Microprobe study of the effect of Li intercalation on the structure of graphite

217

185

A mathematical model to simulate the generation of mechanical stress during the discharge process in a dual porous insertion electrode cell sandwich comprised of lithium cobalt oxide and carbon is presented. The model attributes stress buildup within intercalation electrodes to two different aspects: changes in the lattice volume due to intercalation and phase transformation during the charge/discharge process. The model is used to predict the influence of cell design parameters such as thickness, porosity, and particle size of the electrodes on the magnitude of stress generation. The model developed in this study can be used to understand the mechanical degradation in a porous electrode during an intercalation/deintercalation process, and the use of this model results in an improved design for battery electrodes that are mechanically durable over an extended period of operation.

Section: Negative Electrode (Carbon)-supporting

confidence: 79%

Section: Discussionmentioning

confidence: 99%

Theoretical Analysis of Stresses in a Lithium Ion Cell

Renganathan

Sikha

Santhanagopalan³

et al. 2010

217

185

“…18 However, taking into account the increased I D /I G ratios observed in the Raman spectra of graphitic anodes from tested Li-ion cells we conclude that the crystalline disorder in graphite anodes is limited to the surface of the particle and does not affect the bulk of the material. 3,4 We believe that the local structural damage at the surface of the graphitic electrodes occurs because of non-uniform current density distribution within the graphite electrode. Differences in ionic and electronic resistance within the electrode and the SEI layer contribute to this effect.…”

Section: Discussionmentioning

confidence: 99%

An Investigation of the Effect of Graphite Degradation on Irreversible Capacity in Lithium-ion Cells

Hardwick

Marcinek

Beer

et al. 2008

Self Cite

The effect of surface structural damage on graphitic anodes, commonly observed in tested Li-ion cells, was investigated. Similar surface structural disorder was artificially induced in Mag-10 synthetic graphite anodes using argon-ion sputtering. Raman microscopy, scanning electron microscopy (SEM) and Brunauer Emmett Teller (BET) measurements confirmed that Ar-ion sputtered Mag-10 electrodes display similar degree of surface degradation as the anodes from tested Li-ion cells. Artificially modified Mag-10 anodes showed double the irreversible charge capacity during the first formation cycle, compared to fresh un-altered anodes. Impedance spectroscopy and Fourier transform infrared (FTIR) spectroscopy on surface modified graphite anodes indicated the formation of a thicker and slightly more resistive SEI layer. Gas for the surface modified electrode with no evidence of elevated M w species for the unmodified electrode. The structural disorder induced in the graphite during long-term cycling maybe responsible for the slow and continuous SEI layer reformation, and consequently, the loss of reversible capacity due to the shift of lithium inventory in cycled Li-ion cells.3

“…However, the most dramatic spectral change is observed for the anode cycled at 60˚C, which is expressed by the huge increase of the D/G band intensity ratio and broadening of the G band. The increase of relative average D/G intensity ratios for the cycled anodes indicates that severe structural damage was induced into the graphite during cycling, especially at elevated temperature [16]. The ratio of the integrated peaks from each anode is shown in Table 4.…”

Section: Microraman Analysis Of the Anodementioning

confidence: 99%

“…This (D) band, which is assigned to the A 1g mode, is associated with the breakage of symmetry occurring at the edges of graphite sheets. The relative intensity of the D band vs. G band is attributed to increased carbon disorder [15,16].…”

Section: Microraman Analysis Of the Anodementioning

confidence: 99%

Diagnostic Analysis of Electrodes from High-Power Lithium-Ion Cells Cycled under Different Conditions

Striebel

Shim

Cairns

et al. 2004

Both capacity fade and impedance rise were found to increase with cycling temperature and the span of the DOD. The loss of cycleable Li, most likely due to solvent reduction on the anode, was linear in cell test time and the room temperature cells showed an SEI composition and degree of graphite disorder that roughly correlated with the extent of the Li consumption. However, electrochemical analysis showed that the cathode was controlling the performance loss in the cell. TEM and NMR showed evidence of crystalline defects and degradation of the Li-Ni environment, respectively, though no major new phases were identified, in agreement with the XRD results. FTIR analysis of the cathode revealed no evidence of polymeric deposits on the cathode particles although both Raman and TEM showed evidence of P-containing deposits. Raman mapping showed a noticeable change of the active material/carbon surface concentration ratio for the cathode cycled 1000 times at 100% DOD as compared with that cycled to 70% DOD.