Delicate Structural Control of Si-SiOx-C Composite via High-Speed Spray Pyrolysis for Li-Ion Battery Anodes

Graphene-doped silicon-carbon materials with multi-interface structures for lithium-ion battery anodes

The carbon nanomaterials are usually used to improve the electrical conductivity and stability of silicon (Si) anodes for lithium-ion batteries. However, the Si-based composites containing carbon nanomaterials generally show large specific surface area, leading to severe side reactions that generate large amounts of solid electrolyte interphase films. Herein, we embedded graphene oxide (GO) and silicon nanoparticles (Si NPs) uniformly in pitch matrix by solvent dispersion. The internally doped GO reduces the exposed surface and improves the electrical conductivity of the composite. Meanwhile, the multi-interface structures are constructed inside to limit the domains of Si NPs and improve the structural stability of the material. When evaluated as anodes, the Si/graphene/pitch-based carbon composite anode exhibits the outstanding electrochemical properties, delivering a reversible capacity of 820.8 mAh/g at 50 mA g-1, as well as a capacity retention of 93.6 % after 1000 cycles at 2 A/g. In addition, when assembled with the LiFePO4 cathode, the full cell exhibits an impressive capacity retention of 95 % after 100 cycles at 85 mA g-1. This work provides a valuable design concept for the development of Si/carbon anodes.

Innovative Solutions for High-Performance Silicon Anodes in Lithium-Ion Batteries: Overcoming Challenges and Real-World Applications

Silicon (Si) has emerged as a potent anode material for lithium-ion batteries (LIBs), but faces challenges like low electrical conductivity and significant volume changes during lithiation/delithiation, leading to material pulverization and capacity degradation. Recent research on nanostructured Si aims to mitigate volume expansion and enhance electrochemical performance, yet still grapples with issues like pulverization, unstable solid electrolyte interface (SEI) growth, and interparticle resistance. This review delves into innovative strategies for optimizing Si anodes' electrochemical performance via structural engineering, focusing on the synthesis of Si/C composites, engineering multidimensional nanostructures, and applying non-carbonaceous coatings. Forming a stable SEI is vital to prevent electrolyte decomposition and enhance Li+ transport, thereby stabilizing the Si anode interface and boosting cycling Coulombic efficiency. We also examine groundbreaking advancements such as self-healing polymers and advanced prelithiation methods to improve initial Coulombic efficiency and combat capacity loss. Our review uniquely provides a detailed examination of these strategies in real-world applications, moving beyond theoretical discussions. It offers a critical analysis of these approaches in terms of performance enhancement, scalability, and commercial feasibility. In conclusion, this review presents a comprehensive view and a forward-looking perspective on designing robust, high-performance Si-based anodes the next generation of LIBs.

A Gradient Composite Structure Enables a Stable Microsized Silicon Suboxide-Based Anode for a High-Performance Lithium-Ion Battery

The practical application of microsized anodes is hindered by severe volume changes and fast capacity fading. Herein, we propose a gradient composite strategy and fabricate a silicon suboxide-based composite anode (d-SiO@SiOx/C@C) consisting of a disproportionated microsized SiO inner core, a homogeneous composite SiOx/C interlayer (x ≈ 1.5), and a highly graphitized carbon outer layer. The robust SiOx/C interlayer can realize a gradient abatement of stress and simultaneously connect the inner SiO core and carbon outer layer through covalent bonds. As a result, d-SiO@SiOx/C@C delivers a specific capacity of 1023 mAh/g after 300 cycles at 1 A/g with a retention of >90% and an average Coulombic efficiency of >99.7%. A full cell assembled with a LiNi0.8Co0.15Al0.05O2 cathode displays a remarkable specific energy density of 569 Wh/kg based on total active materials as well as excellent cycling stability. Our strategy provides a promising alternative for designing structurally and electrochemically stable microsized anodes with high capacity.

Ultrathin Carbon Sheet Obtained by Self-Template Method toward Highly Effective Charge Transfer for Si-Based Anodes

A dynamic and stable charge transfer process is the key to exerting lithium storage characteristics of the silicon anode with a large volume change. In this work, the composite with an ultrathin carbon sheet skeleton is prepared by freeze-drying and a copyrolysis process after uniformly mixing citric acid and hydroxylated Si NPs, which is different from traditional conformal carbon coating derived from citric acid. A flexible carbon sheet reduces internal particle (Si-OH@NC) slip and cooperates with interfacial Si-O-C bonding to buffer machinal stress in the electrode during cycling. More importantly, the carbon sheet network increases the point-to-surface contact area between the active material and the conductive agent, ensures continuous electrical connection from the current collector to the active material, and promotes a rapid and stable electron transfer process. Besides, the N-doped C structure with remarkable nucleophilicity guarantees fast ion transport, which is confirmed by theoretical calculation. In this way, the reaction reversibility of the Si-based electrode is further realized during cycles. As a result, the electrode delivers excellent cycle performance (reversible capacity of 1001.9 mAh g-1 at 1 A g-1 after 500 cycles) and rate performance (capacity retention of 86.8 and 65.8% at 1 and 3 A g-1, respectively, compared to 0.2 A g-1). The idea of constructing a highly efficient electrode conductive network through a doped-carbon sheet network is also applicable to other active materials with huge volume changes during lithium storage.

