Si Anode Research Articles

Si anodes via dual strategies of coating Si with a rigid polymer and employing a polymer binder with improved mechanical properties

Si undergoes significant volume change over cycles which degrades the structural integrity and stability of the electrode. This volume change is the primary barrier to the commercialization of Si anodes, and it is more pronounced for Si particle sizes over 150 nm. In this study, a crosslinked polymer binder is developed using poly(acrylic acid-co-acrylamide) (PAAM) with enhanced elasticity compared to the widely used poly(acrylic acid). PAAM is further grafted with boronic acid and dopamine, yielding PAAM-B-D, a binder with improved adhesion due to its 3D crosslinked network. Additionally, 350-nm Si is coated with cyclized polyacrylonitrile (cPAN) and heat-treated to form a conjugated structure. The cPAN-coated Si (cSi) exhibits enhanced conductivity and mechanical stiffness and is used as an active material. The developed Si anode effectively combines cPAN-coated Si with the crosslinked network formed in the PAAM-B-D polymer for enhanced adhesion. The cSi@PAAM-B-D electrode sufficiently maintains its structural integrity and mitigates the Si volume change even with the large-sized 350-nm Si. The cSi@PAAM-B-D exhibits a high initial Coulombic efficiency of 86.5 %, at a Si mass loading of 2 mg cm−2. It also shows a capacity retention of 83.6 % and a high areal capacity of 3 mAh cm−2 after 50 cycles.

The Development of Nano Si Materials in the Application of Lithium-Ion Batteries Anode

Electric vehicles (EVs) have become a practical alternative to conventional fuel vehicles due to their environmental friendliness, high energy efficiency, low operating costs, etc. In EVs, lithium-ion batteries (LIBs) play a crucial role. It provides a power source for EVs and directly affects their performance. Among them, LIBs with silicon nanomaterials as negative electrodes show great potential in improving EV performance. This article aims to conclude Si-based anode LIBs’ present challenges and introduce advanced optimization methods with nano-Si material according to these challenges. It starts with the principle of Li-ion storage in Si. Then, problems faced by pure Si anodes and the preliminarily improved Si-based anodes are listed. Finally, further optimization methods in the nano Si anodes during these years are introduced. The optimization methods mainly include improving the service life of nano-Si-based anode and reducing the cost of manufacture. This comprehensive review provides reference and inspiration for developing Si-based anode LIBs applied in EVs.

Progress in the application of silicon-based materials in lithium-ion batteries anodes

From the battery that powers the remote control to the battery that powers electric cars, lithium-ion batteries (LIBs) are a crucial component of contemporary energy storage. The large theoretical capacity of silicon anodes provides significant benefits inside LIBs. However, the main issue with the conventional silicon bulk anode is its considerable volume expansion, which forms an unstable Solid Electrolyte Interface (SEI) layer during the charge and discharge process and severely reduces battery performance and lifespan. Therefore, to solve these issues, researchers have explored multiple improved silicon anodes, three of which are mentioned in this essay. Firstly, the researchers delve into the usage of nanotechnology. When manipulating silicon particles at the nano-scale, the nano-silicon can mitigate the volume expansion, improving the reaction kinetics. Then, a composite of carbon and silicon is proposed, combining silicon's high capacitance and carbon's high conductivity. After that is the silicon-metal composite, which utilizes metals' mechanical strength and conductivity to stabilize Si anodes further and improve thermal stability. Overall, the significance of this study lies in the exploration of the application of silicon anodes in LIBs, highlighting the potential of these composite materials and advanced technology, which may help guide the future exploration of better silicon anodes.

