Buffer Matrix Research Articles

Coaxial Three-Layered Carbon/Sulfur/Polymer Nanofibers with High Sulfur Content and High Utilization for Lithium-Sulfur Batteries.

Great progress has been made on the cyclability and material utilization in recent development of lithium-sulfur (Li-S) batteries; however, most of the sulfur electrodes reported so far have a considerable low loading of sulfur (60%), which causes a substantial decrease in energy density and is therefore difficult for application in batteries. To deal with this issue, we fabricate a novel sulfur composite with a coaxial three-layered structure, in which sulfur is deposited on carbon fibers and coated with poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS), thus enabling a high sulfur loading of 70.8 wt % without the expense of its electrochemical performance. Benefiting from the rigid conductive framework of carbon fibers and flexible buffering matrix of the polymer for blocking the diffusion loss of discharge intermediates, the as-fabricated composite electrode exhibits a high initial reversible capacity of 1272 mA h g-1 (based on the total mass of the composite), a stable cyclability with a retained capacity of 807 mA h g-1 after 200 cycles, and a high Coulombic efficiency of ∼99% upon extended cycling, offering a new selection for practical application in Li-S batteries.

Multilayer Zn-doped SnO2 hollow nanospheres encapsulated in covalently interconnected three-dimensional graphene foams for high performance lithium-ion batteries

Multilayer Zn-doped SnO2 nanospheres are successfully synthesized by using Sn/Zn bimetal-organic nanoparticles as precursor. These multilayer spheres are found to be very suitable for solving the critical volume expansion problem and mass transfer property due to its high surface area, small crystal size and hollow structure, which is critical for high capacity metal oxide electrodes for lithium-ion batteries. Moreover, the covalently interconnected three-dimensional graphene foams encapsulated these multilayer spheres are successfully obtained through self-assembly effect and chemical cross-linking of graphene oxide nanosheets. The graphene network could further greatly improve the cycling stability and rate capability of the Zn-doped SnO2 spheres electrode due to its flexible buffering matrix and high electric conduction. As a result, the graphene encapsulating multilayer Zn-doped SnO2 spheres anodes exhibit excellent rate capacity and a high reversible capacity of 446mAhg−1 even after 1000 cycles at the current density of 1Ag−1. These excellent electrochemical performances are ascribed to its large specific surface area, fast electron/ion transfer, and stable electrode structure. Furthermore, this strategy using covalently interconnected 3D graphene foams encapsulate the Zn-doped SnO2 spheres not only develops a high performance anode material with long cycle life but also holds great promise for binder-free lithium ion batteries.

Gallium oxide nanorods as novel, safe and durable anode material for Li- and Na-ion batteries

Gallium oxide nanorods prepared by template-free synthesis are reported for the first time as safe and durable anode material for lithium- and sodium-ion batteries. The ambient temperature electrochemical response of the nanorods, tested by cyclic voltammetry and constant-current reversible cycling, is highly satisfying in terms of remarkable stability and capacity retention upon long-term operation (400 cycles), even at high current densities. The newly proposed application of gallium oxide nanorods as electrode material is notable also because this material can preserve the electrical pathway without the need of any “buffer matrix” to compensate for the expansion upon lithium or sodium reversible storage. The highly promising electrochemical performance is attributed to the high aspect ratio and high surface area that stem from the nanorod morphology and which can lead to short diffusion path and fast kinetics of both cations (Li+ or Na+) and electrons.

Nanosized-bismuth-embedded 1D carbon nanofibers as high-performance anodes for lithium-ion and sodium-ion batteries

Bi is a promising candidate for energy storage materials because of its high volumetric capacity, stability in moisture/air, and facile preparation. In this study, the electrochemical performance of nanosized-Bi-embedded one-dimensional (1D) carbon nanofibers (Bi/C nanofibers) as anodes for Li-ion batteries (LIBs) and Na-ion batteries (NIBs) was systematically investigated. The Bi/C nanofibers were prepared using a single-nozzle electrospinning method with a specified Bi source followed by carbothermal reduction. Abundant Bi nanoparticles with diameters of approximately 20 nm were homogeneously dispersed and embedded in the 1D carbon nanofibers, as confirmed by structural and morphological characterization. Electrochemical measurements indicate that the Bi/C nanofiber anodes could deliver a long cycle life for LIBs and a preferable rate performance for NIBs. The superior electrochemical performances of the Bi/C nanofiber anodes are attributed to the 1D carbon nanofiber structure and uniform distribution of Bi nanoparticles embedded in the carbon matrix. This unique embedded structure provides a favorable electron carrier and buffering matrix for the effective release of mechanical stress caused by volume change and prevents the aggregation of Bi nanoparticles.

