Meaning
Quantifies crystallographic strain and particle size distribution gradients by measuring line profile skewness in X-ray diffraction peaks. Asymmetric broadening occurs when non-uniform lithiation or lattice defects create varying d-spacing distributions within active material powders. Characterization of peak asymmetry in diffraction spectra reveals structural degradation during long-term cycling.
Analytical validity stops when instrument optics distortion dominates intrinsic sample diffraction signals.
Structural Skewness
Crystallographic phase changes shift unevenly when active material particles undergo partial transformations during charge or discharge cycles. Inhomogeneous ion distribution produces overlapping diffraction signals with slightly different Bragg angles. In peak asymmetry analysis, calculating the ratio of left half-width to right half-width quantifies internal structural distortion.
Higher asymmetry metrics indicate incomplete phase transition or localized lithium trapping inside the host lattice.
Strain Profile
Lattice strain gradients cause directional shifting of diffraction intensity away from ideal Bragg positions. Micro-cracking within cathode primary particles increases local strain variations under mechanical cycling stresses.
Quality Verification
Material validation protocols use X-ray diffraction profile analysis to screen synthesis lots of active powders. Unintended phase impurity or non-uniform particle synthesis alters peak asymmetry metrics during incoming quality inspection. Supply contracts for cathode active materials stipulate strict limits on diffraction peak profile parameters to ensure lot-to-lot electrochemical consistency.
Deviations in peak shape indicate inadequate calcination or heterogeneous precursor distribution.
