Preparation And Study Of Phosphorus Based Anode Materials ?SnP@C,Se₃P₄@C,GeP₃@C? For High Performance Potassium Ion Batteries

In recent years,the development of new energy has flourished.Lithium-ion batteries have been widely used due to their high energy density.However,a large number of commercial applications of lithium-ion batteries face the problem of limited resources and uneven distribution.The potassium ion secondary rechargeable battery has similar properties to the lithium ion secondary rechargeable battery,and the potassium resource reserves are relatively abundant and widely distributed,so potassium ion batteries has the potential as a low-cost secondary rechargeable battery with high energy density and high voltage.However,conventional anode materials for lithium ion batteries,such as graphite and silicon,have weak electrochemical potassium storage capacity.It is necessary to study a negative electrode material that matches the potassium ion battery system.Phosphorus/carbon composite materials and metal phosphides have high theoretical capacity,and can alleviate the problems of poor conductivity and volume expansion of phosphorus materials,receiving extensive attention.The carbon materials increase the electrical conductivity of the composite electrode material,and improves the cycle stability.However,phosphorus/carbon composites face a major challenge of how to efficiently“binding”phosphorus into the interior of carbon materials.The metal phosphides have a lower redox potential,providing higher specific capacity and better cycle stability.The main contents of this thesis include the following aspects:?1?For the first time,this paper obtained the carbon-supported Sn by hydrothermal method and high temperature reduction.and the carbon-supported Sn reacted with red phosphorus at high temperature,obtaining the metastable trigonal SnP,which broke the limitation of synthesizing SnP under severe conditions such as high temperature and high pressure.The preparation mechanism of SnP was discussed by using the first principle calculation and experiment.Through electrochemical performance testing,the SnP@C electrode maintained a capacity of 355.0 mAh·g^-1 after 100 cycles at a current density of 100mA·g^-1,and the capacity retention rate is 77.94%.The SnP@C electrode maintained a capacity of 215.94 mAh·g^-1 after 200 cycles at a current density of 1000 mA·g^-1,and the capacity retention rate is 87.8%,SnP@C composite anode exhibits excellent electrochemical performance.?2?In this paper,using the characteristics of low melting point of selenium,the commercial carbon material K.J.black is used as the adsorption material to prepare the Se@C composites,and then Se is used as the active reaction site,ie,the anchor point,to induce the red phosphorus vapor to enter the mesoporous carbon.Inside the tiny pipe,P reacts with Se to form a Se₃P₄ compound.The potassium-embedded mechanism of Se₃P₄@C was studied by ex-situ XRD.When the content of Se₃P₄ is 42.9%,the battery can obtain a high capacity of454.03 mAh·g^-1 at a current density of 200 mA·g^-1,and the capacity retention rate reaches86.27%after 100 cycles.When the current density is 1000 mA·g^-1,after 300 cycles the capacity of 200.40 mAh·g^-1 can still be retained,the capacity retention rate is 78.89%,and the average attenuation per cycle is 0.0703%,Se₃P₄@C composite anode exhibits excellent electrochemical performance.?3?In this paper,the GeP₃@C composites was prepared by mechanical ball milling,and its electrochemical performance was tested as anode of potassium-ion batteries.GeP₃ has improved performance compared to P and Ge alone,but there is still a problem of fast capacity degradation.The combination with carbon materials can significantly improve its electrochemical performance.The GeP₃@C composites can get a capacity of 239.38 mAh·g^-1after 50 cycles at a current density of 60 mA·g^-1.The comparative analysis of the electrochemical performance tests of three kinds of phosphorus-based composites shows that the combination of phosphorus and other active components can effectively improve the electrochemical performance of the electrode materials,which is a suitable strategy.The mutual anchoring after the formation of the compound can alleviate the damage caused by the volume change of the material to some extent.At the same time,it can be combined with carbon materials to obtain good protection and conductivity of carbon materials,and the cycle stability and rate performance of the electrode material are remarkably enhanced.Among them,SnP@C and Se₃P₄@C composites show better electrochemical performance,but the capacity attenuation of GeP₃@C composites is still obvious.