Ex-situ X-ray Diffraction Analysis Research Articles

Electrochemical characteristics of electrophoretically deposited nickel antimony oxide anode for lithium-ion rechargeable cells

Lithium‐ion batteries (LIB) are widely used energy storage devices for powering portable electronics, electric transportation, and the grid. In this work, the co-precipitation method synthesizes nickel antimony oxide (NiSb2O6; NSO), a relatively new material for LIB anode. The structure of this material is a tri-rutile phase, wherein the lithium (Li) ions are stored via a conversion-type mechanism. The nickel antimony oxide-carbon black (NSO-CB) electrodes are fabricated using electrophoretic deposition. Ex-situ X-ray diffraction analysis reveals the structural breakdown of NSO into nickel oxide (NiO) and antimony pentaoxide (Sb2O5) after the first discharge. In the voltage range 0.01–2.5V vs. Li+/Li, a stable reversible capacity of 574 mAhg−1 is obtained at a specific current of 0.5Ag-1 after 100 cycles. At a high specific current of 5Ag-1, these electrodes deliver a specific capacity of 370 mAhg−1, equivalent to graphite's theoretical capacity. The full-cell of Li(Ni0.8Co0.1Mn0.1)O2//NSO-CB delivers a nominal voltage of 2.83V vs. Li+/Li and can retain up to 84.2 % of its reversible capacity after 50 cycles. Therefore, electrophoretic deposition is established as a prospective processing technique to implement tri-rutile type NiSb2O6 as an anode material for LIBs.

Chimie Douce Derived K-Based P2-Type Transition Metal(s) Layered Oxides for Secondary K-Ion Batteries

Owing to great societal and technological benefits, there has been a remarkable growth in the industrial demand for enhanced energy storage for many target applications including electric vehicles, aerospace applications, and portable electronics. Secondary K-ion batteries (KIBs) are among the potentially inexpensive candidates for energy storage systems beyond state-of-the-art Li-ion batteries (LIBs). Electrochemical cells based on mobile carrier K+ can provide efficient energy storage because of comparative ionic diffusion in bulk and swift charge transfer at the interface due to weak Lewis’s acidity.1,2 Despite various advantages over LIBs and NIBs, the roadblock of practical KIB implementation lies in identifying suitable cathodes that reversibly (de)intercalate K+ at optimum voltage, swift rate, and with prolonged cycle life.Despite constant efforts to develop new cathodes for K+ -ion batteries, several challenges such as low concentrations of K-ions due to strong electrostatic repulsions between the K+ - K+ ions and difficulty in preparation from direct synthesis routes3 limit its practical application. In this scenario, we have adopted the chimie douce (soft chemistry) method to design the novel layered transition metal oxide cathode from the parent P2 type Na-based system. In addition, we have probed the ion exchange mechanism using X-ray diffraction and transmission electron microscopy (TEM) techniques. Rietveld analysis confirmed the structure having a P2-type stacking sequence with hexagonal symmetry and P6/3mmc space group. Further, we have successfully examined the chemical ion-exchanged novel layered P2- K2/3Co1/3Mn2/3O2 as a cathode for KIB at ambient and high temperatures. It delivered a good capacity (~70 mAh/g) with an average redox potential of 3.0 V along with good cycling stability and coulombic efficiency (CE) in temperature ranging from 25-50 ºC. Ex-situ X-ray diffraction analysis and potentio/galvanostatic titration techniques were used to analyse the K+ insertion mechanism. This study can assist in developing new insertion K+ host materials for viable and reliable practical applications.

