Electrochemical performance enhancement of porous Si lithium-ion battery anode by integrating with optimized carbonaceous materials

Constructing a Stable Integrated Silicon Electrode with Efficient Lithium Storage Performance through Multidimensional Structural Design

Silicon (Si) stands out as a highly promising anode material for next-generation lithium-ion batteries. However, its low intrinsic conductivity and the severe volume changes during the lithiation/delithiation process adversely affect cycling stability and hinder commercial viability. Rational design of electrode architecture to enhance charge transfer and optimize stress distribution of Si is a transformative way to enhance cycling stability, which still remains a great challenge. In this work, we fabricated a stable integrated Si electrode by combining two-dimensional graphene sheets (G), one-dimensional Si nanowires (SiNW), and carbon nanotubes (CNT) through the cyclization process of polyacrylonitrile (PAN). The integrated electrode features a G/SiNW framework enveloped by a conformal coating consisting of cyclized PAN (cPAN) and CNT. This configuration establishes interconnected electron and lithium-ion transport channels, coupled with a rigid-flexible encapsulated coating, ensuring both high conductivity and resistance against the substantial volume changes in the electrode. The unique multidimensional structural design enhances the rate performance, cyclability, and structural stability of the integrated electrode, yielding a gravimetric capacity (based on the total mass of the electrode) of 650 mAh g-1 after 1000 cycles at 3.0 A g-1. When paired with a commercial LiNi0.5Co0.2Mn0.3O2 cathode, the resulting full cell retains 84.8% of its capacity after 160 cycles at 2.0 C and achieves an impressive energy density of 435 Wh kg-1 at 0.5 C, indicating significant potential for practical applications. This study offers valuable insights into comprehensive electrode structure design at the electrode level for Si-based materials.

TiO2-Coated Silicon Nanoparticle Core-Shell Structure for High-Capacity Lithium-Ion Battery Anode Materials

Silicon-based anode materials are considered one of the highly promising anode materials due to their high theoretical energy density; however, problems such as volume effects and solid electrolyte interface film (SEI) instability limit the practical applications. Herein, silicon nanoparticles (SiNPs) are used as the nucleus and anatase titanium dioxide (TiO₂) is used as the buffer layer to form a core-shell structure to adapt to the volume change of the silicon-based material and improve the overall interfacial stability of the electrode. In addition, silver nanowires (AgNWs) doping makes it possible to form a conductive network structure to improve the conductivity of the material. We used the core-shell structure SiNPs@TiO₂/AgNWs composite as an anode material for high-efficiency Li-ion batteries. Compared with the pure SiNPs electrode, the SiNPs@TiO₂/AgNWs electrode exhibits excellent electrochemical performance with a first discharge specific capacity of 3524.2 mAh·g^-1 at a current density of 400 mA·g^-1, which provides a new idea for the preparation of silicon-based anode materials for high-performance lithium-ion batteries.

Integrating highly active graphite nanosheets into microspheres for enhanced lithium storage properties of silicon

Integrating silicon (Si) and graphitic carbon into micron-sized composites by spray-drying holds great potential in developing advanced anodes for high-energy-density lithium-ion batteries (LIBs). However, common graphite particles as graphitic carbon are always too large in three-dimensional size, resulting in inhomogeneous hybridization with nanosized Si (NSi); in addition, the rate capability of graphite is poor owing to sluggish intercalation kinetics. Herein, we integrated graphite nanosheets (GNs) with NSi to prepare porous NSi-GN-C microspheres by spray-drying and subsequent calcination with the assistance of glucose. Two-dimensional GNs with average thickness of ∼80 nm demonstrate superior lithium storage capacity, high conductivity, and flexibility, which could improve the electronic transfer kinetics and structural stability. Moreover, the porous structure buffers the volume expansion of Si during the lithiation process. The obtained NSi-GN-C microspheres manifest excellent electrochemical performance, including high initial coulombic efficiency of 85.9%, excellent rate capability of 94.4% capacity retention after 50 repeated high-rate tests, and good cyclic performance for 500 cycles at 1.0 A g-1. Kinetic analysis and in situ impedance spectra reveal dominant pseudocapacitive behavior with rapid and stable Li+ insertion/extraction processes. Ex situ morphology characterization demonstrates the ultra-stable integrated structure of the NSi-GN-C. The highly active GN demonstrates great potential to improve the lithium storage properties of Si, which provides new opportunity for constructing high-performance anodes for LIBs.

