Viktor Hacker

Thermal-runaway experiments on consumer Li-ion batteries with metal-oxide and olivin-type cathodes

Li-ion batteries play an ever-increasing role in our daily life. Therefore, it is important to understand the potential risks involved with these devices. In this work we demonstrate the thermal runaway characteristics of three types of commercially available Li-ion batteries with the format 18650. The Li-ion batteries were deliberately driven into thermal runaway by overheating under controlled conditions. Cell temperatures up to 850 °C and a gas release of up to 0.27 mol were measured. The main gas components were quantified with gas-chromatography. The safety of Li-ion batteries is determined by their composition, size, energy content, design and quality. This work investigated the influence of different cathode-material chemistry on the safety of commercial graphite-based 18650 cells. The active cathode materials of the three tested cell types were (a) LiFePO4, (b) Li(Ni0.45Mn0.45Co0.10)O2 and (c) a blend of LiCoO2 and Li(Ni0.50Mn0.25Co0.25)O2.

A novel process for stationary hydrogen production: the reformer sponge iron cycle (RESC)

Abstract The reformer sponge iron cycle (RESC) is discussed as a new process for stationary hydrogen production. The RESC is based on the sponge iron reaction process in combination with a reformer unit. The sponge iron reaction process is a cyclic process for water splitting, whereby a syngas is consumed. The syngas reacts with iron oxide (magnetite, Fe3O4) to produce a reduced form of iron oxide (wuestite or iron). The reduced iron oxide is re-oxidised with steam to form magnetite and hydrogen. This process is now combined with the reformer to enhance the overall efficiency considerably. The reformer is operated with methane or liquid hydrocarbons and carbon dioxide and steam out of the sponge iron reaction process off-gas are used for the reforming reaction. Experimental investigations concentrate on the lifetime analysis of the contact mass of the sponge iron reaction process and the catalyst performance under given temperature conditions, and syngas and off-gas compositions as discussed in this paper.

Direct methanol-air fuel cells with membranes plus circulating electrolyte

A new approach for direct methanol–air fuel cells (DMFC), with the advantage of reduced methanol crossover is discussed in this paper. Methanol traces in the circulated electrolyte are recovered and CO2 bubbles in the cells are removed due to the forced methanol–electrolyte stream through the cell. Degradation of the catalyst is reduced since fuel cell electrodes degrade on activated stand without load to a higher extent than under load because high voltage on open circuit promotes carbon oxidation, catalyst changes, etc. Therefore, life expectancy increases with circulating electrolyte by removing the electrolyte from the cells between operating periods.

Thermal runaway of commercial 18650 Li-ion batteries with LFP and NCA cathodes – impact of state of charge and overcharge

Thermal runaway characteristics of two types of commercially available 18650 cells, based on LixFePO4 and Lix (Ni0.80Co0.15Al0.05)O2 were investigated in detail. The cells were preconditioned to state of charge (SOC) values in the range of 0% to 143%; this ensured that the working SOC window as well as overcharge conditions were covered in the experiments. Subsequently a series of temperature-ramp tests was performed with the preconditioned cells. Charged cells went into a thermal runaway, when heated above a critical temperature. The following thermal runaway parameters are provided for each experiment with the two cell types: temperature of a first detected exothermic reaction, maximum cell temperature, amount of produced ventgas and the composition of the ventgas. The dependence of those parameters with respect to the SOC is presented and a model of the major reactions during the thermal runaway is made.

Recent advancements in chemical looping water splitting for the production of hydrogen

Chemical looping water splitting or chemical looping hydrogen is a very promising technology for the production of hydrogen. In recent years extensive research has enabled remarkable leaps towards a successful integration of the chemical looping technology into a future hydrogen infrastructure. Progress has been reported with iron based oxygen carriers for stable hydrogen production capacity over consecutive cycles without significant signs of degradation. The high stability improvements were achieved by adding alien metal oxides or by integrating the active component into a mineral structure which offers excellent resistance towards thermal stress. Prototype systems from small μ-systems up to 50 kW have been operated with promising results. The chemical looping water splitting process was broadened in terms of its application area and utilization of feedstocks using a variety of renewable and fossil resources. The three-reactor system was clearly advantageous due to its flexibility, heat integration capabilities and possibility to produce separate pure streams of hydrogen, CO2 and N2. However two-reactor and single fixed-bed reactor systems were successfully operated as well. This review aims to survey the recently presented literature in detail and systematically summarize the gathered data.

Online stack monitoring tool for dynamically and stationary operated fuel cell systems

The motivation for this development of a new fuel cell stack monitoring system is to establish a much simpler, low-cost stack diagnosis unit feasible for large production volumes. In comparison to conventional cell voltage monitoring (CVM) technology, where up to several hundreds of voltage channels have to be measured, Total Harmonic Distortion Analysis (AVL THDA) significantly reduces the required wiring, contacting and instrumentation. This new approach derives information about critical cell and stack status from only the stack sum voltage. A real-time output signal then indicates whether the stack – in fact every single cell – is operating under safe and reliable conditions. The new technique also detects critical stack operating conditions during load changes, where other monitoring systems usually have difficulty in distinguishing between a change in the voltage of a single cell as a result of load changes or resulting from the occurrence of a critical cell operating status.

