Large ?-conjugated Porous Frameworks As Cathodes For Sodium-ion Batteries

Organic rechargeable sodium-ion batteries(OSIBs)are one of the most appealing alternatives to commercial inorganic lithium-ion batteries because OSIBs can combine the merits of sodium(similar chemical properties with lithium,comparable electrode potential only 0.3 V higher than lithium,resource abundance and possible use of low cost aluminum as current collector for both cathodes and anodes)with the advantages of organic electrodes(diversity,subjective design feasibility of molecular structure,structure flexibility for accommodating large Na-ions(radius:1.02?(Na⁺)vs.0.76?(Li⁺)),eco-friendliness and availability from natural organic sources).Among the kinds of organic materials,carbonyls are promising materials as electrode materials due to the chemical stability of the charged/discharged states,the quantitative electrochemical reaction and the adjustable capacity and electrode potential,although the development of organic electroactive materials is still sluggish in low capacity,cycleability and rate performance.However,the inorganic material of commercial lithium battery is not suitable for a sodium-ions battery,it tends to cause deterioration or failure for sodium-ion batterie.The main reason is that during the charging and discharging process,the larger ionic radius of sodium ions may cause difficulty in embedding/extracting in the material,and even cause pulverization damage of the material structure,which is particularly prominent when the battery is rapidly charged.Therefore,the design of sodium ion battery cathode materials with high specific capacity,good fast charge performance and excellent cycle performance has important scientific significance and application value for promoting the application of sodium ion batteries in energy storage and other fields.But up to now,the research on organic sodium-ion batterie,especially the cathode materials,is still insufficient and the reported organic cathode materials still have some problems,such as low capacity,poor fast charging performance and short cycle life.In order to solve these problems,we designed and synthesized three kinds of large?-conjugated porous frameworks,which utilized the characteristics of conjugated porous polymers to inhibit the dissolution of electrode materials and improve the electrochemical performance of batteries.The main research results are as follows:(1)DAPT-TFP-CPFThe monomers DAPT and TFP were synthesized by the reported literature.The polymer DAPT-TFP-CPF was successfully synthesized by the results of NMR,liquid phase mass spectrometry,elemental analysis,¹³C NMR,FTIR,XRD,XPS,TEM and SEM.In a glove box filled with argon gas,the electrochemical performance of DAPT-TFP-CPF was tested in LANHE-CT2001A test system(Wuhan,China)by mixing DAPT-TFP-CPF with super P(conductive additive)and P VDF(adhesive)at a weight ratio of 5:4:1.The test results show that the performance of conjugated porous polymer DAPT-TFP-CPF cathode is ideal.For example,the charge-discharge capacity remains at 150 m Ah g^-1 after 1000 cycles with the rae of 100 m A g^-1 and 120 m Ah^-1 after more than 1400 cycles with the rate of 1000 m A g^-1.Even at the rate of 2000,5000 m A g^-1,there is still retain more than 100 m Ah g^-1 charge and discharge capacity.These may be due to the conjugated porous polymers can effectively inhibit the dissolution of active materials during the progress of charging and discharging.Moreover,the porous structure is conducive to the implantation/removal of sodium ions,which can enhance the ion transport and improve the electrochemical properties of electrode materials.(2)PT-TABQ-CPFThe conjugated porous polymer PT-TABQ-CPF was prepared by temperature programmed method.The monomers PT and TABQ were synthesized through the reported literature.By the results of NMR,liquid phase mass spectrometry,elemental analysis,¹³C NMR,FTIR,XRD,XPS,TEM and AFM,we can surmise that the synthesized material is our expected large?conjugated porous polymer PT-TABQ-CPF.it exhibited outstanding electrochemical properties during the progress of electrochemical testing.The cathode can deliver a reversible capacity of 200 m Ah g^-1 at the rate of 100 m A g^-1 rates and at the different rate of 50,100,200,500,1000,2000 and 5000 m A g^-1,the reversible capacity of PT-TABQ-CPF were 250,220,200,198,180,150,100 m Ah^-1,respectively,in addition,when the rate returns to 50 m A g^-1,the capacity can rise back to 250 m Ah g^-1.Such outstanding electrochemical performance may be attributed to the large?-conjugated porous polymer inhibiting the dissolution of the material in the electrolyte,thus improving the electrochemical performance of the electrode material.(3)TB-TABQ-CPFOn the basis of the previous two works,in order to further improve the electrochemical performance of the electrode,we prepared the conjugated porous polymer TA-TABQ-CPF with temperature programmed method by using TB and TABQ,due to the higher theoretical specific capacity.The electrochemical performance test data show that the polymer TA-TABQ-CPF has excellent electrochemical performance.For example,after 100 cycles at the rate of 100 m A g^-1,its reversible capacity remains at 243 m Ah^-1,and the coulomb efficiency remains at 100%.At the rate of 1000 m A g^-1,after 2000 cycles,its charge-discharge capacity remains at 180 m Ah g^-1,and the Coulomb efficiency remains at 100%throughout the cycle.In addition,it also have a good rate performance,at the different rate of 50,100,200,500,1000,2000,5000 m A g^-1,the electrode always maintains a stable capacitance output at the rate of 2A or 5A.Moreover,when the rate returns to 50 m A g^-1,the discharge capacity can be recovered to 250 m Ah g^-1.