Synthesis of core-shell-like ZnS/C nanocomposite as improved anode material for lithium ion batteries

ZnS/C nanoparticles with core/shell structure are prepared by a simple solvothermal process followed by an annealing process. The core consists of a quite amount of ultrasmall ZnS nanocrystals (∼10nm) dispersing in in situ formed carbon matrix, which is covered by an outer carbon shell with ∼4nm thickness. The nano-sized ZnS crystals effectively shorten the lithium ion diffusion paths, while the uniform carbon shell, together with the inner amorphous carbon matrix not only provide fast electron conduction, but also act as a buffer matrix to accommodate volume change occurring on electrochemical cycling. Such hierarchical-type microstructure is beneficial concerning electrochemical performance of the proposed composite. When evaluated as an anode material for rechargeable lithium ion batteries, the ZnS/C nanocomposite shows a high specific capacity of 741mAhg−1 at a current density of 0.1Ag−1 after 300 cycles. Even at 5Ag−1, a high reversible capacity of 538mAhg−1 can be still achieved. The lithium diffusion coefficient of ZnS/C electrode is estimated as 6.1×10−11cm2s−1, contributing to the excellent rate performance of the material.

Hollow-sphere ZnSe wrapped around carbon particles as a cycle-stable and high-rate anode material for reversible Li-ion batteries

Hollow-sphere ZnSe is successfully obtained through Ostwald ripening. Carbon nanoparticles are designed and utilized to form a wrapped carbon network as a conductive buffering matrix by subsequent annealing.

Ex Situ Investigation of Anisotropic Interconnection in Silicon-Titanium-Nickel Alloy Anode Material

Herein we investigate the nanostructural evolution of Silicon-Titanium-Nickel (Si-Ti-Ni) ternary alloy material synthesized by melt spinning process for advanced lithium-ion battery anode. The synthesized material was found to have nano-Silicon particles dispersed in the Ti4Ni4Si7 (STN) alloy buffering matrix and was characterized by X-ray diffraction (XRD), High resolution- transmission electron microscope (HR-TEM), Scanning transmission electron microscopes - energy dispersive X-ray spectrometer (STEM-EDS), and electrochemical performance test. The role of STN matrix is to accommodate the volume expansion stresses of the dispersed Si nanoparticles. However, an interesting behavior was observed during cycling. The Si nanoparticles were observed to form interconnection channels growing through the weak STN matrix cracks and evolving to a network isolating the STN matrix into small puddles. This unique nanostructural evolution of Si particles and isolation of the STN matrix failing to offer significant buffering effect to the grown Si network eventually accelerates more volume expansions during cycling due to less mechanical confinement and leads to performance degradation and poor cycle stability.

A novel strategy to prepare Ge@C/rGO hybrids as high-rate anode materials for lithium ion batteries

Abstract Germanium is considered as a promising anode material for lithium ion batteries (LIBs) due to its high-capacity. However, owing to the huge volume variation during cycling, the batteries based on germanium anodes usually show poor cyclability and inferior rate capability. Herein, we demonstrated a novel strategy to uniformly anchor the core-shell structured germanium@carbon (Ge@C) on the reduced graphene oxide (rGO) nanosheets by the strong adhesion of dopamine. In the resulting Ge@C/rGO hybrid, the amorphous carbon layer and rGO nanosheets can effectively reduce the agglomeration of germanium and provide buffer matrix for the volume change in electrochemical lithium reactions. When used as anode materials for LIBs, Ge@C/rGO hybrids deliver a reversible capacity of 1074.4 mA h g−1 at 2C after 600 cycles (with capacity retention of 96.5%) and high rate capability of 436 mA h g−1 at 20C after 200 cycles. The encouraging electrochemical performance clearly demonstrates that Ge@C/rGO hybrids could be a potential anode material with high capacity, excellent rate capability, and good cycling stability for LIBs.

