Impacts of Mg doping on the structural properties and degradation mechanisms of a Li and Mn rich layered oxide cathode for lithium-ion batteries.

The Li- and Mn-rich layered oxide cathode material class is a promising cathode material type for high energy density lithium-ion batteries. However, this cathode material type suffers from layer to spinel structural transition during electrochemical cycling, resulting in energy density losses during repeated cycling. Thus, improving structural stability is an essential key for developing this cathode material family. Elemental doping is a useful strategy to improve the structural properties of cathode materials. This work examines the influences of Mg doping on the structural characteristics and degradation mechanisms of a Li1.2Mn0.4Co0.4O2 cathode material. The results reveal that the prepared cathode materials are a composite, exhibiting phase separation of the Li2MnO3 and LiCoO2 components. Li2MnO3 and LiCoO2 domain sizes decreased as Mg content increased, altering the electrochemical mechanisms of the cathode materials. Moreover, Mg doping can retard phase transition, resulting in reduced structural degradation. Li1.2Mn0.36Mg0.04Co0.4O2 with optimal Mg doping demonstrated improved electrochemical performance. The current work provides deeper understanding about the roles of Mg doping on the structural characteristics and degradation mechanisms of Li-and Mn-rich layered oxide cathode materials, which is an insightful guideline for the future development of high energy density cathode materials for lithium-ion batteries.

A multiscale investigation elucidating the structural complexities and electrochemical properties of layered-layered composite cathode materials synthesized at low temperatures.

Layered-layered composite (xLi2MnO3·(1 -x) LiMO2, M = Mn, Ni, Co, and Fe) cathode materials have attracted much attention as cathodes for high energy density lithium ion batteries. However, these materials are structurally unstable resulting from complicated phase transformation mechanisms during cycling. Additionally, the complex structural characteristics and structural stability of these materials largely depend on their preparation methods. Studying the correlation between multiscale structural properties and preparation methods is important in the development of layered-layered composite cathode materials. In this work, 0.5Li2MnO3·0.5LiCoO2 composite materials were prepared with different heating and cooling rates with a maximum temperature of 600 °C. The structural properties of the 0.5Li2MnO3·0.5LiMO2 composite materials were investigated using combined in situ X-ray absorption spectroscopy (XAS), in situ X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and high resolution transmission electron microscopy (HRTEM) techniques. Heating and cooling rates have no significant effect on either the crystal or local atomic structures of the prepared samples. However, the microstructure was critically important for its impact on electrochemical properties.

Data on effect of electrospinning conditions on morphology and effect of heat-treatment temperature on the cycle and rate properties of core-shell LiFePO4/FeS/C composite fibers for use as cathodes in Li-ion batteries.

The data in this study are related to the research article "Core-shell electrospun and doped LiFePO4/FeS/C composite fibers for Li-ion batteries" [1]. Core-shell LiFePO4/FeS/C composites fiber were prepared via an electrospinning method for use as cathodes in Li-ion batteries. The data presented in this paper showed the effect of electrospinning parameters, including applied voltage, solution flow rate, the concentration of polyvinylpyrrolidone (PVP) (wt%) and a mixed PVP/PEO (polyethylene oxide) (w/w%) polymers on the morphological properties of composites fibers. These data were developed using scanning electron microscopy (SEM). Then, the effect of heat-treatment temperature on fiber morphology was investigated using transmission electron microscopy (TEM). The voltage profile and cycle rate properties of the core-shell LiFePO4/FeS/C composites obtained after various heat treatments were studied.

Rate dependent structural transition and cycling stability of a lithium-rich layered oxide material.

Lithium-rich layered oxide materials, xLi2MnO3·(1 - x)LiMO2 (M = Mn, Fe, Co, Ni, etc.), are a promising candidate for use as cathode materials in the batteries of electric vehicles (EVs). This is due to their high energy density (∼900 W h kg-1), which is larger than those of the currently used commercial cathode materials. Moreover, EV technologies require lithium ion batteries with a high rate performance to achieve short charging times. The high rate property largely depends on the electrochemical properties of the electrodes in these batteries. However, the correlation between the cycling rate, structural stability and electrochemical properties of cathode materials is not clearly understood. In this work, the influence of cycling rate on structural transition behaviors and cycling stability of a 0.5Li2MnO3·0.5LiCoO2 composite-based material was investigated. The experimental results reveal that cycling rates significantly affect the activation of the Li2MnO3 component. A high cycling rate retards Li2MnO3 activation, leading to a smaller spinel phase transition and a higher cycling stability.