Microspheres of Si@Carbon-CNTs composites with a stable 3D interpenetrating structure applied in high-performance lithium-ion battery

The huge volumetric expansion (>300 %) of Si that occurs during the charge-discharge process makes it to have poor cycling ability and weak stable structure. These factors are considered as critical obstacles to the further development of Si as anode for lithium-ion batteries (LIBs). Herein, novel 3D interpenetrating microspheres, i.e., Si@C-CNTs, which consist of silicon nanoparticles interpenetrated with carbon nanotubes (CNTs) and stuck with amorphous carbon (C) have been designed and prepared via a spray-drying assisted approach. As anode of LIBs, Si@C-CNTs microspheres can achieve high silicon loadings of around 86 % and a high initial coulomb efficiency of 80.8 %. The electrodes maintain a reversible specific capacity of 1585.9mAh/g at 500 mA g-1 after 200 cycles, and deliver an excellent rate capability of 756.4 mAh/g at 5 A g-1. The outstanding performance of Si@C-CNTs can be due to their 3D interpenetrating structure and the synergy effect between the CNTs network and amorphous carbon therein. They synergistically act as conductive matrices which significantly improve the conductivity of the composite; they also act binders and reinforcing skeleton which help the composite spheres to have stable structure. Especially, the latter (reinforcing skeleton) alleviates the volumetric effect induced by the expansion and shrinkage of silicon particles during lithiation. The unique architecture provides an ideal model that can be used to design Si-based composite anode for advanced LIBs.

Emerging carbon-based flexible anodes for potassium-ion batteries: Progress and opportunities

In recent years, carbon-based flexible anodes for potassium-ion batteries are increasingly investigated owing to the low reduction potential and abundant reserve of K and the simple preparation process of flexible electrodes. In this review, three main problems on pristine carbon-based flexible anodes are summarized: excessive volume change, repeated SEI growth, and low affinity with K⁺, which thus leads to severe capacity fade, sluggish K⁺ diffusion dynamics, and limited active sites. In this regard, the recent progress on the various modification strategies is introduced in detail, which are categorized as heteroatom-doping, coupling with metal and chalcogenide nanoparticles, and coupling with other carbonaceous materials. It is found that the doping of heteroatoms can bring the five enhancement effects of increasing active sites, improving electrical conductivity, expediting K⁺ diffusion, strengthening structural stability, and enlarging interlayer spacing. The coupling of metal and chalcogenide nanoparticles can largely offset the weakness of the scarcity of K⁺ storage sites and the poor wettability of pristine carbon-based flexible electrodes. The alloy nanoparticles consisting of the electrochemically active and inactive metals can concurrently gain a stable structure and high capacity in comparison to mono-metal nanoparticles. The coupling of the carbonaceous materials with different characteristics can coordinate the advantages of the nanostructure from graphite carbon, the defects and vacancies from amorphous carbon, and the independent structure from support carbon. Finally, the emerging challenges and opportunities for the development of carbon-based flexible anodes are presented.

Enhancing Capacity and Stability of Anionic MOFs as Electrode Material by Cation Exchange

In this study we report on the characterization and use of the anionic metal-organic framework (MOF) JUMP-1, [(Me2NH2)2[Co3(ntb)2(bdc)]] n , alongside with its alkali-metal ion-exchanged analogs JUMP-1(Li) and JUMP-1(Na), as electrode materials for lithium and sodium batteries. Composite electrodes containing these anionic-MOFs were prepared and tested in 1 M lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) in propylene carbonate (PC) and/or 1 M sodium TFSI (NaTFSI) in PC. We showed that the ion-exchanged materials JUMP-1(Li) and JUMP-1(Na) display higher capacities in comparison with the original as-prepared compound JUMP-1 (490 mA∙h∙g-1 vs. 164 mA∙h∙g-1 and 83 mA∙h∙g-1 vs. 73 mA∙h∙g-1 in Li and Na based electrolytes, respectively). Additionally, we showed that the stability of the electrodes containing the ion-exchanged materials is higher than that of JUMP-1, suggesting a form of chemical pre-alkalation works to stabilize them prior to cycling. The results of these studies indicate that the use of designed anionic-MOFs represents a promising strategy for the realization of high performance electrodes suitable for energy storage devices.

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.

