Design Of High Performance Transition Metal Compound Electrodes And The Study On Their Electrochemical Performance

Renewable green energy（solar energy,wind energy,hydropower,etc.）are highly dependent on time,region,weather and other environmental factors and have intermittency characteristic.Therefore,developing the high-efficiency energy storage devices is the key to the popularization and application of clean energy.Secondary battery and supercapacitors are two major options for energy storage systems,which has been widely concerned.Yet,supercapacitor shows higher power density,longer cycle life and more safety and stability than secondary battery,which plays an irreplaceable role in certain application situations.As supercapacitor electrode materials,the composition and structure directly determine the electrochemical performance.Transition metal compounds with intrinsic/extrinsic pseudo-capacitive storage mechanism,showing ultrahigh theoretical specific capacitance,high energy density and low cost,have attracted more and more attentions.However,their poor conductivity,limited active sites and unstable structures seriously hinder their practical application.Based on the problems mentioned above,using a small amount of high conductivity materials,phosphorization or constructing heterostructure to decorated transition metal compound materials for improved conductivity,electrode structure and cycle stability are discussed in this paper,and shows excellent energy storage performance.The main research contents and innovation results are as follows:1.A novel Cu⁰/Cu⁺modified CoO cathode composite was prepared via a facile one-step thermolysis method.Due to the beneficial flower-like nanostructure and the synergetic effect of Cu⁰/Cu⁺modification,the electrochemical performance of CoO electrode has been significantly improved,which results in a significantly enhanced specific capacitance of694.6 F g^-1 at 1.0 A g^-1（four times higher than pristine CoO）and high cyclic stability（93.4%retention over 10 000 cycles）.Furthermore,this modification method is also applicable to other transition metal oxide（such as NiO）with enhanced electrochemical performance.Theoretical calculations further verify that the modification of Cu⁰/Cu⁺can tune the electronic structure of CoO and improve the conductivity and electron transport.2.A novel cathode material of Co P/Cu₃P heterostructured nanoplate is fabricated via a facile phosphorization process.Due to the synergistic effects of high conductivity of Co P and heterostructure,the electrochemical reaction kinetics in the Co P/Cu₃P are significantly enhanced,and the specific capacitance and rate performance are further improved.The Co P/Cu₃P electrode manifests an excellent electrochemical performance of 734.2 F g^-1 at1.0 A g^-1,a superior capability of 53.2%capacitance retention even when the current density increases to 50.0 A g^-1,and an excellent cycling performance.Theoretical calculations further confirm that the heterostructure can effectively tune the electronic structure of Co P,and improve the charge transport.3.A facile in situ polymerization strategy is demonstrated to engineer commercial MoO₃ by adjusting the nano-particles into nanosheets,coating a thin layer of conductive polyaniline and introducing oxygen vacancy.Benefiting from the synergistic effects of enhanced charge transfer kinetics,improved conductivity and robust structural stability,the optimized MoO₃ nanobelts anode material show excellent performance in proton storage.The MoO₃ electrode delivers a record-high performance of 1307.4 F g^-1(236.1 m A h g^-1)at 1.0 A g^-1,excellent rate capability with a capacitance retention of 55.3%at 50.0 A g^-1,and stable cycling performance with a capacitance retention of 95.5%after 6000 cycles.Furthermore,the redox reaction mechanism of the MoO₃ electrode in proton storage has been revealed via micro-structure analysis and ex-situ characterization.4.An effective strategy of in situ polymerization of polyaniline on the surface of annealed Ti₃C₂T_x sheets is proposed with modified surface termination,expanded interlayer spacing and three-dimensional structure.Benefiting from the interconnected structure,enhanced electrochemical activity and efficient ion/electron transport layer,the prepared anode electrode demonstrates an outstanding specific capacitance of 652.3 F g^-1 at 1.0 A g^-1（three times higher than pristine Ti₃C₂T_x）,an impressive rate capability with 80.9%capacitance retention at 50.0 A g^-1,and excellent cycling stability with almost no capacitance loss after 10 000 cycles.Furthermore,the prepared free-stranding film electrode based on modified Ti₃C₂T_x shows a high volumetric capacitance of 2368.1 F cm^-3.