An innovative strategy for constructing multicore yolk-shell Si/C anodes for lithium-ion batteries

The yolk-shell architecture offers a promising solution to the challenges of silicon (Si) anodes in lithium-ion batteries (LIBs), particularly in addressing the significant volume changes that occur during charge and discharge cycles. However, traditional construction methods often rely on sacrificial templates and acid or alkali etching, which limits industrial applicability. In this work, we successfully constructed a silicon/carbon (Si/C) composite with a multicore yolk-shell structure using scalable spray drying technology and in-situ growth of metal-organic frameworks (MOFs) at room temperature. By controlling the spray drying parameters and the size of the MOF, we achieved a controllable adjustment of cavity size and shell integrity without the need for sacrificial templates, facilitating large-scale preparation. Electrochemical characterization shows that the composites exhibit impressive performance, achieving a reversible specific capacity of 1,054.5 mAh g-1 after 100 cycles at 0.5 A g-1, and retaining 734.8 mAh g-1 after 400 cycles at 1 A g-1. Moreover, finite element analysis (FEA) revealed another reason why the yolk-shell structure improves the performance of Si anodes: the presence of cavities promotes ion diffusion processes. This study provides a new synthetic paradigm for preparing Si-C composite materials with yolk shell structure and offers new insights into the improvement mechanism of this structure.

Triple-Layered Noncombustible PEO-Based Solid Electrolyte for Highly Safe Lithium-Metal Batteries

Lithium-metal batteries are currently recognized as promising next-generation technologies owing to their high energy density. Solid polymer electrolytes, particularly those based on polyethylene oxide (PEO), are lauded for their leakage resistance, safety, and flexible design. Despite the ongoing fire safety- and ionic conductivity-related concerns, a novel noncombustible solid polymer electrolytes with superior ionic conductivities are introduced here with additive decabromodiphenyl ethane and zeolite. To enhance the mechanical strength and ensure soft interactions at the electrode interface, a triple-layer structure with self-extinguishing properties and robust ionic conductivity is proposed. Notably, the softness at the electrode interface intensifies as the LiTFSI concentration increases; this higher concentration negatively impacts PEO crystallinity, enhancing the ionic conductivity owing to the presence of free Li+ and TFSI- ions. This novel electrolyte can achieve a conductivity of 1.5 mS cm-1 at 60 °C, maintain anodic stability up to 4.8 V, and exhibit flame retardancy. Furthermore, adding LiTFSI at 60% relative to PEO is shown to reduce LiF formation on the surface, enhancing anode stability. The [LiFePO4/triple-layered electrolyte/Li] lithium-metal batteries are capable of an initial capacity of 153 mAh g-1, sustained superior capacity retention of 87.9%, and high Coulombic efficiency (99.6%) over 1000 cycles at a 1C rate.

Advancing lithium-ion battery performance with heteroatom-based anode architectures for fast charging and high capacity

Electric vehicles (EVs) are on the brink of revolutionizing transportation, but the current lithium-ion batteries (LIBs) used in them have significant limitations in terms of fast-charging capabilities and energy density. This feature article begins by examining the key challenges of using graphite for fast charging and silicon for achieving high energy density in LIBs. Firstly, it explores various design strategies employed by researchers worldwide to improve the fast-charging performance of graphite, such as surface coatings, morphological modifications, and binder design. However, instead of modifying graphite, a more effective approach is to use materials with inherently beneficial properties-specifically, hard carbons. The article then reviews the design strategies for increasing capacity while maintaining structural stability in silicon-based anodes, including encapsulated structures and embedded matrices. Overall, this article provides a comprehensive overview of diverse approaches aimed at advancing both fast-charging capability and energy density in LIBs.

Interface Engineering of Styrenic Polymer Grafted Porous Micro-Silicon/Polyaniline Composite for Enhanced Lithium Storage Anode Materials

Si anode materials are promising candidates for next-generation Li-ion batteries (LIBs) because of their high capacities. However, expansion and low conductivity result in rapid performance degradation. Herein, we present a facile one-pot method for pyrolyzing polystyrene sulfonate (PSS) polymers at low temperatures (≤400 °C) to form a thin carbonaceous layer on the silicon surface. Specifically, micron silicon (mSi) was transformed into porous mSi (por-mSi) by a metal-assisted chemical etching method, and a phenyl-based thin film derived from the thermolysis of PSS formed a strong Si-C/Si-O-C covalent bonding with the Si surface, which helped maintain stable cycle performance by improving the interfacial properties of mSi. Additionally, PSS-grafted por-mSi (por-mSi@PSS) anode was coated with polyaniline (PANI) for endowing additional electrical conductivity. The por-mSi@PSS/PANI anode demonstrated a high reversible capacity of ~1500 mAh g-1 at 0.1 A g-1 after 100 cycles, outperforming or matching the performance reported in recent studies. A thin double layer composed of phenyl moieties and a conductive PANI coating improved the stability of Si-based anodes and provided an effective pathway for Li+ ion transport to the Si interface, suggesting that polymer-modified Si anodes hold significant promise for advanced LIB applications.

