Sr doped Co substituted Li nickelate cathode materials for Li cells with improved cycling and thermal stability

Abstract

Samples of cathode material were synthesized from a highly dispersed precursor containing 0.002 at.% Sr. The synthesis was performed from a mixture of the precursor with some overstoichiometric excess of LiOH at 720 °C in oxygen atmosphere. Part of the samples were coated with a thin film of Li-borate glass. The cathode active material (CAM) was mixed with 15 wt.% of Teflonized acethylene black and pressed on thin Al discs. The cathodes were cycled between 4.20 V and 3.20 V at 1 mA cm−2 first at 25 °C and then at 50 °C, whereafter the cycling continued up to 50–60 cycles. A pulse interruption method was applied to measure the DC area-specific resistivity of the cathodes Rc as a function of the state of discharge x. The evolution of the parameters of the Rc/x plots during cycling lent valuable information on the processes responsible for the degradation of the intercalation compound. The stability of the CAM during overdischarge was evaluated after 10 cycles at 25 °C and 24 cycles at 50 °C at 1 mA cm−2. The cathode was shorted externally for 2 min to 0.00 V. In spite of the large current during the overdischarge the discharge capacity loss in the next cycle was only 3%.