Petroleum Coke As Active Material of Negative Electrode for Lithium-Sulfur Batteries

Abstract

We studied the possibility of using graphite and petroleum coke as active materials of negative electrodes for lithium-sulfur batteries. Petroleum coke was previously subjected to thermochemical activation in its own vapor in an air atmosphere for 10 hours at 800 °C.Positive sulfur electrodes were made by casting a slurry on aluminum foil. The composition of the electrode layer was 70% wt. sulfur, 10% wt. carbon (Ketjenblack EC-600JD), and 20% wt. binder (poly(ethylene) oxide, MW 4x106).The separator was 1 layer of microporous polypropylene Celgard®3501. The electrolyte was 1M LiClO4 in sulfolane.Negative electrodes based on graphite and activated petroleum coke were prepared by slurry casting onto copper foil. The composition of the electrode layer was 94% wt. of the active material (petroleum coke or graphite), 1% wt. of the carbon black (Super P), and 5% wt. of the binder (LA-132).Negative electrodes based on carbon materials were pre-lithiated. For this purpose, cells with a lithium electrode and carbon electrode were assembled and subjected to 5 molding cycles. Figure (a) shows the typical charge-discharge voltage profiles of the semi-cells of Li - Carbon electrode. After 5 molding cycles, the cells were transferred to the glove box and lithiated carbon electrodes were removed from them. Lithium sulfur cells were assembled with these lithiated carbon electrodes.It was shown that regardless of the negative electrodes used, there are two plateau on the discharge voltage profiles of lithium-sulfur cells, corresponding to electrochemical reduction (Figure b):(1) sulfur and high ordered lithium polysulfides through a series of intermediate stages to lithium tetrasulfide:S8 + 4Li+ + 4e- → 2Li2S4 (2) Lithium tetrasulfide to lithium disulfide and lithium sulfide:Li2S4 + 4Li+ + 4e- → 2Li2S + Li2S2. It should be noted that the discharge voltage of lithium-sulfur cells with carbon electrodes is decreased by the magnitude of the voltage of lithium-carbon semi-cells (Figure (a) and (b)).At the initial stages, the rate of decrease in the discharge capacity of lithium-sulfur cells weakly depends on the composition of the negative electrode. Cycling efficiency is 91-92%.Based on the obtained results, it can be concluded that activated petroleum coke can be used as the active material of the negative electrode for lithium-sulfur batteries. This work was performed as part of a Government Order to Ufa Institute of Chemistry of the Russian Academy of Sciences by the Ministry of Science and Higher Education of the Russian Federation (Theme No. AAAA-A17-117011910031-7) Russia and was also financially supported by the Russian Science Foundation (project No 17-73-20115). Figure 1