Self-Templating Construction of 3D Hierarchical Macro-/Mesoporous Silicon from 0D Silica Nanoparticles

Monolithic Layered Silicon Composed of a Crystalline-Amorphous Network for Sustainable Lithium-Ion Battery Anodes

While nanostructural engineering holds promise for improving the stability of high-capacity silicon (Si) anodes in lithium-ion batteries (LIBs), challenges like complex synthesis and the high cost of nano-Si impede its commercial application. In this study, we present a local reduction technique to synthesize micron-scale monolithic layered Si (10-20 μm) with a high tap density of 0.9-1.0 g cm-3 from cost-effective montmorillonite, a natural layered silicate mineral. The created mesoporous structure within each layer, combined with the void spaces between interlayers, effectively mitigates both lateral and vertical expansion throughout repeated lithiation/delithiation cycles. Furthermore, the remaining SiO2 network fortifies the layered structure, preventing it from collapsing during cycling. Half-cell tests reveal a capacity retention of 92% with a reversible capacity of 1130 mAh g-1 over 500 cycles. Moreover, the pouch cell integrated with this Si anode (with a mass loading of 3.0 mg cm-2) and a commercial NCM811 cathode delivers a high energy density of 655 Wh kg-1 (based on the total mass of the cathode and anode) and maintains 82% capacity after 200 cycles. This work demonstrates a cost-efficient and scalable strategy to manufacture high-performance micron Si anodes for the ever-growing demand for high-energy LIBs.

Tailored Yolk-Shell Design to Silicon Microparticles via Scalable and Template-Free Synthesis for Superior Lithium Storage

Micrometer-sized Si particles are beneficial to practical lithium-ion batteries in regard to low cost and high volumetric energy density in comparison with nanostructured Si anodes. However, both the issues of electrical contact loss and overgrowth of solid electrolyte interface for microscale Si induced by colossal volume change still remain to be addressed. Herein, a scalable and template-free method is introduced to fabricate yolk-shell structured Si anode from commercially available Si microparticles. The void is created via a one-step alkali etching process with the remaining silicon core as the yolk, and a double-walled shell is formed from simultaneous in situ growth of the conformal native oxide layer and subsequent carbon coating. In this configuration, the well-defined void spaces allow the Si core to expand without compromising structural integrity, while the double-walled shell acts as a static capsule to confine silicon fragments despite likely particle fracture. Therefore, electrical connectivity is maintained on both the particle and electrode level during deep galvanostatic cycling, and the solid-electrolyte interface is stabilized on the shell surface. Owing to the benefits of tailored design, excellent cycling stability (capacity retention of 95% after 100 cycles) and high coulombic efficiency (99.5%) are realized in a practical full-cell demonstration.

Surfactant-Free Synthesis of Crystalline Mesoporous Metal Oxides by a Seeds/ NaCl-Mediated Growth Strategy

Transitional metal oxides (TMOs) with ultra-high specific surface areas (SSAs), large pore volume, and tailored exposed facets appeal to significant interests in heterogeneous catalysis. Nevertheless, synthesizing the metal oxides with all the above features is challenging. Herein, the so-called seeds/NaCl-mediated growth method is successfully developed based on a bottom-up route. First, the (Brunauer-Emmett-Teller) BET SSAs of TMOs prepared with this method are significantly higher, where the BET SSAs of CeO2 , SnO2 , Nb2 O5 , Fe3 O4 , Mn3 O4 , Mg(OH)2 , and ZrO2 reached 187, 275, 518, 212, 147, 186, and 332 m2  g-1 , respectively. Second, these TMOs exhibit unique mesoporous structures, generated mainly by the aggregation of rod-like or other aspherical primary nanoparticles. More importantly, no environmental-unfriendly organic surfactants or expensive metal alkoxides are involved in this method. Therefore, the entire synthesis protocol fully fitted the "green synthesis" definition, and the corresponding TMOs prepares displayed excellent catalytic performance.

Cu and Ni Co-Doped Porous Si Nanowire Networks as High-Performance Anode Materials for Lithium-Ion Batteries

Due to its extremely high theoretical mass specific capacity, silicon is considered to be the most promising anode material for lithium-ion batteries (LIBs). However, serious volume expansion and poor conductivity limit its commercial application. Herein, dealloying treatments of spray dryed Al-Si-Cu-Ni particles are performed to obtain a Cu/Ni co-doped Si-based anode material with a porous nanowire network structure. The porous structure enables the material to adapt to the volume changes in the cycle process. Moreover, the density functional theory (DFT) calculations show that the co-doping of Cu and Ni can improve the capture ability towards Li, which can accelerate the electron migration rate of the material. Based on the above advantages, the as-prepared material presents excellent electrochemical performance, delivering a reversible capacity of 1092.4 mAh g-1 after 100 cycles at 100 mA g-1. Even after 500 cycles, it still retains 818.7 mAh g-1 at 500 mA g-1. This study is expected to provide ideas for the preparation and optimization of Si-based anodes with good electrochemical performance.

