Li-ion Storage Capacity Research Articles

Green preparation of nanostructured β-MoO3/hexagonal-shaped MoS2/graphene with enhanced lithium-ion storage performance

Metastable monoclinic molybdenum trioxide (β-MoO3) combined with perfect hexagonally-shaped MoS2 and graphene nanosheets are fabricated by facile mechanochemical-molten salt treatment of irregularly-shaped molybdenum disulfide (MoS2) and graphite in air. This hybrid nanostructure exhibits an excellent Li-ion storage performance, outperforming the nanocomposites made of conventional orthorhombic α-MoO3. To this end, ball-milled MoS2 and graphite are treated in the presence of sodium chloride (NaCl) at 900–1200 °C, leading to the preparation of MoS2/MoOx@graphene (MSO@G) nanocomposites in an easily scalable and affordable way. The formation of β-MoO3 is realized at 1100 °C (MSO@G-1100), outperforming the electrochemical performances of other samples and the initial MoS2. Moreover, the influence of binder on the electrochemical performance of MSO@G-1100 is studied, based on which polystyrene acrylic-acrylate (SAE) is found to provide a considerably low charge transfer resistance (27.59 Ω), outperforming conventional binders. The electrode exhibits a reversible Li-ion storage capacity of 878 mAh g−1 after 245 cycles at the current density of 100 mA g−1. The capacitive contribution to the total Li-ion energy storage performance of MSO@G-1100/SAE is found to be significant with the value of around 62% at the potential scan rate of 0.3 mV s−1. This article report on the facile, clean and sustainable preparation of β-MoO3 based nanocomposites with remarkable electrochemical performance.

Electronic, Optical, Mechanical and Li-Ion Storage Properties of Novel Benzotrithiophene-Based Graphdiyne Monolayers Explored by First Principles and Machine Learning

Recently, benzotrithiophene graphdiyne (BTT-GDY), a novel two-dimensional (2D) carbon-based material, was grown via a bottom-up synthesis strategy. Using the BTT-GDY lattice and by replacing the S atoms with N, NH and O, we designed three novel GDY lattices, which we named BTHP-, BTP- and BTF-GDY, respectively. Next, we explored structural, electronic, mechanical, optical, photocatalytic and Li-ion storage properties, as well as carrier mobilities, of novel GDY monolayers. Phonon dispersion relations, mechanical and failure behavior were explored using the machine learning interatomic potentials (MLIPs). The obtained HSE06 results reveal that BTX-GDYs (X = P, F, T) are direct gap semiconductors with band gaps in the range of 2.49–2.65 eV, whereas the BTHP-GDY shows a narrow indirect band gap of 0.06 eV. With appropriate band offsets, good carrier mobilities and a strong capability for the absorption of visible and ultraviolet range of light, BTF- and BTT-GDYs were predicted to be promising candidates for overall photocatalytic water splitting. The BTHP-GDY nanosheet, noticeably, was found to yield an ultrahigh Li-ion storage capacity of over 2400 mAh/g. The obtained findings provide a comprehensive vision of the critical physical properties of the novel BTT-based GDY nanosheets and highlight their potential for applications in nanoelectronics and energy storage and conversion systems.

Electrochemical Conversion of Natural Graphite into Carbon Nanostructures for Energy Storage Applications

Natural graphite minerals with global reserves greater than 320 million tones can be considered as low-cost and highly available precursors for the preparation of high-quality carbon nanostructures with potential applications in energy devices and related areas. Here, the electrochemical conversion of natural graphite minerals into carbon nanostructures, comprising onion-like carbon nanoparticles and multiwall carbon nanotubes (MWCNTs) in high-temperature molten salts are studied. The galvanostatic polarization of electrodes made of such minerals is conducted in molten LiCl and LiCl-NaCl at various current densities, leading to the exfoliation of the minerals into carbon nanostructures. The influence of non-carbon impurities present in the natural graphite mineral, and the current density applied on the characteristics of the resultant nanocarbons are investigated. Moreover, the structural and microstructural properties of the nanocarbons fabricated using natural graphite minerals are compared with those produced using commercially pure graphite electrodes. It is found that the electrochemical nanostructuring of the mineral in molten salt not only increases the surface area of the material, but also increases its electrical conductivity. The high-yield conversion of the mineral into carbon nanostructures is realized at the cathode current density of around 1 A cm-2. The Li- and Na- ion storage performances of this sample are evaluated. The Li-ion storage capacity of the sample is found to be remarkable at around 460 mAh g-1 after 500 charge/discharge cycles at the current density of 200 mA g-1. The green molten salt preparation and the electrochemical performance of nanocarbons is discussed here.

