Preparation And Electrochemical Properties Of Materials Derived From Coordination Polymer

Facing up with energy crisis and worsening environment,the popularization and utilization of clean energy are of significant importance.Limited by the conversion and transmission of these energies,highly-efficient and portable electrochemical storage devices have undergone tremendous development in recent years.As the most widely used energy storage devices commercially,lithium-ion batteries possess the advantages of high capacity,superior energy density and stable charging-discharging performance.However,the safety issues mainly caused by the unavoidable formation of lithium dendrite,as well as insufficient power density and high cost,severely hinder their further applications.Metal-air batteries,such as lithium-air,sodium-air and zinc-air,are considered to be the most promising and widely used power source because they are cheap and superior to capacitors.Although the theoretical potential can reach 1.65 V,the actual discharging voltage is usually lower than 1.4 V,resulting in low power density and poor rate capability.In contrast to zinc-air batteries,zinc-based hybrid batteries(such as Zn-Co3O4 and Ni-Zn batteries)have higher operating voltage and power density.Therefore,in recent years,people have put forward a new concept---the closed zinc battery and zinc-air battery can be knead together at the battery level,so as to obtain a new hybrid battery integrating high voltage,ideal specific capacitance,ideal power and energy density.For the hybrid batteries,the cathode active material plays an important role,the material must have good charging and discharging ability and excellent ORR and OER activity.In this paper,with a Co-based new coordination polymer,[Co(dpdc)(dpphen)]n·2nH2O as a precursor,an ideal cathode material O-Co3O4/MCN was synthesized;an oxygen vacancy rich NiO based composite material with mesoporous carbon modified by N and S atoms as matrix is selected as cathode material,which was synthesized through calcination of NiMOF;the Co3O4@NC composite electrocatalyst based on mesoporous carbon was prepared.The first two tasks are used for hybrid batteries and the last for zinc-air batteries.The first part,to achieve high power/energy density and capacitance/voltage in a safe and cost-effective battery system,a hybrid aqueous Zn battery is assembled by kneading Zn-air and Zn-Co3O4 batteries at the cell level.A new coordination-polymer-derived,oxygen-vacancy-rich Co3O4-based composite is chosen as a cathode material for this hybrid battery.The material is attractive with a specific capacitance of 213.7mAh·g-1 at 1A·g-1.Its rate capability is promising with 62.6%capacitance retained when the current density increases to 20A·g-1.The composite follows a typical four-electron mechanism during the oxygen reduction reaction(ORR).In the oxygen evolution reaction(OER),its overpotential and Tafel slope are 347mV and 79.4mV·dec-1 respectively.For the hybrid aqueous Zn battery,the discharge process is divided into two stages,namely,a Zn-Co3O4 battery and a Zn-air part.With the current density at 1 mA·cm-2,two discharge plateaus locate at 1.72V and 1.02V.In this case,the specific capacitance of the hybrid battery reaches 788mAh·g-1 with an energy density of 921Wh·kg-1.Its peak power density reaches 48.9mW·cm-2 at 34.8mA·cm-2.The charge-discharge platforms and specific capacitance remain stable after continuous experiments for 300 cycles.This work introduces a referable example for the design and fabrication of a high-performance hybrid aqueous Zn battery.The second part,an Ni-Zn battery is a distinguished member in the family of closed Zn-based batteries due to its ideal power density and voltage.However,when it is employed as a power supply for electric vehicles,its defects in terms of specific capacitance and energy density become obvious.Herein,to resolve this problem,a hybrid battery system was created through a combination of Ni-Zn and Zn-air batteries at the cell level.In a hybrid battery system,oxygen vacancy rich NiO with S,N co-modified mesoporous carbon as a matrix was used as the cathode material.This cathode material showed a high specific capacitance of 202.1mAh g-1 at 1.0A g-1.When the current density reduces to 20A·g-1,this value decreases to 130.2 g-1,which implies that 64.4%of specific capacitance was retained.It also exhibits excellent OER and ORR activities.For the hybrid battery system,when the discharge process was carried out at 1mA·cm-2,there were two voltage plateaus at 1.72V and 1.12V,which originated from Ni-Zn and Zn-air,respectively.In this case,its specific capacitance and energy density reaches 800.3mAh g-1 and 961Wh Kg-1,respectively.The hybrid battery also possesses perfect stability during multi-cycle charge-discharge tests.The construction of this hybrid battery system develops a new road to prepare a power supply device with high performance.