Enhanced reversible conversion of Cu2S anodes for Na-ion batteries enabled by carbon nanotubes

Sodium-ion batteries (SIBs) with copper(I) sulfide (Cu2S) anodes has been gaining significant attention because of their relatively high capacity and inherent safety. The highly reversible conversion of Cu/Na2S in charging process to pristine Cu2S is essential for its electrochemical properties. Here, we have prepared Cu2S/carbon nanotube (CNT) anode for SIBs, in which highly-conductive CNTs are employed as a catalyst to promote the reversible reaction kinetics of Cu2S anode. By using a combination of electrochemical and ex-situ X-ray diffraction analysis, we demonstrate that Cu2S/CNT anodes can be converted efficiently and reversibly in comparison with a pure Cu2S anode. CNTs have superior electron conductivity and high surface area, and are therefore used for balancing the poor electronic conductivity of Cu2S and discharged products, as well as physically inhibition of the dissolution of sodium polysulfide. Consequently, a partially reversible conversion reaction is enabled during the charging process. In this study, we are contributing to the design of conversion-type materials that feature reversible mechanisms, opening up new possibilities for materials design.

High‐performance electrodes for Li‐ion cell: Heteroatom‐doped porous carbon/ CoS structure and investigation of their structural and electrochemical properties

As an essential class of anode materials, the synthesis and characterization of CoS@ZIF-12-C composite anode materials are reported. The two-step synthesis of CoS nanoparticles embedded in N-doped porous carbon by using a metal-organic framework (MOF) as the template. After structural characterization of CoS@ZIF-12-C composite materials, the main phase was found as CoS with symmetry of P63mmc. Benefiting from the CoS embedded in porous carbon structure, the half Li-ion battery cell tests of CoS@ZIF-12-C composite materials were performed by a 2-electrode method using CR2032 cells, and the capacities of the cells were measured for 200 cycles using 300 mAg−1 and 500 cycles using 1000 mAg−1. The first discharge capacities of the cells for 1000 mAg−1 were found as 458, 1178, and 815 mAhg−1 for CoS@ZIF-12-C-T, T = 700, 800, and 900°C, respectively. An unexpected capacity increase was observed for the CoS@ZIF-12-C-700 and CoS@ZIF-12-C-900 half cells during the cycling. Ex-situ x-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and cyclic voltammetry (CV) analysis were performed after cycling of the cells for explanations of the capacity increase. Ex-situ XRD analysis of these cells showed phase transitions from crystalline to amorphous type structure, and ex-situ FTIR proves the preservation of the CoS phase during the cycling. A redox reaction mechanism was suggested to explain the cells' battery performance by ex-situ XRD analysis.

Influence of the fluoroethylene carbonate on the electrochemical behavior of Bi3Ge4O12 as Lithium-ion anode

Systematic ex-situ X-ray diffraction (XRD) characterization and electrochemical study revealed the key roles that the cut-off voltage and fluoroethylene carbonate (FEC) additive play on improving electrochemical performance of the Bi3Ge4O12-based (BGO) electrode. The ex-situ XRD analysis revealed that BGO particles suffer multiphase transitions during the (dis)charge reactions, being observed some phases as Bi2O2.33, BiLi3, Li2O, Ge4Li15, Ge2Li7, Ge3Li7, Ge5Li22, Ge4Li9, Bi2O3 and GeO2. The electrochemical evaluation exhibited that the addition of 5 v/v% of FEC in 1.0 M lithium hexafluorophosphate (LiPF6) in ethylene carbonate and diethyl carbonate (EC: DEC) at an applied cut-off voltage (1.5 V vs Li/Li+) improves the specific capacity (29%, delivering 479 mAh g−1), capacity retention (12%) and rate capability (369 mAh g−1 at 1000 mA g−1) of the BGO-based electrode. Also, FEC promotes the formation of a stable solid-electrolyte interface (SEI) layer on the anode at a cut-off voltage of 1.5 V vs Li/Li+. It displays the lowest values of SEI and charge transfer (CT) resistances, and electrode polarization, improving the reversibility of the alloying reactions related to Ge-Li and Bi-Li and maintaining their redox activity after 100 cycles, according to dQ dV−1 data.

