Large-Scale Self-Catalyzed Spongelike Silicon Nano-Network-Based 3D Anodes for High-Capacity Lithium-Ion Batteries

Key developments in magnesiothermic reduction of silica: insights into reactivity and future prospects

Porous Si (p-Si) nanomaterials are an exciting class of inexpensive and abundant materials within the field of energy storage. Specifically, p-Si has been explored in battery anodes to improve charge storage capacity, to generate clean fuels through photocatalysis and photoelectrochemical processes, for the stoichiometric conversion of CO2 to value added chemicals, and as a chemical H2 storage material. p-Si can be made from synthetic, natural, and waste SiO2 sources through a facile and inexpensive method called magnesiothermic reduction (MgTR). This yields a material with tunable properties and excellent energy storage capabilities. In order to tune the physical properties that affect performance metrics of p-Si, a deeper understanding of the mechanism of the MgTR and factors affecting it is required. In this perspective, we review the key developments in MgTR and discuss the thermal management strategies used to control the properties of p-Si. Additionally, we explore future research directions and approaches to bridge the gap between laboratory-scale experiments and industrial applications.

Unlocking the secrets of porous silicon formation: insights into magnesiothermic reduction mechanism using in situ powder X-ray diffraction studies

The magnesiothermic reduction of SiO2 is an important reaction as it is a bulk method that produces porous Si for a wide range of applications directly from SiO2. While its main advantage is potential tunability, the reaction behavior and final product properties are heavily dependent on many parameters including feedstock type. However, a complete understanding of the reaction pathway has not yet been achieved. Here, using in situ X-ray diffraction analysis, for the first time, various pathways through which the magnesiothermic reduction reaction proceeds were mapped. Further, the key parameters and conditions that determine which pathways are favored were determined. It was discovered that the reaction onset temperatures can be as low as 348 ± 7 °C, which is significantly lower when compared to previously reported values. The onset temperature is dependent on the size of Mg particles used in the reaction. Further, Mg2Si was identified as a key intermediate rather than a reaction byproduct during the reduction process. Its rate of consumption is determined by the reaction temperature which needs to be >561 °C. These findings can enable process and product optimization of the magnesiothermic reduction process to manufacture and tune porous Si for a range of applications.

Three-Dimensional Nickel Foam-Based Lithiophilic LPP-Ni3S2@Ni Current Collector for Dendrite-Free Lithium Anode

Lithium metal has been treated as one of the most promising anode materials for next-generation rechargeable batteries due to its extremely high theoretical capacity. However, its practical application is hindered by inhomogeneous lithium deposition and uncontrolled dendrite growth. In this work, we prepared a three-dimensional nickel foam (NF)-based current collector with a lithiophilic interface layer through facile hydrothermal and coating methods. The lithiophilic Ni3S2 array synthesized via a hydrothermal method has been demonstrated to facilitate the nucleation of Li+. Moreover, it has been observed that the outer coating comprising LPP effectively enhances the inward diffusion of Li+. Additionally, this interface layer can serve as an isolating barrier between the electrodes and the electrolyte. The prepared LPP-Ni3S2@Ni shows significant reversibility both in symmetric cells (1200 h, 1 mA cm-2) and half-cells (CE: 99.60%, 500 cycles, 1 mA cm-2) with low interfacial resistance (35 Ω). Full cells with LiFePO4 as a cathode also exhibit promising electrochemical performance with over 76.78% capacity retention over 200 cycles at 1 C.

The "Bloodless" Blood Test: Intradermal Prick Nanoelectronics for the Blood Extraction-Free Multiplex Detection of Protein Biomarkers

Protein biomarkers' detection is of utmost importance for preventive medicine and early detection of illnesses. Today, their detection relies entirely on clinical tests consisting of painful, invasive extraction of large volumes of venous blood; time-consuming postextraction sample manipulation procedures; and mostly label-based complex detection approaches. Here, we report on a point-of-care (POC) diagnosis paradigm based on the application of intradermal finger prick-based electronic nanosensors arrays for protein biomarkers' direct detection and quantification down to the sub-pM range, without the need for blood extraction and sample manipulation steps. The nanobioelectronic array performs biomarker sensing by a rapid intradermal prick-based sampling of proteins biomarkers directly from the capillary blood pool accumulating at the site of the microneedle puncture, requiring only 2 min and less than one microliter of a blood sample for a complete analysis. A 1 mm long microneedle element was optimal in allowing for pain-free dermal sampling with a 100% success rate of reaching and rupturing dermis capillaries. Current common micromachining processes and top-down fabrication techniques allow the nanobioelectronic sensor arrays to provide accurate and reliable clinical diagnostic results using multiple sensing elements in each microneedle and all-in-one direct and label-free multiplex biomarkers detection. Preliminary successful clinical studies performed on human volunteers demonstrated the ability of our intradermal, in-skin, blood extraction-free detection platform to accurately detect protein biomarkers as a plausible POC detection for future replacement of today's invasive clinical blood tests. This approach can be readily extended in the future to detect other clinically relevant circulating biomarkers, such as miRNAs, free-DNAs, exosomes, and small metabolites.

