Layered cathode active materials partially-substituted cobalt with transition metals and spinel active materials have been received more attention due to their cost effectiveness as compared to lithium cobaltate. Scholars have realized with time that the spinel cathode active materials are safe with limited specific capacities while layered cathode active materials possess high specific capacity with safety issues. Presently, layered cathode active materials are more preferred as cathode materials for lithium ion batteries, where nickel-rich layered cathode active materials are front runners except for safety issues, due to their high capacity. To overcome the safety issue challenge, measures, such as the substitution of the transition metal ions with other metal counter ions and the modification of the surface by means of coating with metal oxides, have been put in place.
Nanoparticle coatings on layered cathode active materials have been known to suppress the thermal reaction between the electrode and electrolyte. It has thus been seen necessary to coat or decorate the surface of the cathode since probable exothermic reaction starts from the cathode surface when the electrolyte is decomposed. Extensive studies have been performed on coating materials that inhibit this reaction but little exists about nanofibers-based metal oxides decorated on lithium nickel cobalt aluminum oxide cathode active materials.
Professor Chang Woo Lee and colleagues from the Department of Chemical Engineering, College of Engineering, Kyung Hee University in South Korea proposed a study to modify the surface of lithium nickel cobalt aluminum oxide particles by decorating them with titania nanofibers. They aimed at comparatively studying, with the novel lithium nickel cobalt aluminum oxide, the various quantities of titania nanofibers decorated over lithium nickel cobalt aluminum oxide (LNCA). Their research work is now published in the peer-reviewed journal, Journal of Industrial and Engineering Chemistry.
The researchers commenced their empirical procedure by obtaining titania nanofibers precursor through electrospinning a sol-gel polymeric solution. They then obtained the LNCA precursor. The titania nanofibers precursors were split at 0.5 wt%, 1 wt% and 1.5 wt% before addition of the LNCA precursor powders. The precursor powder mixture was then sintered at 465oC for three hours and then calcined at 850oC for five hours in air. The team then conducted an X-ray photoelectron spectroscopic analysis to investigate the chemical composition of the cycled electrode surface. The team eventually obtained cathode samples and used them to conduct differential scanning calorimetry scans.
The authors also observed that the increase of titania nanofibers decoration over 1wt% ratio showed negative effect during the electrochemical process, as observed using electrochemical impedance spectra for the 1.5wt% titania nanofibers-decorated LNCA. Hence usage of titania nanofibers more than 1wt% was excluded from detailed investigation. The surface modification of LNCA electrodes by 1wt% titania nanofibers decoration greatly increased the cycleability, capacity, and thermal stability of lithium ion batteries at room temperature as well as at elevated temperature. Among titania nanofibers decorated LNCAs, the 1wt% titania nanofibers -decorated LNCA cathode had shown better capacity retention of 89.2% and 81.9% at room and elevated temperature, respectively.
The results of their study second the suggestion of the applicability of titania nanofibers as surface modifiers in order to enhance the electrochemical and thermal properties of lithium ion batteries. Moreover, it has been seen that the capability of the titania nanofibers-decorated LNCA was enhanced compared to that of the pristine LNCA. The onset temperature of thermal decomposition is also shifted towards higher temperature for titania nanofibers-decorated LNCA electrodes than pristine LNCA electrodes.
Subburaj, Yong Nam Jo, K. Prasanna, Ki Jae Kim, Chang Woo Lee. Titanium oxide nanofibers decorated nickel-rich cathodes as high performance electrodes in lithium ion batteries. Journal of Industrial and Engineering Chemistry, volume 51 (2017) pages 223–228.
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