Hierarchically designed SiOx/SiOy bilayer nanomembranes as stable anodes for lithium ion batteries

Stress-Relieving Carboxylated Polythiophene/Single-Walled Carbon Nanotube Conductive Layer for Stable Silicon Microparticle Anodes in Lithium-Ion Batteries

Stress-relieving and electrically conductive single-walled carbon nanotubes (SWNTs) and conjugated polymer, poly[3-(potassium-4-butanoate)thiophene] (PPBT), wrapped silicon microparticles (Si MPs) have been developed as a composite active material to overcome technical challenges such as intrinsically low electrical conductivity, low initial Coulombic efficiency, and stress-induced fracture due to severe volume changes of Si-based anodes for lithium-ion batteries (LIBs). The PPBT/SWNT protective layer surrounding the surface of the microparticles physically limits volume changes and inhibits continuous solid electrolyte interphase (SEI) layer formation that leads to severe pulverization and capacity loss during cycling, thereby maintaining electrode integrity. PPBT/SWNT-coated Si MP anodes exhibited high initial Coulombic efficiency (85%) and stable capacity retention (0.027% decay per cycle) with a reversible capacity of 1894 mA h g-1 after 300 cycles at a current density of 2 A g-1, 3.3 times higher than pristine Si MP anodes. The stress relaxation and underlying mechanism associated with the incorporation of the PPBT/SWNT layer were interpreted by quasi-deterministic and quantitative stress analyses of SWNTs through in situ Raman spectroscopy. PPBT/SWNT@Si MP anodes can maintain reversible stress recovery and 45% less variation in tensile stress compared with SWNT@Si MP anodes during cycling. The results verify the benefits of stress relaxation via a protective capping layer and present an efficient strategy to achieve long cycle life for Si-based anodes for next-generation LIBs.

A Brief Overview of Silicon Nanoparticles as Anode Material: A Transition from Lithium-Ion to Sodium-Ion Batteries

The successful utilization of silicon nanoparticles (Si-NPs) to enhance the performance of Li-ion batteries (LIBs) has demonstrated their potential as high-capacity anode materials for next-generation LIBs. Additionally, the availability and relatively low cost of sodium resources have a significant influence on developing Na-ion batteries (SIBs). Despite the unique properties of Si-NPs as SIBs anode material, limited study has been conducted on their application in these batteries. However, the knowledge gained from using Si-NPs in LIBs can be applied to develop Si-based anodes in SIBs by employing similar strategies to overcome their drawbacks. In this review, a brief history of Si-NPs' usage in LIBs is provided and discuss the strategies employed to overcome the challenges, aiming to inspire and offer valuable insights to guide future research endeavors.

In Situ Hydrogel Polymerization to Form a Flexible Polysaccharide Synergetic Binder Network for Stabilizing SiOx/C Anodes

Today, the commercial application of silicon oxides (SiOx, 1 < x < 2) in lithium-ion batteries (LIBs) still faces the challenge of rapid performance degradation. In this work, by integrating hydrothermal and physicomechanical processes, water-soluble locust bean gum (LBG) and xanthan gum (XG) are utilized to in situ form an LBG@XG binder network to improve the performance of SiOx/C anodes. As a synergy of LBG and XG polysaccharides in hydrogel polymerization, LBG@XG can tightly wrap around SiOx/C particles to prevent plate damage. The flexible SiOx/C anode with the LBG@XG binder exhibits capacity retentions of 74.1% and 76.4% after 1000 cycles at 0.5 A g-1 and 1 A g-1, respectively. The full battery capacity remains stable for 100 cycles at 1 C and the rate performance is excellent (103 mAh g-1 at 3 C). This LBG@XG is demonstrated to be highly electronegative and has a strong attraction to SiOx/C particles, thereby reducing the expansion and increasing the stability of the SiOx/C anodes when coupled with the flexible binder network. In addition to the promising LBG@XG binder, this work also provides a research idea for developing green water-based binders suitable for application in the SiOx/C anodes of LIBs.

Silicon Cutting Waste Derived Silicon Nanosheets with Adjustable Native SiO2 Shell for Highly-Stable Lithiation/Delithiation

Silicon is an excellent candidate for the next generation of ultra-high performance anode materials, with the rapid iteration of the lithium-ion battery industry. High-quality silicon sources are the cornerstone of the development of silicon anodes, and silicon cutting waste (SCW) is one of them while still faces the problems of poor performance and unclear structure-activity relationship. Herein, a simple, efficient, and inexpensive purification method is implemented to reduce impurities in SCW and expose the morphology of nanosheets therein. Furthermore, HF is used to modulate the abundant native O in SCW after thermodynamic and kinetic considerations, realizing the mechanical support for the internal Si in the form of an amorphous SiO₂ shell. Afterward, SCNS@SiO₂ -2.5 with a 1.0 nm thick SiO₂ shell exhibits a reversible capacity of 1583.3 mAh g^-1 after 200 cycles at 0.8 A g^-1 . Ultimately, the molecular dynamics simulations profoundly reveal that the amorphous SiO₂ shell is transformed into the extremely ductile Li_x SiO_y shell to ditch stress and relieve strain during the lithiation/delithiation process.

