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Boron doping of Na$_{0.66}$Mn$_{0.8}$Fe$_{0.2}$O$_{2}$ (NMFO) cathode material improves its specific capacity from 133 to 163 mAh g$^{-1}$ at 0.1~C and capacity retention from 60% to 70% at 1C after 200 cycles. Diffusion coefficient analysis using galvanostatic intermittent titration technique and cyclic voltammetry reveals values in the range of 10$^{-8}$--10$^{-10}$ cm$^{2}$s$^{-1}$. DFT calculations and MD simulations suggest that interstitial tetrahedral sites near vacancies are the dominant incorporation pathways for B and provide insights into Na-ion transport.
Doping a sodium-ion battery cathode with boron can significantly boost its capacity and stability, offering a promising route to improved energy storage.
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.
