Silicon Carbide as a Protective Layer to Stabilize Si-Based Anodes by Inhibiting Chemical Reactions

Enhancing Interfacial Interactions Through Microwave-Irradiated Reduction for the Recycling of Photovoltaic Silicon Waste for Lithium Storage

The application of micro-nano size photovoltaic waste silicon (wSi) as an anode material for lithium-ion battery holds significant practical potential; However, it faces a series of challenges related to the volume expansion of Si during cycling. In this study, a simple, efficient, and eco-friendly microwave method is proposed for the rapid preparation of graphene-coated silicon materials (wSi@rGO) in just a few seconds, in which graphene as the stable interface mitigates structural failure caused by significant volume expansion, enhances electron and ion conductivity, inhibits undesirable side reactions between silicon and electrolyte, and promotes the stability of solid electrolyte interface (SEI). Importantly, the instantaneous high temperature generated by microwaves facilitates the formation of interfacial SiC chemical bonds, which strengthen the interaction between Si and graphene, thereby reducing Si delamination. The wSi@rGO anode exhibits remarkable cycling stability, maintaining a specific capacity of 1100 mA h g-1 over 250 cycles. Furthermore, the assembled wSi@rGO//LiFePO4 full battery demonstrates robust performance, retaining a stable capacity of 150 mA h g-1 after 80 cycles at 0.5 C. This research not only demonstrates a straightforward and efficient microwave technique for synthesizing wSi@rGO anode materials, but also offers an environmentally friendly and economical pathway for recycling photovoltaic waste silicon, contributing positively to carbon peaking and carbon neutrality.

Controllable SiOx Coating Layer Promotes High Stable Si Anode for Lithium-Ion Batteries

Silicon (Si) is considered as one of the most promising candidates for next-generation lithium-ion batteries with high energy density. The main problems are the severe volume expansion and continuous interfacial side reaction of Si that hinder its further application. It can be an effective way by constructing a robust coating layer outside of Si to impede/alleviate the above effect. SiOx with high mechanical strength can largely promote the electrochemical performance of Si. Herein, Si@SiOx material with high specific surface area, high porosity, and controllable coating was synthesized via a simple solid-liquid reaction by LiOH solution etching effect. The etching/oxidation mechanism of Si under alkaline conditions was thoroughly investigated. The surface oxide layer of Si was beneficial to the formation of a solid electrolyte interphase (SEI) with excellent stability and high Li+ conductivity, while its high-porosity structure reduces the volume expansion of the material by approximately 110%. Under the synergistic effect of etching-oxidation, the modified material exhibited superior electrochemical properties. When employed as anode materials, the specific capacity was as high as 3101.5 mAh g-1 and maintained at 841.0 mAh g-1 after 500 cycles at 1 A g-1.

Nanocatalysis in cathode pre-lithiation for lithium-ion batteries: progress and challenges

Pre-lithiation, which is capable of supplying additional active lithium sources to lithium-ion batteries, has been widely accepted as one of the most promising approaches for addressing the issue of active lithium loss during the entire process of initial charging and subsequent cycling. In comparison with anode pre-lithiation, cathode pre-lithiation exhibits a facile operating procedure and good compatibility with current lithium-ion battery production processes. However, cathode pre-lithiation additives suffer from high decomposition voltage and low decomposition efficiency. In view of this, a variety of nanocatalysts have been developed in recent years to enhance the decomposition kinetics of cathode pre-lithiation additives. Nevertheless, a comprehensive review of nanocatalysis in cathode pre-lithiation is still lacking. This timely review aims to present the crucial role of nanocatalysis in cathode pre-lithiation and provide an up-to-date overview of this field. After demonstrating the significance of nanocatalysts for cathode pre-lithiation, recent progress in the application of nanocatalysts for high-efficiency cathode pre-lithiation is briefly introduced. Finally, future challenges and directions for the commercialization of the cathode pre-lithiation technique in conjunction with nanocatalysts are reviewed. The current review provides important insights into nanocatalysis as a cutting-edge strategy for favorable cathode pre-lithiation and builds a bridge between academic research and industrial applications of nanocatalytic cathode pre-lithiation for lithium-ion batteries with high capacity and good cyclability.

