Investigation of Valence Mixing in Sodium-Ion Battery Cathode Material Prussian White by Mössbauer Spectroscopy

At a Glance

Metadata	Details
Publication Date	2022-07-04
Journal	Frontiers in Energy Research
Authors	Tore Ericsson, Lennart Häggström, Dickson O. Ojwang, William R. Brant
Institutions	Uppsala University
Citations	7
Analysis	Full AI Review Included

Technical Documentation & Analysis: Prussian White Cathode Characterization

This document analyzes the research paper “Investigation of Valence Mixing in Sodium-Ion Battery Cathode Material Prussian White by Mössbauer Spectroscopy” and connects the experimental requirements and future applications to the advanced material solutions offered by 6CCVD (6ccvd.com), specialists in MPCVD Single Crystal (SCD) and Polycrystalline Diamond (PCD).

Executive Summary

Core Achievement: Accurate quantification of vacancy content and valence distribution (Fe²⁺/Fe³⁺ mixing) in Prussian White (PW) cathode material for Sodium-Ion Batteries (NIBs).
Methodology: Utilized Mössbauer spectroscopy performed at low temperatures (90 K) to suppress the rapid intervalence charge transfer (IVCT) that obscures room-temperature analysis.
Compositional Validation: The determined sum of iron valences successfully correlated with the sodium content derived from elemental analysis, providing a rigorous validation of the material composition.
Vacancy Confirmation: Analysis confirmed the absence of [Fe(CN)₆]^4- vacancies in the fully sodiated compound (x = 1.8) within experimental error limits.
Technical Value: This approach offers a crucial stepping stone toward rigorous characterization and optimization of iron-based Prussian Blue Analogs (PBAs) for high-performance electrochemical applications.
6CCVD Relevance: The need for high-stability electrochemical analysis and precise thermal management in advanced battery research directly necessitates the use of Boron-Doped Diamond (BDD) electrodes and high-purity SCD substrates.

Technical Specifications

The following hard data points were extracted from the research paper detailing the material properties and experimental conditions:

Parameter	Value	Unit	Context
Theoretical Capacity (PW)	~170	mAhg^-1	Sodium-Ion Battery Cathode Material
Average Voltage Output (PW)	~3.2	V	Comparable to LiFePO₄
Mössbauer Measurement Temperatures	295 and 90	K	Standard and Low-Temperature Analysis
Temperature Stability	< 1	°	Stability during cryogenic (90 K) measurement
Absorber Concentration	10	mg/cm²	PW powder mixed with BN
Nominal x-value (Na content)	1.8, 1.0, 0.5	-	Three different sample compositions investigated
Structural Parameter (x=1.8)	10.474 (1)	Å	Monoclinic P2₁/n, a-axis
Low-Spin Fe Center Shift (x=1.8, 90 K)	-0.094	mm/s	CS (I) for Fe_C²⁺
High-Spin Fe Center Shift (x=1.8, 90 K)	1.258	mm/s	CS (I) for Fe_N²⁺
High-Spin Fe Quadrupole Splitting (x=1.8, 90 K)	0.368	mm/s

Key Methodologies

The experiment focused on using temperature-dependent Mössbauer spectroscopy to resolve valence states in Prussian White:

Sample Preparation: Prussian White (PW) powder with three distinct sodium contents (x = 1.8, 1.0, 0.5) was synthesized.
Absorber Construction: PW powder was ground with Boron Nitride (BN) and sealed into aluminum pockets to achieve a concentration of 10 mg/cm² for Mössbauer analysis.
Spectroscopy Setup: Measurements utilized a constant acceleration vibrator and a ⁵⁷CoRh source. Calibration was performed at 295 K using natural Fe metal foil.
Cryogenic Measurement: Spectra were recorded at 295 K and 90 K using an Oxford gas flow cryostat to observe better-resolved spectra by suppressing intervalence charge transfer (IVCT).
Data Fitting: Spectra were fitted using the least-square Mössbauer fitting program Recoil to determine key parameters (Center Shift, Quadrupole Splitting, Line Width, and Spectral Intensities).
Valence Quantification: Valence distribution was determined by analyzing the linear shift of the isomer shift values for the low-spin Fe_C site, assuming a linear relationship between Fe²⁺ and Fe³⁺ shifts.

6CCVD Solutions & Capabilities

The rigorous characterization and optimization of advanced electrochemical materials like Prussian White require substrates and electrodes with extreme stability, purity, and thermal performance—areas where 6CCVD’s MPCVD diamond materials excel.

