(230j) Anomalous Decrease in Structural Disorder Due to Charge Redistribution in Cr-Doped Li4Ti5O12 Negative-Electrode Materials for High-Rate Li-Ion Batteries

Since one of the main drawbacks of Li4Ti5O12 as a negative-electrode material is its low electronic conductivity, several researchers have attempted to improve the conductivity by narrowing the band gap through transition-metal doping. Herein, we report another, more significant effect of doping in addition to the band gap narrowing, namely, an anomalous decrease in the structural disorder in Li4Ti5O12 upon Cr3+ion doping. Although it is generally recognized that doping with heterogeneous elements increases the structural disorder, the Cr3+ion doping in Li4Ti5O12 demonstrated an unexpected structural phenomenon. From the results of various structural analyses using a synchrotron beam, such anomalous structural changes were revealed to originate from charge redistribution at nearby Ti4+ions. Finally, the capacity was markedly enhanced, especially at high C-rates (125 mAh/g for 10Ccharge/10Cdischarge, 145 mAh/g for 1Ccharge/50Cdischarge) because of both the band gap narrowing and the increased ionic diffusivity due to the decreased structural disorder, but was decreased instead for too-high doping levels.