The effect of electrochemically inactive Ti substituted for Ru in Li_(2)Ru_(1-x)Ti_xO_(3) on structure and electrochemical performance

摘要

The approach of substituting electrochemically active with inactive elements has widely been used to improve the electrochemical performance of Li-rich intercalation cathode materials. This especially is true for Li-rich compounds where almost all of the Li+ions are reversibly(de)intercalated during electrochemical cycling. The beneficial mechanism behind this substitution with electrochemically inactive elements is still not clear yet. Li_(2)RuO_(3) is chosen as basis for a model solid solution system to investigate the effect of electrochemically inactive elements owing to its high specific capacity of more than 300 m Ah g^(-1) and the significant contribution of anion redox mechanism. Herein, Li_(2)Ru_(1-x)Ti_xO_(3) solid solution series are synthesized and the effect of substituting with electrochemical inactive Ti for Ru on structure and electrochemical performance have been comprehensively investigated. The electrochemical performance is significantly improved, especially for Li_(2)Ru_(0.8)Ti_(0.2)O_(3), and the capacity retention after 50 cycles increases from 81% to 90%, as compared to the end member Li_(2)RuO_(3). Results of electrochemical impedance spectroscopy show that Ti substitution reduces the charge transfer impedance, which favors the Li+diffusion across the electrolyte–electrode interface and improves the electronic conductivity. For the first time,nuclear magnetic resonance was utilized to confirm that a small part of Ti ions exchange their position with Li ions in the Li layer. This research provides a better understanding of electrochemical inactive element substitution and strong insights for the functional design of the next generation of Li-rich cathode materials.