Lithium vinylene carbonate

The lithium-storage properties of these Si SiOx/C nanocomposite electrodes were investigated in different electrolyte systems and compared to pure Si nanoparticles. From all the analyzed systems, the Si SiOx-C nanocomposite in conjunction with the solvent vinylene carbonate (VC) to form the solid-electrolyte interface showed the best lithium storage performance in terms of a highly reversible lithium-storage capacity (1100 mAh g-1), excellent cycling performance, and high rate capability (Fig. 7.9). 

Among the various additives tested, vinylene carbonate (VC) might be the most famous in the lithium ion research and development community, although the number of publications related to it seems to be rather small. Its importance can be evidenced by the number of companies that vied for the patent rights for... 

Fig. 2.10 Cycling performance of lithium-ion battery composed of oxygen stoichiometric Lij q AIq j Mn and graphite (MCMB6-28) at RT(open circle) and 60°C (filled circle). Electrolyte contains vinylene carbonate. EC MEC(3 7), 1-M LiPF6, 4.2-S.3 V...

When PC is used as a solvent, the electrolyte continues to decompose at about 0.9 V Vi. LP/Li, as shown in Fig. 4.4, and graphitic (crystalline) carbons cannot be charged due to their exfohation caused by the solvent co-intercalation. This is the reason why EC is dominantly used instead of PC, which was adopted for the first commercial lithium-ion cells with anongraphitic (amorphous) carbon anode. However, the addition of some compounds such as vinylene carbonate (VC) prevents the graphite exfoliation and enables the charge of graphitic carbons, as shown in Fig. 4.4. 

In 1992, Sanyo Electric Company found that vinylene carbonate (VC) (1), the most well-known additive at present, can be used as a solvent in lithium secondary batteries [39],... 

Wang, Y Nakamura, S. Tasaki, K. Balbuena, P.B. Theoretical studies to understand surface chemistry on carbon anodes for lithium-ion batteries how does vinylene carbonate play its role as an electrolyte additive J. Am. Chem. Soc., 2002,124,4408-4421. 

Chen LB, Wang K, Xie XH, Xie JY (2007) Effect of vinylene carbonate (VC) as electrolyte additive on electrochemical performance of Si film anode for lithium ion batteries. J Power Sources 174 538-543... 

Functional electrolyte additives are included in the electrolyte solution to improve battery performance. This concept has been around for some time, tind the basic technology is well established. One early example is the addition of propane sultone to the nonaqueous electrolyte solution of a rechargeable battery using a metallic lithium anode. Although this technology was initially developed for metallic lithium batteries, the use of such additives for LIBs began around 1994. Since then a wide range of additives have been developed. So many different compounds have been used as additives that they are too numerous to mention, but notable examples include vinylene carbonate, propane sultone, phenylcyclohexane, and fluoroethylene carbonate. The selection of additives and determination of their appropriate formulations have become a key aspect of the proprietary know-how of each battery manufacturer, and the search for new additives continues apace. 

Lee HH et al (2005) The function of vinylene carbonate as a thermal additive to electrolyte in lithium batteries. J Appl Electrochem 35 615-623. doi 10.1007/sl0800-005-2700-x... 

SEI formation-boosting additives. There has been a significant interest in the development of electrolyte additives to enhance the stabihty of LiPFe-based electrolytes for lithium-ion batteries [28]. One class of additives, which includes vinylene carbonate (VC) [29] and LiBOB [30, 31], react on the surface of the anode to generate a more stable SEI. Another class of additives includes N,N-dimethylacetamide (DMAc). DMAc reduces the reactivity of LiPFe and inhibits the reactions between the electrolyte and the electrode materials [32-34], Stabilizing the anode SEI and inhibiting the detrimental reactions of the electrolyte with the surface of the electrode materials will extend calendar life and enhance the thermal stability of lithium-ion batteries. 

This irreversible consumption of lithium can be optimized by adding adjuvants into the electrolyte. The use of an adjuvant such as VC Vinylene Carbonate) is often cited in the composition of the electrolyte. It is, like other molecules, considered to be a precursor of the SEI, because it decomposes early on (at high potential), before the other solvents in the electrolyte, forming a fine, homogeneous film on the surface of the graphite particles. The number of lithium ions involved in its decomposition is therefore low, and the irreversible capacity reduced. 

Kim et al. ARC Cathode and electrolyte The effect of lithium bis(oxalato)borate (FiBOB), vinylene carbonate (VC) and succinonitrile (SN) electrolyte additives and FiPFg salt on the reactivity between electrolyte and charged positive electrode material was investigated by ARC. The results shown here suggest that additives and FiPFe salt can play a different role in thermal stability depending on the positive electrode material [44]... 

It has been formd that lithium difluorophosphate modifies the surface chemistry induced by vinylene carbonate and makes a more ionically conductive surface film on the graphite, thus ensuring a good rate capability (43). 

An electrolyte for a rechargeable lithium battery with excellent storage stability at a high temperature has been described (104). The electrolyte for a rechargeable lithium battery includes a nonaque-ous organic solvent, a lithium salt, and an additive. The additive includes vinylene carbonate, fluoroethylene carbonate, and a nitrile-based compound. 

The molecular structure of vinylene carbonate (Figure 9.8b) is substantially similar to that of EC except that the saturated single bond in EC is replaced by an unsaturated double bond. It can also be used as an electrolyte additive for example, it reacts with the lithium at the surface of graphitized carbon (artificial graphite KS-25) and forms a carbonate polymer that helps to form more conductive passivation SEI film. As a result, the irreversible capacity of the EC/DEC solvent combination is reduced and the cycling performance is improved, especially at elevated temperatures. The reactions at the surface of the positive electrode materials reduce the interfacial resistance, but there is no obvious impact on the cycling performance. 

The acidity of the C2 proton (indicated in the scheme above) is estimated as pKa = 24, and this corresponds to a reduction potential of 1.5 V vs Li Li°. The methylation of the C2 proton increases the reduction potential by 300 mV however, this is still not sufficiently negative for lithium battery applications and thus such ILs require the use of additives such as vinylene carbonate (VC), which form a stable solid-electrolyte interphase (SEI) layer, in order to be viable.f " ... 

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