ABSTRACT
With the continuous improvement of the energy density of traction batteries for electric vehicles, the safety of batteries over their entire lifecycle has become the most critical issue in the development of electric vehicles. Abuse of electricity encountered in the application of batteries has a great impact on the safety of traction batteries. In this study, focused on the overdischarge phenomenon that is most likely to be encountered in the practical use of electric vehicles and grid storage, the impact of overdischarge on battery performance degradation is analyzed by neutron imaging technology and its safety hazards is systematically explored, combined with multimethods including electrochemical analysis and structural characterization. Results reveal the deterioration of the internal structure of traction batteries due to the overdischarge behavior and play a guiding role in the testing and evaluation of the safety of traction batteries.
ABSTRACT
Sodium-ion batteries have been considered as one of ideal power sources for energy storage system. However, the choice of cathode material with good cycling stability and high capacity is limited. Herein, a nanocomposite of hierarchical mesoporous iron fluoride and reduced graphene oxide is prepared by an in situ approach. The as-prepared nanocomposite exhibits remarkably high discharge specific capacity of 227.5 mAh/g at 0.1C. Specifically, the discharge specific capacity of the sample still remains 87.5 mAh/g at a high rate of 15C after the 100th cycle. The electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) measurements show that the addition of reduced graphene oxide can effectively reduce the charge transfer resistance and enhance the Na+ diffusion rate in the FeF3·0.33H2O nanoparticles. The structural changes of FeF3·0.33H2O is further investigated by ex-situ XRD, XPS, and ex situ high-resolution transmission electron microscopy.
ABSTRACT
Lithium-rich, Mn-based layered oxides Li2 MnO3 -LiMO2 (M=Ni, Co) have been considered as promising cathode candidates owing to their high capacity. However, the resources shortage and high price of cobalt make it imperious to substitute cobalt with other high-abundance elements. Here, we synthesized a low-cost, cobalt-free, Fe-substituted oxide material, Li(Li0.16 Ni0.19 Fe0.18 Mn0.46 )O2 . It exhibited a high reversible capacity of 169.2â mAh g-1 after 100 cycles and maintained an extraordinarily high discharge potential during cycling. X-ray photoelectron spectroscopy and DFT calculations revealed that super iron FeIV exists in the delithiated state, and oxygen participates in the redox reaction in addition to the Ni2+ /Ni4+ and Fe3+ /Fe4+ redox couples. The anionic oxidation preferentially occurred on oxygen with a Li-O-Li configuration and with oxidized Fe and Ni coordination.
