Study On The Electrochemical Mechanism Of Nickel-based Electrode Materials And Its Application

Supercapacitor is a new type of electrochemical energy storage device with high power density and long cycle life.Supercapacitors have a broad application prospect,however their low energy density has been the main factor hindering their commercialization.The design and development of nickel-based electrode materials is an effective strategy to improve the energy density of supercapacitors,but the low rate-performance and cycling stability are the main obstacles in their application.In this dissertation,the electrochemical mechanism of current collectors was explored and their impact on the electrode material performance evaluation was analyzed.The electrochemical mechanism of nickel-based electrode materials was then studied and used in the design and preparation of materials with high cycle life.The hybrid supercapacitors with high energy density and power density was assembled with the as-prepared material.The main research contents and results of this dissertation are as follows:（1）Study on effect of current collectors on electrochemical performance and the mechanism:the electrochemical mechanisms of Ti foil and nickel foam and their contribution as current collectors to the specific capacity of electrode materials during electrochemical testing were investigated through characterization and electrochemical testing.The results show that Ti foil contributes negligible capacity,and nickel foam cleaned with hydrochloric acid can produce significant capacity that significantly affects the electrochemical performance evaluation on electrode materials.However,the capacity contribution of nickel foam cleaned by acetone can be ignored for high-capacity battery-type materials,indicating that acetone cleaning is the appropriate way to pretreat nickel foam.（2）Study on the electrochemical mechanism of nickel-based electrode materials:based on the two typical materials of Ni₂P and Ni Co₂S₄,the electrochemical reaction mechanism of nickel based materials with high electrical conductivity was investigated in alkaline electrolyte.It was found that the irreversible phase transformation of Ni₂P and Ni Co₂S₄ to hydroxide occurs during the electrochemical reaction process.Also,the main reason for the low cycling stability of Ni₂P and Ni Co₂S₄ is the rapid microstructure destruction of materials caused by the dissolution and recrystallization mechanism of hydroxide after the phase transformation.（3）Preparation and properties of Ni（OH）₂/C electrode materials:based on the afore-mentioned electrochemical mechanism,the Ni（OH）₂/C electrode material with extremely ultra-long cycle life was designed and prepared.This material had a high capacity retention of 102.4%after 150,000 charge-discharge cycles at the current density of 5.0 A g^-1,which was higher than that of most nickel-based battery materials reported so far.The hybrid supercapacitors（HSCs）were assembled with Ni（OH）₂/C as positive electrode and commercial activated carbon（AC）as negative electrode.The HSCs had a high energy density of 43.3Wh kg^-1 at the power density of 721.7 W kg^-1,and still had an energy density of 7.4 Wh kg^-1 at high power density of 11,080.1 W kg^-1.