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Parallel in situ TEM and XRD heating experiments of LiFePO4 precursors obtained by sol-gel method were conducted to study changes and to understand structural and morphological evolution during synthesis annealing, which is one of the most critical stages in preparing rechargeable cathodes based on these materials. Raman spectroscopy and electrochemical testing were also performed and a basic optimization of the final step of the sol-gel process was demonstrated by comparing in situ heating data with the electrochemical performance of materials annealed at different temperatures. The results obtained from these in situ measurements, at different length scales, provided a detailed picture of the structural and morphological changes and provided a better understanding of the electrochemical behavior of the final LiFePO4 material. The study showed a strong dependence between the electrochemical performance of LiFePO4 synthesized by sol-gel method and annealing temperature. The best performance was obtained with a material annealed at 800 °C. [ABSTRACT FROM AUTHOR]

The mechanism of capacity fade of the Li2MnO3·LiMO2 (M = Li, Ni, Co, Mn) composite positive electrode within a full cell was investigated using a combination of operando neutron powder diffraction and transmission X-ray microscopy methods, enabling the phase, crystallographic, and morphological evolution of the material during electrochemical cycling to be understood. The electrode was shown to initially consist of 73(1) wt % R3m LiMO2 with the remaining 27(1) wt % C2/m Li2MnO3 likely existing as an intergrowth. Cracking in the Li2MnO3·LiMO2 electrode particle under operando microscopy observation was revealed to be initiated by the solid-solution reaction of the LiMO2 phase on charge to 4.55 V vs Li+/Li and intensified during further charge to 4.7 V vs Li+/Li during the concurrent two-phase reaction of the LiMO2 phase, involving the largest lattice change of any phase, and oxygen evolution from the Li2MnO3 phase. Notably, significant healing of the generated cracks in the Li2MnO3·LiMO2 electrode particle occurred during subsequent lithiation on discharge, with this rehealing being principally associated with the solid-solution reaction of the LiMO2 phase. This work reveals that while it is the reduction of lattice size of electrode phases during charge that results in cracking of the Li2MnO3·LiMO2 electrode particle, with the extent of cracking correlated to the magnitude of the size change, crack healing is possible in the reverse solid-solution reaction occurring during discharge. Importantly, it is the phase separation during the two-phase reaction of the LiMO2 phase that prevents the complete healing of the electrode particle, leading to pulverization over extended cycling. This work points to the minimization of behavior leading to phase separation, such as two-phase and oxygen evolution, as a key strategy in preventing capacity fade of the electrode. [ABSTRACT FROM AUTHOR]

Mesophase soft carbon (MSC) and mesophase graphite (SMG), for use in comparative studies of high C-rate Lithium Ion Battery (LIB) anodes, were made by heating mesocarbon microbeads (MCMB) at 1300 °C and 3000 °C; respectively. The crystalline structures and morphologies of the MSC, SMG, and commercial hard carbon (HC) were investigated by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy. Additionally, their electrochemical properties, when used as anode materials in LIBs, were also investigated. The results show that MSC has a superior charging rate capability compared to SMG and HC. This is attributed to MSC having a more extensive interlayer spacing than SMG, and a greater number of favorably-oriented pathways when compared to HC. [ABSTRACT FROM AUTHOR]

Spinel LiMn2 − xCoxO4 (0.00 ≦ x ≦ 0.20) powders with small and uniform particle size were successfully synthesized by microwave-induced combustion using lithium nitrate, manganese nitrate, cobalt nitrate, and urea as the starting materials. The LiMn2 − xCoxO4 powders synthesized by microwave-induced combustion were investigated by X-ray diffractometer (XRD), thermogravimeter analyzer (TG), and scanning electron microscopy (SEM). The LiMn2 − xCoxO4 samples were used as cathode materials in lithium-ion batteries, whose discharge capacity and electrochemical characteristics such as the cycling performance were also investigated. The results revealed that the LiMn2 − xCoxO4 cell synthesized by microwave-induced combustion provided a high initial capacity and excellent reversibility compared to the material prepared by solid-state reaction method. [ABSTRACT FROM AUTHOR]