Synergistic Effect of Polymorphs in Doped NaNi0.5Mn0.5O2 Cathode Material for Improving Electrochemical Performances in Na-Batteries

Abstract

Layered NaNi0.5Mn0.5O2, employed as cathode materials in sodium ion batteries, is attracting interest due to its high working potential and high-capacity values, thanks to the big sodium amount hosted in the lattice. Many issues are, however, related to their use, particularly, the complex phase transitions occurring during sodium intercalation/deintercalation, detrimental for the structure stability, and the possible Mn dissolution into the electrolyte. In this paper, the doping with Ti, V, and Cu ions (10% atoms with respect to Ni/Mn amount) was used to stabilize different polymorphs or mixtures of them with the aim to improve the capacity values and cells cyclability. The phases were identified and quantified by means of X-ray powder diffraction with Rietveld structural refinements. Complex voltammograms with broad peaks, due to multiple structural transitions, were disclosed for most of the samples. Ti-doped sample has, in general, the best performances with the highest capacity values (120 mAh/g at C/10), however, at higher currents (1C), Cu-substituted sample also has stable and comparable capacity values.

Physico-Chemical Features of Undoped and Fe/Cu-Doped Na0.67MnO2-Layered Cathodes for Sodium Batteries

“…In all the cases, many redox peaks can be observed, which were an indication of the multiple reactions taking place during sodium intercalation/deintercalation, due to the complex phase's stabilization and to the multiple reactions of the layered polymorphs. For these materials, the redox processes were expected to be mainly due to Mn ions [9,12,31,32]. The most defined phenomena can be observed for the NMO sample (Figure S5A in the Supplementary Materials).…”

Practical Cathodes for Sodium‐Ion Batteries: Who Will Take The Crown?

“…Therefore, compositional modification has been proposed to improve the cycling performance and rate capability of O3-type cathodes. Heterogeneous-atom substitution provides the following benefits: 1) increases the binding energy between TM and O to improve the structural reversibility and reduce the ionic diffusion barrier; [142,143] 2) adjusts the interlayer spacing of the Na layer to improve ion-diffusion kinetics and/or air stability; [144,145] and 3) suppresses the JT effect of Mn 3+ through charge compensation (such as Mg 2+ , Zn 2+ , Cu 2+ , and Li + ). [146][147][148] For example, it was proposed that Al doping can shorten the bond length of TM-O and expand the interlayer spacing of the Na layer by increasing the TM-O bond energy, thereby improving the cycling reversibility and ionic diffusion kinetics of the resulting cathode (NaAl 0.02 Ni 0.49 Mn 0.49 O 2 ).…”

Amorphous Aluminum Oxide-Coated NaFe0.33Ni0.33Mn0.33O2 Cathode Materials: Enhancing Interface Charge Transfer for High-Performance Sodium-Ion Batteries

“…Within the realm of layered positive electrode materials, two prevalent systems are P-type and O-type, based on the arrangement of sodium within octahedral or prismatic environments. , Notably, the O3-type layered positive electrode materials have emerged as the most promising candidates, owing to their high energy density and practical initial Coulombic efficiency. Nonetheless, challenges arise from irreversible structural changes during the insertion and extraction of Na + , which lead to significant degradation in cycling stability owing to grain fragmentation and associated side reactions. − In LIBs, incorporating amorphous aluminum oxide coatings and doping has been proven effective in enhancing the structural stability of materials. − However, conventional approaches typically involve nanoscale particle attachments to the surface, resulting in a suboptimal fraction of coverage. Furthermore, the preservation of a stable crystal structure poses challenges for efficient ion transport.…”