Carbon Microstructure Dependent Li-Ion Storage Behaviors in SiOx /C Anodes

SiO_x anode has a more durable cycle life than Si, being considered competitive to replace the conventional graphite. SiO_x usually serves as composites with carbon to achieve more extended cycle life. However, the carbon microstructure dependent Li-ion storage behaviors in SiO_x /C anode have received insufficient attention. Herein, this work demonstrates that the disorder of carbon can determine the ratio of inter- and intragranular Li-ion diffusions. The resulted variation of platform characteristics will result in different compatibility when matching SiO_x . Rational disorder induced intergranular diffusion can benefit phase transition of SiO_x /C, benefiting the electrochemical performance. Through a series of quantitative calculations and in situ X-ray diffraction characterizations, this work proposes the rational strategy for the future optimization, thus achieving preferable performance of SiO_x /C anode.

Fe3+-Derived Boosted Charge Transfer in an FeSi4P4 Anode for Ultradurable Li-Ion Batteries

Ion and electron transportation determine the electrochemical performance of anodes in metal-ion batteries. This study demonstrates the advantage of charge transfer over mass transport in ensuring ultrastable electrochemical performance. Additionally, charge transfer governs the quality, composition, and morphology of a solid-electrolyte interphase (SEI) film. We develop FeSi₄P₄-carbon nanotube (FSPC) and reduced-FeSi₄P₄-carbon nanotube (R-FSPC) heterostructures. The FSPC contains abundant Fe³⁺ cations and negligible pore contents, whereas R-FSPC predominantly comprises Fe²⁺ and an abundance of nanopores and vacancies. The copious amount of Fe³⁺ ions in FSPC significantly improves charge transfer during Li-ion battery tests and leads to the formation of a thin monotonic SEI film. This prevents the formation of detrimental LiP and crystalline-Li_3.75Si phases and the aggregation of discharging/recharging products and guarantees the reformation of FeSi₄P₄ nanocrystals during delithiation. Thus, FSPC delivers a high initial Coulombic efficiency (>90%), exceptional rate capability (616 mAh g^-1 at 15 A g^-1), and ultrastable symmetric/asymmetric cycling performance (>1000 cycles at ultrahigh current densities). This study deepens our understanding of the effects of electron transport on regulating the structural and electrochemical properties of electrode materials in high-performance batteries.

Dual structure engineering of SiOx-acrylic yarn derived carbon nanofiber based foldable Si anodes for low-cost lithium-ion batteries

Silicon (Si) is attracted much attention due to its outstanding theoretical capacity (4200 mAh/g) as the anode of lithium-ion batteries (LIBs). However, the large volume change and low electron/ion conductivity during the charge and discharge process limit the electrochemical performance of Si-based anodes. Here we demonstrate a foldable acrylic yarn-based composite carbon nanofiber embedded by Si@SiO_x particles (Si@SiO_x-CACNFs) as the anode material. Since the amorphous SiO_x and carbon (C) coating on the outside of the Si particles can provide a double buffer for volume expansion while reducing the contact between the Si core and the electrolyte to form a thin and stable solid electrolyte interface (SEI) film. Simultaneous in-situ electrochemical impedance spectroscopy (in-situ EIS) and galvanostatic intermittent titration technique (GITT) tests show that SiO_x and C have higher ion/electron transport rates, and in addition, using acrylic fiber yarn and Zn(Ac)₂ as raw materials reduces the manufacturing cost and enhanced mechanical properties. Therefore, the half-cell can achieve a high initial Coulombic efficiency (ICE) of 82.3% and a reversible capacity of 1358.2 mAh/g after 180 cycles. It can return to its original shape and remain intact after four consecutive folds, and the soft-pack full battery can also light up LED lights under different bending conditions.

A Novel High-Performance TiO2-x /TiO1-y Ny Coating Material for Silicon Anode in Lithium-Ion Batteries

Protective surface coatings on Si anodes are promising for improving the electrochemical performance of lithium-ion batteries (LIBs). Nevertheless, most coating materials have severe issues, including low initial coulombic efficiency, structural fracture, morphology control, and complicated synthetic processing. In this study, a multifunctional TiO_{2- x} /TiO_{1- y} N_y (TTN) formed via a facile and scalable synthetic process is applied as a coating material for Si anodes. A thin layer of amorphous TiO₂ is uniformly coated onto Si nanoparticles by a simple sol-gel method and then converted into a two phase TiO_{2- x} /TiO_{1- y} N_y via nitridation. The lithiated TiO_2-x provides high ionic and electrical conductivity, while TiO_1-y N_y can improve mechanical strength that alleviates volume change of Si to address capacity fading issue. Owing to these synergetic advantages, TiO_{2- x} /TiO_{1- y} N_y -coated Si (Si@TTN) exhibits excellent electrochemical properties, including a high charge capacity of 1650 mA h g^-1 at 0.1 A g^-1 and 84% capacity retention after 100 cycles at 1 A g^-1 . Moreover, a significantly enhanced rate performance can be achieved at a high current density. This investigation presents a facile and effective coating material to use as the high-capacity silicon anode in the emerging Si anode technology in LIBs.

