Preparation Of Covalent Triazine Framework And Its Application In Novel Secondary Batteries

Lithium-ion batteries are widely used in various electronic devices due to their excellent energy storage performance,which play a very important role in the field of energy storage.Electrode materials are the key factor affecting the performance of Li-ion batteries,and inorganic materials have limited their further development due to their limited resources and environmental problems during the mining process.In contrast,organic electrode materials have the characteristics of high theoretical capacity,green environmental protection,and a wide range of sources,which are considered to be the most potential electrode materials for sustainable green lithium-ion batteries in the future.Due to the high solubility of most organic compounds in organic electrolytes and poor electronic conductivity,their performance in practical applications is unsatisfactory.Therefore in this thesis,a series of covalent triazine frameworks were synthesized through molecular design,and their electrochemical performances as electrode materials for lithium ion batteries and full batteries were deeply studied.The main contents and results are as follows:（1）Using three tetracyanoporphyrins（Cu TPPCN,Co TPPCN and TPPCN）as precursors,three porphyrin-bridged covalent triazine frameworks（CTF-Cu TPP,CTF-Co TPP and CTF-TPP）were synthesized by ionothermal method,ingeniously connecting the porphyrin of the 18πelectron system to the triazine ring.It solves the problem of high solubility of organic compounds in organic electrolytes and ensures good conductivity of polymers.When used as an anode material for lithium-ion batteries in the voltage range of 0.01-3.0 V,CTF-Cu TPP exhibits the best electrochemical performance,for example,the initial discharge and charge capacities of the CTF-Cu TPP are 2035.3/1020.8m Ah g^-1at a current density of 0.1 A g^-1.It exhibits good cycling performance when assembled with Li Co O₂into a full cell,tested in the voltage range of 1.4–3.8 V.A discharge capacity of 103 m Ah g^-1can be achieved at a current density of 50 m A g^-1,and it can be cycled for 900 cycles at a current density of 1 A g^-1with almost no capacity fading.（2）Using melamine（MA）and terephthalaldehyde（PDA）/trialdehyde-based phloroglucinol（TFP）as linking groups and structural units,two imine-linked covalent triazine frameworks（TFP-MA and PDA-MA）with different pore sizes were synthesized by Schiff base reaction,in which linking the triazine rings together with imine bonds solves the dissolving problem of organic compounds in organic electrolytes.Combining carbon nanotubes with the optimium TFP-MA to generate TFP-MA@CNT further enhances the conductivity of organic electrode materials.It was used as an anode material for lithium-ion batteries tested in the voltage range of 0.01-3.0 V.The TFP-MA@CNT exhibits good cycling characteristics,after 1000 charge-discharge cycles at a current density of 1 A g^-1,the reversible capacity of 607.2 m Ah g^-1is still maintained,which is greatly improved compared with the initial reversible capacity.Furthermore,a full cell was assembled using TFP-MA@CNT/Li Co O₂as the anode/cathode materials tested in the voltage range of1.4-3.8 V.The discharge capacity at a current density of 50 m A g^-1is 107.9 m Ah g^-1.After1000 charging and discharging cycles at 1 A g^-1,there is still a charge-discharge capacity of44.6 m Ah g^-1with the capacity retention rate of 74.2%.