density of 1 A g-1. Besides, the Si/Sn@G-C composite exerts enhanced rate performance with 445 mAh g-1 retention at 5 A g-1. This work provides an approach to improve the electrochemical performance of Si anode materials through reasonable compositing with elements from the same family.

Facile fabrication of Si/Sb/Sb2O3/G@C composite electrodes for high-performance Li-ion batteries

Facile fabrication of high-performance Si/Sb/Sb₂O₃/G@C composite materialviathe ball milling and high temperature calcination process is reported.

Carbon free silicon/polyaniline hybrid anodes with 3D conductive structures for superior lithium-ion batteries

We design a carbon-free Si/polyaniline hybrid anode composed of porous Si dendrites and oxalic acid doped polyaniline coatings.

Temperature-Dependent Li Storage Performance in Nanoporous Cu-Ge-Al Alloy

The performance fading process and safety concerns of lithium ion batteries at low temperature (LT) prohibit their application in cold climates. The alloy-type electrodes demonstrate great potentials in stable and dendrite-free anodes at LT. Herein, we report a temperature-dependent Li storage performance in Al-based nanoporous alloy anode. The nanoporous-structured Cu-Ge-Al ternary alloys (NP-CuGeAl) have been designed and prepared by selectively etching Al out. The high-Al-content NP-CuGeAl (acid etching for 6 h, named CGA-6) is composed of multi-intermetallic compounds (denoted as M _xN _y, M, N = Cu, Al, Ge) with bimodal porous architectures. Investigated as anode at room temperature, the CGA-6 delivers a capacity as high as 479.7 mAh g^-1 at 0.5 A g^-1 of over 1020 cycles, and the low-Al-content ones show improved LT electrochemical performance. At -20 °C, the CGA-48 (acid etching for 48 h) shows much better performance as compared with the CGA-6. In Situ transmission electron microscopy and ex situ characterizations confirm that the M _xN _y/Li _zM _xN _y couples are highly reversible and the porous structure is durable upon battery cycling.

One-step mild fabrication of porous core-shelled Si@TiO2 nanocomposite as high performance anode for Li-ion batteries

Nanoporous Si@TiO₂ composites with the unique core-shell architecture are conveniently fabricated through one-step selective dealloying of SiTiAl ternary alloy under mild conditions. The as-prepared composites consist of bimodal Si network skeleton as the core and interconnected TiO₂ nanosponge layer as the shell uniformly distribute on the Si surface to form the porous core-shelled structure. The nanoporous TiO₂ as the outer protective layer not only reduce the violent volume change of electrode materials for stable cycling performance but also shorten the diffusion distance of Li⁺ for high rate capacities. The inner bimodal porous Si possesses an open bicontinuous network structure that can provide the enough empty space and robust backbone to relax the volume variation of composite and guarantee the sufficient electrode-electrolyte contact area. As a result, the optimized nanoporous Si@TiO₂ composite delivers the reversible capacity of 1338.1 and 1174.4 mA h g^-1 at the current densities of 200 and 1000 mA g^-1 after continuous tests for 120 and 100 cycles, respectively. With the advantages of easy preparation, unique architecture, and high lithium storage performances, the porous core-shelled Si@TiO₂ composites demonstrate the promising application potential as an anode material for LIBs.

Fabrication of double core–shell Si-based anode materials with nanostructure for lithium-ion battery

Yolk–shell structure is considered to be a well-designed structure of silicon-based anode. However, there is only one point (point-to-point contact) in the contact region between the silicon core and the shell in this structure, which severely limits the ion transport ability of the electrode. In order to solve this problem, it is important that the core and shell of the core–shell structure are closely linked (face-to-face contact), which ensures good ion diffusion ability. Herein, a double core–shell nanostructure (Si@C@SiO₂) was designed for the first time to improve the cycling performance of the electrode by utilising the unique advantages of the SiO₂ layer and the closely contacted carbon layer. The improved cycling performance was evidenced by comparing the cycling properties of similar yolk–shell structures (Si@void@SiO₂) with equal size of the intermediate shell. Based on the comparison and analysis of the experimental data, Si@C@SiO₂ had more stable cycling performance and exceeded that of Si@void@SiO₂ after the 276^th cycle. More interestingly, the electron/ion transport ability of electrode was further improved by combination of Si@C@SiO₂ with reduced graphene oxide (RGO). Clearly, at a current density of 500 mA g⁻¹, the reversible capacity was 753.8 mA h g⁻¹ after 500 cycles, which was 91% of the specific capacity of the first cycle at this current density.

