Silicon-based Lithium-ion Batteries Research Articles

Understanding the Roles of Electrolyte Additives on the Surface Modification Mechanism of Silicon-Based Anodes in Lithium-Ion Batteries

Silicon is considered as a promising candidate of the anode material for the next generation lithium-ion batteries, due to its substantially higher gravimetric and volumetric capacity compared to conventionally used graphite. Electrolyte additives, fluoroethylene carbonate (FEC) and vinylene carbonate (VC) particularly, are usually applied for silicon-based lithium-ion batteries to tackle the problems such as poor capacity retention and low coulombic efficiency.1-3 In the present work, the decomposition mechanism of FEC as well as the surface modification of Si electrodes were investigated.4 It was observed that the FEC additive degrades at a higher reduction potential prior to the other carbonate solvents. A conformal solid electrolyte interphase (SEI), which consists of the decomposition products of FEC, is instantaneously formed on the silicon electrode as a result. This stable SEI layer sufficiently limits the emergence of cracks and suppresses the additional SEI formation from the decomposition of other electrolyte components. Both of these effects lead to a slower increase in polarization, thus a slower capacity fading, for the FEC containing cell. The differences in the SEI layer, formed with or without the presence of FEC, are schematically demonstrated in Fig 1. Besides, it was also observed that the LiPF6 decomposition can be influenced with the presence of FEC, and this was further studied with a combination of X-ray photoelectron spectroscopy (XPS) and solid-state nuclear magnetic resonance (NMR) techniques. We also demonstrated that by forming an effective SEI layer with the FEC and VC electrolyte additives, the silicon electrodes can be equally well functioning with a novel lithium 4,5-dicyano-2-(trifluoromethyl)imidazolide (LiTDI)-based electrolyte as with the state-of-art LiPF6-based electrolyte.5 Figure 1

One-step solid-state in-situ thermal polymerization of silicon-PEDOT nanocomposites for the application in lithium-ion battery anodes

Abstract The current study presents a one-step solid-state in-situ thermal polymerization approach to prepare silicon nanoparticles-polyethylenedioxythiophene (SiNPs-PEDOT) nanocomposites. The structure-related electrochemical performance of the in-situ polymerized 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT) with SiNPs has been studied for the first time in application to silicon-based lithium-ion battery anodes. Thermal polymerization applied to a solution containing DBEDOT in acetonitrile with suspended silicon nanoparticles resulted in an in-situ formed SiNPs-PEDOT nanocomposite. The structure, morphology, and the corresponding electrochemical performance of the in-situ SiNPs-PEDOT nanocomposites was studied in comparison to a pure PEDOT as well as to the ex-situ polymerized SiNPs-PEDOT nanocomposites using XRD, FTIR, TGA, SEM, TEM, cyclic voltammetry, impedance spectroscopy, and constant current charge-discharge cycles. The XRD, FTIR, and TGA analysis reveal that the in-situ polymerization of monomer is not impeded by the presence of the silicon nanoparticles. The SEMand TEM studies reveal a uniform dispersion of SiNPs within in-situ polymerized PEDOT matrix compared to ex-situ formed SiNPs-PEDOT nanocomposite. In the lithium-ion battery anode, the in-situ polymerized SiNPs-PEDOT nanocomposite demonstrates the enhanced lithiation-delithiation kinetics, conductivity, and rate capability in comparison to the ex-situ SiNPs-PEDOT nanocomposite.

Phase Field Modeling of Lithium-Ion Diffusion and Crack Formation in the Solid Electrolyte Interphase of Silicon-Based Lithium-Ion Battery

Lithium-ion batteries (LIBs) play a key role in portable equipment, electric vehicles, and other energy storage modules. Solid electrolyte interface (SEI) layer cause a significant degradation for lithium-ion batteries’ electrochemical performance. Recently, silicon or Si-based anodes becomes an attractive candidate for the electrode of LIBs due to the low cost and high theoretical specific capacity. However, the mechanism of lithium-ion transport through the SEI layer is not fully understood as well as the crack formation of SEI layer due to silicon severe volume change. A phase field model is employed and developed to simulate the SEI structure and lithium-ion diffusion inside SEI layer including the thermodynamic chemical potential and elastic energy. SEI layer is believed to have multilayered structure; And SEI formation can be regarded as a solidification process. The phase field model is a powerful tool to investigate solidification problems without explicitly tracking the interfaces between the SEI species and electrolyte solution. Two sets of phase field variables are used to describe the microstructure of SEI layer and Lithium-ion transport in SEI layer. One is associated with the volume fraction of the interface. And the other is associated with the concentrations of SEI species. Lithium-ion transport will cause the elastic energy change. Therefore, elastic field needs to be considered in the developed model. And the elastic energy can be applied to investigate the crack initiation and propagation. Most importantly, the present developed model has great potential to be extended to three dimensional spaces for SEI layer spatial growth investigation.

