Silicon-based Composite Anodes Research Articles

Mitigating the volume expansion and enhancing the cycling stability of ferrous fluorosilicate-modified silicon-based composite anodes for lithium-ion batteries

This study introduces an FeSiF6 additive synthesized via the reaction of HF with Si–Fe alloys. It prevents crystalline Li15Si4 formation and promotes stable SEI film, significantly enhancing the cycling stability of silicon-based anodes.

Interphase Regulation by Multifunctional Additive Empowering High Energy Lithium-Ion Batteries with Enhanced Cycle Life and Thermal Safety.

High energy density lithium-ion batteries (LIBs) adopting high-nickel layered oxide cathodes and silicon-based composite anodes always suffer from unsatisfied cycle life and poor safety performance, especially at elevated temperatures. Electrode /electrolyte interphase regulation by functional additives is one of the most economic and efficacious strategies to overcome this shortcoming. Herein, cyano-groups (-CN) are introduced into lithium fluorinated phosphate to synthesize a novel multifunctional additive of lithium tetrafluoro (1,2-dihydroxyethane-1,1,2,2-tetracarbonitrile) phosphate (LiTFTCP), which endows high nickel LiNi0.8 Co0.1 Mn0.1 O2 /SiOx -graphite composite full cell with an ultrahigh cycle life and superior safety characteristics, by adding only 0.5 wt % LiTFTCP into a LiPF6 -carbonate baseline electrolyte. It is revealed that LiTFTCP additive effectively suppresses the HF generation and facilitates the formation of a robust and heat-resistant cyano-enriched CEI layer as well as a stable LiF-enriched SEI layer. The favorable SEI/CEI layers greatly lessen the electrode degradation, electrolyte consumption, thermal-induced gassing and total heat-releasing. This work illuminates the importance of additive molecular engineering and interphase regulation in simultaneously promoting the cycling and thermal safety of LIBs with high-nickel NCMxyz cathode and silicon-based composite anode.

Control of Nanoparticle Dispersion, SEI Composition, and Electrode Morphology Enable Long Cycle Life in High Silicon Content, Nanoparticle-Based Composite Anodes for Lithium-Ion Batteries

Striking a balance between high theoretical capacity, Earth abundance, and compatibility with existing manufacturing infrastructure, silicon is one of the few materials that meets the requirements for a next-generation anode for rechargeable lithium-ion batteries. Due to complications with extreme volume changes during charging/discharging and reactive interfacial chemistries, however, the cycle-life of silicon-based composite anodes is unacceptable for broad use. Developing a majority silicon composite anode formulation that overcomes these challenges and is compatible with current industry manufacturing practices requires materials and chemical engineering solutions that account for both electrode morphology and interfacial chemistry. Here, we synthesize surface-functionalized silicon nanocrystals that enable a highly dispersed and homogeneous slurry that can easily be integrated into standard electrode fabrication process. We use this formulation to print a 76 wt. % silicon composite electrode. We show that the contents and the morphology of the silicon electrolyte interphase – a determining factor in the cycle life of silicon-based anodes – can be controlled with a post-synthetic thermal curing procedure. When paired against a capacity-matched lithium nickel manganese cobalt oxide LiNi0.8Mn0.1Co0.1O2 cathode, the cell retains 72% of its capacity through 1000 charge/discharge cycles while delivering an initial anode specific capacity of nearly 1000 mAh/g and an areal capacity of 2.55 mAh/cm2. Figure 1

Robust Core–Shell Carbon-Coated Silicon-Based Composite Anode with Electrically Interconnected Spherical Framework for Lithium-Ion Battery

Carbon-coated Si/carbon nanotube/graphene oxide (C-Si/CNT/GO) microspheres with a robust core–shell composite structure were successfully fabricated by efficient and scalable spray-drying and chemical vapor deposition (CVD) for application as a lithium-ion battery (LIB) anode. The amphiphilic GO nanoparticles facilitated the uniform dispersion of Si nanoparticles by suppressing the CNT aggregation in the Si/CNT/GO microspheres, efficiently forming a robust Si/CNT/GO microsphere composite structure. The surface of the Si/CNT/GO microsphere composite was coated with carbon using CH4 via CVD to enhance its cycling performance. The four building block components, namely, Si nanoparticles, CNTs, and GO nanoparticles as the core and the carbon-coating layers as the shell, provided high electrochemical capacity, excellent electrical conductivity, efficient buffer space for the volume expansion of the Si nanoparticles, and high structural stability during lithiation/delithiation. The C-Si/CNT/GO composite anode also exhibited excellent electrochemical performance with high specific capacity (2921 mAh g–1 at 100 mA g–1), long cycle life (1542 mAh g–1 at 200 mA g–1 after 100 cycles), and high charge/discharge rate (1506 mAh g–1 at 6 A g–1). This approach for fabricating core–shell structured Si-based composite anodes with excellent electrochemical performance will provide a significant breakthrough for developing next-generation LIBs.

