Low-Cost and Novel Si-Based Gel for Li-Ion Batteries

Scalable engineering of hierarchical layered micro-sized silicon/graphene hybrids via direct foaming for lithium storage

Low-cost micro-sized silicon is an attractive replacement for commercial graphite anodes in advanced lithium-ion batteries (LIBs) but suffers from particle fracture during cycling. Hybridizing micro-sized silicon with conductive carbon materials, especially graphene, is a practical approach to overcome the volume change issue. However, micro-sized silicon/graphene anodes prepared via the conventional technique encounter sluggish Li+ transport due to the lack of efficient electrolyte diffusion channels. Here, we present a facile and scalable method to establish efficient Li+ transport channels through direct foaming from the laminated graphene oxide/micro-sized silicon membrane followed by annealing. The conductive graphene layers and the Li+ transport channels endow the composite material with excellent electronic and ionic conductivity. Moreover, the interconnected graphene layers provide a robust framework for micro-sized silicon particles, allowing them to transform decently in the graphene layer space. Consequently, the prepared hybrid material, namely foamed graphene/micro-sized Si (f-G-Si), can work as a binder-free and free-standing anode without additives and deliver remarkable electrochemical performance. Compared with the control samples, micro-sized silicon wrapped by laminated graphene layers (G-Si) and commercial micro-sized Si, f-G-Si maximizes the utilization of silicon and demonstrates superior performance, disclosing the role of Li+ diffusion channels. This study sheds light on the rational design and manufacture of silicon anodes and beyond.

Facile synthesis of Si/Ge/graphite@C composite with improved tap density and electrochemical performance

Nanoengineering is one of the most effective methods to promote the lithium storage performance of silicon material, which suffers from huge volume changes and poor reaction kinetics during cycling. However, the commercial application of nanostructured silicon is hindered by its high manufacturing cost and low tap density. Herein, a Si/Ge/graphite@C composite was successfully synthesized by ball-milling with subsequent calcination. By introducing Ge, graphite and an amorphous carbon coating, both tap density and electrochemical performance are improved significantly. Benefiting from the synergetic effects of the above components, the Si/Ge/graphite@C composite delivers a reversibility capacity of 474 mA h g-1 at 0.2 A g-1 and stable capacity retention.

Micrometer-Sized SiMgy Ox with Stable Internal Structure Evolution for High-Performance Li-Ion Battery Anodes

In recent years, micrometer-sized Si-based anode materials have attracted intensive attention in the pursuit of energy-storage systems with high energy and low cost. However, the significant volume variation during repeated electrochemical (de)alloying processes will seriously damage the bulk structure of SiO_x microparticles, resulting in rapid performance fade. This work proposes to address the challenge by preparing in situ magnesium-doped SiO_x (SiMg_y O_x ) microparticles with stable structural evolution against Li uptake/release. The homogeneous distribution of magnesium silicate in SiMg_y O_x contributes to building a bonding network inside the particle so that it raises the modulus of lithiated state and restrains the internal cracks due to electrochemical agglomeration of nano-Si. The prepared micrometer-sized SiMg_y O_x anode shows high reversible capacities, stable cycling performance, and low electrode expansion at high areal mass loading. A 21700 cylindrical-type cell based on the SiMg_y O_x -graphite anode and LiNi_0.8 Co_0.15 Al_0.05 O₂ cathode demonstrates a 1000-cycle operation life using industry-recognized electrochemical test procedures, which meets the practical storage requirements for consumer electronics and electric vehicles. This work provides insights on the reasonable structural design of micrometer-sized alloying anode materials toward realization of high-performance Li-ion batteries.

