Li-cycling Properties Research Articles

Effect of molten salt synthesis temperature on TiO2 and Li cycling properties

In this project, we synthesized TiO2 compounds through the molten salt method (MSM) using Ti(IV) oxysulfate, as the Ti source. Molten salts in the ratio of 0.375 M LiNO3:0.180 M NaNO3:0.445 M KNO3 were added and heated at temperatures of 145, 280, 380, and 480 °C for 2 h in air, respectively. A part of the sample prepared at 145 °C was further reheated to 850 °C for 2 h in air. X-ray diffraction studies showed that the amorphous phase was obtained when the sample was prepared at 145 °C, and polycrystalline to crystalline anatase phase was formed when heated from 280 to 850 °C, which is complementary to the results of selected area electron diffraction studies. Electrochemical properties were studied using galvanostatic cycling, cyclic voltammetry, and electrochemical impedance spectroscopy at a current density of 33 mA g−1 (0.1 C rate) and a scan rate of 0.058 mV s−1, in the voltage range 1.0–2.8 V vs. Li. Electrochemical cycling profiles for the amorphous TiO2 samples prepared at 145 °C showed single-phase reaction with a low reversible capacity of 65 mAh g−1, whereas compounds prepared at 280 °C and above showed a two-phase reaction of Li-poor and Li-rich regions with a reversible capacity of 200 mAh g−1. TiO2 produced at 280 °C showed the lowest capacity fading and the lowest impedance value among the investigated samples.

Sandwich-like mesoporous graphene@magnetite@carbon nanosheets for high-rate lithium ion batteries

Sandwich-like mesoporous GS@Fe3O4@C nanosheets with a 2D nanoarchitecture have been successfully synthesized by one-step solvothermal treatment. Such type of 2D nanoarchitecture is made up of a number of Fe3O4 nanoparticles uniformly grown on a graphene sheet and an even amorphous carbon layer covering on their surface. The Li-cycling properties of GS@Fe3O4@C nanosheets have been evaluated by galvanostatic discharge-charge cycling and impedance spectroscopy. Results indicate that the GS@Fe3O4@C nanosheets with about 5 wt % of graphene content provides a very high discharge capacity of 913.2 mAh g−1 at a current densities of 200 mA g−1 after 100 cycles and reveals a stable discharge capacity of 483.2 mAh g−1 at a rate of 1600 mA g−1.

Facile one pot synthesis and Li-cycling properties of MnO2

MnO2 compounds prepared by a molten salt method (MSM) using three different Mn-salts and studied for its electrochemical properties.

Solvothermal synthesis of V2O5/graphene nanocomposites for high performance lithium ion batteries

V2O5 nanoparticles Graphene nanosheets Solvothermal synthesis Electrochemical performance Lithium ion batteries a b s t r a c t In this work, V2O5/graphene nanocomposites have been synthesized by a facile solvothermal approach. The V2O5 nanoparticles, around 20–40 nm in size, were encapsulated in the 2D graphene matrix. The reversible Li-cycling properties of V2O5/graphene have been evaluated by galvanostatic discharge–charge cycling, cyclic voltammetry, and impedance spectroscopy. Compared with the bare V2O5 nanoparticles, the V2O5/graphene nanocomposites exhibited enhanced electrochemical performance with higher reversible capacity and improved cycling stability and rate capability. The graphene nanosheets act not only as an electronically conductive matrix to improve the electronic and ionic conductivity of the composite electrode, but also as a flexible buffer matrix to maintain the structural integrity of the composite electrodes by preventing particle agglomeration, thus leading to the improvement of the electrochemical performance of V2O5.

Li Storage and Impedance Spectroscopy Studies on Co3O4, CoO, and CoN for Li-Ion Batteries

The compounds, CoN, CoO, and Co3O4 were prepared in the form of nano-rod/particles and we investigated the Li-cycling properties, and their use as an anode material. The urea combustion method, nitridation, and carbothermal reduction methods were adopted to prepare Co3O4, CoN, and CoO, respectively. X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and the Brunauer-Emmett-Teller (BET) surface and density methods were used to characterise the materials. Cyclic voltammetry (CV) was performed and galvanostatic cycling tests were also conducted up to 60-70 cycles. The observed reversible capacity of all compounds is of the increasing order CoO, Co3O4, CoN and all compounds showed negligible capacity fading. CoO allows for Li2O and Co metal to form during the discharge cycle, allowing for a high theoretical capacity of 715 mA h g(-1). Co3O4 allows for 4 Li2O and 3Co to form, and has a theoretical capacity of 890 mAhg(-1). CoN is the best anode material of the three because the nitrogen allows for Li3N and Co to form, resulting in an even higher theoretical capacity of 1100 mAhg(-1) due to the Li3N and Co metal formation. Irrespective of morphology the charge profiles of all three compounds showed a major plateaux ~2.0 V vs. Li and potential values are almost unchanged irrespective of crystal structure. Electrochemical impedance spectroscopy (EIS) was performed to understand variation resistance and capacitance values.

