Galvanostatic Charge-discharge Studies Research Articles

Nanocomposites of Copper Sulphide and Graphene Oxide for High-Performance Supercapacitors

Supercapacitors or electrochemical capacitors are receiving greater interest because of their high-power density, long life, low maintenance, and safer operation. The low energy density of such devices needs to improve. In this work, copper sulfide (CuS), a cheap and environment-friendly compound, is used along with graphene oxide (GO) to provide high energy and power densities. CuS nanoparticles and its nanocomposites with GO was synthesized using a facile method for supercapacitor applications. For the synthesis of CuS, an appropriate amount of copper acetate was dissolved in a water-butanol solution for 30 minutes followed by the addition of thiourea. The final solution was then transferred into Teflon-lined stainless-steel autoclave and heated at 180oC for 24 hours. The resulting participate of CuS was recovered using a centrifuge, washed with DI water, and dried in air for 24 hours. A similar procedure was followed for the synthesis of CuS-GO nanocomposite with the addition of appropriate amount of GO in the water-butanol solution prior to the addition of copper acetate and thiourea. Phase purity of the synthesized materials was determined by using X-ray diffraction (XRD) studies. XRD patterns of CuS showed the peaks at 2θ angle of 10.38o, 28.42o, 28.88o, 32.48o, 33.18o, 46.54o, 48.28o, and 59.68o corresponding to (100), (101), (102), (006), (110), (108), (116) planes, respectively, which indicates the covellite CuS hexagonal structure [1,2]. There were no additional peaks found in the XRD pattern of CuS-GO composite, confirming the phase purity of the synthesized materials. TEM images revealed nano-scale morphology of the synthesized particles. The particle size of CuS and CuS/GO composite were found as 95.11 nm, and 64.70 nm, respectively. All the electrochemical measurements were conducted in standard three-electrode configuration, using a platinum wire as a counter electrode and Hg/HgO as a reference electrode. CuS and its composite with graphene oxide on nickel foam were used as working electrodes. All the electrochemical measurements were performed in 3M KOH solution. Electrochemical properties of the synthesized samples were investigated using cyclic voltammetry and galvanostatic charge-discharge studies. The specific capacitance was calculated from cyclic voltammogram, obtained at various scan rate between 10 - 300 mV/s. The specific capacitance of CuS and CuS-GO nanocomposite was found to be 400 and 600 F/g, respectively at a scan rate of 10 mV/s. The detailed results on synthesis, physical, and electrochemical characterization will be presented.

Fabrication of high energy and high power density supercapacitor based on MnCo2O4 nanomaterial

The supercapacitor electrode material MnCo2O4 was successfully prepared by a facile solution combustion method. XRD, FT-IR, UV-DRS, SEM and TEM instruments were employed to study the physico-chemical and surface properties of the MnCo2O4. The electrochemical performance of the MnCo2O4 electrode was evaluated by cyclic voltammetry and galvanostatic charge-discharge studies. The modified electrode shows an excellent cyclic behaviour with a wide potential window of −1.2 to 1.5V. The highest specific capacitance value of MnCo2O4 at the scan rate of 10 mVs−1 was 270 Fg-1 and it shows the enhanced capacitive character of the electrode material. The measured capacitance fading after 1000 cycles was only about 7.6% and this shows the excellent cyclic stability of the material. The maximum energy and power density calculated from the constant charge-discharge cycles were 14.85 Wkg-1 and 495 Whkg−1 respectively. The electrochemistry of MnCo2O4 proves that it can be used as a high energy and power density electrode material for high performance supercapacitors.

