Stable Li-ion Battery Anodes Research Articles

Towards a Higher Energy Density for Lithium-Ion Battery Anodes Via Hierarchically Structured Silicon/Carbon Supraparticles Using Spray Drying

Silicon has a high potential to replace commercial graphite anodes in lithium-ion batteries (LiBs). It can facilitate achieving excellent energy densities because of its high theoretical specific lithiation capacity (Chan et al. 2008). However, major challenges such as rapid capacity fading and low Coulombic efficiency due to the huge volume change (∼300 %) during cycling have seriously hindered its commercialization (Wu et al. 2013). Although nanostructuring has been successful in minimizing volume expansion issues, the electrochemical performance of nano-sized silicon is still limited due to unstable solid-electrolyte interphase, low coating density and overall poor electrical properties due to the higher interparticle resistance (Liu et al. 2014). To tackle those challenges, here we introduce a new concept of post-synthesis spray drying to produce hierarchically structured micro-agglomerates from silicon/carbon (Si/C) composite nanoaggregates synthesized in the gas phase (Amin et al. 2023; Adil Amin et al.).The resulting agglomerates were characterized i) on the powder level by scanning electron microscopy (Fig. 1a) and N2 sorption, ii) on the dispersion level by rheometry and analytical centrifugation, iii) on the electrode level by atomic force microscopy for structure and iv) via electrochemical testing on half-cells for electrochemical performance (Fig. 1b). These results show that electrodes from Si/C supraparticles with the highest concentration of stabilizer exhibit better redispersion stability and excellent first cycle specific discharge capacity as well as better cycling stability as compared to the Si/C composite nanoaggregates (4 wt.% carbon content). Furthermore, compared to the reference electrodes made of nanoaggregates, the more stable supraparticles (3 wt.% stabilizer) showed the highest first Coulombic efficiency. This is due to the reduction of their surface to volume ratio which helps in forming less volume of solid electrolyte interface.To conclude, our investigation suggests how an established industrial process (gas phase synthesis of nanoparticle in a hot-wall reactor) can be combined with scalable one-step spray drying to get dense active materials for LiBs. This enables to fully utilize the new materials’ potential by the right packaging into optimum electrode structures with high performance and longevity. Furthermore, we are of the opinion that this pioneering method can be utilized as a broadly relevant design principle to enhance other (anode) materials that encounter analogous problems of volume expansion. Publication bibliography Amin, Adil; Özcan, Fatih; Loewenich, Moritz; Kilian, Stefan O.; Wiggers, Hartmut; Segets, Doris; Wassmer, Theresa; Bade, Stefan; Lyubina, Julia: Hierarchically Structured Si/C Agglomerates by Spray-Drying. Patent no. PCT / EP 2022/ 052453.Amin, Adil; Loewenich, Moritz; Kilian, Stefan O.; Wassmer, Theresa; Bade, Stefan; Lyubina, Julia et al. (2023): One-Step Non-Reactive Spray Drying Approach to Produce Silicon/Carbon Composite-Based Hierarchically Structured Supraparticles for Lithium-Ion Battery Anodes. In J. Electrochem. Soc. 170 (2), p. 20523. DOI: 10.1149/1945-7111/acb66b.Chan, Candace K.; Peng, Hailin; Liu, Gao; McIlwrath, Kevin; Zhang, Xiao Feng; Huggins, Robert A.; Cui, Yi (2008): High-performance lithium battery anodes using silicon nanowires. In Nature nanotechnology 3 (1), pp. 31–35. DOI: 10.1038/nnano.2007.411.Liu, Nian; Lu, Zhenda; Zhao, Jie; McDowell, Matthew T.; Lee, Hyun-Wook; Zhao, Wenting; Cui, Yi (2014): A pomegranate-inspired nanoscale design for large-volume-change lithium battery anodes. In Nature nanotechnology 9 (3), pp. 187–192. DOI: 10.1038/nnano.2014.6.Wu, Hui; Yu, Guihua; Pan, Lijia; Liu, Nian; McDowell, Matthew T.; Bao, Zhenan; Cui, Yi (2013): Stable Li-ion battery anodes by in-situ polymerization of conducting hydrogel to conformally coat silicon nanoparticles. In Nature communications 4, p. 1943. DOI: 10.1038/ncomms2941. Figure 1

