The Preparation Of Nickel-cobalt Fluorides And Their Electrochemical Performance For Supercapacitors

Recently,the exploitation and application of high-performance supercapacitors electrode materials has been a hot topic in the field of electrochemical energy storage.Among them,new types of transition metal-based electrode materials have attracted particular attention.However,the intrinsic conductivity defect of the transition metal-based electrode materials seriously affects their performance,resulting in low specific capacity,poor rate performance and short cycle life.Therefore,the improvement of such electrode materials has far-reaching significance.In view of above,a novel nickel-cobalt fluoride electrode materials were synthesized.The strong stability characteristics of metal-fluorine bonds and the synergistic effect of nickel and cobalt exerted the electrochemical properties of the entire material and improved its electrochemical performance.Additionally,the energy storage mechanism of materials also was researched.The specific work and conclusions are as follows:1.The ternary Ni-Co-F(Ni:Co = 1:0,16:1,8:1,4:1,2:1,1:1,0:1)tetragonal nanocrystals were solvothermally constructed for supercapacitors' positive electrode materials.The optimal Ni-Co-F(Ni/Co = 2:1)has showed superior performances of specific capacitance,rate capability and charge transfer kinetics(282 C g-1 at 1 A g-1,74%retention/1-16 A g-1,449 ?)than all the other Ni-Co-F candidates.The energy storage behavior is behaved as surface and diffusion mixing control processes,which is between the quasi-capacitance and battery behavior.moreover,the activated carbon(AC)//Ni-Co-F(Ni/Co = 2:1)asymmetric capacitor designed through the charge-balance has delivered superior energy and power densities(18.4 Wh kg-1,6.64 kWkg-1)together with longer cycle life(77%retention after 10,000 cycles at4 Ag-1).2.The perovskite K-Ni-Co-F(Ni:Co = 1:0,8:1,6:1,4:1,3:1,2:1,1:1,1:2,1:3,1:4,1;6,0:1)cubic nanocrystals were synthesized by one-pot solvothermal strategy.The K-Ni-Co-F(Ni:Co = 4:1)materials showed superior specific capacity and rate capability(674.96-543.4 C g-1,1-16 A g-1)than the other K-Ni-Co-F candidates(Ni:Co = 1:0,8:1,6:1,3:1,2:1,1:1,1:2,1:3,1:4,1;6,0:1).The energy storage behavior is mainly based on the diffusion control process,which is close to the battery behavior.Furthermore,the designed(AC)//K-Ni-Co-F(Ni:Co = 4:1)asymmetric capacitor exhibited high energy and power densities(42.7-13.8 Wh kg-1,0.242-18.8 kW kg-1 together with a long cycle life(98%retention/10 000 cycles/4 A g-1).3.A new hybrid hierarchical porous Co(OH)F/Ni(OH)2(Co:Ni = 1:0,3:1,1:1,1:3,0:1)composite materials for supercapacitors were fabricated via one-pot solvothermal method.The Co(OH)F/Ni(OH)2(Co:Ni = 3:1)hybrid showed the more attractive electrochemical performance than the other Co(OH)F/Ni(OH)2 candidates(Co:Ni = 1:0,3:1,1:1,1:3,0:1),exhibiting high specific capacity and rate behavior(104 C g-1 at 1 A g-1)together with excellent cycling stability(116%retention/5000 cycles/6 A g-1).The energy storage behavior is dominated by surface control,showing typical quasi-capacitive behavior.Furthermore,the designed activated carbon(AC)//Co(OH)F/Ni(OH)2(Co:Ni = 3:1)asymmetric capacitor exported both high energy and power densities(13.8-8 Wh kg-1/0.53-4.7 kW kg-1)along with excellent cycle life(121%retention/10,000 cycles/4 A g-1),showing the superior performance than the other AC//Co(OH)F/Ni(OH)2 capacitors(Co:Ni = 1:0,1:1,1:3,0:1).