Preparation, characterization and comparative electrochemical studies of MgMXMn2-XO4 (x=0, 0.5; M= Ni/Co)

In this study, the structural, electrical and electrochemical properties of the compounds MgMxMn2-xO4 [M = Ni/Co: x = 0,0.5] were investigated by preparing the materials by the citric acid assisted simple, cost effective sol-gel method. X-ray Diffraction (XRD) confirmed that Ni/Co doping created a phase transition of MgMn2O4 from tetragonal spinel-structure with a space group of I41/amd to a cubic spinel structure with a space group of Fd-3m. HRTEM and SAED analysis showed the bare compound to be polycrystalline and doped compounds to be single crystalline in nature. SEM analysis showed the agglomerated submicron sized particles for all the three compounds. The electrical properties of the compounds have been investigated through AC impedance spectroscopy. The electrical conductivity of the bare compound MgMn2O4 was found to be 5.09 × 10−6 S/cm at 583 K. Cyclic Voltammetry (CV) and Galvanostatic Charge-Discharge (GCD) studies made by the three electrode system shows that all the samples under study could undergo reversible redox reactions in the aqueous magnesium nitrate solution. MgMn2O4 sample exhibited highest specific discharge capacity of 263 mAh/g at the current density of 30 mA/g.

Camphor sulphonic acid doped novel polycarbazole-g-C3N4 as an efficient electrode material for supercapacitor

The synergistic effect of electric double layer capacitor (EDLC) and pseudo capacitive behaviour of camphor sulphonic acid (CSA) doped PCz-g-C3N4 electrode material for supercapacitor application is studied. The electrochemical behaviour of the prepared electrode material was analysed via cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge studies. The electrode material responded with the specific capacitance calculated to be 199 F g−1 at 1 A g−1 for negative potential window which proves that the material is highly efficient. The PCz-g-C3N4 nanocomposite was synthesized by chemical oxidative polymerization of carbazole using ammonium persulfate as oxidizing agent in ethanol and water media. The structure and elemental analysis were investigated by X-ray diffraction (XRD) and energy dispersive X-ray (EDX) spectroscopy. Fourier transform infrared (FT-IR), high resolution scanning electron microscopy (HR-SEM), high resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy(XPS) techniques are also used to analyse the samples. The active PCz-g-C3N4 electrode material has porous structure and is a prominent material for supercapacitor application.

Soft chemical routes to electrochemically active iron phosphates.

New iron phosphates with related structures have been synthesized using hydrothermal and ion-exchange routes, and their electrochemical properties were investigated. First, NaFe(HPO4)2 was synthesized employing a hydrothermal route and its structure was determined from single-crystal X-ray diffraction data. Subsequent Na+ and partial proton ion exchange with Li+ ion produced a known phase, Li2Fe(H0.5PO4)2, and complete deprotonation of Li2Fe(H0.5PO4)2 with Li+ by employing a solid-state ion-exchange route produced the new phase Li3Fe(PO4)2. The structure of the latter was solved from synchrotron powder X-ray data by employing ab initio methods. All of these phases are highly crystalline, built up of similar connectivities between FeO6 octahedra and PO4 tetrahedral units. Magnetic susceptibility measurements and room-temperature 57Fe Mössbauer spectroscopic studies confirm the 3+ oxidation state of the compounds and their antiferromagnetic ordering with Li2Fe(H0.5PO4)2 showing some interesting metamagnetic behavior. The compounds are stable up to 400 °C and undergo facile electrochemical lithium/sodium insertion through the reduction of Fe3+ to Fe2+. Galvanostatic charge-discharge studies indicate that up to 0.6 lithium ion and 0.5 sodium ion per formula unit can be inserted at average voltages of 3.0 and 2.75 V for lithium and sodium ion batteries, respectively, for NaFe(HPO4)2. The partially Li ion exchanged compound Li2Fe(H0.5PO4)2 showed better cycle life and experimentally achievable capacities up to 0.9 Li insertion with strong dependence on particle size. The electrochemical Li insertion in Li3Fe(PO4)2 was also investigated. The electrochemistry of these three related phases were compared with each other, and their mechanism of Li insertion was investigated by ex situ PXRD.

