In situ formed Si nanoparticle network with micron-sized Si particles for lithium-ion battery anodes

Solid Silicon Nanosheet Sandwiched by Self-Assembled Honeycomb Silicon Nanosheets Enabling Long Life at High Current Density for a Lithium-Ion Battery Anode

A two-dimensional silicon nanosheet (2D Si NS) is promising as a lithium-ion battery anode. However, insufficient cycling life at high current density hampers its practical applications due to its easy fragileness. Rationally engineering the Si micro/nanostructure is promising to address this issue. Unfortunately, the precise construction of a dedicated micro/nanostructure into 2D Si NS meets serious challenges. Herein, a facile strategy is developed to synthesize a sandwich-like honeycomb Si NS/solid Si NS/honeycomb Si NS (h/s/h-Si NS) anode through self-assembled preparation of a sandwich-like honeycomb SiO₂ NS/solid SiO₂ NS/honeycomb SiO₂ NS template, followed by magnesiothermic reduction. This unique structure effectively enhances the mechanical strength, enlarges the specific surface area, and reserves sufficient space to accommodate the anode volume change. A conductive carbon layer is further coated on the h/s/h-Si NS (h/s/h-Si@C NS) to construct a stable electrode/electrolyte interface. The optimal h/s/h-Si@C NS displays outstanding performance with high initial Coulombic efficiency (86%), high reversible capacity (1624 mAh g^-1 after 100 cycles at 1000 mA g^-1), good rate capability (over 1000 mAh g^-1 at 4000 mA g^-1), and long cycling life even at 4000 mA g^-1 (93% retained capacity after 1000 cycles). This work provides a new strategy for constructing high-performance Si electrodes for lithium-ion battery applications.

Hollow Porous N and Co Dual-Doped Silicon@Carbon Nanocube Derived by ZnCo-Bimetallic Metal-Organic Framework toward Advanced Lithium-Ion Battery Anodes

Silicon (Si) has been recognized as a promising alternative to graphite anode materials for advanced lithium-ion batteries (LIBs) owing to its superior theoretical capacity and low discharge voltage. However, Si-based anodes undergo structural pulverization during cycling due to the large volume expansion (ca. 300-400%) and continuous formation of an unstable solid electrolyte interphase (SEI), resulting in fast capacity fading. To address this challenge, a series of different amounts of silicon nanoparticles (Si NPs)-encapsulated hollow porous N-doped/Co-incorporated carbon nanocubes (denoted as p-CoNC@SiX, where X = 50, 80, and 100) as anode materials for LIBs are reported in this paper. These hollow nanocubic materials were derived by facile annealing of different contents of Si NPs-encapsulated Zn/Co-bimetallic zeolitic imidazolate frameworks (ZIF@Si) as self-sacrificial templates. Owing to the advantages of well-defined hollow framework clusters and highly conductive hollow carbon frameworks, the hollow porous p-CoNC@SiX significantly improved the electronic conductivity and Li⁺ diffusion coefficient by an order of magnitude higher than that of Si NPs. The as-prepared p-CoNC@Si80 with 80 wt % Si NPs delivered a continuously increasing specific capacity of 1008 mAh g^-1 at 500 mA g^-1 over 500 cycles, excellent reversible capacity (∼1361 mAh g^-1 at 0.1 A g^-1), and superior rate capability (∼603 mAh g^-1 at 3 A g^-1) along with an unprecedented long-life cyclic stability of ∼1218 mAh g^-1 at 1 A g^-1 over 1000 cycles caused by low volume expansion (9.92%) and suppressed SEI side reactions. These findings provide new insights into the development of highly reversible Si-based anode materials for advanced LIBs.

