Performance criteria and structure refinement of LiNi 0.8 Mn 0.1Co 0.1O2 (NMC 811)

Significance of the topic

LiNi0.8Mn0.1Co0.1O2 (NMC 811) is a leading high-energy-density cathode material for lithium-ion batteries, particularly relevant for electric vehicles and grid storage. Its electrochemical performance (capacity, rate capability, cycle life) is strongly tied to crystal structure, phase purity, cation ordering and oxygen stoichiometry. X-ray diffraction (XRD) is a primary analytical tool to quantify these structural attributes rapidly and non-destructively, enabling materials optimization and quality control in research and production environments.

Objectives and overview of the study

This application note demonstrates the use of the Thermo Scientific ARL X’TRA Companion benchtop XRD system to (i) derive routine performance indicators for NMC 811 from short scans and (ii) perform detailed Rietveld structure refinements from longer high-angle scans. Emphasis is placed on identifying metrics related to long-range ordering, Li–Ni anti-site mixing, lattice parameters and anisotropic atomic displacement parameters (ADPs) that correlate with electrochemical behavior.

Methodology

Measurements were performed on a commercial NMC 811 powder using reflection geometry with Co Kα radiation (λ = 1.790915 Å). Two measurement protocols were used: a fast 10-minute scan (5–90° 2θ) for routine performance criteria and a longer 60-minute scan extending to 143° 2θ for full-profile Rietveld refinement. Data acquisition used a spinning sample, electronic photon-energy filtering to reduce fluorescence, and profile fits based on the fundamental-parameter approach.

Instrumentation used

• Thermo Scientific ARL X’TRA Companion XRD System (θ/θ Bragg–Brentano goniometer, 160 mm radius).
• 600 W X-ray source selectable for Cu or Co radiation; Co Kα used in this study.
• Radial and axial beam collimation via divergence and Soller slits; variable beam knife for reducing air scattering.
• Solid-state pixel detector (55 × 55 µm pitch) enabling rapid data collection.
• Software: Profex/BGMN for Rietveld refinement (fundamental-parameter profile fitting); SolstiX Pronto for instrument control and LIMS integration.

Structure refinement approach

Rietveld refinements started from the Arai et al. α-NaFeO2 (R3m) NMC model. A chemical-sum constraint was applied; anisotropic ADPs were refined for transition-metal (TM) and oxygen sites while Li was treated with isotropic ADP. Li–Ni anti-site mixing and site occupancies were refined within these constraints. Intensities for performance metrics were obtained from profile fits; full structure parameters were derived from the 60-minute high-angle dataset.

Main results and discussion

Phase purity and performance indicators:

• The sample is phase-pure NMC 811.
• Key performance ratios from the 10-minute scan: I003/I104 = 1.37 and c/a = 4.94; the inverse R-factor R = (I006+I102)/I101 = 0.46. These values indicate strong in-plane order and low Li–Ni anti-site mixing, consistent with high Li mobility.

Rietveld refinement (60-minute data):

• Refinement confirms low Li–Ni anti-site mixing on the order of a few percent. Occupancy results reported: Ni-rich TM layer occupancies (examples provided in the study indicate Ni ~0.76–0.79 with Li occupying ~0.01–0.04 on TM sites and complementary Li occupancies on the Li layer ~0.96–0.99).
• Lattice parameters and layer geometry show small but measurable compression of layer thickness and interlayer spacing relative to some literature values (examples: a ≈ 2.871 Å, c ≈ 14.196 Å; layer thicknesses ~4.695–4.732 Å and interlayer distances ~2.592–2.599 Å).
• Anisotropic ADPs align with expected vibration vectors for layered oxides, supporting the physical realism of the refinement model.
• Differences in atomic distances are influenced by more factors than ionic radii differences alone; oxygen vacancies and synthesis-dependent defects can modulate measured parameters (oxygen vacancy content was not quantified in this study).

Comparison with literature:

Refined parameters are comparable to reported NMC 811 samples with low (~3–4%) anti-site mixing. Short-scan performance metrics are sufficient to classify material quality; long high-angle scans are required to extract occupancies and anisotropic thermal parameters reliably.

Benefits and practical applications of the method

• Rapid screening: A 10-minute measurement yields robust performance indicators (I003/I104, c/a, R) suitable for QC workflows and fast materials screening.
• In-depth structural insight: Extended 60-minute scans up to high 2θ allow Rietveld refinements that provide occupancies, precise lattice metrics and anisotropic ADPs — valuable for correlating structure with electrochemical performance and for research on defect chemistry.
• Benchtop convenience: The ARL X’TRA Companion provides a compact solution with fast detectors and software integration for routine lab environments and LIMS connectivity for production traceability.

Future trends and potential applications

• Integration with operando and in situ XRD workflows to monitor phase evolution, lattice changes and oxygen loss during cycling, enabling direct links between structural dynamics and degradation mechanisms.
• Advanced defect characterization combining high-angle XRD with complementary techniques (neutron diffraction, X-ray absorption spectroscopy, electron microscopy) to quantify oxygen vacancies, transition-metal oxidation states and local disorder.
• Automated high-throughput XRD screening combined with machine learning models to predict electrochemical performance from diffraction-derived metrics and accelerate materials discovery.
• Improved treatment of microstructural broadening and preferred orientation in Rietveld models to enhance accuracy of occupancy and ADP determinations for layered cathode materials.

Conclusion

Short, routine XRD scans on the ARL X’TRA Companion reliably deliver performance-relevant metrics for NMC 811, enabling fast quality assessment. For detailed structural characterization — occupancies, anisotropic ADPs and subtle lattice distortions — extended high-angle scans and Rietveld refinement with robust models are required. The combined approach supports both rapid QC and deeper research-driven analyses that inform synthesis optimization and battery performance improvements.

References

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3. H. Arai, M. Tsuda, Y. Sakurai, Journal of Power Sources 2000, 90, 76–81.
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