Study of the Extraction Efficiency of Cathode Material and Its Structural Stability after Extraction

Extraction of the cathode material from disassembled Samsung 18650 cell with LiCoO2 (LCO) chemistry was performed. The effect of dissolving with industrially used organic solvents is compared with the effect of selected ecological options. In successfully separated powders were studied structural changes as a function of aging and storage time. Ex-situ X-ray diffraction analysis was used for observation of differences between materials separated from cell in a fresh state and aged cell. Phase transition happening in the LiCoO2 material during cycling of the battery but also when in contact with air are discussed. Shift of the main peak (0 0 3) and (1 0 4) for the aged cathode material are displayed and discussed.

SnSe nanocomposite chemically-bonded with carbon-coating as an anode material for K-ion batteries with outstanding capacity and cyclability

• A chemically bonded, nanosize SnSe@C composite is fabricated by a scalable method. • The chemically bonded SnSe@C nanocomposite anode is explored for use in K-ion batteries. • The use of amorphous carbon and selenium can significantly suppress the volume expansion of SnSe. • The chemically bonded SnSe@C nanocomposite exhibits excellent cyclability and rate capability. The use of SnSe alloys as anode materials in potassium-ion batteries (PIBs) has recently attracted considerable attention owing to the natural abundance of Sn and Se and the environmental friendliness, high theoretical capacity, and 2D layered structure of SnSe. However, due to the large volumetric change and severe pulverisation during potassiation and depotassiation, they exhibit poor cycling stability in PIBs. In this work, we fabricated a strongly chemically bonded SnSe@C nanocomposite using a simple two-step process consisting of a facile chemical reaction followed by high-energy ball milling. In addition, the introduction of amorphous carbon and selenium effectively suppressed the stress/strain originating from volume expansion during potassiation/depotassiation. The chemically bonded SnSe@C nanocomposite exhibited high initial discharge and charge capacities of 744.8 and 440.7 mAh g −1 , respectively. Even after 50 cycles, it retained a charge capacity of 401 mAh g −1 at 50 mA g −1 , with a coulombic efficiency (CE) of 99.6%. Even at high specific currents of 300 and 500 mA g −1 , the electrode maintained capacities of 270.7 and 203.4 mAh g −1 after 100 and 1000 cycles, respectively, and the CE was almost 100%. Furthermore, a SnSe@C/KFe[Fe(CN) 6 ·xH 2 O] full cell also showed superior cyclability and better rate capability. After 100 cycles, it retained a discharge capacity of 213.9 mAh g −1 at 200 mA g −1 . In addition, the phase transitions in the SnSe@C electrode during potassiation/depotassiation were investigated using ex-situ X-ray diffraction analysis. This work will provide an effective reference for Sn-Se alloy-based anodes for batteries to replace the lithium-ion batteries (LIBs).

Synergetic effects of cation (K+) and anion (S2−)-doping on the structural integrity of Li/Mn-rich layered cathode material with considerable cyclability and high-rate capability for Li-ion batteries

Controlling structural deformations and rapid voltage decay during prolonged cycling has been considered the foremost challenge in improving the cycling and rate performance of Li-rich cathode materials for advanced lithium-ion batteries. In this work, we report an effective strategy for delaying structural variations and inhibiting transition metal migration by co-doping with a large-sized cation and anion. A Li-rich layered composite cathode, namely Li1.165Mn0.495Ni0.165Co0.165O2 (LMNCO; 0.5Li2MnO3-0.5LiMn0.33Ni0.33Co0.33O2) was prepared as the starting material, followed by synthesis of the optimized K+-doped L1.135K0.03Mn0.495Ni0.165Co0.165O2 (LKMNCO) and K+/S2−-doped L1.135K0.03Mn0.495Ni0.165Co0.165O2S0.02 (LKMNCOS) samples via a co-precipitation method. This co-doping strategy retarded structural deformations by significantly suppressing transition metal migration, as evidenced by ex-situ X-ray diffraction analysis at various cycle numbers for the sample cycled at 1.0 C-rate. The K+/S2−-doped sample, i.e., LKMNCOS, exhibited exceptional cycling stability and high-rate capability. Owing to the enhanced structural properties, the co-doped sample delivered an initial charge/discharge capacity of 341/295 mAh g−1 at 0.05 C, with the lowest irreversible capacity loss (ICL) compared to the pristine and K+-doped sample. A discharge capacity of ~129 mAh g−1 was also achieved even after 450 cycles at 1.0 C-rate, with the highest capacity retention ratio (65%) and lowest average capacity decay rate per cycle (~0.07%), suggesting excellent cycling performance. Overall, the results are prospectively beneficial for further development of advanced layered cathodes that undergo layered-to-spinel transformations and demonstrate the efficacy of co-doping for alleviating undesired structural defects.