Enhanced stability and kinetic performance of sandwich Si anode constructed by carbon nanotube and silicon carbide for lithium-ion battery

Owing to highly theoretical capacity of 3579 mAh/g for lithium-ion storage at ambient temperature, silicon (Si) becomes a promising anode material of high-performance lithium-ion batteries (LIBs). However, the large volume change (∼300 %) during lithiation/delithiation and low conductivity of Si are challenging the commercial developments of LIBs with Si anode. Herein, a sandwich structure anode that Si nanoparticles sandwiched between carbon nanotube (CNT) and silicon carbide (SiC) has been successfully constructed by acetylene chemical vapor deposition and magnesiothermic reduction reaction technology. The SiC acts as a stiff layer to inhibit the volumetric stress from Si and the inner graphited CNT plays as the matrix to cushion the volumetric stress and as the conductor to transfer electrons. Moreover, the combination of SiC and CNT can relax the surface stress of carbonaceous interface to synergistically prevent the integrated structure from the degradation to avoid the solid electrolyte interface (SEI) reorganization. In addition, the SiC (111) surface has a strong ability to adsorb fluoroethylene carbonate molecule to further stabilize the SEI. Consequently, the CNT/SiNPs/SiC anode can stably supply the capacity of 1127.2 mAh/g at 0.5 A/g with a 95.6 % capacity retention rate after 200 cycles and an excellent rate capability of 745.5 mAh/g at 4.0 A/g and 85.5 % capacity retention rate after 1000 cycles. The present study could give a guide to develop the functional Si anode through designing a multi-interface with heterostructures.

Modulating porous silicon-carbon anode stability: Carbon/silicon carbide semipermeable layer mitigates silicon-fluorine reaction and enhances lithium-ion transport

Silicon-based material is regarded as one of the most promising anodes for next-generation high-performance lithium-ion batteries (LIBs) due to its high theoretical capacity and low cost. Harnessing silicon carbide's robustness, we designed a novel porous silicon with a sandwich structure of carbon/silicon carbide/Ag-modified porous silicon (Ag-PSi@SiC@C). Different from the conventional SiC interface characterized by a frail connection, a robust dual covalent bond configuration, dependent on SiC and SiOC, has been successfully established. Moreover, the innovative sandwich structure effectively reduces detrimental side reactions on the surface, eases volume expansion, and bolsters the structural integrity of the silicon anode. The incorporation of silver nanoparticles contributes to an improvement in overall electron transport capacity and enhances the kinetics of the overall reaction. Consequently, the Ag-PSi@SiC@C electrode, benefiting from the aforementioned advantages, demonstrates a notably elevated lithium-ion mobility (2.4 * 10-9 cm2·s-1), surpassing that of silicon (5.1 * 10-12 cm2·s-1). The half-cell featuring Ag-PSi@SiC@C as the anode demonstrated robust rate cycling stability at 2.0 A/g, maintaining a capacity of 1321.7 mAh/g, and after 200 cycles, it retained 962.6 mAh/g. Additionally, the full-cell, featuring an Ag-PSi@SiC@C anode and a LiFePO4 (LFP) cathode, exhibits outstanding longevity. Hence, the proposed approach has the potential to unearth novel avenues for the extended exploration of high-performance silicon-carbon anodes for LIBs.

Investigating the Corrosion Resistance of Different SiC Crystal Types: From Energy Sectors to Advanced Applications

Silicon carbide, as a third-generation semiconductor material, plays a pivotal role in various advanced technological applications. Its exceptional stability under extreme conditions has garnered a significant amount of attention. These superior characteristics make silicon carbide an ideal candidate material for high-frequency, high-power electronic devices and applications in harsh environments. In particular, corrosion resistance in natural or artificially acidic and alkaline environments limits the practical application of many other materials. In fields such as chemical engineering, energy conversion, and environmental engineering, materials often face severe chemical erosion, necessitating materials with excellent chemical stability as foundational materials, carriers, or reaction media. Silicon carbide exhibits outstanding performance under these conditions, demonstrating significant resistance to corrosive substances such as hydrochloric acid, sulfuric acid, nitric acid, and alkaline substances such as potassium hydroxide and sodium hydroxide. Despite the well-known chemical stability of silicon carbide, the stability conditions of its different types (such as 3C-, 4H-, and 6H-SiC polycrystals) in acidic and alkaline environments, as well as the specific corrosion mechanisms and differences, warrant further investigation. This Review not only delves deeply into the detailed studies related to this topic but also highlights the current applications of different silicon carbide polycrystals in chemical reaction systems, energy conversion equipment, and recycling processes. Through a comprehensive analysis, this Review aims to bridge research gaps, offering a comparative analysis of the advantages and disadvantages between different polymorphs. It provides material scientists, engineers, and developers with a thorough understanding of silicon carbide's behavior in various chemical environments. This work will propel the research and development of silicon carbide materials under extreme conditions, especially in areas where chemical stability is crucial for device performance and durability. It lays a solid foundation for ultra-high-power, high-integration, high-reliability module architectures, supercomputing chips, and highly safe long-life batteries.

