A two layer silicon/graphite anode for higher energy density Li-ion cells

Silicon is a promising anode material for Lithium-ion batteries (LiBs), offering much higher storage capacity than graphite. However, the main challenge of the usage of silicon, as an anode material in LiBs, is mainly linked to its property of huge volume change during cycling, which leads to internal tension that can deteriorate the silicon network by crack formation. As a result, the performance of the cell would drop radically after a couple of cycles. As the mass loading of pure silicon plays a key role to the cycle life of the anode electrode, thinner silicon anodes (with lower mass loading) tend to provide more cycles, since the mechanical stress is limited, and, consequently, the related cracking and material pulverization becomes less pronounced.

In this work, we propose a new type of anode in a bilayer hybrid configuration, comprised of a thin layer of silicon, which is DC-sputtered on top of the current collector, and an additional mass loading from a graphite slurry, which is coated on top of silicon. In this way, by combining two types of active materials, i.e., pure silicon and graphite, the overall gravimetric specific capacity is increased (compared to a bare graphite anode) and the cycling stability is improved (compared to a bare silicon anode). The optimization of the thickness of both layers (mass loading ratio) and the interface between them have been investigated, since a main trade-off between cycling stability and specific capacity is observed.