Covalently Bonded Silicon/Carbon Nanocomposites as Cycle-Stable Anodes for Li-Ion Batteries

Enhanced Lithium Storage Performance: Dual-Modified Electrospun Si@MnO@CNFs Composites for Advanced Anodes

Due to its many benefits, including high specific capacity, low voltage plateau, and plentiful supplies, silicon-based anode materials are a strong contender to replace graphite anodes. However, silicon has drawbacks such as poor electrical conductivity, abrupt volume changes during the discharge process, and continuous growth of the solid electrolyte interfacial (SEI) film during cycling, which would cause the electrode capacity to degrade quickly. Coating the silicon's exterior with carbon or metal oxide is a popular method to resolve the above-mentioned problems. In light of those above, the liquid-phase approach and electrostatic spinning technique were used in this work to create Si@MnO@CNFs bilayer-coated silicon-based anode materials. Because of the well-thought-out design, MnO and C bilaterally coat the silicon nanoparticles, significantly reducing their volume effect during cycling. Furthermore, manganese oxide has outstanding electrochemical kinetics and an excellent theoretical capacity. The carbon nanofibers' outermost layer increases the material's conductivity and stabilizes the composite material's structure, reducing the volume effect. After 1100 cycles at 2 A g-1, the composite anode material prepared in this work can still maintain a high capacity of 994.4 mAh g-1. This study offers an unusual combination of silicon and MnO that might set the way for the application of silicon-based composites in lithium-ion batteries.

Stabilizing Lithium-Metal Host Anodes by Covalently Binding MgF2 Nanodots to Honeycomb Carbon Nanofibers

Constructing lithiophilic carbon hosts has been regarded as an effective strategy for inhibiting Li dendrite formation and mitigating the volume expansion of Li metal anodes. However, the limitation of lithiophilic carbon hosts by conventional surface decoration methods over long-term cycling hinders their practical application. In this work, a robust host composed of ultrafine MgF2 nanodots covalently bonded to honeycomb carbon nanofibers (MgF2/HCNFs) is created through an in situ solid-state reaction. The composite exhibits ultralight weight, excellent lithiophilicity, and structural stability, contributing to a significantly enhanced energy efficiency and lifespan of the battery. Specifically, the strong covalent bond not only prevents MgF2 nanodots from migrating and aggregating but also enhances the binding energy between Mg and Li during the molten Li infusion process. This allows for the effective and stable regulation of repeated Li plating/stripping. As a result, the MgF2/HCNF-Li electrode delivers a high Coulombic efficiency of 97% after 200 cycles, cycling stably for more than 2000 h. Furthermore, the full cells with a LiFePO4 cathode achieve a capacity retention of 85% after 500 cycles at 0.5C. This work provides a strategy to guide dendrite-free Li deposition patterns toward the development of high-performance Li metal batteries.

Growth of Vertical Graphene Sheets on Silicon Nanoparticles Well-Dispersed on Graphite Particles for High-Performance Lithium-Ion Battery Anode

With rapidly increasing demand for high energy density, silicon (Si) is greatly expected to play an important role as the anode material of lithium-ion batteries (LIBs) due to its high specific capacity. However, large volume expansion for silicon during the charging process is still a serious problem influencing its cycling stability. Here, a Si/C composite of vertical graphene sheets/silicon/carbon/graphite (VGSs@Si/C/G) is reported to address the electrochemical stability issues of Si/graphite anodes, which is prepared by adhering Si nanoparticles on graphite particles with chitosan and then in situ growing VGSs by thermal chemical vapor deposition. As a promising anode material, due to the buffering effect of VGSs and tight bonding between Si and graphite particles, the composite delivers a high reversible capacity of 782.2 mAh g-1 after 1000 cycles with an initial coulombic efficiency of 87.2%. Furthermore, the VGSs@Si/C/G shows a diffusion coefficient of two orders higher than that without growing the VGSs. The full battery using VGSs@Si/C/G anode and LiNi0.8 Co0.1 Mn0.1 O2 cathode achieves a high gravimetric energy density of 343.6 Wh kg-1 , a high capacity retention of 91.5% after 500 cycles and an excellent average CE of 99.9%.