Glucose hydrothermal encapsulation of carbonized silicone polyester to prepare anode materials for lithium batteries with improved cycle stability

A silicon polyester (Si-PET) was synthesized with ethylene glycol and phthalic anhydride, and then it was carbonized and hydrothermally coated with glucose. The formed SiO_x with layered graphene as the 3D network had an amorphous carbon layer. The graphene oxide (rGO) after carbothermal reduction was completely retained in SiO_x, which improved the conductivity of the SiO_x anode material. SiO_x were encapsulated with a flexible amorphous carbon layer on the surface, which can not only improve the electrical performance, but also effectively relieve the huge volume changes of the compound. Further, the key point is that, the solid electrolyte interphase (SEI) film was mainly formed on the surface carbon layer. This would keep a stable SEI film during volume pulverization, and result in a good cycle stability. The SiO_x/C-rGO material maintained a reversible capacity of 660 mA h g⁻¹ at a current density of 100 mA g⁻¹ for 100 cycles, a reversible capacity of 469.7 mA h g⁻¹ at a current density of 200 mA g⁻¹ for 300 cycles. The Coulomb efficiency was maintained at 98% except for the first cycle. After long cycling, the electrode expansion was 16%, which was much lower than those of silicon based materials. Therefore, this article provides a cheap, simple, and commercially valuable anode material for lithium batteries.

Silicon polyester (Si-PET) was synthesized with ethylene glycol and phthalic anhydride, and then it was carbonized and hydrothermally coated with glucose. The forming SiO_x with layered graphene as the 3D network had amorphous carbon layer.

Advances in Si and SiC Materials for High-Performance Supercapacitors toward Integrated Energy Storage Systems

Silicon (Si), as the second most abundant element on Earth, has been a central platform of modern electronics owing to its low mass density and unique semiconductor properties. From an energy perspective, all-in-one integration of power supply systems onto Si-based functional devices is highly desirable, which inspires significant study on Si-based energy storage. Compared to the well-known Si-anode Li-ion batteries, Si-based supercapacitors possess high power density, long life, and simple working mechanisms, which enables their ease of integration onto a wide range of devices and applications. Besides Si, silicon carbide (SiC), as a physicochemically stable wide-bandgap semiconductor, also attracts research attention as an energy storage material in harsh environments. In this review, a detailed overview of latest advances in materials design, synthesis methods, and performances of Si-based and SiC-based supercapacitors will be provided. Some successful integrated devices, future perspectives, and potential research directions are also highlighted and discussed.

Ternary Si-SiO-Al Composite Films as High-Performance Anodes for Lithium-Ion Batteries

Silicon (Si) is a promising anode material for lithium-ion batteries but has long been suffering from low conductivity, drastic volume change, poor cycling performance, etc. Adding SiO, Al, etc. to form Si-based binary composite films can improve some properties but have to give up others. Here, we prepared a ternary Si-SiO-Al composite film anode by adding SiO and Al together into Si using magnetron sputtering. This film has an extraordinary combination of conductivity, specific capacity, cycling stability, rate performance, etc., when compared with its binary and unary counterparts. While both SiO and Al can separately mitigate anode cracking resulting from the huge volume expansion during the lithiation/delithiation cycling process, the synergetic effect of adding SiO and Al together to form a ternary composite film can produce much better results. This film maintains an island structure that can efficiently buffer the volume expansion during the cycling process, giving rise to superior cycling performance and excellent rate performance. In addition, the cosputtered Al improves the electrical conductivity of the anode at the same time. This unique combination of anode properties, together with the low cost, suggests that the Si-SiO-Al composite film has the potential to be commercialized as a binder-free anode for lithium-ion batteries. This work also provides an efficient means to modulate the anode properties with more degrees of freedom.

Vapor-phase production of nanomaterials

The synthesis of nanomaterials, with characteristic dimensions of 1 to 100 nm, is a key component of nanotechnology. Vapor-phase synthesis of nanomaterials has numerous advantages such as high product purity, high-throughput continuous operation, and scalability that have made it the dominant approach for the commercial synthesis of nanomaterials. At the same time, this class of methods has great potential for expanded use in research and development. Here, we present a broad review of progress in vapor-phase nanomaterial synthesis. We describe physically-based vapor-phase synthesis methods including inert gas condensation, spark discharge generation, and pulsed laser ablation; plasma processing methods including thermal- and non-thermal plasma processing; and chemically-based vapor-phase synthesis methods including chemical vapor condensation, flame-based aerosol synthesis, spray pyrolysis, and laser pyrolysis. In addition, we summarize the nanomaterials produced by each method, along with representative applications, and describe the synthesis of the most important materials produced by each method in greater detail.

Zn2+-Imidazole Coordination Crosslinks for Elastic Polymeric Binders in High-Capacity Silicon Electrodes

Recent research has built a consensus that the binder plays a key role in the performance of high-capacity silicon anodes in lithium-ion batteries. These anodes necessitate the use of a binder to maintain the electrode integrity during the immense volume change of silicon during cycling. Here, Zn2+-imidazole coordination crosslinks that are formed to carboxymethyl cellulose backbones in situ during electrode fabrication are reported. The recoverable nature of Zn2+-imidazole coordination bonds and the flexibility of the poly(ethylene glycol) chains are jointly responsible for the high elasticity of the binder network. The high elasticity tightens interparticle contacts and sustains the electrode integrity, both of which are beneficial for long-term cyclability. These electrodes, with their commercial levels of areal capacities, exhibit superior cycle life in full-cells paired with LiNi0.8Co0.15Al0.05O2 cathodes. The present study underlines the importance of highly reversible metal ion-ligand coordination chemistries for binders intended for high capacity alloying-based electrodes.