Clean preparation of Fe2SiO4 coated Fe2O3 integrated with graphene for Li-ion storage application

Ferric oxide (Fe2O3) is an attractive candidate for energy storage applications, including anode of Li-ion batteries due to its low-cost, high availability and large theoretical capacity. However, the mineral suffers from poor cyclability and rate performance due to the combination of rapid disintegration of the compound upon Li-ion insertion and extraction cycles, and poor conductivity of the electrode. Here, for the first time, we report on the clean modification of ferric oxide using corn-derived silica and graphite-derived graphene nanosheets, using a facile calcination-mechanical integration approach, without the involvement of environmentally-problematic raw materials. The product (Fe2O3@Fe2SiO4 @G) consists of ferric oxide particles coated with iron silicate; and these hybrid particles are integrated with graphene nanosheets. The presence of Fe2SiO4 layers could relieve the volume changes of Fe2O3 involved in the cycling, and also improves the ionic conductivity reducing the interfacial resistance between the electrode and the electrolyte, while graphene nanosheets improves the electrical conductivity of the electrode. Thus Fe2O3@Fe2SiO4@G electrode considerably outperforms the initial Fe2O3 with outstanding Li-ion storage capacities of 823 and 422 mA h g−1 recorded at the current densities of 100 and 1000 mA g−1, respectively, after 300 cycles. Pseudocapacitive behavior of the electrode is found to be 76.6% at 1 mV s−1, confirming the promotion of surface interactions in the nanostructured hybrid material. This article suggests a clean way of modifying naturally occurring Fe2O3 to be used as the anode of lithium ion batteries.

Sustainable development of manganese sulfoselenide nanoparticles anchored graphene oxide nanocomposite for high-performance supercapacitor and lithium-ion battery applications

Transition metal chalcogenides have been described as promising electrode materials for supercapacitors due to their low electronegativity, suitable electrical conductivity, comparatively higher specific capacitance, and favorable electrochemical redox regions. However, the poor electrical conductivity and substantial volume fluctuations provide a significant obstacle to industrial use. A new method to develop metal incorporated GO at the time of GO synthesis and subsequent conversion to metal sulfoselenides is proposed and demonstrated here. This novel process incorporates the advantages of both GO and the metal sulfoselenides for electrochemical energy storage applications. The average size of the nanoclusters was 52 nm as identified by Transmission electron microscopy. As pseudocapacitive electrode GO-MnSSe delivered a specific capacitance of 603 F/g at 0.1 A/g in 1 M KCl of aqueous electrolyte, because of their distinct and stable form. The fabricated 2-electrode device showed a specific capacitance of 98.5 mF/cm2 at 80 µA/cm2, showing good retention of 67 % at the end of the 9000 cycles. As Li-ion battery half-cells, at specific currents of 50, 100, 250, and 500 mA/g, GO-MnS delivered a capacity of 587, 378, 273, and 211 mA h/g respectively, reflecting a retention rate of 64 %, while the specific current was increased 10 times. The initial capacity of GO-MnS and GO-MnSSe at 100 mA/g was 494 and 495 mAh/g respectively, and for GO-MnS and GO-MnSSe at 250 mA/g the delivered capacity values were 376 and 363 mA h/g respectively. Coulombic efficiency (CE) for GO, GO-SW (single wash), GO-MnS, and GO-MnSSe were 99.52 %, 99.6 %, 98.7 %, and 99 % respectively at the end of the 100 cycles. Moreover, GO-MnS were cycled at a higher rate of 500 mA/g for 500 cycles which showed a decay initially nevertheless it stabilized after few cycles and showed a retention of 88 % at the end of 500 cycles from 20th cycle. The ex-situ morphological analysis of GO-MnS were conducted as well as the kinetic of the electrode were studied by before and after cycling EIS measurement. As part of this, as an anode for lithium-ion batteries, high Li-ion storage capacity and cyclic stability were observed.

Two Birds with One Stone: Prelithiated Two-Dimensional Nanohybrids as High-Performance Anode Materials for Lithium-Ion Batteries.

