Constructing Novel Si@SnO2 Core-Shell Heterostructures by Facile Self-Assembly of SnO2 Nanowires on Silicon Hollow Nanospheres for Large, Reversible Lithium Storage

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.

Nano-Silicon@Exfoliated Graphite/Pyrolytic Polyaniline Composite of a High-Performance Cathode for Lithium Storage

In this paper, a Si@EG composite was prepared by liquid phase mixing and the elevated temperature solid phase method, while polyaniline was synthesized by the in situ chemical polymerization of aniline monomer to coat the surface of nano-silicon and exfoliated graphite composites (Si@EG). Pyrolytic polyaniline (p-PANI) coating prevents the agglomeration of silicon nanoparticles, forming a good conductive network that effectively alleviates the volume expansion effect of silicon electrodes. SEM, TEM, XRD, Raman, TGA and BET were used to observe the morphology and analyze the structure of the samples. The electrochemical properties of the materials were tested by the constant current charge discharge and cyclic voltammetry (CV) methods. The results show that Si@EG@p-PANI not only inhibits the agglomeration between silicon nanoparticles and forms a good conductive network but also uses the outermost layer of p-PANI carbon coating to effectively alleviate the volume expansion of silicon nanoparticles during cycling. Si@EG@p-PANI had a high initial specific capacity of 1491 mAh g^-1 and still maintains 752 mAh g^-1 after 100 cycles at 100 mA g^-1, which shows that it possesses excellent electrochemical stability and reversibility.

Selenium-Doped Amorphous Black Phosphorus@TiO2/C Heterostructures for High-Performance Li/Na/K Ion Batteries

Heterostructures have been confirmed to demonstrate better electrochemical performance than their individual building blocks, which is not only attributed to the complementary advantages of diverse materials but also to various synergistic effects, such as increased active sites at the heterointerfaces, enhanced kinetics from a built-in electric field, stable structure due to physical or chemical bonding, etc. However, constructing a desired heterostructure remains greatly challenging owing to the mismatch of crystal structures, atomic spacings, and reaction mechanisms between different electrode materials. In this study, an amorphous heterostructure composed of Se-doped black phosphorus and metal-organic framework (MOF)-derived TiO₂/C (Se-BP@TiO₂/C) was successfully fabricated using a simple Se-assisted ball-milling method. In addition to the inherent advantages of heterostructures, the novel material also had considerable free volume in the amorphous domains, which not only buffered the volume change of active materials during cycles but also provided space and interconnected channels for ion diffusion. When used as anode materials for Li/Na/K ion batteries, the Se-BP@TiO₂/C achieved high specific capacities, good cyclability, and fast rate capability. This work opens up a new route to design amorphous heterostructure electrodes for high-performance battery systems.

Improving Lithium-Ion Half-/Full-Cell Performance of WO3 -Protected SnO2 Core-Shell Nanoarchitectures

Anodes derived from SnO₂ offer a greater specific capacity comparative to graphitic carbon in lithium-ion batteries (LIBs); hence, it is imperative to find a simple but effective approach for the fabrication of SnO₂ . The intelligent surfacing of transition metal oxides is one of the favorite strategies to dramatically boost cycling efficiency, and currently most work is primarily aimed at coating and/or compositing with carbon-based materials. Such coating materials, however, face major challenges, including tedious processing and low capacity. This study successfully reports a new and simple WO₃ coating to produce a core-shell structure on the surface of SnO₂ . The empty space permitted natural expansion for the SnO₂ nanostructures, retaining a higher specific capacity for over 100 cycles that did not appear in the pristine SnO₂ without WO₃ shell. Using WO₃ -protected SnO₂ nanoparticles as anode, a coin half-cell battery was designed with Li-foil as counter-electrode. Furthermore, the anode was paired with commercial LiFePO₄ as cathode for a coin-type full cell and tested for lithium storage performance. The WO₃ shell proved to be an effective and strong enhancer for both current rate and specific capacity of SnO₂ nanoarchitectures; additionally, an enhancement of cyclic stability was achieved. The findings demonstrate that the WO₃ can be used for the improvement of cyclic characteristics of other metal oxide materials as a new coating material.

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.