Architectural Engineering Achieves High-Performance Alloying Anodes for Lithium and Sodium Ion Batteries

Tremendous efforts have been dedicated to the development of high-performance electrochemical energy storage devices. The development of lithium- and sodium-ion batteries (LIBs and SIBs) with high energy densities is urgently needed to meet the growing demands for portable electronic devices, electric vehicles, and large-scale smart grids. Anode materials with high theoretical capacities that are based on alloying storage mechanisms are at the forefront of research geared towards high-energy-density LIBs or SIBs. However, they often suffer from severe pulverization and rapid capacity decay due to their huge volume change upon cycling. So far, a wide variety of advanced materials and electrode structures are developed to improve the long-term cyclability of alloying-type materials. This review provides fundamentals of anti-pulverization and cutting-edge concepts that aim to achieve high-performance alloying anodes for LIBs/SIBs from the viewpoint of architectural engineering. The recent progress on the effective strategies of nanostructuring, incorporation of carbon, intermetallics design, and binder engineering is systematically summarized. After that, the relationship between architectural design and electrochemical performance as well as the related charge-storage mechanisms is discussed. Finally, challenges and perspectives of alloying-type anode materials for further development in LIB/SIB applications are proposed.

Manipulating Oxidation of Silicon with Fresh Surface Enabling Stable Battery Anode

Silicon (Si)-based material is a promising anode material for next-generation lithium-ion batteries (LIBs). Herein, we report the fabrication of a silicon oxide-carbon (SiO_x/C) nanocomposite through the reaction between silicon particles with fresh surface and H₂O in a mild hydrothermal condition, as well as conducting carbon coating synchronously. We found that controllable oxidation could be realized for Si particles to produce uniform SiO_x after the removal of the native passivation layer. The uniform oxidation and conductive coating offered the as-fabricated SiO_x/C composite good stability at both particle and electrode level over electrochemical cycling. The as-fabricated SiO_x/C composite delivered a high reversible capacity of 1133 mAh g^-1 at 0.5 A g^-1 with 89.1% capacity retention after 200 cycles. With 15 wt % SiO_x/C composite, graphite-SiO_x/C hybrid electrode displayed a high reversible specific capacity of 496 mAh g^-1 and stable electrochemical cycling with a capacity retention of 90.1% for 100 cycles.

One-Step Low-Temperature Molten Salt Synthesis of Two-Dimensional Si@SiOx@C Hybrids for High-Performance Lithium-Ion Batteries

Various strategies have been developed to mitigate the huge volume expansion of a silicon-based anode during the process of (de)lithiation and accelerate the transport rate of the ions/electrons for lithium-ion batteries (LIBs). Here, we report a one-step synthetic route through a low-temperature eutectic molten salt (LiCl-KCl, 352 °C) to fabricate two-dimensional (2D) silicon-carbon hybrids (Si@SiO_x@MpC), in which the silicon nanoparticles (SiNPs) with an ultrathin SiO_x layer are fully encapsulated by graphene-like carbon nanosheets derived from a low-cost mesophase pitch. The combination of an amorphous graphene-like carbon conductive matrix and a SiO_x protective layer strongly promotes the electrical conductivity, structure stability, and reaction kinetics of the SiNPs. Consequently, the optimized Si@SiO_x@MpC-2 anode delivers large reversible capacity (1239 mAh g^-1 at 1.0 A g^-1), superior rate performance (762 mAh g^-1 at 8 A g^-1), and long cycle life over 600 cycles (degradation rate of only 0.063% every cycle). When coupled with a homemade nano-LiFePO₄ cathode in a full cell, it exhibits a promising energy density of 193.5 Wh kg^-1 and decent cycling stability for 200 cycles at 1C. The methodology driven by salt melt synthesis paves a low-cost way toward simple fabrication and manipulation of silicon-carbon materials in liquid media.

Electrochemical Performance of an Ultrathin Surface Oxide-Modulated Nano-Si Anode Confined in a Graphite Matrix for Highly Reversible Lithium-Ion Batteries

Si-based anode materials have attracted considerable attention for use in high-capacity lithium-ion batteries (LIBs), but their practical application is hindered by huge volume changes and structural instabilities that occur during lithiation/delithiation and low-conductivity. In this regard, we report a novel Si-nanocomposite by modulating the ultrathin surface oxide of nano-Si at a low temperature and highly conductive graphene-graphite matrix. The Si nanoparticles are synthesized by high-energy mechanical milling of micro-Si. The prepared Si/SiO_x@C nanocomposite electrode delivers a high-discharge capacity of 1355 mAh g^-1@300th cycle with an average Coulombic efficiency of 99.5% and a discharge capacity retention of ∼88% at 1C-rate (500 mA g^-1). Remarkably, the nanocomposite exhibits a high initial Coulombic efficiency of ∼87% and excellent charge/discharge rate performance in the range of 0.5-5C. Moreover, a comparative investigation of the three different electrodes nano-Si, Si/SiO_x, and Si/SiO_x@C are presented. The exceptional electrochemical performance of Si/SiO_x@C is owing to the nanosized silicon and ultrathin SiO_x followed by a high-conductivity graphene-graphite matrix, since such a nanostructure is beneficial to suppress the volume changes of silicon, maintain the structural integrity, and enhance the charge transfer during cycling. The proposed nanocomposite and the synthesis method are novel, facile, and cost-effective. Consequently, the Si/SiO_x@C nanocomposite can be a promising candidate for widespread application in next-generation LIB anodes.