Enhanced cycling performance of Se-doped SnS carbon nanofibers as negative electrode for lithium-ion batteries

Se doping has recently demonstrated to be an powerful solution for enhancing the electrochemical performance due to the formation of Se-contained phase, which acts as a buffer matrix against strain and Sn agglomeration upon cycling. In this work, SnS0.9Se0.1 nanoparticles with sub-stoichiometric ratio of Se doping were encapsulated into carbon nanofibers by electrospinning technique. Compared with Se-free samples, Se-doped SnS0.9Se0.1@CNFs electrodes exhibit significantly improved cyclic stability and better rate capability. The degradation of specific capacity is 27% for the former while only 7% for the latter, i.e., 4 times improvement of the cycling stability.

Electrochemically Synthesized Sn Nanodendrites As High-Performance Na-Ion Batteries Anodes

Because of their high energy density, Li-ion batteries have attracted attention as large storage systems over their traditional use for portable and electric vehicle applications. However, there are some concerns about the scarcity, uneven global distribution and high cost of lithium resourced. Compared with Li, Na has the advantages of natural abundance and low cost. Furthermore, Na and Li are in the same main group, exhibiting similar chemical properties, which translates to a resemblance between operational characteristics in Li-ion batteries and Na-ion batteries. Therefore, Na-ion batteries have been suggested for the alternatives to Li-ion batteries for large-scale systems. For the practical use of Na-ion batteries, studies for finding suitable electrode materials with high energy density, good cyclability and rate performance for Na-ion batteries have been actively conducted. Although several cathode materials have been suggested, the anode choices are severely limited because of the unique characteristic of Na. Na-ion cannot be stored much in commercial layered graphite because of its large radius. Si based materials are expected to be the most promising anode for Li-ion batteries, but it is electrochemically inactive with Na. On the contrary, Sn can store 3.75 Na/host-atom (Na15Sn4) resulting a maximum storage capacity of 847 mAh g-1 as an anode for Na-ion battery. Besides the high theoretical capacities, Sn also has advantages as an anode material for Na-ion battery such as low reaction potential and non-toxicity. However, pure Sn anode exhibits poor cyclability due to a loss of electrical contact with the current collector, resulting from a severe volume change (up to approximately 420%) during sodiation/desodiation. To improve the cyclability of Sn electrode, several strategies have been suggested such as introducing carbon or designing Sn-M intermetallic compounds for providing an active or inactive phase that acts as buffer matrix, and synthesizing a micro/nanostructured electrode for facilitating the relaxation of material stress. Among these strategies, synthesizing a nanostructured pure Sn, especially using electrodeposition, should be ideal solution. The material fracture is presumably due to the repeated non-uniform expansion and contraction during alloying and de-alloying. Because of a sluggish kinetic of sodium ion, the diffusion time is large compared to the charge/discharge time for the large sized particles which results uneven sodiation and desodiation states (different phases with different mechanical strengths) inside one particle. These variations in phase lead to stress, which can lead to crack propagation and pulverization. For this reason, nanostructured Sn could greatly reduce the stress induced during sodiation/desodiation by reducing the diffusion time of sodium ions in the electrode. Furthermore, using electrodeposition process, theoretical specific capacity of Sn can be fully used because the Sn anode are deposited directly on the current collector without mixing and drying processes for binder and conductive agent. Recently, we synthesized Sn nanodendrites with nano-sized branches. The Sn nanodendrites exhibited a high reversible capacities and excellent cycle performances. The maximum capacity was measured to be 783.88 mAh g-1 and the charge capacity at 100th cycle was measured to be 759.27 mAh g-1 that correspond to 96.86% of the maximum value. After cycling, the Sn nanodendrites exhibits no loss of active materials and it was attributed to the nano-sized branches greatly reducing the internal stress during sodiation/desodiation.