Silver boosts ultra-long cycle life for metal sulfide lithium-ion battery anodes: Taking AgSbS2 nanowires as an example

Metal sulfide, being a high-capacity anode material, is a promising anode material for rechargeable lithium-ion batteries (LIBs). However, most research efforts have focused on improving their low cycling performance due to multiple combined factors, including low conductivity, huge volume changes, multi-step conversion/alloying reactions, and redox shuttling effect, during the cycling process. Here, we report that by using AgSbS₂ nanowires as LIB anode materials, a record-breaking long cycle life metal sulfide anode has been achieved through the silver synergistic electrochemical performance effect. We found that while the AgSbS₂ nanowire anode is cycled, Ag precipitated out to form a nanocrystal tightly connected with Sb and S and plays a key role in highly-reversible electrochemical performance. Ag can effectively enhance the electrode conductivity, increase ion diffusion rate, serve a diluent huge volume changes during conversion-alloying reactions, improve the absorbability and catalytic ability towards LiPSs to reduce shutting effect of sulfur, and enhanced Li⁺ adsorption. As a result, AgSbS₂ nanowire anodes maintain 90% capacity retention over 5000 and 7000 cycles at the current densities of 500 mA g^-1 and 2000 mA g^-1, respectively, whereas the capacities of Sb₂S₃ nanowire and Sb₂S₃/C nanowire anodes drop rapidly within 10 cycles. The ultra-stable cycle life is superior to the state-of-the-art metal sulfide anodes. Finally, using AgSbS₂ nanowires as the anode combined with the cathode LiNi₅Co₃Mn₂, a full battery after 480 cycles was assembled to verify that its stability (high retention rate of 99.5%) can be used in the current commercial battery architecture. This work solves multiple problems related to shuttling effects and complex reactions of metal sulfide anodes, and provides important progress for the future development of metal sulfide anodes for LIBs.

Realizing Sub-5 nm Red Phosphorus Dispersion in a SiOx/C Matrix for Enhanced Lithium Storage

With high capacity and suitable working plateau, silicon oxide (SiOx) has become a promising lithium-ion battery (LIB) anode material. However, bare SiOx usually suffers from sluggish electron transport and unsatisfactory cyclability. Composting SiOx with a second phase has become an efficient strategy to tackle the current drawbacks. Herein, a P/SiOx/C ternary composite, featuring sub-5 nm red phosphorus (P) clusters uniformly dispersed in a dense SiOx/C matrix has been constructed through an "inside-out" synthesis strategy. The nanosizing of bulk red P sealed in an organosilica matrix is realized by the high-temperature treatment-driven sublimation/diffusion. With the red P amount of ∼7.53 wt %, the P/SiOx/C ternary composite provides a stable discharge capacity of ∼950 mAh g-1 and also manifests a decent rate capability (510 mAh g-1 at 5 A g-1). This study affords a ternary compositing strategy for designing SiOx-based anode materials with desirable electrochemical performance for the next-generation LIBs.

Constructing the Single-Phase Nanotubes with Uniform Dispersion of SiOx and Carbon as Stable Anodes for Lithium-Ion Batteries

SiOx is an attractive anode material for lithium-ion batteries due to its considerable capacity. However, its obvious volume expansion and low conductivity result in poor electrochemical performance. Herein, a novel single-phase nanotube structure with uniform distribution of nanoscale SiOx units and amorphous carbon matrix was fabricated. The hollow nanotube and homogeneously distributed ultrafine SiOx units greatly alleviate volume changes. The amorphous carbon facilitates electron transport throughout the network and offers a buffer to further reduce the volume expansion of SiOx. Benefiting from this unique structure, as-prepared single-phase SiOx/C NTs demonstrate excellent durability and rate capability. Specifically, it delivers a high reversible specific capacity (713 mAh g^-1 at 0.1 A g^-1 after 200 cycles); negligible capacity decay is confirmed after 500 cycles at high density current (544 mAh g^-1 at 1 A g^-1 after 500 cycles).

Flexible Sb-graphene-carbon nanofibers as binder-free anodes for potassium-ion batteries with enhanced properties

Potassium-ion batteries (KIBs) are emerging as attractive alternatives to lithium-ion batteries for the large scale energy storage and conversion systems, in view of the natural abundance and low cost of potassium resources. However, the lack of applicable anodes for reversible accommodation to the large K⁺ limits the application of KIBs. Herein, porous Sb-graphene-carbon (Sb-G-C) nanofibers are fabricated via a scalable and facile electrospinning approach. As an attempt, the nanofibers weaving into flexible mats are introduced as binder-free anode materials of KIBs, presenting a great cycle life (204.95 mAh g^-1 after 100 cycles at 100 mA g^-1), as well as the excellent rate capability (120.83 mAh g^-1 at 1 A g^-1). The superior performances of the Sb-G-C anodes can be derived from the dispersed graphene, which offers enhanced tolerance to the volume change and promotes the electron transportation, accounting for the outstanding cyclability and rate capability. Furthermore, the extrinsic pseudocapacitance created from the 1D porous nanostructure of the Sb-G-C also boosts the K⁺ storage capacity. The presented results may pave a new pathway for future high-performance KIBs.

