Vacuum modification of Aluminum and Copper foil
It is known that etched foil is used to increase the adhesion of the Active Electrode of the battery and supercapacitor to the Current Collector. The size of the tunnels formed in aluminum foil depends on many factors, even on the location of the foil during its etching.
The growth behavior of the tunnel in aluminum foil etching in a different position of foil showed that the maximum length of the tunnel samples in ascending order is: face down, vertically, and placement face up.
Chemical etching does not deletion the oxide film from the surface of the aluminum foil. If the relative increase in the area and the increased roughness of the etched foil increase the adhesion of the Active Electrode, then the presence of an oxide film reduces it. Oxide film increases the chemical resistance of aluminum foil and increases the contact resistance between the Current Collector and the Active Electrode. The dimensions of the etched foil tunnels, namely, the ratio of the tunnel depth to its width is greater than ≥1. This means that filling the tunnel is difficult. The active electrode does not completely fill the tunnel volume, leaving a vacant space. Free space will be occupied by air or electrolyte. In either case, this will increase the Internal Resistance of the battery or supercapacitor. In addition, the distance between the tunnels is very large and this reduces the adhesion force.
Results of AFM studies of aluminum foil modified in vacuum
AFM profilogram of etched and modified Al foil
From the disadvantages of chemically etched foil free aluminum foil modified in vacuum. The surface of the modified foil favorably differs from the etched foil. The mechanical strength of the foil with a vacuum modification is much higher than the foil with chemical etching.
A comparison of the AFM profilogram of the etched and modified foil shows that the filling of the tunnels of the modified foil occurs easily and without free space in the tunnels. This reduces the Internal Resistance of the battery.
Modification creates on the surface of the foil a layer of pure aluminum (without impurities), the chemical resistance of which is higher than the chemical resistance of aluminum foil. On the surface of the modified foil sputtered carbon to increase its chemical resistance and adhesion. The carbon coating provides good electrical and thermal conductivity thanks to its versatile bonding structures derived from sp, sp2, sp3.
The roughness of the modified foil reduces the contact resistance between the Current Collector and the Active Electrode of the battery and the supercapacitor. The carbon coating makes it impossible to form an oxide layer on pure aluminum.
The process of vacuum modification of Aluminum and Copper foil – ecological process. No chemical contamination. The process is easy to manage. Vacuum equipment is much simpler and cheaper than equipment for chemical etching of aluminum foil. Create the same foil by chemical etching is impossible.
This is a new big step in creating the better batteries and supercapacitors.
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