Li7P3S11 double-layer electrolyte for silicon-based all-solid-state batteries: Interface SiS2-doping

Sulfide solid electrolytes is indispensable for developing all-solid-state batteries with Si-based anode for its superior ionic conductivity and excellent mechanical ductility. However, the unfriendly interface between sulfide and silicon still leads to poor cycling performance. Herein, we report a SiS2-doping Li7P3S11 (LPS-xSi) membrane sandwiched between Li7P3S11 electrolyte and Si electrode to form double-layer sulfide electrolyte (LPS-xSi|LPS). LPS-xSi|LPS double-layer contacts well with Si anode and forms Li-Si alloys at the interface to eliminate the adverse side reactions and promote the Li+ transmission of the interface. The LPS-2Si|LPS possesses the highest ionic conductivity of 5.4 × 10−4 S cm−1 at 30 °C. LiIn | LPS-2Si|LPS | LiIn cell works steadily for more than 1000 h at 30 ℃ with 0.1 mA cm−2. The assembled 99 wt.% Si | LPS-2Si|LPS | LiIn cell exhibits an initial discharge capacity of 2208.7 mAh g−1 and remains 339.5 mAh g−1 after 100 cycles.

High‐Performance Yolk‐Shell Structured Silicon‐Carbon Composite Anode Preparation via One‐Step Gas‐Phase Deposition and Etching Technique

AbstractFor producing high‐capacity silicon (Si) anodes, a combined gas‐phase deposition and etching technique is developed to construct yolk‐shell structured silicon‐carbon composites. As a novel etching agent in battery field, NF3 is applied to selectively etch Si to tailor the architecture. Si particles as self‐sacrificed precursor have no need to build artificial or complex templates in advance, thereby greatly simplifying fabrication process and showcasing practicality. As a result, yolk‐shell structured silicon‐carbon composites are successfully fabricated in a single step. Sufficient buffer space between Si and carbon layer accommodates the significant expansion of Si during lithiation, preventing fracture of the carbon layer, which greatly improves service life of Si‐based anodes. Moreover, the refined particle size of Si and abundant pores in inner Si cores enhance the lithiation and de‐lithiation kinetic. Even with a high Si loading of 3.9 mg cm−2, the produced anode exhibits a superior areal capacity of 16.3 mAh cm−2 at 0.2 mA cm−2. Furthermore, at a high current density of 4 A g−1, it demonstrates an excellent capacity of 1114 mAh g−1 after 1000 cycles with a capacity retention of 96.3%. Additionally, with pre‐lithiation, it is successfully paired with an iron trifluoride cathode to construct high‐energy lithium‐ion batteries.

Hybrid 2D/3D carbon framework confined Si with optimized reaction kinetics for highly stable Li-Ion storage

Three-dimensional (3D) conductive skeletons can optimize electron/Li-ion migration kinetics and alleviate stress accumulation for silicon (Si)-based electrodes. In this study, the modified carbon nanotubes (MCNs) are used as a stress-buffering and high-speed conducting framework, and a hierarchical structure of 3D MCNs interspersed with flour-derived 2D N-doped C layer is designed for Si anode via molecular self-assembly and in-situ carbonization strategies. Experimental and theoretical calculations show that the charge redistribution occurred in the fabricated SiOx and N-doped C interfaces, which induced an electric field response and increased the interfacial electron/Li-ion transfer rate. Multiphysics simulations show that the 2D/3D hierarchical structures of carbon can optimize the physicochemical properties, such as a favorable local electronic environment, flexible stress dissipation mechanisms and good thermal stability. The prepared electrode with 77.1 wt% Si@SiOx shows a low volume expansion rate of 23 % and has an excellent Li-ion storage capability (972.1 mAh g−1 at 4000 mA g−1). Moreover, the structural stability of fabricated Si-based electrodes is enhanced, achieving 0.04 % per cycle capacity decay for 500 cycles at 2000 mA g−1. Such integrating the 2D/3D carbon framework to manipulate Si interfacial properties provides fundamental research for other electrodes plagued by significant volume expansion.

