Browsing by Subject "NMC"

Now showing 1 - 3 of 3
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    Geometric and electrochemical characteristics of lithium ion batteries
    (2017-05) Kang, Huixiao; Zhu, Likun
    The geometric and electrochemical characteristics of different lithium ion batteries (LIBs) are investigated in this study. The core work is to study the impact of the calendering process on NMC cathode electrodes performance. X-ray CT image processing by Python, MATLAB, ImageJ and Avizo is utilized in this study. NMC electrodes with different calendering conditions were fabricated to calculate electrochemical properties of the cells. Charge/discharge of the electrodes under 0.1C, 0.2C, 0.4C, 1C, 2C, 4C and 0.1C (retention test) rates were cycled for three times respectively between 4.2 V and 3.0 V. Electrochemical impedance spectroscopy testing was used to further explain the effects of NMC density on rate capability. Geometric properties of NMC electrodes with different calendering conditions were calculated from the computed tomography data of the electrodes. A synchrotron transmission X-ray microscopy tomography system at the Advanced Photon Source of the Argonne National Laboratory was employed to obtain the tomography data. X-ray CT image processing before the data analysis was introduced. Python based Tomopy and ASTRA toolbox were used to filter the original HDF5 data and reconstruction. ImageJ was used to help remove noise, adjust contrast and cropping. Iso2mesh and image processing tool box were used in MATLAB to generate meshed 3D structure of CT data. Geometric properties of NMC electrodes including porosity, pore size distribution, particle size distribution, specific surface area and tortuosity were calculated from the computed tomography data of the electrodes. The geometric and electrochemical analysis show that calendering can increase the electrochemically active area, which lead to improving of the rate capability. However, more calendering will result in crushing of NMC particles, which can reduce the electrode capacity at relatively high C rates. This study shows that the optimum electrochemical performance of NMC electrode at 94:3:3 weight ratio of NMC:binder:carbon black can be achieved by calendering to 3.0 g/cm3 NMC density. LTAP solid electrolyte and NMC cathode material mix electrode-electrolyte X-ray CT data was studied in last chapter. By using 8 kev X-ray energy, we could distinguish NMC active material, LTAP solid electrolyte and the others three phase. On the basis of NMC electrode image processing method, dilation and multiply threshold method is applied to get three-phase 3D geometry. A comparing of connection area between NMC and LTAP of 700psi and 1300psi electrode was analyzed. Geometric properties like tortuosity, di_usion length and e_ective di_usivity were generated from the CT data.
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    In Situ Temperature Evolution and Failure Mechanisms of LiNi0.33Mn0.33Co0.33O2 Cell under Over-Discharge Conditions
    (ECS, 2018-09) Wu, Linmin; Liu, Yadong; Cui, Yi; Zhang, Yi; Zhang, Jing; Mechanical Engineering, School of Engineering and Technology
    In this work, in situ study of commercial 18650 NMC (LiNi0.33Mn0.33Co0.33O2) cells under over-discharge charge conditions (100%, 110%, and 120%) has been performed. Both voltage and cell skin temperature evolutions were simultaneously monitored in situ during discharge process. The results show that there is a clear correlation between the voltage and temperature. For the NMC cell under 120% over-discharge condition, the cell failed after only 1 cycle. The voltage dropped to negative values at the end of the discharge. The skin temperature at the end of discharge increased dramatically to 73°C, indicating strong exothermal reactions happened inside the cell. For the 110% over-discharged cell, the cell failed after 10 cycles. The voltage at the end of the discharge process became negative after the 1st cycle. The cell skin temperature increased from 23.2°C to 61.7°C. The peak temperature in each cycle kept increasing until failure. These implies the micro short circuits were developed during the charge-discharge process. The failed components were examined by SEM/EDX and XRD. The results show substantial aluminum exists inside the failed separators. The results suggest that during the over-discharge process, the alumina inside the separator was reduced to aluminum. The electrons migrate through aluminum channel, leading to the failure of the cells.
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    Three-Dimensional Finite Element Study on Stress Generation in Synchrotron X-Ray Tomography Reconstructed Nickel-Manganese-Cobalt Based Half Cell
    (Elsevier, 2016-12) Wu, Linmin; Xiao, Xianghui; Wen, Youhai; Zhang, Jing; Department of Mechanical Engineering, School of Engineering and Technology
    In this study, the stress generation caused by phase transitions and lithium intercalation of nickel-manganese-cobalt (NMC) based half cell with realistic 3D microstructures has been studied using finite element method. The electrochemical properties and discharged curves under various C rates are studied. The potential drops significantly with the increase of C rates. During the discharge process, for particles isolated from the conductive channels, several particles with no lithium ion intercalation are observed. For particles in the electrochemical network, the lithium ion concentration increases during the discharge process. The stress generation inside NMC particles is calculated coupled with lithium diffusion and phase transitions. The results show the stresses near the concave and convex regions are the highest. The neck regions of the connected particles can break and form several isolated particles. If the isolated particles are not connected with the electrically conductive materials such as carbon and binder, the capacity loses in battery. For isolated particles in the conductive channel, cracks are more likely to form on the surface. Moreover, stresses inside the particles increase dramatically when considering phase transitions. The phase transitions introduce an abrupt volume change and generate the strain mismatch, causing the stresses increase.