Capacity decay

There in an initial steep increase in capacity in the first few cycles which comprise the activation process. After activation, a maximum in electrochemical storage capacity, (2max, is reached. This is usually followed by an almost linear decrease in capacity which may be termed capacity decay. 

With regard to rechargeable cells, a number of laboratory studies have assessed the applicability of the rocking-chair concept to PAN-EC/PC electrolytes with various anode/cathode electrode couples [121-123], Performance studies on cells of the type Li°l PAN-EC/PC-based electrolyte lLiMn20 and carbon I PAN-EC/PC-based electrolyte ILiNi02 show some capacity decline with cycling [121]. For cells with a lithium anode, the capacity decay can be attributed mainly to passivation and loss of lithium by its reaction with... 

Figure 5 shows the data of the capacity decay at various milling times. The pattern of capacity decay with cycle number in Fig. 5 may be fairly well fitted by linear equations. To visually compare the cycle life of electrodes, these linear equations were used to estimate the percent of capacity at the first cycle as a function of cycle number and the results are presented in Fig. 6. As can be seen from this figure, the longer the processing time, the slower the capacity decay. Nevertheless, the change in the rate of the capacity decay with milling time becomes less after 72 h of milling compared with that within 72 h. Consequently, the milled composite ground for 72 h gave the best combination of performance of all the studied electrode materials.

Fig. 5. Variation of the electrode capacity decay with different milling times 1, 1 h 2, 12 h 3, 72 h 4, 240 h.

Reversible capacity decay or reversible insufficient mass utilization (RIMU), perhaps another term for PCL-2 [41]. This is a phenomenon explored by Winsel, Meissner and co-workers at Varta where capacity loss can be reversed by ehanges in charging algorithms or by chemical modifications as noted for PCL-2. 

It has been found that H3PO4 prevents capacity decay of the positive electrode during cycling of gelled lead—acid batteries for electric vehicle applications [21]. Addition of phosphoric acid to VRLAB electrolyte yields stable capacity performance of these batteries in different solar power systems [37]. 

Si, however, involves a fimdamental drawback that needs to be overcome first. When Li is doped into Si, Si expands hugely by 300%. The repeated volume expansion during cycling brings about pulverization of Si and a sharp capacity decay due to the loss of electric contacts between resulting Si fine particles. 

Quite often, simultaneously with the capacity decay, the formation of a barrier layer of lead sulfate (PbS04) is observed between the grid and the active material... 

Higher capacity decay heat removal system... 

The Li4Ce06 compound exhibited good performance with a specific capacity of 200 mAh at an average potential of 1.8 V, showing a capacity decay of only 10 % after 50 cycles. 

Lithium-sulfur batteries suffer from a rapid capacity decay and low energy efficiency because of the low solubility of lithium sulfide (Li2S) in organic solvents and the intrinsic polysulfide shuttle phenomenon. Phosphorus pentasulfide (P2S5) in an organic electrolyte, has been shown to boost the cycling performance of lithium-sulfur batteries. The function of the additive is two-fold (72) ... 

Fig. 20. Influence of the stoichiometric deviation of MiihNij.sCoojAIo j on capacity decay curves at 20"C (charge 186mAg for 2h discharge 93 mAg to -0.6 V vs Hg/HgO) (Sakai et al. 1992a).

Polysuffide shuttle is a phenomenon unique to Li-S batteries with liquid electrolytes. This phenomenon is responsible for high self-discharge, low coulombic efficiency, severe sulfur migration, and fast capacity decay. The polysulfide shutde... 

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