On the diatomite-based nanostructure-preserving material synthesis for energy applications

The present article overviews the current state-of-the-art and future prospects for the use of diatomaceous earth (DE) in the continuously expanding sector of energy science and technology. An eco-friendly direct source of silica and the production of silicon, diatomaceous earth possesses a desirable nano- to micro-structure that offers inherent advantages for optimum performance in existing and new applications in electrochemistry, catalysis, optoelectronics, and biomedical engineering. Silica, silicon and silicon-based materials have proven useful for energy harvesting and storage applications. However, they often encounter setbacks to their commercialization due to the limited capability for the production of materials possessing fascinating microstructures to deliver optimum performance. Despite many current research trends focusing on the means to create the required nano- to micro-structures, the high cost and complex, potentially environmentally harmful chemical synthesis techniques remain a considerable challenge. The present review examines the advances made using diatomaceous earth as a source of silica, silicon-based materials and templates for energy related applications. The main synthesis routes aimed at preserving the highly desirable naturally formed neat nanostructure of diatomaceous earth are assessed in this review that culminates with the discussion of recently developed pathways to achieving the best properties. The trend analysis establishes a clear roadmap for diatomaceous earth as a source material of choice for current and future energy applications.

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.

Silicon-nanoparticle-based composites for advanced lithium-ion battery anodes

Lithium-ion batteries (LIBs) play an important role in modern society. The low capacity of graphite cannot meet the demands of LIBs calling for high power and energy densities. Silicon (Si) is one of the most promising materials instead of graphite, because of its high theoretical capacity, low discharge voltage, low cost, etc. However, Si shows low conductivity of both ions and electrons and exhibits a severe volume change during cycles. Fabricating nano-sized Si and Si-based composites is an effective method to enhance the electrochemical performance of LIB anodes. Using a small size of Si nanoparticles (SiNPs) is likely to avoid the cracking of this material. One critical issue is to disclose different types and electrochemical effects of various coupled materials in the Si-based composites for anode fabrication and optimization. Hence, this paper reviews diverse SiNP-based composites for advanced LIBs from the perspective of composition and electrochemical effects. Almost all kinds of materials that have been coupled with SiNPs for LIB applications are summarized, along with their electrochemical influences on the composites. The integrated materials, including carbon materials, metals, metal oxides, polymers, Si-based materials, transition metal nitrides, carbides, dichalcogenides, alloys, and metal-organic frameworks (MOFs), are comprehensively presented.

Facile Fabrication of High-Performance Si/C Anode Materials via AlCl3-Assisted Magnesiothermic Reduction of Phenyl-Rich Polyhedral Silsesquioxanes

Si/C composites, combining the advantages of both carbon materials and Si materials, have been proposed as the promising material in lithium-ion storage. However, up to now, the most common fabrication methods of Si/C composites are too complicated for practical application. Here, we first use phenyl-substituted cagelike polyhedral silsesquioxane (T_n-Ph, n = 8, 12) as both carbon and silicon precursors to prepare the high-performance Si/C anode materials via a low-temperature and simple AlCl₃-assisted magnesiothermic reduction. AlCl₃ plays two roles in the reduction process, on the one hand, it acts as liquid medium to promote the reduction of siloxane core in such a mild condition (200 °C), and on the other hand, it act as catalyst for phenyl groups polycondensation into carbon materials, which makes the procedure of fabrication feasible and controllable. Impressively, T₁₂-Si/C exhibits an excellent lithium anodic performance with a reversible capacity of 1449.2 mA h g^-1 with a low volume expansion of 16.3% after 100 cycles. Such superior electrochemical performance makes the Si/C composites alternative anode materials for lithium-ion batteries.

Aqueous binder effects of poly(acrylic acid) and carboxy methylated cellulose on anode performance in lithium-ion batteries

The aqueous binder effects of poly(acrylic acid) and carboxy methylated cellulose on metal (oxide) anode performance in lithium-ion batteries were studied.

Applications of 2D MXenes in energy conversion and storage systems

This article provides a comprehensive review of MXene materials and their energy-related applications.

Toward Mechanically Stable Silicon-Based Anodes Using Si/SiO x@C Hierarchical Structures with Well-Controlled Internal Buffer Voids

Low conductivity and structural degradation of silicon-based anodes lead to severe capacity fading, which fundamentally hinders their practical application in Li-ion batteries. Here, we report a scalable Si/SiO _x@C anode architecture, which is constructed simultaneously by sintering a mixture of SiO/sucrose in argon atmosphere, followed by acid etching. The obtained structure features highly uniform Si nanocrystals embedded in silica matrices with well-controlled internal nanovoids, with all of them embraced by carbon shells. Because of the improvement of the volumetric efficiency for accommodating Si active spices and electrical properties, this hierarchical anode design enables the promising electrochemical performance, including a high initial reversible capacity (1210 mAh g^-1), stable cycling performance (90% capacity retention after 100 cycles), and good rate capability (850 mAh g^-1 at 2.0 A g^-1 rate). More notably, the compact heterostructures derived from micro-SiO allow high active mass loading for practical applications and the facile and scalable fabrication strategy makes this electrode material potentially viable for commercialization in Li-ion batteries.