Solid polymer electrolytes with poly(vinyl alcohol) and piperidinium based ionic liquid for Li-ion batteries

We report the preparation of a polymer electrolyte using poly(vinyl alcohol) (PVA) as the polymer network, piperidinium cation based ionic liquid (IL) as a plasticizer and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the lithium source. Various concentrations of the LiTFSI salt were added to the IL to prepare lithium-IL solutions. Polymer membranes were prepared by adding these lithium IL solutions to PVA by solvent casting technique. The melting temperature (Tm) of PVA membrane decreases with the addition of IL confirming that the IL acts as a plasticizer leading to an increase in ionic conductivity. Tan delta (from dynamic mechanical analysis) of the polymer-IL samples show broader α relaxation peaks than pure PVA confirming the increase in segmental motion of the polymer chain. The maximum room temperature conductivity was observed for the membrane with 0.6 m PMPTFSI-LiTFSI (1.2 mS cm−1) and could be correlated to the low viscosity, large number of mobile lithium ions and mobility of lithium ions. Cyclic voltammetry of the polymer electrolytes confirms the reversible redox process (lithium stripping and deposition) and linear sweep voltammetry shows that these electrolytes are stable up to 4.7 V. Galvanostatic charge-discharge studies of the polymer electrolytes in coin cell with LiFePO4 (LFP) cathode delivered a capacity of about 180 mAh g−1 at 60 °C. The cell has an excellent capacity retention property which is observed in retaining the capacity value (170 mAh g−1) equivalent to 99% columbic efficiency after 50 cycles.

Polysulfide diffusion controlled, non-shrinkable, porous, PAN/PES electrospun membrane for high energy Li-S battery application

In recent years, Li-S battery has received much attention owing to its high theoretical specific capacity of 1675 mAh g−1. However, diffusion of the polysulfide across the electrodes during charge-discharge process strictly affects the cell characteristics. To avoid such ion diffusion, usage of an appropriate separator is highly appreciable. A suitable separator, particularly in Li-S system, should act as selective ion diffusion medium and as better electrolyte absorber during the cell operando. Hence, in the present study, polyacrylonitrile-polyethersulfone (PAN/PES) based blend electrospun membrane is developed and employed as separator for the very first time in Li-S system. Physical characteristics such as shrinkage, electrolyte uptake, porosity were studied using various techniques. Concurrently, feasibility of the prepared electrospun membrane in Li-S battery is analysed using various electrochemical studies such cyclic voltammetry, galvanostatic charge-discharge studies and electrochemical impedance spectroscopy. The obtained characteristics of the synthesised membrane were also compared with the commercial Celgard 2320 separator. It is noteworthy to mention that the cell delivered an initial specific capacity of 1175 mAh g−1 at 0.1C for synthesised membrane which surpasses that of commercial one. Upon prolonged cycling, the cell showed more than 90% coulombic efficiency; thus, it clearly reveal the better Li ion diffusivity and control of polysulfide diffusion as compared to commercial separator.

Electrochemistry of Illusive Barbosalite, Fe2+Fe3+2(PO4)2(OH)2: An Iron Phosphate Related to Lipscombite Structure

Barbosalite, an iron hydroxy-phosphate belonging to the family of Lazulite has been synthesized using hydrothermal route and its electrochemical property is investigated for the first time with respect to Li-ion batteries. The structure, as determined from single-crystal X-ray diffraction data, built up of undulating layers of FeO6 octahedra, consisting of trimers and PO4 tetrahedral units. Magnetic susceptibility measurements show predominant overall anti-ferromagnetic interactions and room temperature 57Fe Mössbauer spectroscopic studies confirm the mixed 3+ and 2+ oxidation states of Fe in the compound. The compound is stable up to 400°C and undergo facile electrochemical lithium insertion. Galvanostatic charge-discharge studies indicate that up to 0.7 lithium ions per formula unit can be inserted at an average voltage of 2.6 V. The barbosalite phase seems to undergo irreversible phase transition upon lithiation as evident from the powder X-ray diffraction pattern of the reduced and oxidized phases.