Reprecipitation: A Rapid Synthesis of Micro-Sized Silicon-Graphene Composites for Long-lasting Lithium-Ion Batteries

Silicon microparticles (SiMPs) have gained significant attention as a lithium-ion battery anode material due to their 10 times higher theoretical capacity compared to conventional graphite anodes as well as their much lower production cost than silicon nanoparticles (SiNPs). However, SiMPs have suffered from poorer cycle life relative to SiNPs because their larger size makes them more susceptible to volume changes during charging and discharging. Creating a wrapping structure in which SiMPs are enveloped by carbon layers has proven to be an effective strategy to significantly improve the cycling performance of SiMPs. However, the synthesis processes are complex and time-/energy-consuming and therefore not scalable. In this study, a wrapping structure is created by using a simple, rapid, and scalable "modified reprecipitation method". Graphene oxide (GO) and SiMP dispersion in tetrahydrofuran is injected into n-hexane, in which GO and SiMP by themselves cannot disperse. GO and SiMP therefore aggregate and precipitate immediately after injection to form a wrapping structure. The resulting SiMP/GO film is laser scribed to reduce GO to a laser-scribed graphene (LSG). Simultaneously, SiOx and SiC protection layers form on the SiMPs through the laser process, which alleviates severe volume change. Owing to these desirable characteristics, the modified reprecipitation method successfully doubles the cycle life of SiMP/graphene composites compared to the simple physically mixing method (50.2% vs. 24.0% retention at the 100th cycle). The modified reprecipitation method opens a new synthetic strategy for SiMP/carbon composites.

Macroporous Directed and Interconnected Carbon Architectures Endow Amorphous Silicon Nanodots as Low-Strain and Fast-Charging Anode for Lithium-Ion Batteries

Fabricating low-strain and fast-charging silicon-carbon composite anodes is highly desired but remains a huge challenge for lithium-ion batteries. Herein, we report a unique silicon-carbon composite fabricated by uniformly dispersing amorphous Si nanodots (SiNDs) in carbon nanospheres (SiNDs/C) that are welded on the wall of the macroporous carbon framework (MPCF) by vertical graphene (VG), labeled as MPCF@VG@SiNDs/C. The high dispersity and amorphous features of ultrasmall SiNDs (~ 0.7 nm), the flexible and directed electron/Li+ transport channels of VG, and the MPCF impart the MPCF@VG@SiNDs/C more lithium storage sites, rapid Li+ transport path, and unique low-strain property during Li+ storage. Consequently, the MPCF@VG@SiNDs/C exhibits high cycle stability (1301.4 mAh g-1 at 1 A g-1 after 1000 cycles without apparent decay) and high rate capacity (910.3 mAh g-1, 20 A g-1) in half cells based on industrial electrode standards. The assembled pouch full cell delivers a high energy density (1694.0 Wh L-1; 602.8 Wh kg-1) and an excellent fast-charging capability (498.5 Wh kg-1, charging for 16.8 min at 3 C). This study opens new possibilities for preparing advanced silicon-carbon composite anodes for practical applications.

Silicon-Nanodiamond-Based Anode for a Lithium-Ion Battery

Maintaining the physical integrity of a silicon-based anode, which suffers from damage caused by severe volume changes during cycling, is a top priority in its practical applications. The performance of silicon-flake-based anodes has been significantly improved by mixing nanodiamond powders with silicon flakes for the fabrication of anodes for lithium-ion batteries (LIBs). Nanodiamonds adhere to the surfaces of silicon flakes and are distributed in the binder between flakes. A consistent and robust solid electrolyte interphase (SEI) is promoted by the aid of abundant reactive surface-linked functional groups and exposed dangling bonds of nanodiamonds, leading to enhanced physical integrity of the silicon flakes and the anode. The battery's high-rate discharge capabilities and cycle life are thus improved. SEM, Raman spectroscopy, and XRD were applied to examine the structure and morphology of the anode. Electrochemical performance was evaluated to demonstrate a capacity retention of nearly 75% after 200 cycles, with the final specific capacity exceeding 1000 mAh/g at a test current of 4 mA/cm2. This is attributed to the improved stability of the solid electrolyte interphase (SEI) structure that was achieved by integrating nanodiamonds with silicon flakes in the anode, leading to enhanced cycling stability and rapid charge-discharge performance. The results from this study present an effective strategy of achieving high-cycling-performance by adding nanodiamonds to silicon-flake-based anodes.

