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

Cation substitution of Bi³⁺ with Fe³⁺ in BiOCl leads to the formation of ionically layered Bi_0.7Fe_0.3OCl nanosheets. The synthesis follows a hydrolysis route using bismuth(III) nitrate and iron(III) chloride, followed by postannealing at 500 °C. Room temperature electrical conductivity improves from 6.11 × 10^-8 S/m for BiOCl to 6.80 × 10^-7 S/m for Bi_0.7Fe_0.3OCl. Correspondingly, the activation energy for electrical conduction reduces from 862 meV for pure BiOCl to 310 meV for Bi_0.7Fe_0.3OCl. These data suggest improved charge mobility in Bi_0.7Fe_0.3OCl nanosheets. Density functional theory calculations confirm this behavior by predicting a high density of states near the Fermi level for Bi_0.7Fe_0.3OCl. The improvement in electrical conductivity is exploited in the electrochemical performance of Bi_0.7Fe_0.3OCl nanosheets. The insertion capacity of Li⁺ ions shows an increase of 2.5×, from 215 mAh·.g^-1 for undoped BiOCl to 542 mAh·g^-1 for Bi_0.7Fe_0.3OCl after 50 cycles at a current density of 50 mA·g^-1. Thus, the direct substitution of Bi³⁺ sites with Fe³⁺ in BiOCl results in nanosheets of an ionically layered ternary semiconductor compound which is attractive for Li ion battery anode applications.