Khashayar Bagheri1,2,Vincent Sarou-Kanian1,2,Michael Deschamps1,2,Elodie Salager1,2
CNRS, CEMHTI UPR3079, Université d’Orléans1,Réseau sur le Stockage Electrochimique de l’Energie (RS2E), FR CNRS 34592
Khashayar Bagheri1,2,Vincent Sarou-Kanian1,2,Michael Deschamps1,2,Elodie Salager1,2
CNRS, CEMHTI UPR3079, Université d’Orléans1,Réseau sur le Stockage Electrochimique de l’Energie (RS2E), FR CNRS 34592
<br/>Electrochemical energy storage devices, such as Li-ion or Na-ion batteries, supercapacitors, or hybrid capacitors, are essential for the energy transition. The entire device characterization (<i>In situ</i>) is one of the key elements to obtaining a global understanding of the charge and degradation processes. Nuclear Magnetic Resonance (NMR) spectroscopy is one of the techniques of choice thanks to its ability to detect, non-destructively and with atomic selectivity, the liquid, semi-liquid, crystalline, and amorphous contents of the sample.<br/><br/>Operando NMR spectroscopy of Li-ion batteries is challenging due to the strong heterogeneity of the battery, which results in broadening and distortions of the NMR spectrum. Up to now, most Operando NMR studies used <sup>7</sup>Li NMR spectroscopy to follow lithiation and degradation processes of electrodes displaying highly shifted peaks (lithiation of graphite and silicon, lithium plating). Although the liquid electrolyte located inside the battery provides a narrower and stronger In situ NMR signal, it has not been fully exploited until now.<br/><br/>We will present our efforts to use the liquid <sup>1</sup>H NMR signal of the electrolyte solvent (ether carbonates) to “spy” on the electrodes while benefitting from the higher sensitivity of <sup>1</sup>H NMR compared to <sup>7</sup>Li NMR. Contrary to lithium atoms, hydrogen atoms in the electrolyte solvent are not a direct probe of the state of charge of the electrode. The <sup>1</sup>H NMR spectrum of the electrolyte is however highly sensitive to heterogeneities and interfaces in the battery, especially at the interface with the electrodes.<br/><br/>We demonstrate that the strongly distorted <sup>1</sup>H NMR spectrum of dimethyl carbonate (DMC) in the battery can be used to track the state of charge of the electrodes. A careful analysis of the effect of battery components such as current collectors, separators, and electrodes with various states of charge will be presented. It provides a framework and descriptors for characterizing the distortion of the electrolyte <sup>1</sup>H NMR spectrum arising from the electrodes, with the goal to apply this technique for fast Operando NMR characterization of operating batteries.