Mitigating strategy in lithium dendrite formation in a Li–S cell in accelerated cycling tests

Abstract

Electrochemical impedance analysis, in-situ dilatometry, in-situ electrochemical calorimetry and ex-situ SEM have been shown to be effective diagnostics for studying formation of lithium dendrites in cells. Effect of lithium polysulfides present in the electrolyte in a Li–S cell, on the suppression of fine-dispersed heterogenous non-planar lithium dendrite precipitations during cycling of lithium symmetric cells was studied in accelerated DC cycling tests by a combination of the above techniques. It is shown that deliberate incorporation of lithium polysulfides in electrolyte solutions leads to decreasing rate of accumulation of fine-dispersed lithium (dendrite precipitations) on the surface of a lithium electrode which results in increasing the cycle life of lithium symmetric cells by 200–250% in accelerated tests, thus enhancing safety. It is demonstrated that electrochemical dilatometry and EC calorimetry are sensitive to changes on the surface of lithium electrode and can be used for early identification of dendrite formation during cycling of lithium electrodes. In-situ electrochemical dilatometry can not only identify formation of Li dendrites at early stages but also quantify the growth rate. The presence of high surface area lithium is more corrosive towards the electrolyte and can be monitored by the use of in-situ EC calorimetry for heat generation by corrosion during a cycle. Cycle life is limited by evenness/continuity of electrolyte solution in cell, which must essentially fill internal volume of the cell (all the pores without leaving any “dry area”).