Mechanical Failure Mechanism of Silicon-Based Composite Anodes under Overdischarging Conditions Based on Finite Element Analysis.

Overdischarge is a severe safety issue that can induce severe mechanical failure of electrode materials in lithium-ion batteries. A considerable volume change of silicon-based composite anodes undoubtedly further aggravates the mechanical failure. However, the mechanical failure mechanism of silicon-based composite anodes under overdischarging conditions still lacks in-depth understanding despite many efforts paid under normal charging conditions. Herein, we have modeled and tracked the mechanical failure evolution of silicon/carbon nanofibers, a typical silicon-based anode, under overdischarging conditions based on the finite element simulation, with derived optimization strategies of optimal Young's modulus and stable microstructure. The severe contact damage between silicon nanoparticles and carbon nanofibers, which causes larger shedding and breakage risks, has been found to contribute to mechanical failure. To improve the electrode stability, an optimal Young's modulus interval ranging from ∼75 to ∼150 GPa is found. Furthermore, increasing the embedding depth of silicon nanoparticles in carbon nanofibers has proven to be an effective strategy for improving electrochemical stability due to the faster lithium salt diffusion and more uniform current density distribution, which was further verified by the experimental capacity retention ratio of carbon-coated silicon and silicon/carbon nanofibers (84 vs 75% after 100 cycles). Our results provide meaningful insights into the mechanical failure of silicon-based composite anodes during overdischarging, giving reasonable guidance for electrode safety designs and performance optimization.

Thickness evolution of commercial Li-ion pouch cells with silicon-based composite anodes and NCA cathodes

It is significant to monitor the thickness change of commercial Li-ion pouch cells that are assembled from Si-based electrodes and layered cathodes since the volume variation is critically linked with kinetic reaction mechanism and chemomechanical degradation. In this work, the single-point and full-field measurements are conducted on the thickness evolution of SiOx/C-graphite/lithium nickel-cobalt-aluminum oxide (SiOx-G/NCA) batteries. It is found that an abnormal overshoot that has been rarely observed in the previous studies appears at the beginning of discharge, which is believed to be the combined results between the rapid expansion of NCA and the contraction of graphite related to the state of charge (SOC). Compared with the results of single-point measurement, the spatial displacement distribution obtained from three-dimensional (3D) scanning suggests the full-field thickness evolution of the entire cell scale, which is more feasible and efficient to provide full-field information for supporting pouch cell design and pack integration.

Mechanical and Electrochemical Stability Improvement of SiC-Reinforced Silicon-Based Composite Anode for Li-Ion Batteries

Extreme volume changes and concomitant mechanical instabilities (viz., origin and proliferation of cracking) in Si-based anodes are responsible for premature failure in lithium-ion batteries. Thus,...

Three-Dimensional Resistivity Quantification and Visualization of Silicon-Based Composite Anode Nanostructure Via Scanning Probe Microscopy