Tailoring the Desired Surface Chemistry in Silicon-Based Lithium-Ion Batteries with Electrolyte Additives

The design of safe, high-energy batteries exhibiting prolonged lifetime greatly depends on understanding the surface reactions occurring on the electrode surfaces and the role of the solid electrolyte interphase (SEI) film. Most of the naturally forming SEI films demonstrate undesirable characteristics, such as instability and continuous surface reaction that decrease the capacity of Si-based Li-ion batteries (LIBs). An effective and economic way to modify the surface chemistry in LIBs rather than the Si architecture is by electrolyte additives. The objective of the present study is the examination of the concentration dependence of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) additives on the long-term electrochemical performance of LIBs, as well as the dependence of the SEI formation mechanism on the concentration of the VC and FEC additives. A significant improvement in the cycling performance of Si electrodes can be achieved under operation conditions of optimum VC and FEC concentration. To better understand the additive concentration effect, the reduction mechanisms of VC and FEC were investigated for both Si nanoparticle and Si(100) single crystal working electrodes. Ex-situ ATR-FTIR spectra of Si electrodes for 5% VC additive show a broad peak at a higher wavenumber (1831 cm–1) compared to the EC residual electrolyte (1799 and 1769 cm–1) (Fig. 1). Based on synthesized poly-VC standard spectra, the VC additive reduction compound is assigned to poly-VC or its oligomer, which is consistent with previous reports. However, for Si electrode and FEC additive, the original C=O stretch (1829 and 1802 cm–1) disappears or shifts to a lower wavenumber. The exact reduction product of FEC degradation has not been confirmed yet due to the lack of significant features other than the residual electrolyte. However, it is clear that FEC follows a different reduction path than VC. The reduction path of VC is polymerization with the reduction product remaining a “ring” structure (the C=O peak shifts to a higher wavenumber), whereas the reduction path of FEC is similar to that of ethylene carbonate (EC), leading to a reduction product of open “ring” structure, similar to that produced from EC reduction. More experiments are underway to confirm the different reduction paths of VC and FEC stated above. Acknowledgement This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Freedom CAR and Vehicle Technologies of the U.S. Department of Energy under contract No. DE-AC02-OSCH11231. Figure 1

Understanding the Effect of Different Polymeric Surfactants on Enhancing the Silicon/Reduced Graphene Oxide Anode Performance

Silicon-based lithium-ion battery anodes have brought encouraging results to the current state-of-the-art battery technologies due to their high theoretical capacity, but their large-scale application has been hampered by a large volume change (>300%) of silicon upon lithium insertion and extraction, which leads to severe electrode pulverization and capacity degradation. Polymeric surfactants directing the combination of silicon nanoparticles and reduced graphene oxide have attracted great interest as promising choices for accommodating the huge volume variation of silicon. However, the influence of different polymeric surfactants on improving the electrochemical performance of silicon/reduced graphene oxide (Si/RGO) anodes remains unclear because of the different structural configurations of polymeric surfactants. Here, we systematically study the effect of different polymeric surfactants on enhancing the Si/RGO anode performance. Three of the most well-known polymeric surfactants, poly(sodium 4-styrenesulfonate) (PSS), poly(diallydimethylammonium chloride) (PDDA), and polyvinylpyrrolidone (PVP), were used to direct the combination of silicon nanoparticles and RGO through van der Waals interaction. The Si/RGO anodes made from these composites act as ideal models to investigate and compare how the van der Waals forces between polymeric surfactants and GO affect the final silicon anode performance from both experimental observations and theoretical simulations. We found that the capability of these three surfactants in enhancing long-term cycling stability and high-rate performance of the Si/RGO anodes decreased in the order of PVP > PDDA > PSS.

