| dc.description.abstract | With increasing demands of large-scale electronic applications such as electric vehicles (EVs), lithium ion batteries (LIBs) with high energy density and power density are desired. Recent researches has confirmed that doping quantitative transition metal will increase the Fermi level of the spinel LiNi0.5Mn1.5O4 material, which can improve the cycle performance in high voltage. In addition, to meet the aforementioned requirement, an electrode design that can accommodate more active material loading while reduce additives such as binders and conductive agents without losing any capacity is therefore expected. In the current study, we aim to combine nickel-manganese-chromium based cathode materials and CFs, developing a binder-free LiNi0.5(1-x)Mn1.5(1-x/3)CrxO4 high voltage composite cathode by using electrochemical deposition together with hydrothermal reaction and suction filtration. On the other hand, we develop a binder-free carbon nanotube (CNT)/CF composite anode by using an electrophoretic deposition method.
For the LiNi0.5(1-x)Mn1.5(1-x/3)CrxO4 cathode material. From XRD experiment results, it is found that increasing the calcination time can improve crystal purity, but it also lose oxygen and turn into disproportionate spinel LiNi0.5Mn1.5O4 and LixNi1−xO, so we dope Cr to stabilize the spinel structure of LiNi0.5Mn1.5O4 with increasing crystallinity. The composite cathode demonstrates favorable electrochemical performance against high-voltage operation due to the stronger bonding energy of Cr–O. Among them, the LiCr0.2Ni0.4Mn1.4O4 cathode material exhibits the best cyclic and rate performance. It can deliver the discharge capacity of 135 mAh/g at 0.2 C rate. Even at 5 C rate, it still delivers over 87.4 % capacity retention compared to that of 0.2 C. Through long cycle test, the LiCr0.2Ni0.4Mn1.4O4 cathode material delivers the discharge capacitie of 135.7 mAh/g with 97.6 % capacity retention after 200 cycles.
In addition, the morphology of the CNT/CF composite has been examined using energy-dispersive x-ray spectroscopy, and the results indicate that a CNT layer uniformLy deposites on the CFs. The CNT/CF anode shows better performance than the CF anode in terms of specific capacity, cycling stability, and rate capability. Even at 0.5 C rate, it still delivers discharge capacitie of 283 mAh/g. Through long cycle test, the CNT/CF anode material indicates the discharge capacitiey of 344 mAh/g with 86 % capacity retention after 100 cycles. | en_US |