Microscale Silicon-Based Anodes: Fundamental Understanding and Industrial Prospects for Practical High-Energy Lithium-Ion Batteries

To accelerate the commercial implementation of high-energy batteries, recent research thrusts have turned to the practicality of Si-based electrodes. Although numerous nanostructured Si-based materials with exceptional performance have been reported in the past 20 years, the practical development of high-energy Si-based batteries has been beset by the bias between industrial application with gravimetrical energy shortages and scientific research with volumetric limits. In this context, the microscale design of Si-based anodes with densified microstructure has been deemed as an impactful solution to tackle these critical issues. However, their large-scale application is plagued by inadequate cycling stability. In this review, we present the challenges in Si-based materials design and draw a realistic picture regarding practical electrode engineering. Critical appraisals of recent advances in microscale design of stable Si-based materials are presented, including interfacial tailoring of Si microscale electrode, surface modification of SiO_x microscale electrode, and structural engineering of hierarchical microscale electrode. Thereafter, other practical metrics beyond active material are also explored, such as robust binder design, electrolyte exploration, prelithiation technology, and thick-electrode engineering. Finally, we provide a roadmap starting with material design and ending with the remaining challenges and integrated improvement strategies toward Si-based full cells.

Silicon-Nanographite Aerogel-Based Anodes for High Performance Lithium Ion Batteries

To increase the energy storage density of lithium-ion batteries, silicon anodes have been explored due to their high capacity. One of the main challenges for silicon anodes are large volume variations during the lithiation processes. Recently, several high-performance schemes have been demonstrated with increased life cycles utilizing nanomaterials such as nanoparticles, nanowires, and thin films. However, a method that allows the large-scale production of silicon anodes remains to be demonstrated. Herein, we address this question by suggesting new scalable nanomaterial-based anodes. Si nanoparticles were grown on nanographite flakes by aerogel fabrication route from Si powder and nanographite mixture using polyvinyl alcohol (PVA). This silicon-nanographite aerogel electrode has stable specific capacity even at high current rates and exhibit good cyclic stability. The specific capacity is 455 mAh g⁻¹ for 200^th cycles with a coulombic efficiency of 97% at a current density 100 mA g⁻¹.

Metal-Organic Frameworks-Derived Mesoporous Si/SiOx @NC Nanospheres as a Long-Lifespan Anode Material for Lithium-Ion Batteries

Silicon (Si)-based anode materials with suitable engineered nanostructures generally have improved lithium storage capabilities, which provide great promise for the electrochemical performance in lithium-ion batteries (LIBs). Herein, a metal-organic framework (MOF)-derived unique core-shell Si/SiO_x @NC structure has been synthesized by a facile magnesio-thermic reduction, in which the Si and SiO_x matrix were encapsulated by nitrogen (N)-doped carbon. Importantly, the well-designed nanostructure has enough space to accommodate the volume change during the lithiation/delithiation process. The conductive porous N-doped carbon was optimized through direct carbonization and reduction of SiO₂ into Si/SiO_x simultaneously. Benefiting from the core-shell structure, the synthesized product exhibited enhanced electrochemical performance as an anode material in LIBs. Particularly, the Si/SiO_x @NC-650 anode showed the best reversible capacities up to 724 and 702 mAh g^-1 even after 100 cycles. The excellent cycling stability of Si/SiO_x @NC-650 may be attributed to the core-shell structure as well as the synergistic effect between the Si/SiO_x and MOF-derived N-doped carbon.

A Facile Strategy to Construct Silver-Modified, ZnO-Incorporated and Carbon-Coated Silicon/Porous-Carbon Nanofibers with Enhanced Lithium Storage

For Si anode materials used for lithium ion batteries (LIBs), developing an effective solution to overcome their drawbacks of large volume change and poor electronic conductivity is highly desirable. Here, the composites of ZnO-incorporated and carbon-coated silicon/porous-carbon nanofibers (ZnO-Si@C-PCNFs) are designed and synthesized via a traditional electrospinning method. The prepared ZnO-Si@C-PCNFs can obviously overcome these two drawbacks and provide excellent LIB performance with excellent rate capability and stable long cycling life of 1000 cycles with reversible capacity of 1050 mA h g^-1 at 800 mA g^-1 . Meanwhile, anodes of ZnO-Si@C-PCNFs attached with Ag particles display enhanced LIB performance, maintaining an average capacity of 920 mA h g^-1 at a large current of 1800 mA g^-1 even for 1000 cycles with negligible capacity loss and excellent reversibility. In addition, the assembling method with important practical significance for a simple pouch full cell is designed and used to evaluate the active materials. The Ag/ZnO-Si@C-PCNFs are prelithiated and assembled in full cells using LiNi_0.5 Co_0.2 Mn_0.3 O₂ (NCM523) as cathodes, exhibiting higher energy density (230 W h kg^-1 ) of 18% than that of 195 W h kg^-1 for commercial graphite//NCM523 full pouch cells. Importantly, the comprehensive mechanisms of enhanced electrochemical kinetics originating from ZnO-incorporation and Ag-attachment are revealed in detail.