As an inexpensive and naturally abundant two-dimensional (2D) material, molybdenum disulfide (MoS2) exhibits a high Li-ion storage capacity along with a low volume expansion upon lithiation, rendering it an alternative anode material for lithium-ion batteries (LIBs). However, the challenge of using MoS2-based anodes is their intrinsically low electrical conductivity and unsatisfied cycle stability. To address the above issues, we have exploited a wet chemical technique and integrated MoS2 with highly conductive titanium carbide (Ti3C2) MXene to form a 2D nanohybrid. The binary hybrids were then subjected to an n-butyllithium (n-Buli) treatment to induce both MoS2 deep phase transition and MXene surface functionality modulation simultaneously. We observed a substantial increase in 1T-phase MoS2 content and a clear suppression of -F-containing functional groups in MXene due to the prelithiation process enabled by the n-Buli treatment. Such an approach not only increases the overall network conductivity but also improves Li-ion diffusion kinetics. As a result, the MoS2/Ti3C2 composite with n-Buli treatment delivered a high Li-ion storage capacity (540 mA h g-1 at 100 mA g-1), outstanding cycle stability (up to 300 cycles), and excellent rate capability. This work provides an effective strategy for the structure-property engineering of 2D materials and sheds light on the rational design of high-performance LIBs using 2D-based anode materials.

Graphene nanobuds as a novel anode design paradigm with superior Li-ion storage capacity and rate capability

This work reports the growth of graphene nanobuds (GNB) on Cu foil by chemical vapor deposition and its direct application as an electrode in lithium-ion batteries. The obtained novel GNB anode exhibited a superhigh specific capacity of 2813 mAh g−1 at a current rate of 4 A g−1 with a reversible coulombic efficiency of 78% in the first cycle. The most important advantage of using GNB as an anode was its outstanding cycled performance, maintaining a stable capacity of 1600 mAh g−1 at 8 A g−1 for at least 330 charge/discharge cycles with a coulombic efficiency of 99%. More significantly, the cell still maintained a retention capacity of 870 mAh g−1 when cycled at the very high current rate of 40 A g−1. The exceptional electrochemical performance in storage capacity and rate capability of GNB can be mainly attributed to the nanobuds having more loose space in their adjacent walls and hollow spaces; and to the intrinsic nano-oriented structure of few-layered graphene. This unique structure enables better Li-ion diffusion and higher Li-ion storage capacity. The outstanding electrochemical performance of the GNB as an anode places it as one of the most promising advanced carbon materials for next-generation lithium-ion batteries.

Material Optimization Engineering toward xLiFePO4·yLi3V2(PO4)3 Composites in Application-Oriented Li-Ion Batteries.

The development of LiFePO4 (LFP) in high-power energy storage devices is hampered by its slow Li-ion diffusion kinetics. Constructing the composite electrode materials with vanadium substitution is a scientific endeavor to boost LFP’s power capacity. Herein, a series of xLiFePO4·yLi3V2(PO4)3 (xLFP·yLVP) composites were fabricated using a simple spray-drying approach. We propose that 5LFP·LVP is the optimal choice for Li-ion battery promotion, owning to its excellent Li-ion storage capacity (material energy density of 413.6 W·h·kg−1), strong machining capability (compacted density of 1.82 g·cm−3) and lower raw material cost consumption. Furthermore, the 5LFP·LVP||LTO Li-ion pouch cell also presents prominent energy storage capability. After 300 cycles of a constant current test at 400 mA, 75% of the initial capacity (379.1 mA·h) is achieved, with around 100% of Coulombic efficiency. A capacity retention of 60.3% is displayed for the 300th cycle when discharging at 1200 mA, with the capacity fading by 0.15% per cycle. This prototype provides a valid and scientific attempt to accelerate the development of xLFP·yLVP composites in application-oriented Li-ion batteries.

Lithium storage properties of Ti3C2Tx (Tx = F, Cl, Br) MXenes

In this work, Ti3C2Tx MXene with -F, -Cl and -Br surface terminations are synthesized and the effect of these halogen terminations on the lithium storage properties is investigated. A maximum Li+ storage capacity of 189 mAh/g is achieved with Ti3C2Brx MXene much higher than Ti3C2Clx and Ti3C2Fx with 138 mAh/g and 123 mAh/g, respectively. Density functional theory (DFT) calculation shows that the adsorption formation energy of halogen atoms on Ti atoms follows the trend of Ti-F > Ti-Cl > Ti-Br, leading to the same trend in the content of terminations on corresponding MXenes. In addition, inevitable exposure of MXene to oxygen causes competition between halogen and oxygen. Theoretical results show Ti3C2Brx MXene has the highest Ti to O ratio and the lowest Ti to Br ratio, the high lithium affinity of O explains the maximum Li-ion storage capacity with Ti3C2Brx MXene. This work shed light on the opportunity for achieving improved lithium storage properties of MXene electrodes by regulating the surface chemistry.

