The electrolyte for each of the systems described above is composed of an organic solvent or mixed organic solvent and a lithium containing salt, which provides the conductivity and means for lithium ion transport. Several electrolytes have been used depending on the chemistry of the insertion compound. An example of this type is the Li-TiS2 cell in which the discharge product is a combination of the reactants. Its reaction can be depicted as: The polymeric electrolyte rechargeable lithium cell is similar to the organic electrolyte cell in that it utilizes a solid cathode of the type described above. However, unlike the organic electrolyte type, it utilizes a solid lithium ion conducting polymer as the electrolyte. The performance of this type of cell depends on the transport of lithium ions through the polymer. The transport is improved with temperature. Thus, these systems generally operate close to 100°C. A number of polymers e.g. polyethylene oxide (PEO) and polypropylene oxide (PPO), as well as various copolymers and mixed polymers have been investigated for this electrochemical system. Because of the low ionic conductivity, the major effort has been to find a suitable polymeric electrolyte composition that will provide discharge rates approaching 2 ma/cm2. The reaction in this type of cell is similar to reaction (1). The inorganic electrolyte rechargeable lithium cell contains a porous carbon electrode which serves as the current collector and respository for the salt discharge product. The system receiving most attention utilizes sulfur dioxide (SO2). In one variation of the inorganic electrolyte type, the dissolved salt (LiAlCl4) participates in the reaction. In addition, the carbon in the positive electrode forms a complex with the discharge product. The reaction of this cell can be shown as: In another cell of this type, SO2 functions only as the electrolyte. CuCl2 serves as the positive electrode material. Unfortunately, the use of SO2 has led to safety concerns. The overall reaction for this cell is: The fourth type of rechargeable lithium cell is a high temperature system operating at 375-400°C. The most advanced in the molten salt technology is that using iron sulfide (FeS or FeS2) as the positive electrode. The electrolyte is a eutectic mixture of lithium chloride (LiCl) and potassium chloride (KC1). The lithium electrode is an alloy of aluminum or silicon. The discharge products are not intercalation compounds but simply Li2S and Fe. An example of the high temperature system in which the Li+ in the melt combines with the positive active material is the lithium (aluminum)-iron disulfide (Li(Al)-FeS2) cell. The complete cell discharge involves two reactions, each of which has a specific voltage. The reactions are:
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