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Electrolyte additives are indispensable to enhance the performance of Li-ion batteries. Lithium bis(oxalato)borate (LiBOB) has been explored for many years, as it improves both cathode and anode performance. No consensus regarding its reaction mechanisms has, however, been established. A model operando study combining attenuated total reflection infrared spectroscopy (ATR-FTIR), electrochemical quartz crystal microbalance (EQCM), and online electrochemical mass spectrometry (OEMS) is herein presented to elucidate LiBOB reduction and electrode/electrolyte interphases thus formed. Reduction of the BOB^– ion sets in at ∼1.8 V with solid lithium oxalate and soluble oxalatoborates as the main products. The reduced BOB^– ion also reacts with itself and its environment to evolve CO₂, which in turn impacts the interphase formed on the negative electrode. This study provides further insights into the reduction pathways of LiBOB and how they contribute to the interphase formation.

Introducing small volumes of organosilicon-containing additives as part of lithium-ion battery (LIB) electrolyte engineering has been getting a lot of attention owing to these additives’ multifunctional properties. Tris(trimethylsilyl)phosphate (TMSPa) is a prominent member of this class of additives and scavenges Lewis bases such as water, although the rate at which the reaction occurs and the fate of the resultant product in the battery system still remain unknown. Herein, we have employed complementary nuclear magnetic resonance and gas chromatography–mass spectrometry to systematically study the reactivity of TMSPa with water in conventional organic carbonate solvents mimicking the Li-ion cell environment. The reaction products are identified, and a working reaction pathway is proposed by following the chemical evolution of the products over varying time and temperatures. We found that the main reaction products are trimethylsilanol (TMSOH) and phosphoric acid (H3PO4); however, various P–O–Si-containing intermediates were also found. Similar to water, the Lewis base TMSOH can undergo reaction with TMSPa at room temperature to form hexamethyldisiloxane and can also activate ethylene carbonate (EC) ring-opening reactions at elevated temperatures (≥80 °C), yielding a TMS derivative with ethylene glycol (TMS-EG). While the formation of TMS-EG at the expense of EC is in principle an unwanted parasitic reaction, it should be noted that this reaction is only activated at elevated temperatures in comparison to EC ring-opening by H2O, which takes place at ≥40 °C. Thus, the study underlines the advantages of organo-silicon compounds as electrolyte additives. Elucidating the reaction mechanism in model systems like this is important for future studies of similar additives in order to improve the accuracy of additive exploration in LIBs.

Layered TiS₂ has been proposed as a versatile host material for various battery chemistries. Nevertheless, its compatibility with aqueous electrolytes has not been thoroughly understood. Herein, we report on a reversible hydration process to account for the electrochemical activity and structural evolution of TiS₂ in a relatively dilute electrolyte for sustainable aqueous Li-ion batteries. Solvated water molecules intercalate in TiS₂ layers together with Li⁺ cations, forming a hydrated phase with a nominal formula unit of Li_0.38(H₂O)_2−δTiS₂ as the end-product. We unambiguously confirm the presence of two layers of intercalated water by complementary electrochemical cycling, operando structural characterization, and computational simulation. Such a process is fast and reversible, delivering 60 mAh g^–1 discharge capacity at a current density of 1250 mA g^–1. Our work provides further design principles for high-rate aqueous Li-ion batteries based on reversible water cointercalation.