Novel design of silicon-based lithium-ion battery anode for highly stable cycling at elevated temperature

We demonstrate a facile method for synthesizing silicon particles with a double coating layer consisting of aluminum trifluoride and amorphous carbon to use as an anode material for high-performance lithium-ion batteries at elevated temperatures.

Heading towards novel superior silicon-based lithium-ion batteries: ultrasmall nanoclusters top-down dispersed over synthetic graphite flakes as binary hybrid anodes

Novel scalable ultranano-Si particlesviatop-down dispersion have been developed originally to achieve high performance Si-based anodes with economic benefits heading toward industrial feasibility.

Large-Scale Fabrication, 3D Tomography, and Lithium-Ion Battery Application of Porous Silicon

Recently, silicon-based lithium-ion battery anodes have shown encouraging results, as they can offer high capacities and long cyclic lifetimes. The applications of this technology are largely impeded by the complicated and expensive approaches in producing Si with desired nanostructures. We report a cost-efficient method to produce nanoporous Si particles from metallurgical Si through ball-milling and inexpensive stain-etching. The porosity of porous Si is derived from particle's three-dimensional reconstructions by scanning transmission electron microscopy (STEM) tomography, which shows the particles' highly porous structure when etched under proper conditions. Nanoporous Si anodes with a reversible capacity of 2900 mAh/g was attained at a charging rate of 400 mA/g, and a stable capacity above 1100 mAh/g was retained for extended 600 cycles tested at 2000 mA/g. The synthetic route is low-cost and scalable for mass production, promising Si as a potential anode material for the next-generation lithium-ion batteries with enhanced capacity and energy density.

One-dimensional/two-dimensional hybridization for self-supported binder-free silicon-based lithium ion battery anodes

A unique silicon-based anode for lithium ion batteries is developed via the facile hybridization of one-dimensional silicon nanowires and two-dimensional graphene sheets. The resulting paper-like film holds advantages highly desirable for not only accommodating the volume change of silicon, but also facilitating the fast transport of electron and lithium ions.

Three-Dimensional Metal Scaffold Supported Bicontinuous Silicon Battery Anodes

Silicon-based lithium ion battery anodes are attracting significant attention because of silicon's exceptionally high lithium capacity. However, silicon's large volume change during cycling generally leads to anode pulverization unless the silicon is dispersed throughout a matrix in nanoparticulate form. Because pulverization results in a loss of electric connectivity, the reversible capacity of most silicon anodes dramatically decays within a few cycles. Here we report a three-dimensional (3D) bicontinuous silicon anode formed by depositing a layer of silicon on the surface of a colloidal crystal templated porous nickel metal scaffold, which maintains electrical connectivity during cycling due to the scaffold. The porous metal framework serves to both impart electrical conductivity to the anode and accommodate the large volume change of silicon upon lithiation and delithiation. The initial capacity of the bicontinuous silicon anode is 3568 (silicon basis) and 1450 mAh g(-1) (including the metal framework) at 0.05C. After 100 cycles at 0.3C, 85% of the capacity remains. Compared to a foil-supported silicon film, the 3D bicontinuous silicon anode exhibits significantly improved mechanical stability and cycleability.

Comparing One- and Two-Dimensional Heteronanostructures As Silicon-Based Lithium Ion Battery Anode Materials

The performance of advanced energy conversion and storage devices, such as solar cells, supercapacitors, and lithium (Li) ion batteries, is intimately connected to the electrode design at the nanoscale. To enable significant developments in these research fields, we need detailed information about how the properties of the electrode materials depend on their dimensions and morphologies. This information is currently unavailable, as previous studies have mostly focused on understanding one type of morphology at a time. Here, we report a systematic study to compare the performance of nanostructures enabled by two platforms, one-dimensional nanowires and two-dimensional nanonets. The nanowires and nanonets shared the same composition (titanium disilicide) and similar sizes. Within the framework of Li ion battery applications, they exhibited different stabilities upon lithiation and delithiation (at a rate of 6 A/g), the nanonets-based nanostructures maintaining 90% and the nanowires-based ones 80% of their initial stable capacities after 100 cycles of repeated charge and discharge. The superior stability of the nanonets was ascribed to the two-dimensional connectivity, which afforded better structural stability than nanowires. Information generated by this study should contribute to the design of electrode materials and thereby enable broader applications of complex nanostructures for energy conversion and storage.