Improvement in the Capacity and Safety of Lithium/Inorganic Electrolyte Sulfur Dioxide Rechargeable Cells. Phase 2.

摘要

Our objective was to develop a prototype rechargeable lithium/sulfur dioxide/carbon cell, using practical AA size hardware, in which the electrolyte was to be a sulfur dioxide solution of lithium bromide or thiocyanate, together with a highly soluble cosolute, a second non-lithium salt of the same anion. The cosolute was intended to replace the organic cosolvents familiar from the primary cells, and hopefully, to improve lithium plating efficiency and electrolyte stability during cycling. The primary discharge capacities for AA size cells containing 1.25M CsBr/ 0.12 M LiBr/ So2 were only about 400mAh, while secondary and subsequent capacities were less than 200 mAh. The rates of solvolysis of bromide and of thiocyanate were exacerbated apparently both by the high anion concentrations and by increased lithium ion concentration. We then studied lithium/ sulfur dioxide/ carbon rechargeable cells in which the electrolytes were mixtures of tetrachloroaluminate salts in sulfur dioxide, to take advantage of the better performance, but to face the problem of limited capacity. We determined that the capacity of lithium/ bromine soluble positive cells was being limited by the loss of electrical contact between the carbon and the positive electrode current collector. Also, lithium plating efficiency was poor.