Flower-like carbon with embedded silicon nano particles as an anode material for Li-ion batteries

A novel 3-dimensional (3D) flower-like silicon/carbon composite was synthesized through spray drying method by using NaCl as the sacrificial reagent and was evaluated as an anode material for lithium ion batteries.

Cyclopentadithiophene-benzoic acid copolymers as conductive binders for silicon nanoparticles in anode electrodes of lithium ion batteries

Cyclopentadithiophene-benzoic acid copolymers have been synthesized by direct arylation followed by saponification for use as conductive binders for silicon nanoparticles in anode electrode of lithium ion batteries.

A micro-sized Si–CNT anode for practical application via a one-step, low-cost and green method

Silicon (Si) has been used in Li-ion batteries (LIBs), and considerable progress has been achieved in design and engineering with improved capacity and cycling.

A Tremella-Like Nanostructure of Silicon@void@graphene-Like Nanosheets Composite as an Anode for Lithium-Ion Batteries

Graphene coating is receiving discernable attention to overcome the significant challenges associated with large volume changes and poor conductivity of silicon nanoparticles as anodes for lithium-ion batteries. In this work, a tremella-like nanostructure of silicon@void@graphene-like nanosheets (Si@void@G) composite was successfully synthesized and employed as a high-performance anode material with high capacity, cycling stability, and rate capacity. The Si nanoparticles were first coated with a sacrificial SiO2 layer; then, the nitrogen-doped (N-doped) graphene-like nanosheets were formed on the surface of Si@SiO2 through a one-step carbon-thermal method, and the SiO2 layer was removed subsequently to obtain the Si@void@G composite. The performance improvement is mainly attributed to the good conductivity of N-doped graphene-like nanosheets and the unique design of tremella nanostructure, which provides a void space to allow for the Si nanoparticles expanding upon lithiation. The resulting electrode delivers a capacity of 1497.3 mAh g(-1) at the current density of 0.2 A g(-1) after 100 cycles.

A novel Si/Sn composite with entangled ribbon structure as anode materials for lithium ion battery

A novel Si/Sn composite anode material with unique ribbon structure was synthesized by Mechanical Milling (MM) and the structural transformation was studied in the present work. The microstructure characterization shows that Si/Sn composite with idealized entangled ribbon structured can be obtained by milling the mixture of the starting materials, Si and Sn for 20 h. According to the calculated results based on the XRD data, the as-milled 20 h sample has the smallest avergae crystalline size. It is supposed that the flexible ribbon structure allows for accommodation of intrinsic damage, which significantly improves the fracture toughness of the composite. The charge and discharge tests of the as-milled 20 h sample have been performed with reference to Li⁺/Li at a current density of 400 mA g⁻¹ in the voltage from 1.5 to 0.03 V (vs Li/Li⁺) and the result shows that the initial capacity is ∼1400 mA h g⁻¹, with a retention of ∼1100 mA h g⁻¹ reversible capacity after 50 cycles, which is possible serving as the promising anode material for the lithium ion battery application.

The Effects of Cross-Linking in a Supramolecular Binder on Cycle Life in Silicon Microparticle Anodes

Self-healing supramolecular binder was previously found to enhance the cycling stability of micron-sized silicon particles used as the active material in lithium-ion battery anodes. In this study, we systematically control the density of cross-linking junctions in a modified supramolecular polymer binder in order to better understand how viscoelastic materials properties affect cycling stability. We found that binders with relaxation times on the order of 0.1 s gave the best cycling stability with 80% capacity maintained for over 175 cycles using large silicon particles (∼0.9 um). We attributed this to an improved balance between the viscoelastic stress relaxation in the binder and the stiffness needed to maintain mechanical integrity of the electrode. The more cross-linked binder showed markedly worse performance confirming the need for liquid-like flow in order for our self-healing polymer electrode concept to be effective.