Stable anodes for lithium-ion batteries based on tin-containing silicon oxycarbonitride ceramic nanocomposites

Tin nanoparticles are a promising candidate for Li-ion battery anodes to replace carbon materials due to their high theoretical Li-ion storage capacity (994 mAh/g), which is much higher than that of graphite (372 mAh/g). However, the poor cycling stability of tin emerged from large volume expansion, and contraction remains a challenging issue. To overcome these limitations, we designed Sn-containing silicon oxycarbonitride ceramic nanocomposites (Sn/SiOCN) by the chemical reaction of tin acetate with poly(vinyl)silazane Durazane 1800 in ice bath under argon, followed by the pyrolysis of as-obtained precursors at 1000 °C for 3 h under argon atmosphere. The Sn/SiOCN nanocomposites with different Sn contents are tested as anodes for lithium-ion batteries, delivering a high-discharge capacity of ∼320 mAh/g at a current density of 2220 mA/g and extremely long cycling stability even at high charging rates (approximately 90% of the capacity is maintained after 1000 cycles). The outstanding electrochemical performance of Sn/SiOCN nanocomposites can be attributed to the improved charge transfer process due to the incorporation of metallic Sn nanoparticles into the amorphous SiOCN ceramic matrix, as revealed by electrochemical impedance spectroscopy (EIS) characterization. In situ XRD results confirm the formation of lithium-rich alloy phase Li7Sn2 during the lithiation process.

Metal-Organic Framework Glass Anode with an Exceptional Cycling-Induced Capacity Enhancement for Lithium-Ion Batteries.

Metal-organic frameworks (MOFs) hold great promise as high-energy anode materials for next-generation lithium-ion batteries (LIBs) due to their tunable chemistry, pore structure and abundant reaction sites. However, the pore structure of crystalline MOFs tends to collapse during lithium-ion insertion and extraction, and hence, their electrochemical performances are rather limited. As a critical breakthrough, a MOF glass anode for LIBs has been developed in the present work. In detail, it is fabricated by melt-quenching Cobalt-ZIF-62 (Co(Im)1.75 (bIm)0.25 ) to glass, and then by combining glass with carbon black and binder. The derived anode exhibits high lithium storage capacity (306 mAh g-1 after 1000 cycles at of 2 A g-1 ), outstanding cycling stability, and superior rate performance compared with the crystalline Cobalt-ZIF-62 and the amorphous one prepared by high-energy ball-milling. Importantly, it is found that the Li-ion storage capacity of the MOF glass anode continuously rises with charge-discharge cycling and even tripled after 1000 cycles. Combined spectroscopic and structural analyses, along with density functional theory calculations, reveal the origin of the cycling-induced enhancement of the performances of the MOF glass anode, that is, the increased distortion and local breakage of the CoN coordination bonds making the Li-ion intercalation sites more accessible.

PVP-assisted Self-assembling of lacelike TiP2O7 encapsulated in carbon bracket for advanced Lithium-ion storage

One fundamental issue for developing high-performance lithium-ion batteries (LIBs) locates in the exploration of stable anode materials that can provide stable channels and sufficient active sites for Li-ion shuttling. Polyanionic pyrophosphate-based materials (e.g., TiP2O7) have been considered as the anode materials due to their advantages in ion migration kinetics and cycle stability. However, the large bandgap and strong P-O covalent bond in TiP2O7 result in inferior electron conductivity, limiting its Li-ion storage capability. Herein, a novel lacelike TiP2O7 submicro-spheres with bracket C compounds (TiP2O7@C) were synthesized with PVP-oriented aggregation using one-step hydrothermal and heat treatment method. The pyrolytic carbon coating layer prominently optimizes the electron transfer kinetics, avoids the erosion of organic electrolytes, and stabilizes the hierarchical structure in the ultralong cycle processes. When served as the anode materials for LIBs, the prepared TiP2O7@C composite showed an excellent reversible Li-ion storage capacity of 411.7 mAh g−1 after 700 cycles under a high current density of 1.0 A g−1. The kinetic analysis and pseudocapacitance calculation demonstrated that the tailored structure promotes the electrochemical capability. This proposed strategy displays significant performance benefits, offering a novel pathway to modify the morphology and electron/ion transfer of polyanionic anode materials for LIBs.

