Toward a Metallic Silicon Anode for Practical Lithium-Ion Battery Applications

Abstract

The current state-of-the-art batteries comprising graphite-based anodes are facing its performance limit for the use in automotive applications, thus urging to develop electroactive materials with high capacity and low operating potentials [1]. Si has shown great promise as a next-generation anode, meeting the above requirements in natural abundance. However, unavoidable large volume change upon lithium insertion/extraction causes particle fracture and disintegration of the electrode, resulting in fast degradation of battery along with poor electric conductivity being the main hurdle for fast-chargeable battery design [2]. Recently, interesting breakthroughs have been proposed principally in nanostructuring of Si, composite formation with conductive carbons and mechanically stable binders, which achieved long-term cycle stability and rate capability [3]. Yet, these approaches lead to lowering the electrode density, initial Coulombic efficiency and energy density of battery and thus utilizing the Si microparticles can be rather feasible toward a practical system while stress-driven particle degradation becomes more serious. The existing technologies have focused on coalescing the fractured particles, not preventing itself, and have not considered ionic diffusion of Li-ion across the microparticles as well as the electronic conduction. Herein, we propose the material design concept of Si microparticles by integrating the chalcogen component into the bulk structure through a low temperature doping strategy. The low electric conductivity of intrinsic Si (~10-4 S m-1) with a near-insulator property undergoes a transition into the metallic state via this new method unlike other dopants of boron or phosphorous that only gives extra charge carriers without insulator-to-metal transition. In addition to electronic conduction, the chalcogen chains restrict the saturation of Si dangling bonding during recrystallization process of low temperature doping and create the internal channels inside the crystalline Si lattice. The incorporation of Li-ion channels further increases Li-ion diffusivity without any barriers in case of undoped Si microparticles due to the interfaces of lithium silicide and amorphous Si. Interestingly, chalcogen chains can sustain its internal structure with high flexibility and robustness which is directly corroborated by microscopy analysis, and lithium-induced intermediate can maintain the metallic nature at the interfaces that enhance the Li-ion diffusion over the cycles. Further, the porous but minimized surface area of Si structures increases the initial reversibility, extends the cycle life of battery up to hundreds of cycles with a high structural stability and facilitates fast-charging ability. [1] A. S. Arico, P. Bruce, B. Scrosati, J. M. Tarascon, W. Van Schalkwijk, Nat. Mater. 2005, 4, 366. [2] H. Wu, Y. Cui, Nano Today 2012, 7, 414. [3] J. Ryu, T. Chen, T. Bok, G. Song, J. Ma, C. Hwang, L. Luo, H.-K. Song, J. Cho, C. Wang, S. Zhang, S. Park, Nat. Commun. 2018, 9, 2924