Large-scale synthesis of SiOC composites for stable Li-ion battery anode and dendrite-free Li metal deposition

SiOC is an ideal anode material for Li-ion batteries due to its high specific capacity and low volume fluctuation. However, the large-scale preparation of SiOC still faces challenges such as complex processes and expensive raw materials. Additionally, the excellent compatibility of SiOC with Li-ion implies its inherentpotential for guiding Li metal deposition, but SiOC has rarely been used to investigate the Li metal deposition and/or suppress lithium dendrite growth. In this work, nearly kilogram-scale preparation of SiOC composites was realized using a consecutive chemical vapor deposition method with an inexpensive silane coupling agent as the precursor at the laboratory level. As a result, the as-prepared SiOC as anode exhibits favorable rate performance, negligible volume fluctuations and ultra-long cycle stability (∼2000cycles). Furthermore, SiOC as substrates for guiding lithium metal deposition shows low nucleation overpotential (2.0 mV) and ultra-long cycle stability in half cell (650cycles at 1.0 mA cm−2), symmetrical cell (5000 h at 1.0 mA cm−2) and full cell (800cycles at 1.0C). Density functional theory (DFT) calculation and finite element simulations reveal that the presence of SiOC on the copper foil can not only enable a significant enhancement of Li adsorption but also promote uniform distribution of electric field and Li+ concentration gradient. Finally, SiOC can be used to fabricate an anode-free Li metal battery, further enhancing the energy density of batteries.

Intertwining porous silicon with conducting polymer for high-efficiency stable Li-ion battery anodes

Intertwining porous silicon with conducting polymer for high-efficiency stable Li-ion battery anodes

Insights Into the Degradation Mechanisms of Nanoporous Alloy-Type Lithium-Ion Battery Anodes: A Transmission Electron Microscopy and Small-Angle X-Ray Scattering Study

Alloy-type lithium-ion battery anodes undergo extremely large volume changes of up to ~300% when lithiated.1 The stresses which arise during volume expansion cause pulverization, which typically cuts off electronic pathways to the active material and leads to battery failure. Previous work has demonstrated that nanostructuring alloy-type anodes into nanoporous metals, which consist of bicontinuous networks of active material and pore space, can extend the lifetime of the anode significantly.1,2 Despite these advances, the fundamental mechanisms by which nanoporous alloy-type materials degrade are not well-understood. In this presentation, I will discuss how we elucidated the (de)lithiation behavior and structural degradation of nanoporous alloy-type anodes using both transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). In particular, we observed the evolution of morphological and microstructural features of nanoporous gold by galvanostatically (de)lithiating it to various states of charge, studying its real-space structure with TEM, and corroborating this with statistically representative reciprocal-space information from SAXS. During lithiation, nanoporous gold develops a thick solid electrolyte interphase region which contains trapped nanoparticles of pulverized active material. When delithiated, the volume contraction causes the SEI along with the trapped nanoparticles to break from the surface, resulting in active material loss and battery failure. In addition, we observed the development of a second porous length scale smaller pores on the nanoporous gold ligaments during delithiation, resulting in a hierarchical nanoporous structure. With this insight, we propose a new model for the degradation of nanostructured alloy-type anodes.3 Key Words: TEM, SAXS, Nanoporous Metals, Energy Storage, Alloy-typeReferences(1) Cho, J. Porous Si Anode Materials for Lithium Rechargeable Batteries. J. Mater. Chem. 2010. https://doi.org/10.1039/b923002e.(2) Cook, J. B.; Detsi, E.; Liu, Y.; Liang, Y.-L.; Kim, H.-S.; Petrissans, X.; Dunn, B.; Tolbert, S. H. Nanoporous Tin with a Granular Hierarchical Ligament Morphology as a Highly Stable Li-Ion Battery Anode. ACS Appl. Mater. Interfaces 2017, 9 (1), 293–303. https://doi.org/10.1021/acsami.6b09014.(3) Corsi, J. S.; Welborn, S. S.; Stach, E. A.; Detsi, E. Insights into the Degradation Mechanism of Nanoporous Alloy-Type Li-Ion Battery Anodes. ACS Energy Lett. 2021, 1749–1756. https://doi.org/10.1021/acsenergylett.1c00324. Figure 1

