Silicon Anodes Research Articles

Dramatic Enhancement Enabled by Introducing TiN into Bread-like Porous Si-Carbon Anodes for High-Performance and Safe Lithium Storage.

Doping modifications and surface coatings are effective methods to slow volume dilatation and boost the conductivity in silicon (Si) anodes for lithium-ion batteries (LIBs). Herein, using low-cost ferrosilicon from industrial production as the energy storage material, a bread-like nitrogen-doped carbon shell-coated porous Si embedded with the titanium nitride (TiN) nanoparticle composite (PSi/TiN@NC) was synthesized by simple ball milling, etching, and self-assembly growth processes. Remarkably, the porous Si structure formed by etching the FeSi2 phase in ferrosilicon alloys can provide buffer space for significant volume expansion during lithiation. Highly conductive and stable TiN particles can act as stress absorption sites for Si and improve the electronic conductivity of the material. Furthermore, the nitrogen-doped porous carbon shell further helps to sustain the structural stability of the electrode material and boost the migration rate of Li-ions. Benefiting from its unique synergistic effect of components, the PSi/TiN@NC anode exhibits a reversible discharge capacity up to 1324.2 mAh g-1 with a capacity retention rate of 91.5% after 100 cycles at 0.5 A g-1 (vs fourth discharge). Simultaneously, the electrode also delivers good rate performance and a stable discharge capacity of 923.6 mAh g-1 over 300 cycles. This research can offer a potential economic strategy for the development of high-performance and inexpensive Si-based anodes for LIBs.

Porous silicon/carbon composites as anodes for high-performance lithium-ion batteries

Silicon anodes are promising for use in lithium-ion batteries. However, their practical application is severely limited by their large volume expansion leading to irreversible material fracture and electrical disconnects. This study proposes a new top-down strategy for preparing microsize porous silicon and introduces polyacrylonitrile (PAN) for a nitrogen-doped carbon coating, which is designed to maintain the internal pore volume and lower the expansion of the anode during lithiation and delithiation. We then explore the effect of temperature on the evolution of the structure of PAN and the electrochemical behavior of the composite electrode. After treatment at 400 -, the PAN coating retains a high nitrogen content of 11.35%, confirming the presence of C―N and C―O bonds that improve the ionic-electronic transport properties. This treatment not only results in a more intact carbon layer structure, but also introduces carbon defects, and produces a material that has remarkable stable cycling even at high rates. When cycled at 4 A g−1, the anode had a specific capacity of 857.6 mAh g−1 even after 200 cycles, demonstrating great potential for high-capacity energy storage applications.

Enhanced strain mapping Unveils internal deformation dynamics in Silicon-based lithium-ion batteries during electrochemical cycling

Silicon-based anodes have emerged as a promising advancement in lithium-ion battery technology, offering significantly higher lithium storage capacities than traditional graphite. However, the volumetric expansion of silicon—anodes can swell by up to 300 % during lithiation—presents serious challenges to their structural integrity and electrochemical stability. This study investigates the internal structural dynamics of silicon anodes during lithiation and delithiation cycles. A novel cell design for a 18,650 cylindrical cell featuring micro-sized internal speckles within the silicon anode is presented. This design improves the simulation of electrochemical conditions and allows for precise displacement tracking, mitigating impacts on capacity and cycle performance while enhancing Digital Volume Correlation (DVC) analysis. The research prioritizes reducing scan time and radiation exposure in micro-CT assessments of Li-ion cells, and improves the accuracy of internal strain mapping via DVC. Displacement fields over three charging and discharging cycles are documented. Notably, uneven volumetric changes are observed, with local displacements reaching up to 35 µm in areas smaller than 2.5 mm in radius, which contracted during charging and expanded during discharging. This protocol offers insights into the relationship between electrode mechanics and cell performance, promoting non-destructive evaluations of internal structures in commercial cells.