Near zero-strain silicon oxycarbide interphases for stable Li-ion batteries

We investigate silicon oxycarbide nanotubes that incorporate Si, SiC, and silicon oxycarbide phases, which exhibit near zero-strain volume expansion, leading to reduced electrolyte decomposition. The composite effectively accommodates the formation of c-Li15Si4, as validated by in situ TEM analyses and electrochemical tests, thereby proposing a promising solution for Li-ion battery anodes.

Liquid electrolyte chemistries for solid electrolyte interphase construction on silicon and lithium-metal anodes

Next-generation battery development necessitates the coevolution of liquid electrolyte and electrode chemistries, as their erroneous combinations lead to battery failure. In this regard, priority should be given to the alleviation of the volumetric stress experienced by silicon and lithium-metal anodes during cycling and the mitigation of other problems hindering their commercialization. This review summarizes the advances in sacrificial compound-based volumetric stress-adaptable interfacial engineering, which has primarily driven the development of liquid electrolytes for high-performance lithium batteries. Besides, we discuss how the regulation of lithium-ion solvation structures helps expand the range of electrolyte formulations and thus enhance the quality of solid electrolyte interphases (SEIs), improve lithium-ion desolvation kinetics, and realize longer-lasting SEIs on high-capacity anodes. The presented insights are expected to inspire the design and synthesis of next-generation electrolyte materials and accelerate the development of advanced electrode materials for industrial battery applications.

Insights into Capacity Fading Mechanism and Coating Modification of High-Nickel Cathodes in Lithium-Ion Batteries

Developments in electric vehicles and mobile electronic devices are promoting the demand for lithium-ion batteries with higher capacity and longer lifetime. The performances of lithium-ion batteries are crucially affected by cathode materials, among which ternary cathode materials are the most competitive option with the advantages of high capacity, safety, and cost-effectiveness. However, although high-nickel ternary cathode materials can achieve relatively high specific capacity, they generally have unsatisfactory stability during long-term cycling. In this study, the microscopic mechanisms of the cathode failure and the principle of coating modification in lithium-ion batteries have been comprehensively examined. It has been revealed that the irreversible capacity fading is mainly attributed to the interface chemical reaction, which reduces the transition-metal valence states and generates undesired disordered rock-salt phases. This structural phase transformation at the interface induces the dissolution of transition metals and results in irreversible capacity loss of the cathode. To restrain the occurrence of this process, a LiNbO₃ coating-modified single-crystal LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode material has been prepared. The electrochemical properties as well as the microstructural evolution of the cathode-electrolyte interface during cycling of both the uncoated and coated samples have been comprehensively characterized and compared through impedance spectroscopy testing, SEM-EDX, STEM, and EELS characterization. Additionally, molecular dynamics simulation results confirmed that LiNbO₃ coating can effectively inhibit the dissolution of transition metals while providing stable lithium-ion channels. The experimental results also indicate that the coating modification can effectively improve the cycling stability of the NCM811, with the capacity retention rate for 500 cycles increasing from 19% to 70%. This study is helpful to deepen the understanding of the capacity fading mechanisms, and the coating method is effective at maintaining the structural stability and improving the cycle life of lithium-ion batteries.

Search for New Anode Materials for High Performance Li-Ion Batteries

Owing to an unmatched combination of power and energy density along with cyclic stability, the Li-ion battery has qualified itself to be the highest performing rechargeable battery. Taking both transportable and stationary energy storage requirements into consideration, Li-ion batteries indeed stand tall in comparison to any other existing rechargeable battery technologies. However, graphite, which is still one of the best performing Li-ion anodes, has specific drawbacks in fulfilling the ever-increasing energy and power density requirements of the modern world. Therefore, further research on alternative anode materials is absolutely essential. Equally important is the search for and enhanced use of right earth abundant materials for battery electrodes so as to bring down the costs of the battery systems. In this spotlight article, we discuss the current research progress in the area of alternative anode materials for Li-ion battery, putting our own research work over the past several years into perspective. Starting from conversion anode systems like oxides and sulfides, to insertion cum alloying systems like transition metal carbides, to molecularly engineered open framework systems like metal organic frameworks (MOFs), covalent organic frameworks (COFs), and organic-inorganic hybrid perovskites (OIHPs), this spotlight provides a complete essence of the recent developments in the area of alternative anodes. The possible and potential impact of these new anode materials is detailed and discussed here.