Superior and Reversible Lithium Storage of SnO2/Graphene Composites by Silicon Doping and Carbon Sealing

The poor cycle stability and reversibility seriously hinder the widespread application of SnO₂ materials as anodes for lithium-ion batteries (LIBs). A novel sandwich-architecture composite of Si-doped SnO₂ nanorods and reduced graphene oxide with carbon sealing (Si-SnO₂@G@C) is engineered and fabricated by a facile two-step hydrothermal process and subsequent annealing treatment, which exhibit not only extraordinary rate performance and ultrahigh reversible capacity but also excellent cycle stability and high electrical conductivity as the anode of LIBs. The Si-doped SnO₂ nanoparticles on the surface of graphene were firmly wrapped in the C-coating and formed a porous sandwich structure, which can efficiently prevent the Sn nanoparticles from aggregation and provide more extra space for accommodating the volume variations and more active sites for reactions. The carbon layer also blocks the direct contact of the SnO₂ nanorods with electrolyte and prevents the graphene nanosheets from the restacking. More importantly, the reversibility of lithiation/delithiation reactions can be remarkably improved by the doping silicon. The doped Si not only accelerates the diffusion of Li⁺ but also brings a significant increase in the specific capacity. As a consequence, the Si-SnO₂@G@C nanocomposite can maintain a high capacity of 654 mAh/g at 2 A/g even after 1200 cycles with negligible capacity loss and excellent reversibility with a Coulombic efficiency retention over 99%, which can be capable of the alternative to commercial graphite anodes. This work provides a new strategy for the reasonable design of advanced anode materials with superior and reversible lithium storage capacity.

Quantification on Growing Mass of Solid Electrolyte Interphase and Deposited Mn(II) on the Silicon Anode of LiMn2O4 Full Lithium-Ion Cells

Silicon is considered to be one of the most important high-energy density anode materials for next-generation lithium-ion batteries. A large number of experimental studies on silicon anode have achieved better results, and greatly promoted its practical application potentiality, but almost of them are only tested in metal lithium half batteries. There is still an unavoidable question for commercial applications: what is the performance of the full cell composed of a silicon anode and a manganese-based material cathode? In this paper, the growing solid electrolyte interphase (SEI) and deposited manganese ions of the silicon anode's surface of the spinel lithium manganese oxide LiMn₂O₄/silicon full cells are quantitatively studied during electrochemical cycling, and the SEI performances are tested by differential scanning calorimetry to find out the reason for the rapid decline of reversible capacity in the LiMn₂O₄/silicon system. The experimental results show that manganese ions can make SEI films rapidly grow on the silicon anode and make SEI films more brittle, which results in lower Coulombic efficiency and rapid decline in capacity of the silicon anode.

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.

A hierarchical porous architecture of silicon@TiO2@carbon composite novel anode materials for high performance Li-ion batteries

The excellent electrochemical properties are attributed to the synergistic action of hierarchical porous TiO₂ and carbon layers.

A self-assembled silicon/phenolic resin-based carbon core–shell nanocomposite as an anode material for lithium-ion batteries

Silicon, with advantages such as high theoretical capacity and relatively low working potential, has been regarded as promising when it is used for lithium-ion battery anodes. However, its practical application is impeded by the intrinsic low electrical conductivity and the dramatic volume change during the lithiation/delithiation process, which leads to a rapid capacity fading of the electrode. In this regard, we design silicon nanoparticles homogeneously coated with a phenolic resin-based carbon layer as a core–shell nanocomposite via a facile self-assembly method followed by carbonization. The surrounding carbon shell, confirmed by transmission electron microscopy and Raman spectroscopy, is not only beneficial to the formation of a stable solid electrolyte interface film, but the electrical conductivity of the electrode is also enhanced. A high and stable specific capacity of nearly 1000 mA h g⁻¹ is achieved at C/3 after 200 cycles with a coulombic efficiency of >99.6%. The entire synthesis process is quite simple and easy to scale up, thus having great potential for commercial applications.

A self-assembled silicon/phenolic resin-based carbon core–shell nanocomposite is reported, which exhibits a high and stable reversible capacity and good rate capability.