Microspheres of Si@Carbon-CNTs composites with a stable 3D interpenetrating structure applied in high-performance lithium-ion battery

The huge volumetric expansion (>300 %) of Si that occurs during the charge-discharge process makes it to have poor cycling ability and weak stable structure. These factors are considered as critical obstacles to the further development of Si as anode for lithium-ion batteries (LIBs). Herein, novel 3D interpenetrating microspheres, i.e., Si@C-CNTs, which consist of silicon nanoparticles interpenetrated with carbon nanotubes (CNTs) and stuck with amorphous carbon (C) have been designed and prepared via a spray-drying assisted approach. As anode of LIBs, Si@C-CNTs microspheres can achieve high silicon loadings of around 86 % and a high initial coulomb efficiency of 80.8 %. The electrodes maintain a reversible specific capacity of 1585.9mAh/g at 500 mA g-1 after 200 cycles, and deliver an excellent rate capability of 756.4 mAh/g at 5 A g-1. The outstanding performance of Si@C-CNTs can be due to their 3D interpenetrating structure and the synergy effect between the CNTs network and amorphous carbon therein. They synergistically act as conductive matrices which significantly improve the conductivity of the composite; they also act binders and reinforcing skeleton which help the composite spheres to have stable structure. Especially, the latter (reinforcing skeleton) alleviates the volumetric effect induced by the expansion and shrinkage of silicon particles during lithiation. The unique architecture provides an ideal model that can be used to design Si-based composite anode for advanced LIBs.

High-Temperature Magnesiothermic Reduction Enables HF-Free Synthesis of Porous Silicon with Enhanced Performance as Lithium-Ion Battery Anode

Porous silicon-based anode materials have gained much interest because the porous structure can effectively accommodate volume changes and release mechanical stress, leading to improved cycling performance. Magnesiothermic reduction has emerged as an effective way to convert silica into porous silicon with a good electrochemical performance. However, corrosive HF etching is normally a mandatory step to improve the electrochemical performance of the as-synthesized silicon, which significantly increases the safety risk. This has become one of the major issues that impedes practical application of the magnesiothermic reduction synthesis of the porous silicon anode. Here, a facile HF-free method is reported to synthesize macro-/mesoporous silicon with good cyclic and rate performance by simply increasing the reduction temperature from 700 °C to 800 °C and 900 °C. The mechanism for the structure change resulting from the increased temperature is elaborated. A finite element simulation indicated that the 3D continuous structure formed by the magnesiothermic reduction at 800 °C and 900 °C could undertake the mechanical stress effectively and was responsible for an improved cyclic stability compared to the silicon synthesized at 700 °C.

A Low-Cost SiO x /C@Graphite Composite Derived from Oat Husk as an Advanced Anode for High-Performance Lithium-Ion Batteries

Silicon monoxide (SiO _x ), as a promising anode for the next-generation high-power lithium-ion batteries, has some advantages such as higher lithium storage capacity (∼2400 mAh g^-1), suitable working potential, and smaller volume variations during cycling compared with pure silicon. However, its disadvantages such as its inherent low conductivity and high cost impede its extensive applications. Herein, we have developed a low-cost and high-capacity SiO _x /C@graphite (SCG) composite derived from oat husks by a simple argon/hydrogen reduction method. For further practical application, we also investigated the electrochemical performances of SiO _x mixed with different ratios of graphite. As an advanced anode for lithium-ion batteries, the SCG-1 composite exhibits an excellent electrochemical performance in terms of lithium storage capacity (809.5 mAh g^-1 at 0.5 A g^-1 even after the 250th cycle) and high rate capability (479.7 mAh g^-1 at 1 A g^-1 after the 200th cycle). This work may pave the way for developing a low-cost silicon-based anode derived from biomass with a large reversible capacity and long cycle life in lithium-ion batteries.

Advances of Synthesis Methods for Porous Silicon-Based Anode Materials

Silicon (Si)-based anode materials have been the promising candidates to replace commercial graphite, however, there are challenges in the practical applications of Si-based anode materials, including large volume expansion during Li⁺ insertion/deinsertion and low intrinsic conductivity. To address these problems existed for applications, nanostructured silicon materials, especially Si-based materials with three-dimensional (3D) porous structures have received extensive attention due to their unique advantages in accommodating volume expansion, transportation of lithium-ions, and convenient processing. In this review, we mainly summarize different synthesis methods of porous Si-based materials, including template-etching methods and self-assembly methods. Analysis of the strengths and shortages of the different methods is also provided. The morphology evolution and electrochemical effects of the porous structures on Si-based anodes of different methods are highlighted.