Controlled generation and tuning the oxygen defects in nanofibers of Ca2Fe2O5 toward high and stable Li-ion battery anode

In recent years, oxygen-defect (vacancies) and nanostructured-based materials have been fabricated and applied as electrode materials for lithium-ion batteries (LIBs). However, the individual role of oxygen defects and nanostructuring on the improvement of Li-storage performance is still not clear. In addition, the technique which generates the control amount of oxygen-defects as well as maintains the nanostructured morphology of the electrode materials is highly desirable. Hence, in this work, we have attempted to create the oxygen defects in Ca2Fe2O5 (C2FONF) nanofibers via electrospinning technique and subsequent heat-treatment on as-spun nanofibers such as 700 °C (C2FONF-700), 800 °C (C2FONF-800), and 900 °C (C2FONF-900). All the as-prepared samples are characterized by XRD, FE-SEM, BET, XPS, and I-V characteristics. From the quantification of oxygen defect, it is observed that C2FONF-900 sample consists of the highest number of oxygen defects. As an LIB anode, C2FONF-900 exhibits superior reversible capacity (530 (±10) mAh g−1 at 50 mAg−1 up to 100 cycles), cyclability (370 (±10) mAh g−1 at 1C: 500 mAg−1 up to 100 cycles). Further, the rate capability of C2FONF-900 is found better than the C2FONF-700 and C2FONF-800. Furthermore, the study of capacitive/diffusion-controlled process showed the higher contribution of capacitive capacity in the C2FONF-900 electrodes, which is responsible for their better rate capability. In this study, we have shown that the Li-storage properties of iron-based oxides can be easily improved by tuning their concentration of oxygen defects while maintaining similar fibric nanostructure.

Polymer-Derived SiOC Integrated with a Graphene Aerogel As a Highly Stable Li-Ion Battery Anode.

Amorphous polymer-derived silicon oxycarbide (SiOC) is an attractive candidate for Li-ion battery anodes, as an alternative to graphite, which is limited to a theoretical capacity of 372 mAh/g. However, SiOC tends to exhibit poor transport properties and cycling performance as a result of sparsely distributed carbon clusters and inefficient active sites. To overcome these limitations, we designed and fabricated a layered graphene/SiOC heterostructure by solvent-assisted infiltration of a polymeric precursor into a modified three-dimensional (3D) graphene aerogel skeleton. The use of a high-melting-point solvent facilitated the precursor's freeze drying, which following pyrolysis yielded SiOC as a layer supported on the surface of nitrogen-doped reduced graphene oxide aerogels. The fabrication method employed here modifies the composition and microstructure of the SiOC phase. Among the studied materials, the highest levels of performance were obtained for a sample of moderate SiOC content, in which the graphene network constituted 19.8 wt % of the system. In these materials, a stable reversible charge capacity of 751 mAh/g was achieved at low charge rates. At high charge rates of 1480 mA/g, the capacity retention was ∼95% (352 mAh/g) after 1000 consecutive cycles. At all rates, Coulombic efficiencies >99% were maintained following the first cycle. Performance across all indicators was majorly improved in the graphene aerogel/SiOC nanocomposites, compared with unsupported SiOC. The performance was attributed to mechanisms across multiple length scales. The presence of oxygen-rich SiO4-xCx tetrahedral units and a continuous free-carbon network within the SiOC provides sites for reversible lithiation, while high ionic and electronic transport is provided by the layered graphene/SiOC heterostructure.

NiO nanocrystals encapsulated into a nitrogen-doped porous carbon matrix as highly stable Li-ion battery anodes

Though the carbon matrix is extensively investigated to enhance the electrochemical performances of metal oxides for lithium-ion batteries (LIBs), it is still difficult to expose the whole active sites in the electrode material to participate in electrochemical reactions. Herein, we report a facile MOF-derived strategy for the controlled synthesis of a hybrid structure with NiO nanocrystals uniformly distributed into nitrogen-doped porous carbon matrix (NiO@N–C). In this strategy, the simultaneously generated nitrogen-doped porous carbon matrix can confine the further growth of the resulting NiO nanocrystals during the carbonization process, in which the ultrafine particle sizes of NiO can shorten ion diffusion length and provide abundant exposed active sites for lithium-storage, while the carbon matrix can function as a buffer layer to alleviate the volume expansion. Benefiting from the advantages of the structural features and porous carbon matrix, NiO@N–C delivers a large reversible capacity of 1373 mAh g−1 at 100 mA g−1 after 200 cycles and a remarkable cycling stability up to 1000 cycles at 1 A g−1 with a capacity of 877 mAh g−1, suggesting its potential as an anode material for lithium-ion batteries.

