Preparation And Electrochemical Properties Of P/C Composites For Lithium Ion Batteries

The continuous development of electric vehicles and grid scale storage for renewable sources requires for great energy density,high rate performance,and lower cost electrode materials in LIBs.At present,the defects of lower energy density of commercial graphite system anode materials are gradually highlighted.Finding a new high energy density anode system has become the primary task today.Phosphorus is a potential lithium-ion battery candidate for negative materials because a reversible alloying reaction occurs between phosphorus and Li⁺to produce a lithium-rich phase product Li₃P,which can contribute to a theoretical specific capacity of 2595 mA h g^-1.Among them,red phosphorus is the most suitable one for our target material compared with white phosphorus and black phosphorus due to its wide range of sources,low cost,and stable structure.However,red phosphorus,like other high specific capacity electrode materials,has a poor conductivity and a serious volume expansion during the electrochemical reaction.,In order to solve the above problem,the nanocrystallization of red P and the corresponding targeted structural design is considered to be the most simple and effective strategy.Based on the above idea,this paper prepared a P/biomass-derived porous carbon composite by vaporization-condensation-conversion strategy.The highly developed pore structure and specific surface of the carbon matrix material could promote the conductivity of the Red P composite and accommodate the large volume expansion during cycling.Then,we synthesized a derivative material of red phosphorus Sn₄P₃/MXene composite.The size of Sn₄P₃is nanometerized on the surface of MXene by the solvothermal method.The MXene not only improves the overall conductivity of the composite,but also alleviates the volume expansion of the Sn₄P₃.As a result,the MXene@Sn₄P₃composite exhibits a high rate performance and a good stability.The research content and results obtained are as follows:(1)The P@BDPC composite material was successfully prepared with the biomass-derived porous carbon as a template.The effect of pre-carbonization temperature on the pore size characteristics of porous carbon were studied and an appropriate carbon matrix(BDPC)with high specific surface area and huge micropore volume was obtained from tobacco stem.Furthermore,we synthesized the nano-sized red phosphorous/biomass-derived porous carbon(P@BDPC)via a facile vaporization-condensation-conversion strategy(VCC)and explored the optimal ratio between phosphorus and carbon in the composite material.The results show that the composite material with a phosphorus content of 62.1%exhibits the best electrochemical performance:the initial specific capacity is as high as 1689 mA h g^-1at a current density of 500 mA g^-1with the initial Coulombic efficiency of 91.7%;Furthermore,the P@BDPC electrode materials can delivers a capacity of 599 mA h g^-1at a current density of 30 A g^-1,indicating an improved rate performance;After 600 cycles,the capacity remains is higher than 90%at a current density of 5 A g^-1.(2)Nanosized-SnO₂particles was uniformly grown on the base surface of MXene by solvothermal method.After phosphating,the target product MXene@Sn₄P₃composite was successfully prepared.The results show that the degree of phosphating and the loading of Sn₄P₃play an important role in the performance of the samples.The fully phosphating sample MXene@Sn₄P₃composite exhibits the best overall electrochemical performance.When the addition ratio of SnCl₄·5H₂O to MXene is 5:1,the composite material exhibits the specific capacity of 578 mA h g^-1at a current density of 1 A g^-1with a good cycling performance(the capacity retention rate is higher than 90%after 300 cycles).