Li2SiF6 In Situ Embedded in an Amorphous SiO Matrix to Inhibit Volume Expansion during Prelithiation

Direct contact prelithiation is considered an important means of addressing the low Coulombic efficiency of Si-based anodes. However, few studies have been conducted on the inhibition of volume expansion of Si-based materials and the reduction of side reactions during direct contact prelithiation. In this paper, Li2SiF6 crystals are generated in situ in an amorphous SiO matrix by a thermodynamic reaction between SiO and LiPF6, which is from the viewpoint of contact state at the interface between lithium source and negative electrode as well as the construction of mechanical buffer phase. On the one hand, Li2SiF6 crystals can inhibit the volume expansion of SiO during prelithiation. On the other hand, Li2SiF6 crystals act as an interfacial passivation layer to reduce local currents and inhibit the occurrence of side reactions during direct contact prelithiation. The analysis of the results showed that Li2SiF6 crystals were embedded in an amorphous SiO matrix to prepare the SiO/C composite anode, and the strength of the crystals was utilized to inhibit the volume expansion of SiO during the direct contact prelithiation process. Meanwhile, due to its good ionic conductivity, a strong and tough LiF-rich solid electrolyte interphase (SEI) was constructed, which suppressed the volume expansion of the composite anode for the prelithiation process. The full battery assembled with NCM111 positive electrode still exhibits 94.5% capacity retention after 150 cycles at 0.5C current density.