| The electrode materials of commercial lithium-ion batteries（LIBs）are mainly based on traditional metal-containing cathode materials and carbon-based anode materials.The current electrochemical performance of LIBs can’t meet the increasing demand for high energy and high power density because of the scarcity of resources of inorganic electrode materials,environmental pollution caused by production and recycling processes,limited theoretical capacity and slow reaction kinetics.In addition,the intercalation/deintercalation mechanism of lithium ions in the rigid lattice of metal oxide causes large volume expansion and stress changes,which in turn leads to capacity fading and safety hazards.Organic electrode materials with electrochemically active groups such as C=O,C=N,and N=N have been developed and considered as the most promising ones to replace traditional inorganic electrode materials due to their abundant natural resources,metal-free and light weight,low cost,strong structural designability,environmental friendliness and other advantages.Whereas the high solubility of organic small molecule electrodes in organic electrolytes often leads to poor cycling stability.In contrast,polymer electrodes avoid the dissolution problem,and the long-chain structure can facilitate ion transport and maintain structural integrity during cycling.But most polymer electrodes still face problems such as the decrease of theoretical capacity caused by the introduction of inactive units and the increase of molecular weight,and the unsatisfactory rate performance caused by intrinsic insulating properties.Based on this,the following works are carried out in this paper from two aspects:molecular structure regulation through chain engineering and introduction of conductive carbon skeleton:（1）Using dianhydride and diamine with anthraquinone structure as monomers,a simple and environmentally friendly in-situ hydrothermal polymerization method was used to obtain polyquinoneimines/graphene（PQI@Gr）composites with three-dimensional nanoarray structure.On the one hand,the PQI has a theoretical capacity as high as 228 m Ah g-1 due to the introduction of electroactive linking groups between the imide units,and on the other hand,the three-dimensional nanoarray structure has abundant 3D porous channels and a large number of exposed carbonyl groups,which are beneficial to fast electron transport,fast electrolyte penetration,fast ion diffusion,and efficient utilization of active sites.When the graphene content is 35.8 wt.%,PQI@Gr exhibits a reversible capacity of 205 m Ah g-1 at 0.1 A g-1,an excellent rate performance up to 179.4 m Ah g-1 at 5.0 A g-1,and excellent long-cycle stability with capacity retention of 73%after 10000 cycles at 5.0 A g-1.（2）The polymers PBI-P and PBI-N with both electroactive C=O and benzimidazole rings were synthesized by thermal imidization using acid anhydride and tetramine as monomers.Firstly,the effect of two anhydride structures of PMDA and NTCDA on the electrochemical performance was investigated.Due to more benzene rings and largerπ-conjugated system in the NTCDA structure,PBI-N has a lower LUMO level,more active sites,and faster electron transfer.GO was further introduced for in-situ polymerization,and GO was thermally reduced while PBI-N was generated,and finally PBI-N@Gr composites were obtained.Graphene not only acts as a polymer growth matrix to ensure exposure of active sites and efficient infiltration of electrolytes,but provides efficient electron transport as an internal conductive carbon skeleton in the material as well.Compared with PBI-N,PBI-N@Gr with 15.7 wt.%of graphene has a higher specific reversible charge capacity(1004.4 m Ah g-1),better rate performance(45.9%capacity retention at 2 A g-1)and excellent cycling stability(reversible capacity of 337.5 m Ah g-1 and capacity retention of 76.2%after 2000 cycles at 5 A g-1).（3）Through the in-situ precipitation polymerization of acrylonitrile and GO,followed by heat treatment in air atmosphere,under the synergistic effect of the cyclization oxidation of PAN and the thermal reduction of GO to graphene,graphene-supported OPAN@Gr composites with electroactive C=O and highly conjugated structure are finally obtained.The petal-shaped OPAN grows evenly on both sides of the graphene,which makes the electrolyte better infiltrate,exposes more active sites such as C,N,and O,and shortens the ion diffusion path and accelerates the ion transmission rate.The introduction of the conductive framework graphene ensures the electron transport inside the material,the electronic conductivity of the material is greatly improved,and the material exhibits fast reaction kinetics.When the graphene content is20.6 wt.%,OPAN@Gr exhibits a reversible charge specific capacity as high as 1861.5 m Ah g-1 after 40 cycles at 0.1 A g-1,and the capacity retention is 50.5%after expanding the current density from 0.1 A g-1 to 2 A g-1,the reversible capacity is 382.3 m Ah g-1 after 5000 cycles at10 A g-1,corresponding to a capacity retention rate of 79.9%. |
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