Crack-Free Silicon Monoxide as Anodes for Lithium-Ion Batteries

The volume expansion of Si and SiO particles was investigated using a single-particle battery assembled with a focused ion beam and scanning electron microscopy (FIB-SEM) system. Single Si and SiO particles were galvanostatically charged and discharged as in real batteries. Microstructural changes of the particles were monitored in situ using FIB-SEM from two different angles. The results revealed that the volume expansion of micrometer size particle SiO was not only much smaller than that of Si, but it also kept its original shape with no sign of cracks. This isotropic mechanical property of a SiO particle can be attributed to its microstructure: nanosized Si domains mixed with SiO₂ domains. The nanosized Si domains can mitigate the anisotropic swelling caused by the orientation-dependent lithium-ion insertion; the surrounding SiO₂ domains can act as a buffer to further constrain the localized anisotropic swelling.

Micron-sized SiO x /N-doped carbon composite spheres fabricated with biomass chitosan for high-performance lithium-ion battery anodes

To achieve superior lithium storage performance, SiO x is usually designed into nanostructured SiO x /C composites by complex or expensive methods. Here, micron-sized interconnected SiO x /N-doped carbon (NC) microspheres composed of evenly dispersed SiO x nano-domains and NC have been fabricated by a scalable microemulsion method and following pyrolysis, using vinyltriethoxysilane and chitosan as precursors. The unique structure of the micron-sized SiO x /NC spheres leads to enhanced structural integrity and enables stable long-term cycling (800 cycles at 2 A g-1). Benefiting from the enhanced electron/Li+ diffusion kinetics originated from the unique structure and N-doping, SiO x /NC-2 presents considerable capacitive-controlled Li storage capacity, which leads to outstanding rate capability. Consequently, the assembled SiO x /NC-2//LiFePO4 full cell exhibits superior rate capability (106 mA h g-1 at 4C) and stable long-term cycling at 2C (102 mA h g-1 after 350 cycles). This work opens a new door for the application of chitosan in building micron-sized high-performance SiO x /C anode materials, and to some extent facilitates the recycling of waste seafood shells.

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

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

Two-Dimensional Black Phosphorus Nanomaterials: Emerging Advances in Electrochemical Energy Storage Science

Two-dimensional black phosphorus (2D BP), well known as phosphorene, has triggered tremendous attention since the first discovery in 2014. The unique puckered monolayer structure endows 2D BP intriguing properties, which facilitate its potential applications in various fields, such as catalyst, energy storage, sensor, etc. Owing to the large surface area, good electric conductivity, and high theoretical specific capacity, 2D BP has been widely studied as electrode materials and significantly enhanced the performance of energy storage devices. With the rapid development of energy storage devices based on 2D BP, a timely review on this topic is in demand to further extend the application of 2D BP in energy storage. In this review, recent advances in experimental and theoretical development of 2D BP are presented along with its structures, properties, and synthetic methods. Particularly, their emerging applications in electrochemical energy storage, including Li-/K-/Mg-/Na-ion, Li-S batteries, and supercapacitors, are systematically summarized with milestones as well as the challenges. Benefited from the fast-growing dynamic investigation of 2D BP, some possible improvements and constructive perspectives are provided to guide the design of 2D BP-based energy storage devices with high performance.

Stress-Actuated Spiral Microelectrode for High-Performance Lithium-Ion Microbatteries

Miniaturization of batteries lags behind the success of modern electronic devices. Neither the device volume nor the energy density of microbatteries meets the requirement of microscale electronic devices. The main limitation for pushing the energy density of microbatteries arises from the low mass loading of active materials. However, merely pushing the mass loading through increased electrode thickness is accompanied by the long charge transfer pathway and inferior mechanical properties for long-term operation. Here, a new spiral microelectrode upon stress-actuation accomplishes high mass loading but short charge transfer pathways. At a small footprint area of around 1 mm² , a 21-fold increase of the mass loading is achieved while featuring fast charge transfer at the nanoscale. The spiral microelectrode delivers a maximum area capacity of 1053 µAh cm^-2 with a retention of 67% over 50 cycles. Moreover, the energy density of the cylinder microbattery using the spiral microelectrode as the anode reaches 12.6 mWh cm^-3 at an ultrasmall volume of 3 mm³ . In terms of the device volume and energy density, the cylinder microbattery outperforms most of the current microbattery technologies, and hence provides a new strategy to develop high-performance microbatteries that can be integrated with miniaturized electronic devices.