Porous Si/Fe2O3 Dual Network Anode for Lithium-Ion Battery Application

Benefiting from ultra-high theoretical capacity, silicon (Si) is popular for use in energy storage fields as a Li-ion battery anode material because of its high-performance. However, a serious volume variation happens towards Si anodes in the lithiation/delithiation process, triggering the pulverization of Si and a fast decay in its capacity, which greatly limits its commercial application. In our study, a porous Si/Fe2O3 dual network anode was fabricated using the melt-spinning, ball-milling and dealloying method. The anode material shows good electrochemical performance, delivering a reversible capacity of 697.2 mAh g-1 at 200 mA g-1 after 100 cycles. The high Li storage property is ascribed to the rich mesoporous distribution of the dual network structure, which may adapt the volume variation of the material during the lithiation/delithiation process, shorten the Li-ion diffusion distance and improve the electron transport speed. This study offers a new idea for developing natural ferrosilicon ores into the porous Si-based materials and may prompt the development of natural ores in energy storage fields.

Pomegranate-Like Structured Si@SiOx Composites With High-Capacity for Lithium-Ion Batteries

Silicon anodes with an extremely high theoretical specific capacity of 4,200 mAh g^-1 have been considered as one of the most promising anode materials for next-generation lithium-ion batteries. However, the large volume expansion during lithiation hinders its practical application. In this work, pomegranate-like Si@SiO_x composites were prepared using a simple spray drying process, during which silicon nanoparticles reacted with oxygen and generated SiO_x on the surface. The thickness of the SiO_x layer was tuned by adjusting the drying temperature. In the unique architecture, the SiO_x which serves as the protection layer and the void space in pomegranate-like structure could alleviate the volume expansion during repeated lithium insertion/extraction. As a lithium-ion battery anode, pomegranate-like Si@SiO_x composites dried at 180°C delivered a high specific capacity of 1746.5 mAh g^-1 after 300 cycles at 500 mA g^-1.

Interface-Amorphized Ti3C2@Si/SiOx@TiO2 Anodes with Sandwiched Structures and Stable Lithium Storage

A new two-dimensional material (MXene) has been compounded lately with silicon as anodes for lithium-ion batteries to achieve excellent lithium storage performances on account of its unique properties, such as high electrical conductivities, low ion diffusion barrier, and large surface area. However, the exposed silicon particles may lead to fast capacity decaying upon direct contact with the electrolyte. To solve this issue, the porous silicon and SiO_x are introduced into Ti₃C₂T_x to construct a conductive network, and then Ti₃C₂@Si/SiO_x are covered with amorphous TiO₂ to make a sandwiched Ti₃C₂@Si/SiO_x@TiO₂ composite. Owing to the cooperation of the Ti₃C₂ matrix, Si/SiO_x interlayer, and amorphous TiO₂ layer, the reversible capacity of the Ti₃C₂@Si/SiO_x@TiO₂ composite with a sandwiched structure can be maintained at 939 mA h g^-1 after 100 cycles and enhanced capacity retention capabilities in the initial 10 cycles can be came ture. The combination of these four components also makes the Ti₃C₂@Si/SiO_x@TiO₂ composite material a promising application prospect in lithium-ion batteries.

Carbon/Polymer Bilayer-Coated Si-SiOx Electrodes with Enhanced Electrical Conductivity and Structural Stability

Si-based electrodes offer exceptionally high capacity and energy density for lithium-ion batteries (LIBs),but suffer from poor structural stability and electrical conductivity that hamper their practical applications. To tackle these obstacles, we design a C/polymer bilayer coating deposited on Si-SiO_x microparticles. The inner C coating is used to improve electrical conductivity. The outer C-nanoparticle-reinforced polypyrrole (CNP-PPy) is a polymer matrix composite that can minimize the volumetric expansion of Si-SiO_x and enhance its structural stability during battery operation. Electrodes made of such robust Si-SiO_x@C/CNP-PPy microparticles exhibit excellent cycling performance: 83% capacity retention (794 mAh g^-1) at a 2 C rate after more than 900 cycles for a coin-type half cell, and 80% capacity retention (with initial energy density of 308 Wh kg^-1) after over 1100 cycles for a pouch-type full cell. By comparing the samples with different coatings, an in-depth understanding of the performance enhancement is achieved, i.e., the C/CNP-PPy with cross-link bondings formed in the bilayer coating plays a key role for the improved structural stability. Moreover, a full battery using the Si-SiO_x@C/CNP-PPy electrode successfully drives a car model, demonstrating a bright application prospect of the C/polymer bilayer coating strategy to make future commercial LIBs with high stability and energy density.