Ultrafine SnO2/Sn Nanoparticles Embedded into an In Situ Generated Meso-/Macroporous Carbon Matrix with a Tunable Pore Size

Ultrafine SnO₂/Sn nanoparticles encapsulated into an adjustable meso-/macroporous carbon matrix have been successfully fabricated by the in situ SiO_x sacrificial strategy. The control over the void space in the carbon matrix effectively improves the accessibility of the SnO₂/Sn toward an electrolyte solution. More importantly, the void space also provides an efficient means to accommodate the mechanical stress caused by the volume change of the SnO₂/Sn over cycles. As a result, the enhanced electrolyte accessibility and suppressed mechanical stress improve the electrochemical performance regarding reversible capacity, cyclic stability, and rate capability. A reversible capacity of 1105 mAh g^-1 is still retained after 290 cycles at 200 mAg^-1, and the capacity still can keep at 107 mAh g^-1 at a high current density of 10 A g^-1.

Encasing Prelithiated Silicon Species in the Graphite Scaffold: An Enabling Anode Design for the Highly Reversible, Energy-Dense Cell Model

Si anodes suffer from poor cycling efficiency because of the pulverization induced by volume expansion, lithium trapping in Li-Si alloys, and unfavorable interfacial side reactions with the electrolyte; the comprehensive consideration of the Si anode design is required for their practical deployment. In this article, we develop a cabbage-inspired graphite scaffold to accommodate the volume expansion of silicon particles in interplanar spacing. With further interfacial modification and prelithiation processing, the Si@G/C anode with an areal capacity of 4.4 mA h cm^-2 delivers highly reversible cycling at 0.5 C (Coulombic efficiency of 99.9%) and a mitigated volume expansion of 23%. Furthermore, we scale up the synthetic strategy by producing 10 kg of the Si@G/C composite in the pilot line and pair this anode with a LiNi_0.8Co_0.1Mn_0.1O₂ cathode in a 1 A h pouch-type cell. The full-cell prototype realizes a robust cyclability over 500 cycles (88% capacity retention) and an energy density of 301.3 W h kg^-1 at 0.5 C. Considering the scalable fabrication protocol, holistic electrode formulation design, and harmony integration of key metrics evaluated both in half-cell and full-cell tests, the reversible cycling of the prelithiated silicon species in the graphite scaffold of the composite could enable feasible use of the composite anode in high-energy density lithium batteries.

Rational Design and Mechanical Understanding of Three-Dimensional Macro-/Mesoporous Silicon Lithium-Ion Battery Anodes with a Tunable Pore Size and Wall Thickness

Silicon is regarded as one of the most promising next generation lithium-ion battery anodes due to its exceptional theoretical capacity, appropriate voltage profile, and vast abundance. Nevertheless, huge volume expansion and drastic stress generated upon lithiation cause poor cyclic stability. It has been one of the central issues to improve cyclic performance of silicon-based lithium-ion battery anodes. Constructing hierarchical macro-/mesoporous silicon with a tunable pore size and wall thickness is developed to tackle this issue. Rational structure design, controllable synthesis, and theoretical mechanical simulation are combined together to reveal fundamental mechanisms responsible for an improved cyclic performance. A self-templating strategy is applied using Stöber silica particles as a templating agent and precursor coupled with a magnesiothermic reduction process. Systematic variation of the magnesiothermic reduction time allows good control over the structures of the porous silicon. Finite element mechanical simulations on the porous silicon show that an increased pore size and a reduced wall thickness generate less mechanical stress in average along with an extended lithiation state. Besides the mechanical stress, the evolution of strain and displacement of the porous silicon is also elaborated with the finite element simulation.

Drug Delivery Applications of Three-Dimensional Printed (3DP) Mesoporous Scaffolds

Mesoporous materials are structures characterized by a well-ordered large pore system with uniform porous dimensions ranging between 2 and 50 nm. Typical samples are zeolite, carbon molecular sieves, porous metal oxides, organic and inorganic porous hybrid and pillared materials, silica clathrate and clathrate hydrates compounds. Improvement in biochemistry and materials science led to the design and implementation of different types of porous materials ranging from rigid to soft two-dimensional (2D) and three-dimensional (3D) skeletons. The present review focuses on the use of three-dimensional printed (3DP) mesoporous scaffolds suitable for a wide range of drug delivery applications, due to their intrinsic high surface area and high pore volume. In the first part, the importance of the porosity of materials employed for drug delivery application was discussed focusing on mesoporous materials. At the end of the introduction, hard and soft templating synthesis for the realization of ordered 2D/3D mesostructured porous materials were described. In the second part, 3DP fabrication techniques, including fused deposition modelling, material jetting as inkjet printing, electron beam melting, selective laser sintering, stereolithography and digital light processing, electrospinning, and two-photon polymerization were described. In the last section, through recent bibliographic research, a wide number of 3D printed mesoporous materials, for in vitro and in vivo drug delivery applications, most of which relate to bone cells and tissues, were presented and summarized in a table in which all the technical and bibliographical details were reported. This review highlights, to a very cross-sectional audience, how the interdisciplinarity of certain branches of knowledge, as those of materials science and nano-microfabrication are, represent a growing valuable aid in the advanced forum for the science and technology of pharmaceutics and biopharmaceutics.

