Synthesis And Electrochemical Performance Of Nano-sized ZnS Anode Materials For Lithium-ion Batteries

The rapid development of today's society can greatly promote the process of human social civilization,but this will inevitably have many negative effects on the external environment on which we live:excessive exploitation of non-renewable resources,serious environmental pollution,frequent natural disasters,etc.The emerging energy industry as the three major mainstream industries in the new era has attracted extensive attention of researchers.Lithium-ion battery has become the most mature new energy conversion device because of its advantages of high cycle stability and environmental protection.The negative material,which is an important component of lithium-ion battery,is the key factor to determine its performance.At present,the negative material which has been commercialized is only carbon material.Therefore,a high-performance and low-cost negative electrode for lithium-ion battery has been developed.Material is particularly important.Zinc sulfide(ZnS)has gradually entered the field of vision of researchers because of its theoretical specific capacity as high as 963 mAh/g,abundant reserves,low price and environmental protection.However,the electronic conductivity of ZnS materials is not high and the rate performance is not ideal,and there will be serious volume expansion phenomenon in the process of charging and discharging,and the specific capacity decays rapidly.Therefore,how to solve the above problems of ZnS materials is particularly important.In this paper,nano-sized ZnS materials were prepared by solvothermal method,and ZnS/C materials were synthesized by adding surfactants and carbon-coated modification.Specific research contents are as follows:1.Nano-sized ZnS materials were synthesized by solvothermal method using Zn(NO3)2·6H2O and CH4N2S as reactants and ethylene glycol as solvent without the assistance of other reagents.XRD and SEM results show that the synthesized ZnS material has high purity,good crystallinity and complete crystal structure when the reaction temperature is 160? and the reaction time is 10 h,and the spherical morphology of the synthesized ZnS material is good,the grain distribution is uniform,and the size is about 100 nm.The structure of electrochemical performance test shows that the first lithium intercalation specific capacity of ZnS electrode is 974.4 mAh/g.After 50 cycles,the discharge specific capacity is only 338.8 mAh/g and the capacity retention rate is 34.77%.When the ratio increases to 2.0 C,the discharge specific capacity is only 133.3 mAh/g.2.Nano-sized ZnS material modified by 2 mmol PVP has higher crystallinity and more complete crystal structure.The particle size of the product is uniform,the grain size is between 80?100 nm,the spherical morphology is regular and uniform,and the agglomeration phenomenon is obviously improved.The electrochemical properties of nano-sized ZnS modified by surfactant PVP were characterized and analyzed.It was found that when the current density was 0.1 C,the first discharge specific capacity was 974.4 mAh/g,and after 50 cycles,the discharge specific capacity remained above 420 mAh/g with a capacity retention rate of 52.47%.When the current density was 0.1 C,the reversible discharge specific capacity of nano-ZnS was still maintained.Compared with ZnS before modification,the sample material modified by PVP exhibited better electrochemical properties.3.Using glucose as carbon source,nano-sized ZnS modified by surfactant PVP was selected for carbon-coated modification.The results of XRD,TEM and electrochemical performance test show that the ZnS/C composites synthesized by in-situ carbon coating method with 50 wt%carbon content have high crystallinity and complete crystal structure,uniform particle size,about 80 nm,good monodispersity,high first discharge specific capacity of 1189.8 mAh/g,ideal cycle stability,and the specific discharge capacity after 50 cycles can still be maintained at 948.9 mAh/g.The capacity retention rate is up to 79.75%.The addition of carbon materials can effectively improve the electrochemical properties of ZnS materials.4.ZnO was synthesized by calcining nanometer ZnS materials modified by surfactant PVP at high temperature and then modified by carbon coating to prepare ZnO/C composites.Characterization test results show that the crystallinity of ZnO/C composites is high,and ZnS is completely converted to ZnO after calcination;the product has better grain size,smaller than 100 nm,and there is a slight agglomeration phenomenon;but as lithium ion batteries,the electrochemical performance of ZnO/C composites is poor;the first discharge capacity is 933.1 mAh/g and the discharge ratio increases with the number of cycles.The specific discharge capacity is 368 mAh/g after 50 cycles,and the specific discharge capacity is only 158.8 mAh/g when 2.0 C high rate charge and discharge is realized.Compared with the ZnS/C electrode material,the cyclic stability and rate performance of the ZnO/C electrode materials are not ideal.