Nanocomposite Si-graphite electrodes are a viable option for increasing the energy density and life of lithium-ion battery anodes. In comparison to model systems (e.g., Si wafer and Si thin film), Si nanoparticles, ranging in diameter from tens to hundreds of nanometers, have higher rate capacity and improved fracture toughness.1, 2 However, characterization efforts to better understand localized degradation mechanisms and heterogeneous aging behaviors of distinct components—Si, graphite, binder, and conductive carbon—in Si-based nanocomposite anodes through cycling are hindered by the limited information that can be achieved at the nanoscale using traditional microscopy techniques.To date, high resolution, three-dimensional structural visualization of the Si-based composite electrode has relied upon techniques like X-ray nano-computed tomography3, 4, that provide morphological information but not electronic or chemical information. In this work, we report a novel lab-scale scanning probe microscopy-based approach to map the 3-D nanostructure of composite anodes via contrast in their components’ intrinsic electronic properties. By incorporating experimental nanoscale electronic resistivity data through interpolation, volumes can be extracted to represent distinct constituent phases of the composite electrode. This approach presents an opportunity for relatively high throughput, nanoscale characterization of composite anodes and cathodes to investigate phenomena such as particle dispersion in electrode preparation and electrode evolution through cycling. Ultimately, this technique shows future utility for the multiscale understanding of structural evolution and degradation processes within lithium-ion batteries.Figure 1: Interpolated resistivity layers captured within a Si-Carbon(C) composite electrode, processed to extract C-rich and Si-rich volumes. R. C. de Guzman, J. Yang, M. M.-C. Cheng, S. O. Salley, and K. Y. Simon Ng, Journal of Materials Science, 48 (14), 4823-4833 (2013).S.-L. Chou, J.-Z. Wang, M. Choucair, H.-K. Liu, J. A. Stride, and S.-X. Dou, Electrochemistry Communications, 12 (2), 303-306 (2010).O. O. Taiwo, M. Loveridge, S. D. Beattie, D. P. Finegan, R. Bhagat, D. J. L. Brett, and P. R. Shearing, Electrochimica Acta, 253 85-92 (2017).J. Wu, F. Ma, X. Liu, X. Fan, L. Shen, Z. Wu, X. Ding, X. Han, Y. Deng, W. Hu, and C. Zhong, Small Methods, 3 (10), (2019). Figure 1

SiO2 Is Wasted Space in Single-Nanometer-Scale Silicon Nanoparticle-Based Composite Anodes for Li-Ion Electrochemical Energy Storage

The electrode processing conditions of silicon-based composite anodes play a pivotal role in the resulting interfacial chemical speciation and, thus, the electrochemical cycling behavior of the electrode. Systematically investigating how small chemical changes to the surface of the silicon nanoparticle (NP) affect larger, electrode-level properties is a strategy that will inform design principles to maximize electrode energy density and extend electrode lifetime. Here, we incorporate silicon nanoparticles (NPs) with an average diameter of 5.5 nm synthesized from the gas phase through a nonthermal plasma method into composite anode half-cell coin cells. We perform chemistry to functionalize the native hydride-terminated silicon NP surface with N-methylpyrrolidone (NMP) to improve slurry properties and reduce the silicon reactivity prior to composite electrode fabrication. We construct composite electrodes from these silicon NPs and observe an 86% capacity retention over 100 cycles at a rate of C/5, with an initial silicon specific capacity of 2600 mAh/g. We expose the same Si NPs to water that completely oxidizes these small-diameter NPs to SiO2 and find that the SiO2 NPs in the same electrode configuration exhibit no obvious lithium alloying capacity in the electrochemical potential range of lithium silicide alloy formation. As this result stands in contrast to existing literature, we provide a discussion on the origin of the discrepancies.

Three-Dimensional Mapping of Resistivity and Microstructure of Composite Electrodes for Lithium-Ion Batteries.

Nanoparticle silicon-graphite composite electrodes are a viable way to advance the cycle life and energy density of lithium-ion batteries. However, characterization of composite electrode architectures is complicated by the heterogeneous mixture of electrode components and nanoscale diameter of particles, which falls beneath the lateral and depth resolution of most laboratory-based instruments. In this work, we report an original laboratory-based scanning probe microscopy approach to investigate composite electrode microstructures with nanometer-scale resolution via contrast in the electronic properties of electrode components. Applying this technique to silicon-based composite anodes demonstrates that graphite, SiOx nanoparticles, carbon black, and LiPAA binder are all readily distinguished by their intrinsic electronic properties, with measured electronic resistivity closely matching their known material properties. Resolution is demonstrated by identification of individual nanoparticles as small as ∼20 nm. This technique presents future utility in multiscale characterization to better understand particle dispersion, localized lithiation, and degradation processes in composite electrodes for lithium-ion batteries.

Multi-scale quantification and modeling of aged nanostructured silicon-based composite anodes

Advanced anode material designs utilizing dual phase alloy systems like Si/FeSi2 nano-composites show great potential to decrease the capacity degrading and improve the cycling capability for Lithium (Li)-ion batteries. Here, we present a multi-scale characterization approach to understand the (de-)lithiation and irreversible volumetric changes of the amorphous silicon (a-Si)/crystalline iron-silicide (c-FeSi2) nanoscale phase and its evolution due to cycling, as well as their impact on the proximate pore network. Scattering and 2D/3D imaging techniques are applied to probe the anode structural ageing from nm to μm length scales, after up to 300 charge-discharge cycles, and combined with modeling using the collected image data as an input. We obtain a quantified insight into the inhomogeneous lithiation of the active material induced by the morphology changes due to cycling. The electrochemical performance of Li-ion batteries does not only depend on the active material used, but also on the architecture of its proximity.

