Facile and Scalable Approach To Fabricate Granadilla-like Porous-Structured Silicon-Based Anode for Lithium Ion Batteries

Cu and Ni Co-Doped Porous Si Nanowire Networks as High-Performance Anode Materials for Lithium-Ion Batteries

Due to its extremely high theoretical mass specific capacity, silicon is considered to be the most promising anode material for lithium-ion batteries (LIBs). However, serious volume expansion and poor conductivity limit its commercial application. Herein, dealloying treatments of spray dryed Al-Si-Cu-Ni particles are performed to obtain a Cu/Ni co-doped Si-based anode material with a porous nanowire network structure. The porous structure enables the material to adapt to the volume changes in the cycle process. Moreover, the density functional theory (DFT) calculations show that the co-doping of Cu and Ni can improve the capture ability towards Li, which can accelerate the electron migration rate of the material. Based on the above advantages, the as-prepared material presents excellent electrochemical performance, delivering a reversible capacity of 1092.4 mAh g-1 after 100 cycles at 100 mA g-1. Even after 500 cycles, it still retains 818.7 mAh g-1 at 500 mA g-1. This study is expected to provide ideas for the preparation and optimization of Si-based anodes with good electrochemical performance.

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.

Flexible Porous Silicon/Carbon Fiber Anode for High-Performance Lithium-Ion Batteries

We demonstrate a cross−linked, 3D conductive network structure, porous silicon@carbon nanofiber (P−Si@CNF) anode by magnesium thermal reduction (MR) and the electrospinning methods. The P−Si thermally reduced from silica (SiO₂) preserved the monodisperse spheric morphology which can effectively achieve good dispersion in the carbon matrix. The mesoporous structure of P–Si and internal nanopores can effectively relieve the volume expansion to ensure the structure integrity, and its high specific surface area enhances the multi−position electrical contact with the carbon material to improve the conductivity. Additionally, the electrospun CNFs exhibited 3D conductive frameworks that provide pathways for rapid electron/ion diffusion. Through the structural design, key basic scientific problems such as electron/ion transport and the process of lithiation/delithiation can be solved to enhance the cyclic stability. As expected, the P−Si@CNFs showed a high capacity of 907.3 mAh g⁻¹ after 100 cycles at a current density of 100 mA g⁻¹ and excellent cycling performance, with 625.6 mAh g⁻¹ maintained even after 300 cycles. This work develops an alternative approach to solve the key problem of Si nanoparticles’ uneven dispersion in a carbon matrix.

Engineering Bamboo Leaves Into 3D Macroporous Si@C Composites for Stable Lithium-Ion Battery Anodes

Silicon is considered as the most promising candidate for anodes of next generation lithium-ion batteries owing to its natural abundance and low Li-uptake potential. Building a macroporous structure would alleviate the volume variation and particle fracture of silicon anodes during cycling. However, the common approaches to fabricate macroporous silicon are complex, costly, and high energy-consuming. Herein, bamboo leaves are used as a sustainable and abundant resource to produce macroporous silicon via a scalable magnesiothermic reduction method. The obtained silicon inherits the natural interconnected network from the BLs and the mesopores from the BL-derived silica are engineered into macropores by selective etching after magnesiothermic reduction. These unique structural advantages lead to superior electrochemical performance with efficient electron/ion transport and cycling stability. The macroporous Si@C composite anodes deliver a high capacity of 1,247.7 mAh g⁻¹ after 500 cycles at a current density of 1.0 A g⁻¹ with a remarkable capacity retention of 98.8% and average Coulombic efficiency as high as 99.52% for the same cycle period. Furthermore, the rate capabilities of the Si@C composites are enhanced by conformal carbon coating, which enables the anode to deliver a capacity of 538.2 mAh g⁻¹ at a high current density of 4.0 A g⁻¹ after 1,000 deep cycles. Morphology characterization verifies the structural integrity of the macroporous Si@C composite anodes. This work demonstrated herein provides a simple, economical, and scalable route for the industrial production of macroporous Si anode materials utilizing BLs as a sustainable source for high-performance LIBs.

