Manickam Minakshi

Electrochemical behavior of olivine-type LiMnPO4 in aqueous solutions

The electrochemical behavior of olivine-type lithium manganese phosphate as a cathode material was investigated in a saturated aqueous lithium hydroxide electrolyte. The crystal structure and surface characterization of the olivine type and the products which are formed on its oxidation and subsequent reduction were studied. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and secondary ion mass spectrometry were used for these investigations. was found to be reversibly delithiated/lithiated on electro-oxidation/reduction

The Anodic Behavior of Planar and Porous Zinc Electrodes in Alkaline Electrolyte

The electrochemical performance of planar and porous zinc electrodes in an actual Zn/ MnO 2 battery using lithium hydroxide (LiOH) electrolyte has been investigated. A large discharge capacity of 220 mAh/g is delivered by porous zinc electrodes while planar electrodes only deliver 130 mAh/g. The porous anode improves the rate capability of the rechargeable alkaline battery while enhancing the utilization of the active material. Using scanning electron microscopy and IR spectroscopy, the surface morphology and composition of the Zn anodes were studied at the end of the discharge process. While zincate ions and ZnO products were found after the discharge at the surface of the planar anode, no evidence for these products was found in the porous anode. The porosity of this surface prevents the detrimental buildup of zincate ions at the anodic surface that leads to passivation.

Electrolytic manganese dioxide (EMD): a perspective on worldwide production, reserves and its role in electrochemistry

Electrolytic manganese dioxide (EMD) is the critical component of the cathode material in modern alkaline, lithium, and sodium batteries including electrochemical capacitors and hydrogen production. In terms of environmental and cost considerations, EMD is likely to remain the preferred energy material for the future generation, as it has been in recent decades. Diminishing fossil fuels and increasing oil prices have created the need to derive energy from sustainable sources. The energy storage device from alternative and inexpensive sources, such as low grade manganese ores, has a niche in the renewable energy and portable electronics market. Despite vast manganese sources along with the current activity in producing modified EMD materials from secondary sources, to a surprise, India mostly imports EMD to meet its demand. Keeping this in view, a comprehensive review has been prepared on the synthesis, physical and electrochemical characterization of EMD produced from synthetic solutions and secondary sources. This review summarizes the available EMD sources in the world including Indian deposits and the recent investigations of fundamental advances in understanding the electrochemical mechanism involved in aqueous rechargeable batteries and electrochemical capacitors, thus leading to an improved energy storage performance, which is essential for their long term use in storing renewable energy supply.

Synthesis and Characterization of Li(Co0.5Ni0.5)PO4 Cathode for Li-Ion Aqueous Battery Applications

Olivine-type lithium orthophosphate Li(Co0.5Ni0.5)PO4 was synthesized in a solid state reaction at 800 degrees C in air. Infra-red spectroscopy, x-ray and neutron powder diffraction were used to characterize the as-prepared compound and its electro-oxidized analogue. Rietveld analysis was used to illustrate that the synthesized compound is isostructural with LiNiPO4 and LiCoPO4 with lattice parameters larger than the former and smaller than the latter. The Rietveld-refined Ni:Co ratio was found to be 0.498(4):0.502(4) and no evidence for long-range Ni: Co ordering or mixed Li/Ni/Co cation sites was found. The electro-oxidised electrode showed a mixture of two phases i.e. parent Li(Co0.5Ni0.5)PO4 and lithium extracted Li1-x(Co0.5Ni0.5)PO4 suggesting a delithiation process in aqueous electrolytes. Reversible Li transfer between a Li(Co0.5Ni0.5)PO4 electrode and an aqueous LiOH electrolyte was demonstrated.

The Zn-MnO2 Battery : The Influence of Aqueous LiOH and KOH Electrolytes on the Intercalation Mechanism

Intercalation chemistry of the zinc–manganese dioxide (Zn–MnO2) electrochemical cell aiming at the development of aqueous rechargeable batteries is presented. This study includes electrochemical characterization of MnO2 in saturated aqueous lithium hydroxide (LiOH) and potassium hydroxide (KOH) electrolytes. The lithium insertion into MnO2 results in the formation of LixMnO2. The reversible deintercalation process prevails in the presence of LiOH electrolyte. Rather than the usual protonation (H+) which is apparent in the literature while using KOH electrolyte, in this work, K+ ion insertion into MnO2 is observed. However, the K+ ion insertion is found to be irreversible. The intercalation mechanism is confirmed using various techniques to characterize the discharged MnO2 cathode in LiOH and KOH electrolytes. The influence of small amounts of Bi2O3 (bismuth oxide) additive on the discharge behavior of MnO2 is also discussed.

