Improved Electrochemical Performance and Diffusion kinetics by Boron-doping in Na$_{0.66}$Mn$_{0.8}$Fe$_{0.2}$O$_{2}$ Layered Cathodes for Sodium-Ion Batteries

TL;DR

This study demonstrates that boron doping in Na$_{0.66}$Mn$_{0.8}$Fe$_{0.2}$O$_{2}$ cathodes enhances sodium-ion battery performance by increasing capacity, stability, and understanding diffusion mechanisms through experimental and computational analyses.

Contribution

The paper introduces boron doping as a method to improve electrochemical performance and diffusion kinetics in layered cathodes for sodium-ion batteries, supported by experimental and theoretical insights.

Findings

B-NMFO cathode shows higher specific capacity (163 mAh g$^{-1}$) than undoped NMFO (133 mAh g$^{-1}$).

Capacity retention improves to 70 ext% after 200 cycles at 1 C with boron doping.

Diffusion coefficients are in the range of 10$^{-8}$--10$^{-10}$ cm$^{2}$s$^{-1}$, indicating enhanced ion transport.

Abstract

We report the electrochemical investigation and study the diffusion kinetics of boron doped Na$_{0.66}$Mn$_{0.8}$Fe$_{0.2}$O$_{2}$ (B-NMFO) cathode materials for sodium-ion batteries. Notably, the B-NMFO cathode exhibits improved specific capacity of 163 mAh g$^{-1}$ as compared to 133 mAhg$^{-1}$ at 0.1~C for the NMFO cathode. Further, we observe better capacity retention of 70\% for B-NMFO as compared to the NMFO (60\%) at 1 C after 200 cycles, indicating high structural stability due to the presence of strong B-O bonds. The diffusion coefficient evaluation through galvanostatic intermittent titration technique and cyclic voltammetry, which is found to be in the range of 10$^{-8}$--10$^{-10}$ cm$^{2}$s$^{-1}$. Interestingly, the temperature dependent distribution of relaxation time (DRT) analysis provides a clear understanding about the individual physical processes occurring at different time domains during the electro-chemical testing. Moreover, density functional theory is employed to determine the energetics and the electronic properties of B-NMFO, which suggests that the interstitial tetrahedral sites, especially those next to vacancies, are the dominant incorporation path ways for B in the host structure. Additionally, classical molecular dynamics (MD) simulations are applied to gain insights into the Na-ion transport properties in the bulk structures cathode materials.