Simplified Synthesis of Biomass-Derived Si/C Composites as Stable Anode Materials for Lithium-Ion Batteries

Synthesis of silicon/carbon (Si/C) composites from biomass resources could enable the effective utilization of agricultural products in the battery industry with economical as well as environmental benefits. Herein, a simplified process was developed to synthesize Si/C from biomass, by using a low-cost agricultural byproduct "rice husk (RH)" as a model. This process includes the calcination of RH for SiO₂ /C and the reduction of SiO₂ /C by Al in molten salts at a moderate temperature. This process does not need the removal of carbon before thermal reduction of SiO₂ , which is thought to be necessary to avoid the formation of SiC at elevated temperatures. Thus, carbon derived from biomass can be directly used for Si/C composites for anode materials. The resultant Si/C shows a high reversible capacity of 1309 mAh g^-1 and long cycle life (300 cycles). This research advocates a new and simplified strategy for the synthesis of RH-based biomass-derived Si/C, which is beneficial for low-cost, environmentally friendly, and green energy storage applications.

Laser-Induced Silicon Oxide for Anode-Free Lithium Metal Batteries

The development of a rechargeable Li metal anode (LMA) is an important milestone for improved battery technology. Practical issues hindering LMAs are the formation of Li dendrites and inactive Li during plating and stripping processes, which can cause short circuits, thermal runaway, and low coulombic efficiency (CE). Here, the use of a laser-induced silicon oxide (LI-SiO_x ) layer derived from a commercial adhesive tape to improve the reversibility of Li metal batteries (LMBs) is studied. The silicone-based adhesive of the tape is converted by a commercial infrared laser into a homogeneous porous SiO_x layer deposited directly over the current collector. The coating results in superior performance by suppressing the formation of Li dendrites and inactive Li and presenting higher average CE of 99.3% (2.0 mAh cm^-2 at 2.0 mA cm^-2 ) compared to bare electrodes. The thickness and morphology of the deposited Li is investigated, revealing a different mechanism of Li deposition on coated electrodes. The laser coating affords a method that is fast and avoids the use of toxic organic solvents and extensive drying times. The improved performance with the SiO_x coating is demonstrated in LMB with a zero-excess ("anode-free") configuration where a 100% improved performance is verified.

MOF-derived hollow SiOx nanoparticles wrapped in 3D porous nitrogen-doped graphene aerogel and their superior performance as the anode for lithium-ion batteries

A nanocomposite anode material consisting of metal-organic framework (MOF)-derived hollow SiOx nanoparticles wrapped in three dimensional (3D) nitrogen-doped graphene aerogel (N-GA) has been fabricated through a facile three-step approach, involving MOF-template inducting, self-assembly and nitrogen-doping, freeze-drying and thermal treatment process. The hollow SiOx nanoparticles with an average size of 100-160 nm are distributed on 3D N-GA. Such nanocomposites possess a 3D porous structure with a BET surface area as high as 426.3 m2 g-1. In this nanostructure, the N-GA's property of interconnected porous network enables it to provide pathways for rapid electron transfer and Li+ transport, while the MOF-derived hollow SiOx nanoparticles with void space can accommodate the volume change during a lithiation/delithiation process. As a result, high rate capability (675 mA h g-1 under 50 C) as well as long-life cycling stability (1233.2 mA h g-1 under 10 C, 86% capacity retention over 500 cycles) is achieved.

Collaborative Design of Hollow Nanocubes, In Situ Cross-Linked Binder, and Amorphous Void@SiOx @C as a Three-Pronged Strategy for Ultrastable Lithium Storage

Although silicon-based materials are ideal candidate anodes for high energy density lithium-ion batteries, the large volumetric expansion seriously damages the integrity of the electrodes and impedes commercial processes. Reasonable electrode design based on adjustable structures of silicon and strong binders prepared by a facile method is still a great challenge. Herein, a three-pronged collaborative strategy via hollow nanocubes, amorphous Void@SiO_x @C, and in situ cross-linked polyacrylic acid and d-sorbitol 3D network binder (c-PAA-DS) is adopted to maintain structural/electrode integrality and stability. The all-integrated c-PAA-DS/Void@SiO_x @C electrode delivers excellent mechanical property, which is attributed to ductility of the c-PAA-DS binder and high adhesion energy between Void@SiO_x @C and c-PAA-DS calculated by density functional theory. Benefiting from the synergistic effect of accommodation of the hollow structure, protection of outer carbon shell, amorphous Void@SiO_x @C, and strong adhesive c-PAA-DS binder, c-PAA-DS/Void@SiO_x @C shows excellent electrochemical performance. Long cycling stability with a reversible capacity of 696 mAh g^-1 is obtained, as well as tiny capacity decay after 500 cycles at 0.5 A g^-1 and high-rate performance. The prelithiated Void@SiO_x @C||LiNi_0.5 Co_0.2 Mn_0.3 O₂ (NCM523) full cell is also assembled and shows a reversible capacity of 157 mAh g^-1 at 0.5 C, delivering an excellent capacity retention of 94% after 160 cycles.

