Amorphous germanium-crystalline bismuth films as a promising anode for magnesium-ion batteries

Magnesium-ion batteries(MIBs)are promising alternatives to lithium-ion batteries due to their safety and high theoretical specific capacity,and the abundance of magnesium reserves.However,their anodes and electro-lytes severely restrict the development of MIBs,so alloy-type anodes provide an effective strategy to circum-vent the surface passivation issue encountered with Mg metal in conventional electrolytes.Theoretically,a germanium anode can deliver a high specific capacity of 1476 mAh g?1,but hitherto,no experimental reports have described Ge in MIBs.Herein,we experimentally verified that Ge could reversibly react with Mg 2þions through the design of dual-phase Ge–Bi film electrodes fabricated by magnetron co-sputtering.Notably,a Ge 57 Bi 43 electrode delivered a high specific capacity of 847.5 mAh g?1,owing to the joint alloying reactions of Ge and Bi with Mg,which was much higher than the specific capacity of Bi(around 385 mAh g?1).Moreover,the Ge–Bi anode showed excellent rate performance,good cycling stability,and superior compatibility with conventional electrolytes such as Mg(TFSI)2.More importantly,the Mg storage mechanism of the Ge–Bi anode was unveiled by operando X-ray diffraction,and density functional theory calculations rationalized that the introduction of Bi to form Ge–Bi evidently decreased the defect formation energy and effectively boosted the electrochemical reactivity of Ge with Mg.

Phase-boundary regulation boosting electrochemical reactivity of tin-based anodes for magnesium-ion batteries

Tin(Sn)-based materials are promising anodes for magnesium-ion batteries(MIBs) owing to their low reaction voltages, high theoretical specific capacities and good compatibility with conventional electrolytes. However, relatively arduous alloying reaction and sluggish diffusion kinetics limit their practical applications. Herein, we proposed a general strategy to regulate the electrochemical reactivity and performance of Sn-based anodes for Mg storage through the introduction of the second phase and phase boundary. The biphase Sn–Al, Sn–Pb and Sn–Zn O films were further fabricated via magnetron co-sputtering. Taking Sn–Al as an example, it has been revealed that the introduction of Al can effectively stimulate the electrochemical reaction of Sn with Mg in either nanoscale or bulk through combining experiments with density-functional theory calculations. Specially, the rolled Sn–Al electrode exhibits superior long-term stability over 5,000 cycles. Additionally, the Mg-storage mechanism of the Sn–Al electrode was investigated by operando X-ray diffraction. The Sn–Al anodes also demonstrate good compatibility with simple Mg-salt-based electrolytes like Mg(TFSI)2in full cells. More importantly, it has been authenticated that the activation effect of second phase and phase boundary to Sn is also applicable to Pb and Zn O. Our findings may provide a favorable reference for the development of alloy-type anodes for MIBs.