Chemical Modulation of Local Transition Metal Environment Enables Reversible Oxygen Redox in Mn-Based Layered Cathodes

Abstract

Oxygen redox plays a prominent role in enhancing the energy density of Mn-based layered cathodes. However, understanding the factors affecting the reversibility of oxygen redox is nontrivial due to complicated structural and chemical transformations. Herein, we show that local Mn–O symmetry induced structural/chemical evolutions majorly dictate the reversibility of oxygen redox of Na x Li y Mn1–y O2 in Na cells. Na x Li y Mn1–y O2 with Jahn–Teller distorted MnO6 octahedra undergoes severe Mn dissolution during cycling, which destabilizes the transition metal layer resulting in poor Li retention and irreversible oxygen redox. Jahn–Teller distortion of MnO6 octahedra can be suppressed by modulating the local charge of Mn and Mn–O distance through Mg/Ti dual doping. This leads to reduced Mn dissolution and more reversible oxygen redox. Such stabilization significantly improves the electrochemical performance of Mg/Ti dual doped Na x Li y Mn1–y O2. Through this work, we show that local structural stabilization through local chemical environment modification can promote reversible oxygen redox in layered cathodes.

Dual Honeycomb‐Superlattice Enables Double‐High Activity and Reversibility of Anion Redox for Sodium‐Ion Battery Layered Cathodes

“…The cyclicity meliorates with the increase of the Mg 2+ content in Na 0.67 Mn 1− x Mg x O 2 [9] . The Mg doping in Na 5/6 Li 1/4 Mn 3/4 O 2 enhances the structure stability [10] . More recently, it is noteworthy that the regulation of the superlattice has a great influence on the anion redox during electrochemical processes.…”

Application of Advanced Vibrational Spectroscopy in Revealing Critical Chemical Processes and Phenomena of Electrochemical Energy Storage and Conversion

“…Additionally, the bandwidth of the intrinsic lattice Ce–O vibration F 2g (T 2g ) significantly increases with concentration of oxygen vacancies as well. Fourth, an example of using vibrational spectroscopy to detect short-range bonds and structural orderings is shown in Figure d. − Understanding reversible oxygen oxidation (O 2– → O n – , n < 2) is an important topic for cathode materials research for Li- and Na-ion batteries. − Qiao et al applied operando Raman spectroscopy and directly revealed the formation of O–O bonds in the oxygen sublattice and evolution of the peroxide bonds with battery operation (Figure d), providing valuable information on the nature of oxidized oxygen. An example of using vibrational spectroscopy in amorphous solids is shown in Figure e.…”

Realizing High-Performance Cathodes with Cationic and Anionic Redox Reactions in High-Sodium-Content P2-Type Oxides for Sodium-Ion Batteries

“…To address the drawbacks of Na-deficient P2 oxides, many studies have been performed via ion substitution (such as Li + , Mg 2+ , Cr 3+ , Fe 3+ , Cu 2+ , Al 3+ , etc. ). − For example, Chen’s group found that Mg- and Ti-codoped Na 2/3 [Ni 2/9 Mg 1/9 Mn 5/9 Ti 1/9 ]­O 2 could regulate the crystal structure and enhance the electrochemical properties by suppressing the phase transition . Especially, when weak bonds like Li–O, Mg–O, or Zn–O bonds are introduced in the Na-deficient oxides, the anionic redox reaction O 2– /O n – could be triggered at a high working potential of around 4.2 V, which opens a new path to improve the specific capacity of these oxides. − Na 2/3 [Mg 0.28 Mn 0.72 ]­O 2 is reported to have a high initial charge/discharge capacity of above 150 mAh g –1 due to the contribution of the O redox process, which is close to its theoretical capacity based on the Na content of the compound.…”