Investigation on the Necessity of Low Rates Activation toward Lithium-Sulfur Batteries

Abstract

Low rate activation process is always used in conventional transition metal oxide cathode and fully activates active substances/electrolyte to achieve stable electrochemical performance. However, the related working mechanism in lithium-sulfur (Li- battery is unclear due to the multiple complex chemical reaction steps including the redox of sulfur and the dissolution of polysulfides intermediate. Hence, the influencing mechanism of activation process on Li-S battery is explored by adopting different current densities of 0.05, 0.2, and 1 C in initial three cycles before long-term cycling tests at 0.2 C (denoted by 0.05, 0.2, and 1-battery). 0.05-battery presents the highest initial capacity in activation process, while 0.2-battery presents superior electrochemical performances after 150 cycles. The similar trend can be found in more long-term cycling rates such as 0.02, 0.1, 0.5, and 1 C. Potentiostatically Li₂S precipitation test demonstrates that rapid generation of Li₂S is achieved at higher current density, and S₈-Li₂S_n-Li₂S conversion is accelerated according to Tafel plots. However, interfacial electrochemical and physical characterizations suggest that serious lithium dendrite growth will be induced under high current density. Therefore, considering the reaction kinetics and interfacial properties, low rate activation process is unnecessary when cycling current lower than 1 C for Li-S battery.