Li-S batteries are promising candidate as the next-generation energy-storage systems because of their high theoretical capacities and low cost of raw materials. Nevertheless, several problems, including the shuttling of soluble lithium polysulfide intermediates and pulverization of Li metal anode, remain to make Li-S batteries viable. Although building modified separators/interlayers have overcome above issues to some extent, several challenges still exist: (1) few reported functional separators/interlayers concurrently improved sulfur cathode and lithium metal anode, (2) the main approaches for the modification of separators were complicated and not suitable for large-scale manufacturing, (3) the modification of separators often introduced inert materials with high weight (>0.2 mg cm-2) and large thickness (>0.2 µm).
In view of such a serious situation, Prof. Yongming Sun and co-workers reported the rational design of an ultrathin conductive polymer nanolayer on the pore walls of both surfaces of the separator to provide a stable electrode-separator interface for both Li anode and S cathode for the first time. The functional polypyrrole (PPy) layer not only facilitates homogenous Li+ flux and thus realizes uniform plating and stripping of metallic lithium at the anode side, but also suppresses the migration of the soluble polysulfides at the cathode side. Several important properties of the electrode and Li-S cell are discussed in the manuscript, which include: 1) The in-situ vapor-phase polymerization process enables the functional PPy layer with tiny mass (~0.13 mg cm-2) and thickness (~65nm); 2) A Li||Li symmetrical cell with a PPy modified separator gives a low and stable overpotential (<30 mV) for over 250 hours’ stripping and plating test at 1 mA cm-2 with a fixed areal capacity of 3 mAh cm-2; 3) Using a PPy modified separator, a Li-S cell delivers a high initial areal capacity of 4.7 mAh cm-2 and maintains a high value of 3.6 mA h cm-2 with 75.6% capacity retention after 150 cycles at 0.2 C at a S mass loading of 5.73 mg cm-2. It is believed that the concept of functional electrode-separator interface via engineering an ultrathin and ultralight conductive polymer interfacial nanolayer offers new insight into the development of high-performance Li-S batteries and other electrochemical energy storage devices. The relative work has been published in Energy Storage Materials (Energy Storage Materials, 2019, https://doi.org/10.1016/j.ensm.2019.05.005) with the title of “Engineering stable electrode-separator interfaces with ultrathin conductive polymer layer for practical high-energy-density Li-S batteries”. The first author is Yuanjian Li and the corresponding author is prof. Yongming Sun.