Engineering Carbon Distribution in Silicon-Based Anodes at Multiple Scales

The successful commercialization of promising silicon-based anode materials has been hampered by their poor cycling stability caused by the huge volume change. Integration of the carbon matrix with silicon-based (C/Si-based) anode materials has been demonstrated to be a powerful solution to achieve satisfactory electrochemical performance. This minireview aims to outline recent developments on C/Si-based composites, with the emphasis on the importance of carbon distribution at multiple scales. In addition, the forms of the carbon framework (carbon sources and doping of heteroatoms) have been summarized. Particularly, a novel C/Si-based hybrid with carbon distributed at the atomic scale has been highlighted.

Guidelines and trends for next-generation rechargeable lithium and lithium-ion batteries

This review article summarizes the current trends and provides guidelines towards next-generation rechargeable lithium and lithium-ion battery chemistries.

Hollow Boron-Doped Si/SiOx Nanospheres Embedded in the Vanadium Nitride/Nanopore-Assisted Carbon Conductive Network for Superior Lithium Storage

SiO_x-based anode materials with high capacity and outstanding cycling performance have gained numerous attentions. Nevertheless, the poor electrical conductivity and non-negligible volume change hinder their further application in Li-ion batteries. Herein, we propose a new strategy to construct a hollow nanosphere with boron-doped Si/SiO_x decorated with vanadium nitride (VN) nanoparticles and embedded in a nitrogen-doped, porous, and partial graphitization carbon layer (B-Si/SiO_x@VN/PC). Benefiting from such structural and compositional features, the B-Si/SiO_x@VN/PC electrode exhibits a stable cycling capacity of 1237.1 mA h g^-1 at a current density of 0.5 A g^-1 with an appealing capacity retention of 87.0% after 300 cycles. Additionally, it delivers high-rate capabilities of 1139.4, 940.7, and 653.4 mA h g^-1 at current densities of 2, 5, and 10 A g^-1, respectively, and ranks among the best SiO_x-based anode materials. The outstanding electrochemical performance can be ascribed to the following reasons: (1) its hollow structure makes the Li⁺ transportation length decreased. (2) The existing nanopores facilitate the Li⁺ insertion/desertion and accommodate the volume variation. (3) The nitrogen-doped partial graphitization carbon enhances the electrical conductivity and promotes the formation of stable solid electrolyte interface layers during the repetitive Li⁺ intercalation/extraction process.

Advances in the synthesis and design of nanostructured materials by aerosol spray processes for efficient energy storage

The increasing demand for energy storage has motivated the search for highly efficient electrode materials for use in rechargeable batteries with enhanced energy density and longer cycle life. One of the most promising strategies for achieving improved battery performance is altering the architecture of nanostructured materials employed as electrode materials in the energy storage field. Among numerous synthetic methods suggested for the fabrication of nanostructured materials, aerosol spray techniques such as spray pyrolysis, spray drying, and flame spray pyrolysis are reliable, as they are facile, cost-effective, and continuous processes that enable the synthesis of nanostructured electrode materials with desired morphologies and compositions with controlled stoichiometry. The post-treatment of spray-processed powders enables the fabrication of oxide, sulfide, and selenide nanostructures hybridized with carbonaceous materials including amorphous carbon, reduced graphene oxide, carbon nanotubes, etc. In this article, recent progress in the synthesis of nanostructured electrode materials by spray processes and their general formation mechanisms are discussed in detail. A brief introduction to the working principles of each spray process is given first, and synthetic strategies for the design of electrode materials for lithium-ion, sodium-ion, lithium-sulfur, lithium-selenium, and lithium-oxygen batteries are discussed along with some examples. This analysis sheds light on the synthesis of nanostructured materials by spray processes and paves the way toward the design of other novel and advanced nanostructured materials for high performance electrodes in rechargeable batteries of the future.

Integration of Graphite and Silicon Anodes for the Commercialization of High-Energy Lithium-Ion Batteries

Silicon is considered a most promising anode material for overcoming the theoretical capacity limit of carbonaceous anodes. The use of nanomethods has led to significant progress being made with Si anodes to address the severe volume change during (de)lithiation. However, less progress has been made in the practical application of Si anodes in commercial lithium-ion batteries (LIBs). The drastic increase in the energy demands of diverse industries has led to the co-utilization of Si and graphite resurfacing as a commercially viable method for realizing high energy. Herein, we highlight the necessity for the co-utilization of graphite and Si for commercialization and discuss the development of graphite/Si anodes. Representative Si anodes used in graphite-blended electrodes are covered and a variety of strategies for building graphite/Si composites are organized according to their synthetic methods. The criteria for the co-utilization of graphite and Si are systematically presented. Finally, we provide suggestions for the commercialization of graphite/Si combinations.

