Synthesis And Properties Of Cathode Materials For Secondary Magnesium Battery

The magnesium secondary battery has a theoretical volumetric specific capacity of3832 mAh cm^-3,which is about 5 times that of a commercial lithium as a lithium ion battery(777 mAh cm^-3).Compared with metallic lithium,metallic magnesium has a low electrode potential?-2.37 V?and low price,and it accounts for 13.9%of the earth's crust.The most important thing is the strong Mg-Mg bond.Dendrites are not produced during the reversible deposition process,the safety is extremely high,and it is also friendly to the environment.Therefore,magnesium secondary batteries have attracted great attention from researchers in the past few decades and are considered to be one of the candidates for next generation battery technology.In recent years,research hotspots of magnesium secondary batteries have focused on the development of new cathode materials.In this paper,the CuS cathode material was used as the research object,and the control synthesis of CuS material and the structure and properties of the new CuS electrode were studied.From the perspective of synthetic method design,polyvinylpyrrolidone?PVP?,sodium dodecylbenzenesulfonate?SDBS?and polyvinyl alcohol?PVA?were used as surfactants,and three kinds of pure phase CuS materials with different morphology and different particle sizes were prepared by hydrothermal method,which were called PVP-CuS,SDBS-CuS and PVA-CuS.The physicochemical properties of the above three materials were characterized by XRD?Raman?SEM?EDS?nitrogen adsorption/desorption?constant current charge and discharge and AC impedance tests.The differences in electrochemical performance between the three cathode materials in the magnesium secondary battery system were analyzed.The experimental results show that PVA-CuS has a higher specific surface area and has a relatively lower charge transfer impedance,exhibits the best electrochemical performance.At the current density of 30 mA g^-1,its initial discharge capacity is as high as 445 mAh g^-1,which is about 80%of the theoretical capacity,and after the 10 cycles,the capacity is maintained about 230 mAh g^-1.From the perspective of modification of the positive electrode material and electrode structure,the F-CuS-CNT integration composite flexible film was prepared by PVA-CuS and carbon nanotube layer assembly,which not only improved the conductivity of the material,relieved the volume expansion of the CuS cathode material,but also avoided electrolyte corrodes the current collector after the long cycles,and significantly improved its electrochemical performance.The initial discharge capacity is 479 mAh g^-11 at the current density of 30 mA g^-11 and still maintaining capacity of 165 mAh g^-11 after 100 cycles at the room temperature.The capacity retention rate is 34.4%,which is much higher than the CuS electrode prepared by the conventional coating method.From the perspective of the improvement of the process flow,the CuS@CNT flexible composite film was successfully prepared by one-step hydrothermal method,and the unique bracelet structure exhibited excellent rate performance and cycle performance.At room temperature,the capacity of the first circle reached 428 mAh g^-11 at a current density of 100 mA g^-1and the capacity was still as high as 200 mAh g^-1after 160 cycles.