**7. Conclusions and outlook**

A huge potential for the production of new materials and control their structure lies in the cold plasma. This technology allows us to produce materials in the form of thin films or nanoparticles, with uniform or gradient construction, and with amorphous or nanocrystalline structure, which can be deposited on substrates of any shape. We can also obtain complex composites in this way. A special place among these composites is occupied by 3D systems. The plasma deposited materials may have very high or very low conductivity (both electronic and ionic), may have very high or very low permeability for a given substance and, in the end, may have surprising catalytic and photocatalytic properties. Without a doubt, the cold plasma technology has strongly consolidated its position in the fabrication of thin-film solar cells. Increasingly, however, it is also employed to produce materials for the components of fuel cells and Li-ion batteries, such as electrodes and solid electrolytes. Many times, these elements showed better properties than those prepared by conventional methods. One can expect that in the near future it will be possible to produce efficient and effective anode–(solid electrolyte)–cathode systems in one continuous process consisting of consecutive acts of plasma deposition. Such a construction will eliminate the problem, inter alia, of ensuring proper contact between the electrodes and solid electrolyte. The plasma technology also opens up prospects for the spectacular solutions, such as microbatteries with high aspect ratio electrodes or asymmetrical supercapacitors. It seems also feasible to produce miniaturized 3D cells in which electrodes are formed from carbon nanotubes decorated with nanoparticles of catalytic material (all fabricated by plasma processes), and covered with a plasma-polymer electrolyte. Indeed, the prospects are very promising.

Another issue, which is only briefly mentioned in this Chapter, is the use of cold plasma for surface modification of conventional materials. We can thus improve the properties of "conventional" elements relevant to the construction of electrochemical cells: electrode substrates, electrodes themselves, separators, etc. Research interest in this field of the cold plasma technology is comparable to that which is focused on entirely new materials produced by plasma deposition techniques. The use of the plasma treatment technique in electrochemical cell engineering is a problem, however, so vast that a separate chapter should be devoted to it.