Facile synthesis of ultrafine SnO2 nanoparticles on graphene nanosheets via thermal decomposition of tin-octoate as anode for lithium ion batteries

We demonstrate a facile synthesis of ultrafine SnO2 nanoparticles within graphene nanosheets (GNSs) via thermal decomposition of tin-octoate, in which tin-octoate is firstly blended with GNSs followed by annealing in air at a low temperature (350 °C) and a short time (1 h). As anode for lithium ion batteries, the SnO2/GNSs displays superior cycle and rate performance, delivering reversible capacities of 803 and 682 mA h/g at current densities of 200 and 500 mA/g after 120 cycles, respectively, much higher than that of pure SnO2 and GNSs counterparts (143 and 310 mA h/g at 500 mA/g after 120 cycles, respectively). The enhanced electrochemical performance is attributed to the ultrafine SnO2 nanoparticle size and introduction of GNSs. GNSs prevent the aggregation of the ultrafine SnO2 nanoparticles, which alleviate the stress and also provide more electrochemically active sites for lithium insertion and extraction. Moreover, GNSs with large specific surface area (~363 m2/g) act as a good electrical conductor which greatly improves the electrode conductivity and also an excellent buffer matrix to tolerate the severe volume changes originated from the Li-Sn alloying-dealloying. This work provides a straight-forward synthetic approach for the design of novel composite anode materials with superior electrochemical performance.

Effect of Pore Size Distribution of Carbon Matrix on the Performance of Phosphorus@Carbon Material as Anode for Lithium-Ion Batteries

Phosphorus@carbon composites are alternative anode materials for lithium-ion batteries due to their high specific capacity. Serving as a conductive and buffer matrix, the carbon substrate is important to the performance of the composite. Our results exhibit that the electrochemical performances of phosphorus@carbon composites could be significantly enhanced by pore size distributions of the carbon matrix. The initial Coulombic efficiency of phosphorus@YP-50F reaches 80% and the capacity remains stable at 1370 mAh g–1 after 100 cycles at 300 mA g–1. The work may provide a general strategy for designing or selecting the optimal carbon matrix for phosphorus@carbon performance, and pave the way to practical application in lithium-ion batteries.

High rate capability and long cycle stability of Cr2O3 anode with CNTs for lithium ion batteries

The present study describes the synthesis of nanocomposite materials based on chromium oxide (Cr2O3) nanoparticles and carbon nanotubes (CNTs) (Cr2O3–CNT(x%)) by in-situ chemical co-precipitation method. The physical studies of these materials using a wide range of analytical techniques reveal high surface area and narrow pore size distribution of these nanocomposite materials, indicating homogenous dispersion of Cr2O3 nanoparticles (particle sizes ∼20-30nm) on the surface of CNTs. The first cycle discharge capacity of 1120mAhg-1 for electrodes fabricated from Cr2O3 alone, which is improved for Cr2O3–CNT(0.08%) nanocomposite (1199mAhg-1). This nanocomposite material achieved an overall reversible capacity of 995.3mAhg-1 after 200 cycles, which can be attributed to the high surface area and the large mesoporous volume of Cr2O3 nanoparticles interconnected with highly conducting network of CNTs. At higher current densities, the Cr2O3–CNT(x%) nanocomposite electrodes exhibited high lithium storage capacity compared to the electrode fabricated from Cr2O3 nanoparticles alone. Overall, the Cr2O3–CNT(0.08%) nanocomposite electrode displayed high stability under varying current rates with overall high capacity retention and highest reversible capacity of 719mAhg-1 at a current rate of 2000mAhg-1. This highly enhanced rate capability and excellent cycling stability of Cr2O3–CNT(0.08%) nanocomposite electrode can be ascribed to the synergistic effect of CNTs (anchored with the Cr2O3 nanoparticles). The outcome of this study offers a possibility of improving lithium ion storage of Cr2O3 nanoparticles by carefully controlling their size and shape along with the use of a suitable buffering matrix like CNTs.