Molten synthesis of ZnO.Fe3O4 and Fe2O3 and its electrochemical performance

Fe2O3 and ZnO.Fe3O4 hybrids has been synthesised by molten salt method and tested as anode material for Li-ion batteries. The crystal structure and phase purity was evaluated by X-ray diffraction and the morphology of the final powders was examined by the Scanning electron microscopy. The Li-cycling properties of Fe2O3 and ZnO-Fe3O4 were studied by cyclic voltammery (58μV s−1) and galvanostatic discharge-charge cycling in the voltage range, 0.005- 3V at a current of 60mAg−1. The Fe2O3 samples prepared at 280°C and 900°C showed stable reversible capacities of 600 and 620mAhg−1 at the end of 50 cycles respectively. On the other hand, ZnO.Fe3O4 hybrids showed improved and stable capacity of 820mAhg−1 at the end of the 50th cycle.

Microwave autoclave synthesized multi-layer graphene/single-walled carbon nanotube composites for free-standing lithium-ion battery anodes

Multi-layer graphene sheets have been synthesized by a time-efficient microwave autoclave method and used to form composites in situ with single-walled carbon nanotubes. The application of these composites as flexible free-standing film electrodes was then investigated. According to the transmission electron microscopy and X-ray diffraction characterizations, the average d-spacing of the graphene–single-walled carbon nanotube composites was 0.41nm, which was obviously larger than that of the as-prepared pure graphene (0.36nm). The reversible Li-cycling properties of the free-standing films have been evaluated by galvanostatic discharge–charge cycling and electrochemical impedance spectroscopy. Results showed that the free-standing composite film with 70wt% graphene exhibited the lowest charge transfer resistance and the highest charge capacity of about 303mAhg−1 after 50 cycles, without any noticeable fading.

Graphene Encapsulated Fe3O4 Nanospindles as a Superior Anode Material for Lithium-Ion Batteries

Graphene encapsulated Fe3O4 nanospindles were synthesized by a simple hydrothermal method. From field-emission and transmission electron microscopy results, the Fe3O4 nanospindles with the length of about 260 nm are highly encapsulated in graphene matrix. The reversible Li-cycling properties of graphene encapsulated Fe3O4 nanospindles have been evaluated by galvanostatic discharge-charge cycling and cyclic voltammetry. Results show that graphene encapsulated Fe3O4 nanospindles exhibits a high reversible capacity about 745 mA h g(-1) for the first cycle and a stable capacity of about 558 mA h g(-1) for up to 200th cycle in the voltage range of 0.01-3.0 V at a current density of 100 mA g(-1), indicating excellent cycling stability. The graphene in the composite materials could act not only as lithium storage active materials, but also as an electronically conductive matrix to improve the electrochemical performance of Fe3O4.

(N,F)-Co-doped TiO2: synthesis, anatase–rutile conversion and Li-cycling properties

Nitrogen and fluorine co-doped Ti-oxide, TiO1.9N0.05F0.15 (TiO2(N,F)), with the anatase structure is prepared by the pyro-ammonolysis of TiF3. For the first time it is shown that TiO2(N,F) and anatase-TiO2 are converted to nanosize-rutile structure by high energy ball milling (HEB). The polymorphs are characterised by X-ray diffraction, Rietveld refinement, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and Raman spectra. The Li storage and cycling properties are examined by galvanostatic cycling and cyclic voltammetry in the voltage range 1–2.8 V vs.Li at 30 mA g−1. The performance of TiO2(N,F) is much better than pure anatase-TiO2 and showed a reversible capacity of 95 (±3) mA h g−1 stable up to 25 cycles with a coulombic efficiency of ∼98%. Nano-phase rutile TiO2(N,F) showed an initial reversible capacity of 210 mA h g−1 which slowly degraded to 165 (±3) mA h g−1 after 50 cycles and stabilised between the 50th and 60th cycle whereas the nano-phase rutile-TiO2 (prepared by HEB of anatase-TiO2) exhibited a reversible capacity of 130 (±3) mA h g−1 which is stable in the range, 10–60 cycles. The crystal structure of anatase TiO2(N,F) is not destroyed upon Li-cycling and is confirmed by ex situXRD and HR-TEM.

