Microscopic mechanism of path-dependence on charge–discharge history in lithium iron phosphate cathode analysis using scanning transmission electron microscopy and electron energy-loss spectroscopy spectral imaging

High Spatial Resolution Hyperspectral Imaging with Machine-Learning Techniques

“…We also successfully applied NMF to a series of EELS datasets for the extraction of atom site-specific core-loss spectra, where the relative excitation probabilities of the spectra varied with the diffraction condition because of the electron channeling effects [22][23][24][25]. In these applied data analyses, the nonnegative constraint of the elements of extracted basis spectra and spatial intensity distributions were effective, and the resulting spectra extracted by NMF were consistent with the computational results obtained by first principles calculations [15][16][17][18][19][22][23][24][25].…”

“…Contrary to NMF, the methods mentioned above such as PCA allow the spatial intensities and spectra to have negative values, which hampers the direct physical interpretation of the resolved spectral profiles. We adopted the modified alternating least-square (MALS) fitting algorism of NMF [14] to map the different phases in the degradation of Li battery cathodes [15][16][17][18][19] and the chemical states of nitrogen in nitrogen-doped TiO 2 [20,21]. We also successfully applied NMF to a series of EELS datasets for the extraction of atom site-specific core-loss spectra, where the relative excitation probabilities of the spectra varied with the diffraction condition because of the electron channeling effects [22][23][24][25].…”

Comprehensive analysis of TEM methods for LiFePO4/FePO4 phase mapping: spectroscopic techniques (EFTEM, STEM-EELS) and STEM diffraction techniques (ACOM-TEM)

“…In particular, the conclusions deduced from the STEM-EELS results by Honda et al [8], where a core-shell FP/LFP de/lithiation structure was observed, is in discrepancy to the observation from the ACOM-TEM work from Brunetti et al [12], where a Domino-Cascade model (de/lithiating particle by particle) was confirmed. The limited reliability of EFTEM based phase maps for samples with varying thickness has already been discussed by Sugar et al [11], whereas for diffraction based analysis questions about the reliability arise due to the structural similarity of both phases and the corresponding small difference between the LFP and FP lattice constants, especially for higher index orientations.…”

“…Transmission electron microscopy (TEM) offers various sophisticated methods for LiFePO 4 /FePO 4 (LFP/FP) phase mapping with high spatial resolution [6][7][8][9][10][11][12][13][14][15][16]. The mapping methods can be sorted into two families: one are spectroscopy methods based on the chemical information encoded in the energy spectra; the other are diffraction methods relying on the crystallographic information recorded in diffraction patterns or high resolution (HR)TEM images.…”

“…In the first family of methods, electron energy loss spectroscopy (EELS) was one of forerunners to investigate the Fe-L and O-K edges, Li-K and Fe-M edges as well as the low-loss range resulting from interband transitions and plasma resonances [7,9,[17][18][19]. The approach has been extended to 2 dimensions by combining EELS with scanning transmission electron microscopy (STEM) to obtain STEM-EELS spectral imaging (SI) and, for example, the differences in the O-K and Fe-L core loss spectra in LFP/FP have been used for phase mapping [8]. Alternatively, 2D phase mapping has been implemented by energy filtered transmission electron microscopy (EFTEM) spectral imaging, where the phase has been determined by measuring the chemical shift of the Fe-L 3 edge between the LFP and FP phases [11].…”