Simple Construction of Multistage Stable Silicon-Graphite Hybrid Granules for Lithium-Ion Batteries

Because of its high specific capacity, the silicon-graphite composite (SGC) is regarded as a promising anode for new-generation lithium-ion batteries. However, the frequently employed two-section preparation process, including the modification of silicon seed and followed mixture with graphite, cannot ensure the uniform dispersion of silicon in the graphite matrix, resulting in a stress concentration of aggregated silicon domains and cracks in composite electrodes during cycling. Herein, inspired by powder engineering, the two independent sections are integrated to construct multistage stable silicon-graphite hybrid granules (SGHGs) through wet granulation and carbonization. This method assembles silicon nanoparticles (Si NPs) and graphite and improves compatibility between them, addressing the issue of severe stress concentration caused by uncombined residue of Si NPs. The optimal SGHG prepared with 20% pitch content exhibits a highly reversible specific capacity of 560.0 mAh g^-1 at a current density of 200 mA g^-1 and a considerable stability retention of 86.1% after 1000 cycles at 1 A g^-1 . Moreover, as a practical application, the full cell delivers an outstanding capacity retention of 85.7% after 400 cycles at 2 C. The multistage stable structure constructed by simple wet granulation and carbonization provides theoretical guidance for the preparation of commercial SGC anodes.

High-ICE and High-Capacity Retention Silicon-Based Anode for Lithium-Ion Battery

Silicon-based anodes are promising to replace graphite-based anodes for high-capacity lithium-ion batteries (LIB). However, the charge–discharge cycling suffers from internal stresses created by large volume changes of silicon, which form silicon-lithium compounds, and excessive consumption of lithium by irreversible formation of lithium-containing compounds. Consumption of lithium by the initial conditioning of the anode, as indicated by low initial coulombic efficiency (ICE), and subsequently continuous formation of solid-electrolyte-phase (SEI) on the freshly exposed silicon surface, are among the main issues. A high-performance, silicon-based, high-capacity anode exhibiting 88.8% ICE and the retention of 2 mAh/cm² areal capacity after 200 discharge–charge cycles at the rate of 1 A/g is reported. The anode is made on a copper foil using a mixture of 70%:10%:20% by weight ratio of silicon flakes of 100 × 800 × 800 nm in size, Super P conductivity enhancement additive, and an equal-weight mixture of CMC and SBR binders. Pyrolysis of fabricated anodes at 700 °C in argon environment for 1 h was applied to convert the binders into a porous graphitic carbon structure that encapsulates individual silicon flakes. The porous anode has a mechanically strong and electrically conductive graphitic carbon structure formed by the pyrolyzed binders, which protect individual silicon flakes from excessive reactions with the electrolyte and help keep small pieces of broken silicon flakes together within the carbon structure. The selection and amount of conductivity enhancement additives are shown to be critical to the achievement of both high-ICE and high-capacity retention after long cycling. The Super P conductivity enhancement additive exhibits a smaller effective surface area where SEI forms compared to KB, and thus leads to the best combination of both high-ICE and high-capacity retention. A silicon-based anode exhibiting high capacity, high ICE, and a long cycling life has been achieved by the facile and promising one-step fabrication process.

Durable silicon-carbon composites self-assembled from double-protected heterostructure for lithium-ion batteries

HYPOTHESIS

Silicon-carbon composites have been faced with the contact issues between silicon and carbon in the form of material aggregation and inferior dispersion, leading to electrode cracking or kinetic degradation during cycling. In addition to dispersion improvement from interfacial linkage between self-assembled Si nanoparticles (SiNPs) and carbon fibers (CNFs), the positive influences of high-content carboxymethyl cellulose(CMC) (25 wt%) and amorphous carbon are also expected, respectively after the second-step self-assembly and subsequently sintering.

EXPERIMENTS

A novel composite (i.e. Si-CNF@C) with the decoration of entire SiNPs in the framework of both CNFs and amorphous carbon was prepared via two-step electrostatic self-assembly followed by sintering. Such a composite with heterogeneous nanostructure was used as a lithium-ion battery anode without additional binders or conductive agents.

FINDINGS

SiNPs can be well protected with CNFs and amorphous carbon against the dispersion and contact problems under both effects of electrostatic attraction and chemical bonding. With the double-protected heterostructure, such a novel Si-CNF@C electrode exhibits highly reversible capacities of 1200 mAh g^-1, 982 mAh g^-1, and 849 mAh g^-1 after 100, 500, and 1000 cycles at 0.5 A g^-1, respectively. The long-term cycling stability with a capacity loss of 0.036% per cycle over 1000 cycles is comparable.

Synthesis of Si/Fe2O3-Anchored rGO Frameworks as High-Performance Anodes for Li-Ion Batteries

By virtue of the high theoretical capacity of Si, Si-related materials have been developed as promising anode candidates for high-energy-density batteries. During repeated charge/discharge cycling, however, severe volumetric variation induces the pulverization and peeling of active components, causing rapid capacity decay and even development stagnation in high-capacity batteries. In this study, the Si/Fe2O3-anchored rGO framework was prepared by introducing ball milling into a melt spinning and dealloying process. As the Li-ion battery (LIB) anode, it presents a high reversible capacity of 1744.5 mAh g-1 at 200 mA g-1 after 200 cycles and 889.4 mAh g-1 at 5 A g-1 after 500 cycles. The outstanding electrochemical performance is due to the three-dimensional cross-linked porous framework with a high specific surface area, which is helpful to the transmission of ions and electrons. Moreover, with the cooperation of rGO, the volume expansion of Si is effectively alleviated, thus improving cycling stability. The work provides insights for the design and preparation of Si-based materials for high-performance LIB applications.