Functional properties of electrospun NiO/RuO2 composite carbon nanofibers

One-dimensional (1D) nickel oxide/ruthenium oxide (NiO/RuO2)–carbon composite nanofibers (NiRu–C–NFs) were fabricated via electrospinning of a homogenous mixture of polyacrylonitrile (PAN) and Ni/Ru salt precursors at different ratios followed by heat treatments. The 1D nanostructures of the composite material were characterized by field-emission scanning electron microscopy (FE-SEM), powder X-ray diffraction (XRD), Rietveld refinement and Brunauer–Emmett–Teller (BET) surface area measurements. Li-cycling properties were evaluated using cyclic voltammetry and galvanostatic properties. The asymmetric hybrid supercapacitor studies were carried out with activated carbon as a cathode and NiRu–C–NFs composites as anodes in the cycling range, 0.005–3.0V using 1M LiPF6 (EC;DMC) electrolyte. NiRu–C–NFs fabricated from 5wt% nickel (II) and 15wt% ruthenium (III) precursors showed a capacitance up to ∼60Fg−1 after 30 cycles. Anodic Li-cycling studies of NiRu–C–NF-0 and NiRu–C–NF-2 composite samples showed a reversible capacity of 230 and 350mAhg−1 at current rate of 72mAg−1 at the end of 40th cycle in the voltage range of 0.005–3.0V. Electrochemical impedance studies (EIS) on NiRu–C–NFs showed lower impedance value for 15wt% Ru than the bare sample.

SnO2–Graphene Composite Synthesized via an Ultrafast and Environmentally Friendly Microwave Autoclave Method and Its Use as a Superior Anode for Lithium-Ion Batteries

SnO2–graphene composites have been synthesized by an ultrafast and environmentally friendly microwave autoclave method. From field emission scanning electron microscopy and transmission electron microscopy, it can be determined that the SnO2 nanoparticles, around 4–5 nm in diameter, are uniformly sandwiched between graphene nanosheets containing only a few layers. The successful synthesis demonstrates that in situ loading of SnO2 nanoparticles can be an effective way to prevent graphene nanosheets from being restacked during the reduction. The Li-cycling properties of the materials have been evaluated by galvanostatic discharge–charge cycling and impedance spectroscopy. Results show that the SnO2–graphene composite with a graphene content of 33.3 wt % exhibits a very stable capacity of about 590 mA h g–1 without noticeable fading for up to 200 cycles.

Nano-(V1/2Sb1/2Sn)O4: a high capacity, high rate anode material for Li-ion batteries

Vanadium antimony tin oxide, M (micron size)-(V1/2Sb1/2Sn)O4 with tetragonal rutile structure is prepared for the first time. The N (nanosize, 10–20 nm)-analogue is obtained by high energy ball milling of the above. They are characterized by Rietveld refinement of the X-ray diffraction data, high resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED), density and BET surface area studies. The Li-cycling properties were studied at ambient temperature (24 °C) and at 54 °C by galvanostatic discharge–charge cycling and cyclic voltammetry. Nano-(V1/2Sb1/2Sn)O4 shows stable cycling performance at 24 °C with capacities 450, 435 and 360 (±5) mA h g−1 at rates of 0.43, 1.0 and 3.5 C, respectively, in the range, 0.005–1.0 V vs.Li. These values are stable up to 100 cycles at 0.43 C and up to at least 50 cycles at 1 C and 3.5 C. At 54 °C and at 0.43 C, N-(V1/2Sb1/2Sn)O4 delivers a stable capacity of 440 (±5) mA h g−1 in the range, 5–100 cycles. Under similar conditions the cycling performance of M-(V1/2Sb1/2Sn)O4 is inferior to that of the N-analogue. The M- and N-(V1/2Sb1/2Sn)O4 showed main cathodic and anodic peaks at ∼0.2 V and ∼0.5 V, respectively, by CV. Complementary impedance studies are reported at various voltages and as a function of cycle number to support the Li-cycling mechanism involving alloying–de-alloying reactions of Sn and Sb with Li using (VO) as an inert matrix.

Graphene‐Encapsulated Fe3O4 Nanoparticles with 3D Laminated Structure as Superior Anode in Lithium Ion Batteries

Fe(3)O(4)-graphene composites with three-dimensional laminated structures have been synthesised by a simple in situ hydrothermal method. From field-emission and transmission electron microscopy results, the Fe(3)O(4) nanoparticles, around 3-15 nm in size, are highly encapsulated in a graphene nanosheet matrix. The reversible Li-cycling properties of Fe(3)O(4)-graphene have been evaluated by galvanostatic discharge-charge cycling, cyclic voltammetry and impedance spectroscopy. Results show that the Fe(3)O(4)-graphene nanocomposite with a graphene content of 38.0 wt % exhibits a stable capacity of about 650 mAh g(-1) with no noticeable fading for up to 100 cycles in the voltage range of 0.0-3.0 V. The superior performance of Fe(3)O(4)-graphene is clearly established by comparison of the results with those from bare Fe(3)O(4). The graphene nanosheets in the composite materials could act not only as lithium storage active materials, but also as an electronically conductive matrix to improve the electrochemical performance of Fe(3)O(4).