Study On Energy Storage Characteristics Of Tin-based Carbon Composites Based On Sodium Alginate Crosslinking Reaction

Battery technology is an important energy storage technology.Among them,lithium-ion batteries have attracted much attention as one of the most important energy storage devices.Lithium-ion batteries have high energy density and good cycle life,but the negative graphite,which is commonly used in lithium-ion batteries,has become increasingly difficult to meet current requirements because of its low theoretical specific capacity.Therefore,the development of new anode materials is of great significance.At the same time,sodium ion batteries have received increasing attention as an alternative energy storage system.Tin-based materials have high theoretical specific capacity,suitable voltage windows,and great potential when applied to lithium/sodium ion batteries.Aiming at the problem of electrode degradation caused by the large volume change of tin-based materials during cycling,this paper uses the cross-linking reaction of sodium alginate for carbon coating,meanwhile,introduces elements such as O and P to obtain long-term cycle life and good rate performance lithium/sodium ion battery anode Material system.The main research results obtained are as follows:(1)The cross-linking reaction of sodium alginate with tetravalent tin ions,and the addition of sodium ions affect the reduction temperature of Sn.Based on this,Sn/C composites were prepared,which exhibited a small particle size,a well-developed pore structure,and a carbon matrix with a high degree of graphitization.Applying it to the negative electrode of lithium/sodium ion battery proves that Sn/C has good electrochemical performance(100th cycle for LIB:320 m Ah/g,SIB:122 m Ah/g),but the larger volume expansion still brings more obvious capacity attenuation(attenuation LIB:60%,SIB:73%after the 100th cycle compared to 2rd).(2)Aiming at the problem of excessive volume change of Sn/C,the lower temperature carbonization is used to introduce O element to obtain SnO₂/C composite material prepared based on the sodium alginate cross-linking reaction,which has the same advantages as Sn/C.Ultrafine particle size(3-5 nm),well-developed pore structure,and carbon matrix with high degree of graphitization are obtained.When it is applied to a lithium ion battery,it shows excellent electrochemical performance(0.1A/g:720 m Ah/g,5 A/g:181 m Ah/g).The introduced oxygen element well buffers the volume expansion of the material during cycling.(3)Aiming at the problem of low theoretical specific capacity of SnO₂/C,sodium hypophosphite was used as the phosphorus source,and SnO₂/C was phosphating at low temperature to obtain Sn/Sn₄P₃/C composite material.The material retains the microstructure of SnO₂/C very well,shows a fine particle size,a well-developed pore structure,and a high degree of graphitization of the carbon matrix.The introduction of the P element increases the theoretical specific capacity of the material.When applied to the negative electrode of lithium/sodium ion battery,it presents good electrochemical performance(0.1 A/g,LIB:958 m Ah/g,SIB:156 m Ah/g).By combining the Volt-Ampere characteristic curve,constant current charge-discharge curve and transmission electron microscopy image after cycling,it was found that the reason for the capacity change during the lithium storage process was the combined effect of electrode activation and reversible deposition and decomposition of the electrolyte.In this study,the cross-linking characteristics of sodium alginate and polyvalent metal ions were used to prepare Sn/C and SnO₂ composites,and Sn/Sn₄P₃/C composites were prepared by low-temperature phosphating of SnO₂/C with sodium hypophosphite.The material's energy storage characteristics when applied to the anode of lithium/sodium ion batteries provide a new idea for the research of tin-based anodes.