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.

Silicon as a potential anode material for Li-ion batteries: where size, geometry and structure matter

Silicon has attracted huge attention in the last decade because it has a theoretical capacity ∼10 times that of graphite. However, the practical application of Si is hindered by three major challenges: large volume expansion during cycling (∼300%), low electrical conductivity, and instability of the SEI layer caused by repeated volume changes of the Si material. Significant research efforts have been devoted to addressing these challenges, and significant breakthroughs have been made particularly in the last two years (2014 and 2015). In this review, we have focused on the principles of Si material design, novel synthesis methods to achieve such structural designs, and the synthesis-structure-performance relationships to enhance the properties of Si anodes. To provide a systematic overview of the Si material design strategies, we have grouped the design strategies into several categories: (i) particle-based structures (containing nanoparticles, solid core-shell structures, hollow core-shell structures, and yolk-shell structures), (ii) porous Si designs, (iii) nanowires, nanotubes and nanofibers, (iv) Si-based composites, and (v) unusual designs. Finally, our personal perspectives on outlook are offered with an aim to stimulate further discussion and ideas on the rational design of durable and high performance Si anodes for the next generation Li-ion batteries in the near future.

Towards cost-effective silicon anodes using conductive polyaniline-encapsulated silicon micropowders

To overcome the remaining issues of nanostructured Si anode, we investigated the feasibility towards practically viable Si anode by combining low-cost material precursors with facile and scalable processes.

Metal-Organic Frameworks (MOFs) as Sandwich Coating Cushion for Silicon Anode in Lithium Ion Batteries

A novel metal-organic framework (MOF) sandwich coating method (denoted as MOF-SC) is developed for hybrid Li ion battery electrode preparation, in which the MOF films are casted on the surface of a silicon layer and sandwiched between the active silicon and the separator. The obtained electrodes show improved cycling performance. The areal capacity of the cheap and readily available microsized Si treated with MOF-SC can reach 1700 μAh cm(-2) at 265 μA cm(-2) and maintain at 850 μAh cm(-2) after 50 cycles. Beyond the above, the commercial nanosized Si treated by MOF-SC also shows greatly enhanced areal capacity and outstanding cycle stability, 600 μAh cm(-2) for 100 cycles without any apparent fading. By virtue of the novel structure prepared by the MOFs, this new MOF-SC structure serves as an efficient protection cushion for the drastic volume change of silicon during charge/discharge cycles. Furthermore, this MOF layer, with large pore volume and high surface area, can adsorb electrolyte and allow faster diffusion of Li(+) as evidenced by decreased impedance and improved rate performance.

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

A one-step dealloying method is employed to conveniently fabricate a bimodal porous (BP) Si/Ag composite in high throughput under mild conditions. Upon dealloying the carefully designed SiAgAl ternary alloy in HCl solution at room temperature, the obtained Si/Ag composite has a uniform bicontinuous porous structure in three dimensions with micro-nano bimodal pore size distribution. Compared with the traditional preparation methods for porous Si and Si-based composites, this dealloying route is easily operated and environmentally benign. More importantly, it is convenient to realize the controllable components and uniform distribution of Si and Ag in the product. Owing to the rich porosity of the unique BP structure and the incorporation of highly conductive Ag, the as-made Si/Ag composite possesses the improved conductivity and alleviated volume changes of the Si network during repeated charging and discharging. As expected, the BP Si/Ag anode exhibits high capacity, excellent cycling reversibility, long cycling life and good rate capability for lithium storage. When the current rate is up to 1 A g(-1), BP Si/Ag can deliver a stable reversible capacity above 1000 mA h g(-1), and exhibits a capacity retention of up to 89.2% against the highest capacity after 200 cycles. With the advantages of unique performance and easy preparation, the BP Si/Ag composite holds great application potential as an advanced anode material for Li-ion batteries.