Formicarium-Like Micron Porous Si Synergistically Adjusted by Surface Hard-Soft Nanoencapsulation as Long-Life Lithium-Ion Battery Anode

Micron porous silicon (MPSi) is a promising lithium-ion battery (LIB) anode that can provide enough space to effectively alleviate the volume expansion and large number of transmission channels to rapidly transport the Li-ions. However, a long-term stable MPSi anode at high current density is still a great challenge. Herein, a double-regulated formicarium like-MPSi composite using the surface hard-soft titanium dioxide-few layered MXene nanotemplate (FMPSi@TiO2@FMXene) was designed and synthesized via an in situ assembly strategy as long-life LIB anode. Such hard-soft TiO2-FMXene nanoencapsulation can collaboratively tune the internal/external stress, inhibit the volume expansion, reduce the interfacial reactions, and improve the electrical conductivity of MPSi, resulting in the great enhancement of structural stability and electrochemical performance in cycling even at high current density. Especially, this FMPSi@TiO2@FMXene anode exhibits a high reversible capacity of 1254.9 and 970.4 mAh/g after 500 cycles at 0.5 and 1 A/g, respectively. Moreover, a full cell is assembled with the FMPSi@TiO2@FMXene anode and commercial LiFePO4 (LFP) cathode, exhibiting a high capacity retention rate of 91.6% in 100 cycles. This work provides an effective surface nanoengineering tactic to obtain the structurally stable MPSi anodes by hard-soft nanotemplate for large-scale and long-term LIB application.

Advances in physical vapor deposited silicon/carbon based anode materials for Li-ion batteries

This paper explores the latest developments in physical vapor deposition (PVD) techniques for fabricating silicon-carbon (Si/C) based thin films as anodes of Lithium-Ion batteries (LiBs). Properties of Si/C based materials, such as high thermal stability, electrical conductivity and mechanical strength, have addressed the critical challenges associated with the use silicon as anode material for LiBs, including as volume expansion during lithiation, structural stability and electrode degradation. The review article aims to provide recent advances in the use of Si/C-based thin film materials deposited via PVD processes as anodes for LiBs. PVD deposition processes provide numerous benefits including the precise control over the structure, thickness, morphology, as well as the design of deposited thin-film materials, and this article provides an in-depth analysis on the design and synthesis of Si/C thin films, as well as its electrochemical performance and stability when used as anode for LiBs. The primary aim of this paper is to underscore the advantages provided by PVD processes in overcoming challenges associated with using pure silicon as anode material for LiBs, or in improving the electrochemical performance of Si/C-based anode materials through the design of several Si/C films, covering both multilayer and nanocomposite Si/C film configurations outlined in sections 2 and 3, respectively. Insights into the mechanisms governing lithium-ion insertion/extraction processes within the Si/C matrix are provided, offering an understanding of the material's behavior during battery cycling.

Ag nanoparticle modified porous Si microspheres as high-performance anodes for Li-ion batteries

This study aimed to address the challenges associated with silicon (Si) anode materials in Li-ion batteries, such as their large volume effect and poor electrical conductivity. To overcome these limitations, a novel composite microsphere called pSi/Ag was developed using quartz waste through a combination of high-energy ball-milling, spray drying, and magnesiothermic reduction techniques. The morphology and structure of the pSi/Ag composite were thoroughly characterized using various methods, including X-ray diffraction, field-emission scanning electron microscopy, and transmission electron microscopy. The results revealed that the Ag nanoparticles were uniformly dispersed within the porous micron-sized Si sphere particles, leading to enhanced electrochemical performance compared to pure porous silicon that did not undergo the spray drying process. The use of micron-sized Si prevented the excessive formation of the solid electrolyte interphase film, and the pSi/Ag-5 anode, prepared with 5 wt% AgNO3 as a precursor, demonstrated an impressive initial Coulombic efficiency of 92.8%. Moreover, a high specific capacity of 1251.4 mA h g-1 over 300 cycles at a current density of 4000 mA g-1 was attributed to the improved conductivity provided by the Ag nanoparticles in the Si matrix. The straightforward synthesis method employed in this study to produce pSi/Ag presents a promising approach for the future development of high-performance silicon anodes in Li-ion batteries.