Facile fabrication of sponge-like porous micropillar arrays via an electrochemical process

A large variety of synthetic methods have been developed for hierarchically porous materials by which the performance of a wide range of applications can be dramatically enhanced. Herein, hierarchically porous micropillar arrays are demonstrated by employing electrochemical etching to silicon micropillars. The approach relies on the steering of current flow through the three-dimensional silicon-electrolyte interface to enable nanopores to grow on the entire surface of the micropillars, simultaneously. The pores grow perpendicular to the surface of the micropillars, whereas the pore diameter and porosity vary depending on the locations of the surfaces. The finite element analysis shows that the spatial variation of the pore diameter and porosity is determined by the distribution of current density. Further, the thickness of the porous layer can be tuned by etching time so that sponge-like porous structures are conveniently obtained by regulating the etching time. In addition to the effect of current density flowing through the etched surfaces, the growth of pores also depends on the crystal orientations of the etched surfaces. The etching results on square micropillar arrays and microgroove arrays show that the growth direction and rate of nanopores inside the microstructure also depend on the exposed crystal planes. The facile characteristics of the fabrication method can serve as an effective route for a wide range of applications of porous materials with enhanced capabilities.

Ultrastable Silicon Anode by Three-Dimensional Nanoarchitecture Design

State-of-the-art carbonaceous anodes are approaching their achievable performance limit in Li-ion batteries (LIBs). Silicon has been recognized as one of the most promising anodes for next-generation LIBs because of its advantageous specific capacity and secure working potential. However, the practical implementation of silicon anodes needs to overcome the challenges of substantial volume changes, intrinsic low conductivity, and unstable solid electrolyte interphase (SEI) films. Here, we report an inventive design of a sandwich N-doped graphene@Si@hybrid silicate anode with bicontinuous porous nanoarchitecture, which is expected to simultaneously conquer all these critical issues. In the ingeniously designed hybrid Si anode, the nanoporous N-doped graphene acts as a flexible and conductive support and the amorphous hybrid silicate coating enhances the robustness and suppleness of the electrode and facilitates the formation of stable SEI films. This binder-free and stackable hybrid electrode achieves excellent rate capability and cycling performance (817 mAh/g at 5 C for 10 000 cycles). Paired with LiFePO₄ cathodes, more than 100 stable cycles can be readily realized in full batteries.

Ti3C2Tx MXene Nanosheets as a Robust and Conductive Tight on Si Anodes Significantly Enhance Electrochemical Lithium Storage Performance

Exploring Si-based anode materials with high electrical conductivity and electrode stability is crucial for high-performance lithium-ion batteries (LIBs). Herein, we propose the fabrication of a Si-based composite where Si porous nanospheres (Si p-NSs) are tightly wrapped by Ti₃C₂T_x (T_x stands for the surface groups such as -OH, -F) MXene nanosheets (TNSs) through an interfacial assembly strategy. The TNSs as a conductive and robust tight of the Si p-NSs can effectively improve electron transport and electrode stability, as revealed by substantial characterizations and mechanical simulations. Moreover, the TNSs with rich surface groups enable strong interfacial interactions with the Si p-NS component and a pseudocapacitive behavior, beneficial for fast and stable lithium storage. Consequently, the Si p-NS@TNSs electrode with a high Si content of 85.6% exhibits significantly enhanced battery performance compared with the Si p-NSs electrode such as high reversible capacity (1154 mAh g^-1 at 0.2 A g^-1), long cycling stability (up to 2000 cycles with a 0.026% capacity decay rate per cycle), and excellent rate performances. Notably, the Si p-NS@TNSs electrode-based LIB full cell delivers a high energy uptake of 405 Wh kg^-1, many-times higher than that of the Si p-NSs full cell. This work offers a strategy to develop advanced Si-based anode materials with desirable properties for high-performance LIBs.

A carbon network strategy to synthesize silicon–carbon anodes toward regulated morphologies during molten salt reduction

In this work, a carbon network strategy was proposed to prepare Si/SiO_x/C anodes with regulated morphologies during molten salt reduction.

