Electron paramagnetic resonance imaging for real-time monitoring of Li-ion batteries

Abstract

Batteries for electrical storage are central to any future alternative energy paradigm. The ability to probe the redox mechanisms occurring at electrodes during their operation is essential to improve battery performances. Here we present the first report on Electron Paramagnetic Resonance operando spectroscopy and in situ imaging of a Li-ion battery using Li2Ru0.75Sn0.25O3, a high-capacity (>270 mAh g−1) Li-rich layered oxide, as positive electrode. By monitoring operando the electron paramagnetic resonance signals of Ru5+ and paramagnetic oxygen species, we unambiguously prove the formation of reversible (O2)n− species that contribute to their high capacity. In addition, we visualize by imaging with micrometric resolution the plating/stripping of Li at the negative electrode and highlight the zones of nucleation and growth of Ru5+/oxygen species at the positive electrode. This efficient way to locate ‘electron’-related phenomena opens a new area in the field of battery characterization that should enable future breakthroughs in battery research.

Fundamental interplay between anionic/cationic redox governing the kinetics and thermodynamics of lithium-rich cathodes

“…This is an interesting result which distinguishes LR-NMC from “model” Li 2 Ru 0.75 Sn 0.25 O 3 systems in which cationic and anionic redox are well separated at high and low potentials, respectively. 10,45,46 …”

Editors' Choice—Practical Assessment of Anionic Redox in Li-Rich Layered Oxide Cathodes: A Mixed Blessing for High Energy Li-Ion Batteries

“…The first 3.6 V redox process corresponding to the de-insertion of 0.75 Li per formula unit (theoretical as well as practical capacity of 120 mAh.g −1 ), is known to be purely associated to the oxidation of 0.75 Ru 4+ to Ru 5+ . 4,29 We evaluate the reversibility of this process vs. Li / Li + with GITT. Figure 1a-inset shows a good matching of open-circuit voltages (OCVs) between charge and discharge along with almost complete recovery of capacity that indicates excellent reversibility.…”

“…A total capacity of nearly 240 mAh.g −1 is delivered; out of which about half accounts theoretically for the oxidation of 0.75 Ru 4+ , indicating almost equal capacity contributions from the cationic redox of Ru 4+/5+ and the anionic redox of (O 2 ) 4−/n− . These two processes on discharge can respectively be assigned to the dQ/dV peaks centered around 3.3 V and 3.7 V. 29 In short, the first half of the 'S-shaped'-sloped profile at lower voltages primarily involves cationic redox and after crossing the mid-point (or 50% SOC), oxygen is the major redox species at higher voltages. A deeper charge with CCCV (implying more oxygen oxidation) leads to an expected additional discharge capacity (more intense 3.7 V dQ/dV peak) that is however shifted down to a slightly lower discharge voltage, which is counterintuitive (Fig.…”

Intermediate honeycomb ordering to trigger oxygen redox chemistry in layered battery electrode

“…The [Na 1/3 M 2/3 ]O 2 slabs supply additional Na ions, thereby increasing the reversible capacity while suppressing the over-deintercalation of Na ions from the Na layer. This ‘ A 2− x MO 3 ' strategy has already been adopted in many lithium systems such as Li 2 MnO 3 –LiMO 2 and Li 2 RuO 3 , in which enhanced capacities exceeding a M 4+ /M 3+ one-electron reaction have been achieved through additional oxygen redox contribution161718.…”