Among all the electrode materials used in the vanadium battery,the carbon/graphite felt comprehensive performance is the best,but it still need to do some activation treatment. The commonly used method:heat treatment,acid treatment, electrochemistry treatment etc.
The heat treatment of graphite felt is to put it into the heating equipment, like muffle furnace,to make it oxidation around the surface.
Some scholars have found that if put the un-modified graphite felt into the H2SO4 solution,the surface of the graphite felt is hydrophobic,and it need about 48h to be complete wetting.under 200℃ heating environment,and after that,the wetting time can be reduce to about 30h,and with the heating temperature increasing,the graphite felt is easier to be wetting.
Under the heating temperature at 400℃ in the air environment for 30h,then make the graphite felt used in the vanadium redox flow battery,we could found that,the heating treatment can apparently improve the electrochemistry property of the graphite felt,and can make the energy conversion efficiency of the battery increase from about 70% to 89%.
We could also have a comparation between the modified graphite felt and the un-modifified ones,we could found that the absorption rate of un-modified graphite felt is mearly about 3.2g/g,but the modifified ones,under 400 ℃ environment for 2h,can reach about 10g/g absorption rate.
The reason that heating treatment can improve the graphite felt activation is mainly the heating treatment can improve the directional arrangement of the graphitization,and make the electric resistance come down apparently.
after the experiment and testing,an appropriate condition can make the graphite felt with a minimum electric resistance,make it used in the vanadium battery pack,during the charging and discharging process,the coulomb efficiency can reach more than 90%.