Study on low-temperature performances of Nb16W5O55 anode for lithium-ion batteries

Niobium tungsten oxide Nb16W5O55 is a competitive anode for lithium-ion batteries, while seldom research on low-temperature electrochemical properties. In this paper, Nb16W5O55 is synthesized by solid phase reaction and the effects of operation temperature (25, 0 and −20 °C) on the coulombic efficiency, cycling stability, rate capacity and crystal structure are studied in detail. At 25 °C, Nb16W5O55 electrode can give good cycling stability of 184 mAh g−1 after 404 cycles and rate capacity of 101 mAh g−1 at 4000 mA g−1. By contrast, the electrochemical properties decrease obviously at subambient temperatures. Electrochemical impedance spectroscopy reveal that the sharp increase of the charge-transfer impedance and the decrease of the solid-phase Li+ diffusion coefficient are the essential factors leading to the deterioration of low temperature performances. However, the low temperature mainly affects specific capacities and rate performances, but has little effect on cyclic stability and crystal structure of Nb16W5O55 electrode, indicated by ex-situ X-ray diffraction analysis. These results provide some new insights for the practical application of Nb16W5O55 anode.

Layered P2-Na2/3Co1/2Ti1/2O2 as a high-performance cathode material for sodium-ion batteries

Abstract Layered oxides are regarded as promising cathode materials for sodium-ion batteries. We present Na 2/3 Co 1/2 Ti 1/2 O 2 as a potential new cathode material for sodium-ion batteries. The crystal features and morphology of the pristine powder were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The cathode material is evaluated in galvanostatic charge-discharge and galvanostatic intermittent titration tests, as well as ex-situ X-ray diffraction analysis. Synthesized by a high-temperature solid state reaction, Na 2/3 Co 1/2 Ti 1/2 O 2 crystallizes in P2-type structure with P 6 3 / mmc space group. The material presents reversible electrochemical behavior and delivers a specific discharge capacity of 100 mAh g −1 when tested in Na half cells between 2.0 and 4.2 V (vs. Na + /Na), with capacity retention of 98% after 50 cycles. Furthermore, the electrochemical cycling of this titanium-containing material evidenced a reduction of the potential jumps recorded in the Na x CoO 2 parent phase, revealing a positive impact of Ti substitution for Co. The ex-situ XRD measurements confirmed the reversibility and stability of the material. No structural changes were observed in the XRD patterns, and the P2-type structure was stable during the charge/discharge process between 2.0 and 4.2 V vs. Na + /Na. These outcomes will contribute to the progress of developing low cost electrode materials for sodium-ion batteries.

Synthesis and electrochemical characterization of stoichiometric Cu2S as cathode material with high rate capability for rechargeable lithium batteries