Direct-Contact Prelithiation of Si-C Anode Study as a Function of Time, Pressure, Temperature, and the Cell Ideal Time

Direct-contact prelithiation (PL) is a facile, practical, and scalable method to overcome the first-cycle loss and large volume expansion issues for silicon anode (with 30 wt % Si loading) material, and a detailed study is absent. Here, an understanding of direct-contact PL as a function of the PL time, and the effects of externally applied pressure (weight), microstructure, and operating temperature have been studied. The impact of PL on the Si-C electrode surfaces has been analyzed by electrochemical techniques and different microstructural analyses. The solid electrolyte interface (SEI) layer thickness increases with the increase in PL time and decreases after 2 min of PL time. The ideal PL time was found to be between 15 (PL-15) and 30 (PL-30) min with 83.5 and 97.3% initial Coulombic efficiency (ICE), respectively, for 20 g of externally applied weight. The PL-15 and PL-30 cells showed better cyclic stability than PL-0 (without prelithiation), with more than 90% capacity retention after 500 cycles at 1 A g^-1 current density. The discharge capacities for PL-15 and PL-30 have been observed as highest at 45 °C operating temperature with limited cyclability. We propose here a synchronization strategy in prelithiation time, pressure, and temperature to achieve excellent cell performance.

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.

Observing Two-Dimensional Spontaneous Reaction between a Silicon Electrode and a LiPF6-Based Electrolyte In Situ and in Real Time

Two-dimensional spontaneous reactions between an electrode and an electrolyte are very important for the formation of a solid electrolyte interphase (SEI) but difficult to study because studying such reactions requires surface/interface sensitive techniques with sufficiently structural and temporal resolutions. In this study, we have applied femtosecond broadband sum-frequency generation vibrational spectroscopy (SFG-VS) to investigate the interaction between a silicon electrode and a LiPF₆-based diethyl carbonate electrolyte solution in situ and in real time. We found that two kinds of diethyl carbonate species are present on the silicon surface and their C═O stretching aligns in opposite directions. Intrinsically spontaneous chemical reactions between silicon electrodes and a LiPF₆ electrolyte solution are observed. The reactions generate silicon hydride and cause corrosion of the silicon electrodes. Coating of the silicon surface with a poly(vinyl alcohol) layer can effectively retard and attenuate these reactions. This work demonstrates that SFG-VS can provide a unique and powerful state-of-the-art tool for elucidating the molecular mechanisms of SEI formation.

Operando transmission electron microscopy of battery cycling: thickness dependent breaking of TiO2 coating on Si/SiO2 nanoparticles

Conformal coating of silicon (Si) anode particles is a common strategy for improving their mechanical integrity, to mitigate battery capacity fading due to particle volume expansion, which can result in particle crumbling due to lithiation induced strain and excessive solid-electrolyte interface formation. Here, we use operando transmission electron microscopy in an open cell to show that TiO₂ coatings on Si/SiO₂ particles undergo thickness dependent rupture on battery cycling where thicker coatings crumble more readily than thinner (∼5 nm) coatings, which corroborates the difference in their capacities.

A Review on Recent Advances for Boosting Initial Coulombic Efficiency of Silicon Anodic Lithium Ion batteries

Rechargeable silicon anode lithium ion batteries (SLIBs) have attracted tremendous attention because of their merits, including a high theoretical capacity, low working potential, and abundant natural sources. The past decade has witnessed significant developments in terms of extending the lifespan and maintaining high capacities of SLIBs. However, the detrimental issue of low initial Coulombic efficiency (ICE) toward SLIBs is causing more and more attention in recent years because ICE value is a core index in full battery design that profoundly determines the utilization of active materials and the weight of an assembled battery. Herein, a comprehensive review is presented of recent advances in solutions for improving ICE of SLIBs. From design perspectives, the strategies for boosting ICE of silicon anodes are systematically categorized into several aspects covering structure regulation, prelithiation, interfacial design, binder design, and electrolyte additives. The merits and challenges of various approaches are highlighted and discussed in detail, which provides valuable insights into the rational design and development of state-of-the-art techniques to deal with the deteriorative issue of low ICE of SLIBs. Furthermore, conclusions and future promising research prospects for lifting ICE of SLIBs are proposed at the end of the review.

