Origin of stabilization and destabilization in solid-state redox reaction of oxide ions for lithium-ion batteries

Abstract

Further increase in energy density of lithium batteries is needed for zero emission vehicles. However, energy density is restricted by unavoidable theoretical limits for positive electrodes used in commercial applications. One possibility towards energy densities exceeding these limits is to utilize anion (oxide ion) redox, instead of classical transition metal redox. Nevertheless, origin of activation of the oxide ion and its stabilization mechanism are not fully understood. Here we demonstrate that the suppression of formation of superoxide-like species on lithium extraction results in reversible redox for oxide ions, which is stabilized by the presence of relatively less covalent character of Mn4+ with oxide ions without the sacrifice of electronic conductivity. On the basis of these findings, we report an electrode material, whose metallic constituents consist only of 3d transition metal elements. The material delivers a reversible capacity of 300 mAh g−1 based on solid-state redox reaction of oxide ions.

Synthesis and Electrode Performance of Li₄MoO₅-LiFeO₂ Binary System as Positive Electrode Materials for Rechargeable Lithium Batteries

“…Since superoxide species is chemically unstable, which results in the oxidation and decomposition on further charge to 4.8 V. Indeed, after charge to 4.8 V, intensity of superoxide-like species is significantly weakened, indicating decomposition of superoxide-like species on charge to 4.8 V. Such decomposition reaction of superoxide species leads to oxygen loss, which triggers the structural reconstruction process, and thus Fe and Mo are reduced on discharge. Note that the formation of superoxide species was not evidenced for Li-Nb-Mn system, 8,20 and therefore it is concluded that the suppression of the formation of superoxide-like species is important to improve the reversibility of solid-state redox reaction of oxide ions.…”

Factors Controlling the Redox Activity of Oxygen in Perovskites: From Theory to Application for Catalytic Reactions

“…When removing electron from pure O p states in the bulk, unstable oxyl species would be formed prior to stabilization by charge reorganization. While examples have now been given for the structurally more flexible layered compounds used as Li-ion battery positive electrodes [16,18,20], only rare examples describing the reorganization of lattice oxygen reorganization in the perovskite structure can be found. Indeed, due to the rigidity of the corner-shared octahedral arrangement and the relatively large O-O bond distance, this reorganization is foreseen to be almost impossible for cubic perovskites.…”

“…Identifying the difference between these two types of oxidized species formed under oxidation is also of prime importance for storing extra capacity in Li-ion battery cathode materials, since only the electron removal from lone pair orbitals offers the opportunity to exchange an extra electron upon charging in addition to the one classically exchange from the M-O* bond. Hence, several papers can be found in the literature regarding this phenomenon, with a common agreement in describing the anionic (or oxygen) redox reaction as involving oxygen lone pairs [16][17][18][19][20][21][22][23]. Definitively, it now appears that the chemistry of O-O bond formation, which is the cornerstone of the OER reaction for instance, involves specific electronic levels that we aim to describe in this manuscript.…”

“…The second mechanism invoked the formation of an O-O bond by the reaction of OH − from the electrolyte with deprotonated oxygen atoms. Interestingly, when performing in situ mass spectrometry on 18 O-labeled perovskites, two type of gaseous oxygen were found: 34 O 2 coming from the reactivity of one oxygen from the electrolyte with lattice oxygen and 36 O 2 arising from the combination of two lattice oxygens [6]. Therefore, it is critical to further understand the electronic states respectively involved in these two types of O-O bond formation, denoted respectively acid-base and direct coupling reactions by the homogeneous catalysis community [81,82].…”

Nonstoichiometry and the Origin of Electrochemical Properties of Functional Oxides for Energy Conversion and Storage Technologies

“…[1][2][3][4][5] Therefore, understanding the origin of the functionalities and the governing factors are important knowledge for further development of the energy conversion and storage technologies. The author and coworkers have been studying on understanding the origin of electrochemical properties of layered perovskite type La 2 NiO 4 -based oxides as a model system.…”