Abstract Synthesis of stoichiometric copper sulfide (Cu 2 S) was studied by spray pyrolysis (SP) with heat treatment for different Cu/S molar ratios in the starting solution and different synthesis and annealing temperatures. The sample prepared via SP at 400 °C and then annealed at 460 °C for 2 h showed the stoichiometric Cu/S ratio, which was verified by inductively coupled plasma-optical emission spectroscopy. The X-ray diffraction (XRD) peaks of the sample were indexed to the monoclinic structure with space group P 2 1 / c . The electrochemical performance of the stoichiometric Cu 2 S electrode was investigated by a cycle test and differential capacity analysis. The Cu 2 S electrode coated on an Al foil exhibited a first discharge capacity of 335 mAh g −1 at a charge-discharge rate of 0.1 C, which corresponds to 99.4% of its theoretical capacity. However it showed poor reversibility owing to the corrosion of Al foil by Cu. In contrast, the Cu 2 S electrode coated on Cu foil demonstrated stable cyclability at high charge-discharge rates of up to 30 C. Exsitu XRD analysis showed that a phase transformation from the monoclinic Cu 2 S structure with the space group P 2 1 / c to the tetragonal Cu 1.96 S structure with the space group P 4 3 2 1 2 gradually progressed during the initial five cycles.

Sodium Insertion/Extraction in Carbon-Coated Nanoscale Anatase TiO2

Rechargeable sodium batteries, as the replacement of rechargeable lithium batteries, are attracting much attention for large-scale applications such as electric vehicles and stationary energy storage due to the abundant resource of sodium compared to lithium. Up to now, there are only a few materials which have reasonable performances as negative electrodes of rechargeable sodium batteries, such as alloy materials [1], hard carbon [2], and sodium titanium oxides [3]. Recently, TiO2, an attractive alternative negative electrode material to graphite for rechargeable lithium batteries, was also investigated for rechargeable sodium batteries [4, 5]. However, the reported reversible capacities of TiO2 electrodes are less than 200 mAh g-1 and the Na insertion/extraction mechanism is still unclear. In the previous study, carbon-coated anatase TiO2 (TiO2/C) nanopowders were investigated as negative electrode material for rechargeable sodium battery with Na[FSA]-[C3C1pyrrr][FSA] (FSA = bis(fluorosulfonyl)amide; C3C1pyrr = N-methyl-N-propylpyrrolidinium) ionic liquid electrolyte [6]. In the present study, the electrochemical performance of TiO2/C electrode was further investigated in Na[FSA]-[C3C1pyrrr][FSA] ionic liquid electrolyte, and the Na insertion/extraction mechanism was explored. The TiO2/C electrode shows a high reversible discharge capacity of 275 mAh g-1 at 10 mA g-1 at 363 K. The observed capacity is higher than that reported for anatase TiO2 nanorods (193 mAh g-1 at 10 mA g-1) in organic electrolytes at room temperature [5]. Moreover, this capacity is comparable to that of a hard carbon negative electrode (260 mAh g-1) in Na[FSA]-[C3C1pyrrr][FSA] electrolyte [7]. Since the density of anatase TiO2 (ca. 3.9 g cm-3) is much higher than that of hard carbon (ca. 1.52 g cm-3), the TiO2/C nanopowder electrode is a promising negative electrode material for the rechargeable sodium batteries with high volumetric energy densities. The Na insertion/extraction mechanism was investigated by means of ex-situ X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) spectroscopy and electron diffraction. Ex-situ XRD analysis of the TiO2/C electrodes in the different charged/discharged states show that during the charge process, the anatase TiO2 crystal phase disappears and a new crystal phase is formed. During the discharge process, the newly formed crystal phase disappears and no anatase TiO2 phase appears again. According to the TEM, EDX and electron diffraction studies, the fully discharged TiO2/C electrode is suggested to consist of amorphous TiO2, amorphous Na2TiO3 and cubic TiO phases, and the crystal phase in the fully charged TiO2/C electrode is possibly a solid solution of cubic Na2TiO3 and cubic TiO phases. Thus, amorphous TiO2, amorphous Na2TiO3 and cubic TiO are regarded as active electrode materials, and reversibly react with Na ions to form Na2TiO3•TiO solid solution. The TiO2/C negative electrode also exhibits a high rate capability and good cycling performance. When the charge-discharge rate is increased, the shapes of the charge-discharge curves remain unchanged. The discharge capacities decrease gradually with an increase in the current rate. The TiO2/C electrode shows reversible discharge capacities of 174 and 93 mAh g-1 at current rates of 500 and 2000 mA g-1, respectively, corresponding to about 69 and 37% of the capacity at 20 mA g -1. The discharge capacity is 174 mAh g-1 after 400 cycles at a current rate of 200 mA g-1, exhibiting only 10% drop in capacity. After 1000 cycles, the capacity decreases by approximately 21%. Acknowledgements This study was partly supported by the Advanced Low Carbon Technology Research and Development Program (ALCA, No. 3428) of the Japan Science and Technology Agency (JST) and the “Elements Strategy Initiative to Form Core Research Center" program of the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT).