Electrochemical Sensor of Double-Thiol Linked PProDOT@Si Composite for Simultaneous Detection of Cd(II), Pb(II), and Hg(II)

Heavy metal ions in water, cosmetics, and arable land have become a world-wide issue as they cause a variety of diseases and even death to humans and animals when a certain level is exceeded. Therefore, it is necessary to development a new kind of sensor material for the determination of heavy metal ions. In this paper, we present an electrochemical sensor based on composite material (thiol(-SH) grafted poly(3,4-proplenedioxythiophene) (PProDOT(MeSH)₂)/ porous silicon spheres (Si) composite, denoted as PProDOT(MeSH)₂@Si) from the incorporation of thiol(-SH) grafted poly(3,4-proplenedioxythiophene) (PProDOT(MeSH)₂) with porous silicon spheres (Si) for the electrochemical detection of heavy metal ions (Cd(II), Pb(II), and Hg(II)). The PProDOT(MeSH)₂@Si composite was synthesized via a chemical oxidative polymerization method. The structure and morphology of PProDOT(MeSH)₂@Si composite were characterized by Fourier transform infrared (FT-IR), Ultraviolet-visible spectroscopy (UV-Vis), X-ray diffraction (XRD), scanning electron microscope (SEM), Transmission electron microscope (TEM), and Brunauer-Emmett-Teller (BET). Furthermore, the electrochemical performance of PProDOT(MeSH)₂@Si was evaluated by detecting of Cd(II), Pb(II), and Hg(II) ions using the differential pulse voltammetry (DPV) method. The relationship between structural properties and the electrochemical performance was systematically studied. The results showed that the entry of two thiol-based chains to the monomer unit resulted in an increase in electrochemical sensitivity in PProDOT(MeSH)_2, which was related to the interaction between thiol group(-SH) and heavy metal ions. And, the combination of PProDOT(MeSH)₂ with Si could improve the electrocatalytic efficiency of the electrode material. The PProDOT(MeSH)₂@Si/GCE exhibited high selectivity and sensitivity in the rage of 0.04 to 2.8, 0.024 to 2.8, and 0.16 to 3.2 μM with the detection limit of 0.00575, 0.0027, and 0.0017 µM toward Cd(II), Pb(II), and Hg(II), respectively. The interference studies demonstrated that the PProDOT(MeSH)₂@Si/GCE possessed a low mutual interference and high selectivity for simultaneous detection of Cd(II), Pb(II), and Hg(II) ions.

Necklace-like Si@C nanofibers as robust anode materials for high performance lithium ion batteries

Silicon is believed to be a promising anode material for lithium ion batteries because of its highest theoretical capacity and low discharge potential. However, severe pulverization and capacity fading caused by huge volume change during cycling limits its practical application. In this work, necklace-like N-doped carbon wrapped mesoporous Si nanofibers (NL-Si@C) network has been synthesized via electrospinning method followed by magnesiothermic reduction reaction process to suppress these issues. The mesoporous Si nanospheres are wrapped with N-doped carbon shells network to form yolk-shell structure. Interestingly, the distance of adjacent Si@C nanospheres can be controllably adjusted by different addition amounts of SiO₂ nanospheres. When used as an anode material for lithium ion batteries, the NL-Si@C-0.5 exhibits best cycling stability and rate capability. The excellent electrochemical performances can be ascribed to the necklace-like network structure and N-doped carbon layers, which can ensure fast ions and electrons transportation, facilitate the electrolyte penetration and provide finite voids to allow large volume expansion of inner Si nanoparticles. Moreover, the protective carbon layers are also beneficial to the formation of stable solid electrolyte interface film.

In situ synthesis of porous Si dispersed in carbon nanotube intertwined expanded graphite for high-energy lithium-ion batteries

Silicon (Si) is perceived as one of the most promising anode materials for next-generation lithium-ion batteries (LIBs). For its practical application, superior electrochemical properties, low cost and scalable production are highly required. Herein, we synthesize a carbon nanotube intertwined expanded graphite/porous Si (CNT/EG/pSi) composite through the in situ magnesiothermic reduction method, where porous Si nanoparticles (NPs) are dispersed in the interspaces constructed by EG sheets, with CNTs intertwined throughout the composite, connecting Si NPs and EG sheets. Mesopores within Si NPs can not only shorten the electron and Li+ ion transport distance, but also play an important role in accommodating the huge volume change. EG and CNTs construct a three-dimensional conductive network, improving the electronic conductivity of the composite. Moreover, EG sheets release the excessive local stress over cycles, and CNTs can randomly build new electronic pathways as the structure changes, alleviating the degeneration of the conductive network. Consequently, the CNT/EG/pSi composite exhibits enhanced cycling and rate performances when used as the anode material, delivering reversible specific capacities of 2618 mA h g-1 at 0.2 A g-1 and 1390 mA h g-1 at 4 A g-1, maintaining a capacity of 2152 mA h g-1 after 100 cycles at 0.4 A g-1, with a capacity retention of 84%. This hierarchically structured anode material has a facile and low-cost synthetic route, as well as excellent electrochemical performances, making it attractive for high-performance LIB applications.

