Lithium-manganese dioxide oxide electrodes

On the other hand, the medical condition where the heart beats too fast is known as tachycardia. If untreated, tliis condition may lead to ventricular fibrillation, that is, a condition in which the heart stops beating and shakes uncontrollably and is usually fatal. In 1980, a special device was developed and implanted in patients. It could sense the condition and provide a shock that would stop the fibrillation and restore the normal sinus rhythm via an electrode sutured onto the heart. The device was first powered by a lithium/vanadium pentoxide system later it was replaced by a system using a cathode material of silver vanadium oxide (SVO or Ag2V40ii). This is the actual system used in modem ICDs (implantable cardioverter/defibrillator). Another material used is the lithium/manganese dioxide system. Also, a new system using a sandwich cathode design with an inner cathode material of carbon monofluoride and an external cathode layer of silver vanadium oxide is in wide use. 

Sn-doped Mn02 oxide retained about 71 %, while undoped MnC>2 retained only 40.2% from their initial capacities at 40th cycle. The capacity loss observed in the first cycles in undoped Mn02 was attributed to the small amount of lithium ions inserted in the Mn02 electrode that could not be easily removed from the structure. Similar detrimental effect of cycling on the manganese dioxide structure, but with smaller amplitude, occurred in Sn-Mn02. The reason for a much smaller capacity fade in Sn-doped materials was the enhancement of the structural stability by the presence of the framework Sn ions, which contributed to the reduction of Jahn-Teller ions. 

Some details on the construction of this type of cell are shown in Figure 24.16. The current collector is a sheet of perforated stainless steel. The stainless steel top cap functions as the negative terminal and the stainless steel cell can as the positive terminal of the cell. The polypropylene closure is highly impermeable to water vapour and prevents moisture entering the cell after it has been sealed. The separator is of non-woven polypropylene cloth and contains the electrolyte, a solution of lithium perchlorate in a mixture of propylene carbonate and dimethoxyethane. The lithium negative electrode is punched from sheet lithium and the manganese dioxide cathode is made from a highly active electrolytic oxide. 

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