Effects of TiO2 phase on the performance of Li4Ti5O12 anode for lithium-ion batteries

In recent reports, doping TiO2 phases into Li4Ti5O12 system is an effective approach to improve the electrochemical performance of Li-titanate batteries, and the explanations of this phenomenon are mainly focused on the functions of TiO2 phases at low current density. In this paper, through the ex-situ X-ray diffraction analysis, it is revealed that the crystal structure of rutile-TiO2 in Li4Ti5O12-TiO2 electrode is very different after cycles at high and low current density. Such results can beneficially help us have a fully understanding of Li-ion storage mechanism in multi-phase electrode. Moreover, three kinds of dual and ternary phase Li4Ti5O12-TiO2 composites with the same morphology of nanosheets are fabricated and their electrochemical performances are compared for the first time. These Li4Ti5O12-TiO2 composites exhibit excellent performance at high current density: Li4Ti5O12-rutile-anatase TiO2 electrode delivers a reversible capacity of about 125 mA h g−1 with a total capacity decreasing less than 5% after 2000 cycles at 30 C. Li4Ti5O12-rutile TiO2 nanosheets electrode tested from 1 to 50 C with 100 cycles for each rate delivers a capacity of 108 mA h g−1 at high rate of 50 C, which is 69.2% of the specific capacity at 1 C.

Ex-situ X-ray diffraction analysis of electrode strain at TiO2 atomic layer deposition/α-MoO3 interface in a novel aqueous potassium ion battery

The effect of thin film TiO2 atomic layer deposition (ALD) coating on induced material strain is investigated utilizing ex-situ XRD analysis of a layered-structured α-MoO3 anode. Electrode material lattice expansion is quantified by the examination of ex-situ XRD peak shift, and is performed on both potassiated and potassium-deficient electrodes. Observations of TiO2 ALD coated electrodes reveal significant strain reduction of the electrode material resulting in an increase in the life-cycle of the aqueous cells. The presence of the 10 nm thick amorphous TiO2 ALD layer is found to withhold considerable lattice strain at the thin-film/electrode interface, reducing lattice deformation by 68.2% and exhibits a capacity retention 2.5 times greater than that of the pristine electrode after 20 cycles of operation. The influence of the ALD coating on charge/discharge kinetics and cell capacity is also examined.

Vanadium Oxyfluoride/Few-Layer Graphene Composite as a High-Performance Cathode Material for Lithium Batteries.

Metal oxyfluoride compounds are gathering significant interest as cathode materials for lithium ion batteries at the moment because of their high theoretical capacity and resulting high energy density. In this regard, a new and direct approach is presented to synthesize phase-pure vanadium oxyfluoride (VO2F). The structure of VO2F was identified by Rietveld refinement of the powder X-ray diffraction (XRD) pattern. It crystallizes in a perovskite-type structure with disorder of the oxide and fluoride ions. The as-synthesized VO2F was tested as a cathode material for lithium ion batteries after being surface-coated with few-layer graphene. The VO2F delivered a first discharge capacity of 254 mA h g(-1) and a reversible capacity of 208 mA h g(-1) at a rate of C/20 for the first 20 cycles with an average discharge voltage of 2.84 V, yielding an energy density of 591 W h kg(-1). Improved rate capability that outperforms the previous report has been achieved, showing a discharge capacity of 150 mA h g(-1) for 1 C. The structural changes during lithium insertion and extraction were monitored by ex-situ XRD analysis of the electrodes discharged and charged to various stages. Lithium insertion results in an irreversible structural change of the anion lattice from (3)/4 cubic close packing to hexagonal close packing to accommodate the inserted lithium ions while keeping the overall space-group symmetry. For the first time we have revealed a structural change for the ReO3-type structure of as-prepared VO2F to the RhF3 structure after lithiation/delithiation, with structural changes that have not been observed in previous reports. Furthermore, the new synthetic approach described here would be a platform for the synthesis of new oxyfluoride compounds.

