NMR spectroscopy of coin cell batteries with metal casings.

Abstract

Battery cells with metal casings are commonly considered incompatible with nuclear magnetic resonance (NMR) spectroscopy because the oscillating radio-frequency magnetic fields (“rf fields”) responsible for excitation and detection of NMR active nuclei do not penetrate metals. Here, we show that rf fields can still efficiently penetrate nonmetallic layers of coin cells with metal casings provided “<b>B</b>₁ damming” configurations are avoided. With this understanding, we demonstrate noninvasive high-field in situ ⁷Li and ¹⁹F NMR of coin cells with metal casings using a traditional external NMR coil. This includes the first NMR measurements of an unmodified commercial off-the-shelf rechargeable battery in operando, from which we detect, resolve, and separate ⁷Li NMR signals from elemental Li, anodic β-LiAl, and cathodic Li<i>_x</i>MnO₂ compounds. Real-time changes of β-LiAl lithium diffusion rates and variable β-LiAl ⁷Li NMR Knight shifts are observed and tied to electrochemically driven changes of the β-LiAl defect structure.