Coupling of a conductive Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2 metal-organic framework with silicon nanoparticles for use in high-capacity lithium-ion batteries

A composite of Si nanoparticles (SiNPs) and a two-dimensional (2D) porous conductive Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2 (Ni3(HITP)2) metal-organic framework (MOF), namely Si/Ni3(HITP)2, is suggested as a potential anode material for Li-ion batteries (LIBs). The Ni3(HITP)2 MOF with a carbon backbone and evenly dispersed Ni and N heteroatoms showed high potential for mitigating the volume expansion of Si and enhancing the electronic conductivity as well as Li storage ability of the Si/Ni3(HITP)2 anode. The Si/Ni3(HITP)2 electrode delivered a reversible capacity of 2657 mA h g-1 after 100 cycles of discharge-charge at a rate of 0.1C. Moreover, at a high rate of 1C, the Si/Ni3(HITP)2 electrode maintained a reversible capacity of 876 mA h g-1 even after 1000 cycles. The different rate capacities were 1655, 1129, and 721 mA h g-1 at 5C, 10C and 20C, respectively. The excellent electrochemical performance of the Si/Ni3(HITP)2 electrode in terms of improved cycle life and rate capability results from the open channels of the MOF network, which are beneficial for the movement of Li+ ions through the electrolyte to the electrode and the mitigation of stress by volume expansion of Si. We believe that the coupling of conductive Ni3(HITP)2 with Si is a potential way to make an anode for high-performance LIBs.

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.

Si/a-C Nanocomposites with a Multiple Buffer Structure via One-Step Magnetron Sputtering for Ultrahigh-Stability Lithium-Ion Battery Anodes

Large volume expansion and serious pulverization of silicon are two major challenges for Si-based anode batteries. Herein, a high-mass-load (3.0 g cm^-3) silicon-doped amorphous carbon (Si/a-C) nanocomposite with a hierarchical buffer structure is prepared by one-step magnetron sputtering. The uniform mixing of silicon and carbon is realized on the several-nanometer scale by cosputter deposition of silicon and carbon. The boundary of the primary particles, made up of nanocarbon and nanosilicon, and the boundary of the secondary particles aggregated by the primary particles can provide accommodation space for the volume expansion of silicon and effectively buffer the volume expansion of silicon. Meanwhile, the continuous and uniformly distributed amorphous carbon enhances the conductivity of the Si/a-C nanocomposites. Typically, the 20% Si/a-C cell shows a superior initial discharge capacity of 845.3 mAh g^-1 and achieves excellent cycle performance of up to 1000 cycles (609.4 mAh g^-1) at the current density of 1 A g^-1. Furthermore, the 20% Si/a-C cell exhibits a high capacity of 602.8 mAh g^-1 with the stable discharge/charge rate performance in several extreme conditions (-40-70 °C). In view of the validity and mass productivity of the magnetron sputtering, a potential route for the industrial preparation of the Si/a-C anode nanocomposites is therefore highlighted by this study.

Metal-Organic Frameworks-Derived Mesoporous Si/SiOx @NC Nanospheres as a Long-Lifespan Anode Material for Lithium-Ion Batteries

Silicon (Si)-based anode materials with suitable engineered nanostructures generally have improved lithium storage capabilities, which provide great promise for the electrochemical performance in lithium-ion batteries (LIBs). Herein, a metal-organic framework (MOF)-derived unique core-shell Si/SiO_x @NC structure has been synthesized by a facile magnesio-thermic reduction, in which the Si and SiO_x matrix were encapsulated by nitrogen (N)-doped carbon. Importantly, the well-designed nanostructure has enough space to accommodate the volume change during the lithiation/delithiation process. The conductive porous N-doped carbon was optimized through direct carbonization and reduction of SiO₂ into Si/SiO_x simultaneously. Benefiting from the core-shell structure, the synthesized product exhibited enhanced electrochemical performance as an anode material in LIBs. Particularly, the Si/SiO_x @NC-650 anode showed the best reversible capacities up to 724 and 702 mAh g^-1 even after 100 cycles. The excellent cycling stability of Si/SiO_x @NC-650 may be attributed to the core-shell structure as well as the synergistic effect between the Si/SiO_x and MOF-derived N-doped carbon.

Green Synthesis of Dual Carbon Conductive Network-Encapsulated Hollow SiO x Spheres for Superior Lithium-Ion Batteries

Designing hollow/porous structure is regarded as an effective approach to address the dramatic volumetric variation issue for Si-based anode materials in Li-ion batteries (LIBs). Pioneer studies mainly focused on acid/alkali etching to create hollow/porous structures, which are, however, highly corrosive and may lead to a complicated synthetic process. In this paper, a dual carbon conductive network-encapsulated hollow SiO _x (DC-HSiO _x) is fabricated through a green route, where polyacrylic acid is adopted as an eco-friendly soft template. Low electrical resistance and integrated electrode structure can be maintained during cycles because of the dual carbon conductive networks distributed both on the surface of single particles formed by amorphous carbon and among particles constructed by reduced graphene oxide. Importantly, the hollow space is reserved within SiO _x spheres to accommodate the huge volumetric variation and shorten the transport pathway of Li⁺ ions. As a result, the DC-HSiO _x composite delivers a large reversible capacity of 1113 mA h g^-1 at 0.1 A g^-1, an excellent cycling performance up to 300 cycles with a capacity retention of 92.5% at 0.5 A g^-1, and a good rate capability. Furthermore, the DC-HSiO _x//LiNi_0.8Co_0.1Mn_0.1O₂ full cell exhibits high energy density (419 W h kg^-1) and superior cycling performance. These results render an opportunity for the unique DC-HSiO _x composite as a potential anode material for use in high-performance LIBs.