Achieving high-performance energy storage device of Li3V2(PO4)3 // LiCrTiO4 Li-ion full cell

Active electrode materials are given main responsibility for the electrochemical performance of Li-ion full cells. Hence, it is essential to pursue cost-effective manufacturing techniques for electrode materials. In this study, a green and low-cost strategy is employed to manufacture kg-level monoclinic Li 3 V 2 (PO 4 ) 3 (LVP) and spinel LiCrTiO 4 (LCTO) electrode materials, both of which display excellent Li-ion storage capability with high reversible capacities and a long lifespan. The manufactured LVP || LCTO Li-ion full cells have demonstrated a capacity of 646.5 mA h and an impressive cycling capability of 800 cycles with only 0.36‰ capacity loss per cycle at 500 mA. The higher Li-ion storage capacity of full LIBs is explained by the excellent electrochemical reversibility of Li 3 V 2 (PO 4 ) 3 cathode and LiCrTiO 4 anode. ● A green and low-cost strategy is employed to prepare Li 3 V 2 (PO 4 ) 3 /C (LVP/C). ● LiCrTiO 4 (LCTO) microspheres are constructed with the spray-drying route. ● LVP/C and LCTO both exhibit excellent Li-ion storage capability. ● High-performance energy storage device of LVP//LCTO full LIBs are achieved.

N-Doped Carbon-Wrapped Cobalt–Manganese Oxide Nanosheets Loaded into a Three-Dimensional Graphene Nanonetwork as a Free-Standing Anode for Lithium-Ion Storage

A high-quality and centimeter-level three-dimensional (3D) nitrogen-doped graphene (NG) nanonetwork is synthesized via a chemical vapor deposition method to serve as a substrate and a current collector, which directly germinates active metal oxides to act as a free-standing electrode in lithium-ion batteries. By means of facile electrodeposition and annealing processes, the tetragonal spinel cobalt–manganese oxide nanosheets wrapped with polypyrrole pyrolytic carbon are in situ hybridized with a 3D NG nanonetwork. In particular, the introduced carbon protective layer can enhance the Li-ion storage capacity and cycle stability of the composite electrode. The metallic synergistic effect and rational carbonaceous hybridization jointly provide high-performance charge storage and cycle stability. Notably, the surface-controlled capacitive effect stands out contributing to the total charge storage more than ever in nanostructure electrodes.

Rational design and in-situ formation of nickel–cobalt nitride multi-core/hollow N-doped carbon shell anode for Li-ion batteries

• Nickel–cobalt nitrides with unique multi-core/shell nanostructure are proposed. • Multi-core/shell nanostructures are successfully formed via in-situ thermal annealing process. • Hierarchical composite anodes deliver superior performance for Li-ion batteries. • Structural and morphological evolution at different electrochemical states is elucidated. The construction of a carbon-encapsulated multi-core nanostructure based on transition metal nitride is a preferred approach to efficiently mitigate volume expansion with improved sustainability and to enhance conductivity with more active sites for Li-ion cell reaction. Herein, we report the in-situ formation of carbon-coated nickel–cobalt nitride multi-core nanoparticles encapsulated by hollow N-doped carbon shell via monodispersed Ni 3 [Co(CN) 6 ] 2 Prussian blue analogue/polydopamine precursors using by simultaneous nitridation and calcination process. The (Ni/Co) 3 N multi-core nanoparticles (Ni:Co = 3:2) were highly dispersed in conductive and hollow N-doped carbon shell, thereby (i) mitigating mechanical stress by volume change during the conversion reaction of nitrides, (ii) stabilizing the electrochemical reaction surface with a thin solid electrolyte interphase, and (iii) maintaining the original structure and hierarchical morphologies even after long cycles. The (Ni/Co) 3 N multi-core@hollow N-doped carbon shell demonstrated better electrochemical performance than the (Ni/Co) 3 N@carbon shell without the outer hollow N-doped carbon shell for the Li-ion battery anode, which has an excellent reversible capacity of ~440 mAh g −1 and a stable cycle life of 130 cycles at 200 mA g −1 . The rational synthetic strategy of the unique hybrid nanoarchitecture via in-situ formation of polymer-coated metal–organic frameworks is key in improving the Li-ion storage capacity and cycle stability.

