N3 PHINIX diffraction data from IDONANO helped a Peking University research group publish high-level research results in *Advanced Functional Materials*—precise control of interlayer spacing unlocks the secrets of sodium electrolysis.
Recently, Professor Xiao Yingguo's research group at Peking University Shenzhen Graduate School published their latest research findings in *Advanced Functional Materials*, a top international journal in the field of materials science. The paper, titled "Enhancing the Reversibility of Phase Transition and Anionic Redox Chemistry in O3-Type Sodium-Ion Oxide Cathodes via Precise Alkali-Metal Layer Spacing Modulation," focuses on high-voltage layered oxide cathode materials for sodium-ion batteries and proposes a novel approach to improve the reversibility of phase transitions and anionic redox reactions by precisely controlling the alkali metal interlayer spacing.
More notably, in this work, the research group used an IDONÅNO N3 PHINIX diffractometer to collect XRD data of the samples and combined this with various characterization methods, including neutron diffraction, in-situ XRD, and XAS, to systematically reveal the intrinsic connection between material structure evolution and the improvement of electrochemical performance.
The supplementary materials of the paper clearly state that the XRD patterns of S-Na₁, S-Na₀.₉, S-Na₀.₈, S-Na₀.₇₅, and the control sample NNM were all tested at room temperature using an IDONÅNO N3 PhiniX diffractometer.
Focusing on the challenges of sodium-ion batteries: the "structural costs" behind high capacity
Sodium-ion batteries are considered an important candidate for next-generation energy storage systems due to their abundant resources and cost-effectiveness. However, for O3-type layered oxide cathodes, the materials often face two core bottlenecks at high voltages: firstly, the anion redox reaction is irreversible; secondly, complex phase transitions lead to structural instability. These two problems further induce cation migration, increased interfacial impedance, and rapid capacity decay, thus limiting the practical application potential of the materials. To address this challenge, the Peking University team did not simply rely on surface coating or limiting the cutoff voltage. Instead, they started from the intrinsic structure of the material and proposed altering the interlayer spacing and redox behavior by controlling the initial sodium content. The study focused on a series of O3-type materials, with particular emphasis on comparing two representative samples: S-Na₁ and S-Na₀.₈.
**N3 PHINIX Diffraction Data: Providing Key Support for Structural Determination**
In this work, XRD is the starting point for establishing the "composition-structure-property" correlation. The research team first obtained high-quality diffraction data using an Åndoma N3 PHINIX diffractometer and then performed Rietveld refinement to confirm the differences in crystal structure among samples with different initial sodium contents.
Supplementary materials show that as the initial Na content decreases, the c-axis parameter of the sample gradually increases. Specifically, the c-axis length of S-Na₁ is approximately 16.003 Å (Table S3), while that of S-Na₀.₈ increases to 16.211 Å (Table S5), indicating that reducing the sodium content effectively widens the interlayer spacing. The paper further points out that S-Na₁, S-Na₀.₉, and S-Na₀.₈ can all be indexed as pure O₃ phases with R-3m symmetry, while S-Na₀.₇₅ exhibits P₂/O₃ dual-phase characteristics. This suggests that S-Na₀.₈ represents a key low-sodium content window for maintaining a pure O₃ phase, and also identifies the optimal composition range for subsequent performance optimization.
For materials research, this type of high-quality diffraction data is not only used to "prove the existence of the phase," but more importantly, it establishes a reliable structural baseline for subsequent neutron diffraction, in-situ phase transition analysis, and electrochemical mechanism studies. It can be said that the precise diffraction results provided by N3 PHINIX are one of the important foundational pieces of evidence for this high-level paper.
Figure 1: XRD data of S－Na₁,Na₀.₉, S－Na₀.₈ and Na₀.₇₅ measured by N3 PhiniX and their Rietveld refinement results. Taking S-Na₁ to S-Na₀.₈ of the same phase as an example, as the initial Na content decreases, the c-axis parameter of the material increases from approximately 16.003 Å to 16.211 Å, indicating that the interlayer spacing is effectively controlled, providing a structural basis for subsequent improvements in the reversibility of high-pressure phase transitions and electrochemical performance.
