Scaling up Production and Analysis of Li-rich Nickel Manganese Oxide Cathode for Lithium-ion Batteries
Date Issued
2015
Date
2015
Author(s)
Chu, Yun
Abstract
Among the reported cathode materials so far in the lithium-ion batteries, the class of layered lithium-rich manganese-transition metal oxide composite cathode (abbreviated as LrMOs), xLi2MnO3•(1-x)Li(Mn, M)O2 (M= Mn, Ni, Co), possesses potentially high specific capacity more than 250mAh/g and high average redox potential near 4 V and therefore potential energy density nearly 1000 Wh/kg, which is much higher than those of Li2MnO4, LiNi0.33Co0.33Mn0.33O2 and LiFePO4. With so many advantages, in this thesis, this cathode material wound try to produce in a large amount in Advanced Lithium Electrochemistry Co., Ltd. (Aleees). By directly enlarging the procedure in lab, not only the physical properties but the electrochemical performance needed to be optimized. According to the analyses of Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), crystal size analysis, and electrochemical impedance spectroscopy (EIS), the calcination condition was considered to be a critical factor for its electrochemical properties. Through the modification of the calcination time, heat furnace, and calcination temperature, step by step, the main restriction for the scaling up product that the produce of electrochemical activated MnO2 in the initial charge was overcome. The perfect LrMOs product was successfully synthesized with the production rate of 100 g per batch in Aleees. Furthermore, there was no burn or explosion throughout the security tests for the scaling up LrMOs cell, demonstrated the superb safety of this cathode material. Except for the advantages, on the contrary, LrMOs encountered some fundamental limitations like large first irreversibility, voltage instability, capacity fading, and poor rate performance. Here, the main reason for the voltage fading had been investigated by the cycling test in the low and high voltage windows under 0.1 C (20 mA/g) and 0.3 C (60 mA/g). From the charge/discharge performance, the differential capacity versus voltage (dQ/dV), and normalization curves, the high voltage window cell behaved a more serious polarization and the low voltage window cell had a more apparent voltage fading because of the phase transformation. In conclusion, the low voltage window cell expressed a more prominent phenomenon of voltage fading in 0.1 C (20 mA/g), indicating that the phase transformation was the major factor for the voltage fading. As for 0.3 C (60 mA/g), both cells had similar voltage fading, showing that both phase transformation and internal impedance had similar contributions for the voltage fading. Besides, to solve the obstacle of poor rate performance, especially in the high current density, the effects of cathode mixing had been investigated, by LiFePO4, due to its flat and long plateau. In the beginning, the simulation of cathode mixing was implemented to estimate the results for the cathode mixing with different ratios between them. The results indicated that the influence for the rate performance with fast charging rate was stronger than with slow charging rate. Afterwards, compared with the simulation data, the experimental rate performance results were promulgated in the ratio of 50 : 50 for LrMOs and LiFePO4. However, the experimental rate performance test revealed an inferior results than the simulation. Only when the C-rate in 3 C (525 mA/g), with fast charging rate at different C-rates, the experimental energy density showed a higher value than the simulation one. Maybe, the relatively different particle size distribution of these two cathode materials was the main reason, which may result in the poor lithium ion diffusion between the particles.
Subjects
Li-ion battery
Li-rich layered oxide
voltage fading
phase transformation
cathode mixing
lithium iron phosphate
SDGs
Type
thesis