Surface and Bulk Stabilization of Silicon Anodes with Mixed-Multivalent Additives: Ca(TFSI)₂ and Mg(TFSI)₂

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Silicon anodes offer higher capacity than graphite for next-generation lithium-ion batteries.
• Silicon anodes suffer from poor calendar life due to reactive silicon anions forming unstable solid electrolyte interphase (SEI) layers.
• Unstable SEI layers lead to undesirable side reactions with electrolyte components.

Purpose of the Study:

• To investigate the use of mixed calcium (Ca) and magnesium (Mg) multivalent cations as electrolyte additives for silicon anodes.
• To improve the calendar life of silicon anodes by mitigating reactivity and stabilizing the SEI layer.
• To understand the effect of these mixed salts on the bulk and surface properties of silicon anodes.

Main Methods:

• Utilized a mixture of Ca and Mg multivalent cations as an electrolyte additive for silicon anodes.
• Employed multiple structural characterization techniques to study the effects on anode bulk and surface.
• Conducted coin cell tests to evaluate calendar life performance and side reactions.

Main Results:

• Ca and Mg ions formed thermodynamically stable quaternary Li-Ca-Mg-Si Zintl phases in situ.
• A more stable and denser SEI layer formed on silicon particles, protecting them from side reactions.
• Full cells with mixed cation electrolytes showed enhanced calendar life, lower measured current, and reduced current leakage compared to baseline.

Conclusions:

• Mixed Ca and Mg cations effectively stabilize silicon anodes by forming stable Zintl phases and a robust SEI layer.
• The improved SEI layer reduces side reactions, leading to enhanced calendar life and battery performance.
• Structural analysis confirmed reduced electrode cracking and enhanced cation migration with mixed cation additives.