Adsorption equilibrium polysulphides seesaw: N, O-bis atoms inhibiting effect polysulfide shuttle diaphragm
Lithium-sulfur battery using sulfur as an electrode material, compared with the conventional graphite-based lithium-ion battery, its high theoretical specific capacity and energy density have attracted much attention. During the discharge, S8 Molecular Electronics and gradually gained Li + binding, undergoes a plurality of polysulfide intermediates (Li 2 S x [ after 123], x = 2, 4, 6, 8), eventually converted to Li 2 S, to complete the discharge process.
2 S x , x = 4, 6, 8) which is dissolved in the electrolyte, the positive electrode material from falling down through the porous separator, a negative electrode to the battery, causing the active material the loss of the electrode structure collapses. This process is known as \”polysulfide shuttle effect\”, is a key factor limiting the development of lithium-sulfur batteries. To solve this problem, many researchers dedicated to the design of sulfur cathode, electrolyte regulation and modification of the membrane thereby inhibiting \”polysulfide shuttling effect.\” Reported in the literature but the coating / interlayer modified aperture diaphragm tends to clog the membrane, to restrict the transmission ofs to some extent, increase the internal resistance of the battery. Therefore, the development of new membrane materials, without affecting the transport of lithium ions, polysulfide conversion behavior regulation, a useful modified for a Class ideas. Chongqing University Professor Wei Zidong, Associate Professor Li Cun Pu and other reported the use of hard and soft acid-base reaction reversible capture polysulfide, at the same time does not inhibit migration of lithium ions lithium-sulfur battery separator  ( Small , 2018, 14 (52): 1804277.). Recently, the team cognitive further conversion reaction of the interface, it is reported Based morpholine N, O-bis chemisorption atoms, can be effectively suppressed lithium-sulfur battery separator \”polysulfide shuttle effect\”  ( ACS Appl. Mater. Interfaces , 2020, 10.1021 / acsami.0c04554). By elemental sulfur analysis to multi-step reduction process can be found Li2S, various types of soluble polysulfides transformation involves the reaction of a plurality of interfaces, including solid – liquid interface reaction (S8-Li2S8), liquid – liquid interface reaction (Li2S8 – Li2S4) and liquid – solid interface reaction (Li2S4- Li2S2). With reduction of sulfur cell having constant plateau voltage because loss of various types of polysulfide intermediates of sulfur will result in a subsequent reduction process interrupted, resulting in decrease in battery capacity. Therefore, it is necessary to control various types of polysulfide equivalent to achieve steady charging and discharging of the lithium-sulfur battery. Structure by know chemical analysis, polysulfides Li 2 S x The smaller the x, Li-S bonds closer ionic bond, i.e., lithium the harder the acid, the acid itself, change in hardness of the Li-based chemical adsorption such that a single element, it is difficult to achieve the equivalent of trapping various types of polysulfide. Thereto, as shown, trapping of morpholine as polypropylene diaphragm units introduced polysulfide shuttle 2 inhibition. Morpholine containing two heteroatoms N and O, where O atoms electronegative charge greater concentration, large electron cloud hardness; electrically negative charge dispersion less N atom, the electron cloud of small hardness. Under the control effect of the two atoms to achieve an equivalent adsorption of different hardness polysulfide.
2 S x , x = 4, 6, 8) with piperidine (only one N atom), tetrahydrofuran (only one O atom), the binding energy between it morpholine (N, O atom), as shown in FIG, piperidine and tetrahydrofuran are monoatomic adsorption 4, the binding energy between the multiple levels of polysulfide weak, the difference is also larger; and morpholinyl may be equivalent to three kinds of adsorption polysulfide (Eb ≈-1.5 eV). When a long chain polysulphide side through morpholine, morpholine N, O heteroatoms it to arrest the boat conformation morpholine intermediate form diatomic adsorption, to prevent the loss of polysulfide, lithium-sulfur battery in order to achieve sustained and stable charging and discharging. Binding energy between the
-1 the specific capacity, there good cycle stability and reversibility. Thanks to the protective effect of electrode structure on the rate capability of a battery which also modified diaphragm far better than the polypropylene porous membrane.
Summary: of replacement based on knowledge of the interface conversion polysulphide process, by introducing on the diaphragm with N, O atoms of the two hybrid morpholine as the polysulfide regulatory elements to achieve the equivalent chemical adsorption of soluble polysulfides, soluble polysulfides limitation on the positive side, to ensure that the Li2S8, between the liquid and Li2S6 Li2S4 – liquid-liquid and subsequent conversion of Li2S4 solid transformation can be performed effectively, to achieve a high rate lithium-sulfur battery, charge-discharge sustainable, provides a new high performance research strategies for the development of lithium-sulfur battery.
 Dong Q, Shen R, Li C, et al Construction of soft base tongs on separator to grasp polysulfides from shuttling in lithium-sulfur batteries [J] Small… , 2018, 14 (52): 1804277.  Dong Q, Wang T, Gan R, et al Balancing the Seesaw:… Investigation of a Separator to Grasp Polysulfides with diatomic chemisorption [J] ACS Applied Materials & Interfaces, 2020. DOI: 10.1021 / acsami.0c04554