Encapsulating a Responsive Hydrogel Core for Void Space Modulation in High-Stability Graphene-Wrapped Silicon Anodes

Due to its formidably high theoretical capacity (3590 mAh/g at room temperature), silicon (Si) is expected to replace graphite as the dominant anode for higher energy density lithium (Li)-ion batteries. However, stability issues stemming from silicon's significant volume expansion (∼300%) upon lithiation have slowed down commercialization. Herein, we report the design of a scalable process to engineer core-shell structures capable of buffering this volume expansion, which utilize a core made up of a poly(ethylene oxide)-carboxymethyl cellulose hydrogel and silicon protected by a crumpled graphene shell. The volume expansion of the hydrogel upon exposure to water creates a void space between the Si-Si and Si-rGO interfaces within the core when the gel dries. Unlike sacrificial spacers, the dehydrated hydrogel remains in the core and acts as an elastic Li-ion conductor, which improves the stability and high rate performance. The optimized composite electrodes retain ∼81.7% of their initial capacity (1055 mAh/(g_rGO+gel+Si)) after 320 cycles when an active material loading of 1 mg/cm² is used. At more practical mass loadings (2.5 mg/cm²), the electrodes achieve 2.04 mAh/cm² and retain 79% of this capacity after 200 cycles against a lithium half-cell. Full cells assembled using a lithium ion phosphate cathode lose only 6.7% of their initial capacity over 100 cycles, demonstrating the potential of this nanocomposite anode for use in next-generation Li-ion batteries.

Spider-web-inspired cellulose nanofibrils networking polyaniline-encapsulated silica nanoparticles as anode material of lithium-ion batteries

As the promising anode material of lithium-ion batteries (LIBs), SiO₂ has high theoretical capacity, but the volume expansion severely hinders its application. To address the challenge, inspired by the highly flexible spider-web architecture, the SiO₂@carbonized polyaniline/carbonized 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (SiO₂@cPANI/cTOCNFs) composite was designed, and fabricated via carbonizing the freeze-dried SiO₂@PANI/TOCNFs. The resultant SiO₂@cPANI/cTOCNFs composite exhibited unique spider-web-like nanostructures, providing a double-layer carbon network to protect SiO₂ anode material. The results showed that, the SiO₂@cPANI/cTOCNFs composite as anode material of LIBs offered a reversible capacity of 1103 mAh g^-1 at a current density of 0.1 A g^-1 after 200 cycles, and gave a capacity of 302 mAh g^-1 after 1000 cycles at a current density of 1 A g^-1, exhibiting excellent cycling stability. This study provides a strategy of spider-web-inspired cellulose nanofibrils networking polyaniline-encapsulated silica nanoparticles as anode material of LIBs.

Connecting battery technologies for electric vehicles from battery materials to management

Vehicle electrification has always been a hot topic and gradually become a major role in the automobile manufacturing industry over the last two decades. This paper presented comprehensive discussions and insightful evaluations of both conventional electric vehicle (EV) batteries (such as lead-acid, nickel-based, lithium-ion batteries, etc.) and the state-of-the-art battery technologies (such as all-solid-state, silicon-based, lithium-sulphur, metal-air batteries, etc.). Battery major component materials, operating characteristics, theoretical models, manufacturing processes, and end-of-life management were thoroughly reviewed. Different from other reviews focusing on theoretical studies, this review emphasized the key aspects of battery technologies, commercial applications, and lifecycle management. Useful battery managing technologies such as health prediction, charging and discharging, as well as thermal runaway prevention were thoroughly discussed. Two novel hexagon radar charts of all-round evaluations of most reigning and potential EV battery technologies were created to predict the development trend of the EV battery technologies. It showed that lithium-ion batteries (3.9 points) would be still the dominant product for the current commercial EV power battery market in a short term. However, some cutting-edge technologies such as an all-solid-state battery (3.55 points) and silicon-based battery (3.3 points) are highly likely to be the next-generation EV onboard batteries with both higher specific power and better safety performance.

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.

Controlling Void Space in Crumpled Graphene-Encapsulated Silicon Anodes using Sacrificial Polystyrene Nanoparticles

Silicon anodes have a theoretical capacity of 3590 mAh g^-1 (for Li₁₅ Si₄ , at room temperature), which is tenfold higher than the graphite anodes used in current Li-ion batteries. This, and silicon's natural abundance, makes it one of the most promising materials for next-generation batteries. Encapsulating silicon nanoparticles (Si NPs) in a crumpled graphene shell by spray drying or spray pyrolysis are promising and scalable methods to produce core-shell structures, which buffer the extreme volume change (>300 vol %) caused by (de)lithiaton of silicon. However, capillary forces cause the graphene-based materials to tightly wrap around Si NP clusters, and there is little control over the void space required to further improve cycle life. Herein, a simple strategy is developed to engineer void-space within the core by incorporating varying amounts of similarly sized polystyrene (PS) nanospheres in the spray drier feed mixture. The PS completely decomposes during thermal reduction of the graphene oxide shell and results in Si cores of varying porosity. The best performance is achieved at a 1 : 1 ratio (PS/Si), leading to high capacities of 1638, 1468, and 1179 mAh g^-1 _Si+rGO at 0.1, 1, and 4 A g^-1 , respectively. Moreover, at 1 A g^-1 , the capacity retention is 80.6 % after 200 cycles. At a practical active material loading of 2.4 mg cm^-2 , the electrodes achieve an areal capacity of 2.26 mAh cm^-2 at 1 A g^-1 .

