Synthesis and Electrochemistry Study of P2- and O3-phase Na2/3Fe1/2Mn1/2O2

Electrochemical Performance and Ageing Mechanisms of Sol‐Gel Synthesized Na2/3[Mn3/5Fe2/5]O2 for Sodium‐Ion Batteries

“…The Nyquist plots of Na 2/3 [Mn 3/5 Fe 2/5 ]O 2 cycled in 2.0-4.2 V show two semicircles of which the semicircle at highmedium frequency can be ascribed to the parallel combination of resistance (R sf ) and capacitance (C sf ) due to surface film and the medium-low semicircle due to combination of chargetransfer resistance (R ct ) and double-layer capacitance (C dl ). Similar to our measurements, two semicircles were observed in a previous report for Na 2/3 Fe 1/2 Mn 1/2 O 2 measured after 1 st discharge to 2.0 V. [26] It can be seen that the electrodes initially exhibited high impedance due to surface film resistance as indicated from the diameter of 1 st semicircle. However, the impedance due to surface film decreased upon completing 100 cycles.…”

“…[24] The comparable structural environment for Mn and Fe indicated by the ELNES data is taken as good evidence for a spinel-structured secondary phase with magnetite and hausmannite components. We can exclude that the spinel-structured phase was produced as an artifact of electron beam damage, [27,28] because a time series of the O K edge taken under typical irradiation conditions shows that Na 2/3 [Mn 3/5 Fe 2/5 ]O 2 does not develop the sharp pre-peak of the oxygen K edge (at 530 eV) typical for spinel. The Mn/Fe ratio of the Na-poor phase is also not changed as compared to the pristine material suggesting that a spinel-structured MnÀFe oxide is formed, i. e. a solid solution of hausmannite (Mn 3 O 4 ) and magnetite (Fe 3 O 4 ).…”

Meso-Structure Controlled Synthesis of Sodium Iron-Manganese Oxides Cathode for Low-Cost Na-Ion Batteries

“…[13][14][15][16][17][18][19][20][21][22][23][24] The synthesis method strongly influences the meso-structure of the layered TM oxides. In reviewing the literature (Table I), [25][26][27][28][29][30][31][32][33][34][35][36] solid-state synthesis is the most frequently adopted method for Na x Fe 1-y Mn y O 2 . However, the meso-structure is difficult to control in solid-state synthesis since it entails mixing materials by either ball milling or hand grinding precursors followed by high temperature calcination, producing irregular or plate-like primary particles.…”

Novel Methods for Sodium‐Ion Battery Materials

“…The improved angular resolution and high‐intensity diffraction data are key parameters for the direct observation of fine reaction pathways in electrode materials and assist in the understanding of the (de)intercalation mechanisms in Na‐ion batteries . Na 2/3 Fe 2/3 Mn 1/3 O 2 can form two different phases, O3 and P2, with the same composition by utilizing modified raw materials and synthesis conditions, but with similar electrochemical performance . In order to study the relationship between the initial polymorphs and their phase transitions with the same Na concentration, time‐resolved in situ SXRD was used to investigate their structural evolution .…”