The demand for high-energy lithium ion batteries (LIBs) in portable electronics and automotive applications in particular grows rapidly. Due to the high specific energy of pure silicon (Si) (3579 mAh g 1), intense research has been conducted to implement Si-based anode materials in LIBs. The main challenge of Si anodes is the huge volume expansion upon lithiation and consecutive high irreversible capacities due to continuous formation of solid electrolyte interphase (SEI). In particular, these degradation reactions take place in the first charge/discharge cycles, but also in later cycles on continuously formed fresh surfaces. Approaches to diminish such parasitic side reactions are nano-structuring and embedding Si-particles into a buffering matrix by the synthesis of composites, e.g., Si/SiOx, Si/carbon or Si/SixFey. Pronounced irreversible charge losses at the anode lead to a loss of the so-called “active lithium” and thereby to a rapid capacity loss of Si-based LIB-full cells. To decrease the loss of active lithium and to enable anodes with high Si-contents (≥10 wt.%), pre-lithiation is considered an effective approach.
In this work, electrochemical pre-lithiation without a sacrificial Li metal counter electrode, here defined as ‘electrolytic pre-lithiation’, is investigated. In comparison to the herein investigated electrochemical procedure, pre-lithiation of Si anodes by contact with Li metal or stabilized lithium metal powder (SLMP) feature potential disadvantages. Pre-treatment with pure Li metal foil or powder exhibits severe safety problems due to its high reactivity, whereas the application of SLMP may additionally suffer from cost-inefficiency. As pre-lithiation might take an additional step in the commercial preparation of LIB cells, cost-effectiveness is of great importance. The pre-lithiation via electrolysis of cheap binary lithium salts is therefore appealing for a large scale-application and enables a higher safety during manufacturing.
In this work, the concept of electrolytic pre-lithiation using lithium chloride is fundamentally investigated via electrochemical and spectroscopic techniques. Basic electrochemical properties of the electrolytes used for electrolytic pre-lithiation are evaluated. Pre-lithiation is also validated in cell setups with a sacrificial lithium electrode, and applicability of the concept is shown by performance evaluation in LIB full cells. The impact of the pre-lithiation procedure on the surface (SEI) characteristics of Si-based anodes is systematically analysed by X-ray photoelectron spectroscopy.