PC-based electrolytes

Matsuda and co-workers [39-41] proposed the addition of some inorganic ions, such as Mg2+, Zn2+, In3+, Ga3+, Al3+,and Sn2+, to PC-based electrolytes in order to improve cycle life. They observed the formation of thin layers of Li/M alloys on the electrode surface during the cathodic deposition of lithium on charge-discharge cycling. The resulting films suppress the dendritic deposition of lithium [40, 41]. The Li/Al layer exhibited low and stable resistance in the electrolyte, but the... 

Figure 6. Early stages of intercalation into HOPG above, in EC-based electrolyte below, in PC-based electrolyte [4, 5. ...

LiC104 / PC electrolyte (Fig. 6), a process which was considered to be responsible for the continuing solvent decomposition when graphite is charged in PC-based electrolytes. This showed that, even in EC-based electrolytes, some degree of solvent co-intercalation exists but does not prevent formation of a stable SEI. It is clear that... 

In electrolytes based on solvent mixtures both solvent compounds may react to form films of scarcely soluble materials. PC/THF mixtures yield alkoxides and alkylcarbonates [188] EC/ether blends mainly yield alkylcarbonates, which are thought to be the reason for smaller lithium loss during cycling [188]. PC based electrolytes with LiAsF6and LiC104 form films containing alkylcarbonates which allow the access of other molecules, such... 

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... 

The future remains bright for the use of carbon materials in batteries. In the past several years, several new carbon materials have appeared mesophase pitch fibers, expanded graphite and carbon nanotubes. New electrolyte additives for Li-Ion permit the use of low cost PC based electrolytes with natural graphite anodes. Carbon nanotubes are attractive new materials and it appears that they will be available in quantity in the near future. They have a high ratio of the base plane to edge plain found in HOPG. The ultracapacitor application to deposit an electronically conductive polymer on the surface of a carbon nanotube may be the wave of the future. 

Figure 16. Model In PC based electrolytes, solvent co-intercalation, gas formation and crevice formation in polycrystalline graphite materials are inter-related reactions. In fact, there is a subsequence of reactions (1) PC co-intercalation, (2) gas formation, (3) crevice formation ultimately resulting in exfoliation and macroscopic destruction of graphite [40],...

Test cells using the above graphite materials were evaluated in PC-based electrolytes. For this work, the hybrid pulse power characterization (HPPC) test was performed on cells with the different graphite anodes and PC-based electrolytes to evaluate their high power capabilities. These electrochemical experiments indicate that cells containing the surface-modified natural graphite can meet the power requirement set by the FreedomCar partnership for the hybrid vehicle applications. 

In conclusion, the surface modified natural graphite has good performance in PC based electrolyte and also meets the power requirements for hybrid electrical vehicle applications. Surface carbon coated natural graphite SLC1015 is a very promising material in high power Li-ion batteries with lower cost, reasonable safety, and low irreversible capacity. 

In the early era of lithium ion cell research, Aurbach et al. noticed that the presence of CO2 in the electrolyte had pronounced effects on the lithia-tion behavior of graphitic anodes. A number of electrolytes, which were thought to be incompatible with graphite because they are based on solvents such as methyl formate or THE, delivered much improved performance under 3—6 atm of C02. ° They proposed that CO2 participated in the formation of the SEI by a two-electron process, yielding Li2C03, which assisted in the buildup of the protective surface film. However, in PC-based electrolytes. CO2 presence proved to be ineffective, while, in electrolytes based on carbonate mixtures such as EC/DMC, the... 

Despite the highly efficient performance of crown ethers in reducing the irreversible capacity at the anode side, especially when PC-based electrolytes were used, the toxic nature of these compounds still prevented their application in commercial lithium ion cells. 

A sulfur analogue of EC, ethylene sulfite (ES), was proposed as an additive for PC-based electrolytes by Winter and co-workers,apparently because of its structural similarity to EC and its potential, under reductive conditions, to release SO2, a known additive that effectively suppresses PC decomposition. As the voltammetry in Figure 39 shows, ES in only 5% presence successfully eliminated the exfoliation of the graphite anode, whereas 10% SO2 failed. The irreversible process corresponding to the reduction of ES occurred at --"2.0 V, lower than that of SO2 by 0.80 V however, the quantity of charge associated was much lower. According to the authors, the above apparent gap between the reduction potentials of ES... 

One possible explanation for the broad mle = 44 feature may be found in the thermal decomposition of a lithium alkyl carbonate produced by the reaction between PC and Li, for which C02 would be released at a much lower temperature than the corresponding inorganic carbonate. The formation of such a species has been suggested by Aurbach and co-workers on the basis of in situ and ex situ external reflection FTIR measurements performed in PC-based electrolytes [18]. Support for this assignment was obtained from experiments in which a genuine alkyl carbonate was prepared in UHV by exposing to C02 a layer of lithium alkoxide formed by the adsorption of an alcohol onto the Li surface, as described in Section I.E. 

It decreases from 18 to 6 Q cm2 due to C02 addition, similar to the effect of C02 addition on the behavior of Li electrodes in liquid PC-based electrolyte solutions [14,15].)... 

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