Si@C as a high specific capacity anode material for lithium
batteries
(LIBs) has attracted a lot of attention. However, the severe volume
change during lithium de-embedding causes repeated rupture/reconstruction
of the solid electrolyte interphase (SEI), resulting in poor cycling
stability of the Si-based battery system and thus hindering its application
in commercial batteries. Using electrolyte additives to form an excellent
SEI is considered to be a cost-effective method to meet this challenge.
Here, the classical film-forming additive vinyl carbonate (VC), and
the newly emerging lithium salt additive lithium difluorophosphate
(LiDFP), are chosen as synergistic additives to improve the electrode–electrolyte
interface properties. Final results show that the VC additive generates
flexible polycarbonate components at the electrode/electrolyte interface,
preventing the fragmentation of Si particles. However, the organic
components show high impedance, inhibiting the fast transport of Li+. This defect can be supplemented from the decomposition substances
of the LiDFP additive. The derived inorganic products, such as LiF
and Li3PO4, can strengthen the reaction kinetics
of the electrode, reduce the interfacial impedance, and promote the
Li+ transport. Thus, the synergistic effect of VC and LiDFP
additives builds an effective SEI with good flexibility and high ionic
conductivity and then significantly improves the cycling and rate
stability of Si@C anodes. The experimental results show that the utilization
of LiDFP and VC additives to modify the Si@C anode interface enhances
the capacity retention of the Si@C/Li half-cell after 100 cycles from
68.2% to 85.1%. Besides, the possible mechanism of action between
VC and LiDFP is proposed by using the spectral characterization technique
and density functional theory (DFT) calculations. This research opens
up a new possibility for improvement of SEI, and provides a simple
way to achieve high-performance Si-based LIBs.