Tin Oxide-Carbon-Coated Sepiolite Nanofibers with Enhanced Lithium-Ion Storage Property

Natural sepiolite (Sep) nanofibers were coated with carbon and nanoscale SnO2 to prepare an emerging nanocomposite (SnO2-C@Sep), which exhibited enhanced electrochemical performance. Sepiolite could act as a steady skeleton, carbon coating principally led sepiolite from an isolated to an electric state, and decoration of nanoscale SnO2 was beneficial to the functionization of sepiolite. Cycling performances indicated that SnO2-C@Sep showed higher discharge capacities than commercial SnO2 after 50 cycles. The nanocomposite SnO2-C@Sep possessed enhanced lithium storage properties with stable capacity retention and low cost, which could open up a new strategy to synthesize a variety of functional hybrid materials based on the cheap and abundant clay and commercialization of lithium-metal oxide batteries.

Novel Silicon Doped Tin Oxide-Carbon Microspheres as Anode Material for Lithium Ion Batteries: The Multiple Effects Exerted by Doped Si

Silicon doped tin oxide embedded porous carbon microspheres (Si_y Sn_1-y O_x @C) are synthesized. It is found that the doped Si not only improves the reversibility of lithiation/delithiation reactions, but also prevents Sn from aggregation. In addition, the doped Si introduces extra defects into the carbon matrix and produces Li⁺ conductive Li₄ SiO₄ , which accelerates Li⁺ diffusion. Together with the conductive, porous carbon matrix that provides void space to accommodate the volume change of Sn during charge/discharge cycling, the novel Si_y Sn_1-y O_x @C exhibits excellent electrochemical performance. It shows a high initial columbic efficiency of 75.9%. A charge (delithiation) capacity of 880.32 mA h g^-1 is retained after 150 cycles, i.e., 91% of the initial capacity. These results indicate that the as-synthesized Si_y Sn_1-y O_x @C is a promising anode material for lithium ion batteries.

Tuning the morphologies of fluorine-doped tin oxides in the three-dimensional architecture of graphene for high-performance lithium-ion batteries

The morphology of electrode materials plays an important role in determining the performance of lithium-ion batteries (LIBs). However, studies on determining the most favorable morphology for high-performance LIBs have rarely been reported. In this study, a series of F-doped SnO _x (F-SnO₂ and F-SnO) materials with various morphologies was synthesized using ethylenediamine as a structure-directing agent in a facile hydrothermal process. During the hydrothermal process, the F-SnO _x was embedded in situ into the three-dimensional (3D) architecture of reduced graphene oxide (RGO) to form F-SnO _x @RGO composites. The morphologies and nanostructures of F-SnO _x , i.e., F-SnO₂ nanocrystals, F-SnO nanosheets, and F-SnO₂ aggregated particles, were fully characterized using electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy. Electrochemical characterization indicated that the F-SnO₂ nanocrystals uniformly distributed in the 3D RGO architecture exhibited higher specific capacity, better rate performance, and longer cycling stability than the F-SnO _x with other morphologies. These excellent electrochemical performances were attributed to the uniform distribution of the F-SnO₂ nanocrystals, which significantly alleviated the volume changes of the electrode material and shortened the Li ion diffusion path during lithiation/delithiation processes. The F-SnO₂@RGO composite composed of uniformly distributed F-SnO₂ nanocrystals also exhibited excellent rate performance, as the specific capacities were measured to be 1158 and 648 mA h g^-1 at current densities of 0.1 and 5 A g^-1, respectively.

Heterogeneous Double-Shelled Constructed Fe3O4 Yolk-Shell Magnetite Nanoboxes with Superior Lithium Storage Performances

Among the numerous candidate materials for lithium ion batteries, ferroferric oxide (Fe₃O₄) has been extensively concerned as a prospective anode material because of its high theoretical specific capacity, abundant resources, low cost, and nontoxicity. Here, we designed and fabricated a unique yolk-shell construction by generating heterogeneous double-shelled SnO₂ and nitrogen-doped carbon on Fe₃O₄ yolk (denoted as Fe₃O₄@SnO₂@C-N nanoboxes). The yolk-shell structured Fe₃O₄@SnO₂@C-N nanoboxes have the adjustable void space, which permits the free expansion of Fe₃O₄ yolks without breaking the double shells during the lithiation/delithiation processes, avoiding the structural pulverization. Moreover, the heterogeneous double-shelled SnO₂@C-N can meaningfully improve the electronic conductivity and enhance the lithium storage performance. Two metal oxides also show the specific synergistic effect, promoting the electrochemistry reaction. As a result, this yolk-shell structured Fe₃O₄@SnO₂@C-N exhibits high specific capacity (870 mA h g^-1 at 0.5 A g^-1 after 200 cycles), superior rate capability, and long cycle life (670 mA h g^-1 at 3 A g^-1 after 600 cycles). This design and construction method can be extended to synthesize other yolk-shell nanostructured anode materials with improved electrochemistry performance.