Nitrogen, Oxygen-Codoped Vertical Graphene Arrays Coated 3D Flexible Carbon Nanofibers with High Silicon Content as an Ultrastable Anode for Superior Lithium Storage

Free-standing and foldable electrodes with high energy density and long lifespan have recently elicited attention on the development of lithium-ion batteries (LIBs) for flexible electronic devices. However, both low energy density and slow kinetics in cycling impede their practical applications. In this work, a free-standing and binder-free N, O-codoped 3D vertical graphene carbon nanofibers electrode with ultra-high silicon content (VGAs@Si@CNFs) is developed via electrospinning, subsequent thermal treatment, and chemical vapor deposition processes. The as-prepared VGAs@Si@CNFs electrode exhibits excellent conductivity and flexibility because of the high graphitized carbon nanofiber network and abundant vertical graphene arrays. Such 3D all-carbon architecture can be fabulous for providing a conductive and mechanically robust network, further improving the kinetics and restraining the volume expansion of Si NPs, especially with an ultra-high Si content (>90 wt%). As a result, the VGAs@Si@CNFs composite demonstrates a superior specific capacity (3619.5 mAh g-1 at 0.05 A g-1 ), ultralong lifespan, and outstanding rate capability (1093.1 mAh g-1 after 1500 cycles at 8 A g-1 ) as a free-standing anode for LIBs. It is believed that this work offers an exciting method for developing free-standing and high-energy-density electrodes for other energy storage devices.

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.

Effects of Pyrolysis on High-Capacity Si-Based Anode of Lithium Ion Battery with High Coulombic Efficiency and Long Cycling Life

We report a facile pyrolysis process for the fabrication of a porous silicon-based anode for lithium-ion battery. Silicon flakes of 100 nm × 800 nm × 800 nm were mixed with equal weight of sodium carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) as the binder and the conductivity enhancement additive, Ketjen Black (KB), at the weight ratio of silicon–binder–KB being 70%:20%:10%, respectively. Pyrolysis was carried out at 700 °C in an inert argon environment for one hour. The process converts the binder to graphitic carbon coatings on silicon and a porous carbon structure. The process led to initial coulombic efficiency (ICE) being improved from 67% before pyrolysis to 75% after pyrolysis with the retention of 2.1 mAh/cm² areal capacity after 100 discharge–charge cycles at 1 A/g rate. The improved ICE and cycling performance are attributed to graphitic coatings, which protect silicon from irreversible reactions with the electrolyte to form compounds such as lithium–silicon–fluoride (Li₂SiF₆) and the physical integrity and buffer space provided by the porous carbon structure. By eliminating the adverse effects of KB, the anode made with silicon-to-binder weight ratio of 70%:30% exhibited further improvement of the ICE to approximately 90%. This demonstrated that pyrolysis is a facile and promising one-step process for the fabrication of silicon-based anode with high ICE and long cycling life. This is especially true when the amount and choice of conductivity enhancement additive are optimized.

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.

A surface-engineering-assisted method to synthesize recycled silicon-based anodes with a uniform carbon shell-protective layer for lithium-ion batteries

Yolk-shell silicon/carbon composite encapsulated by uniform carbon shell (Si@C) are becoming an effective method to mitigate volume-related issues of Si-based anodes and maintain an excellent performance for lithium-ion batteries (LIBs). However, a uniform carbon shell in Si@C is difficult to guarantee. Herein, a facile surface-engineering-assisted strategy is described to prepare Si@C composite with low-cost modified recycled waste silicon powders (RWSi) as core coated by a uniform carbon shell-protective layer derived from the pyrolysis of poly (methyl methacrylate) (PMMA) as carbon source (m-RWSi@PMMA-C). In this process, surface-engineering is performed with silane coupling agent kh550 to functionalize the RWSi particles via a silanization reaction, guaranteeing a uniform PMMA coating which will be transformed into carbon shell-protective layer after carbonization. The m-RWSi@PMMA-C electrode delivers an optimal discharge capacity of 1083 mAhg^-1 at 200 mAg^-1 after 200 cycles with an initial capacity of 3176.2 mAhg^-1 and a high initial Coulombic efficiency (ICE) of 75.6%. Based on these results, the recycled silicon-based anode with a uniform carbon shell-protective layer displays great application potential and it also brings a new perspective on silicon-based anodes via surface-engineering method for LIBs.

