The Electrochemical and Structural Changes of Phosphorus-Doped TiO2 through In Situ Raman and In Situ X-Ray Diffraction Analysis.

Doping is a widely employed technique to enhance the functionality of lithium-ion battery materials, tailoring their performance for specific applications. In our study, we employed in situ Raman and in situ X-ray diffraction (XRD) spectroscopic techniques to examine the structural alterations and electrochemical behavior of phosphorus-doped titanium dioxide (TiO2) nanoparticles. This investigation revealed several notable changes: an increase in structural defects, enhanced ionic and electronic conductivity, and a reduction in crystallite size. These alterations facilitated higher lithiation rates and led to the first observed appearance of LiTiO2 in the Raman spectra due to anatase lithiation, resulting in a reversible double-phase transition during the charging and discharging processes. Furthermore, doping with 2, 5, and 10 wt % phosphorus resulted in an initial increase in specific capacity compared to undoped TiO2. However, higher doping levels were associated with diminished capacity retention, pinpointing an optimal doping level for phosphorus. These results underscore the critical role of in situ characterization techniques in understanding doping effects, thereby advancing the performance of anode materials, particularly TiO2, in lithium-ion batteries.

Carbon-coated Ni0.5Mg0.5Fe1.7Mn0.3O4 nanoparticles as a novel anode material for high energy density lithium-ion batteries.

Lithium-ion batteries (LIBs) have gained considerable attention from the scientific community due to their outstanding properties, such as high energy density, low self-discharge, and environmental sustainability. Among the prominent candidates for anode materials in next-generation LIBs are the spinel ferrites, represented by the MFe2O4 series, which offer exceptional theoretical capacities, excellent reversibility, cost-effectiveness, and eco-friendliness. In the scope of this study, Ni0.5Mg0.5Fe1.7Mn0.3O4 nanoparticles were synthesized using a sol-gel synthesis method and subsequently coated with a carbon layer to further enhance their electrochemical performance. TEM images confirmed the presence of the carbon coating layer on the Ni0.5Mg0.5Fe1.7Mn0.3O4/C composite. The analysis of the measured X-ray diffraction (XRD) and Raman spectroscopy results confirmed the formation of nanocrystalline Ni0.5Mg0.5Fe1.7Mn0.3O4 before coating and amorphous carbon in the Ni0.5Mg0.5Fe1.7Mn0.3O4/C after the coating. The Ni0.5Mg0.5Fe1.7Mn0.3O4 anode material exhibited a much higher specific capacity than the traditional graphite material, with initial discharge/charge capacities of 1275 and 874 mA h g-1, respectively, at a 100 mA g-1 current density and a first coulombic efficiency of 68.54%. The long-term cycling test showed a slight capacity fading, retaining approximately 85% of its initial capacity after 75 cycles. Notably, the carbon-coating layer greatly enhanced the stability and slightly increased the capacity of the as-prepared Ni0.5Mg0.5Fe1.7Mn0.3O4. The first discharge/charge capacities of Ni0.5Mg0.5Fe1.7Mn0.3O4/C at 100 mA g-1 current density reached 1032 and 723 mA h g-1, respectively, and a first coulombic efficiency of 70.06%, with an increase of discharge/charge capacities to 826.6 and 806.2 mA h g-1, respectively, after 75 cycles (with a capacity retention of 89.7%), and a high-rate capability of 372 mA h g-1 at 2C. Additionally, a full cell was designed using a Ni0.5Mg0.5Fe1.7Mn0.3O4/C anode and an NMC811 cathode. The output voltage was about 2.8 V, with a high initial specific capacity of 755 mA h g-1 at 0.125C, a high rate-capability of 448 mA h g-1 at 2C, and a high-capacity retention of 91% after 30 cycles at 2C. The carbon coating layer on Ni0.5Mg0.5Fe1.7Mn0.3O4 nanoparticles played a crucial role in the excellent electrochemical performance, providing conducting, buffering, and protective effects.

Sputtered Silicon-Coated Graphite Electrodes as High Cycling Stability and Improved Kinetics Anodes for Lithium Ion Batteries.

Amorphous Si thin films with different thicknesses were deposited on synthetic graphite electrodes by using a simple and scalable one-step physical vapor deposition (PVD) method. The specific capacities and rate capabilities of the produced electrodes were investigated. X-ray diffraction, scanning electron microscopy, Raman spectroscopy, profilometry, cyclic voltammetry, galvanostatic techniques, and in situ Raman spectroscopy were used to investigate their physicochemical and electrochemical properties. Our results demonstrated that the produced Si films covered the bare graphite electrodes completely and uniformly. Si-coated graphite, Si@G, with an optimal thickness of 1 µm exhibited good stability, with an initial discharge capacity of 628.7 mAhg-1, a capacity retention of 96.2%, and a columbic efficiency (CE) higher than 99% at C/3. A discharge capacity of 250 mAh g-1 was attained at a high current rate of 3C, which was over 2.5 times that of a bare graphite electrode, thanks to the high activated surface area (1.5 times that of pristine graphite) and reduced resistance during cycling.