Design Strategies of Si/C Composite Anode for Lithium-Ion Batteries

Silicon-based materials that have higher theoretical specific capacity than other conventional anodes, such as carbon materials, Li₂ TiO₃ materials and Sn-based materials, become a hot topic in research of lithium-ion battery (LIB). However, the low conductivity and large volume expansion of silicon-based materials hinders the commercialization of silicon-based materials. Until recent years, these issues are alleviated by the combination of carbon-based materials. In this review, the preparation of Si/C materials by different synthetic methods in the past decade is reviewed along with their respective advantages and disadvantages. In addition, Si/C materials formed by silicon and different carbon-based materials is summarized, where the influences of carbons on the electrochemical performance of silicon are emphasized. Lastly, future research direction in the material design and optimization of Si/C materials is proposed to fill the current gap in the development of efficient Si/C anode for LIBs.

Nitrogen-plasma doping of carbon film for a high-quality layered Si/C composite anode

The effect of the chemical component and microstructure, not to mention their facile modification, of the coating/wrapping carbon layer on the electrochemical performance of the Si/C composite anode in lithium ion batteries (LIBs) hasn't been actively explored although Si/C has been recognized as one of the most promising route for the high energy density LIBs. Herein we propose a novel nitrogen-plasma doping route to modify the top carbon film in an elaborately constructed layered Si/C composite anode. The electrochemical performance, e.g., the initial coulombic efficiency (CE), cycle stability and specific capacity of the composite anode is drastically improved by this plasma processing due to the increased kinetics of lithium ions. By means of the appropriate adjustment of the N doping ratio and N chemical configuration in the carbon layer through a N₂/H₂ plasma processing, the lithium diffusion rate in the composite anode was memorably increased as the pseudocapacitance effects promoted. The optimized Si/C composite exhibits a high capacity of 1120.7 mA h g^-1 and an initial CE of 80.8% at the current of 2 A g^-1 after a long cycle of 1500, increasing by ~40% of specific capacity and ~29% of the initial CE.

Self-Templated Formation of Fluffy Graphene-Wrapped Ni5P4 Hollow Spheres for Li-Ion Battery Anodes with High Cycling Stability

Transition-metal phosphides have gained great importance in the field of energy conversion and storage such as electrochemical water splitting, fuel cells, and Li-ion batteries. In this study, a rationally designed novel fluffy graphene (FG)-wrapped monophasic Ni₅P₄ (Ni₅P₄@FG) is in-situ-synthesized using a chemical vapor deposition method as a Li-ion battery anode material. The porous and hollow structure of Ni₅P₄ core is greatly helpful for lithium-ion diffusion, and at the same time, the cilia-like graphene nanosheet shell provides an electron-conducting layer and stabilizes the solid electrolyte interface formed on the Ni₅P₄ surface. The Ni₅P₄@FG sample shows a high reversible capacity of 739 mAh g^-1 after 300 cycles at a specific current density of 500 mA g^-1. The high capacity, superior cycling stability, and improved rate capability of Ni₅P₄@FG are ascribed to its unique hierarchical structure. Moreover, the present efficient fabrication methodology of Ni₅P₄@FG has potential to be developed as a general method for the synthesis of other transition-metal phosphides.

In Situ-Formed Artificial Solid Electrolyte Interphase for Boosting the Cycle Stability of Si-Based Anodes for Li-Ion Batteries

Si is being actively developed as one of the most promising high-capacity anodes for next-generation lithium-ion batteries (LIBs). However, low cycling coulombic efficiency (CE) due to the repetitive growth of the solid electrolyte interphase (SEI) film is still an issue for its application in full batteries. Here, we propose a strategy to in situ form an artificial solid electrolyte interphase (ASEI) on the ferrosilicon/carbon (FeSi/C) anode surface by a purposely designed nucleophilic reaction of polysulfides with vinylene carbonate (VC) and fluoroethylene carbonate (FEC) molecules. The as-formed ASEI layer is mechanically dense and ionically conducting and therefore can effectively prevent the electrolyte infiltration and decomposition while allowing Li⁺ transport across, thus stabilizing the interface of the FeSi/C anode. As a result, the ASEI-modified FeSi/C anode exhibits a large reversible capacity of 1409.4 mA h g^-1, an excellent cycling stability over 650 cycles, and a greatly elevated cycling CE of 99.8%, possibly serving as a high-capacity anode of LIBs.