Stress Bearing Mechanism of Reduced Graphene Oxide in Silicon-Based Composite Anodes for Lithium Ion Batteries.

Despite the significant research that has been carried out to improve cycling performance of lithium ion batteries (LIB) with silicon (Si) based composite electrodes, limited studies have been performed on these materials to evaluate the effects of internal microstructural changes and stress evolution on the electrochemical performance. Here, combined ex situ and in situ investigations on the accommodation of volume expansion in Si-based nanocomposite electrodes are reported. This work emphasizes the importance of conductive agents in light of the poor electronic conductivity of Si. A detailed comparison between commonly used carbon black (CB) and reduced graphene oxide (rGO) shows that these materials have substantial effects on microstructural evolution and internal stress in Si based composite electrodes that are employed in lithium ion cells. This study provides the first monitoring of stress evolution in Si-rGO based composite electrode during electrochemical cycling using in situ wafer curvature measurements. The prepared Si-rGO based electrode exhibits almost 10 times lower stress generation and consequently higher cycling performance in electrochemical cells. The resulting 3D networked structure not only acts as an electronic conduit to the encapsulated active materials but also serves as a mini-electrochemical reaction chamber which hinders the formation of the solid electrolyte interphase (SEI) and limits the pulverization of active material and the evolution of severe stress during cycling. Moreover, investigations of the microstructural changes and internal charge transfer resistance in the electrodes after cycling provide further evidence that rGO produces superior structures for energy storage.

Designing of hierarchical mesoporous/macroporous silicon-based composite anode material for low-cost high-performance lithium-ion batteries

A mass-produced and low-cost hierarchical mesoporous/macroporous silicon-based composite material with an ample porous structure and dual carbon protective layers has been rationally designed and constructed. The Si/SiO2@C composite anode materials for LIBs show enhanced electrochemical properties.

Strategies for Overcoming Irreversible Lithium-Ion Losses in Silicon-Based Anodes

Silicon-based anodes are a promising replacement for carbon-based anodes for lithium-ion batteries due to their high specific capacity (3759 mAh/g). However, capacity fading due to irreversible Li+ losses prevent successful pairing up with commercially available cathode materials for a full-cell batteries. It is thought that the continuous reformation of the solid electrolyte interphase and parasitic reactions consume lithium-ions stored in cathode. Here, we will present two different pre-conditioning methods and various cycling strategies (full-potential and constant charge capacity at 1000 mAh/g) with high-surface area porous silicon-based composite anodes with lithium iron phosphate cathodes. Our experiments will demonstrate new methods and strategies for overcoming irreversible losses in silicon-based anode materials.

Effects of the Formulations of Silicon-Based Composite Anodes on their Mechanical, Storage, and Electrochemical Properties.

In this work, the effects of the formulation of silicon-based composite anodes on their mechanical, storage, and electrochemical properties were investigated. The electrode formulation was changed through the use of hydrogenated or modified (through the covalent attachment of a binding additive such as polyacrylic acid) silicon and acetylene black or graphene sheets as conducting additives. A composite anode with a covalently grafted binder had the highest elongation without breakages and strong adhesion to the current collector. These mechanical properties depend significantly on the conductive carbon additive used and the use of graphene sheets instead of acetylene black can improve elongation and adhesion significantly. After 180 days of storage under ambient conditions, the electronic conductivity and discharge capacity of the modified silicon electrode showed much smaller decreases in these properties than those of the hydrogenated silicon composite electrode, indicating that the modification can result in passivation and a constant composition of the active material. Moreover, the composite Si anode has a high packing density. Consequently, thin-film electrodes with very high material loadings can be prepared without decreased electrochemical performance.

