Understanding Challenges of Cathode Materials for Sodium‐Ion Batteries using Synchrotron‐Based X‐Ray Absorption Spectroscopy

Abstract

An in-depth understanding of the electrochemical behavior of cathode materials in a complex chemical environment is critical for the development of state-of-the-art sodium-ion batteries. Advanced synchrotron-based characterization is a powerful tool for collecting valuable information on complicated reaction mechanisms. X-ray absorption spectroscopy can be used to precisely monitor the valence state and corresponding changes during cycling of various elements. Information on the local structure, such as coordination number and bond information can also be extracted from the fitting data in Fourier transform extended X-ray absorption fine structure. In this review, we summarize findings on state-of-the-art cathode materials using ex-situ/in-situ X-ray absorption spectroscopy to probe fundamental discoveries on sodium-ion battery systems and what important and valuable results have been obtained. Further possible improvements and practical operating advice are also discussed in detail. . (a) Crystal structure of Na 3 V 2 (PO 4 ) 2 F 3 with space group Amam. (b) V K-edge XANES spectra at C/10. Reprinted with permission from (a) to (b). [51] Copyright 2017American Chemical Society. (c) Crystal structure of ɛ-VOPO 4 and corresponding charge/discharge curve. V K-edge in-situ XAS spectra of Mo 0.05 V 0.95 OPO 4 for (d) high-voltage discharge and (e) low-voltage discharge.

Probing the charged state of layered positive electrodes in sodium-ion batteries: reaction pathways, stability and opportunities

“…Both ex situ and in situ studies have been carried out on sodium-ion battery systems. 264 Recently, Wang et al studied a P2-type layered material with composition Na 2/3 Zn 1/4 Mn 3/4 O 2 in which the unfavourable P2-O2 transition is suppressed, which signicantly improves the cycling stability and rate capability of the Na x MnO 2 system. 265 In situ XRD conrmed that the transitions were suppressed during cycling to 4.5 V. The authors coupled this with in situ XAS studies to investigate the inuence of Zn-doping on the electronic structure of the material.…”

Designing Advanced Vanadium‐Based Materials to Achieve Electrochemically Active Multielectron Reactions in Sodium/Potassium‐Ion Batteries

“…[ 178 ] The in situ XANES evolution indicates a progressive distortion of the local symmetry with 3d−2p orbital mixing (Figure 14k,l). [ 196 ] In addition, their 51 V MAS NMR results further confirmed the presence of the diamagnetic V 4+ ions. Hu et al.…”

A Cation and Anion Dual Doping Strategy for the Elevation of Titanium Redox Potential for High‐Power Sodium‐Ion Batteries

“…It can be seen that this material is crystallized in acubic symmetry with the space group (P2 1 3, No.1 98), which is very rare and quite interesting among all the polyanionic-based compounds. [39,51,52] Thes turdy 3D open channel framework is made up of linked trimers of PO 3 Ntetrahedra with acentral Na tom, and either TiO 6 or VO 6 octahedra connected with shared Oa toms.T he corresponding illustration is shown in Figure 1b.T he participation of Na toms in the crystal structure of Na 3 Ti 0.5 V 0.5 (PO 3 ) 3 Nresults in both high symmetry and as trong inductive effect between the adjacent V/Ti atoms. [22] Thet hermal stability of the NTVN sample was clearly revealed through thermogravimetric analysis.F rom Figure 1c,t he NTVN precursor stabilized above 642.7 8 8Cw ith aw eight loss of 20.83 %o ft he total initial weight, and the sintered NTVN sample only underwent asmall 4.43 %weight loss,e ven when heated in air.T he surface information was characterized via X-ray photoelectron spectroscopy (XPS).…”