Precycling

IndiAdual cells are usually precycled before assembling into batteries. Tliese early charge—discharge cycles, often called fomiation cycles, improv e the capacity of the cell by increasing the surface area of the active material and effecting cry stal structure changes. 

Figure 29. C Is and O Is XPS spectra for fresh, precycled, and stored graphite anodes. (Reproduced with permission from ref 294 (Figure 17). Copyright 2002 The Electrochemical Society.)...

However, Li2COs was not observed by Andersson and Edstrom in their XPS analysis of the graphitic anode that had been precycled and then stored at 60 °C for 7 days. They found that, during the storage, the original SEI consisting of lithium alkyl carbonate was indeed unstable and disappeared with time, as... 

Figure 30. Capacity loss due to storage at elevated temperatures for Li/graphite half-cells. All cells were precycled at room temperature (cycles 1—3) prior to storage at indicated temperatures for 1 week, followed by continued cycling at room temperature. The electrolytes used were EC/DMC (2 1) and (a) 1.0 M LiPFe or (b) 1.0 M LiBp4. The cells were stored in delithiated states. (Reproduced with permission from ref 277 (Figure 2). Copyright 2001 The Electrochemical Society.)...

Independent from the chemical nature of the supports, pre-cycle lEC media before use to obtain optimal separations. The precycling is recommended especially before first use and after longer storage. 

Several precyclic and photochemical processes for pyrazolo[3,4-, pyridazines, isoxazolo[4,5-, pyridazines, and for-mycene-N6-oxide were discussed in CHEC-II <1996CHEC-II(7)431>. 

Regeneration of cellulose-based columns is most reliably achieved by using the acid/alkali precycling procedure described (see Note 13). 

The purpose of precycling an exchanger is to expose the charged groups that are bound to the matrix. The cellulosic exchangers are discussed here because precycling is most critical to these media. How-... 

Fignre 4-6. The effects of precycling an ion exchange resin on its resolution capabilities. (Copyright W. and R. Balston, Ltd., Maidstone, Kent, England.)... 

Failure to precycle an exchanger results in drastically reduced capacity and resolution (Figure 4-6). The loss in resolution becomes more acute as the size and charge densities of the molecules being separated increases. Therefore, for protein separations on cellulosic exchangers precycling is a critical step. 

Three different pulse techniques were used in this study a) single pulse, b) multipulse experiments, where a series of pulses is introduced, and c) pump-probe experiments, where two different pulses are alternately introduced at a user-specified time interval At. All single pulse and pump-probe experiments consisted of 40 pulse cycles of 3 seconds duration. Directly before the measurement 5 initial precycles were given. The responses of the 40 cycles were averaged to improve the signal/noise ratio. 

In contrast with reversible redox switching of precycled films, the initial redox cycle of Prussian Blue yielded more complex mass responses with much greater irreversible solvation changes. This is dramatically illustrated by the data of Fig. 17 [108], which shows the i-E and AM-E responses to the first redox cycle for each of two nominally identical films, one exposed to H2O and the other to D2O. Although the difference in solvent molar masses is quite small (11%), solvent transfer is such a large component of this initial redox-driven structural change that the overall responses are very different. Somewhat reminiscent of the a-//3-Ni(OH)2 case, this underscores the fact that when the observed response is a sum of individual transfer components (commonly in opposing directions, for example, in response to a volume constraint), a relatively small variation in one component... 

Fig. 10.8 (a) Voltage profiles and (b) capacity retention of bare and AI2O3- and AlPO -coated LiCoO cathodes in coin-type half cells (Li as an anode) with a charge voltage of 4.8 V (precycled at the rates of 0.1 C for the initial 2 cycles, and 0.2 and 0.5 C each for the next two cycles)... 

To investigate the effect of initial cyclic fatigue loading (precoaxing) on creep behavior, five virgin specimens from the same lot were subjected to a series of intermittent cyclic loads for a total of about 5(X),000 cycles In a period of 160 h, Three specimens were precycled c/t ISOCT C and two at 1370 C. 

A precycled specimen (20-09) was then tested under an applied stress of 100 MPa. Test results obtained to date are plotted In Fig. 5. The specimen has accumulated a total strain of about 0.8% and the test Is ongoing. To facilitate comparison, the creep curve of... 

Fig. 5. Comparison of creep behavior of a virgin specimen and that of a precycled specimen tested at 1370°C.

Because of the uncertainty in creep behavior beyond the available data, the true effects of precycling on the creep resistance of this material remain unknown. 

Fig. 6. Enlargement of initial creep behavior of a precycle tensile specimen (20-09) tested of 1370 C under an applied stress of 100 MPa.

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