High-Voltage Electrochemical Properties of Lithium-Rich Spinel Oxides

Abstract

Conventional cathode materials of lithium-ion batteries deliver moderate specific capacity based on the redox reaction of transition metals; using additional oxygen redox reactions in lithium-rich oxides is a strategy to increase their energy density. However, a delithiated layered structure is prone to the irreversible migration of transition metals to lithium-ion layers during oxygen redox reactions, which results in performance degradation. Thus, exploring alternative oxygen redox host frameworks is required to develop high-capacity and durable cathode materials. Herein, we investigated the oxygen redox activity of lithium-rich spinel oxides. First-principles calculations predict that nonbonding O 2p orbitals exist just below the Fermi level of lithium-rich spinel oxides and undergo oxidation through delithiation. Electrochemical measurements demonstrate that delithiation occurs at 5.0 V vs Li/Li + during the first charge, but this high-voltage capacity fades rapidly upon cycling. X-ray absorption/emission spectroscopy, high-resolution transmission electron microscopy, and X-ray diffraction indicate that the oxidized oxide ions are highly unstable to form O 2 molecules accompanied by a reduction of Mn 4+ .

Li-Rich Mn-Based Cathode Materials for Li-Ion Batteries: Progress and Perspective

“…During the initial cycle, the capacity is primarily provided by redox couples, such as Ni 2+ /Ni 3+ , Ni 3+ /Ni 4+ , and O 2− /O − , but the release of lattice oxygen will activate lower voltage redox couples, such as Mn 3+ /Mn 4+ and Co 2+ /Co 3+ , resulting in a continuous decrease in the average valence state of transition metal ions and then accelerate the voltage decay [52]. Meanwhile, a decrease in the Mn element's valence state stimulates the Jahn-Teller effect, which intensifies Mn element dissolution [113,114,117]. Moreover, triggering anionic redox reactions reduces the formation energy and diffusion barriers of oxygen vacancies, leading to nanohole formation and crystal structure transformations [115,118].…”

“…lence state of transition metal ions and then accelerate the voltage decay [52]. Meanwhile, a decrease in the Mn element's valence state stimulates the Jahn-Teller effect, which intensifies Mn element dissolution [113,114,117]. Moreover, triggering anionic redox reactions reduces the formation energy and diffusion barriers of oxygen vacancies, leading to nanohole formation and crystal structure transformations [115,118].…”

Research and Development of Novel Secondary Batteries in Japan

“…In addition to these batteries, the VSI also illustrates novel materials development, theoretical calculations, and characterization for other secondary batteries, such as Li-ion and Na-ion batteries. − …”