Synthesis Methods of Si/C Composite Materials for Lithium-Ion Batteries

Silicon anodes present a high theoretical capacity of 4200 mAh/g, positioning them as strong contenders for improving the performance of lithium-ion batteries. Despite their potential, the practical application of Si anodes is constrained by their significant volumetric expansion (up to 400%) during lithiation/delithiation, which leads to mechanical degradation and loss of electrical contact. This issue contributes to poor cycling stability and hinders their commercial viability, and various silicon–carbon composite fabrication methods have been explored to mitigate these challenges. This review covers key techniques, including ball milling, spray drying, pyrolysis, chemical vapor deposition (CVD), and mechanofusion. Each method has unique benefits; ball milling and spray drying are effective for creating homogeneous composites, whereas pyrolysis and CVD offer high-quality coatings that enhance the mechanical stability of silicon anodes. Mechanofusion has been highlighted for its ability to integrate silicon with carbon materials, showing the potential for further optimization. In light of these advancements, future research should focus on refining these techniques to enhance the stability and performance of Si-based anodes. The optimization of the compounding process has the potential to enhance the performance of silicon anodes by addressing the significant volume change and low conductivity, while simultaneously addressing cost-related concerns.

A Polysaccharide Binder with Carbon Quantum Dots for Improved Flexibility of Si Anodes in Lithium–Ion Batteries

A Polysaccharide Binder with Carbon Quantum Dots for Improved Flexibility of Si Anodes in Lithium–Ion Batteries

Performance Degradation Mechanism of the Si@N, S-Doped Carbon Anode in Sulfide-Based All-Solid-State Batteries.

Silicon (Si) anode is a promising anode material for all-solid-state lithium batteries with ultra-high theoretical specific capacity and low lithium dendrite risk. However, the inevitable vast volume expansion of Si anode during charge/discharge is recognized as a major limitation preventing its commercial application. Herein, an N, S self-doped amorphous carbon layer coated on porous micron-sized Si (p-mSi@C) is designed to construct an electron/ion conducting network while ensuring structural and interfacial stability. Uneven distribution of von mises stresses during p-mSi lithiation leads to irregular volume expansion and even fragmentation. Meanwhile, the growth of by-products at the interface between p-mSi and electrolyte contact leads to a rapid capacity decay. Compared to p-mSi anode, p-mSi@C reduces the risk of fragmentation thanks to the stress-absorbing effect of amorphous carbon, delivering excellent electrochemical performance (2679.65 mAh g-1 at 0.2 mA cm-2 with initial coulombic efficiency of 84%). More importantly, the chemical failure mechanisms of p-mSi and p-mSi@C composite anodes are revealed through structural characterization, chemical analysis, and simulation, which provides the necessary theoretical guidance for practicalization.

Electrochemical in-situ lithiated Li2SiO3 layer promote high performance silicon anode for lithium-ion batteries

Si anode is considered to be one of the most promising candidates for the next-generation lithium-ion batteries (LIBs). However, the severe volume variation of Si (> 300%) during the lithiation/delithiation process results in unstable interface and thus contributes to poor cycling stability. Moreover, the relatively low conductivity derived from the semiconductor nature of Si leads to inferior rate performance. Herein, Li2SiO3 layer with fast lithium-ions transport capability and high mechanical property was formed on Si surface in an in-situ electrochemical method. The relationships between the valence of SiOx and LixSiOy constituents were readily studied. Fortunately, the as-prepared Si@ES-LSO showed great potential to mitigate the expansion and high lithium-ions diffusion coefficient. When employed as anode materials for LIBs, the modified Si anode delivered a specific capacity of 2074.8 mAh g−1 at 1000 mA g−1 with a retention ratio of 98.9% after 100 cycles, demonstrating superior electrochemical performance. This work provides a facial and efficient strategy for the roadmap of Si anode application.