Leak testing of carbon\u2013tin nanocomposites by thermal analysis methods

Electrode materials consisted of tin nanograins encapsulated in different origin carbon buffer matrix (starch or water soluble polymer) were obtained in a simple and inexpensive process. The tin precursor was synthesized using modified reverse nanoemulsion technique (w/o) and then coated by a source of carbon. The composites precursors were pyrolysed, affording formation of C/Sn anode materials. The resulting samples were investigated by powder X-ray diffraction studies in order to verify the structure and calculate crystallites sizes. The morphology of the nanocomposites was characterized by low-temperature nitrogen adsorption method (N2-BET). Thermal analysis measurements (EGA-TG/DTG/DTA and DSC) allowed determining optimal conditions of preparation process and estimating carbon content in the obtained anode materials. Thermogravimetric studies also proved to be highly useful in establishing the leak behaviour of C/Sn nanocomposites. The electrochemical performance of the nanopowders was examined by charge–discharge tests in R2032-type coin cell. The thermal analysis results as well as low-temperature nitrogen adsorption data indicated that the origin of carbon precursor has major impact on morphology and leak behaviour of the obtained carbon buffer matrix. The electrochemical tests showed that better tightness of carbon–tin nanocomposites resulted in higher gravimetric capacity and better cell performance.

Sb2O3 Microstructures As Efficient Anode Material for Sodium-Ion Batteries

With the rapid growth in various advanced technologies such as microelectronics, development of high energy and high power energy storage devices is very essential to power portable electronic devices and the the demand is even more pressing to meet the higher end energy needs for vehicular and large-scale grid storage applications. Lithium ion batteries continue to serve as an excellent choice amongst electrochemical energy storage devices for several decades. However, because of the low abundance and increasing demand for lithium metal, a competent alternative for lithium-ion batteries is being sought after, for quite some time now. Among these alternatives, sodium ion battery (SIB) turns out to be a wise choice, owing to the high abundance of sodium on Earth’s crust, suitable redox properties and similar electrochemical behaviour as that of lithium.[1] Though research on SIBs have started in 1970’s, increasing interest on these systems gained attention over the last few years. Several novel cathode materials have been studied for SIBs in recent years,[2] however, development of efficient anode materials remain a big challenge for the successful implementation of Na-ion battery technology. In the continued search for anodes for SIBs, metal and metal-oxide materials are of great interest because of their potential to deliver high, and stable specific capacities. In particular, antimony-based materials (Sb, Sb2O3) have attracted recent attention due to their high theoretical capacities (660 mAh/g for Sb)[3]. Antimony trioxide (Sb2O3), compared to other metal oxides is unique in such a way that the typical volume expansion issue occurring due to sodiation, gets addressed by the formation of a Na2O ‘buffer matrix’ during the coupled conversion-alloying reaction[4]. Herein, we have synthesized Sb2O3 microstructures that exhibits a unique star-shaped morphology, through hydrothermal method. As-synthesized Sb2O3 has been characterized by using powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Detailed studies on its electrochemical performance as anode material for sodium ion batteries have been carried out by using cyclic voltammetry (CV), galvanostatic charge/discharge cycling and electrochemical impedance spectroscopy (EIS) vs. sodium metal electrode in a standard electrolyte of 1 M NaClO4 in propylene carbonate (PC). The as-synthesized Sb2O3 electrode delivered a stable specific capacity of 510 mAh/g for 30 cycles, at a current rate of 50 mA/g. In order to enhance both the specific capacity and the cycling stability, a graphene network that completely encapsulates Sb2O3 microstructures, forming a 3D interconnected network around it, has also been synthesized and tested as anode for sodium-ion batteries. The composite electrode of graphene-Sb2O3 hydrogel, prepared through simple hydrothermal route, showed excellent rate performance owing to the synergistic effects of highly conducting and interconnected graphene networks along with the pristine high capacity Sb2O3microstructures. The results are discussed and the key challenges will be addressed. The whole approach appears to be quite promising towards fabricating high performance anodes for Na-ion batteries.

How the Conditions of Preparation Process Affect the Electrochemical Properties of C/Sn Anode Materials?