Facile solvothermal synthesis and high supercapacitor performance of NiCo2O4 nanorods

NiCo2O4 nanorod arrays were synthesized employing a facile low-temperature solvothermal approach, followed by post-calcination treatment. The structural, morphological and elemental characterizations were done by diffraction, microscopic and spectroscopic techniques. The prepared sample was studied as an active electrode material for supercapacitor application in 2 M KOH aqueous electrolyte. The cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectral (EIS) studies were carried out to know the electrochemical activity of the prepared material. From the CV study, a high capacitance value of 440 F g−1 was obtained at a scan rate of 5 mV s−1 in a 3-electrode method. Apart from high capacitance value, the prepared electrode depicted 94% initial capacitance retention value after 2000 charge-discharge cycles at a current density of 8 A g−1. The fabricated symmetrical supercapacitor depicted a high energy density of 12.6 Wh kg−1 and a high power density of 4003 W kg−1. This was attributed to the better electrical conductivity of NiCo2O4 nanorods.

Electrochemical performance of hydrothermally synthesized flower-like α-nickel hydroxide

Hydrothermally prepared α-nickel hydroxide had strong hydroxide bond vibrations and carbonate ion is intercalated in the basal spacing between the hydroxide layers. The morphological analysis reveals the flower-like morphology of the material. The electrochemical performance of the material was studied using 2 M KOH as the electrolyte. Cyclic voltammetry curves demonstrate the pseudocapacitive nature of the electrode material. Using galvanostatic charge-discharge studies, the specific capacitance of prepared α-nickel hydroxide was measured to be 516 F g−1 at a current density of 0.5 A g−1. The material exhibited efficient rate stability with 84% capacitance retention even after 1000 redox cycles. A detailed study was performed to correlate the structure and surface morphology of the synthesized α-nickel hydroxide with its redox behavior, specific capacitance, and rate stability. The note-worthy specific capacitance, rate stability, and remarkable morphology supporting efficient ion movement validate that the prepared α-nickel hydroxide could be a significant candidate for supercapacitor electrodes.

Sonochemically recovered silver oxide nanoparticles from the wastewater of photo film processing units as an electrode material for supercapacitor and sensing of 2, 4, 6-trichlorophenol in agricultural soil samples

The present work describes the sensing application and supercapacitive behavior of silver oxide nanoparticles recovered from wastewater of photo film processing units via one-pot green sonochemical recovery process. The recovered silver oxide nanoparticles (Ag2O NPs) were characterized by spectral techniques such as FT-IR, Raman, UV–Vis and analytical tools such as XRD, FE-SEM, TEM, EDX, XPS and BET. In view of Ag2O NPs as electrode material with wide technological applications, the recovered Ag2O NPs were examined for their sensing and supercapacitive behavior. The developed sensor was explored to detect 2, 4, 6-trichlorophenol, and as expected it shows moral parameters which are required of an effective sensor. Therefore, it was exploited for the quantification of 2, 4, 6-trichlorophenol in soil samples from the agricultural area. Cyclic voltammetric (CV), Galvanostatic Charge-Discharge (GCD) and Electrochemical Impedance Spectroscopic (EIS) studies on the recovered Ag2O NPs coated Ni foam electrode depicted the pronounced capacitive behavior. The GCD studies revealed an enhanced electrochemical performance, particularly with the large specific capacitance of 530 F/g at a current density of 1 A/g. The cyclic stability of the electrode material was identified with 88% retention in specific capacitance even after 5000 GCD cycles. These results strongly proved that the recovered Ag2O NPs are potential candidates for sensing and supercapacitor applications.

Synthesis and characterization of carbon supported V2O5 nanotubes and their electrochemical properties

