(566b) Overcoming Micro-Silicon Particle Fracture within Graphene Cages for Stable Battery Anodes

Silicon (Si) has over ten times the theoretical charge capacity of commercial graphite anodes, making it a promising material for enabling next-generation lithium-ion batteries. Nanostructuring has been shown to be fruitful in addressing the problems caused by large Si volume changes (~300%) during battery operation, including particle fracture, loss of electrical contact, and an unstable moving interface. However, nanoscale materials introduce new issues of higher cost and increased surface area for parasitic side reactions, resulting in poor Coulombic efficiencies and challenges for scaling up. Microscale Si powders are low-cost alternatives but, unlike Si nanoparticles, will inevitably fracture and lose electrical contact during charge/discharge. Thus, stable cycling of Si microparticles (SiMP) in batteries have been widely considered to be impossible.

In this work, we develop a method to encapsulate SiMP (diameter ~1-3 μm) within conformally synthesized cages of multilayered graphene [1]. Despite volume expansion and particle fracture, the Si powders remain electrically connected on both the particle and electrode level by the mechanically robust and electrically conductive graphene cage. Furthermore, the chemically inert graphene cage forms a stable interface with the electrolyte. This minimizes irreversible consumption of lithium ions and increases the first-cycle Coulombic efficiency to as high as 93%, approaching the value of commercial graphite (~95%). With these advantages provided by the graphene cage, we demonstrate that even in a full-cell electrochemical test with a finite source of lithium ions, stable cycling (100 cycles; 90% capacity retention) is achieved for the previously nonfunctional microscale Si, bringing Si-based battery anodes one step closer to reality.

[1] Y. Li*, K. Yan*, H.-W. Lee, Z. Lu, N. Liu, Y. Cui. “Growth of conformal graphene cages on micrometre-sized silicon particles as stable battery anodes,” Nature Energy 1 (2016): 15029.

*Denotes equal contribution