Carbon nanotubes-enhanced lithium storage capacity of recovered silicon/carbon anodes produced from solar-grade silicon kerf scrap

Recovered solar-grade silicon kerf scrap is touted as an ideal silicon source for Si-based anodes in advanced lithium-ion batteries (LIBs) whose development is always troubled by the volume expansion and low conductivity. Here, an effective approach for carbon nanotubes (CNTs) enhanced recovered silicon/carbon anodes encapsulated by polymethyl methacrylate (PMMA)-derived carbon coating (Si/CNTs@PMMA-C) is described. The Si/CNTs@PMMA-C anode presents an impressive Li ion storage capacity and long cycle lifespans, delivering a high initial discharge capacity of 3732.7 mAhg−1 and initial coulombic efficiency of 78.2% at 200 mAg−1 with a reversible capacity retention of 1024.8 mAhg−1 after 200th cycle. Moreover, full-cells composed of Si/CNTs@PMMA-C anodes and commercial LiCoO2 cathodes display a good electrochemical performance and high energy density. These excellent electrochemical properties boil down to the synergistic effect of PMMA-derived carbon shell and high-purity recovered silicon; meanwhile, CNTs can further support volume expansion tolerance and electrical conductivity. This effective method can provide a broader practical application prospect for the silicon/carbon composite anodes based on low-cost recovered solar-grade silicon kerf scrap with enhanced electrochemical performance in advanced LIBs.

Hierarchical Co2VO4 yolk-shell microspheres confined by N-doped carbon layer as anode for high-rate lithium-ion batteries

The design of high-performance anodes is crucial for the whole for lithium-ion batteries (LIBs). Binary transition metal oxides (bi-TMOs), especially cobalt vanadates featuring high theoretical lithium storage capacity endow them promising anode materials. However, low electric conductivity as well as tremendous volume change occurring during the process of de−/lithiation restrict their commercialization. Herein, the as-devised novel spinel Co2VO4 yolk-shell microspheres coated with nitrogen-doped carbon shell (Co2VO4@NC) were synthesized by the method of a self-templated solvothermal preparation and following in-situ pyrolysis of polydopamine (PDA) film, which demonstrates excellent properties as anode for LIBs by virtue of the unique spinel structural characteristics, mixed lithium storage mechanism, micro/nanolization of the yolk-shell structure and vital amorphous NC component. In detail, the unique Co2VO4@NC electrode displays the high Li ion storage capacity (1255 mAh g−1 at 0.2 A g−1), the superior cycling stability (1227 mAh g−1 at 0.5 A g−1 after 400 cycles) as well as outstanding reversible capability (remaining 862 mAh g−1 when return to 0.1 A g−1 from 5 A g−1, larger than initial 796 mAh g−1).

Unveiling the stability of Sn/Si/graphite composites for Li-ion storage by physical, electrochemical and computational tools.

Complex materials composed of two and three elements with high Li-ion storage capacity are investigated and tested as lithium-ion battery (LiB) negative electrodes. Namely, anodes containing tin, silicon, and graphite show very good performance because of the large gravimetric and volumetric capacity of silicon and structural support provided by tin and graphite. The performance of the composites during the first cycles was studied using ex situ magic angle spinning (MAS) 7Li Nuclear Magnetic Resonance (NMR), density functional theory (DFT) calculations, and electrochemical techniques. The best performance was obtained for Sn/Si/graphite in a 1 : 1 : 1 proportion, due to an emergent effect of the interaction between Sn and Si. The results suggest a stabilization effect of Sn over Si, providing a physical constraint that prevents Si pulverization. This mechanism ensures good cyclability over more than one hundred cycles, low capacity fading and high specific capacity.