Mechanically and chemically robust sandwich-structured C@Si@C nanotube array Li-ion battery anodes

Stability and high energy densities are essential qualities for emerging battery electrodes. Because of its high specific capacity, silicon has been considered a promising anode candidate. However, the several-fold volume changes during lithiation and delithiation leads to fractures and continuous formation of an unstable solid-electrolyte interphase (SEI) layer, resulting in rapid capacity decay. Here, we present a carbon-silicon-carbon (C@Si@C) nanotube sandwich structure that addresses the mechanical and chemical stability issues commonly associated with Si anodes. The C@Si@C nanotube array exhibits a capacity of ∼2200 mAh g(-1) (∼750 mAh cm(-3)), which significantly exceeds that of a commercial graphite anode, and a nearly constant Coulombic efficiency of ∼98% over 60 cycles. In addition, the C@Si@C nanotube array gives much better capacity and structure stability compared to the Si nanotubes without carbon coatings, the ZnO@C@Si@C nanorods, a Si thin film on Ni foam, and C@Si and Si@C nanotubes. In situ SEM during cycling shows that the tubes expand both inward and outward upon lithiation, as well as elongate, and then revert back to their initial size and shape after delithiation, suggesting stability during volume changes. The mechanical modeling indicates the overall plastic strain in a nanotube is much less than in a nanorod, which may significantly reduce low-cycle fatigue. The sandwich-structured nanotube design is quite general, and may serve as a guide for many emerging anode and cathode systems.

Incorporation of PEDOT:PSS into SnO2/reduced graphene oxide nanocomposite anodes for lithium-ion batteries to achieve ultra-high capacity and cyclic stability

A conducting polymer matrix of PEDOT:PSS is incorporated into SnO₂/reduced graphene oxide composite for increasing the stability of lithium-ion battery anodes.

Coordination-driven self-assembly: construction of a Fe3O4–graphene hybrid 3D framework and its long cycle lifetime for lithium-ion batteries

A three-dimensional graphene framework with uniform distribution of hierarchical Fe₃O₄ spheres was prepared via a one-pot solvothermal method.

Facile synthesis of a mesoporous Co3O4 network for Li-storage via thermal decomposition of an amorphous metal complex

A facile strategy is developed for mass fabrication of porous Co3O4 networks via the thermal decomposition of an amorphous cobalt-based complex. At a low mass loading, the achieved porous Co3O4 network exhibits excellent performance for lithium storage, which has a high capacity of 587 mA h g(-1) after 500 cycles at a current density of 1000 mA g(-1).

Novel design of ultra-fast Si anodes for Li-ion batteries: crystalline Si@amorphous Si encapsulating hard carbon

Nanocrystalline Si (c-Si) dispersed in amorphous Si (a-Si) encapsulating hard carbon (HC) has been synthesized as an anode material for fast chargeable lithium-ion batteries. The HC derived from natural polysaccharide was coated by a thin a-Si layer through chemical vapour deposition (CVD) using silane (SiH₄) as a precursor gas. The HC@c-Si@a-Si anodes showed an excellent cycle retention of 97.8% even after 200 cycles at a 1 C discharge/charge rate. Furthermore, a high capacity retention of ∼54% of its initial reversible capacity at 0.2 C rate was obtained at a high discharge/charge rate of 5 C. Moreover, the LiCoO₂/HC@c-Si@a-Si full-cell showed excellent rate capability and very stable long-term cycle. Even at a rate of 10 C discharge/charge, the capacity retention of the LiCoO₂/HC@c-Si@a-Si full-cell was 50.8% of its capacity at a rate of 1 C discharge/charge and showed a superior cycle retention of 80% after 160 cycles at a rate of 1 C discharge/charge.

Graphene nanosheets encapsulated α-MoO3 nanoribbons with ultrahigh lithium ion storage properties

A facile and effective method has been reported to synthesize graphene-encapsulated α-MoO₃ nanoribbons by self-assembly of negatively charged graphene oxide and positively charged MoO₃ nanoribbons.

Si-Based Anode Materials for Li-Ion Batteries: A Mini Review

Si has been considered as one of the most attractive anode materials for Li-ion batteries (LIBs) because of its high gravimetric and volumetric capacity. Importantly, it is also abundant, cheap, and environmentally benign. In this review, we summarized the recent progress in developments of Si anode materials. First, the electrochemical reaction and failure are outlined, and then, we summarized various methods for improving the battery performance, including those of nanostructuring, alloying, forming hierarchic structures, and using suitable binders. We hope that this review can be of benefit to more intensive investigation of Si-based anode materials.