S. Yuvaraj

Effect of carbon coating on the electrochemical properties of Co2SnO4 for negative electrodes in Li-ion batteries

Co2SnO4 particles were synthesized by a sonochemical method under different pH conditions, followed by carbon coating by a hydrothermal method. The thermal stability and compound formation temperature were identified through thermogravimetric analysis (TGA). The X-ray diffraction (XRD) pattern elucidated the compound formation of Co2SnO4 with cubic structure. Co2SnO4 encapsulated with carbon was confirmed through the TEM and HRTEM analysis and the approximate thickness of carbon was around 20 nm. The pristine-Co2SnO4 and carbon coated Co2SnO4 provided a discharge capacity of 777 mA h g−1 and 780 mA h g−1 at the current density of 40 mA g−1 with the capacity retention of 67% and 81% respectively in the 20th cycle. The charge transfer resistance of carbon coated Co2SnO4 was low when compared to pristine Co2SnO4 which lead to good reversibility of the material. The electrochemical study revealed the excellent electrochemical performance of the carbon coated Co2SnO4 particles with superior cycling stability and electronic conductivity.

An overview of AB2O4- and A2BO4-structured negative electrodes for advanced Li-ion batteries

Energy-storage devices are state-of-the-art devices with many potential technical and domestic applications. Conventionally used batteries do not meet the requirements of electric or plug-in hybrid-electric vehicles due to their insufficient energy and power densities. Graphite is used for the conventional anodes of Li-ion batteries. However, the specific capacity (372 mA h g−1) of a graphite electrode is not sufficient for high-power applications. Therefore, Co-, Ni-, Mn-, and Zn-based simple oxides have been investigated as anode components due to their high specific capacities (500–1000 mA h g−1). Among these, Co-based anodes have demonstrated the best electrochemical performances; however, Cos high cost and toxicity limit its use as an ideal anode component. Recently, mixed-metal oxides with AB2O4 (A = Cu, Co, Ni, Mn, and Zn; B = Co, Mn, and Fe) and A2BO4 (A = Co, Mn, and Fe; B = Sn, Si, Ti, and Ge) structures have received much interest, and their electrochemical performances have been extensively studied. This type of mixed-metal oxide affords the following main advantages: they store charge through conversion as well as alloying–dealloying processes, and they exhibit higher electronic conductivities than that obtained with simple metal oxides. The above points indicate the importance of AB2O4- and A2BO4-structured materials. The present review emphasizes the recent literature on the electrochemical performance of AB2O4- and A2BO4-structured materials and their composites and feasible ways to implement these materials in Li-ion batteries in the near future.

Sonochemical synthesis, structural, magnetic and grain size dependent electrical properties of NdVO4 nanoparticles

NdVO4 nanoparticles are successfully synthesized by efficient sonochemical method using two different structural directing agents like CTAB and P123. The phase formation and functional group analysis are carried out using X-ray diffraction (XRD) and fourier transform infra red (FT-IR) spectra, respectively. Using Scherrer equation the calculated grain sizes are 27 nm, 24 nm and 20 nm corresponding to NdVO4 synthesized by without surfactant, with CTAB and P123, respectively. The TEM images revealed that the shape of NdVO4 particles is rice-like and rod shaped particles while using CTAB and P123 as surfactants. The growth mechanism of NdVO4 nanoparticles is elucidated with the aid of TEM analysis. From electrical analysis, the conductivity of NdVO4 nanoparticles synthesized without surfactant showed a higher conductivity of 5.5703 × 10(-6) S cm(-1). The conductivity of the material depends on grain size and increased with increase in grain size due to the grain size effect. The magnetic measurements indicated the paramagnetic behavior of NdVO4 nanoparticles.

Surfactant-free hydrothermal synthesis of hierarchically structured spherical CuBi2O4 as negative electrodes for Li-ion hybrid capacitors

Hierarchically structured spherical CuBi2O4 particles were prepared using a facile hydrothermal method without using a surfactant over various hydrothermal reaction periods. The prepared CuBi2O4 samples were examined via X-ray diffraction (XRD), which confirmed the formation of a tetragonal crystal structure. The morphological features were analyzed using field emission scanning electron microscopy (FESEM), which elucidated the construction of the hierarchical microspherical CuBi2O4 particles. The plausible growth mechanism of the hierarchical structure was explained in terms of a time-dependent synthesis process and its crystal structure. The uniform hierarchical CuBi2O4 microspheres were used to fabricate a Li-ion hybrid capacitor (Li-HC) along with activated carbon (AC), the generated device delivers a stable specific capacitance of 26.5 F g(-1) over 1500 cycles at a high current density of 1000 mA g(-1) and a capacity retention of ∼86%. The AC/CB2 Li-ion hybrid cell exhibits high energy density and power density values of 24 W h kg(-1) and 300 W kg(-1), respectively.

In situ and ex situ carbon coated Zn2SnO4 nanoparticles as promising negative electrodes for Li-ion batteries

Zinc stannate, Zn2SnO4 nanoparticles are successfully synthesized by a facile hydrothermal method. Subsequently, a layer of carbon is coated on Zn2SnO4 nanoparticles by both in situ and ex situ methods using glucose as a carbon source. The phase purity, carbon content, oxidation state and morphological features are characterized by various techniques. The percentage of carbon present in the Zn2SnO4 is calculated using thermogravimetric analysis. The core–shell structure of Zn2SnO4@C is revealed through high resolution transmission electron microscope images. The electrochemical performance of the Zn2SnO4@C is examined by dQ/dV, charge–discharge, rate capability and electrochemical impedance spectroscopy analysis. Among these, the ex situ carbon coated Zn2SnO4 shows superior cycling stability and it delivered a stable specific discharge capacity of 533 mA h g−1 at 700 mA g−1 over 50 cycle. The EIS analysis indicates that the obtained low charge transfer resistance (Rct) and solid electrolyte interphase (SEI) film resistance (RSEI) of the ex situ carbon coated Zn2SnO4 controls the SEI film thickness on the outer surface of the active material. Overall, the electrochemical analysis elucidates that the ex situ carbon coated Zn2SnO4 shows an excellent cycling stability and good electronic conductivity compared with carbon free and in situ carbon coated Zn2SnO4.

Synthesis and electrochemical performance of Co2TiO4 and its core–shell structure of Co2TiO4@C as negative electrodes for Li-ion batteries

Spinel Co2TiO4 is synthesised using a polymeric precursor method and used as an efficient negative electrode for Li-ion batteries. Precise full-profile Rietveld refinement proves the formation of a single-phase cubic spinel structure with a lattice parameter of a = 8.4190(9) A, which corresponds to the sample composition of Co2.05Ti0.95O4. Subsequently, a carbon coating around Co2TiO4 is achieved through a simple hydrothermal method. TGA analysis implies that Co2TiO4@C consists of 17 wt% carbon, and the presence of D and G bands was confirmed through Raman analysis. Transmission electron microscopy (TEM) is employed to probe the morphological features, as well as to confirm the carbon coating on Co2TiO4. It shows non uniform shape particles with sizes in the range of 400–750 nm and that the thickness of the carbon coating is 10 nm. The superior electrochemical performance of Co2TiO4@C is confirmed by a higher initial discharge–charge capacity (1283/418 mA h g−1), high diffusion coefficient (1.76 × 10−10 cm2 s−1/2) and lower Rct (after 50 cycles). This is attributed to the increased electrical conductivity and the creation of new active sites due to the synergistic effect of the carbon matrix on Co2TiO4, thereby making it a promising candidate for lithium ion battery applications.