Overlithiation of lithium ion batteries often causes a structural transformation of the electrode and capacity degradation and may even lead to severe safety problems. In this study, the electrode structure, surface morphology and compositions at the different overlithiation depths of LiCoO2 cathode material were investigated in detailed by examining the LCO/Li cells and anode-free cells, combined with post-mortem characterizations. When LiCoO2 is found in a slight overlithiation state, the cycle capacity fades slightly and minority of LiCoO2 reduces to CoO and Li2O. After LiCoO2 undergoes a deep overlithiation reaction, a long flat voltage plateau appears at 1.2 V and the cycle performance is greatly deteriorated. SEM and EIS tests show that the single-crystal particles are fractured into small particles with thick-layer formation at the surface and the shape of the EIS curve changes strongly with increasing overlithiation depth. Additionally, as shown by XPS Ar-ion etching and TEM characterization, the LiCoO2 surface is converted into greater amounts of Li2O, CoO and Co metal associated with the severe electrolyte decomposition, and LiF, Li2CO3 and LixPOyFz are the main electrolyte decomposition products. The detailed investigation of the overlithiation mechanism of LiCoO2 provides comprehensive and thorough guidance for understanding the overlithiation mechanism of cathode materials as well as important reference information for practical all-solid-state battery applications.

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Iron oxide/MCM-41 hybrid nanospheres (designated as MMSN) with a large surface area of 1334 m2/g and a uniform diameter of 85 nm have been synthesized via a facile sol-gel route. Transmission electron microscopy (TEM) imagery shows many ultra-small iron oxide nanoparticles evenly distributed inside the mesoporous silica nanospheres. High-resolution TEM image with a corresponding electron diffraction spectrum and Fourier transform infrared spectra confirm the formation of iron oxide nanoparticles while the ordered mesoporous silica structure is maintained. The MMSN present a ferromagnetic property that ensures them a fast response to an applied magnetic field. Moreover, they are proven to be beneficial for loading an anticancer drug—doxorubicin hydrochloride (DOX), because a considerable loading content of 6.0% and a high entrapment efficiency of 90.5% have been achieved. Most notably, these DOX-loaded MMSN display not only a pH-variable but also a magnetic field-controllable drug release behavior. Further, after 48 h co-incubation, the MMSN did not show any significant cytotoxicity against human HepG2 cells even at a high concentration of 250 μg/mL. These results have demonstrated that the prepared MMSN may be potential drug carriers for both magnetic targeting and stimuli-responsive controlled release.

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