How the conditions of preparation process affect the electrochemical properties of C/Sn anode materials? The application of tin in commercially available Li-ion batteries is limited by the poor cyclic performance due to the pulverization caused by cyclic volume changes of elementary cell, during the insertion and extraction processes of lithium ions [1]. Consequently, it results in loss of electrical contact between active material and current collector. One of the ways to overcome this issue is development of tin-carbon nanocomposite, in which nanometric tin grains are encapsulated in a flexible and conductive carbon layers. Such nanocomposites are able to provide appropriate electrochemical properties, only if the formed carbon layer is flexible, has appropriate porosity which featuring local free space to compensate volume changes. The goal of the presented studies is to examine the effects of carbonization temperature as well as origin and content of carbon on the electrochemical performance of carbon-tin nanocomposites. Electrode materials consisted of tin-based nanograins encapsulated in carbon buffer matrix of different origins (starch or water soluble polymer) were obtained in a simple and inexpensive process. The tin precursor (SnO2) was prepared using a modified reverse nanoemulsion method (w/o) and then was coated by a various source of carbon (potato starch or modified poly(N-vinylformamide)) [2,3]. The carbon-tin precursors were pyrolyzed, providing formation of tin-based nanograins encapsulated in buffer matrix. The optimal condition for preparation process was studied using thermal analysis method (EGA-TGA/DTG/SDTA). The structure and the morphology of the samples were characterized by X-Ray diffraction analysis (XRD), low-temperature nitrogen adsorption method (N2-BET) and transmission electron microscopy (TEM) as well. The quality of carbon matrix in resulting composites was determined by Raman spectroscopy (RS) measurements. The working electrodes were prepared from a carbon-tin active material and polyvinylidene fluoride (PVDF) binder in N-methylpyrrolidone (NMP) solvent on copper foil. R-2032 coin type cells were assembled using obtained electrodes combined with Li metal discs as a counter electrode. The electrolyte consisted of a solution of 1M LiPF6in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with EC/DEC molar ratio of 1:1. The lithium cells were characterized by cyclic voltammetry (CV), charge-discharge tests (CELL TEST) as well as electrochemical impedance spectroscopy (EIS). The thermal analysis results enabled determination of the optimal carbonization temperature for obtaining carbon-tin anode materials. N2-BET data as well as TEM images indicated that samples, in which the potato starch was used as a carbon source, have high specific surface area and pore volume as well as reveal presence of the opened pores through the composites. The electrochemical tests showed that better encapsutation of tin nanograins in carbon buffer matrix resulted in higher gravimetric capacity and better cell performance. The C/Sn material in which carbon matrix was fabricated from modified polymer exhibited higher gravimetric capacity and better cell performance (589 mAh g-1 after 70 cycles). The authors acknowledge a financial support from the National Science Centre of Poland under research grant No. 2012/07/N/ST8/03725. [1] S. Ding, X.W. Lou, Nanoscale, 3 (2011) 3586[2] M. Molenda, A. Chojnacka, M. Bakierska, R. Dziembaj, Mater. Technol., 29 (2014) A88[3] A. Chojnacka, M. Molenda, M. Bakierska, R. Dziembaj, Procedia Eng., 98 (2014) 2

Sb-AlxCy-C Nanocomposite Alloy Anodes for Lithium-Ion Batteries

We present a facile approach to making Al-Sb, carbon-modified (Al-Sb-C) nanocomposites for use as new anode materials in lithium-ion batteries (LIB). Alloying is achieved by one step synthesis using high energy mechanical milling (HEMM), producing nanometer-sized alloy particles of Sb-AlxCy-C. Based on electrochemical analyses, we determined that Sb acts as an active material, and both Al and carbon create a hybrid buffering matrix that mitigates the volume expansion of the active material during lithiation/delithiation to a greater degree than that by a pure metallic matrix (AlSb). In addition, we optimized the stoichiometric ratio of Al and Sb with regard to specific capacity and cycling performance. Of the ratios tested, a 1:1 molar ratio of Al and Sb exhibited the best cycling performance (302.5mAhg−1 after 200 charge/discharge cycles). Although our Al-Sb-C composite had low initial coulombic efficiency (∼59%), recovery to∼97% occurred within three cycles, indicating that initial side reactions are quickly reduced over the course of cycling. AlSb-C anodes also showed good rate capability and volumetric capacity. Overall, the new AlSb-C composite is a promising candidate for use as negative electrodes in lithium-ion batteries, providing an alternative to commercially available graphite electrodes.

