Probing the effect of Mg doping on triclinic Na2Mn3O7 transition metal oxide as cathode material for sodium-ion batteries

Mg Substitution Induced TM/Vacancy Disordering and Enhanced Structural Stability in Layered Oxide Cathode Materials

“…Two strong and one weak diffusion minima appear in the plot for the normalized diffusion coefficient, corresponding to the O 2–/ n – at ∼4.2 V, Mn 3+/4+ at ∼2.1 V, and Na + /□ ordering at ∼3.5 V, respectively (Figure S9). However, no such a valley is observed for the Na + /□ ordering in NMMO (Figure S9, inset). The absence of the Na + /□ ordering is beneficial for the Na + diffusion .…”

“…For instance, the P1̅-type layered oxide Na 2 Mn 3 O 7 (Na 4/7 [Mn 6/7 □ 1/7 ]­O 2 , □ for the native vacancies in the TM layer) exhibits an obvious oxygen oxidation with negligible voltage hysteresis. , This is contrary to the common perception that the oxygen oxidation cathode materials usually show a large voltage hysteresis, signifying the voltage fade and irreversible process . However, its rate performance is still poor and the capacity retention is low when it is cycled in a wide range of potential . A new O3 phase is generated at ∼1.6 V and results in a 1.5% volume expansion …”

Modulation of Local Charge Distribution Stabilized the Anionic Redox Process in Mn-Based P2-Type Layered Oxides

“…To further investigate the kinetics and polarization processes of NLZMO materials during charge–discharge cycles, the galvanostatic intermittent titration technique (GITT) was used to calculate the chemical diffusion coefficient ( D x ) of Na + in different charged–discharged states. Figure a,b shows the GITT curves of NLZMO for the first two charge–discharge cycles at a constant current density of 10 mA g –1 in a voltage range of 1.5–4.6 V with a pulse time of 30 min and a relaxation time of 4 h. Fick’s second law can be used to obtain the corresponding diffusion coefficients, and the diffusion coefficients of Na + in different charge–discharge states can be calculated using the following equation: D Na + = 4 π τ true( italicm normalB italicV normalM italicM normalB italicA true) 2 true( normalΔ italicE normals τ false( normald italicE τ / normald τ false) true) 2 , false( τ ≪ italicL 2 / italicD normalNa + false) …”

Anionic Redox Chemistry for Sodium-Ion Batteries: Mechanisms, Advances, and Challenges

“…In Figure a of the annular bright-field scanning transmission electron microscopy image (ABF-STEM), Mn and Mg in TM layer are arranged in honeycomb ordering, where Mg sits in the center of the honeycomb and is surrounded by Mn. Since the Mg–O bond is ionic and similar to Li–O bond in the Li–O–Li configuration, O 2p states are located near the Fermi level with the formation of nonbonding O 2p states. , The charge and discharge curves with specific capacity of ∼160 mAh g –1 are shown in Figure b. The X-ray absorption near-edge spectroscopy (XANES) of Mn K-edge shows no shift during charge, indicating that Mn is not involved for charge compensation.…”

“…As shown in Figure 4c, Mn is tetravalent in the pristine P3- Bruce's group prepared P2-NMMO cathode to verify the origin of extra capacity. 32 In Figure 5a 74,75 The charge and discharge curves with specific capacity of ∼160 mAh g −1 are shown in Figure 5b. The X-ray absorption near-edge spectroscopy (XANES) of Mn K-edge shows no shift during charge, indicating that Mn is not involved for charge compensation.…”