Sustainable Energy Technologies Department
"Synthesis and Characterization of High Energy Density Cathode Materials for Energy Storage"
Presented by Jianming Zheng, PNNL
Friday, January 10, 2014, 11 am
Bldg. 815 1st floor Conference Room
Hosted by: Feng Wang
Safe and high capacity cathode materials are very attractive to develop next generation Hybrid Electric Vehicles (HEV) and Electric Vehicles (EV). The Li-rich Mn-rich (LMR) layered cathode material, here referring to the solid solutions between Li2MnO3 and LiMO2 (M = Ni, Co, Mn) have been found to deliver much higher capacity together with a significant reduction in cost and enhancement in safety compared to the commercially used LiCoO2. However, significant challenges, including voltage decay, long-term cycling instability and poor rate capability, have to be overcome prior to the practical application of these layered cathodes. This presentation will focus on my recent studies on capacity fading mechanism of a representative LMR cathode materials Li[Li0.2Ni0.2Mn0.6]O2 and on how to improve the electrochemical performance by using surface coating/electrolyte additive or by enhancing the atomic scale transition metal (TM) interaction in the material. It is found that corrosion/fragmentation of LMR cathode during repeated cycling is one of the main reasons responsible for the capacity fading. The introduction of an anion receptor TPFPB (tris(pentafluorophenyl)borane) as electrolyte additive could significantly reduce the accumulation of parasitic reaction products and stabilize the interfacial resistances between cathode and electrolyte during extended cycling, thus improving the cycling performance of LMR cathode. In recent study, we have also found that the commonly observed Ni segregation in LMR cathodes could be largely mitigated by improving the uniformly distributed TM ions with controlled synthesis methods. The detailed results will be presented and discussed.