Construction of 3D carbon networks with well-dispersed SiO x nanodomains from gelable building blocks for lithium-ion batteries

Nonstoichiometric silicon oxide (SiO x ) with high theoretical capacity is a promising anode material for lithium-ion batteries (LIBs). However, volume changes and poor electronic conductivity of SiO x are major impediments to its practical application. The modification of SiO x with carbonaceous materials to accommodate volume variations and improve conductivity is a valuable strategy. Nanonetwork-structured (NNS) carbons have been paid great attention because of their unique three-dimensional structure, and high electronic and ionic conductivity. Incorporating SiO x with well-designed NNS carbons is a promising method to prepare high quality electrode materials for lithium-ion batteries. In this work, a fabrication approach is developed to synthesize a 3D carbon network composed of carbonaceous hybrid nanotubes with well-dispersed SiO x nanodomains (CNT@SiO x -C) from 1D gelable bottlebrushes as network building blocks based on molecular-scale interface engineering technology. Herein, nano-sized SiO x particles are embedded into the carbonaceous matrix to prevent their volume change during cycling. The experimental results indicated that the CNT@SiO x -C presents high reversible capacity, remarkable cycle life and high rate capability due to the high dispersion of nano-sized SiO x and conductive 3D carbon nanonetwork.

Silicon oxides: a promising family of anode materials for lithium-ion batteries

Silicon oxides have been recognized as a promising family of anode materials for high-energy lithium-ion batteries (LIBs) owing to their abundant reserve, low cost, environmental friendliness, easy synthesis, and high theoretical capacity. However, the extended application of silicon oxides is severely hampered by the intrinsically low conductivity, large volume change, and low initial coulombic efficiency. Significant efforts have been dedicated to tackling these challenges towards practical applications. This Review focuses on the recent advances in the synthesis and lithium storage properties of silicon oxide-based anode materials. To present the progress in a systematic manner, this review is categorized as follows: (i) SiO-based anode materials, (ii) SiO2-based anode materials, (iii) non-stoichiometric SiOx-based anode materials, and (iv) Si-O-C-based anode materials. Finally, future outlook and our personal perspectives on silicon oxide-based anode materials are presented.

3D porous carbon networks with highly dispersed SiOx by molecular-scale engineering toward stable lithium metal anodes

Benefiting from a high-porosity interconnected structure and lithiophilic SiO_x nanodomains, CNT@SiO_x–C shows great advantages as 3D hosts toward stable Li plating/stripping.

Single-Nanostructured Electrochemical Detection for Intrinsic Mechanism of Energy Storage: Progress and Prospect

Energy storage appliances are active by means of accompanying components for renewable energy resources that play a significant role in the advanced world. To further improve the electrochemical properties of the lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and lithium-sulfur (Li-S) batteries, the electrochemical detection of the intrinsic mechanisms and dynamics of electrodes in batteries is required to guide the rational design of electrodes. Thus, several researches have conducted in situ investigations and real-time observations of electrode evolution, ion diffusion pathways, and side reactions during battery operation at the nanoscale, which are proven to be extremely insightful. However, the in situ cells are required to be compatible for electrochemical tests and are therefore often challenging to operate. In the past few years, tremendous progresses have been made with novel and more advanced in situ electrochemical detection methods for mechanism studies, especially single-nanostructured electrodes. Herein, a comprehensive review of in situ techniques based on single-nanostructured electrodes for studying electrodes changes in LIBs, SIBs, and Li-S batteries, including structure evolution, phase transition, interface formation, and the ion diffusion pathway is provided, which is instructive and meaningful for the optimization of battery systems.

Hierarchical C/SiO x /TiO2 ultrathin nanobelts as anode materials for advanced lithium ion batteries

TiO₂-based nanomaterials are demonstrated to be a promising candidate for next generation lithium ion batteries due to their stable performance and easy preparation. However, their inherent low capacity impedes their wide application compared to commercial carbon nanomaterials. Here we present a unique in situ grafting-graphitization method to achieve a ternary nanocomposite of C/SiO _x /TiO₂ ultrathin nanobelts with a core-shell heterostructure. The obtained ternary nanocomposite integrates the merits of high specific capacity of SiO _x , the excellent mechanical stability of graphite-like carbon and the high reactivity of TiO₂. Cyclic voltammetric curves and cycling performance manifest the optimal ternary nanocomposite and deliver a very high initial specific capacity of ∼1196 mA h g^-1 with both good rate capability (∼200 mA h g^-1 up to 10 C) and especially enhanced cycle stability. Our work demonstrates that building hierarchical core-shell heterostructures is an effective strategy to improve capacity and cycling performance in other composite anodes for electrochemical energy storage materials.