Double core shell structure can not only improve the efficiency of lithium transport, but also effectively alleviate volume expansion.

Improved performances of lithium-ion batteries using intercalated a-Si–Ag thin film layers as electrodes

The laminated construction of an a-Si–Ag thin film electrode is demonstrated, which allows stabilization of the cycling performance of a silicon thin film layer in a lithium-ion battery. A silver thin film plays a determining role in the lithium insertion/extraction process and is incorporated between amorphous Si thin film layers (a-Si/Ag/a-Si), which results in not only high and stable capability, but also the best rate performance compared to that of other electrodes. For the electrode of a-Si/Ag/a-Si, a critical thickness of the silver layer (30 nm) is found; in this case, it exhibits the highest capacity retention of 70% after 200 cycles at a current density of 65.2 μA cm⁻² within the voltage range of 0.01–1.5 V. It is demonstrated that for the a-Si/Ag/a-Si (140/30/140 nm) electrode, enhanced capacity (∼59.1%) is derived from the buffer effect and excellent conductivity of silver layer. Silver interlayer may represent a universal platform for relieving stress in a silicon electrode. In addition, its excellent electrical conductivity will decrease the charge transfer resistance of Si electrode for lithium-ion batteries.

A novel silver interlayer is used to improve the electrochemical performance of the binder-free Si-based thin film anodes.

Facile fabrication of graphene-encapsulated Mn3O4 octahedra cross-linked with a silver network as a high-capacity anode material for lithium ion batteries

Mn₃O₄ octahedra with a bimodal conductive network of nanoporous Ag and graphene nanosheets are simply prepared for better Li storage as an advanced anode material.

Carbon Nanofiber/3D Nanoporous Silicon Hybrids as High Capacity Lithium Storage Materials

Carbon nanofiber (CNF)/3D nanoporous (3DNP) Si hybrid materials were prepared by chemical etching of melt-spun Si/Al-Cu-Fe alloy nanocomposites, followed by carbonization using a pitch. CNFs were successfully grown on the surface of 3DNP Si particles using residual Fe impurities after acidic etching, which acted as a catalyst for the growth of CNFs. The resulting CNF/3DNP Si hybrid materials showed an enhanced cycle performance up to 100 cycles compared to that of the pristine Si/Al-Cu-Fe alloy nanocomposite as well as that of bare 3DNP Si particles. These results indicate that CNFs and the carbon coating layer have a beneficial effect on the capacity retention characteristics of 3DNP Si particles by providing continuous electron-conduction pathways in the electrode during cycling. The approach presented here provides another way to improve the electrochemical performances of porous Si-based high capacity anode materials for lithium-ion batteries.

Integrating Si nanoscale building blocks into micro-sized materials to enable practical applications in lithium-ion batteries

This article highlights recent advances in micro-sized silicon anode materials composed of silicon nanoscale building blocks for lithium-ion batteries. These materials show great potential in practical applications since they combine good cycling stability, high rate performance, and high volumetric capacity. Different preparation methods are introduced and the features and performance of the resulting materials are discussed. Key take-away points are interspersed through the discussion, including comments on the roles of the nanoscale building blocks. Finally, we discuss current challenges and provide an outlook for future development of micro-sized silicon-based anode materials.

Well-constructed silicon-based materials as high-performance lithium-ion battery anodes

Silicon has been considered as one of the most promising anode material alternates for next-generation lithium-ion batteries, because of its high theoretical capacity, environmental friendliness, high safety, low cost, etc. Nevertheless, silicon-based anode materials (especially bulk silicon) suffer from severe capacity fading resulting from their low intrinsic electrical conductivity and great volume variation during lithiation/delithiation processes. To address this challenge, a few special constructions from nanostructures to anchored, flexible, sandwich, core-shell, porous and even integrated structures, have been well designed and fabricated to effectively improve the cycling performance of silicon-based anodes. In view of the fast development of silicon-based anode materials, we summarize their recent progress in structural design principles, preparation methods, morphological characteristics and electrochemical performance by highlighting the material structure. We also point out the associated problems and challenges faced by these anodes and introduce some feasible strategies to further boost their electrochemical performance. Furthermore, we give a few suggestions relating to the developing trends to better mature their practical applications in next-generation lithium-ion batteries.

Recent progress of silicon composites as anode materials for secondary batteries

This review mainly focuses on the latest research achievements of Si composites and their nanostructures as anode materials in lithium-ion batteries. The most recent applications of Si to sodium-ion and magnesium-ion batteries are also included.