Enhanced oxygen redox reversibility and capacity retention of titanium-substituted Na_4/7[□_1/7Ti_1/7Mn_5/7]O₂ in sodium-ion batteries

Abstract

Anion redox reactions offer a means of enhancing the capacity of layered sodium transition metal oxide positive electrode materials. However, oxygen redox reactions typically show limited reversibility and irreversible structural...

Exploiting anion and cation redox chemistry in lithium-rich perovskite oxalate: a novel next-generation Li/Na-ion battery electrode

“…The optical cell (EL-Cell) was assembled and sealed inside an Ar-filled glovebox to avoid air exposure. 23 Further, the pellet electrodes were assembled to perform after cycling charge/discharge X-ray photoelectron spectroscopy (XPS). The XPS data were recorded using a Scienta X-ray photoelectron spectrometer with a monochromatic source.…”

Effect of Ti‐Substitution on the Properties of P3 Structure Na2/3Mn0.8Li0.2O2 Showing a Ribbon Superlattice

“…[16] In addition, Linnell et al revealed no capacity loss for Na 4/7 [ &1/7 Ti 1/7 Mn 5/7 ]O 2 over the voltage range 3.0-4.4 V at 10 mA g À 1 after 50 cycles, whilst Na 4/7 [& 1/7 Mn 6/7 ]O 2 retained only 82 % of its initial discharge capacity, arising from the low electronegativity of Ti that increases the MnÀ O bond strength. [17] Moreover, Na 4/7 [& 1/7 Ti 1/7 Mn 5/7 ]O 2 operates at a higher potential owing to the low electronegativity of Ti which stabilizes the adjacent O 2p orbitals, as evidenced by DFT calculations. [17] These results demonstrate that Ti-substitution is an effective method to stabilize the structure, increase the charge/discharge voltage and enhance the cycling stability for Na 4/7 [& 1/7 Mn 6/7 ]O 2 .…”

“…[17] Moreover, Na 4/7 [& 1/7 Ti 1/7 Mn 5/7 ]O 2 operates at a higher potential owing to the low electronegativity of Ti which stabilizes the adjacent O 2p orbitals, as evidenced by DFT calculations. [17] These results demonstrate that Ti-substitution is an effective method to stabilize the structure, increase the charge/discharge voltage and enhance the cycling stability for Na 4/7 [& 1/7 Mn 6/7 ]O 2 .…”

“…In comparison, Oxy-Na 0.67 Li 0.2 Ti 0.15 Mn 0.65 O 2 main- ChemElectroChem tains 75 % of its initial discharge capacity (187.9 mA h g À 1 ) after 50 cycles, thereby demonstrating the stabilizing role of Ti 4 + -substitution on the cycling performance, consistent with other Ti 4 + -substituted systems. [16,17,[23][24][25] Cao et al [31] reported enhanced performance in P2-Na 0.66 Li 0.22 Ti 0.15 Mn 0.63 O 2 with a honeycomb ordering and assigned this to a reduction in Jahn-Teller distortion on cycling whilst Li et al [25] also reported the effects of Ti 4 + -substitution in P2-Na x Li y Mn 1À y O 2 . They used EPR to suggest that anisotropic coupling between Mn 4 + and O 2 nÀ in the Li doped material is reduced by co-doping thereby enhancing reversibility.…”

“…[12,13] Partial substitution of Mn with Ti has proven to be an effective method to enhance the cycling performance of Na 4/7 [& 1/7 Mn 6/7 ]O 2 . [16,17] Liu et al reported a superior capacity retention of 79 % for Na 4/7 [& 1/7 Ti 1/7 Mn 5/7 ]O 2 compared with 17 % for Na 4/7 [& 1/7 Mn 6/7 ]O 2 between the voltage range 1.5-4.6 V at 50 mA g À 1 over 60 cycles and a ultralow volume change of 0.11 % upon initial charge/discharge. [16] In addition, Linnell et al revealed no capacity loss for Na 4/7 [ &1/7 Ti 1/7 Mn 5/7 ]O 2 over the voltage range 3.0-4.4 V at 10 mA g À 1 after 50 cycles, whilst Na 4/7 [& 1/7 Mn 6/7 ]O 2 retained only 82 % of its initial discharge capacity, arising from the low electronegativity of Ti that increases the MnÀ O bond strength.…”