Dual carbon and void space confined SiOx/C@void@Si/C yolk-shell nanospheres with high-rate performances and outstanding cyclability for lithium-ion batteries anodes

Advances and future perspectives on silicon-based anodes for lithium-ion batteries

Silicon (Si)-based anode has emerged as the most promising anode material for next-generation lithium-ion batteries (LIBs) due to its high specific capacity, suitable operating potential and abundant natural reserves. Nevertheless, the drastic volume effect of Si particles during lithiation/delithiation leads to particle pulverization, electrode structure collapse, and solid electrolyte interfacial (SEI) film instability, which results in a rapid reversible capacity degradation of Si-based anodes. It is essential to deeply analyze the failure mechanism of silicon-based electrodes and explore suitable improvement methods to achieve higher capacity retention. Herein, we systematically summarize the improvement strategies for Si-based anodes, including regulating material particle size, optimizing structure and composition, and exploring new binders, along with their enhancement mechanisms. In addition, the preparation of high-performance Si-based electrodes based on newly developed 3D printing technology in recent years is discussed. Lastly, several possible directions and emerging challenges for Si anode are presented to facilitate further improvement in practical applications. Overall, this review is expected to provide basic understanding and insights into the practical application of Si-based materials in next-generation LIBs negative electrodes.

Hierarchical Porous Structured Si/C Anode Material for Lithium-Ion Batteries by Dual Encapsulating Layers for Enhanced Lithium-Ion and Electron Transports Rates

Silicon (Si) is a promising anode material for next-generation lithium-ion batteries (LIBs) due to its high specific capacity and abundance. However, challenges such as significant volume expansion during cycling and poor electrical conductivity hinder its large-scale application. In this study, the multifunction of sodium polyacrylate (PAAS) utilized to develop a hierarchical porous silicon-carbon anode (Si/SiOx@C) through a simple and efficient method. The hierarchical porous structure successively consists of nano-silicon cores, SiOx encapsulating layers, surrounding space, and phenolic resin-derived carbon shells with carbon chains connecting the SiOx layers and carbon shells in the space. The SiOx nanolayers promote Li⁺ transport, while excess PAAS, removed by washing, generates space for volume expansion, improving cycling performance. Residual carbon chains of PAAS and carbon shells form a conducting carbon network, enhancing electron transport and rate performance. As an anode for LIBs, the composite delivers a high reversible capacity of 685.3 mAh g⁻¹ after 1000 cycles at 1 C with a capacity retention rate of 54.7%. Full cells with the Si/SiOx@C anode and LiNi0.8Co0.1Mn0.1O2 cathode exhibit an excellent capacity retention rate of 96.8% after 200 cycles at 1 C. This work provides a novel approach for the rational design and engineering of advanced LIBs.

Recent progress in Si/Ti3C2Tx MXene anode materials for lithium-ion batteries

Cardiovascular diseases (CVDs) are a major global health issue, causing significant morbidity and mortality worldwide. Early diagnosis and continuous monitoring of physiological signals are crucial for managing cardiovascular diseases, necessitating the development of lightweight and cost-effective wearable devices. These devices should incorporate portable energy storage systems, such as lithium-ion batteries (LIBs). To enhance the durability and consistency of the monitoring systems, there is a need to develop LIBs with high energy density. Silicon-based materials hold great promise for future LIBs anodes due to their high theoretical capacity and cost-efficiency. Despite their potential, silicon-based materials encounter challenges like substantial volume fluctuations and sluggish kinetics. Transition metal carbide, MXene, features a two-dimensional structure, offering advantages in silicon-based anode materials. This review initially presents the potential of silicon-based anodes and then addresses their challenges. Subsequently, the advantages of MXene are systematically reviewed, including unique structure, abundant surface functional groups, excellent electrical conductivity, and excellent ion transport performance. Next, the detailed discussion covers recent advancements in Si/Ti3C2Tx MXene anode materials for LIBs, with a focus on their synthesis methods. Finally, the challenges and future perspectives of synthesizing Si/Ti3C2Tx nanocomposites are examined, aiming to provide a foundational resource for designing advanced materials for high-energy LIBs.