Vanadium pentoxide (V2O5), as one of the most important electrode materials for lithium ions batteries, attracts tremendous attention. Here, carbon supported V2O5 hollow nanotubes are synthesized using carbon fibers as templates through solvothermal reaction with subsequent annealing treatment. Morphological features of the samples are investigated by field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). X-ray diffraction (XRD) patterns confirm the formation of phase-pure structure. Elemental mapping and XPS studies are used to confirm the existence of carbon and V4+ in nanotubes. Electrochemical Li insertion behavior of nanotubes are explored as cathode in half cell configuration (vs. Li) using cyclic voltammetry, galvanostatic charge-discharge studies and rate tests. The V2O5 hollow nanotubes display a good cycling performance with a specific capacity of 237 mA h g−1 after 50 cycles at 100 mA g−1 in the voltage range of 2.0-4.0 V. Moreover, the nanotubes cathode delivers specific capacities of 165.8, 140.3 and 109.6 mA h g−1 at 1000, 2000 and 5000 mA g−1, respectively, indicating a desirable rate capability. The good electrochemical performance of carbon supported V2O5 hollow nanotubes can be attributed to the unique hollow nanotubes and the existence of carbon and V4+.

Pulse-reversal deposition of Ni3S2 thin films on carbon fiber cloths for supercapacitors

In this present work, nanoporous net-like Ni3S2 thin films were successfully electrodeposited on flexible carbon fiber cloths (CFCs) through a facile one-step pulse-reversal electrodeposition (PR) method. The effects of pulse frequency of the PR deposition mode on the microstructure evolution of the deposits and their corresponding capacitance properties as electroactive electrodes for supercapacitors were investigated systematically. After the optimization of pulse frequency, the optimized flexible Ni3S2 electrode was found to be with the unique well-interconnected net-like nanoporous. The subsequent galvanostatic charge-discharge studies showed that the optimized Ni3S2 electrode delivered a superior specific capacitance of about 600 F/g at a constant current density of 1 A/g with 75% capacitance retention even after at relatively high current density of 8 A/g. Moreover, the optimized Ni3S2 electrode retained the 84.6% of initial discharge capacitance after the cycling test at current density of 2 A/g for 2000 cycles. According to the aforementioned electrochemical performance, the NSPR-2 electrode with nanoporous net-like nanostructure could be a potential binder-free electrode for flexible supercapacitors.

Facile microwave-hydrothermal synthesis of NiS nanostructures for supercapacitor applications

In the present investigation, nickel sulphide nanostructures (M, H and MH) have been synthesized through three different methods viz., microwave, hydrothermal and a combination of microwave and hydrothermal. The effect of preparation method on nickel sulphide nanostructures has been investigated through structural, morphological and electrochemical studies. XRD patterns reveal orthorhombic phase of Ni9S8 in the case of M while H and MH exhibit hexagonal NiS structure. SEM micrographs of M, H and MH indicate the nanoflake, spherical and layered structure, respectively. The electrochemical studies have been carried out via cyclic voltammetry, charge-discharge studies and electrochemical impedance analysis. MH provides the largest specific capacitance of 964 F g−1 (from galvanostatic charge-discharge studies at a specific current of 1 A g−1 in 2 M KOH electrolyte) combined with a charge transfer resistance of 0.6 Ω. The MH electrode could provide undiminished capacity retention after 2000 cycles. A symmetric supercapacitor device provides maximum specific capacitance of 119 F g−1 at 1 A g−1 with energy and power densities of 16.5 W h kg−1 and 250 W kg−1. These results imply that MH nanostructure is well suited as a supercapacitor electrode material.

Reversible Mg insertion into chevrel phase Mo6S8 cathode: Preparation, electrochemistry and X-ray photoelectron spectroscopy study

Electrical energy storage is absolute for complete usage of all renewable energy sources. Herein, we have studied the electrochemical performance of Chevrel phase Mo6S8 as cathode material towards rechargeable Mg battery. Solution chemistry route is adopted for the synthesis of Mo6S8. The morphology, phase purity is analyzed by Scanning Electron Microscopy, Transmission Electron Microscopy, and X-Ray Diffraction techniques. The cyclic Voltammetry and Galvanostatic charge-discharge studies confirmed the reversibility of Mg-ion insertion. Herein, Mo6S8 cubes show excellent capacity retention of 70 mAh g−1 for 200 cycles at C/5 rate. The role of CNT in improving rate performance was also demonstrated. The reasonable reversible capacity, rate performance, and cycling stability reveal the feasibility of Mo6S8 material for future rechargeable Mg battery. In order to study the kinetics of Chevrel phase compound upon cycling, EIS study was carried out. The redox process upon insertion/extraction is investigated by X-ray Photoelectron spectroscopy which shows no change in oxidation state of a transition metal.

