Preparation And Electrochemical Performance Research Of Phenyl-based Hyper-crosslinked Polymers-derived Hard Carbon

Hyper-crosslinked polymers（HCPs）are highly crosslinked organic polymers synthesized through Friedel-Crafts alkylation reaction,which have the characteristics of flexible and tunable structures.Using them as precursors to produce hard carbon materials can reduce the production cost of hard carbon negative electrode materials,with the potential to promote sustainable development strategies.Therefore,in this study,the model compound benzene was used as raw material,and phenyl-based hyper-crosslinked polymers and their derived hard carbons were synthesized using an external crosslinking agent method.Hard carbons with different microstructures,specific surface areas,pore structures,and surface chemical properties were prepared by adjusting the catalyst content and crosslinking agent type.The changes in material pore structure and microcrystalline structure before and after carbonization were investigated,and the effect of catalyst content and crosslinking agent type on the structure of derived hard carbon was explored.The electrochemical performance of the prepared hard carbon as a negative electrode material for lithium-ion batteries was tested,and the structure-performance relationship between hard carbon negative electrode material structure and electrochemical performance was studied.First,A highly cross-linked novel hyper-crosslinked polymer（HCPB）was synthesized using benzene and 1,4-dimethoxybenzene through Friedel-Crafts alkylation reaction.The resulting material was carbonized at high temperature to produce derivative hard carbon material（CHCPB）,which exhibited significant performance including large surface area(583m² g^-1),fast ion transport and structural stability.CHCPB also demonstrated a unique layered stacking structure,providing rich storage space for lithium ions,and displaying excellent electrochemical properties.The specific capacity of CHCPB was 699 m Ah g^-1 at 0.1 A g^-1,and even at a high current density of 5 A g^-1,it still showed a specific capacity of 165 m Ah g^-1.After2000 cycles at 2 A g^-1,its reversible capacity could reach 148 m Ah g^-1.By using different proportions of anhydrous Fe Cl₃ as a catalyst in the Friedel-Crafts alkylation reaction,nanoparticle-shaped hyper-crosslinked polymers（HCPB-1）,island-shaped hyper-crosslinked polymers（HCPB-5）,and network-shaped hyper-crosslinked polymers（HCPB-15）were synthesized.The high-temperature carbonization of the precursors produced derived hard carbon materials HC-1,HC-5,and HC-15.Increasing the catalyst concentration within a certain range led to further cross-linking of the polymer,and the decomposition of more cross-linking bridges during high-temperature carbonization increased the micro-and mesopore content of the hard carbon.Among them,the HC-5 sample had a higher specific surface area(947 m² g^-1)and pore volume(0.647 cm³ g^-1),and its rich micro-porous structure and defects provided active sites for lithium-ion storage.The larger interlayer spacing of HC-5also provided favorable conditions for lithium-ion diffusion and transfer,greatly increasing its specific capacity.As a anode electrode material for lithium-ion batteries,HC-5 exhibited a specific capacity of 601.3 m Ah g^-1 at 0.1 A g^-1,and a rate capacity of 159.3 m Ah g^-1 at a high current density of 2 A g^-1.After 200 cycles at 0.2 A g^-1,its reversible capacity reached 337.4m Ah g^-1.Based on the Friedel-Crafts alkylation reaction using different crosslinking agents,benzene-based hyper-crosslinked polymers with different chemical structures were synthesized.After high-temperature treatment,derived hard carbon materials,namely HC-B,HC-M,and HC-H were obtained.Due to their different crosslinking bridges,each material has different surface chemical properties and structural features.HC-B with rigid crosslink bridge exhibits a layered structure,while HC-M and HC-H with flexible crosslink bridge show a particle-like morphology.The hard carbon materials also exhibit different pore characteristics,with specific surface areas of 583,1080,and 353 m² g^-1 and pore volumes of 0.316,0.813,and 0.396 cm³ g^-1 for HC-B,HC-M,and HC-H,respectively.After high-temperature carbonization,the derived hard carbon materials retain some oxygen-containing functional groups,which is beneficial for the accessibility of electrolytes and the conductivity of electrode materials.The abundance of carbonyl groups and larger interlayer spacing in HC-M is advantageous for improving reversible capacity.As a anode electrode material for lithium-ion batteries,HC-M has a specific capacity of up to 632.3 m Ah g^-1 at 0.1 A g^-1 and a rate capacity of 185.7 m Ah g^-1 at a high current density of 2 A g^-1.