Effect of Nb doping on electrochemical properties of LiNi1/3Co1/3Mn1/3O2 at high cutoff voltage for lithium-ion battery

Nb doped cathode materials with the formula LiNi1/3Co1/3Mn1/3−xNbxO2 (x=0, 0.01, 0.02, 0.03) have been prepared successfully by sol–gel method. The effect of Nb substitution on the crystal structure and electrochemical properties of LiNi1/3Co1/3Mn1/3O2 were studied systematically by X-ray diffraction (XRD) and various electrochemical measurements. The results showed Nb substitution played an important role in the good cycling performance of LiNi1/3Co1/3Mn1/3O2. Charge/discharge tests revealed that LiNi1/3Co1/3Mn1/3–0.02Nb0.02O2 showed a capacity retention of 94.1% at 1C after 50 cycles in a high cutoff voltage range (3.0–4.6V), while discharge capacity of LiNi1/3Co1/3Mn1/3O2 remains only 89.4% of that at 1C. Ex-situ XRD analysis and EIS analysis indicated that the improved electrochemical properties of Nb-doped sample result from the more stable structure and lower resistance during the electrochemical cycling.

Enhanced Electrochemical Performance of Sb and Sb2O3 Composite By Electrodeposition for Na-Ion Batteries

Introduction As lithium reserves in natural resource cannot keep up with Li-ion battery market, concerns about a continuous supply of lithium and increasing of lithium price are emerging. Na-ion batteries are considered as an alternative to Li-ion batteries for large-scale applications due to the low-cost and abundance of sodium resources. While a variety of cathodes materials for Na-ion batteries have been reported [1], the availability of anode materials is much rarer. Among the candidates, Sb is very attractive anode materials for Na-ion battery due to high theoretical capacity (660 mAh/g).[2] Currently, sodium storage materials through conversion reaction mechanism have been reported, such as Sb2O4 [3], Sn-SnS-C[4], rGO/Sb2S3 [5], etc. These materials can give higher capacity because of the lower weight of the non-metal elements, as well as improvement of mechanical stability due to buffer matrix. Therefore, in this study, metallic antimony (Sb) and antimony trioxide (Sb2O3) composite were prepared by the electrodeposition from potassium antimony tartrate bath and electrochemical properties of Sb/Sb2O3 composite for Na-ion batteries are investigated. Additionally, the phase transition processes in sodium insertion/deinsertion of Sb/Sb2O3composite is investigated by ex-situ analysis. Experimental Sb/Sb2O3electrodes were prepared by the electrodeposition at a constant current density in a potassium antimony tartrate bath. The electrodeposition was conducted using a standard three-electrode cell; Cu foil was used as a cathode, pure Pt sheet was used as an anode, and a saturated calomel electrode (SCE) was used as a reference electrode. The solution was stirred magnetically at 240 rpm and the electrodeposition was performed at room temperature.The electrochemical properties of the Sb/Sb2O3 electrodes were investigated using two-electrode cell with electrode area of 1 cm2 assembled in an Ar-filled glove box. The cell consists of the Sb/Sb2O3 electrodes as a working electrode, a pure Na as a counter electrode and 1 M NaClO4 dissolved in a mixture of propylene carbonate (PC) and 0.5 vol. % of fluoroethylene carbonate (FEC) as an electrolyte. The electrochemical test was conducted by constant current with a current density of 60 mA/g in the potential range of 0.01 ~ 2.5 V vs. Na/Na+ at 25 oC. The phase transition with cycling was examined by ex-situ X-ray diffraction (XRD), and Raman spectroscopy. Results and discussion Figure 1.