Scalable Synthesis of Biodegradable Black Mesoporous Silicon Nanoparticles for Highly Efficient Photothermal Therapy

Porous silicon (PSi) has attracted wide interest as a potential material for various fields of nanomedicine. However, until now, the application of PSi in photothermal therapy has not been successful due to its low photothermal conversion efficiency. In the present study, biodegradable black PSi (BPSi) nanoparticles were designed and prepared via a high-yield and simple reaction. The PSi nanoparticles possessed a low band gap of 1.34 eV, a high extinction coefficient of 13.2 L/g/cm at 808 nm, a high photothermal conversion efficiency of 33.6%, good photostability, and a large surface area. The nanoparticles had not only excellent photothermal properties surpassing most of the present inorganic photothermal conversion agents (PCAs) but they also displayed good biodegradability, a common problem encountered with the inorganic PCAs. The functionality of the BPSi nanoparticles in photothermal therapy was verified in tumor-bearing mice in vivo. These results showed clearly that the photothermal treatment was highly efficient to inhibit tumor growth. The designed PCA material of BPSi is robust, easy to prepare, biocompatible, and therapeutically extremely efficient and it can be integrated with several other functionalities on the basis of simple silicon chemistry.

Hierarchical Carbon-Coated Ball-Milled Silicon: Synthesis and Applications in Free-Standing Electrodes and High-Voltage Full Lithium-Ion Batteries

Lithium-ion batteries have been regarded as one of the most promising energy storage devices, and development of low-cost batteries with high energy density is highly desired so that the cost per watt-hour ($/Wh) can be minimized. In this work, we report using ball-milled low-cost silicon (Si) as the starting material and subsequent carbon coating to produce low-cost hierarchical carbon-coated (HCC) Si. The obtained particles prepared from different Si sources all show excellent cycling performance of over 1000 mAh/g after 1000 cycles. Interestingly, we observed in situ formation of porous Si, and it is well confined in the carbon shell based on postcycling characterization of the hierarchical carbon-coated metallurgical Si (HCC-M-Si) particles. In addition, lightweight and free-standing electrodes consisting of the HCC-M-Si particles and carbon nanofibers were fabricated, which achieved 1015 mAh/g after 100 cycles based on the total mass of the electrodes. Compared with conventional electrodes, the lightweight and free-standing electrodes significantly improve the energy density by 745%. Furthermore, LiCoO₂ and LiNi_0.5Mn_1.5O₄ cathodes were used to pair up with the HCC-M-Si anode to fabricate full cells. With LiNi_0.5Mn_1.5O₄ as cathode, an energy density up to 547 Wh/kg was achieved by the high-voltage full cell. After 100 cycles, the full cell with a LiNi_0.5Mn_1.5O₄ cathode delivers 46% more energy density than that of the full cell with a LiCoO₂ cathode. The systematic investigation on low-cost Si anodes together with their applications in lightweight free-standing electrodes and high-voltage full cells will shed light on the development of high-energy Si-based lithium-ion batteries for real applications.

Surface Modification of Silicon Nanoparticles by an "Ink" Layer for Advanced Lithium Ion Batteries

Owing to its high specific capacity, silicon is considered as a promising anode material for lithium ion batteries (LIBs). However, the synthesis strategies for previous silicon-based anode materials with a delicate hierarchical structure are complicated or hazardous. Here, Prussian blue analogues (PBAs), widely used in ink, are deposited on the silicon nanoparticle surface (PBAs@Si-450) to modify silicon nanoparticles with transition metal atoms and a N-doped carbon layer. A facile and green synthesis procedure of PBAs@Si-450 nanocomposites was carried out in a coprecipitation process, combined with a thermal treatment process at 450 °C. As-prepared PBAs@Si-450 delivers a reversible charge capacity of 725.02 mAh g^-1 at 0.42 A g^-1 after 200 cycles. Moreover, this PBAs@Si-450 composite exhibits an exceptional rate performance of ∼1203 and 263 mAh g^-1 at current densities of 0.42 and 14 A g^-1, respectively, and fully recovered to 1136 mAh g^-1 with the current density returning to 0.42 A g^-1. Such a novel architecture of PBAs@Si-450 via a facile fabrication process represents a promising candidate with a high-performance silicon-based anode for LIBs.

Green, Scalable, and Controllable Fabrication of Nanoporous Silicon from Commercial Alloy Precursors for High-Energy Lithium-Ion Batteries

Silicon is considered as one of the most favorable anode materials for next-generation lithium-ion batteries. Nanoporous silicon is synthesized via a green, facile, and controllable vacuum distillation method from the commercial Mg₂Si alloy. Nanoporous silicon is formed by the evaporation of low boiling point Mg. In this method, the magnesium metal from the Mg₂Si alloy can be recycled. The pore sizes of nanoporous silicon can be secured by adjusting the distillated temperature and time. The optimized nanoporous silicon (800 °C, 0.5 h) delivers a discharge capacity of 2034 mA h g^-1 at 200 mA g^-1 for 100 cycles, a cycling stability with more than 1180 mA h g^-1 even after 400 cycles at 1000 mA g^-1, and a rate capability of 855 mA h g^-1 at 5000 mA g^-1. The electrochemical properties might be ascribed to its porous structure, which may accommodate large volume change during the cycling process. These results suggest that the green, scalable, and controllable approach may offer a pathway for the commercialization of high-performance Si anodes. This method may also be extended to construct other nanoporous materials.