Constructing Densely Compacted Graphite/Si/SiO2 Ternary Composite Anodes for High-Performance Li-Ion Batteries

Graphite has dominated the market of anode materials for lithium-ion batteries in applications such as consumer electronic devices and electric vehicles. As commercial graphite anodes are approaching their theoretical capacity, significant efforts have been dedicated towards higher capacity by blending capacity-enhancing additives (e.g., Si) with graphite particles. In spite of the improved gravimetric capacity, the areal capacity of such composite anodes might decrease due to excess void spaces and an incompatible material size distribution. Herein, a rational design of compact graphite/Si/SiO₂ ternary composites has been proposed to address the abovementioned issues. Si/SiO₂ clusters with an optimal particle size are homogeneously dispersed in the interstitial spaces between graphite particles to promote the packing density, leading to a higher areal capacity than that of pure graphite with equivalent mass loading or electrode thickness. By taking the full intrinsic advantages of graphite, Si, and SiO₂, the composite electrodes exhibit 553.6 mAh g^-1 after 700 cycles with a capacity retention of 95.2%. Furthermore, the graphite/Si/SiO₂ electrodes demonstrate a high coulombic efficiency with an average of 99.68% from 2nd to 200th cycles and areal capacities above 1.75 mAh cm^-2 during 200 cycles with an areal mass loading as high as 4.04 mg cm^-2. A packing model has been proposed and verified by experimental investigation as a design principle of densely compacted anodes. The effective strategy of introducing Si/SiO₂ clusters into the void spaces between graphite particles provides an alternative solution for implementation of graphite-Si composite anodes in next-generation Li-ion cells.

Recent Advances in Silicon-Based Electrodes: From Fundamental Research toward Practical Applications

The increasing demand for higher-energy-density batteries driven by advancements in electric vehicles, hybrid electric vehicles, and portable electronic devices necessitates the development of alternative anode materials with a specific capacity beyond that of traditional graphite anodes. Here, the state-of-the-art developments made in the rational design of Si-based electrodes and their progression toward practical application are presented. First, a comprehensive overview of fundamental electrochemistry and selected critical challenges is given, including their large volume expansion, unstable solid electrolyte interface (SEI) growth, low initial Coulombic efficiency, low areal capacity, and safety issues. Second, the principles of potential solutions including nanoarchitectured construction, surface/interface engineering, novel binder and electrolyte design, and designing the whole electrode for stability are discussed in detail. Third, applications for Si-based anodes beyond LIBs are highlighted, specifically noting their promise in configurations of Li-S batteries and all-solid-state batteries. Fourth, the electrochemical reaction process, structural evolution, and degradation mechanisms are systematically investigated by advanced in situ and operando characterizations. Finally, the future trends and perspectives with an emphasis on commercialization of Si-based electrodes are provided. Si-based anode materials will be key in helping keep up with the demands for higher energy density in the coming decades.

Electrochemical Performance Enhancement of Micro-Sized Porous Si by Integrating with Nano-Sn and Carbonaceous Materials

Silicon is investigated as one of the most prospective anode materials for next generation lithium ion batteries due to its superior theoretical capacity (3580 mAh g-1), but its commercial application is hindered by its inferior dynamic property and poor cyclic performance. Herein, we presented a facile method for preparing silicon/tin@graphite-amorphous carbon (Si/Sn@G-C) composite through hydrolyzing of SnCl2 on etched Fe-Si alloys, followed by ball milling mixture and carbon pyrolysis reduction processes. Structural characterization indicates that the nano-Sn decorated porous Si particles are coated by graphite and amorphous carbon. The addition of nano-Sn and carbonaceous materials can effectively improve the dynamic performance and the structure stability of the composite. As a result, it exhibits an initial columbic efficiency of 79% and a stable specific capacity of 825.5 mAh g-1 after 300 cycles at a current density of 1 A g-1. Besides, the Si/Sn@G-C composite exerts enhanced rate performance with 445 mAh g-1 retention at 5 A g-1. This work provides an approach to improve the electrochemical performance of Si anode materials through reasonable compositing with elements from the same family.

Porous Si/Fe2O3 Dual Network Anode for Lithium-Ion Battery Application

Benefiting from ultra-high theoretical capacity, silicon (Si) is popular for use in energy storage fields as a Li-ion battery anode material because of its high-performance. However, a serious volume variation happens towards Si anodes in the lithiation/delithiation process, triggering the pulverization of Si and a fast decay in its capacity, which greatly limits its commercial application. In our study, a porous Si/Fe2O3 dual network anode was fabricated using the melt-spinning, ball-milling and dealloying method. The anode material shows good electrochemical performance, delivering a reversible capacity of 697.2 mAh g-1 at 200 mA g-1 after 100 cycles. The high Li storage property is ascribed to the rich mesoporous distribution of the dual network structure, which may adapt the volume variation of the material during the lithiation/delithiation process, shorten the Li-ion diffusion distance and improve the electron transport speed. This study offers a new idea for developing natural ferrosilicon ores into the porous Si-based materials and may prompt the development of natural ores in energy storage fields.