Chemical Overcharge and Overdischarge Protection for Li‐Alloy/Transition‐Metal Sulfide Cells

Abstract

The present lithium-alloy/metal sulfide cells require the careful monitoring of an experimentally established charge cutoff voltage to prevent detrimental overcharge of the cell. The detrimental overcharge results in anodic dissolution of the positive electrode active material or current collector above a critical potential, followed by metal precipitation in the separator as a result of a chemical reaction (Eq. [1]) between lithium dissolved in the electrolyte (Lidissolved) and the transition metal ionsThe metal precipitate short-circuits the cell and terminates cell operation (1). Lithium dissolution from lithium metal or its alloys in molten lithium halides has been verified and studied by several researchers (2-4). In the absence of the transition metal ions in the electrolyte, the dissolved lithium reacts with the positive electrode causing self-discharge of the cell.Overcharge is a serious problem in batteries of Li-alloy/ transition-metal sulfide cells. Maintaining the charge voltage of each cell at or below the voltage limit and simultaneously reaching equal capacity in each series-connected cell of the battery over many cycles are difficult tasks.

A shuttle mechanism for molten-electrolyte lithium batteries

“…The overcharge.tolerant FeS cells at 475°C with the two-phase Li.alloy electrode have demonstrated even higher rates of overcharge tolerance, 3.5 mA/cm 2. [Overcharge tolerance has also been measured for a LiAISi/FeS couple (13).] These cells were operated at higher temperature, 475-500°C, and with an all-lithium electrolyte.…”