Sponge-Like Porous-Conductive Polymer Coating for Ultrastable Silicon Anodes in Lithium-Ion Batteries

Urgent calls for reversible cycling performance of silicon (Si) requires an efficient solution to maintain the silicon-electrolyte interface stable. Herein, a conductive biphenyl-polyoxadiazole (bPOD) layer is coated on Si particles to enhance the electrochemical process and prolong the cells lifespan. The conformal bPOD coatings are mixed ionicelectronic conductors, which not only inhibit the infinite growth of solid electrolyte interphase (SEI) but also endow electrodes with outstanding ion/electrons transport capacity. The superior 3D porous structure in the continuous phase allows the bPOD layers to act like a sponge to buffer volume variation, resulting in high structural stability. The in situ polymerized bPOD coating and it-driven thin LiF-rich SEI layer remarkably improve the lithium storage performance of Si anodes, showing a high reversible specific capacity of 1600 mAh g-1 even after 500 cycles at 1 A g-1 along with excellent rate capacity of over 1500 mAh g-1 at 3 A g-1 . It should be noticed that a long cycle life of 800 cycles with 1065 mAh g-1 at 3 A g-1 can also be achieved with a capacity retention of more than 80%. Therefore,  we  believe this unique polymer coating design paves the way for the widespread adoption of next-generation lithium-ion batteries.

Electron and Ion Transport in Lithium and Lithium-Ion Battery Negative and Positive Composite Electrodes

Electrochemical energy storage systems, specifically lithium and lithium-ion batteries, are ubiquitous in contemporary society with the widespread deployment of portable electronic devices. Emerging storage applications such as integration of renewable energy generation and expanded adoption of electric vehicles present an array of functional demands. Critical to battery function are electron and ion transport as they determine the energy output of the battery under application conditions and what portion of the total energy contained in the battery can be utilized. This review considers electron and ion transport processes for active materials as well as positive and negative composite electrodes. Length and time scales over many orders of magnitude are relevant ranging from atomic arrangements of materials and short times for electron conduction to large format batteries and many years of operation. Characterization over this diversity of scales demands multiple methods to obtain a complete view of the transport processes involved. In addition, we offer a perspective on strategies for enabling rational design of electrodes, the role of continuum modeling, and the fundamental science needed for continued advancement of electrochemical energy storage systems with improved energy density, power, and lifetime.

Strategies for Controlling or Releasing the Influence Due to the Volume Expansion of Silicon inside Si-C Composite Anode for High-Performance Lithium-Ion Batteries

Currently, silicon is considered among the foremost promising anode materials, due to its high capacity, abundant reserves, environmental friendliness, and low working potential. However, the huge volume changes in silicon anode materials can pulverize the material particles and result in the shedding of active materials and the continual rupturing of the solid electrolyte interface film, leading to a short cycle life and rapid capacity decay. Therefore, the practical application of silicon anode materials is hindered. However, carbon recombination may remedy this defect. In silicon/carbon composite anode materials, silicon provides ultra-high capacity, and carbon is used as a buffer, to relieve the volume expansion of silicon; thus, increasing the use of silicon-based anode materials. To ensure the future utilization of silicon as an anode material in lithium-ion batteries, this review considers the dampening effect on the volume expansion of silicon particles by the formation of carbon layers, cavities, and chemical bonds. Silicon-carbon composites are classified herein as coated core-shell structure, hollow core-shell structure, porous structure, and embedded structure. The above structures can adequately accommodate the Si volume expansion, buffer the mechanical stress, and ameliorate the interface/surface stability, with the potential for performance enhancement. Finally, a perspective on future studies on Si-C anodes is suggested. In the future, the rational design of high-capacity Si-C anodes for better lithium-ion batteries will narrow the gap between theoretical research and practical applications.

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.

Carbon-Coated Three-Dimensional MXene/Iron Selenide Ball with Core-Shell Structure for High-Performance Potassium-Ion Batteries

Two-dimensional (2D) MXenes are promising as electrode materials for energy storage, owing to their high electronic conductivity and low diffusion barrier. Unfortunately, similar to most 2D materials, MXene nanosheets easily restack during the electrode preparation, which degrades the electrochemical performance of MXene-based materials. A novel synthetic strategy is proposed for converting MXene into restacking-inhibited three-dimensional (3D) balls coated with iron selenides and carbon. This strategy involves the preparation of Fe₂O₃@carbon/MXene microspheres via a facile ultrasonic spray pyrolysis and subsequent selenization process. Such 3D structuring effectively prevents interlayer restacking, increases the surface area, and accelerates ion transport, while maintaining the attractive properties of MXene. Furthermore, combining iron selenides and carbon with 3D MXene balls offers many more sites for ion storage and enhances the structural robustness of the composite balls. The resultant 3D structured microspheres exhibit a high reversible capacity of 410 mAh g^-1 after 200 cycles at 0.1 A g^-1 in potassium-ion batteries, corresponding to the capacity retention of 97% as calculated based on 100 cycles. Even at a high current density of 5.0 A g^-1, the composite exhibits a discharge capacity of 169 mAh g^-1.

