Silicon is mainly produced by carbothermic reduction of silica. This process generates a by-product called silicon slag, which consists mainly of a mixture of Si, SiC and C. This silicon slag represents considerable energy and material losses. On the other hand, the production of cheaper and more environmentally friendly electrode materials is essential for Li-ion battery manufacturers.

In this study, it is demonstrated that this waste containing 65 wt% Si, 31 wt% SiC and 4 wt% C can be valorized as low-cost high-capacity LiB anode material. After 20 h of high-energy ball-milling, C is fully converted to SiC and a micrometric powder is obtained in which submicrometric SiC inclusions are embedded in a nanocrystalline/amorphous Si matrix (Fig. 1a). This material displays a specific discharge capacity ≥1100 mAh g^-1 at a current density ≤ 0.9 A g^-1 (Fig. 1b) and an areal capacity ≥3.5 mAh cm^-2 for at least 100 cycles (Fig. 1c). Moreover, calendering has no negative impact on the electrode performance (Fig 1d). The dQ/dV curves (Fig. 1e) do not shown intense-sharp anodic peak at about 0.45V characteristic of the delithiation of the c-Li₁₅Si₄ phase, suggesting that its formation is here prevented. This may be beneficial for the electrode cycle life as the formation of c-Li₁₅Si₄ phase is well-known to accentuate the particle cracking. However, a progressive and irreversible increase of the electrode mass and thickness is observed over cycling (reaching 125% and 60% after 200 cycles, respectively) (Fig. 1f), which is mainly attributed to the accumulation of solid electrolyte interphase (SEI) products in the electrode.