Study on ionic conduction of solid-liquid composite electrolyte

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In this study, the composite that contains ceramic ionic and organic solvent is tested as an electrolyte of lithium ion battery. Two-dimensional clays (smectite) were used as ionic conductor and propylene carbonate was used as solvent. The guest cation between aluminosilicate layers of the clay was ion-exchanged by lithium with being soaked in lithium chloride solution. The composite became sticky fluid due to strong interaction between clay and solvent, then its lithium ion conductivity was measured by impedance method.The conductivity of 10ィイD1-3ィエD1Scm at room temperature was obtained for the composite. In pure liquid electrolyte, the same order of conductivity is achieved. This fact indicates that the clay particles in the composite do not prevent from smooth ionic conduction but rather enhance it. Just after preparation of the composite, no ionic species exist in the solvent. The experimental result showing such quite high ionic conduction implies the mechanism that lithium comes out from clay matrix into solvent and takes part in conduction. However, from necessity of electroneutrality, fixed amount of lithium should be accommodated in clay matrix. The conduction oath through clay and solvent is arranged not in parallel but in series. This system is an ideal single ionic conductor and its high conductivity becomes an advantage for practical battery use.The test cell containing this composite electrolyte with lithium anode and LiCoOィイD22ィエD2 cathode show reversible capacity of 70mAhgィイD1-1ィエD1 in the first cycle, the rapid loss was observed in the following ones. On the other hand, the electrolyte sandwiched two lithium sheets show good cycling behavior about lithium deposition and dissolution. This problem is, therefore, considered o stem from interfacial optimization at cathode surface. The improvement of the contact between the composite and cathode may lead to the development of safer lithium ion battery.