Understanding anion-redox reactions in cathode materials of lithium-ion batteries through in situ characterization techniques: a review

Abstract

As the demand for rechargeable lithium-ion batteries (LIBs) with higher energy density increases, the interest in lithium-rich oxide (LRO) with extraordinarily high capacities is surging. The capacity of LRO cathodes exceeds that of conventional layered oxides. This has been attributed to the redox contribution from both cations and anions, either sequentially or simultaneously. However, LROs with notable anion redox suffer from capacity loss and voltage decay during cycling. Therefore, a fundamental understanding of their electrochemical behaviors and related structural evolution is a prerequisite for the successful development of high-capacity LRO cathodes with anion redox activity. However, there is still controversy over their electrochemical behavior and principles of operation. In addition, complicated redox mechanisms and the lack of sufficient analytical tools render the basic study difficult. In this review, we aim to introduce theoretical insights into the anion redox mechanism and in situ analytical instruments that can be used to prove the mechanism and behavior of cathodes with anion redox activity. We summarized the anion redox phenomenon, suggested mechanisms, and discussed the history of development for anion redox in cathode materials of LIBs. Finally, we review the recent progress in identification of reaction mechanisms in LROs and validation of engineering strategies to improve cathode performance based on anion redox through various analytical tools, particularly, in situ characterization techniques. Because unexpected phenomena may occur during cycling, it is crucial to study the kinetic properties of materials in situ under operating conditions, especially for this newly investigated anion redox phenomenon. This review provides a comprehensive perspective on the future direction of studies on materials with anion redox activity.

Zero-Strain Cathodes for Lithium-Based Rechargeable Batteries: A Comprehensive Review

“…82 At high voltage, the oxygen redox reaction contributes to the extraordinary capacity by forming oxidized O n− (n < 2) ions. 83 Unfortunately, the oxidized O n− ion is susceptible to oxygen evolution from the lattice owing to the decreased ion radius and electrostatic force. Oxygen evolution can lead to irreversible phase transition and strong anisotropic lattice strain, resulting in microcracks.…”

Synergistic effect of oxygen vacancy and dual electrocatalysts in activating anion redox in lithia-based cathodes

“…1,2 However, the relatively poor energy density of traditional lithium-ion batteries (LIBs) resulting from the intercalation/deintercalation of Li + ions in heavy transition metal oxides (TMOs) has been one of the most significant barriers for the extension of the driving range of electric vehicles. 3 As the active cathode material, TMOs have been addressed only in terms of cation redox electrochemistry. Therefore, a transition metal cation is the dominant redox center in TMOs, limiting the specific capacity of conventional cathode materials.…”

Recent advances in dendrite-free lithium metal anodes for high-performance batteries

“…Based on Bragg's law, in situ XRD can monitor the lattice parameters in the electrode, which provides a critical support for the in-depth study of the battery operation and failure mechanism. 125–128 In addition, in situ X-ray techniques have applications in in situ X-ray photoelectron spectroscopy (XPS) as well as in in situ X-ray absorption spectroscopy (XAS). 129–132…”

“…Based on Bragg's law, in situ XRD can monitor the lattice parameters in the electrode, which provides a critical support for the in-depth study of the battery operation and failure mechanism. [125][126][127][128] In addition, in situ X-ray techniques have applications in in situ X-ray photoelectron spectroscopy (XPS) as well as in in situ X-ray absorption spectroscopy (XAS). [129][130][131][132] Li et al investigated the stability of the halide solid electrolyte Li 3 InCl 6 in air using synchrotron in situ XRD to reveal the mechanism of decomposition due to water uptake and the decrease in ionic conductivity.…”