Direct Observation of Alternating Octahedral and Prismatic Sodium Layers in O3‐Type Transition Metal Oxides

Abstract

The oxygen stacking of O3-type layered sodium transition metal oxides (O3-NaTMO2) changes dynamically upon topotactic Na extraction and reinsertion. While the phase transition from octahedral to prismatic Na coordination that occurs at intermediate desodiation by TM slab gliding is well understood, the structural evolution at high desodiation, crucial to achieve high reversible capacity, remains mostly uncharted. In this work, the phase transitions of O3-type layered NaTMO2 at high voltage are investigated by combining experimental and computational approaches. We directly observe an OP2-type phase that consists of alternating octahedral and prismatic Na layers by in situ X-ray diffraction and high-resolution scanning transmission electron microscopy. The origin of this peculiar phase is explained by atomic interactions involving Jahn-Teller active Fe 4+ and distortion tolerant Ti 4+ that stabilize the local Na environment. We also rationalize the path-dependent desodiation and resodiation pathways in this material through the different kinetics of the prismatic and octahedral layers, presenting a comprehensive picture about the structural stability of the layered materials upon Na intercalation.

Efficient Stabilization of Na Storage Reversibility by Ti Integration into O′3-Type NaMnO 2

“…Broad diffraction lines observed for the O1 phase suggest the presence of stacking faults along the c-axis direction. For other O3 phases, e.g., Na y Ni 1/3-Fe 1/3 Mn 1/3 O 2[46] and Na y Ti 0.25 Fe 0.25 Co 0.25 Ni 0.25 O 2[47], the formation of an OP2 phase (a sequence of ABCA), which contains alternating octahedral and prismatic sites for sodium ion layers, is evidenced. This phase is regarded as the intergrown layered material of P3-and O1-type structures.…”

Selection of Sodium Salt Electrolyte Compatible with Na0.67Ni0.15Fe0.2Mn0.65O2 Cathode for Sodium‐Ion Batteries

“…The reasons for the phase transition can be summarized as follows: 1) the slip of the TM layer, [ 35 ] 2) the transformation of Na + vacancy ordering, [ 36 ] and 3) the Jahn–Teller effect. [ 23 ] Compared with the NaClO 4 ‐based cell, the plateau in the NaPF 6 ‐based cell is shorter and the polarization is smaller. It indicates an alleviated effect of phase transition for NaPF 6 ‐based cells.…”

“…[22] Owing to the strong corrosiveness of NaTFSI to the current collector, most literatures have used NaPF 6 and NaClO 4 as sodium salt in electrolytes to study various properties of cathode materials. [23][24][25][26][27][28][29] For example, researchers have used NaPF 6 -and NaClO 4 -based electrolytes to study the degradation mechanism of layered cathode materials, respectively. [19,31] However, there are few comparative studies about specific mechanism of these two commonly used electrolytes on cathode surface.…”

Recent Advances in Heterostructured Anode Materials with Multiple Anions for Advanced Alkali‐Ion Batteries

“…Density functional theory (DFT) calculations have been adopted to provide an atomistic explanation of the enhancement of electrochemical kinetics. [91][92][93][94][95] As shown in the band diagram in Figure 2a-c, the conduction and valence band energy levels of materials can be calculated; their difference triggers electron flow in one direction, resulting in built-in electric field at the interface (Figure 2d), which facilitates electron transport. [96] A study by Wang et al theoretically calculated the adsorption energy between alkali-ions and host materials (Co 0.85 Se and S-doped Co 0.85 Se).…”