Inorganic Gel-Derived Metallic Frameworks Enabling High-Performance Silicon Anodes

Metallic matrix materials have emerged as an ideal platform to hybridize with next-generation electrode materials such as silicon for practical applications in Li-ion batteries. However, these metallic species commonly exist in the form of isolated particles, failing to provide enough free space for silicon volume changes as well as continuous charge transport pathways. Herein, three-dimensional (3D) metallic frameworks with interconnected pore channels and conductive skeletons, have been synthesized from inorganic gel precursors as buffering/conducting matrices to boost lithium storage performance of silicon anodes. As a proof-of-concept demonstration, commercial Si particles are in situ immobilized within the Sn-Ni alloy framework via a facile gel-reduction route, and the rearrangement of Si particles during cycling increases the dispersity of Si in the Sn-Ni framework as well as their synergic effects toward lithium storage. The Si@Sn-Ni all-metallic framework manifests high structural integrity, 3D Li⁺/e^- mixed conduction pathway, and synergic effects of interfacial bonding and concurrent reaction dynamics between active Si and Sn, enabling long-term cycle life (1205 mA h g^-1 after 100 cycles at 0.5 A g^-1) and superior rate capability (653 mA h g^-1 at 10 A g^-1).

Fabrication of Lamellar Nanosphere Structure for Effective Stress-Management in Large-Volume-Variation Anodes of High-Energy Lithium-Ion Batteries

The use of high-capacity anode materials to overcome the energy density limits imposed by the utilization of low-theoretical-capacity conventional graphite has recently drawn increased attention. Until now, stress management (including strategies relying on size, surface coating, and free volume control) has been achieved by addressing the critical problems originating from significant anode volume expansion upon lithiation. However, commercially viable alternatives to graphite have not yet been found. A new stress-management strategy relying on the use of a lamellar nanosphere Si anode is proposed. Specifically, nanospheres comprising ≈50 nm Si nanoparticles encapsulated by SiO_x /Si/SiO_x /C layers with thicknesses of <20 nm per layer are synthesized via one-pot chemical vapor deposition in various atmospheres. SiO_x is found to act as a stress management interlayer when it is located between Si and mitigates stress intensification on the surface layer, allowing nanospheres to maintain their morphological integrity and promoting the formation of a stable solid electrolyte interphase layer during cycling. When tested using an industrial protocol, a full cell comprising a nanosphere/graphite blended anode and a lithium cobalt oxide cathode achieve an average energy density of 2440.2 Wh L^-1 (1.72 times higher than that of conventional graphite) with a capacity retention ratio of 80% after 101 cycles.

Electrode Design from "Internal" to "External" for High Stability Silicon Anodes in Lithium-Ion Batteries

Building a stable electrode structure is an effective way to promote the practical applications of Si anode, which has large volume changes during charge/discharge process, in lithium-ion batteries. Herein, we fabricated an integrated electrode structure reinforced from "internal" to "external" to boost the performance of Si nanoparticles (NPs). The electrode contains the conductive polymer of poly(3,4-ethylene dioxythiophene):poly(styrenesulphonic acid) (PEDOT:PSS) as the binder, reduced graphene oxide (rGO), and hydroxylated Si NPs, which help form the "internal" interaction between them through the hydrogen bonding, while the "external" malleable network built by the flexible polymers and two-dimensional rGO sheets as the framework endows the highly flexible network to accommodate the Si expansion and forms long-range conductive network. Thus, the built-integrated electrode by the simple casting method shows high capacity, good rate performance, and long cycling stability. It is noted that such an electrode shows a high areal capacity of 3.29 mA h cm^-2 and a high volumetric capacity of 3290 A h cm^-3 at 0.09 mA cm^-2. The integrated electrode design is promising to promote the practical use of Si anodes and can be extended to other noncarbon anodes with large volume changes.

Nanocrystal Conversion-Assisted Design of Sn-Fe Alloy with a Core-Shell Structure as High-Performance Anodes for Lithium-Ion Batteries

Sn-based alloy materials are strong candidates to replace graphitic carbon as the anode for the next generation lithium-ion batteries because of their much higher gravimetric and volumetric capacity. A series of nanosize Sn _y Fe alloys derived from the chemical transformation of preformed Sn nanoparticles as templates have been synthesized and characterized. An optimized Sn₅Fe/Sn₂Fe anode with a core-shell structure delivered 541 mAh·g^-1 after 200 cycles at the C/2 rate, retaining close to 100% of the initial capacity. Its volumetric capacity is double that of commercial graphitic carbon. It also has an excellent rate performance, delivering 94.8, 84.3, 72.1, and 58.2% of the 0.1 C capacity (679.8 mAh/g) at 0.2, 0.5, 1 and 2 C, respectively. The capacity is recovered upon lowering the rate. The exceptional cycling/rate capability and higher gravimetric/volumetric capacity make the Sn _y Fe alloy a potential candidate as the anode in lithium-ion batteries. The understanding of Sn _y Fe alloys from this work also provides insight for designing other Sn-M (M = Co, Ni, Cu, Mn, etc.) system.

In-Situ Synthesized Si@C Materials for the Lithium Ion Battery: A Mini Review

As an important component, the anode determines the property and development of lithium ion batteries. The synthetic method and the structure design of the negative electrode materials play decisive roles in improving the property of the thus-assembled batteries. Si@C compound materials have been widely used based on their excellent lithium ion intercalation capacity and cyclic stability, in which the in-situ synthetic method can make full use of the structural advantages of the monomer itself, thus improving the electrochemical performance of the anode material. In this paper, the different preparation technologies and composite structures of Si@C compound materials by in-situ synthesis are introduced. The research progress of Si@C compound materials by in-situ synthesis is reviewed, and the prospect of future development of Si@C compound materials has been tentatively commented.

