Analysis of Solid Electrolyte Interphase in Mn-Based Cathode/Graphite Li-Ion Battery with Glow Discharge Optical Emission Spectroscopy

Abstract

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...

Electrochemical, Post-Mortem, and ARC Analysis of Li-Ion Cell Safety in Second-Life Applications

“…16,27,47,51 This fits to the optical appearance of the anode which is black (see inset of Figure 4e). We note that the adhesion of the anode coating from the cell cycled at 45…”

Detection of Li Deposition by Glow Discharge Optical Emission Spectroscopy in Post-Mortem Analysis

“…The linear regression with a correlation coefficient of R 2 = 0.98 proves the accuracy of GD-OES quantification and allows applying the calibrated method on an unknown sample. A similar approach was previously done by Takahara et al 18 Sample with Li plating (sample 1) is created by reconstructing graphite and NMC electrodes from a commercial 16 Ah cell into pouch cells. EC:DMC = 1:1, 1 M LiPF 6 electrolyte and a fresh separator were used in these model cells.…”

“…[15][16][17][18] The present study introduces a novel method to prove Li deposition on graphite anodes of Li-ion batteries by means of GD-OES depth profiling. For comparison, anodes from cells where Li plating is expected (cycling at low temperatures) are compared to anodes without Li plating but initial SEI formation (anodes from fresh cell).…”

Review—Post-Mortem Analysis of Aged Lithium-Ion Batteries: Disassembly Methodology and Physico-Chemical Analysis Techniques

“…Figure 9 shows a schematic overview of degradation mechanisms of electrodes and materials, which is often not distinguished in literature. Electrode degradation includes growth of films on top of electrodes (electrolyte decomposition 16,18,26,28,40,122 or Li deposition 25,45,72 ), clogging of pores of electrodes or the separator, 37 delamination of the separator, 42,95 cracks in the electrode coating 32,42,223 or deformation of electrodes or separator. 9,14,32 Material degradation involves particle cracks, 42,74,75,129,130 exfoliation, 37 changes at particle surfaces, 37,158 film formation on particles, 37,271 dissolution/migration of transition metals, 36,37,272 electrolyte degradation, 175,228,229 or closing of separator pores (e.g.…”

“…Kobayashi et al mentioned that the open circuit voltage (OCV) of aged cells discharged to 2.5 V at C/20 was larger than the OCV of fresh cells due to the increase of internal cell resistance. 12 Hence, the authors held all cells at 3.0 V for over 10 h before disassembly, leading to an OCV of 3.0 V ± 0.01 V. 12 A similar discharge method was used by Takahara et al 26 Kumaresan et al discharged pouch cells in two stages, first with C/33 and after a rest period of 30 min with C/83 to ensure a complete discharge. 73 Disassembly of cells at higher SOCs has been carried out for Tcells, 70 whose capacity is very low (∼0.2 mAh) and therefore the risk is small compared to commercial cells (few Ah).…”