In Situ X‐Ray Diffraction Studies on Structural Changes of a P2 Layered Material during Electrochemical Desodiation/Sodiation

Abstract

3227wileyonlinelibrary.com be adapted almost directly to the sodium system. Sodium equivalents of lithiumcontaining electrode materials, such as oxides, sulfi des, phosphates, pyrophosphates, fl uorophosphates, and alloying metals, have been evaluated as electrode materials for SIBs. [1][2][3][4][5][6] Among the positive electrode materials for SIBs, layered oxides (NaTMO 2 , TM = transition metals) are most attractive due to their large capacity, simple synthesis, and structural stability. [7][8][9][10][11][12][13][14] Various transition metal elements can be substituted into the layered structure, similar to layered lithium compounds, and this will infl uence the structural stability of sodium-ion removal, operating voltage, capacity, and cyclability. In contrast to lithium systems, different stacking structures for Na layered oxides can be examined because of the preferred prismatic coordination of the larger sodium ions. Positive electrode materials with a P2 layered structure by Delmas' notation [ 15 ] have better cyclability and structural stability during electrochemical reactions than those with an O3 layered structure. [ 16 ] The trigonal prismatic site is more favorable for the diffusion of sodium ions, [17][18][19][20] and the diffusion kinetics for Na + can thus be more effi cient in the P2 layered structure compared to those in the O3 layered structure, which is common in lithium intercalation compounds. P2 layered materials with various transition metal compositions for SIBs have been studied, such as Mn-Co, Ni-Mn, and Fe-Mn. [ 9,17,[21][22][23][24][25] Moreover, several approaches for the doping of two-component P2 layered materials with transition metals have also been introduced, [ 8 ] including Co doping on Ni-Mn compounds, [ 26,27 ] Ni doping on Co-Mn systems, [ 28,29 ] and Ni doping on Fe-Mn system. [ 30 ] However, few studies on the Fe-Mn-Co system with P2 stacking have been reported compared to Ni-Fe-Mn or Ni-Co-Mn P2 materials. [ 31,32 ] Co can facilitate the oxidation of Fe atoms, as reported in Li compounds, [ 33 ] and Co can likely stabilize the oxidized state in the layered structure, especially for Fe-containing layered materials. [ 34 ] In addition, Wang et al. reported that Co suppresses the irreversibility of P2-Na 2/3 Mn y Co 1− y O 2 materials. [ 23 ] A similar behavior in the P2-Na-Fe-Co-Mn oxides would be expected.In this paper, P2-Na 0.7 [(Fe 0.5 Mn 0.5 ) 1− x Co x ]O 2 ( x = 0, 0.05, 0.10, and 0.20) was synthesized by a solid-state reaction, and the electrochemical performance of the P2-Fe-Mn-Co system Sodium layered oxides with mixed transition metals have received signifi cant attention as positive electrode candidates for sodium-ion batteries because of their high reversible capacity. The phase transformations of layered compounds during electrochemical reactions are a pivotal feature for understanding the relationship between layered structures and electrochemical properties. A combination of in situ diffraction and ex situ X-ray absorption spectroscopy reveals the phase t...

Na + /vacancy disordering promises high-rate Na-ion batteries

“…4A). It indicates that the c axis is expanding, and the ab plane is contracting because of increased electrostatic repulsion between adjacent oxygen layers and smaller ionic radius, respectively, by Ni 2+ →Ni 3+ ( 33 ). Noticing that no additional diffraction lines beyond the P2 structure are detected, the shape of the (004) peak becomes an asymmetry with a broad feature, which could be attributed to the rearrangement of different in-plane Na orderings ( 34 ).…”

Understanding sodium-ion diffusion in layered P2 and P3 oxides via experiments and first-principles calculations: a bridge between crystal structure and electrochemical performance

“…17,18 Owing to direct Na-ion diffusion and a more open framework, the original structure of the P2 phases is more easily preserved during the sodium extraction process, [19][20][21][22] although a partial P2-O2 phase transition is found in the literature. 23,24 In contrast, the O3 phase always transforms to the P3 phase via gliding of the MeO 2 slabs (1/3, 2/3, 0) that results from the presence of intermediate tetrahedral sites between two octahedral sites ( Figure 1). 25 As two main electrochemical products, the P2 and P3 phases have the same sodium accommodation as prismatic sites.…”

A comprehensive picture of the current rate dependence of the structural evolution of P2-Na2/3Fe2/3Mn1/3O2

“…This estimate also takes into account LIB recycling. [7][8][9][10][11][12] The sodium decient P2-phase and fully sodiated O3-phase, which are classied based on the oxygen layer stacking and the surrounding environment of sodium atoms, have been investigated and compared for their overall electrochemical performance. Consequently, much of the attention has shied towards the search for alternative storage systems.…”