LiFePO 4 has an interesting spin-polarized electronic structure showing a (3dv) 5 (3dV) 1 electron configuration of the Fe 2+ ion. In this work, we have experimentally evidenced the valence electronic structure of LiFePO 4 and of its delithiated compound FePO 4 by X-ray photoelectron spectroscopy (XPS), which allows a visualization of the occupied densities of states (DOS) in the valence band. XPS valence spectra were compared with the DOS obtained from DFT calculations by considering GGA and GGA + U approaches. Thanks to electrochemical extraction/insertion of Li + ions in LiFePO 4 /FePO 4 , it was possible to display the Fe 3d spindown electron of LiFePO 4 , which is not present in the valence spectrum of FePO 4 . We show that the study of XPS valence spectra is an efficient way to access the lithium insertion rate in Li x FePO 4 positive electrode materials for lithium-ion batteries. Besides the contribution to the Li-ion battery field, this paper is also a rare example of experimental evidence of a spin-resolved electronic structure from in-lab XPS experiments.

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A structural model is proposed to explain the abnormal broadening of the (10ℓ) and (20ℓ) lines in the X‐ray diffraction pattern of nickel hydroxide. This model, based on a hypothesis of the presence of stacking faults, allows us to rationalize the empirically established relationship between the presence of such peculiarities in X‐ray diffraction patterns and the good electrochemical behavior of the material. Two types of stacking faults, i.e., growth and deformation faults, corresponding to the existence within the hexagonal oxygen packing of one or two face‐centered cubic oxygen sequences, respectively, have been identified. The simulation, with the DIFFaX program, of the X‐ray diffraction patterns of nickel hydroxide samples has allowed us to determine in a general way the nature and the amount of stacking faults. It is shown that the stability of protons in tetrahedral sites depends on whether they are in the vicinity of a stacking fault or not, and this explains the improvement of both the chargeability of the material and its electronic conductivity in the presence of defects. It is shown as well that stacking faults in the electrochemically active material lead to a more facile transition to the γ phase during overcharge in concentrated electrolyte. © 1999 The Electrochemical Society. All rights reserved.