Enhanced electrochemical performance of LiCoBO3 cathode material for next generation Lithium-ion batteries

Spherical shape, nano-LiCoBO3 is synthesized by sol-gel technique. X-ray diffraction results confirm the presence of monoclinic phase with C2/c space group. Scanning and transmission electron microscopy images depict the existence of the spherical shaped particle with an aggregate diameter range of 5–20 nm. Raman measurement indicates the presence of CoO vibrations in CoO5 polyhedra. X-ray photoelectron spectroscopy confirms the oxidation state of the elements present in the LiCoBO3 material. Galvanostatic charge–discharge studies indicate that the sol-gel derived nano-LiCoBO3 delivers the first charging capacity of 160 mAh g−1 and retaining a discharge capacity of 98 mAh g−1 at the end of 52nd cycle. Formation of spherical shape nanoparticle facilitates electron movement and improves lithium diffusion kinetics, leads to improved electrochemical performance of LiCoBO3 cathode material. An electrochemical study clearly indicates that the sol-gel derived nano-LiCoBO3 has better capacity and cyclic performance compared to previous reports in LiCoBO3.

Facile solvothermal synthesis of BiOI microsquares as a novel electrode material for supercapacitor applications

BiOI microsquares was prepared by using hexamine as surfactant through solvothermal approach and used as electrode material for high performance supercapacitor. The crystalline structure and morphology of the BiOI were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analysis. The electrochemical performance was investigated by using cyclic voltametry (CV) and galvanostatic charge-discharge studies (GCD) using 6M KOH solutions. BiOI electrode exhibits highest specific capacitance of 706Fg−1 at a current density of 2Ag−1. This material retained 55% initial capacitance at a higher current density of 10Ag−1 indicating its better rate performance.

Preparation of High Value Added Activated Carbons from Corncob for Electric Double Layer Capacitors

In this study, corncob-based activated carbons (ACs) were prepared by carbon dioxide (CO2) activation and their use as electrodes in the electrochemical double layer capacitor (EDLC) performed successfully. The effect of activation time (1-7 h) on the surface area and pore structure was detected by nitrogen adsorption-desorption isotherm at 77 K. The electrochemical properties of these corncob-based ACs were evaluated by using cyclic voltammetry (CV), galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) studies. The results showed that the surface area increased to the maximum of 757 m(2) g(-1) with the prolonged activation time. However, when the current density was 50 mA g(-1), the specific capacitance reached to the maximum of 178 F g(-1) in 6 mol L-1 KOH solution when the activation time was 5 h. The capacitance was still up to 157 F g(-1) when increasing the current density to 1000 mA g(-1), indicating a high-rate charge-discharge performance. Furthermore, compared with other reported biomass based ACs, corncob-base ACs showed significantly higher surface specific capacitance (SSC) which means the accessibility and efficient utilization of surface area of these ACs.

Electrochemical performance of polymer electrolytes based on Poly(vinyl alcohol)/Poly(acrylic acid) blend and Pyrrolidinium ionic liquid for lithium rechargeable batteries