Cycling Performance and Interfacial Phenomena of High-Energy Li-Ion Battery with Sulfur-Based Cathode and Silicon-Based Anode

Li-ion battery market is currently expanding from small, portable batteries to electric vehicles and energy storage systems. To meet the demands, more than doubled energy density than that of currently used batteries is required. The energy density of current batteries, which consist of lithium metal oxide cathode and graphite anode materials, is however limited. A general approach to increase the energy density of a battery is the replacement of current cathode and anode active materials to higher capacity materials, and electrolyte that is interfacially compatible to them. Recently, sulfur-based cathode and silicon-based anode materials are considered as one of the most promising active materials for high-energy batteries. Earlier reports on sulfur-based cathode and silicon composite anode in half-cells showed a good cycling performance.1,2 However, there are just a few reports on the full-cell with those materials.3,4 To date, the best performance of full-cell was obtained when being assembled with carbon composite of elemental sulfur cathode, lithiated nanosphere Si/SiOx anode and a polysulfide-containing electrolyte, showing the capacity of 750 mAhg-1 and capacity retention of 85 % at the 500th cycle.3 However, the combination of sulfur-based cathode and silicon-based composite anode in a full-cell face several common issues such as the lack of Li+ source of sulfur cathode, solvent intercalation into graphite anode, and possible interfacial reaction between anode and soluble polysulfide formed during cycling. To overcome those issues, researchers have used Li2S instead of sulfur, fabricated anode with functional binder to prevent solvent intercalation, and modified electrolyte with polysulfide additive.3-5 However, interfacial reaction behavior in full-cells is unknown. In this study, we demonstrate good cycling performance of a full-cell composed of a new micron-sized sulfur-based cathode material and submicron-sized lithiated silicon-based anode material. Correlation between the cycling performance and interfacial phenomena would be discussed in the meeting. Acknowledgements This work was supported under the framework of international cooperation program managed by National Research Foundation of Korea (2015K2A5A3000068) and German Academic Exchange Service (57141898), and by the Ministry of Trade, Industry & Energy (10049609) of Korea, and Nano-Material Technology Development Program by the Ministry of Science, ICT and Future Planning (2009-0082580) of Korea.

Electrochemical Performance of Graphite-Silicon Alloy Composite Anodes Using Cross-Linked Poly(vinyl alcohol) Binder for Lithium-Ion Batteries

The growing demand for rechargeable batteries requires a great improvement in the energy density of current lithium-ion batteries. In order to increase the energy density of lithium-ion batteries, silicon anode materials have been actively studied, because they exhibit a high theoretical capacity, a low reduction potential, are environmentally benign and are low cost.1 However, they suffer from substantial volume changes during cycling, which are highly detrimental to the cycling stability of lithium-ion batteries. The mechanical stresses caused by repeated volume changes can fracture the electrode, which results in poor electrical contacts between the active materials, electronic conductors and current collector. To solve these problems, many studies have been carried out by different approaches such as controlling the particle size and morphology, alloying with inert metals, embedding silicon in a conductive material, and applying several functional binders. In order to obtain the silicon-based composite anodes with high capacity and good cycling stability, we synthesized silicon alloy that was composed of silicon nanoparticles embedded in Al-Fe-Ti-Ni matrix phases. Using these silicon alloy material, we prepared the composite electrodes composed of graphite powder and silicon alloy particles. In these composite anodes, poly(vinyl alcohol) (PVA)s with different degree of cross-linking were employed as polymer binders. The effect of degree of cross-linking on interfacial adhesion and cycling performance of the composite electrodes was investigated to identify optimum processing condition. A systematic study demonstrated that the appropriate cross-linking of PVA made the electrodes mechanically strong and remarkably improved the cycling stability of the electrodes.

Nanostructured Si-Based Anodes for Lithium-Ion Batteries

High capacity electrode materials are searched for commercial applications due to the increase in energy density and power density requirements for lithium-ion secondary cells. Silicon has triggered significant research effort because of its low Li-uptake potential and the high theoretical capacity. However, volume changes during cycling cause pulverization and capacity fade, which is an obstacle of the application of silicon as an anode. Here we present a review of research progress on silicon-based anode materials for lithium-ion batteries, focusing on the effects of the morphology and compound on the electrochemical properties. The reasons of poor cycle performance are discussed. It is pointed out that to control the huge volume change and solid electrolyte interface growth during cycling is an effective way to improve the cycle performance. Outlook for the future development of silicon-based composite anode materials for the application of silicon anodes are finally outlined.

A facile, low-cost synthesis of high-performance silicon-based composite anodes with high tap density for lithium-ion batteries

Micro-sized carbon-coated Si-based composite synthesized by a low-cost and scalable synthetic process exhibits enhanced electrochemical performance with a high tap density of ∼1.34 g cm−3.

Binder-Free Silicon-Based Composite Anodes in Ionic Liquid Electrolytes for Li-Ion Battery

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