Mechanistic understanding of the charge storage processes in FeF₂ aggregates assembled with cylindrical nanoparticles as a cathode material for lithium‐ion batteries by in situ magnetometry

Abstract

Transition metal fluorides (TMFs) cathode materials have shown extraordinary promises for electrochemical energy storage, but the understanding of their electrochemical reaction mechanisms is still a matter of debate due to the complicated and continuous changing in the battery internal environment. Here, we design a novel iron fluoride (FeF2) aggregate assembled with cylindrical nanoparticles as cathode material to build FeF2 lithium‐ion batteries (LIBs) and employ advanced in situ magnetometry to detect their intrinsic electronic structure during cycling in real time. The results show that FeF2 cannot be involved in complete conversion reactions when the FeF2 LIBs operate between the conventional voltage range of 1.0–4.0 V, and that the corresponding conversion ratio of FeF2 can be further estimated. Importantly, we first demonstrate that the spin‐polarized surface capacitance exists in the FeF2 cathode by monitoring the magnetic responses over various voltage ranges. The research presents an original and insightful method to examine the conversion mechanism of TMFs and significantly provides an important reference for the future artificial design of energy systems based on spin‐polarized surface capacitance.

Revealing An Intercalation‐Conversion‐Heterogeneity Hybrid Lithium‐Ion Storage Mechanism in Transition Metal Nitrides Electrodes with Jointly Fast Charging Capability and High Energy Output

“…After the Fe 2 N anode is fully discharged, the peaks at 710.8, 713.9, 724.4, 727.6, 705.4 and 719.2 eV related to Fe 2+ 2p 3/2 , Fe 3+ 2p 3/2 , Fe 2+ 2p 1/2 , Fe 3+ 2p 1/2 , Fe 0 2p 3/2 and Fe 0 2p 1/2 signal are observed in Figure 3b, which could be assigned to Li x Fe 2 N and Fe 0 , implying that a conversion reaction possibly occurred in the Fe 2 N anode. [34][35][36] When the anode returns to a fully charged state, only the peak of Fe 2 N was detected without other Fe-based phases, indicating the excellent reversible electrochemical process. Notably, the ex situ HRTEM images and corresponding fast Fourier transform (FFT) patterns allow direct visualization of the Li-ion intercalation and conversion process in Fe 2 N anode.…”

Multicore–shell iron fluoride@carbon microspheres as a long-life cathode for high-energy lithium batteries

“…7i. 46 The interfacial charge storage therefore allows the FeF 3 cathodes to exhibit higher capacity during electrochemical reactions.…”

Metal Fluoride Cathode Materials for Lithium Rechargeable Batteries: Focus on Iron Fluorides

“…[ 147 ] After that, the electrochemical performance of MFs has made great progress. Various morphologies of MFs, such as NWs, [ 47,128 ] nanoparticles, [ 89,148,149 ] hierarchical mesopores, [ 150–152 ] microspheres, [ 153,154 ] cylindrical nanoparticles, [ 155 ] and amorphous, [ 156,75 ] have been studied. To improve the electrical conductivity, mechanical stability, and other performance metrics (such as kinetic behaviors, side reactions, and dissolution), various nanostructured materials, especially conductive materials with an electron transportation network around the active materials, have been explored.…”