Dramatic Enhancement Enabled by Introducing TiN into Bread-like Porous Si-Carbon Anodes for High-Performance and Safe Lithium Storage

Doping modifications and surface coatings are effective methods to slow volume dilatation and boost the conductivity in silicon (Si) anodes for lithium-ion batteries (LIBs). Herein, using low-cost ferrosilicon from industrial production as the energy storage material, a bread-like nitrogen-doped carbon shell-coated porous Si embedded with the titanium nitride (TiN) nanoparticle composite (PSi/TiN@NC) was synthesized by simple ball milling, etching, and self-assembly growth processes. Remarkably, the porous Si structure formed by etching the FeSi2 phase in ferrosilicon alloys can provide buffer space for significant volume expansion during lithiation. Highly conductive and stable TiN particles can act as stress absorption sites for Si and improve the electronic conductivity of the material. Furthermore, the nitrogen-doped porous carbon shell further helps to sustain the structural stability of the electrode material and boost the migration rate of Li-ions. Benefiting from its unique synergistic effect of components, the PSi/TiN@NC anode exhibits a reversible discharge capacity up to 1324.2 mAh g-1 with a capacity retention rate of 91.5% after 100 cycles at 0.5 A g-1 (vs fourth discharge). Simultaneously, the electrode also delivers good rate performance and a stable discharge capacity of 923.6 mAh g-1 over 300 cycles. This research can offer a potential economic strategy for the development of high-performance and inexpensive Si-based anodes for LIBs.

Tailored Yolk-Shell Design to Silicon Microparticles via Scalable and Template-Free Synthesis for Superior Lithium Storage

Micrometer-sized Si particles are beneficial to practical lithium-ion batteries in regard to low cost and high volumetric energy density in comparison with nanostructured Si anodes. However, both the issues of electrical contact loss and overgrowth of solid electrolyte interface for microscale Si induced by colossal volume change still remain to be addressed. Herein, a scalable and template-free method is introduced to fabricate yolk-shell structured Si anode from commercially available Si microparticles. The void is created via a one-step alkali etching process with the remaining silicon core as the yolk, and a double-walled shell is formed from simultaneous in situ growth of the conformal native oxide layer and subsequent carbon coating. In this configuration, the well-defined void spaces allow the Si core to expand without compromising structural integrity, while the double-walled shell acts as a static capsule to confine silicon fragments despite likely particle fracture. Therefore, electrical connectivity is maintained on both the particle and electrode level during deep galvanostatic cycling, and the solid-electrolyte interface is stabilized on the shell surface. Owing to the benefits of tailored design, excellent cycling stability (capacity retention of 95% after 100 cycles) and high coulombic efficiency (99.5%) are realized in a practical full-cell demonstration.

Binder-Free Intertwined Si and MnO2 Composite Electrode for High-Performance Li-Ion Battery Anode

Silicon is considered as the most felicitous anode material candidate for lithium-ion batteries on account of abundant availability, suitable operating potential, and high specific capacity. Nevertheless, drastic volume expansion during the cycle impedes its practical utilization. Herein, Si and MnO2 (Si-MO) constructed the binder-free intertwined electrode that is reported to effectively improve upon the cycling stability of Si-based materials. The Si-based electrode without a binder has good electrical conductivity, strong adhesion to the substrate, and ample space for mitigating volume expansion. The incorporation of MnO2 establishes a multiphase interface, which mitigates the electrode volume expansion, and supports the electrode structure. Furthermore, MnO2 (∼1230 mAh g-1 theoretical capacity) synergistically enhances the overall capacity of the composite electrodes. Consequently, the Si-MO composite electrode exhibits a reversible specific capacity of 1300 mAh g-1 at 420 mA g-1 and remarkable cycling performance with a specific capacity of 830 mAh g-1 after 500 cycles. In particular, a reversible specific capacity of 837 mAh g-1 at 4200 mA g-1 is achieved and remains stable during 200 cycles. This work provides a potentially feasible way to achieve the Si-based anode commercialization for LIBs.