Supersonically sprayed Fe2O3/C/CNT composites for highly stable Li-ion battery anodes

A synthesized Fe2O3/C composite integrated with carbon nanotubes (CNTs) is deposited via cold spraying and used as a highly stable Li-ion battery anode. The X-ray diffraction pattern of the anode material confirms the coexistence of CNTs and mixed Fe2O3 phases (α and γ). Morphology and elemental mapping analyses are performed using scanning electron microscopy and transmission electron microscopy, respectively. The Fe2O3/C/CNT composite presents the high discharge capacity of 1598 mA·h·g−1 at the current density of 100 mA·g−1. The anode exhibits excellent capacity retention values of 83% and 88% after 100 and 1000 charge–discharge cycles under current densities of 100 and 1000 mA·g−1, respectively. The electrochemical performance of the synthesized Fe2O3/C/CNT composite is superior to that of the Fe2O3/CNT composite prepared by mixing commercially available Fe2O3 and CNTs. This is attributed to the shorter diffusion path of the Li-ions in the relatively smaller Fe2O3 particles and faster charge transfer through the highly conductive CNTs.

Hierarchically Porous Carbon Derived from Biomass Reed Flowers as Highly Stable Li-Ion Battery Anode.

As lithium-ion battery (LIB) anode materials, porous carbons with high specific surface area are highly required because they can well accommodate huge volume expansion/contraction during cycling. In this work, hierarchically porous carbon (HPC) with high specific surface area (~1714.83 m2 g−1) is synthesized from biomass reed flowers. The material presents good cycling stability as an LIB anode, delivering an excellent reversible capacity of 581.2 mAh g−1 after cycling for 100 cycles at a current density of 100 mA g−1, and still remains a reversible capacity of 298.5 mAh g−1 after cycling for 1000 cycles even at 1000 mA g−1. The good electrochemical performance can be ascribed to the high specific surface area of the HPC network, which provides rich and fast paths for electron and ion transfer and provides large contact area and mutual interactions between the electrolyte and active materials. The work proposes a new route for the preparation of low cost carbon-based anodes and may promote the development of other porous carbon materials derived from various biomass carbon sources.

MOF-derived hollow NiCo2O4 nanowires as stable Li-ion battery anodes.

Although binary metal oxides with high theoretical specific capacities and power densities are widely investigated as promising anode materials for lithium-ion batteries (LIBs), their poor cycling stability and huge volume expansion largely limit their extensive application in practical electrode materials. Herein, we report a facile strategy to synthesize hollow NiCo2O4 nanowires through direct calcination of binary metal-organic frameworks (MOFs) in air. When evaluated as an anode material for LIBs, NiCo2O4 nanowires deliver a reversible capacity of 1310 mA h g-1 at a current density of 100 mA g-1 after 100 cycles. Even at a high current density of 1 A g-1, NiCo2O4 nanowires exhibit long-term cycling stability with a capacity of 720 mA h g-1 after 1000 cycles. The outstanding lithium-storage performance can be attributed to the unique structures with 1D porous channels, which are beneficial for the fast transfer of Li+ ions and electrolyte and alleviate the strain caused by the volume expansion during cycling processes.

Synthesis of V-MoS2 Layered Alloys as Stable Li-Ion Battery Anodes

Layered MoS2 nanostructures are attractive candidates as high-capacity anodes for lithium-ion batteries (LIB). However, the low intrinsic electrical conductivity of MoS2 limits its rate performance...

