Synthesis And Properties Of High-Performance Multi-Carbonyl Organic Electrode Materials

As a key energy storage technology,lithium-ion batteries are widely used in electric vehicles,large-scale grid integration,consumer electronics and many other fields,and play an increasingly important role in today’s society.Inorganic transition metal oxide materials are currently the mainstream commercial lithium-ion battery materials,but it has major problems such as non-renewable,expensive,serious environmental pollution,and limited theoretical capacity,and it is increasingly difficult to meet the society’s demand for green-friendly high-performance electrode materials.Compared with inorganic electrode materials,organic electrode materials have attracted widespread attention due to their abundant resources,environmental friendliness and high structural designability.Carbonyl compounds have the advantages of high theoretical capacity and outstanding chemical stability,and are a widely studied class of organic electrode materials.However,carbonyl compounds still have problems such as low conductivity（affecting rate performance）and being soluble in organic electrolytes（affecting cycle stability）,which seriously limits the further application of carbonyl compounds.Focusing on the main challenges of carbonyl compounds,we synthesizes a series of polymer lithium-ion battery materials with multi-carbonyl structure through molecular design,deeply studies and discusses their electrochemical performance,molecular dynamics,lithium storage mechanism,structure-performance relationship,and further expands its application in organic fully symmetric batteries.The specific research content of this paper is as follows:（1）In view of the problems of low actual capacity of traditional polyimide and low capacity at high current rate,we designed and synthesized a new polyimide cathode material（PTN）by introducing an electrochemically active conjugated diketone structure in the diamine part.Compared with traditional polyimide cathode materials without conjugated diketone structure（PPN）,the comprehensive electrochemical performance of PTN has been significantly improved:PTN exhibits high reversible capacity(213 m Ah g^-1),excellent rate performance(78.2%capacity retention at 2000m A g^-1 compared to 50 m A g^-1),outstanding cycle stability(97.3%capacity retention at 2000 m A g^-1 cycle),and has a high energy density of 4417 W kg^-1 at high power density of 380 Wh kg^-1,and its comprehensive energy is one of the highest levels among reported polyimide cathode materials.（2）Based on the research work in the previous chapter,we further explored many factors affecting the electrochemical performance of polyimide cathode materials.At present,most of the existing research focuses on the design and synthesis of electrode materials with novel molecular structures,but the in-depth study of the intrinsic relationship between structure and performance is very lacking.However,the systematic and in-depth study of structure-property relationship is of great significance for the synthesis of new materials.As a typical carbonyl compound,the main shortcoming of polyimide cathode materials lies in their limited capacity.This is mainly determined by several factors such as the density of the active site in the polyimide,the accessibility of the active site and the electrochemical activity of the active site.In this work,we designed and synthesized a series of polyimides containing conjugated/non-conjugated bridges,with/without additional carbonyls,and diamines with different conjugated structures by regulating the structure of diamine monomers.It was found that:1)the introduction of carbonyl groups could increase the active site density of polyimide containing conjugated/non-conjugated diamine structures;2)Improve molecular rigidity and improve molecular accessibility;3)The introduction of conjugated structures between carbonyl groups can improve the activity of the active site.Therefore,the active site density,accessibility and activity of molecules can be improved by regulating the structure of diamine monomers,thereby effectively increasing the capacity of polyimide.On the other hand,improving the active site density,accessibility and activity of polyimide also has a significant effect on the rate performance and cycle stability of polyimide cathode materials.The work in this chapter provides a systematic and in-depth understanding of the structure-function relationship of polyimide electrode materials and may be extended to the molecular design of other organic cathode materials.（3）Based on the previous two works,we introduced a new bridged unit with a lower molecular weight,squaric acid,to overcome the problem of large molecular weight of polyimide bridged groups and repeating units（resulting in limited capacity）,and further tried to explore and expand the application of carbonyl compounds in organic fully symmetric batteries.In this chapter,we synthesized a novel carbonyl compound（PSQ）by polymerizing squaric acids with anthraquinones.The introduction of the square acid bridging structure further improves the density of the active site of the carbonyl compound,so the PSQ has a higher theoretical capacity,and the composite electrode（PSQ-K）after in-situ polymerization with Ketjen black can achieve a high capacity of up to 312 m Ah g^-1.By fusing a variety of efficient molecular design strategies into the PSQ polymer,such as designing an extendedπconjugate system,constructing a donor-acceptor structure to reduce the band gap and rational utilization of intermolecular/intramolecular interactions,we enable the PSQ cathode to simultaneously have high capacity,long cycle stability,and excellent rate performance.Not only that,PSQ can also be used as a negative electrode and exhibits outstanding electrochemical performance.Based on this,we assembled a fully organic symmetrical battery with PSQ as both the positive and negative electrodes of the battery.Thanks to the excellent molecular design of PSQ,PSQ full battery exhibits outstanding comprehensive electrochemical performance:high reversible capacity(capacity 171m Ah g^-1 at 50 m A g^-1),excellent rate performance(99 m Ah g^-1 capacity at 4000m A g^-1)and long cycle life(30000 cycles at 2000 m A g^-1,capacity decay rate of 0.0017%).Its performance is among the best results reported among organic whole batteries.This chapter describes the role of rational utilization of weak intermolecular/intramolecular interactions and the construction of polymers with donor-acceptor structures to solve the problems of solubility and low conductivity of organic electrode materials.This work also provides a new understanding for the molecular design of high-performance and low-cost all-organic symmetric battery electrode materials,which is of great significance for the practical application of organic electrode materials in future sustainable energy storage systems.