A 3D flexible conductive network skeleton by SWCNT-COOH and PVA-PAA enabling high performance for Si anode

Silicon anode undergoes dramatic volume expansion during charge and discharge, causing structural and interfacial instability that severely degrades battery cycling performance. Herein, we propose a three-dimensional (3D) flexible self-standing SiMP/SWCNT-COOH@PVA/PAA anode, in which carboxylation-modified single-walled carbon nanotubes (SWCNT-COOH) construct a highly conductive and flexible skeleton to provide rapid electron transport channels for micron silicon (SiMP), while polyacrylic acid-polyvinyl alcohol (PVA-PAA) cross-linking layer forms a high-strength polymer interface to strengthen the conductive skeleton and helps to maintain the structural integrity of SiMP. The resulting electrode exhibits ultra-high electrical conductance (12406 S m−1) and exceptional mechanical characteristic (tensile strength of 46.95 MPa). More importantly, it demonstrates extremely stable electrochemical properties, with an impressive maximum capacity of approximately 2868.5 mAh g−1 at 0.2C, while retaining an exceptional 96.49 % of capacity even after 100 cycles. A consistent capacity of 1000 mAh g−1 at 1C throughout 1000 cycles is also realized. Furthermore, a flexible full battery based on SiMP/SWCNT-COOH@PVA/PAA anode achieves a discharge capacity of 49.5 mAh g−1 following 100 cycles, and illuminates a LED strip normally under various bending conditions. These results are expected to open a new way towards enhanced performance silicon-based electrodes within flexible LIBs.

Architecting Sturdy Si/Graphite Composite with Lubricative Graphene Nanoplatelets for High-Density Electrodes.

Densification of the electrode by calendering is essential for achieving high-energy density in lithium-ion batteries. However, Si anode, which is regarded as the most promising high-energy substituent of graphite, is vulnerable to the crack during calendering process due to its intrinsic brittleness. Herein, a distinct strategy to prevent the crack and pulverization of Si nanolayer-embedded Graphite (Si/G) composite with graphene nanoplatelets (GNP) is proposed. The thickly coated GNP layer on Si/G by simple mechanofusion process imparts exceptional mechanical strength and lubricative characteristic to the Si/G composite, preventing the crack and pulverization of Si nanolayer against strong external force during calendering process. Accordingly, GNP coated Si/G (GNP-Si/G) composite demonstrates excellent electrochemical performances including superior cycling stability (15.6% higher capacity retention than P-Si/G after 300 cycles in the full-cell) and rate capability under the industrial testing condition including high electrode density (>1.6gcm-3) and high areal capacity (>3.5mAhcm-2). The material design provides a critical insight for practical approach to resolve the fragile properties of Si/G composite during calendering process.

Synergy of Artificial SEI and Electrolyte Additive for Improved Performance of Silicon Electrodes in Li-Ion Batteries.

Maintaining the electrochemically and mechanically stable solid electrolyte interphase (SEI) is of highest importance for the performance of high-capacity anode materials such as silicon (Si). Applying flexible Li-ion permeable coatings to the electrode surface using molecular layer deposition (MLD) offers a strategy to improve the properties of the SEI and greatly contributes to an increase in the cycle life and capacity retention of Si electrodes. In this study, the long-term cycling of Si electrodes with an MLD alucone coating is investigated in the context of more stable SEI formation. When the joined strategy introducing both MLD coating and anFEC electrolyte additive was realized, high performance of Si anodes was achieved, capable of delivering more than 1500 mAh g-1 even after 400 cycles. The reason for the significantly improved longevity is the ability of the alucone layer to react with HF present in LiPF6-based electrolytes already under OCV-like conditions, fluorinating most of the available -OH groups in the alucone structure. This reaction not only partially scavenges hydrofluoric acid but also does not disturb the confining effect of alucone-like fluorinated artificial SEI. This study shows the significance of searching for synergetic solutions, such as a combination of electrode surface modification and electrolyte composition, for maximizing the capacity retention of Si as an active material or as a capacity-enhancing additive to graphite electrodes, and as well can be applied to other high-energy battery materials with large volume changes during cycling.