Manganese Dioxide Cathode in the Presence of TiS2 as Additive on an Aqueous Lithium Secondary Cell

Intercalation of lithium into the vacant sites of a host compound can be achieved electrochemically using nonaqueous electrolytes. The use of aqueous electrolyte is less common because of the reactivity of many lithium intercalation compounds with water. Here, we propose that lithium could be intercalated into the manganese dioxide cathode in a battery using saturated lithium hydroxide as the electrolyte. The positive electrode reaction at MnO2 in this medium is shown to be lithium insertion rather than the usual protonation, and acceptable rechargeability is observed. Using X-ray photoelectron spectroscopy and scanning electron microscope analysis on the discharged cathode material we confirmed the presence of lithium ions in the host structure of MnO2. Further, the incorporation of small amounts (<3 wt %=weight percent) of titanium disulphide (TiS2) additive to the cell MnO2 cathode leads to a significant improvement in cell performance.

Structural characteristics of olivine Li(Mg0.5Ni0.5)PO4 via TEM analysis

The structural characteristics of olivine-type lithium orthophosphate Li(Mg0.5Ni0.5)PO4 synthesized via solid-state reaction have been studied using X-ray diffraction, ion beam technique, scanning electron microscopy, infrared spectroscopy, transmission electron microscopy and energy dispersive X-ray analysis. The parent LiNiPO4 compound can be synthesized in olivine structure without any evidence of secondary phases as impurities. The structural quality of the parent LiNiPO4 in the absence of secondary component phases resulted in the formation of hexagonal closed packed structure. The olivine analogue compound containing mixed M (M = Mg, Ni) cations, Li(Mg0.5Ni0.5)PO4 contained Li3PO4 as a second phase upon synthesis, however a carbothermal reduction method produced a single-phase compound. The redox behaviour of carbon-coated Li(Mg0.5Ni0.5)PO4 cathode in aqueous lithium hydroxide as the electrolyte showed reversible lithium intercalation.

Electrodeposition of manganese dioxide: effect of quaternary amines

The effect of quaternary ammonium salts (tetraethyl ammonium bromide, tetrapropyl ammonium bromide, and tetrabutyl ammonium bromide) on the structural, morphological, and electrochemical characteristics of electrolytic manganese dioxide (EMD) obtained from acidic aqueous sulfate solution has been investigated. Physical characterization of the EMD was achieved by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, differential thermal analysis, and Fourier transform infrared spectroscopy. The charge–discharge profile of the materials was determined to evaluate their potential for alkaline battery applications. The presence of these quaternary ammonium salts as organic additives in the solution increased the current efficiency while decreasing energy consumption during electrochemical deposition of manganese dioxide (MnO2). All the additives influenced the discharge characteristics of the EMD samples significantly, producing a cathode material with increased cumulative discharge capacity relative to EMD prepared in the absence of additives. This is attributed to the ability of the additives to affect the particle size and morphology, and therefore electrochemical activity, of electrodeposited materials; the effects in the case of the additives investigated in this work were positive, producing a material with potential application to battery technology.

Sn – MnO2 Aqueous Rechargeable Battery

Sn-based anodes are currently under investigation as a negative electrode material suitable for lithium-ion batteries using nonaqueous solvents as the electrolyte. However, there is no literature on Sn anodes in aqueous solutions. We present here a class of Sn- MnO2 rechargeable batteries using aqueous lithium hydroxide as the electrolyte. The Sn- MnO2 cell is suitable for a 1 V battery delivering a reversible discharge capacity of 110 mAh/g. This battery presented 85% rechargeability after the 50th cycle. With a view to enhancing the battery capacity, small concentrations (1-5 wt %) of MgO additive were added to the MnO2 cathode and its electrochemical behavior was investigated. The Sn LiOH MnO2 battery exhibited good characteristics indicating its potential as an aqueous rechargeable system.

Co/Mo bimetallic addition to electrolytic manganese dioxide for oxygen generation in acid medium

An efficient electrocatalyst comprising inexpensive and earth-abundant materials for the oxygen evolution reaction (OER) is crucial for the development of water electrolysis. In this work, in-situ addition of cobalt/molybdenum ions to the electrolytic manganese dioxide has been shown to be beneficial for the OER in acid solution as its overpotential performed better (305 mV) than that of the commercial DSA® (341 mV) at 100 mA cm−2. The OER was investigated at ambient temperature in 2 M H2SO4 solution on the modified EMD (MnMoCoO) electrodes. The energy efficiency of the MnMoCoO electrodes improved significantly with the amount of Co in the plating solution. For the electrodeposited catalysts, physico-chemical and electrochemical measurements were conducted including static overpotentials. The better performance of the modified EMD was attributed to an improved charge transfer resistance (Rct; 0.290 Ω cm2), average roughness factor (rf; 429) and decrease in water content in the electrodeposited catalysts. The kinetic parameters obtained on MnMoCoO catalysts were compared and discussed according to the cobalt concentration.