Dual-buffered SnSe@CNFs as negative electrode with outstanding lithium storage performance

Alloying with Se has been recently found to be an effective way to improve the cycling performance because the reduced-Se formations can act as a buffer matrix against the volume change of electrode for IVA materials or anchors S in Li-S batteries during cycling. In this paper, SnSe nanoparticles were dispersed within a carbon fiber matrix with ball milling and electrospinning methods. The uniform nano-architecture with SnSe nanoparticles homogeneously confined in the carbon matrix, which is revealed by X-ray powder diffraction and scanning electron microscope, provides a stable buffer and good electrical conductor for the lithiation/delithiation process. Moreover, Se-based phase acts as an additional stabilizer to alleviate Sn agglomeration during cycling. Such dual-buffered SnSe/C composites thus deliver large reversible capacity of 840mAh/g with ultrastable cycling performance over 100 cycles and demonstrate good rate capacity.

An influence of carbon matrix origin on electrochemical behaviour of carbon-tin anode nanocomposites

Electrode materials in which tin nanograins are encapsulated in carbon matrix obtained from different origin (starch or modified polymer) were examined. Morphology of the C/Sn composites was observed using transmission electron microscopy (TEM). Electrochemical impedance spectroscopy (EIS) analysis in different states of charge (SOC) at initial cycle together with a long term galvanostatic charge-discharge cycling tests allowed determining the influence of carbon coating origin on the electrochemical behaviour of C/Sn nanocomposites. X-ray photoelectron spectroscopy (XPS) measurements of C/Sn materials before cycling and after first cycle were performed to observe changes in surface composition of the material which occur during electrochemical reaction. The results of surface characterization as well as electrochemical studies of C/Sn nanocomposites indicated that the origin of carbon precursor has a major impact on the composites’ morphology and electrochemical behaviour. Long term galvanostatic charge-discharge cycling tests proved that the carbon obtained from MPNVF precursor allows better encapsulation of tin nanograins in the buffer matrix. Furthermore, according to the XPS studies carbon coating based on MPNVF is more chemically stable versus electrolyte, which contributes directly to the improved protection of active material against physical damage. The charge capacity of MPNVF-based composite was 589mAhg−1 after 70 cycles, which constitutes 59% of theoretical metallic tin capacity.

Employment of SnO2:F@Ni3Sn2/Ni nanoclusters composites as an anode material for lithium-ion batteries

Surface modification of SnO2:F particles which obtained from a large-scale electron cyclotron resonance-metal organic chemical vapor deposition system was carried out by two consecutive processes: electroless plating processing and annealing. First, Ni film on the SnO2:F and Ni nanoclusters were observed after Ni electroless plating; the film on the SnO2:F was then converted to Ni3Sn2 after annealing at 800 °C under an argon atmosphere. A Ni3Sn2 bimetallic structure formed instead of NiO during the annealing process because of the presence of carbon impurities in SnO2:F. The surface-modified Ni3Sn2-covered SnO2:F with Ni nanoclusters (SnO2:F@Ni3Sn2/Ni-nc) was employed as an anode material for lithium-ion batteries. The inactive Ni in Ni3Sn2 acts as a buffer matrix against the Sn active material during the charge-discharge reactions, enhancing the electrochemical performance. The Ni nanoclusters in SnO2:F@Ni3Sn2/Ni-nc perform dual functions: they not only improve the conductivity as the contacting media, but also increase the initial columbic efficiency by the decomposition of Li2O—an electrochemically irreversible material. An outstanding reversible capacity of 600.69 mA h g−1 and a coulombic efficiency of 99.23% for SnO2:F@Ni3Sn2/Ni-nc were observed at the 350th cycle under 200 mA g−1 in the our experimental range.