Design Of Large π Molecules With Different Sizes And The Application In Batteries

Energy is the cornerstone of human social development,but in the process of energy development and utilization,reserve crisis and environmental pollution are increasingly prominent.The development and utilization of sustainable clean energy has become an important way to solve the problem effectively.Therefore,there is an urgent need to develop high-performance,environmentally friendly and efficient energy storage devices represented by secondary batteries.The development of high-performance electrode materials is one of the ways to obtain high-efficiency energy storage devices.The development of such materials needs to follow the design principles and specifications of electrode active materials.Generally speaking,good electrical conductivity is a basic requirement for electrode materials.π-Conjugated materials play an extremely important role because of the excellent conductivity and structural tunability.Various novelπ-conjugated materials have been designed and synthesized recently,which brought new impetus to boost the electrochemical energy storage,and have shown broad application prospects.π-Conjugated structure can possess the conductivity and facilitate the rapid charge transfer.Moreover,they can maintain material stability,leading to the long-life cycle of the battery.Considering the observation,π-conjugated materials with different sizes have been synthesized and characterized,and the desired materials have been chosen as the key electrode materials in energy storage devices.The main research results are described as follows.（1）A family ofπ-conjugated small molecules including Vat Red 41,Vat Orange 9,Vat Yellow G,and Vat Bromo mixed with Super-P and binder Poly（vinylidene fluoride）（PVDF）with a mass ratio of 5:4:1 have been utilized as key anode materials in sodium-ion batteries and potassium-ion batteries.The experimental results show that the electrode materials based on Vat Orange 9 and Vat Bromo exhibit good reversible specific capacities in sodium-ion batteries,with capacities of 155 m Ah g^-1 and 150 m Ah g^-1 respectively,when the current density is 50 m A g^-1.Vat Bromo-based electrode material has better cycling stability,at a current density of 200 m A g^-1,and there is no significant decrease in reversible capacity after600 cycles with a capacity retention rate of above 80%.In the potassium-ion battery,the electrode material based on Vat Red 41 has relatively higher reversible specific capacity and better long-cycle stability.After undergoing initial activation,the electrode material exhibits a capacity higher than 200 m Ah g^-1 at different current densities and cycle performance tests at200 m A g^-1 current densities.The results ascertain thatπ-conjugated small molecule systems bearing carbonyl groups have advantages in electron transport and storage,and such features can endow an opportunity forthem to be considered as promising candidates for the application in sustainable secondary electrode materials.（2）An extended large planeπ-conjugated molecule Vat Black BBN was mixed with Super-P and binder Poly（vinylidene fluoride）（PVDF）at a mass ratio of 5:4:1 to be as anode materials,which were used in zinc-ion batteries based on aqueous electrolytes.The results show that the battery exhibits an improved initial capacity of up to 300 m Ah g^-1 at a low current density of 50 m A g^-1.The capacity retention rate is about 80%after 130 cycles at the current density of 200 m A g^-1.More zinc ion intercalation sites can be generated because of the presence of the extendedπ-conjugated system with carbonyl and nitro difunctional groups.The structural feature provides more room for the development of nobleπ-conjugated electrode materials.（3）A largeπ-conjugated molecule poly-1,1,2,2-tetrakis（4-ethynyl-phenyl）ethane（TEPE-PY）has been prepared as anode material and directly applied to lithium-ion batteries,sodium-ion batteries and potassium-ion batteries.The results show that the lithium-ion battery has higher reversible specific capacity than the less stable potassium-ion battery,and its initial reversible specific capacity can reach 250 m Ah g^-1 at the current density of 50 m A g^-1.When charging and discharging at different current densities,it has better cycle stability.When the charge-discharge current density increases gradually and returns to the initial current density again,the reversible capacity increases,indicating that the application of material has an activation process,and the electrochemical performance is more stable after that.The specific capacity of about 70 m Ah g^-1 is obtained at the initial current density of 50 m A g^-1 in the sodium-ion battery.When the current density increases gradually,the capacity does not attenuate significantly,and has a good rate performance.The energy storage mechanism is that the more active sites brought by the largerπ-conjugated polymer system,and large cavities are beneficial to rapid ion transport.This provides a design strategy for the construction of large-scaleπ-conjugated systems.（4）A composite ofπ-conjugated polymers and metal oxides,poly-1,3,5-triethynylbenzene（TEB-PY）encapsulated Sn O₂（Sn O₂@TEB-PY）material has been prepared and used directly as anode material in sodium-ion batteries.The results show that the material presents a high reversible capacity,and the initial capacity can reach 1300m Ah g^-1 at a low current density of 50 m A g^-1.After decaying at high current density,its capacity can be close to the initial capacity after activation when the current density returns to the starting value,inferring a certain reversible reversible.Further optimization can be conducted by regulating the size of Sn O₂ particles and the thickness of TEB-PY cladding layer to explore more reliable cyclic stability.The advantage of the composite material is that the TEB-PY matrix with large specific surface area is coated on the prepared nano-scale Sn O₂surface layer,and the porous carbon structure can increase the contact area between the electrode and the electrolyte,thereby accelerating the electron and Na⁺ion transport.At the same time,TEB-PY cladding layer can restrict the agglomeration of Sn O₂ particles and Sn clusters generated during the sodiumization/de-sodiumization process to a certain extent,and improve the volume expansion.The composite ofπ-conjugated polymers with other materials can be used to improve the electrochemical stability of large-scaleπ-conjugated systems.