Ultralow-strain Ti substituted Mn-vacancy layered oxides with enhanced stability for sodium-ion batteries

Enhanced oxygen redox reversibility and capacity retention of titanium-substituted Na4/7[□1/7Ti1/7Mn5/7]O2 in sodium-ion batteries

“…21 By contrast, Na 4/7 [□ 1/7 Ti 1/7 Mn 5/7 ]O 2 reveals superior cycling stability at 10 and 100 mA g −1 , maintaining 77% and 65%, respectively, of its initial discharge capacity after 50 cycles, showing that Ti-substitution improves the reversibility and cycling performance, consistent with data reported for Na 4/7 [□ 1/7 Ti 1/7 Mn 5/7 ]O 2 by Liu et al and other Ti-substituted materials. 26,27,29,34–41…”

“…1(a)) to a structure which can be well-described in R3m symmetry, demonstrating that the P3 oxygen stacking sequence is preserved (Table S5 †), consistent with the structural evolution observed for Na 4/7 [, 1/7 Mn 6/7 ]O 2 . 22,29 Furthermore, Na 4/7 [, 1/7 Ti 1/7 Mn 5/7 ]O 2 shows a minimal volume contraction of $0.6%. Upon subsequent Na + ion insertion, the PXRD pattern aer discharge to 3.0 V can effectively be modelled using the P 1 space group (Fig.…”

“…27 These results show that Ti-substitution is a proven method to stabilise the structure, smooth the charge/discharge prole, elevate the working potential, and improve the cycling stability. [26][27][28] Liu et al, have recently reported a superior cycling stability 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 within 1.5-4.6 V at 50 mA g À1 , negligible volume change (0.11%) during charge/discharge and no irreversible O 2 evolution upon charge to 4.6 V. 29 The present study aims to understand the role of Ti-substitution on the charge compensation mechanism of Na 1(a) and the results are given in Table S1. † Similarly, the diffraction peaks of the laboratory PXRD pattern of assynthesised Na 4/7 [, 1/7 Mn 6/7 ]O 2 can be indexed using the same model (P 1), as shown in Fig.…”

“…Liu et al , have recently reported a superior cycling stability 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 within 1.5–4.6 V at 50 mA g −1 , negligible volume change (0.11%) during charge/discharge and no irreversible O 2 evolution upon charge to 4.6 V. 29 The present study aims to understand the role of Ti-substitution on the charge compensation mechanism of Na 4/7 [□ 1/7 Mn 6/7 ]O 2 . Herein, we report that Ti-substituted Na 4/7 [□ 1/7 Ti 1/7 Mn 5/7 ]O 2 shows a remarkable improvement over Na 4/7 [□ 1/7 Mn 6/7 ]O 2 for both cation and anion redox stability: for a wide voltage range (1.6–4.4 V) over which both cation (Mn 3+ /Mn 4+ ) and anion (O 2− /O 2 n − ) redox reactions are activated, Na 4/7 [□ 1/7 Ti 1/7 Mn 5/7 ]O 2 delivers higher operating potential, reversible capacity (167 mA h g −1 ), and greater capacity retention of 88% than Na 4/7 [□ 1/7 Mn 6/7 ]O 2 with a lower reversible capacity of 143 mA h g −1 and capacity retention of 76% after 25 cycles at 10 mA g −1 .…”

“…2 This journal is © The Royal Society of Chemistry 2022 maintaining 77% and 65%, respectively, of its initial discharge capacity aer 50 cycles, showing that Ti-substitution improves the reversibility and cycling performance, consistent with data reported for Na 4/7 [, 1/7 Ti 1/7 Mn 5/7 ]O 2 by Liu et al and other Ti-substituted materials. 26,27,29,[34][35][36][37][38][39][40][41] In order to separate the effect of Ti-substitution on oxygen anionic redox from the combined cation and anion redox reactions, cells of Na 4/7 [, 1/7 Mn 6/7 ]O 2 and Na 4/7 [, 1/7 Ti 1/7 Mn 5/7 ]O 2 were cycled galvanostatically between 3.0 and 4.4 V where only oxygen redox couples become active. Fig.…”