Core-Shell Sn@Sioc Nanocomposite Synthesized Via Spray Pyrolysis for LIBs

Lithium-ion batteries (LIBs) have become promising energy storage devices for the consumer electronics and electric vehicles due to their high energy and power density. Anode materials such as Si, Sn and Ge which are alloying with Li+ ions have been attracted as alternatives to conventional graphite due to their very high theoretical capacities. Among the possible candidates, Sn has been thought to be a great anode material that shows high theoretical Li ion storage capacity of 994mAh g-1 and high electrical conductivity. However, the major drawback of tin based anode is their poor cycling stability because of large volme changes (260% for Li22Sn5) during lithiation resulting in pulverization and loss of electrical contact within the electrode. Especially, the repetitive formation and rupture of solid electrolyte interface (SEI) layer continuously deplete the electrolyte. Nanocrystallization can effectively decrease the absolute volume change of every single particle and mitigated the strain improving the cycling stability of Sn anodes. However, preparation methods of nano-Sn have some negative factors, such as the high cost, complex process and reaggregation after cycling. In order to take full advantage of nano-Sn, many studies introduce suitable matrix. These matrix acts as a buffer agents and avoids side reactions by preventing the direct contact of Sn and electrolyte. The common one is carbon matrix works as a conducting medium and enhances the rate performance of electrode. Another one is active metals including Ge-Sn, Sb-Sn and Ag-Sn that can contribute to the overall capacity of the electrodes and long cycling life. Yet these comes with loss of charge storage capacity or large volume expansion. The quest for suitable matrix with high Li ion storage, low volume expansion and sufficient electronic conductivity is important. In this study, silicon oxycarbide (SiOC) was adapted for Sn based anodes. The SiOC consists of silica tetrahedral SiO2, SiOC glass phase and free carbon. This matrix features a high charge storage capacity (~800mAh g-1), low voulme expansion (~7%) and sufficient mechanical strength contributed by SiO2 domains to accommodate the high volume expansion without capacity fading of Sn anode. In particular, the SiOC can suppress the aggreation of metallic Sn at high temperature remaining nano size. First, we obtained the Sn@SiOC nanocomposite with uniformly coated SiOC layer containing metallic Sn nanoparticle by spray pyrolysis and a subsequent carbonization process. The spray pyrolysis is scalable and facile method to synthesize various nanostructure functional materials via one-pot process. Also it can be easily scaled up for mass production. During the spray pyrolysis process, the tin(II) acetate and diphenylsilanediol (DPSD), the starting materials of Sn and SiOC, can be easily vaporized due to its low boiling point. The tin acetate nucleates first due to lower boiling point than DPSD and formates many clusters. Subsequently, DPSD vapors can be deposited onto the Sn clusters via aerosol assisted chemical vapor depsition (AACVD) mechanism. The deposited DPSD vapors lead to formation of coating layer by nucleation, growth and coagulation. Then, the spray pyrolyzed Sn@SiOC nanocomposite thermally treated at the inert atmosphere for growth of carbon network. This approach yields unifomly coated SiOC matrix with Sn nanoparticles of sizes on the order of 40-50nm. Anodes of the Sn@SiOC nanocomposite demonstrate high capacities and better stability against volume change during lithiation and delithiation cycling.

Synthesis of layered silicon-graphene hetero-structures by wet jet milling for high capacity anodes in Li-ion batteries

While silicon-based negative electrode materials have been extensively studied, to develop high capacity lithium-ion batteries (LIBs), implementing a large-scale production method that can be easily transferred to industry, has been a crucial challenge. Here, a scalable wet-jet milling method was developed to prepare a silicon-graphene hybrid material to be used as negative electrode in LIBs. This synthesized composite, when used as an anode in lithium cells, demonstrated high Li ion storage capacity, long cycling stability and high-rate capability. In particular, the electrode exhibited a reversible discharge capacity exceeding 1763 mAh g−1 after 450 cycles with a capacity retention of 98% and a coulombic efficiency of 99.85% (with a current density of 358 mA g−1). This significantly supersedes the performance of a Si-dominant electrode structures. The capacity fade rate after 450 cycles was only 0.005% per cycle in the 0.05–1 V range. This superior electrochemical performance is ascribed to the highly layered, silicon-graphene porous structure, as investigated via focused ion beam in conjunction with scanning electron microscopy tomography. The hybrid electrode could retain 89% of its porosity (under a current density of 358 mA g−1) after 200 cycles compared with only 35% in a Si-dominant electrode. Moreover, this morphology can not only accommodate the large volume strains from active silicon particles, but also maintains robust electrical connectivity. This confers faster transportation of electrons and ions with significant permeation of electrolyte within the electrode. Physicochemical characterisations were performed to further correlate the electrochemical performance with the microstructural dynamics. The excellent performance of the hybrid material along with the scalability of the synthesizing process is a step forward to realize high capacity/energy density LIBs for multiple device applications.