Pre-lithiation, a method of doping Si-based anode with lithium prior to being assembled into a battery cell, has been regarded as one of the most feasible ways to compensate for the amount of active lithium loss during the initial few cycles. From this point of view, a lot of precedent research has successfully verified the effectiveness of pre-inserted lithium in diverse ways. Nevertheless, the majority of them focused more on increasing coulombic efficiency and specific capacity of initial cycles, meaning that the need for advanced cyclability still exists. Building a robust solid electrolyte interphase (SEI) with a slower C-rate during pre-lithiation will be one of the efficient ways to have long-lasting enhancement. However, from long-term capacity retention and industrialization perspectives, it was challenging to satisfy both criteria without a compromise.

The typical pre-lithiation process consists of several steps: lithiating, rinsing, and drying. Among them, rinsing is implemented for washing the remaining lithium salt away before the lithiated anode is transplanted into a full cell. In this study, we tried to utilize this rinsing process in another way, which was to form a more stable SEI by introducing specific additives. Four different additives were used and their effectiveness was calculated respectively depending on whether it is used in the pre-lithiating or rinsing solution.

As a result, it was proven that a small amount of but appropriately designed additives during pre-lithiation could positively influence the long-term cycling properties. In addition, some additives were especially beneficial when used in the rinsing solution, while the other additives showed a better result when mixed with the pre-lithiating solution, implying the possibility of considering the rinsing step as an additional reaction providing place. By applying the additives separately according to their properties rather than simultaneously, we could shorten the entire process time and reduce capacity degradation, attributing to the optimized configuration of SEI. In this regard, this study suggested the importance and possibility of systematic SEI formation through controlling the timing of the use of additives during pre-lithiation.