Studies on multifunctional materials applied to energy storage

Abstract

Structure, phonon, and energy storage density in Sr²⁺-substituted lead-free ferroelectric Ba_1-;xSr_xTiO₃ (BST_x) for compositions x= 0.1, 0.3, and 0.7 were investigated using X-ray diffraction, Raman, and ferroelectric polarization measurements as a function of temperature. The samples were tetragonal for x = 0.1 with a large c/a ratio. The tetragonal anisotropy was decreased upon increasing x and transforming to cubic for x = 0.7. The changes in structural and ferroelectric properties were found to be related to the c/a ratios. The temperature-dependent phonon spectroscopy results indicated a decrease in tetragonal-cubic phase transition temperature, Tc, upon increasing x due to a reduction in the lattice anisotropy. The intensity of ~303 cm^-1 E(TO2) mode decreased gradually with temperature and that finally disappeared around the tetragonal ferroelectric to cubic paraelectric phase at about 100 ℃ and 70 ℃ for x = 0.1 and 0.3, respectively. A gradual reduction in the band gap E_g of BST_x with x was evident from the analysis of UV-Visible absorption spectra. The energy storage density (U_dis) of the ferroelectric capacitors for x = 0.7 was ~0.20 J/cm³ with an energy storage efficiency of ~88% at an applied electric field of 104.6 kV/cm. Nearly room temperature transition temperatures TC and reasonably fair energy storage density of the BST_x capacitors were found.<br /> <br /> The energy storage density of these thin film capacitors was estimated using the measured polarization hysteresis loops and were compared. For x = 0.7, a larger energy storage density (U_re) ~29 J/cm³ with efficiency of ~48 % was estimated at an applied voltage of 1.1 MV/cm. Nearly room temperature transition temperature T_c, larger dielectric constant, and high energy density values of our BST_x thin film capacitors indicate its possible application in high energy storage devices.<br /> <br /> In this study we are reporting electrochemical performance of Ba_0.9 Sr_0.1TiO₃ (BST) having polarization of 14.58 μC/cm² doped sulfur/carbonblack/polyvinylidenefluoride(S/BST/CB/PVDF) composite as cathode materials for Li-S batteries. The performance of fabricated cathodes in terms of structural, electronic, morphological, and electrochemical response have been tested at various concentrations of BST doping. Considering that polar substances have good affinity towards polysulfide and can provide a more stable reacting environment in the cathodic site, trapping polysulfide intermediates via induced permanent dielectric polarizability. It is expected that spontaneous polarization induced by asymmetric crystal structure of ferroelectrics provide internal electric fields and increase chemisorption with heteropolar reactivity. X-ray diffraction spectra confirms tetragonal symmetry (c/a=1.0073), Raman spectroscopic study confirms Raman modes (A₁(TO₁), A₁(TO₂), A₁(TO₃) and A₁(LO₃)) of the tetragonal orientation for BST modified composites. All the compositional cations are observed from SEM images confirm homogeneous distribution of BST in the sulfur cathode system having grain sizes (1-1.5 μm) which is based on microscopic analysis. BST coupled C-S composite cathodes improve the electrochemical performance in comparison with the cathodes composed of C-S. The high capacity for S/BST/CB/PVDF composites of the order of 820 mAh/g @ 100 mA/g have been achieved for the S₅₀BST₃₀CB₁₀PVDF₁₀ composite cathode and very stable response till 100^th cycles attributes polysulfide migration is effectively reducing due to ferroelectric particles doping in the composite cathode. Two plateaus were observed in between 2.3V to 2.0 V and 2.0 V to 1.5 V in the charge/discharge characteristics and high cyclic stability substantiate the superior performance of the designed ferroelectric nanoparticles doped S/CB composite cathode materials due to the efficient reduction in the polysulfide shuttle effect in these composite cathodes. In this study we are reporting the electrochemical performance of Ba_0.9 Sr_0.1TiO₃ (BST) having polarization of 14.58 μC/cm² as an anode for Li-ion batteries. Perovskite structure (ABO₃) anode materials have received much attention because of their mixed electronic and ionic conduction behaviours that make the triple-phase boundary (TPB) extend to the entirely exposed anode surface. Among the variety of these oxides, SrTiO₃-based perovskite compounds are promising Ni-free anode candidates due to their high chemical stability at high temperatures under both oxidizing and reducing atmospheres, and strong resistance to carbon deposition. X-ray diffraction spectra confirm tetragonal symmetry (c/a=1.0073), Raman spectroscopic study confirms Raman modes (A₁(TO₁), A₁(TO₂), A₁(TO₃) and A₁(LO₃)) of the tetragonal orientation for BST. SEM images confirm homogeneous surface of BST having grain sizes (1-1.5 μm). Carbon black was used as the conductive additive PVDF as binder, LiPF₆ as an electrolyte for charge-discharge performance and contribution to the electrochemical properties of the cell in terms of lithium intercalation and de-intercalation. At slow discharge rate, a capacity of approximately 240 mAh g^-1 achieved. It is found that Ba on SrTiO₃ surface helps to facilitate electron transfer thereby improving the capacity and rate performance of BST as Li-ion battery anode material. These results show us that the BST is applicable for the development of lithium-ion batteries. For improving the negative electrode of lithium metal has serious problems as secondary battery use, since it does not have a long enough cyclic life and their safety aspects that need to be considered due to the dendrite formation on the surface of lithium metal electrode during charge/discharge cycles. To solve these problems a locking-chair concept has established, in which the intercalation phenomena has used as an anode reaction for lithium-ion secondary batteries.