Entropymetry for non-destructive structural analysis of LiCoO₂cathodes

Abstract

Entropymetry is proposed as a non-destructive diagnosis tool in detecting structural evolution of LiCoO2 and its nickel-doped derivatives.

An Overview on the Advances of LiCoO2 Cathodes for Lithium‐Ion Batteries

“…[ 85 ] With different SOC, Choi et al monitored the structure changes and the Ni‐doped derivatives by the entropymetry. [ 87 ] Lithium extraction gives a monotonic decline of entropy change (Δ S ) based on progressive vacancy over Li sites, and the presence of a monoclinic intermediate phase inverses the slope of the Δ S profile to reflect its limited atomic configurations with high ordering. Furthermore, Ni‐doping decreases the ordering of the monoclinic phase, decreasing the height amplitude of Δ S profile in the monoclinic regime, suggesting that the increased disorder by Ni‐doping can enhance the stability of the lattice framework, and extend the cycle life with a high cutoff voltage of 4.6 V.…”

Layered Oxide Cathode for Potassium‐Ion Battery: Recent Progress and Prospective

“…When it reaches 1, the as‐synthesized K x MO 2 is likely to stabilize in O3 phase, in which the stacking sequence of oxide layer follows the AB CA BC manner and all K ions localize at the center of octahedral sites, as indicated in Figure 1a. Although many Li‐ [ 32,33 ] and Na‐based [ 34,35 ] layered oxides are stable as the O3 phase, only one O3 phase electrochemically active K x MO 2 compound can be successfully synthesized, suggesting that a wide range of layered K x MO 2 frameworks are unstable especially at high K contents (i.e., K/M = 1). [ 36 ] The reason might be related to the strong electrostatic K + ‐K + repulsion and detailed mechanisms will be described in the subsequent section.…”

Surface-Modified Lithium Cobalt Oxide (LiCoO2) with Enhanced Performance at Higher Rates through Li-Vacancy Ordering in the Monoclinic Phase

“…However, the nature of the interaction between Li + ions in the lattice is repulsive, and some Li-vacancy configurations are preferred in practice. When the quantity of Li + and vacancy differs significantly, the entropy will follow the ideal scenario . Because of electrostatic repulsion between two Li ions, a continuous array of Li-Li configuration is not possible at around 50% Li + occupancy .…”

“…When Li + -Mn + mixing occurs, the ordered nature of the monoclinic phase reduced, indicating that the falling TP H with increasing coating quantity (increasing Mn 3+ amount) denotes the cation mixing. As a result, the TP H of the entropy change profile can be analyzed to evaluate cation mixing . The differences in Δ S profiles before and after cycling are shown in Figure d–g for all samples.…”

“…The layered oxides prefer to order transition when enough vacancies are produced by Li removal during charging. The Li-vacancy ordering becomes considerably more critical from roughly at 4–4.2 V where half of the Li is removed, as it causes an abrupt change in configurational entropy (Δ S ) and may lead to structural instability . Therefore, lowering the Li vacancy ordering is pivotal in the monoclinic phase of LCO to minimize the Δ S .…”