Realizing rapid electrochemical kinetics of Mg2+ in Ti-Nb oxides through a Li+ intercalation activated strategy toward extremely fast charge/discharge dual-ion batteries

The development of practical magnesium batteries is severely hindered by the sluggish solid diffusion processes resulting from the relatively high charge density of Mg 2+ with two unit charges. Therefore, exploiting novel charge storage mechanisms to overcome the inherent kinetic obstruction is urgently needed. Herein, the rapid diffusion kinetics of Mg 2+ in Wadsley-Roth phase TiNb 2 O 7 (TNO) is realized through the electrochemical Li + intercalation boosted approach, contributing to the successful fabrication of high-rate and ultra-long lifespan dual-ion batteries. Through adding lithium salt into the conventional all phenyl complex electrolyte, not only Li + but also Mg 2+ can be intercalated into the TNO, implying the intercalation of Mg 2+ can be activated by the intercalation of Li + . Meanwhile, theoretical calculations reveal that the insertion of Li + can significantly improve the electronic conductivity of TNO and reduce the diffusion energy barrier of Mg 2+ in TNO. Moreover, in-situ Raman and ex-situ X-ray diffraction measurements also indicate the improved structural integrity of TNO with Li + pre-intercalation during cycling. Consequently, such a dual-ion battery system with the TNO cathode and Mg metal anode exhibits a high reversible capacity (243.6 mAh g −1 at 0.1 C) and excellent high-rate cycling stability (capacity retention of 85.1% at 5 C after 2000 cycles)