Identification of LiPF₆Decomposition Products in Li‐Ion Batteries with Endogenous Vanadyl Sensors Using Pulse Electron Paramagnetic Resonance and Density Functional Theory

Abstract

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/aesr.202100121.

Exploring the Solvation Sphere and Spatial Accumulation of Dissolved Transition-Metal Ions in Batteries: A Case Study of Vanadyl Ions Released from V2O5Cathodes

“…Depending on their chemical identity, their contribution can be combined additively. Thereby, the electron donor capacity of the ligand correlates inversely with the A z ( 51 V) contribution because the spin density is delocalized more for strongly donating ligands, as discussed recently …”

“…The cathode film under investigation contains 80 wt % V 2 O 5 (Sigma-Aldrich, 99.95%), 10 wt % carbon black (Alfa Aesar), and 10 wt % poly(vinylidene fluoride) (PVDF, Alfa Aesar) and was prepared as described previously. 16 For electrochemical treatment, Swagelok-type cells were used with metallic lithium (Sigma-Aldrich, 99.9%, 0.38 mm thickness) as a counter and reference electrode and a glass fiber separator (VWR). Additional Celgard 3401 separator was used on either side of the glass fiber separator to avoid sticking and cross-contamination during disassembly.…”

“…Recently, pulse electron paramagnetic resonance (EPR) techniques were introduced for the investigation of battery materials. ,, Hyperfine spectroscopies, which can resolve weak electron–nuclear interactions, are particularly suited to analyze the coordination sphere and identify ligands of a paramagnetic species . For ligand determination, the complementary techniques electron nuclear double resonance (ENDOR) and electron spin echo envelope modulation (ESEEM) techniques can be used .…”

“…For ligand determination, the complementary techniques electron nuclear double resonance (ENDOR) and electron spin echo envelope modulation (ESEEM) techniques can be used . A complete analysis often necessitates accurate prediction of hyperfine coupling constants, a task that can be accomplished with density functional theory (DFT), as discussed in our recent work …”

“…18 A complete analysis often necessitates accurate prediction of hyperfine coupling constants, a task that can be accomplished with density functional theory (DFT), as discussed in our recent work. 16 In principle, all transition-metal ions relevant for current battery chemistries, including cobalt, nickel, manganese, iron, and vanadium, possess paramagnetic electron configurations, a prerequisite for EPR experiments. However, their differing spin multiplicity and d-orbital occupation affect crucial experimental parameters such as electron spin relaxation times, rendering some of them experimentally more accessible than others.…”