Enhancing Electrochemical Performance of Si@CNT Anode by Integrating SrTiO3 Material for High-Capacity Lithium-Ion Batteries

Silicon (Si) has attracted worldwide attention for its ultrahigh theoretical storage capacity (4200 mA h g−1), low mass density (2.33 g cm−3), low operating potential (0.4 V vs. Li/Li+), abundant reserves, environmentally benign nature, and low cost. It is a promising high-energy-density anode material for next-generation lithium-ion batteries (LIBs), offering a replacement for graphite anodes owing to the escalating energy demands in booming automobile and energy storage applications. Unfortunately, the commercialization of silicon anodes is stringently hindered by large volume expansion during lithiation–delithiation, the unstable and detrimental growth of electrode/electrolyte interface layers, sluggish Li-ion diffusion, poor rate performance, and inherently low ion/electron conductivity. These present major safety challenges lead to quick capacity degradation in LIBs. Herein, we present the synergistic effects of nanostructured silicon and SrTiO3 (STO) for use as anodes in Li-ion batteries. Si and STO nanoparticles were incorporated into a multiwalled carbon nanotube (CNT) matrix using a planetary ball-milling process. The mechanical stress resulting from the expansion of Si was transferred via the CNT matrix to the STO. We discovered that the introduction of STO can improve the electrochemical performance of Si/CNT nanocomposite anodes. Experimental measurements and electrochemical impedance spectroscopy provide evidence for the enhanced mobility of Li-ions facilitated by STO. Hence, incorporating STO into the Si@CNT anode yields promising results, exhibiting a high initial Coulombic efficiency of approximately 85%, a reversible specific capacity of ~800 mA h g−1 after 100 cycles at 100 mA g−1, and a high-rate capability of 1400 mA g−1 with a capacity of 800 mA h g−1. Interestingly, it exhibits a capacity of 350 mAh g−1 after 1000 lithiation and delithiation cycles at a high rate of 600 mA hg−1. This result unveils and sheds light on the design of a scalable method for manufacturing Si anodes for next-generation LIBs.

Polyacrylonitrile and aluminum metal dual functionalization interconnected network for superior lithium storage in silicon anode

Currently, silicon-based anode is one of the most promising anode materials that can be applied in next-generation lithium-ion batteries. However, the high activity of the electrode–electrolyte interface and low electronic conductivity of Si anode during the cycling process greatly limits its large-scale application. Aluminum (Al) is the metallic current collector known to promote electronic conductivity and lithium-ion transfer at low cost. However, to our knowledge, scalable interface engineering incorporating Al with carbonized polymer has not been reported. Herein, a polyacrylonitrile (PAN) and aluminum metal dual functionalization interconnected network is achieved via a simple sol-gel method followed by high-temperature calcination to obtain a stable solid electrolyte interphase (SEI) while allowing fast Li+ transmission. The calculated diffusion energy barrier for lithium ions in Al is 0.2198 eV, significantly lower than that in Cu and Fe. Benefiting from the enhanced interfacial protection and kinetics of Si with polyacrylonitrile/Al, the prepared Si@Al@CPAN anode exhibits high lithium storage capacity (2034.90 mAh/g after 150 cycles at 0.84 A/g). At the same time, the prepared Si@Al@CPAN anode outperforms the pure Si anode in rate performance at 12.6 A/g (1116.75 mAh/g vs. 2.84 mAh/g). The present work delivers new design ideas for high-performance Si anode with a multi-functionalization interface.

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.

Reversible silicon anodes enabled by fluorinated inorganic-organic hybrid coating