Ant-nest-like Cu2-xSe@C with biomimetic channels boosts the cycling performance for lithium storage

Controlling the microstructure and composition of electrodes is crucial to enhance their rate capability and cycling stability for lithium storage. Inspired by the highly interconnected network and good mechanical integrity of an ant-nest architecture, herein, a biomimetic strategy is proposed to enhance the electrochemical performance of Cu2-xSe. After facile carbonization and selenization treatments, the 3D Cu-MOF is successfully transformed into the final ant-nest-like Cu2-xSe@C (AN-Cu2-xSe@C). The AN-Cu2-xSe@C is composed of interconnected Cu2-xSe channels with amorphous carbon coated on the outer surface. The 3D interconnected channels within the AN-Cu2-xSe@C provide fast charge transport pathways and enhanced structural integrity to tolerate the large volume fluctuations of Cu2-xSe during cycling. When applied as the anode for lithium storage, the AN-Cu2-xSe@C shows remarkable electrochemical performance with a high capacity of 1452 mA h g-1 after 1200 cycles at 1.0 A g-1 and 879 mA h g-1 after 2500 cycles at 10.0 A g-1, respectively. Mechanism investigations demonstrate that the AN-Cu2-xSe@C experiences complicated conversion-intercalation co-existence reactions upon cycling. The existence of capacitive behaviour (74%) also contributes to the extended cycling performance. Our work offers a new avenue for designing a high performance electrode using the biomimetic concept.

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.

Enhanced Cycle Stability of Crumpled Graphene-Encapsulated Silicon Anodes via Polydopamine Sealing

Despite silicon being a promising candidate for next-generation lithium-ion battery anodes, self-pulverization and the formation of an unstable solid electrolyte interface, caused by the large volume expansion during lithiation/delithiation, have slowed its commercialization. In this work, we expand on a controllable approach to wrap silicon nanoparticles in a crumpled graphene shell by sealing this shell with a polydopamine-based coating. This provides improved structural stability to buffer the volume change of Si, as demonstrated by a remarkable cycle life, with anodes exhibiting a capacity of 1038 mA h/g after 200 cycles at 1 A/g. The resulting composite displays a high capacity of 1672 mA h/g at 0.1 A/g and can still retain 58% when the current density increases to 4 A/g. A systematic investigation of the impact of spray-drying parameters on the crumpled graphene morphology and its impact on battery performance is also provided.

The Positive Effect of ZnS in Waste Tire Carbon as Anode for Lithium-Ion Batteries

There is great demand for high-performance, low-cost electrode materials for anodes of lithium-ion batteries (LIBs). Herein, we report the recovery of carbon materials by treating waste tire rubber via a facile one-step carbonization process. Electrochemical studies revealed that the waste tire carbon anode had a higher reversible capacity than that of commercial graphite and shows the positive effect of ZnS in the waste tire carbon. When used as the anode for LIBs, waste tire carbon shows a high specific capacity of 510.6 mAh·g^-1 at 100 mA·g^-1 with almost 97% capacity retention after 100 cycles. Even at a high rate of 1 A·g^-1, the carbon electrode presents an excellent cyclic capability of 255.1 mAh·g^-1 after 3000 cycles. This high-performance carbon material has many potential applications in LIBs and provide an alternative avenue for the recycling of waste tires.

Scalable Synthesis of Porous SiFe@C Composite with Excellent Lithium Storage

Utilizing cost-effective raw materials to prepare high-performance silicon-based anode materials for lithium-ion batteries (LIBs) is both challenging and attractive. Herein, a porous SiFe@C (pSiFe@C) composite derived from low-cost ferrosilicon is prepared via a scalable three-step procedure, including ball milling, partial etching, and carbon layer coating. The pSiFe@C material integrates the advantages of the mesoporous structure, the partially retained FeSi₂ conductive phase, and a uniform carbon layer (12-16 nm), which can substantially alleviate the huge volume expansion effect in the repeated lithium-ion insertion/extraction processes, effectively stabilizing the solid-electrolyte interphase (SEI) film and markedly enhancing the overall electronic conductivity of the material. Benefiting from the rational structure, the obtained pSiFe@C hybrid material delivers a reversible capacity of 1162.1 mAh g^-1 after 200 cycles at 500 mA g^-1 , with a higher initial coulombic efficiency of 82.30 %. In addition, it shows large discharge capacities of 803.1 and 600.0 mAh g^-1 after 500 cycles at 2 and 4 A g^-1 , respectively, manifesting an excellent electrochemical lithium storage. This work provides a good prospect for the commercial production of silicon-based anode materials for LIBs with a high lithium-storage capacity.

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.