Molecular Understanding of Electrochemical-Mechanical Responses in Carbon-Coated Silicon Nanotubes during Lithiation

Carbon-coated silicon nanotube (SiNT@CNT) anodes show tremendous potential in high-performance lithium ion batteries (LIBs). Unfortunately, to realize the commercial application, it is still required to further optimize the structural design for better durability and safety. Here, the electrochemical and mechanical evolution in lithiated SiNT@CNT nanohybrids are investigated using large-scale atomistic simulations. More importantly, the lithiation responses of SiNW@CNT nanohybrids are also investigated in the same simulation conditions as references. The simulations quantitatively reveal that the inner hole of the SiNT alleviates the compressive stress concentration between a-Li_xSi and C phases, resulting in the SiNT@CNT having a higher Li capacity and faster lithiation rate than SiNW@CNT. The contact mode significantly regulates the stress distribution at the inner hole surface, further affecting the morphological evolution and structural stability. The inner hole of bare SiNT shows good structural stability due to no stress concentration, while that of concentric SiNT@CNT undergoes dramatic shrinkage due to compressive stress concentration, and that of eccentric SiNT@CNT is deformed due to the mismatch of stress distribution. These findings not only enrich the atomic understanding of the electrochemical–mechanical coupled mechanism in lithiated SiNT@CNT nanohybrids but also provide feasible solutions to optimize the charging strategy and tune the nanostructure of SiNT-based electrode materials.

In Situ Construction of High-Performing Compact Si-SiOx-CNx Composites from Polyaminosiloxane for Li-Ion Batteries

Great efforts have been made to design high-performing Si/C composite anodes for Li-ion batteries to improve their energy density and cycling life. However, challenges remain in achieving fast electrical conductivity while accommodating significant electrode volumetric changes. Here, we report a unique Si/C-based anode architecture, a Si-SiO_x-CN_x composite, which is simultaneously constructed via the pyrolysis of a polyaminosiloxane precursor. The obtained structure features high-purity Si nanocrystals embedded in an amorphous silica matrix and then embraced by N-doped carbon layers. Notably, in this structure, all three components derived from the polyaminosiloxane precursor are linked by chemical bonding, forming a compact Si-SiO_x-CN_x triple heterostructure. Because of the improvement in the volumetric efficiency for accommodating Si active materials and electrical properties, this anode design enables promising electrochemical performance, including excellent cycle performance (830 mAh g^-1 after 100 cycles at 0.1 A g^-1) and outstanding rate performance (400 mAh g^-1 at 5 A g^-1). Moreover, this composite anode demonstrates great potential for high-energy Li-ion batteries, where a Si-SiO_x-CN_x//LiNi_0.9Co_0.1O₂ full-cell shows a high capacity of 180 mAh g^-1 as well as stable cycle performance (150 mAh g^-1 after 200 cycles at 0.19 A g^-1).

Effects of SiC and Resorcinol-Formaldehyde (RF) Carbon Coatings on Silicon-Flake-Based Anode of Lithium Ion Battery

Silicon flakes of about 100 × 1000 × 1000 nm in sizes recycled from wastes of silicon wafer manufacturing processes were coated with combined silicon carbide (SiC) and graphitic (Resorcinol-Formaldehyde (RF)) carbon coatings to serve as active materials of the anode of lithium ion battery (LIB). Thermal carbonization of silicon at 1000 °C for 5 h forms 5-nm SiC encapsulating silicon flakes. SiC provides physical strength to help silicon flakes maintain physical integrity and isolating silicon from irreversible reactions with the electrolyte. Lithium diffuses through SiC before alloying with silicon. The SiC buffer layer results in uniform alloying reactions between lithium and silicon on the surface around a silicon flake. RF carbon coatings provide enhanced electrical conductivity of SiC encapsulated silicon flakes. We characterized the coatings and anode by SEM, TEM, FTIR, XRD, cyclic voltammetry (CV), electrochemical impedance spectra (EIS), and electrical resistance measurements. Coin half-cells with combined SiC and RF carbon coatings exhibit an initial Coulombic efficiency (ICE) of 76% and retains a specific capacity of 955 mAh/g at 100th cycle and 850 mAh/g at 150th cycle of repetitive discharge and charge operation. Pre-lithiation of the anode increases the ICE to 97%. The SiC buffer layer reduces local stresses caused by non-uniform volume changes and improves the capacity retention and the cycling life.

