Mo Doping and Electrochemical Activation Co-Induced Vanadium Composite as High-Rate and Long-Life Anode for Ca-Ion Batteries

Calcium-ion batteries have been considered attractive candidates for large-scale energy storage applications due to their natural abundance and low redox potential of Ca^(2+)/Ca.However,current calcium ion technology is still hampered by the lack of high-capacity and long-life electrode materials to accommodate the large Ca^(2+)(1.00Å).Herein,an amorphous vanadium structure induced by Mo doping and in-situ electrochemical activation is reported as a high-rate anode material for calcium ion batteries.The doping of Mo could destroy the lattice stability of VS4 material,enhancing the flexibility of the structure.The following electrochemical activation further converted the material into sulfide and oxides co-dominated composite(defined as MoVSO),which serves as an active material for the storage of Ca^(2+)during cycling.Consequently,this amorphous vanadium structure exhibits excellent rate capability,achieving discharge capacities of 306.7 and 149.2 mAh g^(-1)at 5 and 50 A g^(-1)and an ultra-long cycle life of 2000 cycles with 91.2%capacity retention.These values represent the highest level to date reported for calcium ion batteries.The mechanism studies show that the material undergoes a partial phase transition process to derive MoVSO.This work unveiled the calcium storage mechanism of vanadium sulfide in aqueous electrolytes and accelerated the development of high-performance aqueous calcium ion batteries.

Mechanical Behavior and Microstructure Evolution of a Rolled Magnesium Alloy AZ31B Under Low Stress Triaxiality

Plastic deformation up to final rupture failure of a rolled magnesium（Mg） alloy Mg-3.0Al-1.0Zn-0.34Mn（AZ31B） under low stress triaxiality was investigated.Local strain evolution was quantified by the digital image correlation（DIC） technique analysis with tensile,combined tensile-shear,and shear specimens,corresponding to the stress triaxiality of 1/3,1/6 and 0,respectively.Stress-strain curves show that the yield stress reduces with the decrease in the stress triaxiality,and obviously exhibits different strain hardening response.Electron backscatter diffraction（EBSD） observations reveal that the twinning behavior depends on stress triaxiality.Before fracture,double twinning is the dominant mechanism at the stress triaxiality of 1/3,while extension twinning is prevalent at the stress triaxiality of 0.Moreover,scanning electron microscopy（SEM） shows that the fracture mechanism is transformed from microvoid growth and coalescence to internal void shearing as the stress triaxiality decreases from 1/3 to 0.