(Invited) Using Nanoporous and Nanostructured Materials to Improve Fast Charging and High Capacity Battery Materials

In this talk, we examine ways that solution processed nanostructured materials can be used to address both fundamental and practical issues relevant to next generation electrochemical energy storage. Materials with appropriate porous architectures can be synthesized using a range of solution phase methods, including polymer templating, nanoparticle assembly, and selective dealloying of mixed metal precursors. We begin with nanoporous materials for application in fast charging energy storage systems referred to as pseudocapacitors. Here the goal is both to produce practical new fast charging material, as well as to define the nature of pseudocapacitance in nanostructured materials and to establishing design rules for synthesizing future generations of high rate capability materials. We find that in optimized nanoporous materials, the nanoscale structure and porosity can produce a very desirable combination of electrical connectivity, electrolyte access to the interior of the material, ample surface redox sites, and very short solid-state diffusion lengths for lithium ions, all of which facilitate fast charge and discharge. Perhaps more importantly, many nanoscale materials appear to show suppression of the intercalation induced phase transitions that can cause kinetic limitations in bulk materials. The result is a new family of fast charging nanostructured energy storage materials. In this talk, we will specifically explore anode materials based on nanoporous MoS2, MoO2, and Nb2O5, and nanoporous cathode materials based on LiMn2O4 (LMO) and LiVPO4F (LVPF). A combination of electrochemical kinetics and operando X-ray diffraction allows us to correlate nanometer scale architecture, the speed of charge and discharge, and the presence or absence of intercalation induced phase transitions to show that an optimize nanoporous structure is the key to producing new fast charging energy storage materials. Similar porous architectures can also be used to increase stability and cycle life in high capacity alloy-type anode materials that are being considered as replacements for graphite in traditional lithium ion batteries. Unfortunately, alloy-type anodes suffer from short lifetimes due to large volume changes during lithiation or sodiation. One solution is to use nanoscale porosity to help accommodate those large volume changes. Here we specifically focus on nanoporous Sn and nanoporous SbSn, both of which are synthesized by selective etching, and both of which can be alloyed with either lithium or sodium to produce very high capacity anodes. Using transmission X-ray microscopy (TXM), we are able to directly image changes in both individual grains, and in the pore structure itself upon cycling. We find that porous materials expand much less than bulk materials, because the pores help accommodate the strain. More importantly, we find that porous alloys like nanoporous SbSn are more stable than pure metals because the two components, which alloy at different potentials, help stabilize the pores system so that the alloy can expand into the pores with causing them to break or fracture. This results in significantly improved cycle stability. Taken together, these two families of materials emphasize the key role that can be played by nanoscale porosity in optimizing the properties of next generation energy storage materials. References K. Lesel, J.B. Cook, Y. Yan, T.C. Lin, S.H. Tolbert, “Using Nanoscale Domain Size to Control Charge Storage Kinetics in Pseudocapacitive Nanoporous LiMn2O4 Powders.” ACS Energy Lett. 2017, 2, 2293-2298.B. Cook, T.C. Lin, E. Detsi, J. Nelson Weker, S.H. Tolbert “Using X-ray Microscopy To Understand How Nanoporous Materials Can Be Used To Reduce The Large Volume Change In Alloy Anodes.” Nano Lett., 2017, 17, 870−877.B. Cook, E. Detsi, Y. Liu, Y.-L. Liang, H.-S. Kim, X. Petrissans, B. Dunn, S.H. Tolbert, “Nanoporous Tin with a Granular Hierarchical Ligament Morphology as a Highly Stable Li-Ion Battery Anode.” ACS Appl. Mater. Interfaces, 2017, 9, 293−303.B. Cook, H.-S. Kim, T.C. Lin, C.-H. Lai, B. Dunn, S.H. Tolbert, “Pseudocapacitive Charge Storage in Thick Composite MoS2 Nanocrystal Based Electrodes. Adv. Energy Mater. 2016, 1601283.