Effect of topological patterning on self-rolling of nanomembranes

The effects of topological patterning (i.e., grating and rectangular patterns) on the self-rolling behaviors of heteroepitaxial strained nanomembranes have been systematically studied. An analytical modeling framework, validated through finite-element simulations, has been formulated to predict the resultant curvature of the patterned nanomembrane as the pattern thickness and density vary. The effectiveness of the grating pattern in regulating the rolling direction of the nanomembrane has been demonstrated and quantitatively assessed. Further to the rolling of nanomembranes, a route to achieve predictive design of helical structures has been proposed and showcased. The present study provides new knowledge and mechanistic guidance towards predictive control and tuning of roll-up nanostructures via topological patterning.

SiOx Encapsulated in Graphene Bubble Film: An Ultrastable Li-Ion Battery Anode

SiO_x is proposed as one of the most promising anodes for Li-ion batteries (LIBs) for its advantageous capacity and stable Li uptake/release electrochemistry, yet its practical application is still a big challenge. Here encapsulation of SiO_x nanoparticles into conductive graphene bubble film via a facile and scalable self-assembly in solution is shown. The SiO_x nanoparticles are closely wrapped in multilayered graphene to reconstruct a flake-graphite-like macrostructure, which promises uniform and agglomeration-free distribution of SiO_x in the carbon while ensures a high mechanical strength and a high tap density of the composite. The composites present unprecedented cycling stability and excellent rate capabilities upon Li storage, rendering an opportunity for its anode use in the next-generation high-energy 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.

High Volumetric Energy Density Hybrid Supercapacitors Based on Reduced Graphene Oxide Scrolls

The low volumetric energy density of reduced graphene oxide (rGO)-based electrodes limits its application in commercial electrochemical energy storage devices that require high-performance energy storage capacities in small volumes. The volumetric energy density of rGO-based electrode materials is very low due to their low packing density. A supercapacitor with enhanced packing density and high volumetric energy density is fabricated using doped rGO scrolls (GFNSs) as the electrode material. The restacking of rGO sheets is successfully controlled through synthesizing the doped scroll structures while increasing the packing density. The fabricated cell exhibits an ultrahigh volumetric energy density of 49.66 Wh/L with excellent cycling stability (>10 000 cycles). This unique design strategy for the electrode material has significant potential for the future supercapacitors with high volumetric energy densities.

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

Despite the high theoretical capacity, silicon (Si) anodes in lithium-ion batteries have difficulty in meeting the commercial standards in various aspects. In particular, the huge volume change of Si makes it very challenging to simultaneously achieve high initial Coulombic efficiency (ICE) and long-term cycle life. Herein, we report spray pyrolysis to prepare Si-SiO_x composite using an aqueous precursor solution containing Si nanoparticles, citric acid, and sodium hydroxide (NaOH). In the precursor solution, Si nanoparticles are etched by NaOH with the production of [SiO₄]^4-. During the dynamic course of spray pyrolysis, [SiO₄]^4- transforms to SiO_x matrix and citric acid decomposes to carbon surface layer with the assistance of NaOH that serves as a decomposition catalyst. As a result, a Si-SiO_x composite, in which Si nanodomains are homogeneously embedded in the SiO_x matrix with carbon surface layer, is generated by a one-pot process with a residence time of only 3.5 s in a flow reactor. The optimal composite structure in terms of Si domain size and Si-to-O ratio exhibited excellent electrochemical performance, such as reversible capacity of 1561.9 mAh g^-1 at 0.06C rate and ICE of 80.2% and 87.9% capacity retention after 100 cycles at 1C rate.

Engineered nanomembranes for smart energy storage devices

This review presents recent progress in engineered tubular and planar nanomembranes for smart energy storage applications, especially related to the investigation of fundamental electrochemical kinetics.

Two-dimensional ultra-thin SiOx(0 < x < 2) nanosheets with long-term cycling stability as lithium ion battery anodes

Ultra-thin SiO_xnanosheets, made up of partly-oxidized Si single atomic layers, are preparedviaa one-pot solvothermal method from a Zintl compound CaSi₂. After carbon coating, the SiO_x@C nanosheet composites show high capacity and long-term cycling stability when used as anode materials in lithium ion batteries.

Electrochemical energy storage in Mn2O3 porous nanobars derived from morphology-conserved transformation of benzenetricarboxylate-bridged metal–organic framework

MOF-derived Mn₂O₃ shows a high capacity of ∼410 mA h g⁻¹ as a 2 V anode and an ultrahigh energy density of 147.4 W h kg⁻¹ as a supercapacitor.

