Probing the thermal effects of voltage hysteresis in anionic redox-based lithium-rich cathodes using isothermal calorimetry

Abstract

The commercialization of high-energy batteries with Li-rich cathode materials exhibiting combined cationic/anionic redox processes awaits the elimination of certain practical bottlenecks. Among these, large voltage hysteresis remains the most obscure from a fundamental thermochemical perspective. Here we study this issue by directly measuring via isothermal calorimetry the heat generated by Li/Li 2 Ru 0.75 Sn 0.25 O 3 (Li/LRSO) cells during various cycling conditions, with LRSO being a 'model' Li-rich layered cathode. We show how this heat thermodynamically relates to the lost electrical work that is crucial for practical applications. We further reveal that anionic redox on charging and discharging adopts different metastable paths having non-identical enthalpy potentials such that the overall Li content no longer remains the unique reaction coordinate, unlike in fully path-reversible cationic redox. We elucidate how quasistatic voltage hysteresis is related with heat dissipated due to non-equilibrium entropy production. Overall, this study establishes the great benefits of isothermal calorimetry for enabling energy efficient electrode materials in next-generation batteries.

Eliminating Transition Metal Migration and Anionic Redox to Understand Voltage Hysteresis of Lithium‐Rich Layered Oxides

“…Energy Mater. 2020, 10,1903634 Figure S6, Supporting Information) for reference, the oxidation state of Mo is determined to be somewhere between +4 and +6 after Li-ion extraction, in accordance with the initial charge capacity of 135 mAh g −1 (about 0.8 Li + ). The intensity of the pre-edge peak around 20 005 eV obviously increases after the Li-ion extraction.…”

“…Energy Mater. 2020, 10,1903634 ordering-disordering transformation of the Mo 3 O 13 clusters due to intralayer rearrangement of the Li-TM cations in the initial charging process leads to the obvious voltage hysteresis; 2) the continuous degradation of the Mo 3 O 13 clusters is closely related to the voltage decay. Such fundamental understanding reminds the community of paying attention to the effect of the in-plane rearrangement of the Li-TM ions on the voltage hysteresis and voltage decay though similar M-O clusters are not ubiquitous in the Li-rich layered oxides and we do not rule out the possible contributions of the anionic redox and the interlayer migration of the TM ions to these issues in broader cutoff charge/discharge potential ranges.…”

“…Tarascon and co‐workers believed that the anionic redox plays a vital role in the voltage hysteresis by operando X‐ray absorption spectroscopic (XAS) studies. They recently claimed that the voltage hysteresis is independent of the cationic redox, but is related to the nonequilibrium entropy production of the anionic redox in different metastable paths upon charging and discharging in the Li‐rich layered oxides . However, Chueh and co‐workers believed that the strong coupling between the anionic redox and TM migration results in the regulation of the anionic and cationic redox potential and then the huge voltage hysteresis in LLO.…”

Voltage hysteresis during lithiation/delithiation of graphite associated with meta-stable carbon stackings

“…Surprisingly, the temperature-dependence of the OCV over a wider range than near room temperature (i.e., 20-30 • C) hasn't attracted much attention yet. Varying the temperature under OCV relaxation conditions also allows the entropic and enthalpic origins of the OCV hysteresis to be separated [22,25], allowing greater understanding of the physical origin of that hysteresis.…”

Highly Anisotropic Thermal Transport in LiCoO2

“…The impact of thermal e↵ects on anion redox has recently been highlighted, where heat dissipation contributes to voltage hysteresis upon battery cycling. 28 Investigation of the coupling between the vibrational modes of defects with bulk phonon transport is a worthwhile direction for future research.…”