Applicable Materials

To replicate or extend this research into functional devices or advanced in-situ characterization, 6CCVD recommends the following materials:

Boron-Doped Diamond (BDD): Essential for high-stability electrochemical testing. BDD electrodes offer an exceptionally wide potential window and chemical inertness, ideal for analyzing the long-term stability and degradation pathways of PW cathodes in aggressive NIB electrolytes.
Optical Grade Single Crystal Diamond (SCD): Recommended for use as windows or substrates in advanced spectroscopic setups (e.g., in-situ Mössbauer or Raman analysis). SCD provides superior thermal conductivity, ensuring precise temperature control (critical for the 90 K measurements) and high optical transparency.
Polycrystalline Diamond (PCD) Substrates: Ideal for thermal management in high-power battery testing rigs or integrated sensor packages, ensuring reliable operation and heat dissipation during high-rate cycling tests.

Customization Potential

The complexity of advanced battery research often requires unique geometries and integration methods. 6CCVD provides comprehensive customization capabilities:

Research Requirement	6CCVD Customization Service	Technical Benefit
Specialized Electrode Contacts	Custom Metalization	Internal capability for depositing Au, Pt, Pd, Ti, W, and Cu layers, enabling precise electrical contacts for electrochemical cells or sensor integration onto diamond substrates.
Unique Sample Dimensions	Custom Dimensions & Shaping	We supply plates/wafers up to 125mm (PCD) and custom SCD/PCD thicknesses (0.1µm to 500µm), allowing researchers to design bespoke electrochemical or spectroscopic cells.
Ultra-Smooth Interfaces	Precision Polishing	SCD wafers are polished to Ra < 1nm, and inch-size PCD is polished to Ra < 5nm, critical for minimizing surface defects and ensuring optimal thin-film deposition or sensor performance.
Substrate Thickness Control	Thickness Control (0.1µm to 10mm)	SCD and PCD can be provided in precise thicknesses, from thin films (0.1µm) for low-mass applications to robust substrates (up to 10mm) for structural support.

Engineering Support

6CCVD’s in-house PhD team specializes in applying diamond materials to challenging engineering problems, including advanced electrochemistry and high-power electronics. We can assist researchers in selecting the optimal BDD doping level, SCD orientation, and metalization scheme required for similar Sodium-Ion Battery Cathode Characterization projects, ensuring material properties align perfectly with experimental demands.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Prussian white (PW), Na 2 Fe [Fe(CN) 6 ], is a highly attractive cathode material for sustainable sodium-ion batteries due to its high theoretical capacity of ∼170 mAhg −1 and low-cost synthesis. However, there exists significant variability in the reported electrochemical performance. This variability originates from compositional flexibility possible for all Prussian blue analogs (PBAs) and is exasperated by the difficulty of accurately quantifying the specific composition of PW. This work presents a means of accurately quantifying the vacancy content, valence distribution, and, consequently, the overall composition of PW via Mössbauer spectroscopy. PW cathode material with three different sodium contents was investigated at 295 and 90 K. The observation of only two iron environments for the fully sodiated compound indicated the absence of [Fe(CN) 6 ] 4- vacancies. Due to intervalence charge transfer between iron centers at 295 K, accurate determination of valences was not possible. However, by observing the trend of spectral intensities and center shift for the nitrogen-bound and carbon-bound iron, respectively, at 90 K, valence mixing between the iron sites could be quantified. By accounting for valence mixing, the sum of iron valences agreed with the sodium content determined from elemental analysis. Without an agreement between the total valence sum and the determined composition, there exists uncertainty around the accuracy of the elemental analysis and vacancy content determination. Thus, this study offers one more stepping stone toward a more rigorous characterization of composition in PW, which will enable further optimization of properties for battery applications. More broadly, the approach is valuable for characterizing iron-based PBAs in applications where precise composition, valence determination, and control are desired.

Tech Support

Original Source

DOI: https://doi.org/10.3389/fenrg.2022.909549

References

2022 - Octahedral Tilting in Prussian Blue Analogues [Crossref]
2019 - Selective Control of Composition in Prussian White for Enhanced Material Properties [Crossref]
2018 - Synthesis of Low Vacancies PB with High Electrochemical Performance Using a Facile Method [Crossref]
2018 - Prussian Blue Analogs as Battery Materials [Crossref]
2008 - Magnetic and Optical Bistability Driven by Thermally and Photoinduced Intramolecular Electron Transfer in a Molecular Cobalt−Iron Prussian Blue Analogue [Crossref]
2019 - Novel Acetic Acid Induced Na-Rich Prussian Blue Nanocubes with Iron Defects as Cathodes for Sodium Ion Batteries [Crossref]
2020 - Performance and Degradation of LiFePO4/Graphite Cells: The Impact of Water Contamination and an Evaluation of Common Electrolyte Additives [Crossref]
2006 - Heat-induced Charge Transfer in Cobalt Iron Cyanide [Crossref]
2020 - Influence of Sodium Content on the Thermal Behavior of Low Vacancy Prussian White Cathode Material [Crossref]
2021 - Moisture-Driven Degradation Pathways in Prussian White Cathode Material for Sodium-Ion Batteries [Crossref]