Mechanism of Exact Transition between Cationic and Anionic Redox Activities in Cathode Material Li₂FeSiO₄

Abstract

The discovery of anion redox activity is promising for boosting the capacity of lithium-ion battery (LIB) cathodes. However, fundamental understanding of the mechanisms that trigger the anionic redox is still lacking. Here, using hybrid density functional study combined with experimental soft X-ray absorption spectroscopy (sXAS) measurements, we unambiguously proved thata widely-studied cathode material for LIBs, performs sequent cationic and anionic redox activity through delithiation. Specifically, Fe 2+ is oxidized to Fe 3+ during the first Li-ion extraction per formula unit (f.u.), while the second Li-ion extraction triggered the oxygen redox exclusively. The transition between cationic and anionic redox activities happens exactly at LiFeSiO 4 , with electron and hole polaronic behaviors, respectively. For other polyanionic transition-metal (TM) materials in this family, while Li 2 NiSiO 4 shows similar sequent redox activity as Li 2 FeSiO 4 , Li 2 MnSiO 4 shows the multiple cationic redox (Mn 2+ -Mn 4+ ) during the whole delithiation, and Li 2 CoSiO 4 shows a simultaneous cationic and anionic redox. The present finding not only provides new insights into the oxygen redox activity in polyanionic compounds for rechargeable batteries, but also sheds light on the future design of high-capacity rechargeable batteries. 2 3

Analisis Molekular dan Transpor Ion Natrium Silikat

“…Energi stabilitas yaitu energi dalam keadaan termodinamika pada suatu molekul yang mengalami kesetimbangan kimia dengan lingkungannya (218)(219)(220)(221)(222) . Berikut optimasi energi stability dari molekul Natrium Silikat yang ditinjau menggunakan Chem Ultra 3D:…”

Discovering unusual structures from exception using big data and machine learning techniques

“…2 ) transformation is generally recognized as anionic redox [32], a property that differs from the commonlyknown cationic redox (e.g. the change in valence states of transition metal ions) and is currently a popular topic in materials science.…”

Bulk-Sensitive Soft X-ray Edge Probing for Elucidation of Charge Compensation in Battery Electrodes

“…43 Although the experimental resolution does not allow us to exclude the oxidation beyond Fe(III) with certainty, the formation of Fe(IV) has been rebutted by a complementary operando XANES analysis, see S.I., as well as in multiple other studies. 15,[19][20][21] It should be noted that the pristine sample contained a slight share of Fe 3+ originating from phase impurities.…”

“…The initial hypothesis of more than one electron extraction on the basis of Fe(III) to Fe(IV) transformation proposed by Islam et al 18 and experimentally claimed by Lv et al 13 was not supported by later studies. 14,15,[19][20][21] While the formation of Fe(IV) as the origin of additional capacity at elevated voltage has been rebutted, the role of oxygen as active anionic redox agent has shifted into focus of research. Numerous studies have emerged since the first observation of such anionic redox contribution in layered transition metal oxides about five years ago.…”