Ramchandra S. Kalubarme

Catalytic characteristics of MnO2 nanostructures for the O2 reduction process

Nanorods with an α type MnO(2) structure and a diameter ranging from 25 to 40 nm, along with tipped needles with a β MnO(2) structure and a diameter of 100 nm were obtained. The 25 nm diameter α MnO(2) nanorods showed the best catalytic activity for dissociation of HO(2)(-) formed during oxygen reduction in a KOH solution. The MnO(2) nanostructures preferably followed a two-electron oxygen reduction mechanism in a LiOH solution. The size of the catalyst also affected the specific capacities of the non-aqueous Li/O(2) batteries fabricated using the MnO(2) based air electrode. The highest specific capacity of 1917 mA h g(-1) was obtained for an α MnO(2) nanorod catalyst having a diameter of 25 nm. The cation present in the MnO(2) nanostructures appears to determine the catalytic activity of MnO(2).

Carbon Encapsulated Tin Oxide Nanocomposites: An Efficient Anode for High Performance Sodium-Ion Batteries

The major obstacle in realizing sodium (Na)-ion batteries (NIBs) is the absence of suitable negative electrodes. This is because graphite, a commercially well known anode material for lithium-ion batteries, cannot be utilized as an insertion host for Na ions due to its large ionic size. In this study, a simple and cost-effective hydrothermal method to prepare carbon coated tin oxide (SnO2) nanostructures as an efficient anode material for NIBs was reported as a function of the solvent used. A single phase SnO2 resulted for the ethanol solvent, while a blend of SnO and SnO2 resulted for the DI water and ethylene glycol solvents. The elemental mapping in the transmission electron microscopy confirmed the presence of carbon coating on the SnO2 nanoparticles. In cell tests, the anodes of carbon coated SnO2 prepared in ethanol solvent exhibited stable cycling performance and attained a capacity of about 514 mAh g(-1) on the first charge. With the help of the conductive carbon coating, the SnO2 delivers more capacity at high rates: 304 mAh g(-1) at the 1 C rate, 213 mAh g(-1) at the 2 C rate and 133 mAh g(-1) at the 5 C rate. The excellent cyclability and high rate capability are the result of the formation of a mixed conducting network and uniform carbon coating on the SnO2 nanoparticles.

One step hydrothermal synthesis of a carbon nanotube/cerium oxide nanocomposite and its electrochemical properties.

A carbon nanotube (CNT)/cerium oxide composite was prepared by a one-pot hydrothermal reaction in the presence of KOH and capping agent polyvinylpyrrolidone. The nanocomposite displayed pronounced capacitive behaviour with very small diffusion resistance. The electrochemical performance of the composite electrode in a symmetric supercapacitor displayed a high energy density of 35.9 Wh kg(-1) corresponding to a specific capacitance of 289 F g(-1). These composite electrodes also demonstrated a long cycle life with better capacity retention.

Uniform GeO2 dispersed in nitrogen-doped porous carbon core–shell architecture: an anode material for lithium ion batteries

Germanium oxide (GeO2), which possesses great potential as a high-capacity anode material for lithium ion batteries, has suffered from its poor capacity retention and rate capability due to significant volume changes during lithiation and delithiation. In this study, we introduce a simple synthetic route for producing nanosized GeO2 anchored on a nitrogen-doped carbon matrix (GeO2/N–C) via the sol–gel method followed by a calcination process in an inert argon atmosphere. The GeO2/N–C showed superior electrochemical performance over pure GeO2; almost 91.8% capacity retention of 905 mA h g−1 was shown after 200 cycles at the rate of C/2. Interestingly, even at a high rate of 20C, a specific capacity of 412 mA h g−1 was retained. This unique anode performance of GeO2/N–C is derived from the effective combination of nano-size GeO2 and its uniform distribution in a nitrogen-doped carbon matrix. Herein, the nitrogen doped-carbon matrix not only strengthens the structure but also promotes the lithium diffusion in the GeO2/C–N material. Further, the adaptability of GeO2/N–C as an anode in a full cell configuration in combination with the LiCoO2 cathode was demonstrated by exhibiting high specific capacity and good cyclability.

Simple synthesis of highly catalytic carbon-free MnCo2O4@Ni as an oxygen electrode for rechargeable Li-O2 batteries with long-term stability.

An effective integrated design with a free standing and carbon-free architecture of spinel MnCo2O4 oxide prepared using facile and cost effective hydrothermal method as the oxygen electrode for the Li–O2 battery, is introduced to avoid the parasitic reactions of carbon and binder with discharge products and reaction intermediates, respectively. The highly porous structure of the electrode allows the electrolyte and oxygen to diffuse effectively into the catalytically active sites and hence improve the cell performance. The amorphous Li2O2 will then precipitate and decompose on the surface of free-standing catalyst nanorods. Electrochemical examination demonstrates that the free-standing electrode without carbon support gives the highest specific capacity and the minimum capacity fading among the rechargeable Li–O2 batteries tested. The Li-O2 cell has demonstrated a cyclability of 119 cycles while maintaining a moderate specific capacity of 1000 mAh g−1. Furthermore, the synergistic effect of the fast kinetics of electron transport provided by the free-standing structure and the high electro-catalytic activity of the spinel oxide enables excellent performance of the oxygen electrode for Li-O2 cells.

