Development of Process to Make Silicon Active Material From Halloysite Clay

Abstract

For many years, the potential benefit of using silicon as the active material in anodes has been recognized. The theoretical capacity of silicon is about 10 times that of graphite. The challenge lies in that silicon experiences massive changes in volumes during cycling, on the order of 300%. Such expansion and contraction produce structural deformation that leads to capacity fade [1]. Various methods have been developed to produce nano-structured silicon for anode use, however, the processes tend to be expensive [2].Halloysite is a clay mineral that forms a tubular/cylindrical structure that has shown some promise as a low-cost silicon source for batteries [3]. We use halloysite that is mined locally in Utah, USA to produce silicon. Initial batches of halloysite-derived silicon demonstrated 1800 mAh/g capacity after formation cycles.Often silicon is produced through magnesiothermic, or aluminothermic, reduction of silica. We report on a variation of the process that operates at lower temperatures, does not require HF acid, and allows for recycling of non-reactive species. We will present our progress toward lower-cost and safer production methods and results on potential benefits of impurities in the silicon. Impurities may provide the necessary stability silicon needs for cyclability. Figure 1. BYU-developed process to produce Si powder from AMI’s halloysite for incorporation into high-performance anode films at low cost. References Canham, L., Porous Silicon Formation by Porous Silica Reduction, in Handbook of Porous Silicon, L. Canham, Editor. 2014, Springer International Publishing: Cham. p. 85-92.Hieu, N.S., J.C. Lim, and J.K. Lee, Free-standing silicon nanorods on copper foil as anode for lithium-ion batteries. Microelectronic Engineering, 2012. 89: p. 138-140.Zhou, X., et al., Synthesis of nano-sized silicon from natural halloysite clay and its high performance as anode for lithium-ion batteries. Journal of Power Sources, 2016. 324: p. 33-40. Figure 1