Production of high-energy Li-ion batteries comprising silicon-containing anodes and insertion-type cathodes

Rechargeable Li-based battery technologies utilising silicon, silicon-based, and Si-derivative anodes coupled with high-capacity/high-voltage insertion-type cathodes have reaped significant interest from both academic and industrial sectors. This stems from their practically achievable energy density, offering a new avenue towards the mass-market adoption of electric vehicles and renewable energy sources. Nevertheless, such high-energy systems are limited by their complex chemistry and intrinsic drawbacks. From this perspective, we present the progress, current status, prevailing challenges and mitigating strategies of Li-based battery systems comprising silicon-containing anodes and insertion-type cathodes. This is accompanied by an assessment of their potential to meet the targets for evolving volume- and weight-sensitive applications such as electro-mobility.

Online Monitoring of Transition-Metal Dissolution from a High-Ni-Content Cathode Material

The dissolution of transition metals (TMs) from cathode materials and their deposition on the anode represents a serious degradation process and, with that, a shortcoming of lithium-ion batteries. It occurs particularly at high charge voltages (>4.3 V), contributing to severe capacity loss and thus impeding the increase of cell voltage as a simple measure to increase energy density. We present here for the first time the online detection of dissolved TMs from a Ni-rich layered oxide cathode material with unprecedented potential and time resolution in potentiodynamic scans. To this aid, we used the coupling of an electroanalytical flow cell (EFC) with inductively coupled plasma mass spectrometry (ICP-MS), which is demonstrated to be an ideal tool for a fast performance assessment of new cathode materials from initial cycles. The simultaneous analysis of electrochemical and dissolution data allows hitherto hidden insights into the processes' characteristics and underlying mechanisms.

Dynamically Cross-Linked Polymeric Binder-Made Durable Silicon Anode of a Wide Operating Temperature Li-Ion Battery

The colossal volumetric expansion (up to 300%) of the silicon (Si) anode during repeated charge-discharge cycles destabilizes the electrode structure and causes a drastic drop in capacity. Here in this work, commercial poly(acrylic acid) (PAA) is cross-linked by hydroxypropyl polyrotaxane (HPR) via reversible boronic ester bonds to achieve a water-soluble polymeric binder (PAA-B-HPR) for making the Si anode of the Li-ion battery. Slidable α-cyclodextrins of modified polyrotaxane are allowed to move around when the unwanted volume variation occurs in the course of lithiation and delithiation so that the accumulated internal stress can be equalized throughout the system, while the reversible boronic ester bonds are capable of healing the damages created during manufacturing and service to maintain the electrode integrity. As a result, the Li-ion battery assembled with the Si anode comprised of the PAA-B-HPR binder possesses outstanding specific capacity and cycle stability within a wide temperature range from 25 to 55 °C. Especially, the Si@PAA-B-HPR anode exhibits a discharge specific capacity of 1056 mA h/g at 1.4 A/g after 500 cycles under a higher temperature of 55 °C, and the corresponding capacity fading rate per cycle is only 0.10%. The present work opens an avenue toward the practical application of the Si anode for Li-ion batteries.

Boosting Lithium-Ion Transport Kinetics by Increasing the Local Lithium-Ion Concentration Gradient in Composite Anodes of Lithium-Ion Batteries

Constructing composite electrodes is considered to be a feasible way to realize high-specific-capacity Li-ion batteries. The core-double-shell-structured Si@C@TiO₂ would be an ideal design for such batteries, considering that carbon (C) can buffer the volume change and TiO₂ can constrain the structural deformation of Si. Although the electrochemical performance of the shells themselves is relatively clear, the complexity of the multishell heterointerface always results in an ambiguous understanding about the influence of the heterointerface on the electrochemical properties of the core material. In this work, a multilayer film model that can simplify and simultaneously expand the area of the heterointerface is used to study the heterointerfacial behavior. First, a multilayer film TiO₂/C with different numbers of TiO₂/C heterointerfaces is studied. It shows that the electrochemical performance is enhanced apparently by increasing the number of TiO₂/C heterointerfaces. On the one hand, the TiO₂/C heterointerface exhibits a strong lithium-ion storage capacity. On the other hand, the TiO₂/C heterointerface appears to effectively promote the local Li-ion concentration gradient and thus boost the Li-ion transport kinetics. Then, TiO₂/C is combined with Si to construct a composite anode Si/C/TiO₂. An obvious advantage of TiO₂/C over single TiO₂ and C is observed. The utilization rate of Si is greatly improved in the first cycle and reaches up to 98% in Si/C/TiO₂. The results suggest that the electrochemical performance of Si can be greatly manipulated by the heterointerface between the multishells.

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.