Gassing Behavior of High‐Entropy Oxide Anode and Oxyfluoride Cathode Probed Using Differential Electrochemical Mass Spectrometry

Abstract

Multicomponent materials may exhibit favorable Li‐storage properties because of entropy stabilization. While the first examples of high‐entropy oxides and oxyfluorides show good cycling performance, they suffer from various problems. Here, we report on side reactions leading to gas evolution in Li‐ion cells using rock‐salt (Co0.2Cu0.2Mg0.2Ni0.2Zn0.2)O (HEO) or Li(Co0.2Cu0.2Mg0.2Ni0.2Zn0.2)OF (Li(HEO)F). Differential electrochemical mass spectrometry indicates that a robust solid‐electrolyte interphase layer is formed on the HEO anode, even when using an additive‐free electrolyte. For the Li(HEO)F cathode, the cumulative amount of gases is found by pressure measurements to depend strongly on the upper cutoff potential used during cycling. Cells charged to 5.0 V versus Li+/Li show the evolution of O2, H2, CO2, CO and POF3, with the latter species being indirectly due to lattice O2 release as confirmed by electron energy loss spectroscopy. This result attests to the negative effect that lattice instability at high potentials has on the gassing.

High-entropy energy materials: challenges and new opportunities

“…12 Additionally, using in situ differential electrochemical mass spectrometry (DEMS), the authors revealed that a robust solidelectrolyte interphase (SEI) is formed on the surface of HEO particles, even when using an additive-free electrolyte, further emphasizing the advantage of the proposed entropy-stabilized conversion-type lithium storage mechanism. 79 Notably, the HEO system exhibited a great enhancement in terms of cycling stability when compared to medium-entropy oxide materials (Fig. 9e).…”

“…Entropy stabilization and the occurring interactions between the different incorporated elements endow unique properties of HEMs. In this review, we will focus particularly on the effect that entropy stabilization (and the cocktail effect) has on the applications in electrochemical energy storage, for example, in batteries 12,13,17,18,53,55,69,[76][77][78][79] and supercapacitors. 23,[80][81][82]…”

“…[140][141][142][143][144] Although the preliminary results are promising, further optimizations are needed, especially for preventing side reactions due to gas evolution and surface reconstruction and densification, among others. 79,[145][146][147][148] Rock-salt (CoMgCuNiZn)O was also investigated as chemical anchor of polysulfides in sulfur cathodes for Li-S cells (Fig. 9i).…”

Thermal Analysis of High Entropy Rare Earth Oxides

“…The high entropy design approach was recently applied to carbides [ 4 , 5 ] borides [ 6 , 7 , 8 ], and oxides [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ] for high temperature and battery-related applications. Most of the high entropy compositions that were successfully prepared as single phases are within the 15% limit of atomic radii differences known as a Hume-Rothery [ 19 ] rule to metallurgists and as a Goldschmidt [ 20 ] limit for isomorphic mixtures to mineralogists (the majority of mineral species meet HE definition!…”

Spinel to Rock-Salt Transformation in High Entropy Oxides with Li Incorporation

“…In addition, the recent findings by Bérardan et al on (NiCuZnMgCo) 1−x−y Ga y A x O (with A = Li, Na, K) showed that the charge compensation mechanism when using monovalent elements involves the formation of oxygen vacancies, resulting in a decrease in lattice parameters [18]. Lately, HEOs have been shown to have potential as conversion, intercalation, and insertion materials for application in Liand Na-ion batteries (LIBs and SIBs) [5,13,17,[19][20][21][22]. Nevertheless, the role of Li + in HEO structures (e.g., rock-salt [23] or spinel [24]) and the associated behaviors of the other incorporated elements have not yet been understood.…”