Reversible silicon anodes enabled by fluorinated inorganic-organic hybrid coating

Silicon anodes deliver batteries with energy densities much higher than those based on today’s dominant graphite anodes. However, they commonly exhibit huge volume variations and unfavorable interface stability, causing a gradually diminishing capacity on extended cycling. Most Si-based batteries consisting Si/C composites in industry can only use a very limited amount of Si (<30 % by weight). Exploiting molecular layer deposition (MLD) technique, a fluorine-rich flexible inorganic–organic hybrid alucone (AlFHQ) shell is controllably deposited onto Si electrodes. Employing ex situ XPS and AFM, the AlFHQ film presents reversible electrochemical evolutions in terms of composition and morphology. The interactions the between Li+ and −O−2,3,5,6-fluorobenzene functional groups help to construct a mechanically-chemically robust LiF-rich hybrid solid electrolyte interphase (SEI) on Si anode, delivering enhanced interfacial stability and integrity of electrode. An optimized coating thickness (≈5 nm) for interfacial stabilization and Li+ transport kinetics is demonstrated, namely, Si@AlFHQ-20. The reported fluorine-rich hybrid modification technique endows (a), stable cycling of Si anode (≈3.8 mAh cm−2) with an ultrahigh initial Coulombic efficiency (ICE) of 92.3 %; (b), enhanced rate capability of 1468 mAh/g at 2.0 A g−1 and good cycling performance; and (c), overall cell (Si@AlFHQ-20//LiCoO2@Al2O3) operational stability for more than 100 cycles under stringent cathode conditions (2.68 mAh cm−2, high cutoff voltage at 4.55 V).

Si-P-Cu internally bonded anode: An innovative strategy for low-cost and high-performance pseudocapacitive Li-ion storage

Maintaining the structural integrity of silicon and phosphorus anodes during the Li+ insertion and extraction cycles poses a significant challenge. Inspired by the natural process of plant roots anchoring into soil, we present a simple yet effective method for integrating a SiP anode into the copper current collector. This approach involves subjecting readily available and cost-effective micrometre-sized silicon particles (50–150 μm) and red phosphorus to mechanochemical treatment. Subsequently, the resulting Si/P composite is coated onto copper foil and subjected to annealing treatment, resulting in the formation of an integrated structure, incorporating Cu3Si, Cu3P, and P-doped Si, firmly established within the copper current collector. The electrode obtained (BM-Si@P/Cu-350), promoted by a crosslinked (polyimide) PI binder, outperforms not only the ball-milled Si and red P but also the same electrode in which the annealing process is absent (BM-Si@P/Cu-100). During the mechanochemical treatment, red P acts as both the doping agent and a lubricant, facilitating the grinding of the Si particles into P-doped Si particles in the range of predominantly 200–300 nm; while during the thermal treatment, Si plays a key role in preventing excessive interaction between the P and the Cu current collector. Instead, a tailored rooting of the active material into the current collector is achieved through the formation of Cu3P and Cu3Si phases, not only increasing the mechanical stability of the electrode to endure volume changes during cycling and limit developing cracks, but also enhancing the electrical conductivity of the system. This article suggests a simple and potentially low-cost strategy for the utilization of highly available micrometre-sized silicon and red-P for Li-ion storage applications.

Synergistic Structural Integrity and Remarkable Structural Stability of NC@Si Anodes for Lithium-ion Batteries

The silicon-based anode has attracted wide attention because of its high theoretical specific capacity, which is expected to greatly improve the batteries’ energy density. However, during the charge-discharge cycles, the great volume expansion of the anode active silicon seriously restricts its electrochemical stability. Herein, N-doping carbon-coated silicon microsphere was prepared for lithium-ion batteries. Benefit from the core-shell structure formed from silicon carbon, the volume change of silicon anode during the cycle is well coordinated. What's more, N-doping carbon reduces the reaction energy barrier between silicon and lithium and accelerates the electrochemical reaction, which improves the cycling performance of the battery. The specific capacity of the prepared button battery is as high as 2913.13 mAh g−1 at the current density of 0.21 mA g−1, and the average coulomb efficiency is higher than 99.84% during the cycling. And the capacity of NC@SiO2 anode gradually stabilizes after 500 cycles.

Cycling Aging in Different State of Charge Windows in Lithium-Ion Batteries with Silicon-Dominant Anodes

Reducing the capacity utilization of silicon-containing anodes and choosing the optimal full-cell voltage window improve the lifetime significantly. In this study, we investigate how different voltage windows affect the aging modes with a common 50% cycling depth. First, the cyclic stability, the anode potentials, and the polarization increase are analyzed for the different voltage windows using 70 wt% microscale silicon anodes and NCA cathodes with a lithium metal reference electrode to investigate the electrode-specific characteristics. Further, the underlying aging modes are quantified in the post-mortem analysis. Finally, the anode thickness increase is quantified using a dilatometer setup for different anode lithiations. In contrast to the literature, the highest voltage window is most beneficial for the lifetime since high anode delithiation potentials and high surface increases are avoided. The anode potential at the end-of-discharge, the charge-averaged full-cell potentials, and the resistance increase are a function of the state of health (SoH). The common underlying main aging mechanism is the loss of lithium inventory, followed by the loss of anode active material. In contrast, the loss of cathode active materials only plays a minor role.