Porous Si/Cu Anode with High Initial Coulombic Efficiency and Volumetric Capacity by Comprehensive Utilization of Laser Additive Manufacturing-Chemical Dealloying

Si has been extensively investigated as an anode material for lithium-ion batteries because of its superior theoretical capacity. However, a scalable fabrication method for a Si-based anode with high initial coulombic efficiency (ICE) and large volumetric capacity remains a critical challenge. Herein, we proposed a novel porous Si/Cu anode in which planar Si islands were embedded in the porous Cu matrix through combined laser additive manufacturing and chemical dealloying. The compositions and dimensions of the structure were controlled by metallurgical and chemical reactions during comprehensive interaction. Such a structure has the advantages of micro-sized Si and porous architecture. The planar Si islands decreased the surface area and thus increased ICE. The porous Cu matrix, which acted as both an adhesive-free binder and a conductive network, provided enough access for electrolyte and accommodated volume expansion. The anode structure was well maintained without observable mechanical damage after cycling, demonstrating the high structure stability and integrity. The porous Si/Cu anode showed a high ICE of 93.4% and an initial volumetric capacity of 2131 mAh cm^-3, which retained 1697 mAh cm^-3 after 100 cycles at 0.20 mA cm^-2. Furthermore, the full-cell configuration (porous Si/Cu //LiFePO₄) exhibited a high energy density of 464.9 Wh kg^-1 and a capacity retention of 84.2% after 100 cycles.

Suppressing the Side Reaction by a Selective Blocking Layer to Enhance the Performance of Si-Based Anodes

Building a stable solid electrolyte interphase (SEI) is an effective method to enhance the performance of Si-based materials. However, the general strategy ignores the severe side reaction that originates from the penetration of the fluoride anion which influences the stability of the SEI. In this work, an analytical method is established to study the chemical reaction mechanism between the silicon and electrolyte by combining X-ray diffraction (XRD) with mass spectrometry (MS) technology. Additionally, a selective blocking layer coupling selectivity for the fluoride anion and a high conductivity is coated on the surface of silicon. With the protection of the selective blocking layer, the rate of the side reaction is decreased by 1700 times, and the corresponding SEI thickness is dwindled by 4 times. This work explores the mechanism of the intrinsic chemical reaction and provides future directions for improving Si-based anodes.

Visualizing the Redox Reaction Dynamics of Perovskite Nanocrystals in Real and Reciprocal Space

Redox reaction, involving the gain and loss of electrons between reactants, is one type of common chemical reaction governing fundamental energy issues in nature. However, reports of vividly visualizing such key processes with simultaneous structural determination of new phases that are involved are rare. Here, by achieving simultaneous recording in both real and reciprocal space, we demonstrate in situ imaging of the redox reaction dynamics in perovskite nanocrystals. The thorough atomic-scale movies enable an in-depth understanding of the reaction-induced nucleation and growth mechanism of clusters with the aid of carbon, and a simple way of using SiN films at room temperature to fully prevent the irradiation-induced degradation in perovskites is proposed, in contrast to the costly low-temperature strategy. Real-time atomic-scale imaging in both real and reciprocal space paves the way for revealing various chemical and physical events at targeted nanoscale positions with complementary structural information.

WSi2 nanodot reinforced Si particles as anodes for high performance lithium-ion batteries

Si-based anodes are attracting enormous attention due to the super-high theoretical capacity of silicon (3579 mA h g⁻¹ at room temperature) as an anode of lithium-ion batteries.

A sandwich-like Si/SiC/nanographite sheet as a high performance anode for lithium-ion batteries

Silicon/carbon (Si/C) nanocomposite anodes have attracted great interest for their use in lithium-ion batteries (LIBs). However, Si nanoparticles are difficult to stabilize on a carbon surface. Herein, we solve this stabilization problem by designing a Si/silicon carbide/nanographite sheet (Si/SiC/NanoG) nanocomposite. The Si/SiC/NanoG nanocomposite is synthesized by the magnesium thermal reduction of a mixture of silica (SiO2) nanoparticles and NanoG at low temperature, which results in a sandwich-like structure in which the middle SiC layer serves as a linker to stabilize the Si nanoparticles on the surface of NanoGs. Electrochemical characterization shows that the Si/SiC/NanoG nanocomposite anode exhibits outstanding electrochemical performance (an initial reversible capacity of 1135.4 mA h g-1 and 80.4% capacity retention after 100 cycles at 100 mA g-1). This high capacity retention is due to the strong connection between Si and NanoG through the interfacial SiC layer, which buffers the volume changes during the Li-Si alloying-dealloying process. This research will contribute to the design of advanced Si/C anode materials of LIBs.