Three-Dimensional Monolithically Self-Grown Metal Oxide Highly Dense Nanonetworks as Free-Standing High-Capacity Anodes for Lithium-Ion Batteries

Transition metal oxides (TMOs) have been widely studied as potential next-generation anode materials, owing to their high theoretical gravimetric capacity. However, to date, these anodes syntheses are plagued with time-consuming preparation processes, two-dimensional electrode fabrication, binder requirements, and short operational cycling lives. Here, we present a scalable single-step reagentless process for the synthesis of highly dense Mn₃O₄-based nanonetwork anodes based on a simple thermal treatment transformation of low-grade steel substrates. The monolithic solid-state chemical self-transformation of the steel substrate results in a highly dense forest of Mn₃O₄ nanowires, which transforms the electrochemically inactive steel substrate into an electrochemically highly active anode. The proposed method, beyond greatly improving the current TMO performance, surpasses state-of-the-art commercial silicon anodes in terms of capacity and stability. The three-dimensional self-standing anode exhibits remarkably high capacities (>1500 mA h/g), a stable cycle life (>650 cycles), high Coulombic efficiencies (>99.5%), fast rate performance (>1.5 C), and high areal capacities (>2.5 mA h/cm²). This novel experimental paradigm acts as a milestone for next-generation anode materials in lithium-ion batteries, and pioneers a universal method to transform different kinds of widely available, low-cost, steel substrates into electrochemically active, free-standing anodes and allows for the massive reduction of anode production complexity and costs.

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.

A controlled nucleation and growth of Si nanowires by using a TiN diffusion barrier layer for lithium-ion batteries

Uniform size of Si nanowires (NWs) is highly desirable to enhance the performance of Si NW-based lithium-ion batteries. To achieve a narrow size distribution of Si NWs, the formation of bulk-like Si structures such as islands and chunks needs to be inhibited during nucleation and growth of Si NWs. We developed a simple approach to control the nucleation of Si NWs via interfacial energy tuning between metal catalysts and substrates by introducing a conductive diffusion barrier. Owing to the high interfacial energy between Au and TiN, agglomeration of Au nanoparticle catalysts was restrained on a TiN layer which induced the formation of small Au nanoparticle catalysts on TiN-coated substrates. The resulting Au catalysts led to the nucleation and growth of Si NWs on the TiN layer with higher number density and direct integration of the Si NWs onto current collectors without the formation of bulk-like Si structures. The lithium-ion battery anodes based on Si NWs grown on TiN-coated current collectors showed improved specific gravimetric capacities (>30%) for various charging rates and enhanced capacity retention up to 500 cycles of charging-discharging.

Cross-Linked Sodium Alginate-Sodium Borate Hybrid Binders for High-Capacity Silicon Anodes in Lithium-Ion Batteries

Silicon is considered one of the most promising next-generation anode materials for lithium-ion batteries. It has the advantages of high theoretical specific capacity (4200 mAh·g^-1), which is 10 times larger than that of a commercial graphite anode (372 mAh·g^-1). However, there are some problems such as the pulverization of the electrode and an unstable solid electrolyte interphase (SEI) layer aroused by the huge bulk effect (>300%) of Si during the repeated lithiation/delithiation process. A binder plays a vital role in the conventional lithium-ion batteries that can effectively relieve the bulk expansion stress of a silicon anode. In this work, the inorganic cross-linker sodium borate (SB) and the commonly used binder sodium alginate (SA) were condensed through an esterification reaction and the reaction product was marked as SA-SB. It is found that the mechanical robustness and the peel strength of SA-SB are improved after cross-linking, which is conducive to maintaining the structural stability of the silicon anode in long cycle life. In consequence, the capacity retention of the silicon anode using the SA-SB binder (64.1%) is higher than that of SA (50.6%) after 100 cycles at 0.2 A·g^-1.

