Investigation of the Phase Transition Mechanism in LiFePO₄ Cathode Using In Situ Raman Spectroscopy and 2D Correlation Spectroscopy during Initial Cycle

Lithium storage performance enhanced by lithiation-induced structural phase transitions of fluorinated MXenes

Structural phase transitions in electrode materials of Li-ion batteries (LIBs) often occur along with Li-ion extraction/intercalation during charge and discharge processes. Lithiation-induced phase transition behaviors of two-dimensional fluorinated MXenes were investigated systematically by first-principles density functional calculations. The calculated results show that fluorine atoms in the nine MXenes studied moved from the FCC site (or HCP site for Ta₂CF₂) to the TOP site during Li adsorption. Further all the predicted phase transitions were confirmed by ab initio molecular dynamic simulations. The band structure, density of state, diffusion energy barrier, average voltage and storage capacity were calculated to evaluate the lithium storage properties of fluorinated MXenes, which revealed that V₂CF₂ and Ti₂CF₂ are the optimal candidates for LIB electrode materials. The structural phase transition led to improvements in the cycle stability, storage capacity, average voltage, and other lithium storage properties of the fluorinated MXenes.

A systematic computational investigation of lithiation-induced structural phase transitions of O-functionalized MXenes

Along with Li-ion extraction/intercalation during charge and discharge processes, structural phase transitions often occur in the electrode materials of Li-ion batteries (LIBs). By determining atomic positions before and after Li adsorptions, structural phase transitions of two-dimensional MXenes were investigated systematically using first-principles density functional calculations. The lithiation-induced phase transitions of ten M₂C MXenes with oxygen groups can be divided into three types. No phase transitions occur for Ti-type MXenes including Ti₂CO₂, Zr₂CO₂ and Hf₂CO₂. The oxygens in Ta-type MXenes (Sc₂CO₂, Y₂CO₂, Nb₂CO₂ and Ta₂CO₂) move from one type of octahedral void to another type of octahedral void. However, for Mo-type MXenes including V₂CO₂, Cr₂CO₂ and Mo₂CO₂, the oxygens move from octahedral voids to tetrahedral voids. The mechanisms whether phase transitions happen or not are dependent on the sizes of M ions. Furthermore, all the predicted phase transitions were confirmed by ab initio molecular dynamics simulations. The calculated results of electron localization functions and Bader charge illustrate that there exist strong Coulomb interactions (ionic bonds) between Li and MXene surfaces. The band structure, diffusion energy barrier, open circuit voltage and storage capacity were calculated to evaluate the lithium storage properties of different MXenes, which reveals that V₂CO₂ and Cr₂CO₂ should be optimal candidates as electrode materials for LIBs.

Structural and Electrochemical Properties of Li2O-V2O5-B2O3-Bi2O3 Glass and Glass-Ceramic Cathodes for Lithium-Ion Batteries

In this study, 20Li2O-60V2O5-(20 - x)B2O3-xBi2O3 (x = 5, 7.5, 10 mol%) glass materials have been prepared by the melt-quenching method, and the structure and morphology of the glass materials have been characterized by XRD, FTIR, Raman, and FE-SEM. The results show that the disordered network of the glass is mainly composed of structural motifs, such as VO4, BO3, BiO3, and BiO6. The electrochemical properties of the glass cathode material have been investigated by the galvanostatic charge-discharge method and cyclic voltammetry, and the results show that with the increases of Bi2O3 molar content, the amount of the VO4 group increases, and the network structure of the glass becomes more stable. To further enhance the electrochemical properties, glass-ceramic materials have been obtained by heat treatment, and the effect of the heat treatment temperature on the structure and electrochemical properties of the glass has been studied. The results show that the initial discharge capacity of the glass-ceramic cathode obtained by heat treatment at 280 °C at a current density of 50 mA·g-1 is 333.4 mAh·g-1. In addition, after several cycles of charging and discharging at a high current density of 1000 mA·g-1 and then 10 cycles at 50 mA·g-1, its discharge capacity remains at approximately 300 mAh·g-1 with a capacity retention rate of approximately 90.0%. The results indicate that a proper heat treatment temperature is crucial to improving the electrochemical properties of glass materials. This study provides an approach for the development of new glass cathode materials for lithium-ion batteries.

Antibacterial amorphous magnesium phosphate/graphene oxide for accelerating bone regeneration

Magnesium phosphates (MgP)s have attracted interest as an alternative biomaterial compared to the calcium phosphate (CaP)s compounds in the bone regeneration application in terms of their prominent biodegradability, lack of cytotoxicity, and ability of bone repair stimulation. Among them, amorphous magnesium phosphates (AMP)s indicated a higher rate of resorption, while preserving high osteoblasts viability and proliferation, which is comparable to their CaP peers. However, fast degradation of AMP leads to the initial fast release of Mg²⁺ ions and adverse effects on its excellent biological features. It seems that the addition of graphene oxide (GO) to magnesium phosphate can moderate its degradation rate. Hence, a novel in situ synthesized AMP powders containing 0.05, 0.25, 0.5, and 1 wt% of graphene oxide (AMP/GO) were developed to achieve a favorable degradation rate, desirable antibacterial properties against both Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) accompanying with proper cell viability and proliferation. The incorporation of 0.5 wt% of graphene oxide into the AMP ceramic led to reduce the release of Mg²⁺ ions from 571.2 ± 12.9 mg/L to 372.8 ± 14.7 mg/L and P ions from 354.8 ± 11.9 mg/L to 245.3 ± 9.9 mg/L, at day 10 of immersion in PBS. Besides, AMP/0.5 GO bioceramics were capable of eradicating all bacterial colonies of both strains. On the other hand, MG63 cells viability went up from 143.46% ± 7.54 to 184.46% ± 11.54 on the 7th day of culture in the presence of 0.5 wt% of GO compared to pure AMP ceramic. Furthermore, alizarin red staining and alkaline phosphatase (ALP) activity demonstrated the ability of AMP/GO to maintain the osteogenic phenotype of MG63 cells during 7 days culture. Therefore, it can be concluded that well distributed and in situ synthesized AMP/0.5GO powders can be a promising biomaterial for bone tissue regeneration.

Glycerol's generalized two-dimensional correlation IR/NIR spectroscopy and its principal component analysis

In this manuscript, the fundamental vibration, the combination vibration and the first overtone vibration of the glycerol hydroxyl were studied by near-infrared and infrared spectroscopy. The composition and variation of hydrogen bond were analyzed by two-dimensional correlation spectroscopy and principal component analysis. The analysis revealed five types of hydroxyl and verified the existence of independent, intramolecular, as well as intermolecular, hydrogen bond hydroxyl. The principal component analysis showed that there were three main forms of glycerol association: the first and second principal components explained the majority of the spectral features, and the third was mainly the independent hydroxyl. The results provided insight into the structure of glycerol and illustrated the potential for using these tools in analyzing bonding in even more complex systems.