Influence of the Binder properties on Silicon Anode for Solid-State Batteries

Silicon (Si) has been considered as one of the most promising anode materials because of its high theoretical capacity of 4200 mAh g−1. However, the huge volume change and side reactions upon cycling cause poor cycle performance and limit a use of Si for the commercialization. Recently all solid-state batteries open up new possibilities for an introduction of high capacity electrode materials due to their ability to operate under compression, which can mitigate electrode volume expansion. Herein, we study an effect of multifunctional polymeric binders on silicon anode for all solid-state batteries enabled by a sulfide Li6PS5Cl electrolyte. The Si electrode manufactured by a single rigid polymer shows stable electrochemical properties because of applied external pressure and potential hydrogen bonds between carboxyl groups and Si particles, resulting in a mitigation of a volume change. In addition, an introduction of multifunctional network binders to the Si-based electrode leads to a high discharge capacity of 3000 mAh g−1 and stable cycle performances at room temperature.

Supramolecular-driven construction of multilayered structure by modified hummers method for robust silicon anode

Rational design of nano-structured silicon (Si)-based composites to enhance the structural stability and electrical conductivity is key to developing high-performance lithium-ion batteries. Here, a supramolecular self-assembly strategy is first adopted to prepare Si@rGO composites with multilayered structure through the modified Hummers method. Experimental results demonstrate that Si@SiOx NPs are uniformly distributed in rGO interlayers by supramolecular interaction. In situ Raman results suggest that the multilayer embedded structure can effectively confine the Si NPs and preserve the integrity of the electrode. Theoretical calculations indicate that the imbalanced charge distribution in inner interface shows enhanced dual-interfacial bonding and charge interactions in the Si@SiOx⊂rGO composite, resulting in an interfacial electric-field between Si NPs and rGO for fast ionic and charge migration. The fabricated MSi@SiOx⊂rGO anode with high Si contents (> 60 wt.% Si) exhibits superior Li-ion reaction kinetics (882.4 mAh g−1 at 8 A g−1), durable structural stability (0.031% per cycle capacity attenuation with an average Coulombic efficiency > 99.7%), and low expansion rate. High-mass-loading electrodes show great potential for commercial applications. Full cells assembled with LiCoO2 cathodes also demonstrate outstanding Li-ion storage properties. This work provides insights into the interfacial design of Si@C anodes for advanced Li-ion battery.

Biological small molecule interface-modification fostering resilient interfacial chemistry for silicon-based anodes

Silicon-based materials, particularly at the microscale, are prone to rapid capacity fade due to substantial volume fluctuations during the charge-discharge cycles, significantly impeding their commercial viability. Constructing a stable solid electrolyte interface (SEI) is an effective means to improve the performances of silicon-based anodes. Here small biomolecules, tryptophan (Trp) and phytic acid (PA), are introduced as interface modifiers to optimize the interfacial chemistry of micron-silicon anodes. By engaging in the SEI formation process, these small biomolecules effectively regulate the chemical composition and mechanical properties of the formed SEI, fostering a more cohesive and durable interface. The simultaneous addition of PA and Trp has been observed to yield a synergistic effect, creating a tightly bonded and resilient SEI that confers markedly improved battery performances upon the co-modified micron silicon anodes. Density functional theory calculations reveal charge interactions between these small biomolecules and silicon particles, facilitating effective adsorption onto the silicon surface. Simultaneous adsorption of Trp and PA on silicon surface can significantly enhance adsorption strength, providing a compelling explanation for the observed synergistic effect of Trp and PA co-modification.

Designing multifunctional, 3D cross-linked network binder for actual use in high performance lithium ion batteries silicon based anodes

Binders have been proved to be an economical and effective approach for accelerating the industrial application of silicon based anodes. Herein, a 3D network binder (H-PAN-g-ECH) with multifunctional groups, is constructed by crosslinking polyacrylonitrile (PAN) hydrolysate (H-PAN) with epichlorohydrin (ECH). Strong polar groups carboxylate (-COO-) and amide (-CONH2) obtained from hydrolysis of PAN as well as the original cyanide (-CN) enhance the adhesive ability of H-PAN-g-ECH to not only active material but also current collector, and thus sustain the structure integrity of the electrode. In addition, the network structure proposed by linking H-PAN with short-chain molecules endows H-PAN-g-ECH with facilitated Li-ion transmission and improved mechanical property to accommodate the great volume variation of Si during cycling. The as-prepared H-PAN-g-ECH possesses multiple interfacial adhesion and robust mechanical performance, which improves the electrochemical property of silicon anode with high areal capacity. In combination with good processability, H-PAN-g-ECH is verified to be a superior binder in use of practical Si based anodes.