Graphene Oxides Used as a New "Dual Role" Binder for Stabilizing Silicon Nanoparticles in Lithium-Ion Battery

For the first time, we report that graphene oxide (GO) can be used as a new "dual-role" binder for Si nanoparticles (SiNPs)-based lithium-ion batteries (LIBs). GO not only provides a graphene-like porous 3D framework for accommodating the volume changes of SiNPs during charging/discharging cycles, but also acts as a polymer-like binder that forms strong chemical bonds with SiNPs through its Si-OH functional groups to trap and stabilize SiNPs inside the electrode. Leveraging this unique dual-role of GO binder, we fabricated GO/SiNPs electrodes with remarkably improved performances as compared to using the conventional polyvinylidene fluoride (PVDF) binder. Specifically, the GO/SiNPs electrode showed a specific capacity of 2400 mA h g^-1 at the 50th cycle and 2000 mA h g^-1 at the 100th cycle, whereas the SiNPs/PVDF electrode only showed 456 mAh g^-1 at the 50th cycle and 100 mAh g^-1 at 100th cycle. Moreover, the GO/SiNPs film maintained its structural integrity and formed a stable solid-electrolyte interphase (SEI) film after 100 cycles. These results, combined with the well-established facile synthesis of GO, indicate that GO can be an excellent binder for developing high performance Si-based LIBs.

Scalable 2D Mesoporous Silicon Nanosheets for High-Performance Lithium-Ion Battery Anode

Constructing unique mesoporous 2D Si nanostructures to shorten the lithium-ion diffusion pathway, facilitate interfacial charge transfer, and enlarge the electrode-electrolyte interface offers exciting opportunities in future high-performance lithium-ion batteries. However, simultaneous realization of 2D and mesoporous structures for Si material is quite difficult due to its non-van der Waals structure. Here, the coexistence of both mesoporous and 2D ultrathin nanosheets in the Si anodes and considerably high surface area (381.6 m² g^-1 ) are successfully achieved by a scalable and cost-efficient method. After being encapsulated with the homogeneous carbon layer, the Si/C nanocomposite anodes achieve outstanding reversible capacity, high cycle stability, and excellent rate capability. In particular, the reversible capacity reaches 1072.2 mA h g^-1 at 4 A g^-1 even after 500 cycles. The obvious enhancements can be attributed to the synergistic effect between the unique 2D mesoporous nanostructure and carbon capsulation. Furthermore, full-cell evaluations indicate that the unique Si/C nanostructures have a great potential in the next-generation lithium-ion battery. These findings not only greatly improve the electrochemical performances of Si anode, but also shine some light on designing the unique nanomaterials for various energy devices.

Si nanocrystal solution with stability for one year

Colloidal silicon nanocrystals (SiNCs) are a promising material for next-generation nanostructured devices. High-stability SiNC solutions are required for practical use as well as studies on the properties of SiNC. Here, we show a solution of SiNCs that was stable for one year without aggregation. The stable solution was synthesized by a facile process, i.e., pulsed laser ablation of a Si wafer in isopropyl alcohol (IPA). The long-term stability was due to a large ζ-potential of −50 mV from a SiNC passivation layer composed of oxygen, hydrogen, and alkane groups, according to the results of eight experiments and theoretical calculations. This passivation layer also resulted in good performance as an additive for a conductive polymer film. Namely, a 5-fold enhancement in carrier density was established by the addition of SiNCs into an organic conductive polymer, poly(3-dodecylthiophene), which is useful for solar cells. Furthermore, it was found that fresh (<1 day) and aged (4 months) SiNCs give the same enhancement. The long-term stability was attributed to a great repulsive energy in IPA, whose value was quantified as a function the distance between SiNCs.

A stable nanocrystal for one year without aggregation in a liquid is synthesized by one-step, one-pot, and one-hour process.

Large interlayer spacing vanadium oxide nanotubes as cathodes for high performance sodium ion batteries

Sodium ion batteries (SIBs), as a potential alternative to Li-ion batteries (LIBs), have attracted great attention from researchers.

