Synthesis And Electrochemical Properties Of Mo₆S₈ As Rechargeable Magnesium Batteries Cathode Materials

Lithium-ion batteries have been widely commercialized as more populor energy storage technologies,but lithium-ion batteries are currently facing serious safety issues.Magnesium and lithium are in a diagonal position in the periodic table of the elements,have similar chemical properties,and magnesium is abundant in global reserves.As anode,it has high capacity and safety.Therefore,magnesium ion battery energy storage technology has great development prospect.Currently,the development of magnesium ion batteries is relatively slow.The main factor restricting the development of magnesium ion batteries is the lack of cathode materials that can reversibly insert/extract magnesium ions.The Chevrel phase compound's ability to store magnesium ions quickly has been favored by researchers,but the problem of thermodynamic instability has led to the harsh synthesis of Mo6S8.This article systematically explored a simpler preparation process of Chevrel phase Mo6S8,and studied its electrochemical performance as a cathode material for magnesium ion batteries.Combined with molten salt method and high-temperature solid-phase method,the Chevrel phase Cu2Mo6S8 with uniform particle size was successfully prepared under the condition of holding at 1100?for 24 hours with a particle size of 100 nm to 1.m.After being etched with 8 mol/L HCl,the Chevrel phase Mo6S8 was successfully prepared as a cathode material for magnesium ion batteries and showed excellent cycle stability and rate performance.When the voltage window is 0.5 V to 2 V and the current density is 0.2 C,the specific capacity of Mo6S8 is 123 mAh g-1 at the first cycle,and the specific capacity is 76 mAh g-1 after 50 cycles,and the capacity retention rate is 70.21%.When the mass ratio of raw material to KCl molten salt is 1:4,the phase purity is the highest and the electrochemical performance is the best.The capacity retention rate is good after circulating 70 cycles at a current density of 0.2 C.When the amount of MoS2 added was 1.6 g and the temperature was kept at 1000? for 24 hours,Cu1Mo6Sg was successfully prepared with uniform particle size and the particle size was 100 nm to 500 nm.The product had no obvious agglomeration.Test in the operating voltage window from 0.05 V to 2 V found that 1-Mo6S8 and 2-Mo6Sg had good cycle stability at a current density of 0.2 C,and their reversible capacities were 96.4 mAh g-1 and 101 mAh g-1,respectively.In addition,1-Mo6Sg exhibited 97 mAh g-1,83 mAh g-1,77 mAh g-1,and 65 mAh g-1 at current densities of 0.2 C,0.5 C,1 C,and 2 C,respectively.Using Cu foil as current collector,electrode materials with different coating thickness of Chevrel phase Mo6S8 were prepared.After coating with Cu foil,the phase of the active material changed.Mo6S8 with a coating thickness of 25 ?m and 35 ?m was transformed into Cu1Mo6S8,and Mo6S8 with a coating thickness of 15 ?m was transformed into Cu2Mo6S8.At a current density of 0.2 C,the reversible capacity of the electrode material with a coating thickness of 25 ?m is 117 mAh g-1.After 130 cycles,the capacity is not significantly attenuated and the stability is good.The reversible capacity of the electrode material with a thickness of 15 ?m is 164 mAh g-1,but the cycle stability is poor,because a large amount of dendritic metal Cu appears during the cycle of the electrode material.