Cationically Substituted Bi_0.7Fe_0.3OCl Nanosheets as Li Ion Battery Anodes

Area of Science:

• Materials Science
• Solid-State Chemistry
• Electrochemistry

Background:

• Bismuth oxychloride (BiOCl) is a layered semiconductor with potential applications in energy storage.
• Enhancing the electrical conductivity of BiOCl is crucial for improving its electrochemical performance.
• Cation substitution offers a pathway to tune the electronic properties of BiOCl.

Purpose of the Study:

• To synthesize and characterize iron-substituted bismuth oxychloride (Bi$_{0.7}$Fe$_{0.3}$OCl) nanosheets.
• To investigate the effect of Fe$^{3+}$ substitution on the electrical conductivity and charge transport properties of BiOCl.
• To evaluate the electrochemical performance of Bi$_{0.7}$Fe$_{0.3}$OCl nanosheets as anode materials for lithium-ion batteries.

Main Methods:

• Hydrolysis synthesis route using bismuth(III) nitrate and iron(III) chloride.
• Post-synthesis annealing at 500 °C.
• Room temperature electrical conductivity measurements.
• Density functional theory (DFT) calculations.
• Electrochemical testing for lithium-ion insertion capacity.

Main Results:

• Formation of ionically layered Bi$_{0.7}$Fe$_{0.3}$OCl nanosheets via cation substitution.
• Significant increase in room temperature electrical conductivity from 6.11 × 10$^{-8}$ S/m (BiOCl) to 6.80 × 10$^{-7}$ S/m (Bi$_{0.7}$Fe$_{0.3}$OCl).
• Reduced activation energy for electrical conduction from 862 meV (BiOCl) to 310 meV (Bi$_{0.7}$Fe$_{0.3}$OCl).
• DFT calculations predicted a higher density of states near the Fermi level for Bi$_{0.7}$Fe$_{0.3}$OCl, confirming enhanced charge mobility.
• Achieved a 2.5× increase in Li$^{+}$ ion insertion capacity, from 215 mAh·g$^{-1}$ (BiOCl) to 542 mAh·g$^{-1}$ (Bi$_{0.7}$Fe$_{0.3}$OCl) after 50 cycles.

Conclusions:

• Direct Fe$^{3+}$ substitution for Bi$^{3+}$ in BiOCl effectively creates an ionically layered ternary semiconductor.
• The enhanced electrical conductivity and charge mobility in Bi$_{0.7}$Fe$_{0.3}$OCl are attributed to Fe substitution.
• Bi$_{0.7}$Fe$_{0.3}$OCl nanosheets demonstrate promising potential as anode materials for advanced lithium-ion batteries.