Alloy-Based Anode Materials toward Advanced Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are considered as promising alternatives to lithium-ion batteries owing to the abundant sodium resources. However, the limited energy density, moderate cycling life, and immature manufacture technology of SIBs are the major challenges hindering their practical application. Recently, numerous efforts are devoted to developing novel electrode materials with high specific capacities and long durability. In comparison with carbonaceous materials (e.g., hard carbon), partial Group IVA and VA elements, such as Sn, Sb, and P, possess high theoretical specific capacities for sodium storage based on the alloying reaction mechanism, demonstrating great potential for high-energy SIBs. In this review, the recent research progress of alloy-type anodes and their compounds for sodium storage is summarized. Specific efforts to enhance the electrochemical performance of the alloy-based anode materials are discussed, and the challenges and perspectives regarding these anode materials are proposed.

Rational Design of Three-Dimensional Graphene Encapsulated with Hollow FeP@Carbon Nanocomposite as Outstanding Anode Material for Lithium Ion and Sodium Ion Batteries

Transition metal phosphides have been extensively investigated owing to their high theoretical capacities and relatively low intercalation potentials vs Li/Li⁺, but their practical applications have been hindered by low electrical conductivity and dramatic volume variation during cycling. In this work, an interesting strategy for the rational design of graphene (GR) encapsulated with a hollow FeP@carbon nanocomposite (H-FeP@C@GR) via a combination of a hydrothermal route, a carbon-coating process, phosphidation treatment, and carbothermic reaction is reported. The hollow FeP (H-FeP) nanospheres shelled with thin carbon layers are wonderfully incorporated into the GR matrix, interconnecting to form a three-dimensional (3D) hierarchical architecture. Such a design offers distinct advantages for FeP-based anode materials for both lithium ion batteries (LIBs) and sodium ion batteries (SIBs). For example, the 3D omnibearing conductive networks from the GR skeleton and outer coating carbon can provide an open freeway for electron/ion transport, promoting the electrode reaction kinetics. In addition, the wrapping of an H-FeP nanosphere in a thin carbon layer enables the formation of a solid electrolyte interphase (SEI) on the carbon layer surface instead of on the individual H-FeP surface, preventing the continual re-forming of the SEI. When used as anode materials for LIBs and SIBs, H-FeP@C@GR exhibited excellent electrochemistry performances.

Facile Pyrolyzed N-Doped Binder Network for Stable Si Anodes

Although nanoengineering provides improved stability of Si-based nanostructures, a facile and efficacious method to directly use raw Si practices is still absent. Herein, we report a pyrolyzed N-doped binder network to improve the cycling stability of raw Si particles. Such an N-doped binder network is formed at a conformal pyrolysis condition of the electrode binder using polyacrylonitrile and provides a tight encapsulation of the Si particles with significantly improved cycling stability. In contrast to the single Si particles that pulverize and lose the total capacity at the 20th cycle, the discharge capacity could be retained ∼1700 mA h g^-1 at the 100th cycle for the Si particles imbedded in the pyrolyzed N-doped binder network. Our results demonstrate that such a facile remedy could significantly improve the cycling stability of raw Si particles for high-energy-density lithium-ion batteries.

Facile Synthesis of Si@SiC Composite as an Anode Material for Lithium-Ion Batteries

Here, we propose a simple method for direct synthesis of a Si@SiC composite derived from a SiO₂@C precursor via a Mg thermal reduction method as an anode material for Li-ion batteries. Owing to the extremely high exothermic reaction between SiO₂ and Mg, along with the presence of carbon, SiC can be spontaneously produced with the formation of Si. The synthesized Si@SiC was composed of well-mixed SiC and Si nanocrystallites. The SiC content of the Si@SiC was adjusted by tuning the carbon content of the precursor. Among the resultant Si@SiC materials, the Si@SiC-0.5 sample, which was produced from a precursor containing 4.37 wt % of carbon, exhibits excellent electrochemical characteristics, such as a high first discharge capacity of 1642 mAh g^-1 and 53.9% capacity retention following 200 cycles at a rate of 0.1C. Even at a high rate of 10C, a high reversible capacity of 454 mAh g^-1 was obtained. Surprisingly, at a fixed discharge rate of C/20, the Si@SiC-0.5 electrode delivered a high capacity of 989 mAh g^-1 at a charge rate of 20C. In addition, a full cell fabricated by coupling a lithiated Si@SiC-0.5 anode and a LiCoO₂ cathode exhibits excellent cyclability over 50 cycles. This outstanding electrochemical performance of Si@SiC-0.5 is attributed to the SiC phase, which acts as a buffer layer that stabilizes the nanostructure of the Si active phase and enhances the electrical conductivity of the electrode.

Room-temperature fabrication of a three-dimensional porous silicon framework inspired by a polymer foaming process

A 3D porous silicon framework is fabricated directly based on the whole wafer, which is capable of accommodating nanowires in micron-sized pores.

Simple synthesis of SiGe@C porous microparticles as high-rate anode materials for lithium-ion batteries

We synthesize the PoSiGe@C via the decomposition of Mg₂Si/Mg₂Ge composites, acid pickling and subsequent carbon coating processes, which show excellent cycling and rate performance as anode materials for lithium-ion batteries.