Cobalt oxide thin films for high capacity and stable Li-ion battery anode

Here, we report reactive DC-sputter deposited Co3O4 thin films as a promising and stable Li-ion battery anode. Thin films were deposited on stainless steel by reactive sputtering of cobalt target in O2 atmosphere. X-ray diffraction and X-ray photo electron spectroscopy confirm the formation of Co3O4 crystal structure and absence of other impurities. The electron microscopy analysis shows a columnar growth morphology of the thin films while high resolution images reveal that the film is composed of ultra-small nanoparticles of average size of 5 nm. Fabricated half cells upon cycling between 3.0 and 0.01 V exhibit a stable capacity of 1125 mAh/g at a current density of 1 A/g for 100 cycles. Moreover, the electrode exhibited excellent rate capability and stability at higher rates; at current density of 10 A/g, a capacity close to 1000 mAh/g was observed. The excellent cycling stability of the cell was further confirmed by cycling at a high rate of 25 A/g (28 C) wherein the same was able to retain a capacity of 330 mAh/g even at the end of 1800 cycles. This enhanced performance could be related to the formation of 5-nm primary particles and columnar growth morphology, capable of reducing the lithium ion diffusion lengths and thus offered better kinetics even at high rates.

Nanoporous Tin with a Granular Hierarchical Ligament Morphology as a Highly Stable Li-Ion Battery Anode.

Next generation Li-ion batteries will require negative electrode materials with energy densities many-fold higher than that found in the graphitic carbon currently used in commercial Li-ion batteries. While various nanostructured alloying-type anode materials may satisfy that requirement, such materials do not always exhibit long cycle lifetimes and/or their processing routes are not always suitable for large-scale synthesis. Here, we report on a high-performance anode material for next generation Li-ion batteries made of nanoporous Sn powders with hierarchical ligament morphology. This material system combines both long cycle lifetimes (more than 72% capacity retention after 350 cycles), high capacity (693 mAh/g, nearly twice that of commercial graphitic carbon), good charging/discharging capabilities (545 mAh/g at 1 A/g, 1.5C), and a scalable processing route that involves selective alloy corrosion. The good cycling performance of this system is attributed to its nanoporous architecture and its unique hierarchical ligament morphology, which accommodates the large volume changes taking place during lithiation, as confirmed by synchrotron-based ex-situ X-ray 3D tomography analysis. Our findings are an important step for the development of high-performance Li-ion batteries.

High Energy and Stable Li-Ion Battery Anodes Enabled with 3D Si/C Particulate Nanocomposites Intenally-Wired with Graphene Networks

Silicon is very promising anode materials not only for boosting the energy density of lithium-ion batteries (LIBs) but for replacing the dendrite forming lithium metal anodes in lithium metal free Li-O2and Li-S batteries [1-3]. However, it is challenging to design silicon-based anodes exhibiting stable cycling behavior, high volumetric and specific capacity, and low volume expansion. In this study, we proposed that a sol–gel process can serve as a facile platform for composite materials of high lithium storage capacity. These composite materials consist of silicon nanoparticles (SiNPs) coated with carbon, a small graphene network interconnecting these nanoparticles to form condensed micro-sized particles, and a large fraction of void spaces between nanoparticles and graphene networks in these composites. Since, Si/C composites are internally wired with graphene networks, they are denoted as Si/C-IWGNs hereafter. The Si/C-IWGN samples were simply prepared by carbonizing the composite gels formed in aqueous mixtures consisting of SiNPs and resorcinol (R)–formaldehyde (F) as the carbon precursor and a small amount of graphene oxide (GO) in one-pot reactions. Various Si/C-IWGN samples were prepared with different contents of SiNPs (40 or 50 wt%) and graphene (1, 5 and 10 wt%). Two types of gelation catalysts (C), Na2CO3 or NH4OH, with different concentrations (R/C ratio = 100–500 in molar) were used for forming composite gels. Various electrochemical responses of Si/C-IWGNs, such as cycling stability, volumetric as well as specific capacity, coulombic efficiency, and electrode thickness increase, are thoroughly compared with those of the following reference samples: (1) control composites, Si/C composites, which were prepared without GO addition in the gel formation process and (2) commercial graphite. Finally, we have demonstrated a hybrid strategy to develop a reliable and low cost anode material consisting of mixtures of high capacity Si/CIWGNs and commercial graphite. The characterization and electrochemical responses of this novel composite suggest that graphene networks in Si/C-IWGNs not only provide electrical networks but also generate void spaces (Fig. 1a~c), which are very effective in absorbing large volume expansions of Si to the level comparable to that of commercial graphite (Fig. 1d, inset). Thereby, graphene networks effectively tackled the issue of common electrode pulverization and ensured the cycling stability of Si-based anodes (Fig. 1d) [4]. Compared to commercial graphite, a properly designed Si/C-IWGN composite material exhibited about 420% increase in specific capacity and about 141% increase in volumetric capacity, which was determined on the basis of electrode weight or volume. We devised a reliable and cost-effective hybrid anode using a mixture of Si/C-IWGN and commercial graphite. Si–Gr is a hybrid that offers the capacity level (800–1000 mAh g-1) required to improve the energy density of current LIB cells. Moreover, the volumetric capacity of the Si–Gr electrode is 161% higher than that obtained from commercial graphite [4]. The Si–Gr hybrid also has excellent cycling stability. We conclude that the preparation of Si/C-IWGNs is a scalable process. Moreover, owing to the remarkable electrochemical responses of Si/C-IWGNs, it could be used in manufacturing energy storage devices of high energy density and long cycle life. [1] N.Liu, Z. Lu, J. Zhao, M.T. McDowell, H.-W. Lee, W. Zhao, and Yi Cui, Nat. Nanotechnol., 9, 187-192 (2014). [2] C. Chae, H.-J. Noh, J. K. Lee, B. Scrosati, and Y.-K. Sun, Adv. Funct. Mater,, 24, 3036-3042 (2014). [3] S.-K. Lee, S.-M. Oh, E. Park, B. Scrosati, J. Hassoun, M.-S. Park, Y.- J. Kim, H. Kim, I. Belharouak, and Y.-K. Sun, Nano Lett., 15, 2863-2868 (2015). [4] J. Kim, C. Oh, C. Chae, D.-H. Yeom, J. Choi, N. Kim, E.-S. Oh, and J. K. Lee, J. Mater. Chem. A., 3,18684-18695 (2015). Figure 1. (a) SEM image, (b) TEM image, (c) SEM image of particle cross-section and (d) cycling stability of Si/C and Si/C-IWGNs (Inset shows electrode thickness changes). Figure 1

