Enhancing the Electrochemical Performance of NaCrO₂through Structural Defect Control

Abstract

This study clarifies, for the first time, that misplacement of Cr3+ ions at the Na+ site plays a more important role in dictating the specific capacity and capacity retention over cycles of O3-NaCrO2 cathodes than the Na–O bond length and the NaO2 interlayer spacing do. It is shown that O3-NaCrO2 crystals with a lower degree of misplacement of Cr3+ ions at Na sites and a longer Na–O bond length have higher specific capacity, better capacity retention, and smaller cell impedance. Furthermore, O3-NaCrO2 crystals with a high degree of cation mixing at the Na plane exhibit the formation of some monoclinic O′3-NaCrO2 crystals over 300 charge/discharge cycles between NaCrO2 and Na0.5CrO2 formulas, whereas the rhombohedral structure of O3-NaCrO2 crystals with a low degree of cation mixing at the Na plane is fully reversible. The effects of structural defects discovered in this study are interpreted based on the interference of Cr ions in Na transport on the Na plane and gradual migration of Cr ions to the Na plane during cycles. The insights established in this study will provide guidance in rational design and synthesis of NaCrO2 cathode materials with high specific capacity and long-term cycle stability in the future.

Incommensurately modulated crystal structure of α′ (O′3)-type sodium cobalt oxide Na x CoO2 (x ∼ 0.78)

“…Similar JT distortion is also realized for MnO 6 octahedron in Na 0.93 MnO 2 (Ma et al, 2011), although no detailed structure data was reported. Similarly, no detailed structure data is available for Na x CrO 2 (Luo et al, 2020, Bo et al, 2015. It appears that all these phases have relatively narrow compositionally and thermodynamically stable regions.…”

On the Electrochemical Properties of Carbon-Coated NaCrO2 for Na-Ion Batteries

“…NaCrO 2 , as a promising cathode material for use in Na-ion batteries (NIBs), has been studied extensively [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. One of the important advantages of NaCrO 2 is its high thermal stability and thus good safety [3].…”

“…This irreversible capacity loss has been attributed to the irreversible migration of Cr ions from the octahedral sites in CrO 2 slabs to both tetrahedral and octahedral sites in the Na layer [5,9]. Unfortunately, even for deintercalation of 0.5 moles of Na ions from NaCrO 2 to Na 0.5 CrO 2 , the specific capacity still displays gradual decay over cycles [5,8,[11][12][13][14][15][16][17][18][19], indicating the presence of capacity decay mechanisms even when de/intercalation are between NaCrO 2 and Na 0.5 CrO 2 .…”

“…To minimize the capacity decay of O3-NaCrO 2 , multiple strategies have been studied [7,[11][12][13][14][15][16][17][18][19]. Carbon coating is one of the strategies studied [7,14].…”

Synergistic Engineering of Defects and Architecture in a Co@Co3O4@N-CNT Nanocage toward Li-Ion Batteries and HER

“…Many factors, such as morphology, − crystallinity, − surface porosity, − and defects, − are proven and can affect electrochemical properties and HER activity. A defect engineering strategy can increase electrical conductivity and then accelerate the electron transport. − Wang and his group concentrated on Co 3 O 4– x bubbles with engineered defects and obtained superior durable hybrid Zn-ion batteries and oxygen evolution/reduction (OER/ORR) reactions.…”