Microscopic Behavior of Active Materials Inside a TCNQ-Based Lithium-Ion Rechargeable Battery by in Situ 2D ESR Measurements

Abstract

Real-time spectroscopic measurements in rechargeable batteries are important to understand the electrochemistry of the batteries at the molecular level and improve relevant functionalities. We have applied in situ two-dimensional (2D) electron spin resonance (ESR) spectroscopy to a well-known organic lithium-ion battery, which is composed of 7,7,8,8tetracyanoquinodimethane (TCNQ) as the cathode-active material and a lithium metal anode electrode. The TCNQ rechargeable battery is suitable for investigating electrochemistry in the battery in terms of behavior of electron spin at microscopic levels on both the cathode and anode electrodes. We have discussed two-stage oxidation/reduction reactions of TCNQ, Li deposited/stripped process and their resulting dendritic and/or mossy microstructures, clearly elucidating the cause of the cell capacity degradation upon the charge−discharge cycles. The observed in situ ESR spectra showed that the degradation of the cell capacity was due to the elution of the active molecules, which caused the increase of ion conductivity by the substitution of the electrolyte solution for the adsorbed active materials on the conductive carbon surface. To discriminate paramagnetic species during the charge−discharge process, the generalized 2D correlation spectroscopy has been applied to characterize time-dependent in situ ESR spectra. The correlation analysis with in situ ESR helps us identify the paramagnetic species occurring in the battery cell in a straightforward manner.

Spins at work: probing charging and discharging of organic radical batteries by electron paramagnetic resonance spectroscopy

“…There is increasing interest in both ex situ and in situ spectroelectrochemical (SEC) EPR measurements in research fields ranging from biology to materials science, from redox active systems such as proteins 32 and hydrogenase to catalysis, [33][34][35][36][37] redox-flow batteries 38 and of course ORBs. 16,17 One significant drawback with SEC EPR is the fact that microwave resonators suffer from substantial microwave damping as a result of introducing metal electrodes, polar solvents and ionic salts (i.e., the electrolyte) needed for successful electrochemistry. 39 Microwave damping can be significantly reduced by our novel on-substrate electrode design (see Fig.…”

“…However, also in situ and in operando experiments have recently been demonstrated, providing direct access to the change of the redox state upon charging and discharging of ORBs. 16,17 This opens the intriguing perspective of determining yields for charging and discharging processes by means of in operando quantitative cwEPR spectroscopy. We note that quantitative cwEPR can accurately assess the absolute number of unpaired electron spins in a given volume with high sensitivity.…”

Modulation of Radical Intermediates in Rechargeable Organic Batteries

“…This inspired the researchers to integrate the tri-carbonyl-based units into the extended polymer framework (such as DAAQ-COF and TpPa-COF) [55,56] for high-performance rechargeable batteries. Recently, in situ and ex situ electron paramagnetic resonance (EPR) [26,[57][58][59] technologies have been developed to monitor the dynamic processes of the redox of organic radicals, which will strongly facilitate the development of organic radicals for high-performance rechargeable batteries. The significant works of organic electrodes and organic radicals for rechargeable batteries.…”

“…As shown in Figure 1, given that the atoms in organic materials are connected by covalent bonds with paired electrons, the organic molecules must suffer from a radical state with an unpaired electron when they obtain or lose an electron during the redox processes. [25][26][27] When we consider the electrochemical reaction undergoes one by one electron, the radical states must be the essential intermediates during the redox of organic materials. Thus, the organic radicals should be considered as the special and fundamental intermediate states to investigate the redox processes of organic materials.…”

Machine Learning Isotropic g Values of Radical Polymers

“…Using in operando EPR techniques, evolution of the active material as a function of the state of charge can be studied. − Here, the g value serves as a parameter that can be theoretically computed and experimentally verified to substantiate the required complexity of the simulated system and its similarity to the experimentally investigated states of charge. While simulation of battery systems with realistic complexity for various states of charge is attainable using MD, DFT implementations result in inferior scalability.…”