Scallop-Inspired Shell Engineering of Microparticles for Stable and High Volumetric Capacity Battery Anodes

Building stable and efficient electron and ion transport pathways are critically important for energy storage electrode materials and systems. Herein, a scallop-inspired shell engineering strategy is proposed and demonstrated to confine high volume change silicon microparticles toward the construction of stable and high volumetric capacity binder-free lithium battery anodes. As for each silicon microparticle, the methodology involves an inner sealed but adaptable overlapped graphene shell, and an outer open hollow shell consisting of interconnected reduced graphene oxide, mimicking the scallop structure. The inner closed shell enables simultaneous stabilization of the interfaces of silicon with both carbon and electrolyte, substantially facilitates efficient and rapid transport of both electrons and lithium ions from/to silicon, the outer open hollow shell creates stable and robust transport paths of both electrons and lithium ions throughout the electrode without any sophisticated additives. The resultant self-supported electrode has achieved stable cycling with rapidly increased coulombic efficiency in the early stage, superior rate capability, and remarkably high volumetric capacity upon a facile pressing process. The rational design and engineering of graphene shells of the silicon microparticles developed can provide guidance for the development of a wide range of other high capacity but large volume change electrochemically active materials.

Amorphous red phosphorus incorporated with pyrolyzed bacterial cellulose as a free-standing anode for high-performance lithium ion batteries

Amorphous red phosphorus/pyrolyzed bacterial cellulose (P-PBC) free-standing films are prepared by thermal carbonization and a subsequent vaporization-condensation process. The distinctive bundle-like structure of the flexible pyrolyzed bacterial cellulose (PBC) matrix not only provides sufficient volume to accommodate amorphous red-phosphorus (P) but also restricts the pulverization of red-P during the alternate lithiation/delithiation process. When the mass ratio of raw materials, red-P to PBC, is 70 : 1, the free-standing P-PBC film anode exhibits high reversible capacity based on the mass of the P-PBC film (1039.7 mA h g⁻¹ after 100 cycle at 0.1C, 1C = 2600 mA g⁻¹) and good cycling stability at high current density (capacity retention of 82.84% after 1000 cycles at 2C), indicating its superior electrochemical performances.

A novel freestanding anode was prepared by combining amorphous red-P with a pyrolyzed bacterial cellulose (PBC) matrix for the first time.

Facile Synthesis of Si@SiC Composite as an Anode Material for Lithium-Ion Batteries

Here, we propose a simple method for direct synthesis of a Si@SiC composite derived from a SiO₂@C precursor via a Mg thermal reduction method as an anode material for Li-ion batteries. Owing to the extremely high exothermic reaction between SiO₂ and Mg, along with the presence of carbon, SiC can be spontaneously produced with the formation of Si. The synthesized Si@SiC was composed of well-mixed SiC and Si nanocrystallites. The SiC content of the Si@SiC was adjusted by tuning the carbon content of the precursor. Among the resultant Si@SiC materials, the Si@SiC-0.5 sample, which was produced from a precursor containing 4.37 wt % of carbon, exhibits excellent electrochemical characteristics, such as a high first discharge capacity of 1642 mAh g^-1 and 53.9% capacity retention following 200 cycles at a rate of 0.1C. Even at a high rate of 10C, a high reversible capacity of 454 mAh g^-1 was obtained. Surprisingly, at a fixed discharge rate of C/20, the Si@SiC-0.5 electrode delivered a high capacity of 989 mAh g^-1 at a charge rate of 20C. In addition, a full cell fabricated by coupling a lithiated Si@SiC-0.5 anode and a LiCoO₂ cathode exhibits excellent cyclability over 50 cycles. This outstanding electrochemical performance of Si@SiC-0.5 is attributed to the SiC phase, which acts as a buffer layer that stabilizes the nanostructure of the Si active phase and enhances the electrical conductivity of the electrode.