Enhanced electrochemical properties of fluoride-coated LiCoO2 thin films
The electrochemical properties of fluoride-coated lithium cobalt oxide [LiCoO2] thin films were characterized. Aluminum fluoride [AlF3] and lanthanum fluoride [LaF3] coating layers were fabricated on a pristine LiCoO2 thin film by using a spin-coating process. The AlF3- and LaF3-coated films exhibited a higher rate capability, cyclic performance, and stability at high temperature than the pristine film. This indicates that the AlF3 and LaF3 layers effectively protected the surface of the pristine LiCoO2 film from the reactive electrolyte.
Lithium Cobalt Oxides Functionalized by Conductive Al-doped ZnO Coating as Cathode for High-performance Lithium Ion Batteries
Abstract LiCoO2 (LCO) has been functionally modified with electronic conductive Al-doped ZnO (AZO) via a sol-gel method. The physicochemical characterization results demonstrate that the AZO layer is coated onto the surface of LiCoO2 particles successfully, and the AZO-coated LCO material shows a higher electronic conductivity than pristine sample. The LCO sample coated by 2 wt.% AZO shows the excellent cyclability with a capacity retention of 98.2% after 50 cycles in the voltage range of 2.75–4.5 V under room temperature. More importantly, this material exhibits outstanding rate capability and delivers a quite high capacity of 156 mA h g−1 at the rate of 8 C (1600 mA g−1), corresponding to 86.6% of the capacity at the rate of 0.1 C. Such superior electrochemical performance results from the effective coating of AZO layer which not only acts as a physical protection layer to stabilize the surface structure, but also supplies the conductive networks to decrease charge transfer impedance. The conducting functionalized AZO coating is a facile and efficient approach to improve the electrochemical performance of LCO at a high cut-off voltage of 4.5 V vs. Li+/Li for large-scale application of high energy density lithium ion batteries.
XPS Study on Al2O3- and AlPO4-Coated LiCoO2 Cathode Material for High-Capacity Li Ion Batteries
The impact of aluminum oxide coatings on LiCoO 2 materials for commercial lithium ion batteries has been investigated by X-ray photoelectron spectroscopy (XPS). A low binding energy component in the Al 2p core peak spectra was observed and attributed to the formation of a LiAl x Co (1-x) O 2 solid solution interphase for both Al 2 O 3 - and AlPO 4 -coated LiCoO 2 . The surface chemistry of pristine and Al 2 O 3 -coated LiCoO 2 cathodes and graphite anodes have been investigated after cycling up to 4.2 V or 4.4 V cutoff voltage and after various levels of capacity fade. The Al 2 O 3 coating enhances the capacity retention at both 4.2 V and 4.4 V cutoff voltages. XPS analyses provided evidence of the inhibition of cobalt dissolution from the LiCoO 2 positive electrode by the aluminum coatings. Moreover, the Al 2 O 3 coating lowers the kinetics of degradation of electrolyte species, especially the LiPF 6 salt.