The Safe and Economic Revival of Alkaline Hydrogen/Air Fuel Cells with Circulating Electrolytes, Recommended for Vehicles Using Battery Hybrid Systems and H2 from Ammonia Crackers

Alkaline Fuel Cells (AFCs): The Bacon Fuel Cell, the ApolloNASA Space Shuttle and the Russian Systems, the Allis-Chalmers H2/O2 Tractor, the Union Carbide Corp. H2-O2 GM-Electrovan, the Kordesch Austin-Fuel Cell Hybrid Car, the Eloflux and the Elenco system and the European Space (ESA) Power Plant for HERMES. Also: the Dornier-Siemens and the Swedish Navy systems, Olle Lindstrom s work in Stockholm and in India, The Fuel Cells by Hoechst and von ZeTeK. A Bipolar System was built in Graz and at Apollo Energy Systems, Inc., 2 kW AFCs were tested with NH3. Liquified ammonia, available in low pressure cylinders, can be converted to 75 % H2, 25 % N2 with high efficiency. The capacity per weight and volume of ammonia as fuel surpasses methanol. Ammonia is produced worldwide in amounts of several 100 million tons per year and is produced from natural gas. Ammonia is available on farms. Refrigerators worked safely with ammonia. Internal combustion engines operate on cracked ammonia (a 75 % H2 and 25 % N2 mix) with increased power and higher efficiency 1. Hydrogen/Oxygen (Air) Fuel Cells with Alkaline Electrolytes General Principles (1, 2, 3) Alkaline Fuel Cells (AFCs) operate well at room temperatures, yield the highest voltage at comparable current densities, but the use of KOH requires the removal of CO2 from reformed fuels and control of the CO2 in the air. The electrodes can be built from low-cost porous materials ( e.g. carbon, Ni-foam) with small amounts of catalysts. The components and accessories for a system with circulating electrolyte are fully developed. Alkaline Fuel Cells excel in operating at intermittent duty cycles, like in mobile service, but can also be used in stationary applications, like houses (Solar Power) and on Farms (with Ammonia Cracker). Military applications are looked for in sizes from 150 W to several kW for charging accumulators in the field. Alkaline fuel cells normally use an aqueous solution (30 to 45 wt.%) of potassium hydroxide (KOH) as electrolyte, either mobilized or immobilized. Also, sodium hydroxide (NaOH) would be possible, but has some disadvantages, especially the much lower solubility of sodium carbonate compared to potassium carbonate. Hydroxyl anions diffuse continuously from the cathode to the anode. Most of the reaction water leaves on the anode side through the pores, but a small amount of water vapor is also removed via

High purity pressurised hydrogen production from syngas by the steam-iron process

The production of hydrogen in a fixed bed reactor at a maximum pressure of 50 bar by oxidising an oxygen carrier (Fe2O3/Al2O3/CeO2) with 0.06 g min−1 of steam at 1023 K is discussed. Reductions were performed with synthesis gas at ambient pressure and 1023 K for 90 minutes. The influences of the elevated system pressure on the carbon contamination, the quantification of the contaminations in the produced hydrogen and the oxygen carrier conversion are analysed. The results show that small amounts of carbon depositions are formed during the reduction, which are re-oxidised with steam leading to the contamination of the hydrogen. The hydrogen purity obtained in the experiments is within the range of 99.958% to 99.999% with CO as the main impurity. The amount of contaminations as a result of the oxidation of the solid carbon is not influenced by the elevated system pressure, which confirms the suitability of the reformer steam-iron process in a fixed bed to produce pressurised hydrogen directly from a hydrocarbon feed. The oxygen carrier conversion displays an initial drop followed by a slightly linear decrease. Air-oxidations revealed a regeneration effect on the oxygen carrier conversion, which reversed a part of the conversion losses.

The Effect of Platinum Electrocatalyst on Membrane Degradation in Polymer Electrolyte Fuel Cells.

Membrane degradation is a severe factor limiting the lifetime of polymer electrolyte fuel cells. Therefore, obtaining a deeper knowledge is fundamental in order to establish fuel cells as competitive product. A segmented single cell was operated under open circuit voltage with alternating relative humidity. The influence of the catalyst layer on membrane degradation was evaluated by measuring a membrane without electrodes and a membrane-electrode-assembly under identical conditions. After 100 h of accelerated stress testing the proton conductivity of membrane samples near the anode and cathode was investigated by means of ex situ electrochemical impedance spectroscopy. The membrane sample near the cathode inlet exhibited twofold lower membrane resistance and a resulting twofold higher proton conductivity than the membrane sample near the anode inlet. The results from the fluoride ion analysis have shown that the presence of platinum reduces the fluoride emission rate; which supports conclusions drawn from the literature.

THERMAL STEAM POWER PLANT FIRED BY HYDROGEN AND OXYGEN IN STOICHIOMETRIC RATIO, USING FUEL CELLS AND GAS TURBINE CYCLE COMPONENTS

This proposal fully complies to the demands of a zero emission power plant since only hydrogen and oxygen as obtained from splitting water are provided as fuel in a working gas cycle of pure water. Distributed power plants based on solar radiation, solar heat, wind power and water power from river flow, tidal flow and even wave motion should drive electrolysers producing hydrogen and oxygen. The units are connected with a pipeline system delivering hydrogen and oxygen at high pressure into respective storage tanks in the vicinity of the proposed power plant. So periods of generation of hydrogen and oxygen can overlap and these fuel gases are available to produce peak power according to demand. The proposed plant is an hybrid plant incorporating SOFC fuel cells into an innovative power cycle with steam as working fluid. Twelve fuel cells of 2.5 MW power produce electricity and heat up working fluid from 600 to 800°C. In a succeeding combustion chamber the fuel cell surplus hydrogen as well as the gas turbine hydrogen demand is burned with pure oxygen leading to a working gas (steam) of 1550°C and 40 bar. The working gas is expanded in an innovative cycle producing additional 109 MW of electrical energy. So an overall output of 139 MW can be achieved with a thermal efficiency of 73.8% based on fuel taken from the storage tanks for hydrogen and oxygen at 60 bar.© 2010 ASME