Preparation And Properties Of Zinc Compound/Carbon Composites As Anode Active Material For Sodium-ion Batteries

In order to cope with the energy crisis,it is very important to develop secondary batteries that are efficient and convenient for large-scale energy storage.Due to the scarcity of lithium resources,the price of lithium salt continues to rise,so sodium-ion batteries have become a research hotspot.The sodium source is extensive,the sodium ion battery has higher specific energy,long cycle life and almost no memory effect,which determines the feasibility of sodium ion battery research and development.The negative electrode material of sodium ion battery is an important part in the research of sodium ion battery.Zinc has a theoretical specific capacity of 410 mA·g-1 and can form multiple binary zinc compounds.Zinc-based materials have good application prospects as negative electrodes for sodium ion batteries,but the electrochemical properties have not been good enough.To solve these problems,the preparation of composite materials with carbonaceous materials is proposed.In this thesis,the zincate anode material was taken as the research object,and the one-step hydrothermal method was used to find the zinc compound with high specific capacity and good cycle stability of the anode material of sodium ion battery.Zinc-based/carbon composites were prepared for the problem of unsatisfactory cycling of pure zinc oxide and zinc sulfide electrodes.The structure,morphology and electrochemical properties of the materials were investigated by means of XRD,SEM,constant current charge and discharge,cyclic voltammetry and AC impedance.The effect of reaction conditions on the structure and morphology of the material,as well as the influence of the structure and morphology of the material on the sodium storage performance were analyzed.The experimental results show that ZnS has a higher charge-discharge ratio than ZnO in the zinc-based compounds,but the cycle performance of the two materials is very poor.Furthermore,the preparation of composite materials was carried out.The widely used and inexpensive anhydrous glucose was used as the carbon source,and the ZnS/C(H2NCSNH2)composite prepared by using H2NCSNH2 as the sulfur source was charged for the first time at a current density of 50 mA·g-1.The specific discharge capacity is 226.5 mAh·g-1 and 396.7 mAh·g-1,respectively,and the first coulombic efficiency reaches 57.1%.From the third cycle,the discharge capacity decreases slowly with the number of cycles,and the charge-discharge ratio is very close.After 50 cycles,the discharge capacity is still 161 mAh·g-1,showing good cycle performance.With sodium sulfide as the sulfur source,the first charge-discharge specific capacity of ZnS/C(Na2S)composites at 50 mA·g-1 current density was 493.6 mAh·g-1,909.4 mAh·g-1,respectively.The efficiency is 54.3%,but the charge-discharge ratio is only about 100 mAh·g-1 when it is cycled to the 50th time.Due to the high charge-discharge capacity of ZnS/C(Na2S)composites,the ZnS/C(Na2S)composites were fired at 650 ?,700 ?,750 ? and 800? in N2 atmosphere to investigate the properties of composites with different calcination temperatures impact.ZnS/C-750?composites exhibit good charge-discharge specific capacity and cycle performance at low current densities.At current densities of 200 mAg-1,ZnS/C-650?,ZnS/C-750? and ZnS/C When the 800 ? composite is recycled to 50 times,the charge-discharge ratio is nearly the same,about 200 mAh·g-1.Combined with the results of charge-discharge,cycle and rate performance curves and cyclic voltammetry and AC impedance,the electrochemical performance of ZnS/C750? composites is considered to be the best.In order to improve the first coulombic efficiency and cycle stability of ZnS/C-750 ?composites,ZnS/C was prepared by mechanical ball milling with ZnS/C-750? and tin mud from Shanghai Baosteel tinplate production workshop.SnO2 composite.When charging and discharging at different current densities,the first coulombic efficiency of ZnS/C-SnO2 composites is about 57%,and the first Coulomb efficiency of ZnS/C composites is about 45%,which shows that the introduction of SnO2 significantly improves the electrode.The first coulombic efficiency of the material.In the 50 mA·g-1 charge-discharge curve,in the ZnS/CSnO2 composites obtained by different ball milling time(1h,5h,10h and 15h),the first chargedischarge specific capacity of the electrode material obtained by ball milling for 5h was 496.7 mAh·g-1/905.4 mAh·g-1,the first Coulomb efficiency is 54.8%.In the 200 mA·g-1 constant current circulation curve,the capacity is maintained at 265.3 mAh·g-1/269.5 mAh·g-1 after 50 cycles.The capacity decay rate of each cycle charge and discharge is 0.567%/1.193%.The excellent electrochemical performance of ZnS/C-SnO2 composites may be related to the synergistic effect of materials.The capacity of ZnS/C is high and the electronic conductivity of Sn is excellent.Therefore,the composite has ideal specific capacity and good cycle stability.Considering the charge-discharge ratio capacity and cycle performance of the electrode material and the combined cyclic voltammetry and AC impedance test results,it is considered that the ZnS/C-SnO2 composite obtained by ball milling for 5h has the best electrochemical performance.