Solid electrolyte interphase (SEI) and Mn deposition formed on capacity-degraded graphite electrodes in commercially available Mn-based/Graphite lithium ion batteries were characterized using glow discharge-optical emission spectroscopy (GD-OES). The depth profile of the whole electrode showed a homogeneous distribution of Li and Mn except for the surface region at the initial state. With the progress of degradation, Li and Mn concentrations increased inhomogeneously in the depth-direction of the electrode; the Li and Mn concentrations were high in the outer layer and decreased with depth to the current collector in the degraded electrodes. The SEI layer deposited on the electrode surface was separately analyzed in detail. The GD-OES surface profile was explained by comparing to the XPS analysis results. The amount of Li deposited on the electrode surface was almost constant with the capacity degradation, though the Li concentration in the whole electrode increased along with the capacity degradation. In contrast, the amount of Mn deposition increased with the capacity degradation both in the surface deposition layer and in the whole electrode.Lithium ion batteries (LIBs) have been applied to portable power sources and then extensively to various uses of electric vehicles and stationary devices. An important subject related to LIBs is deterioration during long-term and high-temperature operations. The deterioration mechanism has been studied extensively to date. Solid electrolyte interphase (SEI) growth on the negative electrode is well known to contribute strongly to capacity fading during cycles. 1,2 Formation of the SEI layer on the negative electrode causes irreversible capacity loss in the first few cycles. Even in additional cycles, lithium is consumed continuously as a result of continuous reduction of the electrolyte on the electrode.Lithium manganese oxide spinel, LiMn 2 O 4 (LMO), has been regarded as a promising positive electrode material for large-scale commercial battery because of its low-cost and environmentally friendly characteristics. In the case of LMO cathode, manganese dissolution is a critical factor for deterioration, just as SEI growth is for it. 3,4 Manganese dissolution probably results from acid that is generated by oxidation of the solvent. The dissolved manganese is migrated to the negative electrode. Then it is reduced and deposited as Mn metal on the negative electrode. Finally, it presumably forms manganese compounds such as MnCO 3 . 5 The deposited manganese can enhance the electrolyte decomposition to accelerate SEI growth on the negative electrode. 6 These deposited manganese compounds and SEI growth promote lithium consumption and enhance cell resistance.Recently, capacity fading in commercially available Mnbased/Graphite (LiMn 2 O 4 /LiNi 0.8 Co 0.15 Al 0.05 O 2 mixed cathode and graphite anode) batteries was investigated by Kobayashi et al. 7,8 They performed long-term charge-discharge cycling at the operation temperature of 25 and 45 • C for the cells. They carefully disass...

To find the origin of a large initial irreversible capacity and capacity fading with cycling for Fe-substituted LiCoO 2 (LiCo 1Ϫy Fe y O 2 ), the LiCo 0.8 Fe 0.2 O 2 positive electrode was selected for study by ex situ X-ray diffraction, Co and Fe K-edge X-ray absorption, and 57 Fe Mössbauer spectroscopies. A disordering of Fe ions from 3b͑0, 0, 1/2͒ to 6c͑0, 0, 3/8͒ sites was detected for initial charged samples through X-ray Rietveld analysis and Co and Fe K-edge X-ray absorption near-edge structures and extended X-ray fine structures spectra. The valence state of Fe ions in the 6c site was determined to be a 3ϩ/4ϩ mixed valence state from the isomer shift values obtained by 57 Fe Mössbauer spectra and mean M-O distance values. 50% of the iron ions become disordered after the initial charge process and more than 20% remain in 6c sites after the first and tenth discharge processes. The existence of Fe 3ϩ␦ (0 Ͻ ␦ Ͻ 1) ions on the interstitial 6c site can block fast Li conduction in the Li layer of the layered rock-salt structure (R3m). This leads to a lack of reversibility in Fe-substituted LiCoO 2 positive electrode materials.

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