PEDOT Encapsulated FeOF Nanorod Cathodes for High Energy Lithium-Ion Batteries

Abstract

Conversion-reaction cathodes can potentially double the energy density of current Li-ion batteries. However, the poor cycling stability, low energy efficiency, and low power density of conversion-reaction cathodes limit their applications for Li-ion batteries. Herein, we report a revolutionary advance in a conversion-reaction cathode by developing a core-shell FeOF@PEDOT nanorods, in which partial substitution of fluorine with oxygen in FeF3 substantially enhance the reaction kinetics and reduce the potential hysteresis, while conformal nanolayer PEDOT coating provides a roubst fast electronic connection and prevents the side reactions. The FeOF@PEDOT nanorods deliver a capacity of 560 mA h g(-1) at 10 mA g(-1) with an energy density of >1100 W h kg(-1), which is more than two times higher than the theoretical energy density of LiCoO2. The FeOF@PEDOT nanorods can maintain a capacity of ~430 mA h g(-1) at 50 mA g(-1) (840 W h kg(-1)) for over 150 cycles with capacity decay rate of only 0.04% per cycle, which is 2 orders of magnitude lower than the capacity decay rate ever reported among all conversion-reaction cathodes. Detailed characterizations were conducted to identify the structure and mechanism responsible for these significant improvements that could translate into a Li-ion cell with a 2× increase in energy density.

Microstructural Evolution Of Iron Oxyfluoride/Carbon Nanocomposites Upon Electrochemical Cycling

“…For instance, enhanced cycling stability has been reported for FeOF nanorods after ex situ coating with a thin conducting (PEDOT) polymer. 44 The formation of a surface protective coating can be done also in situ by exposing FeO 0.7 F 1.3 /C nanocomposites to air, resulting in a microstructure consisting of FeO 0.7 F 1.3 /C nanoparticles encapsulated by a thin (1−2 nm) O-rich rocksalt layer. 45 This rocksalt layer was found to be electrochemically inactive, as Fe did not change valence state upon cycling, but provides a protective layer, minimizing reaction with electrolyte.…”

Halide‐Based Materials and Chemistry for Rechargeable Batteries

“…The reversible capacity of FeOF during long cycling was significantly improved by the encapsulation of PEDOT (Figure ), which provided a fine electronic connection for the FeOF particles and prevented side reactions between the Fe 0 nanoparticles formed in situ and the electrolyte. This resulted in a high capacity of about 430 mAh g −1 at 50 mA g −1 for over 150 cycles with a capacity decay rate of only 0.04 % per cycle (Figure h) . Lin et al.…”

In situ surface protection for enhancing stability and performance of conversion-type cathodes

“…Formation losses on the anode as well as slightly higher areal anode capacity typical in practical cells have not been accounted for because these may ultimately be reduced or compensated for. For average cell voltage estimations we considered experimental curves of intercalation cathodes and average potentials of conversion-type cathodes being 0.20-0.25 V lower than theoretical ones (the 0.20-0.25 V value was selected based on many experimental studies [27][28][29] conducted on Li-S and Li-Se cells). In such calculations we pair conversion cathodes with graphite, Si and Li metal anodes, respectively, at the matching capacity and compare energy storage characteristics of such cells with that of cells based on intercalation-type LFP and Ni-, Co-based cathodes [Figs.…”

“…Majority of efforts to overcome such challenges have been focused on particle-level architecture optimizations, including various coatings on the surface of conversion cathode-based (nano)particles, which demonstrated promising trends. [28][29][30][31][32][33][34][35][36][37] Unfortunately, such approaches generally increase complexity and cost of material fabrication and, in most cases, suffer from defects within the protective layers around the individual particles present before or induced after (due to the volume changes) electrochemical cycling.…”