RESUMEN
Lithium-sulfur batteries are believed to possess the feasibility to power electric vehicles in the future ascribed to the competitive energy density. However, soluble polysulfides continuously shuttle between the sulfur electrode and lithium anode across the separator, which dramatically impairs the battery's capacity. Herein, the surface of a polypropylene separator (PP film) is successfully modified with a delicately designed cation-selective polymer layer to suppress the transport of polysulfides. In principle, since bis-sulfonimide anions groups on the backbone of the polymer are immobilized, only cations can pass through the polymer layer. Furthermore, plenty of ethoxy chains in the polymer can facilitate lithium-ion mobility. Consequently, in addition to obstructing the movement of negatively charged polysulfides by the electrostatic repulsive force of fixed anions, the coated multi-functional layer on the PP film also guarantees the smooth conduction of lithium ions. The investigations demonstrate that the battery with the pristine PP film only delivers 228.5â mAh g-1 after 300â cycles at 2â C with a high capacity fading rate of 60.9 %. By contrast, the polymer-coated sample can release 409.4â mAh g-1 under the identical test condition and the capacity fading rate sharply declines to 43.2 %, illustrating superior cycle performance.
RESUMEN
The effect of electrochemically active MnO2 as a coating material on the electrochemical properties of a Li1.2Mn0.54Ni0.13Co0.13O2 (LTMO) cathode material is explored in this article. The structural analysis indicated that the layered structure of the LTMO was unchanged after the modification with MnO2. The morphology inspection demonstrated that the rod-like LTMO particles were encapsulated by a compact coating layer. The MnO2 layer was able to hinder the electrolyte solution from corroding the LTMO particles and optimized the formation of a solid electrolyte interface (SEI). Meanwhile, lithium ions were reversibly inserted into and extracted from MnO2, which afforded an additional capacity. Compared with the bare LTMO, the MnO2-coated sample exhibited enhanced electrochemical performance. After the MnO2 coating, the first discharge capacity rose from 224.2 to 239.1 mAh/g, and the initial irreversible capacity loss declined from 78.2 to 46.0 mAh/g. Meanwhile, the cyclic retention climbed up to 88.2% after 100 cycles at 0.5 C, which was more competitive than that of the bare LTMO with a value of 71.1%. When discharging at a high current density of 2 C, the capacity increased from 100.5 to 136.9 mAh/g after the modification. These investigations may be conducive to the practical application of LTMO in prospective automotive Li-ion batteries.