Fig. 1. Binding strategies of silicon with electrically conductive media.

a Point-mode physical binding of Si with a conventional conductive medium (e.g., carbon black). The large volume change causes pulverization of Si obstructing the contact and induces side reactions, as well as SEI propagation further deteriorating the contact. The ineffective binding or unbinding of Si results in poor cycling stability. b Downsizing of Si. Although resistant to mechanical fracture, the point-mode physical contact is similarly prone to become ineffective, hindering improvement in cycling and rate capability. c Tailoring of the adjacent conductive medium. With the Si/C combination to accommodate the volume change of Si, the cycling stability is improved; yet, this is at the expense of rate capability because the easily weakened point-mode physical binding is still adopted in most cases. d Manipulation of the binding between Si and the adjacent conductive medium. As the point mode of covalent binding is inefficient and unfavorable for the rate capability, the existing covalent binding still encounters risks of being disrupted due to the direct contact and propagating erosion of Si with the electrolyte. e Designing two-dimensional covalent binding for Si. This skin-like binding creates and more importantly, secures a robust and efficient contact between Si and C components, granting stable and fast electron/ion transport from/to the Si upon cycling. It is noteworthy that Li⁺ is defined as lithium ions.