Understanding the Effect of Lithium Nitrate as Additive in Carbonate-Based Electrolytes for Silicon Anodes

Due to its high specific capacity, silicon is one of the most promising anode materials for next-generation lithium-ion batteries. However, its large volumetric changes upon (de)lithiation of ∼300% lead to a rupture/re-formation of the solid-electrolyte interphase (SEI) upon cycling, resulting in continuous electrolyte consumption and irreversible loss of lithium. Therefore, it is crucial to use electrolyte systems that form a more stable SEI that can withstand large volume changes. Here, we investigate lithium nitrate (LiNO₃) and lithium nitrite (LiNO₂) as electrolyte additives. Linear scan voltammetry on carbon black working electrodes in a half-cell configuration with LiNO₃-containing 1 M LiPF₆ in EC/DEC (1/2 v/v) revealed a two-step reduction mechanism, whereby the first reduction peak could be attributed to the conversion of LiNO₃ to LiNO₂, while X-ray photoelectron spectroscopy on harvested electrodes suggests the formation of Li₃N during the second reduction peak. On-line electrochemical mass spectrometry (OEMS) on carbon black electrodes showed that N₂O gas is evolved upon the reduction of LiNO₃- and LiNO₂-containing electrolytes but that the gassing associated with EC reduction is significantly reduced. Furthermore, OEMS and voltammetry were used to examine the redox chemistry of LiNO₂ additive. Finally, LiNO₃ and LiNO₂ additives significantly improved the cycle-life of Si||NCM622 full-cells.