Quantification of Anionic Redox Chemistry in a Prototype Na-Rich Layered Oxide

Abstract

Harnessing anionic redox reactions is of prime importance for boosting the capacity of sodium-ion batteries. However, quantifying the cyclability of anionic redox reactions is still challenging. Herein, we conduct a qualitative and quantitative investigation of the cationic and anionic redox reactions of a prototype Na-rich layered oxide, namely Na3RuO4, by a combination of bulk-sensitive X-ray absorption spectroscopy (XAS) and full-range mapping of resonant inelastic X-ray scattering (mRIXS). We unequivocally reveal that both Ru cations and oxygen anions are involved in the charge compensation process of Na3RuO4. The Ru redox is highly reversible over extended electrochemical cycles; while the cyclability of lattice oxygen redox gradually decreases with the retention of only 36% after 30 cycles, which is mainly responsible for the capacity fading of Na3RuO4. Our findings provide deeper insights into the complex oxygen redox mechanism, which plays a decisive role for designing high-energy Na-rich electrode materials for sodium-ion batteries.

Exploring the Charge Compensation Mechanism of P2-Type Na0.6Mg0.3Mn0.7O2 Cathode Materials for Advanced Sodium-Ion Batteries

“…Combined with the result that manganese is not involved in the redox reaction in this interval, it is very likely that the increase in hybridization strength is partly related to We first discuss the pre-edge features of the bulk-sensitive TFY spectra. Note that the spectral lineshape of two pre-edge peaks is dominated by the valence states of TMs, and the integrated pre-edge intensity (525.5-533.5 eV; marked with shadow region) corresponds to the Mn-O hybridization strength [41,42]. During the first charge process, there are two main changes in this regime.…”

Recent Advances in Electrode Materials with Anion Redox Chemistry for Sodium-Ion Batteries

“…Ru-Based Compounds. The oxygen-redox chemistry was demonstrated in sodium-rich Ru-based cathodes with good structural stability [30][31][32][33][34][35][36][37][38][39][40][41][42]. The first research paper on such materials was published in 2013 by the group of Tamaru et al on Na 2 RuO 3 (R 3 m), in which Ru was stabilized as Ru 4+ [30].…”

“…Na 3 RuO 4 (Na[Na 1/2 Ru 1/2 ]O 2 ) (C2/m) is a further expansion of the Na 2 RuO 3 cathode material toward higher sodium content (O/TM ratio) Ru-based materials with oxygen-redox activity [40][41][42]. The crystal structure of Na 3 RuO 4 is described as a layered structure with a Ru 5+ framework forming isolated tetramers of the edge-sharing RuO 6 octahedra in the Na 1/2 Ru 1/2 O 2 layer (Figure 10(a)) [41].…”

“…The crystal structure of Na 3 RuO 4 is described as a layered structure with a Ru 5+ framework forming isolated tetramers of the edge-sharing RuO 6 octahedra in the Na 1/2 Ru 1/2 O 2 layer (Figure 10(a)) [41]. The reaction mechanism in Na 3 RuO 4 is currently under debate by several groups [40][41][42] [40]. On the basis of the XPS and XANES analyses, the authors claimed that Na extraction/insertion proceeded along the inert redox character of Ru 5+ in the octahedral position.…”

“…The selection of elements in transition metal layers is of great importance in improving the reversibility and controlling the operation voltage of the anionic redox reaction, namely, Na x [A y TM 1-y ]O 2 (A: Li [17][18][19][20][21][22][23][24][25][26][27][28][29], Na [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45], Mg [46][47][48][49][50][51][52][53][54][55][56], Zn [57][58][59][60], Ni [61][62][63][64][65][66]…”