Diversely Doped Uniform Silicon Nanotube Axial Heterostructures Enabled by "Dopant Reflection"

Here, we propose a novel method for the synthesis of extremely uniform, diversely doped silicon nanotube heterostructures. The method, comprising a simple two-step synthesis, exploits the use of a Ge nanowire sacrificial core upon which a multidoping axial pattern can be easily obtained, that is enclosed in an intrinsic Si shell. The Ge-Si core-shell structure is then heated to 750 °C, allowing the migration of dopant elements from the Ge core directly into the Si shell. Removal of the Ge core, via either wet or dry etch, does not impair the crystallinity of the Si shell nor its electrical characteristics, allowing for the formation of a multidoped axially patterned, conformal, and uniform Si nanotube. The precise dopant patterning allows for the extension of Si nanotube applications, which were unattainable because of the inability to precisely control the parameters and uniformity of the nanotubes while doping the structure simultaneously.

Synthesis and electrochemical performance of silicon-nanowire alloy anodes

High-capacity materials are required in order to address the environmental concerns of our modern society, ultimately leading to safe and eco-friendly high-energy batteries. Silicon-nanowire anodes (SiNWs) have the potential to significantly increase the energy density of lithium-ion batteries (LIBs). In order to improve the mechanical durability and the electrochemical performance of SiNW-anodes, we fabricated a silicon–nickel (SiNi) composite anode by electroless deposition of nickel, followed by annealing at high temperature to obtain nickel silicides of different content and composition. The morphology of SiNi-alloy anodes was examined by SEM, in situ TEM and EDS methods in order to understand how different deposition protocols affect the coating of the silicon nanowires. The formation of Ni-silicides was found to occur during thermal treatment at 900 °C. Despite the incomplete shell coverage of SiNWs composed of multiple phases and grains, the electrochemical performance of binder-free and conducting-additive-free SiNi-alloy anodes showed stable electrochemical behavior and higher capacity retention compared to the pristine SiNW anode. Li/SiNW–SiNi_x cells ran at C/2 rate for 200 reversible cycles, exhibiting 0.1%/cycle capacity loss after completion of the SEI formation.

Electroless coating of a silicon nanowires (SiNW) anode (a) followed by annealing, forms nickel silicide layer (b), which enables stable electrochemical behaviour of SiNi-alloy anode and higher capacity retention compared to the pristine SiNW anode (c).

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.

Assembling Nano-Microarchitecture for Electromagnetic Absorbers and Smart Devices

Smart devices, nowadays, are inspiring the infinite vitality and possibilities of intelligent life, such as self-power electromagnetic (EM) nanogenerator and microsensor, smart window, thermally-driven EM absorber, interstellar energy deliverer, and so on. Herein, the latest and most impressive works of 3D nano-micro architectures and their smart EM devices are highly focused on. The most key information, including assembly strategy and mechanism, EM response, and approach-structure-function relationship, is extracted and well-organized with profundity and easy-to-understand approach. The merit and demerit are revealed by comparison. What's more, the brightest and most cutting-edge smart EM devices constructed by 3D nano-micro architectures are reported as highlights, and the device principles are deeply dissected. Finally, a profound and top comment on the fast-growing field as well as challenges are proposed, and the future directions are predicted intelligently.

Self-Catalyzed Vertically Aligned Carbon Nanotube-Silicon Core-Shell Array for Highly Stable, High-Capacity Lithium-Ion Batteries

Here, we report on the simple, catalyst-free preparation and application of carbon nanotube-silicon core-shell composite anodes on stainless steel. The stainless steel mesh structure acts as a self-catalyzing agent for the plasma-enhanced chemical vapor deposition (PECVD) growth of vertically aligned, dense, multiwalled carbon nanotube arrays. The carbon nanotube array then serves as a bed for silicon deposition by the decomposition of silane through chemical vapor deposition (CVD). This approach leads to the formation of highly conductive and stable composite anodes. Silicon deposition on the substrate is controlled in terms of the optimal silicon shell thickness, thus enhancing the performance of the cell. These extremely stable, binder-free composite electrodes were characterized as potential anodes in Li-ion batteries, exhibiting long cycle life (>700 cycles), high gravimetric capacity (>4000 mAh/gSi), low irreversible capacity (<10%), and high Coulombic efficiency (>99.5%). These composite anodes meet the requirements of Li-ion batteries for future portable electronics and electric vehicle applications.