Silicon anodes deliver batteries with energy densities much higher than those based on today’s dominant graphite anodes. However, they commonly exhibit huge volume variations and unfavorable interface stability, causing a gradually diminishing capacity on extended cycling. Most Si-based batteries consisting Si/C composites in industry can only use a very limited amount of Si (<30 % by weight). Exploiting molecular layer deposition (MLD) technique, a fluorine-rich flexible inorganic–organic hybrid alucone (AlFHQ) shell is controllably deposited onto Si electrodes. Employing ex situ XPS and AFM, the AlFHQ film presents reversible electrochemical evolutions in terms of composition and morphology. The interactions the between Li+ and −O−2,3,5,6-fluorobenzene functional groups help to construct a mechanically-chemically robust LiF-rich hybrid solid electrolyte interphase (SEI) on Si anode, delivering enhanced interfacial stability and integrity of electrode. An optimized coating thickness (≈5 nm) for interfacial stabilization and Li+ transport kinetics is demonstrated, namely, Si@AlFHQ-20. The reported fluorine-rich hybrid modification technique endows (a), stable cycling of Si anode (≈3.8 mAh cm−2) with an ultrahigh initial Coulombic efficiency (ICE) of 92.3 %; (b), enhanced rate capability of 1468 mAh/g at 2.0 A g−1 and good cycling performance; and (c), overall cell (Si@AlFHQ-20//LiCoO2@Al2O3) operational stability for more than 100 cycles under stringent cathode conditions (2.68 mAh cm−2, high cutoff voltage at 4.55 V).

Selective Methylation of Cyclic Ether Towards Highly Elastic Solid Electrolyte Interphase for Silicon‐based Anodes

Silicon (Si)‐based anodes offer high theoretical capacity for lithium‐ion batteries but suffer from severe volume changes and continuous solid electrolyte interphase (SEI) degradation. Here, we address these challenges by selective methylation of 1,3‐dioxolane (DOL), thus shifting the unstable bulk polymerization to controlled interfacial reactions and resulting in a highly elastic SEI. Comparative studies of 2‐methyl‐1,3‐dioxolane (2MDOL) and 4‐methyl‐1,3‐dioxolane (4MDOL) reveal that 4MDOL, with its larger ring strain and more stable radical intermediates due to hyperconjugation effect, promotes the formation of high‐molecular‐weight polymeric species at the electrode‐electrolyte interface. This elastic, polymer‐rich SEI effectively accommodates volume changes of Si and inhibits continuous side reactions. Our designed electrolyte enables Si‐based anode to achieve 85.4% capacity retention after 400 cycles at 0.5 C without additives, significantly outperforming conventional carbonate‐based electrolytes. Full cells also demonstrate stable long‐term cycling. This work provides new insights into molecular‐level electrolyte design for high‐performance Si anodes, offering a promising pathway toward next‐generation lithium‐ion batteries with enhanced energy density and longevity.

Are Sulfide‐Based Solid‐State Electrolytes the Best Pair for Si Anodes in Li‐Ion Batteries? (Adv. Energy Mater. 40/2024)

Are Sulfide‐Based Solid‐State Electrolytes the Best Pair for Si Anodes in Li‐Ion Batteries? (Adv. Energy Mater. 40/2024)

Selective Methylation of Cyclic Ether Towards Highly Elastic Solid Electrolyte Interphase for Silicon-based Anodes.

Silicon (Si)-based anodes offer high theoretical capacity for lithium-ion batteries but suffer from severe volume changes and continuous solid electrolyte interphase (SEI) degradation. Here, we address these challenges by selective methylation of 1,3-dioxolane (DOL), thus shifting the unstable bulk polymerization to controlled interfacial reactions and resulting in a highly elastic SEI. Comparative studies of 2-methyl-1,3-dioxolane (2MDOL) and 4-methyl-1,3-dioxolane (4MDOL) reveal that 4MDOL, with its larger ring strain and more stable radical intermediates due to hyperconjugation effect, promotes the formation of high-molecular-weight polymeric species at the electrode-electrolyte interface. This elastic, polymer-rich SEI effectively accommodates volume changes of Si and inhibits continuous side reactions. Our designed electrolyte enables Si-based anode to achieve 85.4% capacity retention after 400 cycles at 0.5 C without additives, significantly outperforming conventional carbonate-based electrolytes. Full cells also demonstrate stable long-term cycling. This work provides new insights into molecular-level electrolyte design for high-performance Si anodes, offering a promising pathway toward next-generation lithium-ion batteries with enhanced energy density and longevity.