Flexible Carbon Nanotubes Confined Yolk-Shelled Silicon-Based Anode with Superior Conductivity for Lithium Storage

The further deployment of silicon-based anode materials is hindered by their poor rate and cycling abilities due to the inferior electrical conductivity and large volumetric changes. Herein, we report a silicon/carbon nanotube (Si/CNT) composite made of an externally grown flexible carbon nanotube (CNT) network to confine inner multiple Silicon (Si) nanoparticles (Si NPs). The in situ generated outer CNTs networks, not only accommodate the large volume changes of inside Si NPs but also to provide fast electronic/ionic diffusion pathways, resulting in a significantly improved cycling stability and rate performance. This Si/CNT composite demonstrated outstanding cycling performance, with 912.8 mAh g-1 maintained after 100 cycles at 100 mA g-1, and excellent rate ability of 650 mAh g-1 at 1 A g-1 after 1000 cycles. Furthermore, the facial and scalable preparation method created in this work will make this new Si-based anode material promising for practical application in the next generation Li-ion batteries.

Improving the Electrochemical Property of Silicon Anodes through Hydrogen-Bonding Cross-Linked Thiourea-Based Polymeric Binders

Binders play a crucial role in the development of silicon (Si) anodes for lithium-ion batteries with high specific energy. The large volume change of Si (∼300%) during repeated discharge and charge processes causes the destruction and separation of electrode materials from the copper (Cu) current collector and ultimately results in poor cycling performance. In the present study, we design and prepare hydrogen-bonding cross-linked thiourea-based polymeric binders (denoted CMC-co-SN) in consideration of their excellent binding interaction with the Cu current collector and low cost as well. The CMC-co-SN binders are formed through in situ thermopolymerization of chain-type carboxymethylcellulose sodium (CMC) with thiourea (SN) in the drying process of Si electrode disks. A tight and physical interlocked layer between the CMC-co-SN binder and Cu current collector is derived from a dendritic nonstoichiometric copper sulfide (Cu_xS) layer on the interface and enhances the binding of electrode materials with the Cu current collector. When applying the CMC-co-SN binders to micro- (∼3 μm) (μSi) and nano- (∼50 nm) (nSi) Si particles, the Si anodes exhibit high initial Coulomb efficiency (91.5% for μSi and 83.2% for nSi) and excellent cyclability (1121 mA h g^-1 for μSi after 140 cycles and 1083 mA h g^-1 for nSi after 300 cycles). The results demonstrate that the CMC-co-SN binders together with a physical interlocked layer have significantly improved the electrochemical performance of Si anodes through strong binding forces with the current collector to maintain electrode integrity and avoid electric contact loss.

Low-cost urchin-like silicon-based anode with superior conductivity for lithium storage applications

Poor rate and cycling performance are the most critical drawbacks for Si-based anodes on account of their inferior conductivity and colossal volumetric expansion during lithiation/delithiation. Here we report the fabrication of structurally-integrated urchin-like Si anode, which provides prominent structural stability and distinguished electron and ion transmission pathways for lithium storage. The inexpensive solid Si waste from organosilane industry after acid-washed and further ball-milling serves as the pristine Si-source in this work. Carbon nanotubes (CNTs) are in-situ grown outside Si microparticles, resulting in an urchin-like structure (Si/CNTs). The optimized Si/CNTs presents ascendant invertible capacity and rate performance, achieving up to 920 mAh g^-1 beyond 100 cycles at 100 mA g ^-1, and a capacity of 606.2 mAh g^-1 at 1 A g ^-1 after long cycling for 1000 cycles. The proposed scalable synthesis can be adopted to advance the performance of other electrode materials with inferior conductivity and enormous volume expansions during cycling.

Silicon nanoparticles coated with nanoporous carbon as a promising anode material for lithium ion batteries

As a promising anode candidate, silicon (Si) nanoparticles have been widely studied for use in lithium ion batteries.

Structure and conductivity enhanced treble-shelled porous silicon as an anode for high-performance lithium-ion batteries

Silicon is regarded as the next generation anode material for lithium-ion batteries because of its high specific capacity, low intercalation potential and abundant reserves. However, huge volume changes during the lithiation and delithiation processes and low electrical conductivity obstruct the practical applications of silicon anodes. In this study, a treble-shelled porous silicon (TS-P-Si) structure was synthesized via a three-step approach. The TS-P-Si anode delivered a capacity of 858.94 mA h g⁻¹ and a capacity retention of 87.8% (753.99 mA h g⁻¹) after being subjected to 400 cycles at a current density of 400 mA g⁻¹. The good cycling performance was due to the unique structure of the inner silicon oxide layer, middle silver nano-particle layer and outer carbon layer, leading to a good conductivity and a decreased volume change of this silicon-based anode.

In this paper, a treble-shelled porous silicon structure is synthesized through three-step approach to enhance the structural stability and conductivity.