MXene/Si@SiO x@C Layer-by-Layer Superstructure with Autoadjustable Function for Superior Stable Lithium Storage

Despite its very high capacity (4200 mAh g^-1), the widespread application of the silicon anode is still hampered by severe volume changes (up to 300%) during cycling, which results in electrical contact loss and thus dramatic capacity fading with poor cycle life. To address this challenge, 3D advanced Mxene/Si-based superstructures including MXene matrix, silicon, SiO _x layer, and nitrogen-doped carbon (MXene/Si@SiO _x@C) in a layer-by-layer manner were rationally designed and fabricated for boosting lithium-ion batteries (LIBs). The MXene/Si@SiO _x@C anode takes the advantages of high Li⁺ ion capacity offered by Si, mechanical stability by the synergistic effect of SiO _x, MXene, and N-doped carbon coating, and excellent structural stability by forming a strong Ti-N bond among the layers. Such an interesting superstructure boosts the lithium storage performance (390 mAh g^-1 with 99.9% Coulombic efficiency and 76.4% capacity retention after 1000 cycles at 10 C) and effectively suppresses electrode swelling only to 12% with no noticeable fracture or pulverization after long-term cycling. Furthermore, a soft package full LIB with MXene/Si@SiO _x@C anode and Li[Ni_0.6Co_0.2Mn_0.2]O₂ (NCM622) cathode was demonstrated, which delivers a stable capacity of 171 mAh g^-1 at 0.2 C, a promising energy density of 485 Wh kg^-1 based on positive active material, as well as good cycling stability for 200 cycles even after bending. The present MXene/Si@SiO _x@C becomes among the best Si-based anode materials for LIBs.

Advances in nanostructures fabricated via spray pyrolysis and their applications in energy storage and conversion

This review provides insight into various nanostructures designed by spray pyrolysis and their applications in energy storage and conversion.

Modified SiO hierarchical structure materials with improved initial coulombic efficiency for advanced lithium-ion battery anodes

Silicon-based anode materials are indispensable components in developing high energy density lithium-ion batteries, yet their practical application still faces great challenges, such as large volume change during the lithiation and delithiation process that causes the pulverization of silicon particles, and continuous formation and reformation of the solid electrolyte interfaces (SEI) which results in a low initial coulombic efficiency. As an endeavor to address these problems, in this study, Si/SiO/Li₂SiO₃@C structures were prepared via a facile method using SiO, pitch powder and Li₂CO₃/PVA solution followed by annealing treatment. The Si/SiO/Li₂SiO₃@C composite shows a great improvement in lithium storage where a high discharge capacity of 1645.47 mA h g⁻¹ was delivered with the 1^st C.E. of 69.05% at 100 mA g⁻¹. These results indicate that the designed method of integrating prelithiation and carbon coating for SiO and the as-prepared macro scale Si/SiO/Li₂SiO₃@C structures are practical for implementation in lithium-ion battery technology.

A simple method of prelithiation of SiO along with carbon coating to achieve high performance SiO-based materials.

Si nanoparticles embedded in 3D carbon framework constructed by sulfur-doped carbon fibers and graphene for anode in lithium-ion battery

3D conductive network constructed with sulfur doped nanofibers and graphene that co-enhance the lithium storage property of the Si anode.

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.

Multiscale Engineered Si/SiO x Nanocomposite Electrodes for Lithium-Ion Batteries Using Layer-by-Layer Spray Deposition

Si-based high-capacity materials have gained much attention as an alternative to graphite in Li-ion battery anodes. Although Si additions to graphite anodes are now commercialized, the fraction of Si that can be usefully exploited is restricted due to its poor cyclability arising from the large volume changes during charge/discharge. Si/SiO _x nanocomposites have also shown promising behavior, such as better capacity retention than Si alone because the amorphous SiO _x helps to accommodate the volume changes of the Si. Here, we demonstrate a new electrode architecture for further advancing the performance of Si/SiO _x nanocomposite anodes using a scalable layer-by-layer atomization spray deposition technique. We show that particulate C interlayers between the current collector and the Si/SiO _x layer and between the separator and the Si/SiO _x layer improved electrical contact and reduced irreversible pulverization of the Si/SiO _x significantly. Overall, the multiscale approach based on microstructuring at the electrode level combined with nanoengineering at the material level improved the capacity, rate capability, and cycling stability compared to that of an anode comprising a random mixture of the same materials.

A Kind of Coordination Complex Cement for the Self-Assembly of Superstructure

Not like the macroscopic building materials, the controllable assembly of blocks into superstructure has not been conquered in microscale, especially for the ordinary particles with shape defects and weak surface activities. Here, a facile route of assembling particles into superstructures utilizing Mo-polydopamine complex as the binder and curing agent is established. A side-by-side adsorption and growth mechanism in a water/ethanol system is derived, and the factors influencing the final structures are verified. This system is suitable to assemble superstructures from particles of different shapes such as nanospheres, nanocubes, nanorods, and hollow spheres in the range from 10 to 500 nm in size. And after high temperature and etching treatment, the generated MoO₂/N/C frameworks with superpore structures derived from different blocks exhibit a high structural plasticity and potential application as multifunctional carriers for energy storage. Rather than the obtained system, our work assembles superstructures from various building blocks and explores more valuable complex cements for superstructures construction.