(a) shows the surface morphology of Sb/Sb2O3 composite prepared by the electrodeposition. Sb/Sb2O3 composite exhibits granular texture and deposited uniformly along the Cu substrate. Energy dispersive spectroscopy (EDS) analysis shows that the electrodeposits are composed of antimony and oxygen. Formation of crystalline Sb2O3 (cubic) as well as metallic Sb (rhombohedral) was confirmed by XRD analysis. Other impurity phases are not detected. (Figure 1. (b))The Sb/Sb2O3 electrode shows improved cycling stability rather than pure Sb electrode. The Sb/Sb2O3 electrode maintains a capacity of 613.2 mAh g-1 after 50 cycles that corresponds to 98.78 % of its initial charge capacity (620.8 mAh g-1) with a high coulombic efficiency above 95 %. In order to determine the reaction reversibility of Sb2O3 with Na+ ion, ex-situ XRD and Raman spectroscopy analysis with cycling were performed. It is confirmed that Sb2O3 reacts with Na+ ion reversibly by ex-situ analysis and reversible formation of Na2O by conversion reaction was expected. Accordingly, superior cycle stability of Sb/Sb2O3 composite results from Na2O which acts as buffer matrix and prevents agglomerating Sb particles. Figure 1 . (a) SEM images and (b) XRD patterns of Sb/Sb2O3composite References [1] M. D. Slater, D. Kim, E. Lee, C. S. Johnson, Advanced Functional Materials 2013, 23, 947.[2] J. Qian, Y. Chen, L. Wu, Y. Cao, X. Ai, H. Yang, Chemical Communications 2012, 48, 7070.[3] Q. Sun, Q. Q. Ren, H. Li, Z. W. Fu, Electrochemistry Communications 2011, 13, 1462.[4] L. Wu, X. Hu, J. Qian, F. Pei, F. Wu, R. Mao, X. Ai, H. Yang, Y. Cao, Journal of Materials Chemistry A 2013, 1, 7181.[5] D. Y. W. Yu, P. V. Prikhodchenko, C. W. Mason, S. K. Batabyal, J. Gun, S. Sladkevich, A. G. Medvedev, O. Lev, Nat Commun 2013, 4.

Solution Mediated Polymorphic Transformation: Form II to Form III Piracetam in Ethanol

The polymorphic transformation of the Piracetam (2-oxo-1-pyrrolidine acetamide) metastable form II to the stable form III has been investigated in ethanol, by ex-situ X-ray diffraction analysis of the solid phase combined with in situ infrared analysis of solution concentrations. The main factors studied were temperature, mass of solids loading, and pretreatment of the loaded solids. At increasing temperature, the solubility ratio decreases and, hence, the transformation driving force decreases. In spite of this, the nucleation induction time of the stable form and the time for completion of the transformation decrease with increasing temperature. The transformation rate is governed by the nucleation and growth of the stable form, with nucleation likely to take place on the faces of the metastable form crystals and the rate increasing with surface area of the metastable form.

Spectroscopic ellipsometry applied for in-situ control of lattice matched III-V growth in MOVPE

Stoichiometry control of lattice matched compound semiconductors during growth is still a challenge for in situ optical techniques. This is because the energy shifts of the semiconductor optical gap induced by strain and stoichiometry compensate one another. Thus conventional critical point analysis for composition measurement is practically impossible. The remaining response of the measured ellipsometric parameters is very small but can be resolved when the signal-to-noise ratio of the ellipsometer is sufficiently high. We exploit this for the closed-loop control of In x Ga 1− x As growth on InP where the trimethylindium (TMIn) flux was directly controlled by the measured optical response in order to reach the desired lattice matched composition ( x=0.53). Ex-situ X-ray diffraction analysis verified ellipsometrically controlled lattice matched growth.