Boron-doped three-dimensional porous carbon framework/carbon shell encapsulated silicon composites for high-performance lithium-ion battery anodes

Deleterious volumetric expansion and poor electrical conductivity seriously hinder the application of Si-based anode materials in lithium-ion batteries (LIBs). Herein, boron-doped three-dimensional (3D) porous carbon framework/carbon shell encapsulated silicon (B-3DCF/Si@C) hybrid composites are successfully prepared by two coating and thermal treatment processes. The presence of 3D porous carbon skeleton and carbon shell effectively improves the mechanical properties of the B-3DCF/Si@C electrode during the cycling process, ensures the stability of the electrical contacts of the silicon particles and stabilizes the solid electrolyte interface (SEI) layer, thus enhancing the electronic conductivity and ion migration efficiency of the anode. The developed B-3DCF/Si@C anode has a high reversible capacity, excellent cycling stability and outstanding rate performance. A reversible capacity of 1288.5 mAh/g is maintained after 600 cycles at a current density of 400 mA g-1. The improved electrochemical performance is demonstrated in a full cell using a LiFePO4-based cathode. This study presents a novel approach that not only mitigates the large volume expansion effects in LIB anode materials, but also provides a reference model for the preparation of porous composites with various functionalities.

Construction of sub micro-nano-structured silicon based anode for lithium-ion batteries

The significant volume change experienced by silicon (Si) anodes during lithiation/delithiation cycles often triggers mechanical-electrochemical failures, undermining their utility in high-energy-density lithium-ion batteries (LIBs). Herein, we propose a sub micro-nano-structured Si based material to address the persistent challenge of mechanic-electrochemical coupling issue during cycling. The mesoporous Si-based composite submicrospheres (M-Si/SiO2/CS) with a high Si/SiO2content of 84.6 wt.% is prepared by magnesiothermic reduction of mesoporous SiO2submicrospheres followed by carbon coating process. M-Si/SiO2/CS anode can maintain a high specific capacity of 740 mAh g-1at 0.5 A g-1after 100 cycles with a lower electrode thickness swelling rate of 63%, and exhibits a good long-term cycling stability of 570 mAh g-1at 1 A g-1after 250 cycles. This remarkable Li-storage performance can be attributed to the synergistic effects of the hierarchical structure and SiO2frameworks. The spherical structure mitigates stress/strain caused by the lithiation/delithiation, while the internal mesopores provide buffer space for Si expansion and obviously shorten the diffusion path for electrolyte/ions. Additionally, the amorphous SiO2matrix not only servers as support for structure stability, but also facilitates the rapid formation of a stable solid electrolyte interphase layer. This unique architecture offers a potential model for designing high-performance Si-based anode for LIBs.

Pristine cobalt humic acid xerogels embedded with ultrafine cobalt sulfide for enhanced and stable lithium-ion storage

The electrochemical performance of pristine metal-organic xerogels as anodes in lithium-ion batteries is reported for the first time. We propose a novel synthesis approach for the in situ generation of highly dispersed, ultrafine cobalt sulfide nanoparticles on humic acid gels (CoSHA). The CoS nanoparticles in CoSHA have an average diameter of approximately 3 nm. CoSHA electrodes demonstrate enhanced lithium storage capacity, delivering a capacity of 662 mAh g-1 at 0.1 A g-1. They also show stable long-term cycling performance, with no capacity decay after 900 cycles at 1.0 A g-1. Furthermore, our experiments indicate that the improved lithium-ion adsorption results from the oxygen-containing functional groups in humic acid and the ultrafine CoS active sites. This study offers a practical methodology for synthesizing ultrafine metal sulfides and new insights into using pristine gel-based electrodes for energy storage and conversion.

