A possible alternative could be represented by the use of sodium instead of lithium in rechargeable batteries, both for its low cost and for its good environmental sustainability . The use of sodium in batteries is only at its early stage, this mainly due to the impossibility of using graphite as active material, as instead happens for Li batteries. This is due to the bigger dimensions of sodium ions compared to lithium ones, with the consequent need for new broader and more open structures, like “hard carbons”, to intercalate the ions . This innovative materials are chiefly obtained as products of pyrolysis and carbonization of synthetic polymers or of organic substances like glucose and saccharose. Recent studies have highlighted that the introduction of nitrogen, phosphorous and magnesium in the organic precursor can lead to carbonaceous materials with an enhanced electrochemical activity when used for electrodes of both Li- and Na-batteries .
The use of algal biomasses as precursors of these carbonaceous materials has been considered in the perspective of a reduction of the environmental impact in batteries production. Algae have different advantages over other biomasses, namely high productivity, no competition with agriculture and the possible recycle, in some cases, of environmentally harmful algal blooms.
This work is therefore focused on the study and application of algal biomasses as alternative materials to the fossil fuel-derived or synthetic ones for the production of non-graphitic open structures (hard carbons) as active materials for Na-ion batteries electrodes. Both commercially available dried algae and algae grown in laboratory controlled conditions are considered. These algae are dried and then decomposed in tubular furnaces under inert nitrogen atmosphere at temperatures comprised between 700 and 1000°C. During the decomposition two different phases are distinguished, the first one, below 500°C, with the decomposition of the organic fraction to give the so-called “biochar”. The formation of hard carbon structures occurs instead above 700°C. The decomposition is monitored with TG analysis, both in inert atmosphere and in air. The products, before and after decomposition, are characterized with optical and SEM microscopes and with XRD analysis.
This organic hard carbon is mixed with carbon black, to enhance the conductivity, and with PVDF as binder, previously dissolved in NMP as organic solvent. The obtained slurry is coated on a copper foil used as current collector. The half coin cell, with metallic sodium as counter electrode and sodium perchlorate in a mixture of ethylene carbonate and diethyl carbonate as electrolyte, is finally assembled. Different cyclic discharge/charge profiles between 2.5 and 0V are performed and the electrochemical performances of the cell analyzed. The performances of these cells are compared to those of identically assembled cells, with the only difference in the use of synthetic hard carbon instead of algae derived ones.
 Noorden, R.V.; “A Better Battery”, Nature, 2014, 507, 26-28.
 Irisarri,E.; Ponrouch, A.; Palacin,M.R.; “Review-Hard Carbon Negative Electrode Materials for Sodium-Ion Batteries”, J.Electroch.Soc., 2015, 162(14), A2476-A2482
 Unur, E.; Brutti, S.; Panero,S.; Scrosati, B.; “Nanoporous Carbon from Hydrothermally Treated Biomassa s Anode Materials for Lithium-Ion Batteries”, Microppor. Mesopor. Mater., 2013, 174, 25-33.