## 1 Introduction  
Over the years several methods for the production of sulfur nanoparticles (SNp) have been developed [1; 2; 3; 4]; among these, the method of the microemulsion is one of the most important due to its flexibility and the excellent control over the size of the particles [5]. These methods use the same chemical reaction between sodium thiosulfate Na\({}_{2}\)S\({}_{2}\)O\({}_{3}\) and hydrochloric acid HCl, but in different fluid dynamic conditions. In general, the preparation of colloidal sulfur (CS) has many advantages [1; 2; 3; 4; 5; 6] such as:  
* The synthesis takes place at room temperature in a single step. * The process is scalable and uses cheap, non-toxic and easily available materials. * The particles obtained are compatible with the traditional techniques to produce lithium batteries and enables the use of electrolytes, binder and conductive materials used in industry today. The concentration of the reactants seems to be one of the most important aspects to control the final size of the particles [5; 7; 8; 9]. In particular, the concentrated solutions of Na\({}_{2}\)S\({}_{2}\)O\({}_{3}\), under normal stirring conditions, cause excessive growth of the particles. On the other hand, excessively dilute solutions do not allow acceptable yields to be obtained and make the successive separation step of the material difficult. Then, the limits of such a procedure are represented by a poor yield (mass of sulfur in volume of solution) and the difficulty of producing nanometer-size particles. In order to obtain particles under submicron size, particularly dilute solutions have to be used to avoid agglomeration. [PERSON] et al. [5; 9] have shown that it is possible to get SNp with an average diameter of about 200 nm by using 5 mm aqueous solution of Na\({}_{2}\)S\({}_{2}\)O\({}_{3}\) and a stoichiometric amount of HCl. However, using different fluid dynamic conditions it is possible to synthesize monodisperse SNp through the spinning disk reactor (SDR) (or rotating disk reactor) technique. The SDR [10; 11] consists of a rotary disc placed horizontally and confined in a cylindrical housing. The reagents, introduced at or near the center of the disc are quickly pushed outward by centrifugal force. In this way, a thin liquid film is formed on the surface of the disk, exhibiting high micro-mixing conditions at reduced residence time. In these conditions, the reaction takes place at the nanoscale and the final solution is collected at the basin of the reactor. Then, the use of the SDR presents a series of advantages which can be summarized as follows:  
* The conditions of micro-mixing can be obtained within the liquid film over the disc surface by using a low amount of energy. * The reduced residence time and the high local supersaturation values limits the growth after the nucleation allowing the production of nanometric size particles. * The use of concentrated solutions allows high yields to be obtained. In addition to this, the synthesis via SDR is a continuous production process that can be easily scaled up for industrial applications. * The particle size distribution of the product may be controlled by means of the operating parameters such as flow rate of the reactants, rotating velocity of the disc and position of the reactant injectors over the disc surface [10; 11]. Therefore, in particular, in this work we want to emphasize that by using the SDR technique under different fluid dynamics conditions, it is possible to obtain monodisperse and nanometric size sulfur particles having higher electrochemical performance as active material in lithium-ion batteries with respect to sulfur particles obtained by colloidal solution. Another fundamental aspect to take into account is the capacity loss for Li-S cell due to the diffusion of polysulfides in solution. The lithium polysulfides (LiS\({}_{\mathrm{x}}\) x = 4; 6; 8) are extremely soluble in traditional electrolytes and their formation, during cycling, causes strong morphological and compositional changes inside the cathode.