Dual immobilization of porous Si by graphene supported anatase TiO2/carbon for high-performance and safe lithium storage

Smart surface coatings have been proven to be an effective strategy to significantly enhance the electronic conductivity and cycling stability of silicon-based anode materials. However, the single/conventional coatings face critical challenges, including low initial Coulomb efficiency (ICE), poor cyclability, and kinetics failure, etc. Hence, we proposed a dual immobilization strategy to synthesize graphene supported anatase TiO2/carbon-coated porous silicon composite (denoted as PSi@TiO2@C/Graphene) using industrial-grade ferrosilicon as lithium storage raw materials through the simple etching, combined with sol-gel and hydrothermal coating processes. In this work, the dual immobilization from the "confinement effect" of the inner TiO2 shell and the "synergistic effect" of the outer carbon shell, improves the kinetics of the electrochemical reaction and ensures the integrity of the electrode material structure during lithiation. Furthermore, the introduction of the graphene substrate offers ample space for dispersing and anchoring the Si-based granules, which in turn provides a stable 3D conductive network between the particles. As a result, the PSi@TiO2@C/Graphene electrode delivers high reversible capacity of 1605.4 mAh g-1 with 93.65% retention at 0.5 A g-1 after 100 cycles (vs. 4th discharge), high initial Coulomb efficiency (82.30%), and superior cyclability of 1159.9 mAh g-1 after 250 cycles. The above results suggest that the particle structure has great potential for applications in Si-based anode and may provide some inspiration for the design of other energy storage materials.

Recent Progress in Silicon-Based Materials for Performance-Enhanced Lithium-Ion Batteries

Silicon (Si) has been considered to be one of the most promising anode materials for high energy density lithium-ion batteries (LIBs) due to its high theoretical capacity, low discharge platform, abundant raw materials and environmental friendliness. However, the large volume changes, unstable solid electrolyte interphase (SEI) formation during cycling and intrinsic low conductivity of Si hinder its practical applications. Various modification strategies have been widely developed to enhance the lithium storage properties of Si-based anodes, including cycling stability and rate capabilities. In this review, recent modification methods to suppress structural collapse and electric conductivity are summarized in terms of structural design, oxide complexing and Si alloys, etc. Moreover, other performance enhancement factors, such as pre-lithiation, surface engineering and binders are briefly discussed. The mechanisms behind the performance enhancement of various Si-based composites characterized by in/ex situ techniques are also reviewed. Finally, we briefly highlight the existing challenges and future development prospects of Si-based anode materials.

Inorganic crosslinked supramolecular binder with fast Self-Healing for high performance silicon based anodes in Lithium-Ion batteries

Capacity retention is one of the key factors affecting the performance of silicon (Si)-based lithium-ion batteries and other energy storage devices. Herein, a three dimension (3D) network self-healing binder (denoted as PVA + LB) consisting of polyvinyl alcohol (PVA) and lithium metaborate (LiBO₂) solution is proposed to improve the cycle stability of Si-based lithium-ion batteries. The reversible capacity of the silicon electrode is maintained at 1767.3 mAh g^-1 after 180 cycles when employing PVA + LB as the binder, exhibiting excellent cycling stability. In addition, the silicon/carbon (Si/C) anode with the PVA + LB binder presents superior electrochemical performance, achieving a stable cycle life with a capacity retention of 73.7% (858.3 mAh g^-1) after 800 cycles at a current density of 1 A g^-1. The high viscosity and flexibility, 3D network structure, and self-healing characteristics of the PVA + LB binder are the main reasons to improve the stability of the Si or Si/C contained electrodes. The novel self-healing binder shows great potential in designing the new generation of silicon-based lithium-ion batteries and even electrochemical energy storage devices.