Silicon Non-Metal Compounds As New Promising Materials for Lithium Ion Batteries

Abstract

Due to an increasing energy demand caused by an expanding global population and the rapid development of new technologies, a high priority to a further development of new battery systems is given. In fact, there is a great interest in Lithium Ion Batteries as they offer a high energy density and a high rate capability [1]. Owing to a high theoretical capacity silicon is a promising anode material to replace commercially used graphite [2]. The electrochemical energy storage originates from an alloying-dealloying mechanism where different lithium-silicon phases like Li12Si7, Li15Si4 or Li22Si5 were formed [2]. This mechanism conducts capacity fading caused by volume expansion during the insertion and extraction of lithium ions. Therefore, nanostructured silicon is expected to meet future criteria defined for new electrochemical energy storage systems. A new promising way to produce silicon nanoparticles is the application of silicon non-metal compounds and their decomposition through an electrochemical in situ conversion mechanism. In addition, the non-metal serves as a Li-containing matrix that buffers the volume expansion during charging and discharging. Moreover, the synthesis of silicon non-metal compounds via planetary ball mill is environmentally benign and easy scalable. Initial studies show that phase-pure produced silicon diphosphide (SiP2) is electrochemical active over a wide potential range. The first discharge cycle reaches a capacity closely to theory (about 3100 mAh/g). Continuous cycling is stable about 100 cycles. Cyclic voltammetry experiments give an insight into the behavior of the redox properties of materials which is in this case very similar compared to pure silicon. From this observation a similar reaction of silicon diphosphide as known from silicon is indicated. Ex situ XRD results confirm the proposed reaction mechanism and refers to the formation of lithium phosphide which serves as buffering matrix. The production of smaller particles is challenging and the large capacity fading after the first cycle needs to be explained and to be overcome. Both points are taken as prospective tasks. [1] C.-M. Park, J.-H. Kim, H. Kim, H.-J. Sohn: Li-alloy based anode materials for secondary batteries. In: Chem. Soc. Rev. VI. 39, 2010, S. 3115–3141. [2] S. Goriparti, E. Miele, F. De Angelis, E. De Fabrizio, R. P. Zaccaria, C. Capiglia: Review on recent progress of nanostructured anode materials for Li-ion batteries. In: J. Power Sources VI. 257, 2014, S. 421–443.