ABSTRACT
The liquid-phase mass transport is the key factor affecting battery stability. The influencing mechanism of liquid-phase mass transport in the separators is still not clear, the internal environment being a complex multi-field during the service life of lithium-ion batteries. The liquid-phase mass transport in the separators is related to the microstructure of the separator and the physicochemical properties of electrolytes. Here, in-situ local electrochemical impedance spectra were developed to investigate local inhomogeneities in the mass transfer process of lithium-ion batteries. The geometric microstructure of the separator affects the mass transfer process, with a reduction in porosity leading to increased overpotentials. There is a competitive relationship among porosity, tortuosity, and membrane thickness in the geometric parameters of the separator, resulting in a peak of polarization. The resistance of the liquid-phase mass transfer process is positively correlated with the viscosity of the electrolyte, making ion migration difficult due to high viscosity. Polarization is closely related to the electrochemical performance, so a phase diagram of battery performance and inhomogeneous mass transfer was developed to guide the design of the battery. This study provides a guiding basis for the development of high stability lithium-ion batteries.
ABSTRACT
Benefits emerging from applying high-entropy ceramics in Li-ion technology are already well-documented in a growing number of papers. However, an intriguing question may be formulated: how can the multicomponent solid solution-type material ensure stable electrochemical performance? Utilizing an example of nonequimolar Sn-based Sn0.8(Co0.2Mg0.2Mn0.2Ni0.2Zn0.2)2.2O4 high-entropy spinel oxide, we provide a comprehensive model explaining the observed very good cyclability. The material exhibits a high specific capacity above 600 mAh g-1 under a specific current of 50 mA g-1 and excellent capacity retention near 100% after 500 cycles under 200 mA g-1. The stability originates from the conversion-alloying reversible reactivity of the amorphous matrix, which forms during the first lithiation from the initial high-entropy structure, and preserves the high level of cation disorder at the atomic scale. In the altered Li-storage mechanism in relation to the simple oxides, the unwanted aggregated metallic grains are not exsolved from the anode and therefore do not form highly lithiated phases characterized by large volumetric changes. Also, the electrochemical activity of Mg from the oxide matrix can be clearly observed. Because the studied compound was prepared by a conventional solid-state route, implementation of the presented approach is facile and appears usable for any oxide anode material containing a high-entropy mixture of elements.
ABSTRACT
Being considered as one of the most potential cathode materials, Li1.15Ni0.17Co0.11Mn0.57O2 draws plenty of attention towards its optimization on cycling and rate performance. The surface coating process provides a longer cycling life and better rate performance for the cathodes. A systematic investigation has been carried out on the nano-AlPO4 coating layer for the Li1.15Ni0.17Co0.11Mn0.57O2 cathode material through a facile in situ dispersion process. The 1% coated cathode material can hold about 90% capacity retention after 100 cycles. Besides, the surface coating enhances the rate ability of Li1.15Ni0.17Co0.11Mn0.57O2, which holds a reversible capacity of 202.3 mAh g-1 at the rate of 1C. Surface information is collected during cycling, which reveals that less side reactions occur on the electrode-electrolyte interface after the coating process for improved cycling and rate performance.