From Structural Control to Performance Leap: S-Na₀.₈ Stands Out
Based on structural optimization, the research group found that samples with lower initial sodium content exhibit significantly better electrochemical performance. The paper shows that the optimized S-Na₀.₈ sample achieved an initial discharge capacity of 174 mAh g⁻¹ at 0.2C (30 mA g⁻¹), maintaining 161 mAh g⁻¹ after 100 cycles, with a capacity retention of 92.5%. After 200 cycles at 1C (150 mA g⁻¹), the capacity retention remained as high as 86.7%.
More importantly, compared to S-Na₁, the initial coulombic efficiency (ICE) of S-Na₀.₈ was significantly improved from 74.3% to 96.2%, indicating that irreversible reactions during high-voltage operation were significantly suppressed. In full-cell testing (using pre-sodium-modified hard carbon as the negative electrode), S-Na₀.₈ also performed exceptionally well: achieving an initial capacity of 154 mAh g⁻¹, and maintaining 81.8% capacity retention after 200 cycles, demonstrating excellent application potential. In contrast, the control sample S-Na₁ only maintained 26.7% capacity retention after 200 cycles, clearly demonstrating superior performance.
The optimized S-Na₀.₈ outperformed S-Na₁ and S-Na₀.₉ in capacity, coulombic efficiency, and long-cycle stability, maintaining its leading position in full-cell performance and showcasing excellent potential for high-pressure sodium storage applications.
**Mechanism Breakthrough: Not Simply "Less Sodium," but Reshaping the High-Pressure Reaction Pathway**
The highlight of this work lies not only in its superior performance but also in its highly complete explanation of the mechanism. In-situ XRD results show that S-Na₁ readily undergoes a significant high-voltage phase transition during charging, forming the OP2 phase, accompanied by substantial interlayer shrinkage and a c-axis change of up to 7.9%. In contrast, S-Na₀.₈ shows only a small amount of the OP2 phase, with a c-axis change of only 2.1% during charging, indicating significantly stronger structural reversibility.
dQ/dV and XAS analyses further demonstrate that a higher initial sodium content causes anion redox to initiate earlier (approximately 3.8 V), thus interrupting the complete oxidation of Ni and inducing more severe lattice slip and structural damage. In S-Na₀.₈, the Ni oxidation process is more complete, and anion redox is delayed until a higher voltage (approximately 4.1 V), resulting in a milder and more reversible overall reaction pathway. In short, this research is not as simple as "adding less sodium," but rather, by controlling the initial Na stoichiometry, it precisely adjusted the interlayer spacing, electronic structure, and redox sequence, ultimately achieving a balance between high capacity and high stability.
**Behind the High-Level Achievements: Support from an Advanced Characterization Platform**
This paper shows that current high-level battery material research increasingly relies on a characterization system that is "multi-scale, multi-method, and strongly correlated." The Peking University team, through a deep integration of experimental design and mechanism analysis, successfully answered the key scientific question of "why S-Na₀.₈ is superior."
The stable, reliable, and high-resolution structural data provided by the Åndoma N3 PHINIX diffractometer played a crucial role in sample phase determination, lattice parameter refinement, and structural evolution studies. This diffractometer employs Cu Kα radiation, boasting high angular resolution and rapid acquisition capabilities, making it ideal for precisely capturing minute lattice variations in layered materials.
For the instrument platform, this achievement further demonstrates that high-quality diffraction data not only serves routine phase analysis but can also become the starting point for elucidating mechanisms in high-level papers. From confirming the basic structure to cross-validating with neutron diffraction and in-situ characterization, the value of XRD data is being continuously amplified.
Conclusion
The research published in *Advanced Functional Materials* by the Peking University research group provides new insights into the high-voltage stabilization of O3-type sodium-ion battery cathode materials and demonstrates the core value of advanced diffraction characterization in cutting-edge materials research. From posing the scientific question to establishing structural evidence, and then to the complete closed loop of performance and mechanism, this achievement not only demonstrates the research group's profound research strength but also highlights the application potential of the Åndoma N3 PHINIX diffractometer in high-end materials characterization.
The birth of high-level results is inseparable from innovative thinking and solid, reliable data support. This is precisely the true value of advanced scientific instruments.
*Data Source Statement: The data cited in this article are all from Li, J. et al., Adv. Funct. Mater. 2026, 16163028, Supplementary Material No. adfm75315-sup-0001-suppmat.docx.*
