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.

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 FeF 3 •0.33H 2 O nanoparticles. The structural changes of FeF 3 •0.33H 2 O is further investigated by ex-situ XRD, XPS, and ex situ high-resolution transmission electron microscopy.

Lithium‐rich, Mn‐based layered oxides Li2MnO3‐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(Li0.16Ni0.19Fe0.18Mn0.46)O2. It exhibited a high reversible capacity of 169.2 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.

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In this paper, we prepared nanostructured γ-MnO2 and used it as the cathode material in a sodium battery. X-ray diffraction (XRD), inductively coupled plasma spectroscopy (ICP), a first-principles calculation, and other tests were carried out to study the structural changes of γ-MnO2 during Na+ (de)­intercalation. A phase transformation of γ-MnO2 to NaMnO2 was found during the first discharge. However, the capacity decayed quickly in EC-based electrolytes due to the dissolution of Mn2+. By replacing the electrolyte with ionic liquid­(IL), Mn2+ dissolution can be effectively alleviated and the cycling of γ-MnO2 can be improved. The capacity is as high as ∼150 mAh/g after 100 cycles in the ionic liqiud.