Scalable Preparation of Ternary Hierarchical Silicon Oxide-Nickel-Graphite Composites for Lithium-Ion Batteries

Silicon monoxide is a promising anode candidate because of its high theoretical capacity and good cycle performance. To solve the problems associated with this material, including large volume changes during charge-discharge processes, we report a ternary hierarchical silicon oxide-nickel-graphite composite prepared by a facile two-step ball-milling method. The composite consists of nano-Si dispersed silicon oxides embedded in nano-Ni/graphite matrices (Si@SiOx /Ni/graphite). In the composite, crystalline nano-Si particles are generated by the mechanochemical reduction of SiO by ball milling with Ni. These nano-Si dispersed oxides have abundant electrochemical activity and can provide high Li-ion storage capacity. Furthermore, the milled nano-Ni/graphite matrices stick well to active materials and interconnect to form a crosslinked framework, which functions as an electrical highway and a mechanical backbone so that all silicon oxide particles become electrochemically active. Owing to these advanced structural and electrochemical characteristics, the composite enhances the utilization efficiency of SiO, accommodates its large volume expansion upon cycling, and has good ionic and electronic conductivity. The composite electrodes thus exhibit substantial improvements in electrochemical performance. This ternary hierarchical Si@SiOx /Ni/graphite composite is a promising candidate anode material for high-energy lithium-ion batteries. Additionally, the mechanochemical ball-milling method is low cost and easy to reproduce, indicating potential for the commercial production of the composite materials.

FeOx and Si nano-dots as dual Li-storage centers bonded with graphene for high performance lithium ion batteries

A novel design based on both FeOx and Si nano-dots bonded with graphene (FeOx·Si@GNS) as dual lithium-storage centers is reported. They show high performance as anode materials for Li-ion batteries with a remarkable reversible capacity of 1160 mA h g(-1) at 0.2 A g(-1), fast charging/discharging rate, and long cycling life (e.g., a capacity retention of 81.7% at 2.0 A g(-1) after 600 cycles). The origin of these high performances comes from the key factors of the high theoretical specific capacity of FeOx and Si, the shorter Li-ion diffusion distance of both nano-dot structures, fast electron conductivity, and the strain relaxation due to volume variations of both nano-dots bonded with graphene nanosheets during cycles.

High-Performance Li-O2 Batteries with Trilayered Pd/MnO x /Pd Nanomembranes

Trilayered Pd/MnO _x /Pd nanomembranes are fabricated as the cathode catalysts for Li-O₂ batteries. The combination of Pd and MnO _x facilitates the transport of electrons, lithium ions, and oxygen-containing intermediates, thus effectively decomposing the discharge product Li₂O₂ and significantly lowering the charge overpotential and enhancing the power efficiency. This is promising for future environmentally friendly applications.

High Performance Li₄Ti₅O12/Si Composite Anodes for Li-Ion Batteries

Improving the energy capacity of spinel Li₄Ti₅O₁₂ (LTO) is very important to utilize it as a high-performance Li-ion battery (LIB) electrode. In this work, LTO/Si composites with different weight ratios were prepared and tested as anodes. The anodic and cathodic peaks from both LTO and silicon were apparent in the composites, indicating that each component was active upon Li⁺ insertion and extraction. The composites with higher Si contents (LTO:Si = 35:35) exhibited superior specific capacity (1004 mAh·g^-1) at lower current densities (0.22 A·g^-1) but the capacity deteriorated at higher current densities. On the other hand, the electrodes with moderate Si contents (LTO:Si = 50:20) were able to deliver stable capacity (100 mAh·g^-1) with good cycling performance, even at a very high current density of 7 A·g^-1. The improvement in specific capacity and rate performance was a direct result of the synergy between LTO and Si; the former can alleviate the stresses from volumetric changes in Si upon cycling, while Si can add to the capacity of the composite. Therefore, it has been demonstrated that the addition of Si and concentration optimization is an easy yet an effective way to produce high performance LTO-based electrodes for lithium-ion batteries.

Encapsulating micro-nano Si/SiO(x) into conjugated nitrogen-doped carbon as binder-free monolithic anodes for advanced lithium ion batteries

Silicon monoxide, a promising silicon-based anode candidate for lithium-ion batteries, has recently attracted much attention for its high theoretical capacity, good cycle stability, low cost, and environmental benignity. Currently, the most critical challenge is to improve its low initial coulombic efficiency and significant volume changes during the charge-discharge processes. Herein, we report a binder-free monolithic electrode structure based on directly encapsulating micro-nano Si/SiOx particles into conjugated nitrogen-doped carbon frameworks to form monolithic, multi-core, cross-linking composite matrices. We utilize micro-nano Si/SiOx reduced by high-energy ball-milling SiO as active materials, and conjugated nitrogen-doped carbon formed by the pyrolysis of polyacrylonitrile both as binders and conductive agents. Owing to the high electrochemical activity of Si/SiOx and the good mechanical resiliency of conjugated nitrogen-doped carbon backbones, this specific composite structure enhances the utilization efficiency of SiO and accommodates its large volume expansion, as well as its good ionic and electronic conductivity. The annealed Si/SiOx/polyacrylonitrile composite electrode exhibits excellent electrochemical properties, including a high initial reversible capacity (2734 mA h g(-1) with 75% coulombic efficiency), stable cycle performance (988 mA h g(-1) after 100 cycles), and good rate capability (800 mA h g(-1) at 1 A g(-1) rate). Because the composite is naturally abundant and shows such excellent electrochemical performance, it is a promising anode candidate material for lithium-ion batteries. The binder-free monolithic architectural design also provides an effective way to prepare other monolithic electrode materials for advanced lithium-ion batteries.