Engineered Nanovoids in Si/C Composites for High Capacity and Stable Li-Ion Battery Anodes

Silicon is an ideal anode material for advanced Li-ion battery (LIB) because it offers a low voltage for charging and the highest specific and volumetric capacities (Li15Si4 » 3,579 mAh g-1 and 8,340 mAh ml-1) among known elements. In spite of these highly appealing features, it has long been a critical challenge to design silicon-based electrode materials in a scalable way which maintain their high capacity over prolonged cycling due to both disastrous electrode pulverization due to huge volume variations (~300%) and the instability of solid-electrolyte interface (SEI) layers. In this study, engineered carbon nanovoids were successfully introduced in the Si/C composites to efficeintly absorb the large volume expansions of silicon in the nanovoids and maintain electrical integrity of electrode as well as cycling stability for prolonged cycles. To explore the idea, chemical binding and electrostatic self-assembly between amine-functionalized Si nanoparticles and SiO2 nanoparticles were employed followed by carbon coating and SiO2 template removal. Thus prepared Si@Nanovoids delivered 1,350 mAh g-1 at the current of 100 mA g-1 and showed stable cycling up to 200 cycles at 500 mA g-1 while the standard Si/C reference electrode lost most of its capacity in 40 cycles. The Si@Nanovoids electrode exhibited minimal volume change thanks to the engineered nanovoids after long cycles. More details in materials synthesis, analysis and electrochemical properties of Si@Nanovoids are to be presented.

Stable Li-ion battery anodes by in-situ polymerization of conducting hydrogel to conformally coat silicon nanoparticles

Silicon has a high-specific capacity as an anode material for Li-ion batteries, and much research has been focused on overcoming the poor cycling stability issue associated with its large volume changes during charging and discharging processes, mostly through nanostructured material design. Here we report incorporation of a conducting polymer hydrogel into Si-based anodes: the hydrogel is polymerized in-situ, resulting in a well-connected three-dimensional network structure consisting of Si nanoparticles conformally coated by the conducting polymer. Such a hierarchical hydrogel framework combines multiple advantageous features, including a continuous electrically conductive polyaniline network, binding with the Si surface through either the crosslinker hydrogen bonding with phytic acid or electrostatic interaction with the positively charged polymer, and porous space for volume expansion of Si particles. With this anode, we demonstrate a cycle life of 5,000 cycles with over 90% capacity retention at current density of 6.0 A g(-1).