Publıcatıons
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In this study, we unravel the effect of Ni doping on the half-cell and full-cell performances of the Na0.67Mn0.5-xNixFe0.43Ti0.07O2 cathode materials where x varies between 0.02 and 0.1. The cyclic voltammetry (CV) analysis of the half-cells is performed at 10 °C, room temperature (RT), and 50 °C to elucidate the redox reaction mechanisms at different temperatures. At the C/2-rate, the excellent capacity retention of the full cell is around 70% after 500 cycles delivering a specific capacity of 103 mAh g−1. Along with the conventional physicochemical characterization methods such as X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Raman and Fourier-transform Infrared Spectroscopies (FTIR), we also utilize X-ray photoelectron spectroscopy (XPS) to bridge the nexus between the performance and the structure properties of the studied materials. Furthermore, we also employ synchrotron-based X-ray Absorption (XAS) to understand the local geometry of the optimized cathode materials in operando.
Intercalation provides to the host materials a means for controlled variation of many physical/chemical properties and dominates the reactions in metal-ion batteries. Of particular interest is the graphite intercalation compounds with intriguing staging structures, which however are still unclear, especially in their nanostructure and dynamic transition mechanism. Herein, the nature of the staging structure and evolution of the lithium (Li)-intercalated graphite was revealed by cryogenic-transmission electron microscopy and other methods at the nanoscale. The intercalated Li-ions distribute unevenly, generating local stress and dislocations in the graphitic structure. Each staging compound is found macroscopically ordered but microscopically inhomogeneous, exhibiting a localized-domains structural model. Our findings uncover the correlation between the long-range ordered structure and short-range domains, refresh the insights on the staging structure and transition of Li-intercalated/deintercalated graphite, and provide effective ways to enhance the reaction kinetic in rechargeable batteries by defect engineering.
Fast-charging lithium-ion batteries are highly required, especially in reducing the mileage anxiety of the widespread electric vehicles. One of the biggest bottlenecks lies in the sluggish kinetics of the Li+ intercalation into the graphite anode; slow intercalation will lead to lithium metal plating, severe side reactions, and safety concerns. The premise to solve these problems is to fully understand the reaction pathways and rate-determining steps of graphite during fast Li+ intercalation. Herein, we compare the Li+ diffusion through the graphite particle, interface, and electrode, uncover the structure of the lithiated graphite at high current densities, and correlate them with the reaction kinetics and electrochemical performances. It is found that the rate-determining steps are highly dependent on the particle size, interphase property, and electrode configuration. Insufficient Li+ diffusion leads to high polarization, incomplete intercalation, and the coexistence of several staging structures.
Here we report on the structural and electrochemical properties of P2-type Na0.67Mn1−xCuxO2 (where x = 0.20–0.50) via various techniques. X-ray diffraction (XRD) reveals a reduction of the unit cell volume upon substitution of Cu elucidated through detailed Rietveld analysis. The cyclic voltammetry (CV) behavior is also affected by the Cu substitution indicating new redox reactions stemming from Cu substitution. Galvanostatic cycling measurements at room temperature show that when x = 0.35 in a P2-type Na0.67Mn1−xCuxO2 cathode active material, the best electrochemical performance is obtained. The Na-ion diffusion rate is found to be strongly dependent upon the environmental temperature. Changes in the valence state and the local structures of P2-type Na0.67Mn1−xCuxO2 during the charge/discharge are investigated through the operando X-ray absorption spectroscopy (XAS) technique.
In this study, we report a facile way to improve the stability of electroplated Silicon (Si) electrodes through heat treatment. Electrodeposition of Si is carried out on a porous current collector followed by the heat treatment under an oxygen-free environment at 300 °C, 350 °C, and 400 °C. It is shown that as the heat treatment temperature increases, the cycling stability of the Si anode also dramatically improves. The Si electrode heat treated at 400 °C also keeps the quality of Si even after exposing the electrode to the air for up to 7 days which relieves the handling burden of Si in the ambient atmosphere. The striking difference allows the Si electrode heat treated at 400 °C to maintain its 77 % capacity even after exposure to air for one week.
In this study, we report a new design paradigm for an electrode preparation method that drastically improves the fast-charging capabilities of a graphite (Gt) anode by controlling the crystallographic orientation. The crystallographic orientation of the Gt electrode is achieved under a dynamic magnetic field using commercially available neodymium magnets. When the slurry of the Gt electrode is tape casted using the conventional method with no magnetic field, the crystallographic orientation is dominated with (002) planes along with other random planes. However, once the slurry of the Gt electrode is casted and dried under a magnetic field, the Gt particles tend to orient themselves along the (100), (101), and (110) planes which are all aligned vertically to the current collector.