Pinning Effect Enhanced Structural Stability toward a Zero‐Strain Layered Cathode for Sodium‐Ion Batteries

Abstract

Layered oxides as the cathode materials of sodiumion batteries are receiving extensive attention due to their high capacity and flexible composition. However,t he layered cathode tends to be thermodynamically and electrochemically unstable during (de)sodiation. Herein, we propose the pinning effect and controllable pinning point in sodium storage layered cathodes to enhance the structural stability and achieve optimal electrochemical performance.0%, 2.5 %and 7.3 %transitionmetal occupancies in Na-site as pinning points are obtained in Na 0.67 Mn 0.5 Co 0.5Àx Fe x O 2 .2 .5 %N a-site pinned by Fe 3+ is beneficial to restrain the potential slab sliding and enhance the structural stability,r esulting in an ultra-low volume variation of 0.6 %a nd maintaining the smooth two-dimensional channel for Na-ion transfer.The Na 0.67 Mn 0.5 Co 0.4 Fe 0.1 O 2 cathode with the optimal Fe 3+ pinning delivers outstanding cycle performance of over 1000 cycles and superior rate capability up to 10 C.

Stabilizing Transition Metal Vacancy Induced Oxygen Redox by Co2+/Co3+ Redox and Sodium‐Site Doping for Layered Cathode Materials

“…Thei nitial galvanostatic charge and discharge (GCD) profiles of MCM-x (x = 0, 1, 2) at 0.1 C(1C= 170 mAh g À1 )between 1.6 and 4.4 Vare shown in Figure 2a.M CM-0 exhibits an initial charge/discharge capacities of 95.6/118.8 mAh g À1 .F or comparison, the specific capacities of MCM-1 and MCM-2 in the first cycle are 96.3/ Angewandte Chemie 144.3 mAh g À1 and 165.9/176 mAh g À1 ,r espectively.M gs ubstitution resulted in the reduction of the capacity below 4.25 V, owing to the dilution of the Co ions concentration with low valence that can be oxidized to higher valence during charging. [15] Interestingly,a sM gc ontent increased to 0.2, af lat voltage plateau with about 110 mAh g À1 in capacity appeared, which is generally considered as the contribution of oxygen redox, thus allowing more Na + extracted from MCM-2. GCD curves in the following cycles are shown in Figure 2b.…”

Synergetic stability enhancement with magnesium and calcium ion substitution for Ni/Mn-based P2-type sodium-ion battery cathodes

“…Here, we prefer to only consider the migration of nickel rather than manganese, since the migration of iron and nickel ions to the AM layers has been observed. 46–50 Meanwhile, our DFT calculation outcomes show that O2 structures with Ni migration are more stable than with Mn migration (Fig. S5 † ).…”

Stabilizing Transition Metal Vacancy Induced Oxygen Redox by Co2+/Co3+ Redox and Sodium‐Site Doping for Layered Cathode Materials

“…Thei nitial galvanostatic charge and discharge (GCD) profiles of MCM-x (x = 0, 1, 2) at 0.1 C(1C= 170 mAh g À1 )between 1.6 and 4.4 Vare shown in Figure 2a.M CM-0 exhibits an initial charge/discharge capacities of 95.6/118.8 mAh g À1 .F or comparison, the specific capacities of MCM-1 and MCM-2 in the first cycle are 96.3/ Angewandte Chemie Forschungsartikel 22198 www.angewandte.de 144.3 mAh g À1 and 165.9/176 mAh g À1 ,r espectively.M gs ubstitution resulted in the reduction of the capacity below 4.25 V, owing to the dilution of the Co ions concentration with low valence that can be oxidized to higher valence during charging. [15] Interestingly,a sM gc ontent increased to 0.2, af lat voltage plateau with about 110 mAh g À1 in capacity appeared, which is generally considered as the contribution of oxygen redox, thus allowing more Na + extracted from MCM-2. GCD curves in the following cycles are shown in Figure 2b.…”

“…For comparison, the specific capacities of MCM‐1 and MCM‐2 in the first cycle are 96.3/144.3 mAh g −1 and 165.9/176 mAh g −1 , respectively. Mg substitution resulted in the reduction of the capacity below 4.25 V, owing to the dilution of the Co ions concentration with low valence that can be oxidized to higher valence during charging [15] . Interestingly, as Mg content increased to 0.2, a flat voltage plateau with about 110 mAh g −1 in capacity appeared, which is generally considered as the contribution of oxygen redox, thus allowing more Na + extracted from MCM‐2.…”