Relationship between Cyclic Properties and Charge-discharge Condition for Li₂Mn_0.4Ru_0.6O₃ and Li₂RuO₃

Abstract

Capacity and voltage retentions upon subsequent cycles for Li₂RuO₃ and Li₂Mn_0.4Ru_0.6O₃ (LMR) under various cut-off voltages have been investigated. The change in average and local structures upon electrochemical cycling were examined by ex-situ XRD and Ru L₃-edge XANES measurements, and the relationship between the cyclic capabilities and the structural changes is discussed. The deteriorations of discharge capacity and average discharge voltage in the subsequent cycles of LMR with a charge cut-off voltage of 4.8 V vs. Li/Li⁺ are remarkably smaller than that with the voltage of 4.2 V. Moreover, LMR exhibits higher average discharge voltage than Li₂RuO₃ under a charge cut-off voltage of 4.8 V. The phase transition behavior of LMR was not similar to Li₂RuO₃ upon electrochemical cycling. Ru L₃-edge XANES spectra measurements reveal that RuO₆ octahedra in LMR charged at 4.2 V are much distorted. The local structure of RuO₆ octahedra is associated with the cyclic capability of LMR and Li₂RuO₃.