SnO2@a-Si core-shell nanowires on free-standing CNT paper as a thin and flexible Li-ion battery anode with high areal capacity

Here, we report 3D hierarchical SnO₂ nanowire (NW) core-amorphous silicon shell on free-standing carbon nanotube paper (SnO₂@a-Si/CNT paper) as an effective anode for flexible lithium-ion battery (LIB) application. This binder-free electrode exhibits a high initial discharge capacity of 3020 mAh g^-1 with a large reversible charge capacity of 1250 mAh g^-1 at a current density of 250 mA g^-1. Compared to other SnO₂ NW or its core-shell nanostructured anodes, the fabricated SnO₂@a-Si/CNT structure demonstrates an outstanding performance with high mass loading (∼5.9 mg cm^-2), high areal capacity (∼5.2 mAh cm^-2), and large volumetric capacity (∼1750 mAh cm^-3) after 25 cycles. Due to the incorporation of CNT paper as the current collector, the weight and thickness of the total electrode is effectively reduced with respect to the conventional LIB anodes. The fabricated electrode has a total thickness of only 30 μm and considering the total weight of the electrode (active mass + current collector), an initial discharge/charge capacity of 2460/1018 mAh g^-1 is obtained. Hence, this thin, lightweight and highly flexible structure is proposed as an excellent candidate for high-performance LIB anode materials, especially in flexible electronics.

High Volumetric Capacity of Hollow Structured SnO2@Si Nanospheres for Lithium-Ion Batteries

A novel design of hollow structured SnO₂@Si nanospheres was presented, which not only demonstrates high volumetric capacity as anode of LIBs, but also prevents aggregation of Sn and confines solid electrolyte interphase thickening. An impressive volumetric specific capacity of 1030 mAh cm^-3 was maintained after 500 cycles. The electrochemical impedance spectroscopy and differential scanning calorimetry indicated that solid electrolyte interphase can be confined in pores of as-prepared hollow structured SnO₂@Si.

Confined Solid Electrolyte Interphase Growth Space with Solid Polymer Electrolyte in Hollow Structured Silicon Anode for Li-Ion Batteries

Silicon anodes for lithium-ion batteries are of much interest owing to their extremely high specific capacity but still face some challenges, especially the tremendous volume change which occurs in cycling and further leads to the disintegration of electrode structure and excessive growth of solid electrolyte interphase (SEI). Here, we designed a novel approach to confine the inward growth of SEI by filling solid polymer electrolyte (SPE) into pores of hollow silicon spheres. The as-prepared composite delivers a high specific capacity of more than 2100 mAh g^-1 and a long-term cycle stability with a reversible capacity of 1350 mAh g^-1 over 500 cycles. The growing behavior of SEI was investigated by electrochemical impedance spectroscopy and differential scanning calorimetry, and the results revealed that SPE occupies the major space of SEI growth and thus confines its excessive growth, which significantly improves cycle performance and Coulombic efficiency of cells embracing hollow silicon spheres.

Structure-preserved 3D porous silicon/reduced graphene oxide materials as anodes for Li-ion batteries

3D porous networks are subject to be destroyed during electrode preparation. Structure-preserved 3D porous Si/rGO anode materials were synthesized by tuning pore size distribution and performed superior electrochemical properties.

Sodium storage in fluorine-rich mesoporous carbon fabricated by low-temperature carbonization of polyvinylidene fluoride with a silica template

A fluorine-rich mesoporous carbon is prepared by low-temperature carbonization of polyvinylidene fluoride with a silica template, exhibiting excellent sodium anodic performances.

Aluminothermic reduction enabled synthesis of silicon hollow microspheres from commercialized silica nanoparticles for superior lithium storage

We report the aluminothermic reduction enabled synthesis of silicon hollow microspheres from commercialized silica nanoparticles by controlled transformation and organization, which exhibit optimized electrochemical performances.