| Due to the advantages of strong molecular designability,wide sources and green environmental protection,the research of organic polymers as electrode materials for lithium-ion batteries has been widely reported.Polyimide is a representative conjugated carbonyl compound,the rich carbonyl group in which makes it have considerable lithium storage capacity and has great potential in improving the energy density of lithium-ion batteries.At the same time,polyimide can also be used as binders in various LIBs systems.Based on the molecular structure and physical characteristics of polyimide,this work intends to fully consider the performance and structural design requirements of lithium-ion battery electrodes in the preparation process,further explore the impact of polyimide molecular structure design on the performance of electrode materials,and explore its multi-functional application in lithium-ion battery cathode materials,so as to achieve the objectives of reducing lithium battery production process and improving energy density.In the first part of this paper,polyimide materials with different structures such as PTTA,PTDA,PMTA and PNDA were synthesized by one pot method.Through the analysis of their physical properties such as thermal stability,crystal phase and morphology,as well as their electrochemical properties such as cycle performance and magnification performance,the influence of polyimide molecular structure on their electrochemical properties was preliminarily explored.By analyzing the charge discharge curves of four polyimides with different molecular structures(PTTA,PTDA,PMTA and PNDA),it is found that the conjugated aromatic ring in the molecular structure of PTTA is the largest,its corresponding theoretical specific capacity is the highest,and its capacity proportion higher than 1.5 V is also the highest.This result shows that the size of conjugated aromatic ring in polyimide structure has a great influence on its capacity performance.The high discharge potential of the negative electrode will greatly reduce the output voltage of the battery,resulting in the reduction of the energy density of the battery.Therefore,the high potential capacity is an inefficient capacity for the negative electrode material.The generation of this high potential capacity should be reduced as much as possible.This requires that the molecular structure of polyimide cathode material based on conjugated carbonyl not only ensures the battery capacity and cycle stability,but also reduces the generation of inefficient capacity and improves the energy density in essence.The second part of this paper is based on the synthesized PMTA as electrode material,combined with the huge volume change of silicon electrode material in the process of charge and discharge,to give full play to the multifunctional role of PMTA as binder,active reversible lithium material,buffer medium and coating material in high-performance silicon anode of lithium-ion battery.The electrochemical properties of MF-PI/Si composite negative electrode materials were improved by introducing multifunctional polyimide(MF-PI)into high-performance silicon negative electrode materials.In MF-PI/Si composite negative electrode,MF-PI as the coating layer of nano-silicon can effectively avoid the volume expansion of silicon negative electrode in the process of charge and discharge and improve the cycle stability of silicon negative electrode.More importantly,this MF-PI with good bonding properties eliminates the addition of secondary binders during the preparation of MF-PI/Si composite electrodes,and its own good bonding properties can maintain the electrode structure stability,which not only saves costs,but also has important significance for improving the overall performance of the battery.Compared with other binders,the excellent electronic conductivity of MF-PI can improve the rate performance of MF-PI/Si composite anode.The excellent conductivity of MF-PI is attributed to the conjugated carbonyl and conjugated π bond in MF-PI benzene ring.More importantly,the electrode using the synthesized MF-PI/Si as the active material and adhesive shows a better electrochemical interface and surface area,which further enhances the electrode dynamics and electrochemical performance.In addition,the good thermal stability of MF-PI/Si also makes the battery work in a relatively high temperature working environment,and the safety performance of the battery has been greatly improved.Therefore,this research on polyimide and silicon composites opens up a new perspective of electrode material design for silicon anode of lithium-ion battery. |
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