Quantification of PF₅ and POF₃ from Side Reactions of LiPF₆ in Li-Ion Batteries

Abstract

The electrochemical oxidation of LiPF 6-based electrolytes is reported to generate POF 3 gas. In order to enable a quantitative analysis of the LiPF 6 decomposition reactions, we aimed to establish calibration factors for POF 3 and PF 5 in on-line electrochemical mass spectrometry (OEMS). Thermal decomposition of dry LiPF 6 is expected to yield PF 5 , but instead all PF 5 is detected as POF 3 in our OEMS setup, rendering a differentiation of the two gases impossible and presenting an artefact which likely occurs with most on-line mass spectrometry systems due to the high reactivity of PF 5. However, we can still determine a cumulative calibration factor for POF 3 + PF 5 (referred to as "POF 3 "), which is then used to investigate the evolution of gases during the oxidation of an EC/LiPF 6 electrolyte on a carbon black electrode. Mechanistic experiments with protons or water added to EC/LiPF 6 electrolyte show that protons trigger the formation of PF 5 , while the kinetics for the hydrolysis of LiPF 6 with water at room temperature are too slow to be detectable. These findings let us conclude that the oxidation of EC generates highly acidic species, which cause the decomposition of PF 6 − to PF 5 and HF; the PF 5 is then detected as POF 3 in the OEMS.

Decoupling Interfacial Reactions at Anode and Cathode by Combining Online Electrochemical Mass Spectroscopy with Anode‐Free Li‐Metal Battery

“…[ 21 ] also figure out the mechanism of EC reduction which provides the CO 2 and CO gaseous products. This is because, due to its higher electron affinity nature than linear carbonates (DEC and EMC), EC solvent undergoes electrochemical reduction reaction for SEI formation [ 22,23 ] , suggesting that the evolution of gases in batteries with in EC based electrolytes preferentially associated with EC decomposition. Scheme shows the possible electrochemical interfacial reduction pathways of EC solvent on the anode surface, mainly responsible for the evolution of CO 2 , CO and C 2 H 4 reductive gases at the Cu current collector.…”

Effects of Film Formation on the Electrodeposition of Lithium

“…22,24 The electrolyte with 1000 ppm water exhibited a more dramatic decrease in water content than that with 100 ppm water (Figure S1). Previous studies have proposed a series of several decomposition reactions for LiPF 6 as follows [Reactions (1)‐(3)]: [25–29] …”

Degradation and Aging Routes of Ni-Rich Cathode Based Li-Ion Batteries

“…They both lead to the formation of low valence transition metal oxides assisted by the loss of oxygen, leading to cations whose salts are more soluble in liquid electrolytes than those composed of high valence transition metal ions are. The oxygen assisted solvent decomposition [(e.g., C 3 H 4 O 3 (EC) + [O] →CO 2 + CO + 2H 2 O)] results in the formation of H 2 O, which, in turn, hydrolyzes the salt (LiPF 6 ↔ LiF + PF 5 ) in the electrolyte solution with the formation of HF (LiPF 6 + H 2 O → POF 3 + 2HF + LiF; POF 3 + H 2 O → HF + HPO 2 F 2 ) [102]. This, in turn, attacks the metal oxide, which results in the formation of slightly more soluble MF 2 salts and H 2 O.…”