Lithiation-delithiation

In-situ x-ray diffraction (XRD) was performed on a coin type cell with a 4x6 mm Kapton window coated with conductive thin copper layer. The graphite electrode was pressed against the Kapton window so as to be reached by the x-ray beam. After several lithiation/delithiation cycles under a C/10 rate between 1.5 and 0V, the cell was fully delithiated up to 1.5V. The cycle capacity achieved with the graphite electrode is about 360mAh/g. The cell was then re-lithiated under a slower rate of C/20. XRD patterns were taken for about five minutes every hour while the cell is under continuous discharge. As result the lithium composition x in LixC6 was incremented by 0.05 between two successive XRD scans. 

Considering the virtually zero solubility of LiF in nonaqueous media, McMillan et al. synthesized the fluorinated counterpart of CIEC. As expected, the shuttle phenomenon was eliminated because of the fluorination, as evidenced by the quantitative Coulombic efficiency, while a similar SEI effect was maintained, since FEC/PC mixed solvent can support reversible lithiation/delithiation of the graphitic anode materials. However, capacity was observed to fade by 37% in 200 cycles. Follow-up work on this solvent has been minimal. 

Figure 53. Stabilization of graphite in PC by LiBOB. Voltage profiles of lithium/graphite half-cells containing 1.0 m lithium salts in neat PC as electrolytes. Only for LiBOB/ PC was the complete lithiation/delithiation cycle achieved. (Reproduced with permission from ref 324 (Figure 1). Copyright 2002 The Electrochemical Society.)...

An important conclusion that these authors drew based on their polarization and EIS studies is that the properties of the SEI film on a graphite anode surface play a far more decisive role in determining the kinetics of the lithiation/delithiation at low temperatures than does the bulk ion conductivity, although it is necessary for the latter to achieve a... 

Figure 27 shows a typical chronopotentiogram of the first lithiation-delithiation cycle of a petroleum coke electrode [357], It demonstrates the irreversible capacity loss due to the carbon s surface reactions (plateau around 1 V versus Li/Li+), the sloping potential profile, and the fact that the maximal reversible capacity is less than that of graphite. However, its structural disorder makes this electrode... 

FIGURE 4.6 Electrochemical lithiation/delithiation of SWNT electrodes effect of sample treatment on potential profile. Top purified SWNT. Middle SWNT ball milled for 1 min. Bottom SWNT ball milled for 10 min. The data were collected at a constant current of 50 mA/g. Reprinted from Ref. [133]. Copyright 2000, with permission from Elsevier. 

It has become possible to imderstand Si s lithiation/delithiation mechanisms due to the use of ex situ and in situ methods. X-ray diffraction (XRD) in situ, nuclear nagnetic resonance (NMR), microscopy techniques in... 

Particles surface chemistry also plays a role in aging processes. Beyond the lithiation/delithiation mechanisms within the bulk of the particles leading to the phases described above, the particles surfaces undergo liieir own... 

Figure 1.14. Diagram of electrochemical reactions during Sn lithiation/delithiation. Reprinted from [U 14c] with permission. Copyright 2014 American Chemical Society)...

M is electrochemically inactive transition metal (M = Fe, Ni, Cu, and Co). M also provides a matrix that buffers volume changes occurring with the lithiation-delithiation processes, therefore the mechanical integrity between Sn nanoparticles and with current collector can be maintained. Both preparation of alloy nanopowders and thin films are popular strategies. 

The last example is THF-PC solutions. Figure 27 shows chronopotentiograms of graphite electrodes that were lithiated-delithiated in THF, THF-PC, 3M, and in THF-PC IM solutions. The difference in behavior is striking. In THF, graphite electrodes fail because THF is not sufficiently reactive to be reduced to passivating... 

Electronic Conductivity, Ionic Diffusivity and Lithiation/Delithiation Mechanism... 

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