A Novel Structured Si‐Based Composite with 2D Structured Graphite for High‐Performance Lithium‐Ion Batteries

AbstractSilicon is a promising alternative to graphite anodes for achieving high‐energy‐density in lithium‐ion batteries (LIBs) because of its high theoretical capacity (3579 mAh g−1). However, silicon anode must be developed to address its disadvantages, such as volume expansion and low electronic conductivity. Therefore, the use of silicon as composed with graphite and carbon anode materials is investigated, which requires properties such as a spherical morphology for high density and encapsulation of silicon particles in the composite. Herein, a graphite@silicon@carbon (Gr@Si@C) micro‐sized spherical anode composite is synthesized by mechanofusion process. This composite comprises an outer surface, middle layer, and core pore, which are formed by the capillary force arising from 2D structured graphite and pitch properties. This structure effectively addresses the intrinsic issues associated with Si. Gr@Si@C exhibits a high capacity of 1622 mAh g−1 and capacity retention of 72.2% after 100 cycles, with a high areal capacity 4.2 mAh cm−2. When Gr@Si@C is blended with commercial graphite, the composite exhibits high capacity retention and average Coulombic efficiency after cycling. The Gr@Si@C blended electrode exhibits a high energy density of 820 Wh L−1 with ≈16% metallic Si in the electrode (40 wt.% composite), enabling the realization of practical commercial LIBs.

Overlooked challenges of interfacial chemistry upon developing high energy density silicon anodes for lithium-ion batteries

Evaluation of silicon (Si) anode performance by the assembled Si||Li half-cells is the primary approach in the development of high-energy-density lithium-ion batteries (LIBs). However, most studies focus solely on the variations of Si anode, the stability of electrolyte on the lithium (Li)-metal counter electrode has been overlooked. Herein, we discovered that the acquired cell performance not only depends on the Li+ (de-)solvation behaviors on the Si anode surface but also was affected significantly by the lithiation overpotential caused by the side reactions on the Li electrode. It is significant to identify this point, as these influences of electrolyte decomposition on the Li electrode have been previously regarded as an integral part of side reactions on the Si anode. We proposed a new perspective of the electrolyte solvation structure and electrode interfacial model to unravel the interfacial behaviors on the Si and Li electrodes respectively. The identified differences in the Li+ solvation and (de-)solvation behaviors not only provide reasons for the varied electrolyte stability in different electrolytes but also interpret the superior performance in tetrahydrofuran (THF)-based electrolytes. This study underscores the importance of understanding electrolyte behavior at the interfaces of individual electrodes to discern the reliability of electrode performance and also introduce a novel principle for designing superior electrolytes for high-energy-density LIBs.

The Synergistic Effect of Cross-Linked and Electrostatic Self-Assembly Si/MXene Composites Anode for Highly Efficient Lithium-Ion Battery

Silicon is a promising anode material for high-performance lithium-ion batteries (LIBs), but its rapid capacity degradation has significantly hindered its large-scale application. In this study, we propose an in situ self-assembly polymerization method to fabricate a stable silicon-based anode by leveraging electrostatic self-assembly technology, in situ esterification, and amidation reactions. The incorporation of a cross-linked polymer, combined with the synergistic effects of electrostatic interactions between negatively charged MXene and positively charged silane-coupling-agent-modified silicon, offers a novel strategy for enhancing the electrochemical performance of LIBs. Notably, annealed electrodes with a 65 wt% nmSi-NH2/MXene ratio demonstrate outstanding electrochemical performance, achieving a capacity of 929.5 mAh g⁻¹ at a current density of 1 A g⁻¹ after 100 charge/discharge cycles. These findings suggest that the integration of cross-linked polymers and electrostatic self-assembly can significantly improve the intercalation and overall electrochemical performance of silicon anodes in lithium-ion batteries.