Composite Gel Polymer Electrolyte Based on Poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) with Modified Aluminum-Doped Lithium Lanthanum Titanate (A-LLTO) for High-Performance Lithium Rechargeable Batteries

A composite gel polymer electrolyte (CGPE) based on poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) polymer that includes Al-doped Li0.33La0.56TiO3 (A-LLTO) particles covered with a modified SiO2 (m-SiO2) layer was fabricated through a simple solution-casting method followed by activation in a liquid electrolyte. The obtained CGPE possessed high ionic conductivity, a large electrochemical stability window, and interfacial stability-all superior to that of the pure gel polymer electrolyte (GPE). In addition, under a highly polarized condition, the CGPE effectively suppressed the growth of Li dendrites due to the improved hardness of the GPE by the addition of inorganic A-LLTO/m-SiO2 particles. Accordingly, the Li-ion polymer and Li-O2 cells employing the CGPE exhibited remarkably improved cyclability compared to cells without CGPE. In particular, the CGPE as a protection layer for the Li metal electrode in a Li-O2 cell was effective in blocking the contamination of the Li electrode by oxygen gas or impurities diffused from the cathode side while suppressing the Li dendrites.

Nanostructured doped ceria for catalytic oxygen reduction and Li2O2 oxidation in non-aqueous electrolytes

Herein, we report the catalytic activities of porous nano-crystalline oxides with surface active sites synthesized by a wet chemical route. Zr doped ceria (ZDC) has been tested as active oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts in air electrodes for Li–O2 batteries. A ZDC-based air electrode exhibits a higher discharge capacity than that of a bare carbon-based air electrode. ZDC loaded in carbon air electrodes delivers a discharge capacity of 8435 mA h g−1. The higher discharge voltages of Li–O2 cells with ZDC, instead of bare carbon, could have originated from the higher oxygen reduction activity of ZDC. These oxides show a lower potential for Li2O2 oxidation than pure carbon. A significant increase in the kinetics for Li2O2 oxidation indicates the influence of the ZDC catalyst on the oxygen evolution reaction. The ORR and OER properties of the catalyst are explained in terms of the high fraction of active defect sites on its surface.

Nickel-titanium oxide as a novel anode material for rechargeable sodium-ion batteries

Nickel-titanium oxide (NiTiO3; NTO) of an ilmenite structure that comprises a layered transition-metal octahedral structure, wherein the zigzag open tunnels are possible routes for Na intercalation, can be a potential anode material for sodium (Na) ion batteries (SIBs). In this study, nanocrystalline NTO particles that are of sizes 3 to 5 nm were prepared using a simple hydrothermal process followed by annealing, and the particles were then tested for SIB applications. The pure-NTO electrode that comprises a hexagonal crystal structure and mesoporous morphology demonstrated a reversible capacity of approximately 521 mA h g−1 that corresponds to a coulombic efficiency of 67% in the first cycle, which further improved to ∼98% in the following cycles, at an applied specific current of 50 mA g−1, and stable cycling performance for 200 cycles. Further, due to the synergetic effect of the porous network structure and high surface area, the NTO electrode exhibited an exceptional rate capability, delivering a capacity of 192 mA h g−1 at a high specific current of 4000 mA g−1. The excellent cyclability and rate capability of the NTO electrode are attributed to the improved electronic conductivity and highly porous microstructure of the NTO material, whereby fast charge transfer and facile diffusion of the Na-ions to the active sites are enabled.

Nickel titanate lithium-ion battery anodes with high reversible capacity and high-rate long-cycle life performance

We demonstrate the impressive performance of sparsely studied nickel titanate anode materials for Li-ion batteries (LIBs). The nickel titanate anode delivers a high reversible discharge capacity of 435 mA h g−1 at a current density of 35 mA g−1, high-rate performance and excellent cycling retention of 96% with a long-term cycling stability at 1500 mA g−1 over 300 cycles. The coulombic efficiency is obtained as high as 98%. This superior nickel titanate electrode material could be used as a safe, low-cost, long cycle life anode material for next-generation LIBs with a high power capability.

Bi-layer lithium phosphorous oxynitride/aluminium substituted lithium lanthanum titanate as a promising solid electrolyte for long-life rechargeable lithium–oxygen batteries

Lithium ion conducting membranes are indispensable for building lithium–air (oxygen) batteries employing aqueous and non-aqueous electrolytes for long-term operation. In this report, we present the high performance of non-aqueous lithium–air batteries, in which a bilayer lithium phosphorous oxynitride/aluminium substituted lithium lanthanum titanate solid electrolyte is employed as a protective layer for a lithium metal electrode and free carbon–manganese dioxide as the cathodic catalyst. Aluminium-doped lithium lanthanum titanate (A-LLTO) pellets were prepared using citrate-gel synthesis followed by pelletization and a sintering process. A thin lithium phosphorous oxynitride (LiPON) layer was then deposited on the A-LLTO using the sputtering method, which was used as a protective interlayer for separating A-LLTO ceramics from the Li metal electrode. With a high ionic conductivity of 2.25 × 10−4 S cm−1 and a large electrochemical stability window of 0–5 V, the LiPON/A-LLTO ceramics showed promising feasibility as a stable solid electrolyte for application in Li–O2 batteries. The aprotic Li–O2 cell containing the Li metal electrode protected by LiPON/A-LLTO exhibited excellent charge–discharge cycling stability with a long life span of 128 cycles under the limited capacity mode of 1000 mA h g−1. After the cycling test, the LiPON/A-LLTO ceramics retained a high ion conductivity of 1.65 × 10−4 S cm−1. In addition, with the introduction of LiPON/A-LLTO, the Li dendrite growth and electrolyte decomposition are effectively suppressed.