Decomposition voltage materials

LijN has a low decomposition potential, 0.445 V, which limits its usefulness as a practical solid electrolyte in batteries. Various Li3N-derivative phases have been synthesised, such as cubic Li5Nl2 with an antifluorite-derivative structure and a related phase in the system, LijN-Lil-LiOH. Some of these have high conductivity and the latter materials in particular are comparable to those of H-doped LijN. They also have a much higher decomposition voltage, 1.5V, but do suffer from increased sensitivity to chemical attack. 

Decomposition potential (voltage) — The onset voltage for electrochemical decomposition of the electrolytic solution or the electrodes. The decomposition can take place due to either oxidation or reduction, or both. The decomposition potentials define the electrochemical window of the system. Its value depends on the salt, solvent, electrode material, temperature, and the existence of materials that can catalyze decomposition reactions, such as Lewis acids. Exact decomposition voltages are hard to reproduce as the onset current of the process is very sensitive to the experimental conditions (e.g., scan rate, temperature, type of electrode, etc.). Decomposi-... 

Availability Low cost Simple handling Nontoxicity Nonflammability High solubility of many salts Low viscosity Low working temperatures Decomposition voltage range at 1.23 V narrow Hydrogen side reactions Hydrolysis of many dissolved materials Reaction of some metals with water... 

Under the conditions achieved in industrial electrolyzers of today (KF-2HF media, 85 °C), the decomposition voltage amounts to 2.9 V. Sufficient stable electrode materials are carbon (anode) and copper or steel (cathode), steel being the cheaper choice. 

Plates of inert metals such as platinum and graphite serve in solid state electrochemical cells to supply electrons to the sample, but block the passage of material and ions for voltages below the thermodynamic decomposition voltage of the SE. The ionic current is blocked since the metals do not contain the required material that can provide the ions. In addition, the metal blocks are applied in a way that blocks the exchange of material with, e.g., the surrounding atmosphere, as well. Not only inert metals can serve for that purpose, but also any electron conductor, whether metal or semiconductor, that stays chemically intact and is impermeable to the material flow either in the form of ions or neutral species. 

Electrical trees consist of visible permanent hoUow channels, resulting from decomposition of the material, and show up clearly in polyethylene and other translucent soHd dielectrics when examined with an optical microscope. Eresh, unstained water trees appear diffuse and temporary. Water trees consist of very fine paths along which moisture has penetrated under the action of a voltage gradient. Considerable force is required to effect this... 

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