Three-dimensional CNTs boosting the conductive confinement structure of silicon/carbon anodes in lithium-ion batteries

In this study, a surface functionalization strategy was proposed to involve carbon nanotubes and silicon nanoparticles encapsulated within carbon derived from a zeolite imidazole framework (ZIF-67). Multidimensional interconnected carbon nanotubes bolster the structural stability and facilitate ion/electron transfer within silicon/carbon composites. Silicon nanoparticles were successfully encapsulated in ZIF-67-derived carbon shells, with carbon nanotubes effectively transferring interfacial stress between silicon and carbon shell during lithiation, where ZIF-67-derived carbon reduces the volume expansion in silicon anodes. As a consequence, the outstanding cycle life and rate performance were demonstrated in the silicon/carbon composites. The specific capacity was maintained at 660 mAh g-1 over 200 cycles at 1 A g-1. The in-situ construction of this conductive confinement structure based on three-dimensional carbon nanotubes offers a promising design approach for advancing silicon/carbon anode technologies.

Ultra‐Durability and Reversible Capacity of Silicon Anodes with Crosslinked Poly‐BIAN Binder in Lithium‐Ion Secondary Batteries for Sturdy Performance

Ultra‐Durability and Reversible Capacity of Silicon Anodes with Crosslinked Poly‐BIAN Binder in Lithium‐Ion Secondary Batteries for Sturdy Performance

Design of Stable Hollow Particles for Silicon Anodes

Design of Stable Hollow Particles for Silicon Anodes

Constructing stress-release layer on Si nanoparticles for high-performance lithium storage

Tailing structures of silicon anode to alleviate the mechanical stress has an important significance in the development of lithium-ion batteries (LIBs). Herein, the stress-released layer of N-doped cubic carbon on the surface of Si nanoparticles (Si@NCC) is explored to stabilize the electrode. Endowed with the unique superiority, the Si@NCC electrode delivers an impressive lithium storage performance with high specific capacity of 630 mAh/g at 0.1 A/g, excellent cycling stability (72.0 % capacity retention after 100 cycles at 0.1 A/g) and good rate capability (375 mAh/g at 2 A/g). It has been demonstrated that the N-doped cubic carbon shell with high conductivity can effectively limit the expansion and agglomeration of Si nanoparticles. Besides, the COMSOL simulations of the stress distributions in materials confirm that the N-doped cubic carbon layer could remarkably decrease the stress originated from the volume expansion of Si nanoparticles during the lithiation. Therefore, this work provides ideas for the mechanical effect of Si-based anodes for lithium storage and sheds lights on the designing advanced materials toward high-performance energy storage devices.

In situ multilevel covalent crosslinking binder with high ionic conductivity for high-performance Si anodes

Silicon (Si) anode has emerged as a promising material for high-energy-density lithium-ion batteries (LIBs), thanks to its high theoretical capacity. However, the commercial application of Si anodes is hindered by inadequate cycling performance and poor interfacial stability, stemming from unfavorable stress conditions. In this study, a multiple crosslinking binder with high ionic conductivity is proposed combining high mechanical strength and high adhesion to current collector and active Si particles by coupling poly(acrylic acid), polyvinyl alcohol, and polyethylene glycol. The designed polymer binder not only efficiently dissipates the inner stress with its multiple crosslinked networks, but also establishes a fast lithium-ion conduction pathway to facilitate the electrode reaction kinetic. The resultant Si anode using the designed binder exhibits significantly improved cycling stability and superior rate performance. This work presents a straightforward yet highly effective method to alleviate the detrimental stress incurred by high-capacity anodes in high-energy LIBs.

Impact of Binder Content and Type on the Electrochemical Performance of Silicon Anode Materials.

Binders are crucial for stabilizing the cycling performance of silicon (Si) materials by preventing Si particle pulverization during lithiation and delithiation. Poly(acrylic acid) (PAA) and carboxymethyl cellulose (CMC) are the two most studied binders for Si electrodes, with PAA being an elastic polymer and CMC a rigid polymer. Starting with the elastic PAA, in this work the impact of binder content on the cycling performance of Si electrodes is studied. It is found that regardless of Si particle size, there is an optimal binder content between 20 % and 25 % for the cycling stability of Si electrodes. On the other hand, the rigid CMC binder results in lower capacity and faster capacity fading for Si electrodes compared with the elastic PAA. AC-impedance analysis reveals that the lower capacity is due to higher grain boundary resistance (Rgb) in CMC-coated electrodes, leading to high charge-transfer resistance (Rct) and increased polarization. This high polarization triggers premature termination during the discharging process (i. e., the lithiation) of Li/Si cells, underutilizing the Si active material. Additionally, the rapid capacity fading of CMC-coated electrodes is attributed to the rigid binder's inferior ability to prevent Si particle pulverization.