Covalent Coupling-Stabilized Transition-Metal Sulfide/Carbon Nanotube Composites for Lithium/Sodium-Ion Batteries

Transition-metal sulfides (TMSs) powered by conversion and/or alloying reactions are considered to be promising anode materials for advanced lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). However, the limited electronic conductivity and large volume expansion severely hinder their practical application. Herein, we report a covalent coupling strategy for TMS-based anode materials using amide linkages to bind TMSs and carbon nanotubes (CNTs). In the synthesis, the thiourea acts as not only the capping agent for morphology control but also the linking agent for the covalent coupling. As a proof of concept, the covalently coupled ZnS/CNT composite (CC-ZnS/CNT) has been prepared, with ZnS nanoparticles (∼10 nm) tightly anchored on CNT bundles. The compact ZnS-CNT heterojunctions are greatly beneficial to facilitating the electron/ion transfer and ensuring structural stability. Due to the strong coupling interaction between ZnS and CNTs, the composite presents prominent pseudocapacitive behavior and highly reversible electrochemical processes, thus leading to superior long-term stability and excellent rate capability, delivering reversible capacities of 333 mAh g^-1 at 2 A g^-1 over 4000 cycles for LIBs and 314 mAh g^-1 at 5 A g^-1 after 500 cycles for SIBs. Consequently, CC-ZnS/CNT exhibits great competence for applications in LIBs and SIBs, and the covalent coupling strategy is proposed as a promising approach for designing high-performance anode materials.

Enveloping a Si/N-doped carbon composite in a CNT-reinforced fibrous network as flexible anodes for high performance lithium-ion batteries

A CNT-reinforced carbonaceous fibers network anchored with N-doped carbon-coated Si (C/Si/CNTs) has been fabricated. Utilized as flexible anodes for lithium-ion batteries, the C/Si/CNT delivers excellent cycling performance and rate capabilities.

On the Interface Design of Si and Multilayer Graphene for a High-Performance Li-Ion Battery Anode

Si/multilayer graphene (mG) is a promising candidate for the next-generation Li-ion battery anode. The highly ordered mG shows intrinsic good stability against the liquid electrolyte and its flexibility to accommodate volume change. Until now, reducing the growth temperature and thus engineering the interphase are a very important research area, but only few studies have been reported. Herein, for the first time, the mG is grown with the Al₂O₃ catalyst at a relatively low temperature of 750 °C, while the thickness is controlled to 2 nm. The growth of mG obeys the Stranski-Krastanov mechanism. Applying a rapid cooling process, a silicon oxycarbide (SiOC) interlayer is in situ-fabricated between the mG coating layer and Si core. The SiOC interlayer is demonstrated to accommodate the volume change of Si and enable faster lithium ion transportation than mG. Taking synergetic advantages of the mG coating layer and SiOC interphase, the cycling stability significantly improved, and a high specific capacity of 990 mA h/g is obtained at 1 A/g after 500 cycles in half cells. A high rate performance of 1164.5 mA h/g at 4 A/g is achieved. Tested in a 1.8 A h pouch cell with LiNi_0.5Mn_0.3Co_0.2O₂ (NMC532) as the cathode, the cell delivers a specific energy of ∼380 W h/kg. The capacity retentions are 93% and 78% after 100 cycles and 200 cycles, respectively. Our work highlights the importance of the interphase design of Si/mG composite anodes, which could also be extended to various core-shell materials in energy storage materials.

Building a Cycle-Stable Fe-Si Alloy/Carbon Nanocomposite Anode for Li-Ion Batteries through a Covalent-Bonding Method

Si is being intensively developed as a safe and high-performance anode for next-generation Li-ion batteries (LIBs); however, its battery application still remains challenging because of its low cycling Coulombic efficiency. To address this issue, we chose a conjugated polymer, polynaphthalene, as a carbon precursor and a low-cost commercial ferrosilicon (Fe-Si) alloy as the active phase to prepare a Fe-Si/C nanocomposite with a core-shell-like architecture through sand milling-assisted covalent-bonding method, followed by a carbonization reaction, thus forming a covalently bonded carbon coating on the surfaces of Fe-Si alloy nanoparticles. Benefitting from the greatly reduced volumetric expansion of Fe-Si alloy cores in the lithiation process and the stable interface provided by the outer carbon shell, the thus-prepared Fe-Si/C nanocomposite exhibits a high structural stability in repeated charge/discharge cycles. The experimental results reveal that the Fe-Si/C composite anode can demonstrate a high reversible capacity of 1316.2 mA h g^-1 with an active mass utilization of 82.6%, a long-term cycle stability of more than 1000 cycles even at a considerably high current rate of 2.0 A g^-1, and, in particular, a high cycling Coulombic efficiency of 99.7%, showing great prospect for application in practical LIBs.