Polymer electrolytes offer the most promising solution to address the all-solid-state battery requirements such as flexibility, leak-proof packing and easy processing. In this study, a polymer blend of 25mol% poly(acrylic acid) (PAA) and 75mol% poly(vinyl alcohol) (PVA) was optimized based on its thermal, mechanical and structural properties. The ionic liquid (IL) electrolyte, 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYRTFSI) with 0.2m lithium bis(trifluoromethansulfonyl)imide (LiTFSI), was added to the polymer blend in different molar ratios. A maximum ionic conductivity of 1mScm−1 is observed at 90°C in the membrane with 70mol% IL. Cyclic voltammetry of the polymer electrolytes shows peaks corresponding to lithium stripping (+0.25V vs. Li+/Li) and deposition (−0.3V vs. Li+/Li) processes indicating the occurrence of a highly reversible redox process. The electrochemical stability window of these polymer electrolytes, as determined by linear sweep voltammetry, extends up to 5V, suggesting that these electrolytes could be suitable for batteries that use high voltage cathode materials. A lithium transference number (tLi+) of 0.4 was determined for the polymer electrolytes by using chronoamperometry and impedance measurements. Galvanostatic charge-discharge studies of the polymer electrolytes in a lithium half-cell with LiCoO2 (LCO) as cathode delivers a capacity of about 100mAhg−1 at 60°C. Coin-type half-cell with LiFePO4 (LFP) cathode and the polymer electrolyte containing 70mol% IL delivered a capacity of 172mAhg−1. Interestingly, the LFP/polymer composite cathode (LFP-C) delivers a higher capacity (215mAhg−1 at 60°C) than the pristine LiFePO4 cathode.

Electrospun SnO2/Lto Composite Sub-Micron Dimpled Spheres As High Performance Anode Material for Lithium Ion Batteries

Introduction: SnO2 is one of the high capacity (782 mAh/g) anode materials used in lithium ion batteries (LIBs) with a tetragonal rutile structure and it alloys at voltage of 0.5V vs Li. However cyclability for SnO2/Sn based materials is very poor due to high volume expansion during alloying with Li ions (charging) and disintegration of structure during de-alloying (discharging) besides the formation of solid electrolyte interface (SEI) at lower operating voltage of the anode. Many attempts have been made to improve the cyclability and minimize the capacity losses of these materials by nanostructuring, making nano composites with graphene and CNT. Even though the results are promising, reproducibility and the scaling up of the electrode material still remains a challenge. Here we present a new way of improving the cyclability with minimum capacity loss using a composite electrode of SnO2 and lithium titanate (LTO). LTO with a cubic spinal structure can intercalate reversibly with Li ions delivering a capacity of 175 mAh/g, theoretically. Low crystal strains during charging –discharging makes the material work even at high charging rates. The combination of SnO2 and LTO can reduce the volume expansion experienced by bare SnO2 during alloying de-alloying reaction as LTO itself is a zero-strain material. Experimental: We have synthesized SnO2/LTO composite using combinational approach of sol-gel and electrospinning. Sol-gel synthesis of nanomaterials is known for obtaining materials with high purity. Electrospinning is a simple and continuous method of nanomaterial fabrication which involves application of high voltage to a viscous solution to yield nanofibers. This combinational approach of sol-gel and electrospinning opens the possibilities to obtain pure inorganic nanomaterial. Further sol-gel/ electrospun based inorganic nanomaterials may be promising as electrodes for LIBs as diffusion path or volume expansion of electrode can be reduced to a greater extent due to the presence of nano grains in porous structures. In this work we present the fabrication of SnO2/LTO composite dimpled spheres prepared by sol-gel/electrospinning followed by measuring their electrochemical performance. LTO and SnO2 sols were prepared in ethanol and mixed in 1:1 ratio followed by ageing prior to electrospinning. As ageing time increased, it resulted in higher viscosity which changed the morphology of SnO2/LTO composite to particles to dimpled spheres to fibers. Electrospun SnO2/LTO dimpled spheres were then calcined in argon and air at different temperature for the required phase formation and to obtain SnO2/LTO and SnO2/LTO/Carbon based dimpled spheres with variation in particle sizes. The synthesized composite structures could minimize the grain growth by creating smaller grains ~40 nm in the sub-micron sized electrospun structures. Results and discussion: FESEM and XRD analysis were carried out to understand their morphology and phase formation respectively. The average grain size was measured to be 25 nm. BET and SAXS were performed for surface area analysis. Electrochemical measurements such as Galvanostatic charge-discharge studies, cyclic voltammetry and impedance spectroscopy were performed. Electrospun SnO2/LTO based composite